WorldWideScience

Sample records for ina ligand sm-o

  1. Evaluation of the exothermicity of the chemi-ionization reaction Sm + OSmO+ + e−

    International Nuclear Information System (INIS)

    Cox, Richard M; Kim, JungSoo; Armentrout, P. B.; Bartlett, Joshua; VanGundy, Robert A.; Heaven, Michael C.; Ard, Shaun G.; Shuman, Nicholas S.; Viggiano, Albert A.; Melko, Joshua J.

    2015-01-01

    The exothermicity of the chemi-ionization reaction Sm + OSmO + + e − has been re-evaluated through the combination of several experimental methods. The thermal reactivity (300–650 K) of Sm + and SmO + with a range of species measured using a selected ion flow tube-mass spectrometer apparatus is reported and provides limits for the bond strength of SmO + , 5.661 eV ≤ D 0 (Sm + -O) ≤ 6.500 eV. A more precise value is measured to be 5.72 5 ± 0.07 eV, bracketed by the observed reactivity of Sm + and SmO + with several species using a guided ion beam tandem mass spectrometer (GIBMS). Combined with the established Sm ionization energy (IE), this value indicates an exothermicity of the title reaction of 0.08 ± 0.07 eV, ∼0.2 eV smaller than previous determinations. In addition, the ionization energy of SmO has been measured by resonantly enhanced two-photon ionization and pulsed-field ionization zero kinetic energy photoelectron spectroscopy to be 5.7427 ± 0.0006 eV, significantly higher than the literature value. Combined with literature bond energies of SmO, this value indicates an exothermicity of the title reaction of 0.14 ± 0.17 eV, independent from and in agreement with the GIBMS result presented here. The evaluated thermochemistry also suggests that D 0 (SmO) = 5.83 ± 0.07 eV, consistent with but more precise than the literature values. Implications of these results for interpretation of chemical release experiments in the thermosphere are discussed

  2. Synthesis, characterization and thermal expansion studies on ThO2-SmO1.5 solid solutions

    International Nuclear Information System (INIS)

    Panneerselvam, G.; Antony, M.P.

    2008-01-01

    Full text: A highly homogeneous Th 1-x Sm x O 2 ; 0 ≤ x ≤ 0.8 solid solutions were synthesized by co-precipitation technique and the co-precipitated samples were sintered at 1473 K. Compositions of the solid solutions were characterized by standard wet-chemical analysis. X-ray diffraction measurements were performed in the sintered pellets for structural analysis, lattice parameter calculation and determination of solid solubility of SmO 1.5 in ThO 2 matrix. Bulk and theoretical densities of solid solutions were also determined. A fluorite structure was observed for ThO 2 -SmO 1.5 solid solutions with 0-55.2 mol % SmO 1.5 . Their thermal expansion coefficients were measured using high temperature X-ray diffraction technique. The mean linear thermal expansivity, αm for ThO 2 -SmO 1.5 solid solutions containing 17.9, 41.7 and 52.0 mole percent of SmO 1.5 were determined in the temperature range 298 to 2000 K for the first time. The mean linear thermal expansion coefficients for ThO 2 -SmO 1.5 solid solutions are 10.47x10 -6 K -1 , 11.16x10 -6 K -1 and 11.45x10 -6 K -1 , respectively. The percentage linear thermal expansion in this temperature range, for ThO 2 -SmO 1.5 solid solutions containing 17.9, 41.7 and 52.0 mol % SmO 1.5 are 1.82,1.94 and 1.99 respectively. It is suggested that the solid solutions are stable up to 2000 K. It is also suggested that the effect and nature of the dopant are the important parameters influenced in the thermal expansion of the ThO 2

  3. Thermochemical studies on complex of [Sm(o-NBA)_3phen]_2

    Institute of Scientific and Technical Information of China (English)

    肖圣雄; 张建军; 李旭; 李强国; 任宁; 李环

    2010-01-01

    A ternary complex [Sm(o-NBA)3phen]2 (o-NBA: o-Nitrobenzoate; phen: 1,10-phenanthroline) was synthesized and characterized by elemental analysis, IR, molar conductance, and thermogravimetric analysis. The dissolution enthalpies of SmCl3·6H2O(s), o-HNBA(s) and phen·H2O(s) in mixed solvent (VHCl :VDMF :VDMSO=2:2:1) were determined by calorimetry at 298.15 K. The enthalpy change of the reaction was determined to be rHmΔθ=252.49±1.60 kJ/mol. Using the relevant data in the literature and a thermochemical recycle ...

  4. InaSAFE applications in disaster preparedness

    Science.gov (United States)

    Pranantyo, Ignatius Ryan; Fadmastuti, Mahardika; Chandra, Fredy

    2015-04-01

    Disaster preparedness activities aim to reduce the impact of disasters by being better prepared to respond when a disaster occurs. In order to better anticipate requirements during a disaster, contingency planning activities can be undertaken prior to a disaster based on a realistic disaster scenario. InaSAFE is a tool that can inform this process. InaSAFE is a free and open source software that estimates the impact to people and infrastructure from potential hazard scenarios. By using InaSAFE, disaster managers can develop scenarios of disaster impacts (people and infrastructures affected) to inform their contingency plan and emergency response operation plan. While InaSAFE provides the software framework exposure data and hazard data are needed as inputs to run this software. Then InaSAFE can be used to forecast the impact of the hazard scenario to the exposure data. InaSAFE outputs include estimates of the number of people, buildings and roads are affected, list of minimum needs (rice and clean water), and response checklist. InaSAFE is developed by Indonesia's National Disaster Management Agency (BNPB) and the Australian Government, through the Australia-Indonesia Facility for Disaster Reduction (AIFDR), in partnership with the World Bank - Global Facility for Disaster Reduction and Recovery (GFDRR). This software has been used in many parts of Indonesia, including Padang, Maumere, Jakarta, and Slamet Mountain for emergency response and contingency planning.

  5. Angle Integrated Photoemission Study of SmO0.85F0.15FeAs

    International Nuclear Information System (INIS)

    Hong-Wei, Ou; Jia-Feng, Zhao; Yan, Zhang; Da-Wei, Shen; Bo, Zhou; Le-Xian, Yang; Cheng, He; Fei, Chen; Min, Xu; Yan, Chen; Dong-Lai, Feng; Tao, Wu; Xian-Hui, Chen

    2008-01-01

    The electronic structure of the new superconductor SmO 1-x F x FeAs (x = 0.15) is studied by angle-integrated photoemission spectroscopy. Our data show a sharp feature very close to the Fermi energy, and a relative flat distribution of the density of states between 0.5eV and 3eV binding energy, which agrees well with the band structure calculations considering an antiferromagnetic ground state. No noticeable gap opening is observed at 12K below the superconducting transition temperature, indicating the existence of large ungapped regions in the Brillouin zone. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  6. Women Fellows of INAE | Women in Science | Initiatives | Indian ...

    Indian Academy of Sciences (India)

    Women Fellows of INAE. INAE - Indian National Academy of Engineering. Ms. Alpa Sheth Civil Engineering. Prof. Bharathi Bhat Electronics & Communication Engineering. Prof. Dipanwita Roy Chowdhury Computer Engineering and Information Technology. Prof. Kamala Krithivasan Computer Engineering and Information ...

  7. Identification of Ina proteins from Fusarium acuminatum

    Science.gov (United States)

    Scheel, Jan Frederik; Kunert, Anna Theresa; Pöschl, Ulrich; Fröhlich-Nowoisky, Janine

    2015-04-01

    Freezing of water above -36° C is based on ice nucleation activity (INA) mediated by ice nucleators (IN) which can be of various origins. Beside mineral IN, biological particles are a potentially important source of atmospheric IN. The best-known biological IN are common plant-associated bacteria. The IN activity of these bacteria is induced by a surface protein on the outer cell membrane, which is fully characterized. In contrast, much less is known about the nature of fungal IN. The fungal genus Fusarium is widely spread throughout the earth. It belongs to the Ascomycota and is one of the most severe fungal pathogens. It can affect a variety of organisms from plants to animals including humans. INA of Fusarium was already described about 30 years ago and INA of Fusarium as well as other fungal genera is assumed to be mediated by proteins or at least to contain a proteinaceous compound. Although many efforts were made the precise INA machinery of Fusarium and other fungal species including the proteins and their corresponding genes remain unidentified. In this study preparations from living fungal samples of F. acuminatum were fractionated by liquid chromatography and IN active fractions were identified by freezing assays. SDS-page and de novo sequencing by mass spectrometry were used to identify the primary structure of the protein. Preliminary results show that the INA protein of F. acuminatum is contained in the early size exclusion chromatography fractions indicating a high molecular size. Moreover we could identify a single protein band from IN active fractions at 130-145 kDa corresponding to sizes of IN proteins from bacterial species. To our knowledge this is for the first time an isolation of a single protein from in vivo samples, which can be assigned as IN active from Fusarium.

  8. Optical emission of InAs nanowires

    International Nuclear Information System (INIS)

    Möller, M; De Lima Jr, M M; Cantarero, A; Chiaramonte, T; Cotta, M A; Iikawa, F

    2012-01-01

    Wurtzite InAs nanowire samples grown by chemical beam epitaxy have been analyzed by photoluminescence spectroscopy. The nanowires exhibit two main optical emission bands at low temperatures. They are attributed to the recombination of carriers in quantum well structures, formed by zincblende–wurtzite alternating layers, and to the donor–acceptor pair. The blue-shift observed in the former emission band when the excitation power is increased is in good agreement with the type-II band alignment between the wurtzite and zincblende sections predicted by previous theoretical works. When increasing the temperature and the excitation power successively, an additional band attributed to the band-to-band recombination from wurtzite InAs appears. We estimated a lower bound for the wurtzite band gap energy of approximately 0.46 eV at low temperature. (paper)

  9. Optical emission of InAs nanowires

    Science.gov (United States)

    Möller, M.; de Lima, M. M., Jr.; Cantarero, A.; Chiaramonte, T.; Cotta, M. A.; Iikawa, F.

    2012-09-01

    Wurtzite InAs nanowire samples grown by chemical beam epitaxy have been analyzed by photoluminescence spectroscopy. The nanowires exhibit two main optical emission bands at low temperatures. They are attributed to the recombination of carriers in quantum well structures, formed by zincblende-wurtzite alternating layers, and to the donor-acceptor pair. The blue-shift observed in the former emission band when the excitation power is increased is in good agreement with the type-II band alignment between the wurtzite and zincblende sections predicted by previous theoretical works. When increasing the temperature and the excitation power successively, an additional band attributed to the band-to-band recombination from wurtzite InAs appears. We estimated a lower bound for the wurtzite band gap energy of approximately 0.46 eV at low temperature.

  10. Electrical characterization of InAs thin films

    Energy Technology Data Exchange (ETDEWEB)

    Botha, L.; Shamba, P.; Botha, J.R. [Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa)

    2008-07-01

    It is known that parallel conduction as a result of surface and /or interface charge accumulation significantly shields the bulk electrical properties of InAs thin films when characterized using Hall measurements. This parallel conduction in InAs can be modeled by using the two-layer model of Nedoluha and Koch [Zeitschrift fuer Physik 132, 608 (1952)]; where an InAs epilayer is treated as consisting of two conductors connected in parallel viz. a bulk and a surface layer. Here, this two-layer model is used to simulate Hall coefficient and conductivity data of InAs thin films ranging from strongly n-doped (n=10{sup 18} cm{sup -3}) to strongly p-doped (p{proportional_to}10{sup 19} cm{sup -3}) material. Conventional Hall approximations, i.e. those that assume uniform conduction from a single band, are then used to predict the apparent carrier concentration and mobility that will be determined from conventional Hall measurements, with the aim of illustrating the error of such a simplified analysis of InAs Hall data. Results show that, in addition to ignoring parallel conduction, the approximations of conventional Hall data analysis have a further inadequacy for p-type InAs, in that the high electron to hole mobility ratio in InAs is not taken into account. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Electrical characterization of InAs thin films

    International Nuclear Information System (INIS)

    Botha, L.; Shamba, P.; Botha, J.R.

    2008-01-01

    It is known that parallel conduction as a result of surface and /or interface charge accumulation significantly shields the bulk electrical properties of InAs thin films when characterized using Hall measurements. This parallel conduction in InAs can be modeled by using the two-layer model of Nedoluha and Koch [Zeitschrift fuer Physik 132, 608 (1952)]; where an InAs epilayer is treated as consisting of two conductors connected in parallel viz. a bulk and a surface layer. Here, this two-layer model is used to simulate Hall coefficient and conductivity data of InAs thin films ranging from strongly n-doped (n=10 18 cm -3 ) to strongly p-doped (p∝10 19 cm -3 ) material. Conventional Hall approximations, i.e. those that assume uniform conduction from a single band, are then used to predict the apparent carrier concentration and mobility that will be determined from conventional Hall measurements, with the aim of illustrating the error of such a simplified analysis of InAs Hall data. Results show that, in addition to ignoring parallel conduction, the approximations of conventional Hall data analysis have a further inadequacy for p-type InAs, in that the high electron to hole mobility ratio in InAs is not taken into account. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Growth and electrical characterization of Zn-doped InAs and InAs1-xSbx

    International Nuclear Information System (INIS)

    Venter, A.; Shamba, P.; Botha, L.; Botha, J.R.

    2009-01-01

    The electrical properties of Zn doped InAs and InAsSb layers grown on semi-insulating GaAs by metal organic vapour phase epitaxy, using dimethyl zinc as the p-type dopant source, have been studied. The influence of dopant flow rate, V/III ratio and substrate orientation on the electrical properties of these InAs and InAs 1-x Sb x layers have been studied at a few appropriate growth temperatures. A promising group V source, tertiary butyl arsenic was used as an alternative to arsenic hydride in the case of InAs growth. The electrical properties of the InAs and InAs 1-x Sb x epitaxial layers were mainly studied by the Hall effect. However, surface accumulation in these materials results in deceptive Hall results being extracted. A two layer model (assuming the layer to consist of two parallel conducting paths viz. surface and bulk) has therefore been used to extract sensible transport properties. In addition, conventional Hall measurements ignores the high electron to hole mobility ratio in InAs and InAsSb leading to erroneous transport properties.

  13. Femtosecond upconverted photocurrent spectroscopy of InAs quantum nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Yamada, Yasuhiro [Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011 (Japan); Tex, David M.; Kanemitsu, Yoshihiko, E-mail: kanemitu@scl.kyoto-u.ac.jp [Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011 (Japan); Japan Science and Technology Agency, CREST, Kyoto University, Uji, Kyoto 611-0011 (Japan); Kamiya, Itaru [Toyota Technological Institute, Nagoya, Aichi 468-8511 (Japan)

    2015-07-06

    The carrier upconversion dynamics in InAs quantum nanostructures are studied for intermediate-band solar-cell applications via ultrafast photoluminescence and photocurrent (PC) spectroscopy based on femtosecond excitation correlation (FEC) techniques. Strong upconverted PC-FEC signals are observed under resonant excitation of quantum well islands (QWIs), which are a few monolayer-thick InAs quantum nanostructures. The PC-FEC signal typically decays within a few hundred picoseconds at room temperature, which corresponds to the carrier lifetime in QWIs. The photoexcited electron and hole lifetimes in InAs QWIs are evaluated as functions of temperature and laser fluence. Our results provide solid evidence for electron–hole–hole Auger process, dominating the carrier upconversion in InAs QWIs at room temperature.

  14. Spin Injection, Manipulation, and Detection, in InAs Nanodevices

    Science.gov (United States)

    Jones, G. M.; Jonker, B. T.; Bennett, B. R.; Meyer, J. R.; Twigg, M. E.; Reinecke, T. L.; Park, D.; Pereverzev, S. V.; Badescu, C. S.; Li, C. H.; Hanbicki, A. T.; van'terve, O.; Vurgaftman, I.

    2008-03-01

    In this talk the authors will discuss their progress using InAs heterostructures to produce spin-polarized injection and detection, as well as manipulation of coherent spin-polarized electrons for a spin-based FET (SpinFET). High-quality n-type InAs heterostructures demonstrate many favorable characteristics necessary to the study of spin dynamics, including 2DEG's with small effective mass (m* = 0.023) and large g-factor (g = -15). Previously, high-mobility InAs heterostructures have been demonstrated in which electrons pass ballistically over hundreds of nanometers up to room temperature. Our devices seek to exploit the strong Spin-Orbit effect present in InAs to manipulate coherent spin-polarized electrons during transport, by producing perpendicular electric field using isolated top-gates fabricated over the electron transport region.

  15. 20 CFR 668.860 - What cash management procedures apply to INA grant funds?

    Science.gov (United States)

    2010-04-01

    ... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false What cash management procedures apply to INA... Administrative Requirements § 668.860 What cash management procedures apply to INA grant funds? INA grantees must... implement the Cash Management Improvement Act, found at 31 CFR part 205, apply by law to most recipients of...

  16. Single-photon generation with InAs quantum dots

    International Nuclear Information System (INIS)

    Santori, Charles; Fattal, David; Vuckovic, Jelena; Solomon, Glenn S; Yamamoto, Yoshihisa

    2004-01-01

    Single-photon generation using InAs quantum dots in pillar microcavities is described. The effects on performance of the excitation wavelength and polarization, and the collection bandwidth and polarization, are studied in detail. The efficiency and photon state purity of these devices have been measured, and issues affecting these parameters are discussed. Prospects for improved devices are also discussed

  17. Past and Present Development of INA's Liberalisation and Privatisation

    International Nuclear Information System (INIS)

    Lesic, A.; Stimac, B.

    2001-01-01

    The paper deals with the historical development aspects of the Croatian oil and gas industry INA. It describes the period from the very start of oil and gas production to the data of establishment of the Croatian state and afterwards. Some important milestones and political and economic events that impacted the development of the Croatian oil industry are described and commented, including changes toward liberalisation and privatisation of the oil and gas sector. The paper emphasises the role of INA in the Croatian economy and proposes some solutions for the liberalisation process and privatisation of the company that could prevent undesirable effects of privatisation and protect the interests of Croatia in the energy sector which is one of the main sectors of economy having influence on other production and service sectors and their competitiveness.(author)

  18. INA's Preparations for Liberalised Energy Market and Privatisation

    International Nuclear Information System (INIS)

    Dragicevic, T.; Kolundzic, S.

    2001-01-01

    Before opening of the market, energy entities must carry out numerous preparations in order to be ready for challenges of a competitive environment. Some preparations refer to legal and organisational issues, but many of them encompass reengineering of business processes, cost reduction schemes and various improvement measures aimed at maintenance or acquisition of a competitive advantage. INA is actively pursuing some of the above measures, but now, by the end of 2001, we also have to deal with preparations for privatisation. These two processes have some important common elements, competitiveness being certainly one of them. INA must work toward improving its competitive strength in the gas sector, in refining, in marketing of oil products, but also in various supporting activities. However, there are constraints that we have to observe, mainly related to social issues.(author)

  19. Reconstruction of an InAs nanowire using geometric tomography

    DEFF Research Database (Denmark)

    Pennington, Robert S.; König, Stefan; Alpers, Andreas

    Geometric tomography and conventional algebraic tomography algorithms are used to reconstruct cross-sections of an InAs nanowire from a tilt series of experimental annular dark-field images. Both algorithms are also applied to a test object to assess what factors affect the reconstruction quality....... When using the present algorithms, geometric tomography is faster, but artifacts in the reconstruction may be difficult to recognize....

  20. 22 CFR 40.68 - Aliens subject to INA 222(g).

    Science.gov (United States)

    2010-04-01

    ... 22 Foreign Relations 1 2010-04-01 2010-04-01 false Aliens subject to INA 222(g). 40.68 Section 40... § 40.68 Aliens subject to INA 222(g). An alien who, under the provisions of INA 222(g), has voided a... new nonimmigrant visa unless the alien complies with the requirements in 22 CFR 41.101 (b) or (c...

  1. Komunikační mix Svatebního salonu INA

    OpenAIRE

    Rybníčková, Michala

    2015-01-01

    Rybníčková, M. Marketing mix for Wedding Boutique INA. Bachelor thesis, Brno: Mendel university in Brno, 2015 This Bechelor thesis focuses on the marketing mix for the company Wedding Boutique INA. Survey results are used to evaluate the effectiveness of marketing tools currently used by INA. Furthermore, the results are used to recommend improvements to the marketing mix. Thesis also includes calculation of costs and scheduling for the year 2015.

  2. Homo- and heteroepitaxial growth behavior of upright InAs nanowires on InAs and GaAs substrates

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, Jens; Gottschalch, Volker; Paetzelt, Hendrik [Institut fuer Anorganische Chemie, Universitaet Leipzig, Johannesallee 29, D-04103 Leipzig (Germany); Wagner, Gerald [Institut fuer Kristallographie und Mineralogie, Universitaet Leipzig, Linnestr. 5, D-04103 Leipzig (Germany); Pietsch, Ulrich [Festkoerperphysik, Universitaet Siegen, D-57068 Siegen (Germany)

    2008-07-01

    Semiconductor nanowires (NW) acquire recently attraction because of promising new application fields in electronics and optoelectronic. We applied the vapor-liquid-solid mechanism with gold seeds in combination with low-pressure metal-organic vapor phase epitaxy (LP-MOVPE) to achieve replicable InAs NW growth with high growth rates. Since the initial alloying of the gold seeds with the substrate material plays a deciding role for the inceptive NW growth, InAs free standing nanowires were grown on GaAs(111)B substrate as well as on InAs/GaAs(111)B quasi-substrate. The influence of the MOVPE parameters will be discussed with respect to NW morphology and real-structure. A special focus will be set on the heteroepitaxial InAs NW growth on GaAs substrates. Gracing-incidence X-ray studies and transmission electron microscopy investigations revealed the existence of a thin Ga{sub x}In{sub 1-x}As graduated alloy layer with embedded crystalline gold alloy particles at the NW substrate interface. The effect of droplet composition on the VLS growth will be presented in a thermodynamic model.

  3. 20 CFR 668.650 - Can INA grantees exclude segments of the eligible population?

    Science.gov (United States)

    2010-04-01

    ... eligible population? 668.650 Section 668.650 Employees' Benefits EMPLOYMENT AND TRAINING ADMINISTRATION... population? (a) No, INA grantees cannot exclude segments of the eligible population. INA grantees must document in their Two Year Plan that a system is in place to afford all members of the eligible population...

  4. Ag-catalyzed InAs nanowires grown on transferable graphite flakes

    DEFF Research Database (Denmark)

    Meyer-Holdt, Jakob; Kanne, Thomas; Sestoft, Joachim E.

    2016-01-01

    on exfoliated graphite flakes by molecular beam epitaxy. Ag catalyzes the InAs nanowire growth selectively on the graphite flakes and not on the underlying InAs substrates. This allows for easy transfer of the flexible graphite flakes with as-grown nanowire ensembles to arbitrary substrates by a micro...

  5. 20 CFR 668.710 - What planning documents must an INA grantee submit?

    Science.gov (United States)

    2010-04-01

    ... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false What planning documents must an INA grantee... Planning/Funding Process § 668.710 What planning documents must an INA grantee submit? Each grantee... participant services and expenditures covering the two-year planning cycle. We will, in consultation with the...

  6. A soft lithographic approach to fabricate InAs nanowire field-effect transistors

    DEFF Research Database (Denmark)

    Madsen, Morten; Lee, S. H.; Shin, S.-H.

    2018-01-01

    -down approach and an epitaxial layer transfer process, using MBE-grown ultrathin InAs as a source wafer. The width of the InAs nanowires was controlled using solvent-assisted nanoscale embossing (SANE), descumming, and etching processes. By optimizing these processes, NWs with a width less than 50 nm were...

  7. Upotreba začina u proizvodnji tradicionalnih sireva

    OpenAIRE

    Josipović, Renata; Markov, Ksenija; Frece, Jadranka; Stanzer, Damir; Cvitković, Ante; Mrvčić, Jasna

    2016-01-01

    Sir je visoko cijenjeni mliječni proizvod u mnogim zemljama svijeta, a posebna pažnja pridaje se tradicionalnim sirevima, koji nisu samo hrana već i dio kulture i obilježja neke zemlje. Zahvaljujući zemljopisnom položaju i klimatsko-vegetacijskoj raznolikosti Republike Hrvatske, u pojedinim regijama razvijena je proizvodnja različitih tradicionalnih sireva uz upotrebu začina. Kod proizvodnje sireva sa začinima, začini se dodaju ili u sir koji se potom oblikuje, ili se sir omata lišćem začinsk...

  8. Nonlinear refraction at the absorption edge in InAs.

    Science.gov (United States)

    Poole, C D; Garmire, E

    1984-08-01

    The results of measurements of nonlinear refraction at the absorption edge in InAs between 68 and 90 K taken with an HF laser are compared with those of a band-gap resonant model in which the contribution of the light-hole band is included and found to account for more than 40% of the observed nonlinear refraction. A generalized expression for the nonlinear index is derived by using the complete Fermi-Dirac distribution function. Good agreement between theory and experiment is obtained, with no free parameters.

  9. Elastic properties and electron transport in InAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Migunov, Vadim

    2013-02-22

    The electron transport and elastic properties of InAs nanowires grown by chemical vapor deposition on InAs (001) substrate were studied experimentally, in-situ in a transmission electron microscope (TEM). A TEM holder allowing the measurement of a nanoforce while simultaneous imaging nanowire bending was used. Diffraction images from local areas of the wire were recorded to correlate elastic properties with the atomic structure of the nanowires. Another TEM holder allowing the application of electrical bias between the nanowire and an apex of a metallic needle while simultaneous imaging the nanowire in TEM or performing electron holography was used to detect mechanical vibrations in mechanical study or holographical observation of the nanowire inner potential in the electron transport studies. The combination of the scanning probe methods with TEM allows to correlate the measured electric and elastic properties of the nanowires with direct identification of their atomic structure. It was found that the nanowires have different atomic structures and different stacking fault defect densities that impacts critically on the elastic properties and electric transport. The unique methods, that were applied in this work, allowed to obtain dependencies of resistivity and Young's modulus of left angle 111 right angle -oriented InAs nanowires on defect density and diameter. It was found that the higher is the defect density the higher are the resistivity and the Young's modulus. Regarding the resistivity, it was deduced that the stacking faults increase the scattering of the electrons in the nanowire. These findings are consistent with the literature, however, the effect described by the other groups is not so pronounced. This difference can be attributed to the significant incompleteness of the physical models used for the data analysis. Regarding the elastic modulus, there are several mechanisms affecting the elasticity of the nanowires discussed in the thesis. It

  10. Polarized and resonant Raman spectroscopy on single InAs nanowires

    Science.gov (United States)

    Möller, M.; de Lima, M. M., Jr.; Cantarero, A.; Dacal, L. C. O.; Madureira, J. R.; Iikawa, F.; Chiaramonte, T.; Cotta, M. A.

    2011-08-01

    We report polarized Raman scattering and resonant Raman scattering studies on single InAs nanowires. Polarized Raman experiments show that the highest scattering intensity is obtained when both the incident and analyzed light polarizations are perpendicular to the nanowire axis. InAs wurtzite optical modes are observed. The obtained wurtzite modes are consistent with the selection rules and also with the results of calculations using an extended rigid-ion model. Additional resonant Raman scattering experiments reveal a redshifted E1 transition for InAs nanowires compared to the bulk zinc-blende InAs transition due to the dominance of the wurtzite phase in the nanowires. Ab initio calculations of the electronic band structure for wurtzite and zinc-blende InAs phases corroborate the observed values for the E1 transitions.

  11. INA-Rxiv: The Missing Puzzle in Indonesia’s Scientific Publishing Workflow

    Science.gov (United States)

    Rahim, R.; Irawan, D. E.; Zulfikar, A.; Hardi, R.; Arliman S, L.; Gultom, E. R.; Ginting, G.; Wahyuni, S. S.; Mesran, M.; Mahjudin, M.; Saputra, I.; Waruwu, F. T.; Suginam, S.; Buulolo, E.; Abraham, J.

    2018-04-01

    INA-Rxiv is the first Indonesia preprint server marking the new development initiated by the open science community. This study aimed at describing the development of INA-Rxiv and its conversations. It usedanalyzer of Inarxiv.id, WhatsApp Group Analyzer, and Twitter Analytics as the tools for data analysis complemented with observation.The results showed that INA-Rxiv users are growing because of the numerous discussions in social media, e.g.WhatsApp,as well as some other positive response of writers who have been using INA- Rxiv. The perspective of growth mindset and the implication of INA-Rxiv movement for filling up the gap in accelerating scientific dissemination process are presented at the end of this article.

  12. Surface Preparation of InAs (110 Using Atomic Hydrogen

    Directory of Open Access Journals (Sweden)

    T.D. Veal

    2002-06-01

    Full Text Available Atomic hydrogen cleaning has been used to produce structurally and electronically damage-free InAs(110 surfaces.  X-ray photoelectron spectroscopy (XPS was used to obtain chemical composition and chemical state information about the surface, before and after the removal of the atmospheric contamination. Low energy electron diffraction (LEED and high-resolution electron-energy-loss spectroscopy (HREELS were also used, respectively, to determine the surface reconstruction and degree of surface ordering, and to probe the adsorbed contaminant vibrational modes and the collective excitations of the clean surface. Clean, ordered and stoichiometric  InAs(110-(1×1 surfaces were obtained by exposure to thermally generated atomic hydrogen at a substrate temperature as low as 400ºC.  Semi-classical dielectric theory analysis of HREEL spectra of the phonon and plasmon excitations of the clean surface indicate that no electronic damage or dopant passivation were induced by the surface preparation method.

  13. Progress in low light-level InAs detectors- towards Geiger-mode detection

    Science.gov (United States)

    Tan, Chee Hing; Ng, Jo Shien; Zhou, Xinxin; David, John; Zhang, Shiyong; Krysa, Andrey

    2017-05-01

    InAs avalanche photodiodes (APDs) can be designed such that only electrons are allowed to initiate impact ionization, leading to the lowest possible excess noise factor. Optimization of wet chemical etching and surface passivation produced mesa APDs with bulk dominated dark current and responsivity that are comparable and higher, respectively, than a commercial InAs detector. Our InAs electron-APDs also show high stability with fluctuation of 0.1% when operated at a gain of 11.2 over 60 s. These InAs APDs can detect very weak signal down to 35 photons per pulse. Fabrication of planar InAs by Be implantation produced planar APDs with bulk dominated dark current. Annealing at 550 °C was necessary to remove implantation damage and to activate Be dopants. Due to minimal diffusion of Be, thick depletion of 8 μm was achieved. Since the avalanche gain increases exponentially with the thickness of avalanche region, our planar APD achieved high gain > 300 at 200 K. Our work suggest that both mesa and planar InAs APDs can exhibit high gain. When combined with a suitable preamplifier, single photon detection using InAs electron-APDs could be achieved.

  14. InAs nanowire formation on InP(001)

    International Nuclear Information System (INIS)

    Parry, H. J.; Ashwin, M. J.; Jones, T. S.

    2006-01-01

    The heteroepitaxial growth of InAs on InP(001) by solid source molecular beam epitaxy has been studied for a range of different growth temperatures and annealing procedures. Atomic force microscopy images show that nanowires are formed for deposition in the temperature range of 400-480 deg. C, and also following high temperature annealing (480 deg. C) after deposition at 400 deg. C. The wires show preferential orientation along and often exhibit pronounced serpentine behavior due to the presence of kinks, an effect that is reduced at increasing growth temperature. The results suggest that the serpentine behavior is related to the degree of initial surface order. Kinks in the wires appear to act as nucleation centers for In adatoms migrating along the wires during annealing, leading to the coexistence of large three-dimensional islands

  15. Self-Assembled InAs Nanowires as Optical Reflectors

    Directory of Open Access Journals (Sweden)

    Francesco Floris

    2017-11-01

    Full Text Available Subwavelength nanostructured surfaces are realized with self-assembled vertically-aligned InAs nanowires, and their functionalities as optical reflectors are investigated. In our system, polarization-resolved specular reflectance displays strong modulations as a function of incident photon energy and angle. An effective-medium model allows one to rationalize the experimental findings in the long wavelength regime, whereas numerical simulations fully reproduce the experimental outcomes in the entire frequency range. The impact of the refractive index of the medium surrounding the nanostructure assembly on the reflectance was estimated. In view of the present results, sensing schemes compatible with microfluidic technologies and routes to innovative nanowire-based optical elements are discussed.

  16. Spin interactions in InAs quantum dots

    Science.gov (United States)

    Doty, M. F.; Ware, M. E.; Stinaff, E. A.; Scheibner, M.; Bracker, A. S.; Gammon, D.; Ponomarev, I. V.; Reinecke, T. L.; Korenev, V. L.

    2006-03-01

    Fine structure splittings in optical spectra of self-assembled InAs quantum dots (QDs) generally arise from spin interactions between particles confined in the dots. We present experimental studies of the fine structure that arises from multiple charges confined in a single dot [1] or in molecular orbitals of coupled pairs of dots. To probe the underlying spin interactions we inject particles with a known spin orientation (by using polarized light to perform photoluminescence excitation spectroscopy experiments) or use a magnetic field to orient and/or mix the spin states. We develop a model of the spin interactions that aids in the development of quantum information processing applications based on controllable interactions between spins confined to QDs. [1] Polarized Fine Structure in the Photoluminescence Excitation Spectrum of a Negatively Charged Quantum Dot, Phys. Rev. Lett. 95, 177403 (2005)

  17. Electronic structure of GaAs with InAs (001) monolayer

    International Nuclear Information System (INIS)

    Tit, N.; Peressi, M.

    1995-04-01

    The effect on the electronic structure of an InAs monomolecular plane inserted in bulk GaAs is investigated theoretically. The (InAs) 1 (GaAs) n (001) strained superlattice is studied via ab-initio self-consistent pseudopotential calculations. Both electrons and holes are localized nearby the inserted InAs monolayer, which therefore acts as a quantum well for all the charge carriers. The small thickness of the inserted InAs slab is responsible of high confinement energies for the charge carriers, and therefore the interband electron-heavy-hole transition energy is close to the energy gap of the bulk GaAs, in agreement with recent experimental data. (author). 18 refs, 4 figs

  18. Wet-chemical passivation of InAs: toward surfaces with high stability and low toxicity.

    Science.gov (United States)

    Jewett, Scott A; Ivanisevic, Albena

    2012-09-18

    In a variety of applications where the electronic and optical characteristics of traditional, siliconbased materials are inadequate, recently researchers have employed semiconductors made from combinations of group III and V elements such as InAs. InAs has a narrow band gap and very high electron mobility in the near-surface region, which makes it an attractive material for high performance transistors, optical applications, and chemical sensing. However, silicon-based materials remain the top semiconductors of choice for biological applications, in part because of their relatively low toxicity. In contrast to silicon, InAs forms an unstable oxide layer under ambient conditions, which can corrode over time and leach toxic indium and arsenic components. To make InAs more attractive for biological applications, researchers have investigated passivation, chemical and electronic stabilization, of the surface by adlayer adsorption. Because of the simplicity, low cost, and flexibility in the type of passivating molecule used, many researchers are currently exploring wet-chemical methods of passivation. This Account summarizes much of the recent work on the chemical passivation of InAs with a particular focus on the chemical stability of the surface and prevention of oxide regrowth. We review the various methods of surface preparation and discuss how crystal orientation affects the chemical properties of the surface. The correct etching of InAs is critical as researchers prepare the surface for subsequent adlayer adsorption. HCl etchants combined with a postetch annealing step allow the tuning of the chemical properties in the near-surface region to either arsenic- or indium-rich environments. Bromine etchants create indium-rich surfaces and do not require annealing after etching; however, bromine etchants are harsh and potentially destructive to the surface. The simultaneous use of NH(4)OH etchants with passivating molecules prevents contact with ambient air that can

  19. Formation of nanogaps in InAs nanowires by selectively etching embedded InP segments.

    Science.gov (United States)

    Schukfeh, M I; Storm, K; Hansen, A; Thelander, C; Hinze, P; Beyer, A; Weimann, T; Samuelson, L; Tornow, M

    2014-11-21

    We present a method to fabricate nanometer scale gaps within InAs nanowires by selectively etching InAs/InP heterostructure nanowires. We used vapor-liquid-solid grown InAs nanowires with embedded InP segments of 10-60 nm length and developed an etching recipe to selectively remove the InP segment. A photo-assisted wet etching process in a mixture of acetic acid and hydrobromic acid gave high selectivity, with accurate removal of InP segments down to 20 nm, leaving the InAs wire largely unattacked, as verified using scanning electron and transmission electron microscopy. The obtained nanogaps in InAs wires have potential as semiconducting electrodes to investigate electronic transport in nanoscale objects. We demonstrate this functionality by dielectrophoretically trapping 30 nm diameter gold nanoparticles into the gap.

  20. Formation of nanogaps in InAs nanowires by selectively etching embedded InP segments

    International Nuclear Information System (INIS)

    Schukfeh, M I; Hansen, A; Tornow, M; Storm, K; Thelander, C; Samuelson, L; Hinze, P; Weimann, T; Beyer, A

    2014-01-01

    We present a method to fabricate nanometer scale gaps within InAs nanowires by selectively etching InAs/InP heterostructure nanowires. We used vapor–liquid–solid grown InAs nanowires with embedded InP segments of 10–60 nm length and developed an etching recipe to selectively remove the InP segment. A photo-assisted wet etching process in a mixture of acetic acid and hydrobromic acid gave high selectivity, with accurate removal of InP segments down to 20 nm, leaving the InAs wire largely unattacked, as verified using scanning electron and transmission electron microscopy. The obtained nanogaps in InAs wires have potential as semiconducting electrodes to investigate electronic transport in nanoscale objects. We demonstrate this functionality by dielectrophoretically trapping 30 nm diameter gold nanoparticles into the gap. (paper)

  1. Linear electro-optic coefficient in multilayer self-organized InAs quantum dot structures

    NARCIS (Netherlands)

    Akca, I.B.; Dana, A.; Aydinli, A.; Rossetti, M.; Li, L.; Dagli, N.; Fiore, A.

    2007-01-01

    The electro-optic coefficients of self-organized InAs quantum dot layers in molecular beam epitaxy grown laser structures in reverse bias have been investigated. Enhanced electrooptic coefficients compared to bulk GaAs were observed.

  2. Electrical characterisation of Sn doped InAs grown by MOVPE

    International Nuclear Information System (INIS)

    Shamba, P.; Botha, L.; Krug, T.; Venter, A.; Botha, J.R.

    2008-01-01

    The feasibility of tetraethyl tin (TESn) as an n-type dopant for InAs is investigated. The electrical properties of Sn doped InAs films grown on semi-insulating GaAs substrates by MOVPE are extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that Sn concentrations can be controlled over 2 orders of magnitude. The Sn doped InAs layers exhibit carrier concentrations between 2.7 x 10 17 and 4.7 x 10 19 cm -3 with 77 K mobilities ranging from 12 000 to 1300 cm 2 /Vs. Furthermore, the influence of the variation of these parameters on the structural properties of InAs are also reported. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. La costituzione dell’INA e il monopolio statale delle assicurazioni (1912-1922 = The constitution of INA and the state monopoly of insurance (1912-1922

    Directory of Open Access Journals (Sweden)

    Serena Potito

    2012-07-01

    Full Text Available Il saggio –basato principalmente su documenti attualmente conservati presso l’Archivio Storico dell’INA, a Roma– esamina le vicende legate alla nascita dell’Istituto, costituito in un regime transitorio di monopolio relativo nel settore delle assicurazioni sulla vita.A causa del suo significato economico e politico, questa speciale forma di monopolio statale diede luogo a molte reazioni nell’ambito finanziario e politico nazionale, pertanto l’INA iniziò i primi anni di attività in una situazione conflittuale ed incerta.Il saggio inoltre approfondisce le ripercussioni sul mercato assicurativo internazionale in seguito alla nascita dell’INA.Durante il decennio di monopolio parziale dell’Istituto nel settore delle assicurazioni sulla vita (1912-1922, le compagnie di assicurazione straniere ritennero compromessi i loro interessi finanziari nel mercato italiano, e lo osteggiarono fino al 1923, quando una nuova legge riformò il mercato assicurativo sulla vita, abolendo il regime di monopolio.The essay –mainly based on documents actually preserved in the Historical Archives of INA, in Rome– examines the events connected with the foundation of the Institute, established in a transient condition of partial monopoly system in life insurance sector. Because of its economic and political meaning, this special form of state monopoly gave rise to many reactions in the financial and political national context, and so INA started its first years of activity in a troubled and unstable situation. The essay also discusses about the repercussions on international insurance market in consequence of the foundation of INA.During the ten-year perior of partial monopoly of the Institute in life insurance sector (1912-1922, foreign insurance companies deemed their financial interest in Italian market jeopardized, and contrasted with it until 1923, when a new act reformed life insurance market, abrogating monopoly system. 

  4. Growth and characterization of InAs quantum dots on silicon

    Energy Technology Data Exchange (ETDEWEB)

    Hansen, L.; Ankudinov, A.; Bensing, F.; Wagner, J.; Wagner, V.; Geurts, J. [Wuerzburg Univ. (Germany). Lehrstuhl fuer Experimentelle Physik 3; Ade, G.; Hinze, P. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Waag, A. [Ulm Univ. (Germany). Abt. Halbleiterphysik

    2001-03-08

    We present a comprehensive investigation of molecular beam epitaxial (MBE) grown InAs quantum dots (QD) on silicon (001) and (111) by reflection high energy electron diffraction (RHEED) and Raman spectroscopy in UHV environment and ex-situ by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Two different ways were developed to prepare up to 10{sup 11} cm{sup -2} InAs QDs on Si(001). One is the conventional mode by exceeding a critical thickness of deposition at which 2D growth changes towards a 3D growth mode. A second way is a dewetting transition, induced by cooling an approximately 1 ML thin 2D InAs layer from growth temperature below a critical temperature at which RHEED indicates the formation of nanoislands. Samples grown in both manners show significant differences in morphology and shape though RHEED, TEM and Raman studies correspondingly indicate strain relaxation. On Si(111) InAs grows in the common temperature range for InAs growth ({proportional_to}400 C) in flat clusters separated by deep trenches. A previous passivation of the Si(111) surface with arsenic at {proportional_to}700 C on the other hand leads to the formation of large InAs nanocrystals. (orig.)

  5. Awareness of the Vysočina Regional Food Labels With Context of Their Media Presence

    Directory of Open Access Journals (Sweden)

    Martina Chalupová

    2016-01-01

    Full Text Available The article presents results of research study that focused on the recognition of the Vysočina regional labels among the consumers in the region in connection with media analysis about the topic. Research among consumers was conducted in each district of Vysočina Region (Jihlava, Žďár nad Sázavou, Třebíč, Havlíčkův Brod and Pelhřimov by interviewing a sample of 819 respondents, selected by quota sampling methods. The research was aimed at analysing the ability of respondents to recognise and differentiate two existing regional labels VYSOČINA Regional Product®, Regional Food Vysočina Region and also nonexistent brand From Our Region Vysočina, created by authors. Data have been processed with correspondence analysis and showed that respondents connect different characteristics with the labels. Media analysis of the Vysočina regional labels revealed that media may help building awareness about the labels but they do not shape respondents’ views on them. Examining the link between the frequency of different types of information in media and their potential impact on the labels’ pereception by consumers have shown distorted image. Stronger consensus between research and media analysis have been examined only on importance of products’ origin, which can be viewed as a logical inference from the name of the labels.

  6. Metalorganic vapour epitaxial growth and infrared characterisation of InAsSb and InAs on InAs substrates

    CSIR Research Space (South Africa)

    Baisitse, TR

    2006-07-01

    Full Text Available Motivation for the research: Interest exists in III-V semiconducting materials (InAs, GaSb, InSb and related alloys) for the detection of infrared radiation; Such materials could be used as alternatives for future infrared detectors and various...

  7. InAs quantum dots as charge storing elements for applications in flash memory devices

    Energy Technology Data Exchange (ETDEWEB)

    Islam, Sk Masiul; Biswas, Pranab [Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302 (India); Banerji, P., E-mail: pallab@matsc.iitkgp.ernet.in [Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302 (India); Chakraborty, S. [Applied Materials Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Sector-I, Kolkata 700 064 (India)

    2015-08-15

    Graphical abstract: - Highlights: • Catalyst-free growth of InAs quantum dots was carried out on high-k ZrO{sub 2}. • Memory device with InAs quantum dots as charge storage nodes are fabricated. • Superior memory window, low leakage and reasonably good retention were observed. • Carrier transport phenomena are explained in both program and erase operations. - Abstract: InAs quantum dots (QDs) were grown by metal organic chemical vapor deposition technique to use them as charge storage nodes. Uniform QDs were formed with average diameter 5 nm and height 5–10 nm with a density of 2 × 10{sup 11} cm{sup −2}. The QDs were grown on high-k dielectric layer (ZrO{sub 2}), which was deposited onto ultra-thin GaP passivated p-GaAs (1 0 0) substrate. A charge storage device with the structure Metal/ZrO{sub 2}/InAs QDs/ZrO{sub 2}/(GaP)GaAs/Metal was fabricated. The devices containing InAs QDs exhibit superior memory window, low leakage current density along with reasonably good charge retention. A suitable electronic band diagram corresponding to programming and erasing operations was proposed to explain the operation.

  8. Electronic and optical properties of graphene-like InAs: An ab initio study

    Science.gov (United States)

    Sohrabi, Leila; Boochani, Arash; Ali Sebt, S.; Mohammad Elahi, S.

    2018-03-01

    The present work initially investigates structural, optical, and electronic properties of graphene-like InAs by using the full potential linear augmented plane wave method in the framework of density functional theory and is then compared with the bulk Indium Arsenide in the wurtzite phase. The lattice parameters are optimized with GGA-PBE and LDA approximations for both 2D- and 3D-InAs. In order to study the electronic properties of graphene-like InAs and bulk InAs in the wurtzite phase, the band gap is calculated by GGA-PBG and GGA-EV approximations. Moreover, optical parameters of graphene-like InAs and bulk InAs such as the real and imaginary parts of dielectric function, electron energy loss function, refractivity, extinction and absorption coefficients, and optical conductivity are investigated. Plasmonic frequencies of 2D- and 3D-InAs are also calculated by using maximum electron energy loss function and the roots of the real part of the dielectric function.

  9. X-ray diffraction analysis of InAs nanowires

    International Nuclear Information System (INIS)

    Davydok, Anton

    2013-01-01

    Semiconductor nanowires have attracted great interest as building blocks for future electronic and optoelectronic devices. The variability of the growth process opens the opportunity to control and combine the various properties tailoring for specific application. It was shown that the electrical and optical characteristics of the nanowires are strongly connected with their structure. Despite intensive research in this field, the growth process is still not fully understood. In particular, extensive real structure investigations are required. Most of the reports dedicated on the structural researches are based on the results of scanning electron microscopy (SEM) or transmission electron microscopy (TEM). SEM provides an image of the surface with nanostructures and is mainly used to describe the morphology of the sample, but it does not bring information about the internal structure, phase composition and defect structure. At the same time, the internal structure can be examined by TEM down to atomic scale. TEM image of good quality are very expensive due to the efforts in sample preparation and in localisation of a single object. All these aspects make the statistical structural analysis difficult. In the present work, X-ray diffraction analysis has been applied for structural investigation of InAs nanowires grown by different techniques. Using various X-ray diffraction geometries, the nanowire systems were investigated in terms of the lattice parameters, phase composition, strains and displacement fields and stacking defects. In particular, realizing grazing incidence diffraction and controlling the penetration depth of X-ray beam, we characterized sample series grown by Au-assisted metal organic phase epitaxy on GaAs [111]B substrate with different growth time. According to the results of SEM and X-ray investigations, a model of the growth process has been proposed. A more detailed analysis was performed on InAs nanowires grown by molecular beam epitaxy (MBE) on

  10. Reduction of dinitrogen ligands

    International Nuclear Information System (INIS)

    Richards, R.L.

    1983-01-01

    Processes of dinitrogen ligand reduction in complexes of transition metals are considered. The basic character of the dinitrogen ligand is underlined. Data on X-ray photoelectronic spectroscopy and intensities of bands ν (N 2 ) in IR-spectra of nitrogen complexes are given. The mechanism of protonation of an edge dinitrogen ligand is discussed. Model systems and mechanism of nitrogenogenase are compared

  11. Growth of InAs Quantum Dots on Germanium Substrate Using Metal Organic Chemical Vapor Deposition Technique

    Directory of Open Access Journals (Sweden)

    Tyagi Renu

    2009-01-01

    Full Text Available Abstract Self-assembled InAs quantum dots (QDs were grown on germanium substrates by metal organic chemical vapor deposition technique. Effects of growth temperature and InAs coverage on the size, density, and height of quantum dots were investigated. Growth temperature was varied from 400 to 450 °C and InAs coverage was varied between 1.40 and 2.35 monolayers (MLs. The surface morphology and structural characteristics of the quantum dots analyzed by atomic force microscope revealed that the density of the InAs quantum dots first increased and then decreased with the amount of InAs coverage; whereas density decreased with increase in growth temperature. It was observed that the size and height of InAs quantum dots increased with increase in both temperature and InAs coverage. The density of QDs was effectively controlled by growth temperature and InAs coverage on GaAs buffer layer.

  12. Channeling study of laser-induced defect generation in InP and InAs

    International Nuclear Information System (INIS)

    Burdel', K.K.; Kashkarov, P.K.; Timoshenko, V.Yu.; Chechenin, N.G.

    1992-01-01

    Damage production in InP and InAs single crystals induced by a ruby-laser pulse irradiation with τ p =20 ms in the energy density region W=0.05-1.0 J/cm 2 is studied by the channeling and Rutherford backscattering techniques. The defect generation threshold was determined to be equal to 0.2 J/cm 2 and 0.55 J/cm 2 for InP and InAs crystals, respectively. Stoichiometric defects in InP crystals were observed at W>=0.5 J/cm 2 . The temperature fields in InP and InAs under laser irradiation were calculated. The experimental observations are considered as a result of a selective evaporation of the components from the melt

  13. InAs film grown on Si(111) by metal organic vapor phase epitaxy

    International Nuclear Information System (INIS)

    Caroff, P; Jeppsson, M; Mandl, B; Wernersson, L-E; Wheeler, D; Seabaugh, A; Keplinger, M; Stangl, J; Bauer, G

    2008-01-01

    We report the successful growth of high quality InAs films directly on Si(111) by Metal Organic Vapor Phase Epitaxy. A nearly mirror-like and uniform InAs film is obtained at 580 0 C for a thickness of 2 μm. We measured a high value of the electron mobility of 5100 cm 2 /Vs at room temperature. The growth is performed using a standard two-step procedure. The influence of the nucleation layer, group V flow rate, and layer thickness on the electrical and morphological properties of the InAs film have been investigated. We present results of our studies by Atomic Force Microscopy, Scanning Electron Microscopy, electrical Hall/van der Pauw and structural X-Ray Diffraction characterization

  14. InAs migration on released, wrinkled InGaAs membranes used as virtual substrate

    International Nuclear Information System (INIS)

    Filipe Covre da Silva, S; Lanzoni, E M; De Araujo Barboza, V; Deneke, Ch; Malachias, A; Kiravittaya, S

    2014-01-01

    Partly released, relaxed and wrinkled InGaAs membranes are used as virtual substrates for overgrowth with InAs. Such samples exhibit different lattice parameters for the unreleased epitaxial parts, the released flat, back-bond areas and the released wrinkled areas. A large InAs migration towards the released membrane is observed with a material accumulation on top of the freestanding wrinkles during overgrowth. A semi-quantitative analysis of the misfit strain shows that the material migrates to the areas of the sample with the lowest misfit strain, which we consider as the areas of the lowest chemical potential of the surface. Material migration is also observed for the edge-supported, freestanding InGaAs membranes found on these samples. Our results show that the released, wrinkled nanomembranes offer a growth template for InAs deposition that fundamentally changes the migration behavior of the deposited material on the growth surface. (paper)

  15. Growth-interruption-induced low-density InAs quantum dots on GaAs

    International Nuclear Information System (INIS)

    Li, L. H.; Alloing, B.; Chauvin, N.; Fiore, A.; Patriarche, G.

    2008-01-01

    We investigate the use of growth interruption to obtain low-density InAs quantum dots (QDs) on GaAs. The process was realized by Ostwald-type ripening of a thin InAs layer. It was found that the optical properties of the QDs as a function of growth interruption strongly depend on InAs growth rate. By using this approach, a low density of QDs (4 dots/μm 2 ) with uniform size distribution was achieved. As compared to QDs grown without growth interruption, a larger energy separation between the QD confined levels was observed, suggesting a situation closer to the ideal zero-dimensional system. Combining with an InGaAs capping layer such as In-rich QDs enable 1.3 μm emission at 4 K

  16. Wavelength tuning of InAs quantum dots grown on InP (100) by chemical-beam epitaxy

    International Nuclear Information System (INIS)

    Gong, Q.; Noetzel, R.; Veldhoven, P.J. van; Eijkemans, T.J.; Wolter, J.H.

    2004-01-01

    We report on an effective way to continuously tune the emission wavelength of InAs quantum dots (QDs) grown on InP (100) by chemical-beam epitaxy. The InAs QD layer is embedded in a GaInAsP layer lattice matched to InP. With an ultrathin GaAs layer inserted between the InAs QD layer and the GaInAsP buffer, the peak wavelength from the InAs QDs can be continuously tuned from above 1.6 μm down to 1.5 μm at room temperature. The major role of the thin GaAs layer is to greatly suppress the As/P exchange during the deposition of InAs and subsequent growth interruption under arsenic flux, as well as to consume the segregated surface In layer floating on the GaInAsP buffer layer

  17. Hall and thermoelectric evaluation of p-type InAs

    Energy Technology Data Exchange (ETDEWEB)

    Wagener, M.C., E-mail: magnus.wagener@nmmu.ac.z [Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Wagener, V.; Botha, J.R. [Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa)

    2009-12-15

    This paper compares the galvanometric and thermoelectric evaluation of the electrical characteristics of narrow gap semiconductors. In particular, the influence of a surface inversion layer is incorporated into the analysis of the temperature-dependent Hall and thermoelectric measurements of p-type InAs. The temperature at which the Seebeck coefficient of p-type material changes sign is shown to be unaffected by the presence of degenerate conduction paths. This finding consequently facilitated the direct determination of the acceptor density of lightly doped thin film InAs.

  18. Spin effects in InAs self-assembled quantum dots

    Directory of Open Access Journals (Sweden)

    Brasil Maria

    2011-01-01

    Full Text Available Abstract We have studied the polarized resolved photoluminescence in an n-type resonant tunneling diode (RTD of GaAs/AlGaAs which incorporates a layer of InAs self-assembled quantum dots (QDs in the center of a GaAs quantum well (QW. We have observed that the QD circular polarization degree depends on applied voltage and light intensity. Our results are explained in terms of the tunneling of minority carriers into the QW, carrier capture by InAs QDs and bias-controlled density of holes in the QW.

  19. Jezdecké stezky v kraji Vysočina

    OpenAIRE

    Bendeová, Tereza

    2014-01-01

    This bachelor thesis discusses the topic of riding trails in the Vysočina region. At the beginning I discuss the role of equestrian tourism in the Czech Republic. There are briefly described origins and conditions of riding trails in the regions and also the list of the public support and grants for development of equestrian tourism. The next part focuses on chosen region and characterizes its natural and cultural heritage. There are also described several trails through the Vysočina region. ...

  20. Electronic Structures of Strained InAs x P1-x by Density Functional Theory.

    Science.gov (United States)

    Lee, Seung Mi; Kim, Min-Young; Kim, Young Heon

    2018-09-01

    We investigated the effects of strain on the electronic structures of InAsxP1-x using quantum mechanical density functional theory calculations. The electronic band gap and electron effective mass decreased with the increase of the uniaxial tensile strain along the [0001] direction of wurtzite InAs0.75P0.25. Therefore, faster electron movements are expected. These theoretical results are in good agreement with the experimental measurements of InAs0.75P0.25 nanowire.

  1. Hall and thermoelectric evaluation of p-type InAs

    International Nuclear Information System (INIS)

    Wagener, M.C.; Wagener, V.; Botha, J.R.

    2009-01-01

    This paper compares the galvanometric and thermoelectric evaluation of the electrical characteristics of narrow gap semiconductors. In particular, the influence of a surface inversion layer is incorporated into the analysis of the temperature-dependent Hall and thermoelectric measurements of p-type InAs. The temperature at which the Seebeck coefficient of p-type material changes sign is shown to be unaffected by the presence of degenerate conduction paths. This finding consequently facilitated the direct determination of the acceptor density of lightly doped thin film InAs.

  2. Ligands in PSI structures

    International Nuclear Information System (INIS)

    Kumar, Abhinav; Chiu, Hsiu-Ju; Axelrod, Herbert L.; Morse, Andrew; Elsliger, Marc-André; Wilson, Ian A.; Deacon, Ashley

    2010-01-01

    A survey of the types and frequency of ligands that are bound to PSI structures is analyzed as well as their utility in functional annotation of previously uncharacterized proteins. Approximately 65% of PSI structures report some type of ligand(s) that is bound in the crystal structure. Here, a description is given of how such ligands are handled and analyzed at the JCSG and a survey of the types, variety and frequency of ligands that are observed in the PSI structures is also compiled and analyzed, including illustrations of how these bound ligands have provided functional clues for annotation of proteins with little or no previous experimental characterization. Furthermore, a web server was developed as a tool to mine and analyze the PSI structures for bound ligands and other identifying features

  3. Syntheses, crystal structures and spectroscopic properties of copper(II)-tetracyanometallate(II) complexes with nicotinamide and isonicotinamide ligands

    Science.gov (United States)

    Sayın, Elvan; Kürkçüoğlu, Güneş Süheyla; Yeşilel, Okan Zafer; Hökelek, Tuncer

    2015-09-01

    Four new one dimensional (1D) cyanide complexes, namely {[Cu(NH3)4(μ-na)][M‧(CN)4]}n and {[Cu(NH3)2(ina)2M‧(μ-CN)2(CN)2]}n (M‧(II) = Pd (1 and 3) or Pt (2 and 4), na:nicotinamide and ina:isonicotinamide) have been synthesized and characterized by elemental, spectral (FT-IR and Raman), and thermal (TG, DTG and DTA) analyses. The crystal structures of complexes 1-3 have been determined by single crystal X-ray diffraction technique. In complexes 1 and 2, na ligand is coordinated to the adjacent Cu(II) ions as a bridging ligand, giving rise to 1D linear cationic chain and the [M‧(CN)4]2- anionic complex acts as a counter ion. Complexes 3 and 4 are also 1D linear chain in which two cyanide ligands bridged neighboring M‧(II) and Cu(II) ions, while ina ligand is coordinated Cu(II) ion through nitrogen atom of pyridine ring. In the complexes, the Cu(II) ions adopt distorted octahedral geometries, while M‧(II) ions are four coordinated with four carbon atoms from cyanide ligands in square-planar geometries. The adjacent chains are further stacked through intermolecular hydrogen bond, Nsbnd Hṡṡṡπ, Csbnd H⋯M‧ and M‧⋯π interactions to form 3D supramolecular networks. Vibration assignments are given for all the observed bands. In addition, thermal stabilities of the compounds are also discussed.

  4. Intrinsic quantum dots in InAs nanowires

    International Nuclear Information System (INIS)

    Weis, Karl Martin Darius

    2013-01-01

    This work deals with InAs nanowire field effect transistors in back gate configuration. In such devices, quantum dots can form at low temperatures in the order of magnitude of a few Kelvin. These dots are henceforth referred to as intrinsic as they are not intentionally defined by electrodes. For the interpretation of their stability diagrams, a thorough knowledge of the structure and transport properties of the nanowires is required. Therefore, first of all, the influence of growth method and doping on the transport properties is studied at room temperature. The wires are grown by two types of metal-organic vapour phase epitaxy: a selective-area (SA-MOVPE) and an Au-catalyzed vapour-liquid-solid method (VLS-MOVPE). Transport data shows that the background doping of VLS-MOVPE wires is higher than for SA-MOVPE wires, but the variability of the transport properties is lower. The polytypism of the SA-MOVPE wires (they are composed of wurtzite and zinc blende segments) is a possible explanation for the second observation. Furthermore, it is shown that the measured transport properties significantly depend on the dielectric environment of the nanowires and on the way the electrical measurements are done (two- or four-terminal configuration). The conductivity is tunable via doping and the gate voltage. Conductivity measurements in the temperature range from 10 K to 300 K show that different transport regimes can occur (partially metallic behaviour for sufficiently high conductivity, otherwise purely semiconducting behaviour). This is attributed to different positions of the Fermi level and thus, a different effect of potential fluctuations. If conductivity and temperature are sufficiently low, the onset of Coulomb blockade is observed for semiconducting samples. It is even possible to tune the very same sample to different regimes via the gate voltage. The semiconducting behaviour observed in many samples contradicts the Thomas-Fermi theory. This is attributed to the

  5. Sensing Responses Based on Transfer Characteristics of InAs Nanowire Field-Effect Transistors

    Science.gov (United States)

    Savelyev, Igor; Blumin, Marina; Wang, Shiliang; Ruda, Harry E.

    2017-01-01

    Nanowire-based field-effect transistors (FETs) have demonstrated considerable promise for a new generation of chemical and biological sensors. Indium arsenide (InAs), by virtue of its high electron mobility and intrinsic surface accumulation layer of electrons, holds properties beneficial for creating high performance sensors that can be used in applications such as point-of-care testing for patients diagnosed with chronic diseases. Here, we propose devices based on a parallel configuration of InAs nanowires and investigate sensor responses from measurements of conductance over time and FET characteristics. The devices were tested in controlled concentrations of vapour containing acetic acid, 2-butanone and methanol. After adsorption of analyte molecules, trends in the transient current and transfer curves are correlated with the nature of the surface interaction. Specifically, we observed proportionality between acetic acid concentration and relative conductance change, off current and surface charge density extracted from subthreshold behaviour. We suggest the origin of the sensing response to acetic acid as a two-part, reversible acid-base and redox reaction between acetic acid, InAs and its native oxide that forms slow, donor-like states at the nanowire surface. We further describe a simple model that is able to distinguish the occurrence of physical versus chemical adsorption by comparing the values of the extracted surface charge density. These studies demonstrate that InAs nanowires can produce a multitude of sensor responses for the purpose of developing next generation, multi-dimensional sensor applications. PMID:28714903

  6. Quantification of Discrete Oxide and Sulfur Layers on Sulfur-Passivated InAs by XPS

    National Research Council Canada - National Science Library

    Petrovykh, D. Y; Sullivan, J. M; Whitman, L. J

    2005-01-01

    .... The S-passivated InAs(001) surface can be modeled as a sulfur-indium-arsenic layer-cake structure, such that characterization requires quantification of both arsenic oxide and sulfur layers that are at most a few monolayers thick...

  7. Charge pumping in InAs nanowires by surface acoustic waves

    NARCIS (Netherlands)

    Roddaro, Stefano; Strambini, Elia; Romeo, Lorenzo; Piazza, Vincenzo; Nilsson, Kristian; Samuelson, Lars; Beltram, Fabio

    2010-01-01

    We investigate the interaction between surface acoustic waves on a piezoelectric LiNbO3 substrate and charge carriers in InAs nanowire transistors. Interdigital transducers are used to excite electromechanical waves on the chip surface and their influence on the transport in the nanowire devices is

  8. Electron Spin Polarization and Detection in InAs Quantum Dots Through p-Shell Trions

    Science.gov (United States)

    2010-01-08

    optical control of spin states in quantum dots. II. EXPERIMENT The QD sample consists of 20 layers of InAs QDs, grown by molecular -beam epitaxy through...anisotropic 2D harmonic poten- tials. The electrons and holes are described by Fock- Darwin states harmonic oscillators with lateral sizes ax and ay in this

  9. Quantum efficiency and oscillator strength of site-controlled InAs quantum dots

    DEFF Research Database (Denmark)

    Albert, F.; Stobbe, Søren; Schneider, C.

    2010-01-01

    We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled InAs quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...

  10. Energy Band Structure Studies Of Zinc-Blende GaAs and InAs ...

    African Journals Online (AJOL)

    A self-consistent calculation of the structural and electronic properties of zinc blende GaAs and InAs has been carried out. The calculations were done using the full potential-linearized augmented plane wave (FPLAPW) method within the density functional theory (DFT). The exchange-correlation energy used is the ...

  11. Positioning of self-assembled InAs quantum dots by focused ion beam implantation

    International Nuclear Information System (INIS)

    Mehta, M.

    2007-01-01

    Self-assembled quantum dots (QDs) are envisioned as building blocks for realization of novel nanoelectronic devices, for which the site-selective growth is highly desirable. This thesis presents a successful route toward selective positioning of self-assembled InAs QDs on patterned GaAs surface by combination of in situ focused ion beam (FIB) implantation and molecular beam epitaxy (MBE) technology. First, a buffer layer of GaAs was grown by MBE before a square array of holes with a pitch of 1-2 μm was fabricated by FIB implantation of Ga and In, ions respectively. Later, an in-situ annealing step followed by InAs deposition was performed. The InAs QDs were preferentially formed in the holes generated by FIB. The influence of ion dose, annealing parameters and InAs amount was investigated in this work. With optimized parameters, more than 50 % single dot occupancy per hole is achieved. Furthermore, the photoluminescence spectra from positioned QDs confirm their good optical quality. (orig.)

