WorldWideScience

Sample records for polarized monolayer culture

  1. A Route to Permanent Valley Polarization in Monolayer MoS2

    KAUST Repository

    Singh, Nirpendra

    2016-10-24

    Realization of permanent valley polarization in Cr-doped monolayer MoS2 is found to be unfeasible because of extended moment formation. Introduction of an additional hole is suggested as a viable solution. V-doped monolayer MoS2 is demonstrated to sustain permanent valley polarization and therefore can serve as a prototype material for valleytronics.

  2. Magnetic field induced polarization enhancement in monolayers of tungsten dichalcogenides: effects of temperature

    Science.gov (United States)

    Smoleński, T.; Kazimierczuk, T.; Goryca, M.; Molas, M. R.; Nogajewski, K.; Faugeras, C.; Potemski, M.; Kossacki, P.

    2018-01-01

    Optical orientation of localized/bound excitons is shown to be effectively enhanced by the application of magnetic fields as low as 20 mT in monolayer WS2. At low temperatures, the evolution of the polarization degree of different emission lines of monolayer WS2 with increasing magnetic fields is analyzed and compared to similar results obtained on a WSe2 monolayer. We study the temperature dependence of this effect up to T=60 K for both materials, focusing on the dynamics of the valley pseudospin relaxation. A rate equation model is used to analyze our data and from the analysis of the width of the polarization dip in magnetic field we conclude that the competition between the dark exciton pseudospin relaxation and the decay of the dark exciton population into the localized states are rather different in these two materials which are representative of the two extreme cases for the ratio of relaxation rate and depolarization rate.

  3. Superior Valley Polarization and Coherence of 2 s Excitons in Monolayer WSe2

    Science.gov (United States)

    Chen, Shao-Yu; Goldstein, Thomas; Tong, Jiayue; Taniguchi, Takashi; Watanabe, Kenji; Yan, Jun

    2018-01-01

    We report the experimental observation of 2 s exciton radiative emission from monolayer tungsten diselenide, enabled by hexagonal boron nitride protected high-quality samples. The 2 s luminescence is highly robust and persists up to 150 K, offering a new quantum entity for manipulating the valley degree of freedom. Remarkably, the 2 s exciton displays superior valley polarization and coherence than 1 s under similar experimental conditions. This observation provides evidence that the Coulomb-exchange-interaction-driven valley-depolarization process, the Maialle-Silva-Sham mechanism, plays an important role in valley excitons of monolayer transition metal dichalcogenides.

  4. Correlation of Effective Dispersive and Polar Surface Energies in Heterogeneous Self-Assembled Monolayer Coatings

    DEFF Research Database (Denmark)

    Zhuang, Yanxin; Hansen, Ole

    2009-01-01

    grown oil oxidized (100) silicon Surfaces in a vapor phase process using five different precursors. Experimentally, effective surface energy components of the fluorocarbon self-assembled monolayers were determined from measured contact angles using the Owens-Wendt-Rabel-Kaelble method. We show......We show, theoretically, that the measured effective dispersive and polar surface energies of a heterogeneous Surface are correlated; the correlation, however, differs whether a Cassic or an Israelachvili and Gee model is assumed. Fluorocarbon self-assembled monolayers with varying coverage were...

  5. Velocity barrier-controlled of spin-valley polarized transport in monolayer WSe2 junction

    Science.gov (United States)

    Qiu, Xuejun; Lv, Qiang; Cao, Zhenzhou

    2018-05-01

    In this work, we have theoretically investigated the influence of velocity barrier on the spin-valley polarized transport in monolayer (ML) WSe2 junction with a large spin-orbit coupling (SOC). Both the spin-valley resolved transmission probabilities and conductance are strong dependent on the velocity barrier, as the velocity barrier decreases to 0.06, a spin-valley polarization of exceeding 90% is observed, which is distinct from the ML MoS2 owing to incommensurable SOC. In addition, the spin-valley polarization is further increased above 95% in a ML WSe2 superlattice, in particular, it's found many extraordinary velocity barrier-dependent transport gaps for multiple barrier due to evanescent tunneling. Our results may open an avenue for the velocity barrier-controlled high-efficiency spin and valley polarizations in ML WSe2-based electronic devices.

  6. Optically initialized robust valley-polarized holes in monolayer WSe2

    KAUST Repository

    Hsu, Wei-Ting

    2015-11-25

    A robust valley polarization is a key prerequisite for exploiting valley pseudospin to carry information in next-generation electronics and optoelectronics. Although monolayer transition metal dichalcogenides with inherent spin–valley coupling offer a unique platform to develop such valleytronic devices, the anticipated long-lived valley pseudospin has not been observed yet. Here we demonstrate that robust valley-polarized holes in monolayer WSe2 can be initialized by optical pumping. Using time-resolved Kerr rotation spectroscopy, we observe a long-lived valley polarization for positive trion with a lifetime approaching 1 ns at low temperatures, which is much longer than the trion recombination lifetime (~10–20 ps). The long-lived valley polarization arises from the transfer of valley pseudospin from photocarriers to resident holes in a specific valley. The optically initialized valley pseudospin of holes remains robust even at room temperature, which opens up the possibility to realize room-temperature valleytronics based on transition metal dichalcogenides.

  7. Spin-orbit-induced spin splittings in polar transition metal dichalcogenide monolayers

    KAUST Repository

    Cheng, Yingchun

    2013-06-01

    The Rashba effect in quasi two-dimensional materials, such as noble metal surfaces and semiconductor heterostructures, has been investigated extensively, while interest in real two-dimensional systems has just emerged with the discovery of graphene. We present ab initio electronic structure, phonon, and molecular-dynamics calculations to study the structural stability and spin-orbit-induced spin splitting in the transition metal dichalcogenide monolayers MXY (M = Mo, W and X, Y = S, Se, Te). In contrast to the non-polar systems with X = Y, in the polar systems with X ≠ Y the Rashba splitting at the Γ-point for the uppermost valence band is caused by the broken mirror symmetry. An enhancement of the splitting can be achieved by increasing the spin-orbit coupling and/or the potential gradient. © Copyright EPLA, 2013.

  8. Large Spin-Valley Polarization in Monolayer MoTe2 on Top of EuO(111)

    KAUST Repository

    Zhang, Qingyun

    2015-12-08

    The electronic properties of monolayer MoTe2 on top of EuO(111) are studied by first-principles calculations. Strong spin polarization is induced in MoTe2, which results in a large valley polarization. In a longitudinal electric field this will result in a valley and spin-polarized charge Hall effect. The direction of the Hall current as well as the valley and spin polarizations can be tuned by an external magnetic field. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Carrier and polarization dynamics in monolayer MoS2: temperature and power dependence

    Science.gov (United States)

    Urbaszek, Bernhard; Lagarde, D.; Bouet, L.; Amand, T.; Marie, X.; Zhu, C. R.; Liu, B. L.; Tan, P. H.

    2014-03-01

    In monolayer (ML) MoS2 optical transitions across the direct bandgap are governed by chiral selection rules, allowing optical k-valley initialization. Here we present the first time resolved photoluminescence (PL) polarization measurements in MoS2 MLs, providing vital information on the electron valley dynamics. Using quasi-resonant excitation of the A-exciton transitions, we can infer that the PL decays within τ ~= 4ps. The PL polarization of Pc ~ 60 % remains nearly constant in time for experiments from 4K - 300K, a necessary condition for the success of future Valley Hall experiments. τ does not vary significantly over this temperature range. This is surprising when considering the decrease of Pc in continuous wave experiments when going from 4K to 300K reported in the literature. By tuning the laser following the shift of the A-exciton resonance with temperature we are able to recover at 300K ~ 80 % of the polarization observed at 4K. For pulsed laser excitation, we observe a decrease of Pc with increasing laser power at all temperatures.

  10. Spin polarization driven by a charge-density wave in monolayer 1T−TaS2

    KAUST Repository

    Zhang, Qingyun

    2014-08-06

    Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer T-phase TaS2. We demonstrate that a charge-density wave is energetically favorable at low temperature, similar to bulk 1T-TaS2. Electron-phonon coupling is found to be essential for the lattice reconstruction. The charge-density wave results in a strong localization of the electronic states near the Fermi level and consequently in spin polarization, transforming the material into a magnetic semiconductor with enhanced electronic correlations. The combination of inherent spin polarization with a semiconducting nature distinguishes the monolayer fundamentally from the bulk compound as well as from other two-dimensional transition metal dichalcogenides. Monolayer T-phase TaS2 therefore has the potential to enable two-dimensional spintronics. © 2014 American Physical Society.

  11. Secretion of endogenous and exogenous proteins from polarized MDCK cell monolayers.

    Science.gov (United States)

    Gottlieb, T A; Beaudry, G; Rizzolo, L; Colman, A; Rindler, M; Adesnik, M; Sabatini, D D

    1986-04-01

    Confluent monolayers of MDCK (Madin-Darby canine kidney) cells provide a widely used system to study the biogenesis of epithelial cell polarity. We now report that these cells are also capable of the vectorial constitutive secretion of a major endogenous product, a glycoprotein of 81 kDa, which is released into the medium from the apical surface within 30 min of its synthesis. This release represents a bona fide exocytotic secretory process and is not the result of proteolytic cleavage of a plasma membrane-associated precursor since, in cells treated with chloroquine, a protein indistinguishable from the mature secretory product accumulated intracellularly. In contrast to the vectorial secretion of the endogenous product, a variety of exogenous exocrine and endocrine proteins synthesized in MDCK cells transfected with the corresponding genes were secreted from both the apical and basolateral surfaces. These included proteins such as rat growth hormone, chicken oviduct lysozyme, bovine gastric prochymosin, and rat salivary gland alpha 2u-globulin, which in their cells of origin are secreted via a regulated pathway, as well as the liver form of the alpha 2u-globulin and the immunoglobulin kappa chain, which are normally released constitutively. These results demonstrate the existence of secretory pathways that lead to both surfaces of MDCK cells and are accessible to the foreign secretory products. They are consistent with the operation of a sorting mechanism in which the polarized secretion of the endogenous product is effected through the recognition of signals that prevent its random distribution within the fluid phase in the cellular endomembrane system.

  12. Anisotropic hybrid excitation modes in monolayer and double-layer phosphorene on polar substrates

    Science.gov (United States)

    Saberi-Pouya, S.; Vazifehshenas, T.; Salavati-fard, T.; Farmanbar, M.

    2017-09-01

    We investigate the anisotropic hybrid surface optical (SO) phonon-plasmon dispersion relations in monolayer and double-layer phosphorene systems located on the polar substrates, such as SiO2, h -BN, and Al2O3 . We calculate these hybrid modes by using the dynamical dielectric function in the random phase approximation in which the electron-electron interaction and long-range electric field generated by the substrate SO phonons via Fröhlich interaction are taken into account. In the long-wavelength limit, we obtain some analytical expressions for the hybrid SO phonon-plasmon dispersion relations which agree with those obtained from the loss function. Our results indicate a strong anisotropy in SO phonon-plasmon modes, which are stronger along the light-mass direction in our heterostructures. Furthermore, we find that the type of substrate has a significant effect on the dispersion relations of the coupled modes. Importantly, the hybrid excitations are apparently sensitive to the misalignment and separation between layers in double-layer phosphorene.

  13. Culture temperature affects human chondrocyte messenger RNA expression in monolayer and pellet culture systems.

    Directory of Open Access Journals (Sweden)

    Akira Ito

    Full Text Available Cell-based therapy has been explored for articular cartilage regeneration. Autologous chondrocyte implantation is a promising cell-based technique for repairing articular cartilage defects. However, there are several issues such as chondrocyte de-differentiation. While numerous studies have been designed to overcome some of these issues, only a few have focused on the thermal environment that can affect chondrocyte metabolism and phenotype. In this study, the effects of different culture temperatures on human chondrocyte metabolism- and phenotype-related gene expression were investigated in 2D and 3D environments. Human chondrocytes were cultured in a monolayer or in a pellet culture system at three different culture temperatures (32°C, 37°C, and 41°C for 3 days. The results showed that the total RNA level, normalized to the threshold cycle value of internal reference genes, was higher at lower temperatures in both culture systems. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH and citrate synthase (CS, which are involved in glycolysis and the citric acid cycle, respectively, were expressed at similar levels at 32°C and 37°C in pellet cultures, but the levels were significantly lower at 41°C. Expression of the chondrogenic markers, collagen type IIA1 (COL2A1 and aggrecan (ACAN, was higher at 37°C than at 32°C and 41°C in both culture systems. However, this phenomenon did not coincide with SRY (sex-determining region Y-box 9 (SOX9, which is a fundamental transcription factor for chondrogenesis, indicating that a SOX9-independent pathway might be involved in this phenomenon. In conclusion, the expression of chondrocyte metabolism-related genes at 32°C was maintained or enhanced compared to that at 37°C. However, chondrogenesis-related genes were further induced at 37°C in both culture systems. Therefore, manipulating the culture temperature may be an advantageous approach for regulating human chondrocyte metabolic activity and

  14. Proteomic Characterization of Primary Mouse Hepatocytes in Collagen Monolayer and Sandwich Culture.

    Science.gov (United States)

    Orsini, Malina; Sperber, Saskia; Noor, Fozia; Hoffmann, Esther; Weber, Susanne N; Hall, Rabea A; Lammert, Frank; Heinzle, Elmar

    2018-01-01

    Dedifferentiation of primary hepatocytes in vitro makes their application in long-term studies difficult. Embedding hepatocytes in a sandwich of extracellular matrix is reported to delay the dedifferentiation process to some extent. In this study, we compared the intracellular proteome of primary mouse hepatocytes (PMH) in conventional monolayer cultures (ML) to collagen sandwich culture (SW) after 1 day and 5 days of cultivation. Quantitative proteome analysis of PMH showed no differences between collagen SW and ML cultures after 1 day. Glycolysis and gluconeogenesis were strongly affected by long-term cultivation in both ML and SW cultures. Interestingly, culture conditions had no effect on cellular lipid metabolism. After 5 days, PMH in collagen SW and ML cultures exhibit characteristic indications of oxidative stress. However, in the SW culture the defense system against oxidative stress is significantly up-regulated to deal with this, whereas in the ML culture a down-regulation of these important enzymes takes place. Regarding the multiple effects of ROS and oxidative stress in cells, we conclude that the down-regulation of these enzymes seem to play a role in the loss of hepatic function observed in the ML cultivation. In addition, enzymes of the urea cycle were clearly down-regulated in ML culture. Proteomics confirms lack in oxidative stress defense mechanisms as the major characteristic of hepatocytes in monolayer cultures compared to sandwich cultures. J. Cell. Biochem. 119: 447-454, 2018. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  15. Human disc cells in monolayer vs 3D culture: cell shape, division and matrix formation

    Directory of Open Access Journals (Sweden)

    Hanley Edward N

    2000-10-01

    Full Text Available Abstract Background The relationship between cell shape, proliferation, and extracellular matrix (ECM production, important aspects of cell behavior, is examined in a little-studied cell type, the human annulus cell from the intervertebral disc, during monolayer vs three-dimensional (3D culture. Results Three experimental studies showed that cells respond specifically to culture microenvironments by changes in cell shape, mitosis and ECM production: 1 Cell passages showed extensive immunohistochemical evidence of Type I and II collagens only in 3D culture. Chondroitin sulfate and keratan sulfate were abundant in both monolayer and 3D cultures. 2 Cells showed significantly greater proliferation in monolayer in the presence of platelet-derived growth factor compared to cells in 3D. 3 Cells on Matrigel™-coated monolayer substrates became rounded and formed nodular colonies, a finding absent during monolayer growth. Conclusions The cell's in vivo interactions with the ECM can regulate shape, gene expression and other cell functions. The shape of the annulus cell changes markedly during life: the young, healthy disc contains spindle shaped cells and abundant collagen. With aging and degeneration, many cells assume a strikingly different appearance, become rounded and are surrounded by unusual accumulations of ECM products. In vitro manipulation of disc cells provides an experimental window for testing how disc cells from given individuals respond when they are grown in environments which direct cells to have either spindle- or rounded-shapes. In vitro assessment of the response of such cells to platelet-derived growth factor and to Matrigel™ showed a continued influence of cell shape even in the presence of a growth factor stimulus. These findings contribute new information to the important issue of the influence of cell shape on cell behavior.

  16. Choroid plexus epithelial monolayers – a cell culture model from porcine brain

    Directory of Open Access Journals (Sweden)

    Reichel Valeska

    2006-12-01

    Full Text Available Abstract Background The goal of the present study was to develop an in vitro choroid plexus (CP epithelial cell culture model for studying transport of protein-mediated drug secretion from blood to cerebrospinal fluid (CSF and vice versa. Methods Cells were isolated by mechanical and enzymatic treatment of freshly isolated porcine plexus tissue. Epithelial cell monolayers were grown and CSF secretion and transepithelial resistance were determined. The expression of f-actin as well as the choroid plexus marker protein transthyretin (TTR, were assessed. The expression of the export proteins p-glycoprotein (Pgp, Abcb1 and multidrug resistance protein 1 (Mrp1, Abcc1 was studied by RT-PCR, Western-blot and immunofluorescence techniques and their functional activity was assessed by transport and uptake experiments. Results Choroid plexus epithelial cells were isolated in high purity and grown to form confluent monolayers. Filter-grown monolayers displayed transendothelial resistance (TEER values in the range of 100 to 150 Ωcm2. Morphologically, the cells showed the typical net work of f-actin and expressed TTR at a high rate. The cultured cells were able to secrete CSF at a rate of 48.2 ± 4.6 μl/cm2/h over 2–3 hours. The ABC-export protein Mrp1 was expressed in the basolateral (blood-facing membranes of cell monolayers and intact tissue. P-glycoprotein showed only low expression within the apical (CSF directed membrane but was located more in sub-apical cell compartments. This finding was paralleled by the lack of directed excretion of p-glycoprotein substrates, verapamil and rhodamine 123. Conclusion It was demonstrated that CP epithelium can be isolated and cultured, with cells growing into intact monolayers, fully differentiating and with properties resembling the tissue in vivo. Thus, the established primary porcine CP model, allowing investigation of complex transport processes, can be used as a reliable tool for analysis of xenobiotic

  17. Thermoprotection of a functional epithelium: heat stress effects on transepithelial transport by flounder renal tubule in primary monolayer culture.

    OpenAIRE

    Brown, M A; Upender, R P; Hightower, L E; Renfro, J L

    1992-01-01

    Primary monolayer cultures of winter flounder renal proximal-tubule cells were used to determine whether transepithelial transport could be protected from the damaging effects of extreme temperature by previous mild heat shock. Renal tubule epithelial cells were enzymatically dispersed and reorganized as confluent monolayer sheets on native rat tail collagen. Transepithelial electrical properties (potential difference, resistance, short-circuit current, and Na(+)-dependent glucose current) an...

  18. Transferrin receptor expression and role in transendothelial transport of transferrin in cultured brain endothelial monolayers

    DEFF Research Database (Denmark)

    Hersom, Maria; Helms, Hans Christian; Pretzer, Natasia

    2016-01-01

    across the endothelial cells by transcytosis. The aim of the present study was to investigate transferrin receptor expression and role in transendothelial transferrin transport in cultured bovine brain endothelial cell monolayers. Transferrin receptor mRNA and protein levels were investigated......Receptor-mediated transcytosis of the transferrin receptor has been suggested as a potential transport system to deliver therapeutic molecules into the brain. Recent studies have however shown that therapeutic antibodies, which have been reported to cross the brain endothelium, reach greater brain...... in endothelial mono-cultures and co-cultures with astrocytes, as well as in freshly isolated brain capillaries using qPCR, immunocytochemistry and Western blotting. Transendothelial transport and luminal association of holo-transferrin was investigated using [125I]holo-transferrin or [59Fe...

  19. Spatiotemporal stability of neonatal rat cardiomyocyte monolayers spontaneous activity is dependent on the culture substrate.

    Directory of Open Access Journals (Sweden)

    Jonathan Boudreau-Béland

    Full Text Available In native conditions, cardiac cells must continuously comply with diverse stimuli necessitating a perpetual adaptation. Polydimethylsiloxane (PDMS is commonly used in cell culture to study cellular response to changes in the mechanical environment. The aim of this study was to evaluate the impact of using PDMS substrates on the properties of spontaneous activity of cardiomyocyte monolayer cultures. We compared PDMS to the gold standard normally used in culture: a glass substrate. Although mean frequency of spontaneous activity remained unaltered, incidence of reentrant activity was significantly higher in samples cultured on glass compared to PDMS substrates. Higher spatial and temporal instability of the spontaneous rate activation was found when cardiomyocytes were cultured on PDMS, and correlated with decreased connexin-43 and increased CaV3.1 and HCN2 mRNA levels. Compared to cultures on glass, cultures on PDMS were associated with the strongest response to isoproterenol and acetylcholine. These results reveal the importance of carefully selecting the culture substrate for studies involving mechanical stimulation, especially for tissue engineering or pharmacological high-throughput screening of cardiac tissue analog.

  20. Towards a defined ECM and small molecule based monolayer culture system for the expansion of mouse and human intestinal stem cells.

    Science.gov (United States)

    Tong, Zhixiang; Martyn, Keir; Yang, Andy; Yin, Xiaolei; Mead, Benjamin E; Joshi, Nitin; Sherman, Nicholas E; Langer, Robert S; Karp, Jeffrey M

    2018-02-01

    Current ISC culture systems face significant challenges such as animal-derived or undefined matrix compositions, batch-to-batch variability (e.g. Matrigel-based organoid culture), and complexity of assaying cell aggregates such as organoids which renders the research and clinical translation of ISCs challenging. Here, through screening for suitable ECM components, we report a defined, collagen based monolayer culture system that supports the growth of mouse and human intestinal epithelial cells (IECs) enriched for an Lgr5 + population comparable or higher to the levels found in a standard Matrigel-based organoid culture. The system, referred to as the Bolstering Lgr5 Transformational (BLT) Sandwich culture, comprises a collagen IV-coated porous substrate and a collagen I gel overlay which sandwich an IEC monolayer in between. The distinct collagen cues synergistically regulate IEC attachment, proliferation, and Lgr5 expression through maximizing the engagement of distinct cell surface adhesion receptors (i.e. integrin α2β1, integrin β4) and cell polarity. Further, we apply our BLT Sandwich system to identify that the addition of a bone morphogenetic protein (BMP) receptor inhibitor (LDN-193189) improves the expansion of Lgr5-GFP + cells from mouse small intestinal crypts by nearly 2.5-fold. Notably, the BLT Sandwich culture is capable of expanding human-derived IECs with higher LGR5 mRNA levels than conventional Matrigel culture, providing superior expansion of human LGR5 + ISCs. Considering the key roles Lgr5 + ISCs play in intestinal epithelial homeostasis and regeneration, we envision that our BLT Sandwich culture system holds great potential for understanding and manipulating ISC biology in vitro (e.g. for modeling ISC-mediated gut diseases) or for expanding a large number of ISCs for clinical utility (e.g. for stem cell therapy). Copyright © 2017 Elsevier Ltd. All rights reserved.

  1. Magnetic and electric control of spin- and valley-polarized transport across tunnel junctions on monolayer WSe2

    Science.gov (United States)

    Tahir, M.; Krstajić, P. M.; Vasilopoulos, P.

    2017-06-01

    The recent experimental realization of high-quality WSe2 leads to the possibility of an efficient manipulation of its spin and valley degrees of freedom. Its electronic properties comprise a huge spin-orbit coupling, a direct band gap, and a strong anisotropic lifting of the degeneracy of the valley degree of freedom in a magnetic field. We evaluate its band structure and study ballistic electron transport through single and double junctions (or barriers) on monolayer WSe2 in the presence of spin Ms and valley Mv Zeeman fields and of an electric potential U . The conductance versus the field Ms or Mv decreases in a fluctuating manner. For a single junction, the spin Ps and valley Pv polarizations rise with M =Mv=2 Ms , reach a value of more than 55 % , and become perfect above U ≈45 meV while for a double junction this change can occur for U ≥50 meV and M ≥5 meV. In certain regions of the (M ,U ) plane Pv becomes perfect. The conductance gc, its spin-up and spin-down components, and both polarizations oscillate with the barrier width d . The ability to isolate various carrier degrees of freedom in WSe2 may render it a promising candidate for new spintronic and valleytronic devices.

  2. Ultrastructural inquiries of the effects of X-radiation on melanocytes in monolayer cultures

    International Nuclear Information System (INIS)

    Hotzel, C.

    1984-01-01

    Melanocytes (HPM-73 cells) in monolayer culture, which in the exponential growth phase were irradiated with an X-ray dose of 8 Gy (800 rad) and 16 Gy (1600 rad), showed ultrastructural changes in the cell wall (for example, microvilli), in elements of the cytoskeleton (microtubules and microfilaments), of the mitochondria and a change in structures containing melanin (melanosomes/pre-melanosomes). As a control, melanocytes incubated in a culture medium containing serum were used. The irradiated cells showed morphologically tangible cell changes. It resulted in a strong development of the cytoskeleton (microtubules and microfilaments), an increase in lysosome-like structures, a re-orientation of cell wall structures in the form of a reduction of wall extensions (decrease in size of microvilli) and an increase in structures containing melanin. It was also noticed that the cells which had received 16 Gy (1600 rad) were damaged more than the cells which had received 8 Gy (800 rad), whereby the more highly irradiated cells still were not understood to be in 'disintegration'. All of these changes should be considered under the aspect of repair mechanisms after cell damage (irradiation). Altogether melanocytes are in comparison to other tumor cells less radiation sensitive. (orig.) [de

  3. EspM inhibits pedestal formation by enterohaemorrhagic Escherichia coli and enteropathogenic E. coli and disrupts the architecture of a polarized epithelial monolayer.

    Science.gov (United States)

    Simovitch, Michal; Sason, Hagit; Cohen, Shulamit; Zahavi, Eitan Erez; Melamed-Book, Naomi; Weiss, Aryeh; Aroeti, Benjamin; Rosenshine, Ilan

    2010-04-01

    Enterohaemorrhagic Escherichia coli and enteropathogenic E. coli are enteropathogens characterized by their ability to induce the host cell to form actin-rich structures, termed pedestals. A type III secretion system, through which the pathogens deliver effector proteins into infected host cells, is essential for their virulence and pedestal formation. Enterohaemorrhagic E. coli encodes two similar effectors, EspM1 and EspM2, which activate the RhoA signalling pathway and induce the formation of stress fibres upon infection of host cells. We confirm these observations and in addition show that EspM inhibits the formation of actin pedestals. Moreover, we show that translocation of EspM into polarized epithelial cells induces dramatic changes in the tight junction localization and in the morphology and architecture of infected polarized monolayers. These changes are manifested by altered localization of the tight junctions and 'bulging out' morphology of the cells. Surprisingly, despite the dramatic changes in their architecture, the cells remain alive and the epithelial monolayer maintains a normal barrier function. Taken together, our results show that the EspM effectors inhibit pedestal formation and induce tight junction mislocalization as well as dramatic changes in the architecture of the polarized monolayer.

  4. Cultured fibroblast monolayers secrete a protein that alters the cellular binding of somatomedin-C/insulinlike growth factor I

    International Nuclear Information System (INIS)

    Clemmons, D.R.; Elgin, R.G.; Han, V.K.; Casella, S.J.; D'Ercole, A.J.; Van Wyk, J.J.

    1986-01-01

    We studied somatomedin-C/insulinlike growth factor (Sm-C/IGF-I) binding to human fibroblasts in both adherent monolayers and in suspension cultures. The addition of Sm-C/IGF-I in concentrations between 0.5 and 10 ng/ml to monolayers cultures resulted in a paradoxical increase in 125 I-Sm-C/IGF-I binding and concentrations between 25 and 300 ng/ml were required to displace the labeled peptide. The addition of unlabeled insulin resulted in no displacement of labeled Sm-C/IGF-I from the adherent cells. When fibroblast suspensions were used Sm-C/IGF-I concentrations between 1 and 10 ng/ml caused displacement, the paradoxical increase in 125 I-Sm-C/IGF-I binding was not detected, and insulin displaced 60% of the labeled peptide. Affinity cross-linking to fibroblast monolayers revealed a 43,000-mol wt 125 I-Sm-C-binding-protein complex that was not detected after cross-linking to suspended cells. The 43,000-mol wt complex was not detected after cross-linking to smooth muscle cell monolayers, and binding studies showed that 125 I-Sm-C/IGF-I was displaced greater than 90% by Sm-C/IGF-I using concentrations between 0.5 and 10 ng/ml. Because fibroblast-conditioned medium contains the 43,000-mol wt complex, smooth muscle cells were incubated with conditioned medium for 24 h prior to initiation of the binding studies. 125 I-Sm-C/IGF-I-binding increased 1.6-fold compared to control cultures and after cross-linking the 43,000-mol wt complex could be detected on the smooth muscle cell surface. Human fibroblast monolayers secrete a protein that binds 125 I-Sm-C/IGF-I which can be transferred to the smooth muscle cell surface and alters 125I-Sm-C/IGF-I binding

  5. Human RPE Stem Cells Grown into Polarized RPE Monolayers on a Polyester Matrix Are Maintained after Grafting into Rabbit Subretinal Space

    Directory of Open Access Journals (Sweden)

    Boris V. Stanzel

    2014-01-01

    Full Text Available Transplantation of the retinal pigment epithelium (RPE is being developed as a cell-replacement therapy for age-related macular degeneration. Human embryonic stem cell (hESC and induced pluripotent stem cell (iPSC-derived RPE are currently translating toward clinic. We introduce the adult human RPE stem cell (hRPESC as an alternative RPE source. Polarized monolayers of adult hRPESC-derived RPE grown on polyester (PET membranes had near-native characteristics. Trephined pieces of RPE monolayers on PET were transplanted subretinally in the rabbit, a large-eyed animal model. After 4 days, retinal edema was observed above the implant, detected by spectral domain optical coherence tomography (SD-OCT and fundoscopy. At 1 week, retinal atrophy overlying the fetal or adult transplant was observed, remaining stable thereafter. Histology obtained 4 weeks after implantation confirmed a continuous polarized human RPE monolayer on PET. Taken together, the xeno-RPE survived with retained characteristics in the subretinal space. These experiments support that adult hRPESC-derived RPE are a potential source for transplantation therapies.

  6. Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

    Directory of Open Access Journals (Sweden)

    Peng Xia

    2017-11-01

    Full Text Available A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF state to low resistance (ON state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

  7. Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

    Science.gov (United States)

    Xia, Peng; Li, Luman; Wang, Pengfei; Gan, Ying; Xu, Wei

    2017-11-01

    A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM) Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF) state to low resistance (ON) state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

  8. [The persistence of the causative agent of amyotrophic leukospongiosis and the astrocyte reaction in monolayer cultures of brain cells].

    Science.gov (United States)

    Poleshchuk, N N; Kvacheva, Z B; Il'kevich, Iu G; Kolomiets, N D

    1990-01-01

    The amyotrophic leukospongiosis (AL) agent which is considered to be an unconventional virus was shown to replicate and amplify in non-neuronal monolayer brain cell cultures. The AL agent persistence was accompanied by complicated morphofunctional changes in astrocytes, some of them developing a specific cytodystrophic process. Phagocytosis in the infected astrocytes came to its end. The dose-dependent effect and selective sensitivity of these cells to the cytodestructive activity of AL was demonstrated. Astrocytes are regarded to be target cells serving as a reservoir for agent amplification.

  9. Differences in growth properties of endometrial cancer in three dimensional (3D) culture and 2D cell monolayer

    International Nuclear Information System (INIS)

    Chitcholtan, Kenny; Asselin, Eric; Parent, Sophie; Sykes, Peter H.; Evans, John J.

    2013-01-01

    Three-dimensional (3D) in vitro models have an invaluable role in understanding the behaviour of tumour cells in a well defined microenvironment. This is because some aspects of tumour characteristics cannot be fully recapitulated in a cell monolayer (2D). In the present study, we compared growth patterns, expression of signalling molecules, and metabolism-associated proteins of endometrial cancer cell lines in 3D and 2D cell cultures. Cancer cells formed spherical structures in 3D reconstituted basement membrane (3D rBM), and the morphological appearance was cell line dependent. Cell differentiation was observed after 8 days in the 3D rBM. There was reduced proliferation, detected by less expression of PCNA in 3D rBM than in 2D cell monolayers. The addition of exogenous epidermal growth factor (EGF) to cancer cells induced phosphorylation of EGFR and Akt in both cell culture conditions. The uptake of glucose was selectively altered in the 3D rBM, but there was a lack of association with Glut-1 expression. The secretion of vascular endothelial growth factor (VEGF) and prostaglandin E 2 (PGE 2 ) was selectively altered in 3D rBM, and it was cell line dependent. Our data demonstrated that 3D rBM as an in vitro model can influence proliferation and metabolism of endometrial cancer cell behaviour compared to 2D cell monolayer. Changes are specific to individual cell types. The use of 3D rBM is, therefore, important in the in vitro study of targeted anticancer therapies.

  10. Differences in growth properties of endometrial cancer in three dimensional (3D) culture and 2D cell monolayer

    Energy Technology Data Exchange (ETDEWEB)

    Chitcholtan, Kenny, E-mail: kenny.chitcholtan@otago.ac.nz [Department of Obstetrics and Gynaecology, University of Otago, Christchurch, 2 Riccarton Avenue, Christchurch 8011 (New Zealand); Asselin, Eric, E-mail: Eric.Asselin@uqtr.ca [Department of Chemistry and Biology, University of Quebec, at Trois-Rivières, C.P. 500, Trois-Rivières, Quebec, Canada G9A 5H7 (Canada); Parent, Sophie, E-mail: Sophie.Parent@uqtr.ca [Department of Chemistry and Biology, University of Quebec, at Trois-Rivières, C.P. 500, Trois-Rivières, Quebec, Canada G9A 5H7 (Canada); Sykes, Peter H., E-mail: peter.sykes@otago.ac.nz [Department of Obstetrics and Gynaecology, University of Otago, Christchurch, 2 Riccarton Avenue, Christchurch 8011 (New Zealand); Evans, John J., E-mail: john.evans@otago.ac.nz [Department of Obstetrics and Gynaecology, University of Otago, Christchurch, 2 Riccarton Avenue, Christchurch 8011 (New Zealand); Centre of Neuroendocrinology and The MacDiarmid Institute of Advanced Materials and Nanotechnology, University of Otago, Christchurch, 2 Riccarton Avenue, Christchurch 8011 (New Zealand)

    2013-01-01

    Three-dimensional (3D) in vitro models have an invaluable role in understanding the behaviour of tumour cells in a well defined microenvironment. This is because some aspects of tumour characteristics cannot be fully recapitulated in a cell monolayer (2D). In the present study, we compared growth patterns, expression of signalling molecules, and metabolism-associated proteins of endometrial cancer cell lines in 3D and 2D cell cultures. Cancer cells formed spherical structures in 3D reconstituted basement membrane (3D rBM), and the morphological appearance was cell line dependent. Cell differentiation was observed after 8 days in the 3D rBM. There was reduced proliferation, detected by less expression of PCNA in 3D rBM than in 2D cell monolayers. The addition of exogenous epidermal growth factor (EGF) to cancer cells induced phosphorylation of EGFR and Akt in both cell culture conditions. The uptake of glucose was selectively altered in the 3D rBM, but there was a lack of association with Glut-1 expression. The secretion of vascular endothelial growth factor (VEGF) and prostaglandin E{sub 2} (PGE{sub 2}) was selectively altered in 3D rBM, and it was cell line dependent. Our data demonstrated that 3D rBM as an in vitro model can influence proliferation and metabolism of endometrial cancer cell behaviour compared to 2D cell monolayer. Changes are specific to individual cell types. The use of 3D rBM is, therefore, important in the in vitro study of targeted anticancer therapies.

  11. Growth and Functionality of Cells Cultured on Conducting and Semi-Conducting Surfaces Modified with Self-Assembled Monolayers (SAMs

    Directory of Open Access Journals (Sweden)

    Rajendra K. Aithal

    2016-02-01

    Full Text Available Bioengineering of dermal and epidermal cells on surface modified substrates is an active area of research. The cytotoxicity, maintenance of cell phenotype and long-term functionality of human dermal fibroblast (HDF cells on conducting indium tin oxide (ITO and semi-conducting, silicon (Si and gallium arsenide (GaAs, surfaces modified with self-assembled monolayers (SAMs containing amino (–NH2 and methyl (–CH3 end groups have been investigated. Contact angle measurements and infrared spectroscopic studies show that the monolayers are conformal and preserve their functional end groups. Morphological analyses indicate that HDFs grow well on all substrates except GaAs, exhibiting their normal spindle-shaped morphology and exhibit no visible signs of stress or cytoplasmic vacuolation. Cell viability analyses indicate little cell death after one week in culture on all substrates except GaAs, where cells died within 6 h. Cells on all surfaces proliferate except on GaAs and GaAs-ODT. Cell growth is observed to be greater on SAM modified ITO and Si-substrates. Preservation of cellular phenotype assessed through type I collagen immunostaining and positive staining of HDF cells were observed on all modified surfaces except that on GaAs. These results suggest that conducting and semi-conducting SAM-modified surfaces support HDF growth and functionality and represent a promising area of bioengineering research.

  12. Differential feedback regulation of cholesterol 7α-hydroxylase mRNA and transcriptional activity by rat bile acids in primary monolayer cultures of rat hepatocytes

    NARCIS (Netherlands)

    Twisk, J.; Lehmann, E.M.; Princen, H.M.G.

    1993-01-01

    We have used primary monolayer cultures of rat hepatocytes to study the effects of physiological concentrations of various bile acids, commonly found in bile of normal rats, on the mechanism of regulation of cholesterol 7α-hydroxylase and bile acid synthesis. Addition of taurocholic acid, the most

  13. The effect of the non-ionic surfactant Brij 30 on the cytotoxicity of adriamycin in monolayer, spheroid and clonogenic culture systems.

    Science.gov (United States)

    Kerr, D J; Wheldon, T E; Russell, J G; Maurer, H R; Florence, A T; Halbert, G W; Freshney, R I; Kaye, S B

    1987-09-01

    The effects of a non-ionic polyoxyethylated lauryl ether surfactant (Brij 30) on monolayer uptake and spheroid penetration of adriamycin have been studied. Co-incubation of adriamycin with Brij 30 increases intracellular adriamycin levels by 2-3-fold. Although, in the concentrations used, Brij 30 alone is not cytotoxic, adriamycin and Brij 30 mixtures are significantly more cytotoxic (monolayer ID90 = 0.6 microgram/ml; disaggregated spheroid ID50 = 1.9 micrograms/ml) and induce significantly longer spheroid growth delay than adriamycin alone (monolayer ID90 = 2.1 micrograms/ml; disaggregated spheroid ID50 = 3.3 micrograms/ml). Adriamycin is equally cytotoxic to mouse normal granulocytes and chronic myeloid leukaemic (M1 cell line) cells in agar clonogenic cultures. The addition of Brij 30 appears to enhance preferentially the activity of adriamycin against these tumour cells relative to the normal granulocytes.

  14. Monte Carlo studies of thermalization of electron-hole pairs in spin-polarized degenerate electron gas in monolayer graphene

    Science.gov (United States)

    Borowik, Piotr; Thobel, Jean-Luc; Adamowicz, Leszek

    2018-02-01

    Monte Carlo method is applied to the study of relaxation of excited electron-hole (e-h) pairs in graphene. The presence of background of spin-polarized electrons, with high density imposing degeneracy conditions, is assumed. To such system, a number of e-h pairs with spin polarization parallel or antiparallel to the background is injected. Two stages of relaxation: thermalization and cooling are clearly distinguished when average particles energy and its standard deviation σ _E are examined. At the very beginning of thermalization phase, holes loose energy to electrons, and after this process is substantially completed, particle distributions reorganize to take a Fermi-Dirac shape. To describe the evolution of and σ _E during thermalization, we define characteristic times τ _ {th} and values at the end of thermalization E_ {th} and σ _ {th}. The dependence of these parameters on various conditions, such as temperature and background density, is presented. It is shown that among the considered parameters, only the standard deviation of electrons energy allows to distinguish between different cases of relative spin polarizations of background and excited electrons.

  15. Repair of wounded monolayers of cultured bovine aortic endothelial cells is inhibited by calcium spirulan, a novel sulfated polysaccharide isolated from Spirulina platensis.

    Science.gov (United States)

    Kaji, Toshiyuki; Fujiwara, Yasuyuki; Inomata, Yuki; Hamada, Chieko; Yamamoto, Chika; Shimada, Satomi; Lee, Jung-Bum; Hayashi, Toshimitsu

    2002-03-08

    Calcium spirulan (Ca-SP) is a novel sulfated polysaccharide isolated from a blue-green alga Spirulina platensis. Ca-SP inhibits thrombin by activation of heparin cofactor II. Therefore, it could serve as an origin of anti-atherogenic medicines. Since maintenance of vascular endothelial cell monolayers is important for prevention of vascular lesions such as atherosclerosis, the effect of Ca-SP at 20 microg/ml or less on the repair of wounded bovine aortic endothelial cell monolayers in culture was investigated in the present study. When the monolayers were wounded and cultured in the presence of Ca-SP, the polysaccharide inhibited the appearance of the cells in the wounded area. The inhibition was also observed even when the repair was promoted by excess basic fibroblast growth factor, which is one of the autocrine growth factors that are involved in the endothelial cell monolayer maintenance. On the other hand, Ca-SP inhibited the cell growth and the incorporation of [3H]thymidine into the acid-insoluble fraction of proliferating endothelial cells, suggesting that Ca-SP inhibits endothelial cell proliferation. From these results, it is concluded that Ca-SP may retard the repair process of damaged vascular endothelium through inhibition of vascular endothelial cell proliferation by induction of a lower ability to respond to stimulation by endogenous basic fibroblast growth factor.

  16. Conditioned Medium of Wharton's Jelly Derived Stem Cells Can Enhance the Cartilage Specific Genes Expression by Chondrocytes in Monolayer and Mass Culture Systems

    Directory of Open Access Journals (Sweden)

    Maryam Hassan Famian

    2017-04-01

    Full Text Available Purpose: Mesenchymal stem cells (MSCs have been introduced for cell therapy strategies in osteoarthritis (OA. Despite of their capacity for differentiation into chondrocyte, there are some evidences about their life-threatening problem after transplantation. So, some researchers shifted on the application of stem cells conditioned medium. The goal of this study is to evaluate whether Wharton's jelly derived stem cell conditioned medium (WJSCs-CM can enhance the gene expression profile by chondrocytes in monolayer and mass culture systems. Methods: Conditioned medium was obtained from WJSCs at fourth passage. Isolated chondrocytes were plated at density of 1×106 for both monolayer and high density culture. Then cells in both groups were divided into control (received medium and experiment group treated with WJ-CM for 3 and 6 days. Samples were prepared to evaluate gene expression profile of collagen II, aggrecan, cartilage oligomeric matrix protein (COMP and sox-9 using real-time RT-PCR. Results: After 3 days, Chondrocytes treated with WJSCs-CM expressed significantly higher level of genes compared to the control group in both culture systems. After 6 days, the expression of genes in monolayer cultivated chondrocytes was decreased but that of the mass culture were up-regulated significantly. Conclusion: WJ-SCs-CM can increase the expression of cartilage-specific genes and can be introduced as a promoting factor for cartilage regeneration.

  17. Salicylate effects on a monolayer culture of gastric mucous cells from adult rats.

    OpenAIRE

    Ota, S; Razandi, M; Sekhon, S; Krause, W J; Terano, A; Hiraishi, H; Ivey, K J

    1988-01-01

    Aspirin, acetyl salicylic acid, damages gastric mucosal cells. This effect is considered related to its inhibition of prostaglandin synthesis. On the other hand, sodium salicylate has been reported to be cytoprotective against drug damage to gastric mucosa in vivo. One reason for this difference is that salicylic acid, unlike acetyl salicylic acid does not inhibit prostaglandin synthesis by gastric mucosa in vivo. Previous studies on tissue culture cells from our laboratory have required gast...

  18. Injection-modulated polarity conversion by charge carrier density control via a self-assembled monolayer for all-solution-processed organic field-effect transistors

    Science.gov (United States)

    Roh, Jeongkyun; Lee, Taesoo; Kang, Chan-Mo; Kwak, Jeonghun; Lang, Philippe; Horowitz, Gilles; Kim, Hyeok; Lee, Changhee

    2017-04-01

    We demonstrated modulation of charge carrier densities in all-solution-processed organic field-effect transistors (OFETs) by modifying the injection properties with self-assembled monolayers (SAMs). The all-solution-processed OFETs based on an n-type polymer with inkjet-printed Ag electrodes were fabricated as a test platform, and the injection properties were modified by the SAMs. Two types of SAMs with different dipole direction, thiophenol (TP) and pentafluorobenzene thiol (PFBT) were employed, modifying the work function of the inkjet-printed Ag (4.9 eV) to 4.66 eV and 5.24 eV with TP and PFBT treatments, respectively. The charge carrier densities were controlled by the SAM treatment in both dominant and non-dominant carrier-channel regimes. This work demonstrates that control of the charge carrier densities can be efficiently achieved by modifying the injection property with SAM treatment; thus, this approach can achieve polarity conversion of the OFETs.

  19. Gold cleaning methods for preparation of cell culture surfaces for self-assembled monolayers of zwitterionic oligopeptides.

    Science.gov (United States)

    Enomoto, Junko; Kageyama, Tatsuto; Myasnikova, Dina; Onishi, Kisaki; Kobayashi, Yuka; Taruno, Yoko; Kanai, Takahiro; Fukuda, Junji

    2018-01-15

    Self-assembled monolayers (SAMs) have been used to elucidate interactions between cells and material surface chemistry. Gold surfaces modified with oligopeptide SAMs exhibit several unique characteristics, such as cell-repulsive surfaces, micropatterns of cell adhesion and non-adhesion regions for control over cell microenvironments, and dynamic release of cells upon external stimuli under culture conditions. However, basic procedures for the preparation of oligopeptide SAMs, including appropriate cleaning methods of the gold surface before modification, have not been fully established. Because gold surfaces are readily contaminated with organic compounds in the air, cleaning methods may be critical for SAM formation. In this study, we examined the effects of four gold cleaning methods: dilute aqua regia, an ozone water, atmospheric plasma, and UV irradiation. Among the methods, UV irradiation most significantly improved the formation of oligopeptide SAMs in terms of repulsion of cells on the surfaces. We fabricated an apparatus with a UV light source, a rotation table, and HEPA filter, to treat a number of gold substrates simultaneously. Furthermore, UV-cleaned gold substrates were capable of detaching cell sheets without serious cell injury. This may potentially provide a stable and robust approach to oligopeptide SAM-based experiments for biomedical studies. Copyright © 2017 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

  20. TU-H-CAMPUS-TeP3-01: Gold Nanoparticle-Enhanced Radiation Therapy in In Vitro A549 Lung Carcinoma: Studies in Both Traditional Monolayer and Three Dimensional Cell Culture Models

    Energy Technology Data Exchange (ETDEWEB)

    Oumano, M [Baystate Medical Center, Springfield, MA (United States); University of Massachusetts Lowell, Lowell, MA (United States); Ngwa, W [University of Massachusetts Lowell, Lowell, MA (United States); Harvard Medical School, Boston, MA (United States); Celli, J; Hempstead, J; Petrovic, L [University of Massachusetts Boston, Boston, MA (United States); Arnoldussen, M; Hanlon, J [Oraya Therapeutics inc., Newark, CA (United States)

    2016-06-15

    Purpose: To measure the increase in in vitro radiosensitivity for A549 lung carcinoma cells due to gold nanoparticle (GNP) radiation dose enhancement in both traditional monolayer and three dimensional (3D) cell culture models. Methods: A γH2AX immunofluorescence assay is performed on monolayer A549 cell culture and quantitatively analyzed to measure the increase in double strand breaks (DSBs) resulting from GNP dose enhancement. A clonogenic survival assay (CSA) is then performed on monolayer A549 cell culture to assess true viability after treatment. And lastly, another γH2AX assay is performed on 3D A549 multicellular nodules overlaid on a bed of growth factor reduced matrigel to measure dose response in a model that better recapitulates treatment response to actual tumors in vivo. Results: The first γH2AX assay performed on the monolayer cell culture shows a significant increase in DSBs due to GNP dose enhancement. The maximum average observed increase in normalized fluorescent intensity for monolayer cell culture is 171% for the 6Gy-treatment groups incubated in 0.556 mg Au/ml solution. The CSA performed on monolayer cell culture also shows considerable GNP dose enhancement. The maximum decrease in the normalized surviving fraction is 12% for the 4Gy-treatment group incubated in 0.556 mg Au/ml. And lastly, the GNP dose enhancement is confirmed to be mitigated in three dimensional cell culture models as compared to the traditional monolayer model. The maximum average observed dose enhancement for 3D cell culture is 19% for the 6Gy-treatment groups and incubated in 0.556 mg Au/ml. Conclusion: A marked increase in radiosensitivity is observed for A549 lung carcinoma cells when treated with GNPs plus radiation as opposed to radiation alone. Traditional monolayer cell culture also shows a much more pronounced radiation dose enhancement than 3D cell culture.

  1. Monolayer culturing and cloning of human pluripotent stem cells on laminin-521-based matrices under xeno-free and chemically defined conditions.

    Science.gov (United States)

    Rodin, Sergey; Antonsson, Liselotte; Hovatta, Outi; Tryggvason, Karl

    2014-10-01

    A robust method for culturing human pluripotent stem (hPS) cells under chemically defined and xeno-free conditions is an important tool for stem cell research and for the development of regenerative medicine. Here, we describe a protocol for monolayer culturing of Oct-4-positive hPS cells on a specific laminin-521 (LN-521) isoform, under xeno-free and chemically defined conditions. The cells are dispersed into single-cell suspension and then plated on LN-521 isoform at densities higher than 5,000 cells per cm², where they attach, migrate and survive by forming small monolayer cell groups. The cells avidly divide and expand horizontally until the entire dish is covered by a confluent monolayer. LN-521, in combination with E-cadherin, allows cloning of individual hPS cells in separate wells of 96-well plates without the presence of rho-associated protein kinase (ROCK) inhibitors or any other inhibitors of anoikis. Characterization of cells maintained for several months in culture reveals pluripotency with a minimal degree of genetic abnormalities.

  2. Experimental Investigation Of Microbially Induced Corrosion Of Test Samples And Effect Of Self-assembled Hydrophobic Monolayers. Exposure Of Test Samples To Continuous Microbial Cultures, Chemical Analysis, And Biochemical Studies

    CERN Document Server

    Laurinavichius, K S

    1998-01-01

    Experimental Investigation Of Microbially Induced Corrosion Of Test Samples And Effect Of Self-assembled Hydrophobic Monolayers. Exposure Of Test Samples To Continuous Microbial Cultures, Chemical Analysis, And Biochemical Studies

  3. A New In Vitro Model to Study Cellular Responses after Thermomechanical Damage in Monolayer Cultures

    Science.gov (United States)

    Hettler, Alice; Werner, Simon; Eick, Stefan; Laufer, Stefan; Weise, Frank

    2013-01-01

    Although electrosurgical instruments are widely used in surgery to cut tissue layers or to achieve hemostasis by coagulation (electrocautery), only little information is available concerning the inflammatory or immune response towards the debris generated. Given the elevated local temperatures required for successful electrocautery, the remaining debris is likely to contain a plethora of compounds entirely novel to the intracorporal setting. A very common in vitro method to study cell migration after mechanical damage is the scratch assay, however, there is no established model for thermomechanical damage to characterise cellular reactions. In this study, we established a new in vitro model to investigate exposure to high temperature in a carefully controlled cell culture system. Heatable thermostat-controlled aluminium stamps were developed to induce local damage in primary human umbilical vein endothelial cells (HUVEC). The thermomechanical damage invoked is reproducibly locally confined, therefore allowing studies, under the same experimental conditions, of cells affected to various degrees as well as of unaffected cells. We show that the unaffected cells surrounding the thermomechanical damage zone are able to migrate into the damaged area, resulting in a complete closure of the ‘wound’ within 48 h. Initial studies have shown that there are significant morphological and biological differences in endothelial cells after thermomechanical damage compared to the mechanical damage inflicted by using the unheated stamp as a control. Accordingly, after thermomechanical damage, cell death as well as cell protection programs were activated. Mononuclear cells adhered in the area adjacent to thermomechanical damage, but not to the zone of mechanical damage. Therefore, our model can help to understand the differences in wound healing during the early phase of regeneration after thermomechanical vs. mechanical damage. Furthermore, this model lends itself to study the

  4. Expression of circadian core clock genes in fibroblasts of human gingiva and periodontal ligament is modulated by L-Mimosine and hypoxia in monolayer and spheroid cultures.

    Science.gov (United States)

    Janjić, Klara; Kurzmann, Christoph; Moritz, Andreas; Agis, Hermann

    2017-07-01

    The circadian clock is involved in a plethora of physiological processes including bone formation and tooth development. While expression of circadian core clock genes was observed in various tissues, their role in the periodontium is unclear. We hypothesized that periodontal cells express circadian core clock genes and that their levels are modulated by hypoxia mimetic agents and hypoxia. Fibroblasts of human gingiva (GF) and periodontal ligament (PDLF) in monolayer and spheroid cultures were treated with the hypoxia mimetic agent L-Mimosine (L-MIM) or hypoxia. Reverse transcription and quantitative PCR were performed to assess the impact on mRNA levels of the circadian core clock genes Clock, Bmal1, Cry1, Cry2, Per1, Per2, and Per3. GF and PDLF expressed Clock, Bmal1, Cry1, Cry2, Per1, Per2, and Per3 in monolayer and spheroid cultures. In monolayer cultures, L-MIM significantly reduced Clock, Cry2, and Per3 mRNA expression in GF and Clock, Cry1, Cry2, Per1, and Per3 in PDLF. Hypoxia significantly reduced Clock, Cry2, and Per3 in GF and Cry1, Cry2, and Per3 in PDLF. In spheroid cultures, L-MIM significantly decreased Clock, Cry1, Cry2, and Per3 in GF and PDLF. Hypoxia significantly decreased Cry2 and Per3 in GF and Clock and Per3 in PDLF. GF and PDLF express circadian core clock genes. The hypoxia mimetic agent L-MIM and hypoxic conditions can decrease the expression of Clock, Cry1-2 and Per1 and Per3. The specific response depends on cell type and culture model. Future studies will show how this effect contributes to periodontal health and disease. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Apical polarity in three-dimensional culture systems: where to now?

    Energy Technology Data Exchange (ETDEWEB)

    Inman, J.L.; Bissell, Mina

    2010-01-21

    Delineation of the mechanisms that establish and maintain the polarity of epithelial tissues is essential to understanding morphogenesis, tissue specificity and cancer. Three-dimensional culture assays provide a useful platform for dissecting these processes but, as discussed in a recent study in BMC Biology on the culture of mammary gland epithelial cells, multiple parameters that influence the model must be taken into account.

  6. Comparison of genotoxic damage in monolayer cell cultures and three-dimensional tissue-like cell assemblies

    Science.gov (United States)

    Behravesh, E.; Emami, K.; Wu, H.; Gonda, S.

    Assessing the biological risks associated with exposure to the high-energy charged particles encountered in space is essential for the success of long-term space exploration. Although prokaryotic and eukaryotic cell models developed in our laboratory and others have advanced our understanding of many aspects of genotoxicity, in vitro models are needed to assess the risk to humans from space radiation insults. Such models must be representative of the cellular interactions present in tissues and capable of quantifying genotoxic damage. Toward this overall goal, the objectives of this study were to examine the effect of the localized microenvironment of cells, cultured as either 2-dimensional (2D) monolayers or 3-dimensional (3D) aggregates, on the rate and type of genotoxic damage resulting from exposure to Fe-charged particles, a significant portion of space radiation. We used rodent transgenic cell lines containing 50-70 copies of a LacI transgene to provide the enhanced sensitivity required to quantify mutational frequency and type in the 1100-bp LacI target as well as assessment of DNA damage to the entire 45-kbp construct. Cultured cells were exposed to high-energy Fe charged particles at Brookhaven National Laboratory's Alternating Gradient Synchrotron facility for a total dose ranging from 0.1 to 2 Gy and allowed to recover for 0-7 days, after which mutational type and frequency were evaluated. The mutational frequency was found to be higher in 3D samples than in 2D samples at all radiation doses. Mutational frequency also was higher at 7 days after irradiation than immediately after exposure. DNA sequencing of the mutant targets revealed that deletional mutations contributed an increasingly high percentage (up to 27%) of all mutations in cells as the dose was increased from 0.5 to 2 Gy. Several mutants also showed large and complex deletions in multiple locations within the LacI target. However, no differences in mutational type were found between the 2D and

  7. Development and Characterization of a Human and Mouse Intestinal Epithelial Cell Monolayer Platform

    Directory of Open Access Journals (Sweden)

    Kenji Kozuka

    2017-12-01

    Full Text Available Summary: We describe the development and characterization of a mouse and human epithelial cell monolayer platform of the small and large intestines, with a broad range of potential applications including the discovery and development of minimally systemic drug candidates. Culture conditions for each intestinal segment were optimized by correlating monolayer global gene expression with the corresponding tissue segment. The monolayers polarized, formed tight junctions, and contained a diversity of intestinal epithelial cell lineages. Ion transport phenotypes of monolayers from the proximal and distal colon and small intestine matched the known and unique physiology of these intestinal segments. The cultures secreted serotonin, GLP-1, and FGF19 and upregulated the epithelial sodium channel in response to known biologically active agents, suggesting intact secretory and absorptive functions. A screen of over 2,000 pharmacologically active compounds for inhibition of potassium ion transport in the mouse distal colon cultures led to the identification of a tool compound. : Siegel and colleagues describe their development of a human and mouse intestinal epithelial cell monolayer platform that maintains the cellular, molecular, and functional characteristics of tissue for each intestinal segment. They demonstrate the platform's application to drug discovery by screening a library of over 2,000 compounds to identify an inhibitor of potassium ion transport in the mouse distal colon. Keywords: intestinal epithelium, organoids, monolayer, colon, small intestine, phenotype screening assays, enteroid, colonoid

  8. A convenient fluorometric method to study sulfur mustard-induced apoptosis in human epidermal keratinocytes monolayer microplate culture.

    Science.gov (United States)

    Ray, Radharaman; Hauck, Stephanie; Kramer, Rachel; Benton, Betty

    2005-01-01

    Sulfur mustard [SM; bis-(2-chloroethyl) sulfide], which causes skin blistering or vesication [(1991). Histo- and cytopathology of acute epithelial lesions. In: Papirmeister, B., Feister, A. J., Robinson, S. I., Ford, R. D., eds. Medical Defense Against Mustard Gas: Toxic Mechanisms and Pharmacological Implications. Boca Raton: CRC Press, pp. 43-78.], is a chemical warfare agent as well as a potential terrorism agent. SM-induced skin blistering is believed to be due to epidermal-dermal detachment as a result of epidermal basal cell death via apoptosis and/or necrosis. Regarding the role of apoptosis in SM pathology in animal skin, the results obtained in several laboratories, including ours, suggest the following: 1) cell death due to SM begins via apoptosis that proceeds to necrosis via an apoptotic-necrotic continuum and 2) inhibiting apoptosis decreases SM-induced microvesication in vivo. To study the mechanisms of SM-induced apoptosis and its prevention in vitro, we have established a convenient fluorometric apoptosis assay using monolayer human epidermal keratinocytes (HEK) adaptable for multiwell plates (24-, 96-, or 384-well) and high-throughput applications. This assay allows replication and multiple types of experimental manipulation in sister cultures so that the apoptotic mechanisms and the effects of test compounds can be compared statistically. SM affects diverse cellular mechanisms, including endoplasmic reticulum (ER) Ca2+ homeostasis, mitochondrial functions, energy metabolism, and death receptors, each of which can independently trigger apoptosis. However, the biochemical pathway in any of these apoptotic mechanisms is characterized by a pathway-specific sequence of caspases, among which caspase-3 is a key member. Therefore, we exposed 80-90% confluent HEK cultures to SM and monitored apoptosis by measuring the fluorescence generated due to hydrolysis of a fluorogenic caspase-3 substrate (acetyl- or benzyl oxycarbonyl

  9. Polarized Airway Epithelial Models for Immunological Co-Culture Studies

    DEFF Research Database (Denmark)

    Papazian, Dick; Würtzen, Peter A; Hansen, Søren Werner Karlskov

    2016-01-01

    of the epithelial response towards environmental antigens and genetic susceptibility, resulting in inflammation and T cell-derived immune responses. In vivo animal models have long been used to study immune homeostasis of the airways but are limited by species restriction and lack of exposure to a natural......Epithelial cells line all cavities and surfaces throughout the body and play a substantial role in maintaining tissue homeostasis. Asthma and other atopic diseases are increasing worldwide and allergic disorders are hypothesized to be a consequence of a combination of dysregulation......-culture models to become powerful tools in the discovery of key molecules dictating immunity and/or tolerance, and for understanding the complex interplay that takes place between mucosa, airway epithelium and resident or infiltrating immune cells. This review focuses on current knowledge and the advantages...

  10. Intensification of the inhibitory effect of X-rays on the growth of Ehrlich ascites tumor cells in monolayer culture by quinacrine (atebrine) or chloroquine (resochine)

    International Nuclear Information System (INIS)

    Biller, H.; Pfab, R.; Hess, F.; Schachtschabel, D.O.; Leising, H.B.

    1980-01-01

    Monolayers of Ehrlich ascites tumor cells in their logarithmic phase of growth were exposed to a single X-ray dose of 1 to 16 Gy. Following exposure, the monolayers were cultured for several days or weeks with or without an addition of 4 x to 6 x 10 -6 M of quinacrine (atebrine) or 3.3 x 10 -5 to 1 x 10 -4 M of chloroquine. Proliferation activity was controlled by the daily microscopical count of representative areas out of the total population. A significant delay resulted from exposure to 4 Gy (particularly during the 1st day), while sole irradiation with 1 or 2 Gy did not much influence the proliferation of the cells. An 8-Gy dose and to a larger extent 16 Gy led to a fall of the cell number down to 20% (8 Gy) or around 10% (16 Gy) of the initial value between the 7th and the 10th day. The cells subsequently multiplied with nearly the growth rate of controls. The inhibitory effect on cells proliferation produced by an exposure to X-rays was distinctly intensified by means of incubation with continuously replaced quinacrine or chloroquine containing culture media. Treatment with 1 x 10 -4 mol chloroquine thus brought about a more pronounced inhibition after pre-irradiation with a single dose of 2 or 8 Gy. If 4 x 10 -6 or 6 x 10 -6 M of quinacrine were added to cultures pretreated with 4 Gy, a more intense inhibition of growth resulted therefrom than from sole treatment with either quinacrine or X-rays. Incubation of cultures pretreated with 8 Gy in the presence of 6 x 10 -6 M quinacrine led to the death of all the cells within 8 days. Quinacrine and chloroquine effects on cells previously exposed to X-rays are discussed in view of the well-known effects these agents exert by inhibiting enzymatic repair processes of DNA damage. (orig.) [de

  11. Polarity establishment, morphogenesis, and cultured plant cells in space

    Science.gov (United States)

    Krikorian, Abraham D.

    1989-01-01

    Plant development entails an orderly progression of cellular events both in terms of time and geometry. There is only circumstantial evidence that, in the controlled environment of the higher plant embryo sac, gravity may play a role in embryo development. It is still not known whether or not normal embryo development and differentiation in higher plants can be expected to take place reliably and efficiently in the micro g space environment. It seems essential that more attention be given to studying aspects of reproductive biology in order to be confident that plants will survive seed to seed to seed in a space environment. Until the time arrives when successive generations of plants can be grown, the best that can be done is utilize the most appropriate systems and begin, piece meal, to accumulate information on important aspects of plant reproduction. Cultured plant cells can play an important role in these activities since they can be grown so as to be morphogenetically competent, and thus can simulate those embryogenic events more usually identified with fertilized eggs in the embryo sac of the ovule in the ovary. Also, they can be manipulated with relative ease. The extreme plasticity of such demonstrably totipotent cell systems provides a means to test environmental effects such as micro g on a potentially free-running entity. The successful manipulation and management of plant cells and propagules in space also has significance for exploitation of biotechnologies in space since such systems, perforce, are an important vehicle whereby many genetic engineering manipulations are achieved.

  12. Drug and radiation sensitivity measurements of successful primary monolayer culturing of human tumor cells using cell-adhesive matrix and supplemented medium

    International Nuclear Information System (INIS)

    Baker, F.L.; Spitzer, G.; Ajani, J.A.

    1986-01-01

    The limitations of the agar suspension culture method for primary culturing of human tumor cells prompted development of a monolayer system optimized for cell adhesion and growth. This method grew 83% of fresh human tumor cell biopsy specimens, cultured and not contaminated, from a heterogeneous group of 396 tumors including lung cancer (93 of 114, 82%); melanoma (54 of 72, 75%); sarcoma (46 of 59, 78%); breast cancer (35 of 39, 90%); ovarian cancer (16 of 21, 76%); and a miscellaneous group consisting of gastrointestinal, genitourinary, mesothelioma, and unknown primaries (78 of 91, 86%). Cell growth was characterized morphologically with Papanicolaoustained coverslip cultures and cytogenetically with Giemsastained metaphase spreads. Morphological features such as nuclear pleomorphism, chromatin condensation, basophilic cytoplasm, and melanin pigmentation were routinely seen. Aneuploid metaphases were seen in 90% of evaluable cultures, with 15 of 28 showing 70% or more aneuploid metaphases. Colony-forming efficiency ranged between 0.01 and 1% of viable tumor cells, with a median efficiency of 0.2%. This culture system uses a low inoculum of 25,000 viable cells per well which permitted chemosensitivity testing of nine drugs at four doses in duplicate from 2.2 X 10(6) viable tumor cells and radiation sensitivity testing at five doses in quadruplicate from 0.6 X 10(6) cells. Cultures were analyzed for survival by computerized image analysis of crystal violet-stained cells. Drug sensitivity studies showed variability in sensitivity and in survival curve shape with exponential cell killing for cisplatin, Adriamycin, and etoposide, and shouldered survival curves for 5-fluorouracil frequently seen. Radiation sensitivity studies also showed variability in both sensitivity and survival curve shape. Many cultures showed exponential cell killing, although others had shouldered survival curves

  13. Perforated monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Regen, S.L.

    1992-12-01

    Goal of this research program is to create ultrathin organic membranes that possess uniform and adjustable pores ( < 7[angstrom] diameter). Such membranes are expected to possess high permeation selectivity (permselectivity) and high permeability, and to provide the basis for energy-efficient methods of molecular separation. Work carried out has demonstrated feasibility of using perforated monolayer''-based composites as molecular sieve membranes. Specifically, composite membranes derived from Langmuir-Blodgett multilayers of the calix[6]arene-based surfactant shown below plus poly[l-(trimethylsilyl)-l-propyne] (PTMSP) were found to exhibit sieving behavior towards He, N[sub 2] and SF[sub 6]. Results of derivative studies that have also been completed are also described in this report.

