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1

Structure of ice crystallized from supercooled water  

PubMed Central

The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. At ambient conditions, ice is considered to exist in two crystalline forms: stable hexagonal ice and metastable cubic ice. Using X-ray diffraction data and Monte Carlo simulations, we show that ice that crystallizes homogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I. Stacking disorder and stacking faults have been reported earlier for metastable ice I, but only for ice crystallizing in mesopores and in samples recrystallized from high-pressure ice phases rather than in water droplets. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder. These findings highlight the need to reevaluate the physical and thermodynamic properties of this metastable ice as a function of the nature and extent of stacking disorder using well-characterized samples.

Malkin, Tamsin L.; Murray, Benjamin J.; Brukhno, Andrey V.; Anwar, Jamshed; Salzmann, Christoph G.

2012-01-01

2

The structure of ice crystallized from supercooled water  

NASA Astrophysics Data System (ADS)

The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. Traditionally ice was thought to exist in two well-crystalline forms: stable hexagonal ice and metastable cubic ice. It has recently been shown, using X-ray diffraction data, that ice which crystallizes homogeneously and heterogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I (ice Isd). This result is consistent with a number of computational studies of the crystallization of water. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder, which raises the question of whether cubic ice exists. New data will be presented which shows significant stacking disorder (or stacking faults on the order of 1 in every 100 layers of ice Ih) in droplets which froze heterogeneously as warm as 257 K. The identification of stacking-disordered ice from heterogeneous ice nucleation supports the hypothesis that the structure of ice that initially crystallises from supercooled water is stacking-disordered ice I, independent of nucleation mechanism, but this ice can relax to the stable hexagonal phase subject to the kinetics of recrystallization. The formation and persistence of stacking disordered ice in the Earth's atmosphere will also be discussed.

Murray, Benjamin

2013-03-01

3

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

PubMed

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 solution. We predict that micrometer-sized particles and nanoparticles have the same equilibrium internal structure. The variation of liquid-vapor surface tension with solute concentration is a key factor in determining whether a solution-embedded ice core or vapor-exposed ice cap is the equilibrium structure of the aerosols. In agreement with experiments, we predict that the structure of mixed-phase HNO3-water particles, representative of polar stratospheric clouds, consists of an ice core surrounded by freeze-concentrated solution. The results of this work are important to determine the phase state and internal structure of sea spray ultrafine aerosols and other mixed-phase particles under atmospherically relevant conditions. PMID:24820354

Hudait, Arpa; Molinero, Valeria

2014-06-01

4

Development of Measurement System for Three-Dimensional Structure of Ice Crystals in Raw Beef Samples  

NASA Astrophysics Data System (ADS)

Micro-Slicer Image Processing System (MSIPS) has been developed for measuring the three-dimensional(3-D) structure and distribution of ice crystals formed in biological materials. The system has functions to reconstruct the 3-D image based on the image data of exposed cross sections obtained by multi-slicing of a frozen sample with the minimum thickness of 1?m and to display the internal structure as well as an arbitrary cross section of the sample choosing observation angles. The effects of freezing conditions on the morphology and distribl1tion of ice crystals were demonstrated quantitatively from the observations of raw beef stained by fluorescent indicator. The 3-D image of the sample demonstrated that the growth of ice columns was restricted by the intrinsic structure of muscle fibers. The proposed method provided a new tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.

Do, Gab-Soo; Sagara, Yasuyuki; Tabata, Mizuho; Kudoh, Ken-Ichi; Higuchi, Toshiro

5

Crystal structure of an insect antifreeze protein and its implications for ice binding.  

PubMed

Antifreeze proteins (AFPs) help some organisms resist freezing by binding to ice crystals and inhibiting their growth. The molecular basis for how these proteins recognize and bind ice is not well understood. The longhorn beetle Rhagium inquisitor can supercool to below -25 °C, in part by synthesizing the most potent antifreeze protein studied thus far (RiAFP). We report the crystal structure of the 13-kDa RiAFP, determined at 1.21 ? resolution using direct methods. The structure, which contains 1,914 nonhydrogen protein atoms in the asymmetric unit, is the largest determined ab initio without heavy atoms. It reveals a compressed ?-solenoid fold in which the top and bottom sheets are held together by a silk-like interdigitation of short side chains. RiAFP is perhaps the most regular structure yet observed. It is a second independently evolved AFP type in beetles. The two beetle AFPs have in common an extremely flat ice-binding surface comprising regular outward-projecting parallel arrays of threonine residues. The more active, wider RiAFP has four (rather than two) of these arrays between which the crystal structure shows the presence of ice-like waters. Molecular dynamics simulations independently reproduce the locations of these ordered crystallographic waters and predict additional waters that together provide an extensive view of the AFP interaction with ice. By matching several planes of hexagonal ice, these waters may help freeze the AFP to the ice surface, thus providing the molecular basis of ice binding. PMID:23486477

Hakim, Aaron; Nguyen, Jennifer B; Basu, Koli; Zhu, Darren F; Thakral, Durga; Davies, Peter L; Isaacs, Farren J; Modis, Yorgo; Meng, Wuyi

2013-04-26

6

Structural transformation in supercooled water controls the crystallization rate of ice.  

PubMed

One of water's unsolved puzzles is the question of what determines the lowest temperature to which it can be cooled before freezing to ice. The supercooled liquid has been probed experimentally to near the homogeneous nucleation temperature, T(H) ? 232 K, yet the mechanism of ice crystallization-including the size and structure of critical nuclei-has not yet been resolved. The heat capacity and compressibility of liquid water anomalously increase on moving into the supercooled region, according to power laws that would diverge (that is, approach infinity) at ~225 K (refs 1, 2), so there may be a link between water's thermodynamic anomalies and the crystallization rate of ice. But probing this link is challenging because fast crystallization prevents experimental studies of the liquid below T(H). And although atomistic studies have captured water crystallization, high computational costs have so far prevented an assessment of the rates and mechanism involved. Here we report coarse-grained molecular simulations with the mW water model in the supercooled regime around T(H) which reveal that a sharp increase in the fraction of four-coordinated molecules in supercooled liquid water explains its anomalous thermodynamics and also controls the rate and mechanisms of ice formation. The results of the simulations and classical nucleation theory using experimental data suggest that the crystallization rate of water reaches a maximum around 225 K, below which ice nuclei form faster than liquid water can equilibrate. This implies a lower limit of metastability of liquid water just below T(H) and well above its glass transition temperature, 136 K. By establishing a relationship between the structural transformation in liquid water and its anomalous thermodynamics and crystallization rate, our findings also provide mechanistic insight into the observed dependence of homogeneous ice nucleation rates on the thermodynamics of water. PMID:22113691

Moore, Emily B; Molinero, Valeria

2011-11-24

7

Stratospheric ice crystals  

NASA Technical Reports Server (NTRS)

In situ sampling of the crystals is described with a NASA high-altitude aircraft to characterize the presence of ice particles and their role in Antarctic ozone chemistry. A NASA wire impactor was employed to collect the crystals, and the device was modified to permit Formvar crystal replication. The size distributions of the columnar crystals show that at the highest altitude the the smallest crystals are collected. The crystals provide surface area for heterogeneous chemical reactions as well as the removal of moisture and particles from the stratosphere and its ozone-related components.

Goodman, Jindra; Pueschel, R. F.; Snetsinger, K. G.; Verma, S.

1990-01-01

8

Bacterial ice crystal controlling proteins.  

PubMed

Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions. PMID:24579057

Lorv, Janet S H; Rose, David R; Glick, Bernard R

2014-01-01

9

Bacterial Ice Crystal Controlling Proteins  

PubMed Central

Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions.

Lorv, Janet S. H.; Rose, David R.; Glick, Bernard R.

2014-01-01

10

Crystal structure and encapsulation dynamics of ice II-structured neon hydrate.  

PubMed

Neon hydrate was synthesized and studied by in situ neutron diffraction at 480 MPa and temperatures ranging from 260 to 70 K. For the first time to our knowledge, we demonstrate that neon atoms can be enclathrated in water molecules to form ice II-structured hydrates. The guest Ne atoms occupy the centers of D2O channels and have substantial freedom of movement owing to the lack of direct bonding between guest molecules and host lattices. Molecular dynamics simulation confirms that the resolved structure where Ne dissolved in ice II is thermodynamically stable at 480 MPa and 260 K. The density distributions indicate that the vibration of Ne atoms is mainly in planes perpendicular to D2O channels, whereas their distributions along the channels are further constrained by interactions between adjacent Ne atoms. PMID:25002464

Yu, Xiaohui; Zhu, Jinlong; Du, Shiyu; Xu, Hongwu; Vogel, Sven C; Han, Jiantao; Germann, Timothy C; Zhang, Jianzhong; Jin, Changqing; Francisco, Joseph S; Zhao, Yusheng

2014-07-22

11

Modeling, simulation, and comparison study of cirrus cloud ice crystals  

Microsoft Academic Search

Various methods and techniques to estimate ice crystals radar response have been developed to study the structure of cirrus clouds. Most methods assume a spherical shape for the ice crystals. This assumption leads to mistakes on the parameter estimation related to the particles' size. In this work, we modeled the shape of ice particles found in cirrus cloud as measured

Jorge M. Villa; Sandra L. Cruz-Pol; Jose G. Colom-Ustariz; Stephen M. Sekelsky

2003-01-01

12

Modeling, Simulation and Comparison Study of Cirrus Clouds' Ice Crystals  

Microsoft Academic Search

Various methods and techniques to estimate ice crystals radar response have been developed to study the structure of cirrus clouds. Most methods assume a spherical shape for the ice crystals. This assumption leads to mistakes on the parameter estimation related to the particles' size. In this work, we modeled the shape of ice particles found in cirrus cloud as measured

Jorge M. Villa; Sandra L. Cruz-Pol; José Colom-Ustáriz; Stephen M. Sekelsky

13

Effects of Ice-Crystal Structure on Halo Formation: Cirrus Cloud Experimental and Ray-Tracing Modeling Studies  

NASA Technical Reports Server (NTRS)

During the 1986 Project FIRE (First International Satellite Cloud Climatology Project Regional Experiment) field campaign, four 22 deg halo-producing cirrus clouds were studied jointly from a ground-based polarization lidar and an instrumented aircraft. The lidar data show the vertical cloud structure and the relative position of the aircraft, which collected a total of 84 slides by impaction, preserving the ice crystals for later microscopic examination. Although many particles were too fragile to survive impaction intact, a large fraction of the identifiable crystals were columns and radial bullet rosettes, with both displaying internal cavitations and radial plate-column combinations. Particles that were solid or displayed only a slight amount of internal structure were relatively rare, which shows that the usual model postulated by halo theorists, i.e., the randomly oriented, solid hexagonal crystal, is inappropriate for typical cirrus clouds. With the aid of new ray-tracing simulations for hexagonal hollow-ended column and bullet-rosette models, we evaluate the effects of more realistic ice-crystal structures on halo formation and lidar depolarization and consider why the common halo is not more common in cirrus clouds.

Sassen, Kenneth; Knight, Nancy C.; Takano, Yoshihide; Heymsfield, Andrew J.

1994-01-01

14

Supernumerary ice-crystal halos?  

Microsoft Academic Search

Geometric-optics singularities in the intensity profiles of refraction halos formed by randomly oriented ice crystals are softened by diffraction and decorated with fine supernumerary fringes. If the crystals have a fixed symmetry axis (as in parhelia), the geometric singularity is a square-root divergence, as in the rainbow. However, the universal curve that describes diffraction is different from the rainbow's Airy

Michael V. Berry

1994-01-01

15

Evolution of crystal fabric: Ice-Age ice versus Holocene ice  

Microsoft Academic Search

Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric

J. H. Kennedy; E. C. Pettit

2009-01-01

16

Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion  

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

17

Retardation of ice crystallization by short peptides  

Microsoft Academic Search

The effect of short peptides on the growth of ice crystals is studied using molecular dynamics simulations. The simulations focus on two sequences (Gly-Pro-Ala-Gly and Gly-Gly-Ala-Gly) that are found in collagen hydrolysate, a substance that is known to retard crystal growth. In the absence of peptides, the growth of ice crystal in the solution with the ice\\/water interface is observed

Jun Soo Kim; Arun Yethiraj

2009-01-01

18

Rheological Implications of the Internal Structure and Crystal Fabrics of the West Antarctic Ice Sheet as Revealed by Deep Core Drilling at Byrd Station.  

National Technical Information Service (NTIS)

Crystalline textures and fabrics of ice cores from the 2164-m-thick ice sheet at Byrd Station, Antarctica, reveal the existence of an anisotropic ice sheet. A gradual but persistent increase in the c-axis preferred orientation of the ice crystals was obse...

A. J. Gow T. Williamson

1976-01-01

19

Ice interaction with offshore structures  

SciTech Connect

Oil platforms and other offshore structures being built in the arctic regions must be able to withstand icebergs, ice islands, and pack ice. This reference explain the effect ice has on offshore structures and demonstrates design and construction methods that allow such structures to survive in harsh, ice-ridden environments. It analyzes the characteristics of sea ice as well as dynamic ice forces on structures. Techniques for ice modeling and field testing facilitate the design and construction of sturdy, offshore constructions. Computer programs included.

Cammaert, A.B.; Muggeridge, D.B.

1988-01-01

20

The Structure of Ice Nanoclusters: Implications for Interstellar Ice Grains  

NASA Technical Reports Server (NTRS)

Crystalline ice nanoclusters and thin-films of pure and impure water ice were deposited and studied in order to evaluate the extent to which surface-related effects control bulk properties. In pure water ice nanoclusters and thin-films of impure water ice, the cubic to hexagonal phase transformation occurs at lower temperatures than in thin-film deposits of pure water ice. In laboratory-grown crystalline ice nanoclusters, approx. 20 nm diameter, a significant proportion of water molecules exists in surface and near-surface environments which have an amorphous or nearly amorphous character. These disordered regions, which are highly reactive, serve to promote transformations or reactions which would otherwise be kinetically hindered. Likewise, dilute impurities such as methanol, sequestered to the surface of thin-films on crystallization, introduce defects into the ice network, thereby allowing sluggish structural transitions to proceed. These structural effects, which are surface phenomena, are believed to play an important role in promoting molecular reactions known to occur within interstellar ice grains in cold molecular clouds, where the first organic compounds are formed.

Delzeit, L.; Blake, David; Uffindell, C.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

21

Colloidal crystallization utilizing interfaces of unidirectionally growing ice crystals  

NASA Astrophysics Data System (ADS)

We show the possibility of unidirectional freezing of colloidal random suspensions as a novel method for growing colloidal crystals. First we confirmed the rejection of polystyrene particles from unidirectionally growing ice-water interfaces by observing color gradations of colloidal crystals formed in front of the interfaces. The rejection of particles from the growing interfaces increased particle concentration in the colloidal crystals. Then we succeeded in achieving colloidal crystallization in front of ice-water interfaces during the unidirectional freezing of water suspensions of polystyrene particles. The colloidal crystals thus obtained exhibited a columnar shape that is typically observed in the unidirectional colloidal crystallization using centrifugation.

Suzuki, Yoshihisa; Sazaki, Gen; Hashimoto, Kaori; Fujiwara, Takahisa; Furukawa, Yoshinori

2013-11-01

22

Artic ice and drilling structures  

SciTech Connect

The sea ice in the southern Beaufort Sea is examined and subdivided into three zones: the fast ice zone, the seasonal pack-ice zone, an the polar pack ice zone. Each zone requires its own type of system. Existing floating drilling systems include ice-strengthened drill ships, conical drilling systems, and floating ice platforms in deep-water land-fast ice. The development of hydrocarbon resources in the Arctic presents great challenges to engineers, since the structures are required to operate safely under various conditions. Significant progress has yet to be made in understanding the behavior of ice.

Sodhl, D.S.

1985-04-01

23

Retardation of ice crystallization by short peptides  

NASA Astrophysics Data System (ADS)

The effect of short peptides on the growth of ice crystals is studied using molecular dynamics simulations. The simulations focus on two sequences (Gly-Pro-Ala-Gly and Gly-Gly-Ala-Gly) that are found in collagen hydrolysate, a substance that is known to retard crystal growth. In the absence of peptides, the growth of ice crystal in the solution with the ice/water interface is observed in at a rate comparable to the experimental data. When peptides are present in the liquid phase, the crystal growth is retarded to a significant extent compared to the pure water. It is found that Gly-Pro-Ala-Gly is more effective (crystallization is up to 5 times slower than in its absence) than Gly-Gly-Ala-Gly (up to 3 times slower) implying that the role of the proline residue is important. The mechanism can be understood in the nature of binding of the peptides to the growing crystal.

Kim, Jun Soo; Yethiraj, Arun

2009-03-01

24

Evolution of crystal fabric: Ice-Age ice versus Holocene ice  

NASA Astrophysics Data System (ADS)

Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric evolution model, based on that developed by Thorsteinsson (2002), to explore the evolution of Ice-Age ice fabric along particle paths for ice within Taylor Glacier, a cold-based outlet glacier of the East Antarctic Ice Sheet. The bulk of the ice within Taylor Glacier consists of Ice-Age and older ice because the Holocene ice has ablated away (there is no Holocene ice remaining within 25km of the terminus, Aciego, 2007). We initialize the evolving fabric based on fabric measurements from Taylor Dome where available (DiPrinzio, 2003) and other ice core records. We compare model results with thin-section data from shallow cores taken near the terminus. As expected, crystal alignment strengthens along the ice particle path. Due to lateral shearing along valley walls and the ice cliffs (terminal ice cliffs are cold in winter and present a resistance to flow), a tilted single maximum is common near the terminus. The highly-aligned fabric of Ice-Age ice is significantly softer than Holocene ice in simple shear parallel to the bed, this softness not only results in faster flow rates for glaciers and ice sheets such as Taylor, but creates a climate-flow-fabric feedback loop through concentrating ice-sheet flow within the Ice-Age ice. Thorsteinsson, T. (2002), Fabric development with nearest-neighbor interaction and dynamic recrystallization, J. Geophys. Res., 107(B1), 2014, doi:10.1029/2001JB000244. S.M. Aciego, K.M. Cuffey, J.L. Kavanaugh, D.L. Morse, J.P. Severinghaus, Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica, Quaternary Research, Volume 68, Issue 3, November 2007, Pages 303-313, ISSN 0033-5894, DOI: 10.1016/j.yqres.2007.07.013. DiPrinzio, Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract C11C-0834, 2003

Kennedy, J. H.; Pettit, E. C.

2009-12-01

25

Light scattering by single ice crystals of cirrus clouds  

NASA Astrophysics Data System (ADS)

In situ measurements of angular scattering intensities (ASIs) related to single ice crystals of cirrus clouds were obtained for the first time with the airborne Polar Nephelometer instrument. These observations were performed in the southern mid-latitudes during the INCA project. The analysis of the data shows that the well marked peaks of the ASIs are undoubtedly attributed to quasi-specular reflections from crystal facets and the refracted rays passed through the ice crystals. Emphasizing that it is not enough to know the shape of the crystal, but also the internal structure is of great importance. Ray tracing simulations reproduce most of the observed ASIs features. The model of surface roughness, which assumes the Weibull statistics, enables to reproduce the quasi-specular external reflection from crystal facets. It follows from the retrievals that the surface of the crystals was deeply rough and the amount of the internal inclusions (air bubbles) was quite high.

Shcherbakov, Valery; Gayet, Jean-François; Jourdan, Olivier; Ström, Johan; Minikin, Andreas

2006-08-01

26

Modeling, simulation, and comparison study of cirrus cloud ice crystals  

NASA Astrophysics Data System (ADS)

Various methods and techniques to estimate ice crystals radar response have been developed to study the structure of cirrus clouds. Most methods assume a spherical shape for the ice crystals. This assumption leads to mistakes on the parameter estimation related to the particles' size. In this work, we modeled the shape of ice particles found in cirrus cloud as measured by airborne instruments, specifically ice bullets. These can be found depending on the temperature and cloud altitude, isolated or in groups of two or more bullets, called bullet rosettes. The model of the bullets was developed using the parameters obtained by airborne measurements from the National Center for Atmospheric Research (NCAR) Video Ice Particle Sampler (VIPS). This is an airborne instrument that takes samples of the cirrus cloud particles sizes. With these sample parameters we created a bullet function in DDSCAT with the actual shape of the bullets. This software allows us to create irregular models of particles using the Discrete Dipole Approximation method. With this model we can analyze the backscattering produced by the bullet and rosette model or reflectivity and compute the total volume backscattering coefficient from the cirrus clouds. Various models of ice crystal habits are compared.

Villa, Jorge M.; Cruz-Pol, Sandra L.; Colom-Ustariz, Jose G.; Sekelsky, Stephen M.

2003-04-01

27

Ice crystals in high clouds and contrails  

NASA Astrophysics Data System (ADS)

In honor of Dr. Helmut K. Weickmann's lifetime achievements, some of his early discoveries on ice crystals in high clouds are resurrected and discussed. It is demonstrated that the shapes and sizes of cloud meteors convey information related to cloud type, cloud duration, cloud amount, cloud radiative forcing, and the environment in which the cloud forms. For example, persistence of a contrail behind an aircraft depends on ice crystal concentration and size distribution, which are governed by the ambient temperature, humidity, and the concentration of ice nuclei. It is suggested that increased air traffic, especially high-flying jets over the past three decades, may have modified global cirrus cloud amount, which in turn may affect surface temperature and global climate.

Parungo, F.

28

Crystallization of amorphous water ice in the solar system.  

PubMed

Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated. PMID:11539415

Jenniskens, P; Blake, D F

1996-12-20

29

Crystallization of amorphous water ice in the solar system  

NASA Technical Reports Server (NTRS)

Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated.

Jenniskens, P.; Blake, D. F.

1996-01-01

30

Extracellular macromolecules in sea-ice: Effects on sea-ice structure and their implications  

NASA Astrophysics Data System (ADS)

Brine inclusions within sea-ice offer a favorable environment for certain marine microorganisms which live and thrive within the ice. These assemblages are a crucial element in the polar ecosystem. Partly entrained by ice platelets into the ice sheet, microorganisms closely interact with the liquid and solid phases of this porous environment (brine and ice), likely influencing their properties. Extracellular polysaccharide substances (EPS) and antifreeze proteins (AFP) have been identified as major elements with the potential to affect ice structure and processes, due to their capability to interact with ice crystals (selected planes in the case of AFPs) and with water molecules and salt ions present in the brine. EPS present in sea water can be selectively retained in the ice during ice formation, with implications for ice structure. Likewise, EPS and AFP released by sea-ice organisms would have a local effect, altering the microenvironment for the benefit of the organism. Macroscopic and microscopic observations showed effects on ice microstructure and a possible increase in brine fraction within the ice caused by AFPs and EPS, implicating changes in ice porosity and permeability. In the following we describe some of the interactions between sea-ice macromolecules, EPS and AFP, and the sea-ice system. We show their influence in ice structure, and discuss probable implications and consequences for microbial survival, distribution of dissolved material between sea-ice and the water column, and possible effects on the seasonal evolution of the ice. All of these could be relevant to the understanding of biogeochemical processes and the limits of habitability, as well as suggest possible applications of these substances.

Ewert, M.; Bayer-Giraldi, M.

2012-04-01

31

Disturbed basal ice seen in radio echo images coincide with zones of big interlocking ice crystals.  

NASA Astrophysics Data System (ADS)

Improvement of the depth sounding radio echo sounding (RES) over Antarctica and Greenland Ice Sheet has made it possible to map the near basal layers that have not been 'seen' earlier due to the very high demand of attenuation needed to reach through more than 3000m of ice. The RES internal reflectors show that the near basal ice at many locations has disturbed layering. At the locations where ice cores reach the bedrock both in Greenland and Antarctica studies of the ice crystal size and orientation show that the near basal ice has big and interlocking ice crystals which suggests the ice is not actively deforming. These observations challenge the often used constitutive equations like Glens flow law in ice sheet modelling. A discussion of the impact of the RES findings on ice sheet modeling and the quest to find the oldest ice in Antarctic based on the anisotropy of the basal ice will follow.

Dahl-Jensen, Dorthe; Gogineni, Sivaprasad; Panton, Christian

2014-05-01

32

Bioprospecting for microbial products that affect ice crystal formation and growth  

Microsoft Academic Search

At low temperatures, some organisms produce proteins that affect ice nucleation, ice crystal structure, and\\/or the process\\u000a of recrystallization. Based on their ice-interacting properties, these proteins provide an advantage to species that commonly\\u000a experience the phase change from water to ice or rarely experience temperatures above the melting point. Substances that bind,\\u000a inhibit or enhance, and control the size, shape,

Brent C. Christner

2010-01-01

33

Specular scattering by preferentially oriented ice crystals.  

PubMed

Scattered light for preferentially oriented ice crystals is divided into specular and diffuse components, where the specular scattering is created by horizontally oriented facets of fluttering crystals. The specular component for a fluttering thin plate modeling these crystals is found analytically. The solution obtained is a two-dimensional (2D) convolution of a geometric optics pattern depending only on flutter and an independent diffraction function. The geometric optics pattern is explicitly expressed through the probability density for particle tilts, and the diffraction function is taken in the Fraunhofer diffraction approximation. The 2D convolution calculated numerically reveals a cumulative enhancement of scattered light in the scattering domain center. Certain possibilities to retrieve both flutter parameters and particle sizes from the specular patterns are discussed. PMID:19571949

Borovoi, Anatoli; Kustova, Natalia

2009-07-01

34

Factors Affecting the Changes of Ice Crystal Form in Ice Cream  

NASA Astrophysics Data System (ADS)

In this study, the shape of ice crystals in ice cream was quantitatively evaluated by introducing fractal analysis. A small droplet of commercial ice cream mix was quickly cooled to about -30°C on the cold stage of microscope. Subsequently, it was heated to -5°C or -10°C and then held for various holding time. Based on the captured images at each holding time, the cross-sectional area and the length of circumference for each ice crystal were measured to calculate fractal dimension using image analysis software. The results showed that the ice crystals were categorized into two groups, e.g. simple-shape and complicated-shape, according to their fractal dimensions. The fractal dimension of ice crystals became lower with increasing holding time and holding temperature. It was also indicated that the growing rate of complicated-shape ice crystals was relatively higher because of aggregation.

Wang, Xin; Watanabe, Manabu; Suzuki, Toru

35

Growth control of ice crystals by poly(vinyl alcohol) and antifreeze protein in ice slurries  

Microsoft Academic Search

Effect of poly(vinyl alcohol) (PVA) in inhibiting an increase in ice crystal size in isothermal ice slurries was investigated, and then compared with the effect of an antifreeze protein (AFP), NaCl, and three other polymers, namely, poly(ethylene glycol), poly(vinyl pyrrolidone), and poly(acrylic acid). First, ice slurries, in which the initial size distribution of ice crystals was known, were isothermally preserved

Takaaki Inada; Poly Rani Modak

2006-01-01

36

New metastable form of ice and its role in the homogeneous crystallization of water.  

PubMed

The homogeneous crystallization of water at low temperature is believed to occur through the direct nucleation of cubic (Ic) and hexagonal (Ih) ices. Here, we provide evidence from molecular simulations that the nucleation of ice proceeds through the formation of a new metastable phase, which we name Ice 0. We find that Ice 0 is structurally similar to the supercooled liquid, and that on growth it gradually converts into a stacking of Ice Ic and Ih. We suggest that this mechanism provides a thermodynamic explanation for the location and pressure dependence of the homogeneous nucleation temperature, and that Ice 0 controls the homogeneous nucleation of low-pressure ices, acting as a precursor to crystallization in accordance with Ostwald's step rule of phases. Our findings show that metastable crystalline phases of water may play roles that have been largely overlooked. PMID:24836734

Russo, John; Romano, Flavio; Tanaka, Hajime

2014-07-01

37

Microscopic pattern of ice crystal growth in the presence of thermal hysteresis proteins  

SciTech Connect

This study examines the effect of thermal hysteresis proteins (THPs) from the winter flounder (Psuedopleuronectes americanus) on the ice-water interface morphology during freezing of aqueous solutions. Experiments were performed using a directional solidification stage, and the development of the two-phase interface was observed through a microscope and recorded by a video system. Unusual ice crystal morphologies were observed, including faceted ice crystal growth along the (1100) crystal plane; spicular or needlelike growth in the (1010) direction; and growth parallel to the c-axis, (0001), consisting of incorporated liquid inclusions bounded by hexagonal prism faces. The observed crystallographic structures can be explained as an effect of the interaction between the THPs and the primary prism faces of ice crystals. This results in an increase in the Gibbs free energy of these planes, followed by ice growth into the supercooled liquid adjacent to these faces.

Coger, R.; Rubinsky, B. (Univ. of California, Berkeley, CA (United States). Dept. of Mechanical Engineering); Fletcher, G. (Memorial Univ. of Newfoundland, St. John's, Newfoundland (Canada))

1994-08-01

38

Strain history of ice shells of the Galilean satellites from radar detection of crystal orientation fabric  

Microsoft Academic Search

Orbital radar sounding has been suggested as a means of determining the subsurface thermal and physical structure of the outer ice I shells of the Galilean satellites. At radar frequencies, the dielectric permittivity of single- and polycrystalline water ice I is anisotropic. Crystal orientation fabric (COF), which is indicative of strain history, can be unambiguously detected by comparing the received

Amy C. Barr; David E. Stillman

2011-01-01

39

Ice mechanics and risks to offshore structures  

SciTech Connect

This volume brings together the results of all salient research development in ice engineering, from smaller scale to full size tests on ice strength and ice mechanics which is essential criteria for the design of safe, cost effective structures. Much of the data has been released from confidential industry files and thus allows, for the first time, a full appraisal of the subject. Contents include - Types and Distribution of Ice, Mechanical Properties, Measurements of Ice-Structure Interaction, and Analysis of Ice Failure and Design Ice Loads. This work is completed with a full literary review and subject index.

Sanderson, T.J.O.

1988-01-01

40

Processes causing electrification of ice crystals in thunderclouds  

NASA Astrophysics Data System (ADS)

Jayaratne and Saunders (1991) have performed a useful service by reporting their laboratory experiments demonstrating, contrary to the findings of Odencrantz and Buecher (1967), that ice crystal charging does not take place in an unmixed cloud of ice crystals. Jayaratne and Saunders' further cold box experiments showing that the ice crystals become electrified when a fan in the cold box is turned on, support their view that an ice-ice charging process takes place on the surfaces of the moving ice-covered fan-blades. Their conclusion, that this phenomenon might be capable of producing each second the several coulombs of charged cloud particles necessary to maintain the electrification of a thundercloud, appears justified. However, because their paper is lacking in experimental details and because it is unknown whether the conditions in their cold chamber accurately duplicate those in a thunderstorm, this point is not possible to resolve. There is good reason to doubt J and S's final conclusion, that "… in thunderstorms, ice crystal charges are similarly acquired by collision processes RATHER THAN BY ANY OTHER MECHANISM". It is puzzling to understand why the authors have chosen to ignore ion attachment, an important ice crystal charging process that does not involve collisions between ice crystals. Beginning with Gish and Wait (1950), numerous investigators have demonstrated that ion currents flow to the tops of thunderclouds as predicted by Wilson (1920). Marshall et al. (1989) and Byrne et al. (1989) have found that ice particles at cloud top carry appreciable charges that appear to be derived from the Wilson current. In an average storm there can be little doubt that this mechanism too could be producing charged ice crystals at the required rate of about a coulomb per second (Vonnegut, 1990).

Vonnegut, B.; Moore, C. B.

41

Ice-Crystal Fallstreaks from Supercooled Liquid Water Parent Clouds  

NASA Technical Reports Server (NTRS)

On 31 December 2001, ice-crystal fallstreaks (e.g., cirrus uncinus, or colloquially "Mare's Tails") from supercooled liquid water parent clouds were observed by ground-based lidars pointed vertically from the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility near Lamont, Oklahoma. The incidence of liquid phase cloud with apparent ice-phase precipitation is investigated. Scenarios for mixed-phase particle nucleation, and fallstreak formation and sustenance are discussed. The observations are unique in the context of the historical reverence given to the commonly observed c h s uncinus fallstreak (wholly ice) versus this seemingly contradictory coincidence of liquid water begetting ice-crystal streaks.

Campbell, James R.; O'C. Starr, David; Welton, Ellsworth J.; Spinhirne, James D.; Ferrare, Richard A.

2003-01-01

42

Backscattering by hexagonal ice crystals of cirrus clouds.  

PubMed

Light backscattering by randomly oriented hexagonal ice crystals of cirrus clouds is considered within the framework of the physical-optics approximation. The fine angular structure of all elements of the Mueller matrix in the vicinity of the exact backward direction is first calculated and discussed. In particular, an approximate equation for the differential scattering cross section is obtained. Its simple spectral dependence is discussed. Also, a hollow of the linear depolarization ratio around the exact backward direction inherent to the long hexagonal columns is revealed. PMID:23903169

Borovoi, Anatoli; Konoshonkin, Alexander; Kustova, Natalia

2013-08-01

43

Diagnosing the Ice Crystal Enhancement Factor in the Tropics  

NASA Technical Reports Server (NTRS)

Recent modeling studies have revealed that ice crystal number concentration is one of the dominant factors in the effect of clouds on radiation. Since the ice crystal enhancement factor and ice nuclei concentration determine the concentration, they are both important in quantifying the contribution of increased ice nuclei to global warming. In this study, long-term cloud-resolving model (CRM) simulations are compared with field observations to estimate the ice crystal enhancement factor in tropical and midlatitudinal clouds, respectively. It is found that the factor in tropical clouds is 10 3-104 times larger than that of mid-latitudinal ones, which makes physical sense because entrainment and detrainment in the Tropics are much stronger than in middle latitudes. The effect of entrainment/detrainment on the enhancement factor, especially in tropical clouds, suggests that cloud microphysical parameterizations should be coupled with subgrid turbulence parameterizations within CRMs to obtain a more accurate depiction of cloud-radiative forcing.

Zeng, Xiping; Tao, Wei-Kuo; Matsui, Toshihisa; Xie, Shaocheng; Lang, Stephen; Zhang, Minghua; Starr, David O'C; Li, Xiaowen; Simpson, Joanne

2009-01-01

44

Radar backscattering properties of nonspherical ice crystals at 94 GHz  

Microsoft Academic Search

The millimeter wavelength radar backscattering properties at 94 GHz for six nonspherical ice crystals, which include hexagonal column, hollow, plate, bullet rosette, aggregate, and droxtal with 46 maximum dimensions ranging from 2 to 10,500 mum, are investigated using the discrete dipole approximation (DDA) method and Lorenz-Mie theory. It is found that the radar backscattering cross sections are sensitive to ice

Gang Hong

2007-01-01

45

Radar backscattering properties of nonspherical ice crystals at 94 GHz  

Microsoft Academic Search

The millimeter wavelength radar backscattering properties at 94 GHz for six nonspherical ice crystals, which include hexagonal column, hollow, plate, bullet rosette, aggregate, and droxtal with 46 maximum dimensions ranging from 2 to 10,500 ?m, are investigated using the discrete dipole approximation (DDA) method and Lorenz-Mie theory. It is found that the radar backscattering cross sections are sensitive to ice

Gang Hong

2007-01-01

46

Enhanced and Oriented Riming of Growing Ice Crystals.  

NASA Astrophysics Data System (ADS)

Geometrically oriented riming was found in Formvar resin replicas of columnar ice crystals collected in cumulus clouds at -6°C during an aircraft field program in Texas. Rimed cloud droplets were found either on the ends of the crystals or in a girdle around the middle. Oriented riming is attributed to preferential collection on growing ice crystals with charge separations between the crystal body and growing ends. Droplet attraction to separated charge regions of growing ice crystals results in enhanced riming and increases the rate of precipitation development. Effects of this process on cloud electrification depend on whether the cloud droplets carry net charges or are polarized. The impact of this oriented riming process on several cloud electrification scenarios is discussed.

Finnegan, William G.; Chai, Steven K.; Detwiler, Andrew

2004-08-01

47

How big should hexagonal ice crystals be to produce halos?  

PubMed

It has been hypothesized that the frequent lack of halos in observations of cirrus and contrails and laboratory measurements is caused by small ice crystal sizes that put the particles outside the geometrical optics domain of size parameters. We test this hypothesis by exploiting a strong similarity of ray tracing phase functions for finite hexagonal and circular ice cylinders and using T-matrix computations of electromagnetic scattering by circular cylinders with size parameters up to 180 in the visible. We conclude that well-defined halos should be observable for ice crystal size parameters of the order of 100 and larger and discuss remote-sensing implications of this result. PMID:18305781

Mishchenko, M I; Macke, A

1999-03-20

48

Forces Generated by High Velocity Impact of Ice on a Rigid Structure  

NASA Technical Reports Server (NTRS)

Tests were conducted to measure the impact forces generated by cylindrical ice projectiles striking a relatively rigid target. Two types of ice projectiles were used, solid clear ice and lower density fabricated ice. Three forms of solid clear ice were tested: single crystal, poly-crystal, and "rejected" poly-crystal (poly-crystal ice in which defects were detected during inspection.) The solid ice had a density of approximately 56 lb/cu ft (0.9 gm/cu cm). A second set of test specimens, termed "low density ice" was manufactured by molding shaved ice into a cylindrical die to produce ice with a density of approximately 40 lb/cu ft (0.65 gm/cu cm). Both the static mechanical characteristics and the crystalline structure of the ice were found to have little effect on the observed transient response. The impact forces generated by low density ice projectiles, which had very low mechanical strength, were comparable to those of full density solid ice. This supports the hypothesis that at a velocity significantly greater than that required to produce fracture in the ice, the mechanical properties become relatively insignificant, and the impact forces are governed by the shape and mass of the projectile.

Pereira, J. Michael; Padula, Santo A., II; Revilock, Duane M.; Melis, Matthew E.

2006-01-01

49

Three-Dimensional Visualization of Ice Crystals in Frozen Materials by Near-Infrared Imaging Spectroscopy  

NASA Astrophysics Data System (ADS)

Micro Slicer Spectral Imaging System (MSSIS) has been applied to observe the three-dimensional(3-D) structure and distribution of ice crystals formed in biological materials. MSSIS is composed of a micro-slicer, near-infrared (NIR) illuminator and spectral imaging system. NIR Spectroscopic analysis using MSSIS confirmed that there are a water absorption band around 965 nm and an ice absorption band around 1025 nm. Spectroscopic images of a frozen agar gel and a piece of raw beef at 1,025 nm were obtained by the MSSIS. These images showed the ice crystals could be clearly distinguished from the other components by the different absorbance. The average area of ice crystals was 6,253 ?m2, and the average distances of major and minor axis were 111?m and 62?m respectively. In addition, the 3-D re-constructed image of the ice crystal morphology revealed that they were formed along with the direction of heat transfer. The proposed method provided a novel tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.

Do, Gab-Soo; Ueno, Shigeaki; Sagara, Yasuyuki; Tsuta, Mizuki; Sugiyama, Junichi

50

Separation of millimeter-wave radar reflectivities of aggregates and pristine ice crystals in a cloud  

Microsoft Academic Search

Millimeter wave radars operating at 35 and 94 GHz are being used for the remote sensing of ice clouds. Two-dimensional particle probe measurements in clouds show that a single type of ice crystals (e.g., column, plate, stellar crystal, etc.) is often observed in a mixture with ice crystal aggregates. This may pose a problem for estimating the ice water content

K. Aydin; T. M. Walsh

1998-01-01

51

Display of ice crystal flutter in atmospheric light pillars  

NASA Astrophysics Data System (ADS)

Specular patterns in the atmosphere caused by ice crystals with preferably horizontal orientation are quantitatively described by use of a bidirectional phase function for a fluttering plate. The main qualitative features of the sun pillars and overground light pillars are explained. Possibilities to retrieve the probability density for orientation of the preferably oriented crystals from the specular patterns are discussed.

Borovoi, Anatoli; Kustova, Natalia

2009-02-01

52

Preferred Ice Crystal Orientation Fabric Measurements within the Greenland Ice Sheet Using Multi-Polarization Radar Data  

NASA Astrophysics Data System (ADS)

Discharge of ice from the Greenland Ice Sheet to the ocean has increased significantly over the last 25 years due to the acceleration of important outlet glaciers. It was reported that the Greenland Ice Sheet contributed about 2.5 m out of about 6 m of sea-level rise during the Eemian interglacial period. The temperatures during Eemian were reported to be about 8o×4o C higher than the mean of the past millennium. Laboratory measurements have shown that glacial ice, characterized by preferred crystal orientation fabric (COF), is three times more deformable than ice with randomly oriented crystalline structures. Layers characterized by preferred ice COF can influence the flow behavior of a glacier or ice sheet. However, COF measurements are typically obtained from ice cores, and thus are very spatially limited and mostly constrained to areas with little ice flow. A more efficient technique to map the extent of ice fabric over larger regions of ice sheets is needed to better understand the effects on large scale ice flow processes. Radar measurements are capable of discriminating between reflections caused by changes in density, electrical permittivity and COF by exploiting the anisotropic and birefringent properties of ice crystals. For this investigation two radar datasets were collected during the survey of the Greenland Eemian Ice Drilling Site (77.45°N 51.06°W) in August 2008, using a ground-based and chirped-pulse Multi-Channel Radar Depth Sounder (MCRDS) developed by the Center for Remote Sensing of Ice Sheets (CReSIS). The radar used two transmit and eight receive antennas at the center frequency of 150 MHz with a bandwidth of 30 MHz. The first data set consisted of polarimatric measurements acquired in a circular pattern (radius: 35 m) with two co-polarized antenna orientations (one transmitter and four receivers oriented with 90° offsets in the directions of the incident H-Field and E-Field, respectively). Analysis of the circular data shows a periodic power variation with four distinct extinction patterns occurring at 90 degree intervals starting at approximately 700 m depth. Furthermore a 20 degree phase change is observed between the E- and H-field data. Both observations suggest that approximately 72% of the 2542m ice column exhibits birefringent anisotropy caused by preferred ice crystal orientation. The second dataset was acquired in a grid pattern consisting of twenty 10-Km 2D lines (NW to SE) spaced at 0.5-Km and three 10-Km lines (NE to SW) spaced at 2.5-Km. Both transmit and eight receive antenna were oriented parallel to the vehicle track, resulting in E-Field co-polarized data. We will determine the dominant COF relative to the ice divide for a 100 square Km region around the NEEM camp using the results from both datasets. The results of this investigation will be compared to the NEEM ice core observations to determine the accuracy of the analysis. In this investigation we will provide a brief overview of the system and experiments and present the results of data analysis.

Velez-Gonzalez, J. A.; JiLu, L.; Leuschen, C.; Gogineni, P.; Van der Veen, C. J.; Tsoflias, G. P.; Drews, R.; Harish, A. R.

2013-12-01

53

Ice-templated structures for biomedical tissue repair: From physics to final scaffolds  

NASA Astrophysics Data System (ADS)

Ice-templating techniques, including freeze-drying and freeze casting, are extremely versatile and can be used with a variety of materials systems. The process relies on the freezing of a water based solution. During freezing, ice nucleates within the solution and concentrates the solute in the regions between the growing crystals. Once the ice is removed via sublimation, the solute remains in a porous structure, which is a negative of the ice. As the final structure of the ice relies on the freezing of the solution, the variables which influence ice nucleation and growth alter the structure of ice-templated scaffolds. Nucleation, the initial step of freezing, can be altered by the type and concentration of solutes within the solution, as well as the set cooling rate before freezing. After nucleation, crystal growth and annealing processes, such as Ostwald ripening, determine the features of the final scaffold. Both crystal growth and annealing are sensitive to many factors including the set freezing temperature and solutes. The porous structures created using ice-templating allow scaffolds to be used for many diverse applications, from microfluidics to biomedical tissue engineering. Within the field of tissue engineering, scaffold structure can influence cellular behavior, and is thus critical for determining the biological stimulus supplied by the scaffold. The research focusing on controlling the ice-templated structure serves as a model for how other ice-templating systems might be tailored, to expand the applications of ice-templated structures to their full potential.

Pawelec, K. M.; Husmann, A.; Best, S. M.; Cameron, R. E.

2014-06-01

54

Crystal Structures as Geobarometers  

NSDL National Science Digital Library

This exercise is based on the recent formulation of a geobarometer based on the crystal structure of clinopyroxene (Nimis, 1995; 1998; 1999). This method relates structural parameters (e.g., the volumes of the unit cell and the M1 polyhedron) to the pressure at which the mineral crystallizes within basic and ultrabasic magmas. students are guided into the American Mineralogist Crystal Structure Database to retrieve and download published crystal structure data for viewing in either the CrystalMaker or Xtaldraw visualization software packages. students are instructed on how to examine the structures to determine pressure-sensitive crystallographic parameters students are then asked a series of questions related to what they learn.

Ratajeski, Kent

55

Derivative Crystal Structures  

Microsoft Academic Search

There exists a class of crystal structures which are derived from others by generalization. These are here designated derivative structures. A special case of derivative structure is the popular ``superstructure.'' The symmetry of a derivative structure is a subgroup of the symmetry of the basic structure. Here the term ``subgroup'' is used in a wider sense than common in mathematical

M. J. Buerger

1947-01-01

56

Crystal Lattice Structures  

NSDL National Science Digital Library

This site provides an index of common crystal lattice structures--arrangements of atoms in a crystalline substance. The structures are indexed by Strukturbericht designation, Pearson symbol, space group, and prototype. Each structure is illustrated and accompanied by a brief description. The structure graphics can be viewed online, downloaded for external viewing, or manipulated in virtual space using a Java applet.

57

Ice Has Structure: H2O  

NSDL National Science Digital Library

This is a lesson about water and water-ice. Learners will explore the molecular geometry and mechanics of ice. They will create a model of H2O, investigate its molecular structure and its consistent shape. Faraday's experiment is used as background. Activities include small group miming, speaking, drawing, and/or writing. This is lesson 2 of 12 in the unit, Exploring Ice in the Solar System.

58

Ice crystal properties retrieval using radar spectral polarimetric measurements within ice\\/mixed-phase clouds  

Microsoft Academic Search

In the field of atmospheric research, ground-based radar systems are often employed to study ice\\/mixed-phase cloud properties based on retrieval techniques. These techniques convert the radar signal backscattered by each bulk of ice crystals being probed within the same radar resolution volume to cloud’s microphysical characteristics. However, the size of a radar resolution volume is often too large compared to

Y. Dufournet

2010-01-01

59

Nanoscale structure intercrystalline interactions in fat crystal networks  

Microsoft Academic Search

The functional attributes of fat-structured food products such as butter, margarine, chocolate, and ice cream are strongly influenced by the structure and physical properties of an underlying fat crystal network present in the material. Fat crystal networks are arranged in a hierarchical manner with characteristic and quantifiable nano and mesoscale structures. Recent studies carried out by our group have demonstrated

Nuria C. Acevedo; Fernanda Peyronel; Alejandro G. Marangoni

2011-01-01

60

Ice-binding proteins that accumulate on different ice crystal planes produce distinct thermal hysteresis dynamics.  

PubMed

Ice-binding proteins that aid the survival of freeze-avoiding, cold-adapted organisms by inhibiting the growth of endogenous ice crystals are called antifreeze proteins (AFPs). The binding of AFPs to ice causes a separation between the melting point and the freezing point of the ice crystal (thermal hysteresis, TH). TH produced by hyperactive AFPs is an order of magnitude higher than that produced by a typical fish AFP. The basis for this difference in activity remains unclear. Here, we have compared the time dependence of TH activity for both hyperactive and moderately active AFPs using a custom-made nanolitre osmometer and a novel microfluidics system. We found that the TH activities of hyperactive AFPs were time-dependent, and that the TH activity of a moderate AFP was almost insensitive to time. Fluorescence microscopy measurement revealed that despite their higher TH activity, hyperactive AFPs from two insects (moth and beetle) took far longer to accumulate on the ice surface than did a moderately active fish AFP. An ice-binding protein from a bacterium that functions as an ice adhesin rather than as an antifreeze had intermediate TH properties. Nevertheless, the accumulation of this ice adhesion protein and the two hyperactive AFPs on the basal plane of ice is distinct and extensive, but not detectable for moderately active AFPs. Basal ice plane binding is the distinguishing feature of antifreeze hyperactivity, which is not strictly needed in fish that require only approximately 1°C of TH. Here, we found a correlation between the accumulation kinetics of the hyperactive AFP at the basal plane and the time sensitivity of the measured TH. PMID:25008081

Drori, Ran; Celik, Yeliz; Davies, Peter L; Braslavsky, Ido

2014-09-01

61

The Examination by Electron Microscope of Ice Crystal Nuclei from Cloud Chamber Experiments  

Microsoft Academic Search

A method is described whereby ice crystals generated in a Bigg-Warner ice nuclei counter may be replicated on Formvar coated slides. The Formvar film, with replicas, is subsequently removed for examination in the electron microscope. The nuclei of the ice crystals remain on the Formvar after sublimation of the ice, and under favorable conditions, may be identified by their morphology

John Rucklidge

1965-01-01

62

Statistical approach to light scattering by convex ice crystals.  

