Theoretical study of the localization of excess electrons at the surface of ice

International Nuclear Information System (INIS)

Hermann, A; Schwerdtfeger, P; Schmidt, W G

2008-01-01

The localization of excess electrons at the basal plane surface of hexagonal ice Ih is investigated theoretically, combining density functional theory (DFT) with a partial self-interaction correction (SIC) scheme, to account for spurious self-interaction effects that artificially delocalize the excess electrons. Starting from energetically favored surface geometries, we find strong localization of excess electrons at surface dangling bonds, in particular for surface adsorbed water monomers and dimers

Communication: Disorder-suppressed vibrational relaxation in vapor-deposited high-density amorphous ice

Science.gov (United States)

Shalit, Andrey; Perakis, Fivos; Hamm, Peter

2014-04-01

We apply two-dimensional infrared spectroscopy to differentiate between the two polyamorphous forms of glassy water, low-density (LDA) and high-density (HDA) amorphous ices, that were obtained by slow vapor deposition at 80 and 11 K, respectively. Both the vibrational lifetime and the bandwidth of the 1-2 transition of the isolated OD stretch vibration of HDO in H2O exhibit characteristic differences when comparing hexagonal (Ih), LDA, and HDA ices, which we attribute to the different local structures - in particular the presence of interstitial waters in HDA ice - that cause different delocalization lengths of intermolecular phonon degrees of freedom. Moreover, temperature dependent measurements show that the vibrational lifetime closely follows the structural transition between HDA and LDA phases.

Nuclear momentum distribution and potential energy surface in hexagonal ice

Science.gov (United States)

Lin, Lin; Morrone, Joseph; Car, Roberto; Parrinello, Michele

2011-03-01

The proton momentum distribution in ice Ih has been recently measured by deep inelastic neutron scattering and calculated from open path integral Car-Parrinello simulation. Here we report a detailed investigation of the relation between momentum distribution and potential energy surface based on both experiment and simulation results. The potential experienced by the proton is largely harmonic and characterized by 3 principal frequencies, which can be associated to weighted averages of phonon frequencies via lattice dynamics calculations. This approach also allows us to examine the importance of quantum effects on the dynamics of the oxygen nuclei close to the melting temperature. Finally we quantify the anharmonicity that is present in the potential acting on the protons. This work is supported by NSF and by DOE.

Kinetically Controlled Two-Step Amorphization and Amorphous-Amorphous Transition in Ice

Science.gov (United States)

Lin, Chuanlong; Yong, Xue; Tse, John S.; Smith, Jesse S.; Sinogeikin, Stanislav V.; Kenney-Benson, Curtis; Shen, Guoyin

2017-09-01

We report the results of in situ structural characterization of the amorphization of crystalline ice Ih under compression and the relaxation of high-density amorphous (HDA) ice under decompression at temperatures between 96 and 160 K by synchrotron x-ray diffraction. The results show that ice Ih transforms to an intermediate crystalline phase at 100 K prior to complete amorphization, which is supported by molecular dynamics calculations. The phase transition pathways show clear temperature dependence: direct amorphization without an intermediate phase is observed at 133 K, while at 145 K a direct Ih-to-IX transformation is observed; decompression of HDA shows a transition to low-density amorphous ice at 96 K and ˜1 Pa , to ice Ic at 135 K and to ice IX at 145 K. These observations show that the amorphization of compressed ice Ih and the recrystallization of decompressed HDA are strongly dependent on temperature and controlled by kinetic barriers. Pressure-induced amorphous ice is an intermediate state in the phase transition from the connected H-bond water network in low pressure ices to the independent and interpenetrating H-bond network of high-pressure ices.

Defect hydrogen vibrations in various phases deuterium ice

International Nuclear Information System (INIS)

Li, J.C.; Wang, Y.; Dong, S.L.; Zhang, P.; Kolesnikov, A.I.

2003-01-01

The inelastic incoherent neutron scattering spectra of D 2 O mixed with a small amount of H 2 O (5% by weight) high density amorphous (hda) ice, ice-VIII, and ice-II have been measured on HET spectrometer at Rutherford Appleton Laboratory (UK). The hydrogen atom in D 2 O ice lattice has three distinguished vibrations: two modes normal to the O---H bond at lower frequency and a stretching mode along the O-H bond at higher frequency. For different ice phases these frequencies are different, it was found that the lower defect mode is at ∼97 meV for ice-II, at about 95 meV for hda-ice and ice-VIII, and they are all lower than the value of 105 meV for ice-Ih. The O-H stretching modes are at 415 meV for ice-II, at 418 meV for hda-ice, and at 425 meV for ice-VIII, which all are much larger than the value for ice-Ih, 406 meV. It was also found that O-D stretching modes in D 2 O ice-VIII is centered at ∼320 meV which is significantly higher than the corresponding value of ∼305 meV for ice-Ih

High density amorphous ice and its phase transition to ice XII

International Nuclear Information System (INIS)

Kohl, I.

2001-07-01

1998 Lobban et al. reported the neutron diffraction data of a new phase of ice, called ice XII, which formed at 260 K on compression of water within the domain of ice V at a pressure of 0.5 GPa. Surprisingly ice XII forms as an incidental product in the preparation of high-density amorphous ice (HDA) on compression of hexagonale ice (ice Ih) at 77 K up to pressures = 1.3 GPa. A decisive experimental detail is the use of an indium container: when compressing ice Ih in a pressure vessel with indium linings, then reproducibly HDA (high density amorphous ice) forms, but without indium randomly scattered relative amounts of ice XII and HDA form. Ice XII forms on compression of ice Ih at 77 K only via HDA, and not directly from ice Ih. Its formation requires a sudden pronounced apparent pressure drop of ca 0.18 GPa at pressures ca 1.1 GPa. These apparent pressure drops can be caused by buildup friction between the piston and the pressure vessel and its sudden release on further compression. I propose that shock-waves generated by apparent pressure drops cause transient local heating and that this induces nucleation and crystal growth. A specific reproducible method to prepare ice XII is heating HDA in a pressure vessel with indium linings at constant pressures (or constant volume). The ice XII (meta-)stability domain extends between ca 158 and 212 K from ca 0.7 to ca 1.5 GPa. DSC (differential scanning calorimetry) and x-ray powder diffraction revealed, that on heating at atmospheric pressure ice XII transforms directly into cubic ice (ice Ic) at 154 K (heating rate 10 K min - 1) and not into an amorphous form before transition to ice Ic. The enthalpy of the ice XII - ice Ic transition is -1.21 ± 0.07 kJ mol -1 . An estimation of the Gibbs free energy at atmospheric pressure and about 140 K results that ice XII is thermodynamically more stable than ice VI. In the heating curve of ice XII a reversible endothermic step can be found at the onset temperature (heating rate

Neutron scattering studies of the phase-transitions of ices by thermal-annealing

International Nuclear Information System (INIS)

Wang, Y.; Kolesnikov, A.; Li, J.C.

1999-01-01

Complete text of publication follows. Inelastic incoherent neutron scattering was used to study the phase-transition process of high-density amorphous (hda) ice produced by pressurising ice-Ih at 16 kbar and 77 K to low-density amorphous (Ida) ice, ice-Ic and ice-Ih by thermobaric treatments. The results show that when annealing temperature is lower than 136 K no obvious phase-transition was observed and transformation of the hda to the lda ice occurs between 136 and 144 K which is very closed to the theoretically calculated value 135 K (1). Comparing the lda spectrum with the vapour deposited low-density amorphous ice (2) shows a number of differences in the translational and vibrational regions, such as the low energy cut off of the vibrational band. On the other hand, the recovered lda from the hda ice has a similar spectrum as ice-Ih. (author)

Helicopter Icing Review.

Science.gov (United States)

1980-09-01

helicopter (i.e. in an icing tunnel or engine test cell ) and therefore can be subjected to controlled icing where spe- cific problems can be safely...evaluation. 69 2.2.5.2 Ice Protection Systems Demonstration Many of the systems noted in 2.2.5.1 can be evaluated in icing test cells or icing wind tunnels...Figure 2-32 illustrates a typical rotor deice system control arrangement. 104 (N >4 A.dO INaH -E- C4) uo U En 9 E-1 H m I ~z O 04 04iH U 0 El4 E-f C E

Role of stacking disorder in ice nucleation.

Science.gov (United States)

Lupi, Laura; Hudait, Arpa; Peters, Baron; Grünwald, Michael; Gotchy Mullen, Ryan; Nguyen, Andrew H; Molinero, Valeria

2017-11-08

The freezing of water affects the processes that determine Earth's climate. Therefore, accurate weather and climate forecasts hinge on good predictions of ice nucleation rates. Such rate predictions are based on extrapolations using classical nucleation theory, which assumes that the structure of nanometre-sized ice crystallites corresponds to that of hexagonal ice, the thermodynamically stable form of bulk ice. However, simulations with various water models find that ice nucleated and grown under atmospheric temperatures is at all sizes stacking-disordered, consisting of random sequences of cubic and hexagonal ice layers. This implies that stacking-disordered ice crystallites either are more stable than hexagonal ice crystallites or form because of non-equilibrium dynamical effects. Both scenarios challenge central tenets of classical nucleation theory. Here we use rare-event sampling and free energy calculations with the mW water model to show that the entropy of mixing cubic and hexagonal layers makes stacking-disordered ice the stable phase for crystallites up to a size of at least 100,000 molecules. We find that stacking-disordered critical crystallites at 230 kelvin are about 14 kilojoules per mole of crystallite more stable than hexagonal crystallites, making their ice nucleation rates more than three orders of magnitude higher than predicted by classical nucleation theory. This effect on nucleation rates is temperature dependent, being the most pronounced at the warmest conditions, and should affect the modelling of cloud formation and ice particle numbers, which are very sensitive to the temperature dependence of ice nucleation rates. We conclude that classical nucleation theory needs to be corrected to include the dependence of the crystallization driving force on the size of the ice crystallite when interpreting and extrapolating ice nucleation rates from experimental laboratory conditions to the temperatures that occur in clouds.

The effects of ice on methane hydrate nucleation: a microcanonical molecular dynamics study.

Science.gov (United States)

Zhang, Zhengcai; Guo, Guang-Jun

2017-07-26

Although ice powders are widely used in gas hydrate formation experiments, the effects of ice on hydrate nucleation and what happens in the quasi-liquid layer of ice are still not well understood. Here, we used high-precision constant energy molecular dynamics simulations to study methane hydrate nucleation from vapor-liquid mixtures exposed to the basal, prismatic, and secondary prismatic planes of hexagonal ice (ice Ih). Although no significant difference is observed in hydrate nucleation processes for these different crystal planes, it is found, more interestingly, that methane hydrate can nucleate either on the ice surface heterogeneously or in the bulk solution phase homogeneously. Several factors are mentioned to be able to promote the heterogeneous nucleation of hydrates, including the adsorption of methane molecules at the solid-liquid interface, hydrogen bonding between hydrate cages and the ice structure, the stronger ability of ice to transfer heat than that of the aqueous solution, and the higher occurrence probability of hydrate cages in the vicinity of the ice surface than in the bulk solution. Meanwhile, however, the other factors including the hydrophilicity of ice and the ice lattice mismatch with clathrate hydrates can inhibit heterogeneous nucleation on the ice surface and virtually promote homogeneous nucleation in the bulk solution. Certainly, the efficiency of ice as a promoter and as an inhibitor for heterogeneous nucleation is different. We estimate that the former is larger than the latter under the working conditions. Additionally, utilizing the benefit of ice to absorb heat, the NVE simulation of hydrate formation with ice can mimic the phenomenon of ice shrinking during the heterogeneous nucleation of hydrates and lower the overly large temperature increase during homogeneous nucleation. These results are helpful in understanding the nucleation mechanism of methane hydrate in the presence of ice.

Molecular Origin of the Vibrational Structure of Ice Ih.

Science.gov (United States)

Moberg, Daniel R; Straight, Shelby C; Knight, Christopher; Paesani, Francesco

2017-06-15

An unambiguous assignment of the vibrational spectra of ice I h remains a matter of debate. This study demonstrates that an accurate representation of many-body interactions between water molecules, combined with an explicit treatment of nuclear quantum effects through many-body molecular dynamics (MB-MD), leads to a unified interpretation of the vibrational spectra of ice I h in terms of the structure and dynamics of the underlying hydrogen-bond network. All features of the infrared and Raman spectra in the OH stretching region can be unambiguously assigned by taking into account both the symmetry and the delocalized nature of the lattice vibrations as well as the local electrostatic environment experienced by each water molecule within the crystal. The high level of agreement with experiment raises prospects for predictive MB-MD simulations that, complementing analogous measurements, will provide molecular-level insights into fundamental processes taking place in bulk ice and on ice surfaces under different thermodynamic conditions.

Mixed quantum/classical approach to OH-stretch inelastic incoherent neutron scattering spectroscopy for ambient and supercooled liquid water and ice Ih

Energy Technology Data Exchange (ETDEWEB)

Shi, L.; Skinner, J. L. [Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2015-07-07

OH-stretch inelastic incoherent neutron scattering (IINS) has been measured to determine the vibrational density of states (VDOS) in the OH-stretch region for liquid water, supercooled water, and ice Ih, providing complementary information to IR and Raman spectroscopies about hydrogen bonding in these phases. In this work, we extend the combined electronic-structure/molecular-dynamics (ES/MD) method, originally developed by Skinner and co-workers to simulate OH-stretch IR and Raman spectra, to the calculation of IINS spectra with small k values. The agreement between theory and experiment in the limit k → 0 is reasonable, further validating the reliability of the ES/MD method in simulating OH-stretch spectroscopy in condensed phases. The connections and differences between IINS and IR spectra are analyzed to illustrate the advantages of IINS over IR in estimating the OH-stretch VDOS.

Mixed quantum/classical approach to OH-stretch inelastic incoherent neutron scattering spectroscopy for ambient and supercooled liquid water and ice Ih

International Nuclear Information System (INIS)

Shi, L.; Skinner, J. L.

2015-01-01

OH-stretch inelastic incoherent neutron scattering (IINS) has been measured to determine the vibrational density of states (VDOS) in the OH-stretch region for liquid water, supercooled water, and ice Ih, providing complementary information to IR and Raman spectroscopies about hydrogen bonding in these phases. In this work, we extend the combined electronic-structure/molecular-dynamics (ES/MD) method, originally developed by Skinner and co-workers to simulate OH-stretch IR and Raman spectra, to the calculation of IINS spectra with small k values. The agreement between theory and experiment in the limit k → 0 is reasonable, further validating the reliability of the ES/MD method in simulating OH-stretch spectroscopy in condensed phases. The connections and differences between IINS and IR spectra are analyzed to illustrate the advantages of IINS over IR in estimating the OH-stretch VDOS

Ice crystal growth under the presence of krypton and methane at low temperature

Science.gov (United States)

Kawauchi, Taizo; Yoda, Yoshitaka; Fukutani, Katsuyuki

2018-02-01

To investigate the influence of foreign gas inclusion on the crystallization of ice, we studied the low-temperature (74 0.2) of Kr and CH4 enhance the formation of ice Ih and increase the crystal size, while at high foreign gas contents (R ⩽ 0.2) that may develop Kr or CH4 crystals below 92 K, the crystal size and relative amount of ice decrease strongly. The maximum ice Ih crystal size in the order of 200 nm was observed with either Kr or CH4 at 92 K for R = 0.2. We propose that Kr and CH4 induce the crystallization of ice by acting as a surfactant.

Review: Evolution of GnIH structure and function

Directory of Open Access Journals (Sweden)

Tomohiro eOsugi

2014-08-01

Full Text Available Discovery of gonadotropin-inhibitory hormone (GnIH in the Japanese quail in 2000 was the first to demonstrate the existence of a hypothalamic neuropeptide inhibiting gonadotropin release. We now know that GnIH regulates reproduction by inhibiting gonadotropin synthesis and release via action on the gonadotropin-releasing hormone (GnRH system and the gonadotrope in various vertebrates. GnIH peptides identified in birds and mammals have a common LPXRF-amide (X = L or Q motif at the C-terminus and inhibits pituitary gonadotropin secretion. However, the function and structure of GnIH peptides were diverse in fish. Goldfish GnIHs possessing a C-terminal LPXRF-amide motif had both stimulatory and inhibitory effects on gonadotropin synthesis or release. The C-terminal sequence of grass puffer and medaka GnIHs were MPQRF-amide. To investigate the evolutionary origin of GnIH and its ancestral structure and function, we searched for GnIH in agnathans, the most ancient lineage of vertebrates. We identified GnIH precursor gene and mature GnIH peptides with C-terminal QPQRF-amide or RPQRF-amide from the brain of sea lamprey. Lamprey GnIH fibers were in close proximity to GnRH-III neurons. Further, one of lamprey GnIHs stimulated the expression of lamprey GnRH-III peptide in the hypothalamus and gonadotropic hormone β mRNA expression in the pituitary. We further identified the ancestral form of GnIH, which had a C-terminal RPQRF-amide, and its receptors in amphioxus, the most basal chordate species. The amphioxus GnIH inhibited cAMP signaling in vitro. In sum, the original forms of GnIH may date back to the time of the emergence of early chordates. GnIH peptides may have had various C-terminal structures slightly different from LPXRF-amide in basal chordates, which had stimulatory and/or inhibitory functions on reproduction. The C-terminal LPXRF-amide structure and its inhibitory function on reproduction may be selected in later-evolved vertebrates, such as

Structures of high and low density amorphous ice by neutron diffraction

International Nuclear Information System (INIS)

Finney, J.L.; Hallbrucker, A.; Kohl, I.; Soper, A.K.; Bowron, D.T.

2002-01-01

Neutron diffraction with isotope substitution is used to determine the structures of high (HDA) and low (LDA) density amorphous ice. Both 'phases' are fully hydrogen bonded, tetrahedral networks, with local order similarities between LDA and ice Ih, and HDA and liquid water. Moving from HDA, through liquid water and LDA to ice Ih, the second shell radial order increases at the expense of spatial order. This is linked to a fifth first neighbor 'interstitial' that restricts the orientations of first shell waters. This 'lynch pin' molecule which keeps the HDA structure intact has implications for the nature of the HDA-LDA transition that bear on the current metastable water debate

What Is IH (Intracranial Hypertension)?

Science.gov (United States)

... Store What is IH? What is IH? Intracranial hypertension literally means that the pressure of cerebrospinal fluid ( ... is too high. “Intracranial” means “within the skull.” “Hypertension” means “high fluid pressure.” To understand how this ...

VOLATILE TRANSPORT INSIDE SUPER-EARTHS BY ENTRAPMENT IN THE WATER-ICE MATRIX

Energy Technology Data Exchange (ETDEWEB)

Levi, A.; Podolak, M. [Department of Geophysics and Planetary Science, Tel Aviv University, Tel Aviv 69978 (Israel); Sasselov, D., E-mail: amitlevi.planetphys@gmail.com [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-05-20

Whether volatiles can be entrapped in a background matrix composing planetary envelopes and be dragged via convection to the surface is a key question in understanding atmospheric fluxes, cycles, and composition. In this paper, we consider super-Earths with an extensive water mantle (i.e., water planets), and the possibility of entrapment of methane in their extensive water-ice envelopes. We adopt the theory developed by van der Waals and Platteeuw for modeling solid solutions, often used for modeling clathrate hydrates, and modify it in order to estimate the thermodynamic stability field of a new phase called methane filled ice Ih. We find that in comparison to water ice VII the filled ice Ih structure may be stable not only at the high pressures but also at the high temperatures expected at the core-water mantle transition boundary of water planets.

Effects Of Field Distortions In Ih-apf Linac

CERN Document Server

Kapin, Valery; Yamada, S

2004-01-01

The project on developing compact medical accelera-tors for the tumor therapy using carbon ions has been started at the National Institute of Radiological Sciences (NIRS). Alternating-phase-focused (APF) linac using an interdigital H-mode (IH) cavity has been proposed for the injector linac. The IH-cavity is doubly ridged circular resonator loaded by the drift-tubes mounted on ridges with supporting stems. The effects of intrinsic and random field distortions in a practical design of the 4-MeV/u 200 MHz IH-APF linac are considered. The intrinsic field distortions in IH-cavity are caused by the asymmetry of the gap field due to presence of the drift-tube supporting stems and pair of ridges. The random field distortions are caused by drift-tube misalignments and non-regular deviations of the voltage distribution from programmed law. The RF fields in IH-cavity have been calculated using Microwave Studio (MWS) code. The effects of field distortions on beam dynamics have been simulated numerically.

Phase changes induced by guest orientational ordering of filled ice Ih methane hydrate under high pressure and low temperature

International Nuclear Information System (INIS)

Hirai, H; Tanaka, T; Yagi, T; Matsuoka, T; Ohishi, Y; Ohtake, M; Yamamoto, Y

2014-01-01

Low-temperature and high-pressure experiments were performed with filled ice Ih structure of methane hydrate under pressure and temperature conditions of 2.0 to 77.0 GPa and 30 to 300 K, respectively, using diamond anvil cells and a helium-refrigeration cryostat. Distinct changes in the axial ratios of the host framework were revealed by In-situ X-ray diffractometry. Splitting in the CH vibration modes of the guest methane molecules, which was previously explained by the orientational ordering of the guest molecules, was observed by Raman spectroscopy. The pressure and temperature conditions at the split of the vibration modes agreed well with those of the axial ratio changes. The results indicated that orientational ordering of the guest methane molecules from orientational disordered-state occurred at high pressures and low temperatures, and that this guest ordering led to the axial ratio changes in the host framework. Existing regions of the guest disordered-phase and the guest ordered-phase were roughly estimated by the X-ray data. In addition, above the pressure of the guest-ordered phase, another high pressure phase was developed at a low-temperature region. The deuterated-water host samples were also examined and isotopic effects on the guest ordering and phase changes were observed.

The phase diagram of water at negative pressures: virtual ices.

Science.gov (United States)

Conde, M M; Vega, C; Tribello, G A; Slater, B

2009-07-21

The phase diagram of water at negative pressures as obtained from computer simulations for two models of water, TIP4P/2005 and TIP5P is presented. Several solid structures with lower densities than ice Ih, so-called virtual ices, were considered as possible candidates to occupy the negative pressure region of the phase diagram of water. In particular the empty hydrate structures sI, sII, and sH and another, recently proposed, low-density ice structure. The relative stabilities of these structures at 0 K was determined using empirical water potentials and density functional theory calculations. By performing free energy calculations and Gibbs-Duhem integration the phase diagram of TIP4P/2005 was determined at negative pressures. The empty hydrates sII and sH appear to be the stable solid phases of water at negative pressures. The phase boundary between ice Ih and sII clathrate occurs at moderate negative pressures, while at large negative pressures sH becomes the most stable phase. This behavior is in reasonable agreement with what is observed in density functional theory calculations.

The Role of Stress-Effected Subgrain Size Distribution in Anelastic Recovery: An Experimental Study on Polycrystalline Ice-Ih

Science.gov (United States)

Caswell, T. E.; Goldsby, D. L.; Cooper, R. F.; Prior, D. J.

2013-12-01

Anelasticity, or time-dependent and recoverable strain, is the source of attenuation at seismic and sub-seismic frequencies, yet the processes governing anelastic recovery are poorly resolved. Numerous experimental studies [e.g., 1-3] have demonstrated that anelasticity occurs via diffusion-effected relaxation along grain boundaries, which leads to a significant grain size sensitivity. Similar studies, however, conducted on deformed single crystals [e.g. 4], coarse-grained metals deforming in dislocation creep [e.g., 5] and polycrystalline ice deforming via a dislocation-accommodated mechanism [6] demonstrate the same frequency dependence, consistent with the grain boundary mechanism, but with no sensitivity to grain size. We postulate that it is the deformation-effected distribution of subgrains, which possesses unique diffusive properties relative to a defect-free lattice, that dominates attenuation in these situations. To test this idea we are conducting creep and stress-drop experiments on polycrystalline ice-Ih with concurrent high-resolution microstructural analysis conducted via Electron Backscatter Diffraction (EBSD) [7] to characterize the relationship between subgrain size distribution and diffusion-effected anelasticity. Our experiments establish the subgrain size distribution in steady-state creep of fine-grained ice-1h at compressional stresses between 0.1-4 MPa, which for the grain sizes and temperatures of our experiments places the rheology squarely within the regime of grain boundary sliding that is accommodated by basal dislocation slip [8]. We then explore the dynamics of the established microstructure, which includes subgrain formation [cf. 9], via stress-drop experiments [e.g. 10]. Experiments of this type allow the characterization of microstructural 'hardness,' i.e., the viscosity of the polycrystalline solid as effected by finite strain, from which we can discern the diffusive kinetics of subgrain boundaries [11, 12]. We are currently

Immersion Freezing of Aluminas: The Effect of Crystallographic Properties on Ice Nucleation

Science.gov (United States)

King, M.; Chong, E.; Freedman, M. A.

2017-12-01

Atmospheric aerosol particles serve as the nuclei for heterogeneous ice nucleation, a process that allows for ice to form at higher temperatures and lower supersaturations with respect to ice. This process is essential to the formation of ice in cirrus clouds. Heterogeneous ice nucleation is affected by many factors including the composition, crystal structure, porosity, and surface area of the particles. However, these factors are not well understood and, as such, are difficult to account for in climate models. To test the effects of crystal structure on ice nucleation, a system of transition aluminas (Al2O3) that differ only in their crystal structure, despite being compositionally similar, were tested using immersion freezing. Particles were immersed in water and placed into a temperature controlled chamber. Freezing events were then recorded as the chamber was cooled to negative 30 °. Alpha-alumina, which is a member of the hexagonal crystal system, showed a significantly higher temperature at which all particles froze in comparison to other samples. This supports the hypothesis that, since a hexagonal crystal structure is the lowest energy state for ice, hexagonal surface structures would best facilitate ice nucleation. However, a similar sample of hexagonal chi-alumina did not show the same results. Further analysis of the samples will be done to characterize surface structures and composition. These conflicting data sets raise interesting questions about the effect of other surface features, such as surface area and porosity, on ice nucleation.

Evolutionary origin and divergence of GnIH and its homologous peptides.

Science.gov (United States)

Tsutsui, Kazuyoshi; Osugi, Tomohiro

2009-03-01

Probing undiscovered hypothalamic neuropeptides that play important roles in the regulation of pituitary function in vertebrates is essential for the progress of neuroendocrinology. In 2000, we discovered a novel hypothalamic dodecapeptide inhibiting gonadotropin release in quail and termed it gonadotropin-inhibitory hormone (GnIH). GnIH acts on the pituitary and gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus via a novel G protein-coupled receptor for GnIH to inhibit gonadal development and maintenance by decreasing gonadotropin release and synthesis. Similar findings were observed in other avian species. Thus, GnIH is a key factor controlling avian reproduction. To give our findings a broader perspective, we also found GnIH homologous peptides in the hypothalamus of other vertebrates, such as mammals, reptiles, amphibians and teleosts. GnIH and its homologs share a common C-terminal LPXRFamide (X=L or Q) motif. A mammalian GnIH homolog also inhibited gonadotropin release in mammals like the GnIH action in birds. In contrast to higher vertebrates, hypophysiotropic activities of GnIH homologs were different in lower vertebrates. To clarify the evolutionary origin of GnIH and its homologs, we further sought to identify novel LPXRFamide peptides from the brain of sea lamprey and hagfish, two extant groups of the oldest lineage of vertebrates, Agnatha. In these agnathans, LPXRFamide peptide and its cDNA were identified only from the brain of hagfish. Based on these findings over the past decade, this paper summarizes the evolutionary origin and divergence of GnIH and its homologous peptides.

Incoherent inelastic neutron scattering measurements on ice VII: Are there two kinds of hydrogen bonds in ice?

International Nuclear Information System (INIS)

Klotz, S.; Strassle, Th.; Philippe, J.; Salzmann, C.G.; Parker, S.F.

2005-01-01

We report the vibrational spectrum of recovered ice VII measured by inelastic incoherent neutron scattering and compare this to similar data of its fully hydrogen-ordered form, ice VIII, under exactly the same conditions (15 K, 1 bar). The spectra of the two phases have their principal features at similar energies, in both the translational and vibrational bands, with a substantial disorder-related broadening in ice VII. In particular, we find no evidence for a peak at 49 meV in ice VII which earlier was associated with the possible existence of two kinds of hydrogen bonds. Additional Raman measurements in ice VII and ice VIII show that the O-H stretching frequencies in the two phases are almost identical. Therefore, the presence of split molecular-optic bands in ice phases, including ordinary ice Ih, is likely related to an incomplete description of the phonon dispersion rather than to a fundamentally new feature in the nature of the hydrogen bond. (authors)

Hexagonal ice in pure water and biological NMR samples

Energy Technology Data Exchange (ETDEWEB)

Bauer, Thomas; Gath, Julia; Hunkeler, Andreas; Ernst, Matthias, E-mail: maer@ethz.ch [ETH Zurich, Physical Chemistry (Switzerland); Böckmann, Anja, E-mail: a.bockmann@ibcp.fr [UMR 5086 CNRS, Université de Lyon 1, Institut de Biologie et Chimie des Protéines (France); Meier, Beat H., E-mail: beme@ethz.ch [ETH Zurich, Physical Chemistry (Switzerland)

2017-01-15

Ice, in addition to “liquid” water and protein, is an important component of protein samples for NMR spectroscopy at subfreezing temperatures but it has rarely been observed spectroscopically in this context. We characterize its spectroscopic behavior in the temperature range from 100 to 273 K, and find that it behaves like pure water ice. The interference of magic-angle spinning (MAS) as well as rf multiple-pulse sequences with Bjerrum-defect motion greatly influences the ice spectra.

Das IHS und die Rolle der Forschungsinstitute

OpenAIRE

Keuschnigg, Christian

2014-01-01

Das Institut für Höhere Studien und wissenschaftliche Forschung (IHS) ist ein unabhängiges Forschungsinstitut und leistet Forschung und Ausbildung auf Spitzenniveau für Politik, Wirtschaft und Gesellschaft. Im Wettbewerb zwischen Universitäten und angewandten Forschungsinstituten ist das IHS einzigartig, weil es unter einem Dach Grundlagenforschung und forschungsnahe Lehre mit angewandter Forschung für die wissenschaftliche Politikberatung verbindet. Mit den drei Disziplinen Ökonomie, Soziolo...

Atypical water lattices and their possible relevance to the amorphous ices: A density functional study

Science.gov (United States)

Anick, David J.

2013-04-01

Of the fifteen known crystalline forms of ice, eleven consist of a single topologically connected hydrogen bond network with four H-bonds at every O. The other four, Ices VI-VIII and XV, consist of two topologically connected networks, each with four H-bonds at every O. The networks interpenetrate but do not share H-bonds. This article presents two new periodic water lattice families whose topological connectivity is "atypical": they consist of many two-dimensional layers that share no H-bonds. Layers are held together only by dispersion forces. Within each layer there are still four H-bonds at each O. Called "Hexagonal Bilayer Water" (HBW) and "Pleated Sheet Water" (PSW), they have computed densities of about 1.1 g/mL and 1.3 g/mL respectively, and nearest neighbor O-coordination is 4.5 to 5.5 and 6 to 8 respectively. Using density functional theory (BLYP-D/TZVP), various proton ordered forms of HBW and PSW are optimized and categorized. There are simple pathways connecting Ice-Ih to HBW and HBW to PSW. Their computed properties suggest similarities to the high density and very high density amorphous ices (HDA and VHDA) respectively. It is unknown whether HDA, VHDA, and Low Density Amorphous Ice (LDA) are fully disordered glasses down to the molecular level, or whether there is some short-range local order. Based on estimated radial distribution functions (RDFs), one proton ordered form of HBW matches HDA best. The idea is explored that HDA could contain islands with this underlying structure, and likewise, that VHDA could contain regions of PSW. A "microlattice model version 1" (MLM1) is presented as a device to compare key experimental data on the amorphous ices with these atypical structures and with a microlattice form of Ice-XI for LDA. Resemblances are found with the amorphs' RDFs, densities, Raman spectra, and transition behaviors. There is not enough information in the static models to assign either a microlattice structure or a partial microlattice

Atypical water lattices and their possible relevance to the amorphous ices: A density functional study

Energy Technology Data Exchange (ETDEWEB)

Anick, David J. [Laboratory for Water and Surface Studies, Department of Chemistry, Pearson Lab, Tufts University, Medford, MA 02155 (United States)

2013-04-15

Of the fifteen known crystalline forms of ice, eleven consist of a single topologically connected hydrogen bond network with four H-bonds at every O. The other four, Ices VI–VIII and XV, consist of two topologically connected networks, each with four H-bonds at every O. The networks interpenetrate but do not share H-bonds. This article presents two new periodic water lattice families whose topological connectivity is “atypical”: they consist of many two-dimensional layers that share no H-bonds. Layers are held together only by dispersion forces. Within each layer there are still four H-bonds at each O. Called “Hexagonal Bilayer Water” (HBW) and “Pleated Sheet Water” (PSW), they have computed densities of about 1.1 g/mL and 1.3 g/mL respectively, and nearest neighbor O-coordination is 4.5 to 5.5 and 6 to 8 respectively. Using density functional theory (BLYP-D/TZVP), various proton ordered forms of HBW and PSW are optimized and categorized. There are simple pathways connecting Ice-Ih to HBW and HBW to PSW. Their computed properties suggest similarities to the high density and very high density amorphous ices (HDA and VHDA) respectively. It is unknown whether HDA, VHDA, and Low Density Amorphous Ice (LDA) are fully disordered glasses down to the molecular level, or whether there is some short-range local order. Based on estimated radial distribution functions (RDFs), one proton ordered form of HBW matches HDA best. The idea is explored that HDA could contain islands with this underlying structure, and likewise, that VHDA could contain regions of PSW. A “microlattice model version 1” (MLM1) is presented as a device to compare key experimental data on the amorphous ices with these atypical structures and with a microlattice form of Ice-XI for LDA. Resemblances are found with the amorphs’ RDFs, densities, Raman spectra, and transition behaviors. There is not enough information in the static models to assign either a microlattice structure or a partial

Atypical water lattices and their possible relevance to the amorphous ices: A density functional study

International Nuclear Information System (INIS)

Anick, David J.

2013-01-01

Of the fifteen known crystalline forms of ice, eleven consist of a single topologically connected hydrogen bond network with four H-bonds at every O. The other four, Ices VI–VIII and XV, consist of two topologically connected networks, each with four H-bonds at every O. The networks interpenetrate but do not share H-bonds. This article presents two new periodic water lattice families whose topological connectivity is “atypical”: they consist of many two-dimensional layers that share no H-bonds. Layers are held together only by dispersion forces. Within each layer there are still four H-bonds at each O. Called “Hexagonal Bilayer Water” (HBW) and “Pleated Sheet Water” (PSW), they have computed densities of about 1.1 g/mL and 1.3 g/mL respectively, and nearest neighbor O-coordination is 4.5 to 5.5 and 6 to 8 respectively. Using density functional theory (BLYP-D/TZVP), various proton ordered forms of HBW and PSW are optimized and categorized. There are simple pathways connecting Ice-Ih to HBW and HBW to PSW. Their computed properties suggest similarities to the high density and very high density amorphous ices (HDA and VHDA) respectively. It is unknown whether HDA, VHDA, and Low Density Amorphous Ice (LDA) are fully disordered glasses down to the molecular level, or whether there is some short-range local order. Based on estimated radial distribution functions (RDFs), one proton ordered form of HBW matches HDA best. The idea is explored that HDA could contain islands with this underlying structure, and likewise, that VHDA could contain regions of PSW. A “microlattice model version 1” (MLM1) is presented as a device to compare key experimental data on the amorphous ices with these atypical structures and with a microlattice form of Ice-XI for LDA. Resemblances are found with the amorphs’ RDFs, densities, Raman spectra, and transition behaviors. There is not enough information in the static models to assign either a microlattice structure or a partial

FFT-enhanced IHS transform method for fusing high-resolution satellite images

Science.gov (United States)

Ling, Y.; Ehlers, M.; Usery, E.L.; Madden, M.

2007-01-01

Existing image fusion techniques such as the intensity-hue-saturation (IHS) transform and principal components analysis (PCA) methods may not be optimal for fusing the new generation commercial high-resolution satellite images such as Ikonos and QuickBird. One problem is color distortion in the fused image, which causes visual changes as well as spectral differences between the original and fused images. In this paper, a fast Fourier transform (FFT)-enhanced IHS method is developed for fusing new generation high-resolution satellite images. This method combines a standard IHS transform with FFT filtering of both the panchromatic image and the intensity component of the original multispectral image. Ikonos and QuickBird data are used to assess the FFT-enhanced IHS transform method. Experimental results indicate that the FFT-enhanced IHS transform method may improve upon the standard IHS transform and the PCA methods in preserving spectral and spatial information. ?? 2006 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).

Review: evolution of GnIH and related peptides structure and function in the chordates.

Science.gov (United States)

Osugi, Tomohiro; Ubuka, Takayoshi; Tsutsui, Kazuyoshi

2014-01-01

Discovery of gonadotropin-inhibitory hormone (GnIH) in the Japanese quail in 2000 was the first to demonstrate the existence of a hypothalamic neuropeptide inhibiting gonadotropin release. We now know that GnIH regulates reproduction by inhibiting gonadotropin synthesis and release via action on the gonadotropin-releasing hormone (GnRH) system and the gonadotrope in various vertebrates. GnIH peptides identified in birds and mammals have a common LPXRF-amide (X = L or Q) motif at the C-terminus and inhibit pituitary gonadotropin secretion. However, the function and structure of GnIH peptides are diverse in fish. Goldfish GnIHs possessing a C-terminal LPXRF-amide motif have both stimulatory and inhibitory effects on gonadotropin synthesis or release. The C-terminal sequence of grass puffer and medaka GnIHs are MPQRF-amide. To investigate the evolutionary origin of GnIH and its ancestral structure and function, we searched for GnIH in agnathans, the most ancient lineage of vertebrates. We identified GnIH precursor gene and mature GnIH peptides with C-terminal QPQRF-amide or RPQRF-amide from the brain of sea lamprey. Lamprey GnIH fibers were in close proximity to GnRH-III neurons. Further, one of lamprey GnIHs stimulated the expression of lamprey GnRH-III peptide in the hypothalamus and gonadotropic hormone β mRNA expression in the pituitary. We further identified the ancestral form of GnIH, which had a C-terminal RPQRF-amide, and its receptors in amphioxus, the most basal chordate species. The amphioxus GnIH inhibited cAMP signaling in vitro. In sum, the original forms of GnIH may date back to the time of the emergence of early chordates. GnIH peptides may have had various C-terminal structures slightly different from LPXRF-amide in basal chordates, which had stimulatory and/or inhibitory functions on reproduction. The C-terminal LPXRF-amide structure and its inhibitory function on reproduction may be selected in later-evolved vertebrates, such as birds and mammals.

Single-scattering properties of ice particles in the microwave regime: Temperature effect on the ice refractive index with implications in remote sensing

International Nuclear Information System (INIS)

Ding, Jiachen; Bi, Lei; Yang, Ping; Kattawar, George W.; Weng, Fuzhong; Liu, Quanhua; Greenwald, Thomas

2017-01-01

An ice crystal single-scattering property database is developed in the microwave spectral region (1 to 874 GHz) to provide the scattering, absorption, and polarization properties of 12 ice crystal habits (10-plate aggregate, 5-plate aggregate, 8-column aggregate, solid hexagonal column, hollow hexagonal column, hexagonal plate, solid bullet rosette, hollow bullet rosette, droxtal, oblate spheroid, prolate spheroid, and sphere) with particle maximum dimensions from 2 µm to 10 mm. For each habit, four temperatures (160, 200, 230, and 270 K) are selected to account for temperature dependence of the ice refractive index. The microphysical and scattering properties include projected area, volume, extinction efficiency, single-scattering albedo, asymmetry factor, and six independent nonzero phase matrix elements (i.e. P_1_1, P_1_2, P_2_2, P_3_3, P_4_3 and P_4_4). The scattering properties are computed by the Invariant Imbedding T-Matrix (II-TM) method and the Improved Geometric Optics Method (IGOM). The computation results show that the temperature dependence of the ice single-scattering properties in the microwave region is significant, particularly at high frequencies. Potential active and passive remote sensing applications of the database are illustrated through radar reflectivity and radiative transfer calculations. For cloud radar applications, ignoring temperature dependence has little effect on ice water content measurements. For passive microwave remote sensing, ignoring temperature dependence may lead to brightness temperature biases up to 5 K in the case of a large ice water path. - Highlights: • Single-scattering properties of ice crystals are computed from 1 to 874 GHz. • Ice refractive index temperature dependence is considered at 160, 200, 230 and 270 K. • Potential applications of the database to microwave remote sensing are illustrated. • Ignoring temperature dependence of ice refractive index can lead to 5 K difference in IWP retrieval

Review: Regulatory mechanisms of gonadotropin-inhibitory hormone (GnIH synthesis and release in photoperiodic animals

Directory of Open Access Journals (Sweden)

Kazuyoshi eTsutsui

2013-04-01

Full Text Available Gonadotropin-inhibitory hormone (GnIH is a novel hypothalamic neuropeptide that was discovered in quail as an inhibitory factor for gonadotropin release. GnIH inhibits gonadotropin synthesis and release in birds through actions on gonadotropin-releasing hormone (GnRH neurons and gonadotropes, mediated via the GnIH receptor (GnIH-R, GPR147. Subsequently, GnIH was identified in mammals and other vertebrates. As in birds, mammalian GnIH inhibits gonadotropin secretion, indicating a conserved role for this neuropeptide in the control of the hypothalamic-pituitary-gonadal (HPG axis across species. Identification of the regulatory mechanisms governing GnIH expression and release is important in understanding the physiological role of the GnIH system. A nocturnal hormone, melatonin, appears to act directly on GnIH neurons through its receptor to induce expression and release of GnIH in quail, a photoperiodic bird. Recently, a similar, but opposite, action of melatonin on the inhibition of expression of mammalian GnIH was shown in hamsters and sheep, photoperiodic mammals. These results in photoperiodic animals demonstrate that GnIH expression is photoperiodically modulated via a melatonin-dependent process. Recent findings indicate that GnIH may be a mediator of stress-induced reproductive disruption in birds and mammals, pointing to a broad role for this neuropeptide in assessing physiological state and modifying reproductive effort accordingly. This paper summarizes the advances made in our knowledge regarding the regulation of GnIH synthesis and release in photoperiodic birds and mammals. This paper also discusses the neuroendocrine integration of environmental signals, such as photoperiods and stress, and internal signals, such as GnIH, melatonin and glucocorticoids, to control avian and mammalian reproduction.

Direct calculation of ice homogeneous nucleation rate for a molecular model of water

Science.gov (United States)

Haji-Akbari, Amir; Debenedetti, Pablo G.

2015-01-01

Ice formation is ubiquitous in nature, with important consequences in a variety of environments, including biological cells, soil, aircraft, transportation infrastructure, and atmospheric clouds. However, its intrinsic kinetics and microscopic mechanism are difficult to discern with current experiments. Molecular simulations of ice nucleation are also challenging, and direct rate calculations have only been performed for coarse-grained models of water. For molecular models, only indirect estimates have been obtained, e.g., by assuming the validity of classical nucleation theory. We use a path sampling approach to perform, to our knowledge, the first direct rate calculation of homogeneous nucleation of ice in a molecular model of water. We use TIP4P/Ice, the most accurate among existing molecular models for studying ice polymorphs. By using a novel topological approach to distinguish different polymorphs, we are able to identify a freezing mechanism that involves a competition between cubic and hexagonal ice in the early stages of nucleation. In this competition, the cubic polymorph takes over because the addition of new topological structural motifs consistent with cubic ice leads to the formation of more compact crystallites. This is not true for topological hexagonal motifs, which give rise to elongated crystallites that are not able to grow. This leads to transition states that are rich in cubic ice, and not the thermodynamically stable hexagonal polymorph. This mechanism provides a molecular explanation for the earlier experimental and computational observations of the preference for cubic ice in the literature. PMID:26240318

Povratna informacija pri matematičnih domačih nalogah

OpenAIRE

Žitko, Urša

2017-01-01

V diplomskem delu je predstavljena povratna informacija pri matematičnih domačih nalogah. V teoretičnem delu so predstavljene domače naloge: njihova zgodovina, namen in več klasifikacij vrst domačih nalog. Domače naloge so namenjene učencem, da z njimi usvojijo in utrdijo obravnavano snov. Domača naloga učencem omogoča učenje uporabe postopkov, ki jih že poznajo, in pridobivanje novih spretnosti za nadaljnje razumevanje snovi. Z rednim pisanjem domačih nalog se učenci naučijo vestnega in sam...

Development of non-duct IH (induction heating) smokeless roaster; Nonduct IH (denjiha yudo kanetsu) muen roaster no kaihatsu

Energy Technology Data Exchange (ETDEWEB)

Matsunaga, K. [Chubu Electric Power Co. Inc., Nagoya (Japan)

1996-11-01

As a part of diffusion and promotion of electric cooking apparatuses, a non-duct IH smokeless roaster has been developed for roast meat restaurants in cooperation with Hitachi Home Tech. Smoke and odor in the room can be removed without using exhaust duct by incorporating smoke and odor processing equipment into the main body. For the developed roaster, IH was adopted as a heat source with less smoke and exhaust gas compared with city gas. Generated smoke and odor are removed by the electrical precipitator and the deodorant catalyst incorporated in the main body. After the treatment, exhaust gas is emitted in the room. This roaster has characteristics as follows. This roaster can be used at high-class roast meat restaurants for avoiding smoke and odor, and can be brought in banqueting hall of hotels. Since it does not have a duct, there is no danger of fire. It is easy to change the layout of guest room. Since the IH system has less exhaust heat than the gas system, increase in room temperature is moderate, which results in the reduction of air conditioning load. 8 figs., 3 tabs.

Possible significance of cubic water-ice, H2O-Ic, in the atmospheric water cycle of Mars

Science.gov (United States)

Gooding, James L.

1988-01-01

The possible formation and potential significance of the cubic ice polymorph on Mars is discussed. When water-ice crystallizes on Earth, the ambient conditions of temperature and pressure result in the formation of the hexagonal ice polymorph; however, on Mars, the much lower termperature and pressures may permit the crystallization of the cubic polymorph. Cubic ice has two properties of possible importance on Mars: it is an excellant nucleator of other volatiles (such as CO2), and it undergoes an exothermic transition to hexagonal ice at temperatures above 170 K. These properties may have significant implications for both martian cloud formation and the development of the seasonal polar caps.

Atypical water lattices and their possible relevance to the amorphous ices: A density functional study

Directory of Open Access Journals (Sweden)

David J. Anick

2013-04-01

Full Text Available Of the fifteen known crystalline forms of ice, eleven consist of a single topologically connected hydrogen bond network with four H-bonds at every O. The other four, Ices VI–VIII and XV, consist of two topologically connected networks, each with four H-bonds at every O. The networks interpenetrate but do not share H-bonds. This article presents two new periodic water lattice families whose topological connectivity is “atypical”: they consist of many two-dimensional layers that share no H-bonds. Layers are held together only by dispersion forces. Within each layer there are still four H-bonds at each O. Called “Hexagonal Bilayer Water” (HBW and “Pleated Sheet Water” (PSW, they have computed densities of about 1.1 g/mL and 1.3 g/mL respectively, and nearest neighbor O-coordination is 4.5 to 5.5 and 6 to 8 respectively. Using density functional theory (BLYP-D/TZVP, various proton ordered forms of HBW and PSW are optimized and categorized. There are simple pathways connecting Ice-Ih to HBW and HBW to PSW. Their computed properties suggest similarities to the high density and very high density amorphous ices (HDA and VHDA respectively. It is unknown whether HDA, VHDA, and Low Density Amorphous Ice (LDA are fully disordered glasses down to the molecular level, or whether there is some short-range local order. Based on estimated radial distribution functions (RDFs, one proton ordered form of HBW matches HDA best. The idea is explored that HDA could contain islands with this underlying structure, and likewise, that VHDA could contain regions of PSW. A “microlattice model version 1” (MLM1 is presented as a device to compare key experimental data on the amorphous ices with these atypical structures and with a microlattice form of Ice-XI for LDA. Resemblances are found with the amorphs’ RDFs, densities, Raman spectra, and transition behaviors. There is not enough information in the static models to assign either a microlattice structure

Hydrophobic Ice Confined between Graphene and MoS2

NARCIS (Netherlands)

Bampoulis, Pantelis; Teernstra, V.J.; Lohse, Detlef; Zandvliet, Henricus J.W.; Poelsema, Bene

2016-01-01

The structure and nature of water confined between hydrophobic molybdenum disulfide (MoS2) and graphene (Gr) are investigated at room temperature by means of atomic force microscopy. We find the formation of two-dimensional (2D) crystalline ice layers. In contrast to the hexagonal ice “bilayers” of

The time-dependence of the defective nature of ice Ic (cubic ice) and its implications for atmospheric science

Science.gov (United States)

Sippel, Christian; Koza, Michael M.; Hansen, Thomas C.; Kuhs, Werner F.

2010-05-01

The possible atmospheric implication of ice Ic (cubic ice) has already been suggested some time ago in the context of snow crystal formation [1]. New findings from air-borne measurements in cirrus clouds and contrails have put ice Ic into the focus of interest to understand the so-called "supersaturation puzzle" [2,3,4]. Our recent microstructural work on ice Ic [5,6] appears to be highly relevant in this context. We have found that ice Ic is characterized by a complex stacking fault pattern, which changes as a function of temperature as well as time. Indeed, from our own [7] and other group's work [8] one knows that (in contrast to earlier believe) ice Ic can form up to temperatures at least as high as 240K - thus in the relevant range for cirrus clouds. We have good preliminary evidence that the "cubicity" (which can be related to stacking fault probabilities) as well as the particle size of ice Ic are the relevant parameters for this correlation. The "cubicity" of stacking faulty ice Ic (established by diffraction) correlates nicely with the increased supersaturation at decreasing temperatures observed in cirrus clouds and contrails, a fact, which may be considered as further evidence for the presence of ice Ic. Recently, we have studied the time-dependency of the changes in both "cubicity" and particle size at various temperatures of relevance for cirrus clouds and contrails by in-situ neutron powder diffraction. The timescales over which changes occur (several to many hours) are similar to the life-time of cirrus clouds and contrails and suggest that the supersaturation situation may change within this time span in the natural environment too. Some accompanying results obtained by cryo-SEM (scanning electron microscopy) work will also be presented and suggest that stacking-faulty ice Ic has kinky surfaces providing many more active centres for heterogeneous reactions on the surface than in the usually assumed stable hexagonal form of ice Ih with its rather

Sum-frequency spectroscopic studies: I. Surface melting of ice, II. Surface alignment of polymers

Energy Technology Data Exchange (ETDEWEB)

Wei, Xing [Univ. of California, Berkeley, CA (United States)

2000-01-01

Surface vibrational spectroscopy via infrared-visible sum-frequency generation (SFG) has been established as a useful tool to study the structures of different kinds of surfaces and interfaces. This technique was used to study the (0001) face of hexagonal ice (Ih). SFG spectra in the O-H stretch frequency range were obtained at various sample temperatures. For the vapor(air)/ice interface, the degree of orientational order of the dangling OH bonds at the surface was measured as a function of temperature. Disordering sets in around 200 K and increases dramatically with temperature, which is strong evidence of surface melting of ice. For the other ice interfaces (silica/OTS/ice and silica/ice), a similar temperature dependence of the hydrogen bonded OH stretch peak was observed; the free OH stretch mode, however, appears to be different from that of the vapor (air)/ice interface due to interactions at the interfaces. The technique was also used to measure the orientational distributions of the polymer chains on a rubbed polyvinyl alcohol surface. Results show that the polymer chains at the surface appear to be well aligned by rubbing, and the adsorbed liquid crystal molecules are aligned, in turn, by the surface polymer chains. A strong correlation exists between the orientational distributions of the polymer chains and the liquid crystal molecules, indicating that the surface-induced bulk alignment of a liquid crystal film by rubbed polymer surfaces is via an orientational epitaxy-like mechanism. This thesis also contains studies on some related issues that are crucial to the above applications. An experiment was designed to measure SFG spectra in both reflection and transmission. The result confirms that SFG in reflection is generally dominated by the surface contribution. Another issue is the motional effect due to fast orientational motion of molecules at a surface or interface. Calculations show that the effect is significant if the molecular orientation varies

The IHS diagnostic X-ray equipment radiation protection program

International Nuclear Information System (INIS)

Knapp, A.; Byrns, G.; Suleiman, O.

1994-01-01

The Indian Health Service (IHS) operates or contracts with Tribal groups to operate 50 hospitals and approximately 165 primary ambulatory care centers. These facilities contain approximately 275 medical and 800 dental diagnostic x-ray machines. IHS environmental health personnel in collaboration with the Food and Drug Administration's (FDA) Center for Devices and Radiological Health (CDRH) developed a diagnostic x-ray protection program including standard survey procedures and menu-driven calculations software. Important features of the program include the evaluation of equipment performance collection of average patient entrance skin exposure (ESE) measurements for selected procedures, and quality assurance. The ESE data, collected using the National Evaluation of X-ray Trends (NEXT) protocol, will be presented. The IHS Diagnostic X-ray Radiation Protection Program is dynamic and is adapting to changes in technology and workload

Cell-Type Specific Development of the Hyperpolarization-Activated Current, Ih, in Prefrontal Cortical Neurons

Directory of Open Access Journals (Sweden)

Sha-Sha Yang

2018-05-01

Full Text Available H-current, also known as hyperpolarization-activated current (Ih, is an inward current generated by the hyperpolarization-activated cyclic nucleotide-gated (HCN cation channels. Ih plays an essential role in regulating neuronal properties, synaptic integration and plasticity, and synchronous activity in the brain. As these biological factors change across development, the brain undergoes varying levels of vulnerability to disorders like schizophrenia that disrupt prefrontal cortex (PFC-dependent function. However, developmental changes in Ih in PFC neurons remains untested. Here, we examine Ih in pyramidal neurons vs. gamma-aminobutyric acid (GABAergic parvalbumin-expressing (PV+ interneurons in developing mouse PFC. Our findings show that the amplitudes of Ih in these cell types are identical during the juvenile period but differ at later time points. In pyramidal neurons, Ih amplitude significantly increases from juvenile to adolescence and follows a similar trend into adulthood. In contrast, the amplitude of Ih in PV+ interneurons decreases from juvenile to adolescence, and does not change from adolescence to adulthood. Moreover, the kinetics of HCN channels in pyramidal neurons is significantly slower than in PV+ interneurons, with a gradual decrease in pyramidal neurons and a gradual increase in PV+ cells across development. Our study reveals distinct developmental trajectories of Ih in pyramidal neurons and PV+ interneurons. The cell-type specific alteration of Ih during the critical period from juvenile to adolescence reflects the contribution of Ih to the maturation of the PFC and PFC-dependent function. These findings are essential for a better understanding of normal PFC function, and for elucidating Ih’s crucial role in the pathophysiology of neurodevelopmental disorders.

Ih current is necessary to maintain normal dopamine fluctuations and sleep consolidation in Drosophila.

Directory of Open Access Journals (Sweden)

Alicia Gonzalo-Gomez

Full Text Available HCN channels are becoming pharmacological targets mainly in cardiac diseases. But apart from their well-known role in heart pacemaking, these channels are widely expressed in the nervous system where they contribute to the neuron firing pattern. Consequently, abolishing Ih current might have detrimental consequences in a big repertoire of behavioral traits. Several studies in mammals have identified the Ih current as an important determinant of the firing activity of dopaminergic neurons, and recent evidences link alterations in this current to various dopamine-related disorders. We used the model organism Drosophila melanogaster to investigate how lack of Ih current affects dopamine levels and the behavioral consequences in the sleep:activity pattern. Unlike mammals, in Drosophila there is only one gene encoding HCN channels. We generated a deficiency of the DmIh core gene region and measured, by HPLC, levels of dopamine. Our data demonstrate daily variations of dopamine in wild-type fly heads. Lack of Ih current dramatically alters dopamine pattern, but different mechanisms seem to operate during light and dark conditions. Behaviorally, DmIh mutant flies display alterations in the rest:activity pattern, and altered circadian rhythms. Our data strongly suggest that Ih current is necessary to prevent dopamine overproduction at dark, while light input allows cycling of dopamine in an Ih current dependent manner. Moreover, lack of Ih current results in behavioral defects that are consistent with altered dopamine levels.

Ocena prehranskega stanja starejših v socialnovarstvenem zavodu

Directory of Open Access Journals (Sweden)

Nika Urh

2017-09-01

Full Text Available Uvod: Eden od dejavnikov kakovosti življenja starejših v socialnovarstvenem zavodu je prehrana. Namen raziskave je bil proučiti prehransko stanje in ponuditi predloge za izboljšanje prehrane starejših v socialnovarstvenem zavodu. Metode: V raziskavi je bila uporabljena kvantitativna opisna metoda raziskovanja. Analizirani so bili dnevni jedilniki v socialnovarstvenem zavodu in na vzorcu starejših (n = 48 izvedena analizo dejanskega vnosa hranil in prehranskega statusa. Prehransko stanje je bilo ugotovljeno na podlagi indeksa telesne mase in vprašalnika Mini prehranski pregled. Vključeni v raziskavo so imeli prehrano, pri kateri dietne prilagoditve niso bile potrebne. Rezultati: Povprečna energijska vrednost ponujenih jedilnikov je znašala 8457 kJ (2021 kcal na dan, 17 hranil je odstopalo od priporočil. Moški (M in ženske (Ž se statistično pomembno razlikujejo v deležu ostanka maščob (μM = 16 %, μŽ = 24 %; p = 0,036, holesterola (μM = 15 %, μŽ = 26 %; p = 0,035, vitamina D (μM = 15 %, μŽ = 27 %; p = 0,017 in vitamina B12 (μM = 17 %, μŽ = 25 %; p = 0,016. Indeks telesne mase je pokazal, da nihče od starejših, ki so bili vključeni v raziskavo, ni bil podhranjen ali v kategoriji debelost III. stopnje. Diskusija in zaključek: Raziskava je potrdila potrebo po sistematičnem spremljanju kakovosti prehrane starejših v socialnovarstvenih zavodih. Da bi starejšim zagotovili ustrezno prehransko oskrbo, je potrebno sodelovanje medpoklicnega tima s starejšimi in njihovimi družinskimi člani.

Dynamics and Structural Details of Amorphous Phases of Ice Determined by Incoherent Inelastic Neutron Scattering

International Nuclear Information System (INIS)

Klug, D.D.; Tulk, C.A.; Svensson, E.C.; Loong, C.

1999-01-01

Incoherent-inelastic neutron scattering data are obtained over the energy range of lattice and internal vibrations of water molecules in phases of ice prepared by pressure-induced amorphization (high-density amorphous ice, hda), by thermal annealing of hda (low-density amorphous ice, lda), and by rapidly cooling water, as well as in ice Ih and Ic . Hydrogen bonding interactions in lda differ significantly from those in the glass obtained by rapid quenching, which has hydrogen-bond interactions characteristic of highly supercooled water. Hydrogen-bond interactions in hda are weaker than in the low-density phases. copyright 1999 The American Physical Society

A Raman spectroscopy study on the effects of intermolecular hydrogen bonding on water molecules absorbed by borosilicate glass surface

Science.gov (United States)

Li, Fabing; Li, Zhanlong; Wang, Ying; Wang, Shenghan; Wang, Xiaojun; Sun, Chenglin; Men, Zhiwei

2018-05-01

The structural forms of water/deuterated water molecules located on the surface of borosilicate capillaries have been first investigated in this study on the basis of the Raman spectral data obtained at different temperatures and under atmospheric pressure for molecules in bulk and also for molecules absorbed by borosilicate glass surface. The strongest two fundamental bands locating at 3063 cm-1 (2438 cm-1) in the recorded Raman spectra are assigned here to the Osbnd H (Osbnd D) bond stretching vibrations and they are compared with the corresponding bands observed at 3124 cm-1 (2325 cm-1) in the Raman spectrum of ice Ih. Our spectroscopic observations have indicated that the structure of water and deuterated water molecules on borosilicate surface is similar to that of ice Ih (hexagonal phase of ice). These observations have also indicated that water molecules locate on the borosilicate surface so as to construct a bilayer structure and that strong and weak intermolecular hydrogen bonds are formed between water/deuterated molecules and silanol groups on borosilicate surface. In accordance with these findings, water and deuterated water molecules at the interface of capillary have a higher melting temperature.

