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1

Vertical gradient freeze GaAs: Growth and electrical properties  

SciTech Connect

We have investigated the influence of silicon contamination prevention methods on the electrical properties of GaAs grown by the Vertical Gradient Freeze (VGF) technique. We report the effectiveness of these methods for GaAs crystals grown from two different starting materials: n-type with resistivities in the range of 10/sup /minus/1/ to 10/sup 3/ ..cap omega..-cm and semi-insulating (SI) with a resistivity of 10/sup 8/ ..cap omega..-cm. We have found that the impurities in the starting materials, specifically boron, carbon and silicon, have an effect on the ability to control silicon contamination with methods that have been reported previously in the literature. We also report the attainment of SI crystals using a PBN crucible, a SI charge and B/sub 2/O/sub 3/ encapsulation. 61 refs., 13 figs., 7 tabs.

Galiano, M.L.

1989-05-01

2

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

3

Growth of LiYF 4 by the seeded vertical gradient freezing technique  

NASA Astrophysics Data System (ADS)

Oriented single crystals of the laser host material LiYF 4, doped with either Er 3+ or Nd 3+, have been grown by seeded vertical gradient freezing (VGF). Successful seeding, requiring a rather high amount of excess LiF in the melt, allowed for the production of crystals of high optical quality. In the case of neodymium doping, the dopant distribution could be related to different convective flow patterns present at different stages of growth.

Rogin, P.; Hulliger, J.

1997-02-01

4

Effects of a traveling magnetic field on vertical gradient freeze growth of cadmium zinc telluride  

NASA Astrophysics Data System (ADS)

The effects of a traveling magnetic field (TMF) on vertical gradient freeze (VGF) growth of cadmium zinc telluride (CZT) are studied using a coupled model of magnetic induction, fluid dynamics, and heat transfer. Simulations are performed to determine the influences of current 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. TMF makes a significant impact on interface shape in the absence of thermal buoyancy, but is ineffectual under realistic conditions in a 4 inch diameter ampoule, for which buoyancy dominates Lorentz force throughout the melt.

Yeckel, Andrew; Derby, Jeffrey J.

2011-09-01

5

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

NASA Astrophysics Data System (ADS)

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 qualitatively with respect to the shapes of the solid-liquid interface and the growth rate.

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

2000-04-01

6

EL2 distributions in vertical gradient freeze GaAs crystals  

SciTech Connect

Spatial distributions of EL2 in undoped, semi-insulating GaAs crystals grown by a novel vertical gradient freeze (VGF) method are reported. As a result of the low-temperature gradients present during growth and post-solidification cooling, these crystals exhibit lower EL2 concentrations and lower dislocation densities than liquid-encapsulated Czochralski crystals. Both the EL2 distribution and dislocation density over the area of a wafer do not display the fourfold symmetric pattern prevalent for LEC-grown GaAs. The radial distributions of EL2 in as-grown VGF crystals have been found to be independent of the dislocation density. Axial and radial Hall-effect measurements are included. Thermal activation energies are also presented and the compensation mechanism for this material is discussed.

Gray, M.L.; Sargent, L.; Blakemore, J.S.; Parsey J.M. Jr.; Clemans, J.E.

1988-06-15

7

GaSb single-crystal growth by vertical gradient freeze  

NASA Astrophysics Data System (ADS)

GaSb 2-inch-diameter ingots doped with Tellurium have been grown by vertical gradient freeze (VGF) in quartz crucibles using an encapsulant. Twinning in the seed or in the cone of the crucible occurred in all growths when crucibles with a 6 mm diameter seed on (1 0 0) orientation and a cone angle to the vertical of 90° or 32.5° were used and in most cases the twins induced nucleation of polycrystalline growth. The amount of twinning could not be reduced by increasing the thermal gradient thereby suppressing the formation of facets. However, the use of full-diameter seeds with a carefully controlled diameter resulted in single-crystal growth of GaSb. First results on the quality of the VGF-grown GaSb:Te are promising. The dislocation density of the GaSb grown from a full-diameter seed is low; around 65 cm -2 at the seeding area and diminishing towards the end of the crystal and the dislocation density of GaSb grown from a 6-mm seed is even lower, around 4 cm -2 near the seed.

Reijnen, L.; Brunton, R.; Grant, I. R.

2005-02-01

8

Growth of 2? InP and GaAs crystals by the vertical gradient freeze (VGF) technique and characterization  

Microsoft Academic Search

InP and GaAs crystals with a diameter of 2? were grown by the vertical gradient freeze (VGF) technique. It is demonstrated by electrical and optical investigations that the VGF technique allows the growth of crystals with a uniform distribution of the dopants in both a macroscopic and a microscopic scale. The etch pit density in the VGF grown crystals is

J. Amon; D. Zemke; B. Hoffmann; G. Müller

1996-01-01

9

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

10

Cu2ZnSnSe4 Photovoltaic Absorber Grown by Vertical Gradient Freeze Technique  

NASA Astrophysics Data System (ADS)

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

Das, Sandip; Mandal, Krishna C.

2013-12-01

11

Fluid flow analysis and vertical gradient freeze crystal growth in a travelling magnetic field  

NASA Astrophysics Data System (ADS)

In bulk crystal growth of semiconductors the concept of remote flow control by means of alternating magnetic fields has attracted considerable interest (see, e.g., te{1,2,3,4,5,6}). In this way the melt flow can be tailored for growth under optimised conditions to improve the crystal properties and/or the growth yield. A promising option is to apply an axially travelling magnetic wave to the melt (Travelling Magnetic Field - TMF). It introduces a mainly axial Lorentz force, which leads to meridional flow patterns. In recent numerical studies te{3}, te{6} the TMF has been recognised to be a versatile and efficient tool to control the heat and mass transport in the melt. For the Vertical Bridgman/Vertical Gradient Freeze (VB/VGF) growth, the beneficial effect of an adequately adjusted TMF-induced flow was clearly demonstrated in te{6} in terms of the reduction of thermal shear stress at the solid-liquid interface. In this paper, we present experimental and numerical results on the TMF driven convection in an isothermal model fluid as well as first VGF-TMF crystal growth experiments. The model investigations are focused on the transition from laminar to instationary flow conditions that should be avoided in crystal growth applications. The VGF experiments were aimed at growing Ga doped germanium single crystals under the influence of the travelling field in a newly developed VGF-TMF equipment. Figs 4, Refs 10.

Lantzsch, R.; Grants, I.; Galindo, V.; Patzold, O.; Gerbeth, G.; Stelter, M.; Croll, A.

2006-12-01

12

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

13

Crystal Growth and Characterization of CdTe Grown by Vertical Gradient Freeze  

NASA Technical Reports Server (NTRS)

In this study, crystals of CdTe were grown from melts by the unseeded vertical gradient freeze method. The quality of grown crystal were studied by various characterization techniques including Synchrotron White Beam X-ray Topography (SWBXT), chemical analysis by glow discharge mass spectroscopy (GDMS), low temperature photoluminescence (PL), and Hall measurements. The SWBXT images from various angles show nearly strain-free grains, grains with inhomogeneous strains, as well as twinning nucleated in the shoulder region of the boule. The GDMS chemical analysis shows the contamination of Ga at a level of 3900 ppb, atomic. The low temperature PL measurement exhibits the characteristic emissions of a Ga-doped sample. The Hall measurements show a resistivity of 1 x l0(exp 7) ohm-cm at room temperature to 3 x 10(exp 9) ohm-cm at 78K with the respective hole and electron concentration of 1.7 x 10(exp 9) cm(exp -3) and 3.9 x 10(exp 7) cm(exp -3) at room temperature.

Su, Ching-Hua; Lehoczky, S. L.; Raghothamachar, B.; Dudley, M.

2007-01-01

14

Vertical gradient freeze of 4 inch Ge crystals in a heater-magnet module  

NASA Astrophysics Data System (ADS)

For the first time 4-in. Ge single crystals were grown using the vertical gradient freeze technique (VGF) in a traveling magnetic field (TMF) generated in a heater-magnet module (HMM). The HMM was placed closely around the growth container inside the chamber of the industrial Bridgman equipment "Kronos". The HMM generates heat and a TMF together. It has a coil-shaped design and replaces the standard meander-type heater. Direct current (DC) for heat production and out-of-phase-accelerated currents (AC) for TMF generation were simultaneously delivered to three equally spaced coil segments connected by star-type wiring. In order to achieve a nearly flat and slightly convex growing interface the AC amplitude, frequency and phase shift have been optimized numerically by using the 3D CrysMAS code and validated by striation analysis on as-grown crystals. Low-field frequencies in the range f=20-50 Hz proved to be of most suitable condition. TMF programming is required to obtain constant interface morphology over the whole growth run. First Ge single crystals grown under nearly optimal conditions show reduced macro- and micro-inhomogeneities, relatively low dislocation density of (3-10)×10 2 cm -2, and high carrier mobility of ?p=2800 cm 2 V -1 s -1.

Frank-Rotsch, Ch.; Rudolph, P.

2009-04-01

15

Vertical gradient freezing of doped gallium antimonide semiconductor crystals using submerged heater growth and electromagnetic stirring  

NASA Astrophysics Data System (ADS)

An investigation of the melt growth of uniformly doped gallium-antimonide (GaSb) semiconductor crystals as well as other III-V alloy crystals with uniform composition are underway at the US Air Force Research Laboratory at Hanscom Air Force Base by the vertical gradient freeze (VGF) method utilizing a submerged heater. Stirring can be induced in the GaSb melt just above the crystal growth interface by applying a small radial electric current in the liquid together with an axial magnetic field. The transport of any dopant and/or alloy component by the stirring can promote better melt homogeneity and allow for more rapid growth rates before the onset of constitutional supercooling. This paper presents a numerical model for the unsteady transport of a dopant during the VGF process by submerged heater growth with a steady axial magnetic field and a steady radial electric current. As the strength of the electromagnetic (EM) stirring increases, the convective dopant transport increases, the dopant transport in the melt reaches a steady state at an earlier time during growth, and the top of the crystal which has solidified after a steady state has been achieved exhibits axial dopant homogeneity. For crystal growth with stronger EM stirring, the crystal exhibits less radial segregation and the axially homogeneous section of the crystal is longer. Dopant distributions in the crystal and in the melt at several different stages during growth are presented.

Ma, Nancy; Bliss, David F.; Iseler, Gerald W.

2003-11-01

16

Flow modelling with relevance to vertical gradient freeze crystal growth under the influence of a travelling magnetic field  

Microsoft Academic Search

Results on the experimental and numerical modelling of the melt flow typically observed in vertical gradient freeze (VGF) crystal growth with a travelling magnetic field (TMF) are presented. Particular attention is paid on the transition from a laminar to a time-dependent flow, which represents a crucial problem in VGF growth. Low-temperature model experiments at around 80°C were performed using a

K. Niemietz; V. Galindo; O. Pätzold; G. Gerbeth; M. Stelter

2011-01-01

17

Numerical simulation of the growth of 2? diameter GaAs crystals by the vertical gradient freeze technique  

NASA Astrophysics Data System (ADS)

We present a global two-dimensional model of a multi-zone-furnace for the growth of GaAs using the bottom-seeded vertical gradient freeze (VGF) technique. The finite element code FIDAP was used to perform calculations of the heat transfer due to radiation and conduction in the whole furnace. The numerical results show a good agreement between measured and calculated temperature distributions in the furnace and calculated/measured power consumptions of the heaters. Quasi-steady-state calculations for a typical growth process were performed and the influence of different growth velocities on the interface shape was analyzed.

Weimann, H.; Amon, J.; Jung, Th.; Müller, G.

1997-10-01

18

Electrical properties of semi-insulating GaAs crystals grown by vertical gradient freeze and liquid encapsulated Czochralski techniques  

NASA Astrophysics Data System (ADS)

Electrical, photoelectrical, luminescent characteristics and the spectra of deep levels are compared for undoped semi-insulating SI-GaAs crystals grown by vertical gradient freeze (VGF) and liquid encapsulated Czochralski (LEC) techniques. It is shown that generally the reverse current of the Schottky diodes prepared on VGF material is considerably lower than for the LEC material which could be a serious advantage for use in radiation detectors. At the same time it is demonstrated that such parameters as photosensitivity and bandedge luminescence efficiency are to a greater extent dependent on the type of the ingots annealing procedure setting up the deep levels spectra in the material than on dislocation density.

Polyakov, A. Y.; Markov, A. V.; Smirnov, N. B.; Govorkov, A. V.

2004-01-01

19

Effect of growth parameters on dislocation generation in InP single crystal grown by the vertical gradient freeze process  

SciTech Connect

The generation and multiplication of dislocations in an indium phosphide (InP) single crystal grown by the vertical gradient freeze (VGF) process is predicted using a crystallographic model. This model couples microscopic dislocation motion and multiplication to macroscopic plastic deformation during the crystal growth process. During growth of an InP crystal, dislocations are generated in the plastically deformed crystal as a result of crystallographic glide caused by excessive thermal stresses. The temperature fields are determined by solving the partial differential equation of heat conduction in a VGF crystal growth system. The effects of growth direction and growth parameters (i.e., imposed temperature gradients, crystal radius and growth rate) on dislocation generation and multiplication in an InP crystal are investigated. Dislocation density patterns on the cross section of an InP crystal are numerically calculated and compared with experimental observations.

Gulluoglu, A.N. (Marmara Univ., Istanbul (Turkey). Dept. of Material Science and Engineering); Tsai, C.T. (Florida Atlantic Univ., Boca Raton, FL (United States). Dept. of Mechanical Engineering)

1999-06-22

20

InGaAs single crystal using a GaAs seed grown with the vertical gradient freeze technique  

NASA Astrophysics Data System (ADS)

We have succeeded in growing the InGaAs single crystal using a GaAs seed with the vertical gradient freeze technique (VGF) with good reproducibility. The orientation of the GaAs seed is (0 0 1). The boundary conditions between the GaAs seed and the InGaAs VGF crystal, the shape of the solid-liquid interface during crystal growth, and the growth mode of the crystal have been studied as basic conditions for the single crystal growth. We found that (1) The polycrystallinity due to the lattice mismatch between the GaAs seed and the InGaAs VGF crystal can be suppressed when the composition difference ? x between the GaAs seed and the InGaAs crystal is less than 0.05. (2) It is possible to make the solid-liquid interface convex toward the melt by reducing the temperature gradient of the growth zone, which prevents other grains occurring near the crucible wall from propagating to the crystal center region. (3) A normal freezing growth mode can be attained by reducing the lowering rate of the furnace temperature, which prevents compositionally abnormal regions from occurring during crystal growth. The InGaAs crystal obtained is 15 mm long and consists of a single crystal region. The diameter of the growth region is 15 mm, which is the same as that of the GaAs seed. The maximum InAs composition is 0.34

Nishijima, Yoshito; Nakajima, Kazuo; Otsubo, Koji; Ishikawa, Hiroshi

1999-03-01

21

Growth of 100-mm-Diameter <100> InP Single Crystals by the Vertical Gradient Freezing Method  

NASA Astrophysics Data System (ADS)

100-mm-diameter <100> undoped InP single crystals were grownby the vertical gradient freezing (VGF) method using a high-pressurefurnace. In order to reduce the temperature fluctuation in the furnacefor preventing twinning during crystal growth, we investigated the gasflow in the furnace by a computer simulation. The simulation resultsshowed that the gas flow was quite unstable because of the collisionbetween the gas and the hot-zone or other gas flows. After wedeveloped a hot-zone to control the gas flow, the temperaturefluctuation near the seed crystal reduced from ±0.3°C to±0.03°C. The axial temperature gradient was lower than10°C/cm and the growth rate was higher than0.4 mm/h. Twin-free 100-mm-diameter single crystals could be obtainedfor the first time under these conditions. The average EPD(Etch PitDensity) of the grown crystals was about 2000 cm-2, less thanthat of the conventional 75-mm-diameter InP LEC (liquid encapsulatedCzochralski) crystals.

Asahi, Toshiaki; Kainosho, Keiji; Kamiya, Tetsuo; Nozaki, Tatsuya; Matsuda, Yuko; Oda, Osamu

1999-02-01

22

Flow modelling with relevance to vertical gradient freeze crystal growth under the influence of a travelling magnetic field  

NASA Astrophysics Data System (ADS)

Results on the experimental and numerical modelling of the melt flow typically observed in vertical gradient freeze (VGF) crystal growth with a travelling magnetic field (TMF) are presented. Particular attention is paid on the transition from a laminar to a time-dependent flow, which represents a crucial problem in VGF growth. Low-temperature model experiments at around 80 °C were performed using a GaInSn melt in a resistance furnace with concentric, separately adjustable heating zones. The TMF was created by an external coil system, and the flow velocity was measured by means of the ultrasonic Doppler velocimetry (UDV). The melt flow was simulated numerically using a finite volume code based on the open source code library OpenFOAM. As a criterion for the stability of the flow the turbulent kinetic energy was calculated under the influence of the TMF and thermal buoyancy. The results obtained are compared to isothermal TMF flow modelling at ambient temperature. The stability limit of the melt flow is found to be significantly influenced by the mutual interaction of buoyant and TMF-driven flows. Both experimental and numerical results show the stabilizing effect of natural, VGF-type buoyancy on the TMF-induced flow.

Niemietz, K.; Galindo, V.; Pätzold, O.; Gerbeth, G.; Stelter, M.

2011-03-01

23

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 -150 V, a room temperature leakage current density of 2.4×10 -6 A/mm 2 was observed which reduced to 7.1×10 -8 A/mm 2 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 -7 cm 2/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

24

Computer-assisted growth of low-EPD GaAs with 3$Prime; diameter by the vertical gradient-freeze technique  

NASA Astrophysics Data System (ADS)

We have grown 3?, silicon-doped GaAs crystals with low dislocation density by the vertical gradient freeze (VGF) method. The thermal conditions in a newly designed, multi-zone VGF-furnace were optimized by the aid of numerical simulation. A computer controlled temperature-time program of the 9 heaters was acquired which allows to keep the axial temperature gradient in the solid (liquid) GaAs at the optimized constant values of 7(2) K/cm during the whole growth process. By using these calculated heater temperatures in real growth experiments, we succeeded in growing 3? single crystals with EPD<500 cm -2.

Amon, J.; Berwian, P.; Müller, G.

1999-03-01

25

Dislocation reduction in sulfur- and germanium-doped indium phosphide single crystals grown by the vertical gradient freeze process: A transient finite-element study  

NASA Astrophysics Data System (ADS)

During the growth of indium phosphide (InP) crystals, dislocations are mostly generated in a plastically deformed crystal due to crystallographic glide caused by excessive thermal stresses. High dislocation density presented in the InP crystal can reduce the performance, lifetime, and reliability of the InP-based microelectronic and optoelectronic devices/circuits. The generation of dislocations in InP single crystals grown from the melt can be predicted by using a transient finite-element model. This model couples microscopic dislocation motion and multiplication to macroscopic plastic deformation during the crystal growth process. The temperature fields in the crystal are determined by solving the partial differential equations of heat transfer for the vertical gradient freeze (VGF) process. These temperature fields are then employed to the transient finite-element model to study the effects of doping impurities and growth parameters (i.e., imposed temperature gradient, crystal radius, and growth rate) on dislocation reduction in InP crystals grown by different VGF processes.

Zhu, X. A.; Tsai, C. T.

2005-02-01

26

Influence of the crucible shape on the formation of facets and twins in the growth of GaAs by the vertical gradient freeze technique  

NASA Astrophysics Data System (ADS)

The influence of the shape of the crucible on the growth of silicon-doped GaAs crystals by the vertical gradient freeze (VGF) technique is investigated by using four different angles ? (60°, 90°, 120°, 144°) of the conical part of the pBN crucible. We find a decrease of the length of the {1 1 1} edge facets in the conical region with increasing cone angle ?. The {1 1 1}As facets are always larger and show a higher tendency to twinning compared to {1 1 1}Ga facets. The model of Hurle (J. Crystal Growth 147 (1995) 239) which correlates the formation of twins with the growth of facets at the three phase boundary (TPB) is confirmed. The maximum angle between the edge facet and the extension of the crystal surface at which the facet should detach from the TPB is found experimentally to be between 95.3° and 107.3°, which corresponds well with the value of 104° calculated by Hurle for encapsulated GaAs.

Amon, J.; Dumke, F.; Müller, G.

1998-04-01

27

Semiconductor apparatus utilizing gradient freeze and liquid-solid techniques  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

28

Measuring the vertical gradient of gravity  

NSDL National Science Digital Library

The free-air effect tells us that as elevation above sea level increases, gravitational acceleration g decreases at the rate of about 0.3086 mgal/meter. This effect is routinely corrected for when making gravity surveys. We will use the LaCoste & Romberg gravimeter to measure the free-air effect in a tall building on campus, and compare with the theoretical value. keywords: gravity; vertical gradient; gravimeter

Sternberg, Rob

29

Vertical gradients of lung density in healthy supine men  

Microsoft Academic Search

Computed tomography was used to determine the vertical gradient of physical density in peripheral lung tissue of 12 healthy supine subjects, at total lung capacity and residual volume. At total lung capacity the mean (SD) density of peripheral lung tissue at the level of the mid right atrium was 0.0715 (0.017) g\\/cm3 and the vertical gradient of density was slight.

A B Millar; D M Denison

1989-01-01

30

Vertical gradient freeze growth with external magnetic fields  

NASA Astrophysics Data System (ADS)

Experimental and numerical results are presented demonstrating the impact of a traveling magnetic field (TMF) on the heat and mass transport in doped, VGF-grown Ge crystals. In growth with TMF a considerable effect on the deflection of the solid-liquid interface is observed, whereas the dopant segregation does not change significantly compared to the growth without field. Furthermore, pronounced striation patterns were found in the crystals indicating a time-dependent melt flow during growth. A combined TMF/DC field is presented which was developed to avoid this effect. Isothermal model experiments using a liquid GaInSn alloy show the capability of the DC field for an effective damping of fluctuations of the flow velocity in qualitative agreement with numerical results.

Lantzsch, R.; Grants, I.; Pätzold, O.; Stelter, M.; Gerbeth, G.

2008-04-01

31

Convective flows in enclosures with vertical temperature or concentration gradients  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

32

Control of interface shape of cadmium zinc telluride grown via an electrodynamic gradient freeze furnace  

Microsoft Academic Search

We consider the feasibility of closed-loop control to control the interface shape of cadmium zinc telluride (CZT) grown via an electrodynamic gradient freeze (EDG) furnace. A simple proportional control algorithm is applied to a quasi-steady-state model to control the interface shape by adjusting the thermal gradient of the furnace temperatures. Three scenarios are enacted: actuation along the entire external boundary,

Lisa Lun; Andrew Yeckel; Jeffrey J. Derby; Prodromos Daoutidis

2007-01-01

33

Vertical CO2-Flux Gradients in the Marine Boundary Layer?  

NASA Astrophysics Data System (ADS)

A classical method to estimate CO2-fluxes through the air/sea-interface consist of measuring the vertical turbulent flux close to the surface by Eddy-Covariance assuming constant flux between the measuring height and the surface. To re-evaluate this assumption, a two level flux measurement was installed on the research platform FINO2 in order to search for vertical flux gradients. The research platform is located at 55° 00' north and 13°09' east in the Baltic Sea between the coasts of Sweden, Denmark and Germany. At FINO2 the water is about 25 meters deep. A 9 meter long boom carrying the flux sensors is mounted at the south-east corner of the platform pointing south. Raw data with 10 Hz sampling rate are stored locally since June 2008 and can be downloaded remotely via satellite-based internet link. CO2-fluxes were calculated with 30 min time resolution applying a standard eddy covariance processing scheme including tilt- and Webb-corrections. In addition, power and cross spectra were calculated for selected (high wind) periods - mainly in order to verify that there are no artifacts due to wind- and wave-induced vibrations of the platform. Our first results over a period of two months in summer 2008 show significant flux gradients over extended periods (1-2 days). Recent runs of mesoscale circulation models, which consider the time dependent sources and sinks of vegetation-covered land, predict patterns of CO2 concentration with horizontal gradients of considerable magnitude. Moreover these model results show that the gradients fade out over open oceans only very gradually on trajectories several hundred kilometers off the coast. We estimate that these horizontal gradients of atmospheric CO2 concentration in combination with vertical gradients of wind speed could be a potential reason for vertical flux gradients. In coastal waters the gradients can result in flux differences between the height of the flux sensor and the sea surface which can amount the same order of magnitude as the surface flux of CO2. We are confident to determine the appearance and the amount of these gradients on the basis of our continuous, long-term measurements and to extrapolate the "real" surface flux.

Krupski, Michael; Peters, Gerhard; Münster, Hans; Ament, Felix

2010-05-01

34

Freezing heat transfer in water-saturated porous media in a vertical rectangular vessel  

Microsoft Academic Search

Numerical and experimental study is performed for the freezing of water-saturated porous media in a vertical rectangular vessel. The governing equations are solved by using a variable transformation and employing a finite difference scheme. The SOR method is utilized to solve numerically the equations. Different size and types of spherical beads are used as the porous media. The temperature of

A. Sasaki; S. Aiba; S. Fukusako

1992-01-01

35

Vertical orbit excursion fixed field alternating gradient accelerators  

NASA Astrophysics Data System (ADS)

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

Brooks, Stephen

2013-08-01

36

Slag and other liquid behavior on vertical surface at near-freezing temperature  

SciTech Connect

Deposition of liquid droplets from turbulent stream to vertical surface and the subsequent transient behavior of the liquid layer are analyzed for the surface temperatures near the freezing point of the liquid. General wave behavior of the equations governing the liquid layer is elucidated. The analysis is applied to the problem of slag layer accumulation on the passage walls of a magnetohydrodynamic regenerative heat exchanger using the coal combustion product as the heat source. The wave behavior predicts the emergence of an accumulation shock that leads to clogging of the passges for certain cyclic operations.

Im, K.H. (Argonne National Lab., IL); Chung, P.M.

1980-11-01

37

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

38

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

Microsoft Academic Search

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

Michael E Loik; Sean P Redar

2003-01-01

39

The role of petioles in light acquisition by Hydrocotyle vulgaris L. in a vertical light gradient  

Microsoft Academic Search

In natural herbaceous vegetation plants are exposed to a vertical light gradient. In experiments, however, morphogenetic\\u000a responses of stoloniferous plants to shade have nearly always been tested under homogeneous shade conditions. In this study\\u000a we simulated a vertical light gradient and found that the response of Hydrocotyle vulgaris in this gradient differed considerably from the responses to homogenous shade. Petioles

L. Leeflang; M. J. A. Werger

1998-01-01

40

Vertical distribution of larval cod ( Gadus morhua) in experimental temperature gradients  

Microsoft Academic Search

Behavioural responses to gradients of temperature and light in the pelagic can potentially regulate the distribution and survival of early life stages of fish. Vertical temperature gradients (strong, mild and no thermocline, range 4–8 °C) were established in transparent experimental plastic bags (15 cm diameter and 1 m depth) to investigate changes in vertical distribution of larval cod in response to temperature and

K. W. Vollset; Ø. Fiksen; A. Folkvord

2009-01-01

41

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

42

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

NASA Astrophysics Data System (ADS)

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

Chang, You-Soon; Shin, Hong-Ryeol

2014-08-01

43

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

PubMed

Vertical hydraulic gradient is commonly measured in rivers, lakes, and streams for studies of groundwater-surface water interaction. While a number of methods with subtle differences have been applied, these methods can generally be separated into two categories; measuring surface water elevation and pressure in the subsurface separately or making direct measurements of the head difference with a manometer. Making separate head measurements allows for the use of electronic pressure sensors, providing large datasets that are particularly useful when the vertical hydraulic gradient fluctuates over time. On the other hand, using a manometer-based method provides an easier and more rapid measurement with a simpler computation to calculate the vertical hydraulic gradient. In this study, we evaluated a wet/wet differential pressure sensor for use in measuring vertical hydraulic gradient. This approach combines the advantage of high-temporal frequency measurements obtained with instrumented piezometers with the simplicity and reduced potential for human-induced error obtained with a manometer board method. Our results showed that the wet/wet differential pressure sensor provided results comparable to more traditional methods, making it an acceptable method for future use. PMID:19664046

Fritz, Brad G; Mackley, Rob D

2010-01-01

44

GOCE derived vertical gravity gradient delineates great earthquake rupture zones along the Chilean margin  

NASA Astrophysics Data System (ADS)

In the south Central Andes region, the Nazca oceanic plate that subducts beneath the South American plate is characterized by a rough topography derived from different oceanic features that collide against the continental margin. These features determine an important segmentation of both the margin and of the interplate zone. The Chilean subduction margin has been characterized by megathrust earthquakes affecting the plate interface with large rupture areas reaching hundreds of kilometers parallel to the trench. The occurrence of these phenomena has been linked, among other causes, to the subduction of sediments that fill the trench and their spatial relation to the relatively prominent oceanic features. We calculated the topography corrected vertical gravity gradient from GOCE satellite data and from EGM2008 model in order to delineate mass heterogeneities related to density variations along the south-central Chile subduction zone. Obtained results show a spatial relation between the subduction of the Nazca oceanic highs and associated along-strike segmentation of the vertical gravity gradients over the interplate zone. We compared our results with the different rupture areas and found a good correspondence with the ellipses for the main earthquakes such as the Valdivia-1960 and Maule-2010 ones. Then, we compared vertical gravity gradients with slip distribution obtained from different models, finding that they are actually correlated with high slip over negative vertical gradient. The GOCE derived gradient adjusts better with the main slip distribution contour since its signal has a characteristic high wavelength. Instead, the EGM2008 model presents a better performance in defining the high frequency anomalies. However, the last results need to be considered only in those regions where the statistical comparison with GOCE data shows a good performance. This is because EGM2008 model data present varying quality of the original terrestrial data, while the quality of the GOCE data is locally homogeneous.

