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1

Design and fabrication of eight zone vertical dynamic gradient freeze system for organic single crystal growth.  

PubMed

Design and construction of the vertical dynamic gradient freeze (VDGF) system operating in the temperature range from 50?°C to 500?°C for growing organic single crystals are described. The design of VDGF system consists of furnace, control system, translation assembly, and image capturing device. Furnace has been constructed with eight zones controlled independently by a dynamic temperature control system for achieving desired thermal environment and multiple temperature gradients, which are essential for the growth of organic single crystals. The transparent furnace enables direct observation to record and monitor the solid-liquid interface and growth of crystals through charge coupled device based video camera. The system is fully computerized hence it is possible to retrieve the complete growth and furnace history. In order to investigate the functioning of the constructed VDGF system for the growth of organic single crystals, a well known organic nonlinear optical single crystal of benzimidazole was grown. The crystalline quality and the optical transmittance of the grown crystal were studied. PMID:24007079

Prabhakaran, S P; Babu, R Ramesh; Ramamurthi, K

2013-08-01

2

Cu2ZnSnSe4 Photovoltaic Absorber Grown by Vertical Gradient Freeze Technique  

NASA Astrophysics Data System (ADS)

High quality large grain single phase Cu2ZnSnSe4 (CZTSe) photovoltaic absorber material was grown by vertical gradient freeze (VGF) technique for the first time. Polycrystalline CZTSe ingot was grown in a vacuum sealed quartz ampoule inside a modified three-zone vertical Bridgman furnace employing a directional cooling. Structural and compositional analyses of the grown crystals were performed by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The grown crystals exhibited highly crystalline tetragonal structure corresponding to kesterite Cu2ZnSnSe4 with lattice parameters of a = 5.696 Å and c = 11.338 Å as evidenced from XRD pattern. Raman spectra showed three characteristic peaks at 171.5, 194.6, and 231.1 cm-1 attributed to kesterite phase CZTSe. No other secondary phases were detected in the grown crystals. Thermoelectric probe measurements showed p-type conductivity of the grown crystals and energy dispersive X-ray spectroscopy (EDS) along the crystal growth direction showed uniform and stoichiometric elemental distribution. Our results show that VGF technique can be used to grow high quality kesterite compounds for photovoltaic application.

Das, Sandip; Mandal, Krishna C.

2013-12-01

3

Electron Backscatter Diffraction Analysis of a CZT Growth Tip from a Vertical Gradient Freeze Furnace  

SciTech Connect

Electronic backscatter diffraction (EBSD) was used to characterize the growth-tip region of a 4.2-cm diameter CdZnTe (CZT) boule grown using low-pressure Bridgman method in a vertical gradient freeze furnace. The boule was sectioned and polished and a section taken along the boule longitudinal centerline with an approximate surface area of 1-cm2 was used for optical and scanning electron microscopy. A collage was assembled using EBSD/SEM images to show morphological features, e.g., twin structure, grain structure, and overall crystal growth direction. Severely twinned regions originating from the tip and side walls were observed. The overall growth orientation was close to <110> and <112> directions. In some regions, the (001) poles of the CZT matrix aligned with the growth direction, while twins aligned such that (111) and (112) poles aligned with the growth direction. In some other areas, (112) or (011) poles of the CZT matrix aligned with the growth direction. New relationships between the CZT matrix and large Te polycrystalline particles were revealed: {11 }CZT??{1 00}Te and {001}CZT??{0 1}Te.

Sundaram, S. K.; Henager, Charles H.; Edwards, Danny J.; Schemer-Kohrn, Alan L.; Bliss, Mary; Riley, Brian J.

2011-08-15

4

Crystal growth of AgIn 1? X Ga X Se 2 crystals grown by a vertical gradient freeze method  

Microsoft Academic Search

AgIn1?XGaXSe2 crystals were grown by a vertical gradient freeze method. All samples were shown to have a chalcopyrite structure and n-type conductivity by means of X-ray diffraction (XRD) and thermoprobe analysis, respectively. Electron probe microanalysis showed all crystals to be In-poor. Lattice constants a and c, calculated from the XRD were found to be proportional to X values in the

Kenji Yoshino; Hironori Komaki; Kousuke Itani; Shigefusa F Chichibu; Youji Akaki; Tetsuo Ikari

2002-01-01

5

Final Report: Property Improvement in CZT via Modeling and Processing Innovations – Te-particles in vertical gradient freeze CZT: Size and Spatial Distributions and Constitutional Supercooling  

SciTech Connect

A section of a vertical gradient freeze CZT boule approximately 2100-mm3 with a planar area of 300-mm2 was prepared and examined using transmitted IR microscopy at various magnifications to determine the three-dimensional spatial and size distributions of Te-particles over large longitudinal and radial length scales. The boule section was approximately 50-mm wide by 60-mm in length by 7-mm thick and was doubly polished for TIR work. Te-particles were imaged through the thickness using extended focal imaging to locate the particles in thickness planes spaced 15-µm apart and then in plane of the image using xy-coordinates of the particle center of mass so that a true three dimensional particle map was assembled for a 1-mm by 45-mm longitudinal strip and for a 1-mm by 50-mm radial strip. Te-particle density distributions were determined as a function of longitudinal and radial positions in these strips, and treating the particles as vertices of a network created a 3D image of the particle spatial distribution. Te-particles exhibited a multi-modal log-normal size density distribution that indicated a slight preference for increasing size with longitudinal growth time, while showing a pronounced cellular network structure throughout the boule that can be correlated to dislocation network sizes in CZT. Higher magnification images revealed a typical Rayleigh-instability pearl string morphology with large and small satellite droplets. This study includes solidification experiments in small crucibles of 30:70 mixtures of Cd:Te to reduce the melting point below 1273 K (1000?C). These solidification experiments were performed over a wide range of cooling rates and clearly demonstrated a growth instability with Te-particle capture that is suggested to be responsible for one of the peaks in the size distribution using size discrimination visualization. The results are discussed with regard to a manifold Te-particle genesis history as 1) Te-particle direct capture from melt-solid growth instabilities, 2) Te-particle formation from dislocation core diffusion and the formation and breakup of Te-tubes, and 3) Te-particle formation due to classical nucleation and growth as precipitates.

Henager, Charles H.; Alvine, Kyle J.; Bliss, Mary; Riley, Brian J.; Stave, Jean A.

2014-10-01

6

Semiconductor apparatus utilizing gradient freeze and liquid-solid techniques  

NASA Technical Reports Server (NTRS)

Transition metals of Group VIII (Co, Rh and Ir) have been prepared as semiconductor compounds with the general formula TSb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor compounds and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor materials having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using vertical gradient freezing techniques and/or liquid phase sintering techniques. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities (up to 1200 cm.sup.2.V.sup.-1.s.sup.-1) and good Seebeck coefficients (up to 150 .mu.VK.sup.-1 between 300.degree. C. and 700.degree. C.). Optimizing the transport properties of semiconductor materials prepared from elemental mixtures Co, Rh, Ir and Sb resulted in a substantial increase in the thermoelectric figure of merit (ZT) at temperatures as high as 400.degree. C. for thermoelectric elements fabricated from such semiconductor materials.

Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

1998-01-01

7

Convective flows in enclosures with vertical temperature or concentration gradients  

NASA Technical Reports Server (NTRS)

The transport process in the fluid phase during the growth of a crystal has a profound influence on the structure and quality of the solid phase. In vertical growth techniques the fluid phase is often subjected to vertical temperature and concentration gradients. The main objective is to obtain more experimental data on convective flows in enclosures with vertical temperature or concentration gradients. Among actual crystal systems the parameters vary widely. The parametric ranges studied for mass transfer are mainly dictated by the electrochemical system employed to impose concentration gradients. Temperature or concentration difference are maintained between two horizontal end walls. The other walls are kept insulated. Experimental measurements and observations were made of the heat transfer or mass transfer, flow patterns, and the mean and fluctuating temperature distribution. The method used to visualize the flow pattern in the thermal cases is an electrochemical pH-indicator method. Laser shadowgraphs are employed to visualize flow patterns in the solutal cases.

Wang, L. W.; Chai, A. T.; Sun, D. J.

1988-01-01

8

Vertical CO2 gradient as an indicator of stratospheric circulation  

NASA Astrophysics Data System (ADS)

It is expected that a possible long-term change of the Brewer-Dobson (BD) circulation is detectable from the change of mean age evaluated from the stratospheric CO2 and SF6 concentrations. However, the result obtained from balloon experiments does not agree with recent model predictions of an accelerating BD circulation with an enhanced mass flux from the tropical troposphere into the stratosphere. This discrepancy between observations and models can be resolved if the poleward transport in the lower stratosphere is enhanced and compensate for increased tropical upwelling. If the poleward transports in the lower and upper layers have been differently changed, there is a possibility that we can detect it as a change of the vertical CO2 gradient. Therefore, the long-term trend of the vertical gradient was examined by using our balloon data. Systematic collections of stratospheric air samples have been carried out over Japan since 1985, using a balloon-borne cryogenic sampler. The stratospheric air samples have been collected almost once a year or two years at 11 assigned heights, ranging from the tropopause to 30 - 35 km. The air samples collected were analyzed for the CO2 and SF6 concentrations and various gases. We used CO2 data observed by 17 balloon experiments during the last 25 years. The average vertical gradients, calculated by applying a least-squares method to the vertical CO2 distributions in the mid-stratosphere, are varying within -0.14 ~ +0.12 ppmv/km with a clear decreasing trend. The average change rate of the vertical CO2 gradient was calculated to be -0.08×0.02 ppmv/km/decade. By applying a statistical testing, it was concluded that the decreasing trend of the vertical CO2 gradient above 20-25 km in the past 25 years is significant with 80 % confidence level. We also calculated CO2-age by comparing CO2 concentration with the convolutions of the age spectrum and the reference function of tropospheric CO2 variation. As a result, we found that the vertical CO2-age gradient has been increased with a rate of +0.05 ×0.01 years/km/decade. These results suggest that the poleward transport in the mid-stratosphere has been weakened in the upper layer more than in the lower layer.

Sugawara, S.; Aoki, S.; Morimoto, S.; Nakazawa, T.; Ishidoya, S.; Toyoda, S.; Honda, H.

2013-12-01

9

Vertical orbit excursion fixed field alternating gradient accelerators  

NASA Astrophysics Data System (ADS)

Fixed field alternating gradient (FFAG) accelerators with vertical orbit excursion (VFFAGs) provide a promising alternative design for rings with fixed-field superconducting magnets. They have a vertical magnetic field component that increases with height in the vertical aperture, yielding a skew quadrupole focusing structure. Scaling-type VFFAGs are found with fixed tunes and no intrinsic limitation on momentum range. This paper presents the first multiparticle tracking of such machines. Proton driver rings to accelerate the 800 MeV beam from the ISIS synchrotron are presented, in terms of both magnet field geometry and longitudinal behavior during acceleration with space charge. The 12 GeV ring produces an output power of at least 2.18 MW. Possible applications of VFFAGs to waste transmutation, hadron therapy, and energy-recovery electron accelerators are also discussed.

Brooks, Stephen

2013-08-01

10

Crystal Growth of CdTe by Gradient Freeze in Universal Multizone Crystallizator (UMC)  

NASA Technical Reports Server (NTRS)

In the case of unsealed melt growth of an array of II-VI compounds, namely, CdTe, CdZnTe and ZnSe, there is a tremendous amount of experimental data describing the correlations between melt conditions and crystal quality. The results imply that the crystallinity quality can be improved if the melt was markedly superheated or long-time held before growth. It is speculated that after high superheating the associated complex dissociate and the spontaneous nucleation is retarded. In this study, crystals of CdTe were grown from melts which have undergone different thermal history by the unseeded gradient freeze method using the Universal Multizone Crystallizator (UMC). The effects of melt conditions on the quality of grown crystal were studied by various characterization techniques, including Synchrotron White Beam X-ray Topography (SWSXT), infrared microscopy, chemical analysis by glow discharge mass spectroscopy (GDMS), electrical conductivity and Hall measurements.

Su, Ching-Hua; Lehoczky, S. L.; Li, C.; Knuteson, D.; Raghothamachar, B.; Dudley, M.; Szoke, J.; Barczy, P.

2004-01-01

11

Microclimate, freezing tolerance, and cold acclimation along an elevation gradient for seedlings of the Great Basin Desert shrub, Artemisia tridentata  

Microsoft Academic Search

Vegetation, microclimate, seedling frequency, freezing tolerance, and cold acclimation were compared for seedlings of Artemisia tridentata collected from 1775, 2175, and 2575 m elevation in the eastern Sierra Nevada, California. Data were used to test the hypothesis that ecotypic differences in stress physiology are important for seedling survival along gradients from desert to montane ecosystems. The vegetation canopy cover and

Michael E Loik; Sean P Redar

2003-01-01

12

MODELING OF THE FREEZING PROCESS FOR FISH IN VERTICAL PLATE FREEZERS  

E-print Network

-unit condenser-unit separator (ammonia in liquid and vapor state) ammonia pump platefreezer The freezing model: Simplified control scheme The freezing system is an ammonia-circle-process and con- sists of [2]: compressor

Gravdahl, Jan Tommy

13

Vertically transmitted symbiont reduces host fitness along temperature gradient.  

PubMed

Parasites with exclusive vertical transmission from host parent to offspring are an evolutionary puzzle. With parasite fitness entirely linked to host reproduction, any fitness cost for infected hosts risks their selective elimination. Environmental conditions likely influence parasite impact and thereby the success of purely vertical transmission strategies. We tested for temperature-dependent virulence of Caedibacter taeniospiralis, a vertically transmitted bacterial symbiont of the protozoan Paramecium tetraurelia. We compared growth of infected and cured host populations at five temperatures (16–32 °C). Infection reduced host density at all temperatures, with a peak of ?30% at 28 °C. These patterns were largely consistent across five infected Paramecium strains. Similar to Wolbachia symbionts, C. taeniospiralis may compensate fitness costs by conferring to the host a ‘killer trait’, targeting uninfected competitors. Considerable loss of infection at 32 °C suggests that killer efficacy is not universal and that limited heat tolerance restricts the conditions for persistence of C. taeniospiralis. PMID:24779056

Dusi, E; Krenek, S; Schrallhammer, M; Sachse, R; Rauch, G; Kaltz, O; Berendonk, T U

2014-04-01

14

Overburden Pressure as a Cause of Vertical Velocity Gradient  

NASA Astrophysics Data System (ADS)

Nonlinear effect of rocks stressed by the overburden pressure causes anisotropy. Evaluation shows that such anisotropy can be significant, reaching several tens of percent and probably more. This result is consistent with common practices, when stacking velocity needs extra corrections with a changing offset. This also implies that at field scales all the rocks are likely to be anisotropic, and this property needs to be accounted for during migration of data, tomography, AVO analysis etc. The laboratory velocity measurements need to be corrected for the nonlinear overburden effects, when applied to the field scales. Nonlinear rock coefficients can be determined from the special laboratory measurements. They also can be evaluated from observation of the nonlinear propagation effects, such as multiple frequency generation. Nonlinear coefficient for Berea sandstone turned out to be by an order of magnitude larger than that estimated from borehole data. This is likely due to low stiffness and low fluid saturation of the used sample. This also suggests possibility of very high velocity gradient at shallow depths in some rocks. An assumption that the amplitudes of the static strains well exceed those related to the dynamic field is not critical. It was made in order to simplify the derivations. If both components are comparable, then the solution would have an additional nonlinear component representing a multiple harmonic. The relations between the nonlinear elastic constants and the elastic constants of the effective TI medium are very simple and allow straightforward estimate of the medium anisotropy induced by an applied stress. There are other causes of anisotropy in rocks besides an applied stress. The rock can possibly be anisotropic on a microscopic (clays) and mesoscopic (sedimentary layering) levels. The combined contribution of all the causes can either reduce or increase the overall effect. Same rock at different depths might have different wave propagation properties. Proper geological interpretation of seismic velocity maps requires application of local depth corrections, which can remove the overburden pressure effects.verage velocity model for Los Angeles basin (blue line) and a least-squares fit (red line) using nonlinear theory.

Korneev, V. A.

2012-12-01

15

Vertical gradient correction for the oceanographic Atlas of the East Asian Seas  

NASA Astrophysics Data System (ADS)

climatology around the East Asian Seas has been developed by an international collaboration between the National Oceanic Data Center and the Korea Oceanic Data Center. It provides reliable information on temperature and salinity climatological fields with high resolution (0.1° × 0.1° by 137 levels). However, there is a problem around near-bottom areas where topographic change is steep and observations are not available near the bottom. This study resolves this problem using a vertical gradient correction method when the profile is statically unstable. The stability is determined based on the Brunt-Väisälä frequency with individual temperature and salinity profiles. Topographic-following mapping technique employing the potential vorticity constraint term is used to construct a vertical gradient database for the temperature and salinity at every grid point. The results show that the correction is effective for eliminating large erroneous vertical gradients around near-bottom areas. In addition, we show the importance of the optimal length scale to construct a precise vertical gradient database in a particular area such as the northern shelf of Taiwan. We expect that our revised high-resolution climatological mean fields will serve as important data for relevant studies around the East Asian Seas.

Chang, You-Soon; Shin, Hong-Ryeol

2014-08-01

16

Creating stiffness gradient polyvinyl alcohol hydrogel using a simple gradual freezing-thawing method to investigate stem cell differentiation behaviors.  

PubMed

Polyvinyl alcohol (PVA) cylindrical hydrogel with a stiffness gradient was prepared using a simple liquid nitrogen (LN2)-contacting gradual freezing and thawing method in order to investigate the effects of substrate stiffness on stem cell differentiation into specific cell types. The prepared cylindrical PVA hydrogel showed a gradually increasing stiffness along the longitudinal direction from the top at approximately 1 kPa to the bottom (LN2 contacted side) at approximately 24 kPa. From the in vitro culture of bone marrow stem cells, it was observed that each soft (?1 kPa) and stiff (?24 kPa) hydrogel section promotes effective neurogenesis and osteogenesis of the cells, respectively, with the tendency to gradually decrease toward the opposing characteristic's side. The stiffness gradient cylindrical PVA hydrogel fabricated using this simple gradual freezing and thawing method can be a useful tool for basic studies, including the determination of optimum stiffness ranges for a variety of stem cell differentiations, as well as the investigation of cell migration in terms of substrate stiffness. PMID:25467820

Kim, Tae Ho; An, Dan Bi; Oh, Se Heang; Kang, Min Kwan; Song, Hyun Hoon; Lee, Jin Ho

2015-02-01

17

The influence of vertical magnetic field gradients on the measured field strength and filling factor in late-type stars  

Microsoft Academic Search

The influence of a vertical gradient of the magnetic field in late type stars on the measurement of magnetic field strengths and filling factors is studied. Line profiles and contribution functions of spectral lines with large Lande factors are calculated in model stellar atmospheres in the presence of a magnetic field with a vertical gradient. It is found that the

U. Grossmann-Doerth; S. K. Solanki

1990-01-01

18

Characteristics of high resolution hydraulic head profiles and vertical gradients in fractured sedimentary rocks  

NASA Astrophysics Data System (ADS)

Accurately identifying the position of vertical hydraulic conductivity (Kv) contrasts is critical to the delineation of hydrogeologic units that serve as the basis for conceptual and numerical models of groundwater flow. High resolution head profiles have identified the position and thickness of Kv contrasts in clayey aquitards but this potential has not yet been thoroughly evaluated in sedimentary rocks. This paper describes an experiment in which head profiles with the highest, technically feasible resolution were obtained using Westbay® multilevel systems (MLS) installed in 15 cored holes at three sedimentary rock research sites with contrasting geologic and flow system conditions. MLSs were installed to maximum depths between 90 and 260 m with 2-5 monitoring zones per 10 m. Head profiles were measured over multiyear periods. The vertical component of hydraulic gradient (i.e., vertical gradient) was calculated for each pair of adjacent monitoring intervals in every MLS and then categorized based on its repeatability to facilitate interpretation of Kv contrasts and comparisons within boreholes, between boreholes at the same site, and between sites. The head and vertical gradient profiles from all three sites display systematic (i.e., simple, geometric) shapes defined by repeatable intervals of no to minimal vertical gradient, indicating relatively high Kv units, bounded by shorter depth intervals with large (up to -50 m/m) vertical gradients, indicating relatively low Kv units. The systematic nature of the profiles suggests flow in regular and interconnected fracture networks rather than dominated by a few key fractures with irregular orientations. The low Kv units were typically thin, with their positions and thicknesses not predicted by lithostratigraphy or detailed lithologic, geophysical, and horizontal hydraulic conductivity data. Hence, the position and thickness of units with contrasting Kv would not be evident if MLSs with the conventional number of monitoring zones had been used. Furthermore, the detailed profiles can be strongly diagnostic of hydrogeologic unit boundaries or layers and can be used to improve the quantitative assessment of flow system conditions that is foundational to understanding contaminant plume migration.

Meyer, Jessica R.; Parker, Beth L.; Cherry, John A.

2014-09-01

19

Free drainage of aqueous foams: Container shape effects on capillarity and vertical gradients  

NASA Astrophysics Data System (ADS)

The standard drainage equation applies only to foam columns of constant cross-sectional area. Here, we generalize to include the effects of arbitrary container shape and develop an exact solution for an exponential, "Eiffel Tower", sample. This geometry largely eliminates vertical wetness gradients, and hence capillary effects, and should permit a clean test of dissipation mechanisms. Agreement with experiment is not achieved at late times, however, highlighting the importance of both boundary conditions and coarsening.

Saint-Jalmes, A.; Vera, M. U.; Durian, D. J.

2000-06-01

20

VERTICAL GRADIENTS IN REGIONAL LUNG DENSITY AND PERFUSION IN THE SUPINE HUMAN LUNG: THE SLINKY® EFFECT  

PubMed Central

In-vivo radioactive tracer and microsphere studies have differing conclusions as to the magnitude of the gravitational effect on the distribution of pulmonary blood flow. We hypothesized that some of the apparent vertical perfusion gradient in-vivo is due to compression of dependent lung increasing local lung density and therefore perfusion/volume. To test this, 6 normal subjects underwent functional MRI with arterial spin labeling during a breath-hold at functional residual capacity, and perfusion quantified in non-overlapping 15mm sagittal slices covering most of the right lung. Lung proton density was measured in the same slices using a short echo 2D-FLASH sequence. Mean perfusion was 1.7 ± 0.6 ml/min/cm3 and was related to vertical height above the dependent lung (slope = ?3%/cm, p < 0.0001). Lung density averaged 0.34 ± 0.08 g/cm3, and was also related to vertical height (slope = ?4.9%/cm, p < 0.0001). By contrast when perfusion was normalized for regional lung density, the slope of the height-perfusion relationship was not significantly different from zero (p = 0.2). This suggests that in-vivo variations in regional lung density affect the interpretation of vertical gradients in pulmonary blood flow and is consistent with a simple conceptual model: that the lung behaves like a Slinky®, a deformable spring distorting under its own weight. The greater density of lung tissue in the dependent regions of the lung is analogous to a greater number of coils in the dependent portion of the vertically oriented spring. This implies that measurements of perfusion in-vivo will be influenced by density distributions and will differ from excised lungs where density gradients are reduced by processing. PMID:17395757

Hopkins, Susan R.; Henderson, A. Cortney; Levin, David L.; Yamada, Kei; Arai, Tatsuya; Buxton, Richard B.; Prisk., G. Kim

2008-01-01

21

Growth of CsI:Tl crystals in carbon coated silica crucibles by the gradient freeze technique  

NASA Astrophysics Data System (ADS)

Single crystals of CsI having different Tl concentrations have been grown by a gradient freeze technique. Carbon films were deposited on the inside surface of fused silica crucibles to avoid sticking of the grown crystals. The crystals could be extracted easily from the crucibles without involving the inversion process at higher temperatures. Effects of varying growth parameters and after-growth thermal treatment on crystal properties like daylight coloration and radiation hardness were studied. Characterization techniques including high resolution X-ray diffraction, induced absorption, photoluminescence, afterglow and thermally stimulated luminescence were employed to evaluate the grown crystals. Gamma-ray detectors were fabricated using the grown crystals that showed good linearity and nearly 7.5% resolution at 662 keV. This established a very simple and low cost method to grow small to medium size (35 mm in diameter and 25 mm in length) CsI crystals for various applications.

Singh, S. G.; Desai, D. G.; Singh, A. K.; Tyagi, M.; Sen, Shashwati; Sinha, A. K.; Gadkari, S. C.; Gupta, S. K.

2012-07-01

22

Effect of temperature gradient on detachment of the crystals grown by vertical directional solidification  

NASA Astrophysics Data System (ADS)

The furnace of the Vertical Directional Solidification (VDS) technique is specially designed to produce increase in temperature with the height and easy control on the temperature gradient. The technique was used for bulk growths of six ingots (12 mm diameter) of InSbBi. The source materials were filled with argon in the quartz ampoules at the pressure 200 torr. The ampoules were synthesized for 50 hr at temperature 850°C. These growths were carried out with the various temperature gradients (12°C/cm to 22°C/cm) at the solid-liquid interface, to study its effect on the detachment of the ingot from the ampoule wall. As grown ingots were partially detached or totally detached.

Maske, D. S.; Joshi, M.; Choudhary, R.; Gadkari, D. B.

2013-02-01

23

Two-Gradient Convection in a Vertical Slot with Maxwell-Cattaneo Heat Conduction  

SciTech Connect

We study the effect of the Maxwell-Cattaneo law of heat conduction (MCHC) on the 1D flow in a vertical slot subject to both vertical and horizontal temperature gradients. The gravitational acceleration is allowed to oscillate, which provides an opportunity to investigate the quantitative contribution of thermal inertia as epitomized by MCHC. The addition of the time derivative in MCHC increases the order of the system. We use a spectral expansion with Rayleigh's beam functions as the basis set, which is especially suited to fourth order boundary value problems (BVP). We show that the time derivative (relaxation of the thermal flux) has a dissipative nature and leads to the appearance of purely real negative eigenvalues. Yet it also increases the absolute value of the imaginary part and decreases the absolute value of the real part of the complex eigenvalues. Thus, the system has a somewhat more oscillatory behavior than the one based on Fourier's heat conduction law (FHC)

Papanicolaou, N. C. [Department of Computer Science, University of Nicosia, P.O. Box 24005, 1700 Nicosia (Cyprus); Christov, C. I. [Department of Mathematics, University of Louisiana at Lafayette, LA 70504-1010 (United States); Jordan, P. M. [Entropy Reversal Consultants (L.L.C), P. O. Box 691, Abita Springs, LA 70420 (United States); Code 7181, Naval Research Lab., Stennis Space Ctr., MS 39529 (United States)

2009-10-29

24

Sunscreening fungal pigments influence the vertical gradient of pendulous lichens in boreal forest canopies.  

PubMed

Pendulous lichens dominate canopies of boreal forests, with dark Bryoria species in the upper canopy vs. light Alectoria and Usnea species in lower canopy. These genera offer important ecosystem services such as winter forage for reindeer and caribou. The mechanism behind this niche separation is poorly understood. We tested the hypothesis that species-specific sunscreening fungal pigments protect underlying symbiotic algae differently against high light, and thus shape the vertical canopy gradient of epiphytes. Three pale species with the reflecting pigment usnic acid (Alectoria sarmentosa, Usnea dasypoga, U. longissima) and three with dark, absorbing melanins (Bryoria capillaris, B. fremontii, B. fuscescens) were compared. We subjected the lichens to desiccation stress with and without light, and assessed their performance with chlorophyll fluorescence. Desiccation alone only affected U. longissima. By contrast, light in combination with desiccation caused photoinhibitory damage in all species. Usnic lichens were significantly more susceptible to light during desiccation than melanic ones. Thus, melanin is a more efficient light-screening pigment than usnic acid. Thereby, the vertical gradient of pendulous lichens in forest canopies is consistent with a shift in type and functioning of sunscreening pigments, from high-light-tolerant Bryoria in the upper to susceptible Alectoria and Usnea in the lower canopy. PMID:25039211

Färber, Leonie; Sølhaug, Knut Asbjorn; Esseen, Per-Anders; Bilger, Wolfgang; Gauslaa, Yngvar

2014-06-01

25

A Spatially Resolved Vertical Temperature Gradient in the HD 163296 Disk  

NASA Astrophysics Data System (ADS)

We analyze sensitive, sub-arcsecond resolution ALMA science verification observations of CO emission lines in the protoplanetary disk hosted by the young, isolated Ae star HD 163296. The observed spatial morphology of the 12CO J = 3-2 emission line is asymmetric across the major axis of the disk; the 12CO J = 2-1 line features a much less pronounced, but similar, asymmetry. The J = 2-1 emission from 12CO and its main isotopologues have no resolved spatial asymmetry. We associate this behavior with the direct signature of a vertical temperature gradient and layered molecular structure in the disk. This is demonstrated using both toy models and more sophisticated calculations assuming non-local thermodynamic equilibrium conditions. A model disk structure is developed to reproduce both the distinctive spatial morphology of the 12CO J = 3-2 line as well as the J = 2-1 emission from the CO isotopologues assuming relative abundances consistent with the interstellar medium. This model disk structure has ? = 1 emitting surfaces for the 12CO emission lines that make an angle of ~15° with respect to the disk midplane. Furthermore, we show that the spatial and spectral sensitivity of these data can distinguish between models that have sub-Keplerian gas velocities due to the vertical extent of the disk and its associated radial pressure gradient (a fractional difference in the bulk gas velocity field of >~ 5%).

Rosenfeld, Katherine A.; Andrews, Sean M.; Hughes, A. Meredith; Wilner, David J.; Qi, Chunhua

2013-09-01

26

The effect of a vertical temperature gradient in the lithosphere on seismic and tectonic waves  

NASA Astrophysics Data System (ADS)

A linear analysis of the stability of the lithosphere considered as a viscoelastic layer with an equilibrium vertical gradient of temperature is carried out. The problem is solved with a complete system of linearized equations of a continuous medium represented in the dimensionless form and containing a set of dimensionless parameters that determine thermomechanical properties of the lithosphere. As a result of the stability analysis, decrements are found that give the time dependence of perturbations and correspond to high-frequency seismic waves and low-frequency tectonic waves. The frequency and velocity of seismic waves are determined by the elasticity and inertial properties of the lithosphere, and their attenuation, by viscous properties of the lithosphere. The temperature gradient existing in the lithosphere influences seismic waves very weakly. On the contrary, the pattern of tectonic waves is controlled by the temperature gradient and viscous properties, while the effect of elastic and inertial properties on these waves is negligibly small. The stability of a viscoelastic lithosphere is examined using such rheological models as the Maxwell, standard linear, and Andrade media (the frequency of tectonic waves is zero in the Maxwell medium).

Birger, B. I.

2008-09-01

27

Longitudinal and Vertical Spatial Gradients in the Distribution of Fish within a Canyon-shaped Reservoir  

NASA Astrophysics Data System (ADS)

The large-scale spatial distribution of fish was investigated within a morphometrically simple canyon-shaped reservoir with a single major tributary and a longitudinal trophic gradient (ímov Reservoir, Czech Republic). Samples of fish were taken by Nordic survey gill nets (several mesh sizes from 8 to 70 mm knot to knot) installed as surface nets at several offshore areas located along the longitudinal axis of the reservoir. Surveys were carried out in late summer during 1999-2003. An obvious distribution gradient of fish was revealed along the longitudinal axis of the ímov Reservoir. The total relative fish abundance and biomass (catch per unit effort) decreased considerably from the upstream end of the reservoir toward the dam. Roach (Rutilus rutilus), bleak (Alburnus alburnus) and bream (Abramis brama) comprised the bulk of catches at all areas. Enhanced dominance of bream was observed in the fish assemblage at the uppermost, more eutrophic area of the reservoir. The highest number of fish species and the highest abundance of young-of-the-year fish were also observed in the tributary area. In the downstream part of the reservoir, gill net surveys along the vertical depth profiles indicated that offshore fish occupied mostly the epilimnion. Extreme flood events affected the ímov Reservoir, however, it seemed they had no significant impact on the gradients described. (

Vaek, Mojmír; Kubeka, Jan; Peterka, Jií; Ech, Martin; Dratík, Vladislav; Hladík, Milan; Prchalová, Marie; Frouzová, Jaroslava

2004-09-01

28

Impacts of freezing and thawing dynamics on foliar litter carbon release in alpine/subalpine forests along an altitudinal gradient in the eastern Tibetan Plateau  

NASA Astrophysics Data System (ADS)

Carbon (C) release from foliar litter is a primary component in C exchange among the atmosphere, vegetation, soil and water from respiration and leaching, but little information is currently related to the effects of freezing and thawing dynamics on C release of foliar litter in cold regions. A 2-year field litter decomposition experiment was conducted along an altitudinal gradient (~ 2700 to ~ 3600 m) to mimic temperature increases in the eastern Tibetan Plateau. C release was investigated for fresh foliar litter of spruce, fir and birch. The onset of the frozen stage, deep frozen stage and thawing stage was partitioned according to changes in the freezing and thawing dynamics of each winter. More rapid 2-year C released from fresh foliar litter at upper elevations compared to lower elevations in the alpine/subalpine region. However, high C release was observed at low altitudes during winter stages, but high altitudes exhibited high C release during growing season stages. The deep frozen stage showed higher rates of C release than other stages in the second year of decomposition. Negative-degree days showing freezing degrees were correlated to C release rates for the deep frozen stages in both years, and this relationship continued for the duration of the experiment, indicating that changes in freezing can directly modify C release from foliar litter. The results suggested that the changed freezing and thawing dynamics could delay the onset of C release in fresh litter in this cold region in the scenario of climate warming.

Fuzhong, W.; Changhui, P.; Jianxiao, Z.; Jian, Z.; Bo, T.; Wanqin, Y.

2014-11-01

29

Individual and population plasticity of the seagrass Zostera noltii along a vertical intertidal gradient  

NASA Astrophysics Data System (ADS)

The seasonal plasticity of individual Zostera noltii architectural, reproductive and elemental content features, of plant epiphyte load and of meadow biomass-density relationships was investigated along a vertical intertidal gradient at Ria Formosa lagoon, southern Portugal. The vertical variability of the seagrass environment was evident in the sediment characteristics, which showed coarser grain size, less organic matter, lower N content and higher ammonium concentration in the low intertidal than in medium and high intertidal. A clear vertical differentiation in Z. noltii morphology was observed from longer and wider leaves, longer and wider internodes and shorter roots at low intertidal, to shorter and narrow leaves, shorter and narrower internodes and longer roots at high intertidal. The leaf size was negatively related to light availability and positively related to nutrient availability whereas the root size was negatively related to nutrient availability. The lower leaf N and P content found in low intertidal plants may reflect a dilution effect of the nutrients due to higher growth rates. Lower N content of low intertidal leaves supports previous findings that the nitrate reductase activity is lower in plants from this level. The higher epiphyte load observed in Z. noltii leaves of the low intertidal may be a consequence of the lower exposure period, but also of higher hydrodynamics that increase the availability of nutrients. No evidence of the influence of the intertidal level on the flowering shoot density was found. The cyclic temporal pattern of the biomass-density relationship was much wider at low and medium intertidal than at high intertidal. At low intertidal, the decline in shoot density during fall and winter was coincident with a biomass decrease and its increase in spring and summer coincided with the biomass increase. In medium and high intertidal, the biomass and density seasonal variations were decoupled. As a result, only at low intertidal there was a significant positive relationship between biomass and density. This suggests that Z. noltii population structure along the intertidal is regulated by different factors. Light is probably the most important factor regulating the population structure in the low intertidal, whereas desiccation is probably the main factor regulating the populations in upper intertidal. Zostera noltii showed a considerable plasticity at a physiological-, plant- and population-level along the intertidal zone, indicative of the species acclimation to the steep environmental gradient of this particular ecosystem.

Cabaço, Susana; Machás, Raquel; Santos, Rui

2009-04-01

30

Impact of changes in freezing and thawing on foliar litter carbon release in alpine/subalpine forests along an altitudinal gradient in the eastern Tibetan Plateau  

NASA Astrophysics Data System (ADS)

Carbon (C) release from foliar litter is a primary component in C exchange between the atmosphere and terrestrial ecosystems, but little information is currently related to the effects of freezing and thawing dynamics on C release of foliar litter in cold regions. A two-year field litter decomposition experiment was conducted along an altitudinal gradient (∼2700 m to ∼3600 m) to mimic temperature increases in the eastern Tibetan Plateau. C release was investigated for fresh foliar litter of spruce, fir and birch. The onset of the frozen stage, deep frozen stage, and thawing stage were partitioned according to changes in freezing and thawing dynamics of each winter. High C release was observed in lower altitudes during winter stages, but higher altitudes exhibited high C release during growing season stages. The deep frozen stage showed higher rates of C release than other stages in the second year of decomposition. Negative degree-days showing freezing degree were correlated to C release rates for the deep frozen stages in both years, and this relationship continued for the duration of the experiment, indicating that changes in freezing can directly modify C release from foliar litter. The results suggested that climate warming could delay the onset of C release in fresh litter in this cold region.

Wu, F.; Peng, C.; Zhu, J.; Zhang, J.; Tan, B.; Yang, W.

2014-06-01

31

Simulation of vertical concentration gradient of influenza viruses in dust resuspended by walking.  

PubMed

Particles are resuspended from the floor by walking and are subject to turbulent transport in the human aerodynamic wake. These processes may generate a vertical concentration gradient of particles. To estimate the magnitude of turbulence generated by walking, we measured the velocity field in the wake from floor to ceiling at 10-cm intervals with a sonic anemometer. The resulting eddy diffusion coefficients varied between 0.06 and 0.20 m(2) /s and were maximal at ~0.75-1 m above the floor, approximately the height of the swinging hand. We applied the eddy diffusion coefficients in an atmospheric transport model to predict concentrations of resuspended influenza virus as a function of the carrier particle size, height in the room, and relative humidity, which affects the resuspension rate coefficient and virus viability. Results indicated that the concentration of resuspended viruses at 1 m above the floor was up to 40% higher than at 2 m, depending on particle size. For exposure to total resuspended viruses, the difference at 1 vs. 2 m was 11-14%. It is possible that shorter people are exposed to higher concentrations of resuspended dust, including pathogens, although experimental evidence is needed to verify this proposition. PMID:25208212

Khare, P; Marr, L C

2014-09-10

32

Freeze drying apparatus  

DOEpatents

The present invention provides methods and apparatus for freeze drying in which a solution, which can be a radioactive salt dissolved within an acid, is frozen into a solid on vertical plates provided within a freeze drying chamber. The solid is sublimated into vapor and condensed in a cold condenser positioned above the freeze drying chamber and connected thereto by a conduit. The vertical positioning of the cold condenser relative to the freeze dryer helps to help prevent substances such as radioactive materials separated from the solution from contaminating the cold condenser. Additionally, the system can be charged with an inert gas to produce a down rush of gas into the freeze drying chamber to also help prevent such substances from contaminating the cold condenser.

Coppa, Nicholas V. (Malvern, PA); Stewart, Paul (Youngstown, NY); Renzi, Ernesto (Youngstown, NY)

2001-01-01

33

Freeze drying method  

DOEpatents

The present invention provides methods and apparatus for freeze drying in which a solution, which can be a radioactive salt dissolved within an acid, is frozen into a solid on vertical plates provided within a freeze drying chamber. The solid is sublimated into vapor and condensed in a cold condenser positioned above the freeze drying chamber and connected thereto by a conduit. The vertical positioning of the cold condenser relative to the freeze dryer helps to help prevent substances such as radioactive materials separated from the solution from contaminating the cold condenser. Additionally, the system can be charged with an inert gas to produce a down rush of gas into the freeze drying chamber to also help prevent such substances from contaminating the cold condenser.

Coppa, Nicholas V. (Malvern, PA); Stewart, Paul (Youngstown, NY); Renzi, Ernesto (Youngstown, NY)

1999-01-01

34

Estimation of the depth to the fresh-water/salt-water interface from vertical head gradients in wells in coastal and island aquifers  

USGS Publications Warehouse

An accurate estimate of the depth to the theoretical interface between fresh, water and salt water is critical to estimates of well yields in coastal and island aquifers. The Ghyben-Herzberg relation, which is commonly used to estimate interface depth, can greatly underestimate or overestimate the fresh-water thickness, because it assumes no vertical head gradients and no vertical flow. Estimation of the interface depth needs to consider the vertical head gradients and aquifer anisotropy that may be present. This paper presents a method to calculate vertical head gradients using water-level measurements made during drilling of a partially penetrating well; the gradient is then used to estimate interface depth. Application of the method to a numerically simulated fresh-water/salt-water system shows that the method is most accurate when the gradient is measured in a deeply penetrating well. Even using a shallow well, the method more accurately estimates the interface position than does the Ghyben-Herzberg relation where substantial vertical head gradients exist. Application of the method to field data shows that drilling, collection methods of water-level data, and aquifer inhomogeneities can cause difficulties, but the effects of these difficulties can be minimized.

Izuka, S.K.; Gingerich, S.B.

1998-01-01

35

Fractionation of large mammalian DNA restriction fragments using vertical pulsed-field gradient gel electrophoresis  

Microsoft Academic Search

A new design for pulsed field gradient (PFG) gel electrophoresis of large (>50 kb) DNA fragments is described. The method eliminates distortion of migration of DNA because of the geometry of the applied electric field, requires a single power supply and a simple switching device, and is extremely simple to use. Parameters investigated include variation in pulse time, conditions of

Katheleen Gardiner; William Laas; David Patterson

1986-01-01

36

Ecophysiological responses of black walnut (Juglans nigra) to plantation thinning along a vertical canopy gradient  

E-print Network

Ecophysiological responses of black walnut (Juglans nigra) to plantation thinning along a vertical Lafayette, IN 47907-2061, USA 1. Introduction Black walnut (Juglans nigra L.) is generally associated oak (Quercus spp.) species. Black walnut is site-sensitive and grows best on deep, fertile, well

37

Bone regeneration using a freeze-dried 3D gradient-structured scaffold incorporating OIC-A006-loaded PLGA microspheres based on ?-TCP/PLGA.  

PubMed

To reveal the latent capacity of the growth factor-like low-molecular-weight material OIC-A006 in tissue regeneration, it is essential to design a porous scaffold in order to concurrently accommodate cells and drug release in a controlled manner. Consequently, we fabricated poly (L-lactide-co-glycolide) (PLGA)-based microspheres with an OIC-A006-loaded gradient-structured ?-TCP/PLGA scaffold by freeze-drying which could then be used for drug delivery and bone regeneration. The OIC-A006-loaded ?-TCP/PLGA scaffold consisted of two parts which loaded different doses of OIC-A006 (6.25 ?M, outside; 12.5 ?M, inside). The porosity, compressive strength, SEM, degradation, and cumulative amount of drug release in vitro were characterized. Furthermore, we confirmed the incorporation of OIC-A006 into the PLGA-based microspheres within the scaffolds using UV-spectrophotometry, and the amount of drug remaining in the scaffold was maintained by 10 % for up to 28 days. The drug release was slower in the normal-structured drug-loaded scaffold. The OIC-A006 released action from the OIC-A006-loaded ?-TCP/PLGA scaffold with ideal the rapeutic prospects in tissue regeneration. In vitro cell culture results showed that this gradient-structured composite scaffold can induce the adhesion and proliferation of rat bone marrow stromal cells towards osteoblasts. These results showed that the newly developed OIC-A006-loaded scaffolds with gradient structure can be potentially applied to bone regeneration in clinical applications. PMID:25577209

Lin, Liulan; Gao, Haitao; Dong, Yangyang

2015-01-01

38

New subdwarfs. III - On obtaining the vertical galactic metallicity gradient from the kinematics of nearby stars  

NASA Astrophysics Data System (ADS)

The combination of the radial velocities of 31 newly identified subdwarfs with data for 83 other subdwarfs from Sandage (1969) expands the sample, to underscore the correlation between velocity in the plane (W(O)) and reduced ultraviolet excess. A chemical gradient evident perpendicular to the plane may be interpreted as the sum of two velocity components with different distributions over metallicity. The distribution of metallicity expected at any height is calculated from the observed sigma and W(O) value distributions in the plane, using both a continuum and a two-component kinematic model. The calculations show that observations of the actual sigma(0.6) distributions in situ, using F and G subdwarfs having brightness values higher than 18, presents powerful conditions on an eventual, realistic model of the chemical gradient observed over the first 5 kpc of the halo.

Sandage, A.

1981-11-01

39

Behavior of a horizontal air curtain subjected to a vertical pressure gradient  

NASA Astrophysics Data System (ADS)

We present the details on an experiment to investigate the behavior of an air curtain that is subjected to a transverse pressure gradient. The setup simulates the conditions that will be present in the Advanced Technology Solar Telescope (ATST), a 4-meter solar observatory that will be built on Haleakala, Hawaii. A test rig was built to replicate the region at which the optical path crosses a temperature and pressure boundary between the telescope mount region, which is at the ambient temperature and pressure, and a warmer, pressurized lab space directly below. Use of an air curtain in place of an optically-transmitting window at the interface would allow science observations at a wider range of scientific wavelengths. With the air curtain exhibiting transitional flow behavior across the boundary, and applied pressure gradients of up to 6.5 Pa, we found that the air curtain was able to hold a pressure gradient of 0.25 Pa. As the applied pressure was increased, transient turbulent regions formed at the interface, and predictable flow behavior only occurred in the region closest to the air curtain blower. Computer modeling is used to validate the test data, identify laminar regions of the air curtain where minimal image distortion would occur, and explore the relationship between the applied pressure, effective pressure difference, and air curtain profile.

Linden, James; Phelps, LeEllen

2012-09-01

40

Use of sinkhole and specific capacity distributions to assess vertical gradients in a karst aquifer  

Microsoft Academic Search

The carbonate-rock aquifer in the Great Valley, West Virginia, USA, was evaluated using a database of 687 sinkholes and 350\\u000a specific capacity tests to assess structural, lithologic, and topographic influences on the groundwater flow system. The enhanced\\u000a permeability of the aquifer is characterized in part by the many sinkholes, springs, and solutionally enlarged fractures throughout\\u000a the valley. Yet, vertical components

Kurt J. McCoy; Mark D. Kozar

2008-01-01

41

Variation in Community Structure across Vertical Intertidal Stress Gradients: How Does It Compare with Horizontal Variation at Different Scales?  

PubMed Central

In rocky intertidal habitats, the pronounced increase in environmental stress from low to high elevations greatly affects community structure, that is, the combined measure of species identity and their relative abundance. Recent studies have shown that ecological variation also occurs along the coastline at a variety of spatial scales. Little is known, however, on how vertical variation compares with horizontal variation measured at increasing spatial scales (in terms of sampling interval). Because broad-scale processes can generate geographical patterns in community structure, we tested the hypothesis that vertical ecological variation is higher than fine-scale horizontal variation but lower than broad-scale horizontal variation. To test this prediction, we compared the variation in community structure across intertidal elevations on rocky shores of Helgoland Island with independent estimates of horizontal variation measured at the scale of patches (quadrats separated by 10s of cm), sites (quadrats separated by a few m), and shores (quadrats separated by 100s to 1000s of m). The multivariate analyses done on community structure supported our prediction. Specifically, vertical variation was significantly higher than patch- and site-scale horizontal variation but lower than shore-scale horizontal variation. Similar patterns were found for the variation in abundance of foundation taxa such as Fucus spp. and Mastocarpus stellatus, suggesting that the effects of these canopy-forming algae, known to function as ecosystem engineers, may explain part of the observed variability in community structure. Our findings suggest that broad-scale processes affecting species performance increase ecological variability relative to the pervasive fine-scale patchiness already described for marine coasts and the well known variation caused by vertical stress gradients. Our results also indicate that experimental research aiming to understand community structure on marine shores should benefit from applying a multi-scale approach. PMID:21887371

Valdivia, Nelson; Scrosati, Ricardo A.; Molis, Markus; Knox, Amanda S.

2011-01-01

42

Denitrification in nitrate-contaminated groundwater: Occurrence in steep vertical geochemical gradients  

USGS Publications Warehouse

A relatively narrow vertical zone (5-6 m thick) of NO3- containing groundwater was identified using multilevel sampling devices in a sand and gravel aquifer on Cape Cod, MA, USA. The aquifer has been chronically contaminated by surface disposal of treated sewage 0.3 km upgradient from the study area. The NO3- zone was anoxic and contained high concentrations of N2O (16.5 ??M), suggesting that it was a zone of active denitrification. Denitrifying activity was confirmed with direct measurement using acetylene block incubations with aquifer core material; the peak rate was 2.4 nmol N reduced (g sed)-1 day-1. Concentrations of dissolved inorganic carbon and N2 were close to atmospheric equilibrium in uncontaminated groundwater, but were more than 2 times higher within the contaminant plume. Excess CO2 and N2 suggested in situ formation with a stoichiometry of C and N mineralized via denitrification of 0.8 (C/N). Denitrification within the aquifer resulted in an increase in the natural ??15N of NO3- (from +13.6 to +42.0%.) and the N2 produced, with an isotopic enrichment factor, ??{lunate}, of -13.9%.. Vertical profiles of NH4+ and ??15N of NH4+ indicated that dissimilatory reduction of NO3- to NH4+ was also occurring but mass balance calculations indicated that denitrification was the predominant process. These results demonstrate that a combination approach using field mass balance, stable isotope analysis, and laboratory incubations yields useful insight as to the significance of denitrification in aquifer sediments and that closely spaced vertical sampling is necessary to adequately quantify the processes controlling C and N transport and transformation within these environments. ?? 1991.

Smith, R.L.; Howes, B.L.; Duff, J.H.

1991-01-01

43

Vertical gradients in photosynthetic light response within an old-growth Douglas-fir and western hemlock canopy.  

PubMed

We examined needle-level light response of photosynthesis across a vertical light gradient within 45-55-m-tall western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees growing in a 400-500-year-old mixed species stand. We determined: (1) whether light-saturated photosynthetic rates, light compensation points, and respiration rates varied from the upper to the lower canopy, and (2) if light-saturated photosynthetic rates, light compensation points, and respiration rates varied between Douglas-fir and western hemlock. Over a 25-m gradient from the canopy top to the lower canopy, mean light-saturated photosynthetic rates, light compensation points, and respiration rates declined in overstory Douglas-fir and western hemlock needles, paralleling a 65% decline in the mean daily photosynthetic photon flux density (PPFD). At the canopy top, increasing light-saturated photosynthetic rates relative to lower canopy needles increased carbon uptake at high PPFD. In the lower canopy, reduced respiration rates relative to upper canopy needles increased carbon uptake at low PPFD by reducing the light compensation point. At all canopy positions, western hemlock had lower mean light-saturated photosynthetic rates, light compensation points and respiration rates than Douglas-fir. As a result, western hemlock had higher net photosynthetic rates at low PPFD, but lower net photosynthetic rates at high PPFD compared with Douglas-fir. PMID:12651440

Lewis, J. D.; McKane, R. B.; Tingey, D. T.; Beedlow, P. A.

2000-04-01

44

Measurement of the Vertical Gradient of the Semidiurnal Tidal Wind Phase in Winter at the 95 Km Level  

NASA Technical Reports Server (NTRS)

When supplemented by absolute reflection height measurements, low frequency wind measurements in the 90-100 km height range become truly competitive in comparison with the more widely used radar meteor wind observations. For example, height profiles of the wind parameters in the so-called meteor zone can be obtained due to the considerable interdiurnal variability of the average nighttime reflection heights controlled by geomagnetic activity. The phase of the semidiurnal tidal wind is particularly height-dependent. The measured vertical gradient of 1/4 h/km in winter corresponds to a vertical wavelength of about 50 km. Wind measurements in the upper atmosphere, at heights between 90 and 100 km, were carried out at the Collm Geophysical Observatory of Karl Marx University Leipzig for a number of years. These measurements use the closely-spaced receiver method and three measuring paths, on 179, 227, and 272 kHz. They take place every day between sunset and sunrise, i.e., nightly. A night in this sense may last as long as 18 hours in winter. Both the measurements and their evaluation are completely automatic, and the prevailing winds and tides are separated.

