Effect of horizontal heat and fluid flow on the vertical temperature distribution in a semiconfining layer

USGS Publications Warehouse

Lu, Ning; Ge, Shemin

1996-01-01

By including the constant flow of heat and fluid in the horizontal direction, we develop an analytical solution for the vertical temperature distribution within the semiconfining layer of a typical aquifer system. The solution is an extension of the previous one-dimensional theory by Bredehoeft and Papadopulos [1965]. It provides a quantitative tool for analyzing the uncertainty of the horizontal heat and fluid flow. The analytical results demonstrate that horizontal flow of heat and fluid, if at values much smaller than those of the vertical, has a negligible effect on the vertical temperature distribution but becomes significant when it is comparable to the vertical.

Phase-Field Simulation of Concentration and Temperature Distribution During Dendritic Growth in a Forced Liquid Metal Flow

NASA Astrophysics Data System (ADS)

Du, Lifei; Zhang, Rong

2014-12-01

A phase-field model with convection is employed to investigate the effect of liquid flow on the dendritic structure formation of a Ni-Cu alloy during rapid solidification. Temperature and solute diffusion are significantly changed with induced liquid metal flow, and distribution changes of concentration and temperature are also analyzed and discussed. The solute segregation is affected due to the concentration diffusion layer thickness change caused by the liquid flow. The flow reduces the solute segregation in the upstream and leads to a fast dendrite growing, while solidifying in the downstream gets constrained with the large solute diffusion layer. Increasing flow velocity increases the asymmetry of dendrite morphology with much more suppressed growth in the downstream. The temperature distribution is also asymmetrical due to the non-uniform latent heat released during solidification coupling with heat diffusion changed by the liquid flow. Therefore, the forced liquid flow significantly affects the dendrite morphology, concentration, and temperature distributions in the solidifying microstructure.

Distribution of blocking temperatures in nano-oxide layers of specular spin valves

NASA Astrophysics Data System (ADS)

Ventura, J.; Araujo, J. P.; Sousa, J. B.; Veloso, A.; Freitas, P. P.

2007-06-01

Specular spin valves show enhanced giant magnetoresistive (GMR) ratio when compared to other, simpler, spin valve structures. The enhancement of GMR results from specular reflection in nano-oxide layers (NOLs) formed by the partial oxidation of the pinned and free layer. These oxides forming the NOL order antiferromagnetically (AFM) below a temperature T ˜175 K. Here, we study the effects of the pinned layer magnetization and its domain structure on the AFM ordering of the NOL by performing field cooling measurements with different cooling fields (H0). We observe enhanced (reduced) exchange field and magnetoresistive ratio for H0>0(<0), i.e., parallel (antiparallel) to the pinned magnetization. These measurements allowed us to confirm the existence of a wide distribution of blocking temperatures (TB) in the NOL of specular spin valves, having a maximum at T ≈175 K, and extending to NOL regions with TB as low as 15 K.

Effect of Index of Refraction on Radiation Characteristics in a Heated Absorbing, Emitting, and Scattering Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1992-01-01

The index of refraction can considerably influence the temperature distribution and radiative heat flow in semitransparent materials such as some ceramics. For external radiant heating, the refractive index influences the amount of energy transmitted into the interior of the material. Emission within a material depends on the square of its refractive index, and hence this emission can be many times that for a biackbody radiating into a vacuum. Since radiation exiting through an interface into a vacuum cannot exceed that of a blackbody, there is extensive reflection at the internal surface of an interface, mostly by total internal reflection. This redistributes energy within the layer and tends to make its temperature distribution more uniform. The purpose of the present analysis is to show that, for radiative equilibrium in a gray layer with diffuse interfaces, the temperature distribution and radiative heat flux for any index of refraction can be obtained very simply from the results for an index of refraction of unity. For the situation studied here, the layer is subjected to external radiative heating incident on each of its surfaces. The material emits, absorbs, and isotropically scatters radiation. For simplicity the index of refraction is unity in the medium surrounding the layer. The surfaces of the layer are assumed diffuse. This is probably a reasonable approximation for a ceramic layer that has not been polished. When transmitted radiation or radiation emitted from the interior reaches the inner surface of an interface, the radiation is diffused and some of it thereby placed into angular directions for which there is total internal reflection. This provides a trapping effect for retaining energy within the layer and tends to equalize its temperature distribution. An analysis of temperature distributions in absorbing-emitting layers, including index of refraction effects, was developed by Gardon (1958) to predict cooling and heat treating of glass plates. The interfaces were optically smooth; the resulting specular reflections were computed from the Fresnel reflection laws. This provides a somewhat different behavior than for diffuse interfaces. A similar application was for heating that occurs in a window of a re-entry vehicle (Fowle et al., 1969). A number of recent papers (Rokhsaz and Dougherty, 1989; Ping and Lallemand, 1989; Crosbie and Shieh, 1990) further examined the effects of Fresnel boundary reflections and nonunity refractive index. Other examples of analyses of both steady and transient heat transfer to single or multiple plane layers (Amlin and Korpela, 1979; Tarshis et al., 1969) have used diffuse assumptions at the interfaces as in the present study

Temperature Distribution in a Composite of Opaque and Semitransparent Spectral Layers

NASA Technical Reports Server (NTRS)

Siegel, Robert

1997-01-01

The analysis of radiative transfer becomes computationally complex for a composite when there are multiple layers and multiple spectral bands. A convenient analytical method is developed for combined radiation and conduction in a composite of alternating semitransparent and opaque layers. The semi- transparent layers absorb, scatter, and emit radiation, and spectral properties with large scattering are included. The two-flux method is used, and its applicability is verified by comparison with a basic solution in the literature. The differential equation in the two-flux method Is solved by deriving a Green's function. The solution technique is applied to analyze radiation effects in a multilayer zirconia thermal barrier coating with internal radiation shields for conditions in an aircraft engine combustor. The zirconia radiative properties are modeled by two spectral bands. Thin opaque layers within the coating are used to decrease radiant transmission that can degrade the zirconia insulating ability. With radiation shields, the temperature distributions more closely approach the opaque limit that provides the lowest metal wall temperatures.

Effect of Index of Refraction on Radiation Characteristics in a Heated Absorbing, Emitting, and Scattering Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1992-01-01

The effect of the index of refraction on the temperature distribution and radiative heat flux in semitransparent materials, such as some ceramics, is investigated analytically. In the case considered here, a plane layer of a ceramic material is subjected to external radiative heating incident on each of its surfaces; the material emits, absorbs, and isotropically scatters radiation. It is shown that, for radiative equilibrium in a gray layer with diffuse interfaces, the temperature distribution and radiative heat flux for any index of refraction can be obtained in a simple manner from the results for an index of refraction of unity.

Experimental study of thermocapillary flows in a thin liquid layer with heat fluxes imposed on the free surface

NASA Technical Reports Server (NTRS)

Lai, Chun-Liang; Greenberg, Paul S.; Chai, An-Ti

1988-01-01

To study thermocapillary flows in a two-dimensional thin liquid layer with heat fluxes imposed on the free surface experimentally, a long tray configuration was employed to simulate the infinite layer. The surface temperature distribution due to thermocapillary convective for different flow regimes was measured and compared with theoretical predictions. A short tray configuration was also employed to study the end wall effects (insulating or conducting). The results show that for a strong convection flow with an insulating wall as the boundary the surface temperature distribution became quite uniform. Consequently, the thermocapillary driving force was greatly reduced. On the other hand, a strong fluid motion always existed adjacent to the conducting wall because of the large surface temperature gradient near the wall.

Ion acceleration and non-Maxwellian electron distributions in a low collisionality, high power helicon plasma source

NASA Astrophysics Data System (ADS)

Li, Yan; Sung, Yung-Ta; Scharer, John

2015-11-01

Ion acceleration through plasma double layer and non-Maxwellian two temperature electron distributions have been observed in Madison Helicon Experiment (MadHeX) operated in high RF power (>1000 W) and low Ar pressure (0.17 mtorr) inductive mode. By applying Optical Emission Spectroscopy (OES) cross-checked with an RF-compensated Langmuir probe (at 13.56 MHz and its second and third harmonics), the fast (>80 eV), untrapped electrons downstream of the double layer have a higher temperature of 13 eV than the trapped bulk electrons upstream with a temperature of 4 eV. The reduction of plasma potential and density observed in the double layer region require an upstream temperature ten times the measured 4 eV if occurring via Boltzmann ambipolar expansion. The hot tail electrons of the non-Maxwellian electron distribution affect the formation and the potential drop of the double layer region. The mechanism behind this has been explored via several non-invasive plasma diagnostics tools. The OES measured electron temperatures and densities are also cross-checked with Atomic Data and Analysis Structure (ADAS) and a millimeter wave interferometer respectively. The IEDF is measured by a four-grid RPA and also cross-checked with argon 668 nm Laser Induced Fluorescence (LIF). An emissive probe has been used to measure the plasma potential.

Fundamental Research on Heat Transfer Characteristics in Shell & Tube Type Ice Forming Cold Energy Storage

NASA Astrophysics Data System (ADS)

Saito, Akio; Utaka, Yoshio; Okawa, Seiji; Ishibashi, Hiroaki

Investigation of heat transfer characteristics in an ice making cold energy storage using a set of horizontal cooling pipes was carried out experimentally. Cooling pipe arrangement, number of pipes used and initial water temperature were varied, and temperature distribution in the tank and the volume of ice formed around the pipe were measured. Natural convection was also observed visually. During the experiment, two kinds of layers were observed. One is the layer where ice forming is interfered by natural convection and its temperature decreases rapidly with an almost uniform temperature distribution, and the other is the layer where ice forms steadily under a stagnant water condition. The former was called that the layer is under a cooling process and the latter that the layer is under an ice forming process. The effect of the experimental parameters, such as the arrangement of the cooling pipes, the number of pipes, the initial water temperature and the flow rate of the cooling medium, on the cooling process and the ice forming process were discussed. Approximate analysis was also carried out and compared with the experimental results. Finally, the relationship between the ice packing factor, which is significant in preventing the blockade, and experimental parameters was discussed.

Room-temperature ferromagnetism in Dy films doped with Ni

NASA Astrophysics Data System (ADS)

Edelman, I.; Ovchinnikov, S.; Markov, V.; Kosyrev, N.; Seredkin, V.; Khudjakov, A.; Bondarenko, G.; Kesler, V.

2008-09-01

Temperature, magnetic field and spectral dependences of magneto-optical effects (MOEs) in bi-layer films Dy (1-x)Ni x-Ni and Dy (1-x)(NiFe) x-NiFe were investigated, x changes from 0 to 0.06. Peculiar behavior of the MOEs was revealed at temperatures essentially exceeding the Curie temperature of bulk Dy which is explained by the magnetic ordering of the Dy layer containing Ni under the action of two factors: Ni impurities distributed homogeneously over the whole Dy layer and atomic contact of this layer with continues Ni layer. The mechanism of the magnetic ordering is suggested to be associated with the change of the density of states of the alloy Dy (1-x)Ni x owing to hybridization with narrow peaks near the Fermi level character for Ni.

Mid-latitude empirical model of the height distribution of atomic oxygen in the MLT region for different solar and geophysical conditions

NASA Astrophysics Data System (ADS)

Semenov, A.; Shefov, N.; Fadel, Kh.

The model of altitude distributions of atomic oxygen in the region of the mesopause and lower thermosphere (MLT) is constructed on the basis of empirical models of variations of the intensities, temperatures and altitudes of maximum of the layers of the emissions of atomic oxygen at 557.7 nm, hydroxyl and Atmospheric system of molecular oxygen. An altitude concentration distribution of neutral components is determined on the basis of systematization of the long-term data of temperature of the middle atmosphere from rocket, nightglow and ionospheric measurements at heights of 30-110 km in middle latitudes. They include dependence on a season, solar activity and a long-term trend. Examples of results of calculation for different months of year for conditions of the lower and higher solar activity are presented. With increasing of solar activity, the height of a layer of a maximum of atomic oxygen becomes lower, and the thickness of the layer increases. There is a high correlation between characteristics of a layer of atomic oxygen and a maximum of temperature at heights of the mesopause and lower thermosphere. This work is supported by grant of ISTC No. 2274.

Turbulent shear stresses in compressible boundary layers

NASA Technical Reports Server (NTRS)

Laderman, A. J.; Demetriades, A.

1979-01-01

Hot-wire anemometer measurements of turbulent shear stresses in a Mach 3 compressible boundary layer were performed in order to investigate the effects of heat transfer on turbulence. Measurements were obtained by an x-probe in a flat plate, zero pressure gradient, two dimensional boundary layer in a wind tunnel with wall to freestream temperature ratios of 0.94 and 0.71. The measured shear stress distributions are found to be in good agreement with previous results, supporting the contention that the shear stress distribution is essentially independent of Mach number and heat transfer for Mach numbers from incompressible to hypersonic and wall to freestream temperature ratios of 0.4 to 1.0. It is also found that corrections for frequency response limitations of the electronic equipment are necessary to determine the correct shear stress distribution, particularly at the walls.

Temperature based Restricted Boltzmann Machines

NASA Astrophysics Data System (ADS)

Li, Guoqi; Deng, Lei; Xu, Yi; Wen, Changyun; Wang, Wei; Pei, Jing; Shi, Luping

2016-01-01

Restricted Boltzmann machines (RBMs), which apply graphical models to learning probability distribution over a set of inputs, have attracted much attention recently since being proposed as building blocks of multi-layer learning systems called deep belief networks (DBNs). Note that temperature is a key factor of the Boltzmann distribution that RBMs originate from. However, none of existing schemes have considered the impact of temperature in the graphical model of DBNs. In this work, we propose temperature based restricted Boltzmann machines (TRBMs) which reveals that temperature is an essential parameter controlling the selectivity of the firing neurons in the hidden layers. We theoretically prove that the effect of temperature can be adjusted by setting the parameter of the sharpness of the logistic function in the proposed TRBMs. The performance of RBMs can be improved by adjusting the temperature parameter of TRBMs. This work provides a comprehensive insights into the deep belief networks and deep learning architectures from a physical point of view.

Novel approach for III-N on Si (111) templates fabrication by low-temperature PA MBE using porous Si layer

NASA Astrophysics Data System (ADS)

Zolotukhin, D.; Seredin, P.; Lenshin, A.; Goloshchapov, D.; Mizerov, A.

2017-11-01

We report on successful growth of GaN nanorods by low-temperature plasma-assisted molecular beam epitaxy on a Si(111) substrate with and without preformed thin porous Si layer (por-Si). The deposited GaN initially forms islands which act as a seed for the wires. Porous structure of the por-Si layer helps to control nucleation islands sizes and achieve homogeneous distribution of the nanorods diameters. In addition 850 nm-thick crack-free GaN layer was formed on Si(111) substrate with preformed por-Si layer.

The Effects of Forming Parameters on Conical Ring Rolling Process

PubMed Central

Meng, Wen; Zhao, Guoqun; Guan, Yanjin

2014-01-01

The plastic penetration condition and biting-in condition of a radial conical ring rolling process with a closed die structure on the top and bottom of driven roll, simplified as RCRRCDS, were established. The reasonable value range of mandrel feed rate in rolling process was deduced. A coupled thermomechanical 3D FE model of RCRRCDS process was established. The changing laws of equivalent plastic strain (PEEQ) and temperature distributions with rolling time were investigated. The effects of ring's outer radius growth rate and rolls sizes on the uniformities of PEEQ and temperature distributions, average rolling force, and average rolling moment were studied. The results indicate that the PEEQ at the inner layer and outer layer of rolled ring are larger than that at the middle layer of ring; the temperatures at the “obtuse angle zone” of ring's cross-section are higher than those at “acute angle zone”; the temperature at the central part of ring is higher than that at the middle part of ring's outer surfaces. As the ring's outer radius growth rate increases at its reasonable value ranges, the uniformities of PEEQ and temperature distributions increase. Finally, the optimal values of the ring's outer radius growth rate and rolls sizes were obtained. PMID:25202716

Heat transfer through turbulent boundary layers - The effects of introduction of and recovery from convex curvature

NASA Technical Reports Server (NTRS)

Simon, T. W.; Moffat, R. J.

1979-01-01

Measurements have been made of the heat transfer through a turbulent boundary layer on a convexly curved isothermal wall and on a flat plate following the curved section. Data were taken for one free-stream velocity and two different ratios of boundary layer thickness to radius of curvature delta/R = 0.051 and delta/R = 0.077. Only small differences were observed in the distribution of heat transfer rates for the two boundary layer thicknesses tested, although differences were noted in the temperature distributions within the boundary layer

Refractive Index and Scattering Effects on Radiative Behavior of a Semitransparent Layer

NASA Technical Reports Server (NTRS)

Spuckler, C. M.; Siegel, R.

1993-01-01

Heat transfer characteristics are analyzed for a plane layer of semitransparent material with refractive index not less than 1. Energy transfer in the material is by conduction, emission, absorption, and isotropic scattering. Each side of the layer is heated by radiation and convection. For a refractive index larger than unity, there is internal reflection of some of the energy within the layer. This, coupled with scattering, has a substantial effect on distributing energy across the layer and altering the temperature distribution from when the refractive index is unity. The effect of scattering is examined by comparisons with results from an earlier paper for an absorbing layer. Results are given for a gray medium with a scattering albedo up to 0.999, and for a two-band spectral variation of the albedo with one band having low absorption. Radiant energy leaving the surface as a result of emission and scattering was examined to determine if it could be used to accurately indicate the surface temperature.

Experimental plasma studies

NASA Technical Reports Server (NTRS)

Dunn, M. G.

1972-01-01

The rate coefficients for the reactions C(+) + e(-) + e(-) yields C + e(-) and CO(+) + e(-) yields C + O were measured over the electron temperature range of approximately 1500 deg K to 7000 deg K. The measurements were performed in CO that had expanded from equilibrium reservoir conditions of 7060 deg K at 17.3 atm pressure and from 6260 deg K at 10.0 atm pressure. Two RAM flight probes were used to measure electron density and electron temperature in the expanding flow of a shock tunnel. Experiments were performed in the inviscid flow with both probes and in the nozzle-wall boundary layer with the constant bias-voltage probe. The distributions of electron density and electron temperature were independently measured using voltage-swept thin-wire probes. Thin-wire Langmuir probes were also used to measure the electron-density and electron-temperature distributions in the boundary layer of a sharp flat plate located on the nozzle centerline. Admittance measurements were performed with the RAM C and RAM C-C S-band antennas in the presence of an ionized boundary layer.

Low Temperature Double-layer Capacitors with Improved Energy Density: An Overview of Recent Development Efforts

NASA Technical Reports Server (NTRS)

Brandon, Erik J.; West, William C.; Smart, Marshall C.; Korenblit, Yair; Kajdos, Adam; Kvit, Alexander; Jagiello, Jacek; Yushin, Gleb

2012-01-01

Electrochemical double-layer capacitors are finding increased use in a wide range of energy storage applications, particularly where high pulse power capabilities are required. Double-layer capacitors store charge at a liquid/solid interface, making them ideal for low temperature power applications, due to the facile kinetic processes associated with the rearrangement of the electrochemical double-layer at these temperatures. Potential low temperature applications include hybrid and electric vehicles, operations in polar regions, high altitude aircraft and aerospace avionics, and distributed environmental and structural health monitoring. State-of-the-art capacitors can typically operate to -40 C, with a subsequent degradation in power performance below room temperature. However, recent efforts focused on advanced electrolyte and electrode systems can enable operation to temperatures as low as -70 C, with capacities similar to room temperature values accompanied by reasonably low equivalent series resistances. This presentation will provide an overview of recent development efforts to extend and improve the wide temperature performance of these devices.

The effect of wall temperature distribution on streaks in compressible turbulent boundary layer

NASA Astrophysics Data System (ADS)

Zhang, Zhao; Tao, Yang; Xiong, Neng; Qian, Fengxue

2018-05-01

The thermal boundary condition at wall is very important for the compressible flow due to the coupling of the energy equation, and a lot of research works about it were carried out in past decades. In most of these works, the wall was assumed as adiabatic or uniform isothermal surface; the flow over a thermal wall with some special temperature distribution was seldom studied. Lagha studied the effect of uniform isothermal wall on the streaks, and pointed out that higher the wall temperature is, the longer the streak (POF, 2011, 23, 015106). So, we designed streamwise stripes of wall temperature distribution on the compressible turbulent boundary layer at Mach 3.0 to learn the effect on the streaks by means of direct numerical simulation in this paper. The mean wall temperature is equal to the adiabatic case approximately, and the width of the temperature stripes is in the same order as the width of the streaks. The streak patterns in near-wall region with different temperature stripes are shown in the paper. Moreover, we find that there is a reduction of friction velocity with the wall temperature stripes when compared with the adiabatic case.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, B.; Lu, S. X.; Li, C. H.

In an atrium measured 120 m by 180 m by 36.5 m high, fire tests were conducted under 'natural filling' and 'mechanical exhaust' conditions by hot smoke test method. The fire size was 8 MW released by an ethanol pool of 3.6 m in diameter. The distribution of vertical temperature profiles above the fire source and the gas layer temperatures were measured. From these measurements, it was shown that the fans successfully exhausted hot smoke to control descending of hot smoke layer and temperature rising rate. The hot smoke layer can be maintained at about 30 m which was almostmore » 2 times of hot layer height in 'natural filling' condition. The temperature risings in both conditions were too low to cause thermal damage to the structure, only 18.6 K and 12 K. The centerline temperature above the fire source and the height of hot smoke layer were calculated using the plume models. The calculated results agreed well with the conclusions obtained from the experiment results.« less

Study of velocity and temperature distributions in boundary layer flow of fourth grade fluid over an exponential stretching sheet

NASA Astrophysics Data System (ADS)

Khan, Najeeb Alam; Saeed, Umair Bin; Sultan, Faqiha; Ullah, Saif; Rehman, Abdul

2018-02-01

This study deals with the investigation of boundary layer flow of a fourth grade fluid and heat transfer over an exponential stretching sheet. For analyzing two heating processes, namely, (i) prescribed surface temperature (PST), and (ii) prescribed heat flux (PHF), the temperature distribution in a fluid has been considered. The suitable transformations associated with the velocity components and temperature, have been employed for reducing the nonlinear model equation to a system of ordinary differential equations. The flow and temperature fields are revealed by solving these reduced nonlinear equations through an effective analytical method. The important findings in this analysis are to observe the effects of viscoelastic, cross-viscous, third grade fluid, and fourth grade fluid parameters on the constructed analytical expression for velocity profile. Likewise, the heat transfer properties are studied for Prandtl and Eckert numbers.

Observation of warm, higher energy electrons transiting a double layer in a helicon plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sung, Yung-Ta, E-mail: ysung2@wisc.edu; Li, Yan; Scharer, John E.

2015-03-15

Measurements of an inductive RF helicon argon plasma double layer with two temperature electron distributions including a fast (>80 eV) tail are observed at 0.17 mTorr Ar pressure. The fast, untrapped electrons observed downstream of the double layer have a higher temperature (13 eV) than the trapped (T{sub e} = 4 eV) electrons. The reduction of plasma potential and density observed in the double layer region would require an upstream temperature ten times the measured 4 eV if occurring via Boltzmann ambipolar expansion. The experimental observation in Madison helicon experiment indicates that fast electrons with substantial density fractions can be created at low helicon operating pressures.

Deployment of titanium thermal barrier for low-temperature carbon nanotube growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, G.Y.; Poa, C.H.P.; Henley, S.J.

2005-12-19

Chemical vapor-synthesized carbon nanotubes are typically grown at temperatures around 600 deg. C. We report on the deployment of a titanium layer to help elevate the constraints on the substrate temperature during plasma-assisted growth. The growth is possible through the lowering of the hydrocarbon content used in the deposition, with the only source of heat provided by the plasma. The nanotubes synthesized have a small diameter distribution, which deviates from the usual trend that the diameter is determined by the thickness of the catalyst film. Simple thermodynamic simulations also show that the quantity of heat, that can be distributed, ismore » determined by the thickness of the titanium layer. Despite the lower synthesis temperature, it is shown that this technique allows for high growth rates as well as better quality nanotubes.« less

Large Eddy Simulations of a Bottom Boundary Layer Under a Shallow Geostrophic Front

NASA Astrophysics Data System (ADS)

Bateman, S. P.; Simeonov, J.; Calantoni, J.

2017-12-01

The unstratified surf zone and the stratified shelf waters are often separated by dynamic fronts that can strongly impact the character of the Ekman bottom boundary layer. Here, we use large eddy simulations to study the turbulent bottom boundary layer associated with a geostrophic current on a stratified shelf of uniform depth. The simulations are initialized with a spatially uniform vertical shear that is in geostrophic balance with a pressure gradient due to a linear horizontal temperature variation. Superposed on the temperature front is a stable vertical temperature gradient. As turbulence develops near the bottom, the turbulence-induced mixing gradually erodes the initial uniform temperature stratification and a well-mixed layer grows in height until the turbulence becomes fully developed. The simulations provide the spatial distribution of the turbulent dissipation and the Reynolds stresses in the fully developed boundary layer. We vary the initial linear stratification and investigate its effect on the height of the bottom boundary layer and the turbulence statistics. The results are compared to previous models and simulations of stratified bottom Ekman layers.

Prediction of temperature and HAZ in thermal-based processes with Gaussian heat source by a hybrid GA-ANN model

NASA Astrophysics Data System (ADS)

Fazli Shahri, Hamid Reza; Mahdavinejad, Ramezanali

2018-02-01

Thermal-based processes with Gaussian heat source often produce excessive temperature which can impose thermally-affected layers in specimens. Therefore, the temperature distribution and Heat Affected Zone (HAZ) of materials are two critical factors which are influenced by different process parameters. Measurement of the HAZ thickness and temperature distribution within the processes are not only difficult but also expensive. This research aims at finding a valuable knowledge on these factors by prediction of the process through a novel combinatory model. In this study, an integrated Artificial Neural Network (ANN) and genetic algorithm (GA) was used to predict the HAZ and temperature distribution of the specimens. To end this, a series of full factorial design of experiments were conducted by applying a Gaussian heat flux on Ti-6Al-4 V at first, then the temperature of the specimen was measured by Infrared thermography. The HAZ width of each sample was investigated through measuring the microhardness. Secondly, the experimental data was used to create a GA-ANN model. The efficiency of GA in design and optimization of the architecture of ANN was investigated. The GA was used to determine the optimal number of neurons in hidden layer, learning rate and momentum coefficient of both output and hidden layers of ANN. Finally, the reliability of models was assessed according to the experimental results and statistical indicators. The results demonstrated that the combinatory model predicted the HAZ and temperature more effective than a trial-and-error ANN model.

Article and method of forming an article

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lacy, Benjamin Paul; Kottilingam, Srikanth Chandrudu; Dutta, Sandip

Provided are an article and a method of forming an article. The method includes providing a metallic powder, heating the metallic powder to a temperature sufficient to joint at least a portion of the metallic powder to form an initial layer, sequentially forming additional layers in a build direction by providing a distributed layer of the metallic powder over the initial layer and heating the distributed layer of the metallic powder, repeating the steps of sequentially forming the additional layers in the build direction to form a portion of the article having a hollow space formed in the build direction,more » and forming an overhang feature extending into the hollow space. The article includes an article formed by the method described herein.« less

Temperature dependence of positron annihilation parameters in Tl-Ba-Ca-Cu-O superconductors

NASA Astrophysics Data System (ADS)

Sundar, C. S.; Bharathi, A.; Ching, W. Y.; Jean, Y. C.; Hor, P. H.; Meng, R. L.; Huang, Z. J.; Chu, C. W.

1990-08-01

The results of positron lifetime and Doppler broadened line-shape parameter measurements as a function of temperature, across Tc, in the Tl-Ba-Ca-Cu-O superconductors are presented. The bulk lifetime in the normal state is found to decrease with the increase in the number of CuO2 layers. Different temperature dependencies of the annihilation parameters are observed in the various Tl systems containing different numbers of CuO2 layers. In the Tl2Ba2Ca2Cu3O10 system, an increase in lifetime is observed below Tc, whereas in Tl2Ba2CaCu2O8, a decrease in lifetime is seen below Tc. In the Tl2Ba2CuO6 system, the lifetime is observed to be temperature independent. The different temperature variations of positron annihilation parameters are discussed in the light of the positron density distribution, obtained with use of the results of the self-consistent orthogonalized linear combination of atomic orbitals band-structure calculations. It is argued that the different temperature dependencies of the annihilation parameters is related to the positron density distribution within the unit cell and arise due to local charge transfer in the vicinity of the CuO2 layer in the superconducting state.

Habitat Parameters for Oxygen Minimum Zone Copepods from the Eastern Tropical North Pacific

NASA Astrophysics Data System (ADS)

Wishner, K. F.; Outram, D.; Grassian, B.

2016-02-01

Oxygen minimum zones (OMZs) affect zooplankton distributions and may be expanding in worldwide spatial and vertical extent from climate change. We studied zooplankton (especially copepod) distributions in the Eastern Tropical North Pacific (ETNP) OMZ, using day-night vertically-stratified MOCNESS tows (0-1000m). Habitat parameters (temperature, oxygen, depth) were defined for abundant copepod species and groups. Zooplankton layers, with a unique suite of species, occurred at upper and lower OMZ oxyclines. At the mesopelagic lower oxycline, there was a layer with a characteristic species assemblage and a sharp 10X biomass increase compared to nearby depths. The lower oxycline layer occurred within a narrow very low oxygen concentration (2µM). At two stations with different OMZ vertical extents, the lower oxycline layer depth changed with OMZ thickness, remaining at the same oxygen concentration but different temperature. Life history habitat (diapause depth, temperature) of the copepod Eucalanus inermis was also affected. In the upper water column at the two stations, large diel vertical migrators (fish, euphausiids) descended to taxon-specific daytime depths in the mid OMZ, regardless of oxygen level, but copepod species distributions showed more variability and sensitivity to habitat parameters. We predict that, with moderate OMZ expansion, the lower oxycline community will likely shift depth, thus re-distributing midwater biomass, species, and processes. In the upper water column, large vertical migrator distributions may be less affected, while smaller taxa (copepods) will likely be sensitive to habitat changes. At some point, the ability to withstand these changes may be exceeded for particular taxa, with consequences for assemblages, trophic webs, and export. In keeping with the session theme, we hope to compare our oceanic findings with others' results from coastal hypoxic situations.

Mathematical modeling of the temperature distribution under the cathode spot of the vacuum arc

NASA Astrophysics Data System (ADS)

Kuznetsov, V. G.; Babushkina, E. S.

2016-07-01

We present a solution to the problem of the temperature distribution under the cathode spot of taking into account melting and spare deposits of metal, brought to boiling temperature on the surface of the cathode spot. The process of heat transfer in the metal is described by the unsteady three dimensional heat conduction equation in Cartesian coordinate system. Similarly, we present a solution to the problem of the temperature distribution in the presence of the pores in the surface layer of the metal. To solve this task we used a numerical method to finite differences and variable directions. We present the calculated data on the distribution of temperature under the cathode spot for different values of spot diameters and speeds its movement.

Studies of heat source driven natural convection

NASA Technical Reports Server (NTRS)

Kulacki, F. A.; Nagle, M. E.; Cassen, P.

1974-01-01

Natural convection energy transport in a horizontal layer of internally heated fluid with a zero heat flux lower boundary, and an isothermal upper boundary, has been studied. Quantitative information on the time-mean temperature distribution and the fluctuating component of temperature about the mean temperature in steady turbulent convection are obtained from a small thermocouple inserted into the layer through the upper bounding plate. Data are also presented on the development of temperature at several vertical positions when the layer is subject to both a sudden increase and to a sudden decrease in power input. For changes of power input from zero to a value corresponding to a Rayleigh number much greater than the critical linear stability theory value, a slight hysteresis in temperature profiles near the upper boundary is observed between the heat-up and cool-down modes.

Transient Heat Transfer in a Semitransparent Radiating Layer with Boundary Convection and Surface Reflections

NASA Technical Reports Server (NTRS)

Siegel, Robert

1996-01-01

Surface convection and refractive index are examined during transient radiative heating or cooling of a grey semitransparent layer with internal absorption, emission and conduction. Each side of the layer is exposed to hot or cold radiative surroundings, while each boundary is heated or cooled by convection. Emission within the layer and internal reflections depend on the layer refractive index. The reflected energy and heat conduction distribute energy across the layer and partially equalize the transient temperature distributions. Solutions are given to demonstrate the effect of radiative heating for layers with various optical thicknesses, the behavior of the layer heated by radiation on one side and convectively cooled on the other, and a layer heated by convection while being cooled by radiation. The numerical method is an implicit finite difference procedure with non-uniform space and time increments. The basic method developed in earlier work is expanded to include external convection and incident radiation.

Heat Transfer Behavior across the Dentino-Enamel Junction in the Human Tooth

PubMed Central

Niu, Lin; Dong, Shao-Jie; Kong, Ting-Ting; Wang, Rong; Zou, Rui; Liu, Qi-Da

2016-01-01

During eating, the teeth usually endure the sharply temperature changes because of different foods. It is of importance to investigate the heat transfer and heat dissipation behavior of the dentino–enamel junction (DEJ) of human tooth since dentine and enamel have different thermophysical properties. The spatial and temporal temperature distributions on the enamel, dentine, and pulpal chamber of both the human tooth and its discontinuous boundaries, were measured using infrared thermography using a stepped temperature increase on the outer boundary of enamel crowns. The thermal diffusivities for enamel and dentine were deduced from the time dependent temperature change at the enamel and dentine layers. The thermal conductivities for enamel and dentine were calculated to be 0.81 Wm-1K-1 and 0.48 Wm-1K-1 respectively. The observed temperature discontinuities across the interfaces between enamel, dentine and pulp-chamber layers were due to the difference of thermal conductivities at interfaces rather than to the phase transformation. The temperature gradient distributes continuously across the enamel and dentine layers and their junction below a temperature of 42°C, whilst a negative thermal resistance is observed at interfaces above 42°C. These results suggest that the microstructure of the dentin-enamel junction (DEJ) junction play an important role in tooth heat transfer and protects the pulp from heat damage. PMID:27662186

Heat Transfer Behavior across the Dentino-Enamel Junction in the Human Tooth.

PubMed

Niu, Lin; Dong, Shao-Jie; Kong, Ting-Ting; Wang, Rong; Zou, Rui; Liu, Qi-Da

During eating, the teeth usually endure the sharply temperature changes because of different foods. It is of importance to investigate the heat transfer and heat dissipation behavior of the dentino-enamel junction (DEJ) of human tooth since dentine and enamel have different thermophysical properties. The spatial and temporal temperature distributions on the enamel, dentine, and pulpal chamber of both the human tooth and its discontinuous boundaries, were measured using infrared thermography using a stepped temperature increase on the outer boundary of enamel crowns. The thermal diffusivities for enamel and dentine were deduced from the time dependent temperature change at the enamel and dentine layers. The thermal conductivities for enamel and dentine were calculated to be 0.81 Wm-1K-1 and 0.48 Wm-1K-1 respectively. The observed temperature discontinuities across the interfaces between enamel, dentine and pulp-chamber layers were due to the difference of thermal conductivities at interfaces rather than to the phase transformation. The temperature gradient distributes continuously across the enamel and dentine layers and their junction below a temperature of 42°C, whilst a negative thermal resistance is observed at interfaces above 42°C. These results suggest that the microstructure of the dentin-enamel junction (DEJ) junction play an important role in tooth heat transfer and protects the pulp from heat damage.

Hydrographic and fish larvae distribution during the "Godzilla El Niño 2015-2016" in the northern end of the shallow oxygen minimum zone of the Eastern Tropical Pacific Ocean

NASA Astrophysics Data System (ADS)

Sánchez-Velasco, L.; Beier, E.; Godínez, V. M.; Barton, E. D.; Santamaría-del-Angel, E.; Jiménez-Rosemberg, S. P. A.; Marinone, S. G.

2017-03-01

Based on hydrographic data and vertical distributions of tropical species of fish larvae (Diogenichthys laternatus, Vinciguerria lucetia, Bregmaceros bathymaster, and Auxis spp.), effects of "Godzilla El Niño 2015-2016" in the shallow oxygen minimum zone off Mexico were analyzed. Zooplankton samples were collected during four cruises, before (February 2010 and April 2012) and during (June 2015 and March 2016) the warm event. Temporal series of sea surface temperature revealed that June 2015 was the warmest June of the last years. Conservative temperature was >2°C higher than normal in the surface mixed layer, and the suboxic layer (4.4 µmol/kg) reached as shallow as 100 m depth. Unexpected results were that larval abundances were relatively high during the warm event, unlike zooplankton volumes, which declined. Before the warm event, V. lucetia and Auxis spp. were more abundant in the surface mixed layer, while B. bathymaster and D. laternatus dominated in the thermocline and shallow hypoxic layer (44 µmol/kg). However, during the event in June 2015, all species were most abundant in the surface mixed layer, which implied that the species adapted to hypoxia had inverted their normal pattern of distribution, possibly as consequence of the rise of the suboxic layer; however, further observations are required to confirm this generality. Results showed no dramatic change in the total larval abundance during the warm event. Nevertheless, a differential response in their vertical distribution was evident in association with changes in the depth of the shallow hypoxic and suboxic layers. This might indicate adaptability of tropical species to prolonged periods of warming in the oceans.

High-fluence Ga-implanted silicon-The effect of annealing and cover layers

NASA Astrophysics Data System (ADS)

Fiedler, J.; Heera, V.; Hübner, R.; Voelskow, M.; Germer, S.; Schmidt, B.; Skorupa, W.

2014-07-01

The influence of SiO2 and SiNx cover layers on the dopant distribution as well as microstructure of high fluence Ga implanted Si after thermal processing is investigated. The annealing temperature determines the layer microstructure and the cover layers influence the obtained Ga profile. Rapid thermal annealing at temperatures up to 750 °C leads to a polycrystalline layer structure containing amorphous Ga-rich precipitates. Already after a short 20 ms flash lamp annealing, a Ga-rich interface layer is observed for implantation through the cover layers. This effect can partly be suppressed by annealing temperatures of at least 900 °C. However, in this case, Ga accumulates in larger, cone-like precipitates without disturbing the surrounding Si lattice parameters. Such a Ga-rich crystalline Si phase does not exist in the equilibrium phase diagram according to which the Ga solubility in Si is less than 0.1 at. %. The Ga-rich areas are capped with SiOx grown during annealing which only can be avoided by the usage of SiNx cover layers.

A random distribution reacting mixing layer model

NASA Technical Reports Server (NTRS)

Jones, Richard A.; Marek, C. John; Myrabo, Leik N.; Nagamatsu, Henry T.

1994-01-01

A methodology for simulation of molecular mixing, and the resulting velocity and temperature fields has been developed. The ideas are applied to the flow conditions present in the NASA Lewis Research Center Planar Reacting Shear Layer (PRSL) facility, and results compared to experimental data. A gaussian transverse turbulent velocity distribution is used in conjunction with a linearly increasing time scale to describe the mixing of different regions of the flow. Equilibrium reaction calculations are then performed on the mix to arrive at a new species composition and temperature. Velocities are determined through summation of momentum contributions. The analysis indicates a combustion efficiency of the order of 80 percent for the reacting mixing layer, and a turbulent Schmidt number of 2/3. The success of the model is attributed to the simulation of large-scale transport of fluid. The favorable comparison shows that a relatively quick and simple PC calculation is capable of simulating the basic flow structure in the reacting and nonreacting shear layer present in the facility given basic assumptions about turbulence properties.

Mechanical properties of nitrogen-rich surface layers on SS304 treated by plasma immersion ion implantation

NASA Astrophysics Data System (ADS)

Fernandes, B. B.; Mändl, S.; Oliveira, R. M.; Ueda, M.

2014-08-01

The formation of hard and wear resistant surface regions for austenitic stainless steel through different nitriding and nitrogen implantation processes at intermediate temperatures is an established technology. As the inserted nitrogen remains in solid solution, an expanded austenite phase is formed, accounting for these surface improvements. However, experiments on long-term behavior and exact wear processes within the expanded austenite layer are still missing. Here, the modified layers were produced using plasma immersion ion implantation with nitrogen gas and had a thickness of up to 4 μm, depending on the processing temperature. Thicker layers or those with higher surface nitrogen contents presented better wear resistance, according to detailed microscopic investigation on abrasion, plastic deformation, cracking and redeposition of material inside the wear tracks. At the same time, cyclic fatigue testing employing a nanoindenter equipped with a diamond ball was carried out at different absolute loads and relative unloadings. As the stress distribution between the modified layer and the substrate changes with increasing load, additional simulations were performed for obtaining these complex stress distributions. While high nitrogen concentration and/or thicker layers improve the wear resistance and hardness, these modifications simultaneously reduce the surface fatigue resistance.

Highly (002) textured large grain bcc Cr{sub 80}Mn{sub 20} seed layer on Cr{sub 50}Ti{sub 50} amorphous layer for FePt-C granular film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeon, Seong-Jae, E-mail: jsjigst@ecei.tohoku.ac.jp; Saito, Shin; Hinata, Shintaro

Effect of bcc Cr{sub 80}Mn{sub 20} seed layer and Cr{sub 50}Ti{sub 50} amorphous texture inducing layer on the heteroepitaxy system in FePt-C granular film was studied by introducing a new concept of the layered structure. The concept suggested that the large grain seed layer in which the crystallographic texture was initially formed on an amorphous layer in the layered structure can reduce the angular distribution of (002) c-axis crystal orientation in the FePt-C granular film owing to heteroepitaxial growth. Structure analysis by X-ray diffraction revealed that (1) when the substrate heating temperature was elevated from 300 °C to 500 °C, grain sizemore » in the seed layer increased from 9.8 nm to 11.6 nm, and then decreased with further increasing the substrate temperature. The reduction of the grain size over 500 °C corresponds to the crystallization of the amorphous texture inducing layer, (2) when the grain size increased from 9.8 nm to 11.6 nm, the angular distribution of the (002) orientation in the seed layer dramatically decreased from 13.7° to 4.1°. It was shown that the large grain seed layer increased the perpendicular hysteresis in FePt-C granular film.« less

Effect of same-temperature GaN cap layer on the InGaN/GaN multiquantum well of green light-emitting diode on silicon substrate.

PubMed

Zheng, Changda; Wang, Li; Mo, Chunlan; Fang, Wenqing; Jiang, Fengyi

2013-01-01

GaN green LED was grown on Si (111) substrate by MOCVD. To enhance the quality of InGaN/GaN MQWs, same-temperature (ST) GaN protection layers with different thickness of 8 Å, 15 Å, and 30 Å were induced after the InGaN quantum wells (QWs) layer. Results show that a relative thicker cap layer is benefit to get InGaN QWs with higher In percent at fixed well temperature and obtain better QW/QB interface. As the cap thickness increases, the indium distribution becomes homogeneous as verified by fluorescence microscope (FLM). The interface of MQWs turns to be abrupt from XRD analysis. The intensity of photoluminescence (PL) spectrum is increased and the FWHM becomes narrow.

Real-time observation of coadsorption layers on Ru(001) using a temperature-programmed ESDIAD/TOF system

NASA Astrophysics Data System (ADS)

Sasaki, T.; Itai, Y.; Iwasawa, Y.

1997-11-01

For the purpose of utilizing ESDIAD as a real-time probe for surface processes, we have developed an instrument which can measure ESDIAD images and time of flight (TOF) spectra of desorbing ions in temperature-programmed surface processes. TOF measurements are carried out to identify the mass and to determine the kinetic energy distribution of the desorbed ions. This temperature-programmed (TP-) ESDIAD/TOF system was used to observe coadsorption layers of methylamine and CO on Ru(001) which have been previously studied by our group using LEED, TPD and HREELS, also drawing upon a comparison of findings with the coadsorption system of CO and ammonia. ESDIAD images acquired for temperature-programmed surface processes in real time were found to provide new insight into the dynamic behaviour of the coadsorption layers. As to the pure adsorption of ammonia and methylamine, the second and the first (chemisorbed) layers can be easily discriminated in their different ESD detection efficiency due to the difference in neutralization rate. The intensity change of H + ions with temperature shows the process of the decomposition of methylamine to be dependent on CO coverage. The intensity of O + originating from CO changes due to the change of CO adsorption site in the reaction process. The angular distribution of H + ions which correspond to CH2NH…Ru species appears at 250-300 K in the presence of high CO pre-coverage.

Refractive Index Effects on Radiation in an Absorbing, Emitting, and Scattering Laminated Layer

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting temperature radiative energy flow in a two-region semitransparent laminated layer in the limit of zero heat conduction. The composite is heated on its two sides by unequal amounts of incident radiation. The two layers of the composite have different refractive indices, and each material absorbs, emits, and isotropically scatters radiation. The interfaces are diffuse, and all interface reflections are included. To illustrate the thermal behavior that is readily calculated from the equations, typical results an given for various optical thicknesses and refractive indices of the layers. Internal reflections have a substantial effect on the temperature distribution and radiative heat flow.

Energy transfer from a pulsed thermal source to He II below 0.3 K.

NASA Technical Reports Server (NTRS)

Pfeifer, C. D.; Luszczynski, K.

1973-01-01

Results of measurements of the angular distribution of the energy flux radiated from a pulsed heater immersed in He II at low temperatures (around 230 mK). It is shown that the energy transfer from a pulsed carbon heater at a relatively high temperature to ambient liquid helium maintained at low temperature cannot be adequately described by the phonon-coupling models. The experimental data on the velocity and angular distribution of the energy flux radiated from the plane of the heater indicate that the energy from the heater is transferred to a layer of hot helium adjacent to the surface of the heater and that this layer acts as the effective source of excitations radiated into the ambient liquid helium. The extent and shape of this source depend on the total energy flux produced by the heater.

Calculations of Laminar Heat Transfer Around Cylinders of Arbitrary Cross Section and Transpiration-Cooled Walls with Application to Turbine Blade Cooling

NASA Technical Reports Server (NTRS)

Eckert, E.R.G.; Livingood, John N.B.

1951-01-01

An approximate method for development of flow and thermal boundary layers in laminar regime on cylinders with arbitrary cross section and transpiration-cooled walls is obtained by use of Karman's integrated momentum equation and an analogous heat-flow equation. Incompressible flow with constant property values throughout boundary layer is assumed. Shape parameters for approximated velocity and temperature profiles and functions necessary for solution of boundary-layer equations are presented as charts, reducing calculations to a minimum. The method is applied to determine local heat-transfer coefficients and surface temperature-cooled turbine blades for a given flow rate. Coolant flow distributions necessary for maintaining uniform blade temperatures are also determined.

Nonlinear Radiation Heat Transfer Effects in the Natural Convective Boundary Layer Flow of Nanofluid Past a Vertical Plate: A Numerical Study

PubMed Central

Mustafa, Meraj; Mushtaq, Ammar; Hayat, Tasawar; Ahmad, Bashir

2014-01-01

The problem of natural convective boundary layer flow of nanofluid past a vertical plate is discussed in the presence of nonlinear radiative heat flux. The effects of magnetic field, Joule heating and viscous dissipation are also taken into consideration. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations via similarity transformations and then solved numerically using the Runge–Kutta fourth-fifth order method with shooting technique. The results reveal an existence of point of inflection for the temperature distribution for sufficiently large wall to ambient temperature ratio. Temperature and thermal boundary layer thickness increase as Brownian motion and thermophoretic effects intensify. Moreover temperature increases and heat transfer from the plate decreases with an increase in the radiation parameter. PMID:25251242

Novel Approach for Modeling of Nonuniform Slag Layers and Air Gap in Continuous Casting Mold

NASA Astrophysics Data System (ADS)

Wang, Xudong; Kong, Lingwei; Yao, Man; Zhang, Xiaobing

2017-02-01

Various kinds of surface defects on the continuous casting slab usually originate from nonuniform heat transfer and mechanical behavior, especially during the initial solidification inside the mold. In this article, a model-coupled inverse heat transfer problem incorporating the effect of slag layers and air gap is developed to study the nonuniform distribution of liquid slag, solid slag, and air gap layers. The model considers not only the formation and evolution of slag layers and air gap but also the temperatures in the mold copper as measured by thermocouples. The simulation results from the model and the measured temperatures from experiments are shown to be in good agreement with each other. At the casting speed of 0.65 m/min, the liquid slag film disappears and transforms into solid slag entirely at about 400 mm away from meniscus, and an air gap begins to form. Until the mold exit, the maximum thickness of the solid slag layer and air gap gradually increases to 1.34 and 0.056 mm, respectively. The results illustrate that the magnitude and nonuniform distribution of the slag layers and air gap along the cross direction, correlating with heat flux between the shell and mold, eventually determine the temperature profiles of the mold hot face and slab surface. The proposed model may provide a convenient approach for analyzing nonuniform heat transfer and mechanical behaviors between the mold and slab in the real casting process.

Nonlinear development and secondary instability of Gortler vortices in hypersonic flows

NASA Technical Reports Server (NTRS)

Fu, Yibin B.; Hall, Philip

1991-01-01

In a hypersonic boundary layer over a wall of variable curvature, the region most susceptible to Goertler vortices is the temperature adjustment layer over which the basic state temperature decreases monotonically to its free stream value. Except for a special wall curvature distribution, the evolution of Goertler vortices trapped in the temperature adjustment layer will in general be strongly affected by the boundary layer growth through the O(M sup 3/2) curvature of the basic state, where M is the free stream Mach number. Only when the local wavenumber becomes as large as of order M sup 3/8, do nonparallel effects become negligible in the determination of stability properties. In the latter case, Goertler vortices will be trapped in a thin layer of O(epsilon sup 1/2) thickness which is embedded in the temperature adjustment layer; here epsilon is the inverse of the local wavenumber. A weakly nonlinear theory is presented in which the initial nonlinear development of Goertler vortices in the neighborhood of the neutral position is studied and two coupled evolution equations are derived. From these, it can be determined whether the vortices are decaying or growing depending on the sign of a constant which is related to wall curvature and the basic state temperature.

Effect of thermal annealing on the photoluminescence of structures with InGaAs/GaAs quantum wells and a low-temperature GaAs layer δ-doped with Mn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalentyeva, I. L.; Vikhrova, O. V., E-mail: istery@rambler.ru; Danilov, Yu. A.

2016-11-15

The effects of isochronal thermal annealing (at 325–725°C) on the radiative properties of InGaAs/GaAs nanoheterostructures containing a low-temperature GaAs layer δ-doped with Mn grown by laser deposition are studied. A decrease in the photoluminescence intensity and increase in the ground transition energy are observed upon thermal impact for quantum wells located near the low-temperature GaAs layer. The distribution of Mn atoms in the initial and annealed structures is obtained by secondary-ion mass spectrometry. A qualitative model of the observed effects of thermal annealing on the radiative properties of the structures is discussed; this model takes into account two main processes:more » diffusion of point defects (primarily gallium vacancies) from the GaAs coating layer deep into the structure and Mn diffusion in both directions by the dissociation mechanism. Magnetization studies show that, as a result of thermal annealing, an increase in the proportion of the ferromagnetic phase at room temperature (presumably, MnAs clusters) in the low-temperature GaAs coating layer takes place.« less

Thermographic process monitoring in powderbed based additive manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krauss, Harald, E-mail: harald.krauss@iwb.tum.de; Zaeh, Michael F.; Zeugner, Thomas

2015-03-31

Selective Laser Melting is utilized to build metallic parts directly from CAD-Data by solidification of thin powder layers through application of a fast scanning laser beam. In this study layerwise monitoring of the temperature distribution is used to gather information about the process stability and the resulting part quality. The heat distribution varies with different kinds of parameters including scan vector length, laser power, layer thickness and inter-part distance in the job layout which in turn influence the resulting part quality. By integration of an off-axis mounted uncooled thermal detector the solidification as well as the layer deposition are monitoredmore » and evaluated. Errors in the generation of new powder layers usually result in a locally varying layer thickness that may cause poor part quality. For effect quantification, the locally applied layer thickness is determined by evaluating the heat-up of the newly deposited powder. During the solidification process space and time-resolved data is used to characterize the zone of elevated temperatures and to derive locally varying heat dissipation properties. Potential quality indicators are evaluated and correlated to the resulting part quality: Thermal diffusivity is derived from a simplified heat dissipation model and evaluated for every pixel and cool-down phase of a layer. This allows the quantification of expected material homogeneity properties. Maximum temperature and time above certain temperatures are measured in order to detect hot spots or delamination issues that may cause a process breakdown. Furthermore, a method for quantification of sputter activity is presented. Since high sputter activity indicates unstable melt dynamics this can be used to identify parameter drifts, improper atmospheric conditions or material binding errors. The resulting surface structure after solidification complicates temperature determination on the one hand but enables the detection of potential surface defects on the other hand. These issues and proper key figures for thermographic monitoring of the Selective Laser Melting process are discussed in the paper. Even though microbolometric temperature measurement is limited to repetition rates in the Hz-regime and sub megapixel resolution, current results show the feasibility of process surveillance by thermography for a limited section of the building platform in a commercial system.« less

Thermographic process monitoring in powderbed based additive manufacturing

NASA Astrophysics Data System (ADS)

Krauss, Harald; Zeugner, Thomas; Zaeh, Michael F.

2015-03-01

Selective Laser Melting is utilized to build metallic parts directly from CAD-Data by solidification of thin powder layers through application of a fast scanning laser beam. In this study layerwise monitoring of the temperature distribution is used to gather information about the process stability and the resulting part quality. The heat distribution varies with different kinds of parameters including scan vector length, laser power, layer thickness and inter-part distance in the job layout which in turn influence the resulting part quality. By integration of an off-axis mounted uncooled thermal detector the solidification as well as the layer deposition are monitored and evaluated. Errors in the generation of new powder layers usually result in a locally varying layer thickness that may cause poor part quality. For effect quantification, the locally applied layer thickness is determined by evaluating the heat-up of the newly deposited powder. During the solidification process space and time-resolved data is used to characterize the zone of elevated temperatures and to derive locally varying heat dissipation properties. Potential quality indicators are evaluated and correlated to the resulting part quality: Thermal diffusivity is derived from a simplified heat dissipation model and evaluated for every pixel and cool-down phase of a layer. This allows the quantification of expected material homogeneity properties. Maximum temperature and time above certain temperatures are measured in order to detect hot spots or delamination issues that may cause a process breakdown. Furthermore, a method for quantification of sputter activity is presented. Since high sputter activity indicates unstable melt dynamics this can be used to identify parameter drifts, improper atmospheric conditions or material binding errors. The resulting surface structure after solidification complicates temperature determination on the one hand but enables the detection of potential surface defects on the other hand. These issues and proper key figures for thermographic monitoring of the Selective Laser Melting process are discussed in the paper. Even though microbolometric temperature measurement is limited to repetition rates in the Hz-regime and sub megapixel resolution, current results show the feasibility of process surveillance by thermography for a limited section of the building platform in a commercial system.

Experimental Investigation of Pool Boiling Heat Transfer Enhancement in Microgravity in the Presence of Electric Fields

NASA Technical Reports Server (NTRS)

Herman, Cila

1999-01-01

In boiling high heat fluxes are possible driven by relatively small temperature differences, which make its use increasingly attractive in aerospace applications. The objective of the research is to develop ways to overcome specific problems associated with boiling in the low gravity environment by substituting the buoyancy force with the electric force to enhance bubble removal from the heated surface. Previous studies indicate that in terrestrial applications nucleate boiling heat transfer can be increased by a factor of 50, as compared to values obtained for the same system without electric fields. The goal of our research is to experimentally explore the mechanisms responsible for EHD heat transfer enhancement in boiling in low gravity conditions, by visualizing the temperature distributions in the vicinity of the heated surface and around the bubble during boiling using real-time holographic interferometry (HI) combined with high-speed cinematography. In the first phase of the project the influence of the electric field on a single bubble is investigated. Pool boiling is simulated by injecting a single bubble through a nozzle into the subcooled liquid or into the thermal boundary layer developed along the flat heater surface. Since the exact location of bubble formation is known, the optical equipment can be aligned and focused accurately, which is an essential requirement for precision measurements of bubble shape, size and deformation, as well as the visualization of temperature fields by HI. The size of the bubble and the frequency of bubble departure can be controlled by suitable selection of nozzle diameter and mass flow rate of vapor. In this approach effects due to the presence of the electric field can be separated from effects caused by the temperature gradients in the thermal boundary layer. The influence of the thermal boundary layer can be investigated after activating the heater at a later stage of the research. For the visualization experiments a test cell was developed. All four vertical walls of the test cell are transparent, and they allow transillumination with laser light for visualization experiments by HI. The bottom electrode is a copper cylinder, which is electrically grounded. The copper block is heated with a resistive heater and it is equipped with 6 thermocouples that provide reference temperatures for the measurements with HI. The top electrode is a mesh electrode. Bubbles are injected with a syringe into the test cell through the bottom electrode. The working fluids presently used in the interferometric visualization experiments, water and PF 5052, satisfy requirements regarding thermophysical, optical and electrical properties. A 30kV power supply equipped with a voltmeter allows to apply the electric field to the electrodes during the experiments. The magnitude of the applied voltage can be adjusted either manually or through the LabVIEW data acquisition and control system connected to a PC. Temperatures of the heated block are recorded using type-T thermocouples, whose output is read by a data acquisition system. Images of the bubbles are recorded with 35mm photographic and 16mm high-speed cameras, scanned and analyzed using various software packages. Visualized temperature fields HI allows the visualization of temperature fields in the vicinity of bubbles during boiling in the form of fringes. Typical visualized temperature distributions around the air bubbles injected into the thermal boundary layer in PF5052 are shown. The temperature of the heated surface is 35 C. The temperature difference for a pair of fringes is approximately 0.05 C. The heat flux applied to the bottom surface is moderate, and the fringe patterns are regular. In the image a bubble penetrating the thermal boundary layer is visible. Because of the axial symmetry of the problem, simplified reconstruction techniques can be applied to recover the temperature field. The thermal plume developing above the heated surface for more intensive heating is shown. The temperature distribution in the liquid is clearly 3D, and tomographic techniques have to be applied to recover the temperature distribution in such a physical situation. A sequence of interferometric images showing the temperature distribution around the rising bubble, recorded with a high-speed camera is shown. Again, the temperature distribution is 3D, and a more complex approach to the evaluation, the tomographic reconstruction has to be taken. Measurement of the temperature distribution from the fringe pattern temperature distributions that yield important information regarding heat transfer are determined. Two algorithms that allow the quantitative evaluation of interferometric fringe patterns and the reconstruction of temperature fields during boiling have been developed at the Heat Transfer Laboratory of the Johns Hopkins University. In the first algorithm the bubble is assumed to be axially symmetrical, which significantly reduces the computational effort for quantifying the temperature distribution around the bubble. For this purpose the thermal boundary layer around the bubble is divided into equidistant concentric shells, and the refractive index is assumed to be constant in each of the shells. Since large temperature gradients are expected in the vicinity of the bubble during boiling, the deflection of the light beam cannot be neglected in boiling experiments. Since the exit angle of the light beam is known, this allows to account for the deflections and phase shifts outside the boundary layer (in the bulk fluid and in the windows of the test cell). Three dimensional temperature distributions in the vicinity of the bubble are reconstructed using tomographic techniques. In tomography, the measurement volume is sliced into 2D planes. In the present study these planes are parallel to the heated surface. The objective is to determine the values of the field parameter of interest in form of the field function in these 2D planes. The field parameter is the change of the refractive index of the liquid in the measurement volume caused by temperature changes. By superimposing data for many 2D planes recorded at the same time instant, the 3D temperature distribution in the measurement volume is recovered.

Advantages of a Vertical High-Resolution Distributed-Temperature-Sensing System Used to Evaluate the Thermal Behavior of Green Roofs

NASA Astrophysics Data System (ADS)

Hausner, M. B.; Suarez, F. I.; Cousiño, J. A.; Victorero, F.; Bonilla, C. A.; Gironas, J. A.; Vera, S.; Bustamante, W.; Rojas, V.; Leiva, E.; Pasten, P.

2015-12-01

Technological innovations used for sustainable urban development, green roofs offer a range of benefits, including reduced heat island effect, rooftop runoff, roof surface temperatures, energy consumption, and noise levels inside buildings, as well as increased urban biodiversity. Green roofs feature layered construction, with the most important layers being the vegetation and the substrate layers located above the traditional roof. These layers provide both insulation and warm season cooling by latent heat flux, reducing the thermal load to the building. To understand and improve the processes driving this thermal energy reduction, it is important to observe the thermal dynamics of a green roof at the appropriate spatial and temporal scales. Traditionally, to observe the thermal behavior of green roofs, a series of thermocouples have been installed at discrete depths within the layers of the roof. Here, we present a vertical high-resolution distributed-temperature-sensing (DTS) system installed in different green roof modules of the Laboratory of Vegetated Infrastructure for Buildings (LIVE -its acronym in Spanish) of the Pontifical Catholic University of Chile. This DTS system allows near-continuous measurement of the thermal profile at spatial and temporal resolutions of approximately 1 cm and 30 s, respectively. In this investigation, the temperature observations from the DTS system are compared with the measurements of a series of thermocouples installed in the green roofs. This comparison makes it possible to assess the value of thermal observations at better spatial and temporal resolutions. We show that the errors associated with lower resolution observations (i.e., from the thermocouples) are propagated in the calculations of the heat fluxes through the different layers of the green roof. Our results highlight the value of having a vertical high-resolution DTS system to observe the thermal dynamics in green roofs.

Two-Flux Method for Transient Radiative Transfer in a Semitransparent Layer

NASA Technical Reports Server (NTRS)

Siegel, Robert

1996-01-01

The two-flux method was used to obtain transient solutions for a plane layer including internal reflections and scattering. The layer was initially at uniform temperature, and was heated or cooled by external radiation and convection. The two-flux equations were examined as a means for evaluating the radiative flux gradient in the transient energy equation. Comparisons of transient temperature distributions using the two-flux method were made with results where the radiative flux gradient was evaluated from the exact radiative transfer equations. Good agreement was obtained for optical thicknesses from 0.5 to 5 and for refractive indices of 1 and 2. Illustrative results obtained with the two-flux method demonstrate the effect of isotropic scattering coupled with changing the refractive index. For small absorption with large scattering the maximum layer temperature is increased when the refractive index is increased. For larger absorption the effect is opposite, and the maximum temperature decreases with increased refractive index .

An Evaluation of a Borided Layer Formed on Ti-6Al-4V Alloy by Means of SMAT and Low-Temperature Boriding

PubMed Central

Yao, Quantong; Sun, Jian; Fu, Yuzhu; Tong, Weiping; Zhang, Hui

2016-01-01

In this paper, a nanocrystalline surface layer without impurities was fabricated on Ti-6Al-4V alloy by means of surface mechanical attrition treatment (SMAT). The grain size in the nanocrystalline layer is about 10 nm and grain morphology displays a random crystallographic orientation distribution. Subsequently, the low-temperature boriding behaviors (at 600 °C) of the SMAT sample, including the phase composition, microstructure, micro-hardness, and brittleness, were investigated in comparison with those of coarse-grained sample borided at 1100 °C. The results showed that the boriding kinetics could be significantly enhanced by SMAT, resulting in the formation of a nano-structured boride layers on Ti-6Al-4V alloy at lower temperature. Compared to the coarse-grained boriding sample, the SMAT boriding sample exhibits a similar hardness value, but improved surface toughness. The satisfactory surface toughness may be attributed to the boriding treatment that was carried out at lower temperature. PMID:28774115

Three-dimensional temporal and spatial distribution of adult Rhyzopertha dominica in stored wheat and corn under different temperatures, moisture contents, and adult densities.

PubMed

Jian, Fuji; Larson, Ron; Jayas, Digvir S; White, Noel D G

2012-08-01

Three-dimensional temporal and spatial distributions of adult Rhyzopertha dominica (F.) at adult densities of 1.0, 5.0, and 10.0 adults per kg grain and at 20 +/- 1, 25 +/- 1, and 30 +/- 1 degrees C were determined in 1.5 t bins filled with wheat (Triticum aestivum L.) with 11.0 +/- 0.8, 13.0 +/- 0.6, and 15.0 +/- 0.5% moisture content (wet basis) or corn (Zea mays L.) with 13.0 +/- 0.2% moisture content (wet basis). At each of five sampled locations, grain was separated into three 15-kg vertical layers, and adult numbers in each layer were counted. Inside both corn and wheat, adults did not prefer any location in the same layer except at high introduced insect density in wheat. The adults were recovered from any layer of the corn and >12, 65, and 45% of adults were recovered in the bottom layer of the corn at 20, 25, and 30 degrees C; respectively. However, <1% of adults were recovered in the bottom layer of wheat. Numbers of adults correlated with those in adjacent locations in both vertical and horizontal directions, and the temporal continuous property existed in both wheat and corn. Adults had highly clumped distribution at any grain temperature and moisture content. This aggregation behavior decreased with the increase of adult density and redistribution speed. Grain type influenced their redistribution speed, and this resulted in the different redistribution patterns inside wheat and corn bulks. These characterized distribution patterns could be used to develop sampling plans and integrated pest management programs in stored grain bins.

Optimal spacing within a tubed, volumetric, cavity receiver suitable for modular molten salt solar towers

NASA Astrophysics Data System (ADS)

Turner, Peter

2016-05-01

A 2-dimensional radiation analysis has been developed to analyse the radiative efficiency of an arrangement of heat transfer tubes distributed in layers but spaced apart to form a tubed, volumetric receiver. Such an arrangement could be suitable for incorporation into a cavity receiver. Much of the benefit of this volumetric approach is gained after using 5 layers although improvements do continue with further layers. The radiation analysis splits each tube into multiple segments in which each segment surface can absorb, reflect and radiate rays depending on its surface temperature. An iterative technique is used to calculate appropriate temperatures depending on the distribution of the net energy absorbed and assuming that the cool heat transfer fluid (molten salt) starts at the front layer and flows back through successive layers to the rear of the cavity. Modelling the finite diameter of each layer of tubes increases the ability of a layer to block radiation scattered at acute angles and this effect is shown to reduce radiation losses by nearly 25% compared to the earlier 1-d analysis. Optimum efficient designs tend to occur when the blockage factor is 0.2 plus the inverse of the number of tube layers. It is beneficial if the distance between successive layers is ≥ 2 times the diameter of individual tubes and in this situation, if the incoming radiation is spread over a range of angles, the performance is insensitive to the degree of any tube positional offset or stagger between layers.

Effect of Same-Temperature GaN Cap Layer on the InGaN/GaN Multiquantum Well of Green Light-Emitting Diode on Silicon Substrate

PubMed Central

Zheng, Changda; Wang, Li; Mo, Chunlan; Fang, Wenqing; Jiang, Fengyi

2013-01-01

GaN green LED was grown on Si (111) substrate by MOCVD. To enhance the quality of InGaN/GaN MQWs, same-temperature (ST) GaN protection layers with different thickness of 8 Å, 15 Å, and 30 Å were induced after the InGaN quantum wells (QWs) layer. Results show that a relative thicker cap layer is benefit to get InGaN QWs with higher In percent at fixed well temperature and obtain better QW/QB interface. As the cap thickness increases, the indium distribution becomes homogeneous as verified by fluorescence microscope (FLM). The interface of MQWs turns to be abrupt from XRD analysis. The intensity of photoluminescence (PL) spectrum is increased and the FWHM becomes narrow. PMID:24369453

Ignition behavior of magnesium powder layers on a plate heated at constant temperature.

PubMed

Chunmiao, Yuan; Dezheng, Huang; Chang, Li; Gang, Li

2013-02-15

The minimum temperature at which dust layers or deposits ignite is considered to be very important in industries where smoldering fires could occur. Experiments were conducted on the self-ignition behavior of magnesium powder layers. The estimated effective thermal conductivity k for modeling is 0.17 W m(-1)K(-1). The minimum ignition temperature (MIT) of magnesium powder layers for four different particle sizes: 6, 47, 104 and 173 μm, are also determined in these experiments. A model was developed describing temperature distribution and its change over time while considering the melting and boiling of magnesium powder. Parameter analysis shown that increasing particle size from 6 to 173 μm increased MIT from 710 to 760 K, and increased thickness of the dust layer led to a decreased MIT. The calculation termination time more than 5000 s didn't significantly impact MIT. Comparing predicted and experimental data showed satisfactory agreement for MIT of magnesium powder layers at various particle sizes. According to the ignition process of magnesium powder layer, a meaningful definition for the most sensitive ignition position (MSIP) was proposed and should be taken into consideration when preventing smoldering fires induced by hot plates. Copyright © 2012 Elsevier B.V. All rights reserved.

Temperature Distributions in Semitransparent Coatings: A Special Two-Flux Solution

NASA Technical Reports Server (NTRS)

Siegel, Robert; Spuckler, Charles M.

1995-01-01

Radiative transfer is analyzed in a semitransparent coating on an opaque substrate and in a semitransparent layer for evaluating thermal protection behavior and ceramic component performance in high temperature applications. Some ceramics are partially transparent for radiative transfer, and at high temperatures internal emission and reflections affect their thermal performance. The behavior is examined for a ceramic component for which interior cooling is not provided. Two conditions are considered: (1) the layer is heated by penetration of radiation from hot surroundings while its external surface is simultaneously film cooled by convection, and (2) the surface is heated by convection while the semitransparent material cools from within by radiant emission leaving through the surface. By using the two-flux method, which has been found to yield good accuracy in previous studies, a special solution is obtained for these conditions. The analytical result includes isotropic scattering and requires only an integration to obtain the temperature distribution within the semitransparent material. Illustrative results are given to demonstrate the nature of the thermal behavior.

High-fluence Ga-implanted silicon—The effect of annealing and cover layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fiedler, J., E-mail: jan.fiedler@hzdr.de; Heera, V.; Hübner, R.

2014-07-14

The influence of SiO{sub 2} and SiN{sub x} cover layers on the dopant distribution as well as microstructure of high fluence Ga implanted Si after thermal processing is investigated. The annealing temperature determines the layer microstructure and the cover layers influence the obtained Ga profile. Rapid thermal annealing at temperatures up to 750 °C leads to a polycrystalline layer structure containing amorphous Ga-rich precipitates. Already after a short 20 ms flash lamp annealing, a Ga-rich interface layer is observed for implantation through the cover layers. This effect can partly be suppressed by annealing temperatures of at least 900 °C. However, in this case,more » Ga accumulates in larger, cone-like precipitates without disturbing the surrounding Si lattice parameters. Such a Ga-rich crystalline Si phase does not exist in the equilibrium phase diagram according to which the Ga solubility in Si is less than 0.1 at. %. The Ga-rich areas are capped with SiO{sub x} grown during annealing which only can be avoided by the usage of SiN{sub x} cover layers.« less

Displacements of Metallic Thermal Protection System Panels During Reentry

NASA Technical Reports Server (NTRS)

Daryabeigi, Kamran; Blosser, Max L.; Wurster, Kathryn E.

2006-01-01

Bowing of metallic thermal protection systems for reentry of a previously proposed single-stage-to-orbit reusable launch vehicle was studied. The outer layer of current metallic thermal protection system concepts typically consists of a honeycomb panel made of a high temperature nickel alloy. During portions of reentry when the thermal protection system is exposed to rapidly varying heating rates, a significant temperature gradient develops across the honeycomb panel thickness, resulting in bowing of the honeycomb panel. The deformations of the honeycomb panel increase the roughness of the outer mold line of the vehicle, which could possibly result in premature boundary layer transition, resulting in significantly higher downstream heating rates. The aerothermal loads and parameters for three locations on the centerline of the windward side of this vehicle were calculated using an engineering code. The transient temperature distributions through a metallic thermal protection system were obtained using 1-D finite volume thermal analysis, and the resulting displacements of the thermal protection system were calculated. The maximum deflection of the thermal protection system throughout the reentry trajectory was 6.4 mm. The maximum ratio of deflection to boundary layer thickness was 0.032. Based on previously developed distributed roughness correlations, it was concluded that these defections will not result in tripping the hypersonic boundary layer.

Epitaxial graphene on SiC(0001): functional electrical microscopy studies and effect of atmosphere.

PubMed

Kazakova, O; Burnett, T L; Patten, J; Yang, L; Yakimova, R

2013-05-31

Surface potential distribution, V(CPD), and evolution of atmospheric adsorbates on few and multiple layers (FLG and MLG) of graphene grown on SiC(0001) substrate have been investigated by electrostatic and Kelvin force microscopy techniques at T = 20-120 °C. The change of the surface potential distribution, ΔV(CPD), between FLG and MLG is shown to be temperature dependent. The enhanced ΔV(CPD) value at 120 °C is associated with desorption of adsorbates at high temperatures and the corresponding change of the carrier balance. The nature of the adsorbates and their evolution with temperature are considered to be related to the process of adsorption and desorption of the atmospheric water on MLG domains. We demonstrate that both the nano- and microscale wettability of the material are strongly dependent on the number of graphene layers.

