Peculiarities of Vibration Characteristics of Amorphous Ices

Science.gov (United States)

Gets, Kirill V.; Subbotin, Oleg S.; Belosludov, Vladimir R.

2012-03-01

Dynamic properties of low (LDA), high (HDA) and very high (VHDA) density amorphous ices were investigated within the approach based on Lattice Dynamics simulations. In this approach, we assume that the short-range molecular order mainly determines the dynamic and thermodynamic properties of amorphous ices. Simulation cell of 512 water molecules with periodical boundary conditions and disordering allows us to study dynamical properties and dispersion curves in the Brillouin zone of pseudo-crystal. Existence of collective phenomena in amorphous ices which is usual for crystals but anomalous for disordered phase was confirmed in our simulations. Molecule amplitudes of delocalized (collective) as well as localized vibrations have been considered.

Relaxation Time of High-Density Amorphous Ice

Science.gov (United States)

Handle, Philip H.; Seidl, Markus; Loerting, Thomas

2012-06-01

Amorphous water plays a fundamental role in astrophysics, cryoelectron microscopy, hydration of matter, and our understanding of anomalous liquid water properties. Yet, the characteristics of the relaxation processes taking place in high-density amorphous ice (HDA) are unknown. We here reveal that the relaxation processes in HDA at 110-135 K at 0.1-0.2 GPa are of collective and global nature, resembling the alpha relaxation in glassy material. Measured relaxation times suggest liquid-like relaxation characteristics in the vicinity of the crystallization temperature at 145 K. By carefully relaxing pressurized HDA for several hours at 135 K, we produce a state that is closer to the ideal glass state than all HDA states discussed so far in literature.

Dynamics anomaly in high-density amorphous ice between 0.7 and 1.1 GPa

Science.gov (United States)

Handle, Philip H.; Loerting, Thomas

2016-02-01

We studied high-density amorphous ices between 0.004 and 1.6 GPa by isobaric in situ volumetry and by subsequent ex situ x-ray diffraction and differential scanning calorimetry at 1 bar. Our observations indicate two processes, namely, relaxation in the amorphous matrix and crystallization, taking place at well-separated time scales. For this reason, we are able to report rate constants of crystallization kX and glass-transition temperatures Tg in an unprecedented pressure range. Tg's agree within ±3 K with earlier work in the small pressure range where there is overlap. Both Tg and kX show a pressure anomaly between 0.7 and 1.1 GPa, namely, a kX minimum and a Tg maximum. This anomalous pressure dependence suggests a continuous phase transition from high- (HDA) to very-high-density amorphous ice (VHDA) and faster hydrogen bond dynamics in VHDA. We speculate this phenomenology can be rationalized by invoking the crossing of a Widom line between 0.7 and 1.1 GPa emanating from a low-lying HDA-VHDA critical point. Furthermore, we interpret the volumetric relaxation of the amorphous matrix to be accompanied by viscosity change to explain the findings such that the liquid state can be accessed prior to the crystallization temperature TX at 0.8 GPa.

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

Vibrational spectra and boson-like excitations in different amorphous forms of ice

International Nuclear Information System (INIS)

Kolesnikov, A.I.; Li, J.C.; Uffindell, C.H.

1999-01-01

Complete text of publication follows. Glasses are very interesting objects in the physics of condensed matter, with many universal properties, such as low-energy excitations (LEE) coexisting with the sound waves and giving an excess of vibrational modes with respect to the crystalline spectrum (the so called 'boson' peak) in Raman and inelastic neutron scattering (INS). Recently it was discovered that films of hydrogenated amorphous silicon do not show such LEE, whereas films of amorphous silicon do [1]. Also, the resonant absorption by two-level systems was observed for the high-density amorphous (hda) ice but not for the low-density amorphous (lda) ice in the far infrared spectra [2]. Thus, the nature of these near universal LEE becomes rather puzzling. This report presents the results of INS studies for hda and lda ice produced by high-pressure treatment and for vapor-deposited lda ice. Clear LEE were observed in the spectra for hda and deposited lda ice unlike their crystalline analogues. (author)

Short, intermediate and long range order in amorphous ices

Science.gov (United States)

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

Water exhibits polyamorphism, i.e., it exists in more than one amorphous state. The most common forms of glassy water are the low-density amorphous (LDA) and the high-density amorphous (HDA) ices. LDA, the most abundant form of ice in the Universe, transforms into HDA upon isothermal compression. We model the transformation of LDA into HDA under isothermal compression with classical molecular dynamics simulations. We analyze the molecular structures with a recently introduced scalar order metric to measure short and intermediate range order. In addition, we rank the structures by their degree of hyperuniformity, i.e.,the extent to which long range density fluctuations are suppressed. F.M. and R.C. acknowledge support from the Department of Energy (DOE) under Grant No. DE-SC0008626.

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

Structure of high-density amorphous ice under pressure

International Nuclear Information System (INIS)

Klotz, S.; Hamel, G.; Loveday, J.S.; Nelmes, R.J.; Guthrie, M.; Soper, A.K.

2002-01-01

We report in situ neutron diffraction studies of high-density amorphous ice (HDA) at 100 K at pressures up to 2.2 GPa. We find that the compression is achieved by a strong contraction (∼20%) of the second neighbor coordination shell, so that at 2.2 GPa it closely approaches the first coordination shell, which itself remains intact in both structure and size. The hydrogen bond orientations suggest an absence of hydrogen bonding between first and second shells and that HDA has increasingly interpenetrating hydrogen bond networks under pressure

Experimental study of the polyamorphism of water. I. The isobaric transitions from amorphous ices to LDA at 4 MPa

Science.gov (United States)

Handle, Philip H.; Loerting, Thomas

2018-03-01

The existence of more than one solid amorphous state of water is an extraordinary feature. Since polyamorphism might be connected to the liquid-liquid critical point hypothesis, it is particularly important to study the relations amongst the different amorphous ices. Here we study the polyamorphic transformations of several high pressure amorphous ices to low-density amorphous ice (LDA) at 4 MPa by isobaric heating utilising in situ volumetry and ex situ X-ray diffraction. We find that very-high density amorphous ice (VHDA) and unannealed high density amorphous ice (HDA) show significant relaxation before transforming to LDA, whereby VHDA is seen to relax toward HDA. By contrast, expanded HDA shows almost no relaxation prior to the transformation. The transition to LDA itself obeys criteria for a first-order-like transition in all cases. In the case of VHDA, even macroscopic phase separation is observed. These findings suggest that HDA and LDA are two clearly distinct polyamorphs. We further present evidence that HDA reaches the metastable equilibrium at 140 K and 0.1 GPa but only comes close to that at 140 K and 0.2 GPa. The most important is the path independence of the amorphous phase reached at 140 K and 0.1 GPa.

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.

Reversible pressure-induced crystal-amorphous structural transformation in ice Ih

Science.gov (United States)

English, Niall J.; Tse, John S.

2014-08-01

Molecular dynamics (MD) simulation of depressurised high-density amorphous ice (HDA) at 80 K and at negative pressures has been performed. Over several attempts, HDA recrystallised to a form close to hexagonal ice Ih, albeit with some defects. The results support the hypothesis that compression of ice-Ih to HDA is a reversible first-order phase transition, with a large hysteresis. Therefore, it would appear that LDA is not truly amorphous. The elastic energy estimated from the area of the hysteresis loop is ca. 4.5 kJ/mol, in some way consistent with experimentally-determined accumulated successive heats of transformations from recovered HDA → ice Ih.

Kinetics of the high- to low-density amorphous water transition

International Nuclear Information System (INIS)

Koza, M M; Schober, H; Fischer, H E; Hansen, T; Fujara, F

2003-01-01

In situ neutron diffraction experiments have been carried out to study the kinetics of the transformation of high-density amorphous (HDA) water into its low-density amorphous state at temperatures 87 K ≤ T ≤ 110 K. It is found that three different stages are comprised in this transformation, namely an annealing process of the high-density matrix followed by a first-order-like transition into a low-density state, which can be further annealed at higher temperatures T ≤ 127 K. The annealing kinetics of the HDA state follows the logarithm of time as found in other systems showing polyamorphism. According to the theory of transformation by nucleation and growth the apparent first-order transition follows an Avrami-Kolmogorov behaviour. An energy barrier ΔE ∼ 33 k Jmol -1 is estimated from the temperature dependence of this transition

Meltwater storage in low-density near-surface bare ice in the Greenland ice sheet ablation zone

Science.gov (United States)

Cooper, Matthew G.; Smith, Laurence C.; Rennermalm, Asa K.; Miège, Clément; Pitcher, Lincoln H.; Ryan, Jonathan C.; Yang, Kang; Cooley, Sarah W.

2018-03-01

We document the density and hydrologic properties of bare, ablating ice in a mid-elevation (1215 m a.s.l.) supraglacial internally drained catchment in the Kangerlussuaq sector of the western Greenland ice sheet. We find low-density (0.43-0.91 g cm-3, μ = 0.69 g cm-3) ice to at least 1.1 m depth below the ice sheet surface. This near-surface, low-density ice consists of alternating layers of water-saturated, porous ice and clear solid ice lenses, overlain by a thin (sheet ablation zone surface. A conservative estimate for the ˜ 63 km2 supraglacial catchment yields 0.009-0.012 km3 of liquid meltwater storage in near-surface, porous ice. Further work is required to determine if these findings are representative of broader areas of the Greenland ice sheet ablation zone, and to assess the implications for sub-seasonal mass balance processes, surface lowering observations from airborne and satellite altimetry, and supraglacial runoff processes.

On the nature of amorphous polymorphism of water

OpenAIRE

Koza, Michael Marek; Geil, Burkhard; Winkel, Katrin; Koehler, Christian; Czeschka, Franz; Scheuermann, Marco; Schober, Helmut; Hansen, Thomas

2005-01-01

We report elastic and inelastic neutron scattering experiments on different amorphous ice modifications. It is shown that an amorphous structure (HDA') indiscernible from the high-density phase (HDA), obtained by compression of crystalline ice, can be formed from the very high-density phase (vHDA) as an intermediate stage of the transition of vHDA into its low-density modification (LDA'). Both, HDA and HDA' exhibit comparable small angle scattering signals characterizing them as structures he...

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)

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.

Investigation of the intermediate- and high-density forms of amorphous ice by molecular dynamics calculations and diffraction experiments

International Nuclear Information System (INIS)

Tse, John S.; Klug, Dennis D.; Guthrie, Malcolm; Benmore, Chris J.; Urquidi, Jacob; Tulk, Chris A.

2005-01-01

The lack of an 'isosbestic' point in the oxygen-oxygen atom radial distribution functions (RDFs) for the HDA→LDA ice transformation at ambient pressure derived from molecular dynamics (MD) calculations show unequivocally that intermediate phases are not equilibrium mixtures of these two amorphous forms. This is supported by x-ray structure factor data, where it is found that linear combinations of the starting and end amorphous forms do not describe intermediate forms of amorphous ice formed during the transformation. This reflects the fact that the x-ray data are heavily weighted to O-O correlations and therefore sensitive to the basic structural changes that occur during the relaxation process. The ice Ih→HDA transformation is also reexamined using MD to identify its thermodynamic nature. This apparently first-order transition induced by a mechanical instability is investigated by compression followed by decompression to negative pressures. In this study we demonstrated that the full van der Waals loop for this transition can be identified

Ice Ih anomalies: Thermal contraction, anomalous volume isotope effect, and pressure-induced amorphization

Science.gov (United States)

Salim, Michael A.; Willow, Soohaeng Yoo; Hirata, So

2016-05-01

Ice Ih displays several anomalous thermodynamic properties such as thermal contraction at low temperatures, an anomalous volume isotope effect (VIE) rendering the volume of D2O ice greater than that of H2O ice, and a pressure-induced transition to the high-density amorphous (HDA) phase. Furthermore, the anomalous VIE increases with temperature, despite its quantum-mechanical origin. Here, embedded-fragment ab initio second-order many-body perturbation (MP2) theory in the quasiharmonic approximation (QHA) is applied to the Gibbs energy of an infinite, proton-disordered crystal of ice Ih at wide ranges of temperatures and pressures. The quantum effect of nuclei moving in anharmonic potentials is taken into account from first principles without any empirical or nonsystematic approximation to either the electronic or vibrational Hamiltonian. MP2 predicts quantitatively correctly the thermal contraction at low temperatures, which is confirmed to originate from the volume-contracting hydrogen-bond bending modes (acoustic phonons). It qualitatively reproduces (but underestimates) the thermal expansion at higher temperatures, caused by the volume-expanding hydrogen-bond stretching (and to a lesser extent librational) modes. The anomalous VIE is found to be the result of subtle cancellations among closely competing isotope effects on volume from all modes. Consequently, even ab initio MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets has difficulty reproducing this anomaly, yielding qualitatively varied predictions of the sign of the VIE depending on such computational details as the choice of the embedding field. However, the temperature growth of the anomalous VIE is reproduced robustly and is ascribed to the librational modes. These solid-state MP2 calculations, as well as MP2 Born-Oppenheimer molecular dynamics, find a volume collapse and a loss of symmetry and long-range order in ice Ih upon pressure loading of 2.35 GPa or higher. Concomitantly, rapid softening of

Ice Ih anomalies: Thermal contraction, anomalous volume isotope effect, and pressure-induced amorphization

Energy Technology Data Exchange (ETDEWEB)

Salim, Michael A.; Willow, Soohaeng Yoo; Hirata, So, E-mail: sohirata@illinois.edu [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801 (United States)

2016-05-28

Ice Ih displays several anomalous thermodynamic properties such as thermal contraction at low temperatures, an anomalous volume isotope effect (VIE) rendering the volume of D{sub 2}O ice greater than that of H{sub 2}O ice, and a pressure-induced transition to the high-density amorphous (HDA) phase. Furthermore, the anomalous VIE increases with temperature, despite its quantum-mechanical origin. Here, embedded-fragment ab initio second-order many-body perturbation (MP2) theory in the quasiharmonic approximation (QHA) is applied to the Gibbs energy of an infinite, proton-disordered crystal of ice Ih at wide ranges of temperatures and pressures. The quantum effect of nuclei moving in anharmonic potentials is taken into account from first principles without any empirical or nonsystematic approximation to either the electronic or vibrational Hamiltonian. MP2 predicts quantitatively correctly the thermal contraction at low temperatures, which is confirmed to originate from the volume-contracting hydrogen-bond bending modes (acoustic phonons). It qualitatively reproduces (but underestimates) the thermal expansion at higher temperatures, caused by the volume-expanding hydrogen-bond stretching (and to a lesser extent librational) modes. The anomalous VIE is found to be the result of subtle cancellations among closely competing isotope effects on volume from all modes. Consequently, even ab initio MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets has difficulty reproducing this anomaly, yielding qualitatively varied predictions of the sign of the VIE depending on such computational details as the choice of the embedding field. However, the temperature growth of the anomalous VIE is reproduced robustly and is ascribed to the librational modes. These solid-state MP2 calculations, as well as MP2 Born–Oppenheimer molecular dynamics, find a volume collapse and a loss of symmetry and long-range order in ice Ih upon pressure loading of 2.35 GPa or higher. Concomitantly, rapid

Amorphous ices explained in terms of nonequilibrium phase transitions in supercooled water

Science.gov (United States)

Limmer, David; Chandler, David

2013-03-01

We analyze the phase diagram of supercooled water out-of-equilibrium using concepts from space-time thermodynamics and the dynamic facilitation theory of the glass transition, together with molecular dynamics simulations. We find that when water is driven out-of-equilibrium, it can exist in multiple amorphous states. In contrast, we find that when water is at equilibrium, it can exist in only one liquid state. The amorphous non-equilibrium states are solids, distinguished from the liquid by their lack of mobility, and distinguished from each other by their different densities and local structure. This finding explains the experimentally observed polyamorphism of water as a class of nonequilibrium phenomena involving glasses of different densities. While the amorphous solids can be long lived, they are thermodynamically unstable. When allowed to relax to equilibrium, they crystallize with pathways that pass first through liquid state configurations and then to ordered ice.

Amorphous ice. A microporous solid: astrophysical implications

International Nuclear Information System (INIS)

Mayer, E.; Pletzer, R.

1987-01-01

Vapour deposited amorphous ice, investigated by N 2 -adsorption at 77 K, was found to be a microporous solid. Micropore volumes between 0.21 and 0.12 cm 3 /g were determined by comparison plots and Dubinin-Radushkevich plots. Warming of the adsorbent to 113 K caused sintering and reduction of apparent surface area by about an order of magnitude; in the presence of adsorbed gas, large amounts of gas were enclosed in the solid. The influence of micropores on the H 2 recombination rate on amorphous ice in interstellar dust and on adsorption of volatile gases in comets is discussed briefly

Formation of ice XII at low temperatures and high pressures

International Nuclear Information System (INIS)

Schober, H.; Koza, M.; Toelle, A.; Fujara, F.

1999-01-01

Complete text of publication follows. Solid water features a large variety of crystalline as well as two amorphous phases. The versatility of water's behavior has been reinforced recently by the identification of still another form of crystalline ice [1]. Ice XII was obtained by cooling liquid water to 260 K at a pressure of 5.5 kbar. Ice XII could be produced in a completely different region of water's phase diagram [2]. Using a. piston-cylinder apparatus ice XII was formed during the production of high-density amorphous ice (HDA) at 77 K as described previously [3]. The amount of crystalline ice XII contamination within the HDA sample varies in a so far unpredictable way with both extremes, i.e. pure HDA as well as pure ice XII. realized. Our results indicate that water's phase diagram needs modification in the region assigned to HDA. Ice XII is characterized as well as its transition towards cubic ice by elastic and inelastic neutron scattering. (author)

Heating- and pressure-induced transformations in amorphous and hexagonal ice: A computer simulation study using the TIP4P/2005 model

Science.gov (United States)

Engstler, Justin; Giovambattista, Nicolas

2017-08-01

We characterize the phase behavior of glassy water by performing extensive out-of-equilibrium molecular dynamics simulations using the TIP4P/2005 water model. Specifically, we study (i) the pressure-induced transformations between low-density (LDA) and high-density amorphous ice (HDA), (ii) the pressure-induced amorphization (PIA) of hexagonal ice (Ih), (iii) the heating-induced LDA-to-HDA transformation at high pressures, (iv) the heating-induced HDA-to-LDA transformation at low and negative pressures, (v) the glass transition temperatures of LDA and HDA as a function of pressure, and (vi) the limit of stability of LDA upon isobaric heating and isothermal decompression (at negative pressures). These transformations are studied systematically, over a wide range of temperatures and pressures, allowing us to construct a P-T phase diagram for glassy TIP4P/2005 water. Our results are in qualitative agreement with experimental observations and with the P-T phase diagram obtained for glassy ST2 water that exhibits a liquid-liquid phase transition and critical point. We also discuss the mechanism for PIA of ice Ih and show that this is a two-step process where first, the hydrogen-bond network (HBN) is distorted and then the HBN abruptly collapses. Remarkably, the collapse of the HB in ice Ih occurs when the average molecular orientations order, a measure of the tetrahedrality of the HBN, is of the same order as in LDA, suggesting a common mechanism for the LDA-to-HDA and Ih-to-HDA transformations.

Visible and ultraviolet emission from pulse irradiated amorphous and polycrystalline H2O ice

International Nuclear Information System (INIS)

Freeman, C.G.; Quickenden, T.I.; Litjens, R.A.J.; Sangster, D.F.

1984-01-01

Luminescence peaking at 405 nm was observed when thin films of amorphous or polycrystalline ice at 97 K were irradiated with a pulsed beam of 0.53 MeV electrons. These emissions differed from the luminescence emitted by crystalline ice in that memory effects were not observed; the peak wavelengths were red shifted by approx.20 nm; and the half-lives were 6--9 ns instead of approx.400 ns. The emission spectra of polycrystalline ice samples produced by rapid deposition or by annealing amorphous ice were similar, but both had substantially lower intensities than amorphous ice spectra

Nature of amorphous polymorphism of water

International Nuclear Information System (INIS)

Koza, M.M.; Schober, H.; Hansen, T.; Geil, B.; Winkel, K.; Koehler, C.; Scheuermann, M.; Czeschka, F.

2005-01-01

We report elastic and inelastic neutron scattering experiments on different amorphous ice modifications. It is shown that an amorphous structure (HDA ' ) indiscernible from the high-density phase (HDA), obtained by compression of crystalline ice, can be formed from the very high-density phase (vHDA) as an intermediate stage of the transition of vHDA into its low-density modification (LDA ' ). Both HDA and HDA ' exhibit comparable small-angle scattering signals characterizing them as structures heterogeneous on a length scale of a few nanometers. The homogeneous structures are the initial and final transition stages vHDA and LDA ' , respectively. Despite their apparent structural identity on a local scale, HDA and HDA ' differ in their transition kinetics explored by in situ experiments. The activation energy of the vHDA-to-LDA ' transition is at least 20 kJ/mol higher than the activation energy of the HDA-to-LDA transition

Polyamorphism in tetrahedral substances: Similarities between silicon and ice

Science.gov (United States)

Garcez, K. M. S.; Antonelli, A.

2015-07-01

Tetrahedral substances, such as silicon, water, germanium, and silica, share various unusual phase behaviors. Among them, the so-called polyamorphism, i.e., the existence of more than one amorphous form, has been intensively investigated in the last three decades. In this work, we study the metastable relations between amorphous states of silicon in a wide range of pressures, using Monte Carlo simulations. Our results indicate that the two amorphous forms of silicon at high pressures, the high density amorphous (HDA) and the very high density amorphous (VHDA), can be decompressed from high pressure (˜20 GPa) down to the tensile regime, where both convert into the same low density amorphous. Such behavior is also observed in ice. While at high pressure (˜20 GPa), HDA is less stable than VHDA, at the pressure of 10 GPa both forms exhibit similar stability. On the other hand, at much lower pressure (˜5 GPa), HDA and VHDA are no longer the most stable forms, and, upon isobaric annealing, an even less dense form of amorphous silicon emerges, the expanded high density amorphous, again in close similarity to what occurs in ice.

THE EFFECT OF DIAMETER ON THE MECHANICAL-PROPERTIES OF AMORPHOUS-CARBON FIBERS FROM LINEAR LOW-DENSITY POLYETHYLENE

NARCIS (Netherlands)

PENNING, JP; LAGCHER, R; PENNINGS, AJ

The mechanical properties of amorphous carbon fibers, derived from linear low density polyethylene strongly depend on the fibre diameter, which may be attributed to the presence of a skin/core structure in these fibres. High strength carbon fibres could thus be prepared by using thin precursor

Electron transfer from electronic excited states to sub-vacuum electron traps in amorphous ice

International Nuclear Information System (INIS)

Vichnevetski, E.; Bass, A.D.; Sanche, L.

2000-01-01

We investigate the electron stimulated yield of electronically excited argon atoms (Ar * ) from monolayer quantities of Ar deposited onto thin films of amorphous ice. Two peaks of narrow width ( - electron-exciton complex into exciton states, by the transfer of an electron into a sub-vacuum electron state within the ice film. However, the 10.7 eV feature is shifted to lower energy since electron attachment to Ar occurs within small pores of amorphous ice. In this case, the excess electron is transferred into an electron trap below the conduction band of the ice layer

FIRST INFRARED BAND STRENGTHS FOR AMORPHOUS CO{sub 2}, AN OVERLOOKED COMPONENT OF INTERSTELLAR ICES

Energy Technology Data Exchange (ETDEWEB)

Gerakines, Perry A.; Hudson, Reggie L., E-mail: Reggie.Hudson@NASA.gov [Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2015-08-01

Solid carbon dioxide (CO{sub 2}) has long been recognized as a component of both interstellar and solar system ices, but a recent literature search has revealed significant qualitative and quantitative discrepancies in the laboratory spectra on which the abundances of extraterrestrial CO{sub 2} are based. Here we report new infrared (IR) spectra of amorphous CO{sub 2}-ice along with band intensities (band strengths) of four mid-IR absorptions, the first such results in the literature. A possible thickness dependence for amorphous-CO{sub 2} IR band shapes and positions also is investigated, and the three discordant reports of amorphous CO{sub 2} spectra in the literature are addressed. Applications of our results are discussed with an emphasis on laboratory investigations and results from astronomical observations. A careful comparison with earlier work shows that the IR spectra calculated from several databases for CO{sub 2} ices, all ices being made near 10 K, are not for amorphous CO{sub 2}, but rather for crystalline CO{sub 2} or crystalline-amorphous mixtures.

On Positronium Formation in Crystalline and Amorphous Ice at Low Positron Energy

DEFF Research Database (Denmark)

Mogensen, O. E.

1986-01-01

The positronium (Ps) yield for ice, measured by Eldrup et al. using a low-energy positron beam, is discussed in terms of the spur model of Ps formation. The pronounced maxima in the Ps yield for crystalline ice at positron energies below 65 eV are well explained by effects due to energy conservat......The positronium (Ps) yield for ice, measured by Eldrup et al. using a low-energy positron beam, is discussed in terms of the spur model of Ps formation. The pronounced maxima in the Ps yield for crystalline ice at positron energies below 65 eV are well explained by effects due to energy...

Pressure-induced transformations in amorphous silicon: A computational study

Energy Technology Data Exchange (ETDEWEB)

Garcez, K. M. S., E-mail: kmgarcez@ufma.br [Universidade Federal do Maranhão, 65700-000 Bacabal, Maranhão (Brazil); Antonelli, A., E-mail: aantone@ifi.unicamp.br [Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, UNICAMP, 13083-859 Campinas, São Paulo (Brazil)

2014-02-14

We study the transformations between amorphous phases of Si through molecular simulations using the environment dependent interatomic potential (EDIP) for Si. Our results show that upon pressure, the material undergoes a transformation from the low density amorphous (LDA) Si to the high density amorphous (HDA) Si. This transformation can be reversed by decompressing the material. This process, however, exhibits clear hysteresis, suggesting that the transformation LDA ↔ HDA is first-order like. The HDA phase is predominantly five-fold coordinated, whereas the LDA phase is the normal tetrahedrally bonded amorphous Si. The HDA phase at 400 K and 20 GPa was submitted to an isobaric annealing up to 800 K, resulting in a denser amorphous phase, which is structurally distinct from the HDA phase. Our results also show that the atomic volume and structure of this new amorphous phase are identical to those of the glass obtained by an isobaric quenching of the liquid in equilibrium at 2000 K and 20 GPa down to 400 K. The similarities between our results and those for amorphous ices suggest that this new phase is the very high density amorphous Si.

Pressure-induced transformations in amorphous silicon: A computational study

Science.gov (United States)

Garcez, K. M. S.; Antonelli, A.

2014-02-01

We study the transformations between amorphous phases of Si through molecular simulations using the environment dependent interatomic potential (EDIP) for Si. Our results show that upon pressure, the material undergoes a transformation from the low density amorphous (LDA) Si to the high density amorphous (HDA) Si. This transformation can be reversed by decompressing the material. This process, however, exhibits clear hysteresis, suggesting that the transformation LDA ↔ HDA is first-order like. The HDA phase is predominantly five-fold coordinated, whereas the LDA phase is the normal tetrahedrally bonded amorphous Si. The HDA phase at 400 K and 20 GPa was submitted to an isobaric annealing up to 800 K, resulting in a denser amorphous phase, which is structurally distinct from the HDA phase. Our results also show that the atomic volume and structure of this new amorphous phase are identical to those of the glass obtained by an isobaric quenching of the liquid in equilibrium at 2000 K and 20 GPa down to 400 K. The similarities between our results and those for amorphous ices suggest that this new phase is the very high density amorphous Si.

Density changes in amorphous Pd80Si20 during low temperature ion irradiation

International Nuclear Information System (INIS)

Schumacher, G.; Birtcher, R.C.; Rehn, L.E.

1994-11-01

Density changes in amorphous Pd 80 Si 20 during ion irradiation below 100K were detected by in situ HVEM measurements of the changes in specimen length as a function of ion fluence. A decrease in mass density as a function of the ion fluence was observed. The saturation value of the change in mass density was determined to be approximately -1.2%

Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy

Energy Technology Data Exchange (ETDEWEB)

McMullan, G., E-mail: gm2@mrc-lmb.cam.ac.uk; Vinothkumar, K.R.; Henderson, R.

2015-11-15

We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of ∼1.1 Å{sup 2} for every incident 300 keV e{sup −}/Å{sup 2}. The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e{sup −}/Å{sup 2} per image with which to observe Thon rings centred around the strong 3.7 Å scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination. - Highlights: • Thon rings can be seen from amorphous ice. • Radiation damage to amorphous ice randomly displaces water molecules. • Each incident 300 keV e{sup −}/Å{sup 2} displaces water molecules on average by ∼1 Å. • Macromolecules embedded in amorphous ice undergo beam induced Brownian motion.

Influence of isotopic disorder on solid state amorphization and polyamorphism in solid H2O -D2O solutions

Science.gov (United States)

Gromnitskaya, E. L.; Danilov, I. V.; Lyapin, A. G.; Brazhkin, V. V.

2015-10-01

We present a low-temperature and high-pressure ultrasonic study of elastic properties of isotopic H2O-D2O solid solutions, comparing their properties with those of the isotopically pure H2O and D2O ices. Measurements were carried out for solid state amorphization (SSA) from 1h to high-density amorphous (HDA) ice upon compression up to 1.8 GPa at 77 K and for the temperature-induced (77 -190 K ) u-HDA (unrelaxed HDA) → e-HDA (expanded HDA) → low-density amorphous (LDA )→1 c cascade of ice transformations near room pressure. There are many similarities in the elasticity behaviour of H2O ,D2O , and H2O-D2O solid solutions, including the softening of the shear elastic modulus as a precursor of SSA and the HDA →LDA transition. We have found significant isotopic effects during H/D substitution, including elastic softening of H2O -D2O solid solutions with respect to the isotopically pure ices in the case of the bulk moduli of ices 1c and 1h and for both bulk and shear elastic moduli of HDA ice at high pressures (>1 GPa ) . This softening is related to the configurational isotopic disorder in the solid solutions. At low pressures, the isotope concentration dependence of the elastic moduli of u-HDA ice changes remarkably and becomes monotonic with pronounced change of the bulk modulus (≈20 %) .

Identifying low and high density amorphous phases during zeolite amorphisation using small and wide angle X-ray scattering

International Nuclear Information System (INIS)

Meneau, F.; Greaves, G.N.

2005-01-01

In situ experiments following the thermal amorphisation of zeolites reveal massive increases in small angle X-ray scattering (SAXS), persisting well beyond the stage where wide angle X-ray scattering (WAXS) can detect that any crystalline phase is present. This heterogeneity in the amorphised phase is attributed to the transition from a low density amorphous phase (LDA) to a high density amorphous phase (HDA) at the glass transition. The fractions of zeolite, LDA and HDA phases obtained from SAXS analysis are discussed in the context of non-linear changes detected in 29 Si solid state NMR during zeolite amorphisation. Whilst the HDA phase is chemically disordered, the LDA phase exhibits much of the Al-Si ordering present in the starting zeolite. These findings are considered in the context of perfect glasses predicted to occur when super strong liquids are supercooled

Experimental Evidence of Low Density Liquid Water under Decompression

Science.gov (United States)

Shen, G.; Lin, C.; Sinogeikin, S. V.; Smith, J.

2017-12-01

Water is not only the most important substance for life, but also plays important roles in liquid science for its anomalous properties. It has been widely accepted that water's anomalies are not a result of simple thermal fluctuation, but are connected to the formation of various structural aggregates in the hydrogen bonding network. Among several proposed scenarios, one model of fluctuations between two different liquids has gradually gained traction. These two liquids are referred to as a low-density liquid (LDL) and a high-density liquid (HDL) with a coexistence line in the deeply supercooled regime at elevated pressure. The LDL-HDL transition ends with decreasing pressure at a liquid-liquid critical point (LLCP) with its Widom line extending to low pressures. Above the Widom line lies mostly HDL which is favored by entropy, while LDL, mostly lying below the Widom line, is favored by enthalpy in the tetrahedral hydrogen bonding network. The origin of water's anomalies can then be explained by the increase in structural fluctuations, as water is cooled down to deeply supercooled temperatures approaching the Widom line. Because both the LLCP and the LDL-HDL transition line lie in water's "no man's land" between the homogeneous nucleation temperature (TH, 232 K) and the crystallization temperature (TX, 150 K), the success of experiments exploring this region has been limited thus far. Using a rapid decompression technique integrated with in situ x-ray diffraction, we observe that a high-pressure ice phase transforms to a low-density noncrystalline (LDN) form upon rapid release of pressure at temperatures of 140-165K. The LDN subsequently crystallizes into ice-Ic through a diffusion-controlled process. The change in crystallization rate with temperature indicates that the LDN is a LDL with its tetrahedrally-coordinated network fully developed and clearly linked to low-density amorphous ices. The observation of the tetrahedral LDL supports the two-liquid model for

Amorphous Dielectric Thin Films with Extremely Low Mechanical Loss

Directory of Open Access Journals (Sweden)

Liu X.

2015-04-01

Full Text Available The ubiquitous low-energy excitations are one of the universal phenomena of amorphous solids. These excitations dominate the acoustic, dielectric, and thermal properties of structurally disordered solids. One exception has been a type of hydrogenated amorphous silicon (a-Si:H with 1 at.% H. Using low temperature elastic and thermal measurements of electron-beam evap-orated amorphous silicon (a-Si, we show that TLS can be eliminated in this system as the films become denser and more structurally ordered under certain deposition conditions. Our results demonstrate that TLS are not intrinsic to the glassy state but instead reside in low density regions of the amorphous network. This work obviates the role hydrogen was previously thought to play in removing TLS in a-Si:H and favors an ideal four-fold covalently bonded amorphous structure as the cause for the disappearance of TLS. Our result supports the notion that a-Si can be made a “perfect glass” with “crystal-like” properties, thus offering an encouraging opportunity to use it as a simple crystal dielectric alternative in applications, such as in modern quantum devices where TLS are the source of dissipation, decoherence and 1/f noise.

Kinetic boundaries and phase transformations of ice i at high pressure

Science.gov (United States)

Wang, Yu; Zhang, Huichao; Yang, Xue; Jiang, Shuqing; Goncharov, Alexander F.

2018-01-01

Raman spectroscopy in diamond anvil cells has been employed to study phase boundaries and transformation kinetics of H2O ice at high pressures up to 16 GPa and temperatures down to 15 K. Ice i formed at nearly isobaric cooling of liquid water transforms on compression to high-density amorphous (HDA) ice at 1.1-3 GPa at 15-100 K and then crystallizes in ice vii with the frozen-in disorder (ice vii') which remains stable up to 14.1 GPa at 80 K and 15.9 GPa at 100 K. Unexpectedly, on decompression of ice vii', it transforms to ice viii in its domain of metastability, and then it relaxes into low-density amorphous (LDA) ice on a subsequent pressure release and warming up. On compression of ice i at 150-170 K, ice ix is crystallized and no HDA ice is found; further compression of ice ix results in the sequential phase transitions to stable ices vi and viii. Cooling ice i to 210 K at 0.3 GPa transforms it to a stable ice ii. Our extensive investigations provide previously missing information on the phase diagram of water, especially on the kinetic paths that result in formation of phases which otherwise are not accessible; these results are keys for understanding the phase relations including the formation of metastable phases. Our observations inform on the ice modifications that can occur naturally in planetary environments and are not accessible for direct observations.

Low-temperature crystallization of amorphous silicon and amorphous germanium by soft X-ray irradiation

Energy Technology Data Exchange (ETDEWEB)

Heya, Akira, E-mail: heya@eng.u-hyogo.ac.jp [Department of Materials Science and Chemistry, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671–2280 (Japan); Kanda, Kazuhiro [Laboratory of Advanced Science and Technology for Industry (LASTI), University of Hyogo, 3-2-1 Koto, Kamigori, Hyogo 678–1205 (Japan); Toko, Kaoru; Sadoh, Taizoh [Department of Electronics, Kyushu University, 744 Nishi-ku, Motooka, Fukuoka 819–0395 (Japan); Amano, Sho [Laboratory of Advanced Science and Technology for Industry (LASTI), University of Hyogo, 3-2-1 Koto, Kamigori, Hyogo 678–1205 (Japan); Matsuo, Naoto [Department of Materials Science and Chemistry, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671–2280 (Japan); Miyamoto, Shuji [Laboratory of Advanced Science and Technology for Industry (LASTI), University of Hyogo, 3-2-1 Koto, Kamigori, Hyogo 678–1205 (Japan); Miyao, Masanobu [Department of Electronics, Kyushu University, 744 Nishi-ku, Motooka, Fukuoka 819–0395 (Japan); Mochizuki, Takayasu [Laboratory of Advanced Science and Technology for Industry (LASTI), University of Hyogo, 3-2-1 Koto, Kamigori, Hyogo 678–1205 (Japan)

2013-05-01

The low-temperature-crystallization effects of soft X-ray irradiation on the structural properties of amorphous Si and amorphous Ge films were investigated. From the differences in crystallization between Si and Ge, it was found that the effects of soft X-ray irradiation on the crystallization strongly depended on the energy band gap and energy level. The crystallization temperatures of the amorphous Si and amorphous Ge films decreased from 953 K to 853 K and 773 K to 663 K, respectively. The decrease in crystallization temperature was also related to atoms transitioning into a quasi-nucleic phase in the films. The ratio of electron excitation and migration effects to thermal effects was controlled using the storage-ring current (photon flux density). Therefore, we believe that low-temperature crystallization can be realized by controlling atomic migration through electron excitation. - Highlights: • This work investigates the crystallization mechanism for soft X-ray irradiation. • The soft X-ray crystallization depended on the energy band gap and energy level. • The decrease in the crystallization temperature for Si and Ge films was 100 K. • This decrement was related to atoms transitioning into a quasi-nucleic phase.

Influence of pressure on the structural properties of liquid D{sub 2}O

Energy Technology Data Exchange (ETDEWEB)

Bellissent-Funel, M.C.

1994-12-31

Results about the structure of liquid water under pressure and using neutron diffraction are presented. The structural data are compared with that of low density amorphous ice (LDA) and of high density amorphous ice (HDA). The low density amorphous ice which is well accounted for a continuous random network model appears as the limit of deeply supercooled water while the high density amorphous ice which is a more disordered form of ice appears as the limit of water under high pressure and at high temperature. (author). 29 refs., 6 figs.

AN INFRARED SPECTROSCOPIC STUDY OF AMORPHOUS AND CRYSTALLINE ICES OF VINYLACETYLENE AND IMPLICATIONS FOR SATURN'S SATELLITE TITAN

International Nuclear Information System (INIS)

Kim, Y. S.; Kaiser, R. I.

2009-01-01

Laboratory infrared spectra of amorphous and crystalline vinylacetylene ices were recorded in the range of 7000-400 cm -1 . The spectra showed several amorphous features in the ice deposited at 10 K, which were then utilized to monitor a phase transition between 93 ± 1 K to form the crystalline structure. Successive heating allows monitoring of the sublimation profile of the vinylacetylene sample in the range of 101-120 K. Considering Titan's surface temperature of 94 K, vinylacetylene ice is likely to be crystalline. Analogous studies on related planetary-bound molecules such as triaceylene and cyanoacetylene may be further warranted to gain better perspectives into the composition of the condensed phases in the Titan's atmosphere (aerosol particles) and of Titan's surface. Based on our studies, we recommend utilizing the ν 1 and ν 16 //ν 11 /ν 17 fundamentals at about 3300 and 650 cm -1 to determine if solid vinylacetylene is crystalline or amorphous on Titan.

Thon rings from amorphous ice and implications of beam-induced Brownian motion in single particle electron cryo-microscopy.

Science.gov (United States)

McMullan, G; Vinothkumar, K R; Henderson, R

2015-11-01

We have recorded dose-fractionated electron cryo-microscope images of thin films of pure flash-frozen amorphous ice and pre-irradiated amorphous carbon on a Falcon II direct electron detector using 300 keV electrons. We observe Thon rings [1] in both the power spectrum of the summed frames and the sum of power spectra from the individual frames. The Thon rings from amorphous carbon images are always more visible in the power spectrum of the summed frames whereas those of amorphous ice are more visible in the sum of power spectra from the individual frames. This difference indicates that while pre-irradiated carbon behaves like a solid during the exposure, amorphous ice behaves like a fluid with the individual water molecules undergoing beam-induced motion. Using the measured variation in the power spectra amplitude with number of electrons per image we deduce that water molecules are randomly displaced by a mean squared distance of ∼1.1 Å(2) for every incident 300 keV e(-)/Å(2). The induced motion leads to an optimal exposure with 300 keV electrons of 4.0 e(-)/Å(2) per image with which to observe Thon rings centred around the strong 3.7 Å scattering peak from amorphous ice. The beam-induced movement of the water molecules generates pseudo-Brownian motion of embedded macromolecules. The resulting blurring of single particle images contributes an additional term, on top of that from radiation damage, to the minimum achievable B-factor for macromolecular structure determination. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Infrared Spectra and Band Strengths of Amorphous and Crystalline N2O

Science.gov (United States)

Hudson, R. L.; Loeffler, M. J.; Gerakines, P. A.

2017-01-01

Infrared transmission spectra from 4000 to 400 cm (exp -1), and associated band strengths and absorption coefficients, are presented for the first time for both amorphous and crystalline N2O. Changes in the spectra as a function of ice thickness and ice temperature are shown. New measurements of density, refractive index, and specific refraction are reported for amorphous and crystalline N2O. Comparisons are made to published results, and the most-likely reason for some recent disagreements in the literature is discussed. As with CO2, its isoelectronic congener, the formation of amorphous N2O is found to require greater care than the formation of amorphous solids from more-polar molecules.

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.

Search for the first-order liquid-to-liquid phase transition in low-temperature confined water by neutron scattering

Science.gov (United States)

Chen, Sow-Hsin; Wang, Zhe; Kolesnikov, Alexander I.; Zhang, Yang; Liu, Kao-Hsiang

2013-02-01

It has been conjectured that a 1st order liquid-to-liquid (L-L) phase transition (LLPT) between high density liquid (HDL) and low density liquid (LDL) in supercooled water may exist, as a thermodynamic extension to the liquid phase of the 1st order transition established between the two bulk solid phases of amorphous ice, the high density amorphous ice (HDA) and the low density amorphous ice (LDA). In this paper, we first recall our previous attempts to establish the existence of the 1st order L-L phase transition through the use of two neutron scattering techniques: a constant Q elastic diffraction study of isobaric temperature scan of the D2O density, namely, the equation of state (EOS) measurements. A pronounced density hysteresis phenomenon in the temperature scan of the density above P = 1500 bar is observed which gives a plausible evidence of crossing the 1st order L-L phase transition line above this pressure; an incoherent quasi-elastic scattering measurements of temperature-dependence of the α-relaxation time of H2O at a series of pressures, namely, the study of the Fragile-to-Strong dynamic crossover (FSC) phenomenon as a function of pressure which we interpreted as the results of crossing the Widom line in the one-phase region. In this new experiment, we used incoherent inelastic neutron scattering (INS) to measure the density of states (DOS) of H atoms in H2O molecules in confined water as function of temperature and pressure, through which we may be able to follow the emergence of the LDL and HDL phases at supercooled temperature and high pressures. We here report for the first time the differences of librational and translational DOSs between the hypothetical HDL and LDL phases, which are similar to the corresponding differences between the well-established HDA and LDA ices. This is plausible evidence that the HDL and LDL phases are the thermodynamic extensions of the corresponding amorphous solid water HDA and LDA ices.

Low-energy electron irradiation induced top-surface nanocrystallization of amorphous carbon film

Science.gov (United States)

Chen, Cheng; Fan, Xue; Diao, Dongfeng

2016-10-01

We report a low-energy electron irradiation method to nanocrystallize the top-surface of amorphous carbon film in electron cyclotron resonance plasma system. The nanostructure evolution of the carbon film as a function of electron irradiation density and time was examined by transmission electron microscope (TEM) and Raman spectroscopy. The results showed that the electron irradiation gave rise to the formation of sp2 nanocrystallites in the film top-surface within 4 nm thickness. The formation of sp2 nanocrystallite was ascribed to the inelastic electron scattering in the top-surface of carbon film. The frictional property of low-energy electron irradiated film was measured by a pin-on-disk tribometer. The sp2 nanocrystallized top-surface induced a lower friction coefficient than that of the original pure amorphous film. This method enables a convenient nanocrystallization of amorphous surface.

Adsorption Energies of Carbon, Nitrogen, and Oxygen Atoms on the Low-temperature Amorphous Water Ice: A Systematic Estimation from Quantum Chemistry Calculations

Science.gov (United States)

Shimonishi, Takashi; Nakatani, Naoki; Furuya, Kenji; Hama, Tetsuya

2018-03-01

We propose a new simple computational model to estimate the adsorption energies of atoms and molecules to low-temperature amorphous water ice, and we present the adsorption energies of carbon (3 P), nitrogen (4 S), and oxygen (3 P) atoms based on quantum chemistry calculations. The adsorption energies were estimated to be 14,100 ± 420 K for carbon, 400 ± 30 K for nitrogen, and 1440 ± 160 K for oxygen. The adsorption energy of oxygen is consistent with experimentally reported values. We found that the binding of a nitrogen atom is purely physisorption, while that of a carbon atom is chemisorption, in which a chemical bond to an O atom of a water molecule is formed. That of an oxygen atom has a dual character, with both physisorption and chemisorption. The chemisorption of atomic carbon also implies the possibility of further chemical reactions to produce molecules bearing a C–O bond, though this may hinder the formation of methane on water ice via sequential hydrogenation of carbon atoms. These properties would have a large impact on the chemical evolution of carbon species in interstellar environments. We also investigated the effects of newly calculated adsorption energies on the chemical compositions of cold dense molecular clouds with the aid of gas-ice astrochemical simulations. We found that abundances of major nitrogen-bearing molecules, such as N2 and NH3, are significantly altered by applying the calculated adsorption energy, because nitrogen atoms can thermally diffuse on surfaces, even at 10 K.

Density of states in Mo-Ru amorphous alloys

International Nuclear Information System (INIS)

Miyakawa, W.

1985-01-01

The density of states is calculated for several compositions of amorphous Mo 1-x Ru x . In order to simulate amorphous clusters, the structures (atomic positions) utilized in the calculations were built from a small dense randomly packed unit of hard spheres with periodic boundary conditions. The density of states is calculated from a tight-binding Hamiltonian with hopping integrals parametrized in terms of the ddσ, ddΠ and ddδ molecular integrals. The results for pure Mo and pure Ru, compared in the canonical band aproximation, agree well with the literature. For binary alloys, the comparison of the calculated density of states with the rigid band aproximation results indicates that a more complex approach than the rigid band model must be used, even when the two atoms have similar bands, with band centers at nearly the same energy. The results also indicate that there is no relation between the peak in the superconducting critical temperature as a function of the number of valence eletrons per atom (e/a) in the region near Mo(e/a=6) and the peak of the density of states at the Fermi level in the same region, as has been sugested by some authors. (Author) [pt

Structural, electronic, and vibrational properties of high-density amorphous silicon: a first-principles molecular-dynamics study.

Science.gov (United States)

Morishita, Tetsuya

2009-05-21

We report a first-principles study of the structural, electronic, and dynamical properties of high-density amorphous (HDA) silicon, which was found to be formed by pressurizing low-density amorphous (LDA) silicon (a normal amorphous Si) [T. Morishita, Phys. Rev. Lett. 93, 055503 (2004); P. F. McMillan, M. Wilson, D. Daisenberger, and D. Machon, Nature Mater. 4, 680 (2005)]. Striking structural differences between HDA and LDA are revealed. The LDA structure holds a tetrahedral network, while the HDA structure contains a highly distorted tetrahedral network. The fifth neighboring atom in HDA tends to be located at an interstitial position of a distorted tetrahedron composed of the first four neighboring atoms. Consequently, the coordination number of HDA is calculated to be approximately 5 unlike that of LDA. The electronic density of state (EDOS) shows that HDA is metallic, which is consistent with a recent experimental measurement of the electronic resistance of HDA Si. We find from local EDOS that highly distorted tetrahedral configurations enhance the metallic nature of HDA. The vibrational density of state (VDOS) also reflects the structural differences between HDA and LDA. Some of the characteristic vibrational modes of LDA are dematerialized in HDA, indicating the degradation of covalent bonds. The overall profile of the VDOS for HDA is found to be an intermediate between that for LDA and liquid Si under pressure (high-density liquid Si).

Thermal desorption of formamide and methylamine from graphite and amorphous water ice surfaces

Science.gov (United States)

Chaabouni, H.; Diana, S.; Nguyen, T.; Dulieu, F.