Schminder, R.; Kurschner, D.

1984-01-01

45

Measurement of the vertical gradient of the semidiurnal tidal wind phase in winter at the 95 km level  

NASA Astrophysics Data System (ADS)

When supplemented by absolute reflection height measurements, low frequency wind measurements in the 90-100 km height range become truly competitive in comparison with the more widely used radar meteor wind observations. For example, height profiles of the wind parameters in the so-called meteor zone can be obtained due to the considerable interdiurnal variability of the average nighttime reflection heights controlled by geomagnetic activity. The phase of the semidiurnal tidal wind is particularly height-dependent. The measured vertical gradient of 1/4 h/km in winter corresponds to a vertical wavelength of about 50 km. Wind measurements in the upper atmosphere, at heights between 90 and 100 km, were carried out at the Collm Geophysical Observatory of Karl Marx University Leipzig for a number of years. These measurements use the closely-spaced receiver method and three measuring paths, on 179, 227, and 272 kHz. They take place every day between sunset and sunrise, i.e., nightly. A night in this sense may last as long as 18 hours in winter. Both the measurements and their evaluation are completely automatic, and the prevailing winds and tides are separated.

Schminder, R.; Kurschner, D.

1984-05-01

46

Observations of BVOC (Biogenic Volatile Organic Compound) Fluxes and Vertical Gradients in a Ponderosa Pine Forest during BEARPEX 2009  

NASA Astrophysics Data System (ADS)

During summer 2009 an intensive field campaign (Biosphere Effects on AeRosols and Photochemistry EXperiment - BEARPEX) took place in Blodgett Forest, a Ponderosa pine forest in the Sierra Nevada Mountains of California. The campaign aimed to investigate biosphere-atmosphere interactions during a period of intense photochemical activity, to elucidate the fate BVOC (Biogenic Volatile Organic Compounds) in the atmosphere, and explore the processes of secondary organic aerosol formation. In this study, a PTR-MS (Proton Transfer Reaction - Mass Spectrometry) was used to measure 19 compounds (masses) including methanol, isoprene + MBO (2-Methyl-3-butene-2-ol), monoterpenes, sesquiterpenes, and some oxygenated BVOCs at 5 heights of a vertical gradient from the forest floor to above the canopy. Fluxes of the 4 dominant BVOCs were measured above the canopy with the Eddy covariance technique. In parallel with BVOC measurements, ozone fluxes and gradients, and meteorological parameters (PAR, temperature, relative humidity, wind speed, and wind direction) were recorded in order to investigate the dependence of BVOC emissions and chemistry on meteorological conditions and to test the hypothesis that BVOC remove atmospheric ozone through gas-phase reactions. BVOCs which are directly emitted from pine trees generally have the highest concentration at the lowest measurement height and the lowest concentration above the canopy. Sesquiterpenes were observed at lower concentration than monoterpenes, but with very similar vertical gradient patterns, indicating their emission patterns are similar. The observed MBO flux was approximately twice the Monoterpene flux. Measured monoterpene canopy scale flux was consistent with modeled emissions based on scaling up from branch enclosure measurements at this site (basal emission rate F30= 0.61 ±0.14 mgC m-2 hr-1 and temperature response ?= 0.15 ±0.09 °C-1). We find that m/z 113, an unidentified OVOCs (oxygenated volatile organic compounds), is clearly produced by both isoprene and terpene oxidation, arriving in air advected to the site from the west indicative of the oxidation of isoprene released by oak trees ~30 km downhill, and also produced from local terpene oxidation and deposited in the pine forest canopy.

Park, J.; Fares, S.; Weber, R.; Goldstein, A.

2010-12-01

47

Active bacterial community structure along vertical redox gradients in Baltic Sea sediment  

SciTech Connect

Community structures of active bacterial populations were investigated along a vertical redox profile in coastal Baltic Sea sediments by terminal-restriction fragment length polymorphism (T-RFLP) and clone library analysis. According to correspondence analysis of T-RFLP results and sequencing of cloned 16S rRNA genes, the microbial community structures at three redox depths (179 mV, -64 mV and -337 mV) differed significantly. The bacterial communities in the community DNA differed from those in bromodeoxyuridine (BrdU)-labeled DNA, indicating that the growing members of the community that incorporated BrdU were not necessarily the most dominant members. The structures of the actively growing bacterial communities were most strongly correlated to organic carbon followed by total nitrogen and redox potentials. Bacterial identification by sequencing of 16S rRNA genes from clones of BrdU-labeled DNA and DNA from reverse transcription PCR (rt-PCR) showed that bacterial taxa involved in nitrogen and sulfur cycling were metabolically active along the redox profiles. Several sequences had low similarities to previously detected sequences indicating that novel lineages of bacteria are present in Baltic Sea sediments. Also, a high number of different 16S rRNA gene sequences representing different phyla were detected at all sampling depths.

Jansson, Janet; Edlund, Anna; Hardeman, Fredrik; Jansson, Janet K.; Sjoling, Sara

2008-05-15

48

Fluid motions and compositional gradients produced by crystallization or melting at vertical boundaries  

NASA Astrophysics Data System (ADS)

The results of a continuing series of laboratory experiments, designed to model the fluid motions which accompany crystallization, are both described and related in a preliminary way to prototype flows in magma chambers. Previous experiments have demonstrated the importance of compositional inhomogeneity, produced by crystallization and melting in a thermal gradient and coupled with double-diffusive effects, in driving convective flows which result in thermal and compositional stratification in an originally homogeneous fluid. The present experiments examine effects produced in tanks cooled at the side, by the upward flow of a less dense boundary layer depleted in the crystallizing component as crystals grow on the side wall. These processes are examined in simple two and three component aqueous systems (H 2O-Na 2CO 3, H 2O-Na 2CO 3-K 2CO 3, H 2O-CuSO 4-Na 2SO 4) with one and two crystallizing phases. In each of these systems, an initially downward flow of a cooled boundary layer against the side wall is reversed as crystallization commences and depletes the boundary layer in the crystallizing component. Accumulation of this cooler but lighter depleted fluid at the top of the chamber produces thermal and compositional layering by a "filling box" mechanism, partly modified by interchange between the boundary layer and the convecting layers outside. When more than one component is present in the solution, the crystallization process produces a differentiated fluid column, i.e. one with compositional gradients which are different for each of the components. The compositional and thermal distributions within the fluid change with time, but finally appear to reach a steady state. These distributions are the integrated result of compositional changes produced by crystallization from a thin boundary layer, a small proportion of the bulk fluid which evolves in composition and temperature independently of the bulk fluid, in a manner controlled by the dynamics of the system. The paths of fluid evolution, and the resulting sequence and abundance of crystalline products, are very different from those predicted on the basis of simple thermally-driven crystallization in the static system. Disequilibrium effects, probably involving different kinetics of crystallization of different crystals, in part determine crystallization in the experimental system; these may or may not be important in real magmatic systems. There is still much to learn before even the behaviour in these simple experimental systems is understood fully, and the application of the results to the interpretation of the behaviour in real magma chambers in even further away. However, it is apparent that dynamic effects provide an additional degree of freedom in crystallization processes, and allow evolution of small increments of solution to compositions much further along crystallization paths than that allowed in static equilibrium systems. Petrologists will have to free their thinking from classical constraints of static systems in order to interpret many magmatic phenomena.

Turner, J. Stewart; Gustafson, Lewis B.

1981-12-01

49

Thermosolutal bifurcation phenomena in porous enclosures subject to vertical temperature and concentration gradients  

NASA Astrophysics Data System (ADS)

The Darcy model with the Boussinesq approximations is used to study double-diffusive instability in a horizontal rectangular porous enclosure subject to two sources of buoyancy. The two vertical walls of the cavity are impermeable and adiabatic while Dirichlet or Neumann boundary conditions on temperature and solute are imposed on the horizontal walls. The onset and development of convection are first investigated using the linear and nonlinear perturbation theories. Depending on the governing parameters of the problem, four different regimes are found to exist, namely the stable diffusive, the subcritical convective, the oscillatory and the augmenting direct regimes. The governing parameters are the thermal Rayleigh number, RT, buoyancy ratio, N, Lewis number, Le, normalized porosity of the porous medium, [epsilon], aspect ratio of the enclosure, A, and the thermal and solutal boundary condition type, [kappa], applied on the horizontal walls. On the basis of the nonlinear perturbation theory and the parallel flow approximation (for slender or shallow enclosures), analytical solutions are derived to predict the flow behaviour. A finite element numerical method is introduced to solve the full governing equations. The results indicate that steady convection can arise at Rayleigh numbers below the supercritical value, indicating the development of subcritical flows. At the vicinity of the threshold of supercritical convection the nonlinear perturbation theory and the parallel flow approximation results are found to agree well with the numerical solution. In the overstable regime, the existence of multiple solutions, for a given set of the governing parameters, is demonstrated. Also, numerical results indicate the possible occurrence of travelling waves in an infinite horizontal enclosure.

Mamou, M.; Vasseur, P.

1999-09-01

50

Spatio-temporal distribution of the timing of start and end of growing season along vertical and horizontal gradients in Japan  

NASA Astrophysics Data System (ADS)

We detected the spatio-temporal variability in the timing of start (SGS) and end of growing season (EGS) in Japan from 2003 to 2012 by analyzing satellite-observed daily green-red vegetation index with a 500-m spatial resolution. We also examined the characteristics of SGS and EGS timing in deciduous broadleaf and needleleaf forests along vertical and horizontal gradients and then evaluated the relationship between their timing and daily mean air temperature. We found that for the timing of SGS and EGS, changes along the vertical gradient in deciduous broadleaf forest tended to be larger than those in deciduous needleleaf forest. For both forest types, changes along the vertical and horizontal gradients in the timing of EGS tended to be smaller than those of SGS. Finally, in both forest types, the sensitivity of the timing of EGS to air temperature was much less than that of SGS. These results suggest that the spatio-temporal variability in the timing of SGS and EGS detected by satellite data, which may be correlated with leaf traits, photosynthetic capacity, and environment conditions, provide useful ground-truthing information along vertical and horizontal gradients.

Nagai, Shin; Saitoh, Taku M.; Nasahara, Kenlo Nishida; Suzuki, Rikie

2015-01-01

51

Spatio-temporal distribution of the timing of start and end of growing season along vertical and horizontal gradients in Japan.  

PubMed

We detected the spatio-temporal variability in the timing of start (SGS) and end of growing season (EGS) in Japan from 2003 to 2012 by analyzing satellite-observed daily green-red vegetation index with a 500-m spatial resolution. We also examined the characteristics of SGS and EGS timing in deciduous broadleaf and needleleaf forests along vertical and horizontal gradients and then evaluated the relationship between their timing and daily mean air temperature. We found that for the timing of SGS and EGS, changes along the vertical gradient in deciduous broadleaf forest tended to be larger than those in deciduous needleleaf forest. For both forest types, changes along the vertical and horizontal gradients in the timing of EGS tended to be smaller than those of SGS. Finally, in both forest types, the sensitivity of the timing of EGS to air temperature was much less than that of SGS. These results suggest that the spatio-temporal variability in the timing of SGS and EGS detected by satellite data, which may be correlated with leaf traits, photosynthetic capacity, and environment conditions, provide useful ground-truthing information along vertical and horizontal gradients. PMID:24781316

Nagai, Shin; Saitoh, Taku M; Nasahara, Kenlo Nishida; Suzuki, Rikie

2015-01-01

52

An electromagnetic sounding experiment in Germany using the vertical gradient of geomagnetic variations observed in a deep borehole  

NASA Astrophysics Data System (ADS)

We have recorded for 13 d, geomagnetic variations simultaneously on the Earth's surface and in a borehole at 832 m depth straight below, with a sampling rate of 1 Hz. In addition, geoelectric variations were observed at the same site near Bad Königshofen in Frankonia, Germany. The penetrated moderately conductive Triassic sediments lie above highly resistive Permian deposits. A presumably crystalline basement begins at 1500-1900 m depth. The purpose of the experiment is to determine the skin effect of geomagnetic variations and to derive from it the equivalent to the magnetotelluric (MT) surface impedance, using the vertical gradient (VG) method of electromagnetic (EM) sounding. In this way, we were able to reproduce all four elements of the MT impedance tensor, except for an unexplained but consistent downward shift of VG phases against MT phases by roughly 15° for the two off-diagonal elements. Hence, our tensor evaluation goes beyond the common practice, to express the skin effect by a single VG transfer function in response to a layered structure. The otherwise good agreement of VG and MT results implies that at our test site, the MT impedance tensor is largely distortion-free and that, for example, its pronounced anisotropy should be regarded as a genuine characteristic of the EM response for a laterally non-uniform or possibly anisotropic deep structure. The drilling site lies within the range of a widespread induction anomaly. We have observed the resulting variations of the vertical magnetic component at the surface and in the borehole and found them to be identical. The thus established absence of a skin effect for the vertical component allows us to treat the sedimentary layer down to the depth of the borehole instrument as a thin sheet, and the pertinent thin-sheet approximation for EM induction forms the basis of our analysis. We have derived the required estimate of conductance from the skin effect of horizontal components, noting that this estimate has to be real valued and the same for all frequencies. We were unable, however, to verify the resulting value of 76 S with independent geoelectric direct current (DC) measurements in the borehole and at the Earth's surface. A model study shows that the thin-sheet conductance, which is relevant for the skin effect, may be substantially higher than the depth-integrated conductivity from DC data. Robust estimates of transfer functions were derived for 20 frequencies from 5.625 to 0.007 cpm, which corresponds to periods from 10 to 10000 s. Squared skin effect coherencies are above 0.9 for periods longer than 20 s and thereby comparable to MT coherencies.

Schmucker, Ulrich; Spitzer, Klaus; Steveling, Erich

2009-09-01

53

[FeFe]-Hydrogenase Abundance and Diversity along a Vertical Redox Gradient in Great Salt Lake, USA  

PubMed Central

The use of [FeFe]-hydrogenase enzymes for the biotechnological production of H2 or other reduced products has been limited by their sensitivity to oxygen (O2). Here, we apply a PCR-directed approach to determine the distribution, abundance, and diversity of hydA gene fragments along co-varying salinity and O2 gradients in a vertical water column of Great Salt Lake (GSL), UT. The distribution of hydA was constrained to water column transects that had high salt and relatively low O2 concentrations. Recovered HydA deduced amino acid sequences were enriched in hydrophilic amino acids relative to HydA from less saline environments. In addition, they harbored interesting variations in the amino acid environment of the complex H-cluster metalloenzyme active site and putative gas transfer channels that may be important for both H2 transfer and O2 susceptibility. A phylogenetic framework was created to infer the accessory cluster composition and quaternary structure of recovered HydA protein sequences based on phylogenetic relationships and the gene contexts of known complete HydA sequences. Numerous recovered HydA are predicted to harbor multiple N- and C-terminal accessory iron-sulfur cluster binding domains and are likely to exist as multisubunit complexes. This study indicates an important role for [FeFe]-hydrogenases in the functioning of the GSL ecosystem and provides new target genes and variants for use in identifying O2 tolerant enzymes for biotechnological applications. PMID:25464382

Boyd, Eric S.; Hamilton, Trinity L.; Swanson, Kevin D.; Howells, Alta E.; Baxter, Bonnie K.; Meuser, Jonathan E.; Posewitz, Matthew C.; Peters, John W.

2014-01-01

54

Spatial Changes in the Bacterial Community Structure along a Vertical Oxygen Gradient in Flooded Paddy Soil Cores  

PubMed Central

Molecular ecology techniques were applied to assess changes in the bacterial community structure along a vertical oxygen gradient in flooded paddy soil cores. Microsensor measurements showed that oxygen was depleted from 140 ?M at the floodwater/soil interface to nondetectable amounts at a depth of approximately 2.0 mm and below. Bacterial 16S rRNA gene (rDNA)-based community fingerprint patterns were obtained from 200-?m-thick soil slices of both the oxic and anoxic zones by using the T-RFLP (terminal restriction fragment length polymorphism) technique. The fingerprints revealed a tremendous shift in the community patterns in correlation to the oxygen depletion measured with depth. 16S rDNA clone sequences recovered from the oxic or anoxic zone directly corresponded to those terminal restriction fragments which were highly characteristic of the respective zone. Comparative sequence analysis of these clones identified members of the ? and ? subclasses of Proteobacteria as the abundant populations in the oxic zone. In contrast, members of clostridial cluster I were determined to be the predominant bacterial group in the oxygen-depleted soil. The extraction of total RNA followed by reverse transcription-PCR of the bacterial 16S rRNA and T-RFLP analysis resulted for both oxic and anoxic zones of flooded soil cores in community fingerprint patterns similar to those obtained by the rDNA-based analysis. This finding suggests that the microbial groups detected on the rDNA level are the metabolically active populations within the oxic and anoxic soil slices examined. PMID:10653747

Lüdemann, Heiner; Arth, Inko; Liesack, Werner

2000-01-01

55

Acclimation of Leaf Nitrogen to Vertical Light Gradient at Anthesis in Wheat Is a Whole-Plant Process That Scales with the Size of the Canopy1[W][OA  

PubMed Central

Vertical leaf nitrogen (N) gradient within a canopy is classically considered as a key adaptation to the local light environment that would tend to maximize canopy photosynthesis. We studied the vertical leaf N gradient with respect to the light gradient for wheat (Triticum aestivum) canopies with the aims of quantifying its modulation by crop N status and genetic variability and analyzing its ecophysiological determinants. The vertical distribution of leaf N and light was analyzed at anthesis for 16 cultivars grown in the field in two consecutive seasons under two levels of N. The N extinction coefficient with respect to light (b) varied with N supply and cultivar. Interestingly, a scaling relationship was observed between b and the size of the canopy for all the cultivars in the different environmental conditions. The scaling coefficient of the b-green area index relationship differed among cultivars, suggesting that cultivars could be more or less adapted to low-productivity environments. We conclude that the acclimation of the leaf N gradient to the light gradient is a whole-plant process that depends on canopy size. This study demonstrates that modeling leaf N distribution and canopy expansion based on the assumption that leaf N distribution parallels that of the light is inappropriate. We provide a robust relationship accounting for vertical leaf N gradient with respect to vertical light gradient as a function of canopy size. PMID:22984122

Moreau, Delphine; Allard, Vincent; Gaju, Oorbessy; Le Gouis, Jacques; Foulkes, M. John; Martre, Pierre

2012-01-01

56

Freezing lake  

NSDL National Science Digital Library

Finite difference solution to mixed conduction-convection limited freezing of a 10 cm thick pool of water, with benchmark against analytical timescales. Requisite software: Gnumeric or Excel to open spreadsheets in source directory.

Powell, Adam C., IV

2005-02-23

57

Vertical structure and horizontal gradients of aerosol extinction coefficients over coastal India inferred from airborne lidar measurements during the Integrated Campaign for Aerosol, Gases and Radiation Budget (ICARB) field campaign  

Microsoft Academic Search

Quantitative estimates of the vertical structure and the spatial gradients of aerosol extinction coefficients have been made from airborne lidar measurements across the coastline into offshore oceanic regions along the east and west coasts of India. The vertical structure revealed the presence of strong, elevated aerosol layers in the altitude region of ?2?4 km, well above the atmospheric boundary layer

S. K. Satheesh; K. Krishna Moorthy; S. Suresh Babu; V. Vinoj; Vijayakumar S. Nair; S. Naseema Beegum; C. B. S. Dutt; D. P. Alappattu; P. K. Kunhikrishnan

2009-01-01

58

Fine-scale horizontal and vertical micro-distribution patterns of testate amoebae along a narrow fen/bog gradient  

E-print Network

1 Fine-scale horizontal and vertical micro-distribution patterns of testate amoebae along a narrow: 2010, 15th June Running headline: Micro-distribution of testate amoebae in Sphagnum hal-00682493.1007/s00248-010-9756-9 #12;2 Abstract1 The ecology of peatland testate amoebae is well studied along

Paris-Sud XI, Université de

59

Large vertical ?13CDIC gradients in Early Triassic seas of the South China craton: Implications for oceanographic changes related to Siberian Traps volcanism  

NASA Astrophysics Data System (ADS)

Vertical gradients in the ?13C of seawater dissolved inorganic carbon (??13CDIC) can be estimated for paleomarine systems based on ?13Ccarb data from sections representing a range of depositional water depths. An analysis of eight Lower Triassic sections from the northern Yangtze Platform and Nanpanjiang Basin, representing water depths of ~ 50 to 500 m, allowed reconstruction of ??13CDIC in Early Triassic seas of the South China craton for seven time slices representing four negative (N) and three positive (P) carbon-isotope excursions: 8.5‰ (N1), 5.8‰ (P1), 3.5‰ (N2), 6.5‰ (P2), 7.8‰ (N3), - 1.9‰ (P3), and 2.2‰ (N4). These values are much larger than vertical ?13CDIC gradients in the modern ocean (~ 1-3‰) due to intensified stratification and reduced vertical mixing in Early Triassic seas. Peaks in ??13CDIC around the PTB (N1) and in the early to mid-Smithian (P2-N3) coincided with episodes of strong climatic warming, reduced marine productivity, and expanded ocean anoxia. The Dienerian-Smithian boundary marks the onset of a major mid-Early Triassic disturbance, commencing ~ 1 Myr after the latest Permian mass extinction, that we link to a second eruptive stage of the Siberian Traps. Inhospitable oceanic conditions generally persisted until the early Spathian, when strong climatic cooling caused re-invigoration of global-ocean circulation, leading to an interval of negative ??13CDIC values and a sharp increase in ?13Ccarb driven by upwelling of nutrient-rich deepwaters. These developments marked the end of the main eruptive stage of the Siberian Traps.

Song, Huyue; Tong, Jinnan; Algeo, Thomas J.; Horacek, Micha; Qiu, Haiou; Song, Haijun; Tian, Li; Chen, Zhong-Qiang

2013-06-01

60

Eddy covariance fluxes and vertical concentration gradient measurements of NO and NO2 over a ponderosa pine ecosystem: observational evidence for within-canopy chemical removal of NOx  

NASA Astrophysics Data System (ADS)

Exchange of NOx (NO+NO2) between the atmosphere and biosphere is important for air quality, climate change, and ecosystem nutrient dynamics. There are few direct ecosystem-scale measurements of the direction and rate of atmosphere-biosphere exchange of NOx. As a result, a complete description of the processes affecting NOx following emission from soils and/or plants as they transit from within the plant/forest canopy to the free atmosphere remains poorly constrained and debated. Here, we describe measurements of NO and NO2 fluxes and vertical concentration gradients made during the Biosphere Effects on AeRosols and Photochemistry EXperiment 2009. In general, during daytime we observe upward fluxes of NO and NO2 with counter-gradient fluxes of NO. We find that NOx fluxes from the forest canopy are smaller than calculated using observed flux-gradient relationships for conserved tracers and also smaller than measured soil NO emissions. We interpret these differences as primarily due to chemistry converting NOx to higher nitrogen oxides within the forest canopy, which might be part of a mechanistic explanation for the "canopy reduction factor" applied to soil NOx emissions in large-scale models.

Min, K.-E.; Pusede, S. E.; Browne, E. C.; LaFranchi, B. W.; Cohen, R. C.

2014-06-01

61

Directional freezing of reproductive cells and organs.  

PubMed

Directional freezing is based on a simple thermodynamic principle where ice crystals are precisely controlled through the sample by regulating the velocity of the sample movement through the predetermined temperature gradient. Directional freezing permits a precise and uniform cooling rate in both small and large volume samples. Directional freezing was used for slow and rapid freezing, as well as for vitrification of oocytes and embryos using the minimum drop size technique. Sperm samples from a wide range of domestic and wild animals were successfully cryopreserved using the directional freezing method. The method enabled, for the first time, successful freezing of a whole ovary and freeze-drying of mammalian cells followed by thawing and transplantation and rehydration, respectively. PMID:22827370

Arav, A; Natan, D

2012-08-01

62

Vertical and longitudinal gradients in HNA-LNA cell abundances and cytometric characteristics in the Mediterranean Sea  

NASA Astrophysics Data System (ADS)

Heterotrophic bacterioplankton abundance and production were investigated with depth (down to bathypelagic layers) and with longitude (from 4.9° E to 32.7° E) along a cruise track across the Mediterranean Sea in early summer 2008. Abundances and flow cytometric characteristics (green fluorescence and side scatter signals) of high nucleic acid (HNA) and low nucleic acid (LNA) bacterial cells were determined using flow cytometry. Contrary to what is generally observed, the relative importance of HNA cells, as a percent of total cells, (%HNA, range 30-69 %) was inversely related to bacterial production (range 0.15-44 ng C l-1 h-1) although the negative relation was weak (log-log regression r2=0.19). The %HNA as well as the mean side scatter of HNA group increased significantly with depth in the meso and bathypelagic layers. Vertical stratification played an important role in influencing the distribution and characteristics of bacterial cells especially with regard to layers located above, within or below the deep chlorophyll maximum. Within a given layer, the relationships between the flow cytometric characteristics and environmental variables such as chlorophyll-a, nutrients or bacterial production changed. Overall, the relationships between HNA and LNA cells and environmental parameters differed vertically more than longitudinally.

van Wambeke, F.; Catala, P.; Pujo-Pay, M.; Lebaron, P.

2011-07-01

63

Changes in hydrocarbon groups, soil ecotoxicity and microbiology along horizontal and vertical contamination gradients in an old landfarming field for oil refinery waste.  

PubMed

Horizontal and vertical contaminant gradients in an old landfarming field for oil refinery waste were characterised with the aim to assess parallel changes in hydrocarbon groups and general, microbiological and ecotoxicological soil characteristics. In the surface soil polar compounds were the most prevalent fraction of heptane-extractable hydrocarbons, superseding GC-FID-resolvable and high-molar-mass aliphatics and aromatics, but there was no indication of their relatively higher mobility or toxicity. The size of the polar fraction correlated poorly with soil physical, chemical and microbiological properties, which were better explained by the total heptane-extractable and total petroleum hydrocarbons (TPH). Deleterious effects on soil microbiology in situ were observed at surprisingly low TPH concentrations (0.3%). Due to the accumulation of polar and complexed degradation products, TPH seems an insufficient measure to assess the quality and monitor the remediation of soil with weathered hydrocarbon contamination. PMID:22243888

Mikkonen, Anu; Hakala, Kati P; Lappi, Kaisa; Kondo, Elina; Vaalama, Anu; Suominen, Leena

2012-03-01

64

When hot water freezes before cold  

E-print Network

I suggest that the origin of the Mpemba effect (the freezing of hot water before cold) is freezing-point depression by solutes, either gaseous or solid, whose solubility decreases with increasing temperature so that they are removed when water is heated. They are concentrated ahead of the freezing front by zone refining in water that has not been heated, reduce the temperature of the freezing front, and thereby reduce the temperature gradient and heat flux, slowing the progress of the front. I present a simple calculation of this effect, and suggest experiments to test this hypothesis.

J. I. Katz

2006-04-27

65

Freeze Technology for Nuclear Applications - 13590  

SciTech Connect

Freezing of soil materials is a complicated process of a number of physical processes: - freezing of pore water in a thermal gradient, - cryogenic suction causing water migration and - ice formation expanding pores inducing frost heave. Structural changes due to increase of effective stress during freezing also take place. The over consolidation gives a powerful dewatering/drying effect and the freeze process causes separation of contaminates. Artificial ground freezing (AGF is a well established technique first practiced in south Wales, as early as 1862. AGF is mostly used to stabilize tunnels and excavations. During the last ten years underwater applications of freeze technologies based on the AGF have been explored in Sweden. The technology can, and has been, used in many different steps in a remediation action. Freeze Sampling where undisturbed samples are removed in both soft and hard sediment/sludge, Freeze Dredging; retrieval of sediment with good precision and minimal redistribution, and Freeze Drying; volume reduction of contaminated sludge/sediment. The application of these technologies in a nuclear or radioactive environment provides several advantages. Sampling by freezing gives for example an advantage of an undisturbed sample taken at a specified depth, salvaging objects by freezing or removal of sludges is other applications of this, for the nuclear industry, novel technology. (authors)

Rostmark, Susanne C.; Knutsson, Sven [Lulea University of Technology (Sweden)] [Lulea University of Technology (Sweden); Lindberg, Maria [Studsvik Nuclear AB, 611 82 Nykoeping (Sweden)] [Studsvik Nuclear AB, 611 82 Nykoeping (Sweden)

2013-07-01

66

Vertical physico-chemical gradients with distinct microbial communities in the hypersaline and heliothermal Lake Ursu (Sovata, Romania).  

PubMed

The effect of vertical physico-chemical stratification on the planktonic microbial community composition of the deep, hypersaline and heliothermal Lake Ursu (Sovata, Romania) was examined in this study. On site and laboratory measurements were performed to determine the physical and chemical variables of the lake water, and culture-based and cultivation-independent techniques were applied to identify the members of microbial communities. The surface of the lake was characterized by a low salinity water layer while the deepest region was extremely saline (up to 300 g/L salinity). Many parameters (e.g. photosynthetically active radiation, dissolved oxygen concentration, pH, redox potential) changed dramatically from 2 to 4 m below the water surface in conjunction with the increasing salinity values. The water temperature reached a maximum at this depth. At around 3 m depth, there was a water layer with high (bacterio) chlorophyll content dominated by Prosthecochloris vibrioformis, a phototrophic green sulfur bacterium. Characteristic microbial communities with various prokaryotic taxa were identified along the different environmental parameters present in the different water layers. Some of these bacteria were known to be heterotrophic and therefore may be involved in the decomposition of lake organic material (e.g. Halomonas, Idiomarina and Pseudoalteromonas) while others in the transformation of sulfur compounds (e.g. Prosthecochloris). Eukaryotic microorganisms identified by molecular methods in the lake water belonged to genera of green algae (Mantionella and Picochlorum), and were restricted mainly to the upper layers. PMID:24531691

Máthé, István; Borsodi, Andrea K; Tóth, Erika M; Felföldi, Tamás; Jurecska, Laura; Krett, Gergely; Kelemen, Zsolt; Elekes, Erzsébet; Barkács, Katalin; Márialigeti, Károly

2014-05-01

67

Tomographic P wave velocity and vertical velocity gradient structure across the geothermal site Groß Schönebeck (NE German Basin): Relationship to lithology, salt tectonics, and thermal regime  

NASA Astrophysics Data System (ADS)

Seismic wide-angle data were collected along a 40-km-long profile centered at the geothermal research well GrSk 3/90 in the Northeast German Basin. Tomographic inversion of travel time data provided a velocity and a vertical velocity gradient model, indicative of Cenozoic to Pre-Permian sediments. Wide-angle reflections are modeled and interpreted as top Zechstein and top Pre-Permian. Changes in velocity gradients are interpreted as the transition from mechanical to chemical compaction at 2-3 km depth, and localized salt structures are imaged, suggesting a previously unknown salt pillow in the southern part of the seismic profile. The Zechstein salt shows decreased velocities in the adjacent salt pillows compared to the salt lows, which is confirmed by sonic log data. This decrease in velocity could be explained by the mobilization of less dense salt, which moved and formed the salt pillows, whereas the denser salt remained in place at the salt lows. We interpret a narrow subvertical low-velocity zone under the salt pillow at GrSk 3/90 as a fault in the deep Permian to Pre-Permian. This WNW-ESE trending fault influenced the location of the salt tectonics and led to the formation of a fault-bounded graben in the Rotliegend sandstones with optimal mechanical conditions for geothermal production. Thermal modeling showed that salt pillows are related to chimney effects, a decrease in temperature, and increasing velocity. The assumed variations in salt lithology, density, and strain must thus be even higher to compensate for the temperature effect.

Bauer, K.; Moeck, I.; Norden, B.; Schulze, A.; Weber, M.; Wirth, H.

2010-08-01

68

Cryoprotectants for freeze drying of drug nano-suspensions: effect of freezing rate.  

PubMed

Drug nanoparticles are often prepared in a liquid medium, and a drying method such as freeze drying is used to convert them to an oral solid dosage form. When the dried form is reconstituted in an aqueous system, it may be redispersed to achieve its original particle size. The redispersibility of dried nanoparticles depends on the parameters of the freeze drying process. In this study, an apparatus with a freezing rate gradient was used to systematically investigate the effect of cryoprotectants on the redispersibility of nanoparticles as a function of freezing rate. Sucrose, lactose, mannitol, and polyethylene glycol were used as cryoprotectants for a naproxen nano-suspension. A fast freezing rate and a high cryoprotectant concentration were generally favored. However, under certain conditions, a slower freezing rate resulted in better redispersibility. This is probably because slow freezing can produce a more cryo-concentrated liquid phase, and the concentrated cryoprotectant in the liquid phase can more effectively protect the nanoparticles. An irreversible aggregation map was constructed as a function of the freezing rate and the cryoprotectant concentration, and shows both the favorable and unfavorable effects of cryoprotectants. PMID:19475555

Lee, Min Kyung; Kim, Min Young; Kim, Sujung; Lee, Jonghwi

2009-12-01

69

Theoretical prediction of 'optimal' freezing programmes.  

PubMed

We have developed a quantitative description of the osmotic behaviour of cells during freezing without a presupposed value of the cooling rate. Instead, at all times the intracellular supercooling is maximised provided that it does not exceed a predetermined value 'p' (e.g., 2 degrees C). This should preclude intracellular ice formation, but also ensures that the osmotic gradient and the CPA concentration gradient are limited, as well as the gradient driven transmembrane fluxes of water and CPA. Using the condition of a constant level of supercooling of p degrees C, equations can be derived to generate non-linear cooling curves in which at all times the cooling rate is maximised (to minimise slow cooling damage), while preventing conditions that could lead to fast cooling damage. Simulations of the osmotic events during freezing, and prediction of the 'optimal' freezing curve can be performed provided that values are available for the membrane permeability coefficients for water (L(p)) and cryoprotectant (P(s)), and their respective activation energies, the initial intracellular osmotically active aqueous volume, and the membrane surface area. Simulations are shown, both with and without permeant solute, to demonstrate how the predicted 'optimal' freezing curve is affected by medium composition, and by membrane permeability and osmotic cell characteristics. PMID:15615612

Woelders, H; Chaveiro, A

2004-12-01

70

Freezing in confined geometries  

NASA Technical Reports Server (NTRS)

Results of detailed structural studies, using elastic neutron scattering, of the freezing of liquid O2 and D2 in porous vycor glass, are presented. The experimental studies have been complemented by computer simulations of the dynamics of freezing of a Lennard-Jones liquid in narrow channels bounded by molecular walls. Results point to a new simple physical interpretation of freezing in confined geometries.

Sokol, P. E.; Ma, W. J.; Herwig, K. W.; Snow, W. M.; Wang, Y.; Koplik, Joel; Banavar, Jayanth R.

1992-01-01

71

Freezing Fish and Shellfish.  

E-print Network

means of preserving the fresh-caught quality of fish and shellfish. Why Freeze? Freezing preserves foods by lowering their tem peratures to a point not conducive to bacterial growth and natural enzyme action. Many spoilage bacteria are destroyed... by freezing, and those that survive are unable to grow at the low temperature. A fresh seafood product can spoil when bacteria are not present. Natural enzymes that help fish digest food and carry on natural metabolism in the cells of the fish...

Nickelson, Ranzell; Reddell, Annette

1980-01-01

72

Effects of oxygen, temperature and light gradients on the vertical distribution of rainbow trout, Oncorhynchus mykiss, in two North Island, New Zealand, lakes differing in trophic status  

Microsoft Academic Search

Vertical distributions of adult rainbow trout (> 25 cm fork length, FL) were determined with a SIMRAD ES470 split?beam echosounder in two 80–90 m deep lakes differing in water quality. Between November 1993 and February 1994, most trout (> 80%) were between 10 and 40 m, within or close to the thermocline. However, a small group of fish occupied colder

D. K. Rowe; B. L. Chisnall

1995-01-01

73

Repeated vitrification/warming of human sperm gives better results than repeated slow programmable freezing  

PubMed Central

In this study, we compared the effects of repeated freezing/thawing of human sperm by our in-house method of rapid freezing with slow programmable freezing. Sperm samples from 11 normozoospermic subjects were processed through density gradients and divided into three aliquots: non-frozen, rapid freezing and slow programmable freezing. Sperm in the rapid freezing group had better motility and viability than those in the slow freezing group (P<0.01) after the first, second and third cycles of freezing/thawing, but there was no difference in morphology. In the second experiment, rapid freezing was repeated three times in 20 subjects. The samples from each thawing cycle were evaluated for DNA fragmentation using the alkaline comet assay. DNA fragmentation began to increase considerably after the second cycle of freezing/thawing, but to a level that was not clinically important. In the third experiment, rapid freezing was done repeatedly in 10 subjects, until no motile sperm were observed after thawing. The median number of repeated freezing/thawing that yielded no motile sperm was seven (range: 5–8, mean: 6.8). In conclusion, we demonstrated that repeated freezing/thawing of processed semen using our rapid freezing method gave better results than standard slow programmable freezing. This method can help maximize the usage of precious cryopreserved sperm samples in assisted reproduction technology. PMID:23064685

Vutyavanich, Teraporn; Lattiwongsakorn, Worashorn; Piromlertamorn, Waraporn; Samchimchom, Sudarat

2012-01-01

74

Freezing and Melting  

NSDL National Science Digital Library

This article tells how the freezing point of a substance is also its melting point. The energy of the substance's molecules changes with temperature, thus with changes in state. Also described is how freezing points can be lowered, or depressed, by adding a substance.

2010-01-01

75

Increased spring freezing vulnerability for alpine shrubs under early snowmelt.  

PubMed

Alpine dwarf shrub communities are phenologically linked with snowmelt timing, so early spring exposure may increase risk of freezing damage during early development, and consequently reduce seasonal growth. We examined whether environmental factors (duration of snow cover, elevation) influenced size and the vulnerability of shrubs to spring freezing along elevational gradients and snow microhabitats by modelling the past frequency of spring freezing events. We sampled biomass and measured the size of Salix herbacea, Vaccinium myrtillus, Vaccinium uliginosum and Loiseleuria procumbens in late spring. Leaves were exposed to freezing temperatures to determine the temperature at which 50% of specimens are killed for each species and sampling site. By linking site snowmelt and temperatures to long-term climate measurements, we extrapolated the frequency of spring freezing events at each elevation, snow microhabitat and per species over 37 years. Snowmelt timing was significantly driven by microhabitat effects, but was independent of elevation. Shrub growth was neither enhanced nor reduced by earlier snowmelt, but decreased with elevation. Freezing resistance was strongly species dependent, and did not differ along the elevation or snowmelt gradient. Microclimate extrapolation suggested that potentially lethal freezing events (in May and June) occurred for three of the four species examined. Freezing events never occurred on late snow beds, and increased in frequency with earlier snowmelt and higher elevation. Extrapolated freezing events showed a slight, non-significant increase over the 37-year record. We suggest that earlier snowmelt does not enhance growth in four dominant alpine shrubs, but increases the risk of lethal spring freezing exposure for less freezing-resistant species. PMID:24435708

Wheeler, J A; Hoch, G; Cortés, A J; Sedlacek, J; Wipf, S; Rixen, C

2014-05-01

76

Freezing in Halide Salts  

NASA Astrophysics Data System (ADS)

The static criterion that the amplitude of the principal peak of the liquid structure factor has a constant value along the freezing line and the onset of freezing are studied from the structure factors and the static dielectric functions of halide salts interacting via the effective pair potentials through the hypernetted-chain approximation. It is observed that the criterion above is restricted to the effective charge difference. The critical value of plasma parameter at freezing is affected by the mobility and number concentration of anions and cations. The distribution of the value of the static dielectric function closest to the wave number axis in the negative region is also determined by the charge difference and the ordering of ions and related to the onset of freezing.

Akdere, ?.; Y?lmaz, M.; Kavanoz, H. B.; Ta?seven, Ç.

2008-06-01

77

Polymerization with freezing  

NASA Astrophysics Data System (ADS)

Irreversible aggregation processes involving reactive and frozen clusters are investigated using the rate equation approach. In aggregation events, two clusters join irreversibly to form a larger cluster; additionally, reactive clusters may spontaneously freeze. Frozen clusters do not participate in merger events. Generally, freezing controls the nature of the aggregation process, as demonstrated by the final distribution of frozen clusters. The cluster mass distribution has a power-law tail, Fk~k-?, when the freezing process is sufficiently slow. Different exponents, ? = 1 and 3, are found for the constant and the product aggregation rates, respectively. For the latter case, the standard polymerization model, either no gels, or a single gel, or even multiple gels, may be produced.

Ben-Naim, E.; Krapivsky, P. L.

2005-12-01

78

The freezing rotation illusion  

Microsoft Academic Search

The “freezing rotation illusion” refers to decrease in perceived speed of a continuously rotating central region when a swaying surround co-rotates. We observed the following effects for rotations: First, when the centre and its surround are turning in the same direction, and their velocities are distinguishable, the perceived speed of the centre is lower than its physical speed. Second, when

Max R. Dürsteler

2008-01-01

79

Animal Anti-Freeze  

NSDL National Science Digital Library

In this outdoor winter activity, learners search for and create hibernation sites that will protect gelatin "animals" from freezing. Learners come to understand that hibernating animals need to take care in selecting a sleeping spot that will provide protection from the winter cold.

Science, Lawrence H.

1982-01-01

80

FREEZE FRAMING MUSLIMS  

Microsoft Academic Search

Western images of Islam and Muslims have been frozen in history and are recycled with mundane regularity. These ‘freeze frames’ emerged at the beginning of Islam and have, over centuries, acquired certain key elements and descriptors. Association of Islam with promiscuity and licentiousness was common during the eight and tenth centuries. The Crusades added war-like violence to the picture, and

Ziauddin Sardar; Merryl Wyn Davies

2010-01-01

81

Modeling soil freezing dynamics  

Technology Transfer Automated Retrieval System (TEKTRAN)

Seasonally frozen soil strongly influences runoff and erosion on large areas of land around the world. In many areas, rain or snowmelt on seasonally frozen soil is the single leading cause of severe runoff and erosion events. As soils freeze, ice blocks the soil pores, greatly diminishing the permea...

82

Freeze-drying of proteins.  

PubMed

Freeze-drying has become one of the most important processes for the preservation of biological products. This chapter provides protocols for freeze-drying of proteins and discusses the importance of formulation, cycle development, and validation. Specific formulations for stabilization of proteins are presented as well as advice on common problems with freeze-drying of proteins. PMID:25428023

Liu, Baolin; Zhou, Xinli

2015-01-01

83

Variation in seedling freezing response is associated with climate in Larrea  

PubMed Central

Variation in freezing severity is hypothesized to have influenced the distribution and evolution of the warm desert evergreen genus Larrea. If this hypothesis is correct, performance and survival of species and populations should vary predictably along gradients of freezing severity. If freezing environment changes in the future, the ability of Larrea to adapt will depend on the structure of variation for freezing resistance within populations. To test whether freezing responses vary among and within Larrea populations, we grew maternal families of seedlings from high and low latitude L. divaricata and high latitude L. tridentata populations in a common garden. We measured survival, projected plant area and dark-adapted chlorophyll fluorescence (Fv/Fm) before and after cold acclimation and for 2 weeks following a single freeze. We detected significant variation in freezing resistance among species and populations. Maternal family lines differed significantly in their responses to cold acclimation and/or freezing for two out of the three populations: among L. tridentata maternal families and among low latitude L. divaricata maternal families. There were no significant differences across maternal families of high latitude L. divaricata. Our results indicate that increased freezing resistance in high latitude populations likely facilitated historical population expansion of both species into colder climates, but this may have occurred to a greater extent for L. tridentata than for L. divaricata. Differences in the structure of variation for cold acclimation and freezing responses among populations suggest potential differences in their ability to evolve in response to future changes in freezing severity. PMID:22068319

Marshall, Diane L.; Maherali, Hafiz; Pockman, William T.

2013-01-01

84

Optimum gradient of mountain paths.  

PubMed

By combining the experiment results of R. Margaria (Atti Accad. Naz. Lincei Memorie 7: 299-368, 1938), regarding the metabolic cost of gradient locomotion, together with recent insights on gait biomechanics, a prediction about the most economical gradient of mountain paths (approximately 25%) is obtained and interpreted. The pendulum-like mechanism of walking produces a waste of mechanical work against gravity within the gradient range of up to 15% (the overall efficiency is dominated by the low transmission efficiency), whereas for steeper values only the muscular efficiency is responsible for the (slight) metabolic change (per meter of vertical displacement) with respect to gradient. The speeds at the optimum gradient turned out to be approximately 0.65 m/s (+0.16 m/s vertical) and 1.50 m/s (-0.36 m/s vertical), for uphill and downhill walking, respectively, and the ascensional energy expenditure was 0.4 and 2.0 ml O2.kg body mass-1.vertical m-1 climbed or descended. When the metabolic power becomes a burden, as in high-altitude mountaineering, the optimum gradient should be reduced. A sample of real mountain path gradients, experimentally measured, mimics the obtained predictions. PMID:8594031

Minetti, A E

1995-11-01

85

The freezing bomb  

NASA Astrophysics Data System (ADS)

The extreme pressures that are generated when water freezes were traditionally demonstrated by sealing a small volume in a massive cast iron 'bomb' and then surrounding it with a freezing mixture of ice and salt. This vessel would dramatically fail by brittle fracture, but no quantitative measurement of bursting pressure was available. Calculation suggests a maximum of about 55 MPa (8000 psi) might have been achieved, with some 2.3% of the water frozen into a hollow shell around the interior of the vessel. In a sufficiently strong alloy steel container the pressure might rise to a maximum of 210 MPa (30 460 psi), this limiting figure being due to the collapse of ordinary ice (ice I) to the denser forms ice II or ice III.

Mills, Allan

2010-03-01

86

Satellite freeze forecast system  

NASA Technical Reports Server (NTRS)

Provisions for back-up operations for the satellite freeze forecast system are discussed including software and hardware maintenance and DS/1000-1V linkage; troubleshooting; and digitized radar usage. The documentation developed; dissemination of data products via television and the IFAS computer network; data base management; predictive models; the installation of and progress towards the operational status of key stations; and digital data acquisition are also considered. The d addition of dew point temperature into the P-model is outlined.

Martsolf, J. D. (principal investigator)

1983-01-01

87

Mechanisms of Freezing lnjuly in Cellular Leve  

NASA Astrophysics Data System (ADS)

The mechanisms of freezing injury in living cells were reviewed. The freezing injury takes place by at least two different factors depending upon cooling rate, those are intracellular freezing and extracellular freezing. The freezing injury caused by extracellular freezing also takes place by two different factors, those are direct and indirect effects by the formation of extracellular ice. These different stresses by freezing cause different damages on the plasma membranes in the same cell. Furthermore, freezing of different cell results in different form of membrane damage. Thus, the occurrence of freezing injury takes place by diverse mechanisms depending upon not only different freezing stresses but also difference of cell type.

Fujikawa, Seizo

88

Eddy covariance emission and deposition flux measurements using proton transfer reaction - time of flight - mass spectrometry (PTR-TOF-MS): comparison with PTR-MS measured vertical gradients and fluxes  

NASA Astrophysics Data System (ADS)

During summer 2010, a proton transfer reaction - time of flight - mass spectrometer (PTR-TOF-MS) and a quadrupole proton transfer reaction mass spectrometer (PTR-MS) were deployed simultaneously for one month in an orange orchard in the Central Valley of California to collect continuous data suitable for eddy covariance (EC) flux calculations. The high time resolution (5 Hz) and high mass resolution (up to 5000 m/?m) data from the PTR-TOF-MS provided the basis for calculating the concentration and flux for a wide range of volatile organic compounds (VOC). Throughout the campaign, 664 mass peaks were detected in mass-to-charge ratios between 10 and 1278. Here we present PTR-TOF-MS EC fluxes of the 27 ion species for which the vertical gradient was simultaneously measured by PTR-MS. These EC flux data were validated through spectral analysis (i.e., co-spectrum, normalized co-spectrum, and ogive). Based on inter-comparison of the two PTR instruments, no significant instrumental biases were found in either mixing ratios or fluxes, and the data showed agreement within 5% on average for methanol and acetone. For the measured biogenic volatile organic compounds (BVOC), the EC fluxes from PTR-TOF-MS were in agreement with the qualitatively inferred flux directions from vertical gradient measurements by PTR-MS. For the 27 selected ion species reported here, the PTR-TOF-MS measured total (24 h) mean net flux of 299 ?g C m-2 h-1. The dominant BVOC emissions from this site were monoterpenes (m/z 81.070 + m/z 137.131 + m/z 95.086, 34%, 102 ?g C m-2 h-1) and methanol (m/z 33.032, 18%, 72 ?g C m-2 h-1). The next largest fluxes were detected at the following masses (attribution in parenthesis): m/z 59.048 (mostly acetone, 12.2%, 36.5 ?g C m-2 h-1), m/z 61.027 (mostly acetic acid, 11.9%, 35.7 ?g C m-2 h-1), m/z 93.069 (para-cymene + toluene, 4.1%, 12.2 ?g C m-2 h-1), m/z 45.033 (acetaldehyde, 3.8%, 11.5 ?g C m-2 h-1), m/z 71.048 (methylvinylketone + methacrolein, 2.4%, 7.1 ?g C m-2 h-1), and m/z 69.071 (isoprene + 2-methyl-3-butene-2-ol, 1.8%, 5.3 ?g C m-2 h-1). Low levels of emission and/or deposition (<1.6% for each, 5.8% in total flux) were observed for the additional reported masses. Overall, our results show that EC flux measurements using PTR-TOF-MS is a powerful new tool for characterizing the biosphere-atmosphere exchange including both emission and deposition for a large range of BVOC and their oxidation products.

Park, J.-H.; Goldstein, A. H.; Timkovsky, J.; Fares, S.; Weber, R.; Karlik, J.; Holzinger, R.

2013-02-01

89

Freeze-Tolerant Condensers  

NASA Technical Reports Server (NTRS)

Two condensers designed for use in dissipating heat carried by working fluids feature two-phase, self-adjusting configurations such that their working lengths automatically vary to suit their input power levels and/or heat-sink temperatures. A key advantage of these condensers is that they can function even if the temperatures of their heat sinks fall below the freezing temperatures of their working fluids and the fluids freeze. The condensers can even be restarted from the frozen condition. The top part of the figure depicts the layout of the first condenser. A two-phase (liquid and vapor) condenser/vapor tube is thermally connected to a heat sink typically, a radiatively or convectively cooled metal panel. A single-phase (liquid) condensate-return tube (return artery) is also thermally connected to the heat sink. At intervals along their lengths, the condenser/vapor tube and the return artery are interconnected through porous plugs. This condenser configuration affords tolerance of freezing, variable effective thermal conductance (such that the return temperature remains nearly constant, independently of the ultimate sink temperature), and overall pressure drop smaller than it would be without the porous interconnections. An additional benefit of this configuration is that the condenser can be made to recover from the completely frozen condition either without using heaters, or else with the help of heaters much smaller than would otherwise be needed. The second condenser affords the same advantages and is based on a similar principle, but it has a different configuration that affords improved flow of working fluid, simplified construction, reduced weight, and faster recovery from a frozen condition.

Crowley, Christopher J.; Elkouhk, Nabil

2004-01-01

90

Freezing of Nonwoody Plant Tissue  

PubMed Central

Temperature recordings of the freezing of plant tissues include two plateaus or regions of reduced slope. During the second of these, small positive spikes were observed. When a completely frozen tissue was thawed and refrozen, neither the second plateau nor the spikes were recorded. Both were present, however, if the initial freezing had been terminated before the second plateau had been reached. The spikes appear to represent the release of heat of crystallization during the freezing of individual cells. Such a freezing and thawing cycle destroys the ability of the cells to remain supercooled in the presence of the ice that is formed as the first plateau is recorded. PMID:16658774

Brown, M. S.; Pereira, E. Sa B.; Finkle, Bernard J.