Impact of Typhoons on the Western Pacific Ocean (ITOP) DRI: Numerical Modeling of Ocean Mixed Layer Turbulence and Entrainment at High Winds

DTIC Science & Technology

2013-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Impact of Typhoons on the Western Pacific Ocean (ITOP...The measurement and modeling activities include a focus on the impact of surface waves, air-sea fluxes and the temperature, salinity and velocity...SUBTITLE Impact of Typhoons on the Western Pacific Ocean (ITOP) DRI: Numerical Modeling of Ocean Mixed Layer Turbulence and Entrainment at High Winds

Surface air temperature in a maritime metropolitan region

Treesearch

J. D. McTaggart-Cowen; J. W. S. Young

1977-01-01

In investigations of the micrometeorology of any area, one of the basic parameters required is the spatial and temporal distribution of the surface air temperature. A mobile instrument mounted on an automobile was used for measuring temperatures within the surface mixed layer. Details are presented of a case study at Saint John, New Brunswick, in a summer period. The...

Transient natural ventilation of a room with a distributed heat source

NASA Astrophysics Data System (ADS)

Fitzgerald, Shaun D.; Woods, Andrew W.

We report on an experimental and theoretical study of the transient flows which develop as a naturally ventilated room adjusts from one temperature to another. We focus on a room heated from below by a uniform heat source, with both high- and low-level ventilation openings. Depending on the initial temperature of the room relative to (i) the final equilibrium temperature and (ii) the exterior temperature, three different modes of ventilation may develop. First, if the room temperature lies between the exterior and the equilibrium temperature, the interior remains well-mixed and gradually heats up to the equilibrium temperature. Secondly, if the room is initially warmer than the equilibrium temperature, then a thermal stratification develops in which the upper layer of originally hot air is displaced upwards by a lower layer of relatively cool inflowing air. At the interface, some mixing occurs owing to the effects of penetrative convection. Thirdly, if the room is initially cooler than the exterior, then on opening the vents, the original air is displaced downwards and a layer of ambient air deepens from above. As this lower layer drains, it is eventually heated to the ambient temperature, and is then able to mix into the overlying layer of external air, and the room becomes well-mixed. For each case, we present new laboratory experiments and compare these with some new quantitative models of the transient flows. We conclude by considering the implications of our work for natural ventilation of large auditoria.

Thermo-Elastic Triangular Sandwich Element for the Complete Stress Field Based on a Single-Layer Theory

NASA Technical Reports Server (NTRS)

Das, M.; Barut, A.; Madenci, E.; Ambur, D. R.

2004-01-01

This study presents a new triangular finite element for modeling thick sandwich panels, subjected to thermo-mechanical loading, based on a {3,2}-order single-layer plate theory. A hybrid energy functional is employed in the derivation of the element because of a C interelement continuity requirement. The single-layer theory is based on five weighted-average field variables arising from the cubic and quadratic representations of the in-plane and transverse displacement fields, respectively. The variations of temperature and distributed loading acting on the top and bottom surfaces are non-uniform. The temperature varies linearly through the thickness.

Radiation forcing by the atmospheric aerosols in the nocturnal boundary layer

NASA Astrophysics Data System (ADS)

Singh, D. K.; Ponnulakshami, V. K.; Mukund, V.; Subramanian, G.; Sreenivas, K. R.

2013-05-01

We have conducted experimental and theoretical studies on the radiation forcing due to suspended aerosols in the nocturnal boundary layer. We present radiative, conductive and convective equilibrium profile for different bottom boundaries where calculated Rayleigh number is higher than the critical Rayleigh number in laboratory conditions. The temperature profile can be fitted using an exponential distribution of aerosols concentration field. We also present the vertical temperature profiles in a nocturnal boundary in the presence of fog in the field. Our results show that during the presence of fog in the atmosphere, the ground temperature is greater than the dew-point temperature. The temperature profiles before and after the formation of fog are also observed to be different.

Tropical Convective Outflow and Near Surface Equivalent Potential Temperatures

NASA Technical Reports Server (NTRS)

Folkins, Ian; Oltmans, Samuel J.; Thompson, Anne M.; Einaudi, Franco (Technical Monitor)

2000-01-01

We use clear sky heating rates to show that convective outflow in the tropics decreases rapidly with height between the 350 K and 360 K potential temperature surfaces (or between roughly 13 and 15 km). There is also a rapid fall-off in the pseudoequivalent potential temperature probability distribution of near surface air parcels between 350 K and 360 K. This suggests that the vertical variation of convective outflow in the upper tropical troposphere is to a large degree determined by the distribution of sub cloud layer entropy.

Test of Monin-Obukhov similarity theory using distributed temperature sensing

NASA Astrophysics Data System (ADS)

Cheng, Y.; Sayde, C.; Li, Q.; Gentine, P.

2017-12-01

Monin-Obukhov similarity theory [Monin and Obukhov, 1954] (MOST) has been widely used to calculate atmospheric surface fluxes applying the structure correction functions [Stull, 1988]. The exact forms of the structure correction functions for momentum and heat, which depend on the vertical gradient velocity and temperature, have been determined empirically mostly from the Kansas experiment [Kaimal et al., 1972]. However, due to the limitation of point measurement, the vertical gradient of temperature and horizontal wind speed are not well captured. Here we propose a way to measure the vertical gradient of temperature and horizontal wind speed with high resolution in space (every 12.7 cm) and time (every second) using the Distributed Temperature Sensing [Selker et al., 2006] (DTS), thus determining the exact form of the structure correction functions of MOST under various stability conditions. Two parallel vertical fiber optics will be placed on a tower at the central facility of ARM SGP site. Vertical air temperature will be measured every 12.7 cm by the fiber optics and horizontal wind speed along fiber will be measured. Then vertical gradient of temperature and horizontal wind speed will be calculated and stability correction functions for momentum and heat will be determined. ReferencesKaimal, J. C., Wyngaard, J. C., Izumi, Y., and Cote, O. R. (1972), Spectral characteristics of surface-layer turbulence, Quarterly Journal of the Royal Meteorological Society, 98(417), 563-589, doi: 10.1002/qj.49709841707. Monin, A., and Obukhov, A. (1954), Basic laws of turbulent mixing in the surface layer of the atmosphere, Contrib. Geophys. Inst. Acad. Sci. USSR, 24(151), 163-187. Selker, J., Thévenaz, L., Huwald, H., Mallet, A., Luxemburg, W., van de Giesen, N., Stejskal, M., Zeman, J., Westhoff, M., and Parlange, M. B. (2006), Distributed fiber-optic temperature sensing for hydrologic systems, Water Resources Research, 42, W12202, doi: 10.1029/2006wr005326. Stull, R. (1988), An Introduction to Boundary Layer Meteorology, pp. 666, Kluwer Academic Publishers, Dordrecht.

Relation between boundary slip mechanisms and waterlike fluid behavior.

PubMed

Ternes, Patricia; Salcedo, Evy; Barbosa, Marcia C

2018-03-01

The slip of a fluid layer in contact with a solid confining surface is investigated for different temperatures and densities using molecular dynamic simulations. We show that for an anomalous waterlike fluid the slip goes as follows: for low levels of shear, defect slip appears and is related to the particle exchange between the fluid layers; at high levels of shear, global slip occurs and is related to the homogeneous distribution of the fluid in the confining surfaces. The oscillations in the transition velocity from defect to global slip are shown to be associated with changes in the layering distribution in the anomalous fluid.

Analysis of nanopore arrangement of porous alumina layers formed by anodizing in oxalic acid at relatively high temperatures

NASA Astrophysics Data System (ADS)

Zaraska, Leszek; Stępniowski, Wojciech J.; Jaskuła, Marian; Sulka, Grzegorz D.

2014-06-01

Anodic aluminum oxide (AAO) layers were formed by a simple two-step anodization in 0.3 M oxalic acid at relatively high temperatures (20-30 °C) and various anodizing potentials (30-65 V). The effect of anodizing conditions on structural features of as-obtained oxides was carefully investigated. A linear and exponential relationships between cell diameter, pore density and anodizing potential were confirmed, respectively. On the other hand, no effect of temperature and duration of anodization on pore spacing and pore density was found. Detailed quantitative and qualitative analyses of hexagonal arrangement of nanopore arrays were performed for all studied samples. The nanopore arrangement was evaluated using various methods based on the fast Fourier transform (FFT) images, Delaunay triangulations (defect maps), pair distribution functions (PDF), and angular distribution functions (ADF). It was found that for short anodizations performed at relatively high temperatures, the optimal anodizing potential that results in formation of nanostructures with the highest degree of pore order is 45 V. No direct effect of temperature and time of anodization on the nanopore arrangement was observed.

Properties of medium-density fiberboard produced in an oil-heated laboratory press

Treesearch

O. Suchsland; G.E. Woodson

1976-01-01

Medium-density fiberboards from pressurized double-disk refined fibers have a close correlation between layer density and layer dynamic modulus of elasticity. Density distribution over the thickness was readily controlled by manipulating platen temperature and applied pressure. Thus, overall modulus of elasticity could be adjusted. In contrast to modulus of elasticity...

The relationship between surface topography, gravity anomalies, and temperature structure of convection

NASA Technical Reports Server (NTRS)

Parsons, B.; Daly, S.

1983-01-01

Consideration is given to the relationship between the temperature structure of mantle convection and the resulting surface topography and gravity anomalies, which are used in its investigation. Integral expressions relating the three variables as a function of wavelength are obtained with the use of Green's function solutions to the equations of motion for the case of constant-viscosity convection in a plane layer subject to a uniform gravitational field. The influence of the boundary conditions, particularly at large wavelengths, is pointed out, and surface topographies and gravity produced by convection are illustrated for a number of simple temperature distributions. It is shown that the upper thermal boundary layer plays an important role in determining the surface observables, while temperatures near the bottom of the layer affect mainly that boundary. This result is consistent with an explanation of geoid anomalies over mid-ocean swells in terms of convection beneath the lithosphere.

Effect of process parameters on hardness, temperature profile and solidification of different layers processed by direct metal laser sintering (DMLS)

NASA Astrophysics Data System (ADS)

Ahmed, Sazzad Hossain; Mian, Ahsan; Srinivasan, Raghavan

2016-07-01

In DMLS process objects are fabricated layer by layer from powdered material by melting induced by a controlled laser beam. Metallic powder melts and solidifies to form a single layer. Solidification map during layer formation is an important route to characterize micro-structure and grain morphology of sintered layer. Generally, solidification leads to columnar, equiaxed or mixture of these two types grain morphology depending on solidification rate and thermal gradient. Eutectic or dendritic structure can be formed in fully equiaxed zone. This dendritic growth has a large effect on material properties. Smaller dendrites generally increase ductility of the layer. Thus, materials can be designed by creating desired grain morphology in certain regions using DMLS process. To accomplish this, hardness, temperature distribution, thermal gradient and solidification cooling rate in processed layers will be studied under change of process variables by using finite element analysis, with specific application to Ti-6Al-4V.

Sheared boundary layers in turbulent Rayleigh-Benard convection

NASA Astrophysics Data System (ADS)

Solomon, T. H.; Gollub, J. P.

1990-05-01

Thermal boundary layers in turbulent Rayleigh-Benard convection are studied experimentally using a novel system in which the convecting fluid is sheared from below with a flowing layer of mercury. Oscillatory shear substantially alters the spatial structure and frequency of the eruptions, with minimal effect on the heat flux (less than 5 percent). The temperature probability distribution function (PDF) just above the lower boundary layer changes from Gaussian to exponential without significant changes in the interior PDF. Implications for theories of 'hard' turbulence are discussed.

Temperature and nitrogen supply interact to determine protein distribution gradients in the wheat grain endosperm.

PubMed

Savill, George P; Michalski, Adam; Powers, Stephen J; Wan, Yongfang; Tosi, Paola; Buchner, Peter; Hawkesford, Malcolm J

2018-05-25

Gradients exist in the distribution of storage proteins in the wheat (Triticum aestivum) endosperm and determine the milling properties and protein recovery rate of the grain. A novel image analysis technique was developed to quantify both the gradients in protein concentration, and the size distribution of protein bodies within the endosperm of wheat plants grown under two different (20 or 28 °C) post-anthesis temperatures, and supplied with a nutrient solution with either high or low nitrogen content. Under all treatment combinations, protein concentration was greater in the endosperm cells closest to the aleurone layer and decreased towards the centre of the two lobes of the grain, i.e. a negative gradient. This was accompanied by a decrease in size of protein bodies from the outer to the inner endosperm layers in all but one of the treatments. Elevated post-anthesis temperature had the effect of increasing the magnitude of the negative gradients in both protein concentration and protein body size, whilst limiting nitrogen supply decreased the gradients.

Analysis of electroluminescence images in small-area circular CdTe solar cells

NASA Astrophysics Data System (ADS)

Bokalič, Matevž; Raguse, John; Sites, James R.; Topič, Marko

2013-09-01

The electroluminescence (EL) imaging process of small area solar cells is investigated in detail to expose optical and electrical effects that influence image acquisition and corrupt the acquired image. An approach to correct the measured EL images and to extract the exact EL radiation as emitted from the photovoltaic device is presented. EL images of circular cadmium telluride (CdTe) solar cells are obtained under different conditions. The power-law relationship between forward injection current and EL emission and a negative temperature coefficient of EL radiation are observed. The distributed Simulation Program with Integrated Circuit Emphasis (SPICE®) model of the circular CdTe solar cell is used to simulate the dark J-V curve and current distribution under the conditions used during EL measurements. Simulation results are presented as circularly averaged EL intensity profiles, which clearly show that the ratio between resistive parameters determines the current distribution in thin-film solar cells. The exact resistance values for front and back contact layers and for CdTe bulk layer are determined at different temperatures, and a negative temperature coefficient for the CdTe bulk resistance is observed.

Raman lidar measurement of water vapor and ice clouds associated with Asian dust layer over Tsukuba, Japan

NASA Astrophysics Data System (ADS)

Sakai, Tetsu; Nagai, Tomohiro; Nakazato, Masahisa; Matsumura, Takatsugu

2004-03-01

The vertical distributions of particle extinction, backscattering, depolarization, and water vapor mixing ratio were measured using a Raman lidar over Tsukuba (36.1°N, 140.1°E), Japan, on 23-24 April 2001. Ice clouds associated with the Asian dust layer were observed at an altitude of ~6-9 km. The relative humidities in the cloud layer were close to the ice saturation values and the temperature at the top of the cloud layer was ~-35°C, suggesting that the Asian dust acted as ice nuclei at the high temperatures. The meteorological analysis suggested that the ice-saturated region was formed near the top of the dust layer where the moist air ascended in slantwise fashion above the cold-frontal zone associated with extratropical cyclone.

The Competition Between a Localised and Distributed Source of Buoyancy

NASA Astrophysics Data System (ADS)

Partridge, Jamie; Linden, Paul

2012-11-01

We propose a new mathematical model to study the competition between localised and distributed sources of buoyancy within a naturally ventilated filling box. The main controlling parameters in this configuration are the buoyancy fluxes of the distributed and local source, specifically their ratio Ψ. The steady state dynamics of the flow are heavily dependent on this parameter. For large Ψ, where the distributed source dominates, we find the space becomes well mixed as expected if driven by an distributed source alone. Conversely, for small Ψ we find the space reaches a stable two layer stratification. This is analogous to the classical case of a purely local source but here the lower layer is buoyant compared to the ambient, due to the constant flux of buoyancy emanating from the distributed source. The ventilation flow rate, buoyancy of the layers and also the location of the interface height, which separates the two layer stratification, are obtainable from the model. To validate the theoretical model, small scale laboratory experiments were carried out. Water was used as the working medium with buoyancy being driven directly by temperature differences. Theoretical results were compared with experimental data and overall good agreement was found. A CASE award project with Arup.

Compressive and rarefactive double layers in non-uniform plasma with q-nonextensive distributed electrons

NASA Astrophysics Data System (ADS)

Shan, S. Ali; Saleem, H.

2018-05-01

Electrostatic solitary waves and double layers (DLs) formed by the coupled ion acoustic (IA) and drift waves have been investigated in non-uniform plasma using q-nonextensive distribution function for the electrons and assuming ions to be cold Ti< Te. It is found that both compressive and rarefactive nonlinear structures (solitary waves and DLs) are possible in such a system. The steeper gradients are supportive for compressive solitary (and double layers) and destructive for rarefactive ones. The q-nonextensivity parameter q and the magnitudes of gradient scale lengths of density and temperature have significant effects on the amplitude of the double layers (and double layers) as well as on the speed of these structures. This theoretical model is general which has been applied here to the F-region ionosphere for illustration.

Experimental investigation of convective stability in a superposed fluid and porous layer when heated from below

NASA Technical Reports Server (NTRS)

Chen, Falin; Chen, C. F.

1989-01-01

Experiments have been carried out in a horizontal superposed fluid and porous layer contained in a test box 24 cm x 12 cm x 4 cm high. The porous layer consisted of 3 mm diameter glass beads, and the fluids used were water, 60 and 90 percent glycerin-water solutions, and 100 percent glycerin. The depth ratio d, which is the ratio of the thickness of the fluid layer to that of the porous layer, varied from 0 to 1.0. Fluids of increasingly higher viscosity were used for cases with larger d in order to keep the temperature difference across the tank within reasonable limits. The size of the convection cells was inferred from temperature measurements made with embedded thermocouples and from temperature distributions at the top of the layer by use of liquid crystal film. The experimental results showed: (1) a precipitous decrease in the critical Rayleigh number as the depth of the fluid layer was increased from zero, and (2) an eightfold decrease in the critical wavelength between d = 0.1 and 0.2. Both of these results were predicted by the linear stability theory reported earlier (Chen and Chen, 1988).

Snow stratigraphic heterogeneity within ground-based passive microwave radiometer footprints: Implications for emission modeling

NASA Astrophysics Data System (ADS)

Rutter, Nick; Sandells, Mel; Derksen, Chris; Toose, Peter; Royer, Alain; Montpetit, Benoit; Langlois, Alex; Lemmetyinen, Juha; Pulliainen, Jouni

2014-03-01

Two-dimensional measurements of snowpack properties (stratigraphic layering, density, grain size, and temperature) were used as inputs to the multilayer Helsinki University of Technology (HUT) microwave emission model at a centimeter-scale horizontal resolution, across a 4.5 m transect of ground-based passive microwave radiometer footprints near Churchill, Manitoba, Canada. Snowpack stratigraphy was complex (between six and eight layers) with only three layers extending continuously throughout the length of the transect. Distributions of one-dimensional simulations, accurately representing complex stratigraphic layering, were evaluated using measured brightness temperatures. Large biases (36 to 68 K) between simulated and measured brightness temperatures were minimized (-0.5 to 0.6 K), within measurement accuracy, through application of grain scaling factors (2.6 to 5.3) at different combinations of frequencies, polarizations, and model extinction coefficients. Grain scaling factors compensated for uncertainty relating optical specific surface area to HUT effective grain size inputs and quantified relative differences in scattering and absorption properties of various extinction coefficients. The HUT model required accurate representation of ice lenses, particularly at horizontal polarization, and large grain scaling factors highlighted the need to consider microstructure beyond the size of individual grains. As variability of extinction coefficients was strongly influenced by the proportion of large (hoar) grains in a vertical profile, it is important to consider simulations from distributions of one-dimensional profiles rather than single profiles, especially in sub-Arctic snowpacks where stratigraphic variability can be high. Model sensitivity experiments suggested that the level of error in field measurements and the new methodological framework used to apply them in a snow emission model were satisfactory. Layer amalgamation showed that a three-layer representation of snowpack stratigraphy reduced the bias of a one-layer representation by about 50%.

Temperature-insensitive vertical-cavity surface-emitting lasers and method for fabrication thereof

DOEpatents

Chow, W.W.; Choquette, K.D.; Gourley, P.L.

1998-01-27

A temperature-insensitive vertical-cavity surface-emitting laser (VCSEL) and method for fabrication thereof are disclosed. The temperature-insensitive VCSEL comprises a quantum-well active region within a resonant cavity, the active region having a gain spectrum with a high-order subband (n {>=} 2) contribution thereto for broadening and flattening the gain spectrum, thereby substantially reducing any variation in operating characteristics of the VCSEL over a temperature range of interest. The method for forming the temperature-insensitive VCSEL comprises the steps of providing a substrate and forming a plurality of layers thereon for providing first and second distributed Bragg reflector (DBR) mirror stacks with an active region sandwiched therebetween, the active region including at least one quantum-well layer providing a gain spectrum having a high-order subband (n {>=} 2) gain contribution, and the DBR mirror stacks having predetermined layer compositions and thicknesses for providing a cavity resonance within a predetermined wavelength range substantially overlapping the gain spectrum. 12 figs.

Temperature-insensitive vertical-cavity surface-emitting lasers and method for fabrication thereof

DOEpatents

Chow, Weng W.; Choquette, Kent D.; Gourley, Paul L.

1998-01-01

A temperature-insensitive vertical-cavity surface-emitting laser (VCSEL) and method for fabrication thereof. The temperature-insensitive VCSEL comprises a quantum-well active region within a resonant cavity, the active region having a gain spectrum with a high-order subband (n.gtoreq.2) contribution thereto for broadening and flattening the gain spectrum, thereby substantially reducing any variation in operating characteristics of the VCSEL over a temperature range of interest. The method for forming the temperature-insensitive VCSEL comprises the steps of providing a substrate and forming a plurality of layers thereon for providing first and second distributed Bragg reflector (DBR) mirror stacks with an active region sandwiched therebetween, the active region including at least one quantum-well layer providing a gain spectrum having a high-order subband (n.gtoreq.2) gain contribution, and the DBR mirror stacks having predetermined layer compositions and thicknesses for providing a cavity resonance within a predetermined wavelength range substantially overlapping the gain spectrum.

Global Distributions of Temperature Variances At Different Stratospheric Altitudes From Gps/met Data

NASA Astrophysics Data System (ADS)

Gavrilov, N. M.; Karpova, N. V.; Jacobi, Ch.

The GPS/MET measurements at altitudes 5 - 35 km are used to obtain global distribu- tions of small-scale temperature variances at different stratospheric altitudes. Individ- ual temperature profiles are smoothed using second order polynomial approximations in 5 - 7 km thick layers centered at 10, 20 and 30 km. Temperature inclinations from the averaged values and their variances obtained for each profile are averaged for each month of year during the GPS/MET experiment. Global distributions of temperature variances have inhomogeneous structure. Locations and latitude distributions of the maxima and minima of the variances depend on altitudes and season. One of the rea- sons for the small-scale temperature perturbations in the stratosphere could be internal gravity waves (IGWs). Some assumptions are made about peculiarities of IGW gener- ation and propagation in the tropo-stratosphere based on the results of GPS/MET data analysis.

Mathematical simulation of surface heating during plasma spraying

NASA Astrophysics Data System (ADS)

Bogdanovich, V. I.; Giorbelidze, M. G.

2017-02-01

A mathematical model of temperature distribution over the flat ‘coating-substrate’ system section during plasma spraying, taking into account a plasma gun travel and coating buildup has been developed. It has been shown that the temperature value in the near-surface layer of the sprayed coating during the plasma gun passage can significantly exceed the temperature values in underlayers.

Chapter 5 - Development of biophysical gradient layers for the LANDFIRE Prototype Project

Treesearch

Lisa Holsinger; Robert E. Keane; Russell Parsons; Eva Karau

2006-01-01

Distributions of plant species are generally continuous, gradually changing across landscapes and blending into each other due to the influence of, and interactions between, a complex array of biophysical gradients (Whittaker 1967; 1975). Key biophysical gradients for understanding vegetation distributions include moisture, temperature, evaporative demand, nutrient...

Observation of the effects of stronger magnetic fields on warm, higher energy electrons and ion beams transiting a double layer in a helicon plasma

NASA Astrophysics Data System (ADS)

Scharer, John; Sung, Yung-Ta; Li, Yan

2017-10-01

Fast, two-temperature electrons (>80 eV, Te =13 eV tail, 4 eV bulk) with substantial tail density fractions are created at low (< = 1.7 mtorr) Ar pressure @ 340 G in the antenna region with nozzle mirror ratio of 1.4 on MadHeX @ 900W. These distributions including a fast tail are observed upstream of a double layer. The fast, untrapped tail electrons measured downstream of the double layer have a higher temperature of 13 eV than the trapped, upstream electrons of 4 eV temperature. Upstream plasma potential fluctuations of + - 30 percent are observed. An RF-compensated Langmuir probe is used to measure the electron temperatures and densities and OES, mm wave IF and an RPA for the IEDF are also utilized. As the magnetic field is increased to 1020 G, an increase in the electron temperature and density upstream of the double layer is observed with Te= 15-25 eV with a primarily single temperature mode. Accelerated ion beam energies in the range of 65-120 eV are observed as the magnetic field is increased from 340 to 850 G. The role of the nozzle, plasma double layer and helicon wave coupling on the EEDF and ion acceleration will be discussed. Research supported in part by the University of Wisconsin.

Spatial temperature distribution in human hairy and glabrous skin after infrared CO2 laser radiation

PubMed Central

2010-01-01

Background CO2 lasers have been used for several decades as an experimental non-touching pain stimulator. The laser energy is absorbed by the water content in the most superficial layers of the skin. The deeper located nociceptors are activated by passive conduction of heat from superficial to deeper skin layers. Methods In the current study, a 2D axial finite element model was developed and validated to describe the spatial temperature distribution in the skin after infrared CO2 laser stimulation. The geometry of the model was based on high resolution ultrasound scans. The simulations were compared to the subjective pain intensity ratings from 16 subjects and to the surface skin temperature distributions measured by an infrared camera. Results The stimulations were sensed significantly slower and less intense in glabrous skin than they were in hairy skin (MANOVA, p < 0.001). The model simulations of superficial temperature correlated with the measured skin surface temperature (r > 0.90, p < 0.001). Of the 16 subjects tested; eight subjects reported pricking pain in the hairy skin following a stimulus of 0.6 J/cm2 (5 W, 0.12 s, d1/e2 = 11.4 mm) only two reported pain to glabrous skin stimulation using the same stimulus intensity. The temperature at the epidermal-dermal junction (depth 50 μm in hairy and depth 133 μm in glabrous skin) was estimated to 46°C for hairy skin stimulation and 39°C for glabrous skin stimulation. Conclusions As compared to previous one dimensional heat distribution models, the current two dimensional model provides new possibilities for detailed studies regarding CO2 laser stimulation intensity, temperature levels and nociceptor activation. PMID:21059226

Target geometrical effects on the stagnation layer formed by colliding a pair of laser produced copper plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fallon, C., E-mail: colm.fallon5@mail.dcu.ie; Hayden, P.; Walsh, N.

We present the results of a time and space resolved optical-spectroscopic study of colliding plasmas formed at the front surfaces of flat and inclined Cu slab targets as a function of both the distance and the wedge angle between them for angles ranging from 100° to 180° (laterally colliding plasmas). The key parameters studied are stagnation layer density, temperature, duration, and kinetics of atomic/ionic spatial distributions and all have been found to vary significantly with wedge angle. It is found that the density and temperature of the stagnation layer decrease with increasing wedge angle. It is also found that themore » larger the wedge angle, the tighter and more well defined the stagnation layer formed.« less

Chemical differentiation of a convecting planetary interior: Consequences for a one-plate planet such as Venus

NASA Technical Reports Server (NTRS)

Parmentier, E. M.; Hess, P. C.

1992-01-01

Chemically depleted mantle forming a buoyant, refractory layer at the top of the mantle can have important implications for the evolution of the interior and surface. On Venus, the large apparent depths of compensation for surface topographic features might be explained if surface topography were supported by variations in the thickness of a 100-200 km thick chemically buoyant mantle layer or by partial melting in the mantle at the base of such a layer. Long volcanic flows seen on the surface may be explained by deep melting that generates low-viscosity MgO-rich magmas. The presence of a shallow refractory mantle layer may also explain the lack of volcanism associated with rifting. As the depleted layer thickens and cools, it becomes denser than the convecting interior and the portion of it that is hot enough to flow can mix with the convecting mantle. Time dependence of the thickness of a depleted layer may create episodic resurfacing events as needed to explain the observed distribution of impact craters on the venusian surface. We consider a planetary structure consisting of a crust, depleted mantle layer, and a thermally and chemically well-mixed convecting mantle. The thermal evolution of the convecting spherical planetary interior is calculated using energy conservation: the time rate of change of thermal energy in the interior is equated to the difference in the rate of radioactive heat production and the rate of heat transfer across the thermal boundary layer. Heat transfer across the thermal boundary layer is parameterized using a standard Nusselt number-Rayleigh number relationship. The radioactive heat production decreases with time corresponding to decay times for the U, Th, and K. The planetary interior cools by the advection of hot mantle at temperature T interior into the thermal boundary layer where it cools conductively. The crust and depleted mantle layers do not convect in our model so that a linear conductive equilibrium temperature distribution is assumed. The rate of melt production is calculated as the product of the volume flux of mantle into the thermal boundary layer and the degree of melting that this mantle undergoes. The volume flux of mantle into the thermal boundary layer is simply the heat flux divided by amount of heat lost in cooling mantle to the average temperature in the thermal boundary layer. The degree of melting is calculated as the temperature difference above the solidus, divided by the latent heat of melting. A maximum degree of melting is prescribed corresponding to the maximum amount of basaltic melt that the mantle can initially generate. As the crust thickens, the pressure at the base of the crust becomes high enough and the temperature remains low enough for basalt to transform to dense eclogite.

A revised model for Jeffrey nanofluid subject to convective condition and heat generation/absorption

PubMed Central

Hayat, Tasawar; Aziz, Arsalan; Muhammad, Taseer; Alsaedi, Ahmed

2017-01-01

Here magnetohydrodynamic (MHD) boundary layer flow of Jeffrey nanofluid by a nonlinear stretching surface is addressed. Heat generation/absorption and convective surface condition effects are considered. Novel features of Brownian motion and thermophoresis are present. A non-uniform applied magnetic field is employed. Boundary layer and small magnetic Reynolds number assumptions are employed in the formulation. A newly developed condition with zero nanoparticles mass flux is imposed. The resulting nonlinear systems are solved. Convergence domains are explicitly identified. Graphs are analyzed for the outcome of sundry variables. Further local Nusselt number is computed and discussed. It is observed that the effects of Hartman number on the temperature and concentration distributions are qualitatively similar. Both temperature and concentration distributions are enhanced for larger Hartman number. PMID:28231298

Investigation of MHD flow structure and fluctuations by potassium lineshape fitting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauman, L.E.

1993-12-31

Multiple Potassium D-line emission absorption spectra from a high temperature, coal-fired flow have been fit to a radiative transfer, boundary layer flow model. The results of fitting spectra from the aerodynamic duct of the Department of Energy Coal-Fired Flow Facility provide information about the thickness and shape of the thermal boundary layer and the bulk potassium seed atom density in a simulated magnetohydrodynamic channel flow. Probability distribution functions for the entire set of more than six thousand spectra clearly indicate the typical values and magnitude of fluctuations for the flow: core temperature of 2538 {plus_minus} 20 K, near wall temperaturemore » of 1945 {plus_minus} 135 K, boundary layer width of about 1 cm, and potassium seed atom density of (5.1 {plus_minus} 0.8)x 10{sup 22}/m{sup 3}. Probability distribution functions for selected times during the eight hours of measurements indicate occasional periods of unstable combustion. In addition, broadband particle parameters during the unstable start of the test may be related to differing particle and gas temperatures. The results clearly demonstrate the ability of lineshape fitting to provide valuable data for diagnosing the high speed turbulent flow.« less

Low-temperature slip along intergrain boundaries

NASA Astrophysics Data System (ADS)

Bakai, A. S.; Lazarev, P. N.

2017-10-01

Equations are derived for slip in a disordered atomic layer which describe diffusive creep as well as high-speed slip at low temperatures. An exact solution for the slip velocity is found in the form of a functional of the distribution function of the threshold shear stresses in the slip layer. The relationship between the microscopic parameters of the theory and the macroscopic properties of metallic glass is established in terms of the Mott intergrain slip model. The calculated rate of deformation of bulk metallic glass is compared with published experimental data.

Simulation of cryolipolysis as a novel method for noninvasive fat layer reduction.

PubMed

Majdabadi, Abbas; Abazari, Mohammad

2016-12-20

Regarding previous problems in conventional liposuction methods, the need for development of new fat removal operations was appreciated. In this study we are going to simulate one of the novel methods, cryolipolysis, aimed to tackle those drawbacks. We think that simulation of clinical procedures contributes considerably in efficacious performance of the operations. To do this we have attempted to simulate temperature distribution in a sample fat of the human body. Using Abaqus software we have presented the graphical display of temperature-time variations within the medium. Findings of our simulation indicate that tissue temperature decreases after cold exposure of about 30 min. It can be seen that the minimum temperature of tissue occurs in shallow layers of the sample and the temperature in deeper layers of the sample remains nearly unchanged. It is clear that cold exposure time of more than the specific time (t > 30 min) does not result in considerable changes. Numerous clinical studies have proved the efficacy of cryolipolysis. This noninvasive technique has eliminated some of drawbacks of conventional methods. Findings of our simulation clearly prove the efficiency of this method, especially for superficial fat layers.

Enhanced electron emission from coated metal targets: Effect of surface thickness on performance

NASA Astrophysics Data System (ADS)

Madas, Saibabu; Mishra, S. K.; Upadhyay Kahaly, Mousumi

2018-03-01

In this work, we establish an analytical formalism to address the temperature dependent electron emission from a metallic target with thin coating, operating at a finite temperature. Taking into account three dimensional parabolic energy dispersion for the target (base) material and suitable thickness dependent energy dispersion for the coating layer, Fermi Dirac statistics of electron energy distribution and Fowler's mechanism of the electron emission, we discuss the dependence of the emission flux on the physical properties such as the Fermi level, work function, thickness of the coating material, and operating temperature. Our systematic estimation of how the thickness of coating affects the emission current demonstrates superior emission characteristics for thin coating layer at high temperature (above 1000 K), whereas in low temperature regime, a better response is expected from thicker coating layer. This underlying fundamental behavior appears to be essentially identical for all configurations when work function of the coating layer is lower than that of the bulk target work function. The analysis and predictions could be useful in designing new coated materials with suitable thickness for applications in the field of thin film devices and field emitters.

Subduction factory in an ampoule: Experiments on sediment-peridotite interaction under temperature gradient conditions

NASA Astrophysics Data System (ADS)

Woodland, A. B.; Bulatov, V. K.; Brey, G. P.; Girnis, A. V.; Höfer, H. E.; Gerdes, A.

2018-02-01

To better understand processes above subducted oceanic slabs, we have undertaken experiments with juxtaposed sediment and peridotite layers at pressures of 7.5 and 10.5 GPa at a controlled temperature gradient from ∼100 to ∼500 °C per a sample length of ∼3 mm. The sediment starting material contains H2O (6.9 wt%) and CO2 (5.9 wt%) and has a major-element composition similar to GLOSS (Plank and Langmuir, 1998) doped with trace elements at 10-100 ppm levels. Several experiments were conducted with ∼0.5 wt% Cl or F. The peridotite layer is composed of natural olivine (66 wt%), orthopyroxene (27 wt%) and garnet (7 wt%) mixed with ∼15 wt% graphite. Several experimental configurations were investigated, but the "basic" setup has the sediment layer at the bottom in the cold zone (400-1200 °C) overlain by peridotite at 900-1500 °C. The temperature distribution was determined by two thermocouples and orthopyroxene-garnet thermometry. Features common to many experiments are (1) the development of multiple layers of various lithologies and a pool of hydrous silicate or carbonate-silicate melt in the hottest part of the capsule; (2) replacement of olivine by orthopyroxene in the metaperidotite; (3) preservation and growth of garnet and local development of magnesite in the metaperidotite layer; (4) enrichment in garnet within the metasediment layer at the contact with the metaperidotite; (5) formation of a clinopyroxene-garnet assemblage at the bottom (the coldest part); (6) presence of K-bearing phases (phlogopite or phengite) and carbonates in the metasediment layer only at temperatures <700 °C; and (7) occurrence of accessory zircon, rutile and phosphates in the coldest regions. In terms of element redistribution, the peridotite becomes strongly enriched in SiO2 compared to the starting composition, and the sediment gains MgO, FeO and Cr2O3. Potassium is fully extracted into the melt, while Na and Ca are largely retained in the coldest part of the metasediment layer in clinopyroxene, Ca-rich garnet and aragonite. The melt is a product of interaction between partial melt or fluid from the sediment and peridotite. It has a silico-carbonatite composition with variable SiO2, MgO, FeO and CaO contents and low Al2O3. The addition of Cl has almost no effect on element distribution, whereas the addition of F results in the appearance of humite-group minerals containing significant amounts of Ti. Trace-element distribution is controlled by pressure, temperature and mineral assemblages. At low temperatures in the sediment layer (<700 °C) Ba, Rb, Sr and Li are much more mobile than REE and HFSE, which results in high Ba/La, Ba/Nb, Sr/Nb etc. (fluid metasomatism). At higher temperatures in the sediment layer, the melt is markedly enriched in Ba, Rb, Sr, LREE and U relative to Ti, MREE and HREE. Negative Nb-Ta and Zr-Hf anomalies in melts are caused by the retention of rutile, zircon and humite-group minerals in the solid residue. Thermodiffusion may affect the ratios of some highly incompatible elements (e.g., Ta/La). Possible applications of the results to natural deep subduction are discussed in view of variations in mineral assemblages and trace element ratios.

Stepwise crystallization and the layered distribution in crystallization kinetics of ultra-thin poly(ethylene terephthalate) film

NASA Astrophysics Data System (ADS)

Zuo, Biao; Xu, Jianquan; Sun, Shuzheng; Liu, Yue; Yang, Juping; Zhang, Li; Wang, Xinping

2016-06-01

Crystallization is an important property of polymeric materials. In conventional viewpoint, the transformation of disordered chains into crystals is usually a spatially homogeneous process (i.e., it occurs simultaneously throughout the sample), that is, the crystallization rate at each local position within the sample is almost the same. Here, we show that crystallization of ultra-thin poly(ethylene terephthalate) (PET) films can occur in the heterogeneous way, exhibiting a stepwise crystallization process. We found that the layered distribution of glass transition dynamics of thin film modifies the corresponding crystallization behavior, giving rise to the layered distribution of the crystallization kinetics of PET films, with an 11-nm-thick surface layer having faster crystallization rate and the underlying layer showing bulk-like behavior. The layered distribution in crystallization kinetics results in a particular stepwise crystallization behavior during heating the sample, with the two cold-crystallization temperatures separated by up to 20 K. Meanwhile, interfacial interaction is crucial for the occurrence of the heterogeneous crystallization, as the thin film crystallizes simultaneously if the interfacial interaction is relatively strong. We anticipate that this mechanism of stepwise crystallization of thin polymeric films will allow new insight into the chain organization in confined environments and permit independent manipulation of localized properties of nanomaterials.

Stepwise crystallization and the layered distribution in crystallization kinetics of ultra-thin poly(ethylene terephthalate) film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zuo, Biao, E-mail: chemizuo@zstu.edu.cn, E-mail: wxinping@yahoo.com; Xu, Jianquan; Sun, Shuzheng

2016-06-21

Crystallization is an important property of polymeric materials. In conventional viewpoint, the transformation of disordered chains into crystals is usually a spatially homogeneous process (i.e., it occurs simultaneously throughout the sample), that is, the crystallization rate at each local position within the sample is almost the same. Here, we show that crystallization of ultra-thin poly(ethylene terephthalate) (PET) films can occur in the heterogeneous way, exhibiting a stepwise crystallization process. We found that the layered distribution of glass transition dynamics of thin film modifies the corresponding crystallization behavior, giving rise to the layered distribution of the crystallization kinetics of PET films,more » with an 11-nm-thick surface layer having faster crystallization rate and the underlying layer showing bulk-like behavior. The layered distribution in crystallization kinetics results in a particular stepwise crystallization behavior during heating the sample, with the two cold-crystallization temperatures separated by up to 20 K. Meanwhile, interfacial interaction is crucial for the occurrence of the heterogeneous crystallization, as the thin film crystallizes simultaneously if the interfacial interaction is relatively strong. We anticipate that this mechanism of stepwise crystallization of thin polymeric films will allow new insight into the chain organization in confined environments and permit independent manipulation of localized properties of nanomaterials.« less

Distribution of Arctic and Pacific copepods and their habitat in the northern Bering Sea and Chukchi Sea

NASA Astrophysics Data System (ADS)

Sasaki, H.; Matsuno, K.; Fujiwara, A.; Onuka, M.; Yamaguchi, A.; Ueno, H.; Watanuki, Y.; Kikuchi, T.

2015-11-01

The advection of warm Pacific water and the reduction of sea-ice extent in the western Arctic Ocean may influence the abundance and distribution of copepods, i.e., a key component in food webs. To understand the factors affecting abundance of copepods in the northern Bering Sea and Chukchi Sea, we constructed habitat models explaining the spatial patterns of the large and small Arctic copepods and the Pacific copepods, separately, using generalized additive models. Copepods were sampled by NORPAC net. Vertical profiles of density, temperature and salinity in the seawater were measured using CTD, and concentration of chlorophyll a in seawater was measured with a fluorometer. The timing of sea-ice retreat was determined using the satellite image. To quantify the structure of water masses, the magnitude of pycnocline and averaged density, temperature and salinity in upper and bottom layers were scored along three axes using principal component analysis (PCA). The structures of water masses indexed by the scores of PCAs were selected as explanatory variables in the best models. Large Arctic copepods were abundant in the water mass with high salinity water in bottom layer or with cold/low salinity water in upper layer and cold/high salinity water in bottom layer, and small Arctic copepods were abundant in the water mass with warm/saline water in upper layer and cold/high salinity water in bottom layers, while Pacific copepods were abundant in the water mass with warm/saline in upper layer and cold/high salinity water in bottom layer. All copepod groups were abundant in areas with deeper depth. Although chlorophyll a in upper and bottom layers were selected as explanatory variables in the best models, apparent trends were not observed. All copepod groups were abundant where the sea-ice retreated at earlier timing. Our study might indicate potential positive effects of the reduction of sea-ice extent on the distribution of all groups of copepods in the Arctic Ocean.

Reduced Fokker-Planck models for fast particle distribution across a transition layer of disparate plasma temperatures

NASA Astrophysics Data System (ADS)

Tang, Xian-Zhu; Berk, H. L.; Guo, Zehua; McDevitt, C. J.

2014-03-01

Across a transition layer of disparate plasma temperatures, the high energy tail of the plasma distribution can have appreciable deviations from the local Maxwellian distribution due to the Knudson layer effect. The Fokker-Planck equation for the tail particle population can be simplified in a series of practically useful limiting cases. The first is the approximation of background Maxwellian distribution for linearizing the collision operator. The second is the supra-thermal particle speed ordering of vTi ≪ v ≪ vTe for the tail ions and vTi ≪ vTe ≪ v for the tail electrons. Keeping both the collisional drag and energy scattering is essential for the collision operator to produce a Maxwellian tail distribution. The Fokker-Planck model for following the tail ion distribution for a given background plasma profile is explicitly worked out for systems of one spatial dimension, in both slab and spherical geometry. A third simplification is an expansion of the tail particle distribution using the spherical harmonics, which are eigenfunctions of the pitch angle scattering operator. This produces a set of coupled Fokker-Planck equations that contain energy-dependent spatial diffusion terms in two coordinates (position and energy), which originate from pitch angle scattering in the original Fokker-Planck equation. It is shown that the well-known diffusive Fokker-Planck model is a poor approximation of the two-mode truncation model, which itself has fundamental deficiency compared with the three-mode truncation model. The cause is the lack of even-symmetry representation in pitch dependence in the two-mode truncation model.

Self-assembled Ag nanoparticle network passivated by a nano-sized ZnO layer for transparent and flexible film heaters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seo, Ki-Won; Kim, Han-Ki, E-mail: imdlhkkim@khu.ac.kr; Kim, Min-Yi

2015-12-15

We investigated a self-assembled Ag nanoparticle network electrode passivated by a nano-sized ZnO layer for use in high-performance transparent and flexible film heaters (TFFHs). The low temperature atomic layer deposition of a nano-sized ZnO layer effectively filled the uncovered area of Ag network and improved the current spreading in the self-assembled Ag network without a change in the sheet resistance and optical transmittance as well as mechanical flexibility. The time-temperature profiles and heat distribution analysis demonstrate that the performance of the TFTH with the ZnO/Ag network is superior to that of a TFFH with Ag nanowire electrodes. In addition, themore » TFTHs with ZnO/Ag network exhibited better stability than the TFFH with a bare Ag network due to the effective current spreading through the nano-sized ZnO layer.« less

Energy management and control of active distribution systems

NASA Astrophysics Data System (ADS)

Shariatzadeh, Farshid

Advancements in the communication, control, computation and information technologies have driven the transition to the next generation active power distribution systems. Novel control techniques and management strategies are required to achieve the efficient, economic and reliable grid. The focus of this work is energy management and control of active distribution systems (ADS) with integrated renewable energy sources (RESs) and demand response (DR). Here, ADS mean automated distribution system with remotely operated controllers and distributed energy resources (DERs). DER as active part of the next generation future distribution system includes: distributed generations (DGs), RESs, energy storage system (ESS), plug-in hybrid electric vehicles (PHEV) and DR. Integration of DR and RESs into ADS is critical to realize the vision of sustainability. The objective of this dissertation is the development of management architecture to control and operate ADS in the presence of DR and RES. One of the most challenging issues for operating ADS is the inherent uncertainty of DR and RES as well as conflicting objective of DER and electric utilities. ADS can consist of different layers such as system layer and building layer and coordination between these layers is essential. In order to address these challenges, multi-layer energy management and control architecture is proposed with robust algorithms in this work. First layer of proposed multi-layer architecture have been implemented at the system layer. Developed AC optimal power flow (AC-OPF) generates fair price for all DR and non-DR loads which is used as a control signal for second layer. Second layer controls DR load at buildings using a developed look-ahead robust controller. Load aggregator collects information from all buildings and send aggregated load to the system optimizer. Due to the different time scale at these two management layers, time coordination scheme is developed. Robust and deterministic controllers are developed to maximize the energy usage from rooftop photovoltaic (PV) generation locally and minimize heat-ventilation and air conditioning (HVAC) consumption while maintaining inside temperature within comfort zone. The performance of the developed multi-layer architecture has been analyzed using test case studies and results show the robustness of developed controller in the presence of uncertainty.

Biothermomechanics of skin tissues

NASA Astrophysics Data System (ADS)

Xu, F.; Lu, T. J.; Seffen, K. A.

Biothermomechanics of skin is highly interdisciplinary involving bioheat transfer, burn damage, biomechanics and neurophysiology. During heating, thermally induced mechanical stress arises due to the thermal denaturation of collagen, resulting in macroscale shrinkage. Thus, the strain, stress, temperature and thermal pain/damage are highly correlated; in other words, the problem is fully coupled. The aim of this study is to develop a computational approach to examine the heat transfer process and the heat-induced mechanical response, so that the differences among the clinically applied heating modalities can be quantified. Exact solutions for temperature, thermal damage and thermal stress for a single-layer skin model were first derived for different boundary conditions. For multilayer models, numerical simulations using the finite difference method (FDM) and finite element method (FEM) were used to analyze the temperature, burn damage and thermal stress distributions in the skin tissue. The results showed that the thermomechanical behavior of skin tissue is very complex: blood perfusion has little effect on thermal damage but large influence on skin temperature distribution, which, in turn, influences significantly the resulting thermal stress field; the stratum corneum layer, although very thin, has a large effect on the thermomechanical behavior of skin, suggesting that it should be properly accounted for in the modeling of skin thermal stresses; the stress caused by non-uniform temperature distribution in the skin may also contribute to the thermal pain sensation.

Summary of experimental heat-transfer results from the turbine hot section facility

NASA Technical Reports Server (NTRS)

Gladden, Herbert J.; Yeh, Fredrick C.

1993-01-01

Experimental data from the turbine Hot Section Facility are presented and discussed. These data include full-coverage film-cooled airfoil results as well as special instrumentation results obtained at simulated real engine conditions. Local measurements of airfoil wall temperature, airfoil gas-path static-pressure distribution, and local heat-transfer coefficient distributions are presented and discussed. In addition, measured gas and coolant temperatures and pressures are presented. These data are also compared with analyses from Euler and boundary-layer codes.

Soil Surface Organic Layers in Alaska's Arctic Foothills: Development, Distribution and Microclimatic Feedbacks

NASA Astrophysics Data System (ADS)

Baughman, C. A.; Mann, D. H.; Verbyla, D.; Valentine, D.; Kunz, M. L.; Heiser, P. A.

2013-12-01

Accumulated organic matter at the ground surface plays an important role in arctic ecosystems. These soil surface organic layers (SSOLs) influence temperature, moisture, and chemistry in the underlying mineral soil and, on a global basis, comprise enormous stores of labile carbon. Understanding the dynamics of SSOLs is prerequisite to modeling the responses of arctic ecosystem processes to climate changes. Here, we ask three questions regarding SSOLs in the Arctic Foothills in northern Alaska: 1) What environmental factors control their spatial distribution? 2) How long do they take to form? 3) What is the relationship between SSOL thickness and mineral soil temperature through the growing season? The best topographically-controlled predictors of SSOL thickness and spatial distribution are duration of sunlight during the growing-season, upslope drainage area, slope gradient, and elevation. SSOLs begin to form within several decades following disturbance but require 500-700 years to reach equilibrium states. Once formed, mature SSOLs lower peak growing-season temperature and mean annual temperature in the underlying mineral horizon by 8° and 3° C respectively, which reduces available growing degree days within the upper mineral soil by nearly 80%. How ongoing climate change in northern Alaska will affect the region's SSOLs is an open and potentially crucial question.

On the Impact of Wind Farms on a Convective Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Lu, Hao; Porté-Agel, Fernando

2015-10-01

With the rapid growth in the number of wind turbines installed worldwide, a demand exists for a clear understanding of how wind farms modify land-atmosphere exchanges. Here, we conduct three-dimensional large-eddy simulations to investigate the impact of wind farms on a convective atmospheric boundary layer. Surface temperature and heat flux are determined using a surface thermal energy balance approach, coupled with the solution of a three-dimensional heat equation in the soil. We study several cases of aligned and staggered wind farms with different streamwise and spanwise spacings. The farms consist of Siemens SWT-2.3-93 wind turbines. Results reveal that, in the presence of wind turbines, the stability of the atmospheric boundary layer is modified, the boundary-layer height is increased, and the magnitude of the surface heat flux is slightly reduced. Results also show an increase in land-surface temperature, a slight reduction in the vertically-integrated temperature, and a heterogeneous spatial distribution of the surface heat flux.

Exchange coupled CoPt/FePtC media for heat assisted magnetic recording

NASA Astrophysics Data System (ADS)

Dutta, Tanmay; Piramanayagam, S. N.; Ru, Tan Hui; Saifullah, M. S. M.; Bhatia, C. S.; Yang, Hyunsoo

2018-04-01

L10 FePtC granular media are being studied as potential future magnetic recording media and are set to be used in conjunction with heat assisted magnetic recording (HAMR) to enable recording at write fields within the range of current day recording heads. Media structures based on a FePtC storage layer and a capping layer can alleviate the switching field distribution (SFD) requirements of HAMR and reduce the noise originating from the writing process. However, the current designs suffer from SFD issues due to high temperature writing. To overcome this problem, we study a CoPt/FePtC exchange coupled composite structure, where FePtC serves as the storage layer and CoPt (with higher Curie temperature, Tc) as the capping layer. CoPt remains ferromagnetic at near Tc of FePtC. Consequently, the counter exchange energy from CoPt would reduce the noise resulting from the adjacent grain interactions during the writing process. CoPt/FePtC bilayer samples with different thicknesses of CoPt were investigated. Our studies found that CoPt forms a continuous layer at a thickness of 6 nm and leads to considerable reduction in the saturation field and its distribution.

Roughness induced transition and heat transfer augmentation in hypersonic environments

NASA Astrophysics Data System (ADS)

Wassel, A. T.; Shih, W. C. L.; Courtney, J. F.

Boundary layer transition and surface heating distributions on graphite, fine weave carbon-carbon, and metallic nosetip materials were derived from surface temperature responses measured in nitrogen environments during both free-flight and track-guided testing in hypersonic environments. Innovative test procedures were developed, and heat transfer results were validated against established theory through experiments using a super-smooth tungsten model. Quantitative definitions of mean transition front locations were established by deriving heat flux distributions from measured temperatures, and comparisons made with existing nosetip transition correlations. Qualitative transition locations were inferred directly from temperature distributions to investigate preferred orientations on fine weave nosetips. Levels of roughness augmented heat transfer were generally shown to be below values predicted by state-of-the-art methods.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, expressions provide the temperature distribution and heat flow for a diffusing medium with a continually varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

NASA Technical Reports Server (NTRS)

Siegel, R.; Spuckler, C. M.

1993-01-01

A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, the analytical expressions provide the temperature distribution and heat flow for a diffusing medium with a continuously varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Nonlinear dynamics of mushy layers induced by external stochastic fluctuations.

PubMed

Alexandrov, Dmitri V; Bashkirtseva, Irina A; Ryashko, Lev B

2018-02-28

The time-dependent process of directional crystallization in the presence of a mushy layer is considered with allowance for arbitrary fluctuations in the atmospheric temperature and friction velocity. A nonlinear set of mushy layer equations and boundary conditions is solved analytically when the heat and mass fluxes at the boundary between the mushy layer and liquid phase are induced by turbulent motion in the liquid and, as a result, have the corresponding convective form. Namely, the 'solid phase-mushy layer' and 'mushy layer-liquid phase' phase transition boundaries as well as the solid fraction, temperature and concentration (salinity) distributions are found. If the atmospheric temperature and friction velocity are constant, the analytical solution takes a parametric form. In the more common case when they represent arbitrary functions of time, the analytical solution is given by means of the standard Cauchy problem. The deterministic and stochastic behaviour of the phase transition process is analysed on the basis of the obtained analytical solutions. In the case of stochastic fluctuations in the atmospheric temperature and friction velocity, the phase transition interfaces (mushy layer boundaries) move faster than in the deterministic case. A cumulative effect of these noise contributions is revealed as well. In other words, when the atmospheric temperature and friction velocity fluctuate simultaneously due to the influence of different external processes and phenomena, the phase transition boundaries move even faster. This article is part of the theme issue 'From atomistic interfaces to dendritic patterns'.This article is part of the theme issue 'From atomistic interfaces to dendritic patterns'. © 2018 The Author(s).

Localization and Ordering of Lipids Around Aquaporin-0: Protein and Lipid Mobility Effects.

PubMed

Briones, Rodolfo; Aponte-Santamaría, Camilo; de Groot, Bert L

2017-01-01

Hydrophobic matching, lipid sorting, and protein oligomerization are key principles by which lipids and proteins organize in biological membranes. The Aquaporin-0 channel (AQP0), solved by electron crystallography (EC) at cryogenic temperatures, is one of the few protein-lipid complexes of which the structure is available in atomic detail. EC and room-temperature molecular dynamics (MD) of dimyristoylglycerophosphocholine (DMPC) annular lipids around AQP0 show similarities, however, crystal-packing and temperature might affect the protein surface or the lipids distribution. To understand the role of temperature, lipid phase, and protein mobility in the localization and ordering of AQP0-lipids, we used MD simulations of an AQP0-DMPC bilayer system. Simulations were performed at physiological and at DMPC gel-phase temperatures. To decouple the protein and lipid mobility effects, we induced gel-phase in the lipids or restrained the protein. We monitored the lipid ordering effects around the protein. Reducing the system temperature or inducing lipid gel-phase had a marginal effect on the annular lipid localization. However, restraining the protein mobility increased the annular lipid localization around the whole AQP0 surface, resembling EC. The distribution of the inter-phosphate and hydrophobic thicknesses showed that stretching of the DMPC annular layer around AQP0 surface is the mechanism that compensates the hydrophobic mismatch in this system. The distribution of the local area-per-lipid and the acyl-chain order parameters showed particular fluid- and gel-like areas that involved several lipid layers. These areas were in contact with the surfaces of higher and lower protein mobility, respectively. We conclude that the AQP0 surfaces induce specific fluid- and gel-phase prone areas. The presence of these areas might guide the AQP0 lipid sorting interactions with other membrane components, and is compatible with the squared array oligomerization of AQP0 tetramers separated by a layer of annular lipids.

Physical Processes Controlling the Spatial Distributions of Relative Humidity in the Tropical Tropopause Layer Over the Pacific

NASA Technical Reports Server (NTRS)

Jensen, Eric J.; Thornberry, Troy D.; Rollins, Andrew W.; Ueyama, Rei; Pfister, Leonhard; Bui, Thaopaul; Diskin, Glenn S.; Digangi, Joshua P.; Hintsa, Eric; Gao, Ru-Shan;

Structure of 18R shifted hexagonal perovskite La{sub 6}MgTi{sub 4}O{sub 18} revisited by neutron diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Fengqi; Kuang, Xiaojun, E-mail: kuangxj@glut.edu.cn

The structure of 18-layer shifted B-site deficient hexagonal perovskite La{sub 6}MgTi{sub 4}O{sub 18} compound has been re-examined by neutron powder diffraction. Structural analysis reveals that La{sub 6}MgTi{sub 4}O{sub 18} compound adopts a 18R octahedral-tilted structure with LaO{sub 3} layer stacking sequence of (hhcccc){sub 3} in space group R{sup {sup -}}3, in contrast with the previously proposed R3m. La{sub 6}MgTi{sub 4}O{sub 18} demonstrates partially ordered Mg cation distribution with a preference on the central octahedral sites over the outer octahedral sites in the cubic perovskite blocks isolated by the single vacant octahedral layers between the two consecutive hexagonal layers. The instabilitymore » of the La{sub 6}MgTi{sub 4}O{sub 18} on alumina ceramic substrate at high temperature and its dependencies of cell parameters and permittivity were characterized as well. - Graphical abstract: 18-layer shifted hexagonal perovskite La{sub 6}MgTi{sub 4}O{sub 18} adopts octahedral-tilted structure in R{sup {sup -}}3 and demonstrates partially ordered Mg distribution in the cubic perovskite blocks isolated by the vacant octahedral layers. - Highlights: • Neutron diffraction reveals an octahedra-tilted structure in R{sup {sup -}}3 for La{sub 6}MgTi{sub 4}O{sub 18}. • Mg/Ti distribution in La{sub 6}MgTi{sub 4}O{sub 18} is partially ordered in the perovskite blocks. • Instability of La{sub 6}MgTi{sub 4}O{sub 18} on alumina ceramic at high temperature is demonstrated.« less

Knudsen and inverse Knudsen layer effect on tail ion distribution and fusion reactivity in inertial confinement fusion targets

NASA Astrophysics Data System (ADS)

McDevitt, C. J.; Tang, X.-Z.; Guo, Z.; Berk, H. L.

2014-10-01

A series of reduced models are used to study the fast ion tail in the vicinity of a transition layer between plasmas at disparate temperatures and densities, which is typical of the gas-pusher interface in inertial confinement fusion targets. Emphasis is placed on utilizing progressively more comprehensive models in order to identify the essential physics for computing the fast ion tail at energies comparable to the Gamow peak. The resulting fast ion tail distribution is subsequently used to compute the fusion reactivity as a function of collisionality and temperature. It is found that while the fast ion distribution can be significantly depleted in the hot spot, leading to a reduction of the fusion reactivity in this region, a surplus of fast ions is present in the neighboring cold region. The presence of this fast ion surplus in the neighboring cold region is shown to lead to a partial recovery of the fusion yield lost in the hot spot.

Development of a laser-induced heat flux technique for measurement of convective heat transfer coefficients in a supersonic flowfield

NASA Technical Reports Server (NTRS)

Porro, A. Robert; Keith, Theo G., Jr.; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.

1991-01-01

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the load surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimental results agreed reasonably well with theoretical predictions of convective heat transfer of flat plate laminar boundary layers. The results indicate that this non-intrusive optical measurement technique has the potential to obtain high quality surface convective heat transfer measurements in high speed flowfields.

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

NASA Technical Reports Server (NTRS)

Porro, A. R.; Keith, T. G., Jr.; Hingst, W. R.

1991-01-01

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high speed flow fields.

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

NASA Technical Reports Server (NTRS)

Porro, A. R.; Keith, T. G., Jr.; Hingst, W. R.

1991-01-01

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high-speed flowfields.

Thermoelectric needle probe for temperature measurements in biological materials.

PubMed

Korn, U; Rav-Noy, Z; Shtrikman, S; Zafrir, M

1980-04-01

In certain biological and medical applications it is important to measure and follow temperature changes inside a body or tissue. Any probe inserted into a tissue causes damage to tissue and distortion to the initial temperature distribution. To minimize this interference, a fine probe is needed. Thus, thin film technology is advantageous and was utilized by us to produce sensitive probes for these applications. The resulting probe is a small thermocouple at the tip of a thin needle (acupuncture stainless steel needle, approximately 0.26 mm in diameter and length in the range 5-10 cm was used). The junction was produced at the needle's tip by coating the needle with thin layers of insulating and thermoelectric materials. The first layer is an insulating one and is composed of polyacrylonitrile (PAN) and polymide produced by plasma polymerization and dip-coating respectively. This layer covers all the needle except the tip. The second layer is a vacuum deposited thermoelectric thin layer of Bi-5% Sb alloy coating also the tip. The third layer is for insulation and protection and is composed of PAN and polyimide. In this arrangement the junction is at the needle's tip, the needle is one conductor, the thermoelectric layer is the other and they are isolated by the plastic layer. The probe is handy and mechanically sturdy. The sensitivity is typically 77 microV/degrees C at room temperature and is constant to within 2% up to 90 degrees C. The response is fast (less than 1 sec) the noise is small, (less than 0.05 degrees C) and because of the small dimension, damage to tissue and disturbance to the measured temperature field are minimal.

Sensitivity of Offshore Surface Fluxes and Sea Breezes to the Spatial Distribution of Sea-Surface Temperature

NASA Astrophysics Data System (ADS)

Lombardo, Kelly; Sinsky, Eric; Edson, James; Whitney, Michael M.; Jia, Yan

2018-03-01

A series of numerical sensitivity experiments is performed to quantify the impact of sea-surface temperature (SST) distribution on offshore surface fluxes and simulated sea-breeze dynamics. The SST simulations of two mid-latitude sea-breeze events over coastal New England are performed using a spatially-uniform SST, as well as spatially-varying SST datasets of 32- and 1-km horizontal resolutions. Offshore surface heat and buoyancy fluxes vary in response to the SST distribution. Local sea-breeze circulations are relatively insensitive, with minimal differences in vertical structure and propagation speed among the experiments. The largest thermal perturbations are confined to the lowest 10% of the sea-breeze column due to the relatively high stability of the mid-Atlantic marine atmospheric boundary layer (ABL) suppressing vertical mixing, resulting in the depth of the marine layer remaining unchanged. Minimal impacts on the column-averaged virtual potential temperature and sea-breeze depth translates to small changes in sea-breeze propagation speed. This indicates that the use of datasets with a fine-scale SST may not produce more accurate sea-breeze simulations in highly stable marine ABL regimes, though may prove more beneficial in less stable sub-tropical environments.

F-16XL ship #1 - CAWAP boundary layer hot film, left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. Hot film is used to measure temperature changes on a surface. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Experiments on aerosol-induced cooling in the nocturnal boundary layer

NASA Astrophysics Data System (ADS)

Sreenivas, K.; Singh, D. K.; Vk, P.; Mukund, V.; Subramanian, G.

2012-12-01

In the nocturnal boundary layer (NBL), under calm & clear-sky conditions, radiation is the principal mode of heat transfer & it determines the temperature distribution close to the ground. Radiative processes thus influence the surface energy budget, & play a decisive role in many micro-meteorological processes including the formation of radiation-fog & inversion layer. Here, we report hyper-cooling of air layers close to the ground that has a radiative origin. Resulting vertical temperature distribution has an anomalous profile with an elevated minimum few decimetres above the ground (known as Lifted Temperature Minimum; LTM). Even though the first observation of this type of profile dates back to 1930s, its origin has not been explained till recently. We report field experiments to elucidate effects of emissivity and other physical properties of the ground on the LTM profile. Field observations clearly indicate that LTM-profiles are observed as a rule in the lowest meter of the NBL. We also demonstrate that the air-layer near the ground, rather than the ground itself, leads the post sunset cooling. This fact changes the very nature of the sensible heat-flux boundary condition. A laboratory experimental setup has been developed that can reproduce LTM. Lab-experiments demonstrate that the high cooling rates observed in the field experiments arise from the presence of aerosols & the intensity of cooling is proportional to aerosol concentration (Fig-1). We have also captured penetrative convection cells in the field experiments (Fig-2). Results presented here thus help in parameterizing transport processes in the NBL.

Effects of temperature distribution on boundary layer stability for a circular cone at Mach 10

NASA Astrophysics Data System (ADS)

Rigney, Jeffrey M.

A CFD analysis was conducted on a circular cone at 3 degrees angle of attack at Mach 10 using US3D and STABL 3D to determine the effect of wall temperature on the stability characteristics that lead to laminar-to-turbulent transition. Wall temperature distributions were manipulated while all other flow inputs and geometric qualities were held constant. Laminar-to-turbulent transition was analyzed for isothermal and adiabatic wall conditions, a simulated short-duration wind tunnel case, and several hot-nose temperature distributions. For this study, stability characteristics include maximum N-factor growth and the corresponding frequency range, disturbance spatial amplification rate and the corresponding modal frequency, and stability neutral point location. STABL 3D analysis indicates that temperature distributions typical of those in short-duration hypersonic wind tunnels do not result in any significant difference on the stability characteristics, as compared to an isothermal wall boundary condition. Hypothetical distributions of much greater temperatures at and past the nose tip do show a trend of dampening of second-mode disturbances, most notably on the leeward ray. The most pronounced differences existed between the isothermal and adiabatic cases.

Rehabilitation reliability of the road pavement structure with recycled base course with foamed bitumen

NASA Astrophysics Data System (ADS)

Buczyński, P.

2018-05-01

This article presents a new approach to reliability assessment of the road structure in which the base layer will be constructed in the process of cold deep recycling with foamed bitumen. In order to properly assess the reliability of the structure with the recycled base, it is necessary to determine the distribution of stress and strain in typical pavement layer systems. The true stress and strain values were established for particular structural layers using the complex modulus (E*) determined based on the master curves. The complex modulus was determined by the direct tension-compression test on cylindrical specimens (DTC-CY) at five temperatures (-7°C, 5°C, 13°C, 25°C, 40°C) and six loading times (0.1 Hz, 0.3 Hz, 1 Hz, 3 Hz, 10 Hz, 20 Hz) in accordance with EN 12697-26 in the linear viscoelasticity (LVE) range for small strains ranging from 25 to 50 με. The master curves of the complex modulus were constructed using the Richards model for the mixtures typically incorporated in structural layers, i.e., SMA11, AC16W, AC22P and MCAS. The values of the modulus characterizing particular layers were determined with temperature distribution in the structure taken into account, when the surface temperature was 40°C. The stress distribution was established for those calculation models. The stress values were used to evaluate the fatigue life under controlled stress conditions (IT-FT). This evaluation, with the controlled stress corresponding to that in the structure, facilitated the quality assessment of the rehabilitated recycled base course. Results showed that the recycled base mixtures having the indirect tensile strength (ITSDRY) similar to the stress in the structure under analysis needed an additional fatigue life evaluation in the indirect tensile test ITT. This approach to the recycled base quality assessment will allow eliminating the damage induced by overloading.

Differences in the efficacy of climate forcings explained by variations in atmospheric boundary layer depth.

PubMed

Davy, Richard; Esau, Igor

2016-05-25

The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. There are also numerous processes that introduce strong, regionalized variations to the overall warming trend. However, the ability of a forcing to change the surface air temperature depends on its spatial and temporal distribution. Here we show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer. This can vary by an order of magnitude on different temporal and spatial scales, and so we get a strongly amplified temperature response in shallow boundary layers. This must be accounted for to assess the efficacy of a climate forcing, and also implies that multiple climate forcings cannot be linearly combined to determine the temperature response.

Physical Limitations of Phosphor layer thickness and concentration for White LEDs.

PubMed

Tan, Cher Ming; Singh, Preetpal; Zhao, Wenyu; Kuo, Hao-Chung

2018-02-05

Increasing phosphor layer thickness and concentration can enhance the lumen flux of white LED (W-LED). In this work, we found that increasing the phosphor layer thickness and concentration can increase its temperature, and there is also a maximum thickness and concentration beyond which their increase will not lead to lumen increase, but only temperature increase. Higher thickness and higher concentration also results in warm light instead of White light. The maximum thickness and concentration are found to be limited by the scattering of light rays with higher % decrease of blue light rays than the yellow light rays. The results obtained in this work can also be used to compute the temperature and thermo-mechanical stress distribution of an encapsulated LED, demonstrating its usefulness to the design of encapsulated LED packages. Simulation software like ANSYS and TracePro are used extensively to verify the root cause mechanisms.

Analysis of Photothermal Characterization of Layered Materials: Design of Optimal Experiments

NASA Technical Reports Server (NTRS)

Cole, Kevin D.

2003-01-01

In this paper numerical calculations are presented for the steady-periodic temperature in layered materials and functionally-graded materials to simulate photothermal methods for the measurement of thermal properties. No laboratory experiments were performed. The temperature is found from a new Green s function formulation which is particularly well-suited to machine calculation. The simulation method is verified by comparison with literature data for a layered material. The method is applied to a class of two-component functionally-graded materials and results for temperature and sensitivity coefficients are presented. An optimality criterion, based on the sensitivity coefficients, is used for choosing what experimental conditions will be needed for photothermal measurements to determine the spatial distribution of thermal properties. This method for optimal experiment design is completely general and may be applied to any photothermal technique and to any functionally-graded material.

Differences in the efficacy of climate forcings explained by variations in atmospheric boundary layer depth

PubMed Central

Davy, Richard; Esau, Igor

2016-01-01

The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. There are also numerous processes that introduce strong, regionalized variations to the overall warming trend. However, the ability of a forcing to change the surface air temperature depends on its spatial and temporal distribution. Here we show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer. This can vary by an order of magnitude on different temporal and spatial scales, and so we get a strongly amplified temperature response in shallow boundary layers. This must be accounted for to assess the efficacy of a climate forcing, and also implies that multiple climate forcings cannot be linearly combined to determine the temperature response. PMID:27221757

Similar solutions for the compressible laminar boundary layer with heat transfer and pressure gradient

NASA Technical Reports Server (NTRS)

Cohen, Clarence B; Reshotko, Eli

1956-01-01

Stewartson's transformation is applied to the laminar compressible boundary-layer equations and the requirement of similarity is introduced, resulting in a set of ordinary nonlinear differential equations previously quoted by Stewartson, but unsolved. The requirements of the system are Prandtl number of 1.0, linear viscosity-temperature relation across the boundary layer, an isothermal surface, and the particular distributions of free-stream velocity consistent with similar solutions. This system admits axial pressure gradients of arbitrary magnitude, heat flux normal to the surface, and arbitrary Mach numbers. The system of differential equations is transformed to integral system, with the velocity ratio as the independent variable. For this system, solutions are found by digital computation for pressure gradients varying from that causing separation to the infinitely favorable gradient and for wall temperatures from absolute zero to twice the free-stream stagnation temperature. Some solutions for separated flows are also presented.

Surface-Induced Near-Field Scaling in the Knudsen Layer of a Rarefied Gas

NASA Astrophysics Data System (ADS)

Gazizulin, R. R.; Maillet, O.; Zhou, X.; Cid, A. Maldonado; Bourgeois, O.; Collin, E.

2018-01-01

We report on experiments performed within the Knudsen boundary layer of a low-pressure gas. The noninvasive probe we use is a suspended nanoelectromechanical string, which interacts with He 4 gas at cryogenic temperatures. When the pressure P is decreased, a reduction of the damping force below molecular friction ∝P had been first reported in Phys. Rev. Lett. 113, 136101 (2014), 10.1103/PhysRevLett.113.136101 and never reproduced since. We demonstrate that this effect is independent of geometry, but dependent on temperature. Within the framework of kinetic theory, this reduction is interpreted as a rarefaction phenomenon, carried through the boundary layer by a deviation from the usual Maxwell-Boltzmann equilibrium distribution induced by surface scattering. Adsorbed atoms are shown to play a key role in the process, which explains why room temperature data fail to reproduce it.

Patterns and Drivers of Vertical Distribution of the Ciliate Community from the Surface to the Abyssopelagic Zone in the Western Pacific Ocean.