2018-04-01

Context. Formamide (NH2CHO) and methylamine (CH3NH2) are known to be the most abundant amine-containing molecules in many astrophysical environments. The presence of these molecules in the gas phase may result from thermal desorption of interstellar ices. Aims: The aim of this work is to determine the values of the desorption energies of formamide and methylamine from analogues of interstellar dust grain surfaces and to understand their interaction with water ice. Methods: Temperature programmed desorption (TPD) experiments of formamide and methylamine ices were performed in the sub-monolayer and monolayer regimes on graphite (HOPG) and non-porous amorphous solid water (np-ASW) ice surfaces at temperatures 40-240 K. The desorption energy distributions of these two molecules were calculated from TPD measurements using a set of independent Polanyi-Wigner equations. Results: The maximum of the desorption of formamide from both graphite and ASW ice surfaces occurs at 176 K after the desorption of H2O molecules, whereas the desorption profile of methylamine depends strongly on the substrate. Solid methylamine starts to desorb below 100 K from the graphite surface. Its desorption from the water ice surface occurs after 120 K and stops during the water ice sublimation around 150 K. It continues to desorb from the graphite surface at temperatures higher than160 K. Conclusions: More than 95% of solid NH2CHO diffuses through the np-ASW ice surface towards the graphitic substrate and is released into the gas phase with a desorption energy distribution Edes = 7460-9380 K, which is measured with the best-fit pre-exponential factor A = 1018 s-1. However, the desorption energy distribution of methylamine from the np-ASW ice surface (Edes = 3850-8420 K) is measured with the best-fit pre-exponential factor A = 1012 s-1. A fraction of solid methylamine monolayer of roughly 0.15 diffuses through the water ice surface towards the HOPG substrate. This small amount of methylamine

Constraining variable density of ice shelves using wide-angle radar measurements

Science.gov (United States)

Drews, Reinhard; Brown, Joel; Matsuoka, Kenichi; Witrant, Emmanuel; Philippe, Morgane; Hubbard, Bryn; Pattyn, Frank

2016-04-01

The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium, for which knowledge of the depth-averaged density is essential. The densification from snow to ice depends on a number of local factors (e.g., temperature and surface mass balance) causing spatial and temporal variations in density-depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar data sets (10 MHz) collected at five sites on Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, Antarctica. We reconstruct depth to internal reflectors, local ice thickness, and firn-air content using a novel algorithm that includes traveltime inversion and ray tracing with a prescribed shape of the depth-density relationship. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggest that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals that the firn inside the channel is 4.7 % denser than that outside the channel. Hydrostatic ice thickness calculations used for determining basal melt rates should account for the denser firn in ice-shelf channels. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

Effects of low-temperature (120 °C) annealing on the carrier concentration and trap density in amorphous indium gallium zinc oxide thin film transistors

Energy Technology Data Exchange (ETDEWEB)

Kim, Jae-sung; Piao, Mingxing; Jang, Ho-Kyun; Kim, Gyu-Tae, E-mail: gtkim@korea.ac.kr [School of Electrical Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Oh, Byung Su [School of Electrical Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Samsung Display Company, Yongin (Korea, Republic of); Joo, Min-Kyu [School of Electrical Engineering, Korea University, Seoul 136-701 (Korea, Republic of); IMEP-LAHC, Grenoble INP, Minatec, CS 50257, 38016 Grenoble (France); Ahn, Seung-Eon [School of Electrical Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Samsung Advanced Institute of Technology, Samsung Electronics Corporations, Yongin 446-712 (Korea, Republic of)

2014-12-28

We report an investigation of the effects of low-temperature annealing on the electrical properties of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). X-ray photoelectron spectroscopy was used to characterize the charge carrier concentration, which is related to the density of oxygen vacancies. The field-effect mobility was found to decrease as a function of the charge carrier concentration, owing to the presence of band-tail states. By employing the transmission line method, we show that the contact resistance did not significantly contribute to the changes in device performance after annealing. In addition, using low-frequency noise analyses, we found that the trap density decreased by a factor of 10 following annealing at 120 °C. The switching operation and on/off ratio of the a-IGZO TFTs improved considerably after low-temperature annealing.

Small scale variability of snow density on Antarctic sea ice

Science.gov (United States)

Wever, N.; Leonard, K. C.; Paul, S.; Jacobi, H. W.; Proksch, M.; Lehning, M.

2016-12-01

Snow on sea ice plays an important role in air-ice-sea interactions. For example, snow may smooth the ice surface when snow drift is occurring, while at the same time it may also generate roughness elements by interactions with the wind. Snow density is a key property in many processes, for example by influencing the thermal conductivity of the snow layer, radiative transfer inside the snow as well as the effects of aerodynamic forcing on the snowpack. We present data from an in-situ measurement campaign in the Weddell Sea during two subsequent cruises of RV Polarstern. By comparing snow density from snow pits and snow micro penetrometer (SMP) measurements, augmented by terrestrial laser scanning (TLS) on an area of 50x50 m2, highly resolved density profiles and surface topology were acquired at a horizontal resolution of approximately 30 cm. Average snow densities are about 280 kg/m3, but the analysis also reveals a high spatial variability in snow density on sea ice in both horizontal and vertical direction, ranging from roughly 170 to 360 kg/m3. This variability is expressed by coherent snow structures over several meters, which disappear over larger distances. A comparison with TLS data indicates that the spatial variability is related to deviations in surface topology. This suggests a strong influence from surface processes, for example wind, on the temporal development of density profiles. The fundamental relationship between density variations, surface roughness and changes therein as investigated in this study are interpreted with respect to larger-scale ice-movement and the ice mass balance.

Carbon Monoxide Hydrogenation on Ice Surfaces.

Science.gov (United States)

Kuwahata, Kazuaki; Ohno, Kaoru

2018-03-14

We have performed density functional calculations to investigate the carbon monoxide hydrogenation reaction (H+CO→HCO), which is important in interstellar clouds. We found that the activation energy of the reaction on amorphous ice is lower than that on crystalline ice. In the course of this study, we demonstrated that it is roughly possible to use the excitation energy of the reactant molecule (CO) in place of the activation energy. This relationship holds also for small water clusters at the CCSD level of calculation and the two-layer-level ONIOM (CCSD : X3LYP) calculation. Generally, since it is computationally demanding to estimate activation energies of chemical reactions in a circumstance of many water molecules, this relationship enables one to determine the activation energy of this reaction on ice surfaces from the knowledge of the excitation energy of CO only. Incorporating quantum-tunneling effects, we discuss the reaction rate on ice surfaces. Our estimate that the reaction rate on amorphous ice is almost twice as large as that on crystalline ice is qualitatively consistent with the experimental evidence reported by Hidaka et al. [Chem. Phys. Lett., 2008, 456, 36.]. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radiation effects in ice: New results

International Nuclear Information System (INIS)

Baragiola, R.A.; Fama, M.; Loeffler, M.J.; Raut, U.; Shi, J.

2008-01-01

Studies of radiation effects in ice are motivated by intrinsic interest and by applications in astronomy. Here we report on new and recent results on radiation effects induced by energetic ions in ice: amorphization of crystalline ice, compaction of microporous amorphous ice, electrostatic charging and dielectric breakdown and correlated structural/chemical changes in the irradiation of water-ammonia ices

OPTICAL CONSTANTS AND BAND STRENGTHS OF CH4:C2H6 ICES IN THE NEAR- AND MID-INFRARED

International Nuclear Information System (INIS)

Molpeceres, Germán; Ortigoso, Juan; Escribano, Rafael; Maté, Belén; Satorre, Miguel Angel; Millán, Carlos

2016-01-01

We present a spectroscopic study of methane–ethane ice mixtures. We have grown CH 4 :C 2 H 6 mixtures with ratios 3:1, 1:1, and 1:3 at 18 and 30 K, plus pure methane and ethane ices, and have studied them in the near-infrared (NIR) and mid-infrared (MIR) ranges. We have determined densities of all species mentioned above. For amorphous ethane grown at 18 and 30 K we have obtained a density of 0.41 and 0.54 g cm −3 , respectively, lower than a previous measurement of the density of the crystalline species, 0.719 g cm −3 . As far as we know this is the first determination of the density of amorphous ethane ice. We have measured band shifts of the main NIR methane and ethane features in the mixtures with respect to the corresponding values in the pure ices. We have estimated band strengths of these bands in the NIR and MIR ranges. In general, intensity decay in methane modes was detected in the mixtures, whereas for ethane no clear tendency was observed. Optical constants of the mixtures at 30 and 18 K have also been evaluated. These values can be used to trace the presence of these species in the surface of trans-Neptunian objects. Furthermore, we have carried out a theoretical calculation of these ice mixtures. Simulation cells for the amorphous solids have been constructed using a Metropolis Monte Carlo procedure. Relaxation of the cells and prediction of infrared spectra have been carried out at density functional theory level.

The Structure of Liquid and Amorphous Hafnia

Directory of Open Access Journals (Sweden)

Leighanne C. Gallington

2017-11-01

Full Text Available Understanding the atomic structure of amorphous solids is important in predicting and tuning their macroscopic behavior. Here, we use a combination of high-energy X-ray diffraction, neutron diffraction, and molecular dynamics simulations to benchmark the atomic interactions in the high temperature stable liquid and low-density amorphous solid states of hafnia. The diffraction results reveal an average Hf–O coordination number of ~7 exists in both the liquid and amorphous nanoparticle forms studied. The measured pair distribution functions are compared to those generated from several simulation models in the literature. We have also performed ab initio and classical molecular dynamics simulations that show density has a strong effect on the polyhedral connectivity. The liquid shows a broad distribution of Hf–Hf interactions, while the formation of low-density amorphous nanoclusters can reproduce the sharp split peak in the Hf–Hf partial pair distribution function observed in experiment. The agglomeration of amorphous nanoparticles condensed from the gas phase is associated with the formation of both edge-sharing and corner-sharing HfO6,7 polyhedra resembling that observed in the monoclinic phase.

Low Density of Top Predators (Seabirds and Marine Mammals in the High Arctic Pack Ice

Directory of Open Access Journals (Sweden)

Claude R. Joiris

2016-01-01

Full Text Available The at-sea distribution of top predators, seabirds and marine mammals, was determined in the high Arctic pack ice on board the icebreaker RV Polarstern in July to September 2014. In total, 1,620 transect counts were realised, lasting 30 min each. The five most numerous seabird species represented 74% of the total of 15,150 individuals registered: kittiwake Rissa tridactyla, fulmar Fulmarus glacialis, puffin Fratercula arctica, Ross’s gull Rhodostethia rosea, and little auk Alle alle. Eight cetacean species were tallied for a total of 330 individuals, mainly white-beaked dolphin Lagenorhynchus albirostris and fin whale Balaenoptera physalus. Five pinniped species were represented by a total of 55 individuals and the polar bear Ursus maritimus was represented by 12 individuals. Four main geographical zones were identified: from Tromsø to the outer marginal ice zone (OMIZ, the Arctic pack ice (close pack ice, CPI, the end of Lomonosov Ridge off Siberia, and the route off Siberia and northern Norway. Important differences were detected between zones, both in species composition and in individual abundance. Low numbers of species and high proportion of individuals for some of them can be considered to reflect very low biodiversity. Numbers encountered in zones 2 to 4 were very low in comparison with other European Arctic seas. The observed differences showed strong patterns.

Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

International Nuclear Information System (INIS)

Astakhov, Oleksandr; Carius, Reinhard; Finger, Friedhelm; Petrusenko, Yuri; Borysenko, Valery; Barankov, Dmytro

2009-01-01

The influence of dangling-bond defects and the position of the Fermi level on the charge carrier transport properties in undoped and phosphorous doped thin-film silicon with structure compositions all the way from highly crystalline to amorphous is investigated. The dangling-bond density is varied reproducibly over several orders of magnitude by electron bombardment and subsequent annealing. The defects are investigated by electron-spin-resonance and photoconductivity spectroscopies. Comparing intrinsic amorphous and microcrystalline silicon, it is found that the relationship between defect density and photoconductivity is different in both undoped materials, while a similar strong influence of the position of the Fermi level on photoconductivity via the charge carrier lifetime is found in the doped materials. The latter allows a quantitative determination of the value of the transport gap energy in microcrystalline silicon. The photoconductivity in intrinsic microcrystalline silicon is, on one hand, considerably less affected by the bombardment but, on the other hand, does not generally recover with annealing of the defects and is independent from the spin density which itself can be annealed back to the as-deposited level. For amorphous silicon and material prepared close to the crystalline growth regime, the results for nonequilibrium transport fit perfectly to a recombination model based on direct capture into neutral dangling bonds over a wide range of defect densities. For the heterogeneous microcrystalline silicon, this model fails completely. The application of photoconductivity spectroscopy in the constant photocurrent mode (CPM) is explored for the entire structure composition range over a wide variation in defect densities. For amorphous silicon previously reported linear correlation between the spin density and the subgap absorption is confirmed for defect densities below 10 18 cm -3 . Beyond this defect level, a sublinear relation is found i.e., not

THE EFFECTS OF EXPERIMENTAL CONDITIONS ON THE REFRACTIVE INDEX AND DENSITY OF LOW-TEMPERATURE ICES: SOLID CARBON DIOXIDE

Energy Technology Data Exchange (ETDEWEB)

Loeffler, M. J.; Moore, M. H.; Gerakines, P. A. [Astrochemistry Laboratory, Code 691, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2016-08-20

We present the first study on the effects of the deposition technique on the measurements of the visible refractive index and the density of a low-temperature ice using solid carbon dioxide (CO{sub 2}) at 14–70 K as an example. While our measurements generally agree with previous studies that show a dependence of index and density on temperature below 50 K, we also find that the measured values depend on the method used to create each sample. Below 50 K, we find that the refractive index varied by as much as 4% and the density by as much as 16% at a single temperature depending on the deposition method. We also show that the Lorentz–Lorenz approximation is valid for solid CO{sub 2} across the full 14–70 K temperature range, regardless of the deposition method used. Since the refractive index and density are important in calculations of optical constants and infrared (IR) band strengths of materials, our results suggest that the deposition method must be considered in cases where n {sub vis} and ρ are not measured in the same experimental setup where the IR spectral measurements are made.

The Effects of Experimental Conditions on the Refractive Index and Density of Low-Temperature Ices: Solid Carbon Dioxide

Science.gov (United States)

Loeffler, M. J.; Moore, M. H.; Gerakines, P. A.

2016-01-01

We present the first study on the effects of the deposition technique on the measurements of the visible refractive index and the density of a low-temperature ice using solid carbon dioxide (CO2) at 14-70 K as an example. While our measurements generally agree with previous studies that show a dependence of index and density on temperature below 50 K, we also find that the measured values depend on the method used to create each sample. Below 50 K, we find that the refractive index varied by as much as 4% and the density by as much as 16% at a single temperature depending on the deposition method. We also show that the Lorentz-Lorenz approximation is valid for solid CO2 across the full 14-70 K temperature range, regardless of the deposition method used. Since the refractive index and density are important in calculations of optical constants and infrared (IR) band strengths of materials, our results suggest that the deposition method must be considered in cases where nvis and ? are not measured in the same experimental setup where the IR spectral measurements are made.

Effective Ice Particle Densities for Cold Anvil Cirrus

Science.gov (United States)

Heymsfield, Andrew J.; Schmitt, Carl G.; Bansemer, Aaron; Baumgardner, Darrel; Weinstock, Elliot M.; Smith, Jessica

2002-01-01

This study derives effective ice particle densities from data collected from the NASA WB-57F aircraft near the tops of anvils during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) in southern Florida in July 2002. The effective density, defined as the ice particle mass divided by the volume of an equivalent diameter liquid sphere, is obtained for particle populations and single sizes containing mixed particle habits using measurements of condensed water content and particle size distributions. The mean effective densities for populations decrease with increasing slopes of the gamma size distributions fitted to the size distributions. The population-mean densities range from near 0.91 g/cu m to 0.15 g/cu m. Effective densities for single sizes obey a power-law with an exponent of about -0.55, somewhat less steep than found from earlier studies. Our interpretations apply to samples where particle sizes are generally below 200-300 microns in maximum dimension because of probe limitations.

Ice crystallization in ultrafine water-salt aerosols: nucleation, ice-solution equilibrium, and internal structure.

Science.gov (United States)

Hudait, Arpa; Molinero, Valeria

2014-06-04

Atmospheric aerosols have a strong influence on Earth's climate. Elucidating the physical state and internal structure of atmospheric aqueous aerosols is essential to predict their gas and water uptake, and the locus and rate of atmospherically important heterogeneous reactions. Ultrafine aerosols with sizes between 3 and 15 nm have been detected in large numbers in the troposphere and tropopause. Nanoscopic aerosols arising from bubble bursting of natural and artificial seawater have been identified in laboratory and field experiments. The internal structure and phase state of these aerosols, however, cannot yet be determined in experiments. Here we use molecular simulations to investigate the phase behavior and internal structure of liquid, vitrified, and crystallized water-salt ultrafine aerosols with radii from 2.5 to 9.5 nm and with up to 10% moles of ions. We find that both ice crystallization and vitrification of the nanodroplets lead to demixing of pure water from the solutions. Vitrification of aqueous nanodroplets yields nanodomains of pure low-density amorphous ice in coexistence with vitrified solute rich aqueous glass. The melting temperature of ice in the aerosols decreases monotonically with an increase of solute fraction and decrease of radius. The simulations reveal that nucleation of ice occurs homogeneously at the subsurface of the water-salt nanoparticles. Subsequent ice growth yields phase-segregated, internally mixed, aerosols with two phases in equilibrium: a concentrated water-salt amorphous mixture and a spherical cap-like ice nanophase. The surface of the crystallized aerosols is heterogeneous, with ice and solution exposed to the vapor. Free energy calculations indicate that as the concentration of salt in the particles, the advance of the crystallization, or the size of the particles increase, the stability of the spherical cap structure increases with respect to the alternative structure in which a core of ice is fully surrounded by

Interaction of D2 with H2O amorphous ice studied by temperature-programmed desorption experiments.

Science.gov (United States)

Amiaud, L; Fillion, J H; Baouche, S; Dulieu, F; Momeni, A; Lemaire, J L

2006-03-07

The gas-surface interaction of molecular hydrogen D2 with a thin film of porous amorphous solid water (ASW) grown at 10 K by slow vapor deposition has been studied by temperature-programmed-desorption (TPD) experiments. Molecular hydrogen diffuses rapidly into the porous network of the ice. The D2 desorption occurring between 10 and 30 K is considered here as a good probe of the effective surface of ASW interacting with the gas. The desorption kinetics have been systematically measured at various coverages. A careful analysis based on the Arrhenius plot method has provided the D2 binding energies as a function of the coverage. Asymmetric and broad distributions of binding energies were found, with a maximum population peaking at low energy. We propose a model for the desorption kinetics that assumes a complete thermal equilibrium of the molecules with the ice film. The sample is characterized by a distribution of adsorption sites that are filled according to a Fermi-Dirac statistic law. The TPD curves can be simulated and fitted to provide the parameters describing the distribution of the molecules as a function of their binding energy. This approach contributes to a correct description of the interaction of molecular hydrogen with the surface of possibly porous grain mantles in the interstellar medium.

PHOTOMETRIC MEASUREMENTS OF H{sub 2}O ICE CRYSTALLINITY ON TRANS-NEPTUNIAN OBJECTS

Energy Technology Data Exchange (ETDEWEB)

Terai, Tsuyoshi [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A‘ohoku Place, Hilo, HI 96720 (United States); Itoh, Yoichi [Center for Astronomy, University of Hyogo, 407-2 Nishigaichi, Sayo-cho, Sayo-gun, Hyogo 679-5313 (Japan); Oasa, Yumiko [Faculty of Education, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570 (Japan); Furusho, Reiko; Watanabe, Junichi, E-mail: tsuyoshi.terai@nao.ac.jp [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2016-08-10

We present a measurement of H{sub 2}O ice crystallinity on the surface of trans-neptunian objects with near-infrared narrow-band imaging. The newly developed photometric technique allows us to efficiently determine the strength of a 1.65 μ m absorption feature in crystalline H{sub 2}O ice. Our data for three large objects—Haumea, Quaoar, and Orcus—which are known to contain crystalline H{sub 2}O ice on the surfaces, show a reasonable result with high fractions of the crystalline phase. It can also be pointed out that if the grain size of H{sub 2}O ice is larger than ∼20 μ m, the crystallinities of these objects are obviously below 1.0, which suggests the presence of the amorphous phase. In particular, Orcus exhibits a high abundance of amorphous H{sub 2}O ice compared to Haumea and Quaoar, possibly indicating a correlation between the bulk density of the bodies and the degree of surface crystallization. We also found the presence of crystalline H{sub 2}O ice on Typhon and 2008 AP{sub 129}, both of which are smaller than the minimum size limit for inducing cryovolcanism as well as a transition from amorphous to crystalline phase through thermal evolution due to the decay of long-lived isotopes.

Kinetic Monte Carlo simulations of water ice porosity: extrapolations of deposition parameters from the laboratory to interstellar space

Science.gov (United States)

Clements, Aspen R.; Berk, Brandon; Cooke, Ilsa R.; Garrod, Robin T.

2018-02-01

Using an off-lattice kinetic Monte Carlo model we reproduce experimental laboratory trends in the density of amorphous solid water (ASW) for varied deposition angle, rate and surface temperature. Extrapolation of the model to conditions appropriate to protoplanetary disks and interstellar dark clouds indicate that these ices may be less porous than laboratory ices.

Amorphous silicon rich silicon nitride optical waveguides for high density integrated optics

DEFF Research Database (Denmark)

Philipp, Hugh T.; Andersen, Karin Nordström; Svendsen, Winnie Edith

2004-01-01

Amorphous silicon rich silicon nitride optical waveguides clad in silica are presented as a high-index contrast platform for high density integrated optics. Performance of different cross-sectional geometries have been measured and are presented with regards to bending loss and insertion loss...

Exact theory of dense amorphous hard spheres in high dimension. II. The high density regime and the Gardner transition.

Science.gov (United States)

Kurchan, Jorge; Parisi, Giorgio; Urbani, Pierfrancesco; Zamponi, Francesco

2013-10-24

We consider the theory of the glass phase and jamming of hard spheres in the large space dimension limit. Building upon the exact expression for the free-energy functional obtained previously, we find that the random first order transition (RFOT) scenario is realized here with two thermodynamic transitions: the usual Kauzmann point associated with entropy crisis and a further transition at higher pressures in which a glassy structure of microstates is developed within each amorphous state. This kind of glass-glass transition into a phase dominating the higher densities was described years ago by Elisabeth Gardner, and may well be a generic feature of RFOT. Microstates that are small excitations of an amorphous matrix-separated by low entropic or energetic barriers-thus emerge naturally, and modify the high pressure (or low temperature) limit of the thermodynamic functions.

Infrared Spectra and Optical Constants of Astronomical Ices: I. Amorphous and Crystalline Acetylene

Science.gov (United States)

Hudson, R. L.; Ferrante, R. F.; Moore, M. H.

2013-01-01

Here we report recent measurements on acetylene (C2H2) ices at temperatures applicable to the outer Solar System and the interstellar medium. New near- and mid-infrared data, including optical constants (n, k), absorption coefficients (alpha), and absolute band strengths (A), are presented for both amorphous and crystalline phases of C2H2 that exist below 70 K. Comparisons are made to earlier work. Electronic versions of the data are made available, as is a computer routine to use our reported n and k values to simulate the observed IR spectra. Suggestions are given for the use of the data and a comparison to a spectrum of Makemake is made.

Structure, thermodynamics, and crystallization of amorphous hafnia

International Nuclear Information System (INIS)

Luo, Xuhui; Demkov, Alexander A.

2015-01-01

We investigate theoretically amorphous hafnia using the first principles melt and quench method. We identify two types of amorphous structures of hafnia. Type I and type II are related to tetragonal and monoclinic hafnia, respectively. We find type II structure to show stronger disorder than type I. Using the phonon density of states, we calculate the specific heat capacity for type II amorphous hafnia. Using the nudged elastic band method, we show that the averaged transition barrier between the type II amorphous hafnia and monoclinic phase is approximately 0.09 eV/HfO 2 . The crystallization temperature is estimated to be 421 K. The calculations suggest an explanation for the low thermal stability of amorphous hafnia

Water’s second glass transition

Science.gov (United States)

Amann-Winkel, Katrin; Gainaru, Catalin; Handle, Philip H.; Seidl, Markus; Nelson, Helge; Böhmer, Roland

2013-01-01

The glassy states of water are of common interest as the majority of H2O in space is in the glassy state and especially because a proper description of this phenomenon is considered to be the key to our understanding why liquid water shows exceptional properties, different from all other liquids. The occurrence of water’s calorimetric glass transition of low-density amorphous ice at 136 K has been discussed controversially for many years because its calorimetric signature is very feeble. Here, we report that high-density amorphous ice at ambient pressure shows a distinct calorimetric glass transitions at 116 K and present evidence that this second glass transition involves liquid-like translational mobility of water molecules. This “double Tg scenario” is related to the coexistence of two liquid phases. The calorimetric signature of the second glass transition is much less feeble, with a heat capacity increase at Tg,2 about five times as large as at Tg,1. By using broadband-dielectric spectroscopy we resolve loss peaks yielding relaxation times near 100 s at 126 K for low-density amorphous ice and at 110 K for high-density amorphous ice as signatures of these two distinct glass transitions. Temperature-dependent dielectric data and heating-rate–dependent calorimetric data allow us to construct the relaxation map for the two distinct phases of water and to extract fragility indices m = 14 for the low-density and m = 20–25 for the high-density liquid. Thus, low-density liquid is classified as the strongest of all liquids known (“superstrong”), and also high-density liquid is classified as a strong liquid. PMID:24101518

Experimental evidence for two distinct deeply supercooled liquid states of water – Response to “Comment on ‘Water's second glass transition”’, by G.P. Johari, Thermochim. Acta (2015)

Energy Technology Data Exchange (ETDEWEB)

Stern, J.; Seidl, M. [Institute of Physical Chemistry, University of Innsbruck, 6020 Innsbruck (Austria); Gainaru, C. [Fakultät Physik, Technische Universität Dortmund, 44221 Dortmund (Germany); Fuentes-Landete, V.; Amann-Winkel, K.; Handle, P.H. [Institute of Physical Chemistry, University of Innsbruck, 6020 Innsbruck (Austria); Köster, K.W.; Nelson, H. [Fakultät Physik, Technische Universität Dortmund, 44221 Dortmund (Germany); Böhmer, R., E-mail: roland.bohmer@tu-dortmund.de [Fakultät Physik, Technische Universität Dortmund, 44221 Dortmund (Germany); Loerting, T., E-mail: thomas.loerting@uibk.ac.at [Institute of Physical Chemistry, University of Innsbruck, 6020 Innsbruck (Austria)

2015-10-10

Highlights: • Two samples of amorphous ices quench-recovered from 140 K to 0.07 GPa are compared. • Calorimetry, X-ray diffraction, dielectric spectroscopy and volumetry are employed. • The two samples are distinct and cannot both be termed “pressure-densified glassy water”. • One route of preparation leads to high- (HDA), and the other to low-density amorphous ice (LDA). • Two distinct glass transitions are observed and interpreted to indicate two liquid H{sub 2}O phases. - Abstract: Recently, our earlier data which led us to conclude that deeply supercooled water displays a second glass transition (Amann-Winkel et al., 2013) was reinterpreted (Johari, 2015). In particular, the increase in heat capacity observed for high-density amorphous ice (HDA) samples at 116 K was reinterpreted to indicate sub-T{sub g} features of low-density amorphous ice's (LDA's) glass transition. We reply to the criticism in detail and report an experiment triggered by the comment on our work. This experiment unequivocally confirms our original interpretation of the observations and reinforces the case for water's second glass transition, its polyamorphism, and the observation of two distinct ultraviscous states of water differing by about 25% in density.

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

Ferroelectricity in high-density H{sub 2}O ice

Energy Technology Data Exchange (ETDEWEB)

Caracas, Razvan, E-mail: razvan.caracas@ens-lyon.fr, E-mail: rhemley@ciw.edu [CNRS, Laboratoire de Géologie de Lyon UMR5276, Ecole Normale Supérieure de Lyon, 46, alleé d’Italie, Université Claude-Bernard Lyon 1, Université de Lyon, 69364 Lyon cedex 07 (France); Hemley, Russell J., E-mail: razvan.caracas@ens-lyon.fr, E-mail: rhemley@ciw.edu [Geophysical Laboratory, 5251 Broad Branch Road NW, Carnegie Institution of Washington, Washington, DC 20015 (United States)

2015-04-07

The origin of longstanding anomalies in experimental studies of the dense solid phases of H{sub 2}O ices VII, VIII, and X is examined using a combination of first-principles theoretical methods. We find that a ferroelectric variant of ice VIII is energetically competitive with the established antiferroelectric form under pressure. The existence of domains of the ferroelectric form within anti-ferroelectric ice can explain previously observed splittings in x-ray diffraction data. The ferroelectric form is stabilized by density and is accompanied by the onset of spontaneous polarization. The presence of local electric fields triggers the preferential parallel orientation of the water molecules in the structure, which could be stabilized in bulk using new high-pressure techniques.

Structure and low temperature thermal relaxation of amorphized germanium

International Nuclear Information System (INIS)

Glover, C.J.; Ridgway, M.C.; Byrne, A.P.; Clerc, C.; Hansen, J.L.; Larsen, A.N.

1999-01-01

The structure of implantation-induced damage in amorphized Ge has been investigated using high resolution extended x-ray absorption fine structure spectroscopy (EXAFS). EXAFS data analysis was performed with the Cumulant Method, allowing a full reconstruction of the interatomic distance distribution (RDF). For the case of MeV implantation at -196 deg C, for an ion-dose range extending two orders of magnitude beyond that required for amorphization, a dose-dependent asymmetric RDF was determined for the amorphous phase including an increase in bond-length as a function of ion dose. Low-temperature thermal annealing resulted in structural relaxation of the amorphous phase as evidenced by a reduction in the centroid, asymmetry and width of the RDF. Such an effect was attributed to the formation (and subsequent annihilation) of three- and five-fold Co-ordinated atoms, comparing favourably to theoretical simulations of the structure of a-Ge

Amorphization Mechanism of Icosahedral Platinum Clusters

International Nuclear Information System (INIS)

Apra, Edoardo; Baletto, Francesca; Ferrando, Riccardo; Fortunelli, Alessandro

2004-01-01

The amorphization mechanism of high-symmetry pt nanoclusters is investigated by a combination of Molecular Dynamics simulations and Density Functional calculations. A general mechanism for amorphization, involving rosette-like structural transformations at fivefold vertices, is proposed. IN the tosette, a fivefold vertex is transformed into a hexagonal ring. We show that for icosahedral Pt nanoclusters, this transformation is associated with an energy gain, so that their most favorable structures have a low symmetry even at icosahedral magic numbers

The effect of empirical potential functions on modeling of amorphous carbon using molecular dynamics method

International Nuclear Information System (INIS)

Li, Longqiu; Xu, Ming; Song, Wenping; Ovcharenko, Andrey; Zhang, Guangyu; Jia, Ding

2013-01-01

Empirical potentials have a strong effect on the hybridization and structure of amorphous carbon and are of great importance in molecular dynamics (MD) simulations. In this work, amorphous carbon at densities ranging from 2.0 to 3.2 g/cm 3 was modeled by a liquid quenching method using Tersoff, 2nd REBO, and ReaxFF empirical potentials. The hybridization, structure and radial distribution function G(r) of carbon atoms were analyzed as a function of the three potentials mentioned above. The ReaxFF potential is capable to model the change of the structure of amorphous carbon and MD results are in a good agreement with experimental results and density function theory (DFT) at low density of 2.6 g/cm 3 and below. The 2nd REBO potential can be used when amorphous carbon has a very low density of 2.4 g/cm 3 and below. Considering the computational efficiency, the Tersoff potential is recommended to model amorphous carbon at a high density of 2.6 g/cm 3 and above. In addition, the influence of the quenching time on the hybridization content obtained with the three potentials is discussed.

Room-temperature low-voltage electroluminescence in amorphous carbon nitride thin films

Science.gov (United States)

Reyes, R.; Legnani, C.; Ribeiro Pinto, P. M.; Cremona, M.; de Araújo, P. J. G.; Achete, C. A.

2003-06-01

White-blue electroluminescent emission with a voltage bias less than 10 V was achieved in rf sputter-deposited amorphous carbon nitride (a-CN) and amorphous silicon carbon nitride (a-SiCN) thin-film-based devices. The heterojunction structures of these devices consist of: Indium tin oxide (ITO), used as a transparent anode; amorphous carbon film as an emission layer, and aluminum as a cathode. The thickness of the carbon films was about 250 Å. In all of the produced diodes, a stable visible emission peaked around 475 nm is observed at room temperature and the emission intensity increases with the current density. For an applied voltage of 14 V, the luminance was about 3 mCd/m2. The electroluminescent properties of the two devices are discussed and compared.

Melting and Pressure-Induced Amorphization of Quartz

OpenAIRE

Badro, James; Gillet, Philippe; Barrat, Jean-Louis

1997-01-01

It has recently been shown that amorphization and melting of ice were intimately linked. In this letter, we infer from molecular dynamics simulations on the SiO2 system that the extension of the quartz melting line in the metastable pressure-temperature domain is the pressure-induced amorphization line. It seems therefore likely that melting is the physical phenomenon responsible for pressure induced amorphization. Moreover, we show that the structure of a "pressure glass" is similar to that ...

Low Bone Density

Science.gov (United States)

... Density Exam/Testing › Low Bone Density Low Bone Density Low bone density is when your bone density ... people with normal bone density. Detecting Low Bone Density A bone density test will determine whether you ...

Low-density to high-density transition in Ce75Al23Si2 metallic glass

International Nuclear Information System (INIS)

Zeng, Q S; Lou, H B; Gong, Y; Wang, X D; Jiang, J Z; Fang, Y Z; Wu, F M; Yang, K; Li, A G; Yan, S; Yu, X H; Lathe, C

2010-01-01

Using in situ high-pressure x-ray diffraction (XRD), we observed a pressure-induced polyamorphic transition from the low-density amorphous (LDA) state to the high-density amorphous (HDA) state in Ce 75 Al 23 Si 2 metallic glass at about 2 GPa and 300 K. The thermal stabilities of both LDA and HDA metallic glasses were further investigated using in situ high-temperature and high-pressure XRD, which revealed different pressure dependences of the onset crystallization temperature (T x ) between them with a turning point at about 2 GPa. Compared with Ce 75 Al 25 metallic glass, minor Si doping shifts the onset polyamorphic transition pressure from 1.5 to 2 GPa and obviously stabilizes both LDA and HDA metallic glasses with higher T x and changes their slopes dT x /dP. The results obtained in this work reveal another polyamorphous metallic glass system by minor alloying (e.g. Si), which could modify the transition pressure and also properties of LDA and HDA metallic glasses. The minor alloying effect reported here is valuable for the development of more polyamorphous metallic glasses, even multicomponent bulk metallic glasses with modified properties, which will trigger more investigations in this field and improve our understanding of polyamorphism and metallic glasses.

Infrared Spectra and Optical Constants of Elusive Amorphous Methane

Science.gov (United States)

Gerakines, Perry A.; Hudson, Reggie L.

2015-01-01

New and accurate laboratory results are reported for amorphous methane (CH4) ice near 10 K for the study of the interstellar medium (ISM) and the outer Solar System. Near- and mid-infrared (IR) data, including spectra, band strengths, absorption coefficients, and optical constants, are presented for the first time for this seldom-studied amorphous solid. The apparent IR band strength near 1300 cm(exp -1) (7.69 micrometer) for amorphous CH4 is found to be about 33% higher than the value long used by IR astronomers to convert spectral observations of interstellar CH4 into CH4 abundances. Although CH4 is most likely to be found in an amorphous phase in the ISM, a comparison of results from various laboratory groups shows that the earlier CH4 band strength at 1300 cm(exp -1) (7.69 micrometer) was derived from IR spectra of ices that were either partially or entirely crystalline CH4 Applications of the new amorphous-CH4 results are discussed, and all optical constants are made available in electronic form.

Radiation Effects in Hydrogen-Laden Porous Water Ice Films: Implications for Interstellar Ices

Science.gov (United States)

Raut, Ujjwal; Baragiola, Raul; Mitchell, Emma; Shi, Jianming

H _{2} is the dominant gas in the dense clouds of the interstellar medium (ISM). At densities of 10 (5) cm (-3) , an H _{2} molecule arrives at the surface of a 0.1 mum-sized, ice-covered dust grain once every few seconds [1]. At 10 K, H _{2} can diffuse into the pores of the ice mantle and adsorb at high-energy binding sites, loading the ice with hydrogen over the lifetime of the cloud. These icy grains are also impacted by galactic cosmic rays and stellar winds (in clouds with embedded protostar). Based on the available cosmic proton flux spectrum [2], we estimate a small impact rate of nearly 1 hit per year on a 0.1 μm sized grain, or 10 (-7) times the impact frequency of the neutral H _{2}. The energy deposited by such impacts can release the adsorbed H _{2} into the gas phase (impact desorption or sputtering). Recently, we have reported on a new process of ion-induced enhanced adsorption, where molecules from the gas phase are incorporated into the film when irradiation is performed in the presence of ambient gas [3]. The interplay between ion-induced ejection and adsorption can be important in determining the gas-solid balance in the ISM. To understand the effects of cosmic rays/stellar winds impacts on interstellar ice immersed in H _{2} gas, we have performed irradiation of porous amorphous ice films loaded with H _{2} through co-deposition or adsorption following growth. The irradiations were performed with 100 keV H (+) using fluxes of 10 (10) -10 (12) H (+) cm (-2) s (-1) at 7 K, in presence of ambient H _{2} at pressures ranging from 10 (-5) to 10 (-8) Torr. Our initial results show a net loss in adsorbed H _{2} during irradiation, from competing ion-induced ejection and adsorption. The H _{2} loss per ion decreases exponentially with fluence, with a cross-section of 10 (-13) cm (2) . In addition to hydrogen removal, irradiation also leads to trapping of H _{2} in the ice film, from closing of the pores during irradiation [4]. As a result, 2.6 percent

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.

Compaction of amorphous iron–boron powder

DEFF Research Database (Denmark)

Hendriksen, Peter Vang; Mørup, Steen; Koch, Christian

1993-01-01

Large scale practical use of bulk amorphous alloys requires the capability of molding the material to a desired design, for instance by compaction of an amorphous powder. This is a difficult task because the sintering temperature is limited by the crystallization temperature of the alloy.1 Here we......, should facilitate a compaction. The passivation layer, however, impedes a compaction. Isostatic pressing at 540 K at a pressure of 200 MPa clearly illustrated this; pellets pressed from passivated powder were much more brittle than pellets pressed from unpassivated powder. The density of the pellets...... was very low ([approximately-equal-to]25% of the density of bulk FeB). We have designed a die for uniaxial pressing in which the compaction can be performed without exposing the powder to air and have obtained densities larger than 60% of that of bulk FeB. We have reported studies of the dependence...

Density model for medium range order in amorphous materials: application to small angle scattering

International Nuclear Information System (INIS)

Boucher, B.; Tournarie, M.; Chieux, P.; Convert, P.

1983-06-01

We consider a family of randomly spaced parallel planes, each plane dressed with a density function, h(x), where x is the distance from the plane. An expression for the volume scattering power from a system of N such families with random orientations in space is derived from Fourier transform of h(x), which can subsequently be determined from experimental observations. This density model is used to interpret the small angle neutron scattering (SANS) results for the amorphous alloy TbCusub(3.54)

A Snow Density Dataset for Improving Surface Boundary Conditions in Greenland Ice Sheet Firn Modeling

Directory of Open Access Journals (Sweden)

Robert S. Fausto

2018-05-01

Full Text Available The surface snow density of glaciers and ice sheets is of fundamental importance in converting volume to mass in both altimetry and surface mass balance studies, yet it is often poorly constrained. Site-specific surface snow densities are typically derived from empirical relations based on temperature and wind speed. These parameterizations commonly calculate the average density of the top meter of snow, thereby systematically overestimating snow density at the actual surface. Therefore, constraining surface snow density to the top 0.1 m can improve boundary conditions in high-resolution firn-evolution modeling. We have compiled an extensive dataset of 200 point measurements of surface snow density from firn cores and snow pits on the Greenland ice sheet. We find that surface snow density within 0.1 m of the surface has an average value of 315 kg m−3 with a standard deviation of 44 kg m−3, and has an insignificant annual air temperature dependency. We demonstrate that two widely-used surface snow density parameterizations dependent on temperature systematically overestimate surface snow density over the Greenland ice sheet by 17–19%, and that using a constant density of 315 kg m−3 may give superior results when applied in surface mass budget modeling.

Evaluation of physicochemical, textural and sensorial characteristics of low-fat or low-sugar synbiotic ice-cream

Directory of Open Access Journals (Sweden)

M Hashemi

2015-08-01

Full Text Available Replacing a part of fat and sugar in ice-cream by inulin and lactulose as prebiotic may create a healthier product. Two low-fat and two low-sugar synbiotic ice-cream samples were manufactured inoculated with Lactobacillus acidophilus or Bacillus coagulans. The physicochemical, textural and sensorial characteristics of the samples were compared with regular ice-cream as control. Low-fat and low-sugar synbiotic ice-cream formulations were prepared by replacing 5% of the fat and sugar contents of the control formula by inulin and lactulose, respectively. According to the results, although the total solids of the ice-cream mixes did not differ significantly, there were significant (p

Low-energy excitations in amorphous films of silicon and germanium

International Nuclear Information System (INIS)

Liu, X.; Pohl, R.O.

1998-01-01

We present measurements of internal friction and shear modulus of amorphous Si (a-Si) and amorphous Ge (a-Ge) films on double-paddle oscillators at 5500 Hz from 0.5 K up to room temperature. The temperature- independent plateau in internal friction below 10 K, which is common to all amorphous solids, also exists in these films. However, its magnitude is smaller than found for all other amorphous solids studied to date. Furthermore, it depends critically on the deposition methods. For a-Si films, it decreases in the sequence of electron-beam evaporation, sputtering, self-ion implantation, and hot-wire chemical-vapor deposition (HWCVD). Annealing can also reduce the internal friction of the amorphous films considerably. Hydrogenated a-Si with 1 at.% H prepared by HWCVD leads to an internal friction more than two orders of magnitude smaller than observed for all other amorphous solids. The internal friction increases after the hydrogen is removed by effusion. Our results are compared with earlier measurements on a-Si and a-Ge films, none of which had the sensitivity achieved here. The variability of the low-energy tunneling states in the a-Si and a-Ge films may be a consequence of the tetrahedrally bonded covalent continuous random network. The perfection of this network, however, depends critically on the preparation conditions, with hydrogen incorporation playing a particularly important role. copyright 1998 The American Physical Society

Molecular simulation strategy for mechanical modeling of amorphous/porous low-dielectric constant materials

NARCIS (Netherlands)

Yuan, C.A.; Sluis, van der O.; Zhang, G.Q.; Ernst, L.J.; Driel, van W.D.; Flower, A.E.; Silfhout, van R.B.R.

2008-01-01

We propose an amorphous/porous molecular connection network generation algorithm for simulating the material stiffness of a low-k material (SiOC:H). Based on a given concentration of the basic building blocks, this algorithm will generate an approximate and large amorphous network. The molecular

On the mechanism of charge transport in low density polyethylene

Science.gov (United States)

Upadhyay, Avnish K.; Reddy, C. C.

2017-08-01

Polyethylene based polymeric insulators, are being increasingly used in the power industry for their inherent advantages over conventional insulation materials. Specifically, modern power cables are almost made with these materials, replacing the mass-impregnated oil-paper cable technology. However, for ultra-high dc voltage applications, the use of these polymeric cables is hindered by ununderstood charge transport and accumulation. The conventional conduction mechanisms (Pool-Frenkel, Schottky, etc.) fail to track high-field charge transport in low density polyethylene, which is semi-crystalline in nature. Until now, attention was devoted mainly to the amorphous region of the material. In this paper, authors propose a novel mechanism for conduction in low density polyethylene, which could successfully track experimental results. As an implication, a novel, substantial relationship is established for electrical conductivity that could be effectively used for understanding conduction and breakdown in polyethylene, which is vital for successful development of ultra-high voltage dc cables.

Experimental study of the polyamorphism of water. II. The isobaric transitions between HDA and VHDA at intermediate and high pressures

Science.gov (United States)

Handle, Philip H.; Loerting, Thomas

2018-03-01

Since the first report of very-high density amorphous ice (VHDA) in 2001 [T. Loerting et al., Phys. Chem. Chem. Phys. 3, 5355-5357 (2001)], the status of VHDA as a distinct amorphous ice has been debated. We here study VHDA and its relation to expanded high density amorphous ice (eHDA) on the basis of isobaric heating experiments. VHDA was heated at 0.1 ≤ p ≤ 0.7 GPa, and eHDA was heated at 1.1 ≤ p ≤ 1.6 GPa to achieve interconversion. The behavior upon heating is monitored using in situ volumetry as well as ex situ X-ray diffraction and differential scanning calorimetry. We do not observe a sharp transition for any of the isobaric experiments. Instead, a continuous expansion (VHDA) or densification (eHDA) marks the interconversion. This suggests that a continuum of states exists between VHDA and HDA, at least in the temperature range studied here. This further suggests that VHDA is the most relaxed amorphous ice at high pressures and eHDA is the most relaxed amorphous ice at intermediate pressures. It remains unclear whether or not HDA and VHDA experience a sharp transition upon isothermal compression/decompression at low temperature.

Nature of metastable amorphous-to-crystalline reversible phase transformations in GaSb

Energy Technology Data Exchange (ETDEWEB)

Kalkan, B. [Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 20015 (United States); Edwards, T. G.; Sen, S. [Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616 (United States); Raoux, S. [IBM T. J. Watson Research Center, Yorktown Heights, New York 10598 (United States)

2013-08-28

The structural, thermodynamic, and kinetic aspects of the transformations between the metastable amorphous and crystalline phases of GaSb are investigated as a function of pressure at ambient temperature using synchrotron x-ray diffraction experiments in a diamond anvil cell. The results are consistent with the hypothesis that the pressure induced crystallization of amorphous GaSb into the β-Sn crystal structure near ∼5 GPa is possibly a manifestation of an underlying polyamorphic phase transition between a semiconducting, low density and a metallic, high density amorphous (LDA and HDA, respectively) phases. In this scenario, the large differences in the thermal crystallization kinetics between amorphous GaSb deposited in thin film form by sputtering and that prepared by laser melt quenching may be related to the relative location of the glass transition temperature of the latter in the pressure-temperature (P-T) space with respect to the location of the critical point that terminate the LDA ↔ HDA transition. The amorphous →β-Sn phase transition is found to be hysteretically reversible as the β-Sn phase undergoes decompressive amorphization near ∼2 GPa due to the lattice instabilities that give rise to density fluctuations in the crystal upon decompression.

Nature of metastable amorphous-to-crystalline reversible phase transformations in GaSb

Science.gov (United States)

Kalkan, B.; Edwards, T. G.; Raoux, S.; Sen, S.

2013-08-01

The structural, thermodynamic, and kinetic aspects of the transformations between the metastable amorphous and crystalline phases of GaSb are investigated as a function of pressure at ambient temperature using synchrotron x-ray diffraction experiments in a diamond anvil cell. The results are consistent with the hypothesis that the pressure induced crystallization of amorphous GaSb into the β-Sn crystal structure near ˜5 GPa is possibly a manifestation of an underlying polyamorphic phase transition between a semiconducting, low density and a metallic, high density amorphous (LDA and HDA, respectively) phases. In this scenario, the large differences in the thermal crystallization kinetics between amorphous GaSb deposited in thin film form by sputtering and that prepared by laser melt quenching may be related to the relative location of the glass transition temperature of the latter in the pressure-temperature (P-T) space with respect to the location of the critical point that terminate the LDA ↔ HDA transition. The amorphous → β-Sn phase transition is found to be hysteretically reversible as the β-Sn phase undergoes decompressive amorphization near ˜2 GPa due to the lattice instabilities that give rise to density fluctuations in the crystal upon decompression.

Nature of metastable amorphous-to-crystalline reversible phase transformations in GaSb

International Nuclear Information System (INIS)

Kalkan, B.; Edwards, T. G.; Sen, S.; Raoux, S.

2013-01-01

The structural, thermodynamic, and kinetic aspects of the transformations between the metastable amorphous and crystalline phases of GaSb are investigated as a function of pressure at ambient temperature using synchrotron x-ray diffraction experiments in a diamond anvil cell. The results are consistent with the hypothesis that the pressure induced crystallization of amorphous GaSb into the β-Sn crystal structure near ∼5 GPa is possibly a manifestation of an underlying polyamorphic phase transition between a semiconducting, low density and a metallic, high density amorphous (LDA and HDA, respectively) phases. In this scenario, the large differences in the thermal crystallization kinetics between amorphous GaSb deposited in thin film form by sputtering and that prepared by laser melt quenching may be related to the relative location of the glass transition temperature of the latter in the pressure-temperature (P-T) space with respect to the location of the critical point that terminate the LDA ↔ HDA transition. The amorphous →β-Sn phase transition is found to be hysteretically reversible as the β-Sn phase undergoes decompressive amorphization near ∼2 GPa due to the lattice instabilities that give rise to density fluctuations in the crystal upon decompression

A new temperature and humidity dependent surface site density approach for deposition ice nucleation

OpenAIRE

I. Steinke; C. Hoose; O. Möhler; P. Connolly; T. Leisner

2014-01-01

Deposition nucleation experiments with Arizona Test Dust (ATD) as a surrogate for mineral dusts were conducted at the AIDA cloud chamber at temperatures between 220 and 250 K. The influence of the aerosol size distribution and the cooling rate on the ice nucleation efficiencies was investigated. Ice nucleation active surface site (INAS) densities were calculated to quantify the ice nucleation efficiency as a function of temperature, humidity and the aerosol ...