1974-01-01

91

Performance Characteristics of an Isothermal Freeze Valve  

SciTech Connect

This document discusses performance characteristics of an isothermal freeze valve. A freeze valve has been specified for draining the DWPF melter at the end of its lifetime. Two freeze valve designs have been evaluated on the Small Cylindrical Melter-2 (SCM-2). In order to size the DWPF freeze valve, the basic principles governing freeze valve behavior need to be identified and understood.

Hailey, A.E.

2001-08-22

92

Freeze-Lining Formation of a Synthetic Lead Slag: Part I. Microstructure Formation  

NASA Astrophysics Data System (ADS)

Recently, freeze linings have been selected more frequently to protect pyrometallurgical reactor walls, due to a number of advantages over conventional refractory linings, such as a self-regenerating capability and the possibility of operating under high-intensity process conditions. A freeze lining is formed on a cooled reactor wall in a time-dependent temperature gradient. A full description of freeze-lining development, including phase formation as a function of temperature, time, and position, is important in understanding freeze-lining formation mechanisms and may be instrumental for the design of a sustainable freeze-lining concept. Freeze-lining formation is therefore investigated in a synthetic lead slag system: PbO-FeO-Fe2O3-ZnO-CaO-SiO2. Lab-scale freeze linings were produced by submerging an air-cooled probe into liquid slag for different times ranging from 1 to 120 minutes. The freeze-lining microstructures were characterized with optical microscopy, scanning electron microscopy (SEM), and electron probe X-ray microanalysis. The results were compared with the results of reference experiments. The freeze-lining formation of the studied slag system is initially dominated by the formation of glass and a highly viscous liquid. After 1 minute, extensive crystallization occurs and further growth of the freeze lining is determined by the growth of the melilite phase, which forms networking crystals. Because the heat transfer occurs very quickly, these melilite crystals form in undercooled liquid. Because the initial solidification rate is high, mass exchange between the freeze lining and bath affects the freeze-lining growth only when the freeze lining almost reaches its steady-state thickness.

Campforts, Mieke; Jak, Evgueni; Blanpain, Bart; Wollants, Patrick

2009-10-01

93

Freezing of living cells  

SciTech Connect

It can be calculated that a living cell will survive more than 5000 years at -196/sup 0/C. This ability to essentially stop biological time has important implications in medicine and agriculture, and in biological research. In medicine the chief implications are in the banking of transplantable tissues and organs and in in vitro fertilization. In agriculture the applications stem in part from the role of frozen embryos in amplifying the number of calves produced by high quanlity cows. The problem is how can cells survive both the cooling to such very low temperatures and the return to normal temperatures. The answers involve fundamental characteristics of cells such as the permeability of their surface membranes to water and solutes. These characteristics determine whether or not cells undergo lethal internal ice formation and other response during freezing and thawing. 27 refs., 12 figs.

Mazur, P.

1985-01-01

94

Snow depth, soil freezing and nitrogen cycling in a northern hardwood forest landscape  

Microsoft Academic Search

Increases in soil freezing associated with decreases in snow cover have been identified as a significant disturbance to nitrogen\\u000a (N) cycling in northern hardwood forests. We created a range of soil freezing intensity through snow manipulation experiments\\u000a along an elevation gradient at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains, NH USA in order to improve\\u000a understanding of

Peter M. Groffman; Janet P. Hardy; Samuel Fashu-Kanu; Charles T. Driscoll; Natalie L. Cleavitt; Timothy J. Fahey; Melany C. Fisk

2011-01-01

95

7.NS Comparing Freezing Points  

NSDL National Science Digital Library

This is a task from the Illustrative Mathematics website that is one part of a complete illustration of the standard to which it is aligned. Each task has at least one solution and some commentary that addresses important asects of the task and its potential use. Here are the first few lines of the commentary for this task: Ocean water freezes at about $-2 \\frac12 ^\\circ C$. Fresh water freezes at $0 ^\\circ C$. Antifreeze, a liquid used in the radiators of cars, freezes at...

96

Freezing Poultry for Home Use  

E-print Network

. ? As you work, keep the cutting surface and utensils clean. ? Work quickly and place the poultry in the freezer as quickly as possible. ? Do not let raw poultry juices contaminate ready-to-eat foods. Answering the following questions will help you decide.... Since most homes do not have a quick-freeze unit and since poultry meat freezes slowly in a regular freezer, use these tips to help your poultry freeze faster. n If you use home-processed poultry, put it in an ice slush bath to chill the carcass...

Davis, Michael

2006-08-31

97

A NEW FREEZING-ULTRAMICROTOME  

PubMed Central

The difficulties in sectioning frozen biological objects for electron microscopic investigations are overcome by Steere's freezing-etching method. In order to test this method and to open up a wide field of application, the new freezing-ultramicrotome has been designed. The apparatus consists of the combination of an ultramicrotome with freezing-drying and shadow-casting installations in the same vacuum container. The preliminary results show, on the one hand, the practicability of all preparational steps and, on the other, that it is possible to resolve internal structures of cell organelles and even macromolecular patterns. PMID:13772269

Moor, H.; Mühlethaler, K.; Waldner, H.; Frey-Wyssling, A.

1961-01-01

98

Temperature and flow measurements on near-freezing aviation fuels in a wing-tank model  

NASA Technical Reports Server (NTRS)

Freezing behavior, pumpability, and temperature profiles for aviation turbine fuels were measured in a 190-liter tank chilled to simulate internal temperature gradients encountered in commercial airplane wing tanks. When the bulk of the fuel was above the specification freezing point, pumpout of the fuel removed all fuel except a layer adhering to the bottom chilled surfaces, and the unpumpable fraction depended on the fuel temperature near these surfaces. When the bulk of the fuel was at or below the freezing point, pumpout ceased when solids blocked the pump inlet, and the unpumpable fraction depended on the overall average temperature.

Friedman, R.; Stockemer, F. J.

1980-01-01

99

TISSUE FREEZING METHODS FOR CRYOSTAT SECTIONING  

E-print Network

that replaces the architecture with a "Swiss Cheese" effect. #12;The object is to freeze so rapidly that water ON THE SUBJECT OF WATER CRYSTAL FORMATION: "FREEZING BIOLOGICAL SAMPLES" Charles W. Scouten & Miles Cunningham OF TISSUE FREEZING 1. Fresh tissue freezing ­ Tissue is in OCT and flash frozen fresh. 2. 4% PFA fixed

Chisholm, Rex L.

100

Fundamentals of freeze-drying.  

PubMed

Given the increasing importance of reducing development time for new pharmaceutical products, formulation and process development scientists must continually look for ways to "work smarter, not harder." Within the product development arena, this means reducing the amount of trial and error empiricism in arriving at a formulation and identification of processing conditions which will result in a quality final dosage form. Characterization of the freezing behavior of the intended formulation is necessary for developing processing conditions which will result in the shortest drying time while maintaining all critical quality attributes of the freeze-dried product. Analysis of frozen systems was discussed in detail, particularly with respect to the glass transition as the physical event underlying collapse during freeze-drying, eutectic mixture formation, and crystallization events upon warming of frozen systems. Experiments to determine how freezing and freeze-drying behavior is affected by changes in the composition of the formulation are often useful in establishing the "robustness" of a formulation. It is not uncommon for seemingly subtle changes in composition of the formulation, such as a change in formulation pH, buffer salt, drug concentration, or an additional excipient, to result in striking differences in freezing and freeze-drying behavior. With regard to selecting a formulation, it is wise to keep the formulation as simple as possible. If a buffer is needed, a minimum concentration should be used. The same principle applies to added salts: If used at all, the concentration should be kept to a minimum. For many proteins a combination of an amorphous excipient, such as a disaccharide, and a crystallizing excipient, such as glycine, will result in a suitable combination of chemical stability and physical stability of the freeze-dried solid. Concepts of heat and mass transfer are valuable in rational design of processing conditions. Heat transfer by conduction--the dominant mechanism of heat transfer in freeze-drying--is inefficient at the pressures used in freeze-drying. Steps should be taken to improve the thermal contact between the product and the shelf of the freeze dryer, such as eliminating metal trays from the drying process. Quantitation of the heat transfer coefficient for the geometry used is a useful way of assessing the impact of changes in the system such as elimination of product trays and changes in the vial. Because heat transfer by conduction through the vapor increases with increasing pressure, the commonly held point of view that "the lower the pressure, the better" is not true with respect to process efficiency. The optimum pressure for a given product is a function of the temperature at which freeze-drying is carried out, and lower pressures are needed at low product temperatures. The controlling resistance to mass transfer is almost always the resistance of the partially dried solids above the submination interface. This resistance can be minimized by avoiding fill volumes of more than about half the volume of the container. The development scientist should also recognize that very high concentrations of solute may not be appropriate for optimum freeze-drying, particularly if the resistance of the dried product layer increases sharply with concentration. Although the last 10 years has seen the publication of a significant body of literature of great value in allowing development scientists and engineers to "work smarter," there is still much work needed in both the science and the technology of freeze-drying. Scientific development is needed for improving analytical methodology for characterization of frozen systems and freeze-dried solids. A better understanding of the relationship between molecular mobility and reactivity is needed to allow accurate prediction of product stability at the intended storage temperature based on accelerated stability at higher temperatures. This requires that the temperature dependence of glass transition-associated mobili

Nail, Steven L; Jiang, Shan; Chongprasert, Suchart; Knopp, Shawn A

2002-01-01

101

Bidirectional quantitative force gradient microscopy  

NASA Astrophysics Data System (ADS)

Dynamic operation modes of scanning force microscopy based on probe resonance frequency detection are very successful methods to study force-related properties of surfaces with high spatial resolution. There are well-recognized approaches to measure vertical force components as well as setups sensitive to lateral force components. Here, we report on a concept of bidirectional force gradient microscopy that enables a direct, fast, and quantitative real space mapping of force component derivatives in both the perpendicular and a lateral direction. It relies solely on multiple-mode flexural cantilever oscillations related to vertical probe excitation and vertical deflection sensing. Exploring this concept we present a cantilever-based sensor setup and corresponding quantitative measurements employing magnetostatic interactions with emphasis on the calculation of mode-dependent spring constants that are the foundation of quantitative force gradient studies.

Reiche, Christopher F.; Vock, Silvia; Neu, Volker; Schultz, Ludwig; Büchner, Bernd; Mühl, Thomas

2015-01-01

102

Geothermal Gradients  

NSDL National Science Digital Library

In this problem set the students use two different equations to calculate a conductive geothermal gradient using a spreadsheet program like Excel. Once they have the geothermal gradient plotted, they are asked to experiment with and comment on the model by changing parameters (e.g. mantle heat flow, thermal conductivity). There is a mix of specific, fill in the blank questions and open-ended questions. This problem set helps develop quantitative problem solving skills using a spreadsheet as a tool, and forces students to think about thermal constraints during igneous and metamorphic processes.

Davidson, Cameron

103

Waves, circulation and vertical dependence  

NASA Astrophysics Data System (ADS)

Longuet-Higgins and Stewart (J Fluid Mech 13:481-504, 1962; Deep-Sea Res 11:529-562, 1964) and later Phillips (1977) introduced the problem of waves incident on a beach, from deep to shallow water. From the wave energy equation and the vertically integrated continuity equation, they inferred velocities to be Stokes drift plus a return current so that the vertical integral of the combined velocities was nil. As a consequence, it can be shown that velocities of the order of Stokes drift rendered the advective term in the momentum equation negligible resulting in a simple balance between the horizontal gradients of the vertically integrated elevation and wave radiation stress terms; the latter was first derived by Longuet-Higgins and Stewart. Mellor (J Phys Oceanogr 33:1978-1989, 2003a), noting that vertically integrated continuity and momentum equations were not able to deal with three-dimensional numerical or analytical ocean models, derived a vertically dependent theory of wave-circulation interaction. It has since been partially revised and the revisions are reviewed here. The theory is comprised of the conventional, three-dimensional, continuity and momentum equations plus a vertically distributed, wave radiation stress term. When applied to the problem of waves incident on a beach with essentially zero turbulence momentum mixing, velocities are very large and the simple balance between elevation and radiation stress gradients no longer prevails. However, when turbulence mixing is reinstated, the vertically dependent radiation stresses produce vertical velocity gradients which then produce turbulent mixing; as a consequence, velocities are reduced, but are still larger by an order of magnitude compared to Stokes drift. Nevertheless, the velocity reduction is sufficient so that elevation set-down obtained from a balance between elevation gradient and radiation stress gradients is nearly coincident with that obtained by the aforementioned papers. This paper includes four appendices. The first appendix demonstrates the numerical process by which Stokes drift is excluded from the turbulence stress parameterization in the momentum equation. A second appendix determines a bottom slope criterion for the application of linear wave relations to the derivation of the wave radiation stress. The third appendix explores the possibility of generalizing results by non-dimensionalization. The final appendix applies the basic theory to a problem introduced by Bennis and Ardhuin (J Phys Oceanogr 41:2008-2012, 2011).

Mellor, George

2013-04-01

104

The role of the geothermal gradient in the emplacement and replenishment of ground ice on Mars  

NASA Technical Reports Server (NTRS)

Knowledge of the mechanisms by which ground ice is emplaced, removed, and potentially replenished, are critical to understanding the climatic and hydrologic behavior of water on Mars, as well as the morphologic evolution of its surface. Because of the strong temperature dependence of the saturated vapor pressure of H2O, the atmospheric emplacement or replenishment of ground ice is prohibited below the depth at which crustal temperatures begin to monotonically increase due to geothermal heating. In contrast, the emplacement and replenishment of ground ice from reservoirs of H2O residing deep within the crust can occur by at least three different thermally-driven processes, involving all three phases of water. In this regard, Clifford has discussed how the presence of a geothermal gradient as small as 15 K/km can give rise to a corresponding vapor pressure gradient sufficient to drive the vertical transport of 1 km of water from a reservoir of ground water at depth to the base of the cryosphere every 10(exp 6) - 10(exp 7) years. This abstract expands on this earlier treatment by considering the influence of thermal gradients on the transport of H2O at temperatures below the freezing point.

Clifford, Stephen M.

1993-01-01

105

Barium titanate-polymer composites produced via directional freezing.  

PubMed

In this study, we use a freeze casting technique to construct ceramic-polymer composites in which the 2 phases are arranged in an electrically parallel configuration. By doing so, the composites exhibit dielectric constant (K) up to 2 orders of magnitude higher than that of composites with ceramic particles randomly dispersed in a polymer matrix. In this technique, an aqueous ceramic slurry was frozen unidirectionally to form ice platelets and ceramic aggregates that were aligned in the temperature gradient direction. Upon freeze-drying, the ice platelets sublimed and left the lamellar ceramic structure intact. The green ceramic body was fired to retain the microstructure, and then the space between ceramic lamellae was infiltrated with a polymer material. The finished composites exhibit the high dielectric constant (1000) of ferroelectric ceramics while maintaining the unique properties of polymer materials such as graceful failure, low dielectric loss, and high dielectric breakdown. PMID:19686976

Gorzkowski, Edward P; Pan, Ming-Jen

2009-08-01

106

Vertical patterns of the flora of seed plants in Dawei Mountain in Yunnan Province, Southwest China  

Microsoft Academic Search

Vertical gradients incorporate multiple resources gradients which vary continuously. Therefore, research on mountain floristic\\u000a patterns along vertical gradients is important to reveal regular patterns of the flora along environmental gradients and to\\u000a understand the changes in biodiversity along these gradients and their biological fitness. This study was designed to explore\\u000a the characteristics of the floral compositions and ecological significance of

Juan Wang; Qin-yan Ma; Fan Du; Yu-ming Yang

2007-01-01

107

Karen Johnson Freeze Fellowship Fund  

Microsoft Academic Search

The Karen Johnson Freeze Fellowship Fund is an initiative of the Foundation for the History of Technology (SHT) and the Society for the History of Technology (SHOT) to encourage research in the field of history of technology in Central, Southeastern, and Eastern Europe. The fund also wants to contribute to the internatio- nal dissemination of research results. The Karen Johnson

J. W. A. Korsten

108

Temperature gradients, not food resource gradients, affect growth rate of migrating Daphnia mendotae in Lake Michigan  

Microsoft Academic Search

Zooplankton production plays a critical role in the Great Lakes ecosystem, and vertical migration, which is exhibited by many zooplankton species, could affect production. We examined the effects of water temperature and food resource gradients on the growth rate of zooplankton undergoing vertical migration in Lake Michigan. In three laboratory experiments, juvenile Daphnia mendotae, native herbivorous cladocerans, were incubated for

Kevin L. Pangle; Scott D. Peacor

2010-01-01

109

Insect Cold-Hardiness: To Freeze or Not to Freeze Richard E. Lee, Jr.  

E-print Network

. The capacity to cold-harden is required for overwintering to survive long-term or short-term exposure to lowInsect Cold-Hardiness: To Freeze or Not to Freeze Richard E. Lee, Jr. BioScience, Vol. 39, No. 5 #12;Insect Cold-hardiness: To Freeze or Not to Freeze How insects survive low temperatures

Lee Jr., Richard E.

110

Freeze chromatography method and apparatus  

DOEpatents

A freeze chromatography method and apparatus are provided which enable separation of the solutes contained in a sample. The apparatus includes an annular column construction comprising cylindrical inner and outer surfaces defining an annular passage therebetween. One of the surfaces is heated and the other cooled while passing an eluent through the annular passageway so that the eluent in contact with the cooled surface freezes and forms a frozen eluent layer thereon. A mixture of solutes dissolved in eluent is passed through the annular passageway in contact with the frozen layer so that the sample solutes in the mixture will tend to migrate either toward or away the frozen layer. The rate at which the mixture flows through the annular passageway is controlled so that the distribution of the sample solutes approaches that at equilibrium and thus a separation between the sample solutes occurs. 3 figs.

Scott, C.D.

1987-04-16

111

Gravity gradient determination with tethered systems  

NASA Technical Reports Server (NTRS)

A detailed investigation of the Earth's gravity field is needed for application to modern solid earth and oceanic investigations. The use of gravity gradiometers presents a technique to measure the intermediate wavelength components of the gravity field. One configuration of a gradiometer involves a tethered pair of masses orbiting the Earth and stabilized by vertical gravity gradient of the earth. A mesurement of the tension in such a system, called the DUMBBELL system is described. It allows the determination of the vertical gradient of the anomalous component of the Earth's gravtiy field. Preliminary analysis of the dynamics, mechanization, expected signal levels and noise environment indicates that the Dumbbell system is feasible.

Kalaghan, P. M.; Colombo, G.

1978-01-01

112

Osmotic Adjustment and the Development of Freezing Resistance in Fragaria virginiana.  

PubMed

Cold temperature acclimation in strawberry (Fragaria virginiana) leaves apparently involves the alteration of cellular osmotic properties. Alterations in leaf osmotic potential were closely correlated with alterations in soluble carbohydrate content of the leaf tissue and changing temperatures. Leaf starch content was inversely related to soluble carbohydrate levels, suggesting that starch is a partial source of osmoticum during osmotic adjustment associated with cold temperature stress. Free amino acid changes were more closely linked to senescence and growth processes while changes in ion content suggested a rapid mobilization of solutes at the onset of freezing temperatures. This was supported by changes in whole plant gradients in leaf osmotic potential before and after exposure to freezing temperatures. In terms of freezing resistance and the role of osmotic adjustment in the development of resistance, it was found that of all leaves undergoing osmotic adjustment only the younger leaves survived, suggesting an age-dependent component to freezing resistance in leaves. Freezing resistance appears to involve alterations in several cellular properties that act in concert to confer a hardy state of the tissue. Although osmotic adjustment may be an important component of the final combination of cellular properties, this study indicates that solute accumulation does not function alone to confer freezing resistance. PMID:16663142

O'neill, S D

1983-08-01

113

Relationship between heat transfer parameters and the characteristic damage variables for the freezing of beef.  

PubMed

One of the most suitable parameters for relating the freezing rate to the volume of drip produced during the thawing of meat is the characteristic time, defined as the time necessary to reduce the temperature of the sample from -1·1°C (initial freezing point in beef) to -7°C (80% of the water frozen). However, as the freezing of beef in factories takes place with important temperature gradients, distributions of these characteristic times must be expected along the pieces of frozen meat. In order to relate these characteristic time distributions to heat transfer parameters under industrial freezing conditions, a mathematical model which simulates the freezing of beef is developed in this paper. The model establishes the heat transfer equations with simultaneous change of phase, taking into account the dependence of the thermal properties with the ice content and considering the anisotropy of the thermal conductivity according to the direction of the fibres. Boundary conditions include the possibility of thermal resistances in the refrigerated interphase. The model developed was compared with laboratory experiments performed under factory freezing conditions and showed a satisfactory agreement between theory and experiment. PMID:22055769

Mascheroni, R H; Calvelo, A

1980-08-01

114

Accurate pressure gradient calculations in hydrostatic atmospheric models  

NASA Technical Reports Server (NTRS)

A method for the accurate calculation of the horizontal pressure gradient acceleration in hydrostatic atmospheric models is presented which is especially useful in situations where the isothermal surfaces are not parallel to the vertical coordinate surfaces. The present method is shown to be exact if the potential temperature lapse rate is constant between the vertical pressure integration limits. The technique is applied to both the integration of the hydrostatic equation and the computation of the slope correction term in the horizontal pressure gradient. A fixed vertical grid and a dynamic grid defined by the significant levels in the vertical temperature distribution are employed.

Carroll, John J.; Mendez-Nunez, Luis R.; Tanrikulu, Saffet

1987-01-01

115

Characteristics of sugar surfactants in stabilizing proteins during freeze-thawing and freeze-drying.  

PubMed

Sugar surfactants with different alkyl chain lengths and sugar head groups were compared for their protein-stabilizing effect during freeze-thawing and freeze-drying. Six enzymes, different in terms of tolerance against inactivation because of freeze-thawing and freeze-drying, were used as model proteins. The enzyme activities that remained after freeze-thawing and freeze-drying in the presence of a sugar surfactant were measured for different types and concentrations of sugar surfactants. Sugar surfactants stabilized all of the tested enzymes both during freeze-thawing and freeze-drying, and a one or two order higher amount of added sugar surfactant was required for achieving protein stabilization during freeze-drying than for the cryoprotection. The comprehensive comparison showed that the C10-C12 esters of sucrose or trehalose were the most effective through the freeze-drying process: the remaining enzyme activities after freeze-thawing and freeze-drying increased at the sugar ester concentrations of 1-10 and 10-100 ?M, respectively, and increased to a greater extent than for the other surfactants at higher concentrations. Results also indicate that, when a decent amount of sugar was also added, the protein-stabilizing effect of a small amount of sugar ester through the freeze-drying process could be enhanced. PMID:24797557

Imamura, Koreyoshi; Murai, Katsuyuki; Korehisa, Tamayo; Shimizu, Noriyuki; Yamahira, Ryo; Matsuura, Tsutashi; Tada, Hiroko; Imanaka, Hiroyuki; Ishida, Naoyuki; Nakanishi, Kazuhiro

2014-06-01

116

Freeze-drying of mammalian sperm.  

PubMed

Long-term preservation of mammalian sperm at suprazero temperatures is desired to save storage and space costs as well as to facilitate transport of preserved samples. This can be accomplished by the freeze-drying of sperm samples. Although freeze-drying results in immotile and membrane-compromised sperm, intracytoplasmic sperm injection (ICSI) can be used to introduce such an immotile sperm into an oocyte and thus start the fertilization process. So far, it has been shown that improved freeze-drying protocols preserve chromosomal integrity and oocyte-activating factor(s) at 4 °C for several years and at ambient temperature for approximately 1 month, which permits shipping freeze-dried samples at ambient temperature. This chapter concisely reviews freeze-drying of mammalian sperm first and then presents a simple freeze-drying protocol. PMID:25428025

Keskintepe, Levent; Eroglu, Ali

2015-01-01

117

Development and design of sludge freezing beds  

SciTech Connect

The purpose of this study was to develop design criteria for a new sludge dewatering unit operation called a sludge freezing bed. This bed uses natural freeze-thaw to condition the sludge for dewatering. The total depth of sludge which can be frozen, thawed and dewatered by this process in a year is the main criterion needed for design. The essential features of a freezing bed which would optimize natural freeze-thaw were identified through a literature review and site visits. Several laboratory tests were conducted to assess the dewaterability of freeze-thaw conditioned sludge at various depths. Water treatment plant sludge and both anaerobically and aerobically digested wastewater sludges were used in these tests. Mathematical models for predicting the design depth were developed and validated with data from other sludge freezing operations. Values for the input parameters to the models were obtained from the literature or from laboratory and pilot-scale experiments.

Martel, C.J.

1987-01-01

118

Freeze-drying of spermatozoa.  

PubMed

Bull semen was diluted to a concentration of 2 X 10(8) cells/ml, cooled to 5 degrees C in 5 h, frozen in 0.025 ml spheres on the surface of solid carbon dioxide, and stored in liquid nitrogen. 50% by volume of the diluent was 325 m0sm Tes:N-tris (hydroxymethyl) methyl-2-amino ethane sulfonic acid titrated to pH 7.2 with 325 m0sm Tris:tris (hydroxymethyl) amino methane. The diluent also contained 30% by volume isotonic sodium citrate and 20% by volume egg yolk. The frozen spermatozoa were freeze-dried in 400 mg quantities in test tubes at -50 degrees C with a condenser at -196 degrees C. Moisture content was determined by weighing the individual samples before and after freeze-drying. Drying the samples for several days at 20 degrees C removed 868 mg from each gram of frozen material and this was considered the zero moisture level. Samples were stored at 20 degrees C or -196 degrees C after freeze-drying. The freezer-dried samples were rehydrated by flooding with five times their original volume of isotonic sodium citrate. Tests of the recovered spermatozoa included percentage motile cells, acrosome damage, enzyme release, protein denaturation, hypotonic swelling and fertility testing. Sperm motility decreased with dryness until it reached zero at 3% moisture. Acrosome morphology and enzyme release appeared normal down to 1% moisture. Preliminary results showed some fertility at all levels of dryness with -196 degrees C storage, and fertility at less than 1% moisture with 20 degrees C storage. Additional fertility testing is underway. PMID:1030432

Larson, E V; Graham, E F

1976-10-01

119

Freezing of stallion epididymal sperm.  

PubMed

Inseminations with frozen-thawed epididymal sperm have resulted in low-pregnancy rates of mares. If fertility of epididymal sperm could be improved, it would help to preserve genetic material from stallions that have suffered severe injuries, been castrated or have died. The aim of the present study was to investigate the effect of different extenders and pre-freezing addition of capacitation media on freezability of epididymal sperm and on storage at 5 degrees C for 24h. In experiment 1, epididymal sperm samples were diluted and subsequently frozen with three different extenders: Botu-Crio, EDTA-Lactose and INRA-82. Motility analysis using computer assisted sperm analyzer (CASA) demonstrated better motility for sperm in Botu-Crio than in the other extenders; EDTA-Lactose yielded better motility than INRA-82 on most evaluated parameters. There was no difference in membrane integrity among the studied extenders. From 18 inseminated mares, 12 (66%) were pregnant 15 days after AI with frozen-thawed epididymal sperm showing that Botu-Crio was able to maintain the fertility potential. In experiment 2, the effect of incubation of epididymal sperm before freezing in three capacitation media (Fert Talp, Sperm Talp, Talp+Progesterone), seminal plasma, or control was tested. Based on post-thaw motility evaluation by CASA, samples incubated in Sperm Talp showed better motility values. There were no differences in plasma or acrosomal membranes or in mitochondrial potential among groups. We concluded that Botu-Crio was better than the other extenders in the ability to preserve epididymal sperm and that pre-freeze addition of Sperm Talp was also beneficial. PMID:18556154

Papa, F O; Melo, C M; Fioratti, E G; Dell'aqua, J A; Zahn, F S; Alvarenga, M A

2008-09-01

120

Predicting freezing for some repulsive potentials.  

PubMed

We propose a simple method to approximately predict the freezing (fluid-solid) phase transition in systems of particles interacting via purely repulsive potentials. The method is based on the striking universality of the freezing curve for the model Yukawa and inverse-power-law interactions. This method is applied to draw an exemplary phase diagram of complex plasmas. We suggest that it can also be used to locate freezing transition in other substances with similar properties of interaction. PMID:20366260

Khrapak, S A; Morfill, G E

2009-12-18

121

Estimation of coastal density gradients  

NASA Astrophysics Data System (ADS)

Density gradients in coastal regions with significant freshwater input are large and variable and are a major control of nearshore circulation. However their measurement is difficult, especially where the gradients are largest close to the coast, with significant uncertainties because of a variety of factors - spatial and time scales are small, tidal currents are strong and water depths shallow. Whilst temperature measurements are relatively straightforward, measurements of salinity (the dominant control of spatial variability) can be less reliable in turbid coastal waters. Liverpool Bay has strong tidal mixing and receives fresh water principally from the Dee, Mersey, Ribble and Conwy estuaries, each with different catchment influences. Horizontal and vertical density gradients are variable both in space and time. The water column stratifies intermittently. A Coastal Observatory has been operational since 2002 with regular (quasi monthly) CTD surveys on a 9 km grid, an situ station, an instrumented ferry travelling between Birkenhead and Dublin and a shore-based HF radar system measuring surface currents and waves. These measurements are complementary, each having different space-time characteristics. For coastal gradients the ferry is particularly useful since measurements are made right from the mouth of Mersey. From measurements at the in situ site alone density gradients can only be estimated from the tidal excursion. A suite of coupled physical, wave and ecological models are run in association with these measurements. The models, here on a 1.8 km grid, enable detailed estimation of nearshore density gradients, provided appropriate river run-off data are available. Examples are presented of the density gradients estimated from the different measurements and models, together with accuracies and uncertainties, showing that systematic time series measurements within a few kilometres of the coast are a high priority. (Here gliders are an exciting prospect for detailed regular measurements to fill this gap.) The consequences for and sensitivity of circulation estimates are presented using both numerical and analytic models.

Howarth, M. J.; Palmer, M. R.; Polton, J. A.; O'Neill, C. K.

2012-04-01

122

Egg freezing: a breakthrough for reproductive autonomy?  

PubMed

This article describes the relatively new technology of freezing human eggs and examines whether egg freezing, specifically when it is used by healthy women as 'insurance' against age-related infertility, is a legitimate exercise of reproductive autonomy. Although egg freezing has the potential to expand women's reproductive options and thus may represent a breakthrough for reproductive autonomy, I argue that without adequate information about likely outcomes and risks, women may be choosing to freeze their eggs in a commercially exploitative context, thus undermining rather than expanding reproductive autonomy. PMID:18945249

Harwood, Karey

2009-01-01

123

Identification, analysis and monitoring of risks of freezing affecting aircraft flying over the Guadarrama Mountains (Spain)  

NASA Astrophysics Data System (ADS)

Freezing is one of the main causes of aircraft accidents registered over the last few decades. This means it is very important to be able to predict this situation so that aircraft can change their routes to avoid freezing risk areas. Also, by using satellites it is possible to observe changes in the horizontal and vertical extension of cloud cover likely to cause freezing in real time as well as microphysical changes in the clouds. The METEOSAT Second Generation (MSG) makes it possible to create different red-green-blue (RGB) compositions that provide a large amount of information associated with the microphysics of clouds, in order to identify super-cooled water clouds that pose a high risk of freezing to aircraft. During the winter of 2011/12 in the Guadarrama Mountains, in the centre of the Iberian Peninsula, a series of scientific flights (conducted by INTA) were organised in order to study the cloud systems that affected this region during the winter. On the flight of the 1st of February 2012, the aircraft was affected by freezing after crossing over a mountain ridge with supercooled large drops (SLD). Although freezing was not expected during that day's flight, the orography caused a series of mesoscale factors that led to the appearance of localised freezing conditions. By analysing this case, we have been able to conclude that the use of satellite images makes it possible to monitor the risk of freezing, especially under specific mesoscale circumstances. Acknowledgements S. Fernández-González acknowledges the grant supported from the FPU program (AP 2010-2093). This study was supported by the following grants: GRANIMETRO (CGL2010-15930); MICROMETEO (IPT-310000-2010-22). The authors would like to thank the INTA for its scientific flights.

Fernández-González, Sergio; Sánchez, José Luis; Gascón, Estíbaliz; Merino, Andrés; Hermida, Lucía; López, Laura; Marcos, José Luis; García-Ortega, Eduardo

2014-05-01

124

Food freezing with simultaneous surface dehydration: approximate prediction of freezing time  

Microsoft Academic Search

Freezing of unpackaged foods induces mass transfer in the form of surface ice sublimation, which in turn modifies heat transfer conditions. At present there are no simplified methods for predicting freezing times when surface dehydration occurs. This paper uses a previously developed model for the simulation of simultaneous heat and mass transfer during food freezing and storage to generate a

Laura A. Campañone; Viviana O. Salvadori; Rodolfo H. Mascheroni

2005-01-01

125

The effect of density gradients on hydrometers  

Microsoft Academic Search

Hydrometers are simple but effective instruments for measuring the density of liquids. In this work, we studied the effect of non-uniform density of liquid on a hydrometer reading. The effect induced by vertical temperature gradients was investigated theoretically and experimentally. A method for compensating for the effect mathematically was developed and tested with experimental data obtained with the MIKES hydrometer

Martti Heinonen; Sampo Sillanpää

2003-01-01

126

Split-sample comparison of directional and liquid nitrogen vapour freezing method on post-thaw semen quality in white rhinoceroses (Ceratotherium simum simum and Ceratotherium simum cottoni).  

PubMed

To increase the quality of cryopreserved sperm in white rhinoceros, the liquid nitrogen vapour (LN vapour) freezing and the multi-thermal gradient directional freezing methods were compared. Sixteen white rhinoceros (Ceratotherium simum sp.) were electro-ejaculated. Semen samples were diluted with cryoextender (Tris, lactose, egg-yolk, DMSO) and aliquoted into straws for LN vapour freezing, and glass hollow tubes for directional freezing. The sperm quality was evaluated before and after freezing by assessing the following parameters: motility, morphologic state, acrosomal integrity and plasma membrane function and integrity (i.e. sperm viability) as defined by the hypo-osmotic swelling. Directional freezing improved the sperm viability by 5.6% (p<0.005), progressive motility score by 34.7% and sperm motility index (SMI) by 8.1% (p<0.005) versus LN vapour freezing. When data was categorized into groups of low (<19%), moderate (20-39%) and high (>40%) percentages of morphologically normal, directional freezing (DF) resulted in 31.4% less abnormal acrosomes for the low quality group as well as 18.7% increase in intact acrosomes and 10.9% increase in motility for the high quality group compared to LN vapour freezing (LN) (p<0.01, p<0.03, p<0.01, respectively). LN showed a significant reduction in sperm head volume (5.7%, p<0.05) compared to the prefreeze; whereas, no significant reduction in head volume was demonstrated after DF. Several additives (xanthenuric acid, cytochalasin D, potassium, EDTA) to the basic cryoextender provided no significant improvement in spermatozoal survival after directional freezing. In conclusion, directional freezing proved to facilitate higher gamete survival compared to LN vapour freezing. This is especially effective in ejaculates of low sperm quality and is important in endangered species where high quality semen donors are often not accessible. These results suggest that directional freezing could be valuable particularly for species with limited freezability of spermatozoa. PMID:18775559

Reid, C E; Hermes, R; Blottner, S; Goeritz, F; Wibbelt, G; Walzer, C; Bryant, B R; Portas, T J; Streich, W J; Hildebrandt, T B

2009-01-15

127

Laboratory experiments on homogeneous and heterogeneous freezing  

NASA Astrophysics Data System (ADS)

The freezing temperature of the binary H_2SO_4 / H_2O solution droplets has been measured in dependence on their acid concentrations by means of acoustic levitation laboratory experiments. Pure solution droplets were analysed, in order to freeze the droplets as far as possible homogeneously. To induce heterogeneous freezing the droplets were contanimated with substances such as graphite, and the minerals kaolin and montmorillonite. The influence of these particles present in the liquid on the freezing temperature was measured. The size radii of the suspended droplets were between 0,4 - 1,1 mm and the concentration of the liquid acid solution was varied between 5 - 25 weight percent. The experiments show that the pure solution can be supercooled well below the equilibrium curve. Furthermore the presence of foreign particles within the solution increases the freezing temperature. The collected data reveal that the quality of the used particles as nuclei for freezing also depends on the particle material properties. Not only the presence of particles in the solution alone influences the freezing temperature of the droplets, but also the chemical composition and the surface charactaristics. In this contribution details of the experimental conditions are presented together with the measured freezing temperatures.

Borrmann, S.; Ettner, M.; Mitra, S. K.; Hannemann, A.; Sommer, C.; Peter, Th.

2003-04-01

128

Refrigeration Requirements for Ice Cream Freezing1  

Microsoft Academic Search

The heat removed from an ice cream mix during freezing is a function of several variables with composition predominating. This investigation compared experimental calorimetric results with predicted refrig- eration requirements. The predictions were obtained by adding the contributions of sensible heat of mix above the initial freezing point, sensible heat of unfrozen mix portion, latent heat and sensible heat of

D. R. Heldman; T. I. Hedrick

1970-01-01

129

Crosswind Shear Gradient Affect on Wake Vortices  

NASA Technical Reports Server (NTRS)

Parametric simulations with a Large Eddy Simulation (LES) model are used to explore the influence of crosswind shear on aircraft wake vortices. Previous studies based on field measurements, laboratory experiments, as well as LES, have shown that the vertical gradient of crosswind shear, i.e. the second vertical derivative of the environmental crosswind, can influence wake vortex transport. The presence of nonlinear vertical shear of the crosswind velocity can reduce the descent rate, causing a wake vortex pair to tilt and change in its lateral separation. The LES parametric studies confirm that the vertical gradient of crosswind shear does influence vortex trajectories. The parametric results also show that vortex decay from the effects of shear are complex since the crosswind shear, along with the vertical gradient of crosswind shear, can affect whether the lateral separation between wake vortices is increased or decreased. If the separation is decreased, the vortex linking time is decreased, and a more rapid decay of wake vortex circulation occurs. If the separation is increased, the time to link is increased, and at least one of the vortices of the vortex pair may have a longer life time than in the case without shear. In some cases, the wake vortices may never link.

Proctor, Fred H.; Ahmad, Nashat N.

2011-01-01

130

Fish With Nature's Anti-freeze  

NSDL National Science Digital Library

Using this material, students will discover that under special experimental conditions, fish have been observed functioning in ice-free cold salt water at a temperature of -6 degrees Centigrade. Research has found that these fish have eight types of anti-freeze molecules which bathe the interior surface of their skin, acting as a barrier to ice propagating in from outside. When the anti-freeze molecules are not present, ice filters through their skin at these temperatures and crystallizes (freezes) their blood and tissues. Students will experiment with lowering the freezing point of a substance, thus causing it to remain liquid at a temperature when it is normally solid. Students will compare their findings with facts about Antarctic ice-fish, which have bodily fluids that remain liquid at temperatures below freezing.

131

RRab Lyrae metallicity gradient in the Galactic bulge  

NASA Astrophysics Data System (ADS)

Aims: We revisit the presence and significance of the Galactic bulge metallicity gradients, using the OGlE-III RR Lyrae sample. Methods: We implemented a Monte Carlo simulation to account for observational uncertainties and systematic errors to test the presence, significance, and spatial variation of RR Lyr photometric metallicity gradients within the Galactic bulge. Furthermore, we take special consideration to identify and account for possible observational and statistical biases, which may introduce an apparent metallicity gradient into the sample. Results: We find a mean Galactic bulge RRab metallicity of -0.97 ± 0.29 dex, a global radial metallicity gradient of -0.016 ± 0.008 dex Kpc-1, and a global vertical metallicity gradient of -0.063 ± 0.013 dex Kpc-1. Furthermore, neither the global radial nor vertical gradients can be explained by random chance, unjustified extrapolation of the metallicity calibration law, or induced by a Malmquist bias.

Sans Fuentes, S. A.; De Ridder, J.

2014-11-01

132

Mimicking the quasi-random assembly of protein fibers in the dermis by freeze-drying method.  

PubMed

Freeze-drying is extensively used for fabrication of porous materials in tissue engineering and biomedical applications, due to its versatility and use of no toxic solvent. However, it has some significant drawbacks. Conventional freeze-drying technique leads to the production of heterogeneous porous structures with side orientated columnar pores. As the top and bottom surfaces of the sample are not in contact with similar environments, different rates of heat transfer in the surfaces and the temperature gradient across the sample establish the preferential direction of heat transfer. To achieve a scaffold with a desirable microstructure for skin tissue engineering, freeze-drying method was modified by controlling the rate of cooling and regulation of heat transfer across the sample during the freezing step. It could create a homogeneous porous structure with more equiaxed non-oriented pores. Freezing the polymeric solution in the aluminum mold enhanced pore interconnectivity relative to the polystyrene mold. Recrystallization process was discussed how to influence the mean pore size of the scaffold when the final freezing temperature varied. Higher final freezing temperature can easily provide the energy required for the recrystallization process, which lead to enlarged ice crystals and resulting pores. PMID:25687012

Ghaleh, Hakimeh; Abbasi, Farhang; Alizadeh, Mina; Khoshfetrat, Ali Baradar

2015-04-01

133

A Wind Tunnel Investigation on Ice Multiplication by Freezing of Waterdrops Falling at Terminal Velocity in Air  

Microsoft Academic Search

The freezing behavior of supercooled waterdrops nucleated by contact with clay particles was studied by means of an experimental setup re_cently described in detail by Pitter and Pruppacher (1973). This setup utilizes the UCLA cloud tunnel, which allows stable suspension of supercooled waterdrops and ice particles in a vertical airstream and also allows retrieval of the t¾ozen particles from the

H. R. Pruppacher; R. J. Schlamp

1975-01-01

134

Development and design of sludge freezing beds  

SciTech Connect

This study develops design criteria for a new sludge dewatering unit operation called a sludge freezing bed. This bed uses natural freeze-thaw to condition the sludge. The total depth of sludge that can be frozen, thawed and dewatered by this process in a year is the main criterion needed for design. Laboratory tests assessed the dewaterability of freeze-thaw conditioned water treatment plant sludge and both anaerobically and aerobically digested wastewater sludges at various depths. Mathematical models for predicting the design depth were developed; values for the input parameters to the models were obtained from the literature or from laboratory and pilot-scale experiments. The dewaterability tests indicated that the depth of sludge that can be applied is not limited by drainability. Up to 2.0 m of each sludge drained in minutes after freeze-thaw conditioning. Except for the aerobically digested sludge, the solids content after drainage is high enough to permit mechanical removal. The physical and thermal characteristics of frozen sludge were found to be equivalent to those of ice. An analysis of the freezing and thawing models reveals that the design of a freezing bed will depend on the duration and intensity of the freezing and thawing seasons.

Martel, C.J.

1988-12-01

135

Evaluation of anti-freeze viscosity modifier for potential external tank applications  

NASA Technical Reports Server (NTRS)

Viscosity modifiers and gelling agents were evaluated in combination with ethylene glycol and dimethyl sulfoxide water eutectics. Pectin and agarose are found to gel these eutectics effectively in low concentration, but the anti-freeze protection afforded by these compositions is found to be marginal in simulations of the intended applications. Oxygen vent shutters and vertical metallic surfaces were simulated, with water supplied as a spray, dropwise, and by condensation from the air.

Lynn, R. O. L.

1981-01-01

136

Hot big bang or slow freeze?  

NASA Astrophysics Data System (ADS)

We confront the big bang for the beginning of the universe with an equivalent picture of a slow freeze - a very cold and slowly evolving universe. In the freeze picture the masses of elementary particles increase and the gravitational constant decreases with cosmic time, while the Newtonian attraction remains unchanged. The freeze and big bang pictures both describe the same observations or physical reality. We present a simple “crossover model” without a big bang singularity. In the infinite past space-time is flat. Our model is compatible with present observations, describing the generation of primordial density fluctuations during inflation as well as the present transition to a dark energy-dominated universe.

Wetterich, C.

2014-09-01

137

Automated Assessment of Pavlovian Conditioned Freezing and Shock Reactivity in Mice Using the Video Freeze System  

PubMed Central

The Pavlovian conditioned freezing paradigm has become a prominent mouse and rat model of learning and memory, as well as of pathological fear. Due to its efficiency, reproducibility and well-defined neurobiology, the paradigm has become widely adopted in large-scale genetic and pharmacological screens. However, one major shortcoming of the use of freezing behavior has been that it has required the use of tedious hand scoring, or a variety of proprietary automated methods that are often poorly validated or difficult to obtain and implement. Here we report an extensive validation of the Video Freeze system in mice, a “turn-key” all-inclusive system for fear conditioning in small animals. Using digital video and near-infrared lighting, the system achieved outstanding performance in scoring both freezing and movement. Given the large-scale adoption of the conditioned freezing paradigm, we encourage similar validation of other automated systems for scoring freezing, or other behaviors. PMID:20953248

Anagnostaras, Stephan G.; Wood, Suzanne C.; Shuman, Tristan; Cai, Denise J.; LeDuc, Arthur D.; Zurn, Karl R.; Zurn, J. Brooks; Sage, Jennifer R.; Herrera, Gerald M.

2009-01-01

138

9 CFR 590.536 - Freezing operations.  

Code of Federal Regulations, 2010 CFR

... FOOD SAFETY AND INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE EGG PRODUCTS INSPECTION INSPECTION OF EGGS AND EGG PRODUCTS (EGG PRODUCTS INSPECTION ACT) Sanitary, Processing, and Facility Requirements § 590.536 Freezing...

2010-01-01

139

9 CFR 590.534 - Freezing facilities.  

Code of Federal Regulations, 2010 CFR

... FOOD SAFETY AND INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE EGG PRODUCTS INSPECTION INSPECTION OF EGGS AND EGG PRODUCTS (EGG PRODUCTS INSPECTION ACT) Sanitary, Processing, and Facility Requirements § 590.534 Freezing...

2010-01-01

140

Cell-encapsulating droplet formation and freezing  

NASA Astrophysics Data System (ADS)

Cell-encapsulating droplets are vitrified for biopreservation applications. The dynamics of micro-droplet formation and its freezing mechanism are analyzed numerically and experimentally. In addition, the microdroplet encapsulation technique is applied to cryopreserve cells.

Ryoun Youn, Jae; Seok Song, Young

2012-09-01

141

Surface freezing of n-octane nanodroplets  

NASA Astrophysics Data System (ADS)

Surface freezing, at temperatures up to a few degrees above the equilibrium melting point, has been observed for intermediate chain length (16? i? 50) n-alkanes [B. M. Ocko, X. Z. Wu, E. B. Sirota, S. K. Sinha, O. Gang and M. Deutsch, Phys. Rev. E, 1997, 55, 3164-3182]. Our recent experimental results suggest that surface freezing is also the first step when highly supercooled nanodroplets of n-octane crystallize. Our data yield surface and bulk nucleation rates on the order of ˜1015/cm2.s and ˜1022/cm3.s, respectively. Complementary molecular dynamics simulations also show that the surface of the droplet freezes almost immediately, and freezing of the remainder of the droplet progresses in a layer-by-layer manner.

Modak, Viraj; Pathak, Harshad; Thayer, Mitchell; Singer, Sherwin; Wyslouzil, Barbara

2013-05-01

142

Freeze Crystallization Processes: Efficiency by Flexibility  

E-print Network

Energy consumption in fractionating solutions by distillation and evaporation can be reduced by 70% to 90% by using freeze crystallization processes. The thermodynamic bases for the substantially lower energy requirements include: 1) The phase...

Heist, J. A.; Barron, T. S.

1983-01-01

143

Freezing tolerance of conifer seeds and germinants.  

PubMed

Survival after freezing was measured for seeds and germinants of four seedlots each of interior spruce (Picea glauca x engelmannii complex), lodgepole pine (Pinus contorta Dougl. ex Loud.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata Donn ex D. Donn). Effects of eight seed treatments on post-freezing survival of seeds and germinants were tested: dry, imbibed and stratified seed, and seed placed in a growth chamber for 2, 5, 10, 15, 20 or 30 days in a 16-h photoperiod and a 22/17 degrees C thermoperiod. Survival was related to the water content of seeds and germinants, germination rate and seedlot origin. After freezing for 3 h at -196 degrees C, dry seed of most seedlots of interior spruce, Douglas-fir and western red cedar had 84-96% germination, whereas lodgepole pine seedlots had 53-82% germination. Freezing tolerance declined significantly after imbibition in lodgepole pine, Douglas-fir and interior spruce seed (western red cedar was not tested), and mean LT50 of imbibed seed of these species was -30, -24.5 and -20 degrees C, respectively. Freezing tolerance continued to decline to a minimum LT50 of -4 to -7 degrees C after 10 days in a growth chamber for interior spruce, Douglas-fir and lodgepole pine, or after 15 days for western red cedar. Minimum freezing tolerance was reached at the stage of rapid hypocotyl elongation. In all species, a slight increase in freezing tolerance of germinants was observed once cotyledons emerged from the seed coat. The decrease in freezing tolerance during the transition from dry to germinating seed correlated with increases in seed water content. Changes in freezing tolerance between 10 and 30 days in the growth chamber were not correlated with seedling water content. Within a species, seedlots differed significantly in freezing tolerance after 2 or 5 days in the growth chamber. Because all seedlots of interior spruce and lodgepole pine germinated quickly, there was no correlation between seedlot hardiness and rate of germination. Germination rate and freezing tolerance of Douglas-fir and western red cedar seedlots was negatively correlated. There was a significant correlation between LT50 after 10 days in the growth chamber and minimum spring temperature at the location of seedlot origin for interior spruce and three seedlots of western red cedar, but no relationship was apparent for lodgepole pine and Douglas-fir. PMID:14652223

Hawkins, B J; Guest, H J; Kolotelo, D

2003-12-01

144

Freezing Characteristics of Rigid Plant Tissues (Development of Cell Tension during Extracellular Freezing).  

PubMed

The freezing characteristics and development of cell tension during extracellular freezing were examined in supercooling stem tissues of riverbank grapes (Vitis riparia) and cold-hardened leaves of live oak (Quercus virginiana) and mountain cranberry (Vaccinium vitis-idaea). Dormant stem xylem and pith tissues of river-bank grapes were resistant to freeze-induced dehydration above the homogeneous nucleation temperature, and they developed cell tension reaching a maximum of 27 MPa. Similarly, extracellular freezing induced cell tension in the leaves of live oak and mountain cranberry. Maximum cell tension in the leaves of live oak was 16.8 MPa and 8.3 MPa in the leaves of mountain cranberry. Following peak tensions in the leaves, a decline in the pressure was observed with progressive freezing. The results suggest that resistance to cell deformation during extracellular freezing due to cell-wall rigidity can lead to reduced cell dehydration and increased cell tension. A relationship to predict freezing behavior in plant tissues based on cell rigidity is presented. Based on cell-water relations and ice nucleation rates, cell-wall rigidity has been shown to effect the freezing characteristics of plant tissues, including freeze-induced dehydration, supercooling, and homogeneous nucleation temperatures. PMID:12226313

Rajashekar, C. B.; Burke, M. J.

1996-06-01

145

Simulation of high pressure freezing processes by enthalpy method  

Microsoft Academic Search

High pressure freezing processes such as pressure assisted freezing (PAF) and high pressure shift freezing (HPSF) are novel technologies that can be used to improve the quality of frozen foods. A one dimensional finite difference numerical model based on the enthalpy formulation was developed to simulate high pressure freezing of tylose, agar gel and potatoes. The Schwartzberg equation was used

T. Norton; A. Delgado; E. Hogan; P. Grace; Da-Wen Sun

2009-01-01

146

Reproducing Black's experiments: freezing point depression and supercooling of water  

Microsoft Academic Search

We carried out two historical experiments referred to by Joseph Black, one on freezing mixtures of salted water with ice and another on freezing supercooled pure water by a small disturbance. The results confirm thermodynamical predictions for the depression of the freezing point of salted water and for the latent heat of freezing of supercooled water respectively, which came after

J. Güémez; C. Fiolhais; M. Fiolhais

2002-01-01

147

Freezing and Thawing Human Embryonic Stem Cells  

NSDL National Science Digital Library

Lia Kent, of Stemgent's Research and Development team, has created this video to demonstrate "the proper technique for rapidly thawing hES cells from liquid nitrogen stocks, plating them on mouse embryonic feeder cells, and slowly freezing them for long-term storage." The video is also accompanied by protocols for thawing and freezing hES cells, discussion, materials, references, a forum for comments, and a PDF of the full text.