PubMed

Within the geometric optics approximation, the phase functions of randomly oriented ice crystals are calculated as a series relative to multiplicity of internal collisions of light inside the particles. In the case of convex crystals, it is shown that the coefficients of the series provide the most information about the crystal shapes, while the angular functions of this series are weakly dependent on the shapes. The prevailing role of the term corresponding to one internal collision is emphasized. Three numbers describing a distribution of the single-collision scattered light among the aureole and halos of 22 degrees and 46 degrees prove to be the basic parameters by which to characterize scattering by hexagonal ice crystals. PMID:16688282

Borovoi, Anatoli; Kustova, Natalia

2006-06-01

63

Effect of the Inhomogeneity of Ice Crystals on Retrieving Ice Cloud Optical Thickness and Effective Particle Size  

NASA Technical Reports Server (NTRS)

Spherical or spheroidal air bubbles are generally trapped in the formation of rapidly growing ice crystals. In this study the single-scattering properties of inhomogeneous ice crystals containing air bubbles are investigated. Specifically, a computational model based on an improved geometric-optics method (IGOM) has been developed to simulate the scattering of light by randomly oriented hexagonal ice crystals containing spherical or spheroidal air bubbles. A combination of the ray-tracing technique and the Monte Carlo method is used. The effect of the air bubbles within ice crystals is to smooth the phase functions, diminish the 22deg and 46deg halo peaks, and substantially reduce the backscatter relative to bubble-free particles. These features vary with the number, sizes, locations and shapes of the air bubbles within ice crystals. Moreover, the asymmetry factors of inhomogeneous ice crystals decrease as the volume of air bubbles increases. Cloud reflectance lookup tables were generated at wavelengths 0.65 m and 2.13 m with different air-bubble conditions to examine the impact of the bubbles on retrieving ice cloud optical thickness and effective particle size. The reflectances simulated for inhomogeneous ice crystals are slightly larger than those computed for homogenous ice crystals at a wavelength of 0.65 microns. Thus, the retrieved cloud optical thicknesses are reduced by employing inhomogeneous ice cloud models. At a wavelength of 2.13 microns, including air bubbles in ice cloud models may also increase the reflectance. This effect implies that the retrieved effective particle sizes for inhomogeneous ice crystals are larger than those retrieved for homogeneous ice crystals, particularly, in the case of large air bubbles.

Xie, Yu; Minnis, Patrick; Hu, Yong X.; Kattawar, George W.; Yang, Ping

2008-01-01

64

Modeling variability in dendritic ice crystal backscattering cross sections at millimeter wavelengths using a modified Rayleigh-Gans theory  

NASA Astrophysics Data System (ADS)

Using the Generalized Multi-particle Mie-method (GMM), Botta et al. (in this issue) [7] created a database of backscattering cross sections for 412 different ice crystal dendrites at X-, Ka- and W-band wavelengths for different incident angles. The Rayleigh-Gans theory, which accounts for interference effects but ignores interactions between different parts of an ice crystal, explains much, but not all, of the variability in the database of backscattering cross sections. Differences between it and the GMM range from -3.5 dB to +2.5 dB and are highly dependent on the incident angle. To explain the residual variability a physically intuitive iterative method was developed to estimate the internal electric field within an ice crystal that accounts for interactions between the neighboring regions within it. After modifying the Rayleigh-Gans theory using this estimated internal electric field, the difference between the estimated backscattering cross sections and those from the GMM method decreased to within 0.5 dB for most of the ice crystals. The largest percentage differences occur when the form factor from the Rayleigh-Gans theory is close to zero. Both interference effects and neighbor interactions are sensitive to the morphology of ice crystals. Improvements in ice-microphysical models are necessary to predict or diagnose internal structures within ice crystals to aid in more accurate interpretation of radar returns. Observations of the morphology of ice crystals are, in turn, necessary to guide the development of such ice-microphysical models and to better understand the statistical properties of ice crystal morphologies in different environmental conditions.

Lu, Yinghui; Clothiaux, Eugene E.; Aydin, Kültegin; Botta, Giovanni; Verlinde, Johannes

2013-12-01

65

Pattern Formation during Ice Crystal Growth -ISS KIBO Experiments-  

NASA Astrophysics Data System (ADS)

Crystal growth experiments of ice in supercooled D2O water were carried out in the Japan Experiment Module KIBO of the International Space Station (ISS) in the period between December 2008 and March 2009. Overview of this project and preliminary results are presented.

Furukawa, Yoshinori; Yokoyama, Etsuro; Yoshizaki, Izumi; Yoda, Shinichi; Tanaka, Tetsuo; Shimaoka, Taro; Sone, Takehiko; Tomobe, Toshiyuki

66

A Critical Look at Ice Crystal Growth Data  

Microsoft Academic Search

I review published data relating to the growth of ice crystals from water vapor under various conditions, and I critically examine the different measurements to determine what useful information can be extracted from each. I show that most, and possibly all, of the existing growth data have been seriously distorted by systematic errors of one form or another, to varying

Kenneth G. Libbrecht

2004-01-01

67

Snow crystal imaging using scanning electron microscopy: III. Glacier ice, snow and biota  

USGS Publications Warehouse

Low-temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow, glacial firn, and glacial ice obtained from South Cascade Glacier in Washington State, USA. Biotic samples consisting of algae (Chlamydomonas nivalis) and ice worms (a species of oligochaetes) were also collected and imaged. In the field, the snow and biological samples were mounted on copper plates, cooled in liquid nitrogen, and stored in dry shipping containers which maintain a temperature of -196??C. The firn and glacier ice samples were obtained by extracting horizontal ice cores, 8 mm in diameter, at different levels from larger standard glaciological (vertical) ice cores 7.5 cm in diameter. These samples were cooled in liquid nitrogen and placed in cryotubes, were stored in the same dry shipping container, and sent to the SEM facility. In the laboratory, the samples were sputter coated with platinum and imaged by a low-temperature SEM. To image the firn and glacier ice samples, the cores were fractured in liquid nitrogen, attached to a specimen holder, and then imaged. While light microscope images of snow and ice are difficult to interpret because of internal reflection and refraction, the SEM images provide a clear and unique view of the surface of the samples because they are generated from electrons emitted or reflected only from the surface of the sample. In addition, the SEM has a great depth of field with a wide range of magnifying capabilities. The resulting images clearly show the individual grains of the seasonal snowpack and the bonding between the snow grains. Images of firn show individual ice crystals, the bonding between the crystals, and connected air spaces. Images of glacier ice show a crystal structure on a scale of 1-2 mm which is considerably smaller than the expected crystal size. Microscopic air bubbles, less than 15 ??m in diameter, clearly marked the boundaries between these crystal-like features. The life forms associated with the glacier were easily imaged and studied. The low-temperature SEM sample collecting and handling methods proved to be operable in the field; the SEM analysis is applicable to glaciological studies and reveals details unattainable by conventional light microscopic methods.Low temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow, glacial firn, and glacial ice obtained from South Cascade Glacier in Washington State, USA. Biotic samples consisting of algae and ice worms were also collected and imaged. The SEM images provide a clear and unique view of the surface of the samples because they are generated from electrons emitted or reflected only from the surface of the sample. The SEM has a great depth of field with a wide range of magnifying capabilities.

Rango, A.; Wergin, W. P.; Erbe, E. F.; Josberger, E. G.

2000-01-01

68

Structural properties of impact ices accreted on aircraft structures  

NASA Technical Reports Server (NTRS)

The structural properties of ice accretions formed on aircraft surfaces are studied. The overall objectives are to measure basic structural properties of impact ices and to develop finite element analytical procedures for use in the design of all deicing systems. The Icing Research Tunnel (IRT) was used to produce simulated natural ice accretion over a wide range of icing conditions. Two different test apparatus were used to measure each of the three basic mechanical properties: tensile, shear, and peeling. Data was obtained on both adhesive shear strength of impact ices and peeling forces for various icing conditions. The influences of various icing parameters such as tunnel air temperature and velocity, icing cloud drop size, material substrate, surface temperature at ice/material interface, and ice thickness were studied. A finite element analysis of the shear test apparatus was developed in order to gain more insight in the evaluation of the test data. A comparison with other investigators was made. The result shows that the adhesive shear strength of impact ice typically varies between 40 and 50 psi, with peak strength reaching 120 psi and is not dependent on the kind of substrate used, the thickness of accreted ice, and tunnel temperature below 4 C.

Scavuzzo, R. J.; Chu, M. L.

1987-01-01

69

Structure and dynamics of amorphous water ice  

NASA Technical Reports Server (NTRS)

Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.

Laufer, D.; Kochavi, E.; Bar-Nun, A.; Owen, T. (Principal Investigator)

1987-01-01

70

Structure and dynamics of amorphous water ice.  

PubMed

Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds. PMID:9942788

Laufer, D; Kochavi, E; Bar-Nun, A

1987-12-15

71

Dynamic pressure-induced dendritic and shock crystal growth of ice VI  

PubMed Central

Crystal growth mechanisms are crucial to understanding the complexity of crystal morphologies in nature and advanced technological materials, such as the faceting and dendrites found in snowflakes and the microstructure and associated strength properties of structural and icy planetary materials. In this article, we present observations of pressure-induced ice VI crystal growth, which have been predicted theoretically, but had never been observed experimentally to our knowledge. Under modulated pressure conditions in a dynamic-diamond anvil cell, rough single ice VI crystal initially grows into well defined octahedral crystal facets. However, as the compression rate increases, the crystal surface dramatically changes from rough to facet, and from convex to concave because of a surface instability, and thereby the growth rate suddenly increases by an order of magnitude. Depending on the compression rate, this discontinuous jump in crystal growth rate or “shock crystal growth” eventually produces 2D carpet-type fractal morphology, and moreover dendrites form under sinusoidal compression, whose crystal morphologies are remarkably similar to those predicted in theoretical simulations under a temperature gradient field. The observed strong dependence of the growth mechanism on compression rate, therefore, suggests a different approach to developing a comprehensive understanding of crystal growth dynamics.

Lee, Geun Woo; Evans, William J.; Yoo, Choong-Shik

2007-01-01

72

Structure of ices on satellites  

NASA Technical Reports Server (NTRS)

The pressure densification of ices, in combination with density changes induced by pore migration in a thermal gradient and the phase transitions of water due to meteoritic bombardment (into either high pressure polymorphs or an amorphous phase) create a complex situation, which is not easily evaluated in either satellites or cometary nuclei. Accordingly, the present findings concerning solar system satellites and comets cannot be rendered quantitative. In general, due to insolation, icy satellites may have slightly warmer surfaces than their interiors. If there are CO2 ice inclusions in satellite water ices, they would have diffused as vapor along pores toward the cold interiors or, if near the surface, would have evaporated. The presence of pores and amorphous ice in cometary nuclei has an important effect on their flare-up and the size of the comas and tails.

Smoluchowski, R.; Mcwilliam, A.

1984-01-01

73

Structure of ices on satellites  

NASA Astrophysics Data System (ADS)

The pressure densification of ices, in combination with density changes induced by pore migration in a thermal gradient and the phase transitions of water due to meteoritic bombardment (into either high pressure polymorphs or an amorphous phase) create a complex situation, which is not easily evaluated in either satellites or cometary nuclei. Accordingly, the present findings concerning solar system satellites and comets cannot be rendered quantitative. In general, due to insolation, icy satellites may have slightly warmer surfaces than their interiors. If there are CO2 ice inclusions in satellite water ices, they would have diffused as vapor along pores toward the cold interiors or, if near the surface, would have evaporated. The presence of pores and amorphous ice in cometary nuclei has an important effect on their flare-up and the size of the comas and tails.

Smoluchowski, R.; McWilliam, A.

1984-05-01

74

The Structure of Ice II  

Microsoft Academic Search

The stability of the high pressure ice forms discovered by Tammann and Bridgman at very low temperatures and atmospheric pressure has made it possible to obtain x-ray powder diffraction photographs of these forms. The experimental procedure is very briefly discussed. An analysis of the ice II diffraction patterns leads to a side-centered orthorhombic cell with a=7.80A, b=4.50A, and c=5.56A. This

Ronald L. McFarlan

1936-01-01

75

Ice crystal growth in a dynamic thermal diffusion chamber  

NASA Technical Reports Server (NTRS)

Ice crystals were grown in a supersaturated environment produced by a dynamic thermal diffusion chamber, which employed two horizontal plates separated by a distance of 2.5 cm. Air was circulated between and along the 1.2 m length of the plates past ice crystals which nucleated and grew from a fiber suspended vertically between the two plates. A zoom stereo microscope with a magnification which ranged from 3X to 80X and both 35 mm still photographs and 16 mm time lapse cine films taken through the microscope were used to study the variation of the shape and linear growth rate of ice crystals as a function of the ambient temperature, the ambient supersaturation, and the forced ventilation velocity. The ambient growth conditions were varied over the range of temperature 0 to -40 C, over the range of supersaturation 4% to 50% with respect to ice, and over the range of forced ventilation velocities 0 cm/s to 20 cm/s.

Keller, V. W.

1980-01-01

76

Laboratory Investigation of Direct Measurement of Ice Water Content, Ice Surface Area, and Effective Radius of Ice Crystals Using a Laser-Diffraction Instrument  

NASA Technical Reports Server (NTRS)

The aircraft microphysics probe, PVM-100A, was tested in the Colorado State University dynamic cloud chamber to establish its ability to measure ice water content (IWC), PSA, and Re in ice clouds. Its response was compared to other means of measuring those ice-cloud parameters that included using FSSP-100 and 230-X 1-D optical probes for ice-crystal concentrations, a film-loop microscope for ice-crystal habits and dimensions, and an in-situ microscope for determining ice-crystal orientation. Intercomparisons were made in ice clouds containing ice crystals ranging in size from about 10 microns to 150 microns diameter, and ice crystals with plate, columnar, dendritic, and spherical shapes. It was not possible to determine conclusively that the PVM accurately measures IWC, PSA, and Re of ice crystals, because heat from the PVM evaporated in part the crystals in its vicinity in the chamber thus affecting its measurements. Similarities in the operating principle of the FSSP and PVM, and a comparison between Re measured by both instruments, suggest, however, that the PVM can make those measurements. The resolution limit of the PVM for IWC measurements was found to be on the order of 0.001 g/cubic m. Algorithms for correcting IWC measured by FSSP and PVM were developed.

Gerber, H.; DeMott, P. J.; Rogers, D. C.

1995-01-01

77

From parallel to single crystallization kinetics in high-density amorphous ice  

NASA Astrophysics Data System (ADS)

The isobaric transformation behavior of unannealed (uHDA) and expanded (eHDA) high-density amorphous ice at pressures up to 0.20 GPa is compared using powder x-ray diffraction and dilatometry. eHDA shows high thermal stability and crystallizes to a single ice phase only, whereas uHDA shows much lower thermal stability and always crystallizes to a mixture of ice phases. Unexpectedly, at low temperatures hexagonal ice grows first from uHDA, whereas this phase never crystallizes from eHDA. This leads us to conclude that hidden structural order in the form of nanocrystalline domains is present in uHDA, which triggers growth of hexagonal ice. By contrast, these ordered domains are absent in eHDA, which appears to be a homogeneous material and, thus, could be considered as a candidate for the low-temperature proxy of the proposed high-density liquid phase of water. The present work provides the basis for further experimental studies aiming at investigating this possibility since it establishes that the well-studied uHDA is not the right material to be studied in this context, whereas the more recently discovered eHDA is.

Seidl, Markus; Amann-Winkel, Katrin; Handle, Philip H.; Zifferer, Gerhard; Loerting, Thomas

2013-11-01

78

Olivine Crystal Structure  

NSDL National Science Digital Library

This exercise is based on recent crystallographic research on the olivine crystal structure published by Redfern et al. (2000). The authors of this study synthesized Fa50 olivine olivine (MgFeSiO4) in an experimental apparatus at temperatures ranging from 100 to 1250 °C, quenched the experiments, and used in situ neutron powder diffraction techniques to investigate changes in the synthesized olivines as a function of temperature. While this study reports cutting-edge materials research carried out with the latest crystallographic techniques, the results are educationally instructive and illustrate important concepts normally covered in an undergraduate mineralogy course. In this exercise, students are guided into the American Mineralogist Crystal Structure Database to retrieve and download published crystal structure data for viewing in either the CrystalMaker or XtalDraw visualization software packages. The students are instructed on how to manipulate the structures and are asked to plot some of the crystallographic data from this study on graphs using a spreadsheet program such as Excel.

Ratajeski, Kent

79

The alignment of ice crystals in changing electric fields  

NASA Astrophysics Data System (ADS)

Orientation of ice crystals in the form of thin plates (diameter up to 30 ?m, thickness 0.5 to a few ?m) was investigated optically for crystals nucleated in a supercooled cloud in a laboratory cold chamber. Random orientation caused by Brownian rotation of small crystals (apparent as twinkling) and alignment caused by airflow resulting from fall motion of larger crystals was changed by application of an electric field either as a step or as an oscillating square wave of variable frequency of order 1-10 Hz. Video records and time exposed still photographs demonstrated crystal fall, oscillation, and orientation changes with electric field magnitude and frequency. Thin film interference colours provided crystal thickness, mass, and moment of inertia. Realignment began for electric fields greater than 0.5-1 kV/m and was complete above 10 kV/m. Measurements of degree of alignment (from random orientation to completely parallel to the electric field) and its time dependence (of order tenths of seconds) are consistent with predictions of a theoretical oscillator model based on electrical torques on ellipsoids in viscous air. In a changing electric field at low frequency, the crystal realignment varies along with the variation field and at high frequency they remain aligned along the average field. These results are applied to larger crystals as occur in the atmosphere with implication for remote sensing of ice by radar and lidar as influenced by local electric fields and with the possibility of their remote measurement by optical observation of changing crystal orientations.

Foster, T. C.; Hallett, J.

80

Crystal structure of daqingshanite  

Microsoft Academic Search

Daqinshanite, a new mineral recently discovered in China, is a kind of strontium-rare earth-bearing phosphate-carbonate. The\\u000a ideal formula is: (Sr, Ca, Ba), RF(PO4)(CO3)3. The mineral belongs to the trigonal system. The intensity data were collected with a single-crystal four-circle diffractometer.\\u000a The lattice parameters are given as:a=10.058(±0.002) Å;c=9.225(±0.003) Å. Space group=R3m,Z=3. The crystal structure was solved by Patterson and electron density

Lulu Ximen; Zhizhong Peng

1985-01-01

81

A Critical Look at Ice Crystal Growth Data  

Microsoft Academic Search

I review published data relating to the growth of ice crystals from water\\u000avapor under various conditions, and I critically examine the different\\u000ameasurements to determine what useful information can be extracted from each. I\\u000ashow that most, and possibly all, of the existing growth data have been\\u000aseriously distorted by systematic errors of one form or another, to varying

Kenneth G. Libbrecht

2004-01-01

82

Structure and Evolution of Ice Dwarf Planets  

NASA Astrophysics Data System (ADS)

Recent discoveries prompt a new assessment of the properties of large, transneptunian objects. With the system barycenter determined by Nix and Hydra and its size by stellar occulation, Charon's density is now known at 1.65 ± 0.06 g cm-3 (Buie et al., A.J. 132, 290, 2006). Structural calculations imply a 60/40 rock/ice ratio, lower than the system as a whole, but still geophysically significant. Early temperatures should have easily reached the ammonia-water ice eutectic, if not water-ice melting. While ice-rock differentiation is not assured in the presence of solid-state convection, convection is now known to be a less efficient heat transport mechanism compared with earlier parameterized convection models. If Charon managed to remain undifferentiated, it should have undergone prolonged cooling and internal conversion of ice I to II, with clear observational consequences. Bodies of the Pluto class mark the transition from solely ice-I shells (differentiation assumed) to shells with lower layers of higher-pressure ice phases (e.g., 2003 UB313); the Pluto class also marks the transition from bodies with Europa-type to Callisto-type oceans (if they have oceans), and if one ignores the possibility of intervening organic-rich layers. Although the very cold surfaces of the ice dwarfs work against the possibility of solid-state convection, the deep ice shells in Pluto-class bodies more than compensate; Pluto itself is near the tipping point for convective shut-down, a late stage in the evolution of large rock-ice bodies in which internal oceans thicken rather than thin. In contrast, the rapidly rotating 2003 EL61, if interpreted as Jacobi ellipsoid, has a density close to 2.6 g cm-3 (Rabinowitz et al., Ap. J. 639, 1238, 2006). This implies a Europa-like structure, 85/15 rock/ice by mass with an 100-km thick ice shell (though no ocean). This work supported by NASA OPR and New Horizons.

McKinnon, William B.; Barr, A. C.

2006-09-01

83

Crystal Lattice Structures  

NSDL National Science Digital Library

The US Naval Research Laboratories (NRL) maintains this Website containing 2-D images (HTML) of 78 crystal lattice structures (e.g., body-centered-cubic, hexagonal-close packed, carbon, silicon). The index of structures can be searched by Pearson Symbol, Space Group, or Strukturbericht Designation. On each page, the structure can be viewed from different perspectives, and information about atomic number, vector diagrams, and atom coordinates is available. The site also contains a bibliography and a programming information page, both with hyperlinks.

84

Nanoscale Ice: Spectroscopic Ellipsometry of Epitaxially-Grown Crystals  

NASA Astrophysics Data System (ADS)

A new laboratory technique has been developed to examine the surface characteristics and kinetics of ice crystals at the nanoscale. Uncertainties remain regarding the fundamental physics of nucleation and depositional growth in atmospheric ice crystals. These molecular-scale uncertainties propagate upward into modeling outcomes at all scales of atmospheric interest: particle models, cloud models, mesoscale models, and climate models. Molecular-scale growth mechanisms and kinetics have been mainly inferred from bulk and particle-scale experiments as well as crystal-growth theory. The precarious nature of the ice surface resisted the first generation of direct nanoscale probing technologies, but new in-situ techniques including ESEM, AFM, and ellipsometry promise to divulge a wealth of new knowledge. Spectroscopic ellipsometry measures changes in the polarization state of light as it reflects off the surface of a thin film. This non-destructive technique is capable of measuring layer thicknesses as small as a single monolayer (~1 Å) and up to thicknesses of ~10 ?m. Other physical parameters including index of refraction and surface roughness are also accessible. At the TCNJ Cloud Physics Laboratory, a Horiba Scientific Auto-SE ellipsometer (440 - 1000 nm spectral range) has been adapted for in-situ measurements of ice crystals. The ice crystals are grown epitaxially on various horizontal substrates in a custom-built static diffusion chamber. The diffusion chamber is housed within a vacuum chamber and an optical path is provided from the ellipsometer light source to sample stage and back to the ellipsometer analyzer at 75° from normal. The diffusion chamber is cooled in two stages, with initial cooling accomplished with a fluid-chilled block and final chilling controlled by two independent thermoelectric cells. A wide range of temperatures, pressures, and saturation ratios are accessible: from 0°C to -30°C, 50mb to atmospheric pressure, and from subsaturated to greater that 200% RHi. Temperature and moisture profiles are continuously determined by platinum resistance thermometers. Optimization of cooling efficiencies are under way and should permit extension of temperature range to -60°C. Ongoing efforts are targeted at kinetic measurements of thickness changes in order to identify growth thresholds as a function of ambient conditions and nucleation mechanism.

Cumiskey, A.; Grippaldi, J.; Magee, N. B.

2011-12-01

85

Crystal Ice Formation of Solution and Its Removal Phenomena on a Vertical Cooled Plate  

NASA Astrophysics Data System (ADS)

Experimental and analytical studies for freezing phenomena of ethylene glycol solution on a vertical cooled polyvinyl-chloride plate have been performed. It is found that the crystal ice formed on the vertical plate is removed from the plate surface due to buoyancy force acting on the crystal ice. It is shown that the crystal ice formed on the vertical plate slides along the plate surface due to buoyancy force and the crystal ice grows in a shape of sheet by joining with the neighbour ice. The number of the removed ice per unit of time is, therefore, decreased as compared to that for the horizontal plate. It is found that the onset of ice removal condition is related to the heat fluxes from the plate surface to the plate and from the plate surface to the solution. The ice removal occurs easily for a vertical plate than for a horizontal one.

Hirata, Tetsuo; Ishikawa, Masaaki; Matsuzaki, You

86

Charge Transfer Process During Collision of Riming Graupel Pellet with Small Ice Crystals within a Thundercloud  

NASA Technical Reports Server (NTRS)

A charge transfer process during the collision of a riming graupel pellet and an ice-crystal at low temperature is proposed. During riming, the surface structure of graupel deviates from perfect crystalline structure. A concept of quasi-solid layer (QSL) formation on the surface is introduced. This QSL contains defects formed during riming. In absence of impurities, positively charged X-defect abundance is considered in the outer layer. These defects are assumed to be the charge carriers during the charge transfer process. Some part of the QSL is stripped off by the colliding ice crystals, which thereby gain some positive charge, leaving the graupel pellet negatively charged. With the proposed model, fC to pC of charge transfer is observed per collision. A transition temperature between -10 C to -15 C is also noted beyond which the QSL concept does not hold. This transition temperature is dependent on the bulk liquid water content of the cloud.

Datta, Saswati; De, Utpal K.; Goswami, K.; Jones, Linwood

1999-01-01

87

An uncoupled multiphase approach towards modeling ice crystals in jet engines  

NASA Astrophysics Data System (ADS)

A recent series of high altitude turbofan engine malfunctions, characterized by flameout and sudden power losses have been reported in recent years. The source of these incidents has been hypothesized to be due to the presence of ice crystals at high altitudes. Ice crystals have been shown to have ballistic trajectories and consequently enter the core engine flow, without getting centrifuged out towards the engine bypass as droplets do. The crystals may melt as they move downstream to higher temperatures in successive stages, or hit a heated surface. The wetted surface may then act as an interface for further crystal impingement, which locally reduces the temperature and could lead to an ice accretion on the components. Ice can accrete to dangerously high levels, causing compressor surge due to blockage of the primary flowpath, vibrational instabilities due to load imbalances of ice on rotating components, mechanical damage of components downstream due to large shed ice fragments, or performance losses if ice enters the combustor, causing a decreased burner efficiency and an eventual flame-out. In order to provide a numerical tool to analyze such situations, FENSAP-ICE has been extended to model mixed-phase flows that combine air, water and ice crystals, and the related ice accretion. DROP3D has been generalized to calculate particle impingement, concentration, and field velocities in an uncoupled approach that neglects any phase change by assuming both ice crystals and supercooled droplets are in thermodynamic equilibrium. ICE3D then accounts for the contribution of ice crystals that stick and melt on an existing water-film and promote ice accretion. The extended ice crystal impingement and ice accretion model has been validated against test data from Cox and Co. and National Research Council icing tests conducted on a NACA0012 airfoil and unheated non-rotating cylinder respectively. The tests show a consistent agreement with respect to experimental profiles in terms of capturing the overall shape, although some of the ice profiles were conservative since they over-predicted the amount of ice accreted. The experimental observations suggest that ice crystals cause splashing of an existing film, and erosion effects when they impact an iced surface, and cause an overall loss in the amount of ice, as well as a general streamlining of the ice profile. This has not been taken into account in the present numerical model. The overall predictions in comparison with other numerical models, however, have improved and are a promising step towards simulating ice-shedding characteristics in a turbomachine.

Nilamdeen, Mohamed Shezad

88

Optical detection and characterization of ice crystals in LACIS  

NASA Astrophysics Data System (ADS)

Tropospheric ice and mixed phase clouds are an integral part of the earth system and their microphysical and radiative properties are strongly coupled e.g. through the complexities of the ice nucleation process. Therefore the investigation of influences of different aerosol particles which act as ice nuclei (IN) on the freezing behaviour of cloud droplets is important and still poses unresolved questions. The Leipzig Aerosol and Cloud Interaction Simulator (LACIS) is used to investigate the IN activity of different natural and artificial aerosol particles (mineral dust, soot etc.) in heterogeneous freezing processes (immersion or deposition freezing). A critical part of LACIS is the particle detection system allowing for size-resolved counting of activated seed particles and discrimination between ice crystals and water droplets. Recently, two instruments have been developed to provide these measurements at the LACIS facility. The Thermally-stabilized Optical Particle Spectrometer (TOPS) is measuring the particle size based on the intensity of light scattered by individual particles into a near-forward (15° to 45°) direction. Two symmetrical forward scattering channels allow for optical determination of the sensing volume, thus reducing the coincidence counting error and the edge zone effect. The backscatter channel (162° to 176°) equipped with a rotatable cross polarizer allows for establishing the change in linear polarization state of the scattered light. The backscatter elevation angle is limited so that the linear depolarization of light scattered by spherical particles of arbitrary size is zero. Any detectable signal in the depolarization channel can be therefore attributed to non-spherical particles (ice crystals). With consideration of the signal in the backscatter channel the separate counting of water drops and ice particle is possible. The Leipzig Ice Scattering Apparatus (LISA) is a modified version of the Small Ice Detector (SID3), developed at the Science and Technology Research Institute at the University of Hertfordshire, UK. The SID instruments have been developed primarily as wing-mounted systems for airborne studies of cloud ice particles. SID3 records the forward scattered light pattern with high angular resolution using an intensified CCD (780 by 582 pixels) at a rate of 20 images per second. In addition to the SID3 capabilities, LISA is able to measure the circular depolarization ratio in the range of scattering angles from 166° to 172°. Whereas particle size, shape and orientation are characterized by the angular distribution of forward-scattered light, the measured value of the circular depolarization can be used to validate the existing theoretical models of light scattering by irregular particles (RTDF, GSVM, T-Matrix, DDA). The first measurements done at the LACIS facility have demonstrated a promising sensitivity of LISA's depolarization channel to the shape of ice crystals. Results showed an increase of the mean circular depolarization ratio from 1.5 (characteristic for the liquid water droplets above 3 µm) to 2.5 for the "just frozen" almost-spherical droplets in the same size range. The presentation will describe details of instruments set up and present some exemplary results from experiments carried out at LACIS and AIDA (KIT) facilities.

Kiselev, Alexei; Clauß, Tina; Niedermeier, Dennis; Hartmann, Susan; Wex, Heike; Stratmann, Frank

2010-05-01

89

The Influence of Radiation on Ice Crystal Spectrum in the Upper Troposphere  

NASA Technical Reports Server (NTRS)

This theoretical study is carried out to investigate the effect of radiation on ice crystal spectrum in the upper troposphere. First, an explicit expression is obtained for the ice crystal growth rate that takes account of radiative and kinetic effects. Second, the expression is used to quantitatively analyze how radiation broadens the ice crystal spectrum and then reveal a new precipitation mechanism in the upper troposphere and the stratosphere. Third, the radiative effect is used to explain the subvisual clouds near the tropopause.

Zeng, Xiping

2008-01-01

90

Ice crystal growth in water vapor at high saturation  

NASA Technical Reports Server (NTRS)

A simple technique is presented for estimating the energy of formation of monolayer icelike clusters at ice-vapor interfaces. Under the assumptions that the ice surfaces are smooth and sparsely covered with monomers, dimers, etc., in near equilibrium with the vapor, and that the bond energies and configurational entropy dominate the energy of formation, it is found that the basal surfaces prefer triangular embryos with an orientation which reverses from layer to layer, whereas the most stable clusters on the prism surfaces are rectangular in configuration. The preferred prism clusters are determined to have a significantly lower critical energy of formation than the basal clusters due to differences in both corner free energy and configurational entropy. This phenomenon provides a mechanism for strongly anisotropic crystal growth at high saturations.

Bartley, D. L.

1976-01-01

91

The chemical, physical and structural properties of estuarine ice in Great Bay, New Hampshire  

USGS Publications Warehouse

The purpose of this study was to provide general information on the chemical, physical and structural properties of estuarine ice and show how it compares with sea ice found at higher latitudes in order to determine whether the ice in Great Bay can be used as an analog in the study of arctic sea ice. Ice cores and water samples were collected during the 1983-1984 winter season at Adams Point in Great Bay, New Hampshire. Concentrations of chloride, nitrogen (as nitrate and nitrite), bromide, phosphate, sulfate and silicate were determined for samples chosen on the basis of identifiable stratigraphic layers (i.e. bubble size and shape, sediment layers, etc.). Similarities between ice formation in Great Bay and those in the arctic regions include the nature of the freezing process and the ice types produced. In addition, the distribution and concentration of chemical constituents were found to be similar to those observed in arctic sea ice. Factors affecting the chemistry of the ice in Great Bay include rainfall during the freezing season, the presence of sediment layers in the ice cores, the nature of incorporation of brine into the crystal structure of the ice and the drainage of brine. ?? 1987.

Meese, D. A.; Gow, A. J.; Mayewski, P. A.; Ficklin, W.; Loder, T. C.

1987-01-01

92

Crystal Ice Formation of Solution and Its Removal Phenomena From Cooled Solid Surface  

NASA Astrophysics Data System (ADS)

Experimental studies for freezing phenomena of ethylene glycol solution on cooled plate have been performed. A polyvinyl chloride as well as an acrylic resin plates are used for the cooled plates. It is found that the crystal ice formed at the cooled plate is removed from the plate due to buoyancy force acting the crystal ice. It means that ice formation on a cooled plate without deposit ice layer is possible by the present method. It is shown that the cooled plate surface is under cooled about 1.0~1.5 degree below the freezing temperature of the solution during the crystal ice formation and its removal phenomena. The degree of under cooled temperature is unaffected by the cooling temperature of the plate. For higher concentration of solution, it is found that the number of the removed crystal ice per unit time is increased and the volume of each removed ice is decreased.

Hirata, Tetsuo; Ishikawa, Masaaki; Nagasaka, Kouji

93

Small, Highly Reflective Ice Crystals in Low-Latitude Cirrus  

NASA Technical Reports Server (NTRS)

At low latitudes, cirrus are ubiquitous and can be in excess of 100 C colder than the surface, limiting the amount of sunlight absorbed by the earth s atmosphere and surface, and reducing its loss of heat. Here we present aircraft measurements within cirrus over southern Florida indicating that ice crystals have smaller sizes and are more reflective than is assumed in most current climate models. If the measurements are generally representative of low-latitude cirrus, they point to a first-order correction to represenntions of how these clouds affect the earth's climate.

Garrett, T. J.; Gerber, H.; Baumgardner, D. G.; Twohy, C. H.; Weinstock, E. M.

2003-01-01

94

Evolution of ice crystal regions on the microscale based on in situ observations  

NASA Astrophysics Data System (ADS)

properties of cirrus clouds largely influence their atmospheric radiative forcing. However, uncertainties remain in simulating/parameterizing the evolution of ice crystals. These uncertainties require more analyses in the Lagrangian view, yet most in situ observations are in the Eulerian view. Here we demonstrate a new method to separate out five phases of ice crystal evolution, using the horizontal spatial relationships between ice supersaturated regions (ISSRs) and ice crystal regions (ICRs). Based on global in situ data sets, we show that the samples of clear-sky ISSRs, ice crystal formation/growth, and evaporation/sedimentation are ~20%, 10%, and 70% of the total ISSR + ICR samples, respectively. In addition, the variance of number-weighted mean diameter (Dc) becomes narrower during the evolution, while the distribution of ice crystal number density (Nc) becomes wider. The new method helps to understand the evolution of ICRs and ISSRs on the microscale by using in situ Eulerian observations.

Diao, Minghui; Zondlo, Mark A.; Heymsfield, Andrew J.; Beaton, Stuart P.; Rogers, David C.

2013-07-01

95

Frustrated polymer crystal structures  

NASA Astrophysics Data System (ADS)

Several crystal structures or polymorphs of chiral or achiral polymers and biopolymers with three fold conformation of the helix have been found to conform to a common and -with one exception(Puterman, M. et al, J. Pol. Sci., Pol. Phys. Ed., 15, 805 (1977))- hitherto unsuspected packing scheme. The trigonal unit-cell contains three isochiral helices; the azimuthal setting of one helix differs significantly from that of the other two, leading to a so-called frustrated packing scheme, in which the environment of conformationally identical helices differs. Two variants of the frustrated scheme are analyzed. Similarities with frustrated two dimensional magnetic systems are underlined. Various examples of frustration in polymer crystallography are illustrated via the elucidation or reinterpretation of crystal phases or polymorphs of polyolefins, polyesters, cellulose derivatives and polypeptides. Structural manifestations (including AFM evidence) and morphological consequences of frustration are presented, which help diagnose the existence of this original packing of polymers.(Work done with L. Cartier, D. Dorset, S. Kopp, T. Okihara, M. Schumacher, W. Stocker.)

Lotz, B.; Strasbourg, 67083

1997-03-01

96

Determination of Ice Crystal Growth Parameters in a Supercooled Cloud Tunnel.  

National Technical Information Service (NTIS)

In order to completely understand the behavior of a dynamically changing ice crystal as it falls through a supercooled cloud, the simultaneous determination of the crystal size, mass, apparent density, and fall velocity is desirable. Based on the experien...

M. W. Kowa

1981-01-01

97

Laboratory studies on the uptake of aromatic hydrocarbons by ice crystals during vapor depositional crystal growth  

NASA Astrophysics Data System (ADS)

Uptake of aromatic hydrocarbons (AH) by ice crystals during vapor deposit growth was investigated in a walk-in cold chamber at temperatures of 242, 251, and 260 K, respectively. Ice crystals were grown from ambient air in the presence of gaseous AH namely: benzene (C 6H 6), toluene (methylbenzene, C 7H 8), the C 8H 10 isomers ethylbenzene, o-, m-, p-xylene (dimethylbenzenes), the C 9H 12 isomers n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene (1,3,5-TMB), 1,2,4-trimethylbenzene (1,2,4-TMB), 1,2,3-trimethylbenzene (1,2,3-TMB), and the C 10H 14 compound tert.-butylbenzene. Gas-phase concentrations calculated at 295 K were 10.3-20.8 ?g m -3. Uptake of AH was detected by analyzing vapor deposited ice with a very sensitive method composed of solid-phase micro-extraction (SPME), followed by gas chromatography/mass spectrometry (GC/MS). Ice crystal size was lower than 1 cm. At water vapor extents of 5.8, 6.0 and 8.1 g m -3, ice crystal shape changed with decreasing temperatures from a column at a temperature of 260 K, to a plate at 251 K, and to a dendrite at 242 K. Experimentally observed ice growth rates were between 3.3 and 13.3×10 -3 g s -1 m -2 and decreased at lower temperatures and lower value of water vapor concentration. Predicted growth rates were mostly slightly higher. Benzene, toluene, ethylbenzene, and xylenes (BTEX) were not detected in ice above their detection limits (DLs) of 25 pg g ice-1 (toluene, ethylbenzene, xylenes) and 125 pg g ice-1 (benzene) over the entire temperature range. Median concentrations of n-propylbenzene, 4-ethyltoluene, 1,3,5-TMB, tert.-butylbenzene, 1,2,4-TMB, and 1,2,3-TMB were between 4 and 176 pg g ice-1 at gas concentrations of 10.3-10.7 ?g m -3 calculated at 295 K. Uptake coefficients ( K) defined as the product of concentration of AH in ice and density of ice related to the product of their concentration in the gas phase and ice mass varied between 0.40 and 10.23. K increased with decreasing temperatures. Values of Gibbs energy (? G) were between -4.5 and 2.4 kJ mol -1 and decreased as temperatures were lowered. From the uptake experiments, the uptake enthalpy (? H) could be determined between -70.6 and -33.9 kJ mol -1. The uptake entropy (? S) was between -281.3 and -126.8 J mol -1 K -1. Values of ? H and ? S were rather similar for 4-ethlytoluene, 1,3,5-TMB and tert.-butylbenzene, whereas 1,2,3-TMB showed much higher values.

Fries, Elke; Starokozhev, Elena; Haunold, Werner; Jaeschke, Wolfgang; Mitra, Subir K.; Borrmann, Stephan; Schmidt, Martin U.

98

Inorganic Crystal Structure Database (ICSD)  

National Institute of Standards and Technology Data Gateway

SRD 84 FIZ/NIST Inorganic Crystal Structure Database (ICSD) (PC database for purchase)   The Inorganic Crystal Structure Database (ICSD) is produced cooperatively by the Fachinformationszentrum Karlsruhe(FIZ) and the National Institute of Standards and Technology (NIST). The ICSD is a comprehensive collection of crystal structure data of inorganic compounds containing more than 140,000 entries and covering the literature from 1915 to the present.

99

Ice/hydrohalite crystallization structures in sub-eutectic freezing experiments in the system NaCl-H20 and possible implications for the properties of frozen brines in Europa: A preliminary report  

NASA Astrophysics Data System (ADS)

Sulfates are likely to be the most abundant solutes in the subsurface Europan liquid ocean. NaCl may also be a significant component of such liquids based on the compositions of stony meteorites like those thought to be among the source materials for the silicates in Europa's interior. The system NaCl-H20 exhibits a eutectic at -20.8°C and 23.3 weight percent NaCl between ice Ih and hydrohalite (NaCl.2H20). This low eutectic temperature compared to Mg and Na sulfate hydrate/ice eutectics indicates that hydrohalite should be among the last salts to crystallize in brine upwellings along rifts and other places where resurfacing by melt extrusion occurs on Europa. We conducted a suite of freezing experiments on NaCl brines with 20.3, 23.3, and 26.6 (saturated) weight percent NaCl by holding these liquids at a few degrees below the eutectic temperature. These runs produced ice-rich, eutectic and hydrohalite-rich aggregates of both phases, respectively, as confirmed by cryogenic x-ray diffraction and x-ray fluorescence spectroscopy. Based on direct observations of crystals forming at the tops and bottoms of the sample chambers and on refractive index measurements of subsequently melted sample material, marked fractional crystallization and segregation by density of ice, hydrohalite, and residual liquids occurred in the 20.3 and 26.6% samples and less so in for the eutectic composition. Crystallization of very fine grained eutectic intergrowths was recognized in cryogenic SEM images of all these samples and they were especially prominent in samples frozen from saturated brine. These samples were very difficult to cleave compared to pure polycrystalline ice, and hence are likely to have high fracture toughness. Direct measurements of this property and also the effects of partial melting on ductile flow rates are planned on such samples. Refracturing of such regions of fine eutectoid ice/hydrohalite intergrowths is likely to be inhibited in refrozen rifts compared to more ice-rich regions on Europa.

Rieck, K.; Kirby, S. H.; Stern, L. A.

2005-12-01

100

75 FR 8116 - Notice Pursuant to the National Cooperative Research and Production Act of 1993-Ice Crystal...  

Federal Register 2010, 2011, 2012, 2013

...National Cooperative Research and Production Act of 1993--Ice Crystal Consortium Notice is hereby given that, on December 31, 2009...15 U.S.C. 4301 et seq. (``the Act''), the Ice Crystal Consortium (``ICC'') has filed written...

2010-02-23

101

Crystal Structure Lab  

NSDL National Science Digital Library

This activity is concerned with crystals, the basic building units that make up rocks and minerals. Students construct a model of the silicon-oxygen tetrahedron and discover that the smallest whole unit that could form a unique crystal is called a unit cell. They learn that a unit cell would have all the properties of a large crystal such as a diamond, but would be only molecular size (submicroscopic). If a crystal starts to form from a slowly cooling magma or from a drying up pool of salty sea water, unit cells add themselves one on top of another in order to develop the large crystals we can see and handle.

Fetcho, Ray

102

Microfluidic experiments reveal that antifreeze proteins bound to ice crystals suffice to prevent their growth  

PubMed Central

Antifreeze proteins (AFPs) are a subset of ice-binding proteins that control ice crystal growth. They have potential for the cryopreservation of cells, tissues, and organs, as well as for production and storage of food and protection of crops from frost. However, the detailed mechanism of action of AFPs is still unclear. Specifically, there is controversy regarding reversibility of binding of AFPs to crystal surfaces. The experimentally observed dependence of activity of AFPs on their concentration in solution appears to indicate that the binding is reversible. Here, by a series of experiments in temperature-controlled microfluidic devices, where the medium surrounding ice crystals can be exchanged, we show that the binding of hyperactive Tenebrio molitor AFP to ice crystals is practically irreversible and that surface-bound AFPs are sufficient to inhibit ice crystal growth even in solutions depleted of AFPs. These findings rule out theories of AFP activity relying on the presence of unbound protein molecules.

Celik, Yeliz; Drori, Ran; Pertaya-Braun, Natalya; Altan, Aysun; Barton, Tyler; Bar-Dolev, Maya; Groisman, Alex; Davies, Peter L.; Braslavsky, Ido

2013-01-01

103

Photonic Crystal Laser Accelerator Structures  

SciTech Connect

Photonic crystals have great potential for use as laser-driven accelerator structures. A photonic crystal is a dielectric structure arranged in a periodic geometry. Like a crystalline solid with its electronic band structure, the modes of a photonic crystal lie in a set of allowed photonic bands. Similarly, it is possible for a photonic crystal to exhibit one or more photonic band gaps, with frequencies in the gap unable to propagate in the crystal. Thus photonic crystals can confine an optical mode in an all-dielectric structure, eliminating the need for metals and their characteristic losses at optical frequencies. We discuss several geometries of photonic crystal accelerator structures. Photonic crystal fibers (PCFs) are optical fibers which can confine a speed-of-light optical mode in vacuum. Planar structures, both two- and three-dimensional, can also confine such a mode, and have the additional advantage that they can be manufactured using common microfabrication techniques such as those used for integrated circuits. This allows for a variety of possible materials, so that dielectrics with desirable optical and radiation-hardness properties can be chosen. We discuss examples of simulated photonic crystal structures to demonstrate the scaling laws and trade-offs involved, and touch on potential fabrication processes.

Cowan, Benjamin M

2003-05-21

104

Directed Discovery of Crystal Structures  

NSDL National Science Digital Library

This contribution is modified from a published exercise "Directed Discovery of Crystal Structures Using Ball-and-Stick Models" [Mogk, 1997] . While the published exercise is based on student exploration of traditional ball-and-stick models of crystal structures, this modified version uses a similar "discovery-based" approach and the latest online crystallographic information and visualization software to teach the spatial relationships and crystal-chemical rules that govern the crystal structures of common minerals and crystalline solids. A few changes in the content have been made from the published exercise, mainly to accommodate the new digital media.

Mogk, Dave; Ratajeski, Kent

105

Effects on skylight at South Pole Station, Antarctica, by ice crystal precipitation in the atmosphere.  

PubMed

Measurements of the radiance and polarization of the skylight at South Pole Station, Antarctica, were made for clear cloud-free skies and cloudless skies with ice crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by ice crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of ice crystal scattering is greatest at the longer wavelengths. PMID:18195749

Fitch, B W; Coulson, K L

1983-01-01

106

Effects on skylight at South Pole Station, Antarctica, by ice crystal precipitation in the atmosphere  

NASA Technical Reports Server (NTRS)

Measurements of the radiance and polarization of the skylight at South Pole Station, Antarctica, were made for clear cloud-free skies and cloudless skies with ice crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by ice crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of ice crystal scattering is greatest at the longer wavelengths.

Fitch, B. W.; Coulson, K. L.

1983-01-01

107

Structure of Ordinary Ice Ih. Part 1: Ideal Structure of Ice.  

National Technical Information Service (NTIS)

This report examines the defect-free structure of ordinary I sub h, reviewing experimental results and theoretical models of the arrangement of oxygen and hydrogen atoms and the electronic structure of ice. Special attention is given to the results of stu...

V. F. Petrenko

1993-01-01

108

Crystal Ice Formation of Solution and Its Removal Phenomena around Vertical Cooled Cylinder  

NASA Astrophysics Data System (ADS)

Experimental and analytical studies for freezing phenomena of ethylene glycol solution around a vertical cooled polyvinyl-chloride cylinder have been performed. It is found that the crystal ice formed around the vertical cylinder is removed from the cylinder surface due to buoyancy force acting on the crystal ice. The crystal ice slides along the cylinder surface due to buoyancy force and grows in a shape of tube by joining with the neighbour ice. It is shown that the onset of ice removal condition is related to the heat flux at the cylinder surface when the latent heat of fusion is discharged with freezing, and that the heat flux ratio of 'from the cylinder surface into the cylinder' to 'from the cylinder surface to the solution' is an important parameter for the onset conditions. The ice removal occurs easily for short cylinders than for long ones.

Hirata, Tetsuo; Ishikawa, Masaaki; Akutsu, Nobuaki

109

Ice breaking in GPCR structural biology  

Microsoft Academic Search

G-protein-coupled receptors (GPCRs) are one of the most challenging targets in structural biology. To successfully solve a high-resolution GPCR structure, several experimental obstacles must be overcome, including expression, extraction, purification, and crystallization. As a result, there are only a handful of unique structures reported from this protein superfamily, which consists of over 800 members. In the past few years, however,

Qiang Zhao; Bei-li Wu

2012-01-01

110

Discrete element analysis of ice loads on ships and structures  

Microsoft Academic Search

In this paper, the versatility of discrete element method (DEM) in modelling ice-related problems is discussed and further demonstrated using the results from the DEM works conducted by the National Research Council's Institute for Ocean Technology (NRC-IOT) using a commercial code DECICE. These works include a wide range of ice-structure and ice-ship interaction problems of current interest, i.e. ice loads

Michael Lau; Karl P. Lawrence; Leo Rothenburg

2011-01-01

111

Direct Visualization of Spruce Budworm Antifreeze Protein Interacting with Ice Crystals: Basal Plane Affinity Confers Hyperactivity  

PubMed Central

Antifreeze proteins (AFPs) protect certain organisms from freezing by adhering to ice crystals, thereby preventing their growth. All AFPs depress the nonequilibrium freezing temperature below the melting point; however AFPs from overwintering insects, such as the spruce budworm (sbw) are 10–100 times more effective than most fish AFPs. It has been proposed that the exceptional activity of these AFPs depends on their ability to prevent ice growth at the basal plane. To test the hypothesis that the hyperactivity of sbwAFP results from direct affinity to the basal plane, we fluorescently tagged sbwAFP and visualized it on the surface of ice crystals using fluorescence microscopy. SbwAFP accumulated at the six prism plane corners and the two basal planes of hexagonal ice crystals. In contrast, fluorescently tagged fish type III AFP did not adhere to the basal planes of a single-crystal ice hemisphere. When ice crystals were grown in the presence of a mixture of type III AFP and sbwAFP, a hybrid crystal shape was produced with sbwAFP bound to the basal planes of truncated bipyramidal crystals. These observations are consistent with the blockage of c-axial growth of ice as a result of direct interaction of sbwAFP with the basal planes.

