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1

Vertical bridgman and gradient freeze growth of III-V compound semiconductors  

SciTech Connect

Major improvements in the structural and electrical perfection of single crystals of III-V compound semiconductors have been achieved by using new vertical Bridgman-type and vertical gradient freeze techniques. A general review of experimental set-ups used for growth of large diameter crystals of GaP, InP and GaAs is presented. Crystal properties and characteristic features are discussed to illustrate advantages and disadvantages of the vertical Bridgman-type growth techniques. 22 refs., 5 figs.

Bourret, E.D.

1990-07-01

2

Growth of 3? and 4? gallium arsenide crystals by the vertical gradient freeze (VGF) method  

Microsoft Academic Search

Results of the vertical gradient freeze (VGF) growth of Si-doped (3?) and semi-insulating (4?) GaAs crystals are shown. The VGF process conditions were optimised with the aid of numerical simulations using the so-called inverse modelling. Experimental results and predictions from the computer simulation (software CrysVUN++) are quantitatively compared with respect to the power versus time profiles of the heaters, and

B. Birkmann; M Rasp; J Stenzenberger; G Müller

2000-01-01

3

Uniformity of 3-in., semi-insulating, vertical-gradient-freeze GaAs wafers  

NASA Astrophysics Data System (ADS)

The uniformity in deep-donor density, dislocation (or etch-pit) density (EPD), resistivity, mobility, and carrier concentration for 3-in., semiinsulating GaAs wafers grown by the vertical-gradient-freeze (VGF) technique were evaluated. Although slight W or U patterns were observed in deep-donor density and EPD along the 110 directions, the overall uniformity was excellent, and comparable to that in the best In-doped and whole-boule-annealed ingots grown by the liquid-encapsulated Czochralski (LEC) technique. Based on results from implant-activation studies on LEC wafers, it is estimated that the measured nonuniformities in EPD and deep-donor density for the VGF wafers would contribute only about 1 percent to implant-activation-efficiency nonuniformities in Si-implanted wafers designed for field-effect transistor applications.

Look, D. C.; Walters, D. C.; Mier, M. G.; Sewell, J. S.; Sizelove, J. S.

1989-07-01

4

Comparison of vertical gradient freeze bulk GaAs and custom grown vertical zone melt bulk GaAs as radiation spectrometers  

Microsoft Academic Search

Custom grown vertical zone melt (VZM) ingots of GaAs have been zone refined and zone leveled. The crystallinity, impurity concentrations, defect concentrations, and electrical properties of the ingots have been studied. Radiation detectors fabricated from the ingots have been compared to radiation detectors fabricated from commercially available vertical gradient freeze (VGF) material. Preliminary results suggest that electrical homogeneity may be

D. S McGregor; H. C Chui; J. E Flatley; R. L Henry; P. E. R Nordquist; R. W Olsen; M Pocha; C. L Wang

1996-01-01

5

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

NASA Astrophysics Data System (ADS)

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.

Prabhakaran, SP.; Babu, R. Ramesh; Ramamurthi, K.

2013-08-01

6

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

7

A novel application of the vertical gradient freeze method to the growth of high quality III-V crystals  

Microsoft Academic Search

A new process for growing high-quality single crystals of the III-V compounds, based on the vertical gradient freeze methods, is described. The method features crystal growth in a boron nitride seeded crucible, with axial and radial thermal gradients that are much lower than in the conventional liquid encapsulated Czochralski technique. This method has been applied to grow large (50-mm diameter)

W. A. Gault; E. M. Monberg; J. E. Clemans

1986-01-01

8

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

9

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

SciTech Connect

The growth-tip region of a high-purity 4.2-cm diameter Ge boule grown using low-pressure Bridgman methods in a vertical gradient freeze furnace was sectioned and polished in preparation for scanning electron microscopy and was characterized using electron backscatter diffraction (EBSD). The boule had a characteristic conical tip region with cone angle of 40? of a right circular cylinder from which a section was taken along the boule longitudinal centerline with an approximate surface area of 4 cm2. The majority of this surface area was characterized using EBSD and an image collage was assembled for the tip region. The grain structure, grain boundary orientation, twin structure, and overall crystal growth direction were determined. A crystal growth direction of approximately <112> was observed, which was also identified as the growth direction of several prominent twins observed in the tip region. The grain structure of the tip region appeared to be controlled by the sidewall nucleation of a stray grain that competed for dominance during growth. Grain boundaries and triple grain junctions were identified as low-energy coincident-site-lattice (CSL) boundaries and junctions of the ?3 and ?9 types.

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

2008-12-15

10

Single phase polycrystalline Cu2ZnSnS4 grown by vertical gradient freeze technique  

NASA Astrophysics Data System (ADS)

We report on the growth of high quality single phase Cu2ZnSnS4 (CZTS) solar absorber material grown by the vertical gradient freeze (VGF) method for the first time. Polycrystalline CZTS ingot was grown in a vacuum sealed quartz ampoule. Structural and compositional analysis of the grown ingot was carried out by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XRD pattern revealed a highly crystalline tetragonal structure with lattice parameters of a=5.429 Å and c=10.847 Å corresponding to kesterite CZTS crystal. Raman spectra confirmed the existence of single phase CZTS without any secondary phases. Energy dispersive X-ray spectroscopy (EDS) and EDS mapping were performed over a large area of the ingot to evaluate the elemental distribution on multiple polycrystals. The grown crystal was nearly stoichiometric with an atomic ratio of Zn/Sn=1.03 and Cu/(Zn+Sn)=0.964. EDS mapping showed a uniform elemental distribution over the polycrystals and a slight Cu-rich and Zn-poor composition at the grain boundaries.

Das, Sandip; Krishna, Ramesh M.; Ma, Shuguo; Mandal, Krishna C.

2013-10-01

11

A novel application of the vertical gradient freeze method to the growth of high quality III-V crystals  

NASA Astrophysics Data System (ADS)

A new process for growing high-quality single crystals of the III-V compounds, based on the vertical gradient freeze methods, is described. The method features crystal growth in a boron nitride seeded crucible, with axial and radial thermal gradients that are much lower than in the conventional liquid encapsulated Czochralski technique. This method has been applied to grow large (50-mm diameter) low-dislocation-density crystals of CaAs, GaP, and InP for uses in optoelectronic and FET devices. In the 750-gg 111-line low-doped ultralow-defect-density seeded InP crystals, the radial uniformity was exceptional, and in silicon-doped 100-line GaAs, a dislocation density of less than 300/sq cm was achieved at low dopant levels. Equipment diagrams and characterization data are included.

Gault, W. A.; Monberg, E. M.; Clemans, J. E.

1986-04-01

12

The prospects for traveling magnetic fields to affect interface shape in the vertical gradient freeze growth of cadmium zinc telluride  

NASA Astrophysics Data System (ADS)

The influence of a traveling magnetic field (TMF) on vertical gradient freeze (VGF) growth of cadmium zinc telluride (CZT) is studied using a coupled model of magnetic induction, fluid dynamics, and heat transfer. Simulations are performed to determine the influences of current, phase shift, and frequency on melt flow and growth interface shape. A downward traveling electromagnetic wave drives flow downward at the wall, which tends to flatten the interface, whereas an upward traveling wave has the opposite effect. An optimum phase shift that maximizes Lorentz force is found to depend only on system geometry. Large currents (?300A) and high frequencies (?500Hz) make a significant impact on interface shape in the absence of thermal buoyancy, but are ineffectual under realistic conditions in a 4 in.-diameter ampoule, for which buoyancy dominates Lorentz force throughout the melt. The results indicate that interface shape in this CZT growth system is strongly governed by furnace heat transfer and is difficult to modify by TMF-driven forced convection.

Yeckel, Andrew; Derby, Jeffrey J.

2013-02-01

13

Characterisation of vertical gradient freeze semi-insulating InP for use as a nuclear radiation detector  

NASA Astrophysics Data System (ADS)

The performance of a nuclear radiation detector fabricated from Vertical Gradient Freeze (VGF) semi-insulating Fe-doped InP was investigated. Pulse height spectra were acquired when the detector was irradiated with alpha particles from 241Am, as a function of temperature and detector bias voltage. The spectroscopic performance of the detector was limited at room temperature due to the presence of a high leakage current. At a bias of -150V, a room temperature leakage current density of 2.4×10-6A/mm2 was observed which reduced to 7.1×10-8A/mm2 at a temperature of -21°C. By biasing the irradiated detector contact at either a negative or positive potential, the charge collection efficiency (CCE) was measured separately for pulses produced predominantly by electron transport and for pulses produced predominantly by hole transport, respectively. At -21°C a maximum CCE of 72% was obtained for the electron signal and 44% for the hole signal. As a function of bias the CCE of the electrons remained constant in the temperature range -21°C to +19°C, whilst that of the holes exhibited a significant variation. By comparison with the Hecht relationship estimates of the carrier mobility-lifetime /(??) products are deduced, which are similar for both holes and electrons and in the range 5×10-7-8×10-7cm2/V. A reduction in /?? is observed at lower temperature for holes, whereas the value for electrons remains constant over the temperature range studied.

El-Abbassi, H.; Rath, S.; Sellin, P. J.

2001-06-01

14

Freezing in a vertical tube  

Microsoft Academic Search

Fundamental heat transfer experiments were performed for freezing of an initially superheated or nonsuperheated liquid in a cooled vertical tube. Measurements were made which yielded information about the freezing front and the frozen mass, about the various energy components extracted from the tube, and about the decay of the initial liquid superheat. Four component energies were identified and evaluated from

E. M. Sparrow; J. A. Broadbent

1983-01-01

15

Visualization of convection in a simulated gradient freeze cell during centrifugation  

Microsoft Academic Search

Experiments were performed in a simulated gradient freeze cell in order to reveal the effect of centrifugation on the convection in the cell. A laser light-cut technique was used for flow visualization. Flow patterns were observed in one vertical and two horizontal cross sections of the cell. Flow velocities were measured via particle displacement tracking velocimetry. Five centrifuge rotation rates

Peter V. Skudarnov; Liya L. Regel; William R. Wilcox

1998-01-01

16

Terrestrial refraction and vertical temperature gradient  

NASA Astrophysics Data System (ADS)

An assessment of the techniques and accuracy of current observations of coefficient of terrestrial refraction, including its diurnal and seasonal variations, is presented. One methodology has employed 1924 measurements of vertical angles between two geodetic stations with either one-way or line refraction techniques. The stations were 15 km apart and at heights of 177 and 361 m. Additional data has been gathered from adjustments of trigonometric leveling traverses with vertical angle capability, using stations 4 km apart. Another network featured lines of 4-23 km, with measurements repeated 12-60 hours sequentially. Mention is also given to measuring light attenuation and evaluation of the vertical refraction angle from the variance of the angle of arrival fluctuations. Formulas for modeling the vertical temperature gradient are discussed.

Mavridis, L. N.

17

Investigation of Crucible Materials in Gradient Freeze Gallium Arsenide Crystal Growth.  

National Technical Information Service (NTIS)

Undoped synthesized GaAs and crystals grown by the gradient freeze method were analyzed by room temperature Hall effect for net carrier density, secondary ion mass spectroscopy for Si and residual impurity concentrations, localized vibrational mode spectr...

J. L. Hurd

1987-01-01

18

Numerical analysis for freezing/melting around vertically arranged four cylinders  

NASA Astrophysics Data System (ADS)

Freezing/melting of water/ice around vertically arranged four horizontal cylinders placed in a rectangular cavity is investigated numerically by using a commercial software package. Freezing/melting is affected by the bottom cylinder distance h from the cavity bottom and by a complicated natural convection as well as the interaction with the flow around each cylinder.

Sugawara, M.; Beer, H.

2009-07-01

19

Numerical analysis for freezing\\/melting around vertically arranged four cylinders  

Microsoft Academic Search

Freezing\\/melting of water\\/ice around vertically arranged four horizontal cylinders placed in a rectangular cavity is investigated\\u000a numerically by using a commercial software package. Freezing\\/melting is affected by the bottom cylinder distance h from the cavity bottom and by a complicated natural convection as well as the interaction with the flow around each cylinder.

M. Sugawara; H. Beer

2009-01-01

20

Estimating Vertical Groundwater Velocities Using Groundwater Thermal Gradients  

NASA Astrophysics Data System (ADS)

An understanding of vertical groundwater flow through unconsolidated deposits is a component for predicting fate and transport of contaminants in the saturated zone. Groundwater movement through heterogeneous glacial deposits common to northern Indiana (USA) provided a test setting for determining if measured vertical groundwater thermal gradients could aid in calculating vertical groundwater velocity estimates. Field procedure was conducted by collecting stratified groundwater temperatures from a series of cased monitoring wells previously advanced through glacial till and outwash sedimentary sequences. Groundwater thermal gradients (temperature-depth profiles) were plotted and matched using automated computer modeling software (Microsoft Excel Solver) with published type curves to derive a dimensionless parameter for estimating vertical groundwater velocities. Data results matched predictions, to include an increase in vertical groundwater velocities during the seasonally wetter Spring; and, higher calculated vertical groundwater velocities for the finer-grained till aquitards when compared to aquifers comprised of coarser-grained outwash deposits. This study shows promise and has gathered interest both in the scientific community and environmental consulting practice for estimating vertical migration rates of contaminants (specifically those affected by advection) within the saturated zone. Government agencies or consultants, for instance, could also potentially apply this estimation technique to measure and map localized recharge rates for developing more accurate wellhead protection zones.

Arriaga, M. A.; Leap, D. I.; Petruccione, J. L.

2007-05-01

21

Full gravity gradient tensors from vertical gravity by cosine transform  

NASA Astrophysics Data System (ADS)

We present a method to calculate the full gravity gradient tensors from pre-existing vertical gravity data using the cosine transform technique and discuss the calculated tensor accuracy when the gravity anomalies are contaminated by noise. Gravity gradient tensors computation on 2D infinite horizontal cylinder and 3D "Y" type dyke models show that the results computed with the DCT technique are more accurate than the FFT technique regardless if the gravity anomalies are contaminated by noise or not. The DCT precision has increased 2 to 3 times from the standard deviation. In application, the gravity gradient tensors of the Hulin basin calculated by DCT and FFT show that the two results are consistent with each other. However, the DCT results are smoother than results computed with FFT. This shows that the proposed method is less affected by noise and can better reflect the fault distribution.

Jiang, Fu-Yu; Huang, Yan; Yan, Ke

2012-06-01

22

Flow visualization and numerical modeling for the gradient freeze configuration during centrifugation  

Microsoft Academic Search

A visualization system was constructed for observation of buoyant convection in the gradient freeze configuration during centrifugation. The buoyant convective flow was observed in the tangential cross-section and two horizontal cross-sections of the test cell. Without centrifugation, the usual axisymmetric flow pattern with a toroidal vortex near the bottom of the test cell was observed. With centrifugation, the flow in

Peter Victorovich Skudarnov

1999-01-01

23

Flow visualization and numerical modeling for the gradient freeze configuration during centrifugation  

NASA Astrophysics Data System (ADS)

A visualization system was constructed for observation of buoyant convection in the gradient freeze configuration during centrifugation. The buoyant convective flow was observed in the tangential cross-section and two horizontal cross-sections of the test cell. Without centrifugation, the usual axisymmetric flow pattern with a toroidal vortex near the bottom of the test cell was observed. With centrifugation, the flow in the test cell was primarily rotational about the cell's vertical axis. Centrifugation also modified the bottom toroidal vortex. This vortex became asymmetric and was pushed toward the bottom of the test cell. A flow pattern transition was observed in the horizontal plane 3 mm above the outer edge of the bottom end cap of the cell. This flow transition occurred at a centrifuge rotation rate of 30 rpm (Taylor number Ta = 5.7 x 105; Grashof number Gr = 8.8 x 103; Froude number Fr = 5.5 x 10-3). A minimum in the flow velocity measured in the 3 mm plane was found at 35 rpm (Ta = 7.8 x 105, Gr = 1.2 x 104; Fr = 6 x 10 -3). This minimum seems to be related to the flow transition. Numerical modeling of the flow visualization experiments was performed using Computational Fluid Dynamics solver FLUENT. Flow patterns calculated in the tangential plane and the 3 mm horizontal plane were in good agreement with those observed in the experiments for rotation rates below 30 rpm (Ta = 5.7 x 105; Gr = 8.8 x 103; Fr = 5.5 x 10-3). The flow velocity computed in the 3 mm plane also agreed well with experiments for rotation rates up to 20 rpm (Ta = 2.5 x 105, Gr = 5.1 x 103; Fr = 3.7 x 10-3). In addition, the numerical modeling predicted a shallow minimum in a mass flow in the vertical direction through surfaces parallel to the bottom of the model cell at a rotation rate of about 10 rpm (Ta = 6.4 x 104, Gr = 4.1 x 103; Fr = 9.8 x 10-4).

Skudarnov, Peter Victorovich

24

Investigation of crucible materials in gradient freeze gallium arsenide crystal growth  

Microsoft Academic Search

Undoped synthesized GaAs and crystals grown by the gradient freeze method were analyzed by room temperature Hall effect for net carrier density, secondary ion mass spectroscopy for Si and residual impurity concentrations, localized vibrational mode spectroscopy for C concentration, and optical absorption for neutral EL2 concentration. Impurity compensation was examined to determine limits for Si content in semi-insulating GaAs. Boules

Hurd

1987-01-01

25

A wet/wet differential pressure sensor for measuring vertical hydraulic gradient  

SciTech Connect

This article describes a new tool for measuring vertical hydraulic gradient in the hyporheic zone. It is essentially an electronic version of an established differential pressure measurement technique.

Fritz, Brad G.; Mackley, Rob D.

2008-12-13

26

How important are internal temperature gradients in french straws during freezing of bovine sperm in nitrogen vapor?  

PubMed

The subject of present work was to predict internal temperature gradients developed during freezing of bovine sperm diluted in extender, packaged in 0.5 ml French plastic straws and suspended in static liquid nitrogen vapor at -100 degree C. For this purpose, a mathematical heat transfer model previously developed to predict freezing times (phase change was considered) of semen/extender packaged in straw was extended to predict internal temperature gradients during the cooling/freezing process. Results showed maximum temperature differences between the centre and the periphery of semen/extender "liquid" column was 1.5 degree C for an external heat transfer coefficient, h = 15 W per (m(2) K), and only 0.5 degree C for h = 5 W per (m(2) K). It is concluded that if a thermocouple wire were inserted in a 0.5 ml plastic straw to monitor the freezing process in nitrogen vapor, its radial position would have little importance since expected internal gradients may be safely neglected. This finding facilitates the interpretation of freezing rates in 0.5 ml plastic straws immersed in nitrogen vapor over liquid nitrogen, a widely used method for cryopreservation of bovine spermatozoa. PMID:23625084

Santos, M V; Sansinena, M; Zaritzky, N; Chirife, J

27

Shoot biomass growth is related to the vertical leaf nitrogen gradient in Salix canopies.  

PubMed

Plant canopy optimization models predict that leaf nitrogen (N) distribution in the canopy will parallel the vertical light gradient, and numerous studies with many species have confirmed this prediction. Further, it is predicted that for a given canopy leaf area, a low vertical light extinction coefficient will promote rapid growth. Therefore, the ideal canopy of fast-growing plants should combine high leaf area index with a low light extinction coefficient; the latter being reflected in a flat vertical leaf N gradient throughout the canopy. Based on data from an experimental Salix stand (six varieties) grown on agricultural land in central Sweden, we tested the hypothesis that shoot growth is correlated with vertical leaf N gradient in canopies of hybrid willows bred for biomass production, which could have implications for Salix breeding. Tree improvement research requires screening of growth-related traits in large numbers of plants, but assessment of canopy leaf N gradients by chemical analysis is expensive, time-consuming and destructive. An alternative to analytical methods is to estimate leaf N gradients nondestructively with an optical chlorophyll meter (SPAD method). Here we provide a specific calibration for interpreting SPAD data measured in hybrid willows grown in biomass plantations on fertile agricultural land. Based on SPAD measurements, a significant and inverse relationship (r(2) = 0.88) was found between shoot biomass growth and vertical leaf N gradient across canopies of six Salix varieties. PMID:17669744

Weih, Martin; Rönnberg-Wästjung, Ann-Christin

2007-11-01

28

Simultaneous observation of vertical gradients of refractivity in the mesosphere and atmosphere using radio occultation data  

NASA Astrophysics Data System (ADS)

Satellites radio emission may be used for radio holographic sounding of the ionosphere, troposphere and terrestrial surface. Generalization of radio holographic method for 3-dimensional case is presented. R sults of detailed retrieving verticale gradients of refractivity in the mesosphere and atmosphere using radio occultation (RO) GPS/MET and CHAMP data are demonstrated. Fine structures in vertical gradient of electron density have been retrieved in sporadic E-layers (heights interval 85-110 km). Maximum values of the positive gradie nts 35109, 38109, 25109, 29109 [m- 3km-1] are located at levels 92, 105km (GPS/MET event 0393) and 93.5, 100 km (GPS/MET event 0583). Vertical distribution of the electron density coincides with its gradient. For considered RO event 0583 the vertical gradient of refractivity found from amplitude channel shows good correspondence at two frequencies and changes in interval +/-2-+/-5 N units/km (between heights 8 10 km) up to +/-0.6-+/-0.8 N units/km--- (between heights 14-21 km) relative to standard values. The corresponding magnitudes of temperature gradient change from negative values 4-9 oK/km at the height 8-14 km to positive 1-3 oK/km above 20.5 km. Sharp changes of temperature gradient +/-6-+/-9 oK/km are found in the tropopause at the heights between 14-20 km. The height of equatorial tropopause is found to be equal 17.6 km in correspondence with UCAR data. Variations in the vertical gradient of refractivity in the atmosphere have been found for CHAMP RO event 09. Vertical gradient of refractivity changes in interval +/-5 N-units/km (height interval 3-10 km) and +/-0.5 N-units/km between levels 11 and 18 km. Vertical distribution of temperature gradient between level 3-37 km reveals features at height 4-6, 9 10 km with positive values of about 69 oK/km.-- Radioholographic RO data analysis may be used for detailed retrieving vertical gradients of refractivity and temperature in the atmosphere and electron density in the lower ionosphere during CHAMP and future COSMIC RO missions. Simultaneous observations of the vertical gradients of refractivity in the atmosphere and ionosphere would be useful for investigation of connections between meteorological and space weather phenomena.

Pavelyev, A.; Wickert, J.; Liou, Y.; Igarashi, K.; Hocke, K.; Huang, C.

29

Method and apparatus for seismic survey including using vertical gradient estimation to separate downgoing seismic wavefield  

US Patent & Trademark Office Database

A vertical gradient estimation technique is used to separate downgoing seismic ghost wavefields. The upgoing reflected seismic wavefield, allows the ghost wavefield to be attenuated to improve signal-to-noise ratio. The vertical gradient estimation technique is applicable to both marine seismic surveying using towed hydrophones, and to land seismic surveying using buried geophones. The technique allows the vertical signal gradient to be estimated from seismic signals measured at a single depth, and is based on a relationship between the measured seismic signals, and the source signature and the Green's function for the survey media. The technique involves determning (20) the source signature for the seismic source, and determining (21) the Green's function for the survey media. Seismic signals are then measured (22). These data are then processed to estimate (24) the vertical signal gradient as a function of source signature, Green's function and the measured seismic signals. Once the vertical signal gradient is estimated, it can be used in processing the measured seismic signals to separate and attenuate (26) the downgoing ghost component of the measured seismic signals.

Corrigan; Dennis (Plano, TX); Weglein; Arthur B. (Grapevine, TX); Thompson; David D. (Plano, TX)

1991-09-24

30

Freezing avoidance of the Antarctic icefishes (Channichthyidae) across thermal gradients in the Southern Ocean  

Microsoft Academic Search

Biogeographic studies separate the Antarctic Notothenioid fish fauna into high- and low-latitude species. Past studies indicate\\u000a that some species found in the high-latitude freezing waters of the High-Antarctic Zone have low-serum hysteresis freezing\\u000a points, while other species restricted to the low-latitude seasonal pack ice zone have higher serum hysteresis freezing points\\u000a above the freezing point of seawater (?1.9°C), but the

Kevin T. Bilyk; Arthur L. DeVries

2010-01-01

31

Importance of closely spaced vertical sampling in delineating chemical and microbiological gradients in groundwater studies  

USGS Publications Warehouse

Vertical gradients of selected chemical constituents, bacterial populations, bacterial activity and electron acceptors were investigated for an unconfined aquifer contaminated with nitrate and organic compounds on Cape Cod, Massachusetts, U.S.A. Fifteen-port multilevel sampling devices (MLS's) were installed within the contaminant plume at the source of the contamination, and at 250 and 2100 m downgradient from the source. Depth profiles of specific conductance and dissolved oxygen at the downgradient sites exhibited vertical gradients that were both steep and inversely related. Narrow zones (2-4 m thick) of high N2O and NH4+ concentrations were also detected within the contaminant plume. A 27-fold change in bacterial abundance; a 35-fold change in frequency of dividing cells (FDC), an indicator of bacterial growth; a 23-fold change in 3H-glucose uptake, a measure of heterotrophic activity; and substantial changes in overall cell morphology were evident within a 9-m vertical interval at 250 m downgradient. The existence of these gradients argues for the need for closely spaced vertical sampling in groundwater studies because small differences in the vertical placement of a well screen can lead to incorrect conclusions about the chemical and microbiological processes within an aquifer.Vertical gradients of selected chemical constituents, bacterial populations, bacterial activity and electron acceptors were investigated for an unconfined aquifer contaminated with nitrate and organic compounds on Cape Cod, Massachusetts, USA. Fifteen-port multilevel sampling devices (MLS's) were installed within the contaminant plume at the source of the contamination, and at 250 and 2100 m downgradient from the source. Depth profiles of specific conductance and dissolved oxygen at the downgradient sites exhibited vertical gradients that were both steep and inversely related. Narrow zones (2-4 m thick) of high N2O and NH4+ concentrations were also detected within the contaminant plume. A 27-fold change in bacterial abundance; a 35-fold change in frequency of dividing cells (FDC), an indicator of bacterial growth; a 23-fold change in 3H-glucose uptake, a measure of heterotrophic activity; and substantial changes in overall cell morphology were evident within a 9-m vertical interval at 250 m downgradient. The existence of these gradients argues for the need for closely spaced vertical sampling in ground-water studies because small differences in the vertical placement of a well screen can lead to incorrect conclusions about the chemical and microbiological processes within an aquifer.

Smith, R. L.; Harvey, R. W.; LeBlanc, D. R.

1991-01-01

32

Daytime HONO vertical gradients during SHARP 2009 in Houston, TX  

NASA Astrophysics Data System (ADS)

Nitrous Acid (HONO) plays an important role in tropospheric chemistry as a precursor of the hydroxyl radical (OH), the most important oxidizing agent in the atmosphere. Nevertheless, the formation mechanisms of HONO are still not completely understood. Recent field observations found unexpectedly high daytime HONO concentrations in both urban and rural areas, which point to unrecognized, most likely photolytically enhanced HONO sources. Several gas-phase, aerosol, and ground surface chemistry mechanisms have been proposed to explain elevated daytime HONO, but atmospheric evidence to favor one over the others is still weak. New information on whether HONO formation occurs in the gas-phase, on aerosol, or at the ground may be derived from observations of the vertical distribution of HONO and its precursor nitrogen dioxide, NO2, as well as from its dependence on solar irradiance or actinic flux. Here we present field observations of HONO, NO2 and other trace gases in three altitude intervals (30-70 m, 70-130 m and 130-300 m) using UCLA's long path DOAS instrument, as well as in situ measurements of OH, NO, photolysis frequencies and solar irradiance, made in Houston, TX, during the Study of Houston Atmospheric Radical Precursor (SHARP) experiment from 20 April to 30 May 2009. The observed HONO mixing ratios were often ten times larger than the expected photostationary state with OH and NO. Larger HONO mixing ratios observed near the ground than aloft imply, but do not clearly prove, that the daytime source of HONO was located at or near the ground. Using a pseudo steady-state (PSS) approach, we calculated the missing daytime HONO formation rates, Punknown, on four sunny days. The NO2-normalized Punknown, Pnorm, showed a clear symmetrical diurnal variation with a maximum around noontime, which was well correlated with actinic flux (NO2 photolysis frequency) and solar irradiance. This behavior, which was found on all clear days in Houston, is a strong indication of a photolytic HONO source. [HONO]/[NO2] ratios also showed a clear diurnal profile, with maxima of 2-3% around noon. PSS calculations show that this behavior cannot be explained by the proposed gas-phase reaction of photoexcited NO2 (NO2*) or any other gas-phase or aerosol photolytic process occurring at similar or longer wavelengths than that of HONO photolysis. HONO formation by aerosol nitrate photolysis in the UV also seems to be unlikely. Pnorm correlated better with solar irradiance (average R2 = 0.85/0.87 for visible/UV) than with actinic flux (R2 = 0.76) on the four sunny days, clearly pointing to HONO being formed at the ground rather than on the aerosol or in the gas-phase. In addition, the observed [HONO]/[NO2] diurnal variation can be explained if the formation of HONO depends on solar irradiance, but not if it depends on the actinic flux. The vertical mixing ratio profiles, together with the stronger correlation with solar irradiance, support the idea that photolytically enhanced NO2 to HONO conversion on the ground was the dominant source of HONO in Houston.

Wong, K. W.; Tsai, C.; Lefer, B.; Haman, C.; Grossberg, N.; Brune, W. H.; Ren, X.; Luke, W.; Stutz, J.

2012-01-01

33

Daytime HONO Vertical Gradients during SHARP 2009 in Houston, TX  

NASA Astrophysics Data System (ADS)

Nitrous Acid (HONO) plays an important role in tropospheric chemistry as a precursor of the hydroxyl radical (OH), the most important oxidizing agent in the atmosphere. Nevertheless, the formation mechanisms of HONO are still not completely understood. Recent field observations found unexpectedly high daytime HONO concentrations in both urban and rural areas, which point to unrecognized, most likely photolytically enhanced HONO sources. Several gas-phase, aerosol, and ground surface chemistry mechanisms have been proposed to explain elevated daytime HONO, but atmospheric evidence to favor one over the others is still weak. New information on whether the HONO formation occurs in the gas-phase, on aerosol, or at the ground may be derived from observations of the vertical distribution of HONO and its precursor nitrogen dioxide, NO2, as well as its dependence on solar radiation or actinic flux. Here we present field observations of HONO, NO2 and other trace gases in three altitude intervals (30-70 m, 70-130 m and 130-300 m) using UCLA's long path DOAS instrument, as well as in situ measurements of OH, NO, photolysis frequencies and solar irradiance, made in Houston, TX, during the Study of Houston Atmospheric Radical Precursor (SHARP) experiment from 20 April to 30 May 2009. The observed HONO mixing ratios were often ten times larger than the expected photostationary state with OH and NO. Larger HONO mixing ratios observed near the ground than aloft, imply, but do not clearly prove, that the daytime source of HONO was located at or near the ground. Using a pseudo steady-state (PSS) approach, we calculated the missing daytime HONO formation rates, Punknown, on four sunny days. The NO2-normalized Punknown, Pnorm, showed a clear symmetrical diurnal variation with a maximum around noontime, which was well correlated with actinic flux (NO2 photolysis) and solar irradiance. This behavior, which was found on all clear days in Houston, is a strong indication of a photolytic HONO source. [HONO]/[NO2] ratios also showed a clear diurnal profile with maxima of 2-3 % around noon. PSS calculations show that this behavior cannot be explained by the proposed NO2?NO2* photolysis or any other gas-phase or aerosol photolytic process occurring at similar or longer wavelengths than that of HONO photolysis. HONO formation by aerosol nitrate photolysis in the UV also seems to be unlikely. Pnorm correlated better with solar irradiance (average R2 = 0.85/0.87 for visible/UV) than with actinic flux (R2 = 0.76) on the four sunny days, clearly pointing to a HONO formation at the ground rather than the aerosol or the gas-phase. In addition, the observed [HONO]/[NO2] diurnal variation can be explained if the formation of HONO depends on solar irradiance but not if it depends on the actinic flux. The vertical mixing ratio profiles together with the stronger correlation of solar irradiance vs. actinic flux support the idea that photolytically enhanced NO2 to HONO conversion on the ground was the dominant source of HONO in Houston.

Wong, K. W.; Tsai, C.; Lefer, B.; Haman, C.; Grossberg, N.; Brune, W. H.; Ren, X.; Luke, W.; Stutz, J.

2011-08-01

34

Freezing around a vertical cylinder immersed in porous media incorporating the natural convection effect  

Microsoft Academic Search

The present paper analyses the freezing heat transfer on a cold cylinder immersed in a superheated liquid-saturated porous medium. The main emphasis of this paper is to clarify the effect of natural convection in the liquid phase on the freezing process. A mathematical model was developed, based on several reasonable assumptions for fluid flow in a liquid phase. The governing

C.-Y. Wang; C. Z. Wu; C. J. Tu; S. Fukusako

1991-01-01

35

A gradient method for interpreting magnetic anomalies due to horizontal circular cylinders, infinite dykes and vertical steps  

Microsoft Academic Search

A new method of interpreting magnetic anomalies of arbitrarily-magnetised horizontal circular cylinders, dipping dykes and\\u000a vertical steps is presented. The method makes use of both horizontal and vertical gradients of the magnetic field of the model\\u000a under consideration, rather than the observed magnetic anomaly. Vertical and horizontal gradients are calculated from the\\u000a observed anomalies, and plotted one against the other

I. V. Radhakrishna Murthy; C. Visweswara Rao; G. Gopala Krishna

1980-01-01

36

Cu-Ni composition gradient for the catalytic synthesis of vertically aligned carbon nanofibers  

SciTech Connect

The influence of catalyst alloy composition on the growth of vertically aligned carbon nanofibers was studied using Cu-Ni thin films. Metals were co-sputtered onto a substrate to form a thin film alloy with a wide compositional gradient, as determined by Auger analysis. Carbon nanofibers were then grown from the gradient catalyst film by plasma enhanced chemical vapor deposition. The alloy composition produced substantial differences in the resulting nanofibers, which varied from branched structures at 81%Ni-19%Cu to high aspect ratio nanocones at 80%Cu-20%Ni. Electron microscopy and spectroscopy techniques also revealed segregation of the initial alloy catalyst particles at certain concentrations.

Klein, Kate L [ORNL; Melechko, Anatoli Vasilievich [ORNL; Rack, Philip D [ORNL; Fowlkes, Jason Davidson [ORNL; Meyer III, Harry M [ORNL; Simpson, Michael L [ORNL

2005-01-01

37

Vertical gravity gradient surveys: field results and interpretations in British Columbia, Canada  

SciTech Connect

Two vertical gravity gradient (VGG) surveys were completed during 1977 in British Columbia. The VGG method utilizes a La Coste and Rouberg model D gravity meter in conjunction with a small gradient tripod. The work indicates that the 'free-air' effect ranges between 2600-2800 E for southwestern British Columbia, which is somewhat lower than the theoretical value of 3086 E. The usefulness of the method in mining exploration is doubtful, especially in hilly or mountainous terrain where VGG values are shown to be very terrain-sensitive. However, the importance of knowing the regional VGG variations is emphasized by the work over the Hat Creek coal deposit, B.C.

Agar, C.A.; Liard, J.O.

1982-06-01

38

Methane flux, vertical gradient and mixing ratio measurements in a tropical forest  

NASA Astrophysics Data System (ADS)

Measurements of CH4 mixing ratio, vertical gradients and turbulent fluxes were carried out in a tropical forest (Reserva Biológica Cuieiras), about 60 km north of Manaus, Brazil. The methane mixing ratio and flux measurements were performed at a height of 53 m (canopy height 35 m). In addition, vertical CH4 gradients were measured within the canopy using custom made air samplers at levels of 2, 16 and 36 m above ground. The methane gradients within the canopy reveal that there is a continuous methane source at the surface. No clear evidence for aerobic methane emission from the canopy was found. The methane fluxes above the canopy are small but consistently show an upward flux with a maximum early in the morning, and the measured fluxes are in agreement with what is expected from the positive CH4 gradient in the canopy. In the morning hours, a strong canopy venting peak is observed for both CH4 and CO2, but for CO2 this peak is then superimposed by photosynthetic uptake, whereas the peak lasts longer for CH4. Monthly averaged diurnal cycles of the CH4 mixing ratio show a decrease during daytime and increase during nighttime. The magnitude of the difference in CH4 mixing ratio between day and night gradually increases throughout the wet season. The fluxes required to explain the nighttime increase are in agreement with the nighttime fluxes measured above the canopy, which implies that the CH4 increase in the nighttime boundary layer originates from local sources.

Querino, C. A. S.; Smeets, C. J. P. P.; Vigano, I.; Holzinger, R.; Moura, V.; Gatti, L. V.; Martinewski, A.; Manzi, A. O.; de Araújo, A. C.; Röckmann, T.

2011-02-01

39

Methane flux, vertical gradient and mixing ratio measurements in a tropical forest  

NASA Astrophysics Data System (ADS)

Measurements of CH4 mixing ratio, vertical gradients and turbulent fluxes were carried out in a tropical forest (Reserva Biológica Cuieiras), about 60 km north of Manaus, Brazil. The methane mixing ratio and flux measurements were performed at a height of 53 m (canopy height 35 m). In addition, vertical CH4 gradients were measured within the canopy using custom made air samplers at levels of 2, 16 and 36 m above ground. The methane gradients within the canopy reveal that there is a continuous methane source at the surface. No clear evidence for aerobic methane emission from the canopy was found. The methane fluxes above the canopy are small but consistently upwards with a maximum early in the morning. The measured fluxes are in agreement with the observed CH4 gradient in the canopy. In the morning hours, a strong canopy venting peak is observed for both CH4 and CO2, but for CO2 this peak is then superimposed by photosynthetic uptake, whereas the peak lasts longer for CH4. Monthly averaged diurnal cycles of the CH4 mixing ratio show a decrease during daytime and increase during nighttime. The magnitude of the difference in CH4 mixing ratio between day and night gradually increases throughout the wet season. The fluxes required to explain the nighttime increase are in agreement with the nighttime fluxes measured above the canopy, which implies that the CH4 increase in the nighttime boundary layer originates from local sources.

Querino, C. A. S.; Smeets, C. J. P. P.; Vigano, I.; Holzinger, R.; Moura, V.; Gatti, L. V.; Martinewski, A.; Manzi, A. O.; de Araújo, A. C.; Röckmann, T.

2011-08-01

40

Estimating Effective Vertical Diffusivity in Shallow Ponds by a Constrained Flux-Gradient Method  

NASA Astrophysics Data System (ADS)

Shallow ponds have been used to mitigate the deleterious effects of storm water run-off by acting as detention/retention basins that sequester run-off associated pollutants in sediments. Studies show that the retention efficiency of these systems can decrease over time as a result of the internal loading of nutrients/contaminants from the sediments back to the water column where they are available for export downstream. Quantifying the vertical transport of gases (down) and sediment derived materials (up) is vital to the modeling and understanding of the processes that contribute to the magnitude of internal loading. A critical parameter is the effective vertical diffusion coefficient: Kz=Dmolecular +Deddy (cm2 sec-1). The flux gradient method for estimating effective vertical thermal diffusivity has been applied with success in large lakes which undergo stratification cycles on seasonal or longer time scales. We offer a constrained version of the flux-gradient method that has been adapted for use in a shallow pond with a daily stratification cycle. The method employs heat as a tracer and assumes that transport in the face of a stable gradient is diffusive. By shrinking the spatial and temporal resolution of measurement to scales appropriate to the system of interest and carefully accounting for internal source and sink terms of heat (e.g solar radiation and sediment heat fluxes) we are able to calculate Kz as a function of time and depth during periods of stable stratification, i.e when the pond is not vertically well-mixed. Results show the magnitude of Kz varies from ca. 10-3 to 10-1 (cm2 sec-1) under stratified conditions depending primarily on the strength of stratification.

Bean, J. R.; Torgersen, T.

