Efficiently reducing transition curvature in heat-assisted magnetic recording with state-of-the-art write heads

NASA Astrophysics Data System (ADS)

Vogler, Christoph; Abert, Claas; Bruckner, Florian; Suess, Dieter

2017-05-01

Curvatures of bit transitions on granular media are a serious problem for the read-back process. We address this fundamental issue and propose a possibility to efficiently reduce transition curvatures with state-of-the-art heat-assisted magnetic recording heads. We compare footprints of conventional with those of the proposed head design on different media, consisting of exchange coupled and single phase grains. Additionally, we investigate the impact of various recording parameters, such as the full width at half maximum (FWHM) of the applied heat pulse and the coercivity gradient near the write temperature of the recording grains. The footprints are calculated with a coarse grained model, based on the Landau-Lifshitz-Bloch equation. The presented simulations show a transition curvature reduction of up to 40%, in the case of a medium with exchange coupled grains and a heat pulse with a FWHM of 40 nm. We further give the reason for the straightening of the bit transitions, by means of basic considerations with regard to the effective recording time window of the write process. Besides the transition curvature reduction, the proposed head design yields an improvement of the transition jitter in both down-track and off-track directions.

A two-beam acoustic system for tissue analysis.

PubMed

Sachs, T D; Janney, C D

1977-03-01

In the 'thermo-acoustic sensing technique' (TAST), a burst of sound, called the 'thermometer' beam is passed through tissue and its transit time is measured. A focused sound field, called the heating field, then warms a small volume in the path of the therometer beam, in proportion to the absorption. Finally, the therometer beam burst is repeated and its transit time subtracted from that of the initial thermometer burst. This difference measures the velocity perturbation in the tissue produced by the heating field. The transit time difference is td = K integral of infinity-infinity IP dchi where K is the instrument constant, I the heating field intensity, and P a perturbation factor which characterizes the tissues. The integration is carried out along the path of the thermometer beam. The perturbation factor is P = (formula: see text) where C is the specific heat, rho the denisty, V the velocity of sound, (formula: see text) the temperature coefficient of velocity and alpha the heating field absorption coefficient which is apparently sensitive to tissue structure and condition. Experiments on a fixed human brain showed an ability to distinguish between various tissue types combined with a spatial resolution of better than 3 mm. Should predictions based on the data and theory prove correct, TAST may become a non-invasive alternative to biopsy.

The quantum phase-transitions of water

NASA Astrophysics Data System (ADS)

Fillaux, François

2017-08-01

It is shown that hexagonal ices and steam are macroscopically quantum condensates, with continuous spacetime-translation symmetry, whereas liquid water is a quantum fluid with broken time-translation symmetry. Fusion and vaporization are quantum phase-transitions. The heat capacities, the latent heats, the phase-transition temperatures, the critical temperature, the molar volume expansion of ice relative to water, as well as neutron scattering data and dielectric measurements are explained. The phase-transition mechanisms along with the key role of quantum interferences and that of Hartley-Shannon's entropy are enlightened. The notions of chemical bond and force-field are questioned.

Transitions to improved confinement regimes induced by changes in heating in zero-dimensional models for tokamak plasmas

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

Zhu, H.; Chapman, S. C.; Max Planck Institute for the Physics of Complex Systems, Dresden

2014-06-15

It is shown that rapid substantial changes in heating rate can induce transitions to improved energy confinement regimes in zero-dimensional models for tokamak plasma phenomenology. We examine for the first time the effect of step changes in heating rate in the models of Kim and Diamond [Phys. Rev. Lett. 90, 185006 (2003)] and Malkov and Diamond [Phys. Plasmas 16, 012504 (2009)], which nonlinearly couple the evolving temperature gradient, micro-turbulence, and a mesoscale flow; and in the extension of Zhu et al. [Phys. Plasmas 20, 042302 (2013)], which couples to a second mesoscale flow component. The temperature gradient rises, as doesmore » the confinement time defined by analogy with the fusion context, while micro-turbulence is suppressed. This outcome is robust against variation of heating rise time and against introduction of an additional variable into the model. It is also demonstrated that oscillating changes in heating rate can drive the level of micro-turbulence through a period-doubling path to chaos, where the amplitude of the oscillatory component of the heating rate is the control parameter.« less

On the approach to Mott's transition in glass-ceramic nanocomposite due to heat treatment

NASA Astrophysics Data System (ADS)

Mahdy, Iman A.; Heikal, Sh.; Abd-Rabo, A. S.; Abdel Ghany, A.; Bahgat, A. A.

2015-07-01

In the present work, the glass-ceramic nanocomposite (GCNC) of the composition 30[0.75 BaTiO3+0.25 PbTiO3]+70 V2O5 (mol. %) was prepared from the parent glass by isothermal heat treatment (HT) at 723 K for different time intervals 0.25, 0.5, 1.5, 2, and 2.5 h, respectively. The bulk density and some related parameters were calculated. X-ray diffraction and Hi-Resolution Transmission Electron Microscope (HRTEM) were used to identify different phases as well as particle size of the precipitated nanocrystals during the heat treatment process. The DC electrical conductivity was enhanced three orders of magnitudes (3×103) by increasing HT time. The resistivity measurements on the other hand as a function of time show an approach to nonmetallic-metallic transition for the prepared NCGC samples. Mott's VRH conduction mechanism was predicted as a result of the increase of the heat treatment time.

Impact of heat treatment on the physical properties of noncrystalline multisolute systems concentrated in frozen aqueous solutions.

PubMed

Izutsu, Ken-ichi; Yomota, Chikako; Kawanishi, Toru

2011-12-01

The purpose of this study was to elucidate the effect of heat treatment on the miscibility of multiple concentrated solutes that mimic biopharmaceutical formulations in frozen solutions. The first heating thermal analysis of frozen solutions containing either a low-molecular-weight saccharide (e.g., sucrose, trehalose, and glucose) or a polymer (e.g., polyvinylpyrrolidone and dextran) and their mixtures from -70°C showed a single transition at glass transition temperature of maximally freeze-concentrated solution (T(g) ') that indicated mixing of the freeze-concentrated multiple solutes. The heat treatment of single-solute and various polymer-rich mixture frozen solutions at temperatures far above their T(g) ' induced additional ice crystallization that shifted the transitions upward in the following scan. Contrarily, the heat treatment of frozen disaccharide-rich solutions induced two-step heat flow changes (T(g) ' splitting) that suggested separation of the solutes into multiple concentrated noncrystalline phases, different in the solute compositions. The extent of the T(g) ' splitting depended on the heat treatment temperature and time. Two-step glass transition was observed in some sucrose and dextran mixture solids, lyophilized after the heat treatment. Increasing mobility of solute molecules during the heat treatment should allow spatial reordering of some concentrated solute mixtures into thermodynamically favorable multiple phases. Copyright © 2011 Wiley-Liss, Inc.