Pertaya, Natalya; Marshall, Christopher B.; Celik, Yeliz; Davies, Peter L.; Braslavsky, Ido

2008-01-01

112

Novel ice structures in carbon nanopores: pressure enhancement effect of confinement.  

PubMed

We report experimental results on the structure and melting behavior of ice confined in multi-walled carbon nanotubes and ordered mesoporous carbon CMK-3, which is the carbon replica of a SBA-15 silica template. The silica template has cylindrical mesopores with micropores connecting the walls of neighboring mesopores. The structure of the carbon replica material CMK-3 consists of carbon rods connected by smaller side-branches, with quasi-cylindrical mesopores of average pore size 4.9 nm and micropores of 0.6 nm. Neutron diffraction and differential scanning calorimetry have been used to determine the structure of the confined ice and the solid-liquid transition temperature. The results are compared with the behavior of water in multi-walled carbon nanotubes of inner diameters of 2.4 nm and 4 nm studied by the same methods. For D(2)O in CMK-3 we find evidence of the existence of nanocrystals of cubic ice and ice IX; the diffraction results also suggest the presence of ice VIII, although this is less conclusive. We find evidence of cubic ice in the case of the carbon nanotubes. For bulk water these crystal forms only occur at temperatures below 170 K in the case of cubic ice, and at pressures of hundreds or thousands of MPa in the case of ice VIII and IX. These phases appear to be stabilized by the confinement. PMID:21451863

Jazdzewska, Monika; Sliwinska-Bartkowiak, Ma?gorzata M; Beskrovnyy, Anatoly I; Vasilovskiy, Sergey G; Ting, Siu-Wa; Chan, Kwong-Yu; Huang, Liangliang; Gubbins, Keith E

2011-05-21

113

Crystals, Part II: Lattices and Structure.  

National Technical Information Service (NTIS)

Lists 715 domestic and foreign references added to the CFSTI collection during the period January 1959 through April 1965. Covers research on crystal lattices and lattice defects, crystal structure, crystal properties, optical properties, crystal processi...

1965-01-01

114

Stability relationship for water droplet crystallization with the NASA Lewis icing spray nozzle  

NASA Technical Reports Server (NTRS)

In order to produce small droplets for icing cloud simulation, high pressure air atomizing nozzles are used. For certain icing testing applications, median drop sizes as small as 5 mm are needed, which require air atomizing pressures greater than 3000 kPa. Isentropic expansion of the ambient temperature atomizing air to atmospheric pressure can result in air stream temperatures of -160 C which results in ice crystals forming in the cloud. To avoid such low temperatures, it is necessary to heat the air and water to high initial temperatures. An icing spray research program was conducted to map the temperatures below which ice crystals form. A soot slide technique was used to determine the presence of crystals in the spray.

Marek, C. John; Bartlett, C. Scott

1988-01-01

115

Stability relationship for water droplet crystallization with the NASA Lewis icing spray  

NASA Technical Reports Server (NTRS)

In order to produce small droplets for icing cloud simulation, high pressure air atomizing nozzles are used. For certain icing testing applications, median drop sizes as small as 5 mm are needed, which require air atomizing pressures greater than 3000 kPa. Isentropic expansion of the ambient temperature atomizing air to atmospheric pressure can result in air stream temperatures of -160 C which results in ice crystals forming in the cloud. To avoid such low temperatures, it is necessary to heat the air and water to high initial temperatures. An icing spray research program was conducted to map the temperatures below which ice crystals form. A soot slide technique was used to determine the presence of crystals in the spray.

Marek, C. John; Bartlett, C. Scott

1987-01-01

116

Thermal Expansion and Crystal Structure  

Microsoft Academic Search

In this investigation, the coefficients of thermal expansion of a number of crystals belonging to two structure types rutile and calcite have been studied by the x-ray method with a view to correlating thermal expansion with crystal structure. The crystals studied are MgF2, ZnF2, NiF2, MnF2, CoF2, FeF2, SnO2, PbO2, TiO2 (rutile), CrO2 and RuO2 belonging to the rutile type

K. V. Krishna Rao

1974-01-01

117

Ground Based Retrievals of Small Ice Crystals and Water Phase in Arctic Cirrus  

NASA Astrophysics Data System (ADS)

The microphysical properties of cirrus clouds are uncertain due to the problem of ice particles shattering at the probe inlet upon sampling. To facilitate better estimation of small ice crystal concentrations in cirrus clouds, a new ground-based remote sensing technique has been used in combination with in situ aircraft measurements. Data from the Mixed-Phase Arctic Cloud Experiment (M-PACE), conducted at the north slope of Alaska (winter 2004), have been used to test a new method for retrieving the liquid water path (LWP) and ice water path (IWP) in mixed phase clouds. The framework of the retrieval algorithm consists of the modified anomalous diffraction approximation or MADA (for mixed phase cloud optical properties), a radar reflectivity-ice microphysics relationship and a temperature-dependent ice particle size distribution (PSD) scheme. Cloud thermal emission measurements made by the ground-based Atmospheric Emitted Radiance Interferometer (AERI) yield information on the total water path (TWP) while reflectivity measurements from the Millimeter Cloud Radar (MMCR) are used to derive the IWP. The AERI is also used to indicate the concentration of small ice crystals (D<50 ?m) relative to the larger ice particles. Combining this small crystal information with the PSD scheme describing the larger particle concentrations yields the retrieved PSD. Small ice crystals are evaluated using the absorption properties of photon tunneling or wave resonance while the liquid water fraction is evaluated using classical Beer's law absorption. While this is still a work in progress, the anticipated products from this AERI-radar retrieval scheme are the IWP, LWP, small-to-large ice crystal number concentration ratio and effective diameter for cirrus, as well as the ice particle number concentration for a given ice water content (IWC).

Mishra, Subhashree; Mitchell, David L.; Deslover, Daniel

2009-03-01

118

A study of the relationship between thunderstorm processes and cloud-top ice crystal size  

NASA Astrophysics Data System (ADS)

Satellite observations and numerical models are used to understand the physical mechanisms responsible for thunderstorms with varying cloud-top ice crystal sizes. Geostationary Operational Environmental Satellite (GOES) data are used to create a three-year climatology of cloud-top 3.9 mum reflectivity, a quantity which is closely correlated with particle size. Maximum mean values are found over the High Plains and Rocky Mountain regions of the U.S., suggesting that convection over that region tends to generate smaller anvil ice crystals than areas throughout much of the eastern U.S. To correct for preferred forward scattering by the cloud-top ice crystals, an effective radius retrieval using GOES is developed. Forward radiative transfer simulations are run for a wide range of cloud-top ice crystal sizes and sun-cloud-satellite scattering angles. The output is used to generate a lookup table, so that GOES-measured radiances may be used along with sun-satellite geometry to obtain an estimate for particle size. Validation of the retrieval shows that the assumed scattering properties perform quite well. To help explain the geographical variation in cloud-top ice crystal size, a composite analysis is performed in the High Plains region by averaging environmental conditions for days which produced both small and large ice crystal storms. Small ice is found to occur with relatively high based storms and steep mid-level lapse rates. Additionally, observational evidence from a pyrocumulonimbus event is presented to show the effect of low-level cloud condensation nuclei (CCN) on cloud-top ice crystal size. Model simulations using the Colorado State University Regional Atmospheric Modeling System (RAMS) are performed to help understand the physical mechanisms responsible for cloud-top ice crystal size. Through a series of sensitivity tests, it is found that larger low-level CCN concentrations lead to smaller anvil ice. In addition, as cloud-base temperature decreases (and cloud-base height increases), storm-top ice crystals get smaller. A weaker updraft strength is found to have very little effect on ice crystal size.

Lindsey, Daniel T.

119

Ultrasonic Velocity Investigations of Crystal Anisotropy in Deep Ice Cores from Antarctica.  

National Technical Information Service (NTIS)

Ice cores from Byrd Station and Little America V have been used to test an ultrasonic technique for evaluating crystal anisotropy in the Antarctic Ice Sheet. P-wave velocities measured parallel and perpendicular to the vertical axes of cores from the 2164...

H. Kohnen A. J. Gow

1979-01-01

120

Structural basis for antifreeze activity of ice-binding protein from arctic yeast.  

PubMed

Arctic yeast Leucosporidium sp. produces a glycosylated ice-binding protein (LeIBP) with a molecular mass of ?25 kDa, which can lower the freezing point below the melting point once it binds to ice. LeIBP is a member of a large class of ice-binding proteins, the structures of which are unknown. Here, we report the crystal structures of non-glycosylated LeIBP and glycosylated LeIBP at 1.57- and 2.43-? resolution, respectively. Structural analysis of the LeIBPs revealed a dimeric right-handed ?-helix fold, which is composed of three parts: a large coiled structural domain, a long helix region (residues 96-115 form a long ?-helix that packs along one face of the ?-helix), and a C-terminal hydrophobic loop region ((243)PFVPAPEVV(251)). Unexpectedly, the C-terminal hydrophobic loop region has an extended conformation pointing away from the body of the coiled structural domain and forms intertwined dimer interactions. In addition, structural analysis of glycosylated LeIBP with sugar moieties attached to Asn(185) provides a basis for interpreting previous biochemical analyses as well as the increased stability and secretion of glycosylated LeIBP. We also determined that the aligned Thr/Ser/Ala residues are critical for ice binding within the B face of LeIBP using site-directed mutagenesis. Although LeIBP has a common ?-helical fold similar to that of canonical hyperactive antifreeze proteins, the ice-binding site is more complex and does not have a simple ice-binding motif. In conclusion, we could identify the ice-binding site of LeIBP and discuss differences in the ice-binding modes compared with other known antifreeze proteins and ice-binding proteins. PMID:22303017

Lee, Jun Hyuck; Park, Ae Kyung; Do, Hackwon; Park, Kyoung Sun; Moh, Sang Hyun; Chi, Young Min; Kim, Hak Jun

2012-03-30

121

An Experimental Study of the Production of Ice Crystals by a Twin-Turboprop Aircraft  

Microsoft Academic Search

The University of Wyoming King Air (KA) research aircraft was used in controlled, in situ experiments to determine whether or not, and under what cloud and aircraft operating conditions, a twin-turboprop aircraft would itself produce ice crystals during passage through clouds containing supercooled liquid water. Such crystals are termed `Aircraft Produced Ice Particles' (APIPs). Computer-aided, air-relative navigation was used to

Robert D. Kelly; Gabor Vali

1991-01-01

122

Spray-ice islands evaluated for Arctic-drilling structures  

SciTech Connect

Comparisons of spray-ice drilling structures for the Beaufort Sea with drilling structures presently in use there show that over a wide range of water depths drilling from spray-ice islands offers significant benefits over the existing alternatives. Both technical and economic comparisons were made. In a water depth of 50 ft, a gravel island for drilling an exploration hole would likely cost between $40 and $60 million. A spray-ice island in the same location would cost less than $10 million. ''Spray-ice'' as used in this article refers to ice made by pumping sea water high up into the air for rapid heat transfer and freezing. The resulting ice has a granular structure and is quite porous.

Juvkam-Wold, H.C.

1986-04-21

123

Crystal Structure of Ettringite  

Microsoft Academic Search

ETTRINGITE (Ca6[Al(OH)6]2(SO4)3.26H2O) occurs as a natural mineral, and is technically important as a hydration product of Portland and supersulphated cements and in its use, as satin white, for coating paper. It forms hexagonal, prismatic crystals which in synthetic material are often highly elongated. Bannister, Hey and Bernal1 obtained unit-cell data (hexagonal: a 11.26, c 21.48 Å, space group P63\\/mmc, Z

A. Moore; H. F. W. TAYLOR

1968-01-01

124

Spray-ice islands evaluated for Arctic-drilling structures  

Microsoft Academic Search

Comparisons of spray-ice drilling structures for the Beaufort Sea with drilling structures presently in use there show that over a wide range of water depths drilling from spray-ice islands offers significant benefits over the existing alternatives. Both technical and economic comparisons were made. In a water depth of 50 ft, a gravel island for drilling an exploration hole would likely

Juvkam-Wold

1986-01-01

125

Arctic ice shelves and ice islands: Origin, growth and disintegration, physical characteristics, structural-stratigraphic variability, and dynamics  

SciTech Connect

Ice shelves are thick, floating ice masses most often associated with Antarctica where they are seaward extensions of the grounded Antarctic ice sheet and sources of many icebergs. However, there are also ice shelves in the Arctic, primarily located along the north coast of Ellesmere Island in the Canadian High Arctic. The only ice shelves in North America and the most extensive in the north polar region, the Ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands, the tabular icebergs of the Arctic Ocean. The present state of knowledge and understanding of these ice features is summarized in this paper. It includes historical background to the discovery and early study of ice shelves and ice islands, including the use of ice islands as floating laboratories for polar geophysical research. Growth mechanisms and age, the former extent and the twentieth century disintegration of the Ellesmere ice shelves, and the processes and mechanisms of ice island calving are summarized. Surface features, thickness, thermal regime, and the size, shape, and numbers of ice islands are discussed. The structural-stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described. Large-scale and small-scale dynamics of ice islands are described, and the results of modeling their drift and recurrence intervals are presented. The conclusion identifies some unanswered questions and future research opportunities and needs. 97 refs., 18 figs.

Jeffries, M.O. (Univ. of Alaska, Fairbanks (United States))

1992-08-01

126

Experimental investigation of the interactions of hyperactive antifreeze proteins with ice crystals  

NASA Astrophysics Data System (ADS)

Antifreeze proteins (AFPs) evolved in cold-adapted organisms and serve to protect them against freezing cold conditions by arresting ice crystal growth and inhibiting ice recrystallization. The freezing point depression by AFPs is defined as thermal hysteresis (TH) and AFPs are classified as hyperactive (hypAFPs) and moderate according to their TH activities. The mechanism of action of AFPs is not well understood. In particular, it is not clear what determines the concentration dependence of TH and whether the binding of AFP to ice is irreversible. Additionally, it is not known why some types of AFP are hyperactive compared to others and it was suggested that hyperactivity might be related to basal plane affinity of hypAFP to ice. The present study utilizes the techniques of microfluidic devices and fluorescence microscopy to study the interaction of AFPs with ice crystals. With novel temperature controlled microfluidic devices, we showed the accumulation and affinity of hypAFPs on the basal plane of ice. This supports the view that hypAFPs adhere to the basal plane. Additionally, for the first time in literature, small ice crystals of 30-50 mum sizes covered with adsorbed GFP tagged hypAFPs were stabilized in supercooled non-AFP solutions for hours with no observed ice growth in temperature controlled microfluidic devices. Repeated TH experiments of ice crystals incubated in AFP solutions before and after the exchange of liquids in microfluidic devices gave the same TH activity. This finding clarifies our understanding of concentration dependence of TH. Furthermore, we found that hypAFPs protect ice against melting as well as freezing, resulting in superheated ice. Ice crystals were superheated up to 0.5°C above their equilibrium melting temperatures and remained stable in this superheated state for hours. Measurements of fast melting velocities added additional evidence to the observed superheating of ice in AFP solutions. The experimental results of the current study provide strong evidence that AFPs bind to ice surfaces via irreversible binding. We have demonstrated that the use of microfluidics in combination with fluorescence microscopy is a valuable technique to study the binding mechanisms of AFPs and the concentration dependence of AFP activity.

Celik, Yeliz

127

Photonic crystal fiber monitors for intracellular ice formation  

NASA Astrophysics Data System (ADS)

An all-silica steering wheel photonic crystal fiber (SW-PCF) device with real-time analysis for cellular temperature sensing is presented. Results are provided for water-filled SW-PCF fibers experiencing cooling down near -40°C. Cellular temperature sensors with fast response times are of interest particularly to the study of cryopreservation, which has been influential in applications such as tissue preservation, food quality control, genetic engineering, as well as drug discovery and in- vitro toxin testing. Results of this investigation are relevant to detection of intracellular ice formation (IIF) and better understanding cell freezing at very low temperatures. IIF detection is determined as a function of absorption occurring within the core of the SW-PCF. The SW-PCF has a 3.3?m core diameter, 125?m outer diameter and steering wheel-like air hole pattern with triangular symmetry, with a 20?m radius. One end of a 0.6m length of the SW-PCF is placed between two thermoelectric coolers, filled with ~0.1?L water. This end is butt coupled to a 0.5m length of single mode fiber (SMF), the distal end of the fiber is then inserted into an optical spectrum analyzer. A near-IR light source is guided through the fiber, such that the absorption of the material in the core can be measured. Spectral characteristics demonstrated by the optical absorption of the water sample were present near the 1300-1700nm window region with strongest peaks at 1350, 1410 and 1460nm, further shifting of the absorption peaks is possible at cryogenic temperatures making this device suitable for IIF monitoring applications.

Battinelli, Emily; Reimlinger, Mark; Wynne, Rosalind

2012-03-01

128

Enhanced alignment of plate ice crystals in a non-uniform electric field  

Microsoft Academic Search

An atmospheric electric field exerts a torque on both column and plate ice crystals. Columns tend to align along the direction of the field. One diameter of plate crystals also aligns parallel to a field, while a non-uniform diverging field leads to further orientation and proscribes a secondary orientation along the direction of least divergence. A laboratory investigation treats the

T. C. Foster; J. Hallett

2008-01-01

129

Single particle measurements of the chemical composition of cirrus ice residue during CRYSTAL-FACE  

NASA Astrophysics Data System (ADS)

The first real-time, in situ, investigation of the chemical composition of the residue of cirrus ice crystals was performed during July 2002. This study was undertaken on a NASA WB-57F high-altitude research aircraft as part of CRYSTAL-FACE, a field campaign which sought to further our understanding of the relation of clouds, water vapor, and climate by characterizing, among other parameters, anvil cirrus formed about the Florida peninsula. A counter flow virtual impactor (CVI) was used to separate cirrus ice from the unactivated interstitial aerosol particles and evaporate condensed-phase water. Residual material, on a crystal-by-crystal basis, was subsequently analyzed using the NOAA Aeronomy Laboratory's Particle Analysis by Laser Mass Spectrometry (PALMS) instrument. Sampling was performed from 5 to 15 km altitude and from 12° to 28° north latitude within cirrus originating over land and ocean. Chemical composition measurements provided several important results. Sea salt was often incorporated into cirrus, consistent with homogeneous ice formation by aerosol particles from the marine boundary layer. Size measurements showed that large particles preferentially froze over smaller ones. Meteoritic material was found within ice crystals, indicative of a relation between stratospheric aerosol particles and tropospheric clouds. Mineral dust was the dominant residue observed in clouds formed during a dust transport event from the Sahara, consistent with a heterogeneous freezing mechanism. These results show that chemical composition and size are important determinants of which aerosol particles form cirrus ice crystals.

Cziczo, D. J.; Murphy, D. M.; Hudson, P. K.; Thomson, D. S.

2004-02-01

130

Ice rule correlations in stuffed spin ice  

NASA Astrophysics Data System (ADS)

Stuffed spin ice is a chemical variation of a spin ice material like Ho2Ti2O7 in which extra magnetic ions are inserted into the crystal structure. Previous studies have shown that the degree of stuffing has very little effect on the residual entropy in the system, which takes a value very close to the spin ice entropy. We argue, however, that the observation of this entropy does not imply long range coherence of the ice rules, that determine the local spin configurations. We have characterized deviations from the ice rules by means of a polarized neutron diffraction study of a single crystal of Ho2+?Ti2-?O7-?/2 with ? = 0.3. Our results demonstrate that the ice rules in stuffed spin ice are strictly valid only over a relatively short range, and that at longer range stuffed spin ice exhibits some characteristics of a ‘cluster glass’, with a tendency to more conventional ferromagnetic correlations.

Aldus, R. J.; Fennell, T.; Deen, P. P.; Ressouche, E.; Lau, G. C.; Cava, R. J.; Bramwell, S. T.

2013-01-01

131

Abrasion of Concrete by Ice in Arctic Sea Structures.  

National Technical Information Service (NTIS)

In arctic sea regions a concrete sea structure is subjected to heavy mechanical loads near the water level due to the moving ice sheets. The determination of the abrasion depth is based on laboratory tests for measuring ice pressures against protruding ag...

S. Huovinen

1990-01-01

132

Crystal Structure of Bi  

SciTech Connect

The room temperature structures of the two-layer Aurivillius phases Bi{sub 2.5}Me{sub 0.5}Nb{sub 2}O{sub 9} (Me=Na, K) have been refined with the Rietveld method from powder neutron diffraction data ({lambda}=1.470 {angstrom}). They consist of (Bi{sub 2}O{sub 2}){sup 2+} layers interleaved with perovskite (Bi{sub 0.5}Me{sub 0.5}Nb{sub 2}O{sub 7}){sup 2-} (Me=Na, K) slabs. The structures were refined in the orthorhombic space group A2{sub 1}am, Z=4, and the unit cell parameters of the two oxides are a= 5.4937(3), b=5.4571(4), c=24.9169(14) {angstrom} and a=5.5005(8), b=5.4958(8), c=25.2524(16) {angstrom}, respectively. The orthorhombic distortion increases with decreasing Me+ cation size in the perovskite layer (Bi/Me){sup 2+} site and the lone pair electrons from the Bi{sup 3+} cation are influencing the site distortion. This is in agreement with other two-layer Aurivillius phases and originates from bonding requirements depending on size and electronic environment.

Borg, Stefan; Svensson, Goeran

2001-02-15

133

The Growth of Atmospheric Ice Crystals: A Summary of Findings in Vertical Supercooled Cloud Tunnel Studies  

Microsoft Academic Search

Measurements of ice crystal growth under free fall in a generation of vertical supercooled cloud tunnels and some static cloud chambers as well as the related theoretical works are summarized.Growth parameters, that is, mass (m), dimensions, apparent density, and fall velocity (w), show extrema at about 5°, 10°, and 15°C where crystals are predominantly column-needle, isometric, and plate-stellar-dendrite, respectively. Crystal

Norihiko Fukuta; Tsuneya Takahashi

1999-01-01

134

Investigation of nucleation, dynamic growth and surface properties of single ice crystals  

NASA Astrophysics Data System (ADS)

Nucleation, dynamic growth and optical light scattering properties of a fixed single ice crystal have been experimentally characterized in dependence of both, the type of the ice nucleus (IN) and the prevailing thermodynamic conditions. The set up was developed based on the laminar flow tube LACIS (Leipzig Aerosol Cloud Interaction Simulator, Stratmann et al., 2004; Hartmann et al., 2011). The flow tube is equipped with a SID3-type (Small Ice Detector, Kaye et al., 2008) instrument called LISA (LACIS Ice Scattering Apparatus) and an additional optical microscope. For the investigations, a single (IN with a dry size of 2-10 micrometer is attached to a thin glass fiber and positioned within the optical measuring volume of LISA. The fixed particle is exposed to the thermodynamically controlled air flow, exiting the flow tube. Temperature and saturation ratio in the measuring volume can be varied on a time scale of 1-2 s by adjusting the humidified gas flow. Dependent on the thermodynamic conditions, ice nucleation and ice particle growth/shrinkage occur and can be studied. Thereby, the LISA instrument is applied to obtain 2-D light scattering patterns, and the additional optical microscope allows a time dependent visualization of the ice crystal. Both devices together allow to investigate the influence of the thermodynamic conditions on ice particle growth, the particle shape and its surface properties (i.e., its surface roughness, Ulanowski et al., 2011; Ulanowski et al., 2012; Ulanowski et al., 2013)). The thermodynamic conditions in the optical measuring volume have been extensively characterized using a) computational fluid dynamics (CFD) calculations, b) temperature and dew-point measurements, and c) evaluation of droplet and ice particle growth data. Furthermore, we successfully performed condensation freezing and deposition nucleation experiments with ATD (Arizona Test Dust), kaolinite, illite and SnomaxTM (Johnson Controls Snow, Colorado, USA) particles. In the experiments we could prove that different types of IN, as well as different temperatures and saturation ratios result in different growth rates and ice crystal shapes, but also in different surface properties. Regarding on single ice crystal, the surface roughness can also be modified by varying the prevailing thermodynamic conditions. Thereby, the surface roughness tends to increase for growing and to decrease for shrinking particles. Here, we will present current results of the thermodynamic characterization measurements and the ongoing ice crystal growth experiments.

Voigtlaender, Jens; Herenz, Paul; Chou, Cédric; Bieligk, Henner; Clauss, Tina; Niedermeier, Dennis; Ritter, Georg; Ulanowski, Joseph Z.; Stratmann, Frank

2014-05-01

135

laboratory studies on the uptake of organic compounds by ice crystals  

NASA Astrophysics Data System (ADS)

Anthropogenic aerosols produced from biomass burning are known to increase the number of cloud condensation nuclei in the atmosphere at most latitudes. This reduces cloud droplet size, which prevents raindrop formation at shallower levels in the atmosphere. Vertical convection processes force particles and water vapor to rise up to the upper troposphere. At lower temperatures, ice crystals are formed via heterogeneous freezing of supercooled droplets containing particles known as ice nuclei (IN) and/or via condensation of supercooled water onto IN directly from the vapor, followed by freezing. Ice crystals grow by vapor deposition, by collision of supercooled drops with ice particles and by collision of ice crystals. The grown ice crystals melt on their way down and turn into rain. Most of the precipitation falling to the surface at midlatitudes originates as ice. The adsorption of organic gases emitted from fossil fuel combustion like BTEX may alter particle growth and sublimation rates in the atmosphere. This may also change precipitation rates, which impact the climate world-wide. Considering importance of ice in atmospheric science, laboratory studies are carried out to quantify organic vapor adsorption onto ice. At temperatures between 0 and -40^oC, organic gases at ppb gas levels are allowed to adsorb to the surface of ice crystals with surface properties similar to atmospheric ice. For the experiments, a vertical ice chamber (stainless-steel) with 10 different screen inserts (stainless-steel) was constructed. The chamber is 39 cm in length and 10,5 cm in diameter. The size of the stainless-steel mesh of the screens was chosen by the size of the ice crystals and is 0.14 cm. The ice chamber is located inside a 2x2 m walk-in cold chamber. Prior to the addition of the organic gases, the precleaned carrier gas of synthetic air is humidified to ice saturation in the walk-in cold chamber by passing the carrier stream through a 10 m long and 5 cm in diameter aluminum pipe. Resulting super cooled droplets are removed by stainless-steel-wool. The carrier gas is mixed outside the ice chamber in various proportions with a defined gas mixture of 60 different organic compounds. This mixture is allowed to flow through the ice chamber at defined pressures and temperatures. The concentrations of the compounds in the gas phase are determined at the inlet and the outlet of the ice chamber by a mobile GC (AirmoVoc1020). Additionally, the amount of adsorbed compounds is determined by a very sensitive method based on solid-phase-micro-extraction (SPME) followed by GC/FID. The resulting sorption coefficients for different gas concentrations are plotted vs the reciprocal of the absolute temperature for all substances. First results dealing with the adsorption properties of the investigated organic compounds.

Fries, E.; Jaeschke, W.

2003-04-01

136

Cirrus Clouds Millimeter-Wave Reflectivity Comparison with In-Situ Ice Crystal Airborne Data  

Microsoft Academic Search

In an effort to evaluate scattering models for particle size distributions of ice crystals within cirrus clouds, simultaneous data was collected during the Department of Energy (DoE) Atmospheric Radiation Measurement (ARM) Cloud Intensive operational period (Cloud IOP) at the Cloud and Radiation Testbed (CART) site in Lamont, Oklahoma, from the NCAR Video Ice Particle Sampler (VIPS) and UMass 33GHz\\/95GHz Cloud

José Morales; Jorge Trabal; Sandra L. Cruz-Pol; Stephen M. Sekelsky

137

American Mineralogist Crystal Structure Database  

NSDL National Science Digital Library

This database provides access to information on every crystal structure published in the American Mineralogist, the Canadian Mineralogist, European Journal of Mineralogy, and Physics and Chemistry of Minerals, as well as selected datasets from other journals. The data are searchable by mineral name, author, chemistry, cell parameters and symmetry, diffraction pattern, and a general search. There are also lists of minerals represented in the database and authors of publications cited.

Downs, R. T.; Hall-Wallace, M.

138

Crystal alignments in the fast ice of Arctic Alaska  

SciTech Connect

Field observations at 60 sites located in the fast or near-fast ice along a 1200-km stretch of the north coast of Alaska between the Bering Strait and Barter Island have shown that the great majority of the ice samples (95%) exhibit striking c axis alignments within the horizontal plane. In all cases the degree of preferred orientation increased with depth in the ice. Representative standard deviations around a mean direction in the horizontal plane are commonly less than +- 10/sup 0/ for samples collected near the bottom of the ice. At a given site the mean c axis direction X-bar/sub 0/ may vary as much as 20/sup 0/ with vertical location in the ice sheet. The c axis allignments in the nearshore region generally parallel the coast, with strong alignments occurring in the lagoon systems between the barrier islands and the coast and seaward of the barrier islands. In passes between islands and in entrances such as the opening to Kotzebue Sound the alignment is parallel to the channel. Only limited observations are available farther seaward over the inner (10- to 50-m isobaths) and outer (50-m isobath to shelf break) shelf regions. These indicate Ne-SW and E-W alignments, respectively, in the Beaufort Sea north of Prudhoe Bay.

Weeks, W.F.; Gow, A.J.

1980-02-20

139

American Mineralogist Crystal Structure Database  

NSDL National Science Digital Library

The American Mineralogist Crystal Structure Database website, maintained by the Mineralogical Society of America and the Mineralogical Association of Canada and sponsored by the National Science Foundation, "includes every structure published in the American Mineralogist, The Canadian Mineralogist, and the European Journal of Mineralogy." The authors are also currently adding data from Physics and Chemistry of Minerals. Users can search the data by minerals, authors, chemistry, cell parameter and symmetry, or by a simple general search. This no frills website allows users to easily find and download data.

140

From the single-scattering properties of ice crystals to climate prediction: A way forward  

NASA Astrophysics Data System (ADS)

Cirrus is composed of non-spherical ice crystals, and against the blue background of the sky, they appear as tenuous wispy clouds, usually located at altitudes greater than about 6 km. Their spatial and temporal distribution about the Earth's atmosphere is significant. With such distributions, their contributions to the Earth's natural greenhouse effect and hydrological cycle are important. Therefore, it is important that climate models are able to predict the radiative effect of cirrus, as well as their contribution to the total amount of ice mass that occurs in the Earth's atmosphere. However, cirrus is composed of ice crystals that can take on a variety of geometrical shapes, from pristine habits such as hexagonal ice columns, hexagonal ice plates and bullet-rosettes, to highly randomized habits, which may have roughened surfaces and/or air cavities. These habits also aggregate together, to form chains of aggregates and compact aggregates. The sizes of these habits may also vary, from about less than 10 ?m, to several cm, with the smaller ice crystals usually existing toward cloud-top and the larger ice crystals existing toward the cloud-bottom. Due to this variability of geometrical complexity, size, and ice mass, predicting the magnitude of the cirrus greenhouse effect has proven problematic. To try to constrain these radiative and hydrological uncertainties, since about 2006 there is now available the A-train constellation of satellites, which attempt to quantify the radiative and hydrological contributions of cirrus to the Earth's atmosphere. The A-train obtains nearly simultaneous measurements of cirrus from across the electromagnetic spectrum. Such simultaneous measurements pose challenges for theoretical scattering models of cirrus, as these models must conserve ice mass and be physically consistent across the electromagnetic spectrum. In this review paper, the microphysical properties of cirrus are summarized. The current idealized habit mixture models that have been proposed to represent the observed variability in ice crystal shape, size and mass are discussed. The theoretical light scattering methods that are currently applied to the idealized habit mixture models to solve for their scattering and absorption properties are discussed. The physical inconsistency of the current approach to parameterize the bulk scattering and absorption properties of cirrus in climate models is highlighted. An alternative parameterization, which couples cloud physics more directly with radiation, is proposed. Such a coupling is required, if climate models are to be physically consistent and radiatively interactive.

Baran, Anthony J.

2012-08-01

141

Formation and structure of refrozen cracks in land-fast first-year sea ice  

NASA Astrophysics Data System (ADS)

This study characterizes the healing process and structure of undeformed, linear, parallel-sided, flooded cracks in land-fast sea ice. Field investigations and refreezing experiments were performed in McMurdo Sound, Ross Sea, Antarctica, between 1998 and 2002. Data from a two-dimensional thermistor array are used to show that the ice-water interface of freezing cracks is arch-shaped due to bidirectional heat flow to the surrounding ice cover and to the atmosphere. Ice growing laterally into the crack is found to desalinate over a prolonged period of time, until the isotherms are approximately horizontal. Superposition of heat flow to the atmosphere and to the host sea ice sheet allows the refreezing progress to be modeled analytically. Close to the ice-air interface, the salinity is higher at the sides of wide refrozen cracks than it is at the center. However, deeper down and in narrower cracks in general, the salinity is higher at the center than at the sides. A finite volume, computational fluid dynamics (CFD) model reproduces the generally arch-shaped alignment of brine pockets. This pattern is attributed to convection in the mushy layer. Crystals are found to grow upstream into the crack due to a salinity gradient in the buoyant convective flow.

Petrich, Chris; Langhorne, Pat J.; Haskell, Tim G.

2007-04-01

142

The crystal structure of dynamin  

PubMed Central

Dynamin-related proteins (DRPs) are multi-domain GTPases that function via oligomerization and GTP-dependent conformational changes to play central roles in regulating membrane structure across phylogenetic kingdoms. How DRPs harness self-assembly and GTP-dependent conformational changes to remodel membranes is not understood. Here we present the crystal structure of an assembly-deficient mammalian endocytic DRP, dynamin 1, lacking the proline-rich domain, in its nucleotide-free state. The dynamin 1 monomer is an extended structure with the GTPase domain and bundle signalling element positioned on top of a long helical stalk with the pleckstrin homology domain flexibly attached on its opposing end. Dynamin 1 dimer and higher order dimer multimers form via interfaces located in the stalk. Analysis of these interfaces provides insight into DRP family member specificity and regulation and provides a framework for understanding the biogenesis of higher order DRP structures and the mechanism of DRP-mediated membrane scission events.

Ford, Marijn G. J.; Jenni, Simon; Nunnari, Jodi

2014-01-01

143

Shear induced structures in crystallizing cocoa butter  

Microsoft Academic Search

Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear

Gianfranco Mazzanti; Sarah E. Guthrie; Eric B. Sirota; Alejandro G. Marangoni; Stefan H. J. Idziak

2004-01-01

144

A Model to Assess the Risk of Ice Accretion Due to Ice Crystal Ingestion in a Turbofan Engine and its Effects on Performance  

NASA Technical Reports Server (NTRS)

The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that were attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was one or more of the following anomalies: degraded engine performance, engine roll back, compressor surge and stall, and flameout of the combustor. The main focus of this research is the development of a computational tool that can estimate whether there is a risk of ice accretion by tracking key parameters through the compression system blade rows at all engine operating points within the flight trajectory. The tool has an engine system thermodynamic cycle code, coupled with a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor blade rows. Assumptions are made to predict the complex physics involved in engine icing. Specifically, the code does not directly estimate ice accretion and does not have models for particle breakup or erosion. Two key parameters have been suggested as conditions that must be met at the same location for ice accretion to occur: the local wet-bulb temperature to be near freezing or below and the local melt ratio must be above 10%. These parameters were deduced from analyzing laboratory icing test data and are the criteria used to predict the possibility of ice accretion within an engine including the specific blade row where it could occur. Once the possibility of accretion is determined from these parameters, the degree of blockage due to ice accretion on the local stator vane can be estimated from an empirical model of ice growth rate and time spent at that operating point in the flight trajectory. The computational tool can be used to assess specific turbine engines to their susceptibility to ice accretion in an ice crystal environment.

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

2013-01-01

145

On the Importance of Small Ice Crystals in Tropical Anvil Cirrus  

NASA Technical Reports Server (NTRS)

In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (< 50 m diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small ]crystals could be artifacts of large ]crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2 ] Dimensional Stereo (2D ]S) probe, which detects particles as small as 10 m. The 2D ]S has detector "arms" instead of an inlet tube. Since the 2D ]S probe surfaces are much further from the sample volume than is the case for the instruments with inlets, it is expected that 2D ]S will be less susceptible to shattering artifacts. In addition, particle inter ]arrival times are used to identify and remove shattering artifacts that occur even with the 2D ]S probe. The number of shattering artifacts identified by the 2D ]S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small ]crystal concentration. The 2D ]S measurements in tropical anvil cirrus suggest that natural small ]crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D ]S ratio of small ]crystal concentrations and large ]crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D ]S large ]crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large ]crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D ]S contribute relatively little cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D ]S ice concentrations in fresh anvil cirrus may often exceed 1 cm.3, and are observed to exceed 10 cm.3 in turrets, they are typically 0.1 cm.3 and rarely exceed 1 cm.3 (<1.4% of the time) in aged anvil cirrus. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus may be caused by ice nucleation driven by either small ]scale convection or gravity waves. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC ]4.

Jensen, E. J.; Lawson, P.; Baker, B.; Pilson, B.; Mo, Q.; Heymsfield, A. J.; Bansemer, A.; Bui, T. P.; McGill, M.; Hlavka, D.; Heymsfield, G.; Platnick, S.; Arnold, G. T.; Tanelli, S.

2009-01-01

146

Elemental composition and morphology of ice-crystal residual particles in cirrus clouds and contrails  

Microsoft Academic Search

Aircraft sampling of residual particles from evaporated ice crystals was performed using a Counterflow Virtual Impactor. Samples of crystals taken in both contrails and cirrus clouds were compared with interstitial aerosols found in natural cirrus. The samples were analyzed with a scanning electron microscope which was equipped with a windowless energy-dispersive X-ray detector (SEM\\/EDX). In the contrail and cirrus cases

A Petzold; J Ström; S Ohlsson; F. P Schröder

1998-01-01

147

Crystal growth of spin-ice pyrochlores by the floating-zone method  

Microsoft Academic Search

Single crystals of RE2Ti2O7 (RE=Y, Tb, Dy and Ho) have been grown by the floating-zone technique in an image furnace in a controlled atmosphere. The effect of annealing the crystals in different atmospheres was studied and found to be very important. Small amounts of Y were doped on the Dy site to study its effect on the spin-ice behaviour. Results

D. Prabhakaran; A. T. Boothroyd

2011-01-01

148

Single particle measurements of the chemical composition of cirrus ice residue during CRYSTAL-FACE  

Microsoft Academic Search

The first real-time, in situ, investigation of the chemical composition of the residue of cirrus ice crystals was performed during July 2002. This study was undertaken on a NASA WB-57F high-altitude research aircraft as part of CRYSTAL-FACE, a field campaign which sought to further our understanding of the relation of clouds, water vapor, and climate by characterizing, among other parameters,

D. J. Cziczo; D. M. Murphy; P. K. Hudson; D. S. Thomson

2004-01-01

149

Structural Transitions in Amorphous Water Ice and Astrophysical Implications  

Microsoft Academic Search

Selected area electron diffraction is used to monitor structural changes of vapor-deposited water ice in vacuum during warm-up from 15 to 188 K. A progression of three amorphous forms of water ice is found with well-defined transitions. The formation of a high-density amorphous form (I_ah) at 15 K is confirmed, and the transition to the more familiar low-density form (I_aI)

Peter Jenniskens; David F. Blake

1994-01-01

150

Crystal Structure of Human ?-Galactosidase  

PubMed Central

GM1 gangliosidosis and Morquio B are autosomal recessive lysosomal storage diseases associated with a neurodegenerative disorder or dwarfism and skeletal abnormalities, respectively. These diseases are caused by deficiencies in the lysosomal enzyme ?-d-galactosidase (?-Gal), which lead to accumulations of the ?-Gal substrates, GM1 ganglioside, and keratan sulfate. ?-Gal is an exoglycosidase that catalyzes the hydrolysis of terminal ?-linked galactose residues. This study shows the crystal structures of human ?-Gal in complex with its catalytic product galactose or with its inhibitor 1-deoxygalactonojirimycin. Human ?-Gal is composed of a catalytic TIM barrel domain followed by ?-domain 1 and ?-domain 2. To gain structural insight into the molecular defects of ?-Gal in the above diseases, the disease-causing mutations were mapped onto the three-dimensional structure. Finally, the possible causes of the diseases are discussed.

Ohto, Umeharu; Usui, Kimihito; Ochi, Toshinari; Yuki, Kenjiro; Satow, Yoshinori; Shimizu, Toshiyuki

2012-01-01

151

Crystallization of amorphous ice as the cause of Comet P/Halley's outburst at 14 AU  

NASA Technical Reports Server (NTRS)

An explanation is provided for the postperihelion eruption of Comet P/Halley, detected in February 1991 and believed to have started three months earlier, namely, the crystallization of amorphous ice taking place in the interior of the porous nucleus, at depths of a few tens of meters, accompanied by the release of trapped gases. Numerical calculations show that for a bulk density of 0.5 g/cu cm and a pore size of 1 micron crystallization occurs on the outbound leg of Comet P/Halley's orbit, at heliocentric distances between 5 AU and 17 AU. The trapped gas is released and flows to the surface through the porous medium. It may also open wider channels, as the internal pressures obtained surpass the tensile strength of cometary ice. The outflowing gas carries with it grains of ice and dust, and thus can explain the large amounts of dust observed in the coma at 14.3 AU and beyond.

Prialnik, D.; Bar-Nun, A.

1992-01-01

152

Flow in Polycrystalline Ice  

NSDL National Science Digital Library

This is a virtual journal article about polycrystalline ice. It focuses on plastic deformation, specific flow characteristics and crystallographic preferred orientations associated with polycrystalline ice within glaciers. Part I covers Polycrystalline aggregates deformed in pure-shear; Dynamic recrystallisation; Grain shape and preferred orientation change; Fabric; Evolution of glacial ice during deformation. Part II covers: Time lapse photography; Glaciers; Dislocations; Bernal-Fowler rule; Generation of defect structures; Crystal structure; Ice; Basal glide; Strain rate for glide on basal systems; Critical resolved shear stress; Non-basal glide; Diffusional flow; Plastic deformation; Primary creep; Secondary creep; Tertiary creep; Deformation maps; Grain growth; Grain size reduction; Anisotropic flow law for ice.

Wilson, Chris

153

The effects of small ice crystals on cirrus infrared radiative properties  

NASA Technical Reports Server (NTRS)

Using a model that combines single-scattering properties for spheroidal and hexagonal ice crystals, the thermal infrared radiative properties of cirrus clouds have been investigated. Infrared scattering and absorption properties for randomly oriented spheroids and hexagons are parameterized based on the anomalous diffraction theory and a geometric ray-tracing method, respectively. Using observed ice crystal size distributions, upwelling radiances at the top of cirrus cloudy atmospheres have been computed. Results show that the presence of small ice crystals can produce significant brightness temperature differences between two infrared wavelengths in the 10-micron window. Theoretical results have been compared with observed brightness temperature differences between 8.35 and 11.16 microns and between 11.16 and 12 microns. The observed values were obtained from the high-spectral resolution interferometer sounder. It is shown that the use of the present nonspherical model for ice crystals in radiative transfer calculations leads to a significantly better interpretation of the observed data than does the use of the spherical model.

Takano, Y.; Liou, K. N.; Minnis, P.

1992-01-01

154

Initial stages in the morphological evolution of vapour-grown ice crystals: A laboratory investigation  

Microsoft Academic Search

SUMMARY We describe experiments to investigate the érst stages in the evolution of small (100-200 ?m) ice crystals levitated in air at temperatures and humidities characteristic of fully glaciated stratiform clouds. We é nd that in these conditions particle morphology is not uniquely determined by environmental temperature and humidity as has commonly been assumed; other parameters, such as the mode

Neil J. Bacon; Marcia B. Baker; Brian D. Swanson

2003-01-01

155

Depolarization of lidar returns by small ice crystals: An application to contrails  

Microsoft Academic Search

Measurements of the lidar linear depolarization ratio delta can be a powerful remote sensing technique for characterizing the microphysics of contrail particles. Since young contrails often consist of relatively small ice crystals, the quantitative interpretation of lidar measurements requires accurate theoretical computations of delta for polydisperse, randomly oriented nonspherical particles with size parameters ranging from zero to at least several

Michael I. Mishchenko; Kenneth Sassen

1998-01-01

156

American Mineralogist Crystal Structure Database  

NSDL National Science Digital Library

This database includes the crystal structure for every mineral published in the American Mineralogist, The Canadian Mineralogist, European Journal of Mineralogy and Physics, and Chemistry of Minerals. Data is now being imported from Acta Crystallographica as well. The database is maintained under the care of the Mineralogical Society of America and the Mineralogical Association of Canada. The data can be displayed or downloaded and are searchable by mineral, author, mineral chemistry, unit cell parameters and symmetry, diffraction pattern, or a general search. Links are provided to additional information and to crystallographic software.

157

The crystal structure of levyne  

Microsoft Academic Search

Summary Levyne, Ca2·7Na0·7K0·2[Al6·3Si11·7O36] · 16.7 H2O, is rhombohedral, space group\\u000a$$R\\\\bar 3m$$\\u000a,ahex=13.338 andchex=23.014 Å. Its crystal structure is built up of layers of single and double six-membered rings of (Si, Al) O4 tetrahedra stacked according the model suggested fifteen years ago byBarrer andKerr. Cations are all disposed along the symmetry axis inside the levyne cage. One particular site is

S. Merlino; E. Galli; A. Alberti

1975-01-01

158

A global classification of snow crystals, ice crystals, and solid precipitation based on observations from middle latitudes to polar regions  

NASA Astrophysics Data System (ADS)

This paper presents an extensive revision of Magono and Lee's (1966) classification of natural snow crystals, which has been widely used in snow and ice studies to describe snow crystal shapes. The new classification catalogs snow crystals and other solid precipitation particles into 121 categories, in contrast to Magono and Lee's 80 categories. Of these, 28 categories were created to classify new types of snow crystals that have been discovered in polar regions since 1968, seven were created after reconsidering the original categories, and six categories were created to classify solid precipitation particles such as frozen cloud particles and small raindrops. Because our observational area extended from middle latitudes (Japan) to polar regions, we refer to our new classification scheme as 'global-scale classification' or 'global classification'. The global classification consists of three levels - general, intermediate, and elementary - which are composed of 8, 39, and 121 categories, respectively. This paper describes the characteristics of each type of snow crystal, ice crystal, and solid precipitation particle.

Kikuchi, Katsuhiro; Kameda, Takao; Higuchi, Keiji; Yamashita, Akira

2013-10-01

159

Nonlinear Phononic Periodic Structures and Granular Crystals.  

National Technical Information Service (NTIS)

In this chapter we describe the dynamic response of nonlinear phononic structures, focusing on granular crystals as the most prominent example. The chapter begins with a brief history of nonlinear lattices and with an introduction to granular crystals. It...

C. Daraio G. Theocharis N. Boechler

2012-01-01

160

The structural consequences of calcium crystal deposition.  

PubMed

Calcium pyrophosphate dihydrate and basic calcium phosphate (BCP) crystals are the most common calcium-containing crystals associated with rheumatic disease. Clinical manifestations of calcium crystal deposition include acute or chronic inflammatory and degenerative arthritides and certain forms of periarthritis. The intra-articular presence of BCP crystals correlates with the degree of radiographic degeneration. Calcium crystal deposition contributes directly to joint degeneration. Vascular calcification is caused by the deposition of calcium hydroxyapatite crystals in the arterial intima. These deposits may contribute to local inflammation and promote further calcification, thus aggravating the atherosclerotic process. Calcium crystal deposition results in substantial structural consequence in humans. PMID:24703349

Durcan, Laura; Bolster, Ferdia; Kavanagh, Eoin C; McCarthy, Geraldine M

2014-05-01

161

Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds  

NASA Astrophysics Data System (ADS)

The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number: Da = kh/D, where h is the width of the 2D calculation domain. Varying the nondimensional Da in the model is equivalent to varying the scale (h) in the model. Our calculations confirm that the crystal/vapor isotopic fractionation approaches the equilibrium value, and the crystals are compact (circular in 2D) as the saturation factor approaches unity (S= 1.0). At higher oversaturation (e.g. S = 1.2), dendritic crystals of millimeter size develop on timescales appropriate to cloud processes, the isotopic fractionations are dominated by kinetic effects, and similar to those predicted by the spherical diffusion model. Dendritic crystals are constrained to be relatively large, with dimension much greater than D/k. The most difficult aspect of the modeling is to account for the large density difference between air and ice, which requires us to use a fictitious higher density for the vapor-oversaturated air and scale the crystal growth time accordingly. A different approach, using a larger scale simulation to derive boundary conditions for a nested smaller scale calculation is in progress. The results to date clarify the controls on dendritic crystal growth, the relationships between saturation state, growth rate, crystal morphology and isotopic fractionation, and provide limits on the value of the accommodation coefficient.

Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.

2006-12-01

162

Characteristic of the ice crystal scattering database for GCOMC/SGLI satellite mission  

NASA Astrophysics Data System (ADS)

In this study, we developed the ice crystal scattering database for ice cloud remote sensing and radiative transfer calculation of the Global Change Observation Mission (GCOMC)/Second Generation Global Imager (SGLI) satellite mission using light scattering methods of the LIght Scattering solver Applicable to particles of arbitrary Shape (LISAS)/ Geometrical-Optics Approximation (GOA), Surface Integral Equations Method of Müller-type (SIEMM), Finite-Difference Time Domain (FDTD), and Improved Geometrical-Optics Method (IGOM). The GCOMC/SGLI mission measures essential geophysical parameters on the Earth's surface and in the atmosphere to facilitate understanding of the global radiation budget, which is scheduled to launch in around 2014 by the JAXA. Computing time and retrieval error of the effective particle radius is a main subject for developing the ice crystal scattering database for GCOMC satellite mission. For developing the suitable database, it is important to optimize the light scattering database based on the specification of the satellite sensor. There are two approaches to optimize a light scattering database: optimizing the complex refractive index grid system and optimizing the wavelength bin for a specific sensor channel. In the former method, a suitable grid system is determined by investigating the radiance error of radiative transfer calculations caused by differing fineness of step size of the complex refractive index. This study focuses on the former case. The grid system of the complex refractive index in the 1.6-?m (SW3) channel of the GCOMC/SGLI satellite sensor was investigated for optimizing the ice crystal scattering database. This grid system is separated into twelve patterns according to the step size of the real and imaginary parts of the refractive index. Specifically, the LISAS/ GOA technique is used to simulate the scattering of light by randomly oriented large hexagonal ice crystals. The difference of radiance with different ice cloud optical thickness and step size of the refractive index is calculated from developed light scattering database using the radiative transfer (R-STAR) solver. The results indicated that the step size of the real part is a significant factor in the difference of radiance. Furthermore, retrieval error of the effective particle radius caused by the sensor noise and error caused by refractive index grid system are investigated. Result indicated that, when step size of the real part is 0.04 with ice cloud optical thickness 8, total error of the effective particle radius is generally smaller than 2-?m. Hence, optimization of the refractive index in the SGLI channel is a significant step toward developing a suitable light scattering database for non-spherical ice crystals. Based on the above result, we developed the ice crystal scattering database for GCOMC satellite mission. Characteristic of the ice crystal scattering database for GCOMC/SGLI was investigated finally. Keywords: GCOMC/SGLI, ice crystal, light scattering method, effective particle radius

Letu, H.; Nakajima, T. Y.; Nagao, T. M.

2012-12-01

163

Ice Rheology Beyond Planet Earth  

Microsoft Academic Search

Barclay Kamb is well known for his seminal work on the motions and internal flow of glaciers, but he was also a pioneer in research on the crystal structures, chemical bonding, and rheologies of the high-pressure phases of ice. In the flow and fracture of terrestrial materials, no rock is more studied than ice. Water ice also has an important

W. B. Durham; S. H. Kirby; L. A. Stern

2001-01-01

164

Model Testing of Structures in Ice: Consideration of Scale Effects.  

National Technical Information Service (NTIS)

The question posed of confidence and scale factor effects of ice model tests is complex. Modelling of the structure is not always straightforward, but in most cases a good representation of the prototype structure can be built. The properties of refrigera...

G. W. Timco

1983-01-01

165

Elementary steps at the surface of ice crystals visualized by advanced optical microscopy  

PubMed Central

Due to the abundance of ice on earth, the phase transition of ice plays crucially important roles in various phenomena in nature. Hence, the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. In this study we demonstrate, by laser confocal microscopy combined with differential interference contrast microscopy, that elementary steps (the growing ends of ubiquitous molecular layers with the minimum height) of ice crystals and their dynamic behavior can be visualized directly at air-ice interfaces. We observed the appearance and lateral growth of two-dimensional islands on ice crystal surfaces. When the steps of neighboring two-dimensional islands coalesced, the contrast of the steps always disappeared completely. We were able to discount the occurrence of steps too small to detect directly because we never observed the associated phenomena that would indicate their presence. In addition, classical two-dimensional nucleation theory does not support the appearance of multilayered two-dimensional islands. Hence, we concluded that two-dimensional islands with elementary height (0.37 and 0.39 nm on basal and prism faces, respectively) were visualized by our optical microscopy. On basal and prism faces, we also observed the spiral growth steps generated by screw dislocations. The distance between adjacent spiral steps on a prism face was about 1/20 of that on a basal face. Hence, the step ledge energy of a prism face was 1/20 of that on a basal face, in accord with the known lower-temperature roughening transition of the prism face.

Sazaki, Gen; Zepeda, Salvador; Nakatsubo, Shunichi; Yokoyama, Etsuro; Furukawa, Yoshinori

2010-01-01

166

Arctic ice island and sea ice movements and mechanical properties: Fourteenth quarterly report, 1 January 1987-31 March 1987. [Sea spray ice bonds to offshore structures  

SciTech Connect

The research program on ice islands has four elements: (1) through the use of satellite imagery, historical records, and aerial photography, to establish a time history of all of the Arctic ice shelves, and thus an historically verified source for ice islands; (2) to establish postioning buoys on the known existing ice islands to track their trajectories daily and to telemeter daily barometer pressure and temperature, via System Argos; (3) to calculate geostrophic winds from global pressure maps and barometric pressure data from the buoys, and relate the observed ice island trajectories to the winds and the internal pack ice forces; (4) to construct a model for ice island motion which will enable a determination of the probability of interaction between ice islands and offshore structures, and which will be verified by comparsion with the experimentally observed trajectory data. Research activities covered in the fourteenth quarter include; ice islands (buoy operation and ice island motion); and mechanical properties of sea spray ice bonds to structures. 2 figs., 6 tabs.

Sackinger, W.M.; Jeffries, M.O.

1987-01-01

167

Functional evaluation of candidate ice structuring proteins using cell-free expression systems.  

PubMed

Ice structuring proteins (ISPs) protect organisms from damage or death by freezing. They depress the non-equilibrium freezing point of water and prevent recrystallization, probably by binding to the surface of ice crystals. Many ISPs have been described and it is likely that many more exist in nature that have not yet been identified. ISPs come in many forms and thus cannot be reliably identified by their structure or consensus ice-binding motifs. Recombinant protein expression is the gold standard for proving the activity of a candidate ISP. Among existing expression systems, cell-free protein expression is the simplest and gives the fastest access to the protein of interest, but selection of the appropriate cell-free expression system is crucial for functionality. Here we describe cell-free expression methods for three ISPs that differ widely in structure and glycosylation status from three organisms: a fish (Macrozoarces americanus), an insect (Dendroides canadensis) and an alga (Chlamydomonas sp. CCMP681). We use both prokaryotic and eukaryotic expression systems for the production of ISPs. An ice recrystallization inhibition assay is used to test functionality. The techniques described here should improve the success of cell-free expression of ISPs in future applications. PMID:23195406

Brödel, A K; Raymond, J A; Duman, J G; Bier, F F; Kubick, S

2013-02-10

168

Simulations of Photonic Crystal and Dielectric Structures  

SciTech Connect

Dielectric materials and photonic crystal structures have electromagnetic properties that could potentially offer great benefits for accelerators. Computer simulation plays a critical role in designing, understanding, and optimizing these structures, especially the non-intuitive photonic crystal structures for which there is no relevant zeroth-order analytic model.

Werner, G. R. [Center for Integrated Plasma Studies, University of Colorado, Boulder, CO 80309 (United States)

2010-11-04

169

Antifreeze protein modulates cell survival during cryopreservation: mediation through influence on ice crystal growth.  

PubMed

Antifreeze proteins (AFPs) are extremely efficient at inhibiting ice recrystallization in frozen solutions. Knight and Duman [Knight, C. A. & Duman, J. G. (1986) Cryobiology 23, 256-263] have proposed that this may be an important function of the proteins in freeze-tolerant organisms. We have tested this proposal in vitro by characterizing the influence of AFP on the recovery of cryopreserved cells, which often can survive cooling and yet subsequently be damaged by ice crystal growth during warming. Relatively low concentrations (e.g., 5-150 micrograms/ml) of winter flounder (Pseudopleuronectes americanus) AFP enhance survival of red blood cells cryopreserved in hydroxyethyl starch solutions. This effect is most apparent in samples warmed at suboptimal rates, i.e., where ice recrystallization would be exaggerated. Cryomicroscopy demonstrates that AFP inhibits ice recrystallization in the extracellular regions during the latter stages of the warming cycle. AFP concentrations that enhance survival of red cells confer partial inhibition of recrystallization. Relatively high concentrations of AFP (e.g., 1.54 mg/ml) are much more effective at inhibiting extracellular recrystallization. However, extensive growth of ice around the cell, and concomitant cell damage, is noted. The mechanism for this AFP-induced ice growth is unknown. We propose that there is a delicate balance between AFP-induced enhancement of cell preservation and AFP-induced enhancement of cell preservation and AFP-induced enhancement of cell damage and that this balance hinges on the degrees of inhibition of ice recrystallization and of preferential growth of ice around the cells. We conclude that, under appropriate conditions, one of the proposed functions of AFPs in nature can be emulated, and perhaps have application, in cryopreservation of materials of biomedical interest. PMID:1409591

Carpenter, J F; Hansen, T N

1992-10-01

170

Single-scattering of preferentially oriented ice crystals at centimeter and millimeter wavelengths  

NASA Astrophysics Data System (ADS)

The scattering properties of frozen cloud and precipitation particles at centimeter and millimeter wavelengths are fundamental for active and passive microwave remote sensing. So far the scattering parameters (scattering-, absorption-, and backscattering cross sections as well as asymmetry factor) have been calculated for randomly oriented particles only. However, some particle types, especially planar crystals, exhibit a preferred horizontal orientation. In this study the scattering and absorption parameters of four different planar ice crystal types have been modeled and exemplarily calculated from 1 GHz to 300 GHz with a freely available software code implementing the Discrete Dipole Approximation (DDA). It is presented how scattering and absorption of horizontally oriented ice crystals turn out for nadir-looking and inclined satellite sensors. The results show that small deviations around the horizontal orientation, as they are reported by relevant papers on cloud microphysics, have only marginal influence. Among all scattering parameters, the backscattering cross section of oriented crystals can differ most with respect to a random orientation. Especially if the incident wave direction is normal to the basal face, the parameter was found to be up to 20 times higher. Therefore the consideration of the orientation especially can be important for active microwave sensors. The more so if horizontally oriented particles and a nadir looking active sensor are involved. Furthermore the existing compilations for the index of refraction of ice at microwave frequencies have been reviewed.

Teschl, F.; Randeu, W. L.; Teschl, R.

2013-01-01

171

Characterizing Single-Scattering Properties of Non-Spherical Ice-Crystal Ensembles  

NASA Astrophysics Data System (ADS)

Retrievals of atmospheric particulate constituents using remote sensing means rely on the characterization of the single-scattering properties of these particulate matters. We are able to characterize with fairly high accuracies the single-scattering properties involving spherical particles, due to the symmetry of their shape. For example, it has been demonstrated that liquid water content, effective radius, and effective variance adequately characterize the single-scattering of an ensemble of spherical cloud water droplets in the visible and near-infrared wavelengths (Hansen and Travis 1974). Such is not the case, however, for non-spherical particles such as ice crystals. In order to characterize the scattering of these non-spherical particles we need to first find realistic representations of their shapes. The Snowfake (Gravner and Griffeath 2009) model is a numerical growth model for ice crystals based on diffusion and vapor deposition. It is capable of “growing” realistic ice crystals with the exquisite fine features observed in nature. Before the advent of Snowfake, single-scattering calculations are performed on shapes described by simplified mathematical formulae, which bear only a rough resemblance to the real ones. With crystals “grown” by the Snowfake model we can be more confident with the representativeness of the single-scattering properties obtained. Single-scattering properties of these particles are calculated using the open-source DDSCAT software developed by Draine and Flatau (2008), based on discrete dipole approximation (DDA). In this presentation we report early results obtained from the effort of characterizing the single-scattering of ensembles of pristine ice crystals using geometric parameters derived from the particle size distribution (PSD) of the ensembles at the wavelengths of current spaceborne radars.

Kuo, K.; Han, Q.; Smith, E. A.

2009-12-01

172

Solvation structure of ice-binding antifreeze proteins  

NASA Astrophysics Data System (ADS)

Antifreeze proteins (AFPs) can be found in organisms which survive at subzero temperatures. They were first discovered in polar fishes since the 1950's [1] and have been isolated meanwhile also from insects, plants, and bacteria. While AFPs shift the freezing point of water below the bulk melting point and hence can prevent recrystallization; the effect is non-colligative and there is a pronounced hysteresis between freezing and melting. For many AFPs it is generally accepted that they function through an irreversible binding to the ice-water interface which leads to a piecewise convex growth front with a lower nonequilibrium freezing point due to the Kelvin effect. Recent molecular dynamics simulations of the AFP from Choristoneura fumiferana reveal that the solvation structures of water at ice-binding and non-ice-binding faces of the protein are crucial for understanding how the AFP binds to the ice surface and how it is protected from being overgrown [2]. We use density functional theory of classical fluids in order to assess the microscopic solvent structure in the vicinity of protein faces with different surface properties. With our method, binding energies of different protein faces to the water-ice-interface can be computed efficiently in a simplified model. [1] Y. Yeh and R.E. Feeney, Chem. Rev. 96, 601 (1996). [2] D.R. Nutt and J.C. Smith, J. Am. Chem. Soc. 130, 13066 (2008).

Hansen-Goos, Hendrik; Wettlaufer, John

2009-03-01

173

Pack-Ice Studies in the Arctic Ocean  

Microsoft Academic Search

The annual stratification of pack ice has been examined. Summer layers are formed either by arrested growth or by thin layers of fresh-water ice. The crystal structure and the salt content of the ice reflect the seasonal cycle. During the growth of ice a pro- nounced orientation of crystalline structure develops; it is determined by vertical as well as by

W. Schwarzacher

1959-01-01

174

Physics of Ice and Snow as Affects Thermal Pressure.  

National Technical Information Service (NTIS)

The physics of ice affects the development and magnitude of thermal ice pressures on lakes and restricted areas of the sea. The crystal structure of ice, the structure of ice covers and snow are related to physical and mechanical properties. Properties ac...

L. Bergdahl

1977-01-01

175

Structure-based characterization and antifreeze properties of a hyperactive ice-binding protein from the Antarctic bacterium Flavobacterium frigoris PS1.  

PubMed

Ice-binding proteins (IBPs) inhibit ice growth through direct interaction with ice crystals to permit the survival of polar organisms in extremely cold environments. FfIBP is an ice-binding protein encoded by the Antarctic bacterium Flavobacterium frigoris PS1. The X-ray crystal structure of FfIBP was determined to 2.1?Å resolution to gain insight into its ice-binding mechanism. The refined structure of FfIBP shows an intramolecular disulfide bond, and analytical ultracentrifugation and analytical size-exclusion chromatography show that it behaves as a monomer in solution. Sequence alignments and structural comparisons of IBPs allowed two groups of IBPs to be defined, depending on sequence differences between the ?2 and ?4 loop regions and the presence of the disulfide bond. Although FfIBP closely resembles Leucosporidium (recently re-classified as Glaciozyma) IBP (LeIBP) in its amino-acid sequence, the thermal hysteresis (TH) activity of FfIBP appears to be tenfold higher than that of LeIBP. A comparison of the FfIBP and LeIBP structures reveals that FfIBP has different ice-binding residues as well as a greater surface area in the ice-binding site. Notably, the ice-binding site of FfIBP is composed of a T-A/G-X-T/N motif, which is similar to the ice-binding residues of hyperactive antifreeze proteins. Thus, it is proposed that the difference in TH activity between FfIBP and LeIBP may arise from the amino-acid composition of the ice-binding site, which correlates with differences in affinity and surface complementarity to the ice crystal. In conclusion, this study provides a molecular basis for understanding the antifreeze mechanism of FfIBP and provides new insights into the reasons for the higher TH activity of FfIBP compared with LeIBP. PMID:24699650

Do, Hackwon; Kim, Soon Jong; Kim, Hak Jun; Lee, Jun Hyuck

2014-04-01

176

Ice  

NSDL National Science Digital Library

When a chunk of ice "twice the size of Manhattan" broke away from the northernmost part of the Antarctic Peninsula in February, ice was at the forefront of scientific news. Now, with the spectacular discovery of bacteria in Antarctic ice and with new evidence of slush beneath the frozen surface of Jupiter's moon Europa, water in its frozen form is once again in the news. The discovery of living organisms in the Antarctic ecosystem, described in the June 26, 1998 issue of Science, is significant because it presents a model for "how life may have arisen and persisted on other worlds." Scientists speculate that if organisms can thrive in the hard ice of Antarctica, they may possibly have done so on Europa and Mars. Galileo's closest approach to Europa occurred on July 21, 1998, offering new images of ice in space. The nine sites listed offer insights and details of the recent findings and discoveries related to ice.

Harris, Kathryn L.

177

Chemical Characterization of Individual Particles and Residuals of Cloud Droplets and Ice Crystals Collected On Board Research Aircraft in the ISDAC 2008 Study  

SciTech Connect

Although it has been shown that size of atmospheric particles has a direct correlation with their ability to act as cloud droplet and ice nuclei, the influence of composition of freshly emitted and aged particles in nucleation processes is poorly understood. In this work we combine data from field measurements of ice nucleation with chemical imaging of the sampled particles to link aerosol composition with ice nucleation ability. Field measurements and sampling were conducted during the Indirect and Semidirect Aerosols Campaign (ISDAC) over Barrow, Alaska, in the springtime of 2008. In-situ ice nucleation measurements were conducted using a Continuous Flow Diffusion Chamber (CFDC). Measured number concentrations of ice nuclei (IN) varied from frequent values of 0.01 per liter to more than 10 per liter. Residuals of airborne droplets and ice crystals were collected through a counterflow virtual impactor (CVI). The compositions of individual atmospheric particles and the residuals were studied using Computer Controlled Scanning Electron Microscopy with Energy Dispersive X-ray analysis (CCSEM/EDX) and Scanning Transmission X-ray Microscopy coupled with Near Edge X-ray Absorption Fine Structure spectroscopy (STXM/NEXAFS). Chemical analysis of cloud particle residuals collected during an episode of high ice nucleation suggests that both size and composition may influence aerosol's ability to act as IN. The STXM/NEXAFS chemical composition maps of individual residuals have characteristic structures of either inorganic or black carbon cores coated by organic materials. In a separate flight, particle samples from a biomass burning plume were collected. Although it has previously been suggested that episodes of biomass burning contribute to increased numbers of highly effective ice nuclei, in this episode we observed that only a small fraction were effective ice nuclei. Most of the particles from the biomass plume episode were smaller in size and were composed of homogeneous organic material without identifiable cores.

Hiranuma, Naruki; Brooks, Sarah D.; Moffet, Ryan C.; Glen, Andrew; Laskin, Alexander; Gilles, Marry K.; Liu, Peter; MacDonald, A. M.; Strapp, J. Walter; McFarquhar, Greg

2013-06-24

178

General equations for the motions of ice crystals and water drops in gravitational and electric fields  

NASA Technical Reports Server (NTRS)

General equations for the Reynolds number of a variety of types of ice crystals and water drops are given in terms of the Davies, Bond, and Knudsen numbers. The equations are in terms of the basic physical parameters of the system and are valid for calculating velocities in gravitational and electric fields over a very wide range of sizes and atmospheric conditions. The equations are asymptotically matched at the bottom and top of the size spectrum, useful when checking large computer codes. A numerical system for specifying the dimensional properties of ice crystals is introduced. Within the limits imposed by such variables as particle density, which have large deviations, the accuracy of velocities appears to be within 10 percent over the entire range of sizes of interest.

Nisbet, John S.

1989-01-01

179

Crystal structure analysis of intermetallic compounds  

NASA Technical Reports Server (NTRS)

Study concerns crystal structures and lattice parameters for a number of new intermetallic compounds. Crystal structure data have been collected on equiatomic compounds, formed between an element of the Sc, Ti, V, or Cr group and an element of the Co or Ni group. The data, obtained by conventional methods, are presented in an easily usable tabular form.

Conner, R. A., Jr.; Downey, J. W.; Dwight, A. E.

1968-01-01

180

Cloud Resolving Simulations of Mixed-Phase Arctic Stratus Observed during BASE: Sensitivity to Concentration of Ice Crystals and Large-Scale Heat and Moisture Advection.  

NASA Astrophysics Data System (ADS)

The authors' previous idealized, two-dimensional cloud resolving model (CRM) simulations of Arctic stratus revealed a surprising sensitivity to the concentrations of ice crystals. In this paper, simulations of an actual case study observed during the Beaufort and Arctic Seas Experiment are performed and the results are compared to the observed data.It is again found in the CRM simulations that the simulated stratus cloud is very sensitive to the concentration of ice crystals. Using midlatitude estimates of the availability of ice forming nuclei (IFN) in the model, the authors find that the concentrations of ice crystals are large enough to result in the almost complete dissipation of otherwise solid, optically thick stratus layers. A tenuous stratus can be maintained in the simulation when the continuous input of moisture through the imposed large-scale advection is strong enough to balance the ice production. However, in association with the large-scale moisture and warm advection, only by reducing the concentration of IFN to 0.3 of the midlatitude estimate values can a persistent, optically thick stratus layer be maintained. The results obtained from the reduced IFN simulation compare reasonably well with observations.The longwave radiative fluxes at the surface are significantly different between the solid stratus and liquid-water-depleted higher ice crystal concentration experiments.This work suggests that transition-season Arctic stratus can be very vulnerable to anthropogenic sources of IFN, which can alter cloud structure sufficiently to affect the rates of melting and freezing of the Arctic Ocean.The authors find that the Hallett-Mossop riming splintering mechanism is not activated in the simulations because the cloud droplets are very small and cloud temperatures are outside the range supporting efficient rime splintering. Thus, the conclusions drawn from the results presented in this paper may be applicable to only a limited class of Arctic stratus.

Jiang, Hongli; Cotton, William R.; Pinto, James O.; Curry, Judy A.; Weissbluth, Michael J.

2000-07-01

181

Ultrafast X-ray probing of water structure below the homogeneous ice nucleation temperature.  

PubMed

Water has a number of anomalous physical properties, and some of these become drastically enhanced on supercooling below the freezing point. Particular interest has focused on thermodynamic response functions that can be described using a normal component and an anomalous component that seems to diverge at about 228 kelvin (refs 1-3). This has prompted debate about conflicting theories that aim to explain many of the anomalous thermodynamic properties of water. One popular theory attributes the divergence to a phase transition between two forms of liquid water occurring in the 'no man's land' that lies below the homogeneous ice nucleation temperature (TH) at approximately 232 kelvin and above about 160 kelvin, and where rapid ice crystallization has prevented any measurements of the bulk liquid phase. In fact, the reliable determination of the structure of liquid water typically requires temperatures above about 250 kelvin. Water crystallization has been inhibited by using nanoconfinement, nanodroplets and association with biomolecules to give liquid samples at temperatures below TH, but such measurements rely on nanoscopic volumes of water where the interaction with the confining surfaces makes the relevance to bulk water unclear. Here we demonstrate that femtosecond X-ray laser pulses can be used to probe the structure of liquid water in micrometre-sized droplets that have been evaporatively cooled below TH. We find experimental evidence for the existence of metastable bulk liquid water down to temperatures of 227(-1)(+2) kelvin in the previously largely unexplored no man's land. We observe a continuous and accelerating increase in structural ordering on supercooling to approximately 229 kelvin, where the number of droplets containing ice crystals increases rapidly. But a few droplets remain liquid for about a millisecond even at this temperature. The hope now is that these observations and our detailed structural data will help identify those theories that best describe and explain the behaviour of water. PMID:24943953

Sellberg, J A; Huang, C; McQueen, T A; Loh, N D; Laksmono, H; Schlesinger, D; Sierra, R G; Nordlund, D; Hampton, C Y; Starodub, D; DePonte, D P; Beye, M; Chen, C; Martin, A V; Barty, A; Wikfeldt, K T; Weiss, T M; Caronna, C; Feldkamp, J; Skinner, L B; Seibert, M M; Messerschmidt, M; Williams, G J; Boutet, S; Pettersson, L G M; Bogan, M J; Nilsson, A

2014-06-19

182

What can polymer crystal structure tell about polymer crystallization processes?  

NASA Astrophysics Data System (ADS)

Contrary to most or all other materials, crystallization of chiral but racemic polymers such as isotactic polypropylene is accompanied by a conformational rearrangement which leads to helical geometries: the building units of the crystal are helical stems, ? 10-20nm long, which can be either right-handed or left-handed. Helical hand cannot be reversed within the crystal structure: it is therefore a permanent marker and an indicator of molecular processes (in particular segregation/selection of helical hands) which take place during crystal growth, and more precisely during the crucial step of "efficient"helical stem deposition. The issue of proper helical hand selection during polymer crystal growth is mainly illustrated with isotactic polypropylene. Its various crystalline polymorphs (?, ?, ? and smectic) display virtually all possible combinations of helical hands, azimuthal settings and even non-parallel orientation of helix axes in space. Furthermore, a specific homoepitaxy which generates a lamellar branching in the ? phase "quadrites"and ?/? composite structures makes it possible a) to determine the helical hand and associated azimuthal setting of every stem in the crystalline entities and b) to determine the impact on the crystal structure and morphology of "mistakes"in helical hand of the depositing stem. Analysis of these morphologies demonstrates that the crystallization of isotactic polypropylene (and by implication of other achiral, helical polymers) is a highly sequential and "substrate-determined"process, i.e. that the depositing stem probes the topography of the growth face prior to attachment. These observations appear difficult to reconcile with crystallization schemes in which molecules (helical segments) are prearranged in a kind of pseudo-crystalline bundle (and as such, are not subjected to the high constraints of crystal symmetry) before deposition as a preassembled entity on the substrate.

Lotz, B.

2000-10-01

183

Photonic Crystal Laser-Driven Accelerator Structures  

SciTech Connect

We discuss simulated photonic crystal structure designs for laser-driven particle acceleration, focusing on three-dimensional planar structures based on the so-called ''woodpile'' lattice. We demonstrate guiding of a speed-of-light accelerating mode by a defect in the photonic crystal lattice and discuss the properties of this mode. We also discuss particle beam dynamics in the structure, presenting a novel method for focusing the beam. In addition we describe some potential coupling methods for the structure.

Cowan, B.; /SLAC

2005-09-19

184

Crystallization media inhibit protein structural dynamics  

NASA Astrophysics Data System (ADS)

The first role of any crystallization solution is to reduce the solubility of proteins, so that it induces protein precipitation. Most times, protein precipitation does not lead to protein crystallization. Do crystallization solutions play any other roles that are crucial for protein crystallization? Here we report our studies that crystallization solutions suppress or inhibit protein structural dynamics. Photoactive yellow protein (PYP), a bacterial blue light photoreceptor protein, is employed as a model system in our study. We use time-resolved FTIR spectroscopic technique to probe the structural dynamics of proteins, including the proton transfer process and global conformational motions. We found that high concentration crystallization solutions (NH4)2SO4 strongly inhibit the structural dynamics of PYP upon blue light excitation. We will examine and discuss the mechanism in which crystallization solutions inhibit protein structural dynamics. The results are expected to provide insights to fundamental understanding of protein crystallization of water-soluble proteins. In addition, the data clearly demonstrates that the structural dynamics observed in crystalline conditions may be far from their natural structural dynamics for studies of protein structure-function relations.

Thubagere, Anupama; Kelemen, Lorand; Kaledhonkar, Sandip; Xie, Aihua

2007-03-01

185

Transition metal complexes with oligopeptides: single crystals and crystal structures.  

PubMed

The coordination chemistry of short chain peptides with transition metals is described in terms of the available crystal structures. Despite their high interest as synthetic models for metalloproteins and as building blocks for molecular materials based on the tuneable properties of oligopeptides, single crystal X-ray diffraction studies are scarce. A perusal of the most relevant results in this field allows us to define the main characteristics of oligopeptide-metal interactions, the fundamental problems for the crystallization of these complexes, and some hints to identify future promising approaches to advance the development of metallopeptide chemistry. PMID:24874062

Lillo, Vanesa; Galán-Mascarós, José Ramón

2014-07-14

186

Crystal Structure of Chabazite K  

SciTech Connect

The crystal structure of the chabazite K with the formula (K{sub 1.33}Na{sub 1.02}Ca{sub 0.84})[Al{sub 4}Si{sub 8}O{sub 24}] {center_dot} 12.17H{sub 2}O from late hydrothermalites in the Khibiny alkaline massif (Kola Peninsula) is established by X-ray diffraction analysis (CAD4 four-circle diffractometer, {lambda}MoK{sub {alpha}} radiation, graphite monochromator, T = 193 K, 2{theta}{sub max} = 70 deg., R{sub 1} = 0.047 for 4745 reflections) on the basis of experimental data (6265 reflections) obtained from a twin (twinning parameter 0.535(1)): a = 13.831(3) A, c = 15.023(5) A, sp. gr. R3-barm, Z = 3, {rho}{sub calcd} = 2.016 g/cm{sup 3} . It is shown that cations occupy five independent positions in large cavities of the tetrahedral Al,Si,O anionic framework in potassium-rich chabazite. A comparative crystallochemical analysis of chabazites of different composition and origin is performed.

Yakubovich, O.V.; Gavrilenko, P.G.; Pekov, I.V. [Moscow State University, Vorob'evy gory, Moscow, 119992 (Russian Federation); Massa, W. [Philipps University, Marburg (Germany)

2005-07-15

187

Ice Construction--Bottom Freezing Techniques for Constructing Shore and Near-Shore Ice Structures.  

National Technical Information Service (NTIS)

New methods and equipment for thickening and strengthening natural sea ice are needed to advance polar operational capabilities. Of the basic categories of techniques for inducing ice growth (ice injection, cold fluid injection, and recirculating fluid), ...

T. L. Culbertson

1971-01-01

188

Crystal structure of a perfect carbyne  

NASA Astrophysics Data System (ADS)

The crystal structure of a perfect carbyne is calculated by the molecular mechanics methods. It is established that the carbyne crystals should consist of polycumulene chains arranged in hexagonal bundles. The unit cell of the perfect carbyne crystal is trigonal and contains one carbon atom. The unit cell parameters are as follows: a = b = c = 0.3580 nm, ? = ? = ? = 118.5°, and space group P3 m1. The perfect carbyne single crystals have a stable structure at room temperature if the length of their constituent chains is larger than 500 nm.

Belenkov, E. A.; Mavrinsky, V. V.

2008-01-01

189

Crystal structure of a perfect carbyne  

SciTech Connect

The crystal structure of a perfect carbyne is calculated by the molecular mechanics methods. It is established that the carbyne crystals should consist of polycumulene chains arranged in hexagonal bundles. The unit cell of the perfect carbyne crystal is trigonal and contains one carbon atom. The unit cell parameters are as follows: a = b = c = 0.3580 nm, {alpha} = {beta} = {gamma} = 118.5{sup o}, and space group P3m1. The perfect carbyne single crystals have a stable structure at room temperature if the length of their constituent chains is larger than 500 nm.

Belenkov, E. A., E-mail: belenkov@csu.ru; Mavrinsky, V. V. [Chelyabinsk State University (Russian Federation)

2008-01-15

190

The dependence of the single-scattering properties of small ice crystals on orientation average, particle shape, and wavelength  

NASA Astrophysics Data System (ADS)

Current methods of representing the bulk scattering properties of cirrus for numerical models and satellite retrieval algorithms require weighting the single-scattering properties of specific shapes and sizes of ice crystals by their observed concentrations. Thus, to determine the influence of cirrus on solar and infrared radiation, as required for climate studies, knowledge of the single-scattering properties of ice crystals is required. Except for a few large ice crystals, most ice crystals do not have preferred orientations. Thus, the corresponding single-scattering properties of ice crystals used for numerical models and remote sensing retrievals are typically calculated assuming random orientations. The Euler's angle, selected using a random number generator, has been exclusively used to determine crystals' orientation for such calculations. When more orientations are used to determine the mean scattering properties, the scattering properties are determined with higher accuracy. However, computational resources limit the number of orientations that can be used in these calculations. Past studies used several efficient orientation-averaging schemes (e.g., quasi-Monte-Carlo and optimal cubature on the sphere) for calculating light scattering properties. These studies mainly focused on small sizes and considered relatively simple shapes, such as spheres and sphere aggregates. Atmospheric ice crystals are non-spherical and their sizes are much larger than those studied previously. In this study, the minimum numbers of orientations needed to determine the single-scattering properties of four different realistically shaped atmospheric ice crystals (i.e., column, droxtal, Gaussian random sphere, and budding Bucky ball) with predefined accuracy levels are determined using the Amsterdam discrete dipole approximation (ADDA) ver. 1.0. The results of the calculations are also used to quantify how the scattering and absorption efficiency, the single-scattering albedo, asymmetry parameter, and scattering phase function depend on sphericity, a parameter that is defined as the ratio of the surface area of a sphere with the same volume of given particle to the surface area of the particle. To generate the random orientations of ice crystals, the Euler's angles are selected using a quasi-Monte-Carlo method that uses a number sequence instead of a random number generator; its efficiency is compared with that of the internal orientation average method of ADDA. Further, simulations with varying sizes of ice crystals determine the influences of ice crystal size on the minimum number of orientations required to achieve the desired accuracy of the single-scattering properties. The results are reported for three different wavelengths of incident light, non-absorbing (0.55 ?m), moderate absorbing (3.78 ?m), and strongly absorbing (11 ?m).

Um, J.; McFarquhar, G. M.

2012-12-01

191

Evaluation of Morphological Change and Aggregation Process of Ice Crystals in Frozen Food by Using Fractal Analysis  

NASA Astrophysics Data System (ADS)

Size and shape of ice crystals in frozen food materials are very important because they affect not only quality of foods but also the viability of industrial processing such as freeze-drying of concentration. In this study, 30%wt sucrose solution is used as test samples. For examining the effect of stabilizerspectine and xantan gum is added to the sucrose solution. They are frozen on the cold stage of microscope to be observed their growing ice crystals under the circumstance of -10°C. Their size and shape are measured and quantitatively evaluated by applying fractal analysis. lce crystal of complicated shape has large fractal dimension, and vice versa. It successflly categorized the ice crystals into two groups; one is a group of large size and complicated shape, and the other is a group of small size and plain shape. The critical crystal size between the two groups is found to become larger with increasing holding time. It suggests a phenomenological model for metamorphoses process of ice crystals. Further, it is indicated that xantan gum is able to suppress the smoothing of ice crystals.

Koshiro, Yoko; Watanabe, Manabu; Takai, Rikuo; Hagiwara, Tomoaki; Suzuki, Toru

192

A new method for producing artificial snow crystals using a mixture of salt and ice  

NASA Astrophysics Data System (ADS)

It has been found that artificial snow crystals can be produced by a simple method using a mixture of salt and ice crushed into sherbet as the cooling material. The freezing mixture of about 100 g was contained in a small styrene cup (85 mm varnothing, 50 mm height). A black acrylic plate (25 mm varnothing, 2 mm thickness) was placed on the freezing mixture in the cup. The cup was placed in a closed plastic box (130×130×65 mm). The water vapour in the air trapped in the plastic box crystallized onto the surface of the acrylic plate and made a crystal 1-2 mm in size in 20 minutes. The artificial crystal is quite similar to natural snow crystals with excellent hexagonal symmetry. A model to explain the process of producing the artificial snow crystal has been proposed, insisting that the electric field due to the static electricity from the acrylic plate plays an important role in making the seeds for the crystal growth.

Suwa, Y.; Myint, H. H.; Kurniawan, H.; Ito, F.; Kagawa, K.

2001-07-01

193

Defect structures in metallic photonic crystals  

SciTech Connect

We have investigated metallic photonic crystals built around a layer-by-layer geometry. Two different crystal structures (face-centered-tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7{endash}8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80{percent}), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations. {copyright} {ital 1996 American Institute of Physics.}

Oezbay, E.; Temelkuran, B. [Department of Physics, Bilkent University, Bilkent, Ankara 06533 (Turkey)] [Department of Physics, Bilkent University, Bilkent, Ankara 06533 (Turkey); Sigalas, M.; Tuttle, G.; Soukoulis, C.M.; Ho, K.M. [Ames Laboratory and Microelectronics Research Center, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory and Microelectronics Research Center, Iowa State University, Ames, Iowa 50011 (United States)

1996-12-01

194

Molecular dynamics studies of ice Ic and the structure I clathrate hydrate of methane. [Empty and filled structure I hydrates of methane  

SciTech Connect

Computer simulations are used to compare and contrast the dynamical behavior of structure I clathrate hydrates with that of ice Ic (cubic lattices). The calculations are based on recently proposed pairwise additive intermolecular potentials for the water molecules. The phonon densities of states of ice Ic and the hydrates are found to be broadly similar, not withstanding their different crystal structures. This fact explains the similarity of the observed heat capacity and infrared data. In the case of the methane hydrate the simulation predicts a distinct dynamical (localized-mode) behavior for methane molecules trapped in each type of cage. 10 figures, 4 tables.

Tse, J.S. (National Research Council of Canada, Ottawa, Ontario); Klein, M.L.; McDonald, I.R.

1983-10-13

195

Ice island creation, drift, recurrences, mechanical properties, and interactions with arctic offshore oil production structures  

SciTech Connect

Research and engineering studies on first-year sea ice for over two decades has resulted in the design, construction, and operation of jacket platforms, of artificial islands, and of massive gravity structures which routinely withstand moving sea ice of thickness up to 2 meters. However, the less-common interactions between such structures and moving multiyear ice ([ge]3 meters thick), and also moving ice islands (10 to 60 meters thick) remain as the unknown and potentially most serious hazard for Arctic offshore structures. In this study, research was addressed across the complete span of remaining questions regarding such features. Ice island components, thickness distributions, scenarios and models for the interactions of massive ice features with offshore structures, all were considered. Ice island morphology and calving studies were directed at the cluster of 19 ice islands produced in a calving from the Ward Hunt Ice Shelf on Ellesmere Island in 1983, and also at a calving from the Milne Ice Shelf in 1988. The statistics of ice island dynamics, on both a short-term small-scale basis and also on a long-term basis, were studied. Typical wind velocities of 5 to 7.5 meters per second led to ice island speeds of about 0.014 of the wind speed, at an angle of 20[degrees] to the right of the wind direction. Ice island samples were tested for their stress/strain characteristics. Compressive strength values ranged from 1.64 MPa at a strain rate of 2 [times] 10[sup [minus]7] s[sup [minus]1] to 6.75 MPa at a strain rate of 1 [times] 10[sup [minus]3] s[sup [minus]1]. Scenarios for ice island/structure interactions were developed, and protective countermeasures such as spray ice and ice rubble barriers were suggested. Additional computer modeling of structure/ice interactions for massive ice features is recommended.

Sackinger, W.M.; Jeffries, M.O.; Li, Fucheng; Lu, Mingchi.

1991-03-01

196

On Understanding Stacking Fault Formation in Ice  

NASA Astrophysics Data System (ADS)

Despite dedicated efforts aimed at revealing possible molecular structures of the ice defects associated with stacking faults in ice (I), these molecular arrangements have remained a puzzle. Here we demonstrate how the reorganization of water molecules on different faces of ice (I) can facilitate formation of stacking faults within a crystal. We show that a pair of point defects can manifest a particular combination of coupled five- and eight-membered rings (5-8 rings). These structural motifs can facilitate a shift in layers within an ice (I) crystal, thereby inducing stacking faults. Furthermore, the presence of molecular solutes such as methane at the ice interface appears to trigger the formation of coupled 5-8 rings. The observation of such coupled 5-8 ring defects provides insights into the possible molecular mechanisms of stacking fault formation in ice (I) and has implications for ice crystal growth phenomenology and the consequent physical and chemical properties of ice.

Pirzadeh, Payman; Kusalik, Peter G.

2012-12-01

197

Introduction to Crystal Structure: Bond Strength  

NSDL National Science Digital Library

This exercise is designed to familiarize students with some basic crystal structures The exercise helps students fully understand the nature and significance of ionic bonds and Pauling's second rule It also builds a bit on Pauling's first rule (radius ratio principle) It is one of several related activities, all of which are intended to help students understand the nature of ionic crystals

Perkins, Dexter

198

SIGNIFICANCE OF TIDAL CHANGE ON ABRASION AREA OF STRUCTURES DUE TO SEA ICE MOVEMENT  

Microsoft Academic Search

When ice movement is very active, hydraulic structures in ice-covered areas suffer abrasion. Especially for offshore structures of reinforced concrete, it is necessary to determine the required cover thickness with high accuracy. This paper describes a method for estimating the size of the active abrasion area, considering local ice pressure distribution, change of water level due to tide, and scatter

Takahiro Takeuchi; Shinji Kioka; Hiroshi Saeki

199

Crystallization of amorphous ice as the cause of comet P/Halley's outburst at 14 AU.  

PubMed

The post-perihelion eruption of comet P/Halley, detected in Feb. 1991 and believed to have started 3 months earlier, can be explained by crystallization of amorphous ice taking place in the interior of the porous nucleus, at depths a few tens of meters, accompanied by the release of trapped gases. Numerical calculations show that for a bulk density of 0.5 g cm-3 and a pore size of 1 millimicron crystallization occurs on the outbound leg of comet P/Halley's orbit, at heliocentric distances between 5 AU and 17 AU. The trapped gas is released and flows to the surface through the porous medium. It may also open wider channels, as the internal pressures obtained surpass the tensile strength of cometary ice. The outflowing gas carries with it grains of ice and dust, and thus can explain the large amounts of dust observed in the coma at 14.3 AU and beyond. The typical decline time of the process is found to be on the order of months, in agreement with observations. The rate of outgassing is two or three orders of magnitude higher than in quiescence. In an asymmetric, non-uniform nucleus--in contrast to the one-dimensional spherical model--the process should occur intermittently, such as was observed for comet P/Halley beyond 5 AU. PMID:11538062

Prialnik, D; Bar-Nun, A

1992-01-01

200

Calorimetric determination of inhibition of ice crystal growth by antifreeze protein in hydroxyethyl starch solutions.  

PubMed Central

Differential scanning calorimetry and cryomicroscopy were used to investigate the effects of type I antifreeze protein (AFP) from winter flounder on 58% solutions of hydroxyethyl starch. The glass, devitrification, and melt transitions noted during rewarming were unaffected by 100 micrograms/ml AFP. Isothermal annealing experiments were undertaken to detect the effects of AFP-induced inhibition of ice crystal growth using calorimetry. A premelt endothermic peak was detected during warming after the annealing procedure. Increasing the duration or the temperature of the annealing for the temperature range from -28 and -18 degrees C resulted in a gradual increase in the enthalpy of the premelt endotherm. This transition was unaffected by 100 micrograms/ml AFP. Annealing between -18 and -10 degrees C resulted in a gradual decrease in the premelt peak enthalpy. This process was inhibited by 100 micrograms/ml AFP. Cryomicroscopic examination of the samples revealed that AFP inhibited ice recrystallization during isothermal annealing at -10 degrees C. Annealing at lower temperatures resulted in minimal ice recrystallization and no visible effect of AFP. Thus, the 100 micrograms/ml AFP to have a detectable influence on thermal events in the calorimeter, conditions must be used that result in significant ice growth without AFP and visible inhibition of this process by AFP. Images FIGURE 8

Hansen, T N; Carpenter, J F

1993-01-01

201

Crystallization and preliminary X-ray crystallographic analysis of an ice-binding protein (FfIBP) from Flavobacterium frigoris PS1.  

PubMed

Ice growth in a cold environment is fatal for polar organisms, not only because of the physical destruction of inner cell organelles but also because of the resulting chemical damage owing to processes such as osmotic shock. The properties of ice-binding proteins (IBPs), which include antifreeze proteins (AFPs), have been characterized and IBPs exhibit the ability to inhibit ice growth by binding to specific ice planes and lowering the freezing point. An ice-binding protein (FfIBP) from the Gram-negative bacterium Flavobacterium frigoris PS1, which was isolated from the Antarctic, has recently been overexpressed. Interestingly, the thermal hysteresis activity of FfIBP was approximately 2.5?K at 50?µM, which is ten times higher than that of the moderately active IBP from Arctic yeast (LeIBP). Although FfIBP closely resembles LeIBP in its amino-acid sequence, the antifreeze activity of FfIBP appears to be much greater than that of LeIBP. In an effort to understand the reason for this difference, an attempt was made to solve the crystal structure of FfIBP. Here, the crystallization and X-ray diffraction data of FfIBP are reported. FfIBP was crystallized using the hanging-drop vapour-diffusion method with 0.1?M sodium acetate pH 4.4 and 3?M sodium chloride as precipitant. A complete diffraction data set was collected to a resolution of 2.9?Å. The crystal belonged to space group P4(1)22, with unit-cell parameters a = b = 69.4, c = 178.2?Å. The asymmetric unit contained one monomer. PMID:22750870

Do, Hackwon; Lee, Jun Hyuck; Lee, Sung Gu; Kim, Hak Jun

2012-07-01

202

Three separate classes of bacterial ice nucleation structures  

SciTech Connect

Studies of the properties of the ice nucleation structure exposed on the surfaces of various bacteria such as Pseudomonas syringae, Erwinia herbicola, or various strains of Ice+ recombinant Escherichia coli have shown that there are clearly three major related but chemically distinct types of structures on these cells. First, the ability of Ice+ cells to nucleate super-cooled D2O has been examined, and it has been found that this ability (relative to the ability of the same cells to nucleate super-cooled H2O) exhibited three characteristic nucleating patterns. The rarest structure, called class A, is found on only a small fraction of cells in a culture, nucleates H2O at temperatures above -4.4 degrees C, and is an effective nucleator of super-cooled D2O. A second class of structure, called class B, is found on a larger portion of the cells, nucleates H2O between -4.8 and -5.7 degrees C, and is a relatively poor nucleator of super-cooled D2O. The class C structure is found on almost all cells and nucleates at -7.6 degrees C or colder. These three classes of structures were also differentiated by their sensitivities to low concentrations of water-miscible organic solvents such as dioxane or dimethyl sulfoxide. Depending on the specific bacterial strain, the addition of these solvents to bacterial suspensions lowered the nucleation activity of the class A structure by 1,000-fold or more. The nucleation activities of class B structures in the same culture were highly resistant to these compounds and were lowered only by 20 to 40%.

Turner, M.A.; Arellano, F.; Kozloff, L.M. (Univ. of California, San Francisco (USA))

1990-05-01

203

ICSD Web: the Inorganic Crystal Structure Database  

NSDL National Science Digital Library

This site contains a free demonstration version of the Inorganic Crystal Structure Database. This database contains a 3325 structure subset of the 76,480 inorganic structures as of 2004. The demo version can be queried and accessed by a web-interface which allows multiple methods of searching, and the resulting crystal structures can then be viewed online (with the CHIME plug-in) or downloaded for viewing with other visualization software. Also included on the site are updates of bug fixes, conditions of use and prices, tips for displaying the structures, a gallery of images, a flash movie, and instructions for installing a ICSD server.

Alan, Hewat

204

Neutron diffraction and NMR relaxation studies of structural variation and phase transformations for water/ice in SBA-15 silica: I. The over-filled case  

NASA Astrophysics Data System (ADS)

Neutron diffraction and NMR relaxation measurements have been made of water/ice in SBA-15, a mesoporous silica constituting an ordered array of cylindrical mesopores of pore diameter ~86 Å, over the temperature range 180-300 K in a cooling and heating cycle. The over-filled sample shows the initial formation of hexagonal ice on the outside of the silica grains, followed by the nucleation of cubic ice inside the pores at a lower temperature. Neutron scattering profiles for the cubic ice peaks are significantly broadened and indicate a defective structure, as observed in previous experiments on ice formation in sol-gel and MCM-type silicas. Below the pore freezing temperature the intensity of the cubic ice peaks exhibit a significant increase, down to the lowest experimental temperature, indicating a reversible conversion of defective ice to ordered ice crystals. The peak profile analysis for the two ice patterns indicates a systematic variation in the position as a function of temperature, giving values of the expansion coefficients that are slightly lower than other measurements for the bulk phase. NMR results on proton relaxation as a function of temperature indicate the presence of a mobile phase for temperatures below pore freezing that supports the view that there is interconversion between brittle and plastic phases of ice.

Liu, E.; Dore, J. C.; Webber, J. B. W.; Khushalani, D.; Jähnert, S.; Findenegg, G. H.; Hansen, T.