2004-12-01

41

Use of vertical temperature gradients for prediction of tidal flat sediment characteristics  

NASA Astrophysics Data System (ADS)

Sediment characteristics largely govern tidal flat morphologic evolution; however, conventional methods of investigating spatial variability in lithology on tidal flats are difficult to employ in these highly dynamic regions. In response, a series of laboratory experiments was designed to investigate the use of temperature diffusion toward sediment characterization. A vertical thermistor array was used to quantify temperature gradients in simulated tidal flat sediments of varying compositions. Thermal conductivity estimates derived from these arrays were similar to measurements from a standard heated needle probe, which substantiates the thermistor methodology. While the thermal diffusivities of dry homogeneous sediments were similar, diffusivities for saturated homogeneous sediments ranged approximately one order of magnitude. The thermal diffusivity of saturated sand was five times the thermal diffusivity of saturated kaolin and more than eight times the thermal diffusivity of saturated bentonite. This suggests that vertical temperature gradients can be used for distinguishing homogeneous saturated sands from homogeneous saturated clays and perhaps even between homogeneous saturated clay types. However, experiments with more realistic tidal flat mixtures were less discriminating. Relationships between thermal diffusivity and percent fines for saturated mixtures varied depending upon clay composition, indicating that clay hydration and/or water content controls thermal gradients. Furthermore, existing models for the bulk conductivity of sediment mixtures were improved only through the use of calibrated estimates of homogeneous end-member conductivity and water content values. Our findings suggest that remotely sensed observations of water content and thermal diffusivity could only be used to qualitatively estimate tidal flat sediment characteristics.

Miselis, Jennifer L.; Holland, K. Todd; Reed, Allen H.; Abelev, Andrei

2012-03-01

42

Use of vertical temperature gradients for prediction of tidal flat sediment characteristics  

USGS Publications Warehouse

Sediment characteristics largely govern tidal flat morphologic evolution; however, conventional methods of investigating spatial variability in lithology on tidal flats are difficult to employ in these highly dynamic regions. In response, a series of laboratory experiments was designed to investigate the use of temperature diffusion toward sediment characterization. A vertical thermistor array was used to quantify temperature gradients in simulated tidal flat sediments of varying compositions. Thermal conductivity estimates derived from these arrays were similar to measurements from a standard heated needle probe, which substantiates the thermistor methodology. While the thermal diffusivities of dry homogeneous sediments were similar, diffusivities for saturated homogeneous sediments ranged approximately one order of magnitude. The thermal diffusivity of saturated sand was five times the thermal diffusivity of saturated kaolin and more than eight times the thermal diffusivity of saturated bentonite. This suggests that vertical temperature gradients can be used for distinguishing homogeneous saturated sands from homogeneous saturated clays and perhaps even between homogeneous saturated clay types. However, experiments with more realistic tidal flat mixtures were less discriminating. Relationships between thermal diffusivity and percent fines for saturated mixtures varied depending upon clay composition, indicating that clay hydration and/or water content controls thermal gradients. Furthermore, existing models for the bulk conductivity of sediment mixtures were improved only through the use of calibrated estimates of homogeneous end-member conductivity and water content values. Our findings suggest that remotely sensed observations of water content and thermal diffusivity could only be used to qualitatively estimate tidal flat sediment characteristics.

Miselis, Jennifer L.; Holland, K. Todd; Reed, Allen H.; Abelev, Andrei

2012-01-01

43

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

44

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

45

Detrimental Effects of Natural Vertical Head Gradients on Chemical and Water Level Measurements in Observation Wells: Identification and Control  

SciTech Connect

It is well known that vertical head gradients exist in natural aquifer systems, and borehole flowmeter data have shown that such gradients commonly set up spontaneous vertical flows in monitoring wells, often called ambient flows. What has not been fully appreciated until recently is the serious detrimental effects such flows can have on solute concentration and hydraulic head measurements in monitoring wells. This communication explores the possibilities of diminishing ambient flows by increasing the hydraulic resistance to vertical flow within monitoring wells and limiting the penetration of such wells. Analyzed also are the surprising effects that vertical gradients may have on the equilibrium water level in a monitoring well. Results are based on collected data, numerical flow simulations, and hydraulic analysis in the near-well vicinity.

Flach, G.P.

2002-12-19

46

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

47

Global grids of gravity anomalies and vertical gravity gradients at 10 km altitude from GOCE gradient data 2009-2011 and polar gravity.  

NASA Astrophysics Data System (ADS)

The GOCE satellite measures gravity gradients which are filtered and transformed to gradients into an Earth-referenced frame by the GOCE High Level processing Facility. More than 80000000 data with 6 components are available from the period 2009-2011. IAG Arctic gravity was used north of 83 deg., while data at the Antarctic was not used due to bureaucratic restrictions by the data-holders. Subsets of the data have been used to produce gridded values at 10 km altitude of gravity anomalies and vertical gravity gradients in 20 deg. x 20 deg. blocks with 10' spacing. Various combinations and densities of data were used to obtain values in areas with known gravity anomalies. The (marginally) best choice was vertical gravity gradients selected with an approximately 0.125 deg spacing. Using Least-Squares Collocation, error-estimates were computed and compared to the difference between the GOCE-grids and grids derived from EGM2008 to deg. 512. In general a good agreement was found, however with some inconsistencies in certain areas. The computation time on a usual server with 24 processors was typically 100 minutes for a block with generally 40000 GOCE vertical gradients as input. The computations will be updated with new Wiener-filtered data in the near future.

Tscherning, Carl Christian; Arabelos, Dimitrios; Reguzzoni, Mirko

2013-04-01

48

Vertical gradients of mineral elements in Pinus sylvestris crown in alkalised soil.  

PubMed

Alkalisation of soil has been assumed to be the principal cause of changes in vertical gradients of nutrients in Pinus sylvestris crown. The long-term influence of alkaline dust pollution (pHH2O 12.3-12.6) emitted from a cement plant on the element composition of soil and needles of Scots pine in different canopy layers was studied. In the polluted area, the pH of soils was >7, and high amounts of Ca, K and Mg were measured in the upper layers of soil (0-30 cm), while the mobility and solubility of some contaminants have decreased, nutrition processes have become complicated, and imbalance of mineral composition of trees was revealed. Reduced N and increased K, Ca and Mg concentrations in needles were observed in the heavily polluted area. Vertical gradients of elements and their ratios in canopies varied depending on the alkalisation level of soil. Needles on the upper-crown shoots had higher concentrations of N, C, Ca and Mg and lower concentrations of P and K compared to the lower layer of the crown. In the unpolluted area, higher concentrations of N, P, K and Ca were found in lower-crown needles and of C and Mg in needles at the top of the canopy. The P/N ratio below 0.125 indicated P deficiency in pines. The ratios N/Ca, N/Mg and N/K had significantly decreased, while the ratios Ca/Mg, K/Mg and K/Ca had a tendency to increase in heavily polluted sample plots. Magnitude of changes of element ratios indicates on the disbalances of availability and translocation of nutrients in the crown of trees. PMID:19015943

Mandre, Malle

2008-11-08

49

Freezing Characteristics of Ethylene-Glycol Solution on the Vertical Cooled Plate  

NASA Astrophysics Data System (ADS)

An experimental study has been performed to investigate the effect of a number of parameters on the characteristics of the frozen layer of solution which formed on the vertical cooled plate being immersed in the forced convection flow. A transparent lucite channel, which has a cross sectional area of 50 mm x 70 mm, and has a length of 500 mm, was utilized for the test section. One side of the test section was made of copper plate as a cooled surface. Ethylene-glycol solution was adopted as a testing liquid. Measurements and visual observations were extensively carried out under a variety of initial concentration, initial temperature, flow velocity of solution, and cooling temperature as parameters. It was found that the characteristics of the frozen layer at the onset and steady state were well classified by both Reynolds Number and the cooling temperature ratio. The correlation equation of the averaged frozen layer thickness was determined.

Fukusako, Shoichiro; Yamada, Masahiko; Morizane, Hisashi

50

Reconstructing the Vertical 14C Gradient of the Baja Margin during the Last Deglaciation  

NASA Astrophysics Data System (ADS)

The radiocarbon activity (?14C) of the atmosphere decreased in two steps during the last deglaciation, coinciding with the well-known Heinrich 1 (H1) and Younger Dryas (YD) stadials. A leading explanation for these periods of decline involves the release of 14C-depleted carbon from a deep, isolated ocean reservoir- a mechanism that may also help to explain the deglacial rise in atmospheric CO2. Reconstructions of intermediate water ?14C near Baja California, Mexico (Marchitto et al., 2007 Science) and in the Arabian Sea (Bryan et al., 2010 Earth Planet. Sci. Lett.) document two intervals of extreme depletion relative to the coeval atmosphere during H1 and the YD that are interpreted as evidence of the return of this aged carbon from the deep reservoir to the upper ocean and atmosphere. Here we report on 14C measurements in additional cores from the Baja margin that expand the depth range of our observations and enable reconstruction of the vertical ?14C gradient. Calendar ages were determined by (1) correlation of diffuse spectral reflectance (DSR, a proxy related to local productivity) with the layer-counted age model in the GISP2 ice core and (2) correlation of raw planktic G. ruber 14C ages to new measurements in core PC08 previously studied by Marchitto et al. (2007). Together these provide a common and consistent calendar age model for margin core PCO8 (depth 705 m), core PC13 from Soledad Basin (sill depth 290 m) and margin core GC38 (depth 1270 m). In preliminary results, G. ruber ?14C data from PC08 exhibit a record of deglacial depletion events that is consistent with partial upward mixing of the intermediate-depth signal to the surface. ?14C at 1270 meters showed relatively little change during H1 and YD, indicating that anomalously depleted water did not penetrate to this depth. The vertical gradient collapsed to within observational uncertainties at the start of the Bølling-Allerød/Antarctic Climate Reversal. Taken together the results support the lateral advection of two pulses of 14C-depleted carbon above 1270 m during H1 and YD with a period of substantial vertical mixing and re-equilibration in between.

Lindsay, C. M.; Lehman, S. J.; Marchitto, T. M.; Ortiz, J. D.; van Geen, A.

2011-12-01

51

AMMONIA AND HYDROGEN SULFIDE FLUX AND DRY DEPOSITION VELOCITY ESTIMATES USING VERTICAL GRADIENT METHOD AT A COMMERCIAL BEEF CATTLE FEEDLOT  

Technology Transfer Automated Retrieval System (TEKTRAN)

Ammonia and hydrogen sulfide flux and dry deposition velocity were estimated using micrometeorological vertical gradient flux method at a commercial cattle feedyard of approximately 50,000 head of beef cattle and average 14.4 m2/head (150 ft2/head) stocking density. During summertime, NH3-N emission...

52

Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999.  

National Technical Information Service (NTIS)

The purpose of this report is to describe vertical gradients in water chemistry in the central High Plains aquifer in southwestern Kansas and the Oklahoma Panhandle. In 1998-99, 18 monitoring wells at nine sites in southwestern Kansas and the Oklahoma Pan...

P. B. McMahon

2001-01-01

53

Local stellar kinematics from RAVE data - III. Radial and vertical metallicity gradients based on red clump stars  

NASA Astrophysics Data System (ADS)

We investigate radial and vertical metallicity gradients for a sample of red clump stars from the RAdial Velocity Experiment (RAVE) Data Release 3. We select a total of 6781 stars, using a selection of colour, surface gravity and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thin or thick disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We derive almost equal metallicity gradients as a function of the Galactocentric distance for the high-probability thin-disc stars and for stars with vertical orbital eccentricities consistent with being dynamically young, ev? 0.07, i.e. d[M/H]/dRm=-0.041 ± 0.003 and d[M/H]/dRm=-0.041 ± 0.007 dex kpc-1. Metallicity gradients as a function of the distance from the Galactic plane for the same populations are steeper, i.e. d[M/H]/dzmax=-0.109 ± 0.008 and d[M/H]/dzmax=-0.260 ± 0.031 dex kpc-1, respectively. Rm and zmax are the arithmetic mean of the perigalactic and apogalactic distances, and the maximum distance to the Galactic plane, respectively. Samples including more thick-disc red clump giant stars show systematically shallower abundance gradients. These findings can be used to distinguish between different formation scenarios of the thick and thin discs.

Bilir, S.; Karaali, S.; Ak, S.; Önal, Ö.; Da?tekin, N. D.; Yontan, T.; Gilmore, G.; Seabroke, G. M.

2012-04-01

54

The stellar kinematics and populations of boxy bulges: cylindrical rotation and vertical gradients  

NASA Astrophysics Data System (ADS)

Boxy and peanut-shaped bulges are seen in about half of edge-on disc galaxies. Comparisons of the photometry and major-axis gas and stellar kinematics of these bulges to simulations of bar formation and evolution indicate that they are bars viewed in projection. If the properties of boxy bulges can be entirely explained by assuming that they are bars, then this may imply that their hosts are pure disc galaxies with no classical bulge. A handful of these bulges, including that of the Milky Way, have been observed to rotate cylindrically, i.e. with a mean stellar velocity independent of height above the disc. In order to assess whether such behaviour is ubiquitous in boxy bulges, and whether a pure disc interpretation is consistent with their stellar populations, we have analysed the stellar kinematics and populations of the boxy or peanut-shaped bulges in a sample of five edge-on galaxies. We placed slits along the major axis of each galaxy and at three offset but parallel positions to build up spatial coverage. The boxy bulge of NGC 3390 rotates perfectly cylindrically within the spatial extent and uncertainties of the data. This is consistent with the metallicity and ?-element enhancement of the bulge, which are the same as in the disc. This galaxy is thus a pure disc galaxy. The boxy bulge of ESO 311-G012 also rotates very close to cylindrically. The boxy bulge of NGC 1381 is neither clearly cylindrically nor non-cylindrically rotating, but it has a negative vertical metallicity gradient and is ?-enhanced with respect to its disc, suggesting a composite bulge comprised of a classical bulge and bar (and possibly a discy pseudo-bulge). The rotation of the peanut-shaped bulge of NGC 5746 is difficult to classify, but the peanut-shaped bulge of IC 4767 does not rotate cylindrically. Thus, even this relatively small sample is sufficient to demonstrate that boxy bulges display a range of rotational and population properties, indicating that they do not form a homogeneous class of object. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile (programmes 64.N-0545, 65.N-0126 and 66.B-0073).

Williams, Michael J.; Zamojski, Michel A.; Bureau, Martin; Kuntschner, Harald; Merrifield, Michael R.; de Zeeuw, P. Tim; Kuijken, Konrad

2011-07-01

55

[A 61-year-old man with progressive gait disturbance, freezing, and vertical gaze paresis who developed esophagus cancer].  

PubMed

We report a 61-year-old Japanese man who died of complications of esophagus cancer surgery. He was well until his 55 years of the age, when he had an onset of speech disturbance and hand writing. He was seen by a neurologist who prescribed Menesit 600 mg/day. His symptoms improved with this medication. In 1993, three years after the onset, he started to show gait disturbance and easy to fall. In 1995, he noted difficulty in eye opening. He visited our clinic on October 26, 1996. On examination, he showed vertical gaze paresis, masked face, nuchal rigidity, small step gait, freezing phenomena, and festination. His mental status was normal. He was treated with 800 mg/day of Menesit, 800 mg/day of L-dops, and 10 mg/day of bromocriptine with little improvement in his symptoms. Cranial CT scan revealed some dilatation of the third ventricle. Subsequent clinical course was one of the slow progression of his parkinsonism. In September of 1997, he noted difficulty in swallowing. He was admitted to the gastrointestinal service of our hospital on October 14, 1997. On admission, neurologic status was essentially similar to the previous one, but he showed more advanced state of his parkinsonism. Upper gastrointestinal series revealed a mass lesion of about 11.5 cm in length protruding into the lower esophagus lumen. Subtotal esophagus resection including the mass was performed on December 2, 1997. The stomach was elevated for anastomosis with the upper esophagus. No metastases were found in the mediastinum except for two lymph nodes in the para-esophageal region. The subsequent course was complicated by marked elevation of GOT, GPT, LDH, total bilirubin as well as direct bilirubin, alkaliphosphatase, and amylase starting in the evening of the surgery. On December 7, leukocytosis and pneumonic shadow were seen involving his right lung. On December 10, he developed cardiopulmonary arrest. He was once resuscitated; however, he developed cardiac arrest again seven hours later and pronounced dead. He was discussed in a neurologic CPC. The chief discussant arrived at the conclusion that the patient had PSP and the cause of the death was ascribed to circulatory disturbance to the liver. The discussant also thought that the terminal course was complicated by cholangitis or cholecystitis, sepsis, and pulmonary embolism. Surgical specimen of the esophagus tumor revealed carcinosarcoma. Postmortem examination revealed yellowish discoloration of the peritoneum and mesenterium, and accumulation of clouded ascites indicating the presence of peritonitis. Inflammatory change extended to the mediastinum. On microscopic examination, various kinds of bacilli and candida spores were seen. The liver was enlarged and a perforation was noted in the gallbladder causing biliary necrosis in the adjacent liver. An extensive infarct was seen in the left lobe of the liver; this was found to be due to obstruction of the hepatic artery at the site of the duodenohepatic mesenterium and obstruction of intrahepatic portal vein secondary to retrograde intrahepatic cholangitis in the left lobe. A piece of surgical threads was seen adjacent to the hepatic artery; foreign body granulomatous reaction was seen surrounding the surgical thread. The rupture of the gallbladder appeared to be due to the obstruction of the left branch of the hepatic artery. Neuropathologic examination revealed extensive degeneration of the pallidum, the substantia nigra, and the subthalamic nucleus and presence of neurofibrillary tangles in the remaining neurons. The neuropathologic findings were consistent with progressive supranuclear palsy, although the pathologic changes in the midbrain tegmentum was only mild gliosis. PMID:9866133

Miyashita, N; Kondo, T; Wakiya, M; Mori, H; Shirai, T; Takubo, H; Mizuno, Y

1998-11-01

56

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

57

Vertical gradients in photosynthetic gas exchange characteristics and refixation of respired CO(2) within boreal forest canopies.  

PubMed

We compared vertical gradients in leaf gas exchange, CO(2) concentrations, and refixation of respired CO(2) in stands of Populus tremuloides Michx., Pinus banksiana Lamb. and Picea mariana (Mill.) B.S.P. at the northern and southern boundaries of the central Canadian boreal forest. Midsummer gas exchange rates in Populus tremuloides were over twice those of the two conifer species, and Pinus banksiana rates were greater than Picea mariana rates. Gas exchange differences among the species were attributed to variation in leaf nitrogen concentration. Despite these differences, ratios of intercellular CO(2) to ambient CO(2) (c(i)/c(a)) were similar among species, indicating a common balance between photosynthesis and stomatal conductance in boreal trees. At night, CO(2) concentrations were high and vertically stratified within the canopy, with maximum concentrations near the soil surface. Daytime CO(2) gradients were reduced and concentrations throughout the canopy were similar to the CO(2) concentration in the well-mixed atmosphere above the canopy space. Photosynthesis had a diurnal pattern opposite to the CO(2) profile, with the highest rates of photosynthesis occurring when CO(2) concentrations and gradients were lowest. After accounting for this diurnal interaction, we determined that photosynthesizing leaves in the understory experienced greater daily CO(2) concentrations than leaves at the top of the canopy. These elevated CO(2) concentrations were the result of plant and soil respiration. We estimated that understory leaves in the Picea mariana and Pinus banksiana stands gained approximately 5 to 6% of their carbon from respired CO(2). PMID:14759908

Brooks, J R; Flanagan, L B; Varney, G T; Ehleringer, J R

1997-01-01

58

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

NASA Astrophysics Data System (ADS)

A relatively narrow vertical zone (5-6 m thick) of NO 3 - 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 NO 3 - zone was anoxic and contained high concentrations of N 2 O (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 N 2 were close to atmospheric equilibrium in uncontaminated groundwater, but were more than 2 times higher within the contaminant plume. Excess CO 2 and N 2 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 15 N of NO 3 - (from +13.6 to +42.0%.) and the N 2 produced, with an isotopic enrichment factor, , of -13.9%.. Vertical profiles of NH 4 + and 15 N of NH 4 + indicated that dissimilatory reduction of NO 3 - to NH 4 + 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.

Smith, Richard L.; Howes, Brian L.; Duff, John H.

1991-07-01

59

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

60

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

61

Fine-scale horizontal and vertical micro-distribution patterns of testate amoebae along a narrow Fen/Bog gradient.  

PubMed

The ecology of peatland testate amoebae is well studied along broad gradient from very wet (pool) to dry (hummock) micro-sites where testate amoebae are often found to respond primarily to the depth to water table (DWT). Much less is known on their responses to finer-scale gradients, and nothing is known of their possible response to phenolic compounds, which play a key role in carbon storage in peatlands. We studied the vertical (0-3, 3-6, and 6-9 cm sampling depths) micro-distribution patterns of testate amoebae in the same microhabitat (Sphagnum fallax lawn) along a narrow ecological gradient between a poor fen with an almost flat and homogeneous Sphagnum carpet (fen) and a "young bog" (bog) with more marked micro-topography and mosaic of poor fen and bog vegetation. We analyzed the relationships between the testate amoeba data and three sets of variables (1) "chemical" (pH, Eh potential, and conductivity), (2) "physical" (water temperature, altitude, i.e., Sphagnum mat micro-topography, and DWT), and (3) phenolic compounds in/from Sphagnum (water-soluble and primarily bound phenolics) as well as the habitat (fen/bog) and the sampling depth. Testate amoeba Shannon H' diversity, equitability J of communities, and total density peaked in lower parts of Sphagnum, but the patterns differed between the fen and bog micro-sites. Redundancy analyses revealed that testate amoeba communities differed significantly in relation to Eh, conductivity, water temperature, altitude, water-soluble phenolics, habitat, and sampling depth, but not to DWT, pH, or primarily bound phenolics. The sensitivity of testate amoebae to weak environmental gradients makes them particularly good integrators of micro-environmental variations and has implications for their use in paleoecology and environmental monitoring. The correlation between testate amoeba communities and the concentration of water-soluble phenolic suggests direct (e.g., physiological) and/or indirect (e.g., through impact on prey organisms) effects on testate amoebae, which requires further research. PMID:20938656

Jassey, Vincent E J; Chiapusio, Geneviève; Mitchell, Edward A D; Binet, Philippe; Toussaint, Marie-Laure; Gilbert, Daniel

2010-10-12

62

Bjerhammar's problem solution using the vertical gravity gradient anomalies (basing on model tests and the example of the geodetic test field near Grybow - the Carpathians, south Poland)  

Microsoft Academic Search

The paper presents studies concerned with the determination of reduced gravity anomalies Ag* after Bjerhammar's conception using the vertical gravity gradient G determined directly by observations in terrain. The redusults of gravity anomaly reduction are presented for global model data and for real gravity field characteristics near Grybow (Cracow district - the Carpathians). The two experiments results pointed out that

M. Barlik; M. Leonczyk

2003-01-01

63

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

64

Research and development on technologies for the preparation of III-V semiconductor materials and on methods for evaluation of the quality of these materials: Gallium arsenide crystals, gradient freeze crystal growth and measurement techniques  

Microsoft Academic Search

A gradient freeze technique was developed for the growth of GaAs crystals with low dislocation densities in closed quartz containers, using directional solidification. Such GaAs substrates are required for the manufacture of infrared light emitting diodes and other III-V devices. Crystal size (up to 1kg) and quality (crystal densities from 1000 to 10,000 cm E-2) are in accordance with present

F. Kuhn-Kuhnenfeld

1981-01-01

65

Vertical gradients in water chemistry in the central High Plains aquifer, southwestern Kansas and Oklahoma panhandle, 1999  

USGS Publications Warehouse

The central High Plains aquifer is the primary source of water for domestic, industrial, and irrigation uses in parts of Colorado, Kansas, New Mexico, Oklahoma, and Texas. Water-level declines of more than 100 feet in some areas of the aquifer have increased the demand for water deeper in the aquifer. The maximum saturated thickness of the aquifer ranged from 500 to 600 feet in 1999. As the demand for deeper water increases, it becomes increasingly important for resource managers to understand how the quality of water in the aquifer changes with depth. In 1998?99, 18 monitoring wells at nine sites in southwestern Kansas and the Oklahoma Panhandle were completed at various depths in the central High Plains aquifer, and one monitoring well was completed in sediments of Permian age underlying the aquifer. Water samples were collected once from each well in 1999 to measure vertical gradients in water chemistry in the aquifer. Tritium concentrations measured in ground water indicate that water samples collected in the upper 30 feet of the aquifer were generally recharged within the last 50 years, whereas all of the water samples collected at depths more than 30 feet below the water table were recharged more than 50 years ago. Dissolved oxygen was present throughout the aquifer, with concentrations ranging from 1.7 to 8.4 mg/L. Water in the central High Plains aquifer was predominantly a calcium-bicarbonate type that exhibited little variability in concentrations of dissolved solids with depth (290 to 642 mg/L). Exceptions occurred in some areas where there had been upward movement of mineralized water from underlying sediments of Permian age and areas where there had been downward movement of mineralized Arkansas River water to the aquifer. Calcium-sulfate and sodium-chloride waters dominated and concentrations of dissolved solids were elevated (862 to 4,030 mg/L) near the base of the aquifer in the areas of upward leakage. Dissolution of gypsum or anhydrite and halite in sediments of Permian age by ground water was the likely source of calcium, sulfate, sodium, and chloride in those waters. Calcium-sodium-sulfate waters dominated, and concentrations of dissolved solids were as large as 4,916 mg/L near the water table in the area of downward leakage. Dissolution of minerals in sedimentary deposits of marine origin in upstream areas of the Arkansas River drainage were the likely sources of calcium, sodium, and sulfate in those waters. Nitrate was detected throughout the aquifer and the background concentration was estimated to be 2.45 mg/L as N. The largest nitrate concentrations (8.28, 22, and 54.4 mg/L as N) occurred in recently recharged water collected adjacent to irrigated fields. Three pesticides (atrazine, metolachlor, simazine) and five pesticide degradation products (alachlor ethanesulfonic acid, alachlor oxanilic acid, deethylatrazine, metolachlor ethanesulfonic acid, metolachlor oxanilic acid) were detected in recently recharged water from six water-table wells. Five of the six wells were adjacent to irrigated fields. These data indicate that concentrations of nitrate and pesticides increased over time in some areas of the aquifer as a result of agricultural activities. Results from this study indicate that vertical gradients in water chemistry existed in the central High Plains aquifer. The chemical gradients resulted from chemical inputs to the aquifer from underlying sediments of Permian age, from the Arkansas River, and from agricultural activities. In areas where those chemical inputs occurred, water quality in the aquifer was impaired and may not have been suitable for some intended uses.

McMahon, Peter B.

2001-01-01

66

Transition from natural-convection-controlled freezing to conduction-controlled freezing  

Microsoft Academic Search

Experiments were performed to study the transition between freezing controlled by natural convection in the liquid adjacent to a freezing interface and freezing controlled by heat conduction in the solidified material. The freezing took place on a cooled vertical tube immersed in an initially superheated liquid contained in an adiabatic-walled vessel. At early and intermediate times, temperature differences throughout the

E. M. Sparrow; J. W. Ramsey; J. S. Harris

1981-01-01

67

Bjerhammar's problem solution using the vertical gravity gradient anomalies (basing on model tests and the example of the geodetic test field near Grybow - the Carpathians, south Poland)  

NASA Astrophysics Data System (ADS)

The paper presents studies concerned with the determination of reduced gravity anomalies Ag* after Bjerhammar's conception using the vertical gravity gradient G determined directly by observations in terrain. The redusults of gravity anomaly reduction are presented for global model data and for real gravity field characteristics near Grybow (Cracow district - the Carpathians). The two experiments results pointed out that introducing the G anomalies demands more detailed process of free-air gravity anomalies reduction and introduction of the gravity reduction before Ag* determination.

Barlik, M.; Leonczyk, M.

2003-04-01

68

Freezing controlled by natural convection  

Microsoft Academic Search

Experiments were performed for freezing under conditions where the liquid phase is either above or at the fusion temperature (i.e., superheated or nonsuperheated liquid). The liquid was housed in a cylindrical containment vessel whose surface was maintained at a uniform, time-invariant temperature during a data run, and the freezing occurred on a cooled vertical tube positioned along the axis of

E. M. Sparrow; J. W. Ramsey; R. G. Kemink

1979-01-01

69

Cell Freeze Liquid Nitrogen Freezing Container  

Center for Biologics Evaluation and Research (CBER)

... Cell Freeze Liquid Nitrogen Freezing Container. Applicant: Charter Medical, Ltd. ... Product: Cell Freeze Liquid Nitrogen Freezing Container. ... More results from www.fda.gov/biologicsbloodvaccines/bloodbloodproducts/approvedproducts

70

Freezing Precipitation.  

National Technical Information Service (NTIS)

This technical note discusses three advection patterns favorable for freezing precipitation. Two graphs were developed based on 503 freezing precipitation occurrences during the past 11 years- a 1000- to 500-mb thickness graph and an 850-mb temperature gr...

E. M. Weber

1998-01-01

71

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.

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

2012-01-01

72

Freezing Rain: An Observational and Theoretical Study  

Microsoft Academic Search

Data from a Doppler radar, an instrumented aircraft, and several rawinsonde observations during freezing rain and ice pellet events have been analyzed for this study. From these data, 34 soundings were obtained that characterized the vertical structure of the atmosphere at the time of the freezing precipitation. These soundings were analyzed to determine the general nature of the vertical structure

Ryan J. Zerr

1997-01-01

73

Horizontal and Vertical Distribution of Soil Macroarthropods Along a Spatio-Temporal Moisture Gradient in Subtropical Central Florida  

Microsoft Academic Search

Distributions of soil macroarthropods were studied monthly for 1 yr (February 2001 to January 2002) in three depth strata (0 Ð 8, 8 Ð16, and 16 Ð24 cm) at six sampling sites along a moisture gradient stretching from the shore of Lake Yale, central Florida, to an upland hammock. Annual mean density of total soil macroarthropods at these sites varied

Jan Frouz; Arshad Ali; Jaroslava Frouzova; Richard J. Lobinske

2004-01-01

74

Eddy covariance fluxes and vertical concentration gradient measurements of NO and NO2 over a ponderosa pine ecosystem: observational evidence for within canopy 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 evidence for the existence of a "canopy reduction factor". We suggest that at this site it is primarily due to chemistry converting NOx to higher nitrogen oxides within the forest canopy.

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

2013-05-01

75

Research and development on technologies for the preparation of III-V semiconductor materials and on methods for evaluation of the quality of these materials: Gallium arsenide crystals, gradient freeze crystal growth and measurement techniques  

NASA Astrophysics Data System (ADS)

A gradient freeze technique was developed for the growth of GaAs crystals with low dislocation densities in closed quartz containers, using directional solidification. Such GaAs substrates are required for the manufacture of infrared light emitting diodes and other III-V devices. Crystal size (up to 1kg) and quality (crystal densities from 1000 to 10,000 cm E-2) are in accordance with present market requirements. The electrical parameters of III-V materials were determined by the van der Pauw method, and also by an eddy current method. Crystal perfection was evaluated by selective photoetching and chemical etching in H2SO4-H202-HF solution. Photoluminescense and photoelasticity measurements were also conducted on the III-V-materials.

Kuhn-Kuhnenfeld, F.

1981-02-01

76

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

77

Comparisons of refractive index gradient and stability profiles measured by balloons and the MU radar at a high vertical resolution in the lower stratosphere  

NASA Astrophysics Data System (ADS)

Many experimental studies have demonstrated that VHF Stratosphere-Troposphere (ST) radar echo power is proportional to the generalized refractive index gradient squared M2 when using a vertically oriented beam. Because humidity is generally negligible above the tropopause, VHF ST radars can thus provide information on the static stability (quantified by the squared Brunt-Väisälä frequency N2) at stratospheric heights and this capability is useful for many scientific applications. Most studies have been performed until now at a vertical resolution of 150 m or more. In the present paper, results of comparisons between radar- and (balloon borne) radiosonde-derived M2 and N2 are shown at a better vertical resolution of 50 m with the MU radar (34.85° N, 136.15° E; Japan) by benefiting from the range resolution improvement provided by the multi-frequency range imaging technique, using the Capon processing method. Owing to favorable winds in the troposphere, the radiosondes did not drift horizontally more than about 30 km from the MU radar site by the time they reached an altitude of 20 km. The measurements were thus simultaneous and almost collocated. Very good agreements have been obtained between both high resolution profiles of M2, as well as profiles of N2. It is also shown that this agreement can still be improved by taking into account a frozen-in advection of the air parcels by a horizontally uniform wind. Therefore, it can be concluded that 1) the range imaging technique with the Capon method really provides substantial range resolution improvement, despite the relatively weak Signal-to-Noise Ratios (SNR) over the analyzed region of the lower stratosphere, 2) the proportionality of the radar echo power to M2 at a vertical scale down to 50 m in the lower stratosphere is experimentally demonstrated, 3) the MU radar can provide stability profiles with a vertical resolution of 50 m at heights where humidity is negligible, 4) stable stratospheric layers as thin as 50 m or less have at least a horizontal extent of a few km to several tens of kilometers and can be considered as frozenly advected over scales of a few tens of minutes.

Luce, H.; Hassenpflug, G.; Yamamoto, M.; Fukao, S.

2007-02-01

78

Optimization of SPRT measurements of freezing in a zinc fixed-point cell  

NASA Astrophysics Data System (ADS)

A numerical model of solute and heat transport in extremely pure materials is described. Its purpose is to characterize the effect of impurities on the freezing curves of metals containing impurities at the level of less than 1 part per million. It is used to simulate experiments performed using a commercially available zinc fixed-point cell for SPRT calibrations. The aim is to determine the effect of different vertical temperature gradients on the freezing curve and to find out whether a range of conditions could be determined where there was a good fit between theory and experiment. For this fixed-point cell, agreement between the model and experiment improves as the distribution coefficient k ? 0. It is found that the model only agrees with the measured freezing curves over the entire freeze for a narrow range of furnace settings where the temperature profile is most uniform. We suggest that this is because if the furnace settings are not optimized, the solid does not grow uniformly, and freezing may continue in regions remote from the SPRT after the material in the vicinity of the SPRT has finished freezing, so distorting the freezing curve. This effect is not present in the model and so the method presented here enables optimization of the furnace to ensure the SPRT is surrounded by a liquid-solid interface over the entire freezing range. We find that the optimum thermal environment is extremely sensitive to the furnace settings; the optimum thermal environment is found when the temperature is slightly cooler at the top of the cell, as measured in the re-entrant well of the cell. We note that optimizing the freezing process is a necessary step towards using a thermal analysis to correct for the effects of impurities in the sample.

Pearce, J. V.; Veltcheva, R. I.; Lowe, D. H.; Malik, Z.; Hunt, J. D.

2012-06-01

79

Throughfall deposition and canopy exchange processes along a vertical gradient within the canopy of beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst).  

PubMed

To assess the impact of air pollution on forest ecosystems, the canopy is usually considered as a constant single layer in interaction with the atmosphere and incident rain, which could influence the measurement accuracy. In this study the variation of througfall deposition and derived dry deposition and canopy exchange were studied along a vertical gradient in the canopy of one European beech (Fagus sylvatica L.) tree and two Norway spruce (Picea abies (L.) Karst) trees. Throughfall and net throughfall deposition of all ions other than H(+) increased significantly with canopy depth in the middle and lower canopy of the beech tree and in the whole canopy of the spruce trees. Moreover, throughfall and net throughfall of all ions in the spruce canopy decreased with increasing distance to the trunk. Dry deposition occurred mainly in the upper canopy and was highest during the growing season for H(+), NH(4)(+), NO(3)(-) and highest during the dormant season for Na(+), Cl(-), SO(4)(2-) (beech and spruce) and K(+), Ca(2+) and Mg(2+) (spruce only). Canopy leaching of K(+), Ca(2+) and Mg(2+) was observed at all canopy levels and was higher for the beech tree compared to the spruce trees. Canopy uptake of inorganic nitrogen and H(+) occurred mainly in the upper canopy, although significant canopy uptake was found in the middle canopy as well. Canopy exchange was always higher during the growing season compared to the dormant season. This spatial and temporal variation indicates that biogeochemical deposition models would benefit from a multilayer approach for shade-tolerant tree species such as beech and spruce. PMID:22325986

Adriaenssens, Sandy; Hansen, Karin; Staelens, Jeroen; Wuyts, Karen; De Schrijver, An; Baeten, Lander; Boeckx, Pascal; Samson, Roeland; Verheyen, Kris

2012-02-09

80

Freezing precipitation in Canada  

Microsoft Academic Search

Renewed interest in freezing precipitation processes and their cause have resulted in a requirement for an updated, detailed climatology of freezing precipitation in Canada. Previous work in this area was very limited in terms of the period of record and the extent of the analysis.In this study national maps were prepared of occurrence frequencies of freezing rain, freezing drizzle and

R. A. Stuart; G. A. Isaac

1999-01-01

81

Time dependence of immersion freezing  

NASA Astrophysics Data System (ADS)

The time dependence of immersion freezing was studied for temperatures between 236 K and 243 K. Droplets with single immersed, size-selected 400 nm and 800 nm kaolinite particles were produced at 300 K, cooled down to supercooled temperatures typical for mixed-phase cloud conditions, and the fraction of frozen droplets with increasing residence time was detected. To simulate the conditions of immersion freezing in mixed-phase clouds we used the Zurich Ice Nucleation Chamber (ZINC) and its vertical extension, the Immersion Mode Cooling chAmber (IMCA). We observed that the frozen fraction of droplets increased with increasing residence time in the chamber. This suggests that there is a time dependence of immersion freezing and supports the importance of a stochastic component in the ice nucleation process. The rate at which droplets freeze was observed to decrease towards higher temperatures and smaller particle sizes. Comparison of the laboratory data with four different ice nucleation models, three based on classical nucleation theory with different representations of the particle surface properties and one singular, suggest that the classical, stochastic approach combined with a distribution of contact angles is able to reproduce the ice nucleation observed in these experiments most accurately. Using the models to calculate the increase in frozen fraction at typical mixed-phase cloud temperatures over an extended period of time, yields an equivalent effect of -1 K temperature shift and an increase in time scale by a factor of ~10.

Welti, A.; Lüönd, F.; Kanji, Z. A.; Stetzer, O.; Lohmann, U.

2012-05-01

82

A study on the vertical profile of bacterial DNA structure in the Puruogangri (Tibetan Plateau) ice core using denaturing gradient gel electrophoresis  

Microsoft Academic Search

The bacterial DNA structures at different depths in the Puruogangri (Tibetan Plateau) ice core (83.45 m) were investigated by the denaturing gradient gel electrophoresis (DGGE) DNA fingerprinting technique. DGGE profiles indicated that the bacterial species diversity in glacial ice is high, and indigenous species represented by common bands in all samples may grow on the glacial surface. Bacterial diversity, as

Xinfang Zhang; Tandong Yao; Lizhe An; Lide Tian; Shijian Xu

2006-01-01

83

Comment on “Depth Estimation of Simple Causative Sources from Gravity Gradient Tensor Invariants and Vertical Component” by B. Oruç in Pure Appl. Geophys. 167 (2010), 1259–1272  

Microsoft Academic Search

estimation. ORUC ¸ (2010) proposes a new method for interpretation of gravity gradient tensor (GGT) data. This method seems interesting from a theoretical point of view, although we have found some flaws in the equations he has derived. In this paper, we correct the introduced equations and describe some theoretical points, briefly. ORUC ¸ (2010) shows that depth to the

Majid Beiki; Laust B. Pedersen

2011-01-01

84

SOIL TEMPERATURE AND FALL FREEZE-THAW EFFECTS ON INFILTRATION AND SOIL MOISTURE MOVEMENT  

Microsoft Academic Search

The quantity of spring snowmelt infiltration and runoff depends on the antecedent soil moisture conditions at the time of soil freezing. Determining the soil moisture status at any particular time during the freezing process requires an understanding of vertical distribution of liquid and frozen water content within the soil profile. This study investigated the effects of soil freezing and thawing

F. C. Kahimba

2006-01-01

85

Does the cryogenic freezing process cause shorter telomeres?  