Álvarez, Orlando; Nacif, Silvina; Gimenez, Mario; Folguera, Andres; Braitenberg, Carla

2014-05-01

45

Bulk Crystal Growth of Nonlinear Optical Organic Materials Using Inverted Vertical Gradient Freeze Method  

NASA Technical Reports Server (NTRS)

A new process for producing large bulk single crystals of benzil (C6H5COCOC6H5) is reported in this paper. Good quality crystals have been successfully grown using this approach to crystal growth. This method seems to be very promising for other thermally stable NLO organic materials also. The entire contents vycor crucible 1.5 inch in diameter and 2 inch deep was converted to single crystal. Purity of the starting growth material is also an important factor in the final quality of the grown crystals. The entire crystal can be very easily taken out of the crucible by simple maneuvering. Initial characterization of the grown crystals indicated that the crystals are as good as other crystals grown by conventional Bridgman Stockbarger technique.

Choi, J.; Cruz, Magda; Metzl, R.; Wang, W. S.; Aggarwal, M. D.; Penn, Benjamin G.; Frazier, Donald O.

1998-01-01

46

Growth of large-diameter ZnTe single crystals by the vertical gradient freezing method  

NASA Astrophysics Data System (ADS)

ZnTe singles crystals (80 mm diameter) were grown by the VGF method without seed crystals. In this method, the high-pressure furnace was used and the melt was encapsulated by B 2O 3 during crystal growth. EPDs of the grown crystals were 5000-10 000 cm -2. The FWHMs of the rocking curve measured by 4-crystal X-ray diffractometry were around 20 arcsec. The crystals grown by the VGF method were of high quality compared with those by other growth methods.

Asahi, T.; Arakawa, A.; Sato, K.

2001-07-01

47

Vertical two-phase flow regimes and pressure gradients: Effect of viscosity  

SciTech Connect

The effect of liquid viscosity on the flow regimes and the corresponding pressure gradients along the vertical two-phase flow was investigated. Experiment was carried out in a vertical transparent tube of 0.019 m in diameter and 3 m in length and the pressure gradients were measured by a U-tube manometer. Water and a 50 vol.% glycerol solution were used as the working fluids whose kinematic viscosities were 0.85 x 10{sup -6} and 4.0 x 10{sup -6} m{sup 2}/s, respectively. In our air-liquid annular two-phase flow, the liquid film of various thicknesses flowed adjacent to the wall and the gas phase flowed at the center of the tube. The superficial air velocity, j{sub air}, was varied between 0.0021 and 58.7 m/s and the superficial liquid velocity, j{sub liquid}, was varied between 0 and 0.1053 m/s. In the bubble, the slug and the slug-churn flow regimes, the pressure gradients decreased with increasing Reynolds number. But in the annular and the mist flow regimes, pressure gradients increased with increasing Reynolds number. Finally, the experimentally measured pressure gradient values were compared and are in good agreement with the theoretical values. (author)

Da Hlaing, Nan; Sirivat, Anuvat; Siemanond, Kitipat [The Petroleum and Petrochemical College, Chulalongkorn University, Soi Chula 12, Phayathai Road, Pathumwan, Bangkok 10330 (Thailand); Wilkes, James O. [Department of Chemical Engineering, The University of Michigan, Ann Arbor, MI 48109-2136 (United States)

2007-05-15

48

Vertical gradients and seasonal variation in stem CO2 efflux within a Norway spruce stand.  

PubMed

Stem CO2 efflux is known to vary seasonally and vertically along tree stems. However, annual tree- and stand-scale efflux estimates are commonly based on measurements made only a few times a year, during daytime and at breast height. In this study, the effect of these simplifying assumptions on annual efflux estimates and their influence on the estimates of the importance of stems in stand-scale carbon cycling are evaluated. In order to assess the strength of seasonal, diurnal and along-stem variability in CO2 efflux, half-hourly measurements were carried out at three heights on three mature Norway spruce (Picea abies (L.) Karst.) trees over a period of 3 years. Making the common assumption of breast height efflux rates being representative of the entire stem was found to result in underestimations of 10-17% in the annual tree-scale CO2 efflux. Upscaling using only daytime measurements from breast height increased the underestimation to 15-20%. Furthermore, the results show that the strength of the vertical gradient varies seasonally, being strongest in the early summer and non-existent during the cool months. The observed seasonality in the vertical CO2 efflux gradient could not be explained by variation in stem temperature, temperature response of the CO2 efflux (Q10), outer-bark permeability, CO2 transport in the xylem or CO2 release from the phloem. However, the estimated CO2 concentration immediately beneath the bark was considerably higher in the upper stem during the main period of diameter growth, coinciding with the strongest vertical efflux gradient. These results suggest that higher growth rates in the upper stem are the main cause for the observed vertical variation in the stem CO2 effluxes. Furthermore, the results indicate that accounting for the vertical efflux variation is essential for assessments of the importance of stems in stand-scale carbon cycling. PMID:24878562

Tarvainen, Lasse; Räntfors, Mats; Wallin, Göran

2014-05-01

49

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

Microsoft Academic Search

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 instaIled within the contaminant plume at the source of the contamination, and at 250 and 2100 m downgradient from the source. Depth profiles of

R. Smith; R HARVEY; D LEBLANC

1991-01-01

50

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

51

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

52

Sensitivity of airborne fluorosensor measurements to linear vertical gradients in chlorophyll concentration  

NASA Technical Reports Server (NTRS)

A semianalytic Monte Carlo radiative transfer simulation model for airborne laser fluorosensors has been extended to investigate the effects of inhomogeneities in the vertical distribution of phytoplankton concentrations in clear seawater. Simulation results for linearly varying step concentrations of chlorophyll are presented. The results indicate that statistically significant differences can be seen under certain conditions in the water Raman-normalized fluorescence signals between nonhomogeneous and homogeneous cases. A statistical test has been used to establish ranges of surface concentrations and/or verticl gradients in which calibration by surface samples would by inappropriate, and the results are discussed.

Venable, D. D.; Punjabi, A. R.; Poole, L. R.

1984-01-01

53

VIEWING THE CONTROVERSY LOSCHMIDT - BOLTZMANN\\/MAXWELL THROUGH MACROSCOPIC MEASUREMENTS OF THE TEMPERATURE GRADIENTS IN VERTICAL COLUMNS OF WATER  

Microsoft Academic Search

In order to clarify the dispute between Loschmidt and Boltzmann\\/Maxwell concerning the existence of a temperature gradient in insulated vertical columns of gas, liquid or solid, macroscopic measurements of t he temperature distribution in water were performed. A negative temperature gradient, cold at the top and warm at the bottom, is found in insulated tubes, while t he outside environment

Roderich W. Graeff

54

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

55

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

56

Numerical simulation of supercritical heat transfer under severe axial density gradient in a narrow vertical tube  

SciTech Connect

A number of computational works have been performed so far for the simulation of heat transfer in a supercritical fluid. The simulations, however, faced a lot of difficulties when heat transfer deteriorates due either to buoyancy or by acceleration. When the bulk temperature approaches the pseudo-critical temperature the fluid experiences a severe axial density gradient on top of a severe radial one. Earlier numerical calculations showed, without exception, unrealistic over-predictions, as soon as the bulk temperature exceeded the pseudo-critical temperature. The over-predictions might have been resulted from an inapplicability of widely-used turbulence models. One of the major causes for the difficulties may probably be an assumption of a constant turbulent Prandtl number. Recent research, both numerical and experimental, indicates that the turbulent Prandtl number is never a constant when the gradient of physical properties is significant. This paper describes the applicability of a variable turbulent Prandtl number to the numerical simulation of heat transfer in supercritical fluids flowing in narrow vertical tubes. (authors)

Bae, Y. Y.; Hong, S. D.; Kim, Y. W. [Korea Atomic Energy Research Inst., 1045 Daedeokdaero, Daejeon (Korea, Republic of)

2012-07-01

57

Estimation of atmospheric trace metal emissions in Vilnius City, Lithuania, using vertical concentration gradient and road tunnel measurement data  

Microsoft Academic Search

A new approach for the estimation of trace metal emissions in Vilnius city was implemented, using vertical concentration profiles in the urban boundary layer and road tunnel measurement data. Heavy metal concentrations were examined in fine and coarse particle fractions using a virtual impactor (cut-off size diameter 2.5?m). Negative vertical concentration gradients were obtained for all metals (Ba, Pb, V,

D. Valiulis; D ?eburnis; J Šakalys; K Kvietkus

2002-01-01

58

Vertical canopy gradient in photosynthesis and monoterpenoid emissions: An insight into the chemistry and physiology behind  

NASA Astrophysics Data System (ADS)

It is well known that vertical canopy gradients and varying sky conditions influence photosynthesis (Pn), specific leaf area (SLA), leaf thickness (LT) and leaf pigments (lutein, â-carotene and chlorophyll). In contrast, little is known about these effects on monoterpenoid (MT) emissions. Our study examines simultaneously measured Pn, MT emissions and the MT/Pn ratio along the canopy of an adult European beech tree (Fagus sylvatica L.) in natural forest conditions. Dynamic branch enclosure systems were used at four heights in the canopy (7, 14, 21 and 25 m) in order to establish relationships and better understand the interaction between Pn and MT emissions under both sunny and cloudy sky conditions. Clear differences in Pn, MT emissions and the MT/Pn ratio were detected within the canopy. The highest Pn rates were observed in the sun leaves at 25 m due to the higher intercepted light levels, whereas MT emissions (and the MT/Pn ratio) were unexpectedly highest in the semi-shaded leaves at 21 m. The higher Pn rates and, apparently contradictory, lower MT emissions in the sun leaves may be explained by the hypothesis of Owen and Peñuelas (2005), stating synthesis of more photo-protective carotenoids may decrease the emissions of volatile isoprenoids (including MTs) because they both share the same biochemical precursors. In addition, leaf traits like SLA, LT and leaf pigments clearly differed with height in the canopy, suggesting that the leaf's physiological status cannot be neglected in future research on biogenic volatile organic compounds (BVOCs) when aiming at developing new and/or improved emission algorithms.

Šimpraga, M.; Verbeeck, H.; Bloemen, J.; Vanhaecke, L.; Demarcke, M.; Joó, E.; Pokorska, O.; Amelynck, C.; Schoon, N.; Dewulf, J.; Van Langenhove, H.; Heinesch, B.; Aubinet, M.; Steppe, K.

2013-12-01

59

Structure and subunit dissociation of the mouse glucocorticoid receptor: rapid analysis using vertical tube rotor sucrose gradients.  

PubMed

The structure and subunit dissociation of the glucocorticoid receptor from the mouse AtT-20 pituitary tumor cell line was analyzed on sucrose gradients using a Beckman VTi 80 vertical tube rotor. This technique afforded a very rapid analysis (65 min) of the variously sedimenting forms compared to swinging-bucket rotor sucrose gradients, which take 16 h to run. Thus, it was possible to detect and study the molybdatestabilized, oligomeric, untransformed receptor (9.1 S) in the presence of 0.3 M KCl. Under similar conditions using the swinging-bucket rotor, only the monomeric, transformed species (3.8 S) was observed. That is, artifactual subunit dissociation was minimized using the vertical tube rotor, allowing the study of the receptor structure in a more native state. Further studies demonstrated that Sephadex LH-20 chromatography causes receptor transformation. Thus, dextran-charcoal adsorption is preferred for the removal of unbound hormone under certain circumstances. Finally, using vertical tube rotor sucrose gradients, it was determined that the transformation of the mouse AtT-20 glucocorticoid receptor involves a conversion of the oligomeric, 9.1 S, untransformed species to a 5.2 S, transformed moiety. This suggests that the 5.2 S, intermediate transformed species may be the physiologically relevant form of this gene regulatory protein. PMID:6712236

Eastman-Reks, S B; Reker, C E; Vedeckis, W V

1984-04-01

60

Natural convection in binary gases driven by combined horizontal thermal and vertical solutal gradients  

Microsoft Academic Search

An investigation of natural convection is presented to examine the influence of a horizontal temperature gradient and a concentration gradient occurring from the bottom to the cold wall in a cavity. As the solutal buoyancy force changes from augmenting to opposing the thermal buoyancy force, the fluid motion switches from unicellular to multicellular flow (fluid motion is up the cold

J. A. Weaver; Raymond Viskanta

1992-01-01

61

Vertical GPS ground motion rates in the Euro-Mediterranean region: new evidence of vertical velocity gradients at different spatial scales along the Nubia-Eurasia plate boundary  

NASA Astrophysics Data System (ADS)

We use 2.5 to 14 years long position time-series from ~1000 continuous GPS stations to study vertical ground motions in the Euro-Mediterranean region and provide a first synoptic view of the vertical velocity field along the broad Nubia-Eurasia plate boundary. By estimating and removing common mode errors in position time-series from the results of a principal component analysis, we obtain a significant gain in the signal-to-noise ratio of the displacements data. Following the results of a maximum likelihood estimation analysis, which gives a mean spectral index ~-0.7, we adopt a power-law + white noise stochastic model in estimating the final vertical rates, and find 95% of the velocities within ×2 mm/yr in the study area, with uncertainties from filtered time-series ~40% smaller than from the unfiltered ones. We evaluate the contribute of the glacial isostatic adjustment (GIA) signal to the vertical velocity budget using two different global models, characterized by distinct rheological layering of the Earth's mantle and different descriptions of the time-history of the mass of continental ice sheets since the Last Glacial Maximum. The analysis carried out allows us to highlight, for the first time, the presence of statistically significant, and spatially coherent, velocity gradients where a higher density of stations is available. We find undulations of the vertical velocity field occurring at different spatial scales both in regions characterized by tectonic activity, like eastern Alps, Apennines and eastern Mediterranean, and regions characterized by low to null tectonic activity, like central Iberia and western Alps. Correcting the observed velocities for GIA, although the two models used predict different GIA velocities and patterns, doesn't change significantly the velocity gradients. A correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area. GIA and weathering processes cannot completely explain the measured rates, and a combination of active tectonics and deep-seated geodynamic processes must be used to explain our observations. Excluding areas where more localized processes are likely, or where subduction/delamination processes may be active, mantle dynamics is the most likely process, but regional mantle modeling is required for a better understanding.

Serpelloni, E.; Faccenna, C.; Spada, G.; Dong, D.; Williams, S. D.

2013-12-01

62

Vertical Gradients in Water Chemistry and Age in the Southern High Plains Aquifer, Texas, 2002  

USGS Publications Warehouse

The southern High Plains aquifer is the primary source of water used for domestic, industrial, and irrigation purposes in parts of New Mexico and Texas. Despite the aquifer's importance to the overall economy of the southern High Plains, fundamental ground-water characteristics, such as vertical gradients in water chemistry and age, remain poorly defined. As part of the U.S. Geological Survey's National Water-Quality Assessment Program, water samples from nested, short-screen monitoring wells installed in the southern High Plains aquifer at two locations (Castro and Hale Counties, Texas) were analyzed for field parameters, major ions, nutrients, trace elements, dissolved organic carbon, pesticides, stable and radioactive isotopes, and dissolved gases to evaluate vertical gradients in water chemistry and age in the aquifer. Tritium measurements indicate that recent (post-1953) recharge was present near the water table and that deeper water was recharged before 1953. Concentrations of dissolved oxygen were largest (2.6 to 5.6 milligrams per liter) at the water table and decreased with depth below the water table. The smallest concentrations were less than 0.5 milligram per liter. The largest major-ion concentrations generally were detected at the water table because of the effects of overlying agricultural activities, as indicated by postbomb tritium concentrations and elevated nitrate and pesticide concentrations at the water table. Below the zone of agricultural influence, major-ion concentrations exhibited small increases with depth and distance along flow paths because of rock/water interactions and mixing with water from the underlying aquifer in rocks of Cretaceous age. The concentration increases primarily were accounted for by dissolved sodium, bicarbonate, chloride, and sulfate. Nitrite plus nitrate concentrations at the water table were 2.0 to 6.1 milligrams per liter as nitrogen, and concentrations substantially decreased with depth in the aquifer to a maximum concentration of 0.55 milligram per liter as nitrogen. Dissolved-gas and nitrogen-isotope data from the deep wells in Castro County indicate that denitrification occurred in the aquifer, removing 74 to more than 97 percent of the nitrate originally present in recharge. There was no evidence of denitrification in the deep part of the aquifer in Hale County. After correcting for denitrification effects, the background concentration of nitrate in water recharged before 1953 ranged from 0.4 to 3.2 milligrams per liter as nitrogen, with an average of 1.6 milligrams per liter as nitrogen. The d15N composition of background nitrate at the time of recharge was estimated to range from 9.6 to 12.3 per mil. Mass-balance models indicate that the decreases in dissolved oxygen and nitrate concentrations and small increases in major-ion concentrations along flow paths can be accounted for by small amounts of silicate-mineral and calcite dissolution; SiO2, goethite, and clay-mineral precipitation; organic-carbon and pyrite oxidation; denitrification; and cation exchange. Mass-balance models for some wells also required mixing with water from the underlying aquifer in rocks of Cretaceous age to achieve mole and isotope balances. Carbon mass transfers identified in the models were used to adjust radiocarbon ages of water samples recharged before 1953. Adjusted radiocarbon ages ranged from less than 1,000 to 9,000 carbon-14 years before present. Radiocarbon ages were more sensitive to uncertainties in the carbon-14 content of recharge than uncertainties in carbon mass transfers, leading to 1-sigma uncertainties of about ?2,000 years in the adjusted ages. Despite these relatively large uncertainties in adjusted radiocarbon ages, it appears that deep water in the aquifer was considerably older (at least 1,000 years) than water near the water table. There was essentially no change in ground-water age with depth in deeper parts of the aquifer, indicating that water in that

McMahon, P.B.; Böhlke, J.K.; Lehman, T.M.

2004-01-01

63

Spatiotemporal variations in vertical gravity gradients at the Campi Flegrei caldera (Italy): a case for source multiplicity during unrest?  

NASA Astrophysics Data System (ADS)

We present an evaluation of residual vertical gravity-height change gradients obtained from gravimetric and elevation data between 1982 and 2000 at the Campi Flegrei caldera (CFc) in Italy. Spatial and temporal variations in the gradients are indicative of multiple causative sources during unrest, in particular for ground subsidence from 1988 onwards. Supported by results obtained from time-series inversion for the period 1988-2000 using a random search approach of a purely elastic earth model and a genetic algorithm accounting for elastic-gravitational effects, we propose a centre of dilatation undergoing predominantly pressure changes yet negligible mass changes as the dominant cause for caldera deflation. Mass fluctuations in randomly active secondary sources along the periphery of the CFc can be best explained by dynamic changes along the caldera boundary (ring) faults.

Gottsmann, Joachim; Camacho, Antonio G.; Tiampo, Kristy F.; Fernández, José

2006-12-01

64

Freeze drying method  

DOEpatents

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

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

1999-01-01

65

Freeze drying apparatus  

DOEpatents

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

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

2001-01-01

66

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

Microsoft Academic Search

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

Scot K. Izuka; Stephen B. Gingerich

1998-01-01

67

Vertical temperature gradients within discharging steam-water boreholes can indicate flow-rate  

SciTech Connect

Few temperature profiles have been taken in flowing geothermal boreholes. The three experiments studied here give a straight line relationship for temperature with depth. This gradient is simply correlated with both hole diameter and flow-rate as in an equation.

James, R.

1980-09-01

68

Dynamic impact of the vertical shear of gradient wind on the tropical cyclone boundary layer wind field  

NASA Astrophysics Data System (ADS)

This work studies the impact of the vertical shear of gradient wind (VSGW) in the free atmosphere on the tropical cyclone boundary layer (TCBL). A new TCBL model is established, which relies on fiveforce balance including the pressure gradient force, Coriolis force, centrifugal force, turbulent friction, and inertial deviation force. This model is then employed to idealize tropical cyclones (TCs) produced by DeMaria's model, under different VSGW conditions (non-VSGW, positive VSGW, negative VSGW, and VSGW increase/decrease along the radial direction). The results show that the free-atmosphere VSGW is particularly important to the intensity of TC. For negative VSGW, the total horizontal velocity in the TCBL is somewhat suppressed. However, with the maximum radial inflow displaced upward and outward, the radial velocity notably intensifies. Consequently, the convergence is enhanced throughout the TCBL, giving rise to a stronger vertical pumping at the TCBL top. In contrast, for positive VSGW, the radial inflow is significantly suppressed, even with divergent outflow in the middle-upper TCBL. For varying VSGW along the radial direction, the results indicate that the sign and value of VSGW is more important than its radial distribution, and the negative VSGW induces stronger convergence and Ekman pumping in the TCBL, which favors the formation and intensification of TC.

Cai, Ninghao; Xu, Xin; Song, Lili; Bai, Lina; Ming, Jie; Wang, Yuan

2014-02-01

69

Natural convection in binary gases driven by combined horizontal thermal and vertical solutal gradients  

SciTech Connect

An investigation of natural convection is presented to examine the influence of a horizontal temperature gradient and a concentration gradient occurring from the bottom to the cold wall in a cavity. As the solutal buoyancy force changes from augmenting to opposing the thermal buoyancy force, the fluid motion switches from unicellular to multicellular flow (fluid motion is up the cold wall and down the hot wall for the bottom counterrotating flow cell). Qualitatively, the agreement between predicted streamlines and smoke flow patterns is generally good. In contrast, agreement between measured and predicted temperature and concentration distributions ranges from fair to poor. Part of the discrepancy can be attributed to experimental error. However, there remains considerable discrepancy between data and predictions due to the idealizations of the mathematical model, which examines only first-order physical effects. An unsteady flow, variable thermophysical properties, conjugate effects, species interdiffusion, and radiation were not accounted for in the model. 31 refs.

Weaver, J.A.; Viskanta, R. (Purdue University, West Lafayette, IN (United States))

1992-01-01

70

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

USGS Publications Warehouse

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

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

1991-01-01

71

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

72

Anisotropy gradients from QL surface waves: Evidence for vertically coherent deformation in the Tibet region  

NASA Astrophysics Data System (ADS)

The India-Eurasia continental collision has not only caused the high uplift of the Tibetan Plateau, but also created a broad diffuse deformation zone in Central Asia. We relate the well-constrained extent of crustal deformation in the Tibet region with underlying mantle deformation by interpreting the quasi-Love (QL) surface wave scattering in the legacy data of Tibet. QL waves are waveform anomalies generated from cross-mode coupling of Earth's free oscillations, mainly through azimuthal anisotropy. Over 50 events with QL observations are identified using recordings in Tibet. The predominant frequency content of the QL waves is near 10 mHz, and reflects peak sensitivity of anisotropy at 150 km depth in the mantle assuming horizontally-oriented symmetry axes. By calculating the delay times between the QL waves and the main Love waves, we back-project the scatterers to cluster in areas like SE Tibet, Sayan Mountain and Iran. Noticeably the spatial distribution of these scatterers borders the crustal deformation pattern quite well, especially at the deformation limits of Central Asia. This linkage suggests a vertically coherent boundary condition through the crust and the upper mantle for the India-Eurasia continental collision in Central Asia.

Chen, Xiaojun; Park, Jeffrey

2013-11-01

73

Vertical distribution of bacterial community structure in the sediments of two eutrophic lakes revealed by denaturing gradient gel electrophoresis (DGGE) and multivariate analysis techniques  

Microsoft Academic Search

Vertical distribution of bacterial community structure was investigated in the sediments of two eutrophic lakes of China,\\u000a Lake Taihu and Lake Xuanwu. Profiles of bacterial communities were generated using a molecular fingerprinting technique, denaturing\\u000a gradient gel electrophoresis (DGGE) followed by DNA sequence analysis, and the results were interpreted with multivariate\\u000a statistical analysis. To assess changes in the genetic diversity of

Jin Zeng; Liuyan Yang; Jiayun Li; Yi Liang; Lin Xiao; Lijuan Jiang; Dayong Zhao

2009-01-01

74

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

NASA Astrophysics Data System (ADS)

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. Résumé Une estimation précise de la profondeur de l'interface théorique entre l'eau douce et l'eau salée est un élément critique dans les estimations de rendement des puits dans les aquifères insulaires et littoraux. La relation de Ghyben-Herzberg, qui est habituellement utilisée pour estimer la profondeur de cette interface, peut fortement sous-estimer ou surestimer l'épaisseur de l'eau douce, parce qu'elle suppose l'absence de gradient vertical de charge et d'écoulement vertical. L'estimation de la profondeur de l'interface requiert de prendre en considération les gradients verticaux de charge et l'éventuelle anisotropie de l'aquifère. Cet article propose une méthode de calcul des gradients verticaux de charge à partir des mesures de niveau piézométrique faites en cours de foration d'un puits incomplet; le gradient est alors utilisé pour estimer la profondeur de l'interface. L'application de cette méthode à un système eau douce - eau salée simulé numériquement montre que la méthode est la plus précise lorsque le gradient est mesuré dans un puits pénétrant profondément dans l'aquifère. Même en utilisant un puits peu profond, la méthode estime la position de l'interface avec plus de précision que ne le fait la relation de Ghyben-Herzberg lorsqu'il existe un gradient vertical de charge bien marqué. L'application de la méthode à des données de terrain montre que la foration, les méthodes de mesure de niveau et les hétérogénéités au sein de l'aquifère peuvent être la cause de difficultés, mais que les effets de ces difficultés peuvent être réduits. Resumen Para la estimación de la productividad de pozos en acuíferos costeros y en islas es necesaria una estimación precisa de la profundidad de la interfaz teórica entre agua dulce y agua salada. La relación de Ghyben-Herzberg, usada habitualmente para estimar la profundidad de la interfaz, puede subestimar o sobrestimar el espesor de agua dulce, al asumir la ausencia de flujos y gradientes verticales. La estimación de la profundidad de la interfaz debe considerar tanto estos gradientes verticales, como la posible anisotropía del acuífero. En este artículo se presenta un método para calcular los gradientes verticales de niveles a partir de las medidas obtenidas durante la perforación de un pozo parcialmente penetrante para, a partir de este gradiente, estimar la profundidad de la interfaz. La aplicación del método a un sistema de agua dulce/agua salada simulado numéricamente muestra que el método es más preciso cuando el gradiente se mide en un pozo profundo. Incluso en el caso de un pozo superficial, el método permite una estimación más precisa de la profundidad de la interfaz que la aplicación de la fórmula de Ghyben-Herzberg, en los casos en l

Izuka, Scot K.; Gingerich, Stephen B.

75

Long-distance abscisic acid signalling under different vertical soil moisture gradients depends on bulk root water potential and average soil water content in the root zone.  

PubMed

To determine how root-to-shoot abscisic acid (ABA) signalling is regulated by vertical soil moisture gradients, root ABA concentration ([ABA](root)), the fraction of root water uptake from, and root water potential of different parts of the root zone, along with bulk root water potential, were measured to test various predictive models of root xylem ABA concentration [RX-ABA](sap). Beans (Phaseolus vulgaris?L. cv. Nassau) were grown in soil columns and received different irrigation treatments (top and basal watering, and withholding water for varying lengths of time) to induce different vertical soil moisture gradients. Root water uptake was measured at four positions within the column by continuously recording volumetric soil water content (?v). Average ?v was inversely related to bulk root water potential (?(root)). In turn, ?(root) was correlated with both average [ABA](root) and [RX-ABA](sap). Despite large gradients in ?v, [ABA](root) and root water potential was homogenous within the root zone. Consequently, unlike some split-root studies, root water uptake fraction from layers with different soil moisture did not influence xylem sap (ABA). This suggests two different patterns of ABA signalling, depending on how soil moisture heterogeneity is distributed within the root zone, which might have implications for implementing water-saving irrigation techniques. PMID:23387513

Puértolas, Jaime; Alcobendas, Rosalía; Alarcón, Juan J; Dodd, Ian C

2013-08-01

76

Vertical GPS ground motion rates in the Euro-Mediterranean region: New evidence of velocity gradients at different spatial scales along the Nubia-Eurasia plate boundary  

NASA Astrophysics Data System (ADS)

use 2.5 to 14 years long position time series from >800 continuous Global Positioning System (GPS) stations to study vertical deformation rates in the Euro-Mediterranean region. We estimate and remove common mode errors in position time series using a principal component analysis, obtaining a significant gain in the signal-to-noise ratio of the displacements data. Following the results of a maximum likelihood estimation analysis, which gives a mean spectral index ~ -0.7, we adopt a power law + white noise stochastic model in estimating the final vertical rates and find 95% of the velocities within ±2 mm/yr, with uncertainties from filtered time series ~40% smaller than from the unfiltered ones. We highlight the presence of statistically significant velocity gradients where the stations density is higher. We find undulations of the vertical velocity field at different spatial scales both in tectonically active regions, like eastern Alps, Apennines, and eastern Mediterranean, and in regions characterized by a low or negligible tectonic activity, like central Iberia and western Alps. A correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area. Glacial isostatic adjustment and weathering processes do not completely explain the measured rates, and a combination of active tectonics and deep-seated geodynamic processes must be invoked. Excluding areas where localized processes are likely, or where subduction processes may be active, mantle dynamics is the most likely process, but regional mantle modeling is required for a better understanding.

Serpelloni, Enrico; Faccenna, Claudio; Spada, Giorgio; Dong, Danan; Williams, Simon D. P.