Determination of Optimal Heat-Storage Thickness of Layer for “Smart Wall” by Methods of Nonlinear Heat Conduction Equations for Phase-transition Materials

NASA Astrophysics Data System (ADS)

Pospelova, I.

2017-11-01

The article suggests an original way of keeping heat load and its compensation for a microclimate system by proposing the “Smart Wall”. The construction consists of specially combined composite materials including phase-transition materials. The method for determination of the layer thickness is proposed for a certain accumulation time. Varying the thickness and composition of the layer it is possible to achieve a low amount of the thermal conductivity coefficient and to obtain various functional characteristics of fences.

A theory of heating of quiet solar corona

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

Wu, C. S., E-mail: cszcwu@msn.com; Institute of Space Science, National Central University, Zhongli 32001, Taiwan; Insitute for Physical Sciences and Technology, University of Maryland, College Park, Maryland 20742

A theory is proposed to discuss the creation of hot solar corona. We pay special attention to the transition region and the low corona, and consider that the sun is quiet. The proposed scenario suggests that the protons are heated by intrinsic Alfvénic turbulence, while the ambient electrons are heated by the hot protons via collisions. The theory contains two prime components: the generation of the Alfvénic fluctuations by the heavy minor ions in the transition region and second, the explanation of the temperature profile in the low solar atmosphere. The proposed heating process operates continuously in time and globallymore » in space.« less

Latent heat of vehicular motion

NASA Astrophysics Data System (ADS)

Ahmadi, Farzad; Berrier, Austin; Habibi, Mohammad; Boreyko, Jonathan

2016-11-01

We have used the thermodynamic concept of latent heat, where a system loses energy due to a solid-to-liquid phase transition, to study the flow of a group of vehicles moving from rest. During traffic flow, drivers keep a large distance from the car in front of them to ensure safe driving. When a group of cars comes to a stop, for example at a red light, drivers voluntarily induce a "phase transition" from this "liquid phase" to a close-packed "solid phase." This phase transition is motivated by the intuition that maximizing displacement before stopping will minimize the overall travel time. To test the effects of latent heat on flow efficiency, a drone captured the dynamics of cars flowing through an intersection on a Smart Road where the initial spacing between cars at the red light was systematically varied. By correlating the experimental results with the Optimal Velocity Model (OVM), we find that the convention of inducing phase transitions at intersections offers no benefit, as the lag time (latent heat) of resumed flow offsets the initial increase in displacement. These findings suggest that in situations where gridlock is not an issue, drivers should not decrease their spacing during stoppages in order to maximize safety with no loss in flow efficiency.

Reversing and nonreversing heat capacity of poly(lactic acid) in the glass transition region by TMDSC

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

Pyda, Marek; Wunderlich, Bernhard

2005-11-01

A study of the glass transition of an amorphous and a semicrystalline poly(lactic acid) (PLA) is performed with adiabatic calorimetry, differential scanning calorimetry (DSC), and temperature-modulated DSC (TMDSC). The reversing, total, and nonreversing apparent heat capacities of samples with different contents of L- and D-lactic acid and with various thermal histories were evaluated. Different modes of TMDSC analyses of amorphous and semicrystalline PLA were compared to the total heat capacity from standard DSC. The enthalpy relaxation and the cold crystallization in the glass transition region are largely irreversible. The melting is largely irreversible, but a 100% reversing fraction is observedmore » at low temperatures from 375 to 420 K, which becomes small inside the major melting peak at about 440 K. From the TMDSC of amorphous PLA, the combined information on endothermic and exothermic enthalpy relaxation and glass transition were deconvoluted into the reversing and nonreversing components. The glass transition temperature from the reversing heat capacity and the enthalpy relaxation peaks from the nonreversing component shift to higher temperature for increasingly annealed PLA. The relaxation times for aging decrease on cooling until the glass transition is reached and then increase. This behavior is linked to cooperativity. All quantitative thermal analyses are based on the heat capacity of the solid and liquid, evaluated earlier with the advanced thermal analysis system (ATHAS).« less

Joule Heating-Induced Metal-Insulator Transition in Epitaxial VO2/TiO2 Devices.

PubMed

Li, Dasheng; Sharma, Abhishek A; Gala, Darshil K; Shukla, Nikhil; Paik, Hanjong; Datta, Suman; Schlom, Darrell G; Bain, James A; Skowronski, Marek

2016-05-25

DC and pulse voltage-induced metal-insulator transition (MIT) in epitaxial VO2 two terminal devices were measured at various stage temperatures. The power needed to switch the device to the ON-state decrease linearly with increasing stage temperature, which can be explained by the Joule heating effect. During transient voltage induced MIT measurement, the incubation time varied across 6 orders of magnitude. Both DC I-V characteristic and incubation times calculated from the electrothermal simulations show good agreement with measured values, indicating Joule heating effect is the cause of MIT with no evidence of electronic effects. The width of the metallic filament in the ON-state of the device was extracted and simulated within the thermal model.

Melting and Freezing of Metals Under the High Pressures of Planetary Interiors

NASA Astrophysics Data System (ADS)