PubMed

We have observed evidence of increased telomere shortening in short-term T-lymphocyte cultures following freezing and thawing of the original inoculum obtained by ficoll-paque gradient centrifugation, compared to T-lymphocytes that were cultured immediately without freezing and thawing from the same blood sample from 3 female and 3 male adults. Because freezing may have similar effects on other cell types, and because telomere shortening may only manifest its effects after many years or decades, we suggest there is a pressing need for evaluation of the effects of freezing on any cells envisioned for clinical applications, including embryo implantation. PMID:22465657

Jenkins, Edmund C; Ye, Lingling; Silverman, Wayne P

2012-03-29

86

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

87

Validation of GOCE time-wise gravity field models using GPS-levelling, gravity, vertical deflections and gravity gradient measurements in Hungary  

NASA Astrophysics Data System (ADS)

With the advantage of satellite gravity gradiometry (SGG) high standard global gravity determination could attain in the static part of the gravitational field. This study presents the validation of the first, second and third generation GOCE-only models using terrestrial data sets in Hungary. GOCE global geopotential models (GGM) are consistent models with global coverage (without the unobserved polar caps of 6.5° spherical radius) in sense that GGMs have been compiled utilizing measurements refer to short time period. Besides GOCE-based GGMs satellite only GRACE models were evaluated to assess the improvements by GOCE observations with respect to GRACE in gravity field determination. EGM2008 as the state-of-the-art model and SRTM3 elevation model were applied to provide that measurements involving Hungarian data sets and model derived gravity field functionals have almost the same spectral content. Results with GPS-levelling and gravity data support that there is an improvement in the determination of medium wavelength constituents of the gravitational field with GOCE models. Although vertical deflections characterize the short wave part of the gravity field, they are also capable to sense the advancement of SGG observations. Our experiences show that torsion balance measurements depict the fine structure of the gravity field, and hence they are not adequate in low-degree GGM validation.

Sz?cs, E.

2012-04-01

88

Polymerization with freezing  

Microsoft Academic Search

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

E. Ben-Naim; P. L. Krapivsky

2005-01-01

89

The Freezing Bomb  

ERIC Educational Resources Information Center

|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.…

Mills, Allan

2010-01-01

90

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

91

Home Freezing of Seafoods.  

National Technical Information Service (NTIS)

Significant advances in freezing technology have been made within the past six years. Information is given on the selection of seafood for home freezing, for its preparation, packaging and storing, and finally on the proper use of the frozen product. Thre...

M. E. Waters

1974-01-01

92

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

93

Experimental system for one-dimensional freezing of undisturbed soil profiles  

Microsoft Academic Search

An inexpensive and easy-to-handle setup for freeze-thaw experiments was developed. The system mimics field conditions, with a relatively deep monolith of undisturbed soil and a soil-air interface as an upper boundary condition. The setup includes a freezing device for vertical freezing of a soil monolith and transducers at several depths in the soil monolith for continuous measurement of unfrozen water

Holger Johnsson; Bo Thunholm; Lars-Christer Lundin

1995-01-01

94

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 standard 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-1) 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.

2012-08-01

95

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

96

Triaxial compression deformation for artificial frozen clay with thermal gradient  

Microsoft Academic Search

In order to study the deformation characteristics of artificial frozen soil with thermal gradient, such as the stress–strain relationship, a series of triaxial compression tests for frozen clay had been conducted by K0DCGF (K0 consolidation, freezing with non-uniform temperature under loading) method and GFC (freezing with non-uniform temperature, isotropic consolidation) method at various consolidation pressures and thermal gradients. Stress–strain curves

Xiaodong Zhao; Guoqing Zhou; Guozhou Chen; Xiangyu Shang; Guangsi Zhao

2011-01-01

97

Ultrasound-Assisted Freezing  

NASA Astrophysics Data System (ADS)

Freezing is a well-known preservation method widely used in the food industry. The advantages of freezing are to a certain degree counterbalanced by the risk of damage caused by the formation and size of ice crystals. Over recent years new approaches have been developed to improve and control the crystallization process, and among these approaches sonocrystallization has proved to be very useful, since it can enhance both the nucleation rate and the crystal growth rate. Although ultrasound has been successfully used for many years in the evaluation of various aspects of foods and in medical applications, the use of power ultrasound to directly improve processes and products is less popular in food manufacturing. Foodstuffs are very complex materials, and research is needed in order to define the specific sound parameters that aid the freezing process and that can later be used for the scale-up and production of commercial frozen food products.

Delgado, A. E.; Sun, Da-Wen

98

Bk060042 Cell Freeze Liquid Nitrogen Freezing Container  

Center for Biologics Evaluation and Research (CBER)

Text Version... NC 21103 Telephone 336 168-6447 F;Jcsirnile 336 774-1150 510(k) Summary Charter Medical Cell Freeze™ Liquid Nitrogen Freezing Container ... More results from www.fda.gov/downloads/biologicsbloodvaccines/bloodbloodproducts

99

Vertical Separation  

Microsoft Academic Search

A simple duopoly model is used to show the advantage to a manufacturer of se lling his product through an independent retailer (vertical separatio n) rather than directly to consumers (vertical integration). Vertical separation is profitable insofar as it induces more friendly behavio r from the rival manufacturer. The authors consider the case where fr anchise fees can be used

Giacomo Bonanno; John Vickers

1988-01-01

100

CryoMACS Freezing Bag  

Center for Biologics Evaluation and Research (CBER)

... CryoMACS Freezing Bag. Applicant: Miltenyi Biotec, Incorporated. 510(k) number: BK090020. Product: CryoMACS Freezing Bag. ... More results from www.fda.gov/biologicsbloodvaccines/bloodbloodproducts/approvedproducts

101

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...

102

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

103

Freezing human ES cells.  

PubMed

Here we demonstrate how our lab freezes HuES human embryonic stem cell lines. A healthy, exponentially expanding culture is washed with PBS to remove residual media that could otherwise quench the Trypsin reaction. Warmed 0.05% Trypsin-EDTA is then added to cover the cells, and the plate allowed to incubate for up to 5 mins at room temperature. During this time cells can be observed rounding, and colonies lifting off the plate surface. Gentle repeated pipetting will remove cells and colonies from the plate surface. Trypsinized cells are placed in a standard conical tube containing pre-warmed hES cell media to quench remaining trypsin, and then spun. Cells are resuspended growth media at a concentration of approximately one million cells in one mL of media, a concentration such that one frozen aliquot is sufficient to resurrect a culture on a 10 cm plate. After cells are adequately resuspended, ice cold freezing media is added at equal volume. Cell suspensions are mixed thoroughly, aliquoted into freezing vials, and allowed to slowly freeze to -80 C over 24 hours. Frozen cells can then moved to the vapor phase of liquid nitrogen for long term storage, or remain at -80 for approximately six months. PMID:18704182

Trish, Erin; Dimos, John; Eggan, Kevin

2006-10-12

104

Freezing Potential of Electrolytic Solutions  

Microsoft Academic Search

The freezing potential for NH3 and NaCl solutions is studied with the experiments being performed at approximately constant freezing rates. The results permit discussion of the transitory and stationary features of the phenomenon. For NH4 solutions, the stationary freezing potential is studied as a function of the growth rate and of the concentration of the solutions. Measurements were also made

Laura Levi; Oscar Milman

1966-01-01

105

Entropy, Disorder, and Freezing  

NASA Astrophysics Data System (ADS)

It is argued that the usual view that entropy is a measure of "disorder" is problematic and that there exist systems at high density, for which packing considerations dominate, where a spatially ordered state has a higher entropy than a disordered one. A classic example is a system of hard-sphere atoms, for which freezing is known to be purely entropy driven. Such a model has relevance to the real world, since it provides a good qualitative (and nearly quantitative) description of solid-liquid coexistence in simple systems such as argon. An analogy based on the packing of suitcases is given to illustrate the main point. A simple classroom demonstration is also described in which an analog simulation of the freezing of hard particles is performed.

Laird, Brian B.

1999-10-01

106

Critical freezing rate in freeze drying nanocrystal dispersions.  

PubMed

Recent advances in nanoparticle technologies have significantly enhanced the oral and parenteral delivery of poorly water-soluble active pharmaceutical ingredients (APIs). However, reports have been limited on the various drying procedures to convert a liquid nanocrystal dispersions into solid dosage forms. The solid dosage form should consist of nanocrystals that can readily reconstitute into their original size upon dissolution in water. Herein, the freeze drying process of nanocrystal dispersions was examined at varying freezing rates (speed of freezing interface). As freezing rate decreases, more particle-particle aggregation developed. A critical freezing rate, below which the dried nanocrystals cannot be re-dispersed, was identified based on the plot of the particle size of reconstituted nanocrystals versus freezing rate. Freeze drying at a freezing rate near the critical value produces dry powders of bimodal particle size distribution after re-dispersion. In addition, API concentration was found to significantly affect the critical freezing rate and therefore the re-dispersibility of dry powders. The concept of critical freezing rate is critical for the development of solid dosage forms of liquid nanocrystal dispersions. PMID:16430987

Lee, Jonghwi; Cheng, Yu

2006-01-23

107

Mechanisms of freezing damage.  

PubMed

Freezing of aqueous systems involves numerous simultaneous changes but this review concentrates on direct effects of the formation of ice and the consequent concentration of solutes in the remaining liquid phase. It is generally believed that cell injury at low cooling rates is principally due to the concentration of both intracellular and extracellular electrolytes and that cryoprotectants act by reducing this build-up. New experimental data are presented to support this explanation; we find that the extent of damage to human red blood cells during freezing in solutions of sodium chloride/glycerol/water can be quantitatively accounted for by the increase in solute concentration. However, we also show that a given degree of damage occurs at lower concentrations of solute in the presence of higher concentrations of glycerol; it appears that glycerol contributes an element of damage itself. Recently published studies from Mazur's laboratory have suggested that the dominant damaging factor at low cooling rates is actually the reduction of the quantity of unfrozen water rather than the corresponding increase in salt concentration that accompanies freezing. These data are re-evaluated, and it is argued that the experimental results could equally well be explained by a susceptibility of cells to shrinkage and re-expansion as the concentration of external impermeant solutes first increases during freezing and then decreases during thawing. It is concluded that external ice probably has no directly damaging effect upon dilute suspensions of cells. However, it is also argued that ice is directly damaging whenever it forms intracellularly, and also when it forms extracellularly in densely packed cell suspensions. In the latter case the damage is probably due to recrystallization of the ice masses during thawing. Extracellular ice also has a directly damaging effect when tissues and organs are frozen. The difficulties of designing experimental methods that will yield unequivocal results is emphasized, and consequently the above conclusions must be regarded as tentative at the present time. PMID:3332492

Pegg, D E

1987-01-01

108

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)  

Microsoft Academic Search

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

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

2009-01-01

109

Gradient-based image deconvolution  

NASA Astrophysics Data System (ADS)

Image restoration and deconvolution from blurry and noisy observation is known to be ill-posed. To stabilize the recovery, total variation (TV) regularization is often utilized for its beneficial edge in preserving the image's property. We take a different approach of TV regularization for image restoration. We first recover horizontal and vertical differences of images individually through some successful deconvolution algorithms. We restore horizontal and vertical difference images separately so that each is more sparse or compressible than the corresponding original image with a TV measure. Then we develop a novel deconvolution method that recovers the horizontal and vertical gradients, respectively, and then estimate the original image from these gradients. Various experiments that compare the effectiveness of the proposed method against the traditional TV methods are presented. Experimental results are provided to show the improved performance of our method for deconvolution problems.

Huang, Heyan; Yang, Hang; Ma, Siliang

2013-01-01

110

Biopotential amplifier for potential gradient measurements  

Microsoft Academic Search

This work proposes a bio-potential amplifier suitable for measurements from an electric potential gradient sensor, in electro-encephalography (EEG). The sensor is an array made by three electrodes placed on the vertices of an equilateral triangle of reduced size. Measuring the gradient requires small separation between electrodes hence, very low amplitude signals, of a few ?V, are obtained. Therefore, it is

Enrique M Spinelli; Carlos H Muravchik

2007-01-01

111

Competitive freezing in gold nanoparticles  

NASA Astrophysics Data System (ADS)

We use molecular dynamics simulations to study the freezing of gold nanoparticles in a size range of N = 309-923 gold atoms and find the clusters freeze to a variety of structures, including icosahedra, decahedra and face-centered cubic type structures. Measurements of the rate of freezing for the different structures reveal that the icosahedral clusters form an order ofmagnitude faster than the remaining structures over the entire range of cluster sizes studied. An analysis of the structural evolution of the icosahedral and decahedral clusters during freezing events suggests that, despite the vast difference in freezing rates, the two structures both initially form the same five-fold symmetric cap, constructed from tetrahedral sub-units of face-centered cubic packed atoms. The slow rate of decahedron freezing may be caused introduction of strain into the structure as it grows along the five-fold symmetric axis of the cluster and the need to form high energy <100> facets.

Asuquo, Cletus C.; Bowles, Richard K.

2013-05-01

112

Magnetic freezing of confined water  

NASA Astrophysics Data System (ADS)

We report results from molecular dynamic simulations of the freezing transition of liquid water in the nanoscale hydrophobic confinement under the influence of a homogeneous external magnetic field of 10 T along the direction perpendicular to the parallel plates. A new phase of bilayer crystalline ice is obtained at an anomalously high freezing temperature of 340 K. The water-to-ice translation is found to be first order. The bilayer ice is built from alternating rows of hexagonal rings and rhombic rings parallel to the confining plates, with a large distortion of the hydrogen bonds. We also investigate the temperature shifts of the freezing transition due to the magnetic field. The freezing temperature, below which the freezing of confined water occurs, shifts to a higher value as the magnetic field enhances. Furthermore, the temperature of the freezing transition of confined water is proportional to the denary logarithm of the external magnetic field.

Zhang, Guangyu; Zhang, Weiwei; Dong, Huijuan

2010-10-01

113

Magnetic freezing of confined water.  

PubMed

We report results from molecular dynamic simulations of the freezing transition of liquid water in the nanoscale hydrophobic confinement under the influence of a homogeneous external magnetic field of 10 T along the direction perpendicular to the parallel plates. A new phase of bilayer crystalline ice is obtained at an anomalously high freezing temperature of 340 K. The water-to-ice translation is found to be first order. The bilayer ice is built from alternating rows of hexagonal rings and rhombic rings parallel to the confining plates, with a large distortion of the hydrogen bonds. We also investigate the temperature shifts of the freezing transition due to the magnetic field. The freezing temperature, below which the freezing of confined water occurs, shifts to a higher value as the magnetic field enhances. Furthermore, the temperature of the freezing transition of confined water is proportional to the denary logarithm of the external magnetic field. PMID:20942551

Zhang, Guangyu; Zhang, Weiwei; Dong, Huijuan

2010-10-01

114

Poromechanics of freezing materials  

NASA Astrophysics Data System (ADS)

When subjected to a uniform cooling below the freezing point a water-infiltrated porous material undergoes a cryo-deformation resulting from various combined actions: (i) the difference of density between the liquid water and the ice crystal, which results in the initial build-up of an in-pore pressure at the onset of crystallization; (ii) the interfacial effects arising between the different constituents, which eventually govern the crystallization process in connection with the pore access radius distribution; (iii) the drainage of the liquid water expelled from the freezing sites towards the air voids; (iv) the cryo-suction process, which drives liquid water towards the already frozen pores as the temperature further decreases; (v) the thermomechanical coupling between the solid matrix, the liquid water and the ice crystal. We work out a comprehensive theory able to encompass this whole set of actions. A macroscopic approach first provides the constitutive equations of freezing poroelastic materials, including the interfacial energy effects. This approach reveals the existence of a thermodynamic state function—namely the liquid saturation degree as a function of the temperature only. The macroscopic ice-dependent poroelastic properties are then upscaled from the knowledge of the elastic properties of the solid matrix, of the pore access radius distribution, and of the capillary curve. The theory is finally illustrated by analysing quantitatively the effects of the cooling rate and of the pore radius distribution upon the cryo-deformation of water-infiltrated porous materials. The theory succeeds in accounting for the experimentally observed shrinkage of embedded air voids, while predicting the partial melting of the ice already formed when the cooling suddenly stops.

Coussy, Olivier

2005-08-01

115

Organic Solutes in Freezing Tolerance  

Microsoft Academic Search

The accumulation of high levels of low-molecular-weight solutes (polyhydric alcohols, saccharides) provides cryoprotection to freeze-tolerant animals by minimizing, via colligative effects, the percentage of body water converted to extracellular ice and the extent of cell volume reduction. Many freeze-tolerant insects accumulate high levels of polyols during autumn cold hardening, whereas freeze-tolerant frogs respond to ice formation in peripheral tissues by

Kenneth B. Storey

1997-01-01

116

A NEW FREEZING-ULTRAMICROTOME  

Microsoft Academic Search

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

H. Moor; K. MtSHLETHALER; H. WALDNER; A. FREY-WYSSLING

1961-01-01

117

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.

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

1974-01-01

118

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

119

Trace gas retrieval including horizontal gradients  

NASA Astrophysics Data System (ADS)

The development of a software package for the retrieval of vertical trace gas profiles from limb sounding measurements led to the analysis of the radiometric effects of inhomogeneous distributions of pressure, temperature and/or trace gases within simulated atmospheric layers as seen by a limb sounding instrument. These inhomogeneities called "horizontal gradients" affect the radiance measured by the instrument and — if unaccounted for - will degrade the retrieval quality of vertical pressure, temperature and/or trace gas profiles. On the other hand, if the retrieval of the vertical profiles is able to support the determination of horizontal gradients and if sufficient additional external knowledge about these gradients is available, then this offers an opportunity to retrieve vertical temperature and trace gas profiles with high accuracy. Several examples will demonstrate typical cases where the use of optimal estimation techniques including a priori knowledge of profiles and covariance data will deliver high quality results.

Kemnitzer, H.; Hilgers, S.; Schwarz, G.; Steck, T.; Clarmann, T. v.; Höpfner, M.; Ressel, K.

120

Letter: freezing theory of rbcl  

Microsoft Academic Search

A criterion for freezing of alkali halides in terms of the principal peak of the liquid charge-charge structure factor SQQ(k) has been given in earlier work. Subsequently, a theory of freezing of both neutral binary alloys and alkali halides has been developed, based on partial liquid structure factors as input information.

M. Rovere; M. P. Tosi; N. H. March

1982-01-01

121

FREEZING RESISTANCE OF NEW ZEALAND TREES AND SHRUBS  

Microsoft Academic Search

SUMMARY: Forty-two native woody species were selected to represent the range of temperature-related ecological gradients in New Zealand. Twigs collected in July (mid-winter) were sent by air to Sapporo, Japan, where they were artificially hardened and then tested for freezing resistance. Although only one plant of each species was sampled from each site in anyone year, results were consistent from

A. SAKAI; P. WARDLE

122

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

123

Thermal Freeze-out Versus Chemical Freeze-out Reexamined  

NASA Astrophysics Data System (ADS)

An alternative, to the commonly used blast-wave, model describing the freeze-out hypersurface is applied to fit the pT-spectra of identified hadrons measured at relativistic heavy-ion collisions at sqrt sNN = 62.4, 130 and 200 GeV. Decays of resonances are taken into account completely. It has turned out that the fitted freeze-out temperature and baryon number chemical potential depend weakly on the centrality of the collision and their values are close to the chemical freeze-out values determined from fits to particle yield ratios.

Prorok, D.

2009-10-01

124

Melting and freezing around a horizontal cylinder placed in a square cavity  

Microsoft Academic Search

Freezing\\/melting of water\\/ice around a horizontal cylinder placed in a square cavity of the inner side length H is investigated numerically. The cylinder is fixed at the centerline of the cavity and placed at various vertical distances\\u000a of h = H\\/3, H\\/2 and 2H\\/3 from the bottom. Melting decreases considerably with increasing cylinder distance h. Freezing shows the utmost effect at h = H\\/2,

M. Sugawara; Y. Komatsu; H. Beer

2008-01-01

125

Positive and negative generalization gradients obtained after equivalent training conditions  

Microsoft Academic Search

Positive and negative gradients were compared on the dimension of angular orientation (tilt) following discrimination training with the presence of a vertical line being positive and its absence being negative for one group of pigeons, and the opposite discrimination for another group. The gradients were initially very similar in form, although the negative gradient became flatter in the course of

Werner K. Honig; C. Alan Boneau; K. R. Burstein; H. S. Pennypacker

1963-01-01

126

Melting and freezing around a horizontal cylinder placed in a square cavity  

NASA Astrophysics Data System (ADS)

Freezing/melting of water/ice around a horizontal cylinder placed in a square cavity of the inner side length H is investigated numerically. The cylinder is fixed at the centerline of the cavity and placed at various vertical distances of h = H/3, H/2 and 2 H/3 from the bottom. Melting decreases considerably with increasing cylinder distance h. Freezing shows the utmost effect at h = H/2, other locations h = H/3 and h = 2 H/3 will considerably retard freezing.

Sugawara, M.; Komatsu, Y.; Beer, H.

2008-11-01

127

Biomimetic Materials by Freeze Casting  

NASA Astrophysics Data System (ADS)

Natural materials, such as bone and abalone nacre, exhibit exceptional mechanical properties, a product of their intricate microstructural organization. Freeze casting is a relatively simple, inexpensive, and adaptable materials processing method to form porous ceramic scaffolds with controllable microstructural features. After infiltration of a second polymeric phase, hybrid ceramic-polymer composites can be fabricated that closely resemble the architecture and mechanical performance of natural bone and nacre. Inspired by the narwhal tusk, magnetic fields applied during freeze casting can be used to further control architectural alignment, resulting in freeze-cast materials with enhanced mechanical properties.

Porter, Michael M.; Mckittrick, Joanna; Meyers, Marc A.

2013-06-01

128

Ethical aspects of social freezing.  

PubMed

The term "social freezing" is used to degrade the reason for freezing eggs to the level of a wish instead of a need. The main problem is that the distinction between "social" and "medical" freezing is very difficult to make and many applications do not fit nicely into one of the categories. The rejection of these applications also suffers from a number of inconsistencies. Given the difficulties in separating the two models, it is proposed that all applications, regardless of the reason, should be evaluated with the same criteria: efficiency, safety and justice. PMID:23972914

Pennings, G

2013-08-21

129

Irradiance gradients  

SciTech Connect

A new method for improving the accuracy of a diffuse interreflection calculation is introduced in a ray tracing context. The information from a hemispherical sampling of the luminous environment is interpreted in a new way to predict the change in irradiance as a function of position and surface orientation. The additional computation involved is modest and the benefit is substantial. An improved interpolation of irradiance resulting from the gradient calculation produces smoother, more accurate renderings. This result is achieved through better utilization of ray samples rather than additional samples or alternate sampling strategies. Thus, the technique is applicable to a variety of global illumination algorithms that use hemicubes or Monte Carlo sampling techniques.

Ward, G.J. [Lawrence Berkeley Lab., CA (United States)]|[Ecole Polytechnique Federale, Lausanne (Switzerland); Heckbert, P.S. [Carnegie-Mellon Univ., Pittsburgh, PA (United States). School of Computer Science]|[Technische Hogeschool Delft (Netherlands). Dept. of Technical Mathematics and Informatics

1992-04-01

130

METALLICITY GRADIENTS OF THICK DISK DWARF STARS  

SciTech Connect

We examine the metallicity distribution of the Galactic thick disk using F, G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release 8. Using the large sample of dwarf stars with proper motions and spectroscopically determined stellar parameters, metallicity gradients in the radial direction for various heights above the Galactic plane and in the vertical direction for various radial distances from the Galaxy center have been found. In particular, we find a vertical metallicity gradient of -0.113 {+-} 0.010 (-0.125 {+-} 0.008) dex kpc{sup -1} using an isochrone (photometric) distance determination in the range 1 kpc <|Z| < 3 kpc, which is the vertical height range most consistent with the thick disk of our Galaxy. In the radial direction, we find metallicity gradients between +0.02 and +0.03 dex kpc{sup -1} for bins in the vertical direction between 1 kpc <|Z| < 3 kpc. Both of these results agree with similar values determined from other populations of stars, but this is the first time a radial metallicity gradient for the thick disk has been found at these vertical heights. We are also able to separate thin and thick disk stars based on kinematic and spatial probabilities in the vertical height range where there is significant overlap of these two populations. This should aid further studies of the metallicity gradients of the disk for vertical heights lower than those studied here but above the solar neighborhood. Metallicity gradients in the thin and thick disks are important probes into possible formation scenarios for our Galaxy and a consistent picture is beginning to emerge from results using large spectroscopic surveys, such as the ones presented here.

Carrell, Kenneth; Chen Yuqin; Zhao Gang, E-mail: carrell@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2012-12-01

131

Vertical mammaplasty.  

PubMed

Current criticisms regarding vertical mammaplasty include problems with poor immediate postoperative appearance, nipple-areola complex malposition, and excessive lower pole length. These problems can be avoided by proper patient selection, by utilizing correct concepts of skin design, and by observing correct glandular resection and closure concepts. Vertical mammaplasty also can result in other problems, such as hypertrophic circumareolar scars and lower pole deformities, including notching, boxy shape, infra-areolar depression, and flatness. These problems are also largely avoidable by using correct technique. Several basic concepts described previously have not proven necessary to achieve good results. Abandoning some of these principles has contributed to the ability to establish an aesthetically ideal breast shape intraoperatively as well as to a decrease in morbidity. This includes eliminating liposuction as a major integral component of the procedure, eliminating suturing the gland to the pectoralis muscle, not undermining the lower pole skin, and avoiding overly wide skin resection and tight wound closure that produces significant lower pole distortion in the early postoperative period. An important concept that has proven reliable is to use a "closed" design that does not predetermine the areolar opening whenever circumstances permit. When this is not possible, a modification that utilizes the smallest possible circumference as an open design is better than a large "mosque." These alternatives allow greater flexibility in determining final nipple position and also reduce the risk of hypertrophic circumareolar scars. Important glandular resection concepts include creating pillars that are attached to both the skin and the chest wall; making them of adequate dimension to avoid postoperative lower pole shape problems, such as flattening; resecting closer to the skin lateral to the pillars to avoid a boxy breast shape; and using a drain both to assist in accurately determining the endpoint of resection and to avoid postoperative seromas. Key closure concepts include approximation of the superior surfaces of the pillars at their base to maintain vertical height and thereby prevent lower pole flattening; approximation of the inferior surfaces of the pillars to the base of the breast to prevent notching; and proper management of the vertical incision by restricting the purse-string suture effect to only the inferior portion of the incision, where there may be skin excess present. Inclusion of these concepts leads to predictable and improved aesthetic results in vertical mammaplasty. This allows full realization of the purported advantages of vertical mammaplasty and allows this method to be utilized with a level of confidence similar to that seen with inverted-T techniques. PMID:15793463

Hidalgo, David A

2005-04-01

132

Freezing of supercooled water nanodroplets  

NASA Astrophysics Data System (ADS)

All three states of water play important roles in nature, from thermostating the atmosphere to providing reactive surfaces environments. The rates at which transitions between the phases occur, the degree to which pure liquid water can be supercooled, and the solid phases that form are all fundamentally interesting questions with strong atmospheric relevance. We have followed and characterized the nucleation, growth, and subsequent freezing of pure water droplets formed in a supersonic nozzle apparatus using both Small Angle X-ray Scattering (SAXS) and Fourier Transform Infrared Spectroscopy (FTIR). Because the droplets have radii r between 3 nm and 6 nm, and the cooling rates are on the order of 5E5 K/s, liquid water only begins to freeze below approximately 215 K. These temperatures are well below the homogeneous freezing limit for bulk water. The experiments show the expected decrease in freezing temperature with decreasing droplet size, or alternatively, with increasing droplet internal pressure.

Wyslouzil, Barbara

2013-03-01

133

Cryoprotective and osmotic responses to cold acclimation and freezing in freeze-tolerant and freeze-intolerant earthworms  

Microsoft Academic Search

In this paper we present the results of physiological responses to winter acclimation and tissue freezing in a freeze-tolerant\\u000a Siberian earthworm, Eisenia nordenskioeldi, and two freeze-intolerant, temperate earthworm species, Lumbricus rubellus and Aporrectodea caliginosa. By analysing the physiological responses to freezing of both types we sought to identify some key factors promoting freeze\\u000a tolerance in earthworms. Winter acclimation was followed

M. Holmstrup; J. P. Costanzo; R. E. Lee Jr

1999-01-01

134

Passive freeze protection for solar collectors  

Microsoft Academic Search

Freeze damage is an important practical problem for water-type solar collectors. This note describes a simple passive concept that can be used to protect water-type solar collectors from freeze damage. Briefly, the water is allowed to freeze. As it freezes, however, it expands against a compliant region, and thus, the expansion does not damage the system. (auth)

L BICKLE

1975-01-01

135

Freezing behaviour of microencapsulated water.  

PubMed

The freezing behaviour of water in polyurea microcapsules was studied through DSC (differential scanning calorimetry) and ESR (electron spin resonance) measurements under a non-equilibrium condition to show that supercooling of water becomes more noticeable with decreasing droplet size of the liquid. Thermodynamics of small systems was found applicable to analyse the experimental findings, even though the process of water freezing in the microcapsules was not of an equilibrium nature. PMID:1328582

Yamane, H; Ohshima, H; Kondo, T

136

Heritage roundtable: the nuclear freeze  

SciTech Connect

The transcript of a panel of foreign policy experts, chaired by former National Security Adviser Richard Allen, debates the proposed nuclear freeze. They consider whether a freeze is a step in the right direction, acting to slow the arms race and contribute to world security, or whether it would aggravate strategic problems by perpetuating an umbalanced situation. Disagreement among the participants makes clear that no one favors nuclear war, but there are differing perspectives on how to continue preventing such a war.

Allen, R.V.; Gray, C.; Kalicki, J.; Pfaltzgraff, R.; Scoville, H.

1982-01-01

137

Freeze concentration of fruit juices.  

PubMed

Concentration of aqueous foods such as fruit juices, milk, beer, wine, coffee, and tea, is a major unit operation in the food industry. Technically feasible processes that are commercially available for the concentration of liquid foods include evaporation, freeze concentration, reverse osmosis, and ultrafiltration. Evaporation is considered to be the most economical and most widely used method of concentration. However, it is not suited for food products with very delicate flavors. Commercial processes for the concentration of such products by membrane separation techniques are not yet available. As compared to the conventional evaporation processes, concentration by freezing is potentially a superior and economic process for aroma-rich liquid foods. In the past, the process, however, was seldom used because of the investment cost and the considerable loss of concentrate in the withdrawn ice, and hence, the quality. Recent technological developments have minimized these two drawbacks associated with the earlier freeze concentration processes. In the coming decade, freeze concentration is seen as a potentially attractive method for the concentration of aroma-rich liquid foods, including fruit juices, coffee, tea, and selected alcoholic beverages. In this article, several aspects of the theoretical considerations behind freeze concentration of fruit juices, the development of new and cheaper designs, and commercially available freeze concentration processes are reviewed. The economics of the process and its application to several other areas of the food industry are also discussed. PMID:6383717

Deshpande, S S; Cheryan, M; Sathe, S K; Salunkhe, D K

1984-01-01

138

Freezing and ice crystals formed in a cylindrical food model: part I. Freezing at atmospheric pressure  

Microsoft Academic Search

Cylindrical gelatin gels were frozen at atmospheric pressure with different operating conditions (air-blast freezing at different air temperatures and brine freezing). A method to calculate a local freezing rate was proposed to take into account the variation of freezing rate as a function of the radius. A linear evolution of the local freezing rate according to the radius was observed

D Chevalier; A Le Bail; M Ghoul

2000-01-01

139

Freeze-Lining Formation of a Synthetic Lead Slag: Part II. Thermal History  

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 lining 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. To model freeze-lining behavior, input data on several assumptions, such as the phase formation and the temperature at the bath-freeze-lining interface during freeze-lining formation, are needed. In order to provide experimental data, the freeze-lining formation of a synthetic lead slag system (PbO-FeO-Fe2O3-ZnO-CaO-SiO2) is investigated. A lab-scale freeze lining was produced by submerging an air-cooled probe into a liquid slag bath for 120 minutes. The temperature evolution during freeze-lining formation was estimated using the experimentally determined position and composition of the phases, the phase-temperature relations predicted with the thermodynamic computer package FactSage, and the results of reference experiments. For the studied slag system, it is concluded that heat transfer is much faster than mass transfer and crystallization. As a result, the liquid in front of the freeze lining undercools. The degree of undercooling depends on the solidification rate. It is concluded that the temperature at the bath-freeze-lining interface varies between the glass transition and liquidus temperatures of the slag bath during freeze-lining formation.

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

2009-10-01

140

Thermoelectromagnetic convection in vertical Bridgman grown germanium silicon  

NASA Astrophysics Data System (ADS)

The effect of thermoelectromagnetic convection (TEMC) was investigated in the system germanium silicon, grown by the vertical Bridgman method under axial static magnetic fields of up to 5 T. TEMC is generated, if thermocurrents, caused by concentration and/or temperature gradients, are running non-parallel to magnetic field lines. Under the influence of strong axial magnetic fields, the macrosegregation along the growth axis changed from a profile typical for normal freezing toward a concentration profile described by diffusive mass transport. At the same time, the segregation pattern on the microscale (i.e. the non-steady distribution of the silicon incorporation perpendicular to the growth axis) changed significantly. Without magnetic field, no evidence of short-range compositional fluctuations has been detected. Growth under static magnetic fields of B?0.5T and B?4T resulted in strong microsegregation. These compositional fluctuations are in the range of a few micrometers up to several hundred micrometers. The strength increased with the field strength and reached a maximum at a magnetic induction of 2 T. These magnetic field induced inhomogeneities are damped with higher magnetic fields and can nearly be eliminated with a magnetic field of 5 T. Due to their coupling to the static magnetic field and their specific shape, they can be attributed to TEMC.

Dold, P.; Szofran, F. R.; Benz, K. W.

2006-05-01

141

Biopotential amplifier for potential gradient measurements  

Microsoft Academic Search

This work proposes a bio-potential amplifier suitable for measurements from an electric potential gradient sensor, in electro-encephalography (EEG). The sensor is an array made by three electrodes placed on the vertices of an equilateral triangle of reduced size. Measuring the gradient requires small separation between electrodes hence, very low amplitude signals, of a few muV, are obtained. Therefore, it is

Andrea N. Bermúdez; Enrique M. Spinelli; Carlos H. Muravchik

2007-01-01

142

Theoretical analysis of specimen cooling rate during impact freezing and liquid-jet freezing of freeze-etch specimens.  

PubMed Central

We have carried out a theoretical analysis of specimen cooling rate under ideal conditions during impact freezing and liquid-jet freezing. The analysis shows that use of liquid helium instead of liquid nitrogen as cooling medium during impact freezing results in an increase in a specimen cooling rate of no more than 30-40%. We have further shown that when both impact freezing and liquid-jet freezing are conducted at liquid nitrogen temperature, the two methods give approximately the same specimen cooling rate under ideal conditions except for a thin outer layer of the specimen. In this region impact freezing yields the highest cooling rate.

Kopstad, G; Elgsaeter, A

1982-01-01

143

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

144

Molecular biology of freezing tolerance.  

PubMed

Winter survival for many kinds of animals involves freeze tolerance, the ability to endure the conversion of about 65% of total body water into extracellular ice and the consequences that freezing imposes including interruption of vital processes (e.g., heartbeat and breathing), cell shrinkage, elevated osmolality, anoxia/ischemia, and potential physical damage from ice. Freeze-tolerant animals include various terrestrially hibernating amphibians and reptiles, many species of insects, and numerous other invertebrates inhabiting both terrestrial and intertidal environments. Well-known strategies of freezing survival include accumulation of low molecular mass carbohydrate cryoprotectants (e.g., glycerol), use of ice nucleating agents/proteins for controlled triggering of ice growth and of antifreeze proteins that inhibit ice recrystallization, and good tolerance of anoxia and dehydration. The present article focuses on more recent advances in our knowledge of the genes and proteins that support freeze tolerance and the metabolic regulatory mechanisms involved. Important roles have been identified for aquaporins and transmembrane channels that move cryoprotectants, heat shock proteins and other chaperones, antioxidant defenses, and metabolic rate depression. Genome and proteome screening has revealed many new potential targets that respond to freezing, in particular implicating cytoskeleton remodeling as a necessary facet of low temperature and/or cell volume adaptation. Key regulatory mechanisms include reversible phosphorylation control of metabolic enzymes and microRNA control of gene transcript expression. These help to remodel metabolism to preserve core functions while suppressing energy expensive metabolic activities such as the cell cycle. All of these advances are providing a much more complete picture of life in the frozen state. PMID:23897687

Storey, Kenneth B; Storey, Janet M

2013-07-01

145

Freeze-dried microarterial allografts  

SciTech Connect

Rehydrated freeze-dried microarterial allografts were implanted to bridge arterial defects using New Zealand White rabbits as the experimental model. Segments of artery from the rabbit ear and thigh were harvested and preserved for a minimum of 2 weeks after freeze-drying. These allografts, approximately 1 mm in diameter and ranging from 1.5 to 2.5 cm in length, were rehydrated and then implanted in low-pressure and high-pressure arterial systems. Poor patency was noted in low-pressure systems in both allografts and autografts, tested in 12 rabbits. In the high-pressure arterial systems, allografts that were freeze-dried and reconstituted failed in a group of 10 rabbits with an 8-week patency rate of 30 percent. Gamma irradiation in an effort to reduce infection and antigenicity of grafts after freeze-drying was associated with a patency rate of 10 percent at 8 weeks in this system in another group of 10 rabbits. Postoperative cyclosporin A therapy was associated with a patency rate of 22.2 percent in the high-pressure arterial system in a 9-rabbit group. Control autografts in this system in a group of 10 rabbits showed a 100 percent patency at 8 weeks. Microarterial grafts depend on perfusion pressure of the vascular bed for long-term patency. Rehydrated freeze-dried microarterial allografts do not seem to function well in lengths of 1 to 2.5 cm when implanted in a high-pressure arterial system. Freeze-dried arterial allografts are probably not antigenic.

Raman, J.; Hargrave, J.C.

1990-02-01

146

Artifacts associated with quick-freezing and freeze-drying.  

PubMed

We have studied the structures produced when nonbiological samples were subjected to quick-freezing and freeze-drying with a liquid helium cooled freeze-slamming device. Samples examined in this way included sodium chloride, sucrose, and Tris buffer. A variety of filamentlike and trabeculumlike structures were formed in these preparations. These structures may represent eutectic mixtures formed during the growth of small ice crystals during the freezing process, and exposed during the rapid sublimation of pure ice during the etching process. Samples of biological membranes (isolated chloroplast membranes) were prepared in various buffers by means of this technique. In distilled water, excellent replicas of membrane surfaces were obtained. In salt solutions, however, the membranes appeared to be embedded in a network of thin filaments appearing very much like a cytoskeletal lattice. It is concluded that extreme caution must be used when employing this preparation technique for studies of cell architecture, and that extensive washing of cell components in distilled water may be necessary to obtain faithful representations of cell structure. PMID:6338243

Miller, K R; Prescott, C S; Jacobs, T L; Lassignal, N L

1983-02-01

147

The Temperature Dependence of Water's Latent Heat of Freezing  

NASA Astrophysics Data System (ADS)

Freezing of water in Earth's atmosphere affects cloud dynamics through the release of the latent heat. The latent heat released is a function of how deeply the cloud water is supercooled before freezing begins - the deeper the supercooling, the less heat is released to the atmosphere. We present new measurements of the temperature dependent latent heat of freezing of water, measured using a Perkin Elmer DSC 7 and a Mettler Toledo Polymer DSC. Both instruments have been calibrated against melting transitions of water, dodecane, undecane,and tetradecane, and both agree within the error of the measurements with values in the literature. However, the two measurements show dramatic differences for the latent heat of freezing of water, which we attribute to the different methods used to extract a heat flux. At higher temperatures our measurements with the Perkin Elmer, which is a power compensation type calorimeter, are comparable to those of Bertolini et al. (1985). At lower temperatures, our measurements diverge from those of Bertolini et al. (1985), which we again attribute to the different principle of operation of the calorimeters. We conclude that temperature gradients within the freezing water play a critical role in the quantity of heat eventually exchanged with the surroundings. Finally, we reconcile the measurements with Kirchhoff's relation, which can be written (??H/?T)p = ?cp where ?H is the enthalpy difference between product and reactant (supercooled water and ice in this case) and ?cp is the difference in their heat capacities. [Bertolini, D., M. Cassettari, and G. Salvetti, Anomalies in the latent-heat of solidification of supercooled water. Chem. Phys. Lett., 119, 553-555, 1985.

Szedlak, A.; Blanchard, A. V.; Kostinski, A. B.; Cantrell, W. H.

2009-12-01

148

BAM Media M30b: Freezing medium  

Center for Food Safety and Applied Nutrition (CFSAN)

... BAM Media M30b: Freezing medium. January 2001. Bacteriological Analytical Manual. M30b Freezing medium for Campylobacter. ... More results from www.fda.gov/food/foodscienceresearch/laboratorymethods

149

Aspects of Freezing Rain Simulation and Testing.  