PubMed

Zhao, Feng; Filker, Sabine; Xu, Kuidong; Huang, Pingping; Zheng, Shan

2017-01-01

The deep sea is one of the largest but least understood ecosystems on earth. Knowledge about the diversity and distribution patterns as well as drivers of microbial eukaryote (including ciliates) along the water column, particularly below the photic zone, is scarce. In this study, we investigated the diversity of pelagic ciliates, the main group of marine microeukaryotes, their vertical distribution from the surface to the abyssopelagic zone, as well as their horizontal distribution over a distance of 1,300 km in the Western Pacific Ocean, using high-throughput DNA and cDNA (complementary DNA) sequencing. No distance-decay relationship could be detected along the horizontal scale; instead, a distinct vertical distribution within the ciliate communities was revealed. The alpha diversity of the ciliate communities in the deep chlorophyll maximum (DCM) and the 200 m layer turned out to be significantly higher compared with the other water layers. The ciliate communities in the 200 m water layer appeared to be more similar to those in deeper layers from 1,000 m to about 5,000 m than to the surface and DCM ciliate communities. Dominant species in the bathypelagic and abyssopelagic zone, particularly some parasites, were also detected in the 200 m layer, but were almost absent in the surface layer. The 200 m layer, therefore, seems to be an important "species bank" for deep ocean layers. Statistical analyses further revealed significant effects of temperature and chlorophyll a on the partitioning of ciliate diversity, indicating that environmental factors are a stronger force in shaping marine pelagic ciliate communities than the geographic distance.

Boundary effects in a quasi-two-dimensional driven granular fluid.

PubMed

Smith, N D; Smith, M I

2017-12-01

The effect of a confining boundary on the spatial variations in granular temperature of a driven quasi-two-dimensional layer of particles is investigated experimentally. The radial drop in the relative granular temperature ΔT/T exhibits a maximum at intermediate particle numbers which coincides with a crossover from kinetic to collisional transport of energy. It is also found that at low particle numbers, the distributions of radial velocities are increasingly asymmetric as one approaches the boundary. The radial and tangential granular temperatures split, and in the tails of the radial velocity distribution there is a higher population of fast moving particles traveling away rather than towards the boundary.

Stress and reliability analyses of multilayered composite cylinder under thermal and mechanical loads

NASA Astrophysics Data System (ADS)

Wang, Xiaohua

The coupling resulting from the mutual influence of material thermal and mechanical parameters is examined in the thermal stress analysis of a multilayered isotropic composite cylinder subjected to sudden axisymmetric external and internal temperature. The method of complex frequency response functions together with the Fourier transform technique is utilized. Because the coupling parameters for some composite materials, such as carbon-carbon, are very small, the effect of coupling is neglected in the orthotropic thermal stress analysis. The stress distributions in multilayered orthotropic cylinders subjected to sudden axisymmetric temperature loading combined with dynamic pressure as well as asymmetric temperature loading are also obtained. The method of Fourier series together with the Laplace transform is utilized in solving the heat conduction equation and thermal stress analysis. For brittle materials, like carbon-carbon composites, the strength variability is represented by two or three parameter Weibull distributions. The 'weakest link' principle which takes into account both the carbon-carbon composite cylinders. The complex frequency response analysis is performed on a multilayered orthotropic cylinder under asymmetrical thermal load. Both deterministic and random thermal stress and reliability analyses can be based on the results of this frequency response analysis. The stress and displacement distributions and reliability of rocket motors under static or dynamic line loads are analyzed by an elasticity approach. Rocket motors are modeled as long hollow multilayered cylinders with an air core, a thick isotropic propellant inner layer and a thin orthotropic kevlar-epoxy case. The case is treated as a single orthotropic layer or a ten layered orthotropic structure. Five material properties and the load are treated as random variable with normal distributions when the reliability of the rocket motor is analyzed by the first-order, second-moment method (FOSM).

Silicanizing Process On Mild Steel Substrate by Using Tronoh Silica Sand: Microstructure, composition and coating growth

NASA Astrophysics Data System (ADS)

Y, Yusnenti F. M.; M, Othman; Mustapha, Mazli; I, MohdYusri

2016-02-01

A new Silicanizing process on formation of coating on mild steel using Tronoh Silica Sand (TSS) is presented. The process was performed in the temperature range 1000- 1100°C and with varying deposition time of 1-4 hours. Influence of the layer and the substrate constituents on the coating compatibility of the whole silicanized layer is described in detail. Morphology and structure of the silicanized layer were investigated by XRF, XRD and SEM. It is observed that diffusion coatings containing high concentrations of silica which profile distribution of SiO2 in the silicanized layer was encountered and the depth from the surface to the substrate was taken as the layer thickness. The results also depicted that a longer deposition time have tendency to produce a looser and larger grain a hence rougher layer. The silicanized layer composed of FeSi and Fe2SiO4 phases with preferred orientation within the experimental range. It is also found that longer deposition time and higher temperature resulted in an increase in SiO2 concentration on the substrate (mild steel).

Anthropogenic Moisture production and its effect on boundary-layer circulations over New York City

Treesearch

Robert D. Bornstein; Yam-Tong Tam

1977-01-01

A heat and moisture excess over New York City is shown to exist by the analysis of helicopter soundings of temperature and wet-bulb depression. The magnitude of the temporal and spatial distribution of anthropogenic moisture emissions in New York City were estimated from fuel-usage data. The URBMET urban boundary-layer model was used to evaluate the effects on the...

[Quantitative apportionment of slope aspect and altitude to soil moisture and temperature and plant distribution on alpine meadow].

PubMed

Niu, Yu Jie; Zhou, Jian Wei; Yang, Si Wei; Wang, Gui Zhen; Liu, Li; Hua, Li Min

2017-05-18

For understanding the effect of aspect and altitude of hill on soil moisture and temperature as well as the vegetation community, we selected an alpine meadow located on a hill in north-eastern Tibet Plateau as our study area. Data on soil moisture and temperature, as well as plant distribution pattern in this mountain ecosystem were collected. We used regression analysis, CCA ordination and variance decomposition, to determine the impacts of the key factors (aspect, altitude, soil temperature and moisture) on plant diversity distribution in 189 sample sites of the hill. The results showed that the plant diversity of shady aspect and bottomland was highest and lowest, respectively. The plant diversity of the shady aspect and on the ridge of the hill increased initially and then decreased with the increasing altitude, but the plant diversity of the sunny aspect increased with the increasing altitude. At 0-30 cm soil layer, the soil temperature of the sunny aspect was higher than that of other aspects, but the soil temperature at 0-20 cm soil layer did not change with the increa-sing altitude. The soil moisture of shady aspect was higher than that of other aspects, and increased with the increasing altitude. The aspect and altitude explained 100% of soil temperature changes and 51.8% of soil moisture variation. Aspect alone explained 72.2% of soil temperature variation and altitude alone explained 51.8% of soil moisture variation, which had the highest contribution rate individually. Most plants were distributed on the shady aspect and on the ridge, and at medium altitude. Sedges mainly grew on the shady aspect, while Gramineae grew on the sunny aspect, the ridge was an ecotone. Cyperaceae, Gramineae and Leguminosae were mainly distributed in low altitude zone. Hill aspect and altitude totally explained 28.6% of plant abundance variation, hill aspect alone explained 19.9% of plant abundance variation. The management of grassland production and ecological restoration in alpine meadow ecosystem should consider the effect of landform on soil and vegetation, and the hill aspect should be priority factor instead of altitude when planning management interventions.

Locating a silane coupling agent in silica-filled rubber composites by EFTEM.

PubMed

Dohi, Hidehiko; Horiuchi, Shin

2007-11-20

A silane coupling agent (SA) was added to silica/rubber composites at different mixing temperatures and the formation of a coupling layer at the silica/rubber interface was investigated by energy-filtering transmission electron microscopy. Bis(triethoxysilypropyl)tetrasulfane (TESPT), which was used as the SA, reacted with the silanol groups on the silica surface and with styrene-butadiene rubber to form an interfacial coupling layer. The silicon and sulfur elemental distributions were analyzed by electron energy loss spectroscopy (EELS) and elemental mapping. The amount of TESPT trapped in the rubber matrix could be qualitatively estimated by EELS, and the in situ formed coupling layer could be characterized by elemental mapping. The result indicated that the formation of the coupling layer was affected by the mixing temperature. The technique described here will contribute to the study of interface-property relationships and the evaluation of the role of SAs in polymeric composites.

Quantum molecular dynamics simulation of structural and thermodynamic properties of NiAl

NASA Astrophysics Data System (ADS)

Karchevskaya, E. S.; Minakov, D. V.; Levashov, P. R.

2018-01-01

In this work, structural and thermodynamic properties of a solid and liquid Ni-Al compound are studied using an ab initio method of quantum molecular dynamics (QMD). Simulations were carried out in 700-3000 K temperature range at atmospheric pressure. Radial distribution functions are analyzed to determine the presence of Ni-Al chemical bonds. Diffusion coefficients for individual components are also calculated. Another goal of this work is the investigation of the reaction propagation in thermally-initiated Ni-Al foils. For this purpose, we performed QMD simulations of Ni-Al layers in the microcanonical ensemble. An exothermic reaction between the solid Ni-Al layers is observed in our simulations at temperature less than the melting temperatures of the components.

Ferromagnetic transition in a simple variant of the Ising model on multiplex networks

NASA Astrophysics Data System (ADS)

Krawiecki, A.

2018-02-01

Multiplex networks consist of a fixed set of nodes connected by several sets of edges which are generated separately and correspond to different networks ("layers"). Here, a simple variant of the Ising model on multiplex networks with two layers is considered, with spins located in the nodes and edges corresponding to ferromagnetic interactions between them. Critical temperatures for the ferromagnetic transition are evaluated for the layers in the form of random Erdös-Rényi graphs or heterogeneous scale-free networks using the mean-field approximation and the replica method, from the replica symmetric solution. Both methods require the use of different "partial" magnetizations, associated with different layers of the multiplex network, and yield qualitatively similar results. If the layers are strongly heterogeneous the critical temperature differs noticeably from that for the Ising model on a network being a superposition of the two layers, evaluated in the mean-field approximation neglecting the effect of the underlying multiplex structure on the correlations between the degrees of nodes. The critical temperature evaluated from the replica symmetric solution depends sensitively on the correlations between the degrees of nodes in different layers and shows satisfactory quantitative agreement with that obtained from Monte Carlo simulations. The critical behavior of the magnetization for the model with strongly heterogeneous layers can depend on the distributions of the degrees of nodes and is then determined by the properties of the most heterogeneous layer.

The Thermocline Layer and Chlorophyll-a Concentration Variability during Southeast Monsoon in the Banda Sea

NASA Astrophysics Data System (ADS)

Pusparini, Nikita; Prasetyo, Budi; Ambariyanto; Widowati, Ita

2017-02-01

Thermocline layer and chlorophyll-a concentration can be used to investigate the upwelling region. This investigation is focused in the Banda Sea because the upwelling event in this area is quite large and has a longer upwelling duration than other waters in Indonesia. In addition, Banda Sea is also influenced by climatic factors such as monsoon. The aim of this research is to determine the validation of secondary data (from satellite imagery data and model) and in situ observation data (from research cruise) and to determine the variability of thermocline layer and chlorophyll-a concentration during Southeast Monsoon in the Banda Sea. The data used in this study were chlorophyll-a concentration, seawater vertical temperature at depths 0-400 meters, and sea surface temperature from remote sensing and in situ data. Spatial and temporal analysis of all parameters was conducted by quantitative descriptive method. The results showed that the variability of thermocline layer and the chlorophyll-a distribution were strongly related to seasonal pattern. In most cases, the estimates of thermocline layer and chlorophyll-a concentration using remote sensing algorithm were higher than in situ measured values. The greatest variability occurred in the eastern Banda Sea during the Southeast Monsoon with shallower thermocline layer, more abundance of chlorophyll-a concentration, and lower sea surface temperature.

Thermal analysis of laser additive manufacturing of aluminium alloys: Experiment and simulation

NASA Astrophysics Data System (ADS)

Bock, Frederic E.; Froend, Martin; Herrnring, Jan; Enz, Josephin; Kashaev, Nikolai; Klusemann, Benjamin

2018-05-01

Laser additive manufacturing (LAM) has become increasingly popular in industry in recent decades because it enables exceptional degrees of freedom regarding the structural design of lightweight components compared to subtractive manufacturing techniques. Laser metal deposition (LMD) of wire-fed material shows in particular the advantages such as high process velocity and efficient use of material compared to other LAM processes. During wire-based LMD, the material is deposited onto a substrate and supplemented by successive layers allowing a layer-wise production of complex three-dimensional structures. Despite the increased productivity of LMD, regarding the ability to process aluminium alloys, there is still a lack in quality and reproducibility due to the inhomogeneous temperature distribution during the process, leading to undesired residual stresses, distortions and inconsistent layer geometries and poor microstructures. In this study, the aluminium alloy AA5087 as wire and AA5754 as substrate material were utilized for LMD. In order to obtain information about the temperature field during LMD, thermocouple and thermography measurements were performed during the process. The temperature measurements were used to validate a finite element model regarding the heat distribution, which will be further used to investigate the temperature field evolution over time. To consider the continuous addition of material within the FE-model, an inactive/active element approach was chosen, where initially deactivated elements are activated corresponding to the deposition of material. The first results of the simulation and the experiments show good agreement. Therefore, the model can be used in the future for LMD process optimization, e.g., in terms of minimizing local variations of the thermal load for each layer.

Surface microstructure and high temperature corrosion resistance of arc-sprayed FeCrAl coating irradiated by high current pulsed electron beam

NASA Astrophysics Data System (ADS)

Hao, Shengzhi; Zhao, Limin; He, Dongyun

2013-10-01

The surface microstructure of arc-sprayed FeCrAl coating irradiated by high current pulsed electron beam (HCPEB) with long pulse duration of 200 μs was characterized by using optical microscopy, scanning electron microscopy and X-ray diffractometry. The distribution of chemical composition in modified surface layer was measured with electron probe micro-analyzer. The high temperature corrosion resistance of FeCrAl coating was tested in a saturated Na2SO4 and K2SO4 solution at 650 °C. After HCPEB irradiation, the coarse surface of arc-sprayed coating was changed as discrete bulged nodules with smooth and compact appearance. When using low energy density of 20 J/cm2, the surface modified layer was continuous entirely with an average melting depth of ˜30 μm. In the surface remelted layer, Fe and Cr elements gave a uniform distribution, while Al and O elements agglomerated particularly at the concave part between nodule structures to form α-Al2O3 phase. After high temperature corrosion tests, the FeCrAl coating treated with HCPEB of 20 J/cm2 remained a glossy surface with weight increment of ˜51 mg/cm2, decreased by 20% as compared to the initial sample. With the increasing energy density of HCPEB irradiation, the integrity of surface modified layer got segmented due to the formation of larger bulged nodules and cracks at the concave parts. For the HCPEB irradiation of 40 J/cm2, the high temperature corrosion resistance of FeCrAl coating was deteriorated drastically.

Laser-assisted selective fusing of thermal sprayed Ni-based self-fluxing alloys by using high-power diode lasers

NASA Astrophysics Data System (ADS)

Chun, Eun-Joon; Kim, Min-Su; Nishikawa, Hiroshi; Park, Changkyoo; Suh, Jeong

2018-03-01

Fusing treatment of Ni-based self-fluxing alloys (Metco-16C and 1276F) was performed using high-power diode lasers to control the temperature of the substrate's surface in real time. The effects of the fusing treatment temperature on the microstructural change and hardness distribution were also investigated. For Metco-16C and 1276F, the macrostructural inhomogeneity (voids) within the thermal sprayed layer decreased considerably as the fusing temperature increased. For both self-fluxing alloys, the optimal temperature for fusing was approximately 1423 K (for Metco-16C) and 1373 K (for 1276F), both of which are within the solid state temperature range; these temperatures maximize the alloy hardness together with the macrostructural homogeneity. In this temperature range, the microstructure consists of a lamellar-structured matrix phase with fine (<5 μm) carbides and borides. Selective fusing for a thermal sprayed layer 0.2-0.5 mm in thickness could be successfully achieved in a high-power diode laser system.

Vertical distribution of bacterial community is associated with the degree of soil organic matter decomposition in the active layer of moist acidic tundra.

PubMed

Kim, Hye Min; Lee, Min Jin; Jung, Ji Young; Hwang, Chung Yeon; Kim, Mincheol; Ro, Hee-Myong; Chun, Jongsik; Lee, Yoo Kyung

2016-11-01

The increasing temperature in Arctic tundra deepens the active layer, which is the upper layer of permafrost soil that experiences repeated thawing and freezing. The increasing of soil temperature and the deepening of active layer seem to affect soil microbial communities. Therefore, information on soil microbial communities at various soil depths is essential to understand their potential responses to climate change in the active layer soil. We investigated the community structure of soil bacteria in the active layer from moist acidic tundra in Council, Alaska. We also interpreted their relationship with some relevant soil physicochemical characteristics along soil depth with a fine scale (5 cm depth interval). The bacterial community structure was found to change along soil depth. The relative abundances of Acidobacteria, Gammaproteobacteria, Planctomycetes, and candidate phylum WPS-2 rapidly decreased with soil depth, while those of Bacteroidetes, Chloroflexi, Gemmatimonadetes, and candidate AD3 rapidly increased. A structural shift was also found in the soil bacterial communities around 20 cm depth, where two organic (upper Oi and lower Oa) horizons are subdivided. The quality and the decomposition degree of organic matter might have influenced the bacterial community structure. Besides the organic matter quality, the vertical distribution of bacterial communities was also found to be related to soil pH and total phosphorus content. This study showed the vertical change of bacterial community in the active layer with a fine scale resolution and the possible influence of the quality of soil organic matter on shaping bacterial community structure.

Boundary-layer cumulus over heterogeneous landscapes: A subgrid GCM parameterization. Final report, December 1991--November 1995

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stull, R.B.; Tripoli, G.

1996-01-08

The authors developed single-column parameterizations for subgrid boundary-layer cumulus clouds. These give cloud onset time, cloud coverage, and ensemble distributions of cloud-base altitudes, cloud-top altitudes, cloud thickness, and the characteristics of cloudy and clear updrafts. They tested and refined the parameterizations against archived data from Spring and Summer 1994 and 1995 intensive operation periods (IOPs) at the Southern Great Plains (SGP) ARM CART site near Lamont, Oklahoma. The authors also found that: cloud-base altitudes are not uniform over a heterogeneous surface; tops of some cumulus clouds can be below the base-altitudes of other cumulus clouds; there is an overlap regionmore » near cloud base where clear and cloudy updrafts exist simultaneously; and the lognormal distribution of cloud sizes scales to the JFD of surface layer air and to the shape of the temperature profile above the boundary layer.« less

Current density and catalyst-coated membrane resistance distribution of hydro-formed metallic bipolar plate fuel cell short stack with 250 cm2 active area

NASA Astrophysics Data System (ADS)

Haase, S.; Moser, M.; Hirschfeld, J. A.; Jozwiak, K.

2016-01-01

An automotive fuel cell with an active area of 250 cm2 is investigated in a 4-cell short stack with a current and temperature distribution device next to the bipolar plate with 560 current and 140 temperature segments. The electrical conductivities of the bipolar plate and gas diffusion layer assembly are determined ex-situ with this current scan shunt module. The applied fuel cell consists of bipolar plates constructed of 75-μm-thick, welded stainless-steel foils and a graphitic coating. The electrical conductivities of the bipolar plate and gas diffusion layer assembly are determined ex-situ with this module with a 6% deviation in in-plane conductivity. The current density distribution is evaluated up to 2.4 A cm-2. The entire cell's investigated volumetric power density is 4.7 kW l-1, and its gravimetric power density is 4.3 kW kg-1 at an average cell voltage of 0.5 V. The current density distribution is determined without influencing the operating cell. In addition, the current density distribution in the catalyst-coated membrane and its effective resistivity distribution with a finite volume discretisation of Ohm's law are evaluated. The deviation between the current density distributions in the catalyst-coated membrane and the bipolar plate is determined.

Plasma potential and electron temperature evaluated by ball-pen and Langmuir probes in the COMPASS tokamak

NASA Astrophysics Data System (ADS)

Dimitrova, M.; Popov, Tsv K.; Adamek, J.; Kovačič, J.; Ivanova, P.; Hasan, E.; López-Bruna, D.; Seidl, J.; Vondráček, P.; Dejarnac, R.; Stöckel, J.; Imríšek, M.; Panek, R.; the COMPASS Team

2017-12-01

The radial distributions of the main plasma parameters in the scrape-off-layer of the COMPASS tokamak are measured during L-mode and H-mode regimes by using both Langmuir and ball-pen probes mounted on a horizontal reciprocating manipulator. The radial profile of the plasma potential derived previously from Langmuir probes data by using the first derivative probe technique is compared with data derived using ball-pen probes. A good agreement can be seen between the data acquired by the two techniques during the L-mode discharge and during the H-mode regime within the inter-ELM periods. In contrast with the first derivative probe technique, the ball-pen probe technique does not require a swept voltage and, therefore, the temporal resolution is only limited by the data acquisition system. In the electron temperature evaluation, in the far scrape-off layer and in the limiter shadow, where the electron energy distribution is Maxwellian, the results from both techniques match well. In the vicinity of the last closed flux surface, where the electron energy distribution function is bi-Maxwellian, the ball-pen probe technique results are in agreement with the high-temperature components of the electron distribution only. We also discuss the application of relatively large Langmuir probes placed in parallel and perpendicularly to the magnetic field lines to studying the main plasma parameters. The results obtained by the two types of the large probes agree well. They are compared with Thomson scattering data for electron temperatures and densities. The results for the electron densities are compared also with the results from ASTRA code calculation of the electron source due to the ionization of the neutrals by fast electrons and the origin of the bi-Maxwellian electron energy distribution function is briefly discussed.

Ion distribution in the hot spot of an inertial confinement fusion plasma

NASA Astrophysics Data System (ADS)

Tang, Xianzhu; Guo, Zehua; Berk, Herb

2012-10-01

Maximizing the fusion gain of inertial confinement fusion (ICF) for inertial fusion energy (IFE) applications leads to the standard scenario of central hot spot ignition followed by propagating burn wave through the cold/dense assembled fuel. The fact that the hot spot is surrounded by cold but dense fuel layer introduces subtle plasma physics which requires a kinetic description. Here we perform Fokker-Planck calculations and kinetic PIC simulations for an ICF plasma initially in pressure balance but having large temperature gradient over a narrow transition layer. The loss of the fast ion tail from the hot spot, which is important for fusion reactivity, is quantified by Fokker-Planck models. The role of electron energy transport and the ambipolar electric field is investigated via kinetic simulations and the fluid moment models. The net effect on both hot spot ion temperature and the ion tail distribution, and hence the fusion reactivity, is elucidated.

Natural convection heat transfer in water near its density maximum

NASA Astrophysics Data System (ADS)

Yen, Yin-Chao

1990-12-01

This monograph reviews and summarizes to date the experimental and analytical results on the effect of water density near its maximum convection, transient flow and temperature structure characteristics: (1) in a vertical enclosure; (2) in a vertical annulus; (3) between horizontal concentric cylinders; (4) in a square enclosure; (5) in a rectangular enclosure; (6) in a horizontal layer; (7) in a circular confined melt layer; and (8) in bulk water during melting. In a layer of water containing a maximum density temperature of 4 C, the onset of convection (the critical number) is found not to be a constant value as in the classical normal fluid but one that varies with the imposed thermal and hydrodynamic boundaries. In horizontal layers, a nearly constant temperature zone forms and continuously expands between the warm and cold boundaries. A minimum heat transfer exists in most of the geometries studied and, in most cases, can be expressed in terms of a density distribution parameter. The effect of this parameter on a cells formation, disappearance and transient structure is discussed, and the effect of split boundary flow on heat transfer is presented.

Neural network modelling of thermal stratification in a solar DHW storage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geczy-Vig, P.; Farkas, I.

2010-05-15

In this study an artificial neural network (ANN) model is introduced for modelling the layer temperatures in a storage tank of a solar thermal system. The model is based on the measured data of a domestic hot water system. The temperatures distribution in the storage tank divided in 8 equal parts in vertical direction were calculated every 5 min using the average 5 min data of solar radiation, ambient temperature, mass flow rate of collector loop, load and the temperature of the layers in previous time steps. The introduced ANN model consists of two parts describing the load periods andmore » the periods between the loads. The identified model gives acceptable results inside the training interval as the average deviation was 0.22 C during the training and 0.24 C during the validation. (author)« less

The airglow layer emission altitude cannot be determined unambiguously from temperature comparison with lidars

NASA Astrophysics Data System (ADS)

Dunker, Tim

2018-05-01

I investigate the nightly mean emission height and width of the OH* (3-1) layer by comparing nightly mean temperatures measured by the ground-based spectrometer GRIPS 9 and the Na lidar at ALOMAR. The data set contains 42 coincident measurements taken between November 2010 and February 2014, when GRIPS 9 was in operation at the ALOMAR observatory (69.3° N, 16.0° E) in northern Norway. To closely resemble the mean temperature measured by GRIPS 9, I weight each nightly mean temperature profile measured by the lidar using Gaussian distributions with 40 different centre altitudes and 40 different full widths at half maximum. In principle, one can thus determine the altitude and width of an airglow layer by finding the minimum temperature difference between the two instruments. On most nights, several combinations of centre altitude and width yield a temperature difference of ±2 K. The generally assumed altitude of 87 km and width of 8 km is never an unambiguous, good solution for any of the measurements. Even for a fixed width of ˜ 8.4 km, one can sometimes find several centre altitudes that yield equally good temperature agreement. Weighted temperatures measured by lidar are not suitable to unambiguously determine the emission height and width of an airglow layer. However, when actual altitude and width data are lacking, a comparison with lidars can provide an estimate of how representative a measured rotational temperature is of an assumed altitude and width. I found the rotational temperature to represent the temperature at the commonly assumed altitude of 87.4 km and width of 8.4 km to within ±16 K, on average. This is not a measurement uncertainty.

Using Distributed Temperature Sensing for measuring vertical temperature profiles and air temperature variance in the roughness sublayer above a forest canopy

NASA Astrophysics Data System (ADS)

Schilperoort, B.; Coenders, M.; Savenije, H. H. G.

2017-12-01

In recent years, the accuracy and resolution of Distributed Temperature Sensing (DTS) machines has increased enough to expand its use in atmospheric sciences. With DTS the temperature of a fiber optic (FO) cable can be measured with a high frequency (1 Hz) and high resolution (0.30 m), for cable lengths up to kilometers. At our measurement site, a patch of 26 to 30 m tall Douglas Fir in mixed forest, we placed FO cables vertically along a 48 m tall flux tower. This gives a high resolution vertical temperature profile above, through, and below the canopy. By using a `bare' FO cable, with a diameter of 0.25 mm, we are able to measure variations in air temperature at a very small timescale, and are able to measure a vertical profile of the air temperature variance. The vertical temperature profiles can be used to study the formation of the stable boundary layer above and in the canopy at a high resolution. It also shows that a stable layer can develop below the canopy, which is not limited to night time conditions but also occurs during daytime. The high frequency measurements can be used to study the gradient of the variance of air temperature over the height. To study how the flux tower itself affects temperature variance measurements, the `bare' FO cable can be placed horizontally under a support structure away from the flux tower. Lastly, by using the hot-wire anemometer principle with DTS, the measurements can be expanded to also include vertical wind profile.

Metallization pattern on solid electrolyte or porous support of sodium battery process

DOEpatents

Kim, Jin Yong; Li, Guosheng; Lu, Xiaochuan; Sprenkle, Vincent L.; Lemmon, John P.

2016-05-31

A new battery configuration and process are detailed. The battery cell includes a solid electrolyte configured with an engineered metallization layer that distributes sodium across the surface of the electrolyte extending the active area of the cathode in contact with the anode during operation. The metallization layer enhances performance, efficiency, and capacity of sodium batteries at intermediate temperatures at or below about 200.degree. C.

Plasma convection and ion beam generation in the plasma sheet boundary layer

NASA Technical Reports Server (NTRS)

Moghaddam-Taaheri, E.; Goertz, C. K.; Smith, R. A.

1991-01-01

Because of the dawn-dusk electric field E(dd), plasma in the magnetotail convects from the lobe toward the central plasma sheet (CPS). In the absence of space or velocity diffusion due to plasma turbulence, convection would yield a steady state distribution function f = V exp (-2/3) g(v exp 2 V exp 2/3), where V is the flux tube volume. Starting with such a distribution function and a plasma beta which varies from beta greater than 1 in the CPS to beta much smaller than 1 in the lobe, the evolution of the ion distribution function was studied considering the combined effects of ion diffusion by kinetic Alfven waves (KAW) in the ULF frequency range (1-10 mHz) and convection due to E(dd) x B drift in the plasma sheet boundary layer (PSBL) and outer central plasma sheet (OCPS). The results show that, during the early stages after launching the KAWs, a beamlike ion distribution forms in the PSBL and at the same time the plasma density and temperature decrease in the OCPS. Following this stage, ions in the beams convect toward the CPS resulting in an increase of the plasma temperature in the OCPS.

Analysis of nanopore arrangement and structural features of anodic alumina layers formed by two-step anodizing in oxalic acid using the dedicated executable software

NASA Astrophysics Data System (ADS)

Zaraska, Leszek; Stępniowski, Wojciech J.; Sulka, Grzegorz D.; Ciepiela, Eryk; Jaskuła, Marian

2014-02-01

Anodic porous alumina layers were fabricated by a two-step self-organized anodization in 0.3 M oxalic acid under various anodizing potentials ranging from 30 to 60 V at two different temperatures (10 and 17 ∘C). The effect of anodizing conditions on structural features and pore arrangement of AAO was investigated in detail by using the dedicated executable publication combined with ImageJ software. With increasing anodizing potential, a linear increase of the average pore diameter, interpore distance, wall thickness and barrier layer thickness, as well as a decrease of the pore density, were observed. In addition, the higher pore diameter and porosity values were obtained for samples anodized at the elevated temperature, independently of the anodizing potential. A degree of pore order was investigated on the basis of Delaunay triangulations (defect maps) and calculation of pair distribution or angle distribution functions (PDF or ADF), respectively. All methods confirmed that in order to obtain nanoporous alumina with the best, hexagonal pore arrangement, the potential of 40 V should be applied during anodization. It was confirmed that the dedicated executable publication can be used to a fast and complex analysis of nanopore arrangement and structural features of nanoporous oxide layers.

Temperature Distribution within a Cold Cap during Nuclear Waste Vitrification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dixon, Derek R.; Schweiger, Michael J.; Riley, Brian J.

2015-07-21

The kinetics of the feed-to-glass conversion affects the waste vitrification rate in an electric melter. The primary area of interest in this conversion process is the cold cap, a layer of reacting feed on top of molten glass. Knowing the temperature profile within a cold cap will help determine its characteristics and relate them to the rate of glass production. The work presented here provides an experimental determination of the temperature distribution within the cold cap. Since a direct measurement of the temperature field within the cold cap is impracticable, an indirect method was developed where the textural features inmore » a laboratory-made cold cap with a high-level waste feed were mapped as a function of position using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. To correlate the temperature distribution to microstructures within the cold cap, microstructures were identified of individual feed samples that were heat treated to set temperatures between 400°C and 1200°C and quenched. The temperature distribution within the cold cap was then established by correlating cold-cap regions with the feed samples of nearly identical structures and was compared with the temperature profile from a mathematical model.« less

Soil surface organic layers in Arctic Alaska: spatial distribution, rates of formation, and microclimatic effects

USGS Publications Warehouse

Baughman, Carson; Mann, Daniel H.; Verbyla, David L.; Kunz, Michael L.

2015-01-01

Organic layers of living and dead vegetation cover the ground surface in many permafrost landscapes and play important roles in ecosystem processes. These soil surface organic layers (SSOLs) store large amounts of carbon and buffer the underlying permafrost and its contained carbon from changes in aboveground climate. Understanding the dynamics of SSOLs is a prerequisite for predicting how permafrost and carbon stocks will respond to warming climate. Here we ask three questions about SSOLs in a representative area of the Arctic Foothills region of northern Alaska: (1) What environmental factors control the thickness of SSOLs and the carbon they store? (2) How long do SSOLs take to develop on newly stabilized point bars? (3) How do SSOLs affect temperature in the underlying ground? Results show that SSOL thickness and distribution correlate with elevation, drainage area, vegetation productivity, and incoming solar radiation. A multiple regression model based on these correlations can simulate spatial distribution of SSOLs and estimate the organic carbon stored there. SSOLs develop within a few decades after a new, sandy, geomorphic surface stabilizes but require 500–700 years to reach steady state thickness. Mature SSOLs lower the growing season temperature and mean annual temperature of the underlying mineral soil by 8 and 3°C, respectively. We suggest that the proximate effects of warming climate on permafrost landscapes now covered by SSOLs will occur indirectly via climate's effects on the frequency, extent, and severity of disturbances like fires and landslides that disrupt the SSOLs and interfere with their protection of the underlying permafrost.

Particle nucleation in the tropical boundary layer and its coupling to marine sulfur sources

PubMed

Clarke; Davis; Kapustin; Eisele; Chen; Paluch; Lenschow; Bandy; Thornton; Moore; Mauldin; Tanner; Litchy; Carroll; Collins; Albercook

1998-10-02

New particle formation in a tropical marine boundary layer setting was characterized during NASA's Pacific Exploratory Mission-Tropics A program. It represents the clearest demonstration to date of aerosol nucleation and growth being linked to the natural marine sulfur cycle. This conclusion was based on real-time observations of dimethylsulfide, sulfur dioxide, sulfuric acid (gas), hydroxide, ozone, temperature, relative humidity, aerosol size and number distribution, and total aerosol surface area. Classic binary nucleation theory predicts no nucleation under the observed marine boundary layer conditions.

Testing fireproof materials in a combustion chamber

NASA Astrophysics Data System (ADS)

Kulhavy, Petr; Martinec, Tomas; Novak, Ondrej; Petru, Michal; Srb, Pavel

This article deals with a prototype concept, real experiment and numerical simulation of a combustion chamber, designed for testing fire resistance some new insulating composite materials. This concept of a device used for testing various materials, providing possibility of monitoring temperatures during controlled gas combustion. As a fuel for the combustion process propane butane mixture has been used and also several kinds of burners with various conditions of inlet air (forced, free) and fuel flows were tested. The tested samples were layered sandwich materials based on various materials or foams, used as fillers in fire shutters. The temperature distribution was measured by using thermocouples. A simulation of whole concept of experimental chamber has been carried out as the non-premixed combustion process in the commercial final volume sw Pyrosim. The result was to design chamber with a construction suitable, according to the international standards, achieve the required values (temperature in time). Model of the combustion based on a stoichiometric defined mixture of gas and the tested layered samples showed good conformity with experimental results - i.e. thermal distribution inside and heat release rate that has gone through the sample.

Heat transfer analysis of skin during thermal therapy using thermal wave equation.

PubMed

Kashcooli, Meisam; Salimpour, Mohammad Reza; Shirani, Ebrahim

2017-02-01

Specifying exact geometry of vessel network and its effect on temperature distribution in living tissues is one of the most complicated problems of the bioheat field. In this paper, the effects of blood vessels on temperature distribution in a skin tissue subjected to various thermal therapy conditions are investigated. Present model consists of counter-current multilevel vessel network embedded in a three-dimensional triple-layered skin structure. Branching angles of vessels are calculated using the physiological principle of minimum work. Length and diameter ratios are specified using length doubling rule and Cube law, respectively. By solving continuity, momentum and energy equations for blood flow and Pennes and modified Pennes bioheat equations for the tissue, temperature distributions in the tissue are measured. Effects of considering modified Pennes bioheat equation are investigated, comprehensively. It is also observed that blood has an impressive role in temperature distribution of the tissue, especially at high temperatures. The effects of different parameters such as boundary conditions, relaxation time, thermal properties of skin, metabolism and pulse heat flux on temperature distribution are investigated. Tremendous effect of boundary condition type at the lower boundary is noted. It seems that neither insulation nor constant temperature at this boundary can completely describe the real physical phenomena. It is expected that real temperature at the lower levels is somewhat between two predicted values. The effect of temperature on the thermal properties of skin tissue is considered. It is shown that considering temperature dependent values for thermal conductivity is important in the temperature distribution estimation of skin tissue; however, the effect of temperature dependent values for specific heat capacity is negligible. It is seen that considering modified Pennes equation in processes with high heat flux during low times is significant. Copyright © 2016 Elsevier Ltd. All rights reserved.

Low-Temperature Growth of Two-Dimensional Layered Chalcogenide Crystals on Liquid.

PubMed

Zhou, Yubing; Deng, Bing; Zhou, Yu; Ren, Xibiao; Yin, Jianbo; Jin, Chuanhong; Liu, Zhongfan; Peng, Hailin

2016-03-09

The growth of high-quality two-dimensional (2D) layered chalcogenide crystals is highly important for practical applications in future electronics, optoelectronics, and photonics. Current route for the synthesis of 2D chalcogenide crystals by vapor deposition method mainly involves an energy intensive high-temperature growth process on solid substrates, often suffering from inhomogeneous nucleation density and grain size distribution. Here, we first demonstrate a facile vapor-phase synthesis of large-area high-quality 2D layered chalcogenide crystals on liquid metal surface with relatively low surface energy at a growth temperature as low as ∼100 °C. Uniform and large-domain-sized 2D crystals of GaSe and GaxIn1-xSe were grown on liquid metal surface even supported on a polyimide film. As-grown 2D GaSe crystals have been fabricated to flexible photodetectors, showing high photoresponse and excellent flexibility. Our strategy of energy-sustainable low-temperature growth on liquid metal surface may open a route to the synthesis of high-quality 2D crystals of Ga-, In-, Bi-, Hg-, Pb-, or Sn-based chalcogenides and halides.

Thermal behavior of an asphalt pavement in the laboratory and in the parking lot.

PubMed

Martinkauppi, J B; Mäkiranta, A; Kiijärvi, J; Hiltunen, E

2015-01-01

The urban, constructed areas are full of buildings and different kinds of pavements and have a noticeable lack of trees and flora. These areas are accumulating the heat from the Sun, people, vehicles, and constructions. One interesting heat collector is the asphalt pavement. How does the heat transfer to different layers under the pavement or does it? What are the temperatures under the pavement in Finland where the winter can be pretty hard? How can those temperatures be measured accurately? These are the main questions this paper gives the preliminary answers to. First the thermal behavior of asphalt and the layers beneath are researched in the laboratory and then the measurement field is bored and dug in the parking in the Western coast of Finland, 63°5'45'' N. Distributed temperature sensing method was found to be a good choice for temperature measurements. Thermal behavior of pavement has been monitored in different layers and the preliminary results have been published here. The goal of this research is to assess the applicability of asphalt pavements for heat energy collection.

Thermal Behavior of an Asphalt Pavement in the Laboratory and in the Parking Lot

PubMed Central

Martinkauppi, J. B.; Mäkiranta, A.; Kiijärvi, J.; Hiltunen, E.

2015-01-01

The urban, constructed areas are full of buildings and different kinds of pavements and have a noticeable lack of trees and flora. These areas are accumulating the heat from the Sun, people, vehicles, and constructions. One interesting heat collector is the asphalt pavement. How does the heat transfer to different layers under the pavement or does it? What are the temperatures under the pavement in Finland where the winter can be pretty hard? How can those temperatures be measured accurately? These are the main questions this paper gives the preliminary answers to. First the thermal behavior of asphalt and the layers beneath are researched in the laboratory and then the measurement field is bored and dug in the parking in the Western coast of Finland, 63°5′45′′ N. Distributed temperature sensing method was found to be a good choice for temperature measurements. Thermal behavior of pavement has been monitored in different layers and the preliminary results have been published here. The goal of this research is to assess the applicability of asphalt pavements for heat energy collection. PMID:25861679

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Continuous-wave distributed-feedback InGaAsP (λ = 1.55 μm) injection heterolasers

NASA Astrophysics Data System (ADS)

Baryshev, V. I.; Golikova, E. G.; Duraev, V. P.; Kuchinskiĭ, V. I.; Kizhaev, K. Yu; Kuksenkov, D. V.; Portnoĭ, E. L.; Smirnitskiĭ, V. B.

1988-11-01

A study was made of stimulated emission from mesa-stripe distributed-feedback lasers in the form of double heterostructures with separate electron and optical confinement. A diffraction grating with a period Λ = 0.46 μm, formed on the surface of the upper waveguide layer by holographic lithography, ensured distributed feedback in the second order. The threshold current for cw operation at room temperature was 35-70 mA, the shift of the emission wavelength with temperature was ~ 0.08 nm/K, and the feedback coefficient deduced from the width of a "Bragg gap" was 110-150 cm- 1.

Membrane catalyst layer for fuel cells

DOEpatents

Wilson, Mahlon S.

1993-01-01

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 .mu.m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm.sup.2. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na.sup.+ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Abundance of fluorescent biological aerosol particles at temperatures conducive to the formation of mixed-phase and cirrus clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Twohy, Cynthia H.; McMeeking, Gavin R.; DeMott, Paul J.

Some types of biological particles are known to nucleate ice at warmer temperatures than mineral dust, with the potential to influence cloud microphysical properties and climate. However, the prevalence of these particle types above the atmospheric boundary layer is not well known. Many types of biological particles fluoresce when exposed to ultraviolet light, and the Wideband Integrated Bioaerosol Sensor takes advantage of this characteristic to perform real-time measurements of fluorescent biological aerosol particles (FBAPs). This instrument was flown on the National Center for Atmospheric Research Gulfstream V aircraft to measure concentrations of fluorescent biological particles from different potential sources andmore » at various altitudes over the US western plains in early autumn. Clear-air number concentrations of FBAPs between 0.8 and 12 µm diameter usually decreased with height and generally were about 10–100 L -1 in the continental boundary layer but always much lower at temperatures colder than 255 K in the free troposphere. At intermediate temperatures where biological ice-nucleating particles may influence mixed-phase cloud formation (255 K ≤ T ≤ 270 K), concentrations of fluorescent particles were the most variable and were occasionally near boundary-layer concentrations. Predicted vertical distributions of ice-nucleating particle concentrations based on FBAP measurements in this temperature regime sometimes reached typical concentrations of primary ice in clouds but were often much lower. If convection was assumed to lift boundary-layer FBAPs without losses to the free troposphere, better agreement between predicted ice-nucleating particle concentrations and typical ice crystal concentrations was achieved. Ice-nucleating particle concentrations were also measured during one flight and showed a decrease with height, and concentrations were consistent with a relationship to FBAPs established previously at the forested surface site below. The vertical distributions of FBAPs measured on five flights were also compared with those for bacteria, fungal spores, and pollen predicted from the EMAC global chemistry–climate model for the same geographic region.« less

Abundance of fluorescent biological aerosol particles at temperatures conducive to the formation of mixed-phase and cirrus clouds

NASA Astrophysics Data System (ADS)

Twohy, Cynthia H.; McMeeking, Gavin R.; DeMott, Paul J.; McCluskey, Christina S.; Hill, Thomas C. J.; Burrows, Susannah M.; Kulkarni, Gourihar R.; Tanarhte, Meryem; Kafle, Durga N.; Toohey, Darin W.

2016-07-01

Some types of biological particles are known to nucleate ice at warmer temperatures than mineral dust, with the potential to influence cloud microphysical properties and climate. However, the prevalence of these particle types above the atmospheric boundary layer is not well known. Many types of biological particles fluoresce when exposed to ultraviolet light, and the Wideband Integrated Bioaerosol Sensor takes advantage of this characteristic to perform real-time measurements of fluorescent biological aerosol particles (FBAPs). This instrument was flown on the National Center for Atmospheric Research Gulfstream V aircraft to measure concentrations of fluorescent biological particles from different potential sources and at various altitudes over the US western plains in early autumn. Clear-air number concentrations of FBAPs between 0.8 and 12 µm diameter usually decreased with height and generally were about 10-100 L-1 in the continental boundary layer but always much lower at temperatures colder than 255 K in the free troposphere. At intermediate temperatures where biological ice-nucleating particles may influence mixed-phase cloud formation (255 K ≤ T ≤ 270 K), concentrations of fluorescent particles were the most variable and were occasionally near boundary-layer concentrations. Predicted vertical distributions of ice-nucleating particle concentrations based on FBAP measurements in this temperature regime sometimes reached typical concentrations of primary ice in clouds but were often much lower. If convection was assumed to lift boundary-layer FBAPs without losses to the free troposphere, better agreement between predicted ice-nucleating particle concentrations and typical ice crystal concentrations was achieved. Ice-nucleating particle concentrations were also measured during one flight and showed a decrease with height, and concentrations were consistent with a relationship to FBAPs established previously at the forested surface site below. The vertical distributions of FBAPs measured on five flights were also compared with those for bacteria, fungal spores, and pollen predicted from the EMAC global chemistry-climate model for the same geographic region.

Ultrafast carrier thermalization and cooling dynamics in few-layer MoS2.

PubMed

Nie, Zhaogang; Long, Run; Sun, Linfeng; Huang, Chung-Che; Zhang, Jun; Xiong, Qihua; Hewak, Daniel W; Shen, Zexiang; Prezhdo, Oleg V; Loh, Zhi-Heng

2014-10-28

Femtosecond optical pump-probe spectroscopy with 10 fs visible pulses is employed to elucidate the ultrafast carrier dynamics of few-layer MoS2. A nonthermal carrier distribution is observed immediately following the photoexcitation of the A and B excitonic transitions by the ultrashort, broadband laser pulse. Carrier thermalization occurs within 20 fs and proceeds via both carrier-carrier and carrier-phonon scattering, as evidenced by the observed dependence of the thermalization time on the carrier density and the sample temperature. The n(-0.37 ± 0.03) scaling of the thermalization time with carrier density suggests that equilibration of the nonthermal carrier distribution occurs via non-Markovian quantum kinetics. Subsequent cooling of the hot Fermi-Dirac carrier distribution occurs on the ∼ 0.6 ps time scale via carrier-phonon scattering. Temperature- and fluence-dependence studies reveal the involvement of hot phonons in the carrier cooling process. Nonadiabatic ab initio molecular dynamics simulations, which predict carrier-carrier and carrier-phonon scattering time scales of 40 fs and 0.5 ps, respectively, lend support to the assignment of the observed carrier dynamics.

Performance Technology Program (PTP-S 2). Volume 9: Evaluation of reentry vehicle nosetip transition and heat transfer in the AEDC hyperballistics track G

NASA Astrophysics Data System (ADS)

Wassel, A. T.; Shih, W. C. L.; Curtis, R. J.

1981-01-01

Boundary layer transition and surface heating distributions on graphite fine weave carbon-carbon, and metallic nosetip materials were derived from surface temperature responses measured in nitrogen environments during both free-flight and track-guided testing in the AEDC Hyperballistics Range/Track G. Innovative test procedures were developed, and heat transfer results were validated against established theory through experiments using a super-smooth tungsten model. Quantitative definitions of mean transition front locations were established by deriving heat flux distributions from measured temperatures, and comparisons made with existing nosetip transition correlations. Qualitative transition locations were inferred directly from temperature distributions to investigate preferred orientations on fine weave nosetips. Levels of roughness augmented heat transfer were generally shown to be below values predicted by state of the art methods.

Surface Evolution of Nano-Textured 4H-SiC Homoepitaxial Layers after High Temperature Treatments: Morphology Characterization and Graphene Growth.

PubMed

Liu, Xingfang; Chen, Yu; Sun, Changzheng; Guan, Min; Zhang, Yang; Zhang, Feng; Sun, Guosheng; Zeng, Yiping

2015-09-18

Nano-textured 4H-SiC homoepitaxial layers (NSiCLs) were grown on 4H-SiC(0001) substrates using a low pressure chemical vapor deposition technique (LPCVD), and subsequently were subjected to high temperature treatments (HTTs) for investigation of their surface morphology evolution and graphene growth. It was found that continuously distributed nano-scale patterns formed on NSiCLs which were about submicrons in-plane and about 100 nanometers out-of-plane in size. After HTTs under vacuum, pattern sizes reduced, and the sizes of the remains were inversely proportional to the treatment time. Referring to Raman spectra, the establishment of multi-layer graphene (MLG) on NSiCL surfaces was observed. MLG with sp ² disorders was obtained from NSiCLs after a high temperature treatment under vacuum at 1700 K for two hours, while MLG without sp ² disorders was obtained under Ar atmosphere at 1900 K.

Analysis and calculation by integral methods of laminar compressible boundary-layer with heat transfer and with and without pressure gradient

NASA Technical Reports Server (NTRS)

Morduchow, Morris

1955-01-01

A survey of integral methods in laminar-boundary-layer analysis is first given. A simple and sufficiently accurate method for practical purposes of calculating the properties (including stability) of the laminar compressible boundary layer in an axial pressure gradient with heat transfer at the wall is presented. For flow over a flat plate, the method is applicable for an arbitrarily prescribed distribution of temperature along the surface and for any given constant Prandtl number close to unity. For flow in a pressure gradient, the method is based on a Prandtl number of unity and a uniform wall temperature. A simple and accurate method of determining the separation point in a compressible flow with an adverse pressure gradient over a surface at a given uniform wall temperature is developed. The analysis is based on an extension of the Karman-Pohlhausen method to the momentum and the thermal energy equations in conjunction with fourth- and especially higher degree velocity and stagnation-enthalpy profiles.

Enhancing the Oxidation Performance of Wrought Ni-Base Superalloy by Minor Additions of Active Elements

NASA Astrophysics Data System (ADS)

Tawancy, H. M.

2016-12-01

We show that the oxidation performance of Cr2O3-forming superalloy based upon the Ni-Cr-W system is significantly improved by the presence of minor concentrations of La, Si and Mn, which outweigh the detrimental effect of high W concentration in the alloy. Although Cr2O3 is known to transform into volatile CrO3 at temperatures ≥950 °C, the respective protection is extended to temperatures reaching 1150 °C, which has also been correlated with the beneficial effects of La, Si and Mn. During high-temperature oxidation, an inner protective La- and Si-modified layer of α-Cr2O3 in contact with the superalloy substrate is developed and shielded by an outermost layer of MnCr2O4. The distribution of La and Si in the inner oxide layer has been characterized down to the scale of transmission electron microscopy, and the possible mechanisms underlying their beneficial effects are elucidated.

Improved fluid dynamics similarity, analysis and verification. Part 5: Analytical and experimental studies of thermal stratification phenomena

NASA Technical Reports Server (NTRS)

Winter, E. R. F.; Schoenhals, R. J.; Haug, R. I.; Libby, T. L.; Nelson, R. N.; Stevenson, W. H.

1968-01-01

The stratification behavior of a contained fluid subjected to transient free convection heat transfer was studied. A rectangular vessel was employed with heat transfer from two opposite walls of the vessel to the fluid. The wall temperature was increased suddenly to initiate the process and was then maintained constant throughout the transient stratification period. Thermocouples were positioned on a post at the center of the vessel. They were adjusted so that temperatures could be measured at the fluid surface and at specific depths beneath the surface. The predicted values of the surface temperature and the stratified layer thickness were found to agree reasonably well with the experimental measurements. The experiments also provided information on the transient centerline temperature distribution and the transient flow distribution.

A means to estimate thermal and kinetic parameters of coal dust layer from hot surface ignition tests.

PubMed

Park, Haejun; Rangwala, Ali S; Dembsey, Nicholas A

2009-08-30

A method to estimate thermal and kinetic parameters of Pittsburgh seam coal subject to thermal runaway is presented using the standard ASTM E 2021 hot surface ignition test apparatus. Parameters include thermal conductivity (k), activation energy (E), coupled term (QA) of heat of reaction (Q) and pre-exponential factor (A) which are required, but rarely known input values to determine the thermal runaway propensity of a dust material. Four different dust layer thicknesses: 6.4, 12.7, 19.1 and 25.4mm, are tested, and among them, a single steady state dust layer temperature profile of 12.7 mm thick dust layer is used to estimate k, E and QA. k is calculated by equating heat flux from the hot surface layer and heat loss rate on the boundary assuming negligible heat generation in the coal dust layer at a low hot surface temperature. E and QA are calculated by optimizing a numerically estimated steady state dust layer temperature distribution to the experimentally obtained temperature profile of a 12.7 mm thick dust layer. Two unknowns, E and QA, are reduced to one from the correlation of E and QA obtained at criticality of thermal runaway. The estimated k is 0.1 W/mK matching the previously reported value. E ranges from 61.7 to 83.1 kJ/mol, and the corresponding QA ranges from 1.7 x 10(9) to 4.8 x 10(11)J/kg s. The mean values of E (72.4 kJ/mol) and QA (2.8 x 10(10)J/kg s) are used to predict the critical hot surface temperatures for other thicknesses, and good agreement is observed between measured and experimental values. Also, the estimated E and QA ranges match the corresponding ranges calculated from the multiple tests method and values reported in previous research.

The evolution of rifting process in the tectonic history of the Earth

NASA Technical Reports Server (NTRS)

Milanovsky, E. E.; Nikishin, A. M.

1985-01-01

The continental rifting is the response of the lithosphere to the oriented tension. The distribution of viscosity in the lithosphere plays an essential role during all stages of the rifting. The viscosity is a function of the temperature, the lithostatic pressure, the rock composition, the deformation rate and other factors. The temperature is the most important factor. The vertical section of continental lithosphere of the rift zone may be divided into the following layers: the upper crust, in which brittle deformation prevails; the medialcrust, in which the role of plastic deformation increases; the lower crust, in which plastic deformation prevails; and the uppermost plastic part of the mantle overlapping asthenosphere. The depth of the boundaries in the crust layers are mainly controlled by the temperature.

Two-Flux and Green's Function Method for Transient Radiative Transfer in a Semi-Transparent Layer

NASA Technical Reports Server (NTRS)

Siegel, Robert

1995-01-01

A method using a Green's function is developed for computing transient temperatures in a semitransparent layer by using the two-flux method coupled with the transient energy equation. Each boundary of the layer is exposed to a hot or cold radiative environment, and is heated or cooled by convection. The layer refractive index is larger than one, and the effect of internal reflections is included with the boundaries assumed diffuse. The analysis accounts for internal emission, absorption, heat conduction, and isotropic scattering. Spectrally dependent radiative properties are included, and transient results are given to illustrate two-band spectral behavior with optically thin and thick bands. Transient results using the present Green's function method are verified for a gray layer by comparison with a finite difference solution of the exact radiative transfer equations; excellent agreement is obtained. The present method requires only moderate computing times and incorporates isotropic scattering without additional complexity. Typical temperature distributions are given to illustrate application of the method by examining the effect of strong radiative heating on one side of a layer with convective cooling on the other side, and the interaction of strong convective heating with radiative cooling from the layer interior.

Four dimensional data assimilation (FDDA) impacts on WRF performance in simulating inversion layer structure and distributions of CMAQ-simulated winter ozone concentrations in Uintah Basin

NASA Astrophysics Data System (ADS)

Tran, Trang; Tran, Huy; Mansfield, Marc; Lyman, Seth; Crosman, Erik

2018-03-01

Four-dimensional data assimilation (FDDA) was applied in WRF-CMAQ model sensitivity tests to study the impact of observational and analysis nudging on model performance in simulating inversion layers and O3 concentration distributions within the Uintah Basin, Utah, U.S.A. in winter 2013. Observational nudging substantially improved WRF model performance in simulating surface wind fields, correcting a 10 °C warm surface temperature bias, correcting overestimation of the planetary boundary layer height (PBLH) and correcting underestimation of inversion strengths produced by regular WRF model physics without nudging. However, the combined effects of poor performance of WRF meteorological model physical parameterization schemes in simulating low clouds, and warm and moist biases in the temperature and moisture initialization and subsequent simulation fields, likely amplified the overestimation of warm clouds during inversion days when observational nudging was applied, impacting the resulting O3 photochemical formation in the chemistry model. To reduce the impact of a moist bias in the simulations on warm cloud formation, nudging with the analysis water mixing ratio above the planetary boundary layer (PBL) was applied. However, due to poor analysis vertical temperature profiles, applying analysis nudging also increased the errors in the modeled inversion layer vertical structure compared to observational nudging. Combining both observational and analysis nudging methods resulted in unrealistically extreme stratified stability that trapped pollutants at the lowest elevations at the center of the Uintah Basin and yielded the worst WRF performance in simulating inversion layer structure among the four sensitivity tests. The results of this study illustrate the importance of carefully considering the representativeness and quality of the observational and model analysis data sets when applying nudging techniques within stable PBLs, and the need to evaluate model results on a basin-wide scale.

Thermal analysis of microlens formation on a sensitized gelatin layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muric, Branka; Pantelic, Dejan; Vasiljevic, Darko

2009-07-01

We analyze a mechanism of direct laser writing of microlenses. We find that thermal effects and photochemical reactions are responsible for microlens formation on a sensitized gelatin layer. An infrared camera was used to assess the temperature distribution during the microlens formation, while the diffraction pattern produced by the microlens itself was used to estimate optical properties. The study of thermal processes enabled us to establish the correlation between thermal and optical parameters.

[Analysis of heat transfer in the biological tissue layer with distributed system of blood vessels].

PubMed

Bogatov, N M; Pelipenko, O N

2005-09-01

Processes of heat transfer in the skin layer with blood vessels were investigated using mathematical modeling. Analysis of influence of a pathological state of blood vessels on heterogeneity of thermal field of the skin surface was carried out. For each site of body surface, there is a certain difference of temperature between normal and pathological sites, being specific for differential diagnosis of diseases of dermal and hypodermic vessels.

Long-term active-layer dynamics: results of 22 years of field observations in Northern Hemisphere permafrost regions.

NASA Astrophysics Data System (ADS)

Shiklomanov, N. I.; Nelson, F. E.; Streletskiy, D. A.; Klene, A. E.; Biskaborn, B. K.

2016-12-01

The uppermost layer of seasonal thawing above permafrost (the active layer) is an important regulator of energy and mass fluxes between the surface and the atmosphere in the polar regions. Active layer monitoring is an important component of efforts to assess the effects of global change in permafrost environments. The Circumpolar Active Layer Monitoring (CALM) program, established in the early 1990s, is designed to observe temporal and spatial variability of the active layer and its response to changes and variations in climatic conditions. The CALM network is an integral part of the Global Terrestrial Network for Permafrost (GTN-P), operating under the auspices of the Global Terrestrial Observing System (GTOS) /Global Climate Observing System (GCOS). Standardized thaw depth observations in the Northern Hemisphere are available for more than 200 GTN-P/CALM sites in the Northern Hemisphere. At each of the sites spatially distributed ALT measurements have been conducted annually by mechanical probing. The locations of sites represent generalized surface and subsurface conditions characteristic of broader regions. The data are assimilated and distributed though the CALM (www.gwu.edu/ calm) and GTN-P (gtnpdatabase.org) online databases. In this presentation we use data from approximately 20 years of continuous observations to examine temporal trends in active-layer thickness for several representative Arctic regions. Results indicate substantial interannual fluctuations in active-layer thickness, primarily in response to variations in air temperature. Decadal trends in ALT vary by region. A progressive increase in ALT has been observed in the Nordic countries, the Russian European North, West Siberia, East Siberia, the Russian Far East, and the Interior of Alaska. North American Arctic sites show no apparent thaw depth trend over 22-years of record. However, combined active layer, ground temperature and heave/subsidence observations conducted in northern Alaska demonstrate a complex, non-linear response of the active-layer/upper permafrost system to changes in climatic conditions.

Soil thermal dynamics, snow cover, and frozen depth under five temperature treatments in an ombrotrophic bog: Constrained forecast with data assimilation: Forecast With Data Assimilation

DOE PAGES

Huang, Yuanyuan; Jiang, Jiang; Ma, Shuang; ...

2017-08-18

We report that accurate simulation of soil thermal dynamics is essential for realistic prediction of soil biogeochemical responses to climate change. To facilitate ecological forecasting at the Spruce and Peatland Responses Under Climatic and Environmental change site, we incorporated a soil temperature module into a Terrestrial ECOsystem (TECO) model by accounting for surface energy budget, snow dynamics, and heat transfer among soil layers and during freeze-thaw events. We conditioned TECO with detailed soil temperature and snow depth observations through data assimilation before the model was used for forecasting. The constrained model reproduced variations in observed temperature from different soil layers,more » the magnitude of snow depth, the timing of snowfall and snowmelt, and the range of frozen depth. The conditioned TECO forecasted probabilistic distributions of soil temperature dynamics in six soil layers, snow, and frozen depths under temperature treatments of +0.0, +2.25, +4.5, +6.75, and +9.0°C. Air warming caused stronger elevation in soil temperature during summer than winter due to winter snow and ice. And soil temperature increased more in shallow soil layers in summer in response to air warming. Whole ecosystem warming (peat + air warmings) generally reduced snow and frozen depths. The accuracy of forecasted snow and frozen depths relied on the precision of weather forcing. Uncertainty is smaller for forecasting soil temperature but large for snow and frozen depths. Lastly, timely and effective soil thermal forecast, constrained through data assimilation that combines process-based understanding and detailed observations, provides boundary conditions for better predictions of future biogeochemical cycles.« less

Soil thermal dynamics, snow cover, and frozen depth under five temperature treatments in an ombrotrophic bog: Constrained forecast with data assimilation: Forecast With Data Assimilation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Yuanyuan; Jiang, Jiang; Ma, Shuang

We report that accurate simulation of soil thermal dynamics is essential for realistic prediction of soil biogeochemical responses to climate change. To facilitate ecological forecasting at the Spruce and Peatland Responses Under Climatic and Environmental change site, we incorporated a soil temperature module into a Terrestrial ECOsystem (TECO) model by accounting for surface energy budget, snow dynamics, and heat transfer among soil layers and during freeze-thaw events. We conditioned TECO with detailed soil temperature and snow depth observations through data assimilation before the model was used for forecasting. The constrained model reproduced variations in observed temperature from different soil layers,more » the magnitude of snow depth, the timing of snowfall and snowmelt, and the range of frozen depth. The conditioned TECO forecasted probabilistic distributions of soil temperature dynamics in six soil layers, snow, and frozen depths under temperature treatments of +0.0, +2.25, +4.5, +6.75, and +9.0°C. Air warming caused stronger elevation in soil temperature during summer than winter due to winter snow and ice. And soil temperature increased more in shallow soil layers in summer in response to air warming. Whole ecosystem warming (peat + air warmings) generally reduced snow and frozen depths. The accuracy of forecasted snow and frozen depths relied on the precision of weather forcing. Uncertainty is smaller for forecasting soil temperature but large for snow and frozen depths. Lastly, timely and effective soil thermal forecast, constrained through data assimilation that combines process-based understanding and detailed observations, provides boundary conditions for better predictions of future biogeochemical cycles.« less

Low-Temperature Alteration of the Seafloor: Impacts on Ocean Chemistry

NASA Astrophysics Data System (ADS)

Coogan, Laurence A.; Gillis, Kathryn M.

2018-05-01

Over 50% of Earth is covered by oceanic crust, the uppermost portion of which is a high-permeability layer of basaltic lavas through which seawater continuously circulates. Fluid flow is driven by heat lost from the oceanic lithosphere; the global fluid flux is dependent on plate creation rates and the thickness and distribution of overlying sediment, which acts as a low-permeability layer impeding seawater access to the crust. Fluid-rock reactions in the crust, and global chemical fluxes, depend on the average temperature in the aquifer, the fluid flux, and the composition of seawater. The average temperature in the aquifer depends largely on bottom water temperature and, to a lesser extent, on the average seafloor sediment thickness. Feedbacks between off-axis chemical fluxes and their controls may play an important role in modulating ocean chemistry and planetary climate on long timescales, but more work is needed to quantify these feedbacks.

Size distribution of carbon layer planes in biochar from different plant type of feedstock with different heating temperatures.

PubMed

Lu, Guan-Yang; Ikeya, Kosuke; Watanabe, Akira

2016-11-01

Biochar application to soil is a strategy to decelerate the increase in the atmospheric carbon concentration. The composition of condensed aromatic clusters appears to be an important determinant of the degradation rate of char in soil. The objective of the present study was to determine the size distribution of carbon layer planes in biochars produced from different types of feedstock (a broadleaf and a coniferous tree and two herbs) using different heating treatment temperatures (HTT; 400 °C-800 °C) using X-ray diffraction 11 band profile analysis. (13)C nuclear magnetic resonance with the phase-adjusted spinning side bands of the chars indicated different spectral features depending on the HTT and similar carbon composition among the plant types at each HTT. Both the content and composition of carbon layer planes in biochar produced using the same HTT were also similar among the plant types. The carbon layer plane size in the 400 °C and 600 °C chars was distributed from 0.24 to 1.68 or 1.92 nm (corresponding to 37 or 52 rings) with the mean size of 0.79-0.92 and 0.80-1.14 nm, respectively. The carbon layer planes in the 800 °C chars ranged from 0.72-0.96 nm (7-14 rings) to 2.64-3.60 nm (91-169 rings) and the mean values were 1.47-1.89 nm. The relative carbon layer plane content in the 600 °C and 800 °C chars was typically 2 and 3 times that in the 400 °C chars. These results indicate the progression of the formation and/or the size development of graphite-like structures, suggesting that a char produced at a higher HTT would have better carbon sequestrating characteristics. Copyright © 2016 Elsevier Ltd. All rights reserved.

Details of Exact Low Prandtl Number Boundary-Layer Solutions for Forced and For Free Convection

NASA Technical Reports Server (NTRS)

Sparrow, E. M.; Gregg, J. L.

1959-01-01

A detailed report is given of exact (numerical) solutions of the laminar-boundary-layer equations for the Prandtl number range appropriate to liquid metals (0.003 to 0.03). Consideration is given to the following situations: (1) forced convection over a flat plate for the conditions of uniform wall temperature and uniform wall heat flux, and (2) free convection over an isothermal vertical plate. Tabulations of the new solutions are given in detail. Results are presented for the heat-transfer and shear-stress characteristics; temperature and velocity distributions are also shown. The heat-transfer results are correlated in terms of dimensionless parameters that vary only slightly over the entire liquid-metal range. Previous analytical and experimental work on low Prandtl number boundary layers is surveyed and compared with the new exact solutions.

Information flow in layered networks of non-monotonic units

NASA Astrophysics Data System (ADS)

Schittler Neves, Fabio; Martim Schubert, Benno; Erichsen, Rubem, Jr.

2015-07-01

Layered neural networks are feedforward structures that yield robust parallel and distributed pattern recognition. Even though much attention has been paid to pattern retrieval properties in such systems, many aspects of their dynamics are not yet well characterized or understood. In this work we study, at different temperatures, the memory activity and information flows through layered networks in which the elements are the simplest binary odd non-monotonic function. Our results show that, considering a standard Hebbian learning approach, the network information content has its maximum always at the monotonic limit, even though the maximum memory capacity can be found at non-monotonic values for small enough temperatures. Furthermore, we show that such systems exhibit rich macroscopic dynamics, including not only fixed point solutions of its iterative map, but also cyclic and chaotic attractors that also carry information.

Thermoelectric Energy Conversion Technology for High-Altitude Airships

NASA Technical Reports Server (NTRS)

Choi, Sang H.; Elliott, James R.; King, Glen C.; Park, Yeonjoon; Kim, Jae-Woo; Chu, Sang-Hyon

2011-01-01

The High Altitude Airship (HAA) has various application potential and mission scenarios that require onboard energy harvesting and power distribution systems. The power technology for HAA maneuverability and mission-oriented applications must come from its surroundings, e.g. solar power. The energy harvesting system considered for HAA is based on the advanced thermoelectric (ATE) materials being developed at NASA Langley Research Center. The materials selected for ATE are silicon germanium (SiGe) and bismuth telluride (Bi2Te3), in multiple layers. The layered structure of the advanced TE materials is specifically engineered to provide maximum efficiency for the corresponding range of operational temperatures. For three layers of the advanced TE materials that operate at high, medium, and low temperatures, correspondingly in a tandem mode, the cascaded efficiency is estimated to be greater than 60 percent.

Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction, volume 1. [theoretical analysis

NASA Technical Reports Server (NTRS)

Omori, S.

1973-01-01

The turbulent kinetic energy equation is coupled with boundary layer equations to solve the characteristics of compressible turbulent boundary layers with mass injection and combustion. The Reynolds stress is related to the turbulent kinetic energy using the Prandtl-Wieghardt formulation. When a lean mixture of hydrogen and nitrogen is injected through a porous plate into the subsonic turbulent boundary layer of air flow and ignited by external means, the turbulent kinetic energy increases twice as much as that of noncombusting flow with the same mass injection rate of nitrogen. The magnitudes of eddy viscosity between combusting and noncombusting flows with injection, however, are almost the same due to temperature effects, while the distributions are different. The velocity profiles are significantly affected by combustion; that is, combustion alters the velocity profile as if the mass injection rate is increased, reducing the skin-friction as a result of a smaller velocity gradient at the wall. If pure hydrogen as a transpiration coolant is injected into a rocket nozzle boundary layer flow of combustion products, the temperature drops significantly across the boundary layer due to the high heat capacity of hydrogen. At a certain distance from the wall, hydrogen reacts with the combustion products, liberating an extensive amount of heat. The resulting large increase in temperature reduces the eddy viscosity in this region.

Analysis of light propagation in quasiregular and hybrid Rudin-Shapiro one-dimensional photonic crystals with superconducting layers

NASA Astrophysics Data System (ADS)

Gómez-Urrea, H. A.; Escorcia-García, J.; Duque, C. A.; Mora-Ramos, M. E.

2017-11-01

The transmittance spectrum of a one-dimensional hybrid photonic crystal built from the suitable arrangement of periodic and quasiregular Rudin-Shapiro heterolayers that include superconducting slabs is investigated. The four-layer Rudin-Shapiro structure is designed with three lossless dielectric layers and a low-temperature superconductor one. The dielectric function of the superconducting layer is modeled by the two-fluid Gorter-Casimir theory, and the transmittance is calculated with the use of the transfer matrix method. The obtained results reveal the presence of a cut-off frequency fc - a forbidden frequency band for propagation - that can be manipulated by changing the width of the superconducting layer, the temperature and the order of the Rudin-Shapiro sequence. In addition, the spatial distribution of the electric field amplitude for the propagating TM modes is also discussed. It is found that the maximum of localized electric field relative intensity - which reaches a value of several tens - corresponds to the frequency values above to the cut-off frequency, at which, the effective dielectric function of the hybrid unit cell becomes zero. The proposed structure could be another possible system for optical device design for temperature-dependent optical devices such as stop-band filters, or as bolometers.

Laser pulse heating of steel mixing with WC particles in a irradiated region

NASA Astrophysics Data System (ADS)

Shuja, S. Z.; Yilbas, B. S.; Ali, H.; Karatas, C.

2016-12-01

Laser pulse heating of steel mixing with tungsten carbide (WC) particles is carried out. Temperature field in the irradiated region is simulated in line with the experimental conditions. In the analysis, a laser pulse parameter is introduced, which defines the laser pulse intensity distribution at the irradiated surface. The influence of the laser parameter on the melt pool size and the maximum temperature increase in the irradiated region is examined. Surface temperature predictions are compared with the experimental data. In addition, the distribution of WC particles and their re-locations in the treated layer, due to combination of the natural convection and Marangoni currents, are predicted. The findings are compared to the experimental data. It is found that surface temperature predictions agree well with the experimental data. The dislocated WC particles form a streamlining in the near region of the melt pool wall, which agree with the experimental findings. The Gaussian distribution of the laser pulse intensity results in the maximum peak temperature and the maximum flow velocity inside the melt pool. In this case, the melt pool depth becomes the largest as compared to those corresponding to other laser pulse intensity distributions at the irradiated surface.

Fluid transition layer between rigid solute and liquid solvent: is there depletion or enrichment?

PubMed

Djikaev, Yuri S; Ruckenstein, Eli

2016-03-21

The fluid layer between solute and liquid solvent is studied by combining the density functional theory with the probabilistic hydrogen bond model. This combination allows one to obtain the equilibrium distribution of fluid molecules, taking into account the hydrogen bond contribution to the external potential whereto they are subjected near the solute. One can find the effective width of the fluid solvent-solute transition layer and fluid average density in that layer, and determine their dependence on temperature, solvent-solute affinity, vicinal hydrogen bond (hb) energy alteration ratio, and solute radius. Numerical calculations are performed for the solvation of a plate and spherical solutes of four different radii in two model solvents (associated liquid and non-associated one) in the temperature range from 293 K to 333 K for various solvent-solute affinities and hydrogen bond energy alteration ratios. The predictions of our model for the effective width and average density of the transition layer are consistent with experiments and simulations. The small-to-large crossover lengthscale for hydrophobic hydration is expected to be about 3-5 nm. Remarkably, characterizing the transition layer with the average density, one can observe that for small hydrophobes, the transition layer becomes enriched with rather than depleted of fluid when the solvent-solute affinity and hb-energy alteration ratio become large enough. The boundary values of solvent-solute affinity and hb-energy alteration ratio, needed for the "depletion-to-enrichment" crossover (in the smoothed density sense), are predicted to decrease with increasing temperature.