Enhanced thermoelectric performance of amorphous Nb based oxynitrides

Science.gov (United States)

Music, Denis; Geyer, Richard W.; Hans, Marcus

2015-12-01

Using density functional theory, amorphous Nb0.27Ru0.06O0.56N0.10 was designed to facilitate a combination of an enhanced Seebeck coefficient and low electrical resistivity. Based on a positive Cauchy pressure, ductile behavior is expected. To verify these predictions, the transport and mechanical properties of amorphous thin films were evaluated. Metallic electrical resistivity and the Seebeck coefficient of -94 μV K-1 are obtained, which is consistent with our predictions. As there is no crack formation, these samples can be perceived as ductile. We demonstrate that the power factor can be increased by an order of magnitude, while keeping the thermal fatigue low.

Synthesis of Fe-based amorphous composite coatings with low purity materials by laser cladding

Energy Technology Data Exchange (ETDEWEB)

Zhu Qingjun [School of Materials Science and Engineering, Shandong University, Jinan 250061 (China)]. E-mail: sduzhu@yahoo.com.cn; Qu Shiyao [School of Materials Science and Engineering, Shandong University, Jinan 250061 (China); Wang Xinhong [School of Materials Science and Engineering, Shandong University, Jinan 250061 (China); Zou Zengda [School of Materials Science and Engineering, Shandong University, Jinan 250061 (China)

2007-06-30

Amorphous composite coatings Fe{sub 38}Ni{sub 30-X}Si{sub 16}B{sub 14}V{sub 2}M {sub X} (X = 0, 1, 2) (M contains Al, Ti, Mo, and C) were prepared with low purity of raw materials by laser cladding. X-ray diffraction and transmission electron microscopy results show that the coating have an amorphous structure with a few crystalline phase on it. The amorphous phase is the primary phase. The glass forming ability as well as the microhardness of the Fe-based alloy made from low purity raw materials can be much enhanced by adding small amount of multi-components. However, the elements addition has its optimal quantity. When X is equal to 1, the microstructure of the coating contains 97.93% amorphous phase and 2.07% crystalline phase on it. As a result, the microhardness of the coating reaches maximum. With further increasing of the additions, the amorphous phase in the coating lessens instead of augment and the crystalline phase begins to accumulate, which result in the decrease of the microhardness.

Mg amorphous alloys for biodegradable implants

International Nuclear Information System (INIS)

Danez, G.P.; Koga, G.Y.; Tonucci, S.; Bolfarini, C.; Kiminami, C.S.; Botta Filho, W.J.

2010-01-01

The use of implants made from amorphous alloys magnesium-based with additions of zinc and calcium are promising. Properties such as biocompatibility, low density, high mechanical strength, low modulus (as compared to alloys such as stainless steel and titanium), corrosion resistance and wear resistance make it attractive for use in implants. Moreover, the by-products of corrosion and wear are not toxic and may contribute to fixation. Aiming to understand the tendency of this amorphous ternary (Mg-Zn-Ca) and expand the information about this system, this work involved the use of the topological criterion of instability (λ) and the criterion of electronegativity (Δe) to the choice of compositions. The alloys were processed into wedge-shaped and analyzed structurally and in X-ray diffraction and scanning electron microscopy. (author)

Inter-annual Variations in Snow/Firn Density over the Greenland Ice Sheet by Combining GRACE gravimetry and Envisat Altimetry

Science.gov (United States)

Su, X.; Shum, C. K.; Guo, J.; Howat, I.; Jezek, K. C.; Luo, Z.; Zhou, Z.

2017-12-01

Satellite altimetry has been used to monitor elevation and volume change of polar ice sheets since the 1990s. In order to derive mass change from the measured volume change, different density assumptions are commonly used in the research community, which may cause discrepancies on accurately estimating ice sheets mass balance. In this study, we investigate the inter-annual anomalies of mass change from GRACE gravimetry and elevation change from Envisat altimetry during years 2003-2009, with the objective of determining inter-annual variations of snow/firn density over the Greenland ice sheet (GrIS). High positive correlations (0.6 or higher) between these two inter-annual anomalies at are found over 93% of the GrIS, which suggests that both techniques detect the same geophysical process at the inter-annual timescale. Interpreting the two anomalies in terms of near surface density variations, over 80% of the GrIS, the inter-annual variation in average density is between the densities of snow and pure ice. In particular, at the Summit of Central Greenland, we validate the satellite data estimated density with the in situ data available from 75 snow pits and 9 ice cores. This study provides constraints on the currently applied density assumptions for the GrIS.

Low-Temperature Preparation of Amorphous-Shell/Nanocrystalline-Core Nanostructured TiO2 Electrodes for Flexible Dye-Sensitized Solar Cells

Directory of Open Access Journals (Sweden)

Dongshe Zhang

2008-01-01

Full Text Available An amorphous shell/nanocrystalline core nanostructured TiO2 electrode was prepared at low temperature, in which the mixture of TiO2 powder and TiCl4 aqueous solution was used as the paste for coating a film and in this film amorphous TiO2 resulted from direct hydrolysis of TiCl4 at 100∘C sintering was produced to connect the particles forming a thick crack-free uniform nanostructured TiO2 film (12 μm, and on which a photoelectrochemical solar cell-based was fabricated, generating a short-circuit photocurrent density of 13.58 mA/cm2, an open-circuit voltage of 0.647 V, and an overall 4.48% light-to-electricity conversion efficiency under 1 sun illumination.

Nature of phase transitions in crystalline and amorphous GeTe-Sb2Te3 phase change materials.

Science.gov (United States)

Kalkan, B; Sen, S; Clark, S M

2011-09-28

The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge(1)Sb(2)Te(4) (GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic → amorphous → orthorhombic → bcc and hexagonal → orthorhombic → bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope. © 2011 American Institute of Physics

Highly featured amorphous silicon nanorod arrays for high-performance lithium-ion batteries

International Nuclear Information System (INIS)

Soleimani-Amiri, Samaneh; Safiabadi Tali, Seied Ali; Azimi, Soheil; Sanaee, Zeinab; Mohajerzadeh, Shamsoddin

2014-01-01

High aspect-ratio vertical structures of amorphous silicon have been realized using hydrogen-assisted low-density plasma reactive ion etching. Amorphous silicon layers with the thicknesses ranging from 0.5 to 10 μm were deposited using radio frequency plasma enhanced chemical vapor deposition technique. Standard photolithography and nanosphere colloidal lithography were employed to realize ultra-small features of the amorphous silicon. The performance of the patterned amorphous silicon structures as a lithium-ion battery electrode was investigated using galvanostatic charge-discharge tests. The patterned structures showed a superior Li-ion battery performance compared to planar amorphous silicon. Such structures are suitable for high current Li-ion battery applications such as electric vehicles

Highly featured amorphous silicon nanorod arrays for high-performance lithium-ion batteries

Energy Technology Data Exchange (ETDEWEB)

Soleimani-Amiri, Samaneh; Safiabadi Tali, Seied Ali; Azimi, Soheil; Sanaee, Zeinab; Mohajerzadeh, Shamsoddin, E-mail: mohajer@ut.ac.ir [Thin Film and Nanoelectronics Lab, Nanoelectronics Center of Excellence, School of Electrical and Computer Engineering, University of Tehran, Tehran 143957131 (Iran, Islamic Republic of)

2014-11-10

High aspect-ratio vertical structures of amorphous silicon have been realized using hydrogen-assisted low-density plasma reactive ion etching. Amorphous silicon layers with the thicknesses ranging from 0.5 to 10 μm were deposited using radio frequency plasma enhanced chemical vapor deposition technique. Standard photolithography and nanosphere colloidal lithography were employed to realize ultra-small features of the amorphous silicon. The performance of the patterned amorphous silicon structures as a lithium-ion battery electrode was investigated using galvanostatic charge-discharge tests. The patterned structures showed a superior Li-ion battery performance compared to planar amorphous silicon. Such structures are suitable for high current Li-ion battery applications such as electric vehicles.

A Snow Density Dataset for Improving Surface Boundary Conditions in Greenland Ice Sheet Firn Modeling

DEFF Research Database (Denmark)

S. Fausto, Robert; E. Box, Jason; Vandecrux, Baptiste Robert Marcel

2018-01-01

The surface snow density of glaciers and ice sheets is of fundamental importance in converting volume to mass in both altimetry and surface mass balance studies, yet it is often poorly constrained. Site-specific surface snow densities are typically derived from empirical relations based...... on temperature and wind speed. These parameterizations commonly calculate the average density of the top meter of snow, thereby systematically overestimating snow density at the actual surface. Therefore, constraining surface snow density to the top 0.1 m can improve boundary conditions in high-resolution firn......-evolution modeling. We have compiled an extensive dataset of 200 point measurements of surface snow density from firn cores and snow pits on the Greenland ice sheet. We find that surface snow density within 0.1 m of the surface has an average value of 315 kg m−3 with a standard deviation of 44 kg m−3, and has...

Contribution to the study of the mechanism of crack in amorphous silica: study by the molecular dynamics of crack in amorphous silica

International Nuclear Information System (INIS)

Van Brutzel, L.

2000-01-01

The aim of this thesis was to understand the mechanism which occurs during the crack at the atomic scale in amorphous silica. The difficulties of the experimental observations at this length scale lead us to use numerical studies by molecular dynamics to access to the dynamical and the thermodynamical informations. We have carried out large simulations with 500000 atoms and studied the structure of the amorphous silica before to studying their behaviours under an imposed strain. The structure of this simulated amorphous silica settled in three length scales. In small length scale between 0 and 5 angstrom glass is composed of tetrahedra, this is close to the crystalline structure. In intermediate length scale between 3 and 10 angstrom tetrahedra are connected together and build rings of different sizes composed in majority between 5 and 7 tetrahedra. In bigger length scale between 15 and 60 angstrom, areas with high density of rings are surrounded by areas with low density of rings. These structural considerations play an important role in initiation and propagation of a crack. Indeed. in this length scale. crack propagates by growth and coalescence of some small cavities which appear in area with low density of rings behind the crack tip. The cavities dissipate the stress with carries away a delay to propagation of the crack. This phenomenons seems ductile and leads to non linear elastic behaviour near the crack tip. We have also shown that the addition of alkali in the amorphous silica changes the structure by creation of nano-porosities and leads to enhance the ductility during the crack propagation. (author)

Experimental evidence of a liquid-liquid transition in interfacial water

Science.gov (United States)

Zanotti, J.-M.; Bellissent-Funel, M.-C.; Chen, S.-H.

2005-07-01

At ambient pressure, bulk liquid water shows an anomalous increase of thermodynamic quantities and apparent divergences of dynamic properties on approaching a temperature Ts of 228 K. At normal pressure, supercooled water spontaneously freezes below the homogeneous nucleation temperature, TH = 235 K. Upon heating, the two forms of Amorphous Solid Water (ASW), LDA (Low Density Amorphous Ice) and HDA (High Density Amorphous Ice), crystallise above TX = 150 K. As a consequence, up to now no experiment has been able to explore the properties of liquid water in this very interesting temperature range between 150 and 235 K. We present nanosecond-time-scale measurements of local rotational and translational dynamics of interfacial, non-crystalline, water from 77 to 280 K. These experimental dynamic results are combined with calorimetric and diffraction data to show that after exhibiting a glass transition at 165 K, interfacial water experiences a first-order liquid-liquid transition at 240 K from a low-density to a high-density liquid. This is the first direct evidence of the existence of a liquid-liquid transition involving water.

Enhanced thermoelectric performance of amorphous Nb based oxynitrides

Energy Technology Data Exchange (ETDEWEB)

Music, Denis, E-mail: music@mch.rwth-aachen.de; Geyer, Richard W.; Hans, Marcus

2015-12-15

Using density functional theory, amorphous Nb{sub 0.27}Ru{sub 0.06}O{sub 0.56}N{sub 0.10} was designed to facilitate a combination of an enhanced Seebeck coefficient and low electrical resistivity. Based on a positive Cauchy pressure, ductile behavior is expected. To verify these predictions, the transport and mechanical properties of amorphous thin films were evaluated. Metallic electrical resistivity and the Seebeck coefficient of −94 µV K{sup −1} are obtained, which is consistent with our predictions. As there is no crack formation, these samples can be perceived as ductile. We demonstrate that the power factor can be increased by an order of magnitude, while keeping the thermal fatigue low.

Enhanced thermoelectric performance of amorphous Nb based oxynitrides

International Nuclear Information System (INIS)

Music, Denis; Geyer, Richard W.; Hans, Marcus

2015-01-01

Using density functional theory, amorphous Nb_0_._2_7Ru_0_._0_6O_0_._5_6N_0_._1_0 was designed to facilitate a combination of an enhanced Seebeck coefficient and low electrical resistivity. Based on a positive Cauchy pressure, ductile behavior is expected. To verify these predictions, the transport and mechanical properties of amorphous thin films were evaluated. Metallic electrical resistivity and the Seebeck coefficient of −94 µV K"−"1 are obtained, which is consistent with our predictions. As there is no crack formation, these samples can be perceived as ductile. We demonstrate that the power factor can be increased by an order of magnitude, while keeping the thermal fatigue low.

Glass-to-cryogenic-liquid transitions in aqueous solutions suggested by crack healing.

Science.gov (United States)

Kim, Chae Un; Tate, Mark W; Gruner, Sol M

2015-09-22

Observation of theorized glass-to-liquid transitions between low-density amorphous (LDA) and high-density amorphous (HDA) water states had been stymied by rapid crystallization below the homogeneous water nucleation temperature (∼235 K at 0.1 MPa). We report optical and X-ray observations suggestive of glass-to-liquid transitions in these states. Crack healing, indicative of liquid, occurs when LDA ice transforms to cubic ice at 160 K, and when HDA ice transforms to the LDA state at temperatures as low as 120 K. X-ray diffraction study of the HDA to LDA transition clearly shows the characteristics of a first-order transition. Study of the glass-to-liquid transitions in nanoconfined aqueous solutions shows them to be independent of the solute concentrations, suggesting that they represent an intrinsic property of water. These findings support theories that LDA and HDA ice are thermodynamically distinct and that they are continuously connected to two different liquid states of water.

Glass-to-cryogenic-liquid transitions in aqueous solutions suggested by crack healing

Science.gov (United States)

Kim, Chae Un; Tate, Mark W.; Gruner, Sol M.

2015-01-01

Observation of theorized glass-to-liquid transitions between low-density amorphous (LDA) and high-density amorphous (HDA) water states had been stymied by rapid crystallization below the homogeneous water nucleation temperature (∼235 K at 0.1 MPa). We report optical and X-ray observations suggestive of glass-to-liquid transitions in these states. Crack healing, indicative of liquid, occurs when LDA ice transforms to cubic ice at 160 K, and when HDA ice transforms to the LDA state at temperatures as low as 120 K. X-ray diffraction study of the HDA to LDA transition clearly shows the characteristics of a first-order transition. Study of the glass-to-liquid transitions in nanoconfined aqueous solutions shows them to be independent of the solute concentrations, suggesting that they represent an intrinsic property of water. These findings support theories that LDA and HDA ice are thermodynamically distinct and that they are continuously connected to two different liquid states of water. PMID:26351671

Crystalline and amorphous H2O on Charon

Science.gov (United States)

Dalle Ore, Cristina M.; Cruikshank, Dale P.; Grundy, Will M.; Ennico, Kimberly; Olkin, Catherine B.; Stern, S. Alan; Young, Leslie A.; Weaver, Harold A.

2015-11-01

Charon, the largest satellite of Pluto, is a gray-colored icy world covered mostly in H2O ice, with spectral evidence for NH3, as previously reported (Cook et al. 2007, Astrophys. J. 663, 1406-1419 Merlin, et al. 2010, Icarus, 210, 930; Cook, et al. 2014, AAS/Division for Planetary Sciences Meeting Abstracts, 46, #401.04). Images from the New Horizons spacecraft reveal a surface with terrains of widely different ages and a moderate degree of localized coloration. The presence of H2O ice in its crystalline form (Brown & Calvin 2000 Science 287, 107-109; Buie & Grundy 2000 Icarus 148, 324-339; Merlin et al, 2010) along with NH3 is consistent with a fresh surface.The phase of H2O ice is a key tracer of variations in temperature and physical conditions on the surface of outer Solar System objects. At Charon’s surface temperature H2O is expected to be amorphous, but ground-based observations (e.g., Merlin et al. 2010) show a clearly crystalline signature. From laboratory experiments it is known that amorphous H2O ice becomes crystalline at temperatures of ~130 K. Other mechanisms that can change the phase of the ice from amorphous to crystalline include micro-meteoritic bombardment (Porter et al. 2010, Icarus, 208, 492) or resurfacing processes such as cryovolcanism.New Horizons observed Charon with the LEISA imaging spectrometer, part of the Ralph instrument (Reuter, D.C., Stern, S.A., Scherrer, J., et al. 2008, Space Science Reviews, 140, 129). Making use of high spatial resolution (better than 10 km/px) and spectral resolving power of 240 in the wavelength range 1.25-2.5 µm, and 560 in the range 2.1-2.25 µm, we report on an analysis of the phase of H2O ice on parts of Charon’s surface with a view to investigate the recent history and evolution of this small but intriguing object.This work was supported by NASA’s New Horizons project.

DETECTIONS OF TRANS-NEPTUNIAN ICE IN PROTOPLANETARY DISKS

Energy Technology Data Exchange (ETDEWEB)

McClure, M. K.; Calvet, N.; Bergin, E.; Cleeves, L. I. [Department of Astronomy, The University of Michigan, 500 Church Street, 830 Dennison Bldg., Ann Arbor, MI 48109 (United States); Espaillat, C. [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); D' Alessio, P. [Centro de Radioastronomía y Astrofísica, Universidad NacionalAUtónoma de México, 58089 Morelia, Michoacán (Mexico); Watson, D. M. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Manoj, P. [Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005 (India); Sargent, B., E-mail: melisma@umich.edu, E-mail: ncalvet@umich.edu, E-mail: ebergin@umich.edu, E-mail: cleeves@umich.edu, E-mail: cce@bu.edu, E-mail: p.dalessio@crya.unam.mx, E-mail: dmw@pas.rochester.edu, E-mail: manoj.puravankara@tifr.res.in, E-mail: baspci@rit.edu [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

2015-02-01

We present Herschel Space Observatory PACS spectra of T Tauri stars, in which we detect amorphous and crystalline water ice features. Using irradiated accretion disk models, we determine the disk structure and ice abundance in each of the systems. Combining a model-independent comparison of the ice feature strength and disk size with a detailed analysis of the model ice location, we estimate that the ice emitting region is at disk radii >30 AU, consistent with a proto-Kuiper belt. Vertically, the ice emits most below the photodesorption zone, consistent with Herschel observations of cold water vapor. The presence of crystallized water ice at a disk location (1) colder than its crystallization temperature and (2) where it should have been re-amorphized in ∼1 Myr suggests that localized generation is occurring; the most likely cause appears to be micrometeorite impact or planetesimal collisions. Based on simple tests with UV models and different ice distributions, we suggest that the SED shape from 20 to 50 μm may probe the location of the water ice snowline in the disk upper layers. This project represents one of the first extra-solar probes of the spatial structure of the cometary ice reservoir thought to deliver water to terrestrial planets.

Nonequilibrium Phase Transitions in Supercooled Water

Science.gov (United States)

Limmer, David; Chandler, David

2012-02-01

We present results of a simulation study of water driven out of equilibrium. Using transition path sampling, we can probe stationary path distributions parameterize by order parameters that are extensive in space and time. We find that by coupling external fields to these parameters, we can drive water through a first order dynamical phase transition into amorphous ice. By varying the initial equilibrium distributions we can probe pathways for the creation of amorphous ices of low and high densities.

Characterisation of the nematode community of a low-activity cold seep in the recently ice-shelf free Larsen B area, Eastern Antarctic Peninsula.

Directory of Open Access Journals (Sweden)

Freija Hauquier

Full Text Available BACKGROUND: Recent climate-induced ice-shelf disintegration in the Larsen A (1995 and B (2002 areas along the Eastern Antarctic Peninsula formed a unique opportunity to assess sub-ice-shelf benthic community structure and led to the discovery of unexplored habitats, including a low-activity methane seep beneath the former Larsen B ice shelf. Since both limited particle sedimentation under previously permanent ice coverage and reduced cold-seep activity are likely to influence benthic meiofauna communities, we characterised the nematode assemblage of this low-activity cold seep and compared it with other, now seasonally ice-free, Larsen A and B stations and other Antarctic shelf areas (Weddell Sea and Drake Passage, as well as cold-seep ecosystems world-wide. PRINCIPAL FINDINGS: The nematode community at the Larsen B seep site differed significantly from other Antarctic sites in terms of dominant genera, diversity and abundance. Densities in the seep samples were high (>2000 individuals per 10 cm(2 and showed below-surface maxima at a sediment depth of 2-3 cm in three out of four replicates. All samples were dominated by one species of the family Monhysteridae, which was identified as a Halomonhystera species that comprised between 80 and 86% of the total community. The combination of high densities, deeper density maxima and dominance of one species is shared by many cold-seep ecosystems world-wide and suggested a possible dependence upon a chemosynthetic food source. Yet stable (13C isotopic signals (ranging between -21.97±0.86‰ and -24.85±1.89‰ were indicative of a phytoplankton-derived food source. CONCLUSION: The recent ice-shelf collapse and enhanced food input from surface phytoplankton blooms were responsible for the shift from oligotrophic pre-collapse conditions to a phytodetritus-based community with high densities and low diversity. The parthenogenetic reproduction of the highly dominant Halomonhystera species is rather unusual

Growth Mechanism for Low Temperature PVD Graphene Synthesis on Copper Using Amorphous Carbon

Science.gov (United States)

Narula, Udit; Tan, Cher Ming; Lai, Chao Sung

2017-03-01

Growth mechanism for synthesizing PVD based Graphene using Amorphous Carbon, catalyzed by Copper is investigated in this work. Different experiments with respect to Amorphous Carbon film thickness, annealing time and temperature are performed for the investigation. Copper film stress and its effect on hydrogen diffusion through the film grain boundaries are found to be the key factors for the growth mechanism, and supported by our Finite Element Modeling. Low temperature growth of Graphene is achieved and the proposed growth mechanism is found to remain valid at low temperatures.

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.

Amorphous metal composites

International Nuclear Information System (INIS)

Byrne, M.A.; Lupinski, J.H.

1984-01-01

This patent discloses an improved amorphous metal composite and process of making the composite. The amorphous metal composite comprises amorphous metal (e.g. iron) and a low molecular weight thermosetting polymer binder. The process comprises placing an amorphous metal in particulate form and a thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite

High pressure synthesis of amorphous TiO2 nanotubes

Directory of Open Access Journals (Sweden)

Quanjun Li

2015-09-01

Full Text Available Amorphous TiO2 nanotubes with diameters of 8-10 nm and length of several nanometers were synthesized by high pressure treatment of anatase TiO2 nanotubes. The structural phase transitions of anatase TiO2 nanotubes were investigated by using in-situ high-pressure synchrotron X-ray diffraction (XRD method. The starting anatase structure is stable up to ∼20GPa, and transforms into a high-density amorphous (HDA form at higher pressure. Pressure-modified high- to low-density transition was observed in the amorphous form upon decompression. The pressure-induced amorphization and polyamorphism are in good agreement with the previous results in ultrafine TiO2 nanoparticles and nanoribbons. The relationship between the LDA form and α-PbO2 phase was revealed by high-resolution transmission electron microscopy (HRTEM study. In addition, the bulk modulus (B0 = 158 GPa of the anatase TiO2 nanotubes is smaller than those of the corresponding bulks and nanoparticles (180-240 GPa. We suggest that the unique open-ended nanotube morphology and nanosize play important roles in the high pressure phase transition of TiO2 nanotubes.

Structure and thermal stability of biodegradable Mg-Zn-Ca based amorphous alloys synthesized by mechanical alloying

Energy Technology Data Exchange (ETDEWEB)

Datta, Moni Kanchan; Chou, Da-Tren; Hong, Daeho; Saha, Partha [Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Chung, Sung Jae [Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Lee, Bouen [Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Sirinterlikci, Arif [Department of Engineering, Robert Morris University, Moon Township, Pittsburgh, PA 15108 (United States); Ramanathan, Madhumati; Roy, Abhijit [Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Kumta, Prashant N., E-mail: matscib@gmail.com [Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (United States); School of Dental Medicine, University of Pittsburgh, Pittsburgh, PA 15261 (United States); Center for Complex Engineered Multifunctional Materials, University of Pittsburgh, Pittsburgh, PA 15261 (United States)

2011-12-15

Room temperature solid state diffusion reaction induced by mechanical alloying (MA) of elemental blends of Mg, Zn and Ca of nominal composition 60 at.% Mg-35 at.% Zn-5 at.% Ca has been studied. Formation of fully amorphous structure has been identified after 5 h of MA performed in a SPEX 8000M shaker mill, with milling continued up to 8 h to confirm the formation of homogeneous amorphous phase. Thermal stability of the amorphous phase has been studied using differential scanning calorimetry (DSC) and isothermal heat treatment at different temperatures. The amorphous powder consolidated using cold isostatic pressing (CIP) showed an envelope density {approx}80% of absolute density, which increased to an envelope density {approx}84% of absolute density after sintering at an optimized temperature of {approx}523 K for 9 h. Electrochemical bio-corrosion testing of the CIP compacted amorphous pellet as well as the sintered pellet performed in Dulbecco's Modified Eagle Medium, showed improved corrosion resistance in comparison to the as-cast pure Mg. Cytotoxicity testing of the CIP compacted amorphous pellet, performed using the MTT assay with MC3T3 osteoblastic cells, showed low cytotoxicity in comparison to the as-cast pure Mg.

Low density lesion in solid mass on CT: Pathologic change and housfield number

International Nuclear Information System (INIS)

Han, Tae Il; Lim, Joo Won; Ryu, Kyung Nam; Ko, Young Tae; Song, Mi Jin; Lee, Dong Ho; Lee, Ju Hie

1994-01-01

We retrospectively reviewed the pathologic changes and housfield unit of the low density lesion in solid mass on CT. Pathologically proved solid mass was evaluated in regard to the shape and margin of the low density in the mass on the CT scans of 23 patient. The CT number of the low density lesion was correlated with the pathologic changes. Pathologic changes of the low density lesions were; necrosis (n=17), hemorrhage (n=13), cyst (n=4), myxoid degeneration (n=2), hyaline degeneration (n=1), fibrosis (n=1), and mixed cellularity (n=1). In 14 cases, more than 2 pathologic changes were seen. In 11 cases, necrosis was associated with hemorrhage. The CT number ranged from 11.5 to 44.9 Housfield unit(HU) (mean, 25.2 HU). The average CT number was 26.9 HU in hemorrhage and necrosis, 17.2 HU in cystic change, 20.9 HU in myxoid degeneration, 35.7 HU in hyaline de generation, 22.3 HU in fibrosis, and 21.4 HU in mixed cellularity. The hemorrhage and necrosis in 17 cases showed irregular margin, amorphous shape, and showed centrifugal distribution. The cystic change in 4 cases showed well defined margin, round shape, and peripheral location in solid mass. The low density lesions in solid mass on CT represented variable pathologic changes; necrosis, hemorrhage, cyst, myxoid degeneration, hyaline degeneration, fibrosis, and mixed cellularity. Pathologic changes would not be differentiated on the basis of CT number

Low-density to high-density transition in Ce{sub 75}Al{sub 23}Si{sub 2} metallic glass

Energy Technology Data Exchange (ETDEWEB)

Zeng, Q S; Lou, H B; Gong, Y; Wang, X D; Jiang, J Z [International Center for New-Structured Materials, Zhejiang University, Hangzhou 310027 (China); Fang, Y Z; Wu, F M [College of Mathematics, Physics and Information Engineering, Zhejiang Normal University, Jinhua 321004, Zhejiang (China); Yang, K; Li, A G; Yan, S; Yu, X H [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201203 (China); Lathe, C, E-mail: qiaoshizeng@gmail.co, E-mail: jiangjz@zju.edu.c [HASYLAB am DESY, Notkestrasse 85, Hamburg D-22603 (Germany)

2010-09-22

Using in situ high-pressure x-ray diffraction (XRD), we observed a pressure-induced polyamorphic transition from the low-density amorphous (LDA) state to the high-density amorphous (HDA) state in Ce{sub 75}Al{sub 23}Si{sub 2} metallic glass at about 2 GPa and 300 K. The thermal stabilities of both LDA and HDA metallic glasses were further investigated using in situ high-temperature and high-pressure XRD, which revealed different pressure dependences of the onset crystallization temperature (T{sub x}) between them with a turning point at about 2 GPa. Compared with Ce{sub 75}Al{sub 25} metallic glass, minor Si doping shifts the onset polyamorphic transition pressure from 1.5 to 2 GPa and obviously stabilizes both LDA and HDA metallic glasses with higher T{sub x} and changes their slopes dT{sub x}/dP. The results obtained in this work reveal another polyamorphous metallic glass system by minor alloying (e.g. Si), which could modify the transition pressure and also properties of LDA and HDA metallic glasses. The minor alloying effect reported here is valuable for the development of more polyamorphous metallic glasses, even multicomponent bulk metallic glasses with modified properties, which will trigger more investigations in this field and improve our understanding of polyamorphism and metallic glasses.

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

In-situ determination of electronic surface and volume defect density of amorphous silicon (a-Si:H) and silicon alloys

International Nuclear Information System (INIS)

Siebke, F.

1992-07-01

The density of localized gap states in the bulk and in the near-surface region of amorphous hydrogenated silicon (a-Si:H) was measured for non oxidized undoped, B-doped and P-doped samples as well as for films with low carbon (C) and germanium (Ge) content. Also the influence of light soaking on the bulk and surface density of states was investigated. The samples were prepared by rf glow discharge in an UHV-system at substrate temperatures between 100degC and 400degC and transferred to the analysis chamber by a vacuum lock. We combined the constant photocurrent method (CPM) and the total-yield photoelectron spectroscopy (TY) to obtain in-situ information about the defect densities. While the first method yields information about the density of states in the bulk, the other method obtains the density of occupied states in the near-surface region. The mean information depth of the TY-measurements is limited by the escape lenght of photoelectrons and can be estimated to 5 nm. In addition to the defect density the position of the Fermi energy was determined for the bulk by dark conductivity measurements and at the surface using a calibrated Kelvin probe. (orig.)

High pressure synthesis of amorphous TiO{sub 2} nanotubes

Energy Technology Data Exchange (ETDEWEB)

Li, Quanjun; Liu, Ran; Wang, Tianyi; Xu, Ke; Dong, Qing; Liu, Bo; Liu, Bingbing, E-mail: liubb@jlu.edu.cn [State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012 (China); Liu, Jing [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

2015-09-15

Amorphous TiO{sub 2} nanotubes with diameters of 8-10 nm and length of several nanometers were synthesized by high pressure treatment of anatase TiO{sub 2} nanotubes. The structural phase transitions of anatase TiO{sub 2} nanotubes were investigated by using in-situ high-pressure synchrotron X-ray diffraction (XRD) method. The starting anatase structure is stable up to ∼20GPa, and transforms into a high-density amorphous (HDA) form at higher pressure. Pressure-modified high- to low-density transition was observed in the amorphous form upon decompression. The pressure-induced amorphization and polyamorphism are in good agreement with the previous results in ultrafine TiO{sub 2} nanoparticles and nanoribbons. The relationship between the LDA form and α-PbO{sub 2} phase was revealed by high-resolution transmission electron microscopy (HRTEM) study. In addition, the bulk modulus (B{sub 0} = 158 GPa) of the anatase TiO{sub 2} nanotubes is smaller than those of the corresponding bulks and nanoparticles (180-240 GPa). We suggest that the unique open-ended nanotube morphology and nanosize play important roles in the high pressure phase transition of TiO{sub 2} nanotubes.

Record low sea-ice concentration in the central Arctic during summer 2010

Science.gov (United States)

Zhao, Jinping; Barber, David; Zhang, Shugang; Yang, Qinghua; Wang, Xiaoyu; Xie, Hongjie

2018-01-01

The Arctic sea-ice extent has shown a declining trend over the past 30 years. Ice coverage reached historic minima in 2007 and again in 2012. This trend has recently been assessed to be unique over at least the last 1450 years. In the summer of 2010, a very low sea-ice concentration (SIC) appeared at high Arctic latitudes—even lower than that of surrounding pack ice at lower latitudes. This striking low ice concentration—referred to here as a record low ice concentration in the central Arctic (CARLIC)—is unique in our analysis period of 2003-15, and has not been previously reported in the literature. The CARLIC was not the result of ice melt, because sea ice was still quite thick based on in-situ ice thickness measurements. Instead, divergent ice drift appears to have been responsible for the CARLIC. A high correlation between SIC and wind stress curl suggests that the sea ice drift during the summer of 2010 responded strongly to the regional wind forcing. The drift trajectories of ice buoys exhibited a transpolar drift in the Atlantic sector and an eastward drift in the Pacific sector, which appeared to benefit the CARLIC in 2010. Under these conditions, more solar energy can penetrate into the open water, increasing melt through increased heat flux to the ocean. We speculate that this divergence of sea ice could occur more often in the coming decades, and impact on hemispheric SIC and feed back to the climate.

Record Low Sea-Ice Concentration in the Central Arctic during Summer 2010

Institute of Scientific and Technical Information of China (English)

Jinping ZHAO; David BARBER; Shugang ZHANG; Qinghua YANG; Xiaoyu WANG; Hongjie XIE

2018-01-01

The Arctic sea-ice extent has shown a declining trend over the past 30 years.Ice coverage reached historic minima in 2007 and again in 2012.This trend has recently been assessed to be unique over at least the last 1450 years.In the summer of 2010,a very low sea-ice concentration (SIC) appeared at high Arctic latitudes—even lower than that of surrounding pack ice at lower latitudes.This striking low ice concentration—referred to here as a record low ice concentration in the central Arctic (CARLIC)—is unique in our analysis period of 2003-15,and has not been previously reported in the literature.The CARLIC was not the result of ice melt,because sea ice was still quite thick based on in-situ ice thickness measurements.Instead,divergent ice drift appears to have been responsible for the CARLIC.A high correlation between SIC and wind stress curl suggests that the sea ice drift during the summer of 2010 responded strongly to the regional wind forcing.The drift trajectories of ice buoys exhibited a transpolar drift in the Atlantic sector and an eastward drift in the Pacific sector,which appeared to benefit the CARLIC in 2010.Under these conditions,more solar energy can penetrate into the open water,increasing melt through increased heat flux to the ocean.We speculate that this divergence of sea ice could occur more often in the coming decades,and impact on hemispheric SIC and feed back to the climate.

Significantly enhanced critical current density in nano-MgB2 grains rapidly formed at low temperature with homogeneous carbon doping

Science.gov (United States)

Liu, Yongchang; Lan, Feng; Ma, Zongqing; Chen, Ning; Li, Huijun; Barua, Shaon; Patel, Dipak; Shahriar, M.; Hossain, Al; Acar, S.; Kim, Jung Ho; Xue Dou, Shi

2015-05-01

High performance MgB2 bulks using carbon-coated amorphous boron as a boron precursor were fabricated by Cu-activated sintering at low temperature (600 °C, below the Mg melting point). Dense nano-MgB2 grains with a high level of homogeneous carbon doping were formed in these MgB2 samples. This type of microstructure can provide a stronger flux pinning force, together with depressed volatility and oxidation of Mg owing to the low-temperature Cu-activated sintering, leading to a significant improvement of critical current density (Jc) in the as-prepared samples. In particular, the value of Jc for the carbon-coated (Mg1.1B2)Cu0.05 sample prepared here is even above 1 × 105 A cm-2 at 20 K, 2 T. The results herein suggest that the combination of low-temperature Cu-activated sintering and employment of carbon-coated amorphous boron as a precursor could be a promising technique for the industrial production of practical MgB2 bulks or wires with excellent Jc, as the carbon-coated amorphous boron powder can be produced commercially at low cost, while the addition of Cu is very convenient and inexpensive.

ICE AND DUST IN THE PRESTELLAR DARK CLOUD LYNDS 183: PREPLANETARY MATTER AT THE LOWEST TEMPERATURES

Energy Technology Data Exchange (ETDEWEB)

Whittet, D. C. B.; Poteet, C. A.; Bajaj, V. M.; Horne, D. [Department of Physics, Applied Physics and Astronomy and New York Center for Astrobiology, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180 (United States); Chiar, J. E. [SETI Institute, Carl Sagan Center, 189 Bernardo Avenue, Mountain View, CA 94043 (United States); Pagani, L. [LERMA, UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l' Observatoire, F-75014 Paris (France); Shenoy, S. S. [SOFIA Science Center, NASA Ames Research Center, MS 232-12, Moffett Field, CA 94035 (United States); Adamson, A. J. [Gemini Observatory, Southern Operations Center, Casilla 603, La Serena (Chile)

2013-09-10

Dust grains are nucleation centers and catalysts for the growth of icy mantles in quiescent interstellar clouds, the products of which may accumulate into preplanetary matter when new stars and solar systems form within the clouds. In this paper, we present the first spectroscopic detections of silicate dust and the molecular ices H{sub 2}O, CO, and CO{sub 2} in the vicinity of the prestellar core L183 (L134N). An infrared photometric survey of the cloud was used to identify reddened background stars, and we present spectra covering solid-state absorption features in the wavelength range 2-20 {mu}m for nine of them. The mean composition of the ices in the best-studied line of sight (toward J15542044-0254073) is H{sub 2}O:CO:CO{sub 2} Almost-Equal-To 100:40:24. The ices are amorphous in structure, indicating that they have been maintained at low temperature ({approx}< 15 K) since formation. The ice column density N(H{sub 2}O) correlates with reddening by dust, exhibiting a threshold effect that corresponds to the transition from unmantled grains in the outer layers of the cloud to ice-mantled grains within, analogous to that observed in other dark clouds. A comparison of results for L183 and the Taurus and IC 5146 dark clouds suggests common behavior, with mantles first appearing in each case at a dust column corresponding to a peak optical depth {tau}{sub 9.7} = 0.15 {+-} 0.03 in the silicate feature. Our results support a previous conclusion that the color excess E{sub J-K} does not obey a simple linear correlation with the total dust column in lines of sight that intercept dense clouds. The most likely explanation is a systematic change in the optical properties of the dust as the density increases.

Structural and phase transformations in the low-temperature annealed amorphous “finemet”-type microwires

Energy Technology Data Exchange (ETDEWEB)

Tcherdyntsev, V.V., E-mail: vvch08@yandex.ru [National University of Science and Technology “MISIS”, Moscow 119049 (Russian Federation); Aleev, A.A. [SSC RF Institute for Theoretical and Experimental Physics, Moscow 117218 (Russian Federation); Churyukanova, M.N.; Kaloshkin, S.D. [National University of Science and Technology “MISIS”, Moscow 119049 (Russian Federation); Medvedeva, E.V. [Institute of Electrophysics, Ural Branch, Russian Academy of Sciences, Yekaterinburg 620016 (Russian Federation); Korchuganova, O.A. [SSC RF Institute for Theoretical and Experimental Physics, Moscow 117218 (Russian Federation); Zhukova, V. [Dpto. de Fns. Mater., UPV/EHU, San Sebastian 20018 (Spain); Zhukov, A.P. [Dpto. de Fns. Mater., UPV/EHU, San Sebastian 20018 (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain)

2014-02-15

Highlights: • Structure and magnetic properties evolution at heating of amorphous microwires was studied. • Relaxation processes in the amorphous phase correlate with an increase in Curie temperature. • Curie temperature change can not be stabilized by a prolonged exposure at pre-crystallization temperatures. • Tomographic atom probe microscopy supports the formation of α-Fe phase precipitations enriched in Si. -- Abstract: Finemet-type glass-coated microwires with amorphous and nanocrystalline structure have been investigated. The relaxation and crystallization processes at heating of amorphous alloy have been studied by DSC method. We observed that the relaxation processes in the amorphous phase correlate with an increasing of the Curie temperature. Additionally a prolonged exposure of the samples below the crystallization temperatures does not stabilize the Curie temperature change. An investigation by the tomographic atom probe microscopy supports the formation of precipitations, probably α-Fe phase, as a result of low-temperature annealing (400 °C, 5 min). We found that the observed nano-sized areas were enriched in silicon.

Structural and phase transformations in the low-temperature annealed amorphous “finemet”-type microwires

International Nuclear Information System (INIS)

Tcherdyntsev, V.V.; Aleev, A.A.; Churyukanova, M.N.; Kaloshkin, S.D.; Medvedeva, E.V.; Korchuganova, O.A.; Zhukova, V.; Zhukov, A.P.

2014-01-01

Highlights: • Structure and magnetic properties evolution at heating of amorphous microwires was studied. • Relaxation processes in the amorphous phase correlate with an increase in Curie temperature. • Curie temperature change can not be stabilized by a prolonged exposure at pre-crystallization temperatures. • Tomographic atom probe microscopy supports the formation of α-Fe phase precipitations enriched in Si. -- Abstract: Finemet-type glass-coated microwires with amorphous and nanocrystalline structure have been investigated. The relaxation and crystallization processes at heating of amorphous alloy have been studied by DSC method. We observed that the relaxation processes in the amorphous phase correlate with an increasing of the Curie temperature. Additionally a prolonged exposure of the samples below the crystallization temperatures does not stabilize the Curie temperature change. An investigation by the tomographic atom probe microscopy supports the formation of precipitations, probably α-Fe phase, as a result of low-temperature annealing (400 °C, 5 min). We found that the observed nano-sized areas were enriched in silicon

Glow discharge-deposited amorphous silicon films for low-cost solar cells

Energy Technology Data Exchange (ETDEWEB)

Grabmaier, J G; Plaettner, R D; Stetter, W [Siemens A.G., Muenchen (Germany, F.R.). Forschungslaboratorien

1980-01-01

Due to their high absorption constant, glow discharge-deposited amorphous silicon (a-Si) films are of great interest for low-cost solar cells. Using SiH/sub 4/ and SiX/sub 4//H/sub 2/ (X = Cl or F) gas mixtures in an inductively or capacitively excited reactor, a-Si films with thicknesses up to several micrometers were deposited on substrates of glass, silica and silicon. The optical and electrical properties of the films were determined by measuring the IR absorption spectra, dark conductivity, photoconductivity, and photoluminescence. Hydrogen, chlorine, or fluorine were incorporated in the films in order to passivate dangling bonds in the amorphous network.

Studies of pulsed laser melting and rapid solidification using amorphous silicon

International Nuclear Information System (INIS)

Lowndes, D.H.; Wood, R.F.

1984-06-01

Pulsed-laser melting of ion implantation-amorphized silicon layers, and subsequent solidification were studied. Measurements of the onset of melting of amorphous silicon layers and of the duration of melting, and modified melting model calculations demonstrated that the thermal conductivity, K/sub a/, of amorphous silicon is very low (K/sub a/ approx. = 0.02 W/cm-K). K/sub a/ is also the dominant parameter determining the dynamical response of amorphous silicon to pulsed laser radiation. TEM indicates that bulk (volume) nucleation occurs directly from the highly undercooled liquid silicon that can be prepared by pulsed laser melting of amorphous silicon layers at low laser energy densities. A modified thermal melting model is presented. The model calculations demonstrate that the release of latent heat by bulk nucleation occurring during the melt-in process is essential to obtaining agreement with observed depths of melting. These calculations also show that this release of latent heat accompanying bulk nucleation can result in the existence of buried molten layers of silicon in the interior of the sample after the surface has solidified. The bulk nucleation implies that the liquid-to-amorphous phase transition (produced using picosecond or uv nanosecond laser pulses) cannot be explained using purely thermodynamic considerations

Vibrational dynamics of amorphous metals by inelastic neutron and raman scattering

International Nuclear Information System (INIS)

Lustig, N.E.

1986-01-01

Time-of-flight inelastic neutron scattering and Raman measurements were performed on amorphous (a-) metals. The neutron-weighted vibrational density of states, G(E), obtained for a-Fe 78 P 22 , a-Ni 82 B 18 and a-Ni 67 B 33 transition metal metalloid alloys (TM-m), indicated two major vibrational bands: a low frequency acoustic-like band and a high frequency optic-like band, derived from TM-TM and TM-m interactions, respectively. Similar neutron measurements were performed on the corresponding polycrystalline (c-) alloys, c-Fe 3 P and c-Ni 2 B. A comparison of the amorphous and crystalline densities of states indicates the elimination of sharp features and the addition of vibrational states at low and high frequencies upon amorphization. The experimental G(E) results for a-Fe 78 P 22 are in good agreement with the theoretically predicted spectrum. A comparison between the a-Ni 67 B 33 and the phenomenologically broadened c-Ni 2 B spectrum indicates a change in the short-range order. This finding is consistent with structural measurements on this alloy. Raman measurements were carried out using interference enhanced Raman spectroscopy (IERS) on thin film Ni-B alloys. The measured spectra provide information about the weighted phonon density of states, and is in good agreement with the neutron results

Amorphous gallium oxide grown by low-temperature PECVD

KAUST Repository

Kobayashi, Eiji

2018-03-02

Owing to the wide application of metal oxides in energy conversion devices, the fabrication of these oxides using conventional, damage-free, and upscalable techniques is of critical importance in the optoelectronics community. Here, the authors demonstrate the growth of hydrogenated amorphous gallium oxide (a-GaO:H) thin-films by plasma-enhanced chemical vapor deposition (PECVD) at temperatures below 200 °C. In this way, conformal films are deposited at high deposition rates, achieving high broadband transparency, wide band gap (3.5-4 eV), and low refractive index (1.6 at 500 nm). The authors link this low refractive index to the presence of nanoscale voids enclosing H, as indicated by electron energy-loss spectroscopy. This work opens the path for further metal-oxide developments by low-temperature, scalable and damage-free PECVD processes.

Combined HRTEM and PEELS analysis of nanoporous and amorphous carbon

International Nuclear Information System (INIS)

Peng, J.L.; Fan, X. D.; Bursill, L.A.

1997-01-01

Both the mass density (1.37 kgm/m 3 ) and sp 2 +sp 3 bonding fraction (0.15) were determined for an unusual nanoporous amorphous carbon consisting of curved single graphitic sheets. A combination of high-resolution transmission electron microscopy (HRTEM) and parallel electron energy loss spectroscopy (PEELS) was used. The values of these two parameters provide important constraints for the determination of the structure of this relatively low density variety of nanoporous carbon. The results are relevant also in the search for negatively-curved Schwarzite-related carbon structures. New date are also presented for highly-oriented pyrollytic graphite (HOPG), chemically vapour deposited (CVD) diamond, C 60 , glassy carbon (GC) and evaporated amorphous carbon (EAC); these are compared with the results for NAC. Kramers-Kronig analysis (KKA) of the low-loss PEELS data shows that the band gaps of both NAC and EAC are collapsed relative to that of CVD diamond. 18 refs., 2 tabs., 3 figs

Combined HRTEM and PEELS analysis of nanoporous and amorphous carbon

Energy Technology Data Exchange (ETDEWEB)

Peng, J.L.; Fan, X. D.; Bursill, L.A.

1997-06-01

Both the mass density (1.37 kgm/m{sup 3}) and sp{sup 2}+sp{sup 3} bonding fraction (0.15) were determined for an unusual nanoporous amorphous carbon consisting of curved single graphitic sheets. A combination of high-resolution transmission electron microscopy (HRTEM) and parallel electron energy loss spectroscopy (PEELS) was used. The values of these two parameters provide important constraints for the determination of the structure of this relatively low density variety of nanoporous carbon. The results are relevant also in the search for negatively-curved Schwarzite-related carbon structures. New date are also presented for highly-oriented pyrollytic graphite (HOPG), chemically vapour deposited (CVD) diamond, C{sub 60}, glassy carbon (GC) and evaporated amorphous carbon (EAC); these are compared with the results for NAC. Kramers-Kronig analysis (KKA) of the low-loss PEELS data shows that the band gaps of both NAC and EAC are collapsed relative to that of CVD diamond. 18 refs., 2 tabs., 3 figs.