Geballe, Zachary Michael

The goal of this thesis is to help improve models of the evolution of cores of the Earth and other planets, and to improve understanding of melting transitions of metals in general. First, I present laboratory studies of high-pressure melting and near-melting phase transitions of two metals. The epsilon-to-B2 phase boundary of FeSi is constrained to 30 +/- 2 GPa with no measurable pressure-dependence from 1200 +/- 200 to 2300 +/- 200 K using x-ray diffraction in laser heated diamond anvil cells. The miscibility of Si in crystalline Fe likely increases at this transition due to the increasing effective ionic radius of Si, evidenced by the coordination change documented here. The result is that silicon is even more miscible in iron in the cores of Mercury and Mars than shown previously. Solid-solid transitions are also documented in AuGa2 from cubic (fluorite-type) to denser phases above 5.5 GPa and 600 K, in close proximity to the reversal in melting curve from negative slope to positive slope, which is also documented here. The change in melting curve therefore seems to be primarily driven by the crystallographic transitions and not the electronic transitions thought to occur at low temperatures. All transitions described here are reversed in the experiments, revealing hysteresis that ranges from 90 K to less than 15 K, and from 7 GPa to less than 2 GPa. This complexity, along with other complexities seen here and in other studies, suggest the need for new experimental techniques to make unambiguous measurements of a variety of equilibrium properties at melting and near melting. To improve future laboratory studies of melting at high pressure, I analyze several varieties of dynamic heating experiments. Laser heating experiments on metals in diamond anvil cells are shown to be at least 5 times less sensitive (and sometimes > 100 times less sensitive) to the latent heat of melting than suggested by published experimental data from pulsed-heating and continuous-heating experiments. Rather, experimentally detected plateaus in temperature likely result from changes in reflectivity of the laser absorber. To reveal a material's energetic properties (latent heat or heat capacity) in the highly conductive environment of diamond cells, heating frequencies >100 kHz should be used, and heat should be deposited uniformly through the material. Specifically, an "adiabaticity parameter'' is presented in Chapter 4 to guide experiments seeking to measure temperature plateaus that reveal the latent heats of first order phase transitions. Focusing on heat capacity alone, two experimental possibilities are described in Chapter 5: relative measures of heat capacity of metallic samples using modulated laser heating at 1 MHz to 1 GHz, and absolute measure of heat capacity using Joule-heating of metallic samples at 1 to 100 MHz frequency. Finally, Chapter 6 shows that a specific experimental design for Joule-heating is feasible: a realistic electrical circuit using two amplifiers and a Wheatstone bridge can couple electrical current into a diamond-cell-sized metal sample and output 20 mu V residual voltage oscillations induced by the sample's 1 MHz temperature oscillations, allowing measurement of the sample's heat capacity with 11% contribution from the insulation. The thermal models of Joule heating in diamond cells are validated by laboratory data of the heat capacity of a nickel foil pressed between thin glass pieces glued to a diamond: measured heat capacities decrease from 100s of % above the actual heat capacity of a 6 mu m-thick nickel sample at ≤ 1 kHz, to within ~ 20% of the actual heat capacity at 30 kHz.

Heat Transfer in a Superelliptic Transition Duct

NASA Technical Reports Server (NTRS)

Poinsatte, Philip; Thurman, Douglas; Hippensteele, Steven

2008-01-01

Local heat transfer measurements were experimentally mapped using a transient liquid-crystal heat transfer technique on the surface of a circular-to-rectangular transition duct. The transition duct had a length-to-diameter ratio of 1.5 and an exit-plane aspect ratio of 3. The crosssectional geometry was defined by the equation of a superellipse. The cross-sectional area was the same at the inlet and exit but varied up to 15 percent higher through the transition. The duct was preheated to a uniform temperature (nominally 64 C) before allowing room temperature air to be suddenly drawn through it. As the surface cooled, the resulting isothermal contours on the duct surface were revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record was made of the surface temperature and time data for all points on the duct surfaces during each test. Using this surface temperature-time data together with the temperature of the air flowing through the model and the initial temperature of the model wall, the heat transfer coefficient was calculated by employing the classic one-dimensional, semi-infinite wall heat transfer conduction model. Test results are reported for inlet diameter-based Reynolds numbers ranging from 0.4x106 to 2.4x106 and two grid-generated freestream turbulence intensities of about 1 percent, which is typical of wind tunnels, and up to 16 percent, which may be more typical of real engine conditions.

Real-time aerodynamic heating and surface temperature calculations for hypersonic flight simulation

NASA Technical Reports Server (NTRS)

Quinn, Robert D.; Gong, Leslie

1990-01-01

A real-time heating algorithm was derived and installed on the Ames Research Center Dryden Flight Research Facility real-time flight simulator. This program can calculate two- and three-dimensional stagnation point surface heating rates and surface temperatures. The two-dimensional calculations can be made with or without leading-edge sweep. In addition, upper and lower surface heating rates and surface temperatures for flat plates, wedges, and cones can be calculated. Laminar or turbulent heating can be calculated, with boundary-layer transition made a function of free-stream Reynolds number and free-stream Mach number. Real-time heating rates and surface temperatures calculated for a generic hypersonic vehicle are presented and compared with more exact values computed by a batch aeroheating program. As these comparisons show, the heating algorithm used on the flight simulator calculates surface heating rates and temperatures well within the accuracy required to evaluate flight profiles for acceptable heating trajectories.

Turbine Vane External Heat Transfer. Volume 2. Numerical Solutions of the Navier-stokes Equations for Two- and Three-dimensional Turbine Cascades with Heat Transfer

NASA Technical Reports Server (NTRS)

Yang, R. J.; Weinberg, B. C.; Shamroth, S. J.; Mcdonald, H.

1985-01-01

The application of the time-dependent ensemble-averaged Navier-Stokes equations to transonic turbine cascade flow fields was examined. In particular, efforts focused on an assessment of the procedure in conjunction with a suitable turbulence model to calculate steady turbine flow fields using an O-type coordinate system. Three cascade configurations were considered. Comparisons were made between the predicted and measured surface pressures and heat transfer distributions wherever available. In general, the pressure predictions were in good agreement with the data. Heat transfer calculations also showed good agreement when an empirical transition model was used. However, further work in the development of laminar-turbulent transitional models is indicated. The calculations showed most of the known features associated with turbine cascade flow fields. These results indicate the ability of the Navier-Stokes analysis to predict, in reasonable amounts of computation time, the surface pressure distribution, heat transfer rates, and viscous flow development for turbine cascades operating at realistic conditions.

Impact of heat treatment on miscibility of proteins and disaccharides in frozen solutions.

PubMed

Izutsu, Ken-ichi; Yomota, Chikako; Okuda, Haruhiro; Kawanishi, Toru; Randolph, Theodore W; Carpenter, John F

2013-10-01

The purpose of this study was to elucidate the effect of heat treatment (annealing) on the miscibility of concentrated protein and disaccharide mixtures in the freezing segment of lyophilization. Frozen solutions containing a protein (e.g., recombinant human albumin, chicken egg lysozyme, bovine plasma immunoglobulin G, or a humanized IgG1k monoclonal antibody) and a non-reducing disaccharide (e.g., sucrose or trehalose) showed single thermal transitions of the solute mixtures (glass transition temperature of maximally freeze-concentrated solutes: T(g)(')) in their first heating scans. Heat treatment (e.g., -5 °C, 30 min) of some disaccharide-rich mixture frozen solutions at temperatures far above their T(g)(') induced two-step T(g)(') transitions in the subsequent scans, suggesting the separation of the solutes into concentrated protein-disaccharide mixture phase and disaccharide phase. Other frozen solutions showed a single transition of the concentrated solute mixture both before and after heat treatment. The apparent effects of the heat treatment temperature and time on the changes in thermal properties suggest molecular reordering of the concentrated solutes from a kinetically fixed mixture state to a more thermodynamically favorable state as a result of increased mobility. The implications of these phenomena on the quality of protein formulations are discussed. Copyright © 2013 Elsevier B.V. All rights reserved.