Phase transitions and kinetic properties of gold nanoparticles confined between two-layer graphene nanosheets

NASA Astrophysics Data System (ADS)

Wang, Gang; Wu, Nanhua; Chen, Jionghua; Wang, Jinjian; Shao, Jingling; Zhu, Xiaolei; Lu, Xiaohua; Guo, Lucun

2016-11-01

The thermodynamic and kinetic behaviors of gold nanoparticles confined between two-layer graphene nanosheets (two-layer-GNSs) are examined and investigated during heating and cooling processes via molecular dynamics (MD) simulation technique. An EAM potential is applied to represent the gold-gold interactions while a Lennard-Jones (L-J) potential is used to describe the gold-GNS interactions. The MD melting temperature of 1345 K for bulk gold is close to the experimental value (1337 K), confirming that the EAM potential used to describe gold-gold interactions is reliable. On the other hand, the melting temperatures of gold clusters supported on graphite bilayer are corrected to the corresponding experimental values by adjusting the εAu-C value. Therefore, the subsequent results from current work are reliable. The gold nanoparticles confined within two-layer GNSs exhibit face center cubic structures, which is similar to those of free gold clusters and bulk gold. The melting points, heats of fusion, and heat capacities of the confined gold nanoparticles are predicted based on the plots of total energies against temperature. The density distribution perpendicular to GNS suggests that the freezing of confined gold nanoparticles starts from outermost layers. The confined gold clusters exhibit layering phenomenon even in liquid state. The transition of order-disorder in each layer is an essential characteristic in structure for the freezing phase transition of the confined gold clusters. Additionally, some vital kinetic data are obtained in terms of classical nucleation theory.

Mapping Surface Temperatures on a Debris-Covered Glacier with an Unmanned Aerial Vehicle

NASA Astrophysics Data System (ADS)

Kraaijenbrink, Philip D. A.; Shea, Joseph M.; Litt, Maxime; Steiner, Jakob F.; Treichler, Désirée; Koch, Inka; Immerzeel, Walter W.

2018-05-01

A mantel of debris cover often accumulates across the surface of glaciers in active mountain ranges with exceptionally steep terrain, such as the Andes, Himalaya and New Zealand Alps. Such a supraglacial debris layer has a major influence on a glacier's surface energy budget, enhancing radiation absorption and melt when the layer is thin, but insulating the ice when thicker than a few cm. Information on spatially distributed debris surface temperature has the potential to provide insight into the properties of the debris, its effects on the ice below and its influence on the near-surface boundary layer. Here, we deploy an unmanned aerial vehicle (UAV) equipped with a thermal infrared sensor on three separate missions over one day to map changing surface temperatures across the debris-covered Lirung Glacier in the Central Himalaya. We present a methodology to georeference and process the acquired thermal imagery, and correct for emissivity and sensor bias. Derived UAV surface temperatures are compared with distributed simultaneous in situ temperature measurements as well as with Landsat 8 thermal satellite imagery. Results show that the UAV-derived surface temperatures vary greatly both spatially and temporally, with -1.4±1.8, 11.0 ±5.2 and 15.3±4.7 °C for the three flights (mean±sd), respectively. The range in surface temperatures over the glacier during the morning is very large with almost 50 °C. Ground-based measurements are generally in agreement with the UAV imagery, but considerable deviations are present that are likely due to differences in measurement technique and approach, and validation is difficult as a result. The difference in spatial and temporal variability captured by the UAV as compared with much coarser satellite imagery is striking and it shows that satellite derived temperature maps should be interpreted with care. We conclude that UAVs provide a suitable means to acquire surface temperature maps of debris-covered glacier surfaces at high spatial and temporal resolution, but that there are caveats with regard to absolute temperature measurement.

Sensitivity analysis of bi-layered ceramic dental restorations.

PubMed

Zhang, Zhongpu; Zhou, Shiwei; Li, Qing; Li, Wei; Swain, Michael V

2012-02-01

The reliability and longevity of ceramic prostheses have become a major concern. The existing studies have focused on some critical issues from clinical perspectives, but more researches are needed to address fundamental sciences and fabrication issues to ensure the longevity and durability of ceramic prostheses. The aim of this paper was to explore how "sensitive" the thermal and mechanical responses, in terms of changes in temperature and thermal residual stress of the bi-layered ceramic systems and crown models will be with respect to the perturbation of the design variables chosen (e.g. layer thickness and heat transfer coefficient) in a quantitative way. In this study, three bi-layered ceramic models with different geometries are considered: (i) a simple bi-layered plate, (ii) a simple bi-layer triangle, and (iii) an axisymmetric bi-layered crown. The layer thickness and convective heat transfer coefficient (or cooling rate) seem to be more sensitive for the porcelain fused on zirconia substrate models. The resultant sensitivities indicate a critical importance of the heat transfer coefficient and thickness ratio of core to veneer on the temperature distributions and residual stresses in each model. The findings provide a quantitative basis for assessing the effects of fabrication uncertainties and optimizing the design of ceramic prostheses. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Studying the effects of the heat stress on the various layers of human skin using damage function

NASA Astrophysics Data System (ADS)

Aijaz, Mir; Khanday, M. A.

2016-03-01

This paper develops a model to identify the effects of thermal stress on temperature distribution and damage in human dermal regions. The design and selection of the model takes into account many factors effecting the temperature distribution of skin, e.g., thermal conductance, perfusion, metabolic heat generation and thermal protective capabilities of the skin. The transient temperature distribution within the region is simulated using a two-dimensional finite element model of the Pennes’ bioheat equation. The relationship between temperature and time is integrated to view the damage caused to human skin by using Henriques’ model Henriques, F. C., Arch. Pathol. 43 (1947) 489-502]. The Henriques’ damage model is found to be more desirable for use in predicting the threshold of thermal damage. This work can be helpful in both emergency medicines as well as to plastic surgeon in deciding upon a course of action for the treatment of different burn injuries.

Disturbance Impacts on Thermal Hot Spots and Hot Moments at the Peatland-Atmosphere Interface

NASA Astrophysics Data System (ADS)

Leonard, R. M.; Kettridge, N.; Devito, K. J.; Petrone, R. M.; Mendoza, C. A.; Waddington, J. M.; Krause, S.

2018-01-01

Soil-surface temperature acts as a master variable driving nonlinear terrestrial ecohydrological, biogeochemical, and micrometeorological processes, inducing short-lived or spatially isolated extremes across heterogeneous landscape surfaces. However, subcanopy soil-surface temperatures have been, to date, characterized through isolated, spatially discrete measurements. Using spatially complex forested northern peatlands as an exemplar ecosystem, we explore the high-resolution spatiotemporal thermal behavior of this critical interface and its response to disturbances by using Fiber-Optic Distributed Temperature Sensing. Soil-surface thermal patterning was identified from 1.9 million temperature measurements under undisturbed, trees removed and vascular subcanopy removed conditions. Removing layers of the structurally diverse vegetation canopy not only increased mean temperatures but it shifted the spatial and temporal distribution, range, and longevity of thermal hot spots and hot moments. We argue that linking hot spots and/or hot moments with spatially variable ecosystem processes and feedbacks is key for predicting ecosystem function and resilience.

Electrical conductivity of rocks at high pressures and temperatures

NASA Technical Reports Server (NTRS)

Parkhomenko, E. I.; Bondarenko, A. T.

1986-01-01

The results of studies of the electrical conductivity in the most widely distributed types of igneous rocks, at temperatures of up to 1200 C, at atmospheric pressure, and also at temperatures of up to 700 C and at pressures of up to 20,000 kg/sq cm are described. The figures of electrical conductivity, of activaation energy and of the preexponential coefficient are presented and the dependence of these parameters on the petrochemical parameters of the rocks are reviewed. The possible electrical conductivities for the depository, granite and basalt layers of the Earth's crust and of the upper mantle are presented, as well as the electrical conductivity distribution to the depth of 200 to 240 km for different geological structures.

Meteorological Drivers of Cold Temperatures in the Western Pacific TTL

NASA Technical Reports Server (NTRS)

Pfister, Leonhard; Ueyama, Rei; Jensen, Eric J.

2017-01-01

During the recent October 2016 aircraft sampling mission of the Tropical Tropopause Layer (POSIDON -- Pacific Oxidants, Sulfur, Ice, Dehydration, and cONvection), Western Pacific October TTL temperatures were anomalously cold due to a combination of La Nina conditions and a very stationary convective pattern. POSIDON also had more October Tropical Cyclones than typical, and tropical cyclones have substantial negative TTL temperatures associated with them. This paper investigates how meteorology in the troposphere drives TTL temperatures, and how these temperatures, coupled with the circulation, produce TTL clouds. We will also compare October TTL cloud distributions in different years, examining the relationship of clouds to October temperature anomalies.

Collisionless slow shocks in magnetotail reconnection

NASA Astrophysics Data System (ADS)

Cremer, Michael; Scholer, Manfred

The kinetic structure of collisionless slow shocks in the magnetotail is studied by solving the Riemann problem of the collapse of a current sheet with a normal magnetic field component using 2-D hybrid simulations. The collapse results in a current layer with a hot isotropic distribution and backstreaming ions in a boundary layer. The lobe plasma outside and within the boundary layer exhibits a large perpendicular to parallel temperature anisotropy. Waves in both regions propagate parallel to the magnetic field. In a second experiment a spatially limited high density beam is injected into a low beta background plasma and the subsequent wave excitation is studied. A model for slow shocks bounding the reconnection layer in the magnetotail is proposed where backstreaming ions first excite obliquely propagating waves by the electromagnetic ion/ion cyclotron instability, which lead to perpendicular heating. The T⊥/T∥ temperature anisotropy subsequently excites parallel propagating Alfvén ion cyclotron waves, which are convected into the slow shock and are refracted in the downstream region.

Origin of condensation nuclei in the springtime polar stratosphere

NASA Technical Reports Server (NTRS)

Zhao, Jingxia; Toon, Owen B.; Turco, Richard P.

1995-01-01

An enhanced sulfate aerosol layer has been observed near 25 km accompanying springtime ozone depletion in the Antarctic stratosphere. We use a one-dimensional aerosol model that includes photochemistry, particle nucleation, condensational growth, coagulation, and sedimentation to study the origin of the layer. Annual cycles of sunlight, temperature, and ozone are incorporated into the model. Our results indicate that binary homogeneous nucleation leads to the formation of very small droplets of sulfuric acid and water under conditions of low temperature and production of H2SO4 following polar sunrise. Photodissociation of carbonyl sulfide (OCS) alone, however, cannot provide sufficient SO2 to create the observed condensation nuclei (CN) layer. When subsidence of SO2 from very high altitudes in the polar night vortex is incorporated into the model, the CN layer is reasonably reproduced. The model predictions, based on the subsidence in polar vortex, agree with in situ measurements of particle concentration, vertical distribution, and persistence during polar spring.

Origin of Condensation Nuclei in the Springtime Polar Stratosphere

NASA Technical Reports Server (NTRS)

Zhao, Jingxia; Toon, Owen B.; Turco, Richard P.

1995-01-01

An enhanced sulfate aerosol layer has been observed near 25 km accompanying springtime ozone depletion in the Antarctic stratosphere. We use a one-dimensional aerosol model that includes photochemistry, particle nucleation, condensational growth, coagulation, and sedimentation to study the origin of the layer. Annual cycles of sunlight, temperature, and ozone are incorporated into the model. Our results indicate that binary homogeneous nucleation leads to the formation of very small droplets of sulfuric acid and water under conditions of low temperature and production of H2SO4 following polar sunrise. Photodissociation of carbonyl sulfide (OCS) alone, however, cannot provide sufficient SO2 to create the observed condensation nuclei (CN) layer. When subsidence of SO2 from very high altitudes in the polar night vortex is incorporated into the model, the CN layer is reasonably reproduced. The model predictions, based on the subsidence in polar vortex, agree with in situ measurements of particle concentration, vertical distribution, and persistence during polar spring.

Improving Representations of Near-Surface Permafrost and Soil Temperature Profiles in the Regional Arctic System Model (RASM)

NASA Astrophysics Data System (ADS)

Gergel, D. R.; Hamman, J.; Nijssen, B.

2017-12-01

Permafrost and seasonally frozen soils are a key characteristic of the terrestrial Arctic, and the fate of near-surface permafrost as a result of climate change is projected to have strong impacts on terrestrial biogeochemistry. The active layer thickness (ALT) is the layer of soil that freezes and thaws annually, and shifts in the depth of the ALT are projected to occur over large areas of the Arctic that are characterized by discontinuous permafrost. Faithful representation of permafrost in land models in climate models is a product of both soil dynamics and the coupling of air and soil temperatures. A common problem is a large bias in simulated ALT due to a model depth that is too shallow. Similarly, soil temperatures often show systematic biases, which lead to biases in air temperature due to poorly modeled air-soil temperature feedbacks in a coupled environment. In this study, we use the Regional Arctic System Model (RASM), a fully-coupled regional earth system model that is run at a 50-km land/atmosphere resolution over a pan-Arctic domain and uses the Variable Infiltration Capacity (VIC) model as its land model. To understand what modeling decisions are necessary to accurately represent near-surface permafrost and soil temperature profiles, we perform a large number of RASM simulations with prescribed atmospheric forcings (e.g. VIC in standalone mode in RASM) while varying the model soil depth, thickness of soil moisture layers, number of soil layers and the distribution of soil nodes. We compare modeled soil temperatures and ALT to observations from the Circumpolar Active Layer Monitoring (CALM) network. CALM observations include annual ALT observations as well as daily soil temperature measurements at three soil depths for three sites in Alaska. In the future, we will use our results to inform our modeling of permafrost dynamics in fully-coupled RASM simulations.

An influence of solar activity on latitudinal distribution of atmospheric ozone and temperature in 2-D radiative-photochemical model

NASA Technical Reports Server (NTRS)

Dyominov, I. G.

1989-01-01

On the basis of the 2-D radiative-photochemical model of the ozone layer at heights 0 to 60 km in the Northern Hemisphere there are revealed and analyzed in detail the characteristic features of the season-altitude-latitude variations of ozone and temperature due to changes of the solar flux during the 11 year cycle, electron and proton precipitations.

Detectability of Delaminations in Solid Rocket Motors with Embedded Stress Sensors

DTIC Science & Technology

2011-10-14

composite grain of hydroxyl-terminated polybutadiene/ammonium perchlorate (HTPB/AP). The insulation layer is ethylene propylene diene monomer ( EPDM ...The temperature-dependent mechanical properties of HTPB/AP and EPDM were obtained from in-house testing at AFRL/RZSM (Edwards AFB). The motor case is...temperature (DBST) sensors and Greg Yandek of AFRL/RZSM for the data collection of EPDM insulation material. Distribution A: Approved for public

Heating requirements and nonadiabatic surface effects for a model in the NTF cryogenic wind tunnel

NASA Technical Reports Server (NTRS)

Macha, J. M.; Landrum, D. B.; Pare, L. A., III; Johnson, C. B.

1988-01-01

A theoretical study has been made of the severity of nonadiabatic surface conditions arising from internal heat sources within a model in a cryogenic wind tunnel. Local surface heating is recognized as having an effect on the development of the boundary layer, which can introduce changes in the flow about the model and affect the wind tunnel data. The geometry was based on the NTF Pathfinder I wind tunnel model. A finite element heat transfer computer code was developed and used to compute the steady state temperature distribution within the body of the model, from which the surface temperature distribution was extracted. Particular three dimensional characteristics of the model were represented with various axisymmetric approximations of the geometry. This analysis identified regions on the surface of the model susceptible to surface heating and the magnitude of the respective surface temperatures. It was found that severe surface heating may occur in particular instances, but could be alleviated with adequate insulating material. The heat flux through the surface of the model was integrated to determine the net heat required to maintain the instrumentation cavity at the prescribed temperature. The influence of the nonadiabatic condition on boundary layer properties and on the validity of the wind tunnel simulation was also investigated.

Analysis of Turbulent Flow and Heat Transfer on a Flat Plate at High Mach Numbers with Variable Fluid Properties

NASA Technical Reports Server (NTRS)

Deissler, R. G.; Loeffler, A. L., Jr.

1959-01-01

A previous analysis of turbulent heat transfer and flow with variable fluid properties in smooth passages is extended to flow over a flat plate at high Mach numbers, and the results are compared with experimental data. Velocity and temperature distributions are calculated for a boundary layer with appreciative effects of frictional heating and external heat transfer. Viscosity and thermal conductivity are assumed to vary as a power or the temperature, while Prandtl number and specific heat are taken as constant. Skin-friction and heat-transfer coefficients are calculated and compared with the incompressible values. The rate of boundary-layer growth is obtained for various Mach numbers.

Effect of Cattaneo-Christov heat flux on Jeffrey fluid flow with variable thermal conductivity

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Javed, Mehwish; Imtiaz, Maria; Alsaedi, Ahmed

2018-03-01

This paper presents the study of Jeffrey fluid flow by a rotating disk with variable thickness. Energy equation is constructed by using Cattaneo-Christov heat flux model with variable thermal conductivity. A system of equations governing the model is obtained by applying boundary layer approximation. Resulting nonlinear partial differential system is transformed to ordinary differential system. Homotopy concept leads to the convergent solutions development. Graphical analysis for velocities and temperature is made to examine the influence of different involved parameters. Thermal relaxation time parameter signifies that temperature for Fourier's heat law is more than Cattaneo-Christov heat flux. A constitutional analysis is made for skin friction coefficient and heat transfer rate. Effects of Prandtl number on temperature distribution and heat transfer rate are scrutinized. It is observed that larger Reynolds number gives illustrious temperature distribution.

Short-term thermal stratification and partial overturning events in a warm polymictic reservoir: effects on distribution of phytoplankton community.

PubMed

Santos, R M; Saggio, A A; Silva, T L R; Negreiros, N F; Rocha, O

2015-01-01

In lentic freshwater ecosystems, patterns of thermal stratification play a considerable part in determining the population dynamics of phytoplankton. In this study we investigated how these thermal patterns and the associated hydrodynamic processes affect the vertical distribution of phytoplankton during two consecutive diel cycles in a warm polymictic urban reservoir in the metropolitan region of São Paulo, Brazil. Water samples were taken and physical, chemical and biological data collected at half-meter intervals of depth along a water column at a fixed site, every 3 hours throughout the 48-hour period. Two events of stratification, followed by deepening of the thermocline occurred during the study period and led to changes in the vertical distribution of phytoplankton populations. Aphanocapsa delicatissima Nägeli was the single dominant species throughout the 48-hour period. In the second diel cycle, the density gradient induced by temperature differences avoided the sedimentation of Mougeotia sp. C. Agardh to the deepest layers. On the other hand, Pseudanabaena galeata Böcher remained in the 4.0-5.5 m deep layer. The thermal structure of the water was directly affected by two meteorological factors: air temperature and wind speed. Changes in the cell density and vertical distribution of the phytoplankton were controlled by the thermal and hydrodynamic events.

Transition Experiments on Blunt Bodies with Isolated Roughness Elements in Hypersonic Free Flight

NASA Technical Reports Server (NTRS)

Reda, Daniel C.; Wilder, Michael C.; Prabhu, Dinesh K.

2010-01-01

Smooth titanium hemispheres with isolated three-dimensional (3D) surface roughness elements were flown in the NASA Ames hypersonic ballistic range through quiescent CO2 and air environments. Global surface intensity (temperature) distributions were optically measured and thermal wakes behind individual roughness elements were analyzed to define tripping effectiveness. Real-gas Navier-Stokes calculations of model flowfields, including laminar boundary layer development in these flowfields, were conducted predict key dimensionless parameters used to correlate transition on blunt bodies in hypersonic flow. For isolated roughness elements totally immersed within the laminar boundary layer, critical roughness Reynolds numbers for flights in air were found to be higher than those measured for flights in CO2, i.e., it was easier to trip the CO2 boundary layer to turbulence. Tripping effectiveness was found to be dependent on trip location within the subsonic region of the blunt body flowfield, with effective tripping being most difficult to achieve for elements positioned closest to the stagnation point. Direct comparisons of critical roughness Reynolds numbers for 3D isolated versus 3D distributed roughness elements for flights in air showed that distributed roughness patterns were significantly more effective at tripping the blunt body laminar boundary layer to turbulence.

Fabrication of fuel cell electrodes and other catalytic structures

DOEpatents

Smith, J.L.

1987-02-11

A porous layer of catalyst material suitable for use as an electrode in a molten carbonate fuel cell includes elongated pores substantially extending across the layer thickness. The catalyst layer is prepared by depositing particulate catalyst material into polymeric flocking on a substrate surface by a procedure such as tape casting. The loaded substrate is heated in a series of steps with rising temperatures to set the tape, thermally decompose the substrate with flocking and sinter bond the catalyst particles into a porous catalytic layer with elongated pores across its thickness. Employed as an electrode, the elongated pores provide distribution of reactant gas into contact with catalyst particles wetted by molten electrolyte. 1 fig.

Fabrication of catalytic electrodes for molten carbonate fuel cells

DOEpatents

Smith, James L.

1988-01-01

A porous layer of catalyst material suitable for use as an electrode in a molten carbonate fuel cell includes elongated pores substantially extending across the layer thickness. The catalyst layer is prepared by depositing particulate catalyst material into polymeric flocking on a substrate surface by a procedure such as tape casting. The loaded substrate is heated in a series of steps with rising temperatures to set the tape, thermally decompose the substrate with flocking and sinter bond the catalyst particles into a porous catalytic layer with elongated pores across its thickness. Employed as an electrode, the elongated pores provide distribution of reactant gas into contact with catalyst particles wetted by molten electrolyte.

Comparison of Summer and Winter California Central Valley Aerosol Distributions from Lidar and MODIS Measurements

NASA Technical Reports Server (NTRS)

Lewis, Jasper; DeYoung, Russell; Ferrare, Richard; Chu, D. Allen

2010-01-01

Aerosol distributions from two aircraft lidar campaigns conducted in the California Central Valley are compared in order to identify seasonal variations. Aircraft lidar flights were conducted in June 2003 and February 2007. While the ground PM(sub 2.5) concentration is highest in the winter, the aerosol optical depth measured from MODIS is highest in the summer. A seasonal comparison shows that PM(sub 2.5) in the winter can exceed summer PM(sub 2.5) by 55%, while summer AOD exceeds winter AOD by 43%. Higher temperatures and wildfires in the summer produce elevated aerosol layers that are detected by satellite measurements, but not surface particulate matter monitors. Temperature inversions, especially during the winter, contribute to higher PM(sub 2.5) measurements at the surface. Measurements of the boundary layer height from lidar instruments provide valuable information need to understand the relationship between satellite measurements of optical depth and in-situ measurements of PM(sub 2.5).

Active and passive controls of Jeffrey nanofluid flow over a nonlinear stretching surface

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Aziz, Arsalan; Muhammad, Taseer; Alsaedi, Ahmed

This communication explores magnetohydrodynamic (MHD) boundary-layer flow of Jeffrey nanofluid over a nonlinear stretching surface with active and passive controls of nanoparticles. A nonlinear stretching surface generates the flow. Effects of thermophoresis and Brownian diffusion are considered. Jeffrey fluid is electrically conducted subject to non-uniform magnetic field. Low magnetic Reynolds number and boundary-layer approximations have been considered in mathematical modelling. The phenomena of impulsing the particles away from the surface in combination with non-zero mass flux condition is known as the condition of zero mass flux. Convergent series solutions for the nonlinear governing system are established through optimal homotopy analysis method (OHAM). Graphs have been sketched in order to analyze that how the temperature and concentration distributions are affected by distinct physical flow parameters. Skin friction coefficient and local Nusselt and Sherwood numbers are also computed and analyzed. Our findings show that the temperature and concentration distributions are increasing functions of Hartman number and thermophoresis parameter.

Variations in VLT/UVES-based OH rotational temperatures for time scales from hours to 15 years

NASA Astrophysics Data System (ADS)

Noll, Stefan; Kimeswenger, Stefan; Proxauf, Bastian; Kausch, Wolfgang; Unterguggenberger, Stefanie; Jones, Amy M.

2017-04-01

Hydroxyl (OH) emission is an important tracer of the climate, chemistry, and dynamics of the Earth's mesopause region. However, the relation of intensity variations in different OH lines is not well understood yet. This is critical for the most popular use of OH lines: the estimate of ambient temperatures based on transitions at low rotational levels of the same band. It is possible that the measured variability of the derived rotational temperature does not coincide with changes in the ambient temperature. Such differences can be caused by varying deviations from the local thermodynamic equilibrium (LTE) for the population distribution over the considered rotational levels. The non-LTE effects depend on the ratio of the thermalising collisions (mostly related to molecular oxygen) and competing radiative transitions or collisions without thermalisation of the rotational level distribution. Therefore, significant changes in the vertical structure of excited OH and its main quenchers can affect the temperature measurements. We have investigated the variability of OH rotational temperatures and the corresponding contributions of non-LTE effects for different OH bands and time scales up to 15 years based on data of the high-resolution echelle spectrograph UVES at the Very Large Telescope at Cerro Paranal in Chile. In order to link the measured rotational temperatures with the structure of the OH emission layer, we have also studied OH emission and kinetic temperature profiles from the multi-channel radiometer SABER on the TIMED satellite taken between 2002 and 2015. The results show that non-LTE contributions can significantly affect the OH rotational temperatures. Their variations can be especially strong during the night and for high upper vibrational levels of the transitions, where amplitudes of several Kelvins can be measured. They appear to be weak if long-term variations such as those caused by the solar cycle are investigated. These differences in the response correlate with changes in the effective height of the OH emission layer and the effective air density in the layer. The latter confirms the expected important role of molecular oxygen for the thermalisation of the OH rotational level populations.

Structural strength assessment of the reconstructed road structure in terms of the loading time and yield criterion

NASA Astrophysics Data System (ADS)

Mazurek, Grzegorz; Iwański, Marek

2018-05-01

This article reports the results of numerical simulations of the stress-strain states in the rebuilt road structure compared to the solutions contained in the Polish Catalogue, with the true characteristics of the layer materials taken into account. In the case analysed, a cold-recycled base layer with foamed bitumen as a recycling agent was used. The presented analysis is complementary to the mandatory in Poland procedure of mechanistic pavement design based on a linear elastic model. The temperature distribution in the road structure was analysed at the reference temperature of 40°C on the asphalt layer surface. The loading time was included in the computer simulations through the use of the classic generalized Maxwell model and thus the stiffness-time history of the layers had to be determined. For this purpose, the dynamic modulus E* tests of the loading time frequency from 0.1 Hz to 20 Hz were carried out, and the yield point was modelled using the Coulomb-Mohr failure criterion calculated on the basis of triaxial compression tests. The analytical solution to the problem was found with ABAQUS. The results demonstrate that the high temperature of asphalt layers and long loading time noticeably reduces the stiffness modulus in those layers. That reduction changes the principal stress levels, which significantly influences the shear stress both in the recycled base layer and in the subgrade soil. Should the yield point be exceeded rapidly in the recycled layer, the horizontal stresses in the asphalt layers will increase and adversely affect the durability of the reconstructed road pavement structure, especially in the zones of slow heavy vehicle traffic.

Evaluation of near-surface temperature, humidity, and equivalent temperature from regional climate models applied in type II downscaling

NASA Astrophysics Data System (ADS)

Pryor, S. C.; Schoof, J. T.

2016-04-01

Atmosphere-surface interactions are important components of local and regional climates due to their key roles in dictating the surface energy balance and partitioning of energy transfer between sensible and latent heat. The degree to which regional climate models (RCMs) represent these processes with veracity is incompletely characterized, as is their ability to capture the drivers of, and magnitude of, equivalent temperature (Te). This leads to uncertainty in the simulation of near-surface temperature and humidity regimes and the extreme heat events of relevance to human health, in both the contemporary and possible future climate states. Reanalysis-nested RCM simulations are evaluated to determine the degree to which they represent the probability distributions of temperature (T), dew point temperature (Td), specific humidity (q) and Te over the central U.S., the conditional probabilities of Td|T, and the coupling of T, q, and Te to soil moisture and meridional moisture advection within the boundary layer (adv(Te)). Output from all RCMs exhibits discrepancies relative to observationally derived time series of near-surface T, q, Td, and Te, and use of a single layer for soil moisture by one of the RCMs does not appear to substantially degrade the simulations of near-surface T and q relative to RCMs that employ a four-layer soil model. Output from MM5I exhibits highest fidelity for the majority of skill metrics applied herein, and importantly most realistically simulates both the coupling of T and Td, and the expected relationships of boundary layer adv(Te) and soil moisture with near-surface T and q.

Microstructure evolution of a ZrC coating layer in TRISO particles during high-temperature annealing

NASA Astrophysics Data System (ADS)

Kim, Daejong; Chun, Young Bum; Ko, Myeong Jin; Lee, Hyeon-Geun; Cho, Moon-Sung; Park, Ji Yeon; Kim, Weon-Ju

2016-10-01

The influence of high-temperature annealing on the microstructure of zirconium carbide (ZrC) was investigated in relation to its application as a coating layer of a nuclear fuel in a very high temperature gas cooled reactor. ZrC was deposited as a constituent coating layer of TRISO coated particles by a fluidized bed chemical vapor deposition method using a ZrCl4-CH4-Ar-H2 system. The grain growth of ZrC during high-temperature annealing was strongly influenced by the co-deposition of free carbon. Sub-stoichiometric ZrC coatings have experienced a significant grain growth during high-temperature annealing at 1800 °C and 1900 °C for 1 h. On the other hand, a dual phase of stoichiometric ZrC and free carbon experienced little grain growth. It was revealed that the free carbon of the as-deposited ZrC was primarily distributed within the ZrC grains but was redistributed to the grain boundaries after annealing. Consequently, carbon at the grain boundary retarded the grain growth of ZrC. Electron backscatter diffraction (EBSD) results showed that as-deposited ZrC had (001) a preferred orientation that kept its favored direction after significant grain growth during annealing. The hardness slightly decreased as the grain growth progressed.

Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy.

PubMed

Eberhardt, S H; Marone, F; Stampanoni, M; Büchi, F N; Schmidt, T J

2014-11-01

Synchrotron-based X-ray tomographic microscopy is investigated for imaging the local distribution and concentration of phosphoric acid in high-temperature polymer electrolyte fuel cells. Phosphoric acid fills the pores of the macro- and microporous fuel cell components. Its concentration in the fuel cell varies over a wide range (40-100 wt% H3PO4). This renders the quantification and concentration determination challenging. The problem is solved by using propagation-based phase contrast imaging and a referencing method. Fuel cell components with known acid concentrations were used to correlate greyscale values and acid concentrations. Thus calibration curves were established for the gas diffusion layer, catalyst layer and membrane in a non-operating fuel cell. The non-destructive imaging methodology was verified by comparing image-based values for acid content and concentration in the gas diffusion layer with those from chemical analysis.

Analysis of Meteorological Data Obtained During Flight in a Supercooled Stratiform Cloud of High Liquid-Water Content

NASA Technical Reports Server (NTRS)

Perkins, Porter J.; Kline, Dwight B.

1951-01-01

Flight icing-rate data obtained in a dense and. abnormally deep supercooled stratiform cloud system indicated the existence of liquid-water contents generally exceeding values in amount and extent previously reported over the midwestern sections of the United States. Additional information obtained during descent through a part of the cloud system indicated liquid-water contents that significantly exceeded theoretical values, especially near the middle of the cloud layer.. The growth of cloud droplets to sizes that resulted in sedimentation from the upper portions of the cloud is considered to be a possible cause of the high water contents near the center of the cloud layer. Flight measurements of the vertical temperature distribution in the cloud layer indicated a rate of change of temperature with altitude exceeding that of the moist adiabatic lapse rate. This excessive rate of change is considered to have contributed to the severity of the condition.

Ice Cloud Formation and Dehydration in the Tropical Tropopause Layer

NASA Technical Reports Server (NTRS)

Jensen, Eric; Pfister, Leonhard; Gore, Warren J. (Technical Monitor)

2002-01-01

Stratospheric water vapor is important not only for its greenhouse forcing, but also because it plays a significant role in stratospheric chemistry. several recent studies have focused on the potential for dehydration due to ice cloud formation in air rising slowly through the tropical tropopause layer. Holton and Gettelman showed that temperature variations associated with horizontal transport of air in the tropopause layer can drive ice cloud formation and dehydration, and Gettelman et al. recently examined the cloud formation and dehydration along kinematic trajectories using simple assumptions about the cloud properties. In this study, we use a Lagrangian, one-dimensional cloud model to further investigate cloud formation and dehydration as air is transported horizontally and vertically through the tropical tropopause layer. Time-height curtains of temperature are extracted from meteorological analyses. The model tracks the growth and sedimentation of individual cloud particles. The regional distribution of clouds simulated in the model is comparable to the subvisible cirrus distribution indicated by SAGE II. The simulated cloud properties depend strongly on the assumed ice supersaturation threshold for ice nucleation. with effective nuclei present (low supersaturation threshold), ice number densities are high (0.1--10 cm(circumflex)-3), and ice crystals do not grow large enough to fall very far, resulting in limited dehydration. With higher supersaturation thresholds, ice number densities are much lower (less than 0.01 cm(circumflex)-3), and ice crystals grow large enough to fall substantially; however, supersaturated air often crosses the tropopause without cloud formation. The clouds typically do not dehydrate the air along trajectories down to the temperature minimum saturation mixing ratio. Rather the water vapor mixing ratio crossing the tropopause along trajectories is typically 10-50% larger than the saturation mixing ratio.

Controlling effects of mesoscale eddies on thermohaline structure and in situ chlorophyll distribution in the western North Pacific

NASA Astrophysics Data System (ADS)

Gao, Wei; Wang, Zhenyan; Zhang, Kainan

2017-11-01

Based on the conductivity, temperature and depth (CTD) data collected at 93 hydrographic stations during a marine cruise and on contemporary satellite altimeter observations, a series of eddies have been observed passing over the stratified upper water of the Parece Vela Basin. The results from hydrographic measurements and in situ chlorophyll fluorescence measurements have revealed that these eddies exerted significant controlling effects on the thermohaline structure and chlorophyll distribution, especially on the prevalent subsurface chlorophyll maximum layer (SCML). Based on these observations and particulate beam attenuation coefficient (cp) data, the in situ phytoplankton bloom around the pycnocline can be largely attributable to the formation of a well-developed SCML in the studied system. The uplift of the cold subsurface water within the cyclone, shoaling the pycnocline to a shallower layer, resulted in a low-temperature anomaly and different salinity anomalies at different depths. This uplift in the cyclone further caused the SCML to appear at a shallower depth with a higher in situ chlorophyll concentration than that in the normal domain. Conversely, the sinking of the warm surface water to the subsurface layer within the anticyclone depressed the pycnocline to a deeper layer and generated a high-temperature anomaly and opposite salinity anomalies compared with the cyclone. The sinking of the pycnocline within the anticyclone considerably influenced the characteristics of the SCML, which had a deeper depth and a lower in situ chlorophyll concentration than that of the normal sea. This study contributes rare quasi-synchronous CTD observations capturing mesoscale eddies and provides valuable descriptions of the variations in the SCML under the influence of mesoscale eddies based on in situ optical measurements from the seldom-discussed western North Pacific.

Micromachined Active Magnetic Regenerator for Low-Temperature Magnetic Coolers

NASA Technical Reports Server (NTRS)

Chen, Weibo; Jaeger, Michael D.

2013-01-01

A design of an Active Magnetic Regenerative Refrigeration (AMRR) system has been developed for space applications. It uses an innovative 3He cryogenic circulator to provide continuous remote/distributed cooling at temperatures in the range of 2 K with a heat sink at about 15 K. A critical component technology for this cooling system is a highly efficient active magnetic regenerator, which is a regenerative heat exchanger with its matrix material made of magnetic refrigerant gadolinium gallium garnet (GGG). Creare Inc. is developing a microchannel GGG regenerator with an anisotropic structured bed for high system thermal efficiency. The regenerator core consists of a stack of thin, single-crystal GGG disks alternating with thin polymer insulating layers. The insulating layers help minimize the axial conduction heat leak, since GGG has a very high thermal conductivity in the regenerator s operating temperature range. The GGG disks contain micro channels with width near 100 micrometers, which enhance the heat transfer between the circulating flow and the refrigerant bed. The unique flow configuration of the GGG plates ensures a uniform flow distribution across the plates. The main fabrication challenges for the regenerator are the machining of high-aspect-ratio microchannels in fragile, single-crystal GGG disks and fabrication and assembly of the GGG insulation layers. Feasibility demonstrations to date include use of an ultrashort- pulse laser to machine microchannels without producing unacceptable microcracking or deposition of recast material, as shown in the figure, and attachment of a thin insulation layer to a GGG disk without obstructing the flow paths. At the time of this reporting, efforts were focused on improving the laser machining process to increase machining speed and further reduce microcracking.

Impact of textural anisotropy on syn-kinematic partial melting of natural gneisses: an experimental approach.

NASA Astrophysics Data System (ADS)

Ganzhorn, Anne-Céline; Trap, Pierre; Arbaret, Laurent; Champallier, Rémi; Fauconnier, Julien; Labrousse, Loic; Prouteau, Gaëlle

2015-04-01

Partial melting of continental crust is a strong weakening process controlling its rheological behavior and ductile flow of orogens. This strength weakening due to partial melting is commonly constrained experimentally on synthetic starting material with derived rheological law. Such analog starting materials are preferentially used because of their well-constrained composition to test the impact of melt fraction, melt viscosity and melt distribution upon rheology. In nature, incipient melting appears in particular locations where mineral and water contents are favorable, leading to stromatic migmatites with foliation-parallel leucosomes. In addition, leucosomes are commonly located in dilatants structural sites like boudin-necks, in pressure shadows, or in fractures within more competent layers of migmatites. The compositional layering is an important parameter controlling melt flow and rheological behavior of migmatite but has not been tackled experimentally for natural starting material. In this contribution we performed in-situ deformation experiments on natural rock samples in order to test the effect of initial gneissic layering on melt distribution, melt flow and rheological response. In-situ deformation experiments using a Paterson apparatus were performed on two partially melted natural gneissic rocks, named NOP1 & PX28. NOP1, sampled in the Western Gneiss Region (Norway), is biotite-muscovite bearing gneiss with a week foliation and no gneissic layering. PX28, sampled from the Sioule Valley series (French Massif Central), is a paragneiss with a very well pronounced layering with quartz-feldspar-rich and biotite-muscovite-rich layers. Experiments were conducted under pure shear condition at axial strain rate varying from 5*10-6 to 10-3 s-1. The main stress component was maintained perpendicular to the main plane of anisotropy. Confining pressure was 3 kbar and temperature ranges were 750°C and 850-900°C for NOP1 and PX28, respectively. For the 750°C experiments NOP1 was previously hydrated at room pressure and temperature. According to melt fraction, deformation of partially molten gneiss induced different strain patterns. For low melt fraction, at 750°C, deformation within the initially isotropic gneiss NOP1 is localized along large scales shear-zones oriented at about 60° from main stress component σ1. In these zones quartz grains are broken and micas are sheared. Melt is present as thin film (≥20 µm) at muscovite-quartz grain boundaries and intrudes quartz aggregates as injections parallel to σ1. For higher melt fraction, at 850°C, deformation is homogeneously distributed. In the layered gneiss PX28, deformation is partitioned between mica-rich and quartz-rich layers. For low melt fraction, at 850°C, numerous conjugate shear-bands crosscut mica-rich layers. Melt is present around muscovite grains and intrudes quartz grains in the favor of fractures. For high melt fractions, at 900°C, melt assisted creep within mica-rich layers is responsible for boudinage of the quartz-feldspar rich layers. Melt-induced veining assists the transport of melt toward inter-boudin zones. Finite strain pattern and melt distribution after deformation of PX28 attest for appearance of strong pressure gradients leading to efficient melt flow. The subsequent melt redistribution strongly enhance strain partitioning and strength weakening, as shown by differential stress vs. strain graphs. Our experiments have successfully reproduced microstructures commonly observed in migmatitic gneisses like boudinage of less fertile layers. Comparison between non-layered and layered gneisses attest for strong influence of compositional anisotropies inherited from the protolith upon melt distribution and migmatite strength.

Design and investigation of de Vries liquid crystals based on 5-phenyl-pyrimidine and (R,R)-2,3-epoxyhexoxy backbone

NASA Astrophysics Data System (ADS)

Sreenilayam, S. P.; Rodriguez-Lojo, D.; Panov, V. P.; Swaminathan, V.; Vij, J. K.; Panarin, Yu. P.; Gorecka, E.; Panov, A.; Stevenson, P. J.

2017-10-01

Calamitic liquid crystals based on 5-phenyl-pyrimidine derivatives have been designed, synthesized, and characterized. The 5-phenyl pyrimidine core was functionalized with a chiral (R,R)-2,3-epoxyhexoxy chain on one side and either siloxane or perfluoro terminated chains on the opposite side. The one involving a perfluorinated chain shows Sm A* phase over a wide temperature range of 82 °C, whereas the siloxane analog exhibits both Sm A* and Sm C* phases over a broad range of temperatures, and a weak first-order Sm A*-Sm C* transition is observed. For the siloxane analog, the reduction factor for the layer shrinkage R (relative to its thickness at the Sm A*-Sm C* transition temperature, TAC) is ˜0.373 , and layer shrinkage is 1.7% at a temperature of 13 °C below the TAC. This compound is considered to have "de Vries smectic" characteristics with the de Vries coefficient CdeVries of ˜0.86 on the scale of zero (maximum-layer shrinkage) to 1 (zero-layer shrinkage). A three-parameter mean-field model is introduced for the orientational distribution function (ODF) to reproduce the electro-optic properties. This model explains the experimental results and leads to the ODF, which exhibits a crossover from the sugar-loaf to diffuse-cone ODF some 3 °C above TAC.

Heat transfer in the turbulent boundary layer with a short strip of surface roughness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, R.P.; Chakroun, W.M.

1992-01-01

The effects of a short strip of surface roughness on heat transfer and fluid flow in the turbulent boundary layer are investigated experimentally. This is done by measuring Stanton number and skin friction distributions and mean velocity, turbulence intensity, and mean temperature profiles in a turbulent boundary layer where the first 0.7 m length is smooth, the next 0.2 m is roughened with 1.27 mm hemispheres spaced 2 base diameters apart and the final 1.5 m is smooth. These results are compared with previously published data from experiments wiht a rough leading portion and smooth final portion and from experimentsmore » on an all-smooth surface. The influence of the roughness is large in the neighborhood of the rough strip, but the Stanton number and skin friction distributions are seen to quickly recover smooth-wall behavior downstream of the rough strip. 19 refs.« less

Integrating remote sensing, field observations, and ground temperature modeling to help address permafrost-related societal challenges around native village of Telida, Interior Alaska

NASA Astrophysics Data System (ADS)

Panda, S. K.; Kholodov, A. L.; Romanovsky, V. E.; Hanson, T.

2017-12-01

The dramatic landscape changes caused by thawing permafrost are wreaking havoc in remote Arctic villages. These changes are directly affecting land use, subsistence access, and adding to the high cost of infrastructure maintenance in remote villages; in some instances, threatening the safety of people who practice subsistence in remote sites. The goal of this project is to study the status and distribution of near-surface permafrost surrounding the Telida village in the Upper Kuskokwim region, and ultimately forecast how permafrost distribution and temperature may evolve in the near-future to help the Telida community better prepare in addressing the engineering, environmental, and subsistence access issues that are emerging with warmer climate and degrading permafrost. We collected baseline data on permafrost distribution, ground temperature, and thaw depth around Telida village during two visits to the study site (August 2016 and 2017) and conducted snow survey in February 2017 in all major landcover types. We mapped landcover, soil, and near-surface permafrost distribution for a 30 square mile area surrounding the Telida village using SPOT pan-sharpened image products (pixel size: 2.5 m) and ground observations. We identified seven major landcover types surrounding the Telida village: Open spruce, Mixed forest, Closed spruce, Wetland, Tall shrub, Deciduous forest, and Low shrub. Open spruce is the most dominant landcover type occupying 33% of the study area. Near-surface permafrost underlies less than 53% of the study area; it is present under Open spruce (active layer thickness: 59±7 cm; permafrost surface temperature: -0.6 °C) and Low shrub landcover types (active layer thickness: 60 cm; permafrost surface temperature: -0.07 °C), sporadic under Closed spruce landcover type, and absent under other landcover types. The mean annual permafrost surface temperature ranges from 0 to -1 °C and coldest permafrost is found under Open spruce landcover type. Permafrost around Telida village is warm and at the verge of thawing. Our ground temperature modeling effort will provide critical knowledge on how permafrost status and distribution around Telida village may evolve in the near future which we hope will help the Telida community in addressing the emerging engineering, environmental, and land use challenges.

Cryogenic Multichannel Pressure Sensor With Electronic Scanning

NASA Technical Reports Server (NTRS)

Hopson, Purnell, Jr.; Chapman, John J.; Kruse, Nancy M. H.

1994-01-01

Array of pressure sensors operates reliably and repeatably over wide temperature range, extending from normal boiling point of water down to boiling point of nitrogen. Sensors accurate and repeat to within 0.1 percent. Operate for 12 months without need for recalibration. Array scanned electronically, sensor readings multiplexed and sent to desktop computer for processing and storage. Used to measure distributions of pressure in research on boundary layers at high Reynolds numbers, achieved by low temperatures.

Feasibility of leakage detection in lake pressure pipes using the Distributed Temperature Sensing Technology

NASA Astrophysics Data System (ADS)

Apperl, Benjamin; Pressl, Alexander; Schulz, Karsten

2016-04-01

This contribution describes a feasibility study carried out in the laboratory for the detection of leakages in lake pressure pipes using high-resolution fiber-optic temperature measurements (DTS). The usage of the DTS technology provides spatiotemporal high-resolution temperature measurements along a fibre optic cable. An opto-electrical device serves both as a light emitter as well as a spectrometer for measuring the scattering of light. The fiber optic cable serves as linear sensor. Measurements can be taken at a spatial resolution of up to 25 cm with a temperature accuracy of higher than 0.1 °C. The first warmer days after the winter stagnation provoke a temperature rise of superficial layers of lakes with barely stable temperature stratification. The warmer layer in the epilimnion differs 4 °C to 5 °C compared to the cold layers in the meta- or hypolimnion before water circulation in spring starts. The warmer water from the surface layer can be rinsed on the entire length of the pipe. Water intrudes at leakages by generating a slightly negative pressure in the pipe. This provokes a local temperature change, in case that the penetrating water (seawater) differs in temperature from the water pumped through the pipe. These temperature changes should be detectable and localized with a DTS cable introduced in the pipe. A laboratory experiment was carried out to determine feasibility as well as limits and problems of this methodology. A 6 m long pipe, submerged in a water tank at constant temperature, was rinsed with water 5-10 °C warmer than the water in the tank. Temperature measurements were taken continuously along the pipe. A negative pressure of 0.1 bar provoked the intrusion of colder water from the tank into the pipe through the leakages, resulting in local temperature changes. Experiments where conducted with different temperature gradients, leakage sizes, number of leaks as well as with different positioning of the DTS cable inside the pipe. Results showed that already small leakages (4mm) can be detected. Problems have arisen from the inside positioning of DTS cable, measuring a reduced temperature difference in the transition layer at the inside wall of the pipe.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, Sazzad Hossain; Mian, Ahsan, E-mail: ahsan.mian@wright.edu; Srinivasan, Raghavan

In DMLS process objects are fabricated layer by layer from powdered material by melting induced by a controlled laser beam. Metallic powder melts and solidifies to form a single layer. Solidification map during layer formation is an important route to characterize micro-structure and grain morphology of sintered layer. Generally, solidification leads to columnar, equiaxed or mixture of these two types grain morphology depending on solidification rate and thermal gradient. Eutectic or dendritic structure can be formed in fully equiaxed zone. This dendritic growth has a large effect on material properties. Smaller dendrites generally increase ductility of the layer. Thus, materialsmore » can be designed by creating desired grain morphology in certain regions using DMLS process. To accomplish this, hardness, temperature distribution, thermal gradient and solidification cooling rate in processed layers will be studied under change of process variables by using finite element analysis, with specific application to Ti-6Al-4V.« less

Ocean haline skin layer and turbulent surface convections

NASA Astrophysics Data System (ADS)

Zhang, Y.; Zhang, X.

2012-04-01

The ocean haline skin layer is of great interest to oceanographic applications, while its attribute is still subject to considerable uncertainty due to observational difficulties. By introducing Batchelor micro-scale, a turbulent surface convection model is developed to determine the depths of various ocean skin layers with same model parameters. These parameters are derived from matching cool skin layer observations. Global distributions of salinity difference across ocean haline layers are then simulated, using surface forcing data mainly from OAFlux project and ISCCP. It is found that, even though both thickness of the haline layer and salinity increment across are greater than the early global simulations, the microwave remote sensing error caused by the haline microlayer effect is still smaller than that from other geophysical error sources. It is shown that forced convections due to sea surface wind stress are dominant over free convections driven by surface cooling in most regions of oceans. The free convection instability is largely controlled by cool skin effect for the thermal microlayer is much thicker and becomes unstable much earlier than the haline microlayer. The similarity of the global distributions of temperature difference and salinity difference across cool and haline skin layers is investigated by comparing their forcing fields of heat fluxes. The turbulent convection model is also found applicable to formulating gas transfer velocity at low wind.

Arctic boundary layer properties and its influence on cloud occurrence frequency, phase and structure in autumn season

NASA Astrophysics Data System (ADS)

Qiu, S.; Dong, X.; Xi, B.

2017-12-01

In this study, autumnal boundary layer characteristics and cloud properties have been investigated using data collected at the Atmospheric Radiation Measurement North Slope of Alaska (ARM NSA) site from January 2002 to December 2008. We found that both cloud and planetary boundary layer (PBL) properties can be well distinguished by surface wind directions. When the ARM NSA site is dominated by a northerly wind during the period September- November, the PBL is at near saturation for all three months; while the maximum RH layer varies from low and thin in September, to higher and thicker in October, and then it becomes close to surface again in November. Both the ceilometer and the MPL derived cloud base heights coincide well with the RH maximum layer in the PBL for all three autumnal months. The frequencies of occurrence of mixed phase clouds in September and October are around 60-80% under a northerly wind, which are about 1.5 times higher than those during a southerly wind. Under northerly wind, the PDFs of PBL temperature and specific humidity are narrow and unimodal, with a peak probability around 0.4-0.5. Under a southerly wind, on the other hand, the PBL is both warmer and wetter than northerly wind profiles, which result in lower RH values (10-15% lower) in September and October; and the PDFs of PBL temperature and specific humidity are more evenly distributed with larger distribution range and lower PDF peak values (<0.3). In September, colder and dryer PBL is more favorable for mixed phase cloud formation, cloud occurrence frequency decreases from 90% to 60% as PBL temperature and specific humidity increase. In October, the frequency of occurrence of mixed phase clouds also decreases from 90% to 50-60% as PBL temperature increases. While in November, it increases first and then decreases with increasing PBL temperature and specific humidity. The frequency of occurrence of mixed phase clouds is linearly correlated to PBL RH values: for all three months, it increases from 20-90% as PBL RH value increases from 50-100%, with R2 values of 0.85-0.95. Liquid-only cloud occurrence frequency has little relationship with PBL RH values, while it increases from 1% to 20% as PBL specific humidity increases from 0-5 g/kg, with R2 values of 0.6-0.85.

Optimization of the defects and the nonradiative lifetime of GaAs/AlGaAs double heterostructures

NASA Astrophysics Data System (ADS)

Cevher, Z.; Folkes, P. A.; Hier, H. S.; VanMil, B. L.; Connelly, B. C.; Beck, W. A.; Ren, Y. H.

2018-04-01

We used Raman scattering and time-resolved photoluminescence spectroscopy to investigate the molecular-beam-epitaxy (MBE) growth parameters that optimize the structural defects and therefore the internal radiative quantum efficiency of MBE-grown GaAs/AlGaAs double heterostructures (DH). The DH structures were grown at two different temperatures and three different As/Ga flux ratios to determine the conditions for an optimized structure with the longest nonradiative minority carrier lifetime. Raman scattering measurements show an improvement in the lattice disorder in the AlGaAs and GaAs layers as the As/Ga flux ratio is reduced from 40 to 15 and as the growth temperature is increased from 550 to 595 °C. The optimized structure is obtained with the As/Ga flux ratio equal to 15 and the substrate temperature 595 °C. This is consistent with the fact that the optimized structure has the longest minority carrier lifetime. Moreover, our Raman studies reveal that incorporation of a distributed Bragg reflector layer between the substrate and DH structures significantly reduces the defect density in the subsequent epitaxial layers.

Mars Science Laboratory Heatshield Aerothermodynamics: Design and Reconstruction

NASA Technical Reports Server (NTRS)

Edquist, Karl T.; Hollis, Brian R.; Johnston, Christopher O.; Bose, Deepak; White, Todd R.; Mahzari, Milad

2013-01-01

The Mars Science Laboratory heatshield was designed to withstand a fully turbulent heat pulse based on test results and computational analysis on a pre-flight design trajectory. Instrumentation on the flight heatshield measured in-depth temperatures in the thermal protection system. The data indicate that boundary layer transition occurred at 5 of 7 thermocouple locations prior to peak heating. Data oscillations at 3 pressure measurement locations may also indicate transition. This paper presents the heatshield temperature and pressure data, possible explanations for the timing of boundary layer transition, and a qualitative comparison of reconstructed and computational heating on the as-flown trajectory. Boundary layer Reynolds numbers that are typically used to predict transition are compared to observed transition at various heatshield locations. A uniform smooth-wall transition Reynolds number does not explain the timing of boundary layer transition observed during flight. A roughness-based Reynolds number supports the possibility of transition due to discrete or distributed roughness elements on the heatshield. However, the distributed roughness height would have needed to be larger than the pre-flight assumption. The instrumentation confirmed the predicted location of maximum turbulent heat flux near the leeside shoulder. The reconstructed heat flux at that location is bounded by smooth-wall turbulent calculations on the reconstructed trajectory, indicating that augmentation due to surface roughness probably did not occur. Turbulent heating on the downstream side of the heatshield nose exceeded smooth-wall computations, indicating that roughness may have augmented heating. The stagnation region also experienced heating that exceeded computational levels, but shock layer radiation does not fully explain the differences.

Understanding Coulomb Scattering Mechanism in Monolayer MoS2 Channel in the Presence of h-BN Buffer Layer.

PubMed

Joo, Min-Kyu; Moon, Byoung Hee; Ji, Hyunjin; Han, Gang Hee; Kim, Hyun; Lee, Gwanmu; Lim, Seong Chu; Suh, Dongseok; Lee, Young Hee

2017-02-08

As the thickness becomes thinner, the importance of Coulomb scattering in two-dimensional layered materials increases because of the close proximity between channel and interfacial layer and the reduced screening effects. The Coulomb scattering in the channel is usually obscured mainly by the Schottky barrier at the contact in the noise measurements. Here, we report low-temperature (T) noise measurements to understand the Coulomb scattering mechanism in the MoS 2 channel in the presence of h-BN buffer layer on the silicon dioxide (SiO 2 ) insulating layer. One essential measure in the noise analysis is the Coulomb scattering parameter (α SC ) which is different for channel materials and electron excess doping concentrations. This was extracted exclusively from a 4-probe method by eliminating the Schottky contact effect. We found that the presence of h-BN on SiO 2 provides the suppression of α SC twice, the reduction of interfacial traps density by 100 times, and the lowered Schottky barrier noise by 50 times compared to those on SiO 2 at T = 25 K. These improvements enable us to successfully identify the main noise source in the channel, which is the trapping-detrapping process at gate dielectrics rather than the charged impurities localized at the channel, as confirmed by fitting the noise features to the carrier number and correlated mobility fluctuation model. Further, the reduction in contact noise at low temperature in our system is attributed to inhomogeneous distributed Schottky barrier height distribution in the metal-MoS 2 contact region.

Neoclassical, semi-collisional tearing mode theory in an axisymmetric torus

NASA Astrophysics Data System (ADS)

Connor, J. W.; Hastie, R. J.; Helander, P.

2017-12-01

A set of layer equations for determining the stability of semi-collisional tearing modes in an axisymmetric torus, incorporating neoclassical physics, in the small ion Larmor radius limit, is provided. These can be used as an inner layer module for inclusion in numerical codes that asymptotically match the layer to toroidal calculations of the tearing mode stability index, \\prime $ . They are more complete than in earlier work and comprise equations for the perturbed electron density and temperature, the ion temperature, Ampère's law and the vorticity equation, amounting to a twelvth-order set of radial differential equations. While the toroidal geometry is kept quite general when treating the classical and Pfirsch-Schlüter transport, parallel bootstrap current and semi-collisional physics, it is assumed that the fraction of trapped particles is small for the banana regime contribution. This is to justify the use of a model collision term when acting on the localised (in velocity space) solutions that remain after the Spitzer solutions have been exploited to account for the bulk of the passing distributions. In this respect, unlike standard neoclassical transport theory, the calculation involves the second Spitzer solution connected with a parallel temperature gradient, because this stability problem involves parallel temperature gradients that cannot occur in equilibrium toroidal transport theory. Furthermore, a calculation of the linearised neoclassical radial transport of toroidal momentum for general geometry is required to complete the vorticity equation. The solutions of the resulting set of equations do not match properly to the ideal magnetohydrodynamic (MHD) equations at large distances from the layer, and a further, intermediate layer involving ion corrections to the electrical conductivity and ion parallel thermal transport is invoked to achieve this matching and allow one to correctly calculate the layer \\prime $ .

Microstructural and mechanical properties of Al2O3/ZrO2 nanomultilayer thin films prepared by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Balakrishnan, G.; Sastikumar, D.; Kuppusami, P.; Babu, R. Venkatesh; Song, Jung Il

2018-02-01

Single layer aluminium oxide (Al2O3), zirconium oxide (ZrO2) and Al2O3/ZrO2 nano multilayer films were deposited on Si (100) substrates at room temperature by pulsed laser deposition. The development of Al2O3/ZrO2 nanolayered structure is an important method used to stabilize the high temperature phase (tetragonal and cubic) of ZrO2 at room temperature. In the Al2O3/ZrO2 multilayer structure, the Al2O3 layer was kept constant at 5 nm, while the ZrO2 layer thickness varied from 5 to 20 nm (5/5, 5/10, 5/15 and 5/20 nm) with a total of 40 bilayers. The X-ray diffraction studies of single layer Al2O3 indicated the γ-Al2O3 of cubic structure, while the single layer ZrO2 indicated both monoclinic and tetragonal phases. The 5/5 and 5/10 nm multilayer films showed the nanocrystalline nature of ZrO2 with tetragonal phase. The high resolution transmission electron microscopy studies indicated the formation of well-defined Al2O3 and ZrO2 layers and that they are of uniform thickness. The atomic force microscopy studies revealed the uniform and dense distribution of nanocrystallites. The nanoindentation studies indicated the hardness of 20.8 ± 1.10 and 10 ± 0.60 GPa, for single layer Al2O3 and ZrO2, respectively, and the hardness of multilayer films varied with bilayer thickness.

Strain transfer analysis of optical fiber based sensors embedded in an asphalt pavement structure

NASA Astrophysics Data System (ADS)

Wang, Huaping; Xiang, Ping

2016-07-01

Asphalt pavement is vulnerable to random damage, such as cracking and rutting, which can be proactively identified by distributed optical fiber sensing technology. However, due to the material nature of optical fibers, a bare fiber is apt to be damaged during the construction process of pavements. Thus, a protective layer is needed for this application. Unfortunately, part of the strain of the host material is absorbed by the protective layer when transferring the strain to the sensing fiber. To account for the strain transfer error, in this paper a theoretical analysis of the strain transfer of a three-layered general model has been carried out by introducing Goodman’s hypothesis to describe the interfacial shear stress relationship. The model considers the viscoelastic behavior of the host material and protective layer. The effects of one crack in the host material and the sensing length on strain transfer relationship are been discussed. To validate the effectiveness of the strain transfer analysis, a flexible asphalt-mastic packaged distributed optical fiber sensor was designed and tested in a laboratory environment to monitor the distributed strain and appearance of cracks in an asphalt concrete beam at two different temperatures. The experimental results indicated that the developed strain transfer formula can significantly reduce the strain transfer error, and that the asphalt-mastic packaged optical fiber sensor can successfully monitor the distributed strain and identify local cracks.

Temperature Effects on the Magnetization and Magnetoimpedance in Ferromagnetic Glass-Covered microwires

NASA Astrophysics Data System (ADS)

Uddin, A.; Evstigneeva, S. A.; Dzhumazoda, A.; Salem, M. M.; Nematov, M. G.; Adam, A. M.; Panina, LV; Morchenko, A. T.

2017-11-01

The effect of temperature on static and dynamic magnetization in Co-based amorphous microwires was investigated with the aim of potential applications in miniature temperature sensors. The wires of two compositions with different magnetostriction and Curie temperature in glass-cover and after removing the glass layer demonstrated very different temperature behaviour of the magnetization loops and magnetoimpedance. The mechanisms of the temperature effects are related to the residual stress distribution due to fast solidification, the difference in thermal expansion coefficient of metal and glass and the proximity to the Curie temperature. The interplay of these factors may result in a very strong temperature dependence of magnetoimpedance in a moderate temperature range (room temperature -373K). Such elements may be incorporated in various composite materials for a local temperature monitoring.

Thermal properties of capacitively coupled electrodes in interstitial hyperthermia.

PubMed

van der Koijk, J F; Crezee, J; Lagendijk, J J

1998-01-01

The multi-electrode current source (MECS) interstitial hyperthermia system which is used for treatment of cancer, employs segmented electrodes inserted in plastic tubes implanted in the treatment volume. The mean power deposition of the individual electrodes is controlled by varying the duty cycle of the RF signal applied to the electrodes, using thermocouples inside the electrodes for thermometry. A non-zero loss angle results in self-heating of the catheter. The thermal influence of self-heating was investigated and an analysis of the measurement of temperatures inside the catheter during and after heating is presented. Analytical models and a high-resolution numerical model were used for the calculation of steady state and transient distributions, respectively. The model results are compared with experimental data obtained in a muscle equivalent phantom. Results indicate that there is no difference between temperature inside and outside the catheter when using lossless catheter materials (e.g. PE and PTFE). Self-heating in the catheter wall has an adverse effect on the uniformity of the stationary temperature distribution and the reliability of temperature measurement with internal thermometry. These problems remain within acceptable limits for mildly lossy materials; the difference between the temperature inside and outside is only 6% when using low-loss Nylon. Analysis of the thermal decay after power-off shows that low-loss materials allow more time to obtain an accurate estimate of the tissue temperature at the catheter wall during power-on. This effect is enhanced by the presence of minute air layers in the applicator. Distortion of temperature gradients along the catheter was also investigated. Key factors are the thermal conduction across the catheter wall, and especially the presence of minute layers of air between consecutive layers of the probe. The distortion extends less than two millimetres, which is acceptable. The simulation results are compatible with measurements in phantoms and show that, if the proper choice of materials is made, the MECS applicator answers our expectations and that the temperature measurement inside the catheter can be used for direct feedback treatment control.

Electron Paramagnetic Resonance Imaging of the Spatial Distribution of Free Radicals in PMR-15 Polyimide Resins

NASA Technical Reports Server (NTRS)

Ahn, Myong K.; Eaton, Sandra S.; Eaton, Gareth R.; Meador, Mary Ann B.

1997-01-01

Prior studies have shown that free radicals generated by heating polyimides above 300 C are stable at room temperature and are involved in thermo-oxidative degradation in the presence of oxygen gas. Electron paramagnetic resonance imaging (EPRI) is a technique to determine the spatial distribution of free radicals. X-band (9.5 GHz) EPR images of PMR-15 polyimide were obtained with a spatial resolution of approximately 0.18 mm along a 2-mm dimension of the sample. In a polyimide sample that was not thermocycled, the radical distribution was uniform along the 2-mm dimension of the sample. For a polyimide sample that was exposed to thermocycling in air for 300 1-h cycles at 335 C, one-dimensional EPRI showed a higher concentration of free radicals in the surface layers than in the bulk sample. A spectral-spatial two-dimensional image showed that the EPR lineshape of the surface layer remained the same as that of the bulk. These EPRI results suggest that the thermo-oxidative degradation of PMR-15 resin involves free radicals present in the oxygen-rich surface layer.

Electron Paramagnetic Resonance Imaging of the Spatial Distribution of Free Radicals in PMR-15 Polyimide Resins

NASA Technical Reports Server (NTRS)

Ahn, Myong K.; Eaton, Sandra S.; Eaton, Gareth R.; Meador, Mary Ann B.

1997-01-01

Prior studies have shown that free radicals generated by heating polyimides above 300 C are stable at room temperature and are involved in thermo-oxidative degradation in the presence of oxygen gas. Electron Paramagnetic Resonance Imaging (EPRI) is a technique to determine the spatial distribution of free radicals. X-band (9.5 GHz) EPR images of PMR-15 polyimide were obtained with a spatial resolution of about 0.18 mm along a 2 mm dimension of the sample. In a polyimide sample that was not thermocycled, the radical distribution was uniform along the 2 mm dimension of the sample. For a polyimide sample that was exposed to thermocycling in air for 300 one-hour cycles at 335 C, one-dimensional EPRI showed a higher concentration of free radicals in the surface layers than in the bulk sample. A spectral-spatial two-dimensional image showed that the EPR lineshape of the surface layer remained the same as that of the bulk. These EPRI results suggest that the thermo-oxidative degradation of PMR-15 resin involves free radicals present in the oxygen-rich surface layer.

Hot cracking susceptibility of fillers 52 and 82 in alloy 690 welding

NASA Astrophysics Data System (ADS)

Wu, Weite; Tsai, C. H.

1999-02-01

The hot cracking susceptibility of fillers 52 and 82 in a alloy 690 weldment is analyzed by the Varestraint test. Weld characteristics, microstructure, hardness distribution, and thermal analysis of the two filler metals are also examined. The weld metal of both fillers develops an extremely dense oxide layer. A stainless steel brush cannot remove the oxide layer, and a grinder may be needed between weld passes to assure a sound weld. Differential temperature analysis (DTA) shows that filler 82 has a lower melting point and a wider melting/solidification temperature differential (Δ T). These characteristics correlate with greater hot cracking susceptibility of filler 82 than 52 in Varestraint tests. The hot cracks are intergranular and are caused by elements segregating in grain boundies.

Characterization of ZrO2 buffer layers for sequentially evaporated Y-Ba-CuO on Si and Al2O3 substrates

NASA Technical Reports Server (NTRS)

Valco, George J.; Rohrer, Norman J.; Pouch, John J.; Warner, Joseph D.; Bhasin, Kul B.

1988-01-01

Thin film high temperature superconductors have the potential to change the microwave technology for space communications systems. For such applications it is desirable that the films be formed on substrates such as Al2O3 which have good microwave properties. The use of ZrO2 buffer layers between Y-Ba-Cu-O and the substrate has been investigated. These superconducting films have been formed by multilayer sequential electron beam evaporation of Cu, BaF2 and Y with subsequent annealing. The three layer sequence of Y/BaF2/Cu is repeated four times for a total of twelve layers. Such a multilayer film, approximately 1 micron thick, deposited directly on SrTiO3 and annealed at 900 C for 45 min produces a film with a superconducting onset of 93 K and critical temperature of 85 K. Auger electron spectroscopy in conjunction with argon ion sputtering was used to obtain the distribution of each element as a function of depth for an unannealed film, the annealed film on SrTiO3 and annealed films on ZrO2 buffer layers. The individual layers were apparent. After annealing, the bulk of the film on SrTiO3 is observed to be fairly uniform while films on the substrates with buffer layers are less uniform. The Y-Ba-Cu-O/ZrO2 interface is broad with a long Ba tail into the ZrO2, suggesting interaction between the film and the buffer layer. The underlying ZrO2/Si interface is sharper. The detailed Auger results are presented and compared with samples annealed at different temperatures and durations.

Tunable metamaterial dual-band terahertz absorber

NASA Astrophysics Data System (ADS)

Luo, C. Y.; Li, Z. Z.; Guo, Z. H.; Yue, J.; Luo, Q.; Yao, G.; Ji, J.; Rao, Y. K.; Li, R. K.; Li, D.; Wang, H. X.; Yao, J. Q.; Ling, F. R.

2015-11-01

We report a design of a temperature controlled tunable dual band terahertz absorber. The compact single unit cell consists of two nested closed square ring resonators and a layer metallic separated by a substrate strontium titanate (STO) dielectric layer. It is found that the absorber has two distinctive absorption peaks at frequencies 0.096 THz and 0.137 THz, whose peaks are attained 97% and 75%. Cooling the absorber from 400 K to 250 K causes about 25% and 27% shift compared to the resonance frequency of room temperature, when we cooling the temperature to 150 K, we could attained both the two tunabilities exceeding 53%. The frequency tunability is owing to the variation of the dielectric constant of the low-temperature co-fired ceramic (LTCC) substrate. The mechanism of the dual band absorber is attributed to the overlapping of dual resonance frequencies, and could be demonstrated by the distributions of the electric field. The method opens up avenues for designing tunable terahertz devices in detection, imaging, and stealth technology.

Understanding and Controlling the Aggregative Growth of Platinum Nanoparticles in Atomic Layer Deposition: An Avenue to Size Selection

PubMed Central

2017-01-01

We present an atomistic understanding of the evolution of the size distribution with temperature and number of cycles in atomic layer deposition (ALD) of Pt nanoparticles (NPs). Atomistic modeling of our experiments teaches us that the NPs grow mostly via NP diffusion and coalescence rather than through single-atom processes such as precursor chemisorption, atom attachment, and Ostwald ripening. In particular, our analysis shows that the NP aggregation takes place during the oxygen half-reaction and that the NP mobility exhibits a size- and temperature-dependent scaling. Finally, we show that contrary to what has been widely reported, in general, one cannot simply control the NP size by the number of cycles alone. Instead, while the amount of Pt deposited can be precisely controlled over a wide range of temperatures, ALD-like precision over the NP size requires low deposition temperatures (e.g., T < 100 °C) when growth is dominated by atom attachment. PMID:28178779

Aging and failure mode of electrochemical double layer capacitors during accelerated constant load tests

NASA Astrophysics Data System (ADS)

Kötz, R.; Ruch, P. W.; Cericola, D.

Electrochemical double layer capacitors of the BCAP0350 type (Maxwell Technologies) were tested under constant load conditions at different voltages and temperatures. The aging of the capacitors was monitored during the test in terms of capacitance, internal resistance and leakage current. Aging was significantly accelerated by elevated temperature or increased voltage. Only for extreme conditions at voltages of 3.5 V or temperatures above 70 °C the capacitors failed due to internal pressure build-up. No other failure events such as open circuit or short circuit were detected. Impedance measurements after the tests showed increased high frequency resistance, an increased distributed resistance and most likely an increase in contact resistance between electrode and current collector together with a loss of capacitance. Capacitors aged at elevated voltages (3.3 V) exhibited a tilting of the low frequency component, which implies an increase in the heterogeneity of the electrode surface. This feature was not observed upon aging at elevated temperatures (70 °C).

Conduit for high temperature transfer of molten semiconductor crystalline material

NASA Technical Reports Server (NTRS)

Fiegl, George (Inventor); Torbet, Walter (Inventor)

1983-01-01

A conduit for high temperature transfer of molten semiconductor crystalline material consists of a composite structure incorporating a quartz transfer tube as the innermost member, with an outer thermally insulating layer designed to serve the dual purposes of minimizing heat losses from the quartz tube and maintaining mechanical strength and rigidity of the conduit at the elevated temperatures encountered. The composite structure ensures that the molten semiconductor material only comes in contact with a material (quartz) with which it is compatible, while the outer layer structure reinforces the quartz tube, which becomes somewhat soft at molten semiconductor temperatures. To further aid in preventing cooling of the molten semiconductor, a distributed, electric resistance heater is in contact with the surface of the quartz tube over most of its length. The quartz tube has short end portions which extend through the surface of the semiconductor melt and which are lef bare of the thermal insulation. The heater is designed to provide an increased heat input per unit area in the region adjacent these end portions.

Preliminary assessment of soil moisture over vegetation

NASA Technical Reports Server (NTRS)

Carlson, T. N.