National Technical Information Service (NTIS)

The paper examines first the available information on freezing rain and freezing drizzle in an attempt to define the applicable parameters, viz. temperature, precipitation rate (or liquid water content), drop size, and wind speed, in order to permit repre...

J. R. Stallabrass

1983-01-01

150

Standardization of Freeze Frame TV Codecs.  

National Technical Information Service (NTIS)

The purpose of this report is to recommend a protocol and a compression technique to be considered as the standard for freeze frame teleconferencing equipments. The recommendations in Section 4 is based on (a) an analysis of freeze frame teleconferencing ...

1990-01-01

151

Variation in vertical stress in the Baram Basin, Brunei: tectonic and geomechanical implications  

Microsoft Academic Search

The vertical or lithostatic stress is an important factor in tectonic and geomechanical studies and is commonly used in the prediction of pore pressures and fracture gradients. However, the vertical stress is not always calculated in situ and the approximation of 1.0psi\\/ft (22.63 MPa\\/km) is often used for the vertical stress gradient. Vertical stress has been determined in 24 fields

M. R. P Tingay; R. R Hillis; C. K Morley; R. E Swarbrick; E. C Okpere

2003-01-01

152

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

153

Freezing Tolerance in Mytilus Edulis.  

National Technical Information Service (NTIS)

Mytilus edulis tolerates freezing to a tissue temperature of -10 deg C, while Venus mercenaria tolerates only -6 deg C. In both species, tissues are injured when 64 per cent of cellular water has been moved to form ice. In Mytilus, 20 percent of cell wate...

R. J. Williams

1969-01-01

154

Ice Accretion in Freezing Rain.  

National Technical Information Service (NTIS)

This report describes a detailed heat-balance ice accretion model, including the important heat fluxes in freezing rain and allowing the accretion of runoff water in the form of icicles. It also presents a simple algorithm for calculating the ice load on ...

K. F. Jones

1996-01-01

155

The vertical profile of radar reflectivity of convective cells: A strong indicator of storm intensity and lightning probability?  

SciTech Connect

Reflectivity data from Doppler radars are used to construct vertical profiles of radar reflectivity (VPRR) of convective cells in mesoscale convective systems (MCSs) in three different environmental regimes. The National Center for Atmospheric Research CP-3 and CP-4 radars are used to calculate median VPRR for MCSs in the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central in 1985. The National Oceanic and Atmospheric Administration-Tropical Ocean Global Atmosphere radar in Darwin, Australia, is used to calculate VPRR for MCSs observed both in oceanic, monsoon regimes and in continental, break period regimes during the wet seasons of 1987/88 and 1988/89. The midlatitude and tropical continental VPRRs both exhibit maximum reflectivity somewhat above the surface and have a gradual decrease in reflectivity with height above the freezing level. In sharp contrast, the tropical oceanic profile has a maximum reflectivity at the lowest level and a very rapid decrease in reflectivity with height beginning just above the freezing level. The tropical oceanic profile in the Darwin area is almost the same shape as that for two other tropical oceanic regimes, leading to the conclustion that it is characteristic. The absolute values of reflectivity in the 0 to 20 C range are compared with values in the literature thought to represent a threshold for rapid storm electrification leading to lightning, about 40 dBZ at -10 C. The large negative vertical gradient of reflectivity in this temperature range for oceanic storms is hypothesized to be a direct result of the characteristically weaker vertical velocities observed in MCSs over tropical oceans..

Zipser, E.J.; Lutz, K.R. [Texas A& M Univ., College Station, TX (United States)

1994-08-01

156

Physiological responses to freezing in hatchlings of freeze-tolerant and -intolerant turtles  

Microsoft Academic Search

Freeze tolerance is a complex cold-hardiness adaptation that has independently evolved in a diverse group of organisms, including several ectothermic vertebrates. Because little is known about the mechanistic basis for freeze tolerance in reptiles, we compared responses to experimental freezing in winter-acclimatized hatchlings representing nine taxa of temperate North American turtles, including ones that tolerated freezing and others that did

Jon P. Costanzo; Patrick J. Baker; Richard E. Lee Jr

2006-01-01

157

Atmospheric Freeze Drying—A Review  

Microsoft Academic Search

This review article focuses on the development of atmospheric freeze drying (AFD): technological aspects, product possibilities, physical properties of products, drying kinetics, modeling, and simulation. The main motivation for developing atmospheric freeze drying as a new drying technology is the desire to reduce the energy consumption compared to vacuum freeze drying while maintaining a high product quality. One technical solution

I. C. Claussen; T. S. Ustad; I. Strømmen; P. M. Walde

2007-01-01

158

Molten salt freeze seal. Final report  

Microsoft Academic Search

This report documents the results of the testing performed at Sandia National Laboratory, Albuquerque, New Mexico, on the applicability of a sodium freeze seal type valve stem in a molten salt environment. The freeze seal tests consisted of cycling the valve stem at set temperature intervals, checking the temperature distribution for freeze plug location, and verifying the actuator forces. In

Corugedo

1985-01-01

159

When hot water freezes before cold  

Microsoft Academic Search

I suggest that the origin of the Mpemba effect (the freezing of hot water before cold) is due to freezing-point depression by solutes, either gaseous or solid, whose solubility decreases with increasing temperature so that they are removed when water is heated. The solutes are concentrated ahead of the freezing front by zone refining in water that has not been

J. I. Katz

2009-01-01

160

Freezing Resistance in Some Antarctic Fishes  

Microsoft Academic Search

Measurements of serum freezing points in three Antarctic marine fishes indicated that they do not freeze in the -1.87 degrees C seawater because their blood is isosmotic to seawater. Concentrations of sodium chloride, urea, and free amino acids in the serum accounted for only half of the freezing-point depression of the serum. A protein containing carbohydrate was isolated which accounted

Arthur L. Devries; Donald E. Wohlschlag

1969-01-01

161

Effects of Yeast Freezing in Frozen Dough  

Microsoft Academic Search

Cereal Chem. 80(4):454-458 The effects of freezing and frozen storage of bread dough and com- pressed yeast on bread quality were studied. Besides, the effects of compressed yeast freezing on cell viability, gas production and release of substances by the yeast cells were examined. Freezing and frozen storage of dough made with fresh yeast had more negative effects on baking

Pablo D. Ribotta; Alberto E. León; María Cristina Añón

2003-01-01

162

a Laboratory Investigation of Droplet Freezing  

Microsoft Academic Search

Laboratory experimentation was undertaken to investigate the effects of various soluble and insoluble nuclei on the freezing temperature of water droplets. The freezing temperature and size of over 15,000 droplets were obtained. Pure water was produced, and subsequently frozen in droplet form. The freezing temperatures of various sizes of pure water droplets were used as a reference standard for the

Thomas E. Hoffer

1961-01-01

163

Freeze-Thaw Processes and Soil Chemistry.  

National Technical Information Service (NTIS)

This review broadly examines the interactions between freeze-thaw processes and soil chemistry, focusing on (1) the effect of solutes on physical properties such as freezing-point depression, unfrozen water and frost heaving, (2) the effect of freeze-thaw...

G. M. Marion

1995-01-01

164

Experimental Observation of the Influence of Furnace Temperature Profile on Convection and Segregation in the Vertical Bridgman Crystal Growth Technique.  

National Technical Information Service (NTIS)

Azulene-doped naphthalene was directionally solidified during the vertical Bridgman-Stockbarger technique. Doping homogeneity and convection were determined as a function of the temperature profile in the furnace and the freezing rate. Convection velociti...

G. T. Neugebauer W. R. Wilcox

1992-01-01

165

Natural Convection between Concentric Vertical Cylinders  

Microsoft Academic Search

The motion of a fluid in the closed annular cavity formed by two concentric vertical cylinders and two horizontal planes has been analyzed by a numerical solution of the equations of motion and energy using a high-speed digital computer. The motion is generated by a radial density gradient caused by the thermal boundary conditions which are, typically: inner cylinder at

G. de Vahl Davis; R. W. Thomas

1969-01-01

166

Freeze Concentration and Its Recent Development  

NASA Astrophysics Data System (ADS)

This article concerns freeze concentration and its recent development. Freeze concentration enables to remove water from aqueous solutions including volatile and heat-sensitive components with less damage to the concentrated solution because of the operation at lower temperature near the freezing point with possibly no gas-liquid boundary. Moreover, the lower latent heat accompanied with ice crystallization provides a possibility of the operation with lower energy consumption. Recently freeze concentration has been applied to the wastewater treatment field. First the principle of freeze concentration will be addressed. Second applications of freeze concentration to the wastewater treatment field will be reviewed, including our recent works. Finally prospective views of freeze concentration will be given.

Wakisaka, Minato; Shirai, Yoshihito

167

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

168

Freeze concentration beats the heat  

Microsoft Academic Search

This paper reports on freeze concentration (FC) which saves energy and money in packaging, shipping, and storing food products. FC---in contrast to existing heat-evaporation processes---retains volatile flavor and aroma compounds in food products so that no additives are required to restore the taste and smell of the original product. In recent tests on orange, grapefruit, and pineapple juices, reconstituted FC

1990-01-01

169

Shadowgraph Study of Gradient Driven Fluctuations  

NASA Astrophysics Data System (ADS)

A fluid or fluid mixture, subjected to a vertical temperature and/or concentration gradient in a gravitational field, exhibits greatly enhanced light scattering at small angles. This effect is caused by coupling between the vertical velocity fluctuations due to thermal energy and the vertically varying refractive index. Physically, small upward or downward moving regions will be displaced into fluid having a refractive index different from that of the moving region, thus giving rise to the enhanced scattering. The scattered intensity is predicted to vary with scattering wave vector q, as q-4, for sufficiently large q, but the divergence is quenched by gravity at small q. In the absence of gravity, the long wavelength fluctuations responsible for the enhanced scattering are predicted to grow until limited by the sample dimensions. It is thus of interest to measure the mean-squared amplitude of such fluctuations in the microgravity environment for comparison with existing theory and ground based measurements. The relevant wave vectors are extremely small, making traditional low-angle light scattering difficult or impossible because of stray elastically scattered light generated by optical surfaces. An alternative technique is offered by the shadowgraph method, which is normally used to visualize fluid flows, but which can also serve as a quantitative tool to measure fluctuations. A somewhat novel shadowgraph apparatus and the necessary data analysis methods will be described. The apparatus uses a spatially coherent, but temporally incoherent, light source consisting of a super-luminescent diode coupled to a single-mode optical fiber in order to achieve extremely high spatial resolution, while avoiding effects caused by interference of light reflected from the various optical surfaces that are present when using laser sources. Results obtained for a critical mixture of aniline and cyclohexane subjected to a vertical temperature gradient will be presented. The sample was confined between two horizontal parallel sapphire plates with a vertical spacing of 1 mm. The temperatures of the sapphire plates were controlled by independent circulating water loops that used Peltier devices to add or remove heat from the room air as required. For a mixture with a temperature gradient, two effects are involved in generating the vertical refractive index gradient, namely thermal expansion and the Soret effect, which generates a concentration gradient in response to the applied temperature gradient. For the aniline/cyclohexane system, the denser component (aniline) migrates toward the colder surface. Consequently, when heating from above, both effects result in the sample density decreasing with altitude and are stabilizing in the sense that no convective motion occurs regardless of the magnitude of the applied temperature gradient. The Soret effect is strong near a binary liquid critical point, and thus the dominant effect is due to the induced concentration gradient. The results clearly show the divergence at low q and the predicted gravitational quenching. Results obtained for different applied temperature gradients at varying temperature differences from the critical temperature, clearly demonstrate the predicted divergence of the thermal diffusion ratio. Thus, the more closely the critical point is approached, the smaller becomes the temperature gradient required to generate the same signal. Two different methods have been used to generate pure concentration gradients. In the first, a sample cell was filled with a single fluid, ethylene glycol, and a denser miscible fluid, water, was added from below thus establishing a sharp interface to begin the experiment. As time went on the two fluids diffused into each other, and large amplitude fluctuations were clearly observed at low q. The effects of gravitational quenching were also evident. In the second method, the aniline/cyclohexane sample was used, and after applying a vertical temperature gradient for several hours, the top and bottom temperatures were set equal and the thermal gradie

Cannell, David; Nikolaenko, Gennady; Giglio, Marzio; Vailati, Alberto; Croccolo, Fabrizio; Meyer, William

2002-11-01

170

The thermodynamics of freezing soils  

NASA Astrophysics Data System (ADS)

In this work a throughout derivation of the soil freezing process is performed, from the thermodynamic equilibrium to the derivation of the water and ice content in the ground. Starting from a capillary tube schematization for the soil and the findings of Loch (1978), the generalized Clapeyron equation may be directly obtained by the Gibbs-Duhem identity. In this equation, however, the ice pressure complicates the formulation as it adds an unknown to the thermodynamic equilibrium. The only way to obtain the common generalized Clapeyron equation often used in literature is to hypothesize the behavior ''freezing=drying'' as proposed by Miller (1963). In this case the pressure at the ice-water interface is equal to the air-water interface, and so the ice pressure may be set constant and equal to the zero gauge pressure given by air pressure. This assumption, often tacitly assumed in literature, implies precise limitations on the physical processes that may be dealt with. In particular, frost heave may not be modeled. The objective of this work is to derive the thermodynamic equilibrium of the ice and water phases in a porous medium, to clarify the ''freezing=drying'' assumption and to propose a fully explicit formulation for the equilibrium where the ice pressure is added to the set of unknowns.

Dall'Amico, Matteo; Rigon, Riccardo; Gruber, Stephan; Endrizzi, Stefano

2010-05-01

171

Freezing induces a loss of freeze tolerance in an overwintering insect.  

PubMed Central

Cold-hardy insects overwinter by one of two main strategies: freeze tolerance and freeze avoidance by supercooling. As a general model, many freeze-tolerant species overwinter in extreme climates, freeze above -10 degrees C via induction by ice-nucleating agents, and once frozen, can survive at temperatures of up to 40 degrees C or more below the initial freezing temperature or supercooling point (SCP). It has been assumed that the SCP of freeze-tolerant insects is unaffected by the freezing process and that the freeze-tolerant state is therefore retained in winter though successive freeze-thaw cycles of the body tissues and fluids. Studies on the freeze-tolerant larva of the hoverfly Syrphus ribesii reveal this assumption to be untrue. When a sample with a mean 'first freeze' SCP of -7.6 degrees C (range of -5 degrees C to -9.5 degrees C) were cooled, either to -10 degrees C or to their individual SCP, on five occasions, the mean SCP was significantly depressed, with some larvae subsequently freezing as low as -28 degrees C. Only larvae that froze at the same consistently high temperature above -10 degrees C were alive after being frozen five times. The wider occurrence of this phenomenon would require a fundamental reassessment of the dynamics and distinctions of the freeze-tolerant and freeze-avoiding strategies of insect overwintering.

Brown, C L; Bale, J S; Walters, K F A

2004-01-01

172

Contact freezing: a review of experimental studies  

NASA Astrophysics Data System (ADS)

This manuscript compiles both theoretical and experimental information on contact freezing with the aim to better understand this potentially important but still not well quantified heterogeneous freezing mode. There is no complete theory that describes contact freezing and how the energy barrier has to be overcome to nucleate an ice crystal by contact freezing. Experiments on contact freezing conducted using the cold plate technique indicate that it can initiate ice formation at warmer temperatures than immersion freezing. Additionally, a qualitative difference in the freezing temperatures between contact and immersion freezing has been found using different instrumentation and different ice nuclei. There is a lack of data on collision rates in most of the reported data, which inhibits a quantitative calculation of the freezing efficiencies. Thus, new or modified instrumentation to study contact nucleation in the laboratory and in the field are needed to identify the conditions at which contact nucleation could occur in the atmosphere. Important questions concerning contact freezing and its potential role for ice cloud formation and climate are also summarized.

Ladino Moreno, L. A.; Stetzer, O.; Lohmann, U.

2013-10-01

173

Improved Cryofixation Applicable to Freeze Etching  

PubMed Central

Freeze etching of solute model systems (e.g., glycerol or ferritin solutions) demonstrates that cryofixation can introduce serious artifacts due to the segregation of the dissolved or dispersed material from the solvent. Since, in principle, this problem can be reduced by increasing the cooling rate, a new technique has been developed which combines spray freezing with freeze etching. This spray-freeze-etching is applied by first spraying the specimen into a liquid cryomedium. The frozen droplets are then “glued” together with butylbenzene to form a regular freeze-etch specimen, while the temperature of the sample is kept at -85°C. The results obtained by spray-freeze-etching are far superior to those obtained by standard freezing. Our results, using 5% glycerol as a test specimen, are equivalent to those obtained by the high-pressure method (1). The reduction of segregation during freezing makes freeze etching a method applicable for the investigation of solute systems. Furthermore, the study of unicellular organisms or cellular fractions by freeze etching without the use of antifreeze is made possible. Images

Bachmann, L.; Schmitt, W. W.

1971-01-01

174

FINITE ELEMENT SURFACE MODEL FOR FLOW AROUND VERTICAL WALL ABUTMENTS  

Microsoft Academic Search

A two-dimensional finite element surface model is developed to determine velocities, depths, and turning angles around vertical wall abutments. The model solves the Reynolds-averaged turbulent flow equations along a horizontal plane passing through the average water surface. This approach is an improvement over the depth-averaged flow models where dispersion terms reflecting vertical effects are neglected. In the model, vertical gradient

A. Molinas; Y. I. Hafez

2000-01-01

175

A study of slag freezing in metallurgical furnaces  

NASA Astrophysics Data System (ADS)

Many smelting and slag-cleaning furnaces operate with cooling systems designed to freeze a slag layer over the refractory to protect it. The fluid flow and heat transfer conditions associated with the freeze layer and mushy zones are poorly understood. This study was conducted to understand the chill layer formation and heat transfer that is required to design cooling systems in pyrometallurgical operations where a slag layer is required to protect the furnace wall. The freeze layer formation and heat transfer in mushy zones were experimentally study at room temperature in a 2-dimensional square cavity differentially heated, using an aqueous solution of calcium chloride to simulate the slag. Reasonable similarity with conditions encountered with copper and nickel smelting systems was achieved (Pr ? 50 and Ra ? 108, in the laminar-turbulent transition). Measurements of velocities were made with the Particle Image Velocimetry (PIV) technique. The freeze layer development was tracked using a digital camera. Direct Numerical Simulations (DNS) of the mean flow using a finite control volume technique with a fixed domain method were also made of the unsteady fluid flow and heat transfer problem. It was found that the macro solidification process is well described using an improved model for high molecular viscosity in the mushy zone. Solid front growth, isothermal profiles, velocity profiles and heat transfer through the walls showed good agreement between the PIV and DNS results. Experimental and numerical velocity profiles close to the freeze layer show a parabolic behaviour in the vertical velocity profile which is completely different from the calculation of heat transfer using a sharp interface model. The reason for this is attributed to the effects of the mushy zone with a high viscosity and high shear stresses acting on that area. In Part III of this Thesis, effects of slag viscosity temperature relationship were analysed with a two-dimensional mathematical model of an electric smelting furnace. The model was focused on the fluid dynamics of the molten slag and the effects over the formation of magnetite-rich slag layer over the walls. The results of the previous experimental and mathematical work, Part I and II, were used to describe mathematically the freeze layer formation on the furnace walls using a fixed-grid model from a highly viscous liquid. Chemical composition of the slag was taken into account through the effect of the viscous activation energy as well the solidus and liquidus temperatures. The results show that the flow pattern is strongly affected in the areas of high viscosity. The results are discussed in terms of heat flux over the refractories and their effects on cooling system design.

Guevara, Fernando

176

Freeze-drying processes and wind erodibility of a clay loam soil in southern Alberta  

SciTech Connect

Freeze-drying has been implicated as a factor causing soil aggregate breakdown on the Canadian Prairies and northern Great Plains. Aggregates of a Dark Brown Chernozemic clay loam soil sampled in October 1993 and January and April 1994 were subjected to repeated cycles of wetting (to 0.1, 0.2 and 0.3 kg kg-1 water contents) freezing, and freeze-drying under laboratory conditions. The October 1993 samples showed less disruption when initially exposed to freeze-drying cycles compared to samples taken in January and April 1994. Using regression analysis, we predicted that 31 freeze-dry cycles were required for the 0.1 kg kg-1 water content aggregates to reach 60% erodible fraction (EF, % aggregates <0.86 mm), 9 cycles for the 0.2 kg kg-1 aggregates and 2 for 0.3 kg kg-1 aggregates. In a field study, conducted over the 1994-1995 winter on a similar clay loam soil, we estimated the number of freeze-drying cycles using large vapor pressure (VPL) and small vapor pressure (VPS) gradients bet ween the soil surface (which had a mean winter water content of {approx}0.1 kg kg-1) and the atmosphere. With solar energy adjustments, we predicted that the number of freeze-dry cycles required for the soil to reach 60% EF was 60 for VPL and 37 for VPS conditions. The latter number was similar to the 31 cycles predicted in the laboratory study of aggregates at 0.1 water content. Our results demonstrate that freeze-drying is an important overwinter process in the breakdown of soil aggregates and hence wind erosion risk in the Canadian prairie region.

Bullock, M S.; Larney, F. J.; McGinn, Sean M.; Izaurralde, R Cesar C.

1999-01-01

177

Seismic velocity gradients in the upper mantle  

SciTech Connect

The radial velocity gradients for P- and S- waves in the upper mantle are of considerable interest for petrological studies of the upper mantle but are difficult to constrain directly. Comparison of three different styles of velocity model, constructed within a common parameterization to give a good fit to the travel times of P- and S-waves to 30{degree}, provide a useful framework for constructing bounds on the radial gradients. For depths from 250-1,000 km a somewhat subjective set of bounds are suggested for the velocity gradients and velocity contrasts at the major discontinuities in an average mantle. One of the most significant factors affecting the estimation of radial gradients is the presence of small-scale heterogeneity in the mantle. Modest heterogeneity, around 1 percent perturbations on scale lengths of about 300 km, can give rise to horizontal velocity gradients which can overwhelm the radial gradients in the shallower parts of the mantle and still be a quarter of the size of the radial gradients at greater depths. However such scales of heterogeneity are unlikely to simulate the presence of additional upper mantle discontinuities for ray paths travelling near vertical.

Kennett, B.L.N.

1991-06-01

178

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

179

Freeze Drying: Potential for Powdered Nanoparticulate Product  

Microsoft Academic Search

Nanoparticles were prepared by using an emulsion solvent evaporation method. Further, the drying of an anti-cancer drug of proprietary nature (nanosized) was carried out by a freeze-drying technique to get a free-flowing powder. A systematic approach was developed to study the freeze-drying technique for polymeric nanoparticles. Initially, the freeze-thawing experiments were carried out with varying concentrations of cryoprotectants to screen

V. V. Patil; P. P. Dandekar; V. B. Patravale; B. N. Thorat

2010-01-01

180

Freeze-Drying Characteristics of Tropical Fruits  

Microsoft Academic Search

The objective of this work was to experimentally determine physical properties such as apparent densities, real densities, and porosity of freeze-dried tropical fruits pulps such as pineapple, Barbados cherry, guava, papaya, and mango, and to carry out nutritional analysis of vitamin C, calcium, and phosphorus in the freeze-dried and in natura pulps. The freeze-dried pulps presented low apparent density and

Ana M. Silveira; José T. Freire

2006-01-01

181

A Bilateral Nuclear-Weapon Freeze  

Microsoft Academic Search

A bilateral nuclear-weapons freeze to stop the arms race is, next to the economy, the major public issue. The author feels that a freeze would lessen the risk of launch-on-warning errors that could lead to nuclear war. Further, a bilateral freeze would preserve the parity of existing US-Soviet arms, but prevent the destabilization of a new counterforce capability. It must

Randall Forsberg

1982-01-01

182

DNA Denaturation Under Freezing in Alkaline Medium  

Microsoft Academic Search

It is generally accepted that DNA conserves its secondary structure after a freeze-thaw cycle. A negligible amount of degradation occurs after this procedure. Degradation becomes appreciable only after multiple cycles of freezing and thawing. In this study, we have found that a single freeze-thaw cycle in alkaline medium (pH ? 10.8) gives rise to denaturation of calf thymus DNA, although

Elena N. Galyuk; Roger M. Wartell; Yury M. Dosin; Dmitri Y. Lando

2009-01-01

183

Predicting Freezing for Some Repulsive Potentials  

SciTech Connect

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.

Khrapak, S. A.; Morfill, G. E. [Max-Planck-Institut fuer extraterrestrische Physik, D-85741 Garching (Germany)

2009-12-18

184

Urban Modification of Freezing-Rain Events  

Microsoft Academic Search

A new national database for freezing-rain occurrences during the 1945-2000 period provided an opportunity for a study of the potential urban effects on freezing-rain events. Numerous past studies of snowfall events in urban areas have defined decreases of 10%-35% related to the urban heat island. The heat island, which acts to elevate near-surface temperatures, could also keep some freezing-rain situations

2003-01-01

185

[Social egg freezing: Which problems?].  

PubMed

In today's society, many women push pregnancy further away from the "right" childbearing age. Assisted reproduction, except egg donation, is unable to fully overcome the effect of age on fertility loss. The effectiveness of oocyte vitrification is demonstrated, and oocyte vitrification is allowed in the French Bioethics law of 2011. In the French law, oocyte' s cryopreservation is proposed to oocyte donors without child. Social egg freezing for non-medical reason is already legal in some countries, but leads to new debates and discussions. PMID:23972923

Belaisch-Allart, J; Brzakowski, M; Chouraqui, A; Grefenstette, I; Mayenga, J-M; Muller, E; Belaid, Y; Kulski, O

2013-08-21

186

Models and Characteristics of Freezing Rain and Freezing Drizzle for Aircraft Icing Applications.  

National Technical Information Service (NTIS)

A large, new database of in-flight measurements of icing-related cloud and atmospheric variables in freezing rain and freezing drizzle conditions is used to help determine the range of temperatures, altitudes, exposure durations, icing intensities, precip...

R. K. Jeck

2010-01-01

187

Reptile freeze tolerance: metabolism and gene expression.  

PubMed

Terrestrially hibernating reptiles that live in seasonally cold climates need effective strategies of cold hardiness to survive the winter. Use of thermally buffered hibernacula is very important but when exposure to temperatures below 0 degrees C cannot be avoided, either freeze avoidance (supercooling) or freeze tolerance strategies can be employed, sometimes by the same species depending on environmental conditions. Several reptile species display ecologically relevant freeze tolerance, surviving for extended times with 50% or more of their total body water frozen. The use of colligative cryoprotectants by reptiles is poorly developed but metabolic and enzymatic adaptations providing anoxia tolerance and antioxidant defense are important aids to freezing survival. New studies using DNA array screening are examining the role of freeze-responsive gene expression. Three categories of freeze responsive genes have been identified from recent screenings of liver and heart from freeze-exposed (5h post-nucleation at -2.5 degrees C) hatchling painted turtles, Chrysemys picta marginata. These genes encode (a) proteins involved in iron binding, (b) enzymes of antioxidant defense, and (c) serine protease inhibitors. The same genes were up-regulated by anoxia exposure (4 h of N2 gas exposure at 5 degrees C) of the hatchlings which suggests that these defenses for freeze tolerance are aimed at counteracting the injurious effects of the ischemia imposed by plasma freezing. PMID:16321368

Storey, Kenneth B

2006-02-01

188

Mechanism of freeze-drying drug nanosuspensions.  

PubMed

Drug nanoparticles prepared in a liquid medium are commonly freeze-dried for the preparation of an oral dosage in solid dosage form. The freezing rate is known to be a critical parameter for redispersible nanoformulations. However, there has been controversy as to whether a fast or slow freezing rate prevents irreversible aggregation. A systematic investigation is presented herein regarding the effect of both the molecular weight of the cryoprotectant and the freezing rate in order to elucidate the mechanism underlying irreversible aggregation. It was found that irreversible aggregation occurred during drying rather than freezing, although a proper freezing rate is critical. A more homogeneous distribution of the cryoprotectant and drug nanoparticles led to more redispersible powders. Thus, keeping the local concentration distribution of the nanoparticles and cryoprotectant fixed during the freezing step plays a critical role in how the freezing rate affects the redispersibility. The kinetic approach of excluding the tendency of ice crystal growth permitted an explanation of the controversial results. This study will facilitate an in-depth understanding of the aggregation process of nanoparticles or proteins during freeze-drying. PMID:22877696

Chung, Nae-Oh; Lee, Min Kyung; Lee, Jonghwi

2012-08-07

189

State diagram of dates: Glass transition, freezing curve and maximal-freeze-concentration condition  

Microsoft Academic Search

The state diagram of Deglet Nour dates was developed using freezing curve, glass transition line, and maximal-freeze-concentration condition. Freezing points and glass transition temperature were measured by differential scanning calorimetry (DSC) as a function of water content. Freezing points were fitted to the Clausius–Clapeyron equation adjusted with un-freezable water, and glass transition was fitted to the Gordon–Taylor model. Glass transition

Nejib Guizani; Ghalib Said Al-Saidi; Mohammad Shafiur Rahman; Salwa Bornaz; Ahmed Ali Al-Alawi

2010-01-01

190

Role of saccharides for the freeze-thawing and freeze drying of liposome  

Microsoft Academic Search

For the preservation of liposomes, freeze-thawing and freeze-drying have been studied by various workers with saccharides (SA) and a freeze-dried liposome preparation is now commercially available. However, the mechanism of stabilizing action of SA in these processes, especially freeze-drying, is not yet fully understood. The interaction of egg yolk phosphatidylcholine (EPC: liquid crystaline state) and DPPC (gel state) liposomes with

Koichiro Miyajima

1997-01-01

191

Ice VI freezing of meat: supercooling and ultrastructural studies  

Microsoft Academic Search

While “classical” freezing (to ice I) is disruptive to the microstructure of meat, freezing to ice VI has been found to preserve it. Ice VI freeze-substitution microscopy showed no traces of structural alteration on muscle fibres compared with the extensive damage caused by ice I freezing. The different signs of the freezing volume changes associated with these two ice phases

Antonio D Molina-Garc??a; Laura Otero; Miriam N Martino; Noem?? E Zaritzky; Jacek Arabas; Janusz Szczepek; Pedro D Sanz

2004-01-01

192

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

193

Effect of power ultrasound on freezing rate during immersion freezing of potatoes  

Microsoft Academic Search

Immersion freezing of potatoes with the aid of power ultrasound was investigated. The effect of power ultrasound on freezing rate was influenced by ultrasound power, exposure time and the freezing phase to which ultrasound was applied. The higher the ultrasound power and the longer the exposure time, the stronger the sonication was. However, the ultrasound power and exposure time should

Bing Li; Da-Wen Sun

2002-01-01

194

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

2008-09-04

195

The investigation of custom grown vertical zone melt semi-insulating bulk gallium arsenide as a radiation spectrometer  

SciTech Connect

Vertical zone melt (VZM) bulk GaAs boules have been zone refined (ZR) and zone leveled (ZL) to reduce EL2 deep donor levels and impurity concentrations with the intent of improving properties for gamma ray detectors. Zr and Zl GaAs boules had background impurity levels and deep donor EL2 concentrations near or below detectable limits. The crystal mosaic of the material at locations near the seed end was slightly superior to commercial liquid encapsulated Czochralski (LEC) material, and nearly equivalent to commercial vertical gradient freeze (VGF) material. The crystal mosaic in ZL material degraded towards the tail end. The homogeneity of the electrical properties for the ZL and ZR VZM material was inferior compared to commercially available bulk GaAs material. Post growth annealing may help to homogenize some electrical properties of the material. The charge collection efficiency of the ZR GaAs detectors was only 30% maximum, and only 25% maximum for the ZL GaAs detectors. Resulting gamma ray spectra was poor from detectors fabricated with the ZL or ZR VZM material. Detectors fabricated from material that was both ZR and ZL did not demonstrate gamma ray resolution, and operated mainly as counters. The poor spectroscopic performance is presently attributed to the inhomogeneity of the electrical properties of the ZR and ZL GaAs materials. Comparisons are made with detectors fabricated from VGF SI bulk GaAs.

McGregor, D.S.; Antolak, A.J. [Sandia National Labs., Livermore, CA (United States); Chui, H.C. [Sandia National Labs., Albuquerque, NM (United States)] [and others

1996-06-01

196

Freezing and Blocking of Water Pipes.  

National Technical Information Service (NTIS)

The topic addressed in this article is the freezing and blockage of water pipes that are full, with the water either flowing or still. It has long been assumed that when the water in a pipe freezes the ice begins to form on the inside surface of the pipe ...

K. L. Carey

1982-01-01

197

Rotary replication for freeze-etching  

PubMed Central

Rotary replication has been adapted to freeze-etching and evaluated using T4 polyheads, erythrocyte ghosts, and chloroplast membranes. Conventional electron microscopy, electron diffraction, and optical diffraction and filtering indicate that platinum-carbon rotary replication renders radially symmetrical contrast and 25 A resolution to freeze-etched specimens so as to clarify subunit structure not normally evident in unidirectional shadow replicas.

1977-01-01

198

Freeze conditioning agents ease winter railcar unloading  

SciTech Connect

A US midwest utility's freeze control programme is described. All coal is treated with a glycol-based freeze control agent. Some rail wagons were treated with a side release agent which stops coal sticking to the metal wagon. The use of calcium chloride or heat to thaw frozen coal is also discussed.

Olson, G.E.

1982-02-01

199

Ground freezing for containment of hazardous waste  

Microsoft Academic Search

The freezing of ground for the containment of subsurface hazardous waste is a promising method that is environmentally friendly and offers a safe alternative to other methods of waste retention in many cases. The frozen soil method offers two concepts for retaining waste. One concept is to freeze the entire waste area into a solid block of frozen soil thus

F. N. Sayles; I. K. Iskandar

1998-01-01

200

FREEZING POINT DEPRESSION OF VARIOUS ICE SLURRIES  

Microsoft Academic Search

Ideal solutions with equal molar concentration have an equal freezing point. The properties that determine heat and mass transfer processes encountered in a secondary cooling cycle are however determined by the mass fraction of solutes. Generally for aqueous solutions, the more freezing point depressant added, the less efficient heat and mass transfer properties. Therefore substances with low molecular weight are

J. W. Meewisse; C. A. Infante Ferreira

201

Freeze Injuries in Avocado Fruit1  

Microsoft Academic Search

Differences were found in the extent of freeze injury among 'Fuerte', 'Hass' and 'Nabal' avocados (Persea americana Mill.). Large 'Fuerte' fruit suffered more than small ones. Relatively high rates of ethylene production and of respiration were found in heavily injured fruit as soon as 1 day after harvest. Keeping quality of freeze-damaged fruit was reduced. It is concluded that the

Y. Fuchs; G. Zauberman; U. Yanko

202

Recovery of White Blood Cells After Freezing.  

National Technical Information Service (NTIS)

Whereas the red cells recover from the actual congelation of all the water freezable at -3C, the neutrophils are already injured when only a fraction of the water freezable at -1.5C is congealed. Electron microscope studies of freeze-dried or freeze-subsi...

B. J. Luyet L. J. Menz G. L. Rapatz D. Rasmussen

1971-01-01

203

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

204

Soil macroaggregate dynamics in a mountain spatial climate gradient  

Microsoft Academic Search

We investigated the response of soil macroaggregate dynamics to soil temperature modification along a spatial gradient located\\u000a on a forested north-facing slope in the southern French Alps, simulating long-term adjustment of soil–plant interactions to\\u000a absence or occurrence of soil frost. Soil macroaggregate (>250 ?m) content of Ah horizons was strongly depleted (72%) in colder\\u000a plots affected by freeze-thaw events, compared to

Lauric Cécillon; Nilvania A. de Mello; Sébastien De Danieli; Jean-Jacques Brun

2010-01-01

205

7 CFR 305.18 - Quick freeze treatment schedule.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Quick freeze treatment schedule. 305...PHYTOSANITARY TREATMENTS Quick Freeze Treatments § 305.18 Quick freeze treatment schedule. (a...United States or its territorial waters, or is otherwise disposed...

2010-01-01

206

7 CFR 305.18 - Quick freeze treatment schedule.  

Code of Federal Regulations, 2010 CFR

...2009-01-01 false Quick freeze treatment schedule. 305...PHYTOSANITARY TREATMENTS Quick Freeze Treatments § 305.18 Quick freeze treatment schedule. (a...United States or its territorial waters, or is otherwise disposed...

2009-01-01

207

BK090020 Summary - CryoMACS Freezing Bag  

Center for Biologics Evaluation and Research (CBER)

Text Version... Primary: Baxter CryocyteTM Freezing Container (BK950049) Secondary: Charter Medical Cell FreezeTM Liquid Nitrogen Freezing Container ... More results from www.fda.gov/downloads/biologicsbloodvaccines/bloodbloodproducts

208

Interdependence of Measures in Pavlovian Conditoned Freezing  

PubMed Central

Pavlovian conditioned freezing is an intensively utilized paradigm that has become a standard model of memory and cognition. Despite its widespread use, the interdependence among each measure commonly reported in fear conditioning studies has not been described. Using mice, we examine the relationship of each common freezing measure (Training Baseline, Post-Shock freezing, Contextual Fear, Tone Baseline, and Tone Fear), as well as baseline locomotor activity measures, to better understand the significance of each. Of particular interest, Post-Shock freezing appears to be a good measure of immediate contextual memory. In contrast, Tone Baseline freezing, as typically measured in a novel context, appears to be contaminated with multiple sources of fear. Finally, Contextual and Tone Fear show a weak interdependence.

Wood, Suzanne C.; Anagnostaras, Stephan G.

2011-01-01

209

DNA denaturation under freezing in alkaline medium.  

PubMed

It is generally accepted that DNA conserves its secondary structure after a freeze-thaw cycle. A negligible amount of degradation occurs after this procedure. Degradation becomes appreciable only after multiple cycles of freezing and thawing. In this study, we have found that a single freeze-thaw cycle in alkaline medium (pH>or=10.8) gives rise to denaturation of calf thymus DNA, although the melting temperature of intact DNA in the solution used for the freeze-thaw experiments is higher than 60 degrees C. The degree of denaturation is almost independent of the regime of freezing. The melting curve obtained after DNA is frozen at -2 degrees C and then thawed is almost the same as after a freezing carried out in liquid nitrogen (-196 degrees C). However, incubation in the same solution at 0 degrees C for 24 hours without freezing does not give rise to any denaturation. The degree of denaturation caused by freezing increases with pH (if pH>or=10.8) and decreases with Na2CO3 concentration at fixed pH and [Na+], although Na2CO3 decreases the melting temperature of intact DNA. A preliminary treatment of DNA with cisplatin or transplatin (0.01 Pt atoms per nucleotide) gives rise to a full recovery of the DNA secondary structure after freezing and thawing similar to what occurs after heating DNA to 100 degrees C and quick cooling. Possible mechanisms that may cause DNA denaturation during a freeze-thaw cycle in alkaline medium are discussed. PMID:19108591

Galyuk, Elena N; Wartell, Roger M; Dosin, Yury M; Lando, Dmitri Y

2009-02-01

210

Advanced Vertical Array Beamformer.  

National Technical Information Service (NTIS)

The advanced vertical array beamformer signal processor accomplishes acoustic beamforming of an underwater vertical array used in shallow water utilizing matched beam processing to suppress generated noise and/or ship radiated noise thereby increasing the...

T. C. Yang J. A. Mobbs

1998-01-01

211

Estimation of PWC gradients over the Kanto Plain using GPS data: Validation and possible meteorological implications  

NASA Astrophysics Data System (ADS)

Simultaneous GPS and water vapor radiometer (WVR) observations were carried out in Tsukuba during May-June 1998, for the validation of precipitable water content (PWC) gradients estimated from single-site GPS data. Slant path PWC observed by WVR were fitted into hourly PWC gradients (WVR gradients) using the least-square method. GPS PWC gradients were retrieved from tropospheric delay gradients that were estimated with GIPSY OASYS 2 package (GIPSY gradients). The results indicate that GIPSY gradients had good, linear correlation with WVR gradients, especially for a large gradient range. Both gradients had spike-shaped, short time-scale (~3 hours) peaks which were mostly associated with synoptic fronts. The GIPSY gradients were also compared with meso-scale PWC gradients calculated from zenith wet delay data of GPS network (NET gradients). The results show that GIPSY gradients did not have very good correlation with NET gradients, and that significant meso-scale discrepancy existed between the two gradients for a cold frontal case on 19 June 1998. One possible reason for this discrepancy is vertical differences in RH gradients, because GIPSY gradients are sensitive to RH gradients around the scale height of humidity (~2500 m) while RH gradients in lowermost level have largest weights for NET gradients. To study PWC gradients associated with the fronts, GPS gradients were compared with other meteorological data over the Kanto Plain for two frontal cases. The results indicate that large PWC gradient zones with horizontal scale of about several tens kilometers in cross-frontal directions were collocated with the surface wind shear zones of the fronts. This suggests that the large PWC gradients were due to humidity discontinuity around the fronts.