Kent, Lia

148

Solutions : FreezePtDepression (20 Variations)  

NSDL National Science Digital Library

It takes 6.86 kg of ethylene glycol (antifreeze) to decrease the freezing point of 6.50 kg of water to -25.0 o F (-31.7 o C). How much sodium chloride (NaCl) would it take to decrease the freezing point of 6.50 kg of water to -25.0 o F? (Assuming all the salt will dissolve in that amount of water.)

149

Freeze-fracture cytochemistry in cell biology.  

PubMed

The term freeze-fracture cytochemistry embraces a series of techniques which share the goal of chemical identification of the structural components viewed in freeze-fracture replicas. As one of the major features of freeze fracture is its ability to provide planar views of membranes, a major emphasis in freeze-fracture cytochemistry is to identify integral membrane proteins, study their spatial organization in the membrane plane, and examine their role in dynamic cellular processes. Effective techniques in freeze-fracture cytochemistry, of wide application in cell biology, are now available. These include fracture-label, label fracture, and the freeze-fracture replica immunolabeling technique (FRIL). In fracture-label, samples are frozen and fractured, thawed for labeling, and finally processed for viewing either by critical-point drying and platinum-carbon replication or by thin-section electron microscopy. Label-fracture involves immunogold labeling a cell suspension, processing as for standard freeze-fracture replication, and then examining the replica without removal of the cellular components. Of greatest versatility, however, is the FRIL technique, in which samples are frozen, fractured, and replicated with platinum-carbon as in standard freeze fracture, and then carefully treated with sodium dodecylsulphate (SDS) to remove all the biological material except a fine layer of molecules attached to the replica itself. Immunogold labeling of these molecules permits the distribution of identified components to be viewed superimposed upon high resolution planar views of replicated membrane structure, for both the plasma membrane and intracellular membranes in cells and tissues. Examples of how these techniques have contributed to our understanding of cardiovascular cell function in health and disease are discussed. PMID:18617035

Severs, Nicholas J; Robenek, Horst

2008-01-01

150

Vertical distribution of larval fish in pelagic waters of southwest Lake Michigan: Implications for growth, survival, and dispersal  

Microsoft Academic Search

Due to variability in biotic and abiotic conditions along a vertical gradient within aquatic systems, the vertical distribution of larval fish can profoundly affect their growth and survival. In large systems such as the Great Lakes, vertical distribution patterns also can influence dispersal and ultimately settlement events. The objective was to describe the diel vertical distribution of the larval fish

Benjamin T. Martin; Sergiusz J. Czesny; David H. Wahl

2011-01-01

151

Near-surface temperature gradient in a coastal upwelling regime  

NASA Astrophysics Data System (ADS)

oceanography, a near homogeneous mixed layer extending from the surface to a seasonal thermocline is a common conceptual basis in physics, chemistry, and biology. In a coastal upwelling region 3 km off the coast in the Mexican Pacific, we measured vertical density gradients with a free-rising CTD and temperature gradients with thermographs at 1, 3, and 5 m depths logging every 5 min during more than a year. No significant salinity gradient was observed down to 10 m depth, and the CTD temperature and density gradients showed no pronounced discontinuity that would suggest a near-surface mixed layer. Thermographs generally logged decreasing temperature with depth with gradients higher than 0.2 K m-1 more than half of the time in the summer between 1 and 3 m, 3 and 5 m and in the winter between 1 and 3 m. Some negative temperature gradients were present and gradients were generally highly variable in time with high peaks lasting fractions of hours to hours. These temporal changes were too rapid to be explained by local heating or cooling. The pattern of positive and negative peaks might be explained by vertical stacks of water layers of different temperatures and different horizontal drift vectors. The observed near-surface gradient has implications for turbulent wind energy transfer, vertical exchange of dissolved and particulate water constituents, the interpretation of remotely sensed SST, and horizontal wind-induced transport.

Maske, H.; Ochoa, J.; Almeda-Jauregui, C. O.; Ruiz-de la Torre, M. C.; Cruz-López, R.; Villegas-Mendoza, J. R.

2014-08-01

152

The effect of density gradients on hydrometers  

NASA Astrophysics Data System (ADS)

Hydrometers are simple but effective instruments for measuring the density of liquids. In this work, we studied the effect of non-uniform density of liquid on a hydrometer reading. The effect induced by vertical temperature gradients was investigated theoretically and experimentally. A method for compensating for the effect mathematically was developed and tested with experimental data obtained with the MIKES hydrometer calibration system. In the tests, the method was found reliable. However, the reliability depends on the available information on the hydrometer dimensions and density gradients.

Heinonen, Martti; Sillanpää, Sampo

2003-05-01

153

Preparation of porous scaffolds by using freeze-extraction and freeze-gelation methods.  

PubMed

Freeze-fixation and freeze-gelation methods are presented in this paper which can be used to prepare highly porous scaffolds without using the time and energy consuming freeze-drying process. The porous structure was generated during the freeze of a polymer solution, following which either the solvent was extracted by a non-solvent or the polymer was gelled under the freezing condition; thus, the porous structure would not be destructed during the subsequent drying stage. Compared with the freeze-drying method, the presented methods are time and energy-saving, with less residual solvent, and easier to be scaled up. Besides, the problem of formation of surface skin can be resolved and the limitation of using solvent with low boiling point can be lifted by the presented methods. With the freeze-extraction and freeze-gelation methods, porous PLLA, PLGA, chitosan and alginate scaffolds were successfully fabricated. In addition to the presentation of the morphologies of the fabricated scaffolds, preliminary data of cell culture on them are as well included in the present work. PMID:14580916

Ho, Ming-Hua; Kuo, Pei-Yun; Hsieh, Hsyue-Jen; Hsien, Tzu-Yang; Hou, Lein-Tuan; Lai, Juin-Yih; Wang, Da-Ming

2004-01-01

154

Freeze Tolerance of Nine Zoysiagrass Cultivars Using Natural Cold Acclimation and Freeze Chambers  

Technology Transfer Automated Retrieval System (TEKTRAN)

Winter hardiness of zoysiagrass (Zoysia spp.) cultivars is an important attribute throughout the biogeographical transition zone, thus the inability to withstand freezing temperatures may limit the use of these cultivars. The objective of this research was to determine the freeze tolerance (LT50) of...

155

Vertical axis wind turbines  

Microsoft Academic Search

A vertical wind turbine having vertical blades, each blade being connected intermediate its ends by a hinge to a support arm having a hub that enables the blades to rotate around a vertical axis, a tie wire connected to the blade at positions spaced along the blade from the hinge, said tie wire engaging a spring-loaded pulley disposed inwardly of

P. E. Delgado; B. A. Holmes

1981-01-01

156

Vertical Map Storage.  

ERIC Educational Resources Information Center

Discusses the superiority of vertical filing of maps in compressor-style vertical units over horizontal filing in drawers, emphasizing such factors as physical protection of the collection, ease of filing and retrieval, and efficient use of space. Disadvantages of vertical filing are also reviewed. (Author/JL)

Perry, Joanne M.

1982-01-01

157

Vertical axis wind turbines  

DOEpatents

A vertical axis wind turbine is described. The wind turbine can include a top ring, a middle ring and a lower ring, wherein a plurality of vertical airfoils are disposed between the rings. For example, three vertical airfoils can be attached between the upper ring and the middle ring. In addition, three more vertical airfoils can be attached between the lower ring and the middle ring. When wind contacts the vertically arranged airfoils the rings begin to spin. By connecting the rings to a center pole which spins an alternator, electricity can be generated from wind.

Krivcov, Vladimir (Miass, RU); Krivospitski, Vladimir (Miass, RU); Maksimov, Vasili (Miass, RU); Halstead, Richard (Rohnert Park, CA); Grahov, Jurij (Miass, RU)

2011-03-08

158

Directional freezing for large volume cryopreservation.  

PubMed

Cryopreservation is currently the method of choice when it comes to long-term preservation of viable biological samples. The process, and consequently the volume of the sample, however, is limited by the ability to achieve homogenous and efficient heat removal. When this cannot be properly managed, ice crystals will grow uncontrollably resulting in extensive damage to the cryopreserved cells or tissues. Directional freezing is a technique that can be used to precisely control heat dissipation and ice crystal growth and morphology even when freezing large volumes. The technique has been used over the years to cryopreserve spermatozoa, oocytes, embryos, tissue slices and whole organs from a wide variety of domestic and wild species. In this chapter a protocol for directional freezing of spermatozoa is described and its benefits and shortcomings are discussed. PMID:25428019

Saragusty, Joseph

2015-01-01

159

Stratospheric Polar Freezing Belt Causes Denitrification  

NASA Technical Reports Server (NTRS)

Trajectory cloud model calculations are presented to show that homogeneous freezing of nitric acid hydrates can produce a polar freezing belt in both hemispheres that can cause denitrification. While hydrate cloud microphysical properties are similar over both poles, the shorter persistence of clouds in the Arctic prevents the depth of the denitrified layers from growing beyond a few kilometers. The 1999-2000 Arctic winter is unique in showing a distinct denitrification profile with a depth of approx. 4.5 km that is nearly half as deep as that computed for a typical Antarctic winter.

Tabazadeh, A.; Jensen, E. J.; Toon, O. B.; Drdla, K.; Schoeberl, M. R.; Gore, Warren J. (Technical Monitor)

2001-01-01

160

Stereo transparency and the disparity gradient limit  

NASA Technical Reports Server (NTRS)

Several studies (Vision Research 15 (1975) 583; Perception 9 (1980) 671) have shown that binocular fusion is limited by the disparity gradient (disparity/distance) separating image points, rather than by their absolute disparity values. Points separated by a gradient >1 appear diplopic. These results are sometimes interpreted as a constraint on human stereo matching, rather than a constraint on fusion. Here we have used psychophysical measurements on stereo transparency to show that human stereo matching is not constrained by a gradient of 1. We created transparent surfaces composed of many pairs of dots, in which each member of a pair was assigned a disparity equal and opposite to the disparity of the other member. For example, each pair could be composed of one dot with a crossed disparity of 6' and the other with uncrossed disparity of 6', vertically separated by a parametrically varied distance. When the vertical separation between the paired dots was small, the disparity gradient for each pair was very steep. Nevertheless, these opponent-disparity dot pairs produced a striking appearance of two transparent surfaces for disparity gradients ranging between 0.5 and 3. The apparent depth separating the two transparent planes was correctly matched to an equivalent disparity defined by two opaque surfaces. A test target presented between the two transparent planes was easily detected, indicating robust segregation of the disparities associated with the paired dots into two transparent surfaces with few mismatches in the target plane. Our simulations using the Tsai-Victor model show that the response profiles produced by scaled disparity-energy mechanisms can account for many of our results on the transparency generated by steep gradients.

McKee, Suzanne P.; Verghese, Preeti

2002-01-01

161

Vortex Formation in Vertically Stratified Protoplanetary Disks  

NASA Astrophysics Data System (ADS)

A central problem of planet formation is how to form large planetesimals in a turbulent protoplanetary disk. Recent work suggests that MRI turbulence would excite such large velocities that the planetesimals would collisionally fragment rather than grow. The structure of chondritic meteorites indicates a gentle nebular environment where chondrules are sorted by size and cemented together rapidly. Although it is well established that anticyclones can concentrate particles that are weakly coupled to the gas in protoplanetary disks, the conditions required for the formation and long-time stability of anticyclones in a vertically stratified disk are still highly uncertain. Fully three dimensional fluid dynamic simulations of protoplanetary disks are computationally expensive when one requires a computational domain that is large compared to the vertical scale height of the disk. An alternative simulation approach is to use potential temperature as the vertical coordinate so that the equations of motion resemble the shallow water equations (Dowling et al. 1998). We have therefore modified a multilayer shallow water simulation code to model the formation of vortices in a vertically stratified protoplanetary disk with a radial entropy gradient. Vertical stratification of the disk is modeled by using multiple layers, where each layer has a different constant value of the entropy. By forcing a slope in the interfaces between the layers, we impose a radial entropy gradient in the disk. Radiative heating and cooling causes vertical mass exchange between adjacent constant entropy layers according to a Newton cooling formula. We find that the formation of anticyclones is robust, and that these vortices actively excite density waves, which in turn, transport angular momentum through the disk. Our simulations therefore yield new insights on how the dusty dead zones of protoplanetary disks can transport angular momentum through the disk by purely hydrodynamic processes. Support from NASA’s Origins of Solar Systems program is gratefully acknowledged.

Stewart, Glen R.

2013-10-01

162

Marine vertical cable multiple attenuation beyond up/down separation  

E-print Network

. 11. 2. 3 Influence of receiver sampling within the cable 11. 3 Pros and cons of F-K dip filtering and Osen's equations 11. 4 Why do we need to go beyond up/down separation?. . 11 . 13 . 13 . 18 . 19 24 25 III MULTIPLE ATTENUATION USING ISMA... summation. It consists in combining the pressure data and its vertical gradient. It assumes that the gradient of the pressure data can be computed from densely spaced receivers in the vertical cable. In this thesis, we will discuss the pros and the cons...

Tran, Andre

2012-06-07

163

Rupture of Cylindrical Ice Model and Tuna Fish during Freezing  

NASA Astrophysics Data System (ADS)

The gape and heave produced on the surface of tuna fish during freezing were confirmed by rupture of cylindrical type ice model. The results of experiment were shown as summarized below; 1) in case of restraining the progress of ice formation of model during freezing,any rupture was produced at not only slow freezing but also quick freezing. It was the same as tuna fish; 2) in case of closing surface of ice model covered perfectly by outside shell ice during slow freezing,it was not ruptured at not only ice model but also tuna fish. On the contrary it was cracked at quick freezing not only ice model but also tuna fish; 3) therefore it was confirmed that the rupture of tuna fish during freezing had been easy to produce at quick freezing.

Ogawa, Yutaka; Uno, Mitsuyo

164

47 CFR 64.1190 - Preferred carrier freezes.  

Code of Federal Regulations, 2010 CFR

...involve a charge to the subscriber. (e) Procedures for lifting preferred carrier freezes. All local exchange carriers who...a minimum, offer subscribers the following procedures for lifting a preferred carrier freeze: (1) A local exchange...

2010-10-01

165

Melting, freezing, and coalescence of gold nanoclusters  

Microsoft Academic Search

We present a detailed molecular-dynamics study of the melting, freezing, and coalescence of gold nanoclusters within the framework of the embedded-atom method. Concerning melting, we find the process first to affect the surface (``premelting''), then to proceed inwards. The curve for the melting temperature vs cluster size is found to agree reasonably well with predictions of phenomenological models based on

Laurent J. Lewis; Pablo Jensen; Jean-Louis Barrat

1997-01-01

166

Freezing of Water Droplet due to Evaporation  

NASA Astrophysics Data System (ADS)

In this study, the feasibility of cooling/freezing of phase change.. materials(PCMs) due to evaporation for cold storage systems was experimentally examined. A pure water was used as the test PCM, since the latent heat due to evaporation of water is about 7 times larger than that due to freezing. A water droplet, the diameter of which was 1-4 mm, was suspended in a test cell by a fine metal wire (O. D.= 100?m),and the cell was suddenly evacuated up to the pressure lower than the triple-point pressure of water, so as to enhance the evaporation from the water surface. Temperature of the droplet was measured by a thermocouple, and the cooling/freezing behavior and the temperature profile of the droplet surface were captured by using a video camera and an IR thermo-camera, respectively. The obtained results showed that the water droplet in the evacuated cell is effectively cooled by the evaporation of water itself, and is frozen within a few seconds through remarkable supercooling state. When the initial temperature of the droplet is slightly higher than the room temperature, boiling phenomena occur in the droplet simultaneously with the freezing due to evaporation. Under such conditions, it was shown that the degree of supercooling of the droplet is reduced by the bubbles generated in the droplet.

Satoh, Isao; Fushinobu, Kazuyoshi; Hashimoto, Yu

167

Strangeness and QGP freeze-out dynamics  

E-print Network

We compare chemical and thermal analysis of the SPS Pb--Pb results at $158A$ GeV, and present a first chemical analysis of RHIC results. We show how a combined analysis of several strange hadron resonances can be used in a study of freeze-out dynamics.

Johann Rafelski; Giorgio Torrieri; Jean Letessier

2001-04-13

168

Freezing in the Antarctic limpet, Nacella concinna.  

PubMed

The process of organismal freezing in the Antarctic limpet, Nacella concinna, is complicated by molluscan biology. Internal ice formation is, in particular, mediated by two factors: (a) the provision of an inoculative target for ice formation in the exposed mucus-secreting foot; and (b) osmoconformity to the marine environment. With regard to the first, direct observations of the independent freezing of pedal mucus support the hypothesis that internal ice formation is delayed by the mucal film. As to the second, ice nucleation parametrics of organismal tissue (head, midgut, gonad, foot) and mucus in both inter- and subtidal populations were characterized by high melting points (range=-4.61 to -6.29 degrees C), with only c.50% of a given sample osmotically active. At this stage it would be premature to ascribe a cryo-adaptive function to the mucus as the protective effects are more readily attributed to the physical properties of the secretion (i.e. viscosity) and their corresponding effects on the rate of heat transfer. As it is difficult to thermally distinguish between the freezing of mucus and the rest of the animal, the question as to whether it is tolerant of internal as well as external ice formation remains problematic, although it may be well suited to the osmotic stresses of organismal freezing. PMID:20599885

Hawes, T C; Worland, M R; Bale, J S

2010-08-01

169

Device and method for determining freezing points  

NASA Technical Reports Server (NTRS)

A freezing point method and device (10) are disclosed. The method and device pertain to an inflection point technique for determining the freezing points of mixtures. In both the method and device (10), the mixture is cooled to a point below its anticipated freezing point and then warmed at a substantially linear rate. During the warming process, the rate of increase of temperature of the mixture is monitored by, for example, thermocouple (28) with the thermocouple output signal being amplified and differentiated by a differentiator (42). The rate of increase of temperature data are analyzed and a peak rate of increase of temperature is identified. In the preferred device (10) a computer (22) is utilized to analyze the rate of increase of temperature data following the warming process. Once the maximum rate of increase of temperature is identified, the corresponding temperature of the mixture is located and earmarked as being substantially equal to the freezing point of the mixture. In a preferred device (10), the computer (22), in addition to collecting the temperature and rate of change of temperature data, controls a programmable power supply (14) to provide a predetermined amount of cooling and warming current to thermoelectric modules (56).

Mathiprakasam, Balakrishnan (Inventor)

1986-01-01

170

Hatchling Turtles Survive Freezing during Winter Hibernation  

Microsoft Academic Search

Hatchlings of the painted turtle (Chrysemys picta marginata) are unique as the only reptile and highest vertebrate life form known to tolerate the natural freezing of extracellular body fluids during winter hibernation. Turtles survived frequent exposures to temperatures as low as -6 degrees C to -8 degrees C in their shallow terrestrial nests over the 1987-1988 winter. Hatchlings collected in

Kenneth B. Storey; Janet M. Storey; Stephen P. J. Brooks; Thomas A. Churchill; Ronald J. Brooks

1988-01-01

171

FREEZE-FRAME: Fast Action Stress Relief.  

ERIC Educational Resources Information Center

Recent scientific research has proven that we can, not only manage our stress, we can even prevent it. Ways to achieve stress management are presented in this book. It details a method called FREEZE-FRAME, a process in which individuals mentally stop the chaos that surrounds them and then calmly contemplate their situation. The text opens with an…

Childre, Doc Lew

172

Monitoring freeze-thaw cycles along north-south Alaskan transects using ERS-1 SAR  

SciTech Connect

Monitoring freeze-thaw cycles of high latitude terrestrial ecosystems is useful for estimating the length of the growing season and annual productivity in the tundra and in boreal forests, for estimating potential damage to living plants due to frost drought, and for evaluating major changes in heat fluxes between land and atmosphere. At microwave frequencies, freezing results in a dramatic decrease of the dielectric constant of soil and vegetation, which significantly alters their radar scattering properties. In this article the authors investigate the possibility of monitoring freeze-thaw cycles of terrestrial ecosystems using C-band frequency (5.3 GHz), vertical transmit and receive polarization, synthetic-aperture radar (SAR) data gathered by the European Space Agency's Earth Remote Sensing satellite (ERS-1). Repeat-pass SAR images are mosaicked together along a north-south transect across Alaska, coregistered, and analyzed using a change detection algorithm that determines when the landscape freezes based on a decrease in radar backscatter greater than 3 dB relative to a known thawed, wet state of the landscape. Air-temperature recordings from seven airport weather stations and in situ observations from three monitored forest stands in interior Alaska concur to indicate SAR accurately maps frozen areas across the entire state. The technique does not apply to open water areas because calm water and frozen water are confused. Elsewhere, ERS-1 SAR could monitor thaw/freeze transitions of terrestrial ecosystems at the regional scale, at a spatial resolution of several tens of meters and independent of cloud cover and vegetation type.

Rignot, E.; Way, J.B. (California Inst. of Tech., Pasadena, CA (United States))

1994-08-01

173

Vertical seismic profile at Pike's Peak, Saskatchewan, Canada: turning rays and velocity anisotropy  

NASA Astrophysics Data System (ADS)

First-arrival traveltimes from a multi-offset vertical seismic profile (VSP) were used to estimate velocity anisotropy in the presence of a vertical velocity gradient. A numerical model consisting of two layers with vertical velocity gradients of 3.1 and 1.2 s-1, respectively, and global anisotropy parameters of ?=0.12±0.02 and ?=0.30±0.06 yielded first-arrival traveltimes that matched the observed traveltimes well. Shallow receivers were found to be crucial for constraining the vertical velocity field and for determining the parameters of anisotropy at depth.

Newrick, Rachel T.; Lawton, Don C.

2003-12-01

174

Aquaporin-Mediated Improvement of Freeze Tolerance of Saccharomyces cerevisiae Is Restricted to Rapid Freezing Conditions  

PubMed Central

Previous observations that aquaporin overexpression increases the freeze tolerance of baker's yeast (Saccharomyces cerevisiae) without negatively affecting the growth or fermentation characteristics held promise for the development of commercial baker's yeast strains used in frozen dough applications. In this study we found that overexpression of the aquaporin-encoding genes AQY1-1 and AQY2-1 improves the freeze tolerance of industrial strain AT25, but only in small doughs under laboratory conditions and not in large doughs under industrial conditions. We found that the difference in the freezing rate is apparently responsible for the difference in the results. We tested six different cooling rates and found that at high cooling rates aquaporin overexpression significantly improved the survival of yeast cells, while at low cooling rates there was no significant effect. Differences in the cultivation conditions and in the thawing rate did not influence the freeze tolerance under the conditions tested. Survival after freezing is determined mainly by two factors, cellular dehydration and intracellular ice crystal formation, which depend in an inverse manner on the cooling velocity. In accordance with this so-called two-factor hypothesis of freezing injury, we suggest that water permeability is limiting, and therefore that aquaporin function is advantageous, only under rapid freezing conditions. If this hypothesis is correct, then aquaporin overexpression is not expected to affect the leavening capacity of yeast cells in large, industrial frozen doughs, which do not freeze rapidly. Our results imply that aquaporin-overexpressing strains have less potential for use in frozen doughs than originally thought. PMID:15184134

Tanghe, An; Van Dijck, Patrick; Colavizza, Didier; Thevelein, Johan M.

2004-01-01

175

Avoid freeze-up of steam traps and their piping  

Microsoft Academic Search

This article addresses the problem of keeping steam traps free of ice in cold weather. The topics of the article include piping configurations and trap types that contribute to freezing, freeze damage, obstructions in piping, insulation of lines to retard freezing, common manifolds for heating of condensate, draining of low points, temperature-actuated devices, and water hammer damage.

OKeefe

1993-01-01

176

Avoid freeze-up of steam traps and their piping  

SciTech Connect

This article addresses the problem of keeping steam traps free of ice in cold weather. The topics of the article include piping configurations and trap types that contribute to freezing, freeze damage, obstructions in piping, insulation of lines to retard freezing, common manifolds for heating of condensate, draining of low points, temperature-actuated devices, and water hammer damage.

O'Keefe, W.

1993-12-01

177

Interspecific analysis of xylem freezing responses in Acer and Betula  

Technology Transfer Automated Retrieval System (TEKTRAN)

Temperate woody plants have evolved two methods for coping with seasonal exposure to sub-zero temperatures. Supercooling is a freeze-avoidance strategy where cells are able to resist the freezing of intracellular water below sub-zero temperatures. Non-supercooling is a freeze-tolerance strategy wh...

178

VISUALIZATION OF FREEZING PROGRESSION IN TURFGRASSES USING INFRARED VIDEO THERMOGRAPHY  

Technology Transfer Automated Retrieval System (TEKTRAN)

Freezing injury can be a significant problem in turfgrasses. Understanding how freezing develops and ramifies throughout the plant could assist in the development of improved management or screening processes for cultivar improvemen. The development of freezing injury is not well understand due pa...

179

Cryomechanical freezing. A model for the heat transfer process  

Microsoft Academic Search

Cryomechanical freezing consists of a two-step process. During the first step, the foodstuff gets into contact with a cryogenic refrigerant for a very short period of time, during which a thin frozen crust is formed. Immediately afterwards, freezing is completed in a conventional cold air-blast freezer. In this work, the heat transfer process during cryomechanical freezing was modelled using the

Miriam E Agnelli; Rodolfo H Mascheroni

2001-01-01

180

Modification of physical properties of freeze-dried rice  

NASA Technical Reports Server (NTRS)

Freeze cycling process consists of alternately freezing and thawing precooked rice for two cycles, rice is then frozen and freeze-dehydrated in vacuum sufficient to remove water from rice by sublimitation. Process modifies rice grain structure and porosity, enabling complete rehydration in one minute in hot water.

Huber, C. S.

1971-01-01

181

Influence of heterogeneous freezing on the microphysical and radiative properties of orographic cirrus clouds  

NASA Astrophysics Data System (ADS)

The influence of heterogeneous freezing on the microphysical and optical properties of orographic cirrus clouds has been simulated with the large eddy simulation model EULAG. Idealised simulations with different concentrations of ice nuclei (IN) in a dynamically dominated regime with high vertical velocities have been performed. Furthermore the temperature at cloud formation as well as the critical supersaturation for initiation of heterogenous freezing have been varied. The shortwave, longwave and net cloud forcing has been calculated under the assumption that the clouds form between 06:00 and 12:00 local time (LT) or between 12:00 and 18:00 LT. In general it can be seen that the onset of homogeneous freezing is shifted in time depending on the IN concentration, as part of the available water vapour is depleted before the critical threshold for homogeneous freezing is reached. Although the high vertical velocities in an orographic gravity wave lead to a strong adiabatic cooling followed by high ice supersaturations, even a small number concentration of IN of the order of 5 L-1 is able to strongly decrease the simulated ice crystal number burden (ICNB), ice water path (IWP) and optical depth of the cloud. In general, the ICNB, IWP and optical depth strongly decrease when the IN concentrations are increased from 0 to 50 L-1. The absolute values of the shortwave, longwave and net cloud forcing are also reduced with increasing IN concentrations. A cloud will produce a net warming or cooling depending on the IN concentration, the temperature and the time of day when the cloud forms. The clouds that form between 06:00 and 12:00 LT are mainly cooling, whereas the clouds with the same microphysical properties can lead to a warming when they form between 12:00 and 18:00 LT. In order to predict the radiative forcing of cirrus clouds it is therefore necessary to take the correct dynamical and thermodynamical processes as well as the possible existence and freezing threshold of heterogeneous IN into account, not only for low vertical velocities but also for dynamically dominated regimes like orographic cirrus.

Joos, H.; Spichtinger, P.; Reutter, P.; Fusina, F.

2014-07-01

182

Cryomicroscopic analysis of freezing in liver of the freeze-tolerant wood frog.  

PubMed

The technique of directional solidification coupled with low-temperature scanning electron microscopy was applied to analyze the freezing of liver slices from the freeze-tolerant frog Rana sylvatica. Micrographs of liver slices from 5 degrees C-acclimated frogs frozen on the directional stage to -7 degrees C showed continuous ice formed along an expanded vasculature with hepatocytes that were shrunken and virtually dehydrated. However, when frogs were given a survivable freezing exposure at -4 degrees C for 24 h, liver slices subsequently frozen in vitro at -7 degrees C were much less shrunken and the presence of intracellular ice crystals (formed when samples were plunged into liquid N2 before microscopy) demonstrated that ample free water remained in these hepatocytes at -7 degrees C. This reduced level of cell dehydration was correlated with the buildup of 280 +/- 61 mumol/g wet wt glucose as a cryoprotectant in liver during the -4 degrees C exposure in vivo. The study provides the first direct cytological analysis of the freezing process in an organ of a freeze-tolerant vertebrate and the first confirmation of the relationship between maintenance of a critical minimum cell volume and freezing survival by these animals. PMID:1636785

Storey, K B; Bischof, J; Rubinsky, B

1992-07-01

183

Gradient index metamaterials.  

PubMed

Metamaterials--artificially structured materials with tailored electromagnetic response--can be designed to have properties difficult or impossible to achieve with traditional materials fabrication methods. Here we present a structured metamaterial, based on conducting split ring resonators (SRRs), which has an effective index of refraction with a constant spatial gradient. We experimentally confirm the gradient by measuring the deflection of a microwave beam by a planar slab of the composite metamaterial over a range of microwave frequencies. The gradient index metamaterial may prove an advantageous alternative approach to the development of gradient index lenses and similar optics, especially at higher frequencies. In particular, the gradient index metamaterial we propose may be suited for terahertz applications, where the magnetic resonant response of SRRs has recently been demonstrated. PMID:15903607

Smith, D R; Mock, J J; Starr, A F; Schurig, D

2005-03-01

184

Vertical axis wind turbines  

Microsoft Academic Search

A vertical axis wind turbine comprises one or more aerofoil section blades attached to a support structure. The blade has at least one part thereof which is acted on by centrifugal forces as the blade rotates with the support structure and thereby caused to increase its angle of inclination to the vertical axis when the speed of rotation increases beyond

Musgrove

1978-01-01

185

Study of freezing-point depression of selected food extracts  

SciTech Connect

The phenomenon of freezing-point depression that accompanies the solute concentration of selected food extracts was investigated to reveal the characteristics of solid-liquid phase equilibrium. The freezing curves of various food extracts did not exhibit ideal solution behavior in the higher concentration range. The experimental data were fitted to new freezing-point depression equations by the method of nonlinear least squares, and the results clearly indicated that the calculated freezing points at various concentrations were in good agreement with the experimental data. Furthermore, by using the determined parameters, the freezing ratio and the activation coefficient were derived.

Tanaka, Fumihiko [Kagoshima Univ. (Japan). Dept. of Agricultural Systems Engineering; Murata, Satoshi; Habara, Kazuhiro; Amaratunga, K.S.P. [Kyushu Univ., Fukuoka (Japan). Dept. of Agricultural Engineering

1996-12-31

186

Gradient Driven Fluctuations  

NASA Technical Reports Server (NTRS)

We have worked with our collaborators at the University of Milan (Professor Marzio Giglio and his group-supported by ASI) to define the science required to measure gradient driven fluctuations in the microgravity environment. Such a study would provide an accurate test of the extent to which the theory of fluctuating hydrodynamics can be used to predict the properties of fluids maintained in a stressed, non-equilibrium state. As mentioned above, the results should also provide direct visual insight into the behavior of a variety of fluid systems containing gradients or interfaces, when placed in the microgravity environment. With support from the current grant, we have identified three key systems for detailed investigation. These three systems are: 1) A single-component fluid to be studied in the presence of a temperature gradient; 2) A mixture of two organic liquids to be studied both in the presence of a temperature gradient, which induces a steady-state concentration gradient, and with the temperature gradient removed, but while the concentration gradient is dying by means of diffusion; 3) Various pairs of liquids undergoing free diffusion, including a proteidbuffer solution and pairs of mixtures having different concentrations, to allow us to vary the differences in fluid properties in a controlled manner.

Cannell, David

2005-01-01

187

Freeze-out parameters: lattice meets experiment.  

PubMed

We present our results for ratios of higher order fluctuations of electric charge as functions of the temperature. These results are obtained in a system of 2+1 quark flavors at physical quark masses and continuum extrapolated. We compare them to preliminary data on higher order moments of the net electric charge distribution from the STAR collaboration. This allows us to determine the freeze-out temperature and chemical potential from first principles. We also show continuum-extrapolated results for ratios of higher order fluctuations of baryon number. These will allow us to test the consistency of the approach, by comparing them to the corresponding experimental data (once they become available) and thus, extracting the freeze-out parameters in an independent way. PMID:23971565

Borsányi, S; Fodor, Z; Katz, S D; Krieg, S; Ratti, C; Szabó, K K

2013-08-01

188

Freezing and melting water in lamellar structures.  

PubMed Central

The manner in which ice forms in lamellar suspensions of dielaidoylphosphatidylethanolamine, dielaidoylphosphatidylcholine, and dioleoylphosphatidylcholine in water depends strongly on the water fraction. For weight fractions between 15 and 9%, the freezing and melting temperatures are significantly depressed below 0 degree C. The ice exhibits a continuous melting transition spanning as much as 20 degrees C. When the water weight fraction is below 9%, ice never forms at temperatures as low as -40 degrees C. We show that when water contained in a lamellar lipid suspension freezes, the ice is not found between the bilayers; it exists as pools of crystalline ice in equilibrium with the bound water associated with the polar lipid headgroups. We have used this effect, together with the known chemical potential of ice, to measure hydration forces between lipid bilayers. We find exponentially decaying hydration repulsion when the bilayers are less than about 7 A apart. For larger separations, we find significant deviations from single exponential decay. PMID:7948683

Gleeson, J T; Erramilli, S; Gruner, S M

1994-01-01

189

Kinetic density functional theory of freezing  

NASA Astrophysics Data System (ADS)

A theory of freezing of a dense hard sphere gas is presented. Starting from a revised Enskog theory, hydrodynamic equations that account for non-local variations in the density but local variations in the flow field are derived using a modified Chapman Enskog procedure. These hydrodynamic equations, which retain structural correlations, are shown to be effectively a time dependent density functional theory. The ability of this theory to capture the solid liquid phase transition is established through analysis and numerical simulations.

Baskaran, Arvind; Baskaran, Aparna; Lowengrub, John

2014-11-01

190

Hadron Freeze-out and QGP Hadronization  

Microsoft Academic Search

Abundances and $m_\\\\bot$-spectra of strange and other hadronic particles emanating from central 158-200 A GeV reactions between nuclei are found to originate from a thermally equilibrated, deconfined source in chemical non-equilibrium. Physical freeze-out parameters and physical conditions (pressure, specific energy, entropy, and strangeness) are evaluated. Five properties of the source we obtain are as expected for direct hadron emission (hadronization)

Johann Rafelski; Jean Letessier

1999-01-01

191

Freeze-branding to permanently mark bats  

Microsoft Academic Search

We tested the effectiveness of freeze-branding as a permanent marking technique on 4 species of bats: Brazilian free-tailed bat (Tadarida brasiliensis), Townsend's big-eared bat (Corynorhinus townsendil), big brown bat (Eptesicus fuscus), and western small-footed myotis (Myotis ciliolabrum). Small copper branding irons (9.3 g and 15.6 g) were cooled in a mixture of dry ice and ethyl alcohol and applied to

Richard E. Sherwin; Shauna Haymond; Rebeccah Olsen

192

Disaggregating meteorites by automated freeze thaw  

NASA Astrophysics Data System (ADS)

An automated freeze-thaw (AFT) instrument for disaggregating meteorites is described. Meteorite samples are immersed in 18.2 M? water and hermetically sealed in a clean 30 ml Teflon vial. This vial and its contents are dipped between baths of liquid nitrogen and hot water over a number of cycles by a dual-stepper motor system controlled by LabView. Uniform and periodic intervals of freezing and thawing induce multiple expansions and contractions, such that cracks propagate along natural flaws in the meteorite for a sufficient number of AFT cycles. For the CR2 chondrite NWA801, the boundaries between different phases (i.e., silicates, metal, matrix) became progressively weaker and allowed for an efficient recovery of 500 individual chondrules and chondrule fragments spanning 0.2-4.7 mm diameters after 243 AFT cycles over 103.3 h. Further FT experiments on a basalt analog showed that the time required for freezing and thawing the same number of cycles can be reduced by a factor of ˜4.

Charles, Christopher R. J.

2011-06-01

193

Disaggregating meteorites by automated freeze thaw.  

PubMed

An automated freeze-thaw (AFT) instrument for disaggregating meteorites is described. Meteorite samples are immersed in 18.2 M? water and hermetically sealed in a clean 30 ml Teflon vial. This vial and its contents are dipped between baths of liquid nitrogen and hot water over a number of cycles by a dual-stepper motor system controlled by LabView. Uniform and periodic intervals of freezing and thawing induce multiple expansions and contractions, such that cracks propagate along natural flaws in the meteorite for a sufficient number of AFT cycles. For the CR2 chondrite NWA801, the boundaries between different phases (i.e., silicates, metal, matrix) became progressively weaker and allowed for an efficient recovery of 500 individual chondrules and chondrule fragments spanning 0.2-4.7 mm diameters after 243 AFT cycles over 103.3 h. Further FT experiments on a basalt analog showed that the time required for freezing and thawing the same number of cycles can be reduced by a factor of ?4. PMID:21721725

Charles, Christopher R J

2011-06-01

194

Atmospheric freeze drying assisted by power ultrasound  

NASA Astrophysics Data System (ADS)

Atmospheric freeze drying (AFD) is considered an alternative to vacuum freeze drying to keep the quality of fresh product. AFD allows continuous drying reducing fix and operating costs, but presents, as main disadvantage, a long drying time required. The application of power ultrasound (US) can accelerate AFD process. The main objective of the present study was to evaluate the application of power ultrasound to improve atmospheric freeze drying of carrot. For that purpose, AFD experiments were carried out with carrot cubes (10 mm side) at constant air velocity (2 ms-1), temperature (-10°C) and relative humidity (10%) with (20.5 kWm-3,USAFD) and without (AFD) ultrasonic application. A diffusion model was used in order to quantify the influence of US in drying kinetics. To evaluate the quality of dry products, rehydration capacity and textural properties were determined. The US application during AFD of carrot involved the increase of drying rate. The effective moisture diffusivity identified in USAFD was 73% higher than in AFD experiments. On the other hand, the rehydration capacity was higher in USAFD than in AFD and the hardness of dried samples did not show significant (p<0.05) differences. Therefore, US application during AFD significantly (p<0.05) sped-up the drying process preserving the quality properties of the dry product.

Santacatalina, J. V.; Cárcel, J. A.; Simal, S.; Garcia-Perez, J. V.; Mulet, A.

2012-12-01

195

Aquaporin Expression Correlates with Freeze Tolerance in Baker's Yeast, and Overexpression Improves Freeze Tolerance in Industrial Strains  

PubMed Central

Little information is available about the precise mechanisms and determinants of freeze resistance in baker's yeast, Saccharomyces cerevisiae. Genomewide gene expression analysis and Northern analysis of different freeze-resistant and freeze-sensitive strains have now revealed a correlation between freeze resistance and the aquaporin genes AQY1 and AQY2. Deletion of these genes in a laboratory strain rendered yeast cells more sensitive to freezing, while overexpression of the respective genes, as well as heterologous expression of the human aquaporin gene hAQP1, improved freeze tolerance. These findings support a role for plasma membrane water transport activity in determination of freeze tolerance in yeast. This appears to be the first clear physiological function identified for microbial aquaporins. We suggest that a rapid, osmotically driven efflux of water during the freezing process reduces intracellular ice crystal formation and resulting cell damage. Aquaporin overexpression also improved maintenance of the viability of industrial yeast strains, both in cell suspensions and in small doughs stored frozen or submitted to freeze-thaw cycles. Furthermore, an aquaporin overexpression transformant could be selected based on its improved freeze-thaw resistance without the need for a selectable marker gene. Since aquaporin overexpression does not seem to affect the growth and fermentation characteristics of yeast, these results open new perspectives for the successful development of freeze-resistant baker's yeast strains for use in frozen dough applications. PMID:12450819

Tanghe, An; Van Dijck, Patrick; Dumortier, Françoise; Teunissen, Aloys; Hohmann, Stefan; Thevelein, Johan M.

2002-01-01

196

Depth-Related Gradients of Viral Activity in Lake Pavin  

PubMed Central

High-resolution vertical sampling and determination of viral and prokaryotic parameters in a deep volcanic lake shows that in the absence of thermal stratification but within light, oxygen, and chlorophyll gradients, host availability empirically is prevalent over the physical and chemical environments and favors lytic over lysogenic “viral life cycles.” PMID:16751565

Colombet, J.; Sime-Ngando, T.; Cauchie, H. M.; Fonty, G.; Hoffmann, L.; Demeure, G.

2006-01-01

197

Inflorescences of alpine cushion plants freeze autonomously and may survive subzero temperatures by supercooling  

PubMed Central

Freezing patterns in the high alpine cushion plants Saxifraga bryoides, Saxifraga caesia, Saxifraga moschata and Silene acaulis were studied by infrared thermography at three reproductive stages (bud, anthesis, fruit development). The single reproductive shoots of a cushion froze independently in all four species at every reproductive stage. Ice formation caused lethal damage to the respective inflorescence. After ice nucleation, which occurred mainly in the stalk or the base of the reproductive shoot, ice propagated throughout that entire shoot, but not into neighboring shoots. However, anatomical ice barriers within cushions were not detected. The naturally occurring temperature gradient within the cushion appeared to interrupt ice propagation thermally. Consequently, every reproductive shoot needed an autonomous ice nucleation event to initiate freezing. Ice nucleation was not only influenced by minimum temperatures but also by the duration of exposure. At moderate subzero exposure temperatures (?4.3 to ?7.7 °C) the number of frozen inflorescences increased exponentially. Due to efficient supercooling, single reproductive shoots remained unfrozen down to ?17.4 °C (cooling rate 6 K h?1). Hence, the observed freezing pattern may be advantageous for frost survival of individual inflorescences and reproductive success of high alpine cushion plants, when during episodic summer frosts damage can be avoided by supercooling. PMID:21151351

Hacker, Jürgen; Ladinig, Ursula; Wagner, Johanna; Neuner, Gilbert

2011-01-01

198

A Four-Zone Furnace for Realization of Silver and Gold Freezing Points  

NASA Astrophysics Data System (ADS)

Recently, the Thermocouple Calibration Laboratory at the National Institute of Standards and Technology has used sodium heat-pipe furnaces for the realization of ITS-90 freezing points of aluminum, silver, and gold. When using a fixed-point cell mounted in a long silica-glass tube that extends to ambient temperature at the top of the furnace, we have observed significant thermal gradients along the well of the fixed-point cell, with the top of the well up to 0.1 K colder than the bottom. Furthermore, the heat-pipe lifetime is limited when used at the gold point (1064.18 °C) for more than a few hundred hours. To address these problems, we have designed and built a four-zone furnace based on a temperature-controlled, graphite isothermal block, suspended inside a three-zone tube furnace. The three-zone furnace is of a commercial design. The graphite block is enclosed in an alloy 600 (Inconel) can, allowing the graphite to be maintained in an argon atmosphere. The argon pressure is maintained at one atmosphere at all temperatures, thereby greatly reducing the stress on the can. Heaters in intimate contact with the can allow temperature control of the fourth inner zone to high accuracy. In this paper, the measured thermal stability and uniformity achieved with this furnace are presented. We also give results of test freezes of a silver freezing-point cell.

Ripple, D. C.; Garrity, K. M.; Meyer, C. W.

2003-09-01

199

Micromachined electrostatic vertical actuator  

DOEpatents

A micromachined vertical actuator utilizing a levitational force, such as in electrostatic comb drives, provides vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control. The micromachined electrostatic vertical actuator provides accurate movement in the sub-micron to micron ranges which is desirable in the phase modulation instrument, such as optical phase shifting. For example, compact, inexpensive, and position controllable micromirrors utilizing an electrostatic vertical actuator can replace the large, expensive, and difficult-to-maintain piezoelectric actuators. A thirty pound piezoelectric actuator with corner cube reflectors, as utilized in a phase shifting diffraction interferometer can be replaced with a micromirror and a lens. For any very precise and small amplitudes of motion` micromachined electrostatic actuation may be used because it is the most compact in size, with low power consumption and has more straightforward sensing and control options.

Lee, Abraham P. (Walnut Creek, CA); Sommargren, Gary E. (Santa Cruz, CA); McConaghy, Charles F. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

1999-10-19

200

Vertical comb array microactuators  

Microsoft Academic Search

A vertical actuator fabricated using a trench-refilled-with-polysilicon (TRiPs) process technology and employing an array of vertical oriented comb electrodes is presented. This actuator structure provides a linear drive to deflection characteristic and a large throw capability which are key features in many sensors, actuators and micromechanisms. The actuation principle and relevant theory is developed, including FastCap simulations for theoretical verification.

Arjun Selvakumar; Khalil Najafi

2003-01-01

201

Automated apparatus for producing gradient gels  

DOEpatents

Apparatus for producing a gradient gel which serves as a standard medium for a two-dimensional analysis of proteins, the gel having a density gradient along its height formed by a variation in gel composition, with the apparatus including first and second pumping means each including a plurality of pumps on a common shaft and driven by a stepping motor capable of providing small incremental changes in pump outputs for the gel ingredients, the motors being controlled, by digital signals from a digital computer, a hollow form or cassette for receiving the gel composition, means for transferring the gel composition including a filler tube extending near the bottom of the cassette, adjustable horizontal and vertical arms for automatically removing and relocating the filler tube in the next cassette, and a digital computer programmed to automatically control the stepping motors, arm movements, and associated sensing operations involving the filling operation.

Anderson, Norman L. (Clarendon Hills, IL)

1986-01-01

202

Automated apparatus for producing gradient gels  

DOEpatents

Apparatus for producing a gradient gel which serves as a standard medium for a two-dimensional analysis of proteins, the gel having a density gradient along its height formed by a variation in gel composition, with the apparatus including first and second pumping means each including a plurality of pumps on a common shaft and driven by a stepping motor capable of providing small incremental changes in pump outputs for the gel ingredients, the motors being controlled, by digital signals from a digital computer, a hollow form or cassette for receiving the gel composition, means for transferring the gel composition including a filler tube extending near the bottom of the cassette, adjustable horizontal and vertical arms for automatically removing and relocating the filler tube in the next cassette, and a digital computer programmed to automatically control the stepping motors, arm movements, and associated sensing operations involving the filling operation.

Anderson, N.L.

1983-11-10

203

Offshore Coastal Wind Speed Gradients: issues for the design and development of large offshore windfarms  

E-print Network

Offshore Coastal Wind Speed Gradients: issues for the design and development of large offshore@globalnet.co.uk · WEB SITE: www.multi-science.co.uk #12;Offshore Coastal Wind Speed Gradients: issues for the design-situ and remote sensing data from offshore wind farms in Denmark, are used to examine both horizontal and vertical

Pryor, Sara C.

204

Simultaneous measurements of wind shear and temperature gradient spectra in the stratosphere  

SciTech Connect

The authors present in this paper the first high resolution analysis of wind shears and temperature gradient measured over 25 m in the low stratosphere. Their power spectral densities deduced by two different methods show that for vertical wavelengths greater than 500 m the behaviors of the temperature and vertical velocity fluctuating field are significantly different from the saturated wave model predictions.

Barat, J.; Cot, C. (Service d'Aeronomie du CNRS, Verrieres le Buisson (France))

1989-10-01

205

Oxygen isotope fractionation during the freezing of seawater  

NASA Astrophysics Data System (ADS)

The dependence of oxygen isotope fractionation on ice growth rate during the freezing of seawater was investigated, focusing on columnar ice, based on laboratory experiments and field observations in McMurdo Sound, Antarctica, and the Sea of Okhotsk. The laboratory experiments were performed in a tank filled with seawater, with sea ice grown under calm conditions at various room temperatures, ranging from -5 to -20 oC, which correspond to the growth rates from 2.2×10-7 to 9.3×10-7 m/s. In McMurdo Sound, the ice growth rate was monitored using thermistor probes for first-year land-fast ice that grew to a thickness of about 2 m, ranging from 0.8×10-7 to 1.7×10-7 m/s. In the Sea of Okhotsk, the growth rate was modeled by coupling the thermodynamic properties of the ice sheet with in-situ meteorological data. Combining these data sets allowed, for the first time, examination of fractionation at a wide range of growth rates from 0.8×10-7 to 9.3×10-7 m/s. In the analysis attempts were made to validate a stagnant boundary-layer (SBL) fractionation model using two independent data sets. Particular interest was in optimizing the parameters used in Eicken's (1998) model that included the effect of brine entrapment during freezing, based on the SBL model. The results show that the slope of the curve showed an abrupt change at the growth rate around 2.0×10-7 m/s and that the optimum values of equilibrium pure ice fractionation factor and boundary layer thickness were significantly different between these two ranges of growth rates. Besides, for practical use the empirical formula which correlates growth rates with effective fractionation coefficient for the whole range of growth rates was also obtained. By applying it to a real sea ice sample collected in the Sea of Okhotsk, it was shown that the vertical profile of oxygen stable isotope fractionation in sea ice is useful to reveal the growth rate history of the sea ice.

Toyota, Takenobu; Smith, Inga; Gough, Alexander; Langhorne, Patricia; Leonard, Gregory; Van Hale, Robert; Mahoney, Andrew; Haskell, Timothy

2013-04-01

206

Vertical axis wind turbines  

SciTech Connect

A vertical wind turbine having vertical blades, each blade being connected intermediate its ends by a hinge to a support arm having a hub that enables the blades to rotate around a vertical axis, a tie wire connected to the blade at positions spaced along the blade from the hinge, said tie wire engaging a spring-loaded pulley disposed inwardly of the blades, the arrangement being such that when the angle of inclination of the blades to the vertical axis alters under the action of centrifugal force the tie wire exerts a force on the pulley opposing the spring force whereby as the turbine speeds up the blades will remain at a predetermined angle of inclination until the force exerted by the wire exceeds the force of the spring. One end of the tie wire can be connected to a position on one blade and connected to another position on another blade so that all of the blades adopt the same angle of inclination to the vertical axis.

Delgado, P.E.; Holmes, B.A.

1981-06-23

207

Impact of Nucleon Mass Shift on the Freeze Out Process  

E-print Network

The freeze out of a massive nucleon gas through a finite layer with time-like normal is studied. The impact of in-medium nucleon mass shift on the freeze out process is investigated. A considerable modification of the thermodynamical variables temperature, flow-velocity, energy density and particle density has been found. Due to the nucleon mass shift the freeze out particle distribution functions are changed noticeably in comparison with evaluations, which use vacuum nucleon mass.