Characterization of structural response to hypersonic boundary-layer transition

DOE PAGES

Riley, Zachary B.; Deshmukh, Rohit; Miller, Brent A.; ...

2016-05-24

The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and theymore » can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.« less

Twin solution calorimeter determines heats of formation of alloys at high temperatures

NASA Technical Reports Server (NTRS)

Darby, J. B., Jr.; Kleb, R.; Kleppa, O. J.

1968-01-01

Calvert-type, twin liquid metal solution calorimeter determines the heats of formation of transition metal alloys at high temperatures. The twin differential calorimeter measures the small heat effects generated over extended periods of time, has maximum operating temperature of 1073 degrees K and an automatic data recording system.

Low Reynolds number kappa-epsilon and empirical transition models for oscillatory pipe flow and heat transfer. M.S. Thesis

NASA Technical Reports Server (NTRS)

Bauer, Christopher

1993-01-01

Stirling engine heat exchangers are shell-and-tube type with oscillatory flow (zero-mean velocity) for the inner fluid. This heat transfer process involves laminar-transition turbulent flow motions under oscillatory flow conditions. A low Reynolds number kappa-epsilon model, (Lam-Bremhorst form), was utilized in the present study to simulate fluid flow and heat transfer in a circular tube. An empirical transition model was used to activate the low Reynolds number k-e model at the appropriate time within the cycle for a given axial location within the tube. The computational results were compared with experimental flow and heat transfer data for: (1) velocity profiles, (2) kinetic energy of turbulence, (3) skin friction factor, (4) temperature profiles, and (5) wall heat flux. The experimental data were obtained for flow in a tube (38 mm diameter and 60 diameter long), with the maximum Reynolds number based on velocity being Re(sub max) = 11840, a dimensionless frequency (Valensi number) of Va = 80.2, at three axial locations X/D = 16, 30 and 44. The agreement between the computations and the experiment is excellent in the laminar portion of the cycle and good in the turbulent portion. Moreover, the location of transition was predicted accurately. The Low Reynolds Number kappa-epsilon model, together with an empirical transition model, is proposed herein to generate the wall heat flux values at different operating parameters than the experimental conditions. Those computational data can be used for testing the much simpler and less accurate one dimensional models utilized in 1-D Stirling Engine design codes.

Experiments of Transient Condensation Heat Transfer on the Heat Flux Senor

NASA Astrophysics Data System (ADS)

Wang, Xuwen; Liu, Qiusheng; Zhu, Zhiqiang; Chen, Xue

2015-09-01

The influence of transient heat transfer in different condensation condition was investigated experimentally in the present paper. Getting condensation heat and mass transfer regularity and characteristics in space can provide theoretical basis for thermodynamic device such as heat pipes, loop heat pipes and capillary pumped loops as well as other fluid management engineering designing. In order to study the condensation process in space, an experimental study has been carried out on the ground for space experiment. The results show that transit heat transfer coefficient of film condensation is related to the condensation film width, the flow condition near the two phase interface and the pressure of the vapor and non-condensable gas in chamber. On the ground, the condensation heat flux on vertical surface is higher than it on horizontal surface. The transit heat flux of film condensation is affected by the temperature of superheated vapor, the temperature of condensation surface and non-condensable gas pressure. Condensation heat flux with vapor forced convection is many times more than it with natural convection. All of heat flux for both vapor forced convection and natural convection condensation in limited chamber declines dramatically over time. The present experiment is preliminary work for our future space experiments of the condensation and heat transfer process onboard the Chinese Spacecraft "TZ-1" to be launched in 2016.

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

Weese, R K; Burnham, A K

Dimensional changes related to temperature cycling of the {beta} and {delta} polymorphs of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) are important for a variety of applications. The coefficient of thermal expansion (CTE) of the {beta} and {delta} phases are measured over a temperature range of -20 C to 215 C by thermo-mechanical analysis (TMA). Dimensional changes associated with the phase transition were also measured, and the time-temperature dependence of the dimensional change is consistent with phase transition kinetics measured earlier by differential scanning calorimetry (DSC). One HMX sample measured by TMA during its initial heating and again three days later during a second heatingmore » showed the {beta}-to-{delta} phase transition a second time, thereby indicating back conversion from {delta}-to-{beta} phase HMX during those three days. DSC was used to measure kinetics of the {delta}-to-{beta} back conversion. The most successful approach was to first heat the material to create the {delta} phase, then after a given period at room temperature, measure the heat absorbed during a second pass through the {beta}-to-{delta} phase transition. Back conversion at room temperature follows nucleation-growth kinetics.« less

Implementation of a Transition Model in a NASA Code and Validation Using Heat Transfer Data on a Turbine Blade

NASA Technical Reports Server (NTRS)

Ameri, Ali A.

2012-01-01

The purpose of this report is to summarize and document the work done to enable a NASA CFD code to model laminar-turbulent transition process on an isolated turbine blade. The ultimate purpose of the present work is to down-select a transition model that would allow the flow simulation of a variable speed power turbine to be accurately performed. The flow modeling in its final form will account for the blade row interactions and their effects on transition which would lead to accurate accounting for losses. The present work only concerns itself with steady flows of variable inlet turbulence. The low Reynolds number k- model of Wilcox and a modified version of the same model will be used for modeling of transition on experimentally measured blade pressure and heat transfer. It will be shown that the k- model and its modified variant fail to simulate the transition with any degree of accuracy. A case is thus made for the adoption of more accurate transition models. Three-equation models based on the work of Mayle on Laminar Kinetic Energy were explored. The three-equation model of Walters and Leylek was thought to be in a relatively mature state of development and was implemented in the Glenn-HT code. Two-dimensional heat transfer predictions of flat plate flow and two-dimensional and three-dimensional heat transfer predictions on a turbine blade were performed and reported herein. Surface heat transfer rate serves as sensitive indicator of transition. With the newly implemented model, it was shown that the simulation of transition process is much improved over the baseline k- model for the single Reynolds number and pressure ratio attempted; while agreement with heat transfer data became more satisfactory. Armed with the new transition model, total-pressure losses of computed three-dimensional flow of E3 tip section cascade were compared to the experimental data for a range of incidence angles. The results obtained, form a partial loss bucket for the chosen blade. In time the loss bucket will be populated with losses at additional incidences. Results obtained thus far will be discussed herein.

Reduction of ion thermal diffusivity associated with the transition of the radial electric field in neutral-beam-heated plasmas in the large helical device.