  12. Diameter dependence of the thermal conductivity of InAs nanowires

    NARCIS (Netherlands)

    Swinkels, M.Y.; van Delft, M.R.; Oliveira, D.S.; Cavalli, A.; Zardo, I.; van der Heijden, R.W.; Bakkers, E.P.A.M.

    2015-01-01

    The diameter dependence of the thermal conductivity of InAs nanowires in the range of 40–1500 nm has been measured. We demonstrate a reduction in thermal conductivity of 80% for 40 nm nanowires, opening the way for further design strategies for nanoscaled thermoelectric materials. Furthermore, we

  13. Study of electron transport in n-type InAs substrate by Monte Carlo ...

    African Journals Online (AJOL)

    It is therefore an iterative process made up from a whole coasting flights stopped by acoustics interactions, polar and non polar optics, piezoelectric, inter-valley, impurity, ionization and surface. By applying this method to the III-V material, case of InAs, we have described the behavior of the carriers from dynamic and ...

  14. High tunability and superluminescence in InAs mid-infrared light emitting diodes

    International Nuclear Information System (INIS)

    Sherstnev, V.V.; Krier, A.; Hill, G.

    2002-01-01

    We report on the observation of super luminescence and high spectral current tunability (181 nm) of InAs light emitting diodes operating at 3.0 μm. The source is based on an optical whispering gallery mode which is generated near the edges of the mesa and which is responsible for the superluminescence. (author)

  15. Pathogenic and Ice-Nucleation Active (INA) Bacteria causing Dieback of Willows in Short Rotation Forestry

    Energy Technology Data Exchange (ETDEWEB)

    Nejad, Pajand

    2005-03-01

    To find out whether bacteria isolated from diseased plant parts can be the main causal agent for the dieback appearing in Salix energy forestry plantations in Sweden during the last few years, and if the joint effects of bacteria and frost injury are synergistic, extensive sampling of shoots from diseased Salix plants was performed. We performed several laboratory and greenhouse investigations and used evaluation techniques on the functions of the Ice-Nucleation Active (INA) bacteria. We carried out a comparison between spring and autumn bacterial communities isolated from within (endophytically) and surface (epiphytically) plant tissues of Salix viminalis. Seasonal variation of bacteria in willow clones with different levels of frost sensitivity and symptoms of bacterial damage was also investigated. We further focussed on possible effect of fertilisation and nutrient availability on the bacterial community in relation to plant dieback in Estonian willow plantations. The identification and detection of INA bacteria which cause damage in combination with frost to willow (Salix spp) plants in late fall, winter and spring was performed using BIOLOG MicroPlate, biochemical tests, selective INA primers and 16S rDNA analysis. To distinguish the character for differentiation between these bacteria morphologically and with respect to growing ability different culture media were used. We studied the temperature, at which ice nucleation occurred for individual bacteria, estimated the population of INA bacteria, effect of growth limiting factors, and evaluated the effect of chemical and physical agents for disruption and possible inhibition of INA among individual bacterial strains. The concentration of carbon, nitrogen and phosphorus on INA is discussed. We demonstrate that among the bacterial isolates recovered from the willow plantations, there were many that were capable of ice nucleation at temperatures between -2 and -10 deg C, many that were capable of inducing a

  16. Effect of growth temperature on the morphology and phonon properties of InAs nanowires on Si substrates

    Directory of Open Access Journals (Sweden)

    Lei Wen

    2011-01-01

    Full Text Available Abstract Catalyst-free, vertical array of InAs nanowires (NWs are grown on Si (111 substrate using MOCVD technique. The as-grown InAs NWs show a zinc-blende crystal structure along a < 111 > direction. It is found that both the density and length of InAs NWs decrease with increasing growth temperatures, while the diameter increases with increasing growth temperature, suggesting that the catalyst-free growth of InAs NWs is governed by the nucleation kinetics. The longitudinal optical and transverse optical (TO mode of InAs NWs present a phonon frequency slightly lower than those of InAs bulk materials, which are speculated to be caused by the defects in the NWs. A surface optical mode is also observed for the InAs NWs, which shifts to lower wave-numbers when the diameter of NWs is decreased, in agreement with the theory prediction. The carrier concentration is extracted to be 2.25 × 1017 cm-3 from the Raman line shape analysis. A splitting of TO modes is also observed. PACS: 62.23.Hj; 81.07.Gf; 63.22.Gh; 61.46.Km

  17. Conductive atomic force microscopy study of InAs growth kinetics on vicinal GaAs (110)

    International Nuclear Information System (INIS)

    Tejedor, Paloma; Diez-Merino, Laura; Beinik, Igor; Teichert, Christian

    2009-01-01

    Conductive atomic force microscopy has been used to investigate the effect of atomic hydrogen and step orientation on the growth behavior of InAs on GaAs (110) misoriented substrates. Samples grown by conventional molecular beam epitaxy exhibit higher conductivity on [110]-multiatomic step edges, where preferential nucleation of InAs nanowires takes place by step decoration. On H-terminated substrates with triangular terraces bounded by [115]-type steps, three-dimensional InAs clusters grow selectively at the terrace apices as a result of a kinetically driven enhancement in upward mass transport via AsH x intermediate species and a reduction in the surface free energy.

  18. InAs nanocrystals on SiO2/Si by molecular beam epitaxy for memory applications

    International Nuclear Information System (INIS)

    Hocevar, Moiera; Regreny, Philippe; Descamps, Armel; Albertini, David; Saint-Girons, Guillaume; Souifi, Abdelkader; Gendry, Michel; Patriarche, Gilles

    2007-01-01

    We studied a memory structure based on InAs nanocrystals grown by molecular beam epitaxy directly on thermal SiO 2 on silicon. Both nanocrystal diameter and density can be controlled by growth parameters. Transmission electron microscopy analysis shows high crystallinity and low size dispersion. In an electrical test structure with a 3.5 nm tunnel oxide, we observed that 80% of the initial injected electrons remain stored in the InAs nanocrystals after 3 months and that the retention time for electrons in InAs nanocrystals is four orders of magnitude higher than in silicon nanocrystals

  19. Schiff base ligand

    Indian Academy of Sciences (India)

    Unknown

    Low-temperature stoichiometric Schiff base reaction in air in 3 : 1 mole ratio between benz- aldehyde and triethylenetetramine (trien) in methanol yields a novel tetraaza µ-bis(bidentate) acyclic ligand L. It was .... electrochemical work was performed as reported in ..... change in ligand shape through change in oxidation.

  20. Ligand modeling and design

    Energy Technology Data Exchange (ETDEWEB)

    Hay, B.P. [Pacific Northwest National Lab., Richland, WA (United States)

    1997-10-01

    The purpose of this work is to develop and implement a molecular design basis for selecting organic ligands that would be used in the cost-effective removal of specific radionuclides from nuclear waste streams. Organic ligands with metal ion specificity are critical components in the development of solvent extraction and ion exchange processes that are highly selective for targeted radionuclides. The traditional approach to the development of such ligands involves lengthy programs of organic synthesis and testing, which in the absence of reliable methods for screening compounds before synthesis, results in wasted research effort. The author`s approach breaks down and simplifies this costly process with the aid of computer-based molecular modeling techniques. Commercial software for organic molecular modeling is being configured to examine the interactions between organic ligands and metal ions, yielding an inexpensive, commercially or readily available computational tool that can be used to predict the structures and energies of ligand-metal complexes. Users will be able to correlate the large body of existing experimental data on structure, solution binding affinity, and metal ion selectivity to develop structural design criteria. These criteria will provide a basis for selecting ligands that can be implemented in separations technologies through collaboration with other DOE national laboratories and private industry. The initial focus will be to select ether-based ligands that can be applied to the recovery and concentration of the alkali and alkaline earth metal ions including cesium, strontium, and radium.

  1. In situ surface and interface study of crystalline (3×1)-O on InAs

    Energy Technology Data Exchange (ETDEWEB)

    Qin, Xiaoye, E-mail: xxq102020@utdallas.edu; Wallace, Robert M., E-mail: rmwallace@utdallas.edu [Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States); Wang, Wei-E.; Rodder, Mark S. [Advanced Logic Lab, Samsung Semiconductor, Inc., Austin, Texas 78754 (United States)

    2016-07-25

    The oxidation behavior of de-capped InAs (100) exposed to O{sub 2} gas at different temperatures is investigated in situ with high resolution of monochromatic x-ray photoelectron spectroscopy and low energy electron diffraction. The oxide chemical states and structure change dramatically with the substrate temperature. A (3 × 1) crystalline oxide layer on InAs is generated in a temperature range of 290–330 °C with a coexistence of In{sub 2}O and As{sub 2}O{sub 3}. The stability of the crystalline oxide upon the atomic layer deposition (ALD) of HfO{sub 2} is studied as well. It is found that the generated (3 × 1) crystalline oxide is stable upon ALD HfO{sub 2} growth at 100 °C.

  2. On the processing of InAs and InSb photodiode applications

    Energy Technology Data Exchange (ETDEWEB)

    Odendaal, V.; Botha, J.R. [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth 6031 (South Africa); Auret, F.D. [Department of Physics, University of Pretoria, Lynnwood road, Hillcrest, Pretoria 0002 (South Africa)

    2008-07-01

    In this paper, potential methods for the surface passivation of InSb and InAs material, covering both compositional extremes of the promising narrow band gap semiconductor InAsSb, are evaluated. Surface states, mostly due to dangling bonds and exposure to the atmosphere, create generation-recombination centres that negatively influence the dark current, stability, efficiency and related noise characteristics of photosensitive devices fabricated from these materials. The effect of various surface treatments, including sulphuric acid based etching, lactic acid based etching, KOH anodising and Na{sub 2}S anodising, on the relative number of surface states is deduced by evaluating the capacitance versus voltage characteristics of metal-insulator-semiconductor structures fabricated on InAs and InSb. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Etching and oxidation of InAs in planar inductively coupled plasma

    Energy Technology Data Exchange (ETDEWEB)

    Dultsev, F.N., E-mail: fdultsev@thermo.isp.nsc.ru [Institute of Semiconductor Physics SB RAS, Lavrentiev av. 13, Novosibirsk 630090 (Russian Federation); Kesler, V.G. [Institute of Semiconductor Physics SB RAS, Lavrentiev av. 13, Novosibirsk 630090 (Russian Federation)

    2009-10-15

    The surface of InAs (1 1 1)A was investigated under plasmachemical etching in the gas mixture CH{sub 4}/H{sub 2}/Ar. Etching was performed using the RF (13.56 MHz) and ICP plasma with the power 30-150 and 50-300 W, respectively; gas pressure in the reactor was 3-10 mTorr. It was demonstrated that the composition of the subsurface layer less than 5 nm thick changes during plasmachemical etching. A method of deep etching of InAs involving ICP plasma and hydrocarbon based chemistry providing the conservation of the surface relief is proposed. Optimal conditions and the composition of the gas phase for plasmachemical etching ensuring acceptable etch rates were selected.

  4. Etching and oxidation of InAs in planar inductively coupled plasma

    Science.gov (United States)

    Dultsev, F. N.; Kesler, V. G.

    2009-10-01

    The surface of InAs (1 1 1)A was investigated under plasmachemical etching in the gas mixture CH 4/H 2/Ar. Etching was performed using the RF (13.56 MHz) and ICP plasma with the power 30-150 and 50-300 W, respectively; gas pressure in the reactor was 3-10 mTorr. It was demonstrated that the composition of the subsurface layer less than 5 nm thick changes during plasmachemical etching. A method of deep etching of InAs involving ICP plasma and hydrocarbon based chemistry providing the conservation of the surface relief is proposed. Optimal conditions and the composition of the gas phase for plasmachemical etching ensuring acceptable etch rates were selected.

  5. Etching and oxidation of InAs in planar inductively coupled plasma

    International Nuclear Information System (INIS)

    Dultsev, F.N.; Kesler, V.G.

    2009-01-01

    The surface of InAs (1 1 1)A was investigated under plasmachemical etching in the gas mixture CH 4 /H 2 /Ar. Etching was performed using the RF (13.56 MHz) and ICP plasma with the power 30-150 and 50-300 W, respectively; gas pressure in the reactor was 3-10 mTorr. It was demonstrated that the composition of the subsurface layer less than 5 nm thick changes during plasmachemical etching. A method of deep etching of InAs involving ICP plasma and hydrocarbon based chemistry providing the conservation of the surface relief is proposed. Optimal conditions and the composition of the gas phase for plasmachemical etching ensuring acceptable etch rates were selected.

  6. Functional display of ice nucleation protein InaZ on the surface of bacterial ghosts.

    Science.gov (United States)

    Kassmannhuber, Johannes; Rauscher, Mascha; Schöner, Lea; Witte, Angela; Lubitz, Werner

    2017-09-03

    In a concept study the ability to induce heterogeneous ice formation by Bacterial Ghosts (BGs) from Escherichia coli carrying ice nucleation protein InaZ from Pseudomonas syringae in their outer membrane was investigated by a droplet-freezing assay of ultra-pure water. As determined by the median freezing temperature and cumulative ice nucleation spectra it could be demonstrated that both the living recombinant E. coli and their corresponding BGs functionally display InaZ on their surface. Under the production conditions chosen both samples belong to type II ice-nucleation particles inducing ice formation at a temperature range of between -5.6 °C and -6.7 °C, respectively. One advantage for the application of such BGs over their living recombinant mother bacteria is that they are non-living native cell envelopes retaining the biophysical properties of ice nucleation and do no longer represent genetically modified organisms (GMOs).

  7. On the processing of InAs and InSb photodiode applications

    International Nuclear Information System (INIS)

    Odendaal, V.; Botha, J.R.; Auret, F.D.

    2008-01-01

    In this paper, potential methods for the surface passivation of InSb and InAs material, covering both compositional extremes of the promising narrow band gap semiconductor InAsSb, are evaluated. Surface states, mostly due to dangling bonds and exposure to the atmosphere, create generation-recombination centres that negatively influence the dark current, stability, efficiency and related noise characteristics of photosensitive devices fabricated from these materials. The effect of various surface treatments, including sulphuric acid based etching, lactic acid based etching, KOH anodising and Na 2 S anodising, on the relative number of surface states is deduced by evaluating the capacitance versus voltage characteristics of metal-insulator-semiconductor structures fabricated on InAs and InSb. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Direct evidence of strain transfer for InAs island growth on compliant Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Marçal, L. A. B.; Magalhães-Paniago, R.; Malachias, Angelo, E-mail: angeloms@fisica.ufmg.br [Universidade Federal de Minas Gerais, Av. Antonio Carlos 6627, CEP 31270-901, Belo Horizonte (Brazil); Richard, M.-I. [European Synchrotron (ESRF), ID01 beamline, CS 40220, 38043 Grenoble Cedex 9 (France); Aix-Marseille University, IM2NP-CNRS, Faculté des Sciences de St Jérôme, 13397 Marseille (France); Cavallo, F. [Center for High Technology Materials, University of New Mexico, 1313 Goddard St., Albuquerque, New Mexico 87106 (United States); University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706 (United States); Lagally, M. G. [University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706 (United States); Schmidt, O. G. [Institute for Integrative Nanosciences, IFW-Dresden, D-01171 Dresden (Germany); Schülli, T. Ü. [European Synchrotron (ESRF), ID01 beamline, CS 40220, 38043 Grenoble Cedex 9 (France); Deneke, Ch. [Laboratório Nacional de Nanotecnologia (LNNano/CNPEM), C.P. 6192, CEP 13083-970, Campinas (Brazil)

    2015-04-13

    Semiconductor heteroepitaxy on top of thin compliant layers has been explored as a path to make inorganic electronics mechanically flexible as well as to integrate materials that cannot be grown directly on rigid substrates. Here, we show direct evidences of strain transfer for InAs islands on freestanding Si thin films (7 nm). Synchrotron X-ray diffraction measurements using a beam size of 300 × 700 nm{sup 2} can directly probe the strain status of the compliant substrate underneath deposited islands. Using a recently developed diffraction mapping technique, three-dimensional reciprocal space maps were reconstructed around the Si (004) peak for specific illuminated positions of the sample. The strain retrieved was analyzed using continuous elasticity theory via Finite-element simulations. The comparison of experiment and simulations yields the amount of strain from the InAs islands, which is transferred to the compliant Si thin film.

  9. Studies on the controlled growth of InAs nanostructures on scission surfaces

    International Nuclear Information System (INIS)

    Bauer, J.

    2006-01-01

    The aim of this thesis was the controlled alignment of self-assembled InAs nano-structures on a {110}-oriented surface. The surface is prestructured with the atomic precision offered by molecular beam epitaxy, using the cleaved edge overgrowth-technique. On all samples grown within this work, the epitaxial template in the first growth step was deposited on a (001)GaAs substrate, while the InAs-layer forming the nanostructures during the second growth step was grown on cleaved {110}-GaAs surfaces. Atomic Force Microscopy (AFM) investigations demonstrate the formation of quantum dot (QD)-like nanostructures on top of the AlAs-stripes. X-ray diffraction measurements on large arrays of aligned quantum dots demonstrate that the quantum dots are formed of pure InAs. First investigations on the optical properties of these nanostructures were done using microphotoluminescence-spectroscopy with both high spatial and spectral resolution. (orig.)

  10. Effects of crossed states on photoluminescence excitation spectroscopy of InAs quantum dots

    Directory of Open Access Journals (Sweden)

    Lin Chien-Hung

    2011-01-01

    Full Text Available Abstract In this report, the influence of the intrinsic transitions between bound-to-delocalized states (crossed states or quasicontinuous density of electron-hole states on photoluminescence excitation (PLE spectra of InAs quantum dots (QDs was investigated. The InAs QDs were different in size, shape, and number of bound states. Results from the PLE spectroscopy at low temperature and under a high magnetic field (up to 14 T were compared. Our findings show that the profile of the PLE resonances associated with the bound transitions disintegrated and broadened. This was attributed to the coupling of the localized QD excited states to the crossed states and scattering of longitudinal acoustical (LA phonons. The degree of spectral linewidth broadening was larger for the excited state in smaller QDs because of the higher crossed joint density of states and scattering rate.

  11. Static and low frequency noise characterization of ultra-thin body InAs MOSFETs

    Science.gov (United States)

    Karatsori, T. A.; Pastorek, M.; Theodorou, C. G.; Fadjie, A.; Wichmann, N.; Desplanque, L.; Wallart, X.; Bollaert, S.; Dimitriadis, C. A.; Ghibaudo, G.

    2018-05-01

    A complete static and low frequency noise characterization of ultra-thin body InAs MOSFETs is presented. Characterization techniques, such as the well-known Y-function method established for Si MOSFETs, are applied in order to extract the electrical parameters and study the behavior of these research grade devices. Additionally, the Lambert-W function parameter extraction methodology valid from weak to strong inversion is also used in order to verify its applicability in these experimental level devices. Moreover, a low-frequency noise characterization of the UTB InAs MOSFETs is presented, revealing carrier trapping/detrapping in slow oxide traps and remote Coulomb scattering as origin of 1/f noise, which allowed for the extraction of the oxide trap areal density. Finally, Lorentzian-like noise is also observed in the sub-micron area devices and attributed to both Random Telegraph Noise from oxide individual traps and g-r noise from the semiconductor interface.

  12. Intermediate band solar cell simulation use InAs quantum dot in GaAs

    International Nuclear Information System (INIS)

    Hendra P, I. B.; Rahayu, F.; Sahdan, M. F.; Darma, Y.

    2015-01-01

    Intermediate band solar cell (IBSC) has become a new approach in increasing solar cell efficiency significantly. One way to create intermediate band is by proposing quantum dots (QD) technology. One of the important aspects in utilizing IBSC is the absorption of light. In this work we simulated the influence of QD arrangement in order to increase absorption coefficient and solar cell efficiency. We also simulated the influence of QD size to capture a wider light spectrum. We present a simple calculation method with low computing power demand. Results show that the increasing in quantum dot size can increase in capturing wider spectrum of light. Arrangement InAs QD in bulk material GaAs can capture wider spectrum of light and increase the absorption coefficient. The arrangement InAs QD 2 nm in GaAs bulk can increase solar cell efficiency up to 49.68%

  13. Shubnikov-de Haas effect study of InAs after transmutation doping at low temperatures

    International Nuclear Information System (INIS)

    Gerstenberg, H.; Mueller, P.

    1990-01-01

    Degenerate InAs single crystals have been irradiated by thermal neutrons below 6 K. The Shubnikov-de Haas effect and the electrical resistivity have been measured as a function of the neutron dose and the annealing temperature. The effects of transmutation doping and simultaneous introduction of lattice defects have been analysed in terms of the conduction electron density and the scattering rates τ ρ -1 - ρne 2 /m * and τ x -1 2πkub(B)X/h/2π (where X is the Dingle temperature). The measured conduction electron density after irradiation and thermal annealing agreed well with the values calculated from the experimental and materials parameters. The effects of radiation damage may qualitatively be explained assuming neutral In vacancies to be the most common type of defect in thermal-neutron-irradiated InAs. A comparison with similar experiments on InSb is given. (author)

  14. Nonlinear absorption and transmission properties of Ge, Te and InAs using tuneable IR FEL

    Energy Technology Data Exchange (ETDEWEB)

    Amirmadhi, F.; Becker, K.; Brau, C.A. [Vanderbilt Univ., Nashville, TN (United States)

    1995-12-31

    Nonlinear absorption properties of Ge, Te and InAs are being investigated using the transmission of FEL optical pulses through these semiconductors (z-scan method). Wavelength, intensity and macropulse dependence are used to differentiate between two-photon and free-carrier absorption properties of these materials. Macropulse dependence is resolved by using a Pockles Cell to chop the 4-{mu}s macropulse down to 100 ns. Results of these experiments will be presented and discussed.

  15. Arsenic flux dependence of island nucleation on InAs(001)

    International Nuclear Information System (INIS)

    Grosse, Frank; Barvosa-Carter, William; Zinck, Jenna; Wheeler, Matthew; Gyure, Mark F.

    2002-01-01

    The initial stages of InAs(001) homoepitaxial growth are investigated using a combination of kinetic Monte Carlo simulations based on ab initio density functional theory and scanning tunneling microscopy. In the two dimensional island nucleation mode investigated, the island number density is found to decrease with increasing As. This behavior is explained by a suppression of the effective In-adatom density leading to a reduction in island nucleation. The relevant microscopic processes responsible for this reduction are identified

  16. Reconstruction of an InAs nanowire using geometric and algebraic tomography

    International Nuclear Information System (INIS)

    Pennington, R S; Boothroyd, C B; König, S; Alpers, A; Dunin-Borkowski, R E

    2011-01-01

    Geometric tomography and conventional algebraic tomography algorithms are used to reconstruct cross-sections of an InAs nanowire from a tilt series of experimental annular dark-field images. Both algorithms are also applied to a test object to assess what factors affect the reconstruction quality. When using the present algorithms, geometric tomography is faster, but artifacts in the reconstruction may be difficult to recognize.

  17. Reconstruction of an InAs nanowire using geometric and algebraic tomography

    DEFF Research Database (Denmark)

    Pennington, Robert S.; König, S.; Alpers, A.

    2011-01-01

    Geometric tomography and conventional algebraic tomography algorithms are used to reconstruct cross-sections of an InAs nanowire from a tilt series of experimental annular dark-field images. Both algorithms are also applied to a test object to assess what factors affect the reconstruction quality....... When using the present algorithms, geometric tomography is faster, but artifacts in the reconstruction may be difficult to recognize....

  18. Steering of quantum waves: Demonstration of Y-junction transistors using InAs quantum wires

    Science.gov (United States)

    Jones, Gregory M.; Qin, Jie; Yang, Chia-Hung; Yang, Ming-Jey

    2005-06-01

    In this paper we demonstrate using an InAs quantum wire Y-branch switch that the electron wave can be switched to exit from the two drains by a lateral gate bias. The gating modifies the electron wave functions as well as their interference pattern, causing the anti-correlated, oscillatory transconductances. Our result suggests a new transistor function in a multiple-lead ballistic quantum wire system.

  19. Fermi energy dependence of the optical emission in core/shell InAs nanowire homostructures

    Science.gov (United States)

    Möller, M.; Oliveira, D. S.; Sahoo, P. K.; Cotta, M. A.; Iikawa, F.; Motisuke, P.; Molina-Sánchez, A.; de Lima, M. M., Jr.; García-Cristóbal, A.; Cantarero, A.

    2017-07-01

    InAs nanowires grown by vapor-liquid-solid (VLS) method are investigated by photoluminescence. We observe that the Fermi energy of all samples is reduced by ˜20 meV when the size of the Au nanoparticle used for catalysis is increased from 5 to 20 nm. Additional capping with a thin InP shell enhances the optical emission and does not affect the Fermi energy. The unexpected behavior of the Fermi energy is attributed to the differences in the residual donor (likely carbon) incorporation in the axial (low) and lateral (high incorporation) growth in the VLS and vapor-solid (VS) methods, respectively. The different impurity incorporation rate in these two regions leads to a core/shell InAs homostructure. In this case, the minority carriers (holes) diffuse to the core due to the built-in electric field created by the radial impurity distribution. As a result, the optical emission is dominated by the core region rather than by the more heavily doped InAs shell. Thus, the photoluminescence spectra and the Fermi energy become sensitive to the core diameter. These results are corroborated by a theoretical model using a self-consistent method to calculate the radial carrier distribution and Fermi energy for distinct diameters of Au nanoparticles.

  20. InP and InAs nanowires hetero- and homojunctions: energetic stability and electronic properties.

    Science.gov (United States)

    Dionízio Moreira, M; Venezuela, P; Miwa, R H

    2010-07-16

    We performed an ab initio total energy investigation, within the density functional theory, of the energetic stability and the electronic properties of hydrogenated InAs/InP nanowire (NW) heterojunctions, as well as InAs and InP homojunctions composed of different structural arrangements, zinc-blend (zb) and wurtzite (w). For InAs/InP NW heterojunctions our results indicate that w and zb NW heterojunctions are quite similar, energetically, for thin NWs. We also examined the robustness of the abrupt interface through an atomic swap at the InAs/InP interface. Our results support the formation of abrupt (non-abrupt) interfaces in w (zb) InAs/InP heterojunctions. Concerning InAs/InP NW-SLs, our results indicate a type-I band alignment, with the energy barrier at the InP layers, in accordance with experimental works. For InAs or InP zb/w homojunctions, we also found a type-I band alignment for thin NWs, however, on increasing the NW diameter both InAs and InP homojunctions exhibit a type-II band alignment.

  1. InP and InAs nanowires hetero- and homojunctions: energetic stability and electronic properties

    International Nuclear Information System (INIS)

    Dionizio Moreira, M; Venezuela, P; Miwa, R H

    2010-01-01

    We performed an ab initio total energy investigation, within the density functional theory, of the energetic stability and the electronic properties of hydrogenated InAs/InP nanowire (NW) heterojunctions, as well as InAs and InP homojunctions composed of different structural arrangements, zinc-blend (zb) and wurtzite (w). For InAs/InP NW heterojunctions our results indicate that w and zb NW heterojunctions are quite similar, energetically, for thin NWs. We also examined the robustness of the abrupt interface through an atomic As↔P swap at the InAs/InP interface. Our results support the formation of abrupt (non-abrupt) interfaces in w (zb) InAs/InP heterojunctions. Concerning InAs/InP NW-SLs, our results indicate a type-I band alignment, with the energy barrier at the InP layers, in accordance with experimental works. For InAs or InP zb/w homojunctions, we also found a type-I band alignment for thin NWs, however, on increasing the NW diameter both InAs and InP homojunctions exhibit a type-II band alignment.

  2. Alloy formation during InAs nanowire growth on GaAs(111)

    Energy Technology Data Exchange (ETDEWEB)

    Davydok, Anton; Saqib, Muhammad; Biermanns, Andreas; Pietsch, Ullrich [Festkoerperphysik, Universitaet Siegen (Germany); Rieger, Torsten; Grap, Thomas; Lepsa, Mihail [Peter Gruenberg Institut 9, Forschungszentrum Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany)

    2012-07-01

    The growth of semiconductor nanowires has attracted significant interest in recent years due to the possible fabrication of novel semiconductor devices for future electronic and opto-electronic applications. A possible way to obtain nanowires is the growth in molecular beam epitaxy on the (111)B oriented surface of the desired substrate, covered by a thin oxide layer. A crucial parameter in this method is the initial thickness of the oxide layer, often determined by an etching procedure. In this contribution, we report on the structural investigation of InAs nanowires grown on GaAs substrates covered by different oxide-layers using X-ray diffraction. In this contribution, we report on the structural investigation of InAs nanowires grown via an In droplet on GaAs substrates covered by different oxide layers using X-ray diffraction. Using a combination of symmetric and asymmetric X-ray diffraction, we observe that for growth on a defective oxide layer, alloy formation takes place and a large amount of InGaAs is formed, whereas for growth on an initially smooth oxide layer, only pure InAs is formed.

  3. The Crystal structure of InAs nanorods grown onto Si[111] substrate

    Energy Technology Data Exchange (ETDEWEB)

    Davydok, Anton; Biermanns, Andreas; Pietsch, Ullrich [Festkoerperphysik, Universitaet Siegen, Walter-Flex-Str. 3,57072, Siegen (Germany); Breuer, Steffen; Dimakis, Manos; Geelhaar, Lutz [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2011-07-01

    Nanowires are of particular interest due to the ability to synthesize heterostructures in the nanometer range. It was found that nearly any AIIIBV semiconductor material can be grown as NWs onto another AIIIBV or group IV [111] substrate independent from lattice mismatch. We presented an X-ray characterization of InAs NRs on Si [111] grown by assist free MBE method. Lattice mismatch of this materials is 11%. For study of strain realizing we concentrated our research on initial stages of growth process investigating samples set with different growth time. Using synchrotron radiation we have performed experiments in symmetrical and asymmetrical out-of plane scattering geometry and grazing-incidence diffraction. Combining the results we were able to characterize the transition between silicon silicon substrate and InAs NWs. We find in-plane lattice mismatch of -0.18% close to the interface compared to InAs bulk material. With help of micro-focus setup we are able measure structural parameters of single NWs to determine the strain accomodation as function of NW size. In particular using asymmetric wurzite-sensitive reflections under coherent beam illumination we could quantify the number of stacking faults. In the talk we present details of the analysis and first simulation results.

  4. Geometric factors in the magnetoresistance of n-doped InAs epilayers

    KAUST Repository

    Sun, Jian

    2013-11-27

    We investigate the magnetoresistance (MR) effect in n-doped InAs and InAs/metal hybrid devices with geometries tailored to elucidate the physical mechanism and the role of geometry in the MR. Despite the isotropic Fermi surface in InAs, we observe a strong intrinsic MR in the InAs epilayer due to the existence of a surface conducting layer. Experimental comparison confirms that the extraordinary MR in the InAs/metal hybrids outperforms the orbital MR in the Corbino disk in terms of both the MR ratio and the magnetic field resolution. The results also indicate the advantage of a two-contact configuration in the hybrid devices over a four-contact one with respect to the magnetic field resolution. This is in contrast to previously reported results, where performance was evaluated in terms of the MR ratio and a four-contact configuration was found to be optimal. By applying Kohler\\'s rule, we find that at temperatures above 75 K the extraordinary MR violates Kohler\\'s rule, due to multiple relaxation rates, whereas the orbital MR obeys it. This finding can be used to distinguish the two geometric effects, the extraordinary MR and the orbital MR, from each other.

  5. GaAs structures with InAs and As quantum dots produced in a single molecular beam epitaxy process

    International Nuclear Information System (INIS)

    Nevedomskii, V. N.; Bert, N. A.; Chaldyshev, V. V.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.

    2009-01-01

    Epitaxial GaAs layers containing InAs semiconductor quantum dots and As metal quantum dots are grown by molecular beam epitaxy. The InAs quantum dots are formed by the Stranskii-Krastanow mechanism, whereas the As quantum dots are self-assembled in the GaAs layer grown at low temperature with a large As excess. The microstructure of the samples is studied by transmission electron microscopy. It is established that the As metal quantum dots formed in the immediate vicinity of the InAs semiconductor quantum dots are larger in size than the As quantum dots formed far from the InAs quantum dots. This is apparently due to the effect of strain fields of the InAs quantum dots upon the self-assembling of As quantum dots. Another phenomenon apparently associated with local strains around the InAs quantum dots is the formation of V-like defects (stacking faults) during the overgrowth of the InAs quantum dots with the GaAs layer by low-temperature molecular beam epitaxy. Such defects have a profound effect on the self-assembling of As quantum dots. Specifically, on high-temperature annealing needed for the formation of large-sized As quantum dots by Ostwald ripening, the V-like defects bring about the dissolution of the As quantum dots in the vicinity of the defects. In this case, excess arsenic most probably diffuses towards the open surface of the sample via the channels of accelerated diffusion in the planes of stacking faults.

  6. Reactive ion etching of GaSb, (Al,Ga)Sb, and InAs for novel device applications

    International Nuclear Information System (INIS)

    LaTulipe, D.C.; Frank, D.J.; Munekata, H.

    1991-01-01

    Although a variety of novel device proposals for GaSb/(Al,Ga)Sb/InAs heterostructures have been made, relatively little is known about processing these materials. The authors of this paper have studied the reactive ion etching characteristics of GaSb, (Al,Ga)Sb, and InAs in both methane/hydrogen and chlorine gas chemistries. At conditions similar to those reported elsewhere for RIE of InP and GaAs in CH 4 /H 2 , the etch rate of (Al,Ga)Sb was found to be near zero, while GaSb and InAs etched at 200 Angstrom/minute. Under conditions where the etch mechanism is primarily physical sputtering, the three compounds etch at similar rates. Etching in Cl 2 was found to yield anistropic profiles, with the etch rate of (Al,Ga)Sb increasing with Al mole fraction, while InAs remains unetched. Damage to the InAs stop layer was investigated by sheet resistance and mobility measurements. These etching techniques were used to fabricate a novel InAs- channel FET composed of these materials. Several scanning electron micrographs of etching results are shown along with preliminary electrical characteristics

  7. Growth and characterization of InAs columnar quantum dots on GaAs substrate

    International Nuclear Information System (INIS)

    Li, L. H.; Patriarche, G.; Rossetti, M.; Fiore, A.

    2007-01-01

    The growth of InAs columnar quantum dots (CQDs) on GaAs substrates by molecular beam epitaxy was investigated. The CQDs were formed by depositing a 1.8 monolayer (ML) InAs seed dot layer and a short period GaAs/InAs superlattice (SL). It was found that the growth of the CQDs is very sensitive to growth interruption (GI) and growth temperature. Both longer GI and higher growth temperature impact the size dispersion of the CQDs, which causes the broadening of photoluminescence (PL) spectrum and the presence of the additional PL peak tails. By properly choosing the GI and the growth temperature, CQDs including GaAs (3 ML)/InAs (0.62 ML) SL with period number up to 35 without plastic relaxation were grown. The corresponding equivalent thickness of the SL is 41 nm which is two times higher than the theoretical critical thickness of the strained InGaAs layer with the same average In composition of 16%. The increase of the critical thickness is partially associated with the formation of the CQDs. Based on a five-stack CQD active region, laser diodes emitting around 1120 nm at room temperature were demonstrated, indicating a high material quality. CQDs with nearly isotropic cross section (20 nmx20 nm dimensions) were formed by depositing a 16-period GaAs (3 ML)/InAs (0.62 ML) SL on an InAs seed dot layer, indicating the feasibility of artificial shape engineering of QDs. Such a structure is expected to be very promising for polarization insensitive device applications, such as semiconductor optical amplifiers

  8. Glutamate receptor ligands

    DEFF Research Database (Denmark)

    Guldbrandt, Mette; Johansen, Tommy N; Frydenvang, Karla Andrea

    2002-01-01

    Homologation and substitution on the carbon backbone of (S)-glutamic acid [(S)-Glu, 1], as well as absolute stereochemistry, are structural parameters of key importance for the pharmacological profile of (S)-Glu receptor ligands. We describe a series of methyl-substituted 2-aminoadipic acid (AA...

  9. Fe-contacts on InAs(100) and InP(100) characterised by conversion electron Mössbauer spectroscopy

    DEFF Research Database (Denmark)

    Damsgaard, Christian Danvad; Gunnlaugsson, H.P; Weyer, G.

    2005-01-01

    We have grown 4 nm thin films of Fe-57 on InAs(100) and InP(100) surfaces by use of MBE and studied the samples by Fe-57 conversion electron Mossbauer spectroscopy. In the case of InAs, the Mossbauer spectrum showed a sextet due to alpha-Fe and a further magnetically split component with slightly...

  10. Characterization of multilayer self-organized InAs quantum dot embedded waveguides at 1.3 and 1.5 μm

    NARCIS (Netherlands)

    Akca, I.B.; Dana, A.; Aydinli, A.; Rossetti, M.; Li, L.; Fiore, A.; Dagli, N.

    2007-01-01

    In this paper, we characterized the electro-optic coefficient and loss of multilayer InAs quantum dot laser structures at 1309 and 1515 nm. Quantum dot waveguides were grown by molecular beam epitaxy, where the active region is formed by three or five layers of self-assembled InAs QDs. Loss

  11. Competitive emissions of InAs (QDs)/GaInAsP/InP grown by GSMBE

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Xiaowen [Huazhong University of Science and Technology, Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Wuhan (China); Chinese Academy of Sciences, National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Shanghai (China); Wang, Qi; Li, Senlin; Chen, C.Q. [Huazhong University of Science and Technology, Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Wuhan (China); Sun, Liaoxin; Luo, X.D.; Zhang, Bo [Chinese Academy of Sciences, National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Shanghai (China)

    2015-04-01

    In this letter, the optical properties of InAs (QDs)/GaInAsP on InP substrate grown by gas source molecular beam epitaxy are investigated. By measuring and analyzing the photoluminescence spectra of InAs (QDs)/GaInAsP/InP at different temperatures and excitation powers, the origin of each emission is verified. And it is found that, with the temperature increasing, the emission intensity of GaInAsP wetting layers decreases firstly (T < 150 K) and then increases from 160 K to room temperature. By analyzing the experimental results of three samples with different QDs' sizes, a competitive emission between InAs QDs and GaInAsP wetting layers is confirmed. (orig.)

  12. Cathodoluminescence imaging and spectroscopy of excited states in InAs self-assembled quantum dots

    International Nuclear Information System (INIS)

    Khatsevich, S.; Rich, D.H.; Kim, Eui-Tae; Madhukar, A.

    2005-01-01

    We have examined state filling and thermal activation of carriers in buried InAs self-assembled quantum dots (SAQDs) with excitation-dependent cathodoluminescence (CL) imaging and spectroscopy. The InAs SAQDs were formed during molecular-beam epitaxial growth of InAs on undoped planar GaAs (001). The intensities of the ground- and excited-state transitions were analyzed as a function of temperature and excitation density to study the thermal activation and reemission of carriers. The thermal activation energies associated with the thermal quenching of the luminescence were measured for ground- and excited-state transitions of the SAQDs, as a function of excitation density. By comparing these activation energies with the ground- and excited-state transition energies, we have considered various processes that describe the reemission of carriers. Thermal quenching of the intensity of the QD ground- and first excited-state transitions at low excitations in the ∼230-300-K temperature range is attributed to dissociation of excitons from the QD states into the InAs wetting layer. At high excitations, much lower activation energies of the ground and excited states are obtained, suggesting that thermal reemission of single holes from QD states into the GaAs matrix is responsible for the observed temperature dependence of the QD luminescence in the ∼230-300-K temperature range. The dependence of the CL intensity of the ground-and first excited-state transition on excitation density was shown to be linear at all temperatures at low-excitation density. This result can be understood by considering that carriers escape and are recaptured as excitons or correlated electron-hole pairs. At sufficiently high excitations, state-filling and spatial smearing effects are observed together with a sublinear dependence of the CL intensity on excitation. Successive filling of the ground and excited states in adjacent groups of QDs that possess different size distributions is assumed to

  13. Making Mn substitutional impurities in InAs using a scanning tunneling microscope.

    Science.gov (United States)

    Song, Young Jae; Erwin, Steven C; Rutter, Gregory M; First, Phillip N; Zhitenev, Nikolai B; Stroscio, Joseph A

    2009-12-01

    We describe in detail an atom-by-atom exchange manipulation technique using a scanning tunneling microscope probe. As-deposited Mn adatoms (Mn(ad)) are exchanged one-by-one with surface In atoms (In(su)) to create a Mn surface-substitutional (Mn(In)) and an exchanged In adatom (In(ad)) by an electron tunneling induced reaction Mn(ad) + In(su) --> Mn(In) + In(ad) on the InAs(110) surface. In combination with density-functional theory and high resolution scanning tunneling microscopy imaging, we have identified the reaction pathway for the Mn and In atom exchange.

  14. Nonlinear absorption and receptivity of the third order in InAs infrared region

    International Nuclear Information System (INIS)

    Musayev, M.A.

    2005-01-01

    Nonlinear absorption and receptivity of the third order and coefficient nonlinear absorption in InAs n-type with different degree of alloying was measured. Obtained score considerably exceed sense, calculated on the basis of the models describing nonlinear receptivity of electrons, situated in the nonparabolic area of conductivity. It was shown that, observable deviations withdraw; if in the calculation apply energy dissipation of electrons. Growth of the efficiency under four-wave interaction in low-energy-gap semiconductors confines nonlinear absorption of interacting waves

  15. Influence of nitrogen on the growth and the properties of InAs quantum dots

    International Nuclear Information System (INIS)

    Schumann, O.

    2004-01-01

    This work investigates the influence of nitrogen incorporation on the growth and the optical properties of InAs quantum dots on GaAs(001) substrates. On the basis of systematic growth interruptions it was shown that the large quantum dots nucleate at dislocations, which are already formed during the growth of the wetting layer. After solving the growth problems, the influence of different combinations of matrix layers on the structural and optical properties of the quantum dots was investigated in the second part of this work. The strain and bandgap of these layers were varied systematically. (orig.)

  16. The third order nonlinear susceptibility of InAs at infrared region

    International Nuclear Information System (INIS)

    Musayev, M.A.

    2008-01-01

    Nonlinear susceptibilities of the third order and coefficient of nonlinear absorption in InAs n-type with a different degree of a doping have been measured. The values of the third order nonlinear susceptibilities have derived from these measurements essentially exceed the values calculated on the basis of model featuring nonlinear susceptibility of electrons, being in conduction-band nonparabolicity. It has been shown that the observable discrepancy has been eliminated, if in calculation a dissipation of energy of electrons has been considered. Growth of efficiency at four-wave mixingin narrow-gap semiconductors has been restricted to nonlinear absorption of interacting waves

  17. Jačina sveze adhezijskih materijala na tvrda zubna tkiva

    OpenAIRE

    Žagar, Polona

    2017-01-01

    Adhezija se odnosi na povezivanje atoma i molekula na kontaktnim površinama različitih materijala. Adhezijske sustave možemo podjeliti prema interakciji sa tvrdim zubnim tkivima na jetkajuće ispirajuće, samojetkajuće i staklenoionomerne sustave. Univerzalni adhezivi su najnovija generacija adheziva na tržištu. Mogu se koristiti kao jetkajući ispirajući i samojetkajući sustavi. U ovom radu je ispitivana jačina adhezijske sveze s caklinom jetkajuće ispirajućim i univerzalnim adheziv...

  18. ODNOS ZAPOSLENIH V VRTCU DO ZDRAVEGA NAČINA ŽIVLJENJA

    OpenAIRE

    Cesarec, Anja

    2009-01-01

    Diplomsko delo predstavlja temo odnos zaposlenih v vrtcu do zdravega načina življenja. Predstavili smo zdravje, dejavnike, ki vplivajo na stopnjo zdravja in dejavnike, ki vplivajo na življenjski slog, kot so kajenje tobaka, način prehranjevanja, telesno aktivnost, uživanje nedovoljenih drog in alkohola ter stres. Posebno poglavje pa je namenjeno skrbi za zdrav način življenja. V empiričnem delu so predstavljeni rezultati raziskave, narejene v vrtcu Rogaška Slatina, enota Izvir. V raziskavo, k...

  19. Theoretical interpretation of the electron mobility behavior in InAs nanowires

    International Nuclear Information System (INIS)

    Marin, E. G.; Ruiz, F. G.; Godoy, A.; Tienda-Luna, I. M.; Martínez-Blanque, C.; Gámiz, F.

    2014-01-01

    This work studies the electron mobility in InAs nanowires (NWs), by solving the Boltzmann Transport Equation under the Momentum Relaxation Time approximation. The numerical solver takes into account the contribution of the main scattering mechanisms present in III-V compound semiconductors. It is validated against experimental field effect-mobility results, showing a very good agreement. The mobility dependence on the nanowire diameter and carrier density is analyzed. It is found that surface roughness and polar optical phonons are the scattering mechanisms that mainly limit the mobility behavior. Finally, we explain the origin of the oscillations observed in the mobility of small NWs at high electric fields.

  20. Spin-lattice relaxation times and knight shift in InSb and InAs

    International Nuclear Information System (INIS)

    Braun, P.; Grande, S.

    1976-01-01

    For a dominant contact interaction between nuclei and conduction electrons the relaxation rate is deduced. The extreme cases of degenerate and non-degenerate semiconductors are separately discussed. At strong degeneracy the product of the Knight shift and relaxation time gives the Korringa relation for metals. Measurements of the NMR spin-lattice relaxation times of 115 InSb and 115 InAs were made between 4.2 and 300 K for strongly degenerated samples. The different relaxation mechanisms are discussed and the experimental and theoretical results are compared. (author)

  1. Growth of InAs Wurtzite Nanocrosses from Hexagonal and Cubic Basis

    DEFF Research Database (Denmark)

    Krizek, Filip; Kanne, Thomas; Razmadze, Davydas

    2017-01-01

    . Two methods use conventional wurtzite nanowire arrays as a 6-fold hexagonal basis for growing single crystal wurtzite nanocrosses. A third method uses the 2-fold cubic symmetry of (100) substrates to form well-defined coherent inclusions of zinc blende in the center of the nanocrosses. We show......Epitaxially connected nanowires allow for the design of electron transport experiments and applications beyond the standard two terminal device geometries. In this Letter, we present growth methods of three distinct types of wurtzite structured InAs nanocrosses via the vapor-liquid-solid mechanism...

  2. Unit Cell Structure of Crystal Polytypes in InAs and InSb Nanowires

    DEFF Research Database (Denmark)

    Kriegner, Dominik; Panse, Christian; Mandl, Bernhard

    2011-01-01

    The atomic distances in hexagonal polytypes of III−V compound semiconductors differ from the values expected from simply a change of the stacking sequence of (111) lattice planes. While these changes were difficult to quantify so far, we accurately determine the lattice parameters of zinc blende......, wurtzite, and 4H polytypes for InAs and InSb nanowires, using X-ray diffraction and transmission electron microscopy. The results are compared to density functional theory calculations. Experiment and theory show that the occurrence of hexagonal bilayers tends to stretch the distances of atomic layers...

  3. Theoretical interpretation of the electron mobility behavior in InAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Marin, E. G., E-mail: egmarin@ugr.es; Ruiz, F. G., E-mail: franruiz@ugr.es; Godoy, A.; Tienda-Luna, I. M.; Martínez-Blanque, C.; Gámiz, F. [Departamento de Electrónica y Tecnología de los Computadores, Facultad de Ciencias, Universidad de Granada, Av. Fuentenueva S/N, 18071 Granada (Spain)

    2014-11-07

    This work studies the electron mobility in InAs nanowires (NWs), by solving the Boltzmann Transport Equation under the Momentum Relaxation Time approximation. The numerical solver takes into account the contribution of the main scattering mechanisms present in III-V compound semiconductors. It is validated against experimental field effect-mobility results, showing a very good agreement. The mobility dependence on the nanowire diameter and carrier density is analyzed. It is found that surface roughness and polar optical phonons are the scattering mechanisms that mainly limit the mobility behavior. Finally, we explain the origin of the oscillations observed in the mobility of small NWs at high electric fields.

  4. Critical Temperature for the Conversion from Wurtzite to Zincblende of the Optical Emission of InAs Nanowires

    KAUST Repository

    Rota, Michele B.

    2017-07-12

    One hour annealing at 300 degrees C changes the optical emission characteristics of InAs nanowires (NWs) from the wurtzite (WZ) phase into that of zincblende (ZB). These results are accounted for by the conversion of a small fraction of the NW WZ metastable structure into the stable ZB structure. Several paths toward the polytype transformation in the configuration space are also demonstrated using first-principles calculations. For lower annealing temperatures, emission which is likely related to WZ polytypes is observed at energies that agree with theoretical predictions. These results demonstrate severe constraints on thermal processes to which devices made from InAs WZ NWs can be exposed.

  5. The photoluminescence decay time of self-assembled InAs quantum dots covered by InGaAs layers

    International Nuclear Information System (INIS)

    Shu, G W; Wang, C K; Wang, J S; Shen, J L; Hsiao, R S; Chou, W C; Chen, J F; Lin, T Y; Ko, C H; Lai, C M

    2006-01-01

    The temperature dependence of the time-resolved photoluminescence (PL) of self-assembled InAs quantum dots (QDs) with InGaAs covering layers was investigated. The PL decay time increases with temperature from 50 to 170 K, and then decreases as the temperature increases further above 170 K. A model based on the phonon-assisted transition between the QD ground state and the continuum state is used to explain the temperature dependence of the PL decay time. This result suggests that the continuum states are important in the carrier capture in self-assembled InAs QDs

  6. Surface morphology and electronic structure of halogen etched InAs (1 1 1)

    Energy Technology Data Exchange (ETDEWEB)

    Eassa, N., E-mail: nashwa.eassa@nmmu.ac.za [Department of Physics, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa); Murape, D.M. [Department of Physics, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa); Betz, R. [Department of Chemistry, Nelson Mandela Metropolitan University (South Africa); Neethling, J.H.; Venter, A.; Botha, J.R. [Department of Physics, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa)

    2012-05-15

    The reaction of halogen-based etchants with n-InAs (1 1 1)A and the resulting surface morphology and surface electronic structure are investigated using field emission scanning electron microscopy and Raman spectroscopy. Using the intensity ratio of the unscreened longitudinal optical (LO) phonon to the transverse optical (TO) phonon in the Raman spectrum, a significant reduction in band bending is deduced after exposure of the InAs surface to HCl:H{sub 2}O, Br-methanol and I-ethanol for moderate times and concentrations. These procedures also lead to smooth and defect-free InAs surfaces. The improvements in surface properties are reversed, however, if the concentrations of the etchants are increased or the etch time is too long. In the worst cases, pit formation and inverted pyramids with {l_brace}1 1 1{r_brace} side facets are observed. The influence of the etchant concentration and etch time on the morphological and electronic properties of the etched surfaces is reported.

  7. Surface morphology and electronic structure of halogen etched InAs (1 1 1)

    International Nuclear Information System (INIS)

    Eassa, N.; Murape, D.M.; Betz, R.; Neethling, J.H.; Venter, A.; Botha, J.R.

    2012-01-01

    The reaction of halogen-based etchants with n-InAs (1 1 1)A and the resulting surface morphology and surface electronic structure are investigated using field emission scanning electron microscopy and Raman spectroscopy. Using the intensity ratio of the unscreened longitudinal optical (LO) phonon to the transverse optical (TO) phonon in the Raman spectrum, a significant reduction in band bending is deduced after exposure of the InAs surface to HCl:H 2 O, Br–methanol and I–ethanol for moderate times and concentrations. These procedures also lead to smooth and defect-free InAs surfaces. The improvements in surface properties are reversed, however, if the concentrations of the etchants are increased or the etch time is too long. In the worst cases, pit formation and inverted pyramids with {1 1 1} side facets are observed. The influence of the etchant concentration and etch time on the morphological and electronic properties of the etched surfaces is reported.

  8. Wet etch methods for InAs nanowire patterning and self-aligned electrical contacts

    Science.gov (United States)

    Fülöp, G.; d'Hollosy, S.; Hofstetter, L.; Baumgartner, A.; Nygård, J.; Schönenberger, C.; Csonka, S.

    2016-05-01

    Advanced synthesis of semiconductor nanowires (NWs) enables their application in diverse fields, notably in chemical and electrical sensing, photovoltaics, or quantum electronic devices. In particular, indium arsenide (InAs) NWs are an ideal platform for quantum devices, e.g. they may host topological Majorana states. While the synthesis has been continously perfected, only a few techniques have been developed to tailor individual NWs after growth. Here we present three wet chemical etch methods for the post-growth morphological engineering of InAs NWs on the sub-100 nm scale. The first two methods allow the formation of self-aligned electrical contacts to etched NWs, while the third method results in conical shaped NW profiles ideal for creating smooth electrical potential gradients and shallow barriers. Low temperature experiments show that NWs with etched segments have stable transport characteristics and can serve as building blocks of quantum electronic devices. As an example we report the formation of a single electrically stable quantum dot between two etched NW segments.

  9. Direct Identification of Atomic-Like Electronic Levels in InAs Nano crystal Quantum Dots

    International Nuclear Information System (INIS)

    Millo, O.; Katz, D.

    1999-01-01

    The size dependent level structure of InAs nano crystals in the range 2-7 nm in diameter is investigated using both tunneling and optical spectroscopies. The tunneling measurements are performed using a cryogenic scanning tunneling microscope on individual nano crystals that, are attached to a gold substrate via dithiol molecules. The tunneling I-V characteristics manifest an interplay between single electron charging and quantum size effects. We are able to directly identify quantum confined states of isolated InAs nano crystals having s and p symmetries. These states are observed in the I-V curves as two and six-fold single electron charging multiplets. Excellent agreement is found between the strongly allowed optical transitions [1] and the spacing of levels detected in the tunneling experiment. This correlation provides new information on the quantum-dot level structure, from which we conclude that the top-most valence band state has both s and p characteristics. The interplay between level structure singles electron charging of the nano crystals obeys an atomic-like Aufbau sequential electron level occupation

  10. X-ray characterization Si-doped InAs nanowires grown on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Saqib, Muhammad; Biermanns, Andreas; Pietsch, Ullrich [Universitaet Siegen, Festkoerperphysik (Germany); Grap, Thomas; Lepsa, Mihail [Forschungszentrum Juelich, Institut fuer Bio- und Nanosysteme (Germany)

    2011-07-01

    Semiconductor nanowires (NW) are of particular interest due to the ability to synthesize single-crystalline 1D epitaxial structures and heterostructures in the nanometer range. However, many details of the growth mechanism are not well understood. In particular, understanding and control of doping mechanisms during NW growth are important issues for technological applications. In this contribution we present a x-ray diffraction study of the influence of Si-doping in InAs NWs grown on GaAs(111) substrates using In-assisted MBE growth. With the help of coplanar and asymmetric x-ray diffraction, we monitor the evolution of the lattice constants and structure of the InAs NWs as function of doping concentration. We observe that increasing the nominal doping concentration leads to the appearance of additional diffraction maxima corresponding to material whose vertical lattice parameter is 1% smaller than that of the undoped nanowires. Those lattice parameters can be attributed with alloy formation in the form of island like crystallites.

  11. Formation of anodic layers on InAs (111)III. Study of the chemical composition

    Energy Technology Data Exchange (ETDEWEB)

    Valisheva, N. A., E-mail: valisheva@thermo.isp.nsc.ru; Tereshchenko, O. E. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Prosvirin, I. P.; Kalinkin, A. V. [Russian Academy of Sciences, Boreskov Institute of Catalysis, Siberian Branch (Russian Federation); Goljashov, V. A. [Novosibirsk State University (Russian Federation); Levtzova, T. A. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Bukhtiyarov, V. I. [Russian Academy of Sciences, Boreskov Institute of Catalysis, Siberian Branch (Russian Federation)

    2012-04-15

    The chemical composition of {approx}20-nm-thick anodic layers grown on InAs (111)III in alkaline and acid electrolytes containing or not containing NH{sub 4}F is studied by X-ray photoelectron spectroscopy. It is shown that the composition of fluorinated layers is controlled by the relation between the concentrations of fluorine and hydroxide ions in the electrolyte and by diffusion processes in the growing layer. Fluorine accumulates at the (anodic layer)/InAs interface. Oxidation of InAs in an acid electrolyte with a low oxygen content and a high NH{sub 4}F content brings about the formation of anodic layers with a high content of fluorine and elemental arsenic and the formation of an oxygen-free InF{sub x}/InAs interface. Fluorinated layers grown in an alkaline electrolyte with a high content of O{sup 2-} and/or OH{sup -} groups contain approximately three times less fluorine and consist of indium and arsenic oxyfluorides. No distinction between the compositions of the layers grown in both types of fluorine-free electrolytes is established.

  12. Transport and performance of a gate all around InAs nanowire transistor

    International Nuclear Information System (INIS)

    Alam, Khairul

    2009-01-01

    The transport physics and performance metrics of a gate all around an InAs nanowire transistor are studied using a three-dimensional quantum simulation. The transistor action of an InAs nanowire transistor occurs by modulating the transmission coefficient of the device. This action is different from a conventional metal-oxide-semiconductor field effect transistor, where the transistor action occurs by modulating the charge in the channel. The device has 82% tunneling current in the off-state and 81% thermal current in the on-state. The two current components become equal at a gate bias at which an approximate source-channel flat-band condition is achieved. Prior to this gate bias, the tunneling current dominates and the thermal current dominates beyond it. The device has an on/off current ratio of 7.84 × 10 5 and an inverse subthreshold slope of 63 mV dec −1 . The transistor operates in the quantum capacitance limit with a normalized transconductance value of 14.43 mS µm −1 , an intrinsic switching delay of 90.1675 fs, and an intrinsic unity current gain frequency of 6.8697 THz

  13. AMPA receptor ligands

    DEFF Research Database (Denmark)

    Strømgaard, Kristian; Mellor, Ian

    2004-01-01

    Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPAR), subtype of the ionotropic glutamate receptors (IGRs), mediate fast synaptic transmission in the central nervous system (CNS), and are involved in many neurological disorders, as well as being a key player in the f......Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPAR), subtype of the ionotropic glutamate receptors (IGRs), mediate fast synaptic transmission in the central nervous system (CNS), and are involved in many neurological disorders, as well as being a key player...... in the formation of memory. Hence, ligands affecting AMPARs are highly important for the study of the structure and function of this receptor, and in this regard polyamine-based ligands, particularly polyamine toxins, are unique as they selectively block Ca2+ -permeable AMPARs. Indeed, endogenous intracellular...

  14. Radiobiology with DNA ligands

    International Nuclear Information System (INIS)

    Weinreich, R.; Argentini, M.; Guenther, I.; Koziorowski, J.; Larsson, B.; Nievergelt-Egido, M.C.; Salt, C.; Wyer, L.; Dos Santos, D.F.; Hansen, H.J.

    1997-01-01

    The paper deals with the following topics: labelling of DNA ligands and other tumour-affinic compounds with 4.15-d 124 I, radiotoxicity of Hoechst 33258 and 33342 and of iodinated Hoechst 33258 in cell cultures, preparation of 76 Br-, 123 I-, and 221 At-labelled 5-halo-2'-deoxyuridine, chemical syntheses of boron derivatives of Hoechst 33258.III., Gadolinium neutron capture therapy

  15. Critical surface phase of α2(2 × 4) reconstructed zig-zag chains on InAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Xiang [Department of Electronic Information Science and Technology, Guizhou University, Guizhou, Guiyang 550025 (China); Zhou, Xun [Department of Electronic Information Science and Technology, Guizhou University, Guizhou, Guiyang 550025 (China); School of Physics and Electronics Science, Guizhou Normal University, Guizhou, Guiyang 550001 (China); Wang, Ji-Hong [Department of Electronic Information Science and Technology, Guizhou University, Guizhou, Guiyang 550025 (China); Luo, Zi-Jiang [Department of Electronic Information Science and Technology, Guizhou University, Guizhou, Guiyang 550025 (China); School of Education Administration, Guizhou University of Finance and Economics, Guizhou, Guiyang 550004 (China); Zhou, Qing; Liu, Ke; Hu, Ming-Zhe [Department of Electronic Information Science and Technology, Guizhou University, Guizhou, Guiyang 550025 (China); Ding, Zhao, E-mail: zding@gzu.edu.cn [Department of Electronic Information Science and Technology, Guizhou University, Guizhou, Guiyang 550025 (China)

    2014-07-01

    The critical condition for InAs(001) surface phase transition has been studied, the surface phase transition of InAs(001) showed discontinuity with hysteresis cycle as a function of substrate temperature. A mixed reconstruction surface and zig-zag chain α2(2 × 4) reconstruction surface have been observed by scanning tunneling microscopy. Considering the interaction and dynamics of surface arsenic atoms, the zig-zag chains of α2(2 × 4) reconstruction were found to be actually caused by the selective adsorption and desorption of surface arsenic dimers, they played a critical role in the surface phase transition between (2 × 4) and (4 × 2). - Highlights: • Discontinuous surface phase transition phenomena on the flat InAs(001) surface • Nanoscale InAs(001) surface observed by scanning tunneling microscopy • “Zig-Zag” chains of α2(2 × 4) reconstruction • Critical role in the surface phase transition between (2 × 4) and (4 × 2)

  16. Self-assembled InAs quantum dots formed by molecular beam epitaxy at low temperature and postgrowth annealing

    NARCIS (Netherlands)

    Zhan, H.H.; Nötzel, R.; Hamhuis, G.J.; Eijkemans, T.J.; Wolter, J.H.

    2003-01-01

    Self-assembled InAs quantum dots are grown at low temperature (LT) by molecular beam epitaxy (MBE) on GaAs substrates. The growth is in situ monitored by reflection high-energy electron diffraction, and ex situ evaluated by atomic force microscopy for the morphological properties, and by

  17. Supercurrent through a spin-split quasi-ballistic point contact in an InAs nanowire

    DEFF Research Database (Denmark)

    Saldaña, J. C. Estrada; Žitko, R.; Cleuziou, J. P.

    2018-01-01

    We study the superconducting proximity effect in an InAs nanowire contacted by Ta-based superconducting electrodes. Using local bottom gates, we control the potential landscape along the nanowire, tuning its conductance to a quasi-ballistic regime. At high magnetic field ($B$), we observe...

  18. Liquid phase epitaxy of abrupt junctions in InAs and studies of injection radiative tunneling processes

    International Nuclear Information System (INIS)

    Bull, D.J.

    1977-01-01

    The p-n junction in a InAs crystal, by liquid phase epitaxy is obtained. The processes of injection and tunneling radiative recombination by emitted radiation from active region of p-n junction for low injection current are studied. (M.C.K.) [pt

  19. Carrier dynamics in InAs quantum dots embedded in InGaAs/GaAs multi quantum well structures

    International Nuclear Information System (INIS)

    Espinola, J L Casas; Dybic, M; Ostapenko, S; Torchynska, T V; Polupan, G

    2007-01-01

    Ground and multi excited state photoluminescence, as well as its temperature dependence, in InAs quantum dots embedded in symmetric In x Ga 1-x As/GaAs (x = 0.15) quantum wells (DWELL) have been investigated. The solution of the set of rate equations for exciton dynamics (relaxation into QWs or QDs and thermal escape) solved by us earlier is used for analysis the variety of thermal activation energies of photoluminescence thermal quenching for ground and multi excited states of InAs QDs. The obtained solutions were used at the discussion of the variety of activation energies of PL thermal quenching in InAs QDs. It is revealed three different regimes of thermally activated quenching of the QD PL intensity. These three regimes were attributed to thermal escape of excitons: i) from the high energy excited states of InAs QDs into the WL with follows exciton re-localization; ii) from the In x Ga 1-x As QWs into the GaAs barrier and iii) from the WL into the GaAs barrier with their subsequent nonradiative recombination in GaAs barrier

  20. 20 CFR 668.700 - What process must an INA grantee use to plan its employment and training services?

    Science.gov (United States)

    2010-04-01

    ... it uses to plan other activities and services. (b) However, in the process of preparing its Two Year... 20 Employees' Benefits 3 2010-04-01 2010-04-01 false What process must an INA grantee use to plan its employment and training services? 668.700 Section 668.700 Employees' Benefits EMPLOYMENT AND...