  14. Action of X-rays and neuraminidase on pinocytotic activity and microtubule-microfilament system of Ehrlich ascites tumor cells in monolayer culture

    Energy Technology Data Exchange (ETDEWEB)

    Pfab, R.; Hess, F.; Schachtschabel, D.O.; Paul, N.; Kern, H.F.

    1981-07-01

    Monolayer cultures of Ehrlich ascites tumor cells in exponential growth phase were treated with X-rays and neuraminidase alone or in combination. A radiation dose of 2 Gy (200 rd) and higher effected a significant inhibition of DNA synthesis and cell proliferation. Neuraminidase treatment in addition to irradiation did not modify the growth-inhibitory irradiation effect. Cells pretreated for 0.5 to 1.0 hours with neuraminidase (in Earle's salt solution) and cultured thereafter (4 h) in serum-containing growth medium exhibited an enhanced development of the microtube-microfilament-system. Morphometric analysis of microtubulus on electronmicroscopic sections revealed a nearly 4-fold increased number in neuraminidase treated cells while the average length of microtubules was similar to controls. Pinocytosis as measured by the ultrastructural uptake of ferritin appeared to be increased following neuraminidase treatment. A connection between neuraminic acid containing components (glycoproteins or glycolipids) of the cell membrane or cell surface, on the one hand, and the cytoskeleton and the endocytotic process of these tumor cells, on the other hand, is suggested.

  15. Human adipose-derived mesenchymal stem cells improve motor functions and are neuroprotective in the 6-hydroxydopamine-rat model for Parkinson's disease when cultured in monolayer cultures but suppress hippocampal neurogenesis and hippocampal memory function when cultured in spheroids.

    Science.gov (United States)

    Berg, Jürgen; Roch, Manfred; Altschüler, Jennifer; Winter, Christine; Schwerk, Anne; Kurtz, Andreas; Steiner, Barbara

    2015-02-01

    Adult human adipose-derived mesenchymal stem cells (MSC) have been reported to induce neuroprotective effects in models for Parkinson's disease (PD). However, these effects strongly depend on the most optimal application of the transplant. In the present study we compared monolayer-cultured (aMSC) and spheroid (sMSC) MSC following transplantation into the substantia nigra (SN) of 6-OHDA lesioned rats regarding effects on the local microenvironment, degeneration of dopaminergic neurons, neurogenesis in the hippocampal DG as well as motor and memory function in the 6-OHDA-rat model for PD. aMSC transplantation significantly increased tyrosine hydroxylase (TH) and brain-derived neurotrophic factor (BDNF) levels in the SN, increased the levels of the glial fibrillary acidic protein (GFAP) and improved motor functions compared to untreated and sMSC treated animals. In contrast, sMSC grafting induced an increased local microgliosis, decreased TH levels in the SN and reduced numbers of newly generated cells in the dentate gyrus (DG) without yet affecting hippocampal learning and memory function. We conclude that the neuroprotective potential of adipose-derived MSC in the rat model of PD crucially depends on the applied cellular phenotype.

  16. Polarized Trafficking of AQP2 Revealed in Three Dimensional Epithelial Culture.

    Directory of Open Access Journals (Sweden)

    William L Rice

    Full Text Available In renal collecting duct (CD principal cells (PCs, vasopressin (VP acts through its receptor, V2R, to increase intracellular cAMP leading to phosphorylation and apical membrane accumulation of the water channel aquaporin 2 (AQP2. The trafficking and function of basolaterally located AQP2 is, however, poorly understood. Here we report the successful application of a 3-dimensional Madin-Darby canine kidney (MDCK epithelial model to study polarized AQP2 trafficking. This model recapitulates the luminal architecture of the CD and bi-polarized distribution of AQP2 as seen in kidney. Without stimulation, AQP2 is located in the subapical and basolateral regions. Treatment with VP, forskolin (FK, or 8-(4-Chlorophenylthio-2'-O-methyladenosine 3',5'-cyclic monophosphate monosodium hydrate (CPT-cAMP leads to translocation of cytosolic AQP2 to the apical membrane, but not to the basolateral membrane. Treating cells with methyl-β-cyclodextrin (mβCD to acutely block endocytosis causes accumulation of AQP2 on the basolateral membrane, but not on the apical membrane. Our data suggest that AQP2 may traffic differently at the apical and basolateral domains in this 3D epithelial model. In addition, application of a panel of phosphorylation specific AQP2 antibodies reveals the polarized, subcellular localization of differentially phosphorylated AQP2 at S256, S261, S264 and S269 in the 3D culture model, which is consistent with observations made in the CDs of VP treated animals, suggesting the preservation of phosphorylation dependent regulatory mechanism of AQP2 trafficking in this model. Therefore we have established a 3D culture model for the study of trafficking and regulation of both the apical and basolaterally targeted AQP2. The new model will enable further characterization of the complex mechanism regulating bi-polarized trafficking of AQP2 in vitro.

  17. Ultrastructural investigations about the effect of X-rays and quinacrine (Atebrin) - alone or in combination - upon Ehrlich ascitic carcinoma cells in monolayer culture

    Energy Technology Data Exchange (ETDEWEB)

    Pfab, R.; Biller, H.; Hess, F.; Schachtschabel, D.O.; Paul, N.

    1983-08-01

    Already two days after an X-ray irradiation with 8 Gy performed during the phase of exponential growth, the cells of an Ehrlich ascitic carcinoma in monolayer culture showed remarkable ultrastructural modifications, e.g. a markedly vacuolized endoplasmic reticulum, swollen mitochondria, increase of lysosome-like structures, and a decrease of microvilli in number and size. Ehrlich ascitic carcinoma cells submitted to an X-ray irradiation with 8 Gy and subsequently incubated with quinacrine (Atebrin) in a concentration of 4x10/sup -6/ M, which alone had no significant effects on growth or ultrastructure, showed severe cellular lesions. The endoplasmic reticulum was still more vacuolized, the mitochondria were severely damaged, lysosome-like structures and residual bodies were increased, and the cellular surfaces had still less microvilli. Microtubules and microfilaments, however, seemed rather increased. The effects of quinacrine (Atebrin) on cells exposed to X-rays were discussed with respect to the known inhibiting action of this substance on DNA synthesis, especially with regard to DNA reparation. The modifications of the microtubule-microfilament system could be correlated to increased intracellular digestive processes involved in the catabolism of radiodamaged structures.

  18. Differential osteogenicity of multiple donor-derived human mesenchymal stem cells and osteoblasts in monolayer, scaffold-based 3D culture and in vivo.

    Science.gov (United States)

    Quent, Verena M C; Theodoropoulos, Christina; Hutmacher, Dietmar W; Reichert, Johannes C

    2016-06-01

    We set out to compare the osteogenicity of human mesenchymal stem (hMSCs) and osteoblasts (hOBs). Upon osteogenic induction in monolayer, hMSCs showed superior matrix mineralization expressing characteristic bone-related genes. For scaffold cultures, both cell types presented spindle-shaped, osteoblast-like morphologies forming a dense, interconnected network of high viability. On the scaffolds, hOBs proliferated faster. A general upregulation of parathyroid hormone-related protein (PTHrP), osteoprotegrin (OPG), receptor activator of NF-κB ligand (RANKL), sclerostin (SOST), and dentin matrix protein 1 (DMP1) was observed for both cell types. Simultaneously, PTHrP, RANKL and DMP-1 expression decreased under osteogenic stimulation, while OPG and SOST increased significantly. Following transplantation into NOD/SCID mice, μCT and histology showed increased bone deposition with hOBs. The bone was vascularized, and amounts further increased for both cell types after recombinant human bone morphogenic protein 7 (rhBMP-7) addition also stimulating osteoclastogenesis. Complete bone organogenesis was evidenced by the presence of osteocytes and hematopoietic precursors. Our study results support the asking to develop 3D cellular models closely mimicking the functions of living tissues suitable for in vivo translation.

  19. Influence of serum extraction from the culture medium and of sublethal X-ray irradiation upon microvilli and invaginations of the membrane of Ehrlich ascites tumor cells in monolayer culture

    Energy Technology Data Exchange (ETDEWEB)

    Laudenbach, G.; Pfab, R.; Hess, F.; Schachtschabel, D.O.

    1984-09-01

    In order to find out modifications of microvilli and invaginations, the cellular surfaces of Ehrlich ascites tumor cells in monolayer culture (basal medium of Eagle + 10% fetal calf serum) were investigated with the aid of electron-microscopic cross-sections. The tumor cells had been cultured without serum 24 hours prior to investigation or irradiated with 2 Gy. Morphometric evaluation after cell culture in a serum-free medium showed a reduced number of microvilli and a diminution of sections of microvilli. As already described before, a reduction of cell proliferation, of the microtubule-microfilament system, and of the endocytosis activity occurs under these serum-free conditions. The number of invaginations (related to a constant membrane part) was reduced by nearly 50% after serum extraction. Similarly to serum extraction, sublethal X-ray irradiation reduced the sections of microvilli, whereas the number of microvilli increased slightly. Contrary to the effect of serum extraction, the irradiated cells showed twice as many invaginations as the non-irradiated control cells. These differences in the surface structures are interpreted as a result of modified growth stimulations (+- serum) and radiogenic reparation processes.

  20. Disorder-dependent valley properties in monolayer WSe2

    KAUST Repository

    Tran, Kha

    2017-07-19

    We investigate the effect of disorder on exciton valley polarization and valley coherence in monolayer WSe2. By analyzing the polarization properties of photoluminescence, the valley coherence (VC) and valley polarization (VP) are quantified across the inhomogeneously broadened exciton resonance. We find that disorder plays a critical role in the exciton VC, while affecting VP less. For different monolayer samples with disorder characterized by their Stokes shift (SS), VC decreases in samples with higher SS while VP does not follow a simple trend. These two methods consistently demonstrate that VC as defined by the degree of linearly polarized photoluminescence is more sensitive to disorder, motivating further theoretical studies.

  1. Large-area and bright pulsed electroluminescence in monolayer semiconductors

    KAUST Repository

    Lien, Der-Hsien

    2018-04-04

    Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electroluminescent device based on transition-metal dichalcogenide monolayers (MoS, WS, MoSe, and WSe) to overcome these problems. Electroluminescence from this dopant-free two-terminal device is obtained by applying an AC voltage between the gate and the semiconductor. Notably, the electroluminescence intensity is weakly dependent on the Schottky barrier height or polarity of the contact. We fabricate a monolayer seven-segment display and achieve the first transparent and bright millimeter-scale light-emitting monolayer semiconductor device.

  2. Perforated monolayers. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Regen. Steven L.

    2000-06-01

    This STI is a final report for a DOE-supported program, ''Perforated Monolayers,'' which focused on the fabrication of ultrathin membranes for gas separations based on Langmuir-Blodgett chemistry.

  3. Antibiotic interaction with phospholipid monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Gambinossi, F.; Mecheri, B.; Caminati, G.; Nocentini, M.; Puggelli, M.; Gabrielli, G

    2002-12-01

    We studied the interactions of tetracycline (TC) antibiotic molecules with phospholipid monolayers with the two-fold aim of elucidating the mechanism of action and providing a first step for the realization of bio-mimetic sensors for such drugs by means of the Langmuir-Blodgett technique. We examined spreading monolayers of three phospholipids in the presence of tetracycline in the subphase by means of surface pressure-area and surface potential-area isotherms as a function of bulk pH. We selected phospholipids with hydrophobic chains of the same length but polar head groups differing either in dimensions and protonation equilibria, i.e. dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE) and dipalmitoylphosphatidic acid (DPPA). The interaction of tetracycline with the three phospholipids was found to be highly dependent on the electric charge of the antibiotic and on the ionization state of the lipid. Significant interactions are established between the negatively charged form of dipalmitoylphosphatidic acid and the zwitterionic form of tetracycline. The drug was found to migrate at the interface where it is adsorbed underneath or/and among the head groups, depending on the surface pressure of the film, whereas penetration through the hydrophobic layer was excluded for all the three phospholipids.

  4. Liver progenitor cells develop cholangiocyte-type epithelial polarity in three-dimensional culture.

    OpenAIRE

    Tanimizu, Naoki; Miyajima, Atsushi; Mostov, Keith E

    2007-01-01

    Cholangiocytes are cellular components of the bile duct system of the liver, which originate from hepatoblasts during embryonic liver development. Although several transcription factors and signaling molecules have been implicated in bile duct development, its molecular mechanism has not been studied in detail. Here, we applied a three-dimensional (3D) culture technique to a liver progenitor cell line, HPPL, to establish an in vitro culture system in which HPPL acquire differentiated cholangi...

  5. Polarization Second Harmonic Generation Discriminates Between Fresh and Aged Starch-Based Adhesives Used in Cultural Heritage.

    Science.gov (United States)

    Psilodimitrakopoulos, Sotiris; Gavgiotaki, Evaggelia; Melessanaki, Kristallia; Tsafas, Vassilis; Filippidis, George

    2016-10-01

    In this work, we report that polarization second harmonic generation (PSHG) microscopy, commonly used in biomedical imaging, can quantitatively discriminate naturally aged from fresh starch-based glues used for conservation or restoration of paintings, works of art on paper, and books. Several samples of fresh and aged (7 years) flour and starch pastes were investigated by use of PSHG. In these types of adhesives, widely used in cultural heritage conservation, second harmonic generation (SHG) contrast originates primarily from the starch granules. It was found that in aged glues, the starch SHG effective orientation (SHG angle, θ) shifts to significantly higher values in comparison to the fresh granules. This shift is attributed to the different degree of granule hydration between fresh and aged adhesives. Thus noninvasive high-resolution nonlinear scattering can be employed to detect and quantify the degree of deterioration of restoration adhesives and to provide guidance toward future conservation treatments.

  6. The three-dimensional cultivation of the carcinoma cell line HepG2 in a perfused chip system leads to a more differentiated phenotype of the cells compared to monolayer culture

    Energy Technology Data Exchange (ETDEWEB)

    Altmann, B; Giselbrecht, S; Weibezahn, K-F; Welle, A; Gottwald, E [Forschungszentrum Karlsruhe, Institute for Biological Interfaces, 76344 Eggenstein-Leopoldshafen (Germany)], E-mail: eric.gottwald@ibg.fzk.de

    2008-09-01

    We describe a polymer chip with a grid-like architecture that it is intended for the three-dimensional cultivation of cells with an active nutrient and gas supply. The chip is typically made from polymethyl methacrylate or polycarbonate but can also be manufactured from biodegradable polymers, such as poly(lactic-co-glycolic acid). Different designs of the chip can be realized. In this study, we evaluated a chip with 506 microcontainers of the size of 300 x 300 x 300 {mu}m that are capable of housing up to 6 million cells, and its suitability as a tissue-specific culture system for the carcinoma cell line HepG2 instead of primary liver cells. Related to an earlier study, where we could show the principal suitability of the system for rat primary cells, we here investigated the system's suitability for the human carcinoma cell line HepG2. The carcinoma cells were used in two different types of chip-containing bioreactors. By confocal laser scanning microscopy, we could show that cellular integrity in the chip culture was maintained and that there were no signs of apoptosis as confirmed by the absence of K18 fragmentation. Gene expression analysis of some liver-specific genes revealed a significantly higher expression of the phase II metabolism genes uridine-diphosphate- glucosyl-transferase (UGT1A1) and glutathione-S-transferase (GST{pi}1) as a marker. Therefore, we conclude that by using a three-dimensional instead of a conventional monolayer culture system, hepatocellular carcinoma cells display a phenotype that resembles more closely the tissue of origin.

  7. ISOLATION AND PRIMARY CULTURES OF HUMAN INTRAHEPATIC BILE DUCTULAR EPITHELIUM

    Science.gov (United States)

    Demetris, A. J.; Markus, B. H.; Saidman, S.; Fung, J. J.; Makowka, L.; Graner, S.; Duquesnoy, R.; Starzl, T. E.

    2010-01-01

    SUMMARY A technique for the isolation of human intrahepatic bile ductular epithelium, and the establishment of primary cultures using a serum- and growth-factor-supplemented medium combined with a connective tissue substrata is described. Initial cell isolates and monolayer cultures display phenotypic characteristics of biliary epithelial cells (low molecular weight prekeratin positive; albumin, alphafetoprotein, and Factor VIII-related antigen negative). Ultrastructural features of the cultured cells show cell polarization with surface microvilli, numerous interepithelial junctional complexes and cytoplasmic intermediate prekeratin filaments. PMID:3131298

  8. Monolayer Superconductivity in WS2

    NARCIS (Netherlands)

    Zheliuk, Oleksandr; Lu, Jianming; Yang, Jie; Ye, Jianting

    Superconductivity in monolayer tungsten disulfide (2H-WS2) is achieved by strong electrostatic electron doping of an electric double-layer transistor (EDLT). Single crystals of WS2 are grown by a scalable method - chemical vapor deposition (CVD) on standard Si/SiO2 substrate. The monolayers are

  9. Transport of monocarboxylic acids at the blood-brain barrier: Studies with monolayers of primary cultured bovine brain capillary endothelial cells

    International Nuclear Information System (INIS)

    Terasaki, T.; Takakuwa, S.; Moritani, S.; Tsuji, A.

    1991-01-01

    The kinetics and mechanism of the transport of monocarboxylic acids (MCAs) were studied by using primary cultured bovine brain capillary endothelial cells. Concentration-dependent uptake of acetic acid was observed, and the kinetic parameters were estimated as follows: the Michaelis constant, Kt, was 3.41 ± 1.87 mM, the maximum uptake rate, Jmax, was 144.7 ± 55.7 nmol/mg of protein/min and the nonsaturable first-order rate constant, Kd, was 6.66 ± 1.98 microliters/mg of protein/min. At medium pH below 7.0, the uptake rate of [3H]acetic acid increased markedly with decreasing medium pH, whereas pH-independent uptake was observed in the presence of 10 mM acetic acid. An energy requirement for [3H]acetic acid uptake was also demonstrated, because metabolic inhibitors (2,4-dinitrophenol and rotenone) reduced significantly the uptake rate (P less than .05). Carbonylcyanide-p-trifluoro-methoxyphenylhydrazone, a protonophore, inhibited significantly the uptake of [3H]acetic acid at medium pH of 5.0 and 6.0, whereas 4,4'-diisothiocyanostilben-2,2'-disulfonic acid did not. Several MCAs inhibited significantly the uptake rate of [3H]acetic acid, whereas di- and tricarboxylic acids did not. The uptake of [3H]acetic acid was competitively inhibited by salicylic acid, with an inhibition constant, Ki, of 3.60 mM, suggesting a common transport system between acetic acid and salicylic acid. Moreover, at the medium pH of 7.4, salicylic acid and valproic acid inhibited significantly the uptake of [3H]acetic acid, demonstrating that the transport of MCA drugs could also be ascribed to the MCA transport system at the physiologic pH

  10. Subcellular topological effect of particle monolayers on cell shapes and functions.

    Science.gov (United States)

    Miura, Manabu; Fujimoto, Keiji

    2006-12-01

    We studied topological effects of subcellular roughness displayed by a closely packed particle monolayer on adhesion and growth of endothelial cells. Poly(styrene-co-acrylamide) (SA) particles were prepared by soap-free emulsion copolymerization. Particle monolayers were prepared by Langmuir-Blodgett deposition using particles, which were 527 (SA053) and 1270 nm (SA127) in diameter. After 24-h incubation, cells tightly adhered on a tissue culture polystyrene dish and randomly spread. On the other hand, cells attached on particle monolayers were stretched into a narrow stalk-like shape. Lamellipodia spread from the leading edge of cells attached on SA053 monolayer to the top of the particles and gradually gathered to form clusters. This shows that cell-cell adhesion became stronger than cell-substrate interaction. Cells attached to SA127 monolayer extended to the reverse side of a particle monolayer and engulfed particles. They remained immobile without migration 24h after incubation. This shows that the inhibition of extensions on SA127 monolayer could inhibit cell migration and cell proliferation. Cell growth on the particle monolayers was suppressed compared with a flat TCPS dish. The number of cells on SA053 gradually increased, whereas that on SA127 decreased with time. When the cell seeding density was increased to 200,000 cells cm(-2), some adherent cells gradually became into contact with adjacent cells. F-actin condensations were formed at the frame of adherent cells and the thin filaments grew from the edges to connect each other with time. For the cell culture on SA053 monolayer, elongated cells showed a little alignment. Cells showed not arrangement of actin stress fibers but F-actin condensation at the contact regions with neighboring cells. Interestingly, the formed cell monolayer could be readily peeled from the particle monolayer. These results indicate that endothelial cells could recognize the surface roughness displayed by particle monolayers and

  11. Treponema pallidum Invades Intercellular Junctions of Endothelial Cell Monolayers

    Science.gov (United States)

    Thomas, D. Denee; Navab, Mahamad; Haake, David A.; Fogelman, Alan M.; Miller, James N.; Lovett, Michael A.

    1988-05-01

    The pathogenesis of syphilis reflects invasive properties of Treponema pallidum, but the actual mode of tissue invasion is unknown. We have found two in vitro parallels of treponemal invasiveness. We tested whether motile T. pallidum could invade host cells by determining the fate of radiolabeled motile organisms added to a HeLa cell monolayer; 26% of treponemes associated with the monolayer in a trypsin-resistant niche, presumably between the monolayer and the surface to which it adhered, but did not attain intracellularity. Attachment of T. pallidum to cultured human and rabbit aortic and human umbilical vein endothelial cells was 2-fold greater than to HeLa cells. We added T. pallidum to aortic endothelial cells grown on membrane filters under conditions in which tight intercellular junctions had formed. T. pallidum was able to pass through the endothelial cell monolayers without altering tight junctions, as measured by electrical resistance. In contrast, heat-killed T. pallidum and the nonpathogen Treponema phagedenis biotype Reiter failed to penetrate the monolayer. Transmission electron micrographs of sections of the monolayer showed T. pallidum in intercellular junctions. Our in vitro observations suggest that these highly motile spirochetes may leave the circulation by invading the junctions between endothelial cells.

  12. Long-term Renewable Human Intestinal Epithelial Stem Cells as Monolayers: A Potential for Clinical Use

    Science.gov (United States)

    Scott, Andrew; Rouch, Joshua D; Jabaji, Ziyad; Khalil, Hassan A; Solorzano, Sergio; Lewis, Michael; Martín, Martín G.; Stelzner, Matthias G.; Dunn, James C.Y.

    2016-01-01

    Purpose Current culture schema for human intestinal stem cells (hISCs) frequently rely on a 3D culture system using Matrigel™, a laminin-rich matrix derived from murine sarcoma that is not suitable for clinical use. We have developed a novel 2D culture system for the in vitro expansion of hISCs as an intestinal epithelial monolayer without the use of Matrigel. Methods Cadaveric duodenal samples were processed to isolate intestinal crypts from the mucosa. Crypts were cultured on a thin coat of type I collagen or laminin. Intestinal epithelial monolayers were supported with growth factors to promote self-renewal or differentiation of the hISCs. Proliferating monolayers were sub-cultured every 4–5 days. Results Intestinal epithelial monolayers were capable of long-term cell renewal. Less differentiated monolayers expressed high levels of gene marker LGR5, while more differentiated monolayers had higher expressions of CDX2, MUC2, LYZ, DEF5, and CHGA. Furthermore, monolayers were capable of passaging into a 3D culture system to generate spheroids and enteroids. Conclusion This 2D system is an important step to expand hISCs for further experimental studies and for clinical cell transplantation. PMID:26995514

  13. Luminescent Organic Semiconducting Langmuir Monolayers.

    Science.gov (United States)

    Agina, Elena V; Mannanov, Artur A; Sizov, Alexey S; Vechter, Olga; Borshchev, Oleg V; Bakirov, Artem V; Shcherbina, Maxim A; Chvalun, Sergei N; Konstantinov, Vladislav G; Bruevich, Vladimir V; Kozlov, Oleg V; Pshenichnikov, Maxim S; Paraschuk, Dmitry Yu; Ponomarenko, Sergei A

    2017-05-31

    In recent years, monolayer organic field-effect devices such as transistors and sensors have demonstrated their high potential. In contrast, monolayer electroluminescent organic field-effect devices are still in their infancy. One of the key challenges here is to create an organic material that self-organizes in a monolayer and combines efficient charge transport with luminescence. Herein, we report a novel organosilicon derivative of oligothiophene-phenylene dimer D2-Und-PTTP-TMS (D2, tetramethyldisiloxane; Und, undecylenic spacer; P, 1,4-phenylene; T, 2,5-thiophene; TMS, trimethylsilyl) that meets these requirements. The self-assembled Langmuir monolayers of the dimer were investigated by steady-state and time-resolved photoluminescence spectroscopy, atomic force microscopy, X-ray reflectometry, and grazing-incidence X-ray diffraction, and their semiconducting properties were evaluated in organic field-effect transistors. We found that the best uniform, fully covered, highly ordered monolayers were semiconducting. Thus, the ordered two-dimensional (2D) packing of conjugated organic molecules in the semiconducting Langmuir monolayer is compatible with its high-yield luminescence, so that 2D molecular aggregation per se does not preclude highly luminescent properties. Our findings pave the way to the rational design of functional materials for monolayer organic light-emitting transistors and other optoelectronic devices.

  14. Electronic and Magnetic Properties of Rare-Earth Metals Doped ZnO Monolayer

    Directory of Open Access Journals (Sweden)

    Changlong Tan

    2015-01-01

    Full Text Available The structural, electronic, and magnetic properties of rare-earth metals doped ZnO monolayer have been investigated using the first-principles calculations. The induced spin polarization is confirmed for Ce, Eu, Gd, and Dy dopings while the induced spin polarization is negligible for Y doping. The localized f states of rare-earth atoms respond to the introduction of a magnetic moment. ZnO monolayer undergoes transition from semiconductor to metal in the presence of Y, Ce, Gd, and Dy doping. More interestingly, Eu doped ZnO monolayer exhibits half-metallic behavior. Our result demonstrates that the RE-doping is an efficient route to modify the magnetic and electronic properties in ZnO monolayer.

  15. Monolayers and mixed-layers on copper towards corrosion protection

    Energy Technology Data Exchange (ETDEWEB)

    Sinapi, F. [Fonds pour la Formation a la Recherche dans l' Industrie et dans l' Agriculture, Rue d' Egmont 5, B-1000 Brussels (Belgium); Julien, S.; Auguste, D.; Hevesi, L.; Delhalle, J. [Laboratory of Chemistry and Electrochemistry of Surfaces, University of Namur, FUNDP, Rue de Bruxelles, 61, B-5000 Namur (Belgium); Mekhalif, Z. [Laboratory of Chemistry and Electrochemistry of Surfaces, University of Namur, FUNDP, Rue de Bruxelles, 61, B-5000 Namur (Belgium)], E-mail: zineb.mekhalif@fundp.ac.be

    2008-05-01

    In order to improve the protection abilities of (3-mercaptopropy)trimethoxysilane (MPTS) self-assembled monolayers on copper surfaces, mixed monolayers have been formed successfully by successive immersions in MPTS and in n-dodecanethiol (DT). A newly synthesised molecule, (11-mercaptoundecyl)trimethoxysilane (MUTS), has also been employed to form a thicker organic film on copper surfaces and, thereby, enhance the inhibitory action of the coating. The grafting has been confirmed by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection adsorption spectroscopy (PM-IRRAS) and water contact angle. The protective efficiency of each protective organic film has been evidenced by cyclic voltammetry (CV) and polarization curve measurements (CP). It was shown that the MUTS and unhydrolyzed MPTS/DT films exhibited significant corrosion protection properties.

  16. Electrokinetics of Polar Liquids in Contact with Non-Polar Surfaces

    OpenAIRE

    Lin, Chih-Hsiu; Ferguson, Gregory S.; Chaudhury, Manoj K.

    2014-01-01

    Zeta potentials of several polar protic (water, ethylene glycol, formamide) as well as polar aprotic (dimethyl sulfoxide) liquids were measured in contact with three non-polar surfaces using closed-cell electro-osmosis. The test surfaces were chemisorbed monolayers of alkyl siloxanes, fluoroalkyl siloxanes and polydimethylsiloxanes (PDMS) grafted on glass slides. All these liquids exhibited substantial electrokinetics in contact with the non-polar surfaces with these observations: the electro...

  17. Phase transitions in surfactant monolayers

    International Nuclear Information System (INIS)

    Casson, B.D.

    1998-01-01

    Two-dimensional phase transitions have been studied in surfactant monolayers at the air/water interface by sum-frequency spectroscopy and ellipsometry. In equilibrium monolayers of medium-chain alcohols C n H 2n+1 OH (n = 9-14) a transition from a two-dimensional crystalline phase to a liquid was observed at temperatures above the bulk melting point. The small population of gauche defects in the solid phase increased only slightly at the phase transition. A model of the hydrocarbon chains as freely rotating rigid rods allowed the area per molecule and chain tilt in the liquid phase to be determined. The area per molecule, chain tilt and density of the liquid phase all increased with increasing chain length, but for each chain length the density was higher than in a bulk liquid hydrocarbon. In a monolayer of decanol adsorbed at the air/water interface a transition from a two-dimensional liquid to a gas was observed. A clear discontinuity in the coefficient of ellipticity as a function of temperature showed that the transition is first-order. This result suggests that liquid-gas phase transitions in surfactant monolayers may be more widespread than once thought. A solid-liquid phase transition has also been studied in mixed monolayers of dodecanol with an anionic surfactant (sodium dodecyl sulphate) and with a homologous series of cationic surfactants (alkyltrimethylammonium bromides: C n TABs, n = 12, 14, 16). The composition and structure of the mixed monolayers was studied above and below the phase transition. At low temperatures the mixed monolayers were as densely packed as a monolayer of pure dodecanol in its solid phase. At a fixed temperature the monolayers under-went a first-order phase transition to form a phase that was less dense and more conformationally disordered. The proportion of ionic surfactant in the mixed monolayer was greatest in the high temperature phase. As the chain length of the C n TAB increased the number of conformational defects

  18. Growth of cells superinoculated onto irradiated and nonirradiated confluent monolayers

    International Nuclear Information System (INIS)

    Matsuoka, H.; Ueo, H.; Sugimachi, K.

    1990-01-01

    We prepared confluent monolayers of normal BALB/c 3T3 cells and compared differences in the growth of four types of cells superinoculated onto these nonirradiated and irradiated monolayers. The test cells were normal BALB/c 3T3 A31 cells, a squamous cell carcinoma from a human esophageal cancer (KSE-1), human fetal fibroblasts, and V-79 cells from Chinese hamster lung fibroblasts. Cell growth was checked by counting the cell number, determining [3H]thymidine incorporation and assessing colony formation. We found that on nonirradiated monolayers, colony formation of human fetal fibroblasts and normal BALB/c 3T3 cells was completely inhibited. On irradiated cells, test cells did exhibit some growth. KSE-1 cells, which had a low clonogenic efficiency on plastic surfaces, formed colonies on both irradiated and nonirradiated cells. On these monolayers, the clonogenic efficiency of V-79 cells was also higher than that on plastic surfaces. We conclude that the nonirradiated monolayer of BALB/c 3T3 cells completely inhibits the growth of superinoculated normal BALB/c 3T3 and human fetal fibroblasts, while on the other hand, they facilitate the growth of neoplastic KSE-1 and V-79 cells by providing a surface for cell adherence and growth, without affecting the presence of normal cells in co-cultures

  19. Structures and shear response of lipid monolayers

    International Nuclear Information System (INIS)

    Dutta, P.; Ketterson, J.B.

    1993-02-01

    This report discusses our work during the last 3 years using x-ray diffraction and shear measurements to study lipid monolayers (membranes). The report is divided into: (1) structure: phase diagram of saturated fatty acid Langmuir monolayers, effect of head group interactions, studies of transferred monolayers (LB films); (2) mechanical properties: fiber=optic capillary wave probe and centrosymmetric trough, mechanical behavior of heneicosanoic acid monolayer phases

  20. Valley-selective optical Stark effect in monolayer WS2

    Science.gov (United States)

    Gedik, Nuh

    Monolayer semiconducting transition-metal dichalcogenides (TMDs) have a pair of valleys that, by time-reversal symmetry, are energetically degenerate. Lifting the valley degeneracy in these materials is of great interest because it would allow for valley specific band engineering and offer additional control in valleytronic applications. In this talk, I will show that circularly polarized light, which breaks time-reversal symmetry, can be used to lift the valley degeneracy by means of the optical Stark effect. We demonstrate that this effect is capable of raising the exciton level in monolayer TMD WS2 by as much as 18 meV in a controllable valley-selective manner. The resulting energy shift is extremely large, comparable to the shift that would be obtained using a very high magnetic field (approximately 100 Tesla). These results offer a novel way to control valley degree of freedom, and may provide a means to realize new valley-selective Floquet topological state of matter.

  1. Metformin affects the features of a human hepatocellular cell line (HepG2) by regulating macrophage polarization in a co-culture microenviroment.

    Science.gov (United States)

    Chen, Miaojiao; Zhang, Jingjing; Hu, Fang; Liu, Shiping; Zhou, Zhiguang

    2015-11-01

    Accumulating evidence suggests an association between diabetes and cancer. Inflammation is a key event that underlies the pathological processes of the two diseases. Metformin displays anti-cancer effects, but the mechanism is not completely clear. This study investigated whether metformin regulated the microenvironment of macrophage polarization to affect the characteristics of HepG2 cells and the possible role of the Notch-signalling pathway. RAW264.7 macrophages were cultured alone or co-cultured with HepG2 cells and treated with metformin. We analysed classical (M1) and alternative (M2) gene expression in RAW264.7 cells using quantitative real-time polymerase chain reaction. Changes in mRNA and protein expressions of Notch signalling in both cell types were also detected using quantitative real-time polymerase chain reaction and Western-blotting analyses. The proliferation, apoptosis and migration of HepG2 cells were detected using Cell Titer 96 AQueous One Solution Cell Proliferation Assay (MTS) (Promega Corporation, Fitchburg, WI, USA), Annexin V-FITC/PI (7SeaPharmTech, Shanghai, China) and the cell scratch assay, respectively. Metformin induced single-cultured RAW264.7 macrophages with an M2 phenotype but attenuated the M2 macrophage differentiation and inhibited monocyte chemoattractant protein-1 (MCP-1) secretion in a co-culture system. The co-cultured group of metformin pretreatment activated Notch signalling in macrophages but repressed it inHepG2 cells. Co-culture also promoted the proliferation and migration of HepG2 cells. However, along with the enhanced apoptosis, the proliferation and the migration of HepG2 cells were remarkably inhibited in another co-culture system with metformin pretreatment. Metformin can skew RAW264.7 macrophages toward different phenotypes according to changes in the microenvironment, which may affect the inflammatory conditions mediated by macrophages, induce apoptosis and inhibit the proliferation and migration of HepG2

  2. Controllable optical bistability and multistability in a graphene monolayer system

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Duo, E-mail: zhangduo10@126.com [School of Electrical and Electronic Engineering, Wuhan Polytechnic University, Wuhan 430023 (China); Sun, Zhaoyu [School of Electrical and Electronic Engineering, Wuhan Polytechnic University, Wuhan 430023 (China); Ding, Chunling [School of Physics and Electronics, Henan University, Kaifeng 475004 (China); Yu, Rong [School of Science, Hubei Province Key Laboratory of Intelligent Robot, Wuhan Institute of Technology, Wuhan 430073 (China); Yang, Xiaoxue [Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2016-02-15

    We theoretically investigate the behavior of optical bistability (OB) and optical multistability (OM) in a graphene monolayer system driven by an elliptically polarized control field and a right-hand circularly polarized probe field. Our numerical results show that it is easy to realize the transition from OB to OM or vice versa by adjusting the frequency detunings of the probe field and the control field, as well as the polarization-dependent phase difference between the two components of the control laser field. The influences of the intensity of the control field and the cooperation parameter on the OB behavior are also discussed in detail. These results may provide some new possibilities for technological applications in optoelectronics and solid-state quantum information science.

  3. Polarization Optics

    OpenAIRE

    Fressengeas, Nicolas

    2010-01-01

    The physics of polarization optics *Polarized light propagation *Partially polarized light; DEA; After a brief introduction to polarization optics, this lecture reviews the basic formalisms for dealing with it: Jones Calculus for totally polarized light and Stokes parameters associated to Mueller Calculus for partially polarized light.

  4. Distinct self-assembly of dithiol monolayers on Au(1 1 1) in water and hexane

    Science.gov (United States)

    Sharif, Aisyah M.; Laffir, Fathima R.; Buckley, D. Noel; Silien, Christophe

    2014-09-01

    The self-assembly of 1,4-benzenedimethanethiol on Au(1 1 1), at low concentration in water and in hexane which are respectively polar and non-polar solvent, has been studied by scanning tunneling microscopy (STM). The data reveal that, on clean Au(1 1 1), a complete and ordered self-assembled monolayer (SAM) of lying-down dithiols can form within a few seconds in water. While in hexane the adsorption is initially impeded by the rapid growth of an ordered hexane film that is gradually replaced by disordered domains of dithiol until completion of a saturated monolayer. Complemented by X-ray photoelectron spectroscopy measurements, the STM images resolve the progression of the self-assembly in both these polar and non-polar solvent, and highlight how the self-assembly depends on the trio solvent, dithiol, and substrate.

  5. Determination of apical membrane polarity in mammary epithelial cell cultures: The role of cell-cell, cell-substratum, and membrane-cytoskeleton interactions

    Energy Technology Data Exchange (ETDEWEB)

    Parry, G.; Beck, J.C.; Moss, L.; Bartley, J. (Lawrence Berkeley Lab., CA (United States)); Ojakian, G.K. (State Univ. of New York, Brooklyn (United States))

    1990-06-01

    The membrane glycoprotein, PAS-O, is a major differentiation antigen on mammary epithelial cells and is located exclusively in the apical domain of the plasma membrane. The authors have used 734B cultured human mammary carcinoma cells as a model system to study the role of tight junctions, cell-substratum contacts, and submembranous cytoskeletal elements in restricting PAS-O to the apical membrane. Immunofluorescence and immunoelectronmicroscopy experiments demonstrated that while tight junctions demarcate PAS-O distribution in confluent cultures, apical polarity could be established at low culture densities when cells could not form tight junctions with neighboring cells. They suggest, then, that interactions between vitronectin and its receptor, are responsible for establishment of membrane domains in the absence of tight junctions. The role of cytoskeletal elements in restricting PAS-O distribution was examined by treating cultures with cytochalasin D, colchicine, or acrylamide. Cytochalasin D led to a redistribution of PAS0O while colchicine and acrylamide did not. They hypothesize that PAS-O is restricted to the apical membrane by interactions with a microfilament network and that the cytoskeletal organization is dependent upon cell-cell and cell-substratum interactions.

  6. Pellet culture model for human primary osteoblasts

    OpenAIRE

    K Jähn; RG Richards; CW Archer; MJ Stoddart

    2010-01-01

    In vitro monolayer culture of human primary osteoblasts (hOBs) often shows unsatisfactory results for extracellular matrix deposition, maturation and calcification. Nevertheless, monolayer culture is still the method of choice for in vitro differentiation of primary osteoblasts. We believe that the delay in mature ECM production by the monolayer cultured osteoblasts is determined by their state of cell maturation. A functional relationship between the inhibition of osteoblast proliferation an...

  7. Our Polar Past

    Science.gov (United States)

    Clary, Renee; Wandersee, James

    2009-01-01

    The study of polar exploration is fascinating and offers students insights into the history, culture, and politics that affect the developing sciences at the farthest ends of Earth. Therefore, the authors think there is value in incorporating polar exploration accounts within modern science classrooms, and so they conducted research to test their…

  8. Polarity inversion of aluminum nitride by direct wafer bonding

    Science.gov (United States)

    Hayashi, Yusuke; Katayama, Ryuji; Akiyama, Toru; Ito, Tomonori; Miyake, Hideto

    2018-03-01

    A novel fabrication process based on direct bonding technologies is proposed and demonstrated to achieve polarity inversion in AlN. High-angle annular dark-field scanning transmission electron microscopy observation clearly showed an atomically flat bonding interface and an abrupt transition from Al polarity (+c) to N polarity (‑c) through a single monolayer. This ideal polarity inversion of III–nitride materials is expected to provide new insight into heteropolar device applications.

  9. Detection of Anatoxin-a and Three Analogs in Anabaena spp. Cultures: New Fluorescence Polarization Assay and Toxin Profile by LC-MS/MS

    Directory of Open Access Journals (Sweden)

    Jon A. Sanchez

    2014-01-01

    Full Text Available Anatoxin-a (ATX is a potent neurotoxin produced by several species of Anabaena spp. Cyanobacteria blooms around the world have been increasing in recent years; therefore, it is urgent to develop sensitive techniques that unequivocally confirm the presence of these toxins in fresh water and cyanobacterial samples. In addition, the identification of different ATX analogues is essential to later determine its toxicity. In this paper we designed a fluorescent polarization (FP method to detect ATXs in water samples. A nicotinic acetylcholine receptor (nAChR labeled with a fluorescein derivative was used to develop this assay. Data showed a direct relationship between the amount of toxin in a sample and the changes in the polarization degree of the emitted light by the labeled nAChR, indicating an interaction between the two molecules. This method was used to measure the amount of ATX in three Anabaena spp. cultures. Results indicate that it is a good method to show ATXs presence in algal samples. In order to check the toxin profile of Anabaena cultures a LC-MS/MS method was also developed. Within this new method, ATX-a, retention time (RT 5 min, and three other molecules with a mass m/z 180.1 eluting at 4.14 min, 5.90 min and 7.14 min with MS/MS spectra characteristic of ATX toxin group not previously identified were detected in the Anabaena spp. cultures. These ATX analogues may have an important role in the toxicity of the sample.

  10. Microculture system for studying monolayers of functional beta-cells.

    Science.gov (United States)

    Dobersen, M J; Scharff, J E; Notkins, A L

    1980-04-01

    A method is described for growing monolayers of newborn rat beta-cells in microculture trays. After disruption of the pancreas with collagenase, islets were isolated by Ficoll density gradient centrifugation, trypsinized to obtain individual cells, and plated in 96-well tissue culture trays. The cells were incubated for the first 3 days in growth medium containing 0.1 mM 3-isobutyl-1-methylxanthine to promote monolayer formation. The cultures could be maintained in a functional state, as defined by their responsiveness to known modulators of insulin secretion, for at least 2 weeks. As few as 1 X 10(3) islet cells/well gave results that were reproducible within +/- 10%. It is suggested that the microculture system for islet cells might prove to be a rapid and reproducible screening technique for studying drugs, viruses, or other agents that affect beta-cell function.

  11. Use of monocyte/endothelial cell co-cultures (in vitro) and a subcutaneous implant mouse model (in vivo) to evaluate a degradable polar hydrophobic ionic polyurethane.

    Science.gov (United States)

    McDonald, Sarah M; Matheson, Loren A; McBane, Joanne E; Kuraitis, Drew; Suuronen, Erik; Santerre, Joseph Paul; Labow, Rosalind S

    2011-12-01

    Potential benefits of co-culturing monocytes (MC) with vascular smooth muscle cells have been reported on for tissue engineering applications with a degradable, polar, hydrophobic, and ionic polyurethane (D-PHI). Since the interaction of MC and endothelial cells (EC) within the blood vessel endothelium is also a process of wound repair it was of interest to investigate their function when cultured on the synthetic D-PHI materials, prior to considering the materials' use in vascular engineering. The co-culture (MC/EC) in vitro studies were carried out on films in 96 well plates and porous scaffold disks were prepared for implant studies in an in vivo subcutaneous mouse model. After 7 days in culture, the MC/EC condition was equal to EC growth but had lower esterase activity (a measure of degradative potential), no pro-inflammatory TNF-α and a relatively high anti-inflammatory IL-10 release while the ECs maintained their functional marker CD31. After explantation of the porous scaffolds, a live/dead stain showed that the cells infiltrating the scaffolds were viable and histological stains (May-Grunwald, Trichrome) demonstrated tissue in growth and extracellular matrix synthesis. Lysates from the implant scaffolds analyzed with a cytokine antibody array showed decreased pro-inflammatory cytokines (IL-6, TNF-α, GM-CSF), increased anti-inflammatory cytokines (IL-10, IL-13, TNF-RI), and increased chemotactic cytokines (MCP-1, MCP-5, RANTES). The low foreign body response elicited by D-PHI when implanted in vivo supported the in vitro studies (EC and MC co-culture), demonstrating that D-PHI promoted EC growth along with an anti-inflammatory MC, further demonstrating its potential as a tissue engineering scaffold for vascular applications. Copyright © 2011 Wiley Periodicals, Inc.

  12. Pellet culture model for human primary osteoblasts.

    Science.gov (United States)

    Jähn, K; Richards, R G; Archer, C W; Stoddart, M J

    2010-09-06

    In vitro monolayer culture of human primary osteoblasts (hOBs) often shows unsatisfactory results for extracellular matrix deposition, maturation and calcification. Nevertheless, monolayer culture is still the method of choice for in vitro differentiation of primary osteoblasts. We believe that the delay in mature ECM production by the monolayer cultured osteoblasts is determined by their state of cell maturation. A functional relationship between the inhibition of osteoblast proliferation and the induction of genes associated with matrix maturation was suggested within a monolayer culture model for rat calvarial osteoblasts. We hypothesize, that a pellet culture model could be utilized to decrease initial proliferation and increase the transformation of osteoblasts into a more mature phenotype. We performed pellet cultures using hOBs and compared their differentiation potential to 2D monolayer cultures. Using the pellet culture model, we were able to generate a population of cuboidal shaped central osteoblastic cells. Increased proliferation, as seen during low-density monolayer culture, was absent in pellet cultures and monolayers seeded at 40,000 cells/cm2. Moreover, the expression pattern of phenotypic markers Runx2, osterix, osteocalcin, col I and E11 mRNA was significantly different depending on whether the cells were cultured in low density monolayer, high density monolayer or pellet culture. We conclude that the transformation of the osteoblast phenotype in vitro to a more mature stage can be achieved more rapidly in 3D culture. Moreover, that dense monolayer leads to the formation of more mature osteoblasts than low-density seeded monolayer, while hOB cells in pellets seem to have transformed even further along the osteoblast phenotype.

  13. Pellet culture model for human primary osteoblasts

    Directory of Open Access Journals (Sweden)

    K Jähn

    2010-09-01

    Full Text Available In vitro monolayer culture of human primary osteoblasts (hOBs often shows unsatisfactory results for extracellular matrix deposition, maturation and calcification. Nevertheless, monolayer culture is still the method of choice for in vitro differentiation of primary osteoblasts. We believe that the delay in mature ECM production by the monolayer cultured osteoblasts is determined by their state of cell maturation. A functional relationship between the inhibition of osteoblast proliferation and the induction of genes associated with matrix maturation was suggested within a monolayer culture model for rat calvarial osteoblasts. We hypothesize, that a pellet culture model could be utilized to decrease initial proliferation and increase the transformation of osteoblasts into a more mature phenotype. We performed pellet cultures using hOBs and compared their differentiation potential to 2D monolayer cultures. Using the pellet culture model, we were able to generate a population of cuboidal shaped central osteoblastic cells. Increased proliferation, as seen during low-density monolayer culture, was absent in pellet cultures and monolayers seeded at 40,000 cells/cm2. Moreover, the expression pattern of phenotypic markers Runx2, osterix, osteocalcin, col I and E11 mRNA was significantly different depending on whether the cells were cultured in low density monolayer, high density monolayer or pellet culture. We conclude that the transformation of the osteoblast phenotype in vitro to a more mature stage can be achieved more rapidly in 3D culture. Moreover, that dense monolayer leads to the formation of more mature osteoblasts than low-density seeded monolayer, while hOB cells in pellets seem to have transformed even further along the osteoblast phenotype.

  14. Permeation of Insulin, Calcitonin and Exenatide across Caco-2 Monolayers: Measurement Using a Rapid, 3-Day System

    Science.gov (United States)

    Gupta, Vivek; Doshi, Nishit; Mitragotri, Samir

    2013-01-01

    Objectives Caco-2 monolayers are one of the most widely used in vitro models for prediction of intestinal permeability of therapeutic molecules. However, the conventional Caco-2 monolayer model has several drawbacks including labor-intensive culture process, unphysiological growth conditions, lack of reproducibility and limited throughput. Here, we report on the use of 3-day Caco-2 monolayers for assessing permeability of polypeptide drugs. Methods The 3-day monolayers were grown in a commercially available transwell set-up, which facilitates rapid development of the Caco-2 monolayers in an intestinal epithelial differentiation mimicking environment. This set-up included use of serum-free medium of defined composition with supplements such as butyric acid, hormones, growth factors, and other metabolites, reported to regulate the differentiation of intestinal epithelial cells in vivo. We measured permeability of 3 different therapeutic polypeptides; insulin, calcitonin, and exenatide across the monolayer. Results Preliminary validation of the monolayer was carried out by confirming dose-dependent permeation of FITC-insulin and sulforhodamine-B. Transport of insulin, calcitonin, and exenatide measured at different loading concentrations suggests that the permeability values obtained with 3-day cultures resemble more closely the values obtained with ex vivo models compared to permeability values obtained with conventional 21-day cultures. Conclusions Short-term 3-day Caco-2 monolayers provide new opportunities for developing reproducible and high-throughput models for screening of therapeutic macromolecules for oral absorption. PMID:23483881

  15. Monolayer atomic crystal molecular superlattices

    Science.gov (United States)

    Wang, Chen; He, Qiyuan; Halim, Udayabagya; Liu, Yuanyue; Zhu, Enbo; Lin, Zhaoyang; Xiao, Hai; Duan, Xidong; Feng, Ziying; Cheng, Rui; Weiss, Nathan O.; Ye, Guojun; Huang, Yun-Chiao; Wu, Hao; Cheng, Hung-Chieh; Shakir, Imran; Liao, Lei; Chen, Xianhui; Goddard, William A., III; Huang, Yu; Duan, Xiangfeng

    2018-03-01

    Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of existing materials. Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility. The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures, but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transistors fabricated from the monolayer phosphorene molecular superlattice show an on/off current ratio exceeding 107, along with excellent mobility and superior stability. We further show that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of varying sizes and symmetries to produce a broad class of superlattices with tailored molecular structures, interlayer distances, phase compositions, electronic and optical properties. These studies define a versatile material platform for fundamental studies and potential technological applications.

  16. Polarized Human Retinal Pigment Epithelium Exhibits Distinct Surface Proteome on Apical and Basal Plasma Membranes.

    Science.gov (United States)

    Khristov, Vladimir; Wan, Qin; Sharma, Ruchi; Lotfi, Mostafa; Maminishkis, Arvydas; Bharti, Kapil

    2018-01-01

    Surface proteins localized on the apical and basal plasma membranes are required for a cell to sense its environment and relay changes in ionic, cytokine, chemokine, and hormone levels to the inside of the cell. In a polarized cell, surface proteins are differentially localized on the apical or the basolateral sides of the cell. The retinal pigment epithelium (RPE) is an example of a polarized cell that performs a variety of functions that are dependent on its polarized state including trafficking of ions, fluid, and metabolites across the RPE monolayer. These functions are absolutely crucial for maintaining the health and integrity of adjacent photoreceptors, the photosensitive cells of the retina. Here we present a series of approaches to identify and validate the polarization state of cultured primary human RPE cells using immunostaining for RPE apical/basolateral markers, polarized cytokine secretion, electrophysiology, fluid transport, phagocytosis, and identification of plasma membrane proteins through cell surface capturing technology. These approaches are currently being used to validate the polarized state and the epithelial phenotype of human induced pluripotent stem (iPS) cell derived RPE cells. This work provides the basis for developing an autologous cell therapy for age-related macular degeneration using patient specific iPS cell derived RPE.

  17. Simulation of a lipid monolayer using molecular dynamics

    Science.gov (United States)

    Kox, A. J.; Michels, J. P. J.; Wiegel, F. W.

    1980-09-01

    Numerical simulation is often a useful tool f or investigating the behaviour of complex systems with many degrees of freedom. Of the two major methods in this field, the Monte Carlo method and the molecular dynamics method, only the first has been applied to realistic models of lipid monolayers1-5. The term lipid monolayer is used here to describe a class of systems consisting of chain molecules on a liquid substrate, the characteristic properties of which can be summarized as follows. (1) The constituent molecules are amphipathic, that is they consist of a hydrophilic (polar) head group and one or more hydrophobic hydrocarbon chains. (2) Due to the amphipathic character of the molecules, the head groups are constrained to the plane of the substrate, whereas the tails are directed outwards from this plane. (3) The collective properties of the molecules are determined by their short-range repulsive and long-range attractive interactions and by the steric repulsion of the tails. We now present what we believe to be the first molecular dynamics simulation of a realistic model of a lipid monolayer. The model system, which has all three properties enumerated above, shows a first order phase transition from an ordered fluid-like state to a disordered, gas-like state.

  18. Bright monolayer tungsten disulfide via exciton and trion chemical modulations.

    Science.gov (United States)

    Tao, Ye; Yu, Xuechao; Li, Jiewei; Liang, Houkun; Zhang, Ying; Huang, Wei; Wang, Qi Jie

    2018-04-05

    Atomically thin transition metal dichalcogenides (TMDCs) with exceptional electrical and optical properties have drawn tremendous attention for use in novel optoelectronic applications as photodetectors, transistors, light emitters, etc. However, electron bound trions formed through the combination of neutral excitons and electrons significantly decrease the photoluminescence (PL) efficiency of TMDCs. In this study, we report a simple yet efficient chemical doping strategy to modulate the optical properties of monolayer tungsten disulfide (WS2). As a demonstrative example, a chemically doped monolayer of WS2 exhibits remarkable PL enhancement of about one order of magnitude higher than that of pristine WS2. This outstanding PL enhancement is attributed to the fact that excess electrons, which promote the formation of electron-bound trions, are reduced in number through charge transfer from WS2 to the chemical dopant. Furthermore, an improved degree of circular polarization from ∼9.0% to ∼41.5% was also observed in the chemically doped WS2 monolayer. This work describes a feasible strategy to manipulate the optical properties of TMDCs via exciton modulation, making TMDCs promising candidates for versatile semiconductor-based photonic devices.

  19. Piezoelectric effect in chemical vapour deposition-grown atomic-monolayer triangular molybdenum disulfide piezotronics

    KAUST Repository

    Qi, Junjie

    2015-06-25

    High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation. These polarization charges alter the Schottky barrier height on both contacts, resulting in a barrier height increase with increasing compressive strain and decrease with increasing tensile strain. The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams. In addition, a new type of MoS2 strain/force sensor built using a monolayer MoS2 triangle is also demonstrated. Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical–electronic nanodevices.

  20. Piezoelectric effect in chemical vapour deposition-grown atomic-monolayer triangular molybdenum disulfide piezotronics

    Science.gov (United States)

    Qi, Junjie; Lan, Yann-Wen; Stieg, Adam Z.; Chen, Jyun-Hong; Zhong, Yuan-Liang; Li, Lain-Jong; Chen, Chii-Dong; Zhang, Yue; Wang, Kang L.

    2015-01-01

    High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation. These polarization charges alter the Schottky barrier height on both contacts, resulting in a barrier height increase with increasing compressive strain and decrease with increasing tensile strain. The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams. In addition, a new type of MoS2 strain/force sensor built using a monolayer MoS2 triangle is also demonstrated. Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical–electronic nanodevices. PMID:26109177

  1. Plasma membrane protein polarity and trafficking in RPE cells: Past, present and future

    Science.gov (United States)

    Lehmann, Guillermo L.; Benedicto, Ignacio; Philp, Nancy J.; Rodriguez-Boulan, Enrique

    2015-01-01

    The retinal pigment epithelium (RPE) comprises a monolayer of polarized pigmented epithelial cells that is strategically interposed between the neural retina and the fenestrated choroid capillaries. The RPE performs a variety of vectorial transport functions (water, ions, metabolites, nutrients and waste products) that regulate the composition of the subretinal space and support the functions of photoreceptors (PRs) and other cells in the neural retina. To this end, RPE cells display a polarized distribution of channels, transporters and receptors in their plasma membrane (PM) that is remarkably different from that found in conventional extra-ocular epithelia, e.g. intestine, kidney, and gall bladder. This characteristic PM protein polarity of RPE cells depends on the interplay of sorting signals in the RPE PM proteins and sorting mechanisms and biosynthetic/recycling trafficking routes in the RPE cell. Although considerable progress has been made in our understanding of the RPE trafficking machinery, most available data have been obtained from immortalized RPE cell lines that only partially maintain the RPE phenotype and by extrapolation of data obtained in the prototype Madin–Darby Canine Kidney (MDCK) cell line. The increasing availability of RPE cell cultures that more closely resemble the RPE in vivo together with the advent of advanced live imaging microscopy techniques provides a platform and an opportunity to rapidly expand our understanding of how polarized protein trafficking contributes to RPE PM polarity. PMID:25152359

  2. Ultrastructural investigations on the effect of X-radiation and quinacrine (Atebrin) of chloroquine (Resochin) - alone and in combination - on cells of a Harding-Passey melanoma in monolayer culture

    Energy Technology Data Exchange (ETDEWEB)

    Pfab, R.; Schachtschabel, D.O.; Kern, H.F.

    1985-11-01

    Monolayer cells of a Harding-Passey melanoma (HPM 73 cells) which were irradiated during the phase of exponential growth with an X-ray dose of 4 Gy or 8 Gy did not show any ultrastructural changes four days after 4 Gy, whereas cells irradiated with 8 Gy showed slight damages such as swollen mitochondria and vacuoles. As shown by the electron microscope, a sole addition of a sublethal quantity (6 x 10/sup -6/ M) of quinacrine (Atebrin) or chloroquine (Resochin) did not lead to significant cell modifications. Those melanoma cells which were pre-irradiated with 8 Gy and then incubated during four days with 6 x 10/sup -6/ M of quinacrine (Atebrin) or 6 x 10/sup -6/ M of chloroquine (Resochin) showed severe damages. There was an increased rate of vacuoles and segregational structures in cytoplasm. The mitochondria were increased and swollen and the cellular surfaces had less microvilli. However, microtubules and microfilaments seemed more distinct. The melanin concentration increased under this treatment. The cell nuclei were increased in volume and seemed to be rather void of chromatin. These reactions of cells on quinacrine (Atebrin) and chloroquine (Resochin) are explained by the known inhibition effect exerted by these substances on DNA synthesis, especially as far as the processes of DNA reparation are concerned. The changes of the microtubule-microfilament system could be due to a correlation with the increase of digestive intracellular processes connected with the catabolism of radiation-damaged structures.

  3. Lateral pressure profiles in lipid monolayers

    NARCIS (Netherlands)

    Baoukina, Svetlana; Marrink, Siewert J.; Tieleman, D. Peter

    2010-01-01

    We have used molecular dynamics simulations with coarse-grained and atomistic models to study the lateral pressure profiles in lipid monolayers. We first consider simple oil/air and oil/water interfaces, and then proceed to lipid monolayers at air/water and oil/water interfaces. The results are

  4. Vapor-transport growth of high optical quality WSe2 monolayers

    Directory of Open Access Journals (Sweden)

    Genevieve Clark

    2014-10-01

    Full Text Available Monolayer transition metal dichalcogenides are atomically thin direct-gap semiconductors that show a variety of novel electronic and optical properties with an optically accessible valley degree of freedom. While they are ideal materials for developing optical-driven valleytronics, the restrictions of exfoliated samples have limited exploration of their potential. Here, we present a physical vapor transport growth method for triangular WSe2 sheets of up to 30 μm in edge length on insulating SiO2 substrates. Characterization using atomic force microscopy and optical microscopy reveals that they are uniform, monolayer crystals. Low temperature photoluminescence shows well resolved and electrically tunable excitonic features similar to those in exfoliated samples, with substantial valley polarization and valley coherence. The monolayers grown using this method are therefore of high enough optical quality for routine use in the investigation of optoelectronics and valleytronics.

  5. Modulating the electronic and optical properties of monolayer arsenene phases by organic molecular doping

    Science.gov (United States)

    Singh, Deobrat; Gupta, Sanjeev K.; Sonvane, Yogesh; Sahoo, Satyaprakash

    2017-12-01

    Recently, arsenene monolayer structure of the arsenic with two phases has displayed semiconducting behavior. We have systematically investigated the electronic and optical properties of single-layer arsenene with two types of functionalized organic molecules; an electrophilic molecule [tetracyanoquinodimethane (TCNQ)] and a nucleophilic molecule [tetrathiafulvalene (TTF)], as an electron acceptor and electron donor, respectively. The interfacial charge transfer between the arsenene monolayer and TCNQ/TTF molecules extensively reduces the band gap of arsenene and accordingly resulted in a p- or n-type semiconducting behavior, respectively. We have also performed the interfacial charge transfer from organic molecules to monolayer arsenene and vice versa. The interfacial surface molecular modification has established an efficient way to develop the light harvesting of arsenene in different polarization directions. Our theoretical investigation suggests that such n- and p-type arsenene semiconductors would broaden the applications in the field of nanoelectronic and optoelectronic devices such as photodiodes and it is also useful for constructing functional electronic systems.

  6. Ferromagnetism induced by point defect in Janus monolayer MoSSe regulated by strain engineering

    Science.gov (United States)

    Meng, Ming; Li, Tinghui; Li, Shaofeng; Liu, Kuili

    2018-03-01

    The formation and regulation of magnetism dependent on introduced defects in the Janus MoSSe monolayer has attracted much attention because of its potential application in spintronics. Here, we present a theoretical study of defect formation in the MoSSe monolayer and its introduced magnetism under external strain. The tensile deformation induced by external strain not only leads to decreases in defect formation energy, but also enhances magnetic characteristics. However, as compressed deformation increases, the magnetism in the structure induced by Se or S defects remains unchanged because this microstructural deformation adequately spin polarizes unpaired electrons of neighboring Mo atoms. Our results suggest the use of point defect and strain engineering in the Janus MoSSe monolayer for spintronics applications.

  7. Self-renewing Monolayer of Primary Colonic or Rectal Epithelial CellsSummary

    Directory of Open Access Journals (Sweden)

    Yuli Wang

    2017-07-01

    Full Text Available Background & Aims: Three-dimensional organoid culture has fundamentally changed the in vitro study of intestinal biology enabling novel assays; however, its use is limited because of an inaccessible luminal compartment and challenges to data gathering in a three-dimensional hydrogel matrix. Long-lived, self-renewing 2-dimensional (2-D tissue cultured from primary colon cells has not been accomplished. Methods: The surface matrix and chemical factors that sustain 2-D mouse colonic and human rectal epithelial cell monolayers with cell repertoires comparable to that in vivo were identified. Results: The monolayers formed organoids or colonoids when placed in standard Matrigel culture. As with the colonoids, the monolayers exhibited compartmentalization of proliferative and differentiated cells, with proliferative cells located near the peripheral edges of growing monolayers and differentiated cells predominated in the central regions. Screening of 77 dietary compounds and metabolites revealed altered proliferation or differentiation of the murine colonic epithelium. When exposed to a subset of the compound library, murine organoids exhibited similar responses to that of the monolayer but with differences that were likely attributable to the inaccessible organoid lumen. The response of the human primary epithelium to a compound subset was distinct from that of both the murine primary epithelium and human tumor cells. Conclusions: This study demonstrates that a self-renewing 2-D murine and human monolayer derived from primary cells can serve as a physiologically relevant assay system for study of stem cell renewal and differentiation and for compound screening. The platform holds transformative potential for personalized and precision medicine and can be applied to emerging areas of disease modeling and microbiome studies. Keywords: Colonic Epithelial Cells, Monolayer, Organoids, Compound Screening

  8. First-principle study of single TM atoms X (X=Fe, Ru or Os) doped monolayer WS2 systems

    Science.gov (United States)

    Zhu, Yuan-Yan; Zhang, Jian-Min

    2018-05-01

    We report the structural, magnetic and electronic properties of the pristine and single TM atoms X (X = Fe, Ru or Os) doped monolayer WS2 systems based on first-principle calculations. The results show that the W-S bond shows a stronger covalent bond, but the covalency is obviously weakened after the substitution of W atom with single X atoms, especially for Ru (4d75s1) with the easily lost electronic configuration. The smaller total energies of the doped systems reveal that the spin-polarized states are energetically favorable than the non-spin-polarized states, and the smallest total energy of -373.918 eV shows the spin-polarized state of the Os doped monolayer WS2 system is most stable among three doped systems. In addition, although the pristine monolayer WS2 system is a nonmagnetic-semiconductor with a direct band gap of 1.813 eV, single TM atoms Fe and Ru doped monolayer WS2 systems transfer to magnetic-HM with the total moments Mtot of 1.993 and 1.962 μB , while single TM atom Os doped monolayer WS2 systems changes to magnetic-metal with the total moments Mtot of 1.569 μB . Moreover, the impurity states with a positive spin splitting energies of 0.543, 0.276 and 0.1999 eV near the Fermi level EF are mainly contributed by X-dxy and X-dx2-y2 states hybridized with its nearest-neighbor atom W-dz2 states for Fe, Ru and Os doped monolayer WS2 system, respectively. Finally, we hope that the present study on monolayer WS2 will provide a useful theoretical guideline for exploring low-dimensional spintronic materials in future experiments.

  9. Fermi Level Pinning at Electrical Metal Contacts of Monolayer Molybdenum Dichalcogenides.

    Science.gov (United States)

    Kim, Changsik; Moon, Inyong; Lee, Daeyeong; Choi, Min Sup; Ahmed, Faisal; Nam, Seunggeol; Cho, Yeonchoo; Shin, Hyeon-Jin; Park, Seongjun; Yoo, Won Jong

    2017-02-28

    Electrical metal contacts to two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) are found to be the key bottleneck to the realization of high device performance due to strong Fermi level pinning and high contact resistances (R c ). Until now, Fermi level pinning of monolayer TMDCs has been reported only theoretically, although that of bulk TMDCs has been reported experimentally. Here, we report the experimental study on Fermi level pinning of monolayer MoS 2 and MoTe 2 by interpreting the thermionic emission results. We also quantitatively compared our results with the theoretical simulation results of the monolayer structure as well as the experimental results of the bulk structure. We measured the pinning factor S to be 0.11 and -0.07 for monolayer MoS 2 and MoTe 2 , respectively, suggesting a much stronger Fermi level pinning effect, a Schottky barrier height (SBH) lower than that by theoretical prediction, and interestingly similar pinning energy levels between monolayer and bulk MoS 2 . Our results further imply that metal work functions have very little influence on contact properties of 2D-material-based devices. Moreover, we found that R c is exponentially proportional to SBH, and these processing parameters can be controlled sensitively upon chemical doping into the 2D materials. These findings provide a practical guideline for depinning Fermi level at the 2D interfaces so that polarity control of TMDC-based semiconductors can be achieved efficiently.

