Note: This page contains sample records for the topic vertical gradient freeze from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Application of an axial magnetic field to vertical gradient freeze GaAs single crystal growth  

Microsoft Academic Search

We have developed a growth technique for vertical gradient freeze GaAs single crystals, in which an axial magnetic field can be applied up to 1500 G. From calculations, the application of an axial magnetic field of 1000 G was found to be enough for suppressing the Marangoni flow and promote the stability of the thermal environment throughout the whole melt

Young Ju Park; Suk-Ki Min; Seung-Ho Hahn; Jong-Kyu Yoon

1995-01-01

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

Microsoft Academic Search

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

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

2000-01-01

4

Vertical gradient freeze growth of ZnGeP2 crystals for nonlinear optical applications  

NASA Astrophysics Data System (ADS)

ZnGeP2 crystal is the leader among nonlinear crystals for middle IR. Large sized ?20×90 mm3 ZGP single crystals have been grown successfully by the vertical gradient freeze technique. The crystallinity and optical properties of as-grown crystals were measured by XRD and transmission spectra respectively. The thermal conductivity was tested using PPMS. The absorption coefficient can be reduced to 0.08 cm-1 at 2 ?m by post-annealing. The fabricated devices were also utilized to demonstrate SHG and OPO experiments for nonlinear optical applications.

Wu, Haixin; Wang, Zhenyou; Ni, Youbao; Mao, Mingsheng; Huang, Changbao; Cheng, Xudong

2012-08-01

5

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

6

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

7

Electron backscatter diffraction of a Ge growth tip from a vertical gradient freeze furnace  

NASA Astrophysics Data System (ADS)

The growth-tip region of a high-purity 4.2-cm-diameter Ge boule grown using low-pressure Bridgman methods in a vertical gradient freeze furnace was sectioned and polished in preparation for scanning electron microscopy and was characterized using electron backscatter diffraction (EBSD). The boule had a characteristic conical tip region with cone angle of 40° of a right circular cylinder from which a section was taken along the boule longitudinal centerline with an approximate surface area of 4 cm 2. The majority of this surface area was characterized using EBSD and an image collage was assembled for the tip region. The grain structure, grain boundary orientation, twin structure, and overall crystal growth direction were determined. A crystal growth direction of approximately <1 1 2> was observed, which was also identified as the growth direction of several prominent twins observed in the tip region. The grain structure of the tip region appeared to be controlled by the sidewall nucleation of a stray grain that competed for dominance during growth. Grain boundaries and triple grain junctions were identified as low-energy coincident-site-lattice (CSL) boundaries and junctions of the ?3 and ?9 types.

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

2008-12-01

8

Electron backscatter diffraction analysis of a CZT growth tip from a vertical gradient freeze furnace  

NASA Astrophysics Data System (ADS)

Electron 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-cm 2 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 <1 1 0> and <1 1 2> directions. In some regions, the (0 0 1) poles of the CZT matrix aligned with the growth direction, while twins aligned such that (1 1 1) and (1 1 2) poles aligned with the growth direction. In some other areas, (1 1 2) or (0 1 1) poles of the CZT matrix aligned with the growth direction. New relationships between the CZT matrix and large Te polycrystalline particles were revealed: {1 1 2¯} CZT??{1 1¯ 0 0} Te and {0 0 1} CZT??{0 1¯ 1¯ 1} Te.

Sundaram, S. K.; Henager, C. H.; Edwards, D. J.; Schemer-Kohrn, A. L.; Bliss, M.; Riley, B. R.

2011-08-01

9

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

10

Single phase polycrystalline Cu2ZnSnS4 grown by vertical gradient freeze technique  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

11

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

12

Investigation on the growth and characterization of 4-aminobenzophenone single crystal by the vertical dynamic gradient freeze technique  

NASA Astrophysics Data System (ADS)

Growth of bulk single crystal of 4-Aminobenzophenone (4-ABP) from the vertical dynamic gradient freeze (VDGF) setup designed with eight zone furnace was investigated. The experimental parameters for the growth of 4-ABP single crystal with respect to the design of VDGF setup are discussed. The eight zones were used to generate multiple temperature gradients over the furnace, and video imaging system helped to capture the real time growth and solid-liquid interface. 4-ABP single crystal with the size of 18 mm diameter and 40 mm length was grown from this investigation. Structural and optical quality of grown crystal was examined by high resolution X-ray diffraction and UV-visible spectral analysis, respectively and the blue emission was also confirmed from the photoluminescence spectrum. Microhardness number of the crystal was estimated at different loads using Vicker's microhardness tester. The size and quality of single crystal grown from the present investigation are compared with the vertical Bridgman grown 4-ABP.

Prabhakaran, SP.; Ramesh Babu, R.; Sukumar, M.; Bhagavannarayana, G.; Ramamurthi, K.

2014-03-01

13

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

14

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

15

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

16

Critique of the vertical gradient of gravity  

NASA Technical Reports Server (NTRS)

Growing interest in high precision studies of the Earth's gravitational field warrant a critical review of precision requirements to yield useful results. Several problems are now under consideration. All of these problems involve, more or less, the precise value of the vertical gradients of gravity. The principle conclusion from this review is that the essential absence of Free Air Vertical Gravity Gradient control and actual values of gravimeter calibrations require serious attention. Large errors in high topography on official published gravity maps also cannot be ignored.

Hammer, Sigmund

1989-01-01

17

Diffusion weighted vertical gradient and spin echo.  

PubMed

In this work, diffusion weighting and parallel imaging is combined with a vertical gradient and spin echo data readout. This sequence was implemented and evaluated on healthy volunteers using a 1.5 and a 3 T whole-body MR system. As the vertical gradient and spin echo trajectory enables a higher k-space velocity in the phase-encoding direction than single-shot echo planar imaging, the geometrical distortions are reduced. When combined with parallel imaging such as generalized autocalibrating partially parallel acquisition, the geometric distortions are reduced even further, while also keeping the minimum echo time reasonably low. However, this combination of a diffusion preparation and multiple refocusing pulses during the vertical gradient and spin echo readout, generally violates the Carr-Purcell-Meiboom-Gill condition, which leads to interferences between echo pathways. To suppress the stimulated echo pathway, refocusing pulses with a sharper slice profiles and an odd/even crusher variation scheme were implemented and evaluated. Being a single-shot acquisition technique, the reconstructed images are robust to rigid-body head motion and spatially varying brain motion, both of which are common sources of artifacts in diffusion MRI. PMID:23008151

Engström, Mathias; Bammer, Roland; Skare, Stefan

2012-12-01

18

Calculation of vertical temperature gradients in heated rooms.  

National Technical Information Service (NTIS)

This paper deals with a simple model which predicts the vertical temperature gradient in a heated room. The gradient is calculated from a dimensionless temperature profile which is determined by two room air temperatures only, the mean temperature in the ...

H. Overby M. Steen-Thoede

1990-01-01

19

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

20

Vertical CO2 gradient as an indicator of stratospheric circulation  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

21

Full gravity gradient tensors from vertical gravity by cosine transform  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

22

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

23

Vertikale temperaturgradienter i rum med konvektive stroemninger. (Vertical temperature gradients in rooms with convective air flow).  

National Technical Information Service (NTIS)

This project deals with measuring and calculation of vertical temperature gradients in radiator heated rooms and measuring of similar vertical gradients in rooms ventilated by displacement ventilation. The project focuses on experimental and theoretical e...

H. Overby

1993-01-01

24

Anomalous segregation during electrodynamic gradient freeze growth of cadmium zinc telluride  

NASA Astrophysics Data System (ADS)

A transient, coupled model has been developed to analyze the segregation of zinc in cadmium zinc telluride (CZT) grown in an electrodynamic gradient freeze (EDG) furnace. The coupled model consists of a local model that solves for time-dependent melt flow, heat transfer, melt-crystal interface position, and zinc distribution in both melt and solid phases and a quasi-steady-state global model that features realistic furnace heat transfer. After verification and validation tests, the model is applied to predict composition patterns in a large-scale CZT EDG growth system previously analyzed by Gasperino et al. [On crucible effects during the growth of cadmium zinc telluride in an electrodynamic gradient freeze furnace, J. Crys. Growth 311 (2009) 2327-2335]. Surprisingly, anomalous zinc segregation is predicted, featuring a non-monotonic axial concentration profile and several local minima and maxima across the boule. A mechanistic explanation is put forth based on the cumulative effect of changes in multi-cellular melt flow structures, a particularly susceptible occurrence for CZT systems. Additional effects of furnace translation rate and solid state diffusion are probed.

Zhang, Nan; Yeckel, Andrew; Burger, Arnold; Cui, Yunlong; Lynn, Kelvin G.; Derby, Jeffrey J.

2011-06-01

25

Freezing tolerance in grasses along an altitudinal gradient in the Venezuelan Andes.  

PubMed

The tropical high Andes experience greater daily temperature oscillations compared to seasonal ones as well as a high frequency of night frost occurrence year round. Survival of organisms, under such environmental conditions, has been determined by selective forces which have evolved into adaptations including avoidance or tolerance to freezing. These adaptations have been studied in different species of trees, shrubs and perennial herbs in páramo ecosystems, while they have not been considered in grasses, an important family of the páramo. In order to understand survival of Poaceae, resistance mechanisms were determined. The study was performed along an altitudinal gradient (2,500-4,200 m a.s.l.) in the páramo. Supercooling capacity and frost injury temperature were determined in nine species in order to establish cold resistance mechanisms. Grasses registered a very low supercooling capacity along the altitudinal gradient, with ice formation between -6 and -3 degrees C. On the other hand, frost injury temperature oscillated between -18 and -7 degrees C. Our results suggest that grasses exhibit freezing tolerance as their main cold resistance mechanism. Since grasses grow at ground level, where greatest heat loss takes place, tolerance may be related to this life form as reported for other small life forms. PMID:17024382

Márquez, Edjuly J; Rada, Fermín; Fariñas, Mario R

2006-12-01

26

On the Vertical Stability of a Rotating Fluid Subject to a Horizontal Temperature Gradient  

Microsoft Academic Search

The vertical potential temperature gradient in the atmosphere is the result of heat transport by radiation and by small- and large-scale motions, with complications due to latent heat release and absorption in condensation and cloud. An idealized model, characterized by the absence of latent heat effects and of a vertical component to the gradient of the impressed temperature field, is

R. Hide

1967-01-01

27

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

28

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

PubMed

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

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

2013-01-01

29

Measurement and calculation of vertical temperature gradients in rooms with convective flows.  

National Technical Information Service (NTIS)

The paper deals with experimental and theoretical examinations of the vertical temperature gradient in rooms with convective flows under transient conditions. The measurements are carried out in a laboratory test room of three different sizes. A small roo...

H. Overby

1994-01-01

30

Determination of the Figure of the Earth from the Anomalies of the Vertical Gravity Gradient.  

National Technical Information Service (NTIS)

A solution of the problem concerning the determination of the figure of the earth's topographic surface from the anomalies of the vertical gravity gradient was first presented in the Interdepartmental Republican Scientific Symposium 'Geodesy, Cartography,...

I. F. Monin

1967-01-01

31

Vertically transmitted symbiont reduces host fitness along temperature gradient.  

PubMed

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

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

2014-04-01

32

Three-dimensional analysis of heat flow, segregation, and interface shape of gradient-freeze crystal growth in a centrifuge  

Microsoft Academic Search

Three-dimensional (3D) heat flow, dopant segregation, and interface shape during crystal growth by a gradient freeze technique in a centrifuge are analyzed by a finite volume method. The basic flow patterns for a fixed geometry (with a concave interface) at different configurations agree well with the previous report (Friedrich et al., J. Crystal Growth 167 (1996) 45). However, the self-consistent

C. W. Lan; C. Y. Tu

2001-01-01

33

The complete gravity gradient tensor derived from the vertical component of gravity: a Fourier transform technique  

NASA Astrophysics Data System (ADS)

A technique has been to developed to determine the complete gravity gradient tensor from pre-existing vertical gravity data using the fast Fourier Transform (FFT). Since direct measurement of the entire gravity gradient tensor is generally unavailable, our technique provides an alternative determination of the gravity gradient tensor components. Traditionally, derivatives of vertical gravity ( gz,x, gz,y, and gz,z) have been the only gravity gradient tensor components that have been computed directly. Gravity gradient tensor components are computed for four different, three-dimensional (3-D), idealized horst-and-graben models, with varying depths to the horst. Comparing the FFT results with calculated gradient components from the 3-D models shows that the RMS error for each component, between the two results, is at most ˜3.3 Eötvos Units. In addition, measured gravity gradient components from an airborne survey over the Wichita Uplift and Anadarko Basin region of southwest Oklahoma compare favorably with the FFT-derived results using available vertical gravity data. No error analysis was attempted between the two results due to a low signal-to-noise ratio in the measured data. Our technique offers a novel way to transform and visualize the available data, and it also offers an inexpensive and previously unavailable subsurface mapping capability.

Mickus, Kevin L.; Hinojosa, Juan Homero

2001-03-01

34

Bulk Crystal Growth of Piezoelectric PMN-PT Crystals Using Gradient Freeze Technique for Improved SHM Sensors  

NASA Technical Reports Server (NTRS)

There has been a growing interest in recent years in lead based perovskite ferroelectric and relaxor ferroelectric solid solutions because of their excellent dielectric, piezoelectric and electrostrictive properties that make them very attractive for various sensing, actuating and structural health monitoring (SHM) applications. We are interested in the development of highly sensitive and efficient PMN-PT sensors based on large single crystals for the structural health monitoring of composite materials that may be used in future spacecrafts. Highly sensitive sensors are needed for detection of defects in these materials because they often tend to fail by distributed and interacting damage modes and much of the damage occurs beneath the top surface of the laminate and not detectable by visual inspection. Research is being carried out for various combinations of solid solutions for PMN-PT piezoelectric materials and bigger size crystals are being sought for improved sensor applications. Single crystals of this material are of interest for sensor applications because of their high piezoelectric coefficient (d33 greater than 1700 pC/N) and electromechanical coefficients (k33 greater than 0.90). For comparison, the commonly used piezoelectric ceramic lead zirconate titanate (PZT) has a d33 of about 600 pC/N and electromechanical coefficients k33 of about 0.75. At the present time, these piezoelectric relaxor crystals are grown by high temperature flux growth method and the size of these crystals are rather small (3x4x5 mm(exp 3). In the present paper, we have attempted to grow bulk single crystals of PMN-PT in a 2 inch diameter platinum crucible and successfully grown a large size crystal of 67%PMN-33%PT using the vertical gradient freeze technique with no flux. Piezoelectric properties of the grown crystals are investigated. PMN-PT plates show excellent piezoelectric properties. Samples were poled under an applied electric field of 5 kV/cm. Dielectric properties at a frequency of 1 kHz are examined. The grown PMN-PT crystals show typical relaxor dielectric properties. Additionally, the thermal properties of the sample are tested. The results are in good agreement with those found in the literature and some are reported for the first time.

Aggarwal, Mohan D.; Kochary, F.; Penn, Benjamin G.; Miller, Jim

2007-01-01

35

Overburden Pressure as a Cause of Vertical Velocity Gradient  

NASA Astrophysics Data System (ADS)

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

Korneev, V. A.

2012-12-01

36

Calculations of the anomalies of the vertical temperature gradient using the horizontal temperature distribution  

Microsoft Academic Search

This paper examines the determination of heat flow at the earth surface in relation to geothermal studies. Anomalies of the vertical temperature gradient can be calculated with the Hilbert transformation of surface temperature measured along a profile. The procedure is carried out with temperature values over the Supetau anticline at the Fergana basin.

R. Roesler; H. Lindner; C. Oelsner

1980-01-01

37

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

Microsoft Academic Search

It is well known that vertical head gradients exist in natural aquifer systems, and borehole flowmeter data have shown that such gradients commonly set up spontaneous vertical flows in monitoring wells, often called ambient flows. What has not been fully appreciated until recently is the serious detrimental effects such flows can have on solute concentration and hydraulic head measurements in

Flach

2002-01-01

38

Detrimental effects of natural vertical head gradients on chemical and water level measurements in observation wells: identification and control  

Microsoft Academic Search

It is well known that vertical head gradients exist in natural aquifer systems, and borehole flowmeter data have shown that such gradients commonly set up spontaneous vertical flows in monitoring wells, often called ambient flows. What has not been fully appreciated until recently is the serious detrimental effects such flows can have on solute concentration [Ground Water 39 (2001) 853

Alper Elçi; Gregory P. Flach; Fred J. Molz

2003-01-01

39

HONO Vertical Gradients during the 2006 TRAMP and the 2009 SHARP experiments in Houston, TX  

NASA Astrophysics Data System (ADS)

Nitrous acid (HONO) plays a significant role in tropospheric photochemistry as a precursor of the hydroxyl radical (OH). Despite the importance of HONO photolysis for the OH budget in the early morning, HONO formation mechanisms are not yet fully understood. In addition, recent observations of higher than expected daytime HONO concentrations are currently unexplained. The vertical distribution of HONO in the morning and during the day can have a considerable impact on its importance for ozone formation in the boundary layer. The observation of vertical profiles is also important to allow a better understanding of HONO formation in the atmosphere. Consequently there is an urgent need to provide observations and detailed model calculations of vertical HONO profiles. During the 2009 SHARP experiment from April 15 to May 29, 2009 in Houston, TX, we performed measurements of HONO, NO2, O3 and other trace gases in three altitude intervals (30-70m, 70 - 130m, and 130 - 300m), using UCLA’s long path DOAS instrument. Vertical gradients of all atmospheric trace gases were frequently observed during stable nights. HONO established negative gradients, with higher concentrations near the ground, indicating that the source of HONO is at or near the ground. Daytime HONO gradients were also observed during some days. Here we compare our results with observations made at the same location in 2006 and with results from a 1-D chemical transport model to elucidate the mechanisms forming HONO in urban areas.

Wong, K.; Tsai, C.; Pikelnaya, O.; Stutz, J.; Fu, D.

2009-12-01

40

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

41

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

42

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

SciTech Connect

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

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

2005-01-01

43

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

44

Diversity and vertical distribution of magnetotactic bacteria along chemical gradients in freshwater microcosms.  

PubMed

The vertical distribution of magnetotactic bacteria along various physico-chemical gradients in freshwater microcosms was analyzed by a combined approach of viable cell counts, 16S rRNA gene analysis, microsensor profiling and biogeochemical methods. The occurrence of magnetotactic bacteria was restricted to a narrow sediment layer overlapping or closely below the maximum oxygen and nitrate penetration depth. Different species showed different preferences within vertical gradients, but the largest proportion (63-98%) of magnetotactic bacteria was detected within the suboxic zone. In one microcosm the community of magnetotactic bacteria was dominated by one species of a coccoid "Alphaproteobacterium", as detected by denaturing gradient gel electrophoresis in sediment horizons from 1 to 10 mm depth. Maximum numbers of magnetotactic bacteria were up to 1.5 x 10(7) cells/cm3, which corresponded to 1% of the total cell number in the upper sediment layer. The occurrence of magnetotactic bacteria coincided with the availability of significant amounts (6-60 microM) of soluble Fe(II), and in one sample with hydrogen sulfide (up to 40 microM). Although various trends were clearly observed, a strict correlation between the distribution of magnetotactic bacteria and individual geochemical parameters was absent. This is discussed in terms of metabolic adaptation of various strains of magnetotactic bacteria to stratified sediments and diversity of the magnetotactic bacterial communities. PMID:16329905

Flies, Christine B; Jonkers, Henk M; de Beer, Dirk; Bosselmann, Katja; Böttcher, Michael E; Schüler, Dirk

2005-04-01

45

The High Precision Calculation of Anomalous Vertical Gravity Gradients die Berechnung von Anomalen Vertikalen Schweregradienten Hoher Praezision.  

National Technical Information Service (NTIS)

Accurate methods for the calculation of anomalous vertical gravity gradients based on the Molodensky theory are presented. The general solution of the mathematical problem leads to a singular inhomogeneous second order integral equation that can be solved...

G. Hein

1977-01-01

46

A SPATIALLY RESOLVED VERTICAL TEMPERATURE GRADIENT IN THE HD 163296 DISK  

SciTech Connect

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

Rosenfeld, Katherine A.; Andrews, Sean M.; Wilner, David J.; Qi, Chunhua [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hughes, A. Meredith [Van Vleck Observatory, Astronomy Department, Wesleyan University, 96 Foss Hill Drive, Middletown, CT 06459 (United States)

2013-09-01

47

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

PubMed

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

Mandre, Malle

2009-12-01

48

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

49

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

50

Seismic ground motion amplification in a 3D sedimentary basin: the effect of the vertical velocity gradient  

NASA Astrophysics Data System (ADS)

Ground motion amplification in sedimentary basins has been observed in some moderate or large earthquakes, such as the 1994 Northridge and 1999 Chi-Chi event. Many numerical studies with simplified 2D models have shown significant effects of the vertical velocity gradient of sediment on basin amplification. However, we need to consider a more realistic 3D model and solve wave equations with 3D numerical methods in order to improve our understanding of basin amplification. In this study, we extend a 2D pseudospectral and finite difference hybrid method to a 3D case and investigate the effects of the vertical velocity gradient for a 3D basin model. Numerical simulations were performed for four basin models with increasing vertical velocity gradients on a PC cluster using 64 processors for 67 108 864 discretized grids. The results show that the vertical velocity gradient enhances basin amplification through strong secondary surface waves and basin trapped waves. The 3D geometry of the basin causes a wave-front focusing effect that contributes significantly to a localized strong amplification with the maximum peak ground velocity in the basin. The results of this study suggest that it is important to consider the detailed properties of sedimentary basins in seismic ground motion studies.

Qin, Yanfang; Wang, Yanbin; Takenaka, Hiroshi; Zhang, Xianbing

2012-12-01

51

Preparative and quantitative isolation of plasma lipoproteins: rapid, single discontinuous density gradient ultracentrifugation in a vertical rotor  

Microsoft Academic Search

A rapid method has been developed for separa- tion of the major plasma lipoproteins from up to 96 ml of plasma by a single ultracentrifugation step. This separa- tion was achieved by a discontinuous density gradient centrifugation between the density range of 1.006 and 1.30 g\\/ml in Sorvall vertical rotors. Each lipoprotein fraction was sharply banded with VLDL at the

Byung H. Chung; Thomas Wilkinson; Jack C. Geer; Jere P. Segrest

52

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

53

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

54

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

55

Vertical gradients in leaf trait diversity in a New Zealand forest  

Microsoft Academic Search

Leaves come in a remarkable diversity of sizes and shapes. However, spatial patterns in leaf trait diversity are rarely investigated\\u000a and poorly resolved. We used a hierarchical approach to evaluate vertical variability in leaf morphology (i.e., leaf trait\\u000a diversity) in 16 common tree and shrub species inhabiting a New Zealand forest. Height-related heterogeneity in leaf area,\\u000a specific leaf area, circularity

Sam Beaumont; K. C. Burns

2009-01-01

56

Depth inversion of a deep homogeneous layer using gravity and vertical gravity gradient disturbance  

NASA Astrophysics Data System (ADS)

In theory, the Moho is determined by the inversion of a homogeneous layer. Furthermore, in mathematical view, the purpose of this work is to find a solution of the Fredholm equation of first kind. In this research, referring the well known achievements by Moritz, Wang and Sjöberg and aiming to apply GOCE in the refining of crust-mantle boundary, we present general expressions of the depth inversion for a deep homogeneous layer using gravity and gravity gradient disturbance in the frequency and space domain. Finally, among others, we verity the formulae through a closed - loop simulation using the GOCO03S model.

Ye, Zhourun; Sneeuw, Nico; Tenzer, Robert; Liu, Lintao

2014-05-01

57

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

NASA Astrophysics Data System (ADS)

A relatively narrow vertical zone (5-6 m thick) of NO 3- containing groundwater was identified using multilevel sampling devices in a sand and gravel aquifer on Cape Cod, MA, USA. The aquifer has been chronically contaminated by surface disposal of treated sewage 0.3 km upgradient from the study area. The NO 3- zone was anoxic and contained high concentrations of N 2O (16.5 ?M), suggesting that it was a zone of active denitrification. Denitrifying activity was confirmed with direct measurement using acetylene block incubations with aquifer core material; the peak rate was 2.4 nmol N reduced (g sed) -1 day -1. Concentrations of dissolved inorganic carbon and N 2 were close to atmospheric equilibrium in uncontaminated groundwater, but were more than 2 times higher within the contaminant plume. Excess CO 2 and N 2 suggested in situ formation with a stoichiometry of C and N mineralized via denitrification of 0.8 (C/N). Denitrification within the aquifer resulted in an increase in the natural ?15N of NO 3- (from +13.6 to +42.0%.) and the N 2 produced, with an isotopic enrichment factor, ?, of -13.9%.. Vertical profiles of NH 4+ and ?15N of NH 4+ indicated that dissimilatory reduction of NO 3- to NH 4+ was also occurring but mass balance calculations indicated that denitrification was the predominant process. These results demonstrate that a combination approach using field mass balance, stable isotope analysis, and laboratory incubations yields useful insight as to the significance of denitrification in aquifer sediments and that closely spaced vertical sampling is necessary to adequately quantify the processes controlling C and N transport and transformation within these environments.