2013-11-01

77

When hot water freezes before cold  

E-print Network

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

J. I. Katz

2006-04-27

78

Freeze Technology for Nuclear Applications - 13590  

SciTech Connect

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

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

2013-07-01

79

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

PubMed

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

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

2014-05-01

80

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

81

VISUALIZATION OF FREEZING DAMAGE  

Microsoft Academic Search

Freeze-cleaving can be used as a direct probe to examine the ultrastructural alterations of biological material due to freezing . We examined the thesis that at least two factors, which are oppositely dependent upon cooling velocity, determine the survival of cells subjected to freezing . According to this thesis, when cells are cooled at rates exceeding a critical velocity, a

HARVEY BANK; PETER MAZUR

1973-01-01

82

Theoretical prediction of ‘optimal’ freezing programmes  

Microsoft Academic Search

We have developed a quantitative description of the osmotic behaviour of cells during freezing without a presupposed value of the cooling rate. Instead, at all times the intracellular supercooling is maximised provided that it does not exceed a predetermined value ‘p’ (e.g., 2°C). This should preclude intracellular ice formation, but also ensures that the osmotic gradient and the CPA concentration

H. Woelders; A. Chaveiro

2004-01-01

83

Freezing in confined geometries  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

84

Freezing Combination Main Dishes  

E-print Network

Making your own frozen prepared foods can be economical. You can cook enough for several meals with little extra effort when you have the time. For best results, remember that freezing maintains, but does not improve, quality. Use only fresh, high-quality food ingredients. Underripe fruits and vegetables lack flavor, and overripe ones are flat and tough, or soft and mushy after freezing. Meat or poultry that is tender before freezing will stay tender after freezing if it is properly prepared, packaged, frozen, and stored. Cleanliness Observe strict cleanliness in preparing food for the home freezer. Freezer temperatures of 0 degrees F or below do not kill bacteria in food; they simply stop bacteria from multiplying. After the frozen food is thawed, bacteria will grow and multiply again. Strict cleanliness keeps the number of bacteria at a minimum before foods are frozen. Foods to Use and Foods to Avoid You may use many of your own favorite recipes for freezing. Prepare the food in the usual way. Cook thoroughly but do not overcook. There may be further cooking when reheated. Foods That Freeze Well • Cooked chicken or turkey in casseroles. • Stews and goulashes made with beef, lamb, pork, or veal. Most vegetables used in these combination dishes, such as peas, carrots, celery, or small quantities of onion also freeze well. However, potatoes may not be satisfactory. • Baked meat loaf. • Cooked dried beans, such as bean soup and baked beans. Because freezing softens beans somewhat, cook until barely tender for best quality. Limit storage time to two weeks if seasoned with ham or bacon. Foods That Do Not Freeze Well The flavor and texture of some foods become poor during freezing. Avoid using these foods. • Cooked egg white toughens. • Mature potatoes which tend to disintegrate, become watery, or darken. New potatoes are better. • Fried foods tend to lose crispness and become soggy. • Avoid freezing cured meats; salt hastens rancidity. • Fresh salad greens, raw tomatoes, raw apples and grapes become soft, soggy, and mushy.

unknown authors

85

Freeze-Thaw  

Microsoft Academic Search

Although attempting to consider the impact of freeze-thaw, the monitoring of associated thermal conditions must, effectively,\\u000a be context free. This is important for several reasons. First, although freeze-thaw is being evaluated, data must be of a\\u000a nature that also allows determination of the spatial and temporal role of other processes. Second, by being ‘holistic’ rather\\u000a than (assumed) ‘specific’ in character

Kevin Hall

86

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

NASA Astrophysics Data System (ADS)

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 estimated by Shannon indices (mean 2.91; SD 0.25; n = 13), was comparable to that of soil habitats and had a positive correlation with Ca2+ concentration (R = 0.71; P < 0.01), a good proxy of dust. This suggested that the soil ecosystem was the main source of bacteria in this glacier. The low similarity indices (0-43%) were found between the ice-core samples, which corresponded to the episodic deposition under defined climatic conditions and low activity of microorganisms in glacial ice. The profiles of bacterial species composition in glacial ice may be a bioindicator of climatic changes or dating.

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

87

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

88

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

89

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

90

Freeze Branding Horses  

E-print Network

Freeze branding of horses has many advantages. It is safe, economical, simple to do and relatively painless. It can be done on horses of any age and does not damage the horse's hide. This publication gives complete, step-by-step instructions...

Householder, Doug; Webb, Gary; Wigington, Sam; Bruemmer, Jason

2001-06-29

91

Cryogenic freezing system  

SciTech Connect

The operation of a prior art freezer installation for freezing food can be improved by: providing air curtains at the doors of the freezer; using a pulse bag filter for separating ice from the air leaving the freezer; and ensuring that the air leaving the freezer is colder than -800 F.

Prentice, A.L.

1982-03-02

92

Freezing Index Maps of Maine.  

National Technical Information Service (NTIS)

The depth of frost penetration can be calculated by means of the modified Berggren formula whose dependent variables are various soils characteristics and air freezing index. Because the last comprehensive study of the distribution of freezing indexes in ...

N. Bigelow

1969-01-01

93

Freezing Poultry for Home Use  

E-print Network

Purchasing fresh poultry in large packages and freezing it in quantities suitable for individual meals can stretch time and food dollars. Topics include packaging needs, cutting, storing and thawing instructions, and freezing pre-cooked meals....

Davis, Michael

2006-08-31

94

NATURAL FREEZING SURVIVAL IN ANIMALS  

Microsoft Academic Search

Natural freeze-tolerance supports the winter survival of many animals including numerous terrestrial insects, many intertidal marine invertebrates, and selected species of terrestrially hibernating amphibians and reptiles. Freeze-tolerant an- imals typically endure the conversion of 50% or more of total body water into extracellular ice and employ a suite of adaptations that counter the negative con- sequences of freezing. Specific adaptations

Kenneth B. Storey; Janet M. Storey

1996-01-01

95

Traditional Gradient Enhanced Gradient  

E-print Network

Recently deep learning has become a field of attention in machine learning (see [1, 2] for a review). Deep learning mainly focuses on applying a deep neural network to various machine learning applications where there are abundant amount of highdimensional training samples either labeled or unlabeled. Especially, it was shown that deep models are able to extract efficient, hierarchical features. Many recent advances in deep learning have shown performances that are far superior to conventional approaches inmany areas including image and speech recognition as wellas multi-modal learning. One of the most widely used models in deep learning is a deep belief network (DBN) which is built by stacking multiple layers ofrestrictedBoltzmannmachines(RBM).ArestrictedBoltzmannmachinethusconstitutesabasicbuildingblockwithitssimple bipartite structure. However, training even this simplified model has been difficult [6]. Training is sensitive to specific choice of learning hyper-parameters aswell as the datarepresentation. We have recently proposed and are developing learning algorithms that could facilitate learning parameters of RBMs. First of all, we proposed the enhanced gradient update rules that are invariant to flipping of variables in RBMs [5]. As shown in Fig. 1 it effectively makes a gradient of weight parameters with respect to hidden units more orthogonal to each other, hence, leading to a reacher set of features learned by RBMs. Then, the adaptive learning rate adapts the learning rate on-the-fly [5], which otherwise,wouldrequireextensivecross-validation. Thirdly,wehaveshownthatwithasimplere-parameterizationoftheenergy functiontrainingRBMswithGaussianvisiblevariablescouldbecomemucheasier[3]. Lastly,wehavedemonstratedthatabetter

Kyunghyun Cho; Juha Karhunen; Figure Theanglesbetweentheupdatedirectionsfortheweightsofanrbmwithhiddenneurons Whitepixelscorrespon

96

Soil Freeze-Thaw Effects on Bank Erodibility and Stability.  

National Technical Information Service (NTIS)

When air temperature is below ground temperature, a thermal gradient is established in the soil that causes the soil to lose heat to the atmosphere. When the soil has lost sufficient heat for soil water to freeze, the newly formed ice changes soil structu...

L. W. Gatto

1995-01-01

97

Effects of freezing on plant mesophyll cells.  

PubMed

Freezing and thawing of leaves of herbaceous plants leads to damage when the freezing temperature falls below a certain tolerance limit, which depends on the plant species and state of acclimation. Such damage is expressed as an irreversible inhibition of photosynthesis observed after thawing. In frost-damaged leaves the capacity of photosynthetic reactions of the thylakoid membranes is impaired. Particularly, the water-oxidation system, photosystems II and I are inhibited. However, it appears that CO2 assimilation is more readily affected by freezing stress than the activity of the thylakoids. The inhibition of CO2 fixation seen in initial stages of damage seems to be independent of thylakoid inactivation. This can be shown by chlorophyll fluorescence analysis made simultaneously with measurement of CO2 assimilation. Fluorescence emission by leaves is strongly influenced by carbon assimilation activity, namely via the redox state of the photosystem II electron acceptor QA (QA-dependent quenching) and via energization of the thylakoid membranes depending on the transthylakoid proton gradient (energy-dependent quenching). Resolution of these components of fluorescence changes provides insight into alterations of the CO2 fixing capacity of the chloroplasts and properties of the thylakoids. The effects of freezing and thawing were studied in detail with isolated mesophyll protoplasts prepared from both non-hardened and cold-acclimated plants of Valerianella locusta L. Freezing damage was characterized by various parameters such as plasma membrane integrity, photosynthetic CO2 assimilation, chlorophyll fluorescence emission and activities of thylakoids isolated from the protoplasts. All tests indicated a substantially increased frost tolerance of protoplasts obtained from cold-acclimated as compared to non-hardened leaves. CO2 assimilation and related fluorescence changes were the most freezing-sensitive parameters in both types of protoplasts. Inactivation of CO2 assimilation was correlated neither to the disintegration of the plasma membrane nor to inactivation of the thylakoids. Experimental data indicate that freeze-thaw treatment affected the light-regulated enzymes of the carbon reduction cycle, such as fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase and ribulose-1,5-bisphosphate carboxylase. Inhibition of light-activation of these enzymes may be based on altered properties of the chloroplast envelope. PMID:3077862

Krause, G H; Grafflage, S; Rumich-Bayer, S; Somersalo, S

1988-01-01

98

Satellite freeze forecast system  

NASA Technical Reports Server (NTRS)

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

Martsolf, J. D. (principal investigator)

1983-01-01

99

Variation in seedling freezing response is associated with climate in Larrea  

PubMed Central

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

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

2013-01-01

100

Freeze Prediction Model  

NASA Technical Reports Server (NTRS)

Measurements of wind speed, net irradiation, and of air, soil, and dew point temperatures in an orchard at the Rock Springs Agricultural Research Center, as well as topographical and climatological data and a description of the major apple growing regions of Pennsylvania were supplied to the University of Florida for use in running the P-model, freeze prediction program. Results show that the P-model appears to have considerable applicability to conditions in Pennsylvania. Even though modifications may have to be made for use in the fruit growing regions, there are advantages for fruit growers with the model in its present form.

Morrow, C. T. (principal investigator)

1981-01-01

101

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

102

Performance Characteristics of an Isothermal Freeze Valve  

SciTech Connect

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

Hailey, A.E.

2001-08-22

103

The effect of water content, cooling rate, and growth temperature on the freezing temperature of 4 Tillandsia species  

E-print Network

in their tissues (Levitt, 1972). Two types of freezing occur in plants: extracellular and intracellular (Asahina, 1978; Levitt, 1972; 1978). Many plants are able to tolerate extracellular freezing (Levitt, 1972; 1978), which results from slow cooling rates (lo...-5oC / hr) (Levitt, 1972) . During extracellular freezing, ice forms in intracellular spaces and / or extracellularly between cell walls and protoplasts (Asahina, 1978; Levitt, 1972) creating a vapor pressure gradient between the ice...

Hagar, Christopher Flint

2012-06-07

104

Understanding Slag Freeze Linings  

NASA Astrophysics Data System (ADS)

Slag freeze linings, the formation of protective deposit layers on the inner walls of furnaces and reactors, are increasingly used in industrial pyrometallurgical processes to ensure that furnace integrity is maintained in these aggressive, high-temperature environments. Most previous studies of freeze-linings have analyzed the formation of slag deposits based solely on heat transfer considerations. These thermal models have assumed that the interface between the stationary frozen layer and the agitated molten bath at steady-state deposit thickness consists of the primary phase, which stays in contact with the bulk liquid at the liquidus temperature. Recent experimental studies, however, have clearly demonstrated that the temperature of the deposit/liquid bath interface can be lower than the liquidus temperature of the bulk liquid. A conceptual framework has been proposed to explain the observations and the factors influencing the microstructure and the temperature of the interface at steady-state conditions. The observations are consistent with a dynamic steady state that is a balance between (I) the rate of nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and (II) the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. It is argued that the assumption that the interface temperature is the liquidus of the bulk material represents only a limiting condition, and that the interface temperature can be between T liquidus and T solidus depending on the process conditions and bath chemistry. These findings have implications for the modeling approach and boundary conditions required to accurately describe these systems. They also indicate the opportunity to integrate considerations of heat and mass flows with the selection of melt chemistries in the design of future high temperature industrial reactors.

Fallah-Mehrjardi, Ata; Hayes, Peter C.; Jak, Evgueni

2014-08-01

105

Understanding Slag Freeze Linings  

NASA Astrophysics Data System (ADS)

Slag freeze linings, the formation of protective deposit layers on the inner walls of furnaces and reactors, are increasingly used in industrial pyrometallurgical processes to ensure that furnace integrity is maintained in these aggressive, high-temperature environments. Most previous studies of freeze-linings have analyzed the formation of slag deposits based solely on heat transfer considerations. These thermal models have assumed that the interface between the stationary frozen layer and the agitated molten bath at steady-state deposit thickness consists of the primary phase, which stays in contact with the bulk liquid at the liquidus temperature. Recent experimental studies, however, have clearly demonstrated that the temperature of the deposit/liquid bath interface can be lower than the liquidus temperature of the bulk liquid. A conceptual framework has been proposed to explain the observations and the factors influencing the microstructure and the temperature of the interface at steady-state conditions. The observations are consistent with a dynamic steady state that is a balance between (I) the rate of nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and (II) the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. It is argued that the assumption that the interface temperature is the liquidus of the bulk material represents only a limiting condition, and that the interface temperature can be between T liquidus and T solidus depending on the process conditions and bath chemistry. These findings have implications for the modeling approach and boundary conditions required to accurately describe these systems. They also indicate the opportunity to integrate considerations of heat and mass flows with the selection of melt chemistries in the design of future high temperature industrial reactors.

Fallah-Mehrjardi, Ata; Hayes, Peter C.; Jak, Evgueni

2014-09-01

106

9 CFR 590.536 - Freezing operations.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Freezing operations. 590...Animal Products FOOD SAFETY AND INSPECTION...Requirements § 590.536 Freezing operations. (a...examination after freezing to determine their fitness for human food. Any such...

2013-01-01

107

9 CFR 590.534 - Freezing facilities.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 2013-01-01 false Freezing facilities. 590.534 ...Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Requirements § 590.534 Freezing facilities. (a) Freezing rooms, either on or off...

2013-01-01

108

9 CFR 590.534 - Freezing facilities.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 2010-01-01 false Freezing facilities. 590.534 ...Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Requirements § 590.534 Freezing facilities. (a) Freezing rooms, either on or off...

2010-01-01

109

9 CFR 590.534 - Freezing facilities.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 2012-01-01 false Freezing facilities. 590.534 ...Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Requirements § 590.534 Freezing facilities. (a) Freezing rooms, either on or off...

2012-01-01

110

9 CFR 590.534 - Freezing facilities.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Freezing facilities. 590.534 ...Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Requirements § 590.534 Freezing facilities. (a) Freezing rooms, either on or off...

2011-01-01

111

9 CFR 590.534 - Freezing facilities.  

...2014-01-01 2014-01-01 false Freezing facilities. 590.534 ...Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Requirements § 590.534 Freezing facilities. (a) Freezing rooms, either on or off...

2014-01-01

112

9 CFR 590.536 - Freezing operations.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 false Freezing operations. 590...Animal Products FOOD SAFETY AND INSPECTION...Requirements § 590.536 Freezing operations. (a...examination after freezing to determine their fitness for human food. Any such...

2012-01-01

113

9 CFR 590.536 - Freezing operations.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Freezing operations. 590...Animal Products FOOD SAFETY AND INSPECTION...Requirements § 590.536 Freezing operations. (a...examination after freezing to determine their fitness for human food. Any such...

2010-01-01

114

9 CFR 590.536 - Freezing operations.  

...2014-01-01 false Freezing operations. 590...Animal Products FOOD SAFETY AND INSPECTION...Requirements § 590.536 Freezing operations. (a...examination after freezing to determine their fitness for human food. Any such...

2014-01-01

115

9 CFR 590.536 - Freezing operations.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 false Freezing operations. 590...Animal Products FOOD SAFETY AND INSPECTION...Requirements § 590.536 Freezing operations. (a...examination after freezing to determine their fitness for human food. Any such...

2011-01-01

116

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

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

117

Assessing vertical soil moisture dynamics using multi-frequency GPR common-midpoint soundings  

NASA Astrophysics Data System (ADS)

SummarySoil moisture measurement techniques are of utmost importance to vadose zone hydrologists. Surface hydrogeophysical methods, such as ground-penetrating radar (GPR), have the capacity to provide field-scale soil moisture information across a range of depth scales. This paper presents an extensive field study using multi-frequency (i.e., 225 MHz, 450 MHz, 900 MHz) GPR common-midpoint (CMP) soundings to monitor a complete annual cycle of soil moisture conditions at three distinct sites. We examine the use of normal-moveout (NMO) velocity analysis applied to CMP data for monitoring highly dynamic vertical soil moisture conditions in a mid-latitude climate consisting of wetting/drying and freeze/thaw cycles with varying degrees of magnitude and vertical velocity gradient. NMO velocity analysis is used to construct interval-velocity-depth models at a fixed location collected every 1-4 weeks. These time-lapse models are combined to construct temporal interval-velocity fields, which are converted into soil moisture content using an appropriate petrophysical relationship. Using these moisture fields, we were able to characterize the vertical distribution and dynamics of soil moisture in the shallow vadose zone. Although the use of multiple antenna frequencies provided varying investigation depths and vertical resolving capabilities, optimal characterization of soil moisture conditions was obtained with high-frequency 900 MHz antennas. The integration of direct ground wave and NMO velocity data from a single CMP sounding allowed us to better refine the shallow soil moisture profile and underlying vadose zone conditions during seasonal wetting, drying and freezing cycles. This study demonstrates the capacity of GPR to characterize vertical moisture dynamics, and highlights the importance of collecting high-resolution data along the air-soil interface to resolve the water content profile from the surface down to the deeper vadose zone conditions.

Steelman, Colby M.; Endres, Anthony L.

2012-05-01

118

7.NS Comparing Freezing Points  

NSDL National Science Digital Library

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

119

Nuclear freeze: myths and realities  

SciTech Connect

A nuclear freeze would create serious problems for US strategic and political interests, and would not achieve the professed goal of a lower probability of nuclear war. It could increase strategic instability and reinforce the morally questionable Mutual Assured Destruction (MAD) approach of using civilian populations as hostages. Compliance would not be verifiable, and Soviet compliance would be doubtful. A review of the strategic and political implications and the basic assumptions of freeze advocates suggests that the movement has proved useful in forcing advocates of other positions to sharpen and refine their arguments. The challenge for freeze opponents is to make it clear to the public that the proposed freeze would benefit the Soviets and to offer viable alternatives for nuclear policy. 15 references.

Weinrod, W.B.

1983-03-03

120

Freezing times of regularly shaped food items  

Microsoft Academic Search

The freezing of food is one of the most significant applications of refrigeration. In order for freezing operations to be cost-effective, it is necessary to optimally design the refrigeration equipment. This requires estimation of the freezing times of foods. Numerous semianalytical\\/empirical methods for predicting food freezing times have been proposed. The designer of food refrigeration facilities is thus faced with

Bryan R. Becker; Brian A. Fricke

1999-01-01

121

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

122

On horizontal wind gradient variability from the stratosphere to the lower troposphere in the Arctic  

Microsoft Academic Search

Previous studies have demonstrated changes in vertical wind shear in recent decades, with implications for upward-propagating planetary waves, the stratospheric polar vortex, and tracer transport. Changes in vertical wind shear combined with horizontal gradients have also been shown to contribute to an increase in vertical gradients in tracer fields, with important implications for vertical transport. In order to explore the

J. V. Lukovich; D. G. Barber

2009-01-01

123

Depth aftereffects mediated by vertical disparities: Evidence for vertical disparity driven calibration of extraretinal signals during stereopsis  

Microsoft Academic Search

Perceptual adaptation often results in a repulsive aftereffect: stimuli are seen as biased away from the adaptation stimulus (Blakemore & Sutton, 1969). Here we report the absence of a repulsive aftereffect for a vertical gradient of vertical disparity (or vertical size ratio, VSR). We exposed observers to a binocular stimulus consisting of horizontal lines. This stimulus contains vertical, but not

Philip A. Duke; Ipek Orucb; Haijiang Qi; Benjamin T. Backus

2006-01-01

124

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

125

Ultrafast microfluidic mixer and freeze-quenching device.  

PubMed

The freeze-quenching technique is extremely useful for trapping meta-stable intermediates populated during fast chemical or biochemical reactions. The application of this technique, however, is limited by the long mixing time of conventional solution mixers and the slow freezing time of cryogenic fluids. To overcome these problems, we have designed and tested a novel microfluidic silicon mixer equipped with a new freeze-quenching device, with which reactions can be followed down to 50 micros. In the microfluidic silicon mixer, seven 10-microm-diameter vertical pillars are arranged perpendicular to the flow direction and in a staggered fashion in the 450-pL mixing chamber to enhance turbulent mixing. The mixed-solution jet, with a cross section of 10 microm x 100 microm, exits from the microfluidic silicon mixer with a linear flow velocity of 20 m/s. It instantaneously freezes on one of two rotating copper wheels maintained at 77 K and is subsequently ground into an ultrafine powder. The ultrafine frozen powder exhibits excellent spectral quality and high packing factor and can be readily transferred between spectroscopic observation cells. The microfluidic mixer was tested by the reaction between azide and myoglobin at pH 5.0. It was found that complete mixing was achieved within the mixing dead time of the mixer (20 micros), and the first observable point for this coupled device was determined to be 50 micros, which is approximately 2 orders of magnitude faster than commercially available instruments. PMID:14710815

Lin, Yu; Gerfen, Gary J; Rousseau, Denis L; Yeh, Syun-Ru

2003-10-15

126

Fuel Cell Freeze Startup and Landscape of FC Freeze Patents  

E-print Network

has a temperature below the freezing temperature of water. The supply of electric current for startup. · Use component/system models to evaluate merits of various solutions from fuel efficiency integrity · Fuel starvation (Elimination of water droplets from flow fields) · Cathode ice formation

127

Effect of acute metabolic acidosis on transmembrane electrolyte gradients in individual renal tubule cells  

Microsoft Academic Search

We studied the effect of acute metabolic acidosis on potassium, sodium and chloride gradients across the apical membrane of proximal and distal tubule cells by determining electrolyte concentrations in individual cells and in tubule fluid employing electron microprobe analysis. Cellular measurements were performed on freeze-dried cryosections of the renal cortex, analysis of tubule fluid electrolyte concentrations on freeze-dried microdroplets of

F.-X. Beck; M. Schramm; A. Dörge; R. Rick; K. Thurau

1988-01-01

128

Transverse freezing of thin liquid films  

NASA Astrophysics Data System (ADS)

A pair of coupled non-linear partial differential equations is derived using lubrication theory that govern the morphology of a thin, liquid film of a pure and a binary metal alloy, bounded by the liquid's solid phase and a passive gas phase. The analysis is motivated by the directional freezing of metallic foams, and is a first attempt to model transverse freezing in thin films that form in foam networks, but also applies to thin film layers in general. Both the no-slip crystal-melt and the free melt-gas interfaces are deformable. The governing pair of non-linear differential equations for the most general case incorporate crystal-melt and melt-gas surface tension, latent heat, heat transfer, volume change, molecular interactions, thermocapillary and dilute phase concentration effects. Linear analysis of a uniform film reveals a variety of instabilities. A unique wavenumber is selected at the onset of instability in the case of an applied temperature gradient with vanishing crystal-melt surface tension. This system reproduces the isothermal result for a rigid solid-liquid interface in which a band of wavenumbers is unstable. A new long-wave instability has been identified, for the case with CM surface tension, that is due to the coupling of the interfaces. Numerical solutions of the fully non-linear system provide film evolution and rupture times, and show that, near the critical conditions, rupture can occur by the growth of standing or traveling waves. The numerics also reveals complex non-linear interactions between unstable modes. It is found that for most unstable initial conditions, the crystal-melt interface retreats by melting away from the tip region of the encroaching melt-gas interface due to a rise in heat flux as the film thins near the rupture point.

Beerman, Michael

129

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

130

Ultrasonic monitoring of food freezing  

Microsoft Academic Search

The time of flight of an ultrasonic pulse moving parallel to the direction of heat flux was measured in blocks of food (gelatin, chicken, beef) during freezing. Echoes were recorded from the food surfaces and from the moving ice front within the food. The changing return times of these echoes were used to calculate the percentage of the food frozen

Halldor Sigfusson; Gregory R. Ziegler; John N. Coupland

2004-01-01

131

Waves, circulation and vertical dependence  

NASA Astrophysics Data System (ADS)

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

Mellor, George

2013-04-01

132

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

133

Freezing: an underutilized food safety technology?  

Microsoft Academic Search

Freezing is an ancient technology for preserving foods. Freezing halts the activities of spoilage microorganisms in and on foods and can preserve some microorganisms for long periods of time. Frozen foods have an excellent overall safety record. The few outbreaks of food-borne illness associated with frozen foods indicate that some, but not all human pathogens are killed by commercial freezing

Douglas L. Archer

2004-01-01

134

Freeze\\/thaw power system. [water expansion  

Microsoft Academic Search

A freeze-thaw power cycle is described that includes a piston driven by the expansion power of a fluid such as water in a cyclinder on freezing and the thawing thereof with alternate, rapid freezing and thawing of the fluid by low and high temperature means with heat transfer rates facilitated by the use of heat pipes or tubes or other

1978-01-01

135

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

136

Biotechnological applications of plant freezing associated Ghislain Breton1  

E-print Network

, freezing tolerance, frozen food, genetic engineering, organ preservation, osmoprotectants, osmotic stress57 Biotechnological applications of plant freezing associated proteins Ghislain Breton1 , Jean and freezing conditions. The identification of these freezing tolerance associated proteins and the elucidation

Sarhan, Fathey

137

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

138

Vertical Farm  

NSDL National Science Digital Library

With the continued growth of the human population of the Earth, there is increasing concern with the planet's ability to provide sustenance for all of its inhabitants. This compelling website by Dickson Despommier and his colleagues at Columbia University provides a worthy alternative to other forms of agriculture: the vertical farm. As Dr. Despommier notes on the site, "..they offer the promise of urban renewal, sustainable production of a safe and varied food supply (year-round crop production), and the eventual repair of ecosystems that have been sacrificed for horizontal farming." The site offers a great deal of information about these vertical farms, a detailed essay on the importance of such farms, a number of potential designs, and a discussion forum. Finally, there are a number of plans that indicate how this type of farm might be effectively created and sustained.

2004-01-01

139

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

140

Exact theory of freeze out  

E-print Network

By considering the kinetic equations for the relic particles and the bath particles supposed in thermal and chemical equilibrium in the early Universe, we show that the problem of finding the present relic abundance is exactly defined by a system of two equations, the usual Boltzmann equation and a new one previously not recognized. The analytical solution of the latter gives the abundance down to a matching temperature that can be identified with freeze out temperature $x_f=m/T_f$, while the usual Boltzmann equation is valid only for $x \\ge x_f$. The dependence of the present relic abundance on the abundance at an intermediate temperature is an exact result and not the consequence of the so called freeze out approximation. We also suggest an analytical approximation that furnishes the relic abundance accurate at the level of $1\\%-2\\%$ in the case of $S$-wave and $P$-wave scattering cross sections.

Cannoni, Mirco

2014-01-01

141

Exact theory of freeze out  

E-print Network

By considering the kinetic equations for the relic particles and the bath particles supposed in thermal and chemical equilibrium in the early Universe, we show that the problem of finding the present relic abundance is exactly defined by a system of two equations, the usual Boltzmann equation and a new one previously not recognized. The analytical solution of the latter gives the abundance down to a matching temperature that can be identified with freeze out temperature $x_f=m/T_f$, while the usual Boltzmann equation is valid only for $x \\ge x_f$. The dependence of the present relic abundance on the abundance at an intermediate temperature is an exact result and not the consequence of the so called freeze out approximation. We also suggest an analytical approximation that furnishes the relic abundance accurate at the level of $1\\%-2\\%$ in the case of $S$-wave and $P$-wave scattering cross sections.

Mirco Cannoni

2014-07-15

142

Commercial Application of Freeze Crystallization  

E-print Network

Comparison The curve for evaporation represenls the installed cost for a multiple effecl, steam driven system. Our cost estimates indicate Ihe total installed capital cost for a mechanical vapor recompression unit would be somewhat higher. We expect... will lower substantially in future generation designs, perhaps even approaching the cost of mechanical vapor recompression evaporation. POWER CONSUMPTION An adherent advantage of freeze crystallization is the low phase change energy required...

Gorgol, R. G.

143

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. PMID:15306323

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

2004-01-01

144

Mapping freeze/thaw boundaries with SMMR data  

NASA Technical Reports Server (NTRS)

Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) data are used to map daily freeze/thaw patterns in the upper Midwest for the Fall of 1984. The combination of a low 37 GHz radiobrightness and a negative 10.7, 18, and 37 GHz spectral gradient, Partial Derivative of Tb with Respect to f, appears to be an effective discriminant for classifying soil as frozen or thawed. The 37 GHz emissivity is less sensitive to soil moisture than are the lower frequency emissivities so that the 37 GHz radiobrightness appears to track soil surface temperature relatively well. The negative gradient for frozen ground is a consequence of volume scatter darkening at shorter microwave wavelengths. This shorter wavelength darkening is not seen in thawed moist soils.

Zuerndorfer, B. W.; England, A. W.; Dobson, M. C.; Ulaby, F. T.

1989-01-01

145

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

146

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

147

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

2012-11-01

148

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

149

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

150

Mechanisms of deterioration of nutrients. [of freeze dried foods  

NASA Technical Reports Server (NTRS)

Methods which produce freeze dried foods of improved quality were examined with emphasis on storage stability. Specific topics discussed include: microstructure of freeze dried systems, investigation of structural changes in freeze dried systems, artificial food matrices, osmotic preconcentration to yield improved quality freeze dried fruits, and storage stability of osmotically preconcentrated freeze dried fruits.

Karel, M.; Flink, J. M.

1976-01-01

151

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

NASA Technical Reports Server (NTRS)

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. It is proposed, as a necessary condition for rapid electrification, that a convective cell must have its updraft speed exceed some threshold value. Based upon field program data, a tentative estimate for the magnitude of this threshold is 6-7 m/s for mean speed and 10-12 m/s for peak speed.

Zipser, Edward J.; Lutz, Kurt R.