  10. Corrosion protection ability of self-assembled monolayer of 3-amino-5-mercapto-1,2,4-triazole on copper electrode

    Energy Technology Data Exchange (ETDEWEB)

    Rajkumar, Ganesan; Sethuraman, Mathur Gopalakrishnan, E-mail: mgsethu@rediffmail.com

    2014-07-01

    The self-assembled monolayer (SAM) of 3-amino-5-mercapto-1,2,4-triazole (AMTa) was formed on a copper surface and characterized using cyclic voltammetry, Fourier Transform Infra-red spectroscopy and scanning electron microscopy. Quantum chemical calculations suggested the stronger interaction between AMTa and copper. The protection ability of SAM has been evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The formed monolayer showed significant protection ability in 1% NaCl medium. The enhanced corrosion protection ability could be due to the compact film structure which blocks the electron transfer from the solution to AMTa monolayer modified copper substrate. - Highlights: • Self-assembled monolayer (SAM) of AMTa has been achieved on copper surface. • Monolayer formed has been duly characterized. • SAM of AMTa has been shown to offer significant protection to copper in NaCl medium.

  11. Acamprosate permeability across Caco-2 cell monolayer is predominantly paracellular

    DEFF Research Database (Denmark)

    Antonescu, Irina-Elena; Steffansen, Bente

    Background. The human oral bioavailability (BA) of acamprosate is 11% and its oral absorption is permeability limited (BCS class III). Acamprosate is not metabolized, therefore it’s BA has the same nominal value as its fraction absorbed (fa). It is however controversial whether the intestinal...... in the different regions of the rodent small intestine and colon. Biopharm Drug Dispos. 2017;38(2):94-114. 2. Avdeef A. Leakiness and size exclusion of paracellular channels in cultured epithelial cell monolayers-interlaboratory comparison. Pharm Res. 2010;27(3):480-9. 3. Avdeef A. Absorption and Drug Development...

  12. Comparison of electronic structure between monolayer silicenes on Ag (111)

    Science.gov (United States)

    Chun-Liang, Lin; Ryuichi, Arafune; Maki, Kawai; Noriaki, Takagi

    2015-08-01

    The electronic structures of monolayer silicenes (4 × 4 and ) grown on Ag (111) surface are studied by scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. While both phases have similar electronic structures around the Fermi level, significant differences are observed in the higher energy unoccupied states. The DFT calculations show that the contributions of Si 3pz orbitals to the unoccupied states are different because of their different buckled configurations. Project supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) through Grants-in-Aid for Scientific Research (Grant Nos. 24241040 and 25110008) and the World Premier International Research Center Initiative (WPI), MEXT, Japan.

  13. Ultrafast generation of pseudo-magnetic field for valley excitons in WSe2 monolayers

    KAUST Repository

    Kim, J.

    2014-12-04

    The valley pseudospin is a degree of freedom that emerges in atomically thin two-dimensional transition metal dichalcogenides (MX2). The capability to manipulate it, in analogy to the control of spin in spintronics, can open up exciting opportunities. Here, we demonstrate that an ultrafast and ultrahigh valley pseudo-magnetic field can be generated by using circularly polarized femtosecond pulses to selectively control the valley degree of freedom in monolayer MX2. Using ultrafast pump-probe spectroscopy, we observed a pure and valley-selective optical Stark effect in WSe2 monolayers from the nonresonant pump, resulting in an energy splitting of more than 10 milli-electron volts between the K and K′ valley exciton transitions. Our study opens up the possibility to coherently manipulate the valley polarization for quantum information applications.

  14. Large-area monolayer hexagonal boron nitride on Pt foil.

    Science.gov (United States)

    Park, Ji-Hoon; Park, Jin Cheol; Yun, Seok Joon; Kim, Hyun; Luong, Dinh Hoa; Kim, Soo Min; Choi, Soo Ho; Yang, Woochul; Kong, Jing; Kim, Ki Kang; Lee, Young Hee

    2014-08-26

    Hexagonal boron nitride (h-BN) has recently been in the spotlight due to its numerous applications including its being an ideal substrate for two-dimensional electronics, a tunneling material for vertical tunneling devices, and a growth template for heterostructures. However, to obtain a large area of h-BN film while maintaining uniform thickness is still challenging and has not been realized. Here, we report the systematical study of h-BN growth on Pt foil by using low pressure chemical vapor deposition with a borazine source. The monolayer h-BN film was obtained over the whole Pt foil (2 × 5 cm(2)) under foil size. A borazine source was catalytically decomposed on the Pt surface, leading to the self-limiting growth of the monolayer without the associating precipitation, which is very similar to the growth of graphene on Cu. The orientation of the h-BN domains was largely confined by the Pt domain, which is confirmed by polarizing optical microscopy (POM) assisted by the nematic liquid crystal (LC) film. The total pressure and orientation of the Pt lattice plane are crucial parameters for thickness control. At high pressure (∼0.5 Torr), thick film was grown on Pt (111), and in contrast, thin film was grown on Pt (001). Our advances in monolayer h-BN growth will play an important role to further develop a high quality h-BN film that can be used for vertical tunneling, optoelectronic devices and growth templates for a variety of heterostructures.

  15. Tunable thermoelectricity in monolayers of MoS2 and other group-VI dichalcogenides

    KAUST Repository

    Tahir, M

    2014-10-31

    We study the thermoelectric properties of monolayers of MoS2 and other group-VI dichalcogenides under circularly polarized off-resonant light. Analytical expressions are derived for the Berry phase mediated magnetic moment, orbital magnetization, as well as thermal and Nernst conductivities. Tuning of the band gap by off-resonant light enhances the spin splitting in both the valence and conduction bands and, thus, leads to a dramatic improvement of the spin and valley thermoelectric properties.

  16. Extended Moment Formation in Monolayer WS2 Doped with 3d Transition-Metals

    KAUST Repository

    Singh, Nirpendra

    2016-08-30

    First-principles calculations with onsite Coulomb interaction and spin-orbit coupling are used to investigate the electronic structure of monolayer WS2 doped substitutionally with 3d transition-metals. While neither W vacancies nor strain induce spin polarization, we demonstrate an unprecedented tendency to extended moment formation under doping. The extended magnetic moments are characterized by dopant-specific spin density patterns with rich structural features involving the nearest neighbor W and S atoms.

  17. Polarity in Mammalian Epithelial Morphogenesis

    OpenAIRE

    Roignot, Julie; Peng, Xiao; Mostov, Keith

    2013-01-01

    Cell polarity is fundamental for the architecture and function of epithelial tissues. Epithelial polarization requires the intervention of several fundamental cell processes, whose integration in space and time is only starting to be elucidated. To understand what governs the building of epithelial tissues during development, it is essential to consider the polarization process in the context of the whole tissue. To this end, the development of three-dimensional organotypic cell culture model...

  18. Large Friction Anisotropy of a Polydiacetylene Monolayer

    International Nuclear Information System (INIS)

    Burns, A.R.; Carpick, R.W.; Sasaki, D.Y.

    1999-01-01

    Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated with the film structure. The film consists of a monolayer of the red form of N-(2-ethanol)- 10,12 pentacosadiynamide, prepared on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy, the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbone. We propose that the backbones impose anisotropic packing of the hydrocarbon side chains which leads to the observed friction anisotropy. Friction anisotropy is therefore a sensitive, optically-independent indicator of polymer backbone direction and monolayer structural properties

  19. Molecular diffusion in monolayer and submonolayer nitrogen

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Bruch, Ludwig Walter

    2001-01-01

    The orientational and translational motions in a monolayer fluid of physisorbed molecular nitrogen are treated using molecular dynamics simulations. Dynamical response functions and several approximations to the coefficient of translational diffusion are determined for adsorption on the basal plane...

  20. Packing of ganglioside-phospholipid monolayers

    DEFF Research Database (Denmark)

    Majewski, J.; Kuhl, T.L.; Kjær, K.

    2001-01-01

    Using synchrotron grazing-incidence x-ray diffraction (GIXD) and reflectivity, the in-plane and out-of-plane structure of mixed ganglioside-phospholipid monolayers was investigated at the air-water interface. Mixed monolayers of 0, 5, 10, 20, and 100 mol% ganglioside GM, and the phospholipid...... dipaimitoylphosphatidylethanolamine (DPPE) were studied in the solid phase at 23 degreesC and a surface pressure of 45 mN/m. At these concentrations and conditions the two components do not phase-separate and no evidence for domain formation was observed. X-ray scattering measurements reveal that GM, is accommodated within the host...... monolayers did not affect hydrocarbon tail packing (fluidization or condensation of the hydrocarbon region). This is in contrast to previous investigations of lipopolymer-lipid mixtures, where the packing structure of phospholipid monolayers was greatly altered by the inclusion of lipids bearing hydrophilic...

  1. Test of endothelial monolayer integrity in the presence or absence of ...

    African Journals Online (AJOL)

    Monolayer cultures of human umbilical vein endothelial cells were established and tested for the effects of endotoxin treatment and anti-TNF-a monoclonal antibodies following endotoxin treatment on albumin permeability and electrical conductance. Application of 40 -g(ml)-1 of endotoxin on human umbilical cord ...

  2. Cultural

    Science.gov (United States)

    Wilbur F. LaPage

    1971-01-01

    A critical look at outdoor recreation research and some underlying premises. The author focuses on the concept of culture as communication and how it influences our perception of problems and our search for solutions. Both outdoor recreation and science are viewed as subcultures that have their own bodies of mythology, making recreation problems more difficult to...

  3. Exciton Binding Energy of Monolayer WS2

    Science.gov (United States)

    Zhu, Bairen; Chen, Xi; Cui, Xiaodong

    2015-03-01

    The optical properties of monolayer transition metal dichalcogenides (TMDC) feature prominent excitonic natures. Here we report an experimental approach to measuring the exciton binding energy of monolayer WS2 with linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE). TP-PLE measurements show the exciton binding energy of 0.71 +/- 0.01 eV around K valley in the Brillouin zone.

  4. STM studies of synthetic peptide monolayers

    Science.gov (United States)

    Bergeron, David J.; Clauss, Wilfried; Pilloud, Denis L.; Leslie Dutton, P.; Johnson, Alan T.

    1998-08-01

    We have used scanning probe microscopy to investigate self-assembled monolayers of chemically synthesized peptides. We find that the peptides form a dense uniform monolayer, above which is found a sparse additional layer. Using scanning tunneling microscopy, submolecular resolution can be obtained, revealing the alpha helices which constitute the peptide. The nature of the images is not significantly affected by the incorporation of redox cofactors (hemes) in the peptides.

  5. Mass spectrometric analysis of monolayer protected nanoparticles

    Science.gov (United States)

    Zhu, Zhengjiang

    Monolayer protected nanoparticles (NPs) include an inorganic core and a monolayer of organic ligands. The wide variety of core materials and the tunable surface monolayers make NPs promising materials for numerous applications. Concerns related to unforeseen human health and environmental impacts of NPs have also been raised. In this thesis, new analytical methods based on mass spectrometry are developed to understand the fate, transport, and biodistributions of NPs in the complex biological systems. A laser desorption/ionization mass spectrometry (LDI-MS) method has been developed to characterize the monolayers on NP surface. LDI-MS allows multiple NPs taken up by cells to be measured and quantified in a multiplexed fashion. The correlations between surface properties of NPs and cellular uptake have also been explored. LDI-MS is further coupled with inductively coupled plasma mass spectrometry (ICP-MS) to quantitatively measure monolayer stability of gold NPs (AuNPs) and quantum dots (QDs), respectively, in live cells. This label-free approach allows correlating monolayer structure and particle size with NP stability in various cellular environments. Finally, uptake, distribution, accumulation, and excretion of NPs in higher order organisms, such as fish and plants, have been investigated to understand the environmental impact of nanomaterials. The results indicate that surface chemistry is a primary determinant. NPs with hydrophilic surfaces are substantially less toxic and present a lower degree of bioaccumulation, making these nanomaterials attractive for sustainable nanotechnology.

  6. cultural

    Directory of Open Access Journals (Sweden)

    Irene Kreutz

    2006-01-01

    Full Text Available Es un estudio cualitativo que adoptó como referencial teorico-motodológico la antropología y la etnografía. Presenta las experiencias vivenciadas por mujeres de una comunidad en el proceso salud-enfermedad, con el objetivo de comprender los determinantes sócio-culturales e históricos de las prácticas de prevención y tratamiento adoptados por el grupo cultural por medio de la entrevista semi-estructurada. Los temas que emergieron fueron: la relación entre la alimentación y lo proceso salud-enfermedad, las relaciones con el sistema de salud oficial y el proceso salud-enfermedad y lo sobrenatural. Los dados revelaron que los moradores de la comunidad investigada tienen un modo particular de explicar sus procedimientos terapéuticos. Consideramos que es papel de los profesionales de la salud en sus prácticas, la adopción de abordajes o enfoques que consideren al individuo en su dimensión sócio-cultural e histórica, considerando la enorme diversidad cultural en nuestro país.

  7. Polarization developments

    International Nuclear Information System (INIS)

    Prescott, C.Y.

    1993-07-01

    Recent developments in laser-driven photoemission sources of polarized electrons have made prospects for highly polarized electron beams in a future linear collider very promising. This talk discusses the experiences with the SLC polarized electron source, the recent progress with research into gallium arsenide and strained gallium arsenide as a photocathode material, and the suitability of these cathode materials for a future linear collider based on the parameters of the several linear collider designs that exist

  8. Effects of irradiated biodegradable polymer in endothelial cell monolayer formation

    Energy Technology Data Exchange (ETDEWEB)

    Arbeitman, Claudia R.; Grosso, Mariela F. del [CONICET – Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Gerencia de Investigación y Aplicaciones, TANDAR-CNEA (Argentina); Behar, Moni [Instituto de Física, UFRGS, Porto Alegre, RS (Brazil); García Bermúdez, Gerardo, E-mail: ggb@tandar.cnea.gov.ar [CONICET – Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Gerencia de Investigación y Aplicaciones, TANDAR-CNEA (Argentina); Escuela de Ciencia y Tecnología, UNSAM (Argentina)

    2013-11-01

    In this work we study cell adhesion, proliferation and cell morphology of endothelial cell cultured on poly-L-lactide acid (PLLA) modified by heavy ion irradiation. Thin films of PLLA samples were irradiated with sulfur (S) at energies of 75 MeV and gold (Au) at 18 MeV ion-beams. Ion beams were provided by the Tandar (Buenos Aires, Argentina) and Tandetron (Porto Alegre, Brazil) accelerators, respectively. The growth of a monolayer of bovine aortic endothelial cells (BAEC) onto unirradiated and irradiated surfaces has been studied by in vitro techniques in static culture. Cell viability and proliferation increased on modified substrates. But the results on unirradiated samples, indicate cell death (necrosis/apoptosis) with the consequent decrease in proliferation. We analyzed the correlation between irradiation parameters and cell metabolism and morphology.

  9. Intact penetratin metabolite permeates across Caco-2 monolayers

    DEFF Research Database (Denmark)

    Birch, Ditlev; Christensen, Malene Vinther; Stærk, Dan

    . Previous studies have demonstrated that cell-penetrating peptides (CPPs) may be used as carriers in order to improve the bioavailability of a therapeutic cargo like insulin after oral administration. Penetratin, a commonly used CPP, has been shown to increase the uptake of insulin across Caco-2 cell......, the aim of the present study was to investigate penetratin metabolites with respect to effects on cellular viability, their epithelial permeation and cell uptake. Methods Extracellular and intracellular degradation of penetratin was assessed by incubation of the carrier peptide on the apical side of Caco......-2 cells cultured on permeable filter inserts and in cell lysates, respectively. The epithelial permeation of penetratin and the formed metabolites was assessed by using Caco-2 monolayers cultured on permeable filter inserts. Results Preliminary data revealed that at least one specific metabolite...

  10. Polarization, political

    NARCIS (Netherlands)

    Wojcieszak, M.; Mazzoleni, G.; Barnhurst, K.G.; Ikeda, K.; Maia, R.C.M.; Wessler, H.

    2015-01-01

    Polarization has been studied in three different forms: on a social, group, and individual level. This entry first focuses on the undisputed phenomenon of elite polarization (i.e., increasing adherence of policy positions among the elites) and also outlines different approaches to assessing mass

  11. Polarization holography

    DEFF Research Database (Denmark)

    Nikolova, L.; Ramanujam, P.S.

    Current research into holography is concerned with applications in optically storing, retrieving, and processing information. Polarization holography has many unique properties compared to conventional holography. It gives results in high efficiency, achromaticity, and special polarization...... properties. This books reviews the research carried out in this field over the last 15 years. The authors provide basic concepts in polarization and the propagation of light through anisotropic materials, before presenting a sound theoretical basis for polarization holography. The fabrication...... and characterization of azobenzene based materials, which remain the most efficient for the purpose, is described in detail. This is followed by a description of other materials that are used in polarization holography. An in-depth description of various applications, including display holography and optical storage...

  12. Electrically tunable magnetic configuration on vacancy-doped GaSe monolayer

    Science.gov (United States)

    Tang, Weiqing; Ke, Congming; Fu, Mingming; Wu, Yaping; Zhang, Chunmiao; Lin, Wei; Lu, Shiqiang; Wu, Zhiming; Yang, Weihuang; Kang, Junyong

    2018-03-01

    Group-IIIA metal-monochalcogenides with the enticing properties have attracted tremendous attention across various scientific disciplines. With the aim to satisfy the multiple demands of device applications, here we report a design framework on GaSe monolayer in an effort to tune the electronic and magnetic properties through a dual modulation of vacancy doping and electric field. A half-metallicity with a 100% spin polarization is generated in a Ga vacancy doped GaSe monolayer due to the nonbonding 4p electronic orbital of the surrounding Se atoms. The stability of magnetic moment is found to be determined by the direction of applied electric field. A switchable magnetic configuration in Ga vacancy doped GaSe monolayer is achieved under a critical electric field of 0.6 V/Å. Electric field induces redistribution of the electronic states. Finally, charge transfers are found to be responsible for the controllable magnetic structure in this system. The magnetic modulation on GaSe monolayer in this work offers some references for the design and fabrication of tunable two-dimensional spintronic device.

  13. Electric field effect of GaAs monolayer from first principles

    Directory of Open Access Journals (Sweden)

    Jiongyao Wu

    2017-03-01

    Full Text Available Using first-principle calculations, we investigate two-dimensional (2D honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.

  14. Growth of cultured porcine retinal pigment epithelial cells

    DEFF Research Database (Denmark)

    Wiencke, A.K.; Kiilgaard, Jens Folke; Nicolini, Jair

    2003-01-01

    To establish and characterize cultures of porcine retinal pigment epithelial (pRPE) cells in order to produce confluent monolayers of cells for transplantation.......To establish and characterize cultures of porcine retinal pigment epithelial (pRPE) cells in order to produce confluent monolayers of cells for transplantation....

  15. Polar Bears

    Science.gov (United States)

    Amstrup, Steven C.; Douglas, David C.; Reynolds, Patricia E.; Rhode, E.B.

    2002-01-01

    Polar bears (Ursus maritimus) are hunted throughout most of their range. In addition to hunting polar bears of the Beaufort Sea region are exposed to mineral and petroleum extraction and related human activities such as shipping road-building, and seismic testing (Stirling 1990).Little was known at the start of this project about how polar bears move about in their environment, and although it was understood that many bears travel across political borders, the boundaries of populations had not been delineated (Amstrup 1986, Amstrup et al. 1986, Amstrup and DeMaster 1988, Garner et al. 1994, Amstrup 1995, Amstrup et al. 1995, Amstrup 2000).As human populations increase and demands for polar bears and other arctic resources escalate, managers must know the sizes and distributions of the polar bear populations. Resource managers also need reliable estimates of breeding rates, reproductive intervals, litter sizes, and survival of young and adults.Our objectives for this research were 1) to determine the seasonal and annual movements of polar bears in the Beaufort Sea, 2) to define the boundaries of the population(s) using this region, 3) to determine the size and status of the Beaufort Sea polar bear population, and 4) to establish reproduction and survival rates (Amstrup 2000).

  16. Dark excitations in monolayer transition metal dichalcogenides

    DEFF Research Database (Denmark)

    Deilmann, Thorsten; Thygesen, Kristian Sommer

    2017-01-01

    Monolayers of transition metal dichalcogenides (TMDCs) possess unique optoelectronic properties, including strongly bound excitons and trions. To date, most studies have focused on optically active excitations, but recent experiments have highlighted the existence of dark states, which are equally...... important in many respects. Here, we use ab initio many-body calculations to unravel the nature of the dark excitations in monolayer MoSe2, MoS2, WSe2, andWS(2). Our results show that all these monolayer TMDCs host dark states as their lowest neutral and charged excitations. We further show that dark...... excitons possess larger binding energies than their bright counterparts while the opposite holds for trions....

  17. Distinct self-assembly of dithiol monolayers on Au(1 1 1) in water and hexane

    Energy Technology Data Exchange (ETDEWEB)

    Sharif, Aisyah M. [Department of Physics and Energy, University of Limerick (Ireland); Materials and Surface Science Institute, University of Limerick (Ireland); Laffir, Fathima R. [Materials and Surface Science Institute, University of Limerick (Ireland); Buckley, D. Noel [Department of Physics and Energy, University of Limerick (Ireland); Materials and Surface Science Institute, University of Limerick (Ireland); Silien, Christophe, E-mail: christophe.silien@ul.ie [Department of Physics and Energy, University of Limerick (Ireland); Materials and Surface Science Institute, University of Limerick (Ireland)

    2014-09-30

    Highlights: • The self-assembly of 1,4-benzenedimethanethiol in water and in hexane is studied. • The initial phase of assembly is revealed for each solvent using STM and XPS. • Water stabilizes an ordered lying-down phase. • Hexane coadsorbs with benzenedimethanethiol and promotes standing-up absorption. - Abstract: The self-assembly of 1,4-benzenedimethanethiol on Au(1 1 1), at low concentration in water and in hexane which are respectively polar and non-polar solvent, has been studied by scanning tunneling microscopy (STM). The data reveal that, on clean Au(1 1 1), a complete and ordered self-assembled monolayer (SAM) of lying-down dithiols can form within a few seconds in water. While in hexane the adsorption is initially impeded by the rapid growth of an ordered hexane film that is gradually replaced by disordered domains of dithiol until completion of a saturated monolayer. Complemented by X-ray photoelectron spectroscopy measurements, the STM images resolve the progression of the self-assembly in both these polar and non-polar solvent, and highlight how the self-assembly depends on the trio solvent, dithiol, and substrate.

  18. Monolayer-by-monolayer growth of platinum films on complex carbon fiber paper structure

    Energy Technology Data Exchange (ETDEWEB)

    Pang, Liuqing; Zhang, Yunxia [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); Liu, Shengzhong, E-mail: szliu@dicp.ac.cn [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); Dalian National Laboratory for Clean Energy, iChEM, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China)

    2017-06-15

    Graphical abstract: A controlled monolayer-by-monolayer deposition process has been developed to fabricate Pt coating on carbon fiber paper with complex network structures using a dual buffer strategy. This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. In fact, the present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value. - Highlights: • Developed a controlled monolayer-by-monolayer Pt deposition using a dual buffer strategy. • The present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value. • This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. - Abstract: A controlled monolayer-by-monolayer deposition process has been developed to fabricate Pt coating on carbon fiber paper with complex network structures using a dual buffer (Au/Ni) strategy. The X-ray diffraction, electrochemical quartz crystal microbalance, current density analyses, and X-ray photoelectron spectroscopy results conclude that the monolayer deposition process accomplishes full coverage on the substrate and that the thickness of the deposition layer can be controlled on a single atom scale. This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. In fact, the present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value.

  19. Large valley splitting in monolayer WS2 by proximity coupling to an insulating antiferromagnetic substrate

    Science.gov (United States)

    Xu, Lei; Yang, Ming; Shen, Lei; Zhou, Jun; Zhu, Tao; Feng, Yuan Ping

    2018-01-01

    Lifting the valley degeneracy is an efficient way to achieve valley polarization for further valleytronics operations. In this Rapid Communication, we demonstrate that a large valley splitting can be obtained in monolayer transition metal dichalcogenides by magnetic proximity coupling to an insulating antiferromagnetic substrate. As an example, we perform first-principles calculations to investigate the electronic structures of monolayer WS2 on the MnO(111) surface. Our calculation results suggest that a large valley splitting of 214 meV, which corresponds to a Zeeman magnetic field of 1516 T, is induced in the valence band of monolayer WS2. The magnitude of valley splitting relies on the strength of interfacial orbital hybridization and can be tuned continually by applying an external out-of-plane pressure and in-plane strain. More interestingly, we find that both spin and valley index will flip when the magnetic ordering of MnO is reversed. Besides, owing to the sizable Berry curvature and time-reversal symmetry breaking in the WS2/MnO heterostructure, a spin- and valley-polarized anomalous Hall current can be generated in the presence of an in-plane electric field, which allows one to detect valleys by the electrical approach. Our results shed light on the realization of valleytronic devices using the antiferromagnetic insulator as the substrate.

  20. Observations of two-dimensional monolayer zinc oxide

    Energy Technology Data Exchange (ETDEWEB)

    Sahoo, Trilochan, E-mail: trilochansahoo@gmail.com [Department of Physics and Nanotechnology, SRM University, Kattankulathur, 603203 Tamilnadu (India); Nayak, Sanjeev K. [Institute of Physics, Martin Luther University Halle-Wittenberg, Von Seckendorff Platz 1, 06120 Halle (Germany); Chelliah, Pandian [Department of Physics and Nanotechnology, SRM University, Kattankulathur, 603203 Tamilnadu (India); Rath, Manasa K.; Parida, Bhaskar [Division of Advanced Materials Engineering, Chonbuk National University, Jeonju 561756 (Korea, Republic of)

    2016-03-15

    Highlights: • Synthesis of planer ZnO nanostructure. • Observation of multilayered and monolayer ZnO. • DFT calculation of (10-10), (11-20) and (0 0 0 1) planes of ZnO. • Stability of non-polar (10-10) and (11-20) planes of ZnO. - Abstract: This letter reports the observations of planar two-dimensional ZnO synthesized using the hydrothermal growth technique. High-resolution transmission electron microscopy revealed the formation of a two-dimensional honeycomb lattice and aggregated structures of layered ZnO. The nonpolar (10-10) and (11-20) planes were present in the X-ray diffraction patterns, but the characteristic (0 0 0 1) peak of bulk ZnO was absent. The study found that nonpolar freestanding ZnO structures composed of a single or few layers may be more stable and may have a higher probability of formation than their polar counterparts. The stability of the nonpolar two-dimensional hexagonal ZnO slabs is supported by density functional theory studies.

  1. Sub-THz Characterisation of Monolayer Graphene

    Directory of Open Access Journals (Sweden)

    Ehsan Dadrasnia

    2014-01-01

    Full Text Available We explore the optical and electrical characteristics of monolayer graphene by using pulsed optoelectronic terahertz time-domain spectroscopy in the frequency range of 325–500 GHz based on fast direct measurements of phase and amplitude. We also show that these parameters can, however, be measured with higher resolution using a free space continuous wave measurement technique associated with a vector network analyzer that offers a good dynamic range. All the scattering parameters (both magnitude and phase are measured simultaneously. The Nicholson-Ross-Weir method is implemented to extract the monolayer graphene parameters at the aforementioned frequency range.

  2. Nonlinear optical studies of organic monolayers

    International Nuclear Information System (INIS)

    Shen, Y.R.

    1988-02-01

    Second-order nonlinear optical effects are forbidden in a medium with inversion symmetry, but are necessarily allowed at a surface where the inversion summary is broken. They are often sufficiently strong so that a submonolayer perturbation of the surface can be readily detected. They can therefore be used as effective tools to study monolayers adsorbed at various interfaces. We discuss here a number of recent experiments in which optical second harmonic generation (SHG) and sum-frequency generation (SFG) are employed to probe and characterize organic monolayers. 15 refs., 5 figs

  3. Self-assembled monolayers on gold nanospheres studied by optical second-harmonic generation

    Science.gov (United States)

    Yamaguchi, T.; Kajikawa, K.

    2008-08-01

    Recently plasmonic biosensors consisting of gold nanoparticles have been developed. In order to understand the response of the biosensors, we have investigated how are gold nanospheres immobilized on a surface covered by a self-assembled monolayer (SAM) which is formed by immersion of the substrate in a solution, by use of surface second-harmonic generation (SHG). The surface immobilized gold nanospheres (SIGNs) are supported by a self-assembled monolayer (SAM) of aminoundecanthiol on a gold thin film. The SIGN substrate was immersed in an ethanol solution of hemicyanine-terminated alkanethiol. The capping angles of the hemicyanine SAM with respect to the top of the SIGN were evaluated from polarization dependence of SHG intensity. The SIGNs are not fully covered with the SAM, and the capping angle is found to be approximately 120 degrees.

  4. The Interface between Gd and Monolayer MoS2: A First-Principles Study

    KAUST Repository

    Zhang, Xuejing

    2014-12-08

    We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface and interface the Gd f states shift to lower energy and new surface/interface Gd d states appear at the Fermi energy, which are strongly hybridized with the Mo 4d states and thus lead to a high spin-polarization (ferromagnetically ordered Mo magnetic moments of 0.15 μB). Gd therefore is an interesting candidate for spin injection into monolayer MoS2.

  5. Quantum description of the optical response of charged monolayer-thick metallic patch nanoantennas

    Science.gov (United States)

    Herrera, Mario Zapata; Kazansky, Andrey K.; Aizpurua, Javier; Borisov, Andrei G.

    2017-06-01

    The optical response of small charged metallic nanodisks of one atomic monolayer thickness is analyzed under the excitation by an incident plane wave and by a localized pointlike dipole. Using the time-dependent density functional theory (TDDFT) and classical electrodynamical calculations we identify the bright and dark plasmon modes and study their evolution under external charging of the nanostructure. For neutral nanodisks, despite their monolayer thickness, the in-plane optical response, as obtained from TDDFT, is in agreement with classical electromagnetic results. The optical response for an incident wave polarized perpendicular to the nanostructure cannot be retrieved classically as it reflects a discrete energy structure of electronic levels. This latter situation appears most sensitive to external charging while the energy of the in-plane plasmon with dipolar character is nearly charge independent.

  6. Possible doping strategies for MoS 2 monolayers: An ab initio study

    KAUST Repository

    Dolui, Kapildeb

    2013-08-14

    Density functional theory is used to systematically study the electronic properties of doped MoS2 monolayers, where the dopants are incorporated both via S/Mo substitution or as adsorbates. Among the possible substitutional dopants at the Mo site, Nb is identified as suitable p-type dopant, while Re is the donor with the lowest activation energy. When dopants are simply adsorbed on a monolayer we find that alkali metals shift the Fermi energy into the MoS2 conduction band, making the system n type. Finally, the adsorption of charged molecules is considered, mimicking an ionic liquid environment. We find that molecules adsorption can lead to both n- and p-type conductivity, depending on the charge polarity of the adsorbed species. © 2013 American Physical Society.

  7. Photoinduced quantum spin and valley Hall effects, and orbital magnetization in monolayer MoS2

    KAUST Repository

    Tahir, M.

    2014-09-22

    We theoretically demonstrate that 100% valley-polarized transport in monolayers of MoS2 and other group-VI dichalcogenides can be obtained using off-resonant circularly polarized light. By tuning the intensity of the off-resonant light the intrinsic band gap in one valley is reduced, while it is enhanced in the other valley, enabling single valley quantum transport. As a consequence, we predict (i) enhancement of the longitudinal electrical conductivity, accompanied by an increase in the spin polarization of the flowing electrons, (ii) enhancement of the intrinsic spin Hall effect, together with a reduction of the intrinsic valley Hall effect, and (iii) enhancement of the orbital magnetic moment and orbital magnetization. These mechanisms provide appealing opportunities to the design of nanoelectronics based on dichalcogenides.

  8. Proliferation of pulmonary endothelial cells: time-lapse cinematography of growth to confluence and restitution of monolayer after wounding.

    Science.gov (United States)

    Ryan, U S; Absher, M; Olazabal, B M; Brown, L M; Ryan, J W

    1982-01-01

    A fundamental characteristic of vascular endothelium is that it exists as a monolayer, a condition that must be met in both vascular growth and repair. Maintenance of the monolayer is important both for the exchange of nutrients and for interactions between blood solutes and endothelial enzymes and transport systems. We have used time-lapse cinematography to compare proliferative behavior of bovine pulmonary endothelial cells in (1) establishment of a monolayer from a low-density seed (7.5 X 10(4) cells in a 60 mm dish) and (2) restitution of a confluent monolayer (approx. 2.9 x 10(6) cells in a 60 mm dish) following a mechanical wound (removal of cells from an area 5 x 15 mm by scraping). Culture 2 was not refed after wounding. In culture 2, approx. 30% of the cells accounted for repopulation (confluence in 40 hr). In culture 1, all cells entered into division. Participating cells of culture 2 began division immediately (69 divisions/filmed area in 10 hr, vs. four divisions in culture 1). Interdivision times (IDT) were longer and relatively constant in culture 1 until near confluence; none were less than 10 h, whereas in 2, 24% of the IDT's were less than or equal to 10 hr. Remarkably, IDTs of culture 2 decreased steadily until confluence was re-established. Cell migration in culture 1 was multidirectional while direction of migration in culture 2 was always into the wound area. Mean migration rate (MIG) in culture 2 was related to the site of origin of the cells, those dividing farthest from the unwounded area had fastest MIGs. Neither culture formed more than a single layer of cells. Although the cell kinetics of cultures 1 and 2 differed, the same goal, confluence, was achieved in either case.

  9. Interaction of plasma apolipoproteins with lipid monolayers

    NARCIS (Netherlands)

    Jackson, R.L.; Pattus, F.; Demel, R.A.

    1979-01-01

    The monolayer technique has been used to study the interaction of lipids with plasma apolipoproteins. Apolipoprotein C-II and C-III from human very low density lipoproteins, apolipoprotein A-I from human high density lipoproteins and arginine-rich protein from swine very low density lipoproteins

  10. Semiconductor monolayer assemblies with oriented crystal faces

    KAUST Repository

    Ma, Guijun

    2012-01-01

    Fabrication of two-dimensional monolayers of crystalline oxide and oxynitride particles was attempted on glass plate substrates. X-Ray diffraction patterns of the assemblies show only specific crystal facets, indicative of the uniform orientation of the particles on the substrate. The selectivity afforded by this immobilization technique enables the organization of randomly distributed polycrystalline powders in a controlled manner.

  11. Nanotubes based on monolayer blue phosphorus

    KAUST Repository

    Montes Muñoz, Enrique

    2016-07-08

    We demonstrate structural stability of monolayer zigzag and armchair blue phosphorus nanotubes by means of molecular dynamics simulations. The vibrational spectrum and electronic band structure are determined and analyzed as functions of the tube diameter and axial strain. The nanotubes are found to be semiconductors with a sensitive indirect band gap that allows flexible tuning.

  12. Shadow mask evaporation through monolayer modified nanostencils

    NARCIS (Netherlands)

    Kolbel, M.; Tjerkstra, R.W.; Brugger, J.P.; van Rijn, C.J.M.; Nijdam, W.; Huskens, Jurriaan; Reinhoudt, David

    2002-01-01

    Gradual clogging of the apertures of nanostencils used as miniature shadow masks in metal evaporations can be reduced by coating the stencil with self-assembled monolayers (SAM). This is quantified by the dimensions (height and volume) of gold features obtained by nanostencil evaporation as measured

  13. Compressibility study of quaternary phospholipid blend monolayers.

    Science.gov (United States)

    Cavalcanti, Leide P; Tho, Ingunn; Konovalov, Oleg; Fossheim, Sigrid; Brandl, Martin

    2011-07-01

    The mechanical properties of liposome membranes are strongly dependent on type and ratio of lipid compounds, which can have important role in drug targeting and release processes when liposome is used as drug carrier. In this work we have used Brewster's angle microscopy to monitor the lateral compression process of lipid monolayers containing as helper lipids either distearoyl phosphatidylethanolamine (DSPE) or dioleoyl phophatidylethanolamine (DOPE) molecules on the Langmuir trough. The compressibility coefficient was determined for lipid blend monolayers containing the helper lipids above, cholesterol, distearoyl phosphatidylcholine (DSPC) and pegylated-DSPE at room temperature. Two variables, the cholesterol fraction and the ratio ρ between the helper lipid (either DSPE or DOPE) and the reference lipid DSPC, were studied by multivariate analysis to evaluate their impact on the compressibility coefficient of the monolayers. The cholesterol level was found to be the most significant variable for DSPE blends while the ratio ρ was the most significant one for DOPE blend monolayers. It was also found that these two variables can exhibit positive interaction and the same compressibility value can be obtained with different blend compositions. Copyright © 2011 Elsevier B.V. All rights reserved.

  14. Mode damping in a commensurate monolayer solid

    DEFF Research Database (Denmark)

    Bruch, Ludwig Walter; Hansen, Flemming Yssing

    1997-01-01

    The normal modes of a commensurate monolayer solid may be damped by mixing with elastic waves of the substrate. This was shown by Hall, Mills, and Black [Phys. Rev. B 32, 4932 (1985)], for perpendicular adsorbate vibrations in the presence of an isotropic elastic medium. That work is generalized...

  15. Imidazolide monolayers for versatile reactive microcontact printing

    NARCIS (Netherlands)

    Hsu, S.H.; Reinhoudt, David; Huskens, Jurriaan; Velders, Aldrik

    2008-01-01

    Imidazolide monolayers prepared from the reaction of amino SAMs with N,N-carbonyldiimidazole (CDI) are used as a versatile platform for surface patterning with amino-, carboxyl- and alcohol-containing compounds through reactive microcontact printing (µCP). To demonstrate the surface reactivity of

  16. Patterned monolayers of nitronyl nitroxide radicals

    NARCIS (Netherlands)

    Mannini, Matteo; Rovai, Donella; Sorace, Lorenzo; Perl, A.; Ravoo, B.J.; Reinhoudt, David

    2008-01-01

    We report here the results of the preliminary characterization of the monolayer obtained both by self-assembling and microcontact printing of a di-alkyl sulfide nitronyl nitroxide derivative, 11-decyl sulfanyl-undecanyl nitronyl nitroxide of which we describe the synthesis. The sulfide unit has been

  17. Fullerene monolayer formation by spray coating

    Czech Academy of Sciences Publication Activity Database

    Červenka, Jiří; Flipse, C.F.J.

    2010-01-01

    Roč. 21, č. 6 (2010), 065302/1-065302/7 ISSN 0957-4484 Institutional research plan: CEZ:AV0Z10100521 Keywords : monolayer * spray coating * fullerene * atomic force microscopy * scanning tunnelling microscopy * electronic structure * graphite * gold Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.644, year: 2010

  18. Elasticity of a quantum monolayer solid

    DEFF Research Database (Denmark)

    Bruch, Ludwig Walter

    1992-01-01

    A perturbation-theory formulation of the zero-temperature elastic constants is used to verify symmetry relations for a (monolayer) triangluar lattice. A generalization of the Cauchy relation between the two elastic constants of the triangular lattice with central-pair-potential interactions...

  19. A Model for Spheroid versus Monolayer Response of SK-N-SH Neuroblastoma Cells to Treatment with 15-Deoxy-PGJ2

    Directory of Open Access Journals (Sweden)

    Dorothy I. Wallace

    2016-01-01

    Full Text Available Researchers have observed that response of tumor cells to treatment varies depending on whether the cells are grown in monolayer, as in vitro spheroids or in vivo. This study uses data from the literature on monolayer treatment of SK-N-SH neuroblastoma cells with 15-deoxy-PGJ2 and couples it with data on growth rates for untreated SK-N-SH neuroblastoma cells grown as multicellular spheroids. A linear model is constructed for untreated and treated monolayer data sets, which is tuned to growth, death, and cell cycle data for the monolayer case for both control and treatment with 15-deoxy-PGJ2. The monolayer model is extended to a five-dimensional nonlinear model of in vitro tumor spheroid growth and treatment that includes compartments of the cell cycle (G1,S,G2/M as well as quiescent (Q and necrotic (N cells. Monolayer treatment data for 15-deoxy-PGJ2 is used to derive a prediction of spheroid response under similar treatments. For short periods of treatment, spheroid response is less pronounced than monolayer response. The simulations suggest that the difference in response to treatment of monolayer versus spheroid cultures observed in laboratory studies is a natural consequence of tumor spheroid physiology rather than any special resistance to treatment.

  20. Essential Function for PDLIM2 in Cell Polarization in Three-Dimensional Cultures by Feedback Regulation of the β1-Integrin–RhoA Signaling Axis

    Directory of Open Access Journals (Sweden)

    Ravi Kiran Deevi

    2014-05-01

    Full Text Available PDLIM2 is a cytoskeletal and nuclear PDZ-LIM domain protein that regulates the stability of Nuclear Factor kappa-B (NFκB and other transcription factors, and is required for polarized cell migration. PDLIM2 expression is suppressed by methylation in different cancers, but is strongly expressed in invasive breast cancer cells that have undergone an Epithelial Mesenchymal Transition (EMT. PDLIM2 is also expressed in non-transformed breast myoepithelial MCF10A cells and here we asked whether it is important for maintaining the polarized, epithelial phenotype of these cells. Suppression of PDLIM2 in MCF10A cells was sufficient to disrupt cell polarization and acini formation with increased proliferation and reduced apoptosis in the luminal space compared to control acini with hollow lumina. Spheroids with suppressed PDLIM2 exhibited increased expression of cell-cell and cell-matrix adhesion proteins including beta 1 (β1 integrin. Interestingly, levels of the Insulin-like growth factor 1 receptor (IGF-1 R and Receptor of activated protein kinase C 1 (RACK1, which scaffolds IGF-1R to β1 integrin, were also increased, indicating a transformed phenotype. Focal Adhesion Kinase (FAK and cofilin phosphorylation, and RhoA Guanosine Triphosphatase (GTPase activity were all enhanced in these spheroids compared to control acini. Importantly, inhibition of either FAK or Rho Kinase (ROCK was sufficient to rescue the polarity defect. We conclude that PDLIM2 expression is essential for feedback regulation of the β1-integrin-RhoA signalling axis and integration of cellular microenvironment signals with gene expression to control the polarity of breast epithelial acini structures. This is a mechanism by which PDLIM2 could mediate tumour suppression in breast epithelium.

  1. Electronic miniband structure, heat capacity and magnetic susceptibility of monolayer and bilayer silicene in TI, VSPM and BI regimes

    Energy Technology Data Exchange (ETDEWEB)

    Yarmohammadi, Mohsen, E-mail: m.yarmohammadi69@gmail.com

    2017-04-11

    In the current work, we theoretically study the electronic band structure (EBS), electronic heat capacity (EHC) and magnetic susceptibility (MS) of three structures including monolayer, AA-stacked and AB-stacked bilayer silicene based on the Kane–Mele Hamiltonian model and Green's function method. The particular attention of this study is paid to the effect of external electric field on the aforementioned physical properties. By variation of the electric field, three phases are found: Topological insulator (TI), valley–spin polarized metal (VSPM) and band insulator (BI). Marvellously, its electronic minibands show that the spin-up contribution of charge carriers with lowest energy bands behaves like relativistic Dirac fermions with linear (parabolic) energy dispersions in monolayer (bilayer) case near the Dirac points. An insightful analysis shows that the maximum and minimum value of EHC peak appear for (AA) AB-stacked bilayer and monolayer silicene in TI (BI) regime while in MS curves appear for (AB) AA-stacked bilayer and monolayer lattices in TI (BI) regime, respectively. Moreover, we have observed a phase transition from antiferromagnetic to ferromagnetic and paramagnetic in the monolayer and bilayer structures in the VSPM regime based on the MS findings, respectively. - Highlights: • Comparison of electronic miniband structure of monolayer and bilayer silicene by using the Kane–Mele model and Green's function technique. • Investigation and comparison the electronic contribution of heat capacity for different configurations of silicene structures. • Observation of phase transition from antiferromagnetic to ferromagnetic and paramagnetic phase in the monolayer and bilayer cases, respectively.

  2. Collective cell streams in epithelial monolayers depend on cell adhesion

    International Nuclear Information System (INIS)

    Czirók, András; Varga, Katalin; Méhes, Előd; Szabó, András

    2013-01-01

    We report spontaneously emerging, randomly oriented, collective streaming behavior within a monolayer culture of a human keratinocyte cell line, and explore the effect of modulating cell adhesions by perturbing the function of calcium-dependent cell adhesion molecules. We demonstrate that decreasing cell adhesion induces narrower and more anisotropic cell streams, reminiscent of decreasing the Taylor scale of turbulent liquids. To explain our empirical findings, we propose a cell-based model that represents the dual nature of cell–cell adhesions. Spring-like connections provide mechanical stability, while a cellular Potts model formalism represents surface-tension driven attachment. By changing the relevance and persistence of mechanical links between cells, we are able to explain the experimentally observed changes in emergent flow patterns. (paper)

  3. Acamprosate permeability across Caco-2 cell monolayer is predominantly paracellular

    DEFF Research Database (Denmark)

    Antonescu, Irina-Elena; Steffansen, Bente

    was mathematically accounting for the unstirred boundary layer permeability (PUBL), the filter permeability (Pf), the intrinsic passive transcellular permeability (Ptrans,0) and Ppara (1-3). The mathematical model thereby accounted for (i) the physical-chemical properties of acamprosate and mannitol (molecular...... role in acamprosate permeability, as only a very low fraction of acamprosate is in the neutral form at pH 7.4. The estimated acamprosate Ppara accounts for nearly 100% of the mathematically determined acamprosate Papp, calc (0.20 ± 0.10 x 10-6 cm/s), which matches well with the experimentally...... in the different regions of the rodent small intestine and colon. Biopharm Drug Dispos. 2017;38(2):94-114. 2. Avdeef A. Leakiness and size exclusion of paracellular channels in cultured epithelial cell monolayers-interlaboratory comparison. Pharm Res. 2010;27(3):480-9. 3. Avdeef A. Absorption and Drug Development...

  4. Study of the ability of self-assembled N-vinylcarbazole monolayers to protect copper against corrosion

    Directory of Open Access Journals (Sweden)

    NAI-XING WANG

    2002-10-01

    Full Text Available N-Vinylcarbazole (NVC monolayers were self-assembled on copper surfaces. The electrochemical properties of the copper surfaces modified by NVC self-assembled monolayers (SAMs were investigated using polarization and electrochemical impedance spectroscopic (EIS methods. The polarization measurements indicated that the NVC SAMs could reduce the rates of the anodic and cathodic reaction on the surface of copper electrodes in 0.5 mol dm-3 NaCl solution. The EIS results showed the NVC formed a closely packed film that was able to inhibit copper corrosion. X-Ray photoelectron spectroscopy (XPS analysis of the copper samples and atomic adsorption analysis of the solution showed that the copper surfaces were covered by NVC SAMs, and the adsorption of NVC on the copper surfaces was accompanied with dissolution of Cu into the solution.

  5. The Shell Structure Effect on the Vapor Selectivity of Monolayer-Protected Gold Nanoparticle Sensors

    Directory of Open Access Journals (Sweden)

    Rui-Xuan Huang

    2014-02-01

    Full Text Available Four types of monolayer-protected gold nanoclusters (MPCs were synthesized and characterized as active layers of vapor sensors. An interdigitated microelectrode (IDE and quartz crystal microbalance (QCM were used to measure the electrical resistance and mass loading changes of MPC films during vapor sorption. The vapor sensing selectivity was influenced by the ligand structure of the monolayer on the surface of gold nanoparticles. The responses of MPC-coated QCM were mainly determined according to the affinity between the vapors and surface ligands of MPCs. The responses to the resistance changes of the MPC films were due to the effectiveness of the swelling when vapor was absorbed. It was observed that resistive sensitivity to polar organics could be greatly enhanced when the MPC contained ligands that contain interior polar functional groups with exterior nonpolar groups. This finding reveals that reducing interparticle attraction by using non-polar exterior groups could increase effective swelling and therefore enhance the sensitivity of MPC-coated chemiresistors.

  6. A Protocol for Isolation and Enriched Monolayer Cultivation of Neural Precursor Cells from Mouse Dentate Gyrus

    OpenAIRE

    Babu, Harish; Claasen, Jan-Hendrik; Kannan, Suresh; Rünker, Annette E.; Palmer, Theo; Kempermann, Gerd

    2011-01-01

    In vitro assays are valuable tools to study the characteristics of adult neural precursor cells under controlled conditions with a defined set of parameters. We here present a detailed protocol based on our previous original publication (Babu et al., 2007) to isolate neural precursor cells from the hippocampus of adult mice and maintain and propagate them as adherent monolayer cultures. The strategy is based on the use of Percoll density gradient centrifugation to enrich precursor cells from ...

  7. A protocol for isolation and enriched monolayer cultivation of neural precursor cells from mouse dentate gyrus

    OpenAIRE

    Harish eBabu; Jan-Hendrik eClaasen; Jan-Hendrik eClaasen; Jan-Hendrik eClaasen; Suresh eKannan; Annette E. Rünker; Theo ePalmer; Gerd eKempermann; Gerd eKempermann

    2011-01-01

    In vitro assays are valuable tools to study the characteristics of adult neural precursor cells under controlled conditions with a defined set of parameters. We here present a detailed protocol based on our previous original publication (Babu et al., Enriched monolayer precursor cell cultures from micro-dissected adult mouse dentate gyrus yield functional granule cell-like neurons, PLoS One 2007, 2:e388) to isolate neural precursor cells from the hippocampus of adult mice and maintain and pro...

  8. Political polarization

    OpenAIRE

    Dixit, Avinash K.; Weibull, Jörgen W.

    2007-01-01

    Failures of government policies often provoke opposite reactions from citizens; some call for a reversal of the policy, whereas others favor its continuation in stronger form. We offer an explanation of such polarization, based on a natural bimodality of preferences in political and economic contexts and consistent with Bayesian rationality.

  9. Political polarization.

    Science.gov (United States)

    Dixit, Avinash K; Weibull, Jörgen W

    2007-05-01

    Failures of government policies often provoke opposite reactions from citizens; some call for a reversal of the policy, whereas others favor its continuation in stronger form. We offer an explanation of such polarization, based on a natural bimodality of preferences in political and economic contexts and consistent with Bayesian rationality.

  10. Elastic properties of cells in the context of confluent cell monolayers: impact of tension and surface area regulation

    OpenAIRE

    Pietuch, Anna; Brückner, Bastian Rouven; Fine, Tamir; Mey, Ingo; Janshoff, Andreas

    2013-01-01

    Epithelial cells usually form a dense continuous cobblestone-like sheet that is frequently exposed to a variety of mechanical challenges encompassing osmotic stress and external forces. The response to external forces was investigated and the question of how individual polar epithelial cells organized in confluent monolayers respond to pharmaceutical stimuli targeting the key players of cellular mechanics was answered. In particular, we ask how epithelial cells respond to changes ...

  11. Digital imaging system and virtual instrument platform for measuring hydraulic conductivity of vascular endothelial monolayers.

    Science.gov (United States)

    Hubert, Christopher G; McJames, Scott W; Mecham, Ian; Dull, Randal O

    2006-03-01

    We have developed an automated, digital imaging system, controlled by two virtual instruments, to measure hydraulic conductivity (Lp) of cultured endothelial monolayers. Live digital images of multiple independent experiments were captured by custom-designed video processing software running in National Instruments LabVIEW 6.1. Fluid displacement data are automatically displayed in real time as both volumetric flux (Jv) and hydraulic conductivity (Lp). A separate data analysis program is used to display permeability values from stored displacement measurements and displays Jv or Lp of each monolayer. Optional statistical filters have been included to aid in data analysis. This new digital permeability system is able to measure flux rates over a dynamic range from 10(-9) cm/s/cm H2O to 10(-4) cm/s/cm H2O. Values obtained for cultured lung microvascular Lp are nearly identical to other cultured endothelial monolayers and also to values obtained in-vivo using the Landis-Michel technique and the split-drop method. The use of a commercially available platform allows the system configuration to be easily modified to suit the experimental needs. The technical development of this system is described in detail.

  12. Molecular tilt on monolayer-protected nanoparticles

    KAUST Repository

    Giomi, L.

    2012-02-01

    The structure of the tilted phase of monolayer-protected nanoparticles is investigated by means of a simple Ginzburg-Landau model. The theory contains two dimensionless parameters representing the preferential tilt angle and the ratio ε between the energy cost due to spatial variations in the tilt of the coating molecules and that of the van der Waals interactions which favors the preferential tilt. We analyze the model for both spherical and octahedral particles. On spherical particles, we find a transition from a tilted phase, at small ε, to a phase where the molecules spontaneously align along the surface normal and tilt disappears. Octahedral particles have an additional phase at small ε characterized by the presence of six topological defects. These defective configurations provide preferred sites for the chemical functionalization of monolayer-protected nanoparticles via place-exchange reactions and their consequent linking to form molecules and bulk materials. Copyright © EPLA, 2012.

  13. Epitaxial growth by monolayer restricted galvanic displacement

    Directory of Open Access Journals (Sweden)

    Vasilić Rastko

    2012-01-01

    Full Text Available The development of a new method for epitaxial growth of metals in solution by galvanic displacement of layers pre-deposited by underpotential deposition (UPD was discussed and experimentally illustrated throughout the lecture. Cyclic voltammetry (CV and scanning tunneling microscopy (STM are employed to carry out and monitor a “quasi-perfect”, two-dimensional growth of Ag on Au(111, Cu on Ag(111, and Cu on Au(111 by repetitive galvanic displacement of underpotentially deposited monolayers. A comparative study emphasizes the displacement stoichiometry as an efficient tool for thickness control during the deposition process and as a key parameter that affects the deposit morphology. The excellent quality of layers deposited by monolayer-restricted galvanic displacement is manifested by a steady UPD voltammetry and ascertained by a flat and uniform surface morphology maintained during the entire growth process.

  14. Investigation of hexadecanethiol self-assembled monolayers on cadmium tin oxide thin films

    International Nuclear Information System (INIS)

    Rhodes, Crissy L.; Brewer, Scott H.; Folmer, Jaap; Franzen, Stefan

    2008-01-01

    This study reports the use of variable angle reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy to investigate the formation of a 1-hexadecanethiol adlayer on cadmium tin oxide (CTO) thin film surfaces. These adlayers appear to be robust, ordered monolayers. The optical and electronic properties of CTO thin films chemically vapor deposited onto glass substrates were also investigated. The reflectance of the CTO films was dependent upon the incident angle of the impinging radiation and revealed a reflectance decrease indicative of a plasma frequency in the mid-IR using p-polarized radiation

  15. Wilhelmy plate artifacts in elastic monolayers

    Science.gov (United States)

    Witten, T. A.; Wang, Jin; Pocivavsek, L.; Lee, K. Y. C.

    2010-01-01

    A recent article [L. Pocivavsek et al., Soft Matter4, 2019 (2008)] by some of us pointed out difficulties in interpreting Wilhelmy plate measurements on elastic Langmuir monolayers that support anisotropic stress. Using a simplified geometry it showed conditions in which the Wilhelmy plate measures significantly different stress from the ambient stress. We correct a serious error in this analysis and strengthen its conclusion, showing that the Wilhelmy stress and the ambient stress can have opposite signs.

  16. Structure of cholesterol/ceramide monolayer mixtures

    DEFF Research Database (Denmark)

    Scheffer, L.; Solomonov, I.; Weygand, M.J.

    2005-01-01

    The structure of monolayers of cholesterol/ ceramide mixtures was investigated using grazing incidence x-ray diffraction, immunofluorescence, and atomic force microscopy techniques. Grazing incidence x-ray diffraction measurements showed the existence of a crystalline mixed phase of the two....... As ceramide incorporates the lipid backbone common to all sphingolipids, this arrangement may be relevant to the understanding of the molecular organization of lipid rafts....

  17. Janus monolayers of transition metal dichalcogenides

    KAUST Repository

    Lu, Ang-Yu

    2017-05-15

    Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS2 monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements.

  18. Diffusive spreading and mixing of fluid monolayers

    International Nuclear Information System (INIS)

    Popescu, M N; Dietrich, S; Oshanin, G

    2005-01-01

    The use of ultra-thin, i.e. monolayer, films plays an important role in the emerging field of nano-fluidics. Since the dynamics of such films is governed by the interplay between substrate-fluid and fluid-fluid interactions, the transport of matter in nanoscale devices may eventually be efficiently controlled by substrate engineering. For such films, the dynamics is expected to be captured by two-dimensional lattice-gas models with interacting particles. Using a lattice-gas model and the non-linear diffusion equation derived from the microscopic dynamics in the continuum limit, we study two problems of relevance in the context of nano-fluidics. The first one is the case in which along the spreading direction of a monolayer a mesoscopic-sized obstacle is present, with a particular focus on the relaxation of the fluid density profile upon encountering and passing the obstacle. The second one is the mixing of two monolayers of different particle species which spread side by side following the merger of two chemical lanes, here defined as domains of high affinity for fluid adsorption surrounded by domains of low affinity for fluid adsorption

  19. Exploring atomic defects in molybdenum disulphide monolayers

    KAUST Repository

    Hong, Jinhua

    2015-02-19

    Defects usually play an important role in tailoring various properties of two-dimensional materials. Defects in two-dimensional monolayer molybdenum disulphide may be responsible for large variation of electric and optical properties. Here we present a comprehensive joint experiment-theory investigation of point defects in monolayer molybdenum disulphide prepared by mechanical exfoliation, physical and chemical vapour deposition. Defect species are systematically identified and their concentrations determined by aberration-corrected scanning transmission electron microscopy, and also studied by ab-initio calculation. Defect density up to 3.5 × 10 13 cm \\'2 is found and the dominant category of defects changes from sulphur vacancy in mechanical exfoliation and chemical vapour deposition samples to molybdenum antisite in physical vapour deposition samples. Influence of defects on electronic structure and charge-carrier mobility are predicted by calculation and observed by electric transport measurement. In light of these results, the growth of ultra-high-quality monolayer molybdenum disulphide appears a primary task for the community pursuing high-performance electronic devices.

  20. Effects of vacancies on spin-dependent behavior of monolayer and bilayer graphene nanoribbons

    Science.gov (United States)

    Safari, E. Keshavarz; Shokri, A. A.; BabaeiPour, M.

    2017-11-01

    In this work, the effect of vacancies on magnetic properties and spin-dependent behaviors of monolayer and bilayer armchair and zigzag graphene nanoribbons is investigated using first principles calculations based on density functional theory (DFT). The armchair and zigzag graphene nanoribbons are composed of 6 rows and 4 rows of carbon atoms with the edges closed by the hydrogen atoms, respectively. Our results show that vacancies affect the magnetic properties and spin polarization of the graphene nanoribbons. It is seen that the monolayer armchair graphene nanoribbon with one vacancy in its supercell (24 carbon sites + 8 hydrogen sites) gives the magnetic moment of 0.79 μB , while magnetic moment in the monolayer zigzag graphene nanoribbon with one vacancy in its supercell (24 carbon sites + 6 hydrogen sites) is 1.72 μB (for site α) and 1.84 μB (for site β). The highest and lowest values of magnetic moment in different configurations of the bilayer armchair (zigzag) graphene nanoribbons with one vacancy in each layer of the supercell give 1.54 μB and 1.29 μB (3.51 μB and 2.72 μB), respectively. Numerical values of the magnetic moment in different configurations depended on the distance of vacancies from each other and from nanoribbon's edge as well as their orientations.

  1. Biomimetic nanoparticles with polynucleotide and PEG mixed-monolayers enhance calcium phosphate mineralization

    Energy Technology Data Exchange (ETDEWEB)

    Vasconcellos, Kayla B.; McHugh, Sean M.; Dapsis, Katherine J.; Petty, Alexander R.; Gerdon, Aren E., E-mail: gerdoar@emmanuel.edu [Emmanuel College (United States)

    2013-09-15

    Biomineralization of hydroxyapatite (Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2}) is of significant importance in biomedical applications such as bone and dental repair, and biomimetic control of mineral formation may lead to more effective restorative procedures. Gold nanoparticles are functional scaffolds on which to assemble multi-component monolayers capable of mimicking protein activity in the templated synthesis of calcium phosphate. The goal of this research was to explore nanoparticle templates with mixed-monolayers of uncharged polar polyethylene glycol (PEG) molecules and highly charged polynucleotide and amino acid molecules in their ability to influence mineralization rates and mineral particle size and morphology. This research demonstrates through time-resolved optical density and dynamic light scattering measurements that the combination of tiopronin, PEG, and DNA presented on a nanoparticle surface decreases nanoparticle aggregation from 59 to 21 nm solvated radius, increases mineralization kinetics from 1.5 Multiplication-Sign 10{sup -3} to 3.1 Multiplication-Sign 10{sup -3} OD/min, and decreases mineral particle size from 685 to 442 nm average radius. FT-IR and TEM data demonstrate that mineralized material, while initially amorphous, transforms to a semi-crystalline material when guided by template interactions. This demonstrates that surface-tailored monolayer protected cluster scaffolds are successful and controllable mineralization templates with further potential for biomedical applications involving calcium phosphate and other biomaterials.

  2. Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains.

    Science.gov (United States)

    Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

    2015-11-05

    A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability.

  3. An oscillating dynamic model of collective cells in a monolayer

    Science.gov (United States)

    Lin, Shao-Zhen; Xue, Shi-Lei; Li, Bo; Feng, Xi-Qiao

    2018-03-01

    Periodic oscillations of collective cells occur in the morphogenesis and organogenesis of various tissues and organs. In this paper, an oscillating cytodynamic model is presented by integrating the chemomechanical interplay between the RhoA effector signaling pathway and cell deformation. We show that both an isolated cell and a cell aggregate can undergo spontaneous oscillations as a result of Hopf bifurcation, upon which the system evolves into a limit cycle of chemomechanical oscillations. The dynamic characteristics are tailored by the mechanical properties of cells (e.g., elasticity, contractility, and intercellular tension) and the chemical reactions involved in the RhoA effector signaling pathway. External forces are found to modulate the oscillation intensity of collective cells in the monolayer and to polarize their oscillations along the direction of external tension. The proposed cytodynamic model can recapitulate the prominent features of cell oscillations observed in a variety of experiments, including both isolated cells (e.g., spreading mouse embryonic fibroblasts, migrating amoeboid cells, and suspending 3T3 fibroblasts) and multicellular systems (e.g., Drosophila embryogenesis and oogenesis).

  4. Mitochondrial ATP Depletion Disrupts Caco-2 Monolayer Integrity and Internalizes Claudin 7.

    Science.gov (United States)

    JanssenDuijghuijsen, Lonneke M; Grefte, Sander; de Boer, Vincent C J; Zeper, Lara; van Dartel, Dorien A M; van der Stelt, Inge; Bekkenkamp-Grovenstein, Melissa; van Norren, Klaske; Wichers, Harry J; Keijer, Jaap

    2017-01-01

    Objective: In vivo studies suggest that intestinal barrier integrity is dependent on mitochondrial ATP production. Here, we aim to provide mechanistic support, using an in vitro model mimicking the oxidative in vivo situation. Methods: Human Caco-2 cells were cultured for 10 days in culture flasks or for 14 days on transwell inserts in either glucose-containing or galactose-containing medium. Mitochondria were visualized and cellular respiration and levels of oxidative phosphorylation (OXPHOS) proteins were determined. Mitochondrial ATP depletion was induced using CCCP, rotenone, or piericidin A (PA). Monolayer permeability was assessed using transepithelial electrical resistance (TEER) and fluorescein flux. Gene expression and cellular distribution of tight junction proteins were analyzed. Results: Caco-2 cells cultured in galactose-containing, but not in glucose-containing, medium showed increased mitochondrial connectivity, oxygen consumption rates and levels of OXPHOS proteins. Inhibition of mitochondrial ATP production using CCCP, rotenone or PA resulted in a dose-dependent increase in Caco-2 monolayer permeability. In-depth studies with PA showed a six fold decrease in cellular ATP and revealed increased gene expression of tight junction proteins ( TJP ) 1 and 2, occludin, and claudin 1, but decreased gene expression of claudin 2 and 7. Of these, claudin 7 was clearly redistributed from the cellular membrane into the cytoplasm, while the others were not (TJP1, occludin) or slightly (claudin 2, actin) affected. In vivo studies suggest that intestinal barrier integrity is dependent on mitochondrial ATP production. Here, we aim to provide mechanistic support, using an in vitro model mimicking the oxidative in vivo situation. Conclusions: Well-functioning mitochondria are essential for maintaining cellular energy status and monolayer integrity of galactose grown Caco-2 cells. Energy depletion-induced Caco-2 monolayer permeability may be facilitated by changes in

  5. Interaction of toremifene with dipalmitoyl-phosphatidyl-glycerol in monolayers at the air–water interface followed by fluorescence microscopy in Langmuir–Blodgett films

    International Nuclear Information System (INIS)

    Romão, Rute I.S.; Maçôas, Ermelinda; Martinho, José M.G.; Gonçalves da Silva, Amélia M.P.S.