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

1991-07-01

58

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

PubMed Central

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

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

2011-01-01

59

Transient buoyancy-driven flow in a vertical cylindrical enclosure with wavy-sidewall due to thermal and concentration gradients  

NASA Astrophysics Data System (ADS)

An axisymmetric transient convection flow, due to thermal and concentration gradients within a vertical cylindrical enclosure with adiabatic wavy sidewall, was studied. The two important cases of enclosure heated from below and heated from the top were studied. An analytical coordinate transformation was used to change the computation domain into a square. The heat and mass transfer were analyzed using non-dimensional parameters which include the cavity aspect ratio, the dimensionless wavelength and amplitude of the wavy-wall, Rayleigh and Prandtl numbers and the buoyancy ratio. For all cases the upper surface is consider as the one with high concentration, while the others are impermeable. Numerical results using a streamfunction formulation were developed. Heatlines and mass lines were used to illustrate the transport phenomena. Average Nusselt and Sherwood numbers were evaluated while the convection patterns arise within the cavity. The wavy-wall was found to promote thermal stratification and low velocity multiple cell patterns for low buoyancy ratio.

Sanchez, Fausto; Martinez, Simon; Ramirez, Hugo; Medina, Abraham

2010-11-01

60

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

NASA Astrophysics Data System (ADS)

During summer 2009 an intensive field campaign (Biosphere Effects on AeRosols and Photochemistry EXperiment - BEARPEX) took place in Blodgett Forest, a Ponderosa pine forest in the Sierra Nevada Mountains of California. The campaign was aimed to understand the biosphere-atmosphere interactions during a period of intense photochemical activity, to elucidate the fate BVOC (Biogenic Volatile Organic Compounds) in the atmosphere, and explore the processes of secondary organic aerosol formation. In this study, a PTR-MS (Proton Transfer Reaction - Mass Spectrometry) was used to measure 19 compounds (masses) including methanol, isoprene + MBO (2-Methyl-3-butene-2-ol), monoterpenes, sesquiterpenes, and some oxygenated BVOCs at 5 heights of a vertical gradient from the forest floor to above the canopy. Fluxes of the 4 dominant BVOCs were measured above the canopy with the Eddy covariance technique. In parallel with BVOC measurements, ozone fluxes and gradients, and meteorological parameters (PAR, temperature, relative humidity, wind speed, and wind direction) were recorded in order to test the dependence of BVOC from meteorological conditions and to test the hypothesis that BVOC remove atmospheric ozone through gas-phase reactions. Data will be compared to previous from the same site collected at different periods of the year to explore the dynamics of BVOC concentration and oxidation products as a function of varying environmental conditions.

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

2009-12-01

61

The Gravitational Potential, Gravitational Acceleration, and Vertical Gravity Gradient of a Rising Thermal Mantle Plume: A Numerical Experiment  

NASA Astrophysics Data System (ADS)

Thermal convection in the mantles of the terrestrial planets is an important mode of heat transfer from the planet's interior. Gravitational instabilities originating at hot, thermal boundary layers at depth, either at the core-mantle boundary or at an interface between the upper mantle and lower mantle, are responsible for a type of convection that gives rise to thermal mantle plumes. Since the inferred horizontal dimensions of mantle plumes as a whole are small compared with their vertical dimensions, it is difficult to observe mantle plumes directly. To better understand the mantle plume's gravitational expression at the surface, the gravitational potential, gravitational acceleration, and vertical gravity gradient of a rising mantle plume are calculated in a series of numerical experiments. An axially symmetric mantle plume is modeled using a composite of spheres and/or disks of various depths, radii, thicknesses, and density contrasts. The density contrast used in the numerical experiments is due to the temperature difference between an isothermal plume and the local geotherm for plumes at depths greater than the depth of pressure-release melt, and is due to the melt density contrast elsewhere. The resulting gravitational quantities for the spheres are obtained with straight-forward, analytical expressions, but those for the disks are obtained by numerical integration. The results of the numerical experiments will be presented.

Hinojosa, Juan H.

2012-10-01

62

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

63

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

PubMed

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

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

2011-02-01

64

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

65

Marine induction studies based on measurements of vertical gradient of scalar magnetic field. A concept and 3-D model studies  

NASA Astrophysics Data System (ADS)

Most of marine EM studies are based on sea-bottom vector measurements which are logistically and instrumentally demanding and rather expensive. Recently Kuvshinov et al (2013) proposed and proved a low-cost and easy-to-deploy magnetic survey concept which exploits sea surface scalar measurements. The concept is based on responses that relate variations of the scalar magnetic field at offshore survey sites with variations of the horizontal magnetic field at onshore base site. These responses are a mixture of elements of tipper and horizontal magnetic tensor, and thus they can be used to probe the electrical conductivity of the Earth. In the present work we introduce alternative responses that relate variations of vertical gradient of the scalar magnetic field at survey sites with variations of the horizontal magnetic field at a base site. We show that these responses are a mixture of elements of inter-site magnetotelluric tensor, and thus they also can be exploited for EM sounding of the Earth. We discuss the results of 3-D model studies aimed to investigate the sensitivity of the newly introduced responses to hypothetic plume structure beneath Hawaii islands.

Kuvshinov, Alexey

2014-05-01

66

Comparison of model-derived and radar-observed freezing-level heights: Implications for vertical reflectivity profile-correction schemes  

NASA Astrophysics Data System (ADS)

In the current operational Met Office scheme for deriving rainfall rates from radar, the height of the enhanced radar return associated with melting snow, the bright band, is determined using the height of the 0 °C isotherm obtained from the Met Office Unified Mesoscale Model (UM) forecast. In this paper the potential errors of using model forecast heights as input to the bright-band correction scheme are investigated. The UM and European Centre for Medium-Range Weather Forecasts (ECMWF) model forecasts of wet-bulb 0 °C isotherm heights (WBZ) are compared with the height of the 'step' increase in reflectivity in the vertical profiles recorded by the vertically pointing 94 GHz Galileo cloud radar at Chilbolton. High-frequency radars do not measure an enhanced 'bright band' at the melting layer, rather a sudden increase of reflectivity as the ice particles become coated in water. This sudden step can be used to locate accurately the height of the WBZ. Results show that the UM predicts the WBZ height with a root-mean-square error of 147 m and a bias of 15 m. This is within the worst-case tolerance of 200 m of the operational bright-band correction scheme. Factors that may influence the accuracy are the presence of deep isothermal layers and timing errors concerning the passage of fronts, but these are found not to be serious. An investigation into the deterioration of the UM 36-hour forecast shows that half the error is introduced at the initialization time, highlighting the fact that further improvements can be achieved through a better definition of the initial state of the atmosphere. The ECMWF forecast is for a longer lead time, but comparison for the same lead-time errors as the UM shows that the performance of the two models is comparable. An alternative approach is to derive the bright-band height from volumetric radar scans at different elevations. This study suggests that, at least in the UK, operational model predictions of the freezing-level height are within the specified 200 m error, but that the use of volumetric scans, even under idealized conditions, cannot achieve this accuracy.

Mittermaier, Marion P.; Illingworth, Anthony J.

2003-01-01

67

Freezing Ice  

NSDL National Science Digital Library

The purpose of this assessment probe is to elicit students' ideas about freezing point. The probe is designed to find out whether students recognize that water freezes at the same time independent of the volume of water.

Eberle, Francis; Tugel, Joyce; Keeley, Page

2007-01-01

68

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

69

Fine-Scale Horizontal and Vertical Microdistribution Patterns of Testate Amoebae Along a Narrow Fen\\/Bog Gradient  

Microsoft Academic Search

The ecology of peatland testate amoebae is well studied along broad gradient from very wet (pool) to dry (hummock) micro-sites\\u000a where testate amoebae are often found to respond primarily to the depth to water table (DWT). Much less is known on their\\u000a responses to finer-scale gradients, and nothing is known of their possible response to phenolic compounds, which play a

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

2011-01-01

70

Freezing lake  

NSDL National Science Digital Library

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

Powell, Adam C., IV

2005-02-23

71

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

73

Formulation of a Lagrangian stochastic model of dispersion in the convective boundary layer with skewed turbulence conditions and vertical density gradient  

NASA Astrophysics Data System (ADS)

The vertical gradient of air density has been included in a skewed probability density function formulation for turbulence in the convective boundary layer and the related drift term for Lagrangian stochastic particle modelling has been obtained based on the well-mixed condition. The formulation has been extended to include unsteady turbulence statistics. Tests were carried out to validate the model including consistency between forward and backward simulations and preservation of well-mixed state with unsteady conditions. The stationary state CBL drift term with density correction was incorporated in the FLEXPART/FLEXPART-WRF Lagrangian models. Currently only the steady state horizontally homogeneous drift term were included. To avoid numerical instability, using the steady homogenous drift in the presence of non-stationary and horizontally non-homogeneous conditions, a re-initialization procedure for particle velocity was used. The criteria for re-initialization and resulting errors were assessed.

cassiani, massimo; stohl, andreas; brioude, jerome

2014-05-01

74

Freezing and Food Safety  

MedlinePLUS

... JSR 286) Actions ${title} Loading... Freezing and Food Safety What Can You Freeze? Is Frozen Food Safe? Does Freezing Destroy Bacteria & Parasites? Freshness & Quality Nutrient Retention Enzymes Packaging Freezer Burn Color Changes Freeze Rapidly Freezer - Refrigerator Temperatures Freezer Storage ...

75

Ultrathin (1 nm) vertically shadowed platinum-carbon replicas for imaging individual molecules in freeze-etched biological DNA and material science metal and plastic specimens.  

PubMed

Single molecule resolution in beam-sensitive, uncoated, noncrystalline materials has heretofore not been possible except in thin (less than or equal to 150 A) platinum-carbon (Pt-C) replicas, which are resistant to electron beam destruction. Previously, the granularity of metal film replicas limited their resolution to greater than or equal to 20 A. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low-angle 20 degrees rotary, 45 degrees unidirectional, and vertical 9.7 +/- 1 A Pt-C films deposited on mica under the same conditions were compared. Vertical replication had a 5 A granularity, the highest resolution, and evenly coated the whole surface. A 45 degrees replication had a 9.5 A granularity, a slightly poorer resolution, and a discontinuous surface coating. The use of 20 degrees rotary replication proved to be unsuitable for high-resolution imaging, with 20-25 A granularity and resolution two to three times poorer. Vertical and 45 degrees Pt-C replicas can visualize the deep-etched DNA helix and the 13.3 A 3(2) helix of pectin in a gel. The DNA double helix, the complex structures of sol-gel glasses, Immobilon filters (polyvinylidene fluoride), a polymethacrylate plastic, the metal oxide surfaces of 440c stainless steel, and aluminum are illustrated. This high-resolution vertical Pt-C replica technique can image in the context of solutions, gels, or solids, single molecular chains 3-7 A wide, their associations, and their conformation. Included in the present article are first time descriptions for removing replicas from metals and plastics and for making high-magnification photographic prints of normal contrast using a reversal rephotographic process. PMID:2809773

Ruben, G C

1989-12-01

76

Freezing and Freeze-Drying  

Microsoft Academic Search

Most biological substances are unstable during storage owing to their high water content. This is why numerous attempts have been made over the last 100 years to prevent, by low temperature freezing, metabolic and biochemical degradations. The transformation of water into ice brings to an end all chemical reactions; however, it might also induce deleterious alterations into the delicate structure

L. Rey; N. W. Pirie; W. E. Whitman; N. Kurti

1975-01-01

77

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

78

Natural Convection in a Vertical Rectangular Cavity Filled with a Non-Newtonian Power Law Fluid and Subjected to a Horizontal Temperature Gradient  

Microsoft Academic Search

A study of natural convection, in a vertical rectangular cavity filled with a non-Newtonian fluid and subjected to uniform heat flux along the vertical side walls, is carried out numerically by solving the full governing equations. In the limit of a tall enclosure, these equations are considerably reduced by using the parallel flow approximation. Solutions for the flow and temperature

M. Lamsaadi; M. Naïmi; M. Hasnaoui; M. Mamou

2006-01-01

79

Modified Model for the Mechanism of Freezing Injury in Erythrocytes.  

National Technical Information Service (NTIS)

The salt concentration theory of freezing injury has been a dominant one since 1953. Recent experiments involving haemolysis of human erythrocytes do not support this theory, however. Damage seems to be caused by an osmotic pressure gradient, and does not...

H. T. Meryman

1968-01-01

80

Inner core freezing and melting: Constraints from seismic body waves  

NASA Astrophysics Data System (ADS)

Hypotheses for the mechanisms of growth of Earth's inner core can be tested from observations of lateral variations of elastic and anelastic properties near the inner core boundary. Differential travel times of PKIKP-PKiKP and the apparent travel time of P waves diffracted around the inner core are consistent with the existence of a stably stratified, globally uniform, region of reduced velocity gradient at the bottom of the outer core. This layer may be a zone of iron enrichment relative to the bulk of the outer core, representing a zone either of crystallization or melting of the inner core. Weak backscattered PKiKP in the equatorial eastern hemisphere can be made consistent with either a hypothesis of freezing or melting. In a melting hypothesis, the eastern hemisphere is texturally older and smoother, with larger crystals or smaller elastic contrasts across grain boundaries providing weaker backscatter to the coda of PKiKP. Additional observations consistent with higher homologous temperature and melting in this region are the existence of a thin low velocity layer in the uppermost inner core inferred from multipathing of PKIKP + PKiKP waves and a bright spot in the amplitude of PKIIKP waves observed at antipodal distances. Alternatively, a freezing hypothesis in the eastern hemisphere is an inner core that is growing radially outward with crystals stretched in the vertical direction. This hypothesis can simultaneously explain weak backscattered PKiKP coda and high attenuation of transmitted PKIKP from the loss of backscattered energy at angles perpendicular to vertically oriented crystals. Strong backscattering observed in the coda of PKiKP sampling the equatorial western hemisphere of the inner core agrees best with a heterogeneity having an isotropic distribution of scale lengths in the uppermost inner core.

Cormier, Vernon F.; Attanayake, Januka; He, Kuang

2011-10-01

81

Periodic ice banding in freezing colloidal dispersions.  

PubMed

Concentrated colloidal alumina dispersions were frozen in a directional solidification apparatus that provides independent control of the freezing rate and temperature gradient. Two distinct steady-state modes of periodic ice banding were observed in the range of freezing rates examined. For each mode, the wavelength between successive bands of segregated ice decreases with increasing freezing rate. At low freezing rates (0.25-3 ?m s(-1)), the ice segregates from the suspension into ice lenses, which are cracklike in appearance, and there is visible structure in the layer of rejected particles in the unfrozen region ahead of the ice lenses. In this regime, we argue that compressive cryosuction forces lead to the irreversible aggregation of the rejected particles into a close-packed cohesive layer. The temperature in the aggregated layer is depressed below the bulk freezing point by more than 2 °C before the ice lenses are encountered; moreover, this undercooled region appears as a light-colored layer. The magnitude of the undercooling and the color change in this region both suggest the presence of pore ice and the formation of a frozen fringe. The possibility of a frozen fringe is supported by a quantitative model of the freezing behavior. At intermediate freezing rates, around 4 ?m s(-1), the pattern of ice segregation is disordered, coinciding with the disappearance of the dark- and light-colored layers. Finally, at high freezing rates (5-10 ?m s(-1)), there is a new mode of periodic ice banding that is no longer cracklike and is absent of any visible structure in the suspension ahead of the ice bands. We discuss the implications of our experimental findings for theories of ice lensing. PMID:23110707

Anderson, Anthony M; Worster, M Grae

2012-12-01

82

Safely Freezing LTL  

Microsoft Academic Search

We consider the safety fragment of linear temporal logic with the freeze quantifier. The freeze quantifier is used to store a value from an infinite domain in a register for later comparison with other such val- ues. We show that, for one register, satisfiability, refinement and model checking problems are decidable. The main result in the paper is that sat-

Ranko Lazic

2006-01-01

83

Freezing and Melting  

NSDL National Science Digital Library

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

2010-01-01

84

Desalting of Seawater by Freezing.  

National Technical Information Service (NTIS)

The economics of the secondary refrigerant freezing process was evaluated with particular emphasis on large freezing plants. It was found that large economies resulted by using normal butane. A study of the secondary refrigerant freezing process using nor...

H. F. Wiegandt J. P. Leinroth P. Harriott

1968-01-01

85

Increased spring freezing vulnerability for alpine shrubs under early snowmelt.  

PubMed

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

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

2014-05-01

86

Controlling the freezing process: a robotic device for rapidly freezing biological tissues with millisecond time resolution.  

PubMed

A robotic cryogenic device was developed which allows freezing of thick biological tissues with millisecond time resolution. The device consists of two horizontally oriented hammers (pre-cooled with liquid N(2)) driven by two linear servo-motors. The tissue sample is bathed in Ringers contained in a chamber which drops rapidly out of the way just as the hammers approach. A third linear motor is vertically oriented, and permits the rapidly dropping chamber to smoothly decelerate. All movements were performed by the three motors and four solenoids controlled by a PC. Mechanical adjustments, that change the size of the gap between the hammers at the end position, permit the final thickness of the frozen tissue to be varied. Here we show that the freezing time increased with the square of the final thickness of the frozen bundle. However, when bundles of different original thicknesses (up to at least 1mm) were compressed to the same final thickness (e.g., 0.2mm), they exhibited nearly equal freezing times. Hence, by being able to adjust the final thickness of the frozen bundles, the device not only speeds the rate of freezing, but standardizes the freezing time for different diameter samples. This permits the use of freezing for accurate determination of the kinetics of cellular processes in biological tissue. PMID:17640628

Tikunov, Boris A; Rome, Lawrence C

2007-10-01

87

Scram or Freeze  

NSDL National Science Digital Library

In this outdoor activity and animal-role-play game, learners discover and uncover the hidden world of "cryptozoa"âorganisms such as spiders, salamanders and slugs that live under objects, like rocks and fallen tree trunks, or in concealed places. When uncovered, some cryptozoa scurry for cover ("scram"), while others remain motionless ("freeze"). Both behaviors help uncovered organisms escape from predators. In the game, learners take the roles of predator or prey and get to scram and freeze, and even growl, until all the prey are caught or reach "shelter." Learners also conduct a cryptozoa survey, by carefully upturning pieces of wood, leaves and rock to find and collect hidden animals. At the end, learners return all organisms to their original positions. The PDF includes safety precautions to protect both learners and the animals they uncover. To adapt the game for hearing impaired learners, instruction signs reading "scram" and "freeze" could be used instead of verbal instructions.

Science, Lawrence H.

1981-01-01

88

Percolation with Constant Freezing  

NASA Astrophysics Data System (ADS)

We introduce and study a model of percolation with constant freezing (PCF) where edges open at constant rate 1 , and clusters freeze at rate ? independently of their size. Our main result is that the infinite volume process can be constructed on any amenable vertex transitive graph. This is in sharp contrast to models of percolation with freezing previously introduced, where the limit is known not to exist. Our interest is in the study of the percolative properties of the final configuration as a function of ? . We also obtain more precise results in the case of trees. Surprisingly the algebraic exponent for the cluster size depends on the degree, suggesting that there is no lower critical dimension for the model. Moreover, even for ?

Mottram, Edward

2014-04-01

89

Percolation with Constant Freezing  

NASA Astrophysics Data System (ADS)

We introduce and study a model of percolation with constant freezing ( PCF) where edges open at constant rate , and clusters freeze at rate independently of their size. Our main result is that the infinite volume process can be constructed on any amenable vertex transitive graph. This is in sharp contrast to models of percolation with freezing previously introduced, where the limit is known not to exist. Our interest is in the study of the percolative properties of the final configuration as a function of . We also obtain more precise results in the case of trees. Surprisingly the algebraic exponent for the cluster size depends on the degree, suggesting that there is no lower critical dimension for the model. Moreover, even for , it is shown that finite clusters have algebraic tail decay, which is a signature of self organised criticality. Partial results are obtained on , and many open questions are discussed.

Mottram, Edward

2014-06-01

90

Heterogeneous freezing of droplets with immersed surface modified mineral dust particles  

Microsoft Academic Search

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

Susan Hartmann

2010-01-01

91

Vertical and temporal shifts in microbial communities in the water column and sediment of saline meromictic Lake Kaiike (Japan), as determined by a 16S rDNA-based analysis, and related to physicochemical gradients.  

PubMed

The vertical and temporal changes in microbial communities were investigated throughout the water column and sediment of the saline meromictic Lake Kaiike by PCR-denaturing gradient gel electrophoresis (DGGE) of 16S rDNA. Marked depth-related changes in microbial communities were observed at the chemocline and the sediment-water interface. However, no major temporal changes in the microbial community below the chemocline were observed during the sampling period, suggesting that the ecosystem in the anoxic zone of Lake Kaiike was nearly stable. Although the sequence of the most conspicuous DGGE band throughout the anoxic water and in the top of the microbial mat was most similar to that of an anoxic, photosynthetic, green sulphur bacterium, Pelodyction luteolum DSM273 (97% similarity), it represented a new phylotype. A comparison of DGGE banding patterns of the water column and sediment samples demonstrated that specific bacteria accumulated on the bottom from the anoxic water layers, and that indigenous microbial populations were present in the sediment. The measurements of bicarbonate assimilation rates showed significant phototrophic assimilation in the chemocline and lithoautotrophic assimilation throughout the anoxic water, but were not clearly linked with net sulphide turnover rates, indicating that sulphur and carbon metabolisms were not directly correlated. PMID:15142251

Koizumi, Yoshikazu; Kojima, Hisaya; Oguri, Kazumasa; Kitazato, Hiroshi; Fukui, Manabu

2004-06-01

92

Temperature and Flow Measurements on Near-Freezing Aviation Fuels in a Wing-Tank Model.  

National Technical Information Service (NTIS)

Freezing behavior, pumpability, and temperature profiles for aviation turbine fuels were measured in a 190-liter tank chilled to simulate internal temperature gradients encountered in commercial airplane wing tanks. When the bulk of the fuel was above the...

R. Friedman F. J. Stockemer

1980-01-01

93

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

94

Visualization of freezing damage.  

PubMed

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 decrease in viability is caused by the presence of intracellular ice; but cells cooled at rates less than this critical velocity do not contain appreciable amounts of intracellular ice and are killed by prolonged exposure to a solution that is altered by the presence of ice. As a test of this hypothesis, we examined freeze-fractured replicas of the yeast Saccharomyces cerevisiae after suspensions had been cooled at rates ranging from 1.8 to 75,000 degrees C/min. Some of the frozen samples were cleaved and replicated immediately in order to minimize artifacts due to sample handling. Other samples were deeply etched or were rewarmed to -20 degrees C and recooled before replication. Yeast cells cooled at or above the rate necessary to preserve maximal viability ( approximately 7 degrees C/min) contained intracellular ice, whereas cells cooled below this rate showed no evidence of intracellular ice. PMID:4572921

Bank, H; Mazur, P

1973-06-01

95

Spatiotemporal measurement of freezing-induced deformation of engineered tissues.  