Agglomeration of amorphous silicon film with high energy density excimer laser irradiation

International Nuclear Information System (INIS)

He Ming; Ishihara, Ryoichi; Metselaar, Wim; Beenakker, Kees

2007-01-01

In this paper, agglomeration phenomena of amorphous Si (α-Si) films due to high energy density excimer laser irradiation are systematically investigated. The agglomeration, which creates holes or breaks the continuous Si film up into spherical beads, is a type of serious damage. Therefore, it determines an upper energy limit for excimer laser crystallization. It is speculated that the agglomeration is caused by the boiling of molten Si. During this process, outbursts of heterogeneously nucleated vapor bubbles are promoted by the poor wetting property of molten silicon on the SiO 2 layer underneath. The onset of the agglomeration is defined by extrapolating the hole density as a function of the energy density of the laser pulse. A SiO 2 capping layer (CL) is introduced on top of the α-Si film to investigate its influence on the agglomeration. It is found that effects of the CL depend on its thickness. The CL with a thickness less than 300 nm can be used to suppress the agglomeration. A thin CL acts as a confining layer and puts a constraint on bubble burst, and hence suppresses the agglomeration

Transportation properties of amorphous state InSb and its metastable middle phase

International Nuclear Information System (INIS)

Cao Xiaowen

1990-09-01

The variation of the substrate temperature induces the metal-semiconductor transition in the condensation InSb films at low temperatrue. The electron conduction is dominant in the metal-type amorphous InSb and the hole in semiconductor-type one. In the metal-type amorphous InSb the electron-electron is correlated under the field above 0.1T in the temperature region of liquid nitrogen. The structure relaxation leads to not only the increase of the short range order but also the change of electron structure in metal-type amorphous InSb. The first conductance jump originates mainly from the increase of Hall mobility of the carrier, i.e. the increase of the short range order, and the system relaxes from the liquid-like to the lattice-like amorphous state. The three types of the crystallization phase transition for the metal-type amorphous InSb present obviously different transportation behaviours. Both metal-type amorphous state and metastable middle phase of InSb all are one of superconducting system with the lowest carrier concentration (n 0 ∼10 18 cm -3 ). Superconducting T c of the metastable middle phase is related to the state density near Fermi surface, i.e. the higher T c corresponds to the higher state density. The quasi-two-dimensional structure is favourable to superconductivity

Determination of ice content in hardened concrete by low-temperature calorimetry

DEFF Research Database (Denmark)

Wu, Min; Johannesson, Björn; Geiker, Mette Rica

2014-01-01

Low-temperature calorimetry has been used to determine the ice content in concrete at different temperatures when exposed to low-temperature environments. However, the analysis of the ice content from the measured data of heat flow is not straightforward. In this study, two important factors...... influencing the ice content calculation are discussed. The importance of the baseline determination for the calculation of the ice content is realized. Two different methods of generating the baseline are discussed. First, the ‘J-baseline’ is discussed which is a recently proposed extrapolation method based...... the ‘J-baseline’ method and the ‘C-baseline’ method can be used to calculate the approximate baseline. The heat of fusion of the water confined in small pores is another important parameter to be considered in ice content calculation. This property must be carefully analyzed in order to accurately...

Extreme Low Light Requirement for Algae Growth Underneath Sea Ice

DEFF Research Database (Denmark)

Hancke, Kasper; Lund-Hansen, Lars C.; Lamare, Maxim L.

2018-01-01

Microalgae colonizing the underside of sea ice in spring are a key component of the Arctic foodweb as they drive early primary production and transport of carbon from the atmosphere to the ocean interior. Onset of the spring bloom of ice algae is typically limited by the availability of light......, and the current consensus is that a few tens-of-centimeters of snow is enough to prevent sufficient solar radiation to reach underneath the sea ice. We challenge this consensus, and investigated the onset and the light requirement of an ice algae spring bloom, and the importance of snow optical properties...... for light penetration. Colonization by ice algae began in May under >1 m of first-year sea ice with approximate to 1 m thick snow cover on top, in NE Greenland. The initial growth of ice algae began at extremely low irradiance (...

What controls the low ice number concentration in the upper troposphere?

Directory of Open Access Journals (Sweden)

C. Zhou

2016-10-01

Full Text Available Cirrus clouds in the tropical tropopause play a key role in regulating the moisture entering the stratosphere through their dehydrating effect. Low ice number concentrations ( <  200 L−1 and high supersaturations (150–160 % have been observed in these clouds. Different mechanisms have been proposed to explain these low ice number concentrations, including the inhibition of homogeneous freezing by the deposition of water vapour onto pre-existing ice crystals, heterogeneous ice formation on glassy organic aerosol ice nuclei (IN, and limiting the formation of ice number from high-frequency gravity waves. In this study, we examined the effect from three different representations of updraft velocities, the effect from pre-existing ice crystals, the effect from different water vapour deposition coefficients (α  =  0.1 or 1, and the effect of 0.1 % of the total secondary organic aerosol (SOA particles acting as IN. Model-simulated ice crystal numbers are compared against an aircraft observational dataset.Including the effect from water vapour deposition on pre-existing ice particles can effectively reduce simulated in-cloud ice number concentrations for all model setups. A larger water vapour deposition coefficient (α  =  1 can also efficiently reduce ice number concentrations at temperatures below 205 K, but less so at higher temperatures. SOA acting as IN is most effective at reducing ice number concentrations when the effective updraft velocities are moderate ( ∼  0.05–0.2 m s−1. However, the effects of including SOA as IN and using (α  =  1 are diminished when the effect from pre-existing ice is included.When a grid-resolved large-scale updraft velocity ( <  0.1 m s−1 is used, the ice nucleation parameterization with homogeneous freezing only or with both homogeneous freezing and heterogeneous nucleation is able to generate low ice number concentrations in good agreement

Monte Carlo kinetics simulations of ice-mantle formation on interstellar grains

Science.gov (United States)

Garrod, Robin

2015-08-01

The majority of interstellar dust-grain chemical kinetics models use rate equations, or alternative population-based simulation methods, to trace the time-dependent formation of grain-surface molecules and ice mantles. Such methods are efficient, but are incapable of considering explicitly the morphologies of the dust grains, the structure of the ices formed thereon, or the influence of local surface composition on the chemistry.A new Monte Carlo chemical kinetics model, MIMICK, is presented here, whose prototype results were published recently (Garrod 2013, ApJ, 778, 158). The model calculates the strengths and positions of the potential mimima on the surface, on the fly, according to the individual pair-wise (van der Waals) bonds between surface species, allowing the structure of the ice to build up naturally as surface diffusion and chemistry occur. The prototype model considered contributions to a surface particle's potential only from contiguous (or "bonded") neighbors; the full model considers contributions from surface constituents from short to long range. Simulations are conducted on a fully 3-D user-generated dust-grain with amorphous surface characteristics. The chemical network has also been extended from the simple water system previously published, and now includes 33 chemical species and 55 reactions. This allows the major interstellar ice components to be simulated, such as water, methane, ammonia and methanol, as well as a small selection of more complex molecules, including methyl formate (HCOOCH3).The new model results indicate that the porosity of interstellar ices are dependent on multiple variables, including gas density, the dust temperature, and the relative accretion rates of key gas-phase species. The results presented also have implications for the formation of complex organic molecules on dust-grain surfaces at very low temperatures.

Intrinsic charge trapping in amorphous oxide films: status and challenges

Science.gov (United States)

Strand, Jack; Kaviani, Moloud; Gao, David; El-Sayed, Al-Moatasem; Afanas’ev, Valeri V.; Shluger, Alexander L.

2018-06-01

We review the current understanding of intrinsic electron and hole trapping in insulating amorphous oxide films on semiconductor and metal substrates. The experimental and theoretical evidences are provided for the existence of intrinsic deep electron and hole trap states stemming from the disorder of amorphous metal oxide networks. We start from presenting the results for amorphous (a) HfO2, chosen due to the availability of highest purity amorphous films, which is vital for studying their intrinsic electronic properties. Exhaustive photo-depopulation spectroscopy measurements and theoretical calculations using density functional theory shed light on the atomic nature of electronic gap states responsible for deep electron trapping observed in a-HfO2. We review theoretical methods used for creating models of amorphous structures and electronic structure calculations of amorphous oxides and outline some of the challenges in modeling defects in amorphous materials. We then discuss theoretical models of electron polarons and bi-polarons in a-HfO2 and demonstrate that these intrinsic states originate from low-coordinated ions and elongated metal-oxygen bonds in the amorphous oxide network. Similarly, holes can be captured at under-coordinated O sites. We then discuss electron and hole trapping in other amorphous oxides, such as a-SiO2, a-Al2O3, a-TiO2. We propose that the presence of low-coordinated ions in amorphous oxides with electron states of significant p and d character near the conduction band minimum can lead to electron trapping and that deep hole trapping should be common to all amorphous oxides. Finally, we demonstrate that bi-electron trapping in a-HfO2 and a-SiO2 weakens Hf(Si)–O bonds and significantly reduces barriers for forming Frenkel defects, neutral O vacancies and O2‑ ions in these materials. These results should be useful for better understanding of electronic properties and structural evolution of thin amorphous films under carrier injection

Contribution to the study of the mechanism of crack in amorphous silica: study by the molecular dynamics of crack in amorphous silica; Contribution a l'etude des mecanismes de rupture dans les amorphes: etude par dynamique moleculaire de la rupture de verre de silice

Energy Technology Data Exchange (ETDEWEB)

Van Brutzel, L

2000-07-01

The aim of this thesis was to understand the mechanism which occurs during the crack at the atomic scale in amorphous silica. The difficulties of the experimental observations at this length scale lead us to use numerical studies by molecular dynamics to access to the dynamical and the thermodynamical informations. We have carried out large simulations with 500000 atoms and studied the structure of the amorphous silica before to studying their behaviours under an imposed strain. The structure of this simulated amorphous silica settled in three length scales. In small length scale between 0 and 5 angstrom glass is composed of tetrahedra, this is close to the crystalline structure. In intermediate length scale between 3 and 10 angstrom tetrahedra are connected together and build rings of different sizes composed in majority between 5 and 7 tetrahedra. In bigger length scale between 15 and 60 angstrom, areas with high density of rings are surrounded by areas with low density of rings. These structural considerations play an important role in initiation and propagation of a crack. Indeed. in this length scale. crack propagates by growth and coalescence of some small cavities which appear in area with low density of rings behind the crack tip. The cavities dissipate the stress with carries away a delay to propagation of the crack. This phenomenons seems ductile and leads to non linear elastic behaviour near the crack tip. We have also shown that the addition of alkali in the amorphous silica changes the structure by creation of nano-porosities and leads to enhance the ductility during the crack propagation. (author)

A COMPREHENSIVE STUDY OF HYDROGEN ADSORBING TO AMORPHOUS WATER ICE: DEFINING ADSORPTION IN CLASSICAL MOLECULAR DYNAMICS

Energy Technology Data Exchange (ETDEWEB)

Dupuy, John L.; Lewis, Steven P.; Stancil, P. C. [Department of Physics and Astronomy and the Center for Simulational Physics, University of Georgia, Athens, GA 30602 (United States)

2016-11-01

Gas–grain and gas–phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas–grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H{sub 2}) in the ISM is the prototypical example of a gas–grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5–400 K] across seven different temperatures of dust grains [10–70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99–0.22.

Physical properties of drawn very low density polyethylene films

Energy Technology Data Exchange (ETDEWEB)

Kim, B.S. [Yeungnam University, Kyongsan (Korea, Republic of); Lee, J.Y. [Korea Institute of Footwear and Leather Technology, Pusan (Korea, Republic of)

1998-05-01

Very low density polyethylene (VLDPE) films were prepared by quenching the pressed melt in ice water. The films were drawn with universal testing machine under constant temperature at four different temperatures, 30, 60, 80, and 110 {sup o} C. Thermal, mechanical properties, grossity, and gas permeability of the drawn VLDPE films as a function of draw ratio were investigated to examine their applicability to packaging. The films showed tow melting peaks, i.e., low temperature endotherm (LTE) and high temperature endotherm (HTE). The melting temperatures were increased with the draw ratio and the drawing temperature. The mechanical properties of the VLDPE film drawn at 80 {sup o} C were superior to those drawn at 110 {sup o} C. The grossity and gas permeability of the VLDPE film drawn at 110 {sup o} C were found to be best among the drawn films.

Low hydrogen containing amorphous carbon films - Growth and electrochemical properties as lithium battery anodes

Energy Technology Data Exchange (ETDEWEB)

Subramanian, V.; Masarapu, Charan; Wei, Bingqing [Department of Mechanical Engineering, University of Delaware, 130 Academy Street, Newark, DE 19716 (United States); Karabacak, Tansel [Department of Applied Science, University of Arkansas at Little Rock, 2801 South University Avenue, Little Rock, AR 72204 (United States); Teki, Ranganath [Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Lu, Toh-Ming [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States)

2010-04-02

Amorphous carbon films were deposited successfully on Cu foils by DC magnetron sputtering technique. Electrochemical performance of the film as lithium battery anode was evaluated across Li metal at 0.2 C rate in a non-aqueous electrolyte. The discharge curves showed unusually low irreversible capacity in the first cycle with a reversible capacity of {proportional_to}810 mAh g{sup -1}, which is at least 2 times higher than that of graphitic carbon. For the first time we report here an amorphous carbon showing such a high reversibility in the first cycle, which is very much limited to the graphitic carbon. The deposited films were extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profilometer for the structural and surface properties. The hydrogen content of the synthesized films was studied using residual gas analysis (RGA). The low hydrogen content and the low specific surface area of the synthesized amorphous carbon film are considered responsible for such a high first cycle columbic efficiency. The growth mechanism and the reasons for enhanced electrochemical performance of the carbon films are discussed. (author)

Low hydrogen containing amorphous carbon films-Growth and electrochemical properties as lithium battery anodes

Science.gov (United States)

Subramanian, V.; Karabacak, Tansel; Masarapu, Charan; Teki, Ranganath; Lu, Toh-Ming; Wei, Bingqing

Amorphous carbon films were deposited successfully on Cu foils by DC magnetron sputtering technique. Electrochemical performance of the film as lithium battery anode was evaluated across Li metal at 0.2 C rate in a non-aqueous electrolyte. The discharge curves showed unusually low irreversible capacity in the first cycle with a reversible capacity of ∼810 mAh g -1, which is at least 2 times higher than that of graphitic carbon. For the first time we report here an amorphous carbon showing such a high reversibility in the first cycle, which is very much limited to the graphitic carbon. The deposited films were extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profilometer for the structural and surface properties. The hydrogen content of the synthesized films was studied using residual gas analysis (RGA). The low hydrogen content and the low specific surface area of the synthesized amorphous carbon film are considered responsible for such a high first cycle columbic efficiency. The growth mechanism and the reasons for enhanced electrochemical performance of the carbon films are discussed.

Differences between pressure-induced densification of LiCl-H{sub 2}O glass and polyamorphic transition of H{sub 2}O

Energy Technology Data Exchange (ETDEWEB)

Suzuki, Yoshiharu; Mishima, Osamu [Polyamorphism Group, Advanced Nano Materials Laboratory, National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki, 305-0044 (Japan)], E-mail: SUZUKI.Yoshiharu@nims.go.jp

2009-04-15

We perform volumetric measurements of LiCl aqueous solution up to 1.00 GPa in the 100-170 K range, examine the pressure-induced vitrification and densification, and draw the pressure-temperature-volume surface. The pressure-induced vitrification of the solution corresponds to the cooling-induced vitrification of the liquid. We found that the volumetric decrease of glassy solution during the densification is continuous and this behavior depends on the glassy state before the compression. Raman profiles of the glassy solutions before and after the densification are similar. In contrast, the polyamorphic transition from low-density amorphous ice (LDA) to high-density amorphous ice (HDA) is discontinuous and their Raman profile before and after the transition is distinct. These results suggest that the densification relates to the structural relaxation and differs intrinsically from the polyamorphic transition. Furthermore, the densification of HDA is observed under high pressure, suggesting that very high-density amorphous ice (VHDA) may be the densified HDA. In order to recognize a polyamorphic transition under a non-equilibrium condition correctly, evidence of not only large volume change but also some distinct structural changes in glassy state is necessary.

Differences between pressure-induced densification of LiCl-H2O glass and polyamorphic transition of H2O

International Nuclear Information System (INIS)

Suzuki, Yoshiharu; Mishima, Osamu

2009-01-01

We perform volumetric measurements of LiCl aqueous solution up to 1.00 GPa in the 100-170 K range, examine the pressure-induced vitrification and densification, and draw the pressure-temperature-volume surface. The pressure-induced vitrification of the solution corresponds to the cooling-induced vitrification of the liquid. We found that the volumetric decrease of glassy solution during the densification is continuous and this behavior depends on the glassy state before the compression. Raman profiles of the glassy solutions before and after the densification are similar. In contrast, the polyamorphic transition from low-density amorphous ice (LDA) to high-density amorphous ice (HDA) is discontinuous and their Raman profile before and after the transition is distinct. These results suggest that the densification relates to the structural relaxation and differs intrinsically from the polyamorphic transition. Furthermore, the densification of HDA is observed under high pressure, suggesting that very high-density amorphous ice (VHDA) may be the densified HDA. In order to recognize a polyamorphic transition under a non-equilibrium condition correctly, evidence of not only large volume change but also some distinct structural changes in glassy state is necessary.

Significantly enhanced critical current density in nano-MgB2 grains rapidly formed at low temperature with homogeneous carbon doping

International Nuclear Information System (INIS)

Liu, Yongchang; Lan, Feng; Ma, Zongqing; Chen, Ning; Li, Huijun; Barua, Shaon; Patel, Dipak; Shahriar, M; Hossain, Al; Kim, Jung Ho; Dou, Shi Xue; Acar, S

2015-01-01

High performance MgB 2 bulks using carbon-coated amorphous boron as a boron precursor were fabricated by Cu-activated sintering at low temperature (600 °C, below the Mg melting point). Dense nano-MgB 2 grains with a high level of homogeneous carbon doping were formed in these MgB 2 samples. This type of microstructure can provide a stronger flux pinning force, together with depressed volatility and oxidation of Mg owing to the low-temperature Cu-activated sintering, leading to a significant improvement of critical current density (J c ) in the as-prepared samples. In particular, the value of J c for the carbon-coated (Mg 1.1 B 2 )Cu 0.05 sample prepared here is even above 1 × 10 5 A cm −2 at 20 K, 2 T. The results herein suggest that the combination of low-temperature Cu-activated sintering and employment of carbon-coated amorphous boron as a precursor could be a promising technique for the industrial production of practical MgB 2 bulks or wires with excellent J c , as the carbon-coated amorphous boron powder can be produced commercially at low cost, while the addition of Cu is very convenient and inexpensive. (paper)

Lithium implantation at low temperature in silicon for sharp buried amorphous layer formation and defect engineering

International Nuclear Information System (INIS)

Oliviero, E.; David, M. L.; Beaufort, M. F.; Barbot, J. F.; Fichtner, P. F. P.

2013-01-01

The crystalline-to-amorphous transformation induced by lithium ion implantation at low temperature has been investigated. The resulting damage structure and its thermal evolution have been studied by a combination of Rutherford backscattering spectroscopy channelling (RBS/C) and cross sectional transmission electron microscopy (XTEM). Lithium low-fluence implantation at liquid nitrogen temperature is shown to produce a three layers structure: an amorphous layer surrounded by two highly damaged layers. A thermal treatment at 400 °C leads to the formation of a sharp amorphous/crystalline interfacial transition and defect annihilation of the front heavily damaged layer. After 600 °C annealing, complete recrystallization takes place and no extended defects are left. Anomalous recrystallization rate is observed with different motion velocities of the a/c interfaces and is ascribed to lithium acting as a surfactant. Moreover, the sharp buried amorphous layer is shown to be an efficient sink for interstitials impeding interstitial supersaturation and {311} defect formation in case of subsequent neon implantation. This study shows that lithium implantation at liquid nitrogen temperature can be suitable to form a sharp buried amorphous layer with a well-defined crystalline front layer, thus having potential applications for defects engineering in the improvement of post-implantation layers quality and for shallow junction formation.

Weak interactions between water and clathrate-forming gases at low pressures

Energy Technology Data Exchange (ETDEWEB)

Thurmer, Konrad; Yuan, Chunqing; Kimmel, Gregory A.; Kay, Bruce D.; Smith, R. Scott

2015-11-01

Using scanning probe microscopy and temperature programed desorption we examined the interaction between water and two common clathrate-forming gases, methane and isobutane, at low temperature and low pressure. Water co-deposited with up to 10-1 mbar methane or 10-5 mbar isobutane at 140 K onto a Pt(111) substrate yielded pure crystalline ice, i.e., the exposure to up to ~107 gas molecules for each deposited water molecule did not have any detectable effect on the growing films. Exposing metastable, less than 2 molecular layers thick, water films to 10-5 mbar methane does not alter their morphology, suggesting that the presence of the Pt(111) surface is not a strong driver for hydrate formation. This weak water-gas interaction at low pressures is supported by our thermal desorption measurements from amorphous solid water and crystalline ice where 1 ML of methane desorbs near ~43 K and isobutane desorbs near ~100 K. Similar desorption temperatures were observed for desorption from amorphous solid water.

Bonding topologies in diamondlike amorphous-carbon films

International Nuclear Information System (INIS)

Siegal, M. P.; Provencio, P. N.; Tallant, D. R.; Simpson, R. L.; Kleinsorge, B.; Milne, W. I.

2000-01-01

The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding topologies of amorphous-carbon (a-C) films. Regions of relatively low density occur near the substrate/film and film/surface interfaces; their thicknesses increase with deposition energy. The ion subplantation growth results in mass density gradients in the bulk portion of a-C in the growth direction; density decreases with distance from the substrate for films grown using ion energies 160 eV. Films grown between these energies are the most diamondlike with relatively uniform bulk density and the highest optical transparencies. Bonding topologies evolve with increasing growth energy consistent with the propagation of subplanted carbon ions inducing a partial transformation of σ- to π-bonded carbon atoms. (c) 2000 American Institute of Physics

Physics of amorphous metals

CERN Document Server

Kovalenko, Nikolai P; Krey, Uwe

2008-01-01

The discovery of bulk metallic glasses has led to a large increase in the industrial importance of amorphous metals, and this is expected to continue. This book is the first to describe the theoretical physics of amorphous metals, including the important theoretical development of the last 20 years.The renowned authors stress the universal aspects in their description of the phonon or magnon low-energy excitations in the amorphous metals, e.g. concerning the remarkable consequences of the properties of these excitations for the thermodynamics at low and intermediate temperatures. Tunneling

Friction and wear measurements of sputtered MoS/sub x/ films amorphized by ion bombardment

International Nuclear Information System (INIS)

Mikkelsen, N.J.; Chevallier, J.; Soerensen, G.; Straede, C.A.

1988-01-01

The present study presents an experimental evidence for amorphization of rf sputtered MoS/sub x/ films by ion bombardment. Even at low doses (3 x 10 15 ions/cm 2 ) of 400 keV argon ions a complete amorphization was confirmed by x-ray diffraction analysis and transmission electron microscopy. As a result of the ion bombardment the film density increased 100% to almost the bulk value for MoS 2 . The friction coefficient for ion beam amorphized MoS/sub x/ was measured to be 0.04 in agreement with the values reported for crystalline films but disagreeing considerably with the friction coefficient of 0.4 previously reported for amorphous films

Electronic transport in amorphous phase-change materials

International Nuclear Information System (INIS)

Luckas, Jennifer Maria

2012-01-01

-GeTe is shown to consist of a shallow and deep defect band in addition to the band tail states. Furthermore, this study on a-GeTe has shown that the data analysis within MPC experiments can be drastically improved. This thesis illustrates on the example of a-GeTe and a-Ge 2 Sb 2 Te 5 , that the problem of unphysical low values for the attempt-to-escape frequency of the order 10 8 s -1 can be resolved by taking the temperature dependence of the band gap into account. In this work the defect state density of three different electrical switching alloys a-GeTe, a-Ge 2 Sb 2 Te 5 and a-Ge 15 Te 85 has been investigated. In a generation-recombination model the threshold field is expected to increase with increasing optical band gap and increasing mid gap-state density. However, a-GeTe, a-Ge 2 Sb 2 Te 5 and a-Ge 15 Te 85 show a large variation in their corresponding electrical threshold fields, which can be not understood by their change in optical band gap value alone. This observation raises the question of the role of localized defect states. MPC experiments reveal that the measured density of mid gap states is observed to decrease with decreasing threshold field known from literature. This result favors a generationrecombination model behind electrical switching in amorphous chalcogenides as originally proposed by Adler. To get a better understanding of resistance drift phenomena this study focuses on the evolution of resistivity on heating and ageing, activation energy of electronic conduction, optical band gap, defect state density, mechanical stress and nearest neighbor ordering in a-GeTe thin films. After heating the samples one hour at 140 C the activation energy for electric conduction increases by 30 meV, while the optical band gap increases by 60 meV. In addition to band gap opening MPC experiments on the same a-GeTe thin film at different sample ages have revealed complex trap kinetics. Ageing results in an increasing concentration of shallow defect states, whereas

Electronic transport in amorphous phase-change materials

Energy Technology Data Exchange (ETDEWEB)

Luckas, Jennifer Maria

2012-09-14

-GeTe is shown to consist of a shallow and deep defect band in addition to the band tail states. Furthermore, this study on a-GeTe has shown that the data analysis within MPC experiments can be drastically improved. This thesis illustrates on the example of a-GeTe and a-Ge{sub 2}Sb{sub 2}Te{sub 5}, that the problem of unphysical low values for the attempt-to-escape frequency of the order 10{sup 8}s{sup -1} can be resolved by taking the temperature dependence of the band gap into account. In this work the defect state density of three different electrical switching alloys a-GeTe, a-Ge{sub 2}Sb{sub 2}Te{sub 5} and a-Ge{sub 15}Te{sub 85} has been investigated. In a generation-recombination model the threshold field is expected to increase with increasing optical band gap and increasing mid gap-state density. However, a-GeTe, a-Ge{sub 2}Sb{sub 2}Te{sub 5} and a-Ge{sub 15}Te{sub 85} show a large variation in their corresponding electrical threshold fields, which can be not understood by their change in optical band gap value alone. This observation raises the question of the role of localized defect states. MPC experiments reveal that the measured density of mid gap states is observed to decrease with decreasing threshold field known from literature. This result favors a generationrecombination model behind electrical switching in amorphous chalcogenides as originally proposed by Adler. To get a better understanding of resistance drift phenomena this study focuses on the evolution of resistivity on heating and ageing, activation energy of electronic conduction, optical band gap, defect state density, mechanical stress and nearest neighbor ordering in a-GeTe thin films. After heating the samples one hour at 140 C the activation energy for electric conduction increases by 30 meV, while the optical band gap increases by 60 meV. In addition to band gap opening MPC experiments on the same a-GeTe thin film at different sample ages have revealed complex trap kinetics. Ageing results

A Density Functional Tight Binding Study of Acetic Acid Adsorption on Crystalline and Amorphous Surfaces of Titania

Directory of Open Access Journals (Sweden)

Sergei Manzhos

2015-02-01

Full Text Available We present a comparative density functional tight binding study of an organic molecule attachment to TiO2 via a carboxylic group, with the example of acetic acid. For the first time, binding to low-energy surfaces of crystalline anatase (101, rutile (110 and (B-TiO2 (001, as well as to the surface of amorphous (a- TiO2 is compared with the same computational setup. On all surfaces, bidentate configurations are identified as providing the strongest adsorption energy, Eads = −1.93, −2.49 and −1.09 eV for anatase, rutile and (B-TiO2, respectively. For monodentate configurations, the strongest Eads = −1.06, −1.11 and −0.86 eV for anatase, rutile and (B-TiO2, respectively. Multiple monodentate and bidentate configurations are identified on a-TiO2 with a distribution of adsorption energies and with the lowest energy configuration having stronger bonding than that of the crystalline counterparts, with Eads up to −4.92 eV for bidentate and −1.83 eV for monodentate adsorption. Amorphous TiO2 can therefore be used to achieve strong anchoring of organic molecules, such as dyes, that bind via a -COOH group. While the presence of the surface leads to a contraction of the band gap vs. the bulk, molecular adsorption caused no appreciable effect on the band structure around the gap in any of the systems.

Heavy ion irradiation of crystalline water ice. Cosmic ray amorphisation cross-section and sputtering yield

Science.gov (United States)

Dartois, E.; Augé, B.; Boduch, P.; Brunetto, R.; Chabot, M.; Domaracka, A.; Ding, J. J.; Kamalou, O.; Lv, X. Y.; Rothard, H.; da Silveira, E. F.; Thomas, J. C.

2015-04-01

Context. Under cosmic irradiation, the interstellar water ice mantles evolve towards a compact amorphous state. Crystalline ice amorphisation was previously monitored mainly in the keV to hundreds of keV ion energies. Aims: We experimentally investigate heavy ion irradiation amorphisation of crystalline ice, at high energies closer to true cosmic rays, and explore the water-ice sputtering yield. Methods: We irradiated thin crystalline ice films with MeV to GeV swift ion beams, produced at the GANIL accelerator. The ice infrared spectral evolution as a function of fluence is monitored with in-situ infrared spectroscopy (induced amorphisation of the initial crystalline state into a compact amorphous phase). Results: The crystalline ice amorphisation cross-section is measured in the high electronic stopping-power range for different temperatures. At large fluence, the ice sputtering is measured on the infrared spectra, and the fitted sputtering-yield dependence, combined with previous measurements, is quadratic over three decades of electronic stopping power. Conclusions: The final state of cosmic ray irradiation for porous amorphous and crystalline ice, as monitored by infrared spectroscopy, is the same, but with a large difference in cross-section, hence in time scale in an astrophysical context. The cosmic ray water-ice sputtering rates compete with the UV photodesorption yields reported in the literature. The prevalence of direct cosmic ray sputtering over cosmic-ray induced photons photodesorption may be particularly true for ices strongly bonded to the ice mantles surfaces, such as hydrogen-bonded ice structures or more generally the so-called polar ices. Experiments performed at the Grand Accélérateur National d'Ions Lourds (GANIL) Caen, France. Part of this work has been financed by the French INSU-CNRS programme "Physique et Chimie du Milieu Interstellaire" (PCMI) and the ANR IGLIAS.

Dust Density Distribution and Imaging Analysis of Different Ice Lines in Protoplanetary Disks

Energy Technology Data Exchange (ETDEWEB)

Pinilla, P. [Department of Astronomy/Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Pohl, A. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Stammler, S. M.; Birnstiel, T., E-mail: pinilla@email.arizona.edu [University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, D-81679 Münich (Germany)

2017-08-10

Recent high angular resolution observations of protoplanetary disks at different wavelengths have revealed several kinds of structures, including multiple bright and dark rings. Embedded planets are the most used explanation for such structures, but there are alternative models capable of shaping the dust in rings as it has been observed. We assume a disk around a Herbig star and investigate the effect that ice lines have on the dust evolution, following the growth, fragmentation, and dynamics of multiple dust size particles, covering from 1 μ m to 2 m sized objects. We use simplified prescriptions of the fragmentation velocity threshold, which is assumed to change radially at the location of one, two, or three ice lines. We assume changes at the radial location of main volatiles, specifically H{sub 2}O, CO{sub 2}, and NH{sub 3}. Radiative transfer calculations are done using the resulting dust density distributions in order to compare with current multiwavelength observations. We find that the structures in the dust density profiles and radial intensities at different wavelengths strongly depend on the disk viscosity. A clear gap of emission can be formed between ice lines and be surrounded by ring-like structures, in particular between the H{sub 2}O and CO{sub 2} (or CO). The gaps are expected to be shallower and narrower at millimeter emission than at near-infrared, opposite to model predictions of particle trapping. In our models, the total gas surface density is not expected to show strong variations, in contrast to other gap-forming scenarios such as embedded giant planets or radial variations of the disk viscosity.

Antarctic krill under sea ice: elevated abundance in a narrow band just south of ice edge.

Science.gov (United States)

Brierley, Andrew S; Fernandes, Paul G; Brandon, Mark A; Armstrong, Frederick; Millard, Nicholas W; McPhail, Steven D; Stevenson, Peter; Pebody, Miles; Perrett, James; Squires, Mark; Bone, Douglas G; Griffiths, Gwyn

2002-03-08

We surveyed Antarctic krill (Euphausia superba) under sea ice using the autonomous underwater vehicle Autosub-2. Krill were concentrated within a band under ice between 1 and 13 kilometers south of the ice edge. Within this band, krill densities were fivefold greater than that of open water. The under-ice environment has long been considered an important habitat for krill, but sampling difficulties have previously prevented direct observations under ice over the scale necessary for robust krill density estimation. Autosub-2 enabled us to make continuous high-resolution measurements of krill density under ice reaching 27 kilometers beyond the ice edge.

Unequal ice-sheet erosional impacts across low-relief shield terrain in northern Fennoscandia

Science.gov (United States)

Ebert, Karin; Hall, Adrian M.; Kleman, Johan; Andersson, Jannike

2015-03-01

Much previous work on Late Cenozoic glacial erosion patterns in bedrock has focussed on mountain areas. Here we identify varying impacts of ice sheet erosion on the low-relief bedrock surface of the Fennoscandian shield, and examine the geological, topographical and glaciological controls on these patterns. We combine GIS-mapping of topographical, hydrological and weathering data with field observations. We identify and investigate areas with similar geology and general low relief that show different degrees of ice sheet erosional impact, despite similar ice cover histories. On two transects with a total area of ~ 84 000 km2 across the northern Fennoscandian shield, we first establish patterns of glacial erosion and then examine why glacially streamlined areas exist adjacent to areas of negligible glacial erosion. The northern transect includes two areas of exceptional glacial preservation, the Parkajoki area in Sweden and the so-called ice divide zone in Finland, each of which preserve tors and deep saprolite covers. The southern transect, overlapping in the northern part with the first transect, includes areas of well developed glacial streamlining, with bedrock areas stripped of loose material and barely any weathering remnants. For both areas, we firstly present contrasting indicators for ice sheet erosional impact: streamlined and non-streamlined inselbergs; parallel and dendritic/rectangular drainage patterns; and the absence and presence of Neogene weathering remnants. This is followed by an investigation of factors that possibly influence ice sheet erosional impact: ice cover history, ice cover duration and thickness, bedrock type and structure, and topography. We find that the erosional impact of the Fennoscandian ice sheet has varied across the study area. Distinct zones of ice sheet erosion are identified in which indicators of either low or high erosion coexist in the same parts of the transects. No direct impact of rock type on glacial erosion patterns

Effect Of Low-Temperature Annealing On The Properties Of Ni-P Amorphous Alloys Deposited Via Electroless Plating

Directory of Open Access Journals (Sweden)

Zhao Guanlin

2015-06-01

Full Text Available Amorphous Ni-P alloys were prepared via electroless plating and annealing at 200°C at different times to obtain different microstructures. The effects of low-temperature annealing on the properties of amorphous Ni-P alloys were studied. The local atomic structure of the annealed amorphous Ni-P alloys was analyzed by calculating the atomic pair distribution function from their X-ray diffraction patterns. The results indicate that the properties of the annealed amorphous Ni-P alloys are closely related to the order atomic cluster size. However, these annealed Ni-P alloys maintained their amorphous structure at different annealing times. The variation in microhardness is in agreement with the change in cluster size. By contrast, the corrosion resistance of the annealed alloys in 3.5 wt% NaCl solution increases with the decrease in order cluster size.

Optical waveguiding in amorphous tellurium oxide thin films

Energy Technology Data Exchange (ETDEWEB)

Nayak, Ranu; Gupta, Vinay; Dawar, A.L.; Sreenivas, K

2003-11-24

Optical waveguiding characteristics of amorphous TeO{sub 2-x} films deposited by reactive sputtering under different O{sub 2}:Ar gas mixtures are investigated on fused quartz and Corning glass substrates. Infra-red absorption band in the range 641-658 cm{sup -1} confirmed the formation of a Te-O bond, and a 20:80 O{sub 2}:Ar gas mixture ratio is found to be optimum for achieving highly uniform and transparent films at a high deposition rate. As grown amorphous films exhibited a large band gap (3.76 eV); a high refractive index value (2.042-2.052) with low dispersion over a wide wavelength range of 500-2000 nm. Optical waveguiding with low propagation loss of 0.26 dB/cm at 633 nm is observed on films subjected to a post-deposition annealing treatment at 200 deg. C. Packing density and etch rates have been determined and correlated with the lowering of optical propagation loss in the annealed films.

Dependence of the saturated light-induced defect density on macroscopic properties of hydrogenated amorphous silicon

OpenAIRE

Park, H. R.; Liu, J. Z.; Roca i Cabarrocas, P.; Maruyama, A.; Isomura, M.; Wagner, S.; Abelson, J. R.; Finger, F.

2008-01-01

We report a study of the saturated light-induced defect density Ns,sat in 37 hydrogenated (and in part fluorinated) amorphous silicon [a-Si:H(F)] films grown in six different reactors under widely different conditions. Ns,sat was attained by exposing the films to light from a krypton ion laser (λ=647.1 nm). Ns,sat is determined by the constant photocurrent method and lies between 5×1016 and 2×1017 cm−3. Ns,sat drops with decreasing optical gap Eopt and hydrogen content cH, but is not correlat...

Bonding topologies in diamondlike amorphous-carbon films

Energy Technology Data Exchange (ETDEWEB)

SIEGAL,MICHAEL P.; PROVENCIO,PAULA P.; TALLANT,DAVID R.; SIMPSON,REGINA L.; KLEINSORGE,B.; MILNE,W.I.

2000-01-27

The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding topologies of amorphous-carbon (a-C) films. Regions of relatively low density occur near the substrate/film and film/surface interfaces and their thicknesses increase with increasing deposition energy. The ion subplantation growth results in mass density gradients in the bulk portion of a-C in the growth direction; density decreases with distance from the substrate for films grown using ion energies < 60 eV and increases for films grown using ion energies > 160 eV. Films grown between these energies are the most diamondlike with relatively uniform bulk density and the highest optical transparencies. Bonding topologies evolve with increasing growth energy consistent with the propagation of subplanted carbon ions inducing a partial transformation of 4-fold to 3-fold coordinated carbon atoms.

Bonding topologies in diamondlike amorphous-carbon films

Energy Technology Data Exchange (ETDEWEB)

Siegal, M. P. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States); Provencio, P. N. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States); Tallant, D. R. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States); Simpson, R. L. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States); Kleinsorge, B. [Department of Engineering, Cambridge University, Cambridge CB2 1PZ, (United Kingdom); Milne, W. I. [Department of Engineering, Cambridge University, Cambridge CB2 1PZ, (United Kingdom)

2000-04-10

The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding topologies of amorphous-carbon (a-C) films. Regions of relatively low density occur near the substrate/film and film/surface interfaces; their thicknesses increase with deposition energy. The ion subplantation growth results in mass density gradients in the bulk portion of a-C in the growth direction; density decreases with distance from the substrate for films grown using ion energies <60 eV and increases for films grown using ion energies >160 eV. Films grown between these energies are the most diamondlike with relatively uniform bulk density and the highest optical transparencies. Bonding topologies evolve with increasing growth energy consistent with the propagation of subplanted carbon ions inducing a partial transformation of {sigma}- to {pi}-bonded carbon atoms. (c) 2000 American Institute of Physics.

Path-integral simulation of ice Ih: The effect of pressure

Science.gov (United States)

Herrero, Carlos P.; Ramírez, Rafael

2011-12-01

The effect of pressure on structural and thermodynamic properties of ice Ih has been studied by means of path-integral molecular dynamics simulations at temperatures between 50 and 300 K. Interatomic interactions were modeled by using the effective q-TIP4P/F potential for flexible water. Positive (compression) and negative (tension) pressures have been considered, which allowed us to approach the limits for the mechanical stability of this solid water phase. We have studied the pressure dependence of the crystal volume, bulk modulus, interatomic distances, atomic delocalization, and kinetic energy. The spinodal point at both negative and positive pressures is derived from the vanishing of the bulk modulus. For P300 K. At positive pressure the spinodal is associated with ice amorphization, and at low temperatures it is found to be between 1.1 and 1.3 GPa. Quantum nuclear effects cause a reduction of the metastability region of ice Ih.

Use of low-frequency Raman spectroscopy and chemometrics for the quantification of crystallinity in amorphous griseofulvin tablets

DEFF Research Database (Denmark)

Mah, Pei T.; Fraser, Sara J.; Reish, Matthew E.

2015-01-01

in stored amorphous samples earlier than the mid-frequency 785 nm Raman system. Overall, this study suggests that low-frequency Raman spectroscopy has at least equally good performance compared to mid-frequency Raman for quantitative analysis of crystallinity in the pharmaceutical setting. More generally......Low-frequency Raman spectroscopy, which directly probes phonon lattice modes of crystal structures, has much unexplored potential for sensitive qualitative and quantitative analysis of crystallinity in drugs and excipients. In this study, the level of crystallinity in tablets containing amorphous...

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.

Infrared Spectra and Optical Constants of Nitrile Ices Relevant to Titan's Atmosphere

Science.gov (United States)

Anderson, Carrie; Ferrante, Robert F.; Moore, W. James; Hudson, Reggie; Moore, Marla H.

2011-01-01

Spectra and optical constants of nitrile ices known or suspected to be in Titan?s atmosphere have been determined from 2.0 to 333.3 microns (approx.5000 to 30/cm). These results are relevant to the ongoing modeling of Cassini CIRS observations of Titan?s winter pole. Ices studied were: HCN, hydrogen cyanide; C2N2, cyanogen; CH3CN, acetonitrile; C2H5CN, propionitrile; and HC3N, cyanoacetylene. Optical constants were calculated, using Kramers-Kronig analysis, for each nitrile ice?s spectrum measured at a variety of temperatures, in both the amorphous- and crystalline phases. Spectra were also measured for many of the nitriles after quenching at the annealing temperature and compared with those of annealed ices. For each of these molecules we also measured the real component, n, of the refractive index for amorphous and crystalline phases at 670 nm. Several examples of the information contained in these new data sets and their usefulness in modeling Titan?s observed features will be presented (e.g., the broad emission feature at 160/cm; Anderson and Samuelson, 2011).

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.

Hydrogen in amorphous silicon

International Nuclear Information System (INIS)

Peercy, P.S.

1980-01-01

The structural aspects of amorphous silicon and the role of hydrogen in this structure are reviewed with emphasis on ion implantation studies. In amorphous silicon produced by Si ion implantation of crystalline silicon, the material reconstructs into a metastable amorphous structure which has optical and electrical properties qualitatively similar to the corresponding properties in high-purity evaporated amorphous silicon. Hydrogen studies further indicate that these structures will accomodate less than or equal to 5 at.% hydrogen and this hydrogen is bonded predominantly in a monohydride (SiH 1 ) site. Larger hydrogen concentrations than this can be achieved under certain conditions, but the excess hydrogen may be attributed to defects and voids in the material. Similarly, glow discharge or sputter deposited amorphous silicon has more desirable electrical and optical properties when the material is prepared with low hydrogen concentration and monohydride bonding. Results of structural studies and hydrogen incorporation in amorphous silicon were discussed relative to the different models proposed for amorphous silicon

An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles

Directory of Open Access Journals (Sweden)

R. W. Saunders

2010-02-01

Full Text Available Nanoparticles of iron oxide (crystalline and amorphous, silicon oxide and magnesium oxide were investigated for their propensity to nucleate ice over the temperature range 180–250 K, using the AIDA chamber in Karlsruhe, Germany.

All samples were observed to initiate ice formation via the deposition mode at threshold ice super-saturations (RHi_thresh ranging from 105% to 140% for temperatures below 220 K. Approximately 10% of amorphous Fe₂O₃ particles (modal diameter = 30 nm generated in situ from a photochemical aerosol reactor, led to ice nucleation at RHi_thresh = 140% at an initial chamber temperature of 182 K. Quantitative analysis using a singular hypothesis treatment provided a fitted function [n_s(190 K=10^{(3.33×s_ice+8.16}] for the variation in ice-active surface site density (n_s:m⁻² with ice saturation (s_ice for Fe₂O₃ nanoparticles. This was implemented in an aerosol-cloud model to determine a predicted deposition (mass accommodation coefficient for water vapour on ice of 0.1 at temperatures appropriate for the upper atmosphere. Classical nucleation theory was used to determine representative contact angles (θ for the different particle compositions. For the in situ generated Fe₂O₃ particles, a slight inverse temperature dependence was observed with θ = 10.5° at 182 K, decreasing to 9.0° at 200 K (compared with 10.2° and 11.4° respectively for the SiO₂ and MgO particle samples at the higher temperature.

These observations indicate that such refractory nanoparticles are relatively efficient materials for the nucleation of ice under the conditions studied in the chamber which correspond to cirrus cloud formation in the upper troposphere. The results also show that Fe₂O₃ particles do not act as ice

A multifunctional setup to record FTIR and UV-vis spectra of organic molecules and their photoproducts in astronomical ices.

Science.gov (United States)

Kofman, V; Witlox, M J A; Bouwman, J; Ten Kate, I L; Linnartz, H

2018-05-01

This article describes a new, multi-functional, high-vacuum ice setup that allows to record the in situ and real-time spectra of vacuum UV (VUV)-irradiated non-volatile molecules embedded in a low-temperature (10 K) amorphous solid water environment. Three complementary diagnostic tools-UV-visible (UV-vis) and Fourier Transform Infrared (FTIR) spectroscopy and temperature-programmed desorption quadrupole mass spectrometry-can be used to simultaneously study the physical and chemical behavior of the organic molecules in the ice upon VUV irradiation. The setup is equipped with a temperature-controlled sublimation oven that enables the controlled homogeneous deposition of solid species such as amino acids, nucleobases, and polycyclic aromatic hydrocarbons (PAHs) in ice mixtures prepared from precursor gases and/or liquids. The resulting ice is photo-processed with a microwave discharge hydrogen lamp, generating VUV radiation with a spectral energy distribution representative for the interstellar medium. The characteristics, performance, and future potential of the system are discussed by describing three different applications. First, a new method is introduced, which uses broadband interference transmission fringes recorded during ice deposition, to determine the wavelength-dependent refractive index, n λ , of amorphous solid water. This approach is also applicable to other solids, pure and mixed. Second, the UV-vis and FTIR spectroscopy of an VUV-irradiated triphenylene:water ice mixture is discussed, monitoring the ionization efficiency of PAHs in interstellar ice environments. The third and final example investigates the stability of solid glycine upon VUV irradiation by monitoring the formation of dissociation products in real time.

A multifunctional setup to record FTIR and UV-vis spectra of organic molecules and their photoproducts in astronomical ices

Science.gov (United States)

Kofman, V.; Witlox, M. J. A.; Bouwman, J.; ten Kate, I. L.; Linnartz, H.

2018-05-01

This article describes a new, multi-functional, high-vacuum ice setup that allows to record the in situ and real-time spectra of vacuum UV (VUV)-irradiated non-volatile molecules embedded in a low-temperature (10 K) amorphous solid water environment. Three complementary diagnostic tools—UV-visible (UV-vis) and Fourier Transform Infrared (FTIR) spectroscopy and temperature-programmed desorption quadrupole mass spectrometry—can be used to simultaneously study the physical and chemical behavior of the organic molecules in the ice upon VUV irradiation. The setup is equipped with a temperature-controlled sublimation oven that enables the controlled homogeneous deposition of solid species such as amino acids, nucleobases, and polycyclic aromatic hydrocarbons (PAHs) in ice mixtures prepared from precursor gases and/or liquids. The resulting ice is photo-processed with a microwave discharge hydrogen lamp, generating VUV radiation with a spectral energy distribution representative for the interstellar medium. The characteristics, performance, and future potential of the system are discussed by describing three different applications. First, a new method is introduced, which uses broadband interference transmission fringes recorded during ice deposition, to determine the wavelength-dependent refractive index, nλ, of amorphous solid water. This approach is also applicable to other solids, pure and mixed. Second, the UV-vis and FTIR spectroscopy of an VUV-irradiated triphenylene:water ice mixture is discussed, monitoring the ionization efficiency of PAHs in interstellar ice environments. The third and final example investigates the stability of solid glycine upon VUV irradiation by monitoring the formation of dissociation products in real time.

Temperature Measurements of the Low-Attenuation Radiographic Ice Ball During CT-Guided Renal Cryoablation

International Nuclear Information System (INIS)

Permpongkosol, Sompol; Link, Richard E.; Kavoussi, Louis R.; Solomon, Stephen B.