    2013-01-01

    Langmuir monolayers of dipalmitoyl-phosphatidyl-glycerol (DPPG) containing toremifene (TOR), an antiestrogen drug derivative of tamoxifen, were prepared in order to study the interaction of the drug with the cell membrane. TOR is not surface active but it remains at the interface in DPPG rich monolayers anchored by electrostatic interaction with the anionic DPPG up to the equimolar composition. The fluidity of mixed monolayers increases up to the TOR mole fraction X TOR = 0.3, remaining practically invariant for higher compositions. Brewster angle microscopy shows that the TOR disturbs the DPPG organization and the liquid condensed (LC) domains of DPPG become undetectable for X TOR ≥ 0.4. Laser scanning confocal fluorescence microscopy images of the LB films doped with rhodamine B-piperazine amide dye confirm the progressive reduction in size of LC domains, from which TOR and rhodamine are excluded. The incorporation of TOR in DPPG monolayers up to the equimolar composition supports the formation of a TOR:DPPG complex (1:1) due to electrostatic interactions between the negatively charged polar groups of DPPG and protonated TOR. - Highlights: • Toremifene (TOR) in dipalmitoyl-phosphatidyl-glycerol (DPPG) monolayers • Electrostatic interactions between DPPG and TOR form a 1:1 complex. • TOR increases the fluidity of DPPG monolayers. • Incorporation of TOR in the fluid phase of DPPG followed by fluorescence imaging

  6. Interactions between an anticancer drug - edelfosine - and cholesterol in Langmuir monolayers

    International Nuclear Information System (INIS)

    Wiecek, Agata; Dynarowicz-Latka, Patrycja; Minones, J.; Conde, Olga; Casas, Matilde

    2008-01-01

    Edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine, abbr. Et-18-OCH 3 ) is a new generation anticancer drug based on a phospholipids-like structure. Since its mechanism of action is believed to be related to the lipids of cellular membrane, we have investigated the interactions between edelfosine and main mammalian sterol: cholesterol, using the Langmuir monolayer technique. The interactions have been analyzed by comparing the experimental curves with theoretical ones, obtained basing on the additivity rule. The observed contraction together with negative deviations from ideality observed on the mean molecular area (A 12 ) vs film composition plots proves the existence of strong attractive forces between edelfosine and cholesterol, which have been quantified with the excess free energy of mixing (ΔG exc ) values, calculated from the surface pressure-area isotherms datapoints. The most negative values of ΔG exc have been found for the mixture of equimolar composition, proving its highest thermodynamic stability and the existence of the strongest interactions between film components. Thus, it has been postulated that at the surface edelfosine and cholesterol form stable complexes of 1:1 stoichiometry. The analysis of the collapse pressure values for the investigated mixed monolayers proves that films of edelfosine mole fraction ≤ 0.5 are miscible within the whole range of surface pressures, while monolayers richer in edelfosine mix in the pressure region below ca. 37.6 mN/m, which corresponds to the collapse of pure edelfosine monolayer. At this very surface pressure, edelfosine is expelled from the mixed monolayer and the remaining film is composed by surface complexes of high stability. The hypothesis of complex formation explains the results performed in vitro on cell cultures, indicating that the increase of cholesterol content significantly reduces the uptake of edelfosine

  7. Promoting Diversity Through Polar Interdisciplinary Coordinated Education (Polar ICE)

    Science.gov (United States)

    McDonnell, J. D.; Hotaling, L. A.; Garza, C.; Van Dyk, P. B.; Hunter-thomson, K. I.; Middendorf, J.; Daniel, A.; Matsumoto, G. I.; Schofield, O.

    2017-12-01

    Polar Interdisciplinary Coordinated Education (ICE) is an education and outreach program designed to provide public access to the Antarctic and Arctic regions through polar data and interactions with the scientists. The program provides multi-faceted science communication training for early career scientists that consist of a face-to face workshop and opportunities to apply these skills. The key components of the scientist training workshop include cultural competency training, deconstructing/decoding science for non-expert audiences, the art of telling science stories, and networking with members of the education and outreach community and reflecting on communication skills. Scientists partner with educators to provide professional development for K-12 educators and support for student research symposia. Polar ICE has initiated a Polar Literacy initiative that provides both a grounding in big ideas in polar science and science communication training designed to underscore the importance of the Polar Regions to the public while promoting interdisciplinary collaborations between scientists and educators. Our ultimate objective is to promote STEM identity through professional development of scientists and educators while developing career awareness of STEM pathways in Polar science.

  8. Seeing phenomena in flatland: studies of monolayers by fluorescence microscopy.

    Science.gov (United States)

    Knobler, C M

    1990-08-24

    Monolayers formed at the interface between air and water can be seen with fluorescence microscopy. This allows the phase behavior of these monolayers to be determined by direct observation and opens up the possibility of following the kinetics of phase transformations in two-dimensional systems. Some unexpected morphologies have been discovered that provide information about the nature of monolayer phases and have connections to pattern formation in other systems.

  9. Transfer plate radioassay using cell monolayers to detect anti-cell surface antibodies synthesized by lymphocyte hybridomas

    International Nuclear Information System (INIS)

    Schneider, M.D.; Eisenbarth, G.S.

    1979-01-01

    A solid phase [ 125 I] Protein A radioassay for anti-cell surface antibodies is described, which employs target cell monolayers cultured on fenestrated polyvinyl chloride 96-well plates ('transfer plates'). The calibrated aperture in the bottom of each well is small enough to retain fluid contents by surface tension during monolayer growth, but also permits fluid to enter the wells when transfer plate are lowered into receptacles containing washing buffer on test sera. To assay for antibodies directed against target cell surface antigens, transfer plates bearing monolayers are inserted into microculture plates with corresponding 96-well geometry, thereby simultaneously sampling 96 wells. This assay allows rapid screening of hundreds of hybrid cell colonies for production of antibodies with desired tissue specificity. (Auth.)

  10. NOx Binding and Dissociation: Enhanced Ferroelectric Surface Chemistry by Catalytic Monolayers

    Science.gov (United States)

    Kakekhani, Arvin; Ismail-Beigi, Sohrab

    2013-03-01

    NOx molecules are regulated air pollutants produced during automotive combustion. As part of an effort to design viable catalysts for NOx decomposition operating at higher temperatures that would allow for improved fuel efficiency, we examine NOx chemistry on ferroelectric perovskite surfaces. Changing the direction of ferroelectric polarization can modify surface electronic properties and may lead to switchable surface chemistry. Here, we describe our recent work on potentially enhanced surface chemistry using catalytic RuO2 monolayers on perovskite ferroelectric substrates. In addition to thermodynamic stabilization of the RuO2 layer, we present results on the polarization-dependent binding of NO, O2, N2, and atomic O and N. We present results showing that one key problem with current catalysts, involving the difficulty of releasing dissociation products (especially oxygen), can be ameliorated by this method. Primary support from Toyota Motor Engineering and Manufacturing, North America, Inc.

  11. A first-principles study on the magnetic properties of nonmetal atom doped phosphorene monolayers.

    Science.gov (United States)

    Zheng, Huiling; Zhang, Jianmin; Yang, Baishun; Du, Xiaobo; Yan, Yu

    2015-07-07

    In order to induce magnetism in two-dimensional semiconductors for their applications in spintronic devices and novel chemical and electronic properties of semiconducting phosphorene, the geometrical structure, electronic and magnetic properties of doped phosphorene monolayers with a series of nonmetal atoms, including H, F, Cl, Br, I, B, C, Si, N, As, O, S and Se, were systematically investigated using first-principles calculations. The results show that although the substitutional doping of H, F, Cl, Br, I, B, N, O, S or Se results in large structural deformation at the doping sites of phosphorene monolayers, all neutral nonmetal atom doped systems are stable. The calculated formation energies reveal that the substitutional doping of numerous nonmetal atoms in phosphorene monolayer are possible under appropriate experimental conditions, and the charged dopants C(-), Si(-), S(+) and Se(+) are stable. Moreover, the substitutional doping of H, F, Cl, Br, I, B, N, As, C(-), Si(-), S(+) or Se(+) cannot induce magnetism in phosphorene monolayer due to the saturation or pairing of valence electrons of dopant and its neighboring P atoms, whereas ground states of neutral C, Si, O, S or Se doped systems are magnetic due to the appearance of an unpaired valence electron of C and Si or the formation of a nonbonding 3p electron of a neighboring P atom around O, S and Se. Furthermore, the magnetic coupling between the moments induced by two Si, O, S or Se are long-range anti-ferromagnetic and the coupling can be attributed to the hybridization interaction involving polarized electrons, whereas the coupling between the moments induced by two C is weak.

  12. Zitterbewegung in monolayer silicene in a magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Romera, E. [Departamento de Física Atómica, Molecular y Nuclear and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Roldán, J.B. [Departamento de Electrónica y Tecnología de Computadores and CITIC, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Santos, F. de los [Departamento de Electromagnetismo y Física de la Materia, and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain)

    2014-07-04

    We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an effective Hamiltonian, we have investigated the autocorrelation function and the density currents in this material. Moreover, we have analyzed other types of periodicities of the system (classical and revival times). Finally, the above results are compared with their counterparts in two other monolayer materials subject to a magnetic field: graphene and MoS{sub 2}. - Highlights: • We study Zitterbewegung in monolayer silicene in a magnetic field. • We have analyzed other types of periodicities in silicene. • The above results are compared with other monolayer materials (graphene and MoS{sub 2})

  13. Anomalously fast kinetics of lipid monolayer buckling

    Science.gov (United States)

    Oppenheimer, Naomi; Diamant, Haim; Witten, Thomas A.

    2013-08-01

    We reexamine previous observations of folding kinetics of compressed lipid monolayers in light of the accepted mechanical buckling mechanism recently proposed by L. Pocivavsek [ScienceSCIEAS0036-807510.1126/science.1154069 320, 912 (2008)]. Using simple models, we set conservative limits on (a) the energy released in the mechanical buckling process and (b) the kinetic energy entailed by the observed folding motion. These limits imply a kinetic energy at least 30 times greater than the energy supplied by the buckling instability. We discuss possible extensions of the accepted picture that might resolve this discrepancy.

  14. Defect-Tolerant Monolayer Transition Metal Dichalcogenides

    DEFF Research Database (Denmark)

    Pandey, Mohnish; Rasmussen, Filip Anselm; Kuhar, Korina

    2016-01-01

    -principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that the TMDs based on group VI and X metals form deep gap states upon creation of a chalcogen (S, Se, Te) vacancy, while the TMDs based on group IV metals form only...... shallow defect levels and are thus predicted to be defect-tolerant. Interestingly, all the defect sensitive TMDs have valence and conduction bands with a very similar orbital composition. This indicates a bonding/antibonding nature of the gap, which in turn suggests that dangling bonds will fall inside...

  15. Fibrinogen monolayer characterization by colloid deposition.

    Science.gov (United States)

    Nattich-Rak, Małgorzata; Adamczyk, Zbigniew; Wasilewska, Monika; Sadowska, Marta

    2013-09-24

    Colloid particle deposition was applied to characterize bovine and human fibrinogen (Fb) monolayers on mica produced by controlled adsorption under diffusion transport at pH 3.5. The surface concentration of Fb was determined by AFM enumeration of single molecules adsorbed over the substrate surface. The electrokinetic properties of Fb monolayers for various ionic strength were studied using the in situ streaming potential measurements. It was shown that Fb adsorbs irreversibly on mica for a broad range of ionic strength of 4 × 10(-4) to 0.15 M, NaCl. The overcharging of initially negative mica surface occurred for fibrinogen surface concentrations higher than 1400 μm(-2). The orientation of fibrinogen molecules in the monolayers was evaluated by the colloid deposition method involving negatively charged polystyrene latex microspheres, 820 nm in diameter. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed, which contradicts the mean-field DLVO predictions. Measurable deposition was observed even at low ionic strength where the minimum approach distance of latex particles to the interface exceeds 70 nm (for 6 × 10(-4) M NaCl). This confirms that, at this pH, fibrinogen molecules adsorb end-on on mica assuming extended conformations with the positive charge located mostly in the end part of the αA chains. This agrees with previous experimental and theoretical results discussed in the literature (Santore, M. M.; Wertz Ch. F. Protein spreading kinetics at liquid-solid interfaces via an adsorption probe method. Langmuir 2005, 21, 10172-10178 (experimental); Adamczyk, Z.; Barbasz, J.; Cieśla, M.; Mechanisms of fibrinogen adsorption at solid substrates. Langmuir, 2011, 25, 6868-6878 (theoretical)). This unusual latex deposition on Fb monolayers was quantitatively interpreted in terms of the model developed in ref 55 (Jin, X.; Wang, N. H. L.; Tarjus, G.; Talbot, J. Irreversible adsorption on nonuniform

  16. Mixed DPPC/POPC Monolayers: All-atom Molecular Dynamics Simulations and Langmuir Monolayer Experiments

    Czech Academy of Sciences Publication Activity Database

    Olžyńska, Agnieszka; Zubek, M.; Roeselová, Martina; Korchowiec, J.; Cwiklik, Lukasz

    2016-01-01

    Roč. 1858, č. 12 (2016), s. 3120-3130 ISSN 0005-2736 R&D Projects: GA ČR GA15-14292S Institutional support: RVO:61388955 ; RVO:61388963 Keywords : phospholipid monolayers * Lung surfactant * molecular dynamics Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.498, year: 2016

  17. Template-Directed Self-Assembly of Alkanethiol Monolayers: Selective Growth on Preexisting Monolayer Edges

    NARCIS (Netherlands)

    Sharpe, R.B.A.; Burdinski, Dirk; Huskens, Jurriaan; Zandvliet, Henricus J.W.; Reinhoudt, David; Poelsema, Bene

    2007-01-01

    Self-assembled monolayers were investigated for their suitability as two-dimensional scaffolds for the selective growth of alkanethiol edge structures. Heterostructures with chemical contrast could be grown, whose dimensions were governed by both the initial pattern sizes and the process time.

  18. Tuning the photo-response in monolayer MoS2 by plasmonic nano-antenna

    Science.gov (United States)

    Li, Jiu; Ji, Qingqing; Chu, Saisai; Zhang, Yanfeng; Li, Yan; Gong, Qihuang; Liu, Kaihui; Shi, Kebin

    2016-03-01

    Monolayer molybdenum disulfide (MoS2) has recently attracted intense interests due to its remarkable optical properties of valley-selected optical response, strong nonlinear wave mixing and photocurrent/photovoltaic generation and many corresponding potential applications. However, the nature of atomic-thin thickness of monolayer MoS2 leads to inefficient light-matter interactions and thereby hinders its optoelectronic applications. Here we report on the enhanced and controllable photo-response in MoS2 by utilizing surface plasmonic resonance based on metallic nano-antenna with characteristic lateral size of 40 × 80 nm. Our nano-antenna is designed to have one plasmonic resonance in the visible range and can enhance the MoS2 photoluminescence intensity up to 10 folds. The intensity enhancement can be effectively tuned simply by the manipulation of incident light polarization. In addition, we can also control the oscillator strength ratio between exciton and trion states by controlling polarization dependent hot carrier doping in MoS2. Our results demonstrate the possibility in controlling the photo-response in broad two-dimensional materials by well-designed nano-antenna and facilitate its coming optoelectronic applications.

  19. Strategic Polarization.

    Science.gov (United States)

    Kalai, Adam; Kalai, Ehud

    2001-08-01

    In joint decision making, similarly minded people may take opposite positions. Consider the example of a marriage in which one spouse gives generously to charity while the other donates nothing. Such "polarization" may misrepresent what is, in actuality, a small discrepancy in preferences. It may be that the donating spouse would like to see 10% of their combined income go to charity each year, while the apparently frugal spouse would like to see 8% donated. A simple game-theoretic analysis suggests that the spouses will end up donating 10% and 0%, respectively. By generalizing this argument to a larger class of games, we provide strategic justification for polarization in many situations such as debates, shared living accommodations, and disciplining children. In some of these examples, an arbitrarily small disagreement in preferences leads to an arbitrarily large loss in utility for all participants. Such small disagreements may also destabilize what, from game-theoretic point of view, is a very stable equilibrium. Copyright 2001 Academic Press.

  20. Serum-free media formulations are cell line-specific and require optimization for microcarrier culture.

    Science.gov (United States)

    Tan, Kah Yong; Teo, Kim Leng; Lim, Jessica F Y; Chen, Allen K L; Choolani, Mahesh; Reuveny, Shaul; Chan, Jerry; Oh, Steve Kw

    2015-08-01

    Mesenchymal stromal cells (MSCs) are being investigated as potential cell therapies for many different indications. Current methods of production rely on traditional monolayer culture on tissue-culture plastic, usually with the use of serum-supplemented growth media. However, the monolayer culturing system has scale-up limitations and may not meet the projected hundreds of billions to trillions batches of cells needed for therapy. Furthermore, serum-free medium offers several advantages over serum-supplemented medium, which may have supply and contaminant issues, leading to many serum-free medium formulations being developed. We cultured seven MSC lines in six different serum-free media and compared their growth between monolayer and microcarrier culture. We show that (i) expansion levels of MSCs in serum-free monolayer cultures may not correlate with expansion in serum-containing media; (ii) optimal culture conditions (serum-free media for monolayer or microcarrier culture) differ for each cell line; (iii) growth in static microcarrier culture does not correlate with growth in stirred spinner culture; (iv) and that early cell attachment and spreading onto microcarriers does not necessarily predict efficiency of cell expansion in agitated microcarrier culture. Current serum-free media developed for monolayer cultures of MSCs may not support MSC proliferation in microcarrier cultures. Further optimization in medium composition will be required for microcarrier suspension culture for each cell line. Copyright © 2015 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.

  1. Cavity plasmon polaritons in monolayer graphene

    International Nuclear Information System (INIS)

    Kotov, O.V.; Lozovik, Yu.E.

    2011-01-01

    Plasmon polaritons in a new system, a monolayer doped graphene embedded in optical microcavity, are studied here. The dispersion law for lower and upper cavity plasmon polaritons is obtained. Peculiarities of Rabi splitting for the system are analyzed; particularly, role of Dirac-like spinor (envelope) wave functions in graphene and corresponding angle factors are considered. Typical Rabi frequencies for maximal (acceptable for Dirac-like electron spectra) Fermi energy and frequencies of polaritons near polariton gap are estimated. The plasmon polaritons in considered system can be used for high-speed information transfer in the THz region. -- Highlights: → Plasmon polaritons in a monolayer doped graphene embedded in optical microcavity, are studied here. → The dispersion law for lower and upper cavity plasmon polaritons is obtained. → Peculiarities of Rabi splitting for the system are analyzed. → Role of Dirac-like wave functions in graphene and corresponding angle factors are considered. → Typical Rabi frequencies and frequencies of polaritons near polariton gap are estimated.

  2. Defect engineering as a versatile route to estimate various scattering mechanisms in monolayer graphene on solid substrates.

    Science.gov (United States)

    Srivastava, Pawan Kumar; Ghosh, Subhasis

    2015-10-14

    It is known that the experimental conditions and growth methods determine the different carrier scatterings responsible for large variation of carrier mobility in graphene monolayers. Here we present a systematic investigation on various possible scattering mechanisms responsible for limiting the carrier mobility in graphene on a solid substrate, like SiO2. This has been possible by defect engineering in graphene monolayers obtained by liquid phase exfoliation of graphite in polar and non-polar solvents with the dielectric constant varying from 2.5 to 64. Lattice defects in graphene monolayers have been characterized by scanning tunnelling microscopy and Raman spectroscopy. Correlation between the results obtained from electrical measurements and the information obtained from Raman spectra have revealed different scattering mechanisms responsible for deciding the carrier mobility. It has been shown that remote interfacial phonons in SiO2 are responsible for limiting the carrier mobility at room temperature whereas, substrate impurities and Raman active point defects in the graphene lattice are the dominant scatterers for limiting the mobility at low temperatures.

  3. Recombinant invasive Lactococcus lactis can transfer DNA vaccines either directly to dendritic cells or across an epithelial cell monolayer.

    Science.gov (United States)

    de Azevedo, Marcela; Meijerink, Marjolein; Taverne, Nico; Pereira, Vanessa Bastos; LeBlanc, Jean Guy; Azevedo, Vasco; Miyoshi, Anderson; Langella, Philippe; Wells, Jerry M; Chatel, Jean-Marc

    2015-09-11

    Lactococcus lactis (L. lactis), a generally regarded as safe (GRAS) bacterium has recently been investigated as a mucosal delivery vehicle for DNA vaccines. Because of its GRAS status, L. lactis represents an attractive alternative to attenuated pathogens. Previous studies showed that eukaryotic expression plasmids could be delivered into intestinal epithelial cells (IECs) by L. lactis, or recombinant invasive strains of L. lactis, leading to heterologous protein expression. Although expression of antigens in IECs might lead to vaccine responses, it would be of interest to know whether uptake of L. lactis DNA vaccines by dendritic cells (DCs) could lead to antigen expression as they are unique in their ability to induce antigen-specific T cell responses. To test this, we incubated mouse bone marrow-derived DCs (BMDCs) with invasive L. lactis strains expressing either Staphylococcus aureus Fibronectin Binding Protein A (LL-FnBPA+), or Listeria monocytogenes mutated Internalin A (LL-mInlA+), both strains carrying a plasmid DNA vaccine (pValac) encoding for the cow milk allergen β-lactoglobulin (BLG). We demonstrated that they can transfect BMDCs, inducing the secretion of the pro-inflammatory cytokine IL-12. We also measured the capacity of strains to invade a polarized monolayer of IECs, mimicking the situation encountered in the gastrointestinal tract. Gentamycin survival assay in these cells showed that LL-mInlA+ is 100 times more invasive than L. lactis. The cross-talk between differentiated IECs, BMDCs and bacteria was also evaluated using an in vitro transwell co-culture model. Co-incubation of strains in this model showed that DCs incubated with LL-mInlA+ containing pValac:BLG could express significant levels of BLG. These results suggest that DCs could sample bacteria containing the DNA vaccine across the epithelial barrier and express the antigen. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

  4. Electronic properties of organic monolayers and molecular devices

    Indian Academy of Sciences (India)

    E-mail: dominique.vuillaume@iemn.univ-lille1.fr. Abstract. We review some of our recent experimental results on charge transport in or- ganic nanostructures such as self-assembled monolayer and monolayers of organic semicon- ductors. We describe a molecular rectifying junction made from a sequential self-assembly.

  5. Self-assembled monolayers of metallosalophenes on gold

    NARCIS (Netherlands)

    Beulen, M.W.J.; van Veggel, F.C.J.M.; Reinhoudt, David

    2000-01-01

    Salophene complexes of transition metals exhibit a reversible electro- chemistry. We have synthesized salophene complexes with sulfur-containing substituents aimed at the formation of self-assembled monolayers on a gold surface. Such monolayers have interesting cation complexating properties. The

  6. Oxygen and hydroxyl adsorption on MS{sub 2} (M = Mo, W, Hf) monolayers: a first-principles molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Iordanidou, K.; Houssa, M.; Afanas' ev, V.V.; Stesmans, A. [Department of Physics and Astronomy, University of Leuven (Belgium); Pourtois, G. [IMEC, Leuven (Belgium)

    2016-11-15

    In this paper, we study the oxygen and hydroxyl adsorption on both pristine and S deficient MS{sub 2} (M = Mo, W, Hf) monolayers, using first-principles molecular dynamics calculations. Our simulations reveal that single-layer HfS{sub 2} suffers severely from oxidation, which results in the formation of strong Hf-O bonds, likely degrading the transport properties of the material. Oxygen adsorption on S deficient monolayers acts as a passivation mechanism, both ''structurally'' by saturating the dangling bonds of neighboring metal atoms and ''electronically'' by removing the S vacancy induced gap states. Hydroxyl adsorption on pristine monolayers generates spin-polarized gap states, and for HfS{sub 2} in particular, causes the Fermi level pinning close to the conduction band edge. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. Salbutamol sulfate absorption across Calu-3 bronchial epithelia cell monolayer is inhibited in the presence of common anionic NSAIDs.

    Science.gov (United States)

    Mamlouk, Mariam; Young, Paul M; Bebawy, Mary; Haghi, Mehra; Mamlouk, Shery; Mulay, Vishwaroop; Traini, Daniela

    2013-05-01

    The aim of this study was to characterize the permeability kinetics of salbutamol sulfate, a commonly used β2-agonist in the treatment of asthma exacerbation, across Calu-3 respiratory epithelial cell monolayers in the presence of non-steroidal anti-inflammatory drugs (NSAIDs), as they have been implicated to be able to modulate organic cation transporters (OCTs). Calu-3 cell monolayers were grown in a liquid covered culture (LCC) configuration on 0.33 cm(2) Transwell polyester cell culture supports. Monolayers, cultured between 11 and 14 days were evaluated for epithelial resistance, tight junction integrity, and expression of OCT using Western blot analysis. The transport of salbutamol across the monolayer was studied as a function of concentration. Directional transport was investigated by assessing apical-basal (a-b) and basal-apical (b-a) directions. The influence of a non-specific OCT inhibitor (tetraethylammonium, TEA) and three NSAIDs (aspirin, ibuprofen, and indomethacin) on the uptake of salbutamol was studied. The flux of salbutamol sulfate increased with increasing concentration before reaching a plateau, suggesting the involvement of a transport-mediated uptake mechanism. Western blot analysis detected the presence of OCT1-3 and N1 and N2 sub-types, suggesting the presence of functioning transporters. The apparent permeability (P(app)) of 0.1 mM salbutamol across the epithelial monolayer displayed directional transport in the a-b direction which was inhibited by ˜70% in the presence of TEA, suggesting OCT-mediated uptake. Likewise, the uptake of 0.1 mM salbutamol was decreased in the presence of all the three NSAIDs, supporting a mechanism whereby NSAIDs inhibit absorption of salbutamol across the bronchial epithelium via effects on the OCT transporters. This study demonstrates that NSAIDs influence the uptake kinetics of salbutamol in an in vitro Calu-3 cell system.

  8. Preparation and structure of a low-density, flat-lying decanethiol monolayer from the densely packed, upright monolayer on gold.

    Science.gov (United States)

    Picraux, Laura B; Zangmeister, Christopher D; Batteas, James D

    2006-01-03

    This study investigates the formation of low-density, flat-lying decanethiol chemisorbed on Au prepared by heating the surface covered with a densely packed, upright monolayer to a surface temperature above that of the onset of desorption. We determined conditions for preparing the low-density phase by observing the evolution of the photoemission spectrum as a function of the surface temperature using polarized ultraviolet light and by utilizing scanning tunneling microscopy. The preparation conditions were similar for single- and polycrystalline gold surfaces. Once the low-density decanethiol phase was formed, reflection absorption infrared spectroscopy was employed to determine the orientation of the carbon chain backbone with respect to the Au surface. The nature of the valance electronic structure for flat-lying decanethiol is described.

  9. A protocol for isolation and enriched monolayer cultivation of neural precursor cells from mouse dentate gyrus

    Directory of Open Access Journals (Sweden)

    Harish eBabu

    2011-07-01

    Full Text Available In vitro assays are valuable tools to study the characteristics of adult neural precursor cells under controlled conditions with a defined set of parameters. We here present a detailed protocol based on our previous original publication (Babu et al., Enriched monolayer precursor cell cultures from micro-dissected adult mouse dentate gyrus yield functional granule cell-like neurons, PLoS One 2007, 2:e388 to isolate neural precursor cells from the hippocampus of adult mice and maintain and propagate them as adherent monolayer cultures. The strategy is based on the use of Percoll density gradient centrifugation to enrich precursor cells from the micro-dissected dentate gyrus. Based on the expression of Nestin and Sox2, a culture-purity of more than 98% can be achieved. The cultures are expanded under serum-free conditions in Neurobasal A medium with addition of the mitogens EGF and FGF2 as well as the supplements Glutamax-1 and B27. Under differentiation conditions, the precursor cells reliably generate approximately 30% neurons with appropriate morphological, molecular and electrophysiological characteristics that might reflect granule cell properties as their in vivo counterpart. We also highlight potential modifications to the protocol.

  10. Precessing deuteron polarization

    International Nuclear Information System (INIS)

    Sitnik, I.M.; Volkov, V.I.; Kirillov, D.A.; Piskunov, N.M.; Plis, Yu.A.

    2002-01-01

    The feasibility of the acceleration in the Nuclotron of deuterons polarized in the horizontal plane is considered. This horizontal polarization is named precessing polarization. The effects of the main magnetic field and synchrotron oscillations are included. The precessing polarization is supposed to be used in studying the polarization parameters of the elastic dp back-scattering and other experiments

  11. Cholesterol strongly affects the organization of lipid monolayers studied as models of the milk fat globule membrane: Condensing effect and change in the lipid domain morphology.

    Science.gov (United States)

    Murthy, Appala Venkata Ramana; Guyomarc'h, Fanny; Paboeuf, Gilles; Vié, Véronique; Lopez, Christelle

    2015-10-01

    The biological membrane that surrounds the milk fat globules exhibits phase separation of polar lipids that is poorly known. The objective of this study was to investigate the role played by cholesterol in the organization of monolayers prepared as models of the milk fat globule membrane (MFGM). Differential scanning calorimetry and X-ray diffraction experiments allowed characterization of the gel to liquid crystalline phase transition temperature of lipids, Tm ~35°C, in vesicles prepared with a MFGM lipid extract. For temperature below Tm, atomic force microscopy revealed phase separation of lipids at 30 mN·m(-1) in Langmuir-Blodgett monolayers of the MFGM lipid extract. The high Tm lipids form liquid condensed (LC) domains that protrude by about 1.5 nm from the continuous liquid expanded (LE) phase. Cholesterol was added to the MFGM extract up to 30% of polar lipids (cholesterol/milk sphingomyelin (MSM) molar ratio of 50/50). Compression isotherms evidenced the condensing effect of the cholesterol onto the MFGM lipid monolayers. Topography of the monolayers showed a decrease in the area of the LC domains and in the height difference H between the LC domains and the continuous LE phase, as the cholesterol content increased in the MFGM lipid monolayers. These results were interpreted in terms of nucleation effects of cholesterol and decrease of the line tension between LC domains and LE phase in the MFGM lipid monolayers. This study revealed the major structural role of cholesterol in the MFGM that could be involved in biological functions of this interface (e.g. mechanisms of milk fat globule digestion). Copyright © 2015 Elsevier B.V. All rights reserved.

  12. Polarization contrast in fluorescence scanning near-field optical microscopy in reflection

    NARCIS (Netherlands)

    Jalocha, A.; Jalocha, A.; van Hulst, N.F.

    1995-01-01

    Polarization contrast is presented in fluorescence images of a Langmuir-Blodgett monolayer obtained with a scanning near-field optical microscope operated in reflection. A tapered optical fiber is used both to excite and to collect the fluorescence. The lateral resolution in the reflection

  13. Polare maskuliniteter

    Directory of Open Access Journals (Sweden)

    Marit Anne Hauan

    2012-05-01

    Full Text Available In this paper my aim is to read and understand the journal of Gerrit de Veer from the last journey of William Barents to the Arctic Regions in 1596 and the journal of captain Junge on his hunting trip from Tromsø to Svalbard in 1834.It is nearly 240 years between this to voyages. The first journal is known as the earliest report from the arctic era. Gerrit de Veer adds instructive copper engravings to his text and give us insight in the crews meeting with this new land. Captain Junges journal is found together with his dead crew in a house in a fjord nearby Ny-Ålesund and has no drawings, but word. Both of these journals may be read as sources of the knowledge and understanding of the polar region. They might also unveil the ideas of how to deal with and survive under the challenges that is given. In addition one can ask if the sources can tell us more about how men describe their challenges. Can the way they expressed themselves in the journals give us an understanding of masculinity? And not least help us to create good questions of the change in the ideas of masculinities which is said to follow the change in understanding of the wilderness.

  14. Interaction of DNA with Cationic Lipid Mixtures-Investigation at Langmuir Lipid Monolayers.

    Science.gov (United States)

    Janich, Christopher; Hädicke, André; Bakowsky, Udo; Brezesinski, Gerald; Wölk, Christian

    2017-10-03

    Four different binary lipid mixtures composed of a cationic lipid and the zwitterionic colipids DOPE or DPPC, which show different DNA transfer activities in cell culture models, were investigated at the soft air/water interface to identify transfection efficiency determining characteristics. Langmuir films are useful models to investigate the interaction between DNA and lipid mixtures in a two-dimensional model system by using different surface sensitive techniques, namely, epifluorescence microscopy and infrared reflection-absorption spectroscopy. Especially, the effect of adsorbed DNA on the properties of the lipid mixtures has been examined. Distinct differences between the lipid composites were found which are caused by the different colipids of the mixtures. DOPE containing lipid mixtures form fluid monolayers with a uniform distribution of the fluorescent probe in the presence and absence of DNA at physiologically relevant surface pressures. Only at high nonphysiological pressures, the lipid monolayer collapses and phase separation was observed if DNA was present in the subphase. In contrast, DPPC containing lipid mixtures show domains in the liquid condensed phase state in the presence and absence of DNA in the subphase. The adsorption of DNA at the positively charged mixed lipid monolayer induces phase separation which is expressed in the morphology and the point of appearance of these domains.

  15. Hypercapnia accelerates wound healing in endothelial cell monolayers exposed to hypoxia.

    Science.gov (United States)

    Tsuji, Takao; Aoshiba, Kazutetsu; Itoh, Masayuki; Nakamura, Hiroyuki; Yamaguchi, Kazuhiro

    2013-01-01

    While tissue hypoxia is known to play a critical role in the process of vascular injury and repair, the effect of hypercapnia on this process remains uncertain. We investigated whether hypercapnia might influence endothelial cell wound healing under the influence of hypoxia. Monolayers of human umbilical venous endothelial cells (HUVECs) were scratch-wounded and incubated under different levels of O2, CO2, and pH in the environment. Inhibition of wound healing was observed in the HUVEC monolayers under the hypoxic condition as compared to the normoxic condition. Both hypercapnic acidosis and buffered hypercapnia, but not normocapnic acidosis improved the rate of wound healing under the influence of hypoxia. The beneficial effect of hypercapnia was associated with stimulation of cell proliferation, without effects on cell adhesion, migration or apoptosis. On the other hand, the stimulatory effect of hypercapnia on wound healing and cell proliferation was not noted under normoxic conditions. These results suggest that hypercapnia, rather than acidosis per se, accelerated the wound healing in HUVEC monolayers cultured under hypoxic conditions. The effect of hypercapnia on wound healing was due, at least in part, to the stimulation of cell proliferation by hypercapnia.

  16. Monolayer adsorption of noble gases on graphene

    Science.gov (United States)

    Maiga, Sidi M.; Gatica, Silvina M.

    2018-02-01

    We report our results of simulations of the adsorption of noble gases (Kr, Ar, Xe) on graphene. For Kr, we consider two configurations: supported and free-standing graphene, where atoms are adsorbed only on one or two sides of the graphene. For Ar and Xe, we studied only the case of supported graphene. For the single-side adsorption, we calculated the two-dimensional gas-liquid critical temperature for each adsorbate. We determined the different phases of the monolayers and constructed the phase diagrams. We found two-dimensional incommensurate solid phases for krypton, argon and xenon, and a two-dimensional commensurate solid phase for krypton. For double side adsorption of Kr, we do not see evidence of an ordering transition driven by the interlayer forces.

  17. Vector assembly of colloids on monolayer substrates

    Science.gov (United States)

    Jiang, Lingxiang; Yang, Shenyu; Tsang, Boyce; Tu, Mei; Granick, Steve

    2017-06-01

    The key to spontaneous and directed assembly is to encode the desired assembly information to building blocks in a programmable and efficient way. In computer graphics, raster graphics encodes images on a single-pixel level, conferring fine details at the expense of large file sizes, whereas vector graphics encrypts shape information into vectors that allow small file sizes and operational transformations. Here, we adapt this raster/vector concept to a 2D colloidal system and realize `vector assembly' by manipulating particles on a colloidal monolayer substrate with optical tweezers. In contrast to raster assembly that assigns optical tweezers to each particle, vector assembly requires a minimal number of optical tweezers that allow operations like chain elongation and shortening. This vector approach enables simple uniform particles to form a vast collection of colloidal arenes and colloidenes, the spontaneous dissociation of which is achieved with precision and stage-by-stage complexity by simply removing the optical tweezers.

  18. Ion beam analysis with monolayer depth resolution

    Science.gov (United States)

    Carstanjen, H. D.

    1998-03-01

    The paper is concerned with the analysis of surfaces and near-surface layers with monolayer depth resolution by means of high resolution Rutherford backscattering (HRBS) and elastic recoil detection (HERDA) of ions with an energy of a few MeV, in combination with an electrostatic spectrometer. With this instrument, which has recently been set up at the 6 MV Pelletron accelerator of the Max-Planck-Institut für Metallforschung in Stuttgart, depth resolutions of 0.1 nm are obtained in HRBS and 0.3 nm in HERDA experiments. This paper gives a short outline of the design and performance of the spectrometer followed by various examples of applications. These comprise examples showing the analyzing power of the instrument, the analysis of an X-ray mirror by HRBS, the study of the initial oxidation of surfaces of aluminum single crystals by HERDA and recent results concerning charge exchange in ion backscattering.

  19. Acid monolayer functionalized iron oxide nanoparticle catalysts

    Science.gov (United States)

    Ikenberry, Myles

    Superparamagnetic iron oxide nanoparticle functionalization is an area of intensely active research, with applications across disciplines such as biomedical science and heterogeneous catalysis. This work demonstrates the functionalization of iron oxide nanoparticles with a quasi-monolayer of 11-sulfoundecanoic acid, 10-phosphono-1-decanesulfonic acid, and 11-aminoundecanoic acid. The carboxylic and phosphonic moieties form bonds to the iron oxide particle core, while the sulfonic acid groups face outward where they are available for catalysis. The particles were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), potentiometric titration, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectrometry (XPS), and dynamic light scattering (DLS). The sulfonic acid functionalized particles were used to catalyze the hydrolysis of sucrose at 80° and starch at 130°, showing a higher activity per acid site than the traditional solid acid catalyst Amberlyst-15, and comparing well against results reported in the literature for sulfonic acid functionalized mesoporous silicas. In sucrose catalysis reactions, the phosphonic-sulfonic nanoparticles (PSNPs) were seen to be incompletely recovered by an external magnetic field, while the carboxylic-sulfonic nanoparticles (CSNPs) showed a trend of increasing activity over the first four recycle runs. Between the two sulfonic ligands, the phosphonates produced a more tightly packed monolayer, which corresponded to a higher sulfonic acid loading, lower agglomeration, lower recoverability through application of an external magnetic field, and higher activity per acid site for the hydrolysis of starch. Functionalizations with 11-aminoundecanoic acid resulted in some amine groups binding to the surfaces of iron oxide nanoparticles. This amine binding is commonly ignored in iron oxide

  20. Three-dimensional Huh7 cell culture system for the study of Hepatitis C virus infection

    Directory of Open Access Journals (Sweden)

    Uprichard Susan L

    2009-07-01

    Full Text Available Abstract Background In order to elucidate how Hepatitis C Virus (HCV interacts with polarized hepatocytes in vivo and how HCV-induced alterations in cellular function contribute to HCV-associated liver disease, a more physiologically relevant hepatocyte culture model is needed. As such, NASA-engineered three-dimensional (3-D rotating wall vessel (RWV bioreactors were used in effort to promote differentiation of HCV-permissive Huh7 hepatoma cells. Results When cultured in the RWV, Huh7 cells became morphologically and transcriptionally distinct from more standard Huh7 two-dimensional (2-D monolayers. Specifically, RWV-cultured Huh7 cells formed complex, multilayered 3-D aggregates in which Phase I and Phase II xenobiotic drug metabolism genes, as well as hepatocyte-specific transcripts (HNF4α, Albumin, TTR and α1AT, were upregulated compared to 2-D cultured Huh7 cells. Immunofluorescence analysis revealed that these HCV-permissive 3-D cultured Huh7 cells were more polarized than their 2D counterparts with the expression of HCV receptors, cell adhesion and tight junction markers (CD81, scavenger receptor class B member 1, claudin-1, occludin, ZO-1, β-Catenin and E-Cadherin significantly increased and exhibiting apical, lateral and/or basolateral localization. Conclusion These findings show that when cultured in 3-D, Huh7 cells acquire a more differentiated hepatocyte-like phenotype. Importantly, we show that these 3D cultures are highly permissive for HCV infection, thus providing an opportunity to study HCV entry and the effects of HCV infection on host cell function in a more physiologically relevant cell culture system.

  1. Polar Lipids Analysis of Cultured Phytoplankton Reveals Significant Inter-taxa Changes, Low Influence of Growth Stage, and Usefulness in Chemotaxonomy.

    Science.gov (United States)

    Cañavate, José Pedro; Armada, Isabel; Hachero-Cruzado, Ismael

    2017-05-01

    The high lipid diversity of microalgae has been used to taxonomically differentiate phytoplankton taxa at the class level. However, important lipids such as phospholipids (PL) and betaine lipids (BL) with potential chemotaxonomy application in phytoplankton ecology have been scarcely studied. The chemotaxonomy value of PL and BL depends on their intraspecific extent of variation as microalgae respond to external changing factors. To determine such effects, lipid class changes occurring at different growth stages in 15 microalgae from ten different classes were analyzed. BL occurred in 14 species and were the less affected lipids by growth stage with diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-b-alanine (DGTA) showing the highest stability. PL were more influenced by growth stage with phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidyletanolamine (PE) declining towards older culture stages in some species. Glycolipids were the more common lipids, and no evident age-related variability pattern could be associated to taxonomic diversity. Selecting BL and PL as descriptor variables optimally distinguished microalgae taxonomic variability at all growth stages. Principal coordinate analysis arranged species through a main tendency from diacylglyceryl-hydroxymethyl-N,N,N-trimethyl-b-alanine (DGCC) containing species (mainly dinoflagellates and haptophytes) to DGTA or PC containing species (mainly cryptophytes). Two diatom classes with similar fatty acid profiles could be distinguished from their respective content in DGTA (Bacillariophyceae) or DGCC (Mediophyceae). In green lineage classes (Trebouxiophyceae, Porphyridophyceae, and Chlorodendrophyceae), PC was a better descriptor than BL. BL and PL explained a higher proportion of microalgae taxonomic variation than did fatty acids and played a complementary role as lipid markers.

  2. Electrically tunable polarizer based on 2D orthorhombic ferrovalley materials

    Science.gov (United States)

    Shen, Xin-Wei; Tong, Wen-Yi; Gong, Shi-Jing; Duan, Chun-Gang

    2018-03-01

    The concept of ferrovalley materials has been proposed very recently. The existence of spontaneous valley polarization, resulting from ferromagnetism, in such hexagonal 2D materials makes nonvolatile valleytronic applications realizable. Here, we introduce a new member of ferrovalley family with orthorhombic lattice, i.e. monolayer group-IV monochalcogenides (GIVMs), in which the intrinsic valley polarization originates from ferroelectricity, instead of ferromagnetism. Combining the group theory analysis and first-principles calculations, we demonstrate that, different from the valley-selective circular dichroism in hexagonal lattice, linearly polarized optical selectivity for valleys exists in the new type of ferrovalley materials. On account of the distinctive property, a prototype of electrically tunable polarizer is realized. In the ferrovalley-based polarizer, a laser beam can be optionally polarized in x- or y-direction, depending on the ferrovalley state controlled by external electric fields. Such a device can be further optimized to emit circularly polarized radiation with specific chirality and to realize the tunability for operating wavelength. Therefore, we show that 2D orthorhombic ferrovalley materials are the promising candidates to provide an advantageous platform to realize the polarizer driven by electric means, which is of great importance in extending the practical applications of valleytronics.

  3. Defect Structure of Localized Excitons in a WSe2 Monolayer

    KAUST Repository

    Zhang, Shuai

    2017-07-26

    The atomic and electronic structure of intrinsic defects in a WSe2 monolayer grown on graphite was revealed by low temperature scanning tunneling microscopy and spectroscopy. Instead of chalcogen vacancies that prevail in other transition metal dichalcogenide materials, intrinsic defects in WSe2 arise surprisingly from single tungsten vacancies, leading to the hole (p-type) doping. Furthermore, we found these defects to dominate the excitonic emission of the WSe2 monolayer at low temperature. Our work provided the first atomic-scale understanding of defect excitons and paved the way toward deciphering the defect structure of single quantum emitters previously discovered in the WSe2 monolayer.

  4. Cross-Polarized Magic-Angle Spinning (sup13)C Nuclear Magnetic Resonance Spectroscopic Characterization of Soil Organic Matter Relative to Culturable Bacterial Species Composition and Sustained Biological Control of Pythium Root Rot.

    Science.gov (United States)

    Boehm, M J; Wu, T; Stone, A G; Kraakman, B; Iannotti, D A; Wilson, G E; Madden, L V; Hoitink, H

    1997-01-01

    We report the use of a model system that examines the dynamics of biological energy availability in organic matter in a sphagnum peat potting mix critical to sustenance of microorganism-mediated biological control of pythium root rot, a soilborne plant disease caused by Pythium ultimum. The concentration of readily degradable carbohydrate in the peat, mostly present as cellulose, was characterized by cross-polarized magic-angle spinning (sup13)C nuclear magnetic resonance spectroscopy. A decrease in the carbohydrate concentration in the mix was observed during the initial 10 weeks after potting as the rate of hydrolysis of fluorescein diacetate declined below a critical threshold level required for biological control of pythium root rot. Throughout this period, total microbial biomass and activity, based on rates of [(sup14)C]acetate incorporation into phospholipids, did not change but shifts in culturable bacterial species composition occurred. Species capable of inducing biocontrol were succeeded by pleomorphic gram-positive genera and putative oligotrophs not or less effective in control. We conclude that sustained efficacy of naturally occurring biocontrol agents was limited by energy availability to this microflora within the organic matter contained in the potting mix. We propose that this critical role of organic matter may be a key factor explaining the variability in efficacy typically encountered in the control of pythium root rot with biocontrol agents.

  5. Mn-Promoted Growth and Photoluminescence of Molybdenum Disulphide Monolayer

    Directory of Open Access Journals (Sweden)

    Shengzhong Jin

    2017-06-01

    Full Text Available Molybdenum disulphide (MoS2 monolayer is a two-dimensional semiconductor material with potential applications in nano electronic devices. However, it is still a challenge to reproducibly synthesize single layer MoS2 in high quality. Herein, we report the growth of monolayer of MoS2 on the SiO2/Si substrate with manganese heterogeneous nucleation. It was shown that the Mn promotes the growth of monolayer MoS2 via heterogeneous nucleation. The growth temperature range expanded two-fold, the nucleation density increased as well. The monolayer prepared in the presence of Mn exhibits a unique red emission peak at 732 nm at room temperature compared to the sample in the absence of Mn.

  6. Experimental study of thermal rectification in suspended monolayer graphene

    Science.gov (United States)

    Wang, Haidong; Hu, Shiqian; Takahashi, Koji; Zhang, Xing; Takamatsu, Hiroshi; Chen, Jie

    2017-06-01

    Thermal rectification is a fundamental phenomenon for active heat flow control. Significant thermal rectification is expected to exist in the asymmetric nanostructures, such as nanowires and thin films. As a one-atom-thick membrane, graphene has attracted much attention for realizing thermal rectification as shown by many molecular dynamics simulations. Here, we experimentally demonstrate thermal rectification in various asymmetric monolayer graphene nanostructures. A large thermal rectification factor of 26% is achieved in a defect-engineered monolayer graphene with nanopores on one side. A thermal rectification factor of 10% is achieved in a pristine monolayer graphene with nanoparticles deposited on one side or with a tapered width. The results indicate that the monolayer graphene has great potential to be used for designing high-performance thermal rectifiers for heat flow control and energy harvesting.

  7. Coexistence of multiple conformations in cysteamine monolayers on Au(111)

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Bilic, A; Reimers, JR

    2005-01-01

    The structural organization, catalytic function, and electronic properties of cysteamine monolayers on Au(111) have been addressed comprehensively by voltammetry, in situ scanning tunneling microscopy (STM) in anaerobic environment, and a priori molecular dynamics (MD) simulation and STM image si...

  8. Thiophene-based monolayer OFETs prepared by Langmuir techniques

    Science.gov (United States)

    Agina, Elena V.; Sizov, Alexey S.; Anisimov, Daniil S.; Trul, Askold A.; Borshchev, Oleg V.; Paraschuk, Dmitry Y.; Shcherbina, Maxim A.; Chvalun, Sergey N.; Ponomarenko, Sergey A.

    2015-08-01

    A novel fast, easily processible and highly reproducible approach to thiophene-based monolayer OFETs fabrication by Langmuir-Blodgett or Langmuir-Schaefer techniques was developed and successfully applied. It is based on selfassembly of organosilicon derivatives of oligothiophenes or benzothienobenzothiophene on the water-air interface. Influence of the conjugation length and the anchor group chemistry of the self-assembling molecules on the monolayer structure and electric performance of monolayer OFETs was systematically investigated. The efficient monolayer OFETs with the charge carrier mobilities up to 0.01 cm2/Vs and on/off ratio up to 106 were fabricated, and their functionality in integrated circuits under normal air conditions was demonstrated.

  9. Monolayer MoS2 heterojunction solar cells

    KAUST Repository

    Tsai, Menglin

    2014-08-26

    We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS 2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS 2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices. © 2014 American Chemical Society.

  10. Phase emerging from intramonolayer cycloaddition on micro-patterned monolayer

    Energy Technology Data Exchange (ETDEWEB)

    Tajuddin, Hairul A.; Manning, Robert J.; Leggett, Graham J.; Williams, Nicholas H. [Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia and Department of Chemistry, University of Sheffield, Sheffield S3 7HF (United Kingdom); Department of Chemistry, University of Sheffield, Sheffield S3 7HF (United Kingdom)

    2012-11-27

    Cu(I)-catalyzed cycloaddition between azide and acetylene, followed by hydrolysis of ester were performed on micro-patterned self-assembled monolayer to produce smaller features. The reactions were initially performed on mixed monolayers and analysed by water contact angle (CA) and confirmed by X-ray Photoelectron Spectroscopy (XPS). The contact angle measurement has shown a drastic wetting of water on the surface of mixed monolayer indicating that the terminal groups on mixed monolayer has changed into carboxylic acid and hydroxyl terminals. The reactions work in a similar way on micro-patterned SAM and analyzed by using friction force microscope. The emerging of the new lines with high friction force on the border suggested a successful intramonolayer reactions on the border of the patterned SAM.

  11. Unsupported single-atom-thick copper oxide monolayers

    Science.gov (United States)

    Yin, Kuibo; Zhang, Yu-Yang; Zhou, Yilong; Sun, Litao; Chisholm, Matthew F.; Pantelides, Sokrates T.; Zhou, Wu

    2017-03-01

    Oxide monolayers may present unique opportunities because of the great diversity of properties of these materials in bulk form. However, reports on oxide monolayers are still limited. Here we report the formation of single-atom-thick copper oxide layers with a square lattice both in graphene pores and on graphene substrates using aberration-corrected scanning transmission electron microscopy. First-principles calculations find that CuO is energetically stable and its calculated lattice spacing matches well with the measured value. Furthermore, free-standing copper oxide monolayers are predicted to be semiconductors with band gaps ∼3 eV. The new wide-bandgap single-atom-thick copper oxide monolayers usher a new frontier to study the highly diverse family of two-dimensional oxides and explore their properties and their potential for new applications.

  12. Tailoring self-assembled monolayers at the electrochemical interface

    Indian Academy of Sciences (India)

    Administrator

    gmail.com. Abstract. The main focus ... facilitates the packing of the molecules in the monolayers and serves as a linker between the head ..... applications of pharmaceutical and food industries. It has been shown recently that SAMs and mixed.

  13. Polarized electron sources

    Energy Technology Data Exchange (ETDEWEB)

    Prepost, R. [Univ. of Wisconsin, Madison, WI (United States)

    1994-12-01

    The fundamentals of polarized electron sources are described with particular application to the Stanford Linear Accelerator Center. The SLAC polarized electron source is based on the principle of polarized photoemission from Gallium Arsenide. Recent developments using epitaxially grown, strained Gallium Arsenide cathodes have made it possible to obtain electron polarization significantly in excess of the conventional 50% polarization limit. The basic principles for Gallium and Arsenide polarized photoemitters are reviewed, and the extension of the basic technique to strained cathode structures is described. Results from laboratory measurements of strained photocathodes as well as operational results from the SLAC polarized source are presented.

  14. Paradox and Polarity: Tools For Managing Complexity

    Science.gov (United States)

    2016-02-09

    personal views and are not necessaril dorsed by the Joint Forces Staff College, the Department of Defense, or any of its corn This paper is entirely my...the governing norm up until the time that events motivate or cause a definite transition to war. Colin Gray writes, “...some cultures , the American...brought wisdom about polarities to Eastern culture , relatively speaking, Western culture has not embraced wisdom of the Tao in either a spiritual

  15. Magnetic brightening and control of dark excitons in monolayer WSe2.

    Science.gov (United States)

    Zhang, Xiao-Xiao; Cao, Ting; Lu, Zhengguang; Lin, Yu-Chuan; Zhang, Fan; Wang, Ying; Li, Zhiqiang; Hone, James C; Robinson, Joshua A; Smirnov, Dmitry; Louie, Steven G; Heinz, Tony F

    2017-09-01

    Monolayer transition metal dichalcogenide crystals, as direct-gap materials with strong light-matter interactions, have attracted much recent attention. Because of their spin-polarized valence bands and a predicted spin splitting at the conduction band edges, the lowest-lying excitons in WX 2 (X = S, Se) are expected to be spin-forbidden and optically dark. To date, however, there has been no direct experimental probe of these dark excitons. Here, we show how an in-plane magnetic field can brighten the dark excitons in monolayer WSe 2 and permit their properties to be observed experimentally. Precise energy levels for both the neutral and charged dark excitons are obtained and compared with ab initio calculations using the GW-BSE approach. As a result of their spin configuration, the brightened dark excitons exhibit much-increased emission and valley lifetimes. These studies directly probe the excitonic spin manifold and reveal the fine spin-splitting at the conduction band edges.

  16. Acetylene chain reaction on hydrogenated boron nitride monolayers: a density functional theory study.

    Science.gov (United States)

    Ponce-Pérez, R; Cocoletzi, Gregorio H; Takeuchi, Noboru

    2017-11-28

    Spin-polarized first-principles total-energy calculations have been performed to investigate the possible chain reaction of acetylene molecules mediated by hydrogen abstraction on hydrogenated hexagonal boron nitride monolayers. Calculations have been done within the periodic density functional theory (DFT), employing the PBE exchange correlation potential, with van der Waals corrections (vdW-DF). Reactions at two different sites have been considered: hydrogen vacancies on top of boron and on top of nitrogen atoms. As previously calculated, at the intermediate state of the reaction, when the acetylene molecule is attached to the surface, the adsorption energy is of the order of -0.82 eV and -0.20 eV (measured with respect to the energy of the non interacting molecule-substrate system) for adsorption on top of boron and nitrogen atoms, respectively. After the hydrogen abstraction takes place, the system gains additional energy, resulting in adsorption energies of -1.52 eV and -1.30 eV, respectively. These results suggest that the chain reaction is energetically favorable. The calculated minimum energy path (MEP) for hydrogen abstraction shows very small energy barriers of the order of 5 meV and 22 meV for the reaction on top of boron and nitrogen atoms, respectively. Finally, the density of states (DOS) evolution study helps to understand the chain reaction mechanism. Graphical abstract Acetylene chain reaction on hydrogenated boron nitride monolayers.

  17. Structural phase transition in monolayer MoTe2 driven by electrostatic doping

    Science.gov (United States)

    Wang, Ying; Xiao, Jun; Zhu, Hanyu; Li, Yao; Alsaid, Yousif; Fong, King Yan; Zhou, Yao; Wang, Siqi; Shi, Wu; Wang, Yuan; Zettl, Alex; Reed, Evan J.; Zhang, Xiang

    2017-10-01

    Monolayers of transition-metal dichalcogenides (TMDs) exhibit numerous crystal phases with distinct structures, symmetries and physical properties. Exploring the physics of transitions between these different structural phases in two dimensions may provide a means of switching material properties, with implications for potential applications. Structural phase transitions in TMDs have so far been induced by thermal or chemical means; purely electrostatic control over crystal phases through electrostatic doping was recently proposed as a theoretical possibility, but has not yet been realized. Here we report the experimental demonstration of an electrostatic-doping-driven phase transition between the hexagonal and monoclinic phases of monolayer molybdenum ditelluride (MoTe2). We find that the phase transition shows a hysteretic loop in Raman spectra, and can be reversed by increasing or decreasing the gate voltage. We also combine second-harmonic generation spectroscopy with polarization-resolved Raman spectroscopy to show that the induced monoclinic phase preserves the crystal orientation of the original hexagonal phase. Moreover, this structural phase transition occurs simultaneously across the whole sample. This electrostatic-doping control of structural phase transition opens up new possibilities for developing phase-change devices based on atomically thin membranes.

  18. Selectively Plasmon-Enhanced Second-Harmonic Generation from Monolayer Tungsten Diselenide on Flexible Substrates

    KAUST Repository

    Wang, Zhuo

    2018-01-04

    Monolayer two-dimensional transition metal dichalcogenides (2D TMDCs) exhibit promising characteristics in miniaturized nonlinear optical frequency converters, due to their inversion asymmetry and large second-order nonlinear susceptibility. However, these materials usually have a very short light interaction lengths with the pump laser because they are atomically thin, such that second-harmonic generation (SHG) is generally inefficient. In this paper, we fabricate a judiciously structured 150-nm-thick planar surface consisting of monolayer tungsten diselenide and sub-20-nm-wide gold trenches on flexible substrates, reporting ~7000-fold SHG enhancement without peak broadening or background in the spectra as compared to WSe2 on as-grown sapphire substrates. Our proof-of-concept experiment yields effective second-order nonlinear susceptibility of 2.1 × 104 pm/V. Three orders of magnitude enhancement is maintained with pump wavelength ranging from 800 nm to 900 nm, breaking the limitation of narrow pump wavelength range for cavity-enhanced SHG. In addition, SHG amplitude can be dynamically controlled via selective excitation of the lateral gap plasmon by rotating the laser polarization. Such fully open, flat and ultrathin profile enables a great variety of functional samples with high SHG from one patterned silicon substrate, favoring scalable production of nonlinear converters. The surface accessibility also enables integration with other optical components for information processing in an ultrathin and flexible form.

  19. Enhanced valley splitting in monolayer WSe2 due to magnetic exchange field.

    Science.gov (United States)

    Zhao, Chuan; Norden, Tenzin; Zhang, Peiyao; Zhao, Puqin; Cheng, Yingchun; Sun, Fan; Parry, James P; Taheri, Payam; Wang, Jieqiong; Yang, Yihang; Scrace, Thomas; Kang, Kaifei; Yang, Sen; Miao, Guo-Xing; Sabirianov, Renat; Kioseoglou, George; Huang, Wei; Petrou, Athos; Zeng, Hao

    2017-08-01

    Exploiting the valley degree of freedom to store and manipulate information provides a novel paradigm for future electronics. A monolayer transition-metal dichalcogenide (TMDC) with a broken inversion symmetry possesses two degenerate yet inequivalent valleys, which offers unique opportunities for valley control through the helicity of light. Lifting the valley degeneracy by Zeeman splitting has been demonstrated recently, which may enable valley control by a magnetic field. However, the realized valley splitting is modest (∼0.2 meV T -1 ). Here we show greatly enhanced valley spitting in monolayer WSe 2 , utilizing the interfacial magnetic exchange field (MEF) from a ferromagnetic EuS substrate. A valley splitting of 2.5 meV is demonstrated at 1 T by magnetoreflectance measurements and corresponds to an effective exchange field of ∼12 T. Moreover, the splitting follows the magnetization of EuS, a hallmark of the MEF. Utilizing the MEF of a magnetic insulator can induce magnetic order and valley and spin polarization in TMDCs, which may enable valleytronic and quantum-computing applications.

  20. Neutral and charged inter-valley biexcitons in monolayer MoSe2

    Science.gov (United States)

    Hao, Kai; Specht, Judith F.; Nagler, Philipp; Xu, Lixiang; Tran, Kha; Singh, Akshay; Dass, Chandriker Kavir; Schüller, Christian; Korn, Tobias; Richter, Marten; Knorr, Andreas; Li, Xiaoqin; Moody, Galan

    2017-06-01

    In atomically thin transition metal dichalcogenides (TMDs), reduced dielectric screening of the Coulomb interaction leads to strongly correlated many-body states, including excitons and trions, that dominate the optical properties. Higher-order states, such as bound biexcitons, are possible but are difficult to identify unambiguously using linear optical spectroscopy methods. Here, we implement polarization-resolved two-dimensional coherent spectroscopy (2DCS) to unravel the complex optical response of monolayer MoSe2 and identify multiple higher-order correlated states. Decisive signatures of neutral and charged inter-valley biexcitons appear in cross-polarized two-dimensional spectra as distinct resonances with respective ~20 and ~5 meV binding energies--similar to recent calculations using variational and Monte Carlo methods. A theoretical model considering the valley-dependent optical selection rules reveals the quantum pathways that give rise to these states. Inter-valley biexcitons identified here, comprising of neutral and charged excitons from different valleys, offer new opportunities for developing ultrathin biexciton lasers and polarization-entangled photon sources.

  1. Ferroelectric transistors with monolayer molybdenum disulfide and ultra-thin aluminum-doped hafnium oxide

    Science.gov (United States)

    Yap, Wui Chung; Jiang, Hao; Liu, Jialun; Xia, Qiangfei; Zhu, Wenjuan

    2017-07-01

    In this letter, we demonstrate ferroelectric memory devices with monolayer molybdenum disulfide (MoS2) as the channel material and aluminum (Al)-doped hafnium oxide (HfO2) as the ferroelectric gate dielectric. Metal-ferroelectric-metal capacitors with 16 nm thick Al-doped HfO2 are fabricated, and a remnant polarization of 3 μC/cm2 under a program/erase voltage of 5 V is observed. The capability of potential 10 years data retention was estimated using extrapolation of the experimental data. Ferroelectric transistors based on embedded ferroelectric HfO2 and MoS2 grown by chemical vapor deposition are fabricated. Clockwise hysteresis is observed at low program/erase voltages due to slow bulk traps located near the 2D/dielectric interface, while counterclockwise hysteresis is observed at high program/erase voltages due to ferroelectric polarization. In addition, the endurances of the devices are tested, and the effects associated with ferroelectric materials, such as the wake-up effect and polarization fatigue, are observed. Reliable writing/reading in MoS2/Al-doped HfO2 ferroelectric transistors over 2 × 104 cycles is achieved. This research can potentially lead to advances of two-dimensional (2D) materials in low-power logic and memory applications.

  2. Nonequilibrium 2-hydroxyoctadecanoic acid monolayers: effect of electrolytes.

    Science.gov (United States)

    Lendrum, Conrad D; Ingham, Bridget; Lin, Binhua; Meron, Mati; Toney, Michael F; McGrath, Kathryn M

    2011-04-19

    2-Hydroxyacids display complex monolayer phase behavior due to the additional hydrogen bonding afforded by the presence of the second hydroxy group. The placement of this group at the position α to the carboxylic acid functionality also introduces the possibility of chelation, a utility important in crystallization including biomineralization. Biomineralization, like many biological processes, is inherently a nonequilibrium process. The nonequilibrium monolayer phase behavior of 2-hydroxyoctadecanoic acid was investigated on each of pure water, calcium chloride, sodium bicarbonate and calcium carbonate crystallizing subphases as a precursor study to a model calcium carbonate biomineralizing system, each at a pH of ∼6. The role of the bicarbonate co-ion in manipulating the monolayer structure was determined by comparison with monolayer phase behavior on a sodium chloride subphase. Monolayer phase behavior was probed using surface pressure/area isotherms, surface potential, Brewster angle microscopy, and synchrotron-based grazing incidence X-ray diffraction and X-ray reflectivity. Complex phase behavior was observed for all but the sodium chloride subphase with hydrogen bonding, electrostatic and steric effects defining the symmetry of the monolayer. On a pure water subphase hydrogen bonding dominates with three phases coexisting at low pressures. Introduction of calcium ions into the aqueous subphase ensures strong cation binding to the surfactant head groups through chelation. The monolayer becomes very unstable in the presence of bicarbonate ions within the subphase due to short-range hydrogen bonding interactions between the monolayer and bicarbonate ions facilitated by the sodium cation enhancing surfactant solubility. The combined effects of electrostatics and hydrogen bonding are observed on the calcium carbonate crystallizing subphase. © 2011 American Chemical Society

  3. Photogalvanic effect in monolayer black phosphorus.

    Science.gov (United States)

    Xie, Yiqun; Zhang, Lei; Zhu, Yu; Liu, Lei; Guo, Hong

    2015-11-13

    We report a first-principles theoretical approach for analyzing linear and circular photogalvanic effects (PGEs) based on density functional theory within the nonequilibrium Green's function formalism. Using this approach we investigate the PGE phenomena in monolayer black phosphorus (MBP) doped with sulfur atoms. The impurity doping breaks the space inversion symmetry of pristine MBP, leading to a C s symmetry with a mirror reflection plane normal to the zigzag direction of the MBP lattice. Governed by this symmetry, a linear PGE is induced in both zigzag and armchair directions, and a circular PGE is induced along the zigzag direction. A robust broadband photoresponse is found from the near-infrared to the visible range for the MBP device. There is a strong anisotropy in PGE: photoresponse in the zigzag direction can be larger by an order of magnitude than that in the armchair direction. We identify the origin of the observed PGE as the inter-band transitions from the impurity and valence bands to the conduction bands, which involves a transfer of angular momentum from photons to electrons.

  4. Specific Ion Effects in Cholesterol Monolayers

    Directory of Open Access Journals (Sweden)

    Teresa Del Castillo-Santaella

    2016-05-01

    Full Text Available The interaction of ions with interfaces and, in particular, the high specificity of these interactions to the particular ions considered, are central questions in the field of surface forces. Here we study the effect of different salts (NaI, NaCl, CaCl2 and MgCl2 on monolayers made of cholesterol molecules, both experimentally (surface area vs. lateral pressure isotherms measured by a Langmuir Film Balance and theoretically (molecular dynamics (MD all-atomic simulations. We found that surface isotherms depend, both quantitatively and qualitatively, on the nature of the ions by altering the shape and features of the isotherm. In line with the experiments, MD simulations show clear evidences of specific ionic effects and also provide molecular level details on ion specific interactions with cholesterol. More importantly, MD simulations show that the interaction of a particular ion with the surface depends strongly on its counterion, a feature ignored so far in most theories of specific ionic effects in surface forces.

  5. Self-Assembled Monolayers for Dental Implants

    Directory of Open Access Journals (Sweden)

    Sidónio C. Freitas

    2018-01-01

    Full Text Available Implant-based therapy is a mature approach to recover the health conditions of patients affected by edentulism. Thousands of dental implants are placed each year since their introduction in the 80s. However, implantology faces challenges that require more research strategies such as new support therapies for a world population with a continuous increase of life expectancy, to control periodontal status and new bioactive surfaces for implants. The present review is focused on self-assembled monolayers (SAMs for dental implant materials as a nanoscale-processing approach to modify titanium surfaces. SAMs represent an easy, accurate, and precise approach to modify surface properties. These are stable, well-defined, and well-organized organic structures that allow to control the chemical properties of the interface at the molecular scale. The ability to control the composition and properties of SAMs precisely through synthesis (i.e., the synthetic chemistry of organic compounds with a wide range of functional groups is well established and in general very simple, being commercially available, combined with the simple methods to pattern their functional groups on complex geometry appliances, makes them a good system for fundamental studies regarding the interaction between surfaces, proteins, and cells, as well as to engineering surfaces in order to develop new biomaterials.