1986-01-01

Modeling of surface energy fluxes was combined with in-situ measurement of surface parameters, specifically the surface sensible heat flux and the substrate soil moisture. A vegetation component was incorporated in the atmospheric/substrate model and subsequently showed that fluxes over vegetation can be very much different than those over bare soil for a given surface-air temperature difference. The temperature signatures measured by a satellite or airborne radiometer should be interpreted in conjunction with surface measurements of modeled parameters. Paradoxically, analyses of the large-scale distribution of soil moisture availability shows that there is a very high correlation between antecedent precipitation and inferred surface moisture availability, even when no specific vegetation parameterization is used in the boundary layer model. Preparatory work was begun in streamlining the present boundary layer model, developing better algorithms for relating surface temperatures to substrate moisture, preparing for participation in the French HAPEX experiment, and analyzing aircraft microwave and radiometric surface temperature data for the 1983 French Beauce experiments.

Atmospheric tides on Venus. III - The planetary boundary layer

NASA Technical Reports Server (NTRS)

Dobrovolskis, A. R.

1983-01-01

Diurnal solar heating of Venus' surface produces variable temperatures, winds, and pressure gradients within a shallow layer at the bottom of the atmosphere. The corresponding asymmetric mass distribution experiences a tidal torque tending to maintain Venus' slow retrograde rotation. It is shown that including viscosity in the boundary layer does not materially affect the balance of torques. On the other hand, friction between the air and ground can reduce the predicted wind speeds from about 5 to about 1 m/sec in the lower atmosphere, more consistent with the observations from Venus landers and descent probes. Implications for aeolian activity on Venus' surface and for future missions are discussed.

Analyses of layer-thickness effects in bilayered dental ceramics subjected to thermal stresses and ring-on-ring tests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsueh, Chun-Hway; Thompson, G. A.; Jadaan, Osama M.

Objectives. The purpose of this study was to analyze the stress distribution through the thickness of bilayered dental ceramics subjected to both thermal stresses and ring-on-ring tests and to systematically examine how the individual layer thickness influences this stress distribution and the failure origin. Methods. Ring-on-ring tests were performed on In-Ceram Alumina/Vitadur Alpha porcelain bilayered disks with porcelain in the tensile side, and In-Ceram Alumina to porcelain layer thickness ratios of 1:2, 1:1, and 2:1 were used to characterize the failure origins as either surface or interface. Based on the thermomechanical properties and thickness of each layer, the cooling temperaturemore » from glass transition temperature, and the ring-on-ring loading configuration, the stress distribution through the thickness of the bilayer was calculated using closed-form solutions. Finite element analyses were also performed to verify the analytical results. Results. The calculated stress distributions showed that the location of maximum tension during testing shifted from the porcelain surface to the In-Ceram Alumina/porcelain interface when the relative layer thickness ratio changed from 1:2 to 1:1 and to 2:1. This trend is in agreement with the experimental observations of the failure origins. Significance. For bilayered dental ceramics subjected to ring-on-ring tests, the location of maximum tension can shift from the surface to the interface depending upon the layer thickness ratio. The closed-form solutions for bilayers subjected to both thermal stresses and ring-on-ring tests are explicitly formulated which allow the biaxial strength of the bilayer to be evaluated.« less

2D- and 3D SIMS investigations on hot-pressed steel powder HS 6-5-3-8.

PubMed

Rosner, M; Pöckl, G; Danninger, H; Hutter, H

2002-10-01

Processing of steel with powder metallurgical methods such as sintering or hot-pressing have proven to be a powerful tool for the production of industrial parts and for components in the automotive industry. Series of steel-powders (HS 6-5-3-8) produced by gas atomization has been hot-pressed in a graphite tube at temperatures from 820 degrees C to 1050 degrees C. The samples have been characterized with a Secondary Electron Microscope (SEM) due to their porosity and then investigated with 2D- and 3D- SIMS. The spatial distribution of the non-metallic impurities and the covering oxide layer of the single particles has been traced dependent to the pressing temperature. Powders pressed at temperatures higher than 880 degrees C exhibited different precipitation behavior of the impurities and an excessive loss of the covering oxide layer of the single powder particles.

Effects of convective ice evaporation on interannual variability of tropical tropopause layer water vapor

NASA Astrophysics Data System (ADS)

Ye, Hao; Dessler, Andrew E.; Yu, Wandi

2018-04-01

Water vapor interannual variability in the tropical tropopause layer (TTL) is investigated using satellite observations and model simulations. We break down the influences of the Brewer-Dobson circulation (BDC), the quasi-biennial oscillation (QBO), and the tropospheric temperature (ΔT) on TTL water vapor as a function of latitude and longitude using a two-dimensional multivariate linear regression. This allows us to examine the spatial distribution of the impact of each process on TTL water vapor. In agreement with expectations, we find that the impacts from the BDC and QBO act on TTL water vapor by changing TTL temperature. For ΔT, we find that TTL temperatures alone cannot explain the influence. We hypothesize a moistening role for the evaporation of convective ice from increased deep convection as the troposphere warms. Tests using a chemistry-climate model, the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM), support this hypothesis.

Monitoring Thermal Status of Ecosystems with MODIS Land-Surface Temperature and Vegetation Index Products

NASA Technical Reports Server (NTRS)

Wan, Zhengming

2002-01-01

The global land-surface temperature (LST) and normalized difference vegetation index (NDVI) products retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) data in 2001 were used in this study. The yearly peak values of NDVI data at 5km grids were used to define six NDVI peak zones from -0.2 to 1 in steps of 0.2, and the monthly NDVI values at each grid were sorted in decreasing order, resulting in 12 layers of NDVI images for each of the NDVI peak zones. The mean and standard deviation of daytime LSTs and day-night LST differences at the grids corresponding to the first layer of NDVI images characterize the thermal status of terrestrial ecosystems in the NDVI peak zones. For the ecosystems in the 0.8-1 NDVI peak zone, daytime LSTs distribute from 0-35 C and day-night LST differences distribute from -2 to 22 C. The daytime LSTs and day-night LST differences corresponding to the remaining layers of NDVI images show that the growth of vegetation is limited at low and high LSTs. LSTs and NDVI may be used to monitor photosynthetic activity and drought, as shown in their applications to a flood-irrigated grassland in California and an unirrigated grassland in Nevada.

GaInAsP/InP lateral-current-injection distributed feedback laser with a-Si surface grating.

PubMed

Shindo, Takahiko; Okumura, Tadashi; Ito, Hitomi; Koguchi, Takayuki; Takahashi, Daisuke; Atsumi, Yuki; Kang, Joonhyun; Osabe, Ryo; Amemiya, Tomohiro; Nishiyama, Nobuhiko; Arai, Shigehisa

2011-01-31

We fabricated a novel lateral-current-injection-type distributed feedback (DFB) laser with amorphous-Si (a-Si) surface grating as a step to realize membrane lasers. This laser consists of a thin GaInAsP core layer grown on a semi-insulating InP substrate and a 30-nm-thick a-Si surface layer for DFB grating. Under a room-temperature continuous-wave condition, a low threshold current of 7.0 mA and high efficiency of 43% from the front facet were obtained for a 2.0-μm stripe width and 300-μm cavity length. A small-signal modulation bandwidth of 4.8 GHz was obtained at a bias current of 30 mA.

A method for coupling a parameterization of the planetary boundary layer with a hydrologic model

NASA Technical Reports Server (NTRS)

Lin, J. D.; Sun, Shu Fen

1986-01-01

Deardorff's parameterization of the planetary boundary layer is adapted to drive a hydrologic model. The method converts the atmospheric conditions measured at the anemometer height at one site to the mean values in the planetary boundary layer; it then uses the planetary boundary layer parameterization and the hydrologic variables to calculate the fluxes of momentum, heat and moisture at the atmosphere-land interface for a different site. A simplified hydrologic model is used for a simulation study of soil moisture and ground temperature on three different land surface covers. The results indicate that this method can be used to drive a spatially distributed hydrologic model by using observed data available at a meteorological station located on or nearby the site.

Charge-density study on layered oxyarsenides (LaO)MAs (M = Mn, Fe, Ni, Zn)

NASA Astrophysics Data System (ADS)

Takase, Kouichi; Hiramoto, Shozo; Fukushima, Tetsuya; Sato, Kazunori; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

2017-12-01

Using synchrotron X-ray powder diffraction, we investigate the charge-density distributions of the layered oxypnictides (LaO)MnAs, (LaO)FeAs, (LaO)NiAs, and (LaO)ZnAs, which are an antiferromagnetic semiconductor, a parent material of an iron-based superconductor, a low-temperature superconductor, and a non-magnetic semiconductor, respectively. For the metallic samples, clear charge densities are observed in both the transition-metal pnictide layers and the rare-earth-oxide layers. However, in the semiconducting samples, there is no finite charge density between the transition-metal element and As. These differences in charge density reflect differences in physical properties. First-principles calculations using density functional theory reproduce the experimental results reasonably well.

Subsurface temperature distribution in a tropical alluvial fan

NASA Astrophysics Data System (ADS)

Chen, Wenfu; Chang, Minhsiang; Chen, Juier; Lu, Wanchung; Huang, Chihc; Wang, Yunshuen

2017-04-01

As a groundwater intensive use country, Taiwan's 1/3 water supplies are derived from groundwater. The major aquifers consist of sand and gravel formed in alluvial fans which border the fronts of central mountains. Thanks to high density of monitoring wells which provide a window to see the details of the subsurface temperature distribution and the thermal regime in an alluvial fan system. Our study area, the Choshui Alluvial Fan, is the largest groundwater basin in Taiwan and, located within an area of 2,000 km2, has a population of over 1.5 million. For this work, we investigated temperature-depth profiles using 70 groundwater monitoring wells during 2000 to 2015. Our results show that the distribution of subsurface temperature is influenced by various factors such as groundwater recharge, groundwater flow field, air temperature and land use. The groundwater recharge zone, hills to the upper fan, contains disturbed and smaller geothermal gradients. The lack of clay layers within the upper fan aquifers and fractures that developed in the hills should cause the convection and mixing of cooler recharge water to groundwater, resulting in smaller geothermal gradients. The groundwater temperatures at a depth to 300 m within the upper fan and hill were approximately only 23-24 °C while the current mean ground surface temperature is approximately 26 °C.

Refractory lining system for high wear area of high temperature reaction vessel

DOEpatents

Hubble, David H.; Ulrich, Klaus H.

1998-01-01

A refractory-lined high temperature reaction vessel comprises a refractory ring lining constructed of refractory brick, a cooler, and a heat transfer medium disposed between the refractory ring lining and the cooler. The refractory brick comprises magnesia (MgO) and graphite. The heat transfer medium contacts the refractory brick and a cooling surface of the cooler, and is composed of a material that accommodates relative movement between the refractory brick and the cooler. The brick is manufactured such that the graphite has an orientation providing a high thermal conductivity in the lengthwise direction through the brick that is higher than the thermal conductivity in directions perpendicular to the lengthwise direction. The graphite preferably is flake graphite, in the range of about 10 to 20 wt %, and has a size distribution selected to provide maximum brick density. The reaction vessel may be used for performing a reaction process including the steps of forming a layer of slag on a melt in the vessel, the slag having a softening point temperature range, and forming a protective frozen layer of slag on the interior-facing surface of the refractory lining in at least a portion of a zone where the surface contacts the layer of slag, the protective frozen layer being maintained at or about the softening point of the slag.

High indium content homogenous InAlN layers grown by plasma-assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kyle, Erin C. H.; Kaun, Stephen W.; Wu, Feng; Bonef, Bastien; Speck, James S.

2016-11-01

InAlN grown by plasma-assisted molecular beam epitaxy often contains a honeycomb microstructure. The honeycomb microstructure consists of 5-10 nm diameter aluminum-rich regions which are surrounded by indium-rich regions. Layers without this microstructure were previously developed for nominally lattice-matched InAlN and have been developed here for higher indium content InAlN. In this study, InAlN was grown in a nitrogen-rich environment with high indium to aluminum flux ratios at low growth temperatures. Samples were characterized by high-resolution x-ray diffraction, atomic force microscopy, high-angle annular dark-field scanning transmission electron microscopy, and atom probe tomography. Atomic force microscopy showed InAlN layers grown at temperatures below 450 °C under nitrogen-rich conditions were free of droplets. InAlN films with indium contents up to 81% were grown at temperatures between 410 and 440 °C. High-angle annular dark-field scanning transmission electron microscopy and atom probe tomography showed no evidence of honeycomb microstructure for samples with indium contents of 34% and 62%. These layers are homogeneous and follow a random alloy distribution. A growth diagram for InAlN of all indium contents is reported.

Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer

NASA Astrophysics Data System (ADS)

Kube, R.; Garcia, O. E.; Theodorsen, A.; Brunner, D.; Kuang, A. Q.; LaBombard, B.; Terry, J. L.

2018-06-01

The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma conditions in an ohmically heated, lower single null diverted discharge. The electron density and temperature are strongly correlated and feature fluctuation statistics similar to the ion saturation current. Both electron density and temperature time series are dominated by intermittent, large-amplitude burst with an exponential distribution of both burst amplitudes and waiting times between them. The characteristic time scale of the large-amplitude bursts is approximately 15 μ {{s}}. Large-amplitude velocity fluctuations feature a slightly faster characteristic time scale and appear at a faster rate than electron density and temperature fluctuations. Describing these time series as a superposition of uncorrelated exponential pulses, we find that probability distribution functions, power spectral densities as well as auto-correlation functions of the data time series agree well with predictions from the stochastic model. The electron particle and heat fluxes present large-amplitude fluctuations. For this low-density plasma, the radial electron heat flux is dominated by convection, that is, correlations of fluctuations in the electron density and radial velocity. Hot and dense blobs contribute only a minute fraction of the total fluctuation driven heat flux.

Substituted Quaternary Ammonium Salts Improve Low-Temperature Performance of Double-Layer Capacitors

NASA Technical Reports Server (NTRS)

Brandon, Erik J.; Smart, Marshall C.; West, William C.

2011-01-01

Double-layer capacitors are unique energy storage devices, capable of supporting large current pulses as well as a very high number of charging and discharging cycles. The performance of doublelayer capacitors is highly dependent on the nature of the electrolyte system used. Many applications, including for electric and fuel cell vehicles, back-up diesel generators, wind generator pitch control back-up power systems, environmental and structural distributed sensors, and spacecraft avionics, can potentially benefit from the use of double-layer capacitors with lower equivalent series resistances (ESRs) over wider temperature limits. Higher ESRs result in decreased power output, which is a particular problem at lower temperatures. Commercially available cells are typically rated for operation down to only 40 C. Previous briefs [for example, Low Temperature Supercapacitors (NPO-44386), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), p. 32, and Supercapacitor Electrolyte Solvents With Liquid Range Below 80 C (NPO-44855), NASA Tech Briefs, Vol. 34, No. 1 (January 2010), p. 44] discussed the use of electrolytes that employed low-melting-point co-solvents to depress the freezing point of traditional acetonitrile-based electrolytes. Using these modified electrolyte formulations can extend the low-temperature operational limit of double-layer capacitors beyond that of commercially available cells. This previous work has shown that although the measured capacitance is relatively insensitive to temperature, the ESR can rise rapidly at low temperatures, due to decreased electrolyte conductance within the pores of the high surface- area carbon electrodes. Most of these advanced electrolyte systems featured tetraethylammonium tetrafluoroborate (TEATFB) as the salt. More recent work at JPL indicates the use of the asymmetric quaternary ammonium salt triethylmethylammonium tetrafluoroborate (TEMATFB) or spiro-(l,l')-bipyrrolidium tetrafluoroborate (SBPBF4) in a 1:1 by volume solvent mixture of acetonitrile (AN) and methyl formate (MF) enables double-layer capacitor cells to operate well below -40 C with a relatively low ESR. Typically, a less than twofold increase in ESR is observed at -65 C relative to room-temperature values, when these modified electrolyte blends are used in prototype cells. Double-layer capacitor coin cells filled with these electrolytes have displayed the lowest measured ESR for an organic electrolyte to date at low temperature (based on a wide range of electrolyte screening studies at JPL). The cells featured high-surface-area (approximately equal to 2,500 m/g) carbon electrodes that were 0.50 mm thick and 1.6 cm in diameter, and coated with a thin layer of platinum to reduce cell resistance. A polyethylene separator was used to electrically isolate the electrodes.

Driving forces: Slab subduction and mantle convection

NASA Technical Reports Server (NTRS)

Hager, Bradford H.

1988-01-01

Mantle convection is the mechanism ultimately responsible for most geological activity at Earth's surface. To zeroth order, the lithosphere is the cold outer thermal boundary layer of the convecting mantle. Subduction of cold dense lithosphere provides tha major source of negative buoyancy driving mantle convection and, hence, surface tectonics. There are, however, importnat differences between plate tectonics and the more familiar convecting systems observed in the laboratory. Most important, the temperature dependence of the effective viscosity of mantle rocks makes the thermal boundary layer mechanically strong, leading to nearly rigid plates. This strength stabilizes the cold boundary layer against small amplitude perturbations and allows it to store substantial gravitational potential energy. Paradoxically, through going faults at subduction zones make the lithosphere there locally weak, allowing rapid convergence, unlike what is observed in laboratory experiments using fluids with temperature dependent viscosities. This bimodal strength distribution of the lithosphere distinguishes plate tectonics from simple convection experiments. In addition, Earth has a buoyant, relatively weak layer (the crust) occupying the upper part of the thermal boundary layer. Phase changes lead to extra sources of heat and bouyancy. These phenomena lead to observed richness of behavior of the plate tectonic style of mantle convection.

Charge carrier relaxation in InGaAs-GaAs quantum wire modulation-doped heterostructures

NASA Astrophysics Data System (ADS)

Kondratenko, S. V.; Iliash, S. A.; Mazur, Yu I.; Kunets, V. P.; Benamara, M.; Salamo, G. J.

2017-09-01

The time dependencies of the carrier relaxation in modulation-doped InGaAs-GaAs low-dimensional structures with quantum wires have been studied as functions of temperature and light excitation levels. The photoconductivity (PC) relaxation follows a stretched exponent with decay constant, which depends on the morphology of InGaAs epitaxial layers, presence of deep traps, and energy disorder due to inhomogeneous distribution of size and composition. A hopping model, where electron tunnels between bands of localized states, gives appropriate interpretation for temperature-independent PC decay across the temperature range 150-290 K. At low temperatures (T < 150 K), multiple trapping-retrapping via 1D states of InGaAs quantum wires (QWRs), sub-bands of two-dimensional electron gas of modulation-doped n-GaAs spacers, as well as defect states in the GaAs environment are the dominant relaxation mechanism. The PC and photoluminescence transients for samples with different morphologies of the InGaAs nanostructures are compared. The relaxation rates are found to be largely dependent on energy disorder due to inhomogeneous distribution of strain, nanostructure size and composition, and piezoelectric fields in and around nanostructures, which have a strong impact on efficiency of carrier exchange between bands of the InGaAs QWRs, GaAs spacers, or wetting layers; presence of local electric fields; and deep traps.

Numerical Investigation of PLIF Gas Seeding for Hypersonic Boundary Layer Flows

NASA Technical Reports Server (NTRS)

Johanson, Craig T.; Danehy, Paul M.

2012-01-01

Numerical simulations of gas-seeding strategies required for planar laser-induced fluorescence (PLIF) in a Mach 10 air flow were performed. The work was performed to understand and quantify adverse effects associated with gas seeding and to compare different flow rates and different types of seed gas. The gas was injected through a slot near the leading edge of a flat plate wedge model used in NASA Langley Research Center's 31- Inch Mach 10 Air Tunnel facility. Nitric oxide, krypton, and iodine gases were simulated at various injection rates. Simulation results showing the deflection of the velocity field for each of the cases are presented. Streamwise distributions of velocity and concentration boundary layer thicknesses as well as vertical distributions of velocity, temperature, and mass distributions are presented for each of the cases. Relative merits of the different seeding strategies are discussed.

Integral gas seal for fuel cell gas distribution assemblies and method of fabrication

DOEpatents

Dettling, Charles J.; Terry, Peter L.

1985-03-19

A porous gas distribution plate assembly for a fuel cell, such as a bipolar assembly, includes an inner impervious region wherein the bipolar assembly has good surface porosity but no through-plane porosity and wherein electrical conductivity through the impervious region is maintained. A hot-pressing process for forming the bipolar assembly includes placing a layer of thermoplastic sealant material between a pair of porous, electrically conductive plates, applying pressure to the assembly at elevated temperature, and allowing the assembly to cool before removing the pressure whereby the layer of sealant material is melted and diffused into the porous plates to form an impervious bond along a common interface between the plates holding the porous plates together. The distribution of sealant within the pores along the surface of the plates provides an effective barrier at their common interface against through-plane transmission of gas.

Method of fabricating an integral gas seal for fuel cell gas distribution assemblies

DOEpatents

Dettling, Charles J.; Terry, Peter L.

1988-03-22

A porous gas distribution plate assembly for a fuel cell, such as a bipolar assembly, includes an inner impervious region wherein the bipolar assembly has good surface porosity but no through-plane porosity and wherein electrical conductivity through the impervious region is maintained. A hot-pressing process for forming the bipolar assembly includes placing a layer of thermoplastic sealant material between a pair of porous, electrically conductive plates, applying pressure to the assembly at elevated temperature, and allowing the assembly to cool before removing the pressure whereby the layer of sealant material is melted and diffused into the porous plates to form an impervious bond along a common interface between the plates holding the porous plates together. The distribution of sealant within the pores along the surface of the plates provides an effective barrier at their common interface against through-plane transmission of gas.

Thermal model for optimization of vascular laser tissue soldering.

PubMed

Bogni, Serge; Stumpp, Oliver; Reinert, Michael; Frenz, Martin

2010-06-01

Laser tissue soldering (LTS) is a promising technique for tissue fusion based on a heat-denaturation process of proteins. Thermal damage of the fused tissue during the laser procedure has always been an important and challenging problem. Particularly in LTS of arterial blood vessels strong heating of the endothelium should be avoided to minimize the risk of thrombosis. A precise knowledge of the temperature distribution within the vessel wall during laser irradiation is inevitable. The authors developed a finite element model (FEM) to simulate the temperature distribution within blood vessels during LTS. Temperature measurements were used to verify and calibrate the model. Different parameters such as laser power, solder absorption coefficient, thickness of the solder layer, cooling of the vessel and continuous vs. pulsed energy deposition were tested to elucidate their impact on the temperature distribution within the soldering joint in order to reduce the amount of further animal experiments. A pulsed irradiation with high laser power and high absorbing solder yields the best results. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Assessing the Nature of the Distribution of Localised States in Bulk GaAsBi.

PubMed

Wilson, Tom; Hylton, Nicholas P; Harada, Yukihiro; Pearce, Phoebe; Alonso-Álvarez, Diego; Mellor, Alex; Richards, Robert D; David, John P R; Ekins-Daukes, Nicholas J

2018-04-24

A comprehensive assessment of the nature of the distribution of sub band-gap energy states in bulk GaAsBi is presented using power and temperature dependent photoluminescence spectroscopy. The observation of a characteristic red-blue-red shift in the peak luminescence energy indicates the presence of short-range alloy disorder in the material. A decrease in the carrier localisation energy demonstrates the strong excitation power dependence of localised state behaviour and is attributed to the filling of energy states furthest from the valence band edge. Analysis of the photoluminescence lineshape at low temperature presents strong evidence for a Gaussian distribution of localised states that extends from the valence band edge. Furthermore, a rate model is employed to understand the non-uniform thermal quenching of the photoluminescence and indicates the presence of two Gaussian-like distributions making up the density of localised states. These components are attributed to the presence of microscopic fluctuations in Bi content, due to short-range alloy disorder across the GaAsBi layer, and the formation of Bi related point defects, resulting from low temperature growth.

Antiparallel pinned NiO spin valve sensor for GMR head application (invited)

NASA Astrophysics Data System (ADS)

Pinarbasi, M.; Metin, S.; Gill, H.; Parker, M.; Gurney, B.; Carey, M.; Tsang, C.

2000-05-01

NiO antiferromagnetic material possesses certain advantages for spin valve applications and has attracted considerable attention. Some of the key advantages are its insulating properties, very high corrosion resistance, less sensitivity to composition, and its low reset temperature. This material, however, has a low blocking temperature which prevents its application to simple spin valve designs. The use of this material in spin valve structures required significant improvements in thermal stability, blocking temperature, and the spin valve design. In the present study, the blocking temperature and the blocking temperature distribution of the NiO films have been improved by depositing the films reactively using ion beam sputtering. A number of improvements in the processing method and deposition system had to be made to allow full NiO spin valve deposition for mass production. Another critical part was the use of antiparallel pinned design in place of the simple design to improve the thermal stability of the NiO spin valves as read elements at disk drive temperatures. The selection of the ferromagnetic pinned layers and the Ru spacer thickness in AP-pinned spin valves has significant impact on the behavior of the devices. These spin valves are all bottom type, NiO/PL1/Ru/PL2/Cu/Co/NiFe/Ta, where the metallic portion of the spin valve is deposited on top of the NiO AF layer. The PL1 and PL2 are ferromagnetic layers comprising NiFe and Co layers. Read elements have been made using these spin valves that delivered areal densities of 12 Gbit/in. These topics and other improvements which resulted in successful use of NiO spin valves as GMR heads in hard disk drives will be discussed.

Coupled granular/continuous medium for thermally stable perpendicular magnetic recording

NASA Astrophysics Data System (ADS)

Sonobe, Y.; Weller, D.; Ikeda, Y.; Takano, K.; Schabes, M. E.; Zeltzer, G.; Do, H.; Yen, B. K.; Best, M. E.

2001-10-01

We studied coupled granular/continuous (CGC) perpendicular media consisting of a continuous multilayer structure and a granular layer. The addition of Co/Pt multilayers decreased the nucleation field from 200 to -1800 Oe and increased the squareness from 0.9 to 1.0. The moment decay at room temperature was significantly reduced from -4.8% to -0.05% per decade. At elevated temperatures, strong exchange coupling between a granular layer and a continuous layer is needed for thermal stability. The exchange-coupled continuous layer reduces thermal demagnetization as it effectively increases the grain size, tightens the grain distribution, and prevents the reversal of individual grains. Magnetic Force Microscope image showed a larger magnetic cluster size for the CGC structure. Compared to the CoCr 18Pt 12 medium, the CGC medium had 2.3 dB higher output. However, the noise for the CGC medium increased with the recording density, while the noise for the CoCr 18Pt 12 medium remained constant from 4 to 15 kfc/mm. Further optimization and noise reduction are still required for future high density recording.

Microstructure and mechanical behavior of Zr substrates coated with FeCrAl and Mo by cold-spraying

NASA Astrophysics Data System (ADS)

Park, Dong Jun; Kim, Hyun Gil; Jung, Yang Il; Park, Jung Hwan; Yang, Jae Ho; Koo, Yang Hyun

2018-06-01

FeCrAl and Mo layers were cold-sprayed onto a Zr surface, with the Mo layer introduced between the FeCrAl coating and the Zr matrix preventing high-temperature interdiffusion. Microstructural characterization of the first-deposited Mo layer and the Zr matrix immediately below the Mo/Zr interface was performed using transmission electron microscopy, and near-interface elemental distributions were obtained using energy-dispersive X-ray spectroscopy. The deformation of the coated Mo powder induced the formation of microbands and mechanically interlocked nanoscale structures. The mechanical behavior of Zr with a coating layer was compared with those characteristic of conventional Zr samples. The coated sample showed smaller strength reduction in the test conducted at elevated temperature. The hardness and fracture morphology of the Zr matrix near the interface region were investigated to determine the effect of impacting Mo particles on the matrix microstructure. The enhanced hardness and cleavage fracture morphology of the Zr matrix immediately below the Mo/Zr interface indicated the occurrence of localized deformation owing to Mo particle impact.

Superplastic Forming/Diffusion Bonding Without Interlayer of 5A90 Al-Li Alloy Hollow Double-Layer Structure

NASA Astrophysics Data System (ADS)

Jiang, Shaosong; Jia, Yong; Lu, Zhen; Shi, Chengcheng; Zhang, Kaifeng

2017-09-01

The hollow double-layer structure of 5A90 Al-Li alloy was fabricated by SPF/DB process in this study. The characteristics and mechanism of 5A90 Al-Li alloy with respect to superplasticity and diffusion bonding were investigated. Tensile tests showed that the optimal elongation of tensile specimens was 243.97% at the temperature of 400 °C and the strain rate of 0.001 s-1. Effect of the surface roughness, bonding temperature and bonding time to determine the microstructure and mechanical properties of diffusion bonding joints was investigated, and the optimum bonding parameters were 540 °C/2.5 h/Ra18. Through the finite element simulation, it could be found that the SPF/DB process of hollow double-layer structure was feasible. The hollow double-layer structure of 5A90 Al-Li alloy was manufactured, showing that the thickness distribution of the bonding area was uniform and the thinnest part was the round corner. The SEM images of diffusion bonding joints showed that sound bonding interfaces were obtained in which no discontinuity existed.

Impact of Typhoons on the Western Pacific Ocean (ITOP) DRI:Numerical Modeling of Ocean Mixed Layer Turbulence and Entrainment at High Winds

DTIC Science & Technology

2013-09-23

DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Impact of Typhoons on the Western Pacific Ocean (ITOP) DRI...measurement and modeling activities include a focus on the impact of surface waves, air- sea fluxes and the temperature, salinity and velocity structure...moment closure (SMC) to represent the impact of Langmuir turbulence. WORK COMPLETED Encouraged by good quantitative comparisons between LES

Investigation of Gas Seeding for Planar Laser-Induced Fluorescence in Hypersonic Boundary Layers

NASA Technical Reports Server (NTRS)

Arisman, C. J.; Johansen, C. T.; Bathel, B. F.; Danehy, P. M.

2015-01-01

Numerical simulations of the gas-seeding strategies required for planar laser-induced fluorescence in a Mach 10 (approximately Mach 8.2 postshock) airflow were performed. The work was performed to understand and quantify the adverse effects associated with gas seeding and to assess various types of seed gas that could potentially be used in future experiments. In prior experiments, NO and NO2 were injected through a slot near the leading edge of a flatplate wedge model used in NASA Langley Research Center's 31 in. Mach 10 air tunnel facility. In this paper, nitric oxide, krypton, and iodine gases were simulated at various injection rates. Simulations showing the deflection of the velocity boundary layer for each of the cases are presented. Streamwise distributions of velocity and concentration boundary-layer thicknesses, as well as vertical distributions of velocity, temperature, and mass distributions, are presented for each of the cases. A comparison between simulated streamwise velocity profiles and experimentally obtained molecular tagging velocimetry profiles using a nitric oxide seeding strategy is performed to verify the influence of such a strategy on the boundary layer. The relative merits of the different seeding strategies are discussed. The results from a custom solver based on OpenFOAM version 2.2.1 are compared against results obtained from ANSYS® Fluent version 6.3.

Theoretical and experimental studies of reentry plasmas

NASA Technical Reports Server (NTRS)

Dunn, M. G.; Kang, S.

1973-01-01

A viscous shock-layer analysis was developed and used to calculate nonequilibrium-flow species distributions in the plasma layer of the RAM vehicle. The theoretical electron-density results obtained are in good agreement with those measured in flight. A circular-aperture flush-mounted antenna was used to obtain a comparison between theoretical and experimental antenna admittance in the presence of ionized boundary layers of low collision frequency. The electron-temperature and electron-density distributions in the boundary layer were independently measured. The antenna admittance was measured using a four-probe microwave reflectometer and these measured values were found to be in good agreement with those predicted. Measurements were also performed with another type of circular-aperture antenna and good agreement was obtained between the calculations and the experimental results. A theoretical analysis has been completed which permits calculation of the nonequilibrium, viscous shock-layer flow field for a sphere-cone body. Results are presented for two different bodies at several different altitudes illustrating the influences of bluntness and chemical nonequilibrium on several gas dynamic parameters of interest. Plane-wave transmission coefficients were calculated for an approximate space-shuttle body using a typical trajectory.

Small scale patches of suspended matter and phytoplankton in the Elbe River estuary, German Bight and tidal flats

NASA Technical Reports Server (NTRS)

Doerffer, R.; Fischer, J.; Stoessel, M.; Brockmann, C.; Grassl, H.

1989-01-01

Landsat 5 TM measurements are found suitable for study of small scale features in coastal waters; three independent factors, namely suspended matter concentration, atmospheric scattering, and sea-surface temperature, were extracted from all seven TM channels on the basis of factor analysis. The distribution of suspended matter in near-surface water layer and sea surface temperature is observable with a spatial resolution of at least 120 x 120 sq m. The high correlation between water depth and suspended matter distribution established by ship-gathered data supports the presently hypothesized control by bottom topography and wind-modified tidal currents of eddy and front formation.

A Conceptual Model for Shear-Induced Phase Behavior in Crystallizing Cocoa Butter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mazzanti,G.; Guthrie, S.; Marangoni, A.

2007-01-01

We propose a conceptual model to explain the quantitative data from synchrotron X-ray diffraction experiments on the shear-induced phase behavior of cocoa butter, the main structural component of chocolate. We captured two-dimensional diffraction patterns from cocoa butter at crystallization temperatures of 17.5, 20.0, and 22.5 {sup o}C under shear rates from 45 to 1440 s{sup -1} and under static conditions. From the simultaneous analysis of the integrated intensity, correlation length, lamellar thickness, and crystalline orientation, we postulate a conceptual model to provide an explanation for the distribution of phases II, IV, V, and X and the kinetics of the process.more » As previously proposed in the literature, we assume that the crystallites grow layer upon layer of slightly different composition. The shear rate and temperature applied define these compositions. Simultaneously, the shear and temperature define the crystalline interface area available for secondary nucleation by promoting segregation and affecting the size distribution of the crystallites. The combination of these factors (composition, area, and size distribution) favors dramatically the early onset of phase V under shear and determines the proportions of phases II, IV, V, and X after the transition. The experimental observations, the methodology used, and the proposed explanation are of fundamental and industrial interest, since the structural properties of crystalline networks are determined by their microstructure and polymorphic crystalline state. Different proportions of the phases will thus result in different characteristics of the final material.« less

Transparent layered YAG ceramics with structured Yb doping produced via tape casting

NASA Astrophysics Data System (ADS)

Hostaša, Jan; Piancastelli, Andreana; Toci, Guido; Vannini, Matteo; Biasini, Valentina

2017-03-01

The flexibility of the ceramic production process, in particular in terms of shaping and spatial control of distribution of active ions, is one of the strong points in favor of transparent ceramics. In high power lasers in particular, where thermal management is a critical issue, the finely controlled design of spatial distribution of the doping ions within the laser gain media can reduce undesired thermally induced effects and large temperature gradients, and thus enhance the efficiency and laser beam quality especially under increased thermal load. In the present work transparent structured YAG ceramics with Yb doping were produced by tape casting followed by thermal compression of assembled tapes and sintered under high vacuum. The thermal compression of variously doped tape cast layers is a very promising method because it allows a high precision and good control over dopant distribution in the sintered material. After sintering, the distribution of Yb across the layers was characterized by SEM-EDX and the thickness of Yb diffusion zones between the layers with different Yb content was measured. Optical homogeneity was assessed by means of optical transmittance mapping of the samples and by 2D scanning of laser output. The effect of structured dopant distribution on laser performance was measured in quasi-CW and CW regime with different duty factors. Slope efficiency values higher than 50% were measured both in quasi-CW and in CW lasing conditions. The results are in good agreement with previously calculated predictions, confirming the beneficial effect of structured doping on laser performances and enlightening the impact of the residual scattering losses. Compared to other processing methods, such as the pressing of granulated powders, tape casting followed by thermal compression leads to straight and narrow interfaces between layers with different composition and allows to build structures composed of extremely thin layers with defined dopant content.

Thermal behaviour of an urban lake during summer

NASA Astrophysics Data System (ADS)

Solcerova, Anna; van de Ven, Frans

2015-04-01

One of the undesirable effects of urbanisation is higher summer air temperatures in cites compared to rural areas. One of the most important self-cooling mechanism of cities is presence of water. Comparative studies showed that from all urban land-use types open water is the most efficient in reducing the heat in its surrounding. Urban water bodies vary from small ponds to big lakes and rivers, but already the presence of a swimming pool in a garden resulted in lower temperatures in the area. Moving and still water both exhibit slightly different patterns with respect to the environment. While ponds tend to respond more to air temperature changes, faster flowing rivers are expected to have more stable temperature over time. There are two major components of cooling effect of a surface water:(1) through evaporation, and (2) by storing heat and increasing its own temperature. This study shows results from a detailed temperature measurements, using Distributed Temperature Sensing (DTS), in an urban lake in Delft (The Netherlands). A two meter tall construction measuring temperature with 2 mm vertical spatial resolution was placed partly in the water, reaching all the way to the muddy underlayer, and partly in the air. Data from continuous two month measurement campaign show the development of water temperature with respect to solar radiation, air temperature, rain and inflow of rainwater from surrounding streets, etc. Most interesting is the 1-2 cm thick layer of colder air right above the water surface. This layer reaches values lower than both the air and the water, which suggests that certain part of the potential cooling capacity of open water is restricted by a small layer of air just above its surface.

Theoretical Investigation of Calculating Temperatures in the Combining Zone of Cu/Fe Composite Plate Jointed by Explosive Welding

NASA Astrophysics Data System (ADS)

Qu, Y. D.; Zhang, W. J.; Kong, X. Q.; Zhao, X.

2016-03-01

The heat-transfer behavior of the interface of Flyer plate (or Base Plate) has great influence on the microcosmic structures, stress distributions, and interface distortion of the welded interface of composite plates by explosive welding. In this paper, the temperature distributions in the combing zone are studied for the case of Cu/Fe composite plate jointed by explosive welding near the lower limit of explosive welding. The results show that Flyer plate (Cu plate) and Base Plate (Fe plate) firstly almost have the same melting rate in the explosive welding process. Then, the melting rate of Cu plate becomes higher than that of Fe plate. Finally, the melt thicknesses of Cu plate and Fe plate trend to be different constants, respectively. Meanwhile, the melting layer of Cu plate is thicker than that of Fe plate. The research could supply some theoretical foundations for calculating the temperature distribution and optimizing the explosive welding parameters of Cu/Fe composite plate to some extent.

Isotope engineering of van der Waals interactions in hexagonal boron nitride

NASA Astrophysics Data System (ADS)

Vuong, T. Q. P.; Liu, S.; van der Lee, A.; Cuscó, R.; Artús, L.; Michel, T.; Valvin, P.; Edgar, J. H.; Cassabois, G.; Gil, B.

2018-02-01

Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes (10B and 11B) compared to those with the natural distribution of boron (20 at% 10B and 80 at% 11B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in 10BN than in 11BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.

Isotope engineering of van der Waals interactions in hexagonal boron nitride.

PubMed

Vuong, T Q P; Liu, S; Van der Lee, A; Cuscó, R; Artús, L; Michel, T; Valvin, P; Edgar, J H; Cassabois, G; Gil, B

2018-02-01

Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes ( 10 B and 11 B) compared to those with the natural distribution of boron (20 at% 10 B and 80 at% 11 B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in 10 BN than in 11 BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.

Investigating Phase-Change-Induced Flow in Gas Diffusion Layers in Fuel Cells with X-ray Computed Tomography

DOE PAGES

Shum, Andrew D.; Parkinson, Dilworth Y.; Xiao, Xianghui; ...

2017-10-07

The performance of polymer-electrolyte fuel cells is heavily dependent on proper management of liquid water. One particular reason is that liquid water can collect in the gas diffusion layers (GDLs) blocking the reactant flow to the catalyst layer. This results in increased mass-transport losses. At higher temperatures, evaporation of water becomes a dominant water-removal mechanism and specifically phase-change-induced (PCI) flow is present due to thermal gradients. This study used synchrotron based micro X-ray computed tomography (CT) to visualize and quantify the water distribution within gas diffusion layers subject to a thermal gradient. Plotting saturation as a function of through-plane distancemore » quantitatively shows water redistribution, where water evaporates at hotter locations and condenses in colder locations. The morphology of the 2 GDLs on the micro-scale, as well as evaporating water clusters, are resolved, indicating that the GDL voids are slightly prolate, whereas water clusters are oblate. From the mean radii of water distributions and visual inspection, it is observed that larger water clusters evaporate faster than smaller ones.« less

A Crystallization-Temperature Profile Through Paleo-Oceanic Crust (Wadi Gideah Transect, Oman Ophiolite): Application of the REE-in-Plagioclase-Clinopyroxene Partitioning Thermometer

NASA Astrophysics Data System (ADS)

Mueller, S.; Hasenclever, J.; Garbe-Schönberg, D.; Koepke, J.; Hoernle, K.

2017-12-01

The accretion mechanisms forming oceanic crust at fast spreading ridges are still under controversial discussion. Thermal, petrological, and geochemical observations predict different end-member models, i.e., the gabbro glacier and the sheeted sill model. They all bear implications for heat transport, temperature distribution, mode of crystallization and hydrothermal heat removal over crustal depth. In a typical MOR setting, temperature is the key factor driving partitioning of incompatible elements during crystallization. LA-ICP-MS data for co-genetic plagioclase and clinopyroxene in gabbros along a transect through the plutonic section of paleo-oceanic crust (Wadi Gideah Transect, Oman ophiolite) reveal that REE partitioning coefficients are relatively constant in the layered gabbro section but increase for the overlying foliated gabbros, with an enhanced offset towards HREEs. Along with a systematic enrichment of REE's with crustal height, these trends are consistent with a system dominated by in-situ crystallization for the lower gabbros and a change in crystallization mode for the upper gabbros. Sun and Liang (2017) used experimental REE partitioning data for calibrating a new REE-in-plagioclase-clinopyroxene thermometer that we used here for establishing the first crystallization-temperature depth profile through oceanic crust that facilitates a direct comparison with thermal models of crustal accretion. Our results indicate crystallization temperatures of about 1220±8°C for the layered gabbros and lower temperatures of 1175±8°C for the foliated gabbros and a thermal minimum above the layered-to-foliated gabbro transition. Our findings are consistent with a hybrid accretion model for the oceanic crust. The thermal minimum is assumed to represent a zone where the descending crystal mushes originating from the axial melt lens meet with mushes that have crystallized in situ. These results can be used to verify and test thermal models (e.g., Maclennan et al., 2004, Theissen-Krah et al., 2016) and their predictions for heat flow and temperature distribution in the crust. Maclennan, J., Hulme, T., & Singh, S. C. (2004), G3, 5(2). / Sun, C., & Liang, Y., (2017), CMP, 172(4). / Theissen-Krah, S., Rüpke, L. H., & Hasenclever, J. (2016), GRL, 43(3).

Impact of micro-porous layer on liquid water distribution at the catalyst layer interface and cell performance in a polymer electrolyte membrane fuel cell

NASA Astrophysics Data System (ADS)

Tabe, Yutaka; Aoyama, Yusuke; Kadowaki, Kazumasa; Suzuki, Kengo; Chikahisa, Takemi

2015-08-01

In polymer electrolyte membrane fuel cells, a gas diffusion layer (GDL) with a micro-porous layer (MPL) gives better anti-flooding performance than GDLs without an MPL. To investigate the function and mechanism of the MPL to suppress water flooding, the liquid water distribution at the cathode catalyst layer (CL) surface are observed by a freezing method; in the method liquid water is immobilized in ice form by rapid freezing, followed by disassembling the cell for observations. The ice covered area is quantified by image processing and cells with and without an MPL are compared. The results show that the MPL suppresses water accumulation at the interface due to smaller pore size and finer contact with the CL, and this results in less water flooding. Investigation of ice formed after -10 °C cold start shutdowns and the temporary performance deterioration at ordinary temperatures also indicates a significant influence of the liquid water accumulating at the interface. The importance of the fine contact between CL and MPL, the relative absence of gaps, is demonstrated by a gas diffusion electrode (GDE) which is directly coated with catalyst ink on the surface of the MPL achieving finer contact of the layers.

Time-dependent dielectric breakdown of atomic-layer-deposited Al2O3 films on GaN

NASA Astrophysics Data System (ADS)

Hiraiwa, Atsushi; Sasaki, Toshio; Okubo, Satoshi; Horikawa, Kiyotaka; Kawarada, Hiroshi

2018-04-01

Atomic-layer-deposited (ALD) Al2O3 films are the most promising surface passivation and gate insulation layers in non-Si semiconductor devices. Here, we carried out an extensive study on the time-dependent dielectric breakdown characteristics of ALD-Al2O3 films formed on homo-epitaxial GaN substrates using two different oxidants at two different ALD temperatures. The breakdown times were approximated by Weibull distributions with average shape parameters of 8 or larger. These values are reasonably consistent with percolation theory predictions and are sufficiently large to neglect the wear-out lifetime distribution in assessing the long-term reliability of the Al2O3 films. The 63% lifetime of the Al2O3 films increases exponentially with a decreasing field, as observed in thermally grown SiO2 films at low fields. This exponential relationship disproves the correlation between the lifetime and the leakage current. Additionally, the lifetime decreases with measurement temperature with the most remarkable reduction observed in high-temperature (450 °C) O3-grown films. This result agrees with that from a previous study, thereby ruling out high-temperature O3 ALD as a gate insulation process. When compared at 200 °C under an equivalent SiO2 field of 4 MV/cm, which is a design guideline for thermal SiO2 on Si, high-temperature H2O-grown Al2O3 films have the longest lifetimes, uniquely achieving the reliability target of 20 years. However, this target is accomplished by a relatively narrow margin and, therefore, improvements in the lifetime are expected to be made, along with efforts to decrease the density of extrinsic Al2O3 defects, if any, to promote the practical use of ALD Al2O3 films.

Experimental Characterization of Radiation Forcing due to Atmospheric Aerosols

NASA Astrophysics Data System (ADS)

Sreenivas, K. R.; Singh, D. K.; Ponnulakshmi, V. K.; Subramanian, G.

2011-11-01

Micro-meteorological processes in the nocturnal atmospheric boundary layer (NBL) including the formation of radiation-fog and the development of inversion layers are controlled by heat transfer and the vertical temperature distribution close to the ground. In a recent study, it has been shown that the temperature profile close to the ground in stably-stratified, NBL is controlled by the radiative forcing due to suspended aerosols. Estimating aerosol forcing is also important in geo-engineering applications to evaluate the use of aerosols to mitigate greenhouse effects. Modeling capability in the above scenarios is limited by our knowledge of this forcing. Here, the design of an experimental setup is presented which can be used for evaluating the IR-radiation forcing on aerosols under either Rayleigh-Benard condition or under conditions corresponding to the NBL. We present results indicating the effect of surface emissivities of the top and bottom boundaries and the aerosol concentration on the temperature profiles. In order to understand the observed enhancement of the convection-threshold, we have determined the conduction-radiation time constant of an aerosol laden air layer. Our results help to explain observed temperature profiles in the NBL, the apparent stability of such profiles and indicate the need to account for the effect of aerosols in climatic/weather models.

Snow control on active layer and permafrost in steep alpine rock walls (Aiguille du Midi, 3842 m a.s.l, Mont Blanc massif)

NASA Astrophysics Data System (ADS)

Magnin, Florence; Westermann, Sebastian; Pogliotti, Paolo; Ravanel, Ludovic; Deline, Philip

2016-04-01

Permafrost degradation through the thickening of the active layer and the rising temperature at depth is a crucial process of rock wall stability. The ongoing increase in rock falls observed during hot periods in mid-latitude mountain ranges is regarded as a result of permafrost degradation. However, the short-term thermal dynamics of alpine rock walls are misunderstood since they result of complex processes related to the interaction of local climate variables, heterogeneous snow cover and heat transfers. As a consequence steady-state and long-term changes that can be approached with simpler process mainly related to air temperature, solar radiations and heat conduction were the most common dynamics to be studied so far. The effect of snow on the bedrock surface temperature is increasingly investigated and has already been demonstrated to be an essential factor of permafrost distribution. Nevertheless, its effect on the year-to-year changes of the active layer thickness and of the permafrost temperature in steep alpine bedrock has not been investigated yet, partly due to the lack of appropriate data. We explore the role of snow accumulations on the active layer and permafrost thermal regime of steep rock walls of a high-elevated site, the Aiguille du Midi (AdM, 3842 m a.s.l, Mont Blanc massif, Western European Alps) by mean of a multi-methods approach. We first analyse six years of temperature records in three 10-m-deep boreholes. Then we describe the snow accumulation patterns on two rock faces by means of automatically processed camera records. Finally, sensitivity analyses of the active layer thickness and permafrost temperature towards timing and magnitude of snow accumulations are performed using the numerical permafrost model CryoGrid 3. The energy balance module is forced with local meteorological measurements on the AdM S face and validated with surface temperature measurements at the weather station location. The heat conduction scheme is calibrated with the temperature measurements in the S-exposed borehole. Results show that the snow may be responsible for permafrost presence while it is absent in the surrounding snow free bedrock. The long lasting of the snow at high elevation, where it can remain until the mid-summer has a delaying effect on the seasonal thaw, which contributes to the lowering of the active layer thickness.

Possible Climatic Signal Recorded by Alkenone Distributions in Sediments from Freshwater and Saline Lakes on the Skarvsnes and Skallen Areas, Antarctica

NASA Astrophysics Data System (ADS)

Sawada, K.; Takeda, M.; Takano, Y.

2014-12-01

The distribution of long-chain (C37 - C39) alkenones in marine sediment has been well documented to record paleo-sea surface temperatures. The alkenones were also found in sediments of terrestrial saline lakes, and recently the calibrations of alkenone unsaturation indices - temperature have been established in continental areas. Furthermore, these biomarkers have been identified in lacustrine sediments on high-latitudinal terrestrial areas such as Greenland and Antarctica. In the present study, the alkenones were identified in the lacustrine sediment cores in freshwater (Lake Naga-ike) and saline lakes (Lake Suribati and Lake Funazoko) on the Skarvsnes, and a saline lake (Lake Skallen Oh-ike) on the Skallen, Antarctica. Here, we report that the alkenone distribution in the Antarctic lakes was examined as paleotemperature proxy. C37-C38 Tetra- and tri-unsaturated alkenones and C37 tetra- and tri-unsaturated alkenoates are identified in all sediment samples. The C37 di-unsaturated (C37:2) alkenones can be identified in sediments of surface layers (0-15 cm) of Lake Naga-ike and layers of 160-190 cm depth, in which age is ca. 3000 years BP by 14C dating, in Lake Skallen Ohike, and alkenone unsaturation index (UK37) is analyzed from these sediments. By using a calibration obtained from a culture strain Chrysotila lamellosa as reported by Nakamura et al. (2014), paleotemperatures are calculated to be 9.2-15ºC in surface sediments of Lake Naga-ike and 6.8-8.6ºC in Lake Skallen Oh-ike, respectively. The estimated temperatures are concordant with summer temperature of lake waters observed in Lake Naga-ike. Also, the highest concentrations of the alkenones and alkenoates are observed in deeper (older) sediment layers from Lake Naga-ikes, which has not been connected the ocean and intruded sea water. This implies that the alkenones are originated from indigenous biological organism(s) in Antarctic lake water. The class distributions (unsaturation ratios) of alkenones varied with core depths in Lake Naga-ike and Lake Suribati, whereas these are nearly constant with core depths in Lake Funazoko. These variations presumably depended on changes of climatic and environmental conditions in lake water. Thus, it is suggested that the alkenone proxies can be applicable for Antarctic climate changes.

Thermal analysis of a growing crystal in an aqueous solution

NASA Astrophysics Data System (ADS)

Shiomi, Yuji; Kuroda, Toshio; Ogawa, Tomoya

1980-10-01

The temperature profiles around growing crystals in aqueous solutions of Rochelle salt were measured with accuracy of 0.005°C in a two-dimensional cell which was used for elimination of thermal convection current in the cell. The temperature distribution became stationary after 2 h from injection of the mother liquid, but the concentration distribution did not become stationary because the diffusion constant of solute in the solution was much smaller than the thermal diffusivity of the solution. The growth rate was linearly proportional to the temperature gradient at every growing interface. Since crystal growth is a typical interaction process between thermal and material flow, the experimental results were analysed by such an interaction model. The analysis confirms that the material flow is limited by diffusion within a layer width of about a few hundreds micrometers on the growing interface.

Aerodynamic heating rate distributions induced by trailing edge controls on hypersonic aircraft configurations at Mach 8

NASA Technical Reports Server (NTRS)

Kaufman, L. G., II; Johnson, C. B.

1984-01-01

Aerodynamic surface heating rate distributions in three dimensional shock wave boundary layer interaction flow regions are presented for a generic set of model configurations representative of the aft portion of hypersonic aircraft. Heat transfer data were obtained using the phase change coating technique (paint) and, at particular spanwise and streamwise stations for sample cases, by the thin wall transient temperature technique (thermocouples). Surface oil flow patterns are also shown. The good accuracy of the detailed heat transfer data, as attested in part by their repeatability, is attributable partially to the comparatively high temperature potential of the NASA-Langley Mach 8 Variable Density Tunnel. The data are well suited to help guide heating analyses of Mach 8 aircraft, and should be considered in formulating improvements to empiric analytic methods for calculating heat transfer rate coefficient distributions.

DNS of moderate-temperature gaseous mixing layers laden with multicomponent-fuel drops

NASA Technical Reports Server (NTRS)

Clercq, P. C. Le; Bellan, J.

2004-01-01

A formulation representing multicomponent-fuel (MC-fuel) composition as a Probability Distribution Function (PDF) depending on the molar weight is used to construct a model of a large number of MC-fuel drops evaporating in a gas flow, so as to assess the extent of fuel specificity on the vapor composition.

Analysis of permafrost depths on Mars

NASA Technical Reports Server (NTRS)

Crescenti, G. H.

1984-01-01

The Martian surface thermal characteristics as they effect the thickness and distribution of the permafrost are discussed. Parameters such as temperature mean, maximum, and minimum, heat flow values, and damping depths are derived and applied to a model of the Martian cryosphere. A comparison is made between the permafrost layers of Earth and Mars.

On the effects of fuel leakage on CO production from household burners as revealed by LIF and CARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van der Meij, C.E.; Mokhov, A.V.; Jacobs, R.A.A.M.

Measurements of the distributions of CO, OH, and temperature in flames from two commonly used, commercially available household burners are presented. The local mole fractions of CO and relative distribution of OH have been obtained using laser-induced fluorescence, while the local temperatures have, been determined by coherent anti-Stokes Raman scattering (CARS). For both burners, burning in the open air, CO formation outside the main flames has been observed and attributed to the leakage of fuel-air mixture at the edges of the flame, where the fuel is subsequently converted to CO in the boundary layer between the flame and the surroundings.more » For a rich-premixed, multiblade burner, which gives Bunsen-like flames, the CO produced by the leaking fuel appears to be oxidized by OH arising from the outer cones of adjacent flames, and burns out to low concentrations. In the case of a lean-premixed burner, the CO produced by fuel leakage remains in the cool boundary layer without adequate burnout. Possible consequences for appliance behavior are discussed.« less

Experimental and theoretical investigations of the quality factor for n+p silicon solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garlick, G.F.J.; Kachare, A.H.

1980-01-01

Many N/sup +/P silicon cells made with silicon from different growth techniques have current-voltage relations of the form: I.I/sub 0/ (exp(qV/AkT) - 1) where the quality factor A is non-integral, is >1 and shows a temperature dependence. The dark forward characteristics of such cells have been measured over a range of temperature and the behavior of the factor A derived from them. A new model is presented on the assumption of non-uniform distributions of recombination levels in the junction depletion layer. This model shows good agreement with experimental data. The cells investigated had evaporated top metallization and so the junctionmore » contamination giving the recombination levels is likely to be a result of junction diffusion and is not specific to the metallization processing. The model needs further development and evaluation in order to apply it to the illuminated cell behavior and also to include any effects of distributed sheet resistance in the N/sup +/ layer. 17 refs.« less

Estimating Planetary Boundary Layer Heights from NOAA Profiler Network Wind Profiler Data

NASA Technical Reports Server (NTRS)

Molod, Andrea M.; Salmun, H.; Dempsey, M

2015-01-01

An algorithm was developed to estimate planetary boundary layer (PBL) heights from hourly archived wind profiler data from the NOAA Profiler Network (NPN) sites located throughout the central United States. Unlike previous studies, the present algorithm has been applied to a long record of publicly available wind profiler signal backscatter data. Under clear conditions, summertime averaged hourly time series of PBL heights compare well with Richardson-number based estimates at the few NPN stations with hourly temperature measurements. Comparisons with clear sky reanalysis based estimates show that the wind profiler PBL heights are lower by approximately 250-500 m. The geographical distribution of daily maximum PBL heights corresponds well with the expected distribution based on patterns of surface temperature and soil moisture. Wind profiler PBL heights were also estimated under mostly cloudy conditions, and are generally higher than both the Richardson number based and reanalysis PBL heights, resulting in a smaller clear-cloudy condition difference. The algorithm presented here was shown to provide a reliable summertime climatology of daytime hourly PBL heights throughout the central United States.

A study on post impingement effects of urea-water solution spray on the heated wall of automotive SCR systems

NASA Astrophysics Data System (ADS)

Shahariar, G. M. H.; Wardana, M. K. A.; Lim, O. T.

2018-04-01

The post impingement effects of urea-water solution spray on the heated wall of automotive SCR systems was numerically investigated in a constant volume chamber using STAR CCM+ CFD code. The turbulence flow was modelled by realizable k-ε two-layer model together with standard wall function and all y+ treatment was applied along with two-layer approach. The Eulerian-Lagrangian approach was used for the modelling of multi phase flow. Urea water solution (UWS) was injected onto the heated wall for the wall temperature of 338, 413, 473, 503 & 573 K. Spray development after impinging on the heated wall was visualized and measured. Droplet size distribution and droplet evaporation rates were also measured, which are vital parameters for the system performance but still not well researched. Specially developed user defined functions (UDF) are implemented to simulate the desired conditions and parameters. The investigation reveals that wall temperature has a great impact on spray development after impingement, droplet size distribution and evaporation. Increasing the wall temperature leads to longer spray front projection length, smaller droplet size and faster droplet evaporation which are preconditions for urea crystallization reduction. The numerical model and parameters are validated comparing with experimental data.

Two-dimensional quasi-double-layers in two-electron-temperature, current-free plasmas

NASA Astrophysics Data System (ADS)

Merino, Mario; Ahedo, Eduardo

2013-02-01

The expansion of a plasma with two disparate electron populations into vacuum and channeled by a divergent magnetic nozzle is analyzed with an axisymmetric model. The purpose is to study the formation and two-dimensional shape of a current-free double-layer in the case when the electric potential steepening can still be treated within the quasineutral approximation. The properties of this quasi-double-layer are investigated in terms of the relative fraction of the high-energy electron population, its radial distribution when injected into the nozzle, and the geometry and intensity of the applied magnetic field. The two-dimensional double layer presents a curved shape, which is dependent on the natural curvature of the equipotential lines in a magnetically expanded plasma and the particular radial distribution of high-energy electrons at injection. The double layer curvature increases the higher the nozzle divergence is, the lower the magnetic strength is, and the more peripherally hot electrons are injected. A central application of the study is the operation of a helicon plasma thruster in space. To this respect, it is shown that the curvature of the double layer does not increment the thrust, it does not modify appreciably the downstream divergence of the plasma beam, but it increases the magnetic-to-pressure thrust ratio. The present study does not attempt to cover current-free double layers involving plasmas with multiple populations of positive ions.

Response of water temperature to surface wave effects in the Baltic Sea: simulations with the coupled NEMO-WAM model

NASA Astrophysics Data System (ADS)

Alari, Victor; Staneva, Joanna; Breivik, Øyvind; Bidlot, Jean-Raymond; Mogensen, Kristian; Janssen, Peter

2016-04-01

The effects of wind waves on the Baltic Sea water temperature has been studied by coupling the hydrodynamical model NEMO with the wave model WAM. The wave forcing terms that have been taken into consideration are: Stokes-Coriolis force, seastate dependent energy flux and sea-state dependent momentum flux. The combined role of these processes as well as their individual contributions on simulated temperature is analysed. The results indicate a pronounced effect of waves on surface temperature, on the distribution of vertical temperature and on upwellinǵs. In northern parts of the Baltic Sea a warming of the surface layer occurs in the wave included simulations. This in turn reduces the cold bias between simulated and measured data. The warming is primarily caused by sea-state dependent energy flux. Wave induced cooling is mostly observed in near coastal areas and is mainly due to Stokes-Coriolis forcing. The latter triggers effect of intensifying upwellings near the coasts, depending on the direction of the wind. The effect of sea-state dependent momentum flux is predominantly to warm the surface layer. During the summer the wave induced water temperature changes were up to 1 °C.

Parameter Estimation for a Thin Layer by Measuring Temperature Induced by a Heat Source

DTIC Science & Technology

2013-01-01

Abdelrazaq, The solution of heat conduction equation with mixed boundary conditions, J. Math. Stat. 2 ( 2006 ) 346-350. [2] R. T. Al-Khairy and Z. M. Al-Ofey...Appl. Math. 2009 (2009) Article ID 604695. [3] G. Araya and G. Gutierrez, Analytical solution for a transient, three-dimensional temperature...distribution due to a moving laser beam, Int. J. Heat and Mass Transfer 49 ( 2006 ) 4124-4131. [4] M. Bertolotti and C. Sibilia, Depth and velocity of the

Time dependent shear stress and temperature distribution over an insulated flat plate moving at hypersonic speed.

NASA Technical Reports Server (NTRS)

Rodkiewicz, C. M.; Gupta, R. N.

1971-01-01

The laminar two-dimensional flow over a stepwise accelerated flat plate moving with hypersonic speed at zero angle of attack is analysed. The governing equations in the self-similar form are linearized and solved numerically for small times. The solutions obtained are the deviations of the velocity and the temperature profiles from those of steady state. The presented results may be used to find the first order boundary layer induced pressure on the plate.

Seasonal Differences in Tropical Western Pacific Cloud Ice, Water Vapor and Aerosols Observed From Space During ATTREX-III and POSIDON

NASA Astrophysics Data System (ADS)

Avery, M. A.; Rosenlof, K. H.; Vaughan, M.; Getzewich, B. J.; Thornberry, T. D.; Gao, R. S.; Rollins, A. W.; Woods, S.; Yorks, J. E.; Jensen, E. J.

2017-12-01

Recent aircraft missions sampling the tropical tropopause layer (TTL) in the tropical Western Pacific have provided a wealth of detailed cloud microphysical and associated aerosol, water vapor and temperature data for understanding processes that regulate stratospheric composition and hydration. This presentation seeks to provide a regional context for these measurements by comparing and contrasting active space-based observations from these time periods (Feb-Mar 2014 for ATTREX-III and Oct 2016 for POSIDON), primarily from the Clouds and Aerosol Lidar with Orthogonal Polarization (CALIOP), with the addition of Cloud Profiling Radar (CPR) and the Cloud-Aerosol Transport System (CATS) where these data sets are available. While the ATTREX III and POSIDON aircraft field missions both took place from Guam in the Western Pacific, there were striking differences between the amount, geographical distribution and properties of cirrus clouds and aerosols in the Tropical TTL. In addition to cloud and aerosol amount and location, we present geometric properties, including cloud top heights, transparent cloud and aerosol layer thicknesses and location of the 532 nm backscatter centroid, which is roughly equivalent to the layer vertical center of mass. We also present differences in the distribution of cirrus cloud extinction coefficients and ice water content, and aerosol optical depths, as detected from space, and compare these with in situ measurements and with temperature and water vapor distributions from the Microwave Limb Sounder (MLS). We find that there is more intense convection reaching the tropical tropopause during the POSIDON mission, and consequently more associated cloud ice observed during POSIDON than during ATTREX-III.

A Flexible Temperature Sensor Based on Reduced Graphene Oxide for Robot Skin Used in Internet of Things.

PubMed

Liu, Guanyu; Tan, Qiulin; Kou, Hairong; Zhang, Lei; Wang, Jinqi; Lv, Wen; Dong, Helei; Xiong, Jijun

2018-05-02

Flexible electronics, which can be distributed on any surface we need, are highly demanded in the development of Internet of Things (IoT), robot technology and electronic skins. Temperature is a fundamental physical parameter, and it is an important indicator in many applications. Therefore, a flexible temperature sensor is required. Here, we report a simple method to fabricate three lightweight, low-cost and flexible temperature sensors, whose sensitive materials are reduced graphene oxide (r-GO), single-walled carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs). By comparing linearity, sensitive and repeatability, we found that the r-GO temperature sensor had the most balanced performance. Furthermore, the r-GO temperature sensor showed good mechanical properties and it could be bent in different angles with negligible resistance change. In addition, the performance of the r-GO temperature sensor remained stable under different kinds of pressure and was unaffected by surrounding environments, like humidity or other gases, because of the insulating layer on its sensitive layer. The easy-fabricated process and economy, together with the remarkable performance of the r-GO temperature sensor, suggest that it is suitable for use as a robot skin or used in the environment of IoT.

Characterization of kerosene distribution around the ignition cavity in a scramjet combustor

NASA Astrophysics Data System (ADS)

Li, Xipeng; Liu, Weidong; Pan, Yu; Yang, Leichao; An, Bin; Zhu, Jiajian

2017-05-01

Kerosene distribution before its ignition in a scramjet combustor with dual cavity was measured using kerosene-PLIF under transverse injection upstream of the cavity and different injection pressures. The simulated flight condition is Ma 5.5, and the isolator entrance has a Mach number of 2.52, a total pressure of 1.6 MPa and a stagnation temperature of 1486 K. Effects of injection pressure on fuel distribution characteristics were analyzed. The majority of kerosene is present in the cavity shear layer as well as its upper region. Kerosene extends gradually into the cavity, almost, at a constant angle. Large scale structures are evident on the windward side of kerosene. The cavity shear layer plays an important role in determining the kerosene distribution and its entrainment into the cavity. The middle part of cavity is the most suitable location for ignition as a result of a favorable local equivalent ratio. As the injection pressure increases, the penetration height gets higher with the rate of increase getting slower at higher injection pressure. Meanwhile, the portion of kerosene entrained into cavity through shear layer becomes smaller as injection pressure increases. However, the kerosene entrained into cavity still increase due to the increased mass flow rate of kerosene.

Chlorine mobility during annealing in N2 in ZrO2 and HfO2 films grown by atomic layer deposition

NASA Astrophysics Data System (ADS)

Ferrari, S.; Scarel, G.; Wiemer, C.; Fanciulli, M.

2002-12-01

Atomic layer deposition (ALD) growth of high-κ dielectric films (ZrO2 and HfO2) was performed using ZrCl4, HfCl4, and H2O as precursors. In this work, we use time of flight secondary ion mass spectrometry to investigate the chlorine distribution in ALD grown ZrO2 and HfO2 films, and its evolution during rapid thermal processes in nitrogen atmosphere. Chlorine outdiffusion is found to depend strongly upon annealing temperature and weakly upon the annealing time. While in ZrO2 chlorine concentration is significantly decreased already at 900 °C, in HfO2 it is extremely stable, even at temperatures as high as 1050 °C.

Hot cracking susceptibility of fillers 52 and 82 in alloy 690 welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, W.; Tsai, C.H.

1999-02-01

The hot cracking susceptibility of fillers 52 and 82 in a alloy 690 weldment is analyzed by the Varestraint test. Weld characteristics, microstructure, hardness distribution, and thermal analysis of the two filler metals are also examined. The weld metal of both fillers develops an extremely dense oxide layer. A stainless steel brush cannot remove the oxide layer, and a grinder may be needed between weld passes to assure a sound weld. Differential temperature analysis (DTA) shows that filler 82 has a lower melting point and a wider melting/solidification temperature differential ({Delta} T). These characteristics correlate with greater hot cracking susceptibilitymore » of filler 82 than 52 in Varestraint tests. The hot cracks are intergranular and are caused by elements segregating in grain boundaries.« less

Effect of gold wire bonding process on angular correlated color temperature uniformity of white light-emitting diode.

PubMed

Wu, Bulong; Luo, Xiaobing; Zheng, Huai; Liu, Sheng

2011-11-21

Gold wire bonding is an important packaging process of lighting emitting diode (LED). In this work, we studied the effect of gold wire bonding on the angular uniformity of correlated color temperature (CCT) in white LEDs whose phosphor layers were coated by freely dispersed coating process. Experimental study indicated that different gold wire bonding impacts the geometry of phosphor layer, and it results in different fluctuation trends of angular CCT at different spatial planes in one LED sample. It also results in various fluctuating amplitudes of angular CCT distributions at the same spatial plane for samples with different wire bonding angles. The gold wire bonding process has important impact on angular uniformity of CCT in LED package. © 2011 Optical Society of America

Strong Eu2+ light emission in Eu silicate through Eu3+ reduction in Eu2O3/Si multilayer deposited on Si substrates

PubMed Central

2013-01-01

Eu2O3/Si multilayer nanostructured films are deposited on Si substrates by magnetron sputtering. Transmission electron microscopy and X-ray diffraction measurements demonstrate that multicrystalline Eu silicate is homogeneously distributed in the film after high-temperature treatment in N2. The Eu2+ silicate is formed by the reaction of Eu2O3 and Si layers, showing an intense and broad room-temperature photoluminescence peak centered at 610 nm. It is found that the Si layer thickness in nanostructures has great influence on Eu ion optical behavior by forming different Eu silicate crystalline phases. These findings open a promising way to prepare efficient Eu2+ materials for photonic application. PMID:23618344

Electron temperature gradient scale at collisionless shocks.

PubMed

Schwartz, Steven J; Henley, Edmund; Mitchell, Jeremy; Krasnoselskikh, Vladimir

2011-11-18

Shock waves are ubiquitous in space and astrophysics. They transform directed flow energy into thermal energy and accelerate energetic particles. The energy repartition is a multiscale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. While large scale features of ion heating are known, the electron heating and smaller scale fields remain poorly understood. We determine for the first time the scale of the electron temperature gradient via electron distributions measured in situ by the Cluster spacecraft. Half of the electron heating coincides with a narrow layer several electron inertial lengths (c/ω(pe)) thick. Consequently, the nonlinear steepening is limited by wave dispersion. The dc electric field must also vary over these small scales, strongly influencing the efficiency of shocks as cosmic ray accelerators.

Optimal doping control of magnetic semiconductors via subsurfactant epitaxy.

PubMed

Zeng, Changgan; Zhang, Zhenyu; van Benthem, Klaus; Chisholm, Matthew F; Weitering, Hanno H

2008-02-15

"Subsurfactant epitaxy" is established as a conceptually new approach for introducing manganese as a magnetic dopant into germanium. A kinetic pathway is devised in which the subsurface interstitial sites on Ge(100) are first selectively populated with Mn, while lateral diffusion and clustering on or underneath the surface are effectively suppressed. Subsequent Ge deposition as a capping layer produces a novel surfactantlike phenomenon as the interstitial Mn atoms float towards newly defined subsurface sites at the growth front. Furthermore, the Mn atoms that failed to float upwards are uniformly distributed within the Ge capping layer. The resulting doping levels of order 0.25 at. % would normally be considered too low for ferromagnetic ordering, but the Curie temperature exceeds room temperature by a comfortable margin. Subsurfactant epitaxy thus enables superior dopant control in magnetic semiconductors.

Variability of temperature and chlorophyll of the Iberian Peninsula near costal ecosystem during an upwelling event for the present climate and a future climate scenario

NASA Astrophysics Data System (ADS)

Lopes, José Fortes; Ferreira, Juan A.; Cardoso, Ana Cristina; Rocha, Alfredo C.

2014-01-01

Understanding the importance and the implication of the climate changes on coastal areas may be one of the major issues for this and next centuries. Climate changes may, indeed, impact the nearshore marine ecosystem, as coastal areas are very sensitive to the strength and the variability of the meteorological forcings. The main purpose of this work is to study temperature and phytoplankton distributions along the Portuguese near coastal zone during upwelling events in the present climate conditions and in a future climate scenario. The SRES-A2 IPCC scenario has been considered. We have used a three-dimensional model for coastal and shelf seas, including the following sub-models: hydrodynamical/physical, biological, sediment and contaminant. The forcings are provided by the interactions at the air-sea, considering the wind intensity and direction with the help of the WRF model (Weather Research and Forecast Model) and the coupled atmosphere-ocean model ECHAM5/MPI-OM. Results show that, for the future climate scenario, there is a reinforcement of the southward wind. The responses of the coastal ecosystem corresponds to the reinforcement of both, the southward (up to 10 cm/s) and the westward (up to 6 cm/s) induced upwelling currents. This, in turn generates an enlargement of the near coast upwelled cold layer, extending up to 60 km, as well as the rise of the warm layer temperature (up to 2.0 °C) and the spreading of the phytoplankton offshore. Significant changes in both the Chl-a vertical and the horizontal distribution patterns have been observed, as the nutrient supply to the upper layers depends on the strength of the upwelling, the bottom topography and orography of the coastal. These results confirm that changes in the strength and eventually the frequency of the upwelling favourable wind impact the phytoplankton distribution, which can have significant effect in the distribution and population of the upper level of the trophic chain of the coastal ecosystem.