2008-01-01

During renal cryoablation a low-attenuation area on CT develops around the cryoprobe. Knowledge of the temperature of the growing low-attenuation area can guide therapy and ensure lethal temperatures. Herein, we report thermocouple results and correlating CT images during the development of the low-attenuation 'radiographic ice ball.' Five patients who underwent percutaneous CT-guided renal cryoablation were identified who had thermocouples inserted and serial intraprocedural CT images that included images with thermocouple measurements of 0 o and sub-0 o C. Thermocouples had been percutaneously placed just beyond the edge of the tumors either to ensure adequate cooling or to ensure safety to adjacent critical structures. Renal cryotherapy under CT guidance produced a growing low-attenuation area corresponding to the radiographic ice ball. When the thermocouple measured 0 o C, CT images showed the thermocouple tip at the edge of the low-attenuation ice ball. At lower temperatures the tip was within the low-attenuation ice ball. We conclude that knowledge of the temperature at the ice ball edge during cryoablation can be used to predict the extent of tissue necrosis and thus provide an estimate of cryotherapy effectiveness during the procedure. Further work is necessary to establish a firm relationship between the thermal conditions and the zone of damage

Inverse Resistance Change Cr2Ge2Te6-Based PCRAM Enabling Ultralow-Energy Amorphization.

Science.gov (United States)

Hatayama, Shogo; Sutou, Yuji; Shindo, Satoshi; Saito, Yuta; Song, Yun-Heub; Ando, Daisuke; Koike, Junichi

2018-01-24

Phase-change random access memory (PCRAM) has attracted much attention for next-generation nonvolatile memory that can replace flash memory and can be used for storage-class memory. Generally, PCRAM relies on the change in the electrical resistance of a phase-change material between high-resistance amorphous (reset) and low-resistance crystalline (set) states. Herein, we present an inverse resistance change PCRAM with Cr 2 Ge 2 Te 6 (CrGT) that shows a high-resistance crystalline reset state and a low-resistance amorphous set state. The inverse resistance change was found to be due to a drastic decrease in the carrier density upon crystallization, which causes a large increase in contact resistivity between CrGT and the electrode. The CrGT memory cell was demonstrated to show fast reversible resistance switching with a much lower operating energy for amorphization than a Ge 2 Sb 2 Te 5 memory cell. This low operating energy in CrGT should be due to a small programmed amorphous volume, which can be realized by a high-resistance crystalline matrix and a dominant contact resistance. Simultaneously, CrGT can break the trade-off relationship between the crystallization temperature and operating speed.

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.

On the density of states of disordered epitaxial graphene

International Nuclear Information System (INIS)

Davydov, S. Yu.

2015-01-01

The study is concerned with two types of disordered epitaxial graphene: (i) graphene with randomly located carbon vacancies and (ii) structurally amorphous graphene. The former type is considered in the coherent potential approximation, and for the latter type, a model of the density of states is proposed. The effects of two types of substrates, specifically, metal and semiconductor substrates are taken into account. The specific features of the density of states of epitaxial graphene at the Dirac point and the edges of the continuous spectrum are analyzed. It is shown that vacancies in epitaxial graphene formed on the metal substrate bring about logarithmic nulling of the density of states of graphene at the Dirac point and the edges of the continuous spectrum. If the Dirac point corresponds to the middle of the band gap of the semiconductor substrate, the linear trend of the density of states to zero in the vicinity of the Dirac point in defect-free graphene transforms into a logarithmic decrease in the presence of vacancies. In both cases, the graphene-substrate interaction is assumed to be weak (quasi-free graphene). In the study of amorphous epitaxial graphene, a simple model of free amorphous graphene is proposed as the initial model, in which account is taken of the nonzero density of states at the Dirac point, and then the interaction of the graphene sheet with the substrate is taken into consideration. It is shown that, near the Dirac point, the quadratic behavior of the density of states of free amorphous graphene transforms into a linear dependence for amorphous epitaxial graphene. In the study, the density of states of free graphene corresponds to the low-energy approximation of the electron spectrum

Amorphous-crystalline transition in thermoelectric NbO2

International Nuclear Information System (INIS)

Music, Denis; Chen, Yen-Ting; Bliem, Pascal; Geyer, Richard W

2015-01-01

Density functional theory was employed to design enhanced amorphous NbO 2 thermoelectrics. The covalent-ionic nature of Nb–O bonding is identical in amorphous NbO 2 and its crystalline counterpart. However, the Anderson localisation occurs in amorphous NbO 2 , which may affect the transport properties. We calculate a multifold increase in the absolute Seebeck coefficient for the amorphous state. These predictions were critically appraised by measuring the Seebeck coefficient of sputtered amorphous and crystalline NbO 2 thin films with the identical short-range order. The first-order phase transition occurs at approximately 550 °C, but amorphous NbO 2 possesses enhanced transport properties at all temperatures. Amorphous NbO 2 , reaching  −173 μV K −1 , exhibits up to a 29% larger absolute Seebeck coefficient value, thereby validating the predictions. (paper)

Oxygen diffusion and reactivity at low temperature on bare amorphous olivine-type silicate

Energy Technology Data Exchange (ETDEWEB)

Minissale, M., E-mail: marco.minissale@obspm.fr; Congiu, E.; Dulieu, F. [LERMA-LAMAp, Université de Cergy-Pontoise, Observatoire de Paris, ENS, UPMC, UMR 8112 du CNRS, 5 Mail Gay Lussac, 95000 Cergy Pontoise Cedex (France)

2014-02-21

The mobility of O atoms at very low temperatures is not generally taken into account, despite O diffusion would add to a series of processes leading to the observed rich molecular diversity in space. We present a study of the mobility and reactivity of O atoms on an amorphous silicate surface. Our results are in the form of reflection absorption infrared spectroscopy and temperature-programmed desorption spectra of O{sub 2} and O{sub 3} produced via two pathways: O + O and O{sub 2} + O, investigated in a submonolayer regime and in the range of temperature between 6.5 and 30 K. All the experiments show that ozone is formed efficiently on silicate at any surface temperature between 6.5 and 30 K. The derived upper limit for the activation barriers of O + O and O{sub 2} + O reactions is ∼150 K/k{sub b}. Ozone formation at low temperatures indicates that fast diffusion of O atoms is at play even at 6.5 K. Through a series of rate equations included in our model, we also address the reaction mechanisms and show that neither the Eley–Rideal nor the hot atom mechanisms alone can explain the experimental values. The rate of diffusion of O atoms, based on modeling results, is much higher than the one generally expected, and the diffusive process proceeds via the Langmuir-Hinshelwood mechanism enhanced by tunnelling. In fact, quantum effects turn out to be a key factor that cannot be neglected in our simulations. Astrophysically, efficient O{sub 3} formation on interstellar dust grains would imply the presence of huge reservoirs of oxygen atoms. Since O{sub 3} is a reservoir of elementary oxygen, and also of OH via its hydrogenation, it could explain the observed concomitance of CO{sub 2} and H{sub 2}O in the ices.

Model of the recrystallization mechanism of amorphous silicon layers created by ion implantation

International Nuclear Information System (INIS)

Drosd, R.M.

1979-11-01

The recrystallization behavior during annealing of thin films of amorphous (α) silicon, in contact with a single crystal silicon substrate (referred to as C), has been studied in the transmission electron microscope (TEM). The amorphous film is created during high dose phosphorus ion implantation at 100 keV. It was found that the crystal substrate orientation and the implantation temperature have dramatic effects on the recrystallizaton rate, and the defect microstructure produced during annealing. Specifically, (100) wafers implanted at 77 0 K contain only a low density of dislocation loops, but when the same wafer is implanted at room temperature the dislocation density is increased drastically. (111) wafers, when implanted at 77 0 K show a high density of microtwins, but as the implantation temperature is increased a gradual increase in the density of dislocation loops is observed along with a reduction of the microtwins. At an implantation temperature of about 100 0 C both orientations give an identical defect microstructure when annealed, which is a dense tangle of dislocations

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.

Electronic structure effects in liquid water studied by photoelectron spectroscopy and density functional theory

Energy Technology Data Exchange (ETDEWEB)

Nordlund, Dennis; Odelius, Michael; Bluhm, Hendrik; Ogasawara, Hirohito; Pettersson, Lars G.M.; Nilsson, Anders

2008-04-29

We present valence photoelectron emission spectra of liquid water in comparison with gas-phase water, ice close to the melting point, low temperature amorphous and crystalline ice. All aggregation states have major electronic structure changes relative to the free molecule, with rehybridization and development of bonding and anti-bonding states accompanying the hydrogen bond formation. Sensitivity to the local structural order, most prominent in the shape and splitting of the occupied 3a{sub 1} orbital, is understood from the electronic structure averaging over various geometrical structures, and reflects the local nature of the orbital interaction.

Glass polymorphism in amorphous germanium probed by first-principles computer simulations

Science.gov (United States)

Mancini, G.; Celino, M.; Iesari, F.; Di Cicco, A.

2016-01-01

The low-density (LDA) to high-density (HDA) transformation in amorphous Ge at high pressure is studied by first-principles molecular dynamics simulations in the framework of density functional theory. Previous experiments are accurately reproduced, including the presence of a well-defined LDA-HDA transition above 8 GPa. The LDA-HDA density increase is found to be about 14%. Pair and bond-angle distributions are obtained in the 0-16 GPa pressure range and allowed us a detailed analysis of the transition. The local fourfold coordination is transformed in an average HDA sixfold coordination associated with different local geometries as confirmed by coordination number analysis and shape of the bond-angle distributions.

Amorphous Ge quantum dots embedded in SiO2 formed by low energy ion implantation

International Nuclear Information System (INIS)

Zhao, J. P.; Huang, D. X.; Jacobson, A. J.; Chen, Z. Y.; Makarenkov, B.; Chu, W. K.; Bahrim, B.; Rabalais, J. W.

2008-01-01

Under ultrahigh vacuum conditions, extremely small Ge nanodots embedded in SiO 2 , i.e., Ge-SiO 2 quantum dot composites, have been formed by ion implantation of 74 Ge + isotope into (0001) Z-cut quartz at a low kinetic energy of 9 keV using varying implantation temperatures. Transmission electron microscopy (TEM) images and micro-Raman scattering show that amorphous Ge nanodots are formed at all temperatures. The formation of amorphous Ge nanodots is different from reported crystalline Ge nanodot formation by high energy ion implantation followed by a necessary high temperature annealing process. At room temperature, a confined spatial distribution of the amorphous Ge nanodots can be obtained. Ge inward diffusion was found to be significantly enhanced by a synergetic effect of high implantation temperature and preferential sputtering of surface oxygen, which induced a much wider and deeper Ge nanodot distribution at elevated implantation temperature. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. Cross-sectional TEM observation and the depth profile of Ge atoms in SiO 2 obtained from x-ray photoelectron spectra revealed a critical Ge concentration for observable amorphous nanodot formation. The mechanism of formation of amorphous Ge nanodots and the change in spatial distribution with implantation temperature are discussed

{sup 2}H-NMR study of amorphous and crystalline high pressure ice phases; {sup 2}H-NMR-Untersuchungen an amorphen und kristallinen Hochdruckeisphasen

Energy Technology Data Exchange (ETDEWEB)

Scheuermann, Marco

2008-10-27

The objective of this work was to produce different high pressure ice phases and measure them at ambient pressure. Temperature dependent relaxation measurements were performed for the first time. All three amorphous ices differ significantly in their temperature dependent T1-values. Applying a heating rate of 1 K/h the transformation of HDA into LDA takes place at a temperature of 105 K. By contrast, warming up VHDA to temperatures above 105 K leads to a relaxed form with relaxation times that resemble the values of HDA. This modification eventually transforms into LDA at 115 K. Our data analysis indicates that this intermediate state is not an inhomogeneous mixture of VHDA and LDA, suggesting that the VHDA/LDA transition is not of a simple first order type. In ice II relaxation measurements and stimulated echo experiments were performed for the first time. The observed temperature of the transition from ice II to cubic ice, 145 K, is consistent with literature data, considering our heating rate of about 1 K/day. The relaxation curves show a bimodal evolution. This is not due to structural heterogeneities, because additional X-ray diffraction measurements exclude a contamination of our samples with other ice phases. The slow relaxing component displays no temperature dependence. The time constant of the fast component reveals Arrhenius-like behaviour, although the activation energy is only 2 kJ/mol. Such a small value can not be attributed to reorientation dynamics as the origin of relaxation in ice II. The decay of the stimulated echo is only about one order of magnitude faster than the decay due to spin-lattice relaxation. The resulting correlation time is temperature independent. Hence, the loss of correlation can not be due to molecular dynamics. But it could stem from spin diffusion, which is known to induce frequency shifts of individual spins in deuteron systems. This interpretation is supported by the analysis of the geometry of the underlying process. The

IceCube Sensitivity for Low-Energy Neutrinos from Nearby Supernovae

Science.gov (United States)

Stamatikos, M.; Abbasi, R.; Berghaus, P.; Chirkin, D.; Desiati, P.; Diaz-Velez, J.; Dumm, J. P.; Eisch, J.; Feintzeig, J.; Hanson, K.;

Low temperature hopping conduction in amorphous Gesub(x)Sesub(1-x)

International Nuclear Information System (INIS)

Mehra, R.M.; Kumar, H.; Agarwal, S.C.; Sikka, P.; Mathur, P.C.

1985-08-01

Bulk amorphous samples of Gesub(x)Sesub(1-x) (0.5<=x<=0.7) were prepared by quenching. Dc conductivity measurements were carried out in the temperature range 77-300 K. In the low temperature region, the conduction occurs due to variable range hopping in the localized states near the Fermi level. The results are explained by Mott, Pollak and Butcher's models. Butcher's model which is based on the equivalent of conduction network is compatible with the results. (author)

Mass balance of the Greenland ice sheet - a study of ICESat data, surface density and firn compaction modelling

DEFF Research Database (Denmark)

Sørensen, L. S.; Simonsen, Sebastian Bjerregaard; Nielsen, K.

2010-01-01

ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique data set for monitoring the changes of the cryosphere. Here we present a novel method for determining the mass balance of the Greenland ice sheet derived from ICESat...... in estimating the mass balance of the Greenland ice sheet. We find firn dynamics and surface densities to be important factors in deriving the mass loss from remote sensing altimetry. The volume change derived from ICESat data is corrected for firn compaction, vertical bedrock movement and an intercampaign...... boundary conditions. We find an annual mass loss of the Greenland ice sheet of 210 ± 21 Gt yr-1 in the period from October 2003 to March 2008. This result is in good agreement with other studies of the Greenland ice sheet mass balance, based on different remote sensing techniques....

Neutron irradiation induced amorphization of silicon carbide

International Nuclear Information System (INIS)

Snead, L.L.; Hay, J.C.

1998-01-01

This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 x 10 25 n/m 2 . Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density (-10.8%), elastic modulus as measured using a nanoindentation technique (-45%), hardness as measured by nanoindentation (-45%), and standard Vickers hardness (-24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C

Influence of the anodic etching current density on the morphology of the porous SiC layer

Directory of Open Access Journals (Sweden)

Anh Tuan Cao

2014-03-01

Full Text Available In this report, we fabricated a porous layer in amorphous SiC thin films by using constant-current anodic etching in an electrolyte of aqueous diluted hydrofluoric acid. The morphology of the porous amorphous SiC layer changed as the anodic current density changed: At low current density, the porous layer had a low pore density and consisted of small pores that branched downward. At moderate current density, the pore size and depth increased, and the pores grew perpendicular to the surface, creating a columnar pore structure. At high current density, the porous structure remained perpendicular, the pore size increased, and the pore depth decreased. We explained the changes in pore size and depth at high current density by the growth of a silicon oxide layer during etching at the tips of the pores.

Continuous Chemistry in Ice Cores

DEFF Research Database (Denmark)

Kjær, Helle Astrid

on parameters involved in the study of photolysis as a source of in situ CO2. The concentration of organic substances in Greenland ice is poorly known due to their low levels and the fact that only a few studies evaluate the concentrations of specific organic compounds. Light does not penetrate deep...... depth was found as a function of wavelength. Further, by computational chemistry hybrid density functional methods (DFT), the four most common conformers of pyruvic acid were investigated in both gas, water and ice using the DFT model CAM-B3LYP with dielectric medium methods. A de rease of the energy...

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

Calorimetric study of water's two glass transitions in the presence of LiCl

Science.gov (United States)

Ruiz, Guadalupe N.; Amann-Winkel, Katrin; Bove, Livia E.; Corti, Horacio R.

2018-01-01

A DSC study of dilute glassy LiCl aqueous solutions in the water-dominated regime provides direct evidence of a glass-to-liquid transition in expanded high density amorphous (eHDA)-type solutions. Similarly, low density amorphous ice (LDA) exhibits a glass transition prior to crystallization to ice Ic. Both glass transition temperatures are independent of the salt concentration, whereas the magnitude of the heat capacity increase differs. By contrast to pure water, the glass transition endpoint for LDA can be accessed in LiCl aqueous solutions above 0.01 mole fraction. Furthermore, we also reveal the endpoint for HDA's glass transition, solving the question on the width of both glass transitions. This suggests that both equilibrated HDL and LDL can be accessed in dilute LiCl solutions, supporting the liquid–liquid transition scenario to understand water's anomalies. PMID:29442107

First-principles study of the amorphous In3SbTe2 phase change compound

Science.gov (United States)

Los, Jan H.; Kühne, Thomas D.; Gabardi, Silvia; Bernasconi, Marco

2013-11-01

Ab initio molecular dynamics simulations based on density functional theory were performed to generate amorphous models of the phase change compound In3SbTe2 by quenching from the melt. In-Sb and In-Te are the most abundant bonds with only a minor fraction of Sb-Te bonds. The bonding geometry in the amorphous phase is, however, strongly dependent on the density in the range 6.448-5.75 g/cm3 that we investigated. While at high density the bonding geometry of In atoms is mostly octahedral-like as in the cubic crystalline phase of the ternary compound In3SbTe2, at low density we observed a sizable fraction of tetrahedral-like geometries similar to those present in the crystalline phase of the two binary compounds InTe and InSb that the ternary system can be thought to be made of. We show that the different ratio between octahedral-like and tetrahedral-like bonding geometries has fingerprints in the optical and vibrational spectra.

Geophysical Investigations of Habitability in Ice-Covered Ocean Worlds

Science.gov (United States)

Vance, Steven D.; Panning, Mark P.; Stähler, Simon; Cammarano, Fabio; Bills, Bruce G.; Tobie, Gabriel; Kamata, Shunichi; Kedar, Sharon; Sotin, Christophe; Pike, William T.; Lorenz, Ralph; Huang, Hsin-Hua; Jackson, Jennifer M.; Banerdt, Bruce

2018-01-01

Geophysical measurements can reveal the structures and thermal states of icy ocean worlds. The interior density, temperature, sound speed, and electrical conductivity thus characterize their habitability. We explore the variability and correlation of these parameters using 1-D internal structure models. We invoke thermodynamic consistency using available thermodynamics of aqueous MgSO4, NaCl (as seawater), and NH3; pure water ice phases I, II, III, V, and VI; silicates; and any metallic core that may be present. Model results suggest, for Europa, that combinations of geophysical parameters might be used to distinguish an oxidized ocean dominated by MgSO4 from a more reduced ocean dominated by NaCl. In contrast with Jupiter's icy ocean moons, Titan and Enceladus have low-density rocky interiors, with minimal or no metallic core. The low-density rocky core of Enceladus may comprise hydrated minerals or anhydrous minerals with high porosity. Cassini gravity data for Titan indicate a high tidal potential Love number (k2>0.6), which requires a dense internal ocean (ρocean>1,200 kg m-3) and icy lithosphere thinner than 100 km. In that case, Titan may have little or no high-pressure ice, or a surprisingly deep water-rock interface more than 500 km below the surface, covered only by ice VI. Ganymede's water-rock interface is the deepest among known ocean worlds, at around 800 km. Its ocean may contain multiple phases of high-pressure ice, which will become buoyant if the ocean is sufficiently salty. Callisto's interior structure may be intermediate to those of Titan and Europa, with a water-rock interface 250 km below the surface covered by ice V but not ice VI.

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

Solubility of crystalline organic compounds in high and low molecular weight amorphous matrices above and below the glass transition by zero enthalpy extrapolation.

Science.gov (United States)

Amharar, Youness; Curtin, Vincent; Gallagher, Kieran H; Healy, Anne Marie

2014-09-10

Pharmaceutical applications which require knowledge of the solubility of a crystalline compound in an amorphous matrix are abundant in the literature. Several methods that allow the determination of such data have been reported, but so far have only been applicable to amorphous polymers above the glass transition of the resulting composites. The current work presents, for the first time, a reliable method for the determination of the solubility of crystalline pharmaceutical compounds in high and low molecular weight amorphous matrices at the glass transition and at room temperature (i.e. below the glass transition temperature), respectively. The solubilities of mannitol and indomethacin in polyvinyl pyrrolidone (PVP) K15 and PVP K25, respectively were measured at different temperatures. Mixtures of undissolved crystalline solute and saturated amorphous phase were obtained by annealing at a given temperature. The solubility at this temperature was then obtained by measuring the melting enthalpy of the crystalline phase, plotting it as a function of composition and extrapolating to zero enthalpy. This new method yielded results in accordance with the predictions reported in the literature. The method was also adapted for the measurement of the solubility of crystalline low molecular weight excipients in amorphous active pharmaceutical ingredients (APIs). The solubility of mannitol, glutaric acid and adipic acid in both indomethacin and sulfadimidine was experimentally determined and successfully compared with the difference between their respective calculated Hildebrand solubility parameters. As expected from the calculations, the dicarboxylic acids exhibited a high solubility in both amorphous indomethacin and sulfadimidine, whereas mannitol was almost insoluble in the same amorphous phases at room temperature. This work constitutes the first report of the methodology for determining an experimentally measured solubility for a low molecular weight crystalline solute

Does a Relationship Between Arctic Low Clouds and Sea Ice Matter?

Science.gov (United States)

Taylor, Patrick C.

2016-01-01

Arctic low clouds strongly affect the Arctic surface energy budget. Through this impact Arctic low clouds influence important aspects of the Arctic climate system, namely surface and atmospheric temperature, sea ice extent and thickness, and atmospheric circulation. Arctic clouds are in turn influenced by these elements of the Arctic climate system, and these interactions create the potential for Arctic cloud-climate feedbacks. To further our understanding of potential Arctic cloudclimate feedbacks, the goal of this paper is to quantify the influence of atmospheric state on the surface cloud radiative effect (CRE) and its covariation with sea ice concentration (SIC). We build on previous research using instantaneous, active remote sensing satellite footprint data from the NASA A-Train. First, the results indicate significant differences in the surface CRE when stratified by atmospheric state. Second, there is a weak covariation between CRE and SIC for most atmospheric conditions. Third, the results show statistically significant differences in the average surface CRE under different SIC values in fall indicating a 3-5 W m(exp -2) larger LW CRE in 0% versus 100% SIC footprints. Because systematic changes on the order of 1 W m(exp -2) are sufficient to explain the observed long-term reductions in sea ice extent, our results indicate a potentially significant amplifying sea ice-cloud feedback, under certain meteorological conditions, that could delay the fall freeze-up and influence the variability in sea ice extent and volume. Lastly, a small change in the frequency of occurrence of atmosphere states may yield a larger Arctic cloud feedback than any cloud response to sea ice.

Electron-irradiation-induced crystallization of amorphous orthophosphates

International Nuclear Information System (INIS)

Meldrum, A.; Ewing, R.C.; Boatner, L.A.

1996-12-01

Amorphous LaPO 4 , EuPO 4 , GdPO 4 , ScPO 4 , and fluorapatite [Ca 5 (PO 4 ) 3 F] were irradiated by electron beam in a TEM. Irradiations were done at -150 to 300 C, 80 to 200 keV, and current densities from 0.3 to 16 A/cm 2 . In all cases, the materials crystallized to form a randomly oriented polycrystalline assemblage. Crystallization is driven dominantly by inelastic processes, although ballistic collisions with target nuclei can be important above 175 keV, particularly in apatite. Using a high current density, crystallization is so fast that continuous lines of crystallites can be ''drawn'' on the amorphous matrix

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.

Amorphous-tetrahedral diamondlike carbon layered structures resulting from film growth energetics

Science.gov (United States)

Siegal, M. P.; Barbour, J. C.; Provencio, P. N.; Tallant, D. R.; Friedmann, T. A.

1998-08-01

High-resolution transmission electron microscopy (HRTEM) shows that amorphous-tetrahedral diamondlike carbon (a-tC) films grown by pulsed-laser deposition on Si(100) consist of three-to-four layers, depending on the growth energetics. We estimate the density of each layer using both HRTEM image contrast and Rutherford backscattering spectrometry. The first carbon layer and final surface layer have relatively low density. The bulk of the film between these two layers has higher density. For films grown under the most energetic conditions, there exists a superdense a-tC layer between the interface and bulk layers. The density of all four layers, and the thickness of the surface and interfacial layers, correlate well with the energetics of the depositing carbon species.

Electron stimulated reactions of methyl iodide coadsorbed with amorphous solid water

International Nuclear Information System (INIS)

Perry, C. C.; Faradzhev, N. S.; Madey, T. E.; Fairbrother, D. H.

2007-01-01

The electron stimulated reactions of methyl iodide (MeI) adsorbed on and suspended within amorphous solid water (ice) were studied using a combination of postirradiation temperature programmed desorption and reflection absorption infrared spectroscopy. For MeI adsorbed on top of amorphous solid water (ice), electron beam irradiation is responsible for both structural and chemical transformations within the overlayer. Electron stimulated reactions of MeI result principally in the formation of methyl radicals and solvated iodide anions. The cross section for electron stimulated decomposition of MeI is comparable to the gas phase value and is only weakly dependent upon the local environment. For both adsorbed MeI and suspended MeI, reactions of methyl radicals within MeI clusters lead to the formation of ethane, ethyl iodide, and diiodomethane. In contrast, reactions between the products of methyl iodide and water dissociation are responsible for the formation of methanol and carbon dioxide. Methane, formed as a result of reactions between methyl radicals and either parent MeI molecules or hydrogen atoms, is also observed. The product distribution is found to depend on the film's initial chemical composition as well as the electron fluence. Results from this study highlight the similarities in the carbon-containing products formed when monohalomethanes coadsorbed with amorphous solid water are irradiated by either electrons or photons

A Low-Stress, Elastic, and Improved Hardness Hydrogenated Amorphous Carbon Film

Directory of Open Access Journals (Sweden)

Qi Wang

2015-01-01

Full Text Available The evolution of hydrogenated amorphous carbon films with fullerene-like microstructure was investigated with a different proportion of hydrogen supply in deposition. The results showed at hydrogen flow rate of 50 sccm, the deposited films showed a lower compressive stress (lower 48.6%, higher elastic recovery (higher 19.6%, near elastic recovery rate 90%, and higher hardness (higher 7.4% compared with the films deposited without hydrogen introduction. Structural analysis showed that the films with relatively high sp2 content and low bonded hydrogen content possessed high hardness, elastic recovery rate, and low compressive stress. It was attributed to the curved graphite microstructure, which can form three-dimensional covalently bonded network.

Mechanisms of aluminium-induced crystallization and layer exchange upon low-temperature annealing of amorphous Si/polycrystalline Al bilayers.

Science.gov (United States)

Wang, J Y; Wang, Z M; Jeurgens, L P H; Mittemeijer, E J

2009-06-01

Aluminium-induced crystallization (ALIC) of amorphous Si and subsequent layer exchange (ALILE) occur in amorphous-Si/polycrystalline-Al bilayers (a-Si/c-Al) upon annealing at temperatures as low as 165 degrees C and were studied by X-ray diffraction and Auger electron spectroscopic depth profiling. It follows that: (i) nucleation of Si crystallization is initiated at Al grain boundaries and not at the a-Si/c-Al interface; (ii) low-temperature annealing results in a large Si grain size in the continuous c-Si layer produced by ALILE. Thermodynamic model calculations show that: (i) Si can "wet" the Al grain boundaries due to the favourable a-Si/c-Al interface energy (as compared to the Al grain-boundary energy); (ii) the wetting-induced a-Si layer at the Al grain boundary can maintain its amorphous state only up to a critical thickness, beyond which nucleation of Si crystallization takes place; and (iii) a tiny driving force controls the kinetics of the layer exchange.

Perpendicular magnetic anisotropy of amorphous ferromagnetic CoSiB/[Pt,Au] multilayer

International Nuclear Information System (INIS)

Jeong, S.; Yim, H. I.

2012-01-01

Perpendicular magnetic anisotropy is being widely studied as a possible candidate for a high density spin-transfer torque magnetic random access memory. The key issues of a high-density spin-transfer torque magnetic random access memory are decreasing the switching current and the high thermal stability. In order to solve these problems, two approaches are suggested: One is the development a new amorphous ferromagnetic material as a pinned layer for a multilayer with a low saturated magnetization (M s ) value because of the interface roughness between the two layers. The other is a search for the most suitable materials with high perpendicular magnetic anisotropy in order to have high thermal stability. In this work, we present an amorphous ferromagnetic Co 75 Si 15 B 10 material and compare the magnetic properties of a [CoSiB (0.3, 0.4, 0.5 nm)/Pt (1.4 nm)] 5 multilayer and new combinations [CoSiB (0.3, 0.4, 0.5 nm)/Au (1.5 nm)] 5 .

Structure of amorphous sulfur

CSIR Research Space (South Africa)

Eichinger, BE

2001-06-01

Full Text Available The lambda-transition of elemental sulfur occurring at about 159°C has long been associated with the conversion of cyclic S8 rings (c-S8) to amorphous polymer (a-S) via a ring opening polymerization. It is demonstrated, with the use of both density...

The location of the second critical point of water

Science.gov (United States)

Kanno, Hitoshi; Miyata, Kuniharu

2006-05-01

Based on the DTA data for homogeneous ice nucleation of emulsified liquid water at low temperatures and high pressures, the location of the second critical point (SCP) of water, which is expected to exist in addition to the normal liquid-vapor critical point, is estimated to be at 145 K pressure). It is shown that SCP is closely associated with the break point of the curve for the homogeneous ice nucleation temperature ( TH) of liquid water and with the transition between low density and high density amorphous solid water (LDA and HDA). Although the existence of SCP has become more realistic, the location seems to be less favorable to the water model of the second-critical-point interpretation.

Amorphous drugs and dosage forms

DEFF Research Database (Denmark)

Grohganz, Holger; Löbmann, K.; Priemel, P.

2013-01-01

The transformation to an amorphous form is one of the most promising approaches to address the low solubility of drug compounds, the latter being an increasing challenge in the development of new drug candidates. However, amorphous forms are high energy solids and tend to recry stallize. New...... formulation principles are needed to ensure the stability of amorphous drug forms. The formation of solid dispersions is still the most investigated approach, but additional approaches are desirable to overcome the shortcomings of solid dispersions. Spatial separation by either coating or the use of micro-containers...... before single molecules are available for the formation of crystal nuclei, thus stabilizing the amorphous form....

Effect of particle surface area on ice active site densities retrieved from droplet freezing spectra

Directory of Open Access Journals (Sweden)

H. Beydoun

2016-10-01

Full Text Available Heterogeneous ice nucleation remains one of the outstanding problems in cloud physics and atmospheric science. Experimental challenges in properly simulating particle-induced freezing processes under atmospherically relevant conditions have largely contributed to the absence of a well-established parameterization of immersion freezing properties. Here, we formulate an ice active, surface-site-based stochastic model of heterogeneous freezing with the unique feature of invoking a continuum assumption on the ice nucleating activity (contact angle of an aerosol particle's surface that requires no assumptions about the size or number of active sites. The result is a particle-specific property g that defines a distribution of local ice nucleation rates. Upon integration, this yields a full freezing probability function for an ice nucleating particle. Current cold plate droplet freezing measurements provide a valuable and inexpensive resource for studying the freezing properties of many atmospheric aerosol systems. We apply our g framework to explain the observed dependence of the freezing temperature of droplets in a cold plate on the concentration of the particle species investigated. Normalizing to the total particle mass or surface area present to derive the commonly used ice nuclei active surface (INAS density (ns often cannot account for the effects of particle concentration, yet concentration is typically varied to span a wider measurable freezing temperature range. A method based on determining what is denoted an ice nucleating species' specific critical surface area is presented and explains the concentration dependence as a result of increasing the variability in ice nucleating active sites between droplets. By applying this method to experimental droplet freezing data from four different systems, we demonstrate its ability to interpret immersion freezing temperature spectra of droplets containing variable particle concentrations. It is shown

Mg amorphous alloys for biodegradable implants; Ligas amorfas de magnesio utilizadas em implantes consumiveis

Energy Technology Data Exchange (ETDEWEB)

Danez, G.P., E-mail: gabidanez@hotmail.co [Universidade Federal de Sao Carlos (PPG-CEMUFSCar), SP (Brazil). Programa de Pos-Graduacao em Ciencia e Engenharia de Materiais; Koga, G.Y.; Tonucci, S.; Bolfarini, C.; Kiminami, C.S.; Botta Filho, W.J. [Universidade Federal de Sao Carlos (DEMa/UFSCar), SP (Brazil). Dept. de Engenharia de Materiais

2010-07-01

The use of implants made from amorphous alloys magnesium-based with additions of zinc and calcium are promising. Properties such as biocompatibility, low density, high mechanical strength, low modulus (as compared to alloys such as stainless steel and titanium), corrosion resistance and wear resistance make it attractive for use in implants. Moreover, the by-products of corrosion and wear are not toxic and may contribute to fixation. Aiming to understand the tendency of this amorphous ternary (Mg-Zn-Ca) and expand the information about this system, this work involved the use of the topological criterion of instability ({lambda}) and the criterion of electronegativity ({Delta}e) to the choice of compositions. The alloys were processed into wedge-shaped and analyzed structurally and in X-ray diffraction and scanning electron microscopy. (author)

Impact of hydrogen dilution on optical properties of intrinsic hydrogenated amorphous silicon films prepared by high density plasma chemical vapor deposition for solar cell applications

Science.gov (United States)

Chen, Huai-Yi; Lee, Yao-Jen; Chang, Chien-Pin; Koo, Horng-Show; Lai, Chiung-Hui

2013-01-01

P-i-n single-junction hydrogenated amorphous silicon (a-Si:H) thin film solar cells were successfully fabricated in this study on a glass substrate by high density plasma chemical vapor deposition (HDP-CVD) at low power of 50 W, low temperature of 200°C and various hydrogen dilution ratios (R). The open circuit voltage (Voc ), short circuit current density (Jsc ), fill factor (FF) and conversion efficiency (η) of the solar cell as well as the refractive index (n) and absorption coefficient (α) of the i-layer at 600 nm wavelength rise with increasing R until an abrupt drop at high hydrogen dilution, i.e. R > 0.95. However, the optical energy bandgap (Eg ) of the i-layer decreases with the R increase. Voc and α are inversely correlated with Eg . The hydrogen content affects the i-layer and p/i interface quality of the a-Si:H thin film solar cell with an optimal value of R = 0.95, which corresponds to solar cell conversion efficiency of 3.85%. The proposed a-Si:H thin film solar cell is expected to be improved in performance.

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.

Research Progress on Fe-based Amorphous Coatings

Directory of Open Access Journals (Sweden)

LIANG Xiu-bing

2017-09-01

Full Text Available The latest research progresses on Fe-based amorphous coatings were reviewed. The typical alloy system and the classification of Fe-based amorphous coatings were clarified. The status, progress and development of the Fe-based amorphous coatings prepared by thermal spray processing and laser cladding process were discussed. The main mechanical properties and potential applications of the Fe-based amorphous coatings were also described. Furthermore, based on the main problems mentioned above, the future development of the Fe-based amorphous coatings was discussed, including the exploitation preparation technologies of high amorphous content of the Fe-based coatings, the development of the low cost and high performance Fe-based coating alloys system, the broadening application of Fe-based amorphous coatings, and so on.

Survival of Lactobacillus acidophilus and Bacillus coagulans in probiotic and low-fat synbiotic ice-creams

Directory of Open Access Journals (Sweden)

M Hashemi

2013-11-01

Full Text Available In this study, survival of Lactobacillus acidophilus and Bacillus coagulans after freezing and during 90 days of storage at -18○C in probiotic and low-fat synbiotic ice-cream was evaluated. Addition to a control group (which was ordinary ice-cream, two probiotic ice-creams were formulated using L. acidophilus and B. coagulans and two synbiotic ice-creams were prepared using the aforementioned microorganisms but replacing 5% of milk-fat with inulin. The total solids of the ice-cream mixes did not differ significantly, however there was a significant difference (p

Low temperature irradiation effects on iron boron based amorphous metallic alloys

International Nuclear Information System (INIS)

Audouard, A.

1982-09-01

Three Fe-B amorphous alloys (Fe 80 B 20 , Fe 27 Mo 2 B 20 and Fe 75 B 25 ) and the crystallized Fe 3 B alloy have been irradiated at the temperature of liquid hydrogen. Electron irradiation and irradiation by 10 B fission fragments induce point defects in amorphous alloys. These defects are characterized by an intrinsic resistivity and a formation volume. The threshold energy for the displacement of iron atoms has also been calculated. Irradiation by 235 U fission fragments induces some important structural modifications in the amorphous alloys [fr

FT-IR investigation of proton transfer in irradiated ice at 90 K in the absence of mobile bjerrum defects

International Nuclear Information System (INIS)

Devlin, J.P.; Richardson, H.H.

1984-01-01

Samples of cubic and amorphous ice containing isolated D 2 O molecules have been prepared using established methods. Radiolysis with 1.7 MeV electrons at 90 K has been observed to convert the D 2 O in H 2 O cubic ice to primarily coupled HOD pairs (HOD) 2 rather than isolated HOD. Based on the assumption that radiolysis produces an abundance of mobile protons but relatively few mobile orientational defects this result was predictable, i.e., the motion of protons through D 2 O sites converts the D 2 O to coupled (HOD) 2 , while extensive conversion of (HOD) 2 units to isolated HOD requires the passage of orientational defects. Thus, the vanishingly small amount of isolated HOD formed during irradiation has been interpreted as evidence that no significant number of mobile orientational defects are produced by radiolysis. The ability to observe (HOD) 2 as a dominant spectroscopic species has added to the credibility of an earlier thermal study of the kinetics of proton motion in ice that was dependent on the quantitative determination of the (HOD) 2 concentration as a function of reaction time. Furthermore, the observation that protons produced radiolytically fall rapidly into shallow traps, from which they are released by modest warming (to approx.130 K), supports a suggestion by Warman that, for a brief period following a radiolysis pulse, mobile protons are in pseudoequilibrium with protons immobilized by association with L defects. The D 2 O isolated in amorphous ice was similarly converted to HOD by mobile protons produced during radiolysis. However, the broader infrared bands of the amorphous samples have prevented assigning the HOD to a particular form [(HOD) 2 or isolated HOD]. The interesting result was the indication that the proton mobility in amorphous ice is comparable to that for cubic ice

Chemical Evolution of Interstellar Methanol Ice Analogs upon Ultraviolet Irradiation: The Role of the Substrate

Science.gov (United States)

Ciaravella, A.; Jiménez-Escobar, A.; Cosentino, G.; Cecchi-Pestellini, C.; Peres, G.; Candia, R.; Collura, A.; Barbera, M.; Di Cicca, G.; Varisco, S.; Venezia, A. M.

2018-05-01

An important issue in the chemistry of interstellar ices is the role of dust materials. In this work, we study the effect of an amorphous water-rich magnesium silicate deposited onto ZnSe windows on the chemical evolution of ultraviolet-irradiated methanol ices. For comparison, we also irradiate similar ices deposited onto bare ZnSe windows. Silicates are produced at relatively low temperatures exploiting a sol–gel technique. The chemical composition of the synthesized material reflects the forsterite stoichiometry. Si–OH groups and magnesium carbonates are incorporated during the process. The results show that the substrate material does affect the chemical evolution of the ice. In particular, the CO2/CO ratio within the ice is larger for methanol ices deposited onto the silicate substrate as a result of concurrent effects: the photolysis of carbonates present in the adopted substrate as a source of CO2, CO, and carbon and oxygen atoms; reactions of water molecules and hydroxyl radicals released from the substrate with the CO formed in the ice by the photolysis of the methanol ice; and changes in the structure and energy of the silicate surface by ultraviolet irradiation, leading to more favorable conditions for chemical reactions or catalysis at the grain surface. The results of our experiments allow such chemical effects contributed by the various substrate material components to be disentangled.

Diffusion of Lithium Ions in Amorphous and Crystalline Poly(ethylene oxide)_3:LiCF_3SO_3 Polymer Electrolytes

International Nuclear Information System (INIS)

Xue, Sha; Liu, Yingdi; Li, Yaping; Teeters, Dale; Crunkleton, Daniel W.; Wang, Sanwu

2017-01-01

The PEO_3:LiCF_3SO_3 polymer electrolyte has attracted significant research due to high conductivity and enhanced stability in lithium polymer batteries. Most experimental studies have shown that amorphous PEO lithium salt electrolytes have higher conductivity than the crystalline ones. Other studies, however, have shown that crystalline PEO salt complexes can conduct ions. As a result, further theoretical investigations are warranted to help clarify the issue. In this work, we use density functional theory with the climbing image nudged elastic band method to investigate the atomic-scale mechanism of lithium ion transport in the polymer electrolytes. We also use density functional theory and ab initio molecular dynamics simulations to obtain the amorphous structure of PEO_3:LiCF_3SO_3. The diffusion pathways and activation energies of lithium ions in both crystalline and amorphous PEO_3:LiCF_3SO_3 are determined. In crystalline PEO_3:LiCF_3SO_3, the activation energy for the low-barrier diffusion pathway is approximately 1.0 eV. In the amorphous phase, the value is 0.6 eV. This result would support the experimental observation that amorphous PEO_3:LiCF_3SO_3 has higher ionic conductivity than the crystalline phase.

Importing low-density ideas to high-density revitalisation

DEFF Research Database (Denmark)

Arnholtz, Jens; Ibsen, Christian Lyhne; Ibsen, Flemming

2016-01-01

Why did union officials from a high-union-density country like Denmark choose to import an organising strategy from low-density countries such as the US and the UK? Drawing on in-depth interviews with key union officials and internal documents, the authors of this article argue two key points. Fi...

Superplasticity of amorphous alloy

International Nuclear Information System (INIS)

Levin, Yu.B.; Likhachev, V.L.; Sen'kov, O.N.

1988-01-01

Results of mechanical tests of Co 57 Ni 10 Fe 5 Si 11 B 17 amorphous alloy are presented and the effect of crystallization, occurring during deformation process, on plastic low characteristics is investiagted. Superplasticity of amorphous tape is investigated. It is shown, that this effect occurs only when during deformation the crystallization takes place. Process model, based on the usage disclination concepts about glass nature, is suggested

Low temperature irradiation effects on iron-boron based amorphous metallic alloys

International Nuclear Information System (INIS)

Audouard, Alain.

1983-01-01

Three iron-boron amorphous alloys and the crystalline Fe 3 B alloy have been irradiated at liquid hydrogen temperature. 2,4 MeV electron irradiation induces the creation of point defects in the amorphous alloys as well as in the crystalline Fe 3 B alloy. These point defects can be assimilated to iron ''Frenkel pairs''. They have been characterized by determining their intrinsic electrical resistivity and their formation volume. The displacement threshold energy of iron atoms has also been determined. 10 B fission fragments induce, in these amorphous alloys, displacement cascades which lead to stable vacancy rich zones. This irradiation also leads to a structural disorder in relation with the presence of defects. 235 U fission fragments irradiation modifies drastically the structure of the amorphous alloys. The results have been interpreted on the basis of the coexistence of two opposite processes which induce local disorder and crystallisation respectively [fr

A mechanistic model for radiation-induced crystallization and amorphization in U3Si

International Nuclear Information System (INIS)

Rest, J.

1994-06-01

Radiation-induced amorphization is assessed. A rate-theory model is formulated wherein amorphous clusters are formed by the damage event These clusters are considered centers of expansion (CE), or excess-free-volume zones. Simultaneously, centers of compression (CC) are created in the material. The CCs are local regions of increased density that travel through the material as an elastic (e.g., acoustic) shock wave. The CEs can be annihilated upon contact with CCs (annihilation probability depends on height of the energy barrier), forming either a crystallized region indistinguishable from the host material, or a region with a slight disorientation (recrystallized grain). Recrystallized grains grow by the accumulation of additional CCs. Full amorphization is calculated on the basis of achieving a fuel volume fraction consistent with the close packing of spherical entities. Amorphization of a recrystallized grain is hindered by the grain boundary. Preirradiation of U 3 Si above the critical temperature for amorphization results in of nanometer-size grains. Subsequent reirradiation below the critical temperature shows that the material has developed a resistance to radiation-induced amorphization higher dose needed to amorphize the preirradiated samples than now preirradiated samples. In the model, it is assumed that grain boundaries act as effective defect sinks, and that enhanced defect annihilation is responsible for retarding amorphization at low temperature. The calculations have been validated against data from ion-irradiation experiments with U 3 Si. To obtain additional validation, the model has also been applied to the ion-induced motion of the interface between crystalline and amorphous phases of U 3 Si. Results of this analysis are compared to data and results of calculations for ion bombardment of Si

ICE AND DUST IN THE PRESTELLAR DARK CLOUD LYNDS 183: PREPLANETARY MATTER AT THE LOWEST TEMPERATURES

International Nuclear Information System (INIS)

Whittet, D. C. B.; Poteet, C. A.; Bajaj, V. M.; Horne, D.; Chiar, J. E.; Pagani, L.; Shenoy, S. S.; Adamson, A. J.

2013-01-01

Dust grains are nucleation centers and catalysts for the growth of icy mantles in quiescent interstellar clouds, the products of which may accumulate into preplanetary matter when new stars and solar systems form within the clouds. In this paper, we present the first spectroscopic detections of silicate dust and the molecular ices H 2 O, CO, and CO 2 in the vicinity of the prestellar core L183 (L134N). An infrared photometric survey of the cloud was used to identify reddened background stars, and we present spectra covering solid-state absorption features in the wavelength range 2-20 μm for nine of them. The mean composition of the ices in the best-studied line of sight (toward J15542044–0254073) is H 2 O:CO:CO 2 ≈ 100:40:24. The ices are amorphous in structure, indicating that they have been maintained at low temperature (∼ 2 O) correlates with reddening by dust, exhibiting a threshold effect that corresponds to the transition from unmantled grains in the outer layers of the cloud to ice-mantled grains within, analogous to that observed in other dark clouds. A comparison of results for L183 and the Taurus and IC 5146 dark clouds suggests common behavior, with mantles first appearing in each case at a dust column corresponding to a peak optical depth τ 9.7 = 0.15 ± 0.03 in the silicate feature. Our results support a previous conclusion that the color excess E J–K does not obey a simple linear correlation with the total dust column in lines of sight that intercept dense clouds. The most likely explanation is a systematic change in the optical properties of the dust as the density increases

Origin of temperature-induced low friction of sputtered Si-containing amorphous carbon coatings

International Nuclear Information System (INIS)

Jantschner, O.; Field, S.K.; Holec, D.; Fian, A.; Music, D.; Schneider, J.M.; Zorn, K.; Mitterer, C.

2015-01-01

This work reports on a tribological study of magnetron-sputtered silicon-containing amorphous carbon thin films vs. their alumina counterparts. Temperature cycling during ball-on-disk tests in humid air revealed a decrease in the coefficient of friction from 0.3 to <0.02 beyond 240 ± 15 °C. Systematic variation of the environment confirmed oxygen to be responsible for the low friction. X-ray photoelectron spectroscopy of the wear tracks indicates oxidation of Si-C bonds and formation of Si-O-C bonds, followed by further oxidation to SiO 2 above 450 °C. Ab initio molecular dynamics simulations of gas interactions with the a-C surface revealed dissociation of O 2 and the formation of oxides. Additional density functional theory calculations of Si incorporation into a graphene layer, resembling the surface of the film, showed preferential attraction of gaseous species (H, O, -OH, H 2 O), to Si-sites as compared to C-sites. Hence, the temperature- and atmosphere-induced changes in friction coefficient can be understood based on correlative X-ray photoelectron spectroscopy and ab initio data: the formation of Si-O-C bonds stemming from a reaction of the as-deposited coating with atmosphere in the tribological contact is observed by theory and experiment

Low thermal budget annealing technique for high performance amorphous In-Ga-ZnO thin film transistors

Directory of Open Access Journals (Sweden)

Joong-Won Shin

2017-07-01

Full Text Available In this paper, we investigate a low thermal budget post-deposition-annealing (PDA process for amorphous In-Ga-ZnO (a-IGZO oxide semiconductor thin-film-transistors (TFTs. To evaluate the electrical characteristics and reliability of the TFTs after the PDA process, microwave annealing (MWA and rapid thermal annealing (RTA methods were applied, and the results were compared with those of the conventional annealing (CTA method. The a-IGZO TFTs fabricated with as-deposited films exhibited poor electrical characteristics; however, their characteristics were improved by the proposed PDA process. The CTA-treated TFTs had excellent electrical properties and stability, but the CTA method required high temperatures and long processing times. In contrast, the fabricated RTA-treated TFTs benefited from the lower thermal budget due to the short process time; however, they exhibited poor stability. The MWA method uses a low temperature (100 °C and short annealing time (2 min because microwaves transfer energy directly to the substrate, and this method effectively removed the defects in the a-IGZO TFTs. Consequently, they had a higher mobility, higher on-off current ratio, lower hysteresis voltage, lower subthreshold swing, and higher interface trap density than TFTs treated with CTA or RTA, and exhibited excellent stability. Based on these results, low thermal budget MWA is a promising technology for use on various substrates in next generation displays.