  6. Magnetic domain formation in monolayer nanoparticle films

    Science.gov (United States)

    Maranville, Brian; Krycka, Kathryn; Borchers, Julie; Hogg, Charles; Majetich, Sara; Ijiri, Yumi

    2009-03-01

    Self-assembled magnetic nanoparticle films offer promise as data storage media, but an understanding of the interactions is missing. Modified Langmuir-Blodgett methods were used to prepare monolayer films of 7 and 11 nm diameter Fe3O4 nanoparticles with large structural domains. Small-angle neutron scattering (SANS) shows a peak at a wavevector Q corresponding to the particle size and spacing, and scattering at intermediate Q indicating possible long-range correlations. We extend to lower Q with off-specular neutron reflectivity, achieving high intensity by sacrificing resolution along one in-plane direction y while retaining high resolution in the other in-plane direction x and the normal direction z. We measure in saturation and zero field to extract magnetic scattering. In high fields, the specular scattering (Qx=0) is increased, consistent with aligned moments. Preliminary results show weak magnetic scattering for nonzero Qx . Since the maximal Qx roughly corresponds to the lowest Q in SANS, the combination of these techniques allows us to quantify field-dependent magnetic domain size.

  7. Equilibrium electrostatics of responsive polyelectrolyte monolayers.

    Science.gov (United States)

    Wang, Kang; Zangmeister, Rebecca A; Levicky, Rastislav

    2009-01-14

    The physical behavior of polyelectrolytes at solid-liquid interfaces presents challenges both in measurement and in interpretation. An informative, yet often overlooked, property that characterizes the equilibrium organization of these systems is their membrane or rest potential. Here a general classification scheme is presented of the relationship between the rest potential and structural response of polyelectrolyte films to salt concentration. A numerical lattice theory, adapted from the polymer community, is used to analyze the rest potential response of end-tethered polyelectrolyte layers in which electrostatics and short-range contact interactions conspire to bring about different structural states. As an experimental quantity the rest potential is a readily accessible, nonperturbing metric of the equilibrium structure of a polyelectrolyte layer. A first set of measurements is reported on monolayers of end-tethered, single-stranded DNA in monovalent (NaCl) and divalent (MgCl(2)) counterion environments. Intriguingly, in NaCl electrolyte at least two different mechanisms appear by which the DNA layers can structurally relax in response to changing salt conditions. In MgCl(2) the layers appear to collapse. The possible molecular mechanisms behind these behaviors are discussed. These studies provide insight into phenomena more generally underlying polyelectrolyte applications in the chemical, environmental, and biotechnological fields.

  8. Myofibroblast keratinocyte growth factor reduces tight junctional integrity and increases claudin-2 levels in polarized Caco-2 cells

    Science.gov (United States)

    Kim, Tae Il; Poulin, Emily J.; Blask, Elliot; Bukhalid, Raghida; Whitehead, Robert H.; Franklin, Jeffrey L.; Coffey, Robert J.

    2013-01-01

    The colonic epithelium is composed of a polarized monolayer sheathed by a layer of pericryptal myofibroblasts (PCMFs). We mimicked these cellular compartments in vitro to assess the effects of paracrine-acting PCMF-derived factors on tight junction (TJ) integrity, as measured by transepithelial electrical resistance (TER). Co-culture with 18Co PCMFs, or basolateral administration of 18Co conditioned medium (CM), significantly reduced TER of polarized Caco-2 cells. Amongst candidate paracrine factors, only keratinocyte growth factor (KGF) reduced Caco-2 TER; basolateral KGF treatment led to time- and concentration-dependent increases in claudin-2 levels. We also demonstrate amphiregulin (AREG), produced largely by Caco-2 cells, increased claudin-2 levels, leading to epidermal growth factor receptor-mediated TER reduction. We propose that colonic epithelial TJ integrity can be modulated by paracrine KGF and autocrine AREG through increased claudin-2 levels. KGF-regulated claudin-2 induction may have implications for inflammatory bowel disease, where both KGF and claudin-2 are upregulated. PMID:22946653

  9. Density determination of langmuir-blodgett monolayer films using x-ray reflectivity technique

    International Nuclear Information System (INIS)

    Damar Yoga Kusuma

    2015-01-01

    Monolayer deposition by Langmuir-Blodgett technique produces monolayer films that are uniform with controllable thickness down to nanometer scale. To evaluate the quality of the monolayer deposition, X-ray reflectivity technique are employed to monitor the monolayers density. Langmuir-Blodgett monolayer with good coverage and uniformity results in film density close to its macroscopic film counterpart whereas films with presence of air gaps shows lower density compared to its macroscopic film counterpart. (author)

  10. Surface Charge Transfer Doping of Monolayer Phosphorene via Molecular Adsorption.

    Science.gov (United States)

    He, Yuanyuan; Xia, Feifei; Shao, Zhibin; Zhao, Jianwei; Jie, Jiansheng

    2015-12-03

    Monolayer phosphorene has attracted much attention owing to its extraordinary electronic, optical, and structural properties. Rationally tuning the electrical transport characteristics of monolayer phosphorene is essential to its applications in electronic and optoelectronic devices. Herein, we study the electronic transport behaviors of monolayer phosphorene with surface charge transfer doping of electrophilic molecules, including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), NO2, and MoO3, using density functional theory combined with the nonequilibrium Green's function formalism. F4TCNQ shows optimal performance in enhancing the p-type conductance of monolayer phosphorene. Static electronic properties indicate that the enhancement is originated from the charge transfer between adsorbed molecule and phosphorene layer. Dynamic transport behaviors demonstrate that additional channels for hole transport in host monolayer phosphorene were generated upon the adsorption of molecule. Our work unveils the great potential of surface charge transfer doping in tuning the electronic properties of monolayer phosphorene and is of significance to its application in high-performance devices.

  11. Biomembrane modeling: molecular dynamics simulation of phospholipid monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, T.R.

    1979-01-01

    As a first step toward a computer model of a biomembrane-like bilayer, a dynamic, deterministric model of a phospholipid monolayer has been constructed. The model moves phospholipid-like centers of force according to an integrated law of motion in finite difference form. Forces on each phospholipid analogue are derived from the gradient of the local potential, itself the sum of Coulombic and short-range terms. The Coulombic term is approximated by use of a finite-difference form of Poisson's equation, while the short-range term results from finite-radius, pairwise summation of a Lennard-Jones potential. Boundary potentials are treated in such a way that the model is effectively infinite in extent in the plane of the monolayer. The two-dimensional virial theorem is used to find the surface pressure of the monolayer as a function of molecular area. Pressure-versus-area curves for simulated monolayers are compared to those of real monolayers. Dependence of the simulator's behavior on Lennard-Jones parameters and the specific geometry of the molecular analogue is discussed. Implications for the physical theory of phospholipid monolayers and bilayers are developed.

  12. Second harmonic generation from hemicyanine self-assembled monolayer on near-hemispherical gold nanoparticles

    Science.gov (United States)

    Tanaka, Daisuke; Yamaguchi, Tatsuya; Gupta, Gaurav; Okawa, Haruki; Hashimoto, Kazuhiko; Kajikawa, Kotaro

    2011-10-01

    Second-harmonic generation (SHG) was observed from hemicyanine-terminated alkanethiolate self-assembled monolayers (SAMs) formed on near-hemispherical gold nanoparticles (GNPs) prepared by annealing a vacuum-evaporated thin gold film deposited on a quartz glass substrate. The hemicyanine SAMs were formed on the near-hemispherical GNP by immersion of the substrate in an ethanol solution of hemicyanine-terminated alkanedisulfide. Polarized SHG measurements with the support of theoretical calculations revealed that the near-hemispherical GNP surfaces are fully covered with the hemicyanine SAMs. This result is in contrast to our previous study that showed that the hemicyanine SAM does not form fully over the spherical GNPs immobilized on a quartz glass substrate.

  13. Inhibition of copper corrosion by the formation of Schiff base self-assembled monolayers

    Science.gov (United States)

    Zhang, Jing; Liu, Zheng; Han, Guo-Cheng; Chen, Shi-Liang; Chen, Zhencheng

    2016-12-01

    Self-assembled monolayers (SAMs) of 4-((2-thiophenecarboxylic acid hydrazide) methylene) benzoic acid (HD2) (denoted as HD2-SAMs) were formed on copper surface. The SAMs were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. Polarization curve and weight loss methods indicated that the highest inhibition efficiency was 93.9% for CO2-saturated simulative oilfield water at a self-assembled time of 3 h. Potential-time curve, electrochemical impedance tests showed that HD2-SAMs on copper surface exhibited excellent inhibition effect at 30 °C. The adsorption behavior of HD2-SAMs on the copper surface followed the Langmuir adsorption isotherm, which was indicative of typically chemical adsorption. Quantum chemistry calculation showed that O and N atoms can interact with Cu atoms by coordination bonds which were the mainly active area of the adsorption of HD2 molecules.

  14. Corrosion Protection of Copper in 3% NaCl Solution by the Fabrication of Thiadiazole Monolayer.

    Science.gov (United States)

    Durainatarajan, P; Prabakaran, M; Ramesh, S; Periasamy, V

    2018-08-01

    In this study, 2-mercapto-1,3,4-thiadiazole (2-MT) self-assembled monolayer (SAM) was formed on copper electrode surface and the resulting 2-MT SAM on copper has been characterized using surface analytical techniques such as Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM) and contact angle measurement (CA). The existence of N and S in the EDX and FT-IR analysis showed that 2-MT molecules were self-assembled on the copper through N and S by chemisorption which indicates the formation of 2-MT SAM on copper surface. Corrosion protection performance of 2-MT SAM on copper was investigated using potentiodynamic polarization studies (PDS), cyclic voltammetry (CV) and scanning electron microscopy (SEM), respectively. Analysis of both electrochemical and SEM analysis results revealed excellent corrosion protection for the copper substrate.

  15. Investigation of non-uniform structure of sulfur doped monolayer for polystyrene hollow microspheres

    International Nuclear Information System (INIS)

    Liu Yiyang; Su Lin; Liu Meifang; Zhang Zhanwen; Li Bo; Chen Sufen

    2012-01-01

    Detailed analysis is carried out to describe the non-uniform structure of sulfur doped monolayer for polystyrene hollow microscopy. The results demonstrate that the appearance of this non-uniform comes from PSS (sodium polystyrene sulfonate, the doped sulfur agent). The film forming capability of PSS is also investigated with infrared image microscopy and polarizing microscope. PSS has a bad performance in film forming, and the ordering aggregates and crystal appear on the surfaces of the film. There is great difference in the thermal properties between the PSS film and the polystyrene film indicated by thermal treatment, and the PSS film is easy to have brittle crack and strip from the polystyrene film. Therefore, PSS is not appropriate for fabricating the hollow microspheres when the content of doped sulfur is high. (authors)

  16. Self-assembled monolayers of shape-persistent macrocycles on graphite: interior design and conformational polymorphism

    Directory of Open Access Journals (Sweden)

    Joscha Vollmeyer

    2014-11-01

    Full Text Available Three shape-persistent naphthylene–phenylene–acetylene macrocycles of identical backbone structures and extraannular substitution patterns but different (empty, apolar, polar nanopore fillings are self-assembled at the solid/liquid interface of highly oriented pyrolytic graphite and 1,2,4-trichlorobenzene. Submolecularly resolved images of the resulting two-dimensional (2D crystalline monolayer patterns are obtained by in situ scanning tunneling microscopy. A concentration-dependent conformational polymorphism is found, and open and more dense packing motifs are observed. For all three compounds alike lattice parameters are found, therefore the intermolecular macrocycle distances are mainly determined by their size and symmetry. This is an excellent example that the graphite acts as a template for the macrocycle organization independent from their specific interior.

  17. Self-assembled monolayers of shape-persistent macrocycles on graphite: interior design and conformational polymorphism.

    Science.gov (United States)

    Vollmeyer, Joscha; Eberhagen, Friederike; Höger, Sigurd; Jester, Stefan-S

    2014-01-01

    Three shape-persistent naphthylene-phenylene-acetylene macrocycles of identical backbone structures and extraannular substitution patterns but different (empty, apolar, polar) nanopore fillings are self-assembled at the solid/liquid interface of highly oriented pyrolytic graphite and 1,2,4-trichlorobenzene. Submolecularly resolved images of the resulting two-dimensional (2D) crystalline monolayer patterns are obtained by in situ scanning tunneling microscopy. A concentration-dependent conformational polymorphism is found, and open and more dense packing motifs are observed. For all three compounds alike lattice parameters are found, therefore the intermolecular macrocycle distances are mainly determined by their size and symmetry. This is an excellent example that the graphite acts as a template for the macrocycle organization independent from their specific interior.

  18. Optical absorption signature of a self-assembled dye monolayer on graphene

    Directory of Open Access Journals (Sweden)

    Tessnim Sghaier

    2016-06-01

    Full Text Available A well-organized monolayer of alkylated perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI has been formed onto CVD graphene transferred on a transparent substrate. Its structure has been probed by scanning tunnelling microscopy and its optical properties by polarized transmission spectroscopy at varying incidence. The results show that the transition dipoles of adsorbed PTCDI are all oriented parallel to the substrate. The maximum absorption is consistent with the measured surface density of molecules and their absorption cross section. The spectrum presents mainly a large red-shift of the absorption line compared with the free molecules dispersed in solution, whereas the relative strengths of the vibronic structures are preserved. These changes are attributed to non-resonant interactions with the graphene layer and the neighbouring molecules.

  19. Covalent Surface Modification of Silicon Oxides with Alcohols in Polar Aprotic Solvents.

    Science.gov (United States)

    Lee, Austin W H; Gates, Byron D

    2017-09-05

    Alcohol-based monolayers were successfully formed on the surfaces of silicon oxides through reactions performed in polar aprotic solvents. Monolayers prepared from alcohol-based reagents have been previously introduced as an alternative approach to covalently modify the surfaces of silicon oxides. These reagents are readily available, widely distributed, and are minimally susceptible to side reactions with ambient moisture. A limitation of using alcohol-based compounds is that previous reactions required relatively high temperatures in neat solutions, which can degrade some alcohol compounds or could lead to other unwanted side reactions during the formation of the monolayers. To overcome these challenges, we investigate the condensation reaction of alcohols on silicon oxides carried out in polar aprotic solvents. In particular, propylene carbonate has been identified as a polar aprotic solvent that is relatively nontoxic, readily accessible, and can facilitate the formation of alcohol-based monolayers. We have successfully demonstrated this approach for tuning the surface chemistry of silicon oxide surfaces with a variety of alcohol containing compounds. The strategy introduced in this research can be utilized to create silicon oxide surfaces with hydrophobic, oleophobic, or charged functionalities.

  20. Broadband Perfect Absorber with Monolayer MoS2and Hexagonal Titanium Nitride Nano-disk Array.

    Science.gov (United States)

    Huo, Dewang; Zhang, Jingwen; Wang, Hao; Ren, Xiaoxuan; Wang, Chao; Su, Hang; Zhao, Hua

    2017-12-01

    A broadband metamaterial absorber (MA) composed of hexagonal-arranged single-sized titanium nitride (TiN) nano-disk array and monolayer molybdenum disulfide (MoS 2 ) is studied using finite-difference time-domain (FDTD) simulations. The structure of TiN nano-disk array/dielectric silica (SiO 2 )/aluminum (Al) is adopted in our design. By optimizing the dimension parameters of the structure, an average absorption of 96.1% is achieved from 400 to 850 nm. In addition, by inserting a monolayer MoS 2 which has high absorption at the short wavelength side underneath the TiN nano-disk array, an average absorption of 98.1% over the entire visible regime from 400 to 850 nm was achieved, with a peak absorption near 100% and absorption over 99% from 475 to 772 nm. Moreover, the absorber presented in this paper is polarization insensitive. This compact and unique design with TiN nano-disk/monolayer MoS 2 / SiO 2 /Al structure may have great potential for applications in photovoltaics and light trapping.

  1. Exciton valley dynamics in monolayer Mo1-xWxSe2 (x = 0, 0.5, 1)

    Science.gov (United States)

    Ye, Jialiang; Niu, Binghui; Li, Ying; Li, Ting; Zhang, Xinhui

    2017-10-01

    We study the exciton valley dynamics in monolayers MoSe2, Mo0.5W0.5Se2, and WSe2 by employing helicity-resolved two-color transient reflection spectroscopy. The valley depolarization dynamics as a function of the excitation laser energy is studied systematically at above-resonant excitation of excitons at 10 K. A longer intervalley scattering time is obtained as the excitation energy approaches the A exciton resonance for the three studied materials. The excitation energy dependence of exciton valley relaxation proves that the long-range electron-hole exchange interaction dominates the intervalley scattering in transition metal dichalcogenide monolayers. The longer valley scattering time and higher valley polarization degree commonly observed for WSe2 than for MoSe2 is discussed to result from the interplay between the intervalley electron-hole exchange interaction and dark-bright exciton scattering, where the existence of energetically lower lying dark excitonic states in monolayer WSe2 favors the suppression of the intervalley electron-hole exchange interaction.

  2. Products and Kinetics of the Reactions of an Alkane Monolayer and a Terminal Alkene Monolayer with NO₃ Radicals

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Simone; Bertram, Allan K.

    2009-01-27

    The reactions of an alkanethiol and a terminal alkenethiol self-assembled monolayer with NO₃ radicals (in the presence of NO₂ and O₂) were studied. For the alkane monolayer, infrared (IR) spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirmed the formation of organonitrates (RONO₂). The observation of organonitrates is in contrast to the recent X-ray photoelectron spectroscopy (XPS) data, which showed very little nitrogen-containing surface species. The identification of organonitrates may help explain why significant volatilization of the organic chain was not observed in recent studies of alkane monolayer oxidation by NO₃ radicals. The reactive uptake coefficient (g) of NO₃ on alkene monolayers determined in our study is higher than the values obtained in a recent study using liquid and solid alkene bulk films. A possible reason for this difference may be the location of the double bond at the interface. Using the g value determined in our studies, we show that under conditions where NO₃ is high the lifetime of an alkene monolayer in the atmosphere may be short (approximately 20 min). XPS, IR, and ToF-SIMS were used to identify surface functional groups after the oxidation of the alkene monolayers by NO₃. The results are consistent with the formation of C-O, aldehyde/ketone, carboxylic groups, and nitrogen containing species.

  3. Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides

    KAUST Repository

    Zheng, Yu Jie

    2016-01-21

    © 2016 American Chemical Society. The nature and extent of electronic screening at heterointerfaces and their consequences on energy level alignment are of profound importance in numerous applications, such as solar cells, electronics etc. The increasing availability of two-dimensional (2D) transition metal dichalcogenides (TMDs) brings additional opportunities for them to be used as interlayers in "van der Waals (vdW) heterostructures" and organic/inorganic flexible devices. These innovations raise the question of the extent to which the 2D TMDs participate actively in dielectric screening at the interface. Here we study perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) monolayers adsorbed on single-layer tungsten diselenide (WSe2), bare graphite, and Au(111) surfaces, revealing a strong dependence of the PTCDA HOMO-LUMO gap on the electronic screening effects from the substrate. The monolayer WSe2 interlayer provides substantial, but not complete, screening at the organic/inorganic interface. Our results lay a foundation for the exploitation of the complex interfacial properties of hybrid systems based on TMD materials.

  4. Alpha-Melanocyte Stimulating Hormone Protects against Cytokine-Induced Barrier Damage in Caco-2 Intestinal Epithelial Monolayers.

    Directory of Open Access Journals (Sweden)

    Judit Váradi

    Full Text Available Alpha-melanocyte-stimulating hormone (α-MSH is a potent anti-inflammatory peptide with cytoprotective effect in various tissues. The present investigation demonstrates the ability of α-MSH to interact with intestinal epithelial cell monolayers and mitigate inflammatory processes of the epithelial barrier. The protective effect of α-MSH was studied on Caco-2 human intestinal epithelial monolayers, which were disrupted by exposure to tumor necrosis factor-α and interleukin-1β. The barrier integrity was assessed by measuring transepithelial electric resistance (TEER and permeability for marker molecules. Caco-2 monolayers were evaluated by immunohistochemistry for expression of melanocortin-1 receptor and tight junction proteins ZO-1 and claudin-4. The activation of nuclear factor kappa beta (NF-κB was detected by fluorescence microscopy and inflammatory cytokine expression was assessed by flow cytometric bead array cytokine assay. Exposure of Caco-2 monolayers to proinflammatory cytokines lowered TEER and increased permeability for fluorescein and albumin, which was accompanied by changes in ZO-1 and claudin-4 immunostaining. α-MSH was able to prevent inflammation-associated decrease of TEER in a dose-dependent manner and reduce the increased permeability for paracellular marker fluorescein. Further immunohistochemistry analysis revealed proinflammatory cytokine induced translocation of the NF-κB p65 subunit into Caco-2 cell nuclei, which was inhibited by α-MSH. As a result the IL-6 and IL-8 production of Caco-2 monolayers were also decreased with different patterns by the addition of α-MSH to the culture medium. In conclusion, Caco-2 cells showed a positive immunostaining for melanocortin-1 receptor and α-MSH protected Caco-2 cells against inflammatory barrier dysfunction and inflammatory activation induced by tumor necrosis factor-α and interleukin-1β cytokines.

  5. Alpha-Melanocyte Stimulating Hormone Protects against Cytokine-Induced Barrier Damage in Caco-2 Intestinal Epithelial Monolayers

    Science.gov (United States)

    Váradi, Judit; Harazin, András; Fenyvesi, Ferenc; Réti-Nagy, Katalin; Gogolák, Péter; Vámosi, György; Bácskay, Ildikó; Fehér, Pálma; Ujhelyi, Zoltán; Vasvári, Gábor; Róka, Eszter; Haines, David; Deli, Mária A.; Vecsernyés, Miklós

    2017-01-01

    Alpha-melanocyte-stimulating hormone (α-MSH) is a potent anti-inflammatory peptide with cytoprotective effect in various tissues. The present investigation demonstrates the ability of α-MSH to interact with intestinal epithelial cell monolayers and mitigate inflammatory processes of the epithelial barrier. The protective effect of α-MSH was studied on Caco-2 human intestinal epithelial monolayers, which were disrupted by exposure to tumor necrosis factor-α and interleukin-1β. The barrier integrity was assessed by measuring transepithelial electric resistance (TEER) and permeability for marker molecules. Caco-2 monolayers were evaluated by immunohistochemistry for expression of melanocortin-1 receptor and tight junction proteins ZO-1 and claudin-4. The activation of nuclear factor kappa beta (NF-κB) was detected by fluorescence microscopy and inflammatory cytokine expression was assessed by flow cytometric bead array cytokine assay. Exposure of Caco-2 monolayers to proinflammatory cytokines lowered TEER and increased permeability for fluorescein and albumin, which was accompanied by changes in ZO-1 and claudin-4 immunostaining. α-MSH was able to prevent inflammation-associated decrease of TEER in a dose-dependent manner and reduce the increased permeability for paracellular marker fluorescein. Further immunohistochemistry analysis revealed proinflammatory cytokine induced translocation of the NF-κB p65 subunit into Caco-2 cell nuclei, which was inhibited by α-MSH. As a result the IL-6 and IL-8 production of Caco-2 monolayers were also decreased with different patterns by the addition of α-MSH to the culture medium. In conclusion, Caco-2 cells showed a positive immunostaining for melanocortin-1 receptor and α-MSH protected Caco-2 cells against inflammatory barrier dysfunction and inflammatory activation induced by tumor necrosis factor-α and interleukin-1β cytokines. PMID:28103316

  6. Geographical Income Polarization

    DEFF Research Database (Denmark)

    Azhar, Hussain; Jonassen, Anders Bruun

    inter municipal income inequality. Counter factual simulations show that rising property prices to a large part explain the rise in polarization. One side-effect of polarization is tendencies towards a parallel polarization of residence location patterns, where low skilled individuals tend to live......In this paper we estimate the degree, composition and development of geographical income polarization based on data at the individual and municipal level in Denmark from 1984 to 2002. Rising income polarization is reconfirmed when applying new polarization measures, the driving force being greater...

  7. Effect of time and deposition method on quality of phosphonic acid modifier self-assembled monolayers on indium zinc oxide

    Energy Technology Data Exchange (ETDEWEB)

    Sang, Lingzi [Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721 (United States); Knesting, Kristina M. [Department of Chemistry, University of Washington, Seattle, WA 98195-1700 (United States); Bulusu, Anuradha [School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Sigdel, Ajaya K. [National Renewable Energy Laboratory, Golden, CO 80401 (United States); Giordano, Anthony J.; Marder, Seth R. [School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (United States); Berry, Joseph J. [National Renewable Energy Laboratory, Golden, CO 80401 (United States); Graham, Samuel [School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Ginger, David S. [Department of Chemistry, University of Washington, Seattle, WA 98195-1700 (United States); Pemberton, Jeanne E., E-mail: pembertn@email.arizona.edu [Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721 (United States)

    2016-12-15

    Highlights: • Deposition of phosphonic acid monolayers on oxides from ethanol solutions occurs by rapid adsorption within 10 s with slower equilibration complete in 48 h. • The slower equilibration step involves molecular reorientation and vacancy filling on the oxide surface. • Soak-free deposition by spray coating and microcontact printing do not provide reproducible, fully-covered, uniform monolayers without substrate etching. • Adjustments to exposure time, substrate temperature, and solution/substrate contact efficiency are necessary to optimize soak-free methods. - Abstract: Phosphonic acid (PA) self-assembled monolayers (SAMs) are utilized at critical interfaces between transparent conductive oxides (TCO) and organic active layers in organic photovoltaic devices (OPVs). The effects of PA deposition method and time on the formation of close-packed, high-quality monolayers is investigated here for SAMs fabricated by solution deposition, micro-contact printing, and spray coating. The solution deposition isotherm for pentafluorinated benzylphosphonic acid (F{sub 5}BnPA) on indium-doped zinc oxide (IZO) is studied using polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS) at room temperature as a model PA/IZO system. Fast surface adsorption occurs within the first min; however, well-oriented high-quality SAMs are reached only after ∼48 h, presumably through a continual process of molecular adsorption/desorption and monolayer filling accompanied by molecular reorientation. Two other rapid, soak-free deposition techniques, micro-contact printing and spray coating, are also explored. SAM quality is compared for deposition of phenyl phosphonic acid (PPA), F{sub 13}-octylphosphonic acid (F{sub 13}OPA), and pentafluorinated benzyl phosphonic acid (F{sub 5}BnPA) by solution deposition, micro-contact printing and spray coating using PM-IRRAS. In contrast to micro-contact printing and spray coating techniques, 48–168 h solution

  8. Mechano-capacitive properties of polarized membranes.

    Science.gov (United States)

    Mosgaard, Lars D; Zecchi, Karis A; Heimburg, Thomas

    2015-10-28

    Biological membranes are capacitors that can be charged by applying a field across the membrane. The charges on the capacitor exert a force on the membrane that leads to electrostriction, i.e. a thinning of the membrane. Since the force is quadratic in voltage, negative and positive voltage have an identical influence on the physics of symmetric membranes. However, this is not the case for a membrane with an asymmetry leading to a permanent electric polarization. Positive and negative voltages of identical magnitude lead to different properties. Such an asymmetry can originate from a lipid composition that is different on the two monolayers of the membrane, or from membrane curvature. The latter effect is called 'flexoelectricity'. As a consequence of permanent polarization, the membrane capacitor is discharged at a voltage different from zero. This leads to interesting electrical phenomena such as outward or inward rectification of membrane permeability. Here, we introduce a generalized theoretical framework, that treats capacitance, polarization, flexoelectricity, piezoelectricity and thermoelectricity in the same language. We show applications to electrostriction, membrane permeability and piezoelectricity and thermoelectricity close to melting transitions, where such effects are especially pronounced.

  9. Low oxygen reduces the modulation to an oxidative phenotype in monolayer-expanded chondrocytes.

    Science.gov (United States)

    Heywood, Hannah K; Lee, David A

    2010-01-01

    Autologous chondrocyte implantation requires a phase of in vitro cell expansion, achieved by monolayer culture under atmospheric oxygen levels. Chondrocytes reside under low oxygen conditions in situ and exhibit a glycolytic metabolism. However, oxidative phosphorylation rises progressively during culture, with concomitant reactive oxygen species production. We determine if the high oxygen environment in vitro provides the transformation stimulus. Articular chondrocytes were cultured in monolayer for up to 14 days under 2%, 5%, or 20% oxygen. Expansion under 2% and 5% oxygen reduced the rate at which the cells developed an oxidative phenotype compared to 20% oxygen. However, at 40 +/- 4 fmol cell(-1) h(-1) the oxygen consumption by chondrocytes expanded under 2% oxygen for 14 days was still 14 times the value observed for freshly isolated cells. Seventy-five to 78% of the increased oxygen consumption was accounted for by oxidative phosphorylation (oligomycin sensitive). Expansion under low oxygen also reduced cellular proliferation and 8-hydroxyguanosine release, a marker of oxidative DNA damage. However, these parameters remained elevated compared to freshly isolated cells. Thus, expansion under physiological oxygen levels reduces, but does not abolish, the induction of an oxidative energy metabolism. We conclude that simply transferring chondrocytes to low oxygen is not sufficient to either maintain or re-establish a normal energy metabolism. Furthermore, a hydrophobic polystyrene culture surface which promotes rounded cell morphology had no effect on the development of an oxidative metabolism. Although the shift towards an oxidative energy metabolism is often accompanied by morphological changes, this study does not support the hypothesis that it is driven by them.

  10. Polarized Light Corridor Demonstrations.

    Science.gov (United States)

    Davies, G. R.

    1990-01-01

    Eleven demonstrations of light polarization are presented. Each includes a brief description of the apparatus and the effect demonstrated. Illustrated are strain patterns, reflection, scattering, the Faraday Effect, interference, double refraction, the polarizing microscope, and optical activity. (CW)

  11. Phase behavior of lipid monolayers containing DPPC and cholesterol analogs.

    Science.gov (United States)

    Stottrup, Benjamin L; Keller, Sarah L

    2006-05-01

    We investigate the miscibility phase behavior of lipid monolayers containing a wide variety of sterols. Six of the sterols satisfy a definition from an earlier study of "membrane-active sterols" in bilayers (cholesterol, epicholesterol, lathosterol, dihydrocholesterol, ergosterol, and desmosterol), and six do not (25-hydroxycholesterol, lanosterol, androstenolone, coprostanol, cholestane, and cholestenone). We find that monolayers containing dipalmitoyl phosphatidylcholine mixed with membrane-active sterols generally produce phase diagrams containing two distinct regions of immiscible liquid phases, whereas those with membrane-inactive sterols generally do not. This observation establishes a correlation between lipid monolayers and bilayers. It also demonstrates that the ability to form two regions of immiscibility in monolayers is not one of the biophysical attributes that explains cholesterol's predominance in animal cell membranes. Furthermore, we find unusual phase behavior for dipalmitoyl phosphatidylcholine monolayers containing 25-hydroxycholesterol, which produce both an upper and a lower miscibility transition. The lower transition correlates with a sharp change of slope in the pressure-area isotherm.

  12. Study of iridium silicide monolayers using density functional theory

    Science.gov (United States)

    Popis, Minh D.; Popis, Sylvester V.; Oncel, Nuri; Hoffmann, Mark R.; ćakır, Deniz

    2018-02-01

    In this study, we investigated physical and electronic properties of possible two-dimensional structures formed by Si (silicon) and Ir (iridium). To this end, different plausible structures were modeled by using density functional theory and the cohesive energies calculated for the geometry of optimized structures, with the lowest equilibrium lattice constants. Among several candidate structures, we identified three mechanically (via elastic constants and Young's modulus), dynamically (via phonon calculations), and thermodynamically stable iridium silicide monolayer structures. The lowest energy structure has a chemical formula of Ir2Si4 (called r-IrSi2), with a rectangular lattice (Pmmn space group). Its cohesive energy was calculated to be -0.248 eV (per IrSi2 unit) with respect to bulk Ir and bulk Si. The band structure indicates that the Ir2Si4 monolayer exhibits metallic properties. Other stable structures have hexagonal (P-3m1) and tetragonal (P4/nmm) cell structures with 0.12 and 0.20 eV/f.u. higher cohesive energies, respectively. Our calculations showed that Ir-Si monolayers are reactive. Although O2 molecules exothermically dissociate on the surface of the free-standing iridium silicide monolayers with large binding energies, H2O molecules bind to the monolayers with a rather weak interaction.

  13. Structure and function evolution of thiolate monolayers on gold

    Energy Technology Data Exchange (ETDEWEB)

    Edwards, Grant Alvin [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (infrared reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  14. Structure and Function Evolution of Thiolate Monolayers on Gold

    Energy Technology Data Exchange (ETDEWEB)

    Edwards, Grant Alvin [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  15. Evidence of indirect gap in monolayer WSe2

    KAUST Repository

    Hsu, Wei-Ting

    2017-10-09

    Monolayer transition metal dichalcogenides, such as MoS2 and WSe2, have been known as direct gap semiconductors and emerged as new optically active materials for novel device applications. Here we reexamine their direct gap properties by investigating the strain effects on the photoluminescence of monolayer MoS2 and WSe2. Instead of applying stress, we investigate the strain effects by imaging the direct exciton populations in monolayer WSe2–MoS2 and MoSe2–WSe2 lateral heterojunctions with inherent strain inhomogeneity. We find that unstrained monolayer WSe2 is actually an indirect gap material, as manifested in the observed photoluminescence intensity–energy correlation, from which the difference between the direct and indirect optical gaps can be extracted by analyzing the exciton thermal populations. Our findings combined with the estimated exciton binding energy further indicate that monolayer WSe2 exhibits an indirect quasiparticle gap, which has to be reconsidered in further studies for its fundamental properties and device applications.

  16. Enhanced piezoelectricity of monolayer phosphorene oxides: a theoretical study.

    Science.gov (United States)

    Yin, Huabing; Zheng, Guang-Ping; Gao, Jingwei; Wang, Yuanxu; Ma, Yuchen

    2017-10-18

    Two-dimensional (2D) piezoelectric materials have potential applications in miniaturized sensors and energy conversion devices. In this work, using first-principles simulations at different scales, we systematically study the electronic structures and piezoelectricity of a series of 2D monolayer phosphorene oxides (POs). Our calculations show that the monolayer POs have tunable band gaps along with remarkable piezoelectric properties. The calculated piezoelectric coefficient d 11 of 54 pm V -1 in POs is much larger than those of 2D transition metal dichalcogenide monolayers and the widely used bulk α-quartz and AlN, and almost reaches the level of the piezoelectric effect in recently discovered 2D GeS. Furthermore, two other considerable piezoelectric coefficients, i.e., d 31 and d 26 with values of -10 pm V -1 and 21 pm V -1 , respectively, are predicted in some monolayer POs. We also examine the correlation between the piezoelectric coefficients and energy stability. The enhancement of piezoelectricity for monolayer phosphorene by oxidation will broaden the applications of phosphorene and phosphorene derivatives in nano-sized electronic and piezotronic devices.

  17. Thermal conductivity of a h-BCN monolayer.

    Science.gov (United States)

    Zhang, Ying-Yan; Pei, Qing-Xiang; Liu, Hong-Yuan; Wei, Ning

    2017-10-18

    A hexagonal graphene-like boron-carbon-nitrogen (h-BCN) monolayer, a new two-dimensional (2D) material, has been synthesized recently. Herein we investigate for the first time the thermal conductivity of this novel 2D material. Using molecular dynamics simulations based on the optimized Tersoff potential, we found that the h-BCN monolayers are isotropic in the basal plane with close thermal conductivity magnitudes. Though h-BCN has the same hexagonal lattice as graphene and hexagonal boron nitride (h-BN), it exhibits a much lower thermal conductivity than the latter two materials. In addition, the thermal conductivity of h-BCN monolayers is found to be size-dependent but less temperature-dependent. Modulation of the thermal conductivity of h-BCN monolayers can also be realized by strain engineering. Compressive strain leads to a monotonic decrease in the thermal conductivity while the tensile strain induces an up-then-down trend in the thermal conductivity. Surprisingly, the small tensile strain can facilitate the heat transport of the h-BCN monolayers.

  18. Piezoelectric effect on the thermal conductivity of monolayer gallium nitride

    Science.gov (United States)

    Zhang, Jin

    2018-01-01

    Using molecular dynamics and density functional theory simulations, in this work, we find that the heat transport property of the monolayer gallium nitride (GaN) can be efficiently tailored by external electric field due to its unique piezoelectric characteristic. As the monolayer GaN possesses different piezoelectric properties in armchair and zigzag directions, different effects of the external electric field on thermal conductivity are observed when it is applied in the armchair and zigzag directions. Our further study reveals that due to the elastoelectric effect in the monolayer GaN, the external electric field changes the Young's modulus and therefore changes the phonon group velocity. Also, due to the inverse piezoelectric effect, the applied electric field induces in-plane stress in the monolayer GaN subject to a length constraint, which results in the change in the lattice anharmonicity and therefore affects the phonon mean free path. Furthermore, for relatively long GaN monolayers, the in-plane stress may trigger the buckling instability, which can significantly reduce the phonon mean free path.

  19. Trichomonas gallinae, in comparison to Tetratrichomonas gallinarum, induces distinctive cytopathogenic effects in tissue cultures.

    Science.gov (United States)

    Amin, Aziza; Bilic, Ivana; Berger, Evelyn; Hess, Michael

    2012-05-25

    In the present study the interaction of three genetically different clonal cultures of Trichomonas gallinae and Tetratrichomonas gallinarum with a permanent chicken liver (LMH) and a permanent quail fibroblast (QT35) cell culture was studied. Proliferation of T. gallinae cells was associated with a disintegration of the cell monolayer. The initial lesions on the LMH monolayer consisted of a progressive accumulation of the flagellate, forming clumps attached to the monolayer. A prolonged incubation time was characterized by appearance of holes in the cell monolayer with accumulation of trichomonads at their periphery. According to the severeness of the monolayer disruption differences among three tested T. gallinae clones were noticed. Furthermore, filtrates obtained either from axenic cultures of T. gallinae or from infected cell cultures produced a cytopathogenic effect similar to the protozoal cells, on both types of cell cultures. However, the destructive effect of the flagellates and their cell-free filtrates was much more pronounced on the LMH monolayer in comparison with the QT35 cells. Furthermore, freshly seeded LMH and QT35 cells suspended in cell-free filtrates of T. gallinae were unable to form a confluent monolayer. In comparison to T. gallinae, clonal cultures of T. gallinarum or their cell-free filtrates produced no effect on both types of monolayers. Interestingly, the cell-free filtrates obtained from both trichomonad species had an effect on the viability of both cell cultures. However, the cytotoxic effect of T. gallinarum filtrates was less severe than that recorded by T. gallinae. Consequently, for the first time a destruction of specified monolayers induced by T. gallinae-free filtrates could be demonstrated. Copyright © 2011 Elsevier B.V. All rights reserved.

  20. Polarized Moessbauer transitions

    International Nuclear Information System (INIS)

    Barb, D.

    1975-01-01

    Theoretical aspects of the emission, absorption and scattering of polarized gamma rays are reviewed for a general case of combined magnetic and electric hyperfine interactions; various possibilities of obtaining polarized gamma sources are described and examples are given of the applications of Moessbauer spectroscopy with polarized gamma rays in solving problems of solid state physics. (A.K.)

  1. Fullerene nanostructures, monolayers and thin films

    International Nuclear Information System (INIS)

    Cotier, B.N.

    2000-10-01

    The interaction of submonolayer, monolayer and multilayer coverages of C 60 with the Ag/Si(111)-(√3x√3)R30 deg. (√3Ag/Si) and Si(111)-7x7 surfaces has been investigated using atomic force microscopy (AFM), photoelectron spectroscopy (PES) and ultra high vacuum scanning tunneling microscopy (UHV-STM). It is shown that it is possible to preserve the √3Ag/Si surface, normally corrupted by exposure to air, in ambient conditions when immersed beneath a few layers of C 60 molecules. Upon removal of the fullerene layers in the UHV-STM some corruption is observed which is linked to the morphology of the fullerene film (defined by the nature of the interaction of C 60 with √3Ag/Si). This technique opens up the possibility of performing experiments on the clean √3Ag/Si surface outside of UHV conditions. With the discovery of techniques whereby structures may be formed that are composed of only a few atoms/molecules, there is a need to perform electrical measurements in order to probe the fascinating properties of these 'nano-scale' devices. Using AFM, PES and STM evaporated metals and ion implantation have been investigated as materials for use in forming sub-micron scale contacts to nanostructures. It is found that ion implantation is a more promising approach after studying the response to annealing of treated surfaces. Electrical measurements between open/short circuited contacts and through Ag films clearly demonstrate the validity of the method, further confirmed by a PES study which probes the chemical nature of the near surface region of ion-implanted samples. Attempts have been made to form nanostructure templates between sub-micron scale contacts as a possible precursor to forming nanostructures. The bonding state of C 60 molecules on the Si(111)-7x7 surface has been in dispute for many years. To properly understand the system a comprehensive AFM, PES and STM study has been performed. PES results indicate covalent bond formation, with the number of bonds

  2. Marrying Excitons and Plasmons in Monolayer Transition-Metal Dichalcogenides

    Science.gov (United States)

    Van Tuan, Dinh; Scharf, Benedikt; Žutić, Igor; Dery, Hanan

    2017-10-01

    Just as photons are the quanta of light, plasmons are the quanta of orchestrated charge-density oscillations in conducting media. Plasmon phenomena in normal metals, superconductors, and doped semiconductors are often driven by long-wavelength Coulomb interactions. However, in crystals whose Fermi surface is comprised of disconnected pockets in the Brillouin zone, collective electron excitations can also attain a shortwave component when electrons transition between these pockets. In this work, we show that the band structure of monolayer transition-metal dichalcogenides gives rise to an intriguing mechanism through which shortwave plasmons are paired up with excitons. The coupling elucidates the origin for the optical sideband that is observed repeatedly in monolayers of WSe2 and WS2 but not understood. The theory makes it clear why exciton-plasmon coupling has the right conditions to manifest itself distinctly only in the optical spectra of electron-doped tungsten-based monolayers.

  3. Nanomechanical resonators based on group IV element monolayers

    Science.gov (United States)

    He, Ji-Dong; Sun, Jia-Sheng; Jiang, Jin-Wu

    2018-04-01

    We perform molecular dynamics simulations to investigate the energy dissipation of the resonant oscillation for the group IV monolayers of puckered configuration, in which the oscillation is driven with different actuation velocities. We find that, in the moderate actuation velocity regime, the nonlinear coupling between the resonant oscillation mode and other high-frequency modes will lead to the non-resonant motion of the system. For the larger actuation velocity, the effective strain generated during the resonant oscillating causes a structural transition from the puckered configuration into the planar configuration, which is a characteristic energy dissipation mechanism for the resonant oscillation of these group IV puckered monolayers. Our findings shed light on mechanical applications of the group IV monolayers in the nanomechanical resonator field.

  4. Infrared spectroscopy of self-assembled monolayer films on silicon

    Science.gov (United States)

    Rowell, N. L.; Tay, Lilin; Boukherroub, R.; Lockwood, D. J.

    2007-07-01

    Infrared vibrational spectroscopy in an attenuated total reflection (ATR) geometry has been employed to investigate the presence of organic thin layers on Si-wafer surfaces. The phenomena have been simulated to show there can be a field enhancement with the presented single-reflection ATR (SR-ATR) approach which is substantially larger than for conventional ATR or specular reflection. In SR-ATR, a discontinuity of the field normal to the film contributes a field enhancement in the lower index thin film causing a two order of magnitude increase in sensitivity. SR-ATR was employed to characterize a single monolayer of undecylenic acid self-assembled on Si(1 1 1) and to investigate a two monolayer system obtained by adding a monolayer of bovine serum albumin protein.

  5. Triptycene-terminated thiolate and selenolate monolayers on Au(111

    Directory of Open Access Journals (Sweden)

    Jinxuan Liu

    2017-04-01

    Full Text Available To study the implications of highly space-demanding organic moieties on the properties of self-assembled monolayers (SAMs, triptycyl thiolates and selenolates with and without methylene spacers on Au(111 surfaces were comprehensively studied using ultra-high vacuum infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and thermal desorption spectroscopy. Due to packing effects, the molecules in all monolayers are substantially tilted. In the presence of a methylene spacer the tilt is slightly less pronounced. The selenolate monolayers exhibit smaller defect densities and therefore are more densely packed than their thiolate analogues. The Se–Au binding energy in the investigated SAMs was found to be higher than the S–Au binding energy.

  6. Self assembled monolayers of octadecyltrichlorosilane for dielectric materials

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Vijay, E-mail: cirivijaypilani@gmail.com [Centre for Nanoscience and Engineering, Indian Institute of Science-Bangalore (India); Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); Puri, Paridhi; Nain, Shivani [Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); Bhat, K. N. [Centre for Nanoscience and Engineering, Indian Institute of Science-Bangalore (India); Sharma, N. N. [Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); School of Automobile, Mechanical & Mechatronics, Manipal University-Jaipur (India)

    2016-04-13

    Treatment of surfaces to change the interaction of fluids with them is a critical step in constructing useful microfluidics devices, especially those used in biological applications. Selective modification of inorganic materials such as Si, SiO{sub 2} and Si{sub 3}N{sub 4} is of great interest in research and technology. We evaluated the chemical formation of OTS self-assembled monolayers on silicon substrates with different dielectric materials. Our investigations were focused on surface modification of formerly used common dielectric materials SiO{sub 2}, Si{sub 3}N{sub 4} and a-poly. The improvement of wetting behaviour and quality of monolayer films were characterized using Atomic force microscope, Scanning electron microscope, Contact angle goniometer, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) monolayer deposited oxide surface.

  7. Measuring the Edge Recombination Velocity of Monolayer Semiconductors.

    Science.gov (United States)

    Zhao, Peida; Amani, Matin; Lien, Der-Hsien; Ahn, Geun Ho; Kiriya, Daisuke; Mastandrea, James P; Ager, Joel W; Yablonovitch, Eli; Chrzan, Daryl C; Javey, Ali

    2017-09-13

    Understanding edge effects and quantifying their impact on the carrier properties of two-dimensional (2D) semiconductors is an essential step toward utilizing this material for high performance electronic and optoelectronic devices. WS 2 monolayers patterned into disks of varying diameters are used to experimentally explore the influence of edges on the material's optical properties. Carrier lifetime measurements show a decrease in the effective lifetime, τ effective , as a function of decreasing diameter, suggesting that the edges are active sites for carrier recombination. Accordingly, we introduce a metric called edge recombination velocity (ERV) to characterize the impact of 2D material edges on nonradiative carrier recombination. The unpassivated WS 2 monolayer disks yield an ERV ∼ 4 × 10 4 cm/s. This work quantifies the nonradiative recombination edge effects in monolayer semiconductors, while simultaneously establishing a practical characterization approach that can be used to experimentally explore edge passivation methods for 2D materials.

  8. Controlled electrodeposition of Au monolayer film on ionic liquid

    Science.gov (United States)

    Ma, Qiang; Pang, Liuqing; Li, Man; Zhang, Yunxia; Ren, Xianpei; Liu, Shengzhong Frank

    2016-05-01

    Gold (Au) nanoparticles have been attractive for centuries for their vibrant appearance enhanced by their interaction with sunlight. Nowadays, there have been tremendous research efforts to develop them for high-tech applications including therapeutic agents, sensors, organic photovoltaics, medical applications, electronics and catalysis. However, there remains to be a challenge to fabricate a monolayer Au coating with complete coverage in controlled fashion. Here we present a facile method to deposit a uniform Au monolayer (ML) film on the [BMIM][PF6] ionic liquid substrate using an electrochemical deposition process. It demonstrates that it is feasible to prepare a solid phase coating on the liquid-based substrate. Moreover, the thickness of the monolayer coating can be controlled to a layer-by-layer accuracy.

  9. Sulfonation of alkyl phenyl ether self-assembled monolayers.

    Science.gov (United States)

    Katash, Irit; Luo, Xianglin; Sukenik, Chaim N

    2010-02-02

    The sulfonation of phenyl ether decorated self-assembled monolayers (SAMs) was studied with an eye toward creating surfaces with a particularly high negative charge density based on a close-packed array of phenyl rings with more than one sulfonic acid group per molecule. The product distribution and kinetics of this process were studied by ultraviolet, infrared, and photoelectron spectroscopies and by monitoring changes in the thickness and wetting properties of the SAM. The sulfonation chemistry could be effected without undermining monolayer integrity and the isomer distribution of ortho- and para-monosulfonated material, along with the percentages of mono- and disulfonated molecules could be established throughout the process. As doubly sulfonated molecules appeared, the reaction slowed drastically. Ultimately, sulfonation stops completely with approximately 60% of the molecules disulfonated and 20% each of the two monosulfonated isomers. This striking constraint on monolayer reactivity and the relationship between the surface chemistry and variations in SAM structure are discussed.

  10. Photo-induced travelling waves in condensed Langmuir monolayers

    CERN Document Server

    Tabe, Y; Yokoyama, H

    2003-01-01

    We report the detailed properties of photo-induced travelling waves in liquid crystalline Langmuir monolayers composed of azobenzene derivatives. When the monolayer, in which the constituent rodlike molecules are coherently tilted from the layer normal, is weakly illuminated to undergo the trans-cis photo-isomerization, spatio-temporal periodic oscillations of the molecular azimuth begin over the entire excited area and propagate as a two-dimensional orientational wave. The wave formation takes place only when the film is formed at an asymmetric interface with broken up-down symmetry and when the chromophores are continuously excited near the long-wavelength edge of absorption to induce repeated photo-isomerizations between the trans and cis forms. Under proper illumination conditions, Langmuir monolayers composed of a wide variety of azobenzene derivatives have been confirmed to exhibit similar travelling waves with velocity proportional to the excitation power irrespective of the degree of amphiphilicity. T...

  11. Effect of a dienogest for an experimental three-dimensional endometrial culture model for endometriosis.

    Science.gov (United States)

    Prechapanich, Japarath; Kajihara, Takeshi; Fujita, Keiko; Sato, Kazuko; Uchino, Satomi; Tanaka, Kayoko; Matsumoto, Sachiko; Akita, Masumi; Nagashima, Masabumi; Brosens, Jan J; Ishihara, Osamu

    2014-12-01

    The pathogenesis of endometriosis remains poorly understood at least in part because early stages of the disease process are difficult to investigate. Previous studies have proposed a three-dimensional fibrin matrix culture model to study human endometriosis. We examined the ultrastructural features of the endometriosis in this model and assessed the effect of a progestin on endometrial outgrowth and apoptosis in this culture system. Endometrial explants were placed in three-dimensional fibrin matrix culture and treated with and without various concentrations of the progestin dienogest. By the second week, endometrial gland-like formation was established in outgrowths both attached to and at a distance from the explants. These cells formed a combination of clumps and tubular monolayers surrounding a central cavity. Electron microscopy demonstrated that these cells are polarized with microvilli on the apical surface, desmosome-like structures, and basement membrane; features consistent with glandular epithelial cells. Outgrowth of endometrial stromal cells and glandular formation was impaired in response to dienogest in a dose-dependent manner. Our study shows that the human endometrial explants cultured in three-dimensional fibrin matrix establish outgrowths that ultrastructurally resemble ectopic endometrial implants. This model may provide insight into the cellular processes leading to endometriosis formation and enables screening of therapeutic compounds.

  12. Langmuir monolayers composed of single and double tail sulfobetaine lipids.

    Science.gov (United States)

    Hazell, Gavin; Gee, Anthony P; Arnold, Thomas; Edler, Karen J; Lewis, Simon E

    2016-07-15

    Owing to structural similarities between sulfobetaine lipids and phospholipids it should be possible to form stable Langmuir monolayers from long tail sulfobetaines. By modification of the density of lipid tail group (number of carbon chains) it should also be possible to modulate the two-dimensional phase behaviour of these lipids and thereby compare with that of equivalent phospholipids. Potentially this could enable the use of such lipids for the wide array of applications that currently use phospholipids. The benefit of using sulfobetaine lipids is that they can be synthesised by a one-step reaction from cheap and readily available starting materials and will degrade via different pathways than natural lipids. The molecular architecture of the lipid can be easily modified allowing the design of lipids for specific purposes. In addition the reversal of the charge within the sulfobetaine head group relative to the charge orientation in phospholipids may modify behaviour and thereby allow for novel uses of these surfactants. Stable Langmuir monolayers were formed composed of single and double tailed sulfobetaine lipids. Surface pressure-area isotherm, Brewster Angle Microscopy and X-ray and neutron reflectometry measurements were conducted to measure the two-dimensional phase behaviour and out-of-plane structure of the monolayers as a function of molecular area. Sulfobetaine lipids are able to form stable Langmuir monolayers with two dimensional phase behaviour analogous to that seen for the well-studied phospholipids. Changing the number of carbon tail groups on the lipid from one to two promotes the existence of a liquid condensed phase due to increased Van der Waals interactions between the tail groups. Thus the structure of the monolayers appears to be defined by the relative sizes of the head and tail groups in a predictable way. However, the presence of sub-phase ions has little effect on the monolayer structure, behaviour that is surprisingly different to

  13. Electron dynamics and optical properties modulation of monolayer MoS{sub 2} by femtosecond laser pulse: a simulation using time-dependent density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Su, Xiaoxing; Jiang, Lan [Beijing Institute of Technology, Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing (China); Wang, Feng [Beijing Institute of Technology, School of Physics, Beijing (China); Su, Gaoshi [Beijing Institute of Technology, School of Mechatronical Engineering, Beijing (China); Qu, Liangti [Beijing Institute of Technology, Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry, Beijing (China); Lu, Yongfeng [University of Nebraska-Lincoln, Department of Electrical Engineering, Lincoln, NE (United States)

    2017-07-15

    In this study, we adopted time-dependent density functional theory to investigate the optical properties of monolayer MoS{sub 2} and the effect of intense few-cycle femtosecond laser pulses on these properties. The electron dynamics of monolayer MoS{sub 2} under few-cycle and multi-cycle laser irradiation were described. The polarization direction of the laser had a marked effect on the energy absorption and electronic excitation of monolayer MoS{sub 2} because of anisotropy. Change in the polarization direction of few-cycle pulse changed the absorbed energy by a factor over 4000. Few-cycle pulse showed a higher sensitivity to the electronic property of material than multi-cycle pulse. The modulation of the dielectric properties of the material was observed on the femtosecond time scale. The negative divergence appeared in the real part of the function at low frequencies and photoinduced blue shift occurred due to Burstein-Moss effect. The irradiation of femtosecond laser caused the dielectric response within the infrared region and introduced anisotropy to the in-plane optical properties. Laser-based engineering of optical properties through controlling transient electron dynamics expands the functionality of MoS{sub 2} and has potential applications in direction-dependent optoelectronic devices. (orig.)

  14. Valley dynamics of intravalley and intervalley multiexcitonic states in monolayer WS2

    Science.gov (United States)

    Fu, Jiyong; Bezerra, Andre; Qu, Fanyao

    2018-03-01

    We present a comprehensive model comprising of a complete set of rate equations, which account for charge transfer among multiexcitonic channels including excitons, trions, and biexcitons, to investigate valley (locked with spin) dynamics in monolayer WS2. The steady-state photoluminescence (PL) spectra, underlying the laser power dependence of excitonic populations, are also determined. Our computed PL for all excitonic states agrees with the experimental data of Paradisanos et al. [Appl. Phys. Lett. 110, 193102 (2017), 10.1063/1.4983285]. We find that the relative weight of PL, stemmed from different excitonic channels, strongly depends on the laser power even under dynamical conditions. Remarkably, the biexciton channel, having the weakest PL intensity at low laser powers, tends to prevail in PL over other excitonic states as the power strengthens. In addition, by accounting for intervalley scatterings, which enable transfer of excitonic states from one valley to the other, we determine the valley polarization, which strongly depends on intervalley scatterings and the exciton generation rates in the two valleys. On the other hand, the valley polarization for all excitonic channels is found almost independent of the laser power, consistent with experimental measurements as well. Finally, the valley dynamics involving both intra- and intervalley trions is discussed. Our model and numerical outcome should be beneficial to experiments especially featuring the interplay of multiexcitonic channels in, e.g., elucidating experimental data, estimating central excitonic quantities including recombination times and transition rates, and in widening possible new experimental scopes.

  15. The Physics of Polarization

    Science.gov (United States)

    Landi Degl'Innocenti, Egidio

    2015-10-01

    The introductory lecture that has been delivered at this Symposium is a condensed version of an extended course held by the author at the XII Canary Island Winter School from November 13 to November 21, 2000. The full series of lectures can be found in Landi Degl'Innocenti (2002). The original reference is organized in 20 Sections that are here itemized: 1. Introduction, 2. Description of polarized radiation, 3. Polarization and optical devices: Jones calculus and Muller matrices, 4. The Fresnel equations, 5. Dichroism and anomalous dispersion, 6. Polarization in everyday life, 7. Polarization due to radiating charges, 8. The linear antenna, 9. Thomson scattering, 10. Rayleigh scattering, 11. A digression on Mie scattering, 12. Bremsstrahlung radiation, 13. Cyclotron radiation, 14. Synchrotron radiation, 15. Polarization in spectral lines, 16. Density matrix and atomic polarization, 17. Radiative transfer and statistical equilibrium equations, 18. The amplification condition in polarized radiative transfer, and 19. Coupling radiative transfer and statistical equilibrium equations.

  16. Photobleaching-activated micropatterning on self-assembled monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Scrimgeour, Jan; Kodali, Vamsi K; Kovari, Daniel T; Curtis, Jennifer E, E-mail: jennifer.curtis@physics.gatech.ed [School of Physics and Petit Institute for Bioengineering and Biosciences (IBB), Georgia Institute of Technology, 837 State St, Atlanta, GA 30332 (United States)

    2010-05-19

    Functional chemical micropatterns were fabricated by exploiting the photobleaching of dye-coupled species near methacrylate self-assembled monolayers. Using this approach we have demonstrated that multiple chemistries can be coupled to the monolayer using a standard fluorescence microscope. The surface bound functional groups remain active and patterns with feature sizes down to 3 {mu}m can be readily achieved with excellent signal-to-noise ratio. Control over the ligand binding density was demonstrated to illustrate the convenient route provided by this platform for fabricating complex spatial gradients in ligand density.

  17. Exciton transport phenomena in monolayer MoS2

    Science.gov (United States)

    Onga, Masaru; Zhang, Yijin; Ideue, Toshiya; Iwasa, Yoshihiro

    Monolayer transition metal dichalcogenides exhibit unique optical phenomena owing to the two-dimensional structure and valley degree of freedom. Many researchers have revealed that excitonic states play an important role in optical response, and have observed the diffusion transport of excitons in this system at room temperature. Here we report exciton transport phenomena in monolayer MoS2 at low temperature through photoluminescence mapping. Our results can provide us a new platform for exciton-based optoelectronics with valley degrees of freedom.

  18. Monolayer structures of alkyl aldehydes: Odd-membered homologues

    International Nuclear Information System (INIS)

    Phillips, T.K.; Clarke, S.M.; Bhinde, T.; Castro, M.A.; Millan, C.; Medina, S.

    2011-01-01

    Crystalline monolayers of three aldehydes with an odd number of carbon atoms in the alkyl chain (C 7 , C 9 and C 11 ) at low coverages are observed by a combination of X-ray and neutron diffraction. Analysis of the diffraction data is discussed and possible monolayer crystal structures are proposed; although unique structures could not be ascertained for all molecules. We conclude that the structures are flat on the surface, with the molecules lying in the plane of the layer. The C 11 homologue is determined to have a plane group of either p2, pgb or pgg, and for the C 7 homologue the p2 plane group is preferred.

  19. Optics and Optoelectronics of Two-dimensional Semiconducting Monolayers and Heterostructures

    Science.gov (United States)

    Ross, Jason Solomon

    Until recently, the physics of truly two-dimensional (2D) excitons could only be explored theoretically. Following the discovery of graphene, many 2D materials were quickly identified and isolated, one system being the semiconducting Group VI-B transition metal dichalcogenides (TMDs). These semiconductors are the first air-stable materials that are atomically thin (three atomics thick), and yet can be produced in arbitrarily large lateral sheets. They have a direct band gap in which confinement leads to large spatial overlap of electrons and holes resulting in strongly coupled excitonic transitions that dominate light-matter interactions. The direct band-gap of monolayer TMDs occurs at the corners of the hexagonal Brillouin zone, referred to as the K valleys. Entirely unique to these materials, excitons in adjacent K valleys selectively couple to light of opposite circular polarization, i.e. the K (K') valley is selective to right (left) circularly polarized photons. This property offers the possible realization of novel devices that will manipulate the valley index, known as valleytronics. Further, creating a stacked heterostructure (HS) of two TMD monolayers of different molecular species can exhibit type-II band alignment leading to the first atomically sharp built-in p-n junction and a bright interlayer exciton with long lifetimes. Being flat 2D sheets, it is easy to couple these materials to nearby systems such as microfabricated electrodes and photonic crystal cavities allowing for unique modulation and device schemes. Here, I employ both optical and electronic techniques to study the unique physics of 2D excitons in TMDs as well as demonstrate some of their first optoelectronic and valleytronic devices. The most notable achievement is perhaps the first demonstrations of both atomically thin and 2D heterostructure light emitting diodes and photovoltaic devices. Other breakthroughs include the first demonstration of exciton charging tunability in a 2D system

  20. Hypoxia/reoxygenation increases the permeability of endothelial cell monolayers: Role of oxygen radicals

    International Nuclear Information System (INIS)

    Inauen, W.; Payne, D.K.; Kvietys, P.R.; Granger, D.N.

    1990-01-01

    We assessed the effect of hypoxia/reoxygenation on 14C-albumin flux across endothelial monolayers. Cultured bovine pulmonary artery endothelial cells were grown to confluence on nitrocellulose filters (pore size 12 microns). The endothelialized filters were mounted in Ussing-type chambers which were filled with cell culture medium (M 199). Equimolar amounts (33 nM) of 14C-labeled and unlabeled albumin were added to the hot and cold chambers, respectively. The monolayers were then exposed to successive periods (90 min) of normoxia (pO2 145 mmHg), hypoxia (pO2 20 mmHg), and reoxygenation (pO2 145 mmHg). A gas bubbling system was used to control media pO2 and to ensure adequate mixing. Four aliquots of culture media were taken during each period in order to calculate the 14C-albumin permeability across the endothelialized filter. In some experiments, either the xanthine oxidase inhibitor, oxypurinol (10 microM), or superoxide dismutase (600 U/mL), was added to the media immediately prior to the experiments. As compared to the normoxic control period, albumin permeability was 1.5 times higher during hypoxia (p less than 0.01) and 2.3 times higher during reoxygenation (p less than 0.01). The reoxygenation-induced increase in albumin permeability was prevented by either oxypurinol or superoxide dismutase. These data indicate that xanthine oxidase-derived oxygen radicals contribute to the hypoxia/reoxygenation-induced endothelial cell dysfunction. The altered endothelial barrier function induced by hypoxia/reoxygenation is consistent with the microvascular dysfunction observed following reperfusion of ischemic tissues

  1. Clientalism and polarized voting: empirical evidence

    NARCIS (Netherlands)

    Gërxhani, K.; Schram, A.

    2009-01-01

    One must take country-specific institutional features into account when analyzing former communist countries’ transformation process to new political institutions. We do so for post-communist Albania, where the regional and cultural polarization that has existed for centuries has evolved to

  2. Advanced chemistry of monolayers at interfaces trends in methodology and technology

    CERN Document Server

    Imae, Toyoko

    2007-01-01

    Advanced Chemistry of Monolayers at Interfaces describes the advanced chemistry of monolayers at interfaces. Focusing on the recent trends of methodology and technology, which are indispensable in monolayer science. They are applied to monolayers of surfactants, amphiphiles, polymers, dendrimers, enzymes, and proteins, which serve many uses.Introduces the methodologies of scanning probe microscopy, surface force instrumentation, surface spectroscopy, surface plasmon optics, reflectometry, and near-field scanning optical microscopy. Modern interface reaction method, lithographic tech

  3. Anomalously temperature-dependent thermal conductivity of monolayer GaN with large deviations from the traditional 1 /T law

    Science.gov (United States)

    Qin, Guangzhao; Qin, Zhenzhen; Wang, Huimin; Hu, Ming

    2017-05-01

    Efficient heat dissipation, which is featured by high thermal conductivity, is one of the crucial issues for the reliability and stability of nanodevices. However, due to the generally fast 1 /T decrease of thermal conductivity with temperature increase, the efficiency of heat dissipation quickly drops down at an elevated temperature caused by the increase of work load in electronic devices. To this end, pursuing semiconductor materials that possess large thermal conductivity at high temperature, i.e., slower decrease of thermal conductivity with temperature increase than the traditional κ ˜1 /T relation, is extremely important to the development of disruptive nanoelectronics. Recently, monolayer gallium nitride (GaN) with a planar honeycomb structure emerges as a promising new two-dimensional material with great potential for applications in nano- and optoelectronics. Here, we report that, despite the commonly established 1 /T relation of thermal conductivity in plenty of materials, monolayer GaN exhibits anomalous behavior that the thermal conductivity almost decreases linearly over a wide temperature range above 300 K, deviating largely from the traditional κ ˜1 /T law. The thermal conductivity at high temperature is much larger than the expected thermal conductivity that follows the general κ ˜1 /T trend, which would be beneficial for applications of monolayer GaN in nano- and optoelectronics in terms of efficient heat dissipation. We perform detailed analysis on the mechanisms underlying the anomalously temperature-dependent thermal conductivity of monolayer GaN in the framework of Boltzmann transport theory and further get insight from the view of electronic structure. Beyond that, we also propose two required conditions for materials that would exhibit similar anomalous temperature dependence of thermal conductivity: large difference in atom mass (huge phonon band gap) and electronegativity (LO-TO splitting due to strong polarization of bond). Our

  4. Microcontact Printing onto Oxide-Free Silicon via Highly Reactive Acid Fluoride-Functionalized Monolayers

    NARCIS (Netherlands)

    Scheres, L.M.W.; Maat, ter J.; Giesbers, M.; Zuilhof, H.

    2010-01-01

    This work describes a new route for patterning organic monolayers on oxide-free silicon by microcontact printing (µCP) on a preformed, reactive, acid-fluoride-terminated monolayer. This indirect printing approach is fast and easily preserves the oxide-free and well-defined monolayer-silicon

  5. Mechanic studies of monolayer formation on H-Si(111) surfaces

    NARCIS (Netherlands)

    Rijksen, B.M.G.

    2012-01-01

    Covalently attached organic monolayers on silicon surfaces form thermally and chemically stable platforms for (bio)functionalization of the surface. Recent advances in monolayer formation – yielding increases in monolayer quality and the complete exclusion of oxygen at modified surfaces – have

  6. Influencing the binding selectivity of self-assembled cyclodextrin monolayers on gold through their architecture

    NARCIS (Netherlands)

    de Jong, M.R.; Huskens, Jurriaan; Reinhoudt, David

    2001-01-01

    Cyclodextrin derivatives modified with seven thioether moieties (1) or with one thiol moiety (2) bind to gold. Monolayers on gold of 1 or mixed monolayers of 2 and mercaptoundecanol were characterized by electrochemistry, wettability, and atomic force microscopy (AFM). Monolayers of 1 are

  7. Electrochemical and structural characterization of self-assembled thiol monolayers on gold

    NARCIS (Netherlands)

    Sondag-Huethorst, J.A.M.