PubMed

In order to cryopreserve functional engineered tissues (ETs), the microstructure of the extracellular matrix (ECM) should be maintained, as well as the cellular viability since the functionality is closely related to the ECM microstructure. Since the post-thaw ECM microstructure is determined by the deformation of ETs during cryopreservation, freezing-induced deformation of ETs was measured with a newly developed quantum dot (QD)-mediated cell image deformetry system using dermal equivalents as a model tissue. The dermal equivalents were constructed by seeding QD-labeled fibroblasts in type I collagen matrices. After 24 h incubation, the ETs were directionally frozen by exposing them to a spatial temperature gradient (from 4 degrees C to -20 degrees C over a distance of 6 mm). While being frozen, the ETs were consecutively imaged, and consecutive pairs of these images were two-dimensionally cross-correlated to determine the local deformation during freezing. The results showed that freezing induced the deformation of ET, and its magnitude varied with both time and location. The maximum local dilatation was 0.006 s(-1) and was always observed at the phase change interface. Due to this local expansion, the unfrozen region in front of the freezing interface experienced compression. This expansion-compression pattern was observed throughout the freezing process. In the unfrozen region, the deformation rate gradually decreased away from the freezing interface. After freezing/thawing, the ET experienced an approximately 28% decrease in thickness and 8% loss in weight. These results indicate that freezing-induced deformation caused the transport of interstitial fluid, and the interstitial fluid was extruded. In summary, the results suggest that complex cell-fluid-matrix interactions occur within ETs during freezing, and these interactions determine the post-thaw ECM microstructure and eventual post-thaw tissue functionality. PMID:20459191

Teo, Ka Yaw; Dutton, J Craig; Han, Bumsoo

2010-03-01

96

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

97

Thermodynamical effects accompanied freezing of two water layers separated by sea ice sheet  

NASA Astrophysics Data System (ADS)

The process of melt pond freezing is very important for generation of sea ice cover thermodynamic and mass balance during winterperiod. However, due to significant difficulties of field measurements the available data of model estimations still have no instrumental confirmation. In May 2009 the authors carried out laboratory experiment on freezing of limited water volume in the University Centre in Svalbard ice tank. In the course of experiment fresh water layer of 27.5 cm thickness at freezing point poured on the 24 cm sea ice layer was cooled during 50 hours at the temperature -10º C and then once again during 60 hours at -20º C. For revealing process typical characteristics the data of continuous measurements of temperature and salinity in different phases were compared with data of numerical computations obtained with thermodynamic model which was formulated in the frames of 1-D equation system (infinite extension of water freezing layer) and adapted to laboratory conditions. The known surprise of the experiment became proximity of calculated and measured estimates of process dynamics that confirmed the adequacy of the problem mathematical statement (excluding probably process finale stage). This effect can be explained by formation of cracks on the upper layer of ice at sharp decreases of air temperature, which temporary compensated hydrostatic pressure growth during freezing of closed water volume. Another compensated mechanism can be migration of brine through the lower layer of ice under influence of vertical pressure gradient and also rejection of gas dissolved in water which increased its compressibility. During 110 hours cooling thickness of water layer between ice layers reduced approximately to 2 cm. According to computations this layer is not chilled completely but keeps as thin brine interlayer within ice body whose thickness (about units of mm) is determined by temperature fluctuations of cooled surface. Nevertheless, despite good coincidence of experimental and model estimates the question of existence of liquid phase under actual conditions is still open and can be clarified in a continuous laboratory experiment. This work was supported by Russian Foundation for Basic Research (Project # 14-05-00677).

Bogorodsky, Petr; Marchenko, Aleksey

2014-05-01

98

Mechanisms of Freezing lnjuly in Cellular Leve  

NASA Astrophysics Data System (ADS)

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

Fujikawa, Seizo

99

Oocyte freezing: here to stay?  

PubMed

Oocyte freezing is an established technology but, in contrast to embryo freezing, it has very limited application in clinical IVF programmes. Is there a chance that oocyte freezing will become an integrated routine in assisted reproductive technology? The delicate cytological architecture of the oocyte with a cold-sensitive spindle and a hardening zona have made the frozen oocyte 'unwanted' in assisted reproductive technology. Nevertheless, empirical improvements in freezing protocols and the use of ICSI for fertilization have led to an increasing number of live births. This mitigates against a simple ban on oocyte freezing. While efficiency of oocyte freezing can certainly be further improved by basic research, it is clear that there are humanitarian reasons for considering oocyte freezing as a future fully utilized assisted reproductive technology. The storage of the female genome as a particulate entity can provide an alternative in case of moral, ethical, legal or religious concerns about embryo freezing. Oocyte freezing can also offer hope for oocyte donation and preservation of fertility for women facing ovarian loss. The message is one of cautious optimism when looking for a place for oocyte freezing in routine assisted reproductive technology. PMID:14640378

Van der Elst, Josiane

2003-01-01

100

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

Microsoft Academic Search

To increase the quality of cryopreserved sperm in white rhinoceros, the liquid nitrogen vapour (LN vapour) freezing and the multi-thermal gradient directional freezing methods were compared. Sixteen white rhinoceros (Ceratotherium simum sp.) were electro-ejaculated. Semen samples were diluted with cryoextender (Tris, lactose, egg-yolk, DMSO) and aliquoted into straws for LN vapour freezing, and glass hollow tubes for directional freezing. The

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

2009-01-01

101

Freeze-Tolerant Condensers  

NASA Technical Reports Server (NTRS)

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

Crowley, Christopher J.; Elkouhk, Nabil

2004-01-01

102

Freezing cold injury.  

PubMed

The pathogenesis of freezing cold injuries (FCI) is not yet entirely understood. Two possible hypothesis emerge: 1) Injury is a direct result of cryogenic insult to the cells. 2) Injury is secondary to vascular stasis which leads to anoxia. In clinical congelatio ice crystallization takes place in the EC-space. When water is transformed into ice, the osmolality in this compartment will increase leading to a passive diffusion of water from the IC-space. Cell dehydration modifies protein structure, alters membrane lipids and cellular pH leading to destructions incompatible with cell survival. Cold induces vasoconstriction of both arterioles and venules, which enhances peripheral filtration and raises plasma viscosity. The stability of red corpuscle aggregates increases and showers of emboli course microvessels. Finally progressive thrombosis will end up in anoxia. The indirect vascular effect has earlier been interpreted similar to that found in non-freezing injuries. Recent studies have, however, shown, that endothelial cells are very sensitive to freezing. The rheologic part of the pathogenesis therefore also seems to depend on a direct injury to cells. The development of FCI does not always depend on ambient temperature and duration of exposure but more to the heat loss subjected to exposed skin. Wind chill, humidity and wetness are all of significance in this matter. From a clinical point of view FCI are best subdivided into superficial and deep injuries. The superficial frostbite is limited to the skin and nearest subcutaneous tissue. A stringing, pinching pain is often the first symptom. The affected area becomes pale or waxy-white and numb.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1811585

Granberg, P O

1991-01-01

103

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

104

Freezing of Nonwoody Plant Tissue  

PubMed Central

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

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

1974-01-01

105

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

106

Development of Freeze Dried Vegetables.  

National Technical Information Service (NTIS)

The development of freeze dried vegetables to be used in the Apollo food system is discussed. After the initial selection and screening of vegetables, several types of freeze dried vegetables were prepared in small batches. From these small batches, two v...

R. W. Larson

1970-01-01

107

Freezing of living cells  

SciTech Connect

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

Mazur, P.

1985-01-01

108

Freeze-drying fungi using a shelf freeze-drier.  

PubMed

Lyophilization, the removal of water by freezing and then volatilization at low pressure and temperature, has been employed as a standard long-term preservation method for many filamentous fungi. The method outlined involves the use of standard shelf freeze-drying and skimmed milk as a suspending solution/lyoprotectant. This approach has been employed to freeze-dry the majority of the 50,000 fungal strains that have been successfully lyophilized at the Centraal bureau voor Schimmelcultures (CBS) culture collection (http://www.cbs.knaw.nl/). PMID:18080466

Tan, C Shu-hui; van Ingen, Cor W; Stalpers, Joost A

2007-01-01

109

Vertical Disintegration  

Microsoft Academic Search

With economies of scale, a vertically integrated firm can lower its upstream cost by supplying downstream competitors. The competitors may strategically choose not to purchase from the integrated firm, unless the latter's price for the intermediate good is sufficiently lower than those of alternative suppliers. In a simple model of dynamic scale economies through learning by doing, equilibrium vertical disintegration

Yongmin Chen

2005-01-01

110

FREEZING RESISTANCE OF NEW ZEALAND TREES AND SHRUBS  

Microsoft Academic Search

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

A. SAKAI; P. WARDLE

111

A NEW FREEZING-ULTRAMICROTOME  

PubMed Central

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

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

1961-01-01

112

Biomimetic Materials by Freeze Casting  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

113

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...

114

Evolution of freezing susceptibility and freezing tolerance in terrestrial arthropods  

Microsoft Academic Search

Abstract – Arthropods have evolved,various adaptations to survive adverse seasons and it has long been discussed why some arthropods are freezing-susceptible and some are freezing-tolerant. However, which mode of frost resistance came,first during the course of evolution? A commonly,held opinion is that no choice of strategy has been offered in evolution, because each species of arthropod may have its own

Ecology Écologie; Philippe Vernon; Guy Vannier

115

Geothermal Gradients  

NSDL National Science Digital Library

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

Davidson, Cameron

116

Freezing of supercooled water nanodroplets  

NASA Astrophysics Data System (ADS)

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

Wyslouzil, Barbara

2013-03-01

117

Freezing of Aqueous Polyvinylpyrrolidone Solutions.  

National Technical Information Service (NTIS)

The freezing of aqueous polyvinylpyrrolidone solutions was studied by means of differential thermal analysis, dilatometry and calorimetry. A differential thermal analysis apparatus for use at low temperatures was constructed. A fast method for the determi...

H. H. G. Jellinek S. Y. Fok

1967-01-01

118

THE VERTICAL  

NASA Technical Reports Server (NTRS)

'THE VERTICAL' computer keyboard is designed to address critical factors which contribute to Repetitive Motion Injuries (RMI) (including Carpal Tunnel Syndrome) in association with computer keyboard usage. This keyboard splits the standard QWERTY design into two halves and positions each half 90 degrees from the desk. In order to access a computer correctly. 'THE VERTICAL' requires users to position their bodies in optimal alignment with the keyboard. The orthopaedically neutral forearm position (with hands palms-in and thumbs-up) reduces nerve compression in the forearm. The vertically arranged keypad halves ameliorate onset occurrence of keyboard-associated RMI. By utilizing visually-reference mirrored mylar surfaces adjustable to the user's eye, the user is able to readily reference any key indicia (reversed) just as they would on a conventional keyboard. Transverse adjustability substantially reduces cumulative musculoskeletal discomfort in the shoulders. 'THE VERTICAL' eliminates the need for an exterior mouse by offering a convenient finger-accessible curser control while the hands remain in the vertically neutral position. The potential commercial application for 'THE VERTICAL' is enormous since the product can effect every person who uses a computer anywhere in the world. Employers and their insurance carriers are spending hundreds of millions of dollars per year as a result of RMI. This keyboard will reduce the risk.

Albert, Stephen L.; Spencer, Jeffrey B.

1994-01-01

119

Fundamentals of freeze-drying.  

PubMed

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

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

2002-01-01

120

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

NASA Technical Reports Server (NTRS)

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

Clifford, Stephen M.

1993-01-01

121

Modification of a variational objective analysis model for new equations for pressure gradient and vertical velocity in the lower troposphere and for spatial resolution and accuracy of satellite data  

NASA Technical Reports Server (NTRS)

Since late 1982 NASA has supported research to develop a numerical variational model for the diagnostic assimilation of conventional and space-based meteorological data. In order to analyze the model components, four variational models are defined dividing the problem naturally according to increasing complexity. The first of these variational models (MODEL I), the subject of this report, contains the two nonlinear horizontal momentum equations, the integrated continuity equation, and the hydrostatic equation. This report summarizes the results of research (1) to improve the way the large nonmeteorological parts of the pressure gradient force are partitioned between the two terms of the pressure gradient force terms of the horizontal momentum equations, (2) to generalize the integrated continuity equation to account for variable pressure thickness over elevated terrain, and (3) to introduce horizontal variation in the precision modulus weights for the observations.

Achtemeier, G. L.

1986-01-01

122

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

123

Freeze-dried microarterial allografts  

SciTech Connect

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

Raman, J.; Hargrave, J.C.

1990-02-01

124

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

125

Vertical mammaplasty.  

PubMed

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

Hidalgo, David A

2005-04-01

126

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

127

Freezing kinetics in overcompressed water  

Microsoft Academic Search

The transformation of water into ice is among the most common first order phase transitions occurring in nature, but it is far from being an ordinary one. Water has unusual physical properties both as a liquid and as a solid due largely to hydrogen bonding effects, which also play a major role in determining the characteristics of its freezing kinetics.

Marina Bastea; Sorin Bastea; John Reaugh; David Reisman

2007-01-01

128

Programmed-Temperature Normal Freezing  

Microsoft Academic Search

A normal freezing apparatus is described where the cooling-bath temperature can be programmed between 0.5 × 10 and 6.0°C\\/mm. Runs with n-hexadecane\\/n-tetradecane test mixtures indicate that improved efficiencies result from programming the cooling bath during the run.

T. H. Gouw

1967-01-01

129

Freezing Tolerance in Mytilus Edulis.  

National Technical Information Service (NTIS)

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

R. J. Williams

1969-01-01

130

Vertical secondary flows in submersed plant-like arrays  

Microsoft Academic Search

Abstract Obstructions that protruded from a laboratory test bed into the benthic boundary,layer were exposed,to gradients in longitudinal velocity (]u\\/]z) that produced,vertical pressure gradients along the surface of the obstruction. These pressure gradients generated vertical secondary,flows that may,have ecological significance for benthic fauna and aquatic macrophytes. Laboratory experiments,demonstrated,that secondary,flows of up to 15% of the local longi- tudinal velocity were,produced,behind,individual

Heidi M. Nepf; Evamaria W. Koch

1999-01-01

131

Energy budgets and temperatures of nyctinastic leaves on freezing nights.  

PubMed

Temperatures of exposed horizontal and vertical soybean leaves (Glycine max [L.] Merr. var. Chippewa) were measured on calm, clear nights with temperatures near freezing. Average leaf-air temperature differences for 5 nights were -1.5 C and -1.0 C for horizontal and vertical leaves respectively. The horizontal leaves were cooler than the vertical leaves. The mean of all observed horizontal-vertical leaf temperature differences was -0.5 C with a maximum average for 1 night of -0.8 C, while maximum differences theoretically attainable in similar leaves were calculated to be -1.7 C. No differences were observed in the extent of frost damage in horizontal and vertical leaves. The apparent reduction in frost damage in vertical leaves observed by Charles Darwin was probably caused by his method of using corks to hold the horizontal leaves and not by leaf orientation. Theoretical considerations and the experimental results indicate that nyctinastic leaf movements probably do not provide significant protection from frost for any plants. PMID:16657763

Schwintzer, C R

1971-08-01

132

Repeated Freeze-Thaw Cycles in Cryosurgery  

Microsoft Academic Search

FREEZING temperatures have been in use in surgery for many years as a means of local tissue destruction. Recent experimental investigation has shown that such freezing will give a reproducible area of cell death provided factors such as the temperature and the duration of application are constant. Additional virtues have been claimed for repeated, as opposed to single, freeze-thaw cycles

William Gill; James Fraser; David C. Carter

1968-01-01

133

When hot water freezes before cold  

Microsoft Academic Search

I suggest that the origin of the Mpemba effect (the freezing of hot water before cold) is 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

J. I. Katz

2006-01-01

134

Molten salt freeze seal. Final report  

Microsoft Academic Search

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

Corugedo

1985-01-01

135

Stone movements and permeability changes in till caused by freezing and thawing  

Microsoft Academic Search

Vertical uplifting of boulders and stones is well known to take place in cold regions. Movements of stones in roads might lead to traffic danger, vehicle failures, and cause breakdown of the road surface with the need of expensive repair as a consequence. In addition, freeze\\/thaw and associated stone movements may cause an increase in permeability, which can lead to

Peter Viklander; Dieter Eigenbrod

2000-01-01

136

Denaturation of ~nzyme Protein by Freeze-Thawing and Freeze-Drying  

Microsoft Academic Search

The effects of freeze-thawing and freeze-drying on catalase, one of globular proteins, were examined for the purpose of investigating relations of the confor­ mation of protein to its stability against freeze-thawing and freeze-drying. Also the water content of the freeze-dried egg albumin, a representative protein, was measured with or without some additives, for the clarification of the mechanism of their

Naofumi HANAFUSA

137

Freeze indicators with a controlled temperature response  

US Patent & Trademark Office Database

A freeze indicator can include an indicator dispersion having an aqueous liquid medium and organic material indicator particles dispersed in the aqueous liquid medium. The indicator dispersion can have an initial appearance before freezing and an irreversibly different appearance after freezing and can exhibit a freeze-onset temperature of about -1.9.degree. C. or higher. Some factors helpful to providing a relatively high freeze onset temperature are employment of a proteinaceous ice-nucleating agent, control of pH, use of a protein stabilizer and control of the ratio of protein stabilizer to ice-nucleating agent.

2012-02-28

138

Breeding bird diversity in relation to environmental gradients in China  

Microsoft Academic Search

Geographic variation in species richness has been explained by different theories such as energy, productivity, energy–water balance, habitat heterogeneity, and freezing tolerance. This study determines which of these theories best account for gradients of breeding bird richness in China. In addition, we develop a best-fit model to account for the relationship between breeding bird richness and environment in China. Breeding

Hong Qian; Silong Wang; Yuanliang Li; Xihua Wang

2009-01-01

139

A study of the impact of freezing on the lyophilization of a concentrated formulation with a high fill depth.  

PubMed

The objective of this study was to evaluate the impact of freezing on the lyophilization of a concentrated formulation with a high fill depth. A model system consisting of a 15-mL fill of 15% (w/w) sulfobutylether 7-beta-cyclodextrin (SBECD) solution in a 30-mL vial was selected for this study. Various freezing methods including single-step freezing, two-step freezing with a super-cooling holding, annealing, vacuum-induced freezing, changing ice habit using tert-butyl-alcohol (TBA), ice nucleation with silver iodide (AgI), as well as combinations of some of the methods, were used in the lyophilization of this model system. This work demonstrated that the freezing process had a significant impact on primary drying rate and product quality of a concentrated formulation with a high fill depth. Annealing, vacuum-induced freezing, and addition of either TBA or an ice nucleating agent (AgI) to the formulation accelerated the subsequent ice sublimation process. Two-step freezing or addition of TBA improved the product quality by eliminating vertical heterogeneity within the cake. The combination of two-step freezing in conjunction with an annealing step was shown to be a method of choice for freezing in the lyophilization of a product with a high fill depth. In addition to being an effective method of freezing, it is most applicable for scaling up. An alternative approach is to add a certain amount of TBA to the formulation, if the TBA-formulation interaction or regulatory concerns can be demonstrated as not being an issue. An evaluation of vial size performed in this study showed that although utilizing large-diameter vials to reduce the fill depth can greatly shorten the cycle time of a single batch, it will substantially decrease the product throughput in a large-scale freeze-dryer. PMID:15926675

Liu, Jinsong; Viverette, Todd; Virgin, Marlin; Anderson, Mitch; Paresh, Dalal

2005-01-01

140

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

141

Optimal Freeze Cycle Length for Renal Cryotherapy  

PubMed Central

Purpose To our knowledge the optimal freeze cycle length in renal cryotherapy is unknown. Ten-minute time based freeze cycles were compared to temperature based freeze cycles to ?20C. Materials and Methods Laparoscopic renal cryotherapy was performed on 16 swine. Time based trials consisted of a double 10-minute freeze separated by a 5-minute thaw. Temperature based trials were double cycles of 1, 5 or 10-minute freeze initiated after 1 of 4 sensors indicated ?20C. A 5-minute active thaw was used between freeze cycles. Control trials consisted of cryoneedle placement for 25 minutes without freeze or thaw. Viability staining and histological analysis were done. Results There was no difference in cellular necrosis between any of the temperature based freeze cycles (p = 0.1). Time based freeze cycles showed more nuclear pyknosis, indicative of necrosis, than the 3 experimental freeze cycles for the renal cortex (p = 0.05) but not for the renal medulla (p = 0.61). Mean time to ?20C for freeze cycle 1 was 19 minutes 10 seconds (range 9 to 46 minutes). In 4 of 21 trials (19%) ?20C was never attained despite freezing for 25 to 63 minutes. Conclusions There was no difference in immediate cellular necrosis among double 1, 5 or 10-minute freeze cycles. Cellular necrosis was evident on histological analysis for trials in which ?20C was attained and in freeze cycles based on time alone. With a standard 10-minute cryoablation period most treated parenchyma 1 cm from the probe never attained ?20C. Cell death appeared to occur at temperatures warmer than ?20C during renal cryotherapy.

Young, Jennifer Lee; Khanifar, Elham; Narula, Navneet; Ortiz-Vanderdys, Cervando Gerardo; Kolla, Surendra Babu; Pick, Donald Lowell; Sountoulides, Petros George; Kaufmann, Oskar Grau; Osann, Kathryn Elizabeth; Huynh, Victor Buu; Kaplan, Adam Geoffrey; Andrade, Lorena Aurora; Louie, Michael Ken; McDougall, Elspeth Marguerita; Clayman, Ralph Victor

2014-01-01

142

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

PubMed Central

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

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

2004-01-01

143

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

144

Estimation of coastal density gradients  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

145

Effects of freeze-thaw cycles on anaerobic microbial processes in an Arctic intertidal mud flat.  

PubMed

Insight into the effects of repeated freezing and thawing on microbial processes in sediments and soils is important for understanding sediment carbon cycling at high latitudes acutely affected by global warming. Microbial responses to repeated freeze-thaw conditions were studied in three complementary experiments using arctic sediment collected from an intertidal flat that is exposed to seasonal freeze-thaw conditions (Ymerbukta, Svalbard, Arctic Ocean). The sediment was subjected to oscillating freeze-thaw incubations, either gradual, from -5 to 4 degrees C, or abrupt, from -20 to 10 degrees C. Concentrations of low-molecular weight carboxylic acids (volatile fatty acids) were measured and sulfate reduction was assessed by measuring (35)S sulfate reduction rates (SRRs). Gradual freeze-thaw incubation decreased microbial activity in the frozen state to 0.25 % of initial levels at 4 degrees C, but activity resumed rapidly reaching >60 % of initial activity in the thawed state. Exposure of sediments to successive large temperature changes (-20 versus 10 degrees C) decreased SRR by 80% of the initial activity, suggesting that a fraction of the bacterial community recovered rapidly from extreme temperature fluctuations. This is supported by 16S rRNA gene-based denaturing gradient gel electrophoresis profiles that revealed persistence of the dominant microbial taxa under repeated freeze-thaw cycles. The fast recovery of the SRRs suggests that carbon mineralization in thawing arctic sediment can resume without delay or substantial growth of microbial populations. PMID:20033071

Sawicka, Joanna E; Robador, Alberto; Hubert, Casey; Jørgensen, Bo Barker; Brüchert, Volker

2010-04-01

146

A cost effective vertical air\\/water solar heating collector  

Microsoft Academic Search

A description is presented of a vertical air\\/water collector which combines high efficiency with low cost. The low-cost characteristics of the total system are obtained by utilizing an air system for heat collection along with a water system for heat storage. The heat exchanger is in the top of the collector. It is protected from freezing, and is available to

T. H. Markowitz; R. L. Hummel

1978-01-01

147

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

PubMed

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

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

2014-06-01

148

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

149

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

150

Freeze Drying: Potential for Powdered Nanoparticulate Product  

Microsoft Academic Search

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

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

2010-01-01

151

Freeze coring soft sediments in tropical lakes  

Microsoft Academic Search

A new freeze corer is described that is specifically designed for operation in warm tropical lakes. It combines the standard wedge-shaped freeze-on container with a 20-liter thermos from which pellets of solid CO2 descend into the wedge to replace those that have sublimated. This extends the duration of effective freezing from ~20 to ~45 min, sufficient to form an adequate

Dirk Veerschuren

2000-01-01

152

Measuring freezing tolerance: survival and regrowth assays.  

PubMed

Screening plants for freezing tolerance under tightly controlled conditions is an invaluable technique for studying freezing tolerance and selecting for improved winterhardiness. Artificial freezing tests of cereal plants historically have used isolated crown and stem tissue prepared by "removing all plant parts 3 cm above and 0.5 cm below the crown tissue" (Fowler et al., Crop Sci 21:896-901, 1981). Here, we describe a method of conducting freezing tolerance tests using intact plants grown in small horticultural containers, including suggested methods for collecting and analyzing the data. PMID:24852624

Skinner, Daniel Z; Garland-Campbell, Kimberly

2014-01-01

153

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

SciTech Connect

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

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

1999-01-01

154

Effect of freeze-drying, freezing and frozen storage of blood plasma on fibrin network characteristics  

Microsoft Academic Search

Introduction: We investigated the effect of freezing, freeze-drying and the duration of frozen storage of blood plasma on fibrin network characteristics of clots subsequently produced. Materials and methods: Fibrin network characteristics of clots made from freeze-dried and frozen plasma were compared to those made from fresh plasma. Freeze-dried pooled plasma was reconstituted and frozen each month for 4 months to

Marlien Pieters; Johann C Jerling; John W Weisel

2002-01-01

155

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

Microsoft Academic Search

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

Koichiro Miyajima

1997-01-01

156

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

157

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

158

Effects of Dissolved Oxygen and Freezing Techniques on the Silver Freezing Point  

Microsoft Academic Search

The freezing point of silver is being considered as a joining point between platinum resistance thermometry and optical pyrometry. Therefore the freezing points of high purity samples of silver have been investigated. An important impurity effect arises from the depression of the freezing point of pure Ag caused by residual dissolved oxygen contents in some samples. Melting range parameters were

G. Bongiovanni; L. Crovini; P. Marcarino

1975-01-01

159

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

160

Boussinesq–Flamant problem in gradient elasticity with surface energy  

Microsoft Academic Search

The strain gradient elasticity theory with surface energy is applied to Boussinesq–Flamant problem. The solution for the vertical displacements at the surface of half space due to the surface normal line load is presented. The theory includes both volumetric and surface energy terms. Boussinesq–Flamant problem in the strain gradient elasticity is solved by means of Fourier transform. The results obtained

Dai Zhou; Bo Jin

2003-01-01

161

Particle Sorting by Repeated Freezing and Thawing  

Microsoft Academic Search

If a hetrogeneous mixture of particles of various sizes is frozen and thawed repeatedly, the particles are sorted into relatively uniform groups by size. The movement of particles depends on the amount of water between the ice-water interface and the particle, the rate of freezing, the distribution of the particles by size, and the orientation of the freeze-thaw plane.