2006-11-01

205

Structures of cyano-biphenyl liquid crystals  

NASA Technical Reports Server (NTRS)

The structures of p-alkyl- p'-cyano- bicyclohexanes, C(n)H(2n+1) (C6H10)(C6H10) CN (n-CCH), and p-alkyl- p'-cyano- biphenyls, C(n)H(2n+1) (C6H4)(C6H4) CN (n-CBP), were studied. It is convenient to use an x ray image intensification device to search for symmetric x ray diffraction patterns. Despite the similarities in molecular structures of these compounds, very different crystal structures were found. For the smectic phase of 2CCH, the structure is close to rhombohedral with threefold symmetry. In contrast, the structure is close to hexagonal close-packed with two molecules per unit cell for 4CCH. Since intermolecular forces may be quite weak for these liquid crystals systems, it appears that crystal structures change considerably when the alkyl chain length is slightly altered. Different structures were also found in the crystalline phase of n-CBP for n = 6 to 9. For n = 7 to 9, the structures are close to monclinic. The structures are reminiscent of the smectic-A liquid crystal structures with the linear molecules slightly tilted away from the c-axis. In contrast, the structure is quite different for n = 6 with the molecules nearly perpendicular to the c-axis.

Chu, Yuan-Chao; Tsang, Tung; Rahimzadeh, E.; Yin, L.

1989-01-01

206

Nanoscale structure of the magnetic induction at monopole defects in artificial spin-ice lattices  

Microsoft Academic Search

Artificially frustrated spin-ice systems are of considerable interest since they simulate the spin frustration and concomitant rich behavior exhibited by atoms on a crystal lattice in naturally occurring spin-ice systems such as pyrochlores. As a result of the magnetic frustration, these systems can exhibit ``magnetic monopole'' type defects, which are an example of an exotic emergent quasiparticle. The local magnetization

C. Phatak; A. K. Petford-Long; O. Heinonen; M. Tanase; M. de Graef

2011-01-01

207

An experimental study of the exposure of a droplet and an ice crystal cloud medium to CO2 laser pulses  

Microsoft Academic Search

The relation of the size and concentration of water droplets and ice particles in clouds created by an exploding ice crystal and a water droplet following exposure to CO2 laser pulses has been investigated experimentally. The intensity of the laser pulses was in the range 0.1-10 MW\\/sq cm, and the duration was 5-6 microseconds. The relationship between the size and

V. A. Belts; O. A. Volkovitskii; A. F. Dobrovolskii; E. V. Ivanov; Iu. V. Nasedkin

1985-01-01

208

Crystal engineering: From design of crystal structures to fabrication of composite crystals  

NASA Astrophysics Data System (ADS)

This thesis reports how to design and control co-crystal structures from a kinetic point of view, and demonstrates the control of crystal morphology through understanding the kinetics and crystal structures. In chapter one, the in-situ atomic force microscope (AFM) was utilized to investigate how side chain on a glycine 2,5-diketopiperazine (GLYDKP) backbone can affect the assembly of GLYDKP, and showed that methyl groups cause larger energy barrier for crystallization. Because the introduction of functional group on the side chain could inevitably slow down the assembly process, a different approach should be considered. Chapter two shows that formic acid at low concentration can accelerate the assembly process without incorporating into the crystal structure. Because formic acid only crystallizes with GLYDKP in concentrated solution, these results prove that co-crystallization is a better method for incorporating functionalized molecules into a solid than direct modification of molecule itself. Chapter three focuses on the rational design of GLYDKP cocrystals by utilizing the observation found in chapter two. Structure of GLYDKP and formic acid crystal was analyzed to search possible guest molecules for cocrystal studies. This method successfully identified eleven molecules that crystallize with GLYDKP, and proved that crystal structure can be controlled through weak interactions such as C-H•••O=C and C-H•••Cl interactions. Chapter four and chapter five explore the possibility of using self-assembled process to control morphology of crystals and surface epitaxy. Metal(II) bis(imidazolium 2,b-pyridinedicarboxylate) complexes were chosen and two morphologies associated with different metal ions were found: rhombohedral (Type I) and rectangular (Type II) crystals. In this study, an additive was found to change the morphology of crystal from type I to type II, and then methods of producing various shapes of composite crystals were also established. These self-assembled procedures of making composite crystals at micron scale are very promising, because the fabrication will only relies on solvent, additives, or combination of them without using sophisticated crystallizers.

Luo, Tzy-Jiun Mark

209

Structural properties of a C120 crystal  

NASA Astrophysics Data System (ADS)

With well-know models used for the study of orientational ordering transition in C60 crystal and with the crystallographic data from G-W. Wang and al.[Nature 387,583(1997)], this work aimed at characterizing a possible orientational ordering transition in C120 crystal. The C120 molecular structure used is based on MNDO optimization. With the same model, we have investigated the effect of the crystal surface on the ordering phase temperature. An orientational ordering phase transition was predicted to take place at 220K in the bulk and 175K at the surface.

Laforge, Christophe; Senet, Patrick; Lambin, Philippe

1998-08-01

210

Radiative properties of visible and subvisible Cirrus: Scattering on hexagonal ice crystals  

NASA Technical Reports Server (NTRS)

One of the main objectives of the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) is to provide a better understanding of the physics of upper level clouds. The focus is on just one specific aspect of cirrus physics, namely on characterizing the radiative properties of single, nonspherical ice particles. The basis for further more extensive studies of the radiative transfer through upper level clouds is provided. Radiation provides a potential mechanism for strong feedback between the divergence of in-cloud radiative flux and the cloud microphysics and ultimately on the dynamics of the cloud. Some aspects of ice cloud microphysics that are relevant to the radiation calculations are described. Next, the Discrete Dipole Approximation (DDA) is introduced and some new results of scattering by irregular crystals are presented. The Anomalous Diffraction Theory (ADT) was adopted to investigate the scattering properties of even larger crystals. In this way the scattering properties of nonspherical particles were determined over a range of particle sizes.

Flatau, Piotr J.; Stephens, Graeme L.; Draine, Bruce T.

1990-01-01

211

Accurate simulation of the optical properties of atmospheric ice crystals with the invariant imbedding T-matrix method  

NASA Astrophysics Data System (ADS)

The invariant imbedding T-matrix method (II-TM) is employed to compute the optical properties of randomly oriented ice crystals of various shapes including hexagonal columns, hollow columns, droxtals, bullet rosettes and aggregates. The II-TM is shown to be numerically stable and capable of obtaining the single-scattering properties of hexagonal ice crystals with size parameters up to 150. The 22° and 46° halo peaks in the phase function of compact hexagonal ice crystals begin to emerge at a size parameter of approximately 80 and tend to become insensitive to particle size as the corresponding size parameter approaches 150. Furthermore, the II-TM solutions are shown to be in agreement with their counterparts based on the discrete dipole approximation (DDA) method and the pseudo-spectral time-domain (PSTD) method. In addition, the accuracy of the improved geometric-optics method (IGOM) is examined for randomly oriented hexagonal ice crystal cases over a wide size-parameter range from the resonant to geometric-optics regimes. The II-TM is also used to study the effects of particle surface roughness and internal inclusions on the single-scattering properties of ice particles.

Bi, Lei; Yang, Ping

2014-05-01

212

Oceanographic frontal structure and biological production at an ice edge  

Microsoft Academic Search

Marginal ice edge zones (MIZ) are unique frontal systems with air-ice-sea interfaces. Phytoplankton blooms, which occur along the edge of the melting ice pack in spring, are strongly related to the air-ice-sea interactive processes. In spring 1982, during a cruise to the Bering Sea ice pack, hydrographic sections, including standard biological oceanographic parameters, were collected across the MIZ showing such

H. J. Niebauer; V. Alexander

1985-01-01

213

Advanced Optical Diagnostics for Ice Crystal Cloud Measurements in the NASA Glenn Propulsion Systems Laboratory  

NASA Technical Reports Server (NTRS)

A light extinction tomography technique has been developed to monitor ice water clouds upstream of a direct connected engine in the Propulsion Systems Laboratory (PSL) at NASA Glenn Research Center (GRC). The system consists of 60 laser diodes with sheet generating optics and 120 detectors mounted around a 36-inch diameter ring. The sources are pulsed sequentially while the detectors acquire line-of-sight extinction data for each laser pulse. Using computed tomography algorithms, the extinction data are analyzed to produce a plot of the relative water content in the measurement plane. To target the low-spatial-frequency nature of ice water clouds, unique tomography algorithms were developed using filtered back-projection methods and direct inversion methods that use Gaussian basis functions. With the availability of a priori knowledge of the mean droplet size and the total water content at some point in the measurement plane, the tomography system can provide near real-time in-situ quantitative full-field total water content data at a measurement plane approximately 5 feet upstream of the engine inlet. Results from ice crystal clouds in the PSL are presented. In addition to the optical tomography technique, laser sheet imaging has also been applied in the PSL to provide planar ice cloud uniformity and relative water content data during facility calibration before the tomography system was available and also as validation data for the tomography system. A comparison between the laser sheet system and light extinction tomography resulting data are also presented. Very good agreement of imaged intensity and water content is demonstrated for both techniques. Also, comparative studies between the two techniques show excellent agreement in calculation of bulk total water content averaged over the center of the pipe.

Bencic, Timothy J.; Fagan, Amy; Van Zante, Judith F.; Kirkegaard, Jonathan P.; Rohler, David P.; Maniyedath, Arjun; Izen, Steven H.

2013-01-01

214

Structural classification of dynamometamorphic transformations of first-year sea ice  

Microsoft Academic Search

This paper considers the main features of the structure of dynamometamorphic transformations of first-year ice. The structural\\u000a classification of these transformations is proposed based on laboratory and natural investigations. It is a logical development\\u000a of the existing structural classification of first-year ice forming in the Arctic seas without the influence of external forcing\\u000a on the ice cover.

K. P. Tyshko

2007-01-01

215

Crystal Distortion of Dy2Ti2O7 at the Spin Ice Transition Temperature  

Microsoft Academic Search

Dy2Ti2O7 with the pyrochlore structure shows a spin ice transition at about 1 K. The Dy3+ ion in this compound has an effective spin Seff=1\\/2. The Dy ions reside on the vertices of corner-linked tetrahedra. Due to a strong single-ion anisotropy, the ground state of Dy3+ is well expressed by an Ising doublet with local quantization axes. We measured the

H. Suzuki; F. Hata; Y. Xue; H. Kaneko; A. Hosomichi; S. Abe; R. Higashinaka; S. Nakatsuji; Y. Maeno

2006-01-01

216

Nonlinear dynamic response of a simple ice-structure interaction model  

SciTech Connect

The problem addressed in the continuous indentation of a ship or offshore structure into an ice sheet. The impacting ship or offshore structure is represented by a mass-spring-dashpot system having a constant velocity relative to the ice sheet. The dynamic response of this simple analogue model of ice-structure interaction is studied in considerable detail. The complicated, highly nonlinear dynamic response is due to intermittent ice breakage and intermittent contact of the structure with the ice. Periodic motions are found and the periodicity for a particular system is dependent upon initial conditions. For a representative system, a Poincare map is presented showing the fixed points. A description of some of the effects of random variations in system parameters is also presented. Some implications of these findings regarding structural design for ice interaction are discussed.

Karr, D.G.; Troesch, A.W.; Wingate, W.C. (Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Naval Architecture and Marine Engineering)

1993-11-01

217

The structure and dynamics of amorphous and crystalline phases of ice  

SciTech Connect

The structures of the high and low-density amorphous phases of ice are studied using several techniques. The diffraction patterns of high and low density amorphous ice are analyzed using reverse Monte Carlo methods and compared with molecular dynamics simulations of these phases. The spectra of crystalline and amorphous phases of ice obtained by Raman and incoherent inelastic neutron scattering are analyzed to yield structural features for comparison with the results of molecular dynamics and Reverse Monte Carlo analysis. The structural details obtained indicate that there are significant differences between the structure of liquid water and the amorphous phases of ice.

Klug, D. D.; Tse, J. S.; Tulk, C. A.; Svensson, E. C.; Swainson, I.; Loong, C.-K.

2000-07-14

218

The crystal structure and crystal chemistry of fernandinite and corvusite  

USGS Publications Warehouse

Using type material of fernandinite from Minasragra, Peru, and corvusite from the Jack Claim, La Sal Mountains, Utah, the properties and crystal chemistry of these minerals have been determined by Rietveld analysis of the powder X-ray-diffraction patterns. The crystal structure of both species is isotypic with the V2O5 -type layer first found for ??-Ag0.68V2O5; it consists of chains of VO6 octahedra linked by opposite corners (parallel to b) condensed by edge-sharing to form the layer. The vanadium has average valence 4.8, and the resulting layer-charge is balanced by varying amounts of Ca, Na, and K in the interlayer region accompanied by labile water. This study has confirmed the validity of fernandinite as a unique mineral species. It is closely related to corvusite, from which it is distinguished on the basis of the dominant interlayer cation: Ca for fernandinite, Na for curvusite. -Authors

Evans, Jr, H. T.; Post, J. E.; Ross, D. R.; Nelen, J. A.

1994-01-01

219

Synthesis and crystal structure of maleopimaric acid.  

PubMed

The title compound maleopimaric acid was synthesized by a Diels-Alder reaction between maleic anhydride and Pinus elliottii engelm oleoresin at room temperature and it was characterized by single crystal X-ray diffraction. The white crystals crystallized in the orthorhombic system, space group P2(12121) with cell dimensions: a = 7.6960 (15) A, b = 11.851 (2) A, c = 24.577 (5) A, alpha = 90 degrees, beta = 90 degrees, gamma = 90 degrees, V = 2241.6(8) A(3), and R(1) = 0.0716, wR(2) = 0.1975. The two fused and unbridged cyclohexane rings form a trans ring junction with chair conformation with two methyl groups in axis positions, the anhydride ring is planar. Crystal water existed in the molecular and stabilized the structure through intermolecular hydrogen bonds. PMID:18626819

Rao, Xiaoping; Song, Zhanqian; Yao, Xujie; Han, Chunrui; Shang, Shibin

2008-01-01

220

Building Crystal Structure Ball Models Using Pre-Drilled Templates: Sheet Structures, Tridymite, and Cristobalite  

NSDL National Science Digital Library

This activity involves building crystal structure ball models in order to strengthen students' understanding of crystalline order, relative atomic size, atomic coordination, crystal chemistry, and crystal symmetry.

Hollocher, Kurt

221

Solar radiative transfer in cirrus clouds. I - Single-scattering and optical properties of hexagonal ice crystals. II - Theory and computations of multiple scattering in an anisotropic medium  

NASA Technical Reports Server (NTRS)

The light scattering and absorption programs of Cai and Liou (1982) and Takano and Jaweera (1985) are extended to include hexagonal ice crystals randomly and horizontally oriented in space. The scattering and polarization results for the ice crystals are calculated. The results are compared with measurement data. The single-scattering properties for horizontally oriented columns and plates are presented and used to explain halos and arcs observed in the atmopshere. In the second section, the theory and computations for multiple scattering in cirrus clouds containing oriented ice crystals are presented. The radiative transfer in clouds composed of horizontally oriented ice crystals is formulated. Also, reflected and transmitted intensities, planetary albedo, and polarization in multiple scattering by ice crystals are discussed.

Takano, Yoshihide; Liou, Kuo-Nan

1989-01-01

222

Crystal structure of Arabidopsis thaliana cytokinin dehydrogenase  

SciTech Connect

Since first discovered in Zea mays, cytokinin dehydrogenase (CKX) genes have been identified in many plants including rice and Arabidopsis thaliana, which possesses CKX homologues (AtCKX1-AtCKX7). So far, the three-dimensional structure of only Z. mays CKX (ZmCKX1) has been determined. The crystal structures of ZmCKX1 have been solved in the native state and in complex with reaction products and a slowly reacting substrate. The structures revealed four glycosylated asparagine residues and a histidine residue covalently linked to FAD. Combined with the structural information, recent biochemical analyses of ZmCKX1 concluded that the final products of the reaction, adenine and a side chain aldehyde, are formed by nonenzymatic hydrolytic cleavage of cytokinin imine products resulting directly from CKX catalysis. Here, we report the crystal structure of AtCKX7 (gene locus At5g21482.1, UniProt code Q9FUJ1).

Bae, Euiyoung; Bingman, Craig A.; Bitto, Eduard; Aceti, David J.; Phillips, Jr., George N. (UW)

2008-08-13

223

Importance of aggregation and small ice crystals in cirrus clouds, based on observations and an ice particle growth model  

NASA Technical Reports Server (NTRS)

The 1 November 1986 FIRE I case study was used to test an ice particle growth model which predicts bimodal size spectra in cirrus clouds. The model was developed from an analytically based model which predicts the height evolution of monomodal ice particle size spectra from the measured ice water content (IWC). Size spectra from the monomodal model are represented by a gamma distribution, N(D) = N(sub o)D(exp nu)exp(-lambda D), where D = ice particle maximum dimension. The slope parameter, lambda, and the parameter N(sub o) are predicted from the IWC through the growth processes of vapor diffusion and aggregation. The model formulation is analytical, computationally efficient, and well suited for incorporation into larger models. The monomodal model has been validated against two other cirrus cloud case studies. From the monomodal size spectra, the size distributions which determine concentrations of ice particles less than about 150 mu m are predicted.

Mitchell, David L.; Chai, Steven K.; Dong, Yayi; Arnott, W. Patrick; Hallett, John

1993-01-01

224

Nanowire-Photonic Crystal Waveguide Hybrid Structure  

Microsoft Academic Search

We propose a class of nanocavities by combining nanowires and photonic crystal waveguides. Three-dimensional finite-difference time-domain techniques have been used to study the structures, and the simulation results show it is easy to achieve nanocavities with mode volumes less than 2(lambda\\/n)3 and Q values over 106 .

Chu-Cai Guo; Myung-Ki Kim; Se-Heon Kim; Yong-Hee Lee

2007-01-01

225

Crystal structure of a plectonemic RNA supercoil  

SciTech Connect

Genome packaging is an essential housekeeping process in virtually all organisms for proper storage and maintenance of genetic information. Although the extent and mechanisms of packaging vary, the process involves the formation of nucleic-acid superstructures. Crystal structures of DNA coiled coils indicate that their geometries can vary according to sequence and/or the presence of stabilizers such as proteins or small molecules. However, such superstructures have not been revealed for RNA. Here we report the crystal structure of an RNA supercoil, which displays one level higher molecular organization than previously reported structures of DNA coiled coils. In the presence of an RNA-binding protein, two interlocking RNA coiled coils of double-stranded RNA, a 'coil of coiled coils', form a plectonemic supercoil. Molecular dynamics simulations suggest that protein-RNA interaction is required for the stability of the supercoiled RNA. This study provides structural insight into higher order packaging mechanisms of nucleic acids.

Stagno, Jason R.; Ma, Buyong; Li, Jess; Altieri, Amanda S.; Byrd, R. Andrew; Ji, Xinhua (NCI); (Maryland)

2012-12-14

226

Structure analysis on synthetic emerald crystals  

NASA Astrophysics Data System (ADS)

Single crystals of emerald synthesized by means of the flux method were adopted for crystallographic analyses. Emerald crystals with a wide range of Cr3+-doping content up to 3.16 wt% Cr2O3 were examined by X-ray single crystal diffraction refinement method. The crystal structures of the emerald crystals were refined to R 1 (all data) of 0.019-0.024 and w R 2 (all data) of 0.061-0.073. When Cr3+ substitutes for Al3+, the main adjustment takes place in the Al-octahedron and Be-tetrahedron. The effect of substitution of Cr3+ for Al3+ in the beryl structure results in progressively lengthening of the Al-O distance, while the length of the other bonds remains nearly unchanged. The substitution of Cr3+ for Al3+ may have caused the expansion of a axis, while keeping the c axis unchanged in the emerald lattice. As a consequence, the Al-O-Si and Al-O-Be bonding angles are found to decrease, while the angle of Si-O-Be increases as the Al-O distance increases during the Cr replacement.

Lee, Pei-Lun; Lee, Jiann-Shing; Huang, Eugene; Liao, Ju-Hsiou

2013-05-01

227

Crystal Structure of Human Enterovirus 71  

SciTech Connect

Enterovirus 71 is a picornavirus associated with fatal neurological illness in infants and young children. Here, we report the crystal structure of enterovirus 71 and show that, unlike in other enteroviruses, the 'pocket factor,' a small molecule that stabilizes the virus, is partly exposed on the floor of the 'canyon.' Thus, the structure of antiviral compounds may require a hydrophilic head group designed to interact with residues at the entrance of the pocket.

Plevka, Pavel; Perera, Rushika; Cardosa, Jane; Kuhn, Richard J.; Rossmann, Michael G. (Purdue); (Sentinext)

2013-04-08

228

The crystal structures of DNA Holliday junctions  

Microsoft Academic Search

Nearly 40 years ago, Holliday proposed a four-stranded complex or junction as the central intermediate in the general mechanism of genetic recombination. During the past two years, six single-crystal structures of such DNA junctions have been determined by three different research groups. These structures all essentially adopt the antiparallel stacked-X conformation, but can be classified into three distinct categories: RNA–DNA

P. Shing Ho; Brandt F Eichman

2001-01-01

229

Crystal and electronic structure of copper sulfides  

Microsoft Academic Search

Copper sulfides with different copper concentration exist in mineral form ranging from CuS to Cu2S. Among these, chalcosite Cu 2S, and digenite Cu1.8S were the subject of extensive research for decades mainly because of their use as the absorber in photovoltaic cells. Yet; their electronic structure is poorly understood because their crystal structure is complex. Most of the results published

Pavel Lukashev

2007-01-01

230

Crystal structure of a nonsymbiotic plant hemoglobin  

Microsoft Academic Search

Background: Nonsymbiotic hemoglobins (nsHbs) form a new class of plant proteins that is distinct genetically and structurally from leghemoglobins. They are found ubiquitously in plants and are expressed in low concentrations in a variety of tissues including roots and leaves. Their function involves a biochemical response to growth under limited O2 conditions.Results: The first X-ray crystal structure of a member

Mark S Hargrove; Eric Allen Brucker; Boguslaw Stec; Gautam Sarath; Raúl Arredondo-Peter; Robert V Klucas; John S Olson; George N Phillips

2000-01-01

231

The Response of Optical Array Spectrometers to Ice and Snow: A Study of Probe Size to Crystal Mass Relationships.  

National Technical Information Service (NTIS)

This report is a summary of work performed by Particle Measuring Systems, Inc., to study the response of Optical Array Spectrometers to ice and snow crystals. The principle objective of this study was to perform laboratory, field and theoretical studies t...

R. G. Knollenberg

1975-01-01

232

Finite-difference time domain method for light scattering by small ice crystals in three-dimensional space  

Microsoft Academic Search

The finite-difference time domain (FDTD) method for the solution of light scattering by nonspherical particles has been developed for small ice crystals of hexagonal shapes including solid and hollow columns, plates, and bullet rosettes commonly occurring in cirrus clouds. To account for absorption, we have introduced the effec- tive permittivity and conductivity to circumvent the required complex calculations in the

Ping Yang; K. N. Liou

1996-01-01

233

Computational studies of crystal structure and bonding.  

PubMed

The analysis, prediction, and control of crystal structures are frontier topics in present-day research in view of their importance for materials science, pharmaceutical sciences, and many other chemical processes. Computational crystallography is nowadays a branch of the chemical and physicals sciences dealing with the study of inner structure, intermolecular bonding, and cohesive energies in crystals. This chapter, mainly focused on organic compounds, first reviews the current methods for X-ray diffraction data treatment, and the new tools available both for quantitative statistical analysis of geometries of intermolecular contacts using crystallographic databases and for the comparison of crystal structures to detect similarities or differences. Quantum chemical methods for the evaluation of intermolecular energies are then reviewed in detail: atoms-in-molecules and other density-based methods, ab initio MO theory, perturbation theory methods, dispersion-supplemented DFT, semiempirical methods and, finally, entirely empirical atom-atom force fields. The superiority of analyses based on energy over analyses based on geometry is highlighted, with caveats on improvised definitions of some intermolecular chemical bonds that are in fact no more than fluxional approach preferences. A perspective is also given on the present status of computational methods for the prediction of crystal structures: in spite of great steps forward, some fundamental obstacles related to the kinetic-thermodynamic dilemma persist. Molecular dynamics and Monte Carlo methods for the simulation of crystal structures and of phase transitions are reviewed. These methods are still at a very speculative stage, but hold promise for substantial future developments. PMID:21506002

Gavezzotti, Angelo

2012-01-01

234

Photonic Crystal Laser-Driven Accelerator Structures  

SciTech Connect

Laser-driven acceleration holds great promise for significantly improving accelerating gradient. However, scaling the conventional process of structure-based acceleration in vacuum down to optical wavelengths requires a substantially different kind of structure. We require an optical waveguide that (1) is constructed out of dielectric materials, (2) has transverse size on the order of a wavelength, and (3) supports a mode with speed-of-light phase velocity in vacuum. Photonic crystals---structures whose electromagnetic properties are spatially periodic---can meet these requirements. We discuss simulated photonic crystal accelerator structures and describe their properties. We begin with a class of two-dimensional structures which serves to illustrate the design considerations and trade-offs involved. We then present a three-dimensional structure, and describe its performance in terms of accelerating gradient and efficiency. We discuss particle beam dynamics in this structure, demonstrating a method for keeping a beam confined to the waveguide. We also discuss material and fabrication considerations. Since accelerating gradient is limited by optical damage to the structure, the damage threshold of the dielectric is a critical parameter. We experimentally measure the damage threshold of silicon for picosecond pulses in the infrared, and determine that our structure is capable of sustaining an accelerating gradient of 300 MV/m at 1550 nm. Finally, we discuss possibilities for manufacturing these structures using common microfabrication techniques.

Cowan, Benjamin M.

2007-08-22

235

Estimation of Cirrus Cloud Effective Ice Crystal Shapes using Visible Reflectances from Dual-Satellite Measurements  

NASA Technical Reports Server (NTRS)

This study develops and examines a multiangle, multisatellite method for determining effective cloud particle shapes from reflectances observed at visible wavelengths. The technique exploits the significant differences in the various cloud particle shape phase functions near the backscatter direction to infer particle shape from a combination of views from a near-backscatter angle and a side scattering angle. Adding-doubling calculations confirm that the optimal viewing combinations include one near-backscatter angle and another between 60" and 150". Sensitivity to shape increases with solar zenith angle. A total of 28 collocated, visible images from pairs of currently operating meteorological satellites with the desired viewing combinations were analyzed for particle shape. Matching reflectances from images with optimal viewing angles clearly separates water droplet from ice crystal clouds. Reflectance pairs from matched pixels containing ice crystals can be explained by the range of selected microphysical models. The most common retrieved shapes correspond to combinations of hexagonal compacts (aspect ratio of unity), hexagonal columns, and bullet rosettes. Although no single microphysical model can account for the observed variability, taken together, the models used for retrieving cloud particle size by the Clouds and the Earth's Radiant Energy System and the Moderate Resolution Imaging Spectroradiometer Projects can account for most of the reflectance variability observed in this limited data set. Additional studies are needed to assess the uncertainties in retrieved shapes due to temporal and spatial mismatches, anisotropic and bright background reflectances, and calibration errors and to validate the retrieved shapes. While applicable to a limited number of dual-satellite viewing combinations for current research and operational meteorological satellites, this approach could be used most extensively to derive effective particle size, shape, and optical depth from a combination of an imaging satellite in an L1 orbit, like Triana, and any other lower Earth orbiting Satellites.

Chepfer, Helene; Minnis, Patrick; Young, David; Nguyen, Louis; Arduini, Robert F.

2002-01-01

236

Laboratory Investigation of Direct Measurement of Ice Water Content, Ice Surface Area, and Effective Radius of Ice Crystals Using a Laser-Diffraction Instrument.  

National Technical Information Service (NTIS)

The aircraft microphysics probe, PVM-100A, was tested in the Colorado State University dynamic cloud chamber to establish its ability to measure ice water content (IWC), PSA, and Re in ice clouds. Its response was compared to other means of measuring thos...

H. Gerber P. J. DeMott D. C. Rogers

1995-01-01

237

Evolution of crystal structures in metallic elements  

NASA Astrophysics Data System (ADS)

Crystal structures of metals are often treated as dense packing of atomic spheres. Face-centered cubic and hexagonal close-packed structures are favored in many metals. Long-period-stacking structures such as 9R are sometimes formed. However, nonclose packed structures such as body centered cubic and ? are formed depending upon chemistry and process conditions. Even in metallic elements, it is a priori unknown how such close/nonclose packed structures are formed and what are their interrelationships. In the present study we show a simple algorithm for automated searching of the phase-transition pathway based upon first-principles calculations, which is applied to systematically pursue the evolution of crystal structures. Following the present algorithm, dynamical stability and interrelationships of different structures generated from a simple cubic structure are revealed for seven metallic elements. Effects of pressure are examined as well. The powerfulness of the automated method to investigate the nature of the phase transition and to predict as-yet-unknown metastable structures is demonstrated.

Togo, Atsushi; Tanaka, Isao

2013-05-01

238

Analysis and Design of an Ice Wall Framing System for an Arctic Drilling Structure  

Microsoft Academic Search

The exterior shell of a concrete base structure for an arctic oil drilling platform must be designed to resist extremely high local ice pressures. Stringent draft criteria for deployment of these structures in shallow waters require that the exterior shells, commonly called ice walls, have minimal weight in conjunction with maximum strength. These conflicting requirements are satisfactorily balanced by the

J. R. Schlechten; R. Fernandes; D. K. Dolan; H. Bivens

1984-01-01

239

Crystal structure of columbite under high pressure  

NASA Astrophysics Data System (ADS)

The structural evolution of two columbites under pressure, one ferrocolumbite from Raode (Africa) and one manganocolumbite from Kragero (Norway), has been determined by single-crystal X-ray diffraction. Structural investigations at high pressure have been carried out on samples which were preliminarily annealed to attain the complete cation-ordered state. For each crystal, five complete datasets have been collected from room pressure up to ca. 7 GPa. Structure refinements converged to final discrepancy factors R ranging between 5.2 and 5.8% for both the crystals. Structure refinements of X-ray diffraction data at different pressures allowed characterisation of the mechanisms by which the columbite structure accommodates variations in pressure. A and B octahedral volumes in both samples decrease linearly as pressure increases, with a larger compression of the larger A site. The difference in polyhedral bulk moduli of the A sites for the two samples does not appear to relate directly to the octahedral sizes, the A site being more compressible in the Fe-rich sample than in the Mn-rich one. By far the most compressible direction in both the analysed samples is along b. The cations are in fact free to move along this direction, thus allowing the octahedral chains to slide over each other; this effect is particularly evident in the manganocolumbite sample which shows a steep shortening of interchain A-B distances along b.

Tarantino, Serena C.; Zema, Michele; Boffa Ballaran, Tiziana

2010-12-01

240

Crystal structure of low-symmetry rondorfite  

SciTech Connect

The crystal structure of an aluminum-rich variety of the mineral rondorfite with the composition Ca{sub 16}[Mg{sub 2}(Si{sub 7}Al)(O{sub 31}OH)]Cl{sub 4} from the skarns of the Verkhne-Chegemskoe plateau (the Kabardino-Balkarian Republic, the Northern Caucasus Region, Russia) was solved in the triclinic space group with the unit-cell parameters a = 15.100(2) A, b = 15.110(2) A, c = 15.092(2) A, {alpha} = 90.06(1) deg., {beta} = 90.01(1) deg., {gamma} = 89.93(1) deg., Z = 4, sp. gr. P1. The structural model consisting of 248 independent atoms was determined by the phase-correction method and refined to R = 3.8% with anisotropic displacement parameters based on all 7156 independent reflections with 7156 F > 3{sigma}(F). The crystal structure is based on pentamers consisting of four Si tetrahedra linked by the central Mg tetrahedron. The structure can formally be refined in the cubic space group (a = 15.105 A, sp. gr. Fd-bar 3, seven independent positions) with anisotropic displacement parameters to R = 2.74% based on 579 reflections with F > 3{sigma}(F) without accounting for more than 1000 observed reflections, which are inconsistent with the cubic symmetry of the crystal structure.

Rastsvetaeva, R. K. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)], E-mail: rast@ns.crys.ras.ru; Zadov, A. E. [NPO Neokhim (Russian Federation); Chukanov, N. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

2008-03-15

241

Crystal structure of low-symmetry rondorfite  

SciTech Connect

The crystal structure of an aluminum-rich variety of the mineral rondorfite with the composition Ca{sub 16}[Mg{sub 2}(Si{sub 7}Al)(O{sub 31}OH)]Cl{sub 4} from the skarns of the Verkhne-Chegemskoe plateau (the Kabardino-Balkarian Republic, the Northern Caucasus Region, Russia) was solved in the triclinic space group with the unit-cell parameters a = 15.100(2) Angstrom-Sign , b = 15.110(2) Angstrom-Sign , c = 15.092(2) Angstrom-Sign , {alpha} = 90.06(1) Degree-Sign , {beta} = 90.01(1) Degree-Sign , {gamma} = 89.93(1) Degree-Sign , Z = 4, sp. gr. P1. The structural model consisting of 248 independent atoms was determined by the phase-correction method and refined to R = 3.8% with anisotropic displacement parameters based on all 7156 independent reflections with 7156 F > 3{sigma}(F). The crystal structure is based on pentamers consisting of four Si tetrahedra linked by the central Mg tetrahedron. The structure can formally be refined in the cubic space group (a = 15.105 Angstrom-Sign , sp. gr. Fd 3 bar , seven independent positions) with anisotropic displacement parameters to R = 2.74% based on 579 reflections with F > 3{sigma}(F) without accounting for more than 1000 observed reflections, which are inconsistent with the cubic symmetry of the crystal structure.

Rastsvetaeva, R. K., E-mail: rast@ns.crys.ras.ru [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Zadov, A. E. [NPO Neokhim (Russian Federation); Chukanov, N. V. [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

2008-03-15

242

Crystal Structure of Toxoplasma gondii Porphobilinogen Synthase  

PubMed Central

Porphobilinogen synthase (PBGS) is essential for heme biosynthesis, but the enzyme of the protozoan parasite Toxoplasma gondii (TgPBGS) differs from that of its human host in several important respects, including subcellular localization, metal ion dependence, and quaternary structural dynamics. We have solved the crystal structure of TgPBGS, which contains an octamer in the crystallographic asymmetric unit. Crystallized in the presence of substrate, each active site contains one molecule of the product porphobilinogen. Unlike prior structures containing a substrate-derived heterocycle directly bound to an active site zinc ion, the product-bound TgPBGS active site contains neither zinc nor magnesium, placing in question the common notion that all PBGS enzymes require an active site metal ion. Unlike human PBGS, the TgPBGS octamer contains magnesium ions at the intersections between pro-octamer dimers, which are presumed to function in allosteric regulation. TgPBGS includes N- and C-terminal regions that differ considerably from previously solved crystal structures. In particular, the C-terminal extension found in all apicomplexan PBGS enzymes forms an intersubunit ?-sheet, stabilizing a pro-octamer dimer and preventing formation of hexamers that can form in human PBGS. The TgPBGS structure suggests strategies for the development of parasite-selective PBGS inhibitors.

Jaffe, Eileen K.; Shanmugam, Dhanasekaran; Gardberg, Anna; Dieterich, Shellie; Sankaran, Banumathi; Stewart, Lance J.; Myler, Peter J.; Roos, David S.

2011-01-01

243

Crystal structure of riboflavin synthase  

SciTech Connect

Riboflavin synthase catalyzes the dismutation of two molecules of 6,7-dimethyl-8-(1'-D-ribityl)-lumazine to yield riboflavin and 4-ribitylamino-5-amino-2,6-dihydroxypyrimidine. The homotrimer of 23 kDa subunits has no cofactor requirements for catalysis. The enzyme is nonexistent in humans and is an attractive target for antimicrobial agents of organisms whose pathogenicity depends on their ability to biosynthesize riboflavin. The first three-dimensional structure of the enzyme was determined at 2.0 {angstrom} resolution using the multiwavelength anomalous diffraction (MAD) method on the Escherichia coli protein containing selenomethionine residues. The homotrimer consists of an asymmetric assembly of monomers, each of which comprises two similar {beta} barrels and a C-terminal {alpha} helix. The similar {beta} barrels within the monomer confirm a prediction of pseudo two-fold symmetry that is inferred from the sequence similarity between the two halves of the protein. The {beta} barrels closely resemble folds found in phthalate dioxygenase reductase and other flavoproteins. The three active sites of the trimer are proposed to lie between pairs of monomers in which residues conserved among species reside, including two Asp-His-Ser triads and dyads of Cys-Ser and His-Thr. The proposed active sites are located where FMN (an analog of riboflavin) is modeled from an overlay of the {beta} barrels of phthalate dioxygenase reductase and riboflavin synthase. In the trimer, one active site is formed, and the other two active sites are wide open and exposed to solvent. The nature of the trimer configuration suggests that only one active site can be formed and be catalytically competent at a time.

Liao, D.-I.; Wawrzak, Z.; Calabrese, J.C.; Viitanen, P.V.; Jordan, D.B. (DuPont); (NWU)

2010-03-05

244

The Surface Structure of Ground Metal Crystals  

NASA Technical Reports Server (NTRS)

The changes produced on metallic surfaces as a result of grinding and polishing are not as yet fully understood. Undoubtedly there is some more or less marked change in the crystal structure, at least, in the top layer. Hereby a diffusion of separated crystal particles may be involved, or, on plastic material, the formation of a layer in greatly deformed state, with possible recrystallization in certain conditions. Czochralski verified the existence of such a layer on tin micro-sections by successive observations of the texture after repeated etching; while Thomassen established, roentgenographically by means of the Debye-Scherrer method, the existence of diffused crystal fractions on the surface of ground and polished tin bars, which he had already observed after turning (on the lathe). (Thickness of this layer - 0.07 mm). Whether this layer borders direct on the undamaged base material or whether deformed intermediate layers form the transition, nothing is known. One observation ty Sachs and Shoji simply states that after the turning of an alpha-brass crystal the disturbance starting from the surface, penetrates fairly deep (approx. 1 mm) into the crystal (proof by recrystallization at 750 C).

Boas, W.; Schmid, E.

1944-01-01

245

The crystal structures of DNA Holliday junctions.  

PubMed

Nearly 40 years ago, Holliday proposed a four-stranded complex or junction as the central intermediate in the general mechanism of genetic recombination. During the past two years, six single-crystal structures of such DNA junctions have been determined by three different research groups. These structures all essentially adopt the antiparallel stacked-X conformation, but can be classified into three distinct categories: RNA-DNA junctions; ACC trinucleotide junctions; and drug-induced junctions. Together, these structures provide insight into how local and distant interactions help to define the detailed and general physical features of Holliday junctions at the atomic level. PMID:11406378

Ho, P S; Eichman, B F

2001-06-01

246

Crystal structure of ultrathin lamellar precipitates  

NASA Astrophysics Data System (ADS)

The crystal structure of lamellar precipitates formed in alloys 1213 (Al-Cu-Ag), V-1461 (Al-Cu-Li) and V-1469 (Al-Cu-Li-Ag) has been studied during age hardening. The experimental studies have been performed using transmission electron microscopy. The precipitates have {111} habits and thicknesses of several atomic planes. In diffraction patterns, these plates give a system of diffuse streaks. These ultrathin plates scatter electrons similar to two-dimensional crystal lattices. It is shown that thin plates of precipitates in alloys 1213, V-1461, and V-1469 give identical systems of diffuse streaks. The two-dimensional crystal lattices that give the system of these streaks have a hexagonal symmetry with the following orientation relationship: {ie481-1} and the lattice parameter a f = 0.495 nm (there is no lattice parameter c f for two-dimensional lattices). A sequence of the steps of reconstruction of the spatial structure of plane precipitates is proposed in terms of their thickness, structures of two-dimensional lattices, and type of precipitates (extrinsic or intrinsic). The influence of Ag on the structure of lamellar precipitates in the V-1469 alloy is discussed.

Alekseev, A. A.; Lukina, E. A.; Klochkova, Yu. Yu.

2013-06-01

247

Crystal structure of ammonia monohydrate phase II.  

PubMed

We have determined the crystal structure of ammonia monohydrate phase II (AMH II) employing a combination of ab initio computational structure prediction and structure solution from neutron powder diffraction data using direct space methods. Neutron powder diffraction data were collected from perdeuterated AMH II using the D2B high-resolution diffractometer at the Institut Laue-Langevin. AMH II crystallizes in space-group Pbca with 16 formula units in a unit-cell of dimensions a = 18.8285(4) A, b = 6.9415(2) A, c = 6.8449(2) A, and V = 894.61(3) A3 [rho(calc)(deuterated) = 1187.56(4) kg m(-3)] at 502 MPa, 180 K. The structure is characterized by sheets of tessellated pentagons formed by orientationally ordered O-D...O, O-D...N, and N-D...O hydrogen-bonds; these sheets are stacked along the a-axis and connected by N-D...O hydrogen bonds alone. With the exception of the simple body-centered-cubic high-pressure phases of ammonia monohydrate and ammonia dihydrate, this is the first complex molecular structure of any of the high-pressure stoichiometric ammonia hydrates to be determined. The powder structure solution is complemented by an ab initio structure prediction using density functional theory which gives an almost identical hydrogen bonding network. PMID:19754191

Fortes, A Dominic; Suard, Emmanuelle; Lemée-Cailleau, Marie-Hélène; Pickard, Christopher J; Needs, Richard J

2009-09-23

248

An Interpretation of the Mechanisms of Ice-Crystal Formation Operative in the Lake Almanor Cloud-Seeding Program.  

NASA Astrophysics Data System (ADS)

In a 1984 85 winter cloud-seeding program at Lake Almanor, California, indium sesquioxide (In2O3) aerosol particle generators were collocated with silver iodide (AgI) aerosol particle generators as a source of inert tracer aerosol. The In2O3 aerosol served as an indicator of the amount of AgI aerosol scavenged. Based on the aerosol emission rates, if AgI aerosol was only captured by scavenging processes, and played no part in forming ice crystals and snowfall, the silver to indium ratio (Ag:In) in the analyzed snow would be 0.8.Analysis of snow samples from the target area produced frequent Ag[ratio]In ratio values in excess of 1.1. In the snowfall at the closest sampling sites to the aerosol generator the high ratios of Ag[ratio]In cannot be explained by the contact-freezing ice formation mechanism. A mechanism with a much faster rate than possible by contact freezing is necessary to produce the high Ag[ratio]In ratios that were observed. Part of the AgI seeding aerosol functioned rapidly to produce ice crystals by a forced condensation-freezing mechanism immediately after generation, and those ice crystals contributed to the snowfall at those sites closest to the generator.

Chai, Steven K.; Finnegan, William G.; Pitter, Richard L.

1993-11-01

249

Structure of Ordinary Ice IH. Part 2: Defects in Ice Volume 1: Point Defects.  

National Technical Information Service (NTIS)

This report examines point defects in ice: molecular defects (vacancies and interstitials), protonic point defects (ions and Bjerrum defects) and electronic point defects (solvated electrons and radicals). Experimental results and theoretical models of th...

V. F. Petrenko R. W. Whitworth

1994-01-01

250

Synchrotron-Based Far-IRAS Investigations of Ice on a Single-Crystal Transition Metal Oxide  

SciTech Connect

Synchrotron-based Far-IR Reflection Absorption Spectroscopy (Far-IRAS) has been used to measure the optical response of multi-layers of water adsorbed on a cleaned and annealed Fe3O4(100) single crystal thin film on MgO(100) substrate in the grazing incidence geometry. Several features of the composite system have been observed. In particular, two derivative-type bands at 700 and 800 cm-1 have been attributed to the librations of ice, and an anti-absorption band at 200 cm-1 has been assigned to the hindered translations of ice.

Hirschmugl, Carol J.; Peden, Charles HF.; Takasaki, M; Collins, M A.; Chambers, Scott A.; G Lawrence Carr and Paul Dumas

1999-10-01

251

Observations on the crystal structures of lueshite  

NASA Astrophysics Data System (ADS)

Laboratory powder XRD patterns of the perovskite-group mineral lueshite from the type locality (Lueshe, Kivu, DRC) and pure NaNbO3 demonstrate that lueshite does not adopt the same space group ( Pbma; #57) as the synthetic compound. The crystal structures of lueshite (2 samples) from Lueshe, Mont Saint-Hilaire (Quebec, Canada) and Sallanlatvi (Kola, Russia) have been determined by single-crystal CCD X-ray diffraction. These room temperature X-ray data for all single-crystal samples can be satisfactorily refined in the orthorhombic space group Pbnm (#62). Cell dimensions, atomic coordinates of the atoms, bond lengths and octahedron tilt angles are given for four crystals. Conventional neutron diffraction patterns for Lueshe lueshite recorded over the temperature range 11-1,000 K confirm that lueshite does not adopt space group Pbma within these temperatures. Neutron diffraction indicates no phase changes on cooling from room temperature to 11 K. None of these neutron diffraction data give satisfactorily refinements but suggest that this is the space group Pbnm. Time-of-flight neutron diffraction patterns for Lueshe lueshite recorded from room temperature to 700 °C demonstrate phase transitions above 550 °C from Cmcm through P4 /mbm to above 650 °C. Cell dimensions and atomic coordinates of the atoms are given for the three high-temperature phases. The room temperature to 400 °C structures cannot be satisfactorily resolved, and it is suggested that the lueshite at room temperature consists of domains of pinned metastable phases with orthorhombic and/or monoclinic structures. However, the sequence of high-temperature phase transitions observed is similar to those determined for synthetic NaTaO3, suggesting that the equilibrated room temperature structure of lueshite is orthorhombic Pbnm.

Mitchell, Roger H.; Burns, Peter C.; Knight, Kevin S.; Howard, Christopher J.; Chakhmouradian, Anton R.

2014-06-01

252

The crystal structure of diphtheria toxin  

Microsoft Academic Search

The crystal structure of the diphtheria toxin dimer at 2.5 Å resolution reveals a Y-shaped molecule of three domains. The catalytic domain, called fragment A, is of the alpha + beta type. Fragment B actually consists of two domains. The transmembrane domain consists of nine alpha-helices, two pairs of which are unusually apolar and may participate in pH-triggered membrane insertion

Seunghyon Choe; Melanie J. Bennett; Gary Fujii; Paul M. G. Curmi; Katherine A. Kantardjieff; R. John Collier; David Eisenberg

1992-01-01

253

Crystal Structures of the ?2-Adrenergic Receptor  

NASA Astrophysics Data System (ADS)

G protein coupled receptors (GPCRs) constitute the largest family of membrane proteins in the human genome, and are responsible for the majority of signal transduction events involving hormones and neuro-transmitters across the cell membrane. GPCRs that bind to diffusible ligands have low natural abundance, are relatively unstable in detergents, and display basal G protein activation even in the absence of ligands. To overcome these problems two approaches were taken to obtain crystal structures of the ?2-adrenergic receptor (?2AR), a well-characterized GPCR that binds cate-cholamine hormones. The receptor was bound to the partial inverse agonist carazolol and co-crystallized with a Fab made to a three-dimensional epitope formed by the third intracellular loop (ICL3), or by replacement of ICL3 with T4 lysozyme. Small crystals were obtained in lipid bicelles (?2AR-Fab) or lipidic cubic phase (?2AR-T4 lysozyme), and diffraction data were obtained using microfocus technology. The structures provide insights into the basal activity of the receptor, the structural features that enable binding of diffusible ligands, and the coupling between ligand binding and G-protein activation.

Weis, William I.; Rosenbaum, Daniel M.; Rasmussen, Søren G. F.; Choi, Hee-Jung; Thian, Foon Sun; Kobilka, Tong Sun; Yao, Xiao-Jie; Day, Peter W.; Parnot, Charles; Fung, Juan J.; Ratnala, Venkata R. P.; Kobilka, Brian K.; Cherezov, Vadim; Hanson, Michael A.; Kuhn, Peter; Stevens, Raymond C.; Edwards, Patricia C.; Schertler, Gebhard F. X.; Burghammer, Manfred; Sanishvili, Ruslan; Fischetti, Robert F.; Masood, Asna; Rohrer, Daniel K.

254

The crystal structure of Hiortdahlite II  

Microsoft Academic Search

Summary The crystal structure of Hiortdahlite II [triclinic P1,a = 11.012(6),b = 10.342(3),c = 7.359 (3) Å,a = 89.92(2)°, ß = 109.21(5)°,y = 90.06(3)°], was determined and refined using 1793 reflections toR1 = 0.069 and R2 = 0.066. The results of the structural study indicated that hiortdahlite II presents the modules which characterize the whole family of minerals related to

S. Merlino; N. Perchiazzi

1987-01-01

255

Fourier Analysis and Structure Determination--Part III: X-ray Crystal Structure Analysis.  

ERIC Educational Resources Information Center

Discussed is single crystal X-ray crystal structure analysis. A common link between the NMR imaging and the traditional X-ray crystal structure analysis is reported. Claims that comparisons aid in the understanding of both techniques. (MVL)

Chesick, John P.