Sticking properties of ice grains

Science.gov (United States)

Jongmanns, M.; Kumm, M.; Wurm, G.; Wolf, D. E.; Teiser, J.

2017-06-01

We study the size dependence of pull-off forces of water ice in laboratory experiments and numerical simulations. To determine the pull-off force in our laboratory experiments, we use a liquid nitrogen cooled centrifuge. Depending on its rotation frequency, spherical ice grains detach due to the centrifugal force which is related to the adhesive properties. Numerical simulations are conducted by means of molecular dynamics simulations of hexagonal ice using a standard coarse-grained water potential. The pull-off force of a single contact between two spherical ice grains is measured due to strain controlled simulations. Both, the experimental study and the simulations reveal a dependence between the pull-off force and the (reduced) particle radii, which differ significantly from the linear dependence of common contact theories.

Effect of cortisol on gonadotropin inhibitory hormone (GnIH) in the cinnamon clownfish, Amphiprion melanopus.

Science.gov (United States)

Choi, Young Jae; Habibi, Hamid R; Kil, Gyung-Suk; Jung, Min-Min; Choi, Cheol Young

2017-04-01

Hypothalamic peptides, gonadotropin-releasing hormone (GnRH) and gonadotropin inhibitory hormone (GnIH), play pivotal roles in the control of reproduction and gonadal maturation in fish. In the present study we tested the possibility that stress-mediated reproductive dysfunction in teleost may involve changes in GnRH and GnIH activity. We studied expression of brain GnIH, GnIH-R, seabream GnRH (sbGnRH), as well as circulating levels of follicle stimulating hormone (FSH), and luteinizing hormone (LH) in the cinnamon clownfish, Amphiprion melanopus. Treatment with cortisol increased GnIH mRNA level, but reduced sbGnRH mRNA and circulating levels of LH and FSH in cinnamon clownfish. Using double immunofluorescence staining, we found expression of both GnIH and GnRH in the diencephalon region of cinnamon clownfish brain. These findings support the hypothesis that cortisol, an indicator of stress, affects reproduction, in part, by increasing GnIH in cinnamon clownfish which contributes to hypothalamic suppression of reproductive function in A. melanopus, a protandrous hermaphroditic fish. Copyright © 2017 Elsevier Inc. All rights reserved.

Configurational entropy of hydrogen-disordered ice polymorphs

International Nuclear Information System (INIS)

Herrero, Carlos P.; Ramírez, Rafael

2014-01-01

The configurational entropy of several H-disordered ice polymorphs is calculated by means of a thermodynamic integration along a path between a totally H-disordered state and one fulfilling the Bernal-Fowler ice rules. A Monte Carlo procedure based on a simple energy model is used, so that the employed thermodynamic path drives the system from high temperatures to the low-temperature limit. This method turns out to be precise enough to give reliable values for the configurational entropy s th of different ice phases in the thermodynamic limit (number of molecules N → ∞). The precision of the method is checked for the ice model on a two-dimensional square lattice. Results for the configurational entropy are given for H-disordered arrangements on several polymorphs, including ices Ih, Ic, II, III, IV, V, VI, and XII. The highest and lowest entropy values correspond to ices VI and XII, respectively, with a difference of 3.3% between them. The dependence of the entropy on the ice structures has been rationalized by comparing it with structural parameters of the various polymorphs, such as the mean ring size. A particularly good correlation has been found between the configurational entropy and the connective constant derived from self-avoiding walks on the ice networks

Experimental and theoretical evidence for bilayer-by-bilayer surface melting of crystalline ice

DEFF Research Database (Denmark)

Sánchez, M. Alejandra; Kling, Tanja; Ishiyama, Tatsuya

2017-01-01

, and its nature, we investigate the surface melting of hexagonal ice by combining noncontact, surfacespecific vibrational sum frequency generation (SFG) spectroscopy and spectra calculated from molecular dynamics simulations. Using SFG, we probe the outermost water layers of distinct single crystalline ice...

42 CFR 137.294 - What is the typical IHS environmental review process for construction projects?

Science.gov (United States)

2010-10-01

... SELF-GOVERNANCE Construction Nepa Process § 137.294 What is the typical IHS environmental review... impact on the environment, and therefore do not require environmental impact statements (EIS). Under current IHS procedures, an environmental review is performed on all construction projects. During the IHS...

Sticking properties of ice grains

Directory of Open Access Journals (Sweden)

Jongmanns M.

2017-01-01

Full Text Available We study the size dependence of pull-off forces of water ice in laboratory experiments and numerical simulations. To determine the pull-off force in our laboratory experiments, we use a liquid nitrogen cooled centrifuge. Depending on its rotation frequency, spherical ice grains detach due to the centrifugal force which is related to the adhesive properties. Numerical simulations are conducted by means of molecular dynamics simulations of hexagonal ice using a standard coarse-grained water potential. The pull-off force of a single contact between two spherical ice grains is measured due to strain controlled simulations. Both, the experimental study and the simulations reveal a dependence between the pull-off force and the (reduced particle radii, which differ significantly from the linear dependence of common contact theories.

Water/ice phase transition: The role of zirconium acetate, a compound with ice-shaping properties

Science.gov (United States)

Marcellini, Moreno; Fernandes, Francisco M.; Dedovets, Dmytro; Deville, Sylvain

2017-04-01

Few compounds feature ice-shaping properties. Zirconium acetate is one of the very few inorganic compounds reported so far to have ice-shaping properties similar to that of ice-shaping proteins, encountered in many organisms living at low temperature. When a zirconium acetate solution is frozen, oriented and perfectly hexagonal ice crystals can be formed and their growth follows the temperature gradient. To shed light on the water/ice phase transition while freezing zirconium acetate solution, we carried out differential scanning calorimetry measurements. From our results, we estimate how many water molecules do not freeze because of their interaction with Zr cations. We estimate the colligative properties of the Zr acetate on the apparent critical temperature. We further show that the phase transition is unaffected by the nature of the base which is used to adjust the pH. Our results provide thus new hints on the ice-shaping mechanism of zirconium acetate.

Effects of Field Distortions in IH-APF Linac for a Compact Medical Accelerator

CERN Document Server

Kapin, Valery; Yamada, Satoru

2004-01-01

The project on developing compact medical accelerators for the tumor therapy using carbon ions has been started at the National Institute of Radiological Sciences (NIRS). Alternating-phase-focused (APF) linac using an interdigital H-mode (IH) cavity has been proposed for the injector linac. The IH-cavity is a doubly ridged circular resonator loaded by the drift-tubes mounted on ridges with supporting stems. The effects of intrinsic and random field distortions in a practical design of the 4-Mev/u 200-MHz IH-APF linac are considered. The intrinsic field distortions in the IH-cavity are caused by an asymmetry of the gap fields due to presence of the stems and pair of ridges. The random field distortions are caused by drift-tube misalignments and non-regular deviations of the gap voltages from programmed values. The RF fields in the IH-cavity have been calculated using Microwave Studio (MWS) code. The effects of field distortions on beam dynamics have been simulated numerically. The intrinsic field distortions a...

42 CFR 137.206 - Why does the IHS need this information?

Science.gov (United States)

2010-10-01

... 42 Public Health 1 2010-10-01 2010-10-01 false Why does the IHS need this information? 137.206 Section 137.206 Public Health PUBLIC HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES INDIAN HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES TRIBAL SELF-GOVERNANCE Operational Provisions Health Status Reports § 137.206 Why does the IHS...

Influence of Ice Cloud Microphysics on Imager-Based Estimates of Earth's Radiation Budget

Science.gov (United States)

Loeb, N. G.; Kato, S.; Minnis, P.; Yang, P.; Sun-Mack, S.; Rose, F. G.; Hong, G.; Ham, S. H.

2016-12-01

A central objective of the Clouds and the Earth's Radiant Energy System (CERES) is to produce a long-term global climate data record of Earth's radiation budget from the TOA down to the surface along with the associated atmospheric and surface properties that influence it. CERES relies on a number of data sources, including broadband radiometers measuring incoming and reflected solar radiation and OLR, high-resolution spectral imagers, meteorological, aerosol and ozone assimilation data, and snow/sea-ice maps based on microwave radiometer data. While the TOA radiation budget is largely determined directly from accurate broadband radiometer measurements, the surface radiation budget is derived indirectly through radiative transfer model calculations initialized using imager-based cloud and aerosol retrievals and meteorological assimilation data. Because ice cloud particles exhibit a wide range of shapes, sizes and habits that cannot be independently retrieved a priori from passive visible/infrared imager measurements, assumptions about the scattering properties of ice clouds are necessary in order to retrieve ice cloud optical properties (e.g., optical depth) from imager radiances and to compute broadband radiative fluxes. This presentation will examine how the choice of an ice cloud particle model impacts computed shortwave (SW) radiative fluxes at the top-of-atmosphere (TOA) and surface. The ice cloud particle models considered correspond to those from prior, current and future CERES data product versions. During the CERES Edition2 (and Edition3) processing, ice cloud particles were assumed to be smooth hexagonal columns. In the Edition4, roughened hexagonal columns are assumed. The CERES team is now working on implementing in a future version an ice cloud particle model comprised of a two-habit ice cloud model consisting of roughened hexagonal columns and aggregates of roughened columnar elements. In each case, we use the same ice particle model in both the

Contribution of corner reflections from oriented ice crystals to backscattering and depolarization characteristics for off-zenith lidar profiling

Science.gov (United States)

Borovoi, Anatoli G.; Konoshonkin, Alexander V.; Kustova, Natalia V.; Veselovskii, Igor A.

2018-06-01

Backscattering Mueller matrix and the depolarization and color ratios for quasi-horizontally oriented hexagonal ice plates have been calculated within the framework of the physical optics approximation. In the case of a tilted lidar, the dependence of the color and depolarization ratios on polarization of the incident light has been analyzed. It is shown that the corner reflection effect inherent to the pristine hexagonal ice crystals results in sharp peaks of both the backscattering cross section and depolarization ratio at the lidar tilts of about 30° off zenith. The experimental results obtained recently by Veselovskii et al. [13] at the lidar tilt of 43° have been interpreted as a partial manifestation of the corner reflection effect. The retrieval of the vertical profile of the ice crystal fraction consisting of quasi-horizontally oriented hexagonal plates has been demonstrated.

Qualidades psicométricas do Inventário de Habilidades Sociais (IHS: estudo sobre a estabilidade temporal e a validade concomitante Psychometric qualities of a Social Skills Inventory (IHS: a study of its temporal stability and concomitant validity

Directory of Open Access Journals (Sweden)

Marina Bandeira

2000-12-01

Full Text Available Esta pesquisa investiga as qualidades psicométricas do Inventário de Habilidades Sociais (IHS em termos de sua validade concomitante e de sua fidedignidade ou estabilidade temporal. Participaram desta pesquisa, 104 estudantes de Psicologia que foram submetidos à aplicação do IHS e da Escala de Assertividade de Rathus. Os resultados mostram uma correlação significativa entre estas duas escalas de avaliação. Os dados referentes à aplicação teste-reteste do IHS, em uma subamostra aleatória de 39 sujeitos, mostram igualmente um correlação significativa entre as duas aplicações. Estes resultados indicam que o IHS possui validade concomitante e fidedignidade ou estabilidade temporal. Estas conclusões complementam os resultados de estudos anteriores sobre as qualidades psicométricas do IHS e recomendam a utilização desta escala para avaliar as habilidades sociais de estudantes universitários no contexto brasileiro.This research investigates the psychometric properties of the Social Skills Inventory (IHS in terms of its concomitant validity and reliability. A sample of 104 psychology students participated in this research. Two scales were applied to the subjects, the IHS and the Rathus Assertiveness Scale. The results showed a significant correlation between the IHS and the Rathus Scale scores. The IHS was also reapplied to a randomized sub-sample of 39 students. The results of this test-retest application also showed a significant correlation between these scores. The results indicate that the IHS has concomitant validity and reliability or temporal stability. This study adds positive results to a previous study investigating some other psychometric properties of the IHS and recommends the use of this scale for the evaluation of college student social skills.

Multi-scale modeling of the mechanical behavior of polycrystalline ice under transient creep.

OpenAIRE

Suquet , Pierre; Moulinec , Hervé; Castelnau , O.; Montagnat , Maurine; Lahellec , Noël; Grennerat , Fanny; Duval , Paul; Brenner , Renald

2012-01-01

International audience; Ice is a challenging material for understanding the overall behavior of polycrystalline materials and more specifically the coupling between elastic and viscous effects during transient creep. At the single crystal level, ice is an hexagonal material with a rather weak elastic anisotropy but with a strong viscoplastic anisotropy. The strain-stress curve of ice single crystals shows a softening behavior depending on the strain-rate. The strong viscous anisotropy of ice ...

Molecular multipole moments of water molecules in ice Ih

International Nuclear Information System (INIS)

Batista, E.R.; Xantheas, S.S.; Jonsson, H.

1998-01-01

We have used an induction model including dipole, dipole endash quadrupole, quadrupole endash quadrupole polarizability and first hyperpolarizability as well as fixed octopole and hexadecapole moments to study the electric field in ice. The self-consistent induction calculations gave an average total dipole moment of 3.09 D, a 67% increase over the dipole moment of an isolated water molecule. A previous, more approximate induction model study by Coulson and Eisenberg [Proc. R. Soc. Lond. A 291, 445 (1966)] suggested a significantly smaller average value of 2.6 D. This value has been used extensively in recent years as a reference point in the development of various polarizable interaction potentials for water as well as for assessment of the convergence of water cluster properties to those of bulk. The reason for this difference is not due to approximations made in the computational scheme of Coulson and Eisenberg but rather due to the use of less accurate values for the molecular multipoles in these earlier calculations. copyright 1998 American Institute of Physics

The defective nature of ice Ic and its implications for atmospheric science

Science.gov (United States)

Kuhs, W. F.; Hansen, T. C.

2009-04-01

The possible atmospheric implication of ice Ic (cubic ice) has already been suggested some time ago in the context of snow crystal formation [1]. New findings from air-borne measurements in cirrus clouds and contrails have put ice Ic into the focus of interest to understand the so-called "supersaturation puzzle" [2,3,4,5]. Our recent microstructural work on ice Ic [6,7] appears to be highly relevant in this context. We have found that ice Ic is characterized by a complex stacking fault pattern, which changes as a function of temperature as well as time. Indeed, from our own [8] and other group's work [9] one knows that (in contrast to earlier believe) ice Ic can form up to temperatures at least as high as 240K - thus in the relevant range for cirrus clouds. We have good preliminary evidence that the "cubicity" (which can be related to stacking fault probabilities) as well as the particle size of ice Ic are the relevant parameters for this correlation. The "cubicity" of stacking faulty ice Ic (established by diffraction) correlates nicely with the increased supersaturation at decreasing temperatures observed in cirrus clouds and contrails, a fact, which may be considered as further evidence for the presence of ice Ic. Moreover, the stacking faults lead to kinks in the outer shapes of the minute ice Ic crystals as seen by cryo scanning electron microscopy (cryo-SEM); these defective sites are likely to play some role in heterogeneous reactions in the atmosphere. The cryo-SEM work suggests that stacking-faulty ice Ic has many more active centres for such reactions than the usually considered thermodynamically stable form, ice Ih. [1] T Kobayashi & T Kuroda (1987) Snow Crystals. In: Morphology of Crystals (ed. I Sunagawa), Terra Scientific Publishing, Tokyo, pp.649-743. [2] DM Murphy (2003) Dehydration in cold clouds is enhanced by a transition from from cubic to hexagonal ice. Geophys.Res.Lett.,30, 2230, doi:10.1029/2003GL018566. [3] RS Gao & 19 other authors (2004

De novo DESIGN AND SYNTHESIS OF AN ICE-BINDING, DENDRIMERIC, POLYPEPTIDE BASED ON INSECT ANTIFREEZE PROTEINS

Directory of Open Access Journals (Sweden)

Ricardo Vera Bravo

2011-12-01

Full Text Available A new strategy is presented for the designand synthesis of peptides that exhibitice-binding and antifreeze activity. Apennant-type dendrimer polypeptidescaffold combining an α-helical backbonewith four short β-strand branches wassynthesized in solid phase using Fmocchemistry in a divergent approach. The51-residue dendrimer was characterizedby reverse phase high performance liquidchromatography, mass spectrometry andcircular dichroism. Each β-strand branchcontained three overlapping TXT aminoacid repeats, an ice-binding motif foundin the ice-binding face of the sprucebudworm (Choristoneura fumiferanaand beetle (Tenebrio molitor antifreezeproteins. Ice crystals in the presence ofthe polypeptide monomer displayed flat,hexagonal plate morphology, similar tothat produced by weakly active antifreezeproteins. An oxidized dimeric form of thedendrimer polypeptide also produced flathexagonal ice crystals and was capableof inhibiting ice crystal growth upontemperature reduction, a phenomenontermed thermal hysteresis, a definingproperty of antifreeze proteins. Linkageof the pennant-type dendrimer to a trifunctionalcascade-type polypeptideproduced a trimeric macromolecule thatgave flat hexagonal ice crystals withhigher thermal hysteresis activity thanthe dimer or monomer and an ice crystal burst pattern similar to that producedby samples containing insect antifreezeproteins. This macromolecule was alsocapable of inhibiting ice recrystallization.

Retrieval of Ice Cloud Properties Using Variable Phase Functions

Science.gov (United States)

Heck, Patrick W.; Minnis, Patrick; Yang, Ping; Chang, Fu-Lung; Palikonda, Rabindra; Arduini, Robert F.; Sun-Mack, Sunny

2009-03-01

An enhancement to NASA Langley's Visible Infrared Solar-infrared Split-window Technique (VISST) is developed to identify and account for situations when errors are induced by using smooth ice crystals. The retrieval scheme incorporates new ice cloud phase functions that utilize hexagonal crystals with roughened surfaces. In some situations, cloud optical depths are reduced, hence, cloud height is increased. Cloud effective particle size also changes with the roughened ice crystal models which results in varied effects on the calculation of ice water path. Once validated and expanded, the new approach will be integrated in the CERES MODIS algorithm and real-time retrievals at Langley.

Ice and water droplets on graphite: A comparison of quantum and classical simulations

International Nuclear Information System (INIS)

Ramírez, Rafael; Singh, Jayant K.; Müller-Plathe, Florian; Böhm, Michael C.

2014-01-01

Ice and water droplets on graphite have been studied by quantum path integral and classical molecular dynamics simulations. The point-charge q-TIP4P/F potential was used to model the interaction between flexible water molecules, while the water-graphite interaction was described by a Lennard-Jones potential previously used to reproduce the macroscopic contact angle of water droplets on graphite. Several energetic and structural properties of water droplets with sizes between 10 2 and 10 3 molecules were analyzed in a temperature interval of 50–350 K. The vibrational density of states of crystalline and amorphous ice drops was correlated to the one of ice Ih to assess the influence of the droplet interface and molecular disorder on the vibrational properties. The average distance of covalent OH bonds is found 0.01 Å larger in the quantum limit than in the classical one. The OO distances are elongated by 0.03 Å in the quantum simulations at 50 K. Bond distance fluctuations are large as a consequence of the zero-point vibrations. The analysis of the H-bond network shows that the liquid droplet is more structured in the classical limit than in the quantum case. The average kinetic and potential energy of the ice and water droplets on graphite has been compared with the values of ice Ih and liquid water as a function of temperature. The droplet kinetic energy shows a temperature dependence similar to the one of liquid water, without apparent discontinuity at temperatures where the droplet is solid. However, the droplet potential energy becomes significantly larger than the one of ice or water at the same temperature. In the quantum limit, the ice droplet is more expanded than in a classical description. Liquid droplets display identical density profiles and liquid-vapor interfaces in the quantum and classical limits. The value of the contact angle is not influenced by quantum effects. Contact angles of droplets decrease as the size of the water droplet increases

Large-Scale Structure and Hyperuniformity of Amorphous Ices

Science.gov (United States)

Martelli, Fausto; Torquato, Salvatore; Giovambattista, Nicolas; Car, Roberto

2017-09-01

We investigate the large-scale structure of amorphous ices and transitions between their different forms by quantifying their large-scale density fluctuations. Specifically, we simulate the isothermal compression of low-density amorphous ice (LDA) and hexagonal ice to produce high-density amorphous ice (HDA). Both HDA and LDA are nearly hyperuniform; i.e., they are characterized by an anomalous suppression of large-scale density fluctuations. By contrast, in correspondence with the nonequilibrium phase transitions to HDA, the presence of structural heterogeneities strongly suppresses the hyperuniformity and the system becomes hyposurficial (devoid of "surface-area fluctuations"). Our investigation challenges the largely accepted "frozen-liquid" picture, which views glasses as structurally arrested liquids. Beyond implications for water, our findings enrich our understanding of pressure-induced structural transformations in glasses.

Photoabsorption of the molecular IH cation at the iodine 3 d absorption edge

Science.gov (United States)

Klumpp, Stephan; Guda, Alexander A.; Schubert, Kaja; Mertens, Karolin; Hellhund, Jonas; Müller, Alfred; Schippers, Stefan; Bari, Sadia; Martins, Michael

2018-03-01

Yields of atomic iodine Iq + (q ≥2 ) fragments resulting from photoexcitation and photoionization of the target ions IH+ and I+ have been measured in the photon-energy range 610-680 eV, which comprises the thresholds for iodine 3 d ionization. The measured ion-yield spectra show two strong and broad resonance features due to the excitation of the 3 d3 /2 ,5 /2 electrons into ɛ f states rather similar for both parent ions. In the 3 d pre-edge range, excitations into (n p π ) -like orbitals and into an additional σ* orbital are found for IH+, which have been identified by comparison of the atomic I+ and molecular IH+ data and with the help of (time-dependent) density functional theory (DFT) and atomic Hartree-Fock calculations. The (5 p π ) orbital is almost atomlike, whereas all other resonances of the IH+ primary ion show a more pronounced molecular character, which is deduced from the chemical shifts of the resonances and the theoretical analysis.

Modelling the viscoplastic behavior and the heterogeneous intracrystalline deformation of columnar ice polycrystals

Energy Technology Data Exchange (ETDEWEB)

Lebensohn, Ricardo A [Los Alamos National Laboratory; Montagnat, Maurine [LGGE (FRANCE); Mansuy, Philippe [MICHELIN (FRANCE); Duval, Paul [LGGE (FRANCE); Philip, A [LGGE (FRANCE)

2008-01-01

A full-field formulation based on Fast Fourier Transforms (FFT) has been adapted and used to predict the micromechanical fields that develop in columnar Ih ice polycrystals deforming in compression by dislocation creep. The predicted intragranular mechanical fields are in qualitative good agreement with experimental observations, in particular those involving the formation of shear and kink bands. These localization bands are associated with the large internal stresses that develop during creep in such anisotropic material, and their location, intensity, morphology and extension are found to depend strongly on the crystallographic orientation of the grains and on their interaction with neighbor crystals. The predictions of the model are also discussed in relation with the deformation of columnar sea and lake ice, and with the mechanical behavior of granular ice of glaciers and polar ice sheets, as well.

Post accelerator of the IH type structure

International Nuclear Information System (INIS)

Chen Ming

2002-01-01

The principle, structure, adjustment of the gap voltage, beam dynamic, RF system and the bunchers of the post-accelerator with Interdigital-H type structure, which was developed by the author and Technical University Munich in four years, is described. The energy of ions with mass of three was increased from 340 keV to 1.74 MeV, when resonant frequency of 84.2 MHz and input RF power of 3 kW. The effective shunt impedance reached to 408 MΩ/m. The commissioning was succeeded with H 3 + ion beams. The output energy of H 3 + ion beams reached the design value. The two harmonic double drift buncher used by the IH structure bunches the beam to the bunches with the width of 360 ps. Then the acceptance of the IH structure is increased to 240 degree. Its shunt impedance is three times higher than former single gap bunchers used by TUM and the length of the buncher system is one fifth of former one only because the use of λ/4 coaxial cavities with double gaps

Long Term Processing Using Integrated Hydropyrolysis plus Hydroconversion (IH2) for the Production of Gasoline and Diesel from Biomass

Energy Technology Data Exchange (ETDEWEB)

Marker, Terry [Gas Technology Institute; Roberts, Michael [Gas Technology Institute; Linck, Martin [Gas Technology Institute; Felix, Larry [Gas Technology Institute; Ortiz-Toral, Pedro [Gas Technology Institute; Wangerow, Jim [Gas Technology Institute; McLeod, Celeste [CRI Catalyst; Del Paggio, Alan [CRI Catalyst; Gephart, John [Johnson Timber; Starr, Jack [Cargill; Hahn, John [Cargill

2013-06-09

Cellulosic and woody biomass can be directly converted to hydrocarbon gasoline and diesel blending components through the use of a new, economical, technology named integrated hydropyrolysis plus hydroconversion (IH2). The IH2 gasoline and diesel blending components are fully compatible with petroleum based gasoline and diesel, contain less than 1% oxygen and have less than 1 total acid number (TAN). The IH2 gasoline is high quality and very close to a drop in fuel. The life cycle analysis (LCA) shows that the use of the IH2 process to convert wood to gasoline and diesel results in a greater than 90% reduction in greenhouse gas emission compared to that found with fossil derived fuels. The technoeconomic analysis showed the conversion of wood using the IH2 process can produce gasoline and diesel at less than $2.00/gallon. In this project, the previously reported semi-continuous small scale IH2 test results were confirmed in a continuous 50 kg/day pilot plant. The continuous IH2 pilot plant used in this project was operated round the clock for over 750 hours and showed good pilot plant operability while consistently producing 26-28 wt % yields of high quality gasoline and diesel product. The IH2 catalyst showed good stability, although more work on catalyst stability is recommended. Additional work is needed to commercialize the IH2 technology including running large particle size biomass, modeling the hydropyrolysis step, studying the effects of process variables and building and operating a 1-50 ton/day demonstration scale plant. The IH2 is a true game changing technology by utilizing U.S. domestic renewable biomass resources to create transportation fuels, sufficient in quantity and quality to substantially reduce our reliance on foreign crude oil. Thus, the IH2 technology offers a path to genuine energy independence for the U. S., along with the creation of a significant number of new U.S. jobs to plant, grow, harvest, and process biomass crops into fungible

Interference phenomena at backscattering by ice crystals of cirrus clouds.

Science.gov (United States)

Borovoi, Anatoli; Kustova, Natalia; Konoshonkin, Alexander

2015-09-21

It is shown that light backscattering by hexagonal ice crystals of cirrus clouds is formed within the physical-optics approximation by both diffraction and interference phenomena. Diffraction determines the angular width of the backscattering peak and interference produces the interference rings inside the peak. By use of a simple model for distortion of the pristine hexagonal shape, we show that the shape distortion leads to both oscillations of the scattering (Mueller) matrix within the backscattering peak and to a strong increase of the depolarization, color, and lidar ratios needed for interpretation of lidar signals.

Single Ih channels in pyramidal neuron dendrites: properties, distribution, and impact on action potential output

NARCIS (Netherlands)

Kole, Maarten H. P.; Hallermann, Stefan; Stuart, Greg J.

2006-01-01

The hyperpolarization-activated cation current (Ih) plays an important role in regulating neuronal excitability, yet its native single-channel properties in the brain are essentially unknown. Here we use variance-mean analysis to study the properties of single Ih channels in the apical dendrites of

Remote Sensing Image Fusion Based on the Combination Grey Absolute Correlation Degree and IHS Transform

Directory of Open Access Journals (Sweden)

Hui LIN

2014-12-01

Full Text Available An improved fusion algorithm for multi-source remote sensing images with high spatial resolution and multi-spectral capacity is proposed based on traditional IHS fusion and grey correlation analysis. Firstly, grey absolute correlation degree is used to discriminate non-edge pixels and edge pixels in high-spatial resolution images, by which the weight of intensity component is identified in order to combine it with high-spatial resolution image. Therefore, image fusion is achieved using IHS inverse transform. The proposed method is applied to ETM+ multi-spectral images and panchromatic image, and Quickbird’s multi-spectral images and panchromatic image respectively. The experiments prove that the fusion method proposed in the paper can efficiently preserve spectral information of the original multi-spectral images while enhancing spatial resolution greatly. By comparison and analysis, the proposed fusion algorithm is better than traditional IHS fusion and fusion method based on grey correlation analysis and IHS transform.

High dendritic expression of Ih in the proximity of the axon origin controls the integrative properties of nigral dopamine neurons.

Science.gov (United States)

Engel, Dominique; Seutin, Vincent

2015-11-15

The hyperpolarization-activated cation current Ih is expressed in dopamine neurons of the substantia nigra, but the subcellular distribution of the current and its role in synaptic integration remain unknown. We used cell-attached patch recordings to determine the localization profile of Ih along the somatodendritic axis of nigral dopamine neurons in slices from young rats. Ih density is higher in axon-bearing dendrites, in a membrane area close to the axon origin, than in the soma and axon-lacking dendrites. Dual current-clamp recordings revealed a similar contribution of Ih to the waveform of single excitatory postsynaptic potentials throughout the somatodendritic domain. The Ih blocker ZD 7288 increased the temporal summation in all dendrites with a comparable effect in axon- and non-axon dendrites. The strategic position of Ih in the proximity of the axon may influence importantly transitions between pacemaker and bursting activities and consequently the downstream release of dopamine. Dendrites of most neurons express voltage-gated ion channels in their membrane. In combination with passive properties, active currents confer to dendrites a high computational potential. The hyperpolarization-activated cation current Ih present in the dendrites of some pyramidal neurons affects their membrane and integration properties, synaptic plasticity and higher functions such as memory. A gradient of increasing h-channel density towards distal dendrites has been found to be responsible for the location independence of excitatory postsynaptic potential (EPSP) waveform and temporal summation in cortical and hippocampal pyramidal cells. However, reports on other cell types revealed that smoother gradients or even linear distributions of Ih can achieve homogeneous temporal summation. Although the existence of a robust, slowly activating Ih current has been repeatedly demonstrated in nigral dopamine neurons, its subcellular distribution and precise role in synaptic integration

Grand Canonical Investigation of the Quasi Liquid Layer of Ice: Is It Liquid?

Science.gov (United States)

Pickering, Ignacio; Paleico, Martin; Sirkin, Yamila A Perez; Scherlis, Damian A; Factorovich, Matías H

2018-05-10

In this study, the solid-vapor equilibrium and the quasi liquid layer (QLL) of ice Ih exposing the basal and primary prismatic faces were explored by means of grand canonical molecular dynamics simulations with the monatomic mW potential. For this model, the solid-vapor equilibrium was found to follow the Clausius-Clapeyron relation in the range examined, from 250 to 270 K, with a Δ H sub of 50 kJ/mol in excellent agreement with the experimental value. The phase diagram of the mW model was constructed for the low pressure region around the triple point. The analysis of the crystallization dynamics during condensation and evaporation revealed that, for the basal face, both processes are highly activated, and in particular cubic ice is formed during condensation, producing stacking-disordered ice. The basal and primary prismatic surfaces of ice Ih were investigated at different temperatures and at their corresponding equilibrium vapor pressures. Our results show that the region known as QLL can be interpreted as the outermost layers of the solid where a partial melting takes place. Solid islands in the nanometer length scale are surrounded by interconnected liquid areas, generating a bidimensional nanophase segregation that spans throughout the entire width of the outermost layer even at 250 K. Two approaches were adopted to quantify the QLL and discussed in light of their ability to reflect this nanophase segregation phenomena. Our results in the μVT ensemble were compared with NPT and NVT simulations for two system sizes. No significant differences were found between the results as a consequence of model system size or of the working ensemble. Nevertheless, certain advantages of performing μVT simulations in order to reproduce the experimental situation are highlighted. On the one hand, the QLL thickness measured out of equilibrium might be affected because of crystallization being slower than condensation. On the other, preliminary simulations of AFM

Hyperpolarization-activated current (I(h)) in vestibular calyx terminals: characterization and role in shaping postsynaptic events.

Science.gov (United States)

Meredith, Frances L; Benke, Tim A; Rennie, Katherine J

2012-12-01

Calyx afferent terminals engulf the basolateral region of type I vestibular hair cells, and synaptic transmission across the vestibular type I hair cell/calyx is not well understood. Calyces express several ionic conductances, which may shape postsynaptic potentials. These include previously described tetrodotoxin-sensitive inward Na(+) currents, voltage-dependent outward K(+) currents and a K(Ca) current. Here, we characterize an inwardly rectifying conductance in gerbil semicircular canal calyx terminals (postnatal days 3-45), sensitive to voltage and to cyclic nucleotides. Using whole-cell patch clamp, we recorded from isolated calyx terminals still attached to their type I hair cells. A slowly activating, noninactivating current (I(h)) was seen with hyperpolarizing voltage steps negative to the resting potential. External Cs(+) (1-5 mM) and ZD7288 (100 μM) blocked the inward current by 97 and 83 %, respectively, confirming that I(h) was carried by hyperpolarization-activated, cyclic nucleotide gated channels. Mean half-activation voltage of I(h) was -123 mV, which shifted to -114 mV in the presence of cAMP. Activation of I(h) was well described with a third order exponential fit to the current (mean time constant of activation, τ, was 190 ms at -139 mV). Activation speeded up significantly (τ=136 and 127 ms, respectively) when intracellular cAMP and cGMP were present, suggesting that in vivo I(h) could be subject to efferent modulation via cyclic nucleotide-dependent mechanisms. In current clamp, hyperpolarizing current steps produced a time-dependent depolarizing sag followed by either a rebound afterdepolarization or an action potential. Spontaneous excitatory postsynaptic potentials (EPSPs) became larger and wider when I(h) was blocked with ZD7288. In a three-dimensional mathematical model of the calyx terminal based on Hodgkin-Huxley type ionic conductances, removal of I(h) similarly increased the EPSP, whereas cAMP slightly decreased simulated EPSP size

X-Ray Absorption Spectra of Amorphous Ices from GW Quasiparticle Calculation

Science.gov (United States)

Kong, Lingzhu; Car, Roberto

2013-03-01

We use a GW approach[2] to compute the x-ray absorption spectra of model low- and high-density amorphous ice structures(LDA and HDA)[3]. We include the structural effects of quantum zero point motion using colored-noise Langevin molecular dynamics[4]. The calculated spectra differences in the main and post edge region between LDA and HDA agree well with experimental observations. We attribute these differences to the presence of interstitial molecules within the first coordination shell range in HDA. This assignment is further supported by a calculation of the spectrum of ice VIII, a high-pressure structure that maximizes the number of interstitial molecules and, accordingly, shows a much weaker post-edge feature. We further rationalize the spectral similarity between HDA and liquid water, and between LDA and ice Ih in terms of the respective similarities in the H-bond network topology and bond angle distributions. Supported by grants DOE-DE-SC0005180, DOE DE-SC0008626 and NSF-CHE-0956500.

Transforming wealth: using the inverse hyperbolic sine (IHS) and splines to predict youth's math achievement.

Science.gov (United States)

Friedline, Terri; Masa, Rainier D; Chowa, Gina A N

2015-01-01

The natural log and categorical transformations commonly applied to wealth for meeting the statistical assumptions of research may not always be appropriate for adjusting for skewness given wealth's unique properties. Finding and applying appropriate transformations is becoming increasingly important as researchers consider wealth as a predictor of well-being. We present an alternative transformation-the inverse hyperbolic sine (IHS)-for simultaneously dealing with skewness and accounting for wealth's unique properties. Using the relationship between household wealth and youth's math achievement as an example, we apply the IHS transformation to wealth data from US and Ghanaian households. We also explore non-linearity and accumulation thresholds by combining IHS transformed wealth with splines. IHS transformed wealth relates to youth's math achievement similarly when compared to categorical and natural log transformations, indicating that it is a viable alternative to other transformations commonly used in research. Non-linear relationships and accumulation thresholds emerge that predict youth's math achievement when splines are incorporated. In US households, accumulating debt relates to decreases in math achievement whereas accumulating assets relates to increases in math achievement. In Ghanaian households, accumulating assets between the 25th and 50th percentiles relates to increases in youth's math achievement. Copyright © 2014 Elsevier Inc. All rights reserved.

42 CFR 137.275 - May Self-Governance Tribes include IHS construction programs in a construction project agreement...

Science.gov (United States)

2010-10-01

... 42 Public Health 1 2010-10-01 2010-10-01 false May Self-Governance Tribes include IHS construction... OF HEALTH AND HUMAN SERVICES TRIBAL SELF-GOVERNANCE Construction Purpose and Scope § 137.275 May Self-Governance Tribes include IHS construction programs in a construction project agreement or in a funding...

Thermal conductivity of hexagonal Si and hexagonal Si nanowires from first-principles

Science.gov (United States)

Raya-Moreno, Martí; Aramberri, Hugo; Seijas-Bellido, Juan Antonio; Cartoixà, Xavier; Rurali, Riccardo

2017-07-01

We calculate the thermal conductivity, κ, of the recently synthesized hexagonal diamond (lonsdaleite) Si using first-principles calculations and solving the Boltzmann Transport Equation. We find values of κ which are around 40% lower than in the common cubic diamond polytype of Si. The trend is similar for [111] Si nanowires, with reductions of the thermal conductivity that are even larger than in the bulk in some diameter range. The Raman active modes are identified, and the role of mid-frequency optical phonons that arise as a consequence of the reduced symmetry of the hexagonal lattice is discussed. We also show briefly that popular classic potentials used in molecular dynamics might not be suited to describe hexagonal polytypes, discussing the case of the Tersoff potential.

High-pass filtering of input signals by the Ih current in a non-spiking neuron, the retinal rod bipolar cell.

Directory of Open Access Journals (Sweden)

Lorenzo Cangiano

Full Text Available Hyperpolarization-activated cyclic nucleotide-sensitive (HCN channels mediate the I(f current in heart and I(h throughout the nervous system. In spiking neurons I(h participates primarily in different forms of rhythmic activity. Little is known, however, about its role in neurons operating with graded potentials as in the retina, where all four channel isoforms are expressed. Intriguing evidence for an involvement of I(h in early visual processing are the side effects reported, in dim light or darkness, by cardiac patients treated with HCN inhibitors. Moreover, electroretinographic recordings indicate that these drugs affect temporal processing in the outer retina. Here we analyzed the functional role of HCN channels in rod bipolar cells (RBCs of the mouse. Perforated-patch recordings in the dark-adapted slice found that RBCs exhibit I(h, and that this is sensitive to the specific blocker ZD7288. RBC input impedance, explored by sinusoidal frequency-modulated current stimuli (0.1-30 Hz, displays band-pass behavior in the range of I(h activation. Theoretical modeling and pharmacological blockade demonstrate that high-pass filtering of input signals by I(h, in combination with low-pass filtering by passive properties, fully accounts for this frequency-tuning. Correcting for the depolarization introduced by shunting through the pipette-membrane seal, leads to predict that in darkness I(h is tonically active in RBCs and quickens their responses to dim light stimuli. Immunohistochemistry targeting candidate subunit isoforms HCN1-2, in combination with markers of RBCs (PKC and rod-RBC synaptic contacts (bassoon, mGluR6, Kv1.3, suggests that RBCs express HCN2 on the tip of their dendrites. The functional properties conferred by I(h onto RBCs may contribute to shape the retina's light response and explain the visual side effects of HCN inhibitors.

Role of Ih in differentiating the dynamics of the gastric and pyloric neurons in the stomatogastric ganglion of the lobster, Homarus americanus.

Science.gov (United States)

Zhu, Lin; Selverston, Allen I; Ayers, Joseph

2016-06-01

The hyperpolarization-activated inward cationic current (Ih) is known to regulate the rhythmicity, excitability, and synaptic transmission in heart cells and many types of neurons across a variety of species, including some pyloric and gastric mill neurons in the stomatogastric ganglion (STG) in Cancer borealis and Panulirus interruptus However, little is known about the role of Ih in regulating the gastric mill dynamics and its contribution to the dynamical bifurcation of the gastric mill and pyloric networks. We investigated the role of Ih in the rhythmic activity and cellular excitability of both the gastric mill neurons (medial gastric, gastric mill) and pyloric neurons (pyloric dilator, lateral pyloric) in Homarus americanus Through testing the burst period between 5 and 50 mM CsCl, and elimination of postinhibitory rebound and voltage sag, we found that 30 mM CsCl can sufficiently block Ih in both the pyloric and gastric mill neurons. Our results show that Ih maintains the excitability of both the pyloric and gastric mill neurons. However, Ih regulates slow oscillations of the pyloric and gastric mill neurons differently. Specifically, blocking Ih diminishes the difference between the pyloric and gastric mill burst periods by increasing the pyloric burst period and decreasing the gastric mill burst period. Moreover, the phase-plane analysis shows that blocking Ih causes the trajectory of slow oscillations of the gastric mill neurons to change toward the pyloric sinusoidal-like trajectories. In addition to regulating the pyloric rhythm, we found that Ih is also essential for the gastric mill rhythms and differentially regulates these two dynamics. Copyright © 2016 the American Physiological Society.

Polarized Radiative Transfer of a Cirrus Cloud Consisting of Randomly Oriented Hexagonal Ice Crystals: The 3 x 3 Approximation for Non-Spherical Particles

Science.gov (United States)

Stamnes, S.; Ou, S. C.; Lin, Z.; Takano, Y.; Tsay, S. C.; Liou, K.N.; Stamnes, K.

2016-01-01

The reflection and transmission of polarized light for a cirrus cloud consisting of randomly oriented hexagonal columns were calculated by two very different vector radiative transfer models. The forward peak of the phase function for the ensemble-averaged ice crystals has a value of order 6 x 10(exp 3) so a truncation procedure was used to help produce numerically efficient yet accurate results. One of these models, the Vectorized Line-by-Line Equivalent model (VLBLE), is based on the doubling- adding principle, while the other is based on a vector discrete ordinates method (VDISORT). A comparison shows that the two models provide very close although not entirely identical results, which can be explained by differences in treatment of single scattering and the representation of the scattering phase matrix. The relative differences in the reflected I and Q Stokes parameters are within 0.5 for I and within 1.5 for Q for all viewing angles. In 1971 Hansen showed that for scattering by spherical particles the 3 x 3 approximation is sufficient to produce accurate results for the reflected radiance I and the degree of polarization (DOP), and he conjectured that these results would hold also for non-spherical particles. Simulations were conducted to test Hansen's conjecture for the cirrus cloud particles considered in this study. It was found that the 3 x 3 approximation also gives accurate results for the transmitted light, and for Q and U in addition to I and DOP. For these non-spherical ice particles the 3 x 3 approximation leads to an absolute error 2 x 10(exp -6) for the reflected and transmitted I, Q and U Stokes parameters. Hence, it appears to be an excellent approximation, which significantly reduces the computational complexity and burden required for multiple scattering calculations.

Izobraževanje starejših odraslih in pomen njihovega izobraževanja za njih same ter družbo

Directory of Open Access Journals (Sweden)

Dušana Findeisen

2009-12-01

Full Text Available Avtorica predstavi pomen izobraževanja starejših odraslih za dejavno staranje v dolgem prehodnem obdobju, imenovanem »čas med delom, upokojitvijo in starostjo«. Ta koncept prehodnega obdobja, prehoda v starost, namreč danes nadomešča starejši koncept pokoja. V tem času ljudje v poznejših letih življenja opravljajo plačano delo, se izobražujejo, se (občasno vračajo na trg dela, delajo prostovoljno. Avtorica piše o prebivalstvenih spremembah in o pomenu izobraženosti vseh in vseh skupin starejših odraslih za soočanje s staranjem družbe. Dušana Findeisen zastane pri vprašanju značilnosti izobraževalnih programov za starejše odrasle, obravnava vrednote, nosilce in oblike izobraževanja starejših. Nazadnje opiše slovensko univerzo za tretje življenjsko obdobje kot konceptualno eno najbolj celostno domišljenih oblik in modelov izobraževanja ljudi v poznejših letih življenja.

Total Hip Arthroplasty in Mucopolysaccharidosis Type IH

Directory of Open Access Journals (Sweden)

S. O'hEireamhoin

2011-01-01

Full Text Available Children affected by mucopolysaccharidosis (MPS type IH (Hurler Syndrome, an autosomal recessive metabolic disorder, are known to experience a range of musculoskeletal manifestations including spinal abnormalities, hand abnormalities, generalised joint stiffness, genu valgum, and hip dysplasia and avascular necrosis. Enzyme therapy, in the form of bone marrow transplantation, significantly increases life expectancy but does not prevent the development of the associated musculoskeletal disorders. We present the case of a 23-year-old woman with a diagnosis of Hurler syndrome with a satisfactory result following uncemented total hip arthroplasty.

Convergent and reciprocal modulation of a leak K+ current and Ih by an inhalational anaesthetic and neurotransmitters in rat brainstem motoneurones

Science.gov (United States)

Sirois, Jay E; Lynch, Carl; Bayliss, Douglas A

2002-01-01

Neurotransmitters and volatile anaesthetics have opposing effects on motoneuronal excitability which appear to reflect contrasting modulation of two types of subthreshold currents. Neurotransmitters increase motoneuronal excitability by inhibiting TWIK-related acid-sensitive K+ channels (TASK) and shifting activation of a hyperpolarization-activated cationic current (Ih) to more depolarized potentials; on the other hand, anaesthetics decrease excitability by activating a TASK-like current and inducing a hyperpolarizing shift in Ih activation. Here, we used whole-cell recording from motoneurones in brainstem slices to test if neurotransmitters (serotonin (5-HT) and noradrenaline (NA)) and an anaesthetic (halothane) indeed compete for modulation of the same ion channels - and we determined which prevails. When applied together under current clamp conditions, 5-HT reversed anaesthetic-induced membrane hyperpolarization and increased motoneuronal excitability. Under voltage clamp conditions, 5-HT and NA overcame most, but not all, of the halothane-induced current. When Ih was blocked with ZD 7288, the neurotransmitters completely inhibited the K+ current activated by halothane; the halothane-sensitive neurotransmitter current reversed at the equilibrium potential for potassium (EK) and displayed properties expected of acid-sensitive, open-rectifier TASK channels. To characterize modulation of Ih in relative isolation, effects of 5-HT and halothane were examined in acidified bath solutions that blocked TASK channels. Under these conditions, 5-HT and halothane each caused their characteristic shift in voltage-dependent gating of Ih. When tested concurrently, however, halothane decreased the neurotransmitter-induced depolarizing shift in Ih activation. Thus, halothane and neurotransmitters converge on TASK and Ih channels with opposite effects; transmitter action prevailed over anaesthetic effects on TASK channels, but not over effects on Ih. These data suggest that

Hexagon solar power panel

Science.gov (United States)

Rubin, I. (Inventor)

1978-01-01

A solar energy panel support is described upon which silicon cells are arrayed. The cells are wafer thin and of two geometrical types, both of the same area and electrical rating, namely hexagon cells and hourglass cells. The hourglass cells are composites of half hexagons. A near perfect nesting relationship of the cells achieves a high density packing whereby optimum energy production per panel area is achieved.

Estimating Regional Mass Balance of Himalayan Glaciers Using Hexagon Imagery: An Automated Approach

Science.gov (United States)

Maurer, J. M.; Rupper, S.

2013-12-01

Currently there is much uncertainty regarding the present and future state of Himalayan glaciers, which supply meltwater for river systems vital to more than 1.4 billion people living throughout Asia. Previous assessments of regional glacier mass balance in the Himalayas using various remote sensing and field-based methods give inconsistent results, and most assessments are over relatively short (e.g., single decade) timescales. This study aims to quantify multi-decadal changes in volume and extent of Himalayan glaciers through efficient use of the large database of declassified 1970-80s era Hexagon stereo imagery. Automation of the DEM extraction process provides an effective workflow for many images to be processed and glacier elevation changes quantified with minimal user input. The tedious procedure of manual ground control point selection necessary for block-bundle adjustment (as ephemeral data is not available for the declassified images) is automated using the Maximally Stable Extremal Regions algorithm, which matches image elements between raw Hexagon images and georeferenced Landsat 15 meter panchromatic images. Additional automated Hexagon DEM processing, co-registration, and bias correction allow for direct comparison with modern ASTER and SRTM elevation data, thus quantifying glacier elevation and area changes over several decades across largely inaccessible mountainous regions. As consistent methodology is used for all glaciers, results will likely reveal significant spatial and temporal patterns in regional ice mass balance. Ultimately, these findings could have important implications for future water resource management in light of environmental change.

Mesoscopic surface roughness of ice crystals pervasive across a wide range of ice crystal conditions

Science.gov (United States)

Magee, N. B.; Miller, A.; Amaral, M.; Cumiskey, A.

2014-11-01

Here we show high-magnification images of hexagonal ice crystals acquired by environmental scanning electron microscopy (ESEM). Most ice crystals were grown and sublimated in the water vapor environment of an FEI-Quanta-200 ESEM, but crystals grown in a laboratory diffusion chamber were also transferred intact and imaged via ESEM. All of these images display prominent mesoscopic topography including linear striations, ridges, islands, steps, peaks, pits, and crevasses; the roughness is not observed to be confined to prism facets. The observations represent the most highly magnified images of ice surfaces yet reported and expand the range of conditions in which rough surface features are known to be conspicuous. Microscale surface topography is seen to be ubiquitously present at temperatures ranging from -10 °C to -40 °C, in supersaturated and subsaturated conditions, on all crystal facets, and irrespective of substrate. Despite the constant presence of surface roughness, the patterns of roughness are observed to be dramatically different between growing and sublimating crystals, and transferred crystals also display qualitatively different patterns of roughness. Crystals are also demonstrated to sometimes exhibit inhibited growth in moderately supersaturated conditions following exposure to near-equilibrium conditions, a phenomenon interpreted as evidence of 2-D nucleation. New knowledge about the characteristics of these features could affect the fundamental understanding of ice surfaces and their physical parameterization in the context of satellite retrievals and cloud modeling. Links to supplemental videos of ice growth and sublimation are provided.

Main types of optical beams giving predominant contributions to the light backscatter for the irregular hexagonal columns

Science.gov (United States)

Shishko, Victor A.; Konoshonkin, Alexander V.; Kustova, Natalia V.; Borovoi, Anatoli G.

2017-11-01

This work presents the estimation of contribution of the main types of optical beams to the light backscatter for randomly oriented hexagonal ice column, the right dihedral angle of which was distorted within the range of 0° (regular particle) to 10°. Calculations were obtained within the physical optics approximation. The wavelength was 532 nm and the refractive index was 1.3116. The results showed that the total contribution of the main types of optical beams to the total backscattering cross section reach the value of 85% at small distortion angle of the hexagonal column and at substantial distortion angle the total contribution of the main types of optical beams decrease up to 55% of the total backscattering cross section. The obtained conclusions can significantly reduce the calculation time in the case when there is no need for high accuracy of the calculation.

The applicability of physical optics in the millimetre and sub-millimetre spectral region. Part II: Application to a three-component model of ice cloud and its evaluation against the bulk single-scattering properties of various other aggregate models

Science.gov (United States)

Baran, Anthony J.; Ishimoto, Hiroshi; Sourdeval, Odran; Hesse, Evelyn; Harlow, Chawn

2018-02-01

The bulk single-scattering properties of various randomly oriented aggregate ice crystal models are compared and contrasted at a number of frequencies between 89 and 874 GHz. The model ice particles consist of the ten-branched plate aggregate, five-branched plate aggregate, eight-branched hexagonal aggregate, Voronoi ice aggregate, six-branched hollow bullet rosette, hexagonal column of aspect ratio unity, and the ten-branched hexagonal aggregate. The bulk single-scattering properties of the latter two ice particle models have been calculated using the light scattering methods described in Part I, which represent the two most extreme members of an ensemble model of cirrus ice crystals. In Part I, it was shown that the method of physical optics could be combined with the T-matrix at a size parameter of about 18 to compute the bulk integral ice optical properties and the phase function in the microwave to sufficient accuracy to be of practical value. Here, the bulk single-scattering properties predicted by the two ensemble model members and the Voronoi model are shown to generally bound those of all other models at frequencies between 89 and 874 GHz, thus representing a three-component model of ice cloud that can be generally applied to the microwave, rather than using many differing ice particle models. Moreover, the Voronoi model and hollow bullet rosette scatter similarly to each other in the microwave. Furthermore, from the various comparisons, the importance of assumed shapes of the particle size distribution as well as cm-sized ice aggregates is demonstrated.

Ice films follow structure zone model morphologies

International Nuclear Information System (INIS)

Cartwright, Julyan H.E.; Escribano, Bruno; Sainz-Diaz, C. Ignacio

2010-01-01

Ice films deposited at temperatures of 6-220 K and at low pressures in situ in a cryo-environmental scanning electron microscope show pronounced morphologies at the mesoscale consistent with the structure zone model of film growth. Water vapour was injected directly inside the chamber at ambient pressures ranging from 10 -4 Pa to 10 2 Pa. Several different substrates were used to exclude the influence of their morphology on the grown films. At the lowest temperatures the ice, which under these conditions is amorphous on the molecular scale, shows the mesoscale morphologies typical of the low-temperature zones of the structure zone model (SZM), including cauliflower, transition, spongelike and matchstick morphologies. Our experiments confirm that the SZM is independent of the chemical nature of the adsorbate, although the intermolecular interactions in water (hydrogen bonds) are different to those in ceramics or metals. At higher temperatures, on the other hand, where the ice is hexagonal crystalline on the molecular scale, it displays a complex palmlike morphology on the mesoscale.

Ice films follow structure zone model morphologies

Energy Technology Data Exchange (ETDEWEB)

Cartwright, Julyan H.E. [Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, E-18071 Granada (Spain); Escribano, Bruno, E-mail: bruno.escribano.salazar@gmail.co [Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, E-18071 Granada (Spain); Sainz-Diaz, C. Ignacio [Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, E-18071 Granada (Spain)

2010-04-02

Ice films deposited at temperatures of 6-220 K and at low pressures in situ in a cryo-environmental scanning electron microscope show pronounced morphologies at the mesoscale consistent with the structure zone model of film growth. Water vapour was injected directly inside the chamber at ambient pressures ranging from 10{sup -4} Pa to 10{sup 2} Pa. Several different substrates were used to exclude the influence of their morphology on the grown films. At the lowest temperatures the ice, which under these conditions is amorphous on the molecular scale, shows the mesoscale morphologies typical of the low-temperature zones of the structure zone model (SZM), including cauliflower, transition, spongelike and matchstick morphologies. Our experiments confirm that the SZM is independent of the chemical nature of the adsorbate, although the intermolecular interactions in water (hydrogen bonds) are different to those in ceramics or metals. At higher temperatures, on the other hand, where the ice is hexagonal crystalline on the molecular scale, it displays a complex palmlike morphology on the mesoscale.

Electrodeposited Silver Nanoparticles Patterned Hexagonally for SERS

International Nuclear Information System (INIS)

Gu, Geun Hoi; Lee, Sue Yeone; Suh, Jung Sang

2010-01-01

We have fabricated hexagonally patterned silver nanoparticles for surface-enhanced Raman scattering (SERS) by electrodepositing silver on the surface of an aluminum plate prepared by completely removing the oxide from anodic aluminum oxide (AAO) templates. Even after completely removing the oxide, well-ordered hexagonal patterns, similar to the shape of graphene, remained on the surface of the aluminum plate. The borders of the hexagonal pattern protruded up to form sorts of nano-mountains at both the sides and apexes of the hexagon, with the apexes protruding even more significantly than the sides. The aluminum plate prepared by completely removing the oxide has been used in the preparation of SERS substrates by sputter-coating of gold or silver on it. Instead of sputter-coating, here we have electro-deposited silver on the aluminum plate. When silver was electro-deposited on the plate, silver nanoparticles were made along the hexagonal margins.

42 CFR 137.95 - May a Self-Governance Tribe purchase goods and services from the IHS on a reimbursable basis?

Science.gov (United States)

2010-10-01

... services from the IHS on a reimbursable basis? 137.95 Section 137.95 Public Health PUBLIC HEALTH SERVICE... Tribe purchase goods and services from the IHS on a reimbursable basis? Yes, a Self-Governance Tribe may...-Governance Tribe, on a reimbursable basis, including payment in advance with subsequent adjustment. Prompt...

Impact of ice particle shape on short-wave radiative forcing: A case study for an arctic ice cloud

International Nuclear Information System (INIS)

Kahnert, Michael; Sandvik, Anne Dagrun; Biryulina, Marina; Stamnes, Jakob J.; Stamnes, Knut

2008-01-01

We used four different non-spherical particle models to compute optical properties of an arctic ice cloud and to simulate corresponding cloud radiative forcings and fluxes. One important finding is that differences in cloud forcing, downward flux at the surface, and absorbed flux in the atmosphere resulting from the use of the four different ice cloud particle models are comparable to differences in these quantities resulting from changing the surface albedo from 0.4 to 0.8, or by varying the ice water content (IWC) by a factor of 2. These findings show that the use of a suitable non-spherical ice cloud particle model is very important for a realistic assessment of the radiative impact of arctic ice clouds. The differences in radiative broadband fluxes predicted by the four different particle models were found to be caused mainly by differences in the optical depth and the asymmetry parameter. These two parameters were found to have nearly the same impact on the predicted cloud forcing. Computations were performed first by assuming a given vertical profile of the particle number density, then by assuming a given profile of the IWC. In both cases, the differences between the cloud radiative forcings computed with the four different non-spherical particle models were found to be of comparable magnitude. This finding shows that precise knowledge of ice particle number density or particle mass is not sufficient for accurate prediction of ice cloud radiative forcing. It is equally important to employ a non-spherical shape model that accurately reproduces the ice particle's dimension-to-volume ratio and its asymmetry parameter. The hexagonal column/plate model with air-bubble inclusions seems to offer the highest degree of flexibility

Complete genome sequence of Pseudomonas rhizosphaerae IH5T (=DSM 16299T), a phosphate-solubilizing rhizobacterium for bacterial biofertilizer.

Science.gov (United States)

Kwak, Yunyoung; Jung, Byung Kwon; Shin, Jae-Ho

2015-01-10

Pseudomonas rhizosphaerae IH5(T) (=DSM 16299(T)), isolated from the rhizospheric soil of grass growing in Spain, has been reported as a novel species of the genus Pseudomonas harboring insoluble phosphorus solubilizing activity. To understanding the multifunctional biofertilizer better, we report the complete genome sequence of P. rhizosphaerae IH5(T). Copyright © 2014 Elsevier B.V. All rights reserved.

Identification and localization of gonadotropin-inhibitory hormone (GnIH) orthologs in the hypothalamus of the red-eared slider turtle, Trachemys scripta elegans.