Arturo E. Corte

1963-01-01

162

Inherent freeze protection for solar water heaters  

SciTech Connect

Research and development of a method for protection of a solar collector from freezing is described. The method is shown to be technically and economically feasible. A prototype water heating system using the inherent freeze protection method was successfully operated during the winter of 1980 to 1981.

Jeter, S.M.; Leonaitis, L.L.; Leonaitis, L.L.

1981-05-01

163

Recovery of White Blood Cells After Freezing.  

National Technical Information Service (NTIS)

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

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

1971-01-01

164

Two simple freeze drying microscope stages  

Microsoft Academic Search

In many instances it is advantageous to make real-time observations of freeze drying phenomena on a microscopic level. Two simple vacuum freeze drying chambers, suitable for use with the optical microscope at higher magnifications (600×), are described and examples of their use are noted.

James M. Flink; Frederik Gejl-Hansen

1978-01-01

165

Can freezing cause floods on Mars?  

Microsoft Academic Search

Floodwaters on Mars likely originated from aquifers confined below a cryosphere. We use an analytical solution to examine freezing-induced pressurization as a mechanism for releasing groundwater. The results suggest that freezing of an aquifer of global extent under the optimal conditions, i.e., perfectly confined and with low compressibility and high permeability relative to the terrestrial analogs, can release enough floodwaters

Chi-yuen Wang; Michael Manga; Jeffrey C. Hanna

2006-01-01

166

Molten Salt Freeze Seal. Final Report.  

National Technical Information Service (NTIS)

This report documents the results of the testing performed at Sandia National Laboratory, Albuquerque, New Mexico, on the applicability of a sodium freeze seal type valve stem in a molten salt environment. The freeze seal tests consisted of cycling the va...

J. J. Corugedo

1985-01-01

167

Fish With Nature's Anti-freeze  

NSDL National Science Digital Library

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

168

Freezing kinetics in overcompressed water  

NASA Astrophysics Data System (ADS)

The transformation of water into ice is among the most common first order phase transitions occurring in nature, but it is far from being an ordinary one. Water has unusual physical properties both as a liquid and as a solid due largely to hydrogen bonding effects, which also play a major role in determining the characteristics of its freezing kinetics. We report high pressure dynamic compression experiments of liquid water along a quasi-adiabatic path leading to the formation of ice VII. We observe dynamic features resembling Van der Waals loops and find that liquid water is compacted to a metastable state close to the ice density before the onset of crystallization. By analyzing the characteristic kinetic time scale involved we estimate the nucleation barrier and conclude that liquid water has been compressed to a high pressure state close to its thermodynamic stability limit.

Bastea, Marina; Bastea, S.; Reaugh, J.; Reisman, D.

2007-03-01

169

Oocyte freezing: timely reproductive insurance?  

PubMed

Cryopreservation of unfertilised oocytes for later use in initiating pregnancy is now a viable technology, with acceptable pregnancy rates (over 20% per thaw cycle). Oocyte cryopreservation used as a form of insurance against "social" (age-related) infertility can improve the lifetime chance of pregnancy in women who defer pregnancy into their late 30s or early 40s. We report two pregnancies using oocytes that were frozen for social rather than medical reasons, as part of a larger series of nine pregnancies using cryopreserved oocytes. Use of oocytes harvested and frozen from women aged under 35 years may more than double the chance of pregnancy for a 41-year-old woman. The disadvantages of oocyte freezing for social infertility reasons include cost, the usual risks associated with in-vitro fertilisation, and the lack of a guarantee of eventual pregnancy. PMID:19296788

Molloy, David; Hall, Barbara A; Ilbery, Mariannne; Irving, Jacqui; Harrison, Keith L

2009-03-01

170

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

171

Impact of freezing/thawing technique on sperm DNA integrity in HIV-1 patients  

PubMed Central

Introduction According french legislation, sperm freezing/thawing procedures are used to prevent ART contaminations in couple with HIV-1 infected men. We determined sperm nuclear fragmentation rate before and after selection and freezing/thawing in HIV-1 14 patients. Methods Two groups of patients were studied: 20 control patients with normal sperm (group 1) and without viral infection and 20 fertile treated HIV-1 patients (group 2). DNA fragmentation was evaluated using terminal uridine nick end labeling, before and after gradient selection, and after cryopreservation and thawing procedures. Results DNA fragmentation rates in fresh semen were increased in HIV patients (6.38% vs 3.39%) (p?freezing/thawing, values were similar to those of fresh semen with an increased rate (p?freezing/thawing procedures, but these two fragmentation rates were not significantly different. Conclusion So, freezing/thawing procedures do not seem to impair sperm DNA and preserve probability of conception for couples with HIV-1 infected men.

Vialard, Francois; Rougier, Nathalie; Aegerther, Philippe; Damond, Florence; Ayel, Jean-Philippe; Yazbeck, Chadi; Hazout, Andre; Selva, Jacqueline

2010-01-01

172

Micromagnetic Modeling Study of Thermal Gradient Effect in Heat-Assisted Magnetic Recording (HAMR)  

Microsoft Academic Search

The performance of heat assisted magnetic recording (HAMR) is simulated using a multilayer micromagnetic model. Recording performance parameters such as signal-to-noise ratio (SNR) were simulated as a function of the vertical thermal gradient in the recording media. Simulation results show that the vertical thermal gradient in the media has to be higher than ( -28 deg\\/nm) in order to have

Adam F. Torabi; Jan Van Ek; Eric Champion; James Wang

2009-01-01

173

Can Propagation of Gas Bubbles Lead to Detached Solidification? Experiments on Freezing of Water  

NASA Technical Reports Server (NTRS)

A vertical Bridgman-Stockbarger apparatus was used to directionally solidify water upward, in the hope that detached solidification would evolve from gas bubbles forming on the wall. A large contact angle of the water on the ampoule wall and a high solubility of the dissolved gas caused gas bubbles or tubes to form only at the ampoule wall, and not in the interior. Gas tubes were often nearly periodically spaced around the ampoule wall, with a spacing that increased with ampoule diameter and decreased with freezing rate. The width of the gas tubes was nearly independent of the ampoule diameter and freezing rate. A high degree of detachment was obtained with a rough, nonwetting coating on the ampoule wall, but full detachment was not achieved. This indicates that detachment does not occur by propagation of a single gas bubble around the periphery of the freezing interface. The convection near the freezing interface influenced gas bubble formation, and was outward for a concave freezing interface and inward for a convex interface.

Wang, Yazhen; Regel, Liya; Wilcox, William R.

2002-01-01

174

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

175

Freeze Denaturation of Fish Muscle Proteins  

NASA Astrophysics Data System (ADS)

Studies on the freeze denaturation of fish muscle proteins were reviewed with emphasis given to changes in their physicochemical and biochemical properties during frozen storage. Denaturation of actomyosin commonly occurs during frozen storage and side-to-side aggregation of myosin molecules apppears to major role in this reaction. The author's group performed freezing studies with isolated preparations of proteins from carp muscle, namely actomyosin, myosin, H-meromyosin, L-meromyosin, and actin. Freeze denaturation occurred with indvidual proteins as well as with their subunits. Not only aggregation but also some conformational changes were observed. Denaturation was inhibited in the presence of added glutamate.

Tsuchiya, Takahide

176

Molten salt freeze seal. Final report  

SciTech Connect

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

Corugedo, J.J.

1985-08-01

177

Numerical computation of magnetothermal convection of water in a vertical cylindrical enclosure  

Microsoft Academic Search

Numerical computations were carried out to clarify the effect of Kelvin force on the flow of water in a vertical cylindrical enclosure heated from below and cooled from above under a vertical magnetic field gradient. Since the Kelvin force that is produced by the magnetic field gradient depends on the position and the size of a circular electric coil, the

Masato Akamatsu; Mitsuo Higano; Yoshio Takahashi; Hiroyuki Ozoe

2005-01-01

178

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

PubMed Central

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

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

2009-01-01

179

Trehalose levels and survival ratio of freeze-tolerant versus freeze-sensitive yeasts.  

PubMed Central

Five freeze-tolerant yeast strains suitable for frozen dough were compared with ordinary commercial bakers' yeast. Kluyveromyces thermotolerans FRI 501 cells showed high survival ability after freezing when their resting cells were fermented for 0 to 180 min in modified liquid medium, and they grew to log and stationary phases. Among the freeze-tolerant strains of Saccharomyces cerevisiae, FRI 413 and FRI 869 showed higher surviving and trehalose-accumulating abilities than other S. cerevisiae strains, but were affected by a prolonged prefermentation period and by growth phases. The freeze tolerance of the yeasts was, to some extent, associated with the basal amount of intracellular trehalose after rapid degradation at the onset of the prefermentation period. In the freeze-sensitive yeasts, the degree of hydrolysis of trehalose may thus be affected by the kind of saccharide, unlike in freeze-tolerant yeasts.

Hino, A; Mihara, K; Nakashima, K; Takano, H

1990-01-01

180

Clinimetrics of freezing of gait.  

PubMed

The clinical assessment of freezing of gait (FOG) provides great challenges. Patients often do not realize what FOG really is. Assessing FOG is further complicated by the episodic, unpredictable, and variable presentation, as well as the complex relationship with medication. Here, we provide some practical recommendations for a standardized clinical approach. During history taking, presence of FOG is best ascertained by asking about the characteristic feeling of "being glued to the floor." Detection of FOG is greatly facilitated by demonstrating what FOG actually looks like, not only to the patient but also to the spouse or other carer. History taking further focuses on the specific circumstances that provoke FOG and on its severity, preferably using standardized questionnaires. Physical examination should be done both during the ON and OFF state, to judge the influence of treatment. Evaluation includes a dedicated "gait trajectory" that features specific triggers to elicit FOG (gait initiation; a narrow passage; dual tasking; and rapid 360 degrees axial turns in both directions). Evaluating the response to external cues has diagnostic importance, and helps to determine possible therapeutic interventions. Because of the tight interplay between FOG and mental functions, the evaluation must include cognitive testing (mainly frontal executive functions) and judgment of mood. Neuroimaging is required for most patients in order to detect underlying pathology, in particular lesions of the frontal lobe or their connections to the basal ganglia. Various quantitative gait assessments have been proposed, but these methods have not proven value for clinical practice. PMID:18668628

Snijders, Anke H; Nijkrake, Maarten J; Bakker, Maaike; Munneke, Marten; Wind, Carina; Bloem, Bastiaan R

2008-01-01

181

A Generalized Correlation for Heat and Mass Transfer in Freezing, Drying, Frying, and Freeze Drying  

Microsoft Academic Search

Experiments on air freezing, deep frying, freeze drying, and air drying on similar samples of 12 mm slice of potato were carried out. The temperature change with time was measured at three locations across the thickness of the potato. All the measurements done on frying, freeze-drying, and air-drying showed the existence of a moving interface that recedes towards the center of

Mohammed Farid; Sally Butcher

2003-01-01

182

Glutathione Protects Lactobacillus sanfranciscensis against Freeze-Thawing, Freeze-Drying, and Cold Treatment  

Microsoft Academic Search

Lactobacillus sanfranciscensis DSM20451 cells containing glutathione (GSH) displayed significantly higher resistance against cold stress induced by freeze-drying, freeze-thawing, and 4°C cold treatment than those without GSH. Cells containing GSH were capable of maintaining their membrane structure intact when exposed to freeze-thawing. In addition, cells containing GSH showed a higher proportion of unsaturated fatty acids in cell membranes upon long-term cold

Juan Zhang; Guo-Cheng Du; Yanping Zhang; Xian-Yan Liao; Miao Wang; Yin Li; Jian Chen

2010-01-01

183

Viability of mass algal cultures preserved by freezing and freeze-drying  

Microsoft Academic Search

The microalgae Chaetoceros sp. and Phaeodactylum tricornutum were grown in semicontinuous 15 1 cultures, a volume commonly used for mid-scale inocula in aquacultural practices. The daily yields were concentrated and stored by freezing and freeze-drying for up to 1 month. After slow or fast freezing without the protective agents glycerol or Me2SO, neither of the microalgae was capable of active

Beatriz Cordero; Domenico Voltolina

1997-01-01

184

Soil macroaggregate dynamics in a mountain spatial climate gradient  

Microsoft Academic Search

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

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

2010-01-01

185

Surface freezing of n-octane nanodroplets  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

186

Steam Consumption Reduction by Eutectic Freeze Crystallization.  

National Technical Information Service (NTIS)

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 fact...

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

1985-01-01

187

Cell-encapsulating droplet formation and freezing  

NASA Astrophysics Data System (ADS)

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

Ryoun Youn, Jae; Seok Song, Young

2012-09-01

188

Energies of freezing and frost desiccation.  

PubMed

A stable cellulose paper system was studied to relate water distribution data, as obtained previously from plant tissues, to the analysis of freezing energy. Water distribution data for the cellulose system were obtained by several techniques and were coordinated with calorimetric data. The effect of the cellulose system on the latent heat of freezing was evaluated to estimate activation energies as functions of the amount of associated liquid water. Similar activation energies of water phase transitions in critical plant tissue systems may be heritable characteristics that affect freezing stress. Adhesion energy, that develops between ice and hydrophilic polymer systems as they compete for liquid water in a complex interface, was suggested as one possible source of freezing stress. This does not occur in frost desiccation. PMID:16658785

Olien, C R

1974-05-01

189

Passive freeze protection for solar collectors  

Microsoft Academic Search

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

L. W. Bickle

1975-01-01

190

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.)

191

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

PubMed Central

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

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

1996-01-01

192

Freeze Drying of Foods for the Armed Services.  

National Technical Information Service (NTIS)

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

J. M. Tuomy

1971-01-01

193

Simulation and application of GPR in Artificial Freezing Engineering  

Microsoft Academic Search

In Artificial Freezing Engineering(AFE), the distribution of freezing soil and its defects are important to engineering safety. Based on relative permittivity measured by vector network analyzer, electromagnetic models of artificial freezing walls were made. Then Ground Penetrating Radar (GPR) exploration of AFE was simulated by Time Domain Finite Element Method (TD-FEM) coupled with freezing temperature calculation. GPR were also used

Song Lei; Zhang Xiaojun; Li Haipeng; Zhang Houquan

2010-01-01

194

A new freeze casting technique for ceramics  

NASA Astrophysics Data System (ADS)

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

Araki, Kiyoshi

195

Effect of freezing rate and dendritic ice formation on concentration profiles of proteins frozen in cylindrical vessels.  

PubMed

The process of freezing protein solutions can perturb the conformation of the protein and potentially lead to aggregate formation during long-term storage in the frozen state. Radial macroscopic freeze concentration and temperature profiles for bovine serum albumin (BSA) solutions in small cylindrical stainless steel vessels were determined for various freezing rates. The measured concentrations of both BSA and immunoglobulin G2, as well as trehalose in sampled ice sections, increased by up to twofold to threefold toward the bottom and radial center for slow freezing rates produced in stagnant air freezers. The concentration and temperature profiles result in density gradients that transport solutes by convective flow. For faster external cooling by either forced convection of air or a liquid coolant, the increased freezing rate raised the ice front velocity resulting in enhanced dendritic ice growth. The ice trapped the solutes more effectively before they were removed from the ice front by diffusion and convection, resulting in more uniform solute concentration profiles. The dynamic temperature profiles from multiple radial thermocouples were consistent with the independently measured freeze concentration profiles. The ability to control the protein concentration profile in the frozen state offers the potential to improve stability of protein in long-term frozen storage. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:1316-1329, 2011. PMID:24081467

Rodrigues, Miguel A; Miller, Maria A; Glass, Matt A; Singh, Satish K; Johnston, Keith P

2011-04-01

196

Modelling the Bicoid gradient.  

PubMed

Morphogen gradients provide embryonic tissues with positional information by inducing target genes at different concentration thresholds and thus at different positions. The Bicoid morphogen gradient in Drosophila melanogaster embryos has recently been analysed quantitatively, yet how it forms remains a matter of controversy. Several biophysical models that rely on production, diffusion and degradation have been formulated to account for the observed dynamics of the Bicoid gradient, but no one model can account for all its characteristics. Here, we discuss how existing data on this gradient fit the various proposed models and what aspects of gradient formation these models fail to explain. We suggest that knowing a few additional parameters, such as the lifetime of Bicoid, would help to identify and develop better models of Bicoid gradient formation. PMID:20570935

Grimm, Oliver; Coppey, Mathieu; Wieschaus, Eric

2010-07-01

197

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

PubMed Central

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

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

2010-01-01

198

Freezing and Freeze-Drying of Serratia Marcescens Suspended in Sodium Chloride.  

National Technical Information Service (NTIS)

Studies were made of the effects of NaCl upon the survival of Serratia marcescens after freezedrying or freeze-thawing. Freeze-dried cells showed lowest survival in the presence of 5% NaCl; higher and lower concentrations yielded higher recovery levels. C...

L. Zimmerman

1964-01-01

199

An Improved Microscope Stage for Direct Observation of Freezing and Freeze Drying  

Microsoft Academic Search

A microscope stage for observation of freezing and freeze drying is described. The stage uses thermoelectric (Peltier) heaters configured in two stages, with circulating fluid as a heat sink on the high temperature side. Lowest attainable sample temperature is about -47°C. Principal advantages of this system are closed-loop control of stage temperature, rapid response to changes in temperature set point,

Steven L. Nail; Lih-Min Her; Christopher P. B. Proffitt; Lisa L. Nail

1994-01-01

200

Investigations on Freezing and Freeze-Drying of Selected Fruits and Vegetables.  

National Technical Information Service (NTIS)

Investigations were made on the mode of invasion of fruit and vegetable tissue by ice and the changes produced by freezing and thawing and freeze-drying of the tissues as well as rehydration evaluations. In general three methods of exploring the effects o...

B. J. Luyet

1968-01-01

201

Resistance to freezing and freeze-drying storage processes of potential probiotic bifidobacteria  

Microsoft Academic Search

The resistance to freezing at -135 °C and freeze-drying of potentially probiot- ic bifidobacteria strains isolated from human habitat and from commercial probiotic prod- ucts already present in the Italian market were tested. The analysis was conducted in two different cryoprotectives, sucrose and skim milk. The strains of Bifidobacterium animalis, the only species found in the commercial probiotic product, were

M. MODESTO; P. MATTARELLI; B. BIAVATI

2004-01-01

202

Freezing of Lennard-Jones-type fluids  

SciTech Connect

We put forward an approximate method to locate the fluid-solid (freezing) phase transition in systems of classical particles interacting via a wide range of Lennard-Jones-type potentials. This method is based on the constancy of the properly normalized second derivative of the interaction potential (freezing indicator) along the freezing curve. As demonstrated recently it yields remarkably good agreement with previous numerical simulation studies of the conventional 12-6 Lennard-Jones (LJ) fluid [S.A.Khrapak, M.Chaudhuri, G.E.Morfill, Phys. Rev. B 134, 052101 (2010)]. In this paper, we test this approach using a wide range of the LJ-type potentials, including LJ n-6 and exp-6 models, and find that it remains sufficiently accurate and reliable in reproducing the corresponding freezing curves, down to the triple-point temperatures. One of the possible application of the method--estimation of the freezing conditions in complex (dusty) plasmas with ''tunable'' interactions--is briefly discussed.

Khrapak, Sergey A. [Max-Planck-Institut fuer Extraterrestrische Physik, D-85741 Garching (Germany); Joint Institute for High Temperatures, 125412 Moscow (Russian Federation); Chaudhuri, Manis; Morfill, Gregor E. [Max-Planck-Institut fuer Extraterrestrische Physik, D-85741 Garching (Germany)

2011-02-07

203

Freeze-stable sialidase activity in human leucocytes: substrate specificity, inhibitor susceptibility, detergent requirements and subcellular localization.  

PubMed Central

Human leucocytes contain a freeze-stable sialidase (neuraminidase; EC 3.2.1.18) activity in addition to the better-characterized lysosomal freeze-labile enzyme. In order to discriminate between the sialidase activities detected with the synthetic fluorimetric substrate 4-methylumbelliferyl-alpha-D-N-acetylneuraminic acid (MU-Neu5Ac), different tritiated sialoglycoconjugate substrates were prepared. Using this sensitive radioactive assay system, leucocyte sialidase activity towards glycoproteins was shown to be labile to repeated freeze-thawing, but a Triton-stimulated activity towards gangliosides was entirely freeze-stable. Assay conditions were optimized for this freeze-stable ganglioside sialidase activity. Subcellular fractionation of mononuclear leucocytes (MNLs) on Percoll-density gradients showed that this ganglioside sialidase activity was entirely associated with the plasma membrane. Study of the detergent requirements showed that MNLs also demonstrated ganglioside sialidase activity when sodium cholate was present in place of Triton. Cholate-stimulated ganglioside sialidase activity was found to be entirely freeze-stable and localized at the plasma membrane. Studies on whole homogenates of MNLs demonstrated that the Triton-stimulated and cholate-stimulated activities showed similar acidic pH optima at < or = 3.9 and were both strongly inhibited by 2-deoxy-2,3-didehydro-N-acetylneuraminic acid and Cu2+, but not by free N-acetylneuraminic acid, N-(4-nitrophenyl)oxamic acid or heparan sulphate. These results suggest that human MNLs contain, in addition to the lysosomal freeze-labile sialidase, a single sialidase activity which is freeze-stable, ganglioside-specific, plasma membrane-associated and stimulated both by Triton and by cholate.

Waters, P J; Corfield, A P; Eisenthal, R; Pennock, C A

1994-01-01

204

Stereo transparency and the disparity gradient limit  

NASA Technical Reports Server (NTRS)

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

McKee, Suzanne P.; Verghese, Preeti

2002-01-01

205

Freeze thaw cycles in Toronto, Canada in a changing climate  

NASA Astrophysics Data System (ADS)

Freeze thaw cycles are examined in Toronto Canada. Using data from 1960 to 1989 for three Toronto area weather stations, trends in freeze thaw activity, the relationship to mean monthly temperature and projections of freeze thaw activity are examined. For downtown Toronto the annual frequency of freeze thaw cycles is decreasing significantly, most notably in the shoulder months of October and April. At the Pearson International Airport and the Toronto Island Airport similar annual trends were not found, however there was evidence of decreased freeze thaw activity in April and October. Polynomial curve fitting provided functional relationships between mean monthly temperature and freeze thaw activity. These relationships enabled the assessment of freeze thaw activity under synthetic warming conditions. The results of this analysis show that the warming of the magnitude typically projected for the rest of this century will not likely generate a significant change in the freeze thaw activity although there are indications that the freeze thaw season will contract.

Ho, E.; Gough, W. A.

2006-01-01

206

Vertical bounce of two vertically aligned balls  

NASA Astrophysics Data System (ADS)

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

Cross, Rod

2007-11-01

207

Mobilization and rupture of LNAPL ganglia during freeze-thaw: two-dimensional cell experiments.  

PubMed

Experiments were conducted on dodecane at residual saturation (21-26%) in a two-dimensional water-saturated glass bead cell (0.5 mm diameter)--to simulate light nonaqueous phase liquid (LNAPL) trapped below the water table--subject to controlled freeze-thaw cycles. The experiments reveal substantial remobilization and rupture of LNAPL ganglia during freeze-thaw, especially during the first few cycles. This includes the detachment and upward mobilization of LNAPL from larger ganglia during upward propagation of the freezing front; the formation of numerous subsinglet ganglia during this transport process, and their entrapment in ice; and the coalescence of such small ganglia during thawing, to form larger singlets. Theoretical calculations suggest that the LNAPL redistribution is caused by large freezing-induced pressure gradients, of up to 6 orders of magnitude higher than the water-LNAPL interfacial (capillary) pressure. The findings have important implications for the understanding and remediation of LNAPLs in cold climate regions. PMID:18754462

Niven, Robert K; Singh, Kamaljit

2008-08-01

208

Vertical axis wind turbines  

DOEpatents

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

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

2011-03-08

209

Ultrastructural study of normal rat glomeruli by the quick-freezing and deep-etching method.  