Thermal Analysis of LED Phosphor Layer

NASA Astrophysics Data System (ADS)

Perera, Ukwatte Lokuliyanage Indika Upendra

Solid-state lighting technology has progressed to a level where light-emitting diode (LED) products are either on par or better than their traditional lighting technology counterparts with respect to efficacy and lifetime. At present, the most common method to create "white" light from LEDs for illumination applications is by using the LED primary radiation and wavelength-converting materials. In this method, the re-emission from the wavelength-converting materials excited by the LED primary radiation is combined with the LED primary radiation to create the "white" light. During this conversion process, heat is generated as a result of conversion inefficiencies and other loss mechanisms in the LED and the wavelength-converting materials. This generated heat, if not properly dissipated, increases the operating temperature, thereby increasing the light output degradation of the system over both the short and long term. The heat generation of the LED and thermal management of the LED have been studied extensively. Methods to effectively dissipate heat from the LEDs and maintain lower LED operating temperature are well understood. However, investigation of factors driving heat generation, the resulting temperature distribution in the phosphor layer, and the influence of the phosphor layer temperature on LED performance and reliability have not received the same focus. The goal of this dissertation was to understand the main factors driving heat and light generation and the transport of light and heat in the wavelength-converting layer of an LED system. Another goal was to understand the interaction between heat and light in the system and to develop and analyze a solution to reduce the wavelength-converting layer operating temperature, thereby improving light output and reliability. Even though past studies have explored generation and transfer separately for light and heat, to the best of the author's knowledge, this is the first study that has analyzed both factors simultaneously to optimize the performance of a phosphor-converted LED system, thus contributing new knowledge to the field. In this dissertation, a theoretical model was developed that modeled both light propagation and heat transfer in the wavelength-converting layer for identifying the factors influencing heat generation. This theoretical model included temperature-dependent phosphor efficiency and light absorption in the phosphor layer geometry. Experimental studies were used to validate the developed model. The model indicated good agreement with the experimental results. The developed theoretical model was then used to model experimental studies. These experiment results were compared with the model predicted results for total radiant power output of LED systems and phosphor layer surface temperature. These comparisons illustrated the effectiveness of a dedicated heat dissipation method in reducing the operating temperature of the wavelength-converting layer, and the contribution of different heat dissipation mechanisms were quantified using the developed numerical model. In addition to these short-term studies, an experiment was conducted to validate the effectiveness of the dedicated wavelength-converting heat sink design to improve system lifetime by reducing phosphor layer operating temperature. The proposed heat sink design decreased the operating temperature of the phosphor layer by ~10°C, improving lifetime by twofold. Finally, this dissertation investigated the potential of the developed theoretical model being used as a tool for prioritizing research tasks and as a design tool during the material selection and system configuration phases.

Two-Flux Green's Function Analysis for Transient Spectral Radiation in a Composite

NASA Technical Reports Server (NTRS)

Siegel, Robert

1996-01-01

An analysis is developed for obtaining transient temperatures in a two-layer semitransparent composite with spectrally dependent properties. Each external boundary of the composite is subjected to radiation and convection. The two-flux radiative transfer equations are solved by deriving a Green's function. This yields the local radiative heat source needed to numerically solve the transient energy equation. An advantage of the two-flux method is that isotropic scattering is included without added complexity. The layer refractive indices are larger than one. This produces internal reflections at the boundaries and the internal interface; the reflections are assumed diffuse. Spectral results using the Green's function method are verified by comparing with numerical solutions using the exact radiative transfer equations. Transient temperature distributions are given to illustrate the effect of radiative heating on one side of a composite with external convective cooling. The protection of a material from incident radiation is illustrated by adding scattering to the layer adjacent to the radiative source.

Strain modulation-enhanced Mg acceptor activation efficiency of Al0.14Ga0.86N/GaN superlattices with AlN interlayer

NASA Astrophysics Data System (ADS)

Wang, Lei; Li, Rui; Li, Ding; Liu, Ningyang; Liu, Lei; Chen, Weihua; Wang, Cunda; Yang, Zhijian; Hu, Xiaodong

2010-02-01

AlN layer was grown as interlayer between undoped GaN and Mg doped Al0.14Ga0.86N/GaN superlattices (SLs) epilayer to modulate the strain distribution between Al0.14Ga0.86N barrier and GaN well layers in SLs sample. Strain relaxation was observed in the SLs sample with AlN interlayer by x-ray diffraction reciprocal space mapping method. The measured hole concentration of SLs sample with AlN interlayer at room temperature was over 1.6×1018 cm-3 but that was only 6.6×1016 cm-3 obtained in SLs sample without AlN interlayer. Variable temperature Hall-effect measurement showed that the acceptor activation energy decreased from 150 to 70 meV after inserting the AlN layer, which indicated that the strain modulation of SLs induced by AlN interlayer was beneficial to the Mg acceptor activation and hole concentration enhancement.

Heat Transfer Retardation at Elevated Temperatures. Phase I. Analysis of Heat Transfer Retardation Configurations and Materials.

DTIC Science & Technology

1983-09-01

perature level effects the flow of the lignin (naturally found in cork) which acts as a binder. Then the bound cork granules are carbonized in an inert...distribution unlimited 17. DISTRIBUTION STATEMENT ( of the abstract entered In Stock 20. it different Inro Report) Same as block 16 I$. SUPPLEMENTARY NOTES 19...applications and was used to estimate the retardation characteristics in terms of an overall thermal resistance and unit weight. Multi-layer

Temporal and spatial temperature distribution in the glabrous skin of rats induced by short-pulse CO2 laser

NASA Astrophysics Data System (ADS)

Lu, Pen-Li; Hsu, Shu-Shen; Tsai, Meng-Li; Jaw, Fu-Shan; Wang, An-Bang; Yen, Chen-Tung

2012-11-01

Pain is a natural alarm that aids the body in avoiding potential danger and can also present as an important indicator in clinics. Infrared laser-evoked potentials can be used as an objective index to evaluate nociception. In animal studies, a short-pulse laser is crucial because it completes the stimulation before escape behavior. The objective of the present study was to obtain the temporal and spatial temperature distributions in the skin caused by the irradiation of a short-pulse laser. A fast speed infrared camera was used to measure the surface temperature caused by a CO2 laser of different durations (25 and 35 ms) and power. The measured results were subsequently implemented with a three-layer finite element model to predict the subsurface temperature. We found that stratum corneum was crucial in the modeling of fast temperature response, and escape behaviors correlated with predictions of temperature at subsurface. Results indicated that the onset latency and duration of activated nociceptors must be carefully considered when interpreting physiological responses evoked by infrared irradiation.

Gradient complex protective coatings for single-crystal turbine blades of high-heat gas turbine engines

NASA Astrophysics Data System (ADS)

Kuznetsov, V. P.; Lesnikov, V. P.; Muboyadzhyan, S. A.; Repina, O. V.

2007-05-01

Complex diffusion-condensation protective coatings characterized by gradient distribution of alloying elements over the thickness due to formation of a diffusion barrier layer on the surface of blades followed by deposition of condensation alloyed layers based on the Ni-Co-Cr-Al-Y system and an external layer based on a NiAl alloyed β-phase and a ZrO2: Y2O3 ceramics are presented. A complex gradient coating possessing unique protective properties at t = 1100-1200°C for single-crystal blades from alloy ZhS36VI for advanced gas turbine engines with gas temperature of 1550°C at the inlet to the turbine is described.

Comparison of Summer and Winter California Central Valley Aerosol Distributions from Lidar and MODIS Measurements

NASA Technical Reports Server (NTRS)

Lewis, Jasper R., Jr.; DeYoung, Russell J.; Chu, D. Allen

2010-01-01

Aerosol distributions from two aircraft lidar campaigns conducted in the California Central Valley are compared in order to identify seasonal variations. Aircraft lidar flights were conducted in June 2003 and February 2008. While the PM2.5 concentration is highest in the winter, the aerosol optical depth measured from MODIS is highest in the summer. A seasonal comparison shows that PM2.5 in the winter can exceed summer PM2.5 by 55%, while summer AOD exceeds winter AOD by 43%. Higher temperatures wildfires in the summer produce elevated aerosol layers that are detected by satellite measurements, but not surface particulate matter monitors. Measurements of the boundary layer height from lidar instruments are necessary to incorporate satellite measurements with air quality measurements.

Temporal variations in supraglacial debris distribution on Baltoro Glacier, Karakoram between 2001 and 2012

NASA Astrophysics Data System (ADS)

Gibson, Morgan J.; Glasser, Neil F.; Quincey, Duncan J.; Mayer, Christoph; Rowan, Ann V.; Irvine-Fynn, Tristram D. L.

2017-10-01

Distribution of supraglacial debris in a glacier system varies spatially and temporally due to differing rates of debris input, transport and deposition. Supraglacial debris distribution governs the thickness of a supraglacial debris layer, an important control on the amount of ablation that occurs under such a debris layer. Characterising supraglacial debris layer thickness on a glacier is therefore key to calculating ablation across a glacier surface. The spatial pattern of debris thickness on Baltoro Glacier has previously been calculated for one discrete point in time (2004) using satellite thermal data and an empirically based relationship between supraglacial debris layer thickness and debris surface temperature identified in the field. Here, the same empirically based relationship was applied to two further datasets (2001, 2012) to calculate debris layer thickness across Baltoro Glacier for three discrete points over an 11-year period (2001, 2004, 2012). Surface velocity and sediment flux were also calculated, as well as debris thickness change between periods. Using these outputs, alongside geomorphological maps of Baltoro Glacier produced for 2001, 2004 and 2012, spatiotemporal changes in debris distribution for a sub-decadal timescale were investigated. Sediment flux remained constant throughout the 11-year period. The greatest changes in debris thickness occurred along medial moraines, the locations of mass movement deposition and areas of interaction between tributary glaciers and the main glacier tongue. The study confirms the occurrence of spatiotemporal changes in supraglacial debris layer thickness on sub-decadal timescales, independent of variation in surface velocity. Instead, variation in rates of debris distribution are primarily attributed to frequency and magnitude of mass movement events over decadal timescales, with climate, regional uplift and erosion rates expected to control debris inputs over centurial to millennial timescales. Inclusion of such spatiotemporal variations in debris thickness in distributed surface energy balance models would increase the accuracy of calculated ablation, leading to a more accurate simulation of glacier mass balance through time, and greater precision in quantification of the response of debris-covered glaciers to climatic change.

Steady state temperature distribution in dermal regions of an irregular tapered shaped human limb with variable eccentricity.

PubMed

Agrawal, M; Pardasani, K R; Adlakha, N

2014-08-01

The investigators in the past have developed some models of temperature distribution in the human limb assuming it as a regular circular or elliptical tapered cylinder. But in reality the limb is not of regular tapered cylindrical shape. The radius and eccentricity are not same throughout the limb. In view of above a model of temperature distribution in the irregular tapered elliptical shaped human limb is proposed for a three dimensional steady state case in this paper. The limb is assumed to be composed of multiple cylindrical substructures with variable radius and eccentricity. The mathematical model incorporates the effect of blood mass flow rate, metabolic activity and thermal conductivity. The outer surface is exposed to the environment and appropriate boundary conditions have been framed. The finite element method has been employed to obtain the solution. The temperature profiles have been computed in the dermal layers of a human limb and used to study the effect of shape, microstructure and biophysical parameters on temperature distribution in human limbs. The proposed model is one of the most realistic model as compared to conventional models as this can be effectively employed to every regular and nonregular structures of the body with variable radius and eccentricity to study the thermal behaviour. Copyright © 2014 Elsevier Ltd. All rights reserved.

Chlorophyll-a thin layers in the Magellan fjord system: The role of the water column stratification

NASA Astrophysics Data System (ADS)

Ríos, Francisco; Kilian, Rolf; Mutschke, Erika

2016-08-01

Fjord systems represent hotspots of primary productivity and organic carbon burial. However, the factors which control the primary production in mid-latitude fjords are poorly understood. In this context, results from the first fine-scale measurements of bio-oceanographic features in the water column of fjords associated with the Strait of Magellan are presented. A submersible fluorescence probe (FP) was used to measure the Chlorophyll-a (Chl-a) concentration in situ, along with conductivity, temperature, hydrostatic pressure (depth) and dissolved oxygen (CTD-O2) of the water column. The Austral spring results of 14 FP-CTD-O2 profiles were used to define the vertical and horizontal patches of the fluorescent pigment distribution and their spatial relations with respect to the observed hydrographic features. Three zones with distinct water structures were defined. In all zones, the 'brown' spectral group (diatoms and dinoflagellates) predominated accounting for >80 wt% of the phytoplankton community. Thin layers with high Chl-a concentration were detected in 50% of the profiles. These layers harbored a substantial amount (30-65 wt%) of the phytoplankton biomass. Stratification was positively correlated to the occurrence of Chl-a thin layers. In stable and highly stratified water columns the integrated Chl-a concentration was higher and frequently located within thin layers whereas well mixed water columns displayed lower values and more homogeneous vertical distribution of Chl-a. These results indicate that mixing/stability processes are important factors accounting to the vertical distribution of Chl-a in Magellan fjords.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shum, Andrew D.; Parkinson, Dilworth Y.; Xiao, Xianghui

The performance of polymer-electrolyte fuel cells is heavily dependent on proper management of liquid water. One particular reason is that liquid water can collect in the gas diffusion layers (GDLs) blocking the reactant flow to the catalyst layer. This results in increased mass-transport losses. At higher temperatures, evaporation of water becomes a dominant water-removal mechanism and specifically phase-change-induced (PCI) flow is present due to thermal gradients. This study used synchrotron based micro X-ray computed tomography (CT) to visualize and quantify the water distribution within gas diffusion layers subject to a thermal gradient. Plotting saturation as a function of through-plane distancemore » quantitatively shows water redistribution, where water evaporates at hotter locations and condenses in colder locations. The morphology of the 2 GDLs on the micro-scale, as well as evaporating water clusters, are resolved, indicating that the GDL voids are slightly prolate, whereas water clusters are oblate. From the mean radii of water distributions and visual inspection, it is observed that larger water clusters evaporate faster than smaller ones.« less

Permafrost Monitoring Sonnblick

NASA Astrophysics Data System (ADS)

Reisenhofer, Stefan; Riedl, Claudia

2014-05-01

Within the project 'Permafrost Monitoring Sonnblick' (PERSON) the spatial distribution of permafrost is investigated by the 'Zentralanstalt für Meteorologie und Geodynamik' (ZAMG) in the Sonnblick area, in the Hohe Tauern in Austria. The aim of PERSON is to identify parameters affecting permafrost (geological, geomorphological, orographical and climatic factors), to determine its spatio-temporal behaviour under present day climate conditions and to estimate its possible future extension under a climate change scenario. PERSON makes use of a permafrost monitoring network that was installed 2005 in the Sonnblick area and is made up by four study sites: On the one hand the spatial extension of permafrost was focused at the ice-dammed lake Pilatus and the rock glacier Zirmsee. On the other hand, at two sites, namely Goldbergspitze and Wintergasse measurements of 'Ground-Surface Temperature' (GST) and 'Bottom Temperatures of the Snow cover' (BTS) are measured. In order to record temperatures in the uppermost layer of the ground and avoid heating by direct solar radiation loggers were buried a few centimetres into the ground or installed in boreholes at depths between 2 and 140 cm. Each of the 'Near Surface Temperature' (NST) borehole mouths is closed up with insulating foam to protect the measurements from atmospheric influence. In addition to these measurements, continuous temperature records from three 20 m deep boreholes located at the southern slope of Hoher Sonnblick are available since 2007, which represent the longest series of its kind in Austria. Furthermore, data from seismic and geoelectric measurements, temperature sensors readings at the surface and extensive meteorological observations from the Sonnblick Observatory are available. Already collected and evaluated data indicate that the thickness of the debris layer around the boreholes reaches a depth of 2 m but no more. The active layer thickness measured in the borehole next to the glacier ranges between 0.7 m and 1.35 m during the past six years and between 0.8 m and 1.04 m from 2008 to 2011 in the borehole nearby the Observatory. The year to year thickness of the active layer mostly depends on depth and duration of the snow cover. Ground temperatures have been slightly increasing during the past three years. The evaluation of the GST data yielded following results: the lower limit of the Permafrost-distribution at the south-east facing slope Goldbergspitze is about 2750m a.s.l. and at the north-west facing slope Wintergasse it is about 2500m a.s.l. Further statements are not yet possible, because of the heterogeneous topography in the study area and the shortness of the records.

Effect of Enhanced Thermal Stability of Alumina Support Layer on Growth of Vertically Aligned Single-Walled Carbon Nanotubes and Their Application in Nanofiltration Membranes.

PubMed

In, Jung Bin; Cho, Kang Rae; Tran, Tung Xuan; Kim, Seok-Min; Wang, Yinmin; Grigoropoulos, Costas P; Noy, Aleksandr; Fornasiero, Francesco

2018-06-07

We investigate the thermal stability of alumina supporting layers sputtered at different conditions and its effect on the growth of aligned single-walled carbon nanotube arrays. Radio frequency magnetron sputtering of alumina under oxygen-argon atmosphere produces a Si-rich alumina alloy film on a silicon substrate. Atomic force microscopy on the annealed catalysts reveals that Si-rich alumina films are more stable than alumina layers with low Si content at the elevated temperatures at which the growth of single-walled carbon nanotubes is initiated. The enhanced thermal stability of the Si-rich alumina layer results in a narrower (< 2.2 nm) diameter distribution of the single-walled carbon nanotubes. Thanks to the smaller diameters of their nanotube pores, membranes fabricated with vertically aligned nanotubes grown on the stable layers display improved ion selectivity.

Electric potential distributions at the interface between plasmasheet clouds

NASA Technical Reports Server (NTRS)

Evans, D. S.; Roth, M.; Lemaire, J.

1987-01-01

At the interface between two plasma clouds with different densities, temperatures, and/or bulk velocities, there are large charge separation electric fields which can be modeled in the framework of a collisionless theory for tangential discontinuities. Two different classes of layers were identified: the first one corresponds to (stable) ion layers which are thicker than one ion Lamor radius; the second one corresponds to (unstable) electron layers which are only a few electron Larmor radii thick. It is suggested that these thin electron layers with large electric potential gradients (up to 400 mV/m) are the regions where large-amplitude electrostatic waves are spontaneously generated. These waves scatter the pitch angles of the ambient plasmasheet electron into the atmospheric loss cone. The unstable electron layers can therefore be considered as the seat of strong pitch angle scattering for the primary auroral electrons.

Effect of Enhanced Thermal Stability of Alumina Support Layer on Growth of Vertically Aligned Single-Walled Carbon Nanotubes and Their Application in Nanofiltration Membranes

NASA Astrophysics Data System (ADS)

In, Jung Bin; Cho, Kang Rae; Tran, Tung Xuan; Kim, Seok-Min; Wang, Yinmin; Grigoropoulos, Costas P.; Noy, Aleksandr; Fornasiero, Francesco

2018-06-01

We investigate the thermal stability of alumina supporting layers sputtered at different conditions and its effect on the growth of aligned single-walled carbon nanotube arrays. Radio frequency magnetron sputtering of alumina under oxygen-argon atmosphere produces a Si-rich alumina alloy film on a silicon substrate. Atomic force microscopy on the annealed catalysts reveals that Si-rich alumina films are more stable than alumina layers with low Si content at the elevated temperatures at which the growth of single-walled carbon nanotubes is initiated. The enhanced thermal stability of the Si-rich alumina layer results in a narrower (< 2.2 nm) diameter distribution of the single-walled carbon nanotubes. Thanks to the smaller diameters of their nanotube pores, membranes fabricated with vertically aligned nanotubes grown on the stable layers display improved ion selectivity.

Flux-transfer losses in helically wound superconducting power cables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clem, John R; Malozemoff, A P

2013-06-25

Minimization of ac losses is essential for economic operation of high-temperature superconductor (HTS) ac power cables. A favorable configuration for the phase conductor of such cables has two counter-wound layers of HTS tape-shaped wires lying next to each other and helically wound around a flexible cylindrical former. However, if magnetic materials such as magnetic substrates of the tapes lie between the two layers, or if the winding pitch angles are not opposite and essentially equal in magnitude to each other, current distributes unequally between the two layers. Then, if at some point in the ac cycle the current of eithermore » of the two layers exceeds its critical current, a large ac loss arises from the transfer of flux between the two layers. A detailed review of the formalism, and its application to the case of paramagnetic substrates including the calculation of this flux-transfer loss, is presented.« less

Surface morphology and interdiffusion of LiF in Alq3-based organic light-emitting devices.

PubMed

Lee, Young Joo; Li, Xiaolong; Kang, Da-Yeon; Park, Seong-Sik; Kim, Jinwoo; Choi, Jeong-Woo; Kim, Hyunjung

2008-09-01

Highly efficient organic light-emitting devices (OLEDs) have been realized by insertion of a thin insulating lithium fluoride (LiF) layer between aluminum (Al) cathode and an electron transport layer, tris-(8-hydroxyquinoline) aluminum (Alq(3)). In this paper, we study the surface morphology of LiF on Alq(3) by synchrotron X-ray scattering and atomic force microscopy (AFM) as a function of thickness of LiF. We also study the interdiffusion of LiF into Al cathode as well as into Alq(3) layer as a function of temperature. Initially, LiF molecules are distributed randomly as clusters on the Alq(3) layer and then gradually form a layer as increasing LiF thickness. The interdiffusion of LiF into Al occurs more actively than into Alq(3) in annealing process. LiF on Alq(3) induces the ordering of Al to (111) direction strongly with increasing LiF thickness.

Refractory lining system for high wear area of high temperature reaction vessel

DOEpatents

Hubble, D.H.; Ulrich, K.H.

1998-04-21

A refractory-lined high temperature reaction vessel comprises a refractory ring lining constructed of refractory brick, a cooler, and a heat transfer medium disposed between the refractory ring lining and the cooler. The refractory brick comprises magnesia (MgO) and graphite. The heat transfer medium contacts the refractory brick and a cooling surface of the cooler, and is composed of a material that accommodates relative movement between the refractory brick and the cooler. The brick is manufactured such that the graphite has an orientation providing a high thermal conductivity in the lengthwise direction through the brick that is higher than the thermal conductivity in directions perpendicular to the lengthwise direction. The graphite preferably is flake graphite, in the range of about 10 to 20 wt %, and has a size distribution selected to provide maximum brick density. The reaction vessel may be used for performing a reaction process including the steps of forming a layer of slag on a melt in the vessel, the slag having a softening point temperature range, and forming a protective frozen layer of slag on the interior-facing surface of the refractory lining in at least a portion of a zone where the surface contacts the layer of slag, the protective frozen layer being maintained at or about the softening point of the slag. 10 figs.

Refractory lining system for high wear area of high temperature reaction vessel

DOEpatents

Hubble, D.H.; Ulrich, K.H.

1998-09-22

A refractory-lined high temperature reaction vessel comprises a refractory ring lining constructed of refractory brick, a cooler, and a heat transfer medium disposed between the refractory ring lining and the cooler. The refractory brick comprises magnesia (MgO) and graphite. The heat transfer medium contacts the refractory brick and a cooling surface of the cooler, and is composed of a material that accommodates relative movement between the refractory brick and the cooler. The brick is manufactured such that the graphite has an orientation providing a high thermal conductivity in the lengthwise direction through the brick that is higher than the thermal conductivity in directions perpendicular to the lengthwise direction. The graphite preferably is flake graphite, in the range of about 10 to 20 wt %, and has a size distribution selected to provide maximum brick density. The reaction vessel may be used for performing a reaction process including the steps of forming a layer of slag on a melt in the vessel, the slag having a softening point temperature range, and forming a protective frozen layer of slag on the interior-facing surface of the refractory lining in at least a portion of a zone where the surface contacts the layer of slag, the protective frozen layer being maintained at or about the softening point of the slag. 10 figs.

Strain-engineering of GaInAsSb overgrown layers and its effects on the optical properties of InAs/GaAs quantum dots

NASA Astrophysics Data System (ADS)

Salhi, A.; Alshaibani, S.; Alaskar, Y.; Albrithen, H.; Albedri, A.; Alyamani, A.

2018-05-01

The effect of antimony incorporation in In0.11Ga0.89As overgrown layers on the optical properties of InAs/GaAs quantum dots grown by molecular beam epitaxy has been studied. The results of photoluminescence, high resolution X-ray diffraction, atomic force microscopy, power and temperature-dependent photoluminescence from 77 K to 300 K have been correlated to characterize the grown samples. The wavelength emission increases with Sb content, and it reaches ∼1367 nm and does not increase further because of Sb incorporation's saturation in the In0.11Ga0.89As layer. To redshift further the wavelength to 1432 nm, a reduction of the growth temperature of the In0.11Ga0.89As1-ySby layer from 500 °C to 440 °C was necessary. This achievement is accompanied by the transformation of the QDs distribution to 2 QDs families. The extracted activation energies suggest that the PL quenching is mainly attributed to the thermal transfer of carriers in the QDs to the higher energy levels in the defects located within the In0.11Ga0.89As1-ySby SRLs. The variation of PL FWHM with temperature was interpreted by carrier thermalization and capture among different QDs within the same QD family or between small and large QD families.

High-quality AlN film grown on a nanosized concave-convex surface sapphire substrate by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Yoshikawa, Akira; Nagatomi, Takaharu; Morishita, Tomohiro; Iwaya, Motoaki; Takeuchi, Tetsuya; Kamiyama, Satoshi; Akasaki, Isamu

2017-10-01

We developed a method for fabricating high-crystal-quality AlN films by combining a randomly distributed nanosized concavo-convex sapphire substrate (NCC-SS) and a three-step growth method optimized for NCC-SS, i.e., a 3-nm-thick nucleation layer (870 °C), a 150-nm-thick high-temperature layer (1250 °C), and a 3.2-μm-thick medium-temperature layer (1110 °C). The NCC-SS is easily fabricated using a conventional metalorganic vapor phase epitaxy reactor equipped with a showerhead plate. The resultant AlN film has a crack-free and single-step surface with a root-mean-square roughness of 0.5 nm. The full-widths at half-maxima of the X-ray rocking curve were 50/250 arcsec for the (0002)/(10-12) planes, revealing that the NCC surface is critical for achieving such a high-quality film. Hexagonal-pyramid-shaped voids at the AlN/NCC-SS interface and confinement of dislocations within the 150-nm-thick high-temperature layer were confirmed. The NCC surface feature and resultant faceted voids play an important role in the growth of high-crystal-quality AlN films, likely via localized and/or disordered growth of AlN at the initial stage, contributing to the alignment of high-crystal-quality nuclei and dislocations.

A MODEL FOR THE TEAR FILM AND OCULAR SURFACE TEMPERATURE FOR PARTIAL BLINKS

PubMed Central

Deng, Quan; Braun, R. J.; Driscoll, T. A.; King-Smith, P. E.

2015-01-01

In this paper, we investigate the dynamics of tear film and the associated temperature variation for partial blinks. We investigate the mechanism of fluid supply during partial blink cycles, and compare the film thickness with observation in vivo. We find that varying the thickness of the fluid layer beneath the moving upper lid improves the agreement for the in vivo measurement of tear film thickness after a half blink. By examining the flux of the fluid, we provide an explanation of this assumption. We also investigate the temperature dynamics both at the ocular surface and inside the simulated anterior chamber. Our simulation results suggest that the ocular surface temperature readjusts rapidly to normal temperature distribution after partial blinks. PMID:25635242

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mensah, P.F.; Stubblefield, M.A.; Pang, S.S.

Thermal characterization of a prepreg fabric used as the bonding material to join composite pipes has been modeled and solved using finite difference modeling (FDM) numerical analysis technique for one dimensional heat transfer through the material. Temperature distributions within the composite pipe joint are predicted. The prepreg material has temperature dependent thermal properties. Thus the resulting boundary value equations are non linear and analytical solutions cannot be obtained. This characterization is pertinent in determining the temperature profile in the prepreg layer during the manufacturing process for optimization purposes. In addition, in order to assess the effects of induced thermal stressmore » in the joint, the temperature profile is needed. The methodology employed in this analysis compares favorably with data from experimentation.« less

Correlation between optical properties surface morphology of porous silicon electrodeposited by Fe3+ ion

NASA Astrophysics Data System (ADS)

Mabrouk, Asma; Lorrain, N.; Haji, M. L.; Oueslati, Meherzi

2015-01-01

In this paper, we analyze the photoluminescence spectra (PL) of porous silicon (PS) layer which is elaborated by electrochemical etching and passivated by Fe3+ ions (PSF) via current density, electro-deposition and temperature measurements. We observe unusual surface morphology of PSF surface and anomalous emission behavior. The PSF surface shows regular distribution of cracks, leaving isolated regions or ;platelets; of nearly uniform thickness. These cracks become more pronounced for high current densities. The temperature dependence of the PL peak energy (EPL) presents anomalous behaviors, i.e., the PL peak energy shows a successive red/blue/redshift (S-shaped behavior) with increasing temperature that we attribute to the existence of strong potential fluctuations induced by the electrochemical etching of PS layers. A competition process between localized and delocalized excitons is used to discuss these PL properties. In this case, the potential confinement plays a key role on the enhancement of PL intensity in PSF. To explain the temperature dependence of the PL intensity, we have proposed a recombination model based on the tunneling and dissociation of excitons.

Transient temperature distributions in simple conducting bodies steadily heated through a laminar boundary layer

NASA Technical Reports Server (NTRS)

Parker, Hermon M

1953-01-01

An analysis is made of the transient heat-conduction effects in three simple semi-infinite bodies: the flat insulated plate, the conical shell, and the slender solid cone. The bodies are assumed to have constant initial temperatures and, at zero time, to begin to move at a constant speed and zero angle of attack through a homogeneous atmosphere. The heat input is taken as that through a laminar boundary layer. Radiation heat transfer and transverse temperature gradients are assumed to be zero. The appropriate heat-conduction equations are solved by an iteration method, the zeroeth-order terms describing the situation in the limit of small time. The method is presented and the solutions are calculated to three orders which are sufficient to give reasonably accurate results when the forward edge has attained one-half the total temperature rise (nose half-rise time). Flight Mach number and air properties occur as parameters in the result. Approximate expressions for the extent of the conduction region and nose half-rise times as functions of the parameters of the problem are presented. (author)

Distribution and removal of organochlorine pesticides in waste clay bricks from an abandoned manufacturing plant using low-temperature thermal desorption technology.

PubMed

Cong, Xin; Li, Fasheng; Kelly, Ryan M; Xue, Nandong

2018-04-01

The distribution of pollutants in waste clay bricks from an organochlorine pesticide-contaminated site was investigated, and removal of the pollutants using a thermal desorption technology was studied. The results showed that the contents of HCHs in both the surface and the inner layer of the bricks were slightly higher than those of DDTs. The total pore volume of the bricks was 37.7 to 41.6% with an increase from external to internal surfaces. The removal efficiency by thermal treatment was within 62 to 83% for HCHs and DDTs in bricks when the temperature was raised from 200 to 250 °C after 1 h. HCHs were more easily removed than DDTs with a higher temperature. Either intraparticle or surface diffusion controls the desorption processes of pollutants in bricks. It was feasible to use the polluted bricks after removal of the pollutants by low-temperature thermal desorption technology.

Defining the Habitat of Pacific Tuna of the Eastern Tropical Pacific from Satellite Imagery, Climatologies, and a Global Circulation Model

NASA Astrophysics Data System (ADS)

Kiefer, D. A.; Hinton, M. G.; Armstrong, E. M.; Harrison, D. P.; Menemenlis, D.; Hu, C.

2016-02-01

With support from NASA's Ecological Forecasting program, we have developed a Tuna Stock Assessment Support System, which merges time series of satellite imagery, a global ocean circulation model, climatology from field surveys, and fisheries data on catch and effort. The purpose of this software is to extract information on the habitat of skipjack, bigeye, and yellowfin tuna in the Eastern Tropical Pacific. The support system is based upon a 50-year record of catch and effort from long-line and purse seine vessels provide by the Inter-American Tropical Tuna Commission. This database, which covers thousands of kilometers of ocean surface, provides monthly information at a 1 degree spatial resolution for the purse seine fleet and 5 degree resolution for the long line fishery. This data is then merged in time and space with satellite imagery of sea surface temperature, chlorophyll, and height, as well as NODC climatologies of oxygen concentration and temperature, and output from NASA's ECCO-2 global circulation model, which provides 3-dimensional simulations of water density, current velocity, mixed layer depth, and sea surface height. Our analyses have yielded a broad range of understanding of the habitat and dynamics both the fish and the fisherman. The purse seine ground, which targets younger tuna, is constrained to waters where the hypoxic layer is shallow. The longline fishery, which targets older tuna, is not constrained by the hypoxic layer and has a much larger distribution. We have characterized the preferences of each species to environmental variables including the depth of the hypoxic layer, the depth of the water column, as well as sea surface height, temperature, and chlorophyll concentration. Finally, the analyses have revealed information on local depletion by fishing, the size distribution of the schools of younger fish, and the impact of ENSO on fishing activities.

Development of a thermal and structural analysis procedure for cooled radial turbines

NASA Technical Reports Server (NTRS)

Kumar, Ganesh N.; Deanna, Russell G.

1988-01-01

A procedure for computing the rotor temperature and stress distributions in a cooled radial turbine is considered. Existing codes for modeling the external mainstream flow and the internal cooling flow are used to compute boundary conditions for the heat transfer and stress analyses. An inviscid, quasi three-dimensional code computes the external free stream velocity. The external velocity is then used in a boundary layer analysis to compute the external heat transfer coefficients. Coolant temperatures are computed by a viscous one-dimensional internal flow code for the momentum and energy equation. These boundary conditions are input to a three-dimensional heat conduction code for calculation of rotor temperatures. The rotor stress distribution may be determined for the given thermal, pressure and centrifugal loading. The procedure is applied to a cooled radial turbine which will be tested at the NASA Lewis Research Center. Representative results from this case are included.

A Numerical Model Study of Nocturnal Drainage Flows with Strong Wind and Temperature Gradients.

NASA Astrophysics Data System (ADS)

Yamada, T.; Bunker, S.

1989-07-01

A second-moment turbulence-closure model described in Yamada and Bunker is used to simulate nocturnal drainage flows observed during the 1984 ASCOT field expedition in Brush Creek, Colorado. In order to simulate the observed strong wind directional shear and temperature gradients, two modifications are added to the model. The strong wind directional shear was maintained by introducing a `nudging' term in the equation of motion to guide the modeled winds in the layers above the ridge top toward the observed wind direction. The second modification was accomplished by reformulating the conservation equation for the potential temperature in such a way that only the deviation from the horizontally averaged value was prognostically computed.The vegetation distribution used in this study is undoubtedly crude. Nevertheless, the present simulation suggests that tall tree canopy can play an important role in producing inhomogeneous wind distribution, particularly in the levels below the canopy top.

Development of a thermal and structural analysis procedure for cooled radial turbines

NASA Technical Reports Server (NTRS)

Kumar, Ganesh N.; Deanna, Russell G.

1988-01-01

A procedure for computing the rotor temperature and stress distributions in a cooled radial turbine are considered. Existing codes for modeling the external mainstream flow and the internal cooling flow are used to compute boundary conditions for the heat transfer and stress analysis. The inviscid, quasi three dimensional code computes the external free stream velocity. The external velocity is then used in a boundary layer analysis to compute the external heat transfer coefficients. Coolant temperatures are computed by a viscous three dimensional internal flow cade for the momentum and energy equation. These boundary conditions are input to a three dimensional heat conduction code for the calculation of rotor temperatures. The rotor stress distribution may be determined for the given thermal, pressure and centrifugal loading. The procedure is applied to a cooled radial turbine which will be tested at the NASA Lewis Research Center. Representative results are given.

Root growth dynamics linked to above-ground growth in walnut (Juglans regia).

PubMed

Contador, Maria Loreto; Comas, Louise H; Metcalf, Samuel G; Stewart, William L; Porris Gomez, Ignacio; Negron, Claudia; Lampinen, Bruce D

2015-07-01

Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature. Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia 'Chandler') using minirhizotron techniques. Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production. The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

High-Resolution Fibre-Optic Temperature Sensing: A New Tool to Study the Two-Dimensional Structure of Atmospheric Surface-Layer Flow

NASA Astrophysics Data System (ADS)

Thomas, Christoph K.; Kennedy, Adam M.; Selker, John S.; Moretti, Ayla; Schroth, Martin H.; Smoot, Alexander R.; Tufillaro, Nicholas B.; Zeeman, Matthias J.

2012-02-01

We present a novel approach based on fibre-optic distributed temperature sensing (DTS) to measure the two-dimensional thermal structure of the surface layer at high resolution (0.25 m, ≈0.5 Hz). Air temperature observations obtained from a vertically-oriented fibre-optics array of approximate dimensions 8 m × 8 m and sonic anemometer data from two levels were collected over a short grass field located in the flat bottom of a wide valley with moderate surface heterogeneity. The objectives of the study were to evaluate the potential of the DTS technique to study small-scale processes in the surface layer over a wide range of atmospheric stability, and to analyze the space-time dynamics of transient cold-air pools in the calm boundary layer. The time response and precision of the fibre-based temperatures were adequate to resolve individual sub-metre sized turbulent and non-turbulent structures, of time scales of seconds, in the convective, neutral, and stable surface layer. Meaningful sensible heat fluxes were computed using the eddy-covariance technique when combined with vertical wind observations. We present a framework that determines the optimal environmental conditions for applying the fibre-optics technique in the surface layer and identifies areas for potentially significant improvements of the DTS performance. The top of the transient cold-air pool was highly non-stationary indicating a superposition of perturbations of different time and length scales. Vertical eddy scales in the strongly stratified transient cold-air pool derived from the DTS data agreed well with the buoyancy length scale computed using the vertical velocity variance and the Brunt-Vaisala frequency, while scales for weak stratification disagreed. The high-resolution DTS technique opens a new window into spatially sampling geophysical fluid flows including turbulent energy exchange.

Active constrained layer damping of geometrically nonlinear vibrations of functionally graded plates using piezoelectric fiber-reinforced composites

NASA Astrophysics Data System (ADS)

Panda, Satyajit; Ray, M. C.

2008-04-01

In this paper, a geometrically nonlinear dynamic analysis has been presented for functionally graded (FG) plates integrated with a patch of active constrained layer damping (ACLD) treatment and subjected to a temperature field. The constraining layer of the ACLD treatment is considered to be made of the piezoelectric fiber-reinforced composite (PFRC) material. The temperature field is assumed to be spatially uniform over the substrate plate surfaces and varied through the thickness of the host FG plates. The temperature-dependent material properties of the FG substrate plates are assumed to be graded in the thickness direction of the plates according to a power-law distribution while the Poisson's ratio is assumed to be a constant over the domain of the plate. The constrained viscoelastic layer of the ACLD treatment is modeled using the Golla-Hughes-McTavish (GHM) method. Based on the first-order shear deformation theory, a three-dimensional finite element model has been developed to model the open-loop and closed-loop nonlinear dynamics of the overall FG substrate plates under the thermal environment. The analysis suggests the potential use of the ACLD treatment with its constraining layer made of the PFRC material for active control of geometrically nonlinear vibrations of FG plates in the absence or the presence of the temperature gradient across the thickness of the plates. It is found that the ACLD treatment is more effective in controlling the geometrically nonlinear vibrations of FG plates than in controlling their linear vibrations. The analysis also reveals that the ACLD patch is more effective for controlling the nonlinear vibrations of FG plates when it is attached to the softest surface of the FG plates than when it is bonded to the stiffest surface of the plates. The effect of piezoelectric fiber orientation in the active constraining PFRC layer on the damping characteristics of the overall FG plates is also discussed.

[Spatial-temporal distribution of bigeye tuna Thunnus obesus in the tropical Atlantic Ocean based on Argo data].

PubMed

Yang, Sheng-long; Jin, Shao-fei; Hua, Cheng-jun; Dai, Yang

2015-02-01

In order to analyze the correlation between spatial-temporal distribution of the bigeye tuna ( Thunnus obesus) and subsurface factors, the study explored the isothermal distribution of subsurface temperatures in the bigeye tuna fishing grounds in the tropical Atlantic Ocean, and built up the spatial overlay chart of the isothermal lines of 9, 12, 13 and 15 °C and monthly CPUE (catch per unit effort) from bigeye tuna long-lines. The results showed that the bigeye tuna mainly distributed in the water layer (150-450 m) below the lower boundary depth of thermocline. At the isothermal line of 12 °C, the bigeye tuna mainly lived in the water layer of 190-260 m, while few individuals were found at water depth more than 400 m. As to the 13 °C isothermal line, high CPUE often appeared at water depth less than 250 m, mainly between 150-230 m, while no CPUE appeared at water depth more than 300 m. The optimum range of subsurface factors calculated by frequency analysis and empirical cumulative distribution function (ECDF) exhibited that the optimum depth range of 12 °C isothermal depth was 190-260 m and the 13 °C isothermal depth was 160-240 m, while the optimum depth difference range of 12 °C isothermal depth was -10 to 100 m and the 13 °C isothermal depth was -40 to 60 m. The study explored the optimum range of subsurface factors (water temperature and depth) that drive horizontal and vertical distribution of bigeye tuna. The preliminary result would help to discover the central fishing ground, instruct fishing depth, and provide theoretical and practical references for the longline production and resource management of bigeye tuna in the Atlantic Ocean.

Synthesis and characterization of magnetic poly(divinyl benzene)/Fe3O4, C/Fe3O4/Fe, and C/Fe onionlike fullerene micrometer-sized particles with a narrow size distribution.

PubMed

Snovski, Ron; Grinblat, Judith; Margel, Shlomo

2011-09-06

Magnetic poly(divinyl benzene)/Fe(3)O(4) microspheres with a narrow size distribution were produced by entrapping the iron pentacarbonyl precursor within the pores of uniform porous poly(divinyl benzene) microspheres prepared in our laboratory, followed by the decomposition in a sealed cell of the entrapped Fe(CO)(5) particles at 300 °C under an inert atmosphere. Magnetic onionlike fullerene microspheres with a narrow size distribution were produced by annealing the obtained PDVB/Fe(3)O(4) particles at 500, 600, 800, and 1100 °C, respectively, under an inert atmosphere. The formation of carbon graphitic layers at low temperatures such as 500 °C is unique and probably obtained because of the presence of the magnetic iron nanoparticles. The annealing temperature allowed control of the composition, size, size distribution, crystallinity, porosity, and magnetic properties of the produced magnetic microspheres. © 2011 American Chemical Society

Localized Electrical Heating System for Various Types of Buildings

NASA Astrophysics Data System (ADS)

Shelehov, I. Y.; Smirnov, E. I.; Inozemsev, V. P.

2017-11-01

The article presents an overview of the factors determining the establishment of zones with high temperature in industrial, public and administrative buildings. The authors state the task on the improvement of the electric energy use efficiency and cost savings associated with the heating of these buildings by infrared electric heater devices. Materials and methods: The experiments were conducted in a room with the sizes of 3x6 m2 with a ceiling height of 3 m, the concrete floor was covered with laminate, in which increments of 250 mm were drilled and installed the thermocouple. In the process, had used the patented heating element with distributed heating layer. Signals from the thermocouples were recorded by instruments of the firm “ARIES” brand TPM138 with the standard software delivered together with devices (Owen Process Manager). The obtained distributions of the temperature fields were imported into MS Excel. Control voltage, current consumption, power was carried out by the device of firm “ARIES” brand of IMS. The results of the study: the article defines the purpose of the study and carried out the characterization of infrared heaters with various types of heating elements. The authors detail the main parameters of different types of infrared heaters, evaluated its possibility for application in other areas where the need to create areas of increased temperature. Discussion and conclusion: the result of this work it was determined that heating appliances that use patented heating element with distributed heating layer, improve thermal performance and bring you maximum comfort at a much greater distance compared to existing similar devices

Study of density distribution in a near-critical simple fluid (19-IML-1)

NASA Technical Reports Server (NTRS)

Michels, Teun

1992-01-01

This experiment uses visual observation, interferometry, and light scattering techniques to observe and analyze the density distribution in SF6 above and below the critical temperature. Below the critical temperature, the fluid system is split up into two coexisting phases, liquid and vapor. The spatial separation of these phases on earth, liquid below and vapor above, is not an intrinsic property of the fluid system; it is merely an effect of the action of the gravity field. At a fixed temperature, the density of each of the coexisting phases is in principle fixed. However, near T sub c where the fluid is strongly compressible, gravity induced hydrostatic forces will result in a gradual decrease in density with increasing height in the sample container. This hydrostatic density profile is even more pronounced in the one phase fluid at temperatures slightly above T sub c. The experiment is set up to study the intrinsic density distributions and equilibration rates of a critical sample in a small container. Interferometry will be used to determine local density and thickness of surface and interface layers. The light scattering data will reveal the size of the density fluctuations on a microscopic scale.

Wind-tunnel experiments of turbulent flow over a surface-mounted 2-D block in a thermally-stratified boundary layer

NASA Astrophysics Data System (ADS)

Zhang, Wei; Markfort, Corey; Porté-Agel, Fernando

2014-11-01

Turbulent flows over complex surface topography have been of great interest in the atmospheric science and wind engineering communities. The geometry of the topography, surface roughness and temperature characteristics as well as the atmospheric thermal stability play important roles in determining momentum and scalar flux distribution. Studies of turbulent flow over simplified topography models, under neutrally stratified boundary-layer conditions, have provided insights into fluid dynamics. However, atmospheric thermal stability has rarely been considered in laboratory experiments, e.g., wind-tunnel experiments. Series of wind-tunnel experiments of thermally-stratified boundary-layer flow over a surface-mounted 2-D block, in a well-controlled boundary-layer wind tunnel, will be presented. Measurements using high-resolution PIV, x-wire/cold-wire anemometry and surface heat flux sensors were conducted to quantify the turbulent flow properties, including the size of the recirculation zone, coherent vortex structures and the subsequent boundary layer recovery. Results will be shown to address thermal stability effects on momentum and scalar flux distribution in the wake, as well as dominant mechanism of turbulent kinetic energy generation and consumption. The authors gratefully acknowledge funding from the Swiss National Foundation (Grant 200021-132122), the National Science Foundation (Grant ATM-0854766) and NASA (Grant NNG06GE256).

The formation of organic (propolis films)/inorganic (layered crystals) interfaces for optoelectronic applications

NASA Astrophysics Data System (ADS)

Drapak, S. I.; Bakhtinov, A. P.; Gavrylyuk, S. V.; Kovalyuk, Z. D.; Lytvyn, O. S.

2008-10-01

Propolis (honeybee glue) organic films were prepared from an alcoholic solution on the surfaces of inorganic layered semiconductors (indium, gallium and bismuth selenides). Atomic force microscopy (AFM) and X-ray diffraction (XRD) are used to characterize structural properties of an organic/inorganic interfaces. It is shown that nanodimensional linear defects and nanodimensional cavities of various shapes are formed on the van der Waals (VDW) surfaces of layered crystals as a result of chemical interaction between the components of propolis (flavonoids, aminoacids and phenolic acids) and the VDW surfaces as well as deformation interaction between the VDW surfaces and propolis films during their polymerization. The nanocavities are formed as a result of the rupture of strong covalent bonds in the upper layers of layered crystals and have the shape of hexagons or triangles in the (0001) plane. The shape, lateral size and distribution of nanodimensional defects on the VDW surfaces depends on the type of crystals, the magnitude and distribution of surface stresses. We have obtained self-organized nanofold structures of propolis/InSe interface. It is established that such heterostructures have photosensitivity in the infrared range hν<1.2 eV (the values of energy gap are 1.2 eV for InSe and 3.07 eV for propolis films at room temperature).

Aircraft microwave observations and simulations of deep convection from 18 to 183 GHz. II - Model results

NASA Technical Reports Server (NTRS)

Yeh, Hwa-Young M.; Prasad, N.; Mack, Robert A.; Adler, Robert F.

1990-01-01

In this June 29, 1986 case study, a radiative transfer model is used to simulate the aircraft multichannel microwave brightness temperatures presented in the Adler et al. (1990) paper and to study the convective storm structure. Ground-based radar data are used to derive hydrometeor profiles of the storm, based on which the microwave upwelling brightness temperatures are calculated. Various vertical hydrometeor phase profiles and the Marshall and Palmer (M-P, 1948) and Sekhon and Srivastava (S-S, 1970) ice particle size distributions are experimented in the model. The results are compared with the aircraft radiometric data. The comparison reveals that the M-P distribution well represents the ice particle size distribution, especially in the upper tropospheric portion of the cloud; the S-S distribution appears to better simulate the ice particle size at the lower portion of the cloud, which has a greater effect on the low-frequency microwave upwelling brightness temperatures; and that, in deep convective regions, significant supercooled liquid water (about 0.5 g/cu m) may be present up to the -30 C layer, while in less convective areas, frozen hydrometeors are predominant above -10 C level.

Molecular dynamics simulation of temperature effects on low energy near-surface cascades and surface damage in Cu

NASA Astrophysics Data System (ADS)

Zhu, Guo; Sun, Jiangping; Guo, Xiongxiong; Zou, Xixi; Zhang, Libin; Gan, Zhiyin

2017-06-01

The temperature effects on near-surface cascades and surface damage in Cu(0 0 1) surface under 500 eV argon ion bombardment were studied using molecular dynamics (MD) method. In present MD model, substrate system was fully relaxed for 1 ns and a read-restart scheme was introduced to save total computation time. The temperature dependence of damage production was calculated. The evolution of near-surface cascades and spatial distribution of adatoms at varying temperature were analyzed and compared. It was found that near-surface vacancies increased with temperature, which was mainly due to the fact that more atoms initially located in top two layers became adatoms with the decrease of surface binding energy. Moreover, with the increase of temperature, displacement cascades altered from channeling-like structure to branching structure, and the length of collision sequence decreased gradually, because a larger portion of energy of primary knock-on atom (PKA) was scattered out of focused chain. Furthermore, increasing temperature reduced the anisotropy of distribution of adatoms, which can be ascribed to that regular registry of surface lattice atoms was changed with the increase of thermal vibration amplitude of surface atoms.

Environmental and biological characteristics of Atlantic bluefin tuna and albacore spawning habitats based on their egg distributions

NASA Astrophysics Data System (ADS)

Reglero, Patricia; Santos, Maria; Balbín, Rosa; Laíz-Carrión, Raul; Alvarez-Berastegui, Diego; Ciannelli, Lorenzo; Jiménez, Elisa; Alemany, Francisco

2017-06-01

Tuna spawning habitats are traditionally characterized using data sets of larvae or gonads from mature adults and concurrent environmental variables. Data on egg distributions have never previously been used since molecular analyses are mandatory to identify tuna eggs to species level. However, in this study we use molecularly derived egg distribution data, in addition to larval data, to characterize hydrographic and biological drivers of the spatial distribution of eggs and larvae of bluefin Thunnus thynnus and albacore tuna Thunnus alalunga in the Balearic Sea, a main spawning area of these species in the Mediterranean. The effects of the hydrography, characterized by salinity, temperature and geostrophic velocity, on the spatial distributions of the eggs and larvae are investigated. Three biological variables are used to describe the productivity in the area: chlorophyll a in the mixed layer, chlorophyll a in the deep chlorophyll maximum and mesozooplankton biomass in the mixed layer. Our results point to the importance of salinity fronts and temperatures above a minimum threshold in shaping the egg and larval distribution of both species. The spatial distribution of the biotic variables was very scattered, and they did not emerge as significant variables in the presence-absence models. However, they became significant when modeling egg and larval abundances. The lack of correlation between the three biotic variables challenges the use of chlorophyll a to describe trophic scenarios for the larvae and suggests that the spatial distribution of resources is not persistent in time. The different patterns in relation to biotic variables across species and stages found in this and other studies indicate a still elusive understanding of the link between trophic levels involving tuna early larval stages. Our ability to improve short-term forecasting and long-term predictions of climate effects on the egg and larval distributions is discussed based on the consistency of the environmentally driven spatial patterns for the two species.

Rocket-borne thermal plasma instrument "MIPEX" for the ionosphere D, E layer in-situ measurements

NASA Astrophysics Data System (ADS)

Fang, H. K.; Chen, A. B. C.; Lin, C. C. H.; Wu, T. J.; Liu, K. S.; Chuang, C. W.

2017-12-01

In this presentation, the design concepts, performances and status of a thermal plasma particle instrument package "Mesosphere and Ionosphere Plasma Exploration complex (MIPEX)", which is going to be installed onboard a NSPO-funded hybrid rocket, to investigate the electrodynamic processes in ionosphere D, E layers above Taiwan are reported. MIPEX is capable of measuring plasma characteristics including ion temperature, ion composition, ion drift, electron temperature and plasma density at densities as low as 1-10 cm-1. This instrument package consists of an improved retarding potential analyzer with a channel electron multiplier (CEM), a simplified ion drift meter and a planar Langmuir probe. To achieve the working atmospheric pressure of CEM at the height of lower D layer ( 70km), a portable vacuum pump is also placed in the package. A prototype set of the MIPEX has been developed and tested in the Space Plasma Operation Chamber (SPOC) at NCKU, where in ionospheric plasma is generated by back-diffusion plasma sources. A plasma density of 10-106 cm-1, ion temperature of 300-1500 K and electron temperature of 1000-3000K is measured and verified. Limited by the flight platform and the performance of the instruments, the in-situ plasma measurements at the Mesosphere and lower Thermosphere is very challenging and rare. MIPEX is capable of extending the altitude of the effective plasma measurement down to 70 km height and this experiment can provide unique high-quality data of the plasma environment to explore the ion distribution and the electrodynamic processes in the Ionosphere D, E layers at dusk.

Effect of shell thickness on the exchange bias blocking temperature and coercivity in Co-CoO core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Thomas, S.; Reethu, K.; Thanveer, T.; Myint, M. T. Z.; Al-Harthi, S. H.

2017-08-01

The exchange bias blocking temperature distribution of naturally oxidized Co-CoO core-shell nanoparticles exhibits two distinct signatures. These are associated with the existence of two magnetic entities which are responsible for the temperature dependence of an exchange bias field. One is from the CoO grains which undergo thermally activated magnetization reversal. The other is from the disordered spins at the Co-CoO interface which exhibits spin-glass-like behavior. We investigated the oxide shell thickness dependence of the exchange bias effect. For particles with a 3 nm thick CoO shell, the predominant contribution to the temperature dependence of exchange bias is the interfacial spin-glass layer. On increasing the shell thickness to 4 nm, the contribution from the spin-glass layer decreases, while upholding the antiferromagnetic grain contribution. For samples with a 4 nm CoO shell, the exchange bias training was minimal. On the other hand, 3 nm samples exhibited both the training effect and a peak in coercivity at an intermediate set temperature Ta. This is explained using a magnetic core-shell model including disordered spins at the interface.

Surface treatment to form a dispersed Y2O3 layer on Zircaloy-4 tubes

NASA Astrophysics Data System (ADS)

Jung, Yang-Il; Kim, Hyun-Gil; Guim, Hwan-Uk; Lim, Yoon-Soo; Park, Jung-Hwan; Park, Dong-Jun; Yang, Jae-Ho

2018-01-01

Zircaloy-4 is a traditional zirconium-based alloy developed for application in nuclear fuel cladding tubes. The surfaces of Zircaloy-4 tubes were treated using a laser beam to increase their mechanical strength. Laser beam scanning of a tube coated with yttrium oxide (Y2O3) resulted in the formation of a dispersed oxide layer in the tube's surface region. Y2O3 particles penetrated the Zircaloy-4 during the laser treatment and were distributed uniformly in the surface region. The thickness of the dispersed oxide layer varied from 50 to 140 μm depending on the laser beam trajectory. The laser treatment also modified the texture of the tube. The preferred basal orientation along the normal to the tube surface disappeared, and a random structure appeared after laser processing. The most obvious result was an increase in the mechanical strength. The tensile strength of Zircaloy-4 increased by 10-20% with the formation of the dispersed oxide layer. The compressive yield stress also increased, by more than 15%. Brittle fracture was observed in the surface-treated samples during tensile and compressive deformation at room temperature; however, the fracture behavior was changed in ductile at elevated temperatures.

Balloon-borne measurements of aerosol, condensation nuclei, and cloud particles in the stratosphere at McMurdo Station, Antarctica, during the spring of 1987

NASA Technical Reports Server (NTRS)

Hofmann, D. J.; Rosen, J. M.; Harder, J. W.; Hereford, J. V.

1989-01-01

Measurements of the vertical profile of particles with condensation nuclei counters and eight channel aerosol detectors at McMurdo Station, Antarctica, in 1987 verified observations made in 1986 concerning the absence of upwelling in the polar vortex and the presence of a condensation nuclei layer in conjunction with the ozone hole region. New observations of a bimodal aerosol size distribution, consisting of a large-particle mode mixed in with the small-particle sulfate mode, at temperatures below -79 C are consistent with the presence of nitric acid-water particles at low concentrations. Higher concentrations of large particles were observed in association with nacreous clouds. An unusual particle layer which contained enhanced concentrations of both the small-particle (sulfate) mode and the large-particle (nitric acid) mode was detected at temperatures below -85 C, suggesting simultaneous nucleation and growth phenomena. The vortex condensation nuclei layer was observed to form at the same time as the ozone hole, indicating that formation of the layer is triggered by photochemical processes and may be important in controlling ozone depletion above 22 km.

Absolute measurements of the triplet-triplet annihilation rate and the charge-carrier recombination layer thickness in working polymer light-emitting diodes based on polyspirobifluorene

NASA Astrophysics Data System (ADS)

Rothe, C.; Al Attar, H. A.; Monkman, A. P.

2005-10-01

The triplet exciton densities in electroluminescent devices prepared from two polyspirobifluorene derivatives have been investigated by means of time-resolved transient triplet absorption as a function of optical and electrical excitation power at 20 K. Because of the low mobility of the triplet excitons at this temperature, the triplet generation profile within the active polymer layer is preserved throughout the triplet lifetime and as a consequence the absolute triplet-triplet annihilation efficiency is not homogeneously distributed but depends on position within the active layer. This then gives a method to measure the charge-carrier recombination layer after electrical excitation relative to the light penetration depth, which is identical to the triplet generation layer after optical excitation. With the latter being obtained from ellipsometry, an absolute value of 5 nm is found for the exciton formation layer in polyspirobifluorene devices. This layer increases to 11 nm if the balance between the electron and the hole mobility is improved by chemically modifying the polymer backbone. Also, and consistent with previous work, triplet diffusion is dispersive at low temperature. As a consequence of this, the triplet-triplet annihilation rate is not a constant in the classical sense but depends on the triplet excitation dose. At 20 K and for typical excitation doses, absolute values of the latter rate are of the order of 10-14cm3s-1 .

Modeling transient heat transfer in nuclear waste repositories.

PubMed

Yang, Shaw-Yang; Yeh, Hund-Der

2009-09-30

The heat of high-level nuclear waste may be generated and released from a canister at final disposal sites. The waste heat may affect the engineering properties of waste canisters, buffers, and backfill material in the emplacement tunnel and the host rock. This study addresses the problem of the heat generated from the waste canister and analyzes the heat distribution between the buffer and the host rock, which is considered as a radial two-layer heat flux problem. A conceptual model is first constructed for the heat conduction in a nuclear waste repository and then mathematical equations are formulated for modeling heat flow distribution at repository sites. The Laplace transforms are employed to develop a solution for the temperature distributions in the buffer and the host rock in the Laplace domain, which is numerically inverted to the time-domain solution using the modified Crump method. The transient temperature distributions for both the single- and multi-borehole cases are simulated in the hypothetical geological repositories of nuclear waste. The results show that the temperature distributions in the thermal field are significantly affected by the decay heat of the waste canister, the thermal properties of the buffer and the host rock, the disposal spacing, and the thickness of the host rock at a nuclear waste repository.

Mixed convection-radiation interaction in boundary-layer flow over horizontal surfaces

NASA Astrophysics Data System (ADS)

Ibrahim, F. S.; Hady, F. M.

1990-06-01

The effect of buoyancy forces and thermal radiation on the steady laminar plane flow over an isothermal horizontal flat plate is investigated within the framework of first-order boundary-layer theory, taking into account the hydrostatic pressure variation normal to the plate. The fluid considered is a gray, absorbing-emitting but nonscattering medium, and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. Both a hot surface facing upward and a cold surface facing downward are considered in the analysis. Numerical results for the local Nusselt number, the local wall shear stress, the local surface heat flux, as well as the velocity and temperature distributions are presented for gases with a Prandtl number of 0.7 for various values of the radiation-conduction parameter, the buoyancy parameter, and the temperature ratio parameter.

The effect of convective boundary condition on MHD mixed convection boundary layer flow over an exponentially stretching vertical sheet

NASA Astrophysics Data System (ADS)

Isa, Siti Suzilliana Putri Mohamed; Arifin, Norihan Md.; Nazar, Roslinda; Bachok, Norfifah; Ali, Fadzilah Md

2017-12-01

A theoretical study that describes the magnetohydrodynamic mixed convection boundary layer flow with heat transfer over an exponentially stretching sheet with an exponential temperature distribution has been presented herein. This study is conducted in the presence of convective heat exchange at the surface and its surroundings. The system is controlled by viscous dissipation and internal heat generation effects. The governing nonlinear partial differential equations are converted into ordinary differential equations by a similarity transformation. The converted equations are then solved numerically using the shooting method. The results related to skin friction coefficient, local Nusselt number, velocity and temperature profiles are presented for several sets of values of the parameters. The effects of the governing parameters on the features of the flow and heat transfer are examined in detail in this study.

Amendment to "Analytical Solution for the Convectively-Mixed Atmospheric Boundary Layer": Inclusion of Subsidence

NASA Astrophysics Data System (ADS)

Ouwersloot, H. G.; de Arellano, J. Vilà-Guerau

2013-09-01

In Ouwersloot and Vilà-Guerau de Arellano (Boundary-Layer Meteorol. doi: 10.1007/s10546-013-9816-z , 2013, this issue), the analytical solutions for the boundary-layer height and scalar evolutions are derived for the convective boundary layer, based on the prognostic equations of mixed-layer slab models without taking subsidence into account. Here, we include and quantify the added effect of subsidence if the subsidence velocity scales linearly with height throughout the atmosphere. This enables analytical analyses for a wider range of observational cases. As a demonstration, the sensitivity of the boundary-layer height and the potential temperature jump to subsidence and the free tropospheric stability is graphically presented. The new relations show the importance of the temporal distribution of the surface buoyancy flux in determining the evolution if there is subsidence.

Boundary layer thermal stresses in angle-ply composite laminates, part 1. [graphite-epoxy composites

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1981-01-01

Thermal boundary-layer stresses (near free edges) and displacements were determined by a an eigenfunction expansion technique and the establishment of an appropriate particular solution. Current solutions in the region away from the singular domain (free edge) are found to be excellent agreement with existing approximate numerical results. As the edge is approached, the singular term controls the near field behavior of the boundary layer. Results are presented for cases of various angle-ply graphite/epoxy laminates with (theta/-theta/theta/theta) configurations. These results show high interlaminar (through-the-thickness) stresses. Thermal boundary-layer thicknesses of different composite systems are determined by examining the strain energy density distribution in composites. It is shown that the boundary-layer thickness depends on the degree of anisotropy of each individual lamina, thermomechanical properties of each ply, and the relative thickness of adjacent layers. The interlaminar thermal stresses are compressive with increasing temperature. The corresponding residual stresses are tensile and may enhance interply delaminations.

Constraints on the formation of layered tektites from the excavation and analysis of layered tektites from northeast Thailand

NASA Astrophysics Data System (ADS)

Fiske, Peter S.

1996-01-01

The size, shape, composition, and vesicle content of 6 kg of layered tektite fragments, excavated near the town of Huai Sai, Thailand, place some constraints on the formation of layered tektites. The mass, shape, and distribution of the fragments are not consistent with an origin as a "puddle" of impact melt but suggest that they were derived from a single equant block. The presence of vesicles up to 7 mm in mean diameter within the tektite fragments suggests that the material was too viscous to allow for significant gravity-driven flow. These results suggest that layered tektites may be analogous to lava bombs, which may have been stretched and deformed in flight but underwent little flow after landing. Rather than being a product of "unusual circumstances," such as multiple impacts, layered tektites may differ from splash-form tektites only in initial temperature of formation, speed of ejection, and small differences in initial composition.

Predicting fundamental and realized distributions based on thermal niche: A case study of a freshwater turtle

NASA Astrophysics Data System (ADS)

Rodrigues, João Fabrício Mota; Coelho, Marco Túlio Pacheco; Ribeiro, Bruno R.

2018-04-01

Species distribution models (SDM) have been broadly used in ecology to address theoretical and practical problems. Currently, there are two main approaches to generate SDMs: (i) correlative, which is based on species occurrences and environmental predictor layers and (ii) process-based models, which are constructed based on species' functional traits and physiological tolerances. The distributions estimated by each approach are based on different components of species niche. Predictions of correlative models approach species realized niches, while predictions of process-based are more akin to species fundamental niche. Here, we integrated the predictions of fundamental and realized distributions of the freshwater turtle Trachemys dorbigni. Fundamental distribution was estimated using data of T. dorbigni's egg incubation temperature, and realized distribution was estimated using species occurrence records. Both types of distributions were estimated using the same regression approaches (logistic regression and support vector machines), both considering macroclimatic and microclimatic temperatures. The realized distribution of T. dorbigni was generally nested in its fundamental distribution reinforcing theoretical assumptions that the species' realized niche is a subset of its fundamental niche. Both modelling algorithms produced similar results but microtemperature generated better results than macrotemperature for the incubation model. Finally, our results reinforce the conclusion that species realized distributions are constrained by other factors other than just thermal tolerances.

A Method for Obtaining High Frequency, Global, IR-Based Convective Cloud Tops for Studies of the TTL

NASA Technical Reports Server (NTRS)

Pfister, Leonhard; Ueyama, Rei; Jensen, Eric; Schoeberl, Mark

2017-01-01

Models of varying complexity that simulate water vapor and clouds in the Tropical Tropopause Layer (TTL) show that including convection directly is essential to properly simulating the water vapor and cloud distribution. In boreal winter, for example, simulations without convection yield a water vapor distribution that is too uniform with longitude, as well as minimal cloud distributions. Two things are important for convective simulations. First, it is important to get the convective cloud top potential temperature correctly, since unrealistically high values (reaching above the cold point tropopause too frequently) will cause excessive hydration of the stratosphere. Second, one must capture the time variation as well, since hydration by convection depends on the local relative humidity (temperature), which has substantial variation on synoptic time scales in the TTL. This paper describes a method for obtaining high frequency (3-hourly) global convective cloud top distributions which can be used in trajectory models. The method uses rainfall thresholds, standard IR brightness temperatures, meteorological temperature analyses, and physically realistic and documented corrections IR brightness temperature corrections to derive cloud top altitudes and potential temperatures. The cloud top altitudes compare well with combined CLOUDSAT and CALIPSO data, both in time-averaged overall vertical and horizontal distributions and in individual cases (correlations of .65-.7). An important finding is that there is significant uncertainty (nearly .5 km) in evaluating the statistical distribution of convective cloud tops even using lidar. Deep convection whose tops are in regions of high relative humidity (such as much of the TTL), will cause clouds to form above the actual convection. It is often difficult to distinguish these clouds from the actual convective cloud due to the uncertainties of evaluating ice water content from lidar measurements. Comparison with models show that calculated cloud top altitudes are generally higher than those calculated by global analyses (e.g., MERRA). Interannual variability in the distribution of convective cloud top altitudes is also investigated.

Differential response of surface temperature and atmospheric temperature to the biogeophysical effects of deforestation

NASA Astrophysics Data System (ADS)

Winckler, J.; Reick, C. H.; Lejeune, Q.; Pongratz, J.

2017-12-01

Deforestation influences temperature locally by changing the water, energy and momentum balance. While most observation-based studies and some modeling studies focused on the effects on surface temperature, other studies focused on the effects on near-surface air temperature. However, these two variables may respond differently to deforestation because changes in albedo and surface roughness may alter the land-atmosphere coupling and thus the vertical temperature distribution. Thus it is unclear whether it is possible to compare studies that assess the impacts of deforestation on these two different variables. Here, we analyze the biogeophysical effects of global-scale deforestation in the climate model MPI-ESM separately for surface temperature, 2m-air temperature and temperature the lowest atmospheric model layer. We investigate why the response of these variables differs by isolating the effects of only changing surface albedo and only changing surface roughness and by separating effects that are induced at the location of deforestation (local effects) from effects that are induced by advection and changes in circulation (nonlocal effects). Concerning surface temperature, we find that the local effects of deforestation lead to a global mean warming which is overcompensated by the nonlocal effects (up to 0.1K local warming versus -0.3K nonlocal cooling). The surface warming in the local effects is largely driven by the change in surface roughness while the cooling in the nonlocal effects is largely driven by the change in surface albedo. The nonlocal effects are largely consistent across surface temperature, 2m-air temperature, and the temperature of the lowest atmospheric layer. However, the local effects strongly differ across the three considered variables. The local effects are strong for surface temperature, but substantially weaker in the 2m-air temperature and largely absent in the lowest atmospheric layer. We conclude that studies focusing on the deforestation effects on surface temperature should not be compared to studies focusing on the effects on air temperature. While the local effects on surface temperature are useful for model evaluation, they might be less relevant for local adaptation and mitigation than previously thought because they might largely be absent in the atmosphere.

Experimental study on the heat transfer characteristics of waste printed circuit boards pyrolysis.

PubMed

Ma, Hongting; Du, Na; Lin, Xueyin; Li, Chen; Lai, Junwen; Li, Zihao

2018-08-15

In order to study the appropriate and advanced technology for recycling waste printed circuit boards (PCBs), a fixed bed pyrolysis device with stirring function has been designed and developed. The effect of rotating speed on the temperature distribution and mass change in the pyrolysis process of FR-4 PCB has been analyzed. The heat transfer and pyrolysis characteristics of different granular layers with and without stirring have been investigated. The results indicate that the stirring can change the main way of heat transfer from conduction to convection in the PCB layers. As the increase of rotating speed, the temperature rising rate of material at the bottom of the pyrolysis furnace gradually decreases, while the heating rate is increasing at the upper layer, and the temperature difference between the upper and bottom layers is gradually reduced. When the rotating speed varies from 0r/min to 18r/min, the weight loss of the material increases from 3.97% to 6.76%, and the overall pyrolysis degree is improved. During the pyrolysis process, the material layer can be divided into three zones along the vertical direction, namely complete pyrolysis zone, partial pyrolysis zone and non-pyrolysis zone. As the rotating speed is 0r/min, the thickness of each zones is 6cm, 6cm and 3cm, respectively. However, when the rotating speed is increased to 18r/min, the non-pyrolysis zone disappears, and the thickness of complete pyrolysis zone and partial pyrolysis zone increase to 9cm and 6cm, respectively. Copyright © 2018 Elsevier B.V. All rights reserved.

Experimental Evaluation of the Effect of Angle-of-attack on the External Aerodynamics and Mass Capture of a Symmetric Three-engine Air-breathing Launch Vehicle Configuration at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Kim, Hyun D.; Frate, Franco C.

2001-01-01

A subscale aerodynamic model of the GTX air-breathing launch vehicle was tested at NASA Glenn Research Center's 10- by 10-Foot Supersonic Wind Tunnel from Mach 2.0 to 3.5 at various angles-of-attack. The objective of the test was to investigate the effect of angle-of-attack on inlet mass capture, inlet diverter effectiveness, and the flowfield at the cowl lip plane. The flow-through inlets were tested with and without boundary-layer diverters. Quantitative measurements such as inlet mass flow rates and pitot-pressure distributions in the cowl lip plane are presented. At a 3deg angle-of-attack, the flow rates for the top and side inlets were within 8 percent of the zero angle-of-attack value, and little distortion was evident at the cowl lip plane. Surface oil flow patterns showing the shock/boundary-layer interaction caused by the inlet spikes are shown. In addition to inlet data, vehicle forebody static pressure distributions, boundary-layer profiles, and temperature-sensitive paint images to evaluate the boundary-layer transition are presented. Three-dimensional parabolized Navier-Stokes computational fluid dynamics calculations of the forebody flowfield are presented and show good agreement with the experimental static pressure distributions and boundary-layer profiles. With the boundary-layer diverters installed, no adverse aerodynamic phenomena were found that would prevent the inlets from operating at the required angles-of-attack. We recommend that phase 2 of the test program be initiated, where inlet contraction ratio and diverter geometry variations will be tested.

Surface topography and electrical properties in Sr2FeMoO6 films studied at cryogenic temperatures

NASA Astrophysics Data System (ADS)

Angervo, I.; Saloaro, M.; Mäkelä, J.; Lehtiö, J.-P.; Huhtinen, H.; Paturi, P.