PubMed

Ida, K; Funaba, H; Kado, S; Narihara, K; Tanaka, K; Takeiri, Y; Nakamura, Y; Ohyabu, N; Yamazaki, K; Yokoyama, M; Murakami, S; Ashikawa, N; deVries, P C; Emoto, M; Goto, M; Idei, H; Ikeda, K; Inagaki, S; Inoue, N; Isobe, M; Itoh, K; Kaneko, O; Kawahata, K; Khlopenkov, K; Komori, A; Kubo, S; Kumazawa, R; Liang, Y; Masuzaki, S; Minami, T; Miyazawa, J; Morisaki, T; Morita, S; Mutoh, T; Muto, S; Nagayama, Y; Nakanishi, H; Nishimura, K; Noda, N; Notake, T; Kobuchi, T; Ohdachi, S; Ohkubo, K; Oka, Y; Osakabe, M; Ozaki, T; Pavlichenko, R O; Peterson, B J; Sagara, A; Saito, K; Sakakibara, S; Sakamoto, R; Sanuki, H; Sasao, H; Sasao, M; Sato, K; Sato, M; Seki, T; Shimozuma, T; Shoji, M; Suzuki, H; Sudo, S; Tamura, N; Toi, K; Tokuzawa, T; Torii, Y; Tsumori, K; Yamamoto, T; Yamada, H; Yamada, I; Yamaguchi, S; Yamamoto, S; Yoshimura, Y; Watanabe, K Y; Watari, T; Hamada, Y; Motojima, O; Fujiwara, M

2001-06-04

Recent large helical device experiments revealed that the transition from ion root to electron root occurred for the first time in neutral-beam-heated discharges, where no nonthermal electrons exist. The measured values of the radial electric field were found to be in qualitative agreement with those estimated by neoclassical theory. A clear reduction of ion thermal diffusivity was observed after the mode transition from ion root to electron root as predicted by neoclassical theory when the neoclassical ion loss is more dominant than the anomalous ion loss.

Thermal Comfort and Energy Consumption Using Different Radiant Heating/Cooling Systems in a Modern Office Building

NASA Astrophysics Data System (ADS)

Nemethova, Ema; Stutterecker, Werner; Schoberer, Thomas

2017-06-01

The aim of the study is to evaluate the potential of enhancing thermal comfort and energy consumption created by three different radiant systems in the newly-built Energetikum office building. A representative office, Simulation room 1/1, was selected from 6 areas equipped with portable sensor groups for the indoor environment monitoring. The presented data obtained from 3 reference weeks; the heating, transition and cooling periods indicate overheating, particularly during the heating and transition period. The values of the indoor air temperature during the heating and transition period could not meet the normative criteria according to standard EN 15251:2007 (cat. II.) for 15-30% of the time intervals evaluated. Consequently, a simulation model of the selected office was created and points to the possibilities of improving the control system, which can lead to an elimination of the problem with overheating. Three different radiant systems - floor heating/ cooling, a thermally active ceiling, and a near-surface thermally active ceiling were implemented in the model. A comparison of their effects on thermal comfort and energy consumption is presented in the paper.

Fragile-to-fragile liquid transition at Tg and stable-glass phase nucleation rate maximum at the Kauzmann temperature TK

NASA Astrophysics Data System (ADS)

Tournier, Robert F.

2014-12-01

An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change Δp accompanying the enthalpy change -Vm×Δp at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at T≤Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atom, touching and interpenetrating, are evaluated from nucleation rates. A fragile-to-fragile liquid transition occurs at Tg without stable-glass formation while a strong glass is stable after transition.

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water.

PubMed

Chiu, Janet; Starr, Francis W; Giovambattista, Nicolas

2014-03-21

Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to-HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T "phase diagram" for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA).

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water

NASA Astrophysics Data System (ADS)

Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas

2014-03-01

Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to-HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T "phase diagram" for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA).

Irreversible phase transitions due to laser-based T-jump heating of precursor Eu:ZrO{sub 2}/Tb:Y{sub 2}O{sub 3} core/shell nanoparticles

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

Gunawidjaja, Ray; Diez-y-Riega, Helena; Eilers, Hergen, E-mail: eilers@wsu.edu

2015-09-15

Amorphous precursors of Eu-doped-ZrO{sub 2}/Tb-doped-Y{sub 2}O{sub 3} (p-Eu:ZrO{sub 2}/p-Tb:Y{sub 2}O{sub 3}) core/shell nanoparticles are rapidly heated to temperatures between 200 °C and 950 °C for periods between 2 s and 60 s using a CO{sub 2} laser. During this heating process the nanoparticles undergo irreversible phase changes. The fluorescence spectra due to Eu{sup 3+} dopants in the core and Tb{sup 3+} dopants in the shell are used to identify distinct phases within the material and to generate time/temperature phase diagrams. Such phase diagrams can potentially help to determine unknown time/temperature histories in thermosensor applications. - Graphical abstract: A CO{sub 2}more » laser is used for rapid heating of p-Eu:ZrO{sub 2}/p-Tb:Y{sub 2}O{sub 3} core/shell nanoparticles. Optical spectra are used to identify distinct phases and to determine its thermal history. - Highlights: • Synthesized oxide precursors of lanthanide doped core/shell nanoparticles. • Heated core/shell nanoparticles via laser-based T-jump technique. • Observed time- and temperature-dependent irreversible phase transition.« less

Precise new shock temperatures in forsterite and in silicate liquids: phase transitions and heat capacity at high pressure

NASA Astrophysics Data System (ADS)

Asimow, P. D.; Fat'yanov, O. V.; Su, C.; Ma, X. J.

2017-12-01

Shock temperature measurements in transparent samples provide key constraints on the phase transitions and thermodynamic properties of materials at high pressure and temperature. Such measurements are necessary, for example, to allow equation of state measurements taken along the Hugoniot to be translated to P-V-T space. We have recently completed a detailed study of the accuracy and reproducibility of calibration of our 6-channel fast pyrometer. We have also introduced improved analysis procedures of the time-dependent multi-wavelength radiance signal that avoid the need for a greybody assumption and therefore have better precision than earlier results. This has motivated (a) renewed study of the shock temperature of forsterite in the superheating, partial melting, and complete melting regimes, (b) pre-heated diopside-anorthite glass shock temperature experiments for comparison to pre-heated silicate liquid equation of state results, and (c) new soda-lime glass shock temperature experiments. Single-crystal synthetic forsterite samples were shocked along (100) to pressures between 120 and 210 GPa on the Caltech two-stage light gas gun. Uncertainties on most results are 50 K. Results above the onset of partial melting at 130 GPa are consistent with Lyzenga and Ahrens (1980) data and show a low P-T slope consistent with a partial melting interval. Complete melting may occur, given sufficient time, at about 210 GPa. The experiment at 120-130 GPa is anomalous, showing two-wave structure and time- and wavelength-dependent scattering suggesting a subsolidus phase transition behind the shock front. The amount of super-heating, if any, is far smaller than claimed by Holland and Ahrens (1997). Steady radiation profiles, high emissivity, and consistency from channel to channel provide high precision (±40 K) in diopside-anorthite liquid shocked from just above the glass transition to high pressure. Temperatures are colder than expected for a model with constant heat capacity, providing direct evidence that multicomponent silicate liquids show a major increase in heat capacity in the P-T range appropriate to terrestrial magma oceans (<150 GPa, <5000 K).