Science.gov (United States)

Ukena, Kazuyoshi; Iwakoshi-Ukena, Eiko; Osugi, Tomohiro; Tsutsui, Kazuyoshi

2016-02-01

Gonadotropin-inhibitory hormone (GnIH) was discovered in 2000 as a novel hypothalamic neuropeptide that inhibited gonadotropin release in the Japanese quail. GnIH and its orthologs have a common C-terminal LPXRFamide (X=L or Q) motif, and have been identified in vertebrates from agnathans to humans, apart from reptiles. In the present study, we characterized a cDNA encoding GnIH orthologs in the brain of the red-eared slider turtle. The deduced precursor protein consisted of 205 amino-acid residues, encoding three putative peptide sequences that included the LPXRFamide motif at their C-termini. In addition, the precursor sequence was most similar to those of avian species. Immunoaffinity purification combined with mass spectrometry confirmed that three mature peptides were produced in the brain. In situ hybridization and immunohistochemistry showed that turtle GnIH-containing cells were restricted to the periventricular hypothalamic nucleus. Immunoreactive fibers were densely distributed in the median eminence. Thus, GnIH and related peptides may act on the pituitary to regulate pituitary hormone release in turtles as well as other vertebrates. Copyright © 2015 Elsevier Inc. All rights reserved.

Crystallization of -type hexagonal ferrites from mechanically

Indian Academy of Sciences (India)

Crystallization of -type hexagonal ferrites from mechanically activated mixtures of barium carbonate and goethite ... Abstract. -type hexagonal ferrite precursor was prepared by a soft mechanochemical ... Bulletin of Materials Science | News.

Essay of accelerator R and D in a small laboratory of an university. Head ion IH linac for fusion material. 1983-1985

International Nuclear Information System (INIS)

Hattori, Toshiyuki

2005-01-01

The linear accelerator of Inter-Digital H type (IH linac) is known to have a high shunt impedance. Research Laboratory for Nuclear Reactors of Tokyo Institute of Technology introduced an IH linac for fusion materials irradiation test in 1983. The beam injector was a tandem electrostatic accelerator. The IH linac was designed and fabricated based on the developmental work at Institute for Nuclear Study of University of Tokyo. The processes of component alignment, cold test and start-up operation are described. Educational aspect of the project is also reviewed. (K.Y.)

Theoretical x-ray absorption investigation of high pressure ice and compressed graphite

International Nuclear Information System (INIS)

Shaw, Dawn M; Tse, John S

2007-01-01

The x-ray absorption spectra (XAS) of high pressure ices II, VIII, and IX have been computed with the Car-Parrinello plane wave pseudopotential method. XAS for the intermediate structures obtained from uniaxial compression of hexagonal graphite along the c-axis are also studied. Whenever possible, comparisons to available experimental results are made. The reliability of the computational methods for the XAS for these structures is discussed

EBSD in Antarctic and Greenland Ice

Science.gov (United States)

Weikusat, Ilka; Kuiper, Ernst-Jan; Pennock, Gill; Sepp, Kipfstuhl; Drury, Martyn

2017-04-01

Ice, particularly the extensive amounts found in the polar ice sheets, impacts directly on the global climate by changing the albedo and indirectly by supplying an enormous water reservoir that affects sea level change. The discharge of material into the oceans is partly controlled by the melt excess over snow accumulation, partly by the dynamic flow of ice. In addition to sliding over bedrock, an ice body deforms gravitationally under its own weight. In order to improve our description of this flow, ice microstructure studies are needed that elucidate the dominant deformation and recrystallization mechanisms involved. Deformation of hexagonal ice is highly anisotropic: ice is easily sheared in the basal plane and is about two orders of magnitude harder parallel to the c-axis. As dislocation creep is the dominant deformation mechanism in polar ice this strong anisotropy needs to be understood in terms of dislocation activity. The high anisotropy of the ice crystal is usually ascribed to a particular behaviour of dislocations in ice, namely the extension of dislocations into partials on the basal plane. Analysis of EBSD data can help our understanding of dislocation activity by characterizing subgrain boundary types thus providing a tool for comprehensive dislocation characterization in polar ice. Cryo-EBSD microstructure in combination with light microscopy measurements from ice core material from Antarctica (EPICA-DML deep ice core) and Greenland (NEEM deep ice core) are presented and interpreted regarding substructure identification and characterization. We examined one depth for each ice core (EDML: 656 m, NEEM: 719 m) to obtain the first comparison of slip system activity from the two ice sheets. The subgrain boundary to grain boundary threshold misorientation was taken to be 3-5° (Weikusat et al. 2011). EBSD analyses suggest that a large portion of edge dislocations with slip systems basal gliding on the basal plane were indeed involved in forming subgrain

Revealing topographic lineaments through IHS enhancement of DEM data. [Digital Elevation Model

Science.gov (United States)

Murdock, Gary

1990-01-01

Intensity-hue-saturation (IHS) processing of slope (dip), aspect (dip direction), and elevation to reveal subtle topographic lineaments which may not be obvious in the unprocessed data are used to enhance digital elevation model (DEM) data from northwestern Nevada. This IHS method of lineament identification was applied to a mosiac of 12 square degrees using a Cray Y-MP8/864. Square arrays from 3 x 3 to 31 x 31 points were tested as well as several different slope enhancements. When relatively few points are used to fit the plane, lineaments of various lengths are observed and a mechanism for lineament classification is described. An area encompassing the gold deposits of the Carlin trend and including the Rain in the southeast to Midas in the northwest is investigated in greater detail. The orientation and density of lineaments may be determined on the gently sloping pediment surface as well as in the more steeply sloping ranges.

Hydrothermal synthesis of hexagonal magnesium hydroxide nanoflakes

International Nuclear Information System (INIS)

Wang, Qiang; Li, Chunhong; Guo, Ming; Sun, Lingna; Hu, Changwen

2014-01-01

Graphical abstract: Hexagonal Mg(OH) 2 nanoflakes were synthesized via hydrothermal method in the presence of PEG-20,000. Results show that PEG-20,000 plays an important role in the formation of this kind of nanostructure. The SAED patterns taken from the different positions on a single hexagonal Mg(OH) 2 nanoflake yielded different crystalline structures. The structure of the nanoflakes are polycrystalline and the probable formation mechanism of Mg(OH) 2 nanoflakes is discussed. - Highlights: • Hexagonal Mg(OH) 2 nanoflakes were synthesized via hydrothermal method. • PEG-20,000 plays an important role in the formation of hexagonal nanostructure. • Mg(OH) 2 nanoflakes show different crystalline structures at different positions. • The probable formation mechanism of hexagonal Mg(OH) 2 nanoflakes was reported. - Abstract: Hexagonal magnesium hydroxide (Mg(OH) 2 ) nanoflakes were successfully synthesized via hydrothermal method in the presence of the surfactant polyethylene glycol 20,000 (PEG-20,000). Results show that PEG-20,000 plays an important role in the formation of this kind of nanostructure. The composition, morphologies and structure of the Mg(OH) 2 nanoflakes were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). The SAED patterns taken from the different positions on a single hexagonal Mg(OH) 2 nanoflake show different crystalline structures. The structure of the nanoflakes are polycrystalline and the probable formation mechanism of Mg(OH) 2 nanoflakes is discussed. Brunauer–Emmett–Teller (BET) analysis were performed to investigate the porous structure and surface area of the as-obtained nanoflakes

Explicit simulation of ice particle habits in a Numerical Weather Prediction Model

Science.gov (United States)

Hashino, Tempei

2007-05-01

This study developed a scheme for explicit simulation of ice particle habits in Numerical Weather Prediction (NWP) Models. The scheme is called Spectral Ice Habit Prediction System (SHIPS), and the goal is to retain growth history of ice particles in the Eulerian dynamics framework. It diagnoses characteristics of ice particles based on a series of particle property variables (PPVs) that reflect history of microphysieal processes and the transport between mass bins and air parcels in space. Therefore, categorization of ice particles typically used in bulk microphysical parameterization and traditional bin models is not necessary, so that errors that stem from the categorization can be avoided. SHIPS predicts polycrystals as well as hexagonal monocrystals based on empirically derived habit frequency and growth rate, and simulates the habit-dependent aggregation and riming processes by use of the stochastic collection equation with predicted PPVs. Idealized two dimensional simulations were performed with SHIPS in a NWP model. The predicted spatial distribution of ice particle habits and types, and evolution of particle size distributions showed good quantitative agreement with observation This comprehensive model of ice particle properties, distributions, and evolution in clouds can be used to better understand problems facing wide range of research disciplines, including microphysics processes, radiative transfer in a cloudy atmosphere, data assimilation, and weather modification.

Četrta konferenca o izobraževanju in učenju starejših

Directory of Open Access Journals (Sweden)

Dušana Findeisen

1998-12-01

Full Text Available Pravijo, da je Univerza v Ulmu "najvišja nemška univerza". Najvišja zato, ker stoji zunaj mesta na vzpetini. Res je, da slovi po svojih tehniških fakultetah, pa vendar v Ulmu niso pozabili na družbene vede. Znanja iz teh ved si je na Univerzi v Ulmu moč pridobiti pri ZAWIW, Univerzitetnem centru za splošno nadaljevalno izobraževanje. Pri tem centru pa je leta 1994 nastal tudi sedež Evropske zveze "Učenje v poznejših letih". Tako je v njenem okviru lani potekala v Ulmu že četrta konferenca, posvečena izobraževanju in učenju starejših odraslih.

Influence of crystal shapes on radiative fluxes in visible wavelength: ice crystals randomly oriented in space

Directory of Open Access Journals (Sweden)

P. Chervet

1996-08-01

Full Text Available Radiative properties of cirrus clouds are one of the major unsolved problems in climate studies and global radiation budget. These clouds are generally composed of various ice-crystal shapes, so we tried to evaluate effects of the ice-crystal shape on radiative fluxes. We calculated radiative fluxes of cirrus clouds with a constant geometrical depth, composed of ice crystals with different shapes (hexagonal columns, bullets, bullet-rosettes, sizes and various concentrations. We considered ice particles randomly oriented in space (3D case and their scattering phase functions were calculated by a ray-tracing method. We calculated radiative fluxes for cirrus layers for different microphysical characteristics by using a discrete-ordinate radiative code. Results showed that the foremost effect of the ice-crystal shape on radiative properties of cirrus clouds was that on the optical thickness, while the variation of the scattering phase function with the ice shape remained less than 3% for our computations. The ice-water content may be a better choice to parameterize the optical properties of cirrus, but the shape effect must be included.

Scattering and absorption of light by ice particles: Solution by a new physical-geometric optics hybrid method

International Nuclear Information System (INIS)

Bi Lei; Yang Ping; Kattawar, George W.; Hu Yongxiang; Baum, Bryan A.

2011-01-01

A new physical-geometric optics hybrid (PGOH) method is developed to compute the scattering and absorption properties of ice particles. This method is suitable for studying the optical properties of ice particles with arbitrary orientations, complex refractive indices (i.e., particles with significant absorption), and size parameters (proportional to the ratio of particle size to incident wavelength) larger than ∼20, and includes consideration of the edge effects necessary for accurate determination of the extinction and absorption efficiencies. Light beams with polygon-shaped cross sections propagate within a particle and are traced by using a beam-splitting technique. The electric field associated with a beam is calculated using a beam-tracing process in which the amplitude and phase variations over the wavefront of the localized wave associated with the beam are considered analytically. The geometric-optics near field for each ray is obtained, and the single-scattering properties of particles are calculated from electromagnetic integral equations. The present method does not assume additional physical simplifications and approximations, except for geometric optics principles, and may be regarded as a 'benchmark' within the framework of the geometric optics approach. The computational time is on the order of seconds for a single-orientation simulation and is essentially independent of the size parameter. The single-scattering properties of oriented hexagonal ice particles (ice plates and hexagons) are presented. The numerical results are compared with those computed from the discrete-dipole-approximation (DDA) method.

Hexagonalization of correlation functions

Energy Technology Data Exchange (ETDEWEB)

Fleury, Thiago [Instituto de Física Teórica, UNESP - University Estadual Paulista,ICTP South American Institute for Fundamental Research,Rua Dr. Bento Teobaldo Ferraz 271, 01140-070, São Paulo, SP (Brazil); Komatsu, Shota [Perimeter Institute for Theoretical Physics,31 Caroline St N Waterloo, Ontario N2L 2Y5 (Canada)

2017-01-30

We propose a nonperturbative framework to study general correlation functions of single-trace operators in N=4 supersymmetric Yang-Mills theory at large N. The basic strategy is to decompose them into fundamental building blocks called the hexagon form factors, which were introduced earlier to study structure constants using integrability. The decomposition is akin to a triangulation of a Riemann surface, and we thus call it hexagonalization. We propose a set of rules to glue the hexagons together based on symmetry, which naturally incorporate the dependence on the conformal and the R-symmetry cross ratios. Our method is conceptually different from the conventional operator product expansion and automatically takes into account multi-trace operators exchanged in OPE channels. To illustrate the idea in simple set-ups, we compute four-point functions of BPS operators of arbitrary lengths and correlation functions of one Konishi operator and three short BPS operators, all at one loop. In all cases, the results are in perfect agreement with the perturbative data. We also suggest that our method can be a useful tool to study conformal integrals, and show it explicitly for the case of ladder integrals.

Hexagonal response matrix using symmetries

International Nuclear Information System (INIS)

Gotoh, Y.

1991-01-01

A response matrix for use in core calculations for nuclear reactors with hexagonal fuel assemblies is presented. It is based on the incoming currents averaged over the half-surface of a hexagonal node by applying symmetry theory. The boundary conditions of the incoming currents on the half-surface of the node are expressed by a complete set of orthogonal vectors which are constructed from symmetrized functions. The expansion coefficients of the functions are determined by the boundary conditions of incoming currents. (author)

Structural Characterization of Hexagonal Braiding Architecture Aided by 3D Printing

Directory of Open Access Journals (Sweden)

Li Zhengning

2018-01-01

Full Text Available Hexagonal braiding method has the advantages of high shape compatibility, interlacing density and high volume fraction. Based on hexagonal braiding method, a hexagonal preform was braided. Then, by following the characteristics of repeatability and concentricity of hexagonal braided preform, the printed geometry structure was got in order to understand and optimize geometric structure to make it more compact like the braided geometric structure. Finally, the unit cells were defined with hexagonal prism to analyze the micro-geometric structure of hexagonal braided preform.

Inhibition of Ice Growth and Recrystallization by Zirconium Acetate and Zirconium Acetate Hydroxide

Science.gov (United States)

Mizrahy, Ortal; Bar-Dolev, Maya; Guy, Shlomit; Braslavsky, Ido

2013-01-01

The control over ice crystal growth, melting, and shaping is important in a variety of fields, including cell and food preservation and ice templating for the production of composite materials. Control over ice growth remains a challenge in industry, and the demand for new cryoprotectants is high. Naturally occurring cryoprotectants, such as antifreeze proteins (AFPs), present one solution for modulating ice crystal growth; however, the production of AFPs is expensive and inefficient. These obstacles can be overcome by identifying synthetic substitutes with similar AFP properties. Zirconium acetate (ZRA) was recently found to induce the formation of hexagonal cavities in materials prepared by ice templating. Here, we continue this line of study and examine the effects of ZRA and a related compound, zirconium acetate hydroxide (ZRAH), on ice growth, shaping, and recrystallization. We found that the growth rate of ice crystals was significantly reduced in the presence of ZRA and ZRAH, and that solutions containing these compounds display a small degree of thermal hysteresis, depending on the solution pH. The compounds were found to inhibit recrystallization in a manner similar to that observed in the presence of AFPs. The favorable properties of ZRA and ZRAH suggest tremendous potential utility in industrial applications. PMID:23555701

Novel high pressure hexagonal OsB2 by mechanochemistry

International Nuclear Information System (INIS)

Xie, Zhilin; Graule, Moritz; Orlovskaya, Nina; Andrew Payzant, E.; Cullen, David A.; Blair, Richard G.

2014-01-01

Hexagonal OsB 2 , a theoretically predicted high-pressure phase, has been synthesized for the first time by a mechanochemical method, i.e., high energy ball milling. X-ray diffraction indicated that formation of hexagonal OsB 2 begins after 2.5 h of milling, and the reaction reaches equilibrium after 18 h of milling. Rietveld refinement of the powder data indicated that hexagonal OsB 2 crystallizes in the P63/mmc space group (No. 194) with lattice parameters of a=2.916 Å and c=7.376 Å. Transmission electron microscopy confirmed the appearance of the hexagonal OsB 2 phase after high energy ball milling. in situ X-ray diffraction experiments showed that the phase is stable from −225 °C to 1050 °C. The hexagonal OsB 2 powder was annealed at 1050 °C for 6 days in vacuo to improve crystallinity and remove strain induced during the mechanochemical synthesis. The structure partially converted to the orthorhombic phase (20 wt%) after fast current assisted sintering of hexagonal OsB 2 at 1500 °C for 5 min. Mechanochemical approaches to the synthesis of hard boride materials allow new phases to be produced that cannot be prepared using conventional methods. - Graphical abstract: High resolution transmission electron micrograph of hexagonal OsB 2 nanocrystallite with corresponding fast Fourier transform and simulated diffraction pattern. - Highlights: • Hexagonal OsB 2 has been synthesized for the first time by mechanochemical method. • Hexagonal OsB 2 crystallizes in P63/mmc space group (No. 194), a=2.916 Å and c=7.376 Å. • The hexagonal structure was confirmed by a transmission electron microscope. • No phase transformation was observed after being annealed at 1050 °C for 6 days. • 20 wt% of h-OsB 2 was transformed to o-OsB 2 after being sintered at 1500 °C for 5 min

Bioinspired Materials for Controlling Ice Nucleation, Growth, and Recrystallization.

Science.gov (United States)

He, Zhiyuan; Liu, Kai; Wang, Jianjun

2018-05-15

Ice formation, mainly consisting of ice nucleation, ice growth, and ice recrystallization, is ubiquitous and crucial in wide-ranging fields from cryobiology to atmospheric physics. Despite active research for more than a century, the mechanism of ice formation is still far from satisfactory. Meanwhile, nature has unique ways of controlling ice formation and can provide resourceful avenues to unravel the mechanism of ice formation. For instance, antifreeze proteins (AFPs) protect living organisms from freezing damage via controlling ice formation, for example, tuning ice nucleation, shaping ice crystals, and inhibiting ice growth and recrystallization. In addition, AFP mimics can have applications in cryopreservation of cells, tissues, and organs, food storage, and anti-icing materials. Therefore, continuous efforts have been made to understand the mechanism of AFPs and design AFP inspired materials. In this Account, we first review our recent research progress in understanding the mechanism of AFPs in controlling ice formation. A Janus effect of AFPs on ice nucleation was discovered, which was achieved via selectively tethering the ice-binding face (IBF) or the non-ice-binding face (NIBF) of AFPs to solid surfaces and investigating specifically the effect of the other face on ice nucleation. Through molecular dynamics (MD) simulation analysis, we observed ordered hexagonal ice-like water structure atop the IBF and disordered water structure atop the NIBF. Therefore, we conclude that the interfacial water plays a critical role in controlling ice formation. Next, we discuss the design and fabrication of AFP mimics with capabilities in tuning ice nucleation and controlling ice shape and growth, as well as inhibiting ice recrystallization. For example, we tuned ice nucleation via modifying solid surfaces with supercharged unfolded polypeptides (SUPs) and polyelectrolyte brushes (PBs) with different counterions. We found graphene oxide (GO) and oxidized quasi

Intrinsic ferromagnetism in hexagonal boron nitride nanosheets

Energy Technology Data Exchange (ETDEWEB)

Si, M. S.; Gao, Daqiang, E-mail: gaodq@lzu.edu.cn, E-mail: xueds@lzu.edu.cn; Yang, Dezheng; Peng, Yong; Zhang, Z. Y.; Xue, Desheng, E-mail: gaodq@lzu.edu.cn, E-mail: xueds@lzu.edu.cn [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Liu, Yushen [Jiangsu Laboratory of Advanced Functional Materials and College of Physics and Engineering, Changshu Institute of Technology, Changshu 215500 (China); Deng, Xiaohui [Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang 421008 (China); Zhang, G. P. [Department of Physics, Indiana State University, Terre Haute, Indiana 47809 (United States)

2014-05-28

Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

Evolution of Planetary Ice-Ocean Systems: Effects of Salinity

Science.gov (United States)

Allu Peddinti, D.; McNamara, A. K.

2015-12-01

Planetary oceanography is enjoying renewed attention thanks to not only the detection of several exoplanetary ocean worlds but also due to the expanding family of ocean worlds within our own star system. Our solar system is now believed to host about nine ocean worlds including Earth, some dwarf planets and few moons of Jupiter and Saturn. Amongst them, Europa, like Earth is thought to have an ice Ih-liquid water system. However, the thickness of the Europan ice-ocean system is much larger than that of the Earth. The evolution of this system would determine the individual thicknesses of the ice shell and the ocean. In turn, these thicknesses can alter the course of evolution of the system. In a pure H2O system, the thickness of the ice shell would govern if heat loss occurs entirely by conduction or if the shell begins to convect as it attains a threshold thickness. This switch between conduction-convection regimes could determine the longevity of the subsurface ocean and hence define the astrobiological potential of the planetary body at any given time. In reality, however, the system is not pure water ice. The detected induced magnetic field infers a saline ocean layer. Salts are expected to act as an anti-freeze allowing a subsurface ocean to persist over long periods but the amount of salts would determine the extent of that effect. In our current study, we use geodynamic models to examine the effect of salinity on the evolution of ice-ocean system. An initial ocean with different salinities is allowed to evolve. The effect of salinity on thickness of the two layers at any time is examined. We also track how salinity controls the switch between conductive-convective modes. The study shows that for a given time period, larger salinities can maintain a thick vigorously convecting ocean while the smaller salinities behave similar to a pure H2O system leading to a thick convecting ice-shell. A range of salinities identified can potentially predict the current state

Bandgap engineered graphene and hexagonal boron nitride

Indian Academy of Sciences (India)

In this article a double-barrier resonant tunnelling diode (DBRTD) has been modelled by taking advantage of single-layer hexagonal lattice of graphene and hexagonal boron nitride (h-BN). The DBRTD performance and operation are explored by means of a self-consistent solution inside the non-equilibrium Green's ...

Chain hexagonal cacti with the extremal eccentric distance sum.

Science.gov (United States)

Qu, Hui; Yu, Guihai

2014-01-01

Eccentric distance sum (EDS), which can predict biological and physical properties, is a topological index based on the eccentricity of a graph. In this paper we characterize the chain hexagonal cactus with the minimal and the maximal eccentric distance sum among all chain hexagonal cacti of length n, respectively. Moreover, we present exact formulas for EDS of two types of hexagonal cacti.

Popular heavy particle beam cancer therapeutic system (3). Development of high efficiency compact incident system-2. Great success of beam test of new APF-IH type DTL

International Nuclear Information System (INIS)

Yamamoto, Kazuo; Iwata, Yoshiyuki

2006-01-01

High efficiency compact incident system consists of an electron cyclotron resonance (ECR) ion source, a radio frequency quadrupole (RFQ) linear accelerator and an interdigital H-mode (IH) drift tube linear accelerator (DTL). IH type DTL and alternating phase focusing (APF) method is explained. Its special features, production, and beam test are reported. The electric field generation method, outline of the APF method, drift tube, IH type DTL, distribution of electric field and voltage, set up of beam test, ECR ion source and incident line, the inside structure of the RFQ type linear accelerator and the APF-IH type DTL, matching Q lens section, beam, emittance, measurement results of momentum dispersion are illustrated. (S.Y.)

Coincidence orientations of grains in hexagonal materials

International Nuclear Information System (INIS)

Grimmer, H.; Warrington, D.H.

1986-06-01

The connection between the rotation matrix in hexagonal lattice coordinates and an angle-axis quadruple is given. The multiplication law of quadruples is derived. It corresponds to multiplying two matrices and gives the effect of two successive rotations. The relation is given between two quadruples that describe the same relative orientation of two lattices due to their hexagonal symmetry; a unique standard description of the relative orientation is proposed. The restrictions satisfied by rotations generating coincidence site lattices (CSLs) are derived for any value of the axial ratio rho = c/a. It is shown that the law for cubic lattices, where the multiplicity SIGMA of the CSL was equal to the least common denominator of the elements of the rotation matrix, does not always hold for hexagonal lattices. A generalisation of this law to lattices of arbitrary symmetry is given and another, quicker method to determine SIGMA for hexagonal lattices is derived. Finally, convenient algorithms are described for determining bases of the CSL and the DSC lattice. (author)

Epitaxial hexagonal materials on IBAD-textured substrates

Science.gov (United States)

Matias, Vladimir; Yung, Christopher

2017-08-15

A multilayer structure including a hexagonal epitaxial layer, such as GaN or other group III-nitride (III-N) semiconductors, a oriented textured layer, and a non-single crystal substrate, and methods for making the same. The textured layer has a crystalline alignment preferably formed by the ion-beam assisted deposition (IBAD) texturing process and can be biaxially aligned. The in-plane crystalline texture of the textured layer is sufficiently low to allow growth of high quality hexagonal material, but can still be significantly greater than the required in-plane crystalline texture of the hexagonal material. The IBAD process enables low-cost, large-area, flexible metal foil substrates to be used as potential alternatives to single-crystal sapphire and silicon for manufacture of electronic devices, enabling scaled-up roll-to-roll, sheet-to-sheet, or similar fabrication processes to be used. The user is able to choose a substrate for its mechanical and thermal properties, such as how well its coefficient of thermal expansion matches that of the hexagonal epitaxial layer, while choosing a textured layer that more closely lattice matches that layer.

Novel high pressure hexagonal OsB2 by mechanochemistry

Science.gov (United States)

Xie, Zhilin; Graule, Moritz; Orlovskaya, Nina; Andrew Payzant, E.; Cullen, David A.; Blair, Richard G.

2014-07-01

Hexagonal OsB2, a theoretically predicted high-pressure phase, has been synthesized for the first time by a mechanochemical method, i.e., high energy ball milling. X-ray diffraction indicated that formation of hexagonal OsB2 begins after 2.5 h of milling, and the reaction reaches equilibrium after 18 h of milling. Rietveld refinement of the powder data indicated that hexagonal OsB2 crystallizes in the P63/mmc space group (No. 194) with lattice parameters of a=2.916 Å and c=7.376 Å. Transmission electron microscopy confirmed the appearance of the hexagonal OsB2 phase after high energy ball milling. in situ X-ray diffraction experiments showed that the phase is stable from -225 °C to 1050 °C. The hexagonal OsB2 powder was annealed at 1050 °C for 6 days in vacuo to improve crystallinity and remove strain induced during the mechanochemical synthesis. The structure partially converted to the orthorhombic phase (20 wt%) after fast current assisted sintering of hexagonal OsB2 at 1500 °C for 5 min. Mechanochemical approaches to the synthesis of hard boride materials allow new phases to be produced that cannot be prepared using conventional methods.

Bifurcation theory for hexagonal agglomeration in economic geography

CERN Document Server

Ikeda, Kiyohiro

2014-01-01

This book contributes to an understanding of how bifurcation theory adapts to the analysis of economic geography. It is easily accessible not only to mathematicians and economists, but also to upper-level undergraduate and graduate students who are interested in nonlinear mathematics. The self-organization of hexagonal agglomeration patterns of industrial regions was first predicted by the central place theory in economic geography based on investigations of southern Germany. The emergence of hexagonal agglomeration in economic geography models was envisaged by Krugman. In this book, after a brief introduction of central place theory and new economic geography, the missing link between them is discovered by elucidating the mechanism of the evolution of bifurcating hexagonal patterns. Pattern formation by such bifurcation is a well-studied topic in nonlinear mathematics, and group-theoretic bifurcation analysis is a well-developed theoretical tool. A finite hexagonal lattice is used to express uniformly distri...

Novel high pressure hexagonal OsB{sub 2} by mechanochemistry

Energy Technology Data Exchange (ETDEWEB)

Xie, Zhilin; Graule, Moritz [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Orlovskaya, Nina, E-mail: Nina.Orlovskaya@ucf.edu [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Andrew Payzant, E. [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Cullen, David A. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Blair, Richard G. [Department of Chemistry, University of Central Florida, Orlando, FL 32816 (United States)

2014-07-01

Hexagonal OsB{sub 2}, a theoretically predicted high-pressure phase, has been synthesized for the first time by a mechanochemical method, i.e., high energy ball milling. X-ray diffraction indicated that formation of hexagonal OsB{sub 2} begins after 2.5 h of milling, and the reaction reaches equilibrium after 18 h of milling. Rietveld refinement of the powder data indicated that hexagonal OsB{sub 2} crystallizes in the P63/mmc space group (No. 194) with lattice parameters of a=2.916 Å and c=7.376 Å. Transmission electron microscopy confirmed the appearance of the hexagonal OsB{sub 2} phase after high energy ball milling. in situ X-ray diffraction experiments showed that the phase is stable from −225 °C to 1050 °C. The hexagonal OsB{sub 2} powder was annealed at 1050 °C for 6 days in vacuo to improve crystallinity and remove strain induced during the mechanochemical synthesis. The structure partially converted to the orthorhombic phase (20 wt%) after fast current assisted sintering of hexagonal OsB{sub 2} at 1500 °C for 5 min. Mechanochemical approaches to the synthesis of hard boride materials allow new phases to be produced that cannot be prepared using conventional methods. - Graphical abstract: High resolution transmission electron micrograph of hexagonal OsB{sub 2} nanocrystallite with corresponding fast Fourier transform and simulated diffraction pattern. - Highlights: • Hexagonal OsB{sub 2} has been synthesized for the first time by mechanochemical method. • Hexagonal OsB{sub 2} crystallizes in P63/mmc space group (No. 194), a=2.916 Å and c=7.376 Å. • The hexagonal structure was confirmed by a transmission electron microscope. • No phase transformation was observed after being annealed at 1050 °C for 6 days. • 20 wt% of h-OsB{sub 2} was transformed to o-OsB{sub 2} after being sintered at 1500 °C for 5 min.

Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe.

Science.gov (United States)

Parker, David S

2017-06-13

We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large T c value is unlikely.

Inserting Stress Analysis of Combined Hexagonal Aluminum Honeycombs

Directory of Open Access Journals (Sweden)

Xiangcheng Li

2016-01-01

Full Text Available Two kinds of hexagonal aluminum honeycombs are tested to study their out-of-plane crushing behavior. In the tests, honeycomb samples, including single hexagonal aluminum honeycomb (SHAH samples and two stack-up combined hexagonal aluminum honeycombs (CHAH samples, are compressed at a fixed quasistatic loading rate. The results show that the inserting process of CHAH can erase the initial peak stress that occurred in SHAH. Meanwhile, energy-absorbing property of combined honeycomb samples is more beneficial than the one of single honeycomb sample with the same thickness if the two types of honeycomb samples are completely crushed. Then, the applicability of the existing theoretical model for single hexagonal honeycomb is discussed, and an area equivalent method is proposed to calculate the crushing stress for nearly regular hexagonal honeycombs. Furthermore, a semiempirical formula is proposed to calculate the inserting plateau stress of two stack-up CHAH, in which structural parameters and mechanics properties of base material are concerned. The results show that the predicted stresses of three kinds of two stack-up combined honeycombs are in good agreement with the experimental data. Based on this study, stress-displacement curve of aluminum honeycombs can be designed in detail, which is very beneficial to optimize the energy-absorbing structures in engineering fields.

Epitaxial hexagonal materials on IBAD-textured substrates

Energy Technology Data Exchange (ETDEWEB)

Matias, Vladimir; Yung, Christopher

2017-08-15

A multilayer structure including a hexagonal epitaxial layer, such as GaN or other group III-nitride (III-N) semiconductors, a <111> oriented textured layer, and a non-single crystal substrate, and methods for making the same. The textured layer has a crystalline alignment preferably formed by the ion-beam assisted deposition (IBAD) texturing process and can be biaxially aligned. The in-plane crystalline texture of the textured layer is sufficiently low to allow growth of high quality hexagonal material, but can still be significantly greater than the required in-plane crystalline texture of the hexagonal material. The IBAD process enables low-cost, large-area, flexible metal foil substrates to be used as potential alternatives to single-crystal sapphire and silicon for manufacture of electronic devices, enabling scaled-up roll-to-roll, sheet-to-sheet, or similar fabrication processes to be used. The user is able to choose a substrate for its mechanical and thermal properties, such as how well its coefficient of thermal expansion matches that of the hexagonal epitaxial layer, while choosing a textured layer that more closely lattice matches that layer.

Controllable synthesis of hexagonal ZnO–carbon core–shell microrods and the removal of ZnO to form hexagonal carbon microtubes

Energy Technology Data Exchange (ETDEWEB)

Xiao, Yong, E-mail: xy91007@163.com [Department of Applied Chemistry, South China Agricultural University, Guangzhou 510642 (China); He, Wenqi; Gao, Chuang [Department of Chemistry and Institute of Nanochemistry, Jinan University, Guangzhou 510632 (China); Zheng, Mingtao; Lie, Bingfu; Liu, Xiaotang [Department of Applied Chemistry, South China Agricultural University, Guangzhou 510642 (China); Liu, Yingliang, E-mail: tliuyl@163.com [Department of Applied Chemistry, South China Agricultural University, Guangzhou 510642 (China)

2013-06-15

A simple and efficient approach was developed to produce regular and uniform shaped hexagonal ZnO–C core–shell micro-rods and carbon micro-tubes. A single-source raw material, zinc acetate dihydrate, has been used for the in situ generation of the hexagonal ZnO–C micro-rods in a sealed autoclave system at 500 °C for 12 h without a catalyst. The resulting products were characterized by X-ray powder diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray analysis and room-temperature photoluminescence spectroscopy (PL). The partial or complete carbon coating on the ZnO surfaces plays an important role in modifying the PL properties. Impacting factors including thermolysis temperature, time and dose of the reactant on the evolution of the hexagonal shape were investigated. A possible formation diagram for the materials has been proposed and discussed based on the features of the reaction system. - Highlights: • Hexagonal ZnO–C core–shell microrods were synthesized by the lower temperature decomposition of zinc acetate. • The novel hexagonal carbon microtubes can gain by simply handling with dilute acid. • The partial or complete carbon coating on the ZnO surfaces plays an important role in modifying the PL properties. • A possible formation diagram for the materials has been proposed.

Characterization of the secondary flow in hexagonal ducts

Science.gov (United States)

Marin, O.; Vinuesa, R.; Obabko, A. V.; Schlatter, P.

2016-12-01

In this work we report the results of DNSs and LESs of the turbulent flow through hexagonal ducts at friction Reynolds numbers based on centerplane wall shear and duct half-height Reτ,c ≃ 180, 360, and 550. The evolution of the Fanning friction factor f with Re is in very good agreement with experimental measurements. A significant disagreement between the DNS and previous RANS simulations was found in the prediction of the in-plane velocity, and is explained through the inability of the RANS model to properly reproduce the secondary flow present in the hexagon. The kinetic energy of the secondary flow integrated over the cross-sectional area yz decreases with Re in the hexagon, whereas it remains constant with Re in square ducts at comparable Reynolds numbers. Close connection between the values of Reynolds stress u w ¯ on the horizontal wall close to the corner and the interaction of bursting events between the horizontal and inclined walls is found. This interaction leads to the formation of the secondary flow, and is less frequent in the hexagon as Re increases due to the 120∘ aperture of its vertex, whereas in the square duct the 90∘ corner leads to the same level of interaction with increasing Re. Analysis of turbulence statistics at the centerplane and the azimuthal variance of the mean flow and the fluctuations shows a close connection between hexagonal ducts and pipe flows, since the hexagon exhibits near-axisymmetric conditions up to a distance of around 0.15DH measured from its center. Spanwise distributions of wall-shear stress show that in square ducts the 90∘ corner sets the location of a high-speed streak at a distance zv+≃50 from it, whereas in hexagons the 120∘ aperture leads to a shorter distance of zv+≃38 . At these locations the root mean square of the wall-shear stresses exhibits an inflection point, which further shows the connections between the near-wall structures and the large-scale motions in the outer flow.

Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe

Energy Technology Data Exchange (ETDEWEB)

Parker, David S. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-06-13

We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large T_c value is unlikely.

Glider-based computing in reaction-diffusion hexagonal cellular automata

International Nuclear Information System (INIS)

Adamatzky, Andrew; Wuensche, Andrew; De Lacy Costello, Benjamin

2006-01-01

A three-state hexagonal cellular automaton, discovered in [Wuensche A. Glider dynamics in 3-value hexagonal cellular automata: the beehive rule. Int J Unconvention Comput, in press], presents a conceptual discrete model of a reaction-diffusion system with inhibitor and activator reagents. The automaton model of reaction-diffusion exhibits mobile localized patterns (gliders) in its space-time dynamics. We show how to implement the basic computational operations with these mobile localizations, and thus demonstrate collision-based logical universality of the hexagonal reaction-diffusion cellular automaton

Remote Sensing of Crystal Shapes in Ice Clouds

Science.gov (United States)

van Diedenhoven, Bastiaan

2017-01-01

Ice crystals in clouds exist in a virtually limitless variation of geometries. The most basic shapes of ice crystals are columnar or plate-like hexagonal prisms with aspect ratios determined by relative humidity and temperature. However, crystals in ice clouds generally display more complex structures owing to aggregation, riming and growth histories through varying temperature and humidity regimes. Crystal shape is relevant for cloud evolution as it affects microphysical properties such as fall speeds and aggregation efficiency. Furthermore, the scattering properties of ice crystals are affected by their general shape, as well as by microscopic features such as surface roughness, impurities and internal structure. To improve the representation of ice clouds in climate models, increased understanding of the global variation of crystal shape and how it relates to, e.g., location, cloud temperature and atmospheric state is crucial. Here, the remote sensing of ice crystal macroscale and microscale structure from airborne and space-based lidar depolarization observations and multi-directional measurements of total and polarized reflectances is reviewed. In addition, a brief overview is given of in situ and laboratory observations of ice crystal shape as well as the optical properties of ice crystals that serve as foundations for the remote sensing approaches. Lidar depolarization is generally found to increase with increasing cloud height and to vary with latitude. Although this variation is generally linked to the variation of ice crystal shape, the interpretation of the depolarization remains largely qualitative and more research is needed before quantitative conclusions about ice shape can be deduced. The angular variation of total and polarized reflectances of ice clouds has been analyzed by numerous studies in order to infer information about ice crystal shapes from them. From these studies it is apparent that pristine crystals with smooth surfaces are generally

Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires

KAUST Repository

Wang, Ping

2015-12-22

Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires (NWs) is demonstrated on InN NWs. In-polarity InN NWs form typical hexagonal structure with pyramidal growth front, whereas N-polarity InN NWs slowly turn to the shape of hexagonal pyramid and then convert to an inverted pyramid growth, forming diagonal pyramids with flat surfaces and finally coalescence with each other. This contrary growth behavior driven by lattice-polarity is most likely due to the relatively lower growth rate of the (0001 ̅) plane, which results from the fact that the diffusion barriers of In and N adatoms on the (0001) plane (0.18 and 1.0 eV, respectively) are about two-fold larger in magnitude than those on the (0001 ̅) plane (0.07 and 0.52 eV), as calculated by first-principles density functional theory (DFT). The formation of diagonal pyramids for the N-polarity hexagonal NWs affords a novel way to locate quantum dot in the kink position, suggesting a new recipe for the fabrication of dot-based devices.

Delicious Low GL space foods by using Low GI materials -IH and Vacuum cooking -

Science.gov (United States)

Katayama, Naomi; Nagasaka, Sanako; Murasaki, Masahiro; Space Agriculture Task Force, J.

Enough life-support systems are necessary to stay in space for a long term. The management of the meal for astronauts is in particular very important. When an astronaut gets sick in outer space, it means death. To astronauts, the delicious good balance space foods are essential for their work. This study was aimed at making balance space foods menu for the healthy space-life. The kitchen utensil has a limit in the space environment. And a method to warm is only heater without fire. Therefore purpose of this study, we make the space foods which make by using vacuum cooking device and the IH heater We made space foods menu to referred to Japanese nutrition standard in 2010. We made space foods menu which are using "brown rice, wheat, soy bean, sweet potato and green-vegetable" and " loach and insects which are silkworm pupa, snail, mud snail, turmait, fly, grasshopper, bee". We use ten health adults as subjects. Ten subjects performed the sensory test of the questionnaire method. There was the sensuality examination in the item of "taste, a fragrance, color, the quantity" and acquired a mark at ten points of perfect scores.. We could make the space foods which we devised with vacuum cooking and IH deliciously. As a result of sensuality examination, the eight points in ten points of perfect scores was appeared. This result showed, our space food menu is delicious. We can store these space foods with a refrigerator for 20 days by making vacuum cooking. This thing is at all important result so that a save is enabled when surplus food was done in future by performing vacuum cooking. We want to make delicious space foods menu with vacuum cooking and IH heater more in future.

77 FR 52748 - 60-Day Proposed Information Collection: Indian Health Service (IHS) Sharing What Works-Best...

Science.gov (United States)

2012-08-30

... DEPARTMENT OF HEALTH AND HUMAN SERVICES Indian Health Service 60-Day Proposed Information Collection: Indian Health Service (IHS) Sharing What Works--Best Practice, Promising Practice, and Local Effort (BPPPLE) Form; Request For Public Comment AGENCY: Indian Health Service, HHS. ACTION: Notice...

Geometrical-optics solution to light scattering by droxtal ice crystals.

Science.gov (United States)

Zhang, Zhibo; Yang, Ping; Kattawar, George W; Tsay, Si-Chee; Baum, Bryan A; Hu, Yongxiang; Heymsfield, Andrew J; Reichardt, Jens

2004-04-20

We investigate the phase matrices of droxtals at wavelengths of 0.66 and 11 microm by using an improved geometrical-optics method. An efficient method is developed to specify the incident rays and the corresponding impinging points on the particle surface necessary to initialize the ray-tracing computations. At the 0.66-microm wavelength, the optical properties of droxtals are different from those of hexagonal ice crystals. At the 11-microm wavelength, the phase functions for droxtals are essentially featureless because of strong absorption within the particles, except for ripple structures that are caused by the phase interference of the diffracted wave.

DUMA - a program to display distributions in hexagonal geometry

International Nuclear Information System (INIS)

Tran Quoc Dung; Makai, M.

1987-09-01

DUMA program displays hexagonal structures applied in WWER-440 reactors or one or two distributions in them. It helps users to display either integer, literal or real arrays in an arbitrary hexagonal structure. Possible applications: displaying reactor core layout, power distribution or activity measurements. (author)

Loading pattern optimization in hexagonal geometry using PANTHER

International Nuclear Information System (INIS)

Parks, G.T.; Knight, M.P.

1996-01-01

The extension of the loading pattern optimization capability of Nuclear Electric's reactor physics code PANTHER to hexagonal geometry cores is described. The variety of search methods available and the code's performance are illustrated by an example in which three search different methods are used in turn in order to find an optimal reload design for a sample hexagonal geometry problem. (author)

A co-ordinate system for reactor physics calculations in hexagonal geometry

International Nuclear Information System (INIS)

Burte, D.P.

1990-01-01

A method for generating all the geometric information concerning typical reactor physics calculations for a basically hexagonal reactor core or its sector involving any of the possible symmetries is presented. The geometrically allowed symmetries for regular hexagons are discussed. The approach is based on the choice of a suitable co-ordinate system, viz. one using three coplanar (including one redundant) axes, each at 120 0 with its cyclically preceding one. A code named KEKULE' is developed for a 2-D, finite difference, one-group diffusion analysis of a hexagonal core using the approach. It can cater to a full hexagonal core as well as to any symmetric sectorial part of it. The main feature of the code is that the input concerning geometry is a bare minimum. It is hoped that the approach presented will be useful even for the calculations for hexagonal fuel assemblies. (author)

Ih equalizes membrane input resistance in a heterogeneous population of fusiform neurons in the dorsal cochlear nucleus.

Directory of Open Access Journals (Sweden)

Cesar Celis Ceballos

2016-10-01

Full Text Available In a neuronal population, several combinations of its ionic conductances are used to attain a specific firing phenotype. Some neurons present heterogeneity in their firing, generally produced by expression of a specific conductance, but how additional conductances vary along in order to homeostatically regulate membrane excitability is less known. Dorsal cochlear nucleus principal neurons, fusiform neurons, display heterogeneous spontaneous action potential activity and thus represent an appropriate model to study the role of different conductances in establishing firing heterogeneity. Particularly, fusiform neurons are divided into quiet, with no spontaneous firing, or active neurons, presenting spontaneous, regular firing. These modes are determined by the expression levels of an intrinsic membrane conductance, an inwardly rectifying potassium current (IKir. In this work, we tested whether other subthreshold conductances vary homeostatically to maintain membrane excitability constant across the two subtypes. We found that Ih expression covaries specifically with IKir in order to maintain membrane resistance constant. The impact of Ih on membrane resistance is dependent on the level of IKir expression, being much smaller in quiet neurons with bigger IKir, but Ih variations are not relevant for creating the quiet and active phenotypes. Finally, we demonstrate that the individual proportion of each conductance, and not their absolute conductance, is relevant for determining the neuronal firing mode. We conclude that in fusiform neurons the variations of their different subthreshold conductances are limited to specific conductances in order to create firing heterogeneity and maintain membrane homeostasis.

Development of an IH-type linac for the acceleration of high current heavy ion beams

Energy Technology Data Exchange (ETDEWEB)

Haehnel, Jan Hendrik

2017-07-20

The Facility for Antiproton and Ion Research (FAIR) at GSI Darmstadt will provide unprecedented intensities of protons and heavy ions up to uranium at energies of up to 29 GeV for protons and 2.7 GeV/u for U{sup 28+}. To achieve high intensities in the synchrotron accelerators, high beam currents have to be provided by the injector linear accelerators. High current heavy ion beams are provided by the Universal Linear Accelerator (UNILAC), which in its current state will not be able to provide the required FAIR beam currents. This thesis deals with the development of upgrades for the UNILAC to ensure its high current capability. The first improvement is a matching section (MEBT) for the interface between the RFQ and the IH-DTL of the existing high current injector HSI at the UNILAC. With this new MEBT section, particle losses are eliminated and the overall beam quality is improved. As a second improvement, a complete replacement of the existing Alvarez-DTL is presented. A combination of efficient IH-type cavities and KONUS beam dynamics results in a reduction of the linac length from about 60 m (Alvarez) to just 23 m (new IH-DTL) while providing the same energy and fulfilling FAIR requirements of a high beam current and beam quality. This thesis contains a detailed beam dynamics design of the new linac including some fundamental investigations of the KONUS beam dynamics concept. A cross-check of the beam dynamics design was performed with two independent multi-particle simulation codes. Detailed error studies were conducted to investigate the influence of manufacturing, alignment and operating errors on the beam dynamics performance. Additionally, all five linac cavities were designed, optimized, and their RF parameters including power requirements calculated to provide a comprehensive linac design.

Development of an IH-type linac for the acceleration of high current heavy ion beams

International Nuclear Information System (INIS)

Haehnel, Jan Hendrik

2017-01-01

The Facility for Antiproton and Ion Research (FAIR) at GSI Darmstadt will provide unprecedented intensities of protons and heavy ions up to uranium at energies of up to 29 GeV for protons and 2.7 GeV/u for U 28+ . To achieve high intensities in the synchrotron accelerators, high beam currents have to be provided by the injector linear accelerators. High current heavy ion beams are provided by the Universal Linear Accelerator (UNILAC), which in its current state will not be able to provide the required FAIR beam currents. This thesis deals with the development of upgrades for the UNILAC to ensure its high current capability. The first improvement is a matching section (MEBT) for the interface between the RFQ and the IH-DTL of the existing high current injector HSI at the UNILAC. With this new MEBT section, particle losses are eliminated and the overall beam quality is improved. As a second improvement, a complete replacement of the existing Alvarez-DTL is presented. A combination of efficient IH-type cavities and KONUS beam dynamics results in a reduction of the linac length from about 60 m (Alvarez) to just 23 m (new IH-DTL) while providing the same energy and fulfilling FAIR requirements of a high beam current and beam quality. This thesis contains a detailed beam dynamics design of the new linac including some fundamental investigations of the KONUS beam dynamics concept. A cross-check of the beam dynamics design was performed with two independent multi-particle simulation codes. Detailed error studies were conducted to investigate the influence of manufacturing, alignment and operating errors on the beam dynamics performance. Additionally, all five linac cavities were designed, optimized, and their RF parameters including power requirements calculated to provide a comprehensive linac design.

Synthesis of hexagonal boron nitride graphene-like few layers

Science.gov (United States)

Yuan, S.; Toury, B.; Journet, C.; Brioude, A.

2014-06-01

Self-standing highly crystallized hexagonal boron nitride (h-BN) mono-, bi- and few-layers have been obtained for the first time via the Polymer Derived Ceramics (PDCs) route by adding lithium nitride (Li3N) micropowders to liquid-state polyborazylene (PBN). Incorporation of Li3N as a crystallization promoter allows the onset of crystallization of h-BN at a lower temperature (1200 °C) than under classical conditions (1800 °C). The hexagonal structure was confirmed by both electron and X-ray diffraction.Self-standing highly crystallized hexagonal boron nitride (h-BN) mono-, bi- and few-layers have been obtained for the first time via the Polymer Derived Ceramics (PDCs) route by adding lithium nitride (Li3N) micropowders to liquid-state polyborazylene (PBN). Incorporation of Li3N as a crystallization promoter allows the onset of crystallization of h-BN at a lower temperature (1200 °C) than under classical conditions (1800 °C). The hexagonal structure was confirmed by both electron and X-ray diffraction. Electronic supplementary information (ESI) available: See DOI: 10.1039/c4nr01017e

Anomalous lattice compressibility of hexagonal Eu{sub 2}O{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Irshad, K.A.; Chandra Shekar, N.V., E-mail: chandru@igcar.gov.in

2017-07-01

Monoclinic Eu{sub 2}O{sub 3} was investigated in a Mao-Bell type diamond anvil cell using angle dispersive x-ray diffraction up to a pressure of 26 GPa. Pressure induced structural phase transition from monoclinic to hexagonal phase was observed at 4.3 GPa with 2% volume collapse. Birch –Murnaghan equation of state fit to the pressure volume data yielded a bulk modulus of 159(9) GPa and 165(6) GPa for the monoclinic and hexagonal phases respectively. Equation of state fitting to the structural parameters yielded an axial compressibility of β{sub a} > β{sub c} > β{sub b} for the parent monoclinic phase, showing the least compressibility along b axis. Contrary to the available reports, an anomalous lattice compressibility behavior is observed for the high pressure hexagonal phase, characterized by pronounced hardening of a axis above 15 GPa. The observed incompressible nature of the hexagonal a axis in the pressure range 15–25 GPa is found to be compensated by doubling the compressibility along the c axis. - Highlights: • Structural phase transition in Eu{sub 2}O{sub 3} from monoclinic to hexagonal phase. • Anomalous lattice compressibility in the hexagonal phase has reported first time. • Quantitative analysis of lattice compressibility.

Hexagonal OsB2: Sintering, microstructure and mechanical properties

International Nuclear Information System (INIS)

Xie, Zhilin; Lugovy, Mykola; Orlovskaya, Nina; Graule, Thomas; Kuebler, Jakob; Mueller, Martin; Gao, Huili; Radovic, Miladin; Cullen, David A.

2015-01-01

Highlights: • ReB 2 -type hexagonal OsB 2 powder has been densified by spark plasma sintering. • The sintered OsB 2 contains ∼80 wt.% hexagonal and ∼20 wt.% orthorhombic phases. • The average grain size of the sintered OsB 2 sample was 0.56 ± 0.26 μm. • H = 31 ± 9 GPa and E = 574 ± 112 GPa measured by nanoindentation. - Abstract: The metastable high pressure ReB 2 -type hexagonal OsB 2 bulk ceramics was produced by spark plasma sintering. The phase composition, microstructure, and mechanical behavior of the sintered OsB 2 were studied by X-ray diffraction, optical microscopy, TEM, SEM, EDS, and nanoindentation. The produced ceramics was rather porous and contained a mixture of hexagonal (∼80 wt.%) and orthorhombic (∼20 wt.%) phases as identified by X-ray diffraction and EBSD analysis. Two boron-rich phases, which do not contain Os, were also identified by TEM and SEM/EDS analysis. Nanoindentation measurements yielded a hardness of 31 ± 9 GPa and Young’s modulus of 574 ± 112 GPa, indicating that the material is rather hard and very stiff; however, it is very prone to crack formation and propagation, which is indicative of a very brittle nature of this material. Improvements in the sintering regime are required in order to produce dense, homogeneous and single phase hexagonal OsB 2 bulk ceramics

42 CFR 136.412 - What questions must the IHS ask as part of the background investigation?

Science.gov (United States)

2010-10-01

..., exploitation, contact, or prostitution; crimes against persons; or offenses committed against children? If yes... Child Protection and Family Violence Prevention § 136.412 What questions must the IHS ask as part of the...: (1) Has the individual been arrested or charged with a crime involving a child? If yes, the...

Study the Postbuckling of Hexagonal Piezoelectric Nanowires with Surface Effect

Directory of Open Access Journals (Sweden)

O. Rahmani

2014-04-01

Full Text Available Piezoelectric nanobeams having circular, rectangular and hexagonal cross-sections are synthesized and used in various Nano structures; however, piezoelectric nanobeams with hexagonal cross-sections have not been studied in detail. In particular, the physical mechanisms of the surface effect and the role of surface stress, surface elasticity and surface piezoelectricity have not been discussed thoroughly. The present study investigated post-buckling behavior of piezoelectric nanobeams by examining surface effects. The energy method was applied to post-buckling of hexagonal nanobeams and the critical buckling voltage and amplitude are derived analytically from bulk and surface material properties and geometric factors.

A nodal expansion method using conformal mapping for hexagonal geometry

International Nuclear Information System (INIS)

Chao, Y.A.; Shatilla, Y.A.

1993-01-01

Hexagonal nodal methods adopting the same transverse integration process used for square nodal methods face the subtle theoretical problem that this process leads to highly singular nonphysical terms in the diffusion equation. Lawrence, in developing the DIF3D-N code, tried to approximate the singular terms with relatively simple polynomials. In the HEX-NOD code, Wagner ignored the singularities to simplify the diffusion equation and introduced compensating terms in the nodal equations to restore the nodal balance relation. More recently developed hexagonal nodal codes, such as HEXPE-DITE and the hexagonal version of PANTHER, used methods similar to Wagner's. It will be shown that for light water reactor applications, these two different approximations significantly degraded the accuracy of the respective method as compared to the established square nodal methods. Alternatively, the method of conformal mapping was suggested to map a hexagon to a rectangle, with the unique feature of leaving the diffusion operator invariant, thereby fundamentally resolving the problems associated with transverse integration. This method is now implemented in the Westinghouse hexagonal nodal code ANC-H. In this paper we report on the results of comparing the three methods for a variety of problems via benchmarking against the fine-mesh finite difference code

Steady squares and hexagons on a subcritical ramp

International Nuclear Information System (INIS)

Hoyle, R.B.

1995-01-01

Steady squares and hexagons on a subcritical ramp are studied, both analytically and numerically, within the framework of the lowest-order amplitude equations. On the subcritical ramp, the external stress or control parameter varies continuously in space from subcritical to supercritical values. At the subcritical end of the ramp, pattern formation is suppressed, and patterns fade away into the conduction solution. It is shown that three-dimensional patterns may change shape on a subcritical ramp. A square pattern becomes a pattern of rolls as it fades, with the roll axes aligned in the direction orthogonal to that in which the control parameter varies. Hexagons in systems with horizontal midplane symmetry become a pattern of rectangles before reaching the conduction solution. There is a suggestion that hexagons in systems which lack this symmetry might fade away through a roll pattern. Numerical simulations are used to illustrate these phenomena

Additive Manufacturing of Dense Hexagonal Boron Nitride Objects

Energy Technology Data Exchange (ETDEWEB)

Marquez Rossy, Andres E [ORNL; Armstrong, Beth L [ORNL; Elliott, Amy M [ORNL; Lara-Curzio, Edgar [ORNL

2017-05-12

The feasibility of manufacturing hexagonal boron nitride objects via additive manufacturing techniques was investigated. It was demonstrated that it is possible to hot-extrude thermoplastic filaments containing uniformly distributed boron nitride particles with a volume concentration as high as 60% and that these thermoplastic filaments can be used as feedstock for 3D-printing objects using a fused deposition system. Objects 3D-printed by fused deposition were subsequently sintered at high temperature to obtain dense ceramic products. In a parallel study the behavior of hexagonal boron nitride in aqueous solutions was investigated. It was shown that the addition of a cationic dispersant to an azeotrope enabled the formulation of slurries with a volume concentration of boron nitride as high as 33%. Although these slurries exhibited complex rheological behavior, the results from this study are encouraging and provide a pathway for manufacturing hexagonal boron nitride objects via robocasting.

Multilayer DNA Origami Packed on Hexagonal and Hybrid Lattices

DEFF Research Database (Denmark)

Ke, Yonggang; Voigt, Niels Vinther; Shih, William M.

2012-01-01

“Scaffolded DNA origami” has been proven to be a powerful and efficient approach to construct two-dimensional or three-dimensional objects with great complexity. Multilayer DNA origami has been demonstrated with helices packing along either honeycomb-lattice geometry or square-lattice geometry....... Here we report successful folding of multilayer DNA origami with helices arranged on a close-packed hexagonal lattice. This arrangement yields a higher density of helical packing and therefore higher resolution of spatial addressing than has been shown previously. We also demonstrate hybrid multilayer...... DNA origami with honeycomb-lattice, square-lattice, and hexagonal-lattice packing of helices all in one design. The availability of hexagonal close-packing of helices extends our ability to build complex structures using DNA nanotechnology....

Multilayer DNA origami packed on hexagonal and hybrid lattices.

Science.gov (United States)

Ke, Yonggang; Voigt, Niels V; Gothelf, Kurt V; Shih, William M

2012-01-25

"Scaffolded DNA origami" has been proven to be a powerful and efficient approach to construct two-dimensional or three-dimensional objects with great complexity. Multilayer DNA origami has been demonstrated with helices packing along either honeycomb-lattice geometry or square-lattice geometry. Here we report successful folding of multilayer DNA origami with helices arranged on a close-packed hexagonal lattice. This arrangement yields a higher density of helical packing and therefore higher resolution of spatial addressing than has been shown previously. We also demonstrate hybrid multilayer DNA origami with honeycomb-lattice, square-lattice, and hexagonal-lattice packing of helices all in one design. The availability of hexagonal close-packing of helices extends our ability to build complex structures using DNA nanotechnology. © 2011 American Chemical Society

On the accuracy of van der Waals inclusive density-functional theory exchange-correlation functionals for ice at ambient and high pressures.

Science.gov (United States)

Santra, Biswajit; Klimes, Jirí; Tkatchenko, Alexandre; Alfè, Dario; Slater, Ben; Michaelides, Angelos; Car, Roberto; Scheffler, Matthias

2013-10-21

Density-functional theory (DFT) has been widely used to study water and ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on ice Ih and six proton ordered phases of ice. Consistent with our previous study [B. Santra, J. Klimeš, D. Alfè, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, and M. Scheffler, Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition pressures of the high-pressure ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high pressures remains and we suggest that because of the stern test the high pressure ice phases pose they should be used in future benchmark studies of simulation methods for water.