PubMed

The ultrastructural features of isolated normal rat glomeruli were investigated using a new splitting technique and the quick-freezing and deep-etching (QF-DE) method. Examinations were also made of in vivo normal rat glomeruli by the QF-DE method to visualize the glomeruli under near natural conditions. Freeze-fractured capillary loops were observed from the capillary lumen or the urinary space. Foot processes were found to be freeze-fractured horizontally, obliquely or vertically to the glomerular basement membrane (GBM), and a glomerular slit diaphragm, which consisted of sheet-like, ladder-like and zipper-like substructures, was clearly identified. The GBM was classified into three zones, which might correspond to those seen in ultrathin sections, including the lamina densa and laminae rarae externa and interna. The lamina densa was composed of a meshwork filled with fine particles, which might represent products of insoluble proteins. In the laminae rarae, filamentous structures consisting of irregular networks could be observed connecting glomerular endothelial or epithelial cells with the lamina densa. Furthermore, the above findings were obtained from investigations at various consecutive levels of freeze-fractured capillary loops from various angles. The three-dimensional ultrastructure of the glomeruli could be demonstrated at high resolution by the QF-DE method. PMID:1774840

Hora, K

1991-09-01

210

Effects of drop freezing on microphysics of an ascending cloud parcel under biomass burning conditions  

NASA Astrophysics Data System (ADS)

There is some evidence that the initiation of warm rain is suppressed in clouds over regions with vegetation fires. Thus, the ice phase becomes important as another possibility to initiate precipitation. Numerical simulations were performed to investigate heterogeneous drop freezing for a biomass-burning situation. An air parcel model with a sectional two-dimensional description of the cloud microphysics was employed with parameterizations for immersion and contact freezing which consider the different ice nucleating efficiencies of various ice nuclei. Three scenarios were simulated resulting to mixed-phase or completely glaciated clouds. According to the high insoluble fraction of the biomass-burning particles drop freezing via immersion and contact modes was very efficient. The preferential freezing of large drops followed by riming (i.e. the deposition of liquid drops on ice particles) and the evaporation of the liquid drops (Bergeron-Findeisen process) caused a further decrease of the liquid drops' effective radius in higher altitudes. In turn ice particle sizes increased so that they could serve as germs for graupel or hailstone formation. The effects of ice initiation on the vertical cloud dynamics were fairly significant leading to a development of the cloud to much higher altitudes than in a warm cloud without ice formation.

Diehl, K.; Simmel, M.; Wurzler, S.

211

Heat transfer coefficient of cryotop during freezing.  

PubMed

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

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

2013-01-01

212

Gradient Estimation Revitalized  

Microsoft Academic Search

We investigate the use of a Fourier-domain derivative error kernel to quantify the error incurred while estimating the gradient of a function from scalar point samples on a regular lattice. We use the error kernel to show that gradient reconstruction quality is significantly enhanced merely by shifting the reconstruction kernel to the centers of the principal lattice directions. Additionally, we

Usman R. Alim; Torsten Möller; Laurent Condat

2010-01-01

213

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

214

Measuring freezing tolerance: electrolyte leakage and chlorophyll fluorescence assays.  

PubMed

Quantitative assessment of freezing tolerance is essential to unravel plant adaptations to cold temperatures. Not only the survival of whole plants but also impairment of detached leaves after a freeze-thaw cycle can be used to accurately quantify plant freezing tolerance in terms of LT50 values. Here we describe two methods to determine the freezing tolerance of detached leaves using different physiological parameters. Firstly, we illustrate how to assess the integrity of (predominantly) the plasma membrane during freezing using an electrolyte leakage assay. Secondly, we provide a chlorophyll fluorescence imaging protocol to determine the freezing tolerance of the photosynthetic apparatus. PMID:24852625

Thalhammer, Anja; Hincha, Dirk K; Zuther, Ellen

2014-01-01

215

Measuring salt and freezing temperature on roads  

NASA Astrophysics Data System (ADS)

Practical monitoring of the amount of salt spread on the road surface for de-icing purposes is technically difficult, especially if it has to be done in a commercially viable way. Possible solutions to this problem are discussed. As it has become customary to refer to the freezing temperature of a salted road, the physical meaning of such a temperature is scrutinised. It turns out that the meaning and the definition of freezing temperature are not clear, and that it also does not have the significance that is often associated with it. Some experimental results of salt measurements on a road are presented.

Turunen, Markus

1997-03-01

216

Freezing Characteristics of Molding Sand with Water by Cold Air Flow for Freeze Mold  

NASA Astrophysics Data System (ADS)

This paper reports the freezing characteristics of sand molded with "the freeze mold method". The freeze mold method is the casting process where little water is added to cast sand then they are frozen and become harden as a mold. Instead of using organic hardener, this molding technology possibly reduces resources and environment loading. We aimed at the practical application of the freeze mold method and chose cold airflow as the medium taking heat away from the mold. At first the sand with water was filled into a rectangular container that is the test section. Then cold air flowed into the container. Consequently, the mold was cooled and frozen by the cold airflow. The freezing behavior of the sample by cold airflow was investigated experimentally under the conditions of added water amount, superficial velocity, inflow air temperature and fixed bed height. As a result, the freezing completion time becomes long as the added water amount increases. However, an increase in the added water amount doesn't influence the pressure loss of the test section so much. Moreover, the empirical equation was derived to predict the freezing completion time.

Horibe, Akihiko; Inaba, Hideo; Haruki, Naoto; Miyagawa, Yasunori

217

Thermal effect of temperature gradient in a field environment chamber served by displacement ventilation system in the tropics  

Microsoft Academic Search

The effect of vertical air temperature gradient on overall and local thermal comfort at different overall thermal sensations and room air temperatures (at 0.6m height) was investigated in a room served by displacement ventilation system. Sixty tropically acclimatized subjects performed sedentary office work for a period of 3h during each session of the experiment. Nominal vertical air temperature gradients between

W. J. Yu; K. W. D. Cheong; K. W. Tham; S. C. Sekhar; R. Kosonen

2007-01-01

218

Gradient Driven Fluctuations  

NASA Technical Reports Server (NTRS)

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

Cannell, David

2005-01-01

219

Vortex Formation in Vertically Stratified Protoplanetary Disks  

NASA Astrophysics Data System (ADS)

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

Stewart, Glen R.

2013-10-01

220

7 CFR 58.638 - Freezing the mix.  

Code of Federal Regulations, 2010 CFR

...false Freezing the mix. 58.638 Section...Continued) AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing Practices), DEPARTMENT...UNDER THE AGRICULTURAL MARKETING ACT OF 1946 AND THE...638 Freezing the mix. After the...

2010-01-01

221

7 CFR 58.638 - Freezing the mix.  

Code of Federal Regulations, 2010 CFR

...2009-01-01 false Freezing the mix. 58.638 Section 58.638 Agriculture...Agriculture (Continued) AGRICULTURAL MARKETING SERVICE, DEPARTMENT OF AGRICULTURE...Procedures § 58.638 Freezing the mix. After the mix enters the...

2009-01-01

222

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

223

Unitarity Constraints on Asymmetric Freeze-In  

SciTech Connect

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

Hook, Anson; /SLAC

2011-08-15

224

Polybutylene pipe freeze/thaw reliability testing  

SciTech Connect

This paper discusses the ability of polybutylene pipe to withstand repeated freezing and thawing. The test apparatus, test procedure, list of chronological events, and results are discussed. Polybutylene piping has potential use in active solar heating systems and integral-collector-storage systems.

Farrington, R.B.

1987-04-01

225

Cryogenic Pipe Freezing - A Theoretical Model.  

National Technical Information Service (NTIS)

A theoretical simplified model for cryogenic pipe freezing, which is based on a steady-state approximation, has been developed in this work. A comparison with experimental results shows a relatively good agreement with the heat flux data obtained from dir...

H. Tinoco

1988-01-01

226

Global Annual Freezing and Thawing Indices  

NSDL National Science Digital Library

The National Snow and Ice Data Center provide these data showing the "cumulative number of degree-days when air temperatures are below and above zero degrees Celsius." Two data files, one each for the freezing and thaw data, and a readme file are available. A Fortran program is provided in the data documentation to read the data that are in flat binary format.

227

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

228

Freezing, Thawing, and Packaging Cells for Transport  

PubMed Central

Cultured mammalian cells are used extensively in cell biology studies. It requires a number of special skills in order to be able to preserve the structure, function, behavior, and biology of the cells in culture. This video describes the basic skills required to freeze and store cells and how to recover frozen stocks.

Ricardo, Richard; Phelan, Katy

2008-01-01

229

Melting, freezing, and coalescence of gold nanoclusters  

Microsoft Academic Search

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

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

1997-01-01

230

Effects of Repeated Freezing on Paper Strength.  

National Technical Information Service (NTIS)

The report describes an investigation into the effects of repeated freezing on paper strength. Six different papers from the Swedish National Testing Institute's collection of tested paper from the period 1920-1921 were chosen. Three papers made of rag pu...

M. Antonsson M. L. Samuelsson

1996-01-01

231

Device and method for determining freezing points  

NASA Technical Reports Server (NTRS)

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

Mathiprakasam, Balakrishnan (Inventor)

1986-01-01

232

The SENSITIVE TO FREEZING2 Gene, Required for Freezing Tolerance in Arabidopsis thaliana, Encodes a ?-Glucosidase  

PubMed Central

The sensitive to freezing2-1 (sfr2-1) mutation causes freezing sensitivity in Arabidopsis thaliana. By mapping, transgenic complementation, and sequencing, sfr2-1 was revealed to be a mutation in gene At3g06510. A new knockout allele was obtained, and its identical freezing-sensitive phenotype confirmed that the SFR2 gene product is essential for freezing tolerance. Transcription of SFR2 was observed to be constitutive rather than stress inducible and was distributed throughout most aerial tissues. SFR2 encodes a protein homologous to family 1 glycosyl hydrolases (?-glycosidases), but the predicted AtSFR2 protein is divergent from all other family 1 ?-glycosidases of Arabidopsis, showing closer homology to the sequences of several ?-glycosidases from thermophilic archea and bacteria. After purification from a heterologous expression system, AtSFR2 displayed a specific hydrolytic activity against ?-d-glucosides.

Thorlby, Glenn; Fourrier, Nicolas; Warren, Gareth

2004-01-01

233

Ultrasonic emissions from conifer xylem exposed to repeated freezing  

Microsoft Academic Search

Ultrasonic emission measurements enable the analysis of xylem cavitation induced by drought and freeze–thaw events. Several studies have indicated that ultrasonic acoustic emissions (UAE) in conifers occur upon freezing and not upon thawing, although classical theory has postulated gas bubble formation during freezing and cavitation during thawing.We analyzed the pattern and quality of freeze–thaw-induced UAE in seven conifers (Abies alba,

Stefan Mayr; Verena Zublasing

2010-01-01

234

Real-time frame-freezing detection system evaluation  

Microsoft Academic Search

This paper describes implementation and evaluation of real-time system for frame-freezing detection in video signals. Frame freezing effect is manifested in cut scenes in video on end-user display devices, which significantly reduces visual quality. In order to efficiently monitor and detect this effect in multimedia systems we propose a realtime frame-freezing detection system that incorporates previously developed frame-freezing detection algorithm.

Darko Lulic; Zoran Marceta; Nikola Vranic; Vladimir Zlokolica; Miodrag Temerinac

2011-01-01

235

Aquaporin-mediated improvement of freeze tolerance of Saccharomyces cerevisiae is restricted to rapid freezing conditions.  

PubMed

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

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

2004-06-01

236

Effect of process conditions on recovery of protein activity after freezing and freeze-drying  

Microsoft Academic Search

The objective of this research was to gain a better understanding of the degree to which recovery of activity of model proteins after freeze-drying can be maximized by manipulation of freeze-dry process conditions in the absence of protective solutes. Catalase, ?-galactosidase and lactate dehydrogenase (LDH) were used as model proteins. All of the three proteins exhibited a concentration-dependent loss of

Shan Jiang; Steven L Nail

1998-01-01

237

Type of automatic gradienter  

NASA Astrophysics Data System (ADS)

Aiming at the requirement that some kinds of big dynamo- electric equipments such as a dam gate of hydro-power plant or a elevator have to keep their balance in the process of being lifted and dropped, a novel and precise gradienter with high resolution and short response time is presented in this article. In this gradienter, the respective hydraulic pressure method is adopted.

Li, Shaohui; He, Liang; Zhang, Gang; Zhang, Zhipeng

2000-05-01

238

Freezing in Parkinson's disease: a spatiotemporal motor disorder beyond gait.  

PubMed

Freezing of gait (FOG) is an incapacitating problem in Parkinson's disease that is difficult to manage therapeutically. We tested the hypothesis that impaired rhythm and amplitude control is a common mechanism of freezing which is also present during other rhythmic tasks. Therefore, we compared the occurrence and spatiotemporal profiles of freezing episodes during upper limb motion, lower limb motion, and FOG. Eleven freezers, 12 non-freezers, and 11 controls performed a rhythmic bilateral finger movement task. The triggering effect of movement speed, amplitude, and coordination pattern was evaluated. Regression slopes and spectral analysis addressed the spatial and temporal kinematic changes inherent to freezing episodes. The FOG Questionnaire score significantly predicted severity of upper limb freezing, present in 9 freezers, and of foot freezing, present in 8 freezers. Similar to gait, small-amplitude movements tended to trigger upper limb freezing, which was preceded by hastened movement and a strong amplitude breakdown. Upper limb freezing power spectra were broadband, including increased energy in the "freeze band" (3-8 Hz). Contrary to FOG, unilateral upper limb freezing was common and occurred mainly on the disease-dominant side. The findings emphasize that a core motor problem underlies freezing which can affect various movement effectors. This deficit may originate on the disease-dominant body side and interfere with amplitude and timing regulation during repetitive limb movements. These results may shift current thinking on the origins of freezing as being not exclusively a gait failure. PMID:22020744

Vercruysse, Sarah; Spildooren, Joke; Heremans, Elke; Vandenbossche, Jochen; Levin, Oron; Wenderoth, Nicole; Swinnen, Stephan P; Janssens, Luc; Vandenberghe, Wim; Nieuwboer, Alice

2012-02-01

239

Modification of physical properties of freeze-dried rice  

NASA Technical Reports Server (NTRS)

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

Huber, C. S.

1971-01-01

240

Avoid freeze-up of steam traps and their piping  

Microsoft Academic Search

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

OKeefe

1993-01-01

241

Factors Influencing Freezing of Supercooled Water in Tender Plants1  

Microsoft Academic Search

Seedlings of beans (Phaseolus vulgaris), corn (Zea mays), and tomatoes (Lycopersicon esculentum) were grown in the greenhouse and then exposed to controlled freezing conditions in a growth chamber. Variables were adjusted to determine the influence of plant water potential, freez- ing time, and external dew formation on the seedlings' susceptibility to frost injury. Freezing, detected visually and by release of

J. W. Cary

1970-01-01

242

Foam-Mat Freeze Drying of Egg White—Mathematical Modeling Part II: Freeze Drying and Modeling  

Microsoft Academic Search

Foam-mat freeze drying is one of the promising methods of drying, which utilizes advantages of both freeze drying and foam-mat drying. Egg white with its excellent foaming properties makes a suitable candidate for foam-mat freeze drying. Experiments were conducted to study foam-mat freeze drying of egg white, in an effort to determine the suitability of this method. Xanthan gum (XG)

Arun Muthukumaran; Cristina Ratti; Vijaya G. S. Raghavan

2008-01-01

243

Microstructure and adsorption properties of gelatinized-tapioca starch beads modified by freezing and a freeze-drying method  

Microsoft Academic Search

The effects of two freezing methods: slow freezing (SF) at -20°C for 24 hours, and quick freezing (QF) at -176°C for 5-10 min and three commercial brands of Golden Chef®, Special Sacoo® or Thaiworld® on moisture content, microstructure, porosity, total bulk volume, adsorption properties (initial adsorption, adsorption capacity and adsorption behaviour) and gel strength of freeze-dried-gelatinized tapioca starch beads (FDTB)

P. Rattanapitigorn; P. Raviyan; C. Khanongnuch; L. Ozimek

244

Subsurface temperatures and geothermal gradients on the North Slope, Alaska  

USGS Publications Warehouse

Geothermal gradients as interpreted from a series of high-resolution stabilized well-bore-temperature surveys from 46 North Slope, Alaska, wells vary laterally and vertically throughout the near-surface sediment (0-2,000 m). The data from these surveys have been used in conjunction with depths of ice-bearing permafrost, as interpreted from 102 well logs, to project geothermal gradients within and below the ice-bearing permafrost sequence. The geothermal gradients calculated from the projected temperature profiles are similar to the geothermal gradients measured in the temperature surveys. Measured and projected geothermal gradients in the ice-bearing permafrost sequence range from 1.5??C/100m in the Prudhoe Bay area to 5.1??C/100m in the National Petroleum Reserve in Alaska (NPRA).

Collett, Timothy, S.; Bird, Kenneth, J.; Magoon, Leslie, B.

1989-01-01

245

Vertical axis windmill  

SciTech Connect

A vertical axis windmill is described which involves a rotatable central vertical shaft having horizontal arms pivotally supporting three sails that are free to function in the wind like the main sail on a sail boat, and means for disabling the sails to allow the windmill to be stopped in a blowing wind.

Campbell, J.S.

1980-04-08

246

Vertical axis wind turbine  

Microsoft Academic Search

A Darrieus-type vertical axis wind turbine is disclosed which includes a vertically extending rotor tube mounted on a support structure with two or three rotor blades of troposkein configuration on the rotor tube for rotating the tube in response to wind energy and thereby drive a generator to produce electrical power. The turbine includes an erection hinge which permits assembly

Kutcher

1984-01-01

247

The effects of freeze drying and freeze drying additives on the prothrombin time and the international sensitivity index  

Microsoft Academic Search

AIM: To determine whether freezing, freeze drying protective additives, or freeze drying of plasma samples from patients on coumarin treatment and from normal individuals affects prothrombin times or the international sensitivity index (ISI) calibration. METHODS: The effect of the addition of the protective additives singly and combined on the prothrombin time of coumarin samples and normal samples before and after

L. Poller; M. Keown; S. A. Shepherd; C. R. Shiach; S. Tabeart

1999-01-01

248

Depth Estimates from Ratios of Gravity, Geoid, and Gravity Gradient Anomalies.  

National Technical Information Service (NTIS)

The utility of combining geoid, gravity, and vertical gravity gradient measurements for delineation of causative mass anomalies is explained and compared with spatial and spectral methods for depth estimation. Depth rules for various source geometries are...

C. Bowin E. Scheer W. Smith

1986-01-01

249

Freeze-on and melt-out on a channelized bed  

NASA Astrophysics Data System (ADS)

The entrainment and release of subglacial sediments are sensitive to changes in both thermal and mechanical forcing. Seepage flows that exchange pore fluids with channelized drainage systems are driven by gradients in pore pressure that control the heterogeneous distribution of effective stress at the glacier bed. The variations in frictional dissipation that result modify the heat balance so that mechanical and thermal heterogeneities are coupled. This can cause freeze-on and melt-out to occur simultaneously on different portions of an initially uniform bed. I explore these thermo-mechanical, drainage--entrainment feedbacks and their implications for the development of subglacial landforms.

Rempel, A. W.

2013-12-01

250

Pan-Arctic Freeze\\/Thaw Algorithm Development Using AMSR-E Data and Satellite Remote Sensing Technique  

Microsoft Academic Search

We have developed an algorithm to determine freeze\\/thaw state in the pan-Arctic region using microwave brightness temperature and surface air temperature. We estimated emissivity using AMSR-E brightness temperature and ground air temperature. We found a strong linear relationship between AMSR-E surface emissivities and surface temperature at 6.9 and 36.5 GHz horizontal and vertical polarizations over arctic land surfaces. The results

M. L. Nirala; J. Kimball; S. Running; K. McDonald; W. Oechel; E. Njoku

2005-01-01

251

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

PubMed

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

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

1980-03-28

252

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

253

Freeze-out parameters: lattice meets experiment.  

PubMed

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

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

2013-08-01

254

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

255

Fundamentals of spray freezing of instant coffee  

Microsoft Academic Search

The freezing of single 2mm diameter droplets of coffee solution in cold moving air down to ?15°C has been studied for 10–50wt.% coffee solutions in a novel temperature monitoring apparatus and in a similar device installed within a nuclear magnetic resonance (NMR) spectrometer. Heat transfer measurements and modelling confirmed that droplet internal temperatures were almost uniform (low Biot number regime),

C. S. MacLeod; J. A. McKittrick; J. P. Hindmarsh; M. L. Johns; D. I. Wilson

2006-01-01

256

Drying a tuberculosis vaccine without freezing  

Microsoft Academic Search

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

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

2007-01-01

257

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

258

Atmospheric freeze drying assisted by power ultrasound  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

259

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

260

Radioluminescence and scintillation results of horizontal gradient freeze grown aliovalently-doped CeBr3.  

SciTech Connect

Strengthening the crystal lattice of lanthanide halides, which are brittle, anisotropic, ionic crystals, may prove to increase the availability and ruggedness of these scintillators for room-temperature gamma-ray spectroscopy applications. Eight aliovalent dopants for CeBr{sub 3} were explored in an effort to find the optimal aliovalent strengthening agent. Eight dopants, CaBr{sub 2}, SrBr{sub 2}, BaBr{sub 2}, ZrBr{sub 4}, HfBr{sub 4}, ZnBr{sub 2}, CdBr[sub 2}, and PbBr{sub 2}, were explored at two levels of doping, 500 and 1000 ppm. From each ingot, samples were harvested for radioluminescence spectrum measurement and scintillation testing. Of the eight dopants explored, only BaBr{sub 2} and PbBr{sub 2} were found to clearly decrease total light yield. ZnBr{sub 2} and CdBr{sub 2} dopants both affected the radioluminescence emission spectrum very little as compared to undoped CeBr{sub 3}. HfBr{sub 2}- and ZnBr{sub 4}-doped CeBr{sub 3} exhibited the highest light yields.

Linnick, C.; Harrison, Mark J.; Doty, F. Patrick; McGregor, D. S.; McCreary, M.; Brinton, S.; Montag, B.

2008-11-01

261

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

262

Electron temperature gradient turbulence.  

PubMed

The first toroidal, gyrokinetic, electromagnetic simulations of small scale plasma turbulence are presented. The turbulence considered is driven by gradients in the electron temperature. It is found that electron temperature gradient (ETG) turbulence can induce experimentally relevant thermal losses in magnetic confinement fusion devices. For typical tokamak parameters, the transport is essentially electrostatic in character. The simulation results are qualitatively consistent with a model that balances linear and secondary mode growth rates. Significant streamer-dominated transport at long wavelengths occurs because the secondary modes that produce saturation become weak in the ETG limit. PMID:11136051

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

2000-12-25

263

Electron Temperature Gradient Turbulence  

SciTech Connect

The first toroidal, gyrokinetic, electromagnetic simulations of small scale plasma turbulence are presented. The turbulence considered is driven by gradients in the electron temperature. It is found that electron temperature gradient (ETG) turbulence can induce experimentally relevant thermal losses in magnetic confinement fusion devices. For typical tokamak parameters, the transport is essentially electrostatic in character. The simulation results are qualitatively consistent with a model that balances linear and secondary mode growth rates. Significant streamer-dominated transport at long wavelengths occurs because the secondary modes that produce saturation become weak in the ETG limit.

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

2000-12-25

264

HIGH GRADIENT INDUCTION ACCELERATOR  

SciTech Connect

A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is stimulated by the desire for compact flash x-ray radiography sources. Research describing an extreme variant of this technology aimed at proton therapy for cancer will be described. Progress in applying this technology to several applications will be reviewed.

Caporaso, G J; Sampayan, S; Chen, Y; Blackfield, D; Harris, J; Hawkins, S; Holmes, C; Krogh, M; Nelson, S; Nunnally, W; Paul, A; Poole, B; Rhodes, M; Sanders, D; Selenes, K; Sullivan, J; Wang, L; Watson, J

2007-06-21

265

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.

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

2011-01-01

266

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

SciTech Connect

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

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

2006-03-15

267

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

268

Paroxysmal Vertical Ocular Dyskinesia.  

National Technical Information Service (NTIS)

Paroxysmal vertical ocular dyskinesia of a previously undescribed nature is reported in a 42-year old woman with demyelinating disease, who was affected with a myelopathy, bilateral amblyopia, and a modified sylvian aqueduct syndrome. Electroencephalograp...

J. B. MacLean J. F. Sassin

1973-01-01

269

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

270

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

271

Glutathione protects Lactobacillus sanfranciscensis against freeze-thawing, freeze-drying, and cold treatment.  