1994-01-01

152

On gradient field theories: gradient magnetostatics and gradient elasticity  

E-print Network

In this work the fundamentals of gradient field theories are presented and reviewed. In particular, the theories of gradient magnetostatics and gradient elasticity are investigated and compared. For gradient magnetostatics, non-singular expressions for the magnetic vector gauge potential, the Biot-Savart law, the Lorentz force and the mutual interaction energy of two electric current loops are derived and discussed. For gradient elasticity, non-singular forms of all dislocation key-formulas (Burgers equation, Mura equation, Peach-Koehler stress equation, Peach-Koehler force equation, and mutual interaction energy of two dislocation loops) are presented. In addition, similarities between an electric current loop and a dislocation loop are pointed out. The obtained fields for both gradient theories are non-singular due to a straightforward and self-consistent regularization.

Lazar, Markus

2014-01-01

153

Innovation in Monitoring Food Freeze Drying  

Microsoft Academic Search

This paper aims to extend the field of application of the pressure rise, test technique, from freeze drying of pharmaceutical or biological products in vials to freeze drying of liquids or foodstuff in trays. The proposed method, which is based on DPE algorithm, has been adapted to monitor the drying of liquids in trays and of individually quick frozen products.

Roberto Pisano; Antonello A. Barresi; Davide Fissore

2011-01-01

154

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

155

Crosswind Shear Gradient Affect on Wake Vortices  

NASA Technical Reports Server (NTRS)

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

Proctor, Fred H.; Ahmad, Nashat N.

2011-01-01

156

Mesoscale monitoring of the soil freeze/thaw boundary from orbital microwave radiometry  

NASA Technical Reports Server (NTRS)

A technique was developed for mapping the spatial extent of frozen soils from the spectral characteristics of the 10.7 to 37 GHz radiobrightness. Through computational models for the spectral radiobrightness of diurnally heated freesing soils, a distinctive radiobrightness signature was identified for frozen soils, and the signature was cast as a discriminant for unsupervised classification. In addition to large area images, local area spatial averages of radiobrightness were calculated for each radiobrightness channel at 7 meteorologic sites within the test region. Local area averages at the meteorologic sites were used to define the preliminary boundaries in the Freeze Indicator discriminate. Freeze Indicator images based upon Nimbus 7, Scanning Multichannel Microwave Radiometer (SMMR) data effectively map temporal variations in the freeze/thaw pattern for the northern Great Plains at the time scale of days. Diurnal thermal gradients have a small but measurable effect upon the SMMR spectral gradient. Scale-space filtering can be used to improve the spatial resolution of a freeze/thaw classified image.

Dobson, Craig; Ulaby, Fawwaz T.; Zuerndorfer, Brian; England, Anthony W.

1990-01-01

157

RRab Lyrae metallicity gradient in the Galactic bulge  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

158

Freezing and thawing or freezing, thawing, and aging effects on beef tenderness.  

PubMed

The objective of this study was to determine the effect of freezing and thawing or freezing and thawing with an additional aging period after frozen storage on the tenderness of longissimus lumborum (LL) and semitendinosus (ST) steaks relative to aged, fresh steaks. Left-side LL and ST (n = 35 each) were obtained from U.S. Select carcasses classified at the grading stand by the U.S. Meat Animal Research Center visible and near-infrared spectroscopy tenderness system to have predicted slice shear force greater than 16.5 kg at 14 d postmortem. At 2 d postmortem, 2.54 cm thick steaks were cut from each muscle and assigned to 1 of the following treatments: 2 d fresh (2FRESH), 2 d freeze + thaw (2FREEZE), 2 d freeze + thaw + 12 d age (2FREEZE+12AGE), 14 d fresh (14FRESH), 14 d freeze + thaw (14FREEZE), 14 d freeze + thaw + 14 d age (14FREEZE+14AGE), and 28 d fresh (28FRESH). Steaks assigned to a freezing treatment were frozen at -26°C for 30 d before thawing/cooking or thawing with an additional aging period at 2°C. Slice shear force for LL and ST was lower (P < 0.01) for 2FREEZE (27.4 and 24.5 kg) and 14FREEZE (22.4 and 22.4 kg) compared to 2FRESH (33.0 and 29.2 kg) and 14FRESH (25.3 and 25.5 kg), respectively. Slice shear force for LL and ST was lower (P < 0.01) for 2FREEZE+12AGE (17.8 and 20.8 kg) and 14FREEZE+14AGE (14.6 and 19.0 kg) compared to 14FRESH (25.3 and 25.5 kg) and 28FRESH (18.7 and 21.7 kg), respectively. Desmin degradation for LL was not different (P > 0.05) between 2FREEZE (21.0%) and 2FRESH (14.6%) or between 14FREEZE (40.4%) and 14FRESH (38.4%); however, desmin degradation was higher (P < 0.06) in 2FREEZE+12AGE (46.7%) and 14FREEZE+14AGE (71.1%) when compared to 14FRESH (38.4%) and 28FRESH (60.5%), respectively. Cooking loss for LL was higher (P < 0.01) in 2FREEZE+12AGE (15.2%) compared to 14FRESH (14.0%) but was not different (P > 0.05) between 14FREEZE+14AGE (15.0%) and 28FRESH (14.3%). Freezing and thawing or a combination of freezing, thawing, and aging resulted in increased tenderness for LL and ST steaks when compared to fresh steaks with the same aging time. These results indicate freezing could be incorporated into normal commercial product distribution processes to improve the consistency of meat tenderness. Researchers who freeze steaks before tenderness assessment should be aware and acknowledge that freezing affects tenderness data. PMID:24671601

Grayson, A L; King, D A; Shackelford, S D; Koohmaraie, M; Wheeler, T L

2014-06-01

159

Exploring the Nature of Contact Freezing  

NASA Astrophysics Data System (ADS)

The freezing of supercooled water droplets upon contact with aerosol particles (contact nucleation of ice) is the least understood mechanism of ice formation in atmospheric clouds. Although experimental evidences suggest that some aerosols can be better IN in the contact than in the immersion mode (that is, triggering ice nucleation at higher temperature), no final explanation of this phenomena currently exists. On the other hand, the contact freezing is believed to be responsible for the enhanced rate of secondary ice formation occasionally observed in LIDAR measurements in the cold mixed phase clouds. Recently we have been able to show that the freezing of supercooled droplets electrodynamically levitated in the laminar flow containing mineral dust particles (kaolinite) is a process solely governed by a rate of collisions between the supercooled droplet and the aerosol particles. We have shown that the probability of droplet freezing on a single contact with aerosol particle may differ over an order of magnitude for kaolinite particles having different genesis and morphology. In this presentation we extend the study of contact nucleation of ice and compare the IN efficiency measured for DMA-selected kaolinite, illite and hematite particles. We show that the freezing probability increases towards unity as the temperature decreases and discuss the functional form of this temperature dependence. We explore the size dependence of the contact freezing probability and show that it scales with the surface area of the particles, thus resembling the immersion freezing behavior. However, for all minerals investigated so far, the contact freezing has been shown to dominate over immersion freezing on the short experimental time scales. Finally, based on the combined ESEM and electron microprobe analysis, we discuss the significance of particle morphology and variability of chemical composition on its IN efficiency in contact mode.

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

2012-12-01

160

Hot big bang or slow freeze?  

E-print Network

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

C. Wetterich

2014-01-21

161

Hot big bang or slow freeze?  

NASA Astrophysics Data System (ADS)

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

Wetterich, C.

2014-09-01

162

Freezing precipitation in the Southeastern United States  

E-print Network

- ample of freezing precipitation coating trees is shown in Fig, 1~ a photograph taken during a storm in College Station~ Texas~ on 6 November 1959 ' It is most ccmmonly referred to as an ice storm, a glaze storm~ or freezing rain (or freezing drizzle... dollars in damages to trees alone Tnese and other significan't sto ms occurring $n tha - ou heastern Wn1tEK3 Sta'tes ( 1 the past 30 years) are listed in Ta?le 1, The amount of ice forming on e~ose i objects varies frc. . storm to storm. According...

Young, William Robert

2012-06-07

163

Shadowgraph Study of Gradient Driven Fluctuations  

NASA Technical Reports Server (NTRS)

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(sup -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

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

2002-01-01

164

Freeze concentration beats the heat  

SciTech Connect

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 juices were found to be superior in taste to juices produced by evaporation and similar to the original pasteurized juices. The dairy industry, which is the largest user of energy for concentration in the food sector, is looking to FC for new products such as frozen concentrated milk as well as better use of the milk by-products of cheese production. The biggest potential for new FC applications is in those industries that consume large amounts of energy for separation processing, according to a 1987 report prepared for EPRI. In the food industry, this includes milk, vinegar, and beer producers. Potential applications also abound in the pulp and paper, pharmaceutical, chemical, and petroleum industries. FC separates substances via crystallization at substantial energy savings.

Rosen, J.

1990-12-01

165

Sublimation of Formaldehyde in Freeze-Drying.  

National Technical Information Service (NTIS)

Formaldehyde solution, commonly used to inactivate bacterial, rickettsial and viral suspensions during the preparation of vaccine, is known to have a deleterious effect on many antigens during freeze-drying. Sublimation of formaldehyde in shell-frozen and...

P. L. Altieri, S. Berman, J. P. Lowenthal

1977-01-01

166

Freeze Crystallization Processes: Efficiency by Flexibility  

E-print Network

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

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

1983-01-01

167

On Freezing and Reactivating Learnt Clauses  

Microsoft Academic Search

\\u000a In this paper, we propose a new dynamic management policy of the learnt clause database in modern sat solvers. It is based on a dynamic freezing and activation principle of the learnt clauses. At a given search state, using\\u000a a relevant selection function, it activates the most promising learnt clauses while freezing irrelevant ones. In this way,\\u000a clauses learned at

Gilles Audemard; Jean-Marie Lagniez; Bertrand Mazure; Lakhdar Saïs

168

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.)

169

Freezing of Xylem Sap Without Cavitation  

PubMed Central

Freezing of stem sections and entire twigs of hemlock (Tsuga canadensis) has been demonstrated to occur without increasing the resistance to the movement of water through the frozen part after rewarming. This was interpreted to mean that freezing did not produce cavitation in the xylem sap even though A) the sap was unquestionably frozen; B) it contained dissolved gases; and C) it was under tension before freezing and after. Freezing stem sections of some other evergreen gymnosperms during the summer again produced no evidence for cavitation of the xylem sap. On the other hand, freezing stem sections of some angiosperms invariably increased the resistance to sap flow leading to wilting and death in a few hours when the sap tension was at normal daytime values at the time of freezing. These results were interpreted to mean that the bordered pits on the tracheids of gymnosperms function to isolate the freezing sap in each tracheid so that the expansion of water upon freezing not only eliminates any existing tension but also develops positive pressure in the sap. Dissolved gases frozen out of solution may then be redissolved under this positive pressure as melting occurs. As the bubbles are reduced in size by this ice pressure developed in an isolated tracheid, further pressure is applied by the surface tension of the water against air. If the bubbles are redissolved or are reduced to sufficient small size by the time the tension returns to the sap as the last ice crystals melt, then the internal pressure from surface tension in any existing small bubbles may exceed the hydrostatic tension of the melted sap and the bubbles cannot expand and will continue to dissolve. PMID:16656485

Hammel, H. T.

1967-01-01

170

Compression of cooked freeze-dried carrots  

E-print Network

. Reduction in volume of up to 18-fold can be obtained by com- pressing dehydrated vegetables (Rabman, 1969). During World War II, the United Kingdom produced dehydrated cabbage and carrots in compressed blocks (Gooding and Rolfe, 1967). Fairbrother (1968...-propanol at low concentration by freeze-drying carbohydrate solutions. J. of Food Sci. 37:617. Flosdorf, E. W. 1949. "Freeze-drying, " Reinhold Publishing Co. , New York. Gooding, E. B. B. and Rolfe, E. J. 1957. Some Recent Work on Dehy- dration...

Macphearson, Bruce Alan

2012-06-07

171

arising from the vertical density gradient and the sloping interface  

E-print Network

, Moderate Resolution Imaging Spectroradiometer (MODIS) Mosaic of Antarctica (MOA) Image Map (National Snow in satellite imagery and the airborne radar survey, in conjunction with the vigorous melt rates here described

Myers, Ransom A.

172

Vertical abundance gradients in Ap-star atmospheres  

NASA Astrophysics Data System (ADS)

A brief review of the theoretical and observational studies of abundance stratification in the atmospheres of late A to early B stars is presented. It includes observational evidence of abundance stratification in classical magnetic Ap stars, and a comparison between theory and observations. An important application of chemically stratified atmospheres is the study of pulsations in cool Ap stars (roAp), where different abundance distributions of groups of elements naturally explain the observed distribution of the pulsational amplitudes and phases across the atmosphere. The influence of magnetic fields on creating the abundance distributions seems to be small.

Ryabchikova, T.

2014-11-01

173

Ris-R-Report Analysis of vertical wind direction and speed  

E-print Network

for LIDAR and vane data 17 4.3 Relation between wsp and 80 m wind speed 18 4.4 Relation between DirectionRisø-R-Report Analysis of vertical wind direction and speed gradients for data from the met. mast Cariou, Rozenn Wagner, Julia Gottschall Title: Analysis of vertical wind direction and speed gradients

174

Near-surface temperature gradient in a coastal upwelling regime  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

175

Eddy-Driven Buoyancy Gradients on Eastern Boundaries and Their Role in the Thermocline  

E-print Network

Eddy-Driven Buoyancy Gradients on Eastern Boundaries and Their Role in the Thermocline PAOLA CESSI that eddy fluxes of buoyancy at the eastern and western boundaries maintain alongshore buoyancy gradients buoyancy gradients normal to the boundary are strong. The eddy fluxes are accompanied by mean vertical

Cessi, Paola

176

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)] [Sandia National Labs., Livermore, CA (United States); Chui, H.C. [Sandia National Labs., Albuquerque, NM (United States)] [and others] [Sandia National Labs., Albuquerque, NM (United States); and others

1996-06-01

177

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

178

UltraViolet Freeze-in  

E-print Network

If dark matter is thermally decoupled from the visible sector, the observed relic density can potentially be obtained via freeze-in production of dark matter. Typically in such models it is assumed that the dark matter is connected to the thermal bath through feeble renormalisable interactions. Here, rather, we consider the case in which the hidden and visible sectors are coupled only via non-renormalisable operators. This is arguably a more generic realisation of the dark matter freeze-in scenario, as it does not require the introduction of diminutive renormalisable couplings. We examine general aspects of freeze-in via non-renormalisable operators in a number of toy models and present several motivated implementations in the context of Beyond the Standard Model physics. Specifically, we study models related to the Peccei-Quinn mechanism and Z' portals.

Elahi, Fatemeh; Unwin, James

2014-01-01

179

Time dependence of immersion freezing: an experimental study on size selected kaolinite particles  

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, 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 for an increase in times scale by one order of magnitude. This suggests that temperature is more important than time.

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

2012-10-01

180

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

PubMed

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 not. Viability rates of hatchlings frozen to -3 degrees C for 72 h ranged from 0 to 100%. Tolerance to freezing was poor in Sternotherus odoratus, Graptemys geographica and Trachemys scripta, intermediate in Chelydra serpentina, and high in Emydoidea blandingii, Chrysemys picta bellii, C. p. marginata, Malaclemys terrapin, and Terrapene ornata, and generally reflected the winter thermal ecology of each taxon. Plasma activity of lactate dehydrogenase (LDH), a novel in vivo index of freeze/thaw damage, corroborated viability assessments and demonstrated that cryoinjury occurred even in surviving turtles. Irrespective of taxon, cryoinjury tended to be higher in smaller individuals and in those having relatively low water contents; however, bases for these associations were not apparent. Screening for certain organic osmolytes that might promote freezing survival by colligatively reducing ice content and limiting cell dehydration showed that the plasma of unfrozen (control) turtles contained small quantities of glucose (1.3-5.8 mmol l(-1)) and lactate (0.6-3.2 mmol l(-1)) and modest amounts of urea (range of mean values for all taxa 8.2-52.3 mmol l(-1)). Frozen/thawed turtles of all taxa accumulated modest amounts of glucose and lactate that jointly raised the plasma solute concentration by 30-100 mmol l(-1). We conclude that organic osmolytes accumulated both before and during freezing may promote survival in species that have evolved a tolerance to freezing, but are not necessarily accumulated for that purpose. PMID:16758216

Costanzo, Jon P; Baker, Patrick J; Lee, Richard E

2006-09-01

181

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

182

GRADIENT CONVERGENCE IN GRADIENT METHODS WITH ERRORS  

E-print Network

/backpropagation method for neural network training, the convergence of which has been the object of much recent analysis [Luo91], [Gai94], [Gri94], [LuT94], [MaS94], [Man93], [Ber95a] (see [BeT96] for our discussion of incre- mental gradient methods and their application to neural network training). The method where the errors wt

Bertsekas, Dimitri

183

Gas-solid flow in vertical tubes  

Microsoft Academic Search

This paper reports on a computational study of fully-developed flow of gas-particle suspensions in vertical pipes which was carried out, using the model proposed recently by Sinclair and Jackson, to understand the predicted scale-up characteristics. It was shown that the model can capture the existence of steady-state multiplicity wherein different pressure gradients can be obtained for the same gas and

Jorge A. Pita; Sankaran Sundaresan

1991-01-01

184

Doering 6/2004 Freezing Cell Lines  

E-print Network

and thawing are below. Reagents/equipment: Sterile freezer vials 50% glycerol, sterile Dry ice/ethanol bath a few times. 5. Freeze the vials on dry ice or in a dry ice/ethanol bath. 6. Store the vials you plan to thaw. Remove the vial you need from the freezer (ideally to dry ice) and quickly scratch

Doering, Tamara

185

TISSUE FREEZING METHODS FOR CRYOSTAT SECTIONING  

E-print Network

, sucrose cryoprotected tissue freezing ­ Tissue is in OCT and may be frozen using dry ice or the flash - and depending on the method prepare liquid nitrogen, isopentane, dry ice. · Label ahead of time - cryo molds, aluminum foil, specimen bags while at room temperature. · Covered Foam cooler with crushed dry ice

Chisholm, Rex L.

186

Freeze fracturing of elastic porous media  

E-print Network

The physical motivation behind this thesis is the phenomenon of fracturing of rocks and other porous media due to ice growth inside pre-existing faults and large pores. My aim is to explain the basic physical processes taking place inside a freezing...

Vlahou, Ioanna

2012-06-12

187

Fast hadron freeze-out generator  

NASA Astrophysics Data System (ADS)

We have developed a fast Monte Carlo procedure of hadron generation that allows one to study and analyze various observables for stable hadrons and hadron resonances produced in ultrarelativistic heavy ion collisions. Particle multiplicities are determined based on the concept of chemical freeze-out. Particles can be generated on the chemical or thermal freeze-out hypersurface represented by a parametrization or a numerical solution of relativistic hydrodynamics with given initial conditions and equation of state. Besides standard spacelike sectors associated with the volume decay, the hypersurface may also include nonspacelike sectors related to the emission from the surface of expanding system. For comparison with other models and experimental data, we demonstrate the results based on the standard parametrizations of the hadron freeze-out hypersurface and flow velocity profile under the assumption of a common chemical and thermal freeze-out. The C++ generator code is written under the ROOT framework and is available for public use at http://uhkm.jinr.ru/.

Amelin, N. S.; Lednicky, R.; Pocheptsov, T. A.; Lokhtin, I. P.; Malinina, L. V.; Snigirev, A. M.; Karpenko, Iu. A.; Sinyukov, Yu. M.

2006-12-01

188

Freeze-Dehydration by Microwave Energy.  

National Technical Information Service (NTIS)

A general unsteady state analysis is used to derive a mathematical model of the freeze-drying process using microwave heating. The temperature and water vapor concentration profiles inside the material being dried are calculated. The model is applied to s...

P. R. F. Peltre

1974-01-01

189

Preservation of flavor in freeze dried green beans  

NASA Technical Reports Server (NTRS)

Before freeze drying, green beans are heated to point at which their cell structure is altered. Beans freeze dried with altered cell structure have improved rehydration properties and retain color, flavor, and texture.

Huber, C. S.; Heidelbaugh, N. D.; Davis, D.

1973-01-01

190

Gradient index metamaterials  

Microsoft Academic Search

Metamaterials---artificially structured materials with tailored electromagnetic response---can be designed to have properties difficult or impossible to achieve with traditional materials fabrication methods. Here we present a structured metamaterial, based on conducting split ring resonators (SRRs), which has an effective index of refraction with a constant spatial gradient. We experimentally confirm the gradient by measuring the deflection of a microwave beam

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

2005-01-01

191

A Natural Policy Gradient  

Microsoft Academic Search

We provide a natural gradient method that represents the steepestdescent direction based on the underlying structure of the parameterspace. Although gradient methods cannot make large changesin the values of the parameters, we show that the natural gradientis moving toward choosing a greedy optimal action rather thanjust a better action. These greedy optimal actions are those thatwould be chosen under one

Sham Kakade

2001-01-01

192

Tandem High-pressure Freezing and Quick Freeze Substitution of Plant Tissues for Transmission Electron Microscopy.  

PubMed

Since the 1940s transmission electron microscopy (TEM) has been providing biologists with ultra-high resolution images of biological materials. Yet, because of laborious and time-consuming protocols that also demand experience in preparation of artifact-free samples, TEM is not considered a user-friendly technique. Traditional sample preparation for TEM used chemical fixatives to preserve cellular structures. High-pressure freezing is the cryofixation of biological samples under high pressures to produce very fast cooling rates, thereby restricting ice formation, which is detrimental to the integrity of cellular ultrastructure. High-pressure freezing and freeze substitution are currently the methods of choice for producing the highest quality morphology in resin sections for TEM. These methods minimize the artifacts normally associated with conventional processing for TEM of thin sections. After cryofixation the frozen water in the sample is replaced with liquid organic solvent at low temperatures, a process called freeze substitution. Freeze substitution is typically carried out over several days in dedicated, costly equipment. A recent innovation allows the process to be completed in three hours, instead of the usual two days. This is typically followed by several more days of sample preparation that includes infiltration and embedding in epoxy resins before sectioning. Here we present a protocol combining high-pressure freezing and quick freeze substitution that enables plant sample fixation to be accomplished within hours. The protocol can readily be adapted for working with other tissues or organisms. Plant tissues are of special concern because of the presence of aerated spaces and water-filled vacuoles that impede ice-free freezing of water. In addition, the process of chemical fixation is especially long in plants due to cell walls impeding the penetration of the chemicals to deep within the tissues. Plant tissues are therefore particularly challenging, but this protocol is reliable and produces samples of the highest quality. PMID:25350384

Bobik, Krzysztof; Dunlap, John R; Burch-Smith, Tessa M

2014-01-01

193

Vertical profiles of condensation nuclei  

NASA Technical Reports Server (NTRS)

Condensation nuclei measurements using a low supersaturation (about 10%) thermal gradient diffusion cloud chamber (TGDCC) and a high supersaturation (about 200%) expansion type instrument were compared on a series of three balloon flights over Laramie, Wyoming. In general, the two instruments produced similar vertical profiles but some discrepancies remain unexplained. Agreement between the two would indicate that the low supersaturations used in the TGDCC were still large enough to cause the instrument to count essentially all of the particles present. The TGDCC condensation nuclei (CN) counter was flown at several sites in both the Northern and Southern Hemispheres. The results indicate the existence of a relative maximum in the CN mixing ratio associated with the upper equatorial troposphere and what appears to be a worldwide constant mixing ratio of CN above 20-25 km.

Rosen, J. M.; Hofmann, D. J.; Kaselau, K. H.

1978-01-01

194

Foliar applied urea improves freezing protection to avocado and peach  

Microsoft Academic Search

The effect of foliar applied urea on freeze hardiness was evaluated under orchard and laboratory conditions. Freezing injury and senescence of avocado (Persea americana Mill.) cv. ‘Hass’ leaves in the orchard was inversely correlated to N content. Three foliar applications of 2% low-biuret urea caused a 26% nitrogen enrichment of leaves. Consequently, leaf freezing hardiness was increased and senescence retarded.

S. Zilkah; Z. Wiesmann; I. Klein; I. David

1996-01-01

195

47 CFR 64.1190 - Preferred carrier freezes.  

Code of Federal Regulations, 2012 CFR

...of the specific procedures necessary to lift a preferred carrier freeze; an explanation...change in carrier selection unless he or she lifts the freeze. (iii) An explanation of...change in carrier selection unless she or he lifts the preferred carrier freeze; and...

2012-10-01

196

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

197

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

198

Offset vertical radar profiling  

USGS Publications Warehouse

Diffraction tomography imaging was applied to VRP data acquired by vertically moving a receiving antenna in a number of wells. This procedure simulated a vertical downhole receiver array. Similarly, a transmitting antenna was sequentially moved along a series of radial lines extending outward from the receiver wells. This provided a sequence of multistatic data sets and, from each data set, a two-dimensional vertical cross-sectional image of spatial variations in wave speed was reconstructed.

Witten, A.; Lane, J.

2003-01-01

199

Study of freezing-point depression of selected food extracts  

SciTech Connect

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

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

1996-12-31

200

Electrochemically generated gradients.  

PubMed

This review surveys recent developments in the field of electrochemically generated gradients. The gradual variation of properties, which is a key characteristic of gradients, is of eminent importance in technology, for example, directional wetting, as well as biology, for example, chemotaxis. Electrochemical techniques offer many benefits, such as the generation of dynamic solution and surface gradients, integration with electronics, and compatibility with automation. An overview is given of newly developed methods, from purely electrochemical techniques to the combination of electrochemistry with other methods. Electrochemically fabricated gradients are employed extensively for biological and technological applications, such as high-throughput screening, high-throughput deposition, and device development, all of which are covered herein. Especially promising are developments towards the study and control of dynamic phenomena, such as the directional motion of molecules, droplets, and cells. PMID:24961906

Krabbenborg, Sven O; Huskens, Jurriaan

2014-08-25

201

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

202

Freeze Thaw Durability of Modern Concrete Mixtures  

E-print Network

Techniques #12;Current Measuring Techniques PCA photo ASTM C 231 PCA photo ASTM C 173 ASTM C 138 #12;Current Measuring Techniques PCA photo ASTM C 231 PCA photo ASTM C 173 ASTM C 138 These only measure volume!!! #12;0.0 0.1 0.2 0.3 0.4 0 2 4 6 8 10 air content ASTM C 231 (%) spacingfactor(mm) recommended for freeze

203

Freeze-branding to permanently mark bats  

Microsoft Academic Search

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

Richard E. Sherwin; Shauna Haymond; Rebeccah Olsen

204

One-stage model of foods freezing  

Microsoft Academic Search

The freezing process in a NaCl eutectic solution is discussed taking into account both a non-constant specific heat and a non-constant thermal conductivity as potential functions of temperature. The non-linearity of the problem is introduced in the heat diffusion equation and in its boundary conditions. A strictly exact solution is used to solve it. By considering only conduction heat transfer

P. D. Sanz; M. Ramos; J. Aguirre-Puente

1999-01-01

205

Freezing and Frozen-Food Storage  

Microsoft Academic Search

\\u000a Food freezing is the preservation process that depends on the reduction of product temperature to levels well below the temperature\\u000a at which ice crystals begin to form within the food. By reducing the temperature of the product to -10 to -20°C, the normal\\u000a reactions that cause deterioration of foods are reduced to negligible or minimal rates. These temperature levels limit

Dennis R. Heldman; Richard W. Hartel

206

Introduction: plant cold acclimation and freezing tolerance.  

PubMed

This introductory chapter provides a brief overview of plant freezing tolerance and cold acclimation and describes the basic concepts and approaches that are currently followed to investigate these phenomena. We highlight the multidisciplinary nature of these investigations and the necessity to use methodologies from different branches of science, such as ecology, genetics, physiology, biochemistry, and biophysics, to come to a complete understanding of the complex adaptive mechanisms underlying plant cold acclimation. PMID:24852623

Hincha, Dirk K; Zuther, Ellen

2014-01-01

207

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

208

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

209

Infrared Freezing of Euclidean QCD observables  

E-print Network

We consider the leading one-chain term in a skeleton expansion for QCD observables and show that for energies Q^2>\\Lambda^2, where Q^2=\\Lambda^2 is the Landau pole in the coupling, the skeleton expansion result is equivalent to the standard Borel integral representation, with ambiguities related to infrared (IR) renormalons. For Q^2skeleton expansion result is equivalent to a previously proposed modified Borel representation where the ambiguities are connected with ultraviolet (UV) renormalons. We investigate the Q^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^2=\\Lambda^2, and then exhibits freezing behaviour, vanishing at Q^2=0. Finiteness at Q^2=\\Lambda^2 implies specific relations between the residues of IR and UV renormalons 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 non-perturbative and perturbative ambiguities we are led to a result for the Q^2 dependence of these observables at all Q^2, in which there is a single undetermined non-perturbative parameter, and which involves the skeleton expansion characteristic function. The observables freeze to zero in the infrared. We briefly consider the freezing behaviour of the Minkowskian R_{e+e-} ratio.

Paul M. Brooks; C. J. Maxwell

2006-04-28

210

Freezing of glycerol-water mixtures under pressure.  

PubMed

We investigated freezing of pure glycerol as well as glycerol-water (GW) mixtures with 3:1 and 3:2 volume fractions as a function of pressure in the 0-10 GPa range by ruby fluorescence spectroscopy and neutron scattering. We find that the glass transition pressure increases from 5.5 GPa for pure glycerol to 6.5 GPa for the 3:1 GW mixture, with unusually small pressure gradients above. For higher water concentrations close to 3:2, phase separation occurs above 2 GPa where most of the water is expelled in the form of ice VII. The results suggest that glycerol is able to effectively hydrogen bond not more than ?2.5 H(2)O molecules per glycerol, which seems to support conclusions from molecular dynamics simulations. The data indicate that these fluids could become important as pressure transmitting media for neutron scattering in the 0-7 GPa range, including at low temperatures. PMID:22689331

Klotz, S; Takemura, K; Strässle, Th; Hansen, Th

2012-08-15

211

Fundamental Technical Elements of Freeze-fracture/Freeze-etch in Biological Electron Microscopy.  