Design and Construction of Power System for Induction Heating (IH) Cooker Using Resonant Converter

International Nuclear Information System (INIS)

Soe Thiri Thandar; Clement Saldanah; Win Khaing Moe

2008-06-01

Induction Heating (IH) systems using electromagnetic induction are developed in many industrial applications in Myanmar. Many industries have benefited from this new breakthrough by implementing induction heating for melting, hardening, and heating. Induction heating cooker is based on high frequency induction heating,electrical and electronic technologies. From the electronic point of view, induction heating cooker is composed of four parts.They are rectifier, filter, high frequency inverter, and resonant load. The purpose of this research is mainly objected to developed an induction heating cooker. The rectifier module is considered as full-bridge rectifier. The second protion of the system is a capacitive filter. The ripple components are minimized by this filter. The third is a high frequency converter to convert the constant DC to high frequency AC by switching the devices alternately. In this research, the Insulated Gate Bipolar Transistor (IGBT) will be used as a power source, and can be driven by the pulse signals from the pulse transformer circuit. In the resonant load, the power consumption is about 500W. Construction and testing has been carried out. The merits of this research work is that IH cooker can be developed because of having less energy consumption, safe, efficient, quick heating, and having efficiency of 90% or more

Thermal stability of hexagonal OsB2

Science.gov (United States)

Xie, Zhilin; Blair, Richard G.; Orlovskaya, Nina; Cullen, David A.; Andrew Payzant, E.

2014-11-01

The synthesis of novel hexagonal ReB2-type OsB2 ceramic powder was performed by high energy ball milling of elemental Os and B powders. Two different sources of B powder have been used for this mechanochemical synthesis. One B powder consisted of a mixture of amorphous and crystalline phases and a mixture of 10B and 11B isotopes with a fine particle size, while another B powder was a purely crystalline (rhombohedral) material consisting of enriched 11B isotope with coarse particle size. The same Os powder was used for the synthesis in both cases. It was established that, in the first case, the hexagonal OsB2 phase was the main product of synthesis with a small quantity of Os2B3 phase present after synthesis as an intermediate product. In the second case, where coarse crystalline 11B powder was used as a raw material, only Os2B3 boride was synthesized mechanochemically. The thermal stability of hexagonal OsB2 powder was studied by heating under argon up to 876 °C and cooling in vacuo down to -225 °C. During the heating, the sacrificial reaction 2OsB2+3O2→2Os+2B2O3 took place due to presence of O2/water vapor molecules in the heating chamber, resulting in the oxidation of B atoms and formation of B2O3 and precipitation of Os metal out of the OsB2 lattice. As a result of such phase changes during heating, the lattice parameters of hexagonal OsB2 changed significantly. The shrinkage of the a lattice parameter was recorded in 276-426 °C temperature range upon heating, which was attributed to the removal of B atoms from the OsB2 lattice due to oxidation followed by the precipitation of Os atoms and formation of Os metal. While significant structural changes occurred upon heating due to presence of O2, the hexagonal OsB2 ceramic demonstrated good phase stability upon cooling in vacuo with linear shrinkage of the lattice parameters and no phase changes detected during cooling.

Comparison of PANTHER nodal solutions in hexagonal-z geometry

International Nuclear Information System (INIS)

Knight, M.; Hutt, P.; Lewis, I.

1995-01-01

The reactor physics code PANTHER has been extended to hexagonal geometries. Steady-state, depletion, and transient calculations with feedback can all be performed. Two hexagonal nodal flux solutions have been developed. In the first method, transverse integration is performed exactly as in the rectangular case. The resulting transverse integrated equation has singular terms, which are simply ignored. The second approach applies a conformal mapping that transforms the hexagon onto a rectangle. Pin power reconstruction has also been developed with both methods. For a benchmark VVER-1000 reactor depletion problem, both methods give accurate results for standard depletion calculations. In the more extreme situation with all rods inserted, the simpler method breaks down. However, the accuracy of the conformal solution was found to be excellent in all cases studied

Some effects of ice crystals on the FSSP measurements in mixed phase clouds

Directory of Open Access Journals (Sweden)

G. Febvre

2012-10-01

Full Text Available In this paper, we show that in mixed phase clouds, the presence of ice crystals may induce wrong FSSP 100 measurements interpretation especially in terms of particle size and subsequent bulk parameters. The presence of ice crystals is generally revealed by a bimodal feature of the particle size distribution (PSD. The combined measurements of the FSSP-100 and the Polar Nephelometer give a coherent description of the effect of the ice crystals on the FSSP-100 response. The FSSP-100 particle size distributions are characterized by a bimodal shape with a second mode peaked between 25 and 35 μm related to ice crystals. This feature is observed with the FSSP-100 at airspeed up to 200 m s⁻¹ and with the FSSP-300 series. In order to assess the size calibration for clouds of ice crystals the response of the FSSP-100 probe has been numerically simulated using a light scattering model of randomly oriented hexagonal ice particles and assuming both smooth and rough crystal surfaces. The results suggest that the second mode, measured between 25 μm and 35 μm, does not necessarily represent true size responses but corresponds to bigger aspherical ice particles. According to simulation results, the sizing understatement would be neglected in the rough case but would be significant with the smooth case. Qualitatively, the Polar Nephelometer phase function suggests that the rough case is the more suitable to describe real crystals. Quantitatively, however, it is difficult to conclude. A review is made to explore different hypotheses explaining the occurrence of the second mode. However, previous cloud in situ measurements suggest that the FSSP-100 secondary mode, peaked in the range 25–35 μm, is likely to be due to the shattering of large ice crystals on the probe inlet. This finding is supported by the rather good relationship between the concentration of particles larger than 20 μm (hypothesized to be ice shattered-fragments measured by the

42 CFR 137.401 - What role does Tribal consultation play in the IHS annual budget request process?

Science.gov (United States)

2010-10-01

... 42 Public Health 1 2010-10-01 2010-10-01 false What role does Tribal consultation play in the IHS annual budget request process? 137.401 Section 137.401 Public Health PUBLIC HEALTH SERVICE, DEPARTMENT OF...-GOVERNANCE Secretarial Responsibilities Budget Request § 137.401 What role does Tribal consultation play in...

A New Approach to Modeling Densities and Equilibria of Ice and Gas Hydrate Phases

Science.gov (United States)

Zyvoloski, G.; Lucia, A.; Lewis, K. C.

2011-12-01

The Gibbs-Helmholtz Constrained (GHC) equation is a new cubic equation of state that was recently derived by Lucia (2010) and Lucia et al. (2011) by constraining the energy parameter in the Soave form of the Redlich-Kwong equation to satisfy the Gibbs-Helmholtz equation. The key attributes of the GHC equation are: 1) It is a multi-scale equation because it uses the internal energy of departure, UD, as a natural bridge between the molecular and bulk phase length scales. 2) It does not require acentric factors, volume translation, regression of parameters to experimental data, binary (kij) interaction parameters, or other forms of empirical correlations. 3) It is a predictive equation of state because it uses a database of values of UD determined from NTP Monte Carlo simulations. 4) It can readily account for differences in molecular size and shape. 5) It has been successfully applied to non-electrolyte mixtures as well as weak and strong aqueous electrolyte mixtures over wide ranges of temperature, pressure and composition to predict liquid density and phase equilibrium with up to four phases. 6) It has been extensively validated with experimental data. 7) The AAD% error between predicted and experimental liquid density is 1% while the AAD% error in phase equilibrium predictions is 2.5%. 8) It has been used successfully within the subsurface flow simulation program FEHM. In this work we describe recent extensions of the multi-scale predictive GHC equation to modeling the phase densities and equilibrium behavior of hexagonal ice and gas hydrates. In particular, we show that radial distribution functions, which can be determined by NTP Monte Carlo simulations, can be used to establish correct standard state fugacities of 1h ice and gas hydrates. From this, it is straightforward to determine both the phase density of ice or gas hydrates as well as any equilibrium involving ice and/or hydrate phases. A number of numerical results for mixtures of N2, O2, CH4, CO2, water

Backscattering Properties of Nonspherical Ice Particles Calculated by Geometrical-Optics-Integral-Equation Method

Directory of Open Access Journals (Sweden)

Masuda Kazuhiko

2016-01-01

Full Text Available Backscattering properties of ice crystal models (Voronoi aggregates (VA, hexagonal columns (COL, and six-branched bullet rosettes (BR6 are calculated by using geometrical-opticsintegral-equation (GOIE method. Characteristics of depolarization ratio (δ and lidar ratio (L of the crystal models are examined. δ (L values are 0.2~0.3 (4~50, 0.3~0.4 (10~25, and 0.5~0.6 (50~100 for COL, BR6, and VA, respectively, at wavelength λ=0.532 μm. It is found that small deformation of COL model could produce significant changes in δ and L.

CMFD and GPU acceleration on method of characteristics for hexagonal cores

International Nuclear Information System (INIS)

Han, Yu; Jiang, Xiaofeng; Wang, Dezhong

2014-01-01

Highlights: • A merged hex-mesh CMFD method solved via tri-diagonal matrix inversion. • Alternative hardware acceleration of using inexpensive GPU. • A hex-core benchmark with solution to confirm two acceleration methods. - Abstract: Coarse Mesh Finite Difference (CMFD) has been widely adopted as an effective way to accelerate the source iteration of transport calculation. However in a core with hexagonal assemblies there are non-hexagonal meshes around the edges of assemblies, causing a problem for CMFD if the CMFD equations are still to be solved via tri-diagonal matrix inversion by simply scanning the whole core meshes in different directions. To solve this problem, we propose an unequal mesh CMFD formulation that combines the non-hexagonal cells on the boundary of neighboring assemblies into non-regular hexagonal cells. We also investigated the alternative hardware acceleration of using graphics processing units (GPU) with graphics card in a personal computer. The tool CUDA is employed, which is a parallel computing platform and programming model invented by the company NVIDIA for harnessing the power of GPU. To investigate and implement these two acceleration methods, a 2-D hexagonal core transport code using the method of characteristics (MOC) is developed. A hexagonal mini-core benchmark problem is established to confirm the accuracy of the MOC code and to assess the effectiveness of CMFD and GPU parallel acceleration. For this benchmark problem, the CMFD acceleration increases the speed 16 times while the GPU acceleration speeds it up 25 times. When used simultaneously, they provide a speed gain of 292 times

CMFD and GPU acceleration on method of characteristics for hexagonal cores

Energy Technology Data Exchange (ETDEWEB)

Han, Yu, E-mail: hanyu1203@gmail.com [School of Nuclear Science and Engineering, Shanghai Jiaotong University, Shanghai 200240 (China); Jiang, Xiaofeng [Shanghai NuStar Nuclear Power Technology Co., Ltd., No. 81 South Qinzhou Road, XuJiaHui District, Shanghai 200000 (China); Wang, Dezhong [School of Nuclear Science and Engineering, Shanghai Jiaotong University, Shanghai 200240 (China)

2014-12-15

Highlights: • A merged hex-mesh CMFD method solved via tri-diagonal matrix inversion. • Alternative hardware acceleration of using inexpensive GPU. • A hex-core benchmark with solution to confirm two acceleration methods. - Abstract: Coarse Mesh Finite Difference (CMFD) has been widely adopted as an effective way to accelerate the source iteration of transport calculation. However in a core with hexagonal assemblies there are non-hexagonal meshes around the edges of assemblies, causing a problem for CMFD if the CMFD equations are still to be solved via tri-diagonal matrix inversion by simply scanning the whole core meshes in different directions. To solve this problem, we propose an unequal mesh CMFD formulation that combines the non-hexagonal cells on the boundary of neighboring assemblies into non-regular hexagonal cells. We also investigated the alternative hardware acceleration of using graphics processing units (GPU) with graphics card in a personal computer. The tool CUDA is employed, which is a parallel computing platform and programming model invented by the company NVIDIA for harnessing the power of GPU. To investigate and implement these two acceleration methods, a 2-D hexagonal core transport code using the method of characteristics (MOC) is developed. A hexagonal mini-core benchmark problem is established to confirm the accuracy of the MOC code and to assess the effectiveness of CMFD and GPU parallel acceleration. For this benchmark problem, the CMFD acceleration increases the speed 16 times while the GPU acceleration speeds it up 25 times. When used simultaneously, they provide a speed gain of 292 times.

Hexagonal OsB{sub 2}: Sintering, microstructure and mechanical properties

Energy Technology Data Exchange (ETDEWEB)

Xie, Zhilin [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Lugovy, Mykola [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Institute for Problems of Materials Science, 3 Krzhizhanivskii Str., Kyiv 03142 (Ukraine); Orlovskaya, Nina, E-mail: Nina.Orlovskaya@ucf.edu [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Graule, Thomas; Kuebler, Jakob [Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for High Performance Ceramics, CH-8600 Dubendorf (Switzerland); Mueller, Martin [Laboratory of Mechanical Metallurgy, EPFL, CH-1015 Lausanne (Switzerland); Gao, Huili [Department of Mechanical Engineering, Texas A& M University, College Station, TX 77843 (United States); Radovic, Miladin [Department of Materials Science and Engineering, Texas A& M University, College Station, TX 77843 (United States); Cullen, David A. [Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)

2015-06-15

Highlights: • ReB{sub 2}-type hexagonal OsB{sub 2} powder has been densified by spark plasma sintering. • The sintered OsB{sub 2} contains ∼80 wt.% hexagonal and ∼20 wt.% orthorhombic phases. • The average grain size of the sintered OsB{sub 2} sample was 0.56 ± 0.26 μm. • H = 31 ± 9 GPa and E = 574 ± 112 GPa measured by nanoindentation. - Abstract: The metastable high pressure ReB{sub 2}-type hexagonal OsB{sub 2} bulk ceramics was produced by spark plasma sintering. The phase composition, microstructure, and mechanical behavior of the sintered OsB{sub 2} were studied by X-ray diffraction, optical microscopy, TEM, SEM, EDS, and nanoindentation. The produced ceramics was rather porous and contained a mixture of hexagonal (∼80 wt.%) and orthorhombic (∼20 wt.%) phases as identified by X-ray diffraction and EBSD analysis. Two boron-rich phases, which do not contain Os, were also identified by TEM and SEM/EDS analysis. Nanoindentation measurements yielded a hardness of 31 ± 9 GPa and Young’s modulus of 574 ± 112 GPa, indicating that the material is rather hard and very stiff; however, it is very prone to crack formation and propagation, which is indicative of a very brittle nature of this material. Improvements in the sintering regime are required in order to produce dense, homogeneous and single phase hexagonal OsB{sub 2} bulk ceramics.

The O H stretching band in ice Ih derived via eV neutron spectroscopy on VESUVIO using the new very low angle detector bank

Science.gov (United States)

Perelli-Cippo, E.; Gorini, G.; Tardocchi, M.; Andreani, C.; Pietropaolo, A.; Senesi, R.; Rhodes, N. J.; Schooneveld, E. M.

2006-06-01

Strong demand exists for an experimental facility enabling new experimental investigations on condensed matter systems based on epithermal neutron scattering at high energy and low momentum transfers. This need will be met by the very low angle detector (VLAD) bank, to be installed on the VESUVIO spectrometer at the ISIS spallation neutron source. The equipment will operate in the scattering angular range 1°<2θ<5°. Scattering measurements from a polycrystalline ice sample using a VLAD prototype demonstrates the effectiveness of the detection technique adopted for the construction of the full detector array. The resulting density of states in ice is 9±2 atoms/cell, in agreement with previous measurements.

Hexagonal undersampling for faster MRI near metallic implants.

Science.gov (United States)

Sveinsson, Bragi; Worters, Pauline W; Gold, Garry E; Hargreaves, Brian A

2015-02-01

Slice encoding for metal artifact correction acquires a three-dimensional image of each excited slice with view-angle tilting to reduce slice and readout direction artifacts respectively, but requires additional imaging time. The purpose of this study was to provide a technique for faster imaging around metallic implants by undersampling k-space. Assuming that areas of slice distortion are localized, hexagonal sampling can reduce imaging time by 50% compared with conventional scans. This work demonstrates this technique by comparisons of fully sampled images with undersampled images, either from simulations from fully acquired data or from data actually undersampled during acquisition, in patients and phantoms. Hexagonal sampling is also shown to be compatible with parallel imaging and partial Fourier acquisitions. Image quality was evaluated using a structural similarity (SSIM) index. Images acquired with hexagonal undersampling had no visible difference in artifact suppression from fully sampled images. The SSIM index indicated high similarity to fully sampled images in all cases. The study demonstrates the ability to reduce scan time by undersampling without compromising image quality. © 2014 Wiley Periodicals, Inc.

Formation of large (≃100 μm ice crystals near the tropical tropopause

Directory of Open Access Journals (Sweden)

M. J. Alexander

2008-03-01

Full Text Available Recent high-altitude aircraft measurements with in situ imaging instruments indicated the presence of relatively large (≃100 μm length, thin (aspect ratios of ≃6:1 or larger hexagonal plate ice crystals near the tropical tropopause in very low concentrations (<0.01 L−1. These crystals were not produced by deep convection or aggregation. We use simple growth-sedimentation calculations as well as detailed cloud simulations to evaluate the conditions required to grow the large crystals. Uncertainties in crystal aspect ratio leave a range of possibilities, which could be constrained by knowledge of the water vapor concentration in the air where the crystal growth occurred. Unfortunately, water vapor measurements made in the cloud formation region near the tropopause with different instruments ranged from <2 ppmv to ≃3.5 ppmv. The higher water vapor concentrations correspond to very large ice supersaturations (relative humidities with respect to ice of about 200%. If the aspect ratios of the hexagonal plate crystals are as small as the image analysis suggests (6:1, see companion paper (Lawson et al., 2008 then growth of the large crystals before they sediment out of the supersaturated layer would only be possible if the water vapor concentration were on the high end of the range indicated by the different measurements (>3 ppmv. On the other hand, if the crystal aspect ratios are quite a bit larger (≃10:1, then H2O concentrations toward the low end of the measurement range (≃2–2.5 ppmv would suffice to grow the large crystals. Gravity-wave driven temperature and vertical wind perturbations only slightly modify the H2O concentrations needed to grow the crystals. We find that it would not be possible to grow the large crystals with water concentrations less than 2 ppmv, even with assumptions of a very high aspect ratio of 15 and steady upward motion of 2 cm s−1 to loft the crystals in the tropopause region. These calculations would seem

Momentum distribution, vibrational dynamics, and the potential of mean force in ice

Science.gov (United States)

Lin, Lin; Morrone, Joseph A.; Car, Roberto; Parrinello, Michele

2011-06-01

By analyzing the momentum distribution obtained from path integral and phonon calculations we find that the protons in hexagonal ice experience an anisotropic quasiharmonic effective potential with three distinct principal frequencies that reflect molecular orientation. Due to the importance of anisotropy, anharmonic features of the environment cannot be extracted from existing experimental distributions that involve the spherical average. The full directional distribution is required, and we give a theoretical prediction for this quantity that could be verified in future experiments. Within the quasiharmonic context, anharmonicity in the ground-state dynamics of the proton is substantial and has quantal origin, a finding that impacts the interpretation of several spectroscopies.

New approach for direct chemical synthesis of hexagonal Co nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Abel, Frank M., E-mail: fabel@udel.edu [Physics and Astronomy, University of Delaware (United States); Tzitzios, Vasilis [Institute of Nanoscience and Nanotechnology, NCSR, Demokritos (Greece); Hadjipanayis, George C. [Physics and Astronomy, University of Delaware (United States)

2016-02-15

In this paper, we explore the possibility of producing hexagonal Cobalt nanoparticles, with high saturation magnetization by direct chemical synthesis. The nanoparticles were synthesized by reduction of anhydrous cobalt (II) chloride by NaBH{sub 4} in tetraglyme at temperatures in the range of 200–270 °C under a nitrogen–hydrogen atmosphere. The reactions were done at high temperatures to allow for the formation of as-made hexagonal cobalt. The size of the particles was controlled by the addition of different surfactants. The best magnetic properties so far were obtained on spherical hexagonal Co nanoparticles with an average size of 45 nm, a saturation magnetization of 143 emu/g and coercivity of 500 Oe. the saturation magnetization and coercivity were further improved by annealing the Co nanoparticles leading to saturation magnetization of 160 emu/g and coercivity of 540 Oe. - Highlights: • We synthesized hexagonal cobalt nanoparticles by a new wet chemical method. • We considered the effects of different surfactants on particles magnetic properties. • The as-made Co nanoparticles had magnetic properties of 143 emu/g and 500 Oe. • After annealing magnetic properties of 160 emu/g and 540 Oe were obtained.

Polyamorphism in Water: Amorphous Ices and their Glassy States

Science.gov (United States)

Amann-Winkel, K.; Boehmer, R.; Fujara, F.; Gainaru, C.; Geil, B.; Loerting, T.

2015-12-01

Water is ubiquitous and of general importance for our environment. But it is also known as the most anomalous liquid. The fundamental origin of the numerous anomalies of water is still under debate. An understanding of these anomalous properties of water is closely linked to an understanding of the phase diagram of the metastable non-crystalline states of ice. The process of pressure induced amorphization of ice was first observed by Mishima et al. [1]. The authors pressurized hexagonal ice at 77 K up to a pressure of 1.6 GPa to form high density amorphous ice (HDA). So far three distinct structural states of amorphous water are known [2], they are called low- (LDA), high- (HDA) and very high density amorphous ice (VHDA). Since the discovery of multiple distinct amorphous states it is controversy discussed whether this phenomenon of polyamorphism at high pressures is connected to the occurrence of more than one supercooled liquid phase [3]. Alternatively, amorphous ices have been suggested to be of nanocrystalline nature, unrelated to liquids. Indeed inelastic X-ray scattering measurements indicate sharp crystal-like phonons in the amorphous ices [4]. In case of LDA the connection to the low-density liquid (LDL) was inferred from several experiments including the observation of a calorimetric glass-to-liquid transition at 136 K and ambient pressure [5]. Recently also the glass transition in HDA was observed at 116 K at ambient pressure [6] and at 140 K at elevated pressure of 1 GPa [7], using calorimetric measurements as well as dielectric spectroscopy. We discuss here the general importance of amorphous ices and their liquid counterparts and present calorimetric and dielectric measurements on LDA and HDA. The good agreement between dielectric and calorimetric results convey for a clearer picture of water's vitrification phenomenon. [1] O. Mishima, L. D. Calvert, and E. Whalley, Nature 314, 76, 1985 [2] D.T. Bowron, J. L. Finney, A. Hallbrucker, et al., J. Chem

The photoexcitation of crystalline ice and amorphous solid water: A molecular dynamics study of outcomes at 11 K and 125 K

Energy Technology Data Exchange (ETDEWEB)

Crouse, J.; Loock, H.-P., E-mail: hploock@chem.queensu.ca; Cann, N. M., E-mail: ncann@chem.queensu.ca [Department of Chemistry, Queen’s University, Kingston, Ontario K7L 3N6 (Canada)

2015-07-21

Photoexcitation of crystalline ice Ih and amorphous solid water at 7-9 eV is examined using molecular dynamics simulations and a fully flexible water model. The probabilities of photofragment desorption, trapping, and recombination are examined for crystalline ice at 11 K and at 125 K and for amorphous solid water at 11 K. For 11 K crystalline ice, a fully rigid water model is also employed for comparison. The kinetic energy of desorbed H atoms and the distance travelled by trapped fragments are correlated to the location and the local environment of the photoexcited water molecule. In all cases, H atom desorption is found to be the most likely outcome in the top bilayer while trapping of all photofragments is most probable deeper in the solid where the likelihood for recombination of the fragments into H{sub 2}O molecules also rises. Trajectory analysis indicates that the local hydrogen bonding network in amorphous solid water is more easily distorted by a photodissociation event compared to crystalline ice. Also, simulations indicate that desorption of OH radicals and H{sub 2}O molecules are more probable in amorphous solid water. The kinetic energy distributions for desorbed H atoms show a peak at high energy in crystalline ice, arising from photoexcited water molecules in the top monolayer. This peak is less pronounced in amorphous solid water. H atoms that are trapped may be displaced by up to ∼10 water cages, but migrate on average 3 water cages. Trapped OH fragments tend to stay near the original solvent cage.

Machined and plastic copings in three-element prostheses with different types of implantabutment joints: a strain gauge comparative analysis

Directory of Open Access Journals (Sweden)

Renato Sussumu Nishioka

2010-06-01

Full Text Available OBJECTIVE: Using strain gauge (SG analysis, the aim of this in vitro study was quantify the strain development during the fixation of three-unit screw implant-supported fixed partial dentures, varying the types of implant-abutment joints and the type of prosthetic coping. The hypotheses were that the type of hexagonal connection would generate different microstrains and the type of copings would produce similar microstrains after prosthetic screws had been tightened onto microunit abutments. MATERIALS AND METHODS: Three dental implants with external (EH and internal (IH hexagonal configurations were inserted into two polyurethane blocks. Microunit abutments were screwed onto their respective implant groups, applying a torque of 20 Ncm. Machined Co-Cr copings (M and plastic prosthetic copings (P were screwed onto the abutments, which received standard wax patterns. The wax patterns were cast in Co-Cr alloy (n=5, forming four groups: G1 EH/M; G2 EH/P; G3 IH/M and G4 IH/P. Four SGs were bonded onto the surface of the block tangentially to the implants, SG 1 mesially to implant 1, SG 2 and SG 3 mesially and distally to implant 2, respectively, and SG 4 distally to implant 3. The superstructure's occlusal screws were tightened onto microunit abutments with 10 Ncm torque using a manual torque driver. The magnitude of microstrain on each SG was recorded in units of microstrain (µε. The data were analyzed statistically by ANOVA and Tukey's test (p0.05. The hypotheses were partially accepted. CONCLUSIONS: It was concluded that the type of hexagonal connection and coping presented similar mechanical behavior under tightening conditions.

Hexagon OPE resummation and multi-Regge kinematics

Energy Technology Data Exchange (ETDEWEB)

Drummond, J.M. [School of Physics & Astronomy, University of Southampton,Highfield, Southampton, SO17 1BJ (United Kingdom); Theory Division, Physics Department, CERN,CH-1211 Geneva 23 (Switzerland); LAPTh, CNRS, Université de Savoie,9 Chemin de Bellevue, F-74941 Annecy-le-Vieux Cedex (France); Papathanasiou, G. [LAPTh, CNRS, Université de Savoie,9 Chemin de Bellevue, F-74941 Annecy-le-Vieux Cedex (France)

2016-02-29

We analyse the OPE contribution of gluon bound states in the double scaling limit of the hexagonal Wilson loop in planar N=4 super Yang-Mills theory. We provide a systematic procedure for perturbatively resumming the contributions from single-particle bound states of gluons and expressing the result order by order in terms of two-variable polylogarithms. We also analyse certain contributions from two-particle gluon bound states and find that, after analytic continuation to the 2→4 Mandelstam region and passing to multi-Regge kinematics (MRK), only the single-particle gluon bound states contribute. From this double-scaled version of MRK we are able to reconstruct the full hexagon remainder function in MRK up to five loops by invoking single-valuedness of the results.

Assessment of the accuracy of the conventional ray-tracing technique: Implications in remote sensing and radiative transfer involving ice clouds

International Nuclear Information System (INIS)

Bi, Lei; Yang, Ping; Liu, Chao; Yi, Bingqi; Baum, Bryan A.; Diedenhoven, Bastiaan van; Iwabuchi, Hironobu

2014-01-01

A fundamental problem in remote sensing and radiative transfer simulations involving ice clouds is the ability to compute accurate optical properties for individual ice particles. While relatively simple and intuitively appealing, the conventional geometric-optics method (CGOM) is used frequently for the solution of light scattering by ice crystals. Due to the approximations in the ray-tracing technique, the CGOM accuracy is not well quantified. The result is that the uncertainties are introduced that can impact many applications. Improvements in the Invariant Imbedding T-matrix method (II-TM) and the Improved Geometric-Optics Method (IGOM) provide a mechanism to assess the aforementioned uncertainties. The results computed by the II-TM+IGOM are considered as a benchmark because the II-TM solves Maxwell's equations from first principles and is applicable to particle size parameters ranging into the domain at which the IGOM has reasonable accuracy. To assess the uncertainties with the CGOM in remote sensing and radiative transfer simulations, two independent optical property datasets of hexagonal columns are developed for sensitivity studies by using the CGOM and the II-TM+IGOM, respectively. Ice cloud bulk optical properties obtained from the two datasets are compared and subsequently applied to retrieve the optical thickness and effective diameter from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements. Additionally, the bulk optical properties are tested in broadband radiative transfer (RT) simulations using the general circulation model (GCM) version of the Rapid Radiative Transfer Model (RRTMG) that is adopted in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM, version 5.1). For MODIS retrievals, the mean bias of uncertainties of applying the CGOM in shortwave bands (0.86 and 2.13 μm) can be up to 5% in the optical thickness and as high as 20% in the effective diameter, depending on cloud optical

New results for loop integrals. AMBRE, CSectors, hexagon

International Nuclear Information System (INIS)

Gluza, Janusz; Kajda, Krzysztof

2009-03-01

We report on the three Mathematica packages hexagon, CSectors, AMBRE. They are useful for the evaluation of one- and two-loop Feynman integrals with a dependence on several kinematical scales. These integrals are typically needed for LHC and ILC applications, but also for higher order corrections at meson factories. hexagon is a new package for the tensor reduction of one-loop 5-point and 6-point functions with rank R=3 and R=4, respectively; AMBRE is a tool for derivations of Mellin-Barnes representations; CSectors is an interface for the package sectordecomposition and allows a convenient, direct evaluation of tensor Feynman integrals. (orig.)

Deep ice and salty oceans of icy worlds, how high pressures influence their thermodynamics and provide constrains on extraterrestrial habitability

Science.gov (United States)

Journaux, B.; Brown, J. M.; Bollengier, O.; Abramson, E.

2017-12-01

As in Earth arctic and Antarctic regions, suspected extraterrestrial deep oceans in icy worlds (i.e. icy moons and water-rich exoplanets) chemistry and thermodynamic state will strongly depend on their equilibrium with H2O ice and present solutes. Na-Mg-Cl-SO4 salt species are currently the main suspected ionic solutes to be present in deep oceans based on remote sensing, magnetic field measurements, cryovolcanism ice grains chemical analysis and chondritic material aqueous alteration chemical models. Unlike on our planet, deep extraterrestrial ocean might also be interacting at depth with high pressure ices (e.g. III, V, VI, VI, X) which have different behavior compared to ice Ih. Unfortunately, the pressures and temperatures inside these hydrospheres differ significantly from the one found in Earth aqueous environments, so most of our current thermodynamic databases do not cover the range of conditions relevant for modeling realistically large icy worlds interiors. Recent experimental results have shown that the presence of solutes, and more particularly salts, in equilibrium with high pressure ices have large effects on the stability, buoyancy and chemistry of all the phases present at these extreme conditions. High pressure in-situ measurements using diamond anvil cell apparatus were operated both at the University of washington and at the European Synchrotron Radiation Facility on aqueous systems phase diagrams with Na-Mg-Cl-SO4 species, salt incorporation in high pressure ices and density inversions between the solid and the fluids. These results suggest a more complex picture of the interior structure, dynamic and chemical evolution of large icy worlds hydrospheres when solutes are taken into account, compared to current models mainly using pure water. Based on our in-situ experimental measurements, we propose the existence of new liquid environments at greater depths and the possibility of solid state transport of solute through the high pressure ices

Modelling snow ice and superimposed ice on landfast sea ice in Kongsfjorden, Svalbard

Directory of Open Access Journals (Sweden)

Caixin Wang

2015-08-01

Full Text Available Snow ice and superimposed ice formation on landfast sea ice in a Svalbard fjord, Kongsfjorden, was investigated with a high-resolution thermodynamic snow and sea-ice model, applying meteorological weather station data as external forcing. The model shows that sea-ice formation occurs both at the ice bottom and at the snow/ice interface. Modelling results indicated that the total snow ice and superimposed ice, which formed at the snow/ice interface, was about 14 cm during the simulation period, accounting for about 15% of the total ice mass and 35% of the total ice growth. Introducing a time-dependent snow density improved the modelled results, and a time-dependent oceanic heat flux parameterization yielded reasonable ice growth at the ice bottom. Model results suggest that weather conditions, in particular air temperature and precipitation, as well as snow thermal properties and surface albedo are the most critical factors for the development of snow ice and superimposed ice in Kongsfjorden. While both warming air and higher precipitation led to increased snow ice and superimposed ice forming in Kongsfjorden in the model runs, the processes were more sensitive to precipitation than to air temperature.

Design considerations for quasi-phase-matching in doubly resonant lithium niobate hexagonal microresonators

CSIR Research Space (South Africa)

Sono, Tleyane J

2017-08-01

Full Text Available Fabrication capabilities of high optical quality hexagonal superstructures by chemical etching of inverted ferroelectric domains in lithium niobate platform suggests a route for efficient implementation of compact hexagonal microcavities...

Diamagnetic response in zigzag hexagonal silicene rings

International Nuclear Information System (INIS)

Xu, Ning; Chen, Qiao; Tian, Hongyu; Ding, Jianwen; Liu, Junfeng

2016-01-01

Highlights: • Hexagonal silicene rings possess unusually large diamagnetic moments. • The magnetic-field-driven spin-up electrons flow anticlockwise and spin-down electrons flow clockwise along the rings. • The large diamagnetic moment is the result of competition of spin-up and spin-down electrons. - Abstract: Hexagonal silicene rings with unusually large diamagnetic moments have been found in a theoretical study of the electronic and magnetic properties. In the presence of effective spin–orbit coupling, the magnetic-field-driven spin-up electrons flow anticlockwise exhibiting colossal diamagnetic moments, while the spin-down electrons flow clockwise exhibiting colossal paramagnetic moments along the rings. The large diamagnetic moment is thus the result of competition of spin-up and spin-down electrons, which can be modulated by spin–orbit coupling strength and exchange field.

Diamagnetic response in zigzag hexagonal silicene rings

Energy Technology Data Exchange (ETDEWEB)

Xu, Ning, E-mail: nxu@ycit.cn [Department of Physics, Yancheng Institute of Technology, Yancheng 224051 (China); Chen, Qiao [Department of Physics, Hunan Institute of Engineering, Xiangtan 411104 (China); Tian, Hongyu [Department of Physics, Yancheng Institute of Technology, Yancheng 224051 (China); Ding, Jianwen [Department of Physics, Xiangtan University, Xiangtan 411105 (China); Liu, Junfeng, E-mail: liu.jf@sustc.edu.cn [Department of Physics, South University of Science and Technology of China, Shenzhen 518055 (China)

2016-09-16

Highlights: • Hexagonal silicene rings possess unusually large diamagnetic moments. • The magnetic-field-driven spin-up electrons flow anticlockwise and spin-down electrons flow clockwise along the rings. • The large diamagnetic moment is the result of competition of spin-up and spin-down electrons. - Abstract: Hexagonal silicene rings with unusually large diamagnetic moments have been found in a theoretical study of the electronic and magnetic properties. In the presence of effective spin–orbit coupling, the magnetic-field-driven spin-up electrons flow anticlockwise exhibiting colossal diamagnetic moments, while the spin-down electrons flow clockwise exhibiting colossal paramagnetic moments along the rings. The large diamagnetic moment is thus the result of competition of spin-up and spin-down electrons, which can be modulated by spin–orbit coupling strength and exchange field.

Analysis of the role of the low threshold currents IT and Ih in intrinsic delta oscillations of thalamocortical neurons

Directory of Open Access Journals (Sweden)

Yimy eAmarillo

2015-05-01

Full Text Available Thalamocortical neurons are involved in the generation and maintenance of brain rhythms associated with global functional states. The repetitive burst firing of TC neurons at delta frequencies (1-4 Hz has been linked to the oscillations recorded during deep sleep and during episodes of absence seizures. To get insight into the biophysical properties that are the basis for intrinsic delta oscillations in these neurons, we performed a bifurcation analysis of a minimal conductance-based thalamocortical neuron model including only the IT channel and the sodium and potassium leak channels. This analysis unveils the dynamics of repetitive burst firing of TC neurons, and describes how the interplay between the amplifying variable mT and the recovering variable hT of the calcium channel IT is sufficient to generate low threshold oscillations in the delta band. We also explored the role of the hyperpolarization activated cationic current Ih in this reduced model and determine that, albeit not required, Ih amplifies and stabilizes the oscillation.

A method based on IHS cylindrical transform model for quality assessment of image fusion

Science.gov (United States)

Zhu, Xiaokun; Jia, Yonghong

2005-10-01

Image fusion technique has been widely applied to remote sensing image analysis and processing, and methods for quality assessment of image fusion in remote sensing have also become the research issues at home and abroad. Traditional assessment methods combine calculation of quantitative indexes and visual interpretation to compare fused images quantificationally and qualitatively. However, in the existing assessment methods, there are two defects: on one hand, most imdexes lack the theoretic support to compare different fusion methods. On the hand, there is not a uniform preference for most of the quantitative assessment indexes when they are applied to estimate the fusion effects. That is, the spatial resolution and spectral feature could not be analyzed synchronously by these indexes and there is not a general method to unify the spatial and spectral feature assessment. So in this paper, on the basis of the approximate general model of four traditional fusion methods, including Intensity Hue Saturation(IHS) triangle transform fusion, High Pass Filter(HPF) fusion, Principal Component Analysis(PCA) fusion, Wavelet Transform(WT) fusion, a correlation coefficient assessment method based on IHS cylindrical transform is proposed. By experiments, this method can not only get the evaluation results of spatial and spectral features on the basis of uniform preference, but also can acquire the comparison between fusion image sources and fused images, and acquire differences among fusion methods. Compared with the traditional assessment methods, the new methods is more intuitionistic, and in accord with subjective estimation.

Thermal conductivity of hexagonal Si, Ge, and Si1-xGex alloys from first-principles

Science.gov (United States)

Gu, Xiaokun; Zhao, C. Y.

2018-05-01

Hexagonal Si and Ge with a lonsdaleite crystal structure are allotropes of silicon and germanium that have recently been synthesized. These materials as well as their alloys are promising candidates for novel applications in optoelectronics. In this paper, we systematically study the phonon transport and thermal conductivity of hexagonal Si, Ge, and their alloys by using the first-principle-based Peierls-Boltzmann transport equation approach. Both three-phonon and four-phonon scatterings are taken into account in the calculations as the phonon scattering mechanisms. The thermal conductivity anisotropy of these materials is identified. While the thermal conductivity parallel to the hexagonal plane for hexagonal Si and Ge is found to be larger than that perpendicular to the hexagonal plane, alloying effectively tunes the thermal conductivity anisotropy by suppressing the thermal conductivity contributions from the middle-frequency phonons. The importance of four-phonon scatterings is assessed by comparing the results with the calculations without including four-phonon scatterings. We find that four-phonon scatterings cannot be ignored in hexagonal Si and Ge as the thermal conductivity would be overestimated by around 10% (40%) at 300 K (900) K. In addition, the phonon mean free path distribution of hexagonal Si, Ge, and their alloys is also discussed.

On the buckling of hexagonal boron nitride nanoribbons via structural mechanics

Science.gov (United States)

Giannopoulos, Georgios I.

2018-03-01

Monolayer hexagonal boron nitride nanoribbons have similar crystal structure as graphene nanoribbons, have excellent mechanical, thermal insulating and dielectric properties and additionally present chemical stability. These allotropes of boron nitride can be used in novel applications, in which graphene is not compatible, to achieve remarkable performance. The purpose of the present work is to provide theoretical estimations regarding the buckling response of hexagonal boron nitride monolayer under compressive axial loadings. For this reason, a structural mechanics method is formulated which employs the exact equilibrium atomistic structure of the specific two-dimensional nanomaterial. In order to represent the interatomic interactions appearing between boron and nitrogen atoms, the Dreiding potential model is adopted which is realized by the use of three-dimensional, two-noded, spring-like finite elements of appropriate stiffness matrices. The critical compressive loads that cause the buckling of hexagonal boron nitride nanoribbons are computed with respect to their size and chirality while some indicative buckled shapes of them are illustrated. Important conclusions arise regarding the effect of the size and chirality on the structural stability of the hexagonal boron nitride monolayers. An analytical buckling formula, which provides good fitting of the numerical outcome, is proposed.

Ice formation in altocumulus clouds over Leipzig: Remote sensing measurements and detailed model simulations

Science.gov (United States)

Simmel, Martin; Bühl, Johannes; Ansmann, Albert; Tegen, Ina

2014-05-01

Over Leipzig, altocumulus clouds are frequently observed using a suite of remote sensing instruments. These observations cover a wide range of heights, temperatures, and microphysical properties of the clouds ranging from purely liquid to heavily frozen. For the current study, two cases were chosen to test the sensitivity of these clouds with respect to several microphysical and dynamical parameters such as aerosol properties (CCN, IN), ice particle shape as well as turbulence. The mixed-phase spectral microphysical model SPECS was coupled to a dynamical model of the Asai-Kasahara type resulting in the model system AK-SPECS. The relatively simple dynamics allows for a fine vertical resolution needed for the rather shallow cloud layers observed. Additionally, the proper description of hydrometeor sedimentation is important especially for the fast growing ice crystals to realistically capture their interaction with the vapour and liquid phase (Bergeron-Findeisen process). Since the focus is on the cloud microphysics, the dynamics in terms of vertical velocity profile is prescribed for the model runs and the feedback of the microphysics on dynamics by release or consumption of latent heat due to phase transfer is not taken into account. The microphysics focuses on (1) ice particle shape allowing hexagonal plates and columns with size-dependant axis ratios and (2) the ice nuclei (IN) budget realized with a prognostic temperature resolved field of potential IN allowing immersion freezing only when active IN and supercooled drops above a certain size threshold are present within a grid cell. Sensitivity studies show for both cases that ice particle shape seems to have the major influence on ice mass formation under otherwise identical conditions. This is due to the effect (1) on terminal fall velocity of the individual ice particle allowing for longer presence times in conditions supersaturated with respect to ice and (2) on water vapour deposition which is enhanced due

Hydrothermal synthesis and magneto-optical properties of Ni-doped ZnO hexagonal columns

International Nuclear Information System (INIS)

Xu, Xingyan; Cao, Chuanbao

2015-01-01

Single crystal Zn 1−x Ni x O (x=0, 0.02, 0.04, 0.06) hexagonal columns have been synthesized by a simple hydrothermal route. The hexagonal columns of the products are about 3 μm in diameter and about 2 μm in thickness. X-ray diffraction (XRD), Ni K-edge XANES spectra and TEM indicate that the as-prepared samples are single-crystalline wurtzite structure and no metallic Ni or other secondary phases are found in the hexagonal columns. Optical absorption and Raman results further confirm the incorporation of Ni 2+ ions in the ZnO lattice. Magnetic measurements indicate that the Zn 1−x Ni x O hexagonal columns exhibited obvious ferromagnetic characteristic at room temperature. The coercive fields (H c ) were obtained to be 135.3, 327.79 and 127.29 Oe for x=0.02, 0.04 and 0.06, respectively. The ferromagnetism was assumed to originate from the exchange interaction between free carriers (holes or electrons) from the valence band and the localized d spins on the Ni ions. - Highlights: • Single crystal Zn 1−x Ni x O (x=0, 0.02, 0.04, 0.06) hexagonal columns were synthesized by a simple hydrothermal method. • The layer-by-layer growth manner of the Zn 1−x Ni x O hexagonal columns was proposed. • Obvious room-temperature ferromagnetic characteristic of Zn 1−x Ni x O are observed and the coercivity (H c ) are 135.3,327.79 and 127.29 Oe for x=0.02, 0.04 and 0.06, respectively. • The exchange interaction between local-spin polarized electrons and conduction electrons is responsible for the room-temperature ferromagnetism in the Zn 1−x Ni x O hexagonal columns

Ice, Ice, Baby!

Science.gov (United States)

Hamilton, C.

2008-12-01

The Center for Remote Sensing of Ice Sheets (CReSIS) has developed an outreach program based on hands-on activities called "Ice, Ice, Baby". These lessons are designed to teach the science principles of displacement, forces of motion, density, and states of matter. These properties are easily taught through the interesting topics of glaciers, icebergs, and sea level rise in K-8 classrooms. The activities are fun, engaging, and simple enough to be used at science fairs and family science nights. Students who have participated in "Ice, Ice, Baby" have successfully taught these to adults and students at informal events. The lessons are based on education standards which are available on our website www.cresis.ku.edu. This presentation will provide information on the activities, survey results from teachers who have used the material, and other suggested material that can be used before and after the activities.

Efficient Offline Waveform Design Using Quincunx/Hexagonal Time-Frequency Lattices

Directory of Open Access Journals (Sweden)

Raouia Ayadi

2017-01-01

Full Text Available Conventional orthogonal frequency division multiplexing (OFDM may turn to be inappropriate for future wireless cellular systems services, because of extreme natural and artificial impairments they are expected to generate. Natural impairments result from higher Doppler and delay spreads, while artificial impairments result from multisource transmissions and synchronization relaxation for closed-loop signaling overhead reduction. These severe impairments induce a dramatic loss in orthogonality between subcarriers and OFDM symbols and lead to a strong increase in intercarrier interference (ICI and intersymbol interference (ISI. To fight against these impairments, we propose here an optimization of the transmit/receive waveforms for filter-bank multicarrier (FBMC systems, with hexagonal time-frequency (TF lattices, operating over severe doubly dispersive channels. For this, we exploit the Ping-pong Optimized Pulse Shaping (POPS paradigm, recently applied to rectangular TF lattices, to design waveforms maximizing the signal-to-interference-plus-noise ratio (SINR for hexagonal TF lattices. We show that FBMC, with hexagonal lattices, offers a strong improvement in SINR with respect to conventional OFDM and an improvement of around 1 dB with respect to POPS-FBMC, with rectangular lattices. Furthermore, we show that hexagonal POPS-FBMC brings more robustness to frequency synchronization errors and offers a 10 dB reduction in out-of-band (OOB emissions, with respect to rectangular POPS-FBMC.

Adiabatic demagnetization of the antiferromagnetic spin-1/2 Heisenberg hexagonal cluster

International Nuclear Information System (INIS)

Deb, Moumita; Ghosh, Asim Kumar

2016-01-01

Exact analytic expressions of eigenvalues of the antiferromagnetic spin-1/2 Heisenberg hexagon in the presence of uniform magnetic field have been obtained. Magnetization process, nature of isentrops and properties of magneto caloric effect in terms of adiabatic demagnetization have been investigated. Theoretical results have been used to study the magneto caloric effect of the spin-1/2 Heisenberg hexagonal compound Cu_3WO_6.

Preparation of triangular and hexagonal silver nanoplates on the surface of quartz substrate

International Nuclear Information System (INIS)

Jia Huiying; Zeng Jianbo; An Jing; Song Wei; Xu Weiqing; Zhao Bing

2008-01-01

In this paper, triangular and hexagonal silver nanoplates were prepared on the surface of quartz substrate using photoreduction of silver ions in the presence of silver seeds. The obtained silver nanoplates were characterized by atomic force microscopy and UV-vis spectroscopy. It was found that the silver seeds played an important role in the formation of triangular and hexagonal silver nanoplates. By varying the irradiation time, nanoplates with different sizes and shapes could be obtained. The growth mechanism for triangular and hexagonal nanoplates prepared on quartz substrate was discussed

Epitaxial Garnets and Hexagonal Ferrites.

Science.gov (United States)

1982-04-20

guide growth of the epitaxial YIG films. Aluminum or gallium substitu- tions for iron were used in combination with lanthanum substitutions for yttrium... gallate spinel sub- strates. There was no difficulty with nucleation in the melt and film quality appeared to be similar to that observed previously...hexagonal ferrites. We succeeded in growing the M-type lead hexaferrite (magnetoplumbite) on gallate spinel substrates. We found that the PbO-based

Electronic properties of Mn-decorated silicene on hexagonal boron nitride

KAUST Repository

Kaloni, Thaneshwor P.; Gangopadhyay, S.; Jones, Burton; Schwingenschlö gl, Udo; Singh, Nirpendra

2013-01-01

We study silicene on hexagonal boron nitride, using first-principles calculations. Since hexagonal boron nitride is semiconducting, the interaction with silicene is weaker than for metallic substrates. It therefore is possible to open a 50 meV band gap in the silicene. We further address the effect of Mn decoration by determining the onsite Hubbard interaction parameter, which turns out to differ significantly for decoration at the top and hollow sites. The induced magnetism in the system is analyzed in detail.

Electronic properties of Mn-decorated silicene on hexagonal boron nitride

KAUST Repository

Kaloni, Thaneshwor P.

2013-12-17

We study silicene on hexagonal boron nitride, using first-principles calculations. Since hexagonal boron nitride is semiconducting, the interaction with silicene is weaker than for metallic substrates. It therefore is possible to open a 50 meV band gap in the silicene. We further address the effect of Mn decoration by determining the onsite Hubbard interaction parameter, which turns out to differ significantly for decoration at the top and hollow sites. The induced magnetism in the system is analyzed in detail.

Thermal stability of hexagonal OsB2

International Nuclear Information System (INIS)

Xie, Zhilin; Blair, Richard G.; Orlovskaya, Nina; Cullen, David A.; Andrew Payzant, E.

2014-01-01

The synthesis of novel hexagonal ReB 2 -type OsB 2 ceramic powder was performed by high energy ball milling of elemental Os and B powders. Two different sources of B powder have been used for this mechanochemical synthesis. One B powder consisted of a mixture of amorphous and crystalline phases and a mixture of 10 B and 11 B isotopes with a fine particle size, while another B powder was a purely crystalline (rhombohedral) material consisting of enriched 11 B isotope with coarse particle size. The same Os powder was used for the synthesis in both cases. It was established that, in the first case, the hexagonal OsB 2 phase was the main product of synthesis with a small quantity of Os 2 B 3 phase present after synthesis as an intermediate product. In the second case, where coarse crystalline 11 B powder was used as a raw material, only Os 2 B 3 boride was synthesized mechanochemically. The thermal stability of hexagonal OsB 2 powder was studied by heating under argon up to 876 °C and cooling in vacuo down to −225 °C. During the heating, the sacrificial reaction 2OsB 2 +3O 2 →2Os+2B 2 O 3 took place due to presence of O 2 /water vapor molecules in the heating chamber, resulting in the oxidation of B atoms and formation of B 2 O 3 and precipitation of Os metal out of the OsB 2 lattice. As a result of such phase changes during heating, the lattice parameters of hexagonal OsB 2 changed significantly. The shrinkage of the a lattice parameter was recorded in 276–426 °C temperature range upon heating, which was attributed to the removal of B atoms from the OsB 2 lattice due to oxidation followed by the precipitation of Os atoms and formation of Os metal. While significant structural changes occurred upon heating due to presence of O 2 , the hexagonal OsB 2 ceramic demonstrated good phase stability upon cooling in vacuo with linear shrinkage of the lattice parameters and no phase changes detected during cooling. - Graphical abstract: The in situ high temperature XRD

Sea ice - Multiyear cycles and white ice

Science.gov (United States)

Ledley, T. S.

1985-01-01

The multiyear thickness cycles represent one of the interesting features of the sea ice studies performed by Semtner (1976) and Washington et al. (1976) with simple thermodynamic models of sea ice. In the present article, a description is given of results which show that the insulating effect of snow on the surface of the sea ice is important in producing these multiyear cycles given the physics included in the model. However, when the formation of white ice is included, the cycles almost disappear. White ice is the ice which forms at the snow-ice interface when the snow layer becomes thick enough to depress the ice below the water level. Water infiltrates the snow by coming through the ice at leads and generally freezes there, forming white ice.

Pressure-induced structural change from hexagonal to fcc metal lattice in scandium trihydride

International Nuclear Information System (INIS)

Ohmura, A.; Machida, A.; Watanuki, T.; Aoki, K.; Nakano, S.; Takemura, K.

2007-01-01

We synthesized scandium hydrides by hydrogenation of a scandium foil with hydrogen fluid under high pressure at ambient temperature. Scandium dihydride (ScH 2 ) and trihydride (ScH 3 ) were prepared near 4 and 5 GPa, respectively. The hydrogenation process and pressure-induced structural changes in ScH 3 were investigated by synchrotron radiation X-ray diffraction measurements up to 54.7 GPa. A structural transition from hexagonal to the fcc lattice began at 30 GPa and was completed at 46 GPa via an intermediate state similar to those reported for other hexagonal trihydrides. The intermediate state was not interpreted in terms of a coexisting state for the low-pressure hexagonal and the high-pressure fcc structures. The onset transition pressure of ScH 3 supported the previously proposed relation that the hexagonal-fcc transition pressure is inversely proportional to the ionic radius of the trihydride

Substrate Integrated Waveguide Cross-Coupling Filter with Multilayer Hexagonal Cavity

Directory of Open Access Journals (Sweden)

B. Wu

2013-01-01

Full Text Available Hexagonal cavities and their applications to multilayer substrate integrated waveguide (SIW filters are presented. The hexagonal SIW cavity which can combine flexibility of rectangular one and performance of circular one is convenient for bandpass filter’s design. Three types of experimental configuration with the same central frequency of 10 GHz and bandwidth of 6%, including three-order and four-order cross-coupling topologies, are constructed and fabricated based on low temperature cofired ceramic (LTCC technology. Both theoretical and experimental results are presented.

Micromolding in inverted polymer opals (MIPO): synthesis of hexagonal mesoporous silica opals

Energy Technology Data Exchange (ETDEWEB)

Yang Sanming; Coombs, N.; Ozin, G.A. [Toronto Univ., Ont. (Canada). Materials Chemistry Research Group

2000-12-15

Regular arrays of hexagonal mesoporous silica spheres are crucial for a number of applications, but until now control of the diameter, dispersity, and packing of the spheres has not proved possible. These authors report a new method-micromolding in inverted polymer opals-that allows the synthesis of such hexagonal mesoporous silica opals for the first time. (orig.)

Molecular interactions with ice: Molecular embedding, adsorption, detection, and release

Energy Technology Data Exchange (ETDEWEB)

Gibson, K. D.; Langlois, Grant G.; Li, Wenxin; Sibener, S. J., E-mail: s-sibener@uchicago.edu [The James Franck Institute and Department of Chemistry, The University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637 (United States); Killelea, Daniel R. [Department of Chemistry and Biochemistry, Loyola University Chicago, 1068 W. Sheridan Ave., Chicago, Illinois 60660 (United States)

2014-11-14

The interaction of atomic and molecular species with water and ice is of fundamental importance for chemistry. In a previous series of publications, we demonstrated that translational energy activates the embedding of Xe and Kr atoms in the near surface region of ice surfaces. In this paper, we show that inert molecular species may be absorbed in a similar fashion. We also revisit Xe embedding, and further probe the nature of the absorption into the selvedge. CF{sub 4} molecules with high translational energies (≥3 eV) were observed to embed in amorphous solid water. Just as with Xe, the initial adsorption rate is strongly activated by translational energy, but the CF{sub 4} embedding probability is much less than for Xe. In addition, a larger molecule, SF{sub 6}, did not embed at the same translational energies that both CF{sub 4} and Xe embedded. The embedding rate for a given energy thus goes in the order Xe > CF{sub 4} > SF{sub 6}. We do not have as much data for Kr, but it appears to have a rate that is between that of Xe and CF{sub 4}. Tentatively, this order suggests that for Xe and CF{sub 4}, which have similar van der Waals radii, the momentum is the key factor in determining whether the incident atom or molecule can penetrate deeply enough below the surface to embed. The more massive SF{sub 6} molecule also has a larger van der Waals radius, which appears to prevent it from stably embedding in the selvedge. We also determined that the maximum depth of embedding is less than the equivalent of four layers of hexagonal ice, while some of the atoms just below the ice surface can escape before ice desorption begins. These results show that energetic ballistic embedding in ice is a general phenomenon, and represents a significant new channel by which incident species can be trapped under conditions where they would otherwise not be bound stably as surface adsorbates. These findings have implications for many fields including environmental science, trace gas

Femtosecond laser direct writing of monocrystalline hexagonal silver prisms

Energy Technology Data Exchange (ETDEWEB)

Vora, Kevin; Kang, SeungYeon; Moebius, Michael [School of Engineering and Applied Sciences, Harvard University, 9 Oxford Street, Cambridge, Massachusetts 02138 (United States); Mazur, Eric [School of Engineering and Applied Sciences, Harvard University, 9 Oxford Street, Cambridge, Massachusetts 02138 (United States); Department of Physics, Harvard University, 9 Oxford Street, Cambridge, Massachusetts 02138 (United States)

2014-10-06

Bottom-up growth methods and top-down patterning techniques are both used to fabricate metal nanostructures, each with a distinct advantage: One creates crystalline structures and the other offers precise positioning. Here, we present a technique that localizes the growth of metal crystals to the focal volume of a laser beam, combining advantages from both approaches. We report the fabrication of silver nanoprisms—hexagonal nanoscale silver crystals—through irradiation with focused femtosecond laser pulses. The growth of these nanoprisms is due to a nonlinear optical interaction between femtosecond laser pulses and a polyvinylpyrrolidone film doped with silver nitrate. The hexagonal nanoprisms have bases hundreds of nanometers in size and the crystal growth occurs over exposure times of less than 1 ms (8 orders of magnitude faster than traditional chemical techniques). Electron backscatter diffraction analysis shows that the hexagonal nanoprisms are monocrystalline. The fabrication method combines advantages from both wet chemistry and femtosecond laser direct-writing to grow silver crystals in targeted locations. The results presented in this letter offer an approach to directly positioning and growing silver crystals on a substrate, which can be used for plasmonic devices.

Femtosecond laser direct writing of monocrystalline hexagonal silver prisms

International Nuclear Information System (INIS)

Vora, Kevin; Kang, SeungYeon; Moebius, Michael; Mazur, Eric

2014-01-01

Bottom-up growth methods and top-down patterning techniques are both used to fabricate metal nanostructures, each with a distinct advantage: One creates crystalline structures and the other offers precise positioning. Here, we present a technique that localizes the growth of metal crystals to the focal volume of a laser beam, combining advantages from both approaches. We report the fabrication of silver nanoprisms—hexagonal nanoscale silver crystals—through irradiation with focused femtosecond laser pulses. The growth of these nanoprisms is due to a nonlinear optical interaction between femtosecond laser pulses and a polyvinylpyrrolidone film doped with silver nitrate. The hexagonal nanoprisms have bases hundreds of nanometers in size and the crystal growth occurs over exposure times of less than 1 ms (8 orders of magnitude faster than traditional chemical techniques). Electron backscatter diffraction analysis shows that the hexagonal nanoprisms are monocrystalline. The fabrication method combines advantages from both wet chemistry and femtosecond laser direct-writing to grow silver crystals in targeted locations. The results presented in this letter offer an approach to directly positioning and growing silver crystals on a substrate, which can be used for plasmonic devices.

Survival and failure modes: platform-switching for internal and external hexagon cemented fixed dental prostheses.

Science.gov (United States)

Anchieta, Rodolfo B; Machado, Lucas S; Hirata, Ronaldo; Coelho, Paulo G; Bonfante, Estevam A

2016-10-01

This study evaluated the probability of survival (reliability) of platform-switched fixed dental prostheses (FDPs) cemented on different implant-abutment connection designs. Eighty-four-three-unit FDPs (molar pontic) were cemented on abutments connected to two implants of external or internal hexagon connection. Four groups (n = 21 each) were established: external hexagon connection and regular platform (ERC); external hexagon connection and switched platform (ESC); internal hexagon and regular platform (IRC); and internal hexagon and switched platform (ISC). Prostheses were subjected to step-stress accelerated life testing in water. Weibull curves and probability of survival for a mission of 100,000 cycles at 400 N (two-sided 90% CI) were calculated. The beta values of 0.22, 0.48, 0.50, and 1.25 for groups ERC, ESC, IRC, and ISC, respectively, indicated a limited role of fatigue in damage accumulation, except for group ISC. Survival decreased for both platform-switched groups (ESC: 74%, and ISC: 59%) compared with the regular matching platform counterparts (ERC: 95%, and IRC: 98%). Characteristic strength was higher only for ERC compared with ESC, but not different between internal connections. Failures chiefly involved the abutment screw. Platform switching decreased the probability of survival of FDPs on both external and internal connections. The absence in loss of characteristic strength observed in internal hexagon connections favor their use compared with platform-switched external hexagon connections. © 2016 Eur J Oral Sci.