S. Zschocke; L. P. Csernai; E. Molnar; J. Manninen; A. Nyiri

2005-10-27

208

Strange hadron resonances and QGP freeze-out  

Microsoft Academic Search

We describe how the abundance and distribution of hyperon resonances can be used to probe freeze-out conditions. We demonstrate that resonance yields allow us to measure the time scales of chemical and thermal freeze-outs. This should permit a direct differentiation between the explosive, sudden and staged adiabatic freeze-out scenarios. We then discuss the meaning of recent experimental results and suggest

G. Torrieri; J. Rafelski

2002-01-01

209

Freeze Tolerant Radiator for an Advanced EMU  

NASA Technical Reports Server (NTRS)

During an Extravehicular Activity (EVA), the astronaut s metabolic heat and the heat produced by the Portable Life Support Unit (PLSS) must be rejected. This heat load is currently rejected by a sublimator, which vents up to eight pounds of water each EVA. However, for advanced space missions of the future, water venting to space needs to be minimized because resupply impacts from earth will be prohibitive. If this heat load could be radiated to space from the PLSS, which has enough surface area to radiate most of the heat, the amount of water now vented could be greatly reduced. Unfortunately, a radiator rejects heat at a relatively constant rate, but the astronauts generate a variable heat load depending on how hard they are working. Without a way to vary the heat removal rate, the astronaut would experience cold discomfort or even frostbite. A proven method allowing a radiator to be turned-down is to sequentially allow tubes that carry the heat transfer fluid to the radiator to freeze. A drawback of current freezable radiators using this method is that they are far to heavy for use on a PLSS, because they use heavy construction to prevent the tubes from bursting as they freeze and thaw. This creates the need for a large radiator to reject most of the heat but with a lightweight tube that doesn t burst as it freezes and thaws. The new freezable radiator for the Extravehicular Mobility Unit (EMU) has features to accommodate the expansion of the radiator fluid when it freezes, and still have the high tube to fin conductance needed to minimize the number and weight of the tubes. Radiator fluid candidates are water and a propylene glycol-water mixture. This design maintains all materials within their elastic limits so that large volume changes can be achieved without breaking the tube. This concept couples this elastic expansion with an extremely lightweight, extremely high conductivity carbon fiber fin that can carry the heat needed to thaw a frozen tube. By using most of the exposed surface area of the PLSS as a radiator, the system can reject about 75% of the highest heat load, and reduce the loss of water through sublimation by a factor of four. The proposed radiator and a small water tank can be no heavier than the current system.

Copeland, Robert J.; Elliott, Jeannine; Weislogel, Mark

2004-01-01

210

Infrared thermal analysis of plant freezing processes.  

PubMed

Infrared thermal analysis is an invaluable technique to study the plant freezing process. In the differential mode infrared thermal analysis allows to localize ice nucleation and ice propagation in whole plants or plant samples at the tissue level. Ice barriers can be visualized, and supercooling of cells, tissues, and organs can be monitored. Places where ice masses are accommodated in the apoplast can be identified. Here, we describe an experimental setting developed in the laboratory in Innsbruck, give detailed information on the practical procedure and preconditions, and give additionally an idea of the problems that can be encountered and how they by special precautions may be overcome. PMID:24852631

Neuner, Gilbert; Kuprian, Edith

2014-01-01

211

The Ammonia Freeze Explosion (AFEX) process  

SciTech Connect

The Ammonia Freeze Explosion (AFEX) process treats lignocellulose with high-pressure liquid ammonia, and then explosively releases the pressure. The combined chemical effect (cellulose decrystallization) and physical effect (increased accessible surface area) dramatically increase lignocellulose susceptibility to enzymatic attack. There are many adjustable parameters in the AFEX process: ammonia loading, water loading, temperature, time, blowdown pressure, and number of treatments. The effect of these parameters on enzymatic susceptibility was explored for three materials: Coastal bermudagrass, bagasse, and newspaper. Nearly quantitative sugar yields were demonstrated for Coastal bermudagrass and bagasse, using a very low enzyme loading (5 IU/g). Newspaper proved to be much more resistant to enzymatic hydrolysis.

Holtzapple, M.T.; Jae-Hoon Jun; Ganesh Ashok; Patibandla, S.L.; Dale, B.E. [Texas A& M Univ., College Station, TX (United States)

1991-12-31

212

Uniform gradient expansions  

E-print Network

Cosmological singularities are often discussed by means of a gradient expansion that can also describe, during a quasi-de Sitter phase, the progressive suppression of curvature inhomogeneities. While the inflationary event horizon is being formed the two mentioned regimes coexist and a uniform expansion can be conceived and applied to the evolution of spatial gradients across the protoinflationary boundary. It is argued that conventional arguments addressing the preinflationary initial conditions are necessary but generally not sufficient to guarantee a homogeneous onset of the conventional inflationary stage.

Giovannini, Massimo

2014-01-01

213

Gradient enhanced spectroscopy  

NASA Astrophysics Data System (ADS)

This paper provides a brief overview of the personal recollections of the authors regarding their contributions to the introduction of shielded gradient technology into NMR spectroscopy during the late 1980s and early 1990s. It provides some background into early probe design and details some of the early technical progress with the use of shielded magnetic field gradients for coherence selection in high resolution NMR and describes the developments at General Electric, the National Institutes of Health, Georgetown University and Johns Hopkins University School of Medicine that ultimately led to this technology becoming commonplace in modern NMR spectroscopy. Most of this early technical work was published in the Journal of Magnetic Resonance.

van Zijl, Peter C.; Hurd, Ralph E.

2011-12-01

214

Food freezing with simultaneous surface dehydration: approximate prediction of weight loss during freezing and storage  

Microsoft Academic Search

Weight loss of unpackaged foods during freezing and later storage is an important quality and economic issue. It is originated on surface ice sublimation due to differences in water activity between food surface and the refrigerating air. Weight loss rate is determined by refrigerating conditions and product characteristics. The modelling of this phenomenon has merited very little attention; at present

Laura A. Campañone; Viviana O. Salvadori; Rodolfo H. Mascheroni

2005-01-01

215

Optical coherence tomography-based freeze-drying microscopy  

PubMed Central

A new type of freeze-drying microscope based upon time-domain optical coherence tomography is presented here (OCT-FDM). The microscope allows for real-time, in situ 3D imaging of pharmaceutical formulations in vials relevant for manufacturing processes with a lateral resolution of <7 ?m and an axial resolution of <5 ?m. Correlation of volumetric structural imaging with product temperature measured during the freeze-drying cycle allowed investigation of structural changes in the product and determination of the temperature at which the freeze-dried cake collapses. This critical temperature is the most important parameter in designing freeze-drying processes of pharmaceutical products. PMID:22254168

Mujat, Mircea; Greco, Kristyn; Galbally-Kinney, Kristin L.; Hammer, Daniel X.; Ferguson, R. Daniel; Iftimia, Nicusor; Mulhall, Phillip; Sharma, Puneet; Pikal, Michael J.; Kessler, William J.

2011-01-01

216

Vertical emitting aperture nanoantennas.  

PubMed

Herein we propose, theoretically investigate, and numerically demonstrate a compact design for a vertical emitter at a wavelength of 1.5 ?m based on nanophotonic aperture antennas coupled to a dielectric waveguide. The structure utilizes a plasmonic antenna placed above a Si3N4 waveguide with a ground plane for breaking the up-down symmetry and increasing the emission efficiency. Three-dimensional (3-D) finite-difference time-domain (FDTD) simulations reveal that up to 60% vertical emission efficiency is possible in a structure only four wavelengths long with a 3 dB bandwidth of over 300 nm. PMID:22555702

Yaacobi, Ami; Timurdogan, Erman; Watts, Michael R

2012-05-01

217

Freezing efficiency of Silver Iodide, ATD and Kaolinite in the contact freezing mode  

NASA Astrophysics Data System (ADS)

The importance of heterogeneous ice nucleation via contact freezing is one of the open questions in the atmospheric science community. In our laboratory, we built the Collision Nucleation CHamber (CLINCH) (Ladino et al. 2011) in which falling cloud droplets can collide with aerosol particles. In this study, contact freezing experiments are conducted to investigate the ice nucleation ability of silver iodide (AgI), kaolinite and Arizona Test Dust (ATD). Silver iodide has been known for its ice nucleation ability since 1940s (Vonnegut 1947) while kaolinite is a clay mineral and known to be a moderate ice nucleus. ATD is a commercial dust sample used by many groups to compare different setups. In CLINCH, size selected aerosol particles collide with water droplets of 80 µm diameter. With the extension in chamber length it is possible to vary the interaction time of ice nuclei and the droplets. Our experiments are performed between -10 to -36 ºC for various concentrations of ice nuclei and different interaction times. The frozen fraction of the droplets is determined using the custom-made depolarization detector IODE (Nicolet et al., 2010). Depolarization of linearly polarized incident laser light is used to determine the ratio of frozen droplets to all droplets. Frozen fractions of the three particle types with different residence times from CLINCH will be presented in this study. The number of collisions between a single droplet and several aerosol particles can be calculated by accounting for the theoretical collision efficiency at the experimental conditions in order to obtain the freezing efficiency (frozen fraction/number of collisions). Nucleation efficiency is compared with other contact freezing studies and with immersion freezing

Nagare, Baban; Marcolli, Claudia; Stetzer, Olaf; Lohmann, Ulrike

2014-05-01

218

Ultrastructure of the echinoderm cuticle after fast-freezing/freeze substitution and conventional chemical fixations.  

PubMed

The cuticles of the pedicellaria primordia in the sea urchin Paracentrotus lividus and of the tube foot disk in the sea star Asterias rubens were preserved by different methods, viz., glutaraldehyde fixation followed by osmium tetroxide postfixation, glutaraldehyde-ruthenium red fixation followed by osmium tetroxide-ruthenium red postfixation, and two fast freezing / freeze substitution methods (FF/FS). The gross ultrastructure of the cuticle as well as the influence of the preservation method on this ultrastructure were identical for the two tissues studied. The cuticle ultrastructure was poorly preserved after glutaraldehyde fixation / osmium tetroxide postfixation. Its preservation was improved after ruthenium red was added in the fixative and postfixative, but the best preservation was consistently achieved using FF/FS. Both low-pressure freezing (plunge freezing) and high-pressure freezing were tested, the latter giving seemingly better results. With these methods, the cuticle appeared to be composed of a proximal lower cuticle, an intermediate upper cuticle, and a distal fuzzy coat. In particular, cryoimmobilization methods emphasized or revealed the occurrence of a well-developed fibrillar lower cuticle in the pedicellaria, the complexity of the upper cuticle which consisted of several zones, and the importance of the usually poorly preserved fuzzy coat that is actually the thickest layer of the cuticle. These observations bring new insights on the functions of the cuticle, and particularly of the fuzzy coat. According to its preservation characteristics, the fuzzy coat presumably consists mostly of proteoglycans. This composition could give it shock absorption and antifouling properties. Furthermore, its important thickness also implies that molecules detected by the short sensory cilia must diffuse through and could be selected by the fuzzy coat. PMID:10738319

Ameye, L; Hermann, R; DuBois, P; Flammang, P

2000-03-15

219

Effect of repeated freeze-thaw cycles on geographically different populations of the freeze-tolerant worm Enchytraeus albidus (Oligochaeta).  

PubMed

Freeze-tolerant organisms survive internal ice formation; however, the adaptations to repeated freeze-thaw cycles are often not well investigated. Here we report how three geographically different populations of Enchytraeus albidus (Germany, Iceland and Svalbard) respond to three temperature treatments - constant thawed (0°C), constant freezing (-5°C) and fluctuating temperature (0 to -5°C) - over a period of 42 days. Survival varied between treatments and populations such that enchytraeids from arctic locations had a higher survival following prolonged freeze periods compared with temperate populations. However, enchytraeids from temperate locations had the same survival rate as arctic populations when exposed to repeated freeze-thaw events. Across all populations, metabolic rate decreased markedly in frozen animals (-5°C) compared with thawed controls (0°C). This decrease is likely due to the lower temperature of frozen animals, but also to the transition to the frozen state per se. Animals exposed to repeated freeze-thaw events had an intermediate metabolic rate and freeze-thaw events were not associated with pronounced excess energetic costs. Overwintering under either condition was not associated with a decrease in lipid content; however, during exposure to constant freezing and repeated freeze-thaw events there was a noticeable decrease in carbohydrate stores over time. Thus, animals exposed to constant freezing showed a decrease in glycogen stores, while both glucose and glycogen content decreased over time when the organisms were exposed to repeated freezing. The results therefore suggest that carbohydrate resources are important as a fuel for E. albidus during freezing whereas lipid resources are of marginal importance. PMID:25214492

Fisker, Karina Vincents; Holmstrup, Martin; Malte, Hans; Overgaard, Johannes

2014-11-01

220

RESPONSES TO FREEZING EXPOSURE OF HATCHLING TURTLES TRACHEMYS SCRIPTA ELEGANS: FACTORS INFLUENCING THE DEVELOPMENT OF FREEZE TOLERANCE BY REPTILES  

Microsoft Academic Search

Summary Hatchling red-eared turtles Trachemys (=Pseudemys) scripta elegans (Wied) from a Louisiana population display a significant ability to withstand the freezing of extracellular body fluids. All animals survived at least 2 h of freezing at -2.5 or —4°C. At -2.5°C, survival declined to 50% after 6h of freezing and no animals recovered after 24 h or longer, when mean ice

THOMAS A. CHURCHILL; KENNETH B. STOREY

221

Method and apparatus for determining vertical heat flux of geothermal field  

DOEpatents

A method and apparatus for determining vertical heat flux of a geothermal field, and mapping the entire field, is based upon an elongated heat-flux transducer (10) comprised of a length of tubing (12) of relatively low thermal conductivity with a thermopile (20) inside for measuring the thermal gradient between the ends of the transducer after it has been positioned in a borehole for a period sufficient for the tube to reach thermal equilibrium. The transducer is thermally coupled to the surrounding earth by a fluid annulus, preferably water or mud. A second transducer comprised of a length of tubing of relatively high thermal conductivity is used for a second thermal gradient measurement. The ratio of the first measurement to the second is then used to determine the earth's thermal conductivity, k.sub..infin., from a precalculated graph, and using the value of thermal conductivity thus determined, then determining the vertical earth temperature gradient, b, from predetermined steady state heat balance equations which relate the undisturbed vertical earth temperature distributions at some distance from the borehole and earth thermal conductivity to the temperature gradients in the transducers and their thermal conductivity. The product of the earth's thermal conductivity, k.sub..infin., and the earth's undisturbed vertical temperature gradient, b, then determines the earth's vertical heat flux. The process can be repeated many times for boreholes of a geothermal field to map vertical heat flux.

Poppendiek, Heinz F. (LaJolla, CA)

1982-01-01

222

Fundamental Boiling and RP-1 Freezing Experiments  

NASA Technical Reports Server (NTRS)

This paper describes results from experiments performed to help understand certain aspects of the MC-1 engine prestart thermal conditioning procedure. The procedure was constrained by the fact that the engine must chill long enough to get quality LOX at the LOX pump inlet but must be short enough to prevent freezing of RP-1 in the fuel pump. A chill test of an MC-1 LOX impeller was performed in LN2 to obtain data on film boiling, transition boiling and impeller temperature histories. The transition boiling data was important to the chill time so a subsequent experiment was performed chilling simple steel plates in LOX to obtain similar data for LOX. To address the fuel freezing concern, two experiments were performed. First, fuel was frozen in a tray and its physical characteristics were observed and temperatures of the fuel were measured. The result was physical characteristics as a function of temperature. Second was an attempt to measure the frozen thickness of RP-1 on a cold wall submerged in warm RP-1 and to develop a method for calculating that thickness for other conditions.

Goode, Brian; Turner, Larry D. (Technical Monitor)

2001-01-01

223

Continuous freezing condenser for phthalic anhydride. [Patented  

SciTech Connect

The increasing outputs of plastics and polymer materials necessitate correspondingly larger outputs of various organic monomers. Phthalic anhydride is one of the source products for organic synthesis. Phthalic anhydride is made in the coking industry by the catalytic vapor-phase oxidation of naphthalene. The product is difficult to isolate from the reaction mixture leaving the static-bed catalytic reactors, since the volume of gases and vapors to be cooled is very large and the phthalic anhydride concentration in the mixture is very low. Continuous freezing condensers have been developed, in which the gas stream is cooled by counterflow contact with a stream of solid granular material on which the phthalic anhydride is condensed. One serious drawback is the need to expend large amounts of heat to remelt the phthalic anhydride crystals. The low strength of the granulated solid substrate leads to dust formation in operation, and the dust contaminates the product. We have developed a condenser in which the freezing and remelting stages take place on metal balls in the same unit and the heat is derived from the incoming reaction mixture. Accordingly, units of large capacity can be constructed giving a higher product yield and lowering the heat consumption in the remelting stage.

Korobchanskii, V.I.; Grebenyuk, A.F.; Korobchanskii, Yu.V.; Il'in, A.P.

1981-01-01

224

Vertical electron transistor (VET) in GaAs with a heterojunction (AlGaAs-GaAs) cathode  

NASA Astrophysics Data System (ADS)

The successful fabrication of submicrometer channel length (0.75 micron) and gate length (0.15 micron) vertical electron transistors with AlGaAs cathodes is reported. Lack of electron velocity enhancement has been proposed to be due to high operating channel temperatures, and low temperature measurements were hindered by carrier freeze-out.

Mishra, U.; Maki, P. A.; Wendt, J. R.; Schaff, W.; Kohn, E.; Eastman, L. F.

1984-02-01

225

Manipulating the Gradient  

ERIC Educational Resources Information Center

We introduce a cooperative learning, group lab for a Calculus III course to facilitate comprehension of the gradient vector and directional derivative concepts. The lab is a hands-on experience allowing students to manipulate a tangent plane and empirically measure the effect of partial derivatives on the direction of optimal ascent. (Contains 7…

Gaze, Eric C.

2005-01-01

226

Freezing stress response in woody tissues observed using low-temperature scanning electron microscopy and freeze substitution techniques.  

PubMed

The objective of the current research was to examine the response of woody plant tissues to freezing stress by using scanning electron microscopy (SEM). Nonsupercooling species red osier dogwood (Cornus stolonifera Michx.), weeping willow (Salix babylonica L.), and corkscrew willow (Salix matsudana Koidz. f. tortuosa Rehd.) survived freezing stress as low as -60 degrees C. Cell collapse of ray parenchyma cells of these species was expected but did not occur. It was concluded that ray parenchyma cells of these species do not fit into either the supercooling or extracellular freezing classifications. Tissues from flowering dogwood (Cornus florida L.), apple (Malus domestica Borkh. cv "Starking III"), red oak (Quercus rubra L.), scarlet oak (Quercus coccinea Muench.), and red ash (Fraxinus pennsylvanica Marsh) were confirmed as supercooling species, and did not survive exposures below -40 degrees C. Ray parenchyma cells of these species did not collapse in response to freezing stress, as was expected. Cell collapse along the margins of voids were observed in bark of all seven species. Voids were the result of extracellular ice crystals formed in the bark during exposure to freezing stress. Tissues prepared by freeze substitution techniques were found to be adequately preserved when compared to those prepared by conventional fixation and low temperature SEM techniques. A freezing protocol for imposing freezing stress at temperatures lower than experienced naturally in the area where the study was conducted was developed that produced responses comparable to those observed in specimens collected in the field during natural freezing events. PMID:16668066

Malone, S R; Ashworth, E N

1991-03-01

227

Probability of freezing in the freeze-avoiding beetle larvae Cucujus clavipes puniceus (Coleoptera: Cucujidae) from interior Alaska.  

PubMed

Freeze-avoiding insects must resist freezing or die. A suite of adaptations to low temperatures, including the production of antifreeze proteins, colligative antifreezes (polyols), and dehydration allows most individuals to prevent freezing below the lowest ambient temperatures experienced in situ; however, there can be a wide variance in the minimum temperatures that individuals of freeze-avoiding species reach before freezing. We used logistic regression to explore factors that affect this variance and to estimate the probability of freezing in larvae of the freeze-avoiding beetle Cucujus clavipes puniceus. We hypothesized that water content ?0.5 mg mg(-1) dry mass would lead to deep supercooling (avoidance of freezing below -58°C). We found a significant interaction between water content and ambient below-snow temperature and a significant difference between individuals collected from two locations in Alaska: Wiseman and Fairbanks. Individuals collected in Wiseman deep supercooled with greater water content and to a greater range of ambient temperatures than individuals collected in Fairbanks, leading to significantly different lethal water contents associated with 50% probability of freezing. PMID:21550349

Sformo, T; McIntyre, J; Walters, K R; Barnes, B M; Duman, J

2011-08-01

228

Aiding Vertical Guidance Understanding  

NASA Technical Reports Server (NTRS)

A two-part study was conducted to evaluate modern flight deck automation and interfaces. In the first part, a survey was performed to validate the existence of automation surprises with current pilots. Results indicated that pilots were often surprised by the behavior of the automation. There were several surprises that were reported more frequently than others. An experimental study was then performed to evaluate (1) the reduction of automation surprises through training specifically for the vertical guidance logic, and (2) a new display that describes the flight guidance in terms of aircraft behaviors instead of control modes. The study was performed in a simulator that was used to run a complete flight with actual airline pilots. Three groups were used to evaluate the guidance display and training. In the training, condition, participants went through a training program for vertical guidance before flying the simulation. In the display condition, participants ran through the same training program and then flew the experimental scenario with the new Guidance-Flight Mode Annunciator (G-FMA). Results showed improved pilot performance when given training specifically for the vertical guidance logic and greater improvements when given the training and the new G-FMA. Using actual behavior of the avionics to design pilot training and FMA is feasible, and when the automated vertical guidance mode of the Flight Management System is engaged, the display of the guidance mode and targets yields improved pilot performance.

Feary, Michael; McCrobie, Daniel; Alkin, Martin; Sherry, Lance; Polson, Peter; Palmer, Everett; McQuinn, Noreen

1998-01-01

229

Construction & Therapy Vertical Integration  

E-print Network

Construction & Therapy Vertical Integration Pilot Project Collaboration Partners Department to work with a local population to realize direct construction. Titled Construction & Therapy the studio will be documented and developed as a therapeutic exercise. The production of the welcome building will be delivered

Strathclyde, University of

230

The Effect of Freezing on the Dynamics of Dike Propagation  

NASA Astrophysics Data System (ADS)

When magma-filled cracks propagate close to the Earth's surface, host rock temperature is well below the magma solidus. Solidification and substantial increase in magma viscosity can occur, are most pronounced near the propagating tip and can slow or arrest the progress of the dike. Quantitative analysis is required to predict whether a given dike will reach the surface to erupt and the duration of the precursor sequence. This challenging physical problem mixes elasticity, fracture mechanics, heat transfer and fluid flow with strong rheologic gradients due to cooling. We describe the propagation behaviour of such a hydraulic fracture using a laboratory experimental system of a crack fed by a constant flux of paraffin wax from a source reservoir propagating through gelatin below the solidus of the wax. The most novel behaviour is an intermittent regime in which cracks periodically stop advancing due to solidification, then swell at constant length while enhancing the elastic deformation in the surrounding solid before propagation resumes. We present a physical model of this system, based on different balances between driving and resistive forces: the former are elastic stress and liquid buoyancy, the latter are fracture resistance at the tip and viscous resistance. The fracture is represented as a head, behind the propagating tip, connected to the source by a narrow tail. Freezing of liquid close to the tip is assumed to enhance fracture resistance according to a cooling law, and propagation is assumed to occur only when the stress exerted by the liquid is enough to overcome fracture resistance. Our theoretical model reproduces intermittent propagation with precise behaviour depending on the controlling stress balances, and provides a tool to analyse natural systems.

Tait, S.; Taisne, B.

2007-12-01

231

SFT: a consistent checkpointing algorithm with shorter freezing time  

Microsoft Academic Search

SFT algorithm, a consistent checkpointing algorithm with shorter freezing time, is presented in this paper. SFT is able to implement fault-tolerance in distributed systems. The features of the algorithm include shorter freezing time, lower overhead, and simple roll backing. To reduce checkpointing time, a special control message (Munblock) is used to ensure that at any given time a process can

Xiaohui Wei; Jiubin Ju

1998-01-01

232

Glassy freezing in relaxor ferroelectric lead magnesium niobate  

Microsoft Academic Search

The freezing process in lead magnesium niobate (PMN) has been investigated by measurements of the frequency-dependent complex dielectric constant and its third harmonic component. The linear complex dielectric susceptibility was analyzed by a temperature-frequency plot in order to determine the temperature dependence of the dielectric relaxation spectrum and to identify the freezing temperature. It was found that both the shape

Adrijan Levstik; Zdravko Kutnjak; Cene Filipic; Rasa. Pirc

1998-01-01

233

Understanding freeze stress in biological tissues: thermodynamics of interfacial water  

Technology Transfer Automated Retrieval System (TEKTRAN)

A thermodynamic approach to distinguish forms of freeze energy that injure plants as the temperature decreases is developed. The pattern resulting from this analysis dictated the sequence of thermal requirements for water to exist as an independent state. Improvement of freezing tolerance in biolo...

234

Logistic Regression Analysis of Freezing Tolerance in Winter Wheat  

Technology Transfer Automated Retrieval System (TEKTRAN)

Four winter wheat cultivars, Eltan, Froid, Kestrel, and Tiber, were cold-acclimated for five weeks and then tested for freezing tolerance in a programmable freezer. The temperature of the soil was recorded every two minutes and the freezing episode was described as five parameters: the minimum temp...

235

Membranes and MEAs at Freezing Temperatures Thomas A. Zawodzinski, Jr.  

E-print Network

Membranes and MEAs at Freezing Temperatures Thomas A. Zawodzinski, Jr. Case Western Reserve #12;5 Conductivity of Membrane at Low T Conductivity drops dramatically below freezing point Note that ~ 6 and increasingly tightly bound as decreases #12;9 DSC thermograms of PEFC membranes (water

236

ORIGINAL PAPER Effect of freezing-thawing on nitrogen mineralization  

E-print Network

ORIGINAL PAPER Effect of freezing-thawing on nitrogen mineralization in vegetation soils of four the effect of freezing-thawing on nitrogen (N) mineralization of four vegetation soils from typical . Soil nitrogen mineralization . Soil water content . Temperate forest . Changbai Mountain 1 Introduction

Boyer, Edmond

237

Freeze After Writing Quasi-Deterministic Parallel Programming with LVars  

E-print Network

Freeze After Writing Quasi-Deterministic Parallel Programming with LVars Lindsey Kuper Indiana: shared memory locations whose semantics are defined in terms of an application- specific lattice. Writes the ability to "freeze" and then read the contents of an LVar directly. Second, we add the ability to attach

Menczer, Filippo

238

FREEZE-FRACTURIN G IN ULTRAHIGH VACUUM AT -196  

Microsoft Academic Search

Conventional freeze-etching is carried out in a vacuum of -10 -~ torr and at a specimen temperature of -100~ The relatively poor topographic resolution of most freeze-etch replicas, and the lack of complementarity of morphological details in double replicas have been thought to be caused by structural distortions during fracturing, and radiation damage during replication. Both phenomena can be reduced

HEINZ GROSS; ENIS BAS; HANS MOOR

239

Research Review Falls and Freezing of Gait in Parkinson's Disease  

E-print Network

Society Key words: Parkinson's disease; falls; gait; freezing; patho- physiology; treatment In recentResearch Review Falls and Freezing of Gait in Parkinson's Disease: A Review of Two Interconnected that are common in Parkinson's disease. Both symp- toms are often incapacitating for affected patients

240

Effect of Freezing on Bacteriologic Culturing of Mastitis Milk Samples  

Microsoft Academic Search

The objective was to determine the effect of freezing and length of freezing in a commercial freezer on the qualitative results of bacteriologic culturing of milk collected from glands of cows with clini- cal or subclinical inwamammary infec- tions. A total of 182 milk samples from cows with clinical mastiffs and 55 milk samples of cows with subclinical mastiffs were

Y. H. Schukken; J. A. H. Smit; F. J. Grommers; D. Vandegeer; A. Brand

1989-01-01

241

Stopping biological time: The freezing of living cells  

SciTech Connect

The fundamental physical-chemical events that occur during the freezing and thawing of cells are outlined and the manner in which cell permeability determines the response of the cell to freezing is discussed both in terms of physical response and in terms of survival. 40 refs., 12 figs.

Mazur, P.

1987-01-01

242

Increasing Freezing Tolerance: Kinase Regulation of ICE1.  

PubMed

Cold temperatures trigger the ICE1-CBF-COR transcriptional cascade in plants, which reprograms gene expression to increase freezing tolerance. In this issue of Developmental Cell, Ding et al. (2015) report that cold stress activates the protein kinase OST1 to phosphorylate and thereby stabilize and stimulate ICE1. This enhances plant tolerance to freezing temperatures. PMID:25669879

Zhan, Xiangqiang; Zhu, Jian-Kang; Lang, Zhaobo

2015-02-01

243

7 CFR 305.18 - Quick freeze treatment schedule.  

Code of Federal Regulations, 2010 CFR

...false Quick freeze treatment schedule. 305.18...Continued) ANIMAL AND PLANT HEALTH INSPECTION SERVICE...AGRICULTURE PHYTOSANITARY TREATMENTS Quick Freeze Treatments...during the 48-hour treatment period, but the temperature...States or its territorial waters, or is otherwise...

2010-01-01

244

Optimum Parameters for Freeze-Drying Decellularized Arterial Scaffolds  

PubMed Central

Decellularized arterial scaffolds have achieved success in advancing toward clinical use as vascular grafts. However, concerns remain regarding long-term preservation and sterilization of these scaffolds. Freeze drying offers a means of overcoming these concerns. In this study, we investigated the effects of various freeze-drying protocols on decellularized porcine carotid arteries and consequently, determined the optimum parameters to fabricate a stable, preserved scaffold with unaltered mechanical properties. Freeze drying by constant slow cooling to two final temperatures ((Tf), ?10°C and ?40°C) versus instant freezing was investigated by histological examination and mechanical testing. Slow cooling to Tf= ?10°C produced a stiffer and less distensible response than the non freeze-dried scaffolds and resulted in disruption to the collagen fibers. The mechanical response of Tf= ?40°C scaffolds demonstrated disruption to the elastin network, which was confirmed with histology. Snap freezing scaffolds in liquid nitrogen and freeze drying to Tf= ?40°C with a precooled shelf at ?60°C produced scaffolds with unaltered mechanical properties and a histology resembling non-freeze-dried scaffolds. The results of this study demonstrate the importance of optimizing the nucleation and ice crystal growth/size to ensure homogenous drying, preventing extracellular matrix disruption and subsequent inferior mechanical properties. This new manufacturing protocol creates the means for the preservation and sterilization of decellularized arterial scaffolds while simultaneously maintaining the mechanical properties of the tissue. PMID:23614758

Sheridan, William S.; Duffy, Garry P.

2013-01-01

245

Physically Accurate Soil Freeze-Thaw Processes in a Global Land Surface Scheme  

NASA Astrophysics Data System (ADS)

Transfer of energy and moisture in frozen soil, and hence the active layer depth, are strongly influenced by the soil freezing curve which specifies liquid moisture content as a function of temperature. However, the curve is typically not represented in global land surface models, with less physically-based approximations being used instead. In this work, we develop a physically accurate model of soil freeze-thaw processes, suitable for use in a global land surface scheme. We incorporated soil freeze-thaw processes into an existing detailed model for the transfer of heat, liquid water and water vapor in soils, including isotope diagnostics - Soil-Litter-Iso (SLI, Haverd & Cuntz 2010), which has been used successfully for water and carbon balances of the Australian continent (Haverd et al. 2013). A unique feature of SLI is that fluxes of energy and moisture are coupled using a single system of linear equations. The extension to include freeze-thaw processes and snow maintains this elegant coupling, requiring only coefficients in the linear equations to be modified. No impedance factor for hydraulic conductivity is needed because of the formulation by matric flux potential rather than pressure head. Iterations are avoided which results in the same computational speed as without freezing. The extended model is evaluated extensively in stand-alone mode (against theoretical predictions, lab experiments and field data) and as part of the CABLE global land surface scheme. SLI accurately solves the classical Stefan problem of a homogeneous medium undergoing a phase change. The model also accurately reproduces the freezing front, which is observed in laboratory experiments (Hansson et al. 2004). SLI was further tested against observations at a permafrost site in Tibet (Weismüller et al. 2011). It reproduces seasonal thawing and freezing of the active layer to within 3 K of the observed soil temperature and to within 10% of the observed volumetric liquid soil moisture. Model-data fusion suggests that model performance is improved when the relatively high thermal conductivity of the ice phase is accounted for. However, the permafrost site is very gravelly so that the model equations for thermal conductivity are at the edge of applicability. The freezing-soil formulation is tested in the presence of snow, using measurements at an orchard site in Idaho. The model reproduces well observed snow-water equivalents and soil temperatures. However, it is highly sensitive to snow emissivity and maximum liquid content of the snow, leading both to modified refreezing of melted water. It is possible that the model would benefit from 1-2 more snow layers to permit simulation of density and temperature gradients in the snow-pack. SLI was run globally on 1°x1° grid as the soil part of the land surface scheme CABLE. We could therefore demonstrate that this detailed and physically-realistic formulation is fast enough to be a feasible alternative to the much simpler default soil-scheme in CABLE. References Hansson et al. (2004) Vadose Zone J 3, 693ff Haverd & Cuntz (2010) J Hydro 388, 434ff Haverd et al. (2013) Biogeosci 10, 2011ff Weismüller et al. (2011) The Cryosphere 5, 741ff

Cuntz, Matthias; Haverd, Vanessa

2014-05-01

246

Physically Accurate Soil Freeze-Thaw Processes in a Global Land Surface Scheme  

NASA Astrophysics Data System (ADS)

Transfer of energy and moisture in frozen soil, and hence the active layer depth, are strongly influenced by the soil freezing curve which specifies liquid moisture content as a function of temperature. However, the curve is typically not represented in global land surface models, with less physically-based approximations being used instead. In this work, we develop a physically accurate model of soil freeze-thaw processes, suitable for use in a global land surface scheme. We incorporated soil freeze-thaw processes into an existing detailed model for the transfer of heat, liquid water and water vapor in soils, including isotope diagnostics - Soil-Litter-Iso (SLI, Haverd & Cuntz 2010), which has been used successfully for water and carbon balances of the Australian continent (Haverd et al. 2013). A unique feature of SLI is that fluxes of energy and moisture are coupled using a single system of linear equations. The extension to include freeze-thaw processes and snow maintains this elegant coupling, requiring only coefficients in the linear equations to be modified. No impedance factor for hydraulic conductivity is needed because of the formulation by matric flux potential rather than pressure head. Iterations are avoided which results in the same computational speed as without freezing. The extended model is evaluated extensively in stand-alone mode (against theoretical predictions, lab experiments and field data) and as part of the CABLE global land surface scheme. SLI accurately solves the classical Stefan problem of a homogeneous medium undergoing a phase change. The model also accurately reproduces the freezing front, which is observed in laboratory experiments (Hansson et al. 2004). SLI was further tested against observations at a permafrost site in Tibet (Weismüller et al. 2011). It reproduces seasonal thawing and freezing of the active layer to within 3 K of the observed soil temperature and to within 10% of the observed volumetric liquid soil moisture. Model-data fusion suggests that model performance is improved when the relatively high thermal conductivity of the ice phase is accounted for. However, the permafrost site is very gravelly so that the model equations for thermal conductivity are at the edge of applicability. The freezing-soil formulation is tested in the presence of snow, using measurements at an orchard site in Idaho. The model reproduces well observed snow-water equivalents and soil temperatures. However, it is highly sensitive to snow emissivity and maximum liquid content of the snow, leading both to modified refreezing of melted water. It is possible that the model would benefit from 1-2 more snow layers to permit simulation of density and temperature gradients in the snow-pack. SLI was run globally on 1x1 degree grid as the soil part of the land surface scheme CABLE. We could therefore demonstrate that this detailed and physically-realistic formulation is fast enough to be a feasible alternative to the much simpler default soil-scheme in CABLE. References Hansson et al. (2004) Vadose Zone J 3, 693ff Haverd & Cuntz (2010) J Hydro 388, 434ff Haverd et al. (2013) Biogeosci 10, 2011ff Weismüller et al. (2011) The Cryosphere 5, 741ff

Cuntz, M.; Haverd, V.

2013-12-01

247

Photomicrographic Investigation of Spontaneous Freezing Temperatures of Supercooled Water Droplets  

NASA Technical Reports Server (NTRS)

A photomicrographic technique for investigating eupercooled. water droplets has been devised and. used. to determine the spontaneous freezing temperatures of eupercooled. water droplets of the size ordinarily found. in the atmosphere. The freezing temperatures of 4527 droplets ranging from 8.75 to 1000 microns in diameter supported on a platinum surface and 571 droplets supported on copper were obtained. The average spontaneous freezing temperature decreased with decrease in the size of the droplets. The effect of size on the spontaneous freezing temperature was particularly marked below 60 microns. Frequency-distribution curves of the spontaneous freezing temperatures observed for droplets of a given size were obtained. Although no droplet froze at a temperature above 20 0 F, all droplets melted at 32 F. Results obtained with a copper support did not differ essentially from those obtained with a platinum surface.

Dorsch, R. G.; Hacker, P. T.

1950-01-01

248

Stress-gradient plasticity.  

PubMed

A new model, stress-gradient plasticity, is presented that provides unique mechanistic insight into size-dependent phenomena in plasticity. This dislocation-based model predicts strengthening of materials when a gradient in stress acts over dislocation source-obstacle configurations. The model has a physical length scale, the spacing of dislocation obstacles, and is validated by several levels of discrete-dislocation simulations. When incorporated into a continuum viscoplastic model, predictions for bending and torsion in polycrystalline metals show excellent agreement with experiments in the initial strengthening and subsequent hardening as a function of both sample-size dependence and grain size, when the operative obstacle spacing is proportional to the grain size. PMID:21911403

Chakravarthy, Srinath S; Curtin, W A

2011-09-20

249

Stress-gradient plasticity  

PubMed Central

A new model, stress-gradient plasticity, is presented that provides unique mechanistic insight into size-dependent phenomena in plasticity. This dislocation-based model predicts strengthening of materials when a gradient in stress acts over dislocation source–obstacle configurations. The model has a physical length scale, the spacing of dislocation obstacles, and is validated by several levels of discrete-dislocation simulations. When incorporated into a continuum viscoplastic model, predictions for bending and torsion in polycrystalline metals show excellent agreement with experiments in the initial strengthening and subsequent hardening as a function of both sample-size dependence and grain size, when the operative obstacle spacing is proportional to the grain size. PMID:21911403

Chakravarthy, Srinath S.; Curtin, W. A.

2011-01-01

250

Crystal structures and freezing of dipolar fluids  

E-print Network

We investigate the crystal structure of classical systems of spherical particles with an embedded point dipole at T=0. The ferroelectric ground state energy is calculated using generalizations of the Ewald summation technique. Due to the reduced symmetry compared to the nonpolar case the crystals are never strictly cubic. For the Stockmayer (i.e., Lennard-Jones plus dipolar) interaction three phases are found upon increasing the dipole moment: hexagonal, body-centered orthorhombic, and body-centered tetragonal. An even richer phase diagram arises for dipolar soft spheres with a purely repulsive inverse power law potential $\\sim r^{-n}$. A crossover between qualitatively different sequences of phases occurs near the exponent $n=12$. The results are applicable to electro- and magnetorheological fluids. In addition to the exact ground state analysis we study freezing of the Stockmayer fluid by density-functional theory.

B. Groh; S. Dietrich

2000-10-21

251

Crystal structures and freezing of dipolar fluids.  

PubMed

We investigate the crystal structure of classical systems of spherical particles with an embedded point dipole at T=0. The ferroelectric ground state energy is calculated using generalizations of the Ewald summation technique. Due to the reduced symmetry compared to the nonpolar case the crystals are never strictly cubic. For the Stockmayer (i.e., Lennard-Jones plus dipolar) interaction three phases are found upon increasing the dipole moment: hexagonal, body-centered orthorhombic, and body-centered tetragonal. An even richer phase diagram arises for dipolar soft spheres with a purely repulsive inverse power law potential approximately r(-n). A crossover between qualitatively different sequences of phases occurs near the exponent n=12. The results are applicable to electro- and magnetorheological fluids. In addition to the exact ground state analysis we study freezing of the Stockmayer fluid by density-functional theory. PMID:11308482

Groh, B; Dietrich, S

2001-02-01

252

Freeze-fracture for scanning electron microscopy.  

PubMed

Two different freeze-fracture methods are explored for preparation of biological material for scanning electron microscopy. In the simpler method the tissues are first fixed and dehydrated. They are then frozen and fractured, and after thawing, critical-point dried. This method has already been used in a number of studies of animal tissues (heart, liver, kidney). It is applied here to the examination of plant material (leaf mesophyll cells). In the second method tissues, or cells, are first infiltrated with cryoprotectant (dimethylsulphoxide) then frozen and fractured, and not fixed until after thawing. The fixed tissues are finally dehydrated and critical-point dried. This method also has previously been used in the study of animal tissues, and is applied here to carrot protoplasts, chicken erythrocytes, and leaf mesophyll cells. PMID:599555

Haggis, G H; Phipps-Todd, B

1977-11-01

253

Heat pump with freeze-up prevention  

DOEpatents

What is disclosed is a heat pump apparatus for conditioning a fluid characterized by a fluid handler and path for circulating the fluid in heat exchange relationship with a refrigerant fluid; at least two refrigerant heat exchangers, one for effecting heat exchange with the fluid and a second for effecting heat exchange between refrigerant and a heat exchange fluid and the ambient air; a compressor for efficiently compressing the refrigerant; at least one throttling valve for throttling liquid refrigerant; a refrigerant circuit; refrigerant; a source of heat exchange fluid; heat exchange fluid circulating device and heat exchange fluid circuit for circulating the heat exchange fluid in heat exchange relationship with the refrigerant; and valves or switches for selecting the heat exchangers and direction of flow of the refrigerant therethrough for selecting a particular mode of operation. The heat exchange fluid prevents freeze up of the second heat exchanger by keeping the temperature above the dew point; and, optionally, provides heat for efficient operation.

Ecker, Amir L. (Dallas, TX)

1981-01-01

254

Solar desalination by freezing and distillation  

NASA Astrophysics Data System (ADS)

It is noted that among seawater desalination processes the absorption-freeze vapor compression processes based on the thermal heat pump, although untested commercially and still in the development stage, appears technically and economically an attractive application of low-grade (exergy) solar heat. The distillation processes proposed here may be conveniently powered by low-grade solar heat (from flat plate solar collectors). It is expected that the scaling problem will be insignificant in comparison with that encountered in the conventional multistage flash process. The novel feature here is the use of enlarged capacity for heat exchange between distillate and brine via latent heat of solid-liquid phase change of a suitable hydrophobic intermediate heat transfer material.

Kvajic, G.

255

Free-energy functional for freezing transitions: Hard sphere systems freezing into crystalline and amorphous structures  

E-print Network

A free-energy functional that contains both the symmetry conserved and symmetry broken parts of the direct pair correlation function has been used to investigate the freezing of a system of hard spheres into crystalline and amorphous structures. The freezing parameters for fluid-crystal transition have been found to be in very good agreement with the results found from simulations. We considered amorphous structures found from the molecular dynamics simulations at packing fractions $\\eta$ lower than the glass close packing fraction $\\eta_{J}$ and investigated their stability compared to that of a homogeneous fluid. The existence of free-energy minimum corresponding to a density distribution of overlapping Gaussians centered around an amorphous lattice depicts the deeply supercooled state with a heterogeneous density profile.

Swarn Lata Singh; Atul S. Bharadwaj; Yashwant Singh

2011-01-31

256

Evaluation and Validation of the Messinger Freezing Fraction  

NASA Technical Reports Server (NTRS)

One of the most important non-dimensional parameters used in ice-accretion modeling and scaling studies is the freezing fraction defined by the heat-balance analysis of Messinger. For fifty years this parameter has been used to indicate how rapidly freezing takes place when super-cooled water strikes a solid body. The value ranges from 0 (no freezing) to 1 (water freezes immediately on impact), and the magnitude has been shown to play a major role in determining the physical appearance of the accreted ice. Because of its importance to ice shape, this parameter and the physics underlying the expressions used to calculate it have been questioned from time to time. Until now, there has been no strong evidence either validating or casting doubt on the current expressions. This paper presents experimental measurements of the leading-edge thickness of a number of ice shapes for a variety of test conditions with nominal freezing fractions from 0.3 to 1.0. From these thickness measurements, experimental freezing fractions were calculated and compared with values found from the Messinger analysis as applied by Ruff. Within the experimental uncertainty of measuring the leading-edge thickness, agreement of the experimental and analytical freezing fraction was very good. It is also shown that values of analytical freezing fraction were entirely consistent with observed ice shapes at and near rime conditions: At an analytical freezing fraction of unity, experimental ice shapes displayed the classic rime shape, while for conditions producing analytical freezing fractions slightly lower than unity, glaze features started to appear.

Anderson, David N.; Tsao, Jen-Ching

2005-01-01

257

Effect of wettability on sessile drop freezing: when superhydrophobicity stimulates an extreme freezing delay.  

PubMed

An increasing number of studies directed at supercooling water droplets on surfaces with different wettabilities have appeared in recent years. This activity has been stimulated by the recognition that water supercooling phenomena can be effectively used to develop methods for protecting outdoor equipment and infrastructure elements against icing and snow accretion. In this article, we discuss the nucleation kinetics of supercooled sessile water droplets on hydrophilic, hydrophobic, and superhydrophobic surfaces under isothermal conditions at temperatures of -8, -10, and -15 °C and a saturated water vapor atmosphere. The statistics of nucleation events for the ensembles of freezing sessile droplets is completed by the detailed analysis of the contact angle temperature dependence and freezing of individual droplets in a saturated vapor atmosphere. We have demonstrated that the most essential freezing delay is characteristic of the superhydrophobic coating on aluminum, with the texture resistant to contact with ice and water. This delay can reach many hours at T = -8 °C and a few minutes at -23 °C. The observed behavior is analyzed on the basis of different nucleation mechanisms. The dissimilarity in the total nucleation rate, detected for two superhydrophobic substrates having the same apparent contact angle of the water drop but different resistivities of surface texture to the contact with water/ice, is associated with the contribution of heterogeneous nucleation on external centers located at the water droplet/air interface. PMID:24491217

Boinovich, Ludmila; Emelyanenko, Alexandre M; Korolev, Vadim V; Pashinin, Andrei S

2014-02-18

258

Effects of freezing on the survival of Escherichia coli and Bacillus and response to UV and chlorine after freezing.  

PubMed

Escherichia coli (E. coli) and Bacillus megaterium bacteria were frozen at -15 degrees C using a freezer and a spray freezing method. The frozen Bacillus spores were also exposed to UV and free chlorine. An average of 4.7-log inactivation was obtained from the spray ice with 2-day storage time, while the freezer freezing only caused 0.84-log reduction with the same storage time. Significantly higher inactivation levels were observed for the E. coli cells with 2-day storage compared with those without storage. The spray freezing was found more effective in killing the E. coli cells, while more cells were sublethally injured by the freezer freezing. Freezing did not kill the Bacillus megaterium spores, but affected their response to UV and chlorine. Greater inactivation levels were observed at higher free chlorine doses or longer contact time, and the UV fluence-response curve showed initial rapid kill followed by tailing for the frozen spores. PMID:17571840

Gao, W; Smith, D W; Li, Y

2007-05-01

259

technology offer Magnetic Gradient Sensor  

E-print Network

technology offer Magnetic Gradient Sensor magnetic gradient sensor, micromechanical structure The invention concerns a sensor for the magnetic field gradient and applies micromechanical structures. Lorentz are typically measured by Hall- sensors which suffer from a large offset and offset drift. For the measurement

Szmolyan, Peter

260

Studies on Freezing RAM Semen in Absence of Glycerol.  

NASA Astrophysics Data System (ADS)

Glycerol is widely used as a major cryoprotective agent for freezing spermatozoa of almost all species. However, it reduces fertility of sheep inseminated cervically compared with intrauterine insemination. Studies were conducted to develop a method and procedure for freezing ram semen in the absence of glycerol. Post -thaw survival of ram spermatozoa frozen in the absence of glycerol was affected by time and temperature after collection and before dilution and time after dilution and before freezing. Increase in time at 5^ circC before or after dilution and before freezing increased both post-thaw motility and number of cells passing through Sephadex filter. A cold dilution method was developed. Slow cooling of fresh ram semen and diluting at 5^circ C 2-3 hr. after collection, then freezing 1 hr. after dilution improved both post-thaw motility and number of cells passing through Sephadex filter compared with immediate dilution at 30-37^circC after collection and freezing 3-4 hr. later (P < 0.05). An extender was developed to freeze ram semen in the absence of glycerol. An increase in post-thaw motility was obtained when semen was extended in TES titrated with Tris to pH 7.0 (TEST) and osmotic pressure of 375-400 mOsm/kg, containing 25-30% (v/v) egg yolk and 10% (v/v) maltose. A special device (boat) for freezing was constructed to insure the same height of the sample above LN _2 and thus the same freezing rate from freeze to freeze. Freezing of semen in 0.25cc straws at 5-10 cm above LN_2 (73.8 to 49.5 ^circC/min) yielded higher post-thaw motility than the rates resulted from freezing at 15 cm above LN_2 or 1 cm above LN _2. Faster Thawing in 37^ circC water for 30 sec. (7.8^ circC/sec.) increased post-thaw motility compared with slower thawing in 5 or 20^circ C water (P < 0.05). A lambing rate of 52.2% was obtained in one fertility trial conducted with ram semen frozen without glycerol and 17.1% in a second trial. One injection (IM) of 15 mg PGF_{2alpha}/ewe for estrus synchronization during breeding season resulted in higher heat response and lambing rate than two injections given 10 days apart.

Abdelnaby, Abdelhady Abdelhakeam

1988-12-01

261

Laser scanning microscopy of broad freezing interfaces with applications to biological cells  

NASA Astrophysics Data System (ADS)

A new, vertical cryostage was used for microscopic observation of broad-front freezing in aqueous solutions. This cryostage complements traditional studies of cell behavior and interface morphology in cryobiology. Traditional systems directionally solidify thin samples perpendicular to the optical axis. Thin samples confer thermal and optical advantages for video brightfield microscopy. However, sample thickness can affect the interface morphology. In the new cryostage, ice propagates parallel to the microscope optical axis. The sample cup is 1 cm tall and 1.5 cm in diameter, with insulated sides and a nitrogen-cooled base to freeze the solution upward. The top of the solution is warmed passively through a cover glass or immersion objective. The freezing solutions contain dilute fluorescein dye, which is visible where it is concentrated by exclusion from the ice. The stage is mounted on a confocal laser-scanning microscope, and thermal control and image capture routines are centralized in a LabView user interface. Filtered water, physiological saline, 9.5% glycerol, and 10% glycerol with PBS were frozen at rates between -2°C/min and -10°C/min and sequential images at one plane were captured. Images distinctly revealed a lamellar interface but could not resolve 3-D morphology. The average lamellar spacing was quantified using image analysis. Physiological saline was frozen in flat glass capillary tubes with 0.05 to 0.4 mm path length, mounted vertically to observe internal ice in cross-section. Lamellae were randomly oriented with respect to the glass, suggesting caution when measuring dendrite spacing in a horizontal cryostage. No correlation between capillary size and lamellar spacing was noted. Cell monolayers and synthetic membranes were mounted horizontally to let a well-developed ice front approach the layer broadly. In transparent membranes, ice-membrane interaction was visible until ice grew over and obscured the membrane. The vertical cryostage improved our ability to observe ice lamellae in cross section. The broad phase front revealed dendrites' interaction with each other, rather than with the container walls. The arrangement permitted immersion objectives, which are normally avoided in cryomicroscopy because of heat transfer. The signal-to-noise ratio was too low for effective confocal microscopy, but laser-scanning microscopy provided good contrast compared to standard epi-fluorescence methods.

Neils, Christopher Martin

2000-09-01

262

Florida Harvester Ant Nest Architecture, Nest Relocation and Soil Carbon Dioxide Gradients  

PubMed Central

Colonies of the Florida harvester ant, Pogonomyrmex badius, excavate species-typical subterranean nests up the 3 m deep with characteristic vertical distribution of chamber area/shape, spacing between levels and vertical arrangement of the ants by age and brood stage. Colonies excavate and occupy a new nest about once a year, and doing so requires that they have information about the depth below ground. Careful excavation and mapping of vacated and new nests revealed that there was no significant difference between the old and new nests in any measure of nest size, shape or arrangement. Colonies essentially built a replicate of the just-vacated nest (although details differed), and they did so in less than a week. The reason for nest relocation is not apparent. Tschinkel noted that the vertical distribution of chamber area, worker age and brood type was strongly correlated to the soil carbon dioxide gradient, and proposed that this gradient serves as a template for nest excavation and vertical distribution. To test this hypothesis, the carbon dioxide gradient of colonies that were just beginning to excavate a new nest was eliminated by boring 6 vent holes around the forming nest, allowing the soil CO2 to diffuse into the atmosphere and eliminating the gradient. Sadly, neither the nest architecture nor the vertical ant distribution of vented nests differed from either unvented control or from their own vacated nest. In a stronger test, workers excavated a new nest under a reversed carbon dioxide gradient (high concentration near the surface, low below). Even under these conditions, the new and old nests did not differ significantly, showing that the soil carbon dioxide gradient does not serve as a template for nest construction or vertical worker distribution. The possible importance of soil CO2 gradients for soil-dwelling animals is discussed. PMID:23555829

Tschinkel, Walter R.