PubMed

Freeze-fracture/freeze-etch describes a process whereby specimens, typically biological or nanomaterial in nature, are frozen, fractured, and replicated to generate a carbon/platinum "cast" intended for examination by transmission electron microscopy. Specimens are subjected to ultrarapid freezing rates, often in the presence of cryoprotective agents to limit ice crystal formation, with subsequent fracturing of the specimen at liquid nitrogen cooled temperatures under high vacuum. The resultant fractured surface is replicated and stabilized by evaporation of carbon and platinum from an angle that confers surface three-dimensional detail to the cast. This technique has proved particularly enlightening for the investigation of cell membranes and their specializations and has contributed considerably to the understanding of cellular form to related cell function. In this report, we survey the instrument requirements and technical protocol for performing freeze-fracture, the associated nomenclature and characteristics of fracture planes, variations on the conventional procedure, and criteria for interpretation of freeze-fracture images. This technique has been widely used for ultrastructural investigation in many areas of cell biology and holds promise as an emerging imaging technique for molecular, nanotechnology, and materials science studies. PMID:25285532

Carson, Johnny L

2014-01-01

212

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

213

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

PubMed Central

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

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

2011-01-01

214

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

PubMed

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

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

2011-01-01

215

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

NASA Astrophysics Data System (ADS)

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

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

2003-09-01

216

Underground structure detection by surface magnetic gradient measurements  

Microsoft Academic Search

This problem involves magnetic induction methods to locate and determine the depth of a subsurface line source of magnetic field. The origin of the field may be self- generated or induced by a surface transmitter. The experimental method requires measuring the horizontal gradient of either the vertical or horizontal component of the field rather than the field itself so as

Robert E. Kelly

2001-01-01

217

Temperature gradient in retort for pyrolysis of carbon containing solids  

Microsoft Academic Search

This patent describes a temperature gradient in retort for pyrolysis of carbon containing solids within a process for retorting oil shale wherein particulate raw oil shale is retorted by passing the raw oil shale into the upper portion of a vertically-elongated retorting vessel having a retorting zone equipped with dispersing elements so constructed and arranged as to substantially limit backmixing

B. G. Spars; R. P. Sieg

1986-01-01

218

Gradient Heterogeneous Surface  

NASA Astrophysics Data System (ADS)

The strength of the interfacial interaction and the length scale over which the interaction occurs are two important factors to understand the polymer blends (Lsp 100 nm), diblock copolymers (Lb 30 nm), cell recognition, random heteropolymer, adhesion (ex. Protein, cell) and wettability on a surface. This has important implications in pattern recognition applications, biosensors and random recognition processes. A gradient pattern is produced on a surface with two different surface energies, analogous to a gradient checkerbroad. Indirectly, this would give some insight on random heteropolymer and multifunctional disordered surfaces and biomimetic recognition between polymer and surfaces. To achieve this, a gradient surface is created to vary the lateral size scale correlation of heterogeneity. Two possible routes will be presented to vary different size scale, for example, from micron to nano scale. Then, the gradient surface will be used as a template to vary the surface interaction, i.e. having one domain hydrophilic and hydrophobic the other. And finally, this lateral size scale correlation having two different interaction sites is used to examine the phase separation of polymer blend films, cell recognition, and diblock copolymer films on this gradient heterogenous surface.

Tsai, Irene; Kimura, Masahiro; Lin, Zhiqun; Stockton, Rebecca; Fadeev, Alex; Jacobson, Bruce; Russell, Thomas P.

2002-03-01

219

Automated apparatus for producing gradient gels  

DOEpatents

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

Anderson, N.L.

1983-11-10

220

Automated apparatus for producing gradient gels  

DOEpatents

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

Anderson, Norman L. (Clarendon Hills, IL)

1986-01-01

221

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

222

Longitudinal chemical gradients in hot Jupiter atmospheres  

NASA Astrophysics Data System (ADS)

We have built a pseudo two-dimensional (altitude and longitude) model to study the chemistry in the atmosphere of hot Jupiters. Our model considers a vertical column of atmosphere that rotates along the equator, mimicking a superrotating wind. We have applied it to the well known exoplanets HD 209458b and HD 189733b. We find that below a certain pressure level, which may be located somewhere between 10 bar and 10 mbar depending on the molecule, the chemical composition is given by thermochemical equilibrium, while about such level, the dynamical time scales for vertical and horizontal mixing compete producing a complex abundance distribution with altitude and longitude. A main conclusion of our study is that some molecules such as CO, H2O, and N2 maintain rather constant abundances with altitude and longitude while others such as CO2, CH4, NH3, and HCN show important abundance gradients as a function of longitude.

Agundez, M.; Parmentier, V.; Venot, O.; Selsis, F.

2013-09-01

223

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

224

High gradient superconducting quadrupoles  

SciTech Connect

Prototype superconducting quadrupoles with a 5 cm aperture and gradient of 16 kG/cm have been built and tested as candidate magnets for the final focus at SLC. The magnets are made from NbTi Tevatron style cable with 10 inner and 14 outer turns per quadrant. Quench performance and multipole data are presented. Design and data for a low current, high gradient quadrupole, similar in cross section but wound with a cable consisting of five insulated conductors are also discussed.

Lundy, R.A.; Brown, B.C.; Carson, J.A.; Fisk, H.E.; Hanft, R.H.; Mantsch, P.M.; McInturff, A.D.; Remsbottom, R.H.

1987-07-01

225

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

226

High gradient electron guns  

SciTech Connect

Experiments have been conducted to determine peak operating gradients attainable in thermionic electron guns. These tests are part of a study of high-current-density, long-life cathodes suitable for use in high power klystrons. We also investigated the use of chromium oxide coating as a means of inhibiting electronic breakdown across the focus electrode anode gap. Field gradients in excess of 280 kV/cm have been achieved for a gun operating at 240 kV with a beam current of 228 A, at pulse widths of the order of 1 {mu}s. 3 refs., 5 figs.

Fant, K.S.; Caryotakis, G.; Koontz, R.F.; Vlieks, A.E. (Stanford Linear Accelerator Center, Menlo Park, CA (USA)); Miram, G. (Miram (G.), Atherton, CA (USA))

1990-08-01

227

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

228

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

229

The Ammonia Freeze Explosion (AFEX) process  

SciTech Connect

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

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

1991-12-31

230

Micromachined electrostatic vertical actuator  

SciTech Connect

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

Lee, A.P.; Sommargren, G.E.; McConaghy, C.F.; Krulevitch, P.A.

1999-10-19

231

Micromachined electrostatic vertical actuator  

DOEpatents

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

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

1999-10-19

232

Free-air gradient observations in Yucca Flat, Nye County, Nevada  

Microsoft Academic Search

In Yucca Flat, Nevada Test Site, the free-air gradient (F) has been calculated from international formulas and from surface gravity data. It has also been determined from measurements on, or near, the ground surface and at an elevated position vertically above. The latter (measured), has been the principal method of determining F at Yucca Flat. The free-air gradient is used

P. S. Powers; D. L. Healey

1985-01-01

233

Limitations of determining density or magnetic boundaries from the horizontal gradient of gravity or pseudogravity data.  

USGS Publications Warehouse

Offsets of horizontal-gradient magnitude maxima (gradient maxima) from a position directly over the boundary are predicted for cases where boundaries are not near-vertical or where several boundaries are close together. These are illustrated by offset equations; other factors which cause offsets are discussed briefly. -after Authors

Grauch, V. J. S.; Cordell, L.

1987-01-01

234

Air-cooled steam condensers non-freeze warranties  

SciTech Connect

What this paper is suggesting is the seller quote a condenser package with a LIMITED NON-FREEZE WARRANTY. Relieve the inexperienced buyer of the responsibility for selecting freeze protection design options. The seller cannot afford to over-design because of the added costs and the need for a competitive price. Yet he cannot under-design and allow the condenser tubes to freeze periodically and then pay the repair bills in accordance with the warranty.

Larinoff, M.W.

1995-09-01

235

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

236

Manipulating the Gradient  

ERIC Educational Resources Information Center

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

Gaze, Eric C.

2005-01-01

237

Gradient Refractive Index Lenses.  

ERIC Educational Resources Information Center

Describes the nature of gradient refractive index (GRIN) lenses, focusing on refraction in these materials, focal length of a thin Wood lens, and on manufacturing of such lenses. Indicates that GRIN lenses of small cross section are in limited production with applications suggested for optical communication and photocopying fields. (JN)

Morton, N.

1984-01-01

238

Gradient Heterogeneous Surface  

Microsoft Academic Search

The strength of the interfacial interaction and the length scale over which the interaction occurs are two important factors to understand the polymer blends (Lsp 100 nm), diblock copolymers (Lb 30 nm), cell recognition, random heteropolymer, adhesion (ex. Protein, cell) and wettability on a surface. This has important implications in pattern recognition applications, biosensors and random recognition processes. A gradient

Irene Tsai; Masahiro Kimura; Zhiqun Lin; Rebecca Stockton; Alex Fadeev; Bruce Jacobson; Thomas P. Russell

2002-01-01

239

Structurally Caused Freezing Point Depression of Biological Tissues  

PubMed Central

When investigating the freezing behaviour (by thermal analysis) of the glycerol-extracted adductor muscle of Mytilus edulis it was observed that the temperature of ice formation in the muscular tissue was up to 1.5°C lower than the freezing point of the embedding liquid, a 0.25 N KCl solution with pH = 4.9 with which the tissue had been equilibrated prior to the freezing experiment. A smaller freezing point depression was observed if the pH values of the embedding 0.25 N KCl solution were above or below pH = 4.9. Reasoning from results obtained previously in analogous experiments with artificial gels, the anomalous freezing depression is explained by the impossibility of growing at the normal freezing temperature regular macroscopic crystals inside the gel, due to the presence of the gel network. The freezing temperature is here determined by the size of the microprisms penetrating the meshes of the network at the lowered freezing temperature. This process leads finally to an ice block of more or less regular structure in which the filaments are embedded. Prerequisite for this hindrance of ideal ice growth is a sufficient tensile strength of the filamental network. The existence of structurally caused freezing point depression in biological tissue is likely to invalidate many conclusions reported in the literature, in which hypertonicity was deduced from cryoscopic data. PMID:13971682

Bloch, Rene; Walters, D. H.; Kuhn, Werner

1963-01-01

240

Optical coherence tomography-based freeze-drying microscopy  

PubMed Central

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

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

2011-01-01

241

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

242

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

2005-04-01

243

Design of a blood-freezing system for leukemia research  

NASA Technical Reports Server (NTRS)

Leukemia research involves the use of cryogenic freezing and storage equipment. In a program being carried out at the National Cancer Institute (NCI), bone marrow (white blood cells) was frozen using a standard cryogenic biological freezer. With this system, it is difficult to maintain the desired rate of freezing and repeatability from sample to sample. A freezing system was developed that satisfies the requirements for a repeatable, constant freezing rate. The system was delivered to NIC and is now operational. This report describes the design of the major subsystems, the analyses, the operating procedure, and final system test results.

Williams, T. E.; Cygnarowicz, T. A.

1978-01-01

244

Gravity Gradients on the Earth's Surface as Deduced from Satellite Orbits  

Microsoft Academic Search

The variation of gravity on the earth's surface is computed in three mutually perpendicular directions: the horizontal anomalous variations along the geocentric latitude and longitude curves, and the vertical component along the plumb line. The numerical results obtained from Kozai's and Gaposchkin's latest harmonic coefficients indicate a correlation between the anomalous vertical gravity gradient and the earth's continental topography.

W. Kohnlein

1967-01-01

245

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

246

[Characteristics of soil net nitrogen mineralization in subalpine/alpine forests of west Sichuan, Southwest China during seasonal freeze-thaw period].  

PubMed

Seasonal freeze-thaw cycle and its change pattern under the scenarios of climate warming might exert strong effects on the soil nitrogen mineralization in alpine forests. In this paper, intact soil cores were collected from the subalpine/alpine forests along an altitudinal gradient in west Sichuan, and an incubation test was conducted to study the soil net nitrogen mineralization rate and the amount of soil mineralized nitrogen in the forests during growth season and seasonal freeze-thaw period under simulated scenarios of global warming. In the test soils, the NH(4+)-N and NO(3-)-N contents both showed a clear tendency of decreased in the period from growth season to the onset stage of freezing, increased at deep freezing stage, and decreased again at the early stage of thawing. The soil net nitrogen mineralization rate and the amount of soil mineralized nitrogen were significantly lower in freeze-thaw period than in growth season, and the soil inorganic nitrogen was obviously immobilized. The soil nitrogen immobilization was stronger at middle altitudes but weaker at high altitudes, as compared with that at low altitudes, possibly due to the variation of soil temperature and its induced different freeze-thaw cycle. During growth period, the soil net nitrogen mineralization rate and the amount of soil mineralized nitrogen showed an obvious increasing trend with the decrease of altitude, and the soil nitrogen mineralization was the strongest at low altitudes, implying that under the scenarios of climate warming, the increase of soil temperature promoted the soil nitrogen mineralization during growth season, and affected the soil nitrogen mineralization rate by increasing the frequency of freeze-thaw cycle and shortening the time period of freeze-thaw. Soil micro-environment could also affect the soil nitrogen mineralization in alpine forest regions. PMID:22720601

Liu, Jin-Ling; Wu, Fu-Zhong; Yang, Wan-Qin; Shi, Pei-Li; Wang, Ao; Yang, Yu-Lian; Wu, Zhi-Chao

2012-03-01

247

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

PubMed

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

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

2014-11-01

248

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

Microsoft Academic Search

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

THOMAS A. CHURCHILL; KENNETH B. STOREY

249

Cytoplasmic structure in organotypic cultures of rat hippocampus prepared by rapid freezing and freeze-substitution fixation.  

PubMed

We have compared rapid freezing followed by freeze-substitution fixation with conventional aldehyde fixation as preparative methods for the electron microscopic study of organotypic cultures of neonatal rat hippocampus. Rapid freezing by contact with a copper block chilled by liquid helium was accomplished without mechanical distortion of superficial structures, and preserved structure to a depth of at least 20 microns without visible ice crystals. Freeze-substitution fixation in acetone/osmium tetroxide, followed by en bloc staining with tannic acid and uranyl acetate, provided satisfactory staining of cytoplasm and organelles. While both preparative techniques yielded generally satisfactory results, rapid freezing provided much better preservation of astrocytic lysosomal inclusions, and afforded new views of intermediate filament substructure. Rapid freezing and freeze-substitution fixation seemed especially well suited to the preservation of short filamentous proteins, such as those forming the membrane cytoskeleton of dendritic spines or those associated with synaptic vesicles. The combination of rapid freezing methods and organotypic culture provides an opportunity to examine cytoplasmic structure in tissue from deep regions of the brain which had previously been inaccessible to rapid freezing techniques. PMID:8497806

Pozzo Miller, L D; Landis, D M

1993-03-01

250

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

PubMed

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 evaluation of bio-samples. An integrated micro analysis device was fabricated which is simple in structure and cheap to make. Preliminary freezing results demonstrated that minor changes in a biological material due to freezing or warming injury might result in a significant deviation of its freezing curve from that of the intact biomaterials. Several potential thermal indexes to quantify the material features were pointed out. Further, experiments were performed on some freezing and thawing processes of small amount of water on a cooling surface to test the effects of droplet sizes, measurement sites, cooling strength, and cooling geometry, etc., on the freezing responses of a water droplet. Their implementation in developing a new micro analysis system were suggested. This freezing curve-based monitoring method may open a new strategy for the evaluation of biomaterials subject to destruction in diverse fields. PMID:12844203

Liu, Jing; Zhou, Yi-Xin

2003-09-01

251

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

PubMed

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

Malone, S R; Ashworth, E N

1991-03-01

252

The effects of haloclines on the vertical distribution and migration of zooplankton  

Microsoft Academic Search

While the influence of horizontal salinity gradients on the distribution and abundance of planktonic organisms in estuaries is relatively well known, the effects of vertical salinity gradients (haloclines) are less well understood. Because biological, chemical, and physical conditions can vary between different salinity strata, an understanding of the behavioral response of zooplankton to haloclines is crucial to understanding the population

Laurence A. Lougee; Stephen M. Bollens; Sean R. Avent

2002-01-01

253

Transition from shear to sideways diffusive instability in a vertical slot  

Microsoft Academic Search

The stability of the steady motion of a fluid confined between two differentially heated rigid vertical plates is considered. The thermosolutal instability occurs when a stable constant vertical salinity gradient is present in the fluid. It has been found that, at moderately large values of the solute Rayleigh number, the instability manifests itself in the form of stationary two-dimensional rolls.

Sivagnanam Thangam; Abdelfattah Zebib; C. F. Chen

1981-01-01

254

Metallicity Gradients in Disks: Do Galaxies Form Inside-Out?  

E-print Network

We examine radial and vertical metallicity gradients using a suite of disk galaxy simulations, supplemented with two classic chemical evolution approaches. We determine the rate of change of gradient and reconcile differences between extant models and observations within the `inside-out' disk growth paradigm. A sample of 25 disks is used, consisting of 19 from our RaDES (Ramses Disk Environment Study) sample, realised with the adaptive mesh refinement code RAMSES. Four disks are selected from the MUGS (McMaster Unbiased Galaxy Simulations) sample, generated with the smoothed particle hydrodynamics (SPH) code GASOLINE, alongside disks from Rahimi et al. (GCD+) and Kobayashi & Nakasato (GRAPE-SPH). Two chemical evolution models of inside-out disk growth were employed to contrast the temporal evolution of their radial gradients with those of the simulations. We find that systematic differences exist between the predicted evolution of radial abundance gradients in the RaDES and chemical evolution models, comp...

Pilkington, K; Gibson, B K; Calura, F; Michel-Dansac, L; Thacker, R J; Molla, M; Matteucci, F; Rahimi, A; Kawata, D; Kobayashi, C; Brook, C B; Stinson, G S; Couchman, H M P; Bailin, J; Wadsley, J

2012-01-01

255

Contribution of the vertical semicircular canals to the caloric nystagmus.  

PubMed

Modulation of the caloric nystagmus in response to repositioning the plane of one vertical semicircular canal from gravitational horizontal to vertical during continuous caloric stimulation was used to measure the vertical canal's contribution to the nystagmus. The rationale was to examine the thermovective response from one vertical canal at a time, after a temperature gradient had been established across its two limbs. The nystagmus was measured and analysed in three dimensions using orthogonal head-referenced coordinates. The magnitude of each semicircular canal's contribution to the overall caloric response, the canal vector, was determined in non-orthogonal, contravariant semicircular canal plane coordinates. By using the canal plane reorientation technique and contravariant canal plane coordinates, we were able to measure the proportional thermovective response magnitude generated by each vertical canal during caloric stimulation. We found that the anterior canal contributed about one-third and the posterior canal about one-tenth as much as the lateral canal did to the overall caloric response magnitude when it was reoriented from horizontal to vertical. Comparison of the eye rotation axis before and after each vertical canal plane reorientation, with the geometry of the stimulated semicircular canals, also showed directional modulation of the caloric nystagmus by the vertical canal response. When one vertical canal plane was horizontal during caloric stimulation, the eye rotation axis aligned with the resultant of the other vertical canal and the lateral canal response axes. After vertical canal plane reorientation, the eye rotation axis realigned towards the resultant of the maximally stimulated vertical canal and the lateral canal, by 55.2+/-33.9 degrees (mean+/-SD) after anterior canal plane reorientation and by 32.3+/-21.2 degrees after posterior canal reorientation. PMID:9840495

Aw, S T; Haslwanter, T; Fetter, M; Heimberger, J; Todd, M J

1998-09-01

256

Stress-gradient plasticity  

PubMed Central

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

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

2011-01-01

257

Observations of mesoscale vertical velocities around frontal zones  

NASA Technical Reports Server (NTRS)

Vertical velocity and reflectivity data obtained with a VHF Doppler radar over a 15-day period in October and November of 1981 are analyzed. Standard radiosonde data and surface observations were used to locate two occluded fronts, two warm fronts, and a cold front that passed the radar site. These fronts are also evident in the radar reflectivity data. Most studies of the vertical circulation patterns associated with mososcale systems have used precipitation and cloud formations as tracers. Unlike other observational techniques, the VHF radar permits the continuous measurement of the three-dimensional air velocity vector in time and height from a fixed location. With the beam in a vertically pointing position, signals are scattered from turbulent variations in the refractive index with half the scale of the radar wavelength and by regions with sudden changes in the refractive index associated with horizontally stratified layers. Generally, the strongest echoes occur at the maximum in the vertical gradient of refractivity, usually at the base of a temperature inversion, such as the tropopause. VHF radars can also be used to locate atmospheric fronts, which are characterized by static stability, large horizontal temperature gradients, large vorticities, and vertical wind shears. These radars can provide the velocity field data needed to study wave motions associated with fronts and compare the actual vertical circulation to theoretical predictions.

Dennis, T. S.; Larsen, M. F.; Rottger, J.

1986-01-01

258

SFT: a consistent checkpointing algorithm with shorter freezing time  

Microsoft Academic Search

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

Xiaohui Wei; Jiubin Ju

1998-01-01

259

ORIGINAL PAPER Effect of freezing-thawing on nitrogen mineralization  

E-print Network

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

Boyer, Edmond

260

Microwave freeze drying of sea cucumber ( Stichopus japonicus)  

Microsoft Academic Search

Freeze drying (FD) yields the best quality of dried sea cucumber but at the cost of long drying time and also the overall cost. Air drying (AD) gives an unacceptably poor quality product. To achieve faster drying along with a high quality product a microwave freeze drying (MFD) technique was developed to dry sea cucumbers. The relationship between corona discharge

Xu Duan; Min Zhang; Arun S. Mujumdar; Shaojin Wang

2010-01-01

261

Prospective Primary School Teachers' Perceptions on Boiling and Freezing  

ERIC Educational Resources Information Center

The aim of this study was to investigate the perceptions of prospective primary school teachers on the physical state of water during the processes of boiling and freezing. There were three stages in the investigation: First, open-ended questions concerning the boiling and freezing of water were given to two groups of prospective primary school…

Senocak, Erdal

2009-01-01

262

Observation of a freezing drizzle episode: A case study  

NASA Astrophysics Data System (ADS)

On 5 February 2012 an episode of freezing precipitation took place in the Guadarrama Mountains, at the center of the Iberian Peninsula. This precipitation affected high elevations, where temperatures remained below freezing because of snow cover that had accumulated from snowfall during the previous days. The case study was recorded by surface synoptic observations (SYNOP) at Navacerrada Pass meteorological observatory (belonging to the National Weather Service of Spain). To study winter cloud systems during the TEcoAgua project, a multichannel ground-based microwave radiometer (MMWR), Micro Rain Radar (MRR-2), and isothermal cloud chamber were installed in the study area, thus permitting the monitoring of the freezing precipitation event. Analysis using Meteosat Second Generation (MSG) satellite data and observations permitted the determination of factors that triggered the freezing precipitation event. Freezing drizzle was interspersed with the passage of a warm and cold front. During frontal passage, mid-level clouds inhibited the generation of freezing drizzle, with snowfall recorded in the study area. However, during the period between the two fronts, an absence of mid-level clouds permitted low-level orographic clouds to persist upwind of the mountain system, producing freezing drizzle at the surface. The decisive factors for the generation of freezing drizzle were high humidity at low levels, weak mesoscale updrafts caused by the topography, stability at mid levels, cloud-top temperatures warmer than - 15 °C, and low concentrations of ice nuclei.

Fernández-González, S.; Valero, F.; Sanchez, Jose L.; Gascón, E.; López, L.; García-Ortega, E.; Merino, A.

2014-11-01

263

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

264

In Vivo Detection of Membrane Injury at Freezing Temperatures  

PubMed Central

The release of hydrogen cyanide from Amelanchier alnifolia was monitored at 30 C and ?10 C following lethal freezing at both slow and fast rates. Assuming that hydrogen cyanide release indicates membrane damage, it was concluded that during a fatal freeze-thaw cycle membrane damage occurred during cell contraction and, therefore, was not dependent upon membrane area expansion during thawing. PMID:16661397

Stout, Darryl G.; Majak, Walter; Reaney, Martin

1980-01-01

265

In vivo detection of membrane injury at freezing temperatures.  

PubMed

The release of hydrogen cyanide from Amelanchier alnifolia was monitored at 30 C and -10 C following lethal freezing at both slow and fast rates. Assuming that hydrogen cyanide release indicates membrane damage, it was concluded that during a fatal freeze-thaw cycle membrane damage occurred during cell contraction and, therefore, was not dependent upon membrane area expansion during thawing. PMID:16661397

Stout, D G; Majak, W; Reaney, M

1980-07-01

266

Industrial applications of freeze concentration technology: Final report  

SciTech Connect

Often more energy-efficient than the separation technologies now in industrial use, freeze concentration techniques also offer advantages in product purity and quality. This applications analysis estimates that widespread adoption of freeze concentration could produce significant national energy savings, along with increasing baseload electricity consumption.

Barron, T.S.; Heist, J.A.; Hunt, K.M.; Wrobel, P.J.

1987-06-01

267

Study of Ice Cream Freezing Process after Treatment with Ultrasound  

Microsoft Academic Search

Application of power ultrasound to Food freezing is a relatively new subject, cavitations is the most significant power which can not only lead to the production of gas bubbles in ice ream but also the occurrence of micro streaming, also it can promote ice nucleation to accelerate the heat and mass transfer process accompanying the freeze process. In this work

A. Mortazavi; F. Tabatabaie

268

Modeling solute segregation during freezing of peatland waters  

Microsoft Academic Search

Freezing of the shallow water in a peatland causes the downward movement of solutes. Field and laboratory data demonstrate that a considerable portion of the solutes are driven into the top soil from the overlying water by freezing. Such solute redistribution phenomena in peatlands are of interest for establishing the geochronology of deposits and determining the nature of pollutant burial.

Robert H. Kadlec; Xiang-Ming Li; Gerald B. Cotten

1988-01-01

269

Freeze-Outs: Transcontinental Analysis and Reform Proposals  

Microsoft Academic Search

One of the most crucial, but systematically neglected, comparative differences between corporate law systems in Europe and in the United States concerns the regulations governing freeze-out transactions in listed corporations. Freeze-outs can be defined as transactions in which the controlling shareholder exercises a legal right to buy out the shares of the minority, and consequently delists the corporation and brings

Marco Ventoruzzo

2010-01-01

270

Freezing of Barley Studied by Infrared Video Thermography  

Microsoft Academic Search

Freezing of barley (Hordeum vulgare), Hordeum murinum, and Holcus lanatus was studied using infrared video thermography. In the field, ice could enter H. lanatus leaves through hydathodes. In laboratory tests with barley, initially 0.4% of the leaf water froze, spreading in alternate strips of high and low freezing intensity longitudinally at 1 to 4 cm s21, and simultaneously spreading laterally

Roger S. Pearce; Michael P. Fuller

2001-01-01

271

Vertical emitting aperture nanoantennas.  

PubMed

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

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

2012-05-01

272

STEFINS: a steel freezing integral simulation program  

SciTech Connect

STEFINS (STEel Freezing INtegral Simulation) is a computer program for the calculation of the rate of solidification of molten steel on solid steel. Such computations arize when investigating core melt accidents in fast reactors. In principle this problem involves a coupled two-dimensional thermal and hydraulic approach. However, by physically reasonable assumptions a decoupled approach has been developed. The transient solidification of molten steel on a cold wall is solved in the direction normal to the molten steel flow and independent from the solution for the molten steel temperature and Nusselt number along the direction of flow. The solutions to the applicable energy equations have been programmed in cylindrical and slab geometries. Internal gamma heating of steel is included.

Frank, M.V.

1980-09-01

273

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

274

Hot water can freeze faster than cold?!?  

E-print Network

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

Jeng, M

2005-01-01

275

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.

276

Hadron Freeze-Out and Unruh Radiation  

E-print Network

We consider hadron production in high energy collisions as an Unruh radiation phenomenon. This mechanism describes the production pattern of newly formed hadrons and is directly applicable at vanishing baryochemical potential, mu = 0. It had already been found to correctly yield the hadronisation temperature, T_h = sqrt(sigma / 2 pi) = 165 MeV in terms of the string tension sigma. Here we show that the Unruh mechanism also predicts hadronic freeze-out conditions, giving s/T_h^3 = 3 pi^2 / 4 = 7.4 in terms of the entropy density s and E/N = \\sqrt(2 pi sigma) = 1.09 for the average energy per hadron. These predictions provide a theoretical basis for previous phenomenological results and are also in accord with recent lattice studies.

Paolo Castorina; Alfredo Iorio; Helmut Satz

2014-09-10

277

Hadron Freeze-Out and Unruh Radiation  

E-print Network

We consider hadron production in high energy collisions as an Unruh radiation phenomenon. This mechanism describes the production pattern of newly formed hadrons and is directly applicable at vanishing baryochemical potential, mu = 0. It had already been found to correctly yield the hadronisation temperature, T_h = sqrt(sigma / 2 pi) = 165 MeV in terms of the string tension sigma. Here we show that the Unruh mechanism also predicts hadronic freeze-out conditions, giving s/T_h^3 = 3 pi^2 / 4 = 7.4 in terms of the entropy density s and E/N = \\sqrt(2 pi sigma) = 1.09 for the average energy per hadron. These predictions provide a theoretical basis for previous phenomenological results and are also in accord with recent lattice studies.