Ice and ocean velocity in the Arctic marginal ice zone: Ice roughness and momentum transfer

Directory of Open Access Journals (Sweden)

Sylvia T. Cole

2017-09-01

Full Text Available The interplay between sea ice concentration, sea ice roughness, ocean stratification, and momentum transfer to the ice and ocean is subject to seasonal and decadal variations that are crucial to understanding the present and future air-ice-ocean system in the Arctic. In this study, continuous observations in the Canada Basin from March through December 2014 were used to investigate spatial differences and temporal changes in under-ice roughness and momentum transfer as the ice cover evolved seasonally. Observations of wind, ice, and ocean properties from four clusters of drifting instrument systems were complemented by direct drill-hole measurements and instrumented overhead flights by NASA operation IceBridge in March, as well as satellite remote sensing imagery about the instrument clusters. Spatially, directly estimated ice-ocean drag coefficients varied by a factor of three with rougher ice associated with smaller multi-year ice floe sizes embedded within the first-year-ice/multi-year-ice conglomerate. Temporal differences in the ice-ocean drag coefficient of 20–30% were observed prior to the mixed layer shoaling in summer and were associated with ice concentrations falling below 100%. The ice-ocean drag coefficient parameterization was found to be invalid in September with low ice concentrations and small ice floe sizes. Maximum momentum transfer to the ice occurred for moderate ice concentrations, and transfer to the ocean for the lowest ice concentrations and shallowest stratification. Wind work and ocean work on the ice were the dominant terms in the kinetic energy budget of the ice throughout the melt season, consistent with free drift conditions. Overall, ice topography, ice concentration, and the shallow summer mixed layer all influenced mixed layer currents and the transfer of momentum within the air-ice-ocean system. The observed changes in momentum transfer show that care must be taken to determine appropriate parameterizations

Ice cream structure modification by ice-binding proteins.

Science.gov (United States)

Kaleda, Aleksei; Tsanev, Robert; Klesment, Tiina; Vilu, Raivo; Laos, Katrin

2018-04-25

Ice-binding proteins (IBPs), also known as antifreeze proteins, were added to ice cream to investigate their effect on structure and texture. Ice recrystallization inhibition was assessed in the ice cream mixes using a novel accelerated microscope assay and the ice cream microstructure was studied using an ice crystal dispersion method. It was found that adding recombinantly produced fish type III IBPs at a concentration 3 mg·L -1 made ice cream hard and crystalline with improved shape preservation during melting. Ice creams made with IBPs (both from winter rye, and type III IBP) had aggregates of ice crystals that entrapped pockets of the ice cream mixture in a rigid network. Larger individual ice crystals and no entrapment in control ice creams was observed. Based on these results a model of ice crystals aggregates formation in the presence of IBPs was proposed. Copyright © 2017 Elsevier Ltd. All rights reserved.

Ice Sheets & Ice Cores

DEFF Research Database (Denmark)

Mikkelsen, Troels Bøgeholm

Since the discovery of the Ice Ages it has been evident that Earth’s climate is liable to undergo dramatic changes. The previous climatic period known as the Last Glacial saw large oscillations in the extent of ice sheets covering the Northern hemisphere. Understanding these oscillations known....... The first part concerns time series analysis of ice core data obtained from the Greenland Ice Sheet. We analyze parts of the time series where DO-events occur using the so-called transfer operator and compare the results with time series from a simple model capable of switching by either undergoing...

Eulerian Method for Ice Crystal Icing

NARCIS (Netherlands)

Norde, Ellen; van der Weide, Edwin Theodorus Antonius; Hoeijmakers, Hendrik Willem Marie

In this study, an ice accretion method aimed at ice crystal icing in turbofan engines is developed and demonstrated for glaciated as well as mixed-phase icing conditions. The particle trajectories are computed by an Eulerian trajectory method. The effects of heat transfer and phase change on the

Design of a broadband hexagonal-shaped zeroth-order resonance antenna with metamaterials

Energy Technology Data Exchange (ETDEWEB)

Woo, Dong Sik; Kim, Kang Wook; Choi, Hyun Chul [Kyungpook National University, Daegu (Korea, Republic of)

2014-11-15

A broadband hexagonal-shaped metamaterials (MTMs)-based zeroth-order resonant (ZOR) antenna was designed and fabricated. The hexagonal shape of a top patch on a mushroom structure makes not only direct-current paths between the two ends of the patch but also round-current paths along the outside of the patch, thereby widening the resonance frequency of the mushroom MTM antenna. According to the shape of the hexagon patch, the presented antenna achieved impedance bandwidth of 58.6% corresponding to ultra-wideband technology. The proposed ZOR antenna was modeled by utilizing a composite right- and left-handed (CRLH) transmission line and provided 4 to 9.3 dBi of the antenna gain with reduced size as compared to conventional microstrip antennas at Ku- to K-band frequencies.

Experimental provocation of 'ice-cream headache' by ice cubes and ice water.

Science.gov (United States)

Mages, Stephan; Hensel, Ole; Zierz, Antonia Maria; Kraya, Torsten; Zierz, Stephan

2017-04-01

Background There are various studies on experimentally provoked 'ice-cream headache' or 'headache attributed to ingestion or inhalation of a cold stimulus' (HICS) using different provocation protocols. The aim of this study was to compare two provocation protocols. Methods Ice cubes pressed to the palate and fast ingestion of ice water were used to provoke HICS and clinical features were compared. Results The ice-water stimulus provoked HICS significantly more often than the ice-cube stimulus (9/77 vs. 39/77). Ice-water-provoked HICS had a significantly shorter latency (median 15 s, range 4-97 s vs. median 68 s, range 27-96 s). There was no difference in pain localisation. Character after ice-cube stimulation was predominantly described as pressing and after ice-water stimulation as stabbing. A second HICS followed in 10/39 (26%) of the headaches provoked by ice water. Lacrimation occurred significantly more often in volunteers with than in those without HICS. Discussion HICS provoked by ice water was more frequent, had a shorter latency, different pain character and higher pain intensity than HICS provoked by ice cubes. The finding of two subsequent HICS attacks in the same volunteers supports the notion that two types of HICS exist. Lacrimation during HICS indicates involvement of the trigeminal-autonomic reflex.

Van der Waals epitaxy and photoresponse of hexagonal tellurium nanoplates on flexible mica sheets.

Science.gov (United States)

Wang, Qisheng; Safdar, Muhammad; Xu, Kai; Mirza, Misbah; Wang, Zhenxing; He, Jun

2014-07-22

Van der Waals epitaxy (vdWE) is of great interest due to its extensive applications in the synthesis of ultrathin two-dimensional (2D) layered materials. However, vdWE of nonlayered functional materials is still not very well documented. Here, although tellurium has a strong tendency to grow into one-dimensional nanoarchitecture due to its chain-like structure, we successfully realize 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. Chemically inert mica surface is found to be crucial for the lateral growth of hexagonal tellurium nanoplates since it (1) facilitates the migration of tellurium adatoms along mica surface and (2) allows a large lattice mismatch. Furthermore, 2D tellurium hexagonal nanoplates-based photodetectors are in situ fabricated on flexible mica sheets. Efficient photoresponse is obtained even after bending the device for 100 times, indicating 2D tellurium hexagonal nanoplates-based photodetectors on mica sheets have a great application potential in flexible and wearable optoelectronic devices. We believe the fundamental understanding of vdWE effect on the growth of 2D tellurium hexagonal nanoplate can pave the way toward leveraging vdWE as a useful channel to realize the 2D geometry of other nonlayered materials.

Thermal performance analysis of optimized hexagonal finned heat sinks in impinging air jet

Energy Technology Data Exchange (ETDEWEB)

Yakut, Kenan, E-mail: kyakut@atauni.edu.tr [Department of Mechanical Engineering, Faculty of Engineering, Atatürk University, 25100, Erzurum (Turkey); Yeşildal, Faruk, E-mail: fayesildal@agri.edu.tr [Department of Mechanical Engineering, Faculty of Patnos Sultan Alparslan Natural Sciences and Engineering, Ağrı İbrahim Çeçen University, 04100, Ağrı (Turkey); Karabey, Altuğ, E-mail: akarabey@yyu.edu.tr [Department of Machinery and Metal Technology, Erciş Vocational High School, Yüzüncü Yıl University, 65400, Van (Turkey); Yakut, Rıdvan, E-mail: ryakut@kafkas.edu.tr [Department of Mechanical Engineering, Faculty of Engineering and Architecture, Kafkas University, 36100, Kars (Turkey)

2016-04-18

In this study, thermal performance analysis of hexagonal finned heat sinks which optimized according to the experimental design and optimization method of Taguchi were investigated. Experiments of air jet impingement on heated hexagonal finned heat sinks were carried out adhering to the L{sub 18}(2{sup 1*}3{sup 6}) orthogonal array test plan. Optimum geometries were determined and named OH-1, OH-2. Enhancement efficiency with the first law of thermodynamics was analyzed for optimized heat sinks with 100, 150, 200 mm heights of hexagonal fin. Nusselt correlations were found out and variations of enhancement efficiency with Reynolds number presented in η–Re graphics.

Magnetic ground state of the multiferroic hexagonal LuFe O3

Science.gov (United States)

Suresh, Pittala; Vijaya Laxmi, K.; Bera, A. K.; Yusuf, S. M.; Chittari, Bheema Lingam; Jung, Jeil; Anil Kumar, P. S.

2018-05-01

The structural, electric, and magnetic properties of bulk hexagonal LuFe O3 are investigated. Single phase hexagonal LuFe O3 has been successfully stabilized in the bulk form without any doping by sol-gel method. The hexagonal crystal structure with P 63c m space group has been confirmed by x-ray-diffraction, neutron-diffraction, and Raman spectroscopy study at room temperature. Neutron diffraction confirms the hexagonal phase of LuFe O3 persists down to 6 K. Further, the x-ray photoelectron spectroscopy established the 3+ oxidation state of Fe ions. The temperature-dependent magnetic dc susceptibility, specific heat, and neutron-diffraction studies confirm an antiferromagnetic ordering below the Néel temperature (TN)˜130 K . Analysis of magnetic neutron-diffraction patterns reveals an in-plane (a b -plane) 120∘ antiferromagnetic structure, characterized by a propagation vector k =(0 0 0 ) with an ordered moment of 2.84 μB/F e3 + at 6 K. The 120∘ antifferomagnetic ordering is further confirmed by spin-orbit coupling density functional theory calculations. The on-site coulomb interaction (U ) and Hund's parameter (JH) on Fe atoms reproduced the neutron-diffraction Γ1 spin pattern among the Fe atoms. P -E loop measurements at room temperature confirm an intrinsic ferroelectricity of the sample with remnant polarization Pr˜0.18 μ C /c m2 . A clear anomaly in the dielectric data is observed at ˜TN revealing the presence of magnetoelectric coupling. A change in the lattice constants at TN has also been found, indicating the presence of a strong magnetoelastic coupling. Thus a coupling between lattice, electric, and magnetic degrees of freedom is established in bulk hexagonal LuFe O3 .

Facile synthesis and characterization of hexagonal NbSe2 nanoplates

International Nuclear Information System (INIS)

Zhang, Xianghua; Zhang, Du; Tang, Hua; Ji, Xiaorui; Zhang, Yi; Tang, Guogang; Li, Changsheng

2014-01-01

Graphical abstract: - Highlights: • Uniform hexagonal NbSe 2 nanoplates were prepared by a simple solid state reaction. • The possible formation mechanism of the NbSe 2 nanoplates was discussed. • The formation of NbSe 2 nanoplates undergoes a series of phase transition. - Abstract: The NbSe 2 nanoplates with hexagonal morphology have been successfully prepared by a facile, environmentally friendly reaction in closed reactor at moderate temperature. The thermal (750 °C) solid-state reaction between the ball-milled mixture of micro-sized Nb and Se yielded a high yield of NbSe 2 nanoplates. The as-prepared products were characterized by XRD, EDS, and SEM. The results showed that the as-prepared products were hexagonal phase NbSe 2 nanoplates with uniform sizes and the formation of NbSe 2 nanoplates underwent a series of phase transition. On the basis of experimental results obtained at different temperatures, a reasonable reaction process and a formation mechanism were proposed. Moreover, the ball milling time played a crucial role in acquiring the homogeneous distribution nanoplates

Ice flow Modelling of the Greenland Ice Sheet

DEFF Research Database (Denmark)

Nielsen, Lisbeth Tangaa

Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others. In t...... a steady state with respect to the reference climate at the end of the simulation and that the mass balance of the ice sheet at this time was more sensitive to recent climate fluctuations than the temperature forcing in the early or mid-Holocene.......Models of ice flow have a range of application in glaciology, including investigating the large-scale response of ice sheets to changes in climate, assimilating data to estimate unknown conditions beneath the ice sheet, and in interpreting proxy records obtained from ice cores, among others....... In this PhD project, the use of ice flow models for the interpretation of the age-structure of the Greenland ice sheet, i.e. the depth within the ice, at which ice deposited at given times are found at present day. Two different observational data sets of this archive were investigated. Further, paleo...

Arctic sea-ice ridges—Safe heavens for sea-ice fauna during periods of extreme ice melt?

Science.gov (United States)

Gradinger, Rolf; Bluhm, Bodil; Iken, Katrin

2010-01-01

The abundances and distribution of metazoan within-ice meiofauna (13 stations) and under-ice fauna (12 stations) were investigated in level sea ice and sea-ice ridges in the Chukchi/Beaufort Seas and Canada Basin in June/July 2005 using a combination of ice coring and SCUBA diving. Ice meiofauna abundance was estimated based on live counts in the bottom 30 cm of level sea ice based on triplicate ice core sampling at each location, and in individual ice chunks from ridges at four locations. Under-ice amphipods were counted in situ in replicate ( N=24-65 per station) 0.25 m 2 quadrats using SCUBA to a maximum water depth of 12 m. In level sea ice, the most abundant ice meiofauna groups were Turbellaria (46%), Nematoda (35%), and Harpacticoida (19%), with overall low abundances per station that ranged from 0.0 to 10.9 ind l -1 (median 0.8 ind l -1). In level ice, low ice algal pigment concentrations (Turbellaria, Nematoda and Harpacticoida also were observed in pressure ridges (0-200 ind l -1, median 40 ind l -1), although values were highly variable and only medians of Turbellaria were significantly higher in ridge ice than in level ice. Median abundances of under-ice amphipods at all ice types (level ice, various ice ridge structures) ranged from 8 to 114 ind m -2 per station and mainly consisted of Apherusa glacialis (87%), Onisimus spp. (7%) and Gammarus wilkitzkii (6%). Highest amphipod abundances were observed in pressure ridges at depths >3 m where abundances were up to 42-fold higher compared with level ice. We propose that the summer ice melt impacted meiofauna and under-ice amphipod abundance and distribution through (a) flushing, and (b) enhanced salinity stress at thinner level sea ice (less than 3 m thickness). We further suggest that pressure ridges, which extend into deeper, high-salinity water, become accumulation regions for ice meiofauna and under-ice amphipods in summer. Pressure ridges thus might be crucial for faunal survival during periods of

42 CFR 136.404 - What does the Indian Child Protection and Family Violence Prevention Act require of the IHS and...

Science.gov (United States)

2010-10-01

... Protection and Family Violence Prevention § 136.404 What does the Indian Child Protection and Family Violence... 42 Public Health 1 2010-10-01 2010-10-01 false What does the Indian Child Protection and Family Violence Prevention Act require of the IHS and Indian Tribes or Tribal organizations receiving funds under...

On the perfect hexagonal packing of rods

International Nuclear Information System (INIS)

Starostin, E L

2006-01-01

In most cases the hexagonal packing of fibrous structures or rods extremizes the energy of interaction between strands. If the strands are not straight, then it is still possible to form a perfect hexatic bundle. Conditions under which the perfect hexagonal packing of curved tubular structures may exist are formulated. Particular attention is given to closed or cycled arrangements of the rods like in the DNA toroids and spools. The closure or return constraints of the bundle result in an allowable group of automorphisms of the cross-sectional hexagonal lattice. The structure of this group is explored. Examples of open helical-like and closed toroidal-like bundles are presented. An expression for the elastic energy of a perfectly packed bundle of thin elastic rods is derived. The energy accounts for both the bending and torsional stiffnesses of the rods. It is shown that equilibria of the bundle correspond to solutions of a variational problem formulated for the curve representing the axis of the bundle. The functional involves a function of the squared curvature under the constraints on the total torsion and the length. The Euler-Lagrange equations are obtained in terms of curvature and torsion and due to the existence of the first integrals the problem is reduced to the quadrature. The three-dimensional shape of the bundle may be readily reconstructed by integration of the Ilyukhin-type equations in special cylindrical coordinates. The results are of universal nature and are applicable to various fibrous structures, in particular, to intramolecular liquid crystals formed by DNA condensed in toroids or packed inside the viral capsids

Electronic structure of nanoparticles of substoichometric hexagonal tungsten oxides

International Nuclear Information System (INIS)

Khyzhun, O Y; Solonin, Y M

2007-01-01

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) methods were used to study the electronic structure of hexagonal h-WO 3 and h-WO 2.8 nanoparticles. For comparison, nanopowder substoichiometric monoclinic tungsten oxides with close content of oxygen atoms, namely m-WO 3 and m-WO 2.77 compounds, were also investigated. For the mentioned oxides, XPS valence-band and corelevel spectra, XES O Kα bands and XAS W L III and O 1s edges were derived. The XPS valence-band spectra and O Kα emission bands in the mentioned hexagonal and monoclinic tungsten oxides were compared on a common energy scale. Both the O Kα bands and XPS valence-band spectra broaden somewhat in the sequences h-WO 3 → h-WO 2.8 and m-WO 3 → m-WO 2.77 , with the half-widths of the spectra being somewhat higher for the hexagonal oxides as compared with those for the monoclinic compounds. The effective positive charge state of tungsten atoms in h-WO 2.8 is very close to that in m-WO 2.77 , but the negative charge states of oxygen atoms are close to each other for all the tungsten oxides under consideration

Simulate-HEX - The multi-group diffusion equation in hexagonal-z geometry

International Nuclear Information System (INIS)

Lindahl, S. O.

2013-01-01

The multigroup diffusion equation is solved for the hexagonal-z geometry by dividing each hexagon into 6 triangles. In each triangle, the Fourier solution of the wave equation is approximated by 8 plane waves to describe the intra-nodal flux accurately. In the end an efficient Finite Difference like equation is obtained. The coefficients of this equation depend on the flux solution itself and they are updated once per power/void iteration. A numerical example demonstrates the high accuracy of the method. (authors)

Room-temperature synthesis and photoluminescence of hexagonal CePO4 nanorods

Science.gov (United States)

Zhu, J.; Zhang, K.; Zhao, H. Y.

2018-01-01

Hexagonal CePO4 nanorods were synthesized via a simple chemical precipitation route at room-temperature without the presence of surfactants and then characterized by powder X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectrometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) spectroscopy. Hexagonal CePO4 nanorods exhibit strong ultraviolet absorption and ultraviolet luminescence, which correspond to the electronic transitions between 4f and 5d state of Ce3+ ions.

Communication: Water on hexagonal boron nitride from diffusion Monte Carlo

Energy Technology Data Exchange (ETDEWEB)

Al-Hamdani, Yasmine S.; Ma, Ming; Michaelides, Angelos, E-mail: angelos.michaelides@ucl.ac.uk [Thomas Young Centre and London Centre for Nanotechnology, 17–19 Gordon Street, London WC1H 0AH (United Kingdom); Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom); Alfè, Dario [Thomas Young Centre and London Centre for Nanotechnology, 17–19 Gordon Street, London WC1H 0AH (United Kingdom); Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT (United Kingdom); Lilienfeld, O. Anatole von [Institute of Physical Chemistry and National Center for Computational Design and Discovery of Novel Materials, Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel (Switzerland); Argonne Leadership Computing Facility, Argonne National Laboratories, 9700 S. Cass Avenue Argonne, Lemont, Illinois 60439 (United States)

2015-05-14

Despite a recent flurry of experimental and simulation studies, an accurate estimate of the interaction strength of water molecules with hexagonal boron nitride is lacking. Here, we report quantum Monte Carlo results for the adsorption of a water monomer on a periodic hexagonal boron nitride sheet, which yield a water monomer interaction energy of −84 ± 5 meV. We use the results to evaluate the performance of several widely used density functional theory (DFT) exchange correlation functionals and find that they all deviate substantially. Differences in interaction energies between different adsorption sites are however better reproduced by DFT.

Phase stabilisation of hexagonal barium titanate doped with transition metals: A computational study

International Nuclear Information System (INIS)

Dawson, J.A.; Freeman, C.L.; Harding, J.H.; Sinclair, D.C.

2013-01-01

Interatomic potentials recently developed for the modelling of BaTiO 3 have been used to explore the stabilisation of the hexagonal polymorph of BaTiO 3 by doping with transition metals (namely Mn, Co, Fe and Ni) at the Ti-site. Classical simulations have been completed on both the cubic and hexagonal polymorphs to investigate the energetic consequences of transition metal doping on each polymorph. Ti-site charge compensation mechanisms have been used for the multi-valent transition metal ions and cluster binding energies have been considered. Simulations show a significant energetic gain when doping occurs at Ti sites in the face sharing dimers (Ti 2 sites) of the hexagonal polymorph compared with the doping of the cubic polymorph. This energetic difference between the two polymorphs is true for all transition metals tested and all charge states and in the case of tri- and tetra-valent dopants negative solution energies are found for the hexagonal polymorph suggesting actual polymorph stabilisation occurs with the incorporation of these ions as observed experimentally. Oxidation during incorporation of Ni 2+ and Fe 3+ ions has also been considered. - Graphical abstract: The representation of the strongest binding energy clusters for tri-valent dopants—(a) Ti 2 /O 1 cluster and (b) Ti 2 /O 2 cluster. Highlights: ► Classical simulations show a significant energetic gain when doping occurs at Ti sites in the face sharing dimers (Ti2 sites) of the hexagonal polymorph compared with the doping of the cubic polymorph. ► This energetic difference between the two polymorphs is true for all transition metals tested and all charge states. ► In the case of tri- and tetra- valent dopants negative solution energies are found for the hexagonal polymorph suggesting actual polymorph stabilisation occurs with the incorporation of these ions

Development and validation of the International Hidradenitis Suppurativa Severity Score System (IHS4), a novel dynamic scoring system to assess HS severity

DEFF Research Database (Denmark)

Zouboulis, C C; Tzellos, T; Kyrgidis, A

2017-01-01

BACKGROUND: A validated tool for the dynamic severity assessment of hidradenitis suppurativa/acne inversa (HS) is lacking. OBJECTIVES: To develop and validate a novel dynamic scoring system to assess the severity of HS. METHODS: A Delphi voting procedure was conducted among the members......, as well as examination for correlation (Spearman's rho) and agreement (Cohen's kappa) with existing scores, were engaged to recognize the variables for a new International HS4 (IHS4) that was established by a second Delphi round. RESULTS: Consensus HS4 was based on number of skin lesions, number of skin....... Three candidate scores were presented to the second Delphi round. The resulting IHS4 score is arrived at by the number of nodules (multiplied by 1) plus the number of abscesses (multiplied by 2) plus the number of draining tunnels (multiplied by 4). A total score of 3 or less signifies mild, 4...

Tensile Behaviour of Welded Wire Mesh and Hexagonal Metal Mesh for Ferrocement Application

Science.gov (United States)

Tanawade, A. G.; Modhera, C. D.

2017-08-01

Tension tests were conducted on welded mesh and hexagonal Metal mesh. Welded Mesh is available in the market in different sizes. The two types are analysed viz. Ø 2.3 mm and Ø 2.7 mm welded mesh, having opening size 31.75 mm × 31.75 mm and 25.4 mm × 25.4 mm respectively. Tensile strength test was performed on samples of welded mesh in three different orientations namely 0°, 30° and 45° degrees with the loading axis and hexagonal Metal mesh of Ø 0.7 mm, having opening 19.05 × 19.05 mm. Experimental tests were conducted on samples of these meshes. The objective of this study was to investigate the behaviour of the welded mesh and hexagonal Metal mesh. The result shows that the tension load carrying capacity of welded mesh of Ø 2.7 mm of 0° orientation is good as compared to Ø2.3 mm mesh and ductility of hexagonal Metal mesh is good in behaviour.

Testing IH Instrumentation: Analysis of 1996-1998 Tank Ventilation Data in Terms of Characterizing a Transient Release

International Nuclear Information System (INIS)

Droppo, James G.

2004-01-01

An analysis is conducted of the 1996-1998 Hanford tank ventilation studies of average ventilation rates to help define characteristics of shorter term releases. This effort is being conducted as part of the design of tests of Industrial Hygiene's (IH) instrumentation ability to detect transient airborne plumes from tanks using current deployment strategies for tank operations. This analysis has improved our understanding of the variability of hourly average tank ventilation processes. However, the analysis was unable to discern the relative importance of emissions due to continuous releases and short-duration bursts of material. The key findings are as follows: (1) The ventilation of relatively well-sealed, passively ventilated tanks appears to be driven by a combination of pressure, buoyancy, and wind influences. The results of a best-fit analysis conducted with a single data set provide information on the hourly emission variability that IH instrumentation will need to detect. (2) Tank ventilation rates and tank emission rates are not the same. The studies found that the measured infiltration rates for a single tank are often a complex function of air exchanges between tanks and air exchanges with outdoor air. This situation greatly limits the usefulness of the ventilation data in defining vapor emission rates. (3) There is no evidence in the data to discern if the routine tank vapor releases occur over a short time (i.e., a puff) or over an extended time (i.e., continuous releases). Based on this analysis of the tank ventilation studies, it is also noted that (1) the hourly averaged emission peaks from the relatively well-sealed passively-vented tanks (such as U-103) are not a simple function of one meteorological parameter--but the peaks often are the result of the coincidence of temporal maximums in pressure, temperature, and wind influences and (2) a mechanistic combination modeling approach and/or field studies may be necessary to understand the short

Moving antiplane shear crack in hexagonal piezoelectric crystals

International Nuclear Information System (INIS)

Tupholme, G.

1998-01-01

Closed form solutions are obtained and discussed for the stress and electric displacement fields around a loaded Griffith-type antiplane shear strip crack moving in hexagonal piezoelectric crystals. Representative numerical results are presented for ZnO and PZT-5H. (author)

Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires

KAUST Repository

Wang, Ping; Yuan, Ying; Zhao, Chao; Wang, Xinqiang; Zheng, Xiantong; Rong, Xin; Wang, Tao; Sheng, Bowen; Wang, Qingxiao; Zhang, Yongqiang; Bian, Lifeng; Yang, Xue-Lin; Xu, Fu-Jun; Qin, Zhixin; Li, Xin-Zheng; Zhang, Xixiang; Shen, Bo

2015-01-01

by first-principles density functional theory (DFT). The formation of diagonal pyramids for the N-polarity hexagonal NWs affords a novel way to locate quantum dot in the kink position, suggesting a new recipe for the fabrication of dot-based devices.

Rate of ice accumulation during ice storms

Energy Technology Data Exchange (ETDEWEB)

Feknous, N. [SNC-Lavalin, Montreal, PQ (Canada); Chouinard, L. [McGill Univ., Montreal, PQ (Canada); Sabourin, G. [Hydro-Quebec, Montreal, PQ (Canada)

2005-07-01

The rate of glaze ice accumulation is the result of a complex process dependent on numerous meteorological and physical factors. The aim of this paper was to estimate the distribution rate of glaze ice accumulation on conductors in southern Quebec for use in the design of mechanical and electrical de-icing devices. The analysis was based on direct observations of ice accumulation collected on passive ice meters. The historical database of Hydro-Quebec, which contains observations at over 140 stations over period of 25 years, was used to compute accumulation rates. Data was processed so that each glaze ice event was numbered in a chronological sequence. Each event consisted of the time series of ice accumulations on each of the 8 cylinders of the ice meters, as well as on 5 of its surfaces. Observed rates were converted to represent the average ice on a 30 mm diameter conductor at 30 m above ground with a span of 300 m. Observations were corrected to account for the water content of the glaze ice as evidenced by the presence of icicles. Results indicated that despite significant spatial variations in the expected severity of ice storms as a function of location, the distribution function for rates of accumulation were fairly similar and could be assumed to be independent of location. It was concluded that the observations from several sites could be combined in order to obtain better estimates of the distribution of hourly rates of ice accumulation. However, the rates were highly variable. For de-icing strategies, it was suggested that average accumulation rates over 12 hour periods were preferable, and that analyses should be performed for other time intervals to account for the variability in ice accumulation rates over time. In addition, accumulation rates did not appear to be highly correlated with average wind speed for maximum hourly accumulation rates. 3 refs., 2 tabs., 10 figs.

Thermodynamics of the hexagonal close-packed iron-nitrogen system from first-principles

DEFF Research Database (Denmark)

Bakkedal, Morten Bjørn

to hexagonal systems and a numerically tractable extended equation of state is developed to describe thermody-namic equilibrium properties at finite temperature.The model is applied to ε-Fe3N specifically. Through the versatility of the model, equi-librium lattice parameters, the bulk modulus, and the thermal......First-principles thermodynamic models are developed for the hexagonal close-packed ε-Fe-N system. The system can be considered as a hexagonal close-packed host lattice of iron atoms and with the nitrogen atoms residing on a sublattice formed by the octahedral interstices. The iron host lattice...... is assumed fixed.The models are developed entirely from first-principles calculations based on fundamen-tal quantum mechanical calculation through the density functional theory approach with the atomic numbers and crystal structures as the only input parameters. A complete thermody-namic description should...

Argentinean adaptation of the Social Skills Inventory IHS-Del-Prette.

Science.gov (United States)

Olaz, Fabián Orlando; Medrano, Leonardo; Greco, María Eugenia; Del Prette, Zilda Aparecida Pereira

2009-11-01

We present the results of the adaptation of the IHS-Del-Prette (Inventario de Habilidades Sociales, in English, Social Skills Inventory) to a sample of Argentinean college students. Firstly, we addressed the backward translation and carried out an equivalence study of the Portuguese and Spanish versions of the scale. The results showed the two versions were equivalent, as we obtained correlations lower than .50 in only 5 items. Secondly, we performed item analysis by calculating discrimination indexes and item-total correlations. Results indicated that the items are sensitive to differentiate between high and low social-skill groups. Exploratory factor analysis carried out with a sample of 602 college students yielded five factors that explained 26.5% of the total variance, although our data did not completely match the original factor structure. We also obtained moderate alpha values for the subscales, but high reliability for the total scale. Lastly, group differences between males and females are presented to provide evidence of validity. We discuss the implications of the results and present future lines of inquiry.

Group of Hexagonal Search Patterns for Motion Estimation and Object Tracking

International Nuclear Information System (INIS)

Elazm, A.A.; Mahmoud, I.I; Hashima, S.M.

2010-01-01

This paper presents a group of fast block matching algorithms based on the hexagon pattern search .A new predicted one point hexagon (POPHEX) algorithm is proposed and compared with other well known algorithms. The comparison of these algorithms and our proposed one is performed for both motion estimation and object tracking. Test video sequences are used to demonstrate the behavior of studied algorithms. All algorithms are implemented in MATLAB environment .Experimental results showed that the proposed algorithm posses less number of search points however its computational overhead is little increased due to prediction procedure.

Characterization of an IceTop tank for the IceCube surface extension IceVeto

Energy Technology Data Exchange (ETDEWEB)

Kemp, Julian; Auffenberg, Jan; Hansmann, Bengt; Rongen, Martin; Stahlberg, Martin; Wiebusch, Christopher [III. Physikalisches Institut B, RWTH Aachen University (Germany); Collaboration: IceCube-Collaboration

2015-07-01

IceTop is an air-shower detector located at the South Pole on the surface above the IceCube detector. It consists of 81 detector stations with two Cherenkov tanks each. The tanks are filled with clear ice and instrumented with two photomultipliers. IceTop detects cosmic-ray induced air-showers above an energy threshold of ∝300 TeV. Muons and neutrinos from these air-showers are the main background for astrophysical neutrino searches with IceCube. The usage of IceTop to veto air-showers largely reduces this background in the field of view. To enlarge the field of view an extension of the surface detector, IceVeto, is planned. Therefore, we investigate the properties of an original IceTop tank as a laboratory reference for the development of new detection module designs. First results of these measurements are presented.

Eu3+-doped Y2O3 hexagonal prisms: Shape-controlled synthesis and tailored luminescence properties

International Nuclear Information System (INIS)

Yang, Errui; Li, Guangshe; Fu, Chaochao; Zheng, Jing; Huang, Xinsong; Xu, Wen; Li, Liping

2015-01-01

In this work, Eu 3+ doped Y 2 O 3 hexagonal prisms were synthesized by a novel two-phase approach, which involves water at the bottom as aqueous phase and oleylamine in the above as oil phase. With this unique reaction system, precursors of hexagonal prisms Y 4 O(OH) 9 (NO 3 ) were first obtained by simply varying the volume ratio of water to oleylamine. Time-dependent experiments were systematically performed to reveal the growth mechanism of the precursor. After subsequent heat treatment, these precursors transformed to Y 2 O 3 hexagonal prisms with controlled diameters and aspect ratios varying from 4 to 19. Such a transformation is preceded via a topotactic process, as indicated by TG-DTA and mass spectra. Eventually, all Eu 3+ doped Y 2 O 3 hexagonal prisms were found to exhibit an intensive red emission at 611 nm, which corresponds to 5 D 0 → 7 F 2 transition of Eu 3+ . With varying the aspect ratio of hexagonal prisms and increasing Eu 3+ concentration in Y 2 O 3 , an optimum external quantum efficiency was achieved. - Graphical abstract: In this work, Eu 3+ doped Y 2 O 3 hexagonal prisms with controlled aspect ratio from 4.4 to 19.3 were synthesized by transformation of the precursor Y 4 O(OH) 9 (NO 3 ) hexagonal prisms from a novel two-phase reaction system. The growth mechanism of the precursor has been systematically investigated, and a topotactic phase transformation from precursors to cubic Y 2 O 3 is for the first time put forward. By the size controlling and aspect ratio adjusting, the luminescence emission intensity as well as external quantum efficiency of Eu 3+ doped Y 2 O 3 hexagonal prisms is further tailored to show an optimum. - Highlights: • Eu 3+ doped Y 2 O 3 hexagonal prisms were synthesized by a novel two-phase approach. • Inheriting mechanism of prisms morphology from Y 4 O(OH) 9 (NO 3 ) to Y 2 O 3 was discussed. • Aspect ratio of prisms was tailored by the volume ratio of water to oleylamine. • Luminescence properties were

Measurements of Neuronal Soma Size and Estimated Peptide Concentrations in Addition to Cell Abundance Offer a Higher Resolution of Seasonal and Reproductive Influences of GnRH-I and GnIH in European Starlings.

Science.gov (United States)

Amorin, Nelson; Calisi, Rebecca M

2015-08-01

Hypothalamic neuropeptides involved in vertebrate reproduction, gonadotropin releasing hormone (GnRH-I) and gonadotropin-inhibitory hormone (GnIH), can vary in the abundance of immunoreactive cells as a function of the reproductive status and nest box occupation of European starlings (Sturnus vulgaris). While using the abundance of cells as an indicator of the activity of neurohormones is informative, incorporating information on cell size (readily observed using immunohistochemistry) can offer a more detailed understanding of environmentally-mediated changes in hormonal dynamics. In this study, we tested the hypothesis that the size of cells' somas and the estimated concentration of peptides in cells immunoreactive (ir) for GnRH-I and GnIH would vary throughout the breeding season and as a function of nest-box status (resident or not). In the absence of a direct assay of protein, we estimated an index of the concentration of hypothalamic peptides via the relative optical density (i.e., the difference between the mean optical density and the optical density of background staining). In support of our hypothesis, we found that GnRH-I- and GnIH-ir soma size and peptide concentration changed both in males and females throughout the breeding season. Somas were largest and estimated peptide concentration was highest mid-season when compared with earlier in the season or to the non-breeding period. For nest-box residents, GnIH-ir soma size and peptide concentration were higher during the middle of the breeding season than earlier in the breeding season, although residence in the nest box was not related to GnRH-I-ir variables. Our results confirm that previously reported changes in cell abundance mimic changes we see in GnRH-I and GnIH-ir soma size and our proxy for peptide concentration. However, investigating changes in the soma of GnRH-I-ir cells revealed a peak in size during the middle of the breeding season, a change not evident when solely examining data on the

Research on the comparison of extension mechanism of cellular automaton based on hexagon grid and rectangular grid

Science.gov (United States)

Zhai, Xiaofang; Zhu, Xinyan; Xiao, Zhifeng; Weng, Jie

2009-10-01

Historically, cellular automata (CA) is a discrete dynamical mathematical structure defined on spatial grid. Research on cellular automata system (CAS) has focused on rule sets and initial condition and has not discussed its adjacency. Thus, the main focus of our study is the effect of adjacency on CA behavior. This paper is to compare rectangular grids with hexagonal grids on their characteristics, strengths and weaknesses. They have great influence on modeling effects and other applications including the role of nearest neighborhood in experimental design. Our researches present that rectangular and hexagonal grids have different characteristics. They are adapted to distinct aspects, and the regular rectangular or square grid is used more often than the hexagonal grid. But their relative merits have not been widely discussed. The rectangular grid is generally preferred because of its symmetry, especially in orthogonal co-ordinate system and the frequent use of raster from Geographic Information System (GIS). However, in terms of complex terrain, uncertain and multidirectional region, we have preferred hexagonal grids and methods to facilitate and simplify the problem. Hexagonal grids can overcome directional warp and have some unique characteristics. For example, hexagonal grids have a simpler and more symmetric nearest neighborhood, which avoids the ambiguities of the rectangular grids. Movement paths or connectivity, the most compact arrangement of pixels, make hexagonal appear great dominance in the process of modeling and analysis. The selection of an appropriate grid should be based on the requirements and objectives of the application. We use rectangular and hexagonal grids respectively for developing city model. At the same time we make use of remote sensing images and acquire 2002 and 2005 land state of Wuhan. On the base of city land state in 2002, we make use of CA to simulate reasonable form of city in 2005. Hereby, these results provide a proof of

The IceProd (IceCube Production) Framework

International Nuclear Information System (INIS)

Díaz-Vélez, J C

2014-01-01

IceProd is a data processing and management framework developed by the IceCube Neutrino Observatory for processing of Monte Carlo simulations and data. IceProd runs as a separate layer on top of middleware or cluster job schedulers and can take advantage of a variety of computing resources including grids such as EGI, OSG, and NorduGrid as well as local clusters running batch systems like HT Condor, PBS, and SGE. This is accomplished by a set of dedicated daemons which process job submission in a coordinated fashion through the use of middleware plug-ins that serve to abstract the details of job submission and job management. IceProd can also manage complex workflow DAGs across distributed computing grids in order to optimize usage of resources. We describe several aspects of IceProd's design and it's applications in collaborative computing environments. We also briefly discuss design aspects of a second generation IceProd, currently being tested in IceCube.

Ice recrystallization inhibition in ice cream as affected by ice structuring proteins from winter wheat grass.

Science.gov (United States)

Regand, A; Goff, H D

2006-01-01

Ice recrystallization in quiescently frozen sucrose solutions that contained some of the ingredients commonly found in ice cream and in ice cream manufactured under commercial conditions, with or without ice structuring proteins (ISP) from cold-acclimated winter wheat grass extract (AWWE), was assessed by bright field microscopy. In sucrose solutions, critical differences in moisture content, viscosity, ionic strength, and other properties derived from the presence of other ingredients (skim milk powder, corn syrup solids, locust bean gum) caused a reduction in ice crystal growth. Significant ISP activity in retarding ice crystal growth was observed in all solutions (44% for the most complex mix) containing 0.13% total protein from AWWE. In heat-shocked ice cream, ice recrystallization rates were significantly reduced 40 and 46% with the addition of 0.0025 and 0.0037% total protein from AWWE. The ISP activity in ice cream was not hindered by its inclusion in mix prior to pasteurization. A synergistic effect between ISP and stabilizer was observed, as ISP activity was reduced in the absence of stabilizer in ice cream formulations. A remarkably smoother texture for ice creams containing ISP after heat-shock storage was evident by sensory evaluation. The efficiency of ISP from AWWE in controlling ice crystal growth in ice cream has been demonstrated.

Hexagonal graphene quantum dots

KAUST Repository

Ghosh, Sumit; Schwingenschlö gl, Udo

2016-01-01

We study hexagonal graphene quantum dots, using density functional theory, to obtain a quantitative description of the electronic properties and their size dependence, considering disk and ring geometries with both armchair and zigzag edges. We show that the electronic properties of quantum dots with armchair edges are more sensitive to structural details than those with zigzag edges. As functions of the inner and outer radii, we find in the case of armchair edges that the size of the band gap follows distinct branches, while in the case of zigzag edges it changes monotonically. This behaviour is further analyzed by studying the ground state wave function and explained in terms of its localisation.

Hexagonal graphene quantum dots

KAUST Repository

Ghosh, Sumit

2016-12-05

We study hexagonal graphene quantum dots, using density functional theory, to obtain a quantitative description of the electronic properties and their size dependence, considering disk and ring geometries with both armchair and zigzag edges. We show that the electronic properties of quantum dots with armchair edges are more sensitive to structural details than those with zigzag edges. As functions of the inner and outer radii, we find in the case of armchair edges that the size of the band gap follows distinct branches, while in the case of zigzag edges it changes monotonically. This behaviour is further analyzed by studying the ground state wave function and explained in terms of its localisation.

The response-matrix based AFEN method for the hexagonal geometry

International Nuclear Information System (INIS)

Noh, Jae Man; Kim, Keung Koo; Zee, Sung Quun; Joo, Hyung Kook; Cho, Byng Oh; Jeong, Hyung Guk; Cho, Jin Young

1998-03-01

The analytic function expansion nodal (AFEN) method, developed to overcome the limitations caused by the transverse integration, has been successfully to predict the neutron behavior in the hexagonal core as well as rectangular core. In the hexagonal node, the transverse leakage resulted from the transverse integration has some singular terms such as delta-function and step-functions near the node center line. In most nodal methods using the transverse integration, the accuracy of nodal method is degraded because the transverse leakage is approximated as a smooth function across the node center line by ignoring singular terms. However, the AFEN method in which there is no transverse leakage term in deriving nodal coupling equations keeps good accuracy for hexagonal node. In this study, the AFEN method which shows excellent accuracy in the hexagonal core analyses is reformulated as a response matrix form. This form of the AFEN method can be implemented easily to nodal codes based on the response matrix method. Therefore, the Coarse Mesh Rebalance (CMR) acceleration technique which is one of main advantages of the response matrix method can be utilized for the AFEN method. The response matrix based AFEN method has been successfully implemented into the MASTER code and its accuracy and computational efficiency were examined by analyzing the two- and three- dimensional benchmark problem of VVER-440. Based on the results, it can be concluded that the newly formulated AFEN method predicts accurately the assembly powers (within 0.2% average error) as well as the effective multiplication factor (within 0.2% average error) as well as the effective multiplication factor (within 20 pcm error). In addition, the CMR acceleration technique is quite efficient in reducing the computation time of the AFEN method by 8 to 10 times. (author). 22 refs., 1 tab., 4 figs

Solution of 2D and 3D hexagonal geometry benchmark problems by using the finite element diffusion code DIFGEN

International Nuclear Information System (INIS)

Gado, J.

1986-02-01

The four group, 2D and 3D hexagonal geometry HTGR benchmark problems and a 2D hexagonal geometry PWR (WWER) benchmark problem have been solved by using the finite element diffusion code DIFGEN. The hexagons (or hexagonal prisms) were subdivided into first order or second order triangles or quadrilaterals (or triangular or quadrilateral prisms). In the 2D HTGR case of the number of the inserted absorber rods was also varied (7, 6, 0 or 37 rods). The calculational results are in a good agreement with the results of other calculations. The larger systematic series of DIFGEN calculations have given a quantitative picture on the convergence properties of various finite element modellings of hexagonal grids in DIFGEN. (orig.)

Misfit of Three Different Implant-Abutment Connections Before and After Cyclic Load Application: An In Vitro Study.

Science.gov (United States)

Gehrke, Sergio Alexandre; Delgado-Ruiz, Rafael Arcesio; Prados Frutos, Juan Carlos; Prados-Privado, María; Dedavid, Berenice Anina; Granero Marín, Jose Manuel; Calvo Guirado, José Luiz

This study aimed to evaluate the misfit of three different implant-abutment connections before and after cycling load. One hundred twenty dental implants and correspondent prefabricated titanium abutments were used. Three different implant-abutment connections were evaluated: Morse taper (MT group), external hexagon (EH group), and internal hexagon (IH group). Forty implants and 40 abutments were used per group. The parameters for the mechanical evaluation were set as: 360,000 cycles, load of 150 N, and frequency of 4 Hz. Samples were sectioned in their longitudinal and transversal axes, and the misfit of the implant-abutment connection was evaluated by scanning electron microscopy analysis. One-way analyses of variance, Tukey post hoc analyses (α = .05), and t test (P .05). Transversally, only the MT group showed full fitting after cycling load compared with the other groups (EH and IH) (P abutment connection in internal, external, and Morse taper connections. In the longitudinal direction, the accommodation decreases and/or eliminates the gap observed initially (before load). In the horizontal direction, Morse cone implant-abutment connections experience a complete accommodation with the elimination of the gap.

Density functional simulations of hexagonal Ge2Sb2Te5 at high pressure

Science.gov (United States)

Caravati, Sebastiano; Sosso, Gabriele C.; Bernasconi, Marco; Parrinello, Michele

2013-03-01

We investigated the structural transformations of the hexagonal phase of Ge2Sb2Te5 under pressure by means of ab initio molecular dynamics with a variable simulation cell. To overcome the enthalpy barriers between the different phases we used metadynamics techniques. We reproduced the hexagonal-to-bcc transformation under pressure found experimentally. The bcc phase retains a partial chemical order, as opposed to a second bcc phase we generated by pressuring the amorphous phase. This structural difference is suggested to be responsible for the memory effect uncovered experimentally, the bcc phase reverting to the amorphous or to the hexagonal phase upon decompression, depending on the type of precursor phase it originates from.

Switching behavior and novel stable states of magnetic hexagonal nanorings

Energy Technology Data Exchange (ETDEWEB)

Yasir Rafique, M., E-mail: myasir.rafique@ciitlahore.edu.pk [Department of Physics, COMSATS Institute of Information Technology, Lahore 54000 (Pakistan); Pan, Liqing; Guo, Zhengang [College of Science and Research Institute for New Energy, China Three Gorges University, Yichang 443002 (China)

2017-06-15

Micromagnetic simulations for Cobalt hexagonal shape nanorings show onion (O) and vortex state (V) along with new state named “tri-domain state”. The tri-domain state is observed in sufficiently large width of ring. The magnetic reversible mechanism and transition of states are explained with help of vector field display. The transitions from one state to other occur by propagation of domain wall. The vertical parts of hexagonal rings play important role in developing the new “tri-domain” state. The behaviors of switching fields from onion to tri-domain (HO-Tr), tri-domain to vortex state (HTr-V) and vortex to onion state and “states size” are discussed in term of geometrical parameter of ring.

Thermal stability of hexagonal OsB{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Xie, Zhilin [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Blair, Richard G. [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Department of Physics, University of Central Florida, Orlando, FL 32816 (United States); Orlovskaya, Nina, E-mail: Nina.Orlovskaya@ucf.edu [Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816 (United States); Cullen, David A. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Andrew Payzant, E. [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)

2014-11-15

The synthesis of novel hexagonal ReB{sub 2}-type OsB{sub 2} ceramic powder was performed by high energy ball milling of elemental Os and B powders. Two different sources of B powder have been used for this mechanochemical synthesis. One B powder consisted of a mixture of amorphous and crystalline phases and a mixture of {sup 10}B and {sup 11}B isotopes with a fine particle size, while another B powder was a purely crystalline (rhombohedral) material consisting of enriched {sup 11}B isotope with coarse particle size. The same Os powder was used for the synthesis in both cases. It was established that, in the first case, the hexagonal OsB{sub 2} phase was the main product of synthesis with a small quantity of Os{sub 2}B{sub 3} phase present after synthesis as an intermediate product. In the second case, where coarse crystalline {sup 11}B powder was used as a raw material, only Os{sub 2}B{sub 3} boride was synthesized mechanochemically. The thermal stability of hexagonal OsB{sub 2} powder was studied by heating under argon up to 876 °C and cooling in vacuo down to −225 °C. During the heating, the sacrificial reaction 2OsB{sub 2}+3O{sub 2}→2Os+2B{sub 2}O{sub 3} took place due to presence of O{sub 2}/water vapor molecules in the heating chamber, resulting in the oxidation of B atoms and formation of B{sub 2}O{sub 3} and precipitation of Os metal out of the OsB{sub 2} lattice. As a result of such phase changes during heating, the lattice parameters of hexagonal OsB{sub 2} changed significantly. The shrinkage of the a lattice parameter was recorded in 276–426 °C temperature range upon heating, which was attributed to the removal of B atoms from the OsB{sub 2} lattice due to oxidation followed by the precipitation of Os atoms and formation of Os metal. While significant structural changes occurred upon heating due to presence of O{sub 2}, the hexagonal OsB{sub 2} ceramic demonstrated good phase stability upon cooling in vacuo with linear shrinkage of the lattice

Synthesis and Isolation of the Titanium-Scandium Endohedral Fullerenes-Sc2 TiC@Ih -C80 , Sc2 TiC@D5h -C80 and Sc2 TiC2 @Ih -C80 : Metal Size Tuning of the Ti(IV) /Ti(III) Redox Potentials.

Science.gov (United States)

Junghans, Katrin; Ghiassi, Kamran B; Samoylova, Nataliya A; Deng, Qingming; Rosenkranz, Marco; Olmstead, Marilyn M; Balch, Alan L; Popov, Alexey A

2016-09-05

The formation of endohedral metallofullerenes (EMFs) in an electric arc is reported for the mixed-metal Sc-Ti system utilizing methane as a reactive gas. Comparison of these results with those from the Sc/CH4 and Ti/CH4 systems as well as syntheses without methane revealed a strong mutual influence of all key components on the product distribution. Whereas a methane atmosphere alone suppresses the formation of empty cage fullerenes, the Ti/CH4 system forms mainly empty cage fullerenes. In contrast, the main fullerene products in the Sc/CH4 system are Sc4 C2 @C80 (the most abundant EMF from this synthesis), Sc3 C2 @C80 , isomers of Sc2 C2 @C82 , and the family Sc2 C2 n (2 n=74, 76, 82, 86, 90, etc.), as well as Sc3 CH@C80 . The Sc-Ti/CH4 system produces the mixed-metal Sc2 TiC@C2 n (2 n=68, 78, 80) and Sc2 TiC2 @C2 n (2 n=80) clusterfullerene families. The molecular structures of the new, transition-metal-containing endohedral fullerenes, Sc2 TiC@Ih -C80 , Sc2 TiC@D5h -C80 , and Sc2 TiC2 @Ih -C80 , were characterized by NMR spectroscopy. The structure of Sc2 TiC@Ih -C80 was also determined by single-crystal X-ray diffraction, which demonstrated the presence of a short Ti=C double bond. Both Sc2 TiC- and Sc2 TiC2 -containing clusterfullerenes have Ti-localized LUMOs. Encapsulation of the redox-active Ti ion inside the fullerene cage enables analysis of the cluster-cage strain in the endohedral fullerenes through electrochemical measurements. © 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Growth and Brilliant Photo-Emission of Crystalline Hexagonal Column of Alq3 Microwires

OpenAIRE

Seokho Kim; Do Hyoung Kim; Jinho Choi; Hojin Lee; Sun-Young Kim; Jung Woon Park; Dong Hyuk Park

2018-01-01

We report the growth and nanoscale luminescence characteristics of 8-hydroxyquinolinato aluminum (Alq3) with a crystalline hexagonal column morphology. Pristine Alq3 nanoparticles (NPs) were prepared using a conventional reprecipitation method. Crystal hexagonal columns of Alq3 were grown by using a surfactant-assisted self-assembly technique as an adjunct to the aforementioned reprecipitation method. The formation and structural properties of the crystalline and non-crystalline Alq3 NPs were...

Polarized Raman spectroscopic study of relaxed high density amorphous ices under pressure.

Science.gov (United States)

Suzuki, Yoshiharu; Tominaga, Yasunori

2010-10-28

We have made high density amorphous ice (HDA) by the pressure-induced amorphization of hexagonal ice at 77 K and measured the volume change on isobaric heating in a pressure range between 0.1 and 1.5 GPa. The volume of HDA on heating below ∼0.35 GPa increases, while the volume of HDA on heating above ∼0.35 GPa decreases. The polarized OH-stretching Raman spectra of the relaxed HDAs are compared with that of the unannealed HDA. The relaxed HDAs are prepared at 0.2 GPa at 130 K and 1.5 GPa at 160 K. It is found that the relatively strong totally symmetric OH-stretching vibration mode around 3100 cm(-1) exists in the depolarized reduced Raman spectrum χ(VH)(") of the unannealed HDA and that its intensity rapidly decreases by relaxation. The χ(VH)(") profiles of the relaxed HDA are similar to those of liquid water. These results indicate that the HDA reaches a nearly equilibrium state by annealing and the intrinsic state of HDA relates to a liquid state. The pressure-volume curve of the relaxed HDA at 140 K seems to be smooth in the pressure range below 1.5 GPa.

Dirac cones in isogonal hexagonal metallic structures

Science.gov (United States)

Wang, Kang

2018-03-01

A honeycomb hexagonal metallic lattice is equivalent to a triangular atomic one and cannot create Dirac cones in its electromagnetic wave spectrum. We study in this work the low-frequency electromagnetic band structures in isogonal hexagonal metallic lattices that are directly related to the honeycomb one and show that such structures can create Dirac cones. The band formation can be described by a tight-binding model that allows investigating, in terms of correlations between local resonance modes, the condition for the Dirac cones and the consequence of the third structure tile sustaining an extra resonance mode in the unit cell that induces band shifts and thus nonlinear deformation of the Dirac cones following the wave vectors departing from the Dirac points. We show further that, under structure deformation, the deformations of the Dirac cones result from two different correlation mechanisms, both reinforced by the lattice's metallic nature, which directly affects the resonance mode correlations. The isogonal structures provide new degrees of freedom for tuning the Dirac cones, allowing adjustment of the cone shape by modulating the structure tiles at the local scale without modifying the lattice periodicity and symmetry.

The Formation and Characterization of GaN Hexagonal Pyramids

Science.gov (United States)

Zhang, Shi-Ying; Xiu, Xiang-Qian; Lin, Zeng-Qin; Hua, Xue-Mei; Xie, Zi-Li; Zhang, Rong; Zheng, You-Dou

2013-05-01

GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method. Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination, producing submicron-sized pyramids. Hexagonal pyramids on the etched GaN with well-defined {101¯1¯} facets and very sharp tips are formed. High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality, and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN. The cathodoluminescence intensity of GaN after etching is significantly increased by three times, which is attributed to the reduction in the internal reflection, high-quality GaN with pyramids and the Bragg effect.

Using ice melting and ice rolling technologies to remove ice from sub-transmission and transmission lines at Manitoba Hydro

International Nuclear Information System (INIS)

Farias, A. R.

1999-01-01

Development of an of an Ice Storm Management program by Manitoba Hydro to reduce ice storm damage to its 8 kV feeders to 115 kV transmission lines, is discussed. The program consists of the de-icing of overhead lines, either by ice melting, or ice rolling. Ice melting involves the placement of a three-phase short at a calculated point. The term ice rolling denotes a process of mechanically stripping the ice from conductors. The most recent major ice storm experienced by Manitoba Hydro was in the winter of 1997/1998. During the period from February 6 to February 17, 1998, a total of 83 'ice melt' procedures were performed to melt the ice from 2,628 km of overhead line (7,883 km of conductor), in addition to 'ice rolling'. This paper describes Manitoba Hydro's 25-years' experience with ice melting and it also describes the advantages and disadvantages of both ice melting and ice rolling. Although not a panacea to combat the effects of ice storms, ice melting was found to be the most effective way of removing ice from overhead transmission and sub-transmission lines. Ice rolling was also found to be effective. Other tools that have been found to be useful by various utilities in combating ice storm damage include improved structure and line design, system design that provide more redundancies and emergency sources, and standby generators at critical load points

Ice shelf fracture parameterization in an ice sheet model

Science.gov (United States)

Sun, Sainan; Cornford, Stephen L.; Moore, John C.; Gladstone, Rupert; Zhao, Liyun

2017-11-01

Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM) to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ˜ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor) fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

Constraining ice sheet history in the Weddell Sea, West Antarctica, using ice fabric at Korff Ice Rise

Science.gov (United States)

Brisbourne, A.; Smith, A.; Kendall, J. M.; Baird, A. F.; Martin, C.; Kingslake, J.

2017-12-01

The grounding history of ice rises (grounded area of independent flow regime within a floating ice shelf) can be used to constrain large scale ice sheet history: ice fabric, resulting from the preferred orientation of ice crystals due to the stress regime, can be used to infer this grounding history. With the aim of measuring the present day ice fabric at Korff Ice Rise, West Antarctica, a multi-azimuth wide-angle seismic experiment was undertaken. Three wide-angle common-midpoint gathers were acquired centred on the apex of the ice rise, at azimuths of 60 degrees to one another, to measure variation in seismic properties with offset and azimuth. Both vertical and horizontal receivers were used to record P and S arrivals including converted phases. Measurements of the variation with offset and azimuth of seismic traveltimes, seismic attenuation and shear wave splitting have been used to quantify seismic anisotropy in the ice column. The observations cannot be reproduced using an isotropic ice column model. Anisotropic ray tracing has been used to test likely models of ice fabric by comparison with the data. A model with a weak girdle fabric overlying a strong cluster fabric provides the best fit to the observations. Fabric of this nature is consistent with Korff Ice Rise having been stable for the order of 10,000 years without any ungrounding or significant change in the ice flow configuration across the ice rise for this period. This observation has significant implications for the ice sheet history of the Weddell Sea sector.

Hexagonal tube behaviour in fuel assemblies under neutron flux in a French fast neutron reactor core

International Nuclear Information System (INIS)

Bernard, A.; Ammann, P.

This paper presents what is obtained in the field of the interpretation by calculation of the post irradiation examination of hexagonal tubes, and in the field of prevision by calculation of the behaviour of hexagonal tubes under fast flux [fr

Fabrication of nickel hydroxide electrodes with open-ended hexagonal nanotube arrays for high capacitance supercapacitors.

Science.gov (United States)

Wu, Mao-Sung; Huang, Kuo-Chih

2011-11-28

A nickel hydroxide electrode with open-ended hexagonal nanotube arrays, prepared by hydrolysis of nickel chloride in the presence of hexagonal ZnO nanorods, shows a very high capacitance of 1328 F g(-1) at a discharge current density of 1 A g(-1) due to the significantly improved ion transport.