  1. Critical surface phase of α2(2 × 4) reconstructed zig-zag chains on InAs(001)

    International Nuclear Information System (INIS)

    Guo, Xiang; Zhou, Xun; Wang, Ji-Hong; Luo, Zi-Jiang; Zhou, Qing; Liu, Ke; Hu, Ming-Zhe; Ding, Zhao

    2014-01-01

    The critical condition for InAs(001) surface phase transition has been studied, the surface phase transition of InAs(001) showed discontinuity with hysteresis cycle as a function of substrate temperature. A mixed reconstruction surface and zig-zag chain α2(2 × 4) reconstruction surface have been observed by scanning tunneling microscopy. Considering the interaction and dynamics of surface arsenic atoms, the zig-zag chains of α2(2 × 4) reconstruction were found to be actually caused by the selective adsorption and desorption of surface arsenic dimers, they played a critical role in the surface phase transition between (2 × 4) and (4 × 2). - Highlights: • Discontinuous surface phase transition phenomena on the flat InAs(001) surface • Nanoscale InAs(001) surface observed by scanning tunneling microscopy • “Zig-Zag” chains of α2(2 × 4) reconstruction • Critical role in the surface phase transition between (2 × 4) and (4 × 2)

  2. Critical Temperature for the Conversion from Wurtzite to Zincblende of the Optical Emission of InAs Nanowires

    KAUST Repository

    Rota, Michele B.; Ameruddin, Amira S.; Wong-Leung, Jennifer; Belabbes, Abderrezak; Gao, Qiang; Miriametro, Antonio; Mura, Francesco; Tan, Hark Hoe; Polimeni, Antonio; Bechstedt, Friedhelm; Jagadish, Chennupati; Capizzi, Mario

    2017-01-01

    One hour annealing at 300 degrees C changes the optical emission characteristics of InAs nanowires (NWs) from the wurtzite (WZ) phase into that of zincblende (ZB). These results are accounted for by the conversion of a small fraction of the NW WZ

  3. Shape analysis of single and stacked InAs quantum dots at the atomic level by cross-sectional STM

    NARCIS (Netherlands)

    Bruls, D.M.; Vugs, J.W.A.M.; Koenraad, P.M.; Skolnick, M.S.; Hopkinson, M.; Wolter, J.H.; Miura, N.; Ando, T.

    2001-01-01

    We present a study of InAs self-assembled quantum dots in GaAs by cross-sectional scanning tunneling microscopy (X-STM). Our results shows that the dots consist of an JnGaAs alloy and that the indium content increases towards the top. The analysis of the height versus base length relation obtained

  4. New process for high optical quality InAs quantum dots grown on patterned GaAs(001) substrates

    NARCIS (Netherlands)

    Alonso-González, Pablo; González, Luisa; González, Yolanda; Fuster, David; Fernández-Martinez, Ivan; Martin-Sánchez, Javier; Abelmann, Leon

    2007-01-01

    This work presents a selective ultraviolet (UV)-ozone oxidation-chemical etching process that has been used, in combination with laser interference lithography (LIL), for the preparation of GaAs patterned substrates. Further molecular beam epitaxy (MBE) growth of InAs results in ordered InAs/GaAs

  5. Bexarotene ligand pharmaceuticals.

    Science.gov (United States)

    Hurst, R E

    2000-12-01

    Bexarotene (LGD-1069), from Ligand, was the first retinoid X receptor (RXR)-selective, antitumor retinoid to enter clinical trials. The company launched the drug for the treatment of cutaneous T-cell lymphoma (CTCL), as Targretin capsules, in the US in January 2000 [359023]. The company filed an NDA for Targretin capsules in June 1999, and for topical gel in December 1999 [329011], [349982] specifically for once-daily oral administration for the treatment of patients with early-stage CTCL who have not tolerated other therapies, patients with refractory or persistent early stage CTCL and patients with refractory advanced stage CTCL. The FDA approved Targretin capsules at the end of December 1999 for once-daily oral treatment of all stages of CTCL in patients refractory to at least one prior systemic therapy, at an initial dose of 300 mg/m2/day. After an NDA was submitted in December 1999 for Targretin gel, the drug received Priority Review status for use as a treatment of cutaneous lesions in patients with stage IA, IB or IIA CTCL [354836]. The FDA issued an approvable letter in June 2000, and granted marketing clearance for CTCL in the same month [370687], [372768], [372769], [373279]. Ligand had received Orphan Drug designation for this indication [329011]. At the request of the FDA, Ligand agreed to carry out certain post-approval phase IV and pharmacokinetic studies [351604]. The company filed an MAA with the EMEA for Targretin Capsules to treat lymphoma in November 1999 [348944]. The NDA for Targretin gel is based on a multicenter phase III trial that was conducted in the US, Canada, Europe and Australia involving 50 patients and a multicenter phase I/II clinical program involving 67 patients. Targretin gel was evaluated for the treatment of patients with early stage CTCL (IA-IIA) who were refractory to, intolerant to, or reached a response plateau for at least 6 months on at least two prior therapies. Efficacy results exceeded the protocol-defined response

  6. Preparation of InAs(0 0 1) surface for spin injection via a chemical route

    International Nuclear Information System (INIS)

    Singh, L J; Oliver, R A; Barber, Z H; Eustace, D A; McComb, D W; Clowes, S K; Gilbertson, A M; Magnus, F; Branford, W R; Cohen, L F; Buckle, L; Buckle, P D; Ashley, T

    2007-01-01

    A wet chemical surface treatment for InAs epilayers is investigated to remove the native semiconductor oxide prior to growth of a MgO tunnel barrier and Co ferromagnetic electrode by dc magnetron sputtering. Use of a HCl etch followed by (NH 4 ) 2 S as the pre-growth surface treatment resulted in pinhole-like features in the tunnel barrier, as observed by conducting atomic force microscopy, but this detrimental effect is avoided if the etch procedure is repeated twice. High resolution transmission electron microscopy revealed that the etched samples had uniform tunnel barriers and reducing the growth temperature of the barrier from 200 to 100 0 C significantly improved the abruptness of the semiconductor/barrier interface. Electrical characterization of barrier properties illustrated that all the etched samples showed parabolic differential conductance curves indicative of tunnelling behaviour at 300 K

  7. ISTRAŽIVANJE ZAGAĐENOSTI MESA, RADNIH POVRŠINA I PRIBORA BAKTERIJAMA RODA PROTEUS

    OpenAIRE

    Hadžiosmanović, Mirza; Živković, Josip; Trešćec, Aida

    1992-01-01

    Istraživan je stupanj zagađenja sirovina i radnih površina tijekom proizvodnje mesnih prerađevina bakterijama roda Proteus. Rezultati su pokazali da je meso peradi zagađeno vrstama roda Proteus u količini od 8,8%, svježe goveđe meso 7,8 % a polutrajne i obarene kobasice neposredno nakon proizvoodnje u količini od 2,8 %. Rezultati pretraga brisova s proizvodnih linija pokazuju da je pripadnika roda Proteus najviše u kobasičarnici (14,6 %), na liniji prerade svinja (11,8 %), goveda (10,9 %), a ...

  8. Surface roughness induced electron mobility degradation in InAs nanowires

    International Nuclear Information System (INIS)

    Wang Fengyun; Yip, Sen Po; Han, Ning; Fok, KitWa; Lin, Hao; Hou, Jared J; Dong, Guofa; Hung, Tak Fu; Chan, K S; Ho, Johnny C

    2013-01-01

    In this work, we present a study of the surface roughness dependent electron mobility in InAs nanowires grown by the nickel-catalyzed chemical vapor deposition method. These nanowires have good crystallinity, well-controlled surface morphology without any surface coating or tapering and an excellent peak field-effect mobility up to 15 000 cm 2 V −1 s −1 when configured into back-gated field-effect nanowire transistors. Detailed electrical characterizations reveal that the electron mobility degrades monotonically with increasing surface roughness and diameter scaling, while low-temperature measurements further decouple the effects of surface/interface traps and phonon scattering, highlighting the dominant impact of surface roughness scattering on the electron mobility for miniaturized and surface disordered nanowires. All these factors suggest that careful consideration of nanowire geometries and surface condition is required for designing devices with optimal performance. (paper)

  9. Fabrication of a complex InAs ring-and-dot structure by droplet epitaxy

    International Nuclear Information System (INIS)

    Noda, Takeshi; Mano, Takaaki

    2008-01-01

    An InAs ring structure accompanying the formation of quantum dots (QDs) was fabricated on (1 0 0)GaAs using droplet epitaxy. The QDs were located in the vicinity of the ring, due to the diffusion of In atoms from the In droplets. In addition, the dots were found to have distributed elliptically and preferentially along the [0 1 1] direction, implying that In itself prefers to diffuse along the [0 1 1] direction, which is the opposite of the favorable diffusion orientation of group III atoms on (1 0 0)GaAs under a commonly used As-stabilized growth condition. This is the first observation of a ring structure accompanying the formation of quantum dots in droplet epitaxy

  10. Mieloencefalite protozoária eqüina (Relato de caso.

    Directory of Open Access Journals (Sweden)

    R. C. Gonçalves

    2005-03-01

    Full Text Available RESUMO :O objetivo deste trabalho foi relatar um caso de mieloencefalite protozoária eqüina no Estado de São Paulo, Brasil. O diagnóstico se baseou nos sinais clínicos, no resultado positivo para anticorpos contra Sarcocystis neurona no soro e no líquor pela técnica de Western blot. Palavras chave: Mieloencefalite, Sarcocystis neurona, eqüinos. SUMMARY: The purpose of this work was to present a case of equine protozoal myeloencephalitis (EPM in the State of São Paulo, Brazil. The diagnosis was based on the clinical sings, the positive results of the serum and cerebrospinal fluid analysis (Western blot for antibodies against Sarcocystis neurona. Keywords: Myeloencephalitis, Sarcocystis neurona,

  11. Time evolution studies of laser induced chemical changes in InAs nanowire using Raman spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pal, Suparna; Aggarwal, R.; Kumari Gupta, Vandna; Ingale, Alka [Laser Physics Application Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, MP (India)

    2014-07-07

    We report the study of time evolution of chemical changes on the surface of an InAs nanowire (NW) on laser irradiation in different power density regime, using Raman spectroscopy for a time span of 8–16 min. Mixture of metastable oxides like InAsO{sub 4,} As{sub 2}O{sub 3} are formed upon oxidation, which are reflected as sharp Raman peaks at ∼240–254 and 180–200 cm{sup −1}. Evidence of removal of arsenic layer by layer is also observed at higher power density. Position controlled laser induced chemical modification on a nanometer scale, without changing the core of the NW, can be useful for NW based device fabrication.

  12. Towards quantitative three-dimensional characterisation of buried InAs quantum dots

    DEFF Research Database (Denmark)

    Kadkhodazadeh, Shima; Semenova, Elizaveta; Schubert, Martin

    2011-01-01

    InAs quantum dots grown on InP or InGaAsP are used for optical communication applications operating in the 1.3 – 1.55 μm wavelength range. It is generally understood that the optical properties of such dots are highly dependent on their structural and chemical profiles. However, morphological...... and compositional measurements of quantum dots using transmission electron microscopy can be ambiguous because the recorded signal is usually a projection through the thickness of the specimen. Here, we discuss the application of scanning transmission electron microscopy tomography to the morphological and chemical...... characterisation of surface and buried quantum dots. We highlight some of the challenges involved and introduce a new specimen preparation method for creating needle-shaped specimens that each contain multiple dots and are suitable for both scanning transmission electron microscopy tomography and atom probe...

  13. Self-assembly of InAs and Si/Ge quantum dots on structured surfaces

    International Nuclear Information System (INIS)

    Patella, F; Sgarlata, A; Arciprete, F; Nufris, S; Szkutnik, P D; Placidi, E; Fanfoni, M; Motta, N; Balzarotti, A

    2004-01-01

    We discuss the self-aggregation process of InAs and Si-Ge quantum dots (QDs) on natural and patterned GaAs(001) and Si(001) and Si(111) surfaces, with reference to our recent studies with scanning tunnelling and atomic force microscopy and current experimental and theoretical works. Various methods for obtaining naturally structured surfaces are briefly surveyed, as the patterning formed by the surface instability and by the strain in mismatched heteroepitaxy, and the latest methods of pre-patterning and growth at selected sites are discussed. Basic topics are also addressed that determine the final morphology of QDs, such as the wetting layer formation, the elastic strain field and the two-dimensional to three-dimensional phase transition

  14. Isolation, Fractionation and Characterization of Catalase from Neurospora crassa (InaCC F226)

    Science.gov (United States)

    Suryani; Ambarsari, L.; Lindawati, E.

    2017-03-01

    Catalase from Indigenous isolate Neurospora crassa InaCC F226 has been isolated, fractionated and characterized. Production of catalase by Neurospora crassa was done by using PDA medium (Potato Dextrosa Agar) and fractionated with ammonium sulphate with 20-80% saturation. Fraction 60% was optimum saturation of ammonium sulphate and had highest specific activity 3339.82 U/mg with purity 6.09 times, total protein 0.920 mg and yield 88.57%. The optimum pH and temperature for catalase activity were at 40°C and pH 7.0, respectively. The metal ions that stimulated catalase activity acted were Ca2+, Mn2+ and Zn2+, and inhibitors were EDTA, Mg2+ and Cu2+. Based on Km and Vmax values were 0.2384 mM and 13.3156 s/mM.

  15. Towards quantitative three-dimensional characterisation of buried InAs quantum dots

    International Nuclear Information System (INIS)

    Kadkhodazadeh, S; Dunin-Borkowski, R E; Semenova, E S; Schubert, M; Yvind, K; Thuvander, M; Stiller, K M

    2011-01-01

    InAs quantum dots grown on InP or InGaAsP are used for optical communication applications operating in the 1.3 – 1.55 μm wavelength range. It is generally understood that the optical properties of such dots are highly dependent on their structural and chemical profiles. However, morphological and compositional measurements of quantum dots using transmission electron microscopy can be ambiguous because the recorded signal is usually a projection through the thickness of the specimen. Here, we discuss the application of scanning transmission electron microscopy tomography to the morphological and chemical characterisation of surface and buried quantum dots. We highlight some of the challenges involved and introduce a new specimen preparation method for creating needle-shaped specimens that each contain multiple dots and are suitable for both scanning transmission electron microscopy tomography and atom probe tomography.

  16. Enhancement of optical properties of InAs quantum dots grown by using periodic arsine interruption

    International Nuclear Information System (INIS)

    Kim, Jungsub; Yang, Changjae; Sim, Uk; Lee, Jaeyel; Yoon, Euijoon; Lee, Youngsoo

    2009-01-01

    We investigated the morphological and optical properties of InAs quantum dots (QDs) grown by using periodic arsine interruption (PAI) and compared them with QDs grown conventionally. In the conventional growth, the formation of large islands was observed, which suppresses the nucleation and growth of QDs. Furthermore, the growth of capping layers was significantly degraded by these large islands. On the other hand, in the PAI growth, the formation of large islands was completely suppressed, resulting in the increase of the density and aspect ratio of QDs and the uniform growth of capping layers. As a result of photoluminescence (PL) measurements, we found that the emission efficiency was enhanced and the full-width-half-maximum was reduced to 32 meV. The temperature dependence of these optical properties also revealed the enhancement of the uniformity of QDs grown by the PAI method.

  17. Anisotropic transport properties of quasiballistic InAs nanowires under high magnetic field

    Science.gov (United States)

    Vigneau, Florian; Zeng, Zaiping; Escoffier, Walter; Caroff, Philippe; Leturcq, Renaud; Niquet, Yann-Michel; Raquet, Bertrand; Goiran, Michel

    2018-03-01

    The magnetoconductance of a long channel InAs nanowire based field effect transistor in the quasiballistic regime under large magnetic field is investigated. The quasi-1D nanowire is fully characterized by a bias voltage spectroscopy and measurements under magnetic field up to 50 T applied either perpendicular or parallel to the nanowire axis lifting the spin and orbital degeneracies of the subbands. Under normal magnetic field, the conductance shows quantized steps due to the backscattering reduction and a decrease due to depopulation of the 1D modes. Under axial magnetic field, a quasioscillatory behavior is evidenced due to the coupling of the magnetic field with the angular momentum of the wave function. In addition the formation of cyclotron orbits is highlighted under high magnetic field. The experimental results are compared with theoretical calculation of the 1D band structure and related parameters.

  18. Detection of nearest neighbors to specific fluorescently tagged ligands in rod outer segment and lymphocyte plasma membranes by photosensitization of 5-iodonaphthyl 1-azide

    International Nuclear Information System (INIS)

    Raviv, Y.; Bercovici, T.; Gitler, C.; Salomon, Y.

    1989-01-01

    Lima bean agglutinin-fluorescein 5-isothiocyanate conjugate (FluNCS-lima bean lectin) interacts with specific receptor molecules on membranes both from the rod outer segment (ROS) of the frog retina and from S49 mouse lymphoma cells. When [125I]-5-iodonaphthyl 1-azide (125I-INA), which freely and randomly partitions into the lipid bilayer, is added to membranes and the suspension is irradiated at 480 nm, the FluNCS-conjugated lectin photosensitizes the [125I]INA but only at discrete sites. This results in the selective labeling of specific proteins: an 88-kDa protein on ROS membranes and a 56-kDa protein on S49 plasma membranes. Labeling is dependent upon the interaction of the FluNCS-lectin with glycosylated receptor sites, since N-acetylgalactosamine, but not methyl alpha-mannoside, blocked labeling of the 56-kDa protein on S49 membranes. In contrast, a random labeling pattern of membrane proteins was observed upon irradiation at 480 nm using other fluorescein conjugates, such as FluNCS-bovine serum albumin (FluNCS-BSA) or FluNCS-soybean trypsin inhibitor (FluNCS-STI), which interact with cell membranes in a nonselective manner, or with N-(fluorescein-5-thiocarbamoyl)-n-undecyclamine (FluNCS-NHC11), which is freely miscible in the membrane lipid. Random labeling was also obtained by direct photoexcitation of [125I]INA at 314 nm, with no distinct labeling of the 88- and 56-kDa proteins in the respective membranes. These results suggest that protein ligands can be used to guide sensitizers to discrete receptor sites and lead to their selective labeling by photosensitized activation of [125I]INA

  19. Ligand Depot: a data warehouse for ligands bound to macromolecules.

    Science.gov (United States)

    Feng, Zukang; Chen, Li; Maddula, Himabindu; Akcan, Ozgur; Oughtred, Rose; Berman, Helen M; Westbrook, John

    2004-09-01

    Ligand Depot is an integrated data resource for finding information about small molecules bound to proteins and nucleic acids. The initial release (version 1.0, November, 2003) focuses on providing chemical and structural information for small molecules found as part of the structures deposited in the Protein Data Bank. Ligand Depot accepts keyword-based queries and also provides a graphical interface for performing chemical substructure searches. A wide variety of web resources that contain information on small molecules may also be accessed through Ligand Depot. Ligand Depot is available at http://ligand-depot.rutgers.edu/. Version 1.0 supports multiple operating systems including Windows, Unix, Linux and the Macintosh operating system. The current drawing tool works in Internet Explorer, Netscape and Mozilla on Windows, Unix and Linux.

  20. A Brief History of INA and ICOH SCNP: International Neurotoxicology Association and International Congress on Occupational Health Scientific Committee on Neurotoxicology and Psychophysiology

    Science.gov (United States)

    Two international scientific societies dedicated to research in neurotoxicology and neurobehavioral toxicology are the International Neurotoxicology Association (INA) and the International Congress on Occupational Health International Symposium on Neurobehavioral Methods and Effe...

  1. The role of strain-driven in migration in the growth of self-assembled InAs quantum dots on InP

    CERN Document Server

    Yoon, S H; Lee, T W; Hwang, H D; Yoon, E J; Kim, Y D

    1999-01-01

    Self-assembled InAs quantum dots (SAQDs) were grown on InP by metalorganic chemical vapor deposition. The amount of excess InAs and the aspect ratio of the SAQD increased with temperature and V/III ratio. It is explained that the As/P exchange reaction at the surface played an important role in the kinetics of SAQD formation. Insertion of a lattice-matched InGaAs buffer layer suppressed the excess InAs formation, and lowered the aspect ratio. Moreover, the dots formed on InGaAs buffer layers were faceted, whereas those on InP were hemispherical, confirming the effect of the As/P exchange reaction. The shape of InAs quantum dots on InGaAs buffer layers was a truncated pyramid with four [136] facets and base edges parallel to directions.

  2. High uniformity of self-organized InAs quantum wires on InAlAs buffers grown on misoriented InP(001)

    International Nuclear Information System (INIS)

    Wang Yuanli; Jin, P.; Ye, X.L.; Zhang, C.L.; Shi, G.X.; Li, R.Y.; Chen, Y.H.; Wang, Z.G.

    2006-01-01

    Highly uniform InAs quantum wires (QWRs) have been obtained on the In 0.5 Al 0.5 As buffer layer grown on the InP substrate 8 (convolutionsign) off (001) towards (111) by molecular-beam epitaxy. The quasi-periodic composition modulation was spontaneously formed in the In 0.5 Al 0.5 As buffer layer on this misoriented InP (001). The width and period of the In-rich bands are about 10 and 40 nm, respectively. The periodic In-rich bands play a major role in the sequent InAs QWRs growth and the InAs QWRs are well positioned atop In-rich bands. The photoluminescence (PL) measurements showed a significant reduction in full width at half maximum and enhanced PL efficiency for InAs QWRs on misoriented InP(001) as compared to that on normal InP(001)

  3. Metal-ligand interactions

    Science.gov (United States)

    Ervin, Kent M.

    Experimental studies of the interactions of small transition-metal cluster anions with carbonyl ligands are reviewed and compared with neutral and cationic clusters. Under thermal conditions, the reaction rates of transition-metal clusters with carbon monoxide are measured as a function of cluster size. Saturation limits for carbon monoxide addition can be related to the geometric structures of the clusters. Both energy-resolved threshold collision-induced dissociation experiments and time-resolved photodissociation experiments are used to measure metal-carbonyl binding energies. For platinum and palladium trimer anions, the carbonyl binding energies are assigned to different geometric binding sites. Platinum and palladium cluster anions catalyse the oxidation of carbon monoxide to carbon dioxide in a full catalytic cycle at thermal energies.

  4. Melatonin: functions and ligands.

    Science.gov (United States)

    Singh, Mahaveer; Jadhav, Hemant R

    2014-09-01

    Melatonin is a chronobiotic substance that acts as synchronizer by stabilizing bodily rhythms. Its synthesis occurs in various locations throughout the body, including the pineal gland, skin, lymphocytes and gastrointestinal tract (GIT). Its synthesis and secretion is controlled by light and dark conditions, whereby light decreases and darkness increases its production. Thus, melatonin is also known as the 'hormone of darkness'. Melatonin and analogs that bind to the melatonin receptors are important because of their role in the management of depression, insomnia, epilepsy, Alzheimer's disease (AD), diabetes, obesity, alopecia, migraine, cancer, and immune and cardiac disorders. In this review, we discuss the mechanism of action of melatonin in these disorders, which could aid in the design of novel melatonin receptor ligands. Copyright © 2014 Elsevier Ltd. All rights reserved.

  5. Electron microscopy of GaAs-based structures with InAs and As quantum dots separated by an AlAs barrier

    International Nuclear Information System (INIS)

    Nevedomskiy, V. N.; Bert, N. A.; Chaldyshev, V. V.; Preobrazhenskiy, V. V.; Putyato, M. A.; Semyagin, B. R.

    2013-01-01

    Electron microscopy studies of GaAs-based structures grown by molecular beam epitaxy and containing arrays of semiconductor InAs quantum dots and metal As quantum dots are performed. The array of InAs quantum dots is formed by the Stranski-Krastanov mechanism and consists of vertically coupled pairs of quantum dots separated by a GaAs spacer 10 nm thick. To separate the arrays of semiconductor and metal quantum dots and to prevent diffusion-induced mixing, the array of InAs quantum dots is overgrown with an AlAs barrier layer 5 or 10 nm thick, after which a GaAs layer is grown at a comparatively low temperature (180°C). The array of As quantum dots is formed in an As-enriched layer of the low-temperature GaAs by means of post-growth annealing at 400–760°C for 15 min. It is established that the AlAs barrier layer has a surface profile corresponding to that of a subbarrier layer with InAs quantum dots. The presence of such a profile causes the formation of V-shaped structural defects upon subsequent overgrowth with the GaAs layer. Besides, it was obtained that AlAs layer is thinned over the InAs quantum dots tops. It is shown that the AlAs barrier layer in the regions between the InAs quantum dots effectively prevents the starting diffusion of excess As at annealing temperatures up to 600°C. However, the concentration of mechanical stresses and the reduced thickness of the AlAs barrier layer near the tops of the InAs quantum dots lead to local barrier breakthroughs and the diffusion of As quantum dots into the region of coupled pairs of InAs quantum dots at higher annealing temperatures

  6. Macrocyclic G-quadruplex ligands

    DEFF Research Database (Denmark)

    Nielsen, M C; Ulven, Trond

    2010-01-01

    are macrocyclic structures which have been modeled after the natural product telomestatin or from porphyrin-based ligands discovered in the late 1990s. These two structural classes of G-quadruplex ligands are reviewed here with special attention to selectivity and structure-activity relationships, and with focus...

  7. Two-color single-photon emission from InAs quantum dots: toward logic information management using quantum light.

    Science.gov (United States)

    Rivas, David; Muñoz-Matutano, Guillermo; Canet-Ferrer, Josep; García-Calzada, Raúl; Trevisi, Giovanna; Seravalli, Luca; Frigeri, Paola; Martínez-Pastor, Juan P

    2014-02-12

    In this work, we propose the use of the Hanbury-Brown and Twiss interferometric technique and a switchable two-color excitation method for evaluating the exciton and noncorrelated electron-hole dynamics associated with single photon emission from indium arsenide (InAs) self-assembled quantum dots (QDs). Using a microstate master equation model we demonstrate that our single QDs are described by nonlinear exciton dynamics. The simultaneous detection of two-color, single photon emission from InAs QDs using these nonlinear dynamics was used to design a NOT AND logic transference function. This computational functionality combines the advantages of working with light/photons as input/output device parameters (all-optical system) and that of a nanodevice (QD size of ∼ 20 nm) while also providing high optical sensitivity (ultralow optical power operational requirements). These system features represent an important and interesting step toward the development of new prototypes for the incoming quantum information technologies.

  8. Increasing the quantum efficiency of GaAs solar cells by embedding InAs quantum dots

    Science.gov (United States)

    Salii, R. A.; Mintairov, S. A.; Nadtochiy, A. M.; Payusov, A. S.; Brunkov, P. N.; Shvarts, M. Z.; Kalyuzhnyy, N. A.

    2016-11-01

    Development of Metalorganic Vapor Phase Epitaxy (MOVPE) technology of InAs quantum dots (QDs) in GaAs for photovoltaic applications is presented. The growth peculiarities in InAs-GaAs lattice-mismatched system were considered. The photoluminescence (PL) intensity dependences on different growth parameters were obtained. The multimodal distribution of QDs by sizes was found using AFM and PL methods. GaAs solar cell nanoheterostructures with imbedded QD arrays were designed and obtained. Ones have been demonstrated a significant increase of quantum efficiency and photogenerated current of QD solar cells due to photo effect in InAs QD array (0.59 mA/cm2 for AM1.5D and 82 mA/cm2 for AM0).

  9. Atomic structures of a monolayer of AlAs, GaAs, and InAs on Si(111)

    International Nuclear Information System (INIS)

    Lee, Geunjung; Yoon, Younggui

    2010-01-01

    We study atomic structures of a monolayer of AlAs, GaAs, and InAs on a Si(111) substrate from first-principles. The surface with the stacking sequence of ...SiSiMAsSiAs is energetically more stable than the surface with the stacking sequence of ...SiSiSiAsMAs, where M is Al, Ga, or In. The atomic structure of the three top layers of the low-energy surfaces are quite robust, irrespective of M, and the atomic structure of the AlAsSiAs terminated surface and that of the GaAsSiAs terminated surface are very similar. For the high-energy AsMAs terminated surfaces, the broken local tetrahedral symmetry plays an important role in the atomic structures. The calculated atomic structures of InAs on the Si(111) substrate depart most from the structure of crystalline Si.

  10. Seeded growth of InP and InAs quantum rods using indium acetate and myristic acid

    International Nuclear Information System (INIS)

    Shweky, Itzhak; Aharoni, Assaf; Mokari, Taleb; Rothenberg, Eli; Nadler, Moshe; Popov, Inna; Banin, Uri

    2006-01-01

    A synthesis of soluble III-V semiconductor quantum rods using gold nanoparticles to direct and catalyze one-dimensional growth is developed. The growth takes place via the solution-liquid-solid (SLS) mechanism where proper precursors are injected into a coordinating solvent. We report the synthesis of InP nanorods using indium acetate and myristic acid with gold nanoparticles as the catalysts in the SLS growth mode. A similar route was successfully developed for the growth of InAs nanorods. We find that the amount of Au catalyst in the reaction is an important parameter to achieve shape control. Transmission electron microscope (TEM) images of InP and InAs nanocrystals revealed that the crystals are mostly rod-shaped, and provide strong evidence for Au presence in one edge. The rods were characterized structurally using X-ray diffraction and high-resolution TEM and optically by absorption and photoluminescence

  11. Optical characterization of InAs quantum wells and dots grown radially on wurtzite InP nanowires

    International Nuclear Information System (INIS)

    Lindgren, David; Kawaguchi, Kenichi; Heurlin, Magnus; Borgström, Magnus T; Pistol, Mats-Erik; Samuelson, Lars; Gustafsson, Anders

    2013-01-01

    Correlated micro-photoluminescence (μPL) and cathodoluminescence (CL) measurements are reported for single core–shell InP–InAs wurtzite nanowires grown using metal–organic vapor phase epitaxy. Samples covering a radial InAs shell thickness of 1–12 ML were investigated. The effective masses for the wurtzite material were determined from the transition energy dependence of the InAs shell thickness, using a model based on linear deformation potential theory. InP cores with segments of mixed zincblende and wurtzite, on which quantum dots nucleated selectively, were also investigated. Narrow peaks were observed by μPL and the spatial origin of the emission was identified with CL imaging. (paper)

  12. The presence of INA proteins on the surface of single cells of Pseudomonas syringae R10.79 isolated from rain

    Science.gov (United States)

    Šantl-Temkiv, Tina; Ling, Meilee; Holm, Stine; Finster, Kai; Boesen, Thomas

    2016-04-01

    One of the important open questions in atmospheric ice nucleation is the impact of bioaerosols on the ice content of mix phase clouds (DeMott and Prenni 2010). Biogenic ice nuclei have a unique capacity of facilitating ice formation at temperatures between -1 and -10 °C. The model biogenic ice nuclei are produced by a few species of plant-surface bacteria, such as Pseudomonas syringae, that are commonly transported through the atmosphere. These bacterial species have highly specialized proteins, the so-called ice nucleation active (INA) proteins, which are exposed at the outer membrane surface of the cell where they promote ice particle formation. The mechanisms behind the onset of INA protein synthesis in single bacterial cells are not well understood. We performed a laboratory study in order to (i) investigate the presence of INA proteins on single bacterial cells and (ii) understand the conditions that induce INA protein production. We previously isolated an INA-positive strain of Pseudomonas syringae from rain samples collected in Denmark. Bacterial cells initiated ice nucleation activity at temperatures ≤-2°C and the cell fragments at temperatures ≤-8°C (Šantl-Temkiv et al 2015). We determined the amino-acid sequence of the INA protein and used the sequence to produce custom-made antibodies (GenScript, Germany). These antibodies were used to specifically stain and visualize the INA protein on the surfaces of single cells, which can then be quantified by a technique called flow cytometry. The synthesis of INA proteins by individual cells was followed during a batch growth experiment. An unusually high proportion of cells that were adapting to the new conditions prior to growth produced INA proteins (~4.4% of all cells). A smaller fraction of actively growing cells was carrying INA proteins (~1.2 % of all cells). The cells that stopped growing due to unfavorable conditions had the lowest fraction of cells carrying INA proteins (~0.5 % of all cells). To

  13. Growth and anisotropic transport properties of self-assembled InAs nanostructures in InP

    International Nuclear Information System (INIS)

    Bierwagen, O.

    2007-01-01

    Self-assembled InAs nanostructures in InP, comprising quantum wells, quantum wires, and quantum dots, are studied in terms of their formation and properties. In particular, the structural, optical, and anisotropic transport properties of the nanostructures are investigated. The focus is a comprehending exploration of the anisotropic in-plane transport in large ensembles of laterally coupled InAs nanostructures. The self-assembled Stranski-Krastanov growth of InAs nanostructures is studied by gas-source molecular beam epitaxy on both nominally oriented and vicinal InP(001). Optical polarization of the interband transitions arising from the nanostructure type is demonstrated by photoluminescence and transmission spectroscopy. The experimentally convenient four-contact van der Pauw Hall measurement of rectangularly shaped semiconductors, usually applied to isotropic systems, is extended to yield the anisotropic transport properties. Temperature dependent transport measurements are performed in large ensembles of laterally closely spaced nanostructures. The transport of quantum wire-, quantum dash- and quantum dot containing samples is highly anisotropic with the principal axes of conductivity aligned to the directions. The direction of higher mobility is [ anti 110], which is parallel to the direction of the quantum wires. In extreme cases, the anisotropies exceed 30 for electrons, and 100 for holes. The extreme anisotropy for holes is due to diffusive transport through extended states in the [ anti 110], and hopping transport through laterally localized states in the [110] direction, within the same sample. A novel 5-terminal electronic switching device based on gate-controlled transport anisotropy is proposed. The gate-control of the transport anisotropy in modulation-doped, self-organized InAs quantum wires embedded in InP is demonstrated. (orig.)

  14. Heterostructures on the basis of GaAs with quantum points of InAs for photo-electric transformers

    Directory of Open Access Journals (Sweden)

    Maronchuk I. E.

    2008-12-01

    Full Text Available Heterostructures based on GaAs with InAs quantum dots obtained in the process of liquid-phase epitaxy by the method of pulse cooling of saturated solution in indium or heterostructures containing quantum dots in the area of the p–n-junction were much worse than control solar cells manufactured on the same structures but without quantum dots. Solar cells containing quantum dots in the p-region were slightly better than control solar cells.

  15. Controlled tuning of the radiative lifetime in InAs self-assembled quantum dots through vertical ordering

    Science.gov (United States)

    Colocci, M.; Vinattieri, A.; Lippi, L.; Bogani, F.; Rosa-Clot, M.; Taddei, S.; Bosacchi, A.; Franchi, S.; Frigeri, P.

    1999-01-01

    Multilayer structures of InAs quantum dots have been studied by means of photoluminescence techniques. A strong increase of the radiative lifetime with increasing number of stacked dot layers has been observed at low temperatures. Moreover, a strong temperature dependence of the radiative lifetime, which is not present in the single layer samples, has been found in the multistacked structures. The observed effects are nicely explained as a consequence of the electronic coupling between electrons and holes induced by vertical ordering.

  16. Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

    Science.gov (United States)

    Qiu, Yueming; Chacon, Rebecca; Uhl, David; Yang, Rui

    2005-01-01

    In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 microns or more near room temperature. InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strainenergy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 microns, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots. In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.

  17. Growth and anisotropic transport properties of self-assembled InAs nanostructures in InP

    Energy Technology Data Exchange (ETDEWEB)

    Bierwagen, O.

    2007-12-20

    Self-assembled InAs nanostructures in InP, comprising quantum wells, quantum wires, and quantum dots, are studied in terms of their formation and properties. In particular, the structural, optical, and anisotropic transport properties of the nanostructures are investigated. The focus is a comprehending exploration of the anisotropic in-plane transport in large ensembles of laterally coupled InAs nanostructures. The self-assembled Stranski-Krastanov growth of InAs nanostructures is studied by gas-source molecular beam epitaxy on both nominally oriented and vicinal InP(001). Optical polarization of the interband transitions arising from the nanostructure type is demonstrated by photoluminescence and transmission spectroscopy. The experimentally convenient four-contact van der Pauw Hall measurement of rectangularly shaped semiconductors, usually applied to isotropic systems, is extended to yield the anisotropic transport properties. Temperature dependent transport measurements are performed in large ensembles of laterally closely spaced nanostructures. The transport of quantum wire-, quantum dash- and quantum dot containing samples is highly anisotropic with the principal axes of conductivity aligned to the <110> directions. The direction of higher mobility is [ anti 110], which is parallel to the direction of the quantum wires. In extreme cases, the anisotropies exceed 30 for electrons, and 100 for holes. The extreme anisotropy for holes is due to diffusive transport through extended states in the [ anti 110], and hopping transport through laterally localized states in the [110] direction, within the same sample. A novel 5-terminal electronic switching device based on gate-controlled transport anisotropy is proposed. The gate-control of the transport anisotropy in modulation-doped, self-organized InAs quantum wires embedded in InP is demonstrated. (orig.)

  18. Quantum Dots obtained by LPE from under-saturated In-As liquid phases on GaAs substrates

    Energy Technology Data Exchange (ETDEWEB)

    Ortiz F E; Mishurnyi V; Gorbatchev A; De Anda F [Universidad Autonoma de San Luis Potosi, Instituto de Investigacion en Comunicacion Optica, Av. Karacorum 1470, Col. Lomas 4a Sec., CP 78210San Luis PotosI (Mexico); Prutskij T, E-mail: fcoe_ov@prodigy.net.mx, E-mail: andre@cactus.iico.uaslp.mx [BUAP, Instituto de Ciencias, Apartado Postal 207, 72000, Puebla (Mexico)

    2011-01-01

    In this work we inform about quantum dots (QD) obtained by Liquid Phase Epitaxy (LPE) on GaAs substrates from under-saturated In-As liquid phases. In our processes, we have prepared saturated In-rich liquid phases by dissolving an InAs wafer at one of the temperatures interval from 450 to 414 C for 60 minutes. The contact between In-As liquid phase and the GaAs substrate was always done at a constant temperature of 444 C for 5 seconds. Thus, the growth temperature for most of the samples was higher than the liquidus temperature. We think that the growth driving force is related to a transient process that occurs when the system is trying to reach equilibrium. Under the atom force microscope (AFM) we have observed nano-islands on the surfaces of the samples obtained from under-saturated liquid phases prepared at 438, 432 and 426 C. The 25 K photoluminescence spectrum shows a peak at a 1.33 eV, in addition to the GaAs related line.

  19. Calculation of Nonlinear Thermoelectric Coefficients of InAs1-xSbx Using Monte Carlo Method

    Energy Technology Data Exchange (ETDEWEB)

    Sadeghian, RB; Bahk, JH; Bian, ZX; Shakouri, A

    2011-12-28

    It was found that the nonlinear Peltier effect could take place and increase the cooling power density when a lightly doped thermoelectric material is under a large electrical field. This effect is due to the Seebeck coefficient enhancement from an electron distribution far from equilibrium. In the nonequilibrium transport regime, the solution of the Boltzmann transport equation in the relaxation-time approximation ceases to apply. The Monte Carlo method, on the other hand, proves to be a capable tool for simulation of semiconductor devices at small scales as well as thermoelectric effects with local nonequilibrium charge distribution. InAs1-xSb is a favorable thermoelectric material for nonlinear operation owing to its high mobility inherited from the binary compounds InSb and InAs. In this work we report simulation results on the nonlinear Peltier power of InAs1-xSb at low doping levels, at room temperature and at low temperatures. The thermoelectric power factor in nonlinear operation is compared with the maximum value that can be achieved with optimal doping in the linear transport regime.

  20. Crystal-phase intergradation in InAs nanostructures grown by van der Waals heteroepitaxy on graphene

    Science.gov (United States)

    Choi, Ji Eun; Yoo, Jinkyoung; Lee, Donghwa; Hong, Young Joon; Fukui, Takashi

    2018-04-01

    This study demonstrates the crystal-phase intergradation of InAs nanostructures grown on graphene via van der Waals epitaxy. InAs nanostructures with diverse diameters are yielded on graphene. High-resolution transmission electron microscopy (HR-TEM) reveals two crystallographic features of (i) wurtzite (WZ)-to-zinc blende (ZB) intergradation along the growth direction of InAs nanostructures and (ii) an increased mean fraction of ZB according to diameter increment. Based on the HR-TEM observations, a crystal-phase intergradation diagram is depicted. We discuss how the formation of a WZ-rich phase during the initial growth stage is an effective way of releasing heterointerfacial stress endowed by the lattice mismatch of InAs/graphene for energy minimization in terms of less in-plane lattice mismatching between WZ-InAs and graphene. The WZ-to-ZB evolution is responsible for the attenuation of the bottom-to-top surface charge interaction as growth proceeds.

  1. Temperature dependence of the transport properties of spin field-effect transistors built with InAs and Si channels

    Science.gov (United States)

    Osintsev, D.; Sverdlov, V.; Stanojević, Z.; Makarov, A.; Selberherr, S.

    2012-05-01

    We study the transport properties of the Datta-Das spin field-effect transistor built on InAs and Si. First, we demonstrate that the amplitude of the magnetoresistance oscillations as a function of the band mismatch between the ferromagnetic contacts and the semiconductor channel made of InAs decreases dramatically with increasing temperature. A shorter InAs channel is needed to create an InAs-based SpinFET which will operate at higher temperatures. Second, we show that the [1 0 0] orientation of the fin is preferable for silicon SpinFETs due to stronger modulation of the conductance as a function of spin-orbit interaction and magnetic field. Short silicon fins can be used for current modulation as a function of the conduction band mismatch between the channel and the ferromagnetic contacts only at relatively low temperatures. In contrast, longer silicon channels allow a TMR modulation at room temperature by changing the strength of the spin-orbit interaction through the gate bias.

  2. Molecular dynamics growth modeling of InAs1-xSbx-based type-II superlattice

    Science.gov (United States)

    Ciani, Anthony J.; Grein, Christoph H.; Irick, Barry; Miao, Maosheng; Kioussis, Nicholas

    2017-09-01

    Type-II strained-layer superlattices (T2SL) based on InAs1-xSbx are a promising photovoltaic detector material technology for thermal imaging; however, Shockley-Read-Hall recombination and generation rates are still too high for thermal imagers based on InAs1-xSbx T2SL to reach their ideal performance. Molecular dynamics simulations using the Stillinger-Weber (SW) empirical potentials are a useful tool to study the growth of tetrahedral coordinated crystals and the nonequilibrium formation of defects within them, including the long-range effects of strain. SW potentials for the possible atomic interactions among {Ga, In, As, Sb} were developed by fitting to ab initio calculations of elastically distorted zinc blende and diamond unit cells. The SW potentials were tested against experimental observations of molecular beam epitaxial (MBE) growth and then used to simulate the MBE growth of InAs/InAs0.5Sb0.5 T2SL on GaSb substrates over a range of processes parameters. The simulations showed and helped to explain Sb cross-incorporation into the InAs T2SL layers, Sb segregation within the InAsSb layers, and identified medium-range defect clusters involving interstitials and their induction of interstitial-vacancy pairs. Defect formation was also found to be affected by growth temperature and flux stoichiometry.

  3. Two novel mixed-ligand complexes containing organosulfonate ligands.

    Science.gov (United States)

    Li, Mingtian; Huang, Jun; Zhou, Xuan; Fang, Hua; Ding, Liyun

    2008-07-01

    The structures reported herein, viz. bis(4-aminonaphthalene-1-sulfonato-kappaO)bis(4,5-diazafluoren-9-one-kappa(2)N,N')copper(II), [Cu(C(10)H(8)NO(3)S)(2)(C(11)H(6)N(2)O)(2)], (I), and poly[[[diaquacadmium(II)]-bis(mu-4-aminonaphthalene-1-sulfonato)-kappa(2)O:N;kappa(2)N:O] dihydrate], {[Cd(C(10)H(8)NO(3)S)(2)(H(2)O)(2)].2H(2)O}(n), (II), are rare examples of sulfonate-containing complexes where the anion does not fulfill a passive charge-balancing role, but takes an active part in coordination as a monodentate and/or bridging ligand. Monomeric complex (I) possesses a crystallographic inversion center at the Cu(II) atom, and the asymmetric unit contains one-half of a Cu atom, one complete 4-aminonaphthalene-1-sulfonate (ans) ligand and one 4,5-diazafluoren-9-one (DAFO) ligand. The Cu(II) atom has an elongated distorted octahedral coordination geometry formed by two O atoms from two monodentate ans ligands and by four N atoms from two DAFO molecules. Complex (II) is polymeric and its crystal structure is built up by one-dimensional chains and solvent water molecules. Here also the cation (a Cd(II) atom) lies on a crystallographic inversion center and adopts a slightly distorted octahedral geometry. Each ans anion serves as a bridging ligand linking two Cd(II) atoms into one-dimensional infinite chains along the [010] direction, with each Cd(II) center coordinated by four ans ligands via O and N atoms and by two aqua ligands. In both structures, there are significant pi-pi stacking interactions between adjacent ligands and hydrogen bonds contribute to the formation of two- and three-dimensional networks.

  4. Strong composition-dependent disorder in InAs1-xNx alloys

    International Nuclear Information System (INIS)

    Benaissa, H.; Zaoui, A.; Ferhat, M.

    2009-01-01

    We investigate the main causes of disorder in the InAs 1-x N x alloys (x = 0, 0.03125, 0.0625, 0.09375, 0.125, 0.25, 0.5, 0.75, 0.875, 0.90625, 0.9375, 0.96875 and 1). The calculation is based on the density-functional theory in the local-density approximation. We use a plane wave-expansion non-norm conserving ab initio Vanderbilt pseudopotentials. To avoid the difficulty of considering the huge number of atomic configurations, we use an appropriate strategy in which we consider four configurations for a given composition where the N atoms are not randomly distributed. We mainly show that the band gap decreases (increases) rapidly with increasing (decreasing) compositions of N. As a consequence the optical band gap bowing is found to be strong and composition dependent. The obtained compounds, from these alloys, may change from semi-conducting to metal (passing to a negative bowing) and could be useful for device applications, especially at certain composition.

  5. Ballistic One-Dimensional InAs Nanowire Cross-Junction Interconnects.

    Science.gov (United States)

    Gooth, Johannes; Borg, Mattias; Schmid, Heinz; Schaller, Vanessa; Wirths, Stephan; Moselund, Kirsten; Luisier, Mathieu; Karg, Siegfried; Riel, Heike

    2017-04-12

    Coherent interconnection of quantum bits remains an ongoing challenge in quantum information technology. Envisioned hardware to achieve this goal is based on semiconductor nanowire (NW) circuits, comprising individual NW devices that are linked through ballistic interconnects. However, maintaining the sensitive ballistic conduction and confinement conditions across NW intersections is a nontrivial problem. Here, we go beyond the characterization of a single NW device and demonstrate ballistic one-dimensional (1D) quantum transport in InAs NW cross-junctions, monolithically integrated on Si. Characteristic 1D conductance plateaus are resolved in field-effect measurements across up to four NW-junctions in series. The 1D ballistic transport and sub-band splitting is preserved for both crossing-directions. We show that the 1D modes of a single injection terminal can be distributed into multiple NW branches. We believe that NW cross-junctions are well-suited as cross-directional communication links for the reliable transfer of quantum information as required for quantum computational systems.

  6. The polarization response in InAs quantum dots: theoretical correlation between composition and electronic properties

    International Nuclear Information System (INIS)

    Usman, Muhammad; O’Reilly, Eoin P; Tasco, Vittorianna; Todaro, Maria Teresa; De Giorgi, Milena; Passaseo, Adriana; Klimeck, Gerhard

    2012-01-01

    III–V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed in an effort to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two-layer composition model, mimicking In segregation and In–Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows us to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response. (paper)

  7. Ambient temperature dependence on emission spectrum of InAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, C.Y.; Yoon, S.F. [School of Electrical and Electronic Engineering, Nanyang Technological University (Singapore); Chua, S.J. [Institute of Materials Research and Engineering, Faculty of Engineering (Singapore)

    2009-04-15

    Semiconductor superluminescent diodes (SLDs) are important broadband light source for fiber optic gyroscope and biomedical imaging. Quantum dots (QDs) have been proposed to be the best candidate for broadband light sources due to the inhomogeneous broadening of the gain spectrum as a result of the inherited size inhomogeneity of the self-assembled QD growth. In this work, the effect of ambient temperature (25-100 C) on the emission spectrum of InAs QDs with wideband emission was investigated. It was found that the full-width at half-maximum (FWHM) of the photoluminescence (PL) spectra remains more than 125 nm throughout the temperature range, and the redshift as function of temperature is approximately 0.27 meV/K. Activation energy of 270 meV is extracted from the Arrhenius plot and the PL quenching at high temperature is attributed to thermally induced carriers escaping out of the In{sub 0.15}Ga{sub 0.85}As strain-reducing layer. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Effect of antimony incorporation on the density, shape, and luminescence of InAs quantum dots

    Science.gov (United States)

    Chen, J. F.; Chiang, C. H.; Wu, Y. H.; Chang, L.; Chi, J. Y.

    2008-07-01

    This work investigates the surfactant effect on exposed and buried InAs quantum dots (QDs) by incorporating Sb into the QD layers with various Sb beam equivalent pressures (BEPs). Secondary ion mass spectroscopy shows the presence of Sb in the exposed and buried QD layers with the Sb intensity in the exposed layer substantially exceeding that in the buried layer. Incorporating Sb can reduce the density of the exposed QDs by more than two orders of magnitude. However, a high Sb BEP yields a surface morphology with a regular periodic structure of ellipsoid terraces. A good room-temperature photoluminescence (PL) at ˜1600 nm from the exposed QDs is observed, suggesting that the Sb incorporation probably improves the emission efficiency by reducing the surface recombination velocity at the surface of the exposed QDs. Increasing Sb BEP causes a blueshift of the emission from the exposed QDs due to a reduction in the dot height as suggested by atomic force microscopy. Increasing Sb BEP can also blueshift the ˜1300 nm emission from the buried QDs by decreasing the dot height. However, a high Sb BEP yields a quantum well-like PL feature formed by the clustering of the buried QDs into an undulated planar layer. These results indicate a marked Sb surfactant effect that can be used to control the density, shape, and luminescence of the exposed and buried QDs.

  9. An Integrated Nonlinear Analysis library - (INA) for solar system plasma turbulence

    Science.gov (United States)

    Munteanu, Costel; Kovacs, Peter; Echim, Marius; Koppan, Andras

    2014-05-01

    We present an integrated software library dedicated to the analysis of time series recorded in space and adapted to investigate turbulence, intermittency and multifractals. The library is written in MATLAB and provides a graphical user interface (GUI) customized for the analysis of space physics data available online like: Coordinated Data Analysis Web (CDAWeb), Automated Multi Dataset Analysis system (AMDA), Planetary Science Archive (PSA), World Data Center Kyoto (WDC), Ulysses Final Archive (UFA) and Cluster Active Archive (CAA). Three main modules are already implemented in INA : the Power Spectral Density (PSD) Analysis, the Wavelet and Intemittency Analysis and the Probability Density Functions (PDF) analysis.The layered structure of the software allows the user to easily switch between different modules/methods while retaining the same time interval for the analysis. The wavelet analysis module includes algorithms to compute and analyse the PSD, the Scalogram, the Local Intermittency Measure (LIM) or the Flatness parameter. The PDF analysis module includes algorithms for computing the PDFs for a range of scales and parameters fully customizable by the user; it also computes the Flatness parameter and enables fast comparison with standard PDF profiles like, for instance, the Gaussian PDF. The library has been already tested on Cluster and Venus Express data and we will show relevant examples. Research supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no 313038/STORM, and a grant of the Romanian Ministry of National Education, CNCS UEFISCDI, project number PN-II-ID PCE-2012-4-0418.

  10. Fabrication and optical properties of multishell InAs quantum dots on GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Xin; Zhang, Xia, E-mail: xzhang@bupt.edu.cn; Li, Junshuai; Cui, Jiangong; Ren, Xiaomin [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

    2015-02-07

    Hybrid nanostructures combining nanowires with quantum dots promote the development of nanoelectronic and nanophotonic devices with integrated functionalities. In this work, we present a complex nanostructure with multishell quantum dots grown on nanowires. 1–4 shells of Stranski-Krastanov InAs quantum dots are grown on the sidewalls of GaAs nanowires by metal organic chemical vapor deposition. Different dot shells are separated by 8 nm GaAs spacer shells. With increasing the number of shells, the quantum dots become sparser and tend to align in one array, which is caused by the shrinkage of facets on which dots prefer to grow as well as the strain fields produced by the lower set of dots which influences the migration of In adatoms. The size of quantum dots increases with the increase of shell number due to enhanced strain fields coupling. The spectra of multishell dots exhibit multiwavelength emission, and each peak corresponds to a dot shell. This hybrid structure may serve as a promising element in nanowire intermediate band solar cells, infrared nanolasers, and photodetectors.

  11. Correcting ligands, metabolites, and pathways

    NARCIS (Netherlands)

    Ott, M.A.; Vriend, G.

    2006-01-01

    BACKGROUND: A wide range of research areas in bioinformatics, molecular biology and medicinal chemistry require precise chemical structure information about molecules and reactions, e.g. drug design, ligand docking, metabolic network reconstruction, and systems biology. Most available databases,

  12. Correlation between the Montreal Cognitive Assessment-Indonesian Version (Moca-INA) and the Mini-Mental State Examination (MMSE) in Elderly.

    Science.gov (United States)

    Rambe, Aldy Safruddin; Fitri, Fasihah Irfani

    2017-12-15

    As the rapid growth of the elderly population and the increased prevalence of Alezheimer's Disease and related disorders, there is an increasing need for effective cognitive screening. The Mini Mental State Examination (MMSE) is the most frequently used screening test of cognitive impairment because of its convenience. The Montreal Cognitive Assessment-Indonesian Version (MoCA-INA) has been validated and recently been used as a cognitive screening tool. The aim of this study was to compare the MMSE and MoCA-INA scores and to determine the correlation between the MMSE and MoCA-INA scores in elderly. This was a cross-sectional study including 83 elderly subjects from November 2016 until June 2017. We performed MMSE and MoCA-INA for assessment of cognitive function and the time between each test was at least 30 minutes. The study included 83 subjects which were consisted of 46 (55.4%) males and 37 (44.6%) females. The mean age was 69.19 ± 4.23 ranging from 65 to 79 years old. The average MMSE scores was 24.96 ± 3.38 (range 14 to 30). The average MoCA-INA scores was 21.06 ± 4.56 (range 5 to 30). The Pearson correlation coefficient between the scores was 0.71 (p<0.005). There were no significant differences of both scores based on history of hypertension, diabetes mellitus and previous stroke, but there was a significant difference in MMSE scores based on level of education. The MoCA-INA score showed a good correlation with the MMSE score. Both tests showed comparable results but MoCA-INA showed lower average with wider range of scores.

  13. On the evolution of InAs thin films grown by molecular beam epitaxy on the GaAs(001) surface

    International Nuclear Information System (INIS)

    Grabowski, Jan

    2010-01-01

    Semiconductor nanostructures are currently of high interest for a wide variety of electronic and optoelectronic applications. A large number of devices, in particular for the optical data transmission in the long-wavelength range, essential in modern communication, are based on InAs/GaAs quantum dot (QD) structures. Though the properties of the InAs/GaAs QDs have been extensively studied, only little is known about the formation and structure of the wetting layer (WL) yet. In the present work, the pathway of the InAs WL evolution is studied in detail. For this purpose, InAs thin films in the range of one monolayer (ML) are deposited on the GaAs(001) surface by molecular beam epitaxy (MBE) and studied by reflection high energy electron diffraction (RHEED) and in particular by scanning tunneling microscopy (STM). The InAs thin films are grown in both typical growth regimes, on the GaAs-c(4 x 4) and the GaAs-β2(2 x 4) reconstructed surface, in a variety of thicknesses starting from submonolayers with 0.09 ML of InAs up to 1.65 ML of InAs exceeding the critical thickness for QD growth. In principle, three growth stages are found. At low InAs coverages, the indium adsorbs in agglomerations of typically eight In atoms at energetically preferable surface sites. In the STM images, the signatures of these In agglomerations appear with a clear bright contrast. A structural model for the initial formation of these signatures is presented, and its electronic and strain related properties are discussed. At an InAs coverage of about 0.67ML the initial surface transforms into a (4 x 3) reconstructed In 2/3 Ga 1/3 As ML and the detailed structure and strain properties of this surface are unraveled. On top of the InGaAs ML further deposited InAs forms a second layer, characterized by a typical zig-zag alignment of (2 x 4) reconstructed unit cells, with an alternating α2/α2-m configuration. In contrast to the previous surface reconstructions, where structural strain is

  14. On the evolution of InAs thin films grown by molecular beam epitaxy on the GaAs(001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Grabowski, Jan

    2010-12-14

    Semiconductor nanostructures are currently of high interest for a wide variety of electronic and optoelectronic applications. A large number of devices, in particular for the optical data transmission in the long-wavelength range, essential in modern communication, are based on InAs/GaAs quantum dot (QD) structures. Though the properties of the InAs/GaAs QDs have been extensively studied, only little is known about the formation and structure of the wetting layer (WL) yet. In the present work, the pathway of the InAs WL evolution is studied in detail. For this purpose, InAs thin films in the range of one monolayer (ML) are deposited on the GaAs(001) surface by molecular beam epitaxy (MBE) and studied by reflection high energy electron diffraction (RHEED) and in particular by scanning tunneling microscopy (STM). The InAs thin films are grown in both typical growth regimes, on the GaAs-c(4 x 4) and the GaAs-{beta}2(2 x 4) reconstructed surface, in a variety of thicknesses starting from submonolayers with 0.09 ML of InAs up to 1.65 ML of InAs exceeding the critical thickness for QD growth. In principle, three growth stages are found. At low InAs coverages, the indium adsorbs in agglomerations of typically eight In atoms at energetically preferable surface sites. In the STM images, the signatures of these In agglomerations appear with a clear bright contrast. A structural model for the initial formation of these signatures is presented, and its electronic and strain related properties are discussed. At an InAs coverage of about 0.67ML the initial surface transforms into a (4 x 3) reconstructed In{sub 2/3}Ga{sub 1/3}As ML and the detailed structure and strain properties of this surface are unraveled. On top of the InGaAs ML further deposited InAs forms a second layer, characterized by a typical zig-zag alignment of (2 x 4) reconstructed unit cells, with an alternating {alpha}2/{alpha}2-m configuration. In contrast to the previous surface reconstructions, where

  15. Growth and electrical characterization of Zn-doped InAs and InAs{sub 1-x}Sb{sub x}

    Energy Technology Data Exchange (ETDEWEB)

    Venter, A., E-mail: andre.venter@nmmu.ac.z [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth (South Africa); Shamba, P.; Botha, L.; Botha, J.R. [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth (South Africa)

    2009-06-01

    The electrical properties of Zn doped InAs and InAsSb layers grown on semi-insulating GaAs by metal organic vapour phase epitaxy, using dimethyl zinc as the p-type dopant source, have been studied. The influence of dopant flow rate, V/III ratio and substrate orientation on the electrical properties of these InAs and InAs{sub 1-x}Sb{sub x} layers have been studied at a few appropriate growth temperatures. A promising group V source, tertiary butyl arsenic was used as an alternative to arsenic hydride in the case of InAs growth. The electrical properties of the InAs and InAs{sub 1-x}Sb{sub x} epitaxial layers were mainly studied by the Hall effect. However, surface accumulation in these materials results in deceptive Hall results being extracted. A two layer model (assuming the layer to consist of two parallel conducting paths viz. surface and bulk) has therefore been used to extract sensible transport properties. In addition, conventional Hall measurements ignores the high electron to hole mobility ratio in InAs and InAsSb leading to erroneous transport properties.

  16. Temperature effect on the growth of Au-free InAs and InAs/GaSb heterostructure nanowires on Si substrate by MOCVD

    Science.gov (United States)

    Kakkerla, Ramesh Kumar; Anandan, Deepak; Hsiao, Chih-Jen; Yu, Hung Wei; Singh, Sankalp Kumar; Chang, Edward Yi

    2018-05-01

    We demonstrate the growth of vertically aligned Au-free InAs and InAs/GaSb heterostructure nanowires on Si (1 1 1) substrate by Metal Organic Chemical Vapor Deposition (MOCVD). The effect of growth temperature on the morphology and growth rate of the InAs and InAs/GaSb heterostructure nanowires (NWs) is investigated. Control over diameter and length of the InAs NWs and the GaSb shell thickness was achieved by using growth temperature. As the GaSb growth temperature increase, GaSb radial growth rate increases due to the increase in alkyl decomposition at the substrate surface. Diffusivity of the adatoms increases as the GaSb growth temperature increase which results in tapered GaSb shell growth. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) measurements revealed that the morphology and shell thickness can be tuned by the growth temperature. Electron microscopy also shows the formation of GaSb both in radial and axial directions outside the InAs NW core can be controlled by the growth temperature. This study demonstrates the control over InAs NWs growth and the GaSb shell thickness can be achieved through proper growth temperature control, such technique is essential for the growth of nanowire for future nano electronic devices, such as Tunnel FET.

  17. 99mTc-MIBI/123I-Na subtraction scanning for localized parathyroid adenoma in patients with asymptomatic/mild primary hyperparathyroidism

    International Nuclear Information System (INIS)

    Tanaka, Yuji; Funahashi, Hiroomi; Imai, Tsuneo

    1996-01-01

    Primary hyperparathyroidism is most commonly detected as a mild elevation of the serum calcium concentration. In the present study, the utility of 99m Tc-methoxyisobutylisonitrile (MIBI) imaging before initial surgery was evaluated for localizing abnormal parathyroid glands in patients with asymptomatic and mild primary hyperparathyroidism. The results were compared with those of thallium-technetium subtraction scanning (TTSS). 99m Tc-MIBI/ 123 I-Na subtraction scanning was performed in 11 patients, and TTSS was performed in 10 of them. The sensitivity was 100% and the positive predictive value was 92% for 99m Tc-MIBI/ 123 I-Na, while the sensitivity was 50% and the positive predictive value was 100% for TTSS. The smallest gland detected weighed 85 mg in 99m Tc-MIBI/ 123 I-Na, and 570 mg in TTSS. There was a difference between the median weight of adenomas which were detected by 99m Tc-MIBI/ 123 I-Na (754 mg), and those which were detected by TTSS (1,195 mg). These results suggest that TTSS parathyroid scintigraphy could give way to 99m Tc-MIBI/ 123 I-Na parathyroid scintigraphy for improved detection of low-weight abnormal parathyroid glands. (author)

  18. LigandRFs: random forest ensemble to identify ligand-binding residues from sequence information alone

    KAUST Repository

    Chen, Peng; Huang, Jianhua Z; Gao, Xin

    2014-01-01

    Protein-ligand binding is important for some proteins to perform their functions. Protein-ligand binding sites are the residues of proteins that physically bind to ligands. Despite of the recent advances in computational prediction

  19. The Effect of INA [(R)-1-O-(1-Pyrenylmethyl)Glycerol] Insertions on the Structure and Biological Activity of a G-Quadruplex from a Critical Kras G-Rich Sequence

    DEFF Research Database (Denmark)

    Cogoi, Susanna; Paramasivan, Manikandan; Xodo, Luigi E.

    2007-01-01

    Quadruplex-forming oligonucleotides containing INA [(R)-1-O-(1-pyrenylmethyl)glycerol] insertions have been designed and studied for their capacity to inhibit the expression of the KRAS oncogene in pancreatic adenocarcinoma cells. It is found that INA can influence the folding topology of the G-q...

  20. STM/STS Measurements of Two-Dimensional Electronic States in Magnetic Fields at Epitaxially Grown InAs(111)A Surfaces

    International Nuclear Information System (INIS)

    Niimi, Y; Kanisawa, K; Kojima, H; Kambara, H; Hirayama, Y; Tarucha, S; Fukuyama, Hiroshi

    2007-01-01

    The local density of states (LDOS) at the epitaxially grown InAs surface on a GaAs substrate was studied at very low temperatures in magnetic fields up to 6 T by scanning tunneling microscopy and spectroscopy. We observed a series of peaks, associated with Landau quantization of the two-dimensional electron system (2DES), in the tunnel spectra just above the subband energy (-80 meV) of the 2DES. The intervals between the peaks are consistent with the estimation from the effective mass of the 2DES at the InAs surface. In a wider energy range, another type of oscillation which was independent of magnetic field was also observed. This oscillation can be explained by the energy dependence of the transmission probability of the tunneling current through the Schottky barrier formed at the interface between the InAs film and GaAs substrate

  1. Simulation of quantum dots size and spacing effect for intermediate band solar cell application based on InAs quantum dots arrangement in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Hendra, P. I. B., E-mail: ib.hendra@gmail.com; Rahayu, F., E-mail: ib.hendra@gmail.com; Darma, Y., E-mail: ib.hendra@gmail.com [Physical Vapor Deposition Laboratory, Physics of Material Electronics Research, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132 (Indonesia)

    2014-03-24

    Intermediate band solar cell (IBSC) has become a promising technology in increasing solar cell efficiency. In this work we compare absorption coefficient profile between InAs quantum dots with GaAs bulk. We calculate the efficiency of GaAs bulk and GaAs doped with 2, 5, and 10 nm InAs quantum dot. Effective distances in quantum dot arrangement based on electron tunneling consideration were also calculated. We presented a simple calculation method with low computing power demand. Results showed that arrangement of quantum dot InAs in GaAs can increase solar cell efficiency from 23.9 % initially up to 60.4%. The effective distance between two quantum dots was found 2 nm in order to give adequate distance to prevent electron tunneling and wave functions overlap.