    1994-01-01

    Self-assembled alkanethiol monolayers on gold are used as model systems in a fundamental study of the potential-dependent wetting and of the galvanic metal deposition. For using such monolayers as model systems, well-defined and ordered monolayers are required. In order to control the

  8. Topography and instability of monolayers near domain boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Diamant, H.; Witten, T. A.; Ege, C.; Gopal, A.; Lee, K. Y. C.

    2001-06-01

    We theoretically study the topography of a biphasic surfactant monolayer in the vicinity of domain boundaries. The differing elastic properties of the two phases generally lead to a nonflat topography of {open_quotes}mesas,{close_quotes} where domains of one phase are elevated with respect to the other phase. The mesas are steep but low, having heights of up to 10 nm. As the monolayer is laterally compressed, the mesas develop overhangs and eventually become unstable at a surface tension of about K({delta}c{sub 0}){sup 2} ({delta}c{sub 0} being the difference in spontaneous curvature and K a bending modulus). In addition, the boundary is found to undergo a topography-induced rippling instability upon compression, if its line tension is smaller than about K{delta}c{sub 0}. The effect of diffuse boundaries on these features and the topographic behavior near a critical point are also examined. We discuss the relevance of our findings to several experimental observations related to surfactant monolayers: (i) small topographic features recently found near domain boundaries; (ii) folding behavior observed in mixed phospholipid monolayers and model lung surfactants; (iii) roughening of domain boundaries seen under lateral compression; (iv) the absence of biphasic structures in tensionless surfactant films.

  9. Overcrowding drives the unjamming transition of gap-free monolayers

    Science.gov (United States)

    Lan, Ganhui; Su, Tao

    Collective cell motility plays central roles in various biological phenomena such as wound healing, cancer metastasis and embryogenesis. These are demonstrations of the unjamming transition in biology. However, contradictory to the typical density-driven jamming in particulate assemblies, cellular systems often get unjammed in highly packed, sometimes overcrowding environments. Here, we investigate monolayers' collective behaviors when cell number changes under the gap-free constraint. We report that overcrowding can unjam gap-free monolayers through increasing isotropic compression. We show that the transition boundary is determined by the isotropic compression and the cell-cell adhesion. Furthermore, we construct the free energy landscape for the T1 topological transition during monolayer rearrangement, and discover that the landscape evolves from single-barrier W shape to double-barrier M shape during the unjamming process. We also discover a distributed-to-disordered morphological transition of cells' geometry, coinciding with the unjamming transition. Our analyses reveal that the overcrowding and adhesion induced unjamming reflects the mechanical yielding of the highly deformable monolayer, suggesting an alternative mechanism that cells may robustly gain collective mobility through proliferation in confined environments, which differs from those caused by loosing up a packed particulate assembly. This work is supported by the GWU College Facilitating Funds.

  10. Illustrative view on the magnetocrystalline anisotropy of adatoms and monolayers

    Czech Academy of Sciences Publication Activity Database

    Šipr, Ondřej; Mankovsky, S.; Polesya, S.; Bornemann, S.; Minár, J.; Ebert, H.

    2016-01-01

    Roč. 93, č. 17 (2016), s. 1-13, č. článku 174409. ISSN 2469-9950 R&D Projects: GA ČR(CZ) GAP108/11/0853 Institutional support: RVO:68378271 Keywords : magnetic anisotropy * adatom * monolayer * spin-orbit coupling Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.836, year: 2016

  11. Ab initio electronic properties of dual phosphorus monolayers in silicon

    DEFF Research Database (Denmark)

    Drumm, Daniel W.; Per, Manolo C.; Budi, Akin

    2014-01-01

    , investigating the fundamental electronic properties of monolayer pairs. Quantitative band splittings and the electronic density are presented, along with effects of the layers’ relative alignment and comments on disordered systems, and for the first time, the effective electronic widths of such device...

  12. Permethylated 12-Vertex p-Carborane Self-Assembled Monolayers

    Czech Academy of Sciences Publication Activity Database

    Scholz, F.; Nothofer, H. G.; Wessels, J. M.; Nelles, G.; Wrochem von, F.; Roy, S.; Chen, X.; Michl, Josef

    2011-01-01

    Roč. 115, č. 46 (2011), s. 22998-23007 ISSN 1932-7447 Grant - others:National Science Foundation(US) CHE-0848477 Institutional research plan: CEZ:AV0Z40550506 Keywords : p-carbone * monolayer * scanning tunneling microscopy * ultraviolet photoelectron spectroscopy * X-ray photoelectron Subject RIV: CC - Organic Chemistry Impact factor: 4.805, year: 2011

  13. Friction of different monolayer lubricants in MEMs interfaces.

    Energy Technology Data Exchange (ETDEWEB)

    Carpick, Robert W. (University of Wisconsin, Madison, WI); Street, Mark D. (University of Wisconsin, Madison, WI); Ashurst, William Robert (Auburn University, Auburn, AL); Corwin, Alex David

    2006-01-01

    This report details results from our last year of work (FY2005) on friction in MEMS as funded by the Campaign 6 program for the Microscale Friction project. We have applied different monolayers to a sensitive MEMS friction tester called the nanotractor. The nanotractor is also a useful actuator that can travel {+-}100 {micro}m in 40 nm steps, and is being considered for several MEMS applications. With this tester, we can find static and dynamic coefficients of friction. We can also quantify deviations from Amontons' and Coulomb's friction laws. Because of the huge surface-to-volume ratio at the microscale, surface properties such as adhesion and friction can dominate device performance, and therefore such deviations are important to quantify and understand. We find that static and dynamic friction depend on the monolayer lubricant applied. The friction data can be modeled with a non-zero adhesion force, which represents a deviation from Amontons' Law. Further, we show preliminary data indicating that the adhesion force depends not only on the monolayer, but also on the normal load applied. Finally, we also observe slip deflections before the transition from static to dynamic friction, and find that they depend on the monolayer.

  14. Direct measurement of the microscale conductivity of conjugated polymer monolayers

    DEFF Research Database (Denmark)

    Bøggild, Peter; Grey, Francois; Hassenkam, T.

    2000-01-01

    The in-plane conductivity of conjugated polymer monolayers is mapped here for the first time on the microscale using a novel scanning micro four-point probe (see Figure). The probe allows the source, drain, and voltage electrodes to be positioned within the same domain and the mapping results...

  15. Self-assembled monolayers on metal oxides : applications in nanotechnology

    NARCIS (Netherlands)

    Yildirim, O.

    2010-01-01

    The thesis describes the use of phosph(on)ate-based self-assembled monolayers (SAMs) to modify and pattern metal oxides. Metal oxides have interesting electronic and magnetic properties such as insulating, semiconducting, metallic, ferromagnetic etc. and SAMs can tailor the surface properties. FePt

  16. Magnetic and Structural Phases of Monolayer 02 on Graphite

    DEFF Research Database (Denmark)

    McTague, J. P.; Nielsen, Mourits

    1976-01-01

    Neutron diffraction studies of O2 thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest...

  17. Melting mechanism in monolayers of flexible rod-shaped molecules

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Taub, H.

    1992-01-01

    The melting of butane and hexane monolayers adsorbed on a graphite basal-plane surface has been studied by molecular-dynamics simulations and experimentally by neutron diffraction. The simulation results are qualitatively consistent with the observed diffraction patterns and suggest a general...

  18. Applications of self-assembled monolayers in materials chemistry

    Indian Academy of Sciences (India)

    Unknown

    Abstract. Self-assembly provides a simple route to organise suitable organic molecules on noble metal and selected nanocluster surfaces by using monolayers of long chain organic molecules with various functionalities like –SH, –COOH, –NH2, silanes etc. These surfaces can be effectively used to build-up interesting ...

  19. Surface plasmon resonance for detecting clenbuterol: Influence of monolayer structure

    Science.gov (United States)

    Suherman; Morita, Kinichi; Kawaguchi, Toshikazu

    2015-03-01

    Surface plasmon resonance sensor equipped with a fabricated immunosensor chip is used for detecting clenbuterol in this study. Since clenbuterol is a small analyte, indirect competitive inhibition immunoassay is employed. For fabricating the immunosurface, the Au-chip was functionalized by succinimidyl-terminated alkanethiol, and the terminal N-hydroxysuccinimide group of the self-assembled monolayer was either replaced with clenbuterol or blocked with ethanolamine. Scanning tunneling microscope experiments and electrochemical measurements depicted the domain structures of the succinimide group of succinimidyl-terminated propanethiol monolayer. The surface concentration and the orientation of succinimide group was significantly dependent on the concentration of dithiobis(succinimidyl) propionate (DSP) used in fabricating the monolayer. Furthermore, the structure of monolayer significantly influenced both the surface concentration and the orientation of clenbuterol on the sensor surface. Consequently, high coverage and standing-up configuration of clenbuterol showed high affinity for clenbuterol antibody. However, high affinity constant exhibited by the sensor surface was coupled with a low sensitivity. By contrast, lowest concentration of DSP solution (0.1 mM) used in fabricating the immunosurface showed a detection sensitivity of 3 ppt - the highest reported sensitivity for clenbuterol. For regeneration the immunosurface, 0.1 M NaOH was used and the same sensor surface could be reused for performing >100 rapid immunoreaction.

  20. Anisotropic growth of buckling-driven wrinkles in graphene monolayer.

    Science.gov (United States)

    Liu, XiaoYi; Wang, FengChao; Wu, HengAn

    2015-02-13

    We theoretically and numerically investigate the growth of buckling-driven wrinkles in graphene monolayers. It is found that the growth of buckling-driven wrinkles in a graphene monolayer is remarkably chirality- and size-dependent. In small sizes, the flexural response of a graphene sheet cannot be accurately described by the classical Euler regime, and the non-continuum effect leads to zigzag-along-preferred buckling. With the increase of size, the width/length ratio α of the compressed region plays an important role in the growth of buckling-driven wrinkles. When α buckling happens in armchair-along compression; when 0.5 buckling. When 1.0 buckling. When α > 3.0, the non-continuum effect and chiral bending stiffness can both be neglected, and the buckling in a graphene monolayer is isotropic. The chirality-along-preferred transition of compressed buckling in a graphene monolayer leads to an improved fundamental understanding of the dynamics mechanism of graphene-based nanodevices, especially for the nanodevices with high frequency response.

  1. Photoresponsive Wettability in Monolayer Films from Sinapinic Acid

    Directory of Open Access Journals (Sweden)

    Cleverson A. S. Moura

    2013-01-01

    Full Text Available Sinapinic acid is an interesting material because it is both antioxidant and antibacterial agent. In addition, when illuminated with ultraviolet light, it can exhibit the so-called photodimerization process. In this paper, we report on the investigation of monolayer films from 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SinA deposited onto poly(allylamine hydrochloride, PAH, films. SinA monolayers were prepared by using the layer-by-layer (LbL self-assembly technique. Adsorption kinetics curves were well fitted by a biexponential function suggesting that the adsorption process is determined by two mechanisms: nucleation and growth of aggregates. By using wetting contact angle analysis, we have found that SinA monolayers exhibit photoresponsive wettability under UV irradiation (365 nm; that is, wettability decreases with increasing UV irradiation time. The photoresponse of wettability was attributed to photodimerization process. This hypothesis was supported by the dependence of surface morphological structure and absorption on UV irradiation time. The mechanism found in the well-known transcinnamic acid crystals is used to explain the photodimerization process in SinA monolayers.

  2. Tailoring self-assembled monolayers at the electrochemical interface

    Indian Academy of Sciences (India)

    Administrator

    SAM could be studied by this method. The IR beam is reflected at a small grazing angle from the monolayer surface and the intensity of the reflected beam is recorded. .... strates a strong decrease in capacity. 3.7b Blocking of electron transfer kinetics: With the decrease in the current for the SAM-covered electrode, one can ...

  3. Applications of self-assembled monolayers in materials chemistry

    Indian Academy of Sciences (India)

    Self-assembly provides a simple route to organise suitable organic molecules on noble metal and selected nanocluster surfaces by using monolayers of long chain organic molecules with various functionalities like -SH, -COOH, -NH2, silanes etc. These surfaces can be effectively used to build-up interesting nano level ...

  4. [Review] Polarization and Polarimetry

    Science.gov (United States)

    Trippe, Sascha

    2014-02-01

    Polarization is a basic property of light and is fundamentally linked to the internal geometry of a source of radiation. Polarimetry complements photometric, spectroscopic, and imaging analyses of sources of radiation and has made possible multiple astrophysical discoveries. In this article I review (i) the physical basics of polarization: electromagnetic waves, photons, and parameterizations; (ii) astrophysical sources of polarization: scattering, synchrotron radiation, active media, and the Zeeman, Goldreich-Kylafis, and Hanle effects, as well as interactions between polarization and matter (like birefringence, Faraday rotation, or the Chandrasekhar-Fermi effect); (iii) observational methodology: on-sky geometry, influence of atmosphere and instrumental polarization, polarization statistics, and observational techniques for radio, optical, and X/γ wavelengths; and (iv) science cases for astronomical polarimetry: solar and stellar physics, planetary system bodies, interstellar matter, astrobiology, astronomical masers, pulsars, galactic magnetic fields, gamma-ray bursts, active galactic nuclei, and cosmic microwave background radiation.

  5. Size dependent gold nanoparticle interaction at nano-micro interface using both monolayer and multilayer (tissue-like) cell models

    Science.gov (United States)

    Yohan, Darren; Yang, Celina; Lu, Xiaofeng; Chithrani, Devika B.

    2016-03-01

    Gold nanoparticles (GNPs) can be used as a model NP system to improve the interface between nanotechnology and medicine since their size and surface properties can be tailored easily. GNPs are being used as radiation dose enhancers and as drug carriers in cancer research. Hence, it is important to know the optimum NP size for uptake not only at monolayer level but also at tissue level. Once GNPs leave tumor vasculature, they enter the tumor tissue. Success of any therapeutic technique using NPs depends on how well NPs penetrate the tumor tissue and reach individual tumor cells. In this work, multicellular layers (MCLs) were grown to model the post-vascular tumor environment. GNPs of 20 nm and 50 nm diameters were used to elucidate the effects of size on the GNP penetration and distribution dynamics. Larger NPs (50 nm) were better at monolayer level, but smaller NPs (20 nm) were at tissue level. The MCLs exhibited a much more extensive extracellular matrix (ECM) than monolayer cell cultures. This increased ECM created a barrier for NP transport and ECM was also dependent on the tumor cell lines. Smaller NPs penetrated better compared to larger NPs. Transport of NPs was better in MDA-MB231 vs MCF-7. This MCL model tissue structures are better tools to optimize NP transport through tissue before using them in animal models. Based on our study, we believe that smaller NPs are better for improved outcome in future cancer therapeutics.

  6. Axially Bound Ruthenium Phthalocyanine Monolayers on Indium Tin Oxide: Structure, Energetics, and Charge Transfer Properties.

    Science.gov (United States)

    Ehamparam, Ramanan; Oquendo, Luis E; Liao, Michael W; Brynnel, Ambjorn K; Ou, Kai-Lin; Armstrong, Neal R; McGrath, Dominic V; Saavedra, S Scott

    2017-08-30

    The efficiency of charge collection at the organic/transparent conducting oxide (TCO) interface in organic photovoltaic (OPV) devices affects overall device efficiency. Modifying the TCO with an electrochemically active molecule may enhance OPV efficiency by providing a charge-transfer pathway between the electrode and the organic active layer, and may also mitigate surface recombination. The synthesis and characterization of phosphonic acid-ruthenium phthalocyanine (RuPcPA) monolayer films on indium tin oxide (ITO), designed to facilitate charge harvesting at ITO electrodes, is presented in this work. The PA group was installed axially relative to the Pc plane so that upon deposition, RuPcPA molecules were preferentially aligned with the ITO surface plane. The tilt angle of 22° between the normal axes to the Pc plane and the ITO surface plane, measured by attenuated total reflectance (ATR) spectroscopy, is consistent with a predominately in-plane orientation. The effect of surface roughness on RuPcPA orientation was modeled, and a correlation was obtained between experimental and theoretical mean tilt angles. Based on electrochemical and spectroelectrochemical studies, RuPcPA monolayers are composed predominately of monomers. Electrochemical impedance spectroscopy (EIS) and potential modulated-ATR (PM-ATR) spectroscopy were used to characterize the electron-transfer (ET) kinetics of these monolayers. A rate constant of 4.0 × 10 3 s -1 was measured using EIS, consistent with a short tunneling distance between the chromophore and the electrode surface. Using PM-ATR, k s,opt values of 2.2 × 10 3 and 2.4 × 10 3 s -1 were measured using TE and TM polarized light, respectively; the similarity of these values is consistent with a narrow molecular orientation distribution and narrow range of tunneling distances. The ionization potential of RuPcPA-modified ITO was measured using ultraviolet photoelectron spectroscopy and the results indicate favorable energetics for

  7. Polarization feedback laser stabilization

    Science.gov (United States)

    Esherick, P.; Owyoung, A.

    1987-09-28

    A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other. 4 figs.

  8. Polarization in Sagittarius A*

    OpenAIRE

    Bower, Geoffrey C.

    2000-01-01

    We summarize the current state of polarization observations of Sagittarius A*, the compact radio source and supermassive black hole candidate in the Galactic Center. These observations are providing new tools for understanding accretion disks, jets and their environments. Linear polarization observations have shown that Sgr A* is unpolarized at frequencies as high as 86 GHz. However, recent single-dish observations indicate that Sgr A* may have strong linear polarization at frequencies higher...

  9. Spin-polarized spin excitation spectroscopy

    International Nuclear Information System (INIS)

    Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J

    2010-01-01

    We report on the spin dependence of elastic and inelastic electron tunneling through transition metal atoms. Mn, Fe and Cu atoms were deposited onto a monolayer of Cu 2 N on Cu(100) and individually addressed with the probe tip of a scanning tunneling microscope. Electrons tunneling between the tip and the substrate exchange energy and spin angular momentum with the surface-bound magnetic atoms. The conservation of energy during the tunneling process results in a distinct onset threshold voltage above which the tunneling electrons create spin excitations in the Mn and Fe atoms. Here we show that the additional conservation of spin angular momentum leads to different cross-sections for spin excitations depending on the relative alignment of the surface spin and the spin of the tunneling electron. For this purpose, we developed a technique for measuring the same local spin with a spin-polarized and a non-spin-polarized tip by exchanging the last apex atom of the probe tip between different transition metal atoms. We derive a quantitative model describing the observed excitation cross-sections on the basis of an exchange scattering process.

  10. Airborne Laser Polarization Sensor

    Science.gov (United States)

    Kalshoven, James, Jr.; Dabney, Philip

    1991-01-01

    Instrument measures polarization characteristics of Earth at three wavelengths. Airborne Laser Polarization Sensor (ALPS) measures optical polarization characteristics of land surface. Designed to be flown at altitudes of approximately 300 m to minimize any polarizing or depolarizing effects of intervening atmosphere and to look along nadir to minimize any effects depending on look angle. Data from measurements used in conjunction with data from ground surveys and aircraft-mounted video recorders to refine mathematical models used in interpretation of higher-altitude polarimetric measurements of reflected sunlight.

  11. Polarization at SLC

    International Nuclear Information System (INIS)

    Swartz, M.L.

    1988-07-01

    The SLAC Linear Collider has been designed to readily accommodate polarized electron beams. Considerable effort has been made to implement a polarized source, a spin rotation system, and a system to monitor the beam polarization. Nearly all major components have been fabricated. At the current time, several source and polarimeter components have been installed. The installation and commissioning of the entire system will take place during available machine shutdown periods as the commissioning of SLC progresses. It is expected that a beam polarization of 45% will be achieved with no loss in luminosity. 13 refs., 15 figs

  12. Vimentin intermediate filaments template microtubule networks to enhance persistence in cell polarity and directed migration

    OpenAIRE

    Gan, Zhuo; Ding, Liya; Burckhardt, Christoph J.; Lowery, Jason; Zaritsky, Assaf; Sitterley, Karlyndsay; Mota, Andressa; Costigliola, Nancy; Starker, Colby G.; Voytas, Daniel F.; Tytell, Jessica; Goldman, Robert D.; Danuser, Gaudenz

    2016-01-01

    Increased expression of vimentin intermediate filaments (VIF) enhances directed cell migration, but the mechanism behind VIF’s effect on motility is not understood. VIF interact with microtubules, whose organization contributes to polarity maintenance in migrating cells. Here we characterize the dynamic coordination of VIF and microtubule networks in wounded monolayers of Retinal Pigment Epithelial cells. By genome editing we fluorescently labelled endogenous vimentin and α-...

  13. The formation of quiescent glomerular endothelial cell monolayer in vitro is strongly dependent on the choice of extracellular matrix coating

    Energy Technology Data Exchange (ETDEWEB)

    Pajęcka, Kamilla, E-mail: kpaj@novonordisk.com [Global Research, Novo Nordisk A/S, Måløv (Denmark); Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus (Denmark); Nielsen, Malik Nygaard [Global Research, Novo Nordisk A/S, Måløv (Denmark); Hansen, Troels Krarup [Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus (Denmark); Williams, Julie M. [Global Research, Novo Nordisk A/S, Måløv (Denmark)

    2017-04-01

    Background and aims: Nephropathy involves pathophysiological changes to the glomerulus. The primary glomerular endothelial cells (GEnCs) have emerged as an important tool for studying glomerulosclerotic mechanisms and in the screening process for drug-candidates. The success of the studies is dependent on the quality of the cell model. Therefore, we set out to establish an easy, reproducible model of the quiescent endothelial monolayer with the use of commercially available extracellular matrices (ECMs). Methods: Primary hGEnCs were seeded on various ECMs. Cell adhesion was monitored by an impedance sensing system. The localization of junctional proteins was assessed by immunofluorescence and the barrier function by passage of fluorescent dextrans and magnitude of VEGF response. Results: All ECM matrices except recombinant human laminin 111 (rhLN111) supported comparable cell proliferation. Culturing hGEnCs on rhLN521, rhLN511 or fibronectin resulted in a physiologically relevant barrier to 70 kDa dextrans which was 82% tighter than that formed on collagen type IV. Furthermore, only hGEnCs cultured on rhLN521 or rhLN511 showed plasma-membrane localized zonula occludens-1 and vascular endothelial cadherin indicative of proper tight and adherens junctions (AJ). Conclusion: We recommend culturing hGEnCs on the mature glomerular basement membrane laminin - rhLN521 – which, as the only commercially available ECM, promotes all of the characteristics of the quiescent hGEnC monolayer: cobblestone morphology, well-defined AJs and physiological perm-selectivity. - Highlights: • rhLN521, rhLN511 and hFN assure physiologically relevant permeability. • rhLN521 and rhLN511 ensure best cell morphology and adherens junction formation. • Collagen IV and I based coating results in disorganized hGEnC monolayer. • Physiologically relevant ECM may lead to down-regulation of self-produced matrices.

  14. The formation of quiescent glomerular endothelial cell monolayer in vitro is strongly dependent on the choice of extracellular matrix coating

    International Nuclear Information System (INIS)

    Pajęcka, Kamilla; Nielsen, Malik Nygaard; Hansen, Troels Krarup; Williams, Julie M.

    2017-01-01

    Background and aims: Nephropathy involves pathophysiological changes to the glomerulus. The primary glomerular endothelial cells (GEnCs) have emerged as an important tool for studying glomerulosclerotic mechanisms and in the screening process for drug-candidates. The success of the studies is dependent on the quality of the cell model. Therefore, we set out to establish an easy, reproducible model of the quiescent endothelial monolayer with the use of commercially available extracellular matrices (ECMs). Methods: Primary hGEnCs were seeded on various ECMs. Cell adhesion was monitored by an impedance sensing system. The localization of junctional proteins was assessed by immunofluorescence and the barrier function by passage of fluorescent dextrans and magnitude of VEGF response. Results: All ECM matrices except recombinant human laminin 111 (rhLN111) supported comparable cell proliferation. Culturing hGEnCs on rhLN521, rhLN511 or fibronectin resulted in a physiologically relevant barrier to 70 kDa dextrans which was 82% tighter than that formed on collagen type IV. Furthermore, only hGEnCs cultured on rhLN521 or rhLN511 showed plasma-membrane localized zonula occludens-1 and vascular endothelial cadherin indicative of proper tight and adherens junctions (AJ). Conclusion: We recommend culturing hGEnCs on the mature glomerular basement membrane laminin - rhLN521 – which, as the only commercially available ECM, promotes all of the characteristics of the quiescent hGEnC monolayer: cobblestone morphology, well-defined AJs and physiological perm-selectivity. - Highlights: • rhLN521, rhLN511 and hFN assure physiologically relevant permeability. • rhLN521 and rhLN511 ensure best cell morphology and adherens junction formation. • Collagen IV and I based coating results in disorganized hGEnC monolayer. • Physiologically relevant ECM may lead to down-regulation of self-produced matrices.

  15. In vitro culture of functionally active buffalo hepatocytes isolated by using a simplified manual perfusion method.

    Directory of Open Access Journals (Sweden)

    Santanu Panda

    Full Text Available In farm animals, there is no suitable cell line available to understand liver-specific functions. This has limited our understanding of liver function and metabolism in farm animals. Culturing and maintenance of functionally active hepatocytes is difficult, since they survive no more than few days. Establishing primary culture of hepatocytes can help in studying cellular metabolism, drug toxicity, hepatocyte specific gene function and regulation. Here we provide a simple in vitro method for isolation and short-term culture of functionally active buffalo hepatocytes.Buffalo hepatocytes were isolated from caudate lobes by using manual enzymatic perfusion and mechanical disruption of liver tissue. Hepatocyte yield was (5.3 ± 0.66×107 cells per gram of liver tissue with a viability of 82.3 ± 3.5%. Freshly isolated hepatocytes were spherical with well contrasted border. After 24 hours of seeding onto fibroblast feeder layer and different extracellular matrices like dry collagen, matrigel and sandwich collagen coated plates, hepatocytes formed confluent monolayer with frequent clusters. Cultured hepatocytes exhibited typical cuboidal and polygonal shape with restored cellular polarity. Cells expressed hepatocyte-specific marker genes or proteins like albumin, hepatocyte nuclear factor 4α, glucose-6-phosphatase, tyrosine aminotransferase, cytochromes, cytokeratin and α1-antitrypsin. Hepatocytes could be immunostained with anti-cytokeratins, anti-albumin and anti α1-antitrypsin antibodies. Abundant lipid droplets were detected in the cytosol of hepatocytes using oil red stain. In vitro cultured hepatocytes could be grown for five days and maintained for up to nine days on buffalo skin fibroblast feeder layer. Cultured hepatocytes were viable for functional studies.We developed a convenient and cost effective technique for hepatocytes isolation for short-term culture that exhibited morphological and functional characteristics of active hepatocytes

  16. RHIC Polarized proton operation

    International Nuclear Information System (INIS)

    Huang, H.; Ahrens, L.; Alekseev, I.G.; Aschenauer, E.; Atoian, G.; Bai, M.; Bazilevsky, A.; Blaskiewicz, M.; Brennan, J.M.; Brown, K.A.; Bruno, D.; Connolly, R.; Dion, A.; D'Ottavio, T.; Drees, K.A.; Fischer, W.; Gardner, C.; Glenn, J.W.; Gu, X.; Harvey, M.; Hayes, T.; Hoff, L.; Hulsart, R.L.; Laster, J.; Liu, C.; Luo, Y.; MacKay, W.W.; Makdisi, Y.; Marr, G.J.; Marusic, A.; Meot, F.; Mernick, K.; Michnoff, R.; Minty, M.; Montag, C.; Morris, J.; Nemesure, S.; Poblaguev, A.; Ptitsyn, V.; Ranjibar, V.; Robert-Demolaize, G.; Roser, T.; Schmidke, B.; Schoefer, V.; Severino, F.; Smirnov, D.; Smith, K.; Steski, D.; Svirida, D.; Tepikian, S.; Trbojevic, D.; Tsoupas, N.; Tuozzolo, J.E.; Wang, G.; Wilinski, M.; Yip, K.; Zaltsman, A.; Zelenski, A.; Zeno, K.; Zhang, S.Y.

    2011-01-01

    The Relativistic Heavy Ion Collider (RHIC) operation as the polarized proton collider presents unique challenges since both luminosity(L) and spin polarization(P) are important. With longitudinally polarized beams at the experiments, the figure of merit is LP 4 . A lot of upgrades and modifications have been made since last polarized proton operation. A 9 MHz rf system is installed to improve longitudinal match at injection and to increase luminosity. The beam dump was upgraded to increase bunch intensity. A vertical survey of RHIC was performed before the run to get better magnet alignment. The orbit control is also improved this year. Additional efforts are put in to improve source polarization and AGS polarization transfer efficiency. To preserve polarization on the ramp, a new working point is chosen such that the vertical tune is near a third order resonance. The overview of the changes and the operation results are presented in this paper. Siberian snakes are essential tools to preserve polarization when accelerating polarized beams to higher energy. At the same time, the higher order resonances still can cause polarization loss. As seen in RHIC, the betatron tune has to be carefully set and maintained on the ramp and during the store to avoid polarization loss. In addition, the orbit control is also critical to preserve polarization. The higher polarization during this run comes from several improvements over last run. First we have a much better orbit on the ramp. The orbit feedback brings down the vertical rms orbit error to 0.1mm, much better than the 0.5mm last run. With correct BPM offset and vertical realignment, this rms orbit error is indeed small. Second, the jump quads in the AGS improved input polarization for RHIC. Third, the vertical tune was pushed further away from 7/10 snake resonance. The tune feedback maintained the tune at the desired value through the ramp. To calibrate the analyzing power of RHIC polarimeters at any energy above

  17. RHIC Polarized proton operation

    Energy Technology Data Exchange (ETDEWEB)

    Huang, H.; Ahrens, L.; Alekseev, I.G.; Aschenauer, E.; Atoian, G.; Bai, M.; Bazilevsky, A.; Blaskiewicz, M.; Brennan, J.M.; Brown, K.A.; Bruno, D.; Connolly, R.; Dion, A.; D' Ottavio, T.; Drees, K.A.; Fischer, W.; Gardner, C.; Glenn, J.W.; Gu, X.; Harvey, M.; Hayes, T.; Hoff, L.; Hulsart, R.L.; Laster, J.; Liu, C.; Luo, Y.; MacKay, W.W.; Makdisi, Y.; Marr, G.J.; Marusic, A.; Meot, F.; Mernick, K.; Michnoff, R,; Minty, M.; Montag, C.; Morris, J.; Nemesure, S.; Poblaguev, A.; Ptitsyn, V.; Ranjibar, V.; Robert-Demolaize, G.; Roser, T.; J.; Severino, F.; Schmidke, B.; Schoefer, V.; Severino, F.; Smirnov, D.; Smith, K.; Steski, D.; Svirida, D.; Tepikian, S.; Trbojevic, D.; Tsoupas, N.; Tuozzolo, J. Wang, G.; Wilinski, M.; Yip, K.; Zaltsman, A.; Zelenski, A.; Zeno, K.; Zhang, S.Y.

    2011-03-28

    The Relativistic Heavy Ion Collider (RHIC) operation as the polarized proton collider presents unique challenges since both luminosity(L) and spin polarization(P) are important. With longitudinally polarized beams at the experiments, the figure of merit is LP{sup 4}. A lot of upgrades and modifications have been made since last polarized proton operation. A 9 MHz rf system is installed to improve longitudinal match at injection and to increase luminosity. The beam dump was upgraded to increase bunch intensity. A vertical survey of RHIC was performed before the run to get better magnet alignment. The orbit control is also improved this year. Additional efforts are put in to improve source polarization and AGS polarization transfer efficiency. To preserve polarization on the ramp, a new working point is chosen such that the vertical tune is near a third order resonance. The overview of the changes and the operation results are presented in this paper. Siberian snakes are essential tools to preserve polarization when accelerating polarized beams to higher energy. At the same time, the higher order resonances still can cause polarization loss. As seen in RHIC, the betatron tune has to be carefully set and maintained on the ramp and during the store to avoid polarization loss. In addition, the orbit control is also critical to preserve polarization. The higher polarization during this run comes from several improvements over last run. First we have a much better orbit on the ramp. The orbit feedback brings down the vertical rms orbit error to 0.1mm, much better than the 0.5mm last run. With correct BPM offset and vertical realignment, this rms orbit error is indeed small. Second, the jump quads in the AGS improved input polarization for RHIC. Third, the vertical tune was pushed further away from 7/10 snake resonance. The tune feedback maintained the tune at the desired value through the ramp. To calibrate the analyzing power of RHIC polarimeters at any energy above

  18. Terahertz polarization imaging

    NARCIS (Netherlands)

    Van der Valk, N.C.J.; Van der Marel, W.A.M.; Planken, P.C.M.

    2005-01-01

    We present a new method to measure the polarization state of a terahertz pulse by using a modified electrooptic sampling setup. To illustrate the power of this method, we show two examples in which the knowledge of the polarization of the terahertz pulse is essential for interpreting the results:

  19. Polarized proton beams

    International Nuclear Information System (INIS)

    Roser, T.

    1995-01-01

    The acceleration of polarized proton beams in circular accelerators is complicated by the presence of numerous depolarizing spin resonances. Careful and tedious minimization of polarization loss at each of these resonances allowed acceleration of polarized proton beams up to 22 GeV. It has been the hope that Siberian Snakes, which are local spin rotators inserted into ring accelerators, would eliminate these resonances and allow acceleration of polarized beams with the same ease and efficiency that is now routine for unpolarized beams. First tests at IUCF with a full Siberian Snake showed that the spin dynamics with a Snake can be understood in detail. The author now has results of the first tests of a partial Siberian Snake at the AGS, accelerating polarized protons to an energy of about 25 GeV. These successful tests of storage and acceleration of polarized proton beams open up new possibilities such as stored polarized beams for internal target experiments and high energy polarized proton colliders

  20. Polar Science Is Cool!

    Science.gov (United States)

    Weeks, Sophie

    2012-01-01

    Children are fascinated by the fact that polar scientists do research in extremely cold and dangerous places. In the Arctic they might be viewed as lunch by a polar bear. In the Antarctic, they could lose toes and fingers to frostbite and the wind is so fast it can rip skin off. They camp on ice in continuous daylight, weeks from any form of…

  1. Emergence of Dirac and quantum spin Hall states in fluorinated monolayer As and AsSb

    KAUST Repository

    Zhang, Qingyun

    2016-01-21

    Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer As and AsSb. While the pristine monolayers are semiconductors (direct band gap at the Γ point), fluorination results in Dirac cones at the K points. Fluorinated monolayer As shows a band gap of 0.16 eV due to spin-orbit coupling, and fluorinated monolayer AsSb a larger band gap of 0.37 eV due to inversion symmetry breaking. Spin-orbit coupling induces spin splitting similar to monolayer MoS2. Phonon calculations confirm that both materials are dynamically stable. Calculations of the edge states of nanoribbons by the tight-binding method demonstrate that fluorinated monolayer As is topologically nontrivial in contrast to fluorinated monolayer AsSb.

  2. Structural, electronic and magnetic properties of Au-based monolayer derivatives in honeycomb structure

    Energy Technology Data Exchange (ETDEWEB)

    Kapoor, Pooja, E-mail: pupooja16@gmail.com; Sharma, Munish; Ahluwalia, P. K. [Physics Department, Himachal Pradesh University, Shimla, Himachal Pradesh, India 171005 (India); Kumar, Ashok [Centre for Physical Sciences, School of Basic and Applied Sciences, Central University of Punjab, Bathinda, India, 151001 (India)

    2016-05-23

    We present electronic properties of atomic layer of Au, Au{sub 2}-N, Au{sub 2}-O and Au{sub 2}-F in graphene-like structure within the framework of density functional theory (DFT). The lattice constant of derived monolayers are found to be higher than the pristine Au monolayer. Au monolayer is metallic in nature with quantum ballistic conductance calculated as 4G{sub 0}. Similarly, Au{sub 2}-N and Au{sub 2}-F monolayers show 4G{sub 0} and 2G{sub 0} quantum conductance respectively while semiconducting nature with calculated band gap of 0.28 eV has been observed for Au{sub 2}-O monolayer. Most interestingly, half metalicity has been predicted for Au{sub 2}-N and Au{sub 2}-F monolayers. Our findings may have importance for the application of these monolayers in nanoelectronic and spintronics.

  3. Precision Polarization of Neutrons

    Science.gov (United States)

    Martin, Elise; Barron-Palos, Libertad; Couture, Aaron; Crawford, Christopher; Chupp, Tim; Danagoulian, Areg; Estes, Mary; Hona, Binita; Jones, Gordon; Klein, Andi; Penttila, Seppo; Sharma, Monisha; Wilburn, Scott

    2009-05-01

    Determining polarization of a cold neutron beam to high precision is required for the next generation neutron decay correlation experiments at the SNS, such as the proposed abBA and PANDA experiments. Precision polarimetry measurements were conducted at Los Alamos National Laboratory with the goal of determining the beam polarization to the level of 10-3 or better. The cold neutrons from FP12 were polarized using optically polarized ^3He gas as a spin filter, which has a highly spin-dependent absorption cross section. A second ^ 3He spin filter was used to analyze the neutron polarization after passing through a resonant RF spin rotator. A discussion of the experiment and results will be given.

  4. Optically polarized 3He

    Science.gov (United States)

    Gentile, T. R.; Nacher, P. J.; Saam, B.; Walker, T. G.

    2018-01-01

    This article reviews the physics and technology of producing large quantities of highly spin-polarized 3He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping. Both technical developments and deeper understanding of the physical processes involved have led to substantial improvements in the capabilities of both methods. For SEOP, the use of spectrally narrowed lasers and K-Rb mixtures has substantially increased the achievable polarization and polarizing rate. For MEOP nearly lossless compression allows for rapid production of polarized 3He and operation in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and revealed new phenomena. Both methods have benefitted from development of storage methods that allow for spin-relaxation times of hundreds of hours, and specialized precision methods for polarimetry. SEOP and MEOP are now widely applied for spin-polarized targets, neutron spin filters, magnetic resonance imaging, and precision measurements. PMID:29503479

  5. Optically polarized 3He

    Science.gov (United States)

    Gentile, T. R.; Nacher, P. J.; Saam, B.; Walker, T. G.

    2017-10-01

    This article reviews the physics and technology of producing large quantities of highly spin-polarized 3He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping. Both technical developments and deeper understanding of the physical processes involved have led to substantial improvements in the capabilities of both methods. For SEOP, the use of spectrally narrowed lasers and K-Rb mixtures has substantially increased the achievable polarization and polarizing rate. For MEOP nearly lossless compression allows for rapid production of polarized 3He and operation in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and revealed new phenomena. Both methods have benefitted from development of storage methods that allow for spin-relaxation times of hundreds of hours, and specialized precision methods for polarimetry. SEOP and MEOP are now widely applied for spin-polarized targets, neutron spin filters, magnetic resonance imaging, and precision measurements.

  6. Parallel Polarization State Generation.

    Science.gov (United States)

    She, Alan; Capasso, Federico

    2016-05-17

    The control of polarization, an essential property of light, is of wide scientific and technological interest. The general problem of generating arbitrary time-varying states of polarization (SOP) has always been mathematically formulated by a series of linear transformations, i.e. a product of matrices, imposing a serial architecture. Here we show a parallel architecture described by a sum of matrices. The theory is experimentally demonstrated by modulating spatially-separated polarization components of a laser using a digital micromirror device that are subsequently beam combined. This method greatly expands the parameter space for engineering devices that control polarization. Consequently, performance characteristics, such as speed, stability, and spectral range, are entirely dictated by the technologies of optical intensity modulation, including absorption, reflection, emission, and scattering. This opens up important prospects for polarization state generation (PSG) with unique performance characteristics with applications in spectroscopic ellipsometry, spectropolarimetry, communications, imaging, and security.

  7. Measuring the Influence of Dielectric Environment on 2D Excitons in Monolayer Semiconductors: Insight from High Magnetic Fields1

    Science.gov (United States)

    Stier, Andreas

    The relatively heavy electrons and holes in monolayer semiconductors such as MoS2 form tightly-bound excitons with large binding energies, thus motivating magneto-optical studies in high magnetic fields. Because 2D excitons in these materials necessarily lie close to a surface, their properties are expected to be strongly influenced by the surrounding dielectric environment. However, systematic studies exploring this role are challenging, in part because the most readily accessible exciton parameter - the exciton's optical transition energy - is largely unaffected by the surrounding medium. Here we show that the role of the dielectric environment can be revealed through its systematic influence on the size of the exciton, which can be directly measured via the diamagnetic shift of the exciton transition in high magnetic fields. Using exfoliated WSe2 monolayers affixed to single-mode optical fibers, we tune the surrounding dielectric environment by encapsulating the monolayers with different materials, and perform polarization resolved low-temperature magneto-absorption studies to 65 tesla. The systematic increase of the exciton's size with dielectric screening, and concurrent two-fold reduction in binding energy (also inferred from these measurements), is quantitatively compared with leading theoretical models based on the Keldysh potential. These results demonstrate how exciton properties can be tuned in future 2D devices and van der Waals heterostructures. 1In collaboration with S.A. Crooker (NHMFL); J. Kono (Rice University); K.M. McCreary, B.T. Jonker (Naval Research Lab); N.P. Wilson, G. Clark, X. Xu (University of Washington).

  8. Monolayer to MTS: using SEM, HIM, TEM and SERS to compare morphology, nanosensor uptake and redox potential in MCF7 cells

    Science.gov (United States)

    Jamieson, L. E.; Bell, A. P.; Harrison, D. J.; Campbell, C. J.

    2015-06-01

    Cellular redox potential is important for the control and regulation of a vast number of processes occurring in cells. When the fine redox potential balance within cells is disturbed it can have serious consequences such as the initiation or progression of disease. It is thought that a redox gradient develops in cancer tumours where the peripheral regions are well oxygenated and internal regions, further from vascular blood supply, become starved of oxygen and hypoxic. This makes treatment of these areas more challenging as, for example, radiotherapy relies on the presence of oxygen. Currently techniques for quantitative analysis of redox gradients are limited. Surface enhanced Raman scattering (SERS) nanosensors (NS) have been used to detect redox potential in a quantitative manner in monolayer cultured cells with many advantages over other techniques. This technique has considerable potential for use in multicellular tumour spheroids (MTS) - a three dimensional (3D) cell model which better mimics the tumour environment and gradients that develop. MTS are a more realistic model of the in vivo cellular morphology and environment and are becoming an increasingly popular in vitro model, replacing traditional monolayer culture. Imaging techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM) and helium ion microscopy (HIM) were used to investigate differences in morphology and NS uptake in monolayer culture compared to MTS. After confirming NS uptake, the first SERS measurements revealing quantitative information on redox potential in MTS were performed.

  9. A Mathematical Model of Neonatal Rat Atrial Monolayers with Constitutively Active Acetylcholine-Mediated K+ Current.

    Directory of Open Access Journals (Sweden)

    Rupamanjari Majumder

    2016-06-01

    Full Text Available Atrial fibrillation (AF is the most frequent form of arrhythmia occurring in the industrialized world. Because of its complex nature, each identified form of AF requires specialized treatment. Thus, an in-depth understanding of the bases of these arrhythmias is essential for therapeutic development. A variety of experimental studies aimed at understanding the mechanisms of AF are performed using primary cultures of neonatal rat atrial cardiomyocytes (NRAMs. Previously, we have shown that the distinct advantage of NRAM cultures is that they allow standardized, systematic, robust re-entry induction in the presence of a constitutively-active acetylcholine-mediated K+ current (IKACh-c. Experimental studies dedicated to mechanistic explorations of AF, using these cultures, often use computer models for detailed electrophysiological investigations. However, currently, no mathematical model for NRAMs is available. Therefore, in the present study we propose the first model for the action potential (AP of a NRAM with constitutively-active acetylcholine-mediated K+ current (IKACh-c. The descriptions of the ionic currents were based on patch-clamp data obtained from neonatal rats. Our monolayer model closely mimics the action potential duration (APD restitution and conduction velocity (CV restitution curves presented in our previous in vitro studies. In addition, the model reproduces the experimentally observed dynamics of spiral wave rotation, in the absence and in the presence of drug interventions, and in the presence of localized myofibroblast heterogeneities.

  10. A protocol for isolation and enriched monolayer cultivation of neural precursor cells from mouse dentate gyrus.

    Science.gov (United States)

    Babu, Harish; Claasen, Jan-Hendrik; Kannan, Suresh; Rünker, Annette E; Palmer, Theo; Kempermann, Gerd

    2011-01-01

    In vitro assays are valuable tools to study the characteristics of adult neural precursor cells under controlled conditions with a defined set of parameters. We here present a detailed protocol based on our previous original publication (Babu et al., 2007) to isolate neural precursor cells from the hippocampus of adult mice and maintain and propagate them as adherent monolayer cultures. The strategy is based on the use of Percoll density gradient centrifugation to enrich precursor cells from the micro-dissected dentate gyrus. Based on the expression of Nestin and Sox2, a culture-purity of more than 98% can be achieved. The cultures are expanded under serum-free conditions in Neurobasal A medium with addition of the mitogens Epidermal growth factor and Fibroblast growth factor 2 as well as the supplements Glutamax-1 and B27. Under differentiation conditions, the precursor cells reliably generate approximately 30% neurons with appropriate morphological, molecular, and electrophysiological characteristics that might reflect granule cell properties as their in vivo counterpart. We also highlight potential modifications to the protocol.

  11. Surface investigation of chitosan film with fatty acid monolayers

    Directory of Open Access Journals (Sweden)

    Esam A. El-hefian

    2009-05-01

    Full Text Available The surface pressure- molecular area (-A isotherm curves of two fatty acids of different chain lengths, i.e. stearic (C18 and arachidic (C20 acids, were obtained by using Langmuir-Blodgett (LB technique. Results showed clear isotherm plots with limiting mean molecular area around 21 Å2 for both acids. However, the monolayer was found to collapse at higher than 33 mN m-1 and 21 mN m-1 for stearic acid and arachidic acid respectively. The effect of Langmuir-Blodgett monolayers of the acids was investigated by atomic force microscopy (AFM. Chitosan film, before and after dipping in water, was also studied by means of AFM so that it could be used for comparison. It was found that the surface of chitosan was more homogeneous and smoother after dipping in water. In addition, more homogeneous surfaces were achieved after transferring a layer of the fatty acid onto the substrate.

  12. Organosilicon derivatives of BTBT for monolayer organic field effect transistors

    Science.gov (United States)

    Agina, Elena V.; Polinskaya, Marina S.; Trul, Askold A.; Chekusova, Viktoria P.; Sizov, Alexey S.; Borshchev, Oleg V.; Ponomarenko, Sergey A.

    2017-08-01

    Synthesis of novel organosilicon derivatives of [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) linked though flexible aliphatic spacers to a disiloxane anchor group is reported. They were successfully used in monolayer OFETs with the charge carrier mobilities up to 0.02 cm2 /Vs, threshold voltage close to 0 V and On/Off ratio up to 10,000. Influence of the chemical structure of the molecules synthesized on the morphology, molecular 2D ordering in the monolayers and their semiconducting properties is considered. The effect of different methods of the ultrathin semiconducting layer preparation, such as Langmuir-Blodgett, Langmuir-Schaefer, spin coating or doctor blade, on the OFET performance is discussed.

  13. MgO monolayer epitaxy on Ni (100)

    Science.gov (United States)

    Sarpi, B.; Putero, M.; Hemeryck, A.; Vizzini, S.

    2017-11-01

    The growth of two-dimensional oxide films with accurate control of their structural and electronic properties is considered challenging for engineering nanotechnological applications. We address here the particular case of MgO ultrathin films grown on Ni (100), a system for which neither crystallization nor extended surface ordering has been established previously in the monolayer range. Using Scanning Tunneling Microscopy and Auger Electron Spectroscopy, we report on experiments showing MgO monolayer (ML) epitaxy on a ferromagnetic nickel surface, down to the limit of atomic thickness. Alternate steps of Mg ML deposition, O2 gas exposure, and ultrahigh vacuum thermal treatment enable the production of a textured film of ordered MgO nano-domains. This study could open interesting prospects for controlled epitaxy of ultrathin oxide films with a high magneto-resistance ratio on ferromagnetic substrates, enabling improvement in high-efficiency spintronics and magnetic tunnel junction devices.

  14. Neutron Reflectivity Measurement for Polymer Dynamics near Graphene Oxide Monolayers

    Science.gov (United States)

    Koo, Jaseung

    We investigated the diffusion dynamics of polymer chains confined between graphene oxide layers using neutron reflectivity (NR). The bilayers of polymethylmetacrylate (PMMA)/ deuterated PMMA (d-PMMA) films and polystyrene (PS)/d-PS films with various film thickness sandwiched between Langmuir-Blodgett (LB) monolayers of graphene oxide (GO) were prepared. From the NR results, we found that PMMA diffusion dynamics was reduced near the GO surface while the PS diffusion was not significantly changed. This is due to the different strength of GO-polymer interaction. In this talk, these diffusion results will be compared with dewetting dynamics of polymer thin films on the GO monolayers. This has given us the basis for development of graphene-based nanoelectronics with high efficiency, such as heterojunction devices for polymer photovoltaic (OPV) applications.

  15. Defective interfering particles in monolayer-propagated Newcastle disease virus

    International Nuclear Information System (INIS)

    Roman, J.M.; Simon, E.H.

    1976-01-01

    Newcastle disease virus (NDV) serially passaged in chick embryo fibroblasts (M-NDV) gives rise to defective interfering (NDV-DI) particles, while NDV passaged in embryonated eggs (E-NDV) does not. Co-infection with these particles and infectious virions results in a 99 percent reduction in yield. Interference is not due to interferon or to prevention of absorption of infectious virions and is specific for NDV. The particles mediating interference sediment at the same velocity as infectious virions. The accumulation of NDV-DI particles in monolayers but not in eggs may be a consequence of the fact that M-NDV virions are larger and probably contain more RNA, or it may reflect differences in NDV replicative processes in eggs and monolayers, or both

  16. Functional Molecular Junctions Derived from Double Self-Assembled Monolayers.

    Science.gov (United States)

    Seo, Sohyeon; Hwang, Eunhee; Cho, Yunhee; Lee, Junghyun; Lee, Hyoyoung

    2017-09-25

    Information processing using molecular junctions is becoming more important as devices are miniaturized to the nanoscale. Herein, we report functional molecular junctions derived from double self-assembled monolayers (SAMs) intercalated between soft graphene electrodes. Newly assembled molecular junctions are fabricated by placing a molecular SAM/(top) electrode on another molecular SAM/(bottom) electrode by using a contact-assembly technique. Double SAMs can provide tunneling conjugation across the van der Waals gap between the terminals of each monolayer and exhibit new electrical functions. Robust contact-assembled molecular junctions can act as platforms for the development of equivalent contact molecular junctions between top and bottom electrodes, which can be applied independently to different kinds of molecules to enhance either the structural complexity or the assembly properties of molecules. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Point defect weakened thermal contraction in monolayer graphene.

    Science.gov (United States)

    Zha, Xian-Hu; Zhang, Rui-Qin; Lin, Zijing

    2014-08-14

    We investigate the thermal expansion behaviors of monolayer graphene and three configurations of graphene with point defects, namely the replacement of one carbon atom with a boron or nitrogen atom, or of two neighboring carbon atoms by boron-nitrogen atoms, based on calculations using first-principles density functional theory. It is found that the thermal contraction of monolayer graphene is significantly decreased by point defects. Moreover, the corresponding temperature for negative linear thermal expansion coefficient with the maximum absolute value is reduced. The cause is determined to be point defects that enhance the mechanical strength of graphene and then reduce the amplitude and phonon frequency of the out-of-plane acoustic vibration mode. Such defect weakening of graphene thermal contraction will be useful in nanotechnology to diminish the mismatching or strain between the graphene and its substrate.

  18. ELECTROCATALYSIS ON SURFACES MODIFIED BY METAL MONOLAYERS DEPOSITED AT UNDERPOTENTIALS.

    Energy Technology Data Exchange (ETDEWEB)

    ADZIC,R.

    2000-12-01

    The remarkable catalytic properties of electrode surfaces modified by monolayer amounts of metal adatoms obtained by underpotential deposition (UPD) have been the subject of a large number of studies during the last couple of decades. This interest stems from the possibility of implementing strictly surface modifications of electrocatalysts in an elegant, well-controlled way, and these bi-metallic surfaces can serve as models for the design of new catalysts. In addition, some of these systems may have potential for practical applications. The UPD of metals, which in general involves the deposition of up to a monolayer of metal on a foreign substrate at potentials positive to the reversible thermodynamic potential, facilitates this type of surface modification, which can be performed repeatedly by potential control. Recent studies of these surfaces and their catalytic properties by new in situ surface structure sensitive techniques have greatly improved the understanding of these systems.

  19. Mixed multilayered vertical heterostructures utilizing strained monolayer WS2

    Science.gov (United States)

    Sheng, Yuewen; Xu, Wenshuo; Wang, Xiaochen; He, Zhengyu; Rong, Youmin; Warner, Jamie H.

    2016-01-01

    Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by CVD directly on Si substrates with SiO2 surface are easily washed off by water and this makes aqueous based transfer methods challenging for creating vertical stacks on the growth substrate. 2D hexagonal Boron Nitride films are used to provide an insulating layer that limits interactions with a top graphene layer and preserve the strong photoluminescence from the WS2. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with atomic thickness depth control and large area coverage.Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by

  20. Exciton diamagnetic shifts and valley Zeeman effects in monolayer WS2 and MoS2 to 65 Tesla

    Science.gov (United States)

    Stier, Andreas V.; McCreary, Kathleen M.; Jonker, Berend T.; Kono, Junichiro; Crooker, Scott A.

    2016-02-01

    In bulk and quantum-confined semiconductors, magneto-optical studies have historically played an essential role in determining the fundamental parameters of excitons (size, binding energy, spin, dimensionality and so on). Here we report low-temperature polarized reflection spectroscopy of atomically thin WS2 and MoS2 in high magnetic fields to 65 T. Both the A and B excitons exhibit similar Zeeman splittings of approximately -230 μeV T-1 (g-factor ~=-4), thereby quantifying the valley Zeeman effect in monolayer transition-metal disulphides. Crucially, these large fields also allow observation of the small quadratic diamagnetic shifts of both A and B excitons in monolayer WS2, from which radii of ~1.53 and ~1.16 nm are calculated. Further, when analysed within a model of non-local dielectric screening, these diamagnetic shifts also constrain estimates of the A and B exciton binding energies (410 and 470 meV, respectively, using a reduced A exciton mass of 0.16 times the free electron mass). These results highlight the utility of high magnetic fields for understanding new two-dimensional materials.

  1. Growth mechanism of largescale MoS2 monolayer by sulfurization of MoO3 film

    Science.gov (United States)

    Taheri, Payam; Wang, Jieqiong; Xing, Hui; Destino, Joel F.; Murat Arik, Mumtaz; Zhao, Chuan; Kang, Kaifei; Blizzard, Brett; Zhang, Lijie; Zhao, Puqin; Huang, Shaoming; Yang, Sen; Bright, Frank V.; Cerne, John; Zeng, Hao

    2016-07-01

    Monolayer two-dimensional transition metal dichalcogenides (TMDCs) such as MoS2 with broken inversion symmetry possesses two degenerate yet inequivalent valleys that can be selectively excited by circularly polarized light. This unique property renders interesting valley physics. The ability to manipulate valley degrees of freedom with light or external field makes them attractive for optoelectronic and spintronic applications. There is great demand for large area monolayer (ML) TMDCs for certain measurements and device applications. Recent reports on large area ML TDMCs focus on chemical vapor deposition growth. In this work, we report a facile approach to grow largescale continuous ML MoS2 nearly free of overgrowth and voids, by sulfurizing evaporated molybdenum trioxide ultrathin films. Photo conductivity scales with device sizes up to 4.5 mm, suggesting excellent film uniformity. The growth mechanism is found to be vaporization, diffusion, sulfurization and lateral growth, all at local micrometer scale. Our approach provides a new pathway for large-area ML TMDC growth and lithography-free device fabrication.

  2. Polarization at the SLC

    Energy Technology Data Exchange (ETDEWEB)

    Moffeit, K.C.

    1988-10-01

    The Stanford Linear collider was designed to accommodate polarized electron beams. Longitudinally polarized electrons colliding with unpolarized positrons at a center of mass energy near the Z/sup 0/ mass can be used as novel and sensitive probes of the electroweak process. A gallium arsenide based photon emission source will provide a beam of longitudinally polarized electrons of about 45 percent polarization. A system of bend magnets and a superconducting solenoid will be used to rotate the spins so that the polarization is preserved while the 1.21 GeV electrons are stored in the damping ring. Another set of bend magnets and two superconducting solenoids orient the spin vectors so that longitudinal polarization of the electrons is achieved at the collision point with the unpolarized positrons. A system to monitor the polarization based on Moller and Compton scattering will be used. Nearly all major components have been fabricated and tested. Subsystems of the source and polarimeters have been installed, and studies are in progress. The installation and commissioning of the entire system will take place during available machine shutdown periods as the commissioning of SLC progresses. 8 refs., 16 figs., 1 tab.

  3. Influence of calcium on ceramide-1-phosphate monolayers

    Directory of Open Access Journals (Sweden)

    Joana S. L. Oliveira

    2016-02-01

    Full Text Available Ceramide-1-phosphate (C1P plays an important role in several biological processes, being identified as a key regulator of many protein functions. For instance, it acts as a mediator of inflammatory responses. The mediation of the inflammation process happens due to the interaction of C1P with the C2 domain of cPLA2α, an effector protein that needs the presence of submicromolar concentrations of calcium ions. The aim of this study was to determine the phase behaviour and structural properties of C1P in the presence and absence of millimolar quantities of calcium in a well-defined pH environment. For that purpose, we used monomolecular films of C1P at the soft air/liquid interface with calcium ions in the subphase. The pH was varied to change the protonation degree of the C1P head group. We used surface pressure versus molecular area isotherms coupled with other monolayer techniques as Brewster angle microscopy (BAM, infrared reflection–absorption spectroscopy (IRRAS and grazing incidence X-ray diffraction (GIXD. The isotherms indicate that C1P monolayers are in a condensed state in the presence of calcium ions, regardless of the pH. At higher pH without calcium ions, the monolayer is in a liquid-expanded state due to repulsion between the negatively charged phosphate groups of the C1P molecules. When divalent calcium ions are added, they are able to bridge the highly charged phosphate groups, enhancing the regular arrangement of the head groups. Similar solidification of the monolayer structure can be seen in the presence of a 150 times larger concentration of monovalent sodium ions. Therefore, calcium ions have clearly a strong affinity for the phosphomonoester of C1P.

  4. Superior Gas Sensing Properties of Monolayer PtSe2

    KAUST Repository

    Sajjad, Muhammad

    2016-12-15

    First-principles calculations of the structural and electronic properties of monolayer 1T-PtSe2 with adsorbed (a) NO2, (b) NO, (c) NH3, (d) H2O, (e) CO2, and (f) CO molecules are discussed. The results point to great potential of the material in gas sensor applications. Superior sensitivity is demonstrated by transport calculations using the nonequilibrium Green\\'s function method.

  5. Shadow-mask evaporation through monolayer-modified nanostencils

    OpenAIRE

    Kolbel, M; Tjerkstra, RW; Brugger, J; van Rijn, CJM; Nijdam, W; Huskens, J; Reinhoudt, DN

    2002-01-01

    Gradual clogging of the apertures of nanostencils used as miniature shadow masks in metal evaporations can be reduced by coating the stencil with self-assembled monolayers (SAM). This is quantified by the dimensions (height and volume) of gold features obtained by nanostencil evaporation as measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM). An increase in material deposition through the apertures by more than 100% can be achieved with SAM-coated stencils, which ...

  6. UV-Induced Reaction Kinetics of Dilinoleoylphosphatidylethanolamine Monolayers

    OpenAIRE

    Viitala, Tapani; Peltonen, Jouko

    1999-01-01

    The UV-induced reactivity of dilinoleoylphosphatidylethanolamine (DLiPE) Langmuir and Langmuir-Blodgett films has been studied by in situ measurements of the changes in the mean molecular area, UV-vis and Fourier transform infrared spectroscopy, and atomic force microscopy (AFM). Optimum orientation and packing density of the DLiPE molecules in the monolayer were achieved by adding uranyl acetate to the subphase. A first-order reaction kinetic model was successfully fitted to the experimental...

  7. In situ Raman spectroelectrochemistry of azobenzene monolayers on glassy carbon.

    Science.gov (United States)

    Itoh, Takashi; McCreery, Richard L

    2007-05-01

    In situ Raman spectra of chemisorbed azobenzene (AB) monolayers on glassy carbon (GC) electrodes were observed under potentiostatic conditions in acetonitrile (ACN) with tetrabutyl-ammonium tetrafluoroborate (TBA-BF4). The Raman intensities of these spectra were high below -1000 mV, and this is attributed to the change in absorbance of AB on GC. In this paper, we describe chemisorbed AB molecules on GC electrode surfaces under potentiostatic conditions.

  8. Vanadium oxide monolayer catalysts. I. Preparation, characterization, and thermal stability

    NARCIS (Netherlands)

    Roozeboom, F.; Fransen, T.; Mars, P.; Gellings, P.J.

    1979-01-01

    Vanadium oxide catalysts of the monolayer type have been prepared by means of chemisorption of vanadate(V)-anions from aqueous solutions and by chemisorption of gaseous V2O3(OH)4. Using Al2O3, Cr2O3, TiO2, CeO2 and ZrO2, catalysts with an approximately complete monomolecular layer of vanadium(V)

  9. Assembly of citrate gold nanoparticles on hydrophilic monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Vikholm-Lundin, Inger, E-mail: inger.vikholm-lundin@uta.fi [University of Tampere, BioMediTech, Tampere (Finland); Fimlab Laboratories Ltd., Tampere (Finland); Rosqvist, Emil; Ihalainen, Petri [Abo Akademi University, Center for Functional Materials, Laboratory of Physical Chemistry (Finland); Munter, Tony [VTT Technical Research Centre of Finland, Process Chemistry end Environmental Engineering, Tampere (Finland); Honkimaa, Anni [University of Tampere, Department of Virology, School of Medicine, Tampere (Finland); Marjomäki, Varpu [University of Jyväskylä, Department of Biological and Environmental Science, Nanoscience Center, Jyväskylä (Finland); Albers, Willem M. [BioNavis Oy Ltd., Ylöjärvi, Tampere (Finland); Peltonen, Jouko [Abo Akademi University, Center for Functional Materials, Laboratory of Physical Chemistry (Finland)

    2016-08-15

    Highlights: • The self-assembled layers were all hydrophilic with Lipa-pTHMMAA exhibiting close to full wetting. • The polyacrylamide layers smoothen the gold surface to a higher extent than the polyethylene glycol and lipoic acid terminated with an amino group. • SPR resonance curves shift to higher angles and become increasingly damped when large nanoparticles assembled on the surface. • Topographical images confirmed that the highest number of particles were assembled on the polyethylene glycol monolayer. • By increasing the interaction time more particles could be assembled on the surface. - Abstract: Self-assembled monolayers (SAMs) as model surfaces were linked onto planar gold films thorough lipoic acid or disulfide groups. The molecules used were polyethylene glycol (EG-S-S), N-[tris-(hydroxymethyl)methyl]acrylamide polymers with and without lipoic acid (Lipa-pTHMMAA and pTHMMAA) and a lipoic acid triazine derivative (Lipa-MF). All the layers, but Lipa-MF with a primary amino group were hydroxyl terminated. The layers were characterized by contact angle measurements and atomic force microscopy, AFM. Citrate stabilized nanoparticles, AuNPs in water and phosphate buffer were allowed to assemble on the layers for 10 min and the binding was followed in real-time with surface plasmon resonance, SPR. The SPR resonance curves were observed to shift to higher angles and become increasingly damped, while also the peaks strongly broaden when large nanoparticles assembled on the surface. Both the angular shift and the damping of the curve was largest for nanoparticles assembling on the EG-S-S monolayer. High amounts of particles were also assembled on the pTHMMAA layer without the lipoic acid group, but the damping of the curve was considerably lower with a more even distribution of the particles. Topographical images confirmed that the highest number of particles were assembled on the polyethylene glycol monolayer. By increasing the interaction time more

  10. Properties of thiolate monolayers formed on different amalgam electrodes

    Czech Academy of Sciences Publication Activity Database

    Josypčuk, Bohdan; Mareček, Vladimír

    2011-01-01

    Roč. 653, 1-2 (2011), s. 7-13 ISSN 1572-6657 R&D Projects: GA AV ČR IAA400400806; GA ČR GAP206/11/1638; GA MŠk(CZ) LC06063 Institutional research plan: CEZ:AV0Z40400503 Keywords : thiolate monolayer * reductive desorption * charge effect Subject RIV: CG - Electrochemistry Impact factor: 2.905, year: 2011

  11. Fabrication of 3D-culture platform with sandwich architecture for preserving liver-specific functions of hepatocytes using 3D bioprinter.

    Science.gov (United States)

    Arai, Kenichi; Yoshida, Toshiko; Okabe, Motonori; Goto, Mitsuaki; Mir, Tanveer Ahmad; Soko, Chika; Tsukamoto, Yoshinari; Akaike, Toshihiro; Nikaido, Toshio; Zhou, Kaixuan; Nakamura, Makoto

    2017-06-01

    The development of new three-dimensional (3D) cell culture system that maintains the physiologically relevant signals of hepatocytes is essential in drug discovery and tissue engineering research. Conventional two-dimensional (2D) culture yields cell growth, proliferation, and differentiation. However, gene expression and signaling profiles can be different from in vivo environment. Here, we report the fabrication of a 3D culture system using an artificial scaffold and our custom-made inkjet 3D bioprinter as a new strategy for studying liver-specific functions of hepatocytes. We built a 3D culture platform for hepatocytes-attachment and formation of cell monolayer by interacting the galactose chain of galactosylated alginate gel (GA-gel) with asialoglycoprotein receptor (ASGPR) of hepatocytes. The 3D geometrical arrangement of cells was controlled by using 3D bioprinter, and cell polarity was controlled with the galactosylated hydrogels. The fabricated GA-gel was able to successfully promote adhesion of hepatocytes. To observe liver-specific functions and to mimic hepatic cord, an additional parallel layer of hepatocytes was generated using two gel sheets. These results indicated that GA-gel biomimetic matrices can be used as a 3D culture system that could be effective for the engineering of liver tissues. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1583-1592, 2017. © 2017 Wiley Periodicals, Inc.

  12. A novel electrospun biphasic scaffold provides optimal three-dimensional topography for in vitro co-culture of airway epithelial and fibroblast cells.