Tracking algorithms for multi-hexagonal assemblies (2D and 3D)

International Nuclear Information System (INIS)

Prabha, Hem; Marleau, Guy; Hébert, Alain

2014-01-01

Highlights: • We present the method of computations of 2D and 3D fluxes in hexagonal assemblies. • Computation of fluxes requires computation of track lengths. • Equations are developed (in 2D and 3D) and are implemented in a program HX7. • The program HX7 is implemented in the NXT module of the code DRAGON. • The tracks are plotted and fluxes are compared with the EXCELT module of DRAGON. - Abstract: Background: There has been a continuous effort to design new reactors and study these reactors under different conditions. Some of these reactors have fuel pins arranged in hexagonal pitch. To study these reactors, development of computational methods and computer codes is required. For this purpose, we have developed algorithms to track two dimensional and three dimensional cluster geometries. These algorithms have been implemented in a subprogram HX7, that is implemented in the code DRAGON (Version 3.06F) to compute neutron flux distributions in these systems. Methods: Computation of the neutron flux distribution requires solution of neutron transport equation. While solving this equation, by using Carlvik’s method of collision probabilities, computation of tracks in the hexagonal geometries is required. In this paper we present equations that we have developed for the computation of tracks in two dimensional (2D) and three dimensional (3D) multi-hexagonal assemblies (with two rotational orientations). These equations have been implemented in a subprogram HX7, to compute tracks in seven hexagonal assemblies. The subprogram HX7 has been implemented in the NXT module of the DRAGON code, where tracks in the pins are computed. Results: The results of our algorithms NXT(+HX7) have been compared with the results obtained by the EXCELT module of DRAGON (Version 3.06F). Conclusions: We find that all the fluxes in 2D and fluxes in the outer pin (3D) are converging to their 3rd decimal places, in both the modules EXCELT and NXT(+HX7). For other regions 3D fluxes

Method for maintenance of ice beds of ice condenser containment

International Nuclear Information System (INIS)

Scrabis, C.M.; Hardin, R.T. Jr.

1987-01-01

This patent describes a method of maintaining ice baskets associated with a nuclear reactor system and disposed in an array of plural such ice baskets, supported in generally vertically oriented and parallel relationship by a lattice support structure which extends between the individual ice baskets and includes lateral supports adjacent the tops of the comprising: selecting an ice basket of the array requiring replenishment of the ice therewithin due to sublimation voids within the ice charges in the basket; isolating the selected ice basket; drilling a hole downwardly through the ice charges in the ice basket in general parallel axial relationship with respect to the cylindrical sidewall of the ice basket, utilizing a rotary drill bit connected through an auger to a rotary drive means; maintaining the rotary drive means in a fixed axial position and reversing the direction of rotation thereof for driving the auger in reverse rotation; and supplying ice in particulate form to the vicinity of the auger and conveying the particulate ice through the drilled hole by continued, reverse rotation of the auger so as to fill the sublimated voids in communication with the drilled hole, from the lowest and through successively higher such voids in the ice charges within the ice basket, and withdrawing the auger from the drilled hole as the voids are filled

Crystallographic Orientation Determination of Hexagonal Structure Crystals by Laser Ultrasonic Technique

International Nuclear Information System (INIS)

Li, W; Coulson, J; Marrow, P; Smith, R J; Clark, M; Sharples, S D; Lainé, S J

2016-01-01

Spatially resolved acoustic spectroscopy (SRAS) is a laser ultrasonic technique that shows qualitative contrast between grains of different orientation, illustrating the sensitivity of acoustic waves to the material structure. The technique has been improved significantly on determining the full orientation of multigrain cubic metals, by comparing the measured surface acoustic wave (SAW) velocity to a pre-calculated model. In this paper we demonstrate the ability of this technique to determine the orientation of hexagonal structure crystals, such as magnesium and titanium based alloys. Because of the isotropy of the SAW velocity on the basal plane (0001) of hexagonal crystals, the slowness surface is shown as a circle. As the plane moves from (0001) towards (112-bar0) or towards (101-bar0), the slowness surface gradually turns into an oval. These acoustic properties increase the difficulty in orientation determination. The orientation results of a grade 1 commercially pure titanium by SRAS is presented, with comparison with electron backscattered diffraction (EBSD) results. Due to the nature of SAWs on hexagonal structure crystals, only the results of Euler angles 1 and 2 are discussed. The error between SRAS and EBSD is also investigated. (paper)

Hexagonally ordered nanoparticles templated using a block copolymer film through Coulombic interactions

International Nuclear Information System (INIS)

Lee, Wonjoo; Lee, Seung Yong; Zhang Xin; Rabin, Oded; Briber, R M

2013-01-01

We present a novel and simple method for forming hexagonal gold nanoparticle arrays that uses Coulombic interactions between negatively charged gold nanoparticles on positively charged vertically oriented poly(4-vinylpyridine) cylinders formed in a spin cast polystyrene-b-poly(4-vinylpyridine) block copolymer film. Exposure of the block copolymer film to dibromobutane vapor quaternizes and crosslinks the poly(4-vinylpyridine) domains which allows for the templated deposition of gold nanoparticles into a self-assembled hexagonal array through electrostatic interactions. These systems can form the basis for sensors or next generation nanoparticle based electronics. (paper)

Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion

Science.gov (United States)

Jorgenson, Philip C. E.; Veres, Joseph P.

2013-01-01

The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that have been attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, and one or more of the following: loss of thrust control (roll back), compressor surge or stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the increase in air temperature causes a portion of the ice crystals to melt. It is hypothesized that this allows the ice-water mixture to cover the metal surfaces of the compressor stationary components which leads to ice accretion through evaporative cooling. Ice accretion causes a blockage which subsequently results in the deterioration in performance of the compressor and engine. The focus of this research is to apply an engine icing computational tool to simulate the flow through a turbofan engine and assess the risk of ice accretion. The tool is comprised of an engine system thermodynamic cycle code, a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor flow path, without modeling the actual ice accretion. A commercial turbofan engine which has previously experienced icing events during operation in a high altitude ice crystal environment has been tested in the Propulsion Systems Laboratory (PSL) altitude test facility at NASA Glenn Research Center. The PSL has the capability to produce a continuous ice cloud which are ingested by the engine during operation over a range of altitude conditions. The PSL test results confirmed that there was ice accretion in the engine due to ice crystal ingestion, at the same simulated altitude operating conditions as experienced previously in

Quasi free-standing silicene in a superlattice with hexagonal boron nitride

KAUST Repository

Kaloni, T. P.

2013-11-12

We study a superlattice of silicene and hexagonal boron nitride by first principles calculations and demonstrate that the interaction between the layers of the superlattice is very small. As a consequence, quasi free-standing silicene is realized in this superlattice. In particular, the Dirac cone of silicene is preserved. Due to the wide band gap of hexagonal boron nitride, the superlattice realizes the characteristic physical phenomena of free-standing silicene. In particular, we address by model calculations the combined effect of the intrinsic spin-orbit coupling and an external electric field, which induces a transition from a semimetal to a topological insulator and further to a band insulator.

Ice shelf fracture parameterization in an ice sheet model

Directory of Open Access Journals (Sweden)

S. Sun

2017-11-01

Full Text Available Floating ice shelves exert a stabilizing force onto the inland ice sheet. However, this buttressing effect is diminished by the fracture process, which on large scales effectively softens the ice, accelerating its flow, increasing calving, and potentially leading to ice shelf breakup. We add a continuum damage model (CDM to the BISICLES ice sheet model, which is intended to model the localized opening of crevasses under stress, the transport of those crevasses through the ice sheet, and the coupling between crevasse depth and the ice flow field and to carry out idealized numerical experiments examining the broad impact on large-scale ice sheet and shelf dynamics. In each case we see a complex pattern of damage evolve over time, with an eventual loss of buttressing approximately equivalent to halving the thickness of the ice shelf. We find that it is possible to achieve a similar ice flow pattern using a simple rule of thumb: introducing an enhancement factor ∼ 10 everywhere in the model domain. However, spatially varying damage (or equivalently, enhancement factor fields set at the start of prognostic calculations to match velocity observations, as is widely done in ice sheet simulations, ought to evolve in time, or grounding line retreat can be slowed by an order of magnitude.

Autonomous Ice Mass Balance Buoys for Seasonal Sea Ice

Science.gov (United States)

Whitlock, J. D.; Planck, C.; Perovich, D. K.; Parno, J. T.; Elder, B. C.; Richter-Menge, J.; Polashenski, C. M.

2017-12-01

The ice mass-balance represents the integration of all surface and ocean heat fluxes and attributing the impact of these forcing fluxes on the ice cover can be accomplished by increasing temporal and spatial measurements. Mass balance information can be used to understand the ongoing changes in the Arctic sea ice cover and to improve predictions of future ice conditions. Thinner seasonal ice in the Arctic necessitates the deployment of Autonomous Ice Mass Balance buoys (IMB's) capable of long-term, in situ data collection in both ice and open ocean. Seasonal IMB's (SIMB's) are free floating IMB's that allow data collection in thick ice, thin ice, during times of transition, and even open water. The newest generation of SIMB aims to increase the number of reliable IMB's in the Arctic by leveraging inexpensive commercial-grade instrumentation when combined with specially developed monitoring hardware. Monitoring tasks are handled by a custom, expandable data logger that provides low-cost flexibility for integrating a large range of instrumentation. The SIMB features ultrasonic sensors for direct measurement of both snow depth and ice thickness and a digital temperature chain (DTC) for temperature measurements every 2cm through both snow and ice. Air temperature and pressure, along with GPS data complete the Arctic picture. Additionally, the new SIMB is more compact to maximize deployment opportunities from multiple types of platforms.

Non-linear triangle-based polynomial expansion nodal method for hexagonal core analysis

International Nuclear Information System (INIS)

Cho, Jin Young; Cho, Byung Oh; Joo, Han Gyu; Zee, Sung Qunn; Park, Sang Yong

2000-09-01

This report is for the implementation of triangle-based polynomial expansion nodal (TPEN) method to MASTER code in conjunction with the coarse mesh finite difference(CMFD) framework for hexagonal core design and analysis. The TPEN method is a variation of the higher order polynomial expansion nodal (HOPEN) method that solves the multi-group neutron diffusion equation in the hexagonal-z geometry. In contrast with the HOPEN method, only two-dimensional intranodal expansion is considered in the TPEN method for a triangular domain. The axial dependence of the intranodal flux is incorporated separately here and it is determined by the nodal expansion method (NEM) for a hexagonal node. For the consistency of node geometry of the MASTER code which is based on hexagon, TPEN solver is coded to solve one hexagonal node which is composed of 6 triangular nodes directly with Gauss elimination scheme. To solve the CMFD linear system efficiently, stabilized bi-conjugate gradient(BiCG) algorithm and Wielandt eigenvalue shift method are adopted. And for the construction of the efficient preconditioner of BiCG algorithm, the incomplete LU(ILU) factorization scheme which has been widely used in two-dimensional problems is used. To apply the ILU factorization scheme to three-dimensional problem, a symmetric Gauss-Seidel Factorization scheme is used. In order to examine the accuracy of the TPEN solution, several eigenvalue benchmark problems and two transient problems, i.e., a realistic VVER1000 and VVER440 rod ejection benchmark problems, were solved and compared with respective references. The results of eigenvalue benchmark problems indicate that non-linear TPEN method is very accurate showing less than 15 pcm of eigenvalue errors and 1% of maximum power errors, and fast enough to solve the three-dimensional VVER-440 problem within 5 seconds on 733MHz PENTIUM-III. In the case of the transient problems, the non-linear TPEN method also shows good results within a few minute of

IceCube systematic errors investigation: Simulation of the ice

Energy Technology Data Exchange (ETDEWEB)

Resconi, Elisa; Wolf, Martin [Max-Planck-Institute for Nuclear Physics, Heidelberg (Germany); Schukraft, Anne [RWTH, Aachen University (Germany)

2010-07-01

IceCube is a neutrino observatory for astroparticle and astronomy research at the South Pole. It uses one cubic kilometer of Antartica's deepest ice (1500 m-2500 m in depth) to detect Cherenkov light, generated by charged particles traveling through the ice, with an array of phototubes encapsulated in glass pressure spheres. The arrival time as well as the charge deposited of the detected photons represent the base measurements that are used for track and energy reconstruction of those charged particles. The optical properties of the deep antarctic ice vary from layer to layer. Measurements of the ice properties and their correct modeling in Monte Carlo simulation is then of primary importance for the correct understanding of the IceCube telescope behavior. After a short summary about the different methods to investigate the ice properties and to calibrate the detector, we show how the simulation obtained by using this information compares to the measured data and how systematic errors due to uncertain ice properties are determined in IceCube.

Scanning tunneling microscopy of hexagonal BN grown on graphite

International Nuclear Information System (INIS)

Fukumoto, H.; Hamada, T.; Endo, T.; Osaka, Y.

1991-01-01

The microscopic surface topography of thin BN x films grown on graphite by electron cyclotron resonance plasma chemical vapor deposition have been imaged with scanning tunneling microscopy in air. The scanning tunneling microscope has generated images of hexagonal BN with atomic resolution

Estruturação de cristais de gelo em soluções aquosas contendo solutos diversos Ice crystals structuring in water solutions containing different solutes

Directory of Open Access Journals (Sweden)

CLÉCIA SILVA CARNEIRO

2000-02-01

Full Text Available Existe uma grande demanda de conhecimentos na área de criopreservação de frutos tropicais com vistas a reduzir os danos celulares provocados por cristais de gelo durante o congelamento. O objetivo deste trabalho foi estudar a capacidade de estruturação de cristais de gelo. Soluções aquosas contendo arabinose, glicose, piridoxina, creatina, metionina, lisina e arginina, foram submetidas a congelamento lento em ar estático e as amostras resultantes examinadas por microscopia ótica sob luz polarizada. Os açúcares arabinose e glicose provocaram nos cristais de gelo estruturações que variaram de uma configuração hexagonal a uma arbórea, dentre outras. Vitaminas hidrossolúveis e compostos hidrofílicos ou hidrofóbicos favoreceram a formação de arranjamentos circulares filamentosos.There is a great demand for information about the cryopreservation of tropical fruits to reduce cell damage caused by ice crystals during freezing. The objective of this work was to study the structuring capacity of ice cristals. Water solutions having arabinose, glucose, pyridoxine, creatine, methionine, lysine and arginine were submitted to a slow freezing process and the resulting samples were examined under an optical microscope under polarized light. Sugars (arabinose and glucose caused a range of structures, from hexagonal to tree-like configurations, among others. Water soluble vitamins and hydrophilic or hydrophobic compounds favored the formation of needles arranged in a circular-type manner.

Hexagon functions and the three-loop remainder function

Energy Technology Data Exchange (ETDEWEB)

Dixon, Lance J.; Drummond, James M.; von Hippel, Matt; Pennington, Jeffrey

2013-12-01

We present the three-loop remainder function, which describes the scattering of six gluons in the maximally-helicity-violating configuration in planar NN = 4 super-Yang-Mills theory, as a function of the three dual conformal cross ratios. The result can be expressed in terms of multiple Goncharov polylogarithms. We also employ a more restricted class of hexagon functions which have the correct branch cuts and certain other restrictions on their symbols. We classify all the hexagon functions through transcendental weight five, using the coproduct for their Hopf algebra iteratively, which amounts to a set of first-order differential equations. The three-loop remainder function is a particular weight-six hexagon function, whose symbol was determined previously. The differential equations can be integrated numerically for generic values of the cross ratios, or analytically in certain kinematic limits, including the near-collinear and multi-Regge limits. These limits allow us to impose constraints from the operator product expansion and multi-Regge factorization directly at the function level, and thereby to fix uniquely a set of Riemann ζ valued constants that could not be fixed at the level of the symbol. The near-collinear limits agree precisely with recent predictions by Basso, Sever and Vieira based on integrability. The multi-Regge limits agree with the factorization formula of Fadin and Lipatov, and determine three constants entering the impact factor at this order. We plot the three-loop remainder function for various slices of the Euclidean region of positive cross ratios, and compare it to the two-loop one. For large ranges of the cross ratios, the ratio of the three-loop to the two-loop remainder function is relatively constant, and close to -7.

FAINT LUMINESCENT RING OVER SATURN’S POLAR HEXAGON

Energy Technology Data Exchange (ETDEWEB)

Adriani, Alberto; D’Aversa, Emiliano; Oliva, Fabrizio; Filacchione, Gianrico [Institute of Space Astrophysics and Planetology of INAF, Via Fosso del Cavaliere 100, I-00133 Rome (Italy); Moriconi, Maria Luisa, E-mail: alberto.adriani@iaps.inaf.it [Institute of Atmospheric Sciences and Climate of CNR, Via Fosso del Cavaliere 100, I-00133 Rome (Italy)

2015-07-20

Springtime insolation is presently advancing across Saturn's north polar region. Early solar radiation scattered through the gaseous giant's atmosphere gives a unique opportunity to sound the atmospheric structure at its upper troposphere/lower stratosphere at high latitudes. Here, we report the detection of a tenuous bright structure in Saturn's northern polar cap corresponding to the hexagon equatorward boundary, observed by Cassini Visual and Infrared Mapping Spectrometer on 2013 June. The structure is spectrally characterized by an anomalously enhanced intensity in the 3610–3730 nm wavelength range and near 2500 nm, pertaining to relatively low opacity windows between strong methane absorption bands. Our first results suggest that a strong forward scattering by tropospheric clouds, higher in respect to the surrounding cloud deck, can be responsible for the enhanced intensity of the feature. This can be consistent with the atmospheric dynamics associated with the jet stream embedded in the polar hexagon. Further investigations at higher spectral resolution are needed to better assess the vertical distribution and microphysics of the clouds in this interesting region.

Manifestations of Kitaev physics in thermodynamic properties of hexagonal iridates and α-RuCl3

Science.gov (United States)

Tsirlin, Alexander

Kitaev model is hard to achieve in real materials. Best candidates available so far are hexagonal iridates M2IrO3 (M = Li and Na) and the recently discovered α-RuCl3 featuring hexagonal layers coupled by weak van der Waals bonding. I will review recent progress in crystal growth of these materials and compare their thermodynamic properties. Both hexagonal iridates and α-RuCl3 feature highly anisotropic Curie-Weiss temperatures that not only differ in magnitude but also change sign depending on the direction of the applied magnetic field. Néel temperatures are largely suppressed compared to the energy scale of the Curie-Weiss temperatures. These experimental observations will be linked to features of the electronic structure and to structural peculiarities associated with deviations from the ideal hexagonal symmetry. I will also discuss how the different nature of ligand atoms affects electronic structure and magnetic superexchange. This work has been done in collaboration with M. Majumder, M. Schmidt, M. Baenitz, F. Freund, and P. Gegenwart.

Sensitivity of open-water ice growth and ice concentration evolution in a coupled atmosphere-ocean-sea ice model

Science.gov (United States)

Shi, Xiaoxu; Lohmann, Gerrit

2017-09-01

A coupled atmosphere-ocean-sea ice model is applied to investigate to what degree the area-thickness distribution of new ice formed in open water affects the ice and ocean properties. Two sensitivity experiments are performed which modify the horizontal-to-vertical aspect ratio of open-water ice growth. The resulting changes in the Arctic sea-ice concentration strongly affect the surface albedo, the ocean heat release to the atmosphere, and the sea-ice production. The changes are further amplified through a positive feedback mechanism among the Arctic sea ice, the Atlantic Meridional Overturning Circulation (AMOC), and the surface air temperature in the Arctic, as the Fram Strait sea ice import influences the freshwater budget in the North Atlantic Ocean. Anomalies in sea-ice transport lead to changes in sea surface properties of the North Atlantic and the strength of AMOC. For the Southern Ocean, the most pronounced change is a warming along the Antarctic Circumpolar Current (ACC), owing to the interhemispheric bipolar seasaw linked to AMOC weakening. Another insight of this study lies on the improvement of our climate model. The ocean component FESOM is a newly developed ocean-sea ice model with an unstructured mesh and multi-resolution. We find that the subpolar sea-ice boundary in the Northern Hemisphere can be improved by tuning the process of open-water ice growth, which strongly influences the sea ice concentration in the marginal ice zone, the North Atlantic circulation, salinity and Arctic sea ice volume. Since the distribution of new ice on open water relies on many uncertain parameters and the knowledge of the detailed processes is currently too crude, it is a challenge to implement the processes realistically into models. Based on our sensitivity experiments, we conclude a pronounced uncertainty related to open-water sea ice growth which could significantly affect the climate system sensitivity.

Winter sea ice export from the Laptev Sea preconditions the local summer sea ice cover and fast ice decay

Directory of Open Access Journals (Sweden)

P. Itkin

2017-10-01

Full Text Available Ice retreat in the eastern Eurasian Arctic is a consequence of atmospheric and oceanic processes and regional feedback mechanisms acting on the ice cover, both in winter and summer. A correct representation of these processes in numerical models is important, since it will improve predictions of sea ice anomalies along the Northeast Passage and beyond. In this study, we highlight the importance of winter ice dynamics for local summer sea ice anomalies in thickness, volume and extent. By means of airborne sea ice thickness surveys made over pack ice areas in the south-eastern Laptev Sea, we show that years of offshore-directed sea ice transport have a thinning effect on the late-winter sea ice cover. To confirm the preconditioning effect of enhanced offshore advection in late winter on the summer sea ice cover, we perform a sensitivity study using a numerical model. Results verify that the preconditioning effect plays a bigger role for the regional ice extent. Furthermore, they indicate an increase in volume export from the Laptev Sea as a consequence of enhanced offshore advection, which has far-reaching consequences for the entire Arctic sea ice mass balance. Moreover we show that ice dynamics in winter not only preconditions local summer ice extent, but also accelerate fast-ice decay.

Face recognition via sparse representation of SIFT feature on hexagonal-sampling image

Science.gov (United States)

Zhang, Daming; Zhang, Xueyong; Li, Lu; Liu, Huayong

2018-04-01

This paper investigates a face recognition approach based on Scale Invariant Feature Transform (SIFT) feature and sparse representation. The approach takes advantage of SIFT which is local feature other than holistic feature in classical Sparse Representation based Classification (SRC) algorithm and possesses strong robustness to expression, pose and illumination variations. Since hexagonal image has more inherit merits than square image to make recognition process more efficient, we extract SIFT keypoint in hexagonal-sampling image. Instead of matching SIFT feature, firstly the sparse representation of each SIFT keypoint is given according the constructed dictionary; secondly these sparse vectors are quantized according dictionary; finally each face image is represented by a histogram and these so-called Bag-of-Words vectors are classified by SVM. Due to use of local feature, the proposed method achieves better result even when the number of training sample is small. In the experiments, the proposed method gave higher face recognition rather than other methods in ORL and Yale B face databases; also, the effectiveness of the hexagonal-sampling in the proposed method is verified.

Achieving a multi-band metamaterial perfect absorber via a hexagonal ring dielectric resonator

Science.gov (United States)

Li, Li-Yang; Wang, Jun; Du, Hong-Liang; Wang, Jia-Fu; Qu, Shao-Bo

2015-06-01

A multi-band absorber composed of high-permittivity hexagonal ring dielectric resonators and a metallic ground plate is designed in the microwave band. Near-unity absorptions around 9.785 GHz, 11.525 GHz, and 12.37 GHz are observed for this metamaterial absorber. The dielectric hexagonal ring resonator is made of microwave ceramics with high permittivity and low loss. The mechanism for the near-unity absorption is investigated via the dielectric resonator theory. It is found that the absorption results from electric and magnetic resonances where enhanced electromagnetic fields are excited inside the dielectric resonator. In addition, the resonance modes of the hexagonal resonator are similar to those of standard rectangle resonators and can be used for analyzing hexagonal absorbers. Our work provides a new research method as well as a solid foundation for designing and analyzing dielectric metamaterial absorbers with complex shapes. Project supported by the National Natural Science Foundation of China (Grant Nos. 61331005, 11204378, 11274389, 11304393, and 61302023), the Aviation Science Foundation of China (Grant Nos. 20132796018 and 20123196015), the Natural Science Foundation for Post-Doctoral Scientists of China (Grant Nos. 2013M532131 and 2013M532221), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2013JM6005), and the Special Funds for Authors of Annual Excellent Doctoral Degree Dissertations of China (Grant No. 201242).

A two-phase flow regime map for a MAPLE-type nuclear research reactor fuel channel: Effect of hexagonal finned bundle

International Nuclear Information System (INIS)

Harvel, G.D.; Chang, J.S.

1997-01-01

A two-phase flow regime map is developed experimentally and theoretically for a vertical hexagonal flow channel with and without a 36-finned rod hexagonal bundle. This type of flow channel is of interest to MAPLE-type nuclear research reactors. The flow regime maps are determined by visual observations and observation of waveforms shown by a capacitance-type void fraction meter. The experimental results show that the inclusion of the finned hexagonal bundle shifts the flow regime transition boundaries toward higher water flow rates. Existing flow regime maps based on pipe flow require slight modifications when applied to the hexagonal flow channel with and without a MAPLE-type finned hexagonal bundle. The proposed theoretical model agrees well with experimental results

Coherent memory functions for finite systems: hexagonal photosynthetic unit

International Nuclear Information System (INIS)

Barvik, I.; Herman, P.

1990-10-01

Coherent memory functions entering the Generalized Master Equation are presented for an hexagonal model of a photosynthetic unit. Influence of an energy heterogeneity on an exciton transfer is an antenna system as well as to a reaction center is investigated. (author). 9 refs, 3 figs

Large scale graphene/hexagonal boron nitride heterostructure for tunable plasmonics

KAUST Repository

Zhang, Kai; Yap, Fungling; Li, Kun; Ng, Changtai; Li, Linjun; Loh, Kianping

2013-01-01

Vertical integration of hexagonal boron nitride (h-BN) and graphene for the fabrication of vertical field-effect transistors or tunneling diodes has stimulated intense interest recently due to the enhanced performance offered by combining

Ice recrystallization inhibition in ice cream by propylene glycol monostearate.

Science.gov (United States)

Aleong, J M; Frochot, S; Goff, H D

2008-11-01

The effectiveness of propylene glycol monostearate (PGMS) to inhibit ice recrystallization was evaluated in ice cream and frozen sucrose solutions. PGMS (0.3%) dramatically reduced ice crystal sizes in ice cream and in sucrose solutions frozen in a scraped-surface freezer before and after heat shock, but had no effect in quiescently frozen solutions. PGMS showed limited emulsifier properties by promoting smaller fat globule size distributions and enhanced partial coalescence in the mix and ice cream, respectively, but at a much lower level compared to conventional ice cream emulsifier. Low temperature scanning electron microscopy revealed highly irregular crystal morphology in both ice cream and sucrose solutions frozen in a scraped-surface freezer. There was strong evidence to suggest that PGMS directly interacts with ice crystals and interferes with normal surface propagation. Shear during freezing may be required for its distribution around the ice and sufficient surface coverage.

Probing topological relations between high-density and low-density regions of 2MASS with hexagon cells

Energy Technology Data Exchange (ETDEWEB)

Wu, Yongfeng [American Physical Society, San Diego, CA (United States); Xiao, Weike, E-mail: yongfeng.wu@maine.edu [Department of Astronautics Engineering, Harbin Institute of Technology, P.O. Box 345, Heilongjiang Province 150001 (China)

2014-02-01

We introduced a new two-dimensional (2D) hexagon technique for probing the topological structure of the universe in which we mapped regions of the sky with high and low galaxy densities onto a 2D lattice of hexagonal unit cells. We defined filled cells as corresponding to high-density regions and empty cells as corresponding to low-density regions. The numbers of filled cells and empty cells were kept the same by controlling the size of the cells. By analyzing the six sides of each hexagon, we could obtain and compare the statistical topological properties of high-density and low-density regions of the universe in order to have a better understanding of the evolution of the universe. We applied this hexagonal method to Two Micron All Sky Survey data and discovered significant topological differences between the high-density and low-density regions. Both regions had significant (>5σ) topological shifts from both the binomial distribution and the random distribution.

Comparison of square and hexagonal fuel lattices for high conversion PWRs

International Nuclear Information System (INIS)

Kotlyar, D.; Shwageraus, E.

2011-01-01

This paper reports on an investigation into fuel design choices of a PWR operating in a self sustainable Th- 233 U fuel cycle. Achieving such self-sustainable with respect to fissile material fuel cycle would practically eliminate concerns over nuclear fuel supply hundreds of years into the future. Moreover, utilization of light water reactor technology and its associated vast experience would allow faster deployment of such fuel cycle without immediate need for development of fast reactor technology, which tends to be more complex and costly. In order to evaluate feasibility of this concept, two types of fuel assembly lattices were considered: square and hexagonal. The hexagonal lattice may offer some advantages over the square one. For example, the fertile blanket fuel can be packed more tightly reducing the blanket volume fraction in the core and potentially allowing to achieve higher core average power density. Furthermore, hexagonal lattice may allow more uniform leakage of neutrons from fissile to fertile regions and therefore more uniform neutron captures in thorium blanket. The calculations were carried out with Monte-Carlo based BGCore system, which includes neutronic, fuel depletion and thermo-hydraulic modules. The results were compared to those obtained from Serpent Monte-Carlo code and deterministic fuel assembly transport code BOXER. One of the major design challenges associated with the square seed-blanket concept is high power peaking due to the high concentration of fissile material in the seed region. In order to explore feasibility of the studied designs, the calculations were extended to include 3D fuel assembly analysis with thermal-hydraulic feedback. The coupled neutronic - thermal-hydraulic calculations were performed with BGCore code system. The analysis showed that both hexagonal and square seed-blanket fuel assembly designs have a potential of achieving net breeding. While no major neutronic advantages were observed for either fuel

7-Hexagon Multifocal Electroretinography for an Objective Functional Assessment of the Macula in 14 Seconds.

Science.gov (United States)

Schönbach, Etienne M; Chaikitmongkol, Voraporn; Annam, Rachel; McDonnell, Emma C; Wolfson, Yulia; Fletcher, Emily; Scholl, Hendrik P N

2017-01-01

We present the multifocal electroretinogram (mfERG) with a 7-hexagon array as an objective test of macular function that can be recorded in 14 s. We provide normal values and investigate its reproducibility and validity. Healthy participants underwent mfERG testing according to International Society for Clinical Electrophysiology of Vision (ISCEV) standards using the Espion Profile/D310 multifocal ERG system (Diagnosys, LLC, Lowell, MA, USA). One standard recording of a 61-hexagon array and 2 repeated recordings of a custom 7-hexagon array were obtained. A total of 13 subjects (mean age 46.9 years) were included. The median response densities were 12.5 nV/deg2 in the center and 5.2 nV/deg2 in the periphery. Intereye correlations were strong in both the center (ρCenter = 0.821; p < 0.0001) and the periphery (ρPeriphery = 0.862; p < 0.0001). Intraeye correlations were even stronger: ρCenter = 0.904 with p < 0.0001 and ρPeriphery = 0.955 with p < 0.0001. Bland-Altman plots demonstrated an acceptable retest mean difference in both the center and periphery, and narrow limits of agreement. We found strong correlations of the center (ρCenter = 0.826; p < 0.0001) and periphery (ρPeriphery = 0.848; p < 0.0001), with recordings obtained by the 61-hexagon method. The 7-hexagon mfERG provides reproducible results in agreement with results obtained according to the ISCEV standard. © 2017 S. Karger AG, Basel.

Torque and Axial Loading Physics for Measuring Atmospheric Icing Load and Icing Rate

OpenAIRE

Mughal, Umair Najeeb; Virk, Muhammad Shakeel

2015-01-01

Measuring icing load and icing rate are important parameters for an atmospheric icing sensor. A new icing sensor has recently been designed and developed at Narvik University College for measuring atmospheric icing rate, icing load and icing type. Unlike the existing atmospheric icing sensors commercially available in market, which uses the axial loading for measuring icing load and icing rate, this new sensory system measures icing load and icing rate using the torque loading physics. The pe...

[Measurement of plasma parameters in cluster hexagon pattern discharge by optical emission spectrum].

Science.gov (United States)

Dong, Li-Fang; Shen, Zhong-Kai; Li, Xin-Chun; Liu, Liang; Lu, Ning; Shang, Jie

2012-09-01

The cluster hexagon pattern was obtained in a dielectric barrier discharge in air/argon for the first time. Three plasma parameters, i. e. the molecular vibrational temperature, the molecular rotational temperature and the average electron energy of individual cluster in cluster hexagon pattern discharge, were studied by changing the air content. The molecular vibrational temperature and the molecular rotational temperature were calculated using the second positive band system of nitrogen molecules (C 3IIu --> B 3IIg) and the first negative band system of nitrogen molecular ions (B 2Sigma(u)+ --> Chi2 Sigma(g)+). The relative intensities of the first negative system of nitrogen molecular ions (391. 4 nm) and nitrogen molecules emission spectrum line (337.1 nm) were analyzed for studying the variations of the electron energy. It was found that the three plasma parameters of individual cluster in cluster hexagon pattern increase with air content increasing from 16% to 24%.

Ice-sheet flow conditions deduced from mechanical tests of ice core

DEFF Research Database (Denmark)

Miyamoto, Atsushi; Narita, Hideki; Hondoh, Takeo

1999-01-01

Uniaxial compression tests were performed on samples of the Greenland Ice Core Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate....... It was revealed that cloudy bands affect ice-deformation processes, but the details remain unclear. Udgivelsesdato: June......Uniaxial compression tests were performed on samples of the Greenland Ice Core Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate......-core samples with basal planes parallel to the horizontal plane of the ice sheet. The ice-flow enhancement factors show a gradual increase with depth down to approximately 2000 m. These results can be interpreted in terms of an increase in the fourth-order Schmid factor. Below 2000 m depth, the flow...

Possible Mechanisms for Turbofan Engine Ice Crystal Icing at High Altitude

Science.gov (United States)

Tsao, Jen-Ching; Struk, Peter M.; Oliver, Michael J.

2016-01-01

A thermodynamic model is presented to describe possible mechanisms of ice formation on unheated surfaces inside a turbofan engine compression system from fully glaciated ice crystal clouds often formed at high altitude near deep convective weather systems. It is shown from the analysis that generally there could be two distinct types of ice formation: (1) when the "surface freezing fraction" is in the range of 0 to 1, dominated by the freezing of water melt from fully or partially melted ice crystals, the ice structure is formed from accretion with strong adhesion to the surface, and (2) when the "surface melting fraction" is the range of 0 to 1, dominated by the further melting of ice crystals, the ice structure is formed from accumulation of un-melted ice crystals with relatively weak bonding to the surface. The model captures important qualitative trends of the fundamental ice-crystal icing phenomenon reported earlier (Refs. 1 and 2) from the research collaboration work by NASA and the National Research Council (NRC) of Canada. Further, preliminary analysis of test data from the 2013 full scale turbofan engine ice crystal icing test (Ref. 3) conducted in the NASA Glenn Propulsion Systems Laboratory (PSL) has also suggested that (1) both types of ice formation occurred during the test, and (2) the model has captured some important qualitative trend of turning on (or off) the ice crystal ice formation process in the tested engine low pressure compressor (LPC) targeted area under different icing conditions that ultimately would lead to (or suppress) an engine core roll back (RB) event.

Sea ice roughness: the key for predicting Arctic summer ice albedo

Science.gov (United States)

Landy, J.; Ehn, J. K.; Tsamados, M.; Stroeve, J.; Barber, D. G.

2017-12-01

Although melt ponds on Arctic sea ice evolve in stages, ice with smoother surface topography typically allows the pond water to spread over a wider area, reducing the ice-albedo and accelerating further melt. Building on this theory, we simulated the distribution of meltwater on a range of statistically-derived topographies to develop a quantitative relationship between premelt sea ice surface roughness and summer ice albedo. Our method, previously applied to ICESat observations of the end-of-winter sea ice roughness, could account for 85% of the variance in AVHRR observations of the summer ice-albedo [Landy et al., 2015]. Consequently, an Arctic-wide reduction in sea ice roughness over the ICESat operational period (from 2003 to 2008) explained a drop in ice-albedo that resulted in a 16% increase in solar heat input to the sea ice cover. Here we will review this work and present new research linking pre-melt sea ice surface roughness observations from Cryosat-2 to summer sea ice albedo over the past six years, examining the potential of winter roughness as a significant new source of sea ice predictability. We will further evaluate the possibility for high-resolution (kilometre-scale) forecasts of summer sea ice albedo from waveform-level Cryosat-2 roughness data in the landfast sea ice zone of the Canadian Arctic. Landy, J. C., J. K. Ehn, and D. G. Barber (2015), Albedo feedback enhanced by smoother Arctic sea ice, Geophys. Res. Lett., 42, 10,714-10,720, doi:10.1002/2015GL066712.

Higher order polynomial expansion nodal method for hexagonal core neutronics analysis

International Nuclear Information System (INIS)

Jin, Young Cho; Chang, Hyo Kim

1998-01-01

A higher-order polynomial expansion nodal(PEN) method is newly formulated as a means to improve the accuracy of the conventional PEN method solutions to multi-group diffusion equations in hexagonal core geometry. The new method is applied to solving various hexagonal core neutronics benchmark problems. The computational accuracy of the higher order PEN method is then compared with that of the conventional PEN method, the analytic function expansion nodal (AFEN) method, and the ANC-H method. It is demonstrated that the higher order PEN method improves the accuracy of the conventional PEN method and that it compares very well with the other nodal methods like the AFEN and ANC-H methods in accuracy

Edge-functionalization of armchair graphene nanoribbons with pentagonal-hexagonal edge structures.

Science.gov (United States)

Ryou, Junga; Park, Jinwoo; Kim, Gunn; Hong, Suklyun

2017-06-21

Using density functional theory calculations, we have studied the edge-functionalization of armchair graphene nanoribbons (AGNRs) with pentagonal-hexagonal edge structures. While the AGNRs with pentagonal-hexagonal edge structures (labeled (5,6)-AGNRs) are metallic, the edge-functionalized (5,6)-AGNRs with substitutional atoms opens a band gap. We find that the band structures of edge-functionalized (5,6)-N-AGNRs by substitution resemble those of defect-free (N-1)-AGNR at the Γ point, whereas those at the X point show the original ones of the defect-free N-AGNR. The overall electronic structures of edge-functionalized (5,6)-AGNRs depend on the number of electrons, supplied by substitutional atoms, at the edges of functionalized (5,6)-AGNRs.

Wave–ice interactions in the neXtSIM sea-ice model

Directory of Open Access Journals (Sweden)

T. D. Williams

2017-09-01

Full Text Available In this paper we describe a waves-in-ice model (WIM, which calculates ice breakage and the wave radiation stress (WRS. This WIM is then coupled to the new sea-ice model neXtSIM, which is based on the elasto-brittle (EB rheology. We highlight some numerical issues involved in the coupling and investigate the impact of the WRS, and of modifying the EB rheology to lower the stiffness of the ice in the area where the ice has broken up (the marginal ice zone or MIZ. In experiments in the absence of wind, we find that wind waves can produce noticeable movement of the ice edge in loose ice (concentration around 70 % – up to 36 km, depending on the material parameters of the ice that are used and the dynamical model used for the broken ice. The ice edge position is unaffected by the WRS if the initial concentration is higher (≳ 0.9. Swell waves (monochromatic waves with low frequency do not affect the ice edge location (even for loose ice, as they are attenuated much less than the higher-frequency components of a wind wave spectrum, and so consequently produce a much lower WRS (by about an order of magnitude at least.In the presence of wind, we find that the wind stress dominates the WRS, which, while large near the ice edge, decays exponentially away from it. This is in contrast to the wind stress, which is applied over a much larger ice area. In this case (when wind is present the dynamical model for the MIZ has more impact than the WRS, although that effect too is relatively modest. When the stiffness in the MIZ is lowered due to ice breakage, we find that on-ice winds produce more compression in the MIZ than in the pack, while off-ice winds can cause the MIZ to be separated from the pack ice.

Understanding Ice Shelf Basal Melting Using Convergent ICEPOD Data Sets: ROSETTA-Ice Study of Ross Ice Shelf

Science.gov (United States)

Bell, R. E.; Frearson, N.; Tinto, K. J.; Das, I.; Fricker, H. A.; Siddoway, C. S.; Padman, L.

2017-12-01

The future stability of the ice shelves surrounding Antarctica will be susceptible to increases in both surface and basal melt as the atmosphere and ocean warm. The ROSETTA-Ice program is targeted at using the ICEPOD airborne technology to produce new constraints on Ross Ice Shelf, the underlying ocean, bathymetry, and geologic setting, using radar sounding, gravimetry and laser altimetry. This convergent approach to studying the ice-shelf and basal processes enables us to develop an understanding of the fundamental controls on ice-shelf evolution. This work leverages the stratigraphy of the ice shelf, which is detected as individual reflectors by the shallow-ice radar and is often associated with surface scour, form close to the grounding line or pinning points on the ice shelf. Surface accumulation on the ice shelf buries these reflectors as the ice flows towards the calving front. This distinctive stratigraphy can be traced across the ice shelf for the major East Antarctic outlet glaciers and West Antarctic ice streams. Changes in the ice thickness below these reflectors are a result of strain and basal melting and freezing. Correcting the estimated thickness changes for strain using RIGGS strain measurements, we can develop decadal-resolution flowline distributions of basal melt. Close to East Antarctica elevated melt-rates (>1 m/yr) are found 60-100 km from the calving front. On the West Antarctic side high melt rates primarily develop within 10 km of the calving front. The East Antarctic side of Ross Ice Shelf is dominated by melt driven by saline water masses that develop in Ross Sea polynyas, while the melting on the West Antarctic side next to Hayes Bank is associated with modified Continental Deep Water transported along the continental shelf. The two sides of Ross Ice Shelf experience differing basal melt in part due to the duality in the underlying geologic structure: the East Antarctic side consists of relatively dense crust, with low amplitude

Ross Ice Shelf, Antarctic Ice and Clouds

Science.gov (United States)

1991-01-01

In this view of Antarctic ice and clouds, (56.5S, 152.0W), the Ross Ice Shelf of Antarctica is almost totally clear, showing stress cracks in the ice surface caused by wind and tidal drift. Clouds on the eastern edge of the picture are associated with an Antarctic cyclone. Winds stirred up these storms have been known to reach hurricane force.

Open-Source Python Modules to Estimate Level Ice Thickness from Ice Charts

Science.gov (United States)

Geiger, C. A.; Deliberty, T. L.; Bernstein, E. R.; Helfrich, S.

2012-12-01

A collaborative research effort between the University of Delaware (UD) and National Ice Center (NIC) addresses the task of providing open-source translations of sea ice stage-of-development into level ice thickness estimates on a 4km grid for the Interactive Multisensor Snow and Ice Mapping System (IMS). The characteristics for stage-of-development are quantified from remote sensing imagery with estimates of level ice thickness categories originating from World Meteorological Organization (WMO) egg coded ice charts codified since the 1970s. Conversions utilize Python scripting modules which transform electronic ice charts with WMO egg code characteristics into five level ice thickness categories, in centimeters, (0-10, 10-30, 30-70, 70-120, >120cm) and five ice types (open water, first year pack ice, fast ice, multiyear ice, and glacial ice with a reserve slot for deformed ice fractions). Both level ice thickness categories and ice concentration fractions are reported with uncertainties propagated based on WMO ice stage ranges which serve as proxy estimates for standard deviation. These products are in preparation for use by NCEP, CMC, and NAVO by 2014 based on their modeling requirements for daily products in near-real time. In addition to development, continuing research tests the value of these estimated products against in situ observations to improve both value and uncertainty estimates.

Whole core transport calculation for the VHTR hexagonal core

International Nuclear Information System (INIS)

Cho, J. Y.; Kim, K. S.; Lee, C. C.; Joo, H. G.

2007-01-01

Recently, the DeCART code which performs the whole core calculation by coupling the radial MOC transport kernel with the axial nodal kernel has equipped a kernel to deal with the hexagonal geometry and applied to the VHTR hexagonal core to examine the accuracy and the computational efficiency of the implemented kernel. The implementation includes a modular ray tracing module based on the hexagonal assembly and a multi-group CMFD module to perform an efficient transport calculation. The requirements for the modular ray are: (1) the assembly based path linking and (2) the complete reflection capabilities. The first requirement is met by adjusting the azimuthal angle and the ray spacing for the modular ray to construct a core ray by the path linking. The second requirement is met by expanding the constructed azimuthal angle in the range of [0,30 degree] to the remained range to reflect completely at the core boundaries. The considered reflecting surface angles for the complete reflection are 30n's (n=1,2,1,12). The CMFD module performs the equivalent diffusion calculation to the radial MOC transport calculation based on the homogenized structure units. The structure units include the hexagonal pin cells and gap cells appearing at the assembly boundary. Therefore, the CMFD module is programmed to deal with the unstructured cells such as the gap cells. The CMFD equation consists of the two parts of (1) the conventional FDM and (2) the current corrective parts. Since the second part of the CMFD equation guarantees the reproducibility of the radial MOC transport solutions for the cell averaged reaction rate and the net current at the cell surfaces, how to build the first part of the CMFD equation is not important. Therefore, the first part of the CMFD equation is roughly built by using the normal distance from the gravity center to the surface. The VHTR core uses helium as a coolant which is realized as a void hole in a neutronics calculation. This void hole which

Polar Ice Caps: a Canary for the Greenland Ice Sheet

Science.gov (United States)

Honsaker, W.; Lowell, T. V.; Sagredo, E.; Kelly, M. A.; Hall, B. L.

2010-12-01

Ice caps are glacier masses that are highly sensitive to climate change. Because of their hypsometry they can have a binary state. When relatively slight changes in the equilibrium line altitude (ELA) either intersect or rise above the land the ice can become established or disappear. Thus these upland ice masses have a fast response time. Here we consider a way to extract the ELA signal from independent ice caps adjacent to the Greenland Ice Sheet margin. It may be that these ice caps are sensitive trackers of climate change that also impact the ice sheet margin. One example is the Istorvet Ice Cap located in Liverpool Land, East Greenland (70.881°N, 22.156°W). The ice cap topography and the underlying bedrock surface dips to the north, with peak elevation of the current ice ranging in elevation from 1050 to 745 m.a.s.l. On the eastern side of the ice mass the outlet glaciers extending down to sea level. The western margin has several small lobes in topographic depressions, with the margin reaching down to 300 m.a.s.l. Topographic highs separate the ice cap into at least 5 main catchments, each having a pair of outlet lobes toward either side of the ice cap. Because of the regional bedrock slope each catchment has its own elevation range. Therefore, as the ELA changes it is possible for some catchments of the ice cap to experience positive mass balance while others have a negative balance. Based on weather observations we estimate the present day ELA to be ~1000 m.a.s.l, meaning mass balance is negative for the majority of the ice cap. By tracking glacier presence/absence in these different catchments, we can reconstruct small changes in the ELA. Another example is the High Ice Cap (informal name) in Milne Land (70.903°N, 25.626°W, 1080 m), East Greenland. Here at least 4 unconformities in ice layers found near the southern margin of the ice cap record changing intervals of accumulation and ablation. Therefore, this location may also be sensitive to slight

Safe Loads on Ice Sheets (Ice Engineering. Number 13)

National Research Council Canada - National Science Library

Haynes, F. D; Carey, Kevin L; Cattabriga, Gioia

1996-01-01

Every winter, ice sheets that grow on lakes and rivers in northern states are used for ice roads, ice bridges, construction platforms, airstrips, and recreational activities, It becomes very important...

Anisotropic Hexagonal Boron Nitride Nanomaterials - Synthesis and Applications

Energy Technology Data Exchange (ETDEWEB)

Han,W.Q.

2008-08-01

Boron nitride (BN) is a synthetic binary compound located between III and V group elements in the Periodic Table. However, its properties, in terms of polymorphism and mechanical characteristics, are rather close to those of carbon compared with other III-V compounds, such as gallium nitride. BN crystallizes into a layered or a tetrahedrally linked structure, like those of graphite and diamond, respectively, depending on the conditions of its preparation, especially the pressure applied. Such correspondence between BN and carbon readily can be understood from their isoelectronic structures [1, 2]. On the other hand, in contrast to graphite, layered BN is transparent and is an insulator. This material has attracted great interest because, similar to carbon, it exists in various polymorphic forms exhibiting very different properties; however, these forms do not correspond strictly to those of carbon. Crystallographically, BN is classified into four polymorphic forms: Hexagonal BN (h-BN) (Figure 1(b)); rhombohedral BN (r-BN); cubic BN (c-BN); and wurtzite BN (w-BN). BN does not occur in nature. In 1842, Balmain [3] obtained BN as a reaction product between molten boric oxide and potassium cyanide under atmospheric pressure. Thereafter, many methods for its synthesis were reported. h-BN and r-BN are formed under ambient pressure. c-BN is synthesized from h-BN under high pressure at high temperature while w-BN is prepared from h-BN under high pressure at room temperature [1]. Each BN layer consists of stacks of hexagonal plate-like units of boron and nitrogen atoms linked by SP{sup 2} hybridized orbits and held together mainly by Van der Waals force (Fig 1(b)). The hexagonal polymorph has two-layered repeating units: AA'AA'... that differ from those in graphite: ABAB... (Figure 1(a)). Within the layers of h-BN there is coincidence between the same phases of the hexagons, although the boron atoms and nitrogen atoms are alternatively located along the c

Hexagon and stripe patterns in dielectric barrier streamer discharge

International Nuclear Information System (INIS)

Dong Lifang; He Yafeng; Yin Zengqian; Chai Zhifang

2004-01-01

We present a specially designed dielectric barrier discharge (DBD) system for the study of pattern formation. Hexagon and stripe patterns have been observed in a streamer discharge in a DBD for the first time. The phase diagram of pattern types as a function of applied voltage is given

Extension of the comet method to 2-D hexagonal geometry

International Nuclear Information System (INIS)

Connolly, Kevin John; Rahnema, Farzad; Zhang, Dingkang

2011-01-01

The capability of the heterogeneous coarse mesh radiation transport (COMET) method developed at Georgia Tech has been expanded. COMET is now able to treat hexagonal geometry in two dimensions, allowing reactor problems to be solved for those next-generation reactors which utilize prismatic block structure and hexagonal lattice geometry in their designs. The COMET method is used to solve whole core reactor analysis problems without resorting to homogenization or low-order transport approximations. The eigenvalue and fission density distribution of the reactor are determined iteratively using response functions. The method has previously proven accurate in solving PWR, BWR, and CANDU eigenvalue problems. In this paper, three simple test cases inspired by high temperature test reactor material cross sections and fuel block geometry are presented. These cases are given not in an attempt to model realistic nuclear power systems, but in order to test the ability of the improved method. Solutions determined by the new hexagonal version of COMET, COMET-Hex, are compared with solutions determined by MCNP5, and the results show the accuracy and efficiency of the improved COMET-Hex method in calculating the eigenvalue and fuel pin fission density in sample full-core problems. COMETHex determines the eigenvalues of these simple problems to an order of within 50 pcm of the reference solutions and all pin fission densities to an average error of 0.2%, and it requires fewer than three minutes to produce these results. (author)

Dark ice dynamics of the south-west Greenland Ice Sheet

Science.gov (United States)

Tedstone, Andrew J.; Bamber, Jonathan L.; Cook, Joseph M.; Williamson, Christopher J.; Fettweis, Xavier; Hodson, Andrew J.; Tranter, Martyn

2017-11-01

Runoff from the Greenland Ice Sheet (GrIS) has increased in recent years due largely to changes in atmospheric circulation and atmospheric warming. Albedo reductions resulting from these changes have amplified surface melting. Some of the largest declines in GrIS albedo have occurred in the ablation zone of the south-west sector and are associated with the development of dark ice surfaces. Field observations at local scales reveal that a variety of light-absorbing impurities (LAIs) can be present on the surface, ranging from inorganic particulates to cryoconite materials and ice algae. Meanwhile, satellite observations show that the areal extent of dark ice has varied significantly between recent successive melt seasons. However, the processes that drive such large interannual variability in dark ice extent remain essentially unconstrained. At present we are therefore unable to project how the albedo of bare ice sectors of the GrIS will evolve in the future, causing uncertainty in the projected sea level contribution from the GrIS over the coming decades. Here we use MODIS satellite imagery to examine dark ice dynamics on the south-west GrIS each year from 2000 to 2016. We quantify dark ice in terms of its annual extent, duration, intensity and timing of first appearance. Not only does dark ice extent vary significantly between years but so too does its duration (from 0 to > 80 % of June-July-August, JJA), intensity and the timing of its first appearance. Comparison of dark ice dynamics with potential meteorological drivers from the regional climate model MAR reveals that the JJA sensible heat flux, the number of positive minimum-air-temperature days and the timing of bare ice appearance are significant interannual synoptic controls. We use these findings to identify the surface processes which are most likely to explain recent dark ice dynamics. We suggest that whilst the spatial distribution of dark ice is best explained by outcropping of particulates from

Solution of the Neutron transport equation in hexagonal geometry using strongly discontinuous nodal schemes; Solucion de la Ecuacion de transporte de neutrones en geometria hexagonal usando esquemas nodales fuertemente discontinuos

Energy Technology Data Exchange (ETDEWEB)

Mugica R, C.A.; Valle G, E. del [IPN, ESFM, Departamento de Ingenieria Nuclear, 07738 Mexico D.F. (Mexico)]. e-mail: cmugica@ipn.mx

2005-07-01

In 2002, E. del Valle and Ernest H. Mund developed a technique to solve numerically the Neutron transport equations in discrete ordinates and hexagonal geometry using two nodal schemes type finite element weakly discontinuous denominated WD{sub 5,3} and WD{sub 12,8} (of their initials in english Weakly Discontinuous). The technique consists on representing each hexagon in the union of three rhombuses each one of which it is transformed in a square in the one that the methods WD{sub 5,3} and WD{sub 12,8} were applied. In this work they are solved the mentioned equations of transport using the same discretization technique by hexagon but using two nodal schemes type finite element strongly discontinuous denominated SD{sub 3} and SD{sub 8} (of their initials in english Strongly Discontinuous). The application in each case as well as a reference problem for those that results are provided for the effective multiplication factor is described. It is carried out a comparison with the obtained results by del Valle and Mund for different discretization meshes so much angular as spatial. (Author)

GPR capabilities for ice thickness sampling of low salinity ice and for detecting oil in ice

Energy Technology Data Exchange (ETDEWEB)

Lalumiere, Louis [Sensors by Design Ltd. (Canada)

2011-07-01

This report discusses the performance and capabilities test of two airborne ground-penetrating radar (GPR) systems of the Bedford Institute of Oceanography (BIO), Noggin 1000 and Noggin 500, for monitoring low salinity snow and ice properties which was used to measure the thickness of brackish ice on Lake Melville in Labrador and on a tidal river in Prince Edward Island. The work of other researchers is documented and the measurement techniques proposed are compared to the actual GPR approach. Different plots of GPR data taken over snow and freshwater ice and over ice with changing salinity are discussed. An interpretation of brackish ice GPR plots done by the Noggin 1000 and Noggin 500 systems is given based on resolution criterion. Additionally, the capability of the BIO helicopter-borne GPR to detect oil-in-ice has been also investigated, and an opinion on the likelihood of the success of GPR as an oil-in-ice detector is given.

Sea Ice Ecosystems

Science.gov (United States)

Arrigo, Kevin R.

2014-01-01

Polar sea ice is one of the largest ecosystems on Earth. The liquid brine fraction of the ice matrix is home to a diverse array of organisms, ranging from tiny archaea to larger fish and invertebrates. These organisms can tolerate high brine salinity and low temperature but do best when conditions are milder. Thriving ice algal communities, generally dominated by diatoms, live at the ice/water interface and in recently flooded surface and interior layers, especially during spring, when temperatures begin to rise. Although protists dominate the sea ice biomass, heterotrophic bacteria are also abundant. The sea ice ecosystem provides food for a host of animals, with crustaceans being the most conspicuous. Uneaten organic matter from the ice sinks through the water column and feeds benthic ecosystems. As sea ice extent declines, ice algae likely contribute a shrinking fraction of the total amount of organic matter produced in polar waters.

Heavy Metal Presence in Two Different Types of Ice Cream: Artisanal Ice Cream (Italian Gelato) and Industrial Ice Cream.

Science.gov (United States)

Conficoni, D; Alberghini, L; Bissacco, E; Ferioli, M; Giaccone, V

2017-03-01

Ice cream, a popular product worldwide, is usually a milk-based product with other types of ingredients (fruit, eggs, cocoa, dried fruit, additives, and others). Different materials are used to obtain the desired taste, texture, consistency, and appearance of the final product. This study surveyed ice cream products available in Italy for heavy metals (lead, cadmium, chromium, tin, and arsenic). The differences between artisanal and industrial ice cream were also investigated because of the importance in the Italian diet and the diffusion of this ready-to-eat food. Ice cream sampling was performed between October 2010 and February 2011 in the northeast of Italy. A total of 100 samples were randomly collected from different sources: 50 industrial samples produced by 19 different brands were collected in coffee bars and supermarkets; 50 artisanal ice cream samples were gathered at nine different artisanal ice cream shops. Ten wooden sticks of industrial ice cream were analyzed in parallel to the ice cream. All samples were negative for arsenic and mercury. None of the artisanal ice cream samples were positive for lead and tin; 18% of the industrial ice cream samples were positive. All positive lead samples were higher than the legal limit stated for milk (0.02 mg/kg). All industrial ice cream samples were negative for cadmium, but cadmium was present in 10% of the artisanal ice cream samples. Chromium was found in 26% of the artisanal and in 58% of the industrial ice cream samples. The heavy metals found in the wooden sticks were different from the corresponding ice cream, pointing out the lack of cross-contamination between the products. Considering the results and the amount of ice cream consumed during the year, contamination through ice cream is a low risk for the Italian population, even though there is need for further analysis.

Domain wall kinetics of lithium niobate single crystals near the hexagonal corner

Energy Technology Data Exchange (ETDEWEB)

Choi, Ju Won [Department of Physics and Photon Science, Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Ko, Do-Kyeong [Department of Physics and Photon Science, Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Advanced Photonics Research Institute, GIST, 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Yu, Nan Ei, E-mail: neyu@gist.ac.kr, E-mail: jhro@pnu.edu [Advanced Photonics Research Institute, GIST, 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Kitamura, Kenji [National Institute for Materials Science, Tsukuba, Ibaraki 305-0044 (Japan); Ro, Jung Hoon, E-mail: neyu@gist.ac.kr, E-mail: jhro@pnu.edu [Department of Biomedical Engineering, School of Medicine, Pusan National University, Busan 602-739 (Korea, Republic of)

2015-03-09

A mesospheric approach based on a simple microscopic 2D Ising model in a hexagonal lattice plane is proposed to explain macroscopic “asymmetric in-out domain wall motion” observation in the (0001) plane of MgO-doped stoichiometric lithium niobate. Under application of an electric field that was higher than the conventional coercive field (E{sub c}) to the ferroelectric crystal, a natural hexagonal domain was obtained with walls that were parallel to the Y-axis of the crystal. When a fraction of the coercive field of around 0.1E{sub c} is applied in the reverse direction, this hexagonal domain is shrunk (moved inward) from the corner site into a shape with a corner angle of around 150° and 15° wall slopes to the Y-axis. A flipped electric field of 0.15E{sub c} is then applied to recover the natural hexagonal shape, and the 150° corner shape changes into a flat wall with 30° slope (moved outward). The differences in corner domain shapes between inward and outward domain motion were analyzed theoretically in terms of corner and wall site energies, which are described using the domain corner angle and wall slope with respect to the crystal Y-axis, respectively. In the inward domain wall motion case, the energy levels of the evolving 150° domain corner and 15° slope walls are most competitive, and could co-exist. In the outward case, the energy levels of corners with angles >180° are highly stable when compared with the possible domain walls; only a flat wall with 30° slope to the Y-axis is possible during outward motion.