2018-03-01

Pulsed laser deposited Sr2FeMoO6 thin films were investigated for the first time with scanning tunneling microscopy and spectroscopy. The results confirm atomic scale layer growth, with step-terrace structure corresponding to a single lattice cell scale. The spectroscopy research reveals a distribution of local electrical properties linked to structural deformation in the initial thin film layers at the film substrate interface. Significant hole structure giving rise to electrically distinctive regions in thinner film also seems to set a thickness limit for the thinnest films to be used in applications.

Tunneling STM/STS and break-junction spectroscopy of the layered nitro-chloride superconductors MNCl (M = Ti, Hf, Zr)

NASA Astrophysics Data System (ADS)

Ekino, Toshikazu; Sugimoto, Akira; Gabovich, Alexander M.; Zheng, Zhanfeng; Zhang, Shuai; Yamanaka, Shoji

2014-05-01

The layered superconductors β-MNCl with the critical temperatures Tc = 14 K (M = Zr) - 25 K (M = Hf) were investigated by means of scanning-tunneling microscopy/spectroscopy and break-junction tunneling spectroscopy. The STM/STS was used to investigate the surface electronic structures in nanometer length scale, while the BJTS was employed to precisely determine the gap characteristics. Both techniques consistently clarified the unusually large size of the superconducting gap. Wide gap distributions with large-scale maximum gap values were also revealed in α-KyTiNCl with a different crystal structure.

Feedback enhanced plasma spray tool

DOEpatents

Gevelber, Michael Alan; Wroblewski, Donald Edward; Fincke, James Russell; Swank, William David; Haggard, Delon C.; Bewley, Randy Lee

2005-11-22

An improved automatic feedback control scheme enhances plasma spraying of powdered material through reduction of process variability and providing better ability to engineer coating structure. The present inventors discovered that controlling centroid position of the spatial distribution along with other output parameters, such as particle temperature, particle velocity, and molten mass flux rate, vastly increases control over the sprayed coating structure, including vertical and horizontal cracks, voids, and porosity. It also allows improved control over graded layers or compositionally varying layers of material, reduces variations, including variation in coating thickness, and allows increasing deposition rate. Various measurement and system control schemes are provided.

Statistical analysis and modeling of intermittent transport events in the tokamak scrape-off layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, Johan, E-mail: anderson.johan@gmail.com; Halpern, Federico D.; Ricci, Paolo

The turbulence observed in the scrape-off-layer of a tokamak is often characterized by intermittent events of bursty nature, a feature which raises concerns about the prediction of heat loads on the physical boundaries of the device. It appears thus necessary to delve into the statistical properties of turbulent physical fields such as density, electrostatic potential, and temperature, focusing on the mathematical expression of tails of the probability distribution functions. The method followed here is to generate statistical information from time-traces of the plasma density stemming from Braginskii-type fluid simulations and check this against a first-principles theoretical model. The analysis ofmore » the numerical simulations indicates that the probability distribution function of the intermittent process contains strong exponential tails, as predicted by the analytical theory.« less

Material distribution in light water reactor-type bundles tested under severe accident conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Noack, V.; Hagen, S.J.L.; Hofmann, P.

1997-02-01

Severe fuel damage experiments simulating small-break loss-of-coolant accidents have been carried out in the CORA out-of-pile test facility at Forschungszentrum Karlsruhe. Rod bundles with electrically heated fuel rod simulators containing annular UO{sub 2} pellets, UO{sub 2} full pellet rods, and absorber rods of two kinds (Ag/In/Cd to represent pressurized water reactor conditions and B{sub 4}C to represent boiling water reactor and VVER-1000 fuel elements) were subjected to temperature transients up to 2,300 K. A special method was applied to determine the axial mass distribution of bundle materials. The low-temperature melt formation by various interactions between zirconium and components of absorbermore » and spacer grids strongly influences the bundle degradation and material relocation. Absorber materials can separate from the fuel by a noncoherent relocation of the materials at different temperatures. The distributions of solidified materials in the different test bundles show a clear dependence on the axial temperature profile. Coolant channel blockages are observed mainly at the lower end of the bundle, i.e., near the lowest elevation at which an oxidation excursion resulting from the highly exothermic zirconium-steam reaction had been experienced. This elevation corresponds with a steep axial temperature gradient in the maximum temperature attained. Oxide layers on Zircaloy result in reduced melt formation.« less

Discussion of flight experiments with an entry research vehicle

NASA Technical Reports Server (NTRS)

Potter, J. L.

1985-01-01

The focus of interest is the maneuvering flight of advanced entry vehicles operating at altitudes above 50 km and at velocities of 5 to 8 km/s. Information resulting in more accurate aerodynamic analysis is sought and measurement techniques that appear to be applicable are identified. Measurements discussed include: shock layer or boundary layer profiles of velocity, temperature, species mass fractions, and other gas properties associated with aerodynamic heating; surface energy transfer process; nonequilibrium flow processes and pressure distribution; separated, vortic leeside flow of nonequilibrium fluid; boundary layer transition on highly swept configurations; and shock and surface slip and gas/surface interaction. Further study should focus on evolving measurement techniques, installation requirements, and on identification of the portions of flights where successful results seem probable.

Characteristics of the near-bottom suspended sediment field over the continental shelf off northern California based on optical attenuation measurements during STRESS and SMILE

NASA Astrophysics Data System (ADS)

Trowbridge, J. H.; Butman, B.; Limeburner, R.

1994-08-01

Time-series measurements of current velocity, optical attenuation and surface wave intensity obtained during the Sediment Transport Events on Shelves and Slopes (STRESS) experiments, combined with shipboard measurements of conductivity, temperature and optical attenuation obtained during the Shelf Mixed Layer Experiment (SMILE), provide a description of the sediment concentration field over the central and outer shelf off northern California. The questions addressed are: (1) existence and characteristics of bottom nepheloid layers and their relationship to bottom mixed layers; (2) characteristics of temporal fluctuations in sediment concentration and their relationship to waves and currents; (3) spatial scales over which suspended sediment concentrations vary horizontally; and (4) vertical distribution of suspended sediment.

Exact solution of conductive heat transfer in cylindrical composite laminate

NASA Astrophysics Data System (ADS)

Kayhani, M. H.; Shariati, M.; Nourozi, M.; Karimi Demneh, M.

2009-11-01

This paper presents an exact solution for steady-state conduction heat transfer in cylindrical composite laminates. This laminate is cylindrical shape and in each lamina, fibers have been wound around the cylinder. In this article heat transfer in composite laminates is being investigated, by using separation of variables method and an analytical relation for temperature distribution in these laminates has been obtained under specific boundary conditions. Also Fourier coefficients in each layer obtain by solving set of equations that related to thermal boundary layer conditions at inside and outside of the cylinder also thermal continuity and heat flux continuity between each layer is considered. In this research LU factorization method has been used to solve the set of equations.

Global model for the lithospheric strength and effective elastic thickness

NASA Astrophysics Data System (ADS)

Tesauro, Magdala; Kaban, Mikhail K.; Cloetingh, Sierd A. P. L.

2013-08-01

Global distribution of the strength and effective elastic thickness (Te) of the lithosphere are estimated using physical parameters from recent crustal and lithospheric models. For the Te estimation we apply a new approach, which provides a possibility to take into account variations of Young modulus (E) within the lithosphere. In view of the large uncertainties affecting strength estimates, we evaluate global strength and Te distributions for possible end-member 'hard' (HRM) and a 'soft' (SRM) rheology models of the continental crust. Temperature within the lithosphere has been estimated using a recent tomography model of Ritsema et al. (2011), which has much higher horizontal resolution than previous global models. Most of the strength is localized in the crust for the HRM and in the mantle for the SRM. These results contribute to the long debates on applicability of the "crème brulée" or "jelly-sandwich" model for the lithosphere structure. Changing from the SRM to HRM turns most of the continental areas from the totally decoupled mode to the fully coupled mode of the lithospheric layers. However, in the areas characterized by a high thermal regime and thick crust, the layers remain decoupled even for the HRM. At the same time, for the inner part of the cratons the lithospheric layers are coupled in both models. Therefore, rheological variations lead to large changes in the integrated strength and Te distribution in the regions characterized by intermediate thermal conditions. In these areas temperature uncertainties have a greater effect, since this parameter principally determines rheological behavior. Comparison of the Te estimates for both models with those determined from the flexural loading and spectral analysis shows that the 'hard' rheology is likely applicable for cratonic areas, whereas the 'soft' rheology is more representative for young orogens.

Vertical profiles of black carbon concentration and particle number size distribution in the North China Plain

NASA Astrophysics Data System (ADS)

Ran, L.; Deng, Z.

2013-12-01

The vertical distribution of aerosols is of great importance to our understanding in the impacts of aerosols on radiation balance and climate, as well as air quality and public health. To better understand and estimate the effects of atmospheric components including trace gases and aerosols on atmospheric environment and climate, an intensive field campaign, Vertical Observations of trace Gases and Aerosols in the North China Plain (VOGA-NCP), was carried out from late July to early August 2013 over a rural site in the polluted NCP. During the campaign, vertical profiles of black carbon (BC) concentration and particle number size distribution were measured respectively by a micro-Aethalometer and an optical particle counter attached to a tethered balloon within 1000 m height. Meteorological parameters, including temperature, relative humidity, wind speed and wind direction, were measured simultaneously by a radiosonde also attached to the tethered balloon. Preliminary results showed distinct diurnal variations of the vertical distribution of aerosol total number concentration and BC concentration, following the development of the mixing layer. Generally, there was a well mixing of aerosols within the mixing layer and a sharp decrease above the mixing layer. Particularly, a small peak of BC concentrations was observed around 400-500 m height for several profiles. Further analysis would be needed to explain such phenomenon. It was also found that measured vertical profiles of BC using the filter-based method might be affected by the vertical distribution of relative humidity.

Effects of local factors and climate on permafrost conditions and distribution in Beiluhe basin, Qinghai-Tibet Plateau, China.

PubMed

Yin, Guoan; Niu, Fujun; Lin, Zhanju; Luo, Jing; Liu, Minghao

2017-03-01

Beiluhe basin is underlain by warm and ice-rich permafrost, and covered by vegetation and soils characteristic of the Qinghai-Tibet Plateau. A field monitoring network was established to investigate permafrost conditions and to assess potential impacts of local factors and climate change. This paper describes the spatial variations in permafrost conditions from instrumented boreholes, controlling environmental factors, and recent thermal evolution of permafrost in the basin. The study area was divided into 10 ecotypes using satellite imagery based classification. The field investigations and cluster analysis of ground temperatures indicated that permafrost underlies most of the ground in swamp meadow, undisturbed alpine meadow, degrading alpine meadow, and desert alpine grassland, but is absent in other cover types. Permafrost-ecotope relations examined over a 2-year (2014-2016) period indicated that: (i) ground surface temperatures varied largely among ecotopes; (ii) annual mean ground temperatures ranged from -1.5 to 0°C in permafrost, indicating sensitive permafrost conditions; (iii) active-layer thicknesses ranged from 1.4m to 3.4m; (iv) ground ice content at the top of permafrost is high, but the active-layer soil is relatively dry. Long-term climate warming has driven thermal changes to permafrost, but ground surface characteristics and soil moisture content strongly influence the ground thermal state. These factors control local-scale spatial variations in permafrost conditions. The warm permafrost in the basin is commonly in thermal disequilibrium, and is sensitive to future climate change. Active-layer thicknesses have increased by at least 42cm and the mean annual ground temperatures have increased by up to 0.2°C in the past 10years over the basin. A permafrost distribution map was produced based on ecotypes, suggesting that permafrost underlies 64% of the study region. Copyright © 2017 Elsevier B.V. All rights reserved.

Kinetics of the melting front movement in process of centrifugal induction surfacing of powder material with nanoscale modificaters

NASA Astrophysics Data System (ADS)

Sasnouski, I.; Kurylionak, A.

2018-03-01

For solving the problem of improving the powder coatings modified by nanostructure components obtained by induction surfacing method tribological characteristics it is necessary to study the kinetics of the powdered layer melting and define the minimum time of melting. For powdered layer predetermined temperature maintenance at sintering mode stage it is required to determine the temperature difference through blank thickness of the for one hundred-day of the define the warm-up swing on of the stocking up by solving the thermal conductivity stationary problem for quill (hollow) cylinder with internal heat source. Herewith, since in practice thickness of the cylinder wall is much less then its diameter and the temperature difference is comparatively small, the thermal conductivity dependence upon the temperature can be treated as negligible. As it was shown by our previous studies, in the induction heating process under powdered material centrifugal surfacing (i.e. before achieving the melting temperature) the temperature distribution in powdered layer thickness may be considered even. Hereinafter, considering the blank part induction heating process quasi-stationarity under Fo big values, it is possible to consider its internal surface heating as developing with constant velocity. As a result of development the melting front movement mathematical model in a powdered material with nanostructure modifiers the minimum surfacing time is defined. It allows to minimize negative impact of thermal influence on formation of applied coating structure, to raise productivity of the process, to lower power inputs and to ensure saving of nonferrous and high alloys by reducing the allowance for machining. The difference of developed mathematical model of melting front movement from previously known is that the surface temperature from which the heat transfer occures is a variable and varies with a time after the linear law.

The influence of the atmospheric boundary layer on nocturnal layers of noctuids and other moths migrating over southern Britain.

PubMed

Wood, Curtis R; Chapman, Jason W; Reynolds, Donald R; Barlow, Janet F; Smith, Alan D; Woiwod, Ian P

2006-03-01

Insects migrating at high altitude over southern Britain have been continuously monitored by automatically operating, vertical-looking radars over a period of several years. During some occasions in the summer months, the migrants were observed to form well-defined layer concentrations, typically at heights of 200-400 m, in the stable night-time atmosphere. Under these conditions, insects are likely to have control over their vertical movements and are selecting flight heights that are favourable for long-range migration. We therefore investigated the factors influencing the formation of these insect layers by comparing radar measurements of the vertical distribution of insect density with meteorological profiles generated by the UK Meteorological Office's (UKMO) Unified Model (UM). Radar-derived measurements of mass and displacement speed, along with data from Rothamsted Insect Survey light traps, provided information on the identity of the migrants. We present here three case studies where noctuid and pyralid moths contributed substantially to the observed layers. The major meteorological factors influencing the layer concentrations appeared to be: (a) the altitude of the warmest air, (b) heights corresponding to temperature preferences or thresholds for sustained migration and (c) on nights when air temperatures are relatively high, wind-speed maxima associated with the nocturnal jet. Back-trajectories indicated that layer duration may have been determined by the distance to the coast. Overall, the unique combination of meteorological data from the UM and insect data from entomological radar described here show considerable promise for systematic studies of high-altitude insect layering.

Biological control of surface temperature in the Arabian Sea

NASA Technical Reports Server (NTRS)

Sathyendranath, Shubha; Gouveia, Albert D.; Shetye, Satish R.; Ravindran, P.; Platt, Trevor

1991-01-01

In the Arabian Sea, the southwest monsoon promotes seasonal upwelling of deep water, which supplies nutrients to the surface layer and leads to a marked increase in phytoplankton growth. Remotely sensed data on ocean color are used here to show that the resulting distribution of phytoplankton exerts a controlling influence on the seasonal evolution of sea surface temperature. This results in a corresponding modification of ocean-atmosphere heat exchange on regional and seasonal scales. It is shown that this biological mechanism may provide an important regulating influence on ocean-atmosphere interactions.

Simulation of nonlinear convective thixotropic liquid with Cattaneo-Christov heat flux

NASA Astrophysics Data System (ADS)

Zubair, M.; Waqas, M.; Hayat, T.; Ayub, M.; Alsaedi, A.

2018-03-01

In this communication we utilized a modified Fourier approach featuring thermal relaxation effect in nonlinear convective flow by a vertical exponentially stretchable surface. Temperature-dependent thermal conductivity describes the heat transfer process. Thixotropic liquid is modeled. Convergent local similar solutions by homotopic approach are obtained. Graphical results for emerging parameters of interest are analyzed. Skin friction is calculated and interpreted. Consideration of larger local buoyancy and nonlinear convection parameters yields an enhancement in velocity distribution. Temperature and thermal layer thickness are reduced for larger thermal relaxation factor.

The Intrinsic Variability in the Water Vapor Saturation Ratio due to Turbulence

NASA Astrophysics Data System (ADS)

Anderson, J. C.; Cantrell, W. H.; Chandrakar, K. K.; Kostinski, A. B.; Niedermeier, D.; Shaw, R. A.

2017-12-01

In the atmosphere, the concentration of water vapor plays an important role in Earth's weather and climate. The mean concentration of water vapor is key to its efficiency as a greenhouse gas; the fluctuations about the mean are important for heat fluxes near the surface of earth. In boundary layer clouds, fluctuations in the water vapor concentration are linked to turbulence. Conditions representative of boundary layer clouds are simulated in Michigan Tech's multiphase, turbulent reaction chamber, the ∏ chamber, where the boundary conditions are controlled and repeatable. Measurements for temperature and water vapor concentration were recorded under forced Rayleigh-Bénard convection. As expected, the distributions for temperature and water vapor concentration broaden as the turbulence becomes more vigorous. From these two measurements the saturation ratio can be calculated. The fluctuations in the water vapor concentration are more important to the variability in the saturation ratio than fluctuations in temperature. In a cloud, these fluctuations in the saturation ratio can result in some cloud droplets experiencing much higher supersaturations. Those "lucky" droplets grow by condensation at a faster rate than other cloud droplets. The difference in the droplet growth rate could contribute to a broadened droplet distribution, which leads to the onset of collision-coalescence. With more intense turbulence these effect will become more pronounced as the fluctuations about the mean saturation ratio become more pronounced.

Anomalous Temperature Dependence in Metal-Black Phosphorus Contact.

PubMed

Li, Xuefei; Grassi, Roberto; Li, Sichao; Li, Tiaoyang; Xiong, Xiong; Low, Tony; Wu, Yanqing

2018-01-10

Metal-semiconductor contact has been the performance limiting problem for electronic devices and also dictates the scaling potential for future generation devices based on novel channel materials. Two-dimensional semiconductors beyond graphene, particularly few layer black phosphorus, have attracted much attention due to their exceptional electronic properties such as anisotropy and high mobility. However, due to its ultrathin body nature, few layer black phosphorus-metal contact behaves differently than conventional Schottky barrier (SB) junctions, and the mechanisms of its carrier transport across such a barrier remain elusive. In this work, we examine the transport characteristic of metal-black phosphorus contact under varying temperature. We elucidated the origin of apparent negative SB heights extracted from classical thermionic emission model and also the phenomenon of metal-insulator transition observed in the current-temperature transistor characteristic. In essence, we found that the SB height can be modulated by the back-gate voltage, which beyond a certain critical point becomes so low that the injected carrier can no longer be described by the conventional thermionic emission theory. The transition from transport dominated by a Maxwell-Boltzmann distribution for the high energy tail states, to that of a Fermi distribution by low energy Fermi sea electrons, is the physical origin of the observed metal-insulator transition. We identified two distinctive tunneling limited transport regimes in the contact: vertical and longitudinal tunneling.

Autumn larval fish assemblages in the northwest African Atlantic coastal zone

NASA Astrophysics Data System (ADS)

Abdelouahab, Hinde; Berraho, Amina; Baibai, Tarik; Agouzouk, Aziz; Makaoui, Ahmed; Errhif, Ahmed

2017-05-01

A study on the assemblage composition and vertical distribution of larval fish was conducted in the southern area of the Moroccan Atlantic coast in Autumn 2011. A total of 1 680 fish larvae taxa were identified from 21 families. The majority of the larvae were present in the upper layers. Clupeids were the most abundant larvae taxa followed by Myctophidae, Gadidae and Sparidae, hence the larval fish assemblages (LFA) were variable in diff erent depth layers. Total fish larvae showed a preference for surface layers, and were mainly found above 75 m depth, with some exceptions. The maximum concentration of fish larvae was concentrated up to 25 m essentially above the thermocline, where chlorophyll a and mesozooplankton were abundant. Spatially, neritic families were located near the coast and at some off shore stations especially in the northern part, while oceanic families were more distributed towards off shore along the study area. Cluster analysis showed a segregation of two groups of larvae. However, a clear separation between neritic families and oceanic families was not found. Multivariate analysis highlighted the relationship between the distribution of larvae of diff erent families and environmental parameters. Temperature and salinity seem to have been the factors that acted on associations of fish larvae. Day/night vertical distributions suggest there was not a very significant vertical migration, probably due to adequate light levels for feeding.

Growth energetics of germanium quantum dots by atomistic simulation

NASA Astrophysics Data System (ADS)

Wagner, Richard Joseph

Strained epitaxial growth of Ge on Si(001) produces self-assembled, nanometer scale islands, or quantum dots. We study this growth by atomistic simulation, computing the energy of island structures to determine when and how islanding occurs. We also describe experimental methods of island growth and characterization in order to understand the relevant physical processes and to interpret experimental observations for comparison with simulation. We show that pyramidal Ge islands with rebonded step {105} facets are energetically favorable compared to growth of planar Ge (2 x 8) on Si(001). We determine how the chemical potential of these islands varies with size, lateral spacing, and wetting layer thickness. We also illustrate the atomic-level structure of these islands with favorable formation energy. Intermixing can occur between the growing Ge film and the Si substrate. We show that although Ge prefers to wet the surface, entropy drives some fraction into the underlying layers. We present a simple model of intermixing by equilibration of the top crystal layers. The equilibration is performed with a flexible lattice Monte Carlo simulation. Ultimately, intermixing produces a temperature-dependent graded Ge concentration. The resulting chemical potential leads to the onset of islanding after 3-4 monolayers of deposition, consistent with experimental observations. The distribution of island sizes on a surface is determined by the relation of island energy to size. We find that there exists a minimum-energy island size due to the interaction of surface energy and bulk relaxation. Applying the calculated chemical potential to the Boltzmann-Gibbs distribution, we predict size distributions as functions of coverage and temperature. The distributions, with peak populations around 86 000 atoms, compare favorably with experiment. This work explores the driving force in growth of Ge on Si(001). The knowledge derived here explains why islanding occurs and provides guidance for the control of island self-assembly to construct useful microelectronic devices from quantum dots.

Electrical and Structural Characterization of Web Dendrite Crystals

NASA Technical Reports Server (NTRS)

Schwuttke, G. H.; Koliwad, K.; Dumas, K. A.

1985-01-01

Minority carrier lifetime distributions in silicon web dendrites are measured. Emphasis is placed on measuring areal homogeneity of lifetime, show its dependency on structural defects, and its unique change during hot processing. The internal gettering action of defect layers present in web crystals and their relation to minority carrier lifetime distributions is discussed. Minority carrier lifetime maps of web dendrites obtained before and after high temperature heat treatment are compared to similar maps obtained from 100 mm diameter Czochralski silicon wafers. Such maps indicate similar or superior areal homogeneity of minority carrier lifetime in webs.

Systems with a constant heat flux with applications to radiative heat transport across nanoscale gaps and layers

NASA Astrophysics Data System (ADS)

Budaev, Bair V.; Bogy, David B.

2018-06-01

We extend the statistical analysis of equilibrium systems to systems with a constant heat flux. This extension leads to natural generalizations of Maxwell-Boltzmann's and Planck's equilibrium energy distributions to energy distributions of systems with a net heat flux. This development provides a long needed foundation for addressing problems of nanoscale heat transport by a systematic method based on a few fundamental principles. As an example, we consider the computation of the radiative heat flux between narrowly spaced half-spaces maintained at different temperatures.

Numerical Study of Nonlinear Structures of Locally Excited Marangoni Convection in the Long-Wave Approximation

NASA Astrophysics Data System (ADS)

Wertgeim, Igor I.

2018-02-01

We investigate stationary and non-stationary solutions of nonlinear equations of the long-wave approximation for the Marangoni convection caused by a localized source of heat or a surface active impurity (surfactant) in a thin horizontal layer of a viscous incompressible fluid with a free surface. The distribution of heat or concentration flux is determined by the uniform vertical gradient of temperature or impurity concentration, distorted by the imposition of a slightly inhomogeneous heating or of surfactant, localized in the horizontal plane. The lower boundary of the layer is considered thermally insulated or impermeable, whereas the upper boundary is free and deformable. The equations obtained in the long-wave approximation are formulated in terms of the amplitudes of the temperature distribution or impurity concentration, deformation of the surface, and vorticity. For a simplification of the problem, a sequence of nonlinear equations is obtained, which in the simplest form leads to a nonlinear Schrödinger equation with a localized potential. The basic state of the system, its dependence on the parameters and stability are investigated. For stationary solutions localized in the region of the surface tension inhomogeneity, domains of parameters corresponding to different spatial patterns are delineated.

An analysis of laminar free-convection flow and heat transfer about a flat plate paralled to the direction of the generating body force

NASA Technical Reports Server (NTRS)

Ostrach, Simon

1953-01-01

The free-convection flow and heat transfer (generated by a body force) about a flat plate parallel to the direction of the body force are formally analyzed and the type of flow is found to be dependent on the Grashof number alone. For large Grashof numbers (which are of interest in aeronautics), the flow is of the boundary-layer type and the problem is reduced in a formal manner, which is analogous to Prandtl's forced-flow boundary-layer theory, to the simultaneous solution of two ordinary differential equations subject to the proper boundary conditions. Velocity and temperature distributions for Prandtl numbers of 0.01, 0.72, 0.733, 1, 1, 10, 100, and 1000 are computed, and it is shown that velocities and Nusselt numbers of the order of magnitude of those encountered in forced-convection flows may be obtained in free-convection flows. The theoretical and experimental velocity and temperature distributions are in good agreement. A flow and a heat-transfer parameter, from which the important physical quantities such as shear stress and heat-transfer rate can be computed, are derived as functions of Prandtl number alone.

Cryolithozone of Western Arctic shelf of Russia

NASA Astrophysics Data System (ADS)

Kholmyanskii, Mikhail; Vladimirov, Maksim; Snopova, Ekaterina; Kartashev, Aleksandr

2017-04-01

We propose a new original version of the structure of the cryolithozone of west Arctic seas of Russia. In contrast to variants of construction of sections and maps based on thermodynamic modeling, the authors have used electrometric, seismic, and thermal data including their own profile measurements by near-field transient electromagnetic technique and seismic profile observations by reflection method. As a result, we defined the spatial characteristics of cryolithozone and managed to differentiate it to several layers, different both in structure and formation time. We confirmed once again that the spatial boundary of cryolithozone, type and thickness of permafrost, chilled rocks and thawed ground are primarily determined by tectonic and oceanographic regimes of the Arctic Ocean and adjacent land in different geological epochs. Permafrost formed on the land in times of cold weather, turn to submarine during flooding and overlap, in the case of the sea transgression, by marine sediments accumulating in the period of warming. We have been able to establish a clear link between the permafrost thickness and the geomorphological structure of the area. This can be explained by the distribution of thermodynamic flows that change the temperature state of previously formed permafrost rocks. Formation in the outer parts of the shelf which took place at ancient conversion stage can be characterized by the structure: • permafrost table - consists of rocks, where the sea water with a temperature below 0 °C has replaced the melted ice; • middle horizon - composed of undisturbed rocks, and the rocks chilled through the lower sieving underlay; As a result of the interpretation and analysis of all the available data, the authors created a map of types of cryolithozone of the Western Arctic shelf of Russia. The following distribution areas are marked on the map: • single-layer cryolithozone (composed of sediments upper Pleistocene and Holocene); • monosyllabic relict permafrost; • two-layer relict permafrost; • three-layered cryolithozone (composed of Holocene rocks and two-layer relict mainly from permafrost rocks); • three-layer cryolithozone (composed of Holocene rocks and two-layer relict mainly from chilled rocks); • post-cryogenic thawed sediments.

Impacts of exhalation flow on the microenvironment around the human body under different room temperatures

NASA Astrophysics Data System (ADS)

Jafari, Mohammad Javad; Gharari, Noradin; Azari, Mansour Rezazade; Ashrafi, Khosro

2018-04-01

Exhalation flow and room temperature can have a considerable effect on the microenvironment in the vicinity of human body. In this study, impacts of exhalation flow and room temperature on the microenvironment around a human body were investigated using a numerical simulation. For this purpose, a computational fluid dynamic program was applied to study thermal plume around a sitting human body at different room temperatures of a calm indoor room by considering the exhalation flow. The simulation was supported by some experimental measurements. Six different room temperatures (18 to 28 °C) with two nose exhalation modes (exhalation and non-exhalation) were investigated. Overhead and breathing zone velocities and temperatures were simulated in different scenarios. This study finds out that the exhalation through the nose has a significant impact on both quantitative and qualitative features of the human microenvironment in different room temperatures. At a given temperature, the exhalation through the nose can change the location and size of maximum velocity at the top of the head. In the breathing zone, the effect of exhalation through the nose on velocity and temperature distribution was pronounced for the point close to mouth. Also, the exhalation through the nose strongly influences the thermal boundary layer on the breathing zone while it only minimally influences the convective boundary layer on the breathing zone. Overall results demonstrate that it is important to take the exhalation flow into consideration in all areas, especially at a quiescent flow condition with low temperature.

Temperature and rate of dehydration of major constituents of carbonaceous chondrites under vacuum conditions

NASA Astrophysics Data System (ADS)

Pohl, Leos; Britt, Daniel

2017-10-01

Some sub-types of carbonaceous chondrites contain a significant amount of hydrated minerals which produce specific absorption lines, typically due to the presence of hydroxyls. However, if these asteroids have come close enough to the Sun during their history, the high temperatures might have resulted in mineral decomposition and consequent loss of hydroxyl (or water) molecules in the surface layer and even to certain depths. Determination of the hydration state of phyllosilicates typically found on asteroids as well as the relative quantities of hydrated to desiccated phyllosilicates relies on experimental data - the temperature and rate of dehydration. Both dehydration temperature and rate depend on pressure. The rate also depends on the temperature. Experimentally determined phase curves for serpentine, that show for example decomposition of antigorite to forsterite and enstatite or talc and water, exist for GPa pressure levels. For antigorite, these temperatures span the range 500-750°C for pressures between 0.1 GPa and 8 GPa. However, these data are not suitable for vacuum environment found on asteroids; further, at lower pressures, the available data suggest a monotonically decreasing dehydration temperature with decreasing pressure. Also, the available data suggest dependence of both dehydration temperature and rate on the grain size distribution of the mineral. We have determined the temperature and rate of dehydration of the serpentine polymorphs antigorite, lizardite, cronstedtite, under high vacuum conditions and for various grain size distributions. The grain size distributions have been determined by particle analyzer and each sample source was also analyzed using X-Ray Diffraction.

Comparison of Euphausia superba, Euphausia crystallorophias, Pleuragramma antarcticum and Environmental Distributions in the Western Ross Sea

NASA Astrophysics Data System (ADS)

Davis, L.; Hofmann, E. E.; Klinck, J. M., II; Dinniman, M.; Pinones, M. A.

2016-02-01

Distributions of Antarctic krill (Euphausia superba), crystal krill (Euphausia crystallorophias), and Antarctic silverfish (Pleuragramma antarcticum) were constructed using observations collected in the western Ross Sea from 1988-2004. Distributions of mixed layer depth (MLD), water temperature below 200 m (an indicator for Circumpolar Deep Water, CDW), and surface speed were obtained from a Ross Sea circulation model; surface chlorophyll and percent sea ice coverage were obtained from satellite observations. The species and environmental distributions were analyzed to determine patterns and correlations. Statistical analyses of the distributions show that the three species are concentrated in specific regions and that their habitats have limited overlap. Antarctic krill are concentrated along the shelf break near Cape Adare and are associated with temperatures >0.5°C and -2°C to -0.75°C, 19-32% sea ice coverage, and high surface flow speeds. Crystal krill are concentrated in Terra Nova Bay in areas with depths of 400-600 m, temperatures < -1.3°, 50% or more sea ice coverage, shallow MLDs (2-36 m), moderate concentrations of chlorophyll (0.44 μg m-3) and low surface speeds (0.08 m s-1). Similarly, Antarctic silverfish are concentrated in Terra Nova Bay and are also found over the continental shelf in areas with depths of 500 m and temperatures of -2°C to -1°C. Additional statistical analyses provide insights into the relative contribution of the different environmental features to producing the distributions of the three species.

Vertical Distribution of Temperature in Transitional Season II and West Monsoon in Western Pacific

NASA Astrophysics Data System (ADS)

Pranoto, Hikari A. H.; Kunarso; Soeyanto, Endro

2018-02-01

Western Pacific is the water mass intersection from both the Northern Pacific and Southern Pacific ocean. The Western Pacific ocean is warm pool area which formed by several warm surface currents. As a warm pool area and also the water mass intersection, western Pacific ocean becomes an interesting study area. The object of this study is to describe the temperature vertical distribution by mooring buoy and temporally in transitional season II (September - November 2014) and west monsoon (December 2014 - February 2015) in Western Pacific. Vertical temperature and wind speed data that was used in this study was recorded by INA-TRITON mooring instrument and obtained from Laboratory of Marine Survey, BPPT. Supporting data of this study was wind vector data from ECMWF to observe the relation between temperature distribution and monsoon. The quantitative approach was used in this study by processing temperature and wind data from INA-TRITON and interpreted graphically. In the area of study, it was found that in transitional season II the range of sea surface temperature to 500-meter depth was about 8.29 - 29.90 °C while in west monsoon was 8.12 - 29.45 °C. According to the research result, the sea SST of western Pacific ocean was related to monsoonal change with SST and wind speed correlation coefficient was 0.78. While the deep layer temperature was affected by water mass flow which passes through the western Pacific Ocean.

How Does CIGS Performance Depend on Temperature at the Microscale?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stuckelberger, Michael E.; Nietzold, Tara; West, Bradley M.

Unveiling the correlation among electrical performance, elemental distribution, and defects at the microscale is crucial for the understanding and improvement of the overall solar cell performance. While this is true in general for solar cells with polycrystalline absorber layers, it is particularly critical for defect engineering of the complex quaternary CuIn xGa 1-xSe 2 (CIGS) material system. Studying these relationships under standard ambient conditions can provide important insights but does not provide input on the behavior of the cell under real operating conditions. In this contribution, we take a close look at the complex temperature dependence of defects and voltagemore » in CIGS at the microscale. We have developed correlative X-raymicroscopymethods and adapted them for temperature-dependent measurements of the locally generated voltage and elemental compositions at the microscale. We have applied these techniques to industrial CIGS solar cells covering temperatures from room temperature up to 100 degrees C. Finally, we find underperforming areas spanning multiple grains that do not correlate with the elemental distribution of major absorber constituents. However, we demonstrate that low-performing areas perform better at higher temperatures relative to the high-performing areas.« less

How Does CIGS Performance Depend on Temperature at the Microscale?

DOE PAGES

Stuckelberger, Michael E.; Nietzold, Tara; West, Bradley M.; ...

2017-11-03

Unveiling the correlation among electrical performance, elemental distribution, and defects at the microscale is crucial for the understanding and improvement of the overall solar cell performance. While this is true in general for solar cells with polycrystalline absorber layers, it is particularly critical for defect engineering of the complex quaternary CuIn xGa 1-xSe 2 (CIGS) material system. Studying these relationships under standard ambient conditions can provide important insights but does not provide input on the behavior of the cell under real operating conditions. In this contribution, we take a close look at the complex temperature dependence of defects and voltagemore » in CIGS at the microscale. We have developed correlative X-raymicroscopymethods and adapted them for temperature-dependent measurements of the locally generated voltage and elemental compositions at the microscale. We have applied these techniques to industrial CIGS solar cells covering temperatures from room temperature up to 100 degrees C. Finally, we find underperforming areas spanning multiple grains that do not correlate with the elemental distribution of major absorber constituents. However, we demonstrate that low-performing areas perform better at higher temperatures relative to the high-performing areas.« less

Structural and chemical evolution of the CdS:O window layer during individual CdTe solar cell processing steps

DOE PAGES

Abbas, A.; Meysing, D. M.; Reese, M. O.; ...

2017-12-01

Oxygenated cadmium sulfide (CdS:O) is often used as the n-type window layer in high-performance CdTe heterojunction solar cells. The as-deposited layer prepared by reactive sputtering is XRD amorphous, with a bulk composition of CdS0.8O1.2. Recently it was shown that this layer undergoes significant transformation during device fabrication, but the roles of the individual high temperature processing steps was unclear. In this work high resolution transmission electron microscopy coupled to elemental analysis was used to understand the evolution of the heterojunction region through the individual high temperature fabrication steps of CdTe deposition, CdCl2 activation, and back contact activation. It is foundmore » that during CdTe deposition by close spaced sublimation at 600 degrees C the CdS:O film undergoes recrystallization, accompanied by a significant (~30%) reduction in thickness. It is observed that oxygen segregates during this step, forming a bi-layer morphology consisting of nanocrystalline CdS adjacent to the tin oxide contact and an oxygen-rich layer adjacent to the CdTe absorber. This bilayer structure is then lost during the 400 degrees C CdCl2 treatment where the film transforms into a heterogeneous structure with cadmium sulfate clusters distributed randomly throughout the window layer. The thickness of window layer remains essentially unchanged after CdCl2 treatment, but a ~25 nm graded interfacial layer between CdTe and the window region is formed. Finally, the rapid thermal processing step used to activate the back contact was found to have a negligible impact on the structure or composition of the heterojunction region.« less

Structural and chemical evolution of the CdS:O window layer during individual CdTe solar cell processing steps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbas, A.; Meysing, D. M.; Reese, M. O.

Oxygenated cadmium sulfide (CdS:O) is often used as the n-type window layer in high-performance CdTe heterojunction solar cells. The as-deposited layer prepared by reactive sputtering is XRD amorphous, with a bulk composition of CdS0.8O1.2. Recently it was shown that this layer undergoes significant transformation during device fabrication, but the roles of the individual high temperature processing steps was unclear. In this work high resolution transmission electron microscopy coupled to elemental analysis was used to understand the evolution of the heterojunction region through the individual high temperature fabrication steps of CdTe deposition, CdCl2 activation, and back contact activation. It is foundmore » that during CdTe deposition by close spaced sublimation at 600 degrees C the CdS:O film undergoes recrystallization, accompanied by a significant (~30%) reduction in thickness. It is observed that oxygen segregates during this step, forming a bi-layer morphology consisting of nanocrystalline CdS adjacent to the tin oxide contact and an oxygen-rich layer adjacent to the CdTe absorber. This bilayer structure is then lost during the 400 degrees C CdCl2 treatment where the film transforms into a heterogeneous structure with cadmium sulfate clusters distributed randomly throughout the window layer. The thickness of window layer remains essentially unchanged after CdCl2 treatment, but a ~25 nm graded interfacial layer between CdTe and the window region is formed. Finally, the rapid thermal processing step used to activate the back contact was found to have a negligible impact on the structure or composition of the heterojunction region.« less

Investigation of irradiation effects induced by self-ion in 6H-SiC combining RBS/C, Raman and XRD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chaabane, Nihed; Debelle, Aurelien; Sattonnay, Gael

2012-01-01

Single crystals of 6H-SiC were irradiated at room temperature and 670 K with 4 MeV C ions at two fluences: 1015 and 1016 cm2 (0.16 and 1.6 dpa at the damage peak). Damage accumulation was studied by a combination of X-ray diffraction (XRD), Raman spectroscopy and Rutherford backscattering spectrometry in channelling geometry (RBS/C) along the [0001] direction. The irradiated layer is found to be composed of a low damage region up to 1.5 lm followed by a region where the disorder level is higher, consistent with SRIM predictions. At room temperature and low fluence, typically 1015 cm2, the strain depthmore » profile follows the dpa depth distribution (with a maximum value of 2%). The disorder is most likely due to small defect clusters. When increasing the fluence up to 1016 cm2, a buried amorphous layer forms, as indicated by e.g. Raman results where the Si C bands become broader or even disappear. At a higher irradiation temperature of 670 K, amorphization is not observed at the same fluence, revealing a dynamic annealing process. However, results tend to suggest that the irradiated layer is highly heterogeneous and composed of different types of defects.« less

Thermal stress analysis of ceramic gas-path seal components for aircraft turbines

NASA Technical Reports Server (NTRS)

Kennedy, F. E.; Bill, R. C.

1979-01-01

Stress and temperature distributions were evaluated numerically for a blade-tip seal system proposed for gas turbine applications. The seal consists of an abradable ceramic layer on metallic backing with intermediate layers between the ceramic layer and metal substrate. The most severe stresses in the seal, as far as failure is concerned, are tensile stresses at the top of the ceramic layer and shear and normal stresses at the layer interfaces. All these stresses reach their maximum values during the deceleration phase of a test engine cycle. A parametric study was carried out to evaluate the influence of various design parameters on these critical stress values. The influences of material properties and geometric parameters of the ceramic, intermediate, and backing layers were investigated. After the parametric study was completed, a seal system was designed which incorporated materials with beneficial elastic and thermal properties in each layer of the seal. An analysis of the proposed seal design shows an appreciable decrease in the magnitude of the maximum critical stresses over those obtained with earlier configurations.

Strain distribution in thin concrete pavement panels under three-point loading to failure with pre-pulse-pump Brillouin optical time domain analysis (Presentation Video)

NASA Astrophysics Data System (ADS)

Bao, Yi; Cain, John; Chen, Yizheng; Huang, Ying; Chen, Genda; Palek, Leonard

2015-04-01

Thin concrete panels reinforced with alloy polymer macro-synthetic fibers have recently been introduced to rapidly and cost-effectively improve the driving condition of existing roadways by laying down a fabric sheet on the roadways, casting a thin layer of concrete, and then cutting the layer into panels. This study is aimed to understand the strain distribution and potential crack development of concrete panels under three-point loading. To this end, six full-size 6ft×6ft×3in concrete panels were tested to failure in the laboratory. They were instrumented with three types of single-mode optical fiber sensors whose performance and ability to measure the strain distribution and detect cracks were compared. Each optical fiber sensor was spliced and calibrated, and then attached to a fabric sheet using adhesive. A thin layer of mortar (0.25 ~ 0.5 in thick) was cast on the fabric sheet. The three types of distributed sensors were bare SM-28e+ fiber, SM-28e+ fiber with a tight buffer, and concrete crack cable, respectively. The concrete crack cable consisted of one SM-28e+ optical fiber with a tight buffer, one SM-28e+ optical fiber with a loose buffer for temperature compensation, and an outside protective tight sheath. Distributed strains were collected from the three optical fiber sensors with pre-pulse-pump Brillouin optical time domain analysis in room temperature. Among the three sensors, the bare fiber was observed to be most fragile during construction and operation, but most sensitive to strain change or micro-cracks. The concrete crack cable was most rugged, but not as sensitive to micro-cracks and robust in micro-crack measurement as the bare fiber. The ruggedness and sensitivity of the fiber with a tight buffer were in between the bare fiber and the concrete crack cable. The strain distribution resulted from the three optical sensors are in good agreement, and can be applied to successfully locate cracks in the concrete panels. It was observed that the three types of fibers were functional until the concrete panels have experienced inelastic deformation, making the distributed strain sensing technology promising for real applications in pavement engineering.

Sequential cryogen spraying for heat flux control at the skin surface

NASA Astrophysics Data System (ADS)

Majaron, Boris; Aguilar, Guillermo; Basinger, Brooke; Randeberg, Lise L.; Svaasand, Lars O.; Lavernia, Enrique J.; Nelson, J. Stuart

2001-05-01

Heat transfer rate at the skin-air interface is of critical importance for the benefits of cryogen spray cooling in combination with laser therapy of shallow subsurface skin lesions, such as port-wine stain birthmarks. With some cryogen spray devices, a layer of liquid cryogen builds up on the skin surface during the spurt, which may impair heat transfer across the skin surface due to relatively low thermal conductivity and potentially higher temperature of the liquid cryogen layer as compared to the spray droplets. While the mass flux of cryogen delivery can be adjusted by varying the atomizing nozzle geometry, this may strongly affect other spray properties, such as lateral spread (cone), droplet size, velocity, and temperature distribution. We present here first experiments with sequential cryogen spraying, which may enable accurate mass flux control through variation of spray duty cycle, while minimally affecting other spray characteristics. The observed increase of cooling rate and efficiency at moderate duty cycle levels supports the above described hypothesis of isolating liquid layer, and demonstrates a novel approach to optimization of cryogen spray devices for individual laser dermatological applications.

Gas Near a Wall: Shortened Mean Free Path, Reduced Viscosity, and the Manifestation of the Knudsen Layer in the Navier-Stokes Solution of a Shear Flow

NASA Astrophysics Data System (ADS)

Abramov, Rafail V.

2018-06-01

For the gas near a solid planar wall, we propose a scaling formula for the mean free path of a molecule as a function of the distance from the wall, under the assumption of a uniform distribution of the incident directions of the molecular free flight. We subsequently impose the same scaling onto the viscosity of the gas near the wall and compute the Navier-Stokes solution of the velocity of a shear flow parallel to the wall. Under the simplifying assumption of constant temperature of the gas, the velocity profile becomes an explicit nonlinear function of the distance from the wall and exhibits a Knudsen boundary layer near the wall. To verify the validity of the obtained formula, we perform the Direct Simulation Monte Carlo computations for the shear flow of argon and nitrogen at normal density and temperature. We find excellent agreement between our velocity approximation and the computed DSMC velocity profiles both within the Knudsen boundary layer and away from it.

The stability of the boundary layer compressible gas with heat and mass transfer from the surface

NASA Astrophysics Data System (ADS)

Gaponov, S. A.; Terekhova, N. M.

2016-10-01

This work continues the research on modeling of the flow regime control in the compressible boundary layer. The effect of the distributed heat and mass transfer on the stability characteristics of the supersonic boundary layer at Mach number M = 5.35 is considered. The main attention is paid to modeling of acoustic disturbances both in conditions of a normal injection, when only the component of the average velocity V is nonzero, and the injection of other direction, including tangential one, when only the component U is nonzero at the wall. It is assumed that the effect of an injection of a homogeneous gas of the different temperature is similar to blowing of the gas of a different density, namely, blowing of the cold gas simulates blowing of the heavy gas and vice versa. Therefore in the present work this modeling is achieved by the change of a temperature factor (heating or cooling of the walls). There are the variant when the so-called locking regime when the velocity perturbations on the porous surface can be taken as zero.

Changes of composition and microstructure of joint interface of tungsten coated carbon by high heat flux

NASA Astrophysics Data System (ADS)

Tokunaga, K.; Matsubara, T.; Miyamoto, Y.; Takao, Y.; Yoshida, N.; Noda, N.; Kubota, Y.; Sogabe, T.; Kato, T.; Plöchl, L.

2000-12-01

Tungsten coatings of 0.5 and 1 mm thickness were successfully deposited by the vacuum plasma spraying (VPS) technique on carbon/carbon fiber composite (CFC), CX-2002U and isotropic fine grained graphite, IG-430U. High heat flux experiments by irradiation of electron beam with uniform profile were performed on the coated samples in order to prove the suitability and load limit of such coating materials. The cross-sectional composition and structure of the interface of VPS-W and carbon material samples were investigated. Compositional analyses showed that the Re/W multi-layer acts as diffusion barrier for carbon and suppresses tungsten carbide formation in the VPS-W layer at high temperature about 1300°C. Microstructure of the joint interface of the sample changed in the case of a peak temperature of about 2800°C. The multi-layer structure completely disappeared and compositional distribution was almost uniform in the interface of the sample after melting and resolidification. The diffusion barrier for carbon is not expected to act in this stage.

Epitaxial growth and magnetic properties of ultraviolet transparent Ga2O3/(Ga1-xFex)2O3 multilayer thin films.

PubMed

Guo, Daoyou; An, Yuehua; Cui, Wei; Zhi, Yusong; Zhao, Xiaolong; Lei, Ming; Li, Linghong; Li, Peigang; Wu, Zhenping; Tang, Weihua

2016-04-28

Multilayer thin films based on the ferromagnetic and ultraviolet transparent semiconductors may be interesting because their magnetic/electronic/photonic properties can be manipulated by the high energy photons. Herein, the Ga2O3/(Ga1-xFex)2O3 multilayer epitaxial thin films were obtained by alternating depositing of wide band gap Ga2O3 layer and Fe ultrathin layer due to inter diffusion between two layers at high temperature using the laser molecular beam epitaxy technique. The multilayer films exhibits a preferred growth orientation of crystal plane, and the crystal lattice expands as Fe replaces Ga site. Fe ions with a mixed valence of Fe(2+) and Fe(3+) are stratified distributed in the film and exhibit obvious agglomerated areas. The multilayer films only show a sharp absorption edge at about 250 nm, indicating a high transparency for ultraviolet light. What's more, the Ga2O3/(Ga1-xFex)2O3 multilayer epitaxial thin films also exhibits room temperature ferromagnetism deriving from the Fe doping Ga2O3.

Active layer monitoring at CALM-S site near J.G.Mendel Station, James Ross Island, eastern Antarctic Peninsula.

PubMed

Hrbáček, Filip; Kňažková, Michaela; Nývlt, Daniel; Láska, Kamil; Mueller, Carsten W; Ondruch, Jakub

2017-12-01

The Circumpolar Active Layer Monitoring - South (CALM-S) site was established in February 2014 on James Ross Island as the first CALM-S site in the eastern Antarctic Peninsula region. The site, located near Johann Gregor Mendel Station, is labelled CALM-S JGM. The grid area is gently sloped (<3°) and has an elevation of between 8 and 11ma.s.l. The lithology of the site consists of the muddy sediments of Holocene marine terrace and clayey-sandy Cretaceous sedimentary rocks, which significantly affect the texture, moisture content, and physical parameters of the ground within the grid. Our objective was to study seasonal and interannual variability of the active layer depth and thermal regime at the CALM-S site, and at two ground temperature measurement profiles, AWS-JGM and AWS-CALM, located in the grid. The mean air temperature in the period March 2013 to February 2016 reached -7.2°C. The mean ground temperature decreased with depth from -5.3°C to -5.4°C at 5cm, to -5.5°C to -5.9°C at 200cm. Active layer thickness was significantly higher at AWS-CALM and ranged between 86cm (2014/15) and 87cm (2015/16), while at AWS-JGM it reached only 51cm (2013/14) to 65cm (2015/16). The mean probed active layer depth increased from 66.4cm in 2013/14 to 78.0cm in 2014/15. Large differences were observed when comparing the minimum (51cm to 59cm) and maximum (100cm to 113cm) probed depths. The distribution of the active layer depth and differences in the thermal regime of the uppermost layer of permafrost at CALM-S JGM clearly show the effect of different lithological properties on the two lithologically distinct parts of the grid. Copyright © 2017 Elsevier B.V. All rights reserved.

Adsorption, Desorption, and Diffusion of Nitrogen in a Model Nanoporous Material: II. Diffusion Limited Kinetics in Amorphous Solid Water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zubkov, Tykhon; Smith, R. Scott; Engstrom, Todd R.

2007-11-14

Tykhon Zubkov, R. Scott Smith, Todd R. Engstrom, and Bruce D. Kay The adsorption, desorption, and diffusion kinetics of N2 on thick (up to ~9 mm) porous films of amorphous solid water (ASW) films were studied using molecular beam techniques and temperature programmed desorption (TPD). Porous ASW films were grown on Pt(111) at low temperature (<30 K) from a collimated H2O beam at glancing incident angles. In thin films (<1 mm), the desorption kinetics are well described by a model that assumes rapid and uniform N2 distribution throughout the film. In thicker films, (>1 mm), N2 adsorption at 27 Kmore » results in a non-uniform distribution where most of N2 is trapped in the outer region of the film. Redistribution of N2 can be induced by thermal annealing. The apparent activation energy for this process is ~7 kJ/mol, which is approximately half of the desorption activation energy at the corresponding coverage. Blocking adsorption sites near the film surface facilitates transport into the film. Despite the onset of limited diffusion, the adsorption kinetics are efficient, precursor-mediated and independent of film thickness. An adsorption mechanism is proposed, in which a high-coverage N2 front propagates into a pore by the rapid transport of physisorbed 2nd layer N2 species on top of the 1st layer chemisorbed layer.« less

Process for making ceramic hot gas filter

DOEpatents

Connolly, Elizabeth Sokolinski; Forsythe, George Daniel; Domanski, Daniel Matthew; Chambers, Jeffrey Allen; Rajendran, Govindasamy Paramasivam

2001-01-01

A ceramic hot-gas candle filter having a porous support of filament-wound oxide ceramic yarn at least partially surrounded by a porous refractory oxide ceramic matrix, and a membrane layer on at least one surface thereof. The membrane layer may be on the outer surface, the inner surface, or both the outer and inner surface of the porous support. The membrane layer may be formed of an ordered arrangement of circularly wound, continuous filament oxide ceramic yarn, a ceramic filler material which is less permeable than the filament-wound support structure, or some combination of continuous filament and filler material. A particularly effective membrane layer features circularly wound filament with gaps intentionally placed between adjacent windings, and a filler material of ceramic particulates uniformly distributed throughout the gap region. The filter can withstand thermal cycling during backpulse cleaning and is resistant to chemical degradation at high temperatures.

Ceramic hot-gas filter

DOEpatents

Connolly, Elizabeth Sokolinski; Forsythe, George Daniel; Domanski, Daniel Matthew; Chambers, Jeffrey Allen; Rajendran, Govindasamy Paramasivam

1999-01-01

A ceramic hot-gas candle filter having a porous support of filament-wound oxide ceramic yarn at least partially surrounded by a porous refractory oxide ceramic matrix, and a membrane layer on at least one surface thereof. The membrane layer may be on the outer surface, the inner surface, or both the outer and inner surface of the porous support. The membrane layer may be formed of an ordered arrangement of circularly wound, continuous filament oxide ceramic yarn, a ceramic filler material which is less permeable than the filament-wound support structure, or some combination of continuous filament and filler material. A particularly effective membrane layer features circularly wound filament with gaps intentionally placed between adjacent windings, and a filler material of ceramic particulates uniformly distributed throughout the gap region. The filter can withstand thermal cycling during backpulse cleaning and is resistant to chemical degradation at high temperatures.

Molecular dynamics studies of interfacial water at the alumina surface.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Argyris, Dr. Dimitrios; Ho, Thomas; Cole, David

2011-01-01

Interfacial water properties at the alumina surface were investigated via all-atom equilibrium molecular dynamics simulations at ambient temperature. Al-terminated and OH-terminated alumina surfaces were considered to assess the structural and dynamic behavior of the first few hydration layers in contact with the substrates. Density profiles suggest water layering up to {approx}10 {angstrom} from the solid substrate. Planar density distribution data indicate that water molecules in the first interfacial layer are organized in well-defined patterns dictated by the atomic terminations of the alumina surface. Interfacial water exhibits preferential orientation and delayed dynamics compared to bulk water. Water exhibits bulk-like behavior atmore » distances greater than {approx}10 {angstrom} from the substrate. The formation of an extended hydrogen bond network within the first few hydration layers illustrates the significance of water?water interactions on the structural properties at the interface.« less

Polyethylene oxide hydration in grafted layers

NASA Astrophysics Data System (ADS)

Dormidontova, Elena; Wang, Zilu

Hydration of water soluble polymers is one of the key-factors defining their conformation and properties, similar to biopolymers. Polyethylene oxide (PEO) is one of the most important biomedical-applications polymers and is known for its reverse temperature solubility due to hydrogen bonding with water. As in many practical applications PEO chains are grafted to surfaces, e.g. of nanoparticles or planar surfaces, it is important to understand PEO hydration in such grafted layers. Using atomistic molecular dynamic simulations we investigate the details of molecular conformation and hydration of PEO end-grafted to gold surfaces. We analyze polymer and water density distribution as a function of distance from the surface for different grafting densities. Based on a detailed analysis of hydrogen bonding between polymer and water in grafted PEO layers, we will discuss the extent of PEO hydration and its implication for polymer conformation, mobility and layer properties. This research is supported by NSF (DMR-1410928).

Ceramic hot-gas filter

DOEpatents

Connolly, E.S.; Forsythe, G.D.; Domanski, D.M.; Chambers, J.A.; Rajendran, G.P.

1999-05-11

A ceramic hot-gas candle filter is described having a porous support of filament-wound oxide ceramic yarn at least partially surrounded by a porous refractory oxide ceramic matrix, and a membrane layer on at least one surface thereof. The membrane layer may be on the outer surface, the inner surface, or both the outer and inner surface of the porous support. The membrane layer may be formed of an ordered arrangement of circularly wound, continuous filament oxide ceramic yarn, a ceramic filler material which is less permeable than the filament-wound support structure, or some combination of continuous filament and filler material. A particularly effective membrane layer features circularly wound filament with gaps intentionally placed between adjacent windings, and a filler material of ceramic particulates uniformly distributed throughout the gap region. The filter can withstand thermal cycling during back pulse cleaning and is resistant to chemical degradation at high temperatures.

Accurate calibration for the quantification of the Al content in AlGaN epitaxial layers by energy-dispersive X-ray spectroscopy in a Transmission Electron Microscope

NASA Astrophysics Data System (ADS)

Amari, H.; Lari, L.; Zhang, H. Y.; Geelhaar, L.; Chèze, C.; Kappers, M. J.; McAleese, C.; Humphreys, C. J.; Walther, T.

2011-11-01

Since the band structure of group III- nitrides presents a direct electronic transition with a band-gap energy covering the range from 3.4 eV for (GaN) to 6.2 eV (for AlN) at room temperature as well as a high thermal conductivity, aluminium gallium nitride (AlGaN) is a strong candidate for high-power and high-temperature electronic devices and short-wavelength (visible and ultraviolet) optoelectronic devices. We report here a study by energy-filtered transmission electron microscopy (EFTEM) and energy-dispersive X-ray spectroscopy (EDXS) of the micro structure and elemental distribution in different aluminium gallium nitride epitaxial layers grown by different research groups. A calibration procedure is out-lined that yields the Al content from EDXS to within ~1 at % precision.

Analysis of the regimes in the scanner-based laser hardening process

NASA Astrophysics Data System (ADS)

Martínez, S.; Lamikiz, A.; Ukar, E.; Calleja, A.; Arrizubieta, J. A.; Lopez de Lacalle, L. N.

2017-03-01

Laser hardening is becoming a consolidated process in different industrial sectors such as the automotive industry or in the die and mold industry. The key to ensure the success in this process is to control the surface temperature and the hardened layer thickness. Furthermore, the development of reliable scanners, based on moving optics for guiding high power lasers at extremely fast speeds allows the rapid motion of laser spots, resulting on tailored shapes of swept areas by the laser. If a scanner is used to sweep a determined area, the laser energy density distribution can be adapted by varying parameters such us the scanning speed or laser power inside this area. Despite its advantages in terms of versatility, the use of scanners for the laser hardening process has not yet been introduced in the thermal hardening industry because of the difficulty of the temperature control and possible non-homogeneous hardness thickness layers. In the present work the laser hardening process with scanning optics applied to AISI 1045 steel has been studied, with special emphasis on the influence of the scanning speed and the results derived from its variation, the evolution of the hardened layer thickness and different strategies for the control of the process temperature. For this purpose, the hardened material has been studied by measuring microhardness at different points and the shape of the hardened layer has also been evaluated. All tests have been performed using an experimental setup designed to keep a nominal temperature value using a closed-loop control. The tests results show two different regimes depending on the scanning speed and feed rate values. The experimental results conclusions have been validated by means of thermal simulations at different conditions.

Measured Two-Dimensional Ice-Wedge Polygon Thermal and Active Layer Dynamics

NASA Astrophysics Data System (ADS)

Cable, W.; Romanovsky, V. E.; Busey, R.

2016-12-01

Ice-wedge polygons are perhaps the most dominant permafrost related features in the arctic landscape. The microtopography of these features, that includes rims, troughs, and high and low polygon centers, alters the local hydrology. During winter, wind redistribution of snow leads to an increased snowpack depth in the low areas, while the slightly higher areas often have very thin snow cover, leading to differences across the landscape in vegetation communities and soil moisture between higher and lower areas. To investigate the effect of microtopographic caused variation in surface conditions on the ground thermal regime, we established temperature transects, composed of five vertical array thermistor probes (VATP), across four different development stages of ice-wedge polygons near Barrow, Alaska. Each VATP had 16 thermistors from the surface to a depth of 1.5 m, for a total of 80 temperature measurements per polygon. We found snow cover, timing and depth, and active layer soil moisture to be major controlling factors in the observed thermal regimes. In troughs and in the centers of low-centered polygons, the combined effect of typically saturated soils and increased snow accumulation resulted in the highest mean annual ground temperatures (MAGT) and latest freezeback dates. While the centers of high-centered polygons, with thinner snow cover and a dryer active layer, had the lowest MAGT, earliest freezeback dates, and shallowest active layer. Refreezing of the active layer initiated at nearly the same time for all locations and polygons however, we found large differences in the proportion of downward versus upward freezing and the length of time required to complete the refreezing process between polygon types and locations. Using our four polygon stages as a space for time substitution, we conclude that ice-wedge degradation resulting in surface subsidence and trough deepening can lead to overall drying of the active layer and increased skewedness of snow distribution. Which in turn leads to shallower active layers, earlier freezeback dates, and lower MAGT. We also find that the large variation in active layer dynamics (active layer depth, downward vs upward freezing, and freezeback date) are important considerations to understanding and scaling biological processes occurring in these landscapes.

Nonmigratory, 12-kHz, deep scattering layers of Sargasso Sea origin in warm-core rings

NASA Astrophysics Data System (ADS)

Conte, Maureen H.; Bishop, James B.; Backus, Richard H.

1986-11-01

Nonmigratory, 12-kHz, deep sound-scattering layers (NMDSLs) were entrained within Sargasso Sea-Gulf Stream waters during the formation of warm-core rings 82B and 82H. At night ring water was easily distinguished from Slope Water by the presence of these well-developed features between 200 and 550 m. The distribution of NMDSLs in 82H as a function of temperature and salinity matched Sargasso Sea distributions, indicating that Sargasso Sea water was present in the center of 82H at the time of its formation. However, the distribution of NMDSLs in the center of 82B a few weeks after its formation was more consistent with the distribution found in Gulf Stream-Sargasso Sea edge water. NMDSLs were a persistent feature of the lower thermostad and upper thermocline of 82B. Their distribution in the upper thermocline approximately paralleled the decrease in thickness of the thermostad and became shallower with increasing distance from ring center. The NMDSLs disappeared at the ring edge when the bottom of the thermostad became shallower than about 100 m. Their distribution within 30 km of ring center changed very little between April and June, whereas those found in the thermocline at greater distances from ring center showed greater dispersion with respect to temperature. Following several Gulf Stream interactions in July, the NMDSLs were significantly shallower, and lay in colder water. The continued presence of the deep NMDSLs in the thermocline, even though the latter was nearly 100 m shallower, indicates that the remaining thermocline had not been significantly exchanged with Gulf Stream or Slope Water during the interactions. The changes in the temperature of the water in which the NMDSLs were found in August suggest that core waters (30 km from ring center in June) were resorbed by the Gulf Stream and that only waters of 30 km radius remained to reform the ring. We found no evidence that the animals composing the NMDSLs adjusted their vertical distributions in response to changes in environmental properties; rather, the temporal changes we observed are best explained by the physical processes affecting ring structure. No qualitative decrease in NMDSL intensity was observed in 82B between April and August, suggesting that the sound scatterers can tolerate significant changes in depth, temperature and salinity. The gonostomatid fish Cyclothone braueri and the physonect siphonophores are possibly sources of the NMDSLs.

Effect of chemical heat release in a temporally evolving mixing layer

NASA Technical Reports Server (NTRS)

Higuera, F. J.; Moser, R. D.

1994-01-01

Two-dimensional numerical simulations of a temporally evolving mixing layer with an exothermic infinitely fast diffusion flame between two unmixed reactants have been carried out in the limit of zero Mach number to study the effect of the heat release on the early stages of the evolution of the flow. Attention has been directed to relatively large values of the oxidizer-to-fuel mass stoichiometric ratio typical of hydrocarbon flames, and initial vorticity distributions thicker than the temperature and species distributions have been chosen to mimic the situation at the outlet of a jet. The results show that, during the stages of the evolution covered by the present simulations, enhancement of combustion occurs by local stretching of the flame without much augmentation of its area. The rate of product generation depends strongly on the initial conditions, which suggests the possibility of controlling the combustion by acting on the flow. Rollup and vortex amalgamation still occur in these reacting flows but are very much affected by the production of new vorticity by baroclinic torques. These torques lead to counter rotating vortex pairs around the flame and, more importantly, in thin layers of light fluid that leave the vicinity of the flame when the Kelvin-Helmholtz instability begins to develop. Propelled by the vortex pairs, these layers wind around, split on reaching high pressure regions, and originate new vortex pairs in a process that ends up building large-scale vortices with a vorticity distribution more complex than for a constant density fluid.

A new solution chemical method to make low dimensional thermoelectric materials

NASA Astrophysics Data System (ADS)

Ding, Zhongfen

2001-11-01

Bismuth telluride and its alloys are currently the best thermoelectric materials known at room temperature and are therefore used for portable solid-state refrigeration. If the thermal electric figure of merit ZT could be improved by a factor of about 3, quiet and rugged solid-state devices could eventually replace conventional compressor based cooling systems. In order to test a theory that improved one-dimensional or two-dimensional materials could enhance ZT due to lower thermal conductivity, we are developing solution processing methods to make low dimensional materials. Bismuth telluride and its p-type and n-type alloys have layered structures consisting of 5 atom thick Te-Bi-Te-Bi-Te sheets, each sheet about 10 A thick. Lithium ions are intercalated into the layered materials using liquid ammonia. The lithium-intercalated materials are then exfoliated in water to form colloidal suspensions with narrow particle size distributions and are stable for more than 24 hours. The layers are then deposited on substrates, which after annealing at low temperatures, form highly c-axis oriented thin films. The exfoliated layers can potentially be restacked with other ions or layered materials in between the sheets to form novel structures. The restacked layers when treated with nitric acid and sonication form high yield nanorod structured materials. This new intercalation and exfoliation followed by sonication method could potentially be used for many other layered materials to make nanorod structured materials. The low dimensional materials are characterized by powder X-ray diffraction, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively coupled plasma (ICP) and dynamic light scattering.

Physics of collisionless scrape-off-layer plasma during normal and off-normal Tokamak operating conditions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hassanein, A.; Konkashbaev, I.

1999-03-15

The structure of a collisionless scrape-off-layer (SOL) plasma in tokamak reactors is being studied to define the electron distribution function and the corresponding sheath potential between the divertor plate and the edge plasma. The collisionless model is shown to be valid during the thermal phase of a plasma disruption, as well as during the newly desired low-recycling normal phase of operation with low-density, high-temperature, edge plasma conditions. An analytical solution is developed by solving the Fokker-Planck equation for electron distribution and balance in the SOL. The solution is in good agreement with numerical studies using Monte-Carlo methods. The analytical solutionsmore » provide an insight to the role of different physical and geometrical processes in a collisionless SOL during disruptions and during the enhanced phase of normal operation over a wide range of parameters.« less

Investigation of transient ignition process in a cavity based scramjet combustor using combined ethylene injectors

NASA Astrophysics Data System (ADS)

Liu, Xiao; Cai, Zun; Tong, Yiheng; Zheng, Hongtao

2017-08-01

Large Eddy Simulation (LES) and experiment were employed to investigate the transient ignition and flame propagation process in a rearwall-expansion cavity scramjet combustor using combined fuel injection schemes. The compressible supersonic solver and three ethylene combustion mechanisms were first validated against experimental data and results show in reasonably good agreement. Fuel injection scheme combining transverse and direct injectors in the cavity provides a benefit mixture distribution and could achieve a successful ignition. Four stages are illustrated in detail from both experiment and LES. After forced ignition in the cavity, initial flame kernel propagates upstream towards the cavity front edge and ignites the mixture, which acts as a continuous pilot flame, and then propagates downstream along the cavity shear layer rapidly to the combustor exit. Cavity shear layer flame stabilization mode can be concluded from the heat release rate and local high temperature distribution during the combustion process.

A particle swarm-based algorithm for optimization of multi-layered and graded dental ceramics.

PubMed

Askari, Ehsan; Flores, Paulo; Silva, Filipe

2018-01-01

The thermal residual stresses (TRSs) generated owing to the cooling down from the processing temperature in layered ceramic systems can lead to crack formation as well as influence the bending stress distribution and the strength of the structure. The purpose of this study is to minimize the thermal residual and bending stresses in dental ceramics to enhance their strength as well as to prevent the structure failure. Analytical parametric models are developed to evaluate thermal residual stresses in zirconia-porcelain multi-layered and graded discs and to simulate the piston-on-ring test. To identify optimal designs of zirconia-based dental restorations, a particle swarm optimizer is also developed. The thickness of each interlayer and compositional distribution are referred to as design variables. The effect of layers number constituting the interlayer between two based materials on the performance of graded prosthetic systems is also investigated. The developed methodology is validated against results available in literature and a finite element model constructed in the present study. Three different cases are considered to determine the optimal design of graded prosthesis based on minimizing (a) TRSs; (b) bending stresses; and (c) both TRS and bending stresses. It is demonstrated that each layer thickness and composition profile have important contributions into the resulting stress field and magnitude. Copyright © 2017 Elsevier Ltd. All rights reserved.

Experimenter's data package for the descending layers rocket

NASA Technical Reports Server (NTRS)

Earle, Greg; Herrero, Fred; Foster, John; Buonsanto, Mike; Satya-Narayana, P.

1992-01-01

In response to a proposal from Science Applications International Corporation (SAIC), NASA Headquarters has approved a sounding rocket mission designed to study the physics of intermediate layers in the Earth's ionosphere at middle latitudes. The experiment will be carried out by a team of scientists and engineers from the NASA Wallops Flight Facility, SAIC, the NASA Goddard Space Flight Center, and the Millstone Hill radar observatory. The mission will involve the launch of an instrumented sounding rocket from the Wallops Island rocket range in the summer of 1994, with the objective of penetrating a descending ionized layer in the E-region between altitudes of 115 and 140 km. Instrumentation aboard the rocket will measure the ion and neutral composition of the layer, its plasma density, driving wind and electric field forces, the thermal ion distribution function, and electron temperature. Depending on payload weight constraints and subject to availability, a particle detector to measure energetic ion and/or electron fluxes near the layer may also be included. This document was prepared as a reference for the NASA payload development and experiment teams, for distribution at the Project Initiation Conference (PIC). The design specifications discussed herein are therefore of a preliminary nature; the intent is to promote open discussions between experimenters and NASA engineers that will lead to a final design capable of achieving the experiment objectives.

Transport lattice models of heat transport in skin with spatially heterogeneous, temperature-dependent perfusion.

PubMed

Gowrishankar, T R; Stewart, Donald A; Martin, Gregory T; Weaver, James C

2004-11-17

Investigation of bioheat transfer problems requires the evaluation of temporal and spatial distributions of temperature. This class of problems has been traditionally addressed using the Pennes bioheat equation. Transport of heat by conduction, and by temperature-dependent, spatially heterogeneous blood perfusion is modeled here using a transport lattice approach. We represent heat transport processes by using a lattice that represents the Pennes bioheat equation in perfused tissues, and diffusion in nonperfused regions. The three layer skin model has a nonperfused viable epidermis, and deeper regions of dermis and subcutaneous tissue with perfusion that is constant or temperature-dependent. Two cases are considered: (1) surface contact heating and (2) spatially distributed heating. The model is relevant to the prediction of the transient and steady state temperature rise for different methods of power deposition within the skin. Accumulated thermal damage is estimated by using an Arrhenius type rate equation at locations where viable tissue temperature exceeds 42 degrees C. Prediction of spatial temperature distributions is also illustrated with a two-dimensional model of skin created from a histological image. The transport lattice approach was validated by comparison with an analytical solution for a slab with homogeneous thermal properties and spatially distributed uniform sink held at constant temperatures at the ends. For typical transcutaneous blood gas sensing conditions the estimated damage is small, even with prolonged skin contact to a 45 degrees C surface. Spatial heterogeneity in skin thermal properties leads to a non-uniform temperature distribution during a 10 GHz electromagnetic field exposure. A realistic two-dimensional model of the skin shows that tissue heterogeneity does not lead to a significant local temperature increase when heated by a hot wire tip. The heat transport system model of the skin was solved by exploiting the mathematical analogy between local thermal models and local electrical (charge transport) models, thereby allowing robust, circuit simulation software to obtain solutions to Kirchhoff's laws for the system model. Transport lattices allow systematic introduction of realistic geometry and spatially heterogeneous heat transport mechanisms. Local representations for both simple, passive functions and more complex local models can be easily and intuitively included into the system model of a tissue.