Aonashi, K.; Shoji, Y.; Ichikawa, R.; Hanado, H.

2000-11-01

212

The effect of soil freezing on N cycling: comparison of two headwater subcatchments with different vegetation and snowpack conditions in the northern Hokkaido Island of Japan  

Microsoft Academic Search

Climate change models predict that the snowpacks of temperate forests will develop later and be shallower resulting in a higher\\u000a propensity for soil freezing. In the northern most island of Japan, Hokkaido, snowpack depth decreases from west to east.\\u000a This snowpack depth gradient provided a unique opportunity to test the effects of variable snowpack and soil freezing on N\\u000a biogeochemistry.

Sheila F. Christopher; Hideaki Shibata; Megumi Ozawa; Yasunori Nakagawa; Myron J. Mitchell

2008-01-01

213

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

214

Gradient sensing during chemotaxis.  

PubMed

Eukaryotic cells have the ability to sense chemoattractant gradients and to migrate toward the sources of attractants. The chemical gradient-guided cell movement is referred to as chemotaxis. Chemoattractants are detected by members of G-protein-coupled receptors (GPCRs) that link to heterotrimeric G-proteins. The GPCR/G-protein sensing machinery is able to translate external chemoattractants fields into intercellular cues, which direct reorganization of the actin cytoskeleton that drives cell movement. Here, I review our current understanding of the formation of chemoattractant gradients in vivo, the GPCR-mediated gradient sensing, and the sophisticated signaling network that guides the function of the actin cytoskeleton. PMID:23880435

Jin, Tian

2013-07-20

215

Scalar Field Gradient Model  

NSDL National Science Digital Library

The Scalar Field Gradient Model displays the gradient of a scalar field using a numerical approximation to the partial derivatives. This simple teaching model also shows how to display and model scalar and vector fields using the EJS. The EJS Scalar Field Gradient Model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_math_ScalarFieldGradient.jar file will run the program if Java is installed.

Christian, Wolfgang

2009-03-14

216

Transmission electron microscopy of thin sections of Drosophila: high-pressure freezing and freeze-substitution.  

PubMed

The state of the art in fine-structure preservation for thin sectioning can be achieved by using fast-freezing technology followed by freeze substitution and embedding in resin. Samples prepared by high-pressure freezing are estimated to be "fixed" in 20-50 msec. Fast freezing also freezes every cell component regardless of its chemistry. Once frozen, tissues can be processed in a variety of ways before viewing in the electron microscope; here we describe only freeze substitution. In freeze substitution, cells are dehydrated at very low temperatures and cell water is replaced with organic solvent at -80°C to -90°C. At this temperature, large molecules such as proteins are immobilized, yet smaller molecules such as water (ice) can be dissolved and replaced with organic solvents, e.g., acetone. The ideal way to do freeze substitution is with a dedicated freeze-substitution device such as the Leica AFS2 system. These devices allow programming of the times and temperatures needed. Alternatively, if this equipment is not available, freeze substitution can still be performed using items commonly found around the laboratory, as is described here. This protocol is useful for preparing thin sections of Drosophila when the best possible preservation of ultrastructure and antigenicity is required. PMID:22474654

McDonald, Kent L; Sharp, David J; Rickoll, Wayne

2012-04-01

217

Vertical bounce of two vertically aligned balls  

NASA Astrophysics Data System (ADS)

When a tennis ball rests on top of a basketball and both drop to the floor together, the tennis ball is projected vertically at high speed. A mass-spring model of the impact, as well as air track data, suggest that the tennis ball should be projected at relatively low speed. Measurements of the forces on each ball and the bounce of vertically aligned superballs are used to resolve the discrepancy.

Cross, Rod

2007-11-01

218

Freeze-thaw stability of water-in-oil emulsions.  

PubMed

Factors influencing water-in-oil emulsion stability during freeze/thaw-cycling, namely interfacial crystallization vs. network crystallization and the sequence of crystallization events (i.e., dispersed vs. continuous phase or vice versa), are assessed. We show that destabilization is most apparent with a liquid-state emulsifier and a continuous oil phase that solidifies prior to the dispersed phase. Emulsions stable to F/T-cycling are obtained when the emulsifier crystallizes at the oil-water interface or in emulsions where the continuous phase crystallizes after the dispersed aqueous phase. The materials used are two food-grade oil-soluble emulsifiers - polyglycerol polyricinoleate (PGPR) and glycerol monostearin (GMS) and two continuous oil phases with differing crystallization temperatures - canola oil and coconut oil. Emulsion stability is assessed with pulsed field gradient NMR droplet size analysis, sedimentation, microscopy and differential scanning calorimetry. This study demonstrates the sequence of crystallization events and the physical state of the surfactant at the oil-water interface strongly impact the freeze-thaw stability of water-in-oil emulsions. PMID:19683718

Ghosh, S; Rousseau, D

2009-07-25

219

Hatchling turtles survive freezing during winter hibernation.  

PubMed Central

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 April 1988 had a mean supercooling point of -3.28 +/- 0.24 degrees C and survived 24 hr of freezing at -4 degrees C with 53.4% +/- 1.98% of total body water as ice. Recovery appeared complete after 20 hr of thawing at 3 degrees C. However, freezing at -10.9 degrees C, resulting in 67% ice, was lethal. A survey of possible cryoprotectants revealed a 2- to 3-fold increase in glucose content of liver and blood and a 3-fold increase in blood glycerol in response to freezing. Although quantitatively low, these responses by spring turtles strongly indicate that these may be the winter-active cryoprotectants. The total amino acid pool of blood also increased 2.25-fold in freezing-exposed turtles, and taurine accounted for 52% of the increase. Most organs accumulated high concentrations of lactate during freezing, a response to the ischemic state imposed by extracellular freezing. Changes in glycogen phosphorylase activity and levels of glucose 6-phosphate and fructose 2,6-bisphosphate were also consistent with a dependence on anaerobic glycolysis during freezing. Studies of the molecular mechanisms of natural freeze tolerance in these turtles may identify protective strategies that can be used in mammalian organ cryopreservation technology.

Storey, K B; Storey, J M; Brooks, S P; Churchill, T A; Brooks, R J

1988-01-01

220

Effects of thermal gradients on the intensity of vortices generated in a cylindrical annulus.  

PubMed

This paper shows the influence of horizontal and vertical temperature gradients on the intensity of vertical vortices, qualitatively similar to dust devils, generated by a convective instability in a cylindrical annulus non-homogeneously heated. The behavior of the vortices formed is studied, showing that the increase of the temperature gradients intensifies the strength of the vortical structures developed and vice versa, small horizontal and vertical temperature gradients lead to weaker vortices or even make them disappear. Consequently, the intensity of the vortices can be controlled thermally by cooling or heating adequately the bottom boundary. PMID:22225369

Navarro, M C; Herrero, H

2011-12-01

221

Molten salt freeze seal. Final report  

SciTech Connect

This report documents the results of the testing performed at Sandia National Laboratory, Albuquerque, New Mexico, on the applicability of a sodium freeze seal type valve stem in a molten salt environment. The freeze seal tests consisted of cycling the valve stem at set temperature intervals, checking the temperature distribution for freeze plug location, and verifying the actuator forces. In addition to the test results, this report also documents the engineering analysis and other tasks performed before testing to form a basis for predicted test conditions and recommendations for the test program.

Corugedo, J.J.

1985-08-01

222

Network velocity gradients in the photosphere. I. Modeling  

NASA Astrophysics Data System (ADS)

We present an extension of the Unno-Rachkovsky solution that provides the theoretical profiles coming out of a Milne-Eddington atmosphere imbedded in a magnetic field, and that then takes a vertical velocity gradient into account. Thus, the theoretical profiles may display asymmetries as do the observed profiles, which facilitates the inversion based on the Unno-Rachkovsky theory, and leads to the additional determination of the vertical velocity gradient. We present UNNOFIT inversion on synthetic data and spectropolarimetric observations performed on an active region of the Sun with the French-Italian telescope THEMIS operated by CNRS and CNR on the island of Tenerife.

Molodij, G.; Bommier, V.; Rayrole, J.

2011-07-01

223

Multiport well design for sampling of ground water at closely spaced vertical intervals  

Microsoft Academic Search

Detailed vertical sampling is useful in aquifers where vertical mixing is limited and steep vertical gradients in chemical concentrations are expected. Samples can be collected at closely spaced vertical intervals from nested wells with short screened intervals. However, this approach may not be appropriate in all situations. An easy-to-construct and easy-to-install multiport sampling well to collect ground-water samples from closely

Geoffrey N. Delin; Matthew K. Landon

1996-01-01

224

Effects of a Descending Lithospheric Slab on Yield Estimates of Aleutian Nuclear Tests. Incorporation of Velocity Gradients in the Synthesis of Complete Seismograms by the Locked Mode Method.  

National Technical Information Service (NTIS)

The locked mode method of synthesizing complete regional seismograms (Harvey, 1981) was modified to include the Langer uniform asymptotic approximation to vertical wave-functions within layers having linear vertical velocity gradients. Good agreement is o...

V. F. Cormier

1990-01-01

225

Salt Water Desalination by the Freezing Method.  

National Technical Information Service (NTIS)

Investigations of the most important units of the new method of salt water desalination by artificial freezing with the help of liquid hydrocarbons (propane-butane mixture) were conducted. Investigation of contact heat transfer processes indicates that th...

I. M. Rutgaizer S. Seitkurbanov V. I. Petrov

1969-01-01

226

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

227

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

228

Vacuum Freezing Multiple Phase Transformation Process Investigation.  

National Technical Information Service (NTIS)

The Vacuum Freezing Multiple Phase Transformation (VFMPT) Process accomplishes vapor liquefaction by desublimation of the vapor on a refrigerated surface, production of a second water vapor of higher temperature than the melting point of ice, and then dir...

C. Y. Cheng W. C. Cheng

1986-01-01

229

Freeze-out Conditions from Lattice QCD  

NASA Astrophysics Data System (ADS)

We describe a procedure for determination of freeze-out parameters of heavy-ion collisions through direct comparisons between experimentally measured higher order cumulants of charge fluctuations and first principle (lattice) QCD calculations.

Mukherjee, Swagato

2013-05-01

230

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

231

Evaporation of water from agitated freezing slurries at low pressure  

Microsoft Academic Search

In an absorptive vacuum freezing process, water evaporates from the freezing solution and condenses on a cold salt solution. Given sufficient condensing capacity, the evaporation rate will be controlled by the freezing solution vapor pressure. The size of the condensing equipment which matches a given evaporation system can be estimated using rate measurements made with low vapor pressure freezing solutions.

L. C. Dickey

1996-01-01

232

Freeze Drying of Foods for the Armed Services.  

National Technical Information Service (NTIS)

The report reviews the development and use of freeze-dried food products for the Armed Services. It covers the various products and ration systems that have been developed, the basic parameters of freeze-drying and freeze-dried foods, commercial freeze-dr...

J. M. Tuomy

1971-01-01

233

A climatological study of surface freezing precipitation in Europe  

Microsoft Academic Search

A climatological study of the occurrence of freezing precipitation at ground level is presented. It is based on reports of freezing precipitation in SYNOP messages from the three winters covering the years 1995-1998. The geographical domain covered is Western and Central Europe, extending northwards to Scandinavia and southwards to North Africa. The types of freezing precipitation selected are freezing rain,

Jean-Marie Carrière; Claude Lainard; Christine Le Bot; Florent Robart

2000-01-01

234

Freezing Tolerance in an Adult Insect  

Microsoft Academic Search

The adult carabid beetle Pterostichus brevicornis tolerates freezing under natural conditions. Laboratory tests confirm that winter beetles tolerate temperatures below -35 degrees C, whereas summer beetles die if frozen at -6.6 degrees C. Winter beetles can be cooled to about -10 degrees C before freezing, and they thaw near -3.5 degrees C. Summer beetles thaw at -0.7 degrees C. To

L. Keith Miller

1969-01-01

235

An inherently freeze protected solar water heater  

SciTech Connect

A solar water heater which uses a roof-contained solar absorber operating a two-phase thermosiphon with splash heat exchanger is described. Such a thermosiphon has operating characteristics which may be exploited to achieve simple and reliable freeze protection. An installation is described and the physical arrangements needed to obtain freeze protection are discussed. The results of a number of tests are presented.

Rush, C.K.

1983-06-01

236

Passive freeze protection for solar collectors  

Microsoft Academic Search

Freeze damage is an important practical problem for water-type solar collectors. In the past, electric resistance heaters, drain systems, and separate ethylene glycol-water collection loops have commonly been used to prevent freezing. These techniques are effective but involve active components such as controls, heaters, valves, solenoids, pumps, heat exchangers, etc., that increase costs, degrade reliability and\\/or reduce overall efficiency. This

L. W. Bickle

1975-01-01

237

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.)

238

Historical recollections of freeze-drying.  

PubMed

The history of freeze-drying is surprisingly recent. Although Altmann used freeze-drying for the preparation of histological sections as early as 1890, his technique went unnoticed for over 40 years. Shackell independently rediscovered the technique in 1909 for the preservation of biologicals. The industrial applications of freeze-drying do not appear to have been appreciated prior to the patients of Tival in 1927 and Elser in 1934, rapidly followed by the important contributions of Flosdorf in the United States and Greaves in England who were largely responsible for making large scale applications of freeze-drying possible. Stimulated particularly by a series of symposia in England and the United States and the renowned courses on freeze-drying organized by Rey in France, the atmosphere in the 1950s and early 60s was one of optimism for the future of freeze-drying, particularly in its application to food stuffs. Many of the dreams of that time remain unfulfilled, largely because of the higher costs of quality processing. Nevertheless, although the optimism may have somewhat dimmed, the promise remains, and economic changes in the future may well stimulate another surge in development. PMID:801137

Meryman, H T

1976-10-01

239

Hydrocarbon exclusion from ground water during freezing  

SciTech Connect

Bench-scale studies were conducted using a constant-head ground-water flow chamber and natural soil. Initial experiments with chlorides and dye were conducted to test the hydraulic and adsorptive characteristics of the chamber. A constant flow of phenol was then introduced into the chamber and contaminant movement with time was monitored under freezing and nonfreezing conditions. The chamber was located in a controlled-temperature room, and freezing fronts were induced from the soil surface downward using cooled Freon circulated through freezer pads placed on the surface of the soil. The results conclusively demonstrate that phenol is excluded from the freezing front and pushed downward through the system. Extensive exclusion of the chemical occurs even though the freezing point of phenol (43 C) is significantly higher than water. The information gained through this research is applicable in cold regions outside Alaska and the Arctic where ground water systems may undergo periodic freezing, and may also be of extreme importance in artificial-freezing scenarios such as those currently being investigated by the Environmental Protection Agency (EPA) as a method of contaminant containment.

Tumeo, M.A.; Davidson, B. (Univ. of Alaska, Fairbanks (United States))

1993-08-01

240

Freezing of living cells: mechanisms and implications  

SciTech Connect

Cells can endure storage at low temperatures such as -196/sup 0/C for centuries. The challenge is to determine how they can survive both the cooling to such temperatures and the subsequent return to physiological conditions. A major factor is whether they freeze intracellularly. They do so if cooling is too rapid, because with rapid cooling insufficient cell water is removed osmotically to eliminate supercooling. Equations have been developed that describe the kinetics of this water loss and permit one to predict the likelihood of intracellular freezing as a function of cooling rate. Such predictions agree well with observations. Although the avoidance of intracellular freezing is usually necessary for survival, it is not sufficient. Slow freezing itself can be injurious. As ice forms outside the cell, the residual unfrozen medium forms channels of decreasing size and increasing solute concentration. The cells lie in the channels and shrink in osmotic response to the rising solute concentration. Prior theories have ascribed slow freezing injury to the concentration of solutes or the cell shrinkage. Recent experiments, however, indicate that the damage is due more to the decrease in the size of the unfrozen channels. This new view of the mechanism of slow freezing injury ought to facilitate the development of procedures for the preservation of complex assemblages of cells of biological, medical, and agricultural significance. 126 references, 18 figures, 2 tables.

Mazur, P.

1984-01-01

241

A new freeze casting technique for ceramics  

NASA Astrophysics Data System (ADS)

A new freeze casting technique for ceramics capable of manufacturing near room temperature with a sublimable vehicle has been developed in order to eliminate expensive processes under extremely cold temperatures in the conventional freeze casting. Fluid concentrated slurries of Al2O 3 powder in molten camphene (C10H16) were successfully prepared at 55°C with a small amount of a dispersant. These slurries were quickly solidified (frozen) at room temperature to yield a rigid solid green body, where the frozen camphene was easily removed by sublimation (freeze-drying) with negligible shrinkage. Sintering was successfully conducted without any special binder burnout process to yield dense sintered bodies (over 98% T.D). An organic alloy with a eutectic composition in the naphthalene (C 10H8)-camphor (C10H16O) binary system with a eutectic temperature of 31°C was also found to be a successful vehicle for the new ceramic freeze casting. The fabrication processes are almost the same as those with camphene. It was found that vehicles with off-eutectic compositions resulted in large voids in the sintered body due to the ceramic particle rejection by pro-eutectic crystals during freezing. At the eutectic composition, fine lamellar microstructure in the solidified vehicle inhibits the particle rejection. The proposed advantages of the new freeze casting technique with a sublimable vehicle include; (1) elimination of extremely cold temperatures used in conventional freeze casting; (2) elimination of troublesome binder burnout process; and (3) fast manufacturing cycle due to quick solidification. Porous ceramic bodies with unique interconnected pore channels were fabricated by the new freeze casting with lower solid content. The unique channels surrounded by fully dense walls have nearly circular cross-sections unlike conventional aqueous freeze casting. The porosity and the channel diameters are controllable by the solid content in the slurry. The unique channels are replicas of entangled dendrites of frozen camphene, which sublimes during freeze-drying process. The unique porous structure with interconnected pore channels, which is completely new, is considered potentially useful in many applications such as filters and implantable bone scaffolds.

Araki, Kiyoshi

242

Density gradient quantum similarity  

NASA Astrophysics Data System (ADS)

Computation of density gradient quantum similarity integrals is analyzed, while comparing such integrals with overlap density quantum similarity measures. Gradient quantum similarity corresponds to another kind of numerical similarity assessment between a pair of molecular frames, which contrarily to the usual up to date quantum similarity definitions are not measures, that is: strictly positive definite integrals. As the density gradient quantum similarity integrals are defined as scalar products of three real functions, they appear to possess a richer structure than the corresponding positive definite density overlap quantum similarity measures, while preserving the overall similarity trends, when the molecular frames are relatively moved in three dimensional space. Numerical results within the atomic shell approximation (ASA) framework are presented as simple examples showing the new performances of the gradient density quantum similarity.

Carbó-Dorca, Ramon; Mercado, Luz Dary

2012-12-01

243

Contrasting effects of high-pressure-assisted freezing and conventional air-freezing on eggplant tissue microstructure  

Microsoft Academic Search

Damage to the microstructure of eggplants frozen by conventional air-freezing methods and by a high-pressure-assisted freezing\\u000a method is compared in this paper. When conventional air-freezing techniques are employed, damage to the microstructure is\\u000a enhanced as the freezing rate diminishes and the sample volume increases. However, when high-pressure-assisted freezing is\\u000a applied, bulk nucleation occurs simultaneously in the whole sample, and the

Laura Otero; María T. Solas; P. D. Sanz; Carlos de Elvira; Juan A. Carrasco

1998-01-01

244

Two-phase frictional pressure drop measurements in U-type wavy tubes subject to horizontal and vertical arrangements  

Microsoft Academic Search

Two-phase frictional pressure gradient is significantly affected by the flow patterns. Though most of the U-type wavy tubes are commonly vertically installed in the air-conditioning and refrigerating systems, yet none investigations had reported the two-phase frictional pressure loss in vertical U-type wavy tubes. This study presents the measurements of R-134a two-phase frictional pressure gradient subject to vertical and horizontal arrangements

Ing Youn Chen; Yu-Shi Wu; Jane-Sunn Liaw; Chi-Chuan Wang

2008-01-01

245

How low-permeability rocks freeze: A laboratory study on resistivity pathways of thawed, supercooled and frozen permafrost rocks  

NASA Astrophysics Data System (ADS)

Resistivity - temperature paths are among the most important proxies in permafrost research. Testing 8 sedimentary, metamorphic and igneous rocks from European permafrost summits, we found evidence that the theoretical background developed in the 70s does not describe the physics of low-permability rocks correctly, which dominate these environments. Saturated rocks with permeabilities below 10 µD have an equilibrium freezing point depression of -0.5°C to -1.55°C and indicate metastable supercooling effects between -0.5 and -1.4 °C. Instantaneous freezing from metastable stages occurs with sudden warming of the rock sample with up to 0.9°C temperature difference. This is due to the spontaneous dissipation of freezing energy subsequent to supercooling. Warming occurs over tens of seconds to a few minutes and coincides with a jump in resistivity. Unfrozen and frozen temperature-resistivity paths match bilinear functions with an R² of 0.88 to 1.00. The frozen temperature-resistivity gradient is 12-34 times steeper that the unfrozen resistivity gradient. Low permeability may decide the ratio of frozen and unfrozen gradients while porosity influences the 0°C resistivity value and the unfrozen gradient. Here we show that separate linear approximation of unfrozen, supercooled and frozen temperature-resistivity behaviour provides a better explanation of involved physics than exponential fits.

Krautblatter, M.; Zisser, N.

2009-04-01

246

Influence of freezing rate on pore structure in freeze-dried collagen-GAG scaffolds  

Microsoft Academic Search

The cellular structure of collagen-glycosaminoglycan (CG) scaffolds used in tissue engineering must be designed to meet a number of constraints with respect to biocompatibility, degradability, pore size, pore structure, and specific surface area. The conventional freeze-drying process for fabricating CG scaffolds creates variable cooling rates throughout the scaffold during freezing, producing a heterogeneous matrix pore structure with a large variation

Fergal J. O’Brien; Brendan A. Harley; Ioannis V. Yannas; Lorna J Gibson

2004-01-01

247

Intracellular freezing and survival in the freeze tolerant alpine cockroach Celatoblatta quinquemaculata  

Microsoft Academic Search

The alpine cockroach Celatoblatta quinquemaculata is common at altitudes of around 1500 m on the Rock and Pillar range of Central Otago, New Zealand where it experiences freezing conditions in the winter. The cockroach is freeze tolerant, but only to c. ?9 °C. The cause of death at temperatures below this is unknown but likely to be due to osmotic

M. R. Worland; D. A. Wharton; S. G. Byars

2004-01-01

248

The hyphae of Uromyces appendiculatus within the leaf tissue after high pressure freezing and freeze substitution  

Microsoft Academic Search

Summary The fine structure of the intercellular dikaryotic hyphae of the biotrophic fungusUromyces appendiculatus was studied. High pressure freezing and freeze substitution were used to achieve a closer approximation of the native state than with conventional fixation and dehydration techniques. In addition to organelles previously described in rust fungi, heavily decorated multivesicular bodies (star bodies) were found close to the

K. Welter; M. Müller; K. Mendgen

1988-01-01

249

IDENTIFICATION OF METABOLITES ASSOCIATED WITH FREEZING TOLERANCE IN CONSTITUTIVELY FREEZING TOLERANT MUTANTS OF ARABIDOPSIS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Many plants develop a better freezing tolerance through a process of cold acclimation (CA), which also results in many changes in metabolite levels. To identify and distinguish metabolites that contribute to the increased freezing tolerance from those that are merely responsive to low temperature st...

250

Predicting Arabidopsis Freezing Tolerance and Heterosis in Freezing Tolerance from Metabolite Composition  

PubMed Central

Heterosis, or hybrid vigor, is one of the most important tools in plant breeding and has previously been demonstrated for plant freezing tolerance. Freezing tolerance is an important trait because it can limit the geographical distribution of plants and their agricultural yield. Plants from temperate climates increase in freezing tolerance during exposure to low, non-freezing temperatures in a process termed ‘cold acclimation’. Metabolite profiling has indicated a major reprogramming of plant metabolism in the cold, but it has remained unclear in previous studies which of these changes are related to freezing tolerance. In the present study, we have used metabolic profiling to discover combinations of metabolites that predict freezing tolerance and its heterosis in Arabidopsis thaliana. We identified compatible solutes and, in particular, the pathway leading to raffinose as crucial statistical predictors for freezing tolerance and its heterosis, while some TCA cycle intermediates contribute only to predicting the heterotic phenotype. This indicates coordinate links between heterosis and metabolic pathways, suggesting that a limited number of regulatory genes may determine the extent of heterosis in this complex trait. In addition, several unidentified metabolites strongly contributed to the prediction of both freezing tolerance and its heterosis and we present an exemplary analysis of one of these, identifying it as a hexose conjugate.

Korn, Marina; Gartner, Tanja; Erban, Alexander; Kopka, Joachim; Selbig, Joachim; Hincha, Dirk K.

2010-01-01

251

The equilibrated state of freezing as a basis for distinguishing lethal stresses of freezing in plants  

Technology Transfer Automated Retrieval System (TEKTRAN)

A model for coordination of stresses that limit winterhardiness in plants based on the thermodynamic equilibrated state of freezing and melting provides a rational basis for distinction of freeze-induced energies which can stress and injure living organisms in various ways. The departure from equili...

252

Representative Values of Icing-Related Variables Aloft in Freezing Rain and Freezing Drizzle  

Microsoft Academic Search

Radiosonde and surface observations in freezing rain (ZR) and freezing drizzle (ZL), and a limited number of aircraftmeasurements in ZR, have been examined for information on the magnitude and altitude dependence of meteorological variablesassociated with aircraft icing in these conditions. The variables include temperature aloft, humidity (clouds), and windshear fromthe radiosondes; surface temperatures, ceiling heights, precipitation type and amount from

Richard K. Jeck

253

Hunger enhances vertical vection.  

PubMed

Hunger was found to facilitate visually induced illusory upward and downward self-motions (vertical vection), but not illusory self-motion in depth (vection in depth). We propose that the origin of this hunger effect lies in the possibility that vertical self-motions (both real and illusory) are more likely to induce changes in visceral state. PMID:23362680

Seno, Takeharu; Ito, Hiroyuki; Sunaga, Shoji; Palmisano, Stephen

2012-01-01

254

Aiding vertical guidance understanding  

Microsoft Academic Search

A study was conducted to evaluate training and displays for the vertical guidance system of a modern glass cockpit airliner. The experiment consisted of a complete flight performed in a fixed-base simulator with airline pilots. Three groups were used to evaluate a new flight mode annunciator display and vertical navigation training. Results showed improved pilot performance with training and significant

Everett Palmer; Martin Alkin; Peter Polson; Daniel McCrobie; Lance Sherry

1999-01-01

255

A Dielectrophoretic Chip With a 3-D Electric Field Gradient  

Microsoft Academic Search

This paper presents the design, fabrication and testing of a new structure of dielectrophoresis (DEP) chip having a three-dimensional (3-D) electric field gradient and an asymmetric distribution of the electric field in the vertical plane. This achievement was possible due to the special configuration of the electrodes: a bulk silicon electrode and a thin amorphous silicon electrode. The thick electrode

Ciprian Iliescu; Liming Yu; Guolin Xu; Francis E. H. Tay

2006-01-01

256

Natural freezing as a wastewater treatment method: E. coli inactivation capacity  

Microsoft Academic Search

Inactivation capacity of E. coli (strain ATCC 15597) in water by natural freezing was examined via two freezing methods: spray freezing and freezing in a freezer. The effect of freezing temperature (?5, ?15 and ?35°C), storage time, freeze–thaw cycles on the survival of the test organism were investigated. In addition, the number of cells injured by the freezing process was

W. Gao; D. W. Smith; Y. Li

2006-01-01

257

Freeze-out Coupling in Hydrodynamics.  

NASA Astrophysics Data System (ADS)

Most hydrodynamical calculations used in heavy-ion physics ignore the effect of freeze-out matter carrying energy and momentum away from the expanding fluid. In a simple one-dimensional model we compare calculated energy density and velocity profiles, with and without interaction between fluid-like and freeze-out parts of the system, in order to estimate the importance of this effect. We use an extended version of the Godunov method( J.-P. Blaizot and J.-Y. Ollitrault, Nucl. Phys.) A458 (1986) 745. to describe the hydrodynamical evolution with freeze-out coupling. It is found that the feedback from freeze-out can have substantial effects on the evolution of the freeze-out surface. The coupling should therefore be taken into account in the next generation of hydrodynamical calculations. Preliminary version available from the LANL archive, nucl- th/9612020.

Lavrenchuk, Boris; Neumann, John J.; Fai, George

1997-04-01

258

Stratospheric Balloon Gradient Geomagnetic Measurements  

NASA Astrophysics Data System (ADS)

The study of the interior structure of the Earth and laws of its evolution is one of the most difficult problems of natural science. Among the geophysical fields the anomaly magnetic field is one of the most informational in questions of the Earth's crust structure. Many important parameters of an environment are expedient for measuring at lower altitudes, than satellite ones. So, one of the alternatives is stratospheric balloon survey. The balloon flight altitudes cover the range from 20 to 50 km. At such altitudes there are steady zone air flows due to which the balloon flight trajectories can be of any direction, including round-the-world (round-the-pole). One of the examples of such sounding system have been designed, developed and maintained at IZMIRAN during already about 20 years. This system consists of three instrumental con-tainers uniformly placed along a vertical 6 km line. System allows measuring a module and vertical gradient of the geomagnetic field along the whole flight trajectory and so one's name is -stratospheric balloon magnetic gradiometer (SMBG). The GPS-receivers, located in each instrumental container, fix the flight coordinates to within several tens meters. Data trans-mission is carried out by Globalstar satellite link. The obtained data are used in solving the problems of deep sounding of the Earth's crust magnetic structure -an extraction of magnetic anomalies, determination of a depth of bedding of magnetoactive rocks and others. The developed launching technology, deployment in flight, assembly, data processing, transfer and landing the containers with the equipment can be used for other similar problems of monitoring and sounding an environment. Useful flight weights of each instrumental container may be reaching 50 kg. More than ten testing flights (1986-2009) at stratospheric altitudes (20-30 km) have proven the reliability of this system.

Filippov, Sergey; Tsvetkov, Yury

259

Local stellar kinematics from RAVE data - II. Radial metallicity gradient  

NASA Astrophysics Data System (ADS)

We investigate radial metallicity gradients for a sample of dwarf stars from the RAdial Velocity Experiment (RAVE) Data Release 3 (DR3). We select a total of approximately 17 000 F-type and G-type dwarfs, using a selection of colour, log g and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thick or thin disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We additionally subsample by colour, to provide samples biased toward young thin-disc and older thin-disc stars. We derive a metallicity gradient as a function of Galactocentric radial distance, i.e. d[M/H]/dRm=-0.051 ± 0.005 dex kpc-1, for the youngest sample, F-type stars with vertical orbital eccentricities ev? 0.04. Samples biased toward older thin-disc stars show systematically shallower abundance gradients.

Co?kuno?Lu, B.; Ak, S.; Bilir, S.; Karaali, S.; Önal, Ö.; Yaz, E.; Gilmore, G.; Seabroke, G. M.

2012-02-01

260

Heat transfer coefficient of cryotop during freezing.  

PubMed

Cryotop is an efficient vitrification method for cryopreservation of oocytes. It has been widely used owing to its simple operation and high freezing rate. Recently, the heat transfer performance of cryotop was studied by numerical simulation in several studies. However, the range of heat transfer coefficient in the simulation is uncertain. In this study, the heat transfer coefficient for cryotop during freezing process was analyzed. The cooling rates of 40 percent ethylene glycol (EG) droplet in cryotop during freezing were measured by ultra-fast measurement system and calculated by numerical simulation at different value of heat transfer coefficient. Compared with the results obtained by two methods, the range of the heat transfer coefficient necessary for the numerical simulation of cryotop was determined, which is between 9000 W/(m(2)·K) and 10000 W/(m (2)·K). PMID:23812315

Li, W J; Zhou, X L; Wang, H S; Liu, B L; Dai, J J

2013-01-01

261

Freeze verification: time for a fresh approach  

SciTech Connect

The administration's claim that some elements of a comprehensive nuclear freeze are unverifiable does not specify the nature of those elements and whether they represent a real threat to national security if we trusted the USSR to comply. The author contends that clandestine development of new weapons will have little strategic effect since both sides already have total destructive power. The risks of noncompliance are largely political and less than the risks of continued arms buildup. Since the USSR would also want the US to be bound by freeze terms, deterrence would come from mutual benefit. Hardliners argue that cheating is easier in a closed society; that our democracy would tend to relax and the USSR would move ahead with its plans for world domination. The author argues that, over time, a freeze would diminish Soviet confidence in its nuclear war fighting capabilities and that adequate verification is possible with monitoring and warning arrangements. (DCK)

Paine, C.

1983-01-01

262

Exponential growth of fingering instabilities of spreading films under horizontal thermal gradients  

Microsoft Academic Search

A thin liquid ribbon deposited on a wettable surface and subjected to a horizontal thermal gradient develops periodic fingers towards the cold region. We present an observation of the exponential growth regime, expected at early times, but not accessible in other driven fingering patterns induced by gravitational flows, spinning drops, or vertical thermal gradients. We have monitored the wavelength ?

J. B. Brzoska; F. Brochard-Wyart; F. Rondelez

1992-01-01

263

Vertical Line Test  

NSDL National Science Digital Library

In this activity, students try to connect given points on a graph in a way that they will pass the vertical line test. If the points can't be made to pass the vertical line test, the student must adjust the points so they will pass the test. This activity allows students to explore the vertical line test for functions. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

2010-01-01

264

Bacterial Community Composition in Lake Tanganyika: Vertical and Horizontal Heterogeneity  

Microsoft Academic Search

Vertical and latitudinal differences in bacterial community composition (BCC) in Lake Tanganyika were studied during the dry season of 2002 by means of denaturing gradient gel electrophoresis analysis of PCR-amplified 16S RNA fragments. Dominant bands were sequenced and identified as members of the Cyanobacteria, Actinobacteria, Nitrospirae, green nonsulfur bacteria, and Firmicutes divisions and the Gamma- and Deltaproteobacteria subdivisions. The BCC

Aaike De Wever; Koenraad Muylaert; Katleen Van der Gucht; Samuel Pirlot; Christine Cocquyt; Jean-Pierre Descy; Pierre-Denis Plisnier; Wim Vyverman

2005-01-01

265

Natural convection in a long vertical cylinder under gravity modulation  

Microsoft Academic Search

The onset of convection in differentially heated cylinders under gravity modulation is examined, with special consideration given to the case of a vertical cylinder of infinite length, when a negative temperature gradient is maintained in the upward direction. The effect of modulation on the stability limits given by linear theory in the standard steady case is analyzed. A method based

M. Wadih; B. Roux

1988-01-01

266

Effect of air freezing, spray freezing, and pressure shift freezing on membrane integrity and viability of Lactobacillus rhamnosus GG  

Microsoft Academic Search

The objective of this work was to assess and compare the impact of three different freezing methods on the physiology of probiotic bacteria based on evaluation of vitality, membrane integrity and special metabolic properties. Lactobacillus rhamnosus GG (LGG) was used as a model strain and was analysed with the plate enumeration method and flowcytometric analyses (FCM) before and after treatment

Marcus Volkert; Edwin Ananta; Cornelius Luscher; Dietrich Knorr

2008-01-01

267

Spatial Distribution of Vertical Shear.  

National Technical Information Service (NTIS)

Spatial variations in small scale vertical shear in the upper ocean are described, relationships between small scale vertical shear and density stratification are investigated, and the potential for predicting mean vertical shear from measurements of the ...

S. L. Patterson F. C. Newman D. M. Rubenstein R. B. Lambert

1981-01-01

268

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

269

Vertical Multijunction Solar Cells.  

National Technical Information Service (NTIS)

A theoretical analysis of the vertical multijunction (VMJ) solar cell was performed which indicated that using silicon certain configurations could be fabricated to satisfy the program objectives. Results indicate that initial AMO efficiencies of 15% can ...

P. M. Stella

1973-01-01

270

Viscosity and the vertical profile of horizontal thermospheric winds  

NASA Astrophysics Data System (ADS)

It is generally assumed that viscosity smoothes out all vertical gradients of the horizontal thermospheric winds above about 150 km, and thus observations of neutral winds at one height can be used at other altitudes in the thermosphere. In this paper we present neutral wind simulations of the May 1997 geomagnetic storm using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. We found that: 1) there are significant variations in the vertical profiles of horizontal neutral winds above 150 km, indicating that previous understandings of vertical gradients of horizontal winds need to be revisited; 2) viscosity is less important when compared with other forcing processes during the storm main phase; and 3) there are strong temporal and spatial changes in both neutral winds and forcing terms, and the relative importance of viscosity in the neutral momentum balance increases during the storm recovery phase.

Wang, W.; Burns, A. G.; Wiltberger, M.; Solomon, S. C.; Killeen, T. L.

2005-12-01

271

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

272

Freeze-Out Effects on n-Channel MOSFET's.  

National Technical Information Service (NTIS)

Surface admittance measurements have been carried out on (100) oriented 1-ohm cm n-channel silicon MOSFET's in the freeze-out regime. The freeze-out temperature accurately determines the amount of compensation. Measurements at different frequencies yield ...

S. Aymeloglu J. N. Zemel

1975-01-01

273

Intraspecific Vertical Stratification as a Mate-Finding Mechanism in Tropical Cockroaches  

Microsoft Academic Search

Cockroaches in a tropical forest stratify vertically both inter- and intraspecifically along micrometerological gradients. At night, low wind speeds and unstable atmospheric conditions result in efficient vertical mixing of the air near the ground. Convective ascent of warm air imparts directionality to the pheromone-dispersion process. The occurrence of males at greater heights than pheromoneemitting conspecific females appears to be a

Coby Schal

1982-01-01

274

Thermal Physiology and Vertical Zonation of Intertidal Animals: Optima, Limits, and Costs of Living1  

Microsoft Academic Search

SYNOPSIS. Temperature's pervasive effects on physiological systems are reflected in the suite of tempera- ture-adaptive differences observed among species from different thermal niches, such as species with dif- ferent vertical distributions (zonations) along the subtidal to intertidal gradient. Among the physiological traits that exhibit adaptive variation related to vertical zonation are whole organism thermal tolerance, heart function, mitochondrial respiration, membrane

GEORGE N. SOMERO

275

Buoyancy measurements and vertical distribution of eggs of sardine ( Sardina pilchardus ) and anchovy ( Engraulis encrasicolus )  

Microsoft Academic Search

Measurements were made of the density and settling velocity of eggs of sardine ( Sardina pilchardus) and anchovy ( Engraulis encrasicolus), using a density-gradient column. These results were related to observed vertical distributions of eggs obtained from stratified vertical distribution sampling in the Bay of Biscay. Eggs of both species had slightly positive buoyancy in local seawater throughout most of

S. H. Coombs; G. Boyra; L. D. Rueda; A. Uriarte; M. Santos; D. V. P. Conway; N. C. Halliday

2004-01-01

276

The Vertical Propagation of Tropospheric Rossby Waves and its Variation with Climate  

Microsoft Academic Search

Rossby wave propagation is theoretically affected by zonal wind gradients, in particular the second derivative of the zonal wind shear in the vertical and meridional directions. Vertical propagation is hindered by the strong winds in the upper troposphere, particularly for short wavelength waves, or by critical levels where the background wind velocity equals the wave phase velocity. In practice, tropospheric

D. H. Rind; J. Perlwitz

2002-01-01

277

Freeze-fracture studies on Pneumocystis carinii  

Microsoft Academic Search

Ultrastructure of the trophozoite of Pneumocystis carinii was studied by the freeze-fracture technique. Nuclei and cytoplasmic organelles such as the endoplasmic reticulum, mitochondria, cytoplasmic vacuoles and small round bodies were observed. The mean number of nuclear pores was 8 per ?m2, which is small compared with that reported for other human pathogenic protozoa. In general, the density of nuclear pores

Hisao Yoshikawa; Hiroyuki Morioka; Yukio Yoshida

1987-01-01

278

Effects of freezing on isolated plant mitochondria  

Microsoft Academic Search

Mitochondria isolated from spinach leaves (Spinacia oleracea L.) and potato tubers (Solanum tuberosum L.) were partly injured when subjected to freezing for 2 to 4 h at-25°C in salt solutions in the absence of cryoprotectants. Damage was manifested by the inactivation of respiratory properties and increase in the permeability of the mitochondrial membranes. Decrease in respiratory control indicated that the

Regina Thebud; Kurt A. Santarius

1981-01-01

279

Hot water can freeze faster than cold?!?  