  2. Inhomogeneous Si-doping of gold-seeded InAs nanowires grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Rolland, Chloe; Coinon, Christophe; Wallart, Xavier; Leturcq, Renaud [Institute of Electronics Microelectronics and Nanotechnology, UMR CNRS 8520, ISEN Department, Avenue Poincare, CS60069, 59652 Villeneuve d' Ascq Cedex (France); Caroff, Philippe [Institute of Electronics Microelectronics and Nanotechnology, UMR CNRS 8520, ISEN Department, Avenue Poincare, CS60069, 59652 Villeneuve d' Ascq Cedex (France); Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200 (Australia)

    2013-06-03

    We have investigated in situ Si doping of InAs nanowires grown by molecular beam epitaxy from gold seeds. The effectiveness of n-type doping is confirmed by electrical measurements showing an increase of the electron density with the Si flux. We also observe an increase of the electron density along the nanowires from the tip to the base, attributed to the dopant incorporation on the nanowire facets whereas no detectable incorporation occurs through the seed. Furthermore, the Si incorporation strongly influences the lateral growth of the nanowires without giving rise to significant tapering, revealing the complex interplay between axial and lateral growth.

  3. Size dependence of the wavefunction of self-assembled InAs quantum dots from time-resolved optical measurements

    DEFF Research Database (Denmark)

    Johansen, Jeppe; Stobbe, Søren; Nikolaev, Ivan S.

    2008-01-01

    and a theoretical model, we determine the striking dependence of the overlap of the electron and hole wavefunctions on the quantum dot size. We conclude that the optical quality is best for large quantum dots, which is important in order to optimally tailor quantum dot emitters for, e.g., quantum electrodynamics......The radiative and nonradiative decay rates of InAs quantum dots are measured by controlling the local density of optical states near an interface. From time-resolved measurements, we extract the oscillator strength and the quantum efficiency and their dependence on emission energy. From our results...

  4. Infrared reflection spectra of multilayer epitaxial heterostructures with embedded InAs and GaAs layers

    International Nuclear Information System (INIS)

    Seredin, P. V.; Domashevskaya, E. P.; Lukin, A. N.; Arsent'ev, I. N.; Vinokurov, D. A.; Tarasov, I. S.

    2008-01-01

    The effect of the thickness of embedded InAs and GaAs layers on the infrared reflection spectra of lattice vibrations for AlInAs/InAs/AlInAs, InGaAs/GaAs/InGaAs, and AlInAs/InGaAs/GaAs/InGaAs/AlInAs multilayer epitaxial heterostructures grown by MOC hydride epitaxy on InP (100) substrates is studied. Relative stresses emerging in the layers surrounding the embedded layers with variation in the number of monolayers from which the quantum dots are formed and with variation the thickness of the layers themselves surrounding the embedded layers are evaluated.

  5. Photoluminescence characteristics of InAs quantum dots grown by STM/MBE site-control technique

    Energy Technology Data Exchange (ETDEWEB)

    Nishikawa, S.; Kohmoto, S.; Nakamura, H.; Ishikawa, T.; Asakawa, K.; Wada, O. [Femtosecond Technology Research Association, Tsukuba, Ibaraki (Japan). FESTA Lab.

    2001-03-08

    This paper describes micro-photoluminescence (PL) analysis of site-controlled QDs (SCQDs) grown using a novel in-situ MBE growth technique in which sites of self-assembled InAs QDs are controlled by forming nanometer deposits using a scanning tunneling microscope (STM) probe. We found from the temperature dependence of PL that the carrier collection at QDs at low temperature is limited by carrier diffusion in the wetting layer. The analysis of PL data considering this effect has indicated that individual QDs grown have high crystalline quality in spite of the addition of an artificial STM process during growth. (orig.)

  6. New process for high optical quality InAs quantum dots grown on patterned GaAs(001) substrates

    International Nuclear Information System (INIS)

    Alonso-Gonzalez, Pablo; Gonzalez, Luisa; Gonzalez, Yolanda; Fuster, David; Fernandez-Martinez, Ivan; Martin-Sanchez, Javier; Abelmann, Leon

    2007-01-01

    This work presents a selective ultraviolet (UV)-ozone oxidation-chemical etching process that has been used, in combination with laser interference lithography (LIL), for the preparation of GaAs patterned substrates. Further molecular beam epitaxy (MBE) growth of InAs results in ordered InAs/GaAs quantum dot (QD) arrays with high optical quality from the first layer of QDs formed on the patterned substrate. The main result is the development of a patterning technology that allows the engineering of customized geometrical displays of QDs with the same optical quality as those formed spontaneously on flat non-patterned substrates

  7. Improved optical properties of InAs quantum dots for intermediate band solar cells by suppression of misfit strain relaxation

    Energy Technology Data Exchange (ETDEWEB)

    Xie, H. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States); School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287-6106 (United States); Prioli, R. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States); Departamento de Física, Pontificia Universidade Católica do Rio de Janeiro, Marques de São Vicente 225, Rio de Janeiro 22452-900 RJ (Brazil); Fischer, A. M.; Ponce, F. A., E-mail: ponce@asu.edu [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States); Kawabata, R. M. S.; Pinto, L. D.; Souza, P. L. [LabSem, CETUC, Pontificia Universidade Católica do Rio de Janeiro, Marques de São Vicente 225, Rio de Janeiro 22452-900 RJ (Brazil); Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores – DISSE – PUC-Rio, RJ (Brazil); Jakomin, R. [Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores – DISSE – PUC-Rio, RJ (Brazil); Campus de Xerem, UFRJ, Duque de Caxias-RJ (Brazil); Pires, M. P. [Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores – DISSE – PUC-Rio, RJ (Brazil); Instituto de Física, UFRJ, Rio de Janeiro-RJ (Brazil)

    2016-07-21

    The properties of InAs quantum dots (QDs) have been studied for application in intermediate band solar cells. It is found that suppression of plastic relaxation in the QDs has a significant effect on the optoelectronic properties. Partial capping plus annealing is shown to be effective in controlling the height of the QDs and in suppressing plastic relaxation. A force balancing model is used to explain the relationship between plastic relaxation and QD height. A strong luminescence has been observed from strained QDs, indicating the presence of localized states in the desired energy range. No luminescence has been observed from plastically relaxed QDs.

  8. Fabrication of GaAs/Al0.3Ga0.7As multiple quantum well nanostructures on (100) si substrate using a 1-nm InAs relief layer.

    Science.gov (United States)

    Oh, H J; Park, S J; Lim, J Y; Cho, N K; Song, J D; Lee, W; Lee, Y J; Myoung, J M; Choi, W J

    2014-04-01

    Nanometer scale thin InAs layer has been incorporated between Si (100) substrate and GaAs/Al0.3Ga0.7As multiple quantum well (MQW) nanostructure in order to reduce the defects generation during the growth of GaAs buffer layer on Si substrate. Observations based on atomic force microscopy (AFM) and transmission electron microscopy (TEM) suggest that initiation and propagation of defect at the Si/GaAs interface could be suppressed by incorporating thin (1 nm in thickness) InAs layer. Consequently, the microstructure and resulting optical properties improved as compared to the MQW structure formed directly on Si substrate without the InAs layer. It was also observed that there exists some limit to the desirable thickness of the InAs layer since the MQW structure having thicker InAs layer (4 nm-thick) showed deteriorated properties.

  9. Stimulated Emission from InAs (GaAs Monolayers Stacks Embedded in Al0.33Ga0.67As Ective Region

    Directory of Open Access Journals (Sweden)

    Dusan Pudis

    2002-01-01

    Full Text Available Our study is focused on the optical and electronic properties of InAs (GaAs monolayers embedded in Al0.33GA0.67As barrier layers investigated by temperature dependencies of electroluminescence spectra. The experimental results obtained from low temperature electroluminescence measurements of InAs (GaAs/Al0.33GA0.67As revealed the excellent emission spectra in the visib le range 630-690 nm. The stimulated emission from these structures across their cleavage planes has been observed at low  temperatures what is highly interesting for potential device applications.

  10. InAs quantum dot growth on AlxGa1−xAs by metalorganic vapor phase epitaxy for intermediate band solar cells

    International Nuclear Information System (INIS)

    Jakomin, R.; Kawabata, R. M. S.; Souza, P. L.; Mourão, R. T.; Pires, M. P.; Micha, D. N.; Xie, H.; Fischer, A. M.; Ponce, F. A.

    2014-01-01

    InAs quantum dot multilayers have been grown using Al x Ga 1−x As spacers with dimensions and compositions near the theoretical values for optimized efficiencies in intermediate band photovoltaic cells. Using an aluminium composition of x = 0.3 and InAs dot vertical dimensions of 5 nm, transitions to an intermediate band with energy close to the ideal theoretical value have been obtained. Optimum size uniformity and density have been achieved by capping the quantum dots with GaAs following the indium-flush method. This approach has also resulted in minimization of crystalline defects in the epilayer structure

  11. Rosetta Ligand docking with flexible XML protocols.

    Science.gov (United States)

    Lemmon, Gordon; Meiler, Jens

    2012-01-01

    RosettaLigand is premiere software for predicting how a protein and a small molecule interact. Benchmark studies demonstrate that 70% of the top scoring RosettaLigand predicted interfaces are within 2Å RMSD from the crystal structure [1]. The latest release of Rosetta ligand software includes many new features, such as (1) docking of multiple ligands simultaneously, (2) representing ligands as fragments for greater flexibility, (3) redesign of the interface during docking, and (4) an XML script based interface that gives the user full control of the ligand docking protocol.

  12. Effect of GaAs interlayer thickness variations on the optical properties of multiple InAs QD structure

    International Nuclear Information System (INIS)

    Park, C.Y.; Park, K.W.; Kim, J.M.; Lee, Y.T.

    2009-01-01

    Multiple InAs/GaAs self-assembled quantum dots (QDs) with vertically stacked structure are grown by molecular beam epitaxy and the effects of GaAs interlayer thickness variation on optical properties are studied. The growth conditions are optimized by in-situ RHEED, AFM, and PL measurement. The five InAs QD layers are embedded in GaAs and Al0.3Ga0.7As layer. The PL intensity is increased with increasing GaAs interlayer thickness. The thin GaAs interlayer has strain field, the strain-induced intermixing of indium atoms in the InAs QDs (blue-shift) can overcompensate for the effect on the increased QD size (red-shift) (H. Heidemeyer et al. Appl. Phys. Lett. 80, 1544 (2002); T. Nakaoka et al. J. Appl. Phys. Lett. 96, 150 (2004)[1, 2], respectively). For the interlayer thickness larger than about 7 nm, the blue-shifts are correlated to the dominant high-energy excited state transitions due to the successive state filling of the ground and higher excited states in the QDs. The energy separation of double PL peaks, originated from two different excited states, was kept at around 50 meV at room temperature. A possible mechanism concerning this phenomenon is also discussed. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Direct radiocarbon dates for Vindija G1 and Velika Pećina Late Pleistocene hominid remains

    Science.gov (United States)

    Smith, Fred H.; Trinkaus, Erik; Pettitt, Paul B.; Karavanić, Ivor; Paunović, Maja

    1999-01-01

    New accelerator mass spectrometry radiocarbon dates taken directly on human remains from the Late Pleistocene sites of Vindija and Velika Pećina in the Hrvatsko Zagorje of Croatia are presented. Hominid specimens from both sites have played critical roles in the development of current perspectives on modern human evolutionary emergence in Europe. Dates of ≈28 thousand years (ka) before the present (B.P.) and ≈29 ka B.P. for two specimens from Vindija G1 establish them as the most recent dated Neandertals in the Eurasian range of these archaic humans. The human frontal bone from Velika Pećina, generally considered one of the earliest representatives of modern humans in Europe, dated to ≈5 ka B.P., rendering it no longer pertinent to discussions of modern human origins. Apart from invalidating the only radiometrically based example of temporal overlap between late Neandertal and early modern human fossil remains from within any region of Europe, these dates raise the question of when early modern humans first dispersed into Europe and have implications for the nature and geographic patterning of biological and cultural interactions between these populations and the Neandertals. PMID:10535913

  14. Design of a multivariable controller for a CANDU 600 MWe nuclear power plant using the INA method

    International Nuclear Information System (INIS)

    Roy, N.; Boisvert, J.; Mensah, S.

    1984-04-01

    The development of large and complex nuclear and process plants requires high-performance control systems, designed with rigorous multivariable techniques. This work is part of an analytical study demonstrating the real potential of multivariable methods. It covers every step in the design of a multi-variable controller for a Gentilly-2 type CANDU 600 MWe nuclear power plant using the Inverse Nyquist Array (INA) method. First the linear design model and its preliminary modifications are described. The design tools are reviewed and the operations required to achieve open-loop diagonal dominance are thoroughly described. Analysis of the closed-loop system is then performed and a feedback matrix is selected to meet the design specifications. The performance of the controller on the linear model is verified by simulation. Finally, the controller is implemented on the reference non-linear model to assess its overall performance. The results show that the INA method can be used successfully to design controllers for large and complex systems

  15. The investigation of alloy formation during InAs nanowires growth on GaAs (111)B substrate

    Energy Technology Data Exchange (ETDEWEB)

    Saqib, Muhammad; Biermanns, Andreas; Davydok, Anton; Pietsch, Ullrich [Festkoerperphysik, Universitaet Siegen, Walter-Flex-Str. 3, Siegen 57072 (Germany); Rieger, Torsten; Grap, Thomas; Lepsa, Mihail [Peter Gruenberg Institute (PGI-9), Forschungzentrum Juelich, Juelich 52425 (Germany)

    2013-07-01

    A possible way to obtain nanowires is the growth in molecular beam epitaxy (MBE) on the (111) oriented surface of the desired substrate, covered by a thin oxide layer. A crucial parameter in this method is the initial thickness of the oxide layer, often determined by an etching procedure. In this contribution, we report on the structural investigation of two different series (etched and unetched) of NWs samples. Vertically aligned InAs nanowires (NWs) doped with Si were self-assisted grown by molecular beam epitaxy on GaAs [111]B substrates covered with a thin SiO{sub x} layer. Using a combination of symmetric and asymmetric X-ray diffraction we study the influence of Si supply on the growth process and nanostructure formation. We find that the number of parasitic crystallites grown between the NWs increases with increasing Si flux. In addition, we observe the formation of a Ga{sub 0.2}In{sub 0.8}As alloy if the growth is performed on samples covered by a defective (etched) oxide layer. This alloy formation is observed within the crystallites and not within the nanowires. The Gallium concentration is determined from the lattice mismatch of the crystallites relative to the InAs nanowires. No alloy formation is found for samples with faultless oxide layers.

  16. Strain in GaAs / InAs core-shell nanowire heterostructures grown on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Biermanns, Andreas; Davydok, Anton; Pietsch, Ullrich [Universitaet Siegen, Festkoerperphysik (Germany); Rieger, Torsten; Lepsa, Mihail Ion [Peter Gruenberg Institut 9, Forschungszentrum Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany)

    2012-07-01

    The growth of semiconductor nanowires (NWs) has attracted significant interest in recent years due to the possible fabrication of novel semiconductor devices for future electronic and opto-electronic applications. Compared to planar heterostructures, the nanowire approach offers an advantage regarding the possibility to form heterostructures between highly lattice mismatched systems, because the free surface of the nanowires allows to relieve the strain more efficiently. One particular way to form heterostructures in the NW geometry, is the fabrication of core-shell devices, in which a NW core is surrounded by a shell of different material. The understanding of the mutual strain between core and shell, as well as the relaxation behavior of the system are crucial for the fabrication of functional devices. In this contribution we report on first X-ray diffraction measurements of GaAs-core/InAs-shell nanowires grown on GaAs(111) by molecular beam epitaxy. Using symmetric- and grazing-incidence X-ray diffraction, the relaxation state of the InAs shell as well as the strain in the GaAs core are measured as function of the InAs shell thickness, showing a gradual relaxation behavior of the shell.

  17. Spin Qubits in GaAs Heterostructures and Gating of InAs Nanowires for Lowtemperature Measurements

    DEFF Research Database (Denmark)

    Nissen, Peter Dahl

    of the contenders in the race to build a large-scale quantum computer, is such a component, and research aiming to build, manipulate and couple spin qubits is looking at many materials systems to nd one where the requirements for fast control and long coherence time can be combined with ecient coupling between...... distant qubits. This thesis presents electric measurement on two of the materials systems currently at the forefront of the spin qubit race, namely InAs nanowires and GaAs/AlGaAs heterostructures. For the InAs nanowires we investigate dierent gating geometries towards the goal of dening stable quantum...... electrodes induces tunable barriers of up to 0:25 eV. From the temperature dependence of the conductance, the barrier height is extracted and mapped as a function of gate voltage. Top and bottom gates are similar to each other in terms of electrostatic couplings (lever arms 0:10:2 eV=V) and threshold...

  18. Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy

    International Nuclear Information System (INIS)

    Joyce, Hannah J; Docherty, Callum J; Lloyd-Hughes, James; Herz, Laura M; Johnston, Michael B; Gao Qiang; Tan, H Hoe; Jagadish, Chennupati

    2013-01-01

    We have performed a comparative study of ultrafast charge carrier dynamics in a range of III–V nanowires using optical pump–terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all samples, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm 2 V −1 s −1 , which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s −1 . This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 10 5   cm s −1 . These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices. (paper)

  19. The influence of atmosphere on performance of pure-phase WZ and ZB InAs nanowire transistors.

    Science.gov (United States)

    Ullah, Abu Rifat; Joyce, Hannah J; Tan, Hoe; Jagadish, Chennupati; Micolich, Adam P

    2017-09-21

    We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs nanowire transistors in several atmospheres: air, dry pure N2 and O2, and N2 bubbled through liquid H2O and alcohols to identify whether phase-related structural/surface differences affect their response. Both WZ and ZB give poor gate characteristics in dry state. Adsorption of polar species reduces off-current by 2-3 orders of magnitude, increases on-off ratio and significantly reduces sub-threshold slope. The key difference is the greater sensitivity of WZ to low adsorbate level. We attribute this to facet structure and its influence on the separation between conduction electrons and surface adsorption sites. We highlight the important role adsorbed species play in nanowire device characterisation. WZ is commonly thought superior to ZB in InAs nanowire transistors. We show this is an artefact of the moderate humidity found in ambient laboratory conditions: WZ and ZB perform equally poorly in the dry gas limit yet equally well in the wet gas limit. We also highlight the vital role density-lowering disorder has in improving gate characteristics, be it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase nanowires. © 2017 IOP Publishing Ltd.

  20. Comparative study of porosification in InAs, InP, ZnSe and ZnCdS

    International Nuclear Information System (INIS)

    Monaico, Eduard; Tiginyanu, Ion; Nielsch, Kornelius; Ursaki, Veaceslav; Colibaba, Gleb; Nedeoglo, Dmitrii; Cojocaru, Ala; Foell Helmut

    2013-01-01

    We report on a comparative study of the pore growth during anodization of a narrow-bandgap III-V compound (InAs), a medium-bandgap III-V one (InP) and wide-bandgap II-VI semiconductors (ZnSe and Zn 0,4 Cd 0,6 S). According to the obtained results, the morphology of the porous layers can be controlled by the composition of the electrolyte and the applied electrochemical parameters. It was evidenced that in the narrow bandgap semiconductor InAs it is difficult to control the mechanism of pore growth. Both current line oriented pores and crystallographically oriented pores were produced in the medium-bandgap material InP. The electrochemical nanostructuring of wide-bandgap semiconductors realized in single crystalline high conductivity samples evidenced only current-line oriented pores. This behavior is explained in terms of difference in the values of electronegativity of the constituent atoms and the degree of ionicity. (authors)

  1. Self-assembled monolayers of alkyl-thiols on InAs: A Kelvin probe force microscopy study

    Science.gov (United States)

    Szwajca, A.; Wei, J.; Schukfeh, M. I.; Tornow, M.

    2015-03-01

    We report on the preparation and characterization of self-assembled monolayers from aliphatic thiols with different chain length and termination on InAs (100) planar surfaces. This included as first step the development and investigation of a thorough chemical InAs surface preparation step using a dedicated bromine/NH4OH-based etching process. Ellipsometry, contact angle measurements and atomic force microscopy (AFM) indicated the formation of smooth, surface conforming monolayers. The molecular tilt angles were obtained as 30 ± 10° with respect to the surface normal. Kelvin probe force microscopy (KPFM) measurements in hand with Parameterized Model number 5 (PM5) calculations of the involved molecular dipoles allowed for an estimation of the molecular packing densities on the surface. We obtained values of up to n = 1014 cm- 2 for the SAMs under study. These are close to what is predicted from a simple geometrical model that would calculate a maximum density of about n = 2.7 × 1014 cm- 2. We take this as additional conformation of the substrate smoothness and quality of our InAs-SAM hybrid layer systems.

  2. The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors

    Science.gov (United States)

    Ullah, A. R.; Joyce, H. J.; Tan, H. H.; Jagadish, C.; Micolich, A. P.

    2017-11-01

    We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs nanowire transistors in several atmospheres: air, dry pure N2 and O2, and N2 bubbled through liquid H2O and alcohols to identify whether phase-related structural/surface differences affect their response. Both WZ and ZB give poor gate characteristics in dry state. Adsorption of polar species reduces off-current by 2-3 orders of magnitude, increases on-off ratio and significantly reduces sub-threshold slope. The key difference is the greater sensitivity of WZ to low adsorbate level. We attribute this to facet structure and its influence on the separation between conduction electrons and surface adsorption sites. We highlight the important role adsorbed species play in nanowire device characterisation. WZ is commonly thought superior to ZB in InAs nanowire transistors. We show this is an artefact of the moderate humidity found in ambient laboratory conditions: WZ and ZB perform equally poorly in the dry gas limit yet equally well in the wet gas limit. We also highlight the vital role density-lowering disorder has in improving gate characteristics, be it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase nanowires.

  3. Self-assembled InAs quantum dots. Properties, modification and emission processes

    International Nuclear Information System (INIS)

    Schramm, A.

    2007-01-01

    In this thesis, structural, optical as well as electronic properties of self-assembled InAs quantum dots (QD) were studied by means of atomic force microscopy (AFM), photoluminescence (PL), capacitance spectroscopy (CV) and capacitance transient spectroscopy (DLTS). The quantum dots were grown with molecular beam epitaxy (MBE) and embedded in Schottky diodes for electrical characterization. In this work growth aspects as well as the electronic structures of QD were discussed. By varying the QD growth parameters it is possible to control the structural, and thus the optical and electronic properties of QD. Two methods are presented. Adjusting the QD growth temperature leads either to small QD with a high areal density or to high QDs with a low density. The structural changes of the QD are reflected in the changes of the optical and electronic properties. The second method is to introduce a growth interruption after capping the QD with thin cap layers. It was shown that capping with AlAs leads to a well-developed alternative to control the QD height and thus the ground-state energies of the QD. A post-growth method modifying the QD properties ist rapid thermal annealing (RTA). Raising the RTA temperature causes a lifting of the QD energy states with respect to the GaAs band edge energy due to In/Ga intermixing processes. A further main part of this work covers the emission processes of charge carriers in QD. Thermal emission, thermally assisted tunneling, and pure tunneling emission are studied by capacitance transient spectroscopy techniques. In DLTS experiments a strong impact of the electric field on the activation energies of electrons was found interfering the correct determination of the QD level energies. This behaviour can be explained by a thermally assisted tunneling model. A modified model taking the Coulomb interaction of occupied QD into account describes the emission rates of the electrons. In order to avoid several emission pathes in the experiments

  4. Influence of bone metastases in the red marrow 131INa internal dosimetry

    International Nuclear Information System (INIS)

    Llina Fuentes, C.S.; Cabrejas, M.I.; Cabrejas, R.

    2008-01-01

    Full text: This research analyses the evaluation of the absorbed dose in the bone marrow for developing a calculation formalism, based on MIRD methodology, to take into account the influence of bone metastases in patients treated with 131 INa due to thyroid differentiated cancer (DTC). A methodology of image processing is stated for later quantification purposes. The dose contribution, mainly electronic, from trabecular bone and cortical bone to red marrow is considered and a general equation is developed to add that contribution. The biodistribution of active bone marrow in adults bone regions is considered from different studies (Cristy (1981), ICRP 70 (1995), Bouchet et al. (2000), ICRP 89 (2004)). It is assumed that the 60% of red marrow is in the axial skeleton, 25% in ribs, femoral head, proximal portion of chimney and breast bone, and 10% in skull and scapula. Accordingly to this distribution, the bone regions with more percentage are included to calculate the influence in the red marrow absorbed dose. The absorbed dose in bone marrow is calculated considering 4 sources: bone marrow, bone tissue with metastases, rest of the bone tissue without metastases and rest of soft tissue. Conversion factors for fifteen regions of the skeleton, obtained from Eckerman Monte Carlo simulations, were used to calculate absorbed dose in each region of bone. The absorbed dose from this formalism is based on specific biokinetic data from patients and dosimetric models. It was considered of interest to compare the results with the biological dosimetry in parallel. From this biological method, the accumulated absorbed dose from previous therapies and also the bone marrow absorbed dose due to the last radioiodine treatment can be obtained in order to compare dose assessment results between the developed formalism and biological dosimetry. The results obtained with the proposed formalism, show that lesions in some bones regions contribute more to the absorbed dose than lesions in

  5. Crystallization of protein–ligand complexes

    International Nuclear Information System (INIS)

    Hassell, Anne M.; An, Gang; Bledsoe, Randy K.; Bynum, Jane M.; Carter, H. Luke III; Deng, Su-Jun J.; Gampe, Robert T.; Grisard, Tamara E.; Madauss, Kevin P.; Nolte, Robert T.; Rocque, Warren J.; Wang, Liping; Weaver, Kurt L.; Williams, Shawn P.; Wisely, G. Bruce; Xu, Robert; Shewchuk, Lisa M.

    2007-01-01

    Methods presented for growing protein–ligand complexes fall into the categories of co-expression of the protein with the ligands of interest, use of the ligands during protein purification, cocrystallization and soaking the ligands into existing crystals. Obtaining diffraction-quality crystals has long been a bottleneck in solving the three-dimensional structures of proteins. Often proteins may be stabilized when they are complexed with a substrate, nucleic acid, cofactor or small molecule. These ligands, on the other hand, have the potential to induce significant conformational changes to the protein and ab initio screening may be required to find a new crystal form. This paper presents an overview of strategies in the following areas for obtaining crystals of protein–ligand complexes: (i) co-expression of the protein with the ligands of interest, (ii) use of the ligands during protein purification, (iii) cocrystallization and (iv) soaks

  6. -Pincer Ligand Family through Ligand Post-Modification

    KAUST Repository

    Huang, Mei-Hui; Hu, Jinsong; Huang, Kuo-Wei

    2017-01-01

    A series of air-stable nickel complexes containing triazine-based PN3P-pincer ligands were synthesized and fully characterized. Complex 3 contains a de-aromatized central triazine ring from the deprotonation of one of the N–H arms. With a post-modification strategy, the Me-PN3P*NiCl complex (3) could be converted into a new class of diimine–traizine PN3P-pincer nickel complexes.

  7. -Pincer Ligand Family through Ligand Post-Modification

    KAUST Repository

    Huang, Mei-Hui

    2017-10-02

    A series of air-stable nickel complexes containing triazine-based PN3P-pincer ligands were synthesized and fully characterized. Complex 3 contains a de-aromatized central triazine ring from the deprotonation of one of the N–H arms. With a post-modification strategy, the Me-PN3P*NiCl complex (3) could be converted into a new class of diimine–traizine PN3P-pincer nickel complexes.

  8. Reactivity of halide and pseudohalide ligands

    International Nuclear Information System (INIS)

    Kukushkin, Yu.N.

    1987-01-01

    Reactivity of halide and pseudohalide (cyanide, azide, thiocyanate, cyanate) ligands tending to form bridge bonds in transition metal (Re, Mo, W) complexes is considered. Complexes where transition metal salts are ligands of other, complex-forming ion, are described. Transformation of innerspheric pseudohalide ligands is an important way of directed synthesis of these metal coordination compounds

  9. Tuning of Rashba/Dresselhaus Spin Splittings by Inserting Ultra-Thin InAs Layers at Interfaces in Insulating GaAs/AlGaAs Quantum Wells.

    Science.gov (United States)

    Yu, Jinling; Zeng, Xiaolin; Cheng, Shuying; Chen, Yonghai; Liu, Yu; Lai, Yunfeng; Zheng, Qiao; Ren, Jun

    2016-12-01

    The ratio of Rashba and Dresselhaus spin splittings of the (001)-grown GaAs/AlGaAs quantum wells (QWs), investigated by the spin photocurrent spectra induced by circular photogalvanic effect (CPGE) at inter-band excitation, has been effectively tuned by changing the well width of QWs and by inserting a one-monolayer-thick InAs layer at interfaces of GaAs/AlGaAs QWs. Reflectance difference spectroscopy (RDS) is also employed to study the interface asymmetry of the QWs, whose results are in good agreement with that obtained by CPGE measurements. It is demonstrated that the inserted ultra-thin InAs layers will not only introduce structure inversion asymmetry (SIA), but also result in additional interface inversion asymmetry (IIA), whose effect is much stronger in QWs with smaller well width. It is also found that the inserted InAs layer brings in larger SIA than IIA. The origins of the additional SIA and IIA introduced by the inserted ultra-thin InAs layer have been discussed.

  10. INFLUENCE OF LOW-ENERGY AR-SPUTTERING ON THE ELECTRONIC-PROPERTIES OF INAS-BASED QUANTUM-WELL STRUCTURES

    NARCIS (Netherlands)

    Magnee, P.H.C.; den Hartog, S.G.; Wees, B.J.van; Klapwijk, T.M; van de Graaf, W.; Borghs, G.

    1995-01-01

    The influence of low energy (80-500 eV) Ar-ion milling cleaning techniques on InAs based quantum well structures is investigated. It is found that both etching with a Kaufmann source and sputter-etching with a rf-plasma enhances the electron density and reduces the mobility. An anneal at 180 degrees

  11. Ligand-regulated peptide aptamers.

    Science.gov (United States)

    Miller, Russell A

    2009-01-01

    The peptide aptamer approach employs high-throughput selection to identify members of a randomized peptide library displayed from a scaffold protein by virtue of their interaction with a target molecule. Extending this approach, we have developed a peptide aptamer scaffold protein that can impart small-molecule control over the aptamer-target interaction. This ligand-regulated peptide (LiRP) scaffold, consisting of the protein domains FKBP12, FRB, and GST, binds to the cell-permeable small-molecule rapamycin and the binding of this molecule can prevent the interaction of the randomizable linker region connecting FKBP12 with FRB. Here we present a detailed protocol for the creation of a peptide aptamer plasmid library, selection of peptide aptamers using the LiRP scaffold in a yeast two-hybrid system, and the screening of those peptide aptamers for a ligand-regulated interaction.

  12. Ligand binding by PDZ domains

    DEFF Research Database (Denmark)

    Chi, Celestine N.; Bach, Anders; Strømgaard, Kristian

    2012-01-01

    , for example, are particularly rich in these domains. The general function of PDZ domains is to bring proteins together within the appropriate cellular compartment, thereby facilitating scaffolding, signaling, and trafficking events. The many functions of PDZ domains under normal physiological as well...... as pathological conditions have been reviewed recently. In this review, we focus on the molecular details of how PDZ domains bind their protein ligands and their potential as drug targets in this context....

  13. Bitopic Ligands and Metastable Binding Sites

    DEFF Research Database (Denmark)

    Fronik, Philipp; Gaiser, Birgit I; Sejer Pedersen, Daniel

    2017-01-01

    of orthosteric binding sites. Bitopic ligands have been employed to address the selectivity problem by combining (linking) an orthosteric ligand with an allosteric modulator, theoretically leading to high-affinity subtype selective ligands. However, it remains a challenge to identify suitable allosteric binding...... that have been reported to date, this type of bitopic ligands would be composed of two identical pharmacophores. Herein, we outline the concept of bitopic ligands, review metastable binding sites, and discuss their potential as a new source of allosteric binding sites....

  14. Radioiodinated ligands for dopamine receptors

    International Nuclear Information System (INIS)

    Kung, H.F.

    1994-01-01

    The dopamine receptor system is important for normal brain function; it is also the apparent action site for various neuroleptic drugs for the treatment of schizophrenia and other metal disorders. In the past few years radioiodinated ligands for single photon emission tomography (SPECT) have been successfully developed and tested in humans: [ 123 I]TISCH for D1 dopamine receptors; [ 123 I]IBZM, epidepride, IBF and FIDA2, four iodobenzamide derivatives, for D2/D3 dopamine receptors. In addition, [ 123 I]β-CIT (RTI-55) and IPT, cocaine derivatives, for the dopamine reuptake site are potentially useful for diagnosis of loss of dopamine neurons. The first iodinated ligand, (R)trans-7-OH-PIPAT, for D3 dopamine receptors, was synthesized and characterized with cloned cell lines (Spodoptera frugiperda, Sf9) expressing the D2 and D3 dopamine receptors and with rat basal forebrain membrane preparations. Most of the known iodobenzamides displayed similar potency in binding to both D2 and D3 dopamine receptors expressed in the cell lines. Initial studies appear to suggest that by fine tuning the structures it may be possible to develop agents specific for D2 and D3 dopamine receptors. It is important to investigate D2/D3 selectivity for this series of potent ligands

  15. Selective area growth of InAs nanowires from SiO2/Si(1 1 1) templates direct-written by focused helium ion beam technology

    Science.gov (United States)

    Yang, Che-Wei; Chen, Wei-Chieh; Chou, Chieh; Lin, Hao-Hsiung

    2018-02-01

    We report on the selective area growth of InAs nanowires on patterned SiO2/Si (1 1 1) nano-holes, prepared by focused helium ion beam technology. We used a single spot mode, in which the focused helium ion beam was fixed on a single point with a He+-ion dosage, ranging from 1.5 pC to 8 pC, to drill the nano-holes. The smallest hole diameter achieved is ∼8 nm. We found that low He+-ion dosage is able to facilitate the nucleation of (1 1 1)B InAs on the highly mismatched Si, leading to the vertical growth of InAs nanowires (NWs). High He-ion dosage, on the contrary, severely damaged Si surface, resulting in tilted and stripe-like NWs. In addition to titled NW grown from (1 1 1)A InAs domain, a new titled growth direction due to defect induced twinning was observed. Cross-sectional TEM images of vertical NWs show mixed wurtizite (WZ) and zincblende (ZB) phases, while WZ phase dominants. The stacking faults resulting from the phase change is proportional to NW diameter, suggesting that the critical diameter of phase turning is larger than 110 nm, the maximum diameter of our NWs. Period of misfit dislocation at the InAs/Si interface of vertical NW is also found larger than the theoretical value when the diameter of heterointerface is smaller than 50 nm, indicating that the small contact area is able to accommodate the large lattice and thermal mismatch between InAs and Si.

  16. Stress evolution during growth of InAs on GaAs measured by an in-situ cantilever beam setup

    Energy Technology Data Exchange (ETDEWEB)

    Hu Dongzhi

    2007-02-13

    The influence of stress on the growth of InAs on GaAs(001) by molecular beam epitaxy (MBE) is investigated in this thesis. Film force curves were measured for InAs deposition under As-rich as well as In-rich growth conditions. The growth under As-rich conditions proceeds in the Stranski- Krastanov growth mode, meaning that quantum dots are formed after the initial growth of a wetting layer. During subsequent growth interruptions or intentional annealing at the growth temperature, the quantum dots undergo ripening. This growth mode of InAs films and the subsequent annealing behavior were studied in detail in this thesis. To understand the influence of strain on the growth mechanisms, the film force curves were analyzed and correlated to the morphological evolution of the InAs films during deposition and especially during annealing. Models were developed to fit and explain the relaxation of the film force measured during the annealing of InAs quantum dots. At temperatures lower than 470 C, quantum dots undergo standard Ostwald ripening. Different mechanisms, such as kinetic and diffusion limited, determine the ripening process. Fits of models based on these mechanisms to the film force relaxation curves, show, that although the relaxation curve for annealing at 440 C can be fitted reasonably well with all the models, the model describing ripening limited by the diffusion along dot boundaries yields a slightly better fit. The relaxation curves obtained at 455 C and 470 C can be fitted very well only with the model in which the ripening is controlled by the attachment/detachment of atoms on the dot surface. Annealing of quantum dots at temperatures higher than 500 C shows a very different behavior. Atomic force microscopy images reveal that the quantum dots ripen first and then dissolve after 450 s-600 s annealing. (orig.)

  17. BIAYA KLAIM INA CBGS DAN BIAYA RIIL PENYAKIT KATASTROPIK RAWAT INAP PESERTA JAMKESMAS DI RUMAH SAKIT STUDI DI 10 RUMAH SAKIT MILIK KEMENTERIAN KESEHATAN JANUARI–MARET 2012

    Directory of Open Access Journals (Sweden)

    Wasis Budiarto

    2013-08-01

    Full Text Available Latar belakang: Implementasi sistem INA-CBGs bagi pasien penyakit katastropik (jantung, kanker, stroke peserta Jamkesmas di rumah sakit, memberikan konsekuensi di satu pihak bahwa penyakit katastropik merupakan ancaman terhadap membengkaknya pembiayaan Jamkesmas di masa datang, sedangkan di pihak lain, rumah sakit merasakan bahwa biaya penggantian klaim INA CBGs lebih rendah dari tarif yang berlaku dirumah sakit. Tujuan: Tujuan penelitian ini untuk memperoleh gambaran biaya pengobatan penyakit katastropik dan perbandingan pembiayaan klaim berdasarkan INA-DRGs dengan biaya pengobatan riil penyakit katastropik dirumah sakit. Jenis penelitian adalah deskriptif menurut perspektif rumah sakit. Metode: Metode pengambilan data dilakukan secara retrospektif yang diambil dari penelusuran dokumen catatan medik pasien penyakit katastropik di 10 rumah sakit selama 3 bulan (Januari–Maret 2012. Analisis data dilakukan secara deskriptif. Hasil: Hasil penelitian menunjukkan bahwa pasien Jamkesmas yang dirawat dengan kasus katastropik terdiri dari penyakit jantung sebesar37,11%, penyakit kanker 23,54% dan sisanya sebesar 39,35% pasien penyakit stroke. Kesimpulan: Biaya pengobatan rawat inap berdasarkan tarif rumah sakit kelas A jauh lebih besar dibandingkan kelas B dan RS Khusus, biaya klaim berdasarkan INA-CBGs jauh lebih besar di rumah sakit kelas A dibanding kelas B dan RS Khusus. Komponen biaya yang banyak peruntukannya adalah biaya akomodasi, tindakan ruangan, pemeriksaan laboratorium, tindakan intervensi nonbedah untuk jantung, tindakan operasi untuk kanker serta biaya obat-obatan. Biaya penggantian klaim penyakit katastropik berdasarkan INA CBGs lebih besar dibandingkan dengan biaya riil berdasarkan tarif rumah sakit, sehingga untuk penyakit katastropik rumah sakit tidak merugi. Untuk itu pelaksanaan kebijakan rujukan berjenjang bagi peserta Jamkesmas harus diawasi secara ketat sehingga pelayanan kesehatan bagi penduduk miskin menjadi lebih terjamin

  18. Stress evolution during growth of InAs on GaAs measured by an in-situ cantilever beam setup

    International Nuclear Information System (INIS)

    Hu Dongzhi

    2007-01-01

    The influence of stress on the growth of InAs on GaAs(001) by molecular beam epitaxy (MBE) is investigated in this thesis. Film force curves were measured for InAs deposition under As-rich as well as In-rich growth conditions. The growth under As-rich conditions proceeds in the Stranski- Krastanov growth mode, meaning that quantum dots are formed after the initial growth of a wetting layer. During subsequent growth interruptions or intentional annealing at the growth temperature, the quantum dots undergo ripening. This growth mode of InAs films and the subsequent annealing behavior were studied in detail in this thesis. To understand the influence of strain on the growth mechanisms, the film force curves were analyzed and correlated to the morphological evolution of the InAs films during deposition and especially during annealing. Models were developed to fit and explain the relaxation of the film force measured during the annealing of InAs quantum dots. At temperatures lower than 470 C, quantum dots undergo standard Ostwald ripening. Different mechanisms, such as kinetic and diffusion limited, determine the ripening process. Fits of models based on these mechanisms to the film force relaxation curves, show, that although the relaxation curve for annealing at 440 C can be fitted reasonably well with all the models, the model describing ripening limited by the diffusion along dot boundaries yields a slightly better fit. The relaxation curves obtained at 455 C and 470 C can be fitted very well only with the model in which the ripening is controlled by the attachment/detachment of atoms on the dot surface. Annealing of quantum dots at temperatures higher than 500 C shows a very different behavior. Atomic force microscopy images reveal that the quantum dots ripen first and then dissolve after 450 s-600 s annealing. (orig.)

  19. International Active Surveillance Study of Women Taking Oral Contraceptives (INAS-OC Study

    Directory of Open Access Journals (Sweden)

    Assmann Anita

    2009-11-01

    Full Text Available Abstract Background A 24-day regimen of contraceptive doses of drospirenone and ethinylestradiol (DRSP/EE 24d was recently launched. This regimen has properties which may be beneficial for certain user populations (e.g., women suffering from premenstrual dysphoric disorder or acne. However, it is unknown whether this extended regimen has an impact on the cardiovascular risk associated with the use of oral contraceptives (OCs. The INternational Active Surveillance study of women taking Oral Contraceptives (INAS-OC is designed to investigate the short- and long-term safety of the new regimen in a population which is representative for the typical user of oral contraceptives. Methods/Design A large, prospective, controlled, non-interventional, long-term cohort study with active surveillance of the study participants has been chosen to ensure reliable and valid results. More than 2,000 gynecologists in the US and 5 European countries (Austria, Germany, Italy, Poland, and Sweden will recruit more than 80,000 OC users. The two to five year follow-up of these women will result in at least 220,000 documented women-years. The main clinical outcomes of interest for the follow-up are deep venous thrombosis, pulmonary embolism, acute myocardial infarction and cerebrovascular accidents. Secondary objectives are general safety, effectiveness and drug utilization pattern of DRSP/EE 24d, return to fertility after stop of OC use, as well as the baseline risk for users of individual OC formulations. Because of the non-interference character of this study, potential participants (first-time users or switchers are informed about the study only after the decision regarding prescription of a new OC. There are no specific medical inclusion or exclusion criteria. Study participation is voluntary and a written informed consent is required. After the baseline questionnaire, follow-up questionnaires will be mailed to the participants every 6 months for up to 5 years after

  20. International Active Surveillance Study of Women Taking Oral Contraceptives (INAS-OC Study).

    Science.gov (United States)

    Dinger, Juergen C; Bardenheuer, Kristina; Assmann, Anita

    2009-11-18

    A 24-day regimen of contraceptive doses of drospirenone and ethinylestradiol (DRSP/EE 24d) was recently launched. This regimen has properties which may be beneficial for certain user populations (e.g., women suffering from premenstrual dysphoric disorder or acne). However, it is unknown whether this extended regimen has an impact on the cardiovascular risk associated with the use of oral contraceptives (OCs). The INternational Active Surveillance study of women taking Oral Contraceptives (INAS-OC) is designed to investigate the short- and long-term safety of the new regimen in a population which is representative for the typical user of oral contraceptives. A large, prospective, controlled, non-interventional, long-term cohort study with active surveillance of the study participants has been chosen to ensure reliable and valid results. More than 2,000 gynecologists in the US and 5 European countries (Austria, Germany, Italy, Poland, and Sweden) will recruit more than 80,000 OC users. The two to five year follow-up of these women will result in at least 220,000 documented women-years. The main clinical outcomes of interest for the follow-up are deep venous thrombosis, pulmonary embolism, acute myocardial infarction and cerebrovascular accidents. Secondary objectives are general safety, effectiveness and drug utilization pattern of DRSP/EE 24d, return to fertility after stop of OC use, as well as the baseline risk for users of individual OC formulations. Because of the non-interference character of this study, potential participants (first-time users or switchers) are informed about the study only after the decision regarding prescription of a new OC. There are no specific medical inclusion or exclusion criteria. Study participation is voluntary and a written informed consent is required. After the baseline questionnaire, follow-up questionnaires will be mailed to the participants every 6 months for up to 5 years after baseline. Self-reported serious adverse events

  1. An efficient atomistic quantum mechanical simulation on InAs band-to-band tunneling field-effect transistors

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhi [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Jiang, Xiang-Wei; Li, Shu-Shen [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Wang, Lin-Wang, E-mail: lwwang@lbl.gov [Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2014-03-24

    We have presented a fully atomistic quantum mechanical simulation method on band-to-band tunneling (BTBT) field-effect transistors (FETs). Our simulation approach is based on the linear combination of bulk band method with empirical pseudopotentials, which is an atomist method beyond the effective-mass approximation or k.p perturbation method, and can be used to simulate real-size devices (∼10{sup 5} atoms) efficiently (∼5 h on a few computational cores). Using this approach, we studied the InAs dual-gate BTBT FETs. The I-V characteristics from our approach agree very well with the tight-binding non-equilibrium Green's function results, yet our method costs much less computationally. In addition, we have studied ways to increase the tunneling current and analyzed the effects of different mechanisms for that purpose.

  2. An efficient atomistic quantum mechanical simulation on InAs band-to-band tunneling field-effect transistors

    International Nuclear Information System (INIS)

    Wang, Zhi; Jiang, Xiang-Wei; Li, Shu-Shen; Wang, Lin-Wang

    2014-01-01

    We have presented a fully atomistic quantum mechanical simulation method on band-to-band tunneling (BTBT) field-effect transistors (FETs). Our simulation approach is based on the linear combination of bulk band method with empirical pseudopotentials, which is an atomist method beyond the effective-mass approximation or k.p perturbation method, and can be used to simulate real-size devices (∼10 5 atoms) efficiently (∼5 h on a few computational cores). Using this approach, we studied the InAs dual-gate BTBT FETs. The I-V characteristics from our approach agree very well with the tight-binding non-equilibrium Green's function results, yet our method costs much less computationally. In addition, we have studied ways to increase the tunneling current and analyzed the effects of different mechanisms for that purpose

  3. Atomic scale characterization of ion-induced amorphization of GaAs and InAs using PAC spectroscopy

    International Nuclear Information System (INIS)

    Dogra, R.; Byrne, A.P.; Ridgway, M.C.

    2005-01-01

    Single crystals of GaAs (100) and InAs (100) were implanted with 1-7 MeV 74 Ge ions over a wide dose range at liquid nitrogen temperature. The implanted substrates were investigated with respect to the damage production by means of perturbed angular correlation spectroscopy based upon hyperfine interactions of nuclear electromagnetic moments of probe nuclei with extra-nuclear fields. The perturbed angular correlation measurements were performed at room temperature utilizing the 111 In/Cd radioisotope probe nuclei. The crystalline, disordered and amorphous probe environments were identified from the measurements. The defect production is described within the framework of different amorphization models. (author). 6 refs., 2 figs

  4. Formation of the InAs-, InSb-, GaAs-, and GaSb-polished surface

    Science.gov (United States)

    Levchenko, Iryna; Tomashyk, Vasyl; Stratiychuk, Iryna; Malanych, Galyna; Korchovyi, Andrii; Kryvyi, Serhii; Kolomys, Oleksandr

    2018-04-01

    The features of the InAs, InSb, GaAs, and GaSb ultra-smooth surface have been investigated using chemical-mechanical polishing with the (NH4)2Cr2O7-HBr-CH2(OH)CH2(OH)-etching solutions. The etching rate of the semiconductors has been measured as a function of the solution saturation by organic solvent (ethylene glycol). It was found that mechanical effect significantly increases the etching rate from 1.5 to 57 µm/min, and the increase of the organic solvent concentration promotes the decrease of the damaged layer-removing rate. According to AFM, RS, HRXRD results, the treatment with the (NH4)2Cr2O7-HBr-ethylene glycol solutions produces the clean surface of the nanosize level (R a < 0.5 nm).

  5. Specific features of electroluminescence in heterostructures with InSb quantum dots in an InAs matrix

    Energy Technology Data Exchange (ETDEWEB)

    Parkhomenko, Ya. A.; Ivanov, E. V.; Moiseev, K. D., E-mail: mkd@iropt2.ioffe.rssi.ru [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

    2013-11-15

    The electrical and electroluminescence properties of a single narrow-gap heterostructure based on a p-n junction in indium arsenide, containing a single layer of InSb quantum dots in the InAs matrix, are studied. The presence of quantum dots has a significant effect on the shape of the reverse branch of the current-voltage characteristic of the heterostructure. Under reverse bias, the room-temperature electroluminescence spectra of the heterostructure with quantum dots, in addition to a negative-luminescence band with a maximum at the wavelength {lambda} = 3.5 {mu}m, contained a positive-luminescence emission band at 3.8 {mu}m, caused by radiative transitions involving localized states of quantum dots at the type-II InSb/InAs heterointerface.

  6. Insights into an original pocket-ligand pair classification: a promising tool for ligand profile prediction.

    Directory of Open Access Journals (Sweden)

    Stéphanie Pérot

    Full Text Available Pockets are today at the cornerstones of modern drug discovery projects and at the crossroad of several research fields, from structural biology to mathematical modeling. Being able to predict if a small molecule could bind to one or more protein targets or if a protein could bind to some given ligands is very useful for drug discovery endeavors, anticipation of binding to off- and anti-targets. To date, several studies explore such questions from chemogenomic approach to reverse docking methods. Most of these studies have been performed either from the viewpoint of ligands or targets. However it seems valuable to use information from both ligands and target binding pockets. Hence, we present a multivariate approach relating ligand properties with protein pocket properties from the analysis of known ligand-protein interactions. We explored and optimized the pocket-ligand pair space by combining pocket and ligand descriptors using Principal Component Analysis and developed a classification engine on this paired space, revealing five main clusters of pocket-ligand pairs sharing specific and similar structural or physico-chemical properties. These pocket-ligand pair clusters highlight correspondences between pocket and ligand topological and physico-chemical properties and capture relevant information with respect to protein-ligand interactions. Based on these pocket-ligand correspondences, a protocol of prediction of clusters sharing similarity in terms of recognition characteristics is developed for a given pocket-ligand complex and gives high performances. It is then extended to cluster prediction for a given pocket in order to acquire knowledge about its expected ligand profile or to cluster prediction for a given ligand in order to acquire knowledge about its expected pocket profile. This prediction approach shows promising results and could contribute to predict some ligand properties critical for binding to a given pocket, and conversely

  7. Insights into an original pocket-ligand pair classification: a promising tool for ligand profile prediction.

    Science.gov (United States)

    Pérot, Stéphanie; Regad, Leslie; Reynès, Christelle; Spérandio, Olivier; Miteva, Maria A; Villoutreix, Bruno O; Camproux, Anne-Claude

    2013-01-01

    Pockets are today at the cornerstones of modern drug discovery projects and at the crossroad of several research fields, from structural biology to mathematical modeling. Being able to predict if a small molecule could bind to one or more protein targets or if a protein could bind to some given ligands is very useful for drug discovery endeavors, anticipation of binding to off- and anti-targets. To date, several studies explore such questions from chemogenomic approach to reverse docking methods. Most of these studies have been performed either from the viewpoint of ligands or targets. However it seems valuable to use information from both ligands and target binding pockets. Hence, we present a multivariate approach relating ligand properties with protein pocket properties from the analysis of known ligand-protein interactions. We explored and optimized the pocket-ligand pair space by combining pocket and ligand descriptors using Principal Component Analysis and developed a classification engine on this paired space, revealing five main clusters of pocket-ligand pairs sharing specific and similar structural or physico-chemical properties. These pocket-ligand pair clusters highlight correspondences between pocket and ligand topological and physico-chemical properties and capture relevant information with respect to protein-ligand interactions. Based on these pocket-ligand correspondences, a protocol of prediction of clusters sharing similarity in terms of recognition characteristics is developed for a given pocket-ligand complex and gives high performances. It is then extended to cluster prediction for a given pocket in order to acquire knowledge about its expected ligand profile or to cluster prediction for a given ligand in order to acquire knowledge about its expected pocket profile. This prediction approach shows promising results and could contribute to predict some ligand properties critical for binding to a given pocket, and conversely, some key pocket

  8. Ligand photo-isomerization triggers conformational changes in iGluR2 ligand binding domain.

    Directory of Open Access Journals (Sweden)

    Tino Wolter

    Full Text Available Neurological glutamate receptors bind a variety of artificial ligands, both agonistic and antagonistic, in addition to glutamate. Studying their small molecule binding properties increases our understanding of the central nervous system and a variety of associated pathologies. The large, oligomeric multidomain membrane protein contains a large and flexible ligand binding domains which undergoes large conformational changes upon binding different ligands. A recent application of glutamate receptors is their activation or inhibition via photo-switchable ligands, making them key systems in the emerging field of optochemical genetics. In this work, we present a theoretical study on the binding mode and complex stability of a novel photo-switchable ligand, ATA-3, which reversibly binds to glutamate receptors ligand binding domains (LBDs. We propose two possible binding modes for this ligand based on flexible ligand docking calculations and show one of them to be analogues to the binding mode of a similar ligand, 2-BnTetAMPA. In long MD simulations, it was observed that transitions between both binding poses involve breaking and reforming the T686-E402 protein hydrogen bond. Simulating the ligand photo-isomerization process shows that the two possible configurations of the ligand azo-group have markedly different complex stabilities and equilibrium binding modes. A strong but slow protein response is observed after ligand configuration changes. This provides a microscopic foundation for the observed difference in ligand activity upon light-switching.

  9. Development of immobilized ligands for actinide separations

    International Nuclear Information System (INIS)

    Paine, R.T.

    1994-01-01

    Primary goals during this grant period were to (1) synthesize new bifunctional chelating ligands, (2) characterize the structural features of the Ln and An coordination complexes formed by these ligands, (3) use structural data to iteratively design new classes of multifunctional ligands, and (4) explore additional routes for attachment of key ligands to solid supports that could be useful for chromatographic separations. Some highlights of recently published work as well as a summary of submitted, unpublished and/or still in progress research are outlined

  10. Prediction of phonon thermal transport in thin GaAs, InAs and InP nanowires by molecular dynamics simulations: influence of the interatomic potential

    Energy Technology Data Exchange (ETDEWEB)

    Carrete, J; Longo, R C; Gallego, L J, E-mail: jesus.carrete@usc.es [Departamento de Fisica de la Materia Condensada, Facultad de Fisica, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela (Spain)

    2011-05-06

    A number of different potentials are currently being used in molecular dynamics simulations of semiconductor nanostructures. Confusion can arise if an inappropriate potential is used. To illustrate this point, we performed direct molecular dynamics simulations to predict the room temperature lattice thermal conductivity {lambda} of thin GaAs, InAs and InP nanowires. In each case, simulations performed using the classical Harrison potential afforded values of {lambda} about an order of magnitude smaller than those obtained using more elaborate potentials (an Abell-Tersoff, as parameterized by Hammerschmidt et al for GaAs and InAs, and a potential of Vashishta type for InP). These results will be a warning to those wishing to use computer simulations to orient the development of quasi-one-dimensional systems as heat sinks or thermoelectric devices.

  11. Growth patterns of self-assembled InAs quantum dots near the two-dimensional to three-dimensional transition

    Science.gov (United States)

    Colocci, M.; Bogani, F.; Carraresi, L.; Mattolini, R.; Bosacchi, A.; Franchi, S.; Frigeri, P.; Rosa-Clot, M.; Taddei, S.

    1997-06-01

    Self-assembled InAs quantum dots have been grown by molecular beam epitaxy in such a way as to obtain a continuous variation of InAs coverages across the wafer. Structured photoluminescence spectra are observed after excitation of a large number of dots; deconvolution into Gaussian components yields narrow emission bands (full width at half-maximum 20-30 meV) separated in energy by an average spacing of 30-40 meV. We ascribe the individual bands of the photoluminescence spectra after low excitation to families of dots with similar shapes and with heights differing by one monolayer, as strongly supported by numerical calculations of the fundamental electronic transitions in quantum dot structures.

  12. Direct-Bandgap InAs Quantum-Dots Have Long-Range Electron--Hole Exchange Whereas Indirect Gap Si Dots Have Short-Range Exchange

    International Nuclear Information System (INIS)

    Juo, J.W.; Franceschetti, A.; Zunger, A.

    2009-01-01

    Excitons in quantum dots manifest a lower-energy spin-forbidden 'dark' state below a spin-allowed 'bright' state; this splitting originates from electron-hole (e-h) exchange interactions, which are strongly enhanced by quantum confinement. The e-h exchange interaction may have both a short-range and a long-range component. Calculating numerically the e-h exchange energies from atomistic pseudopotential wave functions, we show here that in direct-gap quantum dots (such as InAs) the e-h exchange interaction is dominated by the long-range component, whereas in indirect-gap quantum dots (such as Si) only the short-range component survives. As a result, the exciton dark/bright splitting scales as 1/R 2 in InAs dots and 1/R 3 in Si dots, where R is the quantum-dot radius.

  13. In situ doping of catalyst-free InAs nanowires with Si: Growth, polytypism, and local vibrational modes of Si

    Energy Technology Data Exchange (ETDEWEB)

    Dimakis, Emmanouil; Ramsteiner, Manfred; Huang, Chang-Ning; Trampert, Achim; Riechert, Henning; Geelhaar, Lutz [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Davydok, Anton; Biermanns, Andreas; Pietsch, Ullrich [Festkörperphysik, Universität Siegen, Walter-Flex-Str. 3, 57072 Siegen (Germany)

    2013-09-30

    Growth and structural aspects of the in situ doping of InAs nanowires with Si have been investigated. The nanowires were grown catalyst-free on Si(111) substrates by molecular beam epitaxy. The supply of Si influenced the growth kinetics, affecting the nanowire dimensions, but not the degree of structural polytypism, which was always pronounced. As determined by Raman spectroscopy, Si was incorporated as substitutional impurity exclusively on In sites, which makes it a donor. Previously unknown Si-related Raman peaks at 355 and 360 cm{sup −1} were identified, based on their symmetry properties in polarization-dependent measurements, as the two local vibrational modes of an isolated Si impurity on In site along and perpendicular, respectively, to the c-axis of the wurtzite InAs crystal.

  14. Solução concentrada de albumina eqüina na fluidoterapia em eqüinos com desidratação leve a moderada

    OpenAIRE

    Belli,C.B.; Michima,L.E.S.; Latorre,S.M.; Fernandes,W.R.

    2008-01-01

    Avaliou-se o efeito da solução concentrada de albumina eqüina diluída a 5% em solução fisiológica (SF) durante fluidoterapia em eqüinos, após indução de desidratação leve a moderada, utilizando-se cinco eqüinos adultos, sem alterações clínicas. Cada animal passou por dois protocolos de fluidoterapia: apenas com SF (metade sob pressão e metade em fluxo contínuo - grupo-controle); com solução de albumina eqüina e SF (apenas em fluxo contínuo - grupo experimental). Avaliaram-se peso, exame físic...

  15. Growth and optical characteristics of InAs quantum dot structures with tunnel injection quantum wells for 1.55 μ m high-speed lasers

    Science.gov (United States)

    Bauer, Sven; Sichkovskyi, Vitalii; Reithmaier, Johann Peter

    2018-06-01

    InP based lattice matched tunnel injection structures consisting of a InGaAs quantum well, InAlGaAs barrier and InAs quantum dots designed to emit at 1.55 μ m were grown by molecular beam epitaxy and investigated by photoluminescence spectroscopy and atomic force microscopy. The strong influence of quantum well and barrier thicknesses on the samples emission properties at low and room temperatures was investigated. The phenomenon of a decreased photoluminescence linewidth of tunnel injection structures compared to a reference InAs quantum dots sample could be explained by the selection of the emitting dots through the tunneling process. Morphological investigations have not revealed any effect of the injector well on the dot formation and their size distribution. The optimum TI structure design could be defined.

  16. Macrocyclic ligands for uranium complexation

    International Nuclear Information System (INIS)

    Potts, K.T.

    1991-04-01

    A highly preorganized 24-macrocycle containing biuret, thiobiuret and pyridine subunits has been prepared by high dilution ring-closure procedures. Intermediate products to this macrocycle have been utilized to extend this synthetic route to include further representatives where solubility and stability will be influenced by substituent variation. A 1:1 complex has been formed from uranyl acetate and a quinquepyridine derivative, this representing a new type of ligand for the uranyl ion. A very convenient synthetic procedure that will allow the incorporation of these macrocycles into polymeric systems has been developed for the introduction of a vinyl substituent into the 4-position of the pyridine ring. Using triflate, vinyltributyltin and Pd 0 chemistry, this procedure should make a variety of substituted 4-vinylpyridines available for the first time. 3 refs

  17. Studying the InAs quantum points on the vicinal surface of a GaAs crystal by the atomic force microscopy

    CERN Document Server

    Evtikhiev, V P; Kotelnikov, E Y; Matveentsev, A V; Titkov, A N; Shkolnik, A S

    2002-01-01

    The methodology for processing the images, obtained through the atomic force microscopy, is proposed. It is shown by the concrete example, how the parameters of the InAs clusters on the vicinal surface of the GaAs crystal are determined. This makes it possible to calculate the energy levels of the electrons and holes in the quantum point with application of the previously developed cluster spherical model

  18. Improved Saturation Performance in High Speed Waveguide Photodetectors at 1.3 ??sing an Asymmetric InA1GaAs/InGaAsP Structure

    Science.gov (United States)

    Vang, T. A.; Davis, L.; Keo, S.; Forouhar, S. F.

    1996-01-01

    Waveguide photodetector (WGPD) results have recently been presented demonstrating the very large bandwidth-efficiency product potential of these devices. Improved saturation and linearity characteristics are realized in waveguide p-i-n photodetectors at 1.3 ??y using an asymmetric cladding structure with InA1GaAs/InGaAsP in the anode and InGaAsP in the cathode.

  19. Absorption coefficients for interband optical transitions in a strained InAs1−xPx/InP quantum wire

    International Nuclear Information System (INIS)

    Saravanan, S.; John Peter, A.; Lee, Chang Woo

    2014-01-01

    Excitons confined in an InAs 1−x P x /InP (x=0.2) quantum well wire are studied in the presence of magnetic field strength. Numerical calculations are carried out using variational approach within the single band effective mass approximation. The compressive strain contribution to the confinement potential is included throughout the calculations. The energy difference of the ground and the first excited state is investigated in the influence of magnetic field strength taking into account the geometrical confinement effect. The magnetic field induced optical band as a function of wire radius is investigated in the InAs 0.8 P 0.2 /InP quantum well wire. The valence-band anisotropy is included in our theoretical model by employing different hole masses in different spatial directions. The optical gain as a function of incident photon energy is computed in the presence of magnetic field strength. The corresponding 1.55 μm wavelength is achieved for 40 Å InAs 0.8 P 0.2 /InP quantum well wire. We hope that the results could be used for the potential applications in fiber optic communications. -- Highlights: • Magnetic field induced excitons confined in a InAs 1−x P x /InP (x=0.2) quantum well wire are studied. • The compressive strain is included throughout the calculations. • The energy difference of the ground and the first excited state is investigated in the presence of magnetic field strength. • The magnetic field induced optical band with the geometrical confinement is studied. • The optical gain with the photon energy is computed in the presence of magnetic field strength

  20. Combined vertically correlated InAs and GaAsSb quantum dots separated by triangular GaAsSb barrier

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Oswald, Jiří; Pangrác, Jiří; Zíková, Markéta; Kubištová, Jana; Komninou, Ph.; Kioseoglou, J.; Kuldová, Karla; Hulicius, Eduard

    2013-01-01

    Roč. 114, č. 17 (2013), "174305-1"-"174305-5" ISSN 0021-8979 R&D Projects: GA ČR GA13-15286S; GA MŠk 7AMB12GR034; GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : quantum dots * metal-organic vapor phase epitaxy * InAs * GaAs * GaAsSb Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.185, year: 2013

  1. Photoreflectance study of InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs quantum wells

    International Nuclear Information System (INIS)

    Dhifallah, I.; Daoudi, M.; Bardaoui, A.; Eljani, B.; Ouerghi, A.; Chtourou, R.

    2011-01-01

    Photoreflectance and photoluminescence studies were performed to characterize InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs high electron mobility transistors. These structures were grown by Molecular Beam Epitaxy on (1 0 0) oriented GaAs substrates with different silicon-delta-doped layer densities. Interband energy transitions in the InAs ultrathin layer quantum well were observed below the GaAs band gap in the photoreflectance spectra, and assigned to electron-heavy-hole (E e-hh ) and electron-light-hole (E e-lh ) fundamental transitions. These transitions were shifted to lower energy with increasing silicon-δ-doping density. This effect is in good agreement with our theoretical results based on a self-consistent solution of the coupled Schroedinger and Poisson equations and was explained by increased escape of photogenerated carriers and enhanced Quantum Confined Stark Effect in the Si-delta-doped InAs/GaAs QW. In the photoreflectance spectra, not only the channel well interband energy transitions were observed, but also features associated with the GaAs and AlGaAs bulk layers located at about 1.427 and 1.8 eV, respectively. By analyzing the Franz-Keldysh Oscillations observed in the spectral characteristics of Si-δ-doped samples, we have determined the internal electric field introduced by ionized Si-δ-doped centers. We have observed an increase in the electric field in the InAs ultrathin layer with increasing silicon content. The results are explained in terms of doping dependent ionized impurities densities and surface charges. - Research highlights: → Studying HEMTs structures with different silicon doping content. → An increase of the electric field in the InAs layer with increasing Si content. → The interband energy transitions in the HEMTs structures have been obtained from PR. → Experimental and theoretical values of transitions energies were in good agreement.