Low thermal budget annealing technique for high performance amorphous In-Ga-ZnO thin film transistors

Science.gov (United States)

Shin, Joong-Won; Cho, Won-Ju

2017-07-01

In this paper, we investigate a low thermal budget post-deposition-annealing (PDA) process for amorphous In-Ga-ZnO (a-IGZO) oxide semiconductor thin-film-transistors (TFTs). To evaluate the electrical characteristics and reliability of the TFTs after the PDA process, microwave annealing (MWA) and rapid thermal annealing (RTA) methods were applied, and the results were compared with those of the conventional annealing (CTA) method. The a-IGZO TFTs fabricated with as-deposited films exhibited poor electrical characteristics; however, their characteristics were improved by the proposed PDA process. The CTA-treated TFTs had excellent electrical properties and stability, but the CTA method required high temperatures and long processing times. In contrast, the fabricated RTA-treated TFTs benefited from the lower thermal budget due to the short process time; however, they exhibited poor stability. The MWA method uses a low temperature (100 °C) and short annealing time (2 min) because microwaves transfer energy directly to the substrate, and this method effectively removed the defects in the a-IGZO TFTs. Consequently, they had a higher mobility, higher on-off current ratio, lower hysteresis voltage, lower subthreshold swing, and higher interface trap density than TFTs treated with CTA or RTA, and exhibited excellent stability. Based on these results, low thermal budget MWA is a promising technology for use on various substrates in next generation displays.

Low-emissivity coating of amorphous diamond-like carbon/Ag-alloy multilayer on glass

International Nuclear Information System (INIS)

Chiba, Kiyoshi; Takahashi, Toshiyuki; Kageyama, Takashi; Oda, Hironori

2005-01-01

Transparent low-emissivity (low-e) coatings comprising dielectrics of amorphous diamond-like carbon (DLC) and Ag-alloy films are investigated. All films have been prepared by dc magnetron sputtering. An index of refraction of the DLC film deposited in a gas mixture of Ar/H 2 (4%) shows n = 1.80 + 0.047i at 500 nm wavelength. A multilayer stack of DLC (70 nm thick)/Ag 87.5 Cu 12.5 -alloy (10 nm)/DLC (140 nm)/Ag 87.5 Cu 12.5 -alloy (10 nm)/DLC (70 nm) has revealed clear interference spectra with spectra selectivity. This coating performs low emittance less than 0.1 for black body radiation at 297 K, exhibiting a transparent heat mirror property embedded in DLC films

Deuterium in astrophysical ice analogues: Isotope exchange and IR detection sensitivity for HDO

Science.gov (United States)

Escribano, R. M.; Galvez, O.; Mate, B.; Herrero, V. J.

2011-12-01

Among D-bearing molecules, water is especially interesting from an astrophysical point of view. Although the deuterium content of water in astronomical environments is relatively small as compared with other molecules, it holds most valuable information, still largely undeciphered, on the dynamics of formation and evaporation of ice grain mantels in protostellar regions [1], and is crucial for the understanding of the formation of the Solar System and the Earth [2]. In this work, we have used the OD stretching bands of HDO and D2O molecules in various ice mixtures formed by vapor deposition on a cold substrate (see ref [3] for a description of the experimental set-up) to study the sensitivity of the IR technique for the detection of HDO in ice samples, and to monitor processes of H/D isotope exchange in these solids. It is found that the detection sensitivity is strongly dependent on the ice structure. The OD band is extremely broad and tends to disappear into the absorption continuum of H2O for low temperature amorphous samples. Detectable HDO/H2O ratios with this technique may range from a few per cent for amorphous samples to a few per thousand in crystalline ice. These relatively high upper limits and the appreciable dependence of the band shape on temperature, complicating the interpretation of data from many lines of sight, may question the usefulness of this technique. Isotopic H/D exchange in mixed ices of H2O/D2O is found to start at ~ 120 K and is greatly accelerated at 150 K, as crystallization proceeds in the ice. The process is mainly driven by proton transfer assisted by orientational defect mobility. Annealed amorphous samples are more favourable for isotope exchange than samples directly formed in the crystalline phase. The annealing process seems to lead to polycrystalline ice morphology with a higher defect activity. The present data emphasize the relevance of a depletion mechanism for D atoms in hydroxylic bonds in the solid state, recently

Low-temperature behavior of core-softened models: Water and silica behavior

International Nuclear Information System (INIS)

Jagla, E. A.

2001-01-01

A core-softened model of a glass forming fluid is numerically studied in the limit of very low temperatures. The model shows two qualitatively different behaviors depending on the strength of the attraction between particles. For no or low attraction, the changes of density as a function of pressure are smooth, although hysteretic due to mechanical metastabilities. For larger attraction, sudden changes of density upon compressing and decompressing occur. This global mechanical instability is correlated to the existence of a thermodynamic first-order amorphous-amorphous transition. The two different behaviors obtained correspond qualitatively to the different phenomenology observed in silica and water

OPTICAL CONSTANTS AND LAB SPECTRA OF WATER ICE V1.0

Data.gov (United States)

National Aeronautics and Space Administration — Transmission spectra of amorphous and crystalline H2O-ice at temperatures from 20-150 K for a wavelength range from 1.11 to 2.63 microns. These spectra have not been...

OPTICAL CONSTANTS AND LAB SPECTRA OF WATER ICE V1.1

Data.gov (United States)

National Aeronautics and Space Administration — Transmission spectra of amorphous and crystalline H2O-ice at temperatures from 20-150 K for a wavelength range from 1.11 to 2.63 microns. These spectra have not been...

The relation between sea ice thickness and freeboard in the Arctic

Directory of Open Access Journals (Sweden)

V. Alexandrov

2010-09-01

Full Text Available Retrieval of Arctic sea ice thickness from CryoSat-2 radar altimeter freeboard data requires observational data to verify the relation between these two variables. In this study in-situ ice and snow data from 689 observation sites, obtained during the Sever expeditions in the 1980s, have been used to establish an empirical relation between thickness and freeboard of FY ice in late winter. Estimates of mean and variability of snow depth, snow density and ice density were produced on the basis of many field observations. These estimates have been used in the hydrostatic equilibrium equation to retrieve ice thickness as a function of ice freeboard, snow depth and snow/ice density. The accuracy of the ice thickness retrieval has been calculated from the estimated variability in ice and snow parameters and error of ice freeboard measurements. It is found that uncertainties of ice density and freeboard are the major sources of error in ice thickness calculation. For FY ice, retrieval of ≈ 1.0 m (2.0 m thickness has an uncertainty of 46% (37%, and for MY ice, retrieval of 2.4 m (3.0 m thickness has an uncertainty of 20% (18%, assuming that the freeboard error is ± 0.03 m for both ice types. For MY ice the main uncertainty is ice density error, since the freeboard error is relatively smaller than that for FY ice. If the freeboard error can be reduced to 0.01 m by averaging measurements from CryoSat-2, the error in thickness retrieval is reduced to about 32% for a 1.0 m thick FY floe and to about 18% for a 2.4 m thick MY floe. The remaining error is dominated by uncertainty in ice density. Provision of improved ice density data is therefore important for accurate retrieval of ice thickness from CryoSat-2 data.

Tuning Ice Nucleation with Supercharged Polypeptides

NARCIS (Netherlands)

Yang, Huige; Ma, Chao; Li, Kaiyong; Liu, Kai; Loznik, Mark; Teeuwen, Rosalie; van Hest, Jan C. M.; Zhou, Xin; Herrmann, Andreas; Wang, Jianjun

2016-01-01

Supercharged unfolded polypeptides (SUPs) are exploited for controlling ice nucleation via tuning the nature of charge and charge density of SUPs. The results show that positively charged SUPs facilitate ice nucleation, while negatively charged ones suppress it. Moreover, the charge density of the

Low-dose electron energy-loss spectroscopy using electron counting direct detectors.

Science.gov (United States)

Maigné, Alan; Wolf, Matthias

2018-03-01

Since the development of parallel electron energy loss spectroscopy (EELS), charge-coupled devices (CCDs) have been the default detectors for EELS. With the recent development of electron-counting direct-detection cameras, micrographs can be acquired under very low electron doses at significantly improved signal-to-noise ratio. In spectroscopy, in particular in combination with a monochromator, the signal can be extremely weak and the detection limit is principally defined by noise introduced by the detector. Here we report the use of an electron-counting direct-detection camera for EEL spectroscopy. We studied the oxygen K edge of amorphous ice and obtained a signal noise ratio up to 10 times higher than with a conventional CCD.We report the application of electron counting to record time-resolved EEL spectra of a biological protein embedded in amorphous ice, revealing chemical changes observed in situ while exposed by the electron beam. A change in the fine structure of nitrogen K and the carbon K edges were recorded during irradiation. A concentration of 3 at% nitrogen was detected with a total electron dose of only 1.7 e-/Å2, extending the boundaries of EELS signal detection at low electron doses.

More accurate determination of the quantity of ice crystallized at low cooling rates in the glycerol and 1,2-propanediol aqueous solutions: comparison with equilibrium.

Science.gov (United States)

Boutron, P

1984-04-01

It is generally assumed that when cells are cooled at rates close to those corresponding to the maximum of survival, once supercooling has ceased, above the eutectic melting temperature the extracellular ice is in equilibrium with the residual solution. This did not seem evident to us due to the difficulty of ice crystallization in cryoprotective solutions. The maximum quantities of ice crystallized in glycerol and 1,2-propanediol solutions have been calculated from the area of the solidification and fusion peaks obtained with a Perkin-Elmer DSC-2 differential scanning calorimeter. The accuracy has been improved by several corrections: better defined baseline, thermal variation of the heat of fusion of the ice, heat of solution of the water from its melting with the residual solution. More ice crystallizes in the glycerol than in the 1,2-propanediol solutions, of which the amorphous residue contains about 40 to 55% 1,2-propanediol. The equilibrium values are unknown in the presence of 1,2-propanediol. With glycerol, in our experiments, the maximum is first lower than the equilibrium but approaches it as the concentration increases. It is not completely determined by the colligative properties of the solutes.

Applications in the Nuclear Industry for Corrosion-Resistant Amorphous-Metal Thermal-Spray Coatings

International Nuclear Information System (INIS)

Farmer, J; Choi, J

2007-01-01

Amorphous metal and ceramic thermal spray coatings have been developed that can be used to enhance the corrosion resistance of containers for the transportation, aging and disposal of spent nuclear fuel and high-level radioactive wastes. Fe-based amorphous metal formulations with chromium, molybdenum and tungsten have shown the corrosion resistance believed to be necessary for such applications. Rare earth additions enable very low critical cooling rates to be achieved. The boron content of these materials, and their stability at high neutron doses, enable them to serve as high efficiency neutron absorbers for criticality control. Ceramic coatings may provide even greater corrosion resistance for container applications, though the boron-containing amorphous metals are still favored for criticality control applications. These amorphous metal and ceramic materials have been produced as gas atomized powders and applied as near full density, non-porous coatings with the high-velocity oxy-fuel process. This paper summarizes the performance of these coatings as corrosion-resistant barriers, and as neutron absorbers. Relevant corrosion models are also discussed, as well as a cost model to quantify the economic benefits possible with these new materials

Structure and density for As23Se67Ge10 amorphous films

International Nuclear Information System (INIS)

Shchurova, T.N.; Savchenko, N.D.

1999-01-01

The effect of thermal annealing and argon laser irradiation on structure and volume for thin amorphous As 23 Se 67 Ge 10 films deposited by thermal evaporation has been investigated. The short-range structure for the annealed films has been found to be more ordered as compared to the irradiated films. The decrease in film volume under thermal annealing and its increase under laser irradiation have been shown. The changes in film volume have been discussed in the context of non-ergodic model for the amorphous state equilibrium taking into account forces acting from the substrate

Ultra low nanowear in novel chromium/amorphous chromium carbide nanocomposite films

Science.gov (United States)

Yate, Luis; Martínez-de-Olcoz, Leyre; Esteve, Joan; Lousa, Arturo

2017-10-01

In this work, we report the first observation of novel nanocomposite thin films consisting of nanocrystalline chromium embedded in an amorphous chromium carbide matrix (nc-Cr/a-CrC) with relatively high hardness (∼22,3 GPa) and ultra low nanowear. The films were deposited onto silicon substrates using a magnetic filtered cathodic arc deposition system at various negative bias voltages, from 50 to 450 V. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) suggested the co-existence of chromium and chromium carbide phases, while high resolution transmission electron microscopy (HRTEM) confirmed the presence of the nc-Cr/a-CrC structure. The friction coefficient measured with the ball-on disk technique and the nanowear results showed a strong correlation between the macro and nano-tribological properties of the samples. These novel nanocomposite films show promising properties as solid lubricant and wear resistant coatings with relatively high hardness, low friction coefficient and ultra low nanowear.

Interplay of the Glass Transition and the Liquid-Liquid Phase Transition in Water

Science.gov (United States)

Giovambattista, Nicolas; Loerting, Thomas; Lukanov, Boris R.; Starr, Francis W.

2012-01-01

Water has multiple glassy states, often called amorphous ices. Low-density (LDA) and high-density (HDA) amorphous ice are separated by a dramatic, first-order like phase transition. It has been argued that the LDA-HDA transformation connects to a first-order liquid-liquid phase transition (LLPT) above the glass transition temperature Tg. Direct experimental evidence of the LLPT is challenging to obtain, since the LLPT occurs at conditions where water rapidly crystallizes. In this work, we explore the implications of a LLPT on the pressure dependence of Tg(P) for LDA and HDA by performing computer simulations of two water models – one with a LLPT, and one without. In the absence of a LLPT, Tg(P) for all glasses nearly coincide. When there is a LLPT, different glasses exhibit dramatically different Tg(P) which are directly linked with the LLPT. Available experimental data for Tg(P) are only consistent with the scenario including a LLPT. PMID:22550566

Ultrafast carrier dynamics in tetrahedral amorphous carbon: carrier trapping versus electron-hole recombination

International Nuclear Information System (INIS)

Carpene, E; Mancini, E; Dallera, C; Schwen, D; Ronning, C; Silvestri, S De

2007-01-01

We report the investigation of the ultrafast carrier dynamics in thin tetrahedral amorphous carbon films by means of femtosecond time-resolved reflectivity. We estimated the electron-phonon relaxation time of a few hundred femtoseconds and we observed that under low optical excitation photo-generated carriers decay according to two distinct mechanisms attributed to trapping by defect states and direct electron-hole recombination. With high excitation, when photo-carrier and trap densities are comparable, a unique temporal evolution develops, as the time dependence of the trapping process becomes degenerate with the electron-hole recombination. This experimental evidence highlights the role of defects in the ultrafast electronic dynamics and is not specific to this particular form of carbon, but has general validity for amorphous and disordered semiconductors

Low Thermal Conductivity of Bulk Amorphous Si1- x Ge x Containing Nano-Sized Crystalline Particles Synthesized by Ball-Milling Process

Science.gov (United States)

Muthusamy, Omprakash; Nishino, Shunsuke; Ghodke, Swapnil; Inukai, Manabu; Sobota, Robert; Adachi, Masahiro; Kiyama, Makato; Yamamoto, Yoshiyuki; Takeuchi, Tsunehiro; Santhanakrishnan, Harish; Ikeda, Hiroya; Hayakawa, Yasuhiro

2018-06-01

Amorphous Si0.65Ge0.35 powder containing a small amount of nano-sized crystalline particles was synthesized by means of the mechanical alloying process. Hot pressing for 24 h under the pressure of 400 MPa at 823 K, which is below the crystallization temperature, allowed us to obtain bulk amorphous Si-Ge alloy containing a small amount of nanocrystals. The thermal conductivity of the prepared bulk amorphous Si-Ge alloy was extremely low, showing a magnitude of less than 1.35 Wm-1 K-1 over the entire temperature range from 300 K to 700 K. The sound velocity of longitudinal and transverse waves for the bulk amorphous Si0.65Ge0.35 were measured, and the resulting values were 5841 m/s and 2840 m/s, respectively. The estimated mean free path of phonons was kept at the very small value of ˜ 4.2 nm, which was mainly due to the strong scattering limit of phonons in association with the amorphous structure.

Hemodynamics alter arterial low-density lipoprotein metabolism

International Nuclear Information System (INIS)

Warty, V.S.; Calvo, W.J.; Berceli, S.A.; Pham, S.M.; Durham, S.J.; Tanksale, S.K.; Klein, E.C.; Herman, I.M.; Borovetz, H.S.

1989-01-01

We have investigated the role of hemodynamic factors on low-density lipoprotein transport and metabolism in the intact arterial wall. Freshly excised canine carotid blood vessels were exposed to well-defined pulsatile flow in vitro for continuous periods up to 20 hours. We chose to impose the following hemodynamic conditions on our test carotid arteries: normotension, hypertension (at physiologic flow conditions), and hypertension coupled with elevated flow of canine serum perfusate. In several experiments the effect of endothelial denudation was examined in carotid arteries exposed to normotensive pulsatile flow. A trapped ligand method was used for quantitating low-density lipoprotein uptake and metabolism in the arterial wall. The distribution of both intact and degraded low-density lipoprotein fractions was determined from measurements of radiolabelled low-density lipoprotein activity within thin radial sections of perfused arteries. Our results suggest that both hypertensive hemodynamic simulations exacerbate the uptake of low-density lipoprotein within the arterial wall (by a factor of three to nine). The percentage of low-density lipoprotein that undergoes irreversible degradation falls from 41% under normotensive conditions to below 30% when hypertensive conditions are imposed, indicating that degradative processes are not proportionally elevated with the accelerated influx. A similar pattern is observed for deendothelialized vessels

Dynamics of colloidal particles in ice

KAUST Repository

Spannuth, Melissa

2011-01-01

We use x-ray photon correlation spectroscopy (XPCS) to probe the dynamics of colloidal particles in polycrystalline ice. During freezing, the dendritic ice morphology and rejection of particles from the ice created regions of high particle density, where some of the colloids were forced into contact and formed disordered aggregates. The particles in these high density regions underwent ballistic motion, with a characteristic velocity that increased with temperature. This ballistic motion is coupled with both stretched and compressed exponential decays of the intensity autocorrelation function. We suggest that this behavior could result from ice grain boundary migration. © 2011 American Institute of Physics.

Amorphous gallium oxide grown by low-temperature PECVD

KAUST Repository

Kobayashi, Eiji; Boccard, Mathieu; Jeangros, Quentin; Rodkey, Nathan; Vresilovic, Daniel; Hessler-Wyser, Aï cha; Dö beli, Max; Franta, Daniel; De Wolf, Stefaan; Morales-Masis, Monica; Ballif, Christophe

2018-01-01

demonstrate the growth of hydrogenated amorphous gallium oxide (a-GaO:H) thin-films by plasma-enhanced chemical vapor deposition (PECVD) at temperatures below 200 °C. In this way, conformal films are deposited at high deposition rates, achieving high broadband

Low density in liver of idiopathic portal hypertension

International Nuclear Information System (INIS)

Ishito, Hiroyuki

1988-01-01

In order to evaluate the diagnostic value of low density in liver on computed tomography (CT), CT scans of 11 patients with idiopathic portal hypertension (IPH) were compared with those from 22 cirrhotic patients, two patients with scarred liver and 16 normal subjects. Low densities on plain CT scans in patients with IPH were distinctly different from those observed in normal liver. Some of the low densities had irregular shape with unclear margin and were scattered near the liver surface, and others had vessel-like structures with unclear margin and extended as far as near the liver surface. Ten of the 11 patients with IPH had low densities mentioned above, while none of the 22 cirrhotic patients had such low densities. The present results suggest that the presence of low densities in liver on plain CT scan is clinically beneficial in diagnosis of IPH. (author)

Amorphous nickel/cobalt tungsten sulfide electrocatalysts for high-efficiency hydrogen evolution reaction

Energy Technology Data Exchange (ETDEWEB)

Yang, Lun [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Wu, Xinglong, E-mail: hkxlwu@nju.edu.cn [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Department of Physics, NingBo University, NingBo 315001 (China); Zhu, Xiaoshu [Center for Analysis and Testing, Nanjing Normal University, Nanjing 210093 (China); He, Chengyu; Meng, Ming; Gan, Zhixing [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)

2015-06-30

Graphical abstract: - Highlights: • Amorphous nickel/cobalt tungsten sulfides were synthesized by a thermolytic process. • Amorphous NiWS and CoWS could realize hydrogen evolution efficiently. • Ni/Co promotion and annealing alter the porous structure and chemical bonding states. • Active sites on the surface of amorphous WS{sub x} are increased with Ni or Co doping. • Amorphous NiWS and CoWS have immense potentials in water splitting devices. - Abstract: The hydrogen evolution reaction (HER), an appealing solution for future energy supply, requires efficient and inexpensive electrocatalysts with abundant active surface sites. Although crystalline MoS{sub 2} and WS{sub 2} are promising candidates, their activity is dominated by edge sites. Amorphous tungsten sulfide prepared so far lacks the required active sites and its application has thus been hampered. In this work, nickel and cobalt incorporated amorphous tungsten sulfide synthesized by a thermolytic process is demonstrated to enhance the HER efficiency dramatically. The amorphous nickel tungsten sulfide (amorphous NiWS) annealed at 210 °C delivers the best HER performance in this system boasting a Tafel slope of 55 mV per decade and current density of 8.6 mA cm{sup −2} at 250 mV overpotential in a sustained test for 24 h. The introduction of Ni or Co into the catalyst and subsequent thermal treatment alters the porous structure and chemical bonding states thereby increasing the density of active sites on the surface.

Low Density Supersonic Decelerators

Data.gov (United States)

National Aeronautics and Space Administration — The Low-Density Supersonic Decelerator project will demonstrate the use of inflatable structures and advanced parachutes that operate at supersonic speeds to more...

Quantitative orientational characterization if low - density polyethylene blow films by x-ray and birefringence

International Nuclear Information System (INIS)

Taheri Qazvini, N.; Mohammadi, N.; Ghaffarian, R.; Assempour, H.; Haghighatkish, M.

2002-01-01

The effect of two important parameters of film blowing processes, i.e., take-up ration and blow-up ratio, on the overall orientation of low-density blown films have been investigated using birefringence measurements. Furthermore, by combining x-ray diffraction pole figure analysis and birefringence, the White and Spruiell biaxial orientation functions have been determined for aforementioned sample. Within the range of processing condition studied, increasing take-up ratio, increases orientation in both machine and transverse direction. Upon increasing blow-up ratio, orientation in the transverse direction increases and the overall orientation state approaches to equal biaxial one. Characterization of the crystalline regions by pole figure analysis reveals that a and b crystallographic axes preferentially orientate in the film plane and the direction normal to it, respectively. The amorphous regions do not have any preferential orientation

A zero density change phase change memory material: GeTe-O structural characteristics upon crystallisation.

Science.gov (United States)

Zhou, Xilin; Dong, Weiling; Zhang, Hao; Simpson, Robert E

2015-06-11

Oxygen-doped germanium telluride phase change materials are proposed for high temperature applications. Up to 8 at.% oxygen is readily incorporated into GeTe, causing an increased crystallisation temperature and activation energy. The rhombohedral structure of the GeTe crystal is preserved in the oxygen doped films. For higher oxygen concentrations the material is found to phase separate into GeO2 and TeO2, which inhibits the technologically useful abrupt change in properties. Increasing the oxygen content in GeTe-O reduces the difference in film thickness and mass density between the amorphous and crystalline states. For oxygen concentrations between 5 and 6 at.%, the amorphous material and the crystalline material have the same density. Above 6 at.% O doping, crystallisation exhibits an anomalous density change, where the volume of the crystalline state is larger than that of the amorphous. The high thermal stability and zero-density change characteristic of Oxygen-incorporated GeTe, is recommended for efficient and low stress phase change memory devices that may operate at elevated temperatures.

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.

Mixed ice accretion on aircraft wings

Science.gov (United States)

Janjua, Zaid A.; Turnbull, Barbara; Hibberd, Stephen; Choi, Kwing-So

2018-02-01

Ice accretion is a problematic natural phenomenon that affects a wide range of engineering applications including power cables, radio masts, and wind turbines. Accretion on aircraft wings occurs when supercooled water droplets freeze instantaneously on impact to form rime ice or runback as water along the wing to form glaze ice. Most models to date have ignored the accretion of mixed ice, which is a combination of rime and glaze. A parameter we term the "freezing fraction" is defined as the fraction of a supercooled droplet that freezes on impact with the top surface of the accretion ice to explore the concept of mixed ice accretion. Additionally we consider different "packing densities" of rime ice, mimicking the different bulk rime densities observed in nature. Ice accretion is considered in four stages: rime, primary mixed, secondary mixed, and glaze ice. Predictions match with existing models and experimental data in the limiting rime and glaze cases. The mixed ice formulation however provides additional insight into the composition of the overall ice structure, which ultimately influences adhesion and ice thickness, and shows that for similar atmospheric parameter ranges, this simple mixed ice description leads to very different accretion rates. A simple one-dimensional energy balance was solved to show how this freezing fraction parameter increases with decrease in atmospheric temperature, with lower freezing fraction promoting glaze ice accretion.

Anomalous magnetoresistance in amorphous metals

International Nuclear Information System (INIS)

Kuz'menko, V.M.; Vladychkin, A.N.; Mel'nikov, V.I.; Sudovtsev, A.I.

1984-01-01

The magnetoresistance of amorphous Bi, Ca, V and Yb films is investigated in fields up to 4 T at low temperatures. For all metals the magnetoresistance is positive, sharply decreases with growth of temperature and depends anomalously on the magnetic field strength. For amorphous superconductors the results agree satisfactorily with the theory of anomalous magnetoresistance in which allowance is made for scattering of electrons by the superconducting fluctuations

Low density, variation in sintered density and high nitrogen in uranium dioxide

International Nuclear Information System (INIS)

Balakrishna, Palanki; Murty, B.N.; Anuradha, M.; Nageshwara Rao, P.; Jayaraj, R.N.; Ganguly, C.

2000-01-01

Low sintered density and density variation in sintered UO 2 were found to have been caused by non uniformity in the granule feed characteristics to the compacting press. The nitrogen impurity content of sintered UO 2 was found to be sintering furnace related and associated with low sintered density pellets. The problems of low density, variation in sintered density and high nitrogen could be solved by the replacement of the prevailing four punch precompaction by a single punch process; by the introduction of a vibro-sieve for the separation of fine particles from the press feed granules; by innovation in the powder feed shoe design for simultaneous and uniform dispensing of powder in all the die holes; by increasing the final compaction pressure and by modifying the gas flows and preheat temperature in the sintering furnace. (author)

A comparative study on thermal, mechanical and dielectric characteristics of low density polyethylene crosslinked by radiation and chemical methods

International Nuclear Information System (INIS)

Kim, B.H.; Ling, D.Y.; Kim, J.S.

1976-01-01

A comparative study on thermal, static mechanical and dielectric characteristics were made over a temperature range of ca. 20 0 C to 320 0 C and a frequency range of KHZ band on low density polyethylene specimens crosslinked, respectively, by radiation and chemical method. The thermal property of both specimens shows that softening point appears to unchange by crosslinking however, melting and liquidizing temperatures attain rapid increase at the imitation of crosslinking. Mechanical properties show little difference to both specimens crosslinked by different method, further the behaviors were discussed in connection with the relaxation of molecular segments in amorphous phase. Dose dependent dielectric characteristics observed at ambient temperature under several fixed frequencies exhibit extremities at ca. 20 Mrad and the behaviors also were interpreted qualitatively by taking into consideration of dipole concentration change in amorphous phase together with the role of specimen geometry to the depth of oxidative layer. Observing frequency dependent dielectric characteristics, it was also proved that ionic conduction loss is appreciably greater in the specimen prepared by chemical method than that by radiation. (author)

Ab initio simulation of amorphous silicon

International Nuclear Information System (INIS)

Cooper, N.C.; McKenzie, D.R.; Goringe, C.M.

1999-01-01

Full text: A first-principles Car-Parrinello molecular dynamics simulation of amorphous silicon is presented. Density Functional Theory is used to describe the forces between the atoms in a 64 atom supercell which is periodically repeated throughout space in order to generate an infinite network of atoms (a good approximation to a real solid). A quench from the liquid phase is used to achieve a quenched amorphous structure, which is subjected to an annealing cycle to improve its stability. The final, annealed network is in better agreement with experiment than any previous simulation of amorphous silicon. Significantly, the predicted average first-coordination numbers of 3.56 and 3.84 for the quenched and annealed structures from this simulation agree very closely with the experimental values of 3.55 and 3.90 respectively, whereas all previous simulations yielded first coordination numbers greater than 4. This improved agreement in coordination numbers is important because it supports the experimental finding that dangling bonds (which are associated with under-coordinated atoms) are more prevalent than floating bonds (the strained, longer bond of a five coordinate atom) in pure amorphous silicon. Finally, the effect of adding hydrogen to amorphous silicon was investigated by specifically placing hydrogen atoms at the likely defect sites. After a structural relaxation to optimise the positions of these hydrogen atoms, the localised electronic states associated with these defects are absent. Thus hydrogen is responsible for removing these defect states (which are able to trap carriers) from the edge of the band gap of the amorphous silicon. These results confirm the widely held ideas about the effect of hydrogen in producing remarkable improvements in the electronic properties of amorphous silicon

Amorphization, morphological instability and crystallization of krypton ion irradiated germanium

International Nuclear Information System (INIS)

Wang, L.M.; Birtcher, R.C.

1991-01-01

Krypton ion irradiation of crystalline Ge and subsequent thermal annealing were both carried out with in situ transmission electron microscopy observations. The temperature dependence of the amorphization dose, effect of foil thickness, morphological changes during continuous irradiation of the amorphous state as well as the effect of implanted gas have been determined. The dose of 1.5 MeV Kr required for amorphization increases with increasing temperature. At a fixed temperature, the amorphization dose is higher for thicker regions of the specimen. Continuous irradiation of amorphous Ge at room temperature results in a high density of small cavities which grow with increasing dose. Cavities do not coalesce during growth but develop into irregular-shaped holes that eventually transform the amorphous Ge into a sponge-like material. Formation of the spongy structure is independent of Kr implantation. The crystallization temperature and the morphology of recrystallized Ge depend on the Kr + dose. Voids are expelled from recrystallized Ge, while the sponge-like structure is retained after crystallization. (author)

Amorphous and Nanocomposite Materials for Energy-Efficient Electric Motors

Science.gov (United States)

Silveyra, Josefina M.; Xu, Patricia; Keylin, Vladimir; DeGeorge, Vincent; Leary, Alex; McHenry, Michael E.

2016-01-01

We explore amorphous soft-magnetic alloys as candidates for electric motor applications. The Co-rich system combines the benefits of low hysteretic and eddy-current losses while exhibiting negligible magnetostriction and robust mechanical properties. The amorphous precursors can be devitrified to form nanocomposite magnets. The superior characteristics of these materials offer the advantages of ease of handling in the manufacturing processing and low iron losses during motor operation. Co-rich amorphous ribbons were laser-cut to build a stator for a small demonstrator permanent-magnet machine. The motor was tested up to ~30,000 rpm. Finite-element analyses proved that the iron losses of the Co-rich amorphous stator were ~80% smaller than for a Si steel stator in the same motor, at 18,000 rpm (equivalent to an electric frequency of 2.1 kHz). These low-loss soft magnets have great potential for application in highly efficient high-speed electric machines, leading to size reduction as well as reduction or replacement of rare earths in permanent-magnet motors. More studies evaluating further processing techniques for amorphous and nanocomposite materials are needed.

Structure-property relations in amorphous carbon for photovoltaics

International Nuclear Information System (INIS)

Risplendi, Francesca; Cicero, Giancarlo; Bernardi, Marco; Grossman, Jeffrey C.

2014-01-01

Carbon is emerging as a material with great potential for photovoltaics (PV). However, the amorphous form (a-C) has not been studied in detail as a PV material, even though it holds similarities with amorphous Silicon (a-Si) that is widely employed in efficient solar cells. In this work, we correlate the structure, bonding, stoichiometry, and hydrogen content of a-C with properties linked to PV performance such as the electronic structure and optical absorption. We employ first-principles molecular dynamics and density functional theory calculations to generate and analyze a set of a-C structures with a range of densities and hydrogen concentrations. We demonstrate that optical and electronic properties of interest in PV can be widely tuned by varying the density and hydrogen content. For example, sunlight absorption in a-C films can significantly exceed that of a same thickness of a-Si for a range of densities and H contents in a-C. Our results highlight promising features of a-C as the active layer material of thin-film solar cells.

Structure-property relations in amorphous carbon for photovoltaics

Energy Technology Data Exchange (ETDEWEB)

Risplendi, Francesca; Cicero, Giancarlo [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, 10129 Torino (Italy); Bernardi, Marco [Department of Physics, University of California, Berkeley, California 94720 (United States); Grossman, Jeffrey C., E-mail: jcg@mit.edu [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2014-07-28

Carbon is emerging as a material with great potential for photovoltaics (PV). However, the amorphous form (a-C) has not been studied in detail as a PV material, even though it holds similarities with amorphous Silicon (a-Si) that is widely employed in efficient solar cells. In this work, we correlate the structure, bonding, stoichiometry, and hydrogen content of a-C with properties linked to PV performance such as the electronic structure and optical absorption. We employ first-principles molecular dynamics and density functional theory calculations to generate and analyze a set of a-C structures with a range of densities and hydrogen concentrations. We demonstrate that optical and electronic properties of interest in PV can be widely tuned by varying the density and hydrogen content. For example, sunlight absorption in a-C films can significantly exceed that of a same thickness of a-Si for a range of densities and H contents in a-C. Our results highlight promising features of a-C as the active layer material of thin-film solar cells.

Physisorption and desorption of H2, HD and D2 on amorphous solid water ice. Effect on mixing isotopologue on statistical population of adsorption sites.

Science.gov (United States)

Amiaud, Lionel; Fillion, Jean-Hugues; Dulieu, François; Momeni, Anouchah; Lemaire, Jean-Louis

2015-11-28

We study the adsorption and desorption of three isotopologues of molecular hydrogen mixed on 10 ML of porous amorphous water ice (ASW) deposited at 10 K. Thermally programmed desorption (TPD) of H2, D2 and HD adsorbed at 10 K have been performed with different mixings. Various coverages of H2, HD and D2 have been explored and a model taking into account all species adsorbed on the surface is presented in detail. The model we propose allows to extract the parameters required to fully reproduce the desorption of H2, HD and D2 for various coverages and mixtures in the sub-monolayer regime. The model is based on a statistical description of the process in a grand-canonical ensemble where adsorbed molecules are described following a Fermi-Dirac distribution.

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

Permeation of Light Gases through Hexagonal Ice

Directory of Open Access Journals (Sweden)

Luis Gales

2012-09-01

Full Text Available Gas separation using porous solids have attracted great attention due to their energetic applications. There is an enormous economic and environmental interest in the development of improved technologies for relevant processes, such as H₂ production, CO₂ separation or O₂ and N₂ purification from air. New materials are needed for achieving major improvements. Crystalline materials, displaying unidirectional and single-sized pores, preferentially with low pore tortuosity and high pore density, are promising candidates for membrane synthesis. Herein, we study hexagonal ice crystals as an example of this class of materials. By slowly growing ice crystals inside capillary tubes we were able to measure the permeation of several gas species through ice crystals and investigate its relation with both the size of the guest molecules and temperature of the crystal.

Pressure-induced transformations in computer simulations of glassy water

Science.gov (United States)

Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas

2013-11-01

Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a "P-T phase diagram" for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water.

Effect of silane dilution on intrinsic stress in glow discharge hydrogenated amorphous silicon films

Science.gov (United States)

Harbison, J. P.; Williams, A. J.; Lang, D. V.

1984-02-01

Measurements of the intrinsic stress in hydrogenated amorphous silicon (a-Si : H) films grown by rf glow discharge decomposition of silane diluted to varying degrees in argon are presented. Films are found to grow under exceedingly high compressive stress. Low values of macroscopic film density and low stress values are found to correlate with high growth rate. An abrupt drop in stress occurs between 2 and 3% silane at precisely the point where columnar growth morphology appears. No corresponding abrupt change is noted in density, growth rate, or plasma species concentrations as determined by optical emissioin spectroscopy. Finally a model of diffusive incorporation of hydrogen or some gaseous impurity during growth into the bulk of the film behind the growing interface is proposed to explain the results.

Frost flowers on young Arctic sea ice: The climatic, chemical, and microbial significance of an emerging ice type

Science.gov (United States)

Barber, D. G.; Ehn, J. K.; Pućko, M.; Rysgaard, S.; Deming, J. W.; Bowman, J. S.; Papakyriakou, T.; Galley, R. J.; Søgaard, D. H.

2014-10-01

Ongoing changes in Arctic sea ice are increasing the spatial and temporal range of young sea ice types over which frost flowers can occur, yet the significance of frost flowers to ocean-sea ice-atmosphere exchange processes remains poorly understood. Frost flowers form when moisture from seawater becomes available to a cold atmosphere and surface winds are low, allowing for supersaturation of the near-surface boundary layer. Ice grown in a pond cut in young ice at the mouth of Young Sound, NE Greenland, in March 2012, showed that expanding frost flower clusters began forming as soon as the ice formed. The new ice and frost flowers dramatically changed the radiative and thermal environment. The frost flowers were about 5°C colder than the brine surface, with an approximately linear temperature gradient from their base to their upper tips. Salinity and δ18O values indicated that frost flowers primarily originated from the surface brine skim. Ikaite crystals were observed to form within an hour in both frost flowers and the thin pond ice. Average ikaite concentrations were 1013 µmol kg-1 in frost flowers and 1061 µmol kg-1 in the surface slush layer. Chamber flux measurements confirmed an efflux of CO2 at the brine-wetted sea ice surface, in line with expectations from the brine chemistry. Bacteria concentrations generally increased with salinity in frost flowers and the surface slush layer. Bacterial densities and taxa indicated that a selective process occurred at the ice surface and confirmed the general pattern of primary oceanic origin versus negligible atmospheric deposition.

Amorphous carbon nanofibres inducing high specific capacitance of deposited hydrous ruthenium oxide

International Nuclear Information System (INIS)

Barranco, V.; Pico, F.; Ibanez, J.; Lillo-Rodenas, M.A.; Linares-Solano, A.; Kimura, M.; Oya, A.; Rojas, R.M.; Amarilla, J.M.; Rojo, J.M.

2009-01-01

Composites consisting of ruthenium oxide particles deposited on amorphous carbon nanofibres are prepared by a repetitive impregnation procedure. The choice of amorphous carbon nanofibres as support of amorphous ruthenium oxide leads to composites in which the deposited oxide consists of aggregates of extremely small primary particles (1-1.5 nm-size) and showing high porosity (specific surface area of 450 m 2 g -1 ). This special deposition of the oxide seems to favour: (i) high oxide capacitance (1000 Fg -1 ) at high oxide loadings (up to 20 wt%) and (ii) high capacitance retention (ca. 80% from the initial oxide capacitance) at high current densities (200 mA cm -2 ). Amorphous carbon nanofibres are suitable supports for amorphous ruthenium oxide and perhaps for other amorphous oxides acting as active electrode materials.

Ultrafast electron dynamics at alkali/ice structures adsorbed on a metal surface

International Nuclear Information System (INIS)

Meyer, Michael

2011-01-01

The goal of this work is to study the interaction between excess electrons in water ice structures adsorbed on metal surfaces and other charged or neutral species, like alkali ions, or chemically reactive molecules, like chlorofluorocarbons (CFC), respectively. The excess electrons in the ice can interact with the ions directly or indirectly via the hydrogen bonded water molecules. In both cases the presence of the alkali influences the population, localization, and lifetime of electronic states of excess electrons in the ice adlayer. These properties are of great relevance when considering the highly reactive character of the excess electrons, which can mediate chemical reactions by dissociative electron attachment (DEA). The influence of alkali adsorption on electron solvation and transfer dynamics in ice structures is investigated for two types of adsorption configurations using femtosecond time-resolved two-photon photoelectron spectroscopy. In the first system alkali atoms are coadsorbed on top of a wetting amorphous ice film adsorbed on Cu(111). At temperatures between 60 and 100 K alkali adsorption leads to the formation of positively charged alkali ions at the ice/vacuum interface. The interaction between the alkali ions at the surface and the dipole moments of the surrounding water molecules results in a reorientation of the water molecules. As a consequence new electron trapping sites, i.e. at local potential minima, are formed. Photoinjection of excess electrons into these alkali-ion covered amorphous ice layers, results in the trapping of a solvated electron at an alkali-ion/water complex. In contrast to solvation in pure amorphous ice films, where the electrons are located in the bulk of the ice layer, solvated electrons at alkali-ion/water complexes are located at the ice/vacuum interface. They exhibit lifetimes of several picoseconds and show a fast energetic stabilization. With ongoing solvation, i.e. pump-probe time delay, the electron transfer is

Travelling wave resonators fabricated with low-loss hydrogenated amorphous silicon

Science.gov (United States)

Lipka, Timo; Amthor, Julia; Trieu, Hoc Khiem; Müller, Jörg

2013-05-01

Low-loss hydrogenated amorphous silicon is employed for the fabrication of various planar integrated travelling wave resonators. Microring, racetrack, and disk resonators of different dimensions were fabricated with CMOS-compatible processes and systematically investigated. The key properties of notch filter ring resonators as extinction ratio, Q-factor, free spectral range, and the group refractive index were determined for resonators of varying radius, thereby achieving critically coupled photonic systems with high extinction ratios of about 20 dB for both polarizations. Racetrack resonators that are arranged in add/drop configuration and high quality factor microdisk resonators were optically characterized, with the microdisks exhibiting Q-factors of greater than 100000. Four-channel add/drop wavelength-division multiplexing filters that are based on cascaded racetrack resonators are studied. The design, the fabrication, and the optical characterization are presented.

Applications in the Nuclear Industry for Thermal Spray Amorphous Metal and Ceramic Coatings

Science.gov (United States)

Blink, J.; Farmer, J.; Choi, J.; Saw, C.

2009-06-01

Amorphous metal and ceramic thermal spray coatings have been developed with excellent corrosion resistance and neutron absorption. These coatings, with further development, could be cost-effective options to enhance the corrosion resistance of drip shields and waste packages, and limit nuclear criticality in canisters for the transportation, aging, and disposal of spent nuclear fuel. Iron-based amorphous metal formulations with chromium, molybdenum, and tungsten have shown the corrosion resistance believed to be necessary for such applications. Rare earth additions enable very low critical cooling rates to be achieved. The boron content of these materials and their stability at high neutron doses enable them to serve as high efficiency neutron absorbers for criticality control. Ceramic coatings may provide even greater corrosion resistance for waste package and drip shield applications, although the boron-containing amorphous metals are still favored for criticality control applications. These amorphous metal and ceramic materials have been produced as gas-atomized powders and applied as near full density, nonporous coatings with the high-velocity oxy-fuel process. This article summarizes the performance of these coatings as corrosion-resistant barriers and as neutron absorbers. This article also presents a simple cost model to quantify the economic benefits possible with these new materials.

A theoretical and spectroscopic study of co-amorphous naproxen and indomethacin

DEFF Research Database (Denmark)

Löbmann, Korbinian; Laitinen, Riikka; Grohganz, Holger

2013-01-01

. In this study, the co-amorphous drug mixture containing naproxen (NAP) and indomethacin (IND) was investigated using infrared spectroscopy (IR) and quantum mechanical calculations. The structures of both drugs were optimized as monomer, homodimer and heterodimer using density functional theory and used...... for the calculation of IR spectra. Conformational analysis confirmed that the optimized structures were suitable for the theoretical prediction of the spectra. Vibrational modes from the calculation could be matched with experimentally observed spectra for crystalline and amorphous NAP and IND, and it could be shown...... that both drugs exist as homodimers in their respective individual amorphous form. With the results from the experimental single amorphous drugs and theoretical homodimers, a detailed analysis of the experimental co-amorphous and theoretical heterodimer spectra was performed and evaluated. It is suggested...

Oxygen flow effects on electrical properties, stability, and density of states of amorphous In-Ga-Zn-O thin-film transistors

Science.gov (United States)

Lee, Yong-Su; Kai-Hsiang Yu, Eric; Shim, Dong-Hwan; Kong, Hyang-Shik; Bie, Linsen; Kanicki, Jerzy

2014-12-01

To investigate the origin of threshold voltage (Vth) shift of amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs), a combination of bias-temperature stress (BTS) and multi-frequency capacitance-voltage (C-V) measurements were used to evaluate the impact of oxygen partial pressure (PO2) during a-IGZO deposition on TFT electrical properties, electrical stability, and density of states (DOS). The extracted sub-gap DOS was decomposed into exponential bandtail states and Gaussian-like deep-gap states. The peak density of Gaussian-like states is larger for higher PO2. We conclude that the Gaussian-like states are excess/weakly-bonded oxygen in the form of O0 or O1- ions acting as acceptor-like states and are at the origin of TFT threshold voltage shift during positive BTS.

Low Li+ Insertion Barrier Carbon for High Energy Efficient Lithium-Ion Capacitor.

Science.gov (United States)

Lee, Wee Siang Vincent; Huang, Xiaolei; Tan, Teck Leong; Xue, Jun Min

2018-01-17

Lithium-ion capacitor (LIC) is an attractive energy-storage device (ESD) that promises high energy density at moderate power density. However, the key challenge in its design is the low energy efficient negative electrode, which barred the realization of such research system in fulfilling the current ESD technological inadequacy due to its poor overall energy efficiency. Large voltage hysteresis is the main issue behind high energy density alloying/conversion-type materials, which reduces the electrode energy efficiency. Insertion-type material though averted in most research due to the low capacity remains to be highly favorable in commercial application due to its lower voltage hysteresis. To further reduce voltage hysteresis and increase capacity, amorphous carbon with wider interlayer spacing has been demonstrated in the simulation result to significantly reduce Li + insertion barrier. Hence, by employing such amorphous carbon, together with disordered carbon positive electrode, a high energy efficient LIC with round-trip energy efficiency of 84.3% with a maximum energy density of 133 Wh kg -1 at low power density of 210 W kg -1 can be achieved.

Observed aerosol suppression of cloud ice in low-level Arctic mixed-phase clouds

OpenAIRE

Norgren, Matthew S.; Boer, Gijs; Shupe, Matthew D.

2018-01-01

The interactions that occur between aerosols and a mixed-phase cloud system, and the subsequent alteration of the microphysical state of such clouds, is a problem that has yet to be well constrained. Advancing our understanding of aerosol-ice processes is necessary to determine the impact of natural and anthropogenic emissions on Earth’s climate and to improve our capability to predict future climate states. This paper deals specifically with how aerosols influence ice mass production in low-...

Modeling the Effects of Ice Accretion on the Low Pressure Compressor and the Overall Turbofan Engine System Performance

Science.gov (United States)

Veres, Joseph P.; Jorgenson, Philip C. E.; Wright, William B.

2011-01-01

The focus of this study is on utilizing a mean line compressor flow analysis code coupled to an engine system thermodynamic code, to estimate the effects of ice accretion on the low pressure compressor, and quantifying its effects on the engine system throughout a notional flight trajectory. In this paper a temperature range in which engine icing would occur was assumed. This provided a mechanism to locate potential component icing sites and allow the computational tools to add blockages due to ice accretion in a parametric fashion. Ultimately the location and level of blockage due to icing would be provided by an ice accretion code. To proceed, an engine system modeling code and a mean line compressor flow analysis code were utilized to calculate the flow conditions in the fan-core and low pressure compressor and to identify potential locations within the compressor where ice may accrete. In this study, an "additional blockage" due to the accretion of ice on the metal surfaces, has been added to the baseline aerodynamic blockage due to boundary layer, as well as the blade metal blockage. Once the potential locations of ice accretion are identified, the levels of additional blockage due to accretion were parametrically varied to estimate the effects on the low pressure compressor blade row performance operating within the engine system environment. This study includes detailed analysis of compressor and engine performance during cruise and descent operating conditions at several altitudes within the notional flight trajectory. The purpose of this effort is to develop the computer codes to provide a predictive capability to forecast the onset of engine icing events, such that they could ultimately help in the avoidance of these events.