2013-01-01

263

A perfectly balanced method for estimating the internal pressure gradients in ?-coordinate ocean models  

NASA Astrophysics Data System (ADS)

The estimation of the internal pressure gradients (IPG) in ?-coordinate ocean models has been addressed both in text books and in many research papers. In this paper a perfectly balanced method for estimating internal density and pressure gradients is suggested. The method is perfect in the sense that for cases with ? = ?( z), where ? is density and z the vertical coordinate, the numerical estimates of the density and pressure gradients are zero. The method has in addition another important property: for continuous stratification, the estimates of the internal pressure gradients vary continuously with changes in the stratification. The properties of the method are investigated using two very simple vertical column test cases, the seamount case, and two Nordic Seas test cases, one with ? = ?( z) and another more realistic case with ? = ?( x, y, z). For the seamount case and the simple Nordic Seas case, the errors are orders of magnitude smaller than the corresponding errors reported in earlier papers. For the simple vertical column case with non-zero density gradients, the estimates of the gradients produced with the new method converge quadratically towards the true values as the horizontal and vertical grid sizes both tend to zero. The new method may be regarded as a modified second order method calibrated such that the errors are zero for ? = ?( z).

Berntsen, Jarle

264

Vertical heterogeneity in predation pressure in a temperate forest canopy  

PubMed Central

The forest canopy offers a vertical gradient across which variation in predation pressure implies variation in refuge quality for arthropods. Direct and indirect experimental approaches were combined to assess whether canopy strata differ in ability to offer refuge to various arthropod groups. Vertical heterogeneity in impact of avian predators was quantified using exclosure cages in the understory, lower, mid, and upper canopy of a north-temperate deciduous forest near Montreal, Quebec. Bait trials were completed in the same strata to investigate the effects of invertebrate predators. Exclusion of birds yielded higher arthropod densities across all strata, although treatment effects were small for some taxa. Observed gradients in predation pressure were similar for both birds and invertebrate predators; the highest predation pressure was observed in the understory and decreased with height. Our findings support a view of the forest canopy that is heterogeneous with respect to arthropod refuge from natural enemies. PMID:24010017

Aikens, Kathleen R.; Buddle, Christopher M.

2013-01-01

265

Freeze-Thaw Durability of Air-Entrained Concrete  

PubMed Central

One of the most damaging actions affecting concrete is the abrupt temperature change (freeze-thaw cycles). The types of deterioration of concrete structures by cyclic freeze-thaw can be largely classified into surface scaling (characterized by the weight loss) and internal crack growth (characterized by the loss of dynamic modulus of elasticity). The present study explored the durability of concrete made with air-entraining agent subjected to 0, 100, 200, 300, and 400 cycles of freeze-thaw. The experimental study of C20, C25, C30, C40, and C50 air-entrained concrete specimens was completed according to “the test method of long-term and durability on ordinary concrete” GB/T 50082-2009. The dynamic modulus of elasticity and weight loss of specimens were measured after different cycles of freeze-thaw. The influence of freeze-thaw cycles on the relative dynamic modulus of elasticity and weight loss was analyzed. The findings showed that the dynamic modulus of elasticity and weight decreased as the freeze-thaw cycles were repeated. They revealed that the C30, C40, and C50 air-entrained concrete was still durable after 300 cycles of freeze-thaw according to the experimental results. PMID:23576906

Shang, Huai-Shuai; Yi, Ting-Hua

2013-01-01

266

Metabolic changes in Avena sativa crowns recovering from freezing.  

PubMed

Extensive research has been conducted on cold acclimation and freezing tolerance of fall-sown cereal plants due to their economic importance; however, little has been reported on the biochemical changes occurring over time after the freezing conditions are replaced by conditions favorable for recovery and growth such as would occur during spring. In this study, GC-MS was used to detect metabolic changes in the overwintering crown tissue of oat (Avena sativa L.) during a fourteen day time-course after freezing. Metabolomic analysis revealed increases in most amino acids, particularly proline, 5-oxoproline and arginine, which increased greatly in crowns that were frozen compared to controls and correlated very significantly with days after freezing. In contrast, sugar and sugar related metabolites were little changed by freezing, except sucrose and fructose which decreased dramatically. In frozen tissue all TCA cycle metabolites, especially citrate and malate, decreased in relation to unfrozen tissue. Alterations in some amino acid pools after freezing were similar to those observed in cold acclimation whereas most changes in sugar pools after freezing were not. These similarities and differences suggest that there are common as well as unique genetic mechanisms between these two environmental conditions that are crucial to the winter survival of plants. PMID:24675792

Henson, Cynthia A; Duke, Stanley H; Livingston, David P

2014-01-01

267

Dynamical freeze-out in three-fluid hydrodynamics  

SciTech Connect

The freeze-out procedure accepted in a model of three-fluid dynamics is analyzed. This procedure is formulated in terms of drain terms in hydrodynamic equations. The dynamics of freeze-out is illustrated by one-dimensional simulations. It is demonstrated that the resulting freeze-out reveals a nontrivial dynamics depending on initial conditions in the expanding 'fireball'. The freeze-out front is not just defined 'geometrically' on the condition of the freeze-out criterion met but rather is a subject of fluid evolution. It competes with the fluid flow and does not always reach the place where the freeze-out criterion is met. Dynamics of the freeze-out in three-dimensional simulations is analyzed. It is demonstrated that the late stage of central nuclear collisions at the top energies available at the CERN Super Proton Synchrotron is of the form of three (two baryon-rich and one baryon-free) fireballs separated from each other.

Russkikh, V. N.; Ivanov, Yu. B. [Gesellschaft fuer Schwerionenforschung mbH, Planckstr. 1, D-64291 Darmstadt (Germany); Kurchatov Institute, Kurchatov sq. 1, RU-123182 Moscow (Russian Federation)

2007-11-15

268

Metabolic Changes in Avena sativa Crowns Recovering from Freezing  

PubMed Central

Extensive research has been conducted on cold acclimation and freezing tolerance of fall-sown cereal plants due to their economic importance; however, little has been reported on the biochemical changes occurring over time after the freezing conditions are replaced by conditions favorable for recovery and growth such as would occur during spring. In this study, GC-MS was used to detect metabolic changes in the overwintering crown tissue of oat (Avena sativa L.) during a fourteen day time-course after freezing. Metabolomic analysis revealed increases in most amino acids, particularly proline, 5-oxoproline and arginine, which increased greatly in crowns that were frozen compared to controls and correlated very significantly with days after freezing. In contrast, sugar and sugar related metabolites were little changed by freezing, except sucrose and fructose which decreased dramatically. In frozen tissue all TCA cycle metabolites, especially citrate and malate, decreased in relation to unfrozen tissue. Alterations in some amino acid pools after freezing were similar to those observed in cold acclimation whereas most changes in sugar pools after freezing were not. These similarities and differences suggest that there are common as well as unique genetic mechanisms between these two environmental conditions that are crucial to the winter survival of plants. PMID:24675792

Henson, Cynthia A.; Duke, Stanley H.; Livingston, David P.

2014-01-01

269

Freeze-thaw durability of air-entrained concrete.  

PubMed

One of the most damaging actions affecting concrete is the abrupt temperature change (freeze-thaw cycles). The types of deterioration of concrete structures by cyclic freeze-thaw can be largely classified into surface scaling (characterized by the weight loss) and internal crack growth (characterized by the loss of dynamic modulus of elasticity). The present study explored the durability of concrete made with air-entraining agent subjected to 0, 100, 200, 300, and 400 cycles of freeze-thaw. The experimental study of C20, C25, C30, C40, and C50 air-entrained concrete specimens was completed according to "the test method of long-term and durability on ordinary concrete" GB/T 50082-2009. The dynamic modulus of elasticity and weight loss of specimens were measured after different cycles of freeze-thaw. The influence of freeze-thaw cycles on the relative dynamic modulus of elasticity and weight loss was analyzed. The findings showed that the dynamic modulus of elasticity and weight decreased as the freeze-thaw cycles were repeated. They revealed that the C30, C40, and C50 air-entrained concrete was still durable after 300 cycles of freeze-thaw according to the experimental results. PMID:23576906

Shang, Huai-Shuai; Yi, Ting-Hua

2013-01-01

270

Vertical velocity-CCN correlations  

NASA Astrophysics Data System (ADS)

The realization that smaller cloud droplets evaporate more readily (Xue and Feingold 2006; Jiang et al. 2002) gives rise to an anti-indirect aerosol effect (IAE); less cloudiness with pollution. The greater latent heat exchange of the greater evaporation in more polluted clouds adds TKE and buoyancy gradients that can enhance vertical velocity (W), mixing and entrainment (Zhao and Austin 2005). Stronger W can increase horizontal motions, which can further enhance droplet evaporation, which further enhances latent heat exchange and vertical motions, thus, positive feedback. This could also include latent heat released during condensation (Lee and Feingold 2010), which is more rapid for the greater surface areas of the smaller more numerous droplets. These theories imply a positive relationship between within-cloud W variations; i.e., standard deviation of W (?w) and CCN concentration (NCCN) rather than W and NCCN. This implies greater turbulence in polluted clouds, which could possibly counteract the reduction of cloudiness of anti-IAE. During two stratus cloud projects, 50 cloud penetrations in 9 MASE flights and 34 cloud penetrations in 13 POST flights, within-cloud ?w-NCCN showed correlation coefficients (R) of 0.50 and 0.39. Panel a shows similar within-cloud ?w-NCCN R in all altitude bands for 17 RICO flights in small cumulus clouds. R for W-NCCN showed similar values but only at low altitudes. Out-of-cloud ?w-NCCN showed similar high values except at the highest altitudes. Within-cloud ?w showed higher R than within-cloud W with droplet concentrations (Nc), especially at higher altitudes. Panel b for 13 ICE-T cumulus cloud flights in the same location as RICO but during the opposite season, however, showed ?w and W uncorrelated with NCCN at all altitudes; and W and ?w correlated with Nc only at the highest altitudes. On the other hand, out-of-cloud ?w was correlated with NCCN at all altitudes with R similar to the corresponding R of the other projects. Overall these results are consistent with the theories noted above. Supported by NSF AGS-1035230 and DOE SC0009162. Jiang, H., G. Feingold, and W.R. Cotton, 2002: J. Geophys. Res, 107, D24, 4813. Lee, S.-S., and G. Feingold, 2010: Geophys. Res. Lett., 37, L23806. Xue, H., and G. Feingold, 2006: J. Atmos. Sci., 63, 1605-1622. Zhao, M., and P.H. Austin, 2005: J. Atmos. Sci., 62, 1291-1310. Fig. Correlation coefficients (R) between mean and standard deviations of vertical velocity (W; ?w within and outside of clouds) with CCN concentrations at 1% supersaturation (N1%) measured below the clouds and with droplet concentrations (Nc) within various altitude bands.

Hudson, J. G.; Noble, S. R.

2013-12-01

271

Air-Cooled Stack Freeze Tolerance Freeze Failure Modes and Freeze Tolerance Strategies for GenDriveTM Material Handling Application Systems and Stacks Final Scientific Report  

SciTech Connect

Air-cooled stack technology offers the potential for a simpler system architecture (versus liquid-cooled) for applications below 4 kilowatts. The combined cooling and cathode air allows for a reduction in part count and hence a lower cost solution. However, efficient heat rejection challenges escalate as power and ambient temperature increase. For applications in ambient temperatures below freezing, the air-cooled approach has additional challenges associated with not overcooling the fuel cell stack. The focus of this project was freeze tolerance while maintaining all other stack and system requirements. Through this project, Plug Power advanced the state of the art in technology for air-cooled PEM fuel cell stacks and related GenDrive material handling application fuel cell systems. This was accomplished through a collaborative work plan to improve freeze tolerance and mitigate freeze-thaw effect failure modes within innovative material handling equipment fuel cell systems designed for use in freezer forklift applications. Freeze tolerance remains an area where additional research and understanding can help fuel cells to become commercially viable. This project evaluated both stack level and system level solutions to improve fuel cell stack freeze tolerance. At this time, the most cost effective solutions are at the system level. The freeze mitigation strategies developed over the course of this project could be used to drive fuel cell commercialization. The fuel cell system studied in this project was Plug Power's commercially available GenDrive platform providing battery replacement for equipment in the material handling industry. The fuel cell stacks were Ballard's commercially available FCvelocity 9SSL (9SSL) liquid-cooled PEM fuel cell stack and FCvelocity 1020ACS (Mk1020) air-cooled PEM fuel cell stack.

Hancock, David, W.

2012-02-14

272

Immersion freezing on mineral dust particles  

NASA Astrophysics Data System (ADS)

Mineral dust is considered to play a major role in ice cloud nucleation in the troposphere. More than 1.000 Tg of mineral dust are aerosolized from the ground every year, 1-10% of these reach the upper troposphere [1]. At an altitude of about 8 km ice residual particle analysis has shown that about 50% of all ice nuclei (IN) are mineral dust[2]. In principle, natural occurring dusts may either be IN-active themselves or are carriers of organic and/or biological IN. Up to now the ice nucleation, i.e. cloud glaciation, has not been quantized. However, different authors report a high IN-activity for many mineral dust samples, although a systematic comparison between different minerals is still missing. Therefore, we studied selected mineral dust samples which were characterized by X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy before use. Oil immersion measurements were performed on the most common minerals, clay materials and volcanic ash. The median freezing temperatures range from -21°C up to homogenous freezing at 38°C. Even though quite a few dust samples show a reasonable high IN-activity, their median freezing temperatures are low compared to biological samples [3, 4]. Furthermore, heat treatment of the dusts was applied in order to decompose and to denaturize organic and/or biological surfactants. Finally, some dust samples had a high loss of activity and thus were subjects of further experiments. These mineral dust particles were suspended in water and after an incubation time were removed. In some cases the washing water had become IN-active, but lost its activity after enzymatic treatment. The observed high IN-activity can thus be explained by adsorbed biological materials. The results suggest that some mineral dusts are IN-active, and if it is not intrinsic they may even enhance IN-activity of organic and biological IN if these are adsorbed on the dust particle surface. A relatively high IN-activity of the pure mineral dusts was only observed in quartz, clays, and mixed natural dusts (ATD), which are mainly composed of SiO2 and clays. References. [1] C. S. Zender, R. L. Miller and I. Tegen, Eos Trans. AGU, 2004,85, 509. [2] K. A. Pratt, P. J. DeMott, J. R. French, Z. Wang, D. L. Westphal, A. J. Heymsfield, C. H. Twohy, A. J. Prenni, K. A. Prather, Nat. Geosci., 2009, 2, 397-400. [3] B. Pummer, H. Bauer, J. Bernardi, S. Bleicher and H. Grothe, Atmos. Chem. Phys., 2012, 12, 2541-2550. [4] V. T. J. Phillips, C. Andronache, B. Christner, C. E. Morris, D. C. Sands, A. Bansemer, A. Lauer, C. McNaughton and C. Seman, Biogeosciences, 2009, 6, 987-1014.

Zolles, Tobias; Grothe, Hinrich; Pummer, Bernhard

2013-04-01

273

Linear Stability of Return Thermocapillary Flows under Vertical Gravity Modulation  

Microsoft Academic Search

A linear stability analysis of a time-harmonic parallel flow in a slot geometry is presented. A constant temperature gradient applied along the length of a slot with a flat free interface at the top drives a steady thermocapillary return flow. A vertical time-harmonic gravity modulation drives a time-periodic buoyant return flow. The relative strength of the two components is characterized

Vinod Suresh; George Homsy

2000-01-01

274

Freeze-out volume of hot dense fireball  

E-print Network

A thermodynamically consistent excluded volume model is proposed to account for the particle multiplicities obtained from lowest SIS energies to the highest RHIC energies. The chemical freeze-out volumes lying in a slice of one unit of rapidity for pions and kaons are separately inferred from this analysis and the results are compared with the corresponding thermal freeze-out volumes obtained from the Hanbury-Brown Twiss (HBT) pion interferometry. Furthermore, we extract the variations of freeze-out number densities for pions and nucleons with the center-of-mass energy in our model and compare them with the HBT data.

M. Mishra; C. P. Singh

2007-09-27

275

PEM Fuel Cell Freeze Durability and Cold Start Project  

SciTech Connect

UTC has taken advantage of the unique water management opportunities inherent in micro-porous bipolar-plates to improve the cold-start performance of its polymer electrolyte fuel cells (PEFC). Diagnostic experiments were used to determine the limiting factors in micro-porous plate PEFC freeze performance and the causes of any performance decay. Alternative cell materials were evaluated for their freeze performance. Freeze-thaw cycling was also performed to determine micro-porous plate PEFC survivability. Data from these experiments has formed the basis for continuing development of advanced materials capable of supporting DOE's cold-start and durability objectives.

Patterson, T.; O'Neill, Jonathan

2008-01-02

276

322 sperm preservation by freeze-drying in endangered animals.  

PubMed

Sperm preservation is a useful tool for conservation of endangered animals. Freeze-drying sperm have been studied as new preservation method in various mammals as samples can be preserved in a refrigerator at 4°C or ambient temperature. Sperm preservation by freeze-drying is the ultimate method by which sperm can be stored that neither required specialised cryoprotectants nor constant supply of liquid nitrogen. We established the freeze-drying method that mouse and rat sperm could be preserved long-term at 4°C after freeze-drying using a simple solution containing 10mM Tris and 1mM EDTA (TE buffer; 2012 PLoS ONE 7, e35043; 2012 Cryobiology 64, 211-214). Using this method, the fertility of the chimpanzee, giraffe, and jaguar sperm after freeze-drying were estimated. Ejaculated chimpanzee and giraffe and cauda epididymal jaguar sperm were freeze-dried using TE buffer. Sperm were rehydrated with sterile distilled water after storage at 4°C for 1 month. Sperm with normal shape were injected into mouse oocytes in CZB medium with HEPES, and oocytes were then cultured in vitro for 6 to 8h in the same media. In all animals, pronuclei and sperm tail were observed into oocytes without artificial activation after injection of freeze-dried sperm. When chimpanzee, giraffe, and jaguar sperm were injected into oocytes, 86% (12/14), 100% (12/12), and 96% (22/23) of oocytes formed 2 distinct pronuclei. This study demonstrated that the sperm of various animals could be decondensed into the mouse oocytes after freeze-drying using the same protocol. A further advantage is that freeze-dried sperm can be transported oversea at ambient temperature. Freeze-drying preservation without using liquid nitrogen can be protected strongly valuable gametes of endangered animals even in the event of unexpected accidents and disaster such as earthquakes and typhoons. Freeze-drying of sperm has been applied as a "freeze-drying zoo" for conservation of endangered animals (http://www.anim.med.kyoto-u.ac.jp/reproduction/home.aspx). PMID:25472370

Kaneko, T

2014-12-01

277

Vertical Motion Simulator  

NSDL National Science Digital Library

The Vertical Motion Simulator (VMS), at the NASA Ames Research Center, is an advanced flight simulation facility. This Web site provides thorough descriptions of all of the VMS systems. The VMS is a full immersion environment, complete with customizable cockpit, controls, and instrumentation to give the appearance of any aerospace vehicle. One of its most intriguing characteristics is "out-the-window graphics." This allows the pilot to see computer generated imagery of real locations, so virtually everything is identical to the actual flying experience. Even aircraft that are still in the design stage can be simulated on the VMS.

278

'Endurance' Untouched (vertical)  

NASA Technical Reports Server (NTRS)

This navigation camera mosaic, created from images taken by NASA's Mars Exploration Rover Opportunity on sols 115 and 116 (May 21 and 22, 2004) provides a dramatic view of 'Endurance Crater.' The rover engineering team carefully plotted the safest path into the football field-sized crater, eventually easing the rover down the slopes around sol 130 (June 12, 2004). To the upper left of the crater sits the rover's protective heatshield, which sheltered Opportunity as it passed through the martian atmosphere. The 360-degree view is presented in a vertical projection, with geometric and radiometric seam correction.

2004-01-01

279

Vertical slender jets  

NASA Technical Reports Server (NTRS)

The shape of a vertical slender jet of fluid falling steadily under the force of gravity is studied. The problem is formulated as a nonlinear free boundary-value problem for the potential. Surface tension effects are neglected. The use of perturbation expansions results in a system of equations that can be solved by an efficient numerical procedure. Computations were made for jets issuing from orifices in various shapes including an ellipse, a rectangle, and an equilateral triangle. Computational results are presented illustrating the propagation of discontinuities and the formation of thin sheets of fluid.

Geer, J. F.; Strikwerda, J. C.

1980-01-01

280

Is Enceladus' Internal Ocean Doomed to Freeze?  

NASA Astrophysics Data System (ADS)

Enceladus is geologically hyperactive, with plumes of water vapor, other volatiles such as ammonia, and salty particles erupting from its South Polar Terrain. The plumes are spatially associated with a region of greatly increased local heat flux, with a total power output 15.8 × 3.1 GW spread over an area of 70,000 km2 (e.g., Spencer and Nimmo 2013, AREPS 41), corresponding to a regional heat flux of 180-270 mW m-2. Tidal strains of the magnitude only possible in an ice shell that is decoupled from a rocky interior by an internal ocean or regional sea are required to generate this much heat (e.g., Behounkova et al. 2012, Icarus 219). Yet, numerous studies conclude that Enceladus' ocean cannot be in present-day thermodynamic steady state with a conductive or convective ice I shell (e.g., Roberts and Nimmo 2008, Icarus 194; Behounkova et al. 2012). Regardless of where Enceladus' tidal heating is concentrated (i.e., the poles), and regardless of whether its outer ice I shell convects, Enceladus' ocean is predicted to freeze on a geologically rapid time scale, implying that activity on Enceladus is only a transient or episodic phenomenon. These arguments strictly apply only to pure water ice oceans, however. We have previously argued that if the presence of salts or ammonia is allowed for, the ocean may be cooler and can be maintained essentially permanently by tidal heating in the ice above (McKinnon and Barr 2008, LPS XXXIX). Here we elaborate on the conditions under which Enceladus' ocean can be stabilized or even increase in thickness due to present-day tidal heating within the ice shell and the presence of salts and ammonia, which we now know are there (Waite et al. 2009, Nature 460; Postberg et al. 2011, Nature 474). As previous work has found, we cannot explain the present-day heat flow, but there is no fundamental reason that Enceladus' ocean or sea should completely freeze for present-day orbital eccentricities.

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

2013-12-01

281

Inner ear tissue preservation by rapid freezing: improving fixation by high-pressure freezing and hybrid methods.  

PubMed

In the preservation of tissues in as 'close to life' state as possible, rapid freeze fixation has many benefits over conventional chemical fixation. One technique by which rapid freeze-fixation can be achieved, high pressure freezing (HPF), has been shown to enable ice crystal artefact-free freezing and tissue preservation to greater depths (more than 40 ?m) than other quick-freezing methods. Despite increasingly becoming routine in electron microscopy, the use of HPF for the fixation of inner ear tissue has been limited. Assessment of the quality of preservation showed routine HPF techniques were suitable for preparation of inner ear tissues in a variety of species. Good preservation throughout the depth of sensory epithelia was achievable. Comparison to chemically fixed tissue indicated that fresh frozen preparations exhibited overall superior structural preservation of cells. However, HPF fixation caused characteristic artefacts in stereocilia that suggested poor quality freezing of the actin bundles. The hybrid technique of pre-fixation and high pressure freezing was shown to produce cellular preservation throughout the tissue, similar to that seen in HPF alone. Pre-fixation HPF produced consistent high quality preservation of stereociliary actin bundles. Optimising the preparation of samples with minimal artefact formation allows analysis of the links between ultrastructure and function in inner ear tissues. PMID:25016142

Bullen, A; Taylor, R R; Kachar, B; Moores, C; Fleck, R A; Forge, A

2014-09-01

282

Surfactant-induced gradients in the three-dimensional Belousov-Zhabotinsky reaction.  

PubMed

Scroll waves are prominent patterns formed in three-dimensional excitable media, and they are frequently considered highly relevant for some types of cardiac arrhythmias. Experimentally, scroll wave dynamics is often studied by optical tomography in the Belousov-Zhabotinsky reaction, which produces CO(2) as an undesired product. Addition of small concentrations of a surfactant to the reaction medium is a popular method to suppress or retard CO(2) bubble formation. We show that in closed reactors even these low concentrations of surfactants are sufficient to generate vertical gradients of excitability which are due to gradients in CO(2) concentration. In reactors open to the atmosphere such gradients can be avoided. The gradients induce a twist on vertically oriented scroll waves, while a twist is absent in scroll waves in a gradient-free medium. The effects of the CO(2) gradients are reproduced by a numerical study, where we extend the Oregonator model to account for the production of CO(2) and for its advection against the direction of gravity. The numerical simulations confirm the role of solubilized CO(2) as the source of the vertical gradient of excitability in reactors closed to the atmosphere. PMID:22181487

Kupitz, Dennis; Alonso, Sergio; Bär, Markus; Hauser, Marcus J B

2011-11-01

283

Tight junction regulates epidermal calcium ion gradient and differentiation  

SciTech Connect

Research highlights: {yields} We disrupted epidermal tight junction barrier in reconstructed epidermis. {yields} It altered Ca{sup 2+} distribution and consequentially differentiation state as well. {yields} Tight junction should affect epidermal homeostasis by maintaining Ca{sup 2+} gradient. -- Abstract: It is well known that calcium ions (Ca{sup 2+}) induce keratinocyte differentiation. Ca{sup 2+} distributes to form a vertical gradient that peaks at the stratum granulosum. It is thought that the stratum corneum (SC) forms the Ca{sup 2+} gradient since it is considered the only permeability barrier in the skin. However, the epidermal tight junction (TJ) in the granulosum has recently been suggested to restrict molecular movement to assist the SC as a secondary barrier. The objective of this study was to clarify the contribution of the TJ to Ca{sup 2+} gradient and epidermal differentiation in reconstructed human epidermis. When the epidermal TJ barrier was disrupted by sodium caprate treatment, Ca{sup 2+} flux increased and the gradient changed in ion-capture cytochemistry images. Alterations of ultrastructures and proliferation/differentiation markers revealed that both hyperproliferation and precocious differentiation occurred regionally in the epidermis. These results suggest that the TJ plays a crucial role in maintaining epidermal homeostasis by controlling the Ca{sup 2+} gradient.

Kurasawa, Masumi; Maeda, Tetsuo; Oba, Ai; Yamamoto, Takuya [Pola Chemical Industries Inc., 560 Kashio-cho, Totsuka-ku, Yokohama 244-0812 (Japan)] [Pola Chemical Industries Inc., 560 Kashio-cho, Totsuka-ku, Yokohama 244-0812 (Japan); Sasaki, Hiroyuki, E-mail: sasakih@jikei.ac.jp [Division of Fine Morphology, Core Research Facilities, The Jikei University School of Medicine, Minato-ku, Tokyo 105-8461 (Japan) [Division of Fine Morphology, Core Research Facilities, The Jikei University School of Medicine, Minato-ku, Tokyo 105-8461 (Japan); The Center for Advanced Medical Engineering and Infomatics, Osaka University, Osaka 565-0871 (Japan)

2011-03-25

284

Importance of the gradient in photosynthetically active radiation in a vegetation stand for leaf nitrogen allocation in two monocotyledons  

Microsoft Academic Search

Carex acutiformis and Brachypodium pinnatum were grown with a uniform distribution of photosynthetic photon flux density (PFD) with height, and in a vertical PFD gradient similar to the PFD gradient in a leaf canopy. Distribution of organic leaf N and light-saturated rates of photosynthesis were determined. These parameters were also determined on plants growing in a natural vegetation stand. The

Thijs L. Ports; Hans van Rijnberk; Ingeborg Scheurwater; Adrie van der Werf

1993-01-01

285

Melting and Freezing Under the Ross Ice Shelf: Lessons From an Impacted Cavity  

NASA Astrophysics Data System (ADS)

The dimensions of ice shelves are strongly influenced by the temperature and circulation of the underlying ocean. Inflow temperatures vary by about three degrees, with most ice shelves floating in seawater near the in situ freezing point. Circulation under the ice depends on modifications of the thermohaline field by melting, freezing and tidal mixing, which determine the vertical stratification and heat flux. Observations near ice fronts have previously been used to estimate the amount of meltwater present in outflows from ice shelf cavities. While limited by the seasonality and dynamic range of the measurements, along with discrete sampling methods and uncertain source water assumptions, geochemical data add valuable information to the more commonly utilized temperature and salinity fields. Here we evaluate repeat chlorofluorocarbon and thermohaline sections in a region that has experienced a multidecadal decline in shelf water salinity. Inferences about net basal melting are compared with results from numerical models and bottom-moored instruments. Ice shelf cavities are sinks for much of the high salinity shelf water produced by sea ice formation. Outflows from those cavities reflect the properties of shelf water inflows, and affect the salinity and density of downstream bottom water production. We suggest future work that could help to better understand ocean forcing of ice shelf change in an evolving climate.

Jacobs, S. S.; Smethie, W. M.; Assmann, K. M.; Holland, D. M.; Bergamasco, A.

2003-12-01

286

Energy in density gradient  

NASA Astrophysics Data System (ADS)

Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. In the present work, the amount of energy stored in a density gradient is calculated for several specific density profiles in a cylindrical configuration. This is of practical importance for drift wave instability in various plasmas, and, in particular, in its application in models dealing with the heating of solar corona because the instability is accompanied with stochastic heating, so the energy contained in inhomogeneity is effectively transformed into heat. It is shown that even for a rather moderate increase of the density at the axis in magnetic structures in the corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored in such a density gradient becomes several orders of magnitude greater than the amount of total energy losses per unit volume (per second) in quiet regions in the corona. Consequently, within the life-time of a magnetic structure such energy losses can easily be compensated by the stochastic drift wave heating.

Vranjes, J.; Kono, M.

2015-01-01

287

Energy in density gradient  

E-print Network

Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. In the present work the amount of energy stored in a density gradient is calculated for several specific density profiles in a cylindric configuration. This is of practical importance for drift wave instability in various plasmas, and in particular in its application in models dealing with the heating of solar corona because the instability is accompanied with stochastic heating, so the energy contained in inhomogeneity is effectively transformed into heat. It is shown that even for a rather moderate increase of the density at the axis in magnetic structures in the corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored in such a density gradient becomes several orders of magnitude greater than the amount of total energy losses per unit ...

Vranjes, J

2015-01-01

288

Freezing Stress Response in Woody Tissues Observed Using Low-Temperature Scanning Electron Microscopy and Freeze Substitution Techniques 1  

PubMed Central

The objective of the current research was to examine the response of woody plant tissues to freezing stress by using scanning electron microscopy (SEM). Nonsupercooling species red osier dogwood (Cornus stolonifera Michx.), weeping willow (Salix babylonica L.), and corkscrew willow (Salix matsudana Koidz. f. tortuosa Rehd.) survived freezing stress as low as ?60°C. Cell collapse of ray parenchyma cells of these species was expected but did not occur. It was concluded that ray parenchyma cells of these species do not fit into either the supercooling or extracellular freezing classifications. Tissues from flowering dogwood (Cornus florida L.), apple (Malus domestica Borkh. cv “Starking III”), red oak (Quercus rubra L.), scarlet oak (Quercus coccinea Muench.), and red ash (Fraxinus pennsylvanica Marsh) were confirmed as supercooling species, and did not survive exposures below ?40°C. Ray parenchyma cells of these species did not collapse in response to freezing stress, as was expected. Cell collapse along the margins of voids were observed in bark of all seven species. Voids were the result of extracellular ice crystals formed in the bark during exposure to freezing stress. Tissues prepared by freeze substitution techniques were found to be adequately preserved when compared to those prepared by conventional fixation and low temperature SEM techniques. A freezing protocol for imposing freezing stress at temperatures lower than experienced naturally in the area where the study was conducted was developed that produced responses comparable to those observed in specimens collected in the field during natural freezing events. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 PMID:16668066

Malone, Stephen R.; Ashworth, Edward N.

1991-01-01

289

Satellite freeze forecast system: Executive summary  

NASA Technical Reports Server (NTRS)

A satellite-based temperature monitoring and prediction system consisting of a computer controlled acquisition, processing, and display system and the ten automated weather stations called by that computer was developed and transferred to the national weather service. This satellite freeze forecasting system (SFFS) acquires satellite data from either one of two sources, surface data from 10 sites, displays the observed data in the form of color-coded thermal maps and in tables of automated weather station temperatures, computes predicted thermal maps when requested and displays such maps either automatically or manually, archives the data acquired, and makes comparisons with historical data. Except for the last function, SFFS handles these tasks in a highly automated fashion if the user so directs. The predicted thermal maps are the result of two models, one a physical energy budget of the soil and atmosphere interface and the other a statistical relationship between the sites at which the physical model predicts temperatures and each of the pixels of the satellite thermal map.

Martsolf, J. D. (principal investigator)

1983-01-01

290

Adaptation to seasonality and the winter freeze.  

PubMed

Flowering plants initially diversified during the Mesozoic era at least 140 million years ago in regions of the world where temperate seasonal environments were not encountered. Since then several cooling events resulted in the contraction of warm and wet environments and the establishment of novel temperate zones in both hemispheres. In response, less than half of modern angiosperm families have members that evolved specific adaptations to cold seasonal climates, including cold acclimation, freezing tolerance, endodormancy, and vernalization responsiveness. Despite compelling evidence for multiple independent origins, the level of genetic constraint on the evolution of adaptations to seasonal cold is not well understood. However, the recent increase in molecular genetic studies examining the response of model and crop species to seasonal cold offers new insight into the evolutionary lability of these traits. This insight has major implications for our understanding of complex trait evolution, and the potential role of local adaptation in response to past and future climate change. In this review, we discuss the biochemical, morphological, and developmental basis of adaptations to seasonal cold, and synthesize recent literature on the genetic basis of these traits in a phylogenomic context. We find evidence for multiple genetic links between distinct physiological responses to cold, possibly reinforcing the coordinated expression of these traits. Furthermore, repeated recruitment of the same or similar ancestral pathways suggests that land plants might be somewhat pre-adapted to dealing with temperature stress, perhaps making inducible cold traits relatively easy to evolve. PMID:23761798

Preston, Jill C; Sandve, Simen R

2013-01-01

291

Component stress during freeze/thaw cycling  

SciTech Connect

During the past year, the feasibility and usefulness of mathematically modeling the processes occurring in Na/S cells during freeze/thaw (F/T) cycling has been demonstrated with the identification of potential stress producing phenomena. The first strain measurements on functioning cells have been completed that have shown the variable nature of the positive-electrode materials, a factor that may account for the randomness of actual F/T induced failures. Physical property measurements have quantified the important effect the presence of the graphite felt can have on Young's modulus for sulfur. With the completion of the physical-property and strain measurements in the coming year, final modification will be made to the material models contained in the thermo-mechanical code. The strain data will be used to validate the accuracy of the component stress calculations. Once validated, this code can be used to identify and simulate important aspects of various design options and to determine the feasiblity of proposed failure mechanisms. 4 refs., 10 figs., 1 tab.

Braithwaite, J.W.; Subia, S.R.; Stone, C.M.; Hammetter, W.F.

1988-05-23

292

Component stress during freeze/thaw cycling  

NASA Astrophysics Data System (ADS)

During the past year, the feasibility and usefulness of mathematically modeling the processes occurring in Na/S cells during freeze/thaw (F/T) cycling has been demonstrated with the identification of potential stress producing phenomena. The first strain measurements on functioning cells have been completed that have shown the variable nature of the positive-electrode materials, a factor that may account for the randomness of actual F/T induced failures. Physical property measurements have quantified the important effect the presence of the graphite felt can have on Young's modulus for sulfur. With the completion of the physical-property and strain measurements in the coming year, final modification will be made to the material models contained in the thermo-mechanical code. The strain data will be used to validate the accuracy of the component stress calculations. Once validated, this code can be used to identify and simulate important aspects of various design options and to determine the feasibility of proposed failure mechanisms.

Braithwaite, J. W.; Subia, S. R.; Stone, C. M.; Hammetter, W. F.

1988-05-01

293

Hot water can freeze faster than cold?!?  

E-print Network

We review the Mpemba effect, where intially hot water freezes faster than initially cold water. While the effect appears impossible at first sight, it has been seen in numerous experiments, was reported on by Aristotle, Francis Bacon, and Descartes, and has been well-known as folklore around the world. It has a rich and fascinating history, which culminates in the dramatic story of the secondary school student, Erasto Mpemba, who reintroduced the effect to the twentieth century scientific community. The phenomenon, while simple to describe, is deceptively complex, and illustrates numerous important issues about the scientific method: the role of skepticism in scientific inquiry, the influence of theory on experiment and observation, the need for precision in the statement of a scientific hypothesis, and the nature of falsifiability. We survey proposed theoretical mechanisms for the Mpemba effect, and the results of modern experiments on the phenomenon. Studies of the observation that hot water pipes are more likely to burst than cold water pipes are also described.

Monwhea Jeng

2005-12-29

294

Adaptation to seasonality and the winter freeze  

PubMed Central

Flowering plants initially diversified during the Mesozoic era at least 140 million years ago in regions of the world where temperate seasonal environments were not encountered. Since then several cooling events resulted in the contraction of warm and wet environments and the establishment of novel temperate zones in both hemispheres. In response, less than half of modern angiosperm families have members that evolved specific adaptations to cold seasonal climates, including cold acclimation, freezing tolerance, endodormancy, and vernalization responsiveness. Despite compelling evidence for multiple independent origins, the level of genetic constraint on the evolution of adaptations to seasonal cold is not well understood. However, the recent increase in molecular genetic studies examining the response of model and crop species to seasonal cold offers new insight into the evolutionary lability of these traits. This insight has major implications for our understanding of complex trait evolution, and the potential role of local adaptation in response to past and future climate change. In this review, we discuss the biochemical, morphological, and developmental basis of adaptations to seasonal cold, and synthesize recent literature on the genetic basis of these traits in a phylogenomic context. We find evidence for multiple genetic links between distinct physiological responses to cold, possibly reinforcing the coordinated expression of these traits. Furthermore, repeated recruitment of the same or similar ancestral pathways suggests that land plants might be somewhat pre-adapted to dealing with temperature stress, perhaps making inducible cold traits relatively easy to evolve. PMID:23761798

Preston, Jill C.; Sandve, Simen R.

2013-01-01

295

Freeze protection valve for solar heaters  

SciTech Connect

This patent describes a solar heater freeze protection valve apparatus comprising in combination: a valve housing; a remote sensor operatively connected to the valve housing from a remote position, the remote sensor including a bulb containing a liquid adapted to compress and expand with the temperature adjacent the bulb; a piston located in the valve body and slidable responsive to expansion and contraction of the liquid in the remote sensor; a first valve element located in the valve housing and attached to the valve piston for movement; a second valve element located in the valve housing and attached to the housing; a first valve seat in the second valve element forming an opening; a second valve seat positioned in a water passageway to allow the flow of fluid when the second valve element is in an open position and to cut off the flow of fluid when the second valve element is in a closed position. Liquid in a solar heater flows at predetermined temperature readings; and the second valve element is biased in one direction and has a second opening to increase the pressure therebehind when the first valve element closes on the first valve seat. The second valve element closes on the second valve seat.

Cromer, C.J.

1987-07-21

296

Repeated freezing induces oxidative stress and reduces survival in the freeze-tolerant goldenrod gall fly, Eurosta solidaginis.  

PubMed

Freeze tolerant insects must not only survive extracellular ice formation but also the generation of reactive oxygen species (ROS) during oxygen reperfusion upon thawing. Furthermore, diurnal fluctuations in temperature place temperate insects at risk of being exposed to multiple freeze-thaw cycles, yet few studies have examined metrics of survival and oxidative stress in freeze-tolerant insects subjected to successive freezing events. To address this, we assessed survival in larvae of the goldenrod gall fly Eurosta solidaginis, after being subjected to 0, 5, 10, 20, or 30 diurnally repeated cold exposures (RCE) to -18°C or a single freeze to -18°C for 20days. In addition, we measured indicators of oxidative stress, levels of cryoprotectants, and total aqueous antioxidant capacity in animals exposed to the above treatments at 8, 32, or 80h after their final thaw. Repeated freezing and thawing, rather than time spent frozen, reduced survival as only 30% of larvae subjected to 20 or 30 RCE successfully pupated, compared to those subjected to fewer RCE or a single 20d freeze, of which 82% pupated. RCE had little effect on the concentration of the cryoprotectant glycerol (4.26±0.66?gglycerol·ngprotein(-1) for all treatments and time points) or sorbitol (18.8±2.9?gsorbitol·mgprotein(-1) for all treatments and time points); however, sorbitol concentrations were more than twofold higher than controls (16.3±2.2?gsorbitol·mgprotein(-1)) initially after a thaw in larvae subjected to a single extended freeze, but levels returned to values similar to controls at 80h after thaw. Thawing likely produced ROS as total aqueous antioxidant capacities peaked at 1.8-fold higher than controls (14.7±1.6mmoltrolox·ngprotein(-1)) in animals exposed to 5, 10, or 20 RCE. By contrast, aqueous antioxidant capacities were similar to controls in larvae subjected to 30 RCE or the single 20d freeze regardless of time post final thaw, indicating these animals may have had an impaired ability to produce primary antioxidants. Larvae lacking an antioxidant response also had elevated levels of oxidized proteins, nearly twice that of controls (21.8±3.2mmolchloramine-T·mgprotein(-1)). Repeated freezing also lead to substantial oxidative damage to lipids that was independent of aqueous antioxidant capacity; peroxides were, on average, 5.6-fold higher in larvae subjected to 10, 20 or 30 RCE compared to controls (29.1±7.3mmolTMOP·?gprotein(-1)). These data suggest that oxidative stress due to repeated freeze-thaw cycles reduces the capacity of E. solidaginis larvae to survive freezing. PMID:24910457

Doelling, Adam R W; Griffis, Nicole; Williams, Jason B

2014-08-01

297

Infrared spectroscopy of sulfuric acid/water aerosols: Freezing characteristics  

NASA Astrophysics Data System (ADS)

A low-temperature flow cell has been used in conjunction with a Fourier transform infrared (FT-IR) spectrometer to study sulfuric acid/water aerosols. The aerosols were generated with a wide range of composition (28 to 85 wt%), including those characteristic of stratospheric sulfate aerosols, and studied over the temperature range from 240 K to 160 K. The particles exhibited deep supercooling, by as much as 100 K below the freezing point in some cases. Freezing of water ice was observed in the more dilute (<40 wt% sulfuric acid) particles, in agreement with the predictions of Jensen et al. and recent observations by Bertram et al. In contrast with theoretical predictions, however, the entire particle often does not immediately freeze, at least on the timescale of the present experiments (seconds to minutes). Freezing of the entire particle is observed at lower temperatures, well below that characteristic of the polar stratosphere.

Clapp, M. L.; Niedziela, R. F.; Richwine, L. J.; Dransfield, T.; Miller, R. E.; Worsnop, D. R.

1997-04-01

298

Condensation and freezing of droplets on superhydrophobic surfaces.  

PubMed

Superhydrophobic coatings are reported as promising candidates for anti-icing applications. Various studies have shown that as well as having ultra water repellency the surfaces have reduced ice adhesion and can delay water freezing. However, the structure or texture (roughness) of the superhydrophobic surface is subject to degradation during the thermocycling or wetting process. This degradation can impair the superhydrophobicity and the icephobicity of those coatings. In this review, a brief overview of the process of droplet freezing on superhydrophobic coatings is presented with respect to their potential in anti-icing applications. To support this discussion, new data is presented about the condensation of water onto physically decorated substrates, and the associated freezing process which impacts on the freezing of macroscopic droplets on the surface. PMID:24200089

Oberli, Linda; Caruso, Dean; Hall, Colin; Fabretto, Manrico; Murphy, Peter J; Evans, Drew

2014-08-01

299

Normal freezing of ideal ternary systems of the pseudobinary type  

NASA Technical Reports Server (NTRS)

Perfect liquid mixing but no solid diffusion is assumed in normal freezing. In addition, the molar compositions of the freezing solid and remaining liquid, respectively, follow the solidus and liquidus curves of the constitutional diagram. For the linear case, in which both the liquidus and solidus are perfectly straight lines, the normal freezing equation giving the fraction solidified at each melt temperature and the solute concentration profile in the frozen solid was determined as early as 1902, and has since been repeatedly published. Corresponding equations for quadratic, cubic or higher-degree liquidus and solidus lines have also been obtained. The equation of normal freezing for ideal ternary liquid solutions solidified into ideal solid solutions of the pseudobinary type is given. Sample computations with the use of this new equation were made and are given for the Ga-Al-As system.

Li, C. H.

1972-01-01

300

Phase separation during freezing upon warming of aqueous solutions  

NASA Astrophysics Data System (ADS)

Using differential scanning calorimetry, we show that the addition of solute(s) to emulsified water lowers the freezing temperature to <231 K, the homogeneous nucleation temperature of pure bulk water, or even completely suppresses freezing. In the latter case, freezing upon warming occurs above TX ? 150 K and leads to a phase separation into pure ice and a freeze-concentrated solution (FCS) which crystallizes upon further warming. We also show that emulsified 20-21.5 wt. % HCl solutions and the FCS of HCl/H2O solutions transform to glass at Tg ? 127-128 K, i.e., lower than Tg ? 136 K of water. We suggest that water nanodrops adsorbed on fumed silica resemble bulk water more than water confined in nanoscaled confinement and also more than nanoscaled water domains in aqueous solution.

Bogdan, A.; Loerting, T.

2014-11-01

301

even without a freeze plants can be damaged.  

E-print Network

, orchids as well as many aroids, succulent plants and Amazon lilies. It is worth considering movable of water (e.g. a man-made lake ­ heat stored in water and released during a radiational freeze can help

Jawitz, James W.

302

On deriving flux freezing in magnetohydrodynamics by direct differentiation  

NASA Astrophysics Data System (ADS)

The magnetic flux freezing theorem is a basic principle of ideal magnetohydrodynamics (MHD), a commonly used approximation to describe the aspects of astrophysical and laboratory plasmas. The theorem states that the magnetic flux—the integral of magnetic field penetrating a surface—is conserved in time as that surface is distorted in time by fluid motions. Pedagogues of MHD commonly derive flux freezing without showing how to take the material derivative of a general flux integral and/or assuming a vanishing field divergence from the outset. Here I avoid these shortcomings and derive flux freezing by direct differentiation, explicitly using a Jacobian to transform between the evolving field-penetrating surface at different times. The approach is instructive for its generality and helps elucidate the role of magnetic monopoles in breaking flux freezing. The paucity of appearances of this derivation in standard MHD texts suggests that its pedagogic value is underappreciated.

Blackman, Eric G.

2013-03-01

303

Multiphoton imaging of biological samples during freezing and heating  

NASA Astrophysics Data System (ADS)

We applied multiphoton microscopic imaging to observe freezing and heating effects in plant- and animal cell samples. The experimental setups consisted of a multiphoton imaging system and a heating and cooling stage which allows for precise temperature control from liquid nitrogen temperature (-196°C 77 K) up to +600°C (873 K) with heating/freezing rates between 0.01 K/min and 150 K/min. Two multiphoton imaging systems were used: a system based on a modified optical microscope and a flexible mobile system. To illustrate the imaging capabilities, plant leafs as well as animal cells were microscopically imaged in vivo during freezing based on autofluorescence lifetime and intensity of intrinsic molecules. The measurements illustrate the usefulness of multiphoton imaging to investigate freezing effects on animal and plant cells.

Breunig, H. G.; Uchugonova, A.; König, K.

2014-02-01

304

ARCTIC FOUNDATIONS, INC. FREEZE BARRIER SYSTEM - SITE TECHNOLOGY CAPSULE  

EPA Science Inventory

Arctic Foundations, Inc. (AFI), of Anchorage, Alaska has developed a freeze barrier technology designed to prevent the migration of contaminants in groundwater by completely isolating contaminant source areas until appropriate remediation techniques can be applied. With this tec...

305

ARCTIC FOUNDATIONS, INC. FREEZE BARRIER TECHNOLOGY; INNOVATIVE TECHNOLOGY EVALUATION REPORT  

EPA Science Inventory

Arctic Foundations, Inc. (AFI), of Anchorage, Alaska has developed a freeze barrier technology designed to prevent the migration of contaminants in groundwater by completely isolating contaminant source areas until appropriate remediation techniques can be applied. With this tech...

306

Physicothermal Properties of Freeze-Dried Fish Oil Nanocapsules Frozen under Different Conditions  

Microsoft Academic Search

This research compared the effects of vacuum freeze drying (VFD) and conventional freeze drying (CFD) processes on the stability of fish oil–loaded nanocapsules (NCs). For CFD, the NCs showed aggregation that was dependent on the freezing temperature. The encapsulation efficiency of CFD was greater than that of VFD, except at the freezing temperature of ?30°C. From differential scanning calorimetry (DSC)

Piyawan Bejrapha; Sang-Gi Min; Suvimol Surassmo; Mi-Jung Choi

2010-01-01

307

Xylem cavitation caused by drought and freezing stress in four co-occurring Juniperus species  

E-print Network

Xylem cavitation caused by drought and freezing stress in four co-occurring Juniperus species induced by drought but in many cases, not by freezing. Rarely have vulnerability to drought and freezing and distribution of plants in many regions of the world. We studied vulnerability to drought- and freezing- induced

Jackson, Robert B.

308

Prediction of Freezing Times for Regular Multidimensional Foods using Simple Formulae  

Microsoft Academic Search

Freezing is a widely used food preservation technique. The designers and users of freezing equipment need simple prediction methods to calculate the process time. The objective of the present work was to extend the use of a simple prediction method, developed for the freezing of uni-dimensional foods, to the prediction of the freezing times of regular multi-dimensional foods, using different

V. O. Salvadori; A. De Michelis; R. H. Mascheroni

1997-01-01

309

Biphasic Investigation of Tissue Mechanical Response During Freezing Front Propagation  

PubMed Central

Cryopreservation of engineered tissue (ET) has achieved limited success due to limited understanding of freezing-induced biophysical phenomena in ETs, especially fluid-matrix interaction within ETs. To further our understanding of the freezing-induced fluid-matrix interaction, we have developed a biphasic model formulation that simulates the transient heat transfer and volumetric expansion during freezing, its resulting fluid movement in the ET, elastic deformation of the solid matrix and the corresponding pressure redistribution within. Treated as a biphasic material, the ET consists of a porous solid matrix fully saturated with interstitial fluid. Temperature-dependent material properties were employed and phase change was included by incorporating the latent heat of phase change into an effective specific heat term. Model-predicted temperature distribution, the location of the moving freezing front, and the ET deformation rates through the time course compare reasonably well with experiments reported previously. Results from our theoretical model show that behind the marching freezing front, the ET undergoes expansion due to phase change of its fluid contents. It compresses the region preceding the freezing front leading to its fluid expulsion and reduced regional fluid volume fractions. The expelled fluid is forced forward and upward into the region further ahead of the compression zone causing a secondary expansion zone; which then compresses the region further downstream with much reduced intensity. Overall, it forms an alternating expansion-compression pattern which moves with the marching freezing front. The present biphasic model helps us to gain insights into some facets of the freezing process and cryopreservation treatment that could not be gleaned experimentally. Its resulting understanding will ultimately be useful to design and improve cryopreservation protocols for ETs. PMID:22757502

Wright, Jamie; Han, Bumsoo; Chuong, Cheng-Jen

2012-01-01

310

Yukon River ice: freeze-up data (1883-1975)  

SciTech Connect

Freeze-up observations have been sporadically collected on the Yukon River since the late 19th century. This report contains data from 29 different locations on the river; the earliest observations were made in 1883. The purpose is to compile all the presently known data on the freeze-up of the Yukon River for use in future scientific studies and engineering reports. 6 refs.