    Science.gov (United States)

    Morris, G E; Bridge, J C; Brace, L A; Knox, A J; Aylott, J W; Brightling, C E; Ghaemmaghami, A M; Rose, F R A J

    2014-09-01

    Conventional airway in vitro models focus upon the function of individual structural cells cultured in a two-dimensional monolayer, with limited three-dimensional (3D) models of the bronchial mucosa. Electrospinning offers an attractive method to produce defined, porous 3D matrices for cell culture. To investigate the effects of fibre diameter on airway epithelial and fibroblast cell growth and functionality, we manipulated the concentration and deposition rate of the non-degradable polymer polyethylene terephthalate to create fibres with diameters ranging from nanometre to micrometre. The nanofibre scaffold closely resembles the basement membrane of the bronchiole mucosal layer, and epithelial cells cultured at the air-liquid interface on this scaffold showed polarized differentiation. The microfibre scaffold mimics the porous sub-mucosal layer of the airway into which lung fibroblast cells showed good penetration. Using these defined electrospinning parameters we created a biphasic scaffold with 3D topography tailored for optimal growth of both cell types. Epithelial and fibroblast cells were co-cultured onto the apical nanofibre phase and the basal microfibre phase respectively, with enhanced epithelial barrier formation observed upon co-culture. This biphasic scaffold provides a novel 3D in vitro platform optimized to mimic the different microenvironments the cells encounter in vivo on which to investigate key airway structural cell interactions in airway diseases such as asthma.

  13. Self assembly of highly-ordered nanoparticle monolayers.

    Energy Technology Data Exchange (ETDEWEB)

    Bigioni, T. P.; Lin, X.-M.; Nguyen, T. T.; Corwin, E. I.; Witten, T. A.; Jaeger, H. M.; Univ. of Chicago

    2006-01-01

    When a drop of a colloidal solution of nanoparticles dries on a surface, it leaves behind coffee-stain-like rings of material with lace-like patterns or clumps of particles in the interior. These non-uniform mass distributions are manifestations of far-from-equilibrium effects, such as fluid flows and solvent fluctuations during late-stage drying. However, recently a strikingly different drying regime promising highly uniform, long-range-ordered nanocrystal monolayers has been found. Here we make direct, real-time and real-space observations of nanocrystal self-assembly to reveal the mechanism. We show how the morphology of drop-deposited nanoparticle films is controlled by evaporation kinetics and particle interactions with the liquid-air interface. In the presence of an attractive particle-interface interaction, rapid early-stage evaporation dynamically produces a two-dimensional solution of nanoparticles at the liquid-air interface, from which nanoparticle islands nucleate and grow. This self-assembly mechanism produces monolayers with exceptional long-range ordering that are compact over macroscopic areas, despite the far-from-equilibrium evaporation process. This new drop-drying regime is simple, robust and scalable, is insensitive to the substrate material and topography, and has a strong preference for forming monolayer films. As such, it stands out as an excellent candidate for the fabrication of technologically important ultra thin film materials for sensors, optical devices and magnetic storage media.

  14. A trough for improved SFG spectroscopy of lipid monolayers

    Science.gov (United States)

    Franz, Johannes; van Zadel, Marc-Jan; Weidner, Tobias

    2017-05-01

    Lipid monolayers are indispensable model systems for biological membranes. The main advantage over bilayer model systems is that the surface pressure within the layer can be directly and reliably controlled. The sensitive interplay between surface pressure and temperature determines the molecular order within a model membrane and consequently determines the membrane phase behavior. The lipid phase is of crucial importance for a range of membrane functions such as protein interactions and membrane permeability. A very reliable method to probe the structure of lipid monolayers is sum frequency generation (SFG) vibrational spectroscopy. Not only is SFG extremely surface sensitive but it can also directly access critical parameters such as lipid order and orientation, and it can provide valuable information about protein interactions along with interfacial hydration. However, recent studies have shown that temperature gradients caused by high power laser beams perturb the lipid layers and potentially obscure the spectroscopic results. Here we demonstrate how the local heating problem can be effectively reduced by spatially distributing the laser pulses on the sample surface using a translating Langmuir trough for SFG experiments at lipid monolayers. The efficiency of the trough is illustrated by the detection of enhanced molecular order due to reduced heat load.

  15. Strain engineering on transmission carriers of monolayer phosphorene

    Science.gov (United States)

    Zhang, Wei; Li, Feng; Hu, Junsong; Zhang, Ping; Yin, Jiuren; Tang, Xianqiong; Jiang, Yong; Wu, Bozhao; Ding, Yanhuai

    2017-11-01

    The effects of uniaxial strain on the structure, band gap and transmission carriers of monolayer phosphorene were investigated by first-principles calculations. The strain induced semiconductor-metal as well as direct–indirect transitions were studied in monolayer phosphorene. The position of CBM which belonged to indirect gap shifts along the direction of the applied strain. We have concluded the change rules of the carrier effective mass when plane strains are applied. In band structure, the sudden decrease of band gap or the new formation of CBM (VBM) causes the unexpected change in carrier effective mass. The effects of zigzag and armchair strain on the effective electron mass in phosphorene are different. The strain along zigzag direction has effects on the electrons effective mass along both zigzag and armchair direction. By contrast, armchair-direction strain seems to affect only on the free electron mass along zigzag direction. For the holes, the effective masses along zigzag direction are largely affected by plane strains while the effective mass along armchair direction exhibits independence in strain processing. The carrier density of monolayer phosphorene at 300 K is calculated about 1.25× {{10}6} cm‑2, which is greatly influenced by the temperature and strain. Strain engineering is an efficient method to improve the carrier density in phosphorene.

  16. Monolayer MoS{sub 2} self-switching diodes

    Energy Technology Data Exchange (ETDEWEB)

    Al-Dirini, Feras, E-mail: alf@unimelb.edu.au; Hossain, Md Sharafat [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Centre for Neural Engineering, University of Melbourne, Victoria (Australia); Victorian Research Laboratory, National ICT Australia, West Melbourne, Victoria (Australia); Hossain, Faruque M.; Skafidas, Efstratios [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Centre for Neural Engineering, University of Melbourne, Victoria (Australia); Mohammed, Mahmood A. [Princess Sumaya University for Technology, Amman (Jordan); Nirmalathas, Ampalavanapillai [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Melbourne Networked Society Institute (MNSI), University of Melbourne, Victoria (Australia)

    2016-01-28

    This paper presents a new molybdenum disulphide (MoS{sub 2}) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS{sub 2} monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS{sub 2} results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70.

  17. Monolayer MoS2 self-switching diodes

    International Nuclear Information System (INIS)

    Al-Dirini, Feras; Hossain, Md Sharafat; Hossain, Faruque M.; Skafidas, Efstratios; Mohammed, Mahmood A.; Nirmalathas, Ampalavanapillai

    2016-01-01

    This paper presents a new molybdenum disulphide (MoS 2 ) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS 2 monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS 2 results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70

  18. Lipid monolayers and adsorbed polyelectrolytes with different degrees of polymerization.

    Science.gov (United States)

    Ortmann, Thomas; Ahrens, Heiko; Lawrenz, Frank; Gröning, Andreas; Nestler, Peter; Günther, Jens-Uwe; Helm, Christiane A

    2014-06-17

    Polystyrene sulfonate (PSS) of different molecular weight M(w) is adsorbed to oppositely charged DODAB monolayers from dilute solutions (0.01 mmol/L). PSS adsorbs flatly in a lamellar manner, as is shown by X-ray reflectivity and grazing incidence diffraction (exception: PSS with M(w) below 7 kDa adsorbs flatly disordered to the liquid expanded phase). The surface coverage and the separation of the PSS chains are independent of PSS M(w). On monolayer compression, the surface charge density increases by a factor of 2, and the separation of the PSS chains decreases by the same factor. Isotherms show that on increase of PSS M(w) the transition pressure of the LE/LC (liquid expanded/liquid condensed) phase transition decreases. When the contour length exceeds the persistence length (21 nm), the transition pressure is low and constant. For low-M(w) PSS (<7 kDa) the LE/LC transition of the lipids and the disordered/ordered transition of adsorbed PSS occur simultaneously, leading to a maximum in the contour length dependence of the transition enthalpy. These findings show that lipid monolayers at the air/water interface are a suitable model substrate with adjustable surface charge density to study the equilibrium conformation of adsorbed polyelectrolytes as well as their interactions with a model membrane.

  19. Photo-induced travelling waves in condensed Langmuir monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Tabe, Y [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan); Yamamoto, T [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan); Yokoyama, H [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan)

    2003-06-01

    We report the detailed properties of photo-induced travelling waves in liquid crystalline Langmuir monolayers composed of azobenzene derivatives. When the monolayer, in which the constituent rodlike molecules are coherently tilted from the layer normal, is weakly illuminated to undergo the trans-cis photo-isomerization, spatio-temporal periodic oscillations of the molecular azimuth begin over the entire excited area and propagate as a two-dimensional orientational wave. The wave formation takes place only when the film is formed at an asymmetric interface with broken up-down symmetry and when the chromophores are continuously excited near the long-wavelength edge of absorption to induce repeated photo-isomerizations between the trans and cis forms. Under proper illumination conditions, Langmuir monolayers composed of a wide variety of azobenzene derivatives have been confirmed to exhibit similar travelling waves with velocity proportional to the excitation power irrespective of the degree of amphiphilicity. The dynamics can be qualitatively explained by the modified reaction-diffusion model proposed by Reigada, Sagues and Mikhailov.

  20. Gold nanoparticles with patterned surface monolayers for nanomedicine: current perspectives.

    Science.gov (United States)

    Pengo, Paolo; Şologan, Maria; Pasquato, Lucia; Guida, Filomena; Pacor, Sabrina; Tossi, Alessandro; Stellacci, Francesco; Marson, Domenico; Boccardo, Silvia; Pricl, Sabrina; Posocco, Paola

    2017-12-01

    Molecular self-assembly is a topic attracting intense scientific interest. Various strategies have been developed for construction of molecular aggregates with rationally designed properties, geometries, and dimensions that promise to provide solutions to both theoretical and practical problems in areas such as drug delivery, medical diagnostics, and biosensors, to name but a few. In this respect, gold nanoparticles covered with self-assembled monolayers presenting nanoscale surface patterns-typically patched, striped or Janus-like domains-represent an emerging field. These systems are particularly intriguing for use in bio-nanotechnology applications, as presence of such monolayers with three-dimensional (3D) morphology provides nanoparticles with surface-dependent properties that, in turn, affect their biological behavior. Comprehensive understanding of the physicochemical interactions occurring at the interface between these versatile nanomaterials and biological systems is therefore crucial to fully exploit their potential. This review aims to explore the current state of development of such patterned, self-assembled monolayer-protected gold nanoparticles, through step-by-step analysis of their conceptual design, synthetic procedures, predicted and determined surface characteristics, interactions with and performance in biological environments, and experimental and computational methods currently employed for their investigation.

  1. Measurement of Exciton Binding Energy of Monolayer WS2

    Science.gov (United States)

    Chen, Xi; Zhu, Bairen; Cui, Xiaodong

    Excitonic effects are prominent in monolayer crystal of transition metal dichalcogenides (TMDCs) because of spatial confinement and reduced Coulomb screening. Here we use linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE) to measure the exciton binding energy of monolayer WS2. Peaks for excitonic absorptions of the direct gap located at K valley of the Brillouin zone and transitions from multiple points near Γ point of the Brillouin zone, as well as trion side band are shown in the linear absorption spectra of WS2. But there is no gap between distinct excitons and the continuum of the interband transitions. Strong electron-phonon scattering, overlap of excitons around Γ point and the transfer of the oscillator strength from interband continuum to exciton states make it difficult to resolve the electronic interband transition edge even down to 10K. The gap between excited states of the band-edge exciton and the single-particle band is probed by TP-PLE measurements. And the energy difference between 1s exciton and the single-particle gap gives the exciton binding energy of monolayer WS2 to be about 0.71eV. The work is supported by Area of excellency (AoE/P-04/08), CRF of Hong Kong Research Grant Council (HKU9/CRF/13G) and SRT on New Materials of The University of Hong Kong.

  2. Phase diagram of the CF₄ monolayer and bilayer on graphite.

    Science.gov (United States)

    Thomas, Petros; Hess, George B

    2014-05-21

    We report an experimental study of physisorbed monolayers and bilayers of CF4 on graphite using infrared reflection absorption spectroscopy supplemented by ellipsometry. The symmetric C-F stretch mode ν3 near 1283 cm(-1) in the gas is strongly blue shifted in the film by dynamic dipole coupling. This blue shift provides a very sensitive measure of the inter-molecular spacing in the monolayer and, less directly, in the bilayer. We find that important corrections are necessary to the volumetric coverage scales used in previous heat capacity and x-ray diffraction studies of this system. This requires quantitative and some qualitative changes to the previously proposed phase diagram. We find evidence for a new phase transition in the middle of the hexagonal incommensurate region and construct new phase diagrams in both the variables coverage-temperature and chemical potential-temperature. We determine the compressibility and thermal expansion in the low-pressure hexagonal incommensurate phase and values for the entropy change in several phase transitions. Below about 55 K there is evidence of solution of up to 7% of an impurity, most likely CO, in our monolayer but not the bilayer film.

  3. Polarized atomic beams for targets

    International Nuclear Information System (INIS)

    Grueebler, W.

    1984-01-01

    The basic principle of the production of polarized atomic hydrogen and deuterium beams are reviewed. The status of the present available polarization, density and intensity are presented. The improvement of atomic beam density by cooling the hydrogen atoms to low velocity is discussed. The possible use of polarized atomic beams as targets in storage rings is shown. It is proposed that polarized atomic beams can be used to produce polarized gas targets with high polarization and greatly improved density

  4. Polarized scintillator targets

    Science.gov (United States)

    van den Brandt, B.; Bunyatova, E. I.; Hautle, P.; Konter, J. A.; Mango, S.

    2000-05-01

    The hydrogen nuclei in an organic scintillator have been polarized to more than 80% and the deuterons in its fully deuterated version to 24%. The scintillator, doped with TEMPO, has been polarized dynamically in a field of 2.5 T in a vertical dilution refrigerator in which a plastic lightguide transports the scintillation light from the sample in the mixing chamber to a photomultiplier outside the cryostat. Sizeable solid samples with acceptable optical properties and light output have been prepared and successfully operated as "live" polarized targets in nuclear physics experiments.

  5. Polarized scintillator targets

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, B. van den E-mail: vandenbrandt@psi.ch; Bunyatova, E.I.; Hautle, P.; Konter, J.A.; Mango, S

    2000-05-21

    The hydrogen nuclei in an organic scintillator have been polarized to more than 80% and the deuterons in its fully deuterated version to 24%. The scintillator, doped with TEMPO, has been polarized dynamically in a field of 2.5 T in a vertical dilution refrigerator in which a plastic lightguide transports the scintillation light from the sample in the mixing chamber to a photomultiplier outside the cryostat. Sizeable solid samples with acceptable optical properties and light output have been prepared and successfully operated as 'live' polarized targets in nuclear physics experiments.

  6. Heidelberg polarized alkali source

    International Nuclear Information System (INIS)

    Kraemer, D.; Steffens, E.; Jaensch, H.; Philipps Universitaet, Marburg, Germany)

    1984-01-01

    A new atomic beam type polarized alkali ion source has been installed at Heidelberg. In order to improve the beam polarization considerably optical pumping is applied in combination with an adiabatic medium field transition which results in beams in single hyperfine sublevels. The m state population is determined by laser-induced fluorescence spectroscopy. Highly polarized beams (P/sub s/ > 0.9, s = z, zz) with intensities of 30 to 130 μA can be extracted for Li + and Na + , respectively

  7. Polarization measurement in the COMPASS polarized target

    CERN Document Server

    Kondo, K; Baum, G; Berglund, P; Doshita, N; Gautheron, F; Görtz, S; Hasegawa, T; Horikawa, N; Ishimoto, S; Iwata, T; Kisselev, Yu V; Koivuniemi, J H; Le Goff, J M; Magnon, A; Meyer, W; Reicherz, G; Matsuda, T

    2004-01-01

    Continuous wave nuclear magnetic resonance (NMR) is used to determine the target polarization in the COMPASS experiment. The system is made of the so-called Liverpool Q-meters, Yale-cards, and VME modules for data taking and system controlling. In 2001 the NMR coils were embedded in the target material, while in 2002 and 2003 the coils were mounted on the outer surface of the target cells to increase the packing factor of the material. Though the error of the measurement became larger with the outer coils than with the inner coils, we have performed stable measurements throughout the COMPASS run time for 3 years. The maximum polarization was +57% and -53% as the average in the target cells.

  8. Delineating Cultural Models

    Science.gov (United States)

    2010-08-25

    Automatic Control, 49(9), 1520-1533. Olk, H. (2003). Cultural knowledge in translation. ELT Journal , 57(2), 167-174. doi:10.1093/ elt /57.2.167 Ong...culture: A model with local convergence and global polarization. The Journal of Conflict Resolution, 41(2), 203-226. Busemeyer, J. R., & Townsend, J. T...Deffuant, G. (2006). Comparing extremism propagation patterns in continuous opinion models. Journal of Artificial Societies and Social Simulation, 9(3), 8

  9. Monolayer arrangement of fatty hydroxystearic acids on graphite: Influence of hydroxyl groups

    Energy Technology Data Exchange (ETDEWEB)

    Medina, S. [Laboratorio de Rayos-X, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Benítez, J.J.; Castro, M.A. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Cerrillos, C. [Servicio de Microscopía, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Millán, C. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Alba, M.D., E-mail: alba@icmse.csic.es [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain)

    2013-07-31

    Previous studies have indicated that long-chain linear carboxylic acids form commensurate packed crystalline monolayers on graphite even at temperatures above their melting point. This study examines the effect on the monolayer formation and structure of adding one or more secondary hydroxyl, functional groups to the stearic acid skeleton (namely, 12-hydroxystearic and 9,10-dihydroxystearic acid). Moreover, a comparative study of the monolayer formation on recompressed and monocrystalline graphite has been performed through X-ray diffraction (XRD) and Scanning Tunneling Microscopy (STM), respectively. The Differential Scanning Calorimetry (DSC) and XRD data were used to confirm the formation of solid monolayers and XRD data have provided a detailed structural analysis of the monolayers in good correspondence with obtained STM images. DSC and XRD have demonstrated that, in stearic acid and 12-hydroxystearic acid adsorbed onto graphite, the monolayer melted at a higher temperature than the bulk form of the carboxylic acid. However, no difference was observed between the melting point of the monolayer and the bulk form for 9,10-dihydroxystearic acid adsorbed onto graphite. STM results indicated that all acids on the surface have a rectangular p2 monolayer structure, whose lattice parameters were uniaxially commensurate on the a-axis. This structure does not correlate with the initial structure of the pure compounds after dissolving, but it is conditioned to favor a) hydrogen bond formation between the carboxylic groups and b) formation of hydrogen bonds between secondary hydroxyl groups, if spatially permissible. Therefore, the presence of hydroxyl functional groups affects the secondary structure and behavior of stearic acid in the monolayer. - Highlights: • Hydroxyl functional groups affect structure and behavior of acids in the monolayer. • Acids on the surface have a rectangular p2 monolayer structure. • Lattice parameters of acids are uniaxially

  10. Dynamic nuclear spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Stuhrmann, H.B. [GKSS-Forschungszentrum Geesthacht GmbH (Germany)

    1996-11-01

    Polarized neutron scattering from dynamic polarized targets has been applied to various hydrogenous materials at different laboratories. In situ structures of macromolecular components have been determined by nuclear spin contrast variation with an unprecedented precision. The experiments of selective nuclear spin depolarisation not only opened a new dimension to structural studies but also revealed phenomena related to propagation of nuclear spin polarization and the interplay of nuclear polarisation with the electronic spin system. The observation of electron spin label dependent nuclear spin polarisation domains by NMR and polarized neutron scattering opens a way to generalize the method of nuclear spin contrast variation and most importantly it avoids precontrasting by specific deuteration. It also likely might tell us more about the mechanism of dynamic nuclear spin polarisation. (author) 4 figs., refs.

  11. Time Domain Induced Polarization

    DEFF Research Database (Denmark)

    Fiandaca, Gianluca; Auken, Esben; Christiansen, Anders Vest

    2012-01-01

    Time-domain-induced polarization has significantly broadened its field of reference during the last decade, from mineral exploration to environmental geophysics, e.g., for clay and peat identification and landfill characterization. Though, insufficient modeling tools have hitherto limited the use...... of time-domaininduced polarization for wider purposes. For these reasons, a new forward code and inversion algorithm have been developed using the full-time decay of the induced polarization response, together with an accurate description of the transmitter waveform and of the receiver transfer function......%. Furthermore, the presence of low-pass filters in time-domain-induced polarization instruments affects the early times of the acquired decays (typically up to 100 ms) and has to be modeled in the forward response to avoid significant loss of resolution. The developed forward code has been implemented in a 1D...

  12. Polarized proton colliders

    International Nuclear Information System (INIS)

    Roser, T.

    1995-01-01

    High energy polarized beam collisions will open up the unique physics opportunities of studying spin effects in hard processes. This will allow the study of the spin structure of the proton and also the verification of the many well documented expectations of spin effects in perturbative QCD and parity violation in W and Z production. Proposals for polarized proton acceleration for several high energy colliders have been developed. A partial Siberian Snake in the AGS has recently been successfully tested and full Siberian Snakes, spin rotators, and polarimeters for RHIC are being developed to make the acceleration of polarized beams to 250 GeV possible. This allows for the unique possibility of colliding two 250 GeV polarized proton beams at luminosities of up to 2 x 10 32 cm -2 s -1

  13. Anisotropic optical absorption induced by Rashba spin-orbit coupling in monolayer phosphorene

    Science.gov (United States)

    Li, Yuan; Li, Xin; Wan, Qi; Bai, R.; Wen, Z. C.

    2018-04-01

    We obtain the effective Hamiltonian of the phosphorene including the effect of Rashba spin-orbit coupling in the frame work of the low-energy theory. The spin-splitting energy bands show an anisotropy feature for the wave vectors along kx and ky directions, where kx orients to ΓX direction in the k space. We numerically study the optical absorption of the electrons for different wave vectors with Rashba spin-orbit coupling. We find that the spin-flip transition from the valence band to the conduction band induced by the circular polarized light closes to zero with increasing the x-component wave vector when ky equals to zero, while it can be significantly increased to a large value when ky gets a small value. When the wave vector varies along the ky direction, the spin-flip transition can also increase to a large value, however, which shows an anisotropy feature for the optical absorption. Especially, the spin-conserved transitions keep unchanged and have similar varying trends for different wave vectors. This phenomenon provides a novel route for the manipulation of the spin-dependent property of the fermions in the monolayer phosphorene.

  14. High-performance and high-sensitivity applications of graphene transistors with self-assembled monolayers.

    Science.gov (United States)

    Yeh, Chao-Hui; Kumar, Vinod; Moyano, David Ricardo; Wen, Shao-Hsuan; Parashar, Vyom; Hsiao, She-Hsin; Srivastava, Anchal; Saxena, Preeti S; Huang, Kun-Ping; Chang, Chien-Chung; Chiu, Po-Wen

    2016-03-15

    Charge impurities and polar molecules on the surface of dielectric substrates has long been a critical obstacle to using graphene for its niche applications that involve graphene's high mobility and high sensitivity nature. Self-assembled monolayers (SAMs) have been found to effectively reduce the impact of long-range scatterings induced by the external charges. Yet, demonstrations of scalable device applications using the SAMs technique remains missing due to the difficulties in the device fabrication arising from the strong surface tension of the modified dielectric environment. Here, we use patterned SAM arrays to build graphene electronic devices with transport channels confined on the modified areas. For high-mobility applications, both rigid and flexible radio-frequency graphene field-effect transistors (G-FETs) were demonstrated, with extrinsic cutoff frequency and maximum oscillation frequency enhanced by a factor of ~2 on SiO2/Si substrates. For high sensitivity applications, G-FETs were functionalized by monoclonal antibodies specific to cancer biomarker chondroitin sulfate proteoglycan 4, enabling its detection at a concentration of 0.01 fM, five orders of magnitude lower than that detectable by a conventional colorimetric assay. These devices can be very useful in the early diagnosis and monitoring of a malignant disease. Copyright © 2015 Elsevier B.V. All rights reserved.

  15. Synchronization modulation increases transepithelial potentials in MDCK monolayers through Na/K pumps.

    Directory of Open Access Journals (Sweden)

    Vu Tran

    Full Text Available Transepithelial potential (TEP is the voltage across a polarized epithelium. In epithelia that have active transport functions, the force for transmembrane flux of an ion is dictated by the electrochemical gradient in which TEP plays an essential role. In epithelial injury, disruption of the epithelial barrier collapses the TEP at the wound edge, resulting in the establishment of an endogenous wound electric field (∼100 mV/mm that is directed towards the center of the wound. This endogenous electric field is implicated to enhance wound healing by guiding cell migration. We thus seek techniques to enhance the TEP, which may increase the wound electric fields and enhance wound healing. We report a novel technique, termed synchronization modulation (SM using a train of electric pulses to synchronize the Na/K pump activity, and then modulating the pumping cycles to increase the efficiency of the Na/K pumps. Kidney epithelial monolayers (MDCK cells maintain a stable TEP and transepithelial resistance (TER. SM significantly increased TEP over four fold. Either ouabain or digoxin, which block Na/K pump, abolished SM-induced TEP increases. In addition to the pump activity, basolateral distribution of Na/K pumps is essential for an increase in TEP. Our study for the first time developed an electrical approach to significantly increase the TEP. This technique targeting the Na/K pump may be used to modulate TEP, and may have implication in wound healing and in diseases where TEP needs to be modulated.

  16. Inhibition of copper corrosion by the formation of Schiff base self-assembled monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jing [Department of Chemical and Biological Engineering, Guilin University of Technology, Guilin 541004 (China); Liu, Zheng, E-mail: lisa4.6@163.com [Department of Chemical and Biological Engineering, Guilin University of Technology, Guilin 541004 (China); Han, Guo-Cheng, E-mail: hangc1981@163.com [School of Life and Environmental Sciences, Guilin University of Electronic Technology, Guilin 541004 (China); Chen, Shi-Liang [Department of Chemical and Biological Engineering, Guilin University of Technology, Guilin 541004 (China); Chen, Zhencheng [School of Life and Environmental Sciences, Guilin University of Electronic Technology, Guilin 541004 (China)

    2016-12-15

    Highlights: • The highest inhibition efficiency was 93.9% for CO{sub 2}-saturated simulative oilfield water. • HD2-SAMs on copper surface exhibited excellent inhibition effect at 30 °C. • The adsorption behavior of HD2-SAM followed the Langmuir adsorption isotherm. • The adsorption behavior of HD2-SAM is a typically chemical adsorption. - Abstract: Self-assembled monolayers (SAMs) of 4-((2-thiophenecarboxylic acid hydrazide) methylene) benzoic acid (HD2) (denoted as HD2-SAMs) were formed on copper surface. The SAMs were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. Polarization curve and weight loss methods indicated that the highest inhibition efficiency was 93.9% for CO{sub 2}-saturated simulative oilfield water at a self-assembled time of 3 h. Potential-time curve, electrochemical impedance tests showed that HD2-SAMs on copper surface exhibited excellent inhibition effect at 30 °C. The adsorption behavior of HD2-SAMs on the copper surface followed the Langmuir adsorption isotherm, which was indicative of typically chemical adsorption. Quantum chemistry calculation showed that O and N atoms can interact with Cu atoms by coordination bonds which were the mainly active area of the adsorption of HD2 molecules.

  17. Ozone Oxidation of Self-Assembled Monolayers on SiOx-Coated Zinc Selenide Surfaces

    Science.gov (United States)

    McIntire, T. M.; Ryder, O. S.; Finlayson-Pitts, B. J.

    2008-12-01

    Airborne particles are important for visibility, human health, climate, and atmospheric reactions. Atmospheric particles contain a significant fraction of organics and such compounds present on airborne particles are susceptible to oxidation by atmospheric oxidants, such as OH, ozone, halogen atoms, and nitrogen trioxide. Oxidized organics associated with airborne particles are thought to be polar, hygroscopic species with enhanced cloud-nucleating properties. Oxide layers on silicon, or SiO2-coated substrates, act as models of environmentally relevant surfaces such as dust particles upon which organics adsorb. We have shown previously that ozone oxidation of unsaturated self-assembled monolayers (SAMs) on silicon attenuated total reflectance (ATR) crystals leads to the formation of carbonyl groups and micron-sized, hydrophobic organic aggregates surrounded by carbon depleted substrate that do not have increased water uptake as previously assumed. Reported here are further ATR-FTIR studies of the oxidation of alkene SAMs on ZnSe and SiO2-coated ZnSe. These substrates have the advantage that they transmit below 1500 cm-1, allowing detection of additional product species. These experiments show that the loss of C=C and formation of carbonyl groups is also accompanied by formation of a peak at 1110 cm-1, attributed to the secondary ozonide. Details concerning the products and mechanism of ozonolysis of alkene SAMs on surfaces based on these new data are presented and the implications for the oxidation of alkenes on airborne dust particles are discussed.

  18. Plasma polarization spectroscopy

    International Nuclear Information System (INIS)

    Iwamae, Atsushi; Horimoto, Yasuhiro; Fujimoto, Takashi; Hasegawa, Noboru; Sukegawa, Kouta; Kawachi, Tetsuya

    2005-01-01

    The electron velocity distribution function (EVDF) in plasma can be anisotropic in laser-produced plasmas. We have developed a new technique to evaluate the polarization degree of the emission lines in the extreme vacuum ultra violet wavelength region. The polarization of the emission lines and the continuums from the lithium-like nitrogen and from helium- and hydrogen-like carbon in recombining plasma is evaluated. Particle simulation in the velocity space gives the time scale for relaxation of anisotropic EVDFs. (author)

  19. Ultracold Polar Molecules

    Science.gov (United States)

    2016-04-01

    AFRL-AFOSR-UK-TR-2016-0005 Ultracold Polar Molecules Jeremy Hutson UNIVERSITY OF DURHAM Final Report 04/01/2016 DISTRIBUTION A: Distribution approved...DATES COVERED (From - To) 15-Jan-2010 to 14-Jul-2015 4. TITLE AND SUBTITLE Final Report on Grant FA8655-10-1-3033 on Ultracold Polar Molecules 5a...formation of ultracold 87RbCs molecules in their rovibrational ground state by magnetoassociation followed by STIRAP, resulting in 14 papers acknowledging

  20. Hsp Polarization Verification

    Science.gov (United States)

    Bless, Robert

    1991-07-01

    This proposal defines the procedure for determining the instrumental polarization of the polarimetric IDT (IDT#1, POL) on the HSP. 1 of 2 unpolarized standard stars wil be observed using various filter-polarizer combinations. These observations will permit the instrumental polarization to be calibrated. The instrumental polarization must be determined to a high precision in order to vectoriallly remove it from HSP polarization observations to determine the actual astronomical polarization. Final run of proposal will look at one of 2 possible stars previously observed to get another look at the throughput. Revision History: Mark H. Slovak 8/30/88 Translated to V2 proposal instructions (RPSS V6.2) S. Laurent 1/20/89 Updated: Sally Laurent 2/24/89, 3/20/89, 4/13/89, 5/12/89 Modified: P. Stanley 1/15/90 - change to use CTA selected targets only; Fixes for aberration problem - SALM 7/30/90; Based on SV/HSP 1386. New submission changed targets and revised scheduling strategy. Revised: 26 Aug 92 J. Dolan, L. Walter, P. Reppert want to re-run the proposal (3985) one last time to bring down errors.

  1. Radiation Effects on the Cytoskeleton of Endothelial Cells and Endothelial Monolayer Permeability

    International Nuclear Information System (INIS)

    Gabrys, Dorota; Greco, Olga; Patel, Gaurang; Prise, Kevin M.; Tozer, Gillian M.; Kanthou, Chryso

    2007-01-01

    Purpose: To investigate the effects of radiation on the endothelial cytoskeleton and endothelial monolayer permeability and to evaluate associated signaling pathways, which could reveal potential mechanisms of known vascular effects of radiation. Methods and Materials: Cultured endothelial cells were X-ray irradiated, and actin filaments, microtubules, intermediate filaments, and vascular endothelial (VE)-cadherin junctions were examined by immunofluorescence. Permeability was determined by the passage of fluorescent dextran through cell monolayers. Signal transduction pathways were analyzed using RhoA, Rho kinase, and stress-activated protein kinase-p38 (SAPK2/p38) inhibitors by guanosine triphosphate-RhoA activation assay and transfection with RhoAT19N. The levels of junction protein expression and phosphorylation of myosin light chain and SAPK2/p38 were assessed by Western blotting. The radiation effects on cell death were verified by clonogenic assays. Results: Radiation induced rapid and persistent actin stress fiber formation and redistribution of VE-cadherin junctions in microvascular, but not umbilical vein endothelial cells, and microtubules and intermediate filaments remained unaffected. Radiation also caused a rapid and persistent increase in microvascular permeability. RhoA-guanosine triphosphatase and Rho kinase were activated by radiation and caused phosphorylation of downstream myosin light chain and the observed cytoskeletal and permeability changes. SAPK2/p38 was activated by radiation but did not influence either the cytoskeleton or permeability. Conclusion: This study is the first to show rapid activation of the RhoA/Rho kinase by radiation in endothelial cells and has demonstrated a link between this pathway and cytoskeletal remodeling and permeability. The results also suggest that the RhoA pathway might be a useful target for modulating the permeability and other effects of radiation for therapeutic gain

  2. Polarized Light Microscopy

    Science.gov (United States)

    Frandsen, Athela F.

    2016-01-01

    Polarized light microscopy (PLM) is a technique which employs the use of polarizing filters to obtain substantial optical property information about the material which is being observed. This information can be combined with other microscopy techniques to confirm or elucidate the identity of an unknown material, determine whether a particular contaminant is present (as with asbestos analysis), or to provide important information that can be used to refine a manufacturing or chemical process. PLM was the major microscopy technique in use for identification of materials for nearly a century since its introduction in 1834 by William Fox Talbot, as other techniques such as SEM (Scanning Electron Microscopy), FTIR (Fourier Transform Infrared spectroscopy), XPD (X-ray Powder Diffraction), and TEM (Transmission Electron Microscopy) had not yet been developed. Today, it is still the only technique approved by the Environmental Protection Agency (EPA) for asbestos analysis, and is often the technique first applied for identification of unknown materials. PLM uses different configurations in order to determine different material properties. With each configuration additional clues can be gathered, leading to a conclusion of material identity. With no polarizing filter, the microscope can be used just as a stereo optical microscope, and view qualities such as morphology, size, and number of phases. With a single polarizing filter (single polars), additional properties can be established, such as pleochroism, individual refractive indices, and dispersion staining. With two polarizing filters (crossed polars), even more can be deduced: isotropy vs. anisotropy, extinction angle, birefringence/degree of birefringence, sign of elongation, and anomalous polarization colors, among others. With the use of PLM many of these properties can be determined in a matter of seconds, even for those who are not highly trained. McCrone, a leader in the field of polarized light microscopy, often

  3. Establishment of a long-term three-dimensional primary culture of mouse glandular stomach epithelial cells within the stem cell niche

    Energy Technology Data Exchange (ETDEWEB)

    Katano, Takahito [Department of Gastroenterology and Metabolism, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601 (Japan); Ootani, Akifumi [Department of Gastroenterology and GI Endoscopy Center, Shin-Kokura Hospital, Federation of National Public Service Personnel Mutual Aid Associations, 1-3-1 Kanada, Kokurakita-ku, Kitakyushu 803-0816 (Japan); Department of Internal Medicine, Faculty of Medicine, Saga University, 5-1-1 Nabeshima, Saga 849-8501 (Japan); Mizoshita, Tsutomu, E-mail: tmizoshi@med.nagoya-cu.ac.jp [Department of Gastroenterology and Metabolism, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601 (Japan); Tanida, Satoshi; Tsukamoto, Hironobu; Ozeki, Keiji; Ebi, Masahide; Mori, Yoshinori; Kataoka, Hiromi; Kamiya, Takeshi [Department of Gastroenterology and Metabolism, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601 (Japan); Toda, Shuji [Department of Pathology and Microbiology, Faculty of Medicine, Saga University, 5-1-1 Nabeshima, Saga 849-8501 (Japan); Joh, Takashi [Department of Gastroenterology and Metabolism, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601 (Japan)

    2013-03-22

    Highlights: ► We established a 3D culture system to allow long-term culture of stomach cells. ► In this culture system, gastric epithelial cells grew for about 3 months. ► The cultured cells differentiated into multi-units of the stomach. ► This culture method should be useful for elucidating the cause of gastric diseases. -- Abstract: Compared to the small intestine and colon, little is known about stem cells in the stomach because of a lack of specific stem cell markers and an in vitro system that allows long-term culture. Here we describe a long-term three-dimensional (3D) primary gastric culture system within the stem cell niche. Glandular stomach cells from neonatal mice cultured in collagen gel yielded expanding sphere-like structures for 3 months. The wall of the gastrospheres consisted of a highly polarized epithelial monolayer with an outer lining of myofibroblasts. The epithelial cells showed a tall columnar cell shape, basal round nuclei, and mucus-filled cytoplasm as well as expression of MUC5AC, indicating differentiation into gastric surface mucous cells. These cells demonstrated the features of fully differentiated gastric surface mucous cells such as microvilli, junctional complexes, and glycogen and secretory granules. Fewer than 1% of cultured epithelial cells differentiated into enteroendocrine cells. Active proliferation of the epithelial cells and many apoptotic cells in the inner lumen revealed the rapid cell turnover in gastrospheres in vitro. This method enables us to investigate the role of signaling between cell–cell and epithelial–mesenchymal interactions in an environment that is extremely similar to the in vivo environment.

  4. Establishment of a long-term three-dimensional primary culture of mouse glandular stomach epithelial cells within the stem cell niche

    International Nuclear Information System (INIS)

    Katano, Takahito; Ootani, Akifumi; Mizoshita, Tsutomu; Tanida, Satoshi; Tsukamoto, Hironobu; Ozeki, Keiji; Ebi, Masahide; Mori, Yoshinori; Kataoka, Hiromi; Kamiya, Takeshi; Toda, Shuji; Joh, Takashi

    2013-01-01

    Highlights: ► We established a 3D culture system to allow long-term culture of stomach cells. ► In this culture system, gastric epithelial cells grew for about 3 months. ► The cultured cells differentiated into multi-units of the stomach. ► This culture method should be useful for elucidating the cause of gastric diseases. -- Abstract: Compared to the small intestine and colon, little is known about stem cells in the stomach because of a lack of specific stem cell markers and an in vitro system that allows long-term culture. Here we describe a long-term three-dimensional (3D) primary gastric culture system within the stem cell niche. Glandular stomach cells from neonatal mice cultured in collagen gel yielded expanding sphere-like structures for 3 months. The wall of the gastrospheres consisted of a highly polarized epithelial monolayer with an outer lining of myofibroblasts. The epithelial cells showed a tall columnar cell shape, basal round nuclei, and mucus-filled cytoplasm as well as expression of MUC5AC, indicating differentiation into gastric surface mucous cells. These cells demonstrated the features of fully differentiated gastric surface mucous cells such as microvilli, junctional complexes, and glycogen and secretory granules. Fewer than 1% of cultured epithelial cells differentiated into enteroendocrine cells. Active proliferation of the epithelial cells and many apoptotic cells in the inner lumen revealed the rapid cell turnover in gastrospheres in vitro. This method enables us to investigate the role of signaling between cell–cell and epithelial–mesenchymal interactions in an environment that is extremely similar to the in vivo environment

  5. The evolution of tensor polarization

    International Nuclear Information System (INIS)

    Huang, H.; Lee, S.Y.; Ratner, L.

    1993-01-01

    By using the equation of motion for the vector polarization, the spin transfer matrix for spin tensor polarization, the spin transfer matrix for spin tensor polarization is derived. The evolution equation for the tensor polarization is studied in the presence of an isolate spin resonance and in the presence of a spin rotor, or snake

  6. Comparative evaluation of nano-CuO crossing Caco-2 cell monolayers and cellular uptake

    Science.gov (United States)

    Chen, Gao; Lianqin, Zhu; Fenghua, Zhu; Fang, Zheng; Mingming, Song; Kai, Huang

    2015-04-01

    Different concentrations of CuSO4, micro-CuO, and nano-CuO were added to Caco-2 cell monolayers to study the absorption and transport characteristics in this epithelial cell model. Nano-CuO nanoparticles had a diameter of 10-20 nm. Inhibitors of endocytosis were used to explore whether nano-CuO could enter the Caco-2 cell in the form of nanoparticles, and to ascertain the endocytotic pathway that is involved in the transport process. The apparent permeability coefficient ( P app) of CuSO4 and nano-CuO increased with the Cu concentration in the culture medium ( p Caco-2 cells ( p > 0.05). When the Cu concentration in the culture medium was in the range 31.25-500 μM, the P app value of Caco-2 cells incubated with nano-CuO was significantly higher than that obtained with CuSO4. The latter was also significantly higher than that when cells were incubated with micro-CuO ( p Caco-2 cell in the form of nanoparticles, and were found in the cytoplasm, vesicles, lysosomes, and cell nuclei. Several inhibitors of endocytosis effectively prevented the entry of nano-CuO into the Caco-2 cells. It was concluded that nano-CuO particles can enter the Caco-2 cells through several cellular endocytotic pathways.

  7. Collapse of Langmuir monolayer at lower surface pressure: Effect of hydrophobic chain length

    Energy Technology Data Exchange (ETDEWEB)

    Das, Kaushik, E-mail: kaushikdas2089@gmail.com; Kundu, Sarathi [Physical Sciences Division, Institute of Advanced Study in Science and Technology, Vigyan Path, Paschim Boragaon, Garchuk, Guwahati, Assam 781035 (India)

    2016-05-23

    Long chain fatty acid molecules (e.g., stearic and behenic acids) form a monolayer on water surface in the presence of Ba{sup 2+} ions at low subphase pH (≈ 5.5) and remain as a monolayer before collapse generally occurs at higher surface pressure (π{sub c} > 50 mN/m). Monolayer formation is verified from the surface pressure vs. area per molecule (π-A) isotherms and also from the atomic force microscopy (AFM) analysis of the films deposited by single upstroke of hydrophilic Si (001) substrate through the monolayer covered water surface. At high subphase pH (≈ 9.5), barium stearate molecules form multilayer structure at lower surface pressure which is verified from the π-A isotherms and AFM analysis of the film deposited at 25 mN/m. Such monolayer to multilayer structure formation or monolayer collapse at lower surface pressure is unusual as at this surface pressure generally fatty acid salt molecules form a monolayer on the water surface. Formation of bidentate chelate coordination in the metal containing headgroups is the reason for such monolayer to multilayer transition. However, for longer chain barium behenate molecules only monolayer structure is maintained at that high subphase pH (≈ 9.5) due to the presence of relatively more tail-tail hydrophobic interaction.

  8. Active cell-matrix coupling regulates cellular force landscapes of cohesive epithelial monolayers

    Science.gov (United States)

    Zhao, Tiankai; Zhang, Yao; Wei, Qiong; Shi, Xuechen; Zhao, Peng; Chen, Long-Qing; Zhang, Sulin

    2018-03-01

    Epithelial cells can assemble into cohesive monolayers with rich morphologies on substrates due to competition between elastic, edge, and interfacial effects. Here we present a molecularly based thermodynamic model, integrating monolayer and substrate elasticity, and force-mediated focal adhesion formation, to elucidate the active biochemical regulation over the cellular force landscapes in cohesive epithelial monolayers, corroborated by microscopy and immunofluorescence studies. The predicted extracellular traction and intercellular tension are both monolayer size and substrate stiffness dependent, suggestive of cross-talks between intercellular and extracellular activities. Our model sets a firm ground toward a versatile computational framework to uncover the molecular origins of morphogenesis and disease in multicellular epithelia.

  9. Monitoring the hydration of DNA self-assembled monolayers using an extensional nanomechanical resonator

    DEFF Research Database (Denmark)

    Cagliani, Alberto; Kosaka, Priscila; Tamayo, Javier

    2012-01-01

    We have fabricated an ultrasensitive nanomechanical resonator based on the extensional vibration mode to weigh the adsorbed water on self-assembled monolayers of DNA as a function of the relative humidity. The water adsorption isotherms provide the number of adsorbed water molecules per nucleotide...... for monolayers of single stranded (ss) DNA and after hybridization with the complementary DNA strand. Our results differ from previous data obtained with bulk samples, showing the genuine behavior of these self-assembled monolayers. The hybridization cannot be inferred from the water adsorption isotherms due...... on the interaction between water and self-assembled monolayers of nucleic acids....

  10. Thermodynamic and real-space structural evidence of a 2D critical point in phospholipid monolayers

    DEFF Research Database (Denmark)

    Nielsen, Lars K.; Bjørnholm, Thomas; Mouritsen, Ole G.

    2007-01-01

    The two-dimensional phase diagram of phospholipid monolayers at air-water interfaces has been constructed from Langmuir compression isotherms. The coexistence region between the solid and fluid phases of the monolayer ends at the critical temperature of the transition. The small-scale lateral...... structure of the monolayers has been imaged by atomic force microscopy in the nm to mu m range at distinct points in the phase diagram. The lateral structure is immobilized by transferring the monolayer from an air-water interface to a solid mica support using Langmuir-Blodgett techniques. A transfer...

  11. Polarized Electrons at Jefferson Laboratory

    Energy Technology Data Exchange (ETDEWEB)

    Sinclair, C.K.

    1997-12-31

    The CEBAF accelerator at Jefferson laboratory can deliver CW electron beams to three experimental halls simultaneously. A large fraction of the approved scientific program at the lab requires polarized electron beams. Many of these experiments, both polarized and unpolarized, require high average beam current as well. Since all electrons delivered to the experimental halls originate from the same cathode, delivery of polarized beam to a single hall requires using the polarized source to deliver beam to all experiments in simultaneous operation. The polarized source effort at Jefferson Lab is directed at obtaining very long polarized source operational lifetimes at high average current and beam polarization; at developing the capability to deliver all electrons leaving the polarized source to the experimental halls; and at delivering polarized beam to multiple experimental halls simultaneously.initial operational experience with the polarized source will be presented.

  12. Polarized electrons at Jefferson laboratory

    International Nuclear Information System (INIS)

    The CEBAF accelerator at Jefferson laboratory can deliver CW electron beams to three experimental halls simultaneously. A large fraction of the approved scientific program at the lab requires polarized electron beams. Many of these experiments, both polarized and unpolarized, require high average beam current as well. Since all electrons delivered to the experimental halls originate from the same cathode, delivery of polarized beam to a single hall requires using the polarized source to deliver beam to all experiments in simultaneous operation. The polarized source effort at Jefferson Lab is directed at obtaining very long polarized source operational lifetimes at high average current and beam polarization; at developing the capability to deliver all electrons leaving the polarized source to the experimental halls; and at delivering polarized beam to multiple experimental halls simultaneously. Initial operational experience with the polarized source will be presented

  13. Polar low monitoring

    Science.gov (United States)

    Bobylev, Leonid; Zabolotskikh, Elizaveta; Mitnik, Leonid

    2010-05-01

    Polar lows are intense mesoscale atmospheric low pressure weather systems, developing poleward of the main baroclinic zone and associated with high surface wind speeds. Small size and short lifetime, sparse in-situ observations in the regions of their development complicate polar low study. Our knowledge of polar lows and mesocyclones has come almost entirely during the period of satellite remote sensing since, by virtue of their small horizontal scale, it was rarely possible to analyse these lows on conventional weather charts using only the data from the synoptic observing network. However, the effects of intense polar lows have been felt by coastal communities and seafarers since the earliest times. These weather systems are thought to be responsible for the loss of many small vessels over the centuries, although the nature of the storms was not understood and their arrival could not be predicted. The actuality of the polar low research is stipulated by their high destructive power: they are a threat to such businesses as oil and gas exploration, fisheries and shipping. They could worsen because of global warming: a shrinking of sea ice around the North Pole, which thawed to its record minimum in the summer of 2007, is likely to give rise to more powerful storms that form only over open water and can cause hurricane-strength winds. Therefore, study of polar lows, their timely detection, tracking and forecasting represents a challenge for today meteorology. Satellite passive microwave data, starting from Special Sensor Microwave Imager (SSM/I) onboard Defense Meteorological Satellite Program (DMSP) satellite, remain invaluable source of regularly available remotely sensed data to study polar lows. The sounding in this spectral range has several advantages in comparison with observations in visible and infrared ranges and Synthetic Aperture Radar (SAR) data: independence on day time and clouds, regularity and high temporal resolution in Polar Regions. Satellite

  14. Polarized protons at RHIC

    International Nuclear Information System (INIS)

    Tannenbaum, M.J.

    1990-12-01

    The Physics case is presented for the use of polarized protons at RHIC for one or two months each year. This would provide a facility with polarizations of approx-gt 50% high luminosity ∼2.0 x 10 32 cm -2 s -1 , the possibility of both longitudinal and transverse polarization at the interaction regions, and frequent polarization reversal for control of systematic errors. The annual integrated luminosity for such running (∼10 6 sec per year) would be ∫ Ldt = 2 x 10 38 cm -2 -- roughly 20 times the total luminosity integrated in ∼ 10 years of operation of the CERN Collider (∼10 inverse picobarns, 10 37 cm -2 ). This facility would be unique in the ability to perform parity-violating measurements and polarization test of QCD. Also, the existence of p-p collisions in a new energy range would permit the study of ''classical'' reactions like the total cross section and elastic scattering, etc., and serve as a complement to measurements from p-bar p colliders. 11 refs

  15. The Bochum Polarized Target

    International Nuclear Information System (INIS)

    Reicherz, G.; Goertz, S.; Harmsen, J.; Heckmann, J.; Meier, A.; Meyer, W.; Radtke, E.

    2001-01-01

    The Bochum 'Polarized Target' group develops the target material 6 LiD for the COMPASS experiment at CERN. Several different materials like alcohols, alcanes and ammonia are under investigation. Solid State Targets are polarized in magnetic fields higher than B=2.5T and at temperatures below T=1K. For the Dynamic Nuclear Polarization process, paramagnetic centers are induced chemically or by irradiation with ionizing beams. The radical density is a critical factor for optimization of polarization and relaxation times at adequate magnetic fields and temperatures. In a high sensitive EPR--apparatus, an evaporator and a dilution cryostat with a continuous wave NMR--system, the materials are investigated and optimized. To improve the polarization measurement, the Liverpool NMR-box is modified by exchanging the fixed capacitor for a varicap diode which not only makes the tuning very easy but also provides a continuously tuned circuit. The dependence of the signal area upon the circuit current is measured and it is shown that it follows a linear function

  16. In-line Fiber Polarizer

    OpenAIRE

    Perumalsamy, Priya

    1998-01-01

    Polarizers and polarization devices are important components in fiber optic communication and sensor systems. There is a growing need for efficient low loss components that are compatible with optical fibers. An all fiber in-line polarizer is a more desirable alternative that could be placed at appropriate intervals along communication links. An in-line fiber polarizer was fabricated and tested. The in-line fiber polarizer operates by coupling optical energy propagatin...

  17. Transport of curcumin derivatives in Caco-2 cell monolayers.

    Science.gov (United States)

    Zeng, Zhen; Shen, Zhe L; Zhai, Shuo; Xu, Jia L; Liang, Hui; Shen, Qin; Li, Qing Y

    2017-08-01

    Curcumin (Cur) is a strong natural antioxidant, who can prevent multiple diseases such as anti-cancer, anti-inflammatory, have a resistance to alzheimer's disease and various malignant diseases. But it has poor oral bioavailability due to its poor aqueous solubility, as well as instability. While its novel derivatives (CB and FE), showed better anti-tumor activity, better anti-oxidant activity and better stability than the original drug (Cur). The aim of this study was to study the intestinal transport of Cur, CB and FE using an in vitro Caco-2 cell monolayer model. The results showed that Cur had a lower permeability coefficient (1.13×10 -6 ±0.11×10 -6 cm/s) for apical-to-basolated (AP-BL) transport at 25μM, while the transport rate for AP to BL flux of CB (3.18×10 -6 ±0.31×10 -6 cm/s) and FE (5.28×10 -6 ±0.83×10 -6 cm/s) were significantly greater than that of Cur. The efflux ratio (ER) value at the concentration of 25μM was 1.31 for Cur, 1.26 for CB and 1.33 for FE, suggesting there was no active efflux involved in the translocation across the Caco-2 cell monolayers for the three compounds. Furthermore, the transport flux of CB and FE was in a concentration dependent manner, suggesting the intestinal transport mechanism in them was passive transport. In summary, the results demonstrated that both the intestinal permeability of CB and FE across Caco-2 cell monolayers was significantly improved compare to Cur. Thus they might show a higher oral bioavailability in vivo, and show the potential application in clinic or nutraceutical. Copyright © 2017 Elsevier B.V. All rights reserved.

  18. Metal adsorption on monolayer blue phosphorene: A first principles study

    Science.gov (United States)

    Khan, Imran; Son, Jicheol; Hong, Jisang

    2018-01-01

    We investigated the electronic structure, adsorption energies, magnetic properties, dipole moment and work function of metal adatoms (Mg, Cr, Mo, Pd, Pt, and Au) adsorption on a blue phosphorene monolayer. For Mg, Pt and Au metals, the most stable state was found in hollow site while for Cr, Mo and Pd metals we found an adsorption in valley site. We suggest that the Pd and Pt atoms prefer 2D growth mode while the Mg, Cr, Mo and Au atoms prefer 3D island growth mode on monolayer phosphorene. The electronic band structures and magnetic properties were dependent on the doping site and dopant materials. For instance, the semiconducting features were preserved in Mg, Pd, Pt, and Au doped systems. However, the Cr and Mo doped systems displayed half-metallic band structures. The total magnetic moment of 4.05, 2.0 and 0.77 μB /impurity atom were obtained in Cr, Mo and Au doped systems whereas the Mg, Pd and Pt doped systems remained nonmagnetic. We also investigated the magnetic interaction between two transition metal impurities. We observed ferromagnetic coupling between two transition metal impurities in Cr and Mo doped systems while the Au doped system displayed almost degenerated magnetic state. For Mg, Cr, and Mo adsorptions, we found relatively large values of dipole moments compared to those in the Pd, Pt and Au adsorptions. This resulted in a significant suppression of the work function in Mg, Cr and Mo adsorptions. Overall, adsorption can tune the physical and magnetic properties of phosphorene monolayer.

  19. Fabrication, characterization, and applications of nanometer-scale features within organomercaptan self- assembled monolayers

    Science.gov (United States)

    Schoer, Jonathan Kevin

    1997-10-01

    Nanometer-scale features in organomercaptan self- assembled monolayers (SAMs) on Au(111) substrates were prepared by three methods: electrochemical enhancement of adventitious defects, electrochemical enhancement of template-molecule-induced pores, and scanning tunneling microscopy (STM)-induced patterning. The resulting features were characterized by electrochemistry, scanning electron microscopy (STM), and electrochemical STM (ECSTM). Finally, we applied STM-induced patterning methods to lithographic fabrication of features with critical dimensions resists and barrier layers to electron and mass transfer. Further, the nanometer-scale features act as nanometer- size electrodes. Measurements of the physical dimensions of nanometer- scale features by STM can be combined with microelectrode theory to calculate a value for the limiting current. Comparison of this value with that obtained directly from conventional electrochemistry provides qualitative agreement. From in-depth studies of the mechanistic aspects of STM- induced patterning of organomercaptan SAMs we determined that this process is controlled by a complex combination of parameters defined by both the instrument and the chemical and physical properties of materials in the vicinity of the tip. In particular, the patterning is dependent on the magnitude and polarity of the gap bias, the Coulomb dose, and the composition of the gap. From this information we propose a detailed multi-step model for STM-induced removal of n-alkanethiol SAMs from Au surfaces. The model is partially based on our observation that high tip bias ([>]~[+]2.30 V) results in removal of SAMs by Faradaic electrochemical processes in which the n-octadecyl mercaptan monolayer is: (1) disrupted by the tip, (2) electrochemically desorbed, and (3) removed by the scanning action of the tip. Further, we determined that at biases above a second threshold (~[+]4.0 V) the patterning becomes irreproducible because the patterning mechanism changes to

  20. Acanthamoeba culbertsoni isolated from a clinical case with intraocular dissemination: Structure and in vitro analysis of the interaction with hamster cornea and MDCK epithelial cell monolayers.

    Science.gov (United States)

    González-Robles, Arturo; Omaña-Molina, Maritza; Salazar-Villatoro, Lizbeth; Flores-Maldonado, Catalina; Lorenzo-Morales, Jacob; Reyes-Batlle, María; Arnalich-Montiel, Francisco; Martínez-Palomo, Adolfo

    2017-12-01

    Acanthamoeba culbertsoni trophozoites, previously isolated from a human keratitis case with severe intraocular damage, were maintained in axenic culture. Co-incubation of amoebae with MDCK cell monolayers demonstrated an apparent preference of the amoebae to introduce themselves between the cells. The trophozoites appeared to cross the cell monolayer through the tight junctions, which resulted in decreased trans-epithelial resistance (TER) measurements. Unexpectedly, after co-incubation of amoebae with hamster corneas, we observed that the trophozoites were able to cross the different cell layers and reach the corneal stroma after only 12 h of interaction, in contrast to other Acanthamoeba species. These observations suggest that this A. culbertsoni isolate is particularly pathogenic. Further research with diverse methodologies needs to be performed to explain the unique behavior of this Acanthamoeba strain. Copyright © 2017 Elsevier Inc. All rights reserved.

  1. Fractal growth in impurity-controlled solidification in lipid monolayers

    DEFF Research Database (Denmark)

    Fogedby, Hans C.; Sørensen, Erik Schwartz; Mouritsen, Ole G.

    1987-01-01

    A simple two-dimensional microscopic model is proposed to describe solidifcation processes in systems with impurities which are miscible only in the fluid phase. Computer simulation of the model shows that the resulting solids are fractal over a wide range of impurity concentrations and impurity...... diffusional constants. A fractal-forming mechanism is suggested for impurity-controlled solidification which is consistent with recent experimental observations of fractal growth of solid phospholipid domains in monolayers. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....

  2. Friction anisotropy-driven domain imaging on exfoliated monolayer graphene.

    Science.gov (United States)

    Choi, Jin Sik; Kim, Jin-Soo; Byun, Ik-Su; Lee, Duk Hyun; Lee, Mi Jung; Park, Bae Ho; Lee, Changgu; Yoon, Duhee; Cheong, Hyeonsik; Lee, Ki Ho; Son, Young-Woo; Park, Jeong Young; Salmeron, Miquel

    2011-07-29

    Graphene produced by exfoliation has not been able to provide an ideal graphene with performance comparable to that predicted by theory, and structural and/or electronic defects have been proposed as one cause of reduced performance. We report the observation of domains on exfoliated monolayer graphene that differ by their friction characteristics, as measured by friction force microscopy. Angle-dependent scanning revealed friction anisotropy with a periodicity of 180° on each friction domain. The friction anisotropy decreased as the applied load increased. We propose that the domains arise from ripple distortions that give rise to anisotropic friction in each domain as a result of the anisotropic puckering of the graphene.

  3. Hybrid plasmonic/semiconductor nanoparticle monolayer assemblies as hyperbolic metamaterials

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Ozel, Tuncay; Mutlugun, Evren

    2014-01-01

    We show that hybrid nanostructures made of alternating colloidal semiconductor quantum dot and metal nanoparticle monolayers can function as multilayer hyperbolic meta-materials. By choosing the thickness of the spacer between the quantum dot and nanoparticle layers, one can achieve the indefinite...... effective permittivity tensor of the structure. This results in increased photonic density of states and strong enhancement of quantum dot luminescence, in line with recent experimental results. Our findings demonstrate that hyperbolic metamaterials can increase the radiative decay rate of emission centers...

  4. The dependence of lipid monolayer lipolysis on surface pressure.

    OpenAIRE

    Hall, D G

    1992-01-01

    Brönsted-Bjerrum theory [Brönsted (1922) Z. Phys. Chem. 102, 169-207; (1925) Z. Phys. Chem. 115, 337-364; Bjerrum (1924) Z. Phys. Chem. 108, 82-100] as applied to reactions at interfaces is used to interpret published data on the lipolysis of dinonanoyl phosphatidylcholine monolayers by pancreatic phospholipase A2. Reasonable quantitative agreement between theoretical and experimental results occurs when the reported effects of surface pressure on the amount of adsorbed enzyme are used togeth...

  5. Temperature effects in a nonlinear model of monolayer Scheibe aggregates

    DEFF Research Database (Denmark)

    Bang, Ole; Christiansen, Peter Leth; If, F.

    1994-01-01

    of the complicated spectrum of the noise are considered: time independent, spatially white noise, simply corresponding to disorder in the arrangement of the molecules, and pure white noise. Parameter values are found by comparison with experiments by Mobius and Kuhn [Isr. J. Chem. 18, 375 (1979)] and order......A nonlinear dynamical model of molecular monolayers arranged in Scheibe aggregates is derived from a proper Hamiltonian. Thermal fluctuations of the phonons are included. The resulting equation for the excitons is the two dimensional nonlinear Schrodinger equation with noise. Two limits...

  6. Nanocomposite Materials of Alternately Stacked C60 Monolayer and Graphene

    International Nuclear Information System (INIS)

    Ishikawa, M.; Miura, K.; Kamiya, S.; Yoshimoto, S.; Suzuki, M.; Kuwahara, D.; Sasaki, N.

    2010-01-01

    We synthesized the novel nanocomposite consisting alternately of a stacked single graphene sheet and a C 60 monolayer by using the graphite intercalation technique in which alkylamine molecules help intercalate large C 60 molecules into the graphite. Moreover, it is found that the intercalated C 60 molecules can rotate in between single graphene sheets by using C 13 NMR measurements. This preparation method provides a general way for intercalating huge fullerene molecules into graphite, which will lead to promising materials with novel mechanical, physical, and electrical properties.

  7. Nanocomposite Materials of Alternately Stacked C60 Monolayer and Graphene

    Directory of Open Access Journals (Sweden)

    Makoto Ishikawa

    2010-01-01

    Full Text Available We synthesized the novel nanocomposite consisting alternately of a stacked single graphene sheet and a C60 monolayer by using the graphite intercalation technique in which alkylamine molecules help intercalate large C60 molecules into the graphite. Moreover, it is found that the intercalated C60 molecules can rotate in between single graphene sheets by using C13 NMR measurements. This preparation method provides a general way for intercalating huge fullerene molecules into graphite, which will lead to promising materials with novel mechanical, physical, and electrical properties.

  8. Kinetics of monolayer graphene growth by segregation on Pd(111)

    International Nuclear Information System (INIS)

    Mok, H. S.; Murata, Y.; Kodambaka, S.; Ebnonnasir, A.; Ciobanu, C. V.; Nie, S.; McCarty, K. F.

    2014-01-01

    Using in situ low-energy electron microscopy and density functional theory calculations, we follow the growth of monolayer graphene on Pd(111) via surface segregation of bulk-dissolved carbon. Upon lowering the substrate temperature, nucleation of graphene begins on graphene-free Pd surface and continues to occur during graphene growth. Measurements of graphene growth rates and Pd surface work functions establish that this continued nucleation is due to increasing C adatom concentration on the Pd surface with time. We attribute this anomalous phenomenon to a large barrier for attachment of C adatoms to graphene coupled with a strong binding of the non-graphitic C to the Pd surface

  9. Switchable Polarization in Mn Embedded Graphene.

    Science.gov (United States)

    Noor-A-Alam, Mohammad; Ullah, Hamid; Shin, Young-Han

    2018-03-14

    Graphene, despite its many unique properties, is neither intrinsically polar due to inversion symmetry nor magnetic. However, based on density functional theory, we find that Mn, one of transition metals, embedded in single or double vacancy (Mn@SV and Mn@DV) in a graphene monolayer induces a dipole moment perpendicular to the sheet, which can be switched from up to down by Mn penetration through the graphene. Such switching could be realized by an external stimuli introduced through the tip of a scanning probe microscope, as already utilized in the studies of molecular switches. We estimate the energy barriers for dipole switching, which are found to be 2.60 eV and 0.28 eV for Mn@SV and Mn@DV, respectively. However, by applying biaxial tensile strain, we propose a mechanism for tuning the barrier. We find that 10% biaxial tensile strain, which is already experimentally achievable in graphene-like two-dimensional materials, can significantly reduce the barrier to 0.16 eV in Mn@SV. Moreover, in agreement with previous studies, we find a high magnetic moment of 3 μ B for both Mn@SV and Mn@DV, promising the potential of these structures in spintronics as well as in nanoscale electro-mechanical or memory devices.

  10. Temperature-dependent Raman spectroscopy studies of the interface coupling effect of monolayer ReSe2 single crystals on Au foils

    Science.gov (United States)

    Jiang, Shaolong; Zhao, Liyun; Shi, Yuping; Xie, Chunyu; Zhang, Na; Zhang, Zhepeng; Huan, Yahuan; Yang, Pengfei; Hong, Min; Zhou, Xiebo; Shi, Jianping; Zhang, Qing; Zhang, Yanfeng

    2018-05-01

    Rhenium diselenide (ReSe2), which bears in-plane anisotropic optical and electrical properties, is of considerable interest for its excellent applications in novel devices, such as polarization-sensitive photodetectors and integrated polarization-controllers. However, great challenges to date in the controllable synthesis of high-quality ReSe2 have hindered its in-depth investigations and practical applications. Herein, we report a feasible synthesis of monolayer single-crystal ReSe2 flakes on the Au foil substrate by using a chemical vapor deposition route. Particularly, we focus on the temperature-dependent Raman spectroscopy investigations of monolayer ReSe2 grown on Au foils, which present concurrent red shifts of Eg-like and Ag-like modes with increasing measurement temperature from 77–290 K. Linear temperature dependences of both modes are revealed and explained from the anharmonic vibration of the ReSe2 lattice. More importantly, the strong interaction of ReSe2 with Au, with respect to that with SiO2/Si, is further confirmed by temperature-dependent Raman characterization. This work is thus proposed to shed light on the optical and thermal properties of such anisotropic two-dimensional three-atom-thick materials.

  11. Political Competition and Polarization

    DEFF Research Database (Denmark)

    Schultz, Christian

    This paper considers political competition and the consequences of political polarization when parties are better informed about how the economy functions than voters are. Specifically, parties know the cost producing a public good, voters do not. An incumbent's choice of policy acts like a signa...... for costs before an upcoming election. It is shown that the more polarized the political parties the more distorted the incumbent's policy choice.......This paper considers political competition and the consequences of political polarization when parties are better informed about how the economy functions than voters are. Specifically, parties know the cost producing a public good, voters do not. An incumbent's choice of policy acts like a signal...