Melting, glass transition, and apparent heat capacity of α-D-glucose by thermal analysis.

PubMed

Magoń, A; Pyda, M

2011-11-29

The thermal behaviors of α-D-glucose in the melting and glass transition regions were examined utilizing the calorimetric methods of standard differential scanning calorimetry (DSC), standard temperature-modulated differential scanning calorimetry (TMDSC), quasi-isothermal temperature-modulated differential scanning calorimetry (quasi-TMDSC), and thermogravimetric analysis (TGA). The quantitative thermal analyses of experimental data of crystalline and amorphous α-D-glucose were performed based on heat capacities. The total, apparent and reversingheat capacities, and phase transitions were evaluated on heating and cooling. The melting temperature (T(m)) of a crystalline carbohydrate such as α-D-glucose, shows a heating rate dependence, with the melting peak shifted to lower temperature for a lower heating rate, and with superheating of around 25K. The superheating of crystalline α-D-glucose is observed as shifting the melting peak for higher heating rates, above the equilibrium melting temperature due to of the slow melting process. The equilibrium melting temperature and heat of fusion of crystalline α-D-glucose were estimated. Changes of reversing heat capacity evaluated by TMDSC at glass transition (T(g)) of amorphous and melting process at T(m) of fully crystalline α-D-glucose are similar. In both, the amorphous and crystalline phases, the same origin of heat capacity changes, in the T(g) and T(m) area, are attributable to molecular rotational motion. Degradation occurs simultaneously with the melting process of the crystalline phase. The stability of crystalline α-D-glucose was examined by TGA and TMDSC in the melting region, with the degradation shown to be resulting from changes of mass with temperature and time. The experimental heat capacities of fully crystalline and amorphous α-D-glucose were analyzed in reference to the solid, vibrational, and liquid heat capacities, which were approximated based on the ATHAS scheme and Data Bank. Copyright © 2011 Elsevier Ltd. All rights reserved.

Transition process leading to microbubble emission boiling on horizontal circular heated surface in subcooled pool

NASA Astrophysics Data System (ADS)

Ueno, Ichiro; Ando, Jun; Horiuchi, Kazuna; Saiki, Takahito; Kaneko, Toshihiro

2016-11-01

Microbubble emission boiling (MEB) produces a higher heat flux than critical heat flux (CHF) and therefore has been investigated in terms of its heat transfer characteristics as well as the conditions under which MEB occurs. Its physical mechanism, however, is not yet clearly understood. We carried out a series of experiments to examine boiling on horizontal circular heated surfaces of 5 mm and of 10 mm in diameter, in a subcooled pool, paying close attention to the transition process to MEB. High-speed observation results show that, in the MEB regime, the growth, condensation, and collapse of the vapor bubbles occur within a very short time. In addition, a number of fine bubbles are emitted from the collapse of the vapor bubbles. By tracking these tiny bubbles, we clearly visualize that the collapse of the vapor bubbles drives the liquid near the bubbles towards the heated surface, such that the convection field around the vapor bubbles under MEB significantly differs from that under nucleate boiling. Moreover, the axial temperature gradient in a heated block (quasi-heat flux) indicates a clear difference between nucleate boiling and MEB. A combination of quasi-heat flux and the measurement of the behavior of the vapor bubbles allows us to discuss the transition to MEB. This work was financially supported by the 45th Research Grant in Natural Sciences from The Mitsubishi Foundation (2014 - 2015), and by Research Grant for Boiler and Pressurized Vessels from The Japan Boiler Association (2016).

Long-Time Variation of Magnetic Structure in (Pr xLa 1-x)Co 2Si 2: Coexistence of Slow and Fast Processes in Magnetic Phase Transition

DOE PAGES

Motoya, Kiyoichiro; Hagihala, Masato; Shigeoka, Toru; ...

2017-03-14

In this paper, long-time variations of the magnetic structure in PrCo 2Si 2 and (Pr 0.98La 0.02)Co 2Si 2 were studied by magnetization and time-resolved neutron scattering measurements. The amplitudes of magnetic Bragg peaks showed marked time variations after cooling or heating across the magnetic transition temperature T 1 between two different antiferromagnetic phases. However, the amplitude of the time variation decreased rapidly with increasing distance from T 1. Finally, we analyzed the results on the basis of a phase transition model that includes the coexistence of fast and slow processes.

Neutron Scattering Analysis of Water's Glass Transition and Micropore Collapse in Amorphous Solid Water.

PubMed

Hill, Catherine R; Mitterdorfer, Christian; Youngs, Tristan G A; Bowron, Daniel T; Fraser, Helen J; Loerting, Thomas

2016-05-27

The question of the nature of water's glass transition has continued to be disputed over many years. Here we use slow heating scans (0.4  K min^{-1}) of compact amorphous solid water deposited at 77 K and an analysis of the accompanying changes in the small-angle neutron scattering signal, to study mesoscale changes in the ice network topology. From the data we infer the onset of rotational diffusion at 115 K, a sudden switchover from nondiffusive motion and enthalpy relaxation of the network at <121  K to diffusive motion across sample grains and sudden pore collapse at >121  K, in excellent agreement with the glass transition onset deduced from heat capacity and dielectric measurements. This indicates that water's glass transition is linked with long-range transport of water molecules on the time scale of minutes and, thus, clarifies its nature. Furthermore, the slow heating rates combined with the high crystallization resistance of the amorphous sample allow us to identify the glass transition end point at 136 K, which is well separated from the crystallization onset at 144 K-in contrast to all earlier experiments in the field.

3D filling simulation of micro- and nanostructures in comparison to iso- and variothermal injection moulding trials

NASA Astrophysics Data System (ADS)

Rytka, C.; Lungershausen, J.; Kristiansen, P. M.; Neyer, A.