Microsoft Academic Search

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

Monwhea Jeng

2005-01-01

280

Freeze verification: time for a fresh approach  

Microsoft Academic Search

The administration's claim that some elements of a comprehensive nuclear freeze are unverifiable does not specify the nature of those elements and whether they represent a real threat to national security if we trusted the USSR to comply. The author contends that clandestine development of new weapons will have little strategic effect since both sides already have total destructive power.

Paine

1983-01-01

281

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

282

Scaling-Up Eutectic Freeze Crystallization  

Microsoft Academic Search

A novel crystallization technology, Eutectic Freeze Crystallization (EFC) has been investigated and further developed in this thesis work. EFC operates around the eutectic temperature and composition of aqueous solutions and can be used for recovery of (valuable) dissolved salts (and\\/or or acids) and water from a wide variety of aqueous process streams. Using EFC, processes producing large quantities of saline

F. E. Genceli

2008-01-01

283

Freeze-Drying Various Strains of Shigella.  

National Technical Information Service (NTIS)

Of six candidate strains of Shigella prepared in Brain Heart Infusion broth as freeze-dried vaccine, low survival rates were obtained with two of the most promising strains. Survival rates with these two strains were increased to acceptable levels when th...

S. Berman P. L. Altieri A. Groffinger J. P. Lowenthal S. B. Formal

1968-01-01

284

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

285

Method for freezing edible marine animals  

US Patent & Trademark Office Database

Various methods useful in connection with catching and freezing fish are disclosed. Also disclosed is an immersion freezer. In preferred embodiments, fish or other items to be frozen are immersed in a cooling medium. The cooling medium comprises an organic cooling agent, which preferably is a carbohydrate, sugar alcohol, glycoside, or non-toxic oil.

Knauf; Jeff (Sitka, AK)

2006-05-23

286

Unitarity Constraints on Asymmetric Freeze-In  

SciTech Connect

This paper considers unitarity and CPT constraints on asymmetric freeze-in, the use of freeze-in to store baryon number in a dark sector. In this scenario, Sakharov's out of equilibrium condition is satisfied by placing the visible and hidden sectors at different temperatures while a net visible baryon number is produced by storing negative baryon number in a dark sector. It is shown that unitarity and CPT lead to unexpected cancellations. In particular, the transfer of baryon number cancels completely at leading order. This note has shown that if two sectors are in thermal equilibrium with themselves, but not with each other, then the leading effect transferring conserved quantities between the two sectors is of order the the weak coupling connecting them to the third power. When freeze-in is used to produce a net baryon number density, the leading order effect comes from {Omicron}({lambda}{sup 3}) diagrams where the intermediate state that goes on-shell has a different visible baryon number than the final state visible baryon number. Models in which the correct baryon number is generated with freeze-in as the dominant source of abundance, typically require {lambda} {approx}> 10{sup -6} and m{sub bath} {approx}> TeV. m{sub bath} is the mass of the visible particle which communicates with the hidden sector. The lower window is potentially observable at the LHC.

Hook, Anson; /SLAC

2011-08-15

287

Food Freezing in the Intermediate Fluidized Bed.  

National Technical Information Service (NTIS)

A new food freezing method has been investigated using the so-called intermediate fluidized bed in which the food was fluidized together with small particles for aid of the fluidization and heat transfer of the food. Formed alumina and refined salt partic...

M. Yumiyama

1988-01-01

288

Gradient-Index Optics.  

National Technical Information Service (NTIS)

SAIC has performed an effort to advance the state of the art in gradient-index (GRIN) nanolayered polymer optics. The goal of this study was to take significant risks off the table with regard to practical high-performance GRIN optical designs. The DARPA ...

N. Shatz

2010-01-01

289

Gradient Armor System.  

National Technical Information Service (NTIS)

The patent application describes an armor system comprising a ceramic matrix having a gradient of fine ductile metallic particles dispersed therein in an amount of from 0.0% commencing at the front or impact surface of the armor to about 2 to 15% by volum...

M. L. Wilkins A. C. Holt C. F. Cline K. E. Fromschner

1970-01-01

290

Power from salinity gradients  

Microsoft Academic Search

A large source of energy exists at the interface between water bodies of different salinities. Two techniques, pressure-retarded osmosis and reverse electrodialysis, appear to be promising entrees into this energy source. Although the present cost of membranes suitable to these methods is too high, a research and development effort should make this salinity gradient energy competitive with other energy sources.

G Wick

1978-01-01

291

Freezing and anoxia tolerance of slugs: a metabolic perspective  

Microsoft Academic Search

Freezing survival was assessed in three species of terrestrial slugs, a holarctic but native North American species, Deroceras laeve, and two species introduced from Europe, D. reticulatum and Arion\\u000a circumscriptus. The introduced species showed very poor freezing survival. Supercooling points of the introduced species were quite high\\u000a (??3°C) and their freezing survival was very poor, limited to short-term freezing at

Kenneth B. Storey; Janet M. Storey; Thomas A. Churchill

2007-01-01

292

Effect of freezing and thawing processes on soil aggregate stability  

Microsoft Academic Search

The effect of freezing and thawing on wet aggregate stability of soils formed on different parent materials was determined for different aggregate size groups (0.0–1.0; 1.0–2.0; and 2.0–4.0 mm), different water contents and for various freezing and thawing cycles (three, six and nine times) and freezing temperatures (?4 and ?18 °C). The initial wet aggregate stability decreased with freeze–thaw treatments

Taskin Oztas; Ferhan Fayetorbay

2003-01-01

293

Do stratospheric aerosol droplets freeze above the ice frost point?  

Microsoft Academic Search

Laboratory experiments are presented which show that liquid stratospheric aerosol droplets under polar winter conditions do not freeze for temperatures higher than the water ice saturation temperature (frost point). Calorimetric measurements of the freezing of supercooled H2SO4\\/HNO3\\/H2O bulk solutions with concentrations typical of the polar stratospheric aerosol exhibit very small freezing rates, which exclude the possibility of homogeneous freezing of

T. Koop; U. M. Biermann; W. Raber; B. P. Luo; P. J. Crutzen; Th. Peter

1995-01-01

294

Conditional and unconditional components of post-shock freezing  

Microsoft Academic Search

Rats received shocks in one apparatus, and post-shock “freezing” was then assessed in that apparatus or in a different one.\\u000a The assessment of freezing was made immediately after shock or after a 24-hour delay. Post-shock freezing was reduced when\\u000a the animals were tested in a different apparatus from that in which shocks had been administered. No reduction in freezing\\u000a was

Michael S. Fanselow

1980-01-01

295

Freezing rate determination by the isotopic composition of the ice  

Microsoft Academic Search

The distribution of an isotopic species, HDO (deuterium) or H218O (oxygen), in ice formed by the migration of a well-defined freezing front in water is dependent on the freezing rate. Development of a box diffusion model combined with the boundary layer concept leads to a possibility of prediction of the freezing rate in nature by the determination of the isotopic

Roland Souchez; Jean-Louis Tison; Jean Jouzel

1987-01-01

296

Behavior of water below the freezing point in PEFCs  

Microsoft Academic Search

This study investigates the phenomenon of water freezing below the freezing point in polymer electrolyte fuel cell (PEFCs). Water generated on the surface of the catalyst layer was observed simultaneously with visible and infrared images. Surprisingly, it was found that water generated below the freezing point is in the liquid state and that the temperature rises to 0°C at the

Yuji Ishikawa; T. Morita; K. Nakata; K. Yoshida; M. Shiozawa

2007-01-01

297

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

298

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

299

Simulation of Heat Transfer in Freezing Soils Using ABAQUS  

Microsoft Academic Search

Freezing saturated soils are mixtures of solid particles, water, and ice. Heat transfer in freezing soils is a complex process because of the multi-phase nature of the mixture. The phase change of the liquid part adds complexity, since not all water changes phase at the freezing temperature. Difficulties with convergence are known to appear when simulating the process. A numerical

Ming Zhu; Radoslaw L. Michalowski

300

Molecular dynamics simulations of freezing of water and salt solutions  

Microsoft Academic Search

Results of extensive molecular dynamics simulations of freezing of neat water and aqueous sodium chloride solutions are reported. The process of water freezing in contact with an ice patch is analyzed at a molecular level and a robust simulation protocol within the employed force field is established. Upon addition of a small amount of NaCl brine rejection from the freezing

Luboš Vrbka; Pavel Jungwirth

2007-01-01

301

Nucleation of Freezing in Supercooled Water by Cavitation  

Microsoft Academic Search

NUCLEATION of freezing in supercooled liquids by cavitation has been ascribed to a momentary large increase in the degree of supercooling, induced by the high transient pressures generated by a collapsing cavity. This is a plausible mechanism for substances which contract on freezing; for substances such as water, which expand on freezing, it seems less satisfactory1. Hickling2, however, has proposed

M. N. Plooster

1968-01-01

302

Recent Progress in the Freeze-Etching Technique  

Microsoft Academic Search

The freeze-etching technique must be improved if structures at the molecular size level are to be seen. The limitations of the technique are discussed here together with the progress made in alleviating them. The vitrification of living specimens is limited by the fact that very high freezing rates are needed. The critical freezing rate can be lowered on the one

H. Moor

1971-01-01

303

Sources of Data on Freezing Rain and Resulting Damages  

Microsoft Academic Search

Freezing rain produces major damages each year in the United States, and various affected groups continue to seek data on the incidence and losses produced by freezing rain. The various kinds of data available about freezing rain and related damages have been identified and assessed as part of a project to develop long-term databases. Data include long-term records of the

Tamara G. Creech

2003-01-01

304

Core drilling through the ross ice shelf (antarctica) confirmed Basal freezing.  

PubMed

New techniques that have been used to obtain a continuous ice core through the whole 416-meter thickness of the Ross Ice Shelf at Camp J-9 have demonstrated that the bottom 6 meters of the ice shelf consists of sea ice. The rate of basal freezing that is forming this ice is estimated by different methods to be 2 centimeters of ice per year. The sea ice is composed of large vertical crystals, which form the waffle-like lower boundary of the shelf. A distinct alignment of the crystals throughout the sea ice layer suggests the presence of persistent long-term currents beneath the ice shelf. PMID:17779616

Zotikov, I A; Zagorodnov, V S; Raikovsky, J V

1980-03-28

305

Freezing survival, body ice content and blood composition of the freeze-tolerant European common lizard, Lacerta vivipara  

Microsoft Academic Search

To investigate the freeze tolerance of the European common lizard, Lacerta vivipara, we froze 17 individuals to body temperatures as low as -4 °C under controlled laboratory conditions. The data show that this species tolerates the freezing of 50% of total body water and can survive freezing exposures of at least 24-h duration. Currently, this represents the best known development

Y. Voituron; J. Storey; C. Grenot; K. Storey

2002-01-01

306

Freezing curve-based monitoring to quickly evaluate the viability of biological materials subject to freezing or thermal injury  

Microsoft Academic Search

This paper is aimed at investigating the roles of freezing dynamics of a liquid droplet to characterize the properties of the material. In particular, freezing curve-based monitoring was proposed to quickly evaluate the viability of biological materials subject to freezing, re-warming, or other kinds of injury, which is an extremely important issue in practices such as cryobiology, hyperthermia, or freshness

Jing Liu; Yi-Xin Zhou

2003-01-01

307

Effects of Freeze\\/Thaw Index, Air Temperature, and Snow Cover on Seasonal Freeze and Thaw Depths in Russia  

Microsoft Academic Search

Seasonal freezing and thawing processes in cold regions play an exceedingly important role in ecosystem diversity, productivity, and the Arctic hydrological system in general. Long-term changes in seasonal freeze and thaw depths are also important indicators of climate change. Only sparse observational measurements of seasonal freeze and thaw depths are available in permafrost and seasonally frozen ground regions. However, soil

O. W. Frauenfeld; T. Zhang; R. G. Barry; D. Gilichinsky; A. J. Etringer

2003-01-01

308

Purification of very high density lipoproteins by differential density gradient ultracentrifugation.  

PubMed

Differential density gradient ultracentrifugation procedures, utilizing a vertical rotor, were developed for the preparative purification of very high density lipoproteins (VHDL, density greater than 1.21 g/ml). The VHDLs of several insect species were purified as follows. An initial density gradient ultracentrifugation step removed lipoproteins of lower density from the VHDL-fraction, which partially separated from the nonlipoproteins present in the infranatant. A complete separation was achieved by a second centrifugation step employing a modified gradient system. The use of a vertical rotor and specially designed discontinuous gradients allows a relatively fast, efficient, and economical isolation of the class of very high density lipoproteins. Similar gradient systems should be useful for the detection and purification of VHDLs from other sources. PMID:3578796

Haunerland, N H; Ryan, R O; Law, J H; Bowers, W S

1987-03-01

309

Fish antifreeze protein and the freezing and recrystallization of ice.  

PubMed

Antifreeze glycopeptide and peptides from the blood of polar fishes prevent the growth of ice crystals in water at temperatures down to approximately 1 degree C below freezing point, but do not appreciably influence the equilibrium freezing point. This freezing point hysteresis must be a disequilibrium effect, or it would violate Gibbs' phase rule, but the separate freezing and melting points are experimentally very definite: ice neither melts nor freezes perceptibly within the 'hysteresis gap', for periods of hours or days. We report here unusual crystal faces on ice crystals grown from solutions of very low concentrations of the anti-freeze glycopeptides and peptides. This is a clue to the mechanism of freezing inhibition, and it may be the basis of a simple, very sensitive test for antifreeze material. Very low concentrations of the antifreeze protein are also remarkably effective in preventing the recrystallization of ice. PMID:6700733

Knight, C A; DeVries, A L; Oolman, L D

310

Chiral condensate and chemical freeze-out  

NASA Astrophysics Data System (ADS)

We consider a chemical freeze-out mechanism which is based on a strong medium dependence of the rates for inelastic flavor-equilibrating collisions based on the delocalization of hadronic wave functions and growing hadronic radii when approaching the chiral restoration. We investigate the role of mesonic (pion) and baryonic (nucleon) fluctuations for melting the chiral condensate in the phase diagram in the ( T, ?)-plane. We apply the PNJL model beyond mean-field and present an effective generalization of the chiral perturbation theory result which accounts for the medium dependence of the pion decay constant while preserving the GMOR relation. We demonstrate within a schematic resonance gas model consisting of a variable number of pionic and nucleonic degrees of freedom that within the above model a quantitative explanation of the hadonic freeze-out curve and its phenomenological conditions can be given.

Blaschke, D. B.; Berdermann, J.; Cleymans, J.; Redlich, K.

2011-12-01

311

Freezing and melting water in lamellar structures.  

PubMed

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

1994-08-01

312

Ground freezing for containment of hazardous waste  

SciTech Connect

The freezing of ground for the containment of subsurface hazardous waste is a promising method that is environmentally friendly and offers a safe alternative to other methods of waste retention in many cases. The frozen soil method offers two concepts for retaining waste. One concept is to freeze the entire waste area into a solid block of frozen soil thus locking the waste in situ. For small areas where the contaminated soil does not include vessels that would rupture from frost action, this concept may be simpler to install. A second concept, of course, is to create a frozen soil barrier to confine the waste within prescribed unfrozen soil boundaries; initial research in this area was funded by EPA, Cincinnati, OH, and the Army Corps of Engineers. The paper discusses advantages and limitations, a case study from Oak Ridge, TN, and a mesh generation program that simulates the cryogenic technology.

Sayles, F.N.; Iskandar, I.K.

1998-07-01

313

Study of Transient Nuclei near Freezing  

NASA Astrophysics Data System (ADS)

The molasses tail in dense hard core fluids is investigated by extensive event-driven molecular dynamics simulation through the orientational autocorrelation functions. Near the fluid- solid phase transition, there exist three regimes in the relaxation of the pair orientational autocorrelation function, namely the kinetic, molasses (stretched exponential), and diffusional power decay. The density dependence of both the molasses and diffusional power regimes are evaluated and the latter compares with theoretical predictions in three dimensions. The largest cluster at the freezing density of only a few sphere diameter in size persist for only about 30 picoseconds (˜2.8 x10-11[s]). The most striking observation through the bond orientatinal order parameter is the dramatic increase of the cluster size as the freezing density is approached.

Isobe, Masaharu; Alder, Berni

2011-03-01

314

Study of Transient Nuclei near Freezing  

NASA Astrophysics Data System (ADS)

The molasses tail in dense hard core fluids is investigated by extensive event-driven molecular dynamics simulation through the orientational autocorrelation functions. Near the fluid-solid phase transition, there exist three regimes in the relaxation of the pair orientational autocorrelation function, namely the kinetic, molasses (stretched exponential), and diffusional power decay. The density dependence of both the molasses and diffusional power regimes are evaluated and the latter compares with theoretical predictions in three dimensions. The largest cluster at the freezing density of only a few sphere diameter in size persist for only about 30 picoseconds (˜ 2.8 × 10(-11) [s]). The most striking observation through the bond orientatinal order parameter is the dramatic increase of the cluster size as the freezing density is approached.

Isobe, M.; Alder, B. J.

315

Freeze-Out Parameters: Lattice Meets Experiment  

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

316

Freezing of colloidal suspensions in confined spaces  

SciTech Connect

Simulation and experimental techniques have been developed to study the phase properties of a fluid confined between two closely-spaced walls and applied to investigate systems of charge-stabilized colloidal suspensions between repulsive smooth walls in contact with a reservoir. The phase behavior of confined suspensions is studied as a function of bulk particle volume fraction, surface charge, and wall separation. Complete crystallization within a fixed-size gap at sufficiently small wall separation occurs at bulk volume fractions well below the bulk freezing volume fraction. The simulations show a strong dependence of the freezing transition on a preferred wall separation corresponding to an integral number of layers. The simulation predictions match experimental observations at wall separations from five to ten particle diameters. 42 refs., 10 figs., 1 tab.

Hug, J.E.; Swol, F. van; Zukoski, C.F. (Univ. of Illinois, Urbana, IL (United States))

1995-01-01

317

Drying a tuberculosis vaccine without freezing  

Microsoft Academic Search

With the increasing incidence of tuberculosis and drug resistant disease in developing countries due to HIV\\/AIDS, there is a need for vaccines that are more effective than the present bacillus Calmette-Guérin (BCG) vaccine. We demonstrate that BCG vaccine can be dried without traditional freezing and maintained with remarkable refrigerated and room-temperature stability for months through spray drying. Studies with a

Y.-L. Wong; Samantha Sampson; W. A. Germishuizen; Sunali Goonesekera; Giovanni Caponetti; Jerry Sadoff; B. R. Bloom; David Edwards

2007-01-01

318

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

319

Phase diagram for freeze-dried persimmon  

Microsoft Academic Search

Phase transitions of freeze-dried persimmon in a large range of moisture content were determined by differential scanning calorimetry (DSC). In order to study this transitions at low and intermediate moisture content domains, samples were conditioned by adsorption at various water activities (aw=0.11–0.90) at 25°C. For the high moisture content region, samples were obtained by water addition. At aw?0.75 two glass

P. J. A. Sobral; V. R. N. Telis; A. M. Q. B. Habitante; A. Sereno

2001-01-01

320

Hydrocarbon exclusion from ground water during freezing  

Microsoft Academic Search

Bench-scale studies were conducted using a constant-head ground-water flow chamber and natural soil. Initial experiments with chlorides and dye were conducted to test the hydraulic and adsorptive characteristics of the chamber. A constant flow of phenol was then introduced into the chamber and contaminant movement with time was monitored under freezing and nonfreezing conditions. The chamber was located in a

Mark A. Tumeo; Bret Davidson

1993-01-01

321

Vogel-Fulcher freezing in relaxor ferroelectrics  

SciTech Connect

A physical mechanism for the freezing of polar nanoregions (PNRs) in relaxor ferroelectrics is presented. Assuming that the activation energy for the reorientation of a cluster of PNRs scales with the mean volume of the cluster, the characteristic relaxation time {tau} is found to diverge as the cluster volume reaches the percolation limit. Applying the mean field theory of continuum percolation, the familiar Vogel-Fulcher equation for the temperature dependence of {tau} is derived.

Pirc, R.; Blinc, R. [Jozef Stefan Institute, P.O. Box 3000, 1001 Ljubljana (Slovenia)

2007-07-01

322

Solar desalination by freezing and distillation  

Microsoft Academic Search

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

G. Kvajic

1981-01-01

323

Fluctuations in US Freezing Rain Days  

Microsoft Academic Search

Freezing rain occurrences during a 50-year period, 1949\\/1950–1998\\/1999, derived from carefully examined records of 161 first-order stations distributed across the United States, were assessed for temporal fluctuations and trends. Classification of station fluctuations based on five 10-year periods revealed five unique distribution types in areas east of the Rockies. One of these five distributions, for stations located in the western

David Changnon; Russell Bigley

2005-01-01

324

Comparison of chemical freeze-out criteria in heavy-ion collisions  

SciTech Connect

One of the most remarkable results to emerge from heavy-ion collisions over the past two decades is the striking regularity shown by particle yields at all energies. This has led to several very successful proposals describing particle yields over a very wide range of beam energies, reaching from 1A GeV up to 200A GeV, using only one or two parameters. A systematic comparison of these proposals is presented here. The conditions of fixed energy per particle, baryon+anti-baryon density, normalized entropy density as well as percolation model are investigated. The results are compared with the most recent chemical freeze-out parameters obtained in the thermal-statistical analysis of particle yields. The sensitivity and dependence of the results on parameters is analyzed and discussed. It is shown that in the energy range above the top energy of the BNL Alternating Gradient Synchrotron within present accuracies, all chemical freeze-out criteria give a fairly good description of the particle yields. However, the low energy heavy-ion data favor the constant energy per particle as a unified condition of chemical particle freeze-out. This condition also shows the weakest sensitivity on model assumptions and parameters.

Cleymans, J.; Oeschler, H.; Redlich, K.; Wheaton, S. [UCT-CERN Research Centre and Department of Physics, University of Cape Town, Rondebosch 7701 (South Africa); Darmstadt University of Technology, D-64289 Darmstadt, Germany and UCT-CERN Research Centre and Department of Physics, University of Cape Town, Rondebosch 7701 (South Africa); Institute of Theoretical Physics, University of Wroclaw, Pl. Maksa Borna 9, 50-204 Wroclaw, Poland and CERN TH, CH 1211 Geneva 23 (Switzerland); UCT-CERN Research Centre and Department of Physics, University of Cape Town, Rondebosch 7701, South Africa and Darmstadt University of Technology, D-64289 Darmstadt (Germany)

2006-03-15

325

Numerical simulation of the interaction of biological cells with an ice front during freezing  

NASA Astrophysics Data System (ADS)

The goal of this study is a better understanding of the interaction between cells and a solidification front during a cryopreservation process. This technique of freezing is commonly used to conserve biological material for long periods at low temperatures. However the biophysical mechanisms of cell injuries during freezing are difficult to understand because a cell is a very sophisticated microstructure interacting with its environment. We have developed a finite element model to simulate the response of cells to an advancing solidification front. A special front-tracking technique is used to compute the motion of the cell membrane and the ice front during freezing. The model solves the conductive heat transfer equation and the diffusion equation of a solute on a domain containing three phases: one or more cells, the extra-cellular solution and the growing ice. This solid phase growing from a binary salt solution rejects the solute in the liquid phase and increases the solute gradient around the cell. This induces the shrinkage of the cell. The model is used to simulate the engulfment of one cell modelling a red blood cell by an advancing solidification front initially planar or not is computed. We compare the incorporation of a cell with that of a solid particle.

Carin, M.; Jaeger, M.

2001-12-01

326

Vertical Bargraph Display.  

National Technical Information Service (NTIS)

The program involves the generation of an advance approach to electronic aircraft instrumentation. The display media is a twisted nematic liquid crystal display (TN LCD). The instrument was designed as a one-for-one replacement for the existing vertical b...

S. Aftergut G. M. Gozeba C. R. Stein R. L. Skovholt W. W. Thurlow

1975-01-01

327

Vertical Differentiation among Occupations.  

ERIC Educational Resources Information Center

|It is reported that research on the socioeconomic achievement process has begun to generate anomalous findings, many of which involve occupational status as conventionally measured. The author proposes a theory of vertical occupational differentiation based on the role activities of occupational incumbents. (Author/RLV)|

Spaeth, Joe L.

1979-01-01

328

Steam consumption reduction by eutectic freeze crystallization  

SciTech Connect

Steam production in American beet sugar factories can be reduced by 600 pounds per ton of beets by using hydrate freeze crystallization in place of pan evaporators for sugar crystallization. This is a relatively constant number, regardless of current factory energy use. Further reduction is limited by the juice heating needs in the purification operations. Steam for juice heating is 20 to 30% on beets, or 400 to 600 pounds of steam per ton. In efficient factories this is about the steam flow to the evaporators when the pan crystallizers are replaced by freeze crystallization. An approach is described here for a rapid evaluation of effects on the steam balance of basic process changes. It provides a visual guide to restructuring the steam balance that simplifies optimization when such changes are made. The graphic approach is useful in illustrating methods of reducing energy use in a sugar factory, in addition to the current analysis of integration of the hydrate freeze process. For example, membrane and vapor recompression evaporators for juice concentration must be accompanied by major factory modifications to produce any net savings of steam. The reason is the needs for specific steam quantity and quality for the pan evaporators and juice heaters, supplied through the current evaporator trains. Reduction of the steam rate below 25 to 35% on beets will require changes to the conventional juice purification process.

Bichsel, S.E.; Cleary, M.; Barron, T.S.; Heist, J.A.

1985-01-01

329

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

330

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

331

Improve online freeze and cloud point control  

SciTech Connect

To improve financial performance, petroleum refiners want tighter control on individual processing units. Consequently, modern refineries are moving product-quality analytical functions closer to process. Historically, processing units sent product samples to the laboratory and made adjustments based on analytical results. In some cases, the lag time between sample procurement an data return could be several hours. During this time, the unit could be producing off-spec product or operating in a nonoptimized mode while waiting on lab results. Under these conditions, the cost to the refinery could mean the difference between a profit or loss. Many quality requirements are associated with the refined products. Some are regulatory mandates, others are market or seasonally driven and some are driven by yield and process optimization objectives. For example, freeze and cloud point are process control parameters that can increase yields and improve financial performance. Opting to use online analyzers to monitor/control freeze and cloud point specifications has potential economical advantages. The paper discusses freeze and cloud point data, common problems with analyzers, and two case histories of monitoring petroleum refinery streams.

Davidson, F.; Tsang, C. [Phase Technology, Richmond, British Columbia (Canada)

1997-01-01

332

Intracellular freezing, viability, and composition of fat body cells from freeze-intolerant larvae of Sarcophaga crassipalpis.  

PubMed

Although it is often assumed that survival of freezing requires that ice formation must be restricted to extracellular compartments, fat body cells from freeze-tolerant larvae of the gall fly, Eurosta solidaginis (Diptera, Tephritidae) survive intracellular freezing. Furthermore, these cells are highly susceptible to inoculative freezing by external ice, undergo extensive lipid coalescence upon thawing, and survive freezing better when glycerol is added to the suspension medium. To determine whether these traits are required for intracellular freeze tolerance or whether they are incidental and possessed by fat body cells in general, we investigated the capacity of fat body cells from nondiapause-destined and diapause-destined (i.e., cold-hardy) larvae of the freeze-intolerant flesh fly Sarcophaga crassipalpis (Diptera, Sarcophagidae) to survive intracellular freezing. Fat body cells from both types of larvae were highly susceptible to inoculative freezing; all cells froze between -3.7 to -6.2 degrees C. The highest rates for survival of intracellular freezing occurred at -5 degrees C. The addition of glycerol to the media markedly increased survival rates. Upon thawing, the fat body cells showed little or no lipid coalescence. Fat body cells from E. solidaginis had a water content of only 35% compared to cells from S. crassipalpis larvae that had 52-55%; cells with less water may be less likely to be damaged by mechanical forces during intracellular freezing. PMID:11746564

Davis, D J; Lee, R E

2001-12-01

333

Gradient echo MRI  

PubMed Central

Background: Recent studies have demonstrated that gradient echo (GRE) MRI sequences are as accurate as CT for the detection of intracerebral hemorrhage (ICH) in the context of acute stroke. However, many physicians who currently read acute stroke imaging studies may be unfamiliar with interpretation of GRE images. Methods: An NIH Web-based training program was developed including a pretest, tutorial, and posttest. Physicians involved in the care of acute stroke patients were encouraged to participate. The tutorial covered acute, chronic, and mimic hemorrhages as they appear on CT, diffusion-weighted imaging, and GRE sequences. Ability of users to identify ICH presence, type, and age on GRE was compared from the pretest to posttest timepoint. Results: A total of 104 users completed the tutorial. Specialties represented included general radiology (42%), general neurology (16%), neuroradiology (15%), stroke neurology (14%), emergency medicine (1%), and other (12%). Median overall score improved pretest to posttest from 66.7% to 83.3%, p < 0.001. Improvement by category was as follows: acute ICH, 66.7%–100%, p < 0.001; chronic ICH, 33.3%–66.7%, p < 0.001; ICH negatives/mimics, 100%–100%, p = 0.787. Sensitivity for identification of acute hemorrhage improved from 68.2% to 96.4%. Conclusions: Physicians involved in acute stroke care achieved significant improvement in gradient echo (GRE) hemorrhage interpretation after completing the NIH GRE MRI tutorial. This indicates that a Web-based tutorial may be a viable option for the widespread education of physicians to achieve an acceptable level of diagnostic accuracy at reading GRE MRI, thus enabling confident acute stroke treatment decisions. GLOSSARY AHA/ASA = American Heart Association/American Stroke Association; CME = continuing medical education; DWI = diffusion-weighted imaging; GRE = gradient echo; ICH = intracerebral hemorrhage; tPA = tissue plasminogen activator.

Copenhaver, B R.; Shin, J; Warach, S; Butman, J A.; Saver, J L.; Kidwell, C S.

2009-01-01

334

Magnetic shielding for the Fermilab Vertical Cavity Test Facility  

SciTech Connect

A superconducting RF cavity has to be shielded from magnetic fields present during cool down below the critical temperature to avoid freezing in the magnetic flux at localized impurities, thereby degrading the cavity intrinsic quality factor Q{sub 0}. The magnetic shielding designed for the Fermilab vertical cavity test facility (VCTF), a facility for CW RF vertical testing of bare ILC 1.3 GHz 9-cell SRF cavities, was recently completed. For the magnetic shielding design, we used two cylindrical layers: a room temperature 'outer' shield of Amumetal (80% Ni alloy), and a 2K 'inner' shield of Cryoperm 10. The magnetic and mechanical design of the magnetic shielding and measurement of the remanent magnetic field inside the shielding are described.

Ginsburg, Camille M.; Reid, Clark; Sergatskov, Dmitri A.; /Fermilab

2008-09-01

335

3-D radial gravity gradient inversion  

NASA Astrophysics Data System (ADS)

We have presented a joint inversion of all gravity-gradient tensor components to estimate the shape of an isolated 3-D geological body located in subsurface. The method assumes the knowledge about the depth to the top and density contrast of the source. The geological body is approximated by an interpretation model formed by an ensemble of vertically juxtaposed 3-D right prisms, each one with known thickness and density contrast. All prisms forming the interpretation model have a polygonal horizontal cross-section that approximates a depth slice of the body. Each polygon defining a horizontal cross-section has the same fixed number of vertices, which are equally spaced from 0° to 360° and have their horizontal locations described in polar coordinates referred to an arbitrary origin inside the polygon. Although the number of vertices forming each polygon is known, the horizontal coordinates of these vertices are unknown. To retrieve a set of juxtaposed depth slices of the body, and consequently, its shape, our method estimates the radii of all vertices and the horizontal Cartesian coordinates of all arbitrary origins defining the geometry of all polygons describing the horizontal cross-sections of the prisms forming the interpretation model. To obtain a stable estimate that fits the observed data, we impose constraints on the shape of the estimated body. These constraints are imposed through the well-known zeroth- and first-order Tikhonov regularizations allowing, for example, the estimate of vertical or dipping bodies. If the data do not have enough in-depth resolution, the proposed inverse method can obtain a set of stable estimates fitting the observed data with different maximum depths. To analyse the data resolution and deal with this possible ambiguity, we plot the ?2-norm of the residuals (s) against the estimated volume (vp) produced by a set of estimated sources having different maximum depths. If this s × vp curve (s as a function of vp) shows a well-defined minimum of s, the data have enough resolution to recover the shape of the body entirely. Conversely, if the observed data do not have enough resolution, some estimates with different maximum depths produce practically the same minimum value of s on the s × vp curve. In this case, the best estimate among a suite of estimates producing equally data fits is the one fitting the gravity-gradient data and producing the minima of both the source's bottom depth and volume. The histograms of the residuals can be used to quantify and remove systematic errors in the data. After removing these errors, we confirmed the ability of our method to recover the source geometry entirely (or its upper part only), if the data have sufficient (or insufficient) in-depth resolution. By inverting the gravity-gradient data from a survey over the Vinton salt dome (Louisiana, USA) with a density contrast of 0.55 g cm-3, we estimated a massive cap rock whose maximum depth attains 460 ± 10 m and its shallowest portion is elongated in the northeast-southwest direction.

Oliveira, Vanderlei C.; Barbosa, Valéria C. F.

2013-11-01

336

Heuristic numerical and analytical models of the hydrologic controls over vertical solute transport in a domed peat bog, Jura Mountains, Switzerland  

Microsoft Academic Search

We report the results of numerical and analytical simulations to test the hypothesis that downward vertical flow of porewater from the crests of domed alpine and kettle bogs controls vertical porewater distributions of major solutes such as Ca and Mg. The domed Etang de la Gruère bog (EGr), Switzerland, characterized by a vertical downward gradient of 0·04 and stratified layers

Jeffrey M. McKenzie; Donald I. Siegel; William Shotyk; Philipp Steinmann; Gabriele Pfunder

2002-01-01

337

The vertical distribution of phytoplankton in stratified water columns.  

PubMed

What determines the vertical distribution of phytoplankton in different aquatic environments remains an open question. To address this question, we develop a model to explore how phytoplankton respond through growth and movement to opposing resource gradients and different mixing conditions. We assume stratification creates a well-mixed surface layer on top of a poorly mixed deep layer and nutrients are supplied from multiple depth-dependent sources. Intraspecific competition leads to a unique strategic equilibrium for phytoplankton, which allows us to classify the distinct vertical distributions that can exist. Biomass can occur as a benthic layer (BL), a deep chlorophyll maximum (DCM), or in the mixed layer (ML), or as a combination of BL+ML or DCM+ML. The ML biomass can be limited by nutrients, light, or both. We predict how the vertical distribution, relative resource limitation, and biomass of phytoplankton will change across environmental gradients. We parameterized our model to represent potentially light and phosphorus limited freshwater lakes, but the model is applicable to a broad range of vertically stratified systems. Increasing nutrient input from the sediments or to the mixed layer increases light limitation, shifts phytoplankton towards the surface, and increases total biomass. Increasing background light attenuation increases light limitation, shifts the phytoplankton towards the surface, and generally decreases total biomass. Increasing mixed layer depth increases, decreases, or has no effect on light limitation and total biomass. Our model is able to replicate the diverse vertical distributions observed in nature and explain what underlying mechanisms drive these distributions. PMID:20932846

Mellard, Jarad P; Yoshiyama, Kohei; Litchman, Elena; Klausmeier, Christopher A

2011-01-21

338

Freezing and ice crystals formed in a cylindrical food model: part II. Comparison between freezing at atmospheric pressure and pressure-shift freezing  

Microsoft Academic Search

Cylindrical gelatin gels were pressure-shift frozen at different pressure levels (100, 150 and 200 MPa). Temperature and pressure profiles were compared and the maximum supercooling obtained after pressure release was evaluated. A comparison between the freezing steps at atmospheric pressure and those of pressure-shift freezing was carried out to compare the time steps during the processes. The degree of supercooling

D. Chevalier; A. Le Bail; M. Ghoul

2000-01-01

339

Speciation along environmental gradients  

NASA Astrophysics Data System (ADS)

Traditional discussions of speciation are based on geographical patterns of species ranges. In allopatric speciation, long-term geographical isolation generates reproductively isolated and spatially segregated descendant species. In the absence of geographical barriers, diversification is hindered by gene flow. Yet a growing body of phylogenetic and experimental data suggests that closely related species often occur in sympatry or have adjacent ranges in regions over which environmental changes are gradual and do not prevent gene flow. Theory has identified a variety of evolutionary processes that can result in speciation under sympatric conditions, with some recent advances concentrating on the phenomenon of evolutionary branching. Here we establish a link between geographical patterns and ecological processes of speciation by studying evolutionary branching in spatially structured populations. We show that along an environmental gradient, evolutionary branching can occur much more easily than in non-spatial models. This facilitation is most pronounced for gradients of intermediate slope. Moreover, spatial evolutionary branching readily generates patterns of spatial segregation and abutment between the emerging species. Our results highlight the importance of local processes of adaptive divergence for geographical patterns of speciation, and caution against pitfalls of inferring past speciation processes from present biogeographical patterns.

Doebeli, Michael; Dieckmann, Ulf

2003-01-01

340

Cold hardiness and supercooling along an altitudinal gradient in andean giant rosette species  

Microsoft Academic Search

Factors affecting supercooling capacity and cold hardiness were investigated in leaves of ten giant rosette species of the genus Espeletia (Compositae). These species grow along a 2,800–4,200 m elevation gradient in the Venezuelan Andes. In this high tropical environment, freezing frequently occurs every night, particularly above 3,300 m, but lasts for only a few hours. Supercooling capacty is linearly related

G. Goldstein; F. Rada; A. Azocar

1985-01-01

341

Jamming in Vertical Channels  

NASA Astrophysics Data System (ADS)

We study jamming of low aspect-ratio cylindrical Delrin grains in a vertical channel. Grain heights are less than their diameter so the grains resemble antacid tablets, coins, or poker chips. These grains are allowed to fall through a vertical channel with a square cross section where the channel width is greater than the diameter of a grain and constant throughout the length of the channel with no obstructions or constrictions. Grains are sometimes observed to form jams, stable structures supported by the channel walls with no support beneath them. The probability of jam occurrence and the strength or robustness of a jam is effected by grain and channel sizes. We will present experimental measurements of the jamming probability and jam strength in this system and discuss the relationship of these results to other experiments and theories.

Baxter, G. William; Steel, Fiona

2011-03-01

342

Jamming in Vertical Channels  

NASA Astrophysics Data System (ADS)

We experimentally study jamming of cylindrical grains in a vertical channel. The grains have a low aspect-ratio (height/diameter < 1) so their shape is like antacid tablets or poker chips. They are allowed to fall through a vertical channel with a square cross section. The channel width is greater than the diameter of a grain and constant throughout the length of the channel with no obstructions or constrictions. It is observed that grains sometimes jam in this apparatus. In a jam, grains form a stable structure from one side of the channel to the other with nothing beneath them. Jams may be strong enough to support additional grains above. The probability of a jam occurring is a function of the grain height and diameter. We will present experimental measurements of the jamming probability in this system and discuss the relationship of these results to other experiments and theories.