  2. CXCR4 Ligands : The Next Big Hit?

    NARCIS (Netherlands)

    Walenkamp, Annemiek M. E.; Lapa, Constantin; Herrmann, Ken; Wester, Hans-Juergen

    2017-01-01

    The G protein-coupled protein receptor C-X-C chemokine receptor 4 (CXCR4) is an attractive target for cancer diagnosis and treatment, as it is overexpressed in many solid and hematologic cancers. Binding of its ligand, C-X-C chemokine ligand 12 (CXCL12), results in receptor internalization and

  3. Ligand-receptor Interactions by NMR Spectroscopy

    Directory of Open Access Journals (Sweden)

    Novak. P.

    2008-04-01

    Full Text Available Today NMR spectroscopy is a method of choice for elucidation of interactions between biomolecules and the potential ligands. Knowledge on these interactions is an essential prerequisite for the rational drug design. The most important contribution of NMR to drug design a few years ago was the 3D structure determination of proteins. Besides delivering the 3D structures of the free proteins as a raw material for the modeling studies on ligand binding, NMR can directly yield valuable experimental data on the biologically important protein-ligand complexes. In addition to X-ray diffraction, NMR spectroscopy can provide information on the internal protein dynamics ordynamics of intermolecular interactions. Changes in NMR parameters allow us to detect ("SAR by NMR" and quantitatively determine binding affinities (titration, diffusion NMR experiments, etc. of potential ligands. Also, it is possible to determine the binding site and conformations of ligands, receptors and receptor-ligand complexes with the help of NMR methods such as tr-NOESY. Epitopes or functional groups responsible for binding of ligands to the receptor can be identified by employing STD or WaterLOGSY experiments. In this review are described some of the most frequent NMR methods for the characterization of the interactions between biomolecules and ligands, together with their advantages and disadvantages.

  4. Autocrine signal transmission with extracellular ligand degradation

    Science.gov (United States)

    Muratov, C B; Posta, F; Shvartsman, S Y

    2009-03-01

    Traveling waves of cell signaling in epithelial layers orchestrate a number of important processes in developing and adult tissues. These waves can be mediated by positive feedback autocrine loops, a mode of cell signaling where binding of a diffusible extracellular ligand to a cell surface receptor can lead to further ligand release. We formulate and analyze a biophysical model that accounts for ligand-induced ligand release, extracellular ligand diffusion and ligand-receptor interaction. We focus on the case when the main mode for ligand degradation is extracellular and analyze the problem with the sharp threshold positive feedback nonlinearity. We derive expressions that link the speed of propagation and other characteristics of traveling waves to the parameters of the biophysical processes, such as diffusion rates, receptor expression level, etc. Analyzing the derived expressions we found that traveling waves in such systems can exhibit a number of unusual properties, e.g. non-monotonic dependence of the speed of propagation on ligand diffusivity. Our results for the fully developed traveling fronts can be used to analyze wave initiation from localized perturbations, a scenario that frequently arises in the in vitro models of epithelial wound healing, and guide future modeling studies of cell communication in epithelial layers.

  5. Organotellurium ligands – designing and complexation reactions

    Indian Academy of Sciences (India)

    Unknown

    membered rings it is negative and ~30 ppm only. Keywords. Organotellurium ligands; hybrid telluroether; platinum metal complexes; tellurium-125 NMR. 1. Introduction. Tellurium is the noblest metalloid which may act as a Lewis acid as well as Lewis base. The ligand chemistry of tellurium, which acts as a 'soft' donor, was ...

  6. Composition, morphology and surface recombination rate of HCl-isopropanol treated and vacuum annealed InAs(1 1 1)A surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kesler, V.G., E-mail: kesler@isp.nsc.ru [Institute of Semiconductor Physics SB RAS, Lavrentiev av., 13, Novosibirsk 630090 (Russian Federation); Seleznev, V.A.; Kovchavtsev, A.P.; Guzev, A.A. [Institute of Semiconductor Physics SB RAS, Lavrentiev av., 13, Novosibirsk 630090 (Russian Federation)

    2010-05-01

    X-ray photoelectron spectroscopy and atomic force microscopy were used to examine the chemical composition and surface morphology of InAs(1 1 1)A surface chemically etched in isopropanol-hydrochloric acid solution (HCl-iPA) and subsequently annealed in vacuum in the temperature range 200-500 deg. C. Etching for 2-30 min resulted in the formation of 'pits' and 'hillocks' on the sample surface, respectively 1-2 nm deep and high, with lateral dimensions 50-100 nm. The observed local formations, whose density was up to 3 x 10{sup 8} cm{sup -2}, entirely vanished from the surface after the samples were vacuum-annealed at temperatures above 300 deg. C. Using a direct method, electron beam microanalysis, we have determined that the defects of the hillock type includes oxygen and excessive As, while the 'pits' proved to be identical in their chemical composition to InAs. Vacuum anneals were found to cause a decrease in As surface concentration relative to In on InAs surface, with a concomitant rise of surface recombination rate.

  7. Composition, morphology and surface recombination rate of HCl-isopropanol treated and vacuum annealed InAs(1 1 1)A surfaces

    Science.gov (United States)

    Kesler, V. G.; Seleznev, V. A.; Kovchavtsev, A. P.; Guzev, A. A.

    2010-05-01

    X-ray photoelectron spectroscopy and atomic force microscopy were used to examine the chemical composition and surface morphology of InAs(1 1 1)A surface chemically etched in isopropanol-hydrochloric acid solution (HCl-iPA) and subsequently annealed in vacuum in the temperature range 200-500 °C. Etching for 2-30 min resulted in the formation of "pits" and "hillocks" on the sample surface, respectively 1-2 nm deep and high, with lateral dimensions 50-100 nm. The observed local formations, whose density was up to 3 × 10 8 cm -2, entirely vanished from the surface after the samples were vacuum-annealed at temperatures above 300 °C. Using a direct method, electron beam microanalysis, we have determined that the defects of the hillock type includes oxygen and excessive As, while the "pits" proved to be identical in their chemical composition to InAs. Vacuum anneals were found to cause a decrease in As surface concentration relative to In on InAs surface, with a concomitant rise of surface recombination rate.

  8. Composition, morphology and surface recombination rate of HCl-isopropanol treated and vacuum annealed InAs(1 1 1)A surfaces

    International Nuclear Information System (INIS)

    Kesler, V.G.; Seleznev, V.A.; Kovchavtsev, A.P.; Guzev, A.A.

    2010-01-01

    X-ray photoelectron spectroscopy and atomic force microscopy were used to examine the chemical composition and surface morphology of InAs(1 1 1)A surface chemically etched in isopropanol-hydrochloric acid solution (HCl-iPA) and subsequently annealed in vacuum in the temperature range 200-500 deg. C. Etching for 2-30 min resulted in the formation of 'pits' and 'hillocks' on the sample surface, respectively 1-2 nm deep and high, with lateral dimensions 50-100 nm. The observed local formations, whose density was up to 3 x 10 8 cm -2 , entirely vanished from the surface after the samples were vacuum-annealed at temperatures above 300 deg. C. Using a direct method, electron beam microanalysis, we have determined that the defects of the hillock type includes oxygen and excessive As, while the 'pits' proved to be identical in their chemical composition to InAs. Vacuum anneals were found to cause a decrease in As surface concentration relative to In on InAs surface, with a concomitant rise of surface recombination rate.

  9. Controlling the size of InAs quantum dots on Si1-xGex/Si(0 0 1) by metalorganic vapor-phase epitaxy

    International Nuclear Information System (INIS)

    Kawaguchi, Kenichi; Ebe, Hiroji; Ekawa, Mitsuru; Sugama, Akio; Arakawa, Yasuhiko

    2009-01-01

    The formation of III-V InAs quantum dots (QDs) on group-IV Si 1-x Ge x /Si(0 0 1) was investigated by metalorganic vapor-phase epitaxy. Two types of QDs, round-shaped QDs and giant QDs elongated in the [1 1 0] or [1,-1,0] direction, were observed in a growth condition of low V/III ratios. An increase in the V/III ratio and AsH 3 preflow during the cooling process was found to suppress the formation of giant QDs. It was considered that replacing the H-stabilized SiGe surface with the As-stabilized surface was necessary for increasing the QD nucleation. The size and density of InAs QDs on SiGe were controllable as well as that on III-V semiconductor buffer layers, and InAs QDs with a density as high as 5 x 10 10 cm -2 were obtained.

  10. A modified gradient approach for the growth of low-density InAs quantum dot molecules by molecular beam epitaxy

    Science.gov (United States)

    Sharma, Nandlal; Reuter, Dirk

    2017-11-01

    Two vertically stacked quantum dots that are electronically coupled, so called quantum dot molecules, are of great interest for the realization of solid state building blocks for quantum communication networks. We present a modified gradient approach to realize InAs quantum dot molecules with a low areal density so that single quantum dot molecules can be optically addressed. The individual quantum dot layers were prepared by solid source molecular beam epitaxy depositing InAs on GaAs(100). The bottom quantum dot layer has been grown without substrate rotation resulting in an In-gradient across the surface, which translated into a density gradient with low quantum dot density in a certain region of the wafer. For the top quantum dot layer, separated from the bottom quantum dot layer by a 6 nm thick GaAs barrier, various InAs amounts were deposited without an In-gradient. In spite of the absence of an In-gradient, a pronounced density gradient is observed for the top quantum dots. Even for an In-amount slightly below the critical thickness for a single dot layer, a density gradient in the top quantum dot layer, which seems to reproduce the density gradient in the bottom layer, is observed. For more or less In, respectively, deviations from this behavior occur. We suggest that the obvious influence of the bottom quantum dot layer on the growth of the top quantum dots is due to the strain field induced by the buried dots.

  11. Contactless electroreflectance and photoluminescence of InAs quantum dots with GaInNAs barriers grown on GaAs substrate

    International Nuclear Information System (INIS)

    Motyka, M.; Kudrawiec, R.; Misiewicz, J.; Pucicki, D.; Tlaczala, M.; Fischer, M.; Marquardt, B.; Forchel, A.

    2007-01-01

    InAs quantum dots (QDs) with GaInNAs barriers grown on (001) GaAs substrate by molecular beam epitaxy have been studied by contactless electroreflectance (CER) and photoluminescence (PL) spectroscopies. It has been observed that the overgrowth of self-organized InAs QDs with GaInNAs layers effectively tunes the QD emission to the 1.3 μm spectral region. In case of PL spectra only one peak related to QD emission has been observed. In the case of CER spectra, in addition to a CER feature corresponding to the QD ground state, a rich spectrum of CER resonances related to optical transitions in InAs/GaInNAs/GaAs QW has been observed. It has been concluded that the application of GaInNAs instead InGaAs leads to better control of emission wavelength from InAs QDs since strains in GaInNAs can be tuned from compressive to tensile. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Thermal conductivity of InAs quantum dot stacks using AlAs strain compensating layers on InP substrate

    International Nuclear Information System (INIS)

    Salman, S.; Folliot, H.; Le Pouliquen, J.; Chevalier, N.; Rohel, T.; Paranthoën, C.; Bertru, N.; Labbé, C.; Letoublon, A.; Le Corre, A.

    2012-01-01

    Highlights: ► The thermal conductivity of InAs on InP (1 1 3)B quantum dots stacks is measured. ► The growth of a close stack of 100 layers of InAs using AlAs strain compensating layers is presented. ► New data on the thermal conductivity of InP n-doped susbtrate are given. - Abstract: The growth and thermal conductivity of InAs quantum dot (QD) stacks embedded in GaInAs matrix with AlAs compensating layers deposited on (1 1 3)B InP substrate are presented. The effect of the strain compensating AlAs layer is demonstrated through Atomic Force Microscopy (AFM) and X-ray diffraction structural analysis. The thermal conductivity (2.7 W/m K at 300 K) measured by the 3ω method reveals to be clearly reduced in comparison with a bulk InGaAs layer (5 W/m K). In addition, the thermal conductivity measurements of S doped InP substrates and the SiN insulating layer used in the 3ω method in the 20–200 °C range are also presented. An empirical law is proposed for the S doped InP substrate, which slightly differs from previously presented results.

  13. Formation of InAs/GaAs quantum dots from a subcritical InAs wetting layer: A reflection high-energy electron diffraction and theoretical study

    International Nuclear Information System (INIS)

    Song, H. Z.; Usuki, T.; Nakata, Y.; Yokoyama, N.; Sasakura, H.; Muto, S.

    2006-01-01

    InAs/GaAs quantum dots (QD's) are formed by postgrowth annealing of an InAs wetting layer thinner than the critical thickness for the transition from two- (2D) to three-dimensional (3D) growth mode. Reflection high energy electron diffraction is used to monitor the QD formation. Based on a mean-field theory [Phys. Rev. Lett. 79, 897 (1997)], the time evolution of total QD's volume, first increasing and finally saturating, is well explained by precursors forming during wetting layer growth and converting into nucleated QD's after growth stop. Both the saturation QD's volume and the QD nucleation rate depend exponentially on the InAs coverage. These behaviors and their temperature and InAs growth rate dependences are essentially understandable in the frame of the mean-field theory. Similar analysis to conventional QD growth suggests that the often observed significant mass transport from wetting layer to QD's can be ascribed to the precursors existing before 2D-3D growth mode transition

  14. Improvement of the optical quality of site-controlled InAs quantum dots by a double stack growth technique in wet-chemically etched holes

    Energy Technology Data Exchange (ETDEWEB)

    Pfau, Tino Johannes; Gushterov, Aleksander; Reithmaier, Johann-Peter [Technische Physik, INA, Universitaet Kassel (Germany); Cestier, Isabelle; Eisenstein, Gadi [Electrical Engineering Dept., Technion, Haifa (Israel); Linder, Evgany; Gershoni, David [Solid State Institute and Physics Dept., Technion, Haifa (Israel)

    2010-07-01

    The optimization of the wet-chemically etching of holes and a special MBE growth stack technique allows enlarging the site-control of low density InAs QDs on GaAs substrates up to a buffer layer thickness of 55 nm. The strain of InAs QDs, grown in the etched holes, reduces the hole closing, so that a pre-patterned surface is conserved for the second QD layer. The distance of 50 nm GaAs between the two QD layers exceeds drastically the maximum vertical alignment based on pure strain coupling (20 nm). Compared to stacks with several QD layers, this method avoids electronic coupling between the different QD layers and reduces the problems to distinguish the dots of different layers optically. Confocal microphotoluminescence reveals a significant diminution of the low temperature photoluminescence linewidth of the second InAs QD layer to an average value of 505{+-}53 {mu}eV and a minimum width of 460 {mu}eV compared to 2 to 4 meV for QDs grown on thin buffer layers. The increase of the buffer layer thickness decreases the influence of the surface defects caused by prepatterning.

  15. Effects of growth temperature and arsenic pressure on size distribution and density of InAs quantum dots on Si (001)

    International Nuclear Information System (INIS)

    Zhao, Z.M.; Hul'ko, O.; Kim, H.J.; Liu, J.; Shi, B.; Xie, Y.H.

    2005-01-01

    InAs self-assembled quantum dots (QDs) were grown on Si (001) substrates via molecular beam epitaxy. The size distribution and density of InAs QDs grown under different conditions were studied using plan-view transmission electron microscopy. Dot density was shown to strongly depend on arsenic beam equivalent pressure (BEP) ranging from 2.8x10 -5 to 1.2x10 -3 Pa. In contrast, dot density was nearly independent of substrate temperature from 295 to 410 deg. C under constant arsenic BEP, while broadening of size distribution was observed with increasing temperature. The mechanism accounting for some of the main features of the experimental observations is discussed. Finally, InAs quantum dots with optimized narrow size distribution and high density were grown at low arsenic BEP of 7.2 x10 -5 Pa and low temperature of 250 deg. C followed by annealing at arsenic BEP of 1.9 x10 -4 Pa and temperature of 410 deg. C

  16. Comparison of the reactivity of alkyl and alkyl amine precursors with native oxide GaAs(100) and InAs(100) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Henegar, A.J., E-mail: henegar1@umbc.edu; Gougousi, T., E-mail: gougousi@umbc.edu

    2016-12-30

    Graphical abstract: The interaction of the native oxides of GaAs(100) and InAs(100) with alkyl (trimethyl aluminum) and alkyl amine (tetrakis dimethylamino titanium) precursors during thermal atomic layer deposition (ALD) of Al{sub 2}O{sub 3} and TiO{sub 2} is compared. Al{sub 2}O{sub 3} if found to be a significantly better barrier against the transport of the surface native oxide during the film deposition as well as after post-deposition heat treatment. This superior blocking ability also limits the removal of the native oxides during the Al{sub 2}O{sub 3} ALD process. - Highlights: • Native oxide diffusion is required for continuous native oxide removal. • The diffusion barrier capabilities of Al{sub 2}O{sub 3} limits native oxide removal during ALD. • Arsenic oxide exhibits higher mobility from InAs compared to GaAs substrates. • Oxygen scavenging from the surface by trimethyl aluminum is confirmed. - Abstract: In this manuscript we compare the interaction of alkyl (trimethyl aluminum) and alkyl amine (tetrakis dimethylamino titanium) precursors during thermal atomic layer deposition with III-V native oxides. For that purpose we deposit Al{sub 2}O{sub 3} and TiO{sub 2}, using H{sub 2}O as the oxidizer, on GaAs(100) and InAs(100) native oxide surfaces. We find that there are distinct differences in the behavior of the two films. For the Al{sub 2}O{sub 3} ALD very little native oxide removal happens after the first few ALD cycles while the interaction of the alkyl amine precursor for TiO{sub 2} and the native oxides continues well after the surface has been covered with 2 nm of TiO{sub 2}. This difference is traced to the superior properties of Al{sub 2}O{sub 3} as a diffusion barrier. Differences are also found in the behavior of the arsenic oxides of the InAs and GaAs substrates. The arsenic oxides from the InAs surface are found to mix more efficiently in the growing dielectric film than those from the GaAs surface. This difference is attributed to

  17. Comparison of the reactivity of alkyl and alkyl amine precursors with native oxide GaAs(100) and InAs(100) surfaces

    International Nuclear Information System (INIS)

    Henegar, A.J.; Gougousi, T.

    2016-01-01

    Graphical abstract: The interaction of the native oxides of GaAs(100) and InAs(100) with alkyl (trimethyl aluminum) and alkyl amine (tetrakis dimethylamino titanium) precursors during thermal atomic layer deposition (ALD) of Al_2O_3 and TiO_2 is compared. Al_2O_3 if found to be a significantly better barrier against the transport of the surface native oxide during the film deposition as well as after post-deposition heat treatment. This superior blocking ability also limits the removal of the native oxides during the Al_2O_3 ALD process. - Highlights: • Native oxide diffusion is required for continuous native oxide removal. • The diffusion barrier capabilities of Al_2O_3 limits native oxide removal during ALD. • Arsenic oxide exhibits higher mobility from InAs compared to GaAs substrates. • Oxygen scavenging from the surface by trimethyl aluminum is confirmed. - Abstract: In this manuscript we compare the interaction of alkyl (trimethyl aluminum) and alkyl amine (tetrakis dimethylamino titanium) precursors during thermal atomic layer deposition with III-V native oxides. For that purpose we deposit Al_2O_3 and TiO_2, using H_2O as the oxidizer, on GaAs(100) and InAs(100) native oxide surfaces. We find that there are distinct differences in the behavior of the two films. For the Al_2O_3 ALD very little native oxide removal happens after the first few ALD cycles while the interaction of the alkyl amine precursor for TiO_2 and the native oxides continues well after the surface has been covered with 2 nm of TiO_2. This difference is traced to the superior properties of Al_2O_3 as a diffusion barrier. Differences are also found in the behavior of the arsenic oxides of the InAs and GaAs substrates. The arsenic oxides from the InAs surface are found to mix more efficiently in the growing dielectric film than those from the GaAs surface. This difference is attributed to lower native oxide stability as well as an initial diffusion path formation by the indium oxides.

  18. Correcting ligands, metabolites, and pathways

    Directory of Open Access Journals (Sweden)

    Vriend Gert

    2006-11-01

    Full Text Available Abstract Background A wide range of research areas in bioinformatics, molecular biology and medicinal chemistry require precise chemical structure information about molecules and reactions, e.g. drug design, ligand docking, metabolic network reconstruction, and systems biology. Most available databases, however, treat chemical structures more as illustrations than as a datafield in its own right. Lack of chemical accuracy impedes progress in the areas mentioned above. We present a database of metabolites called BioMeta that augments the existing pathway databases by explicitly assessing the validity, correctness, and completeness of chemical structure and reaction information. Description The main bulk of the data in BioMeta were obtained from the KEGG Ligand database. We developed a tool for chemical structure validation which assesses the chemical validity and stereochemical completeness of a molecule description. The validation tool was used to examine the compounds in BioMeta, showing that a relatively small number of compounds had an incorrect constitution (connectivity only, not considering stereochemistry and that a considerable number (about one third had incomplete or even incorrect stereochemistry. We made a large effort to correct the errors and to complete the structural descriptions. A total of 1468 structures were corrected and/or completed. We also established the reaction balance of the reactions in BioMeta and corrected 55% of the unbalanced (stoichiometrically incorrect reactions in an automatic procedure. The BioMeta database was implemented in PostgreSQL and provided with a web-based interface. Conclusion We demonstrate that the validation of metabolite structures and reactions is a feasible and worthwhile undertaking, and that the validation results can be used to trigger corrections and improvements to BioMeta, our metabolite database. BioMeta provides some tools for rational drug design, reaction searches, and

  19. Interaction and Cooperative Nucleation of InAsSbP Quantum Dots and Pits on InAs(100 Substrate

    Directory of Open Access Journals (Sweden)

    Gambaryan Karen

    2009-01-01

    Full Text Available Abstract An example of InAsSbP quaternary quantum dots (QDs, pits and dots–pits cooperative structures’ growth on InAs(100 substrates by liquid phase epitaxy (LPE is reported. The interaction and surface morphology of the dots–pits combinations are investigated by the high-resolution scanning electron microscope. Bimodal growth mechanism for the both QDs and pits nucleation is observed. Cooperative structures consist of the QDs banded by pits, as well as the “large” pits banded by the quantum wires are detected. The composition of the islands and the pits edges is found to be quaternary, enriched by antimony and phosphorus, respectively. This repartition is caused by dissociation of the wetting layer, followed by migration (surface diffusion of the Sb and P atoms in opposite directions. The “small” QDs average density ranges from 0.8 to 2 × 109 cm−2, with heights and widths dimensions from 2 to 20 nm and 5 to 45 nm, respectively. The average density of the “small” pits is equal to (6–10 × 109 cm−2 with dimensions of 5–40 nm in width and depth. Lifshits–Slezov-like distribution for the amount and surface density of both “small” QDs and pits versus their average diameter is experimentally detected. A displacement of the absorption edge toward the long wavelength region and enlargement toward the short wavelength region is detected by the Fourier transform infrared spectrometry.

  20. Role of Bruton's tyrosine kinase (BTK) in growth and metastasis of INA6 myeloma cells

    International Nuclear Information System (INIS)

    Bam, R; Venkateshaiah, S U; Khan, S; Ling, W; Randal, S S; Li, X; Zhang, Q; Rhee, F van; Barlogie, B; Epstein, J; Yaccoby, S

    2014-01-01

    Bruton's tyrosine kinase (BTK) and the chemokine receptor CXCR4 are linked in various hematologic malignancies. The aim of the study was to understand the role of BTK in myeloma cell growth and metastasis using the stably BTK knockdown luciferase-expressing INA6 myeloma line. BTK knockdown had reduced adhesion to stroma and migration of myeloma cells toward stromal cell-derived factor-1. BTK knockdown had no effect on short-term in vitro growth of myeloma cells, although clonogenicity was inhibited and myeloma cell growth was promoted in coculture with osteoclasts. In severe combined immunodeficient-rab mice with contralaterally implanted pieces of bones, BTK knockdown in myeloma cells promoted their proliferation and growth in the primary bone but suppressed metastasis to the contralateral bone. BTK knockdown myeloma cells had altered the expression of genes associated with adhesion and proliferation and increased mammalian target of rapamycin signaling. In 176 paired clinical samples, BTK and CXCR4 expression was lower in myeloma cells purified from a focal lesion than from a random site. BTK expression in random-site samples was correlated with proportions of myeloma cells expressing cell surface CXCR4. Our findings highlight intratumoral heterogeneity of myeloma cells in the bone marrow microenvironment and suggest that BTK is involved in determining proliferative, quiescent or metastatic phenotypes of myeloma cells

  1. Coherent Transport in a Linear Triple Quantum Dot Made from a Pure-Phase InAs Nanowire.

    Science.gov (United States)

    Wang, Ji-Yin; Huang, Shaoyun; Huang, Guang-Yao; Pan, Dong; Zhao, Jianhua; Xu, H Q

    2017-07-12

    A highly tunable linear triple quantum dot (TQD) device is realized in a single-crystalline pure-phase InAs nanowire using a local finger gate technique. The electrical measurements show that the charge stability diagram of the TQD can be represented by three kinds of current lines of different slopes and a simulation performed based on a capacitance matrix model confirms the experiment. We show that each current line observable in the charge stability diagram is associated with a case where a QD is on resonance with the Fermi level of the source and drain reservoirs. At a triple point where two current lines of different slopes move together but show anticrossing, two QDs are on resonance with the Fermi level of the reservoirs. We demonstrate that an energetically degenerated quadruple point at which all three QDs are on resonance with the Fermi level of the reservoirs can be built by moving two separated triple points together via sophistically tuning of energy levels in the three QDs. We also demonstrate the achievement of direct coherent electron transfer between the two remote QDs in the TQD, realizing a long-distance coherent quantum bus operation. Such a long-distance coherent coupling could be used to investigate coherent spin teleportation and superexchange effects and to construct a spin qubit with an improved long coherent time and with spin state detection solely by sensing the charge states.

  2. Study of the transport phenomena in III-V materials by the Monte Carlo method: application to INAS

    International Nuclear Information System (INIS)

    Bouazza, B.; Amer, L.; Guen-Bouazza, A.; Sayeh, C.; Chabanne-Sari, N.E.; Gontrand, C.

    2004-01-01

    Full text.The microelectronic comprehension of the phenomena which describes the behavior of the carriers in semiconductor materials requires the knowledge of energy distribution function. This distribution function is obtained by the resolution of Boltzmann equation which is very hard to solve analytically. Other methods based on modeling are actually successfully used to solve this equation. This Monte Carlo method is among of the most methods used for studying electronics components operations. It consists to follow the evolution of electron packets in real space, where each electron subjected to the electric field present in material goes interact with the crystal lattice. It is therefore an iterative process made up from a whole coasting flights stopped by acoustics interactions, polar and non polar optics, piezoelectric, inter-valley, impurity, ionization and surface. By applying this method to the III-V material: InAs. We can describe the behavior of the carriers from dynamic and energetic point of view (variation speed according to the field). The simulation is applied, taking into account variation of the carriers according to time in the non stationary mode, and the effect of temperature, and measurements doping. Results obtained are shown to be comparable to those of the theory

  3. Magnetoresistance engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates

    Science.gov (United States)

    Fábián, G.; Makk, P.; Madsen, M. H.; Nygârd, J.; Schönenberger, C.; Baumgartner, A.

    2016-11-01

    We present magnetoresistance (MR) experiments on an InAs nanowire quantum dot device with two ferromagnetic sidegates (FSGs) in a split-gate geometry. The wire segment can be electrically tuned to a single dot or to a double dot regime using the FSGs and a backgate. In both regimes we find a strong MR and a sharp MR switching of up to 25% at the field at which the magnetizations of the FSGs are inverted by the external field. The sign and amplitude of the MR and the MR switching can both be tuned electrically by the FSGs. In a double dot regime close to pinch-off we find two sharp transitions in the conductance, reminiscent of tunneling MR (TMR) between two ferromagnetic contacts, with one transition near zero and one at the FSG switching fields. These surprisingly rich characteristics we explain in several simple resonant tunneling models. For example, the TMR-like MR can be understood as a stray-field controlled transitions between singlet and triplet double dot states. Such local magnetic fields are the key elements in various proposals to engineer novel states of matter and may be used for testing electron spin based Bell inequalities.

  4. Autocrine signal transmission with extracellular ligand degradation

    International Nuclear Information System (INIS)

    Muratov, C B; Posta, F; Shvartsman, S Y

    2009-01-01

    Traveling waves of cell signaling in epithelial layers orchestrate a number of important processes in developing and adult tissues. These waves can be mediated by positive feedback autocrine loops, a mode of cell signaling where binding of a diffusible extracellular ligand to a cell surface receptor can lead to further ligand release. We formulate and analyze a biophysical model that accounts for ligand-induced ligand release, extracellular ligand diffusion and ligand–receptor interaction. We focus on the case when the main mode for ligand degradation is extracellular and analyze the problem with the sharp threshold positive feedback nonlinearity. We derive expressions that link the speed of propagation and other characteristics of traveling waves to the parameters of the biophysical processes, such as diffusion rates, receptor expression level, etc. Analyzing the derived expressions we found that traveling waves in such systems can exhibit a number of unusual properties, e.g. non-monotonic dependence of the speed of propagation on ligand diffusivity. Our results for the fully developed traveling fronts can be used to analyze wave initiation from localized perturbations, a scenario that frequently arises in the in vitro models of epithelial wound healing, and guide future modeling studies of cell communication in epithelial layers

  5. Radiation induced ligand loss from cobalt complexes

    International Nuclear Information System (INIS)

    Funston, A. M.; McFadyen, W.D.; Tregloan, P.A.

    2000-01-01

    Full text: Due to the rapid nature of ligand dissociation from cobalt(II) complexes the study of the rate of ligand dissociation necessitates the use of a technique such as pulse radiolysis. This allows the rapid reduction of the corresponding cobalt(III) complex by a reducing radical, such as the aquated electron, to form the cobalt(II) complex. However, to date, no systematic study of either the mechanism of reduction or the influence of the electronic structure on the rate of ligand dissociation has been carried out. In order to understand these processes more fully the mechanism of reduction of a range of related cobalt(III) complexes by the aquated electron and the subsequent rate of ligand dissociation from the resulting cobalt(II) complexes is being investigated. It has been found that a number of processes are observed following the initial rapid reaction of the cobalt(III) complex with the aquated electron. Ultimately ligand loss is observed. Depending upon the complex, the initial processes observed may include the formation of coordinated radicals and electron transfer within the complex. For complexes containing aromatic ligands such as 2,2'-bipyridine, 1,10-phenanthroline and dipyrido[3,2-a:2',3'-c]phenazine the formation of a coordinated radical is observed as the initial reduction step. The kinetics of ligand dissociation of these complexes has been determined. The loss of monodentate ligands is fast and has been indistinguishable from the reduction processes when aromatic ligands are also present in the complex. However, for diamine chelates and diimine chelates spectra of the transient species can be resolved

  6. Labeled receptor ligands for spect

    International Nuclear Information System (INIS)

    Kung, H.F.

    1989-01-01

    Receptor specific imaging agents for single photon emission computed tomography (SPECT) can potentially be useful in the understanding of basic biochemistry and pharmacology of receptors. SPECT images may also provide tools for evaluation of density and binding kinetics of a specific receptor, information important for diagnosis and patient management. Basic requirements for receptor imaging agents are: (a) they are labeled with short-lived isotopes, (b) they show high selectivity and specific uptake, (c) they exhibit high target/background ratio, and (d) they can be modeled to obtain quantitative information. Several good examples of CNS receptor specific ligands labeled with I-123 have been developed, including iodoQNB, iodoestrogen iodobenzadiazepine, iodobenazepine, iodobenzamides for muscarinic, estrogen benzadiazepine, D-1 and D-2 dopamine receptors. With the advent of newer and faster SPECT imaging devices, it may be feasible to quantitate the receptor density by in vivo imaging techniques. These new brain imaging agents can provide unique diagnostic information, which may not be available through other imaging modalities, such as CT and MRI

  7. A Versatile Dinucleating Ligand Containing Sulfonamide Groups

    DEFF Research Database (Denmark)

    Sundberg, Jonas; Witt, Hannes; Cameron, Lisa

    2014-01-01

    ligand can be prepared in aqueous solutions using only divalent metal ions. Two of the copper(II) complexes, [Cu2(psmp)(OH)] and [Cu2(psmp)(OAc)2]-, demonstrate the anticipated 1:2 ligand/metal stoichiometry and show that the dimetallic binding site created for exogenous ligands possesses high inherent...... of antiferromagnetic coupling. This is corroborated computationally by broken-symmetry density functional theory, which for isotropic modeling of the coupling predicts an antiferromagnetic coupling strength of J = 70.5 cm-1....

  8. Ligand based pharmacophore modelling of anticancer histone ...

    African Journals Online (AJOL)

    USER

    2010-06-21

    Jun 21, 2010 ... The study was carried out using the software Ligand Scout (version .... Computer Science, for his great help and support. We are also grateful to Faculty of Engineering and applied. Sciences, Mohammad .... Aided Mol. Design ...

  9. Synthesis and characterization β-ketoamine ligands

    Science.gov (United States)

    Zaid, Nurzati Amani Mohamed; Hassan, Nur Hasyareeda; Karim, Nurul Huda Abd

    2018-04-01

    β-ketoamine ligands are important members of heterodonor ligand because of their ease of preparation and modification of both steric and/or electronic effects. Complexes with β-ketoamine has received much less attention and there has been no study about this complex with β-ketoamine in ionic liquid reported. Two type of β-ketoamine ligands which are 4-amino-3-pentene-2-onato (A) and 3-amino-2-butenoic acid methyl ester (B) have been synthesized in this work. The resulting compound formed was characterized using standard spectroscopic and structural techniques which includes 1H and 13C, NMR spectroscopy and FTIR spectroscopy. The 1H and 13C NMR spectrum displayed all the expected signals with correct integration and multiplicity. And it is proved that there are some differences between two ligands as observed in NMR and FTIR spectrum.

  10. EGFR Activation by Spatially Restricted Ligands

    National Research Council Canada - National Science Library

    Clouse, Katherine N; Goodrich, Jennifer S

    2006-01-01

    ...) activity has been associated with an increased prognosis of breast cancer. During cogenesis in Drosophila melanogaster local Egfr activation by the spatially-restricted TGFalpha-like ligand Gurken (Grk...

  11. EGFR Activation by Spatially Restricted Ligands

    National Research Council Canada - National Science Library

    Goodrich, Jennifer S

    2005-01-01

    ...) activity has been associated with an increased prognosis of breast cancer. During oogenesis in Drosophila melanogaster, local EGFR activation by the spatially restricted TGF alpha-like ligand, Gurken (Grk...

  12. Cell-specific targeting by heterobivalent ligands.

    Science.gov (United States)

    Josan, Jatinder S; Handl, Heather L; Sankaranarayanan, Rajesh; Xu, Liping; Lynch, Ronald M; Vagner, Josef; Mash, Eugene A; Hruby, Victor J; Gillies, Robert J

    2011-07-20

    Current cancer therapies exploit either differential metabolism or targeting to specific individual gene products that are overexpressed in aberrant cells. The work described herein proposes an alternative approach--to specifically target combinations of cell-surface receptors using heteromultivalent ligands ("receptor combination approach"). As a proof-of-concept that functionally unrelated receptors can be noncovalently cross-linked with high avidity and specificity, a series of heterobivalent ligands (htBVLs) were constructed from analogues of the melanocortin peptide ligand ([Nle(4), dPhe(7)]-α-MSH) and the cholecystokinin peptide ligand (CCK-8). Binding of these ligands to cells expressing the human Melanocortin-4 receptor and the Cholecystokinin-2 receptor was analyzed. The MSH(7) and CCK(6) were tethered with linkers of varying rigidity and length, constructed from natural and/or synthetic building blocks. Modeling data suggest that a linker length of 20-50 Å is needed to simultaneously bind these two different G-protein coupled receptors (GPCRs). These ligands exhibited up to 24-fold enhancement in binding affinity to cells that expressed both (bivalent binding), compared to cells with only one (monovalent binding) of the cognate receptors. The htBVLs had up to 50-fold higher affinity than that of a monomeric CCK ligand, i.e., Ac-CCK(6)-NH(2). Cell-surface targeting of these two cell types with labeled heteromultivalent ligand demonstrated high avidity and specificity, thereby validating the receptor combination approach. This ability to noncovalently cross-link heterologous receptors and target individual cells using a receptor combination approach opens up new possibilities for specific cell targeting in vivo for therapy or imaging.

  13. Time-resolved x-ray diffraction measurements of high-density InAs quantum dots on Sb/GaAs layers and the suppression of coalescence by Sb-irradiated growth interruption

    International Nuclear Information System (INIS)

    Kakuda, Naoki; Yamaguchi, Koichi; Kaizu, Toshiyuki; Takahasi, Masamitu; Fujikawa, Seiji

    2010-01-01

    Self-assembly of high-density InAs quantum dots (QDs) on Sb-irradiated GaAs buffer layers was observed in-situ by a time-resolved X-ray diffraction (XRD) technique using a combination of XRD and molecular beam epitaxy. Evolution of dot height and lattice constant was analyzed during InAs QD growth and subsequent growth interruption (GI), and as a result, dislocated giant dots due to coalescence and coherent dots were separately evaluated. An Sb-irradiated GI (Sb-GI) method to be applied after InAs growth was attempted for the suppression of coalescence. Using this method, the XRD intensity of giant dots decreased, and the photoluminescence intensity of InAs QDs was enhanced. High-density InAs QDs without giant dots were produced by using the combination of the QD growth on the Sb-irradiated GaAs buffer layers and the Sb-GI. (author)

  14. Comparison between mini mental state examination (MMSE) and Montreal cognitive assessment Indonesian version (MoCA-Ina) as an early detection of cognitive impairments in post-stroke patients

    Science.gov (United States)

    Lestari, S.; Mistivani, I.; Rumende, C. M.; Kusumaningsih, W.

    2017-08-01

    Mild cognitive impairment (MCI) is defined as cognitive impairment that may never develop into dementia. Cognitive impairment is one long-term complication of a stroke. The Mini Mental State Examination (MMSE), which is commonly used as a screening tool for cognitive impairment, has a low sensitivity to detect cognitive impairment, especially MCI. Alternatively, the Montreal Cognitive Assessment Indonesian version (MoCA-Ina) has been reported to have a higher sensitivity than the MMSE. The aim of this study was to compare the proportion of MCI identified between the MMSE and MoCA-Ina in stroke patients. This was a cross-sectional study of stroke outpatients who attended the Polyclinic Neuromuscular Division, Rehabilitation Department, and Polyclinic Stroke, Neurology Department Cipto Mangunkusumo General Hospital, Jakarta. The proportion of MCI identified using the MMSE was 31.03% compared to 72.41% when using the MoCA-Ina. This difference was statistically significant (Fisher’s exact test, p = 0.033). The proportion of MCI in stroke patients was higher when using the MoCA-Ina compared to the MMSE. The MoCA-Ina should be used as an alternative in the early detection of MCI in stroke patients, especially those undergoing rehabilitation.

  15. Semiconductor Quantum Dots with Photoresponsive Ligands.

    Science.gov (United States)

    Sansalone, Lorenzo; Tang, Sicheng; Zhang, Yang; Thapaliya, Ek Raj; Raymo, Françisco M; Garcia-Amorós, Jaume

    2016-10-01

    Photochromic or photocaged ligands can be anchored to the outer shell of semiconductor quantum dots in order to control the photophysical properties of these inorganic nanocrystals with optical stimulations. One of the two interconvertible states of the photoresponsive ligands can be designed to accept either an electron or energy from the excited quantum dots and quench their luminescence. Under these conditions, the reversible transformations of photochromic ligands or the irreversible cleavage of photocaged counterparts translates into the possibility to switch luminescence with external control. As an alternative to regulating the photophysics of a quantum dot via the photochemistry of its ligands, the photochemistry of the latter can be controlled by relying on the photophysics of the former. The transfer of excitation energy from a quantum dot to a photocaged ligand populates the excited state of the species adsorbed on the nanocrystal to induce a photochemical reaction. This mechanism, in conjunction with the large two-photon absorption cross section of quantum dots, can be exploited to release nitric oxide or to generate singlet oxygen under near-infrared irradiation. Thus, the combination of semiconductor quantum dots and photoresponsive ligands offers the opportunity to assemble nanostructured constructs with specific functions on the basis of electron or energy transfer processes. The photoswitchable luminescence and ability to photoinduce the release of reactive chemicals, associated with the resulting systems, can be particularly valuable in biomedical research and can, ultimately, lead to the realization of imaging probes for diagnostic applications as well as to therapeutic agents for the treatment of cancer.

  16. Designer TGFβ superfamily ligands with diversified functionality.

    Directory of Open Access Journals (Sweden)

    George P Allendorph

    Full Text Available Transforming Growth Factor--beta (TGFβ superfamily ligands, including Activins, Growth and Differentiation Factors (GDFs, and Bone Morphogenetic Proteins (BMPs, are excellent targets for protein-based therapeutics because of their pervasiveness in numerous developmental and cellular processes. We developed a strategy termed RASCH (Random Assembly of Segmental Chimera and Heteromer, to engineer chemically-refoldable TGFβ superfamily ligands with unique signaling properties. One of these engineered ligands, AB208, created from Activin-βA and BMP-2 sequences, exhibits the refolding characteristics of BMP-2 while possessing Activin-like signaling attributes. Further, we find several additional ligands, AB204, AB211, and AB215, which initiate the intracellular Smad1-mediated signaling pathways more strongly than BMP-2 but show no sensitivity to the natural BMP antagonist Noggin unlike natural BMP-2. In another design, incorporation of a short N-terminal segment from BMP-2 was sufficient to enable chemical refolding of BMP-9, without which was never produced nor refolded. Our studies show that the RASCH strategy enables us to expand the functional repertoire of TGFβ superfamily ligands through development of novel chimeric TGFβ ligands with diverse biological and clinical values.

  17. LigandRFs: random forest ensemble to identify ligand-binding residues from sequence information alone

    KAUST Repository

    Chen, Peng

    2014-12-03

    Background Protein-ligand binding is important for some proteins to perform their functions. Protein-ligand binding sites are the residues of proteins that physically bind to ligands. Despite of the recent advances in computational prediction for protein-ligand binding sites, the state-of-the-art methods search for similar, known structures of the query and predict the binding sites based on the solved structures. However, such structural information is not commonly available. Results In this paper, we propose a sequence-based approach to identify protein-ligand binding residues. We propose a combination technique to reduce the effects of different sliding residue windows in the process of encoding input feature vectors. Moreover, due to the highly imbalanced samples between the ligand-binding sites and non ligand-binding sites, we construct several balanced data sets, for each of which a random forest (RF)-based classifier is trained. The ensemble of these RF classifiers forms a sequence-based protein-ligand binding site predictor. Conclusions Experimental results on CASP9 and CASP8 data sets demonstrate that our method compares favorably with the state-of-the-art protein-ligand binding site prediction methods.

  18. Characterization of free-standing InAs quantum membranes by standing wave hard x-ray photoemission spectroscopy

    Science.gov (United States)

    Conti, G.; Nemšák, S.; Kuo, C.-T.; Gehlmann, M.; Conlon, C.; Keqi, A.; Rattanachata, A.; Karslıoǧlu, O.; Mueller, J.; Sethian, J.; Bluhm, H.; Rault, J. E.; Rueff, J. P.; Fang, H.; Javey, A.; Fadley, C. S.

    2018-05-01

    Free-standing nanoribbons of InAs quantum membranes (QMs) transferred onto a (Si/Mo) multilayer mirror substrate are characterized by hard x-ray photoemission spectroscopy (HXPS) and by standing-wave HXPS (SW-HXPS). Information on the chemical composition and on the chemical states of the elements within the nanoribbons was obtained by HXPS and on the quantitative depth profiles by SW-HXPS. By comparing the experimental SW-HXPS rocking curves to x-ray optical calculations, the chemical depth profile of the InAs(QM) and its interfaces were quantitatively derived with ångström precision. We determined that (i) the exposure to air induced the formation of an InAsO4 layer on top of the stoichiometric InAs(QM); (ii) the top interface between the air-side InAsO4 and the InAs(QM) is not sharp, indicating that interdiffusion occurs between these two layers; (iii) the bottom interface between the InAs(QM) and the native oxide SiO2 on top of the (Si/Mo) substrate is abrupt. In addition, the valence band offset (VBO) between the InAs(QM) and the SiO2/(Si/Mo) substrate was determined by HXPS. The value of VBO = 0.2 ± 0.04 eV is in good agreement with literature results obtained by electrical characterization, giving a clear indication of the formation of a well-defined and abrupt InAs/SiO2 heterojunction. We have demonstrated that HXPS and SW-HXPS are non-destructive, powerful methods for characterizing interfaces and for providing chemical depth profiles of nanostructures, quantum membranes, and 2D layered materials.

  19. Characterization of free-standing InAs quantum membranes by standing wave hard x-ray photoemission spectroscopy

    Directory of Open Access Journals (Sweden)

    G. Conti

    2018-05-01

    Full Text Available Free-standing nanoribbons of InAs quantum membranes (QMs transferred onto a (Si/Mo multilayer mirror substrate are characterized by hard x-ray photoemission spectroscopy (HXPS and by standing-wave HXPS (SW-HXPS. Information on the chemical composition and on the chemical states of the elements within the nanoribbons was obtained by HXPS and on the quantitative depth profiles by SW-HXPS. By comparing the experimental SW-HXPS rocking curves to x-ray optical calculations, the chemical depth profile of the InAs(QM and its interfaces were quantitatively derived with ångström precision. We determined that (i the exposure to air induced the formation of an InAsO4 layer on top of the stoichiometric InAs(QM; (ii the top interface between the air-side InAsO4 and the InAs(QM is not sharp, indicating that interdiffusion occurs between these two layers; (iii the bottom interface between the InAs(QM and the native oxide SiO2 on top of the (Si/Mo substrate is abrupt. In addition, the valence band offset (VBO between the InAs(QM and the SiO2/(Si/Mo substrate was determined by HXPS. The value of VBO = 0.2 ± 0.04 eV is in good agreement with literature results obtained by electrical characterization, giving a clear indication of the formation of a well-defined and abrupt InAs/SiO2 heterojunction. We have demonstrated that HXPS and SW-HXPS are non-destructive, powerful methods for characterizing interfaces and for providing chemical depth profiles of nanostructures, quantum membranes, and 2D layered materials.

  20. [Exposure to benzene and hematologic changes in workers at the Ina-Oki Drnisplast factory in Drnis].

    Science.gov (United States)

    Mikulandra, O; Cala, D; Marković, V; Zorić, A

    1993-12-01

    In the summer of 1984 workers in the "INA-OKI Drnisplast" factory frequently complained about headaches, weight loss and irregular menstrual cycles. According to the factory engineers that might have been due to an altered composition of the paints and glues that were used in the manufacturing process that year. Those had been found to lack specifications of chemical composition. Experts from the Institute for the Safety at Work from Zagreb were called in to perform measurements of organic solvents content in the workroom air. Benzene concentrations were found to be up to five times higher than the maximum permissible levels, those of toluene up to three times and of cyclohexane up to ten times higher. The polluted part of the factory was closed down, changes were introduced into the working process (use of paints was stopped, only glues without benzene content were allowed and proper ventilation was installed) and all the workers, twenty in all, received medical treatment. After three months the working process was resumed. In 1989 all the twenty workers underwent a control medical examination. All showed signs of recovery, both objective and subjective. Their blood tests values were within normal range. All the workers continued working, save one who retired in 1988 upon recommendation of a disability commission. The cause of disablement was occupational disease--benzene poisoning. On the basis of this experience emphasis is placed on the importance, in working with benzene, of complying with the Legislation on working capacity assessment for jobs requiring special working conditions and with the Safety at work act.

  1. Emission and elastic strain in InGaAs/GaAs quantum wells with embedded InAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Vega-Macotela, L.G.; Polupan, G. [ESIME - Instituto Politecnico Nacional, Mexico D.F. 07738 (Mexico); Shcherbyna, Ye. [National Technical University-' ' KPI' ' , Kiev 03057 (Ukraine)

    2012-07-15

    Photoluminescence (PL) spectra have been studied in the symmetric GaAs/In{sub 0.15}Ga{sub 0.85}As/GaAs quantum wells (QWs) with embedded InAs quantum dots (QDs), grown at different temperatures from the range 470-535 C. The increase of QD growth temperature is accompanied by decreasing the QD surface density and the enlargement of QD lateral diameters. Simultaneously the variation of the PL intensity and PL peak positions none monotonously have been detected. To understand the reason of the variation of PL intensity and peak positions the PL temperature dependences and the X-ray diffraction (XRD) at low angles (1.75-1.92 ) have been studied. The fitting procedure is applied to analysis the temperature shift of PL peak positions. Fitting has been done on the base of empirical expression for the band gap shrinkage that uses the Einstein temperature parameter. The character non monotonous for the Ga/In inter diffusion versus QD growth temperatures has been revealed. The XRD study has detected the high intensity peaks that corresponds to the diffraction of X-ray beam from the (311) crystal planes in GaAs QWs. The position of XRD peaks in the structures with QD grown at 490-510 C is very close to the angles related to the diffraction from (311) planes in the bulk GaAs. In QD structures with QD grown at 470 and 525-535 C the (311) XRD peaks shift to the higher diffraction angles that testifies on the essential compressive strains in these structures. The reason of the variation non monotonously of elastic strain versus QD densities has been discussed (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Synthesis and characterization of mixed ligand chiral nanoclusters

    KAUST Repository

    Guven, Zekiye P.

    2016-06-22

    Chiral mixed ligand silver nanoclusters were synthesized in the presence of a chiral and an achiral ligand. While the chiral ligand led mostly to the formation of nanoparticles, the presence of the achiral ligand drastically increased the yield of nanoclusters with enhanced chiral properties. © 2016 The Royal Society of Chemistry.

  3. Synthesis and characterization of mixed ligand chiral nanoclusters

    KAUST Repository

    Guven, Zekiye P.; Ustbas, Burcin; Harkness, Kellen M.; Coskun, Hikmet; Joshi, Chakra Prasad; Besong, Tabot M.D.; Stellacci, Francesco; Bakr, Osman; Akbulut, Ozge

    2016-01-01

    Chiral mixed ligand silver nanoclusters were synthesized in the presence of a chiral and an achiral ligand. While the chiral ligand led mostly to the formation of nanoparticles, the presence of the achiral ligand drastically increased the yield of nanoclusters with enhanced chiral properties. © 2016 The Royal Society of Chemistry.

  4. Impact of protein and ligand impurities on ITC-derived protein-ligand thermodynamics.

    Science.gov (United States)

    Grüner, Stefan; Neeb, Manuel; Barandun, Luzi Jakob; Sielaff, Frank; Hohn, Christoph; Kojima, Shun; Steinmetzer, Torsten; Diederich, François; Klebe, Gerhard

    2014-09-01

    The thermodynamic characterization of protein-ligand interactions by isothermal titration calorimetry (ITC) is a powerful tool in drug design, giving valuable insight into the interaction driving forces. ITC is thought to require protein and ligand solutions of high quality, meaning both the absence of contaminants as well as accurately determined concentrations. Ligands synthesized to deviating purity and protein of different pureness were titrated by ITC. Data curation was attempted also considering information from analytical techniques to correct stoichiometry. We used trypsin and tRNA-guanine transglycosylase (TGT), together with high affinity ligands to investigate the effect of errors in protein concentration as well as the impact of ligand impurities on the apparent thermodynamics. We found that errors in protein concentration did not change the thermodynamic properties obtained significantly. However, most ligand impurities led to pronounced changes in binding enthalpy. If protein binding of the respective impurity is not expected, the actual ligand concentration was corrected for and the thus revised data compared to thermodynamic properties obtained with the respective pure ligand. Even in these cases, we observed differences in binding enthalpy of about 4kJ⋅mol(-1), which is considered significant. Our results indicate that ligand purity is the critical parameter to monitor if accurate thermodynamic data of a protein-ligand complex are to be recorded. Furthermore, artificially changing fitting parameters to obtain a sound interaction stoichiometry in the presence of uncharacterized ligand impurities may lead to thermodynamic parameters significantly deviating from the accurate thermodynamic signature. Copyright © 2014 Elsevier B.V. All rights reserved.

  5. Adsorbed layers on (111)InAs faces in contact with In-As-Cl-H gas phase, and the possibility of phase transitions in the adsorbed layers

    Science.gov (United States)

    Chernov, A. A.; Ruzaikin, M. P.

    1981-04-01

    Adsorption of various species existing in the In-As-Cl-H CVD gaseous system on both InAs (111) faces is considered. Arsenic is supposed to be adsorbed in the form of triangles As 3 and tetrahedrons As 4, each of them occupying 3 atomic sites above In or As atoms on (111)In or (111)As, respectively. The system of polyatomic adsorption equations was used to find the coverages of the faces by various species. Admolecule-surface bond strengths are taken to be equal to the ones for the single bonds in molecules. Pauling electronegativities were used to find the effective charges of the atoms in the adsorption layer. Thus, the dipole moments of adsorbed molecules which arise are directed along the In-As bonds in the InAs lattice. With this geometry, the calculated electrostatic dipole-dipole attraction between InCl molecules forming a dense layer on (111)As exceeds 12 kcal/mol. Thus, condensation of the two-dimensional gas of adsorbed InCl molecules should be expected. Corresponding S-shape isotherms θ( P) are calculated for different As 3 vapor pressures, θ and P being the surface coverage and bulk vapor pressure of InCl. Intervals of {InCl 3}/{H 2} ratios at different temperatures where the two-dimensional condensation may occur, are presented for realistic CVD conditions. Two-dimensional condensation may result in sharp changes in kinetic coefficient and thus in autho-oscillations in growth rate and doping level creating periodic superstructures. Nucleation and CVD growth processes are discussed.

  6. ANALYSIS OF INA-CBG’S FARE AND GOVERNOR REGULATION FAREON SURGERY AT INPATIENT ROOM OF UNDATA REGIONAL PUBLIC HOSPITAL IN PALU

    Directory of Open Access Journals (Sweden)

    Muh. Ryman Napirah

    2016-03-01

    Full Text Available Aim: In order to determine the fares of surgery, there are two types of fares used by hospitals namely Indonesian Case Based Groups fare (INA-CBG s and Governor Regulation fare. This study aimed to identify and analyze both types of fares in orthopedic surgery, general, eyes, midwifery, mouth, ENT, urology at inpatient room of Undata Regional Public Hospital in Palu during year 2014. Method: This was a quantitative study with descriptive approach with 46 cases as the number of surgery. Data were collected through observation and analysis of secondary data were gotten from medical record, pharmaceutical installation of IBS/IDR, inpatient therapy room (Matahari, Aster, and Teratai pavilions and cashier of inpatient room in form of cost details and patient data from January to December 2014. Data Presentation was formed on tables, where the existing fares are grouped based on the component of each cost then summed and calculated the deviation between the two types of fares. Results: This study indicated that orthopedic surgery with deviation of Rp 11.311.365, general surgery with deviation of Rp 6.438.409, eyes surgery with deviation of Rp 45.173.741, midwifery surgery with deviation of Rp 6.645.765, oral surgery with deviation of Rp 6.105.659, and urological surgery with deviation of Rp. 3.809.959. Conclusion: It can be concluded that INA-CBG's fares are higher than Governor Regulation fares except orthopedic surgery, where the Governor Regulation faresare higher than INA-CBG’s fares.

  7. Expression of nociceptive ligands in canine osteosarcoma.

    Science.gov (United States)

    Shor, S; Fadl-Alla, B A; Pondenis, H C; Zhang, X; Wycislo, K L; Lezmi, S; Fan, T M

    2015-01-01

    Canine osteosarcoma (OS) is associated with localized pain as a result of tissue injury from tumor infiltration and peritumoral inflammation. Malignant bone pain is caused by stimulation of peripheral pain receptors, termed nociceptors, which reside in the localized tumor microenvironment, including the periosteal and intramedullary bone cavities. Several nociceptive ligands have been determined to participate directly or indirectly in generating bone pain associated with diverse skeletal abnormalities. Canine OS cells actively produce nociceptive ligands with the capacity to directly or indirectly activate peripheral pain receptors residing in the bone tumor microenvironment. Ten dogs with appendicular OS. Expression of nerve growth factor, endothelin-1, and microsomal prostaglandin E synthase-1 was characterized in OS cell lines and naturally occurring OS samples. In 10 dogs with OS, circulating concentrations of nociceptive ligands were quantified and correlated with subjective pain scores and tumor volume in patients treated with standardized palliative therapies. Canine OS cells express and secrete nerve growth factor, endothelin-1, and prostaglandin E2. Naturally occurring OS samples uniformly express nociceptive ligands. In a subset of OS-bearing dogs, circulating nociceptive ligand concentrations were detectable but failed to correlate with pain status. Localized foci of nerve terminal proliferation were identified in a minority of primary bone tumor samples. Canine OS cells express nociceptive ligands, potentially permitting active participation of OS cells in the generation of malignant bone pain. Specific inhibitors of nociceptive ligand signaling pathways might improve pain control in dogs with OS. Copyright © 2015 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of American College of Veterinary Internal Medicine.

  8. InAs0.45P0.55/InP strained multiple quantum wells intermixed by inductively coupled plasma etching

    International Nuclear Information System (INIS)

    Cao, Meng; Wu, Hui-Zhen; Lao, Yan-Feng; Cao, Chun-Fang; Liu, Cheng

    2009-01-01

    The intermixing effect on InAs 0.45 P 0.55 /InP strained multiple quantum wells (SMQWs) by inductively coupled plasma (ICP) etching and rapid thermal annealing (RTA) is investigated. Experiments show that the process of ICP etching followed RTA induces the blue shift of low temperature photoluminescence (PL) peaks of QWs. With increasing etching depth, the PL intensities are firstly enhanced and then diminished. This phenomenon is attributed to the variation of surface roughness and microstructure transformation inside the QW structure during ICP processing.

  9. GaAsSb-capped InAs QD type-II solar cell structures improvement by composition profiling of layers surrounding QD

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Vyskočil, Jan; Zíková, Markéta; Oswald, Jiří; Pangrác, Jiří; Petříček, Otto

    2017-01-01

    Roč. 4, č. 2 (2017), s. 1-8, č. článku 025502. ISSN 2053-1591 R&D Projects: GA ČR(CZ) GP14-21285P; GA MŠk(CZ) LO1603 Institutional support: RVO:68378271 Keywords : GaAsSb * InAs * InGaAs * quantum dot * solar cells * MOVPE Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.068, year: 2016

  10. Photoreflectance study of InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Dhifallah, I., E-mail: ines.dhifallah@gmail.co [Laboratoire de Photovoltaique, des Semiconducteurs et des Nanostructures, Centre de Recherche et des Technologies de l' energie, BP 95 Hammam-Lif 2050 (Tunisia); Daoudi, M.; Bardaoui, A. [Laboratoire de Photovoltaique, des Semiconducteurs et des Nanostructures, Centre de Recherche et des Technologies de l' energie, BP 95 Hammam-Lif 2050 (Tunisia); Eljani, B. [Unite de recherche sur les Hetero-Epitaxie et Applications, Faculte des Sciences de Monastir (Tunisia); Ouerghi, A. [Laboratoire de Photonique et de Nanostructures, CNRS Route de Nozay 91 46a0, Marcoussis (France); Chtourou, R. [Laboratoire de Photovoltaique, des Semiconducteurs et des Nanostructures, Centre de Recherche et des Technologies de l' energie, BP 95 Hammam-Lif 2050 (Tunisia)

    2011-05-15

    Photoreflectance and photoluminescence studies were performed to characterize InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs high electron mobility transistors. These structures were grown by Molecular Beam Epitaxy on (1 0 0) oriented GaAs substrates with different silicon-delta-doped layer densities. Interband energy transitions in the InAs ultrathin layer quantum well were observed below the GaAs band gap in the photoreflectance spectra, and assigned to electron-heavy-hole (E{sub e-hh}) and electron-light-hole (E{sub e-lh}) fundamental transitions. These transitions were shifted to lower energy with increasing silicon-{delta}-doping density. This effect is in good agreement with our theoretical results based on a self-consistent solution of the coupled Schroedinger and Poisson equations and was explained by increased escape of photogenerated carriers and enhanced Quantum Confined Stark Effect in the Si-delta-doped InAs/GaAs QW. In the photoreflectance spectra, not only the channel well interband energy transitions were observed, but also features associated with the GaAs and AlGaAs bulk layers located at about 1.427 and 1.8 eV, respectively. By analyzing the Franz-Keldysh Oscillations observed in the spectral characteristics of Si-{delta}-doped samples, we have determined the internal electric field introduced by ionized Si-{delta}-doped centers. We have observed an increase in the electric field in the InAs ultrathin layer with increasing silicon content. The results are explained in terms of doping dependent ionized impurities densities and surface charges. - Research highlights: {yields} Studying HEMTs structures with different silicon doping content. {yields} An increase of the electric field in the InAs layer with increasing Si content. {yields} The interband energy transitions in the HEMTs structures have been obtained from PR. {yields} Experimental and theoretical values of transitions energies were in good agreement.

  11. Structural Disorder in Colloidal InAs and CdSe Nanocrystals Observed by X-Ray Absorption Near-Edge Spectroscopy

    International Nuclear Information System (INIS)

    Hamad, K.S.; Hamad, K.S.; Roth, R.; Roth, R.; Rockenberger, J.; Rockenberger, J.; Alivisatos, A.P.; Alivisatos, A.P.; Buuren, T. van

    1999-01-01

    We report the observation of size dependent structural disorder by x-ray absorption near-edge spectroscopy (XANES) in InAs and CdSe nanocrystals 17 - 80 Angstrom in diameter. XANES of the In and Cd M 4,5 edges yields features that are sharp for the bulk solid but broaden considerably as the size of the particle decreases. FEFF7 multiple-scattering simulations reproduce the size dependent broadening of the spectra if a bulklike surface reconstruction of a spherical nanocrystal model is included. This illustrates that XANES is sensitive to the structure of the entire nanocrystal including the surface. copyright 1999 The American Physical Society

  12. Cave bear (Ursus spelaeus Rosenmüller & Heinroth males' den from Velika Pećina in Duboka Near Kučevo, Eastern Serbia

    Directory of Open Access Journals (Sweden)

    Dimitrijević Vesna M.

    2002-01-01

    Full Text Available More a 100 years after the first research in the cave Velika pećina in Duboka near Kučevo cave bear remains were discovered in a small chamber cut off from the passable channels by a 7 m high slope. A whole skull, bones of a forearm in articulation, and other skeleton parts were laying on the cave floor encrusted in travertine cover and in some places overgrown by stalagmites. Bones belonged to adult males, which found there the shelter to hibernate, in a short epizode that ended by closing the channels that once linked this part of the cave to a surface.

  13. Influência da heparina sódica na ocorrência de laminite eqüina induzida por sobrecarga de carboidratos

    OpenAIRE

    Martins Filho,L.P.; Fagliari,J.J.; Moraes,J.R.E.; Sampaio,R.C.; Oliveira,J.A.; Lacerda Neto,J.C.

    2008-01-01

    Avaliou-se a eficiência da infusão intravenosa de heparina sódica (100UI/kg/8h, a partir de 24h após o fornecimento de carboidrato, até completar 48h) no controle da laminite eqüina experimentalmente induzida por sobrecarga de carboidrato (17,6g de amido de milho/kg de peso corpóreo). Foram utilizados 15 eqüinos adultos, distribuídos em três grupos experimentais: GI (grupo-controle); GII (grupo laminite) e GIII (grupo laminite+heparina). Posteriormente ao fornecimento de carboidrato, os anima...

  14. Magnetic-field-induced Fermi-edge singularity in the tunneling current through an InAs self-assembled quantum dot

    International Nuclear Information System (INIS)

    Khanin, Yu. N.; Vdovin, E. E.; Eaves, L.; Larkin, I. A.; Patane, A.; Makarovskii, O. N.; Henini, M.

    2007-01-01

    The results of the investigation of tunneling transport through a GaAs/(AlGa)As/GaAs single-barrier heterostructure containing InAs self-assembled quantum dots at low temperatures are reported. An anomalous increase in the tunneling current through the quantum dots has been observed in the presence of a magnetic field both parallel and perpendicular to the current. This increase is a manifestation of a Fermi-edge singularity appearing in the current due to the interaction of a tunneling electron with the electron gas in an emitter

  15. Characterization of highly stacked InAs quantum dot layers on InP substrate for a planar saturable absorber at 1.5 μm band

    International Nuclear Information System (INIS)

    Inoue, Jun; Akahane, Kouichi; Yamamoto, Naokatsu; Isu, Toshiro; Tsuchiya, Masahiro

    2006-01-01

    We examined the absorption saturation properties in the 1.5 μm band of novel highly stacked InAs quantum dot layers. The transmission change at vertical incidence based on the saturable absorption of the quantum dots was more than 1%. This value is as large as the reflection changes of previously reported 1-μm-band quantum dot saturable absorber with interference enhancement. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Immobilisation of ligands by radio-derivatized polymers; Immobilisering av ligander med radioderiverte polymerer

    Energy Technology Data Exchange (ETDEWEB)

    Varga, J.M.; Fritsch, P.