Neutron noise calculations in a hexagonal geometry and comparison with analytical solutions

International Nuclear Information System (INIS)

Tran, H. N.; Demaziere, C.

2012-01-01

This paper presents the development of a neutronic and kinetic solver for hexagonal geometries. The tool is developed based on the diffusion theory with multi-energy groups and multi-groups of delayed neutron precursors allowing the solutions of forward and adjoint problems of static and dynamic states, and is applicable to both thermal and fast systems with hexagonal geometries. In the dynamic problems, the small stationary fluctuations of macroscopic cross sections are considered as noise sources, and then the induced first order noise is calculated fully in the frequency domain. Numerical algorithms for solving the static and noise equations are implemented with a spatial discretization based on finite differences and a power iterative solution. A coarse mesh finite difference method has been adopted for speeding up the convergence. Since no other numerical tool could calculate frequency-dependent noise in hexagonal geometry, validation calculations have been performed and benchmarked to analytical solutions based on a 2-D homogeneous system with two-energy groups and one-group of delayed neutron precursor, in which point-like perturbations of thermal absorption cross section at central and non-central positions are considered as noise sources. (authors)

Applying machine learning methods for characterization of hexagonal prisms from their 2D scattering patterns - an investigation using modelled scattering data

Science.gov (United States)

Salawu, Emmanuel Oluwatobi; Hesse, Evelyn; Stopford, Chris; Davey, Neil; Sun, Yi

2017-11-01

Better understanding and characterization of cloud particles, whose properties and distributions affect climate and weather, are essential for the understanding of present climate and climate change. Since imaging cloud probes have limitations of optical resolution, especially for small particles (with diameter < 25 μm), instruments like the Small Ice Detector (SID) probes, which capture high-resolution spatial light scattering patterns from individual particles down to 1 μm in size, have been developed. In this work, we have proposed a method using Machine Learning techniques to estimate simulated particles' orientation-averaged projected sizes (PAD) and aspect ratio from their 2D scattering patterns. The two-dimensional light scattering patterns (2DLSP) of hexagonal prisms are computed using the Ray Tracing with Diffraction on Facets (RTDF) model. The 2DLSP cover the same angular range as the SID probes. We generated 2DLSP for 162 hexagonal prisms at 133 orientations for each. In a first step, the 2DLSP were transformed into rotation-invariant Zernike moments (ZMs), which are particularly suitable for analyses of pattern symmetry. Then we used ZMs, summed intensities, and root mean square contrast as inputs to the advanced Machine Learning methods. We created one random forests classifier for predicting prism orientation, 133 orientation-specific (OS) support vector classification models for predicting the prism aspect-ratios, 133 OS support vector regression models for estimating prism sizes, and another 133 OS Support Vector Regression (SVR) models for estimating the size PADs. We have achieved a high accuracy of 0.99 in predicting prism aspect ratios, and a low value of normalized mean square error of 0.004 for estimating the particle's size and size PADs.

Model for lattice dynamics of hexagonal close packed metals

Energy Technology Data Exchange (ETDEWEB)

Singh, R K [Tata Inst. of Fundamental Research, Bombay (India); Kumar, S [Meerut Coll. (India). Dept. of Physics

1977-11-19

A lattice dynamical model, which satisfies the requirements of translational invariance as well as the static equilibrium of hexagonal close packed lattice, has been proposed and applied to study the phonon dispersion relations in magnesium. The results revealed by this model have been claimed to be better than earlier ones.

The response of grounded ice to ocean temperature forcing in a coupled ice sheet-ice shelf-ocean cavity model

Science.gov (United States)

Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.

2010-12-01

Ice shelves provide a pathway for the heat content of the ocean to influence continental ice sheets. Changes in the rate or location of basal melting can alter their geometry and effect changes in stress conditions at the grounding line, leading to a grounded ice response. Recent observations of ice streams and ice shelves in the Amundsen Sea sector of West Antarctica have been consistent with this story. On the other hand, ice dynamics in the grounding zone control flux into the shelf and thus ice shelf geometry, which has a strong influence on the circulation in the cavity beneath the shelf. Thus the coupling between the two systems, ocean and ice sheet-ice shelf, can be quite strong. We examine the response of the ice sheet-ice shelf-ocean cavity system to changes in ocean temperature using a recently developed coupled model. The coupled model consists a 3-D ocean model (GFDL's Generalized Ocean Layered Dynamics model, or GOLD) to a two-dimensional ice sheet-ice shelf model (Goldberg et al, 2009), and allows for changing cavity geometry and a migrating grounding line. Steady states of the coupled system are found even under considerable forcing. The ice shelf morphology and basal melt rate patterns of the steady states exhibit detailed structure, and furthermore seem to be unique and robust. The relationship between temperature forcing and area-averaged melt rate is influenced by the response of ice shelf morphology to thermal forcing, and is found to be sublinear in the range of forcing considered. However, results suggest that area-averaged melt rate is not the best predictor of overall system response, as grounding line stability depends on local aspects of the basal melt field. Goldberg, D N, D M Holland and C G Schoof, 2009. Grounding line movement and ice shelf buttressing in marine ice sheets, Journal of Geophysical Research-Earth Surfaces, 114, F04026.

Thermal conductivity of ultra-thin chemical vapor deposited hexagonal boron nitride films

International Nuclear Information System (INIS)

Alam, M. T.; Haque, M. A.; Bresnehan, M. S.; Robinson, J. A.

2014-01-01

Thermal conductivity of freestanding 10 nm and 20 nm thick chemical vapor deposited hexagonal boron nitride films was measured using both steady state and transient techniques. The measured value for both thicknesses, about 100 ± 10 W m −1 K −1 , is lower than the bulk basal plane value (390 W m −1 K −1 ) due to the imperfections in the specimen microstructure. Impressively, this value is still 100 times higher than conventional dielectrics. Considering scalability and ease of integration, hexagonal boron nitride grown over large area is an excellent candidate for thermal management in two dimensional materials-based nanoelectronics

Comparison of turbulent flow through hexagram and hexagon orifices in circular pipes using large-eddy simulation

Energy Technology Data Exchange (ETDEWEB)

Wang, Wei; Nicolleau, Franck C G A; Qin, Ning, E-mail: n.qin@sheffield.ac.uk [Department of Mechanical Engineering, The University of Sheffield, Sheffield, S1 3JD (United Kingdom)

2016-04-15

Characteristics of turbulent flow through a circular, a hexagon and a hexagram orifice with the same flow area in circular pipes are investigated using wall-modelled large-eddy simulation. Good agreements to available experimental data were obtained in both the mean velocity and turbulent kinetic energy. The hexagram orifice with alternating convex and concave corners introduces outwards radial velocity around the concave corners downstream of the orifice plate stronger than the hexagon orifice. The stronger outwards radial velocity transfers high momentum from the pipe centre towards the pipe wall to energize the orifice-forced vortex sheet rolling-up and leads to a delayed vortex break-down. Correspondingly, the hexagram has a more gradual flow recovery to a pipe flow and a reduced pressure drop than the hexagon orifice. Both the hexagon and hexagram orifices show an axis-switching phenomenon, which is observed from both the streamwise velocity and turbulent kinetic energy contours. To the best knowledge of the authors, this is the first comparison of orifice-forced turbulence development, mixing and flow dynamics between a regular and a fractal-based polygonal orifice. (paper)

Laboratory studies of the growth, sublimation, and light- scattering properties of single levitated ice particles

Science.gov (United States)

Bacon, Neil Julian

2001-12-01

I describe experiments to investigate the properties of microscopic ice particles. The goal of the work was to measure parameters that are important in cloud processes and radiative transfer, using a novel technique that avoids the use of substrates. The experiments were conducted in two separate electrodynamic balance chambers. Single, charged ice particles were formed from frost particles or from droplets frozen either homogeneously or heteroge neously with a bionucleant. The particles were trapped at temperatures between -38°C and -4°C and grown or sublimated according to the temperature gradient in the cham ber. I describe observations of breakup of sublimating frost particles, measurements of light scattering by hexagonal crystals, and observations of the morphology of ice particles grown from frozen water droplets and frost particles. The breaking strength of frost particles was an order of magnitude less than that of bulk ice. Light scattering features not previously observed were analyzed and related to crystal dimension. Initial results from a computer model failed to reproduce these features. The widths of scattering peaks suggest that surface roughness may play a role in determining the angular distribution of scattered light. Ice particle mass evolution was found to be consistent with diffusion- limited growth. Crystals grown slowly from frozen droplets adopted isometric habits, while faster growth resulted in thin side-planes, although there was not an exact correspondence between growth conditions and particle morphology. From the morphological transition, I infer lower limits for the critical supersaturation for layer nucleation on the prism face of 2.4% at -15°C, 4.4% at -20°C, and 3.1% at -25°C. Analytic expressions for the size dependence of facet stability are developed, indicating a strong dependence of stability on both crystal size and surface kinetics, and compared with data. I discuss the role of complex particle morphologies in

Tolerance measurements on internal- and external-hexagon implants.

Science.gov (United States)

Braian, Michael; De Bruyn, Hugo; Fransson, Håkan; Christersson, Cecilia; Wennerberg, Ann

2014-01-01

To measure the horizontal machining tolerances of the interface between internal- and external-hexagon implants and analogs with corresponding components after delivery from the manufacturer. These values may be a valuable tool for evaluating increasing misfit caused by fabrication, processing, and wear. Seven implants and seven analogs with external- and internal-hexagon connections (Biomet 3i) with corresponding prefabricated gold cylinders and gold screws, prefabricated cylindric plastic cylinders, and laboratory screws were studied. One set of components from the external and internal groups was measured manually and digitally. Measurements from the test subjects were compared with identical measurements from the virtual model to obtain threshold values. The virtual model was then used to obtain optimally oriented cuts. The horizontal machining tolerances for castable plastic abutments on external implants were 12 ± 89 μm, and for internal implants they were 86 ± 47 μm. Tolerance measurements on prefabricated gold abutments for external implants were 44 ± 9 μm, and for internal implants they were 58 ± 28 μm. The groups with metallic components showed the smallest tolerance at external group and internal group. The prefabricated plastic cylinder groups ranged from external and internal connection.

Changes on the ice plain of Ice Stream B and Ross Ice Shelf

Science.gov (United States)

Shabtaie, Sion

1993-01-01

During the 1970's and 1980's, nearly 200 stations from which accurate, three dimensional position fixes have been obtained from TRANSIT satellites were occupied throughout the Ross Ice Shelf. We have transformed the elevations obtained by satellite altimetry to the same geodetic datum, and then applied a second transformation to reduce the geodetic heights to elevations above mean sea level using the GEM-10C geoidal height. On the IGY Ross Ice Shelf traverse between Oct. 1957 and Feb. 1958, an accurate method of barometric altimetry was used on a loop around the ice shelf that was directly tied to the sea at both ends of the travel route, thus providing absolute elevations. Comparisons of the two sets of data at 32 station pairs on floating ice show a mean difference of 0 +/- 1 m. The elevation data were also compared with theoretical values of elevations for a hydrostatically floating ice shelf. The mean difference between theoretical and measured values of elevations is -2 +/- 1 m.

The applicability of physical optics in the millimetre and sub-millimetre spectral region. Part I: The ray tracing with diffraction on facets method

Science.gov (United States)

Baran, A. J.; Hesse, Evelyn; Sourdeval, Odran

2017-03-01

Future satellite missions, from 2022 onwards, will obtain near-global measurements of cirrus at microwave and sub-millimetre frequencies. To realise the potential of these observations, fast and accurate light-scattering methods are required to calculate scattered millimetre and sub-millimetre intensities from complex ice crystals. Here, the applicability of the ray tracing with diffraction on facets method (RTDF) in predicting the bulk scalar optical properties and phase functions of randomly oriented hexagonal ice columns and hexagonal ice aggregates at millimetre frequencies is investigated. The applicability of RTDF is shown to be acceptable down to size parameters of about 18, between the frequencies of 243 and 874 GHz. It is demonstrated that RTDF is generally well within about 10% of T-matrix solutions obtained for the scalar optical properties assuming hexagonal ice columns. Moreover, on replacing electromagnetic scalar optical property solutions obtained for the hexagonal ice aggregate with the RTDF counterparts at size parameter values of about 18 or greater, the bulk scalar optical properties can be calculated to generally well within ±5% of an electromagnetic-based database. The RTDF-derived bulk scalar optical properties result in brightness temperature errors to generally within about ±4 K at 874 GHz. Differing microphysics assumptions can easily exceed such errors. Similar findings are found for the bulk scattering phase functions. This finding is owing to the scattering solutions being dominated by the processes of diffraction and reflection, both being well described by RTDF. The impact of centimetre-sized complex ice crystals on interpreting cirrus polarisation measurements at sub-millimetre frequencies is discussed.

High-resolution electron microscopy on incommensurate long-period superstructures of hexagonal-close-packed Cu-Sb alloy

International Nuclear Information System (INIS)

Onozuka, T.; Kakehashi, S.; Takahashi, T.; Hirabayashi, M.

1989-01-01

Hexagonal incommensurate long-period superstructures of the Cu-Sb alloys containing 18-20 at.% Sb have been investigated by means of superstructure imaging using a high-resolution electron microscope. Honeycomb-type distributions of hexagonal domains consisting of the commensurate superstructure of type 7a 0 -2H are observed. The incommensurabilities of superstructure can be interpreted well with a hexagonal model composed of the 7a 0 -2H domains surrounded by domain walls which contain higher Sb content than the domain interior. The observed image contrast is reproduced well with multislice computer simulations based on the structure models proposed for the 7a 0 -2H domain and the domain wall. (orig.)

High-resolution electron microscopy on incommensurate long-period superstructures of hexagonal-close-packed Cu-Sb alloy

Energy Technology Data Exchange (ETDEWEB)

Onozuka, T.; Kakehashi, S.; Takahashi, T.; Hirabayashi, M. (Tohoku Univ., Sendai (Japan). Inst. for Materials Research)

1989-06-01

Hexagonal incommensurate long-period superstructures of the Cu-Sb alloys containing 18-20 at.% Sb have been investigated by means of superstructure imaging using a high-resolution electron microscope. Honeycomb-type distributions of hexagonal domains consisting of the commensurate superstructure of type 7a{sub 0}-2H are observed. The incommensurabilities of superstructure can be interpreted well with a hexagonal model composed of the 7a{sub 0}-2H domains surrounded by domain walls which contain higher Sb content than the domain interior. The observed image contrast is reproduced well with multislice computer simulations based on the structure models proposed for the 7a{sub 0}-2H domain and the domain wall. (orig.).

Surface charge conductivity of a topological insulator in a magnetic field: The effect of hexagonal warping

Science.gov (United States)

Akzyanov, R. S.; Rakhmanov, A. L.

2018-02-01

We investigate the influence of hexagonal warping on the transport properties of topological insulators. We study the charge conductivity within Kubo formalism in the first Born approximation using low-energy expansion of the Hamiltonian near the Dirac point. The effects of disorder, magnetic field, and chemical-potential value are analyzed in detail. We find that the presence of hexagonal warping significantly affects the conductivity of the topological insulator. In particular, it gives rise to the growth of the longitudinal conductivity with the increase of the disorder and anisotropic anomalous in-plane magnetoresistance. Hexagonal warping also affects the quantum anomalous Hall effect and anomalous out-of-plane magnetoresistance. The obtained results are consistent with the experimental data.

Duality of Ross Ice Shelf systems: crustal boundary, ice sheet processes and ocean circulation from ROSETTA-Ice surveys

Science.gov (United States)

Tinto, K. J.; Siddoway, C. S.; Padman, L.; Fricker, H. A.; Das, I.; Porter, D. F.; Springer, S. R.; Siegfried, M. R.; Caratori Tontini, F.; Bell, R. E.

2017-12-01

Bathymetry beneath Antarctic ice shelves controls sub-ice-shelf ocean circulation and has a major influence on the stability and dynamics of the ice sheets. Beneath the Ross Ice Shelf, the sea-floor bathymetry is a product of both tectonics and glacial processes, and is influenced by the processes it controls. New aerogeophysical surveys have revealed a fundamental crustal boundary bisecting the Ross Ice Shelf and imparting a duality to the Ross Ice Shelf systems, encompassing bathymetry, ocean circulation and ice flow history. The ROSETTA-Ice surveys were designed to increase the resolution of Ross Ice Shelf mapping from the 55 km RIGGS survey of the 1970s to a 10 km survey grid, flown over three years from New York Air National Guard LC130s. Radar, LiDAR, gravity and magnetic instruments provide a top to bottom profile of the ice shelf and the underlying seafloor, with 20 km resolution achieved in the first two survey seasons (2015 and 2016). ALAMO ocean-profiling floats deployed in the 2016 season are measuring the temperature and salinity of water entering and exiting the sub-ice water cavity. A significant east-west contrast in the character of the magnetic and gravity fields reveals that the lithospheric boundary between East and West Antarctica exists not at the base of the Transantarctic Mountains (TAM), as previously thought, but 300 km further east. The newly-identified boundary spatially coincides with the southward extension of the Central High, a rib of shallow basement identified in the Ross Sea. The East Antarctic side is characterized by lower amplitude magnetic anomalies and denser TAM-type lithosphere compared to the West Antarctic side. The crustal structure imparts a fundamental duality on the overlying ice and ocean, with deeper bathymetry and thinner ice on the East Antarctic side creating a larger sub-ice cavity for ocean circulation. The West Antarctic side has a shallower seabed, more restricted ocean access and a more complex history of

Multiyear ice transport and small scale sea ice deformation near the Alaska coast measured by air-deployable Ice Trackers

Science.gov (United States)

Mahoney, A. R.; Kasper, J.; Winsor, P.

2015-12-01

Highly complex patterns of ice motion and deformation were captured by fifteen satellite-telemetered GPS buoys (known as Ice Trackers) deployed near Barrow, Alaska, in spring 2015. Two pentagonal clusters of buoys were deployed on pack ice by helicopter in the Beaufort Sea between 20 and 80 km offshore. During deployment, ice motion in the study region was effectively zero, but two days later the buoys captured a rapid transport event in which multiyear ice from the Beaufort Sea was flushed into the Chukchi Sea. During this event, westward ice motion began in the Chukchi Sea and propagated eastward. This created new openings in the ice and led to rapid elongation of the clusters as the westernmost buoys accelerated away from their neighbors to the east. The buoys tracked ice velocities of over 1.5 ms-1, with fastest motion occurring closest to the coast indicating strong current shear. Three days later, ice motion reversed and the two clusters became intermingled, rendering divergence calculations based on the area enclosed by clusters invalid. The data show no detectable difference in velocity between first year and multiyear ice floes, but Lagrangian timeseries of SAR imagery centered on each buoy show that first year ice underwent significant small-scale deformation during the event. The five remaining buoys were deployed by local residents on prominent ridges embedded in the landfast ice within 16 km of Barrow in order to track the fate of such features after they detached from the coast. Break-up of the landfast ice took place over a period of several days and, although the buoys each initially followed a similar eastward trajectory around Point Barrow into the Beaufort Sea, they rapidly dispersed over an area more than 50 km across. With rapid environmental and socio-economic change in the Arctic, understanding the complexity of nearshore ice motion is increasingly important for predict future changes in the ice and the tracking ice-related hazards

Bibliography of Ice Properties and Forecasting Related to Transportation in Ice-Covered Waters.

Science.gov (United States)

1980-09-01

N. and Tabata , T., Ice study in the Gulf of Peschanskii, I.S., Ice science and ice technology, Bothnia, III: observations on large grains of ice...ice and by Sterrett, K.F., The arctic environment and the hitting ice floes. Results of these measurements have arctic surface effect vehicle, Cold...ice growth, temperature 26-3673 effects, ice cover thickness. 28-557 Determining contact stresses when a ship’s stem hits the ice, Kheisin, D.E

Structure of water in mesoporous organosilica by calorimetry and inelastic neutron scattering

Science.gov (United States)

Levy, Esthy; Kolesnikov, Alexander I.; Li, Jichen; Mastai, Yitzhak

2009-01-01

In this paper, we describe the preparation of mesoporous organosilica samples with hydrophilic or hydrophobic organic functionality inside the silica channel. We synthesized mesoporous organosilica of identical pore sizes based on two different organic surface functionality namely hydrophobic (based on octyltriethoxysilane OTES) and hydrophilic (3-aminopropyltriethoxysilane ATES) and MCM-41 was used as a reference system. The structure of water/ice in those porous silica samples have been investigated over a range temperatures by differential scanning calorimetry (DSC) and inelastic neutron scattering (INS). INS study revealed that water confined in hydrophobic mesoporous organosilica shows vibrational behavior strongly different than bulk water. It consists of two states: water with strong and weak hydrogen bonds (with ratio 1:2.65, respectively), compared to ice-Ih. The corresponding O-O distances in these water states are 2.67 and 2.87 Ǻ, which strongly differ compared to ice-Ih (2.76 Ǻ). INS spectra for water in hydrophilic mesoporous organosilica ATES show behavior similar to bulk water, but with greater degree of disorder.

Fabrication Improvement of Cold Forging Hexagonal Nuts by Computational Analysis and Experiment Verification

Directory of Open Access Journals (Sweden)

Shao-Yi Hsia

2015-01-01

Full Text Available Cold forging has played a critical role in fasteners and has been applied to the automobile industry, construction industry, aerospace industry, and living products so that cold forging presents the opportunities for manufacturing more products. By using computer simulation, this study attempts to analyze the process of creating machine parts, such as hexagonal nuts. The DEFORM-3D forming software is applied to analyze the process at various stages in the computer simulation, and the compression test is also used for the flow stress equation in order to compare the differences between the experimental results and the equation that is built into the computer simulation software. At the same time, the metallography and hardness of experiments are utilized to understand the cold forging characteristics of hexagonal nuts. The research results would benefit machinery businesses to realize the forging load and forming conditions at various stages before the fastener formation. In addition to planning proper die design and production, the quality of the produced hexagonal nuts would be more stable to promote industrial competitiveness.

Influence of winter sea-ice motion on summer ice cover in the Arctic

Directory of Open Access Journals (Sweden)

Noriaki Kimura

2013-11-01

Full Text Available Summer sea-ice cover in the Arctic varies largely from year to year owing to several factors. This study examines one such factor, the relationship between interannual difference in winter ice motion and ice area in the following summer. A daily-ice velocity product on a 37.5-km resolution grid is prepared using the satellite passive microwave sensor Advanced Microwave Scanning Radiometer—Earth Observing System data for the nine years of 2003–2011. Derived daily-ice motion reveals the dynamic modification of the winter ice cover. The winter ice divergence/convergence is strongly related to the summer ice cover in some regions; the correlation coefficient between the winter ice convergence and summer ice area ranges between 0.5 and 0.9 in areas with high interannual variability. This relation implies that the winter ice redistribution controls the spring ice thickness and the summer ice cover.

Hydrothermal synthesis and formation mechanism of hexagonal yttrium hydroxide fluoride nanobundles

International Nuclear Information System (INIS)

Tian, Li; Sun, QiLiang; Zhao, RuiNi; He, HuiLin; Xue, JianRong; Lin, Jun

2013-01-01

Graphical abstract: The formation of yttrium hydroxide fluorides nanobundles can be expressed as a precipitation transformation from cubic NaYF 4 to hexagonal NaYF 4 and to hexagonal Y(OH) 2.02 F 0.98 owing to ion exchange. - Highlights: • Novel Y(OH) 2.02 F 0.98 nanobundles have been successfully prepared by hydrothermal method. • The branched nanobundles composed of numerous oriented-attached nanoparticles has been studied. • The growth mechanism is proposed to be ion exchange and precipitation transformation. - Abstract: This article presents the fabrication of hexagonal yttrium hydroxide fluoride nanobundles via one-pot hydrothermal process, using yttrium nitrate, sodium hydroxide and ammonia fluoride as raw materials to react in propanetriol solvent. The X-ray diffraction pattern clearly reveals that the grown product is pure yttrium hydroxide fluoride, namely Y(OH) 2.02 F 0.98 . The morphology and microstructure of the synthesized product is testified to be nanobundles composed of numerous oriented-attached nanoparticles as observed from the field emission scanning electron microscopy (FESEM). The chemical composition was analyzed by the energy dispersive spectrum (EDS), confirming the phase transformation of the products which was clearly consistent with the result of XRD analysis. It is proposed that the growth of yttrium hydroxide fluoride nanobundles be attributed to ion exchange and precipitation transformation

Ab Initio Molecular Dynamics and Lattice Dynamics-Based Force Field for Modeling Hexagonal Boron Nitride in Mechanical and Interfacial Applications.

Science.gov (United States)

Govind Rajan, Ananth; Strano, Michael S; Blankschtein, Daniel

2018-04-05

Hexagonal boron nitride (hBN) is an up-and-coming two-dimensional material, with applications in electronic devices, tribology, and separation membranes. Herein, we utilize density-functional-theory-based ab initio molecular dynamics (MD) simulations and lattice dynamics calculations to develop a classical force field (FF) for modeling hBN. The FF predicts the crystal structure, elastic constants, and phonon dispersion relation of hBN with good accuracy and exhibits remarkable agreement with the interlayer binding energy predicted by random phase approximation calculations. We demonstrate the importance of including Coulombic interactions but excluding 1-4 intrasheet interactions to obtain the correct phonon dispersion relation. We find that improper dihedrals do not modify the bulk mechanical properties and the extent of thermal vibrations in hBN, although they impact its flexural rigidity. Combining the FF with the accurate TIP4P/Ice water model yields excellent agreement with interaction energies predicted by quantum Monte Carlo calculations. Our FF should enable an accurate description of hBN interfaces in classical MD simulations.

Forecasting Turbine Icing Events

DEFF Research Database (Denmark)

Davis, Neil; Hahmann, Andrea N.; Clausen, Niels-Erik

2012-01-01

In this study, we present a method for forecasting icing events. The method is validated at two European wind farms in with known icing events. The icing model used was developed using current ice accretion methods, and newly developed ablation algorithms. The model is driven by inputs from the WRF...... mesoscale model, allowing for both climatological estimates of icing and short term icing forecasts. The current model was able to detect periods of icing reasonably well at the warmer site. However at the cold climate site, the model was not able to remove ice quickly enough leading to large ice...

State of Arctic Sea Ice North of Svalbard during N-ICE2015

Science.gov (United States)

Rösel, Anja; King, Jennifer; Gerland, Sebastian

2016-04-01

The N-ICE2015 cruise, led by the Norwegian Polar Institute, was a drift experiment with the research vessel R/V Lance from January to June 2015, where the ship started the drift North of Svalbard at 83°14.45' N, 21°31.41' E. The drift was repeated as soon as the vessel drifted free. Altogether, 4 ice stations where installed and the complex ocean-sea ice-atmosphere system was studied with an interdisciplinary Approach. During the N-ICE2015 cruise, extensive ice thickness and snow depth measurements were performed during both, winter and summer conditions. Total ice and snow thickness was measured with ground-based and airborne electromagnetic instruments; snow depth was measured with a GPS snow depth probe. Additionally, ice mass balance and snow buoys were deployed. Snow and ice thickness measurements were performed on repeated transects to quantify the ice growth or loss as well as the snow accumulation and melt rate. Additionally, we collected independent values on surveys to determine the general ice thickness distribution. Average snow depths of 32 cm on first year ice, and 52 cm on multi-year ice were measured in January, the mean snow depth on all ice types even increased until end of March to 49 cm. The average total ice and snow thickness in winter conditions was 1.92 m. During winter we found a small growth rate on multi-year ice of about 15 cm in 2 months, due to above-average snow depths and some extraordinary storm events that came along with mild temperatures. In contrast thereto, we also were able to study new ice formation and thin ice on newly formed leads. In summer conditions an enormous melt rate, mainly driven by a warm Atlantic water inflow in the marginal ice zone, was observed during two ice stations with melt rates of up to 20 cm per 24 hours. To reinforce the local measurements around the ship and to confirm their significance on a larger scale, we compare them to airborne thickness measurements and classified SAR-satellite scenes. The

Ice Cream

NARCIS (Netherlands)

Scholten, E.

2014-01-01

Ice cream is a popular dessert, which owes its sensorial properties (mouth feel) to its complex microstructure. The microstructure is a result of the combination of the ingredients and the production process. Ice cream is produced by simultaneous freezing and shearing of the ice cream mix, which

Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet

Science.gov (United States)

Margold, Martin; Stokes, Chris R.; Clark, Chris D.

2018-06-01

This paper reconstructs the deglaciation of the Laurentide Ice Sheet (LIS; including the Innuitian Ice Sheet) from the Last Glacial Maximum (LGM), with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides. We build on a recent inventory of Laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the LIS, which we depict in a series of palaeogeographic maps. Results show that the drainage network at the LGM was similar to modern-day Antarctica. The majority of the ice streams were marine terminating and topographically-controlled and many of these continued to function late into the deglaciation, until the ice sheet lost its marine margin. Ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build-up, peak-phase and collapse of the Cordilleran-Laurentide ice saddle. The south-eastern marine margin in Atlantic Canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the LGM. In contrast, the ice streams draining towards the north-western and north-eastern marine margins in the Beaufort Sea and in Baffin Bay appear to have remained stable throughout most of the Late Glacial, and some of them continued to function until after the Younger Dryas (YD). The YD influenced the dynamics of the deglaciation, but there remains uncertainty about the response of the ice sheet in several sectors. We tentatively ascribe the switching-on of some major ice streams during this period (e.g. M'Clintock Channel Ice Stream at the north-west margin), but for other large ice streams whose timing partially overlaps with the YD, the drivers are less clear and ice-dynamical processes, rather than effects of climate and surface mass balance are viewed as more likely drivers. Retreat

Saturnian north polar region: a triangle inside the hexagon?

Science.gov (United States)

Kochemasov, Gennady G.

2010-05-01

The famous and "mysterious" stable hexagon structure around the North Pole of Saturn was earlier interpreted as projections of faces of a structural tetrahedron [1]. This "hidden" simplest Plato's polyhedron is a result of an interference of four fundamental (wave 1) warping waves having in any rotating celestial body four directions: orthogonal and diagonal. Origin of the warping waves in any celestial body is due to their movements in elliptical keplerian orbits with periodically changing accelerations. The structural tetrahedron is an intrinsic geometric feature marking the celestial bodies ubiquitous tectonic dichotomy as in a tetrahedron always there is an opposition of a face (expansion) and a vertex (contraction). In the saturnian case the tetrahedron shows a face at the north and a vertex at the south. Morphologically this is manifested by the hexagon and opposing it in the south a vertex. Blue and pink hues of the northern and southern hemispheres also underline the tectonic dichotomy. These geometric expressions are enforced by a subtle dark equilateral triangle appearing in the image PIA11682 also around the north pole and inside the hexagon (the triangle side is about 15000 km long). One angle of the triangle is clearly visible, another one just shows itself and the third one is barely distinguished. The sides of the triangle are not strait lines but slightly broken amidst lines what makes the triangle appear a bit hexagonal (spherical) and the angle is a bit bigger than 60 degrees of a classical equilateral triangle (~70 degrees). The central part of the triangle is not imaged (a black hole in the PIA11682). This image also confirms that the wide northern polar region is also densely "peppered" with bright cloudy more or less isometric spots on average 400 to 800 km across as in other latitudinal belts of Saturn [2, 3, 4]. Earlier they were observed in IR wavelengths, now they show themselves in visible wavelengths. Their origin and size were

Improved ice loss estimate of the northwestern Greenland ice sheet

DEFF Research Database (Denmark)

Kjeldsen, Kristian Kjellerup; Khan, Shfaqat Abbas; Wahr, J.

2013-01-01

We estimate ice volume change rates in the northwest Greenland drainage basin during 2003–2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Elevation changes are often reported to be largest near the frontal portion of outlet glaciers. To improve the volume change...... estimate, we supplement the ICESat data with altimeter surveys from NASA's Airborne Topographic Mapper from 2002 to 2010 and NASA's Land, Vegetation and Ice Sensor from 2010. The Airborne data are mainly concentrated along the ice margin and thus have a significant impact on the estimate of the volume...... change. Our results show that adding Airborne Topographic Mapper and Land, Vegetation and Ice Sensor data to the ICESat data increases the catchment-wide estimate of ice volume loss by 11%, mainly due to an improved volume loss estimate along the ice sheet margin. Furthermore, our results show...

Response of hexagonal fuel assembly coupled with internal hydrodynamics

International Nuclear Information System (INIS)

Marchertas, A.H.; Julke, R.T.

1975-01-01

For safety considerations of sodium cooled fast breeder reactors the mechanistic accident-initiating conditions must be studied. In previous investigations of such initiating accidents the models assumed axisymmetric configurations and in general neglected the coupling effects with the subassembly boundary. This paper presents a more precise treatment of the subassembly boundary and also provides feedback of the boundary response to the pressure source. This is accomplished by marking use of two computer codes: REXCO-HT and SADCAT. The internal hydrodynamics of the fuel subassembly is simulated by the REXCO-HT code which possesses certain models of fuel-coolant interactions (MFCI) to be used as a pressure source. The hexagonal boundary of the fuel subassembly is modeled by the SADCAT code. Since both codes involve explicit time integration, coupling between the two is effected at each time step. The pressure at the outside boundary of the REXCO-HT model provides the loading on the SADCAT model. Given the load, the SADCAT model yields the three-dimensional deformation of the hexagonal boundary. With the deformation known, the outside REXCO-HT model boundary is adjusted and the computation cycle of the coupling is completed. In effect, the coupling of the two codes substitutes a cylindrical vessel of the REXCO-HT code by a hexagonal duct. It is shown by the use of this procedure that the assumption of a cylindrical vessel of the same thickness as that of the hexcan is quite erroneous. The maximum deformation of the flat of the hexcan in the illustrative examples is larger by as much as one order of magnitude. The maximum strains at the inside CORNER of the hexcan are also underestimated by a similar amount

Delamination of hexagonal boron nitride in a stirred media mill

International Nuclear Information System (INIS)

Damm, C.; Körner, J.; Peukert, W.

2013-01-01

A scalable process for delamination of hexagonal boron nitride in an aqueous solution of the non-ionic surfactant TWEEN85 using a stirred media mill is presented. The size of the ZrO 2 beads used as grinding media governs the dimensions of the ground boron nitride particles as atomic force microscopic investigations (AFM) reveal: the mean flakes thickness decreases from 3.5 to 1.5 nm and the ratio between mean flake area and mean flake thickness increases from 2,200 to 5,800 nm if the grinding media size is reduced from 0.8 to 0.1 mm. This result shows that a high number of stress events in combination with low stress energy (small grinding media) facilitate delamination of the layered material whereas at high stress energies in combination with a low number of stress events (large grinding media) breakage of the layers dominates over delamination. The results of particle height analyses by AFM show that few-layer structures have been formed by stirred media milling. This result is in agreement with the layer thickness dependence of the delamination energy for hexagonal boron nitride. The concentration of nanoparticles remaining dispersed after centrifugation of the ground suspension increases with grinding time and with decreasing grinding media size. After 5 h of grinding using 0.1 mm ZrO 2 grinding media the yield of nanoparticle formation is about 5 wt%. The nanoparticles exhibit the typical Raman peak for hexagonal boron nitride at 1,366 cm −1 showing that the in-plane order in the milled platelets is remained.

Computational study of packing a collagen-like molecule: quasi-hexagonal vs "Smith" collagen microfibril model.

Science.gov (United States)

Lee, J; Scheraga, H A; Rackovsky, S

1996-01-01

The lateral packing of a collagen-like molecule, CH3CO-(Gly-L-Pro-L-Pro)4-NHCH3, has been examined by energy minimization with the ECEPP/3 force field. Two current packing models, the Smith collagen microfibril twisted equilateral pentagonal model and the quasi-hexagonal packing model, have been extensively investigated. In treating the Smith microfibril model, energy minimization was carried out on various conformations including those with the symmetry of equivalent packing, i.e., in which the triple helices were arranged equivalently with respect to each other. Both models are based on the experimental observation of the characteristic axial periodicity, D = 67 nm, of light and dark bands, indicating that, if any superstructure exists, it should consist of five triple helices. The quasi-hexagonal packing structure is found to be energetically more favorable than the Smith microfibril model by as much as 31.2 kcal/mol of five triple helices. This is because the quasi-hexagonal packing geometry provides more nonbonded interaction possibilities between triple helices than does the Smith microfibril geometry. Our results are consistent with recent x-ray studies with synthetic collagen-like molecules and rat tail tendon, in which the data were interpreted as being consistent with either a quasi-hexagonal or a square-triangular structure.

Tropospheric characteristics over sea ice during N-ICE2015

Science.gov (United States)

Kayser, Markus; Maturilli, Marion; Graham, Robert; Hudson, Stephen; Cohen, Lana; Rinke, Annette; Kim, Joo-Hong; Park, Sang-Jong; Moon, Woosok; Granskog, Mats

2017-04-01

Over recent years, the Arctic Ocean region has shifted towards a younger and thinner sea-ice regime. The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in this new ice regime north of Svalbard. Here we analyze upper-air measurements made by radiosondes launched twice daily together with surface meteorology observations during N-ICE2015 from January to June 2015. We study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, sudden increases in moisture content and temperature, temperature inversions and boundary layer dynamics. The influence of synoptic cyclones is strongest under polar night conditions, when radiative cooling is most effective and the moisture content is low. We find that transitions between the radiatively clear and opaque state are the largest drivers of changes to temperature inversion and stability characteristics in the boundary layer during winter. In spring radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. The unique N-ICE2015 dataset is used for case studies investigating changes in the vertical structure of the atmosphere under varying synoptic conditions. The goal is to deepen our understanding of synoptic interactions within the Arctic climate system, to improve model performance, as well as to identify gaps in instrumentation, which precludes further investigations.

Arctic multiyear ice classification and summer ice cover using passive microwave satellite data

Science.gov (United States)

Comiso, J. C.

1990-08-01

The ability to classify and monitor Arctic multiyear sea ice cover using multispectral passive microwave data is studied. Sea ice concentration maps during several summer minima have been analyzed to obtain estimates of ice surviving the summer. The results are compared with multiyear ice concentrations derived from data the following winter, using an algorithm that assumes a certain emissivity for multiyear ice. The multiyear ice cover inferred from the winter data is approximately 25 to 40% less than the summer ice cover minimum, suggesting that even during winter when the emissivity of sea ice is most stable, passive microwave data may account for only a fraction of the total multiyear ice cover. The difference of about 2×106 km2 is considerably more than estimates of advection through Fram Strait during the intervening period. It appears that as in the Antarctic, some multiyear ice floes in the Arctic, especially those near the summer marginal ice zone, have first-year ice or intermediate signatures in the subsequent winter. A likely mechanism for this is the intrusion of seawater into the snow-ice interface, which often occurs near the marginal ice zone or in areas where snow load is heavy. Spatial variations in melt and melt ponding effects also contribute to the complexity of the microwave emissivity of multiyear ice. Hence the multiyear ice data should be studied in conjunction with the previous summer ice data to obtain a more complete characterization of the state of the Arctic ice cover. The total extent and actual areas of the summertime Arctic pack ice were estimated to be 8.4×106 km2 and 6.2×106 km2, respectively, and exhibit small interannual variability during the years 1979 through 1985, suggesting a relatively stable ice cover.

Experimental investigation of the coolability of blocked hexagonal bundles

Energy Technology Data Exchange (ETDEWEB)

Hózer, Zoltán, E-mail: zoltan.hozer@energia.mta.hu; Nagy, Imre; Kunstár, Mihály; Szabó, Péter; Vér, Nóra; Farkas, Róbert; Trosztel, István; Vimi, András

2017-06-15

Highlights: • Experiments were performed with electrically heated hexagonal fuel bundles. • Coolability of ballooned VVER-440 type bundle was confirmed up to high blockage rate. • Pellet relocation effect causes delay in the cool-down of the bundle. • The bypass line does not prevent the reflood of ballooned fuel rods. - Abstract: The CODEX-COOL experimental series was carried out in order to evaluate the effect of ballooning and pellet relocation in hexagonal bundles on the coolability of fuel rods after a LOCA event. The effects of blockage geometry, coolant flowrate, initial temperature and axial profile were investigated. The experimental results confirmed that a VVER bundle up to 80% blockage rate remains coolable after a LOCA event under design basis conditions. The ballooned section creates some obstacles for the cooling water during reflood of the bundle, but this effect causes only a short delay in the cooling down of the hot fuel rods. The accumulation of fuel pellet debris in the ballooned volume results in a local power peak, which leads to further slowing down of quench front.

Lake Ontario Shore Protection Study: Literature Review Report.

Science.gov (United States)

1979-07-01

PokING ICE FrikPATION GCVERK THIS ! ELECI10N. CAUILk (UNCENh14AluhS IN. SNOb ICE SAhPLES bEAL HIGHLY VARIIABLE# HLwtVjks CATAQK CLCEKTkIILNS a0 ALL... APPEAL WHICH IS CIVIOUb IC EVERY VISIL. IhIS Al’PiAL IS MADE Ed’ OF A LA64*1 NUMBER OF COMPONENTS# EACH OF WHICH ADDS A FACET TC Int Ti.,AL. NO FACET

Evidence for graphite-like hexagonal AlN nanosheets epitaxially grown on single crystal Ag(111)

Energy Technology Data Exchange (ETDEWEB)

Tsipas, P.; Kassavetis, S.; Tsoutsou, D.; Xenogiannopoulou, E.; Golias, E.; Giamini, S. A.; Dimoulas, A. [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece); Grazianetti, C.; Fanciulli, M. [Laboratorio MDM, IMM-CNR, I-20864, Agrate Brianza (MB) (Italy); Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, I-20126, Milano (Italy); Chiappe, D.; Molle, A. [Laboratorio MDM, IMM-CNR, I-20864, Agrate Brianza (MB) (Italy)

2013-12-16

Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals. Electron diffraction and scanning tunneling microscopy provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy indicating a reduced energy bandgap as expected for hexagonal AlN.

There goes the sea ice: following Arctic sea ice parcels and their properties.

Science.gov (United States)

Tschudi, M. A.; Tooth, M.; Meier, W.; Stewart, S.

2017-12-01

Arctic sea ice distribution has changed considerably over the last couple of decades. Sea ice extent record minimums have been observed in recent years, the distribution of ice age now heavily favors younger ice, and sea ice is likely thinning. This new state of the Arctic sea ice cover has several impacts, including effects on marine life, feedback on the warming of the ocean and atmosphere, and on the future evolution of the ice pack. The shift in the state of the ice cover, from a pack dominated by older ice, to the current state of a pack with mostly young ice, impacts specific properties of the ice pack, and consequently the pack's response to the changing Arctic climate. For example, younger ice typically contains more numerous melt ponds during the melt season, resulting in a lower albedo. First-year ice is typically thinner and more fragile than multi-year ice, making it more susceptible to dynamic and thermodynamic forcing. To investigate the response of the ice pack to climate forcing during summertime melt, we have developed a database that tracks individual Arctic sea ice parcels along with associated properties as these parcels advect during the summer. Our database tracks parcels in the Beaufort Sea, from 1985 - present, along with variables such as ice surface temperature, albedo, ice concentration, and convergence. We are using this database to deduce how these thousands of tracked parcels fare during summer melt, i.e. what fraction of the parcels advect through the Beaufort, and what fraction melts out? The tracked variables describe the thermodynamic and dynamic forcing on these parcels during their journey. This database will also be made available to all interested investigators, after it is published in the near future. The attached image shows the ice surface temperature of all parcels (right) that advected through the Beaufort Sea region (left) in 2014.

Development of a Capacitive Ice Sensor to Measure Ice Growth in Real Time

Directory of Open Access Journals (Sweden)

Xiang Zhi

2015-03-01

Full Text Available This paper presents the development of the capacitive sensor to measure the growth of ice on a fuel pipe surface in real time. The ice sensor consists of pairs of electrodes to detect the change in capacitance and a thermocouple temperature sensor to examine the ice formation situation. In addition, an environmental chamber was specially designed to control the humidity and temperature to simulate the ice formation conditions. From the humidity, a water film is formed on the ice sensor, which results in an increase in capacitance. Ice nucleation occurs, followed by the rapid formation of frost ice that decreases the capacitance suddenly. The capacitance is saturated. The developed ice sensor explains the ice growth providing information about the icing temperature in real time.

Development of a capacitive ice sensor to measure ice growth in real time.

Science.gov (United States)

Zhi, Xiang; Cho, Hyo Chang; Wang, Bo; Ahn, Cheol Hee; Moon, Hyeong Soon; Go, Jeung Sang

2015-03-19

This paper presents the development of the capacitive sensor to measure the growth of ice on a fuel pipe surface in real time. The ice sensor consists of pairs of electrodes to detect the change in capacitance and a thermocouple temperature sensor to examine the ice formation situation. In addition, an environmental chamber was specially designed to control the humidity and temperature to simulate the ice formation conditions. From the humidity, a water film is formed on the ice sensor, which results in an increase in capacitance. Ice nucleation occurs, followed by the rapid formation of frost ice that decreases the capacitance suddenly. The capacitance is saturated. The developed ice sensor explains the ice growth providing information about the icing temperature in real time.

Dead-ice environments

DEFF Research Database (Denmark)

Krüger, Johannes; Kjær, Kurt H.; Schomacker, Anders

2010-01-01

glacier environment. The scientific challenges are to answer the key questions. What are the conditions for dead-ice formation? From which sources does the sediment cover originate? Which melting and reworking processes act in the ice-cored moraines? What is the rate of de-icing in the ice-cored moraines...

Synthesis of hexagonal ultrathin tungsten oxide nanowires with diameters below 5 nm for enhanced photocatalytic performance

Science.gov (United States)

Lu, Huidan; Zhu, Qin; Zhang, Mengying; Yan, Yi; Liu, Yongping; Li, Ming; Yang, Zhishu; Geng, Peng

2018-04-01

Semiconductor with one dimension (1D) ultrathin nanostructure has been proved to be a promising nanomaterial in photocatalytic field. Great efforts were made on preparation of monoclinic ultrathin tungsten oxide nanowires. However, non-monoclinic phase tungsten oxides with 1D ultrathin structure, especially less than 5 nm width, have not been reported. Herein, we report the synthesis of hexagonal ultrathin tungsten oxide nanowires (U-WOx NW) by modified hydrothermal method. Microstructure characterization showed that U-WOx NW have the diameters of 1-3 nm below 5 nm and are hexagonal phase sub-stoichiometric WOx. U-WOx NW show absorption tail in the visible and near infrared region due to oxygen vacancies. For improving further photocatalytic performance, Ag co-catalyst was grown directly onto U-WOx NW surface by in situ redox reaction. Photocatalytic measurements revealed hexagonal U-WOx NW have better photodegradation activity, compared with commercial WO3(C-WO3) and oxidized U-WOx NW, ascribe to larger surface area, short diffusion length of photo-generated charge carriers and visible absorption of oxygen-vacancy-rich hexagonal ultrathin nanostructures. Moreover, the photocatalytic activity and stability of U-WOx NW using Ag co-catalyst were further improved.

Ice bridges and ridges in the Maxwell-EB sea ice rheology

Directory of Open Access Journals (Sweden)

V. Dansereau

2017-09-01

Full Text Available This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB, is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a Mohr–Coulomb damage criterion that allows for pure (uniaxial and biaxial tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.

Ice bridges and ridges in the Maxwell-EB sea ice rheology

Science.gov (United States)

Dansereau, Véronique; Weiss, Jérôme; Saramito, Pierre; Lattes, Philippe; Coche, Edmond

2017-09-01

This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB), is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a Mohr-Coulomb damage criterion that allows for pure (uniaxial and biaxial) tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.

Ice formation and growth shape bacterial community structure in Baltic Sea drift ice.

Science.gov (United States)

Eronen-Rasimus, Eeva; Lyra, Christina; Rintala, Janne-Markus; Jürgens, Klaus; Ikonen, Vilma; Kaartokallio, Hermanni

2015-02-01

Drift ice, open water and under-ice water bacterial communities covering several developmental stages from open water to thick ice were studied in the northern Baltic Sea. The bacterial communities were assessed with 16S rRNA gene terminal-restriction fragment length polymorphism and cloning, together with bacterial abundance and production measurements. In the early stages, open water and pancake ice were dominated by Alphaproteobacteria and Actinobacteria, which are common bacterial groups in Baltic Sea wintertime surface waters. The pancake ice bacterial communities were similar to the open-water communities, suggesting that the parent water determines the sea-ice bacterial community in the early stages of sea-ice formation. In consolidated young and thick ice, the bacterial communities were significantly different from water bacterial communities as well as from each other, indicating community development in Baltic Sea drift ice along with ice-type changes. The thick ice was dominated by typical sea-ice genera from classes Flavobacteria and Gammaproteobacteria, similar to those in polar sea-ice bacterial communities. Since the thick ice bacterial community was remarkably different from that of the parent seawater, results indicate that thick ice bacterial communities were recruited from the rarer members of the seawater bacterial community. © FEMS 2014. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris.

Science.gov (United States)

Stickley, Catherine E; St John, Kristen; Koç, Nalân; Jordan, Richard W; Passchier, Sandra; Pearce, Richard B; Kearns, Lance E

2009-07-16

Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic, contain ice-rafted debris (IRD) back to the middle Eocene epoch, prompting recent suggestions that ice appeared in the Arctic about 46 million years (Myr) ago. However, because IRD can be transported by icebergs (derived from land-based ice) and also by sea ice, IRD records are restricted to providing a history of general ice-rafting only. It is critical to differentiate sea ice from glacial (land-based) ice as climate feedback mechanisms vary and global impacts differ between these systems: sea ice directly affects ocean-atmosphere exchanges, whereas land-based ice affects sea level and consequently ocean acidity. An earlier report assumed that sea ice was prevalent in the middle Eocene Arctic on the basis of IRD, and although somewhat preliminary supportive evidence exists, these data are neither comprehensive nor quantified. Here we show the presence of middle Eocene Arctic sea ice from an extraordinary abundance of a group of sea-ice-dependent fossil diatoms (Synedropsis spp.). Analysis of quartz grain textural characteristics further supports sea ice as the dominant transporter of IRD at this time. Together with new information on cosmopolitan diatoms and existing IRD records, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas approximately 47.5 Myr ago, followed approximately 0.5 Myr later by the onset of seasonally paced sea-ice formation in offshore areas of the central Arctic. Our data establish a 2-Myr record of sea ice, documenting the transition from a warm, ice-free environment to one dominated by winter sea ice at the start of the middle Eocene climatic cooling phase.

Band gap effects of hexagonal boron nitride using oxygen plasma

International Nuclear Information System (INIS)

Sevak Singh, Ram; Leong Chow, Wai; Yingjie Tay, Roland; Hon Tsang, Siu; Mallick, Govind; Tong Teo, Edwin Hang

2014-01-01

Tuning of band gap of hexagonal boron nitride (h-BN) has been a challenging problem due to its inherent chemical stability and inertness. In this work, we report the changes in band gaps in a few layers of chemical vapor deposition processed as-grown h-BN using a simple oxygen plasma treatment. Optical absorption spectra show a trend of band gap narrowing monotonically from 6 eV of pristine h-BN to 4.31 eV when exposed to oxygen plasma for 12 s. The narrowing of band gap causes the reduction in electrical resistance by ∼100 fold. The x-ray photoelectron spectroscopy results of plasma treated hexagonal boron nitride surface show the predominant doping of oxygen for the nitrogen vacancy. Energy sub-band formations inside the band gap of h-BN, due to the incorporation of oxygen dopants, cause a red shift in absorption edge corresponding to the band gap narrowing

Band gap effects of hexagonal boron nitride using oxygen plasma

Energy Technology Data Exchange (ETDEWEB)

Sevak Singh, Ram; Leong Chow, Wai [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Yingjie Tay, Roland [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Temasek Laboratories-NTU, 50 Nanyang Avenue, Singapore 639798 (Singapore); Hon Tsang, Siu [Temasek Laboratories-NTU, 50 Nanyang Avenue, Singapore 639798 (Singapore); Mallick, Govind [Temasek Laboratories-NTU, 50 Nanyang Avenue, Singapore 639798 (Singapore); Weapons and Materials Research Directorate, U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005 (United States); Tong Teo, Edwin Hang, E-mail: htteo@ntu.edu.sg [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore)

2014-04-21

Tuning of band gap of hexagonal boron nitride (h-BN) has been a challenging problem due to its inherent chemical stability and inertness. In this work, we report the changes in band gaps in a few layers of chemical vapor deposition processed as-grown h-BN using a simple oxygen plasma treatment. Optical absorption spectra show a trend of band gap narrowing monotonically from 6 eV of pristine h-BN to 4.31 eV when exposed to oxygen plasma for 12 s. The narrowing of band gap causes the reduction in electrical resistance by ∼100 fold. The x-ray photoelectron spectroscopy results of plasma treated hexagonal boron nitride surface show the predominant doping of oxygen for the nitrogen vacancy. Energy sub-band formations inside the band gap of h-BN, due to the incorporation of oxygen dopants, cause a red shift in absorption edge corresponding to the band gap narrowing.

A natural ice boom

Energy Technology Data Exchange (ETDEWEB)

Hopper, H.R. [Manitoba Hydro, Winnipeg, MB (Canada)

1998-10-01

Planning for ice jams and ice movements are critical on the Nelson River in northern Manitoba in designing cofferdams. Experience on the St. Lawrence River demonstrated the possibility of exercising some control over ice action by judicious placement of log booms or ice control structures. The success of experiments with man-made controls led to field tests in which an ice sheet of sufficient magnitude and competence was introduced into the open water stream of the Nelson River. The ice sheet was subsequently jammed in a narrow channel, thereby creating a natural ice bridge or boom upstream of a proposed hydro development. Under favourable conditions, this boom would initiate the progression of the ice cover from its location upstream, cutting off the downstream reach from the ice producing potential of the upstream reach. Although ice would still be generated downstream, the length of the reach between the ice boom and the development site would be short enough that ice jamming at the development site would never occur. Although problems in blasting prevented the introduction of a competent ice sheet into the main stream of the river at the location chosen, sufficient confidence in the theory was gained to warrant further consideration. 4 refs., 1 tab., 10 figs.

Inhibition of ice crystal growth in ice cream mix by gelatin hydrolysate.

Science.gov (United States)

Damodaran, Srinivasan

2007-12-26

The inhibition of ice crystal growth in ice cream mix by gelatin hydrolysate produced by papain action was studied. The ice crystal growth was monitored by thermal cycling between -14 and -12 degrees C at a rate of one cycle per 3 min. It is shown that the hydrolysate fraction containing peptides in the molecular weight range of about 2000-5000 Da exhibited the highest inhibitory activity on ice crystal growth in ice cream mix, whereas fractions containing peptides greater than 7000 Da did not inhibit ice crystal growth. The size distribution of gelatin peptides formed in the hydrolysate was influenced by the pH of hydrolysis. The optimum hydrolysis conditions for producing peptides with maximum ice crystal growth inhibitory activity was pH 7 at 37 degrees C for 10 min at a papain to gelatin ratio of 1:100. However, this may depend on the type and source of gelatin. The possible mechanism of ice crystal growth inhibition by peptides from gelatin is discussed. Molecular modeling of model gelatin peptides revealed that they form an oxygen triad plane at the C-terminus with oxygen-oxygen distances similar to those found in ice nuclei. Binding of this oxygen triad plane to the prism face of ice nuclei via hydrogen bonding appears to be the mechanism by which gelatin hydrolysate might be inhibiting ice crystal growth in ice cream mix.

Quasi free-standing silicene in a superlattice with hexagonal boron nitride

KAUST Repository

Kaloni, T. P.; Tahir, M.; Schwingenschlö gl, Udo

2013-01-01

We study a superlattice of silicene and hexagonal boron nitride by first principles calculations and demonstrate that the interaction between the layers of the superlattice is very small. As a consequence, quasi free-standing silicene is realized

Structural, magnetic and electrical properties of the hexagonal ferrites MFeO3 (M=Y, Yb, In)

International Nuclear Information System (INIS)

Downie, Lewis J.; Goff, Richard J.; Kockelmann, Winfried; Forder, Sue D.; Parker, Julia E.; Morrison, Finlay D.; Lightfoot, Philip

2012-01-01

The hexagonal ferrites MFeO 3 (M=Y, Yb, In) have been studied using a combination of neutron and X-ray powder diffraction, magnetic susceptibility, dielectric measurements and 57 Fe Mössbauer spectroscopy. This study confirms the previously reported crystal structure of InFeO 3 (YAlO 3 structure type, space group P6 3 /mmc), but YFeO 3 and YbFeO 3 both show a lowering of symmetry to at most P6 3 cm (ferrielectric YMnO 3 structure type). However, Mössbauer spectroscopy shows at least two distinct Fe sites for both YFeO 3 and YbFeO 3 and we suggest that the best model to rationalise this involves phase separation into more than one similar hexagonal YMnO 3 -like phase. Rietveld analysis of the neutron diffraction data was carried out using two hexagonal phases as a simplest case scenario. In both YFeO 3 and YbFeO 3 , distinct dielectric anomalies are observed near 130 K and 150 K, respectively. These are tentatively correlated with weak anomalies in magnetic susceptibility and lattice parameters, for YFeO 3 and YbFeO 3 , respectively, which may suggest a weak magnetoelectric effect. Comparison of neutron and X-ray powder diffraction shows evidence of long-range magnetic order in both YFeO 3 and YbFeO 3 at low temperatures. Due to poor sample crystallinity, the compositional and structural effects underlying the phase separation and possible magnetoelectric phenomena cannot be ascertained. - Graphical abstract: Hexagonal MFeO 3 (M=Y, Yb) exhibit phase separation into two YMnO 3 -like phases. Variable temperature crystallographic, electrical and magnetic studies suggest weak correlations between electrical and magnetic responses and long-range magnetic order at low temperature. Highlights: ► Multi-technique study of multiferroic hexagonal MFeO 3 . ► Phase separation into two similar hexagonal phases. ► Weak coupling of electrical and magnetic responses. ► Long-range magnetic order at low T.

Ice targets

International Nuclear Information System (INIS)

Pacheco, C.; Stark, C.; Tanaka, N.; Hodgkins, D.; Barnhart, J.; Kosty, J.