1989-01-01

256

Examining Crystal Fabric Develoment in Ice: Cryo EBSD, Deformation Experiments and the Link to En-glacial Reflectivity  

NASA Astrophysics Data System (ADS)

Over the past few years, cryogenic electron back-scatter diffraction (Cryo-EBSD) has been increasingly used to examine micro-structures in both natural and experimentally deformed ice samples on a micron-scale. Experiments that investigate grain size-sensitive behavior require working on fine-grained ice. These samples present a number of experimental challenges. Issues that present particular difficulties include stable mounting of ice samples, transport of mounted samples and producing a planar, frost-free and damage-free surface. Recent work at the new Otago Ice Deformation Lab has led to the development of a number of experimental methods that help overcome these challenges and enable routine EBSD analysis of fine-grained ice. A brief outline of these experimental methods and some EBSD results from variably deformed ice samples will be presented. Shear deformation experiments on polycrystalline ice are being conducted in order to further explore the relationships between deformation, processes of recrystallization, and the development of anisotropic fabrics that lead to en-glacial seismic reflections. Self-contained, refrigerated deformation units fitted with digital controllers and hardware have been designed for unconfined deformation experiments on polycrystalline synthetic ice. Methods of analysis, from time-lapse photography to random-point tracking, are being employed for monitoring strain in real time. Various methods have been explored for monitoring the development of anisotropic fabrics in ice during progressive deformation. Ultra-sonic transducers can be used to monitor wave velocity changes in various orientations in materials under strain. These experiments have been designed with the objective of quantifying the relationship between deformation fabrics and en-glacial seismic reflectivity observed in thick grounded ice sheets.

Vaughan, Matthew; Prior, David; Seidemann, Meike; Gorman, Andrew; Lilly, Kat; Langhorne, Pat; Easingwood, Richard; Golding, Narayana; Durham, Bill

2014-05-01

257

Crystal Structure, Chemical Binding, and Lattice Properties  

NASA Astrophysics Data System (ADS)

This chapter starts with an overview of the ZnO crystal structure and its conjunction to the chemical binding. ZnO commonly occurs in the wurtzite structure. This fact is closely related to its tetrahedral bond symmetry and its prominent bond polarity. The main part of the first section deals with the ZnO wurtzite crystal lattice, its symmetry properties, and its geometrical parameters. Besides wurtzite ZnO, the other polytypes, zinc-blende and rocksalt ZnO are also briefly discussed. Subsequently, lattice constant variations and crystal lattice deformations are treated. This discussion starts with static lattice constant variations, induced by temperature or by pressure, as well as strain-induced static lattice deformation, which reduces the crystal symmetry. The impact of this symmetry reduction on the electrical polarization is the piezo effect, which is very much pronounced in ZnO and is exploited in many applications. See also Chap. 13. Dynamic lattice deformations manifest themselves as phonons and, in case of doping, as phonon-plasmon mixed states. The section devoted to phonons starts with a consideration of the vibration eigenmodes and their dispersion curves. Special attention is paid to the investigation of phonons by optical spectroscopy. The methods applied for this purpose are infrared spectroscopy and, more often, Raman spectroscopy. The latter method is very common for the structural quality assessment of ZnO bulk crystals and layers; it is also frequently used for the study of the incorporation of dopant and alloying atoms in the ZnO crystal lattice. Thus, it plays an important role with regard to possible optoelectronics and spintronics applications of ZnO. The final section of this chapter focuses on phonon-plasmon mixed states. These eigenstates occur in doped ZnO due to the strong coupling between collective free-carrier oscillations and lattice vibrations, which occurs due to the high bond polarity. Owing to the direct correlation of the plasmon-phonon modes to the electronic doping, they are an inherent property of ZnO samples, when applied in (opto-) electronics and spintronics. See also Chap. 12.

Geurts, J.

258

Crystallization and Characterization of Galdieria sulphuraria RUBISCO in Two Crystal Forms: Structural Phase Transition Observed in P21 Crystal Form  

Microsoft Academic Search

We have isolated ribulose-1,5-bisphosphate-carboxylase\\/oxygenase (RUBISCO) from the red algae Galdieria Sulphuraria . The protein crystallized in two different crystal forms, the I422 crystal form being obtained from hi gh salt and the P2 1 crystal form being obtained from lower concentration of salt and PEG. We report here the crystallization, preliminary stages of structure determination and t he detection of

Michael Baranowski; Boguslaw Stec

2007-01-01

259

Formation of ridges on Europa above crystallizing water bodies inside the ice shell  

NASA Astrophysics Data System (ADS)

Jupiter’s second Galilean satellite, Europa, is a Moon-sized body with an icy shell and global ocean approximately 100 km thick surrounding a rocky interior. Its surface displays extensive tectonic activity in a geologically recent past. Europa’s most ubiquitous surface features, double ridges, have a central trough flanked by two raised edifices. Double ridges can extend hundreds of kilometers and appear genetically related to cracks formed in the Europan ice shell. The origin of the raised flanks has been the center of much debate and many models have been proposed. There are also ridges without a central trough, single ridges. These ridges are far less common than their double ridge counterparts. However, there are locations where along-strike changes in ridge type appear to occur. We explore an elastic model in which the ridges form in response to crystallization of a liquid water intrusion. In our model, liquid water fills tension cracks that open in the Europan crust in response to tidal stress or perhaps overpressure of a subsurface ocean. The crack would be long and essentially continuous, similar to dikes on Earth, explaining the remarkable continuity and lack of segmentation of Europan ridges. The freezing of the water would cause a volume expansion, compressing and buckling the adjacent crust. We find that the geometry of the intruding water body controls the shape of the resulting ridges, with single ridges forming above sill-like intrusions and double ridges above dike-like intrusions. In order to match the ridge heights observed for double ridges we would need approximately 1.5 km2 of water intruded at a shallow depth in the ice shell, potentially over the course of multiple events. Deeper intrusions result in a broader, lower amplitude ridge than shallow intrusions.

Johnston, Stephanie A.; Montési, Laurent G. J.

2014-07-01

260

The structural changes of water ice I during warmup  

NASA Technical Reports Server (NTRS)

The polymorph transitions of vapor deposited water ice I during warmup from 15 K to 210 K was mapped by means of selected area electron diffraction. The polymorph transitions account for many phenomena observed in laboratory analog studies of cometary outgassing and radial diffusion in UV photolyzed interstellar ices.

Jenniskens, Peter; Blake, David F.

1994-01-01

261

Structural changes of filled ice Ic structure for hydrogen hydrate under high pressure.  

PubMed

High-pressure experiments of hydrogen hydrate, filled ice Ic structure, were performed using a diamond-anvil cell in the pressure range of 0.1-80.3 GPa at room temperature. In situ x-ray diffractometry (XRD) revealed that structural changes took place at approximately 35-40 and 55-60 GPa, and that the high-pressure phase of hydrogen hydrate survived up to at least 80.3 GPa. Raman spectroscopy showed that the changes in vibrational mode for the hydrogen molecules in hydrogen hydrate occurred at around 40 and 60 GPa, and these results were consistent with those of the XRD. At about 40 GPa, the intermolecular distance of host water molecules consisting the framework attained the critical distance of symmetrization of the hydrogen bond for water molecules, which suggested that symmetrization of the hydrogen bond occurred at around 40 GPa. The symmetrization might introduce some structural change in the filled ice Ic structure. In addition, the existence of the high-pressure phase above 55-60 GPa implies that a denser structure than that of filled ice Ic may exist in hydrogen hydrate. PMID:19071926

Machida, Shin-ichi; Hirai, Hisako; Kawamura, Taro; Yamamoto, Yoshitaka; Yagi, Takehiko

2008-12-14

262

Ikaite crystals in melting sea ice - implications for pCO2 and pH levels in Arctic surface waters  

NASA Astrophysics Data System (ADS)

A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO2 exchange. This has been complicated by the recent discoveries of ikaite (a polymorph of CaCO3·6H2O) in Arctic and Antarctic sea ice, which indicate that multiple chemical transformations occur in sea ice with a possible effect on CO2 and pH conditions in surface waters. Here, we report on biogeochemical conditions, microscopic examinations and x-ray diffraction analysis of single crystals from a melting 1.7 km2 (0.5-1 m thick) drifting ice floe in the Fram Strait during summer. Our findings show that ikaite crystals are present throughout the sea ice but with larger crystals appearing in the upper ice layers. Ikaite crystals placed at elevated temperatures disintegrated into smaller crystallites and dissolved. During our field campaign in late June, melt reduced the ice floe thickness by 0.2 m per week and resulted in an estimated 3.8 ppm decrease of pCO2 in the ocean surface mixed layer. This corresponds to an air-sea CO2 uptake of 10.6 mmol m-2 sea ice d-1 or to 3.3 ton km-2 ice floe week-1. This is markedly higher than the estimated primary production within the ice floe of 0.3-1.3 mmol m-2 sea ice d-1. Finally, the presence of ikaite in sea ice and the dissolution of the mineral during melting of the sea ice and mixing of the melt water into the surface oceanic mixed layer accounted for half of the estimated pCO2 uptake.

Rysgaard, S.; Glud, R. N.; Lennert, K.; Cooper, M.; Halden, N.; Leakey, R. J. G.; Hawthorne, F. C.; Barber, D.

2012-08-01

263

Structural map of flow variability and propagation behavior in the Ross Ice Shelf  

NASA Astrophysics Data System (ADS)

Fracture geometries in the Ross Ice Shelf, observable using visible band satellite imagery from the MODIS Mosaic of Antarctica (MOA) and the Landsat Image Mosaic of Antarctica (LIMA) provide a unique opportunity to study fracture propagation behavior and discharge variability in the ice streams and outlet glaciers feeding the shelf. Propagation is driven by changes in fracture length, near-field stress conditions, and the material properties of the ice. Changes in ice stream discharge and the development of "sticky spots," in both ice streams and within the shelf, lead to redirection of flow, changes in lateral gradients of ice velocity, and the propagation of fractures in response to changes in near-field stresses. The propagation behaviors most commonly observed in the ice shelf are the growth in the transverse direction of a fracture that formed within a shear zone and mechanical interactions between adjacent fracture tips. We use fracture mechanics theory and remote-sensed imagery to categorize fracture patterns and longitudinal zones of fractured ice in the Ross Ice Shelf. Near current sites of formation, simple fracture geometries and principal stresses are used to illustrate physical processes related to the formation and propagation of fractures. To compute flow lines and principal stresses, we derive a velocity map of the Ross Ice Shelf by merging two velocity datasets using a combination of statistical methods. A structural map of fracture geometries, relict shear margins, and structural boundaries is constructed. Using the ice shelf features, present-day flow lines, and principal stresses, we investigate the manner in which principal stresses affect fracture formation and propagation behavior and the variability of ice stream discharge into the shelf.

LeDoux, C. M.; Hulbe, C. L.

2011-12-01

264

Geometry of Crystal Structure with Defects. I. Euclidean Picture  

NASA Astrophysics Data System (ADS)

Continuously distributed defects of crystal structure are considered. The starting point is the Euclidean geometry of the ideal crystal lattice and the topological description of the distortion of the crystal structure. It is shown how the non-Euclidean geometry of distorted crystal structure, as well as the basic assumptions of the phenomenological plasticity theory concerning the deformation of a continuum, are related to those theories. A form for an affine connection describing continuously distributed dislocations is proposed.

Trzesowski, Andrzej

1987-04-01

265

The First Mammalian Aldehyde Oxidase Crystal Structure  

PubMed Central

Aldehyde oxidases (AOXs) are homodimeric proteins belonging to the xanthine oxidase family of molybdenum-containing enzymes. Each 150-kDa monomer contains a FAD redox cofactor, two spectroscopically distinct [2Fe-2S] clusters, and a molybdenum cofactor located within the protein active site. AOXs are characterized by broad range substrate specificity, oxidizing different aldehydes and aromatic N-heterocycles. Despite increasing recognition of its role in the metabolism of drugs and xenobiotics, the physiological function of the protein is still largely unknown. We have crystallized and solved the crystal structure of mouse liver aldehyde oxidase 3 to 2.9 ?. This is the first mammalian AOX whose structure has been solved. The structure provides important insights into the protein active center and further evidence on the catalytic differences characterizing AOX and xanthine oxidoreductase. The mouse liver aldehyde oxidase 3 three-dimensional structure combined with kinetic, mutagenesis data, molecular docking, and molecular dynamics studies make a decisive contribution to understand the molecular basis of its rather broad substrate specificity.

Coelho, Catarina; Mahro, Martin; Trincao, Jose; Carvalho, Alexandra T. P.; Ramos, Maria Joao; Terao, Mineko; Garattini, Enrico; Leimkuhler, Silke; Romao, Maria Joao

2012-01-01

266

Ikaite crystals in melting sea ice - implications for pCO2 and pH levels in Arctic surface waters  

NASA Astrophysics Data System (ADS)

A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO2 exchange. This has been complicated by the recent discoveries of ikaite (CaCO3·6H2O) in Arctic and Antarctic sea ice, which indicate that multiple chemical transformations occur in sea ice with a possible effect on CO2 and pH conditions in surface waters. Here we report on biogeochemical conditions, microscopic examinations and x-ray diffraction analysis of single crystals from an actively melting 1.7 km2 (0.5-1 m thick) drifting ice floe in the Fram Strait during summer. Our findings show that ikaite crystals are present throughout the sea ice but with larger crystals appearing in the upper ice layers. Ikaite crystals placed at elevated temperatures gradually disintegrated into smaller crystallites and dissolved. During our field campaign in late June, melt reduced the ice flow thickness by ca. 0.2 m per week and resulted in an estimated 1.6 ppm decrease of pCO2 in the ocean surface mixed layer. This corresponds to an air-sea CO2 uptake of 11 mmol m-2 sea ice d-1 or to 3.5 ton km-2 ice floe week-1.

Rysgaard, S.; Glud, R. N.; Lennert, K.; Cooper, M.; Halden, N.; Leakey, R. J. G.; Hawthorne, F. C.; Barber, D.

2012-03-01

267

Ice Cover as a Factor Driving Microbial Community Structure in the Laurentian Great Lakes  

NASA Astrophysics Data System (ADS)

Lakes serve as rapid responding sentinels of human influence on the natural environment rendering them powerful tools to advance our understanding of a changing climate on microbial community structure and function. Whereas we possess a baseline knowledge of microbial diversity in the Great Lakes, we know little about how these communities respond to the manifestations of climate change. Through collaboration with U.S.- and Canadian Coast Guards, winter surveys have been conducted on Lake Erie since 2007. The surveys have captured extremes in ice extent ranging from expansive ice cover through 2011 to nearly ice-free waters in winter 2012, a condition driven by a warm positive Arctic Oscillation. We showed that dramatic changes in annual ice cover were accompanied by equally dramatic shifts in phytoplankton community structure. Expansive ice cover documented for Lake Erie in winters 2010 and 2011 supported ice-associated phytoplankton blooms dominated by physiologically robust, filamentous centric diatoms. Transcriptomic analysis of the winter bloom offers insights into the success of this psychrophilic community. By comparison, ice free conditions promoted the growth of small-sized cells supported by analysis of size-fractionated chlorophyll a and flow cytometry. The phytoplankton community in winter 2013 was dominated by microplankton-sized filamentous diatoms, coincident with expansive ice cover and thus returning to the size structure of the 2010 and 2011 communities. Reduced size is recognized as a universal ecological response to global warming in aquatic systems although it usually marks a response to climate warming over multiple years, not a single season as reported here. Fig. 1. Winter surveys conducted on Lake Erie over two years demonstrated tight coupling between microplankton Chl a biomass and total Chl a during winter 2010-11 (purple, green), a year of expansive ice cover. A warm positive Arctic Oscillation resulted in negligible ice cover on Lake Erie in 2011-12. Coincident with the ice-free conditions, a strong departure from a microplankton-dominated system was documented (red, yellow).

McKay, R. M.; Beall, B.; Oyserman, B.; Smith, D.; Bullerjahn, G.; Morris, P.; Twiss, M. R.

2013-12-01

268

Ice island creation, drift, recurrences, mechanical properties, and interactions with arctic offshore oil production structures. Final report  

SciTech Connect

Research and engineering studies on first-year sea ice for over two decades has resulted in the design, construction, and operation of jacket platforms, of artificial islands, and of massive gravity structures which routinely withstand moving sea ice of thickness up to 2 meters. However, the less-common interactions between such structures and moving multiyear ice ({ge}3 meters thick), and also moving ice islands (10 to 60 meters thick) remain as the unknown and potentially most serious hazard for Arctic offshore structures. In this study, research was addressed across the complete span of remaining questions regarding such features. Ice island components, thickness distributions, scenarios and models for the interactions of massive ice features with offshore structures, all were considered. Ice island morphology and calving studies were directed at the cluster of 19 ice islands produced in a calving from the Ward Hunt Ice Shelf on Ellesmere Island in 1983, and also at a calving from the Milne Ice Shelf in 1988. The statistics of ice island dynamics, on both a short-term small-scale basis and also on a long-term basis, were studied. Typical wind velocities of 5 to 7.5 meters per second led to ice island speeds of about 0.014 of the wind speed, at an angle of 20{degrees} to the right of the wind direction. Ice island samples were tested for their stress/strain characteristics. Compressive strength values ranged from 1.64 MPa at a strain rate of 2 {times} 10{sup {minus}7} s{sup {minus}1} to 6.75 MPa at a strain rate of 1 {times} 10{sup {minus}3} s{sup {minus}1}. Scenarios for ice island/structure interactions were developed, and protective countermeasures such as spray ice and ice rubble barriers were suggested. Additional computer modeling of structure/ice interactions for massive ice features is recommended.

Sackinger, W.M.; Jeffries, M.O.; Li, Fucheng; Lu, Mingchi

1991-03-01

269

Crystal structure of the dynein motor domain.  

PubMed

Dyneins are microtubule-based motor proteins that power ciliary beating, transport intracellular cargos, and help to construct the mitotic spindle. Evolved from ring-shaped hexameric AAA-family adenosine triphosphatases (ATPases), dynein's large size and complexity have posed challenges for understanding its structure and mechanism. Here, we present a 6 angstrom crystal structure of a functional dimer of two ~300-kilodalton motor domains of yeast cytoplasmic dynein. The structure reveals an unusual asymmetric arrangement of ATPase domains in the ring-shaped motor domain, the manner in which the mechanical element interacts with the ATPase ring, and an unexpected interaction between two coiled coils that create a base for the microtubule binding domain. The arrangement of these elements provides clues as to how adenosine triphosphate-driven conformational changes might be transmitted across the motor domain. PMID:21330489

Carter, Andrew P; Cho, Carol; Jin, Lan; Vale, Ronald D

2011-03-01

270

High-frequency microwave anti-/de-icing system for carbon-reinforced airfoil structures  

NASA Astrophysics Data System (ADS)

An aircraft may be subjected to icing for a variety of meteorological reasons during the flight. Ice formation on the plane and in particular on the aerodynamically carrying structures adversely affects the flight behaviour. Conventional de-icing methods for aluminum wings are characterised by a high energy consumption during the flight and slow ice melting due to thermal diffusion of the heat in the wing material. In addition to advanced turbines, novel materials and composites have to be used in order to reduce the weight and, hence, the fuel consumption. These composite materials have a far worse thermal conductivity than metals and undergo delamination when hot air systems, resistance or ohmic heating mats are used. In the paper, the unique advantages of a novel High Frequency Microwave Anti-/De-icing System for large future aircraft with carbon reinforced leading edge structures are presented.

Feher, Lambert; Thumm, Manfred

2001-08-01

271

Development of a structural concept to resist impacts from multiyear ice floes, ridges, and icebergs  

SciTech Connect

Large multi-year ice features and icebergs may have masses ranging up to 20 million tons or more and may move in the open water at speeds up to 1 knot, thus developing tremendous kinetic energy. A stepped structure concept has been developed to resist these impacts and to transfer the resultant forces and moments into the foundation thus developing a relatively high concentrated reaction force against the ice tending to spall and split it, thus causing a multi-modal failure of the ice, as well as using up kinetic energy at a relatively controlled rate. Calculated ice forces and ice failure modes will be presented. The stepped structure concept is primarily applicable to production platforms in water depths of 50 to 200 meters, which are subject to impact of large ice features such as multi-year ridges, floes, and icebergs The resulting global ice loads are reduced by 50 percent or more as compared to those developed by a vertical or a steep sided structure. Overturning moments are reduced, thus reducing maxima soil bearing values. The structure itself is efficient in its use of structural materials, and is practicable for construction in prestressed reinforced concrete or steel/ concrete hybrid construction. It has acceptable draft during tow and can carry a fully outfitted deck. It is stable during all stages of installation.

Gerwick, B.C.; Potter, R.E.; Rojansky, M.

1984-05-01

272

The Crystal Structure of Triuranyl Diphosphate Tetrahydrate  

Microsoft Academic Search

The hydrated neutral uranyl phosphate, (UO2)3(PO4)2(H2O)4, was synthesized by hydrothermal methods. Intensity data were collected using MoK? radiation and a CCD-based area detector. The crystal structure was solved by direct methods and refined by full-matrix least-squares techniques to agreement indices wR2=0.116 for all data, and R1=0.040, calculated for the 2764 unique observed reflections (?Fo??4?F). The compound is orthorhombic, space group

Andrew J. Locock; Peter C. Burns

2002-01-01

273

Crystal Structure of Marburg Virus VP24.  

PubMed

The VP24 protein plays an essential, albeit poorly understood role in the filovirus life cycle. VP24 is only 30% identical between Marburg virus and the ebolaviruses. Furthermore, VP24 from the ebolaviruses is immunosuppressive, while that of Marburg virus is not. The crystal structure of Marburg virus VP24, presented here, reveals that although the core is similar between the viral genera, Marburg VP24 is distinguished by a projecting ?-shelf and an alternate conformation of the N-terminal polypeptide. PMID:24574400

Zhang, Adrianna P P; Bornholdt, Zachary A; Abelson, Dafna M; Saphire, Erica Ollmann

2014-05-01

274

Elasticity of some mantle crystal structures. II.  

NASA Technical Reports Server (NTRS)

The single-crystal elastic constants are determined as a function of pressure and temperature for rutile structure germanium dioxide (GeO2). The data are qualitatively similar to those of rutile TiO2 measured by Manghnani (1969). The compressibility in the c direction is less than one-half that in the a direction, the pressure derivative of the shear constant is negative, and the pressure derivative of the bulk modulus has a relatively high value of about 6.2. According to an elastic strain energy theory, the negative shear modulus derivative implies that the kinetic barrier to diffusion decreases with increasing pressure.

Wang, H.; Simmons, G.

1973-01-01

275

Radiation effects in water ice: A near-edge x-ray absorption fine structure study  

NASA Astrophysics Data System (ADS)

The changes in the structure and composition of vapor-deposited ice films irradiated at 20 K with soft x-ray photons (3-900 eV) and their subsequent evolution with temperatures between 20 and 150 K have been investigated by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) at the oxygen K edge. We observe the hydroxyl OH, the atomic oxygen O, and the hydroperoxyl HO2 radicals, as well as the oxygen O2 and hydrogen peroxide H2O2 molecules in irradiated porous amorphous solid water (p-ASW) and crystalline (Icryst) ice films. The evolution of their concentrations with the temperature indicates that HO2, O2, and H2O2 result from a simple step reaction fuelled by OH, where O2 is a product of HO2 and HO2 a product of H2O2. The local order of ice is also modified, whatever the initial structure is. The crystalline ice Icryst becomes amorphous. The high-density amorphous phase (Iah) of ice is observed after irradiation of the p-ASW film, whose initial structure is the normal low-density form of the amorphous ice (Ial). The phase Iah is thus peculiar to irradiated ice and does not exist in the as-deposited ice films. A new ``very high density'' amorphous phase-we call Iavh-is obtained after warming at 50 K the irradiated p-ASW ice. This phase is stable up to 90 K and partially transforms into crystalline ice at 150 K.

Laffon, C.; Lacombe, S.; Bournel, F.; Parent, Ph.

2006-11-01

276

Energy benchmarks for water clusters and ice structures from an embedded many-body expansion.  

PubMed

We show how an embedded many-body expansion (EMBE) can be used to calculate accurate ab initio energies of water clusters and ice structures using wavefunction-based methods. We use the EMBE described recently by Bygrave et al. [J. Chem. Phys. 137, 164102 (2012)], in which the terms in the expansion are obtained from calculations on monomers, dimers, etc., acted on by an approximate representation of the embedding field due to all other molecules in the system, this field being a sum of Coulomb and exchange-repulsion fields. Our strategy is to separate the total energy of the system into Hartree-Fock and correlation parts, using the EMBE only for the correlation energy, with the Hartree-Fock energy calculated using standard molecular quantum chemistry for clusters and plane-wave methods for crystals. Our tests on a range of different water clusters up to the 16-mer show that for the second-order Møller-Plesset (MP2) method the EMBE truncated at 2-body level reproduces to better than 0.1 mE(h)/monomer the correlation energy from standard methods. The use of EMBE for computing coupled-cluster energies of clusters is also discussed. For the ice structures Ih, II, and VIII, we find that MP2 energies near the complete basis-set limit reproduce very well the experimental values of the absolute and relative binding energies, but that the use of coupled-cluster methods for many-body correlation (non-additive dispersion) is essential for a full description. Possible future applications of the EMBE approach are suggested. PMID:24070273

Gillan, M J; Alfè, D; Bygrave, P J; Taylor, C R; Manby, F R

2013-09-21

277

Energy benchmarks for water clusters and ice structures from an embedded many-body expansion  

NASA Astrophysics Data System (ADS)

We show how an embedded many-body expansion (EMBE) can be used to calculate accurate ab initio energies of water clusters and ice structures using wavefunction-based methods. We use the EMBE described recently by Bygrave et al. [J. Chem. Phys. 137, 164102 (2012)], in which the terms in the expansion are obtained from calculations on monomers, dimers, etc., acted on by an approximate representation of the embedding field due to all other molecules in the system, this field being a sum of Coulomb and exchange-repulsion fields. Our strategy is to separate the total energy of the system into Hartree-Fock and correlation parts, using the EMBE only for the correlation energy, with the Hartree-Fock energy calculated using standard molecular quantum chemistry for clusters and plane-wave methods for crystals. Our tests on a range of different water clusters up to the 16-mer show that for the second-order Møller-Plesset (MP2) method the EMBE truncated at 2-body level reproduces to better than 0.1 mEh/monomer the correlation energy from standard methods. The use of EMBE for computing coupled-cluster energies of clusters is also discussed. For the ice structures Ih, II, and VIII, we find that MP2 energies near the complete basis-set limit reproduce very well the experimental values of the absolute and relative binding energies, but that the use of coupled-cluster methods for many-body correlation (non-additive dispersion) is essential for a full description. Possible future applications of the EMBE approach are suggested.

Gillan, M. J.; Alfè, D.; Bygrave, P. J.; Taylor, C. R.; Manby, F. R.

2013-09-01

278

Crystal Distortion of Dy2Ti2O7 at the Spin Ice Transition Temperature  

SciTech Connect

Dy2Ti2O7 with the pyrochlore structure shows a spin ice transition at about 1 K. The Dy3+ ion in this compound has an effective spin Seff=1/2. The Dy ions reside on the vertices of corner-linked tetrahedra. Due to a strong single-ion anisotropy, the ground state of Dy3+ is well expressed by an Ising doublet with local <111> quantization axes. We measured the x-ray diffraction for a Dy2Ti2O7 powder sample between 0.15 K. and 20 K. The lattice spacing increases drastically between 1.5 K and about 1 K, with decreasing temperature. The lattice spacing of the (222) diffraction is considerably larger than the other directions.

Suzuki, H.; Hata, F.; Xue, Y.; Kaneko, H.; Hosomichi, A.; Abe, S. [Department of Physics, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan); Higashinaka, R.; Nakatsuji, S.; Maeno, Y. [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)

2006-09-07

279

Crystal structure of the Baykovite mineral  

SciTech Connect

The X-ray crystal structure of baykovite, [Ca{sub 1.07}Mg{sub 0.62}Ti{sub 0.31}(Al{sub 0.55}Si{sub 0.45}){sub 2}O{sub 6}][Al(Mg{sub 0.77}Ti{sub 1.17}Al{sub 0.06}){sub 2}O{sub 4}] - a mineral of the enigmatite structural group - was determined: sp gr. P{bar 1}, a = 10.425(2), b = 10.799(2), c = 8.924(2) {Angstrom}, {alpha} = 105.98(2), {beta} = 96.05(2), {gamma} = 124.76(1){degrees}, V= 748.425, Z= 2, and R = 0.046. Baykovite is shown to be close to rhoenite varieties, which are characterized by their anomalous composition with a high content of titanium in two oxidation states: Ti{sup +3} and Ti{sup +4}. The structures of enigmatite-group compounds are described as disomatic structures formed from spinel and pyroxene moieties. A scheme of cation distribution over the equivalent positions in the enigmatite-group structures is proposed based on the assumption that individual fragments inherit the main features of the parent structures. 8 refs., 2 figs., 5 tabs.

Arakcheeva, A.V. [Baikov Institute of Metallurgy, Moscow (Russian Federation)

1995-03-01

280

Computational prediction of organic crystal structures and polymorphism  

NASA Astrophysics Data System (ADS)

The development of a robust manufacturing process for solid organic materials, such as pharmaceuticals, can be complicated when the molecules crystallize in different solid forms, including polymorphs. The diverse challenges to computational chemistry in computing the relative thermodynamic stability of different potential crystal structures for a range of organic molecules are outlined. Once the crystal structures which are thermodynamically feasible have been obtained, then comparison with the experimentally known polymorphs can provide interesting insights into crystallization behaviour. Although the computational prediction of polymorphism requires modelling the kinetic factors that can influence crystallization, the computational prediction of the crystal energy landscape is already a valuable complement to experimental searches for polymorphs.

Price, S. L.

281

Structural and spectroscopic studies on calcium succinate single crystals  

NASA Astrophysics Data System (ADS)

Calcium succinate crystals have been grown by gel aided solution growth technique. The structure of the crystal is solved by single crystal XRD analysis. The Crystal structure of the title compound is triclinic having space group P(1) Powder XRD studies confirmed the good crystalline nature of the sample. The different functional groups and their assigned vibrations are discussed by FT-IR and FT Raman spectroscopic studies.

Binitha, M. P.; Pradyumnan, P. P.

2014-04-01

282

Crystal structure of yeast Sco1.  

PubMed

The Sco family of proteins are involved in the assembly of the dinuclear CuA site in cytochrome c oxidase (COX), the terminal enzyme in aerobic respiration. These proteins, which are found in both eukaryotes and prokaryotes, are characterized by a conserved CXXXC sequence motif that binds copper ions and that has also been proposed to perform a thiol:disulfide oxidoreductase function. The crystal structures of Saccharomyces cerevisiae apo Sco1 (apo-ySco1) and Sco1 in the presence of copper ions (Cu-ySco1) were determined to 1.8- and 2.3-A resolutions, respectively. Yeast Sco1 exhibits a thioredoxin-like fold, similar to that observed for human Sco1 and a homolog from Bacillus subtilis. The Cu-ySco1 structure, obtained by soaking apo-ySco1 crystals in copper ions, reveals an unexpected copper-binding site involving Cys181 and Cys216, cysteine residues present in ySco1 but not in other homologs. The conserved CXXXC cysteines, Cys148 and Cys152, can undergo redox chemistry in the crystal. An essential histidine residue, His239, is located on a highly flexible loop, denoted the Sco loop, and can adopt positions proximal to both pairs of cysteines. Interactions between ySco1 and its partner proteins yeast Cox17 and yeast COX2 are likely to occur via complementary electrostatic surfaces. This high-resolution model of a eukaryotic Sco protein provides new insight into Sco copper binding and function. PMID:16570183

Abajian, Carnie; Rosenzweig, Amy C

2006-06-01

283

Snow Crystals  

NSDL National Science Digital Library

This site describes snow crystals and snowflakes. Although a common meteorological phenomenon, snow crystal growth is a fascinating and poorly understood process, in which remarkably complex and beautifully symmetric structures appear, quite literally, out of thin air. The many facets of snow crystals are described here, along with the attempts to understand their formation. Site highlights include research on creating designer snow crystals in the laboratory, the history of early snow crystal observations, snow crystal photography, properties of frozen precipitation, and a snow crystal primer for a short course in snow crystal physics - what snow crystals are, how they form, and why they form the way they do. Information is offered on snow crystal classification, preservation, and unusual crystal forms. An extensive image gallery of lab-created crystal forms is available, with enlargeable thumbnail images. There are even instructions for users on how to create crystals. This could be made into a classroom activity, as the science of the growth is explained. Snowflake Physics discusses diffusion, dendrite growth, ice surface physics, electric growth, and ice properties. A vast list of related links is also provided.

Libbrecht, Kenneth

284

Crystal structure of human nicotinamide riboside kinase.  

PubMed

Nicotinamide riboside kinase (NRK) has an important role in the biosynthesis of NAD(+) as well as the activation of tiazofurin and other NR analogs for anticancer therapy. NRK belongs to the deoxynucleoside kinase and nucleoside monophosphate (NMP) kinase superfamily, although the degree of sequence conservation is very low. We report here the crystal structures of human NRK1 in a binary complex with the reaction product nicotinamide mononucleotide (NMN) at 1.5 A resolution and in a ternary complex with ADP and tiazofurin at 2.7 A resolution. The active site is located in a groove between the central parallel beta sheet core and the LID and NMP-binding domains. The hydroxyl groups on the ribose of NR are recognized by Asp56 and Arg129, and Asp36 is the general base of the enzyme. Mutation of residues in the active site can abolish the catalytic activity of the enzyme, confirming the structural observations. PMID:17698003

Khan, Javed A; Xiang, Song; Tong, Liang

2007-08-01

285

Crystal Structure of Human Nicotinamide Riboside Kinase  

SciTech Connect

Nicotinamide riboside kinase (NRK) has an important role in the biosynthesis of NAD{sup +} as well as the activation of tiazofurin and other NR analogs for anticancer therapy. NRK belongs to the deoxynucleoside kinase and nucleoside monophosphate (NMP) kinase superfamily, although the degree of sequence conservation is very low. We report here the crystal structures of human NRK1 in a binary complex with the reaction product nicotinamide mononucleotide (NMN) at 1.5 {angstrom} resolution and in a ternary complex with ADP and tiazofurin at 2.7 {angstrom} resolution. The active site is located in a groove between the central parallel {beta} sheet core and the LID and NMP-binding domains. The hydroxyl groups on the ribose of NR are recognized by Asp56 and Arg129, and Asp36 is the general base of the enzyme. Mutation of residues in the active site can abolish the catalytic activity of the enzyme, confirming the structural observations.

Khan,J.; Xiang, S.; Tong, L.

2007-01-01

286

Rotating micro-structures in Antarctic cold basal ice: implications for glacier flow and its interpretation  

Microsoft Academic Search

Structural analyses were conducted in the basal zone of an Antarctic glacier. The studied basal ice sequence was retrieved\\u000a from a 20-m-long subglacial tunnel dug at the margin of the glacier and is at the temperature of ?17°C. For the first time,\\u000a rotating clast systems embedded within debris-rich ice were thin-sectioned using specially designed cutting techniques. The\\u000a observed structures reflect

Denis Samyn; Sean J. Fitzsimons; Reginald D. Lorrain

2010-01-01

287

Crystal Structure of Human Spermine Synthase  

PubMed Central

The crystal structures of two ternary complexes of human spermine synthase (EC 2.5.1.22), one with 5?-methylthioadenosine and spermidine and the other with 5?-methylthioadenosine and spermine, have been solved. They show that the enzyme is a dimer of two identical subunits. Each monomer has three domains: a C-terminal domain, which contains the active site and is similar in structure to spermidine synthase; a central domain made up of four ?-strands; and an N-terminal domain with remarkable structural similarity to S-adenosylmethionine decarboxylase, the enzyme that forms the aminopropyl donor substrate. Dimerization occurs mainly through interactions between the N-terminal domains. Deletion of the N-terminal domain led to a complete loss of spermine synthase activity, suggesting that dimerization may be required for activity. The structures provide an outline of the active site and a plausible model for catalysis. The active site is similar to those of spermidine synthases but has a larger substrate-binding pocket able to accommodate longer substrates. Two residues (Asp201 and Asp276) that are conserved in aminopropyltransferases appear to play a key part in the catalytic mechanism, and this role was supported by the results of site-directed mutagenesis. The spermine synthase·5?-methylthioadenosine structure provides a plausible explanation for the potent inhibition of the reaction by this product and the stronger inhibition of spermine synthase compared with spermidine synthase. An analysis to trace possible evolutionary origins of spermine synthase is also described.

Wu, Hong; Min, Jinrong; Zeng, Hong; McCloskey, Diane E.; Ikeguchi, Yoshihiko; Loppnau, Peter; Michael, Anthony J.; Pegg, Anthony E.; Plotnikov, Alexander N.

2008-01-01

288

Evidence of ice crystals at cloud top of Arctic boundary-layer mixed-phase clouds derived from airborne remote sensing  

NASA Astrophysics Data System (ADS)

The vertical distribution of ice crystals in Arctic boundary-layer mixed-phase (ABM) clouds was investigated by airborne remote-sensing and in situ measurements during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. Information on the spectral absorption of solar radiation by ice and liquid water cloud particles is derived from airborne measurements of solar spectral radiation reflected by these clouds. It is shown by calculation of the vertical weighting function of the measurements that the observed absorption of solar radiation is dominated by the upper cloud layers (50% within 200 m from cloud top). This vertical weighting function is shifted even closer to cloud top for wavelengths where absorption by ice dominates. On this basis an indicator of the vertical distribution of ice crystals in ABM clouds is designed. Applying in situ measured microphysical properties, the cloud-top reflectivity was calculated by radiative transfer simulations and compared to the measurements. It is found that ice crystals near cloud top (mixed-phase cloud top layer) are necessary to reproduce the measurements at wavelengths where absorption by ice dominates. The observation of backscatter glories on the cloud top generally indicating liquid water droplets does not contradict the postulated presence of ice crystals. Radiative transfer simulations reproduce the observed glories even if the cloud top layer is of mixed-phase character.

Ehrlich, A.; Wendisch, M.; Bierwirth, E.; Gayet, J.-F.; Mioche, G.; Lampert, A.; Mayer, B.

2009-12-01

289

Evidence of ice crystals at cloud top of Arctic boundary-layer mixed-phase clouds derived from airborne remote sensing  

NASA Astrophysics Data System (ADS)

The vertical distribution of ice crystals in Arctic boundary-layer mixed-phase (ABM) clouds was investigated by airborne remote sensing and in situ measurements during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. From airborne measurements of spectral solar radiation reflected by the ABM clouds information on the spectral absorption of solar radiation by ice and liquid water cloud particles is derived. It is shown by calculation of the vertical weighting function of the measurements that the observed absorption of solar radiation is dominated by the upper cloud layers (50% within 200 m from cloud top). This vertical weighting function is shifted even closer to cloud top for wavelengths where absorption by ice is dominating. On this basis an indicator of the vertical distribution of ice crystals in ABM clouds is designed. Applying the in situ measured microphysical properties, the cloud top reflectance was calculated by radiative transfer simulations and compared to measurements. It is found that ice crystals near cloud top (mixed-phase cloud top layer) are necessary to reproduce the measurements at wavelengths where absorption by ice is dominating. The observation of backscatter glories on top of the ABM clouds generally indicating liquid water droplets does not contradict the postulated presence of ice crystals. Radiative transfer simulations reproduce the observed glories even if the cloud top layer is of mixed-phase character.

Ehrlich, A.; Wendisch, M.; Bierwirth, E.; Gayet, J.-F.; Mioche, G.; Lampert, A.; Mayer, B.

2009-06-01

290

Midlatitude Cirrus Clouds Derived from Hurricane Nora: A Case Study with Implications for Ice Crystal Nucleation and Shape  

NASA Technical Reports Server (NTRS)

Hurricane Nora traveled up the Bala Peninsula coast in the unusually warm El Nino waters of September 1997, until rapidly decaying as it approached Southern California on 24 September. The anvil cirrus blowoff from the final surge of tropical convection became embedded in subtropical flow that advected the cirrus across the western US, where it was studied from the Facility for Atmospheric Remote Sensing (FARS) in Salt Lake City, Utah. A day later, the cirrus shield remnants were redirected southward by midlatitude circulations into the Southern Great Plains, providing a case study opportunity for the research aircraft and ground-based remote sensors assembled at the Clouds and Radiation Testbed (CART) site in northern Oklahoma. Using these comprehensive resources and new remote sensing cloud retrieval algorithms, the microphysical and radiative cloud properties of this unusual cirrus event are uniquely characterized. Importantly, at both the FARS and CART sites the cirrus generated spectacular optical displays, which acted as a tracer for the hurricane cirrus, despite the limited lifetimes of individual ice crystals. Lidar polarization data indicate widespread regions of uniform ice plate orientations, and in situ particle masticator data show a preponderance of pristine, solid hexagonal plates and columns. It is suggested that these unusual aspects are the result of the mode of cirrus particle nucleation, presumably involving the lofting of sea-salt nuclei in thunderstorm updrafts into the upper troposphere. This created a reservoir of haze particles that continued to produce halide-saltcontaminated ice crystals during the extended period of cirrus cloud maintenance. The reference that marine microliters are embedded in the replicas of ice crystals collected over the CART site points to the longevity of marine effects. Various nucleation scenarios proposed for cirrus clouds based on this and other studies, and the implications for understanding cirrus radiative properties or a global scale, are discussed.

Sassen, Kenneth; Arnott, W. Patrick; OCStarr, David; Mace, Gerald G.; Wang, Zhien; Poellot, Michael R.

2002-01-01

291

The effect of dynamic compression on phase transformation: Solidification of water and crystal growth of ice VI using dynamic diamond anvil cell  

NASA Astrophysics Data System (ADS)

The kinetics of phase transformation depends on how driving parameters are applied. Under high pressure, compression rate can give different paths of phase transformation. For this purpose, we have developed a new device, called dynamic diamond anvil cell (d-DAC), which can modulate a given static pressure with various compression rate and type. Using d-DAC, liquid water can be overpressurized up to 75 % in ice VI phase field without crystallization, and after transforms to metastable iceVII phase in the stable ice VI pressure field. Interestingly, when fast sinusoidal compression is applied, the crystal morphology of ice VI surrounded by liquid water dramatically changes to fractal and dendritic shape. In this talk, we will describe the details of crystallization, following a brief description of the technical development of d-DAC.

Lee, Geun Woo; Evans, William; Yoo, Choong-Shik

2007-03-01

292

Southern Ocean frontal structure and sea-ice formation rates revealed by elephant seals  

PubMed Central

Polar regions are particularly sensitive to climate change, with the potential for significant feedbacks between ocean circulation, sea ice, and the ocean carbon cycle. However, the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited, especially in the Southern Ocean, where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea-ice formation is poorly known. Here, we show that southern elephant seals (Mirounga leonina) equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms. In particular, seals provided a 30-fold increase in hydrographic profiles from the sea-ice zone, allowing the major fronts to be mapped south of 60°S and sea-ice formation rates to be inferred from changes in upper ocean salinity. Sea-ice production rates peaked in early winter (April–May) during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between May and August, in agreement with a three-dimensional coupled ocean–sea-ice model. By measuring the high-latitude ocean during winter, elephant seals fill a “blind spot” in our sampling coverage, enabling the establishment of a truly global ocean-observing system.

Charrassin, J.-B.; Hindell, M.; Rintoul, S. R.; Roquet, F.; Sokolov, S.; Biuw, M.; Costa, D.; Boehme, L.; Lovell, P.; Coleman, R.; Timmermann, R.; Meijers, A.; Meredith, M.; Park, Y.-H.; Bailleul, F.; Goebel, M.; Tremblay, Y.; Bost, C.-A.; McMahon, C. R.; Field, I. C.; Fedak, M. A.; Guinet, C.

2008-01-01

293

Morphology, crystal structure, phase transitions and blend compatibility of thermotropic liquid crystal terpolyesters  

Microsoft Academic Search

The morphology, crystal structure, phase transitions and blend compatibility of a series of semiflexible thermotropic liquid crystal terpolyesters (LCPs) were studied to understand their crystallization behavior and establish relationships between their microstructure and physical properties. Main characterization methods were electron microscopy and diffraction, and differential scanning calorimetry. The LCPs were composed of equimolar amounts of p-oxybenzoate, p-dioxyphenyl, and aliphatic segments,

Clara Lena Gonzalez-Costoso

1997-01-01

294

Ganymede?s internal structure including thermodynamics of magnesium sulfate oceans in contact with ice  

NASA Astrophysics Data System (ADS)

The large icy moons of Jupiter contain vast quantities of liquid water, a key ingredient for life. Ganymede and Callisto are weaker candidates for habitability than Europa, in part because of the model-based assumption that high-pressure ice layers cover their seafloors and prevent significant water-rock interaction. Water-rock interactions may occur, however, if heating at the rock-ice interface melts the high pressure ice. Highly saline fluids would be gravitationally stable, and might accumulate under the ice due to upward migration, refreezing, and fractionation of salt from less concentrated liquids. To assess the influence of salinity on Ganymede?s internal structure, we use available phase-equilibrium data to calculate activity coefficients and predict the freezing of water ice in the presence of aqueous magnesium sulfate. We couple this new equation of state with thermal profiles in Ganymede?s interior-employing recently published thermodynamic data for the aqueous phase-to estimate the thicknesses of layers of ice I, III, V, and VI. We compute core and silicate mantle radii consistent with available constraints on Ganymede?s mass and gravitational moment of inertia. Mantle radii range from 800 to 900 km for the values of salt and heat flux considered here (4-44 mW m-2 and 0 to 10 wt% MgSO4). Ocean concentrations with salinity higher than 10 wt% have little high pressure ice. Even in a Ganymede ocean that is mostly liquid, achieving such high ocean salinity is permissible for the range of likely S/Si ratios. However, elevated salinity requires a smaller silicate mantle radius to satisfy mass and moment-of-inertia constraints, so ice VI is always present in Ganymede?s ocean. For lower values of heat flux, oceans with salinity as low as 3 wt% can co-exist with ice III. Available experimental data indicate that ice phases III and VI become buoyant for salinity higher than 5 wt% and 10 wt%, respectively. Similar behavior probably occurs for ice V at salinities higher than 10 wt%. Flotation can occur over tens of kilometers of depth, indicating the possibility for upward ‘snow’ or other exotic modes of heat and material transport. We assess Ganymede?s interior structure for oceans with magnesium sulfate. New activity models predict freezing of ice in magnesium sulfate solutions. High ocean salinities are permitted by constraints on Ganymede?s sulfur content. Stability under high pressure ice implies water rock contact and layered oceans. Upward ‘snow’ of high-pressure ices occurs in the lower depths of salty oceans.

Vance, Steve; Bouffard, Mathieu; Choukroun, Mathieu; Sotin, Christophe

2014-06-01

295

Crystal structure of Junin virus nucleoprotein.  

PubMed

Junin virus (JUNV) has been identified as the aetiological agent of Argentine haemorrhagic fever (AHF), which is a serious public health problem with approximately 5 million people at risk. It is treated as a potential bioterrorism agent because of its rapid transmission by aerosols. JUNV is a negative-sense ssRNA virus that belongs to the genus Arenavirus within the family Arenaviridae, and its genomic RNA contains two segments encoding four proteins. Among these, the nucleoprotein (NP) has essential roles in viral RNA synthesis and immune suppression, but the molecular mechanisms of its actions are only partially understood. Here, we determined a 2.2 Å crystal structure of the C-terminal domain of JUNV NP. This structure showed high similarity to the Lassa fever virus (LASV) NP C-terminal domain. However, both the structure and function of JUNV NP showed differences compared with LASV NP. This study extends our structural insight into the negative-sense ssRNA virus NPs. PMID:23884367

Zhang, Yinjie; Li, Le; Liu, Xiang; Dong, Shishang; Wang, Wenming; Huo, Tong; Guo, Yu; Rao, Zihe; Yang, Cheng

2013-10-01

296

In situ proteolysis for protein crystallization and structure determination.  

PubMed

We tested the general applicability of in situ proteolysis to form protein crystals suitable for structure determination by adding a protease (chymotrypsin or trypsin) digestion step to crystallization trials of 55 bacterial and 14 human proteins that had proven recalcitrant to our best efforts at crystallization or structure determination. This is a work in progress; so far we determined structures of 9 bacterial proteins and the human aminoimidazole ribonucleotide synthetase (AIRS) domain. PMID:17982461

Dong, Aiping; Xu, Xiaohui; Edwards, Aled M; Chang, Changsoo; Chruszcz, Maksymilian; Cuff, Marianne; Cymborowski, Marcin; Di Leo, Rosa; Egorova, Olga; Evdokimova, Elena; Filippova, Ekaterina; Gu, Jun; Guthrie, Jennifer; Ignatchenko, Alexandr; Joachimiak, Andrzej; Klostermann, Natalie; Kim, Youngchang; Korniyenko, Yuri; Minor, Wladek; Que, Qiuni; Savchenko, Alexei; Skarina, Tatiana; Tan, Kemin; Yakunin, Alexander; Yee, Adelinda; Yim, Veronica; Zhang, Rongguang; Zheng, Hong; Akutsu, Masato; Arrowsmith, Cheryl; Avvakumov, George V; Bochkarev, Alexey; Dahlgren, Lars-Göran; Dhe-Paganon, Sirano; Dimov, Slav; Dombrovski, Ludmila; Finerty, Patrick; Flodin, Susanne; Flores, Alex; Gräslund, Susanne; Hammerström, Martin; Herman, Maria Dolores; Hong, Bum-Soo; Hui, Raymond; Johansson, Ida; Liu, Yongson; Nilsson, Martina; Nedyalkova, Lyudmila; Nordlund, Pär; Nyman, Tomas; Min, Jinrong; Ouyang, Hui; Park, Hee-won; Qi, Chao; Rabeh, Wael; Shen, Limin; Shen, Yang; Sukumard, Deepthi; Tempel, Wolfram; Tong, Yufeng; Tresagues, Lionel; Vedadi, Masoud; Walker, John R; Weigelt, Johan; Welin, Martin; Wu, Hong; Xiao, Ting; Zeng, Hong; Zhu, Haizhong

2007-12-01

297

Ice Cream  

NSDL National Science Digital Library

In this chemistry activity, learners use the lowered freezing point of water to chill another mixture (ice cream) to the solid state. Learners will record the temperature of the ice before and after mixing it with the ice cream ingredients and discover that adding a solute to a solvent lowers the freezing point of that solvent (also known as a colligative property). This activity can also be used to introduce learners to crystallization.