    1995-01-30

    The invention relates to radio-derivatized polymers and a method of producing them by contacting non-polymerizable conjugands with radiolysable polymers in the presence of irradiation. The resulting radio-derivatized polymers can be further linked with ligand of organic or inorganic nature to immobilize such ligands. 2 figs., 5 tabs.

  17. A General Ligand Design for Gold Catalysis allowing Ligand-Directed Anti Nucleophilic Attack of Alkynes

    Science.gov (United States)

    Wang, Yanzhao; Wang, Zhixun; Li, Yuxue; Wu, Gongde; Cao, Zheng; Zhang, Liming

    2014-01-01

    Most homogenous gold catalyses demand ≥0.5 mol % catalyst loading. Due to the high cost of gold, these reactions are unlikely to be applicable in medium or large scale applications. Here we disclose a novel ligand design based on the privileged biphenyl-2-phosphine framework that offers a potentially general approach to dramatically lowering catalyst loading. In this design, an amide group at the 3’ position of the ligand framework directs and promotes nucleophilic attack at the ligand gold complex-activated alkyne, which is unprecedented in homogeneous gold catalysis considering the spatial challenge of using ligand to reach antiapproaching nucleophile in a linear P-Au-alkyne centroid structure. With such a ligand, the gold(I) complex becomes highly efficient in catalyzing acid addition to alkynes, with a turnover number up to 99,000. Density functional theory calculations support the role of the amide moiety in directing the attack of carboxylic acid via hydrogen bonding. PMID:24704803

  18. A new class of PN3-pincer ligands for metal–ligand cooperative catalysis

    KAUST Repository

    Li, Huaifeng

    2014-12-01

    Work on a new class of PN3-pincer ligands for metal-ligand cooperative catalysis is reviewed. While the field of the pyridine-based PN3-transition metal pincer complexes is still relatively young, many important applications of these complexes have already emerged. In several cases, the PN3-pincer complexes for metal-ligand cooperative catalysis result in significantly improved or unprecedented activities. The synthesis and coordination chemistry of PN3-pincer ligands are briefly summarized first to cover the synthetic routes for their preparation, followed by a focus review on their applications in catalysis. A specific emphasis is placed on the later section about the role of PN3-pincer ligands\\' dearomatization-rearomatization steps during the catalytic cycles. The mechanistic insights from density functional theory (DFT) calculations are also discussed.

  19. A new class of PN3-pincer ligands for metal–ligand cooperative catalysis

    KAUST Repository

    Li, Huaifeng; Zheng, Bin; Huang, Kuo-Wei

    2014-01-01

    Work on a new class of PN3-pincer ligands for metal-ligand cooperative catalysis is reviewed. While the field of the pyridine-based PN3-transition metal pincer complexes is still relatively young, many important applications of these complexes have already emerged. In several cases, the PN3-pincer complexes for metal-ligand cooperative catalysis result in significantly improved or unprecedented activities. The synthesis and coordination chemistry of PN3-pincer ligands are briefly summarized first to cover the synthetic routes for their preparation, followed by a focus review on their applications in catalysis. A specific emphasis is placed on the later section about the role of PN3-pincer ligands' dearomatization-rearomatization steps during the catalytic cycles. The mechanistic insights from density functional theory (DFT) calculations are also discussed.

  20. Effects of PPARγ ligands on vascular tone.

    Science.gov (United States)

    Salomone, Salvatore; Drago, Filippo

    2012-06-01

    Peroxisome Proliferator-Activated Receptor γ (PPARγ), originally described as a transcription factor for genes of carbohydrate and lipid metabolism, has been more recently studied in the context of cardiovascular pathophysiology. Here, we review the available data on PPARγ ligands as modulator of vascular tone. PPARγ ligands include: thiazolidinediones (used in the treatment of type 2 diabetes mellitus), glitazars (bind and activate both PPARγ and PPARα), and other experimental drugs (still in development) that exploit the chemistry of thiazolidinediones as a scaffold for PPARγ-independent pharmacological properties. In this review, we examine both short (mostly from in vitro data)- and long (mostly from in vivo data)-term effects of PPARγ ligands that extend from PPARγ-independent vascular effects to PPARγ-dependent gene expression. Because endothelium is a master regulator of vascular tone, we have attempted to differentiate between endothelium-dependent and endothelium-independent effects of PPARγ ligands. Based on available data, we conclude that PPARγ ligands appear to influence vascular tone in different experimental paradigms, most often in terms of vasodilatation (potentially increasing blood flow to some tissues). These effects on vascular tone, although potentially beneficial, must be weighed against specific cardiovascular warnings that may apply to some drugs, such as rosiglitazone.

  1. LIBRA: LIgand Binding site Recognition Application.

    Science.gov (United States)

    Hung, Le Viet; Caprari, Silvia; Bizai, Massimiliano; Toti, Daniele; Polticelli, Fabio

    2015-12-15

    In recent years, structural genomics and ab initio molecular modeling activities are leading to the availability of a large number of structural models of proteins whose biochemical function is not known. The aim of this study was the development of a novel software tool that, given a protein's structural model, predicts the presence and identity of active sites and/or ligand binding sites. The algorithm implemented by ligand binding site recognition application (LIBRA) is based on a graph theory approach to find the largest subset of similar residues between an input protein and a collection of known functional sites. The algorithm makes use of two predefined databases for active sites and ligand binding sites, respectively, derived from the Catalytic Site Atlas and the Protein Data Bank. Tests indicate that LIBRA is able to identify the correct binding/active site in 90% of the cases analyzed, 90% of which feature the identified site as ranking first. As far as ligand binding site recognition is concerned, LIBRA outperforms other structure-based ligand binding sites detection tools with which it has been compared. The application, developed in Java SE 7 with a Swing GUI embedding a JMol applet, can be run on any OS equipped with a suitable Java Virtual Machine (JVM), and is available at the following URL: http://www.computationalbiology.it/software/LIBRAv1.zip. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

  2. Dockomatic - automated ligand creation and docking.

    Science.gov (United States)

    Bullock, Casey W; Jacob, Reed B; McDougal, Owen M; Hampikian, Greg; Andersen, Tim

    2010-11-08

    The application of computational modeling to rationally design drugs and characterize macro biomolecular receptors has proven increasingly useful due to the accessibility of computing clusters and clouds. AutoDock is a well-known and powerful software program used to model ligand to receptor binding interactions. In its current version, AutoDock requires significant amounts of user time to setup and run jobs, and collect results. This paper presents DockoMatic, a user friendly Graphical User Interface (GUI) application that eases and automates the creation and management of AutoDock jobs for high throughput screening of ligand to receptor interactions. DockoMatic allows the user to invoke and manage AutoDock jobs on a single computer or cluster, including jobs for evaluating secondary ligand interactions. It also automates the process of collecting, summarizing, and viewing results. In addition, DockoMatic automates creation of peptide ligand .pdb files from strings of single-letter amino acid abbreviations. DockoMatic significantly reduces the complexity of managing multiple AutoDock jobs by facilitating ligand and AutoDock job creation and management.

  3. Dockomatic - automated ligand creation and docking

    Directory of Open Access Journals (Sweden)

    Hampikian Greg

    2010-11-01

    Full Text Available Abstract Background The application of computational modeling to rationally design drugs and characterize macro biomolecular receptors has proven increasingly useful due to the accessibility of computing clusters and clouds. AutoDock is a well-known and powerful software program used to model ligand to receptor binding interactions. In its current version, AutoDock requires significant amounts of user time to setup and run jobs, and collect results. This paper presents DockoMatic, a user friendly Graphical User Interface (GUI application that eases and automates the creation and management of AutoDock jobs for high throughput screening of ligand to receptor interactions. Results DockoMatic allows the user to invoke and manage AutoDock jobs on a single computer or cluster, including jobs for evaluating secondary ligand interactions. It also automates the process of collecting, summarizing, and viewing results. In addition, DockoMatic automates creation of peptide ligand .pdb files from strings of single-letter amino acid abbreviations. Conclusions DockoMatic significantly reduces the complexity of managing multiple AutoDock jobs by facilitating ligand and AutoDock job creation and management.

  4. Ligand identification using electron-density map correlations

    International Nuclear Information System (INIS)

    Terwilliger, Thomas C.; Adams, Paul D.; Moriarty, Nigel W.; Cohn, Judith D.

    2007-01-01

    An automated ligand-fitting procedure is applied to (F o − F c )exp(iϕ c ) difference density for 200 commonly found ligands from macromolecular structures in the Protein Data Bank to identify ligands from density maps. A procedure for the identification of ligands bound in crystal structures of macromolecules is described. Two characteristics of the density corresponding to a ligand are used in the identification procedure. One is the correlation of the ligand density with each of a set of test ligands after optimization of the fit of that ligand to the density. The other is the correlation of a fingerprint of the density with the fingerprint of model density for each possible ligand. The fingerprints consist of an ordered list of correlations of each the test ligands with the density. The two characteristics are scored using a Z-score approach in which the correlations are normalized to the mean and standard deviation of correlations found for a variety of mismatched ligand-density pairs, so that the Z scores are related to the probability of observing a particular value of the correlation by chance. The procedure was tested with a set of 200 of the most commonly found ligands in the Protein Data Bank, collectively representing 57% of all ligands in the Protein Data Bank. Using a combination of these two characteristics of ligand density, ranked lists of ligand identifications were made for representative (F o − F c )exp(iϕ c ) difference density from entries in the Protein Data Bank. In 48% of the 200 cases, the correct ligand was at the top of the ranked list of ligands. This approach may be useful in identification of unknown ligands in new macromolecular structures as well as in the identification of which ligands in a mixture have bound to a macromolecule

  5. Ligand sphere conversions in terminal carbide complexes

    DEFF Research Database (Denmark)

    Morsing, Thorbjørn Juul; Reinholdt, Anders; Sauer, Stephan P. A.

    2016-01-01

    Metathesis is introduced as a preparative route to terminal carbide complexes. The chloride ligands of the terminal carbide complex [RuC(Cl)2(PCy3)2] (RuC) can be exchanged, paving the way for a systematic variation of the ligand sphere. A series of substituted complexes, including the first...... example of a cationic terminal carbide complex, [RuC(Cl)(CH3CN)(PCy3)2]+, is described and characterized by NMR, MS, X-ray crystallography, and computational studies. The experimentally observed irregular variation of the carbide 13C chemical shift is shown to be accurately reproduced by DFT, which also...... demonstrates that details of the coordination geometry affect the carbide chemical shift equally as much as variations in the nature of the auxiliary ligands. Furthermore, the kinetics of formation of the sqaure pyramidal dicyano complex, trans-[RuC(CN)2(PCy3)2], from RuC has been examined and the reaction...

  6. Characteristic molecular vibrations of adenosine receptor ligands.

    Science.gov (United States)

    Chee, Hyun Keun; Yang, Jin-San; Joung, Je-Gun; Zhang, Byoung-Tak; Oh, S June

    2015-02-13

    Although the regulation of membrane receptor activation is known to be crucial for molecular signal transduction, the molecular mechanism underlying receptor activation is not fully elucidated. Here we study the physicochemical nature of membrane receptor behavior by investigating the characteristic molecular vibrations of receptor ligands using computational chemistry and informatics methods. By using information gain, t-tests, and support vector machines, we have identified highly informative features of adenosine receptor (AdoR) ligand and corresponding functional amino acid residues such as Asn (6.55) of AdoR that has informative significance and is indispensable for ligand recognition of AdoRs. These findings may provide new perspectives and insights into the fundamental mechanism of class A G protein-coupled receptor activation. Copyright © 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  7. Supramolecular architectures constructed using angular bipyridyl ligands

    International Nuclear Information System (INIS)

    Barnett, Sarah Ann

    2003-01-01

    This work details the synthesis and characterization of a series of coordination frameworks that are formed using bidentate angular N-donor ligands. Pyrimidine was reacted with metal(ll) nitrate salts. Reactions using Cd(NO 3 ) 2 receive particular focus and the analogous reactions using the linear ligand, pyrazine, were studied for comparison. In all cases, two-dimensional coordination networks were prepared. Structural diversity is observed for the Cd(ll) centres including metal-nitrate bridging. In contrast, first row transition metal nitrates form isostructural one-dimensional chains with only the bridging N-donor ligands generating polymeric propagation. The angular ligand, 2,4-bis(4-pyridyl)-1,3,5-triazine (dpt), was reacted with Cd(NO 3 ) 2 and Zn(NO 3 ) 2 . Whereas Zn(NO 3 ) 2 compounds exhibit solvent mediated polymorphism, a range of structures were obtained for the reactions with Cd(NO 3 ) 2 , including the first example of a doubly parallel interpenetrated 4.8 2 net. 4,7-phenanthroline, was reacted with various metal(ll) nitrates as well as cobalt(ll) and copper(ll) halides. The ability of 4,7-phenanthroline to act as both a N-donor ligand and a hydrogen bond acceptor has been discussed. Reactions of CuSCN with pyrimidine yield an unusual three-dimensional structure in which polymeric propagation is not a result of ligand bridging. The reaction of CuSCN with dpt yielded structural supramolecular isomers. (author)

  8. Probing into hybrid organic-molecule and InAs quantum-dots nanosystem with multistacked dots-in-a-well units

    Science.gov (United States)

    Chen, Miaoxiang; Kobashi, Kazufumi

    2012-09-01

    Hybridizing air-stable organic-molecules with advanced III-V semiconductor quantum-dots (QDs) structures can be utilized to create a new generation of biochemical sensing devices. In order to enhance their optical performances, the active regions in these QDs structures commonly consist of multistacked dots-in-a-well (DWELL) units. The effects of grafted molecules on the performances of the QDs structures with multistacked DWELLs, however, still remain unclear. Here, we show the significant improvements in the optical properties of InAs QDs in a hybrid nanosystem obtained by grafting biocompatible diazonium salt compound (amine donor) atop InAs QDs structure. Since its interface between the QDs structure and molecular monolayer retains an uncontaminated and non-oxidized condition, the nanosystem is an ideal platform to study the intrinsic properties of charge-carrier transport inside the system. Because of the complexity of the energy-levels in the QDs structure due to the existing surface QDs and DWELLs, selective excitation wavelengths (400, 633, and 885 nm, respectively) with different photo-energies are used to exactly analyze the complete charging mechanism in these QDs. A clear view of charge-carrier transfer inside the nanosystem is revealed by employing photoluminescence technique under selective-wavelength excitations. The present work provides new quantitative evidences for exploiting inorganic QDs applications in complex biological systems.

  9. Probing into hybrid organic-molecule and InAs quantum-dots nanosystem with multistacked dots-in-a-well units

    Energy Technology Data Exchange (ETDEWEB)

    Chen Miaoxiang [Department of Micro- and Nano technology, Technical University of Denmark, Orsteds Plads, 2800 Kgs. Lyngby (Denmark); Kobashi, Kazufumi [Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565 (Japan)

    2012-09-15

    Hybridizing air-stable organic-molecules with advanced III-V semiconductor quantum-dots (QDs) structures can be utilized to create a new generation of biochemical sensing devices. In order to enhance their optical performances, the active regions in these QDs structures commonly consist of multistacked dots-in-a-well (DWELL) units. The effects of grafted molecules on the performances of the QDs structures with multistacked DWELLs, however, still remain unclear. Here, we show the significant improvements in the optical properties of InAs QDs in a hybrid nanosystem obtained by grafting biocompatible diazonium salt compound (amine donor) atop InAs QDs structure. Since its interface between the QDs structure and molecular monolayer retains an uncontaminated and non-oxidized condition, the nanosystem is an ideal platform to study the intrinsic properties of charge-carrier transport inside the system. Because of the complexity of the energy-levels in the QDs structure due to the existing surface QDs and DWELLs, selective excitation wavelengths (400, 633, and 885 nm, respectively) with different photo-energies are used to exactly analyze the complete charging mechanism in these QDs. A clear view of charge-carrier transfer inside the nanosystem is revealed by employing photoluminescence technique under selective-wavelength excitations. The present work provides new quantitative evidences for exploiting inorganic QDs applications in complex biological systems.

  10. Determination of the burn-up in fuels of the MTR type by means of gamma spectroscopy with crystal of INa(Tl)

    International Nuclear Information System (INIS)

    Kestelman, A.J.

    1988-01-01

    One of the responsibilities of the Laboratory of Analysis by Neutronic Activation of the RA-6 reactor is to determine the burn-up in fuels of the MTR type. In order to gain experience, up to the arrival of the hyperpure Germanium detector (HPGe) to be used in normal operation, preliminary measurements with a crystal of INa(Tl) were made. The fuel elements used are originated in the RA-3 reactor, with a decay superior to the thirteen years. For this reason, the unique visible photoelectric peak is the one of Cs-137, owing to the low resolution of the INa(Tl). After preliminary measurements, the profiles of burn-up, rectified by attenuation, were measured. Once the efficiency of the detector was determined, the calculation of the burn-up was made; for the element No. 144, a value of 21.6 ± 2.9 g was obtained to be compared with the value 21.9 g which was the evaluation made by the operators. (Author) [es

  11. Auger recombination in p-type InAs and in Gasub(x)Insub(1-x)As solid solutions

    International Nuclear Information System (INIS)

    Zotova, N.V.; Yassievich, I.N.

    1977-01-01

    The probability of the Auger recombination in p-type semiconductors, which is accompanied by transition of the second hole into the zone, splitted by spin-orbital interaction, was calculated. The above process is effective when the energy of spin-orbital splitting off Δ is close to the forbidden zone energy Esub(g), which takes place in the case of InAs, GaSb and solid solutions based on these compounds. The calculation is performed for the non-degenerate hole gas at a finite difference of Esub(g) - Δ. By means of the study of radiative recombination in InAs and Gasub(x)Insub(1-x)As solid solutions with small contents of GaAs (0 17 cm -3 . It is found that the quantum yield of radiative recombination increases sharply in Gasub(x)Insub(1-x)As solid solutions with the increase of x, which is associated with the increase of the difference of Esub(g) - Δ; the radiative recombination intensity increases in correspondence with the theoretical calculation made

  12. GaAs metal-oxide-semiconductor based non-volatile flash memory devices with InAs quantum dots as charge storage nodes

    Energy Technology Data Exchange (ETDEWEB)

    Islam, Sk Masiul, E-mail: masiulelt@gmail.com; Chowdhury, Sisir; Sarkar, Krishnendu; Nagabhushan, B.; Banerji, P. [Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302 (India); Chakraborty, S. [Applied Materials Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Sector-I, Kolkata 700 064 (India); Mukherjee, Rabibrata [Department of Chemical Engineering, Indian Institute of Technology, Kharagpur 721302 (India)

    2015-06-24

    Ultra-thin InP passivated GaAs metal-oxide-semiconductor based non-volatile flash memory devices were fabricated using InAs quantum dots (QDs) as charge storing elements by metal organic chemical vapor deposition technique to study the efficacy of the QDs as charge storage elements. The grown QDs were embedded between two high-k dielectric such as HfO{sub 2} and ZrO{sub 2}, which were used for tunneling and control oxide layers, respectively. The size and density of the QDs were found to be 5 nm and 1.8×10{sup 11} cm{sup −2}, respectively. The device with a structure Metal/ZrO{sub 2}/InAs QDs/HfO{sub 2}/GaAs/Metal shows maximum memory window equivalent to 6.87 V. The device also exhibits low leakage current density of the order of 10{sup −6} A/cm{sup 2} and reasonably good charge retention characteristics. The low value of leakage current in the fabricated memory device is attributed to the Coulomb blockade effect influenced by quantum confinement as well as reduction of interface trap states by ultra-thin InP passivation on GaAs prior to HfO{sub 2} deposition.

  13. Deterministic self-organization: Ordered positioning of InAs quantum dots by self-organized anisotropic strain engineering on patterned GaAs(311)B

    International Nuclear Information System (INIS)

    Selcuk, E.; Hamhuis, G.J.; Noetzel, R.

    2009-01-01

    Laterally ordered InGaAs quantum dot (QD) arrays, InAs QD molecules, and single InAs QDs in a spot-like periodic arrangement are created by self-organized anisotropic strain engineering of InGaAs/GaAs superlattice (SL) templates on planar GaAs (311)B substrates in molecular beam epitaxy. On shallow- and deep-patterned substrates the respectively generated steps and facets guide the self-organization process during SL template formation to create more complex ordering such as periodic stripes, depending on pattern design. Here we demonstrate for patterns such as shallow- and deepetched round holes and deep-etched zigzag mesas that the self-organized periodic arrangement of QD molecules and single QDs is spatially locked to the pattern sidewalls and corners. This extends the concept of guided self-organization to deterministic self-organization. Absolute position control of the QDs is achieved without one-to-one pattern definition. This guarantees the excellent arrangement control of the ordered QD molecules and single QDs with strong photoluminescence emission up to room temperature, which is required for future quantum functional devices. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Studies on the controlled growth of InAs nanostructures on scission surfaces; Untersuchungen zum kontrollierten Wachstum von InAs-Nanostrukturen auf Spaltflaechen

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, J.

    2006-01-15

    The aim of this thesis was the controlled alignment of self-assembled InAs nano-structures on a {l_brace}110{r_brace}-oriented surface. The surface is prestructured with the atomic precision offered by molecular beam epitaxy, using the cleaved edge overgrowth-technique. On all samples grown within this work, the epitaxial template in the first growth step was deposited on a (001)GaAs substrate, while the InAs-layer forming the nanostructures during the second growth step was grown on cleaved {l_brace}110{r_brace}-GaAs surfaces. Atomic Force Microscopy (AFM) investigations demonstrate the formation of quantum dot (QD)-like nanostructures on top of the AlAs-stripes. X-ray diffraction measurements on large arrays of aligned quantum dots demonstrate that the quantum dots are formed of pure InAs. First investigations on the optical properties of these nanostructures were done using microphotoluminescence-spectroscopy with both high spatial and spectral resolution. (orig.)

  15. Strong Ligand-Protein Interactions Derived from Diffuse Ligand Interactions with Loose Binding Sites.

    Science.gov (United States)

    Marsh, Lorraine

    2015-01-01

    Many systems in biology rely on binding of ligands to target proteins in a single high-affinity conformation with a favorable ΔG. Alternatively, interactions of ligands with protein regions that allow diffuse binding, distributed over multiple sites and conformations, can exhibit favorable ΔG because of their higher entropy. Diffuse binding may be biologically important for multidrug transporters and carrier proteins. A fine-grained computational method for numerical integration of total binding ΔG arising from diffuse regional interaction of a ligand in multiple conformations using a Markov Chain Monte Carlo (MCMC) approach is presented. This method yields a metric that quantifies the influence on overall ligand affinity of ligand binding to multiple, distinct sites within a protein binding region. This metric is essentially a measure of dispersion in equilibrium ligand binding and depends on both the number of potential sites of interaction and the distribution of their individual predicted affinities. Analysis of test cases indicates that, for some ligand/protein pairs involving transporters and carrier proteins, diffuse binding contributes greatly to total affinity, whereas in other cases the influence is modest. This approach may be useful for studying situations where "nonspecific" interactions contribute to biological function.

  16. Interaction of calreticulin with CD40 ligand, TRAIL and Fas ligand

    DEFF Research Database (Denmark)

    Duus, K; Pagh, R T; Holmskov, U

    2007-01-01

    is utilized by many other functionally diverse molecules and in this work the interaction of calreticulin with C1q and structurally similar molecules was investigated. In addition to C1q and MBL, CD40 ligand (CD40L), tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL) were...... found to bind calreticulin strongly. A low level or no binding was observed for adiponectin, tumour necrosis factor-alpha (TNF-alpha), CD30L, surfactant protein-A and -D and collagen VIII. The interaction with calreticulin required a conformational change in CD40L, TRAIL and FasL and showed the same...

  17. Ligand Exchange Kinetics of Environmentally Relevant Metals

    Energy Technology Data Exchange (ETDEWEB)

    Panasci, Adele Frances [Univ. of California, Davis, CA (United States)

    2014-07-15

    The interactions of ground water with minerals and contaminants are of broad interest for geochemists but are not well understood. Experiments on the molecular scale can determine reaction parameters (i.e. rates of ligand exchange, activation entropy, activation entropy, and activation volume) that can be used in computations to gain insight into reactions that occur in natural groundwaters. Experiments to determine the rate of isotopic ligand exchange for three environmentally relevant metals, rhodium (Rh), iron (Fe), and neptunium (Np), are described. Many environmental transformations of metals (e.g. reduction) in soil occur at trivalent centers, Fe(III) in particular. Contaminant ions absorb to mineral surfaces via ligand exchange, and the reversal of this reaction can be dangerous, releasing contaminants into the environment. Ferric iron is difficult to study spectroscopically because most of its complexes are paramagnetic and are generally reactive toward ligand exchange; therefore, Rh(III), which is diamagnetic and less reactive, was used to study substitution reactions that are analogous to those that occur on mineral oxide surfaces. Studies on both Np(V) and Np(VI) are important in their own right, as 237Np is a radioactive transuranic element with a half-life of 2 million years.

  18. Ligand iron catalysts for selective hydrogenation

    Science.gov (United States)

    Casey, Charles P.; Guan, Hairong

    2010-11-16

    Disclosed are iron ligand catalysts for selective hydrogenation of aldehydes, ketones and imines. A catalyst such as dicarbonyl iron hydride hydroxycyclopentadiene) complex uses the OH on the five member ring and hydrogen linked to the iron to facilitate hydrogenation reactions, particularly in the presence of hydrogen gas.

  19. Programmed Death-Ligand 1 Immunohistochemistry Testing

    DEFF Research Database (Denmark)

    Büttner, Reinhard; Gosney, John R; Skov, Birgit Guldhammer

    2017-01-01

    Purpose Three programmed death-1/programmed death-ligand 1 (PD-L1) inhibitors are currently approved for treatment of non-small-cell lung cancer (NSCLC). Treatment with pembrolizumab in NSCLC requires PD-L1 immunohistochemistry (IHC) testing. Nivolumab and atezolizumab are approved without PD-L1...

  20. Versatile phosphite ligands based on silsesquioxane backbones

    NARCIS (Netherlands)

    van der Vlugt, JI; Ackerstaff, J; Dijkstra, TW; Mills, AM; Kooijman, H; Spek, AL; Meetsma, A; Abbenhuis, HCL; Vogt, D

    Silsesquioxanes are employed as ligand backbones for the synthesis of novel phosphite compounds with 3,3'-5,5'-tetrakis(tert-butyl)-2,2'-di-oxa-1,1'-biphenyl substituents. Both mono- and bidentate phosphites are prepared in good yields. Two types of silsesquioxanes are employed as starting

  1. Complex laterally ordered InGaAs and InAs quantum dots by guided self-organized anisotropic strain engineering on artificially patterned GaAs (3 1 1)B substrates

    NARCIS (Netherlands)

    Selçuk, E.; Hamhuis, G.J.; Nötzel, R.

    2009-01-01

    Self-organized anisotropic strain engineering is combined with growth on artificially patterned GaAs (3 1 1)B substrates to realize complex lateral ordering of InGaAs and InAs quantum dots (QDs) guided by steps and facets generated along the pattern sidewalls. Depending on the pattern design, size,

  2. Physical properties of metal–insulator–semiconductor structures based on n-GaAs with InAs quantum dots deposited onto the surface of an n-GaAs layer

    Energy Technology Data Exchange (ETDEWEB)

    Tikhov, S. V.; Gorshkov, O. N.; Koryazhkina, M. N., E-mail: mahavenok@mail.ru; Kasatkin, A. P.; Antonov, I. N.; Vihrova, O. V.; Morozov, A. I. [Lobachevsky State University of Nizhny Novgorod (NNSU) (Russian Federation)

    2016-12-15

    The properties of metal–insulator–semiconductor (MIS) structures based on n-GaAs in which silicon oxide and yttria-stabilized zirconia and hafnia are used as the insulator containing InAs quantum dots, which are embedded at the insulator/n-GaAs interface, are investigated. The structures manifest the resistive switching and synaptic behavior.

  3. Ammonia formation by metal-ligand cooperative hydrogenolysis of a nitrido ligand

    Science.gov (United States)

    Askevold, Bjorn; Nieto, Jorge Torres; Tussupbayev, Samat; Diefenbach, Martin; Herdtweck, Eberhardt; Holthausen, Max C.; Schneider, Sven

    2011-07-01

    Bioinspired hydrogenation of N2 to ammonia at ambient conditions by stepwise nitrogen protonation/reduction with metal complexes in solution has experienced remarkable progress. In contrast, the highly desirable direct hydrogenation with H2 remains difficult. In analogy to the heterogeneously catalysed Haber-Bosch process, such a reaction is conceivable via metal-centred N2 splitting and unprecedented hydrogenolysis of the nitrido ligands to ammonia. We report the synthesis of a ruthenium(IV) nitrido complex. The high nucleophilicity of the nitrido ligand is demonstrated by unusual N-C coupling with π-acidic CO. Furthermore, the terminal nitrido ligand undergoes facile hydrogenolysis with H2 at ambient conditions to produce ammonia in high yield. Kinetic and quantum chemical examinations of this reaction suggest cooperative behaviour of a phosphorus-nitrogen-phosphorus pincer ligand in rate-determining heterolytic hydrogen splitting.

  4. Dynamic ligand-based pharmacophore modeling and virtual ...

    Indian Academy of Sciences (India)

    Five ligand-based pharmacophore models were generated from 40 different .... the Phase module of the Schrodinger program.35 Each model consisted of six types of ... ligand preparation included the OPLS_2005 force field and to retain the ...

  5. Substrate coated with receptor and labelled ligand for assays

    International Nuclear Information System (INIS)

    1980-01-01

    Improvements in the procedures for assaying ligands are described. The assay consists of a polystyrene tube on which receptors are present for both the ligand to be assayed and a radioactively labelled form of the ligand. The receptors on the bottom portion of the tube are also coated with labelled ligands, thus eliminating the necessity for separate addition of the labelled ligand and sample during an assay. Examples of ligands to which this method is applicable include polypeptides, nucleotides, nucleosides and proteins. Specific examples are given in which the ligand to be assayed is digoxin, the labelled form of the ligand is 3-0-succinyl digoxyigenin tyrosine ( 125 I) and the receptor is digoxin antibody. (U.K.)

  6. Role of ligand-ligand vs. core-core interactions in gold nanoclusters.

    Science.gov (United States)

    Milowska, Karolina Z; Stolarczyk, Jacek K

    2016-05-14

    The controlled assembly of ligand-coated gold nanoclusters (NCs) into larger structures paves the way for new applications ranging from electronics to nanomedicine. Here, we demonstrate through rigorous density functional theory (DFT) calculations employing novel functionals accounting for van der Waals forces that the ligand-ligand interactions determine whether stable assemblies can be formed. The study of NCs with different core sizes, symmetry forms, ligand lengths, mutual crystal orientations, and in the presence of a solvent suggests that core-to-core van der Waals interactions play a lesser role in the assembly. The dominant interactions originate from combination of steric effects, augmented by ligand bundling on NC facets, and related to them changes in electronic properties induced by neighbouring NCs. We also show that, in contrast to standard colloidal theory approach, DFT correctly reproduces the surprising experimental trends in the strength of the inter-particle interaction observed when varying the length of the ligands. The results underpin the importance of understanding NC interactions in designing gold NCs for a specific function.

  7. AutoSite: an automated approach for pseudo-ligands prediction—from ligand-binding sites identification to predicting key ligand atoms

    Science.gov (United States)

    Ravindranath, Pradeep Anand; Sanner, Michel F.

    2016-01-01

    Motivation: The identification of ligand-binding sites from a protein structure facilitates computational drug design and optimization, and protein function assignment. We introduce AutoSite: an efficient software tool for identifying ligand-binding sites and predicting pseudo ligand corresponding to each binding site identified. Binding sites are reported as clusters of 3D points called fills in which every point is labelled as hydrophobic or as hydrogen bond donor or acceptor. From these fills AutoSite derives feature points: a set of putative positions of hydrophobic-, and hydrogen-bond forming ligand atoms. Results: We show that AutoSite identifies ligand-binding sites with higher accuracy than other leading methods, and produces fills that better matches the ligand shape and properties, than the fills obtained with a software program with similar capabilities, AutoLigand. In addition, we demonstrate that for the Astex Diverse Set, the feature points identify 79% of hydrophobic ligand atoms, and 81% and 62% of the hydrogen acceptor and donor hydrogen ligand atoms interacting with the receptor, and predict 81.2% of water molecules mediating interactions between ligand and receptor. Finally, we illustrate potential uses of the predicted feature points in the context of lead optimization in drug discovery projects. Availability and Implementation: http://adfr.scripps.edu/AutoDockFR/autosite.html Contact: sanner@scripps.edu Supplementary information: Supplementary data are available at Bioinformatics online. PMID:27354702

  8. Effects of InAlAs strain reducing layer on the photoluminescence properties of InAs quantum dots embedded in InGaAs/GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Lingmin, E-mail: konglm@qq.com [School of Marine Science and Technology, Zhejiang Ocean University, Zhoushan 316000 (China); Sun, Wei [SEM School of Electromechanical Engineering, Weifang Engineering Vocational College, Qingzhou 262500 (China); Feng, Zhe Chuan, E-mail: zcfeng@nut.edu.tw [Institute of Photonics and Optoelectronics, Department of Electrical Engineering, and Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei 106-17, Taiwan (China); Xie, Sheng [School of Electronic and Information Engineering, Tianjin University, Tianjin 300072 (China); Zhou, Yunqing; Wang, Rui; Zhang, Cunxi; Zong, Zhaocun; Wang, Hongxia; Qiao, Qian [Department of Physics, Zhejiang Ocean University, Zhoushan 316000 (China); Wu, Zhengyun [Department of Physics, Xiamen University, Xiamen 361005 China (China)

    2014-07-01

    Two kinds of self-assembled quantum dots (QDs) embedded within InGaAs/GaAs quantum wells were grown by molecular beam epitaxy: one was capped with an InAlAs strain reducing (SR) layer, while the other was not. Their emission dynamics was investigated by time-resolved and temperature dependent (TD) photoluminescence (PL) measurements. A significant redshift can be observed in the emission peak position of InAs QDs with thin InAlAs SR cap layer, which results from SR effects. Different behaviors of the integrated PL intensity for the samples with or without InAlAs layer may be ascribed to the reduced carrier transition at higher temperature for the higher energy barrier of the InAlAs layer, and the TD mode of carrier migration. The PL decay time of quantum dots grown with InAlAs layer was much longer than that without the layer, which implies that the InAlAs layer with higher energy barrier may enhance the quantum restriction of carriers in InAs QDs. These observations are discussed from the viewpoint of strain compensation and potential barrier variation with SR layers. Our experiments also demonstrate that the main mode of carrier migration is quantum tunneling effect at lower temperature, while it is quantum transition at higher temperature. The results demonstrate the importance of InAlAs SR layer for the optical quality of InAs QDs. - Highlights: • InAs quantum dots (QDs) were grown on GaAs. • A thin InAlAs layer was grown on InAs QDs. • Temperature dependent photoluminescence (PL) and time-resolved PL were carried out. • Both a redshift and a double exponential decay of PL emission were generated by the InAlAs layer.

  9. A response calculus for immobilized T cell receptor ligands

    DEFF Research Database (Denmark)

    Andersen, P S; Menné, C; Mariuzza, R A

    2001-01-01

    determine the level of T cell activation. When fitted to T cell responses against purified ligands immobilized on plastic surfaces, the 2D-affinity model adequately simulated changes in cellular activation as a result of varying ligand affinity and ligand density. These observations further demonstrated...

  10. Fullerenes as a new type of ligands for transition metals

    International Nuclear Information System (INIS)

    Sokolov, V.I.

    2007-01-01

    Fullerenes are considered as ligands in transition metal π-complexes. The following aspects are discussed: metals able to form π-complexes with fullerenes (Zr, V, Ta, Mo, W, Re, Ru, etc.); haptic numbers; homo- and hetero ligand complexes; ligand compatibility with fullerenes for different metals, including fullerenes with a disturbed structure of conjugation [ru

  11. New pinene-derived pyridines as bidentate chiral ligands

    Czech Academy of Sciences Publication Activity Database

    Malkov, A. V.; Stewart-Liddon, A.; Teplý, Filip; Kobr, L.; Muir, K. W.; Haigh, D.; Kočovský, P.

    2008-01-01

    Roč. 64, č. 18 (2008), s. 4011-4025 ISSN 0040-4020 Institutional research plan: CEZ:AV0Z40550506 Keywords : chiral ligands * transition metal catalysis * asymmetric catalysis * pyridine ligands * oxazoline ligands Subject RIV: CC - Organic Chemistry Impact factor: 2.897, year: 2008

  12. Engineering bacterial surface displayed human norovirus capsid proteins: A novel system to explore interaction between norovirus and ligands

    Directory of Open Access Journals (Sweden)

    Mengya eNiu

    2015-12-01

    Full Text Available Human noroviruses (HuNoVs are major contributors to acute nonbacterial gastroenteritis outbreaks. Many aspects of HuNoVs are poorly understood due to both the current inability to culture HuNoVs, and the lack of efficient small animal models. Surrogates for HuNoVs, such as recombinant viral like particles (VLPs expressed in eukaryotic system or P particles expressed in prokaryotic system, have been used for studies in immunology and interaction between the virus and its receptors. However, it is difficult to use VLPs or P particles to collect or isolate potential ligands binding to these recombinant capsid proteins. In this study, a new strategy was used to collect HuNoVs binding ligands through the use of ice nucleation protein (INP to display recombinant capsid proteins of HuNoVs on bacterial surfaces. The viral protein-ligand complex could be easily separated by a low speed centrifugation step. This system was also used to explore interaction between recombinant capsid proteins of HuNoVs and their receptors. In this system, the VP1 capsid encoding gene (ORF2 and the protruding domain (P domain encoding gene (3’ terminal fragment of ORF2 of HuNoVs GI.1 and GII.4 were fused with 5’ terminal fragment of ice nucleation protein encoding gene (inaQn. The results demonstrated that the recombinant VP1 and P domains of HuNoVs were expressed and anchored on the surface of Escherichia coli BL21 cells after the bacteria were transformed with the corresponding plasmids. Both cell surface displayed VP1 and P domains could be recognized by HuNoVs specific antibodies and interact with the viral histo-blood group antigens receptors. In both cases, displayed P domains had better binding abilities than VP1. This new strategy of using displayed HuNoVs capsid proteins on the bacterial surface could be utilized to separate HuNoVs binding components from complex samples, to investigate interaction between the virus and its receptors, as well as to develop an

  13. Sigma-2 receptor ligands QSAR model dataset

    Directory of Open Access Journals (Sweden)

    Antonio Rescifina

    2017-08-01

    Full Text Available The data have been obtained from the Sigma-2 Receptor Selective Ligands Database (S2RSLDB and refined according to the QSAR requirements. These data provide information about a set of 548 Sigma-2 (σ2 receptor ligands selective over Sigma-1 (σ1 receptor. The development of the QSAR model has been undertaken with the use of CORAL software using SMILES, molecular graphs and hybrid descriptors (SMILES and graph together. Data here reported include the regression for σ2 receptor pKi QSAR models. The QSAR model was also employed to predict the σ2 receptor pKi values of the FDA approved drugs that are herewith included.

  14. Metal-ligand cooperative activation of nitriles by a ruthenium complex with a de-aromatized PNN pincer ligand

    NARCIS (Netherlands)

    Eijsink, Linda E; Perdriau, Sébastien C P; de Vries, Johannes G; Otten, Edwin

    2016-01-01

    The pincer complex (PNN)RuH(CO), with a de-aromatized pyridine in the ligand backbone, is shown to react with nitriles in a metal-ligand cooperative manner. This leads to the formation of a series of complexes with new Ru-N(nitrile) and C(ligand)-C(nitrile) bonds. The initial nitrile cycloaddition

  15. Mālama I Ka `Āina, Sustainability: learning from Hawai`i's displaced place and culture-based science standard

    Science.gov (United States)

    Chinn, Pauline W. U.

    2011-03-01

    This response to Mitchell and Mueller's "A philosophical analysis of David Orr's theory of ecological literacy" comments on their critique of Orr's use of the phrase "ecological crisis" and what I perceive as their conflicting views of "crisis." I present my views on ecological crisis informed by standpoint theory and the definition of crisis as turning point. I connect the concept of turning point to tipping point as used in ecology to describe potentially irreversible changes in coupled social-ecological systems. I suggest that sustainable societies may provide models of adaptive learning in which monitoring of ecological phenomena is coupled to human behavior to mitigate threats to sustainability before a crisis/tipping point is reached. Finally, I discuss the Hawai`i State Department of Education's removal of its Indigenous science content standard Mālama I Ka `Āina, Sustainability and its continued use in community-based projects.

  16. Mobility in excess of 106 cm2/V s in InAs quantum wells grown on lattice mismatched InP substrates

    Science.gov (United States)

    Hatke, A. T.; Wang, T.; Thomas, C.; Gardner, G. C.; Manfra, M. J.

    2017-10-01

    We investigate the transport properties of a two-dimensional electron gas residing in strained composite quantum wells of In0.75Ga0.25As/InAs/In0.75Ga0.25As cladded with In0.75Al0.25As barriers grown metamorphically on insulating InP substrates. By optimizing the widths of the In0.75Ga0.25As layers, the In0.75Al0.25As barrier, and the InAs quantum well, we demonstrate mobility in excess of 1 ×106 cm2/V s. Mobility vs. density data indicate that scattering is dominated by a residual three dimensional distribution of charged impurities. We extract the effective Rashba parameter and spin-orbit length for these composite quantum wells.

  17. Phospholipid analysis and fractional reconstitution of the ice nucleation protein activity purified from Escherichia coli overexpressing the inaZ gene of Pseudomonas syringae.

    Science.gov (United States)

    Palaiomylitou, M A; Kalimanis, A; Koukkou, A I; Drainas, C; Anastassopoulos, E; Panopoulos, N J; Ekateriniadou, L V; Kyriakidis, D A

    1998-08-01

    Ice nucleation protein was partially purified from the membrane fraction of E. coli carrying inaZ from Pseudomonas syringae. The ice nucleation protein was totally localized in the bacterial envelope and was extracted by either salt (0.25 M NH4Cl) or the nonionic detergent Tween 20. The extracted protein was partially purified by sequential passage through DEAE-52 cellulose and Sephacryl-S400 columns. The activity of the purified protein was lost after treatment with phospholipase C, and its activity was subsequently restored by addition of the naturally occurring lipid phosphatidylethanolamine. These results suggest that ice nucleation proteins have a requirement for lipids that reconstitute a physiological hydrophobic environment similar to the one existing in vivo, to attain and maintain a structure that enables ice catalysis. Copyright 1998 Academic Press.

  18. Minority carrier lifetime and dark current measurements in mid-wavelength infrared InAs0.91Sb0.09 alloy nBn photodetectors

    Science.gov (United States)

    Olson, B. V.; Kim, J. K.; Kadlec, E. A.; Klem, J. F.; Hawkins, S. D.; Leonhardt, D.; Coon, W. T.; Fortune, T. R.; Cavaliere, M. A.; Tauke-Pedretti, A.; Shaner, E. A.

    2015-11-01

    Carrier lifetime and dark current measurements are reported for a mid-wavelength infrared InAs0.91Sb0.09 alloy nBn photodetector. Minority carrier lifetimes are measured using a non-contact time-resolved microwave technique on unprocessed portions of the nBn wafer and the Auger recombination Bloch function parameter is determined to be |F1F2|=0.292 . The measured lifetimes are also used to calculate the expected diffusion dark current of the nBn devices and are compared with the experimental dark current measured in processed photodetector pixels from the same wafer. Excellent agreement is found between the two, highlighting the important relationship between lifetimes and diffusion currents in nBn photodetectors.

  19. X-ray investigation of the interface structure of free standing InAs nanowires grown on GaAs[ anti 1 anti 1 anti 1]{sub B}

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, Jens; Gottschalch, Volker; Wagner, Gerald [Universitaet Leipzig, Halbleiterchemie, Leipzig (Germany); Pietsch, Ullrich; Davydok, Anton; Biermanns, Andreas [Universitaet Siegen, Festkoerperphysik, Siegen (Germany); Grenzer, Joerg [Forschungszentrum Rossendorf, Institut fuer Ionenstrahlphysik und Materialforschung, Dresden (Germany)

    2009-09-15

    The heteroepitaxial growth process of InAs nanowires (NW) on GaAs[ anti 1 anti 1 anti 1]{sub B} substrate was investigated by X-ray grazing-incidence diffraction using synchrotron radiation. For crystal growth we applied the vapor-liquid-solid (VLS) growth mechanism via gold seeds. The general sample structure was extracted from various electron microscopic and X-ray diffraction experiments. We found a closed Ga{sub x}In{sub 1-x} As graduated alloy layer at the substrate to NW interface which was formed in the initial stage of VLS growth with a Au-Ga-In liquid alloy. With ongoing growth time a transition from this VLS layer growth to the conventional VLS NW growth was observed. The structural properties of both VLS grown crystal types were examined. Furthermore, we discuss the VLS layer growth process. (orig.)

  20. Longer than 1.9 μm photoluminescence emission from InAs quantum structure on GaAs (001) substrate

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Ke; Ma, Wenquan, E-mail: wqma@semi.ac.cn; Huang, Jianliang; Zhang, Yanhua; Cao, Yulian; Huang, Wenjun; Luo, Shuai; Yang, Tao [Institute of Semiconductors, Chinese Academy of Sciences, Qinghua East Road A 35, Beijing 100083 (China)

    2015-07-27

    We report on photoluminescence (PL) emission with long wavelength for quantum structure by the sub-monolayer (SML) growth technique on GaAs (001) substrate. It is found that the PL emission wavelength can be controlled by controlling the SML InAs deposition amount. At 12 K, the PL peak position of the grown samples changes from about 1.66 to 1.78 μm. At 120 K, the PL emission of a sample reaches 1.91 μm. The physical mechanism responsible for the measured long wavelength PL emission may be related to strong In segregation and intermixing effects occurred in the structure grown by SML growth technique.

  1. Valence Band Structure of InAs1-xBix and InSb1-xBix Alloy Semiconductors Calculated Using Valence Band Anticrossing Model

    Directory of Open Access Journals (Sweden)

    D. P. Samajdar

    2014-01-01

    Full Text Available The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs1-xBix and InSb1-xBix alloy systems. It is found that both the heavy/light hole, and spin-orbit split E+ levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E− energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data.

  2. Terahertz tunable detection in self-switching diodes based on high mobility semiconductors: InGaAs, InAs and InSb

    International Nuclear Information System (INIS)

    Iniguez-de-la-Torre, I; Rodilla, H; Mateos, J; Pardo, D; Gonzalez, T; Song, A M

    2009-01-01

    In this work we report on the use of high mobility materials in the channel of self-switching diodes as potential candidates for terahertz operation. By means of Monte Carlo simulations we envisage the feasibility of tuneable-by-geometry detection in the terahertz range. The low effective mass of InAs and InSb in relation to InGaAs enhances ballistic transport inside the diode, thus improving the amplitude and quality factor of the resonance found in the detection spectra of self-switching diodes. The frequency of the resonant peak is also increased with the use of these narrow band gap semiconductors. The analysis of the noise spectra provides useful information about the origin of the resonance. By decreasing temperature below 300 K, a clear improvement in detection sensitivity is also achieved.

  3. Terahertz tunable detection in self-switching diodes based on high mobility semiconductors: InGaAs, InAs and InSb

    Energy Technology Data Exchange (ETDEWEB)

    Iniguez-de-la-Torre, I; Rodilla, H; Mateos, J; Pardo, D; Gonzalez, T [Departamento de Fisica Aplicada, Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca (Spain); Song, A M, E-mail: indy@usal.e [School of Electrical and Electronic Engineering, University of Manchester, Manchester M60 1QD (United Kingdom)

    2009-11-15

    In this work we report on the use of high mobility materials in the channel of self-switching diodes as potential candidates for terahertz operation. By means of Monte Carlo simulations we envisage the feasibility of tuneable-by-geometry detection in the terahertz range. The low effective mass of InAs and InSb in relation to InGaAs enhances ballistic transport inside the diode, thus improving the amplitude and quality factor of the resonance found in the detection spectra of self-switching diodes. The frequency of the resonant peak is also increased with the use of these narrow band gap semiconductors. The analysis of the noise spectra provides useful information about the origin of the resonance. By decreasing temperature below 300 K, a clear improvement in detection sensitivity is also achieved.

  4. Surface Brillouin scattering measurement of the elastic constants of single crystal InAs0.91Sb0.09

    International Nuclear Information System (INIS)

    Kotane, L M; Comins, J D; Every, A G; Botha, J R

    2011-01-01

    Surface Brillouin scattering of light has been used to measure the angular dependence of the Rayleigh surface acoustic wave (SAW), pseudo surface acoustic wave (PSAW) and longitudinal lateral wave (LLW) speeds in a (100)-oriented single crystal of the ternary semiconductor alloy InAs 0.91 Sb 0.09 . The wave speed measurements have been used to determine the room temperature values of the elastic constants C 11 , C 12 and C 44 of the alloy. A simple and robust fitting procedure has been implemented for recovering the elastic constants, in which the merit function is constructed from explicit secular functions that determine the surface and lateral wave speeds in the [001] and [011] crystallographic directions. In the fitting, relatively larger weighting factors have been assigned to the SAW and PSAW data because of the greater precision with which the surface modes can be measured as compared with the lateral wave.

  5. EGFR Activation by Spatially Restricted Ligands

    Science.gov (United States)

    2006-06-01

    the level of ligand production, that result in human breast cancer. We have integrated genetic and biochemical methods to study (1) the effects of a...and spindle-B encode components of the RAD52 DNA repair pathway and affect meiosis and patterning in Drosophila oogenesis. Genes Dev 12, 2711-2723...findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision

  6. Selective oxoanion separation using a tripodal ligand

    Energy Technology Data Exchange (ETDEWEB)

    Custelcean, Radu; Moyer, Bruce A.; Rajbanshi, Arbin

    2016-02-16

    The present invention relates to urea-functionalized crystalline capsules self-assembled by sodium or potassium cation coordination and by hydrogen-bonding water bridges to selectively encapsulate tetrahedral divalent oxoanions from highly competitive aqueous alkaline solutions and methods using this system for selective anion separations from industrial solutions. The method involves competitive crystallizations using a tripodal tris(urea) functionalized ligand and, in particular, provides a viable approach to sulfate separation from nuclear wastes.

  7. Targeting Selectins and Their Ligands in Cancer

    Directory of Open Access Journals (Sweden)

    Alessandro eNatoni

    2016-04-01

    Full Text Available Aberrant glycosylation is a hallmark of cancer cells with increased evidence pointing to a role in tumor progression. In particular, aberrant sialylation of glycoproteins and glycolipids have been linked to increased immune cell evasion, drug evasion, drug resistance, tumor invasiveness, and vascular dissemination leading to metastases. Hypersialylation of cancer cells is largely the result of overexpression of sialyltransferases. Humans differentially express twenty different sialyltransferases in a tissue-specific manner, each of which catalyze the attachment of sialic acids via different glycosidic linkages (2-3; 2-6 or 2-8 to the underlying glycan chain. One important mechanism whereby overexpression of sialyltransferases contributes to an enhanced metastatic phenotype is via the generation of selectin ligands. Selectin ligand function requires the expression of sialyl-Lewis X and its structural-isomer sialyl-Lewis A, which are synthesized by the combined action of alpha 1-3-fucosyltransferases, 2-3-sialyltransferases, 1-4-galactosyltranferases, and N-acetyl--glucosaminyltransferases. The α2-3-sialyltransferases ST3Gal4 and ST3Gal6 are critical to the generation of functional E- and P-selectin ligands and overexpression of these sialyltransferases have been linked to increased risk of metastatic disease in solid tumors and poor outcome in multiple myeloma. Thus, targeting selectins and their ligands as well as the enzymes involved in their generation, in particular sialyltransferases, could be beneficial to many cancer patients. Potential strategies include sialyltransferase inhibition and the use of selectin antagonists, such as glycomimetic drugs and antibodies. Here, we review ongoing efforts to optimize the potency and selectivity of sialyltransferase inhibitors, including the potential for targeted delivery approaches, as well as evaluate the potential utility of selectin inhibitors, which are now in early clinical

  8. Determination of ligand binding modes in weak protein–ligand complexes using sparse NMR data

    Energy Technology Data Exchange (ETDEWEB)

    Mohanty, Biswaranjan; Williams, Martin L.; Doak, Bradley C.; Vazirani, Mansha; Ilyichova, Olga [Monash University, Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences (Australia); Wang, Geqing [La Trobe University, La Trobe Institute for Molecular Bioscience (Australia); Bermel, Wolfgang [Bruker Biospin GmbH (Germany); Simpson, Jamie S.; Chalmers, David K. [Monash University, Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences (Australia); King, Glenn F. [The University of Queensland, Institute for Molecular Bioscience (Australia); Mobli, Mehdi, E-mail: m.mobli@uq.edu.au [The University of Queensland, Centre for Advanced Imaging (Australia); Scanlon, Martin J., E-mail: martin.scanlon@monash.edu [Monash University, Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences (Australia)

    2016-11-15

    We describe a general approach to determine the binding pose of small molecules in weakly bound protein–ligand complexes by deriving distance constraints between the ligand and methyl groups from all methyl-containing residues of the protein. We demonstrate that using a single sample, which can be prepared without the use of expensive precursors, it is possible to generate high-resolution data rapidly and obtain the resonance assignments of Ile, Leu, Val, Ala and Thr methyl groups using triple resonance scalar correlation data. The same sample may be used to obtain Met {sup ε}CH{sub 3} assignments using NOESY-based methods, although the superior sensitivity of NOESY using [U-{sup 13}C,{sup 15}N]-labeled protein makes the use of this second sample more efficient. We describe a structural model for a weakly binding ligand bound to its target protein, DsbA, derived from intermolecular methyl-to-ligand nuclear Overhauser enhancements, and demonstrate that the ability to assign all methyl resonances in the spectrum is essential to derive an accurate model of the structure. Once the methyl assignments have been obtained, this approach provides a rapid means to generate structural models for weakly bound protein–ligand complexes. Such weak complexes are often found at the beginning of programs of fragment based drug design and can be challenging to characterize using X-ray crystallography.

  9. ProBiS-ligands: a web server for prediction of ligands by examination of protein binding sites.

    Science.gov (United States)

    Konc, Janez; Janežič, Dušanka

    2014-07-01

    The ProBiS-ligands web server predicts binding of ligands to a protein structure. Starting with a protein structure or binding site, ProBiS-ligands first identifies template proteins in the Protein Data Bank that share similar binding sites. Based on the superimpositions of the query protein and the similar binding sites found, the server then transposes the ligand structures from those sites to the query protein. Such ligand prediction supports many activities, e.g. drug repurposing. The ProBiS-ligands web server, an extension of the ProBiS web server, is open and free to all users at http://probis.cmm.ki.si/ligands. © The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.

  10. Spectrophotometric method for determination of bifunctional macrocyclic ligands in macrocyclic ligand-protein conjugates

    International Nuclear Information System (INIS)

    Dadachova, E.; Chappell, L.L.; Brechbiel, M.W.

    1999-01-01

    A simple spectrophotometric assay for determination of bifunctional polyazacarboxylate-macrocyclic ligands of different sizes that are conjugated to proteins has been developed for: 12-membered macrocycle DOTA (2-[4-nitrobenzyl]-1, 4, 7, 10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) and analogs, the 15-membered PEPA macrocycle (2-[4-nitrobenzyl]-1,4,7,10,13-pentaazacyclopentadecane-N,N',N'',N''',N'''' -pentaacetic acid), and the large 18-membered macrocycle HEHA (1,4,7,10,13,16-hexaazacyclooctadecane-N,N',N'',N''',N''''-hexaacetic acid). The method is based on titration of the blue-colored 1:1 Pb(II)-Arsenazo III (AAIII) complex with the polyazacarboxylate macrocyclic ligand in the concentration range of 0-2.5 μM, wherein color change occurring upon transchelation of the Pb(II) from the AAIII to the polyazamacrocyclic ligand is monitored at 656 nm. The assay is performed at ambient temperature within 20 min without any interfering interaction between the protein and Pb(II)-AA(III) complex. Thus, this method also provides a ligand-to-protein ratio (L/P ratio) that reflects the effective number of ligands per protein molecule available to radiolabeling. The method is not suitable for 14-membered TETA macrocycle (2-[4-nitrobenzyl]-1, 4, 8, 11-tetraazacyclotetradecane N,N',N'',N'''-tetraacetic acid) because of low stability constant of Pb(II)-TETA complex. The method is rapid, simple and may be customized for other polyazacarboxylate macrocyclic ligands

  11. Ligand cluster-based protein network and ePlatton, a multi-target ligand finder.

    Science.gov (United States)

    Du, Yu; Shi, Tieliu

    2016-01-01

    Small molecules are information carriers that make cells aware of external changes and couple internal metabolic and signalling pathway systems with each other. In some specific physiological status, natural or artificial molecules are used to interact with selective biological targets to activate or inhibit their functions to achieve expected biological and physiological output. Millions of years of evolution have optimized biological processes and pathways and now the endocrine and immune system cannot work properly without some key small molecules. In the past thousands of years, the human race has managed to find many medicines against diseases by trail-and-error experience. In the recent decades, with the deepening understanding of life and the progress of molecular biology, researchers spare no effort to design molecules targeting one or two key enzymes and receptors related to corresponding diseases. But recent studies in pharmacogenomics have shown that polypharmacology may be necessary for the effects of drugs, which challenge the paradigm, 'one drug, one target, one disease'. Nowadays, cheminformatics and structural biology can help us reasonably take advantage of the polypharmacology to design next-generation promiscuous drugs and drug combination therapies. 234,591 protein-ligand interactions were extracted from ChEMBL. By the 2D structure similarity, 13,769 ligand emerged from 156,151 distinct ligands which were recognized by 1477 proteins. Ligand cluster- and sequence-based protein networks (LCBN, SBN) were constructed, compared and analysed. For assisting compound designing, exploring polypharmacology and finding possible drug combination, we integrated the pathway, disease, drug adverse reaction and the relationship of targets and ligand clusters into the web platform, ePlatton, which is available at http://www.megabionet.org/eplatton. Although there were some disagreements between the LCBN and SBN, communities in both networks were largely the same

  12. Towards ligand docking including explicit interface water molecules.

    Directory of Open Access Journals (Sweden)

    Gordon Lemmon

    Full Text Available Small molecule docking predicts the interaction of a small molecule ligand with a protein at atomic-detail accuracy including position and conformation the ligand but also conformational changes of the protein upon ligand binding. While successful in the majority of cases, docking algorithms including RosettaLigand fail in some cases to predict the correct protein/ligand complex structure. In this study we show that simultaneous docking of explicit interface water molecules greatly improves Rosetta's ability to distinguish correct from incorrect ligand poses. This result holds true for both protein-centric water docking wherein waters are located relative to the protein binding site and ligand-centric water docking wherein waters move with the ligand during docking. Protein-centric docking is used to model 99 HIV-1 protease/protease inhibitor structures. We find protease inhibitor placement improving at a ratio of 9:1 when one critical interface water molecule is included in the docking simulation. Ligand-centric docking is applied to 341 structures from the CSAR benchmark of diverse protein/ligand complexes [1]. Across this diverse dataset we see up to 56% recovery of failed docking studies, when waters are included in the docking simulation.

  13. Measurements of the spin-orbit interaction and Landé g factor in a pure-phase InAs nanowire double quantum dot in the Pauli spin-blockade regime

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jiyin; Huang, Shaoyun, E-mail: hqxu@pku.edu.cn, E-mail: syhuang@pku.edu.cn; Lei, Zijin [Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China); Pan, Dong; Zhao, Jianhua [State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Xu, H. Q., E-mail: hqxu@pku.edu.cn, E-mail: syhuang@pku.edu.cn [Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China); Division of Solid State Physics, Lund University, Box 118, S-22100 Lund (Sweden)

    2016-08-01

    We demonstrate direct measurements of the spin-orbit interaction and Landé g factors in a semiconductor nanowire double quantum dot. The device is made from a single-crystal pure-phase InAs nanowire on top of an array of finger gates on a Si/SiO{sub 2} substrate and the measurements are performed in the Pauli spin-blockade regime. It is found that the double quantum dot exhibits a large singlet-triplet energy splitting of Δ{sub ST} ∼ 2.3 meV, a strong spin-orbit interaction of Δ{sub SO} ∼ 140 μeV, and a large and strongly level-dependent Landé g factor of ∼12.5. These results imply that single-crystal pure-phase InAs nanowires are desired semiconductor nanostructures for applications in quantum information technologies.

  14. InAs quantum dot growth on Al{sub x}Ga{sub 1−x}As by metalorganic vapor phase epitaxy for intermediate band solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Jakomin, R., E-mail: robertojakomin@xerem.ufrj.br [Campus de Xerém, Universidade Federal do Rio de Janeiro, UFRJ, Duque de Caxias-RJ (Brazil); Campus de Xerém, Universidade Federal do Rio de Janeiro, UFRJ, Duque de Caxias-RJ (Brazil); Kawabata, R. M. S.; Souza, P. L. [Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutoires–DISSE–PUC-Rio, RJ (Brazil); Pontificia Universidade Católica do Rio de Janeiro, Marques de São Vicente 225, Rio de Janeiro, 22452-900 RJ (Brazil); Mourão, R. T.; Pires, M. P. [Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutoires–DISSE–PUC-Rio, RJ (Brazil); Instituto de Física, Universidade Federal do Rio de Janeiro, UFRJ, Rio de Janeiro-RJ (Brazil); Micha, D. N. [Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutoires–DISSE–PUC-Rio, RJ (Brazil); Instituto de Física, Universidade Federal do Rio de Janeiro, UFRJ, Rio de Janeiro-RJ (Brazil); Coordenação de Licenciatura em Física, CEFET/RJ, Petrópolis-RJ (Brazil); Xie, H.; Fischer, A. M.; Ponce, F. A. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States)

    2014-09-07

    InAs quantum dot multilayers have been grown using Al{sub x}Ga{sub 1−x}As spacers with dimensions and compositions near the theoretical values for optimized efficiencies in intermediate band photovoltaic cells. Using an aluminium composition of x = 0.3 and InAs dot vertical dimensions of 5 nm, transitions to an intermediate band with energy close to the ideal theoretical value have been obtained. Optimum size uniformity and density have been achieved by capping the quantum dots with GaAs following the indium-flush method. This approach has also resulted in minimization of crystalline defects in the epilayer structure.

  15. Predicting Nanocrystal Shape through Consideration of Surface-Ligand Interactions

    KAUST Repository

    Bealing, Clive R.

    2012-03-27

    Density functional calculations for the binding energy of oleic acid-based ligands on Pb-rich {100} and {111} facets of PbSe nanocrystals determine the surface energies as a function of ligand coverage. Oleic acid is expected to bind to the nanocrystal surface in the form of lead oleate. The Wulff construction predicts the thermodynamic equilibrium shape of the PbSe nanocrystals. The equilibrium shape is a function of the ligand surface coverage, which can be controlled by changing the concentration of oleic acid during synthesis. The different binding energy of the ligand on the {100} and {111} facets results in different equilibrium ligand coverages on the facets, and a transition in the equilibrium shape from octahedral to cubic is predicted when increasing the ligand concentration during synthesis. © 2012 American Chemical Society.

  16. Prediction of GPCR-Ligand Binding Using Machine Learning Algorithms

    Directory of Open Access Journals (Sweden)

    Sangmin Seo

    2018-01-01

    Full Text Available We propose a novel method that predicts binding of G-protein coupled receptors (GPCRs and ligands. The proposed method uses hub and cycle structures of ligands and amino acid motif sequences of GPCRs, rather than the 3D structure of a receptor or similarity of receptors or ligands. The experimental results show that these new features can be effective in predicting GPCR-ligand binding (average area under the curve [AUC] of 0.944, because they are thought to include hidden properties of good ligand-receptor binding. Using the proposed method, we were able to identify novel ligand-GPCR bindings, some of which are supported by several studies.

  17. Mixed ligand chelates of rare earths in aqueous solution

    International Nuclear Information System (INIS)

    Lakhani, S.U.; Thakur, G.S.; Sangal, S.P.

    1981-01-01

    Mixed ligand chelates of the 1:1 trivalent lanthanoids-EDTA, HEDTA and NTA chelates-1, 2-Dihydroxybenzene (Pyrocatechol) have been investigated at 35degC and 0.2 M ionic strength maintained by NaC10 4 . The formation of mixed ligand chelates has been found in all cases. The formation of mixed ligand chelates with EDTA shows the coordination number of lanthanoids to be eight, while the mixed ligand chelates with HEDTA and NTA shows the coordination number to be seven and six respectively. The stability constants of mixed ligand chelates are smaller than the binary complexes. The order of stability constants with respect to primary ligands follows the order NTA>HEDTA>EDTA. With respect to metal ions the stability constants increases with the decrease in ionic radii such as Gd< Er< Yb. (author)

  18. New ' Bucky- ligands'. Potentially Monoanionic Terdentate Diamino Aryl Pincer Ligands Anchored to C60

    NARCIS (Netherlands)

    Koten, G. van; Meijer, M.D.; Gossage, R.A.; Jastrzebski, J.T.B.H.