2016-06-01

Flow simulations can cut down both costs and time for the development of injection moulded polymer parts with functional surfaces used in life science and optical applications. We simulated the polymer melt flow into 3D micro- and nanostructures with Moldflow and Comsol and compared the results to real iso- and variothermal injection moulding trials below, at and above the transition temperature of the polymer. By adjusting the heat transfer coefficient and the transition temperature in the simulation it was possible to achieve good correlation with experimental findings at different processing conditions (mould temperature, injection velocity) for two polymers, namely polymethylmethacrylate and amorphous polyamide. The macroscopic model can be scaled down in volume and number of elements to save computational time for microstructure simulation and to enable first and foremost the nanostructure simulation, as long as local boundary conditions such as flow front speed are transferred correctly. The heat transfer boundary condition used in Moldflow was further evaluated in Comsol. Results showed that the heat transfer coefficient needs to be increased compared to macroscopic moulding in order to represent interfacial polymer/mould effects correctly. The transition temperature is most important in the packing phase for variothermal injection moulding.

On a Heat Exchange Problem under Sharply Changing External Conditions

NASA Astrophysics Data System (ADS)

Khishchenko, K. V.; Charakhch'yan, A. A.; Shurshalov, L. V.

2018-02-01

The heat exchange problem between carbon particles and an external environment (water) is stated and investigated based on the equations of heat conducting compressible fluid. The environment parameters are supposed to undergo large and fast variations. In the time of about 100 μs, the temperature of the environment first increases from the normal one to 2400 K, is preserved at this level for about 60 μs, and then decreases to 300 K during approximately 50 μs. At the same periods of time, the pressure of the external environment increases from the normal one to 67 GPa, is preserved at this level, and then decreases to zero. Under such external conditions, the heating of graphite particles of various sizes, their phase transition to the diamond phase, and the subsequent unloading and cooling almost to the initial values of the pressure and temperature without the reverse transition from the diamond to the graphite phase are investigated. Conclusions about the maximal size of diamond particles that can be obtained in experiments on the shock compression of the mixture of graphite with water are drawn.

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.

Current-driven orbital order-disorder transition in LaMnO3

NASA Astrophysics Data System (ADS)

Mondal, Parthasarathi; Bhattacharya, Dipten; Mandal, P.

2011-08-01

We report a significant influence of electric current on the orbital order-disorder transition in LaMnO3. The transition temperature TOO, thermal hysteresis in the resistivity ρ versus temperature T plot around TOO, and latent heat L associated with the transition decrease with an increase in current density. Eventually, at a critical current density, L reaches zero. The transition zone, on the other hand, broadens with an increase in current density. The states at ordered, disordered, and transition zones are all found to be stable within the time window from ˜10-3 to ˜104 s.

Heat exchanger and related methods

DOEpatents

Turner, Terry D.; McKellar, Michael G.

2015-12-22

Heat exchangers include a housing having an inlet and an outlet and forming a portion of a transition chamber. A heating member may form another portion of the transition chamber. The heating member includes a first end having a first opening and a second end having a second opening larger than the first opening. Methods of conveying a fluid include supplying a first fluid into a transition chamber of a heat exchanger, supplying a second fluid into the transition chamber, and altering a state of a portion of the first fluid with the second fluid. Methods of sublimating solid particles include conveying a first fluid comprising a material in a solid state into a transition chamber, heating the material to a gaseous state by directing a second fluid through a heating member and mixing the first fluid and the second fluid.

Experimental Investigation of Roughness Effects on Transition Onset and Turbulent Heating Augmentation on a Hemisphere at Mach 6 and Mach 10

NASA Technical Reports Server (NTRS)

Hollis, Brian R.

2017-01-01

An experimental investigation of the effects of distributed surface roughness on boundary-layer transition and turbulent heating has been conducted. Hypersonic wind tunnel testing was performed using hemispherical models with surface roughness patterns simulating those produced by heat shield ablation. Global aeroheating and transition onset data were obtained using phosphor thermography at Mach 6 and Mach 10 over a range of roughness heights and free stream Reynolds numbers sufficient to produce laminar, transitional and turbulent flow. Upstream movement of the transition onset location and increasing heating augmentation over predicted smooth-wall levels were observed with both increasing roughness heights and increasing free stream Reynolds numbers. The experimental heating data are presented herein, as are comparisons to smooth-wall heat transfer distributions from computational flow-field simulations. The transition onset data are also tabulated, and correlations of these data are presented.

Thermophysical Parameters of Organic PCM Coconut Oil from T-History Method and Its Potential as Thermal Energy Storage in Indonesia

NASA Astrophysics Data System (ADS)

Silalahi, Alfriska O.; Sukmawati, Nissa; Sutjahja, I. M.; Kurnia, D.; Wonorahardjo, S.

2017-07-01

The thermophysical parameters of organic phase change material (PCM) of coconut oil (co_oil) have been studied by analyzing the temperature vs time data during liquid-solid phase transition (solidification process) based on T-history method, adopting the original version and its modified form to extract the values of mean specific heats of the solid and liquid co_oil and the heat of fusion related to phase transition of co_oil. We found that the liquid-solid phase transition occurs rather gradually, which might be due to the fact that co_oil consists of many kinds of fatty acids with the largest amount of lauric acid (about 50%), with relatively small supercooling degree. For this reason, the end of phase transition region become smeared out, although the inflection point in the temperature derivative is clearly observed signifying the drastic temperature variation between the phase transition and solid phase periods. The data have led to the values of mean specific heat of the solid and liquid co_oil that are comparable to the pure lauric acid, while the value for heat of fusion is resemble to those of the DSC result, both from references data. The advantage of co_oil as the potential sensible and latent TES for room-temperature conditioning application in Indonesia is discussed in terms of its rather broad working temperature range due to its mixture composition characteristic.

Comparison of Theoretical and Experimental Heat-Transfer Characteristics of Bodies of Revolution at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Scherrer, Richard

1951-01-01

An investigation of the three important factors that determine convective heat-transfer characteristics at supersonic speeds, location boundary-layer transition, recovery factor, and heat-transfer parameter has been performed at Mach numbers from 1.49 to 1.18. The bodies of revolution that were tested had, in most cases, laminar boundary layers, and the test results have been compared with available theory. Boundary-layer transition was found to be affected by heat transfer. Adding heat to a laminar boundary layer caused transition to move forward on the test body, while removing heat caused transition to move rearward. These experimental results and the implications of boundary-layer-stability theory are in qualitative agreement.

MHD Modeling of Coronal Loops: the Transition Region Throat

NASA Technical Reports Server (NTRS)

Guarrasi, M.; Reale, F.; Orlando, S.; Mignone, A.; Klimchuk, J. A.