Castorina, Paolo; Satz, Helmut

2014-01-01

278

Freeze-fracture cytochemistry: partition of glycophorin in freeze- fractured human erythrocyte membranes  

PubMed Central

Thin-section and critical-point-dried fracture-labeled preparations are used to determine the distribution and partition of glycophorin- associated wheat germ agglutinin (WGA) binding sites over protoplasmic and exoplasmic faces of freeze-fractured human erythrocyte membranes. Most wheat germ agglutinin binding sites are found over exoplasmic faces. Label is sparse over the protoplasmic faces. These results contrast with previous observations of the partition of band 3 component where biochemical analysis and fracture-label of concanavalin A (Con A) binding sites show preferential partition of this transmembrane protein with the protoplasmic face. Presence of characteristic proportions of WGA and Con A binding sites over each fracture face is interpreted to indicate the operation of a stochastic process during freeze-fracture. This process appears modulated by the relative expression of each transmembrane protein at either surface as well as by their association to components of the erythrocyte membrane skeleton. PMID:7096449

1982-01-01

279

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

E-print Network

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

Swarn Lata Singh; Atul S. Bharadwaj; Yashwant Singh

2011-01-31

280

A search for the Mpemba effect: When hot water freezes faster then cold water  

E-print Network

An explanation for why hot water will sometime freeze more rapidly than cold water is offered. Two specimens of water from the same source will often have different spontaneous freezing temperatures; that is, the temperature at which freezing begins. When both specimens supercool and the spontaneous freezing temperature of the hot water is higher than that of the cold water, then the hot water will usually freeze first, if all other conditions are equal and remain so during cooling. The probability that the hot water will freeze first if it has the higher spontaneous freezing temperature will be larger for a larger difference in spontaneous freezing temperature. Heating the water may lower, raise or not change the spontaneous freezing temperature. The keys to observing hot water freezing before cold water are supercooling the water and having a significant difference in the spontaneous freezing temperature of the two water specimens. We observed hot water freezing before cold water 28 times in 28 attempts und...

Brownridge, James D

2010-01-01

281

9 CFR 381.66 - Temperatures and chilling and freezing procedures.  

Code of Federal Regulations, 2011 CFR

...Temperatures and chilling and freezing procedures. 381.66 Section...Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Temperatures and chilling and freezing procedures. (a) General...necessary for chilling and freezing ready-to-cook...

2011-01-01

282

9 CFR 381.66 - Temperatures and chilling and freezing procedures.  

Code of Federal Regulations, 2012 CFR

...Temperatures and chilling and freezing procedures. 381.66 Section...Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Temperatures and chilling and freezing procedures. (a) General...necessary for chilling and freezing ready-to-cook...

2012-01-01

283

9 CFR 381.66 - Temperatures and chilling and freezing procedures.  

Code of Federal Regulations, 2013 CFR

...Temperatures and chilling and freezing procedures. 381.66 Section...Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Temperatures and chilling and freezing procedures. (a) General...necessary for chilling and freezing ready-to-cook...

2013-01-01

284

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

NASA Astrophysics Data System (ADS)

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

Cuntz, M.; Haverd, V.

2013-12-01

285

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

286

Freezing and anoxia tolerance of slugs: a metabolic perspective.  

PubMed

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 circumscriptus. The introduced species showed very poor freezing survival. Supercooling points of the introduced species were quite high ( approximately -3 degrees C) and their freezing survival was very poor, limited to short-term freezing at -1.2 to -1.5 degrees C and low ice contents (23-44%). D. laeve showed a significant elevation of supercooling point between slugs collected in the autumn (-4.8 degrees C +/- 0.5) and those collected early in the spring (-3.1 degrees C +/- 0.4). This species also showed substantial freezing survival which was greater for spring-collected slugs (100% survival of 1 h freezing at -2 degrees C with an ice content of 65%) than for autumn animals (100% survival for 1 h at -1 degrees C with approximately 40% ice). Carbohydrate and amino acid responses to freezing and anoxia exposures were compared in the two Deroceras species. D. laeve showed a strong hyperglycemic response to freezing, a 100-fold increase in glucose levels that suggested that glucose may have a cryoprotective function in this species. D. reticulatum did not accumulate glucose and neither species produced glycerol or lactate. Both species showed typical responses to anoxia (aspartate and glutamate catabolism, alanine and succinate accumulation) and D. laeve also showed this pattern during freezing, suggesting a natural switch to anaerobiosis to support freezing survival. PMID:17628806

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

2007-11-01

287

Evaluation and Validation of the Messinger Freezing Fraction  

NASA Technical Reports Server (NTRS)

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

Anderson, David N.; Tsao, Jen-Ching

2005-01-01

288

Inoculation triggers freezing at high subzerotemperatures in a freeze-tolerant frog (Rana sylvatica)and insect (Eurosta solidaginis)  

E-print Network

sylvatica)and insect (Eurosta solidaginis) hcr R. LnyNr, Jn.l OhioUniversity- Belmont,45425National .Road.Inoculationtriggersfreezingat high subzerotemperaturesin a freeze-tolerantfrog (Rana sylvatica) and insdct(Eurosta solidaginis possibility in two freeze-tolerantanimals,the wood frog, Ranasylvatica, andthegoldenrodgall fly, Eurosta

Lee Jr., Richard E.

289

Feasibility of high pressure freezing with freeze substitution after long-term storage in chemical fixatives.  

PubMed

Fixation of biological samples is an important process especially related to histological and ultrastructural studies. Chemical fixation was the primary method of fixing tissue for transmission electron microscopy for many years, as it provides adequate preservation of the morphology of cells and organelles. High pressure freezing (HPF) and freeze substitution (FS) is a newer alternative method that rapidly freezes non-cryoprotected samples that are then slowly heated in the FS medium, allowing penetration of the tissue to insure adequate fixation. This study addresses several issues related to tissue preservation for electron microscopy. Using mice liver tissue as model the difference between samples fixed chemically or with HPF immediately after excision, or stored before chemical or HPF fixation were tested with specific focus on the nuclear membrane. Findings are that immediate HPF is the method of choice compared to chemical fixation. Of the chemical fixatives, immediate fixation with 2.5% glutaraldehyde (GA)/formaldehyde (FA) is the best in preserving membrane morphology, 2.5% GA can be used as alternative for stored and then chemically processed samples, with 10% formalin being suitable as a storage medium only if followed by HPF fixation. Overall, storage leads to lower ultrastructural preservation, but HPF with FS can minimize these artifacts relative to other processing protocols. PMID:23818457

Venter, Chantelle; Van Der Merwe, Christiaan Frederick; Oberholzer, Hester Magdalena; Bester, Megan Jean; Taute, Helena

2013-09-01

290

Aiding Vertical Guidance Understanding  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

291

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

PubMed

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

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

2007-05-01

292

Method and apparatus for determining vertical heat flux of geothermal field  

DOEpatents

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

Poppendiek, Heinz F. (LaJolla, CA)

1982-01-01

293

Two-Zone Bridgman Furnace With Sharp Thermal Gradient  

NASA Technical Reports Server (NTRS)

Two-zone vertical directional-solidification furnace designed and built to grow crystals from stoichiometric and nonstoichiometric melts and from solutions. Includes conventional wire heater in lower zone, tubular silicon carbide heating element in upper zone, and thermal baffle between zones. Temperature gradients up to 125 degrees centigrade per centimeter achieved in the crystal-growth region. Sharper gradient enables both faster growth and better separation between solid and liquid. Furnace used in laboratory or industrial setting for growth of crystals from congruently melting materials as well as for growth of compounds formed by peritectic reactions.

Borshchevsky, Alex; Caillat, Thierry; Fleurial, Jean-Pierre

1994-01-01

294

Studies on Freezing RAM Semen in Absence of Glycerol.  

NASA Astrophysics Data System (ADS)

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

Abdelnaby, Abdelhady Abdelhakeam

1988-12-01

295

The effect of water-soluble polymers on the microstructure and properties of freeze-cast alumina ceramics  

NASA Astrophysics Data System (ADS)

Porous ceramics can be divided into three separate classes based on their pore size: microporous ceramics with pores less than 2 nm, mesoporous ceramics with pores in the range of 2--50 nm and macroporous ceramics with pores that are greater than 50 nm. In particular, macroporous ceramics are used in a variety of applications such as refractories, molten metal filtration, diesel particulate filters, heterogeneous catalyst supports and biomedical scaffolds. Freeze casting is a novel method used to create macroporous ceramics. In this method growing ice crystals act as a template for the pores and are solidified, often directionally, through a ceramic dispersion and removed from the green body through a freeze drying procedure. This method has attracted some attention over the past few years due to its relative simplicity, flexibility and environmental friendliness. On top of this freeze casting is capable of producing materials with high pore volume fractions, which is an advantage over processing by packing and necking of particles, where the pore volume fraction is typically less than 50%. Many of the basic processing variables that affect the freeze cast microstructure, such as the temperature gradient, interfacial velocity and solid loading of the dispersion have been well established in the literature. On the other hand, areas such as the effect of additives on the microstructure and mechanical properties have not been covered in great detail. In this study the concept of constitutional supercooling from basic solidification theory is used to explain the effects of two water-soluble polymers, polyethylene glycol and polyvinyl alcohol, on the microstructure of freeze cast alumina ceramics. In addition, changes in the observed microstructure will be related to experimentally determined values of permeability and compressive strength.

Pekor, Christopher Michael

296

Convection in drying and freezing ground  

NASA Astrophysics Data System (ADS)

In this paper, we analyse the drying of a soil composed of particles, water and solute impurities, and study the occurrence of convective instabilities during evaporation. We find that the main driving force for instability is the formation of a concentration gradient at the soil surface due to the evaporation of water. A similar phenomenon may occur during the thawing of frozen ground in Arctic regions.

Faizal, Mir; Peppin, Stephen

2014-08-01

297

Water Relations of Pachysandra Leaves during Freezing and Thawing 1  

PubMed Central

The evergreen herb Pachysandra terminalis becomes moderately frost-hardy in winter. The water relations of its frost-hardy leaves were studied during a freeze-thaw cycle. Leaf water potentials, measured by psychrometry at subfreezing temperatures, were identical with those of ice, indicating equilibrium freezing. Microscopic observations showed extracellular freezing of tissue water. As evidenced by thermal analysis, the freezing process starts with the crystallization of a minor volume which was identified as apoplasmic water. The following long-lasting exotherm indicated slow export of water from the protoplasts driven by extracellular crystallization. In partially frozen leaves, the fractions of liquid water were measured at several subfreezing temperatures by nuclear magnetic resonance spectroscopy. They were consistently greater than those calculated from the osmotic potentials of cellular fluid, and the differences increased with decreasing temperature. About 50% of the differences could be abolished by freeze-killing of the leaf and was thus ascribed to the effect of a (negative) pressure reinforcing the osmotic potential. The persistent part of the differences may have reflected a matric component. At ?7°C, the absolute values of both potentials were ?1.7 megapascals each. The water relations of Pachysandra leaves clearly indicate nonideal equilibrium freezing where negative pressures and matric potentials contribute to the leaf water potential and thus alleviate freeze-dehydration of the tissue. ImagesFigure 1Figure 5 PMID:16668501

Zhu, Jian-Jun; Beck, Erwin

1991-01-01

298

Metabolic Changes in Avena sativa Crowns Recovering from Freezing  

PubMed Central

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

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

2014-01-01

299

Metabolic changes in Avena sativa crowns recovering from freezing.  

PubMed

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

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

2014-01-01

300

Immersion freezing on mineral dust particles  

NASA Astrophysics Data System (ADS)

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

Zolles, Tobias; Grothe, Hinrich; Pummer, Bernhard

2013-04-01

301

Is Enceladus' Internal Ocean Doomed to Freeze?  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

302

Freezing and Melting, Precipitation Type, and Numerical Weather Prediction  

NSDL National Science Digital Library

This Webcast 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.

Comet

2002-07-03

303

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

304

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

305

Florida harvester ant nest architecture, nest relocation and soil carbon dioxide gradients.  

PubMed

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

Tschinkel, Walter R

2013-01-01

306

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

PubMed Central

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

Tschinkel, Walter R.

2013-01-01

307

The role of subglacial drainage and basal freeze-on for ice streams  

NASA Astrophysics Data System (ADS)

The Siple Coast ice streams are major discharge routes for ice in the West Antarctic. Observations suggest that their fast flow is due to sliding along a water-saturated bed, with variations in velocities and ice stream width on decadal to centennial time scales. These variations include the migration of ice stream margins, where the fast flow slows down to the speed of the surrounding ice, which in contrast appears to be frozen to the underlying bed. Using a coupled ice-sediment model we investigate the roles of basal freeze-on, subglacial drainage, and feedbacks between fast flow and heat dissipation for ice-stream evolution. The ice is modeled as a vertically uniform plug flow. The sediment model allows for lateral motion of melt water in the sediment and changes in the thickness of the water-saturated sediment layer due to melting and freezing processes. Dynamical feedbacks in the energy balance include both frictional heating along the bed and lateral shear heating. Using this model, we study the evolution and possible steady states of ice streams. We find that no steady-state ice stream configurations are possible in the absence of subglacial drainage. Moreover, the bed outside of the fast flowing region will eventually freeze onto the ice, which prohibits outward migration of ice stream margins due to subglacial drainage. Possible steady state configurations are investigated in detail. Hence, subglacial drainage must play an important role for ice stream behaviour, but drainage-driven margin migration is possible to a limited extent only, as ice stream margins are believed to coincide with the boundary between a frozen and temperate bed.

Haseloff, M.; Schoof, C.

2012-12-01

308

Satellite freeze forecast system: Executive summary  

NASA Technical Reports Server (NTRS)

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

Martsolf, J. D. (principal investigator)

1983-01-01

309

Adaptation to seasonality and the winter freeze  

PubMed Central

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

Preston, Jill C.; Sandve, Simen R.

2013-01-01

310

Hot water can freeze faster than cold?!?  

E-print Network

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

Monwhea Jeng

2005-12-29

311

GPR utilization in artificial freezing engineering  

NASA Astrophysics Data System (ADS)

To utilize ground penetrating radar (GPR) in artificial freezing engineering (AFE), the electromagnetic parameters (EMP) of frozen soil were measured using a vector network analyser, which showed that the dielectric permittivity and electric conductivity change abruptly at the boundary between the frozen and the non-frozen soil. Then similarity criteria of GPR model experiments were deduced, and GPR laboratory model experiments and field explorations of AFE were carried out. It was found that for AFE, the GPR travel time and profile characters of anomalies in model experiments were similar to those in field explorations, while the amplitude of GPR signals in laboratory model experiments were much stronger than those in field explorations. Numerical simulations were also implemented to analyse the relationship between model experiments and field explorations, which further told us why we could easily find the targets by GPR in the laboratory but not in field explorations. The outputs showed that GPR could be used to detect the thickness of the frozen wall and to find unfrozen soil defects, even though the amplitude of the reflective signals were much weaker than those of laboratory experiments. The research findings have an important theoretical value for AFE and permafrost region engineering, and the deduced GPR similarity criteria could be widely used in other GPR model experiments.

Song, Lei; Yang, Weihao; Huang, Jiahui; Li, Haipeng; Zhang, Xiaojun

2013-06-01

312

Drying a tuberculosis vaccine without freezing.  

PubMed

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 model Mycobacterium (Mycobacterium smegmatis) revealed that by removing salts and cryoprotectant (e.g., glycerol) from bacterial suspensions, the significant osmotic pressures that are normally produced on bacterial membranes through droplet drying can be reduced sufficiently to minimize loss of viability on drying by up to 2 orders of magnitude. By placing the bacteria in a matrix of leucine, high-yield, free-flowing, "vial-fillable" powders of bacteria (including M. smegmatis and M. bovis BCG) can be produced. These powders show relatively minor losses of activity after maintenance at 4 degrees C and 25 degrees C up to and beyond 4 months. Comparisons with lyophilized material prepared both with the same formulation and with a commercial formulation reveal that the spray-dried BCG has better overall viability on drying. PMID:17299039

Wong, Yun-Ling; Sampson, Samantha; Germishuizen, Willem Andreas; Goonesekera, Sunali; Caponetti, Giovanni; Sadoff, Jerry; Bloom, Barry R; Edwards, David

2007-02-20

313

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

PubMed Central

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

Malone, Stephen R.; Ashworth, Edward N.

1991-01-01

314

Underground structure detection by surface magnetic gradient measurements  

NASA Astrophysics Data System (ADS)

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

Kelly, Robert E.

2001-11-01

315

Hierarchically deflated conjugate gradient  

E-print Network

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

P A Boyle

2014-02-11

316

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

317

Charge gradient microscopy  

PubMed Central

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

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

2014-01-01

318

Charge gradient microscopy.  

PubMed

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

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

2014-05-01

319

Tight junction regulates epidermal calcium ion gradient and differentiation  

SciTech Connect

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

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

2011-03-25

320

Spray irrigation effects on surface-layer stability in an experimental citrus orchard during winter freezes  

SciTech Connect

Observations taken by two surface radiation and energy budget stations deployed in the University of Florida/Institute for Food and Agricultural Service experimental citrus orchard in Ginesville, Florida, have been analyzed to identify the effects of sprayer irrigation on thermal stability and circulation processes within the orchard during three 1992 winter freeze episodes. Lapse rates of temperature observed from a micrometeorological tower near the center of the orchard were also recorded during periods of irrigation for incorporation into the analysis. Comparisons of the near-surface temperature lapse rates observed with the two energy budget stations show consistency between the two sites and with the tower-based lapse rates taken over a vertical layer from 1.5 to 15 m above ground level. A theoretical framework was developed that demonstrates that turbulent-scale processes originating within the canopy, driven by latent heat release associated with condensation and freezing processes from water vapor and liquid water released from sprayer nozzles, can destabilize lapse rates and promote warm air mixing above the orchard canopy. The orchard data were then analyzed in the context of the theory for evidence of local overturning and displacement of surface layer air, with warmer air from aloft driven by locally buoyant plumes generated by water vapor injected into the orchard during the irrigation periods. 14 refs., 6 figs.

Cooper, H.J.; Smith, E.A. [Florida State Univ., Tallahassee, FL (United States)] [Florida State Univ., Tallahassee, FL (United States); Martsolf, J.D. [Univ. of Florida, Gainesville, FL (United States)] [Univ. of Florida, Gainesville, FL (United States)

1997-02-01

321

Phase separation during freezing upon warming of aqueous solutions  

NASA Astrophysics Data System (ADS)

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

Bogdan, A.; Loerting, T.

2014-11-01

322

Phase separation during freezing upon warming of aqueous solutions.  

PubMed

Using differential scanning calorimetry, we show that the addition of solute(s) to emulsified water lowers the freezing temperature to <231 K, the homogeneous nucleation temperature of pure bulk water, or even completely suppresses freezing. In the latter case, freezing upon warming occurs above TX ? 150 K and leads to a phase separation into pure ice and a freeze-concentrated solution (FCS) which crystallizes upon further warming. We also show that emulsified 20-21.5 wt. % HCl solutions and the FCS of HCl/H2O solutions transform to glass at Tg ? 127-128 K, i.e., lower than Tg ? 136 K of water. We suggest that water nanodrops adsorbed on fumed silica resemble bulk water more than water confined in nanoscaled confinement and also more than nanoscaled water domains in aqueous solution. PMID:25399198

Bogdan, A; Loerting, T

2014-11-14

323

Freezing in Sealed Capillaries for Preparation of Frozen Hydrated Sections  

PubMed Central

We have investigated the freezing of specimens in a confined volume for preparation of vitreous samples for cryosectioning. With 15% dextran as a cryoprotectant, a sample sealed in a copper tube begins to freeze into crystalline ice when plunged into liquid ethane. Crystallization rapidly causes an increase in the pressure to the point that much of the sample freezes in a vitreous state. We used synchrotron X-ray diffraction of samples frozen with various amounts of dextran to characterize the ice phases and crystal orientation, providing insights on the freezing process. We have characterized cryosections obtained from these samples to explore the optimum amount of cryoprotectant. Images of cryosectioned bacteria frozen with various levels of cryoprotectant illustrate effects of cryoprotectant concentration. PMID:22077543

Yakovlev, Sergey; Downing, Kenneth H.

2014-01-01

324

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

EPA Science Inventory

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

325

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

EPA Science Inventory

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

326

Condensation and freezing of droplets on superhydrophobic surfaces.  

PubMed

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

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

2014-08-01

327

The Hazards of Debt: Rollover Freezes, Incentives, and Bailouts  

E-print Network

We investigate the trade-off between incentive provision and inefficient rollover freezes for a firm financed with short-term debt. First, debt maturity that is too short-term is inefficient, even with incentive provision. ...

Cheng, Ing-Haw

328

Universality of tip singularity formation in freezing water drops.  

PubMed

A drop of water deposited on a cold plate freezes into an ice drop with a pointy tip. While this phenomenon clearly finds its origin in the expansion of water upon freezing, a quantitative description of the tip singularity has remained elusive. Here we demonstrate how the geometry of the freezing front, determined by heat transfer considerations, is crucial for the tip formation. We perform systematic measurements of the angles of the conical tip, and reveal the dynamics of the solidification front in a Hele-Shaw geometry. It is found that the cone angle is independent of substrate temperature and wetting angle, suggesting a universal, self-similar mechanism that does not depend on the rate of solidification. We propose a model for the freezing front and derive resulting tip angles analytically, in good agreement with the experiments. PMID:25126922

Marín, A G; Enríquez, O R; Brunet, P; Colinet, P; Snoeijer, J H

2014-08-01

329

Vertical variations of boundary layer chemistry in the urban environment of Boston  

NASA Astrophysics Data System (ADS)

Boundary layer chemistry in urban areas is often strongly influenced by surface emissions of NOx and VOCs. Vertical mixing in combination with chemical transformations leads to distinctive vertical profiles of reactive trace gases. Chemistry, therefore, varies with altitude in the lowest 50 m, in particular in the stable nocturnal boundary layer. The influence of vertical mixing on chemistry in the lowest part of the boundary layer is often not accurately described, and a better understanding is needed to improve our ability to model urban air pollution. During the NEAQS/NAOPEX field campaign in July-August, 2002, vertical distributions of NO2, O3, HONO, HCHO, NO3, and several other trace gases were measured in the lowest 10 - 50 m of the atmosphere with a long-path differential optical absorption spectroscopy instrument in a residential area in Boston, MA. Various meteorological parameters were also monitored at the same location. Clear vertical trace gas concentration gradients were observed. In particular, during nights with strong stabilities, nocturnal boundary layer chemistry was clearly altitude dependent. Positive gradients of O3 and NO3 developed as a result of the fast chemical reactions with NO emitted at the surface. Negative NO2 and HONO gradients point to the vertical variation of the heterogeneous NO2-HONO conversion process, suggesting the importance of heterogeneous chemistry at the ground and building walls. With the transition from the stable boundary layer to a convective layer after sunrise, the vertical profiles regressed. However, vertical gradients of HCHO and O3 were observed in the afternoon on most days of this study. The observations suggest that ground-based emissions and fast photochemistry can lead to vertical profiles of trace gases in an urban boundary layer even during daytime. The vertical stratification of boundary layer chemistry, which depends on many factors including mixing strength, fast photochemistry and the emission strength, will be discussed.

Wang, S.; Geyer, A.; Stutz, J.

2003-12-01

330

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

331

When the Melting and Freezing Points are not the Same  

Microsoft Academic Search

Almost every solid has a melting point, and almost every liquid has a freezing point. These two points are one and the same, just viewed from different perspectives: ice melts at zero degrees Celsius--the highest temperature at which it can be a stable solid--whereas water freezes at zero degrees C--the lowest temperature at which it can be a stable liquid.

R. Stephen Berry

1990-01-01

332

Successful pregnancies with directional freezing of large volume buck semen  

Microsoft Academic Search

Artificial insemination with frozen-thawed buck semen shows variable results which depend on many factors related to semen quality and the cryopreservation processing. We conducted experiments based on a new freezing method, directional freezing, of large volumes (8ml). In the first experiment semen from three Saanen bucks, ages 1–2-years-old and genetically selected for milk improvement, was frozen individually. Two to three-years-old

H. Gacitua; A. Arav

2005-01-01

333

Three keys to the radiation of angiosperms into freezing environments.  

PubMed

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

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

2014-02-01

334

Correlation estimates ethane plant's carbon-dioxide freezing pressure  

Microsoft Academic Search

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

Trebble

1983-01-01

335

A climatological analysis of the freeze period of Texas  

E-print Network

A CLIMATOLOGICAL ANALYSIS OF THE FREEZE PERIOD OF TEKAS A Thesis by CHRISTOPHER ALAN DONAHUE Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE... December 1991 Major Subject: Meteorology A CLIMATOLOGICAL ANALYSIS OF THE FREEZE PERIOD OF TEXAS A Thesis by CHRISTOPHER ALAN DONAHUE Approved as to style and content by: ohn F. Gri ths (Chair of Committee) Gerald R. North (Member) Michael T. L...

Donahue, Christopher Alan

2012-06-07

336

Freeze concentration of dairy products Phase 2. Final report  

SciTech Connect

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

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

1993-09-01

337

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

338

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

339

Liver glycogen, glucose mobilization and freezing survival in chorus frogs, Pseudacris triseriata  

Microsoft Academic Search

We compared liver glycogen stores and glucose mobilization during freezing among winters in chorus frogs, Pseudacris triseriata, where populations varied in freezing survival. We also characterized tissue glycogen levels across the annual cycle. Frogs with low liver glycogen stores mobilized low amounts of glucose during freezing, and these were correlated with population variation in freezing survival. Moreover, liver glycogen stores

Jennifer L. Jenkins; David L. Swanson

2005-01-01

340

Application of the SAFES (systematic approach to food engineering systems) methodology to strawberry freezing process  

Microsoft Academic Search

SAFES methodology has been applied in strawberry freezing process using data from references. Three cases of freezing have been studied. All of them start from the refrigerated temperature (Tc) and there is a first stage of cooling until the initial freezing temperature (Tm) is reached. However, the changes of components depend on the temperature reached and the rate of freezing.

M. L. Castelló; P. J. Fito; A. Argüelles

2007-01-01

341

Reptile freeze tolerance: Metabolism and gene expression q Kenneth B. Storey *  

E-print Network

to temperatures below 0 °C cannot be avoided, either freeze avoidance (supercooling) or freeze toleranceReview Reptile freeze tolerance: Metabolism and gene expression q Kenneth B. Storey * Institute reptile species display ecologically relevant freeze tolerance, sur- viving for extended times with 50

Storey, Kenneth B.

342

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

E-print Network

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

Jackson, Robert B.

343

Mechanisms of deterioration of nutrients. [improved quality of freeze-dried foods  

NASA Technical Reports Server (NTRS)

Methods for improving the quality of freeze-dried foods were investigated. Areas discussed include: (1) microstructure of freeze-dried systems, (2) structural changes in freeze-dried systems, (3) artificial food matrices, and (4) osmotic preconcentration to yield improved freeze-dried products.

Karel, M.; Flink, J. M.

1978-01-01

344

Gradient optimization and nonlinear control  

NASA Technical Reports Server (NTRS)

The book represents an introduction to computation in control by an iterative, gradient, numerical method, where linearity is not assumed. The general language and approach used are those of elementary functional analysis. The particular gradient method that is emphasized and used is conjugate gradient descent, a well known method exhibiting quadratic convergence while requiring very little more computation than simple steepest descent. Constraints are not dealt with directly, but rather the approach is to introduce them as penalty terms in the criterion. General conjugate gradient descent methods are developed and applied to problems in control.

Hasdorff, L.

1976-01-01

345

Gradient boosting machines, a tutorial  

PubMed Central

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

Natekin, Alexey; Knoll, Alois

2013-01-01

346

Cryo-fixation by self-pressurized rapid freezing.  

PubMed

High-pressure freeze fixation is the method of choice to arrest instantly all dynamic and physiological processes inside cells, tissues, and small organisms. Embedded in vitreous ice, such samples can be further processed by freeze substitution or directly analyzed in their fully hydrated state by cryo-electron microscopy of vitreous sections (CEMOVIS) to explore cellular ultrastructure as close as possible to the native state. Here, we describe the procedure of self-pressurized rapid freezing as fast, easy-to-use, and low-cost freeze fixation method, avoiding the usage of a high-pressure freezing (HPF) apparatus. Cells or small organisms are placed in capillary metal tubes, which are tightly closed and plunged directly into liquid ethane cooled by liquid nitrogen. In parts of the tube, crystalline ice is formed and builds up pressure sufficient for the liquid-glass transition of the remaining specimen. The quality of samples is equivalent to preparations by conventional HPF apparatus, allowing for high-resolution cryo-EM applications or for freeze substitution and plastic embedding. PMID:24357364

Grabenbauer, Markus; Han, Hong-Mei; Huebinger, Jan

2014-01-01

347

Viability of freeze dried microencapsulated human retinal pigment epithelial cells.  

PubMed

Encapsulated human retinal pigment epithelial cell line ARPE-19 has been successfully used in experimental cell therapy of retinal degenerations and Parkinson's disease, but the long-term storage of encapsulated cells is still an unresolved question. Reconstitution of viable encapsulated cells from dry form would benefit the development of cell therapy products. We freeze dried and reconstituted microencapsulated ARPE19 and ARPE19-SEAP cells. Cross-linked alginate matrix with polycation (poly-l-lysine, cationic starch) coating was used for microencapsulation. Cell viability was assessed with fluorescence microscopy and oxygen consumption of the cells. Freeze dried and reconstituted cell microcapsules were imaged using scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM). We show partial viability of microencapsulated cells after freeze-drying. Unlike poly-l-lysine (PLL) coating, cationic starch supported microcapsule shape and cell viability during freeze-drying. Trehalose pre-treatment augmented cell viability. Likewise, some lyoprotectants (trehalose, glycerol) enabled preservation of cell viability. Upon reconstitution the freeze dried cell microcapsules rapidly regained their original spherical shape. This proof-of-concept study demonstrates that microencapsulated cells can retain their viability during freeze-drying. Therefore, this approach can be further optimized for the benefit of cell therapy product development. PMID:22820032

Wikström, Jonna; Elomaa, Matti; Nevala, Laura; Räikkönen, Johanna; Heljo, Petteri; Urtti, Arto; Yliperttula, Marjo

2012-09-29

348

Low-temperature brewing by freeze-dried immobilized cells.  