    1998-01-01

    Two new methanofullerenes have been prepared by the reaction of C{6}{0} with diazo substituted, potentially monoanionic, terdentate diamino aryl ligands, yielding a mixture of the open valence [5, 6]- and closed valence [6,6]-isomers. Single isomers of the pure [6,6]-methanofullerenes were obtained

  19. LASSO-ligand activity by surface similarity order: a new tool for ligand based virtual screening.

    Science.gov (United States)

    Reid, Darryl; Sadjad, Bashir S; Zsoldos, Zsolt; Simon, Aniko

    2008-01-01

    Virtual Ligand Screening (VLS) has become an integral part of the drug discovery process for many pharmaceutical companies. Ligand similarity searches provide a very powerful method of screening large databases of ligands to identify possible hits. If these hits belong to new chemotypes the method is deemed even more successful. eHiTS LASSO uses a new interacting surface point types (ISPT) molecular descriptor that is generated from the 3D structure of the ligand, but unlike most 3D descriptors it is conformation independent. Combined with a neural network machine learning technique, LASSO screens molecular databases at an ultra fast speed of 1 million structures in under 1 min on a standard PC. The results obtained from eHiTS LASSO trained on relatively small training sets of just 2, 4 or 8 actives are presented using the diverse directory of useful decoys (DUD) dataset. It is shown that over a wide range of receptor families, eHiTS LASSO is consistently able to enrich screened databases and provides scaffold hopping ability.

  20. LASSO—ligand activity by surface similarity order: a new tool for ligand based virtual screening

    Science.gov (United States)

    Reid, Darryl; Sadjad, Bashir S.; Zsoldos, Zsolt; Simon, Aniko

    2008-06-01

    Virtual Ligand Screening (VLS) has become an integral part of the drug discovery process for many pharmaceutical companies. Ligand similarity searches provide a very powerful method of screening large databases of ligands to identify possible hits. If these hits belong to new chemotypes the method is deemed even more successful. eHiTS LASSO uses a new interacting surface point types (ISPT) molecular descriptor that is generated from the 3D structure of the ligand, but unlike most 3D descriptors it is conformation independent. Combined with a neural network machine learning technique, LASSO screens molecular databases at an ultra fast speed of 1 million structures in under 1 min on a standard PC. The results obtained from eHiTS LASSO trained on relatively small training sets of just 2, 4 or 8 actives are presented using the diverse directory of useful decoys (DUD) dataset. It is shown that over a wide range of receptor families, eHiTS LASSO is consistently able to enrich screened databases and provides scaffold hopping ability.

  1. New synthetic routes toward enantiopure nitrogen donor ligands

    OpenAIRE

    Sala, Xavier; Rodríguez, Anna M.; Rodríguez, Montserrat; Romero, Isabel; Parella, Teodor; Zelewsky, Alexander von; Llobet, Antoni; Benet-Buchholz, Jordi

    2008-01-01

    New polypyridylic chiral ligands, having either C₃ or lower symmetry, have been prepared via a de novo construction of the pyridine nucleus by means of Kröhnke methodology in the key step. The chiral moieties of these ligands originate from the monoterpen chiral pool, namely (-)-α-pinene ((-)-14, (-)-15) and (-)-myrtenal ((-)-9, (-)-10). Extension of the above-mentioned asymmetric synthesis procedure to the preparation of enantiopure derivatives of some commonly used polypyridylic ligands has...

  2. Selectivity in ligand recognition of G-quadruplex loops.

    Science.gov (United States)

    Campbell, Nancy H; Patel, Manisha; Tofa, Amina B; Ghosh, Ragina; Parkinson, Gary N; Neidle, Stephen

    2009-03-03

    A series of disubstituted acridine ligands have been cocrystallized with a bimolecular DNA G-quadruplex. The ligands have a range of cyclic amino end groups of varying size. The crystal structures show that the diagonal loop in this quadruplex results in a large cavity for these groups, in contrast to the steric constraints imposed by propeller loops in human telomeric quadruplexes. We conclude that the nature of the loop has a significant influence on ligand selectivity for particular quadruplex folds.

  3. Singular Value Decomposition and Ligand Binding Analysis

    Directory of Open Access Journals (Sweden)

    André Luiz Galo

    2013-01-01

    Full Text Available Singular values decomposition (SVD is one of the most important computations in linear algebra because of its vast application for data analysis. It is particularly useful for resolving problems involving least-squares minimization, the determination of matrix rank, and the solution of certain problems involving Euclidean norms. Such problems arise in the spectral analysis of ligand binding to macromolecule. Here, we present a spectral data analysis method using SVD (SVD analysis and nonlinear fitting to determine the binding characteristics of intercalating drugs to DNA. This methodology reduces noise and identifies distinct spectral species similar to traditional principal component analysis as well as fitting nonlinear binding parameters. We applied SVD analysis to investigate the interaction of actinomycin D and daunomycin with native DNA. This methodology does not require prior knowledge of ligand molar extinction coefficients (free and bound, which potentially limits binding analysis. Data are acquired simply by reconstructing the experimental data and by adjusting the product of deconvoluted matrices and the matrix of model coefficients determined by the Scatchard and McGee and von Hippel equation.

  4. Spectrochemical study on different ligand neodymium complexes

    International Nuclear Information System (INIS)

    Khomenko, V.S.; Lozinskij, M.O.; Fialkov, Yu.A.; Krasovskaya, L.I.; Rasshinina, T.A.; AN Ukrainskoj SSR, Kiev. Inst. Organicheskoj Khimii)

    1986-01-01

    A series of new adducts of neodymium complexes with 1, 1, 1, 5, 5, 5-hexafluoropentadione - 2, 4 and 2-heptafluoropropoxy-1, 1, 1, 2-tetrafluoro-5-phenylpentadione-3, 5: Nd(HFPTFPhPD) 3 x2H 2 O, Nd(HFPTFPhPD) 3 xDipy, Nd(HFPTFPhPD) 3 xPhen, Nd(HFPTFPhPD) 3 xDphen, Nd(HFA) 3 x2H 2 O, Nd(HFA) 3 xDipy, Nd(HFA) 3 xPhen, Nd(HFA) 3 xDphen, have been synthesized. Ways of their fragmentation under electron impact are established. Bond strength of additional ligands with central atom in the complexes studied is evaluated. Data on decomposition mechanisms of bicharged ions have been obtained for the first time. Addition of bis-heterocycles to neodymium three-ligand complexes changes the properties of the complexes - their thermal stability and photochemical stability increase, in certain cases their volatility increases

  5. Novel Somatostatin Receptor Ligands Therapies for Acromegaly

    Directory of Open Access Journals (Sweden)

    Rosa Maria Paragliola

    2018-03-01

    Full Text Available Surgery is considered the treatment of choice in acromegaly, but patients with persistent disease after surgery or in whom surgery cannot be considered require medical therapy. Somatostatin receptor ligands (SRLs octreotide (OCT, lanreotide, and the more recently approved pasireotide, characterized by a broader receptor ligand binding profile, are considered the mainstay in the medical management of acromegaly. However, in the attempt to offer a more efficacious and better tolerated medical approach, recent research has been aimed to override some limitations related to the use of currently approved drugs and novel SRLs therapies, with potential attractive features, have been proposed. These include both new formulation of older molecules and new molecules. Novel OCT formulations are aimed in particular to improve patients’ compliance and to reduce injection discomfort. They include an investigational ready-to-use subcutaneous depot OCT formulation (CAM2029, delivered via prefilled syringes and oral OCT that uses a “transient permeability enhancer” technology, which allows for OCT oral absorption. Another new delivery system is a long-lasting OCT implant (VP-003, which provide stable doses of OCT throughout a period of several months. Finally, a new SRL DG3173 (somatoprim seems to be more selective for GH secretion, suggesting possible advantages in the presence of hyperglycemia or diabetes. How much these innovations will actually be beneficial to acromegaly patients in real clinical practice remains to be seen.

  6. Use of Remotely Piloted Aircraft System (RPAS) in the analysis of historical landslide occurred in 1885 in the Rječina River Valley, Croatia

    Science.gov (United States)

    Dugonjić Jovančević, Sanja; Peranić, Josip; Ružić, Igor; Arbanas, Željko; Kalajžić, Duje; Benac, Čedomir

    2016-04-01

    Numerous instability phenomena have been recorded in the Rječina River Valley, near the City of Rijeka, in the past 250 years. Large landslides triggered by rainfall and floods, were registered on both sides of the Valley. Landslide inventory in the Valley was established based on recorded historical events and LiDAR imagery. The Rječina River is a typical karstic river 18.7km long, originating from the Gorski Kotar Mountains. The central part of the Valley, belongs to the dominant morphostructural unit that strikes in the northwest-southeast direction along the Rječina River. Karstified limestone rock mass is visible on the top of the slopes, while the flysch rock mass is present on the lower slopes and at the bottom of the Valley. Different types of movements can be distinguished in the area, such as the sliding of slope deposits over the flysch bedrock, rockfalls from limestone cliffs, sliding of huge rocky blocks, and active landslide on the north-eastern slope. The paper presents investigation of the dormant landslide located on the south-western slope of the Valley, which was recorded in 1870 in numerous historical descriptions. Due to intense and long-term rainfall, the landslide was reactivated in 1885, destroying and damaging houses in the eastern part of the Grohovo Village. To predict possible reactivation of the dormant landslide on the south-western side of the Valley, 2D stability back analyses were performed on the basis of landslide features, in order to approximate the position of sliding surface and landslide dimensions. The landslide topography is very steep, and the slope is covered by unstable debris material, so therefore hard to perform any terrestrial geodetic survey. Consumer-grade DJI Phantom 2 Remotely Piloted Aircraft System (RPAS) was used to provide the data about the present slope topography. The landslide 3D point cloud was derived from approximately 200 photographs taken with RPAS, using structure-from-motion (SfM) photogrammetry

  7. Crystallization of bi-functional ligand protein complexes.

    Science.gov (United States)

    Antoni, Claudia; Vera, Laura; Devel, Laurent; Catalani, Maria Pia; Czarny, Bertrand; Cassar-Lajeunesse, Evelyn; Nuti, Elisa; Rossello, Armando; Dive, Vincent; Stura, Enrico Adriano

    2013-06-01

    Homodimerization is important in signal transduction and can play a crucial role in many other biological systems. To obtaining structural information for the design of molecules able to control the signalization pathways, the proteins involved will have to be crystallized in complex with ligands that induce dimerization. Bi-functional drugs have been generated by linking two ligands together chemically and the relative crystallizability of complexes with mono-functional and bi-functional ligands has been evaluated. There are problems associated with crystallization with such ligands, but overall, the advantages appear to be greater than the drawbacks. The study involves two matrix metalloproteinases, MMP-12 and MMP-9. Using flexible and rigid linkers we show that it is possible to control the crystal packing and that by changing the ligand-enzyme stoichiometric ratio, one can toggle between having one bi-functional ligand binding to two enzymes and having the same ligand bound to each enzyme. The nature of linker and its point of attachment on the ligand can be varied to aid crystallization, and such variations can also provide valuable structural information about the interactions made by the linker with the protein. We report here the crystallization and structure determination of seven ligand-dimerized complexes. These results suggest that the use of bi-functional drugs can be extended beyond the realm of protein dimerization to include all drug design projects. Copyright © 2013 Elsevier Inc. All rights reserved.

  8. Superior serum half life of albumin tagged TNF ligands

    International Nuclear Information System (INIS)

    Mueller, Nicole; Schneider, Britta; Pfizenmaier, Klaus; Wajant, Harald

    2010-01-01

    Due to their immune stimulating and apoptosis inducing properties, ligands of the TNF family attract increasing interest as therapeutic proteins. A general limitation of in vivo applications of recombinant soluble TNF ligands is their notoriously rapid clearance from circulation. To improve the serum half life of the TNF family members TNF, TWEAK and TRAIL, we genetically fused soluble variants of these molecules to human serum albumin (HSA). The serum albumin-TNF ligand fusion proteins were found to be of similar bioactivity as the corresponding HSA-less counterparts. Upon intravenous injection (i.v.), serum half life of HSA-TNF ligand fusion proteins, as determined by ELISA, was around 15 h as compared to approximately 1 h for all of the recombinant control TNF ligands without HSA domain. Moreover, serum samples collected 6 or 24 h after i.v. injection still contained high TNF ligand bioactivity, demonstrating that there is only limited degradation/inactivation of circulating HSA-TNF ligand fusion proteins in vivo. In a xenotransplantation model, significantly less of the HSA-TRAIL fusion protein compared to the respective control TRAIL protein was required to achieve inhibition of tumor growth indicating that the increased half life of HSA-TNF ligand fusion proteins translates into better therapeutic action in vivo. In conclusion, our data suggest that genetic fusion to serum albumin is a powerful and generally applicable mean to improve bioavailability and in vivo activity of TNF ligands.

  9. Spectra of fluorinated rare earth. beta. -diketonates with added ligands

    Energy Technology Data Exchange (ETDEWEB)

    Khomenko, V.S.; Lozinskij, M.O.; Fialkov, Yu.A.; Rasshinina, T.A.; Krasovskaya, L.I. (AN Belorusskoj SSR, Minsk. Inst. Fiziki; AN Ukrainskoj SSR, Kiev. Inst. Organicheskoj Khimii)

    1984-01-01

    Different-ligand rare earth complexes are synthesized. Fluorated ..beta..-diketones, triethylphosphine oxide and trifluoracetic acid are used as active ligands. Mass-spectra of low and high resolution are taken at the energy of ionizing electrons of 70 eV, as well as luminescence spectra of complexes. Fragmentation ways of complexes decomposition under electron shock are studied. A series of changing the bound strength of additional ligands with europium in mixed complexes is determined. It is shown that the introduction of additional ligands can purposefully change physical and chemical properties of complexes.

  10. Implicit ligand theory for relative binding free energies

    Science.gov (United States)

    Nguyen, Trung Hai; Minh, David D. L.

    2018-03-01

    Implicit ligand theory enables noncovalent binding free energies to be calculated based on an exponential average of the binding potential of mean force (BPMF)—the binding free energy between a flexible ligand and rigid receptor—over a precomputed ensemble of receptor configurations. In the original formalism, receptor configurations were drawn from or reweighted to the apo ensemble. Here we show that BPMFs averaged over a holo ensemble yield binding free energies relative to the reference ligand that specifies the ensemble. When using receptor snapshots from an alchemical simulation with a single ligand, the new statistical estimator outperforms the original.

  11. Strain, size and composition of InAs quantum sticks, embedded in InP, determined via X-ray anomalous diffraction and diffraction anomalous fine structure in grazing incidence

    International Nuclear Information System (INIS)

    Letoublon, A.; Favre-Nicolin, V.; Renevier, H.; Proietti, M.G.; Monat, C.; Gendry, M.; Marty, O.; Priester, C.

    2005-01-01

    We report on the study of strain, size and composition of small-size encapsulated semiconductor nanostructures. We show that the partial structure factor of As atoms in InAs stick-like nanostructures (quantum sticks), embedded in InP, can be directly extracted from grazing incidence anomalous X-ray diffraction maps at the As K-edge. We have recovered the average height and strain of the islands and determined their composition. The average height of the quantum sticks (QSs), as deduced from the width of the structure factor profile is 2.54 nm. The InAs out of plane deformation, relative to InP, is equal to 6.1%. Fixed-Q anomalous diffraction spectra, measured at the As K-edge, in grazing incidence provide clear evidence of pure InAs QSs. This is confirmed by the analysis of the diffraction anomalous fine structure (DAFS) that also gives a direct way to recover the strain accomodation inside the quantum sticks. Finite difference method calculations reproduce well the diffraction data. Chemical mixing at interfaces is at most 1 ML. This paper shows that ultimate application of anomalous diffraction and DAFS together with reciprocal space maps is a powerful method to sudy the structural properties of nanostructures

  12. Calculating the mean time to capture for tethered ligands and its effect on the chemical equilibrium of bound ligand pairs.

    Science.gov (United States)

    Shen, Lu; Decker, Caitlin G; Maynard, Heather D; Levine, Alex J

    2016-09-01

    We present here the calculation of the mean time to capture of a tethered ligand to the receptor. This calculation is then used to determine the shift in the partitioning between (1) free, (2) singly bound, and (3) doubly bound ligands in chemical equilibrium as a function of the length of the tether. These calculations are used in the research article Fibroblast Growth Factor 2 Dimer with Superagonist in vitro Activity Improves Granulation Tissue Formation During Wound Healing (Decker et al., in press [1]) to explain quantitatively how changes in polymeric linker length in the ligand dimers modifies the efficacy of these molecules relative to that of free ligands.

  13. Role of ligands in permanganate oxidation of organics.

    Science.gov (United States)

    Jiang, Jin; Pang, Su-Yan; Ma, Jun

    2010-06-01

    We previously demonstrated that several ligands such as phosphate, pyrophosphate, EDTA, and humic acid could significantly enhance permanganate oxidation of triclosan (one phenolic biocide), which was explained by the contribution of ligand-stabilized reactive manganese intermediates in situ formed upon permanganate reduction. To further understand the underlying mechanism, we comparatively investigated the influence of ligands on permanganate oxidation of bisphenol A (BPA, one phenolic endocrine-disrupting chemical), carbamazepine (CBZ, a pharmaceutical containing the olefinic group), and methyl p-tolyl sulfoxide (TMSO, a typical oxygen-atom acceptor). Selected ligands exerted oxidation enhancement for BPA but had negligible influence for CBZ and TMSO. This was mainly attributed to the effects of identified Mn(III) complexes, which would otherwise disproportionate spontaneously in the absence of ligands. The one-electron oxidant Mn(III) species exhibited no reactivity toward CBZ and TMSO for which the two-electron oxygen donation may be the primary oxidation mechanism but readily oxidized BPA. The latter case was a function of pH, the complexing ligand, and the molar [Mn(III)]:[ligand] ratio, generally consistent with the patterns of ligand-affected permanganate oxidation. Moreover, the combination of the one-electron reduction of Mn(III) (Mn(III) + e(-) -->Mn(II)) and the Mn(VII)/Mn(II) reaction in excess ligands (Mn(VII) + 4Mn(II) ----> (ligands) 5Mn(III)) suggested a catalytic role of the Mn(III)/Mn(II) pair in permanganate oxidation of some phenolics in the presence of ligands.

  14. Synthesis and complexation of acyclic dithiolate ligands

    International Nuclear Information System (INIS)

    Ashford, L.

    1999-11-01

    Four approaches to ring substituted and unsubstituted N,N'-bis(o-mercaptobenzyliden)propylenediaminate ligands are described using N,N-dimethylcarbamate as a thiolate protecting group. Of the four basic methods, substitution, reduction, rearrangement and oxidation, the latter two successfully synthesise the aldehyde precursor. Rearrangement of the thiocarbamoyl group to the protected thiophenol is shown to be facilitated by a para-nitro substiuent. Ni(II) and Cu(II) complexes of N,N'-bis(p-nitro-o-mercaptobenzyliden)-propylenediaminate are synthesised by reaction of 2-formyl-4-nitro-N,N-dimethylcarbamoyI thiophenol, [Ni(OAc) 2 ].4(H 2 O) and 1,3-diaminopropane. The para-unsubstituted Ni(II) complex, Nickel-[N,N'-bis(o-mercaptobenzyliden) propylenediaminate] is prepared via reaction of the aldehyde, 2-formyl-N,N-dimethylcarbamoyl thiophenol with [Ni(OAc) 2 ].4(H 2 O) and 1,3-diaminopropane. The analogous carbamoyl-protected amine ligands, N,N'-dimethyl-N.N'-di[2-(N'',N''-dimethylcarbamyl)mercapto] benzyl-1,3-propane-diamine and N,N'-dimethyl-N,N'-di[2-(N'',N''-dimethylcarbamyl)mercapto] benzyl-1,2-ethane-diamine are also studied. The tertiary-butyl-protected diimine ligand, N,N'-bis-(o-mercaptobenzylidene)-propylenediaminate is prepared from 2-(tert-butylsulfanyl)benzaldehyde and 1,3-diaminopropane. Reaction with [Ni(H 2 O) 6 ]Cl 2 gives Nickel-[N,N'-bis(o-mercaptobenzyliden)-propylenediaminate], the crystal structure showing a distorted square-planar Ni(II) centre. Reaction with ZnCl 2 gives Zinc-[N,N'-bis(o-mercaptobenzyliden)propylenediaminate]dichloride. The crystal structure shows the thiolate donors remain protected and uncoordinated. The Zn(II) ion is coordinated by two imine donors and two chloride ions in a tetrahedral environment. In reactions with Ag(I) and Hg(II), N,N'-bis-(o-mercaptobenzylidene)-propylenediaminate acts as a reductant giving the free metals. Structural data and NMR and IR spectroscopic data for Nickel

  15. Competitive growth mechanisms of InAs quantum dots on InxGa1-xAs layer during post growth interruption

    International Nuclear Information System (INIS)

    Yang, Changjae; Kim, Jungsub; Sim, Uk; Lee, Jaeyel; Choi, Won Jun; Yoon, Euijoon

    2010-01-01

    We investigated the effect of the post growth interruption (GI) on InAs quantum dots (QDs) grown on In x Ga 1-x As strained buffer layers (SBL). When QDs were grown on the 5 and 10% In content SBLs by using post GI, the size of QDs increased as its density decreased. Based on the 50 meV red-shift of PL in these cases, the transport of materials between QDs leads to the increase of QD size with maintaining its composition during the post GI. On the other hand, when using SBLs with the 15 and 20% In contents, the size of QDs increased, but its density was a little reduced. In addition, PL results were observed blue-shifted by about 20 meV and 2 meV, respectively. Considering the interruption of source gases during the post GI, these observations are strong evidence of the Ga incorporation from 15 and 20% In content SBLs. Therefore, these results imply that the dominant mechanism which increases the size of QDs during the post GI depends on the growth condition of SBL.

  16. Accurate evaluation of subband structure in a carrier accumulation layer at an n-type InAs surface: LDF calculation combined with high-resolution photoelectron spectroscopy

    Directory of Open Access Journals (Sweden)

    Takeshi Inaoka

    2012-12-01

    Full Text Available Adsorption on an n-type InAs surface often induces a gradual formation of a carrier-accumulation layer at the surface. By means of high-resolution photoelectron spectroscopy (PES, Betti et al. made a systematic observation of subbands in the accumulation layer in the formation process. Incorporating a highly nonparabolic (NP dispersion of the conduction band into the local-density-functional (LDF formalism, we examine the subband structure in the accumulation-layer formation process. Combining the LDF calculation with the PES experiment, we make an accurate evaluation of the accumulated-carrier density, the subband-edge energies, and the subband energy dispersion at each formation stage. Our theoretical calculation can reproduce the three observed subbands quantitatively. The subband dispersion, which deviates downward from that of the projected bulk conduction band with an increase in wave number, becomes significantly weaker in the formation process. Accurate evaluation of the NP subband dispersion at each formation stage is indispensable in making a quantitative analysis of collective electronic excitations and transport properties in the subbands.

  17. Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using in situ X-ray diffraction

    International Nuclear Information System (INIS)

    Shimomura, Kenichi; Ohshita, Yoshio; Kamiya, Itaru; Suzuki, Hidetoshi; Sasaki, Takuo; Takahasi, Masamitu

    2015-01-01

    Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures

  18. Wetting layer states in low density InAs/InGaAs quantum dots from sub-critical InAs coverages

    International Nuclear Information System (INIS)

    Seravalli, L; Trevisi, G; Frigeri, P; Rossi, F; Buffagni, E; Ferrari, C

    2013-01-01

    In this work we study the properties of wetting layers in InAs/InGaAs/GaAs quantum dot (QD) structures suitable for single photon emission; the mandatory low density of QDs is obtained by an molecular beam epitaxy (MBE) approach based on the deposition of sub-critical InAs coverages followed by post-growth annealing. Such a growth regime is fundamentally different from the Stranski–Krastanow (SK) one commonly used for the deposition of QDs. By fitting x-ray diffraction (XRD) spectra, ten-steps composition profiles were derived and used as inputs of model calculations of the two-dimensional quantum energy system: model results were validated by comparison with photoluminescence spectra. A strong reduction of In molar fraction in wetting layers in comparison with SK structures was found, causing a larger wavefunction delocalization for carriers that populate the wetting layer energy levels. Moreover, by considering the limits for strain relaxation when In x Ga 1−x As capping layers are used, we grew structures with the highest possible values of x to study the modifications of the energy system. When x = 0.20 the electron–heavy hole overlap is almost halved and the carriers' probability of being in the first nanometre of the wetting layer is reduced by 60%. These results will be useful for advanced design of QD nanostructures for single photon sources. (paper)

  19. Native oxide transport and removal during the atomic layer deposition of Ta{sub 2}O{sub 5} on InAs(100) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Henegar, Alex J.; Gougousi, Theodosia, E-mail: gougousi@umbc.edu [Department of Physics, UMBC, Baltimore, Maryland 21250 (United States)

    2016-05-15

    Atomic layer deposition (ALD) was used to deposit Ta{sub 2}O{sub 5} on etched and native oxide-covered InAs(100) using pentakis dimethyl amino tantalum and H{sub 2}O at 200–300 °C. The transport and removal of the native oxides during the ALD process was investigated using x-ray photoelectron spectroscopy (XPS). Depositions above 200 °C on etched surfaces protected the interface from reoxidation. On native oxide-covered surfaces, depositions resulted in enhanced native oxide removal at higher temperatures. The arsenic oxides were completely removed above 250 °C after 3 nm of film growth, but some of the As{sub 2}O{sub 3} remained in the film at lower temperatures. Angle-resolved and sputter depth profiling XPS confirmed indium and arsenic oxide migration into the Ta{sub 2}O{sub 5} film at deposition temperatures as low as 200 °C. Continuous removal of both arsenic and indium oxides was confirmed even after the deposition of several monolayers of a coalesced Ta{sub 2}O{sub 5} film, and it was demonstrated that native oxide transport is a prevalent component of the interface “clean-up” mechanism.

  20. Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using in situ X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Shimomura, Kenichi; Ohshita, Yoshio; Kamiya, Itaru, E-mail: kamiya@toyota-ti.ac.jp [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Suzuki, Hidetoshi [Faculty of Engineering, University of Miyazaki, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192 (Japan); Sasaki, Takuo; Takahasi, Masamitu [Quantum Beam Science Center, Japan Atomic Energy Agency, Koto 1-1-1, Sayo-cho, Hyogo 679-5148 (Japan)

    2015-11-14

    Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures.

  1. Observation of infrared absorption of InAs quantum dot structures in AlGaAs matrix toward high-efficiency solar cells

    Science.gov (United States)

    Yoshikawa, Hirofumi; Watanabe, Katsuyuki; Kotani, Teruhisa; Izumi, Makoto; Iwamoto, Satoshi; Arakawa, Yasuhiko

    2018-06-01

    In accordance with the detailed balance limit model of single-intermediate-band solar cells (IBSCs), the optimum matrix bandgap and IB–conduction band (CB) energy gap are ∼1.9 and 0.7 eV, respectively. We present the room-temperature polarized infrared absorption of 20 stacked InAs quantum dot (QD) structures in the Al0.32Ga0.68As matrix with a bandgap of ∼1.9 eV for the design of high-efficiency IBSCs by using a multipass waveguide geometry. We find that the IB–CB absorption is almost independent of the light polarization, and estimate the magnitude of the absorption per QD layer to be ∼0.01%. We also find that the IB–CB absorption edge of QD structures with a wide-gap matrix is ∼0.41 eV. These results indicate that both the significant increase in the magnitude of IB–CB absorption and the lower energy of the IB state for the higher IB–CB energy gap are necessary toward the realization of high-efficiency IBSCs.

  2. Coherent dynamics of excitons in a stack of self-assembled InAs quantum dots at 1.5-μm waveband

    International Nuclear Information System (INIS)

    Ishi-Hayase, J.; Akahane, K.; Yamamoto, N.; Kujiraoka, M.; Inoue, J.; Ema, K.; Tsuchiya, M.; Sasaki, M.

    2006-01-01

    We investigate the excitonic dephasing in a stack of self-assembled quantum dots (SAQDs) by using a four-wave-mixing (FWM) technique performed in the optical telecomm-fiber wavelength region at 6 K. A sample used in our experiment is a 150-layer stack of InAs SAQDs embedded in InGaAlAs grown on InP(3 1 1)B substrate fabricated by molecular beam epitaxy. By using a novel strain-controlled technique, the resonant wavelength of the exciton ground state (GS) ranges from 1.25 to 1.5 μm which is much longer than that in typical In(Ga)As SAQDs. In the weak excitation region, the intrinsic dephasing time of excitons at the excitation wavelength of 1.43 μm reaches 770 ps which is much longer than that in most SAQDs with the resonant wavelength of <1 μm. We also find a strong anisotoropy of the signal intensity with respect to the crystal axis attributed to the orientation of InP(3 1 1)B substrate and the elongated shape of QDs

  3. Radiation sensitization by an iodine-labelled DNA ligand

    Energy Technology Data Exchange (ETDEWEB)

    Martin, R F; Murray, V; D' Cunha, G; Pardee, M; Haigh, A; Hodgson, G S [Peter MacCallum Cancer Inst., Melbourne (Australia); Kampouris, E; Kelly, D P [Melbourne Univ., Parkville (Australia)

    1990-05-01

    An iodinated DNA ligand, iodoHoechst 33258, which binds in the minor groove of DNA, enhances DNA strand breakage and cell killing by UV-A irradiation. The sites of UV-induced strand breaks reflect the known sequence specificity of the ligand. (author).

  4. Identifying Marine Copper-Binding Ligands in Seawater

    Science.gov (United States)

    Whitby, H.; Hollibaugh, J. T.; Maldonado, M. T.; Ouchi, S.; van den Berg, S. M.

    2016-02-01

    Complexation reactions are important because they affect the bioavailability of trace metals such as copper and iron. For example, organic complexation can determine whether copper is a limiting or a toxic micronutrient at natural levels. Copper competes with iron for complexing ligands, and when iron is limiting, copper can also substitute for iron in some metabolic pathways. The speciation of copper can be measured using complexing capacity titrations, which provide the concentration of individual ligand classes (L1, L2 etc.) and the complex stabilities (log K). Using methods recently developed in our laboratory, we show that the ligands within these classes can be measured independently of titrations, thus confirming the titration method and simultaneously identifying the ligands within each class. Thiols were identified as the L1 ligand class and humic compounds as the weaker L2 class in samples from coastal Georgia, USA, collected monthly from April to December. Log K values of the ligand complexes were consistent with values expected for thiols and humic substances. Recent results from culture studies and from samples collected along Line P, a coastal - oceanic transect in the HNLC region of the NE subarctic Pacific, will be presented in comparison to the estuarine results. This comparison will help to broaden our perspective on copper complexation and the ligands responsible, furthering our understanding of ligand sources and life cycles.

  5. Some new IIB group complexes of an imidazolidine ligand ...

    Indian Academy of Sciences (India)

    The spectral data indicate that the ligand is coordinated to zinc(II) as a bidentate ligand in imidazolidine form but it binds to ..... confirmed by determination of the minimum inhibitory ...... Yue F, Gang L, Xiu-Mei T, Ji-De W and Wei W 2008. Chin.

  6. Mixed-Ligand Complexes Of Nickel (II) With 2-Acetylpyridine ...

    African Journals Online (AJOL)

    The preparation and spectral properties of five nickel (II) mixed-ligands complexes (Ni [2-Actsc.Y]CI2), derived from 2-acetylpyridinethiosermicarbazones and some nitrogen/sulphur monodentate ligands such as thiophene, ammonia, picoline, pyridine and aniline are described. The complexes have been characterized on ...

  7. Synthesis of meta-substituted monodentate phosphinite ligands and ...

    Indian Academy of Sciences (India)

    SATEJ S DESHMUKH

    from organic synthesis, phosphinite ligands find appli- cations in a variety of ... thesis of meta-substituted phosphinite ligands is rarely reported.18 This is most ... 1.9 μm; mobile phase used, 90% methanol + 10% water +. 0.1% formic acid) ...

  8. The Evaluation of Novel Camphor-derived Pyridyl Ligands as ...

    African Journals Online (AJOL)

    NJD

    2009-03-03

    Mar 3, 2009 ... The structures of the copper (II) complexes of the ligands were calculated using ONIOM density functional theory and the results suggest that chiral induction to the alkene functional group is indeed lacking. This explains the moderate experimental selectivities obtained. KEYWORDS. Camphor ligands ...

  9. The Evaluation of Novel Camphor-derived Pyridyl Ligands as ...

    African Journals Online (AJOL)

    The structures of the copper (II) complexes of the ligands were calculated using ONIOM density functional theory and the results suggest that chiral induction to the alkene functional group is indeed lacking. This explains the moderate experimental selectivities obtained. Keywords: Camphor ligands, asymmetric catalysis, ...

  10. THERMODYNAMICS OF PROTEIN-LIGAND INTERACTIONS AND THEIR ANALYSIS

    Directory of Open Access Journals (Sweden)

    Rummi Devi Saini

    2017-11-01

    Full Text Available Physiological processes are controlled mainly by intermolecular recognition mechanisms which involve protein–protein and protein–ligand interactions with a high specificity and affinity to form a specific complex. Proteins being an important class of macromolecules in biological systems, it is important to understand their actions through binding to other molecules of proteins or ligands. In fact, the binding of low molecular weight ligands to proteins plays a significant role in regulating biological processes such as cellular metabolism and signal transmission. Therefore knowledge of the protein–ligand interactions and the knowledge of the mechanisms involved in the protein-ligand recognition and binding are key in understanding biology at molecular level which will facilitate the discovery, design, and development of drugs. In this review, the mechanisms involved in protein–ligand binding, the binding kinetics, thermodynamic concepts and binding driving forces are discussed. Thermodynamic mechanisms involved in a few important protein-ligand binding are described. Various spectroscopic, non-spectroscopic and computational method for analysis of protein–ligand binding are also discussed.

  11. Polymerization catalysts containing electron-withdrawing amide ligands

    Science.gov (United States)

    Watkin, John G.; Click, Damon R.

    2002-01-01

    The present invention describes methods of making a series of amine-containing organic compounds which are used as ligands for group 3-10 and lanthanide metal compounds. The ligands have electron-withdrawing groups bonded to them. The metal compounds, when combined with a cocatalyst, are catalysts for the polymerization of olefins.

  12. Mixed ligand chelate therapy for plutonium and cadmium poisoning

    Energy Technology Data Exchange (ETDEWEB)

    Schubert, J; Derr, S K [Hope Coll., Holland, MI (USA)

    1978-09-28

    Some experiments with mice are described in which complete removal of tissue deposits of /sup 239/Pu and prevention of mortality in animals given lethal doses of Cd were achieved using a mixed ligand chelate treatment (MLC). The mixed ligand consisted of diethylenetriaminepentaacetic acid and salicylic acid.

  13. Immobilisation of ligands by radio-derivatized polymers

    International Nuclear Information System (INIS)

    Varga, J.M.; Fritsch, P.

    1995-01-01

    The invention relates to radio-derivatized polymers and a method of producing them by contacting non-polymerizable conjugands with radiolysable polymers in the presence of irradiation. The resulting radio-derivatized polymers can be further linked with ligand of organic or inorganic nature to immobilize such ligands. 2 figs., 5 tabs

  14. Correcting binding parameters for interacting ligand-lattice systems

    Science.gov (United States)

    Hervy, Jordan; Bicout, Dominique J.

    2017-07-01

    Binding of ligands to macromolecules is central to many functional and regulatory biological processes. Key parameters characterizing ligand-macromolecule interactions are the stoichiometry, inducing the number of ligands per macromolecule binding site, and the dissociation constant, quantifying the ligand-binding site affinity. Both these parameters can be obtained from analyses of classical saturation experiments using the standard binding equation that offers the great advantage of mathematical simplicity but becomes an approximation for situations of interest when a ligand binds and covers more than one single binding site on the macromolecule. Using the framework of car-parking problem with latticelike macromolecules where each ligand can cover simultaneously several consecutive binding sites, we showed that employing the standard analysis leads to underestimation of binding parameters, i.e., ligands appear larger than they actually are and their affinity is also greater than it is. Therefore, we have derived expressions allowing to determine the ligand size and true binding parameters (stoichiometry and dissociation constant) as a function of apparent binding parameters retrieved from standard saturation experiments.

  15. Predicting Nanocrystal Shape through Consideration of Surface-Ligand Interactions

    KAUST Repository

    Bealing, Clive R.; Baumgardner, William J.; Choi, Joshua J.; Hanrath, Tobias; Hennig, Richard G.

    2012-01-01

    Density functional calculations for the binding energy of oleic acid-based ligands on Pb-rich {100} and {111} facets of PbSe nanocrystals determine the surface energies as a function of ligand coverage. Oleic acid is expected to bind

  16. Lanthanide(III) complexes with tridentate Schiff base ligand ...

    African Journals Online (AJOL)

    The X-ray study reveals isotopic Nd/Sm binuclear structures were each metal ion is nine-coordinated in the same fashion. Both metal centers have distorted tricapped trigonal prism geometry, with the Schiff base acting as tridentate ligand. The DPPH· radical scavenging effects of the Schiff base ligand and its Ln(III) ...

  17. Models of protein-ligand crystal structures: trust, but verify.

    Science.gov (United States)

    Deller, Marc C; Rupp, Bernhard

    2015-09-01

    X-ray crystallography provides the most accurate models of protein-ligand structures. These models serve as the foundation of many computational methods including structure prediction, molecular modelling, and structure-based drug design. The success of these computational methods ultimately depends on the quality of the underlying protein-ligand models. X-ray crystallography offers the unparalleled advantage of a clear mathematical formalism relating the experimental data to the protein-ligand model. In the case of X-ray crystallography, the primary experimental evidence is the electron density of the molecules forming the crystal. The first step in the generation of an accurate and precise crystallographic model is the interpretation of the electron density of the crystal, typically carried out by construction of an atomic model. The atomic model must then be validated for fit to the experimental electron density and also for agreement with prior expectations of stereochemistry. Stringent validation of protein-ligand models has become possible as a result of the mandatory deposition of primary diffraction data, and many computational tools are now available to aid in the validation process. Validation of protein-ligand complexes has revealed some instances of overenthusiastic interpretation of ligand density. Fundamental concepts and metrics of protein-ligand quality validation are discussed and we highlight software tools to assist in this process. It is essential that end users select high quality protein-ligand models for their computational and biological studies, and we provide an overview of how this can be achieved.

  18. Ligand Binding Domain Protein in Tetracycline-Inducible Expression

    African Journals Online (AJOL)

    Purpose: To investigate tetracycline-inducible expression system for producing clinically usable, highquality liver X receptor ligand-binding domain recombinant protein. Methods: In this study, we have expressed and purified the recombinant liver X receptor β-ligand binding domain proteins in E. coli using a tetracycline ...

  19. Novel peptide ligand with high binding capacity for antibody purification

    DEFF Research Database (Denmark)

    Lund, L. N.; Gustavsson, P. E.; Michael, R.

    2012-01-01

    Small synthetic ligands for protein purification have become increasingly interesting with the growing need for cheap chromatographic materials for protein purification and especially for the purification of monoclonal antibodies (mAbs). Today, Protein A-based chromatographic resins are the most...... commonly used capture step in mAb down stream processing; however, the use of Protein A chromatography is less attractive due to toxic ligand leakage as well as high cost. Whether used as an alternative to the Protein A chromatographic media or as a subsequent polishing step, small synthetic peptide...... ligands have an advantage over biological ligands; they are cheaper to produce, ligand leakage by enzymatic degradation is either eliminated or significantly reduced, and they can in general better withstand cleaning in place (CIP) conditions such as 0.1 M NaOH. Here, we present a novel synthetic peptide...

  20. Identification and characterization of PPARα ligands in the hippocampus.

    Science.gov (United States)

    Roy, Avik; Kundu, Madhuchhanda; Jana, Malabendu; Mishra, Rama K; Yung, Yeni; Luan, Chi-Hao; Gonzalez, Frank J; Pahan, Kalipada

    2016-12-01

    Peroxisome proliferator-activated receptor-α (PPARα) regulates hepatic fatty acid catabolism and mediates the metabolic response to starvation. Recently we found that PPARα is constitutively activated in nuclei of hippocampal neurons and controls plasticity via direct transcriptional activation of CREB. Here we report the discovery of three endogenous PPARα ligands-3-hydroxy-(2,2)-dimethyl butyrate, hexadecanamide, and 9-octadecenamide-in mouse brain hippocampus. Mass spectrometric detection of these compounds in mouse hippocampal nuclear extracts, in silico interaction studies, time-resolved FRET analyses, and thermal shift assay results clearly indicated that these three compounds served as ligands of PPARα. Site-directed mutagenesis studies further revealed that PPARα Y464 and Y314 are involved in binding these hippocampal ligands. Moreover, these ligands activated PPARα and upregulated the synaptic function of hippocampal neurons. These results highlight the discovery of hippocampal ligands of PPARα capable of modulating synaptic functions.

  1. Ligand Electron Density Shape Recognition Using 3D Zernike Descriptors

    Science.gov (United States)

    Gunasekaran, Prasad; Grandison, Scott; Cowtan, Kevin; Mak, Lora; Lawson, David M.; Morris, Richard J.

    We present a novel approach to crystallographic ligand density interpretation based on Zernike shape descriptors. Electron density for a bound ligand is expanded in an orthogonal polynomial series (3D Zernike polynomials) and the coefficients from this expansion are employed to construct rotation-invariant descriptors. These descriptors can be compared highly efficiently against large databases of descriptors computed from other molecules. In this manuscript we describe this process and show initial results from an electron density interpretation study on a dataset containing over a hundred OMIT maps. We could identify the correct ligand as the first hit in about 30 % of the cases, within the top five in a further 30 % of the cases, and giving rise to an 80 % probability of getting the correct ligand within the top ten matches. In all but a few examples, the top hit was highly similar to the correct ligand in both shape and chemistry. Further extensions and intrinsic limitations of the method are discussed.

  2. Automated identification of crystallographic ligands using sparse-density representations

    International Nuclear Information System (INIS)

    Carolan, C. G.; Lamzin, V. S.

    2014-01-01

    A novel procedure for identifying ligands in macromolecular crystallographic electron-density maps is introduced. Density clusters in such maps can be rapidly attributed to one of 82 different ligands in an automated manner. A novel procedure for the automatic identification of ligands in macromolecular crystallographic electron-density maps is introduced. It is based on the sparse parameterization of density clusters and the matching of the pseudo-atomic grids thus created to conformationally variant ligands using mathematical descriptors of molecular shape, size and topology. In large-scale tests on experimental data derived from the Protein Data Bank, the procedure could quickly identify the deposited ligand within the top-ranked compounds from a database of candidates. This indicates the suitability of the method for the identification of binding entities in fragment-based drug screening and in model completion in macromolecular structure determination

  3. The affinity of the uranyl ion for nitrogen donor ligands

    International Nuclear Information System (INIS)

    Jarvis, N.V.; De Sousa, A.S.; Hancock, R.D.

    1992-01-01

    Established ligand design principles are used to predict the solution chemistry of UO 2 2+ with nitrogen donor ligands which do not contain carboxylate donors. pK a 's of the nitrogen donors are lowered by addition of hydroxylalkyl groups causing UO 2 2+ to have a greater affinity for these ligands than for hydroxide. Potentiometric studies using the ligands N,N,N',N',N''-pentakis(2-hydroxypropyl)-1,4,7-triazaheptane; N,N,N',N',N''-pentakis(2-hydroxyethyl)-1,4,7-triazaheptane; N,N,N',N'-tetrakis(2-hydroxypropyl)1,2-diaminoethane, N,N,N',N'-tetrakis(2-hydroxyethyl)-trans-1,2-diaminocyclohexane; 1,4,8,11-tetrakis(2-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane and N,N-bis(2-hydroxyethyl)glycine with UO 2 2+ showed that UO 2 2+ has a considerable aqueous solution chemistry with these ligands. (orig.)

  4. Regulation mechanisms of the FLT3-ligand after irradiation

    International Nuclear Information System (INIS)

    Prat-Lepesant, M.

    2005-06-01

    The hematopoietic compartment is one of the most severely damaged after chemotherapy, radiotherapy or accidental irradiations. Whatever its origin, the resulting damage to the bone marrow remains difficult to evaluate. Thus, it would be of great interest to get a biological indicator of residual hematopoiesis in order to adapt the treatment to each clinical situation. Recent results indicated that the plasma Flt3 ligand concentration was increased in patients suffering from either acquired or induced aplasia, suggesting that Flt3 ligand might be useful as a biological indicator of bone marrow status. We thus followed in a mouse model as well as in several clinical situations the variations in plasma Flt3 ligand concentration, after either homogeneous or heterogeneous irradiations. These variations were correlated to the number of hematopoietic progenitors and to other parameters such as duration and depth of pancytopenia. The results indicated that the concentration of Flt3 ligand in the blood reflects the bone marrow status, and that the follow-up of plasma Flt3 ligand concentration could give predictive information about the bone marrow function and the duration and severity of pancytopenia and thrombocytopenia. Nevertheless, the clinical use of Flt3 ligand as a biological indicator of bone marrow damage require the knowledge of the mechanisms regulating the variations in plasma Flt3 ligand concentration. We thus developed a study in the mouse model. The results indicated that the variations in plasma Flt3 ligand variations were not solely due to a balance between its production by lymphoid cells and its consumption by hematopoietic cells. Moreover, we showed that T lymphocytes are not the main regulator of plasma Flt3 ligand concentration as previously suggested, and that other cell types, possibly including bone marrow stromal cells, might be strongly implicated. These results also suggest that the Flt3 ligand is a main systemic regulator of hematopoiesis

  5. Cellular trafficking of quantum dot-ligand bioconjugates and their induction of changes in normal routing of unconjugated ligands

    DEFF Research Database (Denmark)

    Tekle, Christina; van Deurs, Bo; Sandvig, Kirsten

    2008-01-01

    Can quantum dots (Qdots) act as relevant intracellular probes to investigate routing of ligands in live cells? The intracellular trafficking of Qdots that were coupled to the plant toxin ricin, Shiga toxin, or the ligand transferrin (Tf) was studied by confocal fluorescence microscopy. The Tf...

  6. Gas adsorption and gas mixture separations using mixed-ligand MOF material

    Science.gov (United States)

    Hupp, Joseph T [Northfield, IL; Mulfort, Karen L [Chicago, IL; Snurr, Randall Q [Evanston, IL; Bae, Youn-Sang [Evanston, IL

    2011-01-04

    A method of separating a mixture of carbon dioxiode and hydrocarbon gas using a mixed-ligand, metal-organic framework (MOF) material having metal ions coordinated to carboxylate ligands and pyridyl ligands.

  7. Regulation mechanisms of the FLT3-ligand after irradiation; Mecanismes de regulation du FLT3-ligand apres irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Prat-Lepesant, M

    2005-06-15

    The hematopoietic compartment is one of the most severely damaged after chemotherapy, radiotherapy or accidental irradiations. Whatever its origin, the resulting damage to the bone marrow remains difficult to evaluate. Thus, it would be of great interest to get a biological indicator of residual hematopoiesis in order to adapt the treatment to each clinical situation. Recent results indicated that the plasma Flt3 ligand concentration was increased in patients suffering from either acquired or induced aplasia, suggesting that Flt3 ligand might be useful as a biological indicator of bone marrow status. We thus followed in a mouse model as well as in several clinical situations the variations in plasma Flt3 ligand concentration, after either homogeneous or heterogeneous irradiations. These variations were correlated to the number of hematopoietic progenitors and to other parameters such as duration and depth of pancytopenia. The results indicated that the concentration of Flt3 ligand in the blood reflects the bone marrow status, and that the follow-up of plasma Flt3 ligand concentration could give predictive information about the bone marrow function and the duration and severity of pancytopenia and thrombocytopenia. Nevertheless, the clinical use of Flt3 ligand as a biological indicator of bone marrow damage require the knowledge of the mechanisms regulating the variations in plasma Flt3 ligand concentration. We thus developed a study in the mouse model. The results indicated that the variations in plasma Flt3 ligand variations were not solely due to a balance between its production by lymphoid cells and its consumption by hematopoietic cells. Moreover, we showed that T lymphocytes are not the main regulator of plasma Flt3 ligand concentration as previously suggested, and that other cell types, possibly including bone marrow stromal cells, might be strongly implicated. These results also suggest that the Flt3 ligand is a main systemic regulator of hematopoiesis

  8. Effects of electrostatic interactions on ligand dissociation kinetics

    Science.gov (United States)

    Erbaş, Aykut; de la Cruz, Monica Olvera; Marko, John F.

    2018-02-01

    We study unbinding of multivalent cationic ligands from oppositely charged polymeric binding sites sparsely grafted on a flat neutral substrate. Our molecular dynamics simulations are suggested by single-molecule studies of protein-DNA interactions. We consider univalent salt concentrations spanning roughly a 1000-fold range, together with various concentrations of excess ligands in solution. To reveal the ionic effects on unbinding kinetics of spontaneous and facilitated dissociation mechanisms, we treat electrostatic interactions both at a Debye-Hückel (DH) (or implicit ions, i.e., use of an electrostatic potential with a prescribed decay length) level and by the more precise approach of considering all ionic species explicitly in the simulations. We find that the DH approach systematically overestimates unbinding rates, relative to the calculations where all ion pairs are present explicitly in solution, although many aspects of the two types of calculation are qualitatively similar. For facilitated dissociation (FD) (acceleration of unbinding by free ligands in solution) explicit-ion simulations lead to unbinding at lower free-ligand concentrations. Our simulations predict a variety of FD regimes as a function of free-ligand and ion concentrations; a particularly interesting regime is at intermediate concentrations of ligands where nonelectrostatic binding strength controls FD. We conclude that explicit-ion electrostatic modeling is an essential component to quantitatively tackle problems in molecular ligand dissociation, including nucleic-acid-binding proteins.

  9. Database of ligand-induced domain movements in enzymes

    Directory of Open Access Journals (Sweden)

    Hayward Steven

    2009-03-01

    Full Text Available Abstract Background Conformational change induced by the binding of a substrate or coenzyme is a poorly understood stage in the process of enzyme catalysed reactions. For enzymes that exhibit a domain movement, the conformational change can be clearly characterized and therefore the opportunity exists to gain an understanding of the mechanisms involved. The development of the non-redundant database of protein domain movements contains examples of ligand-induced domain movements in enzymes, but this valuable data has remained unexploited. Description The domain movements in the non-redundant database of protein domain movements are those found by applying the DynDom program to pairs of crystallographic structures contained in Protein Data Bank files. For each pair of structures cross-checking ligands in their Protein Data Bank files with the KEGG-LIGAND database and using methods that search for ligands that contact the enzyme in one conformation but not the other, the non-redundant database of protein domain movements was refined down to a set of 203 enzymes where a domain movement is apparently triggered by the binding of a functional ligand. For these cases, ligand binding information, including hydrogen bonds and salt-bridges between the ligand and specific residues on the enzyme is presented in the context of dynamical information such as the regions that form the dynamic domains, the hinge bending residues, and the hinge axes. Conclusion The presentation at a single website of data on interactions between a ligand and specific residues on the enzyme alongside data on the movement that these interactions induce, should lead to new insights into the mechanisms of these enzymes in particular, and help in trying to understand the general process of ligand-induced domain closure in enzymes. The website can be found at: http://www.cmp.uea.ac.uk/dyndom/enzymeList.do

  10. Calculation of protein-ligand binding affinities.

    Science.gov (United States)

    Gilson, Michael K; Zhou, Huan-Xiang

    2007-01-01

    Accurate methods of computing the affinity of a small molecule with a protein are needed to speed the discovery of new medications and biological probes. This paper reviews physics-based models of binding, beginning with a summary of the changes in potential energy, solvation energy, and configurational entropy that influence affinity, and a theoretical overview to frame the discussion of specific computational approaches. Important advances are reported in modeling protein-ligand energetics, such as the incorporation of electronic polarization and the use of quantum mechanical methods. Recent calculations suggest that changes in configurational entropy strongly oppose binding and must be included if accurate affinities are to be obtained. The linear interaction energy (LIE) and molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) methods are analyzed, as are free energy pathway methods, which show promise and may be ready for more extensive testing. Ultimately, major improvements in modeling accuracy will likely require advances on multiple fronts, as well as continued validation against experiment.

  11. Constitutive and ligand-induced TCR degradation

    DEFF Research Database (Denmark)

    von Essen, Marina; Bonefeld, Charlotte Menné; Siersma, Volkert

    2004-01-01

    Modulation of TCR expression levels is a central event during T cell development and activation, and it probably plays an important role in adjusting T cell responsiveness. Conflicting data have been published on down-regulation and degradation rates of the individual TCR subunits, and several di...... to the lysosomes. Similar results were obtained in studies of primary human Vbeta8+ T cells stimulated with superantigen. Based on these results, the simplest model for TCR internalization, sorting, and degradation is proposed.......Modulation of TCR expression levels is a central event during T cell development and activation, and it probably plays an important role in adjusting T cell responsiveness. Conflicting data have been published on down-regulation and degradation rates of the individual TCR subunits, and several...... divergent models for TCR down-regulation and degradation have been suggested. The aims of this study were to determine the rate constants for constitutive and ligand-induced TCR degradation and to determine whether the TCR subunits segregate or are processed as an intact unit during TCR down...

  12. The coordination chemistry of macrocyclic ligands II

    International Nuclear Information System (INIS)

    Klimes, J.; Knoechel, A.; Rudolph, G.

    1977-01-01

    Compounds of UO 2 (NO 3 ) 2 .6H 2 0 or Th(NO 3 ) 4 .5H 2 0 with five selected crown ethers were prepared according to the method described in Knoeckel et al., Inorg.Nucl.Chem.Lett.; 11:787 (1975). The products were characterized by chemical analysis, NMR, IR and Raman spectroscopy. The results are analyzed and discussed. It is shown that the NO 3 groups remain free after combination, and the H 2 0 groups form the bonds to the polyether. It is concluded that the polyether molecule is attached to two units of UO 2 (NO 3 ) 2 .2H 2 0 (or Th(NO 3 ) 4 .3H 2 0), one each side of the polyether. This would be contrary to the assumption in previous publications, that the U0 2 2+ and Th 4+ ions were coordinated inside the macrocyclic ligand structure. The present hypothesis, however, agrees with a recently published x-ray structure for the uranium compound. In view of the new proposed structure it is suggested that the compounds should be regarded as adducts rather than complexes. (U.K.)

  13. Complexes of technetium with polyhydric ligands

    International Nuclear Information System (INIS)

    Hwang, L.L.Y.; Ronca, N.; Solomon, N.A.; Steigman, J.

    1985-01-01

    Polyhydric complexes of Tc(V) show absorption bands near 500 nm, with molar absorptivity coefficients of about 100. The shorter-chain compounds like ethylene glycol produce complexes which quickly disproportionate to Tc(IV) (as TcO 2 ) and Tc(VII) (as TcO 4 - ) on acidification. The longer-chain ligands like mannitol and gluconate do not. However, while the mannitol complex shows no change in spectrum from pH 12 to pH 3, the gluconate and glucoheptonate compounds show a definite spectral change on acidification, starting at pH 5. Electrophoresis similarity showed a change in mobility with pH for Tc-glucoheptonate, but none for Tc-mannitol. It was concluded that the carboxylic acid group of glucoheptonate was not binding the technetium. In 25 molal choline chloride the glucoheptonate-Tc mole ratio was 1:1 or less. A similar result emerged from a similar experiment in methylcellosolve as solvent. (author)

  14. Electrolytic formation of technetium complexes with π-acceptor ligands

    International Nuclear Information System (INIS)

    Cerda, F.; Kremer, C.; Gambino, D.; Kremer, E.

    1994-01-01

    Electrolytic reduction of pertechnetate was performed in aqueous solution containing π-acceptor ligands. Cyanide and 1,10-phenanthroline were the selected ligands. In both cases, electrolyses produced a cathodic TcO 2 deposit and soluble Tc complexes. When cyanide was the ligand, the complexes formed were [Tc(CN) 6 ] 5- and [TcO 2 (CN) 4 ] 3- . When working with the amine, [Tc(phen) 3 ] 2+ and another positively charged species were found after reaction. Results are compared with previous studies with amines, and the usefulness of the electrolytic route to obtain Tc complexes is evaluated. (author) 11 refs.; 2 figs.; 1 tab

  15. Synthesis and study of new oxazoline-based ligands

    OpenAIRE

    Tilliet, Mélanie

    2008-01-01

    This thesis deals with the study of oxazoline-based ligands in metal-catalyzed asymmetric reactions. The first part describes the synthesis of six new bifunctinal pyridine-bis(oxazoline) ligands and their applications in asymmetric metal-catalysis. These ligands, in addition to a Lewis acid coordination site, are equipped with a Lewis basic part in the 4-position of the oxazoline rings. Dual activation by means of this system was probed in cyanide addition to aldehydes. The second part is con...

  16. NKG2D and its ligands in cancer.

    Science.gov (United States)

    Dhar, Payal; Wu, Jennifer D

    2018-04-01

    NKG2D is an activating immune receptor expressed by NK and effector T cells. Induced expression of NKG2D ligand on tumor cell surface during oncogenic insults renders cancer cells susceptible to immune destruction. In advanced human cancers, tumor cells shed NKG2D ligand to produce an immune soluble form as a means of immune evasion. Soluble NKG2D ligands have been associated with poor clinical prognosis in cancer patients. Harnessing NKG2D pathway is considered a viable avenue in cancer immunotherapy over recent years. In this review, we will discuss the progress and perspectives. Copyright © 2018. Published by Elsevier Ltd.

  17. Entangled zinc-ditetrazolate frameworks involving in situ ligand synthesis and topological modulation by various secondary N-donor ligands

    International Nuclear Information System (INIS)

    Li Yunwu; Chen Weilin; Wang Yonghui; Li Yangguang; Wang Enbo

    2009-01-01

    The introduction of various secondary N-donor ligands into an in situ ditetrazolate-ligand synthesis system of terephthalonitrile, NaN 3 and ZnCl 2 led to the formation of three new entangled frameworks Zn(pdtz)(4,4'-bipy).3H 2 O (1), [Zn(pdtz)(bpp)] 2 .3H 2 O (2) and Zn(pdtz) 0.5 (N 3 )(2,2'-bipy) (3) (4,4'-bipy=4,4'-bipyridine; bpp=1,3-bis(4-pyridyl)propane; 2,2'-bipy=2,2'-bipyridine; H 2 pdtz=5,5'-1,4-phenylene-ditetrazole). The formation of pdtz 2- ligand involves the Sharpless [2+3] cycloaddition reaction between terephthalonitrile and NaN 3 in the presence of Zn 2+ ion as a Lewis-acid catalyst under hydrothermal conditions. Compound 1 exhibits a fivefold interpenetrating 3D framework based on the diamondoid topology. Compound 2 displays a twofold parallel interpenetrating framework based on the wavelike individual network. Compound 3 possesses a 2D puckered network. These new Zn-ditetrazolate frameworks are highly dependent on the modulation of different secondary N-donor ligands. Their luminescent properties were investigated. - Graphical abstract: Three new entangled frameworks were prepared by an in situ ditetrazolate-ligand synthesis system assisted with various auxiliary N-donor ligands. The entangled structures can be modulated by different secondary ligands.

  18. Formation of mixed ligand complexes of UO22+ involving some nitrogen and oxygen donor ligands

    International Nuclear Information System (INIS)

    Singh, Mamta; Ram Nayan

    1996-01-01

    The complexation reactions of UO 2 2+ ion with nitrogen and oxygen donor ligands, 1-amino-2-naphthol-4-sulphonic acid, o-aminophenol (ap), 2-hydroxybenzoic acid (sa), 3-carboxy-4-hydroxybenzenesulphonic acid (ss) and 1,2-dihydroxybenzene (ca) have been investigated in aqueous solution employing the pH-titration technique. Analysis of the experimental data recorded at 25 degC and at an ionic strength of 0.10 M KNO 3 indicates formation of binary, hydroxo and ternary complexes of uranium. Formation constant values of the existing species have been evaluated and the results have been discussed. (author). 21 refs., 2 figs., 2 tabs

  19. Screening of agricultural wastes as a medium production of catalase for enzymatic fuel cell by Neurospora crassa InaCC F226

    Science.gov (United States)

    Santoso, Pugoh; Yopi

    2017-12-01

    Explorations of local microorganisms from Indonesia that can produce of catalase are still limited. Neurospora crassa is a fungus which resulting of two kinds of catalase, namely catalase-1 and catalase-3. We studied the production of catalase by Neurospora crassa (no. F226) from Indonesia Culture Collection (InaCC) in Solid State Fermentation (SSF). Among four screened agro wastes (corn cob, rice straw, oil palm empty fruit bunches, and bagasse), rice straw and oil palm empty fruit bunches (OPEFB) were remarked as the most promising substrate suited for the excellent growth and adequate production of catalase. Based on the result, the method of solid state fermentation was suitable to production of catalase. It is caused that the medium served to maintain microbial growth and metabolism. The filamentous filament is more suitable for living on solid media because it has a high tolerance to low water activity, and it has a high potential to excrete hydrolytic enzymes that caused of its morphology. The filamentous filament morphology allows the fungus to form colonies and penetrate the solid substrates in order to obtain nutrients. The results showed that the highest catalase activity was obtained on rice straw and oil palm empty fruit bunches medium with catalase activity of 39.1 U/mL and 37,7 U/mL in 50% moisture content medium, respectively. Optimization of humidity and pH medium in the rice straw were investigated which is the highest activity obtained in 30% moisture content and pH medium of 6. The catalase activity was reached in the value of 53.761 U/mL and 56.903 U/mL by incubated 48 hours and 96 hours, respectively.

  20. Cytotoxicity of an 125I-labelled DNA ligand

    International Nuclear Information System (INIS)

    Karagiannis, T.C.; Lobachevsky, P.N.; Martin, R.F.

    2000-01-01

    The subcellular distribution and cytotoxicity of a DNA-binding ligand [ 125 I]-Hoechst 33258 following incubation of K562 cells with the drug was investigated. The ability of a radical scavenger, dimethyl sulphoxide, to protect cells from the 125 I-decay induced cell death was also studied. Three different concentrations and specific activities of the drug were used to provide different ligand : DNA binding ratios. The results demonstrated a trend toward improved delivery of the ligand to the nucleus and to chromatin at higher ligand concentrations, with concomitant increased sensitivity to 125 I-decay induced cytotoxicity and decreased protection by dimethyl sulphoxide. This correlation of radiobiological parameters with subcellular drug distribution is consistent with the classical dogma that attributes cytotoxicity to DNA double-stranded breakage in the vicinity of the site of decay, where the high LET nature of the damage confers minimal sensitivity to radical scavenging

  1. Epibatidine-derivatives: ligands for the neuronal nicotinic acetylcholine receptor

    International Nuclear Information System (INIS)

    Westera, G.; Patt, J.T.; Jankowski, K.; Bertrand, D.; Spang, J.; Schubiger, P.A.

    1997-01-01

    Epibatidine, isolated from the Ecuadorian frog Epipedobates tricolar, has been synthesized. 11 C-N-methyl derivate is investigated as useful nicotinergic receptor ligand by electrophysiological methods and in vivo mice experiments. (author) 2 figs., 7 refs

  2. PET and Hormone Receptor Ligands in Breast Cancer

    National Research Council Canada - National Science Library

    Gemignani, Mary

    2006-01-01

    .... To investigate this further, this project's objectives are: To evaluate the use of estrogen-like ligands labeled with positron emitters in preoperatively determining the ER status of breast cancer using PET...

  3. Unique advantages of organometallic supporting ligands for uranium complexes

    Energy Technology Data Exchange (ETDEWEB)

    Diaconescu, Paula L. [Univ. of California, Los Angeles, CA (United States); Garcia, Evan [Univ. of California, Los Angeles, CA (United States)

    2014-05-31

    The objective of our research project was to study the reactivity of uranium complexes supported by ferrocene-based ligands. In addition, this research provides training of graduate students as the next generation of actinide scientists.

  4. Unique advantages of organometallic supporting ligands for uranium complexes

    International Nuclear Information System (INIS)

    Diaconescu, Paula L.; Garcia, Evan

    2014-01-01

    The objective of our research project was to study the reactivity of uranium complexes supported by ferrocene-based ligands. In addition, this research provides training of graduate students as the next generation of actinide scientists.

  5. Ligand Binding Domain Protein in Tetracycline-Inducible Expression ...

    African Journals Online (AJOL)

    binding domain proteins in E. coli using a tetracycline inducible system. To allow for ... development of molecular ligands with improved therapeutic windows. Keywords: Nuclear receptor ..... functional recombinant cannabinoid receptor CB2 in ...

  6. related apoptosis-inducing ligand in transplastomic tobacco

    African Journals Online (AJOL)

    -inducing ligand (sTRAIL) can, as the whole length TRAIL protein, bind with its receptors and specifically induce the apoptosis of cancer cells; therefore, it has been developed as a potential therapeutic agent for various cancer treatments.

  7. Dysprosium complexes with the tetraphenylporphyrin macrocyclic ligand

    International Nuclear Information System (INIS)

    Martinez M, V.; Padilla, J.; Ramirez, F.M.