Low-latitude ice cores and freshwater availability

Science.gov (United States)

Kehrwald, Natalie Marie

2009-12-01

Recent retreat of Tibetan Plateau glaciers affects at least half a billion people. Himalayan glaciers seasonally release meltwater into tributaries of the Indus, Ganges, and Brahmaputra Rivers and supply freshwater necessary to support agricultural and economic practices. Tibetan Plateau glaciers are retreating more rapidly than mountain glaciers elsewhere in the world, and this retreat is accelerating. The Naimona'nyi (30°27'N; 81°91'E, 6050 m a.s.l), Guliya (35°17'N; 81°29'E, 6710 m a.s.l.) and Dasuopu (28°23'N; 85°43'E, 7200 m a.s.l.) ice cores place this recent retreat into a longer time perspective through quantifying climate parameters such as past temperature, aridity, and atmospheric chemistry. Naimona'nyi has not accumulated mass since at least 1950, as evidenced by the virtual lack of radiogenic isotopes (36Cl, 3 H, and beta radioactivity) present in the ice core. These isotopes were produced by U.S. and Soviet atmospheric thermonuclear bomb tests conducted in the 1950s and 1960s and provide independent dating horizons for the ice cores. Lead-210 dates imply that the uppermost preserved glacial ice on Naimona'nyi formed during the 1940s. While this is the highest documented glacial thinning in the world other glaciers at elevations similar to that of Naimona'nyi, such as Kilimanjaro (3°4'S; 37°21'E, 5893 m a.s.l.), are also losing mass at their summits. The global scope of high-elevation glacial thinning suggests that ablation on the Earth's highest ice fields may be more prevalent as global mean temperatures continue to increase. Glacial thinning has not been taken into account in future projections of regional freshwater availability, and the net mass loss indicates that Himalayan glaciers currently store less freshwater than assumed in models. The acceleration of Tibetan Plateau glacial retreat has been hypothesized to be due in part to deposition of black carbon (BC) from biomass burning on to ice fields, thereby lowering the reflectivity of

Low-density moderation in the storage of PWR fuel assemblies

International Nuclear Information System (INIS)

Alcorn, F.M.

1987-01-01

The nuclear criticality safety of PWR fuel storage arrays requires that the potential of low-density moderation within the array be considered. The calculated criticality effect of low-density moderation in a typical PWR fuel assembly array is described in this paper. Calculated reactivity due to low-density moderation can vary significantly between physics codes that have been validated for well moderated systems. The availability of appropriate benchmark experiments for low-density moderation is quite limited; attempts to validate against the one set of suitable experiments at low density have been disappointing. Calculations indicate that a typical array may be unacceptable should the array be subjected to interstitial moderation equivalent to 5 % of full density water. Array parameters (such as spacing and size) will dramatically affect the calculated maximum K-eff at low-density moderation. Administrative and engineered control may be necessary to assure maintenance of safety at low-density moderation. Potential sources for low-density moderation are discussed; in general, accidentally achieving degrees of low-density moderation which might lead to a compromise of safety are not credible. (author)

Hybrid glasses from strong and fragile metal-organic framework liquids.

Science.gov (United States)

Bennett, Thomas D; Tan, Jin-Chong; Yue, Yuanzheng; Baxter, Emma; Ducati, Caterina; Terrill, Nick J; Yeung, Hamish H-M; Zhou, Zhongfu; Chen, Wenlin; Henke, Sebastian; Cheetham, Anthony K; Greaves, G Neville

2015-08-28

Hybrid glasses connect the emerging field of metal-organic frameworks (MOFs) with the glass formation, amorphization and melting processes of these chemically versatile systems. Though inorganic zeolites collapse around the glass transition and melt at higher temperatures, the relationship between amorphization and melting has so far not been investigated. Here we show how heating MOFs of zeolitic topology first results in a low density 'perfect' glass, similar to those formed in ice, silicon and disaccharides. This order-order transition leads to a super-strong liquid of low fragility that dynamically controls collapse, before a subsequent order-disorder transition, which creates a more fragile high-density liquid. After crystallization to a dense phase, which can be remelted, subsequent quenching results in a bulk glass, virtually identical to the high-density phase. We provide evidence that the wide-ranging melting temperatures of zeolitic MOFs are related to their network topologies and opens up the possibility of 'melt-casting' MOF glasses.

Thermal conductivity of sputtered amorphous Ge films

International Nuclear Information System (INIS)

Zhan, Tianzhuo; Xu, Yibin; Goto, Masahiro; Tanaka, Yoshihisa; Kato, Ryozo; Sasaki, Michiko; Kagawa, Yutaka

2014-01-01

We measured the thermal conductivity of amorphous Ge films prepared by magnetron sputtering. The thermal conductivity was significantly higher than the value predicted by the minimum thermal conductivity model and increased with deposition temperature. We found that variations in sound velocity and Ge film density were not the main factors in the high thermal conductivity. Fast Fourier transform patterns of transmission electron micrographs revealed that short-range order in the Ge films was responsible for their high thermal conductivity. The results provide experimental evidences to understand the underlying nature of the variation of phonon mean free path in amorphous solids

Emerging trends in the stabilization of amorphous drugs.

Science.gov (United States)

Laitinen, Riikka; Löbmann, Korbinian; Strachan, Clare J; Grohganz, Holger; Rades, Thomas

2013-08-30

The number of active pharmaceutical substances having high therapeutic potential but low water solubility is constantly increasing, making it difficult to formulate these compounds as oral dosage forms. The solubility and dissolution rate, and thus potentially the bioavailability, of these poorly water-soluble drugs can be increased by the formation of stabilized amorphous forms. Currently, formulation as solid polymer dispersions is the preferred method to enhance drug dissolution and to stabilize the amorphous form of a drug. The purpose of this review is to highlight emerging alternative methods to amorphous polymer dispersions for stabilizing the amorphous form of drugs. First, an overview of the properties and stabilization mechanisms of amorphous forms is provided. Subsequently, formulation approaches such as the preparation of co-amorphous small-molecule mixtures and the use of mesoporous silicon and silica-based carriers are presented as potential means to increase the stability of amorphous pharmaceuticals. Copyright © 2012 Elsevier B.V. All rights reserved.

Electron Density Dropout Near Enceladus in the Context of Water-Vapor and Water-Ice

Science.gov (United States)

Farrell, W. M.; Kurth, W. S.; Gurnett, D. A.; Johnson, R. E.; Kaiser, M. L.; Wahlund, J.-E.; Waite, J. H., Jr.

2009-01-01

On 12 March 2008, the Cassini spacecraft made a close encounter with the Saturnian moon Enceladus, passing within 52 km of the moon. The spacecraft trajectory was intentionally-oriented in a southerly direction to create a close alignment with the intense water-dominated plumes emitted from the south polar region. During the passage, the Cassini Radio and Plasma Wave System (RPWS) detected two distinct radio signatures: 1) Impulses associated with small water-ice dust grain impacts and 2) an upper hybrid (UH) resonance emission that both intensified and displayed a sharp frequency decrease in the near-vicinity of the moon. The frequency decrease of the UH emission is associated with an unexpectedly sharp decrease in electron density from approximately 90 el/cubic cm to below 20 el/cubic cm that occurs on a time scale of a minute near the closest encounter with the moon. In this work, we consider a number of scenarios to explain this sharp electron dropout, but surmise that electron absorption by ice grains is the most likely process.

Distributions of crystals and gas bubbles in reservoir ice during growth period

Directory of Open Access Journals (Sweden)

Zhi-jun Li

2011-06-01

Full Text Available In order to understand the dominant factors of the physical properties of ice in ice thermodynamics and mechanics, in-situ observations of ice growth and decay processes were carried out. Two samplings were conducted in the fast and steady ice growth stages. Ice pieces were used to observe ice crystals and gas bubbles in ice, and to measure the ice density. Vertical profiles of the type and size of ice crystals, shape and size of gas bubbles, and gas bubble content, as well as the ice density, were obtained. The results show that the upper layer of the ice pieces is granular ice and the lower layer is columnar ice; the average crystal size increases with the ice depth and remains steady in the fast and steady ice growth stages; the shape of gas bubbles in the upper layer of ice pieces is spherical with higher total content, and the shape in the middle and lower layers is cylinder with lower total content; the gas bubble size and content vary with the ice growth stage; and the ice density decreases with the increase of the gas bubble content.

Spring snow conditions on Arctic sea ice north of Svalbard, during the Norwegian Young Sea ICE (N-ICE2015) expedition

Science.gov (United States)

Gallet, Jean-Charles; Merkouriadi, Ioanna; Liston, Glen E.; Polashenski, Chris; Hudson, Stephen; Rösel, Anja; Gerland, Sebastian

2017-10-01

Snow is crucial over sea ice due to its conflicting role in reflecting the incoming solar energy and reducing the heat transfer so that its temporal and spatial variability are important to estimate. During the Norwegian Young Sea ICE (N-ICE2015) campaign, snow physical properties and variability were examined, and results from April until mid-June 2015 are presented here. Overall, the snow thickness was about 20 cm higher than the climatology for second-year ice, with an average of 55 ± 27 cm and 32 ± 20 cm on first-year ice. The average density was 350-400 kg m-3 in spring, with higher values in June due to melting. Due to flooding in March, larger variability in snow water equivalent was observed. However, the snow structure was quite homogeneous in spring due to warmer weather and lower amount of storms passing over the field camp. The snow was mostly consisted of wind slab, faceted, and depth hoar type crystals with occasional fresh snow. These observations highlight the more dynamic character of evolution of snow properties over sea ice compared to previous observations, due to more variable sea ice and weather conditions in this area. The snowpack was isothermal as early as 10 June with the first onset of melt clearly identified in early June. Based on our observations, we estimate than snow could be accurately represented by a three to four layers modeling approach, in order to better consider the high variability of snow thickness and density together with the rapid metamorphose of the snow in springtime.

Effect of low level doping of boron and phosphorus on the properties of amorphous silicon films

International Nuclear Information System (INIS)

Tran, N.T.; Epstein, K.A.; Grimmer, D.P.; Vernstrom, G.D.

1987-01-01

Effect of the low level doping of boron and phosphorus on the properties of amorphous silicon films (a-Si:H) were studied. Doping level of both boron and phosphorus was in the range of 10/sup 17/ atoms/cm/sup 3/. Apparent improvement in the stability of dark and photoconductivity of a-Si: films upon low level doping does not result from the elimination of light-induced defects. The stability of the dark and photoconductivity upon doping is an indication of pinning of the Fermi level

Ethane Ices in the Outer Solar System: Spectroscopy and Chemistry

Science.gov (United States)

Hudson, R. L.; Moore, M. H.; Raines, L. L.

2009-01-01

We report recent experiments on ethane ices made at temperatures applicable to the outer Solar System. New near- and mid-infrared data for crystalline and amorphous ethane, including new spectra for a seldom-studied solid phase that exists at 35-55 K, are presented along with radiation-chemical experiments showing the formation of more-complex hydrocarbons

The influence of structural changes on electrical and magnetic characteristics of amorphous powder of the nixmoy alloy

Directory of Open Access Journals (Sweden)

Ribić-Zelenović Lenka

2006-01-01

Full Text Available Nickel and molybdenum alloy powder was electrodeposited on a titanium cathode from a NiSO4⋅7H2O and (NH46 Mo7O24⋅4H2O ammonium solution. The desired chemical composition, structure, size and shape of particles in the powder samples were achieved by an appropriate choice of electrolysis parameters (current density, composition and temperature of the solution, cathode material and electrolysis duration. Metal coatings form in the current density range 15 mA cm-2density is greater than 40mA cm-2 then powders form. The chemical composition of powder samples depends on the current density of electrodeposition. The molybdenum content in the powder increases with the increase of current density (in the low current density range, while in the higher current density range the molybdenum content in the alloy decreases with the increase of the current density of deposition. Smaller sized particles form at higher current density. X-ray analysis, differential scanning calorimetric and measurements of the temperature dependence of electric resistance and magnetic permeability of the powder samples were all used to establish a predominantly amorphous structure of the powder samples formed at the current density of j≥70mA cm-2. The crystalline particle content in the powder samples increases with the decrease of the current density of deposition. Powder heating causes structural changes. The process of thermal stabilization of nickel and molybdenum amorphous powders takes place in the temperature interval from 463K to 573K and causes a decrease in electrical resistance and increase in magnetic permeability. The crystallization temperature depends on the value of current density of powder electrodeposition. Powder formed at j=180 mA cm-2 begins to crystallize at 573K, while the powder deposited at j=50 mA cm-2 begins to crystallize at 673K. Crystallization of the powder causes a decrease in electric resistivity and magnetic

Amorphous silicon thin-film solar cells on glass fiber textiles

Energy Technology Data Exchange (ETDEWEB)

Plentz, Jonathan, E-mail: jonathan.plentz@leibniz-ipht.de; Andrä, Gudrun; Pliewischkies, Torsten; Brückner, Uwe; Eisenhawer, Björn; Falk, Fritz

2016-02-15

Graphical abstract: - Highlights: • Amorphous silicon solar cells on textile glass fiber fabrics are demonstrated. • Open circuit voltages of 883 mV show shunt-free contacting on non-planar fabrics. • Short-circuit current densities of 3.7 mA/cm{sup 2} are limited by transmission losses. • Fill factors of 43.1% and pseudo fill factors of 70.2% show high series resistance. • Efficiencies of 1.4% and pseudo efficiencies of 2.1% realized on textile fabrics. - Abstract: In this contribution, amorphous silicon thin-film solar cells on textile glass fiber fabrics for smart textiles are prepared and the photovoltaic performance is characterized. These solar cells on fabrics delivered open circuit voltages up to 883 mV. This shows that shunt-free contacting of the solar cells was successful, even in case of non-planar fabrics. The short-circuit current densities up to 3.7 mA/cm{sup 2} are limited by transmission losses in a 10 nm thin titanium layer, which was used as a semi-transparent contact. The low conductivity of this layer limits the fill factor to 43.1%. Pseudo fill factors, neglecting the series resistance, up to 70.2% were measured. Efficiencies up to 1.4% and pseudo efficiencies up to 2.1% were realized on textile fabrics. A transparent conductive oxide could further improve the efficiency to above 5%.

Physical stabilization of low-molecular-weight amorphous drugs in the solid state: a material science approach.

Science.gov (United States)

Qi, Sheng; McAuley, William J; Yang, Ziyi; Tipduangta, Pratchaya

2014-07-01

Use of the amorphous state is considered to be one of the most effective approaches for improving the dissolution and subsequent oral bioavailability of poorly water-soluble drugs. However as the amorphous state has much higher physical instability in comparison with its crystalline counterpart, stabilization of amorphous drugs in a solid-dosage form presents a major challenge to formulators. The currently used approaches for stabilizing amorphous drug are discussed in this article with respect to their preparation, mechanism of stabilization and limitations. In order to realize the potential of amorphous formulations, significant efforts are required to enable the prediction of formulation performance. This will facilitate the development of computational tools that can inform a rapid and rational formulation development process for amorphous drugs.

The Stabilization of Amorphous Zopiclone in an Amorphous Solid Dispersion.

Science.gov (United States)

Milne, Marnus; Liebenberg, Wilna; Aucamp, Marique

2015-10-01

Zopiclone is a poorly soluble psychotherapeutic agent. The aim of this study was to prepare and characterize an amorphous form of zopiclone as well as the characterization and performance of a stable amorphous solid dispersion. The amorphous form was prepared by the well-known method of quench-cooling of the melt. The solid dispersion was prepared by a solvent evaporation method of zopiclone, polyvinylpyrrolidone-25 (PVP-25), and methanol, followed by freeze-drying. The physico-chemical properties and stability of amorphous zopiclone and the solid dispersion was studied using differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), hot-stage microscopy (HSM), X-ray diffractometry (XRD), solubility, and dissolution studies. The zopiclone amorphous solid-state form was determined to be a fragile glass; it was concluded that the stability of the amorphous form is influenced by both temperature and water. Exposure of amorphous zopiclone to moisture results in rapid transformation of the amorphous form to the crystalline dihydrated form. In comparison, the amorphous solid dispersion proved to be more stable with increased aqueous solubility.

Annealing effect on spin density of broken bonds and on the structure of amorphous germanium

International Nuclear Information System (INIS)

Bukhan'ko, F.N.; Okunev, V.D.; Samojlenko, Z.A.

1989-01-01

Dependence of volumetric spin density of broken bonds in a-Ge films, produced by cathode sputtering in argon, on the annealing temperature is investigated by ESR method. The film structure is controlled by the X-ray method. Two ESR lines with g=2.019 and g=2.003, their intensities changing non-monotonously with annealing temperature are observed. The line with g=2.019 is typical of only amorphous germanium state, and the line with g=2.003 is preserved after film crystallization. Under comparison of results with structural data a conclusion is made that the observed lines in ESR spectra are linked with broken bonds in peripheral regions of two types of clusters. The line with g=2.003 is conditioned by broken bonds in the peripheral cluster regions with standard cubic atom packing and the line with g=2.019 is linked with clusters of hexagonal type which is not typical of crystalline germanium standard structure

Measurement of the fracture toughness of polycrystalline bubbly ice from an Antarctic ice core

Directory of Open Access Journals (Sweden)

J. Christmann

2015-05-01

Full Text Available The critical fracture toughness is a material parameter describing the resistance of a cracked body to further crack extension. It is an important parameter for simulating and predicting the breakup behavior of ice shelves from the calving of single icebergs to the disintegration of entire ice shelves over a wide range of length scales. The fracture toughness values are calculated with equations that are derived from an elastic stress analysis. Additionally, an X-ray computer tomography (CT scanner was used to identify the density as a function of depth. The critical fracture toughness of 91 Antarctic bubbly ice samples with densities between 840 and 870 kg m−3 has been determined by applying a four-point bending technique on single-edge v-notched beam samples. The examined ice core was drilled 70 m north of Kohnen Station, Dronnning Maud Land (75°00' S, 00°04' E; 2882 m. Supplementary data are available at doi:10.1594/PANGAEA.835321.

Paramagnetic defects in hydrogenated amorphous carbon powders

International Nuclear Information System (INIS)

Keeble, D J; Robb, K M; Smith, G M; Mkami, H El; Rodil, S E; Robertson, J

2003-01-01

Hydrogenated amorphous carbon materials typically contain high concentrations of paramagnetic defects, the density of which can be quantified by electron paramagnetic resonance (EPR). In this work EPR measurements near 9.5, 94, and 189 GHz have been performed on polymeric and diamond-like hydrogenated amorphous carbon (a-C:H) powder samples. A similar single resonance line was observed at all frequencies for the two forms of a-C:H studied. No contributions to the spectrum from centres with resolved anisotropic g-values as reported earlier were detected. An increase in linewidth with microwave frequency was observed. Possible contributions to this frequency dependence are discussed

MELCOR 1.8.1 assessment: PNL Ice Condenser Aerosol Experiments

International Nuclear Information System (INIS)

Gross, R.J.

1993-06-01

The MELCOR code was used to simulate PNL's Ice Condenser Experiments 11-6 and 16-11. In these experiments, ZnS was injected into a mixing chamber, and the combined steam/air/aerosol mixture flowed into an ice condenser which was l4.7m tall. Experiment 11-6 was a low flow test; Experiment l6-1l was a high flow test. Temperatures in the ice condenser region and particle retention were measured in these tests. MELCOR predictions compared very well to the experimental data. The MELCOR calculations were also compared to CONTAIN code calculations for the same tests. A number of sensitivity studies were performed. It as found that simulation time step, aerosol parameters such as the number of MAEROS components and sections used and the particle density, and ice condenser parameters such as the energy capacity of the ice, ice heat transfer coefficient multiplier, and ice heat structure characteristic length all could affect the results. Thermal/hydraulic parameters such as control volume equilibrium assumptions, flow loss coefficients, and the bubble rise model were found to affect the results less significantly. MELCOR results were not machine dependent for this problem

Amorphous metal based nanoelectromechanical switch

KAUST Repository

Mayet, Abdulilah M.; Smith, Casey; Hussain, Muhammad Mustafa

2013-01-01

Nanoelectromechanical (NEM) switch is an interesting ultra-low power option which can operate in the harsh environment and can be a complementary element in complex digital circuitry. Although significant advancement is happening in this field, report on ultra-low voltage (pull-in) switch which offers high switching speed and area efficiency is yet to be made. One key challenge to achieve such characteristics is to fabricate nano-scale switches with amorphous metal so the shape and dimensional integrity are maintained to achieve the desired performance. Therefore, we report a tungsten alloy based amorphous metal with fabrication process development of laterally actuated dual gated NEM switches with 100 nm width and 200 nm air-gap to result in <5 volts of actuation voltage (Vpull-in). © 2013 IEEE.

Amorphous metal based nanoelectromechanical switch

KAUST Repository

Mayet, Abdulilah M.

2013-04-01

Nanoelectromechanical (NEM) switch is an interesting ultra-low power option which can operate in the harsh environment and can be a complementary element in complex digital circuitry. Although significant advancement is happening in this field, report on ultra-low voltage (pull-in) switch which offers high switching speed and area efficiency is yet to be made. One key challenge to achieve such characteristics is to fabricate nano-scale switches with amorphous metal so the shape and dimensional integrity are maintained to achieve the desired performance. Therefore, we report a tungsten alloy based amorphous metal with fabrication process development of laterally actuated dual gated NEM switches with 100 nm width and 200 nm air-gap to result in <5 volts of actuation voltage (Vpull-in). © 2013 IEEE.

Results of Low Power Deicer tests on a swept inlet component in the NASA Lewis Icing Research Tunnel

Science.gov (United States)

Bond, Thomas H.; Shin, Jaiwon

1993-01-01

Tests were conducted under a USAF/NASA Low Power Deicer program on two expulsive technologies to examine system performance on hardware representative of a modern aircraft part. The BF Goodrich Electro-Expulsive Deicing System and Pneumatic Impulse Ice Protection system were installed on a swept, compound curve, engine inlet component with varying leading edge radius, and tested through a range of icing and system operating conditions in the NASA Lewis Icing Research Tunnel. A description of the experimental procedure and results, including residual ice thickness, shed ice particle size, and changes in system energy/pressure characteristics are presented.

The Influence of Ice Properties on Borehole Deformation at the West Antarctic Ice Sheet Divide

Science.gov (United States)

Sinkler, E.; Pettit, E. C.; Obbard, R. W.

2017-12-01

It is widely known that ice flow is affected by many properties, including crystal fabric and impurities, though these relationships are not fully understood. This study uses data from the West Antarctic Ice Sheet (WAIS) Divide borehole to better determine the influence of such properties on ice flow. The WAIS Divide borehole, the byproduct of the 2006-2012 coring project, offers a unique opportunity to study deep Antarctic Ice. Thanks to the work of many researchers, extensive data on ice properties are available from both coring and borehole logging at this site. The borehole, kept open with a density-approximating fluid, closes and tilts due to ice flow. We have tracked this deformation over two years using a set of repeat measurements with an Acoustic Televiewer. This tool acts as an acoustic caliper allowing us to view cross-sections of the borehole shape and size with up to 1.25 degree azimuthal resolution and a depth resolution as high as 1.4 mm. In addition, the tool collects tilt and azimuth data. These measurements are compared to a 1D Glen's Flow Law model for borehole closure that uses density differences between the ice and borehole fluid as its driving force and incorporates temperature effects. This is then compared to ice properties like crystal fabric and impurities in order to determine the influence of these properties on ice deformation at this site. Crystal fabric has appeared as an important factor in this study.This work builds on that of others who have studied in-situ deep ice through borehole deformation (e.g. Paterson, 1977 and Dahl-Jensen and Gundestrup, 1987). Our results have implications for ice flow modeling and therefore interpretation of depth-age relationships in deep ice cores.

A theory-based parameterization for heterogeneous ice nucleation and implications for the simulation of ice processes in atmospheric models

Science.gov (United States)

Savre, J.; Ekman, A. M. L.

2015-05-01

A new parameterization for heterogeneous ice nucleation constrained by laboratory data and based on classical nucleation theory is introduced. Key features of the parameterization include the following: a consistent and modular modeling framework for treating condensation/immersion and deposition freezing, the possibility to consider various potential ice nucleating particle types (e.g., dust, black carbon, and bacteria), and the possibility to account for an aerosol size distribution. The ice nucleating ability of each aerosol type is described using a contact angle (θ) probability density function (PDF). A new modeling strategy is described to allow the θ PDF to evolve in time so that the most efficient ice nuclei (associated with the lowest θ values) are progressively removed as they nucleate ice. A computationally efficient quasi Monte Carlo method is used to integrate the computed ice nucleation rates over both size and contact angle distributions. The parameterization is employed in a parcel model, forced by an ensemble of Lagrangian trajectories extracted from a three-dimensional simulation of a springtime low-level Arctic mixed-phase cloud, in order to evaluate the accuracy and convergence of the method using different settings. The same model setup is then employed to examine the importance of various parameters for the simulated ice production. Modeling the time evolution of the θ PDF is found to be particularly crucial; assuming a time-independent θ PDF significantly overestimates the ice nucleation rates. It is stressed that the capacity of black carbon (BC) to form ice in the condensation/immersion freezing mode is highly uncertain, in particular at temperatures warmer than -20°C. In its current version, the parameterization most likely overestimates ice initiation by BC.

First-principles study of crystalline and amorphous AlMgB14-based materials

International Nuclear Information System (INIS)

Ivashchenko, V. I.; Shevchenko, V. I.; Turchi, P. E. A.; Veprek, S.; Leszczynski, Jerzy; Gorb, Leonid; Hill, Frances

2016-01-01

We report first-principles investigations of crystalline and amorphous boron and M1 x M2 y X z B 14−z (M1, M2 = Al, Mg, Li, Na, Y; X = Ti, C, Si) phases (so-called “BAM” materials). Phase stability is analyzed in terms of formation energy and dynamical stability. The atomic configurations as well as the electronic and phonon density states of these phases are compared. Amorphous boron consists of distorted icosahedra, icosahedron fragments, and dioctahedra, connected by an amorphous network. The presence of metal atoms in amorphous BAM materials precludes the formation of icosahedra. For all the amorphous structures considered here, the Fermi level is located in the mobility gap independent of the number of valence electrons. The intra-icosahedral vibrations are localized in the range of 800 cm −1 , whereas the inter-icosahedral vibrations appear at higher wavenumbers. The amorphization leads to an enhancement of the vibrations in the range of 1100–1250 cm −1 . The mechanical properties of BAM materials are investigated at equilibrium and under shear and tensile strain. The anisotropy of the ideal shear and tensile strengths is explained in terms of a layered structure of the B 12 units. The strength of amorphous BAM materials is lower than that of the crystalline counterparts because of the partial fragmentation of the boron icosahedra in amorphous structures. The strength enhancement found experimentally for amorphous boron-based films is very likely related to an increase in film density, and the presence of oxygen impurities. For crystalline BAM materials, the icosahedra are preserved during elongation upon tension as well as upon shear in the (010)[100] slip system.

Does low surface brightness mean low density?

NARCIS (Netherlands)

deBlok, WJG; McGaugh, SS

1996-01-01

We compare the dynamical properties of two galaxies at identical positions on the Tully-Fisher relation, but with different surface brightnesses. We find that the low surface brightness galaxy UGC 128 has a higher mass-to-light ratio, and yet has lower mass densities than the high surface brightness

Deep-level transient spectroscopy on an amorphous InGaZnO4 Schottky diode

NARCIS (Netherlands)

Chasin, A.; Simoen, E.; Bhoolokam, A.; Nag, M.; Genoe, J.; Gielen, G.; Heremans, P.

2014-01-01

The first direct measurement is reported of the bulk density of deep states in amorphous IGZO (indium-gallium-zinc oxide) semiconductor by means of deep-level transient spectroscopy (DLTS). The device under test is a Schottky diode of amorphous IGZO semiconductor on a palladium (Pd) Schottky-barrier

Using containerless methods to develop amorphous pharmaceuticals.

Science.gov (United States)

Weber, J K R; Benmore, C J; Suthar, K J; Tamalonis, A J; Alderman, O L G; Sendelbach, S; Kondev, V; Yarger, J; Rey, C A; Byrn, S R

2017-01-01

Many pipeline drugs have low solubility in their crystalline state and require compounding in special dosage forms to increase bioavailability for oral administration. The use of amorphous formulations increases solubility and uptake of active pharmaceutical ingredients. These forms are rapidly gaining commercial importance for both pre-clinical and clinical use. Synthesis of amorphous drugs was performed using an acoustic levitation containerless processing method and spray drying. The structure of the products was investigated using in-situ high energy X-ray diffraction. Selected solvents for processing drugs were investigated using acoustic levitation. The stability of amorphous samples was measured using X-ray diffraction. Samples processed using both spray drying and containerless synthesis were compared. We review methods for making amorphous pharmaceuticals and present data on materials made by containerless processing and spray drying. It was shown that containerless processing using acoustic levitation can be used to make phase-pure forms of drugs that are known to be difficult to amorphize. The stability and structure of the materials was investigated in the context of developing and making clinically useful formulations. Amorphous compounds are emerging as an important component of drug development and for the oral delivery of drugs with low solubility. Containerless techniques can be used to efficiently synthesize small quantities of pure amorphous forms that are potentially useful in pre-clinical trials and for use in the optimization of clinical products. Developing new pharmaceutical products is an essential enterprise to improve patient outcomes. The development and application of amorphous pharmaceuticals to increase absorption is rapidly gaining importance and it provides opportunities for breakthrough research on new drugs. There is an urgent need to solve problems associated with making formulations that are both stable and that provide high

Fracture properties of hydrogenated amorphous silicon carbide thin films

International Nuclear Information System (INIS)

Matsuda, Y.; King, S.W.; Bielefeld, J.; Xu, J.; Dauskardt, R.H.

2012-01-01

The cohesive fracture properties of hydrogenated amorphous silicon carbide (a-SiC:H) thin films in moist environments are reported. Films with stoichiometric compositions (C/Si ≈ 1) exhibited a decreasing cohesive fracture energy with decreasing film density similar to other silica-based hybrid organic–inorganic films. However, lower density a-SiC:H films with non-stoichiometric compositions (C/Si ≈ 5) exhibited much higher cohesive fracture energy than the films with higher density stoichiometric compositions. One of the non-stoichiometric films exhibited fracture energy (∼9.5 J m −2 ) greater than that of dense silica glasses. The increased fracture energy was due to crack-tip plasticity, as demonstrated by significant pileup formation during nanoindentation and a fracture energy dependence on film thickness. The a-SiC:H films also exhibited a very low sensitivity to moisture-assisted cracking compared with other silica-based hybrid films. A new atomistic fracture model is presented to describe the observed moisture-assisted cracking in terms of the limited Si-O-Si suboxide bond formation that occurs in the films.

Topside electron density at low latitudes

International Nuclear Information System (INIS)

Ezquer, R.G.; Cabrera, M.A.; Flores, R.F.; Mosert, M.

2002-01-01

The validity of IRI to predict the electron density at the topside electron density profile over the low latitude region is checked. The comparison with measurements obtained with the Taiyo satellite during low solar activity shows that, the disagreement between prediction and measurement is lower than 40% for 70% of considered cases. These IRI predictions are better than those obtained in a previous work at the southern peak of the equatorial anomaly for high solar activity. Additional studies for low solar activity, using ionosonde data as input parameters in the model, are needed in order to check if the observed deviations are due to the predicted peak characteristics or to the predicted shape of the topside profile. (author)

Structural characterization of amorphous materials applied to low-k organosilicate materials

Energy Technology Data Exchange (ETDEWEB)

Raymunt, Alexandra Cooper, E-mail: amc442@cornell.edu; Clancy, Paulette

2014-07-01

We present a methodology to create computational atomistic-level models of porous amorphous materials, in particular, an organosilicate structure for ultra-low dielectric constant (ULK) materials known as “SiCOH.” The method combines the ability to satisfy geometric and chemical constraints with subsequent molecular dynamics (MD) techniques as a way to capture the complexities of the porous and amorphous nature of these materials. The motivation for studying ULK materials arises from a desire to understand the origin of the material's weak mechanical properties. The first step towards understanding how these materials might behave under processing conditions that are intended to improve their mechanical properties is to develop a suitable computational model of the material and hence is the focus of this paper. We define the atomic-scale topology of ULK materials that have been produced by chemical vapor deposition-like experimental techniques. Specifically, we have developed a method of defining the initial atom configurations and interactions, as well as a method to rearrange these starting configurations into relaxed structures. The main advantage of our described approach is the ability of our structure generation method to maintain a random distribution of relevant structural motifs throughout the structure, without relying on large unit cells and periodic boundaries to approximate the behavior of this complex material. The minimization of the different models was accomplished using replica exchange molecular dynamics (REMD). Following the generation of the ‘equilibrium’ configurations that result from REMD for a ULK material of a pre-specified composition, we demonstrate that its structural properties, including bonding topology, porosity and pore size distribution are similar to experimentally used ULK materials. - Highlights: • Method for creating a model of a low dielectric constant organosilicate material • Method of defining porosity in

Synthesis and densification of Cu-coated Ni-based amorphous composite powders

International Nuclear Information System (INIS)

Kim, Yong-Jin; Kim, Byoung-Kee; Kim, Jin-Chun

2007-01-01

Spherical Ni 57 Zr 20 Ti 16 Si 2 Sn 3 (numbers indicate at.%) amorphous powders were produced by the gas atomization process, and ductile Cu phase was coated on the Ni-based amorphous powders by the spray drying process in order to increase the ductility of the consolidated amorphous alloy. The characteristics of the as-prepared powders and the consolidation behaviors of Cu-coated Ni-based amorphous composite powders were investigated. The atomization was conducted at 1450 deg. C under the vacuum of 10 -2 mbar. The Ni-based amorphous powders and Cu nitrate solution were mixed and sprayed at temperature of 130 deg. C. After spray drying and reduction treatment, the sub-micron size Cu powders were coated successfully on the surface of the atomized Ni amorphous powders. The spark plasma sintering process was applied to study the densification behavior of the Cu-coated composite powders. Thickness of the Cu layer was less than 1 μm. The compacts obtained by SPS showed high relative density of over 98% and its hardness was over 800 Hv

Neutron diffraction and thermal studies of amorphous CS2 realised by low-temperature vapour deposition

International Nuclear Information System (INIS)

Yamamuro, O.; Matsuo, T.; Onoda-Yamamuro, N.; Takeda, K.; Munemura, H.; Tanaka, S.; Misawa, M.

2003-01-01

We have succeeded in preparing amorphous carbon disulphide (CS 2 ) by depositing its vapour on a cold substrate at 10 K. Complete formation of the amorphous state has been confirmed by neutron diffraction and differential thermal analysis (DTA). The amorphous sample crystallized at ca. 70 K, which is lower than the hypothetical glass transition temperature (92 K) estimated from the DTA data of the (CS 2 ) x (S 2 Cl 2 ) 1-x binary mixture. CS 2 , a symmetric linear tri-atomic molecule, is the simplest of the amorphized molecular substances whose structural and thermal information has been reported so far. Comparison of the static structure factors S(Q) has shown that the orientational correlation of CS 2 molecules may be much stronger in the amorphous state than in the liquid state at higher temperature. (authors)

Effect of γ-(Fe,Ni) crystal-size stabilization in Fe-Ni-B amorphous ribbon

Science.gov (United States)

Gorshenkov, M. V.; Glezer, A. M.; Korchuganova, O. A.; Aleev, A. A.; Shurygina, N. A.

2017-02-01

The effect of stabilizing crystal size in a melt-quenched amorphous Fe50Ni33B17 ribbon is described upon crystallization in a temperature range of 360-400°C. The shape, size, volume fraction, and volume density have been investigated by transmission electron microscopy and X-ray diffraction methods. The formation of an amorphous layer of the Fe50Ni29B21 compound was found by means of atomic-probe tomography at the boundary of the crystallite-amorphous phase. The stabilization of crystal sizes during annealing is due to the formation of a barrier amorphous layer that has a crystallization temperature that exceeds the crystallization temperature of the matrix amorphous alloy.

Low-frequency magnetization processes in chemically etched Co-based amorphous ribbons

International Nuclear Information System (INIS)

Betancourt, I.; Martinez, L.A.; Valenzuela, R.

2005-01-01

In this report we present a study of the magnetization processes for Co-based amorphous ribbons at low frequencies (10 Hz-13 MHz) as a function of decreasing thicknesses attained by chemical etching. Reversible domain-wall bulging, characterized by initial permeability and relaxation frequency, was monitored by means of inductance measurements. The real part of inductance (proportional to initial permeability) exhibited a decreasing trend with diminishing ribbon thickness, together with an increasing tendency for the relaxation frequency. For high amplitude of the ac field (leading to domain-wall unpinning), reduced ribbon thickness showed a deleterious-enhancement effect on irreversible domain-wall displacement, which was observed for both real and imaginary inductance spectroscopic plots. Results are interpreted in terms of reduced domain-wall pinning distances resulting from thinner alloy samples

Aero-thermal optimization of in-flight electro-thermal ice protection systems in transient de-icing mode

International Nuclear Information System (INIS)

Pourbagian, Mahdi; Habashi, Wagdi G.

2015-01-01

Highlights: • We introduce an efficient methodology for the optimization of a de-icing system. • We can replace the expensive CHT simulation by ROM without loosing much accuracy. • We propose different criteria affecting the energy usage and aerodynamic performance. • These criteria can significantly improve the performance of the de-icing system. - Abstract: Even if electro-thermal ice protection systems (IPS) consume less energy when operating in de-icing mode than in anti-icing mode, they still need to be optimized for energy usage. The optimization, however, should also take into account the effect of the de-icing system on the aerodynamic performance. The present work offers an optimization framework in which both thermal and aerodynamic viewpoints are taken into account in formulating various objective and constraint functions by considering the energy consumption, the thickness, the volume, the shape and the location of the accreted ice on the surface as the key parameters affecting the energy usage and the aerodynamic performance. The design variables include the power density and the activation time of the electric heating blankets. A derivative-free technique, called the mesh adaptive direct search (MADS) method, is used to carry out the optimization process, which would normally need a large number of unsteady conjugate heat transfer (CHT) calculations for the IPS simulation. To avoid such prohibitive computations, reduced-order modeling (ROM) is used to construct simplified low-dimensional CHT models. The approach is illustrated through several test cases, in which different combinations of objective and constraint functions, design variables and cycling sequence patterns are examined. In these test cases, the energy consumption is significantly reduced compared to the experiments by improving the spatial and temporal distribution of the thermal energy usage. The results show the benefits of the approach in bringing energy, safety and

Solid state photochemistry. Subpanel A-2(b): Metastability in hydrogenated amorphous silicon

Energy Technology Data Exchange (ETDEWEB)

Carlson, D. [Solarex Corporation, Newton, PA (United States)

1996-09-01

All device quality amorphous silicon based materials exhibit degradation in electronic properties when exposed to sunlight. The photo-induced defects are associated with Si dangling bonds that are created by the recombination and/or trapping of photogenerated carriers. The defects are metastable and can be annealed out at temperatures of about 150 to 200 degrees Centigrade. The density of metastable defects is larger in films that are contaminated with > 10{sup 19} per cubic cm of impurities such as oxygen, carbon and nitrogen. However, recent experimental results indicate that some metastable defects are still present in films with very low impurity concentrations. The photo-induced defects typically saturate after 100 to 1000 hours of exposure to one sun illumination depending on the deposition conditions. There is also experimental evidence that photo-induced structural changes are occurring in the amorphous silicon based materials and that hydrogen may be playing an important role in both the photo-induced structural changes and in the creation of metastable defects.

Proceedings of the frontiers of hydrogen complexity

International Nuclear Information System (INIS)

Yamamuro, Osamu

2000-05-01

The discussion meeting on complex systems containing hydrogen and/or hydrogen bondings were held at High Energy Accelerator Research Organization (KEK), Japan, in December, 1999, and the proceedings of the papers presented, 18 oral and 20 poster presentations, are included in the present report. Study on water structure using neutron scattering in these 50 years is activated by appearance of new research techniques: Pulsed neutron sources and easy preparation method of amorphous ices, high density amorphous (HDA) and low density amorphous (LDA) one. Both techniques may bring about possibility of elucidation of the dynamics of water structure. Pulsed neutron sources make possible to carry out measurements in a wider Q-w space, thus extending excitations to higher levels. HDA state can be kept in lower temperatures while maintaining the same density as that of liquid water. Research fields relevant to the present discussion include super-cooled liquid, glassy state, supercritical liquid, polymers, gels and micro-emulsions. Other research techniques for this study include X-ray and photon scattering, NMR, dielectric relaxation phenomena, calorimetric measurement, and computer simulations. (S.Ohno)

Ice Chemistry in Interstellar Dense Molecular Clouds, Protostellar Disks, and Comets

Science.gov (United States)

Sandford, Scott A.

2015-01-01

Despite the low temperatures (T less than 20K), low pressures, and low molecular densities found in much of the cosmos, considerable chemistry is expected to occur in many astronomical environments. Much of this chemistry happens in icy grain mantles on dust grains and is driven by ionizing radiation. This ionizing radiation breaks chemical bonds of molecules in the ices and creates a host of ions and radicals that can react at the ambient temperature or when the parent ice is subsequently warmed. Experiments that similar these conditions have demonstrated a rich chemistry associated with these environments that leads to a wide variety of organic products. Many of these products are of considerable interest to astrobiology. For example, the irradiation of simple ices has been shown to abiotically produce amino acids, nucleobases, quinones, and amphiphiles, all compounds that play key roles in modern biochemistry. This suggests extraterrestrial chemistry could have played a role in the origin of life on Earth and, by extension, do so on planets in other stellar systems.

A Bulk Microphysics Parameterization with Multiple Ice Precipitation Categories.

Science.gov (United States)

Straka, Jerry M.; Mansell, Edward R.

2005-04-01

A single-moment bulk microphysics scheme with multiple ice precipitation categories is described. It has 2 liquid hydrometeor categories (cloud droplets and rain) and 10 ice categories that are characterized by habit, size, and density—two ice crystal habits (column and plate), rimed cloud ice, snow (ice crystal aggregates), three categories of graupel with different densities and intercepts, frozen drops, small hail, and large hail. The concept of riming history is implemented for conversions among the graupel and frozen drops categories. The multiple precipitation ice categories allow a range of particle densities and fall velocities for simulating a variety of convective storms with minimal parameter tuning. The scheme is applied to two cases—an idealized continental multicell storm that demonstrates the ice precipitation process, and a small Florida maritime storm in which the warm rain process is important.

Electrical and optical properties of amorphous indium zinc oxide films

International Nuclear Information System (INIS)

Ito, N.; Sato, Y.; Song, P.K.; Kaijio, A.; Inoue, K.; Shigesato, Y.

2006-01-01

Valence electron control and electron transport mechanisms on the amorphous indium zinc oxide (IZO) films were investigated. The amorphous IZO films were deposited by dc magnetron sputtering using an oxide ceramic IZO target (89.3 wt.% In 2 O 3 and 10.7 wt.% ZnO). N-type impurity dopings, such as Sn, Al or F, could not lead to the increase in carrier density in the IZO. Whereas, H 2 introduction into the IZO deposition process was confirmed to be effective to increase carrier density. By 30% H 2 introduction into the deposition process, carrier density increased from 3.08 x 10 2 to 7.65 x 10 2 cm -3 , which must be originated in generations of oxygen vacancies or interstitial Zn 2+ ions. Decrease in the transmittance in the near infrared region and increase in the optical band gap were observed with the H 2 introduction, which corresponded to the increase in carrier density. The lowest resistivity of 3.39 x 10 -4 Ω cm was obtained by 10% H 2 introduction without substrate heating during the deposition

Evaluation of real-time ice concentration inside pipeline by the refractive index method

Energy Technology Data Exchange (ETDEWEB)

Lee, Dong Gyu; Kang, Chae Dong [Chonbuk National University, Jeonju (Korea, Republic of); Chung, Dong Yeol; Peck, Jong Hyeon [KITECH, Cheonan (Korea, Republic of)

2015-05-15

Ice fraction (or ice concentration, IC) of the ice slurry flowing through the pipe is very difficult to measure directly and in real time in ice slurry type system in thermal energy storage system. Measuring IC is very important to calculate the capacity of cold energy supplied through a pipeline. Ice fraction measurement methods have been reported as using density, electric resistance, electric conductivity, freezing point etc. However, the conventional methods are not perfect in terms of the resolution and accuracy. In this study, a new method is suggested to measure the IC of the ice slurry flowing through a pipe, which is used for a refractometer with low electrical noise and high resolution. To measure IC of the flowing ice slurry aqueous solution in pipe, it was installed in the test section to mass flow meter, refractometer, cyclone, and RTD Resistance temperature detector) sensor. From the experiment, IC measurement method by using refractive index showed better result than others for the ice slurry in pipeline flowing or slurry tank.

Heterogeneous Ice Nucleation Ability of NaCl and Sea Salt Aerosol Particles at Cirrus Temperatures

Science.gov (United States)

Wagner, Robert; Kaufmann, Julia; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Ullrich, Romy; Leisner, Thomas

2018-03-01

In situ measurements of the composition of heterogeneous cirrus ice cloud residuals have indicated a substantial contribution of sea salt in sampling regions above the ocean. We have investigated the heterogeneous ice nucleation ability of sodium chloride (NaCl) and sea salt aerosol (SSA) particles at cirrus cloud temperatures between 235 and 200 K in the Aerosol Interaction and Dynamics in the Atmosphere aerosol and cloud chamber. Effloresced NaCl particles were found to act as ice nucleating particles in the deposition nucleation mode at temperatures below about 225 K, with freezing onsets in terms of the ice saturation ratio, Sice, between 1.28 and 1.40. Above 225 K, the crystalline NaCl particles deliquesced and nucleated ice homogeneously. The heterogeneous ice nucleation efficiency was rather similar for the two crystalline forms of NaCl (anhydrous NaCl and NaCl dihydrate). Mixed-phase (solid/liquid) SSA particles were found to act as ice nucleating particles in the immersion freezing mode at temperatures below about 220 K, with freezing onsets in terms of Sice between 1.24 and 1.42. Above 220 K, the SSA particles fully deliquesced and nucleated ice homogeneously. Ice nucleation active surface site densities of the SSA particles were found to be in the range between 1.0 · 1010 and 1.0 · 1011 m-2 at T < 220 K. These values are of the same order of magnitude as ice nucleation active surface site densities recently determined for desert dust, suggesting a potential contribution of SSA particles to low-temperature heterogeneous ice nucleation in the atmosphere.

Amorphous NiFe-OH/NiFeP Electrocatalyst Fabricated at Low Temperature for Water Oxidation Applications

KAUST Repository

Liang, Hanfeng

2017-04-11

Water splitting driven by electricity or sunlight is one of the most promising ways to address the global terawatt energy needs of future societies; however, its large-scale application is limited by the sluggish kinetics of the oxygen evolution reaction (OER). NiFe-based compounds, mainly oxides and hydroxides, are well-known OER catalysts and have been intensively studied; however, the utilization of the synergistic effect between two different NiFe-based materials to further boost the OER performance has not been achieved to date. Here, we report the rapid conversion of NiFe double hydroxide into metallic NiFeP using PH3 plasma treatment and further construction of amorphous NiFe hydroxide/NiFeP/Ni foam as efficient and stable oxygen-evolving anodes. The strong electronic interactions between NiFe hydroxide and NiFeP significantly lower the adsorption energy of H2O on the hybrid and thus lead to enhanced OER performance. As a result, the hybrid catalyst can deliver a geometrical current density of 300 mA cm–2 at an extremely low overpotential (258 mV, after ohmic-drop correction), along with a small Tafel slope of 39 mV decade–1 and outstanding long-term durability in alkaline media.

Disentangling neighbors and extended range density oscillations in monatomic amorphous semiconductors.

Science.gov (United States)

Roorda, S; Martin, C; Droui, M; Chicoine, M; Kazimirov, A; Kycia, S

2012-06-22

High energy x-ray diffraction measurements of pure amorphous Ge were made and its radial distribution function (RDF) was determined at high resolution, revealing new information on the atomic structure of amorphous semiconductors. Fine structure in the second peak in the RDF provides evidence that a fraction of third neighbors are closer than some second neighbors; taking this into account leads to a narrow distribution of tetrahedral bond angles, (8.5 ± 0.1)°. A small peak which appears near 5 Å upon thermal annealing shows that some ordering in the dihedral bond-angle distribution takes place during structural relaxation. Extended range order is detected (in both a-Ge and a-Si) which persists to beyond 20 Å, and both the periodicity and its decay length increase upon thermal annealing. Previously, the effect of structural relaxation was only detected at intermediate range, involving reduced tetrahedral bond-angle distortions. These results enhance our understanding of the atomic order in continuous random networks and place significantly more stringent requirements on computer models intending to describe these networks, or their alternatives which attempt to describe the structure in terms of an arrangement of paracrystals.