House, The S.

2014-01-28

298

Datamining Protein Structure Databanks for Crystallization Patterns of Proteins  

Microsoft Academic Search

A study of 345 protein structures selected among 1500 structures determined by Nuclear Magnetic Resonance (NMR) methods, revealed useful correlation between crystallization properties and several parameters for the studied proteins. NMR methods of structure determination do not require the growth of protein crystals, and hence allow comparison of properties of proteins that have or have not been the subject of

Homayoun Valafar; James H. Prestegard; Faramarz Valafar

2002-01-01

299

Some Lower Valence Vanadium Fluorides: Their Crystal Distortions, Domain Structures, Modulated Structures, Ferrimagnetism, and Composition Dependence.  

ERIC Educational Resources Information Center

Describes some contemporary concepts unique to the structure of advanced solids, i.e., their crystal distortions, domain structures, modulated structures, ferrimagnetism, and composition dependence. (Author/CS)

Hong, Y. S.; And Others

1980-01-01

300

Disorder in the crystals of trans-4-fluoroazoxybenzene. Synthesis, spectral properties, crystal structures and DFT calculations  

Microsoft Academic Search

Two crystals of trans-4-fluoroazoxybenzene were obtained using two different methods. Oxidation of 4-fluoroazobenzene provided crystals of trans-4-fluoroazoxybenzene (I) consisting of two isomers; 51% alpha (ONN) and 49% beta (NNO) isomer. From trans-amino-azoxybenzenes in Schiemann reaction it were obtained crystals of trans-4-fluoro-NNO-azoxybenzenes (II, beta isomer) containing 4.7% of the alpha-isomer according to the HPLC analysis. The crystal structures of I and

Krzysztof Ejsmont; Andrzej A. Domanski; Janusz B. Kyziol; Jacek Zaleski

2005-01-01

301

Disorder in the crystals of trans-4-fluoroazoxybenzene. Synthesis, spectral properties, crystal structures and DFT calculations  

Microsoft Academic Search

Two crystals of trans-4-fluoroazoxybenzene were obtained using two different methods. Oxidation of 4-fluoroazobenzene provided crystals of trans-4-fluoroazoxybenzene (I) consisting of two isomers; 51% ? (ONN) and 49% ? (NNO) isomer. From trans-amino-azoxybenzenes in Schiemann reaction it were obtained crystals of trans-4-fluoro-NNO-azoxybenzenes (II, ? isomer) containing 4.7% of the ?-isomer according to the HPLC analysis. The crystal structures of I and

Krzysztof Ejsmont; Andrzej A. Doma?ski; Janusz B. Kyzio?; Jacek Zaleski

2005-01-01

302

The hierarchical structure of glacial climatic oscillations: Interactions between ice-sheet dynamics and climate  

SciTech Connect

Abrupt climatic oscillations around the North Atlantic have been identified recently in Greenland ice cores as well as in North Atlantic marine sediment cores. The good correlation between the {open_quote}Dansgaard Oeschger events{close_quote} in the ice and the {open_quote}Heinrich events{close_quote} in the ocean suggests climate, in the North Atlantic region, underwent several massive reorganizations in the last glacial period. A characteristic feature seems to be their hierarchical structure. Every 7 to 10-thousand years, when the temperature is close to its minimum, the ice-sheet undergoes a massive iceberg discharge. This Heinrich event is followed by an abrupt warming. then by other oscillations, each lasting between one and two thousand years. These secondary oscillations do not have a clear signature in marine sediments but constitute most of the{open_quote} Dansgaard-Oeschger events{close_quote} found in the ice. A simplified model coupling an ice-sheet and an ocean basin, to illustrate how the interactions between these two components can lead to such a hierarchical structure. The ice-sheet model exhibits internal oscillations composed of growing phases and basal ice melting phases that induce massive iceberg discharges. These fresh water inputs in the ocean stop for a moment the thermohaline circulation, enhancing the temperature contrast between low- and high-latitudes. Just after this event, the thermohaline circulation restarts and an abrupt warming of high-latitude regions is observed. For some parameter values, these warmer temperatures have some influence on the ice-sheet, inducing secondary oscillations similar to those found in paleoclimatic records. Although the mechanism presented here may be too grossly simplified. it nevertheless underlines the potential importance of the coupling between ice-sheet dynamics and oceanic thermohaline circulation on the structure of the climatic records during the last glacial period. 33 refs., 14 figs., 1 tab.

Paillard, D. [Centre d`Etudes de Saclay, Gif sur Yvette (France)] [Centre d`Etudes de Saclay, Gif sur Yvette (France)

1995-04-01

303

Positron Annihilation and Electronic Lattice Structure in Insulator Crystals  

Microsoft Academic Search

The dimensions of the electronic lattice structure of the hexagonal quartz crystal and the fcc CaF2 crystal have been measured by resolving characteristic markings on the angular-correlation curves as observed for the two gamma quanta emitted in the annihilation of positrons with electrons in these crystals.

Werner Brandt; Gérard Coussot; Robert Paulin

1969-01-01

304

Ocean circulation off east Antarctica affects ecosystem structure and sea-ice extent.  

PubMed

Sea ice and oceanic boundaries have a dominant effect in structuring Antarctic marine ecosystems. Satellite imagery and historical data have identified the southern boundary of the Antarctic Circumpolar Current as a site of enhanced biological productivity. Meso-scale surveys off the Antarctic peninsula have related the abundances of Antarctic krill (Euphausia superba) and salps (Salpa thompsoni) to inter-annual variations in sea-ice extent. Here we have examined the ecosystem structure and oceanography spanning 3,500 km of the east Antarctic coastline, linking the scales of local surveys and global observations. Between 80 degrees and 150 degrees E there is a threefold variation in the extent of annual sea-ice cover, enabling us to examine the regional effects of sea ice and ocean circulation on biological productivity. Phytoplankton, primary productivity, Antarctic krill, whales and seabirds were concentrated where winter sea-ice extent is maximal, whereas salps were located where the sea-ice extent is minimal. We found enhanced biological activity south of the southern boundary of the Antarctic Circumpolar Current rather than in association with it. We propose that along this coastline ocean circulation determines both the sea-ice conditions and the level of biological productivity at all trophic levels. PMID:10952309

Nicol, S; Pauly, T; Bindoff, N L; Wright, S; Thiele, D; Hosie, G W; Strutton, P G; Woehler, E

2000-08-01

305

Ocean circulation off east Antarctica affects ecosystem structure and sea-ice extent  

NASA Astrophysics Data System (ADS)

Sea ice and oceanic boundaries have a dominant effect in structuring Antarctic marine ecosystems. Satellite imagery and historical data have identified the southern boundary of the Antarctic Circumpolar Current as a site of enhanced biological productivity. Meso-scale surveys off the Antarctic peninsula have related the abundances of Antarctic krill (Euphausia superba) and salps (Salpa thompsoni) to inter-annual variations in sea-ice extent. Here we have examined the ecosystem structure and oceanography spanning 3,500km of the east Antarctic coastline, linking the scales of local surveys and global observations. Between 80° and 150°E there is a threefold variation in the extent of annual sea-ice cover, enabling us to examine the regional effects of sea ice and ocean circulation on biological productivity. Phytoplankton, primary productivity, Antarctic krill, whales and seabirds were concentrated where winter sea-ice extent is maximal, whereas salps were located where the sea-ice extent is minimal. We found enhanced biological activity south of the southern boundary of the Antarctic Circumpolar Current rather than in association with it. We propose that along this coastline ocean circulation determines both the sea-ice conditions and the level of biological productivity at all trophic levels.

Nicol, Stephen; Pauly, Tim; Bindoff, Nathan L.; Wright, Simon; Thiele, Deborah; Hosie, Graham W.; Strutton, Peter G.; Woehler, Eric

2000-08-01

306

Crystal structure of oligoacenes under high pressure  

SciTech Connect

We report crystal structures of anthracene, tetracene, and pentacene under pressure. Energy dispersive x-ray diffraction experiments up to 9 GPa were performed. Quasiharmonic lattice dynamics calculations are compared to the experimental results and show excellent agreement. The results are discussed with particular emphasis on the pressure dependence of the unit cell dimensions and the rearrangement of the molecules. The high pressure data also allow an analysis of the equation of state of these substances as a function of molecular length. We report the bulk modulus of tetracene and pentacene (B{sub 0}=9.0 and 9.6 GPa, respectively) and its pressure derivative (B{sub 0}{sup '}=7.9 and 6.4, respectively). We find that the unit-cell volume and bulk modulus at ambient pressure follow a linear relationship with the molecular length.

Oehzelt, M.; Aichholzer, A.; Resel, R.; Heimel, G.; Venuti, E.; Della Valle, R. G. [Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz (Austria); School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States); Dipartimento di Chimica Fisica e Inorganica and INSTM-UdR Bologna, Universita di Bologna, Viale Risorgimento 4, I-40136 Bologna (Italy)

2006-09-01

307

Crystal structure of a snake venom cardiotoxin  

SciTech Connect

Cardiotoxin V/sup II/4 from Naja mossambica crystallizes in space group P6/sub 1/ (a = b = 73.9 A; c = 59.0 A) with two molecules of toxin (molecular mass = 6715 Da) in the asymmetric unit. The structure was solved by using a combination of multiple isomorphous replacement and density modification methods. Model building and least-squares refinement led to an agreement factor of 27% for a data set to 3-A resolution prior to any inclusion of solvent molecules. The topology of the molecule is similar to that found in short and long snake neurotoxins, which block the nicotinic acetylcholine receptor. Major differences occur in the conformation of the central loop, resulting in a change in the concavity of the molecule. Hydrophobic residues are clustered in two distinct areas. The existence of stable dimeric entities in the crystalline state, with the formation of a six-stranded antiparallel ..beta.. sheet, may be functionally relevant.

Rees, B.; Samama, J.P.; Thierry, J.C.; Gilibert, M.; Fischer, J.; Schweitz, H.; Lazdunski, M.; Moras, D.

1987-05-01

308

Tunable photonic structures from liquid crystal elastomers  

NASA Astrophysics Data System (ADS)

We investigated one-dimensional and two-dimensional optical diffraction structures fabricated in thin films of a sidechain light-sensitive liquid crystal elastomer (SC-LS-LCEs) by optical holographic lithography methods. The emphasis was on analysis of modifications of the periodicity of the recorded patterns induced by application of an external strain and by temperature modifications. The results show that due to rubber elasticity of the LCE films, relative modifications of the periodicity by 10% can easily be reached. In most cases tuning is reversible and linear with respect to the strain. Temperature induced tuning is most efficient in the region of phase transition from the nematic to the paranematic phase and provides relative periodicity modifications up to 30%.

Gregorc, Marko; Li, Hui; Domenici, Valentina; Drevenšek-Olenik, Irena

2012-11-01

309

Stability relationship for water droplet crystallization with the NASA Lewis icing spray nozzle  

Microsoft Academic Search

In order to produce small droplets for icing cloud simulation, high pressure air atomizing nozzles are used. For certain icing testing applications, median drop sizes as small as 5 mm are needed, which require air atomizing pressures greater than 3000 kPa. Isentropic expansion of the ambient temperature atomizing air to atmospheric pressure can result in air stream temperatures of -160

C. John Marek; C. Scott Bartlett

1988-01-01

310

Scattering of Polarized Light by Ice Crystals and Monodispersed Ellipsoidal Latex Particles  

Microsoft Academic Search

The large coolable and evacuable aerosol chamber AIDA is used as a cloud chamber to study processes of ice formation in atmospheric clouds and in the upper troposphere. In- tensity and depolarization of forward- and back-scattered laser radiation is measured, caused by particles in a small scattering volume far from the walls. Droplet freezing and growth of the ice particles

A. Nink; H. Bunz; O. Möhler; M. Schnaiter; R. Tiede; U. Schurath

311

Optical spectra of orientationally disordered crystals. VI. The Raman spectrum of the translational lattice vibrations of ice Ih  

Microsoft Academic Search

The Raman spectrum of the translational vibrations of polycrystalline ice Ih has been investigated in the range 350-20 cm-1. All the vibrations are Raman active, and there is much fine structure, presumably due to particular points in the Brillouin zone. Tentative assignments are suggested for some of the features. The theory of the Raman scattering by the translational vibrations of

P. T. T. Wong; E. Whalley

1976-01-01

312

Links between the structure of an Antarctic shallow-water community and ice-scour frequency  

Microsoft Academic Search

Ice is a major structuring force in marine and freshwater environments at high latitudes. Although recovery from scouring has been quantified in time, the frequency of scouring in the Antarctic has not. We placed grids of markers at 9–17 m depth at two sites, to study ice-scouring over 2 years at Adelaide island (Antarctic Peninsula). We quantified the time scale of scour

Kirsty M. Brown; Keiron P. P. Fraser; David K. A. Barnes; Lloyd S. Peck

2004-01-01

313

Cryogenic structure and ice content of lacustrine sediments in the Yukon River Basin, Alaska  

NASA Astrophysics Data System (ADS)

Lacustrine sediments often present a significant part of the upper permafrost of plains and lowlands of Alaska. Lacustrine sediments in their contemporary state vary from ice-poor to extremely ice-rich. The ice content depends on initial conditions of freezing and further history of permafrost development, which can include partial degradation and recovery of permafrost. In Alaska, the primary mechanism of freezing and cryogenic structure formation of lacustrine sediments is para-syngenetic (term by E.M. Katasonov, 1978), typical of sediments accumulated in lakes surrounded by permafrost. Though the freezing of such sediments occurs before or immediately after the termination of sedimentation (similar to syngenetic permafrost), the freezing conditions and cryogenic structure of para-syngenetic permafrost are similar to epigenetic permafrost. The ice lenses in para-syngenetic sediments are often inclined, and the ice content is relatively small in the central parts of refrozen taliks. This type of ice distribution is generally governed by the migration of water to multidirectional fronts of freezing. We studied the cryogenic structure of lacustrine sediments across different regions of the Yukon River Basin, Alaska, including Koyukuk Flats (Hozatka Lake area), Innoko Lowlands, and Tanana-Kuskokwim Lowlands (Lake Minchumina area). Study sites are located in the discontinuous permafrost zone, where permafrost was encountered mainly within uplifted peat plateaus. Field work included study of natural exposures and drilling. The upper part of studied sections is formed by frozen organic soils up to 2-3 -m -thick underlain by lacustrine silt, which is mostly ice-rich. Volume of visible ice in silt reaches at places 40% and more. A combination of layered and reticulate cryostructures is the most typical and common cryostructure assemblage. The thickness of ice lenses generally varies from 1 to 5 cm and occasionally reaches 10 cm. Aggradation of ice during the freezing of lacustrine silt caused a sufficient heave of the ground surface. Remnants of peat plateaus are surrounded by unfrozen bogs and fens, a result of thawing and settling of ice-rich lacustrine silt. Thermokarst scars initially form at places where ice-rich silt is not protected by a thick layer of organic soil. Further development of thermokarst bogs is related mostly to lateral enlargement of thaw bulbs and collapsing of the margins of peat plateaus. Lacustrine silt within taliks is covered by woody peat accumulated under forests during the permafrost plateau stage and then by aquatic sphagnum peat accumulated after collapse.

Kanevskiy, M. Z.; Jorgenson, M. T.; Shur, Y.; O'Donnell, J.; Harden, J. W.; Fortier, D.

2009-12-01

314

Polarimetric radar observation of ice crystals and aggregates: Backscattering modeling of signatures from C to Ka band  

NASA Astrophysics Data System (ADS)

Hydrometeor classification using polarimetric Doppler weather radar is based on the characteristic polarimetric signature for each hydrometeor class. This signature can be obtained by either experimental campaigns or by proper electromagnetic modelling. Both approaches have advantages and drawbacks: the experimental approach is not easy to conduct as it requires co-located measurements of a weather radar with in-situ sampler (usually installed aboard an aircraft); moreover, it is generally strictly related to the measurement configuration (e.g., frequency, range) it is performed. Of course, experimental campaigns are needed for definitive validation, but the modelling approach exhibits a high flexibility in terms of system and meteorological parameters very well suited for retrieval algorithm design. On the other hand, a model approach is heavily dependent on the model capability to represent hydrometeor volumes in a realistic way. Within the electromagnetic scattering modelling of hydrometeor radar response, a well known technique to simulate the radar backscattering from an ensemble of particle is based on the T-matrix algorithm (Kim, 2006). The T-matrix model is based on the equivalence principle and can ensure numerical convergence for a small set of canonical shapes such as ellipsoids. These shapes are useful to represent raindrops and vertically-oriented small crystals, but are largely unrealistic when dealing with ice aggregates and crystals. In this work we use a different approach to the scattering modelling that fits well for classes like ice crystals and aggregates of different shapes and sizes: the discrete dipole approximation (DDA). The DDA model lets us simulate almost any kind of particle under the hypothesis it can be approximated as a three dimensional array of dipoles that generate the scattering field (the wavelength should be large compared to the distance between dipoles). The DDA code used is DDSCAT, developed by Draine and Flatau (2004), which computes the scattering by a single randomly oriented particle. With this approach a variety of hydrometeor shapes have been simulated: cylindrical ice crystals, aggregates of ice cylinders, snow crystals, mixed-phase particles, etc. From DDA it has been possible to obtain the polarimetric signature for ground-based radars at C and X band for these hydrometeor classes after solving some heavy computational issues. An equivalent spheroid model has been also developed for the ice hydrometeor classes in order to use a T-matrix code, faster than DDA, to simulate ice crystals-equivalent spheroids (Weinman and Kim, 2007). Numerical results will be discussed analyzing the sensitivity of the DDA model to the particle shape, wavelength, size distribution and orientation. The accuracy of T-matrix approximation of the ensemble particle polarimetric signature will be also evaluated within the context of hydrometeor classification schemes based on either fuzzy-logic or Bayesian techniques.

Botta, G.; Montopoli, M.; Marzano, F. S.

2009-04-01

315

Validation and Determination of Ice Water Content - Radar Reflectivity Relationships during CRYSTAL-FACE: Flight Requirements for Future Comparisons  

NASA Technical Reports Server (NTRS)

In order for clouds to be more accurately represented in global circulation models (GCM), there is need for improved understanding of the properties of ice such as the total water in ice clouds, called ice water content (IWC), ice particle sizes and their shapes. Improved representation of clouds in models will enable GCMs to better predict for example, how changes in emissions of pollutants affect cloud formation and evolution, upper tropospheric water vapor, and the radiative budget of the atmosphere that is crucial for climate change studies. An extensive cloud measurement campaign called CRYSTAL-FACE was conducted during Summer 2002 using instrumented aircraft and a variety of instruments to measure properties of ice clouds. This paper deals with the measurement of IWC using the Harvard water vapor and total water instruments on the NASA WB-57 high-altitude aircraft. The IWC is measured directly by these instruments at the altitude of the WB-57, and it is compared with remote measurements from the Goddard Cloud Radar System (CRS) on the NASA ER-2. CRS measures vertical profiles of radar reflectivity from which IWC can be estimated at the WB-57 altitude. The IWC measurements obtained from the Harvard instruments and CRS were found to be within 20-30% of each other. Part of this difference was attributed to errors associated with comparing two measurements that are not collocated in time an space since both aircraft were not in identical locations. This study provides some credibility to the Harvard and CRS-derived IWC measurements that are in general difficult to validate except through consistency checks using different measurement approaches.

Sayres, D. S.; Smith, J. B.; Pittman, J. V.; Weinstock, E. M.; Anderson, J. G.; Heymsfield, G.; Fridland, A. M.; Ackerman, A. S.

2007-01-01

316

Three-Dimensional Photonic Crystal Laser-Driven Accelerator Structures  

SciTech Connect

We discuss simulated photonic crystal structure designs for laser-driven particle acceleration, focusing on three-dimensional planar structures based on the so-called ''woodpile'' lattice. We describe guiding of a speed-of-light accelerating mode by a defect in the photonic crystal lattice and discuss the properties of this mode, including particle beam dynamics and potential coupling methods for the structure. We also discuss possible materials and power sources for this structure and their effects on performance parameters, as well as possible manufacturing techniques and the required tolerances. In addition we describe the computational technique and possible improvements in numerical modeling that would aid development of photonic crystal structures.

Cowan, B.; /SLAC

2006-09-07

317

Use of Pom Pons to Illustrate Cubic Crystal Structures.  

ERIC Educational Resources Information Center

Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)

Cady, Susan G.

1997-01-01

318

Growth and crystal structure of the BeAl 6O 10 single crystals  

NASA Astrophysics Data System (ADS)

Unlike earlier published works we have established incongruent melting for the compound BeAl 6O 10 (BHA). The conditions of growing crystals from their own melt with a superstoichiometric excess of BeO, using the Czochralski method, have been determined. The nature of inclusions in grown BHA crystals is described. On the basis of X-ray crystal structure analysis and data of spectroscopic studies the symmetry and space group of BHA crystal structure have been refined, as well as uncertainties arising in their interpretation are discussed.

Alimpiev, A. I.; Merkulov, A. A.; Solntsev, V. P.; Tsvetkov, E. G.; Matrosov, V. N.; Pestryakov, E. V.

2002-04-01

319

Refinement of the crystal structure of rutherfordine.  

SciTech Connect

Rutherfordine, UO{sub 2}CO{sub 3} is orthorhombic, a 4.840(1), b 9.273(2), c 4.298(1) Angstroms, V192.90(7) Angstroms{sup 3}, space group lmm2,Z=2. The structure was refined to an R index of 2.2% on the basis of 306 unique data [|F{sub o}|/{sigma}(|F{sub o}|)>5] measured with MoK{alpha} X-radiation on a single-crystal diffractometer. The structure consists of neutral sheets of edge- and corner-sharing (UO{sub 8}) hexagonal bipyramids and (CO{sub 3}) triangles, as originally proposed by Christ et al. (1955); our refinement, however shows that (CO{sub 3}) groups in alternate layers have the same orientation, not opposite orientations as originally reported. The refined value of the U-O (uranyl) distance is strongly affected by the details of the absorption correction, ranging from 1.71 to 1.80 Angstroms as a function of the plate-glancing angle used in an empirical psi-scan absorption correction and as a function of the type of weighting scheme used in the refinement. The Gaussian-quadrature method of integration also shows similar problems, but they are less extreme. The preferred value for the U-O (uranyl) distance in rutherfordine is {approx}1.745 Angstroms; as rutherfordine contains no H atoms, the O(uranyl) atom is [1]-coordinated, and should have the shortest U-O(uranyl) distance stereochemically possible. The current work suggests that U-O(uranyl) values less than 1.745 Angstrom reported in other studies are adversely affected by less-than-optimum absorption corrections.

Finch, R. J.; Cooper, M. A.; Hawthorne, F. C.; Ewing, R. C.; Chemical Engineering; Univ. of Manitoba; Univ. of Michigan

1999-01-01

320

Crystal Structure of a "Nonfoldable" Insulin  

PubMed Central

Protein evolution is constrained by folding efficiency (“foldability”) and the implicit threat of toxic misfolding. A model is provided by proinsulin, whose misfolding is associated with ?-cell dysfunction and diabetes mellitus. An insulin analogue containing a subtle core substitution (LeuA16 ? Val) is biologically active, and its crystal structure recapitulates that of the wild-type protein. As a seeming paradox, however, ValA16 blocks both insulin chain combination and the in vitro refolding of proinsulin. Disulfide pairing in mammalian cell culture is likewise inefficient, leading to misfolding, endoplasmic reticular stress, and proteosome-mediated degradation. ValA16 destabilizes the native state and so presumably perturbs a partial fold that directs initial disulfide pairing. Substitutions elsewhere in the core similarly destabilize the native state but, unlike ValA16, preserve folding efficiency. We propose that LeuA16 stabilizes nonlocal interactions between nascent ?-helices in the A- and B-domains to facilitate initial pairing of CysA20 and CysB19, thus surmounting their wide separation in sequence. Although ValA16 is likely to destabilize this proto-core, its structural effects are mitigated once folding is achieved. Classical studies of insulin chain combination in vitro have illuminated the impact of off-pathway reactions on the efficiency of native disulfide pairing. The capability of a polypeptide sequence to fold within the endoplasmic reticulum may likewise be influenced by kinetic or thermodynamic partitioning among on- and off-pathway disulfide intermediates. The properties of [ValA16]insulin and [ValA16]proinsulin demonstrate that essential contributions of conserved residues to folding may be inapparent once the native state is achieved.

Liu, Ming; Wan, Zhu-li; Chu, Ying-Chi; Aladdin, Hassan; Klaproth, Birgit; Choquette, Meredith; Hua, Qing-xin; Mackin, Robert B.; Rao, J. Sunil; De Meyts, Pierre; Katsoyannis, Panayotis G.; Arvan, Peter; Weiss, Michael A.

2009-01-01

321

Effect of the grain boundary of ice crystals in a frozen gelatin solution on the dielectric properties at a subzero temperature.  

PubMed

The effect of the grain boundary of ice crystals in a frozen gelatin solution on the dielectric properties was investigated by the combination of a dielectric spectrometer and image analysis. A micro-slicer image processing system (MSIPS) was applied to measure the grain boundary properties as the perimeter density and number density of ice crystals. The perimeter density and number density of the ice crystals increased with increasing freezing rate. The dielectric properties of the frozen gelatin solution at various freezing rates were measured in the frequency range of 100 Hz to 100 kHz at -40 degrees C. The relaxation time did not affect the grain boundary properties. The perimeter density and number density significantly affected dielectric parameter epsilon(0)-epsilon(infinity) and electrical conductivity sigma(0). These results indicate that the dielectric spectrometer could be used to estimate the grain boundary properties in a frozen gelatin solution. PMID:19897916

Ueno, Shigeaki; Shirakashi, Ryo; Kudoh, Ken-ichi; Higuchi, Toshiro; Do, Gab-Soo; Araki, Tetsuya; Sagara, Yasuyuki

2009-11-01

322

Anisotropic domain structure of KTiOPO{sub 4} crystals  

SciTech Connect

Highly anisotropic ferroelectric domain structure is observed in KTiOPO{sub 4} (KTP) crystals reversed by low electric field. The applied Miller--Weinreich model for sidewise motion of domain walls indicates that this anisotropy results from the peculiarities of KTP crystal lattice. The domain nuclei of dozen nanometer size, imaged by atomic force microscopy method, demonstrate regular hexagonal forms. The orientation of domain walls of the elementary nuclei coincides with the orientation of the facets of macroscopic KTP crystals. The observed strong domain elongation along one principal crystal axis allows us to improve tailoring of ferroelectric domain engineered structures for nonlinear optical converters. {copyright} 2001 American Institute of Physics.

Urenski, P.; Lesnykh, M.; Rosenwaks, Y.; Rosenman, G.; Molotskii, M.

2001-08-15

323

Spectroscopic, thermal and structural studies on manganous malate crystals  

NASA Astrophysics Data System (ADS)

Prismatic crystals of manganous malate have been prepared by controlled ionic diffusion in hydrosilica gel. The structure was elucidated using single crystal X-ray diffraction. The crystals are orthorhombic with space group Pbca. Vibrations of the functional groups were identified by the FTIR spectrum. Thermogravimetric and differential thermal analyses (TG-DTA) were carried out to explore the thermal decomposition pattern of the material. Structural information derived from FTIR and TG-DTA studies is in conformity with the single crystal XRD data.

Thomas, J.; Lincy, A.; Mahalakshmi, V.; Saban, K. V.

2013-01-01

324

Freezing and melting behavior of an octyl ?-D-glucoside-water binary system--inhibitory effect of octyl ?-D-glucoside on ice crystal formation.  

PubMed

Phase transition behavior of lyotropic liquid crystals of an octyl ?-D-glucoside (OG)-water binary system during ice freezing and melting was studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Not the thermotropic, but the lyotropic phase transition due to the change of OG concentration during ice freezing and melting was observed. The concentration-temperature phase diagram of the binary system was constructed. Melting temperature of ice, T(m), lyotropic phase transition temperature, T(tr), and glass transition temperatures of unfrozen phases in the absence and presence of ice, T(g) and T(g)', were shown in the phase diagram. The phase diagram indicated that the OG aqueous system was concentrated to ca. 90-92 wt% by ice freezing and exhibited glass transition at T(g)'. An observation of the concentration-gradient specimen by the cryo-POM showed the evidence of the inhibitory effects of OG on nucleation and growth of ice crystals in the extremely high OG concentration system in which the lamellar liquid crystalline phase was formed. This study provided the importance of the influence of concentration change by ice freezing on the behaviour of the sugar-based surfactant-water system under low temperature conditions. PMID:23133837

Ogawa, Shigesaburo; Asakura, Kouichi; Osanai, Shuichi

2012-12-21

325

Synthesis, crystal structure and vibrational spectroscopy of a nonlinear optical crystal: L-arginine maleate dihydrate  

NASA Astrophysics Data System (ADS)

From the aqueous solution containing L-arginine and maleic acid (C 4H 4O 4), crystals of L-arginine maleate dihydrate were grown. The crystal structure was determined by single crystal X-ray diffraction. In the triclinic unit cell (space group P1), the molecule contains one L-arginine cation, one maleate anion and two water molecules. The crystal can be described as an inclusion complex from its layer structure. The basic unit in L-arginine layer is centrosymmetric and the maleate anions exist in coplanarity. Hydrogen bond plays a great role in the construction of the crystal and nonlinear optical properties. The crystal was characterized by infrared (IR) and Raman spectra. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder second harmonic generation (SHG) experiment was investigated to explore its NLO properties.

Sun, Z. H.; Yu, W. T.; Cheng, X. F.; Wang, X. Q.; Zhang, G. H.; Yu, G.; Fan, H. L.; Xu, D.

2008-02-01

326

Retrieval of Surface Solar Radiation Budget under Ice Cloud Sky: Uncertainty Analysis and Parameterization  

Microsoft Academic Search

This study investigates and accounts for the influence of various ice cloud parameters on the retrieval of the surface solar radiation budget (SSRB) from reflected flux at the top of the atmosphere (TOA). The optical properties of ice clouds depend on ice crystal shape, size distribution, water content, and the vertical profiles of geometric and microphysical structure. As a result,

Ying Zhang; Zhanqing Li; Andreas Macke

2002-01-01

327

An unconventional bilayer ice structure on a NaCl(001) film.  

PubMed

Water-solid interactions are of broad importance both in nature and technology. The hexagonal bilayer model based on the Bernal-Fowler-Pauling ice rules has been widely adopted to describe water structuring at interfaces. Using a cryogenic scanning tunnelling microscope, here we report a new type of two-dimensional ice-like bilayer structure built from cyclic water tetramers on an insulating NaCl(001) film, which is completely beyond this conventional bilayer picture. A novel bridging mechanism allows the interconnection of water tetramers to form chains, flakes and eventually a two-dimensional extended ice bilayer containing a regular array of Bjerrum D-type defects. Ab initio density functional theory calculations substantiate this bridging growth mode and reveal a striking proton-disordered ice structure. The formation of the periodic Bjerrum defects with unusually high density may have a crucial role as H donor sites in directing multilayer ice growth and in catalysing heterogeneous chemical reactions on water-coated salt surfaces. PMID:24874452

Chen, Ji; Guo, Jing; Meng, Xiangzhi; Peng, Jinbo; Sheng, Jiming; Xu, Limei; Jiang, Ying; Li, Xin-Zheng; Wang, En-Ge

2014-01-01

328

Size, separation, structural order, and mass density of molecules packing in water and ice  

PubMed Central

The structural symmetry and molecular separation in water and ice remain uncertain. We present herewith a solution to unifying the density, the structure order and symmetry, the size (H-O length dH), and the separation (dOO = dL + dH or the O:H length dL) of molecules packing in water and ice in terms of statistic mean. This solution reconciles: i) the dL and the dH symmetrization of the O:H-O bond in compressed ice, ii) the dOO relaxation of cooling water and ice and, iii) the dOO expansion of a dimer and between molecules at water surface. With any one of the dOO, the density ?(g·cm?3), the dL, and the dH, as a known input, one can resolve the rest quantities using this solution that is probing conditions or methods independent. We clarified that: i) liquid water prefers statistically the mono-phase of tetrahedrally-coordinated structure with fluctuation, ii) the low-density phase (supersolid phase as it is strongly polarized with even lower density) exists only in regions consisting molecules with fewer than four neighbors and, iii) repulsion between electron pairs on adjacent oxygen atoms dictates the cooperative relaxation of the segmented O:H-O bond, which is responsible for the performance of water and ice.

Huang, Yongli; Zhang, Xi; Ma, Zengsheng; Li, Wen; Zhou, Yichun; Zhou, Ji; Zheng, Weitao; Sun, Chang Q.

2013-01-01

329

Size, separation, structural order, and mass density of molecules packing in water and ice  

NASA Astrophysics Data System (ADS)

The structural symmetry and molecular separation in water and ice remain uncertain. We present herewith a solution to unifying the density, the structure order and symmetry, the size (H-O length dH), and the separation (dOO = dL + dH or the O:H length dL) of molecules packing in water and ice in terms of statistic mean. This solution reconciles: i) the dL and the dH symmetrization of the O:H-O bond in compressed ice, ii) the dOO relaxation of cooling water and ice and, iii) the dOO expansion of a dimer and between molecules at water surface. With any one of the dOO, the density ?(g.cm-3), the dL, and the dH, as a known input, one can resolve the rest quantities using this solution that is probing conditions or methods independent. We clarified that: i) liquid water prefers statistically the mono-phase of tetrahedrally-coordinated structure with fluctuation, ii) the low-density phase (supersolid phase as it is strongly polarized with even lower density) exists only in regions consisting molecules with fewer than four neighbors and, iii) repulsion between electron pairs on adjacent oxygen atoms dictates the cooperative relaxation of the segmented O:H-O bond, which is responsible for the performance of water and ice.

Huang, Yongli; Zhang, Xi; Ma, Zengsheng; Li, Wen; Zhou, Yichun; Zhou, Ji; Zheng, Weitao; Sun, Chang Q.

2013-10-01

330

Evolutionary Crystal Structure Prediction and Novel High-Pressure Phases  

Microsoft Academic Search

\\u000a Prediction of stable crystal structures at given pressure-temperature conditions, based only on the knowledge of the chemical\\u000a composition, is a central problem of condensed matter physics. This extremely challenging problem is often termed “crystal\\u000a structure prediction problem”, and recently developed evolutionary algorithm USPEX (Universal Structure Predictor: Evolutionary\\u000a Xtallography) made an important progress in solving it, enabling efficient and reliable prediction

Artem R. Oganov; Yanming Ma; Andriy O. Lyakhov; Mario Valle; Carlo Gatti

2010-01-01

331

Structural study of Langmuir liquid crystal monolayer  

NASA Astrophysics Data System (ADS)

A systematic study is reported on monolayer characteristics of Ferroelectric Liquid Crystal (FLC) at the air-water interface, using surface pressure and surface potential isotherms at different temperatures. Dipole moment is calculated by using Helmholtz equation. No significant influence from the sub phase temperature was detected because liquid crystal remains in Sm-C* phase in temperature range 5°C-40°C. FLC was deposited on smooth quartz substrate with good transfer ratio. AFM topography reveals uniform deposition of liquid crystals having well defined domains.

Kaur, Ramneek; Raina, K. K.

2014-04-01

332

Novel photonic crystal cavities and related structures.  

SciTech Connect

The key accomplishment of this project is to achieve a much more in-depth understanding of the thermal emission physics of metallic photonic crystal through theoretical modeling and experimental measurements. An improved transfer matrix technique was developed to enable incorporation of complex dielectric function. Together with microscopic theory describing emitter radiative and non-radiative relaxation dynamics, a non-equilibrium thermal emission model is developed. Finally, experimental methodology was developed to measure absolute emissivity of photonic crystal at high temperatures with accuracy of +/-2%. Accurate emissivity measurements allow us to validate the procedure to treat the effect of the photonic crystal substrate.

Luk, Ting Shan

2007-11-01

333

In vivo protein crystallization opens new routes in structural biology  

PubMed Central

Protein crystallization in cells has been observed several times in nature. However, owing to their small size these crystals have not yet been used for X-ray crystallographic analysis. We prepared nano-sized in vivo–grown crystals of Trypanosoma brucei enzymes and applied the emerging method of free-electron laser-based serial femtosecond crystallography to record interpretable diffraction data. This combined approach will open new opportunities in structural systems biology.

Koopmann, Rudolf; Cupelli, Karolina; Redecke, Lars; Nass, Karol; DePonte, Daniel P; White, Thomas A; Stellato, Francesco; Rehders, Dirk; Liang, Mengning; Andreasson, Jakob; Aquila, Andrew; Bajt, Sasa; Barthelmess, Miriam; Barty, Anton; Bogan, Michael J; Bostedt, Christoph; Boutet, Sebastien; Bozek, John D; Caleman, Carl; Coppola, Nicola; Davidsson, Jan; Doak, R Bruce; Ekeberg, Tomas; Epp, Sascha W; Erk, Benjamin; Fleckenstein, Holger; Foucar, Lutz; Graafsma, Heinz; Gumprecht, Lars; Hajdu, Janos; Hampton, Christina Y; Hartmann, Andreas; Hartmann, Robert; Hauser, Gunter; Hirsemann, Helmut; Holl, Peter; Hunter, Mark S; Kassemeyer, Stephan; Kirian, Richard A; Lomb, Lukas; Maia, Filipe R N C; Kimmel, Nils; Martin, Andrew V; Messerschmidt, Marc; Reich, Christian; Rolles, Daniel; Rudek, Benedikt; Rudenko, Artem; Schlichting, Ilme; Schulz, Joachim; Seibert, M Marvin; Shoeman, Robert L; Sierra, Raymond G; Soltau, Heike; Stern, Stephan; Struder, Lothar; Timneanu, Nicusor; Ullrich, Joachim; Wang, Xiaoyu; Weidenspointner, Georg; Weierstall, Uwe; Williams, Garth J; Wunderer, Cornelia B; Fromme, Petra; Spence, John C H; Stehle, Thilo; Chapman, Henry N; Betzel, Christian; Duszenko, Michael

2012-01-01

334

Crystal and magnetic structure of the uranium digermanide UGe 2  

Microsoft Academic Search

The crystal structure of the uranium digermanide UGe2 was determined and refined from single crystal X-ray diffraction data to R = 0.040, Rw = 0.052. UGe2 crystallizes with the orthorhombic ZrGa2 type (Cmcm) instead of the ZrSi2 type (Cmcm) as was previously assumed on the basis of rather old and unreliable results. Our magnetic study of a polycrystalline are melted

P. Boulet; A. Daoudi; M. Potel; H. Noël; G. M. Gross; G. André; F. Bourée

1997-01-01

335

Crystal structure of interleukin 8: Symbiosis of NMR and crystallography  

Microsoft Academic Search

The crystal structure of a host defense system chemotactic factor, interleukin 8, has been solved by molecular replacement using as a model the solution structure derived from nuclear magnetic resonance experiments. The structure was refined with 2 â« x-ray data to an R factor of 0.817. A comparison indicates some potential differences between the structure in solution and in the

E. T. Baldwin; I. T. Weber; R. St. Charles; Jiancheng Xuan; Kouji Matsushima; A. Wlodawer; E. Appella; G. M. Clore; A. M. Gronenborn; Masaki Yamada; B. F. P. Edwards

1991-01-01

336

III-Nitride LEDs with photonic crystal structures.  

SciTech Connect

Electrical operation of III-Nitride light emitting diodes (LEDs) with photonic crystal structures is demonstrated. Employing photonic crystal structures in III-Nitride LEDs is a method to increase light extraction efficiency and directionality. The photonic crystal is a triangular lattice formed by dry etching into the III-Nitride LED. A range of lattice constants is considered (a {approx} 270-340nm). The III-Nitride LED layers include a tunnel junction providing good lateral current spreading without a semi-absorbing metal current spreader as is typically done in conventional III-Nitride LEDs. These photonic crystal III-Nitride LED structures are unique because they allow for carrier recombination and light generation proximal to the photonic crystal (light extraction area) yet displaced from the absorbing metal contact. The photonic crystal Bragg scatters what would have otherwise been guided modes out of the LED, increasing the extraction efficiency. The far-field light radiation patterns are heavily modified compared to the typical III-Nitride LED's Lambertian output. The photonic crystal affects the light propagation out of the LED surface, and the radiation pattern changes with lattice size. LEDs with photonic crystals are compared to similar III-Nitride LEDs without the photonic crystal in terms of extraction, directionality, and emission spectra.

Wendt, Joel Robert; Sigalas, M. M. (Agilent Technologies, Palo Alto, CA); Epler, J. E. (Lumileds Lighting, San Jose, CA); Krames, M. R. (Lumileds Lighting, San Jose, CA); Li, D. (University of New Mexico, Albuquerque NM); Brueck, Stephen R. J. (University of New Mexico, Albuquerque NM); Shagam, M. (Boston University, Boston, MA); Gardner, N. F. (Lumileds Lighting, San Jose, CA); Wierer, Jonathan J. (Lumileds Lighting, San Jose, CA)

2005-02-01

337

III-nitride LEDs with photonic crystal structures  

NASA Astrophysics Data System (ADS)

Electrical operation of III-Nitride light emitting diodes (LEDs) with photonic crystal structures is demonstrated. Employing photonic crystal structures in III-Nitride LEDs is a method to increase light extraction efficiency and directionality. The photonic crystal is a triangular lattice formed by dry etching into the III-Nitride LED. A range of lattice constants is considered (a ~ 270 - 340nm). The III-Nitride LED layers include a tunnel junction providing good lateral current spreading without a semi-absorbing metal current spreader as is typically done in conventional III-Nitride LEDs. These photonic crystal III-Nitride LED structures are unique because they allow for carrier recombination and light generation proximal to the photonic crystal (light extraction area) yet displaced from the absorbing metal contact. The photonic crystal Bragg scatters what would have otherwise been guided modes out of the LED, increasing the extraction efficiency. The far-field light radiation patterns are heavily modified compared to the typical III-Nitride LED"s Lambertian output. The photonic crystal affects the light propagation out of the LED surface, and the radiation pattern changes with lattice size. LEDs with photonic crystals are compared to similar III-Nitride LEDs without the photonic crystal in terms of extraction, directionality, and emission spectra.

Wierer, Jonathan J.; Krames, Michael R.; Epler, John E.; Gardner, Nathan F.; Wendt, Joel R.; Sigalas, Mihail M.; Brueck, Steven R. J.; Li, Dong; Shagam, Michael

2005-03-01

338

Crystal structure and characterization of pyrroloquinoline quinone disodium trihydrate  

PubMed Central

Background Pyrroloquinoline quinone (PQQ), a tricarboxylic acid, has attracted attention as a growth factor, and its application to supplements and cosmetics is underway. The product used for these purposes is a water-soluble salt of PQQ disodium. Although in the past, PQQ disodiumpentahydrates with a high water concentration were used, currently, low hydration crystals of PQQ disodiumpentahydrates are preferred. Results We prepared a crystal of PQQ disodium trihydrate in a solution of ethanol and water, studied its structure, and analyzed its properties. In the prepared crystal, the sodium atom interacted with the oxygen atom of two carboxylic acids as well as two quinones of the PQQ disodium trihydrate. In addition, the hydration water of the prepared crystal was less than that of the conventional PQQ disodium crystal. From the results of this study, it was found that the color and the near-infrared (NIR) spectrum of the prepared crystal changed depending on the water content in the dried samples. Conclusions The water content in the dried samples was restored to that in the trihydrate crystal by placing the samples in a humid environment. In addition, the results of X-ray diffraction (XRD) and X-ray diffraction-differential calorimetry (XRD-DSC) analyses show that the phase of the trihydrate crystal changed when the crystallization water was eliminated. The dried crystal has two crystalline forms that are restored to the original trihydrate crystals in 20% relative humidity (RH). This crystalline (PQQ disodium trihydrate) is stable under normal environment.

2012-01-01

339

Characterization of crystal structure in binary mixtures of latex globules.  

PubMed

Colloidal crystals formed by two types of polystyrene particles of different sizes (94 and 141 nm) at various number ratios (94:141 nm) are studied. Experiments showed that the formation time of crystals lengthens as the number ratio of the two components approaches 1:1. The dependence of the mean interparticle distance (D(0)), crystal structure and alloy structure on the number ratio of the two types of particles was studied by means of Kossel diffraction technique and reflection spectra. The results showed that as the number ratio decreased, the mean interparticle distance (D(0)) became larger. And the colloidal crystal in binary mixtures is more preferably to form the bcc structure. This study found that binary systems form the substitutional solid solution (sss)-type alloy structure in all cases except when the number ratio of two types of particles is 5:1, which results instead in the superlattice structure. PMID:18674779

Liu, Lei; Xu, Shenghua; Liu, Jie; Sun, Zhiwei

2008-10-01

340

Supercooled Droplets and Ice Crystals in Mixed-Phase Clouds: Numerical Simulations Considering Isotropic Turbulence of the Ambient Flow Field  

NASA Astrophysics Data System (ADS)

In midlatitudes the formation and evolution of precipitation is the result of a chain of processes taking place in mixed-phase clouds. Due to the coexistence of supercooled water drops and ice particles in such clouds mutual interactions by collisions, i.e. riming and aggregation, take place leading to ice hydrometeors of a large precipitation size. In the past these collision mechanisms have been investigated - besides laboratory measurements - by numerical simulations of the collision process where trajectories of the participating hydrometeors have been calculated as occurring in an environment at rest (Pruppacher and Klett, Kluwer Academic Publishers, Dordrecht, 1997). However, as it is well-known the flow field in clouds is almost always turbulent (Siebert et al., Atmos. Res. 97 (2010) 426-437) except in undiluted updrafts of single strong convective clouds. And it has been argued that turbulence may enhance precipitation formation. As a consequence turbulence effects on the collisional interaction of cloud and other heavy particles came into focus during the last decade and gave rise to the description in terms of radial distribution function, mean radial relative velocity and the collection efficiency all derived from numerical simulations. Up to now mostly the turbulence influence on cloud droplet/cloud droplet collisions has been investigated (Ayala et al., New J. Phys. 10 (2008) 075015), (Bec et al., J. Fluid Mech. 646 (2010) 527-536). Much less is known about the influence of turbulence on particles in mixed phase clouds. This is mainly due to the various and complex shapes of the ice particles depending on the temperature, the supersaturation, and their life time. Hence, our knowledge about the behavior of ice crystals in turbulence is based on wind tunnel experiments. In the early stage ice crystals often have the shape of hexagonal plates or needles. In theoretical and numerical studies these are commonly approximated by ellipsoids. However, except in (Pinsky and Khain, Atmos. Res. 47-48 (1998) 69-86) only laminar flows have been considered so far. Therefore we have developed a numerical experiment with a novel setup (Kunnen et al., under review in Atmos. Res. (2013)). Therein synthetic turbulence is generated at the inflow and is then advected by a mean flow through the domain. The full Navier-Stokes equations are solved using a DNS method on an Eulerian Cartesian grid. The evolving decaying turbulence shares similarities with the grid-generated turbulence of wind tunnels. In this flow several million particle spheres as well as ellipsoids are advanced in a Lagrangian manner in order to represent the supercooled droplets and ice crystals out of a small region of a mixed-phase cloud. Statistics will be gathered about the orientation, the sedimentation velocities, the clustering, and the relative velocities of these particles. From this basis collision kernels can be calculated. These are input parameters for cloud models estimating the evolution of precipitation.

Siewert, Christoph; Kunnen, Rudie; Meinke, Matthias; Schröder, Wolfgang; Beheng, Klaus

2013-04-01

341

Growth and Structure of Single-Crystal Films.  

National Technical Information Service (NTIS)

This research project was concerned with basic research on the growth and structure of single-crystal films of metals obtained by evaporation in ultra-high vaccum onto two types of substrates: mica and metal single-crystal films. The films were prepared i...

E. Grunbaum

1968-01-01

342

The importance of crystal structure to the water treatment industry  

SciTech Connect

The intention of this paper is to provide additional insights into the area of crystal structure, dispersion and crystal modification, particularly for the calcium salts of carbonate and sulphate. The application of the discussed approaches to real life systems will go a long way to ensure scale-free heat transfer equipment.

Caplan, G.