PubMed

Lactobacillus sanfranciscensis DSM20451 cells containing glutathione (GSH) displayed significantly higher resistance against cold stress induced by freeze-drying, freeze-thawing, and 4 degrees C cold treatment than those without GSH. Cells containing GSH were capable of maintaining their membrane structure intact when exposed to freeze-thawing. In addition, cells containing GSH showed a higher proportion of unsaturated fatty acids in cell membranes upon long-term cold treatment. Subsequent studies revealed that the protective role of GSH against cryodamage of the cell membrane is partly due to preventing peroxidation of membrane fatty acids and protecting Na(+),K(+)-ATPase. Intracellular accumulation of GSH enhanced the survival and the biotechnological performance of L. sanfranciscensis, suggesting that the robustness of starters for sourdough fermentation can be improved by selecting GSH-accumulating strains. Moreover, the results of this study may represent a further example of mechanisms for stress responses in lactic acid bacteria. PMID:20208023

Zhang, Juan; Du, Guo-Cheng; Zhang, Yanping; Liao, Xian-Yan; Wang, Miao; Li, Yin; Chen, Jian

2010-05-01

272

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

273

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

274

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

SciTech Connect

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

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

1989-10-01

275

Movement and Vertical Coupling of Adiabatic Baroclinic Tropical Cyclones*.  

NASA Astrophysics Data System (ADS)

The vertical coupling and movement of an adiabatic baroclinic tropical cyclone (TC) are investigated through two numerical experiments in which the TC is affected by either a vertical environmental shear or a differential beta drift. In both cases, the initial response of the symmetric vortex is to tilt in the vertical. In response to the vertical tilt, a three-dimensional asymmetric circulation with a typical radius of 100 km develops within the TC core region. In addition, the wavenumber-one potential vorticity (PV) anomalies develop with positive anomalies downtilt (uptilt) above (below) the maximum PV level in order to maintain a balanced state between the thermal and dynamical fields. On a beta plane, in contrast to the beta gyres, the mesoscale asymmetric circulation is a pair of counterrotating inner gyres centered at the radius of maximum wind. As a result, the resulting three-dimensional mesoscale asymmetric circulation, not the penetration flow, plays an important role in the vertical coupling of adiabatic baroclinic vortices. In both cases, the TC motion is not simply due to the advection of the symmetric PV component by the asymmetric (ventilation) flow. The horizontal advection of the asymmetric PV anomalies by the symmetric cyclonic flow and the vertical PV advection associated with the asymmetric vertical motion also considerably contribute to the TC motion. The latter two processes also play a critical role in the vertical coupling of the baroclinic TC due to the presence of the vertical PV gradient.

Wu, Liguang; Wang, Bin

2001-07-01

276

Transverse gradients of azimuthal velocity in a global disk model of the Milky Way Galaxy  

Microsoft Academic Search

This work aims to estimate the vertical gradients in rotational velocity of\\u000aGalaxy. This is performed in the framework of a global thin disk model\\u000aapproximation. The predicted gradient values coincide with the observed\\u000avertical falloff in the Galaxy rotation curve. The gradient is estimated based\\u000aon a statistical analysis of trajectories of test bodies in the gravitational\\u000afield of

Joanna Ja?ocha; ?ukasz Bratek; Marek Kutschera; Piotr Skindzier

2010-01-01

277

Two-dimensional freezing criteria for crystallizing colloidal monolayers  

NASA Astrophysics Data System (ADS)

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 Löwen-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; Alsayed, Ahmed M.; Yodh, Arjun G.; Han, Yilong

2010-04-01

278

Two-dimensional freezing criteria for crystallizing colloidal monolayers.  

PubMed

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 Lowen-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. PMID:20423183

Wang, Ziren; Alsayed, Ahmed M; Yodh, Arjun G; Han, Yilong

2010-04-21

279

Nappe emplacement under lateral pressure gradient  

NASA Astrophysics Data System (ADS)

New thin viscous approximation is under development specifically targeted to model spontaneous initiation and tens of kilometers horizontal displacement of tectonic nappes. Nappes are few kilometers thing and tens of kilometers long rock units trusted towards foreland often preserving internal lithological consistency and laying at near horizontal position at the end of the emplacement. Significant shear stresses and deviation of principal stresses from vertical is required to explain this very peculiar strain localization style from mechanical point of view. There is also a need for the explanation of their common appearances in most collisional settings. Both pure shear thin sheet and flexural models kinematically eliminate nappes formation. Spreading viscous sheet models, such as used to model glaciers, are also not applicable as the direction of motion is upward, against gravity. The reason for this discrepancy is the hydrostatic pressure approximation of the gravity-driven spreading models. Actually, the thin sheet approximation is not sensitive to the assumptions made on pressure profile. Lateral non-lithostatic pressure gradient-driven viscous sheet model is appropriate for modeling of nappes. In turn, significant non-lithostatic pressure must be supported by flexural rigidity of overlying and underlying units. Lateral gradients of this non-lithostatic pressure are responsible for the significant shear stress and, therefore, deviation of principal stress from vertical.

Podladchikov, Yury; Schmalholz, Stefan

2014-05-01

280

Verticality in hydroelectric machines  

SciTech Connect

Everyone who erects a vertical hydroelectric machine makes an effort to put the machine together so that its elements are vertical. A plumb line (or its optical equivalent) is a practical starting point for aligning the stationary parts of the machine - the generator stator, turbine case, and bearings. This does not mean, though, that the machine parts must be in near-perfect vertical orientation for the machine to perform well. Verticality is sometimes over-emphasized when procedures are undertaken to achieve good machine alignment. If the generator rotor, the connecting shaft, and the turbine runner are centered in stationary parts that are well-aligned along the same axis angle, this angle can depart from true vertical by a significant amount without ill effect. Mechanical balance does not often play a large part in determining how well a generator rotor is centered in the air gap. Magnetic forces are much more important. This is why it is desirable to maintain air gap variations around the machine to less than 5 percent from the average. However, this is sometimes difficult, especially if bearing clearances are large.

O'Kelly, F.

1991-12-01

281

Freeze Tolerant Radiator for an Advanced EMU  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

282

A remote controlled freeze corer for sampling unconsolidated surface sediments  

Microsoft Academic Search

A new coring device is presented which allows the recovery of loose watery surface sediments and the water\\/sediment interface\\u000a byin situ freezing, resulting in well preserved samples. The instrument consists of a tripod with adjustable legs, a hydraulic system,\\u000a an insulated thermos (with two electrical pumps), and a wedge-shaped freeze box. Alcohol chilled with dry ice is the freezing\\u000a agent.

A. F. Lotter; I. Renberg; H. Hansson; R. Stöckli; M. Sturm

1997-01-01

283

A remote controlled freeze corer for sampling unconsolidated surface sediments  

Microsoft Academic Search

A new coring device is presented which allows the recovery of loose watery surface sediments and\\u000athe water\\/sediment interface by in situ freezing, resulting in well preserved samples. The instrument\\u000aconsists of a tripod with adjustable legs, a hydraulic system, an insulated thermos (with two\\u000aelectrical pumps), and a wedge-shaped freeze box. Alcohol chilled with dry ice is the freezing

A. F. Lotter; I. Renberg; H. Hansson; R. Stöckli; M. Sturm

1997-01-01

284

Monitoring Shallow Freeze and Thaw Processes Using High Frequency Surface Ground Penetrating Radar  

NASA Astrophysics Data System (ADS)

High frequency GPR (225-900 MHz) was used for the high resolution, non-invasive monitoring of freeze and thaw processes in the shallow subsurface (i.e., within 1.5 meters of the surface) at three sites with different soil types (sand, sandy loam and silt loam). Both common midpoint (CMP) gathers and constant offset reflection profiles were repeatedly done over 2 m transects at each site. CMP gathers were used to monitor direct ground wave propagation and determine vertical velocity profiles; reflection profiles were used to image reflectivity variations and observe near vertical reflection event traveltimes. Direct ground waves were significantly attenuated during the initial freezing process due to interference with short period reflections; modelling results indicate that this phenomenon occurs until the frozen surface layer exceeds 15 cm in thickness for 450 MHz data. Differences in shallow surface freezing rates between sites were inferred from the direct wave data. Direct wave velocities indicate that surface thawing occurred rapidly in late March even though snowpack melting commenced in early March. CMP velocity profiles show the progressive development of the frozen zone and indicate the presence of liquid water in this zone one week prior to the surface thaw. Reflection profiling monitored the development of a continuous reflection event interpreted to be the interface at the base of frozen zone. Significantly diminished reflectivity of stratigraphic interfaces was observed above this interface. Measured reflection event traveltimes indicate the deeper section underwent drainage after the shallow frozen zone development terminated the seasonal autumn recharge. In addition, reflection traveltime data also found the thaw recharge started one week prior to the surface thaw.

Steelman, C. M.; Endres, A. L.

2007-12-01

285

Toward fractional gradient elasticity  

NASA Astrophysics Data System (ADS)

The use of an extension of gradient elasticity through the inclusion of spatial derivatives of fractional order to describe the power law type of non-locality is discussed. Two phenomenological possibilities are explored. The first is based on the Caputo fractional derivatives in one dimension. The second involves the Riesz fractional derivative in three dimensions. Explicit solutions of the corresponding fractional differential equations are obtained in both cases. In the first case, stress equilibrium in a Caputo elastic bar requires the existence of a nonzero internal body force to equilibrate it. In the second case, in a Riesz-type gradient elastic continuum under the action of a point load, the displacement may or may not be singular depending on the order of the fractional derivative assumed.

Tarasov, Vasily E.; Aifantis, Elias C.

2014-05-01

286

The 630 nm MIG and the vertical neutral wind in the low latitude nighttime thermosphere  

Microsoft Academic Search

It is shown that large negative divergences (gradients) in the horizontal neutral wind in the equatorial thermosphere can support downward neutral winds in excess of 20 m\\/s. With attention to the meridional and vertical winds only, the pressure tendency equation is used to derive the expression Uz0 ? ??Uy \\/?y? H for the vertical wind Uz0 at the reference altitude

F. A. Herrero; J. W. Meriwether

1994-01-01

287

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

Microsoft Academic Search

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

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

2004-01-01

288

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

Microsoft Academic Search

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

M. W. Woo; A. S. Mujumdar

2010-01-01

289

Viscoelastic analysis of interaction between freezing wall and outer shaft wall in freeze sinking  

Microsoft Academic Search

In order to reasonably determine the external load of outer freezing shaft wall, it is necessary to conduct interaction study between frozen soil wall and outer shaft wall. First, based on the characteristic of three-stage compressive deformation of foam board, a relational expression of such radial deformations as frozen soil wall, outer shaft wall, and foam board is established; then

Yan-sen Wang; Zhi-jiang Yang; Wei-hao Yang

2009-01-01

290

Fabrication of porous ceramics by freeze-casting\\/freeze-drying. Final report, April 1991December 1992  

Microsoft Academic Search

Porous ceramics have many applications in the gas industry, including gas separation, filtration, catalyst supports and substrates, lightweight insulation, and burners. The report explores the fabrication of porous ceramics by a new approach involving the use of cryogenic processing techniques such as freeze-drying, to characterize the materials formed in this way, and to evaluate the potential of the techniques for

S. M. Johnson; M. I. Gusman

1993-01-01

291

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

292

Freezing and Melting, Precipitation Type, and Numerical Weather Prediction  

NSDL National Science Digital Library

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

Spangler, Tim

2002-01-01

293

A molecular dynamics study of freezing in a confined geometry  

NASA Technical Reports Server (NTRS)

The dynamics of freezing of a Lennard-Jones liquid in narrow channels bounded by molecular walls is studied by computer simulation. The time development of ordering is quantified and a novel freezing mechanism is observed. The liquid forms layers and subsequent in-plane ordering within a layer is accompanied by a sharpening of the layer in the transverse direction. The effects of channel size, the methods of quench, the liquid-wall interaction and the roughness of walls on the freezing mechanism are elucidated. Comparison with recent experiments on freezing in confined geometries is presented.

Ma, Wen-Jong; Banavar, Jayanth R.; Koplik, Joel

1992-01-01

294

A calorimeter to detect freezing in supercooled water droplets  

NASA Astrophysics Data System (ADS)

This apparatus suspends a 1 ?l water droplet on an ultraminiature thermistor and uses a Peltier cooling device to supercool the droplet. Electrical connections to the thermistor allow the temperature of the droplet to be constantly monitored, and they also permit direct electrical heating of the droplet after freezing has occurred. Deionized water droplets can be readily supercooled to temperatures of -20 °C before freezing, and repeated determinations of the freezing temperature for the same droplet are straightforward. The temperature characteristics of the phase change are very well defined, and the apparatus therefore permits many other investigations on the provocation of freezing in a supercooled droplet.

Harrison, R. G.; Lodge, B. N.

1998-11-01

295

Optical coherence tomography-based freeze-drying microscopy  

PubMed Central

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

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

2011-01-01

296

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

297

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

298

Vertical breast reduction.  

PubMed

The vertical approach to breast reduction surgery has achieved increasing popularity. The learning curve can be a problem for surgeons starting to incorporate vertical techniques into their practices; the medial pedicle approach is outlined in detail. Designing and creating the medial pedicle is straightforward and rotating it into position is easy. An elegant curve to the lower pole of the reduced breast can thus be created. Current concepts related to the skin brassiere, breast sutures, and the longevity of results are reviewed. It is important for the surgeon to understand that the skin resection pattern and the pedicle design are separate issues when discussing breast reduction surgery. PMID:20574477

Hall-Findlay, Elizabeth J

2004-08-01

299

Fundamental Boiling and RP-1 Freezing Experiments  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

300

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

PubMed

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

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

2012-11-20

301

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

302

Vertical axis windmill  

SciTech Connect

A vertical axis windmill has a blade pivotally connected to a rotatable support structure on an axis passing through its center of gravity which is arranged to lie forward of its aerodynamic center whereby the blade automatically swings outwardly and inwardly when moving on the windward and leeward sides respectively of the axis of rotation of said support means.

Zheug, Y.K.

1984-03-06

303

Vertical shaft windmill  

SciTech Connect

A vertical shaft has several equally spaced blades mounted thereon. Each blade consists of an inboard section and an outboard section skew hinged to the inboard section. The inboard sections automatically adjust their positions with respect to the fixed inboard sections with changes in velocity of the wind. This windmill design automatically governs the maximum rotational speed of shaft.

Grana, D.C.; Inge, S.V. Jr.

1983-11-15

304

Vertical shaft windmill  

NASA Technical Reports Server (NTRS)

A vertical shaft has several equally spaced blades mounted. Each blade consists of an inboard section and an outboard section skew hinged to the inboard section. The inboard sections automatically adjust their positions with respect to the fixed inboard sections with changes in velocity of the wind. This windmill design automatically governs the maximum rotational speed of shaft.

Grana, D. C.; Inge, S. V., Jr. (inventors)

1983-01-01

305

Improved vertical scanning interferometry  

Microsoft Academic Search

Vertical scanning interferometers are routinely used for the measurement of optical fiber connectors. There are increasing needs for measurements of such items as machined surfaces, contact lenses, paint texture, cell structure, and integrated circuit devices, to name a few. These structures have too much depth, or are too rough, to measure with standard interferometry methods. Phase- measurement interferometry methods are

Akiko Harasaki; Joanna Schmidt; James C. Wyant

2000-01-01

306

Developing Vertical File Resources.  

ERIC Educational Resources Information Center

Describes how to develop vertical file resources for school libraries. Discusses the importance of having primary sources that are not available in other formats; sources for obtaining materials, including the Internet and printed sources; how to organize the materials; providing access; and promoting the collection. (LRW)

Smallwood, Carol

1998-01-01

307

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

308

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.

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

2014-01-01

309

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

310

Rational design of an influenza subunit vaccine powder with sugar glass technology: Preventing conformational changes of haemagglutinin during freezing and freeze-drying  

Microsoft Academic Search

The development of a stable influenza subunit vaccine in the dry state was investigated. The influence of various carbohydrates, buffer types and freezing rates on the integrity of haemagglutinin after freeze-thawing or freeze-drying was investigated with a range of analytical and immunological methods. The use of fast freezing, Hepes buffer and carbohydrates (trehalose, inulin or dextran) as cryo- and lyoprotectants

J. P. Amorij; J. Meulenaar; W. L. J. Hinrichs; T. Stegmann; A. Huckriede; F. Coenen; H. W. Frijlink

2007-01-01

311

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

Microsoft Academic Search

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

G. Goldstein; F. Rada; A. Azocar

1985-01-01

312

Large ion concentration gradients below the equatorial F peak.  

NASA Technical Reports Server (NTRS)

Very large vertical and longitudinal gradients in the ion concentrations are observed below the F peak near the magnetic equator with the retarding potential analyzer on Ogo 6. Ion concentration 'bite outs' of up to a factor of 1000 are observed above 400 km. They appear to be associated with the bottomside of the nighttime F layer. The ion composition in the minima may contain large fractions of ions heavier than O(+) (e.g., NO(+) and Fe(+)). It is suggested that convective electric fields associated with spread F steepen the bottomside of the F layer and also introduce longitudinal irregularities in the vertical ion concentration profiles.

Hanson, W. B.; Sanatani, S.

1973-01-01

313

Stopping biological time: The freezing of living cells  

SciTech Connect

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

Mazur, P.

1987-01-01

314

Heat of Freezing and Melting of Sea Ice.  

National Technical Information Service (NTIS)

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

D. Anderson

1966-01-01

315

Evaluation of Human Sperm Function After Repeated Freezing and Thawing  

Microsoft Academic Search

Sperm storage via freezing has been useful for men who have difficulty masturbating during assisted reproductive tech- nology (ART) programs and before impotency caused by chemo- therapy, vasectomy, and other procedures. Studies were undertaken to evaluate the extent of cryoinjury to sperm after repeated freezing and thawing. The results showed that normozoospermic and oligo- zoospermic sperm survived after 3 repeated

ENOKA BANDULARATNE; ARIFF BONGSO

2002-01-01

316

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

317

Free(z)ing Degrees of Freedom in Skill Acquisition  

Microsoft Academic Search

This study reports an empirical investigation into Bernstein's (1967) ideas that in the early stages of the acquisition of a movement skill the coordination problem is reduced by an initial freezing out of degrees of freedom, followed later in the learning process by the release of these degrees of freedom and their incorporation into a dynamic, controllable system. “Freezing” degrees

Beatrix Vereijken; Richard E. A. van Emmerik; H. T. A. Whiting; Karl M. Newell

1992-01-01

318

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

NSDL National Science Digital Library

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

Aquarium, New E.

2011-01-01

319

TOPICAL REVIEW: Confinement effects on freezing and melting  

Microsoft Academic Search

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

Hugo K. Christenson

2001-01-01

320

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

321

A multilayer freezer for freeze concentration of liquid milk  

Microsoft Academic Search

Over the past few decades, much progress has been made in the development of freeze concentration technology, and commercial freeze concentration plants have been established around the world. However, high costs still limit its use in many potential applications.A continuous, multilayer freezer was designed, constructed, and operated under different conditions. This process used a series of chambers, mounted as layers

Zhonglai Zhang; Richard W. Hartel

1996-01-01

322

Volume-Restricted Freezing of Living Cells and Tissues.  

National Technical Information Service (NTIS)

The effect of constant-volume freezing on the survival of red blood cells in diluted rabbit blood and of Artemia Salina (brine shrimp) in dimethyl sulfoxide (DMSO)-saline solution was examined. Constant-volume freezing significantly improved red-blood-cel...

S. D. Engstrom Y. E. Chu W. F. Sung M. S. Giroux

1977-01-01

323

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

NASA Astrophysics Data System (ADS)

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

Cuntz, Matthias; Haverd, Vanessa

2014-05-01

324

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

325

Freezing D2O clay gels.  

PubMed

To obtain the T1 surface value in smectites/D2O diluted suspensions or gels, as was obtained on a monolayer deuterated clay, we freeze them. The broad Pake's doublets similar to ice doublets and with the same T1 show that we can separate frozen from unfrozen D2O. The latter exhibits a narrower line and a single T1 and is attributed to the liquid surface water layer in rapid exchange with the nearby supercooled water, the quantity of which diminishes with the lowering of the temperature depending on the gel porosity. It is possible to measure the supercooled water quantity and to correct the T1 measured values to extract the T1 surface. The value extrapolated at room temperature allows the complete clay surface area measurement. The example of a montmorillonite is given and a comparison with laponite is made. PMID:9803898

Letellier, M

1998-01-01

326

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

327

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 important for sea ice modelling and ship operations. Here a method to detect the thickness of sea ice up to 50 cm during the freeze-up 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 anticorrelation 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 algorithm sensitive to thin sea ice up to 50 cm thickness. The algorithm shows high correlation 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.

2014-03-01

328

An improved microscope stage for direct observation of freezing and freeze drying.  

PubMed

A microscope stage for observation of freezing and freeze drying is described. The stage uses thermoelectric (Peltier) heaters configured in two stages, with circulating fluid as a heat sink on the high temperature side. Lowest attainable sample temperature is about -47 degrees C. Principal advantages of this system are closed-loop control of stage temperature, rapid response to changes in temperature set point, and improved documentation of experiments by use of a video recorder system with a character generator which allows display of sample identity and temperature. Accuracy of measuring the sample temperature in the field of view was validated by comparing observed values of eutectic melting with published values for a series of solutes with eutectic temperatures in the range from -2 degrees C to -32 degrees C. Good agreement was obtained throughout this range. PMID:7971708

Nail, S L; Her, L M; Proffitt, C P; Nail, L L

1994-08-01

329

3-D radial gravity gradient inversion  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

330

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

331

Fabrication of porous ceramics by freeze-casting/freeze-drying. Final report, April 1991-December 1992  

SciTech Connect

Porous ceramics have many applications in the gas industry, including gas separation, filtration, catalyst supports and substrates, lightweight insulation, and burners. The report explores the fabrication of porous ceramics by a new approach involving the use of cryogenic processing techniques such as freeze-drying, to characterize the materials formed in this way, and to evaluate the potential of the techniques for making porous ceramics for specific gas industry applications.

Johnson, S.M.; Gusman, M.I.

1993-04-01

332

Long-term stability of sterically stabilized liposomes by freezing and freeze-drying: Effects of cryoprotectants on structure  

Microsoft Academic Search

Liposomes are widely investigated for their use as drug delivery systems, where they have to meet strict stability criteria. Hence, it is of common interest to establish appropriate storage conditions to improve the shelf life of liposomes. In general, long-term stability can be achieved by freezing as well as freeze-drying, and different carbohydrates or polyalcohols, such as mannitol or glycerol

Brigitte Stark; Georg Pabst; Ruth Prassl

2010-01-01

333

Freeze-Spray Processing of Layered Ceramic Composites (Preprint).  

National Technical Information Service (NTIS)

Thermal gradients and associated stresses are critical in designing with ceramic composites having low thermal conductivity. In order to reduce the stresses from thermal gradients, compositional gradients are employed in designing of composite structures....

A. Abbott F. Dogan O. Jongprateep Q. Fu

2006-01-01

334

Vertical vector face lift.  

PubMed

Facial rejuvenation using local anesthesia has evolved in the past decade as a safer option for patients seeking fewer complications and minimal downtime. Mini- and short-scar face lifts using more conservative incision lengths and extent of undermining can be effective in the younger patient with lower face laxity and minimal loose, elastotic neck skin. By incorporating both an anterior and posterior approach and using an incision length between the mini and more traditional face lift, the Vertical Vector Face Lift can achieve longer-lasting and natural results with lesser cost and risk. Submentoplasty and liposuction of the neck and jawline, fundamental components of the vertical vector face lift, act synergistically with superficial musculoaponeurotic system plication to reestablish a more youthful, sculpted cervicomental angle, even in patients with prominent jowls. Dramatic results can be achieved in the right patient by combining with other procedures such as injectable fillers, chin implants, laser resurfacing, or upper and lower blepharoplasties. PMID:21276163

Somoano, Brian; Chan, Joanna; Morganroth, Greg

2011-01-01

335

Structures of turbulent boundary layers with adverse pressure gradients  

NASA Astrophysics Data System (ADS)

Turbulent structures in spanwise/wall-normal plane of the turbulent boundary layers (TBLs) subjected to adverse pressure gradients (APGs) were investigated by analyzing the DNS database of Lee & Sung (2009). Probability density functions of the strength of the vortex cores normalized by their r.m.s. values displayed that strong swirling motions are frequently observed on the APG TBLs than zero pressure gradient TBLs. Influence of APGs on the population trends of spanwise vortex cores showed that those have a local maximum at the outer region for APG TBLs which might be due to the maximum Reynolds shear stress. Moreover, two-point correlations and linear stochastic estimations were scrutinized to provide statistical evidence for hairpin packet motions in the vertical plane of the TBLs with APGs. We found that wall-normal extent of the contours is elongated vertically owing to the strong swirling motion of the individual vortex located in the wake region or wake-type detached structures.