PubMed

We propose a novel biocatalyst in brewing. A cryotolerant strain of Saccharomyces cerevisiae was immobilized on delignified cellulosic material followed by freeze-drying of the immobilized cells without the use of any cryoprotectant. The freeze-dried immobilized biocatalyst was used in repeated-batch fermentation of wort and showed reduced fermentation time and increased productivities as compared with free freeze-dried cells (FFDCs). It also demonstrated suitability for low-temperature brewing (5 and 0 degrees C). The fermentation time in repeated-batch fermentations at 15 degrees C was 1.5-2 d for a period of 13 mo, showing a high operational stability of the system. At 0 degrees C the freeze-dried immobilized biocatalyst showed a 2- to 3.5-fold decrease in fermentation time in comparison with FFDCs. Polyphenol contents, bitterness, and diacetyl concentration were lower in beers produced by freeze-dried immobilized cells as compared with FFDCs. At 0 degrees C polyphenols were 40% lower than at 15 degrees C. Higher alcohols were reduced and ethyl acetate increased in comparison with FFDCs. Amyl alcohols at 0 degrees C were lower than half of their content at 15 degrees C, while ethyl acetate was 31 mg/L at 0 degrees C and 18 mg/L at 15 degrees C. These data justify the improved aroma and taste of beers produced by freeze-dried immobilized biocatalyst mainly at low temperatures. PMID:11996222

Bekatorou, Argyro; Soupioni, Magda J; Koutinas, Athanasios A; Kanellaki, Maria E

2002-02-01

349

Freeze concentration of dairy products, Phase 1: Final report  

SciTech Connect

The objective of this study was to explore freeze concentration as a process to replace thermal evaporation in the dairy industry. The goals of the study were to save energy by converting concentration processes to an efficient, electrically powered, refrigeration system, and to create higher quality and innovative products that might bring new life to a nature dairy market. A small freeze concentration pilot plant was used to concentrate products for quality comparisons, for physical and chemical analytical determinations, and to discover any equipment/product attributes or limitations. Data was correlated to compare operating economics of freeze concentrations superior to the fresh feedstock in sensory and functionality tests upon reconstitution. Laboratory testing showed equal or superior quality in resulting spray dried powders from freeze concentrates. Freeze concentration was shown to be economically competitive with thermal processes and second generation freezing technology is projected to produce a substantially less expensive product and offer other advantages over current thermally produced goods. 31 figs., 14 tabs.

Luksas, A.; Ahmed, S.; Johnson, T.A.

1989-03-01

350

Freeze avoidance: a dehydrating moss gathers no ice.  

PubMed

Using cryo-SEM with EDX fundamental structural and mechanical properties of the moss Ceratodon purpureus (Hedw.) Brid. were studied in relation to tolerance of freezing temperatures. In contrast to more complex plants, no ice accumulated within the moss during the freezing event. External ice induced desiccation with the response being a function of cell type; water-filled hydroid cells cavitated and were embolized at -4 °C while parenchyma cells of the inner cortex exhibited cytorrhysis, decreasing to ? 20% of their original volume at a nadir temperature of -20 °C. Chlorophyll fluorescence showed that these winter acclimated mosses displayed no evidence of damage after thawing from -20 °C while GCMS showed that sugar concentrations were not sufficient to confer this level of freezing tolerance. In addition, differential scanning calorimetry showed internal ice nucleation occurred in hydrated moss at ?-12 °C while desiccated moss showed no evidence of freezing with lowering of nadir temperature to -20 °C. Therefore the rapid dehydration of the moss provides an elegantly simple solution to the problem of freezing; remove that which freezes. PMID:20525002

Lenné, Thomas; Bryant, Gary; Hocart, Charles H; Huang, Cheng X; Ball, Marilyn C

2010-10-01

351

Freezing of barley studied by infrared video thermography.  

PubMed

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

Pearce, R S; Fuller, M P

2001-01-01

352

Freezing of Barley Studied by Infrared Video Thermography1  

PubMed Central

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

Pearce, Roger S.; Fuller, Michael P.

2001-01-01

353

An Experimental Investigation of the Effect of Pressure Gradient on Gas-oil Relative Permeability in Iranian Carbonate Rocks  

Microsoft Academic Search

The authors examine the effect of pressure gradient on gas-oil relative permeability in horizontal and vertical immiscible displacement. The experiments are conducted on a core from lower Dalan formation in the South Pars oilfield of Iran, in constant pressure, unsteady-state condition, and different pressure gradients. The Toth method is used for calculating the relative permeability and plotting proper curves. Data

A. Keshavarz; H. Vatanparast; M. Zargar; A. Kalantari Asl; M. Haghighi

2012-01-01

354

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

PubMed Central

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

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

2011-01-01

355

Critical gradient formula for toroidal electron temperature gradient modes  

Microsoft Academic Search

Under certain conditions, the electron heat transport induced by electron temperature gradient (ETG) streamers is sufficiently large and sensitive with respect to the normalized electron temperature gradient to represent a possible cause for electron temperature profile consistency (``stiffness''). Here, linear gyrokinetic simulations of toroidal ETG modes in tokamak core and edge plasmas are presented. An algebraic formula for the threshold

F. Jenko; W. Dorland; G. W. Hammett

2001-01-01

356

Vertical solar louver project  

NASA Astrophysics Data System (ADS)

The thermal network analysis computer program MICROPAS was used to analyze Vertical Solar Louvers and other reference solar designs in eight selected climates. The results have been used to generate a set of correlation coefficients for use in performance predictions by the Solar Load Ratio method. At low mass VSL were shown to be superior to ordinary direct gain and equal to the trombe wall systems in energy savings. The energy savings advantage of VSL over direct gain disappears in comparable systems of high mass. Identical solar water tanks of oval cross section were compared in the water wall and VSL configurations.

Bier, C. J.

1984-09-01

357

Vertical Motion Simulator  

NSDL National Science Digital Library

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

358

'Endurance' Untouched (vertical)  

NASA Technical Reports Server (NTRS)

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

2004-01-01

359

Inhibition, Executive Function, and Freezing of Gait  

PubMed Central

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

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

2014-01-01

360

Vertical profiles of ethane and propane in the stratosphere  

Microsoft Academic Search

Stratospheric measurements of the C2H6 mixing ratio up to 30 km and of the C3H8 mixing ratio up to 18 km altitude are reported. The observed vertical gradient of C2H6 is much weaker than that calculated from a one-dimensional steady state model, indicating lower concentrations of atomic chlorine in the lower stratosphere than those predicted by models. From the measured

J. Rudolph; D. H. Ehhalt; A. Toennissen

1981-01-01

361

Optimization of Intensification of Freeze-Drying Rate of Banana: Combined Applications of IR Radiation and Cryogenic Freezing  

Microsoft Academic Search

A programmed experimental study on infrared (IR) aided freeze-drying of cryogenically (LN2) frozen heat sensitive material viz. banana (Musa acuminata) rendered faster moisture separation rate compared to the conventionally frozen samples. Response surface methodology (RSM) could determine the simultaneous optimal freeze-drying conditions of 59.78°C IR temperature, 10 mm sample thickness and 5 h drying time corresponding to minimum moisture content of 4.11%,

M. Bera; R. Chakraborty; P. Bhattacharya

2012-01-01

362

FROST - FReezing Of coated and uncoated duST particles  

NASA Astrophysics Data System (ADS)

In April 2008, the measurement campaign FROST (FReezing Of coated and uncoated duST particles) was conducted at the ACCENT (Atmospheric Composition Change - the European NeTwork of excellence) infrastructure site LACIS (Leipzig Aerosol Cloud Interaction Simulator). During the campaign, size selected coated and uncoated Arizona Test Dust (ATD) particles were characterized with respect to shape, chemical composition, hygroscopic growth and activation, and their ability to act as IN (Ice Nuclei). The ATD particles were dispersed by means of a fluidized bed generator. Coatings were applied in different furnaces, operated at different temperatures. The coatings were either succinic acid, sulphuric acid, or ammonium sulphate. A DMA (Differential Mobility Analyzer) was used for selecting particles with a mobility diameter of 300 nm. The following measurements were done: Three AMS (Aerosol Mass Spectrometers, e.g. Schneider et al. (2005) and references therein) were used to determine particle composition. Particles were collected on grids for subsequent TEM (Transmission Electron Micoscropy) analysis. Hygroscopic growth factors were determined by means of a HH-TDMA (High Humidity Tandem Differential Mobility Analyzer) that measured up to relative humidities (RH) of 98% (Hennig et al. (2005)). The critical super-saturations needed for the activation of the investigated particles into cloud droplets were measured with a continuous flow CCNc (Cloud Condensation Nucleus counter) from DMT (Droplet Measurement Technologies, Roberts and Nenes (2005)). The LACIS flow tube was extended to a length of 8 m, so LACIS could be used to examine the immersion freezing behaviour of the coated and uncoated ATD particles. By a bulk analysis and by the AMS measurements, the ATD particles were found to contain water soluble material, however in small quantities. By means of the online AMS measurements, it was possible to distinguish between thin and thick H2SO4 coatings. For the thin coatings, the H2SO4 was found to have reacted with material contained in the ATD, so that almost no free H2SO4 was found. For the thick coatings, obtained at higher coating temperatures, H2SO4 was detected. In general, uncoated particles and those coated with thin coatings of H2SO4 or of succinic acid, showed almost no hygroscopic growth. Particles coated with thicker coatings of H2SO4 and of ammonium sulphate grew noticeably above 95% RH (growth factors of about 1.1 at 98% RH). Both, coated and uncoated ATD particles, were found to activate at atmospherically relevant super-saturations (0.35% for pure ATD, 0.2% for succinic acid and thin H2SO4 coatings, 0.15% for thick H2SO4 and for ammonium sulphate coatings). Combining measured hygroscopic growth with activation data, a dynamic shape factor of the ATD particles of about 1.8 was derived, corroborating the deviation of the particle shape from that of a sphere. Uncoated ATD particles and particles coated with succinic acid or thin coatings of H2SO4 nucleated ice at higher temperatures, i.e. were more efficient IN, than particles with thick H2SO4 or ammonium sulphate coatings. Although the latter two were similar in hygroscopic growth and activation behaviour, they differed in their ability to act as IN, with ATD particles coated with ammonium sulphate being the most ineffective IN. This finding suggests that the investigated particle's ability to act as IN might not be related to water activity for the immersion freezing processes investigated in this study. References: Hennig, T., A. Massling, F. Brechtel, and A. Wiedensohler (2005), A tandem DMA for highly temperature-stabilized hygroscopic particle growth measurements between 90% and 98% relative humidity, J. Aerosol Sci., 36, 10, 1210-1223. Roberts, G., and A. Nenes (2005), A continuous-flow streamwise thermal-gradient CCN chamber for atmospheric measurements, Aerosol Sci. Technol., 39, 206-221. Schneider, J., N. Hock, S. Weimer, S. Borrmann, U. Kirchner, R. Vogt, and V. Scheer (2005), Nucleation particles in Diesel exhaust: Composition inferred from in situ mass sp

Wex, H.

2009-04-01

363

HIF-1? involvement in low temperature and anoxia survival by a freeze tolerant insect  

Microsoft Academic Search

Winter survival for many insect species relies on the ability to endure the freezing of extracellular body fluids. Because\\u000a freezing impedes oxygen delivery to tissues, one component of natural freeze tolerance is a well-developed anoxia\\/ischemia\\u000a resistance. The present study explores the responses of the hypoxia-inducible factor-1? (HIF-1?) to cold, freezing and anoxia\\u000a exposures in the freeze tolerant goldenrod gall fly

Pier Morin; David C. McMullen; Kenneth B. Storey

2005-01-01

364

Time course for cryoprotectant synthesis in the freeze-tolerant chorus frog, Pseudacris triseriata  

Microsoft Academic Search

Increases in liver glycogen phosphorylase activity, along with inhibition of glycogen synthetase and phosphofructokinase-1, are associated with elevated cryoprotectant (glucose) levels during freezing in some freeze-tolerant anurans. In contrast, freeze-tolerant chorus frogs, Pseudacris triseriata, accumulate glucose during freezing but exhibit no increase in phosphorylase activity following 24-h freezing bouts. In the present study, chorus frogs were frozen for 5- and

Joshua R Edwards; Karen L Koster; David L Swanson

2000-01-01

365

Repeated freeze–thaw cycles induce embolism in drought stressed conifers (Norway spruce, stone pine)  

Microsoft Academic Search

Freezing and thawing lead to xylem embolism when gas bubbles caused by ice formation expand during the thaw process. However, previous experimental studies indicated that conifers are resistant to freezing-induced embolism, unless xylem pressure becomes very negative during the freezing. In this study, we show that conifers experienced freezing-induced embolism when exposed to repeated freeze–thaw cycles and simultaneously to drought.

Stefan Mayr; Andreas Gruber; Helmut Bauer

2003-01-01

366

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

367

Thermal Gradient Fining of Glass  

NASA Technical Reports Server (NTRS)

Molten glass fined (cleared of bubbles) by heating with suitable temperature gradient, according to preliminary experiments. Temperature gradient produces force on gas bubbles trapped in molten glass pushing bubbles to higher temperature region where they are collected. Concept demonstrated in experiments on Earth and on rocket.

Wilcox, W.

1983-01-01

368

Empirical equation estimates geothermal gradients  

SciTech Connect

An empirical equation can estimate geothermal (natural) temperature profiles in new exploration areas. These gradients are useful for cement slurry and mud design and for improving electrical and temperature log interpretation. Downhole circulating temperature logs and surface outlet temperatures are used for predicting the geothermal gradients.

Kutasov, I.M. (MultiSpectrum Technologies, Santa Monica, CA (United States))

1995-01-02

369

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

370

Freeze-thaw cycles enhance decellularization of large tendons.  

PubMed

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

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

2014-04-01

371

Measuring and modeling hemoglobin aggregation below the freezing temperature.  

PubMed

Freezing of protein solutions is required for many applications such as storage, transport, or lyophilization; however, freezing has inherent risks for protein integrity. It is difficult to study protein stability below the freezing temperature because phase separation constrains solute concentration in solution. In this work, we developed an isochoric method to study protein aggregation in solutions at -5, -10, -15, and -20 °C. Lowering the temperature below the freezing point in a fixed volume prevents the aqueous solution from freezing, as pressure rises until equilibrium (P,T) is reached. Aggregation rates of bovine hemoglobin (BHb) increased at lower temperature (-20 °C) and higher BHb concentration. However, the addition of sucrose substantially decreased the aggregation rate and prevented aggregation when the concentration reached 300 g/L. The unfolding thermodynamics of BHb was studied using fluorescence, and the fraction of unfolded protein as a function of temperature was determined. A mathematical model was applied to describe BHb aggregation below the freezing temperature. This model was able to predict the aggregation curves for various storage temperatures and initial concentrations of BHb. The aggregation mechanism was revealed to be mediated by an unfolded state, followed by a fast growth of aggregates that readily precipitate. The aggregation kinetics increased for lower temperature because of the higher fraction of unfolded BHb closer to the cold denaturation temperature. Overall, the results obtained herein suggest that the isochoric method could provide a relatively simple approach to obtain fundamental thermodynamic information about the protein and the aggregation mechanism, thus providing a new approach to developing accelerated formulation studies below the freezing temperature. PMID:23808610

Rosa, Mónica; Lopes, Carlos; Melo, Eduardo P; Singh, Satish K; Geraldes, Vitor; Rodrigues, Miguel A

2013-08-01

372

Freeze-Thaw Cycles Enhance Decellularization of Large Tendons  

PubMed Central

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

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

2014-01-01

373

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

PubMed Central

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

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

2014-01-01

374

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

375

Ultrastructural effects of lethal freezing on brain, muscle and Malpighian tubules from freeze-tolerant larvae of the gall fly, Eurosta solidaginis  

Microsoft Academic Search

In preparation for winter low temperatures, larvae of the gall fly, Eurosta solidaginis, accumulate the cryoprotectants glycerol, sorbitol, and trehalose. The fat body cells of these freeze-tolerant larvae can survive intracellular freezing to ?80°C for 48 h even though no whole larvae survive this treatment. We hypothesized that some other tissue was more susceptible to freezing and therefore may be

Stephen D Collins; Allan L Allenspach; Richard E Lee

1997-01-01

376

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

PubMed

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. PMID:17578108

Sheridan, T E; Katschke, M R; Wells, K D

2007-02-01

377

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

378

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

2012-11-01

379

Preparation of Chitosan Nanocompositeswith a Macroporous Structure by Unidirectional Freezing and Subsequent Freeze-Drying  

PubMed Central

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

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

2014-01-01

380

Monitoring Seasonal Landscape Freeze/Thaw Processes with SMAP  

NASA Astrophysics Data System (ADS)

Major science objectives of SMAP support understanding of processes linking terrestrial water, energy and carbon cycles and quantify net carbon flux. The landscape transition between seasonally frozen and non- frozen conditions occurs each year over more than 50 million km2 of the global biosphere, affecting hydrological and ecological processes and associated trace gas dynamics profoundly. The SMAP suite of data products will include maps of landscape freeze/thaw state derived from L-band radar at 1-3 km spatial resolution with a 2-day refresh rate for the high northern latitudes (i.e. latitudes above 50 degrees north). Satellite active and passive microwave remote sensing can be applied to detect large changes in landscape dielectric properties associated with water transitioning between frozen and non-frozen conditions. In the northern high latitudes, seasonal freeze/thaw transitions associated with this process dominate time-series microwave remote sensing signatures. The SMAP freeze/thaw algorithm employs a temporal change detection scheme to delineate freeze/thaw state changes associated with temporal variations in landscape dielectric properties. Development of the algorithm follows from application of legacy data sets provided by satellite radars, both scatterometers and Synthetic Aperture Radars (SARs), and radiometers. This presentation reviews algorithm development and applications, and associated SMAP science objectives addressed through the derived freeze/thaw data products. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, and at the University of Montana under contract to the National Aeronautics and Space Administration.

McDonald, K. C.; Kimball, J. S.

2008-12-01

381

A modified homogeneous freezing rate parameterization for aqueous solution droplets  

NASA Astrophysics Data System (ADS)

It is still a matter of debate wether cirrus cloud formation is dominated by heterogeneous ice nucleation, leading to low ice crystal number concentrations, or is also influenced by homogeneous freezing of solution aerosols leading to higher ice crystal number concentrations. Part of the discussion is due to the fact that current models seem to overestimate ice crystal numbers from homogeneous freezing compared to measurements, though the formation rate of cirrus ice crystals by homogeneous freezing of aqueous particles is believed to be well understood and formulated in terms of e.g. the concept of effective freezing temperatures or the water activity dependent ice nucleation rates. Series of recent cirrus cloud simulation experiments at the cloud chamber facility AIDA at the Karlsruhe Institute of Technology at temperatures between -40°C and -80°C together with process modeling studies demonstrated, that the freezing formulations tend to show a low bias in the humidity onset thresholds for homogeneous ice formation at temperatures below about 210 K, and furthermore overestimate the ice formation rate by at least a factor of 2. The experimental results will be summarized and a new empirical fit to the experimental data will be suggested for use in atmospheric models.

Moehler, O.; Benz, S.; Hoehler, K.; Wagner, R.

2012-12-01

382

Units of freezing of deep supercooled water in woody xylem.  

PubMed

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

Hong, S G; Sucoff, E

1980-07-01

383

Temperature profiles in high gradient furnaces  

NASA Technical Reports Server (NTRS)

Accurate temperature measurement of the furnace environment is very important in both the science and technology of crystal growth as well as many other materials processing operations. A high degree of both accuracy and precision is acutely needed in the directional solidification of compound semiconductors in which the temperature profiles control the freezing isotherm which, in turn, affects the composition of the growth with a concomitant feedback perturbation on the temperature profile. Directional solidification requires a furnace configuration that will transport heat through the sample being grown. A common growth procedure is the Bridgman Stockbarger technique which basically consists of a hot zone and a cold zone separated by an insulator. In a normal growth procedure the material, contained in an ampoule, is melted in the hot zone and is then moved relative to the furnace toward the cold zone and solidification occurs in the insulated region. Since the primary path of heat between the hot and cold zones is through the sample, both axial and radial temperature gradients exist in the region of the growth interface. There is a need to know the temperature profile of the growth furnace with the crystal that is to be grown as the thermal load. However it is usually not feasible to insert thermocouples inside an ampoule and thermocouples attached to the outside wall of the ampoule have both a thermal and a mechanical contact problem as well as a view angle problem. The objective is to present a technique of calibrating a furnace with a thermal load that closely matches the sample to be grown and to describe procedures that circumvent both the thermal and mechanical contact problems.

Fripp, A. L.; Debnam, W. J.; Woodell, G. A.; Berry, R.; Crouch, R. K.; Sorokach, S. K.

1989-01-01

384

Heterogeneous freezing of droplets with immersed surface modified mineral dust particles  

NASA Astrophysics Data System (ADS)

In the framework of the international measurement campaign FROST II (FReezing Of duST), the heterogeneous freezing of droplets with an immersed surface modified size-segregated mineral dust particles was investigated at LACIS (Leipzig Aerosol Cloud Interaction Simulator, Stratmann et al. 2004). The following measurements were done: LACIS, CFDC (Continuous Flow thermal gradient Diffusion Chamber, Rogers (1988)) and FINCH (Fast Ice Nucleus Chamber Counter, Bundke et al (2008)) were used to analyze the immersion freezing behavior of the treated Arizona Test Dust (ATD) particles at different temperature regimes. The ability to act as IN (Ice Nucleus) in the deposition nucleation mode was quantified by the PINC (Portable Ice Nucleation Chamber) and the CFDC instrument. AMS (Aerosol Mass Spectrometers, e.g. Schneider et al. (2005)) and ATOFMS (Aerosol Time-Of-Flight Mass Spectrometer) measurements were applied to determine particle composition. The hygroscopic growth and the critical super-saturations needed for droplet activation were determined by means of an H-TDMA (Humidity-Tandem Differential Mobility Analyzer) and CCN counter (Cloud Condensation Nucleus counter, Droplet Measurement Technologies, Roberts and Nenes (2005)). The 300 nm ATD particles were chemically and physically treated by coating with sulphuric acid (H2SO4, three different coating thicknesses) and ammonium sulphate ((NH4)2SO4) or by thermal treatment with a thermodenuder operating at 250°C. The H2SO4 coating modified the particles by reacting with particle material, forming soluble sulfates and therefore changing surface properties. AMS showed free H2SO4 only for thick H2SO4 coatings. In the heated section of the thermodenuder coating materials were evaporated partly and the surface properties of the particles were additionally altered. Uncoated particles and those coated with thin coatings of H2SO4, showed almost no hygroscopic growth. Particles coated with thicker coatings of H2SO4 and of (NH4)2SO4 grew noticeably above 95% relative humidity. All investigated particles were found to activate at atmospherically relevant super-saturations. All kinds of treatment lower the IN-ability, whereas the deposition nucleation was more sensitive to treatments than the immersion freezing mode. Considering the immersion freezing behavior, pure ATD particles and particles coated with thin coatings of H2SO4 were more efficient IN, than particles with thick H2SO4 or (NH4)2SO4 coatings. Thermal treatments of the particles led to further decrease of the IN capability except for particles coated with (NH4)2SO4, where the heating did not effect the immersion freezing behavior likely due to their already reduced IN ability. In order to specify the temperature-dependent immersion freezing, two parameterization based on either stochastic or singular hypothesis were performed. From both theoretical approaches it can be concluded that the treatments lead to particle surface modifications lowering the nucleation efficiency. References: Bundke, U., B. Nillius, et al. (2008), The fast Ice Nucleus chamber FINCH, Atmospheric Research 90(2-4): 180-186. Rader, D. J. and P. H. McMurry (1986), Application of the Tandem Differential Mobility Analyzer to studies of droplet growth or evaporation, J. Aerosol Sci., Vol. 17, No. 5, pp. 771-787. Roberts, G., and A. Nenes (2005), A continuous-flow streamwise thermal-gradient CCN chamber for atmospheric measurements, Aerosol Sci. Technol., 39, 206-221. Schneider, J., N. Hock, S. Weimer, S. Borrmann, U. Kirchner, R. Vogt, and V. Scheer (2005), Nucleation particles in Diesel exhaust: Composition inferred from in situ mass spectrometric analysis, Environ. Sci. Technol., 39, 6153-6161. Rogers,D .C. (1988), Developmenot f a continuousflow thermal gradient diffusion chamber for ice nucleation studies. Atmospheric Research, 22, 149-181. Stratmann, F., A. Kiselev, S. Wurzler, M. Wendisch, J. Heintzenberg, R. J. Charlson, K. Diehl, H. Wex, and S. Schmidt (2004), Laboratory studies and numerical simulations of cloud droplet formation under realistic super

Hartmann, Susan

2010-05-01

385

Particle-size dependence of immersion freezing: Investigation of INUIT test aerosol particles with freely suspended water drops.  

NASA Astrophysics Data System (ADS)

One goal of the research group INUIT (Ice Nuclei research UnIT) is to investigate the efficiencies of several test ice nuclei under comparable conditions but with different experimental techniques. In the present studies, two methods are used: the Mainz vertical wind tunnel and an acoustic levitator placed inside a cold chamber. In both cases drops are freely levitated, either at their terminal velocity in the wind tunnel updraft or around the nodes of a standing ultrasonic wave in the acoustic levitator. Thus, heat transfer conditions are well approximated, and wall contact effects on freezing as well as electrical charges of the drops are avoided. Drop radii are 370 ?m and 1 mm, respectively. In the wind tunnel, drops are investigated at constant temperatures within a certain time period and the onset of freezing is observed directly. In the acoustic levitator, the drop temperature decreases during the experiments and is measured by an in-situ calibrated Infrared thermometer. The onset of freezing is indicated by a rapid rise of the drop surface temperature because of the release of latent heat. Investigated test ice nuclei are Snomax® as a proxy of biological particles and illite NX as well as K-feldspar as represents of mineral dust. The particle concentrations are 1 × 10-12 to 3 × 10-6 g Snomax® per drop and 5 × 10-9 to 5 × 10-5 g mineral dust per drop. Freezing temperatures are between -2 and -18° C in case of Snomax® and between -14 and -26° C in case of mineral dust. The lower the particle masses per drop the lower are the freezing temperatures. For similar particle concentrations in the drops, the median freezing temperatures determined by the two techniques agree well within the measurement errors. With the knowledge of the specific particle surface area of the mineral dusts, the results are interpreted also in terms of particle surface area per drop. Results from the wind tunnel experiments which are performed at constant temperatures indicate that the freezing times are shorter the lower the temperatures are. For evaluation and comparisons of the data, two models of heterogeneous freezing are applied, the stochastic and the time-independent singular description. The nucleation rate coefficients J(T) as well as the surface densities of active sites ns(T) or the numbers of active sites nm(T) are determined from the experimental data. It is shown that both models are suited to describe the present heterogeneous freezing results for the range of investigated particle masses or surface areas per drop. The comparison of the results from the two experimental techniques evaluated with the time-independent singular model indicates an excellent agreement within the measurement errors.

Diehl, Karoline; Debertshäuser, Michael; Eppers, Oliver; Jantsch, Evelyn; Mitra, Subir K.

2014-05-01

386

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

PubMed

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 degrees 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 also examined by using different growth media. The bacteria frozen at the warmer temperature (-5 degrees C) was most sensitive to storage and freeze-thaw cycles as compared to those frozen at -15 and -35 degrees C. In general, greater inactivation efficiencies were achieved under longer storage time and warmer freezing temperature conditions. Freezing and thawing caused cell injury. More cells were injured when frozen at -15 degrees C. The percentage of cells injured decreased as freeze-thaw cycles increased. The spray-freezing process was found more effective in killing the cells. On average, the log reduction rate for the spray ice with two-day storage time was about 4 log units higher than those without any storage after freezing. The results indicated that the natural freezing processes are not only cost-effective techniques for chemical and physical contaminant removal from wastewater or enhancing sludge dewaterability in cold regions but also effective in reducing E. coli concentration. PMID:16740289

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

2006-07-01

387

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

388

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

389

Immersion freezing by SnomaxTM particles: Comparison of results from different instruments  

NASA Astrophysics Data System (ADS)

Within the DFG funded research unit INUIT (Ice Nucleation research UnIT, FOR 1525), an effort was made to compare results on immersion freezing from a suite of different instruments. Besides mineral dusts, SnomaxTM was picked as one of the substances that were examined by all participating groups. Here, the comparison of the results for SnomaxTM is presented. Every participating group used SnomaxTM from the same batch and, as far as possible, the same particle generation set-up. Instruments participating in the comparison were, in alphabetical order, an acoustic levitator (Diehl et al., 2009), AIDA (Connolly et al., 2009), BINARY (Budke et al., 2013), FINCH (Bundke et al., 2008), LACIS (Hartmann et al., 2011), PINC (Chou et al., 2011) and the Mainz vertical windtunnel (Diehl et al., 2011). Some of the instruments examined droplets directly produced from SnomaxTM suspensions, where the suspensions could have a wide range of concentrations. Other instruments used size segregated particles which were generated via atomization from a SnomaxTM suspension and subsequent drying, followed by size selection with a DMA (Differential Mobility Analyzer). These particles were then activated to droplets and cooled subsequently. For these, the number of ice nucleation active protein complexes present in the droplets depended on the original particle size (for details see e.g. Hartmann et al., 2013). Also, the different measurements spanned a range of different time scales. The shortest residence time of roughly 1 second was used for LACIS measurements, and the longest one was about 6 seconds used in the BINARY setup with a cooling rate of 1 K/min. All data were evaluated using two different approaches: 1) a time dependent approach following Classical Nucleation Theory which included the use of a contact angle distribution (see Niedermeier et al., 2014); 2) a singular approach using an active site density per mass (see Vali, 1971, Murray et al., 2012). Both approaches were found to work equally well, hence freezing by SnomaxTM can be considered to show no time dependence. Particularly data from LACIS and BINARY, i.e. from the "fastest" and "slowest" measurements, were found to agree very well. Acknowledgement: This work was done within the framework of the DFG funded Ice Nucleation research UnIT (INUIT, FOR 1525). Literature Budke et al. (2013), Investigation of Heterogeneous Ice Nucleation Using a Novel Optical Freezing Array, AIP Conference Proceedings, 1527, 949-951, doi: 10.1064/1.4803429. Bundke et al. (2008), The fast Ice Nucleus chamber FINCH, Atmos. Res. 90, 180-186. Chou et al. (2011), Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps, Atmos. Chem. Phys., 11, 4725-4738. Connolly, et al. (2009), Studies of heterogeneous freezing by three different desert dust samples, Atmos. Chem. Phys., 9, 2805-2824. Diehl et al. (2011), The Mainz vertical wind tunnel facility: A review of 25 years of laboratory experiments on cloud physics and chemistry. In: J.D. Pereira (Ed.), Wind tunnels: Aerodynamics, models, and experiments. Nova Science Publishers, Inc., Chapter 2. Diehl et al. (2009), Homogeneous freezing of single sulfuric and nitric acid solution drops levitated in an acoustic trap, Atm. Res., 94, 356-361, doi:10.1016/j.atmosres.2009.06.001. Hartmann et al. (2011), Homogeneous and heterogeneous ice nucleation at LACIS: Operating principle and theoretical studies, Atmos. Chem. Phys., 11, 1753-1767. Hartmann et al. (2013), Immersion freezing of ice nucleating active protein complexes, Atmos. Chem. Phys., 13, 5751-5766. Murray et al. (2012), Ice nucleation by particles immersed in supercooled cloud droplets, Chem. Soc. Rev., 41, 6519-6554. Niedermeier et al. (2014), A computationally-efficient description of heterogeneous freezing: A simplified version of the Soccer ball model, Geophys. Res. Lett., 10.1002/2013GL058684. Vali, G. (1971), Quantitative evaluation of experimental results on heterogeneous freezing nucleation of supercooled liquids, J. Atmos. Sci., 28(3), 402-409.