Baxter, G. William; McCausland, Jeffrey; Steel, Fiona

2010-03-01

343

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

344

Vertical axis wind turbine  

Microsoft Academic Search

A vertical axis wind turbine is provided based on the co-pending application ser. No. 890,998, filed Mar. 28, 1978, now U.S. Pat. No. 4,204,805. In this improved system the centrifugal forces of rotation produce no bending moments in the air foil spars. Also, the center of mass, the center of useful aerodynamic pressure and the center of main bearing supported

Bolie

1981-01-01

345

Two-dimensional freezing criteria for crystallizing colloidal monolayers  

SciTech Connect

Video microscopy was employed to explore crystallization of colloidal monolayers composed of diameter-tunable microgel spheres. Two-dimensional (2D) colloidal liquids were frozen homogenously into polycrystalline solids, and four 2D criteria for freezing were experimentally tested in thermal systems for the first time: the Hansen-Verlet freezing rule, the Loewen-Palberg-Simon dynamical freezing criterion, and two other rules based, respectively, on the split shoulder of the radial distribution function and on the distribution of the shape factor of Voronoi polygons. Importantly, these freezing criteria, usually applied in the context of single crystals, were demonstrated to apply to the formation of polycrystalline solids. At the freezing point, we also observed a peak in the fluctuations of the orientational order parameter and a percolation transition associated with caged particles. Speculation about these percolated clusters of caged particles casts light on solidification mechanisms and dynamic heterogeneity in freezing.

Wang Ziren; Han Yilong [Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay (Hong Kong); Alsayed, Ahmed M. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, Pennsylvania 19104 (United States); Complex Assemblies of Soft Matter, CNRS/UPENN/Rhodia UMI 3254, Bristol, Pennsylvania 19007 (United States); Yodh, Arjun G. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, Pennsylvania 19104 (United States)

2010-04-21

346

On the size dependence of contact freezing probability  

NASA Astrophysics Data System (ADS)

The contact freezing of supercooled water droplets electrodynamically levitated in the aerosol flow containing clay mineral particles has been investigated in the temperature range from -27°C to -34°C. The aerosol generation system employs a multistage impactor to narrow down the size distribution of aerosol. We use mobility selected illite clay mineral particles of four characteristic diameters to investigate the influence of particle size onto the freezing probability in the contact mode. Our preliminary results show that the contact freezing probability is proportional to the square of particle size (surface area), a feature which is normally attributed to the immersion freezing efficacy of atmospheric ice active particles. Along with the observed temperature and material dependence of contact freezing, this finding provides a new basis for approaching the question of similarity between the contact and immersion freezing.

Kiselev, Alexei; Hoffmann, Nadine; Duft, Denis; Leisner, Thomas

2013-05-01

347

Development of a low-cost system for measuring conditional time-averaged gradients of SO2 and NH3.  

PubMed

A conditional time-averaged gradient (COTAG) system has been developed to provide direct long-term (weekly to monthly) average flux gradient measurements for a range of trace gases, between land and atmosphere. Over daily periods, atmospheric conditions can range from high stability, where the vertical gradients of ambient concentration are enhanced due to very small diffusivity, to highly unstable conditions, in which concentration gradients are small due to the intense turbulent activity of the surface layer. The large vertical gradients generated by high stability would bias the estimate of the actual flux: to avoid this, the COTAG system samples conditionally, within a carefully refined range of stability. A comparison with a continuous flux gradient system suggested that the removal of stable conditions from the sampling period does not substantially modify the evaluation of the long-term fluxes. PMID:19184491

Famulari, D; Fowler, D; Nemitz, E; Hargreaves, K J; Storeton-West, R L; Rutherford, G; Tang, Y S; Sutton, M A; Weston, K J

2009-01-30

348

Convergent tracer tests in multilayered aquifers: The importance of vertical flow in the injection borehole  

NASA Astrophysics Data System (ADS)

A mathematical model describing the steady state flows in a forced gradient tracer test between an injection and pumping borehole in a multilayered sandstone aquifer has been developed that includes the effect of vertically variable background heads. A second model describing the recovery of tracer from a layer in which there are discharges due to vertical flow in the injection borehole is also presented. Application of the models to field tracer test data indicates that the observed recoveries, which are not proportional to the abstraction rate in each layer, are consistent with the hydraulic behavior of the aquifer when natural vertical head gradients are taken into account. Investigation with the models illustrates that the vertical distribution of tracer recovery depends strongly upon the background heads and that tracer tests conducted in the same aquifer, but at different times, may interrogate different aquifer layers. It is also shown generally that for a given abstraction rate the vertical distribution of tracer recovery in small-scale tracer tests is controlled largely by the transmissivity distribution but that as the spatial scale of the test increases, the distribution of recovery becomes proportional to the discharges from the injection borehole because of vertical flows within it, which may be natural or induced by pumping in the monitoring borehole. Uncertainties inherent in the design of forced gradient tracer tests in multilayered aquifers and the problems of applying the results of such tests to natural gradient contaminant migration are discussed.

Riley, Michael S.; Tellam, John H.; Greswell, Richard B.; Durand, VéRonique; Aller, Maria F.

2011-07-01

349

Infrared freezing of Euclidean QCD observables  

SciTech Connect

We consider the leading one-chain term in a skeleton expansion for QCD observables and show that for energies Q{sup 2}>{lambda}{sup 2}, where Q{sup 2}={lambda}{sup 2} is the Landau pole of the coupling, the skeleton expansion result is equivalent to the standard Borel integral representation, with ambiguities related to infrared (IR) renormalons. For Q{sup 2}<{lambda}{sup 2} the skeleton expansion result is equivalent to a previously proposed modified Borel representation where the ambiguities are connected with ultraviolet (UV) renormalons. We investigate the Q{sup 2}-dependence of the perturbative corrections to the Adler-D function, the GLS sum rule and the polarized and unpolarized Bjorken sum rules. In all these cases the one-chain result changes sign in the vicinity of Q{sup 2}={lambda}{sup 2}, and then exhibits freezing behavior, vanishing at Q{sup 2}=0. Finiteness at Q{sup 2}={lambda}{sup 2} implies specific relations between the residues of IR and UV renormalon singularities in the Borel plane. These relations, only one of which has previously been noted (though it remained unexplained), are shown to follow from the continuity of the characteristic function in the skeleton expansion. By considering the compensation of nonperturbative and perturbative ambiguities we are led to a result for the Q{sup 2}-dependence of these observables at all Q{sup 2}, in which there is a single undetermined nonperturbative parameter, and which involves the skeleton expansion characteristic function. The observables freeze to zero in the infrared. We briefly consider the freezing behavior of the Minkowskian R{sub e{sup +}}{sub e{sup -}} ratio.

Brooks, Paul M.; Maxwell, C. J. [Institute for Particle Physics Phenomenology, University of Durham, South Road, DH1 3LE (United Kingdom)

2006-09-15

350

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

351

Nitrous oxide emissions from soil during freezing and thawing periods  

Microsoft Academic Search

In a laboratory investigation, the processes of N2O emissions during freezing\\/thawing periods were studied. Four undisturbed soil columns from an agricultural site were subjected to two freeze\\/thaw cycles. Two periods of higher N2O emissions were detected, a period of elevated N2O emissions during continuous soil freezing and a period of brief peak emissions during thawing. Soil respiration indicated that microorganisms

R Teepe; R Brumme; F Beese

2001-01-01

352

Vertical heterogeneity in predation pressure in a temperate forest canopy.  

PubMed

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; Timms, Laura L; Buddle, Christopher M

2013-08-22

353

Dynamics of gravity-induced gradients in soap film thicknesses  

NASA Astrophysics Data System (ADS)

We demonstrate a direct measurement of thickness gradients in vertical soap films with a resonant differential interferometer, i.e., the Jamin-Fabry-Perot interferometer. Two regimes are investigated: thick colored films with gravity- and capillarity-induced gradients, and silvery-gray to common black films which are quasi-independent of gravity. In the colored zone, our differential method is an ideal tool with which to isolate the large thickness instabilities of the film reaching 17 nm/mm that characterize the end of its drainage. Using the so-called F2 law of such an interferometer, thermal-induced thickness variations as small as 1 nm are isolated in the gradient-free common black film.

Ropars, G.; Chauvat, D.; Le Floch, A.; O'Sullivan-Hale, M. N.; Boyd, R. W.

2006-06-01

354

A vortex pair near a density gradient interface  

NASA Astrophysics Data System (ADS)

The dynamics of a vortex pair in a stratified atmosphere near a density gradient interface is considered here using direct numerical simulations. A density-gradient interface has continuous density but discontinuous gradient of density, and is a common model of the tropopause. The vortex pair is released below the interface and allowed to propagate vertically toward the interface. The anelastic approximation of the Navier-Stokes equations are treated using a spectral method, and the initial vortex has a Gaussian distribution of vorticity. The results show that strong vortices propagate through the interface without much change in dynamics. Weaker vortices will dissipate energy when they reach the interface and although a remnant of the vortex pair transits the interface, it does not achieve the same altitude that it would have without the interface. Overall, the interface is not a barrier to vortex pairs, but would be expected to change the distribution of energy in more complicated flows.

Shaw, Surupa; Jenkins, Nick; McHugh, John

2011-11-01

355

Adaptive dictionary learning in sparse gradient domain for image recovery.  

PubMed

Image recovery from undersampled data has always been challenging due to its implicit ill-posed nature but becomes fascinating with the emerging compressed sensing (CS) theory. This paper proposes a novel gradient based dictionary learning method for image recovery, which effectively integrates the popular total variation (TV) and dictionary learning technique into the same framework. Specifically, we first train dictionaries from the horizontal and vertical gradients of the image and then reconstruct the desired image using the sparse representations of both derivatives. The proposed method enables local features in the gradient images to be captured effectively, and can be viewed as an adaptive extension of the TV regularization. The results of various experiments on MR images consistently demonstrate that the proposed algorithm efficiently recovers images and presents advantages over the current leading CS reconstruction approaches. PMID:23955749

Liu, Qiegen; Wang, Shanshan; Ying, Leslie; Peng, Xi; Zhu, Yanjie; Liang, Dong

2013-08-15

356

Gradient drift irregularities in mid-latitude sporadic E  

SciTech Connect

Three-meter E region irregularities observed by a portable 50-MHz radar on the island of Guadeloupe in June 1977 are shown to have the same properties as 3-m irregularities generated by the gradient drift instability at the equator and in the auroral zones. The irregularities occur when intense sporadic E patches are know to occur, suggesting that they are generated by the gradient drift instability acting on the large vertical gradients in sporadic E patches. Large, rapid E region drift variations observed on two occasions suggest either that the E region electric fields are structured and less than 450 km in horizontal extent, or that E and F region fields couple and decouple intermittently during ionospheric sunset.

Ecklund, W.L.; Carter, D.A.; Balsley, B.B.

1981-02-01

357

Freezing on heating of liquid solutions.  

PubMed

We report a reversible liquid-solid transition upon heating of a simple solution composed of a-cyclodextrine (alpha CD), water, and 4-methylpyridine. These solutions are homogeneous and transparent at ambient temperature and solidify when heated to temperatures between 45 degrees and 75 degrees. Quasielastic and elastic neutron scattering show that molecular motions are slowed down in the solid and that crystalline order is established. The solution "freezes on heating." This process is fully reversible, on cooling the solid melts. A rearrangement of hydrogen bonds is postulated to be responsible for the observed phenomenon. PMID:15352791

Plazanet, M; Floare, C; Johnson, M R; Schweins, R; Trommsdorff, H P

2004-09-15

358

Freezing on heating of liquid solutions  

NASA Astrophysics Data System (ADS)

We report a reversible liquid-solid transition upon heating of a simple solution composed of a-cyclodextrine (?CD), water, and 4-methylpyridine. These solutions are homogeneous and transparent at ambient temperature and solidify when heated to temperatures between 45° and 75°. Quasielastic and elastic neutron scattering show that molecular motions are slowed down in the solid and that crystalline order is established. The solution ``freezes on heating.'' This process is fully reversible, on cooling the solid melts. A rearrangement of hydrogen bonds is postulated to be responsible for the observed phenomenon.

Plazanet, M.; Floare, C.; Johnson, M. R.; Schweins, R.; Trommsdorff, H. P.

2004-09-01

359

Scanning temperature gradient focusing.  

PubMed

Temperature gradient focusing (TGF) is a recently developed technique for the simultaneous concentration and electrophoretic separation of ionic analytes in microfluidic channels. One drawback to TGF as it has previously been described is the limited peak capacity; only a small number of analyte peaks (approximately 2-3) can be simultaneously focused and separated. In this paper, we report on a variation of the TGF method whereby the bulk flow rate is varied over time so that a large number of analytes can be sequentially focused, moved past a fixed detection point, and flushed to waste. In addition to improved peak capacity, the detection limits of the scanning TGF method can be adjusted on-the-fly, as needed for different samples. Finally, scanning TGF provides a technique by which high-resolution, high-peak-capacity electrophoretic separations can be performed in simple, straight, and short microfluidic channels. PMID:17037919

Hoebel, Stacey J; Balss, Karin M; Jones, Barbara J; Malliaris, Constantin D; Munson, Matthew S; Vreeland, Wyatt N; Ross, David

2006-10-15

360

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

361

Conjugate gradient Mojette reconstruction  

NASA Astrophysics Data System (ADS)

Iterative methods are now recognized as powerful tools to solve inverse problems such as tomographic reconstruction. In this paper, the main goal is to present a new reconstruction algorithm made from two components. An iterative algorithm, namely the Conjugate Gradient (CG) method, is used to solve the tomographic problem in the least square (LS) sense for our specific discrete Mojette geometry. The results are compared (with the same geometry) to the corresponding Mojette Filtered Back Projection (FBP) method. In the fist part of the paper, we recall the discrete geometry used to define the projection M and backprojection M* operators. In the second part, the CG algorithm is presented within the context of the Mojette geometry. Noise is then added onto these Mojette projections with respect to the sampling and reconstructions are performed. Finally the Toeplitz block Toeplitz (TBT) character of M*M is demonstrated.

Servieres, Myriam; Idier, Jerome; Normand, Niccolas; Guedon, Jean-Pierre

2005-04-01

362

Tectorial Membrane Stiffness Gradients  

PubMed Central

The mammalian inner ear processes sound with high sensitivity and fine resolution over a wide frequency range. The underlying mechanism for this remarkable ability is the “cochlear amplifier”, which operates by modifying cochlear micromechanics. However, it is largely unknown how the cochlea implements this modification. Although gradual improvements in experimental techniques have yielded ever-better descriptions of gross basilar membrane vibration, the internal workings of the organ of Corti and of the tectorial membrane have resisted exploration. Although measurements of cochlear function in mice with a gene mutation for ?-tectorin indicate the tectorial membrane's key role in the mechanoelectrical transformation by the inner ear, direct experimental data on the tectorial membrane's physical properties are limited, and only a few direct measurements on tectorial micromechanics are available. Using the hemicochlea, we are able to show that a tectorial membrane stiffness gradient exists along the cochlea, similar to that of the basilar membrane. In artificial perilymph (but with low calcium), the transversal and radial driving point stiffnesses change at a rate of –4.0 dB/mm and ?4.9 dB/mm, respectively, along the length of the cochlear spiral. In artificial endolymph, the stiffness gradient for the transversal component was –3.4 dB/mm. Combined with the changes in tectorial membrane dimensions from base to apex, the radial stiffness changes would be able to provide a second frequency-place map in the cochlea. Young's modulus, which was obtained from measurements performed in the transversal direction, decreased by ?2.6 dB/mm from base to apex.

Richter, Claus-Peter; Emadi, Gulam; Getnick, Geoffrey; Quesnel, Alicia; Dallos, Peter

2007-01-01

363

A variant of a slam freezing device for electron microscopy.  

PubMed

A home-made slam freezing device is presented that allows reproducible results in freezing various unfixed tissues. The heart of the device is an aluminum socket, which harbors a plunger that is set in motion by a spring. At the end of the plunger there is an electromagnet which holds the sample on a sheet metal planchette. During stop freezing the electrical contacts are interrupted and the plunger can be withdrawn leaving the specimen on the cooled copper block. This guarantees freezing of not only solid tissues, but also cell suspensions, such as blood or bone marrow. PMID:8148433

Lemke, C; Schwerdtfeger, M; Pöhlmann, I; Sammler, G; Linss, W

1994-01-01

364

Experimental quantification of contact freezing in an electrodynamic balance  

NASA Astrophysics Data System (ADS)

Heterogeneous nucleation of ice in a supercooled water droplet induced by external contact with a dry aerosol particle has long been known to be more effective than freezing induced by the same nucleus immersed in the droplet. However, the experimental quantification of contact freezing is challenging. Here we report an experimental method to determine the temperature-dependent ice nucleation probability of size-selected aerosol particles. The method is based on the suspension of supercooled charged water droplets in a laminar flow of air containing aerosol particles as contact freezing nuclei. The rate of droplet-particle collisions is calculated numerically with account for Coulomb attraction, drag force and induced dipole interaction between charged droplet and aerosol particles. The calculation is verified by direct counting of aerosol particles collected by a levitated droplet. By repeating the experiment on individual droplets for a sufficient number of times, we are able to reproduce the statistical freezing behavior of a large ensemble of supercooled droplets and measure the average rate of freezing events. The freezing rate is equal to the product of the droplet-particle collision rate and the probability of freezing on a single contact, the latter being a function of temperature, size and composition of the contact ice nuclei. Based on these observations, we show that for the types of particles investigated so far, contact freezing is the dominating freezing mechanism on the timescale of our experiment.

Hoffmann, N.; Kiselev, A.; Rzesanke, D.; Duft, D.; Leisner, T.

2013-09-01

365

Anoxia tolerance and freeze tolerance in hatchling turtles.  

PubMed

Freezing survival in hatchling turtles may be limited by ischemic anoxia in frozen tissues and the associated accumulation of lactate and reactive oxygen species (ROS). To determine whether mechanisms for coping with anoxia are also important in freeze tolerance, we examined the association between capacities for freezing survival and anoxia tolerance in hatchlings of seven species of turtles. Tolerance to freezing (-2.5 degrees C) was high in Emydoidea blandingii, Chrysemys picta, Terrapene ornata, and Malaclemys terrapin and low in Graptemys geographica, Chelydra serpentina, and Trachemys scripta. Hatchlings survived in a N(2) atmosphere at 4 degrees C for periods ranging from 17 d (M. terrapin) to 50 d (G. geographica), but survival time was not associated with freeze tolerance. Lactate accumulated during both stresses, but plasma levels in frozen/thawed turtles were well below those found in anoxia-exposed animals. Activity of the antioxidant enzyme catalase in liver increased markedly with anoxia exposure in most species, but increased with freezing/thawing only in species with low freeze tolerance. Our results suggest that whereas oxygen deprivation occurs during somatic freezing, freeze tolerance is not limited by anoxia tolerance in hatchling turtles. PMID:15739066

Dinkelacker, S A; Costanzo, J P; Lee, R E

2005-03-01

366

Freezing and Melting, Precipitation Type, and Numerical Weather Prediction  

NSDL National Science Digital Library

This Webcast, Freezing and Melting, Precipitation Type, and Numerical Weather Prediction, is based on a COMET classroom presentation by Dr. Gary Lackmann at the 2nd MSC Winter Weather Course held in Boulder, Colorado on 22 February 2002. Dr. Lackmann reviews the basic thermodynamics of freezing and melting and how operational models represent these processes. He also touches upon the biases that occur in the models by looking at examples of melting snow aloft, melting snow at the surface, freezing aloft (ice pellets), and freezing rain. Dr. Lackmann is a faculty member in the Department of Marine, Earth, and Atmospheric Sciences at North Carolina State University.

Spangler, Tim

2002-01-01

367

Identification of chaperones in freeze tolerance in Saccharomyces cerevisiae.  

PubMed

Exposure to low temperatures reduces protein folding rates and induces the cold denaturation of proteins. Considering the roles played by chaperones in facilitating protein folding and preventing protein aggregation, chaperones must exist that confer tolerance to cold stress. Here, yeast strains lacking individual chaperones were screened for reduced freezing tolerance. In total, 19 of 82 chaperone-deleted strains tested were more sensitive to freeze-thaw treatment than wild-type cells. The reintroduction of the respective chaperone genes into the deletion mutants recovered the freeze tolerance. The freeze sensitivity of the chaperone-knockout strains was also retained in the presence of 20% glycerol. PMID:23124761

Naicker, Mahendran Chinnamara; Seul Jo, I; Im, Hana

2012-11-04

368

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.

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

369

Possible Application of Bacterial Condensation Freezing to Artificial Rainfall Enhancement.  

NASA Astrophysics Data System (ADS)

Both gram-positive and gram-negative bacteria become excellent condensation nuclei when lyophilized to dryness. The same freeze-dry procedure does not inactivate the highly effective freezing nuclei produced by ice nucleation active bacteria. Therefore, irrespective of their contact nucleation potential, ice nucleation-active bacteria ought to effect condensation freezing at 10°C of warmer in cloud systems. Output from a numerical cloud model suggests that the condensation freezing capability of ice nucleation-active bacteria at warmer temperatures could be exploited to produce rainfall from clouds too warm to respond positively to inorganic nucleants like silver iodide.

Levin, Z.; Yankofsky, S. A.; Pardes, D.; Magal, N.

1987-09-01

370

Reversible Photoinhibition in Antarctic Moss during Freezing and Thawing.  

PubMed

Tolerance of antarctic moss to freezing and thawing stress was investigated using chlorophyll a fluorescence. Freezing in darkness caused reductions in Fv/Fm (ratio of variable to maximum fluorescence) and Fo (initial fluorescence) that were reversible upon thawing. Reductions in Fv/Fm and Fo during freezing in darkness indicate a reduction in the potential efficiency of photosystem II that may be due to conformational changes in pigment-protein complexes due to desiccation associated with freezing. The absorption of light during freezing further reduced Fv/Fm and Fo but was also reversible. Using dithiothreitol (DTT), which inhibits the formation of the carotenoid zeaxanthin, we found reduced flurorescence quenching during freezing and reduced concentrations of zeaxanthin and antheraxanthin after freezing in DTT-treated moss. Reduced concentrations of zeaxanthin and antheraxanthin in DTT-treated moss were partially associated with reductions in nonphotochemical fluorescence quenching. The reversible photoinhibition observed in antarctic moss during freezing indicates the existence of processes that protect from photoinhibitory damage in environments where freezing temperatures occur in conjunction with high solar radiation levels. These processes may limit the need for repair cycles that require temperatures favorable for enzyme activity. PMID:12228644

Lovelock, C. E.; Jackson, A. E.; Melick, D. R.; Seppelt, R. D.

1995-11-01

371

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

372

Effects of electrode materials on freezing of supercooled water in electric freeze control  

Microsoft Academic Search

In order to clarify effects of electric charge on freezing of supercooled water, experiments were carried out with various kinds of electrodes in supercooled water. Water sample was kept in a test tube and cooled down at a constant cooling rate. When the water sample was maintained under a supercooling state, an electric charge was applied to the water sample

Tsutomu Hozumi; Akio Saito; Seiji Okawa; Kazuharu Watanabe

2003-01-01

373

Effects of shapes of electrodes on freezing of supercooled water in electric freeze control  

Microsoft Academic Search

In order to clarify the effects of electric charge on freezing of supercooled water, experiments were carried out. Two kinds of shapes were used for tips of electrodes. One was the sharp end surface. The other was the flat end surface. Aluminum was selected as the material. Water sample was kept in a test tube and cooled down at a

Tsutomu Hozumi; Akio Saito; Seiji Okawa; Yoichiro Eshita

2005-01-01

374

Effects of Electric and Magnetic Field on Freezing and Possible Relevance in Freeze Drying  

Microsoft Academic Search

Application of an electric or magnetic field can significantly affect the freezing characteristics of water. A DC electric field will tend to induce ice nucleation at a lower degree of supercooling, and there is evidence to show that an AC electric field delays the onset of ice nucleation. Industrial research has shown that a magnetic field can be used to

M. W. Woo; A. S. Mujumdar

2010-01-01

375

High-pressure freezing and freeze substitution of Arabidopsis for electron microscopy.  

PubMed

The objectives of electron microscopy ultrastructural studies are to examine cellular architecture and relate the cell's structural machinery to dynamic functional roles. This aspiration is difficult to achieve if specimens have not been adequately preserved in a "living state"; hence specimen preparation is of the utmost importance for the success of any electron micrographic study. High-pressure freezing (HPF)/freeze substitution (FS) has long been recognized as the primer technique for the preservation of ultrastructure in biological samples. In most cases a basic HPF/freeze substitution protocol is sufficient to obtain superior ultrastructural preservation and structural contrast, which allows one to use more advanced microscopy techniques such as 3D electron tomography. However, for plant tissues, which have a thick cell wall, large water-filled vacuoles, and air spaces (all of which are detrimental to cryopreservation), these basic HPF/FS protocols often yield undesirable results. In particular, ice crystal artifacts and the staining of membrane systems are often poorly or negatively stained, which make 3D segmentation of a tomogram difficult. To overcome these problems, various aspects of the HPF/FS protocol can be altered, including the cryo-filler(s) used, freeze substitution cocktail, and the resin infiltration process. This chapter will describe these modifications for the preparation of plant tissues for routine electron microscopic studies, immunocytochemistry, and 3D tomographic electron imaging. PMID:24057382

Austin, Jotham R

2014-01-01

376

Development of a low-cost system for measuring conditional time-averaged gradients of SO 2 and NH 3  

Microsoft Academic Search

A conditional time-averaged gradient (COTAG) system has been developed to provide direct long-term (weekly to monthly) average\\u000a flux gradient measurements for a range of trace gases, between land and atmosphere. Over daily periods, atmospheric conditions\\u000a can range from high stability, where the vertical gradients of ambient concentration are enhanced due to very small diffusivity,\\u000a to highly unstable conditions, in which

D. Famulari; D. Fowler; E. Nemitz; K. J. Hargreaves; R. L. Storeton-West; G. Rutherford; Y. S. Tang; M. A. Sutton; K. J. Weston

2010-01-01

377

Zone Freezing Study for Pyrochemical Process Waste Minimization  

SciTech Connect

Pyroprocessing technology is a non-aqueous separation process for treatment of used nuclear fuel. At the heart of pyroprocessing lies the electrorefiner, which electrochemically dissolves uranium from the used fuel at the anode and deposits it onto a cathode. During this operation, sodium, transuranics, and fission product chlorides accumulate in the electrolyte salt (LiCl-KCl). These contaminates change the characteristics of the salt overtime and as a result, large volumes of contaminated salt are being removed, reprocessed and stored as radioactive waste. To reduce the storage volumes and improve recycling process for cost minimization, a salt purification method called zone freezing has been proposed at Korea Atomic Energy Research Institute (KAERI). Zone freezing is melt crystallization process similar to the vertical Bridgeman method. In this process, the eutectic salt is slowly cooled axially from top to bottom. As solidification occurs, the fission products are rejected from the solid interface and forced into the liquid phase. The resulting product is a grown crystal with the bulk of the fission products near the bottom of the salt ingot, where they can be easily be sectioned and removed. Despite successful feasibility report from KAERI on this process, there were many unexplored parameters to help understanding and improving its operational routines. Thus, this becomes the main motivation of this proposed study. The majority of this work has been focused on the CsCl-LiCl-KCl ternary salt. CeCl3-LiCl-KCl was also investigated to check whether or not this process is feasible for the trivalent species—surrogate for rare-earths and transuranics. For the main part of the work, several parameters were varied, they are: (1) the retort advancement rate—1.8, 3.2, and 5.0 mm/hr, (2) the crucible lid configurations—lid versus no-lid, (3) the amount or size of mixture—50 and 400 g, (4) the composition of CsCl in the salt—1, 3, and 5 wt%, and (5) the temperature differences between the high and low furnace zones—200 and 300 ?C. During each experiment, the temperatures at selected locations around the crucible were measured and recorded to provide temperature profiles. Following each experiment, samples were collected and elemental analysis was done to determine the composition of iii the salt. Several models—non-mixed, well-mixed, Favier, and hybrid—were explored to describe the zone freezing process. For CsCl-LiCl-KCl system, experimental results indicate that through this process up to 90% of the used salt can be recycled, effectively reducing waste volume by a factor of ten. The optimal configuration was found to be a 5.0 mm/hr rate with a lid configuration and a ?T of 200°C. The larger 400 g mixtures had recycle percentages similar to the 50 g mixtures; however, the throughput per time was greater for the 400 g case. As a result, the 400 g case is recommended. For the CeCl3-LiCl-KCl system, the result implies that it is possible to use this process to separate the rare-earth and transuranics chlorides. Different models were applied to only CsCl ternary system. The best fit model was the hybrid model as a result of a solute transport transition from non- mixed to well-mixed throughout the growing process.

Ammon Williams

2012-05-01

378

Anisotropic Ion Temperature Gradient Instabilities  

Microsoft Academic Search

The effects of anisotropic temperature gradient and collisions on the ion-temperature-gradient (ITG) instabilities have been investigated by using kinetic theory. In the slab limit, the ITG mode is driven unstable by coupling between the transit resonance and ion temperature gradients. While eta_{rm i|} (eta_{rm i| } equiv partiallnT_ {i|}\\/partiallnn, where T_{rm i|} is the perpendicular ion temperature and n is

Hao Song

1994-01-01

379

Gradient elution in capillary electrochromatography  

Microsoft Academic Search

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

D. S. Anex; D. J. Rakestraw; Chao Yan; R. Dadoo; R. N. Zare

1997-01-01

380

To Freeze or Not to Freeze? An Evolutionary Perspective on the Cold?Hardiness Strategies of Overwintering Ectotherms  

Microsoft Academic Search

We address the question of whether freeze-tolerance, freeze-avoidance, or mixed strategy represents the best adaptation for overwintering ectotherms to endure severe winter. To this end, we develop an optimization fitness model that takes into account different physiological parameters such as energetic level, the phys- iological stress associated with each strategy, and climatic variables. The results show that the freeze-tolerance strategy

Yann Voituron; Nicolas Mouquet; Claire de Mazancourt; Jean Clobert

2002-01-01

381

Morphological study of endothelial cells during freezing  

NASA Astrophysics Data System (ADS)

Microvascular injury is recognized as a major tissue damage mechanism of ablative cryosurgery. Endothelial cells lining the vessel wall are thought to be the initial target of freezing. However, details of this injury mechanism are not yet completely understood. In this study, ECMatrix™ 625 was used to mimic the tumour environment and to allow the endothelial cells cultured in vitro to form the tube-like structure of the vasculature. The influence of water dehydration on the integrity of this structure was investigated. It was found that the initial cell shape change was mainly controlled by water dehydration, dependent on the cooling rate, resulting in the shrinkage of cells in the direction normal to the free surface. As the cooling was prolonged and temperature was lowered, further cell shape change could be induced by the chilling effects on intracellular proteins, and focal adhesions to the basement membrane. Quantitative analysis showed that the freezing induced dehydration greatly enhanced the cell surface stresses, especially in the axial direction. This could be one of the major causes of the final breaking of the cell junction and cell detachment.

Zhang, A.; Xu, L. X.; Sandison, G. A.; Cheng, S.

2006-12-01

382

Morphological study of endothelial cells during freezing.  

PubMed

Microvascular injury is recognized as a major tissue damage mechanism of ablative cryosurgery. Endothelial cells lining the vessel wall are thought to be the initial target of freezing. However, details of this injury mechanism are not yet completely understood. In this study, ECMatrix 625 was used to mimic the tumour environment and to allow the endothelial cells cultured in vitro to form the tube-like structure of the vasculature. The influence of water dehydration on the integrity of this structure was investigated. It was found that the initial cell shape change was mainly controlled by water dehydration, dependent on the cooling rate, resulting in the shrinkage of cells in the direction normal to the free surface. As the cooling was prolonged and temperature was lowered, further cell shape change could be induced by the chilling effects on intracellular proteins, and focal adhesions to the basement membrane. Quantitative analysis showed that the freezing induced dehydration greatly enhanced the cell surface stresses, especially in the axial direction. This could be one of the major causes of the final breaking of the cell junction and cell detachment. PMID:17110769

Zhang, A; Xu, L X; Sandison, G A; Cheng, S

2006-11-02

383

On the Freezing Process with Supercooling  

NASA Astrophysics Data System (ADS)

Experiments and statistical analysis were carried out to study the effect of cooling rate and surface area on freezing temperature of supercooled water attached to a heat transfer surface. Electrolytically polished copper disk was used and experiments were carried out under three kinds of fixed cooling rates (0.05K/s, 0.2K/s & 0.8K/s). In a case of experiments under high cooling rate, non-uniform temperature distribution existed on the surface, so the analytical method introduced in the former paper could not be applied. Hence another method was introduced here. The heat transfer surface was divided into a few parts so that in each part a temperature distribution on the surface kept uniform. The probability for the whole surface was taken as a combination of the probability for each part. By using this method, the probability of ice appearance within a unit surface area in unit time interval was calculated for each series of cooling rate. The results were compared and was observed that the probability of ice appearance was independent of the cooling rate and the area used for the experiment. Hence the reliability of using the method to predict the most probable freezing temperature of supercooled water introduced in this paper was clarified.

Saito, Akio; Okawa, Seiji; Tamaki, Atsushi

384

Immersion freezing of birch pollen washing water  

NASA Astrophysics Data System (ADS)

In the present study, the immersion freezing behavior of birch pollen, i.e. its ice nucleating active (INA) macromolecules, was investigated at the Leipzig Aerosol Cloud Interaction Simulator (LACIS). For that, washing water of two different birch pollen samples with different regional origin (Northern birch and Southern birch) were used. The immersion freezing of droplets generated from the pollen washing water was already observed at temperatures higher than -20 °C, for both samples. Main differences between the Northern birch pollen and the Southern birch pollen were obvious in a temperature range, between -18 °C and -24 °C, where the ice fraction increased with decreasing temperature. There, the Northern birch pollen washing water featured two different slopes, with one being steeper and one being similar to the slope of the Southern birch pollen washing water. As we assume single INA macromolecules being the reason for the ice nucleation, we concluded that the Northern birch pollen are able to produce at least two different types of INA macromolecules. We were able to determine the heterogeneous nucleation rates for both INA macromolecule types and so could explain the ice nucleation behavior of both, the Southern and the Northern birch pollen washing water.

Augustin, S.; Hartmann, S.; Pummer, B.; Grothe, H.; Niedermeier, D.; Clauss, T.; Voigtländer, J.; Tomsche, L.; Wex, H.; Stratmann, F.

2012-12-01

385

Vertically moored platform anchoring  

SciTech Connect

An improved system is disclosed for anchoring a floating vessel which is anchored only by parallel and essentially vertical conduits. The anchoring load is carried by units of concentric pipes including an outer riser pipe and inner strings of casing. Drilling wells and/or production of oil and gas or like operations are conducted through these casings. The tension of the inner casing string is transmitted to the floating vessel through the upper end of the outer riser pipe. The system prevents excessive buildup of stresses in the upper end of the inner casing due to the bending caused by excursions caused by the waves, the wind and the current.

Blenkarn, K.A.; Beynet, P.A.

1984-02-14

386

Freezing survival, body ice content and blood composition of the freeze-tolerant European common lizard, Lacerta vivipara.  

PubMed

To investigate the freeze tolerance of the European common lizard, Lacerta vivipara, we froze 17 individuals to body temperatures as low as -4 degrees C under controlled laboratory conditions. The data show that this species tolerates the freezing of 50% of total body water and can survive freezing exposures of at least 24-h duration. Currently, this represents the best known development of freeze tolerance among squamate reptiles. Freezing stimulated a significant increase in blood glucose levels (16.15+/- 1.73 micromol x ml(-1) for controls versus 25.06 +/- 2.92 micromol x ml(-1) after thawing) but this increase had no significant effect on serum osmolality which was unchanged between control and freeze-exposed lizards (506.0 +/- 23.8 mosmol x l(-1) versus 501.0 +/- 25.3 mosmol x l(-1), respectively). Tests that assessed the possible presence of antifreeze proteins in lizard blood were negative. Recovery at 5 degrees C after freezing was assessed by measurements of the mean time for the return of breathing (5.9 +/- 0.5 h) and of the righting reflex (44.8 +/- 4.5 h). Because this species hibernates in wet substrates inoculative freezing may frequently occur in nature and the substantial freeze tolerance of this lizard should play a key role in its winter survival. PMID:11824405

Voituron, Y; Storey, J M; Grenot, C; Storey, K B

2002-01-01

387

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

2011-04-28

388

Effect of long-term freezing and freeze-thaw cycles on indigenous and inoculated microorganisms in dewatered blackwater.  

PubMed

Wastewater treatment in many Arctic regions is inadequate, even nonexisting. Natural freezing of wastewater in those areas may be beneficial for reduction of microorganisms. The aim of this study was to investigate the effect of long-term freezing, and repeated freezing and thawing, on indigenous coliforms, fecal streptococci, and antibiotic-resistant (AR) bacteria, and inoculated Salmonella Enteriditis and E. coli bacteriophage ?X174 in dewatered blackwater. At the end of the long-term freezing experiment (10 months), an MPN recovery study was done, including the microbial groups that had shown the largest reduction, using tryptone soy broth at incubation temperatures of 10 and 20 °C overnight for the coliforms and AR bacteria, and buffered peptone water at incubation temperature of 37 °C for 18-20 h for Salmonella. Fecal streptococci were more resistant to long-term freezing than the coliform group. Total number of AR bacteria decreased slowly but constantly over the 10-month freezing period. Salmonella rapidly decreased and were nondetectable within a week but exhibited some recovery after 10 months of freezing, whereas limited or no recovery of coliforms and AR-bacteria was detected. Bacteriophages showed limited reduction during the long-term freezing. Repeated freezing and thawing increased the reduction of all tested microbial groups markedly. PMID:23113759

Gunnarsdóttir, Ragnhildur; Müller, Karoline; Jensen, Pernille Erland; Jenssen, Petter Deinboll; Villumsen, Arne

2012-11-05

389

Gradient waveform synthesis for magnetic propulsion using MRI gradient coils  

NASA Astrophysics Data System (ADS)

Navigating an untethered micro device in a living subject is of great interest for both diagnostic and therapeutic applications. Magnetic propulsion of an untethered device carrying a magnetic core in it is one of the promising methods to navigate the device. MRI gradients coils are thought to be suitable for navigating the device since they are capable of magnetic propulsion in any direction while providing magnetic resonance images. For precise navigation of the device, especially in the peripheral region of the gradient coils, the concomitant gradient fields, as well as the linear gradient fields in the main magnetic field direction, should be considered in driving the gradient coils. For simple gradient coil configurations, the Maxwell coil in the z-direction and the Golay coil in the x- and y-directions, we have calculated the magnetic force fields, which are not necessarily the same as the conventional linear gradient fields of MRI. Using the calculated magnetic force fields, we have synthesized gradient waveforms to navigate the device along a desired path.

Han, B. H.; Park, S.; Lee, S. Y.

2008-09-01

390

Gradient waveform synthesis for magnetic propulsion using MRI gradient coils.  

PubMed

Navigating an untethered micro device in a living subject is of great interest for both diagnostic and therapeutic applications. Magnetic propulsion of an untethered device carrying a magnetic core in it is one of the promising methods to navigate the device. MRI gradients coils are thought to be suitable for navigating the device since they are capable of magnetic propulsion in any direction while providing magnetic resonance images. For precise navigation of the device, especially in the peripheral region of the gradient coils, the concomitant gradient fields, as well as the linear gradient fields in the main magnetic field direction, should be considered in driving the gradient coils. For simple gradient coil configurations, the Maxwell coil in the z-direction and the Golay coil in the x- and y-directions, we have calculated the magnetic force fields, which are not necessarily the same as the conventional linear gradient fields of MRI. Using the calculated magnetic force fields, we have synthesized gradient waveforms to navigate the device along a desired path. PMID:18695296

Han, B H; Park, S; Lee, S Y

2008-08-11

391

Torsional nystagmus during vertical pursuit.  