Lee, Jin; Sung, Hyung Jin

2009-11-01

336

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

NASA Astrophysics Data System (ADS)

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

Hirata, Tetsuo; Ishikawa, Masaaki; Akutsu, Nobuaki

337

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

338

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.

Tschinkel, Walter R.

2013-01-01

339

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

340

The effects of freeze drying and freeze drying additives on the prothrombin time and the international sensitivity index.  

PubMed Central

AIM: To determine whether freezing, freeze drying protective additives, or freeze drying of plasma samples from patients on coumarin treatment and from normal individuals affects prothrombin times or the international sensitivity index (ISI) calibration. METHODS: The effect of the addition of the protective additives singly and combined on the prothrombin time of coumarin samples and normal samples before and after freeze drying was observed using high and low ISI reference thromboplastins. ISI values were also determined. RESULTS: Freezing caused a prolongation of prothrombin time in the normal plasma samples with both reagents, which was significant with the low ISI human. Prolongation (non-significant) of the prothrombin time in coumarin plasma samples occurred with the human reagent only. Significant prolongation of normal prothrombin time by some of the protective additives before and after freeze drying was observed with both thromboplastins but to a greater extent with the human. Significant prolongation of prothrombin time in coumarin plasma samples was observed, but again was more marked with human thromboplastin. An approximate ISI was determined on the 20 coumarin samples. The only marked ISI change was with the WHO human thromboplastin after freeze drying of plasma, where a decrease from 0.95 to 0.90 was observed, corresponding to a marked prothrombin ratio increase. CONCLUSIONS: Freeze drying additives and the freeze drying procedure prolong normal and coumarin prothrombin times, with low ISI thromboplastin. Less marked prolongations occurred with a high ISI rabbit reagent, coumarin samples showing more significant prolongations. Marked ISI change in freeze dried plasma was only recorded with the low ISI ECAA human reagent. Frozen normal plasma samples cannot be used with confidence for ISI calibrations.

Poller, L; Keown, M; Shepherd, S A; Shiach, C R; Tabeart, S

1999-01-01

341

Tectorial Membrane Stiffness Gradients  

PubMed Central

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

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

2007-01-01

342

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

NASA Astrophysics Data System (ADS)

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

Neils, Christopher Martin

2000-09-01

343

Non linear inversion of gravity gradients and the GGI gradiometer  

NASA Astrophysics Data System (ADS)

All gradiometers currently operating for exploration in the field are based on Lockheed Martin's GGI gradiometer. The working of this gradiometer is described and a method for robust non linear inversion of gravity gradients is presented. The inversion method involves obtaining the gradient response of a trial body consisting of vertical rectangular prisms. The inversion adjusts the depth to the tops or bases of the prisms. In the trial model all the prisms are not required to have the same area of cross section or the same density (which can also be allowed to vary with depth). The depth to the tops and bottoms of each prism can also be different. This response is compared with the observed values of gradient and through an iterative procedure, the difference is minimized in a least square sense to arrive at a best fitting model by varying the position of the tops or bottoms of the prisms. Each gradient can be individually inverted or one or more gradients can be jointly inverted. The method is extended to invert gravity values individually or jointly with gradient values. The use of Differential Curvature, a quantity which is directly obtained by current gradiometers in use and which is an invariant under a rotation in the horizontal plane, is emphasized. Synthetic examples as well as a field example of inversion are given.

Talwani, Manik

2011-12-01

344

Nanoparticle manipulation by thermal gradient  

PubMed Central

A method was proposed to manipulate nanoparticles through a thermal gradient. The motion of a fullerene molecule enclosed inside a (10, 10) carbon nanotube with a thermal gradient was studied by molecular dynamics simulations. We created a one-dimensional potential valley by imposing a symmetrical thermal gradient inside the nanotube. When the temperature gradient was large enough, the fullerene sank into the valley and became trapped. The escaping velocities of the fullerene were evaluated based on the relationship between thermal gradient and thermophoretic force. We then introduced a new way to manipulate the position of nanoparticles by translating the position of thermostats with desirable thermal gradients. Compared to nanomanipulation using a scanning tunneling microscope or an atomic force microscope, our method for nanomanipulation has a great advantage by not requiring a direct contact between the probe and the object.

2012-01-01

345

Nanoparticle manipulation by thermal gradient.  

PubMed

A method was proposed to manipulate nanoparticles through a thermal gradient. The motion of a fullerene molecule enclosed inside a (10, 10) carbon nanotube with a thermal gradient was studied by molecular dynamics simulations. We created a one-dimensional potential valley by imposing a symmetrical thermal gradient inside the nanotube. When the temperature gradient was large enough, the fullerene sank into the valley and became trapped. The escaping velocities of the fullerene were evaluated based on the relationship between thermal gradient and thermophoretic force. We then introduced a new way to manipulate the position of nanoparticles by translating the position of thermostats with desirable thermal gradients. Compared to nanomanipulation using a scanning tunneling microscope or an atomic force microscope, our method for nanomanipulation has a great advantage by not requiring a direct contact between the probe and the object. PMID:22364240

Wei, Ning; Wang, Hui-Qiong; Zheng, Jin-Cheng

2012-01-01

346

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

347

Freeze-thaw durability of air-entrained concrete.  

PubMed

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

Shang, Huai-Shuai; Yi, Ting-Hua

2013-01-01

348

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.

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

2014-01-01

349

Gradient index in borate glasses  

NASA Astrophysics Data System (ADS)

A number of aluminum-borate glasses has been developed for producing gradient index glasses by exchanging. Both positive and negative axial gradient were fabricated in the glasses by exchange of Li+ for Na+ and Na+ for Li+, respectively. Index change to 0.03 and gradient index Abble number larger than +100 were achieved. The diffusion coefficients of Na+ and Li+ in borate glasses were calculated by fitting the profiles of refractive index to complimentary error function.

Sun, Yunan; Kindred, Douglas S.; Moore, Duncan T.

1994-08-01

350

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

351

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

PubMed

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

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

2011-11-01

352

Freeze Tape Casting of Functionally Graded Porous Ceramics  

NASA Technical Reports Server (NTRS)

Freeze tape casting is a means of making preforms of ceramic sheets that, upon subsequent completion of fabrication processing, can have anisotropic and/or functionally graded properties that notably include aligned and graded porosity. Freeze tape casting was developed to enable optimization of the microstructures of porous ceramic components for use as solid oxide electrodes in fuel cells: Through alignment and grading of pores, one can tailor surface areas and diffusion channels for flows of gas and liquid species involved in fuel-cell reactions. Freeze tape casting offers similar benefits for fabrication of optimally porous ceramics for use as catalysts, gas sensors, and filters.

Sofie, Stephen W.

2007-01-01

353

Delayed freezing of water droplet on silver nanocolumnar thin film  

NASA Astrophysics Data System (ADS)

Silver nanocolumns were grown on Si substrate using glancing angle deposition method. Interestingly, the cold nanocolumnar surface was observed to make a delay of more than 62 s in freezing compared to the conventional silver thin film. The observed delay in freezing on silver nanocolumns is explainable in terms of reduction in effective liquid-solid interface area within the framework of Cassie-Baxter model. This study shows the possibility of using silver nanocolumnar films in ice free coatings and surfaces with tunable freezing properties.

Singh, Dhruv P.; Singh, Jitendra P.

2013-06-01

354

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

355

The 630 nm MIG and the vertical neutral wind in the low latitude nighttime thermosphere  

NASA Astrophysics Data System (ADS)

It is shown that large negative divergences (gradients) in the horizontal neutral wind in the equatorial thermosphere can support downward neutral winds in excess of 20 m/s. With attention to the meridional and vertical winds only, the pressure tendency equation is used to derive the expression Uz0 approximately equals (Partial derivative Uy/Partial derivative y)H for the vertical wind Uz0 at the reference altitude for the pressure tendency equation; H is the atmospheric density scale height, and (Partial derivative Uy/Partial derivative y) is the meridional wind gradient. The velocity gradient associated with the Meridional Intensity Gradient (MIG) of the O1D) emission (630 nm) at low latitudes is used to estimate the vertical neutral wind in the MIG region. Velocity gradients derived from MIG data are about 0.5 (m/s)/km) or more, indicating that the MIG region may contain downward neutral winds in excess of 20 m/s. Though direct measurements of the vertical wind are scarce, Fabry-Perot interferometer data of the equatorial F-region above Natal, Brazil, showed downward winds of 30 m/s occurring during a strong meridional wind convergence in 1982. In-situ measurements with the WATS instrument on the DE-2 satellite also show large vertical neutral winds in the equatorial region.

Herrero, F. A.; Meriwether, J. W., Jr.

1994-01-01

356

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

PubMed

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

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

2010-02-01

357

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

NASA Astrophysics Data System (ADS)

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

Hirata, Tetsuo; Ishikawa, Masaaki; Matsuzaki, You

358

The vertical distribution of soluble gases in the troposphere  

NASA Technical Reports Server (NTRS)

The thermodynamic properties of several water-soluble gases are reviewed to determine the likely effect of the atmospheric water cycle on their vertical profiles. It is found that gaseous HCl, HNO3, and HBr are sufficiently soluble in water to suggest that their vertical profiles in the troposphere have a similar shape to that of water vapor. It is predicted that HCl, HNO3, and HBr exhibit a steep negative gradient with altitude roughly equal to the altitude gradient of water vapor. Therefore, ground-based sources of inorganic chlorine, odd nitrogen, and inorganic bromine compounds are not likely to affect the stratosphere directly in the mean. Calculations also show that while SO2 and NH3 are significantly affected by the atmospheric water cycle, their abundances may not decrease with altitude as rapidly as does that of water vapor.

Stedman, D. H.; Chameides, W. L.; Cicerone, R. J.

1975-01-01

359

Vertical blind assembly  

US Patent & Trademark Office Database

A vertical blind assembly includes an elongate header casing and two sets of louvers movably supported in adjacent channels within the header casing, including a first set of plain louvers structured to be moved horizontally along the length of the first channel, and a second set of louvers which are molded and configured in a decorative, three-dimensional pattern and structured to be moved horizontally along the length of the second channel so that they are positioned in front of the first set of louvers.

1997-01-28

360

'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

361

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.

362

Heat Transfer Control in Quiescent Air with Thermal Gradient by Magnetizing Force Under both Gravitational and Nongravitational Fields  

Microsoft Academic Search

Two-dimensional numerical computations were carried out to clarify the influence of magnetizing force on quiescent air with thermal gradient in a vertical cylindrical container under both gravitational and nongravitational fields. Several sizes and axial positions of a circular electric coil were tested so that the magnetizing force depended on the magnetic gradient. Under both gravitational and nongravitational fields, the convection

Masato Akamatsu; Mitsuo Higano; Yoshio Takahashi; Hiroyuki Ozoe

2005-01-01

363

Characterization of a laboratory-scale container for freezing protein solutions with detailed evaluation of a freezing process simulation.  

PubMed

A 300-mL stainless steel freeze container was constructed to enable QbD (Quality by Design)-compliant investigations and the optimization of freezing and thawing (F/T) processes of protein pharmaceuticals at moderate volumes. A characterization of the freezing performance was conducted with respect to freezing kinetics, temperature profiling, cryoconcentration, and stability of the frozen protein. Computational fluid dynamic (CFD) simulations of temperature and phase transition were established to facilitate process scaling and process analytics as well as customization of future freeze containers. Protein cryoconcentration was determined from ice-core samples using bovine serum albumin. Activity, aggregation, and structural perturbation were studied in frozen rabbit muscle l-lactic dehydrogenase (LDH) solution. CFD simulations provided good qualitative and quantitative agreement with highly resolved experimental measurements of temperature and phase transition, allowing also the estimation of spatial cryoconcentration patterns. LDH exhibited stability against freezing in the laboratory-scale system, suggesting a protective effect of cryoconcentration at certain conditions. The combination of the laboratory-scale freeze container with accurate CFD modeling will allow deeper investigations of F/T processes at advanced scale and thus represents an important step towards a better process understanding. PMID:24338205

Roessl, Ulrich; Jajcevic, Dalibor; Leitgeb, Stefan; Khinast, Johannes G; Nidetzky, Bernd

2014-02-01

364

Reduced gradient bubble model.  

PubMed

An approach to decompression modeling, the reduced gradient bubble model (RGBM), is developed from the critical phase hypothesis. The phase limit is introduced, extended, and applied within bubble-nucleation theory proposed by Yount. Much is different in the RGBM algorithm, on both theoretical and applied sides, with a focus on permissible bubble excesses rather than just dissolved gas buildup, something of a departure from traditional models. Overall, the approach is conservative, with changes in parameter settings affording flexibility. Marginal profiles permitted by tables and meters are restricted by the bubble algorithm. Highlighted features of the conservative algorithm include: (1) reduced no-stop time limits from the varying-permeability model (VPM); (2) short safety stops (or shallow swimming ascents) in the 10-20 feet of sea water (fsw) zone; (3) ascent and descent rates of 60 fsw/min, or slower; (4) restricted repetitive exposures, particularly beyond 100 fsw, based on reduced permissible bubble excess; (5) restricted spike (shallow-to-deep) exposures based on excitation of additional micronuclei; (6) restricted multi-day activity based on regeneration of micronuclei; (7) consistent treatment of altitude diving within model framework; (8) algorithm linked to bubble-nucleation theory and experiment. Coupled to medical reports about the long term effects of breathing pressurized gases and shortcomings in dissolved gas models, conservative modeling seems prudent. PMID:2276850

Wienke, B R

1990-11-01

365

Utilization of polysaccharide coatings to improve freeze–thaw and freeze–dry stability of protein-coated lipid droplets  

Microsoft Academic Search

The impact of freezing–thawing and freeze–drying on the physical stability of oil-in-water (O\\/W) emulsions containing protein-coated and protein\\/polysaccharide-coated droplets has been studied. O\\/W emulsions (2wt% corn oil, 0.12wt% ?-lactoglobulin, pH 3.5) were prepared that contained either 0 or 0.2wt% pectin or ?-carrageenan, and 0–8wt% maltodextrin. The emulsions were then subjected to either freeze–thaw cycling (?20°C, 22h; +30°C, 2h; ×2) or

Saehun Mun; Younghee Cho; Eric Andrew Decker; David Julian McClements

2008-01-01

366

Universal Public Argument and the Failure of Nuclear Freeze.  

ERIC Educational Resources Information Center

Examines the strategy of universalization during the nuclear freeze movement of 1981-82 by drawing upon the insights of Celeste Condit and William Bailey. Identifies strengths and weaknesses of the Condit/Bailey concepts and suggests modifications. (KEH)

King, Andrew; Petress, Kenneth

1990-01-01

367

Freezing Phenomena in Adsorbed Water as Studied by NMR  

NASA Astrophysics Data System (ADS)

The freezing of water adsorbed on high-surface-area materials such as silica gel, controlled-pore glass, and activated charcoal is investigated with NMR methods. Part of the pore water freezes at the temperature predicted by the Kelvin equation and the rest of the water does not freeze in the sense that it does not assume the structure of ice on cooling below this freezing point. This bound water exhibits a distribution of correlation times, and information about the width of this distribution is obtained. Values for the activation enthalpy of the bound water are also deduced. An alternative method for the determination of the pore volume of an adsorbent is proposed and it is shown that. for adsorbents with small pores ( r < 100 Å), this method results in a much better estimate for the total pore volume than the more common mercury-intrusion method.

Overloop, K.; Vangerven, L.

368

Normal freezing of ideal ternary systems of the pseudobinary type  

NASA Technical Reports Server (NTRS)

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

Li, C. H.

1972-01-01

369

A Quantitative Approach to Casting Solidification: Freezing of Cast Iron.  

National Technical Information Service (NTIS)

The separate processes involved in casting solidification, such as eutectic nucleation and growth, have been previously studied separately in controlled experiments. The interaction of the separate processes has now been treated, using the freezing of cas...

W. Oldfield

1966-01-01

370

Procedures to Minimize Mechanical Damage to Freeze-Dried Foods.  

National Technical Information Service (NTIS)

The objective of the studies reported herein was to develop procedures principally to minimize mechanical breakage during handling and transport, while retaining or improving other quality characteristics of ten meat/seafood products. The effects of freez...

E. Seltzer S. C. Sharma

1975-01-01

371

Multiphoton imaging of biological samples during freezing and heating  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

372

On deriving flux freezing in magnetohydrodynamics by direct differentiation  

NASA Astrophysics Data System (ADS)

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

Blackman, Eric G.

2013-03-01

373

Dewatering Florida Phosphate Pebble Rock Slime by Freezing Techniques.  

National Technical Information Service (NTIS)

Freezing to dewater typical Florida phosphate rock slime as demonstrated in laboratory tests appeared to have potential commercial use because of indicated moderate energy requirements, good compaction of dewatered solids, and effective recovery of usable...

E. W. Collins I. L. Feld M. H. Stanczyk

1971-01-01

374

Long-term storage of bionanodevices by freezing and lyophilization.  

PubMed

Successful long-term storage of a "smart dust" device integrating biomolecular motors and complex protein assemblies has been demonstrated using freezing or lyophilization, which implies that fabrication and application can be separated even for complex bionanodevices. PMID:16929405

Seetharam, Raviraja; Wada, Yuuko; Ramachandran, Sujatha; Hess, Henry; Satir, Peter

2006-09-01

375

Freezing Test for Evaluating Relative Frost Susceptibility of Various Soils.  

National Technical Information Service (NTIS)

The report presents a description of the equipment and procedures used in the laboratory test of the relative frost susceptibility of different soils on Corps of Engineers construction projects and includes typical results of freezing tests of natural soi...

C. W. Kaplar

1974-01-01

376

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

377

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

378

Metallicity Gradients in Elliptical Galaxies  

NASA Technical Reports Server (NTRS)

The study of metalicity gradients is an examination of the relics of the first epoch of star formation and, thus, another issue that metallicity gradients can address is the relationship between chemical and dynamical evolution during the initial phase of star formation.

Hanlan, Patricia C.; Schombert, James M.; Barsony, Mary; Rakos, Karl D.

1993-01-01

379

Edge dislocation in gradient elasticity  

Microsoft Academic Search

The present paper is a natural continuation of the authors` previous work where they have considered the screw dislocation in gradient elasticity. They consider two dislocation configurations: a separate edge dislocation and a dipole of edge dislocations. The gradient solutions presented have been obtained by two different ways, i.e., in total displacements and in elastic strains with both leading to

M. Yu. Gutkin; E. C. Aifantis

1997-01-01

380

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

381

Rapid Gradient-Echo Imaging  

PubMed Central

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

Hargreaves, Brian

2012-01-01

382

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

383

Viability of spores after repeate freezing and thawing shocks  

Microsoft Academic Search

Survival of spores of the fungusRhizopus nigricans after repeated freezing and thawing was investigated. The cooling rate was 104°C\\/min. Dry spores were fully inactive after 32 repeated shocks. About one-half of spores were killed after 8 repetitions.\\u000a The water content did not change the resistance, swollen spores reacted to shocks much like dry ones. The sensitivity of spores\\u000a to freezing-thawing

O. Ne?as; M. Gabriel

1978-01-01

384

MEMBRANE DIFFERENTIATIONS IN FREEZE-FRACTURED MAMMALIAN SPERM  

Microsoft Academic Search

A correlated thin-sectioning and freeze-fracturing study has been made of guinea pig and rat spermatozoa. In sections, the cell membrane over the acrosome has a concanavalin A and ruthenium red reactive glycocalyx which exhibits an ordered pattern related to the lattice of crystalline domains within the plane of the mem- brane revealed by freeze-fracturing. The cleaved acrosomal membrane also shows

DANIEL S. FRIEND; DON W. FAWCETT

1974-01-01

385

A new TDR sensor for accurate freeze–thaw measurement  

Microsoft Academic Search

The variation of soil properties during freezing–thawing cycles, especially the reduction of subgrade strength during the thawing process, is the major cause of pavement damage in cold regions. This paper introduces the development and evaluation of an innovative guided electromagnetic (EM) wave [time domain reflectometry (TDR)] tube sensor to non-destructively monitor the freezing–thawing process. Experimental evaluation indicates that the sensor

Xinbao Yu; Yan Liu; Javanni Gonzalez; Bill Yu

2011-01-01

386

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

SciTech Connect

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

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

1984-01-01

387

Freeze-drying of microorganisms using a simple apparatus  

Microsoft Academic Search

The advantages of freeze-drying are obvious. It is a convenient method for the preservation and long-term storage of a wide variety of microorganisms. However, special precautions are needed for the preservation of microorganisms sensitive to dessication, light, oxygen, osmotic pressure, surface tension and other factors. During several years of experimentation I have developed various new methods and have optimized freeze-drying

Khursheed A. Malik; Mascheroder Weg

1992-01-01

388

Segregation freezing as the cause of suction force for ice lens formation  

Microsoft Academic Search

A new freezing mechanism, called segregation freezing, is proposed to explain the generation of the suction force that draws pore water up to the freezing surface of a growing ice lens. The segregation freezing temperature is derived by applying thermodynamics to a soil mechanics concept that distinguishes the effective pressure from the neutral pressure. The frost-heaving pressure is formulated in

S. Takagi

1978-01-01

389

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

Microsoft Academic Search

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,

James D. Brownridge

2010-01-01

390

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

391

Gradient elution in capillary electrochromatography  

SciTech Connect

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

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

1997-08-01

392

Review: freeze concentration technology applied to dairy products.  

PubMed

Freeze concentration is a process of concentrating liquid products by freezing the water content and subsequently removing the so-formed ice crystals from the food system. In dairy processing, this technology offers the advantage of minimizing the heat abuse of sensitive milk components, such as proteins and flavors. It thus provides an opportunity for producing dairy ingredients with enhanced functional and organoleptic qualities. By freeze concentration, skim milk has been concentrated up to 40 wt% total solids (TS) and whole milk up to 44 wt% TS. Lactose and lipids are more concentrated in the ice fraction than in the concentrated fraction. Proteins (casein and whey protein) decrease the ice growth rate and the high viscosity is a limiting factor for the freeze concentration of both skim milk and whole milk. In this study, the most important studies relating to the suspension, block and layer freeze concentration of milk are summarized, analyzing results and indicating how freeze concentration process efficiency of dairy products can be improved. PMID:21364040

Sánchez, J; Hernández, E; Auleda, J M; Raventós, M

2011-02-01

393

Identification of Arabidopsis mutants with altered freezing tolerance.  

PubMed

Low temperature is an important determinant in the configuration of natural plant communities and defines the range of distribution and growth of important crops. Some plants, including Arabidopsis, have evolved sophisticated adaptive mechanisms to tolerate low and freezing temperatures. Central to this adaptation is the process of cold acclimation. By means of this process, many plants from temperate regions are able to develop or increase their freezing tolerance in response to low, nonfreezing temperatures. The identification and characterization of factors involved in freezing tolerance are crucial to understand the molecular mechanisms underlying the cold acclimation response and have a potential interest to improve crop tolerance to freezing temperatures. Many genes implicated in cold acclimation have been identified in numerous plant species by using molecular approaches followed by reverse genetic analysis. Remarkably, however, direct genetic analyses have not been conveniently exploited in their capacity for identifying genes with pivotal roles in that adaptive response. In this chapter, we describe a protocol for evaluating the freezing tolerance of both non-acclimated and cold-acclimated Arabidopsis plants. This protocol allows the accurate and simple screening of mutant collections for the identification of novel factors involved in freezing tolerance and cold acclimation. PMID:24852630

Perea-Resa, Carlos; Salinas, Julio

2014-01-01

394

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

395

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.

Pearce, Roger S.; Fuller, Michael P.

2001-01-01

396

Florida Citrus Freezes and Polar Anticyclones in the Great Plains.  

NASA Astrophysics Data System (ADS)

Severe Florida citrus freezes since 1880 are identified and described in terms of the horticultural damage, overall frequency of occurrence, and association with polar anticyclone outbreaks in the plains of southern Canada and the United States. The most severe `advective' freezes are associated with strong cold anticyclones having tracks southward across the plains to Texas with subsequent northeastward movement. Other anticyclones move in a track somewhat east of this and ultimately pass over Florida or the eastern Gulf of Mexico. Over 80% of the worst Florida citrus freezes are associated with anticyclones with central pressures in excess of 1045 mb moving along these paths. However, anticyclones of similar intensity with more zonally oriented paths across higher latitudes are associated with minor citrus damage. The major freezes tend to be clustered in time in the 1890s and since 1977. On interdecadal time scales, the recent freezes are not linked to higher winter mean pressure in the northern plains, and there has not been an unusually high frequency of strong anticyclones in recent decades, compared to earlier this century. Compared to the freeze-free period of 1948-57, the winters of 1977-86 are characterized by a more amplified 500-mb mean standing wave pattern across North America. This is linked to changes in the Pacific/North American upper-air teleconnection pattern, the index for which had much lower values (characterized by zonal flow) prior to 1958.