Fountain, A.G.; Vaughn, B.H.

1984-01-01

311

Freeze concentration of dairy products Phase 2. Final report  

SciTech Connect

An efficient, electrically driven freeze concentration system offers potential for substantially increasing electricity demand while providing the mature dairy industry with new products for domestic and export markets together with enhanced production efficiencies. Consumer tests indicate that dairy products manufactured from freeze-concentrated ingredients are either preferred or considered equivalent in quality to fresh milk-based products. Economic analyses indicate that this technology should be competitive with thermal evaporation processes on a commercial basis.

Best, D.E.; Vasavada, K.C.

1993-09-01

312

Three keys to the radiation of angiosperms into freezing environments.  

PubMed

Early flowering plants are thought to have been woody species restricted to warm habitats. This lineage has since radiated into almost every climate, with manifold growth forms. As angiosperms spread and climate changed, they evolved mechanisms to cope with episodic freezing. To explore the evolution of traits underpinning the ability to persist in freezing conditions, we assembled a large species-level database of growth habit (woody or herbaceous; 49,064 species), as well as leaf phenology (evergreen or deciduous), diameter of hydraulic conduits (that is, xylem vessels and tracheids) and climate occupancies (exposure to freezing). To model the evolution of species' traits and climate occupancies, we combined these data with an unparalleled dated molecular phylogeny (32,223 species) for land plants. Here we show that woody clades successfully moved into freezing-prone environments by either possessing transport networks of small safe conduits and/or shutting down hydraulic function by dropping leaves during freezing. Herbaceous species largely avoided freezing periods by senescing cheaply constructed aboveground tissue. Growth habit has long been considered labile, but we find that growth habit was less labile than climate occupancy. Additionally, freezing environments were largely filled by lineages that had already become herbs or, when remaining woody, already had small conduits (that is, the trait evolved before the climate occupancy). By contrast, most deciduous woody lineages had an evolutionary shift to seasonally shedding their leaves only after exposure to freezing (that is, the climate occupancy evolved before the trait). For angiosperms to inhabit novel cold environments they had to gain new structural and functional trait solutions; our results suggest that many of these solutions were probably acquired before their foray into the cold. PMID:24362564

Zanne, Amy E; Tank, David C; Cornwell, William K; Eastman, Jonathan M; Smith, Stephen A; FitzJohn, Richard G; McGlinn, Daniel J; O'Meara, Brian C; Moles, Angela T; Reich, Peter B; Royer, Dana L; Soltis, Douglas E; Stevens, Peter F; Westoby, Mark; Wright, Ian J; Aarssen, Lonnie; Bertin, Robert I; Calaminus, Andre; Govaerts, Rafaël; Hemmings, Frank; Leishman, Michelle R; Oleksyn, Jacek; Soltis, Pamela S; Swenson, Nathan G; Warman, Laura; Beaulieu, Jeremy M

2014-02-01

313

Correlation estimates ethane plant's carbon-dioxide freezing pressure  

Microsoft Academic Search

This paper describes a new correlation model which allows quick calculation of the expected COâ freezing pressure in a turboexpander ethane extraction plant. It presents a program for use with the TI-58 calculator which incorporates the correlation equations. If the recommended 2,750 kPa minimum COâ freezing pressure is applied, then 73% ethane recovery is the maximum level that could safely

Trebble

1983-01-01

314

Effect of air voids on salt scaling and internal freezing  

Microsoft Academic Search

By combining calorimetric measurements with dilatometry, it has been possible to calculate the contributions of thermal expansion, pore pressure, and crystallization pressure of ice to the strain observed in a mortar during freezing\\/thawing cycles. Air-entrained mortars contract upon freezing, while non-air-entrained mortars expand. The expansion of the latter is attributed primarily to hydraulic pressure, owing to the rapid growth of

Zhenhua Sun; George W. Scherer

2010-01-01

315

Freezing of barley studied by infrared video thermography.  

PubMed

Freezing of barley (Hordeum vulgare), Hordeum murinum, and Holcus lanatus was studied using infrared video thermography. In the field, ice could enter H. lanatus leaves through hydathodes. In laboratory tests with barley, initially 0.4% of the leaf water froze, spreading in alternate strips of high and low freezing intensity longitudinally at 1 to 4 cm s(-1), and simultaneously spreading laterally at 0.3 cm s(-1). Similar results were obtained in the field with H. lanatus. A distinct second, more intense, freezing event spread slowly from the margins of the leaves toward the midrib. Organs of uprooted barley tested in the laboratory froze in this order: nucleated leaf, roots, older leaves, younger leaves, and secondary tillers. When ice spread from one leaf to the rest of the plant the crown delayed spread to the roots and other leaves. There was a longer delay above than below -2 degrees C, helping to protect the crown from freezing during mild frosts. Initial spread of freezing was not damaging. However, the initial spread is a prerequisite for the second freezing event, which can cause damage. The route of the initial spread of ice may be extracellular, drawing water from more gel-like parts of the cell wall. PMID:11154332

Pearce, R S; Fuller, M P

2001-01-01

316

Tissue Triage and Freezing for Models of Skeletal Muscle Disease  

PubMed Central

Skeletal muscle is a unique tissue because of its structure and function, which requires specific protocols for tissue collection to obtain optimal results from functional, cellular, molecular, and pathological evaluations. Due to the subtlety of some pathological abnormalities seen in congenital muscle disorders and the potential for fixation to interfere with the recognition of these features, pathological evaluation of frozen muscle is preferable to fixed muscle when evaluating skeletal muscle for congenital muscle disease. Additionally, the potential to produce severe freezing artifacts in muscle requires specific precautions when freezing skeletal muscle for histological examination that are not commonly used when freezing other tissues. This manuscript describes a protocol for rapid freezing of skeletal muscle using isopentane (2-methylbutane) cooled with liquid nitrogen to preserve optimal skeletal muscle morphology. This procedure is also effective for freezing tissue intended for genetic or protein expression studies. Furthermore, we have integrated our freezing protocol into a broader procedure that also describes preferred methods for the short term triage of tissue for (1) single fiber functional studies and (2) myoblast cell culture, with a focus on the minimum effort necessary to collect tissue and transport it to specialized research or reference labs to complete these studies. Overall, this manuscript provides an outline of how fresh tissue can be effectively distributed for a variety of phenotypic studies and thereby provides standard operating procedures (SOPs) for pathological studies related to congenital muscle disease. PMID:25078247

Meng, Hui; Janssen, Paul M.L.; Grange, Robert W.; Yang, Lin; Beggs, Alan H.; Swanson, Lindsay C.; Cossette, Stacy A.; Frase, Alison; Childers, Martin K.; Granzier, Henk; Gussoni, Emanuela; Lawlor, Michael W.

2014-01-01

317

Charge gradient microscopy.  

PubMed

Here we present a simple and fast method to reliably image polarization charges using charge gradient microscopy (CGM). We collected the current from the grounded CGM probe while scanning a periodically poled lithium niobate single crystal and single-crystal LiTaO3 thin film on the Cr electrode. We observed current signals at the domains and domain walls originating from the displacement current and the relocation or removal of surface charges, which enabled us to visualize the ferroelectric domains at a scan frequency above 78 Hz over 10 ?m. We envision that CGM can be used in high-speed ferroelectric domain imaging and piezoelectric energy-harvesting devices. PMID:24760831

Hong, Seungbum; Tong, Sheng; Park, Woon Ik; Hiranaga, Yoshiomi; Cho, Yasuo; Roelofs, Andreas

2014-05-01

318

Hierarchically deflated conjugate gradient  

E-print Network

We present a multi-level algorithm for the solution of five dimensional chiral fermion formulations, including domain wall and Mobius Fermions. The algorithm operates on the red-black preconditioned Hermitian operator, and directly accelerates conjugate gradients on the normal equations. The coarse grid representation of this matrix is next-to-next-to-next-to-nearest neighbour and multiple algorithmic advances are introduced, which help minimise the overhead of the coarse grid. The treatment of the coarse grids is purely four dimensional, and the bulk of the coarse grid operations are nearest neighbour. The intrinsic cost of most of the coarse grid operations is therefore comparable to those for the Wilson case. We also document the implementation of this algorithm in the BAGEL/Bfm software package and report on the measured performance gains the algorithm brings to simulations at the physical point on IBM BlueGene/Q hardware.

P A Boyle

2014-02-11

319

Gradient index polymer optics  

NASA Astrophysics Data System (ADS)

The design, fabrication, and properties of one of a new class of gradient-index lenses are reported. The lens is an f/2.25 GRIN singlet based on a nanolayered polymer composite material, designed to correct for spherical aberration. The light gathering and focusing properties of the polymer lens are compared to a homogeneous BK7 glass singlet with a similar f-number. The modulation transfer function of the polymer GRIN lens exceeded that of the homogeneous glass lens at all spatial frequencies and was as much as 3 times better at 5 cyc/mm. The weight of the polymer lens was approximately an order of magnitude less than the homogeneous glass lens.

Beadie, G.; Fleet, E.; Rosenberg, A.; Lane, Paul A.; Shirk, James S.; Kamdar, A. R.; Ponting, M.; Hiltner, A.; Baer, E.

2008-08-01

320

ON-LINE TOOLS FOR PROPER VERTICAL POSITIONING OF VERTICAL SAMPLING INTERVALS DURING SITE ASSESSMENT  

EPA Science Inventory

This presentation presents on-line tools for proper vertical positioning of vertical sampling intervals during site assessment. Proper vertical sample interval selection is critical for generate data on the vertical distribution of contamination. Without vertical delineation, th...

321

A numerical study of scalar gradients in Kelvin-Helmholtz billows  

NASA Technical Reports Server (NTRS)

A high resolution numerical technique is used to model the development of a periodically perturbed shear layer imbedded in an initially vertical gradient of a passive scalar. The technique follows the development of the vorticity through an initial linear growth state and well into the nonlinear development of Kelvin-Helmholtz billows, in the zero-viscosity, zero-diffusion limit. The resulting scalar distribution rapidly develops regions of extremely sharp scalar gradients, which wind around the periodically spaced vortical low gradient cores. Vertical cross sections through different parts of the billow structure are presented and compared with rocket measurements of electron density fine structure in the mesosphere. Gradient limits imposed by finite diffusion are calculated, and implications for atmospheric radar observations are discussed.

Parker, J. W.; Bowhill, S. A.

1989-01-01

322

Ultrastructure of hypertrophic cartilage: histochemical procedures compared with high pressure freezing and freeze substitution.  

PubMed

The effect of cationic dyes on the ultrastructure of hypertrophic cartilage was compared with results obtained with modern cryotechniques in studies on rat epiphyseal growth plate. Addition of alcian blue, acridine orange, cupromeronic blue, ruthenium hexamine trichloride, ruthenium red, or safranin O to conventional glutaraldehyde/osmium tetroxide fixatives to a large extent resulted in prevention of chondrocyte shrinkage except for alcian blue which showed poor tissue penetration. The fine structure of the matrix in pericellular and territorial compartments appeared very coarse with areas of high contrast in tissue exposed to fixatives containing cationic dyes. This indicates structural collapse and precipitation of electron-dense material, a pattern clearly differing from that observed in specimens prepared by the cryotechniques. The dyes giving a pattern most similar to that seen after high pressure freezing, freeze substitution, and low temperature embedding were acridine orange and safranin O. It is concluded that studies of matrix ultrastructure down to the molecular level necessitate the application of cryotechniques. PMID:7529658

Engfeldt, B; Reinholt, F P; Hultenby, K; Widholm, S M; Müller, M

1994-10-01

323

Imaging the Endothelial Glycocalyx In Vitro by Rapid Freezing/Freeze Substitution Transmission Electron Microscopy  

PubMed Central

Objective Recent publications questioned the validity of endothelial cell (EC) culture studies of glycocalyx (GCX) function, due to findings that GCX in vitro may be substantially thinner than in vivo. The assessment of thickness differences is complicated by GCX collapse during dehydration for traditional electron microscopy. We measured in vitro GCX thickness using rapid freezing/freeze substitution transmission electron microscopy (RF/FS-TEM), taking advantage of high spatial resolution provided by TEM and the capability to stably preserve the GCX in its hydrated configuration by RF/FS. Methods and Results Bovine aortic and rat fat pad endothelial cells (BAEC and RFPEC) were subjected to conventional- or RF/FS-TEM. Conventionally preserved BAEC GCX was ~0.040 ?m in thickness. RF/FS-TEM revealed impressively thick BAEC GCX of ~11 ?m and RFPEC GCX of ~5 ?m. RF/FS-TEM also discerned GCX structure and thickness variations due to heparinase III enzyme treatment and extracellular protein removal, respectively. Immunoconfocal studies confirmed that the in vitro GCX is several microns thick and is comprised of extensive and well integrated heparan sulfate, hyaluronic acid, and protein layers. Conclusions New observations by RF/FS-TEM reveal substantial GCX layers on cultured EC, supporting their continued use for fundamental studies of GCX and its function in the vasculature. PMID:21474821

Ebong, Eno E; Macaluso, Frank P; Spray, David C; Tarbell, John M

2011-01-01

324

Gradient boosting machines, a tutorial  

PubMed Central

Gradient boosting machines are a family of powerful machine-learning techniques that have shown considerable success in a wide range of practical applications. They are highly customizable to the particular needs of the application, like being learned with respect to different loss functions. This article gives a tutorial introduction into the methodology of gradient boosting methods with a strong focus on machine learning aspects of modeling. A theoretical information is complemented with descriptive examples and illustrations which cover all the stages of the gradient boosting model design. Considerations on handling the model complexity are discussed. Three practical examples of gradient boosting applications are presented and comprehensively analyzed. PMID:24409142

Natekin, Alexey; Knoll, Alois

2013-01-01

325

Immersion freezing of biological particles at LACIS  

NASA Astrophysics Data System (ADS)

Biological particles, especially bacteria being ubiquitous in the atmosphere, belong to the most efficient ice nuclei (IN) (Möhler, 2008) and hence might have a large impact on weather and climate. In this study, the immersion freezing behavior of different size segregated biological particles is investigated at the laminar flow tube LACIS (Leipzig Aerosol Cloud Interaction Simulator, Hartmann et al., 2011). For these experiments, SNOMAX and outer membrane vesicles (OMV) are used as IN. SNOMAX industrially produced from Pseudomonas-syringae bacteria, which are very ice nucleation active, can be seen as a proxy for ice nucleating bacteria in general. On the surface of these bacteria, ice nucleating proteins that initiate the freezing are situated (Maki et al., 1974). Additionally, it has been found that some ice nucleating bacteria strains have the ability to produce OMV, i.e., strangulated parts of the bacterial cell consisting of the same membrane material (Phelps et al., 1986). These OMV might contain the same ice nucleating proteins on their surface and thus might be able to nucleate ice as well. The OMV used in our experiments were extracted from bacteria cultivated from rain samples collected in Denmark from 30 m height. In our experiments, the biological particles are suspended in air via atomization, size selected by means of a Differential Mobility Particle Sizer, and then fed into LACIS. In LACIS, well defined droplets are produced by activating the biological particles to cloud droplets, so that each droplet contains only one biological particle. By decreasing the temperature in LACIS, these droplets are frozen. To determine the ice fraction, i.e., the fraction of frozen droplets to all particles, the liquid and frozen droplets are distinguished by means of a newly self-built optical device, which is positioned under LACIS, using the depolarization of light scattered by a single particle. The ice fractions are measured as a function of temperature and then used to determine nucleation rates. For 650 nm and 800 nm SNOMAX particles, the ice fraction versus temperature is a very steep function and almost linear within the temperature range between -3°C and -10°C. The ice fraction observed for the OMV is close to the detection limit, in a range of about 1 %, implying that only a small fraction of the OMV are ice nucleating active. Hartmann, S., et al. (2011), Homogeneous and heterogeneous ice nucleation at LACIS: operating principle and theoretical studies, Atmos. Chem. Phys., 11(4), 1753-1767. Maki, L. R., et al. (1974), Ice nucleation induced by Pseudomonas-syringae, Appl. Microbiol., 28(3), 456-459. Möhler, O., et al. (2008), Heterogeneous ice nucleation activity of bacteria: new laboratory experiments at simulated cloud conditions, Biogeosciences, 5(5), 1425-1435. Phelps, P., et al. (1986), Release of cell-free ice nuclei by erwina-herbicola, J. Bacteriol., 167(2), 496-502.

Clauss, T.; Hartmann, S.; Temkiv, T. S.; Augustin, S.; Gosewinkel Karlson, U.; Sahyoun, M. M.; Niedermeier, D.; Wex, H.; Voigtländer, J.; Raddatz, M.; Stratmann, F.

2012-04-01

326

Inhibition, Executive Function, and Freezing of Gait  

PubMed Central

Background Studies suggest that freezing of gait (FoG) in people with Parkinson’s disease (PD) is associated with declines in executive function (EF). However, EF is multi-faceted, including three dissociable components: inhibiting prepotent responses, switching between task sets, and updating working memory. Objective This study investigated which aspect of EF is most strongly associated with FoG in PD. Method Three groups were studied: adults with PD (with and without FoG) and age-matched, healthy adults. All participants completed a battery of cognitive tasks previously shown to discriminate among the three EF components. Participants also completed a turning-in-place task that was scored for FoG by neurologists blind to subjects’ self-reported FoG. Results Compared to both other groups, participants with FoG showed significant performance deficits in tasks associated with inhibitory control, even after accounting for differences in disease severity, but no significant deficits in task-switching or updating working memory. Surprisingly, the strongest effect was an intermittent tendency of participants with FoG to hesitate, and thus miss the response window, on go trials in the Go-Nogo task. The FoG group also made slower responses in the conflict condition of the Stroop task. Physician-rated FoG scores were correlated both with failures to respond on go trials and with failures to inhibit responses on nogo trials in the Go-Nogo task. Conclusion These results suggest that FoG is associated with a specific inability to appropriately engage and release inhibition, rather than with a general executive deficit. PMID:24496099

Cohen, Rajal G.; Klein, Krystal A.; Nomura, Mariko; Fleming, Michael; Mancini, Martina; Giladi, Nir; Nutt, John G.; Horak, Fay B.

2014-01-01

327

Measurement of electric field and gradient in the plasma sheath using clusters of floating microspheres  

SciTech Connect

A method for measuring the time-averaged vertical electric field and its gradient in the plasma sheath using clusters with n=2 or 3 floating microspheres of known mass is described. The particle charge q is found by determining the ratio of the breathing frequency to the center-of-mass frequency for horizontal (in-plane) oscillations. The electric field at the position of the particles is then calculated using the measured charge-to-mass ratio, and the electric-field gradient is determined from the vertical resonance frequency. The Debye length is also found. Experimental results are in agreement with a simple sheath model.

Sheridan, T. E.; Katschke, M. R.; Wells, K. D. [Department of Physics and Astronomy, Ohio Northern University, Ada, Ohio 45810 (United States)

2007-02-15

328

Simultaneous measurement of gravity acceleration and gravity gradient with an atom interferometer  

SciTech Connect

We demonstrate a method to measure the gravitational acceleration with a dual cloud atom interferometer; the use of simultaneous atom interferometers reduces the effect of seismic noise on the gravity measurement. At the same time, the apparatus is capable of accurate measurements of the vertical gravity gradient. The ability to determine the gravity acceleration and gravity gradient simultaneously and with the same instrument opens interesting perspectives in geophysical applications.

Sorrentino, F.; Lien, Y.-H.; Rosi, G.; Tino, G. M. [Dipartimento di Fisica e Astronomia and LENS, Universita di Firenze, INFN Sezione di Firenze, via Sansone 1, I-50019 Sesto Fiorentino (Italy); Bertoldi, A. [Laboratoire Charles Fabry de l'Institut d'Optique, CNRS and Universite Paris-Sud Campus Polytechnique, RD 128, F-91127 Palaiseau cedex (France); Bodart, Q. [Dipartimento di Fisica e Astronomia and LENS, Universita di Firenze, INFN Sezione di Firenze, via Sansone 1, I-50019 Sesto Fiorentino (Italy); European Space Agency, Research and Scientific Support Department, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands); Cacciapuoti, L. [European Space Agency, Research and Scientific Support Department, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands); Angelis, M. de [Istituto di Fisica Applicata 'Nello Carrara' CNR, via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Prevedelli, M. [Dipartimento di Fisica dell'Universita di Bologna, Via Irnerio 46, I-40126, Bologna (Italy)

2012-09-10

329

Vertical allometry: fact or fiction?  

PubMed

In pharmacokinetics, vertical allometry is referred to the clearance of a drug when the predicted human clearance is substantially higher than the observed human clearance. Vertical allometry was initially reported for diazepam based on a 33-fold higher human predicted clearance than the observed human clearance. In recent years, it has been found that many other drugs besides diazepam, can be classified as drugs which exhibit vertical allometry. Over the years, many questions regarding vertical allometry have been raised. For example, (1) How to define and identify the vertical allometry? (2) How much difference should be between predicted and observed human clearance values before a drug could be declared 'a drug which follows vertical allometry'? (3) If somehow one can identify vertical allometry from animal data, how this information can be used for reasonably accurate prediction of clearance in humans? This report attempts to answer the aforementioned questions. The concept of vertical allometry at this time remains complex and obscure but with more extensive works one can have better understanding of 'vertical allometry'. PMID:24534003

Mahmood, Iftekhar; Boxenbaum, Harold

2014-04-01

330

Freeze-thaw cycles enhance decellularization of large tendons.  

PubMed

The use of decellularized tendon tissue as a scaffold for tendon tissue engineering provides great opportunities for future clinical and current research applications. The aim of this study was to assess the effect of repetitive freeze-thaw cycles and two different detergents, t-octyl-phenoxypolyethoxyethanol (Triton X-100) and sodium dodecyl sulfate (SDS), on decellularization effectiveness and cytocompatibility in large tendons. Freshly collected equine superficial and deep digital flexor tendons were subjected to decellularization according to four different protocols (1 and 2: freeze-thaw cycles combined with either Triton X-100 or SDS; 3 and 4: Triton X-100 or SDS). Decellularization effectiveness was assessed based on the reduction of vital cell counts, histologically visible nuclei, and DNA content. Transmission electron microscopy was performed to evaluate cellular and extracellular matrix integrity. Further, cytocompatibility of scaffolds that had been decellularized according to the protocols including freeze-thaw cycles (protocols 1 and 2) was assessed by seeding the scaffolds with superparamagnetic iron oxide labeled mesenchymal stromal cells and monitoring the cells histologically and by magnetic resonance imaging for two weeks. Decellularization was significantly more effective when using the protocols including freeze-thaw cycles, leaving only roughly 1% residual nuclei and 20% residual DNA, whereas samples that had not undergone additional freeze-thaw cycles contained roughly 20% residual nuclei and 40% residual DNA. No morphological extracellular matrix alterations due to decellularization could be observed. Scaffolds prepared by both protocols including freeze-thaw cycles were cytocompatible, but the cell distribution into the scaffold tended to be better in scaffolds that had been decellularized using freeze-thaw cycles combined with Triton X-100 instead of SDS. PMID:23879725

Burk, Janina; Erbe, Ina; Berner, Dagmar; Kacza, Johannes; Kasper, Cornelia; Pfeiffer, Bastian; Winter, Karsten; Brehm, Walter

2014-04-01

331

Does Anxiety Cause Freezing of Gait in Parkinson's Disease?  

PubMed Central

Individuals with Parkinson's disease (PD) commonly experience freezing of gait under time constraints, in narrow spaces, and in the dark. One commonality between these different situations is that they may all provoke anxiety, yet anxiety has never been directly examined as a cause of FOG. In this study, virtual reality was used to induce anxiety and evaluate whether it directly causes FOG. Fourteen patients with PD and freezing of gait (Freezers) and 17 PD without freezing of gait (Non-Freezers) were instructed to walk in two virtual environments: (i) across a plank that was located on the ground (LOW), (ii) across a plank above a deep pit (HIGH). Multiple synchronized motion capture cameras updated participants' movement through the virtual environment in real-time, while their gait was recorded. Anxiety levels were evaluated after each trial using self-assessment manikins. Freezers performed the experiment on two separate occasions (in their ON and OFF state). Freezers reported higher levels of anxiety compared to Non-Freezers (p<0.001) and all patients reported greater levels of anxiety when walking across the HIGH plank compared to the LOW (p<0.001). Freezers experienced significantly more freezing of gait episodes (p?=?0.013) and spent a significantly greater percentage of each trial frozen (p?=?0.005) when crossing the HIGH plank. This finding was even more pronounced when comparing Freezers in their OFF state. Freezers also had greater step length variability in the HIGH compared to the LOW condition, while the step length variability in Non-Freezers did not change. In conclusion, this was the first study to directly compare freezing of gait in anxious and non-anxious situations. These results present strong evidence that anxiety is an important mechanism underlying freezing of gait and supports the notion that the limbic system may have a profound contribution to freezing in PD. PMID:25250691

Ehgoetz Martens, Kaylena A.; Ellard, Colin G.; Almeida, Quincy J.

2014-01-01

332

Density Gradients in Chemistry Teaching  

ERIC Educational Resources Information Center

Outlines experiments in which a density gradient might be used to advantage. A density gradient consists of a column of liquid, the composition and density of which varies along its length. The procedure can be used in analysis of solutions and mixtures and in density measures of solids. (Author/TS)

Miller, P. J.

1972-01-01

333

Height and gradient from shading  

Microsoft Academic Search

The method described here for recovering the shape of a surface from a shaded image can deal with complex, wrinkled surfaces. Integrability can be enforced easily because both surface height and gradient are represented (A gra- dient field is integrable if it is the gradient of some surface height function). The robustness of the method stems in part from linearization

Berthold K. P. Horn

1990-01-01

334

Rapid Gradient-Echo Imaging  

PubMed Central

Gradient echo sequences are widely used in magnetic resonance imaging (MRI) for numerous applications ranging from angiography to perfusion to functional MRI. Compared with spin-echo techniques, the very short repetition times of gradient-echo methods enable very rapid 2D and 3D imaging, but also lead to complicated “steady states.” Signal and contrast behavior can be described graphically and mathematically, and depends strongly on the type of spoiling: fully balanced (no spoiling), gradient spoiling, or RF-spoiling. These spoiling options trade off between high signal and pure T1 contrast while the flip angle also affects image contrast in all cases, both of which can be demonstrated theoretically and in image examples. As with spin-echo sequences, magnetization preparation can be added to gradient-echo sequences to alter image contrast. Gradient echo sequences are widely used for numerous applications such as 3D perfusion imaging, functional MRI, cardiac imaging and MR angiography. PMID:23097185

Hargreaves, Brian

2012-01-01

335

Vertically reciprocating auger  

NASA Technical Reports Server (NTRS)

The mathematical model and test results developed for the Vertically Reciprocating Auger (VRA) are summarized. The VRA is a device capable of transporting cuttings that result from below surface drilling. It was developed chiefly for the lunar surface, where conventional fluid flushing while drilling would not be practical. The VRA uses only reciprocating motion and transports material through reflections with the surface above. Particles are reflected forward and land ahead of radially placed fences, which prevent the particles from rolling back down the auger. Three input wave forms are considered to drive the auger. A modified sawtooth wave form was chosen for testing, over a modified square wave or sine wave, due to its simplicity and effectiveness. The three-dimensional mathematical model predicted a sand throughput rate of 0.2667 pounds/stroke, while the actual test setup transported 0.075 pounds/stroke. Based on this result, a correction factor of 0.281 is suggested for a modified sawtooth input.

Etheridge, Mark; Morgan, Scott; Fain, Robert; Pearson, Jonathan; Weldi, Kevin; Woodrough, Stephen B., Jr.

1988-01-01

336

Modelling the vertical thermal stratification in the North Sea - advantages of using adaptive coordinates  

NASA Astrophysics Data System (ADS)

The seasonal stratification in the North Sea which is characterised by a sharp summer thermocline oscillating on semi-diurnal (tidal and inertial) timescales has been studied in a numerical model (GETM) of the coupled system North Sea / Baltic Sea. The setup includes three nested grids: a 4 nm one for the North Atlantic, a 1 nm grid for the North Sea / Baltic Sea and a 600 m grid for the southern North Sea. The model results are analysed for the period 2003-2012. To validate the modelling system, point measurements but also vertical Scanfish-transect covering the entire North Sea are used. To assess the impact of the vertical coordinate system, a twin experiment is started: a) a run with fixed sigma-coordinates and b) a run with adaptive coordinates with an adaptation towards stratification. The differences are quantified in terms of Potential Energy Anomaly, bottom and surface temperature differences and numerical mixing. The results indicate that the adaptive coordinates show an excellent performance in reproducing the location of the thermocline and the temperature gradient across the thermocline. Whereas the sigma coordinates also match the thermocline-location, its vertical gradient is significantly underestimated. In the vicinity of the thermocline the adaptive coordinates allow for a vertical grid spacing of down to 5-10 cm, which is hardly feasible in classical vertical coordinate systems. Additionally, the minimum vertical viscosity/diffusivity at the thermocline is one order of magnitude lower than for sigma coordinates. Transforming the vertical gradient and diffusivity into a vertical flux gives higher values for sigma coordinates and allow for an higher exchange across the thermocline. Here the results for the adaptive coordinates show the expected blocking behaviour. The better representation of vertical gradients by using adaptive coordinates reduces the numerical mixing and thus the artificial effects of the numerics. Since the adaptive coordinates are spatially and temporal varying, they allow for the oscillation of the coordinate lines with the moving thermocline due to internal waves or internal tides. This gives lower values of numerical mixing. The total stratified area during the summer does not vary much between the two runs. Only in the southern part of the North Sea significant differences are visible. Our results show that vertical adaptive coordinates are beneficial in modelling regions with spatial and temporal varying stratification. Although the adaptive coordinates introduce computational overhead of roughly 10% for hydrodynamic runs, this is compensated by the excellent performance in reproducing vertical gradients. Moreover, the overhead is negligible in biogeochemical applications where most of the computational time is spend in the advection routines.

Gräwe, Ulf; Holtermann, Peter; Klingbeil, Knut; Burchard, Hans

2013-04-01

337

Gradient elution in capillary electrochromatography  

SciTech Connect

In analogy to pressure-driven gradient techniques in high-performance liquid chromatography, a system has been developed for delivering electroosmotically-driven solvent gradients for capillary electrochromatography (CEC). Dynamic gradients with sub-mL/min flow rates are generated by merging two electroosmotic flows that are regulated by computer-controlled voltages. These flows are delivered by two fused-silica capillary arms attached to a T-connector, where they mix and then flow into a capillary column that has been electrokinetically packed with 3-mm reversed-phase particles. The inlet of one capillary arm is placed in a solution reservoir containing one mobile phase and the inlet of the other is placed in a second reservoir containing a second mobile phase. Two independent computer-controlled programmable high-voltage power supplies (0-50 kV)--one providing an increasing ramp and the other providing a decreasing ramp--are used to apply variable high-voltage potentials to the mobile phase reservoirs to regulate the electroosmotic flow in each arm. The ratio of the electroosmotic flow rates between the two arms is changed with time according to the computer-controlled voltages to deliver the required gradient profile to the separation column. Experiments were performed to confirm the composition of the mobile phase during a gradient run and to determine the change of the composition in response to the programmed voltage profile. To demonstrate the performance of electroosmotically-driven gradient elution in CEC, a mixture of 16 polycyclic aromatic hydrocarbons (PAHs) was separated in less than 90 minutes. This gradient technique is expected to be well-suited for generating not only solvent gradients in CEC, but also other types of gradients such as pH- and ionic-strength gradients in capillary electrokinetic separations and analyses.

Anex, D.; Rakestraw, D.J. [Sandia National Labs., Livermore, CA (United States); Yan, Chao; Dadoo, R.; Zare, R.N. [Stanford Univ., CA (United States). Dept. of Chemistry

1997-08-01

338

The Gains from Vertical Scaling  

ERIC Educational Resources Information Center

It is often assumed that a vertical scale is necessary when value-added models depend upon the gain scores of students across two or more points in time. This article examines the conditions under which the scale transformations associated with the vertical scaling process would be expected to have a significant impact on normative interpretations…

Briggs, Derek C.; Domingue, Ben

2013-01-01

339

Measuring Growth with Vertical Scales  

ERIC Educational Resources Information Center

A vertical score scale is needed to measure growth across multiple tests in terms of absolute changes in magnitude. Since the warrant for subsequent growth interpretations depends upon the assumption that the scale has interval properties, the validation of a vertical scale would seem to require methods for distinguishing interval scales from…

Briggs, Derek C.

2013-01-01

340

Vertical axis wind turbine motor  

Microsoft Academic Search

A wind power conversion turbine motor has a body supported to rotate about a vertical axis and carrying a plurality of substantially upright vanes substantially spaced from the vertical axis and circumferentially spaced from one another so that wind thrusting propulsively against outer sides of the vanes can move across the space circumscribed by the vanes and thrust propulsively against

Rumsey

1977-01-01

341

Modeling Verticality Estimation During Locomotion  

E-print Network

for gravitational vertical estimation is introduced including an inclinometer combined with an imu, as proposed´eal, Qc, Canada 3 Laboratoire de Physiologie de la Perception et de l'Action, Coll`ege de France, Paris, France Abstract Estimation of the gravitational vertical is a fundamental problem faced by locomoting

Hayward, Vincent

342

Preparation of chitosan nanocompositeswith a macroporous structure by unidirectional freezing and subsequent freeze-drying.  

PubMed

Chitosan is the N-deacetylated derivative of chitin, a naturally abundant mucopolysaccharide that consists of 2-acetamido-2-deoxy-?-d-glucose through a ? (1?4) linkage and is found in nature as the supporting material of crustaceans, insects, etc. Chitosan has been strongly recommended as a suitable functional material because of its excellent biocompatibility, biodegradability, non-toxicity, and adsorption properties. Boosting all these excellent properties to obtain unprecedented performances requires the core competences of materials chemists to design and develop novel processing strategies that ultimately allow tailoring the structure and/or the composition of the resulting chitosan-based materials. For instance, the preparation of macroporous materials is challenging in catalysis, biocatalysis and biomedicine, because the resulting materials will offer a desirable combination of high internal reactive surface area and straightforward molecular transport through broad "highways" leading to such a surface. Moreover, chitosan-based composites made of two or more distinct components will produce structural or functional properties not present in materials composed of one single component. Our group has been working lately on cryogenic processes based on the unidirectional freezing of water slurries and/or hydrogels, the subsequent freeze-drying of which produce macroporous materials with a well-patterned structure. We have applied this process to different gels and colloidal suspensions of inorganic, organic, and hybrid materials. In this review, we will describe the application of the process to chitosan solutions and gels typically containing a second component (e.g., metal and ceramic nanoparticles, or carbon nanotubes) for the formation of chitosan nanocomposites with a macroporous structure. We will also discuss the role played by this tailored composition and structure in the ultimate performance of these materials. PMID:25421320

Aranaz, Inmaculada; Gutiérrez, María C; Ferrer, María Luisa; del Monte, Francisco

2014-11-01

343

Arabidopsis ESK1 encodes a novel regulator of freezing tolerance.  

PubMed

The eskimo1 (esk1) mutation of Arabidopsis resulted in a 5.5 degrees C improvement in freezing tolerance in the absence of cold acclimation. Here we show that the increase in freezing tolerance is not associated with any increase in the ability to survive drought or salt stresses, which are similar to freezing in their induction of cellular dehydration. Genome-wide comparisons of gene expression between esk1-1 and wild type indicate that mutations at esk1 result in altered expression of transcription factors and signaling components and of a set of stress-responsive genes. Interestingly, the list of 312 genes regulated by ESK1 shows greater overlap with sets of genes regulated by salt, osmotic and abscisic acid treatments than with genes regulated by cold acclimation or by the transcription factors CBF3 and ICE1, which have been shown to control genetic pathways for freezing tolerance. Map-based cloning identified the esk1 locus as At3g55990. The wild-type ESK1 gene encodes a 57-kDa protein and is a member of a large gene family of DUF231 domain proteins whose members encode a total of 45 proteins of unknown function. Our results indicate that ESK1 is a novel negative regulator of cold acclimation. Mutations in the ESK1 gene provide strong freezing tolerance through genetic regulation that is apparently very different from previously described genetic mechanisms of cold acclimation. PMID:17316173

Xin, Zhanguo; Mandaokar, Ajin; Chen, Junping; Last, Robert L; Browse, John

2007-03-01

344

'Banking time': egg freezing and the negotiation of future fertility.  

PubMed

This paper examines the relatively recent practice of non-medical egg freezing, in which women bank their eggs for later use in conceiving a child. Non-medical egg freezing has only been available for about the last five years, as new vitrification techniques have made the success rates for actual conception more reliable than the earlier method of slow freezing. I draw on interviews with both clinicians and women who have banked their eggs to consider how this novel practice articulates with broader issues about the relationship between sexuality, reproduction and the political economy of household formation. Non-medical egg-freezing provides a technical solution to a number of different problems women face with regard to the elongation of the life course, the extension of education, the cost of household establishment and the iterative nature of relationship formation, thematised by the ubiquity of internet dating among the interviewees. I focus on the ways women used egg freezing to manage and reconcile different forms of time. PMID:25247927

Waldby, Catherine

2014-09-23

345

Units of freezing of deep supercooled water in woody xylem.  

PubMed

The low temperature exotherms (LTE) of 1-year-old twigs of Haralson apple (Malus pumila Mill.), shagbark hickory (Carya ovata [Mill.] K. Koch), green ash (Fraxinus pennsylvanica Marsh), honey locust (Gleditsia triacanthos L.), American chestnut (Castanea dentata [Marsh] Borkh.), and red oak (Quercus rubra L.) were determined by differential thermal analysis (DTA). In one type of experiment freezing during a DTA experiment was halted for up to 2.5 hours after part of the supercooled water had frozen at temperatures between -25 and -42 C. Upon resumption of cooling the freezing started within 2 C of the stopping temperature. In a second type of experiment living and dead cells were microscopically observed in the same ray after partial freezing in the DTA apparatus. In another experiment, the LTE persisted even after tangential and radial sectioning of the twig to 0.13 millimeters. In a final experiment the LTE of a single multiseriate ray of red oak had the same shape as the LTE of wood with many uniseriate rays.These experiments confirm that the deep supercooled water in woody xylem or pith freezes in numerous independent events over a span of as much as 20 C. The units which freeze in an event are single cells or small groups of cells. Ice grows very slowly if at all from these units, and water moves very slowly from unfrozen cells to frozen ones. Deep supercooling of ray parenchyma does not require an intact ray. PMID:16661390

Hong, S G; Sucoff, E

1980-07-01

346

[Cryopreservation of thyroid pieces--optimal freezing condition and recovery].  

PubMed

We have studied the cryopreservation of thyroid pieces for the purpose of autotransplantation. In this paper, the optimal freezing condition was investigated by comparing the survival cells of the cryopreserved thyroid pieces under various freezing conditions, including cooling rate, freezing medium, cryoprotectant, size of pieces and prefreezing incubation. The recovery regarded as survival rate was also evaluated. Based on the results, the optimal freezing condition was that 1 mm 3 of the thyroid pieces in the freezing medium, consisted of culture medium supplemented with 10% of fetal bovine serum and 10% of dimethylsulfoxide, were cooled slowly until -80 degrees C with prefreezing incubation at 4 degrees C for 1 hour and kept in liquid nitrogen for preservation. The number of survival cells under the optimal condition was 1.24-2.03 (1.71 +/- 0.40) x 10(6)/0.1 g tissue, and recovery was 25.2-58.0 (45.5 +/- 14.6)%. This high survival rate suggests the possibility that the cryopreserved thyroid pieces are utilized as the autografts maintaining the intact follicles. PMID:8309467

Kitamura, Y; Shimizu, K; Nagahama, M; Shoji, T

1994-01-01

347

Line-of-sight electron density gradients as deduced from an empirical ionospheric model  

NASA Technical Reports Server (NTRS)

A topside ionospheric model (Bent Ionospheric Model) was developed for an accurate prediction of integrated total electron content (TEC), from a global data acquired for the years 1962 to 1969. In this paper the effects of line-of-sight electron density gradients on ground to satellite measurements are discussed. The results of analyses show that in the presence of increasing density gradients, deduced values of vertical electron content or slab thicknesses will be too large, while for decreasing gradients these values will be smaller than they should be.

Nesterczuk, G.; Kozelsky, J. K.; Behuncik, J. A.

1976-01-01

348

A sampler for quantifying the vertical distribution of macroinvertebrates in shallow wetlands  

USGS Publications Warehouse

A sampler for quantifying the vertical distribution of aquatic macroinvertebrates in wetlands is described. This device will facilitate quantitative sampling of macroinvertebrates in waterfowl ecology and related studies. Because it simultaneously collects benthic and pelagic invertebrates the sampler reduces bias associated with sampling macroinvertebrates that occupy the benthic-pelagic interface of wetlands. The sampling device also separates benthic and pelagic macroinvertebrates into separate vertical profiles to facilitate studies of distribution patterns or the influence of chemical and physical gradients on invertebrate vertical distribution.

MacKay, J.; Euliss, N.H., Jr.

1993-01-01

349

Progression of fusion during rapid freezing for electron microscopy.  

PubMed

The method used to determine the rate of fusion was based on the large difference in the dielectric constants of water and ice. A thin (50--60 micrometers) slice of a gelatin gel was used as the dielectric in a plate condenser. The slice was placed on a metal electrode built in a specimen carrier which was dropped on a silver freezing surface kept at below 70 K, forming the other plate of the condenser. Freezing of the gelatin causes a marked decrease in a 20,000 cycle current passing through the condenser. Since the thickness of the layer of frozen material was shown to be a function of the reciprocal of the current, it was possible to determine the course of fusion of the section. Freezing started at a high rate which declined during the first 5 ms but then increased again and usually became quite high at the end of fusion. PMID:379347

Van Harreveld, A; Trubatch, J

1979-04-01

350

Amides as cryoprotectants for freezing stallion semen: a review.  

PubMed

Stallion semen cryopreservation, despite its impact on the horse industry, is not an established technology. During the last years, a number of modifications have been proposed to the freezing process, however, a large population of stallions still have poor semen quality and fertility after frozen-thawed. Glycerol toxicity could be a reason for the variation on stallion sperm freezability. There are limited publications concerning the use of alternative cryoprotectants for equine sperm. Glycerol is contraceptive for some species and other cryoprotectors, such as amides, have been show to be a good option for freezing semen of these species. Recent reports have shown encouraging data respecting the use of amides as cryoprotectants for stallions, with more remarkable improvements for semen from stallions that freeze poorly when glycerol is used. PMID:16099609

Alvarenga, M A; Papa, F O; Landim-Alvarenga, F C; Medeiros, A S L

2005-10-01

351

A case history of a tunnel constructed by ground freezing  

NASA Astrophysics Data System (ADS)

Artificial ground freezing was used for structural support and groundwater control for a 37 m long, 3.2 m diameter tunnel located about 2 m beneath high speed railroad lines in Syracuse, New York. A double row of freeze pipes spaced approximately 0.9 m on-center was used around the periphery of the tunnel above the spring line, while only a single row of freeze pipes was required below the spring line. Excavation of the frozen soil within the tunnel was accomplished with a small road header tunnel boring machine. The results of in situ testing of frozen soil, laboratory testing of frozen soils, computer analysis to predict stress deformation-time characteristics under static and cyclic loading, the instrumentation program including a comparison of estimated and measured performance are discussed.

Lacy, H. S.; Jones, J. S., Jr.; Gidlow, B.

352

Thermal stresses from large volumetric expansion during freezing of biomaterials.  

PubMed

Thermal stresses were studied in freezing of biomaterials containing significant amounts of water. An apparent specific heat formulation of the energy equation and a viscoelastic model for the mechanics problem were used to analyze the transient axi-symmetric freezing of a long cylinder. Viscoelastic properties were measured in an Instron machine. Results show that, before phase change occurs at any location, both radial and circumferential stresses are tensile and keep increasing until phase change begins. The maximum principal tensile stress during phase change increases with a decrease in boundary temperature (faster cooling). This is consistent with experimentally observed fractures at a lower boundary temperature. Large volumetric expansion during water to ice transformation was shown to be the primary contributor to large stress development. For very rapid freezing, relaxation may not be significant, and an elastic model may be sufficient. PMID:10412455

Shi, X; Datta, A K; Mukherjee, Y

1998-12-01

353

High-freezing-point fuels used for aviation turbine engines  

NASA Technical Reports Server (NTRS)

Broadened-specification aviation fuels could be produced from a greater fraction of crude source material with improvements in fuel supply and price. These fuels, particularly those with increased final boiling temperatures, would have higher freezing temperatures than current aviation turbine fuels. The higher-freezing-point fuels can be substituted in the majority of present commercial flights, since temperature data indicate that in-flight fuel temperatures are relatively mild. For the small but significant fraction of commercial flights where low fuel temperatures make higher freezing-point fuel use unacceptable, adaptations to the fuel or fuel system may be made to accommodate this fuel. Several techniques are discussed. Fuel heating is the most promising concept. One simple system design uses existing heat rejection from the fuel-lubricating oil cooler, another uses an engine-driven generator for electrical heating. Both systems offer advantages that outweigh the obvious penalties.

Friedman, R.

1979-01-01

354

Transcript expression of the freeze responsive gene fr10 in Rana sylvatica during freezing, anoxia, dehydration, and development.  

PubMed

Freeze tolerance is a critical winter survival strategy for the wood frog, Rana sylvatica. In response to freezing, a number of genes are upregulated to facilitate the survival response. This includes fr10, a novel freeze-responsive gene first identified in R. sylvatica. This study analyzes the transcriptional expression of fr10 in seven tissues in response to freezing, anoxia, and dehydration stress, and throughout the Gosner stages of tadpole development. Transcription of fr10 increased overall in response to 24 h of freezing, with significant increases in expression detected in testes, heart, brain, and lung when compared to control tissues. When exposed to anoxia; heart, lung, and kidney tissues experienced a significant increase, while the transcription of fr10 in response to 40 % dehydration was found to significantly increase in both heart and brain tissues. An analysis of the transcription of fr10 throughout the development of the wood frog showed a relatively constant expression; with slightly lower transcription levels observed in two of the seven Gosner stages. Based on these results, it is predicted that fr10 has multiple roles depending on the needs and stresses experienced by the wood frog. It has conclusively been shown to act as a cryoprotectant, with possible additional roles in anoxia, dehydration, and development. In the future, it is hoped that further knowledge of the mechanism of action of FR10 will allow for increased stress tolerance in human cells and tissues. PMID:25280399

Sullivan, K J; Biggar, K K; Storey, K B

2015-01-01

355

High field gradient particle accelerator  

DOEpatents

A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications is disclosed. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle. 10 figs.

Nation, J.A.; Greenwald, S.

1989-05-30

356

High field gradient particle accelerator  

DOEpatents

A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle.

Nation, John A. (Ithaca, NY); Greenwald, Shlomo (Haifa, IL)

1989-01-01

357

Freezing Tolerance of Citrus, Spinach, and Petunia Leaf Tissue 1  

PubMed Central

Seasonal variations in freezing tolerance, water content, water and osmotic potential, and levels of soluble sugars of leaves of field-grown Valencia orange (Citrus sinensis) trees were studied to determine the ability of citrus trees to cold acclimate under natural conditions. Controlled environmental studies of young potted citrus trees, spinach (Spinacia pleracea), and petunia (Petunia hybrids) were carried out to study the water relations during cold acclimation under less variable conditions. During the coolest weeks of the winter, leaf water content and osmotic potential of field-grown trees decreased about 20 to 25%, while soluble sugars increased by 100%. At the same time, freezing tolerance increased from lethal temperature for 50% (LT50) of ?2.8 to ?3.8°C. In contrast, citrus leaves cold acclimated at a constant 10°C in growth chambers were freezing tolerant to about ?6°C. The calculated freezing induced cellular dehydration at the LT50 remained relatively constant for field-grown leaves throughout the year, but increased for leaves of plants cold acclimated at 10°C in a controlled environment. Spinach leaves cold acclimated at 5°C tolerated increased cellular dehydration compared to nonacclimated leaves. Cold acclimated petunia leaves increased in freezing tolerance by decreasing osmotic potential, but had no capacity to change cellular dehydration sensitivity. The result suggest that two cold acclimation mechanisms are involved in both citrus and spinach leaves and only one in petunia leaves. The common mechanism in all three species tested was a minor increase in tolerance (about ?1°C) resulting from low temperature induced osmotic adjustment, and the second in citrus and spinach was a noncolligative mechanism that increased the cellular resistance to freeze hydration. PMID:16666563

Yelenosky, George; Guy, Charles L.

1989-01-01

358

High freezing point fuels used for aviation turbine engines  

NASA Technical Reports Server (NTRS)

Broadened-specification aviation fuels could be produced from a greater fraction of crude source material with improvements in fuel supply and price. These fuels, particularly those with increased final boiling temperatures, would have higher freezing temperatures than current aviation turbine fuels. For the small but significant fraction of commercial flights where low fuel temperatures make higher freezing-point fuel use unacceptable, adaptations to the fuel or fuel system may be made to accommodate this fuel. Several techniques are discussed. Fuel heating is the most promising concept. One simple design uses existing heat rejection from the fuel-lubricating oil cooler, another uses an engine-driven generator for electrical heating.

Friedman, R.

1979-01-01

359

Freeze-out conditions from fluctuations of conserved charges  

NASA Astrophysics Data System (ADS)

The latest results on fluctuations of electric charge and baryon number, simulated on the lattice by the Wuppertal-Budapest Collaboration, are compared to the moments of multiplicity distribution of the corresponding conserved charges, measured in heavy ion collision experiments by the STAR Collaboration. The purpose of this study is to extract the chemical freeze-out parameters (temperature and chemical potential) as a function of the collision energy, from first principles. Consistency between the freeze-out parameters obtained through the two different conserved charges used in the analysis is discussed.

Ratti, C.; Borsanyi, S.; Fodor, Z.; Katz, S. D.; Krieg, S.; Szabo, K. K.

2014-11-01

360

Correlation estimates ethane plant's carbon-dioxide freezing pressure  

SciTech Connect

This paper describes a new correlation model which allows quick calculation of the expected CO/sub 2/ freezing pressure in a turboexpander ethane extraction plant. It presents a program for use with the TI-58 calculator which incorporates the correlation equations. If the recommended 2,750 kPa minimum CO/sub 2/ freezing pressure is applied, then 73% ethane recovery is the maximum level that could safely be achieved with a demethanizer pressure of 1,723 kPa. The correlation model is applied to a straddle plant.

Trebble, M.A.

1983-01-31

361

Cirrus crystal nucleation by homogeneous freezing of solution droplets  

NASA Technical Reports Server (NTRS)

A numerical model consisting of a system of differential equations is used to study cirrus crystal nucleation in a rising parcel containing a distribution of cloud condensation nuclei. The evolution of the particle population and the thermodynamic variables in the parcel are examined. The results suggest that, if homogeneous freezing is not considered, liquid water should be detected below -40 C. If homogeneous freezing is considered, the rapid growth of ice crystals and vapor depletion prevent water saturation from being reached. It is shown that the likelihood of a droplet being frozen is increased by lower temperatures, larger droplet diameter, or lower solution density.

Heymsfield, Andrew J.; Sabin, Robert M.

1989-01-01

362

Gradient characterization in magnetic resonance imaging  

E-print Network

Special magnetic resonance (MR) scans, such as spiral imaging and echo-planar imaging, require speed and gradient accuracy while putting high demands on the MR gradient system that may cause gradient distortion. Additionally, ...

Cheng, Joseph Yitan

2007-01-01

363

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2014 CFR

...25 2014-07-01 2014-07-01 false Salinity gradients. 230.25 Section 230.25 ...Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity gradients form where salt water from the...