    1992-04-01

    In this report, the results obtained on the synthesis, characterization and study of the chemical behavior of dysprosium complex with the acetylacetone chelating agent (Hacac) and the tetraphenylporphyrin macrocyclic ligand (H 2 TFP) are given. Based on the literature but according to our necessities and interest, the appropriate methodology settled down from the synthesis of prime matters until the obtaining and characterization of the products. The acetyl acetonate complex was obtained of mono hydrated dysprosium [Dy(acac) 3 . H 2 0] and trihydrated [Dy(acac) 3 .3 H 2 0], the mono tetra phenyl porphyrinate [Dy(TFP)(acac). 2 ac] the double sandwich of the dysprosium porphyrinate [Dy(TFP) 2 ] and the triple sandwich of the dysprosium porphyrinate [Dy(TFP) 3 . 2 TCB] (TCB = trichlorobenzene). Its were characterized by their melting points, solubility, IR, UV, TGA and DTA both first and besides the techniques already mentioned for NMR'H, RPE and Magnetic susceptibility the three last complexes. From the spectroscopic point of view, IR and RPE its suggested the existence of a complex of inverse mixed valence [Dy(TFP) 2- (TFP) 1- ] for the Dy(TFP) 2 as a result of the existence of the free radical (TFP' 1- and that it was not in none of the other porphyrin compounds. In the NMR'H spectra of the compounds were not observed signals in the region from 0 to 10 ppm that which shows that the dysprosium complexes in special those of the porphyrin type are highly paramagnetic and its could be used as displacement reagents, creators of images and contrast agents of great utility in these days in studies of NMR, technique today by today used in medical diagnoses. (Author)

  8. Photodiode 1 × 64 linear array based on a double p-InAsSbP/n-InAs{sub 0.92}Sb{sub 0.08}/n{sup +}-InAs heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Il’inskaya, N. D., E-mail: ioffeled@mail.ru; Karandashev, S. A. [Russian Academy of Sciences, Ioffe Institute (Russian Federation); Karpukhina, N. G. [Limited Liability Company Ioffe LED Ltd. (Russian Federation); Lavrov, A. A.; Matveev, B. A.; Remennyi, M. A.; Stus, N. M.; Usikova, A. A. [Russian Academy of Sciences, Ioffe Institute (Russian Federation)

    2016-05-15

    The results of studies of the current–voltage characteristics and of the photoelectric and luminescence properties of a monolithic diode 1 × 64 linear array based on p-InAsSbP/n-InAsSb/n{sup +}-InAs with the n{sup +}-InAs-substrate side illuminated and sensitive in the region of 4-μm are reported. An analysis is performed of the mechanisms of current flow in the temperature range of 77–353 K and also of the photosensitivity and the speed of response taking into account the spatial distribution of nonequilibrium radiation and the data of capacitance–voltage measurements.

  9. Influence of nitrogen on the growth and the properties of InAs quantum dots; Einfluss von Stickstoff auf das Wachstum und die Eigenschaften von InAs-Quantenpunkten

    Energy Technology Data Exchange (ETDEWEB)

    Schumann, O.

    2004-11-01

    This work investigates the influence of nitrogen incorporation on the growth and the optical properties of InAs quantum dots on GaAs(001) substrates. On the basis of systematic growth interruptions it was shown that the large quantum dots nucleate at dislocations, which are already formed during the growth of the wetting layer. After solving the growth problems, the influence of different combinations of matrix layers on the structural and optical properties of the quantum dots was investigated in the second part of this work. The strain and bandgap of these layers were varied systematically. (orig.)

  10. Tetrapyrroles as Endogenous TSPO Ligands in Eukaryotes and Prokaryotes: Comparisons with Synthetic Ligands

    Directory of Open Access Journals (Sweden)

    Leo Veenman

    2016-06-01

    Full Text Available The 18 kDa translocator protein (TSPO is highly 0conserved in eukaryotes and prokaryotes. Since its discovery in 1977, numerous studies established the TSPO’s importance for life essential functions. For these studies, synthetic TSPO ligands typically are applied. Tetrapyrroles present endogenous ligands for the TSPO. Tetrapyrroles are also evolutionarily conserved and regulate multiple functions. TSPO and tetrapyrroles regulate each other. In animals TSPO-tetrapyrrole interactions range from effects on embryonic development to metabolism, programmed cell death, response to stress, injury and disease, and even to life span extension. In animals TSPOs are primarily located in mitochondria. In plants TSPOs are also present in plastids, the nuclear fraction, the endoplasmic reticulum, and Golgi stacks. This may contribute to translocation of tetrapyrrole intermediates across organelles’ membranes. As in animals, plant TSPO binds heme and protoporphyrin IX. TSPO-tetrapyrrole interactions in plants appear to relate to development as well as stress conditions, including salt tolerance, abscisic acid-induced stress, reactive oxygen species homeostasis, and finally cell death regulation. In bacteria, TSPO is important for switching from aerobic to anaerobic metabolism, including the regulation of photosynthesis. As in mitochondria, in bacteria TSPO is located in the outer membrane. TSPO-tetrapyrrole interactions may be part of the establishment of the bacterial-eukaryote relationships, i.e., mitochondrial-eukaryote and plastid-plant endosymbiotic relationships.

  11. A new class of modular chiral ligands with fluxional groups.

    Science.gov (United States)

    Sibi, Mukund P; Zhang, Ruzhou; Manyem, Shankar

    2003-08-06

    In ligand design for asymmetric catalysis, the usual norm is to derive the face shielding elements from a chiral source. New ligands in which the face shielding is determined by fluxional groups are introduced. Their design, modular synthesis, and experiments to demonstrate the significance of the fluxional groups are discussed. The advantage is that the fluxional groups, introduced at a later stage, allow for simple tuning of the face shielding group.

  12. Reversible Size Control of Silver Nanoclusters via Ligand-exchange

    KAUST Repository

    Bootharaju, Megalamane Siddaramappa

    2015-05-21

    The properties of atomically monodisperse noble metal nanoclusters (NCs) are intricately intertwined with their precise molecular formula. The vast majority of size-specific NC syntheses start from the reduction of the metal salt and thiol ligand mixture. Only in gold was it recently shown that ligand-exchange could induce the growth of NCs from one atomically precise species to another; a process of yet unknown reversibility. Here, we present a process for the ligand-exchange-induced growth of atomically precise silver NCs, in a biphasic liquid-liquid system, which is particularly of interest because of its complete reversibility and ability to occur at room temperature. We explore this phenomenon in-depth using Ag35(SG)18 [SG= glutathionate] and Ag44(4-FTP)30 [4-FTP= 4-fluorothiophenol] as model systems. We show that the ligand-exchange conversion of Ag35(SG)18 into Ag44(4-FTP)30 is rapid (< 5 min) and direct, while the reverse process proceeds slowly through intermediate cluster sizes. We adapt a recently developed theory of reverse Ostwald ripening to model the NCs’ interconvertibility. The model’s predictions are in good agreement with the experimental observations, and they highlight the importance of small changes in the ligand-metal binding energy in determining the final equilibrium NC size. Based on the insight provided by this model, we demonstrated experimentally that by varying the choice of ligands, ligand-exchange can be used to obtain different sized NCs. The findings in this work establish ligand-exchange as a versatile tool for tuning cluster sizes.

  13. Ligand-promoted protein folding by biased kinetic partitioning.

    Science.gov (United States)

    Hingorani, Karan S; Metcalf, Matthew C; Deming, Derrick T; Garman, Scott C; Powers, Evan T; Gierasch, Lila M

    2017-04-01

    Protein folding in cells occurs in the presence of high concentrations of endogenous binding partners, and exogenous binding partners have been exploited as pharmacological chaperones. A combined mathematical modeling and experimental approach shows that a ligand improves the folding of a destabilized protein by biasing the kinetic partitioning between folding and alternative fates (aggregation or degradation). Computationally predicted inhibition of test protein aggregation and degradation as a function of ligand concentration are validated by experiments in two disparate cellular systems.

  14. Ligand assisted cleavage of uranium oxo-clusters

    Energy Technology Data Exchange (ETDEWEB)

    Nocton, Gregory; Pecaut, Jacques; Mazzanti, Marinella [Laboratoire de Reconnaissance Ionique et Chimie de Coordination, Service de Chimie Inorganique et Biologique, UMR-E 3 CEA-UJF, CEA/DSM/INAC, CEA-Grenoble, 38054 Grenoble, Cedex 09 (France); Filinchuk, Yaroslav [Swiss Norwegian Beam Lines (SNBL) at the European Synchrotron Radiation Facility (ESRF), rue Jules Horowitz, 38043 Grenoble (France)

    2010-07-01

    Dibenzoylmethanate replaces the bridging triflate ligands in uranium triflate poly-oxo-clusters and cleaves the U{sub 12}O{sub 20} core yielding the new [U{sub 6}O{sub 4}(OH){sub 4}({eta}-dbm){sub 12}] dibenzoylmethanate (dbm{sup -}) cluster which slowly dissociates into a monomeric complex. This reactivity demonstrates the importance of bridging ligands in stabilizing uranium poly-oxo-clusters. (authors)

  15. Reversible Size Control of Silver Nanoclusters via Ligand-exchange

    KAUST Repository

    Bootharaju, Megalamane Siddaramappa; Burlakov, Victor M.; Besong, Tabot M.D.; Joshi, Chakra Prasad; AbdulHalim, L; Black, David; Whetten, Robert; Goriely, Alain; Bakr, Osman

    2015-01-01

    The properties of atomically monodisperse noble metal nanoclusters (NCs) are intricately intertwined with their precise molecular formula. The vast majority of size-specific NC syntheses start from the reduction of the metal salt and thiol ligand mixture. Only in gold was it recently shown that ligand-exchange could induce the growth of NCs from one atomically precise species to another; a process of yet unknown reversibility. Here, we present a process for the ligand-exchange-induced growth of atomically precise silver NCs, in a biphasic liquid-liquid system, which is particularly of interest because of its complete reversibility and ability to occur at room temperature. We explore this phenomenon in-depth using Ag35(SG)18 [SG= glutathionate] and Ag44(4-FTP)30 [4-FTP= 4-fluorothiophenol] as model systems. We show that the ligand-exchange conversion of Ag35(SG)18 into Ag44(4-FTP)30 is rapid (< 5 min) and direct, while the reverse process proceeds slowly through intermediate cluster sizes. We adapt a recently developed theory of reverse Ostwald ripening to model the NCs’ interconvertibility. The model’s predictions are in good agreement with the experimental observations, and they highlight the importance of small changes in the ligand-metal binding energy in determining the final equilibrium NC size. Based on the insight provided by this model, we demonstrated experimentally that by varying the choice of ligands, ligand-exchange can be used to obtain different sized NCs. The findings in this work establish ligand-exchange as a versatile tool for tuning cluster sizes.

  16. Models of protein–ligand crystal structures: trust, but verify

    Science.gov (United States)

    Deller, Marc C.

    2015-01-01

    X-ray crystallography provides the most accurate models of protein–ligand structures. These models serve as the foundation of many computational methods including structure prediction, molecular modelling, and structure-based drug design. The success of these computational methods ultimately depends on the quality of the underlying protein–ligand models. X-ray crystallography offers the unparalleled advantage of a clear mathematical formalism relating the experimental data to the protein–ligand model. In the case of X-ray crystallography, the primary experimental evidence is the electron density of the molecules forming the crystal. The first step in the generation of an accurate and precise crystallographic model is the interpretation of the electron density of the crystal, typically carried out by construction of an atomic model. The atomic model must then be validated for fit to the experimental electron density and also for agreement with prior expectations of stereochemistry. Stringent validation of protein–ligand models has become possible as a result of the mandatory deposition of primary diffraction data, and many computational tools are now available to aid in the validation process. Validation of protein–ligand complexes has revealed some instances of overenthusiastic interpretation of ligand density. Fundamental concepts and metrics of protein–ligand quality validation are discussed and we highlight software tools to assist in this process. It is essential that end users select high quality protein–ligand models for their computational and biological studies, and we provide an overview of how this can be achieved. PMID:25665575

  17. Metallogel formation in aqueous DMSO by perfluoroalkyl decorated terpyridine ligands.

    Science.gov (United States)

    Tatikonda, Rajendhraprasad; Bhowmik, Sandip; Rissanen, Kari; Haukka, Matti; Cametti, Massimo

    2016-08-09

    Terpyridine based ligands 1 and 2, decorated with a C8F17 perfluorinated tag, are able to form stable thermoreversible gels in the presence of several d-block metal chloride salts. The gel systems obtained have been characterized by NMR, X-ray diffraction, electron microscopies and Tgel experiments in order to gain insights into the observed different behaviour of the two similar ligands, also in terms of the effect of additional common anionic species.

  18. Prediction of ligand effects in platinum-amyloid-β coordination.

    Science.gov (United States)

    Turner, Matthew; Deeth, Robert J; Platts, James A

    2017-08-01

    Ligand field molecular mechanics (LFMM) and semi-empirical Parametric Model 7 (PM7) methods are applied to a series of six Pt II -Ligand systems binding to the N-terminal domain of the amyloid-β (Aβ) peptide. Molecular dynamics using a combined LFMM/Assisted Model Building with Energy Refinement (AMBER) approach is used to explore the conformational freedom of the peptide fragment, and identifies favourable platinum binding modes and peptide conformations for each ligand investigated. Platinum coordination is found to depend on the nature of the ligand, providing evidence that binding mode may be controlled by suitable ligand design. Boltzmann populations at 310K indicate that each Pt-Aβ complex has a small number of thermodynamically accessible states. Ramachandran maps are constructed for the sampled Pt-Aβ conformations and secondary structural analysis of the obtained complex structures is performed and contrasted with the free peptide; coordination of these platinum complexes disrupts existing secondary structure in the Aβ peptide and promotes formation of ligand-specific turn-type secondary structure. Copyright © 2017 Elsevier Inc. All rights reserved.

  19. Ligand recognition by RAR and RXR receptors: binding and selectivity.

    Science.gov (United States)

    Sussman, Fredy; de Lera, Angel R

    2005-10-06

    Fundamental biological functions, most notably embriogenesis, cell growth, cell differentiation, and cell apoptosis, are in part regulated by a complex genomic network that starts with the binding (and activation) of retinoids to their cognate receptors, members of the superfamily of nuclear receptors. We have studied ligand recognition of retinoic receptors (RXRalpha and RARgamma) using a molecular-mechanics-based docking method. The protocol used in this work is able to rank the affinity of pairs of ligands for a single retinoid receptor, the highest values corresponding to those that adapt better to the shape of the binding site and generate the optimal set of electrostatic and apolar interactions with the receptor. Moreover, our studies shed light onto some of the energetic contributions to retinoid receptor ligand selectivity. In this regard we show that there is a difference in polarity between the binding site regions that anchor the carboxylate in RAR and RXR, which translates itself into large differences in the energy of interaction of both receptors with the same ligand. We observe that the latter energy change is canceled off by the solvation energy penalty upon binding. This energy compensation is borne out as well by experiments that address the effect of site-directed mutagenesis on ligand binding to RARgamma. The hypothesis that the difference in binding site polarity might be exploited to build RXR-selective ligands is tested with some compounds having a thiazolidinedione anchoring group.

  20. Predicting Efficient Antenna Ligands for Tb(III) Emission

    Energy Technology Data Exchange (ETDEWEB)

    Samuel, Amanda P.S.; Xu, Jide; Raymond, Kenneth

    2008-10-06

    A series of highly luminescent Tb(III) complexes of para-substituted 2-hydroxyisophthalamide ligands (5LI-IAM-X) has been prepared (X = H, CH{sub 3}, (C=O)NHCH{sub 3}, SO{sub 3}{sup -}, NO{sub 2}, OCH{sub 3}, F, Cl, Br) to probe the effect of substituting the isophthalamide ring on ligand and Tb(III) emission in order to establish a method for predicting the effects of chromophore modification on Tb(III) luminescence. The energies of the ligand singlet and triplet excited states are found to increase linearly with the {pi}-withdrawing ability of the substituent. The experimental results are supported by time-dependent density functional theory (TD-DFT) calculations performed on model systems, which predict ligand singlet and triplet energies within {approx}5% of the experimental values. The quantum yield ({Phi}) values of the Tb(III) complex increases with the triplet energy of the ligand, which is in part due to the decreased non-radiative deactivation caused by thermal repopulation of the triplet. Together, the experimental and theoretical results serve as a predictive tool that can be used to guide the synthesis of ligands used to sensitize lanthanide luminescence.

  1. The affinity plutonium(IV) for nitrogen donor ligands

    International Nuclear Information System (INIS)

    Jarvis, N.V.; Hancock, R.D.

    1994-01-01

    Established ligand design principles are used to predict the solution chemistry of Pu(IV) with nitrogen donor ligands which do not contain carboxylate donors. pK a 's of the nitrogen donors are lowered by addition of hydroxyalkyl groups causing Pu(IV) to have a greater affinity for these ligands than for hydroxide. Potentiometric studies using the ligands N,N,N'N',N''-pentakis(2-hydroxypropyl)-1,4,7-triazaheptane; N,N,N',N',N''-pentakis(2-hydroxyethyl)-1,4,7-triazaheptane; N,N,N',N',N'-tetrakis(2-hydroxyethyl)-1,2-diaminoethane; N,N,N',N'-tetrakis(2-hydroxyethyl)-trans-1,2-diaminocyclohexane; 1,4,8,11-tetrakis(2-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane and N,N-bis(2-hydroxyethyl)glycine with Pu(IV) showed that Pu(IV) has a considerable aqueous solution chemistry with these ligands. Data were processed by the ESTA library of programs and stability constants for all the systems are reported. Implications for selective ligand design for Pu(IV) are discussed. (orig.)

  2. A Ferrocene-Based Catecholamide Ligand: the Consequences of Ligand Swivel for Directed Supramolecular Self-Assembly

    Energy Technology Data Exchange (ETDEWEB)

    Mugridge, Jeffrey; Fiedler, Dorothea; Raymond, Kenneth

    2010-02-04

    A ferrocene-based biscatecholamide ligand was prepared and investigated for the formation of metal-ligand supramolecular assemblies with different metals. Reaction with Ge(IV) resulted in the formation of a variety of Ge{sub n}L{sub m} coordination complexes, including [Ge{sub 2}L{sub 3}]{sup 4-} and [Ge{sub 2}L{sub 2}({mu}-OMe){sub 2}]{sup 2-}. The ligand's ability to swivel about the ferrocenyl linker and adopt different conformations accounts for formation of many different Ge{sub n}L{sub m} species. This study demonstrates why conformational ligand rigidity is essential in the rational design and directed self-assembly of supramolecular complexes.

  3. Secondary ligand-directed assembly of Co(II) coordination polymers based on a pyridine carboxylate ligand

    International Nuclear Information System (INIS)

    Cao, Ke-Li; Zhang, Yi-Ping; Cai, Yi-Ni; Xu, Xiao-Wei; Feng, Yun-Long

    2014-01-01

    To investigate the influence of hydrogen bonds and secondary ligands on the structures and properties of the resulting frameworks, five new Co(II) compounds have been synthesized by the reactions of Co(II) salts and 3,5-bis(pyridin-4-ylmethoxy)benzoic acid (HL) with four rationally selected dicarboxylic acid ligands. Without secondary ligand, we got one compound [CoL 2 (H 2 O) 2 ] n ·2nH 2 O (1), which possesses a 1D chain structure. In the presence of ancillary ligands, namely, 1,3-adamantanedicarboxylic acid (H 2 adbc), terephthalic acid (H 2 tpa), thiophene-2,5-dicarboxylic acid (H 2 tdc) and 1,4-benzenedithioacetic acid (H 2 bdtc), four 3D structures [Co 2 L 2 (adbc)] n ·nH 2 O (2), [Co 2 L 2 (tpa)] n (3), [Co 2 L 2 (tdc)] n (4), [Co 2 L 2 (bdtc)(H 2 O)] n (5) were obtained, respectively. It can be observed from the architectures of 1–5 that hydrogen bonds and secondary ligands both have great effects on the spatial connective fashions, resulting in the formation of various dimensional compounds. The XRPD, TGA data of title polymers and the magnetic properties for 2 and 5 have also been investigated. - Graphical abstract: The structural differences show that the ancillary ligands have great effects on the spatial connective fashions, resulting in the formation of various dimensional compounds. - Highlights: • Five new Co(II) coordination polymers have been synthesized by solvothermal reactions based on 3,5-bis(pyridin-4-ylmethoxy)benzoic acid (HL). • The long-flexible ligand (HL) is a good candidate to produce interpenetrating architectures. • The secondary dicarboxylic acid ligands play important roles in the spatial connective fashions and the formation of various dimensional compounds. • The magnetism studies show that both 2 and 5 exhibit antiferromagnetic interactions

  4. Quantitative analysis of protein-ligand interactions by NMR.

    Science.gov (United States)

    Furukawa, Ayako; Konuma, Tsuyoshi; Yanaka, Saeko; Sugase, Kenji

    2016-08-01

    Protein-ligand interactions have been commonly studied through static structures of the protein-ligand complex. Recently, however, there has been increasing interest in investigating the dynamics of protein-ligand interactions both for fundamental understanding of the underlying mechanisms and for drug development. NMR is a versatile and powerful tool, especially because it provides site-specific quantitative information. NMR has widely been used to determine the dissociation constant (KD), in particular, for relatively weak interactions. The simplest NMR method is a chemical-shift titration experiment, in which the chemical-shift changes of a protein in response to ligand titration are measured. There are other quantitative NMR methods, but they mostly apply only to interactions in the fast-exchange regime. These methods derive the dissociation constant from population-averaged NMR quantities of the free and bound states of a protein or ligand. In contrast, the recent advent of new relaxation-based experiments, including R2 relaxation dispersion and ZZ-exchange, has enabled us to obtain kinetic information on protein-ligand interactions in the intermediate- and slow-exchange regimes. Based on R2 dispersion or ZZ-exchange, methods that can determine the association rate, kon, dissociation rate, koff, and KD have been developed. In these approaches, R2 dispersion or ZZ-exchange curves are measured for multiple samples with different protein and/or ligand concentration ratios, and the relaxation data are fitted to theoretical kinetic models. It is critical to choose an appropriate kinetic model, such as the two- or three-state exchange model, to derive the correct kinetic information. The R2 dispersion and ZZ-exchange methods are suitable for the analysis of protein-ligand interactions with a micromolar or sub-micromolar dissociation constant but not for very weak interactions, which are typical in very fast exchange. This contrasts with the NMR methods that are used

  5. Biotechnological Fluorescent Ligands of the Bradykinin B1 Receptor: Protein Ligands for a Peptide Receptor.

    Directory of Open Access Journals (Sweden)

    Xavier Charest-Morin

    Full Text Available The bradykinin (BK B1 receptor (B1R is a peculiar G protein coupled receptor that is strongly regulated to the point of being inducible in immunopathology. Limited clinical evidence suggests that its expression in peripheral blood mononuclear cells is a biomarker of active inflammatory states. In an effort to develop a novel imaging/diagnostic tool, we report the rational design and testing of a fusion protein that is a ligand of the human B1R but not likely to label peptidases. This ligand is composed of a fluorescent protein (FP (enhanced green FP [EGFP] or mCherry prolonged at its N-terminus by a spacer peptide and a classical peptide agonist or antagonist (des-Arg9-BK, [Leu8]des-Arg9-BK, respectively. The design of the spacer-ligand joint peptide was validated by a competition assay for [3H]Lys-des-Arg9-BK binding to the human B1R applied to 4 synthetic peptides of 18 or 19 residues. The labeling of B1R-expressing cells with EGFP or mCherry fused with 7 of such peptides was performed in parallel (microscopy. Both assays indicated that the best design was FP-(Asn-Glyn-Lys-des-Arg9-BK; n = 15 was superior to n = 5, suggesting benefits from minimizing steric hindrance between the FP and the receptor. Cell labeling concerned mostly plasma membranes and was inhibited by a B1R antagonist. EGFP-(Asn-Gly15-Lys-des-Arg9-BK competed for the binding of [3H]Lys-des-Arg9-BK to human recombinant B1R, being only 10-fold less potent than the unlabeled form of Lys-des-Arg9-BK to do so. The fusion protein did not label HEK 293a cells expressing recombinant human BK B2 receptors or angiotensin converting enzyme. This study identifies a modular C-terminal sequence that can be adapted to protein cargoes, conferring high affinity for the BK B1R, with possible applications in diagnostic cytofluorometry, histology and drug delivery (e.g., in oncology.

  6. Essential role of conformational selection in ligand binding.

    Science.gov (United States)

    Vogt, Austin D; Pozzi, Nicola; Chen, Zhiwei; Di Cera, Enrico

    2014-02-01

    Two competing and mutually exclusive mechanisms of ligand recognition - conformational selection and induced fit - have dominated our interpretation of ligand binding in biological macromolecules for almost six decades. Conformational selection posits the pre-existence of multiple conformations of the macromolecule from which the ligand selects the optimal one. Induced fit, on the other hand, postulates the existence of conformational rearrangements of the original conformation into an optimal one that are induced by binding of the ligand. In the former case, conformational transitions precede the binding event; in the latter, conformational changes follow the binding step. Kineticists have used a facile criterion to distinguish between the two mechanisms based on the dependence of the rate of relaxation to equilibrium, kobs, on the ligand concentration, [L]. A value of kobs decreasing hyperbolically with [L] has been seen as diagnostic of conformational selection, while a value of kobs increasing hyperbolically with [L] has been considered diagnostic of induced fit. However, this simple conclusion is only valid under the rather unrealistic assumption of conformational transitions being much slower than binding and dissociation events. In general, induced fit only produces values of kobs that increase with [L] but conformational selection is more versatile and is associated with values of kobs that increase with, decrease with or are independent of [L]. The richer repertoire of kinetic properties of conformational selection applies to kinetic mechanisms with single or multiple saturable relaxations and explains the behavior of nearly all experimental systems reported in the literature thus far. Conformational selection is always sufficient and often necessary to account for the relaxation kinetics of ligand binding to a biological macromolecule and is therefore an essential component of any binding mechanism. On the other hand, induced fit is never necessary and

  7. Ligand-specific conformational changes in the alpha1 glycine receptor ligand-binding domain

    DEFF Research Database (Denmark)

    Pless, Stephan Alexander; Lynch, Joseph W

    2009-01-01

    , and by the antagonist, strychnine. Voltage-clamp fluorometry involves labeling introduced cysteines with environmentally sensitive fluorophores and inferring structural rearrangements from ligand-induced fluorescence changes. In the inner beta-sheet, we labeled residues in loop 2 and in binding domain loops D and E....... At each position, strychnine and glycine induced distinct maximal fluorescence responses. The pre-M1 domain responded similarly; at each of four labeled positions glycine produced a strong fluorescence signal, whereas strychnine did not. This suggests that glycine induces conformational changes...... in the inner beta-sheet and pre-M1 domain that may be important for activation, desensitization, or both. In contrast, most labeled residues in loops C and F yielded fluorescence changes identical in magnitude for glycine and strychnine. A notable exception was H201C in loop C. This labeled residue responded...

  8. Microassay for measurement of binding of radiolabelled ligands to cell surface molecules

    International Nuclear Information System (INIS)

    Woof, J.M.; Burton, D.R.

    1988-01-01

    An improved technique for measuring the binding of radiolabelled ligands to cell surface molecules has been developed by modification of a procedure using centrifugation through a water-immiscible oil to separate free and cell-bound ligand. It maximises the percentage of ligand bound since cell-bound and free ligand can be separated easily and reproducibly even when very small reaction volumes are used. This permits low levels of ligand radiolabelling and relatively low numbers of cells to be used

  9. Self-assembled InAs quantum dots. Properties, modification and emission processes; Selbstorganisierte InAs-Quantenpunkte. Eigenschaften, Modifizierung und Emissionsprozesse

    Energy Technology Data Exchange (ETDEWEB)

    Schramm, A.

    2007-09-06

    In this thesis, structural, optical as well as electronic properties of self-assembled InAs quantum dots (QD) were studied by means of atomic force microscopy (AFM), photoluminescence (PL), capacitance spectroscopy (CV) and capacitance transient spectroscopy (DLTS). The quantum dots were grown with molecular beam epitaxy (MBE) and embedded in Schottky diodes for electrical characterization. In this work growth aspects as well as the electronic structures of QD were discussed. By varying the QD growth parameters it is possible to control the structural, and thus the optical and electronic properties of QD. Two methods are presented. Adjusting the QD growth temperature leads either to small QD with a high areal density or to high QDs with a low density. The structural changes of the QD are reflected in the changes of the optical and electronic properties. The second method is to introduce a growth interruption after capping the QD with thin cap layers. It was shown that capping with AlAs leads to a well-developed alternative to control the QD height and thus the ground-state energies of the QD. A post-growth method modifying the QD properties ist rapid thermal annealing (RTA). Raising the RTA temperature causes a lifting of the QD energy states with respect to the GaAs band edge energy due to In/Ga intermixing processes. A further main part of this work covers the emission processes of charge carriers in QD. Thermal emission, thermally assisted tunneling, and pure tunneling emission are studied by capacitance transient spectroscopy techniques. In DLTS experiments a strong impact of the electric field on the activation energies of electrons was found interfering the correct determination of the QD level energies. This behaviour can be explained by a thermally assisted tunneling model. A modified model taking the Coulomb interaction of occupied QD into account describes the emission rates of the electrons. In order to avoid several emission pathes in the experiments

  10. Using chemical shift perturbation to characterise ligand binding.

    Science.gov (United States)

    Williamson, Mike P

    2013-08-01

    Chemical shift perturbation (CSP, chemical shift mapping or complexation-induced changes in chemical shift, CIS) follows changes in the chemical shifts of a protein when a ligand is added, and uses these to determine the location of the binding site, the affinity of the ligand, and/or possibly the structure of the complex. A key factor in determining the appearance of spectra during a titration is the exchange rate between free and bound, or more specifically the off-rate koff. When koff is greater than the chemical shift difference between free and bound, which typically equates to an affinity Kd weaker than about 3μM, then exchange is fast on the chemical shift timescale. Under these circumstances, the observed shift is the population-weighted average of free and bound, which allows Kd to be determined from measurement of peak positions, provided the measurements are made appropriately. (1)H shifts are influenced to a large extent by through-space interactions, whereas (13)Cα and (13)Cβ shifts are influenced more by through-bond effects. (15)N and (13)C' shifts are influenced both by through-bond and by through-space (hydrogen bonding) interactions. For determining the location of a bound ligand on the basis of shift change, the most appropriate method is therefore usually to measure (15)N HSQC spectra, calculate the geometrical distance moved by the peak, weighting (15)N shifts by a factor of about 0.14 compared to (1)H shifts, and select those residues for which the weighted shift change is larger than the standard deviation of the shift for all residues. Other methods are discussed, in particular the measurement of (13)CH3 signals. Slow to intermediate exchange rates lead to line broadening, and make Kd values very difficult to obtain. There is no good way to distinguish changes in chemical shift due to direct binding of the ligand from changes in chemical shift due to allosteric change. Ligand binding at multiple sites can often be characterised, by

  11. The chemistry of separations ligand degradation by organic radical cations

    International Nuclear Information System (INIS)

    Mezyk, S.P.; Horne, G.P.; Mincher, B.J.; Zalupski, P.R.; Cook, A.R.; Wishart, J.F.

    2016-01-01

    Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexing agents and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R"."+), carbon-centered radicals (R".), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R"."+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with 2 ligands: CMPO and TODGA. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved. (authors)

  12. New synthetic routes toward enantiopure nitrogen donor ligands.

    Science.gov (United States)

    Sala, Xavier; Rodríguez, Anna M; Rodríguez, Montserrat; Romero, Isabel; Parella, Teodor; von Zelewsky, Alexander; Llobet, Antoni; Benet-Buchholz, Jordi

    2006-12-08

    New polypyridylic chiral ligands, having either C3 or lower symmetry, have been prepared via a de novo construction of the pyridine nucleus by means of Kröhnke methodology in the key step. The chiral moieties of these ligands originate from the monoterpen chiral pool, namely (-)-alpha-pinene ((-)-14, (-)-15) and (-)-myrtenal ((-)-9, (-)-10). Extension of the above-mentioned asymmetric synthesis procedure to the preparation of enantiopure derivatives of some commonly used polypyridylic ligands has been achieved through a new aldehyde building block ((-)-16). As an example, the synthesis of a chiral derivative of N,N-bis(2-pyridylmethyl)ethylamine (bpea) ligand, (-)-19, has been performed to illustrate the viability of the method. The coordinative ability of the ligands has been tested through the synthesis and characterization of complexes [Mn((-)-19)Br2], (-)-20, and [RuCl((-)-10)(bpy)](BF4), (-)-21. Some preliminary results related to the enantioselective catalytic epoxidation of styrene with the ruthenium complex are also presented.

  13. A grand unified model for liganded gold clusters

    Science.gov (United States)

    Xu, Wen Wu; Zhu, Beien; Zeng, Xiao Cheng; Gao, Yi

    2016-12-01

    A grand unified model (GUM) is developed to achieve fundamental understanding of rich structures of all 71 liganded gold clusters reported to date. Inspired by the quark model by which composite particles (for example, protons and neutrons) are formed by combining three quarks (or flavours), here gold atoms are assigned three `flavours' (namely, bottom, middle and top) to represent three possible valence states. The `composite particles' in GUM are categorized into two groups: variants of triangular elementary block Au3(2e) and tetrahedral elementary block Au4(2e), all satisfying the duet rule (2e) of the valence shell, akin to the octet rule in general chemistry. The elementary blocks, when packed together, form the cores of liganded gold clusters. With the GUM, structures of 71 liganded gold clusters and their growth mechanism can be deciphered altogether. Although GUM is a predictive heuristic and may not be necessarily reflective of the actual electronic structure, several highly stable liganded gold clusters are predicted, thereby offering GUM-guided synthesis of liganded gold clusters by design.

  14. Receptor-ligand binding sites and virtual screening.

    Science.gov (United States)

    Hattotuwagama, Channa K; Davies, Matthew N; Flower, Darren R

    2006-01-01

    Within the pharmaceutical industry, the ultimate source of continuing profitability is the unremitting process of drug discovery. To be profitable, drugs must be marketable: legally novel, safe and relatively free of side effects, efficacious, and ideally inexpensive to produce. While drug discovery was once typified by a haphazard and empirical process, it is now increasingly driven by both knowledge of the receptor-mediated basis of disease and how drug molecules interact with receptors and the wider physiome. Medicinal chemistry postulates that to understand a congeneric ligand series, or set thereof, is to understand the nature and requirements of a ligand binding site. Likewise, structural molecular biology posits that to understand a binding site is to understand the nature of ligands bound therein. Reality sits somewhere between these extremes, yet subsumes them both. Complementary to rules of ligand design, arising through decades of medicinal chemistry, structural biology and computational chemistry are able to elucidate the nature of binding site-ligand interactions, facilitating, at both pragmatic and conceptual levels, the drug discovery process.

  15. Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands

    Energy Technology Data Exchange (ETDEWEB)

    Neale, Nathan R [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Carroll, Gerard [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Limpens, Rens [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2018-04-16

    The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups - alkyls, amides, and alkoxides - on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative to alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands - not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals - are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. These results reveal a potentially broadly applicable correlation between the optoelectronic properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.

  16. Tuning Confinement in Colloidal Silicon Nanocrystals with Saturated Surface Ligands.

    Science.gov (United States)

    Carroll, Gerard M; Limpens, Rens; Neale, Nathan R

    2018-05-09

    The optical properties of silicon nanocrystals (Si NCs) are a subject of intense study and continued debate. In particular, Si NC photoluminescence (PL) properties are known to depend strongly on the surface chemistry, resulting in electron-hole recombination pathways derived from the Si NC band-edge, surface-state defects, or combined NC-conjugated ligand hybrid states. In this Letter, we perform a comparison of three different saturated surface functional groups-alkyls, amides, and alkoxides-on nonthermal plasma-synthesized Si NCs. We find a systematic and size-dependent high-energy (blue) shift in the PL spectrum of Si NCs with amide and alkoxy functionalization relative to alkyl. Time-resolved photoluminescence and transient absorption spectroscopies reveal no change in the excited-state dynamics between Si NCs functionalized with alkyl, amide, or alkoxide ligands, showing for the first time that saturated ligands-not only surface-derived charge-transfer states or hybridization between NC and low-lying ligand orbitals-are responsible for tuning the Si NC optical properties. To explain these PL shifts we propose that the atom bound to the Si NC surface strongly interacts with the Si NC electronic wave function and modulates the Si NC quantum confinement. These results reveal a potentially broadly applicable correlation between the optoelectronic properties of Si NCs and related quantum-confined structures based on the interaction between NC surfaces and the ligand binding group.

  17. Cloud computing for protein-ligand binding site comparison.

    Science.gov (United States)

    Hung, Che-Lun; Hua, Guan-Jie

    2013-01-01

    The proteome-wide analysis of protein-ligand binding sites and their interactions with ligands is important in structure-based drug design and in understanding ligand cross reactivity and toxicity. The well-known and commonly used software, SMAP, has been designed for 3D ligand binding site comparison and similarity searching of a structural proteome. SMAP can also predict drug side effects and reassign existing drugs to new indications. However, the computing scale of SMAP is limited. We have developed a high availability, high performance system that expands the comparison scale of SMAP. This cloud computing service, called Cloud-PLBS, combines the SMAP and Hadoop frameworks and is deployed on a virtual cloud computing platform. To handle the vast amount of experimental data on protein-ligand binding site pairs, Cloud-PLBS exploits the MapReduce paradigm as a management and parallelizing tool. Cloud-PLBS provides a web portal and scalability through which biologists can address a wide range of computer-intensive questions in biology and drug discovery.

  18. The chemistry of separations ligand degradation by organic radical cations

    Energy Technology Data Exchange (ETDEWEB)

    Mezyk, S.P.; Horne, G.P. [California State University at Long Beach, Long Beach, CA 90840 (United States); Mincher, B.J.; Zalupski, P.R. [Idaho National Laboratory, Idaho Falls, ID 83415 (United States); Cook, A.R.; Wishart, J.F. [Chemistry Department, Brookhaven National Laboratory, New York, 11973 (United States)

    2016-07-01

    Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexing agents and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R{sup .+}), carbon-centered radicals (R{sup .}), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R{sup .+} as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with 2 ligands: CMPO and TODGA. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved. (authors)

  19. The affinity of the uranyl ion for nitrogen donor ligands

    Energy Technology Data Exchange (ETDEWEB)

    Jarvis, N.V. (Atomic Energy Corp. of South Africa Ltd., Pretoria (South Africa). Dept. of Process Technology); De Sousa, A.S.; Hancock, R.D. (Univ. of the Witwatersrand, Johannesburg (South Africa). Centre for Molecular Design)

    1992-01-01

    Established ligand design principles are used to predict the solution chemistry of UO[sub 2][sup 2+] with nitrogen donor ligands which do not contain carboxylate donors. pK[sub a]'s of the nitrogen donors are lowered by addition of hydroxylalkyl groups causing UO[sub 2][sup 2+] to have a greater affinity for these ligands than for hydroxide. Potentiometric studies using the ligands N,N,N',N',N''-pentakis(2-hydroxypropyl)-1,4,7-triazaheptane; N,N,N',N',N''-pentakis(2-hydroxyethyl)-1,4,7-triazaheptane; N,N,N',N'-tetrakis(2-hydroxypropyl)1,2-diaminoethane, N,N,N',N'-tetrakis(2-hydroxyethyl)-trans-1,2-diaminocyclohexane; 1,4,8,11-tetrakis(2-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane and N,N-bis(2-hydroxyethyl)glycine with UO[sub 2][sup 2+] showed that UO[sub 2][sup 2+] has a considerable aqueous solution chemistry with these ligands. (orig.).

  20. Selective extraction of trivalent actinides with hard-soft mixed donor ligands: role of intra-ligand synergism

    International Nuclear Information System (INIS)

    Ghanty, Tapan K.

    2016-01-01

    In recent years, considerable attention has been given to understand the coordination chemistry of trivalent lanthanide (Ln) and actinide (An) with various ligands because of its close link with the nuclear waste management processes. It is well known that lanthanide-actinide separation is a challenging and difficult task because of very similar chemical properties of these two series of ions, which are associated with similar ionic radii and coordination numbers. Recently, we have introduced a new concept, 'intra-ligand synergism', where hard donor atom, such as, oxygen preferentially binds to trivalent actinides (An(III)) as compared to the valence iso-electronic trivalent lanthanides (Ln(III)) in presence of another soft donor centre. In the present work, the conventional concept of selective complexation of actinides with soft donor ligands (either S or N donor) has been modified through exploiting this concept, and thereby the higher selectivity of 1,10-phenanthroline-2,9-dicarboxylamide (PDAM) based ligands, namely PDAM and its isobutyl and decyl derivatives towards Am(III) ion has been predicted theoretically through density functional calculations. Subsequently, several such amide derivatives have been synthesized to optimize the solubility of the ligands in organic phase. Finally, solvent extraction experiments have been carried out to validate the theoretical prediction on the selectivity of oxygen donor ligands towards Am(III) as compared to Eu(III), and a maximum separation factor of about 51 has been achieved experimentally using 2,9-bis(N-decylaminocarbonyl)-1,10-phenanthroline ligand. The separation factor is increased with the decrease in pH, which is very interesting since extraction of the Am 3+ ion is considered to be important under highly acidic conditions from the nuclear waste management point of view. (author)

  1. Conformational diversity of flexible ligand in metal-organic frameworks controlled by size-matching mixed ligands

    International Nuclear Information System (INIS)

    Hua, Xiu-Ni; Qin, Lan; Yan, Xiao-Zhi; Yu, Lei; Xie, Yi-Xin; Han, Lei

    2015-01-01

    Hydrothermal reactions of N-auxiliary flexible exo-bidentate ligand 1,3-bis(4-pyridyl)propane (bpp) and carboxylates ligands naphthalene-2,6-dicarboxylic acid (2,6-H_2ndc) or 4,4′-(hydroxymethylene)dibenzoic acid (H_2hmdb), in the presence of cadmium(II) salts have given rise to two novel metal-organic frameworks based on flexible ligands (FL-MOFs), namely, [Cd_2(2,6-ndc)_2(bpp)(DMF)]·2DMF (1) and [Cd_3(hmdb)_3(bpp)]·2DMF·2EtOH (2) (DMF=N,N-Dimethylformamide). Single-crystal X-ray diffraction analyses revealed that compound 1 exhibits a three-dimensional self-penetrating 6-connected framework based on dinuclear cluster second building unit. Compound 2 displays an infinite three-dimensional ‘Lucky Clover’ shape (2,10)-connected network based on the trinuclear cluster and V-shaped organic linkers. The flexible bpp ligand displays different conformations in 1 and 2, which are successfully controlled by size-matching mixed ligands during the self-assembly process. - Graphical abstract: Compound 1 exhibits a 3D self-penetrating 6-connected framework based on dinuclear cluster, and 2 displays an infinite 3D ‘Lucky Clover’ shape (2,10)-connected network based on the trinuclear cluster. The flexible 1,3-bis(4-pyridyl)propane ligand displays different conformations in 1 and 2, which successfully controlled by size-matching mixed ligands during the self-assembly process.

  2. Conformational diversity of flexible ligand in metal-organic frameworks controlled by size-matching mixed ligands

    Energy Technology Data Exchange (ETDEWEB)

    Hua, Xiu-Ni; Qin, Lan; Yan, Xiao-Zhi; Yu, Lei; Xie, Yi-Xin; Han, Lei, E-mail: hanlei@nbu.edu.cn

    2015-12-15

    Hydrothermal reactions of N-auxiliary flexible exo-bidentate ligand 1,3-bis(4-pyridyl)propane (bpp) and carboxylates ligands naphthalene-2,6-dicarboxylic acid (2,6-H{sub 2}ndc) or 4,4′-(hydroxymethylene)dibenzoic acid (H{sub 2}hmdb), in the presence of cadmium(II) salts have given rise to two novel metal-organic frameworks based on flexible ligands (FL-MOFs), namely, [Cd{sub 2}(2,6-ndc){sub 2}(bpp)(DMF)]·2DMF (1) and [Cd{sub 3}(hmdb){sub 3}(bpp)]·2DMF·2EtOH (2) (DMF=N,N-Dimethylformamide). Single-crystal X-ray diffraction analyses revealed that compound 1 exhibits a three-dimensional self-penetrating 6-connected framework based on dinuclear cluster second building unit. Compound 2 displays an infinite three-dimensional ‘Lucky Clover’ shape (2,10)-connected network based on the trinuclear cluster and V-shaped organic linkers. The flexible bpp ligand displays different conformations in 1 and 2, which are successfully controlled by size-matching mixed ligands during the self-assembly process. - Graphical abstract: Compound 1 exhibits a 3D self-penetrating 6-connected framework based on dinuclear cluster, and 2 displays an infinite 3D ‘Lucky Clover’ shape (2,10)-connected network based on the trinuclear cluster. The flexible 1,3-bis(4-pyridyl)propane ligand displays different conformations in 1 and 2, which successfully controlled by size-matching mixed ligands during the self-assembly process.

  3. Designing multiple ligands - medicinal chemistry strategies and challenges.

    Science.gov (United States)

    Morphy, Richard; Rankovic, Zoran

    2009-01-01

    It has been widely recognised over the recent years that parallel modulation of multiple biological targets can be beneficial for treatment of diseases with complex etiologies such as cancer asthma, and psychiatric disease. In this article, current strategies for the generation of ligands with a specific multi-target profile (designed multiple ligands or DMLs) are described and a number of illustrative example are given. Designing multiple ligands is frequently a challenging endeavour for medicinal chemists, with the need to appropriately balance affinity for 2 or more targets whilst obtaining physicochemical and pharmacokinetic properties that are consistent with the administration of an oral drug. Given that the properties of DMLs are influenced to a large extent by the proteomic superfamily to which the targets belong and the lead generation strategy that is pursued, an early assessment of the feasibility of any given DML project is essential.

  4. Evaluation of macrocyclic hydroxyisophthalamide ligands as chelators for zirconium-89.

    Science.gov (United States)

    Bhatt, Nikunj B; Pandya, Darpan N; Xu, Jide; Tatum, David; Magda, Darren; Wadas, Thaddeus J

    2017-01-01

    The development of bifunctional chelators (BFCs) for zirconium-89 immuno-PET applications is an area of active research. Herein we report the synthesis and evaluation of octadentate hydroxyisophthalamide ligands (1 and 2) as zirconium-89 chelators. While both radiometal complexes could be prepared quantitatively and with excellent specific activity, preparation of 89Zr-1 required elevated temperature and an increased reaction time. 89Zr-1 was more stable than 89Zr-2 when challenged in vitro by excess DTPA or serum proteins and in vivo during acute biodistribution studies. Differences in radiometal complex stability arise from structural changes between the two ligand systems, and suggest further ligand optimization is necessary to enhance 89Zr chelation.

  5. Evaluation of macrocyclic hydroxyisophthalamide ligands as chelators for zirconium-89.

    Directory of Open Access Journals (Sweden)

    Nikunj B Bhatt

    Full Text Available The development of bifunctional chelators (BFCs for zirconium-89 immuno-PET applications is an area of active research. Herein we report the synthesis and evaluation of octadentate hydroxyisophthalamide ligands (1 and 2 as zirconium-89 chelators. While both radiometal complexes could be prepared quantitatively and with excellent specific activity, preparation of 89Zr-1 required elevated temperature and an increased reaction time. 89Zr-1 was more stable than 89Zr-2 when challenged in vitro by excess DTPA or serum proteins and in vivo during acute biodistribution studies. Differences in radiometal complex stability arise from structural changes between the two ligand systems, and suggest further ligand optimization is necessary to enhance 89Zr chelation.

  6. Ligand screening by saturation-transfer difference (STD) NMR spectroscopy.

    Energy Technology Data Exchange (ETDEWEB)

    Krishnan, V V

    2005-04-26

    NMR based methods to screen for high-affinity ligands have become an indispensable tool for designing rationalized drugs, as these offer a combination of good experimental design of the screening process and data interpretation methods, which together provide unprecedented information on the complex nature of protein-ligand interactions. These methods rely on measuring direct changes in the spectral parameters, that are often simpler than the complex experimental procedures used to study structure and dynamics of proteins. The goal of this review article is to provide the basic details of NMR based ligand-screening methods, with particular focus on the saturation transfer difference (STD) experiment. In addition, we provide an overview of other NMR experimental methods and a practical guide on how to go about designing and implementing them.

  7. Lanthanide and actinide complexation studies with tetradentate 'N' donor ligands

    International Nuclear Information System (INIS)

    Bhattacharyya, A.; Mohapatra, M.; Mohapatra, P.K.; Rawat, N.; Tomar, B.S.; Gadly, T.; Ghosh, S.K.; Manna, D.; Ghanty, T.K.

    2014-01-01

    Because of their similar charge and chemical behaviour separation of trivalent actinides and lanthanides is an important and challenging task in nuclear fuel cycle. Soft (S,N) donor ligands show selectivity towards the trivalent actinides over the lanthanides. Out of various 'N' donor ligands studied, bis(1,2,4)triazinyl bipyridine (BTBP) and bis(1,2,4)triazinyl phenanthroline (BTPhen) were found to be most promising. In order to understand the separation behaviour of these ligands, their complexation studies with these 'f' block elements are essential. In the present work, complexation studies of various lanthanide ions (La 3+ , Eu 3+ and Er 3+ ) was studied with ethyl derivatives of BTBP (C 2 BTBP) and BTBPhen (C 2 BTPhen) and pentyl derivative of BTBP (C 5 BTBP) in acetonitrile medium using UV-Vis spectrophotometry, fluorescence spectroscopy and solution calorimetry. Computational studies were also carried out to understand the experimental results

  8. Analytical developments for screening of lanthanides/ligands interactions

    International Nuclear Information System (INIS)

    Varenne, F.

    2012-01-01

    This work investigates the potential of hyphenated capillary electrophoresis and inductively coupled mass spectrometry to classify different ligands according to their europium binding affinity in a hydro-organic medium. On the one hand, this method enables to evaluate the affinity of phosphorus-containing ligands in less than two hours and using less than 15 ng of ligand. On the other hand, complexation constants could be determined. The results are in excellent agreement with the values obtained by spectrophotometric titrations.Moreover, a library of copolymers for solid/liquid extraction of europium is investigated. The extraction protocol enables to classify copolymers according to their europium affinity in a hydro-organic medium. This screening requires 60 mg of copolymers. For the most promising recognition properties and selectivity La 3+ /Eu 3+ /Lu 3+ are evaluated. (author)

  9. Xanthene and Xanthone Derivatives as G-Quadruplex Stabilizing Ligands

    Directory of Open Access Journals (Sweden)

    Alessandro Altieri

    2013-10-01

    Full Text Available Following previous studies on anthraquinone and acridine-based G-quadruplex ligands, here we present a study of similar aromatic cores, with the specific aim of increasing G-quadruplex binding and selectivity with respect to duplex DNA. Synthesized compounds include two and three-side chain xanthone and xanthene derivatives, as well as a dimeric “bridged” form. ESI and FRET measurements suggest that all the studied molecules are good G-quadruplex ligands, both at telomeres and on G-quadruplex forming sequences of oncogene promoters. The dimeric compound and the three-side chain xanthone derivative have been shown to represent the best compounds emerging from the different series of ligands presented here, having also high selectivity for G-quadruplex structures with respect to duplex DNA. Molecular modeling simulations are in broad agreement with the experimental data.

  10. Ligands Exchange Process on Gold Nanoparticles in Acetone Solution

    Science.gov (United States)

    Hu, C. L.; Mu, Y. Y.; Bian, Z. C.; Luo, Z. H.; Luo, K.; Huang, A. Z.

    2018-05-01

    The ligands exchange process on gold nanoparticles (GNPs) was proceeded by using hydrophobic group (PPh3) and hydrophilic group (THPO) in acetone solution. The FTIR and XPS results demonstrated that part of THPO was replaced by PPh3 which was dissolved in polar solution (acetone); the results were in accordance with the electrochemical analysis where the differential capacity decreased with increasing exchange time. After 12 h, the exchange process terminated and the final ratio of PPh3 and THPO was about 1.4: 1. This ratio remained unchanged although the PPh3 and THPO modified GNPs re-dispersed in the PPh3 acetone solution demonstrating the stable adsorption of both ligands after exchanging for 12 h. The TEM images showed that the gold nanoparticles were self-assembled from scattered to arranged morphology due to the existence of hydrophilic and hydrophobic ligands and led to Janus gold nanoparticles.

  11. A tandem regression-outlier analysis of a ligand cellular system for key structural modifications around ligand binding.

    Science.gov (United States)

    Lin, Ying-Ting

    2013-04-30

    A tandem technique of hard equipment is often used for the chemical analysis of a single cell to first isolate and then detect the wanted identities. The first part is the separation of wanted chemicals from the bulk of a cell; the second part is the actual detection of the important identities. To identify the key structural modifications around ligand binding, the present study aims to develop a counterpart of tandem technique for cheminformatics. A statistical regression and its outliers act as a computational technique for separation. A PPARγ (peroxisome proliferator-activated receptor gamma) agonist cellular system was subjected to such an investigation. Results show that this tandem regression-outlier analysis, or the prioritization of the context equations tagged with features of the outliers, is an effective regression technique of cheminformatics to detect key structural modifications, as well as their tendency of impact to ligand binding. The key structural modifications around ligand binding are effectively extracted or characterized out of cellular reactions. This is because molecular binding is the paramount factor in such ligand cellular system and key structural modifications around ligand binding are expected to create outliers. Therefore, such outliers can be captured by this tandem regression-outlier analysis.

  12. Systematic study of ligand structures of metal oxide EUV nanoparticle photoresists

    KAUST Repository

    Jiang, Jing

    2015-03-19

    Ligand stabilized metal oxide nanoparticle resists are promising candidates for EUV lithography due to their high sensitivity for high-resolution patterning and high etching resistance. As ligand exchange is responsible for the patterning mechanism, we systematically studied the influence of ligand structures of metal oxide EUV nanoparticles on their sensitivity and dissolution behavior. ZrO2 nanoparticles were protected with various aromatic ligands with electron withdrawing and electron donating groups. These nanoparticles have lower sensitivity compared to those with aliphatic ligands suggesting the structures of these ligands is more important than their pka on resist sensitivity. The influence of ligand structure was further studied by comparing the nanoparticles’ solubility for a single type ligand to mixtures of ligands. The mixture of nanoparticles showed improved pattern quality. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  13. Spectroscopic study of cadmium (II) complexes with heterocyclic dithiocarbamate ligands

    International Nuclear Information System (INIS)

    Garcia-Fontan, S.; Rodriguez-Seoane, P.; Casas, J.S.; Sordo, J.; Jones, M.M.

    1993-01-01

    Cadmium(II) dithiocarbamates [Cd(dtc) 2 ] (dtc=4-carboxamidopiperidine-1-carbodithioate, morpholine-1-carbodithioate or 4-(2-hydroxyethyl)piperazine-1-carbodithioate) and [Cd(dtc) 2 ].H 2 O (dtc=4-hydroxypiperidine-1-carbodithioate} have been prepared and characterized by thermal analysis and IR and NMR ( 13 C, 113 Cd) spectrometry. Two of these ligands have previously been shown capable of removing cadmium from its aged in vivo storage sites. The use of solid state 13 C NMR measurements to establish the coordination mode of the dithiocarbomate ligands is also examined and the difficulties which arise are discussed. (orig.)

  14. Contrasting roles for TLR ligands in HIV-1 pathogenesis.

    Directory of Open Access Journals (Sweden)

    Beda Brichacek

    2010-09-01

    Full Text Available The first line of a host's response to various pathogens is triggered by their engagement of cellular pattern recognition receptors (PRRs. Binding of microbial ligands to these receptors leads to the induction of a variety of cellular factors that alter intracellular and extracellular environment and interfere directly or indirectly with the life cycle of the triggering pathogen. Such changes may also affect any coinfecting microbe. Using ligands to Toll-like receptors (TLRs 5 and 9, we examined their effect on human immunodeficiency virus (HIV-1 replication in lymphoid tissue ex vivo. We found marked differences in the outcomes of such treatment. While flagellin (TLR5 agonist treatment enhanced replication of CC chemokine receptor 5 (CCR 5-tropic and CXC chemokine receptor 4 (CXCR4-tropic HIV-1, treatment with oligodeoxynucleotide (ODN M362 (TLR9 agonist suppressed both viral variants. The differential effects of these TLR ligands on HIV-1 replication correlated with changes in production of CC chemokines CCL3, CCL4, CCL5, and of CXC chemokines CXCL10, and CXCL12 in the ligand-treated HIV-1-infected tissues. The nature and/or magnitude of these changes were dependent on the ligand as well as on the HIV-1 viral strain. Moreover, the tested ligands differed in their ability to induce cellular activation as evaluated by the expression of the cluster of differentiation markers (CD 25, CD38, CD39, CD69, CD154, and human leukocyte antigen D related (HLA-DR as well as of a cell proliferation marker, Ki67, and of CCR5. No significant effect of the ligand treatment was observed on apoptosis and cell death/loss in the treated lymphoid tissue ex vivo. Our results suggest that binding of microbial ligands to TLRs is one of the mechanisms that mediate interactions between coinfected microbes and HIV-1 in human tissues. Thus, the engagement of appropriate TLRs by microbial molecules or their mimetic might become a new strategy for HIV therapy or prevention.

  15. Designer ligands: The search for metal ion selectivity

    Directory of Open Access Journals (Sweden)

    Perry T. Kaye

    2011-03-01

    Full Text Available The paper reviews research conducted at Rhodes University towards the development of metal-selective ligands. The research has focused on the rational design, synthesis and evaluation of novel ligands for use in the formation of copper complexes as biomimetic models of the metalloenzyme, tyrosinase, and for the selective extraction of silver, nickel and platinum group metal ions in the presence of contaminating metal ions. Attention has also been given to the development of efficient, metal-selective molecular imprinted polymers.

  16. Introducing various ligands into superhalogen anions reduces their electronic stabilities

    Science.gov (United States)

    Smuczyńska, Sylwia; Skurski, Piotr

    2008-02-01

    The vertical electron detachment energies (VDE) of six NaX2- anions (where X = F, Cl, Br) were calculated at the OVGF level with the 6-311++G(3df) basis sets. In all the cases studied the VDE exceeds the electron affinity of chlorine atom and thus those species were classified as superhalogen anions. The largest vertical binding energy was found for the NaF2- system (6.644 eV). The strong VDE dependence on the ligand type, ligand-central atom distance, and the character of the highest occupied molecular orbital (HOMO) was observed and discussed.

  17. Long ligands reinforce biological adhesion under shear flow

    Science.gov (United States)

    Belyaev, Aleksey V.

    2018-04-01

    In this work, computer modeling has been used to show that longer ligands allow biological cells (e.g., blood platelets) to withstand stronger flows after their adhesion to solid walls. A mechanistic model of polymer-mediated ligand-receptor adhesion between a microparticle (cell) and a flat wall has been developed. The theoretical threshold between adherent and non-adherent regimes has been derived analytically and confirmed by simulations. These results lead to a deeper understanding of numerous biophysical processes, e.g., arterial thrombosis, and to the design of new biomimetic colloid-polymer systems.

  18. Force loading explains spatial sensing of ligands by cells

    Science.gov (United States)

    Oria, Roger; Wiegand, Tina; Escribano, Jorge; Elosegui-Artola, Alberto; Uriarte, Juan Jose; Moreno-Pulido, Cristian; Platzman, Ilia; Delcanale, Pietro; Albertazzi, Lorenzo; Navajas, Daniel; Trepat, Xavier; García-Aznar, José Manuel; Cavalcanti-Adam, Elisabetta Ada; Roca-Cusachs, Pere

    2017-12-01

    Cells can sense the density and distribution of extracellular matrix (ECM) molecules by means of individual integrin proteins and larger, integrin-containing adhesion complexes within the cell membrane. This spatial sensing drives cellular activity in a variety of normal and pathological contexts. Previous studies of cells on rigid glass surfaces have shown that spatial sensing of ECM ligands takes place at the nanometre scale, with integrin clustering and subsequent formation of focal adhesions impaired when single integrin-ligand bonds are separated by more than a few tens of nanometres. It has thus been suggested that a crosslinking ‘adaptor’ protein of this size might connect integrins to the actin cytoskeleton, acting as a molecular ruler that senses ligand spacing directly. Here, we develop gels whose rigidity and nanometre-scale distribution of ECM ligands can be controlled and altered. We find that increasing the spacing between ligands promotes the growth of focal adhesions on low-rigidity substrates, but leads to adhesion collapse on more-rigid substrates. Furthermore, disordering the ligand distribution drastically increases adhesion growth, but reduces the rigidity threshold for adhesion collapse. The growth and collapse of focal adhesions are mirrored by, respectively, the nuclear or cytosolic localization of the transcriptional regulator protein YAP. We explain these findings not through direct sensing of ligand spacing, but by using an expanded computational molecular-clutch model, in which individual integrin-ECM bonds—the molecular clutches—respond to force loading by recruiting extra integrins, up to a maximum value. This generates more clutches, redistributing the overall force among them, and reducing the force loading per clutch. At high rigidity and high ligand spacing, maximum recruitment is reached, preventing further force redistribution and leading to adhesion collapse. Measurements of cellular traction forces and actin flow speeds

  19. Structural, magnetic, and lattice-dynamical interface properties of epitactical iron films on InAs(001) and GaAs(001) substrates; Strukturelle, magnetische und gitterdynamische Grenzflaecheneigenschaften von epitaktischen Eisenfilmen auf InAs(001)- und GaAs(001)-Substraten

    Energy Technology Data Exchange (ETDEWEB)

    Peters, Robert

    2009-07-14

    In this thesis the structure, magnetism and interface properties of ferromagnet-semiconductor hybrid structures were investigated. The main goal of this thesis was to obtain information on physical properties at the interface between a ferromagnetic metal and a III-V semiconductor (SC). For this purpose Fe films that serve as ferromagnetic contacts were deposited in ultrahigh vacuum (UHV) on InAs(001) and GaAs(001) substrates, respectively, and investigated. Both systems are interesting model systems with respect to electrical spin injection from a ferromagnetic metal into a semiconductor. In order for spin injection to occur, it is known that a Schottky barrier must form at the Fe/SC interface. Film growth and film structure were investigated in-situ in UHV by electron diffraction (RHEED) and ex-situ by X-ray diffraction. For determining the magnetic properties {sup 57}Fe conversion electron Moessbauer spectroscopy (CEMS) combines with {sup 57}Fe probe-layer technique was employed at different temperatures. Further, the partial Fe phonon density of states (PDOS) at the Fe/InAs (001) interface was determined by nuclear resonant inelastic X-ray scattering (NRIXS) from a {sup 57}Fe probe-layer. The CEM spectra (at room temperature) provided relatively high values of the average hyperfine magnetic field of left angle B{sub hf} right angle {proportional_to} 27 T and of the most-probable hyperfine magnetic field of B{sub hf,} {sub peak} {proportional_to} 30 T. This provides evidence for relativ high average Fe magnetic moments of {proportional_to} 1.8 {mu}{sub B}. The partial Fe phonon density of states (PDOS) at the Fe/InAs(001) interface is remarkably modified as compared to that of bulk bcc Fe. Using magnetometry and {sup 57}Fe CEMS, a strong temperature dependent magnetization directions was observed for Fe/Tb multilayers on InAs(001). Furthermore it is shown that such Fe/Tb multilayers on p-InAs(001) with perpendicular spin texture are useful as potential

  20. Glucagon-like peptide-1 receptor ligand interactions: structural cross talk between ligands and the extracellular domain.

    Directory of Open Access Journals (Sweden)

    Graham M West

    Full Text Available Activation of the glucagon-like peptide-1 receptor (GLP-1R in pancreatic β-cells potentiates insulin production and is a current therapeutic target for the treatment of type 2 diabetes mellitus (T2DM. Like other class B G protein-coupled receptors (GPCRs, the GLP-1R contains an N-terminal extracellular ligand binding domain. N-terminal truncations on the peptide agonist generate antagonists capable of binding to the extracellular domain, but not capable of activating full length receptor. The main objective of this study was to use Hydrogen/deuterium exchange (HDX to identify how the amide hydrogen bonding network of peptide ligands and the extracellular domain of GLP-1R (nGLP-1R were altered by binding interactions and to then use this platform to validate direct binding events for putative GLP-1R small molecule ligands. The HDX studies presented here for two glucagon-like peptide-1 receptor (GLP-1R peptide ligands indicates that the antagonist exendin-4[9-39] is significantly destabilized in the presence of nonionic detergents as compared to the agonist exendin-4. Furthermore, HDX can detect stabilization of exendin-4 and exendin-4[9-39] hydrogen bonding networks at the N-terminal helix [Val19 to Lys27] upon binding to the N-terminal extracellular domain of GLP-1R (nGLP-1R. In addition we show hydrogen bonding network stabilization on nGLP-1R in response to ligand binding, and validate direct binding events with the extracellular domain of the receptor for putative GLP-1R small molecule ligands.