PubMed

We examined three patients with cavernous angioma within the middle cerebellar peduncle. Each patient had an unusual ocular motor finding: the appearance of a strong torsional nystagmus during vertical pursuit. The uncalled-for torsion changed direction when vertical pursuit changed direction. In one patient, we recorded eye movements with the magnetic field technique using a combined direction and torsion eye coil. The slow-phase velocity of the inappropriate torsional nystagmus was linearly related to the slow-phase velocity of vertical smooth pursuit, and changed direction when vertical pursuit changed direction. This torsional nystagmus also appeared during fixation suppression of the vertical vestibulo-ocular reflex (VOR), but was minimal during vertical head rotation when fixing a stationary target in the light. We suggest that inappropriately directed eye movements during pursuit might be another ocular motor sign of cerebellar dysfunction. Furthermore, we speculate that the signals used for vertical smooth pursuit are, at some stage, encoded in a semicircular canal VOR coordinate framework. To illustrate, for the vertical semicircular canals, vertical and torsional motion are combined on the same cells, with the anterior semicircular canals mediating upward movements and the posterior semicircular canals mediating downward movements. For the right labyrinth, however, both vertical semicircular canals produce clockwise slow phases (ipsilateral eye intorts, contralateral eye extorts). The opposite is true for the vertical semicircular canals in the left labyrinth; counterclockwise slow phases are produced. Hence, to generate a pure vertical VOR, the anterior or posterior semicircular canals on both sides of the head must be excited so that opposite-directed torsional components cancel. Thus, if pursuit were organized in a way similar to the VOR, pure vertical pursuit would require that oppositely-directed torsional components cancel in normals. If this did not happen, a residual torsional nystagmus could appear during attempted vertical pursuit. PMID:8797162

FitzGibbon, E J; Calvert, P C; Dieterich, M; Brandt, T; Zee, D S

1996-06-01

392

Embolism formation during freezing in the wood of Picea abies.  

PubMed

Freeze-thaw events can cause embolism in plant xylem. According to classical theory, gas bubbles are formed during freezing and expand during thawing. Conifers have proved to be very resistant to freeze-thaw induced embolism, because bubbles in tracheids are small and redissolve during thawing. In contrast, increasing embolism rates upon consecutive freeze-thaw events were observed that cannot be explained by the classical mechanism. In this study, embolism formation during freeze-thaw events was analyzed via ultrasonic and Cryo-scanning electron microscope techniques. Twigs of Picea abies L. Karst. were subjected to up to 120 freeze-thaw cycles during which ultrasonic acoustic emissions, xylem temperature, and diameter variations were registered. In addition, the extent and cross-sectional pattern of embolism were analyzed with staining experiments and Cryo-scanning electron microscope observations. Embolism increased with the number of freeze-thaw events in twigs previously dehydrated to a water potential of -2.8 MPa. In these twigs, acoustic emissions were registered, while saturated twigs showed low, and totally dehydrated twigs showed no, acoustic activity. Acoustic emissions were detected only during the freezing process. This means that embolism was formed during freezing, which is in contradiction to the classical theory of freeze-thaw induced embolism. The clustered pattern of embolized tracheids in cross sections indicates that air spread from a dysfunctional tracheid to adjacent functional ones. We hypothesize that the low water potential of the growing ice front led to a decrease of the potential in nearby tracheids. This may result in freezing-induced air seeding. PMID:17041033

Mayr, Stefan; Cochard, Hervé; Améglio, Thierry; Kikuta, Silvia B

2006-10-13

393

Inclusion of velocity gradients in the Unno solution for magnetic field diagnostic from spectropolarimetric data  

NASA Astrophysics Data System (ADS)

We present an extension of the Unno-Rachkovsky solution that provides the theoretical profiles coming out of a Milne-Eddington atmosphere imbedded in a magnetic field, to the additional taking into account of a vertical velocity gradient. Thus, the theoretical profiles may display asymmetries as do the observed profiles, which facilitates the inversion based on the Unno-Rachkovsky theory, and leads to the additional determination of the vertical velocity gradient. We present UNNOFIT inversion on spectropolarimetric data performed on an active region of the Sun with the french-italian telescope THEMIS operated by CNRS and CNR on the island of Tenerife.

Molodij, Guillaume; Bommier, Véronique

2011-06-01

394

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

395

A one-dimensional model of vertical stratification of Lake Shira focussed on winter conditions and ice cover  

Microsoft Academic Search

In meromictic lakes such as Lake Shira, horizontal inhomogeneity is small in comparison with vertical gradients. To determine\\u000a the vertical distribution of temperature, salinity, and density of water in a deep zone of a Lake Shira, or other saline lakes,\\u000a a one-dimensional (in vertical direction) mathematical model is presented. A special feature of this model is that it takes\\u000a into

S. N. Genova; V. M. Belolipetskii; D. Y. Rogozin; A. G. Degermendzhy; W. M. Mooij

2010-01-01

396

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

397

Small scale gradient effects on isopods (Crustacea: Oniscidea) in karstic sinkholes  

Microsoft Academic Search

We studied abundance and diversity patterns of terrestrial isopod assemblages along a ‘micro-scale’ vertical gradient in sinkholes\\u000a in the Aggtelek National Park, Hungary. Time restricted manual sampling yielded ten native species, including endemic and\\u000a rare ones. Along the gradient we found no major differences in species richness and -composition, and abundance decreased\\u000a from the bottoms to the upper zones of

Ferenc Vilisics; Péter Sólymos; Antal Nagy; Roland Farkas; Zita Kemencei; Elisabeth Hornung

2011-01-01

398

Bacterial Community Composition in Lake Tanganyika: Vertical and Horizontal Heterogeneity  

PubMed Central

Vertical and latitudinal differences in bacterial community composition (BCC) in Lake Tanganyika were studied during the dry season of 2002 by means of denaturing gradient gel electrophoresis analysis of PCR-amplified 16S RNA fragments. Dominant bands were sequenced and identified as members of the Cyanobacteria, Actinobacteria, Nitrospirae, green nonsulfur bacteria, and Firmicutes divisions and the Gamma- and Deltaproteobacteria subdivisions. The BCC in the lake displayed both vertical and latitudinal variation. Vertical changes in BCC were related to the thermal water column stratification, which influences oxygen and nutrient concentrations. Latitudinal variation was related to upwelling of deep water and increased primary production in the south of the lake. The number of bands per sample increased with bacterial production in the epilimnion of the lake, suggesting a positive diversity-productivity relationship.

De Wever, Aaike; Muylaert, Koenraad; Van der Gucht, Katleen; Pirlot, Samuel; Cocquyt, Christine; Descy, Jean-Pierre; Plisnier, Pierre-Denis; Vyverman, Wim

2005-01-01

399

Geothermal gradient map of Colorado  

SciTech Connect

Reported bottom hole temperatures (BHT) were taken from 12,000 oil and gas wells provided by the Colorado Oil and Gas Conservation Commission files. Average annual surface temperatures were subtracted from the BHT and then divided by the depth to give a gradient. To eliminate as many sources of error as possible, the gradient values were averaged for each township and contoured.

Repplier, F.N.; Fargo, R.L.

1981-01-01

400

Geothermal gradient map of Colorado  

Microsoft Academic Search

Reported bottom hole temperatures (BHT) were taken from 12,000 oil and gas wells provided by the Colorado Oil and Gas Conservation Commission files. Average annual surface temperatures were subtracted from the BHT and then divided by the depth to give a gradient. To eliminate as many sources of error as possible, the gradient values were averaged for each township and

F. N. Repplier; R. L. Fargo

1981-01-01

401

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

402

Multilayer High-Gradient Insulators  

SciTech Connect

Multilayer High-Gradient Insulators are vacuum insulating structures composed of thin, alternating layers of dielectric and metal. They are currently being developed for application to high-current accelerators and related pulsed power systems. This paper describes some of the High-Gradient Insulator research currently being conducted at Lawrence Livermore National Laboratory.

Harris, J R

2006-08-16

403

Ponds Freeze in Winter -- Why Doesn't the Ocean?  

NSDL National Science Digital Library

In this activity, learners explore how salt water freezes in comparison to fresh water. Use this experiment to consider how pond animals survive cold winters in comparison to animals that live in the ocean. This resource includes information about freezing points as well as examples of how different animals respond to the winter cold.

Aquarium, New E.

2011-01-01

404

Freezing of Random and Designed Heteropolymers: Replica Solution Without Replicas  

Microsoft Academic Search

The freezing transition of heteropolymers is an interesting physical phenomenon with implications for protein folding. The Random Energy Model (REM) has been used to model this transition and has been previously derived using the replica trick directly from the nature of interactions between monomers. In this talk, we present an alternative approach to derive the freezing transition, reproducing the results

Vijay S. Pande; Alexander Yu. Grosberg; Toyoichi Tanaka

1996-01-01

405

TOPICAL REVIEW: Confinement effects on freezing and melting  

Microsoft Academic Search

A review of experimental work on freezing and melting in confinement is presented. A range of systems, from metal oxide gels to porous glasses to novel nanoporous materials, is discussed. Features such as melting-point depression, hysteresis between freezing and melting, modifications to bulk solid structure and solid-solid transitions are reviewed for substances such as helium, organic fluids, water and metals.

Hugo K. Christenson

2001-01-01

406

Heat of Freezing and Melting of Sea Ice.  

National Technical Information Service (NTIS)

Computations are presented which show that the latent heat of freezing ice in equilibrium with sea water is less than that associated with freezing pure water at 0C. The difference is due primarily to a temperature effect that is opposed to some extent by...

D. Anderson

1966-01-01

407

Terrorist asset-freezing – Continuing flaws in the current scheme  

Microsoft Academic Search

The Terrorist Asset-Freezing etc Act 2010 came into force on 17 December 2010. The 2010 Act repealed the previous Temporary Provisions Act. This article does not purport to provide comprehensive coverage of the Act; it outlines four main areas of concern that arose in respect of the Draft Terrorist Asset-Freezing Bill and that now arise in respect of the Terrorist

Adam Tomkins; Helen Fenwick; Liora Lazarus

2011-01-01

408

Freeze concentration of sugarcane juice in a jaggery making process  

Microsoft Academic Search

A heat pump based Freeze Concentration System (FCS) is proposed to concentrate sugarcane juice from 20 to 40 Brix in a jaggery making process. Further concentration of the juice is carried out in a boiling pan. Inclusion analysis is carried out to estimate sucrose loss in the ice formed in a layer freezing process. A mathematical model is developed taking

Milind V. Rane; Siddharth K. Jabade

2005-01-01

409

Standard Reference Material 1744: Aluminum Freezing-Point Standard.  

National Technical Information Service (NTIS)

The freezing point of aluminum (660.323 deg. C) is a defining fixed point of the International Temperature Scale of 1990 (ITS-90). Realization of this freezing point is performed using a fixed-point cell containing high purity (greater than or equal to 99...

G. F. Strouse

1995-01-01

410

Freeze-Drying Process to Avoid Resist Pattern Collapse  

Microsoft Academic Search

Freeze-drying, which is a surface-tension-free process, was applied in resist processing to avoid resist pattern collapse and the mechanism was investigated. The freeze-drying, in which tert-butylalcohol was used, prevents resist patterns from collapsing. The driving force of collapse is surface tension of the rinsing liquid.

Toshihiko Tanaka; Mitsuaki Morigami; Hiroaki Oizumi; Taro Ogawa

1993-01-01

411

Some Factors Affecting the Freezing Point of Milk1  

Microsoft Academic Search

The freezing point of milk has served for over 30 years as an official method (2) for detecting adulteration of milk with added water. Current investigations (4, 7, 10) have indicated that the present standard of - 0.550 ° C. is too low for the average freezing point of milk, and that average values frequently fall be- tween -- 0.535

I. Sato; C. L. Hankinson; I. A. Gould; T. V. Armstrong

1957-01-01

412

Analysis of stresses during the freezing of solid spherical foods  

Microsoft Academic Search

An analytical model is presented to calculate thermal stresses and strains during the freezing of a spherical food, taking into account both the expansion during phase change and subsequent thermal contraction due to temperature decrease. The Young modulus and Poisson ratio are assumed to undergo a step change at the freezing point. The expansion due to phase change cause a

Q. Tuan Pham; Alain Le Bail; Brice Tremeac

2006-01-01

413

Stabilization of Lipid Bilayer Vesicles by Sucrose during Freezing  

Microsoft Academic Search

The freeze-induced fusion and leakage of small unilamellar vesicles (SUV) of natural and synthetic phosphatidylcholines and the suppression of these processes by sucrose was studied by electron microscopy, by high-resolution NMR, and by ESR techniques. During slow freezing of SUV suspensions in water, the lipid was compressed into a small interstitial volume and transformed into a multilamellar aggregate without vesicular

G. Strauss; H. Hauser

1986-01-01

414

Corn Seed Germination and Vigor Following Freezing during Seed Development  

Microsoft Academic Search

The potential for an early autumn frost to reduce corn (Zea mays L.) seed quality is a concern for seed producers. This study evaluated the effect of freezing rate, freezing temperature (26, 211C) and duration (4, 6 h), ear attachment, and endosperm composition on seed germination and vigor (accelerated aging (AA) and cold test) during seed development and maturation of

James Woltz; Dennis M. TeKrony; Dennis B. Egli

2006-01-01

415

Factors Affecting the Quality of Freeze-Dried Green Beans.  

National Technical Information Service (NTIS)

The effect of extended blanching, sulfiting and packaging on the quality of freeze-dried green beans prepared from commercially frozen products and stored for six months at 100F were investigated. Results indicated that acceptable freeze-dried green beans...

A. R. Rahman G. R. Taylor K. Miller K. R. Johnson

1969-01-01

416

Adaptive Control of Freeze-Form Extrusion Fabrication Processes (Preprint).  

National Technical Information Service (NTIS)

Freeze-form Extrusion Fabrication (FEF) is an additive manufacturing process that extrudes high solids loading aqueous ceramic pastes in a layer-by- layer fashion below the paste freezing temperature for component fabrication. Due to effects such as the a...

M. C. Leu R. G. Landers X. Zhao

2008-01-01

417

Freezing-Thawing Processes in Glass Fiber Board  

Microsoft Academic Search

For the prevention of vapor condensation and accompanying damage in cold regions, the behavior of water and ice in porous materials should be understood. In this study, experiments on the freezing-thawing processes in a glass fiber board, which is a typical insu lation, were conducted. The freezing-thawing processes were analyzed with the use of si multaneous heat and moisture transfer

S. Hokoi; M. Hatano; M. Matsumoto; M. K. Kumaran

2000-01-01

418

Freeze-drying of filamentous fungi and yeasts  

Microsoft Academic Search

The aim of this thesis was to optimize the freeze-drying protocol for fungi in general and for those genera that do not survive this preservation method, in particular. To this end, the influence of the cooling rate, the lyoprotectant and the drying process itself was examined. Since most fungi belong to the Basidiomycota and Ascomycota, this thesis focused on freeze-drying

C. S. Tan

2011-01-01

419

Promising freeze protection alternatives in solar domestic hot water systems  

Microsoft Academic Search

Since the gains associated with solar thermal energy technologies are comparatively small in relation to the required capital investment, it is vital to maximize conversion efficiency. While providing the necessary function of freeze protection, the heat exchanger commonly included in solar domestic water heating systems represents a system inefficiency. This thesis explores two alternate methods of providing freeze protection without

1997-01-01

420

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...

421

A simple model for freezing rain ice loads  

Microsoft Academic Search

There are many models for hindcasting ice loads from meteorological data measured during freezing rain storms. Each model is based on the physics of the ice accretion process and on empirical observations. However, these models predict significantly different ice loads for the same freezing rain storm, making it difficult to use model results to determine design ice loads. In this

Kathleen F Jones

1998-01-01

422

Does Hot Water Freeze Faster Than Cold Water?  

NSDL National Science Digital Library

In this activity, conduct an experiment to find out if hot water can actually freeze faster than cold water. Investigate how impurities affect the freezing rate of varying temperatures of water. This activity guide includes a step-by-step instructional video.

Center, Saint L.

2013-01-17

423

The role of seawater freezing in the formation of subsurface brines  

NASA Astrophysics Data System (ADS)

Several mechanisms (evaporation, water-rock interaction, ultra-filtration) have been suggested to explain the evolution of ubiquitous Ca-chloride subsurface brines. In the present paper, the freezing of seawater in polar regions, and in even wider areas during glacial periods, is proposed as an additional possible path of brine formation. Four detailed seawater freezing experiments to -14°C (resulting in a concentration factor of about 5) were carried out, and Na, K, Ca, Mg, Sr, Cl, SO 4, and Br were analysed in the residual brines and in the ice. Br and Sr, whose behavior during the freezing of seawater is reported here for the first time, show a conservative behavior throughout the studied temperature range. Our data and earlier literature show that the high salinities, which are common in subsurface brines (>300 g/l), may be obtained by the removal of H 2O as ice in the primary glacial environment. The decrease in the Na/Cl ratio is caused by the crystallization of mirabilite (Na 2SO 4 · 10H 2O), supplemented by hydrohalite (NaCl · 2H 2O). Sulfate is removed both in mirabilite and by bacterial reduction. The brine then migrates to the subsurface, heats-up under the local geothermal gradient, and interacts with the adjacent rocks. At this stage, it may be diluted by meteoric waters, its Mg/Ca ratio decreases (dolomitization and chloritization), the SO 4/Cl ratio varies according to the local gypsum-anhydrite equilibrium conditions, and the Ca/(SO 4 + HCO 3) ratio increases as a result of dolomitization or chloritization. The interaction with rocks in the subsurface may affect both the original 87Sr /86Sr and the 18O /16O ratios of the brine. Although several of the processes which lead to the formation of Ca-chloride brines are common for both the evaporative and the freezing models, the Na-Br-Cl relationship in a given brine can be used to discriminate between the two modes of brine evolution. Several subsurface brines from the Canadian Shield and one brine from Finland are used as examples of the seawater freezing model, and an explanation is proposed for the necessary mass production of brines in glacial environments.

Herut, Barak; Starinsky, Avraham; Katz, Amitai; Bein, Amos

1990-01-01

424

Responses to freezing exposure of hatchling turtles Trachemys scripta elegans: factors influencing the development of freeze tolerance by reptiles.  

PubMed

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 degrees C. At -2.5 degrees C, survival declined to 50% after 6 h of freezing and no animals recovered after 24 h or longer, when mean ice content reached 54.7 +/- 1.4% of total body water. At -4 degrees C, all turtles recovered from 4 h of freezing exposure with a mean ice content of 49.6 +/- 2.4%, but survival dropped sharply thereafter with no animals recovering after 8 h, when ice content had reached 64.5 +/- 0.7%. Survival times were substantially shorter and percentage ice values greater than comparable values for hatchling painted turtles (Chrysemys picta (Schneider)) from northern populations subjected to identical freezing exposures. The ability to synthesize cryoprotectants in response to freezing was poorly developed in T. s. elegans; maximal accumulation of glucose was only 3.2 mumol g-1 wet mass in liver. Lactate content increased two- to threefold in oxygen-sensitive organs (heart and brain) during freezing, but levels of lactate and other putative cryoprotectants were unchanged in other organs. Total free amino acid content rose significantly in liver, muscle and blood during freezing; increased taurine concentration was primarily responsible for the changes in liver and blood. The capacity for freezing survival by T. s. elegans hatchlings from southern populations would be of limited use for hibernation in a cold climate, but the metabolic responses to freezing displayed by these animals might be enhanced by northern populations to increase their freeze tolerance. PMID:1634864

Churchill, T A; Storey, K B

1992-06-01

425

Study of Multi-Phase Ejectors for Freezing Process Desalination Systems.  

National Technical Information Service (NTIS)

A theoretical study was made of freezing process Multiple-Phase Ejector (MPE) desalination systems. To establish a baseline, an ideal reversible freezing process desalination system was compared to the ideal direct contact freezing MPE desalination system...

C. A. Kemper G. F. Harper S. William Gouse J. H. Leigh

1964-01-01

426

14 CFR 25.1455 - Draining of fluids subject to freezing.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 2013-01-01 false Draining of fluids subject to freezing. 25.1455 Section 25...Miscellaneous Equipment § 25.1455 Draining of fluids subject to freezing. If fluids subject to freezing may be drained...

2013-01-01

427

Observation of picometer vertical emittance with a vertical undulator.  

PubMed

Using a vertical undulator, picometer vertical electron beam emittances have been observed at the Australian Synchrotron storage ring. An APPLE-II type undulator was phased to produce a horizontal magnetic field, which creates a synchrotron radiation field that is very sensitive to the vertical electron beam emittance. The measured ratios of undulator spectral peak heights are evaluated by fitting to simulations of the apparatus. With this apparatus immediately available at most existing electron and positron storage rings, we find this to be an appropriate and novel vertical emittance diagnostic. PMID:23215388

Wootton, K P; Boland, M J; Dowd, R; Tan, Y-R E; Cowie, B C C; Papaphilippou, Y; Taylor, G N; Rassool, R P

2012-11-08

428

Observation of Picometer Vertical Emittance with a Vertical Undulator  

NASA Astrophysics Data System (ADS)

Using a vertical undulator, picometer vertical electron beam emittances have been observed at the Australian Synchrotron storage ring. An APPLE-II type undulator was phased to produce a horizontal magnetic field, which creates a synchrotron radiation field that is very sensitive to the vertical electron beam emittance. The measured ratios of undulator spectral peak heights are evaluated by fitting to simulations of the apparatus. With this apparatus immediately available at most existing electron and positron storage rings, we find this to be an appropriate and novel vertical emittance diagnostic.

Wootton, K. P.; Boland, M. J.; Dowd, R.; Tan, Y.-R. E.; Cowie, B. C. C.; Papaphilippou, Y.; Taylor, G. N.; Rassool, R. P.

2012-11-01

429

Facile Route to Vertically Aligned High-Aspect Ratio Block Copolymer Films via Dynamic Zone Annealing  

NASA Astrophysics Data System (ADS)

Directed assembly of block copolymers (BCP) can be used to fabricate a diversity of nanostructures useful for nanotech applications. The ability to vertically orient etchable high aspect ratio (˜30) ordered BCP domains on flexible substrates via continuous processing methods are particularly attractive for nanomanufacturing. We apply sharp dynamic cold zone annealing (CZA-S) to create etchable, and predominantly vertically oriented 30nm cylindrical domains in 1 ?m thick poly(styrene-b-methylmethacrylate) films on low thermal conductivity rigid (quartz) and flexible (PDMS & Kapton) substrates. Under similar static conditions, temporally stable vertical cylinders form within a narrow zone above a critical temperature gradient. Primary ordering mechanism of CZA-S involves sweeping this vertically orienting zone created at maximum thermal gradient. An optimal speed is needed since the process competes with preferential surface wetting dynamics that favors parallel orientation. GISAXS of etched BCP films confirms internal morphology.

Singh, Gurpreet; Kulkarni, Manish; Yager, Kevin; Smilgies, Detlef; Bucknall, David; Karim, Alamgir

2012-02-01

430

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

431

Gradient elution in capillary electrochromatography.  

PubMed

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 submicroliter per minute 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-?m 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) [Formula: see text] one providing an increasing ramp and the other providing a decreasing ramp [Formula: see text] 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 was separated in less than 90 min. 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. PMID:21619344

Yan, C; Dadoo, R; Zare, R N; Rakestraw, D J; Anex, D S

1996-09-01

432

Two features at the two-dimensional freezing transitions.  

PubMed

We studied the two-dimensional freezing transitions in monolayers of microgel colloidal spheres with short-ranged repulsions in video-microscopy experiments, and monolayers of hard disks, and Yukawa particles in simulations. These systems share two common features at the freezing points: (1) the bimodal distribution profile of the local orientational order parameter; (2) the two-body excess entropy, s(2), reaches -4.5±0.5?k(B). Both features are robust and sensitive to the freezing points, so that they can potentially serve as empirical freezing criteria in two dimensions. Compared with the conventional freezing criteria, the first feature has no finite-size ambiguities and can be resolved adequately with much less statistics; and the second feature can be directly measured in macroscopic experiments without the need for microscopic information. PMID:21261367

Wang, Ziren; Qi, Weikai; Peng, Yi; Alsayed, Ahmed M; Chen, Yong; Tong, Penger; Han, Yilong

2011-01-21

433

MHD modeling of the double-gradient (kink) magnetic instability  

NASA Astrophysics Data System (ADS)

The paper presents the detailed numerical investigation of the "double-gradient mode," which is believed to be responsible for the magnetotail flapping oscillations—the fast vertical (normal to the layer) oscillations of the Earth's magnetotail plasma sheet with a quasiperiod ˜100-200 s. The instability is studied using the magnetotail near-equilibrium configuration. For the first time, linear three-dimensional numerical analysis is complemented with full 3-D MHD simulations. It is known that the "double-gradient mode" has unstable solutions in the region of the tailward growth of the magnetic field component, normal to the current sheet. The unstable kink branch of the mode is the focus of our study. Linear MHD code results agree with the theory, and the growth rate is found to be close to the peak value, provided by the analytical estimates. Full 3-D simulations are initialized with the numerically relaxed magnetotail equilibrium, similar to the linear code initial condition. The calculations show that current layer with tailward gradient of the normal component of the magnetic field is unstable to wavelengths longer than the curvature radius of the field line. The segment of the current sheet with the earthward gradient of the normal component makes some stabilizing effect (the same effect is registered in the linearized MHD simulations) due to the minimum of the total pressure localized in the center of the sheet. The overall growth rate is close to the theoretical double-gradient estimate averaged over the computational domain.

Korovinskiy, D. B.; Divin, A.; Erkaev, N. V.; Ivanova, V. V.; Ivanov, I. B.; Semenov, V. S.; Lapenta, G.; Markidis, S.; Biernat, H. K.; Zellinger, M.

2013-03-01

434

Comp aratrve Ultrastructure of Fat Body Cells of Freeze-susceptible and Freeze-tolerant Eurosta solidaginis Larvae After Chemical Fixation and High Pressure Freezing  

Microsoft Academic Search

Cold-hard- ening includes the elevation of the supercooling point, the temperature at which body water spontaneously freezes, and the accumulation of the low-molecular-mass cryoprotectants, glycerol, sorbitol and trehalose. Although it is generally believed that freezing survival is only possible if the ice lattice is restricted to the extracellular space, the larval fat body cells survive intracellular ice formation. Fat body

R. TODD MORASON; ALLAN L. ALLENSPACH; RICHARD E. LEE JR

435

Gradient zone boundary control in salt gradient solar ponds  

DOEpatents

A method and apparatus for suppressing zone boundary migration in a salt gradient solar pond includes extending perforated membranes across the pond at the boundaries, between the convective and non-convective zones, the perforations being small enough in size to prevent individual turbulence disturbances from penetrating the hole, but being large enough to allow easy molecular diffusion of salt thereby preventing the formation of convective zones in the gradient layer. The total area of the perforations is a sizable fraction of the membrane area to allow sufficient salt diffusion while preventing turbulent entrainment into the gradient zone.

Hull, John R. (Downers Grove, IL)

1984-01-01

436

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

437

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.

438

The Importance of Slag Engineering in Freeze-Lining Applications  

NASA Astrophysics Data System (ADS)

Freeze linings are frequently used to protect the reactor wall in pyrometallurgical processes. In order to minimize reactor wall corrosion, the stability of a freeze lining has to be guaranteed. To illustrate the importance of slag engineering in the optimization of freeze-lining behavior, the freeze-lining formation of six synthetic lead slags is studied. Lab-scale freeze linings are obtained using a cooled-probe technique and their microstructures are characterized using light optical microscopy (LOM) and microprobe analysis. The results show that slag engineering can have a major impact on the operative freeze-lining formation mechanisms. Some slag properties found to affect the freeze-lining formation are the viscosity, the temperature stability range of the relevant phases, the type of phases that form (interlocking or not), and the crystallization behavior of the slag. The operational demands of a protective freeze lining are defined by the authors as follows: (1) a rapid formation to limit the contact between the reactor wall and the corrosive bath material and (2) a sufficient stability during changes in heat input from the bath and in bath composition. From the comparison of the microstructural features of the freeze linings formed with the studied slags, it is concluded that these demands can be fulfilled with the growth of an initial layer dominated by the presence of interlocking crystals in combination with the subsequent formation of a high-melting crystalline layer at the bath-freeze-lining interface, which is in equilibrium with the slag bath and the composition of which differs sufficiently from the bath composition.

Campforts, Mieke; Blanpain, Bart; Wollants, Patrick

2009-10-01

439

Spray freezing into liquid versus spray-freeze drying: Influence of atomization on protein aggregation and biological activity  

Microsoft Academic Search

Protein aggregation and enzyme activity were compared for reconstituted lysozyme particles produced by two cryogenic technologies, spray freezing into liquid (SFL) and spray-freeze drying (SFD). The particles were characterized by enzyme activity measurements, scanning electron microscopy (SEM), light scattering, X-ray photoelectron spectroscopy (XPS) and BET specific surface area analysis. Highly porous microparticle aggregates of protein nanoparticles, observed by SEM, were

Zhongshui Yu; Keith P. Johnston; Robert O. Williams III

2006-01-01

440

Effects of freezing rates and cryoprotectant on thermal expansion of articular cartilage during freezing process.  

PubMed

The intact articular cartilage has not yet been successfully preserved at low temperature most likely due to the volume expansion from water to ice during freezing. The objective of this current study focuses on examining thermal expansion behavior of articular cartilage (AC) during freezing from 0 degree C to -100 degree C. Thermo Mechanical Analysis (TMA) was used to investigate the effects of different concentrations of dimethyl sulphoxide (DMSO) (0%, 10%, 30% and 60% v/v) and different freezing rates (1 C/min, 3 C/min and 5 C/min). The results showed that: (1) the inhomogeneous thermal expansion (or contraction) presents due to inhomogeneous water distributions in articular cartilage during freezing, which also may be the most likely reason that the matrix has been damaged in cryopreserved intact articular cartilage; (2) at the phase transition temperature range, the maximum thermal strain change value for 5C/min is approximately 1.45 times than that for 1 C/min, but the maximum thermal expansion coefficient of the later is about six times than that of the former; (3) the thermal expansion coefficient decreases with increasing cooling rate at the unfrozen temperature region, but some opposite results are obtained at the frozen temperature region; (4) the higher the DMSO concentration is, at the phase change temperature region, the smaller the thermal strain change as well as the maximum thermal expansion coefficient are, but DMSO concentration exhibits little effect on the thermal expansion coefficient at both unfrozen and frozen region. Once the DMSO concentration increasing enough, e.g. 60% v/v, the thermal strain decreases linearly and smoothly without any abrupt change due to little or no ice crystal forms (i.e. vitrification) in frozen articular cartilage. This study may improve our understanding of the thermal expansion (or contraction) behavior of cryopreserved articular cartilage and it may be useful for the future study on cryopreservation of intact articular cartilage. PMID:23995399

Xu, Y; Sun, H J; Lv, Y; Zou, J C; Lin, B L; Hua, T C

441

Dynamics of geckos running vertically  

Microsoft Academic Search

Geckos with adhesive toe pads rapidly climb even smooth vertical surfaces. We challenged geckos (Hemidactylus garnotii) to climb up a smooth vertical track that contained a force platform. Geckos climbed vertically at up to 77·cm·s -1 with a stride frequency of 15·Hz using a trotting gait. During each step, whole body fore-aft, lateral and normal forces all decreased to zero

K. Autumn; S. T. Hsieh; D. M. Dudek; J. Chen; C. Chitaphan; R. J. Full

2006-01-01

442

Coupled resonator vertical cavity laser  

SciTech Connect

The monolithic integration of coupled resonators within a vertical cavity laser opens up new possibilities due to the unique ability to tailor the interaction between the cavities. The authors report the first electrically injected coupled resonator vertical-cavity laser diode and demonstrate novel characteristics arising from the cavity coupling, including methods for external modulation of the laser. A coupled mode theory is used model the output modulation of the coupled resonator vertical cavity laser.

Choquette, K.D.; Chow, W.W.; Hou, H.Q.; Geib, K.M.; Hammons, B.E.

1998-01-01

443

30.VERTIGO AND VERTICALITY IN  

Microsoft Academic Search

The vertical dimension is crucial to Super Monkey Ball on all levels1, and invites us to meditate on vertigo and verticality, falling and failing in the construc- tion of space and game-play in this game and in comput- er-games as such. In Super Monkey Ball, the vertical dimension should be mastered (landing on tiny islands with the ball glider), avoided

Troels Degn Johansson

444

4. VIEW OF VERTICAL BORING MACHINE. (Bullard) Vertical turning lathe ...  

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

4. VIEW OF VERTICAL BORING MACHINE. (Bullard) Vertical turning lathe (VTL). Machining the fixture for GE Turboshroud. G.S. O'Brien, operator. - Juniata Shops, Machine Shop No. 1, East of Fourth Avenue at Third Street, Altoona, Blair County, PA

445

Temperature versus salinity gradients below the ocean mixed layer  

NASA Astrophysics Data System (ADS)

We characterize the global ocean seasonal variability of the temperature versus salinity gradients in the transition layer just below the mixed layer using observations of conductivity temperature and depth and profiling float data from the National Ocean Data Center's World Ocean Data set. The balance of these gradients determines the temperature versus salinity control at the mixed layer depth (MLD). We define the MLD as the shallowest of the isothermal, isohaline, and isopycnal layer depths (ITLD, IHLD, and IPLD), each with a shared dependence on a 0.2°C temperature offset. Data are gridded monthly using a variational technique that minimizes the squared analysis slope and data misfit. Surface layers of vertically uniform temperature, salinity, and density have substantially different characteristics. By examining differences between IPLD, ITLD, and IHLD, we determine the annual evolution of temperature or salinity or both temperature and salinity vertical gradients responsible for the observed MLD. We find ITLD determines MLD for 63% and IHLD for 14% of the global ocean. The remaining 23% of the ocean has both ITLD and IHLD nearly identical. It is found that temperature tends to control MLD where surface heat fluxes are large and precipitation is small. Conversely, salinity controls MLD where precipitation is large and surface heat fluxes are small. In the tropical ocean, salinity controls MLD where surface heat fluxes can be moderate but precipitation is very large and dominant.

Helber, Robert W.; Kara, A. Birol; Richman, James G.; Carnes, Michael R.; Barron, Charlie N.; Hurlburt, Harley E.; Boyer, Timothy

2012-05-01

446

Light gradients and optical microniches in coral tissues.  

PubMed

Light quantity and quality are among the most important factors determining the physiology and stress response of zooxanthellate corals. Yet, almost nothing is known about the light field that Symbiodinium experiences within their coral host, and the basic optical properties of coral tissue are unknown. We used scalar irradiance microprobes to characterize vertical and lateral light gradients within and across tissues of several coral species. Our results revealed the presence of steep light gradients with photosynthetically available radiation decreasing by about one order of magnitude from the tissue surface to the coral skeleton. Surface scalar irradiance was consistently higher over polyp tissue than over coenosarc tissue in faviid corals. Coral bleaching increased surface scalar irradiance by ~150% (between 500 and 700 nm) relative to a healthy coral. Photosynthesis peaked around 300 ?m within the tissue, which corresponded to a zone exhibiting strongest depletion of scalar irradiance. Deeper coral tissue layers, e.g., ~1000 ?m into aboral polyp tissues, harbor optical microniches, where only ~10% of the incident irradiance remains. We conclude that the optical microenvironment of corals exhibits strong lateral and vertical gradients of scalar irradiance, which are affected by both tissue and skeleton optical properties. Our results imply that zooxanthellae populations inhabit a strongly heterogeneous light environment and highlight the presence of different optical microniches in corals; an important finding for understanding the photobiology, stress response, as well as the phenotypic and genotypic plasticity of coral symbionts. PMID:22969755

Wangpraseurt, Daniel; Larkum, Anthony W D; Ralph, Peter J; Kühl, Michael

2012-08-27

447

Radial metallicity gradient from RAVE DR3 (Coskunoglu+, 2012)  

NASA Astrophysics Data System (ADS)

We investigate radial metallicity gradients for a sample of dwarf stars from the RAdial Velocity Experiment (RAVE) Data Release 3 (DR3, Cat. III/265). We select a total of approximately 17000 F-type and G-type dwarfs, using a selection of colour, log g and uncertainty in the derived space motion, and calculate for each star a probabilistic (kinematic) population assignment to a thick or thin disc using space motion and additionally another (dynamical) assignment using stellar vertical orbital eccentricity. We additionally subsample by colour, to provide samples biased toward young thin-disc and older thin-disc stars. We derive a metallicity gradient as a function of Galactocentric radial distance, i.e. d[M/H]/dRm=-0.051+/-0.005dex/kpc, for the youngest sample, F-type stars with vertical orbital eccentricities ev<=0.04. Samples biased toward older thin-disc stars show systematically shallower abundance gradients. (1 data file).

Coskunoglu, B.; Ak, S.; Bilir, S.; Karaali, S.; Onal, O.; Yaz, E.; Gilmore, G.; Seabroke, G. M.

2012-07-01

448

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

449

Local structure, fluctuations, and freezing in two dimensions  

NASA Astrophysics Data System (ADS)

Starting from the concept of local solidlike order in two-dimensional (2D) liquids we introduce and quantify the corresponding ensembles of fluctuations, using a probabilistic-based method of local-structure analysis (LSA). A systematic LSA (including size dependence) was performed for a hard disk and 2D Lennard-Jones systems, simulated using Monte Carlo and molecular-dynamics methods. We find that the onset of freezing is accompanied by a dramatic crossover between ensembles of fluctuations. Some universal features related to the onset of freezing in two dimensions are found and corresponding freezing criteria are formulated: (i) the liquid starts to freeze when the concentration of solidlike atoms constitutes 0.50-0.56, and (ii) a Lindemann-like freezing criterion: the rms fluctuation constitutes, at the onset, 0.12-0.13. Those criteria offer an effective method for a localization of the onset of freezing in computer simulations. We point out, in this context, that in computer simulations there is a possibility that all quantitative characterizations of the onset of freezing are related to a metastable range. This important methodological topic is discussed briefly in the light of recent results both for 2D and 3D systems.

Mitus, A. C.; Patashinski, A. Z.; Patrykiejew, A.; Sokolowski, S.

2002-11-01

450

The Freeze Risk to Florida Citrus. Part 1: Investment Decisions.  

NASA Astrophysics Data System (ADS)

In the 1980s Florida was struck by an unusual series of severe freezes that caused enormous damage to citrus groves. While citrus acreage in relatively freeze-free parts of the state has expanded rapidly since these freezes, serious questions remain about the commercial viability of growing citrus crops in some central Florida counties. This paper considers the role that freeze risk plays in the investment decisions of citrus growers. A simplified example is used to estimate tolerable levels of freeze risk for individuals evaluating the investment at different discount rates, and to show the impact of changes in the risk level. Changes in estimated freeze risk in the 1980s are computed over the historical temperature record, and related to the growers' replanting decisions. It is concluded that the computed changes in the probability of a killing freeze would be sufficient to alter the citrus planting decisions of some investors. Furthermore, the longest available climate record should be used to estimate the risk of such low-probability extreme events.

Miller, Kathleen A.; Downton, Mary W.

1993-02-01

451

Levodopa changes the severity of freezing in Parkinson's disease.  

PubMed

Oral levodopa has been proposed to be one of the more effective medications to alleviate freezing of gait, but there is limited data on its efficacy. We evaluated the gait phenomenology of 20 Parkinson's disease patients with freezing of gait before and 60 min after a standardized levodopa dose using a rating scale based on the assumption that festination and akinetic freezing share a common pathophysiology. Levodopa abolished festination and freezing in 20% of patients (p < 0.0001), and reduced the freezing sum score from a median of 15 (IQR 6.75-27.5) to 3.5 (1-11.25), p < 0.001) in all but one of the remainder. Pre-dose ratings correlated with post-dose ratings, in that those patients with lower pre-dose item-scores also showed lower post-dose outcome scores. Levodopa's effect on both festination and akinetic freezing was linear, thereby supporting the concept that festination and freezing are variants on a continuity of episodic gait disorders in PD. PMID:23642712

Fietzek, Urban M; Zwosta, Jens; Schroeteler, Frauke E; Ziegler, Kerstin; Ceballos-Baumann, Andres O

2013-05-01

452

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

453

Empirical sea ice thickness retrieval during the freeze up period from SMOS high incident angle observations  

NASA Astrophysics Data System (ADS)

Sea ice thickness information is needed for climate modeling and ship operations. Here a method to detect the thickness of sea ice up to 50 cm during the freezeup season based on high incidence angle observations of the Soil Moisture and Ocean Salinity (SMOS) satellite working at 1.4 GHz is suggested. By comparison of thermodynamic ice growth data with SMOS brightness temperatures, a high correlation to intensity and an anti correlation to the difference between vertically and horizontally polarised brightness temperatures at incidence angles between 40 and 50 ° are found and used to develop an empirical retrieval sensitive to thin sea ice up to 50 cm thickness. It shows high correlations with ice thickness data from airborne measurements and reasonable ice thickness patterns for the Arctic freeze up period.

Huntemann, M.; Heygster, G.; Kaleschke, L.; Krumpen, T.; Mäkynen, M.; Drusch, M.

2013-08-01