1979-12-01

This report presents a description of ice targets that were constructed for research work at the High Resolution Spectrometer (HRS) and at the Energetic Pion Channel and Spectrometer (EPICS). Reasons for using these ice targets and the instructions for their construction are given. Results of research using ice targets will be published at a later date

Eu{sup 3+}-doped Y{sub 2}O{sub 3} hexagonal prisms: Shape-controlled synthesis and tailored luminescence properties

Energy Technology Data Exchange (ETDEWEB)

Yang, Errui [Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Li, Guangshe [Fujian Provincial Key Laboratory of Nanomaterials, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Fu, Chaochao; Zheng, Jing [Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Huang, Xinsong [Fujian Provincial Key Laboratory of Nanomaterials, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China); Xu, Wen [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012 (China); Li, Liping, E-mail: lipingli@fjirsm.ac.cn [Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002 (China)

2015-10-25

In this work, Eu{sup 3+} doped Y{sub 2}O{sub 3} hexagonal prisms were synthesized by a novel two-phase approach, which involves water at the bottom as aqueous phase and oleylamine in the above as oil phase. With this unique reaction system, precursors of hexagonal prisms Y{sub 4}O(OH){sub 9}(NO{sub 3}) were first obtained by simply varying the volume ratio of water to oleylamine. Time-dependent experiments were systematically performed to reveal the growth mechanism of the precursor. After subsequent heat treatment, these precursors transformed to Y{sub 2}O{sub 3} hexagonal prisms with controlled diameters and aspect ratios varying from 4 to 19. Such a transformation is preceded via a topotactic process, as indicated by TG-DTA and mass spectra. Eventually, all Eu{sup 3+} doped Y{sub 2}O{sub 3} hexagonal prisms were found to exhibit an intensive red emission at 611 nm, which corresponds to {sup 5}D{sub 0}→{sup 7}F{sub 2} transition of Eu{sup 3+}. With varying the aspect ratio of hexagonal prisms and increasing Eu{sup 3+} concentration in Y{sub 2}O{sub 3}, an optimum external quantum efficiency was achieved. - Graphical abstract: In this work, Eu{sup 3+} doped Y{sub 2}O{sub 3} hexagonal prisms with controlled aspect ratio from 4.4 to 19.3 were synthesized by transformation of the precursor Y{sub 4}O(OH){sub 9}(NO{sub 3}) hexagonal prisms from a novel two-phase reaction system. The growth mechanism of the precursor has been systematically investigated, and a topotactic phase transformation from precursors to cubic Y{sub 2}O{sub 3} is for the first time put forward. By the size controlling and aspect ratio adjusting, the luminescence emission intensity as well as external quantum efficiency of Eu{sup 3+} doped Y{sub 2}O{sub 3} hexagonal prisms is further tailored to show an optimum. - Highlights: • Eu{sup 3+} doped Y{sub 2}O{sub 3} hexagonal prisms were synthesized by a novel two-phase approach. • Inheriting mechanism of prisms morphology from Y{sub 4}O(OH){sub 9

Sea Ice

Science.gov (United States)

Perovich, D.; Gerland, S.; Hendricks, S.; Meier, Walter N.; Nicolaus, M.; Richter-Menge, J.; Tschudi, M.

2013-01-01

During 2013, Arctic sea ice extent remained well below normal, but the September 2013 minimum extent was substantially higher than the record-breaking minimum in 2012. Nonetheless, the minimum was still much lower than normal and the long-term trend Arctic September extent is -13.7 per decade relative to the 1981-2010 average. The less extreme conditions this year compared to 2012 were due to cooler temperatures and wind patterns that favored retention of ice through the summer. Sea ice thickness and volume remained near record-low levels, though indications are of slightly thicker ice compared to the record low of 2012.

Sea ice and pollution-modulated changes in Greenland ice core methanesulfonate and bromine

Science.gov (United States)

Maselli, Olivia J.; Chellman, Nathan J.; Grieman, Mackenzie; Layman, Lawrence; McConnell, Joseph R.; Pasteris, Daniel; Rhodes, Rachael H.; Saltzman, Eric; Sigl, Michael

2017-01-01

Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its future evolution. Methanesulfonate (MSA) and bromine concentrations preserved in ice cores have both been proposed as indicators of past sea ice conditions. In this study, two ice cores from central and north-eastern Greenland were analysed at sub-annual resolution for MSA (CH3SO3H) and bromine, covering the time period 1750-2010. We examine correlations between ice core MSA and the HadISST1 ICE sea ice dataset and consult back trajectories to infer the likely source regions. A strong correlation between the low-frequency MSA and bromine records during pre-industrial times indicates that both chemical species are likely linked to processes occurring on or near sea ice in the same source regions. The positive correlation between ice core MSA and bromine persists until the mid-20th century, when the acidity of Greenland ice begins to increase markedly due to increased fossil fuel emissions. After that time, MSA levels decrease as a result of declining sea ice extent but bromine levels increase. We consider several possible explanations and ultimately suggest that increased acidity, specifically nitric acid, of snow on sea ice stimulates the release of reactive Br from sea ice, resulting in increased transport and deposition on the Greenland ice sheet.

Synthesis and magnetic properties of hexagonal Y(Mn,Cu)O3 multiferroic materials

International Nuclear Information System (INIS)

Jeuvrey, L.; Peña, O.; Moure, A.; Moure, C.

2012-01-01

Single-phase hexagonal-type solid solutions based on the multiferroic YMnO 3 material were synthesized by a modified Pechini process. Copper doping at the B-site (YMn 1−x Cu x O 3 ; x 1+y MnO 3 ; y 3+ two-dimensional lattice. The magnetic transition at T N decreases from 70 K down to 49 K, when x(Cu) goes from 0 to 15 at%. Weak ferromagnetic Mn 3+ –Mn 4+ interactions created by the substitution of Mn 3+ by Cu 2+ , are visible through the coercive field and spontaneous magnetization but do not modify the overall magnetic frustration. Presence of Mn 3+ –Mn 4+ pairs leads to an increase of the electrical conductivity due to thermally-activated small-polaron hopping mechanisms. Results show that local ferromagnetic interactions can coexist within the frustrated state in the hexagonal polar structure. - Highlights: ► Hexagonal-type solid solutions of Y(Mn,Cu)O 3 synthesized by Pechini process. ► Chemical substitution at B site inhibits geometrical magnetic frustration. ► Magnetic transition decreases with Cu-doping. ► Local ferromagnetic Mn–Mn interactions coexist with the frustrated state.

Direct numerical simulation of turbulence and heat transfer in a hexagonal shaped duct

Science.gov (United States)

Marin, Oana; Obabko, Aleks; Schlatter, Philipp

2014-11-01

Flows in hexagonal shapes frequently occur in nuclear reactor applications, and are also present in honeycomb-shaped settling chambers for e.g. wind tunnels. Whereas wall-bounded turbulence has been studied comprehensively in two-dimensional channels, and to a lesser degree also in square and rectangular ducts and triangles, only very limited data for hexagonal ducts is available, including resistance correlations and mean profiles. Here, we use resolved spectral-element simulations to compute velocity and temperature in fully-developed (periodic) hexagonal duct flow. The Reynolds number, based on the fixed flow rate and the hydraulic diameter, ranges between 2000 and 20000. The temperature assumes constant wall flux or constant wall temperature. First DNS results are focused on the mean characteristics such a head loss, Nusselt number, and critical Reynolds number for sustained turbulence. Profiles, both for mean and fluctuating quantities, are extracted and discussed in the context of square ducts and pipes. Comparisons to existing experiments, RANS and empirical correlations are supplied as well. The results show a complicated and fine-scale pattern of the in-plane secondary flow, which clearly affects the momentum and temperature distribution throughout the cross section.

Little Ice Age Fluctuations of Quelccaya Ice Cap, Peru

Science.gov (United States)

Stroup, J. S.; Kelly, M. A.; Lowell, T.

2009-12-01

A record of the past extents of Quelccaya Ice Cap (QIC) provides valuable information about tropical climate change from late glacial to recent time. Here, we examine the timing and regional significance of fluctuations of QIC during the Little Ice Age (LIA; ~1300-1850 AD). One prominent set of moraines, known as the Huancane I moraines, is located ~1 km from the present-day western ice cap margin and provides a near-continuous outline of the most recent advance of QIC. This moraine set was radiocarbon dated (~298 ± 134 and 831 ± 87 yr BP) by Mercer and Palacios (1977) and presented as some of the first evidence for cooling in the tropics during the Little Ice Age. Recent field investigations in the QIC region focused on refining the chronology of the Huancane I moraines. In 2008, new stratigraphic sections exposed by local lake-flooding events revealed multiple layers of peat within the Huancane I moraines. In both 2008 and 2009, samples were obtained for 10Be dating of boulders on Huancane I moraines. A combination of radiocarbon and 10Be ages indicate that the Huancane I moraines were deposited by ice cap expansion after ~3800 yr BP and likely by multiple advances at approximately 1000, 600, 400, and 200 yr BP. Radiocarbon and 10Be chronologies of the Huancane I moraines are compared with the Quelccaya ice core records (Thompson et al., 1985; 1986; 2006). Accumulation data from the ice core records are interpreted to indicate a significant wet period at ~1500-1700 AD followed by a significant drought at ~1720-1860 AD. We examine ice marginal fluctuations during these times to determine influence of such events on the ice cap extent.

Influence of strontium on the cubic to ordered hexagonal phase

Indian Academy of Sciences (India)

... Refresher Courses · Symposia · Live Streaming. Home; Journals; Bulletin of Materials Science; Volume 23; Issue 6. Influence of strontium on the cubic to ordered hexagonal phase transformation in barium magnesium niobate. M Thirumal A K Ganguli. Phase Transitions Volume 23 Issue 6 December 2000 pp 495-498 ...

Polymer- and salt-induced toroids of hexagonal DNA.

OpenAIRE

Ubbink, J; Odijk, T

1995-01-01

A model is proposed for polymer- and salt-induced toroidal condensates of DNA, based on a recent theory of the undulation enhancement of the electrostatic interaction in the bulk hexagonal phase of semiflexible polyions. In a continuum approximation, the thermodynamic potential of a monomolecular toroid may be split up in bulk, surface, and curvature contributions. With the help of an approximate analytical minimization procedure, the optimal torus dimensions are calculated as a function of t...

Extension of the analytic nodal diffusion solver ANDES to triangular-Z geometry and coupling with COBRA-IIIc for hexagonal core analysis

International Nuclear Information System (INIS)

Lozano, Juan-Andres; Jimenez, Javier; Garcia-Herranz, Nuria; Aragones, Jose-Maria

2010-01-01

In this paper the extension of the multigroup nodal diffusion code ANDES, based on the Analytic Coarse Mesh Finite Difference (ACMFD) method, from Cartesian to hexagonal geometry is presented, as well as its coupling with the thermal-hydraulic (TH) code COBRA-IIIc for hexagonal core analysis. In extending the ACMFD method to hexagonal assemblies, triangular-Z nodes are used. In the radial plane, a direct transverse integration procedure is applied along the three directions that are orthogonal to the triangle interfaces. The triangular nodalization avoids the singularities, that appear when applying transverse integration to hexagonal nodes, and allows the advantage of the mesh subdivision capabilities implicit within that geometry. As for the thermal-hydraulics, the extension of the coupling scheme to hexagonal geometry has been performed with the capability to model the core using either assembly-wise channels (hexagonal mesh) or a higher refinement with six channels per fuel assembly (triangular mesh). Achieving this level of TH mesh refinement with COBRA-IIIc code provides a better estimation of the in-core 3D flow distribution, improving the TH core modelling. The neutronics and thermal-hydraulics coupled code, ANDES/COBRA-IIIc, previously verified in Cartesian geometry core analysis, can also be applied now to full three-dimensional VVER core problems, as well as to other thermal and fast hexagonal core designs. Verification results are provided, corresponding to the different cases of the OECD/NEA-NSC VVER-1000 Coolant Transient Benchmarks.

Bronze-mean hexagonal quasicrystal

Science.gov (United States)

Dotera, Tomonari; Bekku, Shinichi; Ziherl, Primož

2017-10-01

The most striking feature of conventional quasicrystals is their non-traditional symmetry characterized by icosahedral, dodecagonal, decagonal or octagonal axes. The symmetry and the aperiodicity of these materials stem from an irrational ratio of two or more length scales controlling their structure, the best-known examples being the Penrose and the Ammann-Beenker tiling as two-dimensional models related to the golden and the silver mean, respectively. Surprisingly, no other metallic-mean tilings have been discovered so far. Here we propose a self-similar bronze-mean hexagonal pattern, which may be viewed as a projection of a higher-dimensional periodic lattice with a Koch-like snowflake projection window. We use numerical simulations to demonstrate that a disordered variant of this quasicrystal can be materialized in soft polymeric colloidal particles with a core-shell architecture. Moreover, by varying the geometry of the pattern we generate a continuous sequence of structures, which provide an alternative interpretation of quasicrystalline approximants observed in several metal-silicon alloys.

The phenomenon of resilient rotary curvature of hexagon selenium nanothin crystals grate around [001] within the framework of asymmetrical theory of resiliency

International Nuclear Information System (INIS)

Malkov, V.B.; Agalakov, S.P.; Malkov, A.V.; Malkov, O.V.; Pushin, V.G.; Shul'gin, B.V.

2008-01-01

The research of resilient rotary curvature of hexagon selenium nanothin (80-100 nm) crystals grate the method of translucent electronic microscopy. In view of the fact that reasons of resilient rotary curvature of hexagon selenium nanothin crystals grate around [001] remained not found out, the analysis of models of resilient rotary curvature of hexagon selenium crystals grate is conducted.

How Will Sea Ice Loss Affect the Greenland Ice Sheet? On the Puzzling Features of Greenland Ice-Core Isotopic Composition

Science.gov (United States)

Pausata, Francesco S. R.; Legrande, Allegra N.; Roberts, William H. G.

2016-01-01

The modern cryosphere, Earth's frozen water regime, is in fast transition. Greenland ice cores show how fast theses changes can be, presenting evidence of up to 15 C warming events over timescales of less than a decade. These events, called Dansgaard/Oeschger (D/O) events, are believed to be associated with rapid changes in Arctic sea ice, although the underlying mechanisms are still unclear. The modern demise of Arctic sea ice may, in turn, instigate abrupt changes on the Greenland Ice Sheet. The Arctic Sea Ice and Greenland Ice Sheet Sensitivity (Ice2Ice Chttps://ice2ice.b.uib.noD) initiative, sponsored by the European Research Council, seeks to quantify these past rapid changes to improve our understanding of what the future may hold for the Arctic. Twenty scientists gathered in Copenhagen as part of this initiative to discuss the most recent observational, technological, and model developments toward quantifying the mechanisms behind past climate changes in Greenland. Much of the discussion focused on the causes behind the changes in stable water isotopes recorded in ice cores. The participants discussed sources of variability for stable water isotopes and framed ways that new studies could improve understanding of modern climate. The participants also discussed how climate models could provide insights into the relative roles of local and nonlocal processes in affecting stable water isotopes within the Greenland Ice Sheet. Presentations of modeling results showed how a change in the source or seasonality of precipitation could occur not only between glacial and modern climates but also between abrupt events. Recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. Further, indications from recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. This feature complicates

Arctic landfast sea ice

Science.gov (United States)

Konig, Christof S.

Landfast ice is sea ice which forms and remains fixed along a coast, where it is attached either to the shore, or held between shoals or grounded icebergs. Landfast ice fundamentally modifies the momentum exchange between atmosphere and ocean, as compared to pack ice. It thus affects the heat and freshwater exchange between air and ocean and impacts on the location of ocean upwelling and downwelling zones. Further, the landfast ice edge is essential for numerous Arctic mammals and Inupiat who depend on them for their subsistence. The current generation of sea ice models is not capable of reproducing certain aspects of landfast ice formation, maintenance, and disintegration even when the spatial resolution would be sufficient to resolve such features. In my work I develop a new ice model that permits the existence of landfast sea ice even in the presence of offshore winds, as is observed in mature. Based on viscous-plastic as well as elastic-viscous-plastic ice dynamics I add tensile strength to the ice rheology and re-derive the equations as well as numerical methods to solve them. Through numerical experiments on simplified domains, the effects of those changes are demonstrated. It is found that the modifications enable landfast ice modeling, as desired. The elastic-viscous-plastic rheology leads to initial velocity fluctuations within the landfast ice that weaken the ice sheet and break it up much faster than theoretically predicted. Solving the viscous-plastic rheology using an implicit numerical method avoids those waves and comes much closer to theoretical predictions. Improvements in landfast ice modeling can only verified in comparison to observed data. I have extracted landfast sea ice data of several decades from several sources to create a landfast sea ice climatology that can be used for that purpose. Statistical analysis of the data shows several factors that significantly influence landfast ice distribution: distance from the coastline, ocean depth, as

Sodium-Doped Mesoporous Ni2P2O7 Hexagonal Tablets for High-Performance Flexible All-Solid-State Hybrid Supercapacitors.

Science.gov (United States)

Wei, Chengzhen; Cheng, Cheng; Wang, Shanshan; Xu, Yazhou; Wang, Jindi; Pang, Huan

2015-08-01

A simple hydrothermal method has been developed to prepare hexagonal tablet precursors, which are then transformed into porous sodium-doped Ni2P2O7 hexagonal tablets by a simple calcination method. The obtained samples were evaluated as electrode materials for supercapacitors. Electrochemical measurements show that the electrode based on the porous sodium-doped Ni2P2O7 hexagonal tablets exhibits a specific capacitance of 557.7 F g(-1) at a current density of 1.2 A g(-1) . Furthermore, the porous sodium-doped Ni2P2O7 hexagonal tablets were successfully used to construct flexible solid-state hybrid supercapacitors. The device is highly flexible and achieves a maximum energy density of 23.4 Wh kg(-1) and a good cycling stability after 5000 cycles, which confirms that the porous sodium-doped Ni2P2 O7 hexagonal tablets are promising active materials for flexible supercapacitors. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

2D of hexagonal plasmonic necklaces for enhanced second harmonic generation

DEFF Research Database (Denmark)

Gómez-Tornero, Alejandro; Tserkezis, Christos; Mateos, Luis

2017-01-01

Hexagonal plasmonic necklaces of silver nanoparticles organized in 2D superlattices on functional ferroelectric templates are fabricated in large-scale spatial regions by using a surfactant-free photo-deposition process. The plasmonic necklaces support broad radiative plasmonic resonances allowing...

Diagonal form factors and hexagon form factors

International Nuclear Information System (INIS)

Jiang, Yunfeng; Petrovskii, Andrei

2016-01-01

We study the heavy-heavy-light (HHL) three-point functions in the planar N=4 super-Yang-Mills theory using the recently proposed hexagon bootstrap program http://arxiv.org/abs/1505.06745. We prove the conjecture of Bajnok, Janik and Wereszczynski http://dx.doi.org/10.1007/JHEP09(2014)050 on the polynomial L-dependence of HHL structure constant up to the leading finite-size corrections, where L is the length of the heavy operators. The proof is presented for a specific set-up but the method can be applied to more general situations.

Diagonal form factors and hexagon form factors

Energy Technology Data Exchange (ETDEWEB)

Jiang, Yunfeng [Institute for Theoretical Physics, ETH Zürich,Honggerberg, Zürich, 8093 (Switzerland); Petrovskii, Andrei [Institut de Physique Théorique, CEA, URA 2306 CNRS Saclay,Gif-sur-Yvette, F91191 (France)

2016-07-25

We study the heavy-heavy-light (HHL) three-point functions in the planar N=4 super-Yang-Mills theory using the recently proposed hexagon bootstrap program http://arxiv.org/abs/1505.06745. We prove the conjecture of Bajnok, Janik and Wereszczynski http://dx.doi.org/10.1007/JHEP09(2014)050 on the polynomial L-dependence of HHL structure constant up to the leading finite-size corrections, where L is the length of the heavy operators. The proof is presented for a specific set-up but the method can be applied to more general situations.

Ice slurry applications

Energy Technology Data Exchange (ETDEWEB)

Kauffeld, M. [Karlsruhe University of Applied Sciences, Moltkestr. 30, 76133 Karlsruhe (Germany); Wang, M.J.; Goldstein, V. [Sunwell Technologies Inc., 180 Caster Avenue, Woodbridge, L4L 5Y (Canada); Kasza, K.E. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

2010-12-15

The role of secondary refrigerants is expected to grow as the focus on the reduction of greenhouse gas emissions increases. The effectiveness of secondary refrigerants can be improved when phase changing media are introduced in place of single-phase media. Operating at temperatures below the freezing point of water, ice slurry facilitates several efficiency improvements such as reductions in pumping energy consumption as well as lowering the required temperature difference in heat exchangers due to the beneficial thermo-physical properties of ice slurry. Research has shown that ice slurry can be engineered to have ideal ice particle characteristics so that it can be easily stored in tanks without agglomeration and then be extractable for pumping at very high ice fraction without plugging. In addition ice slurry can be used in many direct contact food and medical protective cooling applications. This paper provides an overview of the latest developments in ice slurry technology. (author)

Factors Affecting the Changes of Ice Crystal Form in Ice Cream

Science.gov (United States)

Wang, Xin; Watanabe, Manabu; Suzuki, Toru

In this study, the shape of ice crystals in ice cream was quantitatively evaluated by introducing fractal analysis. A small droplet of commercial ice cream mix was quickly cooled to about -30°C on the cold stage of microscope. Subsequently, it was heated to -5°C or -10°C and then held for various holding time. Based on the captured images at each holding time, the cross-sectional area and the length of circumference for each ice crystal were measured to calculate fractal dimension using image analysis software. The results showed that the ice crystals were categorized into two groups, e.g. simple-shape and complicated-shape, according to their fractal dimensions. The fractal dimension of ice crystals became lower with increasing holding time and holding temperature. It was also indicated that the growing rate of complicated-shape ice crystals was relatively higher because of aggregation.

Mapping Ross Ice Shelf with ROSETTA-Ice airborne laser altimetry

Science.gov (United States)

Becker, M. K.; Fricker, H. A.; Padman, L.; Bell, R. E.; Siegfried, M. R.; Dieck, C. C. M.

2017-12-01

The Ross Ocean and ice Shelf Environment and Tectonic setting Through Aerogeophysical surveys and modeling (ROSETTA-Ice) project combines airborne glaciological, geological, and oceanographic observations to enhance our understanding of the history and dynamics of the large ( 500,000 square km) Ross Ice Shelf (RIS). Here, we focus on the Light Detection And Ranging (LiDAR) data collected in 2015 and 2016. This data set represents a significant advance in resolution: Whereas the last attempt to systematically map RIS (the surface-based RIGGS program in the 1970s) was at 55 km grid spacing, the ROSETTA-Ice grid has 10-20 km line spacing and much higher along-track resolution. We discuss two different strategies for processing the raw LiDAR data: one that requires proprietary software (Riegl's RiPROCESS package), and one that employs open-source programs and libraries. With the processed elevation data, we are able to resolve fine-scale ice-shelf features such as the "rampart-moat" ice-front morphology, which has previously been observed on and modeled for icebergs. This feature is also visible in the ROSETTA-Ice shallow-ice radar data; comparing the laser data with radargrams provides insight into the processes leading to their formation. Near-surface firn state and total firn air content can also be investigated through combined analysis of laser altimetry and radar data. By performing similar analyses with data from the radar altimeter aboard CryoSat-2, we demonstrate the utility of the ROSETTA-Ice LiDAR data set in satellite validation efforts. The incorporation of the LiDAR data from the third and final field season (December 2017) will allow us to construct a DEM and an ice thickness map of RIS for the austral summers of 2015-2017. These products will be used to validate and extend observations of height changes from satellite radar and laser altimetry, as well as to update regional models of ocean circulation and ice dynamics.

Capabilities and performance of Elmer/Ice, a new-generation ice sheet model

Directory of Open Access Journals (Sweden)

O. Gagliardini

2013-08-01

Full Text Available The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

Solution of the Neutron transport equation in hexagonal geometry using strongly discontinuous nodal schemes

International Nuclear Information System (INIS)

Mugica R, C.A.; Valle G, E. del

2005-01-01

In 2002, E. del Valle and Ernest H. Mund developed a technique to solve numerically the Neutron transport equations in discrete ordinates and hexagonal geometry using two nodal schemes type finite element weakly discontinuous denominated WD 5,3 and WD 12,8 (of their initials in english Weakly Discontinuous). The technique consists on representing each hexagon in the union of three rhombuses each one of which it is transformed in a square in the one that the methods WD 5,3 and WD 12,8 were applied. In this work they are solved the mentioned equations of transport using the same discretization technique by hexagon but using two nodal schemes type finite element strongly discontinuous denominated SD 3 and SD 8 (of their initials in english Strongly Discontinuous). The application in each case as well as a reference problem for those that results are provided for the effective multiplication factor is described. It is carried out a comparison with the obtained results by del Valle and Mund for different discretization meshes so much angular as spatial. (Author)

Characterizing Arctic Sea Ice Topography Using High-Resolution IceBridge Data

Science.gov (United States)

Petty, Alek; Tsamados, Michel; Kurtz, Nathan; Farrell, Sinead; Newman, Thomas; Harbeck, Jeremy; Feltham, Daniel; Richter-Menge, Jackie

2016-01-01

We present an analysis of Arctic sea ice topography using high resolution, three-dimensional, surface elevation data from the Airborne Topographic Mapper, flown as part of NASA's Operation IceBridge mission. Surface features in the sea ice cover are detected using a newly developed surface feature picking algorithm. We derive information regarding the height, volume and geometry of surface features from 2009-2014 within the Beaufort/Chukchi and Central Arctic regions. The results are delineated by ice type to estimate the topographic variability across first-year and multi-year ice regimes.

Arctic sea ice decline contributes to thinning lake ice trend in northern Alaska

Science.gov (United States)

Alexeev, Vladimir; Arp, Christopher D.; Jones, Benjamin M.; Cai, Lei

2016-01-01

Field measurements, satellite observations, and models document a thinning trend in seasonal Arctic lake ice growth, causing a shift from bedfast to floating ice conditions. September sea ice concentrations in the Arctic Ocean since 1991 correlate well (r = +0.69,p Research and Forecasting model output produced a 7% decrease in lake ice growth when 2007/08 sea ice was imposed on 1991/92 climatology and a 9% increase in lake ice growth for the opposing experiment. Here, we clearly link early winter 'ocean-effect' snowfall and warming to reduced lake ice growth. Future reductions in sea ice extent will alter hydrological, biogeochemical, and habitat functioning of Arctic lakes and cause sub-lake permafrost thaw.

Stochastic ice stream dynamics.

Science.gov (United States)

Mantelli, Elisa; Bertagni, Matteo Bernard; Ridolfi, Luca

2016-08-09

Ice streams are narrow corridors of fast-flowing ice that constitute the arterial drainage network of ice sheets. Therefore, changes in ice stream flow are key to understanding paleoclimate, sea level changes, and rapid disintegration of ice sheets during deglaciation. The dynamics of ice flow are tightly coupled to the climate system through atmospheric temperature and snow recharge, which are known exhibit stochastic variability. Here we focus on the interplay between stochastic climate forcing and ice stream temporal dynamics. Our work demonstrates that realistic climate fluctuations are able to (i) induce the coexistence of dynamic behaviors that would be incompatible in a purely deterministic system and (ii) drive ice stream flow away from the regime expected in a steady climate. We conclude that environmental noise appears to be crucial to interpreting the past behavior of ice sheets, as well as to predicting their future evolution.

Autonomous Aerial Ice Observation for Ice Defense

Directory of Open Access Journals (Sweden)

Joakim Haugen

2014-10-01

Full Text Available One of the tasks in ice defense is to gather information about the surrounding ice environment using various sensor platforms. In this manuscript we identify two monitoring tasks known in literature, namely dynamic coverage and target tracking, and motivate how these tasks are relevant in ice defense using RPAS. An optimization-based path planning concept is outlined for solving these tasks. A path planner for the target tracking problem is elaborated in more detail and a hybrid experiment, which consists of both a real fixed-wing aircraft and simulated objects, is included to show the applicability of the proposed framework.

Controls on Arctic sea ice from first-year and multi-year ice survival rates

Science.gov (United States)

Armour, K.; Bitz, C. M.; Hunke, E. C.; Thompson, L.

2009-12-01

The recent decrease in Arctic sea ice cover has transpired with a significant loss of multi-year (MY) ice. The transition to an Arctic that is populated by thinner first-year (FY) sea ice has important implications for future trends in area and volume. We develop a reduced model for Arctic sea ice with which we investigate how the survivability of FY and MY ice control various aspects of the sea-ice system. We demonstrate that Arctic sea-ice area and volume behave approximately as first-order autoregressive processes, which allows for a simple interpretation of September sea-ice in which its mean state, variability, and sensitivity to climate forcing can be described naturally in terms of the average survival rates of FY and MY ice. This model, used in concert with a sea-ice simulation that traces FY and MY ice areas to estimate the survival rates, reveals that small trends in the ice survival rates explain the decline in total Arctic ice area, and the relatively larger loss of MY ice area, over the period 1979-2006. Additionally, our model allows for a calculation of the persistence time scales of September area and volume anomalies. A relatively short memory time scale for ice area (~ 1 year) implies that Arctic ice area is nearly in equilibrium with long-term climate forcing at all times, and therefore observed trends in area are a clear indication of a changing climate. A longer memory time scale for ice volume (~ 5 years) suggests that volume can be out of equilibrium with climate forcing for long periods of time, and therefore trends in ice volume are difficult to distinguish from its natural variability. With our reduced model, we demonstrate the connection between memory time scale and sensitivity to climate forcing, and discuss the implications that a changing memory time scale has on the trajectory of ice area and volume in a warming climate. Our findings indicate that it is unlikely that a “tipping point” in September ice area and volume will be

Defect mediated van der Waals epitaxy of hexagonal boron nitride on graphene

Science.gov (United States)

Heilmann, M.; Bashouti, M.; Riechert, H.; Lopes, J. M. J.

2018-04-01

Van der Waals heterostructures comprising of hexagonal boron nitride and graphene are promising building blocks for novel two-dimensional devices such as atomically thin transistors or capacitors. However, demonstrators of those devices have been so far mostly fabricated by mechanical assembly, a non-scalable and time-consuming method, where transfer processes can contaminate the surfaces. Here, we investigate a direct growth process for the fabrication of insulating hexagonal boron nitride on high quality epitaxial graphene using plasma assisted molecular beam epitaxy. Samples were grown at varying temperatures and times and studied using atomic force microscopy, revealing a growth process limited by desorption at high temperatures. Nucleation was mostly commencing from morphological defects in epitaxial graphene, such as step edges or wrinkles. Raman spectroscopy combined with x-ray photoelectron measurements confirm the formation of hexagonal boron nitride and prove the resilience of graphene against the nitrogen plasma used during the growth process. The electrical properties and defects in the heterostructures were studied with high lateral resolution by tunneling current and Kelvin probe force measurements. This correlated approach revealed a nucleation apart from morphological defects in epitaxial graphene, which is mediated by point defects. The presented results help understanding the nucleation and growth behavior during van der Waals epitaxy of 2D materials, and point out a route for a scalable production of van der Waals heterostructures.

Computation of 3D neutron fluxes in one pin hexagonal cell

International Nuclear Information System (INIS)

Prabha, Hem; Marleau, Guy

2013-01-01

Highlights: ► Computations of 3D neutron fluxes in one pin hexagonal cell is performed by Carlvik’s method of collision probability. ► Carlvik’s method requires computation of track lengths in the geometry. ► Equations are developed to compute tracks, in 2D and 3D, in hexagons and are implemented in a program HX7. ► The program HX7 is implemented in NXT module of the code DRAGON, where tracks in pins are computed. ► The tracks are plotted and fluxes are compared with the EXCELT module of the code DRAGON. - Abstract: In this paper we are presenting the method of computation of three dimensional (3D) neutron fluxes in one pin hexagonal cell. Carlvik’s collision probability method of solving neutron transport equation for computing fluxes has been used here. This method can consider exact geometrical details of the given geometry. While using this method, track length computations are required to be done. We have described here the method of computing tracks in one 3D hexagon. A program HX7 has been developed for this purpose. This program has been implemented in the NXT module of the code DRAGON, where tracks in the pins are computed. For computing tracks in 3D, first we use the tracks computed in the two dimensions (2D) and then we project them in the third dimension. We have developed equations for this purpose. In both the regions, fuel pin as well as in the moderator surrounding the pin the fluxes are assumed to be uniform. A uniform source is assumed in the moderator region. Reflecting boundary conditions are applied on all the sides as well as on the top and bottom surfaces. One group 2D and 3D fluxes are compared with the respective results obtained by the EXCELT module of DRAGON. To check the computations, tracks are plotted and errors in the computations are obtained. It is observed by using both the modules EXCELT and NXT that the fluxes in the pins converge faster and in the moderator region fluxes converge very slowly

The future of ice sheets and sea ice: between reversible retreat and unstoppable loss.

Science.gov (United States)

Notz, Dirk

2009-12-08

We discuss the existence of cryospheric "tipping points" in the Earth's climate system. Such critical thresholds have been suggested to exist for the disappearance of Arctic sea ice and the retreat of ice sheets: Once these ice masses have shrunk below an anticipated critical extent, the ice-albedo feedback might lead to the irreversible and unstoppable loss of the remaining ice. We here give an overview of our current understanding of such threshold behavior. By using conceptual arguments, we review the recent findings that such a tipping point probably does not exist for the loss of Arctic summer sea ice. Hence, in a cooler climate, sea ice could recover rapidly from the loss it has experienced in recent years. In addition, we discuss why this recent rapid retreat of Arctic summer sea ice might largely be a consequence of a slow shift in ice-thickness distribution, which will lead to strongly increased year-to-year variability of the Arctic summer sea-ice extent. This variability will render seasonal forecasts of the Arctic summer sea-ice extent increasingly difficult. We also discuss why, in contrast to Arctic summer sea ice, a tipping point is more likely to exist for the loss of the Greenland ice sheet and the West Antarctic ice sheet.

SmaggIce 2.0: Additional Capabilities for Interactive Grid Generation of Iced Airfoils

Science.gov (United States)

Kreeger, Richard E.; Baez, Marivell; Braun, Donald C.; Schilling, Herbert W.; Vickerman, Mary B.

2008-01-01

The Surface Modeling and Grid Generation for Iced Airfoils (SmaggIce) software toolkit has been extended to allow interactive grid generation for multi-element iced airfoils. The essential phases of an icing effects study include geometry preparation, block creation and grid generation. SmaggIce Version 2.0 now includes these main capabilities for both single and multi-element airfoils, plus an improved flow solver interface and a variety of additional tools to enhance the efficiency and accuracy of icing effects studies. An overview of these features is given, especially the new multi-element blocking strategy using the multiple wakes method. Examples are given which illustrate the capabilities of SmaggIce for conducting an icing effects study for both single and multi-element airfoils.

Winter snow conditions on Arctic sea ice north of Svalbard during the Norwegian young sea ICE (N-ICE2015) expedition

Science.gov (United States)

Merkouriadi, Ioanna; Gallet, Jean-Charles; Graham, Robert M.; Liston, Glen E.; Polashenski, Chris; Rösel, Anja; Gerland, Sebastian

2017-10-01

Snow is a crucial component of the Arctic sea ice system. Its thickness and thermal properties control heat conduction and radiative fluxes across the ocean, ice, and atmosphere interfaces. Hence, observations of the evolution of snow depth, density, thermal conductivity, and stratigraphy are crucial for the development of detailed snow numerical models predicting energy transfer through the snow pack. Snow depth is also a major uncertainty in predicting ice thickness using remote sensing algorithms. Here we examine the winter spatial and temporal evolution of snow physical properties on first-year (FYI) and second-year ice (SYI) in the Atlantic sector of the Arctic Ocean, during the Norwegian young sea ICE (N-ICE2015) expedition (January to March 2015). During N-ICE2015, the snow pack consisted of faceted grains (47%), depth hoar (28%), and wind slab (13%), indicating very different snow stratigraphy compared to what was observed in the Pacific sector of the Arctic Ocean during the SHEBA campaign (1997-1998). Average snow bulk density was 345 kg m-3 and it varied with ice type. Snow depth was 41 ± 19 cm in January and 56 ± 17 cm in February, which is significantly greater than earlier suggestions for this region. The snow water equivalent was 14.5 ± 5.3 cm over first-year ice and 19 ± 5.4 cm over second-year ice.

Removable cruciform for ice condenser ice basket

International Nuclear Information System (INIS)

Scrabis, C.M.; Mazza, G.E.; Golick, L.R.; Pomaibo, P.

1987-01-01

A removable cruciform for use in an ice basket having a generally cylindrical sidewall defining a central, vertical axis of the ice basket and plural, generally annular retaining rings secured to the interior of the cylindrical sidewall of the ice basket at predetermined, spaced elevations throughout the axial height of the ice basket is described comprising: a pair of brackets, each comprising a central, base portion having parallel longitudinal edges and a pair of integral legs extending at corresponding angles relative to the base portion from the perspective parallel longitudinal edges thereof; a pair of support plate assemblies secured to and extending in parallel, spaced relationship from one of the pair of brackets; a pair of slide support plates secured to the other of the pair of brackets and extending therefrom in spaced, parallel relationship; and spring means received within the housing and engaging the base portions of the brackets and applying a resilient biasing force thereto for maintaining the spaced relationship thereof

Solution of two-dimensional diffusion equation for hexagonal cells by the finite Fourier transformation

International Nuclear Information System (INIS)

Kobayashi, Keisuke

1975-01-01

A method of solution is presented for a monoenergetic diffusion equation in two-dimensional hexagonal cells by a finite Fourier transformation. Up to the present, the solution by the finite Fourier transformation has been developed for x-y, r-z and x-y-z geometries, and the flux and current at the boundary are obtained in terms of Fourier series. It is shown here that the method can be applied to hexagonal cells and the expansion of boundary values in a Legendre polynomials gives numerically a higher accuracy than is obtained by a Fourier series. (orig.) [de

Acoustic phonons in the hexagonal perovskite CsNiCl3 around the Gamma-point

DEFF Research Database (Denmark)

Visser, D.; Monteith, A.R.; Rønnow, H.M.

2000-01-01

The acoustic phonon dispersion curves of the hexagonal perovskite CsNiCl3 were measured at room temperature in the vicinity of the Gamma-point along the [0 0 1] and [1 1 0] directions. The derived velocity of sound values for the longitudinal and transverse acoustic phonons are compared with the ......The acoustic phonon dispersion curves of the hexagonal perovskite CsNiCl3 were measured at room temperature in the vicinity of the Gamma-point along the [0 0 1] and [1 1 0] directions. The derived velocity of sound values for the longitudinal and transverse acoustic phonons are compared...

Bacterial Ice Crystal Controlling Proteins

Science.gov (United States)

Lorv, Janet S. H.; Rose, David R.; Glick, Bernard R.

2014-01-01

Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions. PMID:24579057

First-principles calculations on double-walled inorganic nanotubes with hexagonal chiralities

International Nuclear Information System (INIS)

Zhukovskii, Yuri F; Evarestov, Robert A; Bandura, Andrei V; Losev, Maxim V

2011-01-01

The two sets of commensurate double-walled boron nitride and titania hexagonally-structured nanotubes (DW BN and TiO 2 NTs) possessing either armchair- or zigzag-type chiralities have been considered, i.e., (n 1 ,n 1 )-(n 2 ,n 2 ) or (n 1 ,0)-(n 2 ,0), respectively. For symmetry analysis of these nanotubes, the line symmetry groups for one-periodic (1D) nanostructures with rotohelical symmetry have been applied. To analyze the structural and electronic properties of hexagonal DW NTs, a series of large-scale ab initio DFT-LCAO calculations have been performed using the hybrid Hartree-Fock/Kohn-Sham exchange-correlation functional PBE0 (as implemented in CRYSTAL-09 code). To establish the optimal inter-shell distances within DW NTs corresponding to the minima of calculated total energy, the chiral indices n 1 and n 2 of the constituent single-walled (SW) nanotubes have been successively varied.

Astronomical Ice: The Effects of Treating Ice as a Porous Media on the Dynamics and Evolution of Extraterrestrial Ice-Ocean Environments

Science.gov (United States)

Buffo, J.; Schmidt, B. E.

2015-12-01

With the prevalence of water and ice rich environments in the solar system, and likely the universe, becoming more apparent, understanding the evolutionary dynamics and physical processes of such locales is of great importance. Piqued interest arises from the understanding that the persistence of all known life depends on the presence of liquid water. As in situ investigation is currently infeasible, accurate numerical modeling is the best technique to demystify these environments. We will discuss an evolving model of ice-ocean interaction aimed at realistically describing the behavior of the ice-ocean interface by treating basal ice as a porous media, and its possible implications on the formation of astrobiological niches. Treating ice as a porous media drastically affects the thermodynamic properties it exhibits. Thus inclusion of this phenomenon is critical in accurately representing the dynamics and evolution of all ice-ocean environments. This model utilizes equations that describe the dynamics of sea ice when it is treated as a porous media (Hunke et. al. 2011), coupled with a basal melt and accretion model (Holland and Jenkins 1999). Combined, these two models produce the most accurate description of the processes occurring at the base of terrestrial sea ice and ice shelves, capable of resolving variations within the ice due to environmental pressures. While these models were designed for application to terrestrial environments, the physics occurring at any ice-water interface is identical, and these models can be used to represent the evolution of a variety of icy astronomical bodies. As terrestrial ice shelves provide a close analog to planetary ice-ocean environments, we truth test the models validity against observations of ice shelves. We apply this model to the ice-ocean interface of the icy Galilean moon Europa. We include profiles of temperature, salinity, solid fraction, and Darcy velocity, as well as temporally and spatially varying melt and

Thermodynamics of high-pressure ice polymorphs : ices III and V

NARCIS (Netherlands)

Tchijov, [No Value; Ayala, RB; Leon, GC; Nagornov, O

Thermodynamic properties of high-pressure ice polymorphs, ices III and V, are studied theoretically. The results of TIP4P molecular dynamics simulations in the NPT ensemble are used to calculate the temperature dependence of the specific volume of ices III and V at pressures 0.25 and 0.5 GPa,

Export of Ice-Cavity Water from Pine Island Ice Shelf, West Antarctica

Science.gov (United States)

Thurnherr, Andreas; Jacobs, Stanley; Dutrieux, Pierre

2013-04-01

Stability of the West Antarctic Ice Sheet is sensitive to changes in melting at the bottom of floating ice shelves that form the seaward extensions of Antarctic glaciers flowing into the ocean. Not least because observations in the cavities beneath ice shelves are difficult, heat fluxes and melt rates have been inferred from oceanographic measurements obtained near the ice edge (calving fronts). Here, we report on a set of hydrographic and velocity data collected in early 2009 near the calving front of the Amundsen Sea's fast-moving and (until recently) accelerating Pine Island Glacier and its associated ice shelf. CTD profiles collected along the southern half of the meridionally-trending ice front show clear evidence for export of ice-cavity water. That water was carried in the upper ocean along the ice front by a southward current that is possibly related to a striking clockwise gyre that dominated the (summertime) upper-ocean circulation in Pine Island Bay. Signatures of ice-cavity water appear unrelated to current direction along most of the ice front, suggesting that cross-frontal exchange is dominated by temporal variability. However, repeated hydrographic and velocity measurements in a small "ice cove" at the southern end of the calving front show a persistent strong (mean velocity peaking near 0.5 ms-1) outflow of ice-cavity water in the upper 500 m. While surface features (boils) suggested upwelling from deep below the ice shelf, vertical velocity measurements reveal 1) that the mean upwelling within the confines of the cove was too weak to feed the observed outflow, and 2) that large high-frequency internal waves dominated the vertical motion of water inside the cove. These observations indicate that water exchange between the Pine Island Ice Shelf cavity and the Amundsen sea is strongly asymmetric with weak broad inflow at depth and concentrated surface-intensified outflow of melt-laden deep water at the southern edge of the calving front. The lack of

Observation and modeling of snow melt and superimposed ice formation on sea ice

OpenAIRE

Nicolaus, Marcel; Haas, Christian

2004-01-01

Sea ice plays a key role within the global climate system. It covers some 7% of earths surface and processes a strong seasonal cycle. Snow on sea ice even amplifies the importance of sea ice in the coupled atmosphere-ice-ocean system, because it dominates surface properties and energy balance (incl. albedo).Several quantitative observations of summer sea ice and its snow cover show the formation of superimposed ice and a gap layer underneath, which was found to be associated to high standing ...

RTk/SN Solutions of the Two-Dimensional Multigroup Transport Equations in Hexagonal Geometry

International Nuclear Information System (INIS)

Valle, Edmundo del; Mund, Ernest H.

2004-01-01

This paper describes an extension to the hexagonal geometry of some weakly discontinuous nodal finite element schemes developed by Hennart and del Valle for the two-dimensional discrete ordinates transport equation in quadrangular geometry. The extension is carried out in a way similar to the extension to the hexagonal geometry of nodal element schemes for the diffusion equation using a composite mapping technique suggested by Hennart, Mund, and del Valle. The combination of the weakly discontinuous nodal transport scheme and the composite mapping is new and is detailed in the main section of the paper. The algorithm efficiency is shown numerically through some benchmark calculations on classical problems widely referred to in the literature

Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films.

Science.gov (United States)

Cao, Shi-Gu; Li, Yunsong; Wu, Hong-Hui; Wang, Jie; Huang, Baoling; Zhang, Tong-Yi

2017-08-09

The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO 3 ) with a special thermomechanical treatment (TMT), where BaTiO 3 nanothin films under various stresses are annealed at temperature of 575 °C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials.

Evaluation of the hexagonal and spherical model of vocational interests in the young people in Serbia and Bulgaria

Directory of Open Access Journals (Sweden)

Hedrih Vladimir

2016-01-01

Full Text Available The aim of this study was to validate Holland’s hexagonal and Tracey’s spherical model of vocational interests in young adults in Serbia and Bulgaria. To this end, 1250 participants, 560 from Serbia and 690 from Bulgaria, filled in Serbian and Bulgarian versions of the Personal Globe Inventory (PGI, Tracey, 2002. Hubert and Arabie’s randomization test of hypothetical orders, multidimensional scaling with fixed coordinates, Myors test and exploratory factor analysis were used. The results showed that the hexagonal and spherical models well explained the structure of vocational interests in both samples. The level of fit of the hexagonal model to the data obtained by using the PGI was generally higher than those established in the studies that used other Holland-based instruments. Furthermore, the levels of fit of both hexagonal and spherical model were in the same range like those obtained in previous studies in other countries. The results also pointed out a remarkable similarity in the structure of vocational interests in the Bulgarian and Serbian samples. [Projekat Ministarstva nauke Republike Srbije, br. 179002

The effect of ice-cream-scoop water on the hygiene of ice cream.

Science.gov (United States)

Wilson, I. G.; Heaney, J. C.; Weatherup, S. T.

1997-01-01

A survey of unopened ice cream, ice cream in use, and ice-cream-scoop water (n = 91) was conducted to determine the effect of scoop water hygiene on the microbiological quality of ice cream. An aerobic plate count around 10(6) c.f.u. ml-1 was the modal value for scoop waters. Unopened ice creams generally had counts around 10(3)-10(4) c.f.u. ml-1 and this increased by one order of magnitude when in use. Many scoop waters had low coliform counts, but almost half contained > 100 c.f.u. ml-1. E. coli was isolated in 18% of ice creams in use, and in 10% of unopened ice creams. S. aureus was not detected in any sample. Statistical analysis showed strong associations between indicator organisms and increased counts in ice cream in use. EC guidelines for indicator organisms in ice cream were exceeded by up to 56% of samples. PMID:9287941

Surface lowering of the debris-covered area of Kanchenjunga Glacier in the eastern Nepal Himalaya since 1975, as revealed by Hexagon KH-9 and ALOS satellite observations

Science.gov (United States)

Lamsal, Damodar; Fujita, Koji; Sakai, Akiko

2017-12-01

This study presents the geodetic mass balance of Kanchenjunga Glacier, one of the largest debris-covered glaciers in the easternmost Nepal Himalaya, which possesses a negative mass balance of -0.18 ± 0.17 m w.e. a-1 for the 1975-2010 study period, estimated using digital elevation models (DEMs) generated from Hexagon KH-9 and ALOS PRISM stereo images. Accurate DEMs, with a relative uncertainty of ±5.5 m, were generated from the intensive and manual editing of triangulated irregular network (TIN) models on a stereo MirrorTM/3D Monitor. The glacier ice-flow velocity field was also calculated using a feature-tracking method that was applied to two ALOS orthoimages taken in 2010. The elevation differences between the two DEMs highlight considerable surface lowering across the debris-covered area, and a slight thickening in the accumulation area of Kanchenjunga Glacier between 1975 and 2010. The magnitude and gradient of surface lowering are similar among the six glacier tributaries, even though they are situated at different elevations, which may reflect variations in the ice-flow velocity field. The pattern of surface lowering correlates well with the ice-flow velocity field over the debris-covered portion of the main tributary, suggesting that the glacier dynamics significantly affect surface lowering by altering the emergence velocity along the glacier, particularly in the compressive ablation area. Surface-lowering patterns partially correspond to the supraglacial pond area fraction of the glacier, with enhanced surface lowering observed in areas that possess a larger pond area fraction. These findings support the hypothesis that supraglacial ponds may intensify ice wastage and play a key role in the heterogeneous surface lowering of debris-covered glaciers. The estimated mass loss of Kanchenjunga Glacier is moderate compared with other debris-covered glaciers in neighboring Himalayan regions, which may be due to the lower pond area fraction of Kanchenjunga

Proceedings of the 19. IAHR international symposium on ice : using new technology to understand water-ice interaction

International Nuclear Information System (INIS)

Jasek, M.; Andrishak, R.; Siddiqui, A.

2008-01-01

This conference provided a venue for scientists, engineers and researchers an opportunity to expand their knowledge of water-ice interactions with reference to water resources, river and coastal hydraulics, risk analysis, energy and the environment. The the theme of new technology falls into 3 basic groups, notably measurement and instrumentation; remote sensing; and numerical simulation. The thermal regime of rivers was discussed along with ice mechanics, ice hydraulics, ice structures and modelling ice phenomena. The titles of the sessions were: river ice, glaciers and climate change; freeze-up processes on rivers and oceans; river ice-structure interactions; numerical simulations in ice engineering; river-ice break-up and ice jam formation; ice measurement; Grasse River ice evaluation; evaluation of structural ice control alternatives; remote sensing; hydropower and dam decommissioning; mechanical behaviour of river ice, ice covered flow and thermal modelling; mathematical and computer model formulations for ice friction and sea ice; ice bergs and ice navigation; ice crushing processes; sea ice and shore/structure interactions; ice properties, testing and physical modelling; ice actions on compliant structures; oil spills in ice; desalination, ice thickness and climate change; and, sea ice ridges. The conference featured 123 presentations, of which 20 have been catalogued separately for inclusion in this database. refs., tabs., figs

Structural domain walls in polar hexagonal manganites

Science.gov (United States)

Kumagai, Yu

2014-03-01

The domain structure in the multiferroic hexagonal manganites is currently intensely investigated, motivated by the observation of intriguing sixfold topological defects at their meeting points [Choi, T. et al,. Nature Mater. 9, 253 (2010).] and nanoscale electrical conductivity at the domain walls [Wu, W. et al., Phys. Rev. Lett. 108, 077203 (2012).; Meier, D. et al., Nature Mater. 11, 284 (2012).], as well as reports of coupling between ferroelectricity, magnetism and structural antiphase domains [Geng, Y. et al., Nano Lett. 12, 6055 (2012).]. The detailed structure of the domain walls, as well as the origin of such couplings, however, was previously not fully understood. In the present study, we have used first-principles density functional theory to calculate the structure and properties of the low-energy structural domain walls in the hexagonal manganites [Kumagai, Y. and Spaldin, N. A., Nature Commun. 4, 1540 (2013).]. We find that the lowest energy domain walls are atomically sharp, with {210}orientation, explaining the orientation of recently observed stripe domains and suggesting their topological protection [Chae, S. C. et al., Phys. Rev. Lett. 108, 167603 (2012).]. We also explain why ferroelectric domain walls are always simultaneously antiphase walls, propose a mechanism for ferroelectric switching through domain-wall motion, and suggest an atomistic structure for the cores of the sixfold topological defects. This work was supported by ETH Zurich, the European Research Council FP7 Advanced Grants program me (grant number 291151), the JSPS Postdoctoral Fellowships for Research Abroad, and the MEXT Elements Strategy Initiative to Form Core Research Center TIES.

Windows in Arctic sea ice: Light transmission and ice algae in a refrozen lead

Science.gov (United States)

Kauko, Hanna M.; Taskjelle, Torbjørn; Assmy, Philipp; Pavlov, Alexey K.; Mundy, C. J.; Duarte, Pedro; Fernández-Méndez, Mar; Olsen, Lasse M.; Hudson, Stephen R.; Johnsen, Geir; Elliott, Ashley; Wang, Feiyue; Granskog, Mats A.

2017-06-01

The Arctic Ocean is rapidly changing from thicker multiyear to thinner first-year ice cover, with significant consequences for radiative transfer through the ice pack and light availability for algal growth. A thinner, more dynamic ice cover will possibly result in more frequent leads, covered by newly formed ice with little snow cover. We studied a refrozen lead (≤0.27 m ice) in drifting pack ice north of Svalbard (80.5-81.8°N) in May-June 2015 during the Norwegian young sea ICE expedition (N-ICE2015). We measured downwelling incident and ice-transmitted spectral irradiance, and colored dissolved organic matter (CDOM), particle absorption, ultraviolet (UV)-protecting mycosporine-like amino acids (MAAs), and chlorophyll a (Chl a) in melted sea ice samples. We found occasionally very high MAA concentrations (up to 39 mg m-3, mean 4.5 ± 7.8 mg m-3) and MAA to Chl a ratios (up to 6.3, mean 1.2 ± 1.3). Disagreement in modeled and observed transmittance in the UV range let us conclude that MAA signatures in CDOM absorption spectra may be artifacts due to osmotic shock during ice melting. Although observed PAR (photosynthetically active radiation) transmittance through the thin ice was significantly higher than that of the adjacent thicker ice with deep snow cover, ice algal standing stocks were low (≤2.31 mg Chl a m-2) and similar to the adjacent ice. Ice algal accumulation in the lead was possibly delayed by the low inoculum and the time needed for photoacclimation to the high-light environment. However, leads are important for phytoplankton growth by acting like windows into the water column.

Vortex solitons at the interface separating square and hexagonal lattices

Energy Technology Data Exchange (ETDEWEB)

Jović Savić, Dragana, E-mail: jovic@ipb.ac.rs; Piper, Aleksandra; Žikić, Radomir; Timotijević, Dejan

2015-06-19

Vortex solitons at the interface separating two different photonic lattices – square and hexagonal – are demonstrated numerically. We consider the conditions for the existence of discrete vortex states at such interfaces and develop a concise picture of different scenarios of the vortex solutions behavior. Various vortices with different size and topological charges are considered, as well as various lattice interfaces. A novel type of discrete vortex surface solitons in a form of five-lobe solution is observed. Besides stable three-lobe and six-lobe discrete surface modes propagating for long distances, we observe various oscillatory vortex surface solitons, as well as dynamical instabilities of different kinds of solutions and study their angular momentum. Dynamical instabilities occur for higher values of the propagation constant, or at higher beam powers. - Highlights: • We demonstrate vortex solitons at the square–hexagonal photonic lattice interface. • A novel type of five-lobe surface vortex solitons is observed. • Different phase structures of surface solutions are studied. • Orbital angular momentum transfer of such solutions is investigated.

Sea Ice Summer Camp: Bringing Together Arctic Sea Ice Modelers and Observers

Science.gov (United States)

Perovich, D. K.; Holland, M. M.

2016-12-01

The Arctic sea ice has undergone dramatic change and numerical models project this to continue for the foreseeable future. Understanding the mechanisms behind sea ice loss and its consequences for the larger Arctic and global systems is of critical importance if we are to anticipate and plan for the future. One impediment to progress is a disconnect between the observational and modeling communities. A sea ice summer camp was held in Barrow Alaska from 26 May to 1 June 2016 to overcome this impediment and better integrate the sea ice community. The 25 participants were a mix of modelers and observers from 13 different institutions at career stages from graduate student to senior scientist. The summer camp provided an accelerated program on sea ice observations and models and also fostered future collaborative interdisciplinary activities. Each morning was spent in the classroom with a daily lecture on an aspect of modeling or remote sensing followed by practical exercises. Topics included using models to assess sensitivity, to test hypotheses and to explore sources of uncertainty in future Arctic sea ice loss. The afternoons were spent on the ice making observations. There were four observational activities; albedo observations, ice thickness measurements, ice coring and physical properties, and ice morphology surveys. The last field day consisted of a grand challenge where the group formulated a hypothesis, developed an observational and modeling strategy to test the hypothesis, and then integrated the observations and model results. The impacts of changing sea ice are being felt today in Barrow Alaska. We opened a dialog with Barrow community members to further understand these changes. This included an evening discussion with two Barrow sea ice experts and a community presentation of our work in a public lecture at the Inupiat Heritage Center.

Ice Thickness, Melting Rates and Styles of Activity in Ice-Volcano Interaction

Science.gov (United States)

Gudmundsson, M. T.

2005-12-01

In most cases when eruptions occur within glaciers they lead to rapid ice melting, jokulhlaups and/or lahars. Many parameters influence the style of activity and its impact on the environment. These include ice thickness (size of glacier), bedrock geometry, magma flow rate and magma composition. The eruptions that have been observed can roughly be divided into: (1) eruptions under several hundred meters thick ice on a relatively flat bedrock, (2) eruptions on flat or sloping bed through relatively thin ice, and (3) volcanism where effects are limitied to confinement of lava flows or melting of ice by pyroclastic flows or surges. This last category (ice-contact volcanism) need not cause much ice melting. Many of the deposits formed by Pleistocene volcanism in Iceland, British Columbia and Antarctica belong to the first category. An important difference between this type of activity and submarine activity (where pressure is hydrostatic) is that pressure at vents may in many cases be much lower than glaciostatic due to partial support of ice cover over vents by the surrounding glacier. Reduced pressure favours explosive activity. Thus the effusive/explosive transition may occur several hundred metres underneath the ice surface. Explosive fragmentation of magma leads to much higher rates of heat transfer than does effusive eruption of pillow lavas, and hence much higher melting rates. This effect of reduced pressure at vents will be less pronounced in a large ice sheet than in a smaller glacier or ice cap, since the hydraulic gradient that drives water away from an eruption site will be lower in the large glacier. This may have implications for form and type of eruption deposits and their relationship with ice thickness and glacier size.

Ice, Ice, Baby: A Program for Sustained, Classroom-Based K-8 Teacher Professional Development

Science.gov (United States)

Hamilton, C.

2009-12-01

Ice, Ice, Baby is a K-8 science program created by the education team at the Center for the Remote Sensing of Ice Sheets (CReSIS), an NSF-funded science and technology center headquartered at the University of Kansas. The twenty-four hands-on activities, which constitute the Ice, Ice, Baby curriculum, were developed to help students understand the role of polar ice sheets in sea level rise. These activities, presented in classrooms by CReSIS' Educational Outreach Coordinator, demonstrate many of the scientific properties of ice, including displacement and density. Student journals are utilized with each lesson as a strategy for improving students' science process skills. Journals also help the instructor identify misconceptions, assess comprehension, and provide students with a year-long science reference log. Pre- and post- assessments are given to both teachers and students before and after the program, providing data for evaluation and improvement of the Ice, Ice, Baby program. While students are actively engaged in hands-on learning about the unusual topics of ice sheets, glaciers, icebergs and sea ice, the CReSIS' Educational Coordinator is able to model best practices in science education, such as questioning and inquiry-based methods of instruction. In this way, the Ice, Ice, Baby program also serves as ongoing, in-class, professional development for teachers. Teachers are also provided supplemental activities to do with their classes between CReSIS' visits to encourage additional science lessons, reinforce concepts taught in the Ice, Ice, Baby program, and to foster teachers' progression toward more reform-based science instruction.

Ice-Shelf Flexure and Tidal Forcing of Bindschadler Ice Stream, West Antarctica

Science.gov (United States)

Walker, Ryan T.; Parizek, Bryron R.; Alley, Richard B.; Brunt, Kelly M.; Anandakrishnan, Sridhar

2014-01-01

Viscoelastic models of ice-shelf flexure and ice-stream velocity perturbations are combined into a single efficient flowline model to study tidal forcing of grounded ice. The magnitude and timing of icestream response to tidally driven changes in hydrostatic pressure and/or basal drag are found to depend significantly on bed rheology, with only a perfectly plastic bed allowing instantaneous velocity response at the grounding line. The model can reasonably reproduce GPS observations near the grounding zone of Bindschadler Ice Stream (formerly Ice Stream D) on semidiurnal time scales; however, other forcings such as tidally driven ice-shelf slope transverse to the flowline and flexurally driven till deformation must also be considered if diurnal motion is to be matched

Simulation of an extended surface detector IceVeto for IceCube-Gen2