1986-01-01

343

Electronic structure of Cr{sup 3+} in forsterite crystals  

SciTech Connect

Specific properties of silicate crystals that make them promising in applications as active media for IR tunable lasers are discussed. The energy level structure of Cr{sup 3+} ions in a forsterite crystal field is analyzed. 4 refs., 3 tabs.

Avanesov, A.G.; Zhorin, V.V.; Pisarenko, V.F. [Kuban` State Univ., Krasnodar (Russian Federation)

1994-11-01

344

Structural, spectral and mechanical studies of bimetallic crystal: cadmium manganese thiocyanate single crystals  

NASA Astrophysics Data System (ADS)

A nonlinear optical bimetallic thiocyanate complex crystal, cadmium manganese thiocyanate (CMTC) has been successfully synthesized. The growth of single crystals of cadmium manganese thiocyanate has been accomplished from aqueous solution using slow evaporation method. The presence of manganese and cadmium in the synthesized material was confirmed through energy dispersive spectrum (EDS) analysis. Structural analysis was carried out using powder X-ray diffractometer (PXRD) and crystalline perfection of the grown crystals was ascertained by high-resolution X-ray diffraction (HRXRD) analysis. Fourier transform infrared (FTIR) spectrum was taken to confirm the functional groups. The transmittance spectrum of the crystal in the UV-visible region has been recorded and the cutoff wavelength has been determined. The dielectric measurements for the crystals were performed for various frequencies and temperatures. The mechanical properties were evaluated by Vickers microhardness testing, which reveals hardness and stiffness constant of the crystals.

Manikandan, M.; Vijaya Prasath, G.; Bhagavannarayan, G.; Vijayan, N.; Mahalingam, T.; Ravi, G.

2012-09-01

345

Three-dimensional structure of respiratory complex I from Escherichia coli in ice in the presence of nucleotides.  

PubMed

Complex I (NADH:ubiquinone oxidoreductase) is the largest protein complex of bacterial and mitochondrial respiratory chains. The first three-dimensional structure of bacterial complex I in vitrified ice was determined by electron cryo-microscopy and single particle analysis. The structure of the Escherichia coli enzyme incubated with either NAD(+) (as a reference) or NADH was calculated to 35 and 39 A resolution, respectively. The X-ray structure of the peripheral arm of Thermus thermophilus complex I was docked into the reference EM structure. The model obtained indicates that Fe-S cluster N2 is close to the membrane domain interface, allowing for effective electron transfer to membrane-embedded quinone. At the current resolution, the structures in the presence of NAD(+) or NADH are similar. Additionally, side-view class averages were calculated for the negatively stained bovine enzyme. The structures of bovine complex I in the presence of either NAD(+) or NADH also appeared to be similar. These observations indicate that conformational changes upon reduction with NADH, suggested to occur by a range of studies, are smaller than had been thought previously. The model of the entire bacterial complex I could be built from the crystal structures of subcomplexes using the EM envelope described here. PMID:18433710

Morgan, David J; Sazanov, Leonid A

2008-01-01

346

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.  

PubMed

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. PMID:6713947

Boutron, P

1984-04-01

347

The Arctic Cone Exploration Structure: A Mobile Offshore Drilling Unit for Heavy Ice Cover  

Microsoft Academic Search

This paper reports on the results of a rig development program which began in 1981 to design a mobile drilling unit which could operate beyond the 50 ft depth contour in the most exposed ice conditions. The Arctic Cone Exploration Structure (ACES) project has produced the design of what is likely to be the prototype for heavy-duty, bottom-founded mobile rigs

R. C. Byrd; R. Coleman; R. Weiss; L. Boaz; E. Sauve; R. M. White

1984-01-01

348

Observations of Ship Performance and the Structure of Fast Ice Channels in the Northern Baltic Sea.  

National Technical Information Service (NTIS)

Field data of the structure of fast ice ship channels in the northern Baltic Sea, and of the performance characteristics of ships in these channels are presented. The field work was done in two areas in the Bay of Bothnia during March 15 to 21, 1990. Obse...

B. Veitch M. Leppaeranta P. Kujala P. Kosloff

1991-01-01

349

Dynamics of Artificial Kagome `Spin Ice' In Geometrically Frustrated Permalloy Nano Structures  

Microsoft Academic Search

Thin films of ferro-magnetic material with lithographically designed geometries can be used as an analog for the study of spin ice or frustrated systems. Here we study the magnetic structure and magnetization dynamics of permalloy thin films in a frustrated, hexagonal geometry using Transmission Lorentz Microscopy. The permalloy films are evaporated through patterns defined by conventional electron beam lithography to

Yi Qi; Todd Brintlinger; John Cumings

2007-01-01

350

Ultrasound-initiated structural transformations in liquid crystals (A review)  

Microsoft Academic Search

The results of the studies of structural transformations in liquid crystal layers with homeotropic and planar macrostructures\\u000a in the fields of longitudinal, surface, and shear ultrasonic waves are systematized and generalized.

O. A. Kapustina

2008-01-01

351

Crystal Structure and Molecular Motion of Solid Carbon Disulfide.  

National Technical Information Service (NTIS)

The crystal structure of CS2 was determined at two temperatures from intensity data measured with a proportional counter and a modified Weissenberg apparatus. The orthorhombic cell exhibited marked anisotropic thermal expansion. Positional and anisotropic...

N. C. Baenziger W. L. Duax

1967-01-01

352

A Trireticulate Crystal Structure: Trihydrogen Cobalticyanide and Trisilver Cobalticyanide.  

National Technical Information Service (NTIS)

The crystals trisilver cobalticyanide and trihydrogen cobalticyanide have been shown to have a trireticulate structure, with nearly regular cobalticyanide octahedra connected by nitrogen-silver-nitrogen bonds or by hydrogen bonds between the nitrogen atom...

L. Pauling P. Pauling

1968-01-01

353

Stabilities of filled ice II structure of hydrogen and helium hydrates at low temperatures and high pressures  

NASA Astrophysics Data System (ADS)

Hydrogen hydrate is expected to be a hydrogen storage material, because it can contain relatively high hydrogen and its synthetic condition is mild comparable to industrial production. Three phases of hydrogen hydrate have been known so for. One is a clathrate hydrate sII [1], and others are filled ice II structure and filled ice Ic structure [2]. The ratio of water to hydrogen molecules for these phases are1:3, 1:6, 1:1, respectively. The clathrate sII containing only hydrogen molecules is stable only in a lower temperature region. At room temperature, above about 0.8 GPa filled ice II and above 2.5 GPa filled ice Ic are formed. The latter one survives at least up to 90 GPa [3]. However, investigations in low temperature and high pressure region have been limited. In this study, low temperature and high pressure experiments were performed by using diamond anvil cells and a helium-refrigeration cryostat in a region of 0.2 to 4.5 GPa and 130 to 300 K. X-ray diffractometry (XRD) showed a series of phase change from sII to filled ice Ic via filled ice II. For example, at 220K, sII transformed to filled ice II at approximately 0.7 GPa and further transformed to filled ice Ic structure at about 2.0 GPa. The present results experimentally confirmed the previously predicted phase boundaries. For filled ice II structure, Raman spectroscopy revealed that pressure dependency of vibration mode of guest hydrogen molecules and OH stretching mode of host water molecules changed at approximately 2.5 GPa. The XRD also showed change in axial ratio at the same pressure. These result suggested that state of filled ice II structure changed at about 2.5 GPa. Helium hydrate is known to form filled ice II structure [4], but high pressure study has not been yet fully performed. Similar experiments were carried out in a region of 0.2 to 5.0 GPa and 200 to 300 K. The results showed that the filled ice II structure did not transformed to filled ice Ic structure, but decomposed into helium and ice VI or VIII without transition to filled ice Ic structure as expected. [1] W. L. Mao et al., Science, 2002, 297, 2247-2249. [2] W. L. Vos et al, Phys. Rev. Lett. 1993, 71, 3150-3153. [3] H. Hirai et al., Amer. Mineralogist, 2006, 91, 826-830. [4] D. Londono et al., J. Chem. Phys., 1992, 97, 547.-552.

Hirai, H.; Umeda, A.; Fujii, T.; Machida, S.; Shinozaki, A.; Kawamura, T.; Yamamoto, Y.; Yagi, T.

2011-12-01

354

Allophycocyanin and phycocyanin crystal structures reveal facets of phycobilisome assembly.  

PubMed

X-ray crystal structures of the isolated phycobiliprotein components of the phycobilisome have provided high resolution details to the description of this light harvesting complex at different levels of complexity and detail. The linker-independent assembly of trimers into hexamers in crystal lattices of previously determined structures has been observed in almost all of the phycocyanin (PC) and allophycocyanin (APC) structures available in the Protein Data Bank. In this paper we describe the X-ray crystal structures of PC and APC from Synechococcus elongatus sp. PCC 7942, PC from Synechocystis sp. PCC 6803 and PC from Thermosynechococcus vulcanus crystallized in the presence of urea. All five structures are highly similar to other PC and APC structures on the levels of subunits, monomers and trimers. The Synechococcus APC forms a unique loose hexamer that may show the structural requirements for core assembly and rod attachment. While the Synechococcus PC assembles into the canonical hexamer, it does not further assemble into rods. Unlike most PC structures, the Synechocystis PC fails to form hexamers. Addition of low concentrations of urea to T. vulcanus PC inhibits this proteins propensity to form hexamers, resulting in a crystal lattice composed of trimers. The molecular source of these differences in assembly and their relevance to the phycobilisome structure is discussed. PMID:23201474

Marx, Ailie; Adir, Noam

2013-03-01

355

Crystal Structure of KinS2-I.  

National Technical Information Service (NTIS)

An X-ray single-crystal structure determination has confirmed that KInS2-I has the TIGaSe2 structure. The bonding in KIn S2-I is highly covalent and exhibits both two-dimensional and three-dimensinal features. The structure is comprised of layers of verte...

C. K. Lowe-Ma D. O. Kipp T. A. Vanderan

1990-01-01

356

Crystal Structure of Bacillus subtilis ?-Amylase in Complex with Acarbose  

PubMed Central

The crystal structure of Bacillus subtilis ?-amylase, in complex with the pseudotetrasaccharide inhibitor acarbose, revealed an hexasaccharide in the active site as a result of transglycosylation. After comparison with the known structure of the catalytic-site mutant complexed with the native substrate maltopentaose, it is suggested that the present structure represents a mimic intermediate in the initial stage of the catalytic process.

Kagawa, Masayuki; Fujimoto, Zui; Momma, Mitsuru; Takase, Kenji; Mizuno, Hiroshi

2003-01-01

357

Vortex structure in superconducting iron pnictide single crystals  

NASA Astrophysics Data System (ADS)

The vortex structure in the iron pnictide single crystals Ba1- x K x Fe2As2 and Sr1- x K x Fe2As2 of the 122 type and SmFeAsO1- x F x of the 1111 type has been investigated using the decoration method. In all of the crystals under investigation, no regular vortex lattice has been revealed in the magnetic field range up to 200 Oe. The disordered vortex structure is discussed in view of the vortex pinning in single crystals.

Vinnikov, L. Ya.; Artemova, T. M.; Veshchunov, I. S.; Zhigadlo, N. D.; Karpinski, J.; Popovich, P.; Sun, D. L.; Lin, C. T.; Boris, A. V.

2009-10-01

358

X-ray crystal structures of a severely desiccated protein.  

PubMed

Unlike most protein crystals, form IX of bovine pancreatic ribonuclease A diffracts well when severely dehydrated. Crystal structures have been solved after 2.5 and 4 days of desiccation with CaSO4, at 1.9 and 2.0 A resolution, respectively. The two desiccated structures are very similar. An RMS displacement of 1.6 A is observed for main-chain atoms in each structure when compared to the hydrated crystal structure with some large rearrangements observed in loop regions. The structural changes are the result of intermolecular contacts formed by strong electrostatic interactions in the absence of a high dielectric medium. The electron density is very diffuse for some surface loops, consistent with a very disordered structure. This disorder is related to the conformational changes. These results help explain conformational changes during the lyophilization of protein and the associated phenomena of denaturation and molecular memory. PMID:10548049

Bell, J A

1999-10-01

359

Quantitative crystal structure descriptors from multiplicative congruential generators.  

PubMed

Special types of number-theoretic relations, termed multiplicative congruential generators (MCGs), exhibit an intrinsic sublattice structure. This has considerable implications within the crystallographic realm, namely for the coordinate description of crystal structures for which MCGs allow for a concise way of encoding the numerical structural information. Thus, a conceptual framework is established, with some focus on layered superstructures, which proposes the use of MCGs as a tool for the quantitative description of crystal structures. The multiplicative congruential method eventually affords an algorithmic generation of three-dimensional crystal structures with a near-uniform distribution of atoms, whereas a linearization procedure facilitates their combinatorial enumeration and classification. The outlook for homometric structures and dual-space crystallography is given. Some generalizations and extensions are formulated in addition, revealing the connections of MCGs with geometric algebra, discrete dynamical systems (iterative maps), as well as certain quasicrystal approximants. PMID:22338652

Hornfeck, Wolfgang

2012-03-01

360

Electron-stimulated desorption of D+ from D2O ice: Surface structure and electronic excitations  

NASA Astrophysics Data System (ADS)

We present a study of the electron-stimulated desorption of deuterium cations (D+) from thin (1-40 ML) D2O ice films vapor deposited on a Pt(111) substrate. Measurements of the total yield and velocity distributions as a function of temperature from 90 to 200 K show that the D+ yield changes with film thickness, surface temperature, and ice phase. We observe two energy thresholds for cation emission, near 25 and 40 eV, which are weakly dependent upon the ice temperature and phase. The cation time-of-flight (TOF) distribution is at least bimodal, indicating multiple desorption channels. A decomposition of the TOF distributions into ``fast'' and ``slow'' channels shows structure as a function of excitation energy, film thickness, and temperature. The D+ yield generally increases with temperature, rising near 120 K on amorphous ice, and near 135 K on crystalline ice. The amorphous-crystalline phase transition at ~160 K causes a drop in total desorption yield. The temperature dependence of D- desorption via the 2B1 dissociative electron attachment resonance is very similar to the slow D+ yield, and likely involves similar restructuring and lifetime effects. The data collectively suggest that a thermally activated reduction of surface hydrogen bonding increases the lifetime of the excited states responsible for ion desorption, and that these lifetime effects are strongest for excited states involving a1 bands

Sieger, M. T.; Simpson, W. C.; Orlando, T. M.

1997-08-01

361

De-icing: recovery of diffraction intensities in the presence of ice rings.  

PubMed

Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality. PMID:20516627

Chapman, Michael S; Somasundaram, Thayumanasamy

2010-06-01

362

De-icing: recovery of diffraction intensities in the presence of ice rings  

PubMed Central

Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality.

Chapman, Michael S.; Somasundaram, Thayumanasamy

2010-01-01

363

High density amorphous ice at room temperature  

PubMed Central

The phase diagram of water is both unusual and complex, exhibiting a wide range of polymorphs including proton-ordered or disordered forms. In addition, a variety of stable and metastable forms are observed. The richness of H2O phases attests the versatility of hydrogen-bonded network structures that include kinetically stable amorphous ices. Information of the amorphous solids, however, is rarely available especially for the stability field and transformation dynamics—but all reported to exist below the crystallization temperature of approximately 150–170 K below 4–5 GPa. Here, we present the evidence of high density amorphous (HDA) ice formed well above the crystallization temperature at 1 GPa—well inside the so-called “no-man’s land.” It is formed from metastable ice VII in the stability field of ice VI under rapid compression using dynamic-diamond anvil cell (d-DAC) and results from structural similarities between HDA and ice VII. The formation follows an interfacial growth mechanism unlike the melting process. Nevertheless, the occurrence of HDA along the extrapolated melt line of ice VII resembles the ice Ih-to-HDA transition, indicating that structural instabilities of parent ice VII and Ih drive the pressure-induced amorphization.

Chen, Jing-Yin; Yoo, Choong-Shik

2011-01-01

364

Isothermal Ice-Crystallization Kinetics in the Gas-Diffusion Layer of a Proton-Exchange-Membrane Fuel Cell  

SciTech Connect

Nucleation and growth of ice in the fibrous gas-diffusion layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are investigated using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear icecrystallization rate expression is developed using Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nucleation theory. A validated rate expression is now available for predicting icecrystallization kinetics in GDLs.

Dursch, Thomas J.; Ciontea, Monica A.; Radke, Clayton J.; Weber, Adam Z.

2011-11-11

365

Ice Flora (Bottom Type): A Mechanism of Primary Production in Polar Seas and the Growth of Diatoms in Sea Ice.  

National Technical Information Service (NTIS)

A field survey off Barrow in the summer of 1964 revealed that sea ice in the Arctic develops a layered structure through the growth of diatoms. The diatoms increase in brine solutions which occur in the microfissures between fine crystals of sea ice and f...

H. Meguro K. Ito H. Fukushima

1967-01-01

366

Some formation peculiarities of physical and mechanical ice characteristics in hummocky formations  

Microsoft Academic Search

Main differences are considered in the formation of physical and mechanical ice properties in hummocky formations as compared\\u000a with level areas of the ice cover. The results of laboratory and field investigations demonstrate that these differences are\\u000a caused both by dynamometamorphic transformations of crystal ice structure as a result of the compression of ice fields before\\u000a the beginning of hummocky

K. P. Tyshko

2010-01-01

367

Optical Spectra of Orientationally Disordered Crystals. II. Infrared Spectrum of Ice Ih and Ice Ic from 360 to 50 cm-1  

Microsoft Academic Search

The far-infrared spectra in the range 360–50 cm?1 of ice Ih and ice Ic made from H2O and from D2O, and of vitreous ice made made from H2O have been investigated. The spectra are due to essentially purely translational vibrations, and have been interpreted using the theory of the spectra of orientationally disordered phases developed in the preceding paper. There

J. E. Bertie; E. Whalley

1967-01-01

368

The spin ice Ho(2)Ti(2)O(7) versus the spin liquid Tb(2)Ti(2)O(7): field-induced magnetic structures.  

PubMed

We studied the field-induced magnetic structures of Ho(2)Ti(2)O(7) spin ice by means of single-crystal neutron diffraction with a magnetic field applied along a [110] direction. These structures are compared to those of the spin liquid Tb(2)Ti(2)O(7) previously measured in similar experimental conditions. For both compounds, magnetic structures of two types with k = 0 and k = (0, 0, 1) propagation vectors coexist at low temperature (1.6 K) and high applied field (7 T). The k = 0 structures are described by the basis functions of the same irreducible representation for both Tb(2)Ti(2)O(7) and Ho(2)Ti(2)O(7). On the other hand, the k = (0, 0, 1) structures of Tb(2)Ti(2)O(7) and Ho(2)Ti(2)O(7) correspond to different irreducible representations, leading to different magnetic structures. PMID:21471634

Sazonov, A P; Gukasov, A; Mirebeau, I

2011-04-27

369

Crystal Structures of Two Putative Phosphoheptose  

SciTech Connect

Structural genomic centers use both NMR spectroscopic and X-ray crystallographic methods to determine three-dimensional structures of proteins on a genomic scale in a high-throughput mode and to deposit in the PDB. The main goal of structural genomics is to determine a large number of protein structures to complement the ever-expanding database of genome sequences. Another role of structural genomics is to delineate the correspondence between sequence and structure space; a number of protein structures from otherwise unrelated (i.e., 8-10% sequence identity) families often prove to have remarkably similar folds. This finding, in turn, allows better understanding of the structure-function relationships in those proteins for which either structures are not available or cannot be experimentally determined.

Seetharaman,J.; Rajashankar, K.; Solarzano, V.; Kniewel, R.; Lima, C.; Bonanno, J.; Burley, S.; Swaminathan, S.

2006-01-01

370

Measurements of HNO3 and NOy on Cirrus Ice Particles and in Solution Aerosols During CRYSTAL-FACE  

NASA Astrophysics Data System (ADS)

NOx (NO + NO2) is central to tropospheric O3 production. The larger family of gases with which NOx interconverts, NOy, or total reactive nitrogen, includes HNO3. One potential mechanism for the removal and/or vertical transport of NOy is via uptake on ice particles and aerosols. NOx is unlikely to be subject to such uptake, and HNO3 is likely the most significant NOy species subject to uptake. Thus the uptake of HNO3 has the potential to affect indirectly the O3 budget of the atmospehre [Lawrence and Crutzen, Tellus, 1998; Meier and Hendricks, JGR, 2002]. To assess the degree of uptake, condensed-phase HNO3 and NOy were measured during CRYSTAL-FACE by instruments in adjacent pallets on the WB57. The instruments employed nearly identical inlets for the enhanced (anisokinetic) sampling of condensed-phase species. Each instrument employed a second inlet for the measurement of the gas-phase plus small-particle fraction. Differences in the small-particle sampling by these latter inlets has proven beneficial for the inference of condensed-phase HNO3 on particles with diameters of order 1 micron. This talk will emphasize the southern survey flight of 9 July 2002, for which we infer the presence of condensed-phase HNO3 in ternary solutions of H2O, H2SO4, and HNO3. Ice was found in greater and lesser amounts in the presence of the aerosols, but ice appears to have played little role in the uptake of HNO3 here, as the aerosols compete very effectively for the HNO3 in this particular case, due to the relatively large particle volume and the low temperatures. In addition, the condensed-phase NOy measurements are compared to the condensed-phase HNO3 measurements described in another presentation at this meeting (Popp et al.) Overall the condensed-phase HNO3 and NOy amounts are similar to one another and give no indication that other NOy species are taken up by cirrus ice particles.

Weinheimer, A. J.; Knapp, D. J.; Montzka, D. D.; Ridley, B. A.; Popp, P. J.; Gao, R. S.; Marcy, T. P.; Fahey, D. W.; Baumgardner, D.; Anderson, B. E.; Wilson, J. C.; Lee, S. H.; Reeves, J. M.; Lafleur, B. G.; Hilbert, H.; Schmit, O.; Herman, R. L.; Weinstock, E. M.; Smith, J. B.; Sayres, D. W.; Vellovic, J.; Anderson, J. G.; Bui, T. P.; Bowen, S. W.; Pfister, L.; Dean-Day, J.; Chang, C.

2003-12-01

371

Crystallization of dienelactone hydrolase in two space groups: structural changes caused by crystal packing.  

PubMed

Dienelactone hydrolase (DLH) is a monomeric protein with a simple ?/?-hydrolase fold structure. It readily crystallizes in space group P212121 from either a phosphate or ammonium sulfate precipitation buffer. Here, the structure of DLH at 1.85?Å resolution crystallized in space group C2 with two molecules in the asymmetric unit is reported. When crystallized in space group P212121 DLH has either phosphates or sulfates bound to the protein in crucial locations, one of which is located in the active site, preventing substrate/inhibitor binding. Another is located on the surface of the enzyme coordinated by side chains from two different molecules. Crystallization in space group C2 from a sodium citrate buffer results in new crystallographic protein-protein interfaces. The protein backbone is highly similar, but new crystal contacts cause changes in side-chain orientations and in loop positioning. In regions not involved in crystal contacts, there is little change in backbone or side-chain configuration. The flexibility of surface loops and the adaptability of side chains are important factors enabling DLH to adapt and form different crystal lattices. PMID:25005082

Porter, Joanne L; Carr, Paul D; Collyer, Charles A; Ollis, David L

2014-07-01

372

Single-crystal growth, crystal and electronic structure of NaCoO 2  

Microsoft Academic Search

Single crystals of NaCoO2 have been successfully synthesized for the first time by a flux method at 1323K. A single-crystal X-ray diffraction study confirmed the trigonal R3?m space group and the lattice parameters a=2.8897(15)A?, c=15.609(3)A?. The crystal structure has been refined to the conventional values R=1.9% and wR=2.1% for 309 independent observed reflections. The electron density distribution of NaCoO2 has

Yasuhiko Takahashi; Yoshito Gotoh; Junji Akimoto

2003-01-01

373

Datamining protein structure databanks for crystallization patterns of proteins.  

PubMed

A study of 345 protein structures selected among 1,500 structures determined by nuclear magnetic resonance (NMR) methods, revealed useful correlations between crystallization properties and several parameters for the studied proteins. NMR methods of structure determination do not require the growth of protein crystals, and hence allow comparison of properties of proteins that have or have not been the subject of crystallographic approaches. One- and two-dimensional statistical analyses of the data confirmed a hypothesized relation between the size of the molecule and its crystallization potential. Furthermore, two-dimensional Bayesian analysis revealed a significant relationship between relative ratio of different secondary structures and the likelihood of success for crystallization trials. The most immediate result is an apparent correlation of crystallization potential with protein size. Further analysis of the data revealed a relationship between the unstructured fraction of proteins and the success of its crystallization. Utilization of Bayesian analysis on the latter correlation resulted in a prediction performance of about 64%, whereas a two-dimensional Bayesian analysis succeeded with a performance of about 75%. PMID:12594078

Valafar, Homayoun; Prestegard, James H; Valafar, Faramarz

2002-12-01

374

Crystal and quasicrystal structures in Al-Mn-Si alloys  

Microsoft Academic Search

It is shown that the alpha-(AlMnSi) crystal structure is closely (and systematically) related to that of the icosahedral Al-Mn-Si alloys. Using a modification of the 'projection' method of generating icosahedral structures from six-dimensional lattices, a simple description of the alpha-(AlMnSi) structure is found. This structure, and (it is conjectured) the icosahedral one, can also be described as a packing of

Veit Elser; C. L. Henley

1985-01-01

375

CO2 (dry ice) cleaning system  

NASA Technical Reports Server (NTRS)

Tomco Equipment Company has participated in the dry ice (solid carbon dioxide, CO2) cleaning industry for over ten years as a pioneer in the manufacturer of high density, dry ice cleaning pellet production equipment. For over four years Tomco high density pelletizers have been available to the dry ice cleaning industry. Approximately one year ago Tomco introduced the DI-250, a new dry ice blast unit making Tomco a single source supplier for sublimable media, particle blast, cleaning systems. This new blast unit is an all pneumatic, single discharge hose device. It meters the insertion of 1/8 inch diameter (or smaller), high density, dry ice pellets into a high pressure, propellant gas stream. The dry ice and propellant streams are controlled and mixed from the blast cabinet. From there the mixture is transported to the nozzle where the pellets are accelerated to an appropriate blasting velocity. When directed to impact upon a target area, these dry ice pellets have sufficient energy to effectively remove most surface coatings through dry, abrasive contact. The meta-stable, dry ice pellets used for CO2 cleaning, while labeled 'high density,' are less dense than alternate, abrasive, particle blast media. In addition, after contacting the target surface, they return to their equilibrium condition: a superheated gas state. Most currently used grit blasting media are silicon dioxide based, which possess a sharp tetrahedral molecular structure. Silicon dioxide crystal structures will always produce smaller sharp-edged replicas of the original crystal upon fracture. Larger, softer dry ice pellets do not share the same sharp-edged crystalline structures as their non-sublimable counterparts when broken. In fact, upon contact with the target surface, dry ice pellets will plastically deform and break apart. As such, dry ice cleaning is less harmful to sensitive substrates, workers and the environment than chemical or abrasive cleaning systems. Dry ice cleaning system components include: a dry ice pellet supply, a non-reactive propellant gas source, a pellet and propellant metering device, and a media transport and acceleration hose and nozzle arrangement. Dry ice cleaning system operating parameters include: choice of propellant gas, its pressure and temperature, dry ice mass flow rate, dry ice pellet size and shape, and acceleration nozzle configuration. These parameters may be modified to fit different applications. The growth of the dry ice cleaning industry will depend upon timely data acquisition of the effects that independent changes in these parameters have on cleaning rates, with respect to different surface coating and substrate combinations. With this data, optimization of cleaning rates for particular applications will be possible. The analysis of the applicable range of modulation of these parameters, within system component mechanical constraints, has just begun.

Barnett, Donald M.

1995-01-01

376

The Cloud Particle Spectrometer with Polarization Detection (CPSPD): A next generation open-path cloud probe for distinguishing liquid cloud droplets from ice crystals  

NASA Astrophysics Data System (ADS)

The differentiation of small water droplets and ice crystals by in situ measurements, in the size range < 50 ?m, remains a challenge and the lack of such measurements is an obstacle to progress in understanding ice formation in clouds. A new microphysical instrument, the Cloud Particle Spectrometer with Polarization Detection (CPSPD), has been developed that measures light intensity scattered (in forward and backward directions) by individual cloud particles that pass through a focused laser beam and derives their size and thermodynamic phase (liquid or ice) in the optical diameter range from 2 to 50 ?m. The optical equivalent diameter is derived from the light scattered in the forward direction. The change in polarization state of the incident light, caused by interaction with the cloud particle, is determined from the polarized components of the backscattered light. The CPSPD, along with several other cloud microphysical probes, has been flown on the University of North Dakota Citation aircraft in mixed phase clouds. It has also been deployed and operated at the Zugspitze research station studying mountain clouds. The preliminary results show that liquid cloud droplets can be distinguished from ice crystals and that the ice fraction can be estimated; an important parameter for better understanding of cloud processes, particularly that of glaciation.

Baumgardner, Darrel; Newton, Roy; Krämer, Martina; Meyer, Jessica; Beyer, Alexander; Wendisch, Manfred; Vochezer, Paul

2014-06-01

377

Single-crystal structure of a covalent organic framework.  

PubMed

The crystal structure of a new covalent organic framework, termed COF-320, is determined by single-crystal 3D electron diffraction using the rotation electron diffraction (RED) method for data collection. The COF crystals are prepared by an imine condensation of tetra-(4-anilyl)methane and 4,4'-biphenyldialdehyde in 1,4-dioxane at 120 °C to produce a highly porous 9-fold interwoven diamond net. COF-320 exhibits permanent porosity with a Langmuir surface area of 2400 m(2)/g and a methane total uptake of 15.0 wt % (176 cm(3)/cm(3)) at 25 °C and 80 bar. The successful determination of the structure of COF-320 directly from single-crystal samples is an important advance in the development of COF chemistry. PMID:24143961

Zhang, Yue-Biao; Su, Jie; Furukawa, Hiroyasu; Yun, Yifeng; Gándara, Felipe; Duong, Adam; Zou, Xiaodong; Yaghi, Omar M

2013-11-01

378

Crystal structure of potassium titanyl phosphate doped with zirconium  

SciTech Connect

This paper reports on the results of precision X-ray structural investigations of single crystals of the compounds KTi{sub 0.96}Zr{sub 0.04}OPO{sub 4} (at 293 K) and KTi{sub 0.97}Zr{sub 0.03}OPO{sub 4} (at 293 and 105 K). No significant splitting of the positions occupied by potassium atoms is revealed. This result is in agreement with a considerable decrease in the electrical conductivity of potassium titanyl phosphate KTiOPO{sub 4} (KTP) crystals doped with zirconium (KTP: Zr) as compared to crystals of undoped potassium titanyl phosphate. It is established that the difference between the Ti-O bond lengths in chains formed by titanium octahedra is not a single structural parameter responsible for the nonlinear optical properties of crystals in this series.

Alekseeva, O. A., E-mail: olalex@ns.crys.ras.ru; Dudka, A. P.; Sorokina, N. I. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Pietraszko, A. [Polish Academy of Sciences, Institute of Low Temperature and Structure Research (Poland); Rabadanov, M. Kh. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Agapova, E. I.; Voronkova, V. I. [Lomonosov Moscow State University (Russian Federation); Simonov, V. I. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)

2007-07-15

379

Crystal structure of ScB/sub 12/  

SciTech Connect

The crystal structure of scandium dodecaboride was determined. The research material was a single crystal derived from an ingot obtained by fusion of metallic Sc and finely crystalline boron in an electric-arc furnace (Ar atmosphere). We used Laue, rotation, and inverse-lattice photography methods. The data confirmed that ScB/sub 12/ has a face-centered cubic structure. The investigation showed that with regard to the composition and structure of the resulting borides Sc exhibits complete analogy with Zr and is less similar to yttrium-group rare earth metals, for which the formation of tetraborides and hexaborides is characteristic.

Bruskov, V.A.; Zavalii, L.V.; Kuz'ma, Yu.B.

1988-08-01

380

Vulcanite, CuTe: hydrothermal synthesis and crystal structure refinement  

Microsoft Academic Search

Summary   The crystal structure of the mineral vulcanite, CuTe [a?=?3.155(1), b?=?4.092(1), c?=?6.956(1)?Å; Z?=?2; space group: Pmmn,\\u000a No. 59] exhibits a pronounced layer structure with Te-Te distances between the CuTe layers of 4.019(1)?Å. Within a range up\\u000a to 4.2?Å the individual Cu atom is [4Te+4Cu+2Cu], the individual Te atom [4Cu+2Te+4Te] coordinated. Crystals of vulcanite\\u000a suitable for the present structure investigation were

F. Pertlik

2001-01-01

381

Symmetry building Monte Carlo-based crystal structure prediction  

NASA Astrophysics Data System (ADS)

Methods are presented that allow for the automatic increase and preservation of symmetry during global optimization of crystal structures. This systematic building of symmetry allows for its incorporation into structure prediction simulations even when the space group information is not known a priori. It is shown that simulations that build and maintain symmetry converge much more rapidly to ground state crystal structures than when symmetry is ignored, allowing for the treatment of unit cells much larger than would otherwise be possible, especially when beginning from the P1 space group.

Michel, Kyle Jay; Wolverton, C.

2014-05-01

382

Atomic- Resolution Crystal Structure of the Antiviral Lectin Scytovirin  

SciTech Connect

The crystal structures of the natural and recombinant antiviral lectin scytovirin (SVN) were solved by single-wavelength anomalous scattering and refined with data extending to 1.3 Angstroms and 1.0 Angstroms resolution, respectively. A molecule of SVN consists of a single chain 95 amino acids long, with an almost perfect sequence repeat that creates two very similar domains (RMS deviation 0.25 Angstroms for 40 pairs of Ca atoms). The crystal structure differs significantly from a previously published NMR structure of the same protein, with the RMS deviations calculated separately for the N- and C-terminal domains of 5.3 Angstroms and 3.7 Angstroms, respectively, and a very different relationship between the two domains. In addition, the disulfide bonding pattern of the crystal structures differs from that described in the previously published mass spectrometry and NMR studies.

Moulaei,T.; Botos, I.; Ziolkowska, N.; Bokesch, H.; Krumpe, L.; McKee, T.; O'Keefe, B.; Dauter, Z.; Wlodawer, A.

2007-01-01

383

Crystal structure of a theta-class glutathione transferase.  

PubMed Central

Glutathione S-transferases (GSTs) are a family of enzymes involved in the cellular detoxification of xenotoxins. Cytosolic GSTs have been grouped into four evolutionary classes for which there are representative crystal structures of three of them. Here we report the first crystal structure of a theta-class GST. So far, all available GST crystal structures suggest that a strictly conserved tyrosine near the N-terminus plays a critical role in the reaction mechanism and such a role has been convincingly demonstrated by site-directed mutagenesis. Surprisingly, the equivalent residue in the theta-class structure is not in the active site, but its role appears to have been replaced by either a nearby serine or by another tyrosine residue located in the C-terminal domain of the enzyme. Images

Wilce, M C; Board, P G; Feil, S C; Parker, M W

1995-01-01

384

Optical and structural properties of chalcone NLO single crystals  

NASA Astrophysics Data System (ADS)

Organic compound (E)-1-(4-methoxyphenyl)-3-(2,3,5-trichlorophenyl)prop-2-en-1-one [MPTCPP] with molecular formula C 16H 11Cl 3O 2 was synthesized using Claisen-Schmidt condensation reaction method. 1H NMR spectra was recorded to identify the various functional groups present in the compound and confirm the chemical structure. The single crystals were grown using slow evaporation solution growth technique. The UV-Visible spectrum study reveals that the crystal is transparent in the entire visible region and the absorption is observed at 364 nm. The Kurtz powder second harmonic generation (SHG) test shows that the MPTCPP is NLO active and its SHG efficiency is three times that of urea. Single crystal XRD study shows that the compound crystallizes in the monoclinic system with a space group Cc. The corresponding lattice parameters of the crystal are a = 28.215(5) Å, b = 3.9740(4) Å, c = 16.178(3) Å and V = 1503.0(4) Å 3. The micro hardness test was carried out and the work hardening coefficient value ( n) of the crystal was found to be 1.48. This indicates that the crystal is hard and is suitable for device application. The thermal study reveals that the thermal stability of the crystal is good.

Rajesh Kumar, P. C.; Ravindrachary, V.; Janardhana, K.; Manjunath, H. R.; Karegouda, Prakash; Crasta, Vincent; Sridhar, M. A.

2011-11-01

385

Refined Crystal Structures of Unligated Adenylosuccinate Synthetase from Escherichia coli  

Microsoft Academic Search

Crystal structures of unligated adenylosuccinate synthetase fromEscherichia coliin space groupsP21andP212121have been refined toR-factors of 0.199 and 0.206 against data to 2.0 and 2.5 Å, respectively. Bond lengths and angles deviate from expected values by 0.011 Å and 1.7° for theP21crystal form and by 0.015 Å and 1.7° for theP212121crystal form. The fold of the polypeptide chain is dominated by a

M. Mercedes Silva; Bradley W. Poland; Chad R. Hoffman; Herbert J. Fromm; Richard B. Honzatko

1995-01-01

386

Chemical space sampling in virtual screening by different crystal structures.  

PubMed

Retrospective virtual screening experiments were carried out to investigate the effects of combining hit lists from different crystal structures of the same target using consensus scoring. An in-house High Throughput Screening (HTS) dataset from PI3K-? was used and docked against five diverse PI3K-? crystal structures. The results show that consensus scoring prioritizes compounds that score moderately against individual crystal structures and is thus complementary to individual crystal structure screening leading to an increase in the diversity of hits. Enrichment factors (EFs) of the consensus score for two or three structures are often as high as or higher than the EF of the individual structures used in the consensus score. Combining four or five structures in the consensus score generally yields lower enrichments. Compounds in the top 500 of the consensus score that are also found in the top 500 of an individual X-ray structure used in the consensus score calculations yield the largest number of hits with the lowest number of false positives. PMID:20958920

Brooijmans, Natasja; Humblet, Christine

2010-12-01

387

Photonic crystals of diamond spheres with the opal structure  

NASA Astrophysics Data System (ADS)

Opal samples consisting of diamond spheres have been synthesized by chemical deposition in microwave plasma from a CH4/H2 mixture using templates of silicon inverse opal. The optical investigations have confirmed that the periodic structures prepared are structurally perfect three-dimensional photonic crystals.

Sovyk, D. N.; Ralchenko, V. G.; Kurdyukov, D. A.; Grudinkin, S. A.; Golubev, V. G.; Khomich, A. A.; Konov, V. I.

2013-05-01

388

Crystal structure of simple metals at high pressures  

Microsoft Academic Search

The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 14–17, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a

Olga Degtyareva; Olga

2010-01-01

389

Etching effect on periodic domain structures of lithium niobate crystals  

Microsoft Academic Search

In order to improve the knowledge of the domain structure in LiNbO3 crystals, the effect of the etching process with HF:HNO3 (1:2 by vol.) has been studied. It has been found, by analyzing the superficial composition with the secondary ion mass spectrometry technique, that during the etching treatment, the fluorine ion diffuses into the crystal, mainly along the positive ferroelectric

V. Bermúdez; F Caccavale; C Sada; F Segato; E Diéguez

1998-01-01

390

Etching effect on periodic domain structures of lithium niobate crystals  

NASA Astrophysics Data System (ADS)

In order to improve the knowledge of the domain structure in LiNbO 3 crystals, the effect of the etching process with HF : HNO 3 (1 : 2 by vol.) has been studied. It has been found, by analyzing the superficial composition with the secondary ion mass spectrometry technique, that during the etching treatment, the fluorine ion diffuses into the crystal, mainly along the positive ferroelectric domain.

Bermúdez, V.; Caccavale, F.; Sada, C.; Segato, F.; Diéguez, E.

1998-07-01

391

Structure of blue phase III of cholesteric liquid crystals.  

PubMed

We report large scale simulations of the blue phases of cholesteric liquid crystals. Our results suggest a structure for blue phase III, the blue fog, which has been the subject of a long debate in liquid crystal physics. We propose that blue phase III is an amorphous network of disclination lines, which is thermodynamically and kinetically stabilized over crystalline blue phases at intermediate chiralities. This amorphous network becomes ordered under an applied electric field, as seen in experiments. PMID:21469836

Henrich, O; Stratford, K; Cates, M E; Marenduzzo, D

2011-03-11

392

The Host Guest Co-Crystal Approach to Supramolecular Structure  

Microsoft Academic Search

A host-guest co-crystal approach to supramolecular structure has been developed. Molecular functionalities have been identified that will self assemble via hydrogen bonds to give one dimensional ?-networks with defined intermolecular distances. Host molecules based on these functionalites can be co-crystallized with guest molecules, the characteristic distance defined by the host is thus imposed on the guest. Using this strategy, functional

John J. Kane; Tam Nguyen; Jun Xiao; Frank W. Fowler; Joseph W. Lauher

2001-01-01

393

Crystal structure of the extracellular segment of integrin V3  

Microsoft Academic Search

Integrins are heterodimeric receptors that mediate divalent cation-dependent cell-cell and cell-matrix adhesion through tightly regulated interactions with ligands. We have solved the crystal structure of the extracellular portion of integrin V{sup }3 at 3.1 Angstroms resolution. Its 12 domains assemble into an ovoid 'head' and two 'tails.' In the crystal, V{sup }3 is severely bent at a defined region in

J.-P. Xiong; T. Stehle; B. Diefenbach; R. Zhang; R. Dunker; D. L. Scott; A. Joachimiak; S. L. Goodman; M. A. Arnaout; Merck KGaA

2001-01-01

394

Observation and Analysis of Polymer Crystal Structures at the Stem Level. Implications Regarding Polymer Crystallization Processes.  

NASA Astrophysics Data System (ADS)

The building element of chain folded polymer crystals is the individual stem that spans the lamellar thickness. For chiral but racemic helical polymers such as polyolefins (e.g. isotactic and syndiotactic polypropylene and poly(1-butene)), stems can be right- or left-handed helices. These polymers can exist in various crystal polymorphs that are either "racemic" or "chiral" (made of both, or of only one helical hand). Upon crystallization, each stem has a conformational "choice", but must adapt to the crystal structure and, once crystallized, is characterized by a "conformational tag" (right or left hand). Various means exist to determine or observe helical hands in polyolefin lamellae: Atomic Force Microscopy on epitaxially crystallized samples, or, for the alpha phase of isotactic polypropylene, analysis of its specific lamellar branching. These observations and analyses indicate that the helical hand of stems is tightly determined by the substrate or growth face topography, i.e. indicate that the depositing stem probes and adapts to the surface structure prior to successful attachment. This "post-mortem" analysis of the crystal structure and stem chirality emphasizes the "sequential" nature of the growth process (successive attachment of individual stems). It is in line with early views on polymer crystallization. It is at variance with recently introduced models or scenarios that assume either some pre-ordering of the polymer melt as a result of spinodal decomposition and/or accretion of polymer chains in pseudo-crystalline bundles followed by (solid state) reorganization of the bundles to generate fully grown lamellae.

Lotz, Bernard

2003-03-01

395

Crystal and Magnetic Structure of UNi0.52  

NASA Astrophysics Data System (ADS)

We report the single crystal neutron diffraction studies done to resolve the room-temperature structure and the magnetic structure at 25 K of Uranium antimonide, UNi0.5Sb2. The time-of-flight single-crystal neutron diffraction experiments at room temperature and 25 K were done on the Single Crystal Diffractometer, SCD, at Los Alamos Neutron Science Center. Previous X-ray single crystal and neutron powder diffraction studies could not unambiguously resolve the structure because of the presence of hkl/2 type reflections. The studies were done on a 2 x 1 x 0.5 mm3 crystal and half-indexed reflections were observed corroborating the observations in previous studies. The room temperature structure that accounts for all the observed reflections is determined to be tetragonal P42/n m c with lattice parameters a = 4.333(2) å and c = 17.868(6) å respectively. The compound is found to order antiferromagnetically at 162 K and has a simple antiferromagnetic structure at 25 K with propagation vector q = (0, 0, 0) and with a moment of 1.82?B/U atom.

Kothapalli, Karunakar; Torikachvili, Milton; Nasreen, Farzana; Nakotte, Heinrich

2010-10-01

396

Fine Structure of Electron Diffraction Beams from a Gold Crystal and from a Silver Film on a Gold Crystal  

Microsoft Academic Search

A study of the diffraction of low-speed electrons from a gold crystal has been made under the same conditions as those previously used for a silver crystal to determine the extent to which the previously observed fine structure characteristics depend on the nature of the atoms composing the crystal. For normal incidence there are many differences in the positions, structure,

H. E. Farnsworth

1933-01-01

397

Optimal modeling of atomic fluctuations in protein crystal structures for weak crystal contact interactions  

NASA Astrophysics Data System (ADS)

The accurate modeling of protein dynamics in crystalline states holds keys to the understanding of protein dynamics relevant to functions. In this study, we used coarse-grained elastic network models (ENMs) to explore the atomic fluctuations of a protein structure that interacts with its crystalline environment, and evaluated the modeling results using the anisotropic displacement parameters (ADPs) obtained from x-ray crystallography. To ensure the robustness of modeling results, we used three ENM schemes for assigning force constant combined with three boundary conditions for treating the crystalline environment. To explore the role of crystal contact interactions in the modeling of ADPs, we varied the strength of interactions between a protein structure and its environment. For a list of 83 high-resolution crystal structures, we found that the optimal modeling of ADPs, as assessed by a variety of metrics, is achieved for weak protein-environment interactions (compared to the interactions within a protein structure). As a result, the ADPs are dominated by contributions from rigid-body motions of the entire protein structure, and the internal protein dynamics is only weakly perturbed by crystal packing. Our finding of weak crystal contact interactions is also corroborated by the calculations of residue-residue contact energy within a protein structure and between protein molecules using a statistical potential.

Hafner, Jeffrey; Zheng, Wenjun

2010-01-01

398

Structural characterization of water/ice formation in SBA-15 silicas: III. The triplet profile for 86 Å pore diameter.  

PubMed

The diffraction results for the formation of ice in 86 Å diameter pores of a SBA-15 silica sample are analysed to provide information on the characteristics of the ice created in the pores. The asymmetric triplet at ?1.7 Å(-1), which involves several overlapping peaks, is particularly relevant to the different ice phases and contains a number of components that can be individually identified. The use of a set of three peaks with an asymmetric profile to represent the possibility of facetted growth in the pores was found to give an unsatisfactory fit to the data. The alternative method involving the introduction of additional peaks with a normal symmetric profile was found to give excellent fits with five components and was the preferred analytic procedure. Three peaks could be directly linked to the positions for the triplet of hexagonal ice, I(h), and one of the other two broad peaks could be associated with a form of amorphous ice. The variation of the peak intensity (and position) was systematic with temperature for both cooling and heating runs. The results indicate that a disordered state of ice is formed as a component with the defective crystalline ices. The position of a broad diffraction peak is intermediate between that of high-density and low-density amorphous ice. The remaining component peak is less broad but does not relate directly to any of the known ice phases and cannot be assigned to any specific structural feature at the present time. PMID:21694289

Seyed-Yazdi, J; Farman, H; Dore, John C; Webber, J Beau W; Findenegg, G H

2008-05-21

399

What's An Ice Core?  

NSDL National Science Digital Library

This animation starts with a schematic illustration of glacier growth and then introduces six different methods that researchers use when studying ice cores in order to deduce the climate of the past. The research methods that are briefly introduced are ice layering, pollen, oxygen isotopes, ice crystals and gases trapped inside, and other chemistry.

History, The A.

400

Bathymetry and geological structures beneath the Ross Ice Shelf at the mouth of Whillans Ice Stream, West Antarctica, modeled from ground-based gravity measurements  

NASA Astrophysics Data System (ADS)

gravity data reveal important geologic controls on the location and behavior of the grounding zone of Whillans Ice Stream (WIS), West Antarctica. Grounding zones of ice sheets and contiguous ice shelves are important for understanding ice sheet dynamics, as key processes that influence the grounded ice and its discharge into the ocean occur in these regions. Here, we model the bathymetry and shallow geological structures beneath the Ross Ice Shelf in an embayment of the WIS grounding zone using gravity data collected on the ground, in conjunction with seismic and radar data. We find that the region of shallow ocean water (<~50 m) is extensive; oceanographic models suggest that grounding zones exhibiting thin ocean cavities with gently sloping ice-ocean interfaces are likely to be tidally well mixed, leading to slower basal melting than would occur in a thicker, stratified water column. Beneath the ocean water column, we model a fault and a sedimentary basin in a half-graben, filled with two layers of sediments. The total thickness of the sediment layer is 900 to 1250 m in the half-graben, and 600 to 800 m on the upthrown block, and the basement depth is no more than 2000 m. We observe that the upper, softer sediment is thinnest near the modern grounding line and may possibly pinch out near our grid, and that the modeled fault is roughly parallel to part the grounding. We therefore hypothesize that the WIS grounding line stabilized in its current location in part due to the subglacial geology.

Muto, Atsuhiro; Christianson, Knut; Horgan, Huw J.; Anandakrishnan, Sridhar; Alley, Richard B.

2013-08-01

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