Macro controlling of copper oxide deposition processes and spray mode by using home-made fully computerized spray pyrolysis system

NASA Astrophysics Data System (ADS)

Essa, Mohammed Sh.; Chiad, Bahaa T.; Shafeeq, Omer Sh.

2017-09-01

Thin Films of Copper Oxide (CuO) absorption layer have been deposited using home-made Fully Computerized Spray Pyrolysis Deposition system FCSPD on glass substrates, at the nozzle to substrate distance equal to 20,35 cm, and computerized spray mode (continues spray, macro-control spray). The substrate temperature has been kept at 450 °c with the optional user can enter temperature tolerance values ± 5 °C. Also that fixed molar concentration of 0.1 M, and 2D platform speed or deposition platform speed of 4mm/s. more than 1000 instruction program code, and specific design of graphical user interface GUI to fully control the deposition process and real-time monitoring and controlling the deposition temperature at every 200 ms. The changing in the temperature has been recorded during deposition processes, in addition to all deposition parameters. The films have been characterized to evaluate the thermal distribution over the X, Y movable hot plate, the structure and optical energy gap, thermal and temperature distribution exhibited a good and uniform distribution over 20 cm2 hot plate area, X-ray diffraction (XRD) measurement revealed that the films are polycrystalline in nature and can be assigned to monoclinic CuO structure. Optical band gap varies from 1.5-1.66 eV depending on deposition parameter.

Finite element method simulating temperature distribution in skin induced by 980-nm pulsed laser based on pain stimulation.

PubMed

Wang, Han; Dong, Xiao-Xi; Yang, Ji-Chun; Huang, He; Li, Ying-Xin; Zhang, Hai-Xia

2017-07-01

For predicting the temperature distribution within skin tissue in 980-nm laser-evoked potentials (LEPs) experiments, a five-layer finite element model (FEM-5) was constructed based on Pennes bio-heat conduction equation and the Lambert-Beer law. The prediction results of the FEM-5 model were verified by ex vivo pig skin and in vivo rat experiments. Thirty ex vivo pig skin samples were used to verify the temperature distribution predicted by the model. The output energy of the laser was 1.8, 3, and 4.4 J. The laser spot radius was 1 mm. The experiment time was 30 s. The laser stimulated the surface of the ex vivo pig skin beginning at 10 s and lasted for 40 ms. A thermocouple thermometer was used to measure the temperature of the surface and internal layers of the ex vivo pig skin, and the sampling frequency was set to 60 Hz. For the in vivo experiments, nine adult male Wistar rats weighing 180 ± 10 g were used to verify the prediction results of the model by tail-flick latency. The output energy of the laser was 1.4 and 2.08 J. The pulsed width was 40 ms. The laser spot radius was 1 mm. The Pearson product-moment correlation and Kruskal-Wallis test were used to analyze the correlation and the difference of data. The results of all experiments showed that the measured and predicted data had no significant difference (P > 0.05) and good correlation (r > 0.9). The safe laser output energy range (1.8-3 J) was also predicted. Using the FEM-5 model prediction, the effective pain depth could be accurately controlled, and the nociceptors could be selectively activated. The FEM-5 model can be extended to guide experimental research and clinical applications for humans.

Numerical study of heterogeneous mean temperature and shock wave in a resonator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yano, Takeru

2015-10-28

When a frequency of gas oscillation in an acoustic resonator is sufficiently close to one of resonant frequencies of the resonator, the amplitude of gas oscillation becomes large and hence the nonlinear effect manifests itself. Then, if the dissipation effects due to viscosity and thermal conductivity of the gas are sufficiently small, the gas oscillation may evolve into the acoustic shock wave, in the so-called consonant resonators. At the shock front, the kinetic energy of gas oscillation is converted into heat by the dissipation process inside the shock layer, and therefore the temperature of the gas in the resonator rises.more » Since the acoustic shock wave travels in the resonator repeatedly over and over again, the temperature rise becomes noticeable in due course of time even if the shock wave is weak. We numerically study the gas oscillation with shock wave in a resonator of square cross section by solving the initial and boundary value problem of the system of three-dimensional Navier-Stokes equations with a finite difference method. In this case, the heat conduction across the boundary layer on the wall of resonator causes a spatially heterogeneous distribution of mean (time-averaged) gas temperature.« less

Evolution of Helium Bubbles and Discs in Irradiated 6H-SiC during Post-Implantation Annealing.

PubMed

Shen, Qiang; Zhou, Wei; Ran, Guang; Li, Ruixiang; Feng, Qijie; Li, Ning

2017-01-24

The single crystal 6H-SiC with [0001] crystal direction irradiated by 400 keV He⁺ ions with 1 × 10 17 ions/cm² fluence at 400 °C were annealed at 600, 900, 1200 and 1400 °C for different durations. The evolution of helium bubbles and discs was investigated by transmission electron microscopy. An irradiated layer distributed with fine helium bubbles was formed with a width of ~170 nm after helium ion irradiation. The size of gas bubbles increased with increasing annealing time and temperature and finally reached stable values at a given annealing temperature. According to the relationship between the bubble radii and annealing time, an empirical formula for calculating the bubble radii at the annealing temperature ranged from 600 to 1400 °C was given by fitting the experiment data. Planar bubble clusters (discs) were found to form on (0001) crystal plane at both sides of the bubble layer when the annealing temperature was at the range of 800-1200 °C. The mechanism of bubble growth during post-implantation annealing and the formation of bubble discs were also analyzed and discussed.

Surface heating and patchiness in the coastal ocean off central California during a wind relaxation event

NASA Technical Reports Server (NTRS)

Ramp, Steven R.; Garwood, Roland W.; Snow, Richard L.; Davis, Curtiss O.

1991-01-01

The difference between the temperature of the ocean at 4-cm and 2-m depth was continuously monitored during a cruise to the coastal transition zone off Point Arena, California, during June 1987. The two temperatures were coincident most of the time but diverged during one nearshore leg of the cruise where large temperature differences of up to 4.7 C were observed between the 4-cm and 2-m sensors, in areas which were separated by regions where the two temperatures were coincident as usual. The spatial scale of this 'patchy' thermal structure was about 5-10 km. A mixed layer model (Garwood, 1977) was used to simulate the near surface stratification when forced by the observed wind stress, surface heating, and optical clarity of the water. The model produced a thin strongly stratified surface layer at stations where exceptionally high turbidity was observed but did not produce such features otherwise. This simple model could not explain the horizontal patchiness in the thermal structure, which was likely due to patchiness in the near-surface chlorophyll distributions or to submesoscale variability of the surface wind stress.

Transient Analysis of Thermal Protection System for X-33 Aircraft using MSC/NASTRAN

NASA Technical Reports Server (NTRS)

Miura, Hirokazu; Chargin, M. K.; Bowles, J.; Tam, T.; Chu, D.; Chainyk, M.; Green, Michael J. (Technical Monitor)

1997-01-01

X-33 is an advanced technology demonstrator vehicle for the Reusable Launch Vehicle (RLV) program. The thermal protection system (TPS) for the X-33 is composed of complex layers of materials to protect internal components, while withstanding severe external temperatures induced by aerodynamic heating during high speed flight. It also serves as the vehicle aeroshell in some regions using a stand-off design. MSC/NASTRAN thermal analysis capability was used to predict transient temperature distribution (within the TPS) throughout a mission, from launch through the cool-off period after landing. In this paper, a typical analysis model, representing a point on the vehicle where the liquid oxygen tank is closest to the outer mold line, is described. The maximum temperature difference between the outer mold line and the internal surface of the liquid oxygen tank can exceed 1500 F. One dimensional thermal models are used to select the materials and determine the thickness of each layer for minimum weight while insuring that all materials remain within the allowable temperature range. The purpose of working with three dimensional (3D) comprehensive models using MSC/NASTRAN is to assess the 3D radiation effects and the thermal conduction heat shorts of the support fixtures.

Mechanisms of impact of greenhouse gases on the Earth's ozone layer in the Polar Regions

NASA Astrophysics Data System (ADS)

Zadorozhny, Alexander; Dyominov, Igor

A numerical 2-D zonally averaged interactive dynamical radiative-photochemical model of the atmosphere including aerosol physics is used to examine the impact of the greenhouse gases CO2, CH4, and N2O on the future long-term changes of the Earth's ozone layer, in particular on its expected recovery after reduction of anthropogenic discharges of chlorine and bromine compounds into the atmosphere. The model allows calculating self-consistently diabatic circu-lation, temperature, gaseous composition of the troposphere and stratosphere at latitudes from the North to South Poles, as well as distribution of sulphate aerosol particles and polar strato-spheric clouds (PSCs) of types I and II. The scenarios of expected changes of the anthropogenic pollutants for the period from 1980 through 2050 are taken from Climate Change 2001. The processes, which determine the influence of anthropogenic growth of atmospheric abun-dance of the greenhouse gases on the long-term changes of the Earth's ozone layer in the Polar Regions, have been studied in details. Expected cooling of the stratosphere caused by increases of greenhouse gases, most importantly CO2, essentially influences the ozone layer by two ways: through temperature dependencies of the gas phase reaction rates and through enhancement of polar ozone depletion via increased PSC formation. The model calculations show that a weak-ness in efficiencies of all gas phase catalytic cycles of the ozone destruction due to cooling of the stratosphere is a dominant mechanism of the impact of the greenhouse gases on the ozone layer in Antarctic as well as at the lower latitudes. This mechanism leads to a significant acceleration of the ozone layer recovery here because of the greenhouse gases growth. On the contrary, the mechanism of the impact of the greenhouse gases on the ozone through PSC modification be-gins to be more effective in Arctic in comparison with the gas phase mechanism in springs after about 2020, which leads to retard the expected recovery of the ozone layer here. The difference in the impact of the greenhouse gases on the ozone layer at the southern and northern polar latitudes through PCS modification is determined by the difference in temperature regimes of the Polar Regions. The mechanism of the impact of the greenhouse gases on the polar ozone by means of modification of sulphate aerosol distribution in the atmosphere has been revealed and investigated, too. Numerical experiments show that enhancement of the surface area density of sulphate aerosol in the stratosphere caused by the growth of the greenhouse gases will reduce significantly the ozone depletion during the Antarctic ozone hole.

The thermal impact of aquifer thermal energy storage (ATES) systems: a case study in the Netherlands, combining monitoring and modeling

NASA Astrophysics Data System (ADS)

Visser, Philip W.; Kooi, Henk; Stuyfzand, Pieter J.

2015-05-01

Results are presented of a comprehensive thermal impact study on an aquifer thermal energy storage (ATES) system in Bilthoven, the Netherlands. The study involved monitoring of the thermal impact and modeling of the three-dimensional temperature evolution of the storage aquifer and over- and underlying units. Special attention was paid to non-uniformity of the background temperature, which varies laterally and vertically in the aquifer. Two models were applied with different levels of detail regarding initial conditions and heterogeneity of hydraulic and thermal properties: a fine-scale heterogeneity model which construed the lateral and vertical temperature distribution more realistically, and a simplified model which represented the aquifer system with only a limited number of homogeneous layers. Fine-scale heterogeneity was shown to be important to accurately model the ATES-impacted vertical temperature distribution and the maximum and minimum temperatures in the storage aquifer, and the spatial extent of the thermal plumes. The fine-scale heterogeneity model resulted in larger thermally impacted areas and larger temperature anomalies than the simplified model. The models showed that scattered and scarce monitoring data of ATES-induced temperatures can be interpreted in a useful way by groundwater and heat transport modeling, resulting in a realistic assessment of the thermal impact.

Two-dimensional microclimate distribution within and above a crop canopy in an arid environment: Modeling and observational studies

NASA Astrophysics Data System (ADS)

Naot, O.; Mahrer, Y.

1991-08-01

A numerical two-dimensional model based on higher-order closure assumptions is developed to simulate the horizontal microclimate distribution over an irrigated field in arid surroundings. The model considers heat, mass, momentum, and radiative fluxes in the soil-plant-atmosphere system. Its vertical domain extends through the whole planetary boundary layer. The model requires temporal solar and atmospheric radiation data, as well as temporal boundary conditions for wind-speed, air temperature, and humidity. These boundary conditions are specified by an auxiliary mesoscale model and are incorporated in the microscale model by a nudging method. Vegetation parameters (canopy height, leaf-angle orientation distribution, leaf-area index, photometric properties, root-density distribution), soil texture, and soil-hydraulic and photometric properties are considered. The model is tested using meteorological data obtained in a drip-irrigated cotton field located in an extremely arid area, where strong fetch effects are expected. Four masts located 50 m before the leading edge of the field and 10, 30, and 100 m inward from the leading edge are used to measure various meteorological parameters and their horizontal and vertical gradients. Calculated values of air and soil temperatures, wind-speed, net radiation and soil, latent, and sensible heat fluxes agreed well with measurements. Large horizontal gradients of air temperature are both observed and measured within the canopy in the first 40 m of the leading edge. Rate of evapotranspiration at both the upwind and the downwind edges of the field are higher by more than 15% of the midfield value. Model calculations show that a stable thermal stratification is maintained above the whole field for 24 h. The aerodynamic and thermal internal boundary layer (IBL) growth is proportional to the square root of the fetch. This is also the observed rate of growth of the thermal IBL over a cool sea surface.

Spatial distribution and vertical migrations of fish larvae communities off Northwestern Iberia sampled with LHPR and Bongo nets

NASA Astrophysics Data System (ADS)

Garrido, Susana; Santos, A. Miguel P.; dos Santos, Antonina; Ré, Pedro

2009-10-01

The spatial distribution and diel vertical migration of fish larvae were studied in relation to the environmental conditions off NW Iberia during May 2002. Larvae from 23 families were identified, the most abundant were the Clupeidae, Gobiidae, Callionymidae, Blenniidae, Sparidae and Labridae. Sardina pilchardus was the most abundant species, mean concentrations 1 order of magnitude higher than the other fish larvae species. Larval horizontal distribution was mainly related to upwelling-driven circulation, resulting in an offshore increase of larval abundance while the vertical distribution was closely associated to the Western Iberia Buoyant Plume. Despite this general trend, taxon-specific relationships between the distribution of larvae and environmental variables were observed, and temperature was an important regressor explaining the distribution of most taxa. A comparison between ichthyoplankton samples collected alternatively with the LHPR and Bongo nets resulted in captures of larvae ≈1 order of magnitude higher for the LHPR, probably related to its higher towing speed. The spatial distribution and relative composition of larvae were also different for both nets, although the most frequent/abundant groups were the same. A fixed station sampled for 69-h showed diel vertical migrations performed by the larvae, with the highest larval concentrations occurring at surface layers during the night and most larvae being found in the neuston layer only during that period.

Modeling short-term concentration fluctuations of semi-volatile pollutants in the soil-plant-atmosphere system.

PubMed

Bao, Zhongwen; Haberer, Christina M; Maier, Uli; Beckingham, Barbara; Amos, Richard T; Grathwohl, Peter

2016-11-01

Temperature changes can drive cycling of semi-volatile pollutants between different environmental compartments (e.g. atmosphere, soil, plants). To evaluate the impact of daily temperature changes on atmospheric concentration fluctuations we employed a physically based model coupling soil, plants and the atmosphere, which accounts for heat transport, effective gas diffusion, sorption and biodegradation in the soil as well as eddy diffusion and photochemical oxidation in the atmospheric boundary layer of varying heights. The model results suggest that temperature-driven re-volatilization and uptake in soils cannot fully explain significant diurnal concentration fluctuations of atmospheric pollutants as for example observed for polychlorinated biphenyls (PCBs). This holds even for relatively low water contents (high gas diffusivity) and high sorption capacity of the topsoil (high organic carbon content and high pollutant concentration in the topsoil). Observed concentration fluctuations, however, can be easily matched if a rapidly-exchanging environmental compartment, such as a plant layer, is introduced. At elevated temperatures, plants release organic pollutants, which are rapidly distributed in the atmosphere by eddy diffusion. For photosensitive compounds, e.g. some polycyclic aromatic hydrocarbons (PAHs), decreasing atmospheric concentrations would be expected during daytime for the bare soil scenario. This decline is buffered by a plant layer, which acts as a ground-level reservoir. The modeling results emphasize the importance of a rapidly-exchanging compartment above ground to explain short-term atmospheric concentration fluctuations. Copyright © 2016 Elsevier B.V. All rights reserved.

Effectiveness of distributed temperature measurements for early detection of piping in river embankments

NASA Astrophysics Data System (ADS)

Bersan, Silvia; Koelewijn, André R.; Simonini, Paolo

2018-02-01

Internal erosion is the cause of a significant percentage of failure and incidents involving both dams and river embankments in many countries. In the past 20 years the use of fibre-optic Distributed Temperature Sensing (DTS) in dams has proved to be an effective tool for the detection of leakages and internal erosion. This work investigates the effectiveness of DTS for dike monitoring, focusing on the early detection of backward erosion piping, a mechanism that affects the foundation layer of structures resting on permeable, sandy soils. The paper presents data from a piping test performed on a large-scale experimental dike equipped with a DTS system together with a large number of accompanying sensors. The effect of seepage and piping on the temperature field is analysed, eventually identifying the processes that cause the onset of thermal anomalies around piping channels and thus enable their early detection. Making use of dimensional analysis, the factors that influence this thermal response of a dike foundation are identified. Finally some tools are provided that can be helpful for the design of monitoring systems and for the interpretation of temperature data.

Elevation alters ecosystem properties across temperate treelines globally

NASA Astrophysics Data System (ADS)

Mayor, Jordan R.; Sanders, Nathan J.; Classen, Aimée T.; Bardgett, Richard D.; Clément, Jean-Christophe; Fajardo, Alex; Lavorel, Sandra; Sundqvist, Maja K.; Bahn, Michael; Chisholm, Chelsea; Cieraad, Ellen; Gedalof, Ze'Ev; Grigulis, Karl; Kudo, Gaku; Oberski, Daniel L.; Wardle, David A.

2017-01-01

Temperature is a primary driver of the distribution of biodiversity as well as of ecosystem boundaries. Declining temperature with increasing elevation in montane systems has long been recognized as a major factor shaping plant community biodiversity, metabolic processes, and ecosystem dynamics. Elevational gradients, as thermoclines, also enable prediction of long-term ecological responses to climate warming. One of the most striking manifestations of increasing elevation is the abrupt transitions from forest to treeless alpine tundra. However, whether there are globally consistent above- and belowground responses to these transitions remains an open question. To disentangle the direct and indirect effects of temperature on ecosystem properties, here we evaluate replicate treeline ecotones in seven temperate regions of the world. We find that declining temperatures with increasing elevation did not affect tree leaf nutrient concentrations, but did reduce ground-layer community-weighted plant nitrogen, leading to the strong stoichiometric convergence of ground-layer plant community nitrogen to phosphorus ratios across all regions. Further, elevation-driven changes in plant nutrients were associated with changes in soil organic matter content and quality (carbon to nitrogen ratios) and microbial properties. Combined, our identification of direct and indirect temperature controls over plant communities and soil properties in seven contrasting regions suggests that future warming may disrupt the functional properties of montane ecosystems, particularly where plant community reorganization outpaces treeline advance.

Elevation alters ecosystem properties across temperate treelines globally.

PubMed

Mayor, Jordan R; Sanders, Nathan J; Classen, Aimée T; Bardgett, Richard D; Clément, Jean-Christophe; Fajardo, Alex; Lavorel, Sandra; Sundqvist, Maja K; Bahn, Michael; Chisholm, Chelsea; Cieraad, Ellen; Gedalof, Ze'ev; Grigulis, Karl; Kudo, Gaku; Oberski, Daniel L; Wardle, David A

2017-02-02

Temperature is a primary driver of the distribution of biodiversity as well as of ecosystem boundaries. Declining temperature with increasing elevation in montane systems has long been recognized as a major factor shaping plant community biodiversity, metabolic processes, and ecosystem dynamics. Elevational gradients, as thermoclines, also enable prediction of long-term ecological responses to climate warming. One of the most striking manifestations of increasing elevation is the abrupt transitions from forest to treeless alpine tundra. However, whether there are globally consistent above- and belowground responses to these transitions remains an open question. To disentangle the direct and indirect effects of temperature on ecosystem properties, here we evaluate replicate treeline ecotones in seven temperate regions of the world. We find that declining temperatures with increasing elevation did not affect tree leaf nutrient concentrations, but did reduce ground-layer community-weighted plant nitrogen, leading to the strong stoichiometric convergence of ground-layer plant community nitrogen to phosphorus ratios across all regions. Further, elevation-driven changes in plant nutrients were associated with changes in soil organic matter content and quality (carbon to nitrogen ratios) and microbial properties. Combined, our identification of direct and indirect temperature controls over plant communities and soil properties in seven contrasting regions suggests that future warming may disrupt the functional properties of montane ecosystems, particularly where plant community reorganization outpaces treeline advance.

Sensitivity of boundary layer variables to PBL schemes over the central Tibetan Plateau

NASA Astrophysics Data System (ADS)

Xu, L.; Liu, H.; Wang, L.; Du, Q.; Liu, Y.

2017-12-01

Planetary Boundary Layer (PBL) parameterization schemes play critical role in numerical weather prediction and research. They describe physical processes associated with the momentum, heat and humidity exchange between land surface and atmosphere. In this study, two non-local (YSU and ACM2) and two local (MYJ and BouLac) planetary boundary layer parameterization schemes in the Weather Research and Forecasting (WRF) model have been tested over the central Tibetan Plateau regarding of their capability to model boundary layer parameters relevant for surface energy exchange. The model performance has been evaluated against measurements from the Third Tibetan Plateau atmospheric scientific experiment (TIPEX-III). Simulated meteorological parameters and turbulence fluxes have been compared with observations through standard statistical measures. Model results show acceptable behavior, but no particular scheme produces best performance for all locations and parameters. All PBL schemes underestimate near surface air temperatures over the Tibetan Plateau. By investigating the surface energy budget components, the results suggest that downward longwave radiation and sensible heat flux are the main factors causing the lower near surface temperature. Because the downward longwave radiation and sensible heat flux are respectively affected by atmosphere moisture and land-atmosphere coupling, improvements in water vapor distribution and land-atmosphere energy exchange is meaningful for better presentation of PBL physical processes over the central Tibetan Plateau.

Experimental characterization of fire-induced response of rigid polyurethane foam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chu, T.Y.; Gill, W.; Moore, J.W.

1995-12-31

Reported is the result of an experimental investigation of fire-induced response of a 96 kg/m{sup 3} closed cell rigid polyurethane foam. The specimen is 0.37 m in diameter, and 152 mm thick, placed in a cylindrical test vessel. The fire condition is simulated by heating the bottom of the test vessel to 1283 K using a radiant heat source. Real-time x-ray shows that the degradation process involves the progression of a charring front into the virgin material. The charred region has a regular and graded structure consisting of a packed bubble outer layer and successive layers of thin shells. Themore » layer-to-layer permeability appears to be poor. There are indications that gas vents laterally. The shell-like structure might be the result of lateral venting. Although the foam degradation process is quite complicated, the in-depth temperature responses in the uncharted foam appear to be consistent with steady state ablation. The measured temperature responses are well represented by the exponential distribution for steady state ablation. An estimate of the thermal diffusivity of the foam is obtained from the ablation model. The experiment is part of a more comprehensive program to develop material response models of foams and encapsulants.« less

LIDAR detection of forest fire smoke above Sofia

NASA Astrophysics Data System (ADS)

Grigorov, Ivan; Deleva, Atanaska; Stoyanov, Dimitar; Kolev, Nikolay; Kolarov, Georgi

2015-01-01

The distribution of aerosol load in the atmosphere due to two forest fires near Sofia (the capital city of Bulgaria) was studied using two aerosol lidars which operated at 510.6 nm and 1064 nm. Experimental data is presented as 2D-heatmaps of the evolution of attenuated backscatter coefficient profiles and mean profile of the aerosol backscatter coefficient, calculated for each lidar observation. Backscatter related Angstrom exponent was used as a criterion in particle size estimation of detected smoke layers. Calculated minimal values at altitudes where the aerosol layer was observed corresponded to predominant fraction of coarse aerosol. Dust-transport forecast maps and calculations of backward trajectories were employed to make conclusions about aerosol's origin. They confirmed the local transport of smoke aerosol over the city and lidar station. DREAM forecast maps predicted neither cloud cover, nor Saharan load in the air above Sofia on the days of measurements. The results of lidar observations are discussed in conjunction with meteorological situation, aiming to better explain the reason for the observed aerosol stratification. The data of regular radio sounding of the atmosphere showed a characteristic behavior with small differences of the values between the air temperature and dew-point temperature profiles at aerosol smoke layer altitude. So the resulting stratification revealed the existence of atmospheric layers with aerosol trapping properties.

Ocean barrier layers' effect on tropical cyclone intensification.

PubMed

Balaguru, Karthik; Chang, Ping; Saravanan, R; Leung, L Ruby; Xu, Zhao; Li, Mingkui; Hsieh, Jen-Shan

2012-09-04

Improving a tropical cyclone's forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone's path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are "quasi-permanent" features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropical cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity.

Intermediate coating layer for high temperature rubbing seals for rotary regenerators

DOEpatents

Schienle, James L.; Strangman, Thomas E.

1995-01-01

A metallic regenerator seal is provided having multi-layer coating comprising a NiCrAlY bond layer, a yttria stabilized zirconia (YSZ) intermediate layer, and a ceramic high temperature solid lubricant surface layer comprising zinc oxide, calcium fluoride, and tin oxide. Because of the YSZ intermediate layer, the coating is thermodynamically stable and resists swelling at high temperatures.

Large scale patterns in vertical distribution and behaviour of mesopelagic scattering layers

NASA Astrophysics Data System (ADS)

Klevjer, T. A.; Irigoien, X.; Røstad, A.; Fraile-Nuez, E.; Benítez-Barrios, V. M.; Kaartvedt., S.

2016-01-01

Recent studies suggest that previous estimates of mesopelagic biomasses are severely biased, with the new, higher estimates underlining the need to unveil behaviourally mediated coupling between shallow and deep ocean habitats. We analysed vertical distribution and diel vertical migration (DVM) of mesopelagic acoustic scattering layers (SLs) recorded at 38 kHz across oceanographic regimes encountered during the circumglobal Malaspina expedition. Mesopelagic SLs were observed in all areas covered, but vertical distributions and DVM patterns varied markedly. The distribution of mesopelagic backscatter was deepest in the southern Indian Ocean (weighted mean daytime depth: WMD 590 m) and shallowest at the oxygen minimum zone in the eastern Pacific (WMD 350 m). DVM was evident in all areas covered, on average ~50% of mesopelagic backscatter made daily excursions from mesopelagic depths to shallow waters. There were marked differences in migrating proportions between the regions, ranging from ~20% in the Indian Ocean to ~90% in the Eastern Pacific. Overall the data suggest strong spatial gradients in mesopelagic DVM patterns, with implied ecological and biogeochemical consequences. Our results suggest that parts of this spatial variability can be explained by horizontal patterns in physical-chemical properties of water masses, such as oxygen, temperature and turbidity.

Large scale patterns in vertical distribution and behaviour of mesopelagic scattering layers.

PubMed

Klevjer, T A; Irigoien, X; Røstad, A; Fraile-Nuez, E; Benítez-Barrios, V M; Kaartvedt, S

2016-01-27

Recent studies suggest that previous estimates of mesopelagic biomasses are severely biased, with the new, higher estimates underlining the need to unveil behaviourally mediated coupling between shallow and deep ocean habitats. We analysed vertical distribution and diel vertical migration (DVM) of mesopelagic acoustic scattering layers (SLs) recorded at 38 kHz across oceanographic regimes encountered during the circumglobal Malaspina expedition. Mesopelagic SLs were observed in all areas covered, but vertical distributions and DVM patterns varied markedly. The distribution of mesopelagic backscatter was deepest in the southern Indian Ocean (weighted mean daytime depth: WMD 590 m) and shallowest at the oxygen minimum zone in the eastern Pacific (WMD 350 m). DVM was evident in all areas covered, on average ~50% of mesopelagic backscatter made daily excursions from mesopelagic depths to shallow waters. There were marked differences in migrating proportions between the regions, ranging from ~20% in the Indian Ocean to ~90% in the Eastern Pacific. Overall the data suggest strong spatial gradients in mesopelagic DVM patterns, with implied ecological and biogeochemical consequences. Our results suggest that parts of this spatial variability can be explained by horizontal patterns in physical-chemical properties of water masses, such as oxygen, temperature and turbidity.

Microstructure investigations of U3Si2 implanted by high-energy Xe ions at 600 °C

NASA Astrophysics Data System (ADS)

Miao, Yinbin; Harp, Jason; Mo, Kun; Kim, Yeon Soo; Zhu, Shaofei; Yacout, Abdellatif M.

2018-05-01

The microstructure investigations on a high-energy Xe-implanted U3Si2 pellet were performed. The promising accident tolerant fuel (ATF) candidate, U3Si2, was irradiated by 84 MeV Xe ions at 600 °C at Argonne Tandem Linac Accelerator System (ATLAS). The characterizations of the Xe implanted sample were conducted using advanced transmission electron microscopy (TEM) techniques. An oxidation layer was observed on the sample surface after irradiation under the ∼10-5 Pa vacuum. The study on the oxidation layer not only unveils the readily oxidation behavior of U3Si2 under high-temperature irradiation conditions, but also develops an understanding of its oxidation mechanism. Intragranular Xe bubbles with bimodal size distribution were observed within the Xe deposition region of the sample induced by 84 MeV Xe ion implantation. At the irradiation temperature of 600 °C, the gaseous swelling strain contributed by intragranular bubbles was found to be insignificant, indicating an acceptable fission gas behavior of U3Si2 as a light water reactor (LWR) fuel operating at such a temperature.

Idebenone-loaded solid lipid nanoparticles for drug delivery to the skin: in vitro evaluation.

PubMed

Montenegro, Lucia; Sinico, Chiara; Castangia, Ines; Carbone, Claudia; Puglisi, Giovanni

2012-09-15

Idebenone (IDE), a synthetic derivative of ubiquinone, shows a potent antioxidant activity that could be beneficial in the treatment of skin oxidative damages. In this work, the feasibility of targeting IDE into the upper layers of the skin by topical application of IDE-loaded solid lipid nanoparticles (SLN) was evaluated. SLN loading different amounts of IDE were prepared by the phase inversion temperature method using cetyl palmitate as solid lipid and three different non-ionic surfactants: ceteth-20, isoceteth-20 and oleth-20. All IDE loaded SLN showed a mean particle size in the range of 30-49 nm and a single peak in size distribution. In vitro permeation/penetration experiments were performed on pig skin using Franz-type diffusion cells. IDE penetration into the different skin layers depended on the type of SLN used while no IDE permeation occurred from all the SLN under investigation. The highest IDE content was found in the epidermis when SLN contained ceteth-20 or isoceteth-20 as surfactant while IDE distribution into the upper skin layers depended on the amount of IDE loaded when oleth-20 was used as surfactant. These results suggest that the SLN tested could be an interesting carrier for IDE targeting to the upper skin layers. Copyright © 2012 Elsevier B.V. All rights reserved.

Solidification of a binary mixture

NASA Technical Reports Server (NTRS)

Antar, B. N.

1982-01-01

The time dependent concentration and temperature profiles of a finite layer of a binary mixture are investigated during solidification. The coupled time dependent Stefan problem is solved numerically using an implicit finite differencing algorithm with the method of lines. Specifically, the temporal operator is approximated via an implicit finite difference operator resulting in a coupled set of ordinary differential equations for the spatial distribution of the temperature and concentration for each time. Since the resulting differential equations set form a boundary value problem with matching conditions at an unknown spatial point, the method of invariant imbedding is used for its solution.

Spatial and temporal distribution of pore gas concentrations during mainstream large-scale trough composting in China.

PubMed

Zeng, Jianfei; Shen, Xiuli; Sun, Xiaoxi; Liu, Ning; Han, Lujia; Huang, Guangqun

2018-05-01

With the advantages of high treatment capacity and low operational cost, large-scale trough composting has become one of the mainstream composting patterns in composting plants in China. This study measured concentrations of O 2 , CO 2 , CH 4 and NH 3 on-site to investigate the spatial and temporal distribution of pore gas concentrations during mainstream large-scale trough composting in China. The results showed that the temperature in the center of the pile was obviously higher than that in the side of the pile. Pore O 2 concentration rapidly decreased and maintained <5% (in volume) for 38 days or more in both the center and side of the pile and effective O 2 diffusion occurred at most in every two contiguous layers. Pore CO 2 and CH 4 concentrations at each measurement point were positively correlated (0.436 ≤ r ≤ 0.570, P < 0.01) and the concentrations in the side of the pile were obviously lower than those in the center. The top layer exhibited highest pore O 2 concentration and lowest CO 2 and CH 4 concentrations, and the bottom layer was on the contrary. No significant differences in pore NH 3 concentrations between different layers or between different measurement points in the same layer were found. Therefore, mixing the center and the side of the pile when mechanical turning and adjusting the height of the pile according to the physical properties of bulking agents are suggested to optimize the oxygen distribution and promote the composting process during large-scale trough composting when the pile was naturally aerated, which will contribute to improving the current undesirable atmosphere environment in China. Copyright © 2018 Elsevier Ltd. All rights reserved.

Temperature distribution by the effect of groundwater flow in an aquifer thermal energy storage system model

NASA Astrophysics Data System (ADS)

Shim, B.

2005-12-01

Aquifer thermal energy storage (ATES) can be a cost-effective and renewable energy source, depending on site-specific thermohydraulic conditions. To design an effective ATES system, the understanding of thermohydraulic processes is necessary. The heat transfer phenomena of an aquifer heat storage system are simulated with the scenario of heat pump operation of pumping and waste water reinjection in a two layered confined aquifer model having the effect of groundwater movement. Temperature distribution of the aquifer model is generated, and hydraulic heads and temperature variations are monitored at both wells during simulation days. The average groundwater velocities are determined with two assumed hydraulic gradients set by boundary conditions, and the effect of groundwater flow are shown at the generated thermal distributions at three different depth slices. The generated temperature contour lines at the hydraulic gradient of 0.001 are shaped circular, and the center is moved less than 5 m to the east in 365 days. However at the hydraulic gradient of 0.01, the contour centers of the east well at each depth slice are moved near the east boundary and the movement of temperature distribution is increased at the lower aquifer. By the analysis of thermal interference data between two wells the efficiency of a heat pump operation model is validated, and the variation of heads is monitored at injection, pumping and stabilized state. The thermal efficiency of the ATES system model is represented as highly depended on groundwater flow velocity and direction. Therefore the hydrogeologic condition for the system site should be carefully surveyed.

Dynamics of water in synthetic saponite clays: Effect of trivalent ion substitution

NASA Astrophysics Data System (ADS)

Mitra, S.; Prabhudesai, S. A.; Chakrabarty, D.; Sharma, V. K.; Vicente, M. A.; Embs, J. P.; Mukhopadhyay, R.

2013-06-01

Saponite clay belongs to the phyllosilicate family and is comprised of layers of Si(IV) tetrahedra and Al(III) or Mg(II) octahedra with definite interlayer spacing. In these systems, the trivalent ion substitutions in the tetrahedral layers lead to negative charge on the layers. Here we report the dynamics of water contained in [Si6.97Al1.03][Ni6.00]O20(OH)4[Na1.03]·28H2O (SAP-1) and [Si7.13Fe0.86][Ni6.00]O20(OH)4[Na0.86]·14H2O (SAP-2) saponite clays in the temperature range 200-310 K as studied by quasielastic neutron scattering technique. Particularly the effect of the ion substitution towards the dynamics of water is addressed here. Data analysis is carried out using the relaxing cage model. The existence of distribution in relaxation times indicated that the water molecules in saponite clay have a different local environment which leads to complex diffusion behavior. It is found that water exists in a supercooled state in the temperature range up to 235 K. However, some of the water molecules are found to be immobile in the temperature range 240-285 K. The fraction of immobile water decreases with increase in temperature. At higher temperatures, some of the water molecules in the hydration shells or those near the surface start participating in the diffusion process and at 293 K, almost all water molecules contribute to the dynamics. Diffusivity of water in both SAP-1 and SAP-2 are found to be lower in comparison to the bulk, and within the two samples of saponite clay diffusivity in SAP-1 is found to be lower compared to SAP-2; this has been explained on the basis of the charge on the tetrahedral layers and the charge balancing cations in the interlayer spacing.

Observations and Parameterizations of Particle Size Distributions in Deep Tropical Cirrus and Stratiform Precipitation Clouds: Results from In-Situ Observations in TRMM Field Campaigns

NASA Technical Reports Server (NTRS)

Heymsfield, Andrew J.; Bansemer, Aaron; Field, Paul R.; Durden, Stephen L.; Stith, Jeffrey L.; Dye, James E.; Hall, William; Grainger, Cedric A.

2002-01-01

In this study, we report on the evolution of particle size distributions (PSDs) and habits as measured during slow, Lagrangian-type spiral descents through deep subtropical and tropical cloud layers in Florida, Brazil, and Kwajalein, Marshall Islands, most of which were precipitating. The objective of the flight patterns was to learn more about how the PSDs evolved in the vertical and to obtain information of the vertical structure of microphysical properties. New instrumentation yielding better information on the concentrations of particles in the size (D) range between 0.2 and 2 cm, as well as improved particle imagery, produced more comprehensive observations for tropical stratiform precipitation regions and anvils than have been available previously. Collocated radar observations provided additional information on the vertical structure of the cloud layers sampled. Most of the spirals began at cloud top, with temperatures (T) as low as -50 C, and ended at cloud base or below the melting layer (ML). The PSDs broadened from cloud top towards cloud base, with the largest particles increasing in size from several millimeters at cloud top to one centimeter or larger towards cloud base. Some continued growth was noted in the upper part of the ML. Concentrations of particles less than 1 mm in size decreased with decreasing height. The result was a consistent change in the PSDs in the vertical. Similarly, systematic changes in the size dependence of the particle cross-sectional area was noted with decreasing height. Aggregation-as ascertained from both the changes in the PSDs and evolution of particle habits as observed in high detail with the cloud particle imager (CPI) probe-was responsible for these trends. The PSDs were generally well-represented by gamma distributions of the form N = N0 gamma D microns e- lambda gamma D that were fitted to the PSDs over 1-km horizontal intervals throughout the spirals. The intercept (N0 gamma), slope (lambda gamma), and dispersion (microns) values were derived for each PSD. Exponential curves (N = N0e- lambdaD; micron = 0) were also fitted to the distributions. The lambda gamma values for given spirals varied systematically with temperature as did the values of lambda (exponential), and the data generally conformed to values found in previous studies involving exponential fits to size distributions in mid-latitude frontal and cirrus layers. Considerable variability often noted in the PSD properties during the loops of individual spirals was manifested primarily in large changes in N0 gamma and N0, but micron, lambda gamma and lambda remained fairly stable. Temperature is not found to be the sole factor controlling lambda gamma or lambda but is a primary one. Direct relationships were found between lambda gamma and N0 gamma or lambda gamma and micron for the gamma distributions and lambda and N0 for the exponential. The latter relationship was not found as distinctly in earlier studies; observed PSDs in this study had better fidelity with less scatter. The micron values changed monotonically with T over the range of temperatures and were directly related to N0 gamma or lambda gamma, thereby reducing the number of variables in the PSD functional equation to two. In the upper part of the ML, N0 and lambda continued to decrease, and in the lower part these values began to increase as the largest particles melted. We developed general expressions relating various bulk microphysical, radar, and radiative transfer-related variables to N0 gamma and lambda gamma, useful for both tropical and mid-latitude clouds. These relationships facilitate the specification of a number of bulk properties in cloud and climate models. The results presented in this paper apply best to temperatures between 0 and -40 C, for which the measured radar reflectivities fall in the range of 0 to 25 dBZe.

A comparative study of the tail ion distribution with reduced Fokker-Planck models

NASA Astrophysics Data System (ADS)

McDevitt, C. J.; Tang, Xian-Zhu; Guo, Zehua; Berk, H. L.

2014-03-01

A series of reduced models are used to study the fast ion tail in the vicinity of a transition layer between plasmas at disparate temperatures and densities, which is typical of the gas and pusher interface in inertial confinement fusion targets. Emphasis is placed on utilizing progressively more comprehensive models in order to identify the essential physics for computing the fast ion tail at energies comparable to the Gamow peak. The resulting fast ion tail distribution is subsequently used to compute the fusion reactivity as a function of collisionality and temperature. While a significant reduction of the fusion reactivity in the hot spot compared to the nominal Maxwellian case is present, this reduction is found to be partially recovered by an increase of the fusion reactivity in the neighboring cold region.

Ionomer equivalent weight structuring in the cathode catalyst layer of automotive fuel cells: Effect on performance, current density distribution and electrochemical impedance spectra

NASA Astrophysics Data System (ADS)

Herden, Susanne; Hirschfeld, Julian A.; Lohri, Cyrill; Perchthaler, Markus; Haase, Stefan

2017-10-01

To improve the performance of proton exchange membrane fuel cells, membrane electrode assemblies (MEAs) with segmented cathode electrodes have been manufactured. Electrodes with a higher and lower ionomer equivalent weight (EW) were used and analyzed using current density and temperature distribution, polarization curve, temperature sweep and electrochemical impedance spectroscopy measurements. These were performed using automotive metallic bipolar plates and operating conditions. Measurement data were used to manufacture an optimized segmented cathode electrode. We were able to show that our results are transferable from a small scale hardware to automotive application and that an ionomer EW segmentation of the cathode leads to performance improvement in a broad spectrum of operating conditions. Furthermore, we confirmed our results by using in-situ electrochemical impedance spectroscopy.

[Distribution characteristics of dissolved oxygen and mechanism of hypoxia in the upper estuarine zone of the Daliaohe River].

PubMed

Yang, Li-Na; Li, Zheng-Yan; Zhang, Xue-Qing

2011-01-01

Based on field surveys in the upper estuarine zone of the Daliaohe River in Spring and Summer of 2009, the spatial and temporal distributions of dissolved oxygen were analyzed and the mechanism of hypoxia were preliminarily discussed. The results indicated that DO concentrations were higher in the river mouth and lower in the upper reaches, higher in surface layers and lower in bottom concerning its spatial distribution. For its temporal distribution, DO concentrations were higher in daytime and lower at night, higher in Spring and lower in Summer. The DO concentrations in the upper estuarine zone of the Daliaohe River in Summer ranged between 1.36-4.77 mg/L with an average of 3.44 mg/L. The concentrations in the lower reaches were higher with an average of 3.94 mg/L. A large hypoxia area was recorded in Summer in the upper reaches of the estuary starting from about 45 km away from the river gate with an average DO concentration of 2.33 mg/L and a minimum of 1.36 mg/L. The correlation analysis showed that DO concentration was significantly correlated with nutrients and permanganate index. Excessive discharge of nutrients and organic pollutants were, therefore, main factors causing hypoxia, and water column stratification due to temperature rise in Summer in surface layers led to further reduction of DO in bottom layers of the water.

Solid state dewetting of thin plasmonic films under focused cw-laser irradiation

DOE PAGES

Abbott, William M.; Corbett, Simon; Cunningham, Graeme; ...

2017-12-21

Elevated temperatures and large thermal gradients are a significant source of component failure in microelectronics, and is the limiting factor in heat-assisted magnetic recording (HAMR). Here, we have investigated the effect of solid-state dewetting in Au thin films, as a function of local temperature, film thickness, and substrate adhesion. In this work, a localised temperature rise is induced in thin (≤ 50 nm) polycrystalline Au films on SiO 2 substrates via focused continuous-wave laser irradiation at 488 nm. The magnitude and distribution of the total temperature rise is measured using CCD-based thermoreflectance. This also allows a sensitive measurement of themore » temperature at which dewetting occurs, showing that for thin (≤ 50 nm) Au films without adhesion layers, rapid dewetting can occur at temperatures as low as 50° C. The time decay of the reflected light from the illuminating laser is used to monitor locally the dynamics of solid state dewetting. TEM diffraction analysis shows significant changes in the microstructure and crystallographic texture of the films as far as 10 µm away from the illuminated area. The use of a thin metallic adhesion layer (such as Ti or Cr) is shown to significantly improve the adhesion of the Au to the substrate and reduce the tendency towards dewetting, but does not entirely protect it from changes to the crystallographic texture.« less

Solid state dewetting of thin plasmonic films under focused cw-laser irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbott, William M.; Corbett, Simon; Cunningham, Graeme

Elevated temperatures and large thermal gradients are a significant source of component failure in microelectronics, and is the limiting factor in heat-assisted magnetic recording (HAMR). Here, we have investigated the effect of solid-state dewetting in Au thin films, as a function of local temperature, film thickness, and substrate adhesion. In this work, a localised temperature rise is induced in thin (≤ 50 nm) polycrystalline Au films on SiO 2 substrates via focused continuous-wave laser irradiation at 488 nm. The magnitude and distribution of the total temperature rise is measured using CCD-based thermoreflectance. This also allows a sensitive measurement of themore » temperature at which dewetting occurs, showing that for thin (≤ 50 nm) Au films without adhesion layers, rapid dewetting can occur at temperatures as low as 50° C. The time decay of the reflected light from the illuminating laser is used to monitor locally the dynamics of solid state dewetting. TEM diffraction analysis shows significant changes in the microstructure and crystallographic texture of the films as far as 10 µm away from the illuminated area. The use of a thin metallic adhesion layer (such as Ti or Cr) is shown to significantly improve the adhesion of the Au to the substrate and reduce the tendency towards dewetting, but does not entirely protect it from changes to the crystallographic texture.« less

Interhemispheric comparison of atmospheric circulation features as evaluated from Nimbus satellite data

NASA Technical Reports Server (NTRS)

Reiter, E. R.; Vonderhaar, T. H.; Adler, R. F.; Srivatsangam, S.; Fields, A.

1973-01-01

A relationship is established between relative geostrophic vorticity on an isobaric surface and the Laplacian of the underlying layer-mean temperature. This relationship is used to investigate the distribution of vorticity and baroclinicity in a jet-stream model which is constantly recurrent in the winter troposphere. The investigation shows that the baroclinic and vorticity fields of the extratropical troposphere must be bifurcated with two extrema in the middle and subpolar latitudes. This pattern is present in daily tropospheric meridional cross-sections. The reasons for the disappearance of bifurcation in the time-and-longitude averaged distributions are discussed.

Biogenic nitric oxide emission from a spruce forest soil in mountainous terrain

NASA Astrophysics Data System (ADS)

Falge, Eva; Bargsten, Anika; Behrendt, Thomas; Meixner, Franz X.

2010-05-01

The process-based spatial simulation model SVAT-CN was used to estimate biogenic nitric oxide (NO) emission by soils of a Norway spruce forest (Weidenbrunnen) in the Fichtelgebirge, Germany. SVAT-CN core is a combination of a multiple-layer soil water balance model and a multi-layered canopy gas exchange model. The soil modules comprise a flexible hybrid between a layered bucket model and classical basic liquid flow theory. Further soil processes include: heat transport, distribution of transpiration demand proportionally to soil resistance, reduction of leaf physiological parameters with limiting soil moisture. Spruce forest soils usually are characterized by a thick organic layer (raw humus), with the topmost centimetres being the location where most of the biogenic NO is produced. Within individual spruce forest stands the understory might be composed of patches characterized by different species (e.g. Vaccinium myrtillus, Picea abies, Deschampsia caespitosa), and NO production potentials. The effect of soil physical and chemical parameters and understory types on NO emission from the organic layer was investigated in laboratory incubation and fumigation experiments on soils sampled below the various understory covers found at the Weidenbrunnen site. Results from the laboratory experiments were used to parameterize multi-factorial regression models of soil NO emission with respect to its response to soil temperature and moisture. Parameterization of the spatial model SVAT-CN includes horizontal heterogeneity of over- and understory PAI, understory species distribution, soil texture, bulk density, thickness of organic layer. Simulations are run for intensive observations periods of 2007 and 2008 of the EGER (ExchanGE processes in mountainous Regions) project, a late summer/fall and an early summer period, providing estimates for different understory types (young spruce, blueberry, grass, and moss/litter patches). Validation of the model is being carried out at point scale, by comparison with measured soil moisture and temperature data at 12 locations at the Weidenbrunnen site. In addition model output is compared to soil NO emission data from dynamic chambers. Understory type was found to have a strong influence on the magnitude of soil NO emissions, with emissions from blueberry and young spruce one order of magnitude larger than those from grass or moss/litter patches.

Numerical study of active control of mixing in electro-osmotic flows by temperature difference using lattice Boltzmann methods.

PubMed

Alizadeh, A; Wang, J K; Pooyan, S; Mirbozorgi, S A; Wang, M

2013-10-01

In this paper, the effect of temperature difference between inlet flow and walls on the electro-osmotic flow through a two-dimensional microchannel is investigated. The main objective is to study the effect of temperature variations on the distribution of ions and consequently internal electric potential field, electric body force, and velocity fields in an electro-osmotic flow. We assume constant temperature and zeta potential on walls and use the mean temperature of each cross section to characterize the Boltzmann ion distribution across the channel. Based on these assumptions, the multiphysical transports are still able to be described by the classical Poisson-Boltzmann model. In this work, the Navier-Stokes equation for fluid flow, the Poisson-Boltzmann equation for ion distribution, and the energy equation for heat transfer are solved by a couple lattice Boltzmann method. The modeling results indicate that the temperature difference between walls and the inlet solution may lead to two symmetrical vortices at the entrance region of the microchannel which is appropriate for mixing enhancements. The advantage of this phenomenon for active control of mixing in electro-osmotic flow is the manageability of the vortex scale without extra efforts. For instance, the effective domain of this pattern could broaden by the following modulations: decreasing the external electric potential field, decreasing the electric double layer thickness, or increasing the temperature difference between inlet flow and walls. This work may provide a novel strategy for design or optimization of microsystems. Copyright © 2013 Elsevier Inc. All rights reserved.

Tuning Nanocrystal Surface Depletion by Controlling Dopant Distribution as a Route Toward Enhanced Film Conductivity

NASA Astrophysics Data System (ADS)

Staller, Corey M.; Robinson, Zachary L.; Agrawal, Ankit; Gibbs, Stephen L.; Greenberg, Benjamin L.; Lounis, Sebastien D.; Kortshagen, Uwe R.; Milliron, Delia J.

2018-05-01

Electron conduction through bare metal oxide nanocrystal (NC) films is hindered by surface depletion regions resulting from the presence of surface states. We control the radial dopant distribution in tin-doped indium oxide (ITO) NCs as a means to manipulate the NC depletion width. We find in films of ITO NCs of equal overall dopant concentration that those with dopant-enriched surfaces show decreased depletion width and increased conductivity. Variable temperature conductivity data shows electron localization length increases and associated depletion width decreases monotonically with increased density of dopants near the NC surface. We calculate band profiles for NCs of differing radial dopant distributions and, in agreement with variable temperature conductivity fits, find NCs with dopant-enriched surfaces have narrower depletion widths and longer localization lengths than those with dopant-enriched cores. Following amelioration of NC surface depletion by atomic layer deposition of alumina, all films of equal overall dopant concentration have similar conductivity. Variable temperature conductivity measurements on alumina-capped films indicate all films behave as granular metals. Herein, we conclude that dopant-enriched surfaces decrease the near-surface depletion region, which directly increases the electron localization length and conductivity of NC films.

Gain and temperature in a slit nozzle supersonic chemical oxygen-iodine laser with transonic and supersonic injection of iodine

NASA Astrophysics Data System (ADS)

Rosenwaks, Salman; Barmashenko, Boris D.; Bruins, Esther; Furman, Dov; Rybalkin, Victor; Katz, Arje

2002-05-01

Spatial distributions of the gain and temperament across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser as a function of the iodine and secondary nitrogen flow rate, jet penetration parameter and gas pumping rate. The mixing efficiency for supersonic injection of iodine is found to be much larger than for transonic injection, the maximum values of the gain being approximately 0.65 percent/cm for both injection schemes. Measurements of the gain distribution as a function of the iodine molar flow rate nI2 were carried out. For transonic injection the optimal value of nI2 at the flow centerline is smaller than that at the off axis location. The temperature is distributed homogeneously across the flow, increasing only in the narrow boundary layers near the walls. Opening a leak downstream of the cavity in order to decease the Mach number results in a decrease of the gain and increase of the temperature. The mixing efficiency in this case is much larger than for closed leak.

Tuning Nanocrystal Surface Depletion by Controlling Dopant Distribution as a Route Toward Enhanced Film Conductivity.

PubMed

Staller, Corey M; Robinson, Zachary L; Agrawal, Ankit; Gibbs, Stephen L; Greenberg, Benjamin L; Lounis, Sebastien D; Kortshagen, Uwe R; Milliron, Delia J

2018-05-09

Electron conduction through bare metal oxide nanocrystal (NC) films is hindered by surface depletion regions resulting from the presence of surface states. We control the radial dopant distribution in tin-doped indium oxide (ITO) NCs as a means to manipulate the NC depletion width. We find in films of ITO NCs of equal overall dopant concentration that those with dopant-enriched surfaces show decreased depletion width and increased conductivity. Variable temperature conductivity data show electron localization length increases and associated depletion width decreases monotonically with increased density of dopants near the NC surface. We calculate band profiles for NCs of differing radial dopant distributions and in agreement with variable temperature conductivity fits find NCs with dopant-enriched surfaces have narrower depletion widths and longer localization lengths than those with dopant-enriched cores. Following amelioration of NC surface depletion by atomic layer deposition of alumina, all films of equal overall dopant concentration have similar conductivity. Variable temperature conductivity measurements on alumina-capped films indicate all films behave as granular metals. Herein, we conclude that dopant-enriched surfaces decrease the near-surface depletion region, which directly increases the electron localization length and conductivity of NC films.

Transition Effects on Heating in the Wake of a Blunt Body

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Perkins, John N.

1997-01-01

A series of aerodynamic heating tests was conducted on a 70-deg sphere-cone planetary entry vehicle model in a Mach 10 perfect-gas wind tunnel at freestream Reynolds numbers based on diameter of 8.23x104 to 3.15x105. Surface heating distributions were determined from temperature time-histories measured on the model and on its support sting using thin-film resistance gages. The experimental heating data were compared to computations made using an axisymmetric/2D, laminar, perfect-gas Navier-Stokes solver. Agreement between computational and experimental heating distributions to within, or slightly greater than, the experimental uncertainty was obtained on the forebody and afterbody of the entry vehicle as well as on the sting upstream of the free-shear-layer reattachment point. However, the distributions began to diverge near the reattachment point, with the experimental heating becoming increasingly greater than the computed heating with distance downstream from the reattachment point. It was concluded that this divergence was due to transition of the wake free shear layer just upstream of the reattachment point on the sting.

Statistical Analyses of Satellite Cloud Object Data From CERES. Part 4; Boundary-layer Cloud Objects During 1998 El Nino

NASA Technical Reports Server (NTRS)

Xu, Kuan-Man; Wong, Takmeng; Wielicki, Bruce A.; Parker, Lindsay

2006-01-01

Three boundary-layer cloud object types, stratus, stratocumulus and cumulus, that occurred over the Pacific Ocean during January-August 1998, are identified from the CERES (Clouds and the Earth s Radiant Energy System) single scanner footprint (SSF) data from the TRMM (Tropical Rainfall Measuring Mission) satellite. This study emphasizes the differences and similarities in the characteristics of each cloud-object type between the tropical and subtropical regions and among different size categories and among small geographic areas. Both the frequencies of occurrence and statistical distributions of cloud physical properties are analyzed. In terms of frequencies of occurrence, stratocumulus clouds dominate the entire boundary layer cloud population in all regions and among all size categories. Stratus clouds are more prevalent in the subtropics and near the coastal regions, while cumulus clouds are relatively prevalent over open ocean and the equatorial regions, particularly, within the small size categories. The largest size category of stratus cloud objects occurs more frequently in the subtropics than in the tropics and has much larger average size than its cumulus and stratocumulus counterparts. Each of the three cloud object types exhibits small differences in statistical distributions of cloud optical depth, liquid water path, TOA albedo and perhaps cloud-top height, but large differences in those of cloud-top temperature and OLR between the tropics and subtropics. Differences in the sea surface temperature (SST) distributions between the tropics and subtropics influence some of the cloud macrophysical properties, but cloud microphysical properties and albedo for each cloud object type are likely determined by (local) boundary-layer dynamics and structures. Systematic variations of cloud optical depth, TOA albedo, cloud-top height, OLR and SST with cloud object sizes are pronounced for the stratocumulus and stratus types, which are related to systematic variations of the strength of inversion with cloud object sizes, produced by large-scale subsidence. The differences in cloud macrophysical properties over small regions are significantly larger than those of cloud microphysical properties and TOA albedo, suggesting a greater control of (local) large-scale dynamics and other factors on cloud object properties. When the three cloud object types are combined, the relative population among the three types is the most important factor for determining the cloud object properties in a Pacific transect where the transition of boundary-layer cloud types takes place.

Temperature determination of shock layer using spectroscopic techniques

NASA Technical Reports Server (NTRS)

Akundi, Murty A.

1989-01-01

Shock layer temperature profiles are obtained through analysis of radiation from shock layers produced by a blunt body inserted in an arc jet flow. Spectral measurements of N2(+) have been made at 0.5 inch, 1.0 inch, and 1.4 inches from the blunt body. A technique is developed to measure the vibrational and rotational temperatures of N2(+). Temperature profiles from the radiation layers show a high temperature near the shock front and decreasing temperature near the boundary layer. Precise temperature measurements could not be made using this technique due to the limited resolution. Use of a high resolution grating will help to make a more accurate temperature determination. Laser induced fluorescence technique is much better since it gives the scope for selective excitation and a better spacial resolution.

Contemporary dynamics of active layer thickness of Northeastern Eurasia: evidence of climate warming, cooling or cyclicity?

NASA Astrophysics Data System (ADS)

Maslakov, A.; Tregubov, O.; Ruzanov, V.; Fedorov-Davydov, D.; Davydov, S. P.; Shiklomanov, N. I.; Streletskiy, D. A.

2017-12-01

Active layer is an intermediate position between the atmosphere and permafrost. It develops in warm period of the year in cryolithozone. Active layer thickness (ALT), or seasonal thaw depth is sensitive to the changes of the weather and climate; it also defines the intensity of such processes as thermokarst and thermal erosion, which have great impact on Arctic infrastructure. Active layer formation mechanism and natural factors affecting its spatial distribution are well studied on the regional scale, but high local variability of ALT brings uncertainty to the modelled results; it also forms multidirectional trends in interannual variations of ALT. This study presents the results of long-term observations of the seasonal thaw dynamics in Northeastern tip of Eurasia. The data is presented by field measurements, conducted in framework of Circumpolar Active Layer Monitoring (CALM) program and study materials of Dionisiya field permafrost station. The key sites are located in three areas: Kolyma lowland (NE Yakutia), Anadyr lowland (SW Chukotka) and Chukchi peninsula (Eastern Chukotka). They represent natural conditions ranging from typical tundra to northern taiga, developed on continuous permafrost extent. The analysis of interannual fluctuations of ALT and summer air temperatures detected common patterns and trends: the majority of considered monitoring sites demonstrates deepening of thaw depths, which was traced in 1980-1990s, following increasing summer air temperature. This period was followed by relative stabilization of ALT in 2000-2010s. Nevertheless, several sites in Kolyma lowland and in Eastern Chukotka demonstrate persistent ALT increase during 2000-2010, even despite of summer temperatures stabilization. At the same time monitoring sites in Dionisiya permafrost station show shrinking of seasonal thaw in 2005-2015. Presented study shows ambiguity of cryosphere response to climate changes and identifies the need for further studies of interaction between active layer and natural conditions.

Development of Naphthalene PLIF for Visualizing Ablation Products From a Space Capsule Heat Shield

NASA Technical Reports Server (NTRS)

Combs, C. S.; Clemens, N. T.; Danehy, P. M.

2014-01-01

The Orion Multi-Purpose Crew Vehicle (MPCV) will use an ablative heat shield. To better design this heat shield and others that will undergo planetary entry, an improved understanding of the ablation process would be beneficial. Here, a technique developed at The University of Texas at Austin that uses planar laser-induced fluorescence (PLIF) of a low-temperature sublimating ablator (naphthalene) to enable visualization of the ablation products in a hypersonic flow is applied. Although high-temperature ablation is difficult and expensive to recreate in a laboratory environment, low-temperature sublimation creates a limited physics problem that can be used to explore ablation-product transport in a hypersonic flow-field. In the current work, a subscale capsule reentry vehicle model with a solid naphthalene heat shield has been tested in a Mach 5 wind tunnel. The PLIF technique provides images of the spatial distribution of sublimated naphthalene in the heat-shield boundary layer, separated shear layer, and backshell recirculation region. Visualizations of the capsule shear layer using both naphthalene PLIF and Schlieren imaging compared favorably. PLIF images have shown high concentrations of naphthalene in the capsule separated flow region, intermittent turbulent structures on the heat shield surface, and interesting details of the capsule shear layer structure. It was shown that, in general, the capsule shear layer appears to be more unsteady at lower angels of attack. The PLIF images demonstrated that during a wind tunnel run, as the model heated up, the rate of naphthalene ablation increased, since the PLIF signal increased steadily over the course of a run. Additionally, the shear layer became increasingly unsteady over the course of a wind tunnel run, likely because of increased surface roughness but also possibly because of the increased blowing. Regions with a relatively low concentration of naphthalene were also identified in the capsule backshell recirculation region and are most likely the result of cross-flow-induced vortices on the capsule afterbody.

Defect-driven flexochemical coupling in thin ferroelectric films

NASA Astrophysics Data System (ADS)

Eliseev, Eugene A.; Vorotiahin, Ivan S.; Fomichov, Yevhen M.; Glinchuk, Maya D.; Kalinin, Sergei V.; Genenko, Yuri A.; Morozovska, Anna N.

2018-01-01

Using the Landau-Ginzburg-Devonshire theory, we considered the impact of the flexoelectrochemical coupling on the size effects in polar properties and phase transitions of thin ferroelectric films with a layer of elastic defects. We investigated a typical case, when defects fill a thin layer below the top film surface with a constant concentration creating an additional gradient of elastic fields. The defective surface of the film is not covered with an electrode, but instead with an ultrathin layer of ambient screening charges, characterized by a surface screening length. Obtained results revealed an unexpectedly strong effect of the joint action of Vegard stresses and flexoelectric effect (shortly flexochemical coupling) on the ferroelectric transition temperature, distribution of the spontaneous polarization and elastic fields, domain wall structure and period in thin PbTi O3 films containing a layer of elastic defects. A nontrivial result is the persistence of ferroelectricity at film thicknesses below 4 nm, temperatures lower than 350 K, and relatively high surface screening length (˜0.1 nm ) . The origin of this phenomenon is the flexoelectric coupling leading to the rebuilding of the domain structure in the film (namely the cross-over from c-domain stripes to a-type closure domains) when its thickness decreases below 4 nm. The ferroelectricity persistence is facilitated by negative Vegard effect. For positive Vegard effect, thicker films exhibit the appearance of pronounced maxima on the thickness dependence of the transition temperature, whose position and height can be controlled by the defect type and concentration. The revealed features may have important implications for miniaturization of ferroelectric-based devices.

Diversity and distribution of deep-sea shrimps in the Ross Sea region of Antarctica.

PubMed

Basher, Zeenatul; Bowden, David A; Costello, Mark J

2014-01-01

Although decapod crustaceans are widespread in the oceans, only Natantia (shrimps) are common in the Antarctic. Because remoteness, depth and ice cover restrict sampling in the South Ocean, species distribution modelling is a useful tool for evaluating distributions. We used physical specimen and towed camera data to describe the diversity and distribution of shrimps in the Ross Sea region of Antarctica. Eight shrimp species were recorded: Chorismus antarcticus; Notocrangon antarcticus; Nematocarcinus lanceopes; Dendrobranchiata; Pasiphaea scotiae; Pasiphaea cf. ledoyeri; Petalidium sp., and a new species of Lebbeus. For the two most common species, N. antarcticus and N. lanceopes, we used maximum entropy modelling, based on records of 60 specimens and over 1130 observations across 23 sites in depths from 269 m to 3433 m, to predict distributions in relation to environmental variables. Two independent sets of environmental data layers at 0.05° and 0.5° resolution respectively, showed how spatial resolution affected the model. Chorismus antarcticus and N. antarcticus were found only on the continental shelf and upper slopes, while N. lanceopes, Lebbeus n. sp., Dendrobranchiata, Petalidium sp., Pasiphaea cf. ledoyeri, and Pasiphaea scotiae were found on the slopes, seamounts and abyssal plain. The environmental variables that contributed most to models for N. antarcticus were depth, chlorophyll-a concentration, temperature, and salinity, and for N. lanceopes were depth, ice concentration, seabed slope/rugosity, and temperature. The relative ranking, but not the composition of these variables changed in models using different spatial resolutions, and the predicted extent of suitable habitat was smaller in models using the finer-scale environmental layers. Our modelling indicated that shrimps were widespread throughout the Ross Sea region and were thus likely to play important functional role in the ecosystem, and that the spatial resolution of data needs to be considered both in the use of species distribution models.

Diversity and Distribution of Deep-Sea Shrimps in the Ross Sea Region of Antarctica

PubMed Central

Basher, Zeenatul; Bowden, David A.; Costello, Mark J.

2014-01-01

Although decapod crustaceans are widespread in the oceans, only Natantia (shrimps) are common in the Antarctic. Because remoteness, depth and ice cover restrict sampling in the South Ocean, species distribution modelling is a useful tool for evaluating distributions. We used physical specimen and towed camera data to describe the diversity and distribution of shrimps in the Ross Sea region of Antarctica. Eight shrimp species were recorded: Chorismus antarcticus; Notocrangon antarcticus; Nematocarcinus lanceopes; Dendrobranchiata; Pasiphaea scotiae; Pasiphaea cf. ledoyeri; Petalidium sp., and a new species of Lebbeus. For the two most common species, N. antarcticus and N. lanceopes, we used maximum entropy modelling, based on records of 60 specimens and over 1130 observations across 23 sites in depths from 269 m to 3433 m, to predict distributions in relation to environmental variables. Two independent sets of environmental data layers at 0.05° and 0.5° resolution respectively, showed how spatial resolution affected the model. Chorismus antarcticus and N. antarcticus were found only on the continental shelf and upper slopes, while N. lanceopes, Lebbeus n. sp., Dendrobranchiata, Petalidium sp., Pasiphaea cf. ledoyeri, and Pasiphaea scotiae were found on the slopes, seamounts and abyssal plain. The environmental variables that contributed most to models for N. antarcticus were depth, chlorophyll-a concentration, temperature, and salinity, and for N. lanceopes were depth, ice concentration, seabed slope/rugosity, and temperature. The relative ranking, but not the composition of these variables changed in models using different spatial resolutions, and the predicted extent of suitable habitat was smaller in models using the finer-scale environmental layers. Our modelling indicated that shrimps were widespread throughout the Ross Sea region and were thus likely to play important functional role in the ecosystem, and that the spatial resolution of data needs to be considered both in the use of species distribution models. PMID:25051333

Permafrost conditions at the Upper Kuskokwim river area and its influence on local communities.

NASA Astrophysics Data System (ADS)

Kholodov, A. L.; Panda, S. K.; Hanson, T.

2017-12-01

Research area located within the zone of discontinuous permafrost distribution. Recent mean annual air temperature here is close to the 0C. It means, that taking in consideration warming influence of the snow cower during winter, mean annual temperature at the ground surface is well above freezing point. It means that presence or absence of permafrost here completely controlled by the ecological conditions. Based on remote sensing data and the surveys conducted in 2016-17 we selected 6 main ecotypes typical for this area: black spruce boreal forest, wetlands, low and tall shrubs, deciduous and mixed forest. Most of them (low shrubs, deciduous and mixed forest) represent different stages of area recovering after forest fires that was confirmed by the presence of ashy layer close to ground surface in soil pits had been dug within these landscapes. Permafrost was observed only within 2 of them: low shrubs and black spruce boreal forest. Within these types of terrain temperature at the bottom of active layer varies from -0.2/-0.5C at the areas of low shrubs, recovered after relatively recent (approximately 30-50 years old) fires to -1/-1.5 within black spruce forest. Active (seasonally thawed) layer as thick as 0.6 to 0.8 m. Warmest ecotypes for the area are tall shrubs and deciduous forest, temperature at the depth close to 1 m is about +3C. At the mixed forest temperature at the same depth consists of +1/+2C. Active (seasonally frozen) layer thickness within permafrost free areas is 1-1.5 m at the drained sites and about 0.5 within wetlands. Ice-rich permafrost underlying the active layer was noticed only within the black spruce forest. Areas which are free of permafrost are much better drained, typical moisture of mineral soil is less than 30% versus 45-50% in seasonally thawed layer. The current state of permafrost and the fact that it presence completely depends on ecosystems limits land use abilities of local inhabitants. Any changes of forest coverage or organic layer thickness will lead to permafrost degradation and initiate thermokarst process or dryness of the area that increases risk of wild fires. Also, shallow soil freezing within wetlands makes shorter the safe period of snow machines operation. Current research should help local communities make more informed decisions in adaptation of resources management and land use.

Modeling of transitional flows

NASA Technical Reports Server (NTRS)

Lund, Thomas S.

1988-01-01

An effort directed at developing improved transitional models was initiated. The focus of this work was concentrated on the critical assessment of a popular existing transitional model developed by McDonald and Fish in 1972. The objective of this effort was to identify the shortcomings of the McDonald-Fish model and to use the insights gained to suggest modifications or alterations of the basic model. In order to evaluate the transitional model, a compressible boundary layer code was required. Accordingly, a two-dimensional compressible boundary layer code was developed. The program was based on a three-point fully implicit finite difference algorithm where the equations were solved in an uncoupled manner with second order extrapolation used to evaluate the non-linear coefficients. Iteration was offered as an option if the extrapolation error could not be tolerated. The differencing scheme was arranged to be second order in both spatial directions on an arbitrarily stretched mesh. A variety of boundary condition options were implemented including specification of an external pressure gradient, specification of a wall temperature distribution, and specification of an external temperature distribution. Overall the results of the initial phase of this work indicate that the McDonald-Fish model does a poor job at predicting the details of the turbulent flow structure during the transition region.

The behavior of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient. Ph.D. Thesis - Washington Univ., Seattle, Aug. 1972

NASA Technical Reports Server (NTRS)

Rose, W. C.

1973-01-01

The results of an experimental investigation of the mean- and fluctuating-flow properties of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient are presented. The turbulent boundary layer developed on the wall of an axially symmetric nozzle and test section whose nominal free-stream Mach number and boundary-layer thickness Reynolds number were 4 and 100,000, respectively. The adverse pressure gradient was induced by an externally generated conical shock wave. Mean and time-averaged fluctuating-flow data, including the complete experimental Reynolds stress tensor and experimental turbulent mass- and heat-transfer rates are presented for the boundary layer and external flow, upstream, within and downstream of the pressure gradient. The mean-flow data include distributions of total temperature throughout the region of interest. The turbulent mixing properties of the flow were determined experimentally with a hot-wire anemometer. The calibration of the wires and the interpretation of the data are discussed. From the results of the investigation, it is concluded that the shock-wave - boundary-layer interaction significantly alters the turbulent mixing characteristics of the boundary layer.

Ocean barrier layers’ effect on tropical cyclone intensification

PubMed Central

Balaguru, Karthik; Chang, Ping; Saravanan, R.; Leung, L. Ruby; Xu, Zhao; Li, Mingkui; Hsieh, Jen-Shan

2012-01-01

Improving a tropical cyclone’s forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone’s path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are “quasi-permanent” features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropical cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity. PMID:22891298

Ocean Barrier Layers’ Effect on Tropical Cyclone Intensification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balaguru, Karthik; Chang, P.; Saravanan, R.

2012-09-04

Improving a tropical cyclone's forecast and mitigating its destructive potential requires knowledge of various environmental factors that influence the cyclone's path and intensity. Herein, using a combination of observations and model simulations, we systematically demonstrate that tropical cyclone intensification is significantly affected by salinity-induced barrier layers, which are 'quasi-permanent' features in the upper tropical oceans. When tropical cyclones pass over regions with barrier layers, the increased stratification and stability within the layer reduce storm-induced vertical mixing and sea surface temperature cooling. This causes an increase in enthalpy flux from the ocean to the atmosphere and, consequently, an intensification of tropicalmore » cyclones. On average, the tropical cyclone intensification rate is nearly 50% higher over regions with barrier layers, compared to regions without. Our finding, which underscores the importance of observing not only the upper-ocean thermal structure but also the salinity structure in deep tropical barrier layer regions, may be a key to more skillful predictions of tropical cyclone intensities through improved ocean state estimates and simulations of barrier layer processes. As the hydrological cycle responds to global warming, any associated changes in the barrier layer distribution must be considered in projecting future tropical cyclone activity.« less