Rogers, Jeffrey C.; Rohli, Robert V.

1991-11-01

397

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

398

Zooplankton biomass abundance and allometric patterns along an eutrophic gradient at Furnas Reservoir (Minas Gerais Brazil)  

Microsoft Academic Search

ABSTRACT: Zooplankton biomass, abundance and allometric patterns along an eutrophic gradient at Furnas reservoir (Minas Gerais, Brazil). The aim of this study was to describe the zooplankton composition, allometry, abundance and biomass along a trophic gradient at Furnas Reservoir.,Furnas,dam,is located,few,kilometres,downstream,the,mouth,of Sapucaí,River (Minas Gerais, Brazil), being one of the biggest reservoir in Brazilian Southwest (1440 Km, ). Zooplankton,was,sampled,by vertical,hauls,in three,different,campaigns along

399

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

NASA Astrophysics Data System (ADS)

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

Sorrentino, F.; Bertoldi, A.; Bodart, Q.; Cacciapuoti, L.; de Angelis, M.; Lien, Y.-H.; Prevedelli, M.; Rosi, G.; Tino, G. M.

2012-09-01

400

The vertical structure of geostrophic turbulence: statistical mechanics approach.  

NASA Astrophysics Data System (ADS)

The vertical structure of freely evolving, continuously stratified, quasi-geostrophic turbulence is investigated. We predict the final state organization, and in particular its vertical structure, using statistical mechanics and these predictions are tested against numerical simulations. In general, the conservation laws, and in particular that enstrophy is conserved layer-wise, prevent complete barotropization, i.e., the tendency to reach the gravest vertical mode. The peculiar role of the beta-effect, i.e. of the existence of planetary vorticity gradients, is discussed. In particular, it is shown that increasing beta increases the tendency toward barotropization through turbulent stirring. In addition, it is shown that in the presence of sufficiently large bottom topography anomalies, an initial surface-intensified velocity field evolves towards a bottom-trapped mean current following iso-contours of topography.

Venaille, A.; Vallis, G. K.; Griffies, S. M.

2012-04-01

401

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.

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

2014-01-01

402

Drying of Fennel Plants: Oven, Freeze Drying, Effect of Freeze-Drying Time, and Use of Biopolymers  

Microsoft Academic Search

Fennel plants were oven and freeze dried. The influence of freeze-drying time on the concentration of the two main components, trans-anethole and isoanethole, of its essential oil was evaluated. Drying time up to 15 h led to 50% reduction of moisture content with minor increase in volatile losses, whereas drying time greater than 15 h resulted in a dried product with an

Chryssavgi Gardeli; Vasiliki Evageliou; Christoforos Poulos; Stavrianos Yanniotis; Michael Komaitis

2010-01-01

403

Phosphoglycerate kinase 1 expression responds to freezing, anoxia, and dehydration stresses in the freeze tolerant wood frog, Rana sylvatica  

Microsoft Academic Search

Natural freezing survival by wood frogs (Rana sylvatica) involves multiple organ- specific changes in gene expression. Screening of a cDNA library made from brain of frozen frogs revealed freeze-responsive up-regulation of the glycolytic enzyme, phosphoglycerate kinase 1 (PGK1). Northern blots showed an approximately two-fold increase in pgk1 transcripts in brain of frozen frogs whereas PGK1 protein levels rose by three-

Shaobo Wu; Janet M. Storey; Kenneth B. Storey

2009-01-01

404

Preparation of 3-D regenerated fibroin scaffolds with freeze drying method and freeze drying\\/foaming technique  

Microsoft Academic Search

Although three-dimensional fibroin scaffolds have been prepared with freeze drying method, the porosity and pore sizes still\\u000a can not satisfy the requirement of tissue engineering. In this article, fibroin porous scaffold with high porosity and > 100?m\\u000a diameter interconnected pores was firstly prepared with freeze drying method through adjusting fibroin concentration. The\\u000a morphology of different scaffolds lyophilized from different fibroin

Qiang Lv; QingLing Feng

2006-01-01

405

Encapsulation and sustained release from biodegradable microcapsules made by emulsification\\/freeze drying and spray\\/freeze drying  

Microsoft Academic Search

Hollow biodegradable poly(dl-lactide) (PLA) particles with porous shell walls were prepared by freeze drying small droplets of PLA solution formed by emulsification or spraying. The hollow freeze-dried particles were dispersed in water, and the resulting aqueous suspensions were exposed to plasticizing solvents, either dichloromethane or compressed carbon dioxide. The plasticizing solvent causes the pores in the shell wall to close,

Weisi Yin; M. Z. Yates

2009-01-01

406

Measuring changes in protein secondary structure in-situ during freezing and freeze-drying using infrared microscopy  

Microsoft Academic Search

The goal of this research was twofold, (1) determine the feasibility of combining a freeze-dry microscopy stage with an infrared microscope as a method of in-situ measurement of protein secondary structure in the liquid, frozen and freeze-dried states, and (2) use this instrumentation to gain a better understanding at the molecular level of the mechanism of loss of integrity of

John J Schwegman

2004-01-01

407

Preparation of poly( L-lactic acid) honeycomb monolith structure by unidirectional freezing and freeze-drying  

Microsoft Academic Search

Honeycomb monolith structured porous poly(L-lactic acid) (PLLA) was successfully fabricated by combining pseudo steady state unidirectional freezing and freeze-drying techniques. Dehydrated 1,4-dioxane was used as a solvent for PLLA and the single-phase mixture was unidirectionally frozen by lowering the sample tube into liquid nitrogen at a constant rate. The 1,4-dioxane crystal was nucleated in the solution and grown in the

Jin-Woong Kim; Kentaro Taki; Shinsuke Nagamine; Masahiro Ohshima

2008-01-01

408

Fabrication of HA\\/PHBV composite scaffolds through the emulsion freezing\\/freeze-drying process and characterisation of the scaffolds  

Microsoft Academic Search

Biodegradable polymer-based scaffolds containing osteoconductive hydroxyapatite (HA) particles can be very useful for bone\\u000a tissue engineering. In this investigation, HA nanoparticles were incorporated in poly(hydroxybutyrate-co-valerate) (PHBV) polymer to fabricate osteoconductive composite scaffolds. PHBV and HA\\/PHBV scaffolds were made using an\\u000a emulsion freezing\\/freeze-drying technique. The scaffolds produced were subsequently characterized using several techniques.\\u000a It was found that the scaffolds were highly

Naznin Sultana; Min Wang

2008-01-01

409

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

410

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

411

Freezing and Melting Characteristics of a Sand Mold Containing Water on the Freeze Mold Method Process Using Cold Airflow  

NASA Astrophysics Data System (ADS)

This paper reports the freezing and melting characteristics of a sand mold containing water on the freeze mold method. In the freeze mold method, water in the cast sand is frozen and the sand mold becomes hard without caking additives. In this study, the sand mold was cooled by cold airflow for using the freeze mold method in practical applications. In the experiments, the sand containing water was filled into a rectangular container, and then cold air of -30°C was flowed into the container. After water in the sand was frozen, molten aluminum alloy of 900°C was cast into the sand mold to make a test piece. The freezing and melting behavior of water in the sand was investigated experimentally under the various water amount conditions. As a result, it was found that water of 1 mass% in the sand was evaporated by the cold airflow in the freezing process. In the casting process, the movement of evaporation interface becomes slow as the water amount in the sand increases, on the other hand, the movement of melting interface is not influenced by the water amount so much.

Horibe, Akihiko; Inaba, Hideo; Haruki, Naoto; Miyagawa, Yasunori

412

Exponentiated Gradient Versus Gradient Descent for Linear Predictors  

Microsoft Academic Search

We consider two algorithms for on-line prediction based on a linear model. The algorithms are the well-known gradient descent (GD) algorithm and a new algorithm, which we call EG±. They both maintain a weight vector using simple updates. For the GD algorithm, the update is based on subtracting the gradient of the squared error made on a prediction. The EG±algorithm

Jyrki Kivinen; Manfred K. Warmuth

1997-01-01

413

High field gradient particle accelerator  

DOEpatents

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

Nation, J.A.; Greenwald, S.

1989-05-30

414

High field gradient particle accelerator  

DOEpatents

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

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

1989-01-01

415

Modeling the Arecibo nighttime F{sub 2} layer 2. Ionospheric gradients  

SciTech Connect

The servo model is extended and used to fit horizontal gradients in the F{sub 2} layer height and density and to estimate the zonal Pedersen current and its zonal and meridional gradient. Horizontal gradients were measured from the Arecibo Observatory during the following five nights: August 16-17 and 17-18, 1982; and October 4-5, 5-6, and 9-10, 1983. The model gradients are driven by nonzero current gradients, which are applied as needed to fit the measured gradients in the F{sub 2} peak. The gradient is calculated self-consistently in the model. The divergence of the Pedersen current can be deduced when the current flows zonally and is found to differ from zero. This is a consequence of zonal divergence of the model zonal current. Expressions are derived for the divergence of the Hall current and for the curl of the current in the presence of ionospheric gradients. The vertical vorticity of the F region current is determined from the radar and optical measurements and the mass spectrometer/incoherent scatter (MSIS) neutral densities. Both neutral and plasma motions generate current vorticity equally as expected from the F region dynamo. The measured velocity gradients produce more current gradients and vorticity than the measured conductance gradients. The nighttime current may be irrotational or have constant vorticity. Large current gradients occur in conjunction with observed descents of the F{sub 2} peak height. The gradients are interpreted as due to the midnight pressure bulge at low latitudes. Short-period gravity waves of meteorological origin are ruled out as they were not observed and are limited in their ability to reach ionospheric heights. The harmonic analysis used to obtain horizontal wind gradients is largely unaffected by spatially uniform wind accelerations. Therefore the deduced spatial variations in the measured winds are unlikely to be due to temporal variations. 49 refs., 13 figs.

Melendez-Alvira, D.J. [Naval Research Lab., Washington, DC (United States)] [Naval Research Lab., Washington, DC (United States); Burnside, R.G. [Arecibo Observatory (Puerto Rico)] [Arecibo Observatory (Puerto Rico); Walker, J.C.G. [Univ. of Michigan, Ann Arbor, MI (United States)] [Univ. of Michigan, Ann Arbor, MI (United States)

1994-12-01

416

Effect of freeze-chilling, in comparison with fresh, chilling and freezing, on some quality parameters of raw whiting, mackerel and salmon portions  

Microsoft Academic Search

Freeze-chilling involves freezing and frozen storage followed by thawing and chilled storage. It offers logistic benefits for fish packers as it enables packaged fillets to be held frozen and then released into the chill chain as required. Trials with whiting, mackerel and salmon fillets\\/portions indicated no difference in odour scores (raw samples) between freeze-chilled and chilled samples; however, freeze-chilled salmon

John D. Fagan; T. Ronan Gormley; Mary U?? Mhuircheartaigh

2003-01-01

417

Up-regulation of acidic ribosomal phosphoprotein P0 in response to freezing or anoxia in the freeze tolerant wood frog, Rana sylvatica  

Microsoft Academic Search

Natural freezing survival by the wood frog, Rana sylvatica, involves multiple organ-specific, freeze-responsive changes in gene expression. The present study provides the first report of freeze-responsive genes in brain. Differential screening of a cDNA library made from brain of frozen wood frogs revealed a freeze-responsive clone encoding a protein of 315 amino acids that was identified as the acidic ribosomal

Shaobo Wu; Kenneth B. Storey

2005-01-01

418

Vertical Dimension in Complete Dentures.  

National Technical Information Service (NTIS)

The video demonstrates proportional and functional methods to establish a tentative vertical dimension for the edentulous patient. It emphasizes the correlation of this dimension with the centric relation.

1994-01-01

419

Vertical quantum dot with a vertically coupled charge detector  

Microsoft Academic Search

We fabricated a vertical quantum dot equipped with a charge detector. The dot current flows vertically between the top and bottom contacts. The charge detector is formed at the bottom contact layer with a current channel constricted to the region just under the dot. This channel current is reduced by addition of an extra electron onto the dot due to

Koichiro Zaitsu; Yosuke Kitamura; Keiji Ono; Seigo Tarucha

2008-01-01

420

Risk factors for freezing of gait in Parkinson's disease.  

PubMed

Freezing of gait is an episodic gait disorder that may occur in patients with Parkinson's disease. The risk factors for this disorder are poorly understood. To determine the relevant risk factors for this condition, we screened 160 consecutive patients with Parkinson's disease for freezing of gait and assessed 36 potentially related variables. Freezers and non-freezers were compared using statistical univariate analysis, followed by bivariate and multivariate logistic regression, receiver operating characteristics curves and Kaplan-Meier estimates. Seventy-one patients (44.4%) reported freezing of gait. At onset, the mean disease duration was 8.1±6.3years. Freezers experienced falls more frequently than non-freezers (57.7% vs 23.6%, p<0.001). Disease duration was the independent variable most associated with freezing of gait (OR=1.10, 95% CI=1.01-1.19, p=0.020). Its specificity was 77%, but its sensitivity was low, and Hoehn and Yahr staging and the UPDRS (part III) score showed similar accuracy to that of disease duration in predicting freezers. Previous antiparkinsonian treatments and predominant motor signs (tremor/akinesia-rigidity subtypes) at the onset of Parkinson's disease were not related to freezing of gait. Patients who developed Parkinson's disease before the age of 60years experienced freezing of gait earlier than older patients (log-rank, p<0.005). Freezing of gait is a common and disabling motor complication of Parkinson's disease that is related to the progression of the disease. It is not primarily associated with dopamine replacement therapy and may occur early in young patients. PMID:22795382

Contreras, Ana; Grandas, Francisco

2012-09-15

421

Experience Modulates Vicarious Freezing in Rats: A Model for Empathy  

PubMed Central

The study of the neural basis of emotional empathy has received a surge of interest in recent years but mostly employing human neuroimaging. A simpler animal model would pave the way for systematic single cell recordings and invasive manipulations of the brain regions implicated in empathy. Recent evidence has been put forward for the existence of empathy in rodents. In this study, we describe a potential model of empathy in female rats, in which we studied interactions between two rats: a witness observes a demonstrator experiencing a series of footshocks. By comparing the reaction of witnesses with or without previous footshock experience, we examine the role of prior experience as a modulator of empathy. We show that witnesses having previously experienced footshocks, but not naïve ones, display vicarious freezing behavior upon witnessing a cage-mate experiencing footshocks. Strikingly, the demonstrator's behavior was in turn modulated by the behavior of the witness: demonstrators froze more following footshocks if their witness froze more. Previous experiments have shown that rats emit ultrasonic vocalizations (USVs) when receiving footshocks. Thus, the role of USV in triggering vicarious freezing in our paradigm is examined. We found that experienced witness-demonstrator pairs emitted more USVs than naïve witness-demonstrator pairs, but the number of USVs was correlated with freezing in demonstrators, not in witnesses. Furthermore, playing back the USVs, recorded from witness-demonstrator pairs during the empathy test, did not induce vicarious freezing behavior in experienced witnesses. Thus, our findings confirm that vicarious freezing can be triggered in rats, and moreover it can be modulated by prior experience. Additionally, our result suggests that vicarious freezing is not triggered by USVs per se and it influences back onto the behavior of the demonstrator that had elicited the vicarious freezing in witnesses, introducing a paradigm to study empathy as a social loop.

Atsak, Piray; Orre, Marie; Bakker, Petra; Cerliani, Leonardo; Roozendaal, Benno

2011-01-01

422

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

423

Enhanced Aqueous Dissolution of a Poorly Water Soluble Drug by Novel Particle Engineering Technology: Spray-Freezing into Liquid with Atmospheric Freeze-Drying  

Microsoft Academic Search

Purpose. The purpose of this work was to investigate spray-freezing into liquid (SFL) and atmospheric freeze-drying (ATMFD) as industrial processes for producing micronized SFL powders with enhanced aqueous dissolution. Micronized SFL powders dried by ATMFD were compared with vacuum freeze-dried SFL powders.

True L. Rogers; Andrew C. Nelsen; Marazban Sarkari; Timothy J. Young; Keith P. Johnston; Robert O. Williams

2003-01-01

424

NIF optics phase gradient specification.  

National Technical Information Service (NTIS)

A root-mean-square (rms) phase gradient specification seems to allow a good connection between the NIF optics quality and focal spot requirements. Measurements on Beamlet optics individually, and as a chain, indicate they meet the assumptions necessary to...

J. Auerbach J. Hunt K. Manes L. Lawson W. Williams

1997-01-01

425

Generalized gradient and contour program  

USGS Publications Warehouse

This program computes estimates of gradients, prepares contour maps, and plots various sets of data provided by the user on the CalComp plotters. The gradients represent the maximum rates of change of a real variable Z=f(X,Y) with respect to the twodimensional rectangle on which the function is defined. The contours are lines of equal Z values. The program also plots special line data sets provided by the user.

Hellman, Marshall Strong

1972-01-01

426

Control in bioreactors showing gradients  

Microsoft Academic Search

In large-scale bioreactors gradients often occur as a result of non-ideal mixing. This phenomenon complicates design and control of large-scale bioreactors. Gradients in the oxygen concentration can be modeled with a two-compartment model of the liquid phase. Application of this model had been suggested for the control of the dissolved oxygen concentration with a batch gluconic acid fermentation process as

S. R. Weijers; G. Honderd; K. Ch. A. M. Luyben

1990-01-01

427

The 630 nm MIG and the vertical neutral wind in the low latitude nighttime thermosphere  

Microsoft Academic Search

It is shown that large negative divergences (gradients) in the horizontal neutral wind in the equatorial thermosphere can support downward neutral winds in excess of 20 m\\/s. With attention to the meridional and vertical winds only, the pressure tendency equation is used to derive the expression U[sub zO] [approx] [l angle][partial derivative]U[sub y]\\/[partial derivative]y[r angle]H for the vertical wind U[sub

F. A. Herrero; J.W. Jr. Meriwether

1994-01-01

428

The 630 nm MIG and the vertical neutral wind in the low latitude nighttime thermosphere  

Microsoft Academic Search

It is shown that large negative divergences (gradients) in the horizontal neutral wind in the equatorial thermosphere can support downward neutral winds in excess of 20 m\\/s. With attention to the meridional and vertical winds only, the pressure tendency equation is used to derive the expression Uz0 approximately equals (Partial derivative Uy\\/Partial derivative y)H for the vertical wind Uz0 at

F. A. Herrero; J. W. Meriwether Jr.

1994-01-01

429

Light gradients and optical microniches in coral tissues  

PubMed Central

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

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

2012-01-01

430

Jet Stream and Horizontal Temperature Gradients  

NSDL National Science Digital Library

This applet explores the relationship between wind speed, jet streams and temperature gradients. The text explains jet streams and polar front jets and their relationship to temperature gradients. Questions about pressure gradients and wind are also provided.

Ackerman, Steve; Whittaker, Tom

431

Freezing-induced fluid-matrix interaction in poroelastic material  

PubMed Central

Freezing of biological tissue is emerging in various biomedical applications. The success of these applications requires precise control of the tissue functionality, which is closely associated with the microstructure of the extracellular matrix (ECM). In the present study, the spatiotemporal effects of freezing on the ECM were experimentally and theoretically investigated by approximating biological tissue as a poroelastic material saturated with interstitial fluid. The experiments with type I collagen gel showed that its matrix underwent two distinct levels of structural changes due to freezing : enlarged pore structure of the matrix and increased collagen fibril diameters. The extent of these changes was augmented as the freezing temperature was lowered. The theoretical model suggested that the interstitial fluid might be transported toward the unfrozen region from the phase change interface due to the volumetric expansion associated with the water-ice phase change, and the transported fluid could interact with the matrix and enlarge its pore structure. The model also illustrated the effects of matrix structural properties on this interaction including initial porosity, hydraulic conductivity and elastic modulus. These results imply that an identical macroscopic freezing protocol may result in different microstructural alterations of poroelastic materials depending on the structural properties of the matrix. This may be relevant to understanding the tissue-type dependent outcomes of cryomedicine applications and be useful in designing cryomedicine applications for a wide variety of tissues.

Han, Bumsoo; Miller, Jeffrey D.; Jung, Jun K.

2008-01-01

432

Antibody staining in C. elegans using "freeze-cracking".  

PubMed

To stain C. elegans with antibodies, the relatively impermeable cuticle must be bypassed by chemical or mechanical methods. "Freeze-cracking" is one method used to physically pull the cuticle from nematodes by compressing nematodes between two adherent slides, freezing them, and pulling the slides apart. Freeze-cracking provides a simple and rapid way to gain access to the tissues without chemical treatment and can be used with a variety of fixatives. However, it leads to the loss of many of the specimens and the required compression mechanically distorts the sample. Practice is required to maximize recovery of samples with good morphology. Freeze-cracking can be optimized for specific fixation conditions, recovery of samples, or low non-specific staining, but not for all parameters at once. For antibodies that require very hard fixation conditions and tolerate the chemical treatments needed to chemically permeabilize the cuticle, treatment of intact nematodes in solution may be preferred. If the antibody requires a lighter fix or if the optimum fixation conditions are unknown, freeze-cracking provides a very useful way to rapidly assay the antibody and can yield specific subcellular and cellular localization information for the antigen of interest. PMID:24145964

Duerr, Janet S

2013-01-01

433

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

434

Measuring Growth with Vertical Scales  

ERIC Educational Resources Information Center

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

Briggs, Derek C.

2013-01-01

435

Vertical strabismus in monofixation syndrome  

Microsoft Academic Search

Purpose: The manifest angle of the horizontal deviation in monofixation syndrome (MFS) has been reported to reach a maximum of 8 to 10 PD. Review of the literature, however, revealed no studies about the vertical deviation associated with MFS. The purpose of this study is to evaluate the range of the angle of the vertical deviation in MFS. Methods: Forty

Dong Gyu Choi; Sherwin J. Isenberg

2001-01-01

436

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

437

The Gains from Vertical Scaling  

ERIC Educational Resources Information Center

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

Briggs, Derek C.; Domingue, Ben

2013-01-01

438

Prediction of mechanical properties of multilayer gradient hydroxyapatite reinforced poly(vinyl alcohol) gel biomaterial.  

PubMed

Functional graded materials provided us one new concept for artificial articular cartilage design with graded component and graded structure. In this article, a novel functional material design was proposed by functionalizing hydroxyapatite (HA) particles in poly(vinyl alcohol) (PVA) hydrogel. The goal of the present study was to fabricate a multilayer gradient HA/PVA gel biocomposites through layer-by-layer casting method combining with freeze/thaw cycle technology and establish a mechanical model to predict the compressive mechanical properties of multilayer gradient gel biocomposites. The results showed that the compressive strength of the multilayer gradient gel biocomposites increased with the rise of HA content, but it presented decreasing trend with the rise of interlayer gradient concentration of HA particles. Furthermore, the compressive strength of multilayer gradient biocomposites would be approximately predicted by the established mechanical model. The maximum error between theoretical compressive strength predicted by the model and the experimental strength is less than 7%. On the other hand, the compressive mechanical properties of multilayer gradient composites could be designed and controlled by the mechanical model as established in this study. PMID:23359553

Yusong, Pan; Qianqian, Shen; Chengling, Pan; Jing, Wang

2013-07-01

439

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

440

On computing gradients of potential field data in the space domain  

NASA Astrophysics Data System (ADS)

Accurate and robust computation of gradients of potential field data are crucial in potential field-data processing and also in data-based interpretation. The standard Fourier domain approach in gradient computation, although computationally efficient, is flawed due to its sensitivity to noise in the data. A robust space domain technique in computing both the horizontal and vertical gradients of equally spaced 2D potential field data is formalized. The method uses moving polynomial interpolation in 2D to compute the x- and y-components of the horizontal gradient of the 2D data, and provides optimal low-pass filtering to the noisy data as well. The amount of filtering depends on the order of polynomial and the dimension of the filter window. The vertical gradient is computed through a Hilbert transform of the x- and y-components of the horizontal gradient in the space domain using a sinc interpolation method, where a regularization technique and a conjugate gradient solver are used to determine the sinc bases which are used to compute the Hilbert transform. Numerical experiments on synthetically generated 2D data contaminated with varied levels of random noise were carried out and a comparison of the present technique with the standard Fourier domain technique was also made. The applicability of the method to the field data was also tested.

Roy, Indrajit G.

2013-06-01

441

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

PubMed

Phase transition behavior of lyotropic liquid crystals of an octyl ?-D-glucoside (OG)-water binary system during ice freezing and meltin