2014-07-01

364

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2013 CFR

...26 2013-07-01 2013-07-01 false Salinity gradients. 230.25 Section 230.25 ...Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity gradients form where salt water from the...

2013-07-01

365

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2012 CFR

...26 2012-07-01 2011-07-01 true Salinity gradients. 230.25 Section 230.25 ...Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity gradients form where salt water from the...

2012-07-01

366

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2011 CFR

...25 2011-07-01 2011-07-01 false Salinity gradients. 230.25 Section 230.25 ...Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity gradients form where salt water from the...

2011-07-01

367

COMPUTATIONAL COMPLEXITY OF INEXACT GRADIENT ...  

E-print Network

In Figure 5.2 we also plot the evolution of the states and inputs over the simulation .... 80EU/2010); Sectoral Operational Programme Human Resources ... [6] M.R. Hestenes, Multiplier and gradient methods, Journal of Optimization and ...

2012-11-02

368

Vertical distribution of mercury species at two sites in the Western Black Sea  

Microsoft Academic Search

The Black Sea is a unique natural laboratory for studying the biogeochemical cycling of mercury (Hg), a toxic metal present at trace levels in natural waters. The strong vertical density gradient in the Black Sea results in little ventilation of deep waters and therefore anoxic and sulfidic conditions at depth. In this way, the water column of the Black Sea

Carl H. Lamborg; O?uz Yi?iterhan; William F. Fitzgerald; Prentiss H. Balcom; Chad R. Hammerschmidt; James Murray

2008-01-01

369

Prospecting for near vertical aquifers in low temperature geothermal areas in Iceland  

SciTech Connect

This paper deals with the problem of locating permeable near vertical dykes, faults and fractures which serve as aquifers in low temperature areas in Iceland. Four different methods are discussed, geological mapping, ground magnetic measurements, head-on resistivity profiling and shallow temperature gradient holes. Examples of successful use of the methods are given.

Flovenz, O.G.; Georgsson, L.S.

1982-10-01

370

Vertically Aligned Nanocomposite Thin Films  

E-print Network

Vertically aligned nanocomposite (VAN) thin films have recently stimulated significant research interest to achieve better material functionality or multifunctionalities. In VAN thin films, both phases grow epitaxially in parallel on given...

Bi, Zhenxing

2012-07-16

371

Vertically scanned laser sheet microscopy  

NASA Astrophysics Data System (ADS)

Laser sheet microscopy is a widely used imaging technique for imaging the three-dimensional distribution of a fluorescence signal in fixed tissue or small organisms. In laser sheet microscopy, the stripe artifacts caused by high absorption or high scattering structures are very common, greatly affecting image quality. To solve this problem, we report here a two-step procedure which consists of continuously acquiring laser sheet images while vertically displacing the sample, and then using the variational stationary noise remover (VSNR) method to further reduce the remaining stripes. Images from a cleared murine colon acquired with a vertical scan are compared with common stitching procedures demonstrating that vertically scanned light sheet microscopy greatly improves the performance of current light sheet microscopy approaches without the need for complex changes to the imaging setup and allows imaging of elongated samples, extending the field of view in the vertical direction.

Dong, Di; Arranz, Alicia; Zhu, Shouping; Yang, Yujie; Shi, Liangliang; Wang, Jun; Shen, Chen; Tian, Jie; Ripoll, Jorge

2014-10-01

372

Vertical axis wind turbine airfoil  

DOEpatents

A vertical axis wind turbine airfoil is described. The wind turbine airfoil can include a leading edge, a trailing edge, an upper curved surface, a lower curved surface, and a centerline running between the upper surface and the lower surface and from the leading edge to the trailing edge. The airfoil can be configured so that the distance between the centerline and the upper surface is the same as the distance between the centerline and the lower surface at all points along the length of the airfoil. A plurality of such airfoils can be included in a vertical axis wind turbine. These airfoils can be vertically disposed and can rotate about a vertical axis.

Krivcov, Vladimir; Krivospitski, Vladimir; Maksimov, Vasili; Halstead, Richard; Grahov, Jurij Vasiljevich

2012-12-18

373

Long-term geoelectrical monitoring of laboratory freeze-thaw experiments on bedrock samples  

NASA Astrophysics Data System (ADS)

Much attention has recently focussed on the continuous and near-real-time geophysical monitoring of permafrost-affected bedrock with permanently installed sensor arrays. It is hoped that such efforts will enhance process understanding in such environments (permafrost degradation, weathering mechanisms) and augment our capability to predict future instabilities of rock walls and slopes. With regard to electrical methods for example, recent work has demonstrated that temperature-calibrated electrical resistivity tomography (ERT) is capable of imaging recession and re-advance of rock permafrost in response to the ambient temperature regime. However, field experience also shows that several fundamental improvements to ERT methodology are still required to achieve the desired sensitivity, spatial-temporal resolution and long-term robustness that must underpin continuous geophysical measurements. We have applied 4D geoelectrical tomography to monitoring laboratory experiments simulating permafrost growth, persistence and thaw in bedrock over a period of 26 months. Six water-saturated samples of limestone and chalk of varying porosity represented lithologies commonly affected by permafrost-related instability. Time-lapse imaging of the samples was undertaken during multiple successive freeze-thaw cycles, emulating annual seasonal change over several decades. Further experimental control was provided by simultaneous measurements of vertical profiles of temperature and moisture content within the bedrock samples. These experiments have helped develop an alternative methodology for the volumetric imaging of permafrost bedrock and tracking active layer dynamics. Capacitive resistivity imaging (CRI), a technique based upon low-frequency, capacitively-coupled measurements emulates ERT methodology, but without the need for galvanic contact on frozen rock. The latter is perceived as a key potential weakness, which could lead to significant limitations as a result of the variable quality of contact between sensors and the host material as it freezes and thaws. Our experiments have directly compared the CRI and ERT approaches. Numerical simulation of dense capacitive multi-sensor geometries shows that the basic assumptions of CRI remain valid for our experimental setup; as a consequence, conventional ERT methodology (including time-lapse inversion) becomes applicable to the capacitive measurements. Permafrost processes tend to be multi-scale in space and time; any imaging technique must therefore be capable of resolving subtle changes in rock properties over a range of spatial scales and long periods of time. Frequent data acquisition (three times per 24-hour period) allowed us to obtain 3D resistivity models of all samples as the freeze-thaw experiment progressed. Data from different stages of the simulated seasonal cycles show that CRI is capable of imaging temperature-dominated changes in resistivity, associated with an approximate temperature range between 20°C and -5°C. Volumetric temperature models of the samples were obtained using calibration curves determined by separate freeze-thaw experiments using identical material. Below the freezing point temperature dominates the resistivity response and the resistivity-based temperature models show very good agreement with point estimates from temperature probes. The CRI and ERT methodologies both hold promise for the systematic and strategic assessment of the thermal state of bedrock permafrost in the field using geoelectrical monitoring.

Kuras, Oliver; Uhlemann, Sebastian; Murton, Julian; Krautblatter, Michael

2014-05-01

374

Air-Cooled Stack Freeze Tolerance; Freeze Failure Modes and Freeze Tolerance Strategies for; GenDriveTM Material Handling Application Systems and Stacks; Final Scientific Report  

Microsoft Academic Search

Air-cooled stack technology offers the potential for a simpler system architecture (versus liquid-cooled) for applications below 4 kilowatts. The combined cooling and cathode air allows for a reduction in part count and hence a lower cost solution. However, efficient heat rejection challenges escalate as power and ambient temperature increase. For applications in ambient temperatures below freezing, the air-cooled approach has

2012-01-01

375

Natural Vertical Flow in the Los Azufres, Mexico, Geothermal Reservoir  

SciTech Connect

This work focuses on estimating the mass (M) and energy (E) flow rates, the permeability k, and the relative permeability functions R{sub L} and R{sub V} associated with the natural vertical flow in the reservoir. To estimate M and E we used the standard 1-D vertical equations for two-phase flow, complemented with boundary conditions at the boiling and dew interfaces. These boundary conditions were derived in an earlier stage of this study that established an approximate 1-D vertical model of the reservoir. The estimated values of M and E were then used together with the previously established liquid saturation vertical profile of the reservoir, and the differential equation expressing the pressure gradient, to fit, by trial and error, the observed natural pressure profile. The accuracy of the fit depends on the assumed value for the vertical permeability and on the chosen forms for the relative permeability functions. They estimated M {approx} 6.9 x 10{sup -8} kg m{sup -2} s{sup -1} and E {approx} 0.2 W m{sup -2}. These results lie well within the ample ranges of mass and energy flowrates per unit area found in geothermal fields worldwide. The estimated values of M and E support the previous inference that there is an extensive caprock in the reservoir. The best fit to the natural pressure gradient implies a vertical permeability of about 0.08 mD, residual water- and steam-saturations of about 0.04 and 0.00 respectively, and ''fracture relative permeabilities'' (i.e., R{sub L} + R{sub V} = 1). This work addresses a major obstacle for a successful analysis of the Los Azufres geothermal reservoir, which is characterized by an extensive two-phase region: the former unavailability of reasonably reliable relative permeability functions. Furthermore, the present characterization of the vertical natural flow provides important constraints for both lumped- and distributed-parameter models of the reservoir. Finally, this work gives information on reservoir properties that would be difficult to obtain by other means.

Iglesias, E.R.; Arellano, V.M.; Ortiz-Ramirez, J.

1986-01-21

376

Ground-based measurements of immersion freezing in the eastern Mediterranean  

E-print Network

Ice nuclei were measured in immersion-freezing mode in the eastern Mediterranean region using the FRIDGE-TAU (FRankfurt Ice-nuclei Deposition freezinG Experiment, the Tel Aviv University version) chamber. Aerosol particles ...

Levin, Z.

377

Inactivation of Kudoa septempunctata in olive flounder meat by liquid freezing.  

PubMed

Kudoa septempunctata in olive flounder meat was inactivated using 3 distinct freezing methods?liquid freezing for 5 min, air blast freezing at ?30? for 5 h, and ?80? for 1 h. The fracture curve of olive flounder meat subjected to liquid freezing resembled that of meat stored at 4?, indicating that the structure of olive flounder muscle was well preserved. In contrast, air blast freezing induced the disappearance of the fracture point in the fracture curve, indicating that there was deterioration in the meat quality. Liquid freezing preserved the transparency of olive flounder meat to the same degree as that of meat stored at 4°C. However, air blast freezing induced meat cloudiness. These results indicate that liquid freezing can be used for K. septempunctata inactivation without affecting the meat quality. PMID:25252645

Ohnishi, Takahiro; Akuzawa, Sayuri; Furusawa, Hiroko; Yoshinari, Tomoya; Kamata, Yoichi; Sugita-Konishi, Yoshiko

2014-01-01

378

9 CFR 381.66 - Temperatures and chilling and freezing procedures.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 2012-01-01 false Temperatures and chilling and freezing procedures...Operating Procedures § 381.66 Temperatures and chilling and freezing procedures. (a) General. Temperatures and procedures that are...

2012-01-01

379

9 CFR 354.244 - Temperatures and cooling and freezing procedures.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Temperatures and cooling and freezing procedures...Contamination of Products § 354.244 Temperatures and cooling and freezing procedures. Temperatures and procedures which are...

2011-01-01

380

9 CFR 354.244 - Temperatures and cooling and freezing procedures.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 2012-01-01 false Temperatures and cooling and freezing procedures...Contamination of Products § 354.244 Temperatures and cooling and freezing procedures. Temperatures and procedures which are...

2012-01-01

381

9 CFR 381.66 - Temperatures and chilling and freezing procedures.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 2010-01-01 false Temperatures and chilling and freezing procedures...Operating Procedures § 381.66 Temperatures and chilling and freezing procedures. (a) General. Temperatures and procedures that are...

2010-01-01

382

9 CFR 354.244 - Temperatures and cooling and freezing procedures.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 2013-01-01 false Temperatures and cooling and freezing procedures...Contamination of Products § 354.244 Temperatures and cooling and freezing procedures. Temperatures and procedures which are...

2013-01-01

383

9 CFR 381.66 - Temperatures and chilling and freezing procedures.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Temperatures and chilling and freezing procedures...Operating Procedures § 381.66 Temperatures and chilling and freezing procedures. (a) General. Temperatures and procedures that are...

2011-01-01

384

9 CFR 381.66 - Temperatures and chilling and freezing procedures.  

Code of Federal Regulations, 2014 CFR

...2014-01-01 2014-01-01 false Temperatures and chilling and freezing procedures...Operating Procedures § 381.66 Temperatures and chilling and freezing procedures. (a) General. Temperatures and procedures that are...

2014-01-01

385

9 CFR 354.244 - Temperatures and cooling and freezing procedures.  

Code of Federal Regulations, 2014 CFR

...2014-01-01 2014-01-01 false Temperatures and cooling and freezing procedures...Contamination of Products § 354.244 Temperatures and cooling and freezing procedures. Temperatures and procedures which are...

2014-01-01

386

9 CFR 381.66 - Temperatures and chilling and freezing procedures.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 2013-01-01 false Temperatures and chilling and freezing procedures...Operating Procedures § 381.66 Temperatures and chilling and freezing procedures. (a) General. Temperatures and procedures that are...

2013-01-01

387

9 CFR 354.244 - Temperatures and cooling and freezing procedures.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 2010-01-01 false Temperatures and cooling and freezing procedures...Contamination of Products § 354.244 Temperatures and cooling and freezing procedures. Temperatures and procedures which are...

2010-01-01

388

Impact of Thermal History on Tolerance of Meloidogyne hapla Second-stage Juveniles to External Freezing  

PubMed Central

Low temperature induced physiological changes that increased the ability of second-stage juveniles of Meloidogyne hapla to survive external freezing. Second-stage juveniles in polyethylene glycol solution were exposed to -4 , 0, 4, or 24 C, and then their survival was determined after ice-induced freezing of the suspensions at - 4 C for 24 hours. Survival was greatest for juveniles exposed to 4 C before freezing. Some juveniles were killed by exposure to - 4 C before freezing of the suspensions. The percentage of juveniles surviving freezing increased from about 30% to 80% within 12 hours of exposure to 4 C. This tolerance of external freezing was lost during subsequent exposure to 24 C. Longer exposures, of 1 to 15 days, to low temperature did not increase the percentage surviving external freezing, as compared to the 12-hour exposure, but reduced the tolerance of external freezing lost during subsequent exposure to 24 C for 48 hours. PMID:19282993

Forge, T. A.; MacGuidwin, A. E.

1992-01-01

389

Experimental research of "microcable in a microconduct" system stability to effect of freezing water  

NASA Astrophysics Data System (ADS)

Results of experimental researches of "optical microcable in a microduct" system stability to effect of freezing water are presented. It is shown this system is steadier to water freezing in comparison to lighten optical cable in protective polymer tube.

Andreev, Vladimir A.; Burdin, Vladimir A.; Nikulina, Tatiana G.; Alekhin, Ivan N.; Gavryushin, Sergey A.; Nikulin, Aleksey G.; Praporshchikov, Denis E.

2011-12-01

390

VOLATILE EMISSIONS OF NAVEL ORANGES AS PREDICTORS OF FREEZE DAMAGE  

Technology Transfer Automated Retrieval System (TEKTRAN)

Volative emissions of navel orange fruit were evaluated as a means for predicting and gauging freeze damage. The fruit were subjected to -5C or -7C treatments in a laboratory freezer for various time periods of 2 to 9.5 hours, and stored at 23C for 1, 2, or 7 days, after which the emission of volat...

391

FREEZING SWINE EMBRYOS: DO SUCCESS RATES DIFFER BETWEEN BREEDS?  

Technology Transfer Automated Retrieval System (TEKTRAN)

Successful freezing, or cryopreservation, of embryos could greatly impact the pork industry, serving as a tool for conservation of valuable germplasm and enhancing biosecurity for transfer of genetic material. Pig embryos are very sensitive to cooling and few reports have shown successful developmen...

392

Freezing resistance improvement of Lactobacillus reuteri by using cell immobilization  

Microsoft Academic Search

Lactobacillus reuteri shows certain beneficial effects to human health and is recognized as a probiotic. However, its application in frozen foods is still not popular because of its low survival during freezing and frozen storage. Cell immobilization technique could effectively exert protection effects to microbial cells in order to enhance their endurance to unfavorable environmental conditions as well as to

Jen-Horng Tsen; Hui-Ying Huang; Yeu-Pyng Lin; V. An-Erl King

2007-01-01

393

GENERAL VIEW OF SHARP FREEZE ROOM ON LEVEL 2; LOOKING ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

GENERAL VIEW OF SHARP FREEZE ROOM ON LEVEL 2; LOOKING WEST; PIPES ON CEILING CARRIED COMPRESSED AMMONIA; NOTE NONBEARING GLAZED TILE WALLS BETWEEN COLUMNS; FLOORS ARE BRICK - Rath Packing Company, Cooler Building, Sycamore Street between Elm & Eighteenth Streets, Waterloo, Black Hawk County, IA

394

Freezing of parallel hard cubes with rounded edges.  

PubMed

The freezing transition in a classical three-dimensional system of rounded hard cubes with fixed, equal orientations is studied by computer simulation and fundamental-measure density functional theory. By switching the rounding parameter s from zero to one, one can smoothly interpolate between cubes with sharp edges and hard spheres. The equilibrium phase diagram of rounded parallel hard cubes is computed as a function of their volume fraction and the rounding parameter s. The second order freezing transition known for oriented cubes at s = 0 is found to be persistent up to s = 0.65. The fluid freezes into a simple-cubic crystal which exhibits a large vacancy concentration. Upon a further increase of s, the continuous freezing is replaced by a first-order transition into either a sheared simple cubic lattice or a deformed face-centered cubic lattice with two possible unit cells: body-centered orthorhombic or base-centered monoclinic. In principle, a system of parallel cubes could be realized in experiments on colloids using advanced synthesis techniques and a combination of external fields. PMID:22502532

Marechal, Matthieu; Zimmermann, Urs; Löwen, Hartmut

2012-04-14

395

De-aggregated reliability analysis of freezing rain hazard  

Microsoft Academic Search

This work addresses issues for improving the estimation of the recurrence rate and the distribution in severity of extreme ice events in the Montreal area, which is required in order to determine design criteria for structures such as electric transmission lines. Some of the limitations of current methods for studying extreme freezing rain events are due to the relatively short

Reza Erfani

2010-01-01

396

Workshop on Sub-Freezing Effects February 1, 2005  

E-print Network

Workshop on Sub-Freezing Effects February 1, 2005 MEA and Interfacial Issues in Low Temperature Membrane Interfaces · Many within electrodes · Between electrodes and membrane (skin layer?) · Other FC Comparing MEA Cross-Section Before/After ~2200 Durability Test Membrane Cathode Anode B A B Detached Segment

397

How Circulation of Water Affects Freezing in Ponds  

ERIC Educational Resources Information Center

One means of preventing the top of a pond from freezing involves running a circulating pump near the bottom to agitate the surface and expose it to air throughout the winter months. This phenomenon is similar to that of the flowing of streams in subzero temperatures and to the running of taps to prevent pipe bursts in winter. All of these cases…

Moreau, Theresa; Lamontagne, Robert; Letzring, Daniel

2007-01-01

398

Self-Freeze Linear Decompressors for Low Power Testing  

E-print Network

Self-Freeze Linear Decompressors for Low Power Testing V. Tenentes and X. Kavousianos Dept in the ATE (Automatic Test Equipment) memory, and they are downloaded on chip where they are decompressed. Increased switching activity during the scan in-out process is responsible for increased average power

Kavousianos, Xrysovalantis

399

Who'll Warm to a Tuition Freeze?  

ERIC Educational Resources Information Center

Examines the recent decision by Williams College (Massachusetts) to freeze tuition. Notes effect of the booming economy on the value of institutional endowments. Suggests that the school's exercise of price leadership is unlikely to foster the needed discussion of college pricing, but rather will be seen by peer institutions as a brief misbegotten…

Breneman, David W.

2000-01-01

400

The Freezing Point Depression Law in Physical Chemistry.  

ERIC Educational Resources Information Center

Suggests a change in physical chemistry courses to use a slightly more complicated but significantly more useful generalization of the simple freezing point depression law. Lists reasons for the change and presents the treatment of solid-liquid equilibria where solid-solution is allowed. Provides a mathematical treatment. (MVL)

Franzen, Hugo F.

1988-01-01

401

COMBINED REVERSE OSMOSIS AND FREEZE CONCENTRATION OF BLEACH PLANT EFFLUENTS  

EPA Science Inventory

Reverse osmosis (RO) and freeze concentration (FC) were evaluated at three different pulp and paper mills as tools for concentrating bleach plant effluents. By these concentration processes, the feed effluent was divided into two streams. The clean water stream approached drinkin...

402

Influence of freezing conditions on ice crystallisation in ice cream  

Microsoft Academic Search

Successful optimisation of the ice cream freezing process to deliver a product with small ice crystals, and therefore a smooth texture, requires an understanding of the mechanisms of ice crystallisation. The purpose of this work was to relate the processing variables available to the ice cream manufacturer to measured ice crystal size distributions, with a view to elucidating the dominant

A. B. Russell; P. E. Cheney; S. D. Wantling

1999-01-01

403

Sinkholes in West-central Florida, Freeze Event of 2010  

USGS Multimedia Gallery

Sinkholes damage roadways and require constant maintenance for road safety. More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting lows as farmers pumped water to irrigate their plants for protection ...

404

Dynamic modelling for a submerged freeze microgripper using thermal networks  

E-print Network

Dynamic modelling for a submerged freeze microgripper using thermal networks Beatriz L in this paper is designed to operate in a completely submerged manner in an aqueous medium. The handling is focused on the modelling of the thermal microhandling system using electrical analogy. The submerged

Boyer, Edmond

405

Carbohydrates in oat tillers and their relationship to freezing survival  

Technology Transfer Automated Retrieval System (TEKTRAN)

In grasses the crown is a complex organ from which tillers arise and eventually produce the flower-bearing structure where seeds are eventually born. We have observed that in oats not all tillers have the same ability to survive freezing and while an entire plant may be produced from one surviving ...

406

Fructan mobilization during recovery from freezing in winter oat crowns  

Technology Transfer Automated Retrieval System (TEKTRAN)

Fructan, which is a carbohydrate polymer similar to starch but based on fructose, is an important cryoprotectant in plants. But how the plant uses this carbohydrate to improve freezing resistance is controversial. We are reporting here results of the first analysis of fructan changes that occur du...

407

Sinkholes in West-central Florida, Freeze Event of 2010  

USGS Multimedia Gallery

More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting lows as farmers pumped water to irrigate their plants for protection from the cold temperatures. The sinkholes destroyed homes, roads and se...

408

Sinkholes in West-central Florida, Freeze Event of 2010  

USGS Multimedia Gallery

Sinkholes affect structures as well as many types of supporting infrastructure such as buried utilities lines seen here. More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting lows ...

409

Sinkholes in West-central Florida, Freeze Event of 2010  

USGS Multimedia Gallery

A sinkhole formed in a roadway caused traffic to detour around it while it is filled in, stabilized and repaved. More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting lows as farmers pumped water to...

410

Sinkholes in West-central Florida, Freeze Event of 2010  

USGS Multimedia Gallery

Cracks shown here in the exterior and supporting structures of this home are indicative of subsidence damage associated with sinkhole activity. More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting l...

411

Sinkholes in West-central Florida, Freeze Event of 2010  

USGS Multimedia Gallery

Sinkholes affect roadway safety and require constant maintenance and monitoring. More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting lows as farmers pumped water to irrigate their plants for p...

412

Sinkholes in West-central Florida, Freeze Event of 2010  

USGS Multimedia Gallery

A section of a strawberry field that was destroyed by a sinkhole and filled in, as is done with many sinkholes if possible. More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting lows as farmers pump...

413

Sinkholes in West-central Florida, Freeze Event of 2010  

USGS Multimedia Gallery

The entire root perimeter of this tree collapsed in response to subsidence activity. More than 110 sinkholes formed in the Dover area of Florida during a freeze event in January 2010. Ground water levels dropped to record-setting lows as farmers pumped water to irrigate their plants for pr...

414

Weight loss during freezing and storage of unpackaged foods  

Microsoft Academic Search

Dehydration of unwrapped foods occurs during freezing and frozen storage. Coupled heat and mass balances were proposed incorporating solidification of water and sublimation of ice. The mathematical model was solved using an implicit finite-differences method, with a variable grid to follow the moving sublimation front. The model evaluates temperature and water concentration profiles and was used to predict the kinetics

L. A. Campañone; V. O. Salvadori; R. H. Mascheroni

2001-01-01

415

Simulation of a Combined Microwave and Radiant Freeze Dryer  

Microsoft Academic Search

A mathematical model was developed to aid the development of a combined microwave and radiant freeze dryer. By considering the limitations of the condensation capacity and the vacuum system in the boundary conditions, a more realistic simulation was developed. The phenomenon of solid entrainment during sublimation and its effects on the drying process were also examined.

H. B. Arsem; Y. H. Ma

1990-01-01

416

Freezing resistance of antifreeze-deficient larval Antarctic fish.  

PubMed

Antarctic notothenioids, along with many other polar marine fishes, have evolved biological antifreeze proteins (AFPs) to survive in their icy environments. The larvae of Antarctic notothenioid fish hatch into the same frigid environment inhabited by the adults, suggesting that they must also be protected by sufficient AFPs, but this has never been verified. We have determined the contribution of AFPs to the freezing resistance of the larvae of three species: Gymnodraco acuticeps, Pagothenia borchgrevinki and Pleuragramma antarcticum. Of the three, only P. borchgrevinki larvae are protected by high, adult levels of AFPs. Hatchling G. acuticeps and P. antarcticum have drastically inadequate AFP concentrations to avoid freezing at the ambient seawater temperature (-1.91 degrees C). We raised G. acuticeps larvae and measured the AFP levels in their blood for approximately 5 months post hatching. Larval serum freezing point was -1.34+/-0.04 degrees C at the time of hatch; it began to decrease only after 30 days post hatch (d.p.h.), and finally reached the adult value (-2.61+/-0.03 degrees C) by 147 d.p.h. Additionally, AFP concentrations in their intestinal fluids were very low at hatching, and did not increase with age throughout a sampling period of 84 d.p.h. Surviving in a freezing environment without adequate AFP protection suggests that other mechanisms of larval freezing resistance exist. Accordingly, we found that G. acuticeps hatchlings survived to -3.6+/-0.1 degrees C while in contact with external ice, but only survived to -1.5+/-0.0 degrees C when ice was artificially introduced into their tissues. P. antarcticum larvae were similarly resistant to organismal freezing. The gills of all three species were found to be underdeveloped at the time of hatch, minimizing the risk of ice introduction through these delicate structures. Thus, an intact integument, underdeveloped gill structures and other physical barriers to ice propagation may contribute significantly to the freezing resistance and survival of these larval fishes in the icy conditions of the Southern Ocean. PMID:16424091

Cziko, Paul A; Evans, Clive W; Cheng, Chi-Hing C; DeVries, Arthur L

2006-02-01

417

Adaptive phenotypic diversification along a temperature-depth gradient.  

PubMed

Theoretical models suggest that sympatric speciation along environmental gradients might be common in nature. Here we present the first data-based model of evolutionary diversification along a continuous environmental gradient. On the basis of genetic analyses, it has been suggested that a pair of coregonid fishes (Coregonus spp.) in a postglacial German lake originated by sympatric speciation. Within this lake, the two species segregate vertically and show metabolic adaptations to, as well as behavioral preferences for, correspondingly different temperatures. We test the plausibility of the hypothesis that this diversifying process has been driven by adaptations to different thermal microhabitats along the lake's temperature-depth gradient. Using an adaptive-dynamics model that is calibrated with empirical data and allows the gradual evolution of a quantitative trait describing optimal foraging temperature, we show that under the specific environmental conditions in the lake, evolutionary branching of a hypothetical ancestral population into two distinct phenotypes may have occurred. We also show that the resultant evolutionary diversification yields two stably coexisting populations with trait values and depth distributions that are in agreement with those currently observed in the lake. We conclude that divergent thermal adaptations along the temperature-depth gradient might have brought about the two species observed today. PMID:23933726

Ohlberger, Jan; Brännström, Åke; Dieckmann, Ulf

2013-09-01

418

The Metallicity Gradient of the Old Galactic Bulge Population  

NASA Astrophysics Data System (ADS)

Understanding the structure, formation and evolution of the Galactic Bulge requires the proper determination of spatial metallicity gradients in both the radial and vertical directions. RR Lyrae pulsators, known to be excellent distance indicators, may hold the key to determining these gradients. Jurcsik and Kovacs (A&A 312:111, 1996) has shown that RR Lyrae light curves and the phase difference of their Fourier decomposition, ? 31, can be used to estimate photometric metallicities. The existence of galactic bulge metallicity gradients is a currently debated topic that would help pinpoint the Galaxy's formation and evolution. A recent study of the OGLE-III Galactic Bulge RR Lyrae Population by Pietrukowicz et al. (ApJ 750:169, 2012) suggests that the spatial distribution is uniform. We investigate how small a gradient would be detectable within the current S/N levels of the present data set, given the random and systematic errors associated with the derivation of a photometric metallicity versus spatial position relationship.

Sans Fuentes, Sara Alejandra; De Ridder, Joris

419

Gravity Induced Formation of Concentration Gradients in Supersaturated Binary Solutions  

NASA Technical Reports Server (NTRS)

Experimental and theoretical studies of the formation of solute concentration gradient in supersaturated binary solutions in a gravitational field were carried out. The formation of solute concentration gradient was associated with the gravity induced redistribution of subcritical solute clusters. The birth-death process of the new solute-rich phase domains (subcritical solute clusters) was described in terms of the time-dependent Ginzburg Landau model developed for metastable state relaxation in binary (solute + solvent) non-critical solutions in the presence of a gravitational field. A new mathematical Ansatz was developed for solution of the model equations. This Ansatz has allowed to approach for the first time the following important problems: (1) Microstructure of solute distribution inside of the subcritical solute clusters. The analytical results obtained demonstrate that solute inside of the subcritical solute clusters is heterogeneously distributed with a spatially periodic structure. (2) Macrostructure of the solute subcritical clusters distribution in a gravitational field. The subcritical solute clusters are found to be distributed heterogeneously in a gravitational field. This heterogeneity, which is due to the heterogeneous birth-death process of the subcritical solute clusters in a gravitational field, initiates a noticeable solute concentration gradient in vertical columns of supersaturated binary solutions. An analysis and comparison of theoretical results and experimental data related to the solute concentration gradient formation in a gravitational field are presented. It is also demonstrated that the critical radius of solute clusters (radius of nucleation) and induction time are gravity-dependent.

Izmailov, Alexander F.; Myerson, Allan S.

1996-01-01

420

Impaired regulation of stride variability in Parkinson's disease subjects with freezing of gait  

Microsoft Academic Search

  \\u000a Patients with Parkinson's disease (PD) often experience freezing of gait, a debilitating phenomenon during which the subject\\u000a suddenly becomes unable to start walking or to continue to move forward. Little is known about the gait of those subjects\\u000a with PD who experience freezing of gait or the pathophysiology of freezing. One possibility is that freezing of gait is a

J. M. Hausdorff; J. D. Schaafsma; Y. Balash; A. L. Bartels; T. Gurevich; N. Giladi

2003-01-01

421

Underground structure detection by surface magnetic gradient measurements  

SciTech Connect

This problem involves magnetic induction methods to locate and determine the depth of a subsurface line source of magnetic field. The origin of the field may be self-generated or induced by a surface transmitter. The experimental method requires measuring the horizontal gradient of either the vertical or horizontal component of the field rather than the field itself so as to increase signal to noise ratio. A mathematical outline is presented and experimental results are discussed. Keywords: underground detection, electromagnetic theory, magnetic induction, tunnels, underground structures, imaging

Kelly, R. E. (Robert E.)

2001-01-01

422

Refractive phenomena in the shock wave dispersion with variable gradients  

SciTech Connect

In this article the refraction effects in the weak shock wave (SW) dispersion on an interface with a temperature variation between two mediums are described. In the case of a finite-gradient boundary, the effect of the SW dispersion is remarkably stronger than in the case of a step change in parameters. In the former case the vertical component of velocity for the transmitted SW (the refraction effect) must be taken into account. Results of comparative calculations based on the two-dimensional model corrected for the refraction effect show significant differences in the shapes of the dispersed SW fronts.

Markhotok, A.; Popovic, S. [Department of Physics, Old Dominion University, Norfolk, Virginia, 23529 (United States)

2010-06-15

423

Method of freezing living cells and tissues with improved subsequent survival  

DOEpatents

This invention relates to an improved method for freezing red blood cells, ther living cells, or tissues with improved subsequent survival, wherein constant-volume freezing is utilized that results in significantly improved survival compared with constant-pressure freezing; optimization is attainable through the use of different vessel geometries, cooling baths and warming baths, and sample concentrations.

Senkan, Selim M. (Oak Ridge, TN); Hirsch, Gerald P. (Oak Ridge, TN)

1980-01-01

424

Drought increases freezing tolerance of both leaves and xylem of Larrea tridentatapce_2224 43..51  

E-print Network

Drought increases freezing tolerance of both leaves and xylem of Larrea tridentatapce_2224 43, New Mexico 87131, USA ABSTRACT Drought and freezing are both known to limit desert plant distributions, but the interaction of these stressors is poorly understood. Drought may increase freezing tolerance in leaves while

Pockman, William T.

425

Gelatin-Filtered Consomme: A Practical Demonstration of the Freezing and Thawing Processes  

ERIC Educational Resources Information Center

Freezing is a key food processing and preservation technique widely used in the food industry. Application of best freezing and storage practices extends the shelf-life of foods for several months, while retaining much of the original quality of the fresh food. During freezing, as well as its counterpart process, thawing, a number of critical…

Lahne, Jacob B.; Schmidt, Shelly J.

2010-01-01

426

Comparative studies on tolerance of Medicago truncatula and Medicago falcata to freezing  

Microsoft Academic Search

Medicago falcata is a legume species that exhibits great capacity of tolerance to abiotic stresses. To elucidate the mechanism underlying\\u000a tolerance of M. falcata to freezing, we compared the characteristics of M. falcata in response to cold acclimation and freezing with those of the legume model plant Medicago truncatula. M. falcata seedlings were more tolerant to freezing than M. truncatula,

Li-Li Zhang; Min-Gui Zhao; Qiu-Ying Tian; Wen-Hao Zhang

427

Factors that influence freezing in the subAntarctic springtail Tullbergia antarctica  

Microsoft Academic Search

Effects of 12 biotic and abiotic factors on the freezing point of the sub-Antarctic springtail, Tullbergia antarctica, were investigated. Repeated cooling of individual springtails five times resulted in very similar freezing points suggesting that ice nucleation in this freeze-susceptible species is likely to be initiated by intrinsic factors rather than being a stochastic event. Mean supercooling point (SCP) was influenced

M. Roger Worland

2005-01-01

428

Exposure to ultraviolet light as a means of predicting damage in oranges exposed to freezing conditions  

Technology Transfer Automated Retrieval System (TEKTRAN)

Current methods of evaluating whether an orange has been damaged by a period of freezing temperatures require fruit to be cut and physically examined for signs of freeze damage. This method is destructive, slow, and inaccurate and relies on visual evaluation. Visual symptoms of freeze damage may t...

429

Exploring high-density baryonic matter: Maximum freeze-out density  

E-print Network

The hadronic freeze-out line is calculated in terms of the net baryon density and the energy density instead of the usual T and mu_B. This analysis makes it apparent that the freeze-out density exhibits a maximum as the collision energy is decreased. This maximum freeze-out density is well within the parameters of the proposed NICA accelerator.

J. Randrup; J. Cleymans

2009-05-18

430

21 CFR 864.9225 - Cell-freezing apparatus and reagents for in vitro diagnostic use.  

Code of Federal Regulations, 2012 CFR

...2012-04-01 2012-04-01 false Cell-freezing apparatus and reagents for...Blood and Blood Products § 864.9225 Cell-freezing apparatus and reagents for in...diagnostic use. (a) Identification. Cell-freezing apparatus and reagents...

2012-04-01

431

21 CFR 864.9225 - Cell-freezing apparatus and reagents for in vitro diagnostic use.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Cell-freezing apparatus and reagents for...Blood and Blood Products § 864.9225 Cell-freezing apparatus and reagents for in...diagnostic use. (a) Identification. Cell-freezing apparatus and reagents...

2010-04-01

432

21 CFR 864.9225 - Cell-freezing apparatus and reagents for in vitro diagnostic use.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Cell-freezing apparatus and reagents for...Blood and Blood Products § 864.9225 Cell-freezing apparatus and reagents for in...diagnostic use. (a) Identification. Cell-freezing apparatus and reagents...

2013-04-01

433

21 CFR 864.9225 - Cell-freezing apparatus and reagents for in vitro diagnostic use.  

Code of Federal Regulations, 2011 CFR

...2011-04-01 2011-04-01 false Cell-freezing apparatus and reagents for...Blood and Blood Products § 864.9225 Cell-freezing apparatus and reagents for in...diagnostic use. (a) Identification. Cell-freezing apparatus and reagents...

2011-04-01

434

21 CFR 864.9225 - Cell-freezing apparatus and reagents for in vitro diagnostic use.  

Code of Federal Regulations, 2014 CFR

...2014-04-01 2014-04-01 false Cell-freezing apparatus and reagents for...Blood and Blood Products § 864.9225 Cell-freezing apparatus and reagents for in...diagnostic use. (a) Identification. Cell-freezing apparatus and reagents...

2014-04-01

435

Freezing Points of Bulking Agents Used in Manufacture of Low-Calorie Frozen Desserts1  

Microsoft Academic Search

Freezing points of solutions of poly- dextrose, polydextrose partially neu- tralized with potassium hydroxide, sor- bitol, and microcrystalline cellulose at concentrations commonly used in frozen desserts were compared with those of similar concentrations of sucrose. Solu- tions of polydextrose and polydextrose partially neutralized with potassium hy- droxide exhibited higher freezing points. Freezing points of sorbitol solutions were lower and microcrystalline

Robert J. Baer; Kirk A. Baldwin

1984-01-01

436

Optimal freezing and thawing for the survival of periphheral nerves in severed rabbit limbs  

PubMed Central

This study aimed to investigate the optimal freezing and thawing procedures for the survival of peripheral nerves in severed rabbit limbs. Twenty New Zealand White rabbits were randomized into four groups: normal control, slow-freezing fast-thawing, slow-freezing slow-thawing, fast-freezing fast-thawing, with five animals in each group. The hind limbs of the rabbits were severed at 1 cm above the knee joint. The severed limbs were cryopreserved with various freezing and thawing procedures. The sciatic nerves were harvested and trypsinized into single nerve fibers for morphological evaluation. The cell viability of the nerve fibers was examined by staining with Calcein-AM and propidium iodide. The fluorescent intensity of the nerve fibers was measured with a laser scanning confocal microscope. The morphology of the nerve fibers in the slow-freezing fast-thawing group was very similar with that of the normal control group, with only mild demyelination. The slow-freezing fast-thawing group and slow-freezing slow-thawing group showed severely damaged nerve fibers. The fluorescent intensities of the nerve fibers was significantly different among the four groups, with a decreasing order of normal control, slow-freezing fast-thawing, slow-freezing slow-thawing, and fast-freezing fast-thawing (P < 0.05). Of the various cryopreservative procedures, slow-freezing fast thawing has the minimal effects on the survival of nerve fibers in severed rabbit limbs.

Zhu, Zexing; Qiao, Lin; Zhao, Yandong; Zhang, Shuming

2014-01-01

437

The 2007 California Citrus Freeze: Vulnerability, Poverty, and Unemployment Issues of Farmworkers  

ERIC Educational Resources Information Center

In January of 2007, freezing temperatures destroyed citrus and vegetable crops in California. By May 2007, more than 9,000 freeze-related unemployment applications had been fled. Through face-to-face interviews, this study documents the experience of 63 farmworkers to find out how they survived the freeze and accessed services. Findings revealed…

Orozco, Graciela Leon

2010-01-01

438

Using Sprinklers to Protect Blueberries from Spring Freezes Mark Longstroth, MSUE Extension Educator  

E-print Network

Using Sprinklers to Protect Blueberries from Spring Freezes Mark Longstroth, MSUE Extension Many blueberry growers use sprinkler systems to protect blueberry flowers from spring freezes the plant down colder than the air temperature as the ice evaporates. Protection with sprinklers The freeze

Isaacs, Rufus

439

METALLICITY GRADIENTS THROUGH DISK INSTABILITY: A SIMPLE MODEL FOR THE MILKY WAY'S BOXY BULGE  

SciTech Connect

Observations show a clear vertical metallicity gradient in the Galactic bulge, which is often taken as a signature of dissipative processes in the formation of a classical bulge. Various evidence shows, however, that the Milky Way is a barred galaxy with a boxy bulge representing the inner three-dimensional part of the bar. Here we show with a secular evolution N-body model that a boxy bulge formed through bar and buckling instabilities can show vertical metallicity gradients similar to the observed gradient if the initial axisymmetric disk had a comparable radial metallicity gradient. In this framework, the range of metallicities in bulge fields constrains the chemical structure of the Galactic disk at early times before bar formation. Our secular evolution model was previously shown to reproduce inner Galaxy star counts and we show here that it also has cylindrical rotation. We use it to predict a full mean metallicity map across the Galactic bulge from a simple metallicity model for the initial disk. This map shows a general outward gradient on the sky as well as longitudinal perspective asymmetries. We also briefly comment on interpreting metallicity gradient observations in external boxy bulges.

Martinez-Valpuesta, Inma; Gerhard, Ortwin, E-mail: imv@mpe.mpg.de, E-mail: gerhard@mpe.mpg.de [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany)

2013-03-20

440

The influence of ocean surface temperature gradient and continentality on the Walker circulation. II - Prescribed global changes  

NASA Technical Reports Server (NTRS)

The series of experiments presently used to investigate the mechanisms responsible for forcing the global Walker circulation features worldwide changes in ocean surface temperatures (OSTs), topography, and/or continents. The primary factor affecting circulation is noted to be the global distribution of continents and oceans; while OST gradients are also important, topography emerges as comparatively unimportant. Continentality and OST gradients force the model atmosphere through the introduction of zonal variations in surface heating. The vertical motions to which they give rise yield moisture convergence and condensation variations which reinforce vertical motions. The forcing by OST gradients is partly nonlocal, and the atmospheric response is effected by continentality. In all cases, vertical motion zonal variations correlate with precipitation.

Stone, P. H.; Chervin, R. M.

1984-01-01

441

Vertical saccades in dyslexic children.  

PubMed

Vertical saccades have never been studied in dyslexic children. We examined vertical visually guided saccades in fifty-six dyslexic children (mean age: 10.5±2.56 years old) and fifty-six age matched non dyslexic children (mean age: 10.3±1.74 years old). Binocular eye movements were recorded using an infrared video-oculography system (mobileEBT®, e(ye)BRAIN). Dyslexic children showed significantly longer latency than the non dyslexic group, also the occurrence of anticipatory and express saccades was more important in dyslexic than in non dyslexic children. The gain and the mean velocity values were significantly smaller in dyslexic than in non dyslexic children. Finally, the up-down asymmetry reported in normal population for the gain and the velocity of vertical saccades was observed in dyslexic children and interestingly, dyslexic children also reported an up-down asymmetry for the mean latency. Taken together all these findings suggested impairment in cortical areas responsible of vertical saccades performance and also at peripheral level of the extra-ocular oblique muscles; moreover, a visuo-attentionnal bias could explain the up-down asymmetry reported for the vertical saccade triggering. PMID:25151607

Tiadi, Aimé; Seassau, Magali; Bui-Quoc, Emmanuel; Gerard, Christophe-Loïc; Bucci, Maria Pia

2014-11-01

442

Dielectric gradient metasurface optical elements.  

PubMed

Gradient metasurfaces are two-dimensional optical elements capable of manipulating light by imparting local, space-variant phase changes on an incident electromagnetic wave. These surfaces have thus far been constructed from nanometallic optical antennas, and high diffraction efficiencies have been limited to operation in reflection mode. We describe the experimental realization and operation of dielectric gradient metasurface optical elements capable of also achieving high efficiencies in transmission mode in the visible spectrum. Ultrathin gratings, lenses, and axicons have been realized by patterning a 100-nanometer-thick Si layer into a dense arrangement of Si nanobeam antennas. The use of semiconductors can broaden the general applicability of gradient metasurfaces, as they offer facile integration with electronics and can be realized by mature semiconductor fabrication technologies. PMID:25035488

Lin, Dianmin; Fan, Pengyu; Hasman, Erez; Brongersma, Mark L

2014-07-18

443

Neglected locked vertical patellar dislocation.  

PubMed

Patellar dislocations occurring about the vertical and horizontal axis are rare and irreducible. The neglected patellar dislocation is still rarer. We describe the clinical presentation and management of a case of neglected vertical patellar dislocation in a 6 year-old boy who sustained an external rotational strain with a laterally directed force to his knee. Initially the diagnosis was missed and 2 months later open reduction was done. The increased tension generated by the rotation of the lateral extensor retinaculum kept the patella locked in the lateral gutter even with the knee in full extension. Traumatic patellar dislocation with rotation around a vertical axis has been described earlier, but no such neglected case has been reported to the best of our knowledge. PMID:23162154

Gupta, Rakesh Kumar; Gupta, Vinay; Sangwan, Sukhbir Singh; Kamboj, Pradeep

2012-09-01

444

Method of total field reconstruction from aeromagnetic gradients data  

NASA Astrophysics Data System (ADS)

The total field reconstructed from the measured gradient data is diurnal free. It is important approach to eliminate diurnal for some survey area that is not possible to have a base-station magnetometer. In this work, method of total field reconstruction from gradients data in frequency domain was investigated. Transformation of potential field by fast Fourier transform technique in frequency domain is common used, the equations describing these geophysical problems are often much simpler when expressed in frequency terms, and the computation speed is very fast, this is very important for large dataset of aeromagnetic survey. The widely used fast Fourier transform technique, applied to total field reconstruction has a major difficulty which is those expressions of transform operators are undefined when u or v equal to zero or u and v are simultaneously equal to zero (u is the frequency in x-direction and v is the frequency in y-direction), the operators can not be sampled at these frequencies. Consequently, the traditional Fourier methods are not applicable for these singular points. Shift sampling theory proposed by Chai etal is employed for resolving this problem, and the method is illustrated by application to theoretical and field data. The performance of the method was assessed using theoretical magnetic total field and gradient anomaly produced by three prisms. Comparisons of the computed results with theoretical total field show excellent agreement in anomaly shapes and amplitude. All mean relative errors of computed total field are less than 2%, in contrast, the results calculated from vertical gradient and calculated from longitudinal and transverse gradients by using Hilbert transform relations are better, the mean relative errors are less than 1%. In addition, random noise was added to theoretical gradient data to test the feasibility of the method. Model tests indicate that the algorithm is stable and produces good results.The technique was tested on aeromagnetic gradients data collected by three axis airborne gradiometer. Comparisons of the calculated results with measured total field show good agreement in anomaly shapes, but the amplitudes are not good agree with the measured total field for most of the region, there are more obvious long-period errors, the total fields obtained from gradients can eliminate diurnal problem but have other errors. The errors source need to be analyzed further.

Li, H.; Yu, H.

2013-12-01

445

Spatial and temporal variations of meiofaunal communities from the western sector of the Gulf of Batabanó, Cuba: III. Vertical distribution.  

PubMed

The vertical distribution of meiofauna within subtidal sediments was studied in four stations pertaining to mangrove or muddy flats habitats. In 2003, replicated samples were taken in dry (February) and wet (July) seasons at the Bacunagua Inlet, southwestern coast of Cuba. The abundance and number of meiofaunal taxa exhibited a vertical gradient possibly due to changes in the concentrations of oxygen and hydrogen sulphide, rather than food availability along this gradient. Nematodes are capable of distributing themselves throughout the whole sediment column due to their ability to tolerate reducing conditions; however depletion of communities along depth was evident. Their presence in deeper sediments (6 - 10 cm) suggests that certain species are adequately adapted to spend their entire life cycle in these harsh environments (where soluble tannins and decomposing organic matter predominate). Copepods showed a strong limitation to vertical distribution (concentrating in the top 2 cm), possibly in response to a sharp vertical decline in oxygenation within these organically enriched sediments. PMID:19419033

Armenteros, M; Williams, J P; Creagh, B; Capetillo, N

2008-09-01

446

Structural interpretation of southern part of western Anatolian using analytic signal of the second order gravity gradients and discrete wavelet transform analysis  

NASA Astrophysics Data System (ADS)

In this work, gravity anomalies have been analyzed using gradient analytic signal (GAS) obtained from the square root of the sum of the squares of the second complex and vertical gradients. The gravity anomalies have been decomposed at 1, 2 and 3 levels with Haar mother wavelet. The DWT leads to a decomposition of the approximation coefficients in four distinct components: the approximation, horizontal, vertical and diagonal. I have tested the maxima of the magnitude computed from the square root of the sum of the squares of the horizontal, vertical and diagonal components (HVDM), and maxima of GAS in imaging the source edges in theoretical examples, with and without random Gaussian noise.

Oruç, B.

2014-04-01

447

Measurements of vertical bar Vcb vertical bar and vertical bar Vub vertical bar at BaBar  

SciTech Connect

We report results from the BABAR Collaboration on the semileptonic B decays, highlighting the measurements of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix elements Vub and Vcb. We describe the techniques used to obtain the matrix element |Vcb| using the measurement of the inclusive B {yields} Xclv process and a large sample of exclusive B {yields} D*lv decays. The vertical bar Vub vertical bar matrix elements has been measured studying different kinematic variables of the B {yields} Xulv process, and also with the exclusive reconstruction of B {yields} {pi}({rho})lv decays.

Rotondo, M. [Dipartimento di Fisica Galileo Galilei, Via Marzolo 8, Padova 35131 (Italy)

2005-10-12

448

Convection in vertical Bridgman configurations  

NASA Technical Reports Server (NTRS)

We are interested in tracing the convective profiles of vertical Bridgman growth in two configurations, the pure Rayleigh convective mode and the combined Rayleigh-Marangoni mode. In order to do so, we conducted a numerical investigation that involved a finite volume calculation. The governing equations were integrated about a cell volume, using the Gauss Theorem and the volume variables like temperature and velocity were related to the surface variables. In order to solve for the pressure field, we employed the continuity equation and the residuals resulted in a Poisson equation. Results and comments for the Rayleigh and Marangoni problems in a vertical cylinder or Bridgman configuration are given.

Narayanan, Ranga

1991-01-01

449

Vertical motion simulator familiarization guide  

NASA Technical Reports Server (NTRS)

The Vertical Motion Simulator Familiarization Guide provides a synoptic description of the Vertical Motion Simulator (VMS) and descriptions of the various simulation components and systems. The intended audience is the community of scientists and engineers who employ the VMS for research and development. The concept of a research simulator system is introduced and the building block nature of the VMS is emphasized. Individual sections describe all the hardware elements in terms of general properties and capabilities. Also included are an example of a typical VMS simulation which graphically illustrates the composition of the system and shows the signal flow among the elements and a glossary of specialized terms, abbreviations, and acronyms.

Danek, George L.

1993-01-01

450

Edge Detection in Potential-Field Gradient Tensor Data by Use of Improved Horizontal Analytical Signal Methods  

NASA Astrophysics Data System (ADS)

Potential-field gradient tensor data contain nine signal components. They include higher-frequency signals than potential field data, which can help delineation of small-scale features of the sources. Edge-detection technology has been widely used to delineate the edges of the sources. We need to develop a new edge detector to process gradient tensor data. Many methods are used to recognize the edges of data. The analytical signal method is a widely used edge-detection filter. We make some improvements to the analytical signal method so it can process potential-field gradient tensor data. We define new filters based on the horizontal directional analytical signal and the second-order horizontal directional analytical signal. To display the large and small amplitude edges simultaneously, we present two normalization methods: use of th