Wex, Heike; Stratmann, Frank; Rösch, Michael; Niedermeier, Dennis; Nilius, Björn; Möhler, Ottmar; Mitra, Subir K.; Koop, Thomas; Jantsch, Evelyn; Hiranuma, Naruki; Diehl, Karoline; Curtius, Joachim; Budke, Carsten; Boose, Yvonne; Augustin, Stefanie

2014-05-01

390

Shaping Morphogen Gradients by Proteoglycans  

PubMed Central

During development, secreted morphogens such as Wnt, Hedgehog (Hh), and BMP emit from their producing cells in a morphogenetic field, and specify different cell fates in a direct concentration-dependent manner. Understanding how morphogens form their concentration gradients to pattern tissues has been a central issue in developmental biology. Various experimental studies from Drosophila have led to several models to explain the formation of morphogen gradients. Over the past decade, one of the main findings in this field is the characterization of heparan sulfate proteoglycan (HSPG) as an essential regulator for morphogen gradient formation. Genetic and cell biological studies have showed that HSPGs can regulate morphogen activities at various steps including control of morphogen movement, signaling, and intracellular trafficking. Here, we review these data, highlighting recent findings that reveal mechanistic roles of HSPGs in controlling morphogen gradient formation. PMID:20066107

Yan, Dong; Lin, Xinhua

2009-01-01

391

Height and Gradient from Shading  

E-print Network

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. ...

Horn, Berthold K.P.

1989-05-01

392

Ice cube maker with new freeze and harvest control  

SciTech Connect

A method of making ice cubes is described comprising the steps of (a) sensing the size of ice frozen upon an evaporator; (b) initiating a hot gas defrost of the evaporator upon the sensing of a predetermined size of ice, and thereby and thereafter harvesting the ice from the evaporator; (c) dropping the ice off of the evaporator and against a curtain; (d) opening the curtain with the dropping ice; (e) changing the mode of a photoelectric emitter-receiver with the curtain during the opening; and (f) terminating the hot gas defrost and restarting a freeze cycle in response to the mode changing, and freezing a subsequent quantity of ice.

Josten, M.H.; Merrill, T.L.; Schneider, K.W.; Utter, R.F.

1988-03-29

393

FREEZING AND THAWING RESISTANCE OF CONCRETE WITH INITIAL CRACK  

NASA Astrophysics Data System (ADS)

Freezing and thawing resistance of concrete with an initial crack was investigated. The specimens were classified into plane concrete, fiber reinforced concrete, and reinforced concrete. In the tests of plane concrete with an initial crack, the crack grows seriously by the frozen expansion pressure of the water infiltrated into the crack, though the concrete material had high resistance to freezing and thawing. In the experimental results of fiber reinforced concrete, the long polypropylene fiber was useful to prevent the spalling of concrete cover, though the crack growth was not prevented. Moreover, in the experimental results of reinforced concrfete, it was shown that the crack growth was effectively prevented by steel reinforcing bar.

Naito, Hideki; Hayashi, Hiroshi; Saiki, Yusuke; Sando, Koichi; Koga, Hideyuki; Suzuki, Motoyuki

394

Correlation estimates ethane plant's carbon-dioxide freezing pressure  

SciTech Connect

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

Trebble, M.A.

1983-01-31

395

Time dependent freezing of water under dynamic compression.  

SciTech Connect

Using shock wave reverberation experiments, water samples were quasi-isentropically compressed between silica and sapphire plates to peak pressures of 1-5 GPa on nanosecond time scales. Real time optical transmission measurements were used to examine changes in the compressed samples. Although the ice VII phase is thermodynamically favored above 2 GPa, the liquid state was initially preserved and subsequent freezing occurred over hundreds of nanoseconds only for the silica cells. Images detailing the formation and growth of the solid phase were obtained. These results provide unambiguous evidence of bulk water freezing on such short time scales.

Dolan, Daniel H., III (Washington State University, Pullman, WA)

2003-07-01

396

Porosity gradients in marine sediments  

E-print Network

of Department) May 1990 ABSTRACT Porosity Gradients in Marine Sediments. (May 1990) Khalid Mahmood, B. Sc. , Punjab University; M. Sc. , Punjab University Chair of Advisory Committee: Dr. William R. Bryant Porosity versus depth profiles from over 110... of Department) May 1990 ABSTRACT Porosity Gradients in Marine Sediments. (May 1990) Khalid Mahmood, B. Sc. , Punjab University; M. Sc. , Punjab University Chair of Advisory Committee: Dr. William R. Bryant Porosity versus depth profiles from over 110...

Mahmood, Khalid

2012-06-07

397

Electron temperature gradient driven turbulence  

Microsoft Academic Search

Collisionless electron-temperature-gradient-driven (ETG) turbulence in toroidal geometry is studied via nonlinear numerical simulations. To this aim, two massively parallel, fully gyrokinetic Vlasov codes are used, both including electromagnetic effects. Somewhat surprisingly, and unlike in the analogous case of ion-temperature-gradient-driven (ITG) turbulence, we find that the turbulent electron heat flux is significantly underpredicted by simple mixing length estimates in a certain

F. Jenko; W. Dorland; M. Kotschenreuther; B. N. Rogers

2000-01-01

398

Correlated Knowledge Gradients: Example alternatives  

E-print Network

Correlated Knowledge Gradients: Example -4 -2 0 2 4 alternatives value 0 10 20 30 -10 -8 -6 -4 -2 0;Correlated Knowledge Gradients: Example -4 -2 0 2 4 alternatives value 0 10 20 30 -10 -8 -6 -4 -2 0 num measurements log(KGfactor) 0 10 20 30 0 0.5 1 1.5 2 num measurements opportunitycost #12;Correlated Knowledge

Keinan, Alon

399

Gradient characterization in magnetic resonance imaging  

E-print Network

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

Cheng, Joseph Yitan

2007-01-01

400

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2010 CFR

...24 2010-07-01 2010-07-01 false Salinity gradients. 230.25 Section 230.25 ...Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity gradients form where salt water from the...

2010-07-01

401

40 CFR 230.25 - Salinity gradients.  

Code of Federal Regulations, 2011 CFR

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

2011-07-01

402

Functions and Vertical Line Test  

NSDL National Science Digital Library

This lesson is designed to introduce students to the vertical line test for functions as well as practice plotting points and drawing simple functions. The lesson provides links to discussions and activities related to the vertical line test and functions as well as suggested ways to integrate them into the lesson.

2010-01-01

403

Influence of Nocturnal Vertical Stability on Daytime Chemistry: A One-dimensional Model Study  

NASA Astrophysics Data System (ADS)

Nocturnal chemistry can play an important role in determining the initial conditions for photochemistry of the next day, through the chemical removal and conversion of air pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOC). The quantification of these processes is challenging because radiation cooling leads to the suppression of turbulence and vertical mixing. Consequently, emissions at the ground are only slowly transported vertically and vertical concentration gradients develop for many trace gases, making nocturnal chemistry dependent on altitude and vertical stability. The stable nocturnal boundary layer which is often capped by a neutrally stratified residual layer breaks up after sunrise and a vertically well-mixed boundary layer forms. The transition from a vertically non-uniform chemical regime to a well-mixed boundary layer makes the assessment of the influence of nocturnal vertical stability on daytime chemistry challenging. Here we present one-dimensional (1-D) chemical transport model calculations for different nighttime vertical stability (stable, weakly stable and neutral) and different O3 formation regimes, i.e. NOx- vs VOC-sensitive. We investigate the influence of nocturnal vertical stability on O3 formation during the next day by analyzing the vertically integrated nocturnal loss of NOx, and the concentrations of NOx and O3 during the next day. Our results show that the impact of nocturnal chemistry depends on whether O3 formation occurs under NOx- or VOC-sensitive conditions.

Wong, K.; Stutz, J.

2007-12-01

404

Underground thermo-erosion of ice wedges: numerical simulation of tunnel freeze- back  

NASA Astrophysics Data System (ADS)

On Bylot Island in the Eastern Canadian Arctic archipelago, Fortier et al. (2007) observed and characterized the formation and development of tunnels initiated by the process of underground thermo-erosion of ice wedges networks. These tunnels often collapsed during the course of one or two summers and developed into gullies. However, observations of such tunnels in permafrost exposures indicate that they can be preserved in the permafrost record. The objective of this study is to estimate the freeze-back time of tunnels filled with water and slurry in cold and warm permafrost conditions. Ultimately, the goal is to evaluate time the tunnels remain "open"" for groundwater flow. We used numerical thermal modeling to conduct simple simulations of the conductive heat transfer during freeze-back of the tunnels. The thermal analyses were performed using the GeoslopeTM unsteady finite element heat conduction model TEMP/W. We used Bylot Island, Nunavut, Canada (Mean air temperature around -15 C) as a cold permafrost study case and Beaver Creek, Yukon Territory, Canada (Mean annual air temperature around -5.5C) as a warm permafrost study case. The air temperature was converted to ground surface temperature by the n-factor method. Zero heat flux was applied at the vertical and bottom boundaries due to the permafrost which is several tens to hundreds of meters thick. Based on previous studies, we simulated tunnels partly cut in ice-wedges and in the adjacent permafrost. The syngenetic permafrost of the case studies was assumed to be fully saturated with 110% gravimetric water content. The geometry of the tunnels was based on field measurements on Bylot Island. We considered three scenarios for the slurry filling the tunnels: 1) 100% water; 2) fully saturated sand with 30% gravimetric water content; and 3) an air layer at the top of the tunnel with water and saturated sands partly filling the bottom of the tunnel. We used three water/slurry temperatures: 1) 0.5C which simulates the water temperature of early snowmelt run-off, a period of active underground thermo- erosion; 2) 2C corresponding to the water temperature of run-off over a partly frozen active layer, which is typical for early summer undergrouns thermo-erosion ; 3) 5C and 15C corresponding to the water temperature lakes at the end of August on Bylot Island and at Beaver Creek respectively. This scenario simulates underground thermo-erosion due to lake drainage through ice wedges. The volumetric heat capacity of the ground was calculated as the sum of the volumetric heat capacities of the three phases multiplied by their volumetric fractions. The thermal conductivity of the permafrost and slurry was calculated by the geometric mean model. The apparent heat capacity method was applied to deal with latent heat generation. The initial permafrost temperature was -12C for the cold permafrost case and -2.5C for the warm permafrost case. The results suggest that thermo-erosion of ice wedges creates underground water flow paths that remain unfrozen for significant period of time, particularly in warm permafrost conditions. Tunnels entirely filled with water took about 1.5 to 2 times longer to freeze back. The presence of air pockets in the tunnel significantly delayed the freeze back time. In the cold permafrost cases, the tunnels froze back in about 3 to 6 months whereas they required between 8 months to about 3 years to freeze back in the warm permafrost cases.

Kim, K.; Fortier, D.

2008-12-01

405

Computational analysis of fluid dynamics in pharmaceutical freeze-drying.  

PubMed

Analysis of water vapor flows encountered in pharmaceutical freeze-drying systems, laboratory-scale and industrial, is presented based on the computational fluid dynamics (CFD) techniques. The flows under continuum gas conditions are analyzed using the solution of the Navier-Stokes equations whereas the rarefied flow solutions are obtained by the direct simulation Monte Carlo (DSMC) method for the Boltzmann equation. Examples of application of CFD techniques to laboratory-scale and industrial scale freeze-drying processes are discussed with an emphasis on the utility of CFD for improvement of design and experimental characterization of pharmaceutical freeze-drying hardware and processes. The current article presents a two-dimensional simulation of a laboratory scale dryer with an emphasis on the importance of drying conditions and hardware design on process control and a three-dimensional simulation of an industrial dryer containing a comparison of the obtained results with analytical viscous flow solutions. It was found that the presence of clean in place (CIP)/sterilize in place (SIP) piping in the duct lead to significant changes in the flow field characteristics. The simulation results for vapor flow rates in an industrial freeze-dryer have been compared to tunable diode laser absorption spectroscopy (TDLAS) and gravimetric measurements. PMID:19569225

Alexeenko, Alina A; Ganguly, Arnab; Nail, Steven L

2009-09-01

406

De-aggregated reliability analysis of freezing rain hazard  

Microsoft Academic Search

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

Reza Erfani

2010-01-01

407

Computer simulations on multiprobe freezing of irregularly shaped tumors  

Microsoft Academic Search

Cryosurgery is particularly suitable for the treatment of unresectable liver tumors. However, a major bottleneck is encountered during the treatment of large-sized irregularly shaped tumors. Large and complex liver tumors have varying degree of shape irregularity. Adopting a multiprobe freezing model, simulations for an irregularly shaped liver tumor were conducted. The model, validated with both in-vitro data from an experimental

K. J. Chua

2011-01-01

408

Anticipating InfertilityEgg Freezing, Genetic Preservation, and Risk  

Microsoft Academic Search

This article discusses the new reproductive technology of egg freezing in the context of existing literature on gender, medicalization, and infertility. What is unique about this technology is its use by women who are not currently infertile but who may anticipate a future diagnosis. This circumstance gives rise to a new ontological category of “anticipated infertility.” The author draws on

Lauren Jade Martin

2010-01-01

409

47 CFR 64.1190 - Preferred carrier freezes.  

Code of Federal Regulations, 2013 CFR

...TO COMMON CARRIERS Changes in Preferred Telecommunications...freeze) prevents a change in a subscriber's...be unable to make a change in carrier selection...explanation of any charges associated with the preferred carrier...response unit, or similar mechanism that records the...

2013-10-01

410

Freezing-induced ordering of block copolymer micelles.  

PubMed

We demonstrate here the ordering of block copolymer micelles by ice templating, below 0 °C. We used this for the preparation of silica monoliths that present an ice-templated macroporosity, combined with a 2D hexagonal mesostructure templated by the addition of P123. We propose a mechanism triggered by the progressive freezing-induced concentration. PMID:25198174

Dhainaut, Jérémy; Piana, Giulia; Deville, Sylvain; Guizard, Christian; Klotz, Michaela

2014-10-25

411

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

E-print Network

' of Water in Proton Conductors ? Freezing (bulk), bound freezable, bound non freezable water states claimedControlling Phenomena High ( > 0.04 S/cm)Low ( Proton Conductivity Grotthuss (hopping) Vehicular (water for conduction at very low water contents associated with tight binding of water and protons

412

Heat transfer with freezing in a scraped surface heat exchanger  

Microsoft Academic Search

An experimental study was carried out on a scraped surface heat exchanger used for freezing of water–ethanol mixture and aqueous sucrose solution. The influence of various parameters on heat transfer intensity was established: product type and composition, flow rate, blade rotation speed, distance between blades and wall. During starting (transient period) the solution is first supercooled, then ice crystals appear

Mohamed Ben Lakhdar; Rosalia Cerecero; Graciela Alvarez; Jacques Guilpart; Denis Flick; André Lallemand

2005-01-01

413

Freeze-cast hydroxyapatite scaffolds for bone tissue engineering applications.  

PubMed

Freeze casting of aqueous suspensions was investigated as a method for preparing porous hydroxyapatite (HA) scaffolds for eventual application to bone tissue engineering. Suspensions of HA particles (10-20 volume percent) were frozen unidirectionally in a cylindrical mold placed on a cold steel substrate (-20 degrees C). After sublimation of the ice, sintering for 3 h at 1350 degrees C produced constructs with dense HA lamellae, with porosity of approximately 50%, and inter-lamellar pore widths of 5-30 microm. These constructs had compressive strengths of 12 +/- 1 MPa and 5 +/- 1 MPa in the directions parallel and perpendicular to the freezing direction, respectively. Manipulation of the microstructure was achieved by modifying the solvent composition of the suspension used for freeze casting. The use of water-glycerol mixtures (20 wt% glycerol) resulted in the production of constructs with finer pores (1-10 microm) and a larger number of dendritic growth connecting the HA lamellae, and higher strength. On the other hand, the use of water-dioxane mixtures (60 wt% dioxane) resulted in a cellular-type microstructure with larger pores (90-110 microm). The mechanical response showed high strain tolerance (5-10% at the maximum stress), high strain for failure (>20%) and sensitivity to the loading rate. The favorable mechanical behavior of the porous constructs, coupled with the ability to modify their microstructure, indicates the potential of the present freeze casting route for the production of porous scaffolds for bone tissue engineering. PMID:18458369

Fu, Qiang; Rahaman, Mohamed N; Dogan, Fatih; Bal, B Sonny

2008-06-01

414

The path from chemical to thermal freeze-out  

E-print Network

The evolution of a hadronic system after its chemical decomposition is described through a model that conserves the hadronic multiplicities to their values at chemical freeze-out. The state of the system is found as function of temperature and the corresponding baryon density is evaluated. The baryon density at thermal decoupling is also computed.

Kapoyannis, A S

2001-01-01

415

Human Platelets Loaded with Trehalose Survive Freeze-Drying  

Microsoft Academic Search

Human blood platelets are stored in blood banks for 5 days, after which they are discarded, by federal regulation. This short lifetime has led to a chronic shortage of platelets, a problem that is particularly acute in immunosuppressed patients, such as those with AIDS. We report here that platelets can be preserved by freeze-drying them with trehalose, a sugar found

Willem F. Wolkers; Naomi J. Walker; Fern Tablin; John H. Crowe

2001-01-01

416

Structure related changes during moistening of freeze dried apple tissue  

Microsoft Academic Search

The knowledge and interpretation of the relationships between structure and properties in foods is of considerable interest. In the present work, freeze dried apple tissue was assumed as a basic plant food structure and some chemical and physical changes associated with a gradual moistening were monitored in order to (a) observe their reciprocal interactions, (b) clarify whether they could be

E. Venir; M. Munari; A. Tonizzo; E. Maltini

2007-01-01

417

Measurement of Freezing Point Depression of Selected Food Solutions  

NASA Astrophysics Data System (ADS)

Freezing point depression of selected food solutions were measured at various concentrations in order to reveal the characteristics of solid-liquid phase equilibrium. The measurement were carried out on a hand made apparatus that was calibrated before the measurement by some of selected reagents (acid and sugar) with known thermal properties. The results revealed that the freezing point depression of selected food solutions deviated from the behavior of the ideal solution with increasing solute concentration, so the water activity for non-ideal solution were introduced to the freezing point depression equation. Further, assuming that the heat of fusion was a equation of temperature, thus the following new equation was led, ln {(1-Xs)/(l-Xs+?·Xs + ?·Xs2)} = A(1/To - 1/Tf) - Bln(To/Tf) The goodness of fit of the equation showed the best results. Futhermore, by using the parameters a formula of freezing ratio and the relative water activities, which showed deviation from the ideal solution, were derived.

Murata, Satoshi; Tanaka, Fumihiko; Matsuoka, Takahisa

418

Analysis of Food Freezing by Slot Jet Impingement  

Microsoft Academic Search

In this study, numerical simulation using Computational Fluid Dynamics (CFD) was conducted to predict the effect of various parameters on freezing time of slab shaped food by a slot air impingement. Continuity, momentum and energy equations were solved using Fluent 6.0 a commercial Computational Fluid Dynamics (CFD) solver. In order to model the turbulent air flow, the standard Reynolds Stress

M. Jafari; P. Alavi

2008-01-01

419

Bundle design protects air-cooled condensers from freezing  

Microsoft Academic Search

Air-cooled steam condensers used in turbine exhaust systems are subject to costly freeze damage to finned tubes during the winter. These condensers also are vulnerable to loss of thermal performance in summer. Loss of thermal performance is not due to an increased ambient air temperature; it comes from a degraded heat transfer capability resulting from gas-blanketed tubes. The author discusses

Larinoff

1990-01-01

420

FREEZING WATER CLEANING A POSSIBLE IMPROVEMENT IN SRF CAVITY RINSING*  

E-print Network

method of high pressure rinsing - freezing water cleaning - consists in preliminary cooling down the cavity to be rinsed. Expansion of water in the phase transition to ice can lift particles from particles and finally the rinsing turns into regular high pressure rinsing. INTRODUCTION High-pressure water

421

References on Compression of Freeze-Dried Foods.  

National Technical Information Service (NTIS)

This report attempts to assemble the references to the R&D work conducted in the area of freeze-dried and compressed foods. Sixty-eight technical reports with authors summaries, 69 journal articles and papers, 27 patents, and 17 specifications and Limited...

S. E. Wallen, J. M. Tuomy, G. C. Walker

1978-01-01

422

A novel approach to sterile pharmaceutical freeze-drying.  

PubMed

A novel approach has been developed that enables sterile pharmaceutical products to be freeze-dried in the open laboratory without specialist facilities. The product is filled into vials, semi-stoppered and sealed inside one, followed by a second, sterilization pouch under class 100 conditions. The product is then freeze-dried in the laboratory where the vials are shelf-stoppered before being returned to class 100, unwrapped and crimped. The sterilization pouches increased the resistance to water vapor movement during sublimation, thereby increasing the sublimation time and product temperature. Ovine immunoglobulins were double wrapped and lyophilized (as above) adjusting the primary drying time and shelf temperature for increased product temperature and, therefore, prevention of collapse. Ovine immunoglobulin G formulations freeze-dried to ? 1.1% residual moisture with no effect on protein aggregation or biological activity. The process was simulated with tryptone soya broth and no growth of contaminating microbial cells was observed after incubation at 35 °C for 2 weeks. Although increasing lyophilization time, this approach offers significant plant and validation cost savings when sterile freeze-drying small numbers of vials thereby making the manufacture of treatments for neglected and orphan diseases more viable economically. PMID:23323966

Cherry, Christopher Lee Albert; Millward, Huw; Cooper, Rose; Landon, John

2014-02-01

423

Subliming Ice Surfaces: Freeze-Etch Electron Microscopy  

Microsoft Academic Search

Vacuum sublimation of oriented single crystals of ice at temperatures from -110 to -60 degrees Celsius was studied by electron microscopy with the freeze-etch technique. Sublimation etches the ice surface to produce pits and asperities and above -85 degrees Celsius causes extreme surface roughening. The etch pits are ascribed to surface dislocations, and the extreme roughening is ascribed to the

J. Gordon Davy; Daniel Branton

1970-01-01

424

The Freezing Point Depression Law in Physical Chemistry.  

ERIC Educational Resources Information Center

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

Franzen, Hugo F.

1988-01-01

425

A sledge microtome for high resolution subsampling of freeze cores  

E-print Network

interface, which is A. L. Macumber (&) Á R. T. Patterson Á L. A. Neville Department of Earth SciencesNOTES A sledge microtome for high resolution subsampling of freeze cores Andrew L. Macumber · R. Timothy Patterson · Lisa A. Neville · Hendrik Falck Received: 6 August 2010 / Accepted: 2 December 2010

Patterson, Timothy

426

Freezing, fragmentation, and charge separation in sonic sprayed water droplets  

NASA Astrophysics Data System (ADS)

Water droplets are generated by sonic spray, transferred into vacuum through a capillary interface, and then passed through two image charge detectors separated by a drift region. The image charge detectors measure the charge and velocity of each droplet. For around 1% of the droplets, the charge changes significantly between the detectors. In some cases it increases, in others it decreases, and for some droplets the charge changes polarity. We attribute the charge changing behavior to fragmentation caused by freezing. Simulations indicate that the time required for a droplet to cool and freeze in vacuum depends on its size, and that droplets with radii of 1-2 [mu]m have the right size to freeze between the two detectors. These sizes correspond to the smaller end of the distribution present in the experiment. When the charge on a droplet increases or changes polarity, fragmentation must be accompanied by charge separation where fragments carry away opposite charges. In some cases, two fission fragments were observed in the second charge detector. We show examples where the droplet breaks apart to give fragments of the same charge and opposite charges. The fragmentation and charge changing behavior found here is consistent with what has been found in the freezing of larger suspended and supported droplets.

Zilch, Lloyd W.; Maze, Joshua T.; Smith, John W.; Jarrold, Martin F.

2009-06-01

427

Protein spheres prepared by drop jet freeze drying.  

PubMed

In spray freeze drying (SFD) solutions are frozen by spraying into a very cold environment and subsequently dried by sublimation. In contrast to conventional freeze drying, spray freeze drying has the possibility to produce flowable lyophilizates which offers a variety of new pharmaceutical applications. Here, a drop jet nozzle is proposed as liquid dispenser that is able to produce droplets with a very narrow size distribution compared to standard methods. The drop jet nozzle is mounted in a spray tower designed to prevent direct contact of the product with the freezing medium. Various formulations have been tested containing lysozyme as model protein and stabilizers such as bovine serum albumin, polyvinylpyrrolidone or dextran in various concentrations and mannitol. Excellent free flowing and nearly monodispersed, porous particles are produced where particle properties can be controlled by formulation and process conditions. The particle diameter varied between 231 ± 3 ?m and 310 ± 10 ?m depending on the formulation composition. The lysozyme activity was >94 ± 5% for all formulations exhibiting a full preservation of enzyme activity. This new method is very promising for the production of nearly monodisperse particulate lyophilizates in various therapeutic applications. PMID:22960322

Eggerstedt, Sören N; Dietzel, Mathias; Sommerfeld, Martin; Süverkrüp, Richard; Lamprecht, Alf

2012-11-15

428

Cryopreservation of Spermatozoa from Freeze-Tolerant and -Intolerant Anurans  

E-print Network

bovine serum or glutathione), and combinations of these cryoprotectants and supplements. Me2SO and fetal bovine serum were the most effective cryoprotectant and supplement, respectively, in reducing sperm lysis bovine serum. Thus, this combination was used to cryopreserve spermatozoa from the freeze

Lee Jr., Richard E.

429

Connectivity of the pedunculopontine nucleus in parkinsonian freezing of gait  

E-print Network

(FOG) patients, compared with non-FOG PD and healthy controls using diffusion tensor imaging techniques showed connectivity with the cerebellum in controls and non-FOG PD. FOG patients showed absence the connectivity of the PPN freezing of gait (FOG) patients, compared with non-FOG PD and healthy controls. Methods

Hansen, Peter

430

Freeze and restart of the DWPF Scale Glass Melter  

Microsoft Academic Search

After over two years of successful demonstration of many design and operating concepts of the DWPF Melter system, the last Scale Glass Melter campaign was initiated on 6\\/9\\/88 and consisted of two parts; (1) simulation of noble metal buildup and (2) freeze and subsequent restart of the melter under various scenarios. The objectives were to simulate a prolonged power loss

1989-01-01

431

Io's Atmospheric Freeze-out Dynamics in the Presence of a Non-condensable Species  

SciTech Connect

One dimensional direct simulation Monte Carlo (DSMC) simulations are used to examine the effect of a trace non-condensable species on the freeze-out dynamics of Io's sulfur dioxide sublimation atmosphere during eclipse and egress. Due to finite ballistic times, essentially no collapse occurs during the first 10 minutes of eclipse at altitudes above {approx}100 km, and hence immediately after ingress auroral emission morphology above 100 km should resemble that of the immediate pre-eclipse state. In the absence of a non-condensable species the sublimation SO2 atmosphere will freeze-out (collapse) during eclipse as the surface temperature drops. However, rapid collapse is prevented by the presence of even a small amount of a perfect non-condensable species due to the formation of a static diffusion layer several mean free paths thick near the surface. The higher the non-condensable mole fraction, the longer the collapse time. The effect of a weakly condensable gas species (non-zero sticking/reaction coefficient) was examined since real gas species may not be perfectly non-condensable at realistic surface temperatures. It is found that even a small sticking coefficient dramatically reduces the effect of the diffusion layer on the dynamics. If the sticking coefficient of the non-condensable exceeds {approx}0.25 the collapse dynamics are effectively the same as if there was no non-condensable present. This sensitivity results because the loss of non-condensable to the surface reduces the effective diffusion layer size and the formation of an effective diffusion layer requires that the layer be stationary which does not occur if the surface is a sink. As the surface temperature increases during egress from eclipse the sublimating SO2 gas pushes the non-condensable diffusion layer up to higher altitudes once it becomes dense enough to be collisional. This vertical species stratification should alter the auroral emissions after egress.

Moore, Chris H.; Goldstein, David B.; Varghese, Philip L.; Trafton, Laurence M.; Stewart, Benedicte D.; Walker, Andrew C. [University of Texas at Austin, Department of Aerospace Engineering, 210 E. 24th St. W.R. Woolrich Laboratories, 1 University Station C0600 Austin, Tx. 78712 (United States)

2008-12-31

432

9 CFR 354.244 - Temperatures and cooling and freezing procedures.  

Code of Federal Regulations, 2010 CFR

...Temperatures and cooling and freezing procedures. 354.244 Section 354.244 Animals and Animal Products FOOD SAFETY AND...and Precautions Against Contamination of Products § 354.244 Temperatures and cooling and freezing...

2010-01-01

433

Inactivation of Kudoa septempunctata in Olive Flounder Meat by Liquid Freezing.  

PubMed

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

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

2014-01-01

434

Ground-based measurements of immersion freezing in the eastern Mediterranean  

E-print Network

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

Levin, Z.