Effect of vacuum-packaging and low dose gamma irradiation on the microbial, bio-chemical quality and shelf life of peeled shrimp (Litopenaeus vannamei) during ice storage

International Nuclear Information System (INIS)

Bojayanaik, Manjanaik; Naroth, Kavya; Prasad, Surjith; Shetty, Veena; Hiriyur, Somashekarappa; Patil, Rajashekar

2015-01-01

The present investigation was carried out to see the combined effect of vacuum packaging and low dose gamma irradiation (3kGy) on the shelf life of peeled and undeveined shrimp (Litopeanus vannamie) during ice storage. The fresh farm raised shrimps were peeled and un deveined, packed in high density polyethylene bags (aerobic and vacuum packaging) and were divided into four groups viz. control (C), Irradiated (I), Vacuum packed (V) and vacuum-packed with irradiation (VI). The two groups (I and VI) were irradiated at 3 kGy (Dose rate at the rate 6.043 kGy/hr) and aseptically stored in ice in an insulated polystyrene box. All the samples were periodically analysed for microbial (Total bacterial load, total Coliform, Faecal Coliforms, Staphylococcus, Salmonella, Vibrios and E. coli) and bio chemical (TVB-N, TMA, TBARS and pH) quality. The results revealed that the combination of low dose gamma irradiation and vacuum packaging had a significant effect on microbial load (p>0.05). The TVB-N, TMA-N, TBARS and pH were significantly lower in vacuum packed with irradiation when compare to non-irradiated and aerobically packed shrimp (p> 0.05), and shelf life of peeled shrimp extended up to 21 days in ice storage. (author)

Study of low energy Si5- and Cs- implantation induced amorphization effects in Si(1 0 0)

International Nuclear Information System (INIS)

Lenka, H P; Joseph, B; Kuiri, P K; Sahu, G; Mahapatra, D P; Mishra, P; Ghose, D

2008-01-01

The damage growth and surface modifications in Si(1 0 0), induced by 25 keV Si 5 - cluster ions, as a function of fluence, φ, has been studied using atomic force microscopy (AFM) and channelling Rutherford backscattering spectrometry (RBS/C). RBS/C results indicate a nonlinear growth in damage from which it has been possible to get a threshold fluence, φ 0 , for amorphization as 2.5 x 10 13 ions cm -2 . For φ below φ 0 , a growth in damage as well as surface roughness has been observed. At a φ of 1 x 10 14 ions cm -2 , damage saturation coupled with a much reduced surface roughness has been found. In this case a power spectrum analysis of AFM data showed a significant drop in spectral density, as compared with the same obtained for a fluence, φ 0 . This drop, together with damage saturation, can be correlated with a transition to a stress relaxed amorphous phase. Irradiation with similar mass Cs - ions, at the same energy and fluence, has been found to result in a reduced accumulation of defects in the near surface region leading to reduced surface features.

Molecular dynamics study of amorphous pocket formation in Si at low energies and its application to improve binary collision models

International Nuclear Information System (INIS)

Santos, Ivan; Marques, Luis A.; Pelaz, Lourdes; Lopez, Pedro

2007-01-01

In this paper, we present classical molecular dynamics results about the formation of amorphous pockets in silicon for energy transfers below the displacement threshold. While in binary collision simulations ions with different masses generate the same number of Frenkel pairs for the same deposited nuclear energy, in molecular dynamics simulations the amount of damage and its complexity increase with ion mass. We demonstrate that low-energy transfers to target atoms are able to generate complex damage structures. We have determined the conditions that have to be fulfilled to produce amorphous pockets, showing that the order-disorder transition depends on the particular competition between melting and heat diffusion processes. We have incorporated these molecular dynamics results in an improved binary collision model that is able to provide a good description of damage with a very low computational cost

Trapping of CH4, CO, and CO2 in Amorphous Water Ice

Science.gov (United States)

Mastrapa, R. M. E.; Brown, R. H.; Anicich, V. G.; Cohen, B. A.; Dai, W.; Lunine, J. I.

1999-09-01

In this study, CO, CH4, and CO2 were trapped in H2O at temperatures as low as 20 K and pressures between 10-5 and 10-8 Torr. IR spectra were taken of each sample before sublimation to confirm the presence of volatiles. The samples were then heated at rates from 0.25 K/min to 1 K/min and the escape ranges were measured with a mass spectrometer. The volatiles escaped from the ice mixtures in temperature ranges similar to those found in previous work (1, 2, 3), namely 48-52 K, 145-160 K, 170-185 K. H2O is released from 150 K to 185 K. However, the temperature range of escape is strongly dependent on deposition temperature and heating rate. If the deposition temperature is below the point where the solid volatile rapidly sublimates in the ambient environment of our experiment, then the first range of volatile escape is centered around it's sublimation point, and there is little of the volatile remaining from 170-185 K. The location of the third escape range shifts to lower temperatures with slower sublimation rate. It was determined that 0.5 K/min is the ideal sample heating rate to determine these escape ranges. In our data, the infrared spectrum of CO trapped in water ice shows a splitting of the 2145 cm-1 solid CO line into two bands at 2343 cm-1 and 2135 cm-1. These shifts are similar to those seen by Sandford, et al. (4). (1) Bar-Nun, A., G. Herman, D. Laufer, and M. L. Rappaport, (1985), Icarus, 63, 317-332. (2) Bar-Nun, A., J. Dror, E. Kochavi, and D. Laufer, (1987), Physical Review B, 35, no. 5, 2427-2435. (3) Hudson, R. L., and B. Donn, (1991), Icarus, 94, 326-332. (4) Sandford, S. A., L. J. Allamandola, A. G. G. M. Tielens, and G. J. Valero, (1988), Astrophysical Journal, 329, 498-510.

Molecular hydrogen formation on surfaces of astrophysical interest: first results on water ice at very low temperature and on graphite at high temperature

International Nuclear Information System (INIS)

Baouche, Saoud

2004-01-01

As the generally admitted mechanism of formation of the H_2 molecule in the interstellar medium (ISM) is a catalytic reaction between two atoms of H on the surface of cosmic powder grains, where grains are supposed to be carbons or silicates and could have ice coats, this research thesis aims at providing some elements about the efficiency of this reaction, what happens to the bound energy released after formation of the H_2 molecule. The author first describes the FORMOLISM experiment (Formation of molecule in the ISM), and then reports the study of the source of H or D atoms which is a very important component of the experiment. He reports and comments results obtained on the formation of H_2 and D_2 molecules on amorphous water ice. He reports the study of the dynamics of formation of the D_2 molecule on a graphite surface by using the laser-aided associative adsorption technique

Evolution of Mars’ Northern Polar Seasonal CO2 deposits: variations in surface brightness and bulk density

Science.gov (United States)

Mount, Christopher P.; Titus, Timothy N.

2015-01-01

Small scale variations of seasonal ice are explored at different geomorphic units on the Northern Polar Seasonal Cap (NPSC). We use seasonal rock shadow measurements, combined with visible and thermal observations, to calculate density over time. The coupling of volume density and albedo allows us to determine the microphysical state of the seasonal CO2 ice. We find two distinct endmembers across the NPSC: 1) Snow deposits may anneal to form an overlying slab layer that fractures. These low density deposits maintain relatively constant densities over springtime. 2) Porous slab deposits likely anneal rapidly in early spring and fracture in late spring. These high density deposits dramatically increase in density over time. The endmembers appear to be correlated with latitude.

A Bayesian Retrieval of Greenland Ice Sheet Internal Temperature from Ultra-wideband Software-defined Microwave Radiometer (UWBRAD) Measurements

Science.gov (United States)

Duan, Y.; Durand, M. T.; Jezek, K. C.; Yardim, C.; Bringer, A.; Aksoy, M.; Johnson, J. T.

2017-12-01

The ultra-wideband software-defined microwave radiometer (UWBRAD) is designed to provide ice sheet internal temperature product via measuring low frequency microwave emission. Twelve channels ranging from 0.5 to 2.0 GHz are covered by the instrument. A Greenland air-borne demonstration was demonstrated in September 2016, provided first demonstration of Ultra-wideband radiometer observations of geophysical scenes, including ice sheets. Another flight is planned for September 2017 for acquiring measurements in central ice sheet. A Bayesian framework is designed to retrieve the ice sheet internal temperature from simulated UWBRAD brightness temperature (Tb) measurements over Greenland flight path with limited prior information of the ground. A 1-D heat-flow model, the Robin Model, was used to model the ice sheet internal temperature profile with ground information. Synthetic UWBRAD Tb observations was generated via the partially coherent radiation transfer model, which utilizes the Robin model temperature profile and an exponential fit of ice density from Borehole measurement as input, and corrupted with noise. The effective surface temperature, geothermal heat flux, the variance of upper layer ice density, and the variance of fine scale density variation at deeper ice sheet were treated as unknown variables within the retrieval framework. Each parameter is defined with its possible range and set to be uniformly distributed. The Markov Chain Monte Carlo (MCMC) approach is applied to make the unknown parameters randomly walk in the parameter space. We investigate whether the variables can be improved over priors using the MCMC approach and contribute to the temperature retrieval theoretically. UWBRAD measurements near camp century from 2016 was also treated with the MCMC to examine the framework with scattering effect. The fine scale density fluctuation is an important parameter. It is the most sensitive yet highly unknown parameter in the estimation framework

Modeling and characterization of the low frequency noise behavior for amorphous InGaZnO thin film transistors in the subthreshold region

Science.gov (United States)

Cai, Minxi; Yao, Ruohe

2017-10-01

An analytical model of the low-frequency noise (LFN) for amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) in the subthreshold region is developed. For a-IGZO TFTs, relations between the device noise and the subgap defects are characterized based on the dominant multiple trapping and release (MTR) mechanism. The LFN is considered to be contributed from trapping/detrapping of carriers both into the border traps and the subgap density of states (DOS). It is revealed that the LFN behavior of a-IGZO TFTs in the subthreshold region is significantly influenced by the distribution of tail states, where MTR process prevails. The 1/f α (with α < 1) spectrum of the drain current noise is also related to the characteristic temperature of the tail states. The new method is introduced to calculate the LFN of devices by extracting the LFN-related DOS parameters from the current-voltage characteristics.

Thick and low-stress PECVD amorphous silicon for MEMS applications

International Nuclear Information System (INIS)

Iliescu, Ciprian; Chen Bangtao

2008-01-01

This paper presents a solution for the deposition of thick amorphous silicon (α-Si:H) in PECVD reactors for MEMS applications, such as sacrificial layer or mask layer for dry or wet etching of glass. This achievement was possible by tuning the deposition parameters to a 'zero' value of the residual stress in the α-Si:H layer. The influence of the process parameters, such as power, frequency mode, temperature, pressure and SiH 4 /Ar flow rates for tuning the residual stress and for a good deposition rate is analyzed. The deposition of low-stress and thick (more than 12 µm in our case) α-Si:H layers was possible without generation of hillock defects (previously reported in literature for layers thicker then 2 µm). Finally, the paper presents some MEMS applications of such a deposited α-Si:H layer: masking layer for deep wet etching as well as dry etching of glass, and sacrificial layer for dry or wet release

An IR investigation of solid amorphous ethanol - Spectra, properties, and phase changes

Science.gov (United States)

Hudson, Reggie L.

2017-12-01

Mid- and far-infrared spectra of condensed ethanol (CH3CH2OH) at 10-160 K are presented, with a special focus on amorphous ethanol, the form of greatest astrochemical interest, and with special attention given to changes at 155-160 K. Infrared spectra of amorphous and crystalline forms are shown. The refractive index at 670 nm of amorphous ethanol at 16 K is reported, along with three IR band strengths and a density. A comparison is made to recent work on the isoelectronic compound ethanethiol (CH3CH2SH), and several astrochemical applications are suggested for future study.

Anomalously-dense firn in an ice-shelf channel revealed by wide-angle radar

Science.gov (United States)

Drews, R.; Brown, J.; Matsuoka, K.; Witrant, E.; Philippe, M.; Hubbard, B.; Pattyn, F.

2015-10-01

The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium for which knowledge of the depth-averaged density is essential. The densification from snow to ice depends on a number of local factors (e.g. temperature and surface mass balance) causing spatial and temporal variations in density-depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar datasets (10 MHz) collected at five sites on Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, Antarctica. Using a novel algorithm including traveltime inversion and raytracing with a prescribed shape of the depth-density relationship, we show that the depth to internal reflectors, the local ice thickness and depth-averaged densities can reliably be reconstructed. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggests that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals 10 % denser firn inside compared to outside the channel. The denser firn in the ice-shelf channel should be accounted for when using the hydrostatic ice thickness for determining basal melt rates. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

First-principles study of crystalline and amorphous AlMgB{sub 14}-based materials

Energy Technology Data Exchange (ETDEWEB)

Ivashchenko, V. I.; Shevchenko, V. I., E-mail: shev@materials.kiev.ua [Institute of Problems of Material Science, National Academy of Science of Ukraine, Krzhyzhanosky Str. 3, 03142 Kyiv (Ukraine); Turchi, P. E. A. [Lawrence Livermore National Laboratory (L-352), P.O. Box 808, Livermore, California 94551 (United States); Veprek, S. [Department of Chemistry, Technical University Munich, Lichtenbergstrasse 4, D-85747 Garching (Germany); Leszczynski, Jerzy [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, Mississippi 39217 (United States); Gorb, Leonid [Department of Chemistry and Biochemistry, Interdisciplinary Center for Nanotoxicity, Jackson State University, Jackson, Mississippi 39217 (United States); Badger Technical Services, LLC, Vicksburg, Mississippi 39180 (United States); Hill, Frances [U.S. Army ERDC, Vicksburg, Mississippi 39180 (United States)

2016-05-28

We report first-principles investigations of crystalline and amorphous boron and M1{sub x}M2{sub y}X{sub z}B{sub 14−z} (M1, M2 = Al, Mg, Li, Na, Y; X = Ti, C, Si) phases (so-called “BAM” materials). Phase stability is analyzed in terms of formation energy and dynamical stability. The atomic configurations as well as the electronic and phonon density states of these phases are compared. Amorphous boron consists of distorted icosahedra, icosahedron fragments, and dioctahedra, connected by an amorphous network. The presence of metal atoms in amorphous BAM materials precludes the formation of icosahedra. For all the amorphous structures considered here, the Fermi level is located in the mobility gap independent of the number of valence electrons. The intra-icosahedral vibrations are localized in the range of 800 cm{sup −1}, whereas the inter-icosahedral vibrations appear at higher wavenumbers. The amorphization leads to an enhancement of the vibrations in the range of 1100–1250 cm{sup −1}. The mechanical properties of BAM materials are investigated at equilibrium and under shear and tensile strain. The anisotropy of the ideal shear and tensile strengths is explained in terms of a layered structure of the B{sub 12} units. The strength of amorphous BAM materials is lower than that of the crystalline counterparts because of the partial fragmentation of the boron icosahedra in amorphous structures. The strength enhancement found experimentally for amorphous boron-based films is very likely related to an increase in film density, and the presence of oxygen impurities. For crystalline BAM materials, the icosahedra are preserved during elongation upon tension as well as upon shear in the (010)[100] slip system.

LAKE ICE DETECTION IN LOW-RESOLUTION OPTICAL SATELLITE IMAGES

Directory of Open Access Journals (Sweden)

M. Tom

2018-05-01

Full Text Available Monitoring and analyzing the (decreasing trends in lake freezing provides important information for climate research. Multi-temporal satellite images are a natural data source to survey ice on lakes. In this paper, we describe a method for lake ice monitoring, which uses low spatial resolution (250 m–1000 m satellite images to determine whether a lake is frozen or not. We report results on four selected lakes in Switzerland: Sihl, Sils, Silvaplana and St. Moritz. These lakes have different properties regarding area, altitude, surrounding topography and freezing frequency, describing cases of medium to high difficulty. Digitized Open Street Map (OSM lake outlines are back-projected on to the image space after generalization. As a pre-processing step, the absolute geolocation error of the lake outlines is corrected by matching the projected outlines to the images. We define the lake ice detection as a two-class (frozen, non-frozen semantic segmentation problem. Several spectral channels of the multi-spectral satellite data are used, both reflective and emissive (thermal. Only the cloud-free (clean pixels which lie completely inside the lake are analyzed. The most useful channels to solve the problem are selected with xgboost and visual analysis of histograms of reference data, while the classification is done with non-linear support vector machine (SVM. We show experimentally that this straight-forward approach works well with both MODIS and VIIRS satellite imagery. Moreover, we show that the algorithm produces consistent results when tested on data from multiple winters.

Lake Ice Detection in Low-Resolution Optical Satellite Images

Science.gov (United States)

Tom, M.; Kälin, U.; Sütterlin, M.; Baltsavias, E.; Schindler, K.

2018-05-01

Monitoring and analyzing the (decreasing) trends in lake freezing provides important information for climate research. Multi-temporal satellite images are a natural data source to survey ice on lakes. In this paper, we describe a method for lake ice monitoring, which uses low spatial resolution (250 m-1000 m) satellite images to determine whether a lake is frozen or not. We report results on four selected lakes in Switzerland: Sihl, Sils, Silvaplana and St. Moritz. These lakes have different properties regarding area, altitude, surrounding topography and freezing frequency, describing cases of medium to high difficulty. Digitized Open Street Map (OSM) lake outlines are back-projected on to the image space after generalization. As a pre-processing step, the absolute geolocation error of the lake outlines is corrected by matching the projected outlines to the images. We define the lake ice detection as a two-class (frozen, non-frozen) semantic segmentation problem. Several spectral channels of the multi-spectral satellite data are used, both reflective and emissive (thermal). Only the cloud-free (clean) pixels which lie completely inside the lake are analyzed. The most useful channels to solve the problem are selected with xgboost and visual analysis of histograms of reference data, while the classification is done with non-linear support vector machine (SVM). We show experimentally that this straight-forward approach works well with both MODIS and VIIRS satellite imagery. Moreover, we show that the algorithm produces consistent results when tested on data from multiple winters.

Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1−xKxFe2As2 superconductors

KAUST Repository

Wang, Lei

2011-06-01

We report here an atomic resolution study of the structure and composition of the grain boundaries in polycrystallineSr0.6K0.4Fe2As2superconductor. A large fraction of grain boundaries contain amorphous layers larger than the coherence length, while some others contain nanometer-scale crystallites sandwiched in between amorphous layers. We also find that there is significant oxygen enrichment at the grain boundaries. Such results explain the relatively low transport critical current density (Jc) of polycrystalline samples with respect to that of bicrystal films.

Sea-ice deformation in a coupled ocean–sea-ice model and in satellite remote sensing data

Directory of Open Access Journals (Sweden)

G. Spreen

2017-07-01

Full Text Available A realistic representation of sea-ice deformation in models is important for accurate simulation of the sea-ice mass balance. Simulated sea-ice deformation from numerical simulations with 4.5, 9, and 18 km horizontal grid spacing and a viscous–plastic (VP sea-ice rheology are compared with synthetic aperture radar (SAR satellite observations (RGPS, RADARSAT Geophysical Processor System for the time period 1996–2008. All three simulations can reproduce the large-scale ice deformation patterns, but small-scale sea-ice deformations and linear kinematic features (LKFs are not adequately reproduced. The mean sea-ice total deformation rate is about 40 % lower in all model solutions than in the satellite observations, especially in the seasonal sea-ice zone. A decrease in model grid spacing, however, produces a higher density and more localized ice deformation features. The 4.5 km simulation produces some linear kinematic features, but not with the right frequency. The dependence on length scale and probability density functions (PDFs of absolute divergence and shear for all three model solutions show a power-law scaling behavior similar to RGPS observations, contrary to what was found in some previous studies. Overall, the 4.5 km simulation produces the most realistic divergence, vorticity, and shear when compared with RGPS data. This study provides an evaluation of high and coarse-resolution viscous–plastic sea-ice simulations based on spatial distribution, time series, and power-law scaling metrics.

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.

Amorphous silicon radiation detectors

Science.gov (United States)

Street, Robert A.; Perez-Mendez, Victor; Kaplan, Selig N.

1992-01-01

Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification.

Interaction between rare-earth ions and amorphous silicon nanoclusters produced at low processing temperatures

Energy Technology Data Exchange (ETDEWEB)

Meldrum, A. [Department of Physics, University of Alberta, Edmonton, T6G2J1 (Canada)]. E-mail: ameldrum@ualberta.ca; Hryciw, A. [Department of Physics, University of Alberta, Edmonton, T6G2J1 (Canada); MacDonald, A.N. [Department of Physics, University of Alberta, Edmonton, T6G2J1 (Canada); Blois, C. [Department of Physics, University of Alberta, Edmonton, T6G2J1 (Canada); Clement, T. [Department of Electrical and Computer Engineering, University of Alberta, Edmonton, T6G2V4 (Canada); De Corby, R. [Department of Electrical and Computer Engineering, University of Alberta, Edmonton, T6G2V4 (Canada); Wang, J. [Department of Physics, Chinese University of Hong Kong, Shatin, Hong Kong (China); Li Quan [Department of Physics, Chinese University of Hong Kong, Shatin, Hong Kong (China)

2006-12-15

Temperatures of 1000 deg. C and higher are a significant problem for the incorporation of erbium-doped silicon nanocrystal devices into standard silicon technology, and make the fabrication of contacts and reflectors in light emitting devices difficult. In the present work, we use energy-filtered TEM imaging techniques to show the formation of size-controlled amorphous silicon nanoclusters in SiO films annealed between 400 and 500 deg. C. The PL properties of such films are characteristic of amorphous silicon, and the spectrum can be controlled via a statistical size effect-as opposed to quantum confinement-that has previously been proposed for porous amorphous silicon. Finally, we show that amorphous nanoclusters sensitize the luminescence from the rare-earth ions Er, Nd, Yb, and Tm with excitation cross-sections similar in magnitude to erbium-doped silicon nanocrystal composites, and with a similar nonresonant energy transfer mechanism.

Excessively High Vapor Pressure of Al-based Amorphous Alloys

Directory of Open Access Journals (Sweden)

Jae Im Jeong

2015-10-01

Full Text Available Aluminum-based amorphous alloys exhibited an abnormally high vapor pressure at their approximate glass transition temperatures. The vapor pressure was confirmed by the formation of Al nanocrystallites from condensation, which was attributed to weight loss of the amorphous alloys. The amount of weight loss varied with the amorphous alloy compositions and was inversely proportional to their glass-forming ability. The vapor pressure of the amorphous alloys around 573 K was close to the vapor pressure of crystalline Al near its melting temperature, 873 K. Our results strongly suggest the possibility of fabricating nanocrystallites or thin films by evaporation at low temperatures.

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

Amorphization of thiamine chloride hydrochloride: A study of the crystallization inhibitor properties of different polymers in thiamine chloride hydrochloride amorphous solid dispersions.

Science.gov (United States)

Arioglu-Tuncil, Seda; Bhardwaj, Vivekanand; Taylor, Lynne S; Mauer, Lisa J

2017-09-01

Amorphous solid dispersions of thiamine chloride hydrochloride (THCl) were created using a variety of polymers with different physicochemical properties in order to investigate how effective the various polymers were as THCl crystallization inhibitors. THCl:polymer dispersions were prepared by lyophilizing solutions of THCl and amorphous polymers (guar gum, pectin, κ-carrageenan, gelatin, and polyvinylpyrrolidone (PVP)). These dispersions were stored at select temperature (25 and 40°C) and relative humidity (0, 23, 32, 54, 75, and 85% RH) conditions and monitored at different time points using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). Moisture sorption isotherms of all samples were also obtained. Initially amorphous THCl was produced in the presence of ≥40% w/w pectin, κ-carrageenan, gelatin, and guar gum or ≥60% w/w PVP. Trends in polymer THCl crystallization inhibition (pectin≥κ-carrageenan>gelatin>guar gum≫PVP) were primarily based on the ability of the polymer to interact with THCl via hydrogen bonding and/or ionic interactions. The onset of THCl crystallization from the amorphous dispersions was also related to storage conditions. THCl remained amorphous at low RH conditions (0 and 23% RH) in all 1:1 dispersions except THCl:PVP. THCl crystallized in some dispersions below the glass transition temperature (T g ) but remained amorphous in others at T~T g . At high RHs (75 and 85% RH), THCl crystallized within one day in all samples. Given the ease of THCl amorphization in the presence of a variety of polymers, even at higher vitamin concentrations than would be found in foods, it is likely that THCl is amorphous in many low moisture foods. Copyright © 2017 Elsevier Ltd. All rights reserved.

On The Importance of Connecting Laboratory Measurements of Ice Crystal Growth with Model Parameterizations: Predicting Ice Particle Properties

Science.gov (United States)

Harrington, J. Y.

2017-12-01

Parameterizing the growth of ice particles in numerical models is at an interesting cross-roads. Most parameterizations developed in the past, including some that I have developed, parse model ice into numerous categories based primarily on the growth mode of the particle. Models routinely possess smaller ice, snow crystals, aggregates, graupel, and hail. The snow and ice categories in some models are further split into subcategories to account for the various shapes of ice. There has been a relatively recent shift towards a new class of microphysical models that predict the properties of ice particles instead of using multiple categories and subcategories. Particle property models predict the physical characteristics of ice, such as aspect ratio, maximum dimension, effective density, rime density, effective area, and so forth. These models are attractive in the sense that particle characteristics evolve naturally in time and space without the need for numerous (and somewhat artificial) transitions among pre-defined classes. However, particle property models often require fundamental parameters that are typically derived from laboratory measurements. For instance, the evolution of particle shape during vapor depositional growth requires knowledge of the growth efficiencies for the various axis of the crystals, which in turn depends on surface parameters that can only be determined in the laboratory. The evolution of particle shapes and density during riming, aggregation, and melting require data on the redistribution of mass across a crystals axis as that crystal collects water drops, ice crystals, or melts. Predicting the evolution of particle properties based on laboratory-determined parameters has a substantial influence on the evolution of some cloud systems. Radiatively-driven cirrus clouds show a broader range of competition between heterogeneous nucleation and homogeneous freezing when ice crystal properties are predicted. Even strongly convective squall

Electronic structure of xenon implanted with low energy in amorphous silicon

International Nuclear Information System (INIS)

Barbieri, P.F.; Landers, R.; Oliveira, M.H. de; Alvarez, F.; Marques, F.C.

2007-01-01

Electronic structure of Xe implanted in amorphous silicon (a-Si) films are investigated. Xe atoms were implanted with low energy by ion beam assisted deposition (IBAD) technique during growth of the a-Si films. The Xe implantation energy varied in the 0-300 eV energy range. X-ray photoelectron spectroscopy (XPS), X-ray Auger excited spectroscopy (XAES) and X-ray absorption spectroscopy (XAS) were used for investigating the Xe electronic structure. The Xe M 4 N 45 N 45 transitions were measured to extract the Auger parameter and to analyze the initial state and relaxation contributions. It was found that the binding energy variation is mainly due to initial state contribution. The relaxation energy variation also shows that the Xe trapped environment depends on the implantation energy. XAS measurements reveals that Xe atoms are dispersed in the a-Si matrix

Amorphous and crystalline aerosol particles interacting with water vapor: conceptual framework and experimental evidence for restructuring, phase transitions and kinetic limitations

Directory of Open Access Journals (Sweden)

T. Koop

2009-12-01

Full Text Available Interactions with water are crucial for the properties, transformation and climate effects of atmospheric aerosols. Here we present a conceptual framework for the interaction of amorphous aerosol particles with water vapor, outlining characteristic features and differences in comparison to crystalline particles. We used a hygroscopicity tandem differential mobility analyzer (H-TDMA to characterize the hydration and dehydration of crystalline ammonium sulfate, amorphous oxalic acid and amorphous levoglucosan particles (diameter ~100 nm, relative humidity 5–95% at 298 K. The experimental data and accompanying Köhler model calculations provide new insights into particle microstructure, surface adsorption, bulk absorption, phase transitions and hygroscopic growth. The results of these and related investigations lead to the following conclusions:

(1 Many organic substances, including carboxylic acids, carbohydrates and proteins, tend to form amorphous rather than crystalline phases upon drying of aqueous solution droplets. Depending on viscosity and microstructure, the amorphous phases can be classified as glasses, rubbers, gels or viscous liquids.

(2 Amorphous organic substances tend to absorb water vapor and undergo gradual deliquescence and hygroscopic growth at lower relative humidity than their crystalline counterparts.

(3 In the course of hydration and dehydration, certain organic substances can form rubber- or gel-like structures (supramolecular networks and undergo transitions between swollen and collapsed network structures.

(4 Organic gels or (semi-solid amorphous shells (glassy, rubbery, ultra-viscous with low molecular diffusivity can kinetically limit the uptake and release of water and may influence the hygroscopic growth and activation of aerosol particles as cloud condensation nuclei (CCN and ice nuclei (IN. Moreover, (semi-solid amorphous phases may influence the uptake of gaseous photo

The use of low density high accuracy (LDHA) data for correction of high density low accuracy (HDLA) point cloud

Science.gov (United States)

Rak, Michal Bartosz; Wozniak, Adam; Mayer, J. R. R.

2016-06-01

Coordinate measuring techniques rely on computer processing of coordinate values of points gathered from physical surfaces using contact or non-contact methods. Contact measurements are characterized by low density and high accuracy. On the other hand optical methods gather high density data of the whole object in a short time but with accuracy at least one order of magnitude lower than for contact measurements. Thus the drawback of contact methods is low density of data, while for non-contact methods it is low accuracy. In this paper a method for fusion of data from two measurements of fundamentally different nature: high density low accuracy (HDLA) and low density high accuracy (LDHA) is presented to overcome the limitations of both measuring methods. In the proposed method the concept of virtual markers is used to find a representation of pairs of corresponding characteristic points in both sets of data. In each pair the coordinates of the point from contact measurements is treated as a reference for the corresponding point from non-contact measurement. Transformation enabling displacement of characteristic points from optical measurement to their match from contact measurements is determined and applied to the whole point cloud. The efficiency of the proposed algorithm was evaluated by comparison with data from a coordinate measuring machine (CMM). Three surfaces were used for this evaluation: plane, turbine blade and engine cover. For the planar surface the achieved improvement was of around 200 μm. Similar results were obtained for the turbine blade but for the engine cover the improvement was smaller. For both freeform surfaces the improvement was higher for raw data than for data after creation of mesh of triangles.

Influence of irradiation spectrum and implanted ions on the amorphization of ceramics

International Nuclear Information System (INIS)

Zinkle, S.J.; Snead, L.L.

1995-01-01

Polycrystalline Al2O3, magnesium aluminate spinel (MgAl2O4), MgO, Si3N4, and SiC were irradiated with various ions at 200-450 K, and microstructures were examined following irradiation using cross-section TEM. Amorphization was not observed in any of the irradiated oxide ceramics, despsite damage energy densities up to ∼7 keV/atom (70 displacements per atom). On the other hand, SiC readily amorphized after damage levels of ∼0.4 dpa at room temperature (RT). Si3N4 exhibited intermediate behavior; irradiation with Fe 2+ ions at RT produced amorphization in the implanted ion region after damage levels of ∼1 dpa. However, irradiated regions outside the implanted ion region did not amorphize even after damage levels > 5 dpa. The amorphous layer in the Fe-implanted region of Si3N4 did not appear if the specimen was simultaneoulsy irradiated with 1-MeV He + ions at RT. By comparison with published results, it is concluded that the implantation of certain chemical species has a pronounced effect on the amorphization threshold dose of all five materials. Intense ionizing radiation inhibits amorphization in Si3N4, but does not appear to significantly influence the amorphization of SiC

Experimental study of natural convection melting of ice in salt solutions

International Nuclear Information System (INIS)

Fang, L.J.; Cheung, F.B.; Linehan, J.H.; Pedersen, D.R.

1984-01-01

The solid-liquid interface morphology and the micro-physical process near the moving phase boundary during natural convection melting of a horizontal layer of ice by an overlying pool of salt solution were studied experimentally. A cathetometer which amplifies the interface region was used to measure the ice melting rate. Also measured were the temperature transients of the liquid pool. Within the temperature and the density ratio ranges explored, the ice melting rate was found to be very sensitive to the ratio of pool-to-ice melt density but independent of pool-to-ice temperature difference. By varying the density ratio, three different flow regimes and morphologies of the solid-liquid interface were observed, with melt streamers emanating from the crests of the wavy interface into the pool in all three cases. The measured wavelengths (spacing) between the streamers for four different pairs of materials were correlated with the density ratio and found to agree favorably with the predictions of Taylor instability theory

Demographic, ecological, and physiological responses of ringed seals to an abrupt decline in sea ice availability.

Science.gov (United States)

Ferguson, Steven H; Young, Brent G; Yurkowski, David J; Anderson, Randi; Willing, Cornelia; Nielsen, Ole

2017-01-01

To assess whether demographic declines of Arctic species at the southern limit of their range will be gradual or punctuated, we compared large-scale environmental patterns including sea ice dynamics to ringed seal ( Pusa hispida ) reproduction, body condition, recruitment, and stress in Hudson Bay from 2003 to 2013. Aerial surveys suggested a gradual decline in seal density from 1995 to 2013, with the lowest density occurring in 2013. Body condition decreased and stress (cortisol) increased over time in relation to longer open water periods. The 2010 open water period in Hudson Bay coincided with extremes in large-scale atmospheric patterns (North Atlantic Oscillation, Arctic Oscillation, El Nino-Southern Oscillation) resulting in the earliest spring breakup and the latest ice formation on record. The warming event was coincident with high stress level, low ovulation rate, low pregnancy rate, few pups in the Inuit harvest, and observations of sick seals. Results provide evidence of changes in the condition of Arctic marine mammals in relation to climate mediated sea ice dynamics. We conclude that although negative demographic responses of Hudson Bay seals are occurring gradually with diminishing sea ice, a recent episodic environmental event played a significant role in a punctuated population decline.

INFRARED SPECTRA AND OPTICAL CONSTANTS OF NITRILE ICES RELEVANT TO TITAN's ATMOSPHERE

International Nuclear Information System (INIS)

Moore, Marla H.; Hudson, Reggie; Ferrante, Robert F.; James Moore, W.

2010-01-01

Spectra and optical constants of nitrile ices known or suspected to be in Titan's atmosphere are presented from 2.0 to 333.3 μm (∼5000-30 cm -1 ). These results are relevant to the ongoing modeling of Cassini CIRS observations of Titan's winter pole. Ices studied are: HCN, hydrogen cyanide; C 2 N 2 , cyanogen; CH 3 CN, acetonitrile; C 2 H 5 CN, propionitrile; and HC 3 N, cyanoacetylene. For each of these molecules, we also report new cryogenic measurements of the real refractive index, n, determined in both the amorphous and crystalline phases at 670 nm. These new values have been incorporated into our optical constant calculations. Spectra were measured and optical constants were calculated for each nitrile at a variety of temperatures, including, but not limited to, 20, 35, 50, 75, 95, and 110 K, in both the amorphous phase and the crystalline phase. This laboratory effort used a dedicated FTIR spectrometer to record transmission spectra of thin-film ice samples. Laser interference was used to measure film thickness during condensation onto a transparent cold window attached to the tail section of a closed-cycle helium cryostat. Optical constants, real (n) and imaginary (k) refractive indices, were determined using Kramers-Kronig analysis. Our calculation reproduces the complete spectrum, including all interference effects.

Bilateral anterior thalamic low densities in descending transtentorial herniation

Energy Technology Data Exchange (ETDEWEB)

Nagashima, Chikao; Watanabe, Takao

1985-02-01

Round, well-demarcated, symmetrical low densities in a bilateral thalamus in a case of descending transtentorial herniation due secondarily to acute traumatic left subdural hematoma are reported. An 8-year-old boy, on whom emergency surgery was refused by his parents, showed a marked shift due to the hematoma on admission; this was followed by a low density in the left PCA territory and round, equivocal hypodensities in the anterior thalamus 44 hours post-trauma. The equivocal hypodensities became definite, well-demarcated, round low densities situated symmetrically in the anterior thalamus on the 39th day post-trauma. Akinetic mutism was noted at this time. The symmetrical low densities and the PCA-territory low density persisted as late as the 39th day post-trauma, suggesting infarcts. The downward stretch of the bilateral thalamoperforators, which was effected by a narrowing of the interpeduncular fossa with an approximation of the bilateral perforators, plus a downward shift of the PCA due to descending transtentorial herniation, was assumed to be the mechanism involved. (author).

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.

Ultraviolet spectrophotometry of comet Giacobini-Zinner during the ICE encounter. [International Cometary Explorer (ICE)

Science.gov (United States)

Ahearn, Michael F.; Mcfadden, Lucy A.; Feldman, Paul D.; Boehnhardt, Hermann; Rahe, Juergen; Festou, Michael; Brandt, John C.; Maran, Stephen P.; Niedner, Malcom B.; Smith, Andrew M.

1986-01-01

The IUE spectrophotometry of Comet P/Giacobini-Zinner was acquired in support of the International Cometary Explorer (ICE) mission. The abundances (or upper limits) of UV-active species were calculated. During the ICE encounter the H2O production rate was 3 times 10 to the 28th power/sec, + or - 50%, consistent with values derived from the ICE experiments. Comparison of the abundance of CO2(+) ions with the total electron density measured by the plasma electron experiment on ICE indicates a deficiency of ions relative to electrons indicating a population of ions not detected by remote sensing. The absence of detectable Mg(+) rules out this species as a possible ion of M/Q = 24 detected by the Ion Composition Instrument, part of the ICE complement of instruments.

Atomistic modeling of defect evolution in Si for amorphizing and subamorphizing implants

International Nuclear Information System (INIS)

Lopez, Pedro; Pelaz, Lourdes; Marques, Luis A.; Santos, Ivan; Aboy, Maria; Barbolla, Juan

2004-01-01

Solid phase epitaxial regrowth of pre-amorphizing implants has received significant attention as a method to achieve high dopant activation with minimal diffusion at low implant temperatures and suppress channelling. Therefore, a good understanding of the amorphization and regrowth mechanisms is required in process simulators. We present an atomistic amorphization and recrystallization model that uses the interstitial-vacancy (I-V) pair as a building block to describe the amorphous phase. I-V pairs are locally characterized by the number of neighbouring I-V pairs. This feature captures the damage generation and the dynamical annealing during ion implantation, and also explains the annealing behaviour of amorphous layers and amorphous pockets

Using cloud ice flux to parametrise large-scale lightning

Directory of Open Access Journals (Sweden)

D. L. Finney

2014-12-01

Full Text Available Lightning is an important natural source of nitrogen oxide especially in the middle and upper troposphere. Hence, it is essential to represent lightning in chemistry transport and coupled chemistry–climate models. Using ERA-Interim meteorological reanalysis data we compare the lightning flash density distributions produced using several existing lightning parametrisations, as well as a new parametrisation developed on the basis of upward cloud ice flux at 440 hPa. The use of ice flux forms a link to the non-inductive charging mechanism of thunderstorms. Spatial and temporal distributions of lightning flash density are compared to tropical and subtropical observations for 2007–2011 from the Lightning Imaging Sensor (LIS on the Tropical Rainfall Measuring Mission (TRMM satellite. The well-used lightning flash parametrisation based on cloud-top height has large biases but the derived annual total flash density has a better spatial correlation with the LIS observations than other existing parametrisations. A comparison of flash density simulated by the different schemes shows that the cloud-top height parametrisation has many more instances of moderate flash densities and fewer low and high extremes compared to the other parametrisations. Other studies in the literature have shown that this feature of the cloud-top height parametrisation is in contrast to lightning observations over certain regions. Our new ice flux parametrisation shows a clear improvement over all the existing parametrisations with lower root mean square errors (RMSEs and better spatial correlations with the observations for distributions of annual total, and seasonal and interannual variations. The greatest improvement with the new parametrisation is a more realistic representation of the zonal distribution with a better balance between tropical and subtropical lightning flash estimates. The new parametrisation is appropriate for testing in chemistry transport and chemistry�

submitter Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of α-pinene

CERN Document Server

Ignatius, Karoliina; Järvinen, Emma; Nichman, Leonid; Fuchs, Claudia; Gordon, Hamish; Herenz, Paul; Hoyle, Christopher R; Duplissy, Jonathan; Garimella, Sarvesh; Dias, Antonio; Frege, Carla; Höppel, Niko; Tröstl, Jasmin; Wagner, Robert; Yan, Chao; Amorim, Antonio; Baltensperger, Urs; Curtius, Joachim; Donahue, Neil M; Gallagher, Martin W; Kirkby, Jasper; Kulmala, Markku; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Tomé, Antonio; Virtanen, Annele; Worsnop, Douglas; Stratmann, Frank

2016-01-01

There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate heterogeneous ice nucleation and thus influence cloud properties. However, experimental ice nucleation studies of biogenic SOA are scarce. Here, we investigated the ice nucleation ability of viscous SOA particles. The SOA particles were produced from the ozone initiated oxidation of α-pinene in an aerosol chamber at temperatures in the range from −38 to −10 ◦C at 5–15 % relative humidity with respect to water to ensure their formation in a highly viscous phase state, i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with different sizes was investigated with a new continuous flow diffusion chamber. For the first time, we observed heterogeneous ice nucleation of viscous α-pinene SOA for ice saturation ratios between 1.3 and 1.4 significantly below the homogeneous freezing limit. The maximum frozen fraction...

Impurity-defect complexes in hydrogenated amorphous silicon

International Nuclear Information System (INIS)

Yang, L.H.; Fong, C.Y.; Nichols, C.S.

1991-01-01

The two most outstanding features observed for dopants in hydrogenated amorphous silicon (a-Si:H)-a shift in the Fermi level accompanied by an increase in the defect density and an absence of degenerate doping have previously been postulated to stem from the formation of substitutional dopant-dangling bond complexes. Using first-principles self-consistent pseudopotential calculations in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results. The authors have studied the electronic and structural properties of substitutional fourfold-coordinated phosphorus and boron at the second neighbor position to a dangling bond defect. This paper demonstrates that such impurity-defect complexes can account for the general features observed experimentally in doped a-Si:H

Aging mechanisms in amorphous phase-change materials.

Science.gov (United States)

Raty, Jean Yves; Zhang, Wei; Luckas, Jennifer; Chen, Chao; Mazzarello, Riccardo; Bichara, Christophe; Wuttig, Matthias

2015-06-24

Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to a drift in the electrical resistance, which hinders the development of ultrahigh density storage devices. Here we elucidate the aging process in amorphous GeTe, a prototypical phase-change material, by advanced numerical simulations, photothermal deflection spectroscopy and impedance spectroscopy experiments. We show that aging is accompanied by a progressive change of the local chemical order towards the crystalline one. Yet, the glass evolves towards a covalent amorphous network with increasing Peierls distortion, whose structural and electronic properties drift away from those of the resonantly bonded crystal. This behaviour sets phase-change materials apart from conventional glass-forming systems, which display the same local structure and bonding in both phases.

Non-localized deformation in Cu−Zr multi-layer amorphous films under tension

Energy Technology Data Exchange (ETDEWEB)

Zhong, C. [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Zhang, H. [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9 (Canada); Cao, Q.P.; Wang, X.D. [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Zhang, D.X. [State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027 (China); Hu, J.W. [Hangzhou Workers Amateur University, Hangzhou 310027 (China); Liaw, P.K. [Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996 (United States); Jiang, J.Z., E-mail: jiangjz@zju.edu.cn [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China)

2016-09-05

In metallic glasses (MGs), plastic deformation at room temperature is dominated by highly localized shear bands. Here we report the non-localized deformation under tension in Cu−Zr multi-layer MGs with a pure amorphous structure using large-scale atomistic simulations. It is demonstrated that amorphous samples with high layer numbers, composed of Cu{sub 64}Zr{sub 36} and Cu{sub 40}Zr{sub 60}, or Cu{sub 64}Zr{sub 36} and Cu{sub 50}Zr{sub 50}, present obviously non-localized deformation behavior. We reveal that the deformation behavior of the multi-layer-structured MG films is related but not determined by the deformation behavior of the composed individual layers. The criterion for the deformation mode change for MGs with a pure amorphous structure, in generally, was suggested, i.e., the competition between the elastic-energy density stored and the energy density needed for forming one mature shear band in MGs. Our results provide a promising strategy for designing tensile ductile MGs with a pure amorphous structure at room temperature. - Highlights: • Tensile deformation behaviors in multi-layer MG films. • Films with high layer numbers confirmed with a non-localized deformation behavior. • The deformation mode is reasonably controlled by whether U{sub p} larger than U{sub SB.}.

Amorphous structure evolution of high power diode laser cladded Fe–Co–B–Si–Nb coatings

International Nuclear Information System (INIS)

Zhu Yanyan; Li Zhuguo; Huang Jian; Li Min; Li Ruifeng; Wu Yixiong

2012-01-01

Highlights: ► Fabricated amorphous composited coating by high power diode laser cladding with single track. ► Lower dilution and higher scanning speed are desired to obtain higher amorphous phase fraction. ► White spots phase with high content of Nb embedded in the amorphous matrix. - Abstract: Fe–Co–B–Si–Nb coatings were fabricated on the surface of low carbon steel using high power diode laser cladding of [(Fe 0.5 Co 0.5 ) 0.75 B 0.2 Si 0.05 ] 95.7 Nb 4.3 amorphous powders at three different scanning speeds of 6, 17 and 50 m/s. At each scanning speed, laser power was optimized to obtain low dilution ratio. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy with energy dispersive spectrometer and electron probe micro analysis were carried out to characterize the microstructure and chemical composition of the cladded coatings. Differential scanning calorimetry was also carried out to investigate the fraction of the amorphous phase. The results showed that dilution ratio and scanning speed were the two main factors for fabricating Fe–Co–B–Si–Nb amorphous coating by high power diode laser cladding. Low dilution ratio was crucial for the formation of amorphous phase. When the dilution ratio was low, the fraction of amorphous phase in the cladded coatings increased upon increasing the scanning speed.

Low pCO2 under sea-ice melt in the Canada Basin of the western Arctic Ocean

Science.gov (United States)

Kosugi, Naohiro; Sasano, Daisuke; Ishii, Masao; Nishino, Shigeto; Uchida, Hiroshi; Yoshikawa-Inoue, Hisayuki

2017-12-01

In September 2013, we observed an expanse of surface water with low CO2 partial pressure (pCO2sea) (Ocean. The large undersaturation of CO2 in this region was the result of massive primary production after the sea-ice retreat in June and July. In the surface of the Canada Basin, salinity was low ( 20 µmol kg-1) in the subsurface low pCO2sea layer in the Canada Basin indicated significant net primary production undersea and/or in preformed condition. If these low pCO2sea layers surface by wind mixing, they will act as additional CO2 sinks; however, this is unlikely because intensification of stratification by sea-ice melt inhibits mixing across the halocline.

Extreme Low Light Requirement for Algae Growth Underneath Sea Ice: A Case Study From Station Nord, NE Greenland

Science.gov (United States)

Hancke, Kasper; Lund-Hansen, Lars C.; Lamare, Maxim L.; Højlund Pedersen, Stine; King, Martin D.; Andersen, Per; Sorrell, Brian K.

2018-02-01

Microalgae colonizing the underside of sea ice in spring are a key component of the Arctic foodweb as they drive early primary production and transport of carbon from the atmosphere to the ocean interior. Onset of the spring bloom of ice algae is typically limited by the availability of light, and the current consensus is that a few tens-of-centimeters of snow is enough to prevent sufficient solar radiation to reach underneath the sea ice. We challenge this consensus, and investigated the onset and the light requirement of an ice algae spring bloom, and the importance of snow optical properties for light penetration. Colonization by ice algae began in May under >1 m of first-year sea ice with ˜1 m thick snow cover on top, in NE Greenland. The initial growth of ice algae began at extremely low irradiance (automated high-frequency temperature profiles. We propose that changes in snow optical properties, caused by temperature-driven snow metamorphosis, was the primary driver for allowing sufficient light to penetrate through the thick snow and initiate algae growth below the sea ice. This was supported by radiative-transfer modeling of light attenuation. Implications are an earlier productivity by ice algae in Arctic sea ice than recognized previously.

Density functional/molecular dynamics simulations of nucleus-driven crystallization of amorphous Ge2Sb2Te5

Energy Technology Data Exchange (ETDEWEB)

Akola, Jaakko [Department of Physics, Tampere University of Technology (Finland); COMP Centre of Excellence, Department of Applied Physics, Aalto University (Finland); GRSS and PGI-1, Forschungszentrum Juelich (Germany); Kalikka, Janne; Larrucea, Julen [Nanoscience Center, Department of Physics, University of Jyvaeskylae (Finland); Jones, Robert O. [GRSS and PGI-1, Forschungszentrum Juelich (Germany)

2013-07-01

Early stages of nucleus-driven crystallization of the prototype phase change material Ge{sub 2}Sb{sub 2}Te{sub 5} have been studied by massively-parallel density functional/molecular dynamics simulations for amorphous samples (460 and 648 atoms) at 500, 600, and 700 K. All systems assumed a fixed cubic seed of 58 atoms and 6 vacancies in order to achieve sub-nanosecond phase transition. Crystallization occurs within 600 ps for the 460-atom system at 600 and 700 K, and signs of crystallization (nucleus growth, percolation) are present in the others. Crystallization is accompanied by an increase in the number of ABAB squares (A: Ge,Sb, B: Te), and atoms of all elements move significantly. The evolution of cavities/vacancies is closely monitored. The existence of Te-Te, Ge-Ge, Ge-Sb, and Sb-Sb (wrong) bonds is an inevitable consequence of rapid crystallization.

Gamma irradiation effects in low density polyethylene

International Nuclear Information System (INIS)

Ono, Lilian S.; Scagliusi, Sandra R.; Cardoso, Elisabeth E.L.; Lugao, Ademar B.

2011-01-01