  12. Physics of polarized targets

    CERN Document Server

    Niinikoski, Tapio

    2014-01-01

    For developing, building and operating solid polarized targets we need to understand several fields of physics that have seen sub stantial advances during the last 50 years. W e shall briefly review a selection of those that are important today. These are: 1) quantum statistical methods to describe saturation and relaxation in magnetic resonance; 2) equal spin temperature model for dy namic nuclear polarization; 3 ) weak saturation during NMR polarization measurement; 4 ) refrigeration using the quantum fluid properties of helium isotopes. These, combined with superconducting magnet technologies, permit today to reach nearly complete pola rization of almost any nuclear spins. Targets can be operated in frozen spin mode in rather low and inhomogeneous field of any orientation, and in DNP mode in beams of high intensity. Beyond such experiments of nuclear and particle physics, applications a re also emerging in macromolecular chemistry and in magnetic resonance imaging. This talk is a tribute to Michel Borghini...

  13. No More Polarization, Please!

    DEFF Research Database (Denmark)

    Hansen, Mia Reinholt

    The organizational science literature on motivation has for long been polarized into two main positions; the organizational economic position focusing on extrinsic motivation and the organizational behavior position emphasizing intrinsic motivation. With the rise of the knowledge economy...... and the increasing levels of complexities it entails, such polarization is not fruitful in the attempt to explain motivation of organizational members. This paper claims that a more nuanced perspective on motivation, acknowledging the co-existence of intrinsic and extrinsic motivation, the possible interaction...... between the two as well as different types of motivations filling in the gap between the two polar types, is urgently needed in the organizational science literature. By drawing on the research on intrinsic and extrinsic motivation conducted in social psychology and combining this with contributions from...

  14. Polarized source upgrading

    International Nuclear Information System (INIS)

    Clegg, T.B.; Rummel, R.L.; Carter, E.P.; Westerfeldt, C.R.; Lovette, A.W.; Edwards, S.E.

    1985-01-01

    The decision was made this past year to move the Lamb-shift polarized ion source which was first installed in the laboratory in 1970. The motivation was the need to improve the flexibility of spin-axis orientation by installing the ion source with a new Wien-filter spin precessor which is capable of rotating physically about the beam axis. The move of the polarized source was accomplished in approximately two months, with the accelerator being turned off for experiments during approximately four weeks of this time. The occasion of the move provided the opportunity to rewire completely the entire polarized ion source frame and to rebuild approximately half of the electronic chassis on the source. The result is an ion source which is now logically wired and carefully documented. Beams obtained from the source are much more stable than those previously available

  15. A lunar polar expedition

    Science.gov (United States)

    Dowling, Richard; Staehle, Robert L.; Svitek, Tomas

    1992-09-01

    Advanced exploration and development in harsh environments require mastery of basic human survival skill. Expeditions into the lethal climates of Earth's polar regions offer useful lessons for tommorrow's lunar pioneers. In Arctic and Antarctic exploration, 'wintering over' was a crucial milestone. The ability to establish a supply base and survive months of polar cold and darkness made extensive travel and exploration possible. Because of the possibility of near-constant solar illumination, the lunar polar regions, unlike Earth's may offer the most hospitable site for habitation. The World Space Foundation is examining a scenario for establishing a five-person expeditionary team on the lunar north pole for one year. This paper is a status report on a point design addressing site selection, transportation, power, and life support requirements.

  16. POLARIZED NEUTRONS IN RHIC

    Energy Technology Data Exchange (ETDEWEB)

    COURANT,E.D.

    1998-04-27

    There does not appear to be any obvious way to accelerate neutrons, polarized or otherwise, to high energies by themselves. To investigate the behavior of polarized neutrons the authors therefore have to obtain them by accelerating them as components of heavier nuclei, and then sorting out the contribution of the neutrons in the analysis of the reactions produced by the heavy ion beams. The best neutron carriers for this purpose are probably {sup 3}He nuclei and deuterons. A polarized deuteron is primarily a combination of a proton and a neutron with their spins pointing in the same direction; in the {sup 3}He nucleus the spins of the two protons are opposite and the net spin (and magnetic moment) is almost the same as that of a free neutron. Polarized ions other than protons may be accelerated, stored and collided in a ring such as RHIC provided the techniques proposed for polarized proton operation can be adapted (or replaced by other strategies) for these ions. To accelerate polarized particles in a ring, one must make provisions for overcoming the depolarizing resonances that occur at certain energies. These resonances arise when the spin tune (ratio of spin precession frequency to orbit frequency) resonates with a component present in the horizontal field. The horizontal field oscillates with the vertical motion of the particles (due to vertical focusing); its frequency spectrum is dominated by the vertical oscillation frequency and its modulation by the periodic structure of the accelerator ring. In addition, the magnet imperfections that distort the closed orbit vertically contain all integral Fourier harmonics of the orbit frequency.

  17. Proteoglycan from salmon nasal cartridge promotes in vitro wound healing of fibroblast monolayers via the CD44 receptor

    Energy Technology Data Exchange (ETDEWEB)

    Ito, Gen; Kobayashi, Takeshi; Takeda, Yoshie [Department of Physiology, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550 (Japan); Sokabe, Masahiro, E-mail: msokabe@med.nagoya-u.ac.jp [Department of Physiology, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550 (Japan); Mechanobiology Laboratory, Nagoya University Graduate School of Medicine, Nagoya, Aichi 466-8550 (Japan); Mechanobiology Institute Singapore, National University of Singapore, Singapore 117411 (Singapore)

    2015-01-16

    Highlights: • Proteoglycan from salmon nasal cartridge (SNC-PG) promoted wound healing in fibroblast monolayers. • SNC-PG stimulated both cell proliferation and cell migration. • Interaction between chondroitin sulfate-units and CD44 is responsible for the effect. - Abstract: Proteoglycans (PGs) are involved in various cellular functions including cell growth, adhesion, and differentiation; however, their physiological roles are not fully understood. In this study, we examined the effect of PG purified from salmon nasal cartilage (SNC-PG) on wound closure using tissue-cultured cell monolayers, an in vitro wound-healing assay. The results indicated that SNC-PG significantly promoted wound closure in NIH/3T3 cell monolayers by stimulating both cell proliferation and cell migration. SNC-PG was effective in concentrations from 0.1 to 10 μg/ml, but showed much less effect at higher concentrations (100–1000 μg/ml). The effect of SNC-PG was abolished by chondroitinase ABC, indicating that chondroitin sulfates (CSs), a major component of glycosaminoglycans (GAGs) in SNC-PG, are crucial for the SNC-PG effect. Furthermore, chondroitin 6-sulfate (C-6-S), a major CS of SNC-PG GAGs, could partially reproduce the SNC-PG effect and partially inhibit the binding of SNC-PG to cells, suggesting that SNC-PG exerts its effect through an interaction between the GAGs in SNC-PG and the cell surface. Neutralization by anti-CD44 antibodies or CD44 knockdown abolished SNC-PG binding to the cells and the SNC-PG effect on wound closure. These results suggest that interactions between CS-rich GAG-chains of SNC-PG and CD44 on the cell surface are responsible for the SNC-PG effect on wound closure.

  18. Airborne acrolein induces keratin-8 (Ser-73) hyperphosphorylation and intermediate filament ubiquitination in bronchiolar lung cell monolayers.

    Science.gov (United States)

    Burcham, Philip C; Raso, Albert; Henry, Peter J

    2014-05-07

    The combustion product acrolein is a key mediator of pulmonary edema in victims of smoke inhalation injury. Since studying acrolein toxicity in conventional in vitro systems is complicated by reactivity with nucleophilic culture media constituents, we explored an exposure system which delivers airborne acrolein directly to lung cell monolayers at the air-liquid interface. Calu-3 lung adenocarcinoma cells were maintained on membrane inserts such that the basal surface was bathed in nucleophile-free media while the upper surface remained in contact with acrolein-containing air. Cells were exposed to airborne acrolein for 30 min before they were allowed to recover in fresh media, with cell sampling at defined time points to allow evaluation of toxicity and protein damage. After prior exposure to acrolein, cell ATP levels remained close to controls for 4h but decreased in an exposure-dependent manner by 24h. A loss of transepithelial electrical resistance and increased permeability to fluorescein isothiocyanate-labeled dextran preceded ATP loss. Use of antibody arrays to monitor protein expression in exposed monolayers identified strong upregulation of phospho-keratin-8 (Ser(73)) as an early consequence of acrolein exposure. These changes were accompanied by chemical damage to keratin-8 and other intermediate filament family members, while acrolein exposure also resulted in controlled ubiquitination of high mass proteins within the intermediate filament extracts. These findings confirm the usefulness of systems allowing delivery of airborne smoke constituents to lung cell monolayers during studies of the molecular basis for acute smoke intoxication injury. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  19. Dark Polar Dunes

    Science.gov (United States)

    2005-01-01

    20 January 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, acquired during northern summer in December 2004, shows dark, windblown sand dunes in the north polar region of Mars. A vast sea of sand dunes nearly surrounds the north polar cap. These landforms are located near 80.3oN, 144.1oW. Light-toned features in the image are exposures of the substrate that underlies the dune field. The image covers an area about 3 km (1.9 mi) wide and is illuminated by sunlight from the lower left.

  20. Imaging with Polarized Neutrons

    Directory of Open Access Journals (Sweden)

    Nikolay Kardjilov

    2018-01-01

    Full Text Available Owing to their zero charge, neutrons are able to pass through thick layers of matter (typically several centimeters while being sensitive to magnetic fields due to their intrinsic magnetic moment. Therefore, in addition to the conventional attenuation contrast image, the magnetic field inside and around a sample can be visualized by detecting changes of polarization in a transmitted beam. The method is based on the spatially resolved measurement of the cumulative precession angles of a collimated, polarized, monochromatic neutron beam that traverses a magnetic field or sample.

  1. The polar mesosphere

    International Nuclear Information System (INIS)

    Morris, Ray; Murphy, Damian

    2008-01-01

    The mesosphere region, which lies at the edge of space, contains the coldest layer of the Earth's atmosphere, with summer temperatures as low as minus 130 °C. In this extreme environment ice aerosol layers have appeared since the dawn of industrialization—whose existence may arguably be linked to human influence—on yet another layer of the Earth's fragile atmosphere. Ground-based and space-based experiments conducted in the Arctic and Antarctic during the International Polar Year (IPY) aim to address limitations in our knowledge and to advance our understanding of thermal and dynamical processes at play in the polar mesosphere

  2. Internal polarized targets

    Energy Technology Data Exchange (ETDEWEB)

    Kinney, E.R.; Coulter, K.; Gilman, R.; Holt, R.J.; Kowalczyk, R.S.; Napolitano, J.; Potterveld, D.H.; Young, L. (Argonne National Lab., IL (USA)); Mishnev, S.I.; Nikolenko, D.M.; Popov, S.G.; Rachek, I.A.; Temnykh, A.B.; Toporkov, D.K.; Tsentalovich, E.P.; Wojtsekhowski, B.B. (AN SSSR, Novosibirsk (USSR). Inst. Yadernoj Fiziki)

    1989-01-01

    Internal polarized targets offer a number of advantages over external targets. After a brief review of the basic motivation and principles behind internal polarized targets, the technical aspects of the atomic storage cell will be discussed in particular. Sources of depolarization and the means by which their effects can be ameliorated will be described, especially depolarization by the intense magnetic fields arising from the circulating particle beam. The experience of the Argonne Novosibirsk collaboration with the use of a storage cell in a 2 GeV electron storage ring will be the focus of this technical discussion. 17 refs., 11 figs.

  3. AGS polarized H- source

    International Nuclear Information System (INIS)

    Kponou, A.; Alessi, J.G.; Sluyters, T.

    1985-01-01

    The AGS polarized H - source is now operational. During a month-long experimental physics run in July 1984, pulses equivalent to 15 μA x 300 μs (approx. 3 x 10 10 protons) were injected into the RFQ preaccelerator. Beam polarization, measured at 200 MeV, was approx. 75%. After the run, a program to increase the H - yield of the source was begun and significant progress has been made. The H - current is now frequently 20 to 30 μA. A description of the source and some details of our operating experience are given. We also briefly describe the improvement program

  4. Molecular modeling of alkyl and alkenyl monolayers on hydrogen-terminated Si(111).

    Science.gov (United States)

    Scheres, Luc; Rijksen, Bart; Giesbers, Marcel; Zuilhof, Han

    2011-02-01

    On H-Si(111) surfaces monolayer formation with 1-alkenes results in alkyl monolayers with a Si-C-C linkage, while 1-alkynes yield alkenyl monolayers with a Si-C═C linkage. Recently, considerable structural differences between both types of monolayers were observed, including an increased thickness, improved packing, and higher surface coverage for the alkenyl monolayers. The precise origin thereof could experimentally not be clarified yet. Therefore, octadecyl and octadecenyl monolayers on Si(111) were studied in detail by molecular modeling via PCFF molecular mechanics calculations on periodically repeated slabs of modified surfaces. After energy minimization the packing energies, structural properties, close contacts, and deformations of the Si surfaces of monolayers structures with various substitution percentages and substitution patterns were analyzed. For the octadecyl monolayers all data pointed to a substitution percentage close to 50-55%, which is due the size of the CH(2) groups near the Si surface. This agrees with literature and the experimentally determined coverage of octadecyl monolayers. For the octadecenyl monolayers the minimum in packing energy per chain is calculated around 60% coverage, i.e., close to the experimentally observed value of 65% [Scheres et al. Langmuir 2010, 26, 4790], and this packing energy is less dependent on the substitution percentage than calculated for alkyl layers. Analysis of the chain conformations, close contacts, and Si surface deformation clarifies this, since even at coverages above 60% a relatively low number of close contacts and a negligible deformation of the Si was observed. In order to evaluate the thermodynamic feasibility of the monolayer structures, we estimated the binding energies of 1-alkenes and 1-alkynes to the hydrogen-terminated Si surface at a range of surface coverages by composite high-quality G3 calculations and determined the total energy of monolayer formation by adding the packing energies

  5. The physics of polarization

    Science.gov (United States)

    Landi Degl'Innocenti, Egidio

    This course is intended to give a description of the basic physical concepts which underlie the study and the interpretation of polarization phenomena. Apart from a brief historical introduction (Sect. 1), the course is organized in three parts. A first part (Sects. 2 - 6) covers the most relevant facts about the polarization phenomena that are typically encountered in laboratory applications and in everyday life. In Sect. 2, the modern description of polarization in terms of the Stokes parameters is recalled, whereas Sect. 3 is devoted to introduce the basic tools of laboratory polarimetry, such as the Jones calculus and the Mueller matrices. The polarization phenomena which are met in the reflection and refraction of a beam of radiation at the separation surface between two dielectrics, or between a dielectric and a metal, are recalled in Sect. 4. Finally, Sect. 5 gives an introduction to the phenomena of dichroism and of anomalous dispersion and Sect. 6 summarizes the polarization phenomena that are commonly encountered in everyday life. The second part of this course (Sects. 7-14) deals with the description, within the formalism of classical physics, of the spectro-polarimetric properties of the radiation emitted by accelerated charges. Such properties are derived by taking as starting point the Liénard and Wiechert equations that are recalled and discussed in Sect. 7 both in the general case and in the non-relativistic approximation. The results are developed to find the percentage polarization, the radiation diagram, the cross-section and the spectral characteristics of the radiation emitted in different phenomena particularly relevant from the astrophysical point of view. The emission of a linear antenna is derived in Sect. 8. The other Sections are devoted to Thomson scattering (Sect. 9), Rayleigh scattering (Sect. 10), Mie scattering (Sect. 11), bremsstrahlung radiation (Sect. 12), cyclotron radiation (Sect. 13), and synchrotron radiation (Sect. 14

  6. Polarized Proton Collisions at RHIC

    CERN Document Server

    Bai, Mei; Alekseev, Igor G; Alessi, James; Beebe-Wang, Joanne; Blaskiewicz, Michael; Bravar, Alessandro; Brennan, Joseph M; Bruno, Donald; Bunce, Gerry; Butler, John J; Cameron, Peter; Connolly, Roger; De Long, Joseph; Drees, Angelika; Fischer, Wolfram; Ganetis, George; Gardner, Chris J; Glenn, Joseph; Hayes, Thomas; Hseuh Hsiao Chaun; Huang, Haixin; Ingrassia, Peter; Iriso, Ubaldo; Laster, Jonathan S; Lee, Roger C; Luccio, Alfredo U; Luo, Yun; MacKay, William W; Makdisi, Yousef; Marr, Gregory J; Marusic, Al; McIntyre, Gary; Michnoff, Robert; Montag, Christoph; Morris, John; Nicoletti, Tony; Oddo, Peter; Oerter, Brian; Osamu, Jinnouchi; Pilat, Fulvia Caterina; Ptitsyn, Vadim; Roser, Thomas; Satogata, Todd; Smith, Kevin T; Svirida, Dima; Tepikian, Steven; Tomas, Rogelio; Trbojevic, Dejan; Tsoupas, Nicholaos; Tuozzolo, Joseph; Vetter, Kurt; Wilinski, Michelle; Zaltsman, Alex; Zelenski, Anatoli; Zeno, Keith; Zhang, S Y

    2005-01-01

    The Relativistic Heavy Ion Collider~(RHIC) provides not only collisions of ions but also collisions of polarized protons. In a circular accelerator, the polarization of polarized proton beam can be partially or fully lost when a spin depolarizing resonance is encountered. To preserve the beam polarization during acceleration, two full Siberian snakes were employed in RHIC to avoid depolarizing resonances. In 2003, polarized proton beams were accelerated to 100~GeV and collided in RHIC. Beams were brought into collisions with longitudinal polarization at the experiments STAR and PHENIX by using spin rotators. RHIC polarized proton run experience demonstrates that optimizing polarization transmission efficiency and improving luminosity performance are significant challenges. Currently, the luminosity lifetime in RHIC is limited by the beam-beam effect. The current state of RHIC polarized proton program, including its dedicated physics run in 2005 and efforts to optimize luminosity production in beam-beam limite...

  7. Simvastatin Ameliorates Matrix Stiffness-Mediated Endothelial Monolayer Disruption.

    Directory of Open Access Journals (Sweden)

    Marsha C Lampi

    Full Text Available Arterial stiffening accompanies both aging and atherosclerosis, and age-related stiffening of the arterial intima increases RhoA activity and cell contractility contributing to increased endothelium permeability. Notably, statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA reductase inhibitors whose pleiotropic effects include disrupting small GTPase activity; therefore, we hypothesized the statin simvastatin could be used to attenuate RhoA activity and inhibit the deleterious effects of increased age-related matrix stiffness on endothelial barrier function. Using polyacrylamide gels with stiffnesses of 2.5, 5, and 10 kPa to mimic the physiological stiffness of young and aged arteries, endothelial cells were grown to confluence and treated with simvastatin. Our data indicate that RhoA and phosphorylated myosin light chain activity increase with matrix stiffness but are attenuated when treated with the statin. Increases in cell contractility, cell-cell junction size, and indirect measurements of intercellular tension that increase with matrix stiffness, and are correlated with matrix stiffness-dependent increases in monolayer permeability, also decrease with statin treatment. Furthermore, we report that simvastatin increases activated Rac1 levels that contribute to endothelial barrier enhancing cytoskeletal reorganization. Simvastatin, which is prescribed clinically due to its ability to lower cholesterol, alters the endothelial cell response to increased matrix stiffness to restore endothelial monolayer barrier function, and therefore, presents a possible therapeutic intervention to prevent atherogenesis initiated by age-related arterial stiffening.

  8. Investigating phosphonate monolayer stability on ALD oxide surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Branch, Brittany [Nanoscience and Microsystems Engineering and Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87131 (United States); Dubey, Manish [Lujan Center, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Anderson, Aaron S. [Physical Chemistry and Applied Spectroscopy, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Artyushkova, Kateryna [Nanoscience and Microsystems Engineering and Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87131 (United States); Baldwin, J. Kevin [Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Petsev, Dimiter [Nanoscience and Microsystems Engineering and Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87131 (United States); Dattelbaum, Andrew M., E-mail: amdattel@lanl.gov [Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2014-01-01

    We report a series of studies aimed at investigating the stability of phosphonate self-assembled monolayers (SAMs) made from octadecylphosphonic acid (ODPA) or a perfluorinated phosphonic acid (PFPA) on hafnium and aluminum oxide surfaces deposited by atomic layer deposition (ALD). The monolayers were deposited by a series of techniques including self-assembly from solution, tethering by aggregation and growth, and the Langmuir–Blodgett (LB) method. SAMs prepared by LB method were primarily used in our stability investigations because they were found to be the most uniform and reproducible. All films deposited on ALD oxide-coated substrates were characterized by means of water contact angle measurements, spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS data conclusively showed covalent phosphonate formation on both substrates. SAMs formed on both Al{sub 2}O{sub 3} and HfO{sub 2} were stable upon exposure to water. PFPA SAMs on HfO{sub 2} were found to be the most stable SAMs studied here in either water or phosphate buffer (PBS) at room temperature. We also show that similar silane-based SAMs made from octadecyltrichlorosilane (OTS) on silicon oxide (SiO{sub 2}) are less stable in PBS than phosphonate SAMs on atomic layer deposited HfO{sub 2} substrates. These data suggest that phosphonate SAMs should be considered for use in (bio)molecular sensing and actuator devices that utilize ALD and require longer-term stability under aqueous conditions.

  9. Anisotropic Negative Differential Resistance in Monolayer Black Phosphorus

    Science.gov (United States)

    Zhang, Wanting; Kang, Peng; Chen, Huahui

    2018-01-01

    The tremendous potential application in emerging two-dimensional layered materials such as black phosphorus (BP) has attracted great attention as nanoscale devices. In this paper, the effect of anisotropic negative differential resistance (NDR) in monolayer black phosphorus field-effect transistors (FETs) is reported by the first-principles computational study based on the non-equilibrium Green’s function approach combined with density functional theory. The transport properties including current-voltage (I-V) relation and transmission spectrum of monolayer BP are investigated at different gate voltages (Vg). Further studies indicate that NDR occurs at a specific gate voltage in the armchair direction rather than in the zigzag direction. The decrease of current in I-V characteristics can be understood from the generation of non-conducting states region moving towards the Fermi level resulting in a reduction of the integration within corresponding energy range in the transmission spectrum. Our results offer useful guidance for designing FETs and other potential applications in nanoelectronic devices based on BP.

  10. Tension-Enhanced Hydrogen Evolution Reaction on Vanadium Disulfide Monolayer.

    Science.gov (United States)

    Pan, Hui

    2016-12-01

    Water electrolysis is an efficient way for hydrogen production. Finding efficient, cheap, and eco-friendly electrocatalysts is essential to the development of this technology. In the work, we present a first-principles study on the effects of tension on the hydrogen evolution reaction of a novel electrocatalyst, vanadium disulfide (VS2) monolayer. Two electrocatalytic processes, individual and collective processes, are investigated. We show that the catalytic ability of VS2 monolayer at higher hydrogen coverage can be efficiently improved by escalating tension. We find that the individual process is easier to occur in a wide range of hydrogen coverage and the collective process is possible at a certain hydrogen coverage under the same tension. The best hydrogen evolution reaction with near-zero Gibbs free energy can be achieved by tuning tension. We further show that the change of catalytic activity with tension and hydrogen coverage is induced by the change of free carrier density around the Fermi level, that is, higher carrier density, better catalytic performance. It is expected that tension can be a simple way to improve the catalytic activity, leading to the design of novel electrocatalysts for efficient hydrogen production from water electrolysis.

  11. Photolysis of incorporated benzophenone derivatives inside compressed lipid monolayers

    Directory of Open Access Journals (Sweden)

    DEJAN Z. MARKOVIC

    2001-05-01

    Full Text Available The goal of this work was to study the possibility of the occurrence of radical-type lipid peroxidation of the lipid constituents on biomembranes, in compressed monolayers, having lipoidal benzophenone photosensitizers incorporated. The triplets of the photosensitizer abstract allylic and doubly-allylic hydrogen atoms from anticonjugated moities of the lipid molecules. The results simultaneously confirmed the occurrence of H-abstraction (and so the initiation of the peroxidizing chain mechanism, and the absence of the formation of lipid peroxides. The reason lies in "cage effect": the highly restricted spacial area of compressed lipid monolayers limits the mobility of the created radicals (lipid radicals and ketyl radicals and leads to their recombination, thus preventing the propagation step of the chain mechanism. With certain reservations it may be concluded that these results have a clear implication on real biomembranes: the structure of which is one of themain factors preventing the spread of the chain reaction, and the formation of lipid peroxides.

  12. Evidence for superconductivity in Li-decorated monolayer graphene.

    Science.gov (United States)

    Ludbrook, B M; Levy, G; Nigge, P; Zonno, M; Schneider, M; Dvorak, D J; Veenstra, C N; Zhdanovich, S; Wong, D; Dosanjh, P; Straßer, C; Stöhr, A; Forti, S; Ast, C R; Starke, U; Damascelli, A

    2015-09-22

    Monolayer graphene exhibits many spectacular electronic properties, with superconductivity being arguably the most notable exception. It was theoretically proposed that superconductivity might be induced by enhancing the electron-phonon coupling through the decoration of graphene with an alkali adatom superlattice [Profeta G, Calandra M, Mauri F (2012) Nat Phys 8(2):131-134]. Although experiments have shown an adatom-induced enhancement of the electron-phonon coupling, superconductivity has never been observed. Using angle-resolved photoemission spectroscopy (ARPES), we show that lithium deposited on graphene at low temperature strongly modifies the phonon density of states, leading to an enhancement of the electron-phonon coupling of up to λ ≃ 0.58. On part of the graphene-derived π*-band Fermi surface, we then observe the opening of a Δ ≃ 0.9-meV temperature-dependent pairing gap. This result suggests for the first time, to our knowledge, that Li-decorated monolayer graphene is indeed superconducting, with Tc ≃ 5.9 K.

  13. Control of Magnetic Order in Monolayer Films by Substrate Tuning

    Science.gov (United States)

    Heinze, Stefan; Ferriani, Paolo; Turek, Ilja; Bihlmayer, Gustav; Blügel, Stefan

    2007-03-01

    Surprisingly, antiferromagnetic order has recently been observed in a monolayer (ML) film of Fe on W(001) [1] and a novel, nanoscale magnetic structure has been discovered for a ML Fe on Ir(111) [2] showing the crucial influence of the substrate. Here, we therefore propose to tailor exchange interactions in magnetic monolayer films by tuning the adjacent non-magnetic substrate. Using first-principles calculations based on density functional theory, we demonstrate a ferromagnetic-antiferromagnetic phase transition for one ML Fe on a Tax W1-x(001) surface as a function of the Ta concentration. At the Ta concentration of the transition, the nearest-neighbor exchange interaction becomes negligible and exchange terms beyond nearest-neighbors and higher order spin interactions beyond the Heisenberg Hamiltonian become crucial. In this regime, the accessible magnetic phase space is dramatically enhanced, and we study complex magnetic order such as spin-spiral states, multiple-q states, or even disordered local moment states. [1] A. Kubetzka, et al., Phys. Rev. Lett.94, 087204 (2005). [2] K. von Bergmann, et al., Phys. Rev.Lett. 96, 167203 (2006).

  14. Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides

    KAUST Repository

    Moody, Galan

    2016-03-14

    Transition metal dichalcogenides (TMDs) have garnered considerable interest in recent years owing to their layer thickness-dependent optoelectronic properties. In monolayer TMDs, the large carrier effective masses, strong quantum confinement, and reduced dielectric screening lead to pronounced exciton resonances with remarkably large binding energies and coupled spin and valley degrees of freedom (valley excitons). Coherent control of valley excitons for atomically thin optoelectronics and valleytronics requires understanding and quantifying sources of exciton decoherence. In this work, we reveal how exciton-exciton and exciton-phonon scattering influence the coherent quantum dynamics of valley excitons in monolayer TMDs, specifically tungsten diselenide (WSe2), using two-dimensional coherent spectroscopy. Excitation-density and temperature dependent measurements of the homogeneous linewidth (inversely proportional to the optical coherence time) reveal that exciton-exciton and exciton-phonon interactions are significantly stronger compared to quasi-2D quantum wells and 3D bulk materials. The residual homogeneous linewidth extrapolated to zero excitation density and temperature is ~1:6 meV (equivalent to a coherence time of 0.4 ps), which is limited only by the population recombination lifetime in this sample. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  15. In situ scanning tunneling microscope tip treatment device for spin polarization imaging

    Science.gov (United States)

    Li, An-Ping [Oak Ridge, TN; Jianxing, Ma [Oak Ridge, TN; Shen, Jian [Knoxville, TN

    2008-04-22

    A tip treatment device for use in an ultrahigh vacuum in situ scanning tunneling microscope (STM). The device provides spin polarization functionality to new or existing variable temperature STM systems. The tip treatment device readily converts a conventional STM to a spin-polarized tip, and thereby converts a standard STM system into a spin-polarized STM system. The tip treatment device also has functions of tip cleaning and tip flashing a STM tip to high temperature (>2000.degree. C.) in an extremely localized fashion. Tip coating functions can also be carried out, providing the tip sharp end with monolayers of coating materials including magnetic films. The device is also fully compatible with ultrahigh vacuum sample transfer setups.

  16. Giant bulk photovoltaic effect and spontaneous polarization of single-layer monochalcogenides

    Science.gov (United States)

    Rangel, Tonatiuh; Fregoso, Benjamin M.; Mendoza, Bernardo S.; Morimoto, Takahiro; Moore, Joel E.; Neaton, Jeffrey B.

    We implement and use a first-principles density functional theory approach to calculate the shift current response of monolayer group-IV monochalcogenides. We find a larger effective three- dimensional effective polarization ( 1.9 C/m2) and shift current ( 200 μA/V2) than have been previously observed in common ferroelectrics. By using a one-dimensional Rice-Mele tight-binding model we investigate the shift-current tensor along the polarization axis, its relation with polarization, and the conditions under which shift-current reaches a maximum. Importantly, our calculations predict that shift current can be largest in the UV visible range, indicating the potential of these materials for optoelectronic applications. BMF and TR share equal contributions. We acknowledge AFOSR MURI, Conacyt, NERSC, the Gordon and Betty Moore Foundation and the DOE.

  17. Lobbying and political polarization

    OpenAIRE

    Ursprung, Heinrich W.

    2002-01-01

    Standard spatial models of political competition give rise to equilibria in which the competing political parties or candidates converge to a common position. In this paper I show how political polarization can be generated in models that focus on the nexus between pre-election interest group lobbying and electoral competition.

  18. Fluorescence confocal polarizing microscopy

    Indian Academy of Sciences (India)

    Much of the modern understanding of orientational order in liquid crystals (LCs) is based on polarizing microscopy (PM). A PM image bears only two-dimensional (2D) information, integrating the 3D pattern of optical birefringence over the path of light. Recently, we proposed a technique to image 3D director patterns by ...

  19. Polarization of Bremsstrahlung

    International Nuclear Information System (INIS)

    Miller, J.

    1957-01-01

    The numerical results for the polarization of Bremsstrahlung are presented. The multiple scattering of electrons in the target is taken into account. The angular-and photon energy dependences are seen on the curves for an incident 25 MeV electron energy. (Author) [fr

  20. DESY: HERA polarization

    International Nuclear Information System (INIS)

    Anon.

    1992-01-01

    The new HERA electron-proton collider at DESY in Hamburg achieved the first luminosity for electron-proton collisions on 19 October last year. Only one month later, on 20 November, HERA passed another important milestone with the observation of transverse electron polarization

  1. Titan Polar Landscape Evolution

    Science.gov (United States)

    Moore, Jeffrey M.

    2016-01-01

    With the ongoing Cassini-era observations and studies of Titan it is clear that the intensity and distribution of surface processes (particularly fluvial erosion by methane and Aeolian transport) has changed through time. Currently however, alternate hypotheses substantially differ among specific scenarios with respect to the effects of atmospheric evolution, seasonal changes, and endogenic processes. We have studied the evolution of Titan's polar region through a combination of analysis of imaging, elevation data, and geomorphic mapping, spatially explicit simulations of landform evolution, and quantitative comparison of the simulated landscapes with corresponding Titan morphology. We have quantitatively evaluated alternate scenarios for the landform evolution of Titan's polar terrain. The investigations have been guided by recent geomorphic mapping and topographic characterization of the polar regions that are used to frame hypotheses of process interactions, which have been evaluated using simulation modeling. Topographic information about Titan's polar region is be based on SAR-Topography and altimetry archived on PDS, SAR-based stereo radar-grammetry, radar-sounding lake depth measurements, and superposition relationships between geomorphologic map units, which we will use to create a generalized topographic map.

  2. Graphics of polar figure

    International Nuclear Information System (INIS)

    Macias B, L.R.

    1991-11-01

    The objective of this work, is that starting from a data file coming from a spectra that has been softened, and of the one that have been generated its coordinates to project it in stereographic form, to create the corresponding polar figure making use of the Cyber computer of the ININ by means of the GRAPHOS package. This work only requires a Beta, Fi and Intensity (I) enter data file. It starts of the existence of a softened spectra of which have been generated already with these data, making use of some language that in this case was FORTRAN for the Cyber computer, a program is generated supported in the Graphos package that allows starting of a reading of the Beta, Fi, I file, to generate the points in a stereographic projection and that it culminates with the graph of the corresponding polar figure. The program will request the pertinent information that is wanted to capture in the polar figure just as: date, name of the enter file, indexes of the polar figure, number of levels, radio of the stereographic projection (cms.), crystalline system to which belongs the sample, name the neuter graph file by create and to add the own general data. (Author)

  3. Electrokinetics of polar liquids in contact with nonpolar surfaces.

    Science.gov (United States)

    Lin, Chih-Hsiu; Ferguson, Gregory S; Chaudhury, Manoj K

    2013-06-25

    Zeta potentials of several polar protic (water, ethylene glycol, and formamide) as well as polar aprotic (dimethyl sulfoxide) liquids were measured in contact with three nonpolar surfaces using closed-cell electroosmosis. The test surfaces were chemisorbed monolayers of alkyl siloxanes, fluoroalkyl siloxanes, and polydimethylsiloxanes (PDMS) grafted on glass slides. All these liquids exhibited substantial electrokinetics in contact with the nonpolar surfaces with these observations: the electrokinetic effect on the fluorocarbon-coated surface is the strongest and on a PDMS grafted surface, the effect is the weakest. Even though these hygroscopic liquids contain small amounts of water, the current models of charging based on the adsorption of hydroxide ions at the interface or the dissociation of pre-existing functionalities (e.g., silanol groups) appear to be insufficient to account for the various facets of the experimental observations. The results illustrate how ubiquitous the phenomenon of electrokinetics is with polar liquids contacting such apparently passive nonpolar surfaces. We hope that these results will inspire further experimental and theoretical studies in this important area of research that has potential practical implications.

  4. Ordering and dynamics of oligo(phenylene ethynylene) self-assembled monolayers on Au(111)

    NARCIS (Netherlands)

    Wu, Hairong; Sotthewes, Kai; Schön, Peter Manfred; Vancso, Gyula J.; Zandvliet, Henricus J.W.

    2015-01-01

    Self-assembled monolayers of 4-[4′-(phenylethynyl)-phenylethynyl]-benzenethiolate (PPB-S) molecules on flame annealed Au(111) have been investigated by ultra-high vacuum scanning tunneling microscopy. We have found a hitherto unknown self-assembled monolayer phase. This phase consists of a

  5. Pressure-area isotherm of a lipid monolayer from molecular dynamics simulations

    NARCIS (Netherlands)

    Baoukina, Svetlana; Monticelli, Luca; Marrink, Siewert J.; Tieleman, D. Peter

    2007-01-01

    We calculated the pressure-area isotherm of a dipalmitoyl-phosphatidylcholine (DPPC) lipid monolayer from molecular dynamics simulations using a coarse-grained molecular model. We characterized the monolayer structure, geometry, and phases directly from the simulations and compared the calculated

  6. Electrochemistry of Surface-Grafted Stimulus-Responsive Monolayers of Poly(ferrocenyldimethylsilane) on Gold

    NARCIS (Netherlands)

    Péter, M.; Lammertink, Rob G.H.; Hempenius, Mark A.; Vancso, Gyula J.

    2005-01-01

    Poly(ferrocenyldimethylsilane)s with various degrees of polymerization and featuring a thiol end group were chemically end-grafted onto gold substrates by self-assembly, forming redox-active monolayers. The monolayers were characterized by contact angle measurements, Fourier transform infrared

  7. Intramolecular and Lattice Melting in n-Alkane Monolayers: An Analog of Melting in Lipid Bilayers

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Herwig, K.W.; Matthies, B.

    1999-01-01

    Molecular dynamics (MD) simulations and neutron diffraction experiments have been performed on n-dotriacontane (n-C32D66) monolayers adsorbed on a graphite basal-plane surface. The diffraction experiments show little change in the crystalline monolayer structure up to a temperature of similar...

  8. Crystallization of Isotactic Poly(methylmethacrylate) in Monolayers and Thin Films

    NARCIS (Netherlands)

    Brinkhuis, R.H.G.; Schouten, A.J.

    Langmuir-Blodgett monolayers of isotactic PMMA exhibit a pressure-induced transition upon compression, that can be described in terms of a two-dimensional crystallization process, analogous to a normal melt crystallization. These water surface crystallized monolayers can be used to prepare highly

  9. Structure of solid monolayers and multilayers of n-hexane on graphite

    Indian Academy of Sciences (India)

    Unknown

    Abstract. We present all-atom molecular dynamics simulations of n-hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid.

  10. Effect of lipid composition and packing on the adsorption of apolipoproteins to lipid monolayers

    International Nuclear Information System (INIS)

    Ibdah, J.A.; Lund-Katz, S.; Phillips, M.C.

    1987-01-01

    The monolayer system has been used to study the effects of lipoprotein surface lipid composition and packing on the affinities of apolipoproteins for the surfaces of lipoprotein particles. The adsorption of apolipoproteins injected beneath lipid monolayers prepared with pure lipids or lipoprotein surface lipids is evaluated by monitoring the surface pressure of the film and the surface concentration (Gamma) of 14 C-labelled apolipoprotein. At a given initial film pressure (π/sub i/) there is a higher adsorption of human apo A-I to unsaturated phosphatidylcholine (PC) monolayers compared to saturated PC monolayers (e.g., at π/sub i/ = 10 mN/m, Gamma = 0.35 and 0.06 mg/m 2 for egg PC and distearoyl PC, respectively, with 3 x 10 -4 mg/ml apo A-I in the subphase). In addition, adsorption of apo A-I is less to an egg sphingomyelin monolayer than to an egg PC monolayer. The adsorption of apo A-I to PC monolayers is decreased by addition of cholesterol. Generally, apo A-I adsorption diminishes as the lipid molecular area decreases. Apo A-I adsorbs more to monolayers prepared with HDL 3 surface lipids than with LDL surface lipids. These studies suggest that lipoprotein surface lipid composition and packing are crucial factors influencing the transfer and exchange of apolipoproteins among various lipoprotein classes during metabolism of lipoprotein particles

  11. Simulation studies of pore and domain formation in a phospholipid monolayer

    NARCIS (Netherlands)

    Knecht, Volker; Muller, M; Bonn, M; Marrink, SJ; Mark, AE

    2005-01-01

    Despite extensive study the phase behavior of phospholipid monolayers at an air-water interface is still not fully understood. In particular recent vibrational sum-frequency generation (VSFG) spectra of DPPC monolayers as a function of area density show a sharp transition in the order of the lipid

  12. A self-assembled monolayer-assisted surface microfabrication and release technique

    NARCIS (Netherlands)

    Kim, B.J.; Liebau, M.; Huskens, Jurriaan; Reinhoudt, David; Brugger, J.P.

    2001-01-01

    This paper describes a method of thin film and MEMS processing which uses self-assembled monolayers as ultra-thin organic surface coating to enable a simple removal of microfabricated devices off the surface without wet chemical etching. A 1.5-nm thick self-assembled monolayer of

  13. Gas sensing with self-assembled monolayer field-effect transistors

    NARCIS (Netherlands)

    Andringa, Anne-Marije; Spijkman, Mark-Jan; Smits, Edsger C. P.; Mathijssen, Simon G. J.; van Hal, Paul A.; Setayesh, Sepas; Willard, Nico P.; Borshchev, Oleg V.; Ponomarenko, Sergei A.; Blom, Paul W. M.; de Leeuw, Dago M.

    A new sensitive gas sensor based on a self-assembled monolayer field-effect transistor (SAMFET) was used to detect the biomarker nitric oxide. A SAMFET based sensor is highly sensitive because the analyte and the active channel are separated by only one monolayer. SAMFETs were functionalised for

  14. Characteristics of volume polarization holography with linear polarization light

    Science.gov (United States)

    Zang, Jinliang; Wu, An'an; Liu, Ying; Wang, Jue; Lin, Xiao; Tan, Xiaodi; Shimura, Tsutomu; Kuroda, Kazuo

    2015-10-01

    Volume polarization holographic recording in phenanthrenequinone-doped poly(methyl methacrylate) (PQ-PMMA) photopolymer with linear polarized light is obtained. The characteristics of the volume polarization hologram are experimentally investigated. It is found that beyond the paraxial approximation the polarization states of the holographic reconstruction light are generally different from the signal light. Based on vector wave theoretical analyses and material properties, the special exposure condition for correctly holographic reconstruction is obtained and experimentally demonstrated.

  15. Radiation-induced apoptosis in human ovarian carcinoma cells growing as a monolayer and as multicell spheroids.

    Science.gov (United States)

    Filippovich, I V; Sorokina, N I; Robillard, N; Chatal, J F

    1997-09-04

    Response to external gamma irradiation was studied in a human ovarian carcinoma cell line (OVCAR 3) growing as a monolayer and as multicell spheroids. Necrosis and apoptosis were documented using Trypan-blue uptake and acridine-orange staining, respectively, and apoptosis was quantified using a terminal deoxynucleotidyl transferase assay. Exposure of OVCAR 3 cells growing as a monolayer to 137Cs gamma radiation at a dose of 10 Gy produced 30-40% apoptosis 72 hr after irradiation. Cell-cycle analysis of irradiated cells showed an accumulation of cells in G2/M phase 24 hr after irradiation and then a decline at 48 hr in conjunction with apoptosis onset. The loss of G0/G1 cells in irradiated cultures suggested a preferential entry into apoptosis. No increase in apoptotic cell number was observed in OVCAR 3 spheroids after irradiation, and the cells probably died as a result of necrosis. When spheroids were disrupted immediately after irradiation to obtain a cell suspension, minor apoptosis was observed in association with a marked increase in TB-positive cell number after 96 hr of incubation following irradiation. Thus, a relationship was found between radiation-induced apoptosis and the cell cycle. Results with spheroids suggested the possible involvement of cell-to-cell interactions in apoptosis regulation.

  16. Topological insulator behavior of WS{sub 2} monolayer with square-octagon ring structure

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Ashok, E-mail: ashok@cup.ac.in [Centre for Physical Sciences, School of Basic and Applied Sciences, Central University of Punjab, Bathinda, India 151001 (India); Pandey, Ravindra [Department of Physics, Michigan Technological University Houghton, MI (United States); Ahluwalia, P. K. [Department of Physics, Himachal Pradesh University Shimla, India, 171005 (India); Tankeshwar, K. [Department of Physics, Panjab University Chandigarh, India 160014 (India)

    2016-05-23

    We report electronic behavior of an allotrope of monolayer WS{sub 2} with a square octagon ring structure, refereed to as (so-WS{sub 2}) within state-of-the-art density functional theory (DFT) calculations. The WS{sub 2} monolayer shows semi-metallic characteristics with Dirac-cone like features around Γ. Unlike p-orbital’s Dirac-cone in graphene, the Dirac-cone in the so-WS{sub 2} monolayer originates from the d-electrons of the W atom in the lattice. Most interestingly, the spin-orbit interaction associated with d-electrons induce a finite band-gap that results into the metal-semiconductor transition and topological insulator-like behavior in the so-WS{sub 2} monolayer. These characteristics suggest the so-WS{sub 2} monolayer to be a promising candidate for the next-generation electronic and spintronics devices.

  17. Surface Chemistry and Spectroscopic Study of a Cholera Toxin B Langmuir Monolayer.

    Science.gov (United States)

    Sharma, Shiv K; Seven, Elif S; Micic, Miodrag; Li, Shanghao; Leblanc, Roger M

    2018-02-20

    In this article, we explored the surface chemistry properties of a cholera toxin B (CTB) monolayer at the air-subphase interface and investigated the change in interfacial properties through in situ spectroscopy. The study showed that the impact of the blue shift was negligible, suggesting that the CTB molecules were minimally affected by the subphase molecules. The stability of the CTB monolayer was studied by maintaining the constant surface pressure for a long time and also by using the compression-decompression cycle experiments. The high stability of the Langmuir monolayer of CTB clearly showed that the driving force of CTB going to the amphiphilic membrane was its amphiphilic nature. In addition, no major change was detected in the various in situ spectroscopy results (such as UV-vis, fluorescence, and IR ER) of the CTB Langmuir monolayer with the increase in surface pressure. This indicates that no aggregation occurs in the Langmuir monolayer of CTB.

  18. DPPC Monolayers Exhibit an Additional Phase Transition at High Surface Pressure

    DEFF Research Database (Denmark)

    Shen, Chen; de la Serna, Jorge B.; Struth, Bernd

    2015-01-01

    Pulmonary surfactant forms a monolayer at the air/aqueous interface within the lung. During the breath process, the surface pressure (Π) periodically varies from ~40mN/m up to ~70mN/m. The film is mechanically stable during this rapid and reversible expansion. Pulmonary surfactant consists of ~90......% of lipid with 10% integrated proteins. Among its lipid compounds, di-palmitoyl-phosphatidylcholine (DPPC) dominates (~45wt%). DPPC is the only known lipid that can be compressed to very high surface pressure (~70mN/m) before its monolayer collapses. Most probably, this feature contributes to the mechanical...... stability of the alveoli monolayer. Still, to the best of our knowledge, some details of the compression isotherm presented here and the related structures of the DPPC monolayer were not studied so far. The liquid-expanded/liquid-condensed phase transition of the DPPC monolayer at ~10mN/m is well known...

  19. Experiments with Fermilab polarized proton and polarized antiproton beams

    International Nuclear Information System (INIS)

    Yokosawa, A.

    1990-01-01

    We summarize activities concerning the Fermilab polarized beams. They include a brief description of the polarized-beam facility, measurements of beam polarization by polarimeters, asymmetry measurements in the π degree production at high p perpendicular and in the Λ (Σ degree), π ± , π degree production at large x F , and Δσ L (pp, bar pp) measurements. 18 refs

  20. NUCLEON POLARIZATION IN 3-BODY MODELS OF POLARIZED LI-6

    NARCIS (Netherlands)

    SCHELLINGERHOUT, NW; KOK, LP; COON, SA; ADAM, RM

    1993-01-01

    Just as He-3 --> can be approximately characterized as a polarized neutron target, polarized Li-6D has been advocated as a good isoscalar nuclear target for the extraction of the polarized gluon content of the nucleon. The original argument rests upon a presumed ''alpha + deuteron'' picture of Li-6,

  1. Chemo-sensitivity of Two-dimensional Monolayer and Three-dimensional Spheroid of Breast Cancer MCF-7 Cells to Daunorubicin, Docetaxel, and Arsenic Disulfide.

    Science.gov (United States)

    Uematsu, Nami; Zhao, Yuxue; Kiyomi, Anna; Yuan, B O; Onda, Kenji; Tanaka, Sachiko; Sugiyama, Kentaro; Sugiura, Munetoshi; Takagi, Norio; Hayakawa, Akemi; Hirano, Toshihiko

    2018-04-01

    Chemo-sensitivity of two-dimensional (2D) monolayers and three-dimensional (3D) spheroids of human breast cancer MCF-7 cells were investigated. MCF-7 cells were cultured in monolayers or spheroids established using a thermo-reversible gelatin polymer, in the presence of daunorubicin, docetaxel, or As 2 S 2 Cell proliferation was examined by a Cell Counting Kit-8 assay. Daunorubicin, docetaxel, and As 2 S 2 dose-dependently decreased the MCF-7 cell proliferation in both 2D- and 3D-culture systems. The 3D spheroids were less sensitive to these agents than the 2D cultured cells. Verapamil, an inhibitor of P-glycoprotein, partially enhanced the antiproliferative effects of the agents. DL-buthionine-(S, R)-sulfoximine significantly increased (p<0.05), while N-acetyl-L-cysteine significantly inhibited the antiproliferative effects of As 2 S 2 (p<0.003). The 3D spheroids showed less sensitivity to the antiprolliferative efficacies of anticancer agents than the 2D cultured cells. P-Glycoprotein is suggested to be partially implicated in drug resistance. Reduction of cellular glutathione level enhanced the As 2 S 2 cytotoxicity. Copyright© 2018, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.

  2. Geomagnetic polarity transitions

    Science.gov (United States)

    Merrill, Ronald T.; McFadden, Phillip L.

    1999-05-01

    The top of Earth's liquid outer core is nearly 2900 km beneath Earth's surface, so we will never be able to observe it directly. This hot, dense, molten iron-rich body is continuously in motion and is the source of Earth's magnetic field. One of the most dynamic manifestations at Earth's surface of this fluid body is, perhaps, a reversal of the geomagnetic field. Unfortunately, the most recent polarity transition occurred at about 780 ka, so we have never observed a transition directly. It seems that a polarity transition spans many human lifetimes, so no human will ever witness the phenomenon in its entirety. Thus we are left with the tantalizing prospect that paleomagnetic records of polarity transitions may betray some of the secrets of the deep Earth. Certainly, if there are systematics in the reversal process and they can be documented, then this will reveal substantial information about the nature of the lowermost mantle and of the outer core. Despite their slowness on a human timescale, polarity transitions occur almost instantaneously on a geological timescale. This rapidity, together with limitations in the paleomagnetic recording process, prohibits a comprehensive description of any reversal transition both now and into the foreseeable future, which limits the questions that may at this stage be sensibly asked. The natural model for the geomagnetic field is a set of spherical harmonic components, and we are not able to obtain a reliable model for even the first few harmonic terms during a transition. Nevertheless, it is possible, in principle, to make statements about the harmonic character of a geomagnetic polarity transition without having a rigorous spherical harmonic description of one. For example, harmonic descriptions of recent geomagnetic polarity transitions that are purely zonal can be ruled out (a zonal harmonic does not change along a line of latitude). Gleaning information about transitions has proven to be difficult, but it does seem

  3. Polarized electron beams at SLAC

    International Nuclear Information System (INIS)

    Moffeit, K.C.

    1992-11-01

    SLAC has successfully accelerated high energy polarized electrons for the Stanford Linear Collider and fixed polarized nuclear target experiments. The polarized electron beams at SLAC use a gallium arsenide (GaAlAs for E-142) photon emission source to provide the beam of polarized electrons with polarization of approximately 28% (41% for E-142). While the beam emittance is reduced in the damping ring for SLC operation a system of bend magnets and superconducting solenoids preserve and orient the spin direction for maximum longitudinal polarization at the collision point. The electron polarization is monitored with a Compton scattering polarimeter, and was typically 22% at the e+e- collision point for the 1992 run. Improvements are discussed to increase the source polarization and to reduce the depolarization effects between the source and the collision point

  4. Analytical polarization calculations beyond SLIM

    International Nuclear Information System (INIS)

    Barber, D.P.

    1989-01-01

    A comparison is made between the theories of Bell and Leinaas and of Derbenev and Kondratenko for the spin polarization in electron storage rings. A calculation of polarization in HERA using the program SMILE of Mane is presented

  5. On Determinants of Political Polarization

    OpenAIRE

    Grechyna, Daryna

    2015-01-01

    Political polarization has been shown to significantly influence a country's economic performance. However, little is known about the drivers of political polarization. In this article, we aim to identify the main determinants of political polarization using Bayesian Model Averaging to overcome the problem of model uncertainty. We find that the level of trust within a country and the degree of income inequality are the most robust determinants of political polarization.

  6. Micro- and Nanopatterning of Functional Organic Monolayers on Oxide-Free Silicon by Laser-Induced Photothermal Desorption

    NARCIS (Netherlands)

    Scheres, L.; Klingebiel, B.; Maat, ter J.; Giesbers, M.; Jong, de J.H.S.G.M.; Hartmann, N.; Zuilhof, H.

    2010-01-01

    The photothermal laser patterning of functional organic monolayers, prepared on oxide-free hydrogen-terminated silicon, and subsequent backfilling of the laser-written lines with a second organic monolayer that differs in its terminal functionality, is described. Since the thermal monolayer

  7. Boc-protected ω-amino alkanedithiols provide chemically and thermally stable amine-terminated monolayers on gold.

    Science.gov (United States)

    Lee, Han Ju; Jamison, Andrew C; Lee, T Randall

    2015-02-24

    Four custom-designed bidentate adsorbates having either ammonium or Boc-protected amino termini and either methanethiol or ethanethioate headgroups were prepared for the purpose of generating amine-terminated self-assembled monolayers (SAMs) on evaporated gold surfaces. These adsorbates utilize a phenyl-based framework to connect the headgroups to a single hexadecyloxy chain, extending the amino functionality away from the surface of gold, providing two regions within the adsorbate structure where intermolecular interactions contribute to the stability of the fully formed thin film. The structural features of the resulting SAMs were characterized by ellipsometry, X-ray photoelectron spectroscopy, and polarization modulation infrared reflection-absorption spectroscopy. The collected data were compared to those of eight additional SAMs formed from analogous monodentate alkanethiols and alkanethioacetates having either a similar aromatic framework or a simple alkyl chain connecting the headgroup to the tailgroup. The analysis of the data obtained for the full set of SAMs revealed that both the tailgroup and headgroup influenced the formation of a well-packed monolayer, with the Boc-protected amine-terminated alkanethiols producing films with superior surface bonding and adsorbate packing as compared to those formed with ammonium tailgroups or alkanethioacetate headgroups. A comparison of the structural differences before and after deprotection of the Boc-protected amine-terminated thiolate SAMs revealed that the bidentate adsorbate was the most resistant to desorption during the Boc-deprotection procedure. Furthermore, solution-phase thermal desorption tests performed to evaluate the thermal stability of the Boc-deprotected amine-terminated alkanethiolate films provided further evidence of the enhanced stability associated with SAMs formed from these bidentate adsorbates.

  8. Polarized electrogowdy spacetimes censored

    Energy Technology Data Exchange (ETDEWEB)

    Nungesser, Ernesto, E-mail: ernesto.nungesser@aei.mpg.d [Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Am Muehlenberg 1, 14476 Potsdam (Germany)

    2010-05-01

    A sketch of the proof of strong cosmic censorship is presented for a class of solutions of the Einstein-Maxwell equations, those with polarized Gowdy symmetry. A key element of the argument is the observation that by means of a suitable choice of variables the central equations in this problem can be written in a form where they are identical to the central equations for general (i.e. non-polarized) vacuum Gowdy spacetimes. Using this it is seen that the results of Ringstroem on strong cosmic censorship in the vacuum case have implications for the Einstein-Maxwell case. Working out the geometrical meaning of these analytical results leads to the main conclusion.

  9. Failure Processes in Embedded Monolayer Graphene under Axial Compression

    Science.gov (United States)

    Androulidakis, Charalampos; Koukaras, Emmanuel N.; Frank, Otakar; Tsoukleri, Georgia; Sfyris, Dimitris; Parthenios, John; Pugno, Nicola; Papagelis, Konstantinos; Novoselov, Kostya S.; Galiotis, Costas

    2014-01-01

    Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of –0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1–2 nm. These results were compared with DFT computations performed on analogue coronene/PMMA oligomers and a reasonable agreement was obtained. PMID:24920340

  10. Shear rheology of lipid monolayers and insights on membrane fluidity

    Science.gov (United States)

    Espinosa, Gabriel; López-Montero, Iván; Monroy, Francisco; Langevin, Dominique

    2011-01-01

    The concept of membrane fluidity usually refers to a high molecular mobility inside the lipid bilayer which enables lateral diffusion of embedded proteins. Fluids have the ability to flow under an applied shear stress whereas solids resist shear deformations. Biological membranes require both properties for their function: high lateral fluidity and structural rigidity. Consequently, an adequate account must include, in addition to viscosity, the possibility for a nonzero shear modulus. This knowledge is still lacking as measurements of membrane shear properties have remained incomplete so far. In the present contribution we report a surface shear rheology study of different lipid monolayers that model distinct biologically relevant situations. The results evidence a large variety of mechanical behavior under lateral shear flow. PMID:21444777

  11. Monolayer phosphorene under time-dependent magnetic field

    Science.gov (United States)

    Nascimento, J. P. G.; Aguiar, V.; Guedes, I.

    2018-02-01

    We obtain the exact wave function of a monolayer phosphorene under a low-intensity time-dependent magnetic field using the dynamical invariant method. We calculate the quantum-mechanical energy expectation value and the transition probability for a constant and an oscillatory magnetic field. For the former we observe that the Landau level energy varies linearly with the quantum numbers n and m and the magnetic field intensity B0. No transition takes place. For the latter, we observe that the energy oscillates in time, increasing linearly with the Landau level n and m and nonlinearly with the magnetic field. The (k , l) →(n , m) transitions take place only for l = m. We investigate the (0,0) →(n , 0) and (1 , l) and (2 , l) probability transitions.

  12. A self assembled monolayer based microfluidic sensor for urea detection

    Science.gov (United States)

    Srivastava, Saurabh; Solanki, Pratima R.; Kaushik, Ajeet; Ali, Md. Azahar; Srivastava, Anchal; Malhotra, B. D.

    2011-07-01

    Urease (Urs) and glutamate dehydrogenase (GLDH) have been covalently co-immobilized onto a self-assembled monolayer (SAM) comprising of 10-carboxy-1-decanthiol (CDT) via EDC-NHS chemistry deposited onto one of the two patterned gold (Au) electrodes for estimation of urea using poly(dimethylsiloxane) based microfluidic channels (2 cm × 200 μm × 200 μm). The CDT/Au and Urs-GLDH/CDT/Au electrodes have been characterized using Fourier transform infrared (FTIR) spectroscopy, contact angle (CA), atomic force microscopy (AFM) and electrochemical cyclic voltammetry (CV) techniques. The electrochemical response measurement of a Urs-GLDH/CDT/Au bioelectrode obtained as a function of urea concentration using CV yield linearity as 10 to 100 mg dl-1, detection limit as 9 mg dl-1 and high sensitivity as 7.5 μA mM-1 cm-2.

  13. Nanobubble induced formation of quantum emitters in monolayer semiconductors

    Science.gov (United States)

    Shepard, Gabriella D.; Ajayi, Obafunso A.; Li, Xiangzhi; Zhu, X.-Y.; Hone, James; Strauf, Stefan

    2017-06-01

    The recent discovery of exciton quantum emitters in transition metal dichalcogenides (TMDCs) has triggered renewed interest of localized excitons in low-dimensional systems. Open questions remain about the microscopic origin previously attributed to dopants and/or defects as well as strain potentials. Here we show that the quantum emitters can be deliberately induced by nanobubble formation in WSe2 and BN/WSe2 heterostructures. Correlations of atomic-force microscope and hyperspectral photoluminescence images reveal that the origin of quantum emitters and trion disorder is extrinsic and related to 10 nm tall nanobubbles and 70 nm tall wrinkles, respectively. We further demonstrate that ‘hot stamping’ results in the absence of 0D quantum emitters and trion disorder. The demonstrated technique is useful for advances in nanolasers and deterministic formation of cavity-QED systems in monolayer materials.

  14. Graphene growth by conversion of aromatic self-assembled monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Turchanin, Andrey [Institute of Physical Chemistry, Friedrich Schiller University Jena (Germany); Jena Center for Soft Matter (JCSM), Jena (Germany); Center for Energy and Environmental Chemistry Jena (CEEC), Jena (Germany); Abbe Center of Photonics (ACP), Jena (Germany)

    2017-11-15

    Despite present diversity of graphene production methods there is still a high demand for improvement of the existing production schemes or development of new. Here a method is reviewed to produce graphene employing aromatic self-assembled monolayers (SAMs) as molecular precursors. This method is based on electron irradiation induced crosslinking of aromatic SAMs resulting in their conversion into carbon nanomembranes (CNMs) with high thermal stability and subsequent pyrolysis of CNMs into graphene in vacuum or in the inert atmosphere. Depending on the production conditions, such as chemical structure of molecular precursors, irradiation and annealing parameters, various properties of the produced graphene sheets including shape, crystallinity, thickness, optical properties and electric transport can be adjusted. The assembly of CNM/graphene van der Waals heterostructures opens a flexible route to non-destructive chemical functionalization of graphene for a variety of applications in electronic and photonic devices. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Resilient Nodeless d -Wave Superconductivity in Monolayer FeSe

    Science.gov (United States)

    Agterberg, D. F.; Shishidou, T.; O'Halloran, J.; Brydon, P. M. R.; Weinert, M.

    2017-12-01

    Monolayer FeSe exhibits the highest transition temperature among the iron based superconductors and appears to be fully gapped, seemingly consistent with s -wave superconductivity. Here, we develop a theory for the superconductivity based on coupling to fluctuations of checkerboard magnetic order (which has the same translation symmetry as the lattice). The electronic states are described by a symmetry based k .p -like theory and naturally account for the states observed by angle resolved photoemission spectroscopy. We show that a prediction of this theory is that the resultant superconducting state is a fully gapped, nodeless, d -wave state. This state, which would usually have nodes, stays nodeless because, as seen experimentally, the relevant spin-orbit coupling has an energy scale smaller than the superconducting gap.

  16. Thermal conductivity of bulk and monolayer MoS2

    KAUST Repository

    Gandi, Appala

    2016-02-26

    © Copyright EPLA, 2016. We show that the lattice contribution to the thermal conductivity of MoS2 strongly dominates the carrier contribution in a broad temperature range from 300 to 800 K. Since theoretical insight into the lattice contribution is largely missing, though it would be essential for materials design, we solve the Boltzmann transport equation for the phonons self-consistently in order to evaluate the phonon lifetimes. In addition, the length scale for transition between diffusive and ballistic transport is determined. The low out-of-plane thermal conductivity of bulk MoS2 (2.3 Wm-1K-1 at 300 K) is useful for thermoelectric applications. On the other hand, the thermal conductivity of monolayer MoS2 (131 Wm-1K-1 at 300 K) is comparable to that of Si.

  17. Engineering monolayer poration for rapid exfoliation of microbial membranes.

    Science.gov (United States)

    Pyne, Alice; Pfeil, Marc-Philipp; Bennett, Isabel; Ravi, Jascindra; Iavicoli, Patrizia; Lamarre, Baptiste; Roethke, Anita; Ray, Santanu; Jiang, Haibo; Bella, Angelo; Reisinger, Bernd; Yin, Daniel; Little, Benjamin; Muñoz-García, Juan C; Cerasoli, Eleonora; Judge, Peter J; Faruqui, Nilofar; Calzolai, Luigi; Henrion, Andre; Martyna, Glenn J; Grovenor, Chris R M; Crain, Jason; Hoogenboom, Bart W; Watts, Anthony; Ryadnov, Maxim G

    2017-02-01

    The spread of bacterial resistance to traditional antibiotics continues to stimulate the search for alternative antimicrobial strategies. All forms of life, from bacteria to humans, are postulated to rely on a fundamental host defense mechanism, which exploits the formation of open pores in microbial phospholipid bilayers. Here we predict that transmembrane poration is not necessary for antimicrobial activity and reveal a distinct poration mechanism that targets the outer leaflet of phospholipid bilayers. Using a combination of molecular-scale and real-time imaging, spectroscopy and spectrometry approaches, we introduce a structural motif with a universal insertion mode in reconstituted membranes and live bacteria. We demonstrate that this motif rapidly assembles into monolayer pits that coalesce during progressive membrane exfoliation, leading to bacterial cell death within minutes. The findings offer a new physical basis for designing effective antibiotics.

  18. Evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer techniques.

    Science.gov (United States)

    Schöne, Anne-Christin; Roch, Toralf; Schulz, Burkhard; Lendlein, Andreas

    2017-05-01

    Polymeric biomaterials are of specific relevance in medical and pharmaceutical applications due to their wide range of tailorable properties and functionalities. The knowledge about interactions of biomaterials with their biological environment is of crucial importance for developing highly sophisticated medical devices. To achieve optimal in vivo performance, a description at the molecular level is required to gain better understanding about the surface of synthetic materials for tailoring their properties. This is still challenging and requires the comprehensive characterization of morphological structures, polymer chain arrangements and degradation behaviour. The review discusses selected aspects for evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer methods as powerful techniques for studying interfacial properties, such as morphological and degradation processes. The combination of spectroscopic, microscopic and scattering methods with the Langmuir techniques adapted to polymers can substantially improve the understanding of their in vivo behaviour. © 2017 The Author(s).

  19. Nanoscale Nitrogen Doping in Silicon by Self-Assembled Monolayers.

    Science.gov (United States)

    Guan, Bin; Siampour, Hamidreza; Fan, Zhao; Wang, Shun; Kong, Xiang Yang; Mesli, Abdelmadjid; Zhang, Jian; Dan, Yaping

    2015-07-31

    This Report presents a nitrogen-doping method by chemically forming self-assembled monolayers on silicon. Van der Pauw technique, secondary-ion mass spectroscopy and low temperature Hall effect measurements are employed to characterize the nitrogen dopants. The experimental data show that the diffusion coefficient of nitrogen dopants is 3.66 × 10(-15) cm(2) s(-1), 2 orders magnitude lower than that of phosphorus dopants in silicon. It is found that less than 1% of nitrogen dopants exhibit electrical activity. The analysis of Hall effect data at low temperatures indicates that the donor energy level for nitrogen dopants is located at 189 meV below the conduction band, consistent with the literature value.

  20. Perforated monolayers. Progress report, July 1, 1990--December 31, 1992

    Energy Technology Data Exchange (ETDEWEB)

    Regen, S.L.

    1992-12-01

    Goal of this research program is to create ultrathin organic membranes that possess uniform and adjustable pores ( < 7{angstrom} diameter). Such membranes are expected to possess high permeation selectivity (permselectivity) and high permeability, and to provide the basis for energy-efficient methods of molecular separation. Work carried out has demonstrated feasibility of using ``perforated monolayer``-based composites as molecular sieve membranes. Specifically, composite membranes derived from Langmuir-Blodgett multilayers of the calix[6]arene-based surfactant shown below plus poly[l-(trimethylsilyl)-l-propyne] (PTMSP) were found to exhibit sieving behavior towards He, N{sub 2} and SF{sub 6}. Results of derivative studies that have also been completed are also described in this report.