2014-01-01

Context. The expansion of coronal loops in the transition region may considerably influence the diagnostics of the plasma emission measure. The cross-sectional area of the loops is expected to depend on the temperature and pressure, and might be sensitive to the heating rate. Aims. The approach here is to study the area response to slow changes in the coronal heating rate, and check the current interpretation in terms of steady heating models. Methods. We study the area response with a time-dependent 2D magnetohydrodynamic (MHD) loop model, including the description of the expanding magnetic field, coronal heating and losses by thermal conduction, and radiation from optically thin plasma. We run a simulation for a loop 50 Mm long and quasi-statically heated to about 4 millikelvin. Results. We find that the area can change substantially with the quasi-steady heating rate, e.g., by approx. 40% at 0.5 millikelvin as the loop temperature varies between 1 millikelvin and 4 millikelvin, and, therefore, affects the interpretation of the differential emission measure vs. temperature (DEM(T)) curves.

Experimental process investigation of a latent heat energy storage system with a staggered heat exchanger with different phase change materials for solar thermal energy storage applications

NASA Astrophysics Data System (ADS)

Tsolakoglou, Nikolas P.; Koukou, Maria K.; Vrachopoulos, Michalis Gr.; Tachos, Nikolaos; Lymberis, Kostas; Stathopoulos, Vassilis

2017-11-01

This work investigates melting and solidification processes of four different Phase Change Materials (PCM) used as latent heat thermal storage system. The experimental rig was consisted of an insulated tank, filled with the under investigation PCM, a staggered heat exchanger to supply or extract heat from the PCM cavity and a water pump to circulate Heat Transfer Fluid (HTF). Both charging (melting) and discharging (solidification) processes were conducted for two different HTF flow rates. The main scope of this work was to develop a first approach and to investigate the behaviour of PCM under various load conditions (different HTF flow rates). Results show that different HTF flow rates affect melting and solidification time periods; in both processes time was reduced while HTF flow rate was increased but in differentways due to the transition from conduction to convection heat transfer mechanisms.

The quiescent chromospheres and transition regions of active dwarf stars - What are we learning from recent observations and models?

NASA Technical Reports Server (NTRS)

Linsky, J. L.

1983-01-01

Progress in understanding active dwarf stars based on recent IUE, Einstein, and ground-based observations is reviewed. The extent of magnetic field control over nonflare phenomena in active dwarf stars is considered, and the spatial homogeneity and time variability of active dwarf atmospheres is discussed. The possibility that solar like flux tubes can explain enhanced heating in active dwarf stars in examined, and the roles of systematic flows in active dwarf star atmospheres are considered. The relation between heating rates in different layers of active dwarf stars is summarized, and the mechanism of chromosphere and transition region heating in these stars are discussed. The results of one-component and two-component models of active dwarf stars are addressed.

First order transitions by conduction calorimetry: Application to deuterated potassium dihydrogen phosphate ferroelastic crystal under uniaxial pressure

NASA Astrophysics Data System (ADS)

Gallardo, M. C.; Jiménez, J.; Koralewski, M.; del Cerro, J.

1997-03-01

The specific heat c and the heat power W exchanged by a Deuterated Potassium Dihydrogen Phosphate ferroelectric-ferroelastic crystal have been measured simultaneously for both decreasing and increasing temperature at a low constant rate (0.06 K/h) between 175 and 240 K. The measurements were carried out under controlled uniaxial stresses of 0.3 and 4.5±0.1 bar applied to face (110). At Tt=207.9 K, a first order transition is produced with anomalous specific heat behavior in the interval where the transition heat appears. This anomalous behavior is explained in terms of the temperature variation of the heat power during the transition. During cooling, the transition occurs with coexistence of phases, while during heating it seems that metastable states are reached. Excluding data affected by the transition heat, the specific heat behavior agrees with the predictions of a 2-4-6 Landau potential in the range of 4-15 K below Tt while logarithmic behavior is obtained in the range from Tt to 1 K below Tt. Data obtained under 0.3 and 4.5 bar uniaxial stresses exhibit the same behavior.

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.

Simulating the Thermal Response of High Explosives on Time Scales of Days to Microseconds

NASA Astrophysics Data System (ADS)

Yoh, Jack J.; McClelland, Matthew A.

2004-07-01

We present an overview of computational techniques for simulating the thermal cookoff of high explosives using a multi-physics hydrodynamics code, ALE3D. Recent improvements to the code have aided our computational capability in modeling the response of energetic materials systems exposed to extreme thermal environments, such as fires. We consider an idealized model process for a confined explosive involving the transition from slow heating to rapid deflagration in which the time scale changes from days to hundreds of microseconds. The heating stage involves thermal expansion and decomposition according to an Arrhenius kinetics model while a pressure-dependent burn model is employed during the explosive phase. We describe and demonstrate the numerical strategies employed to make the transition from slow to fast dynamics.

Sandia and NJ TRANSIT Authority Developing Resilient Power Grid

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

Hanley, Charles J.; Ellis, Abraham

2014-11-01

Through the memorandum of understanding between the Depratment of Energy (DOE), the New Jersey Transit Authority (NJ Transit), and the New Jersey Board of Public Utilities, Sandia National Labs is assisting NJ Transit in developing NJ TransitGrid: an electric microgrid that will include a large-scale gas-fired generation facility and distributed energy resources (photovoltaics [PV], energy storage, electric vehicles, combined heat and power [CHP]) to supply reliable power during storms or other times of significant power failure. The NJ TransitGrid was awarded $410M from the Department of Transportation to develop a first-of-its-kind electric microgrid capable of supplying highly-reliable power.

A Second Glass Transition in Pressure Collapsed Type II Clathrate Hydrates.

PubMed

Andersson, Ove; Häussermann, Ulrich

2018-04-19

Type II clathrate hydrates (CHs) M·17 H 2 O, with M = tetrahydrofuran (THF) or 1,3-dioxolane, are known to collapse, or amorphize, on pressurization to ∼1.3 GPa in the temperature range 77-140 K. On heating at 1 GPa, these pressure-amorphized CH states show a weak, stretched sigmoid-shaped, heat-capacity increase because of a glass transition. Here we use thermal conductivity and heat capacity measurements to show that also type II CH with M = cyclobutanone (CB) collapses on isothermal pressurization and undergoes a similar, weak, glass transition upon heating at 1 GPa. Furthermore, we reveal for both THF CH and CB CH a second, much more pronounced, glass transition at temperatures above the thermally weak glass transition on heating in the 0.2-0.7 GPa range. This result suggests the general occurrence of two glass transitions in water-rich (94 mol %) pressure-collapsed CHs. Because of a large increase in dielectric permittivity concurrently as the weak heat capacity increase, the first glass transition must be due to kinetic unfreezing of water molecules. The thermal features of the second glass transition, measured on isobaric temperature cycling, are typical of a glass-liquid-glass transition, which suggests that pressure-amorphized CHs transform reversibly to liquids.

The use of transition region characteristics to improve the numerical simulation of heat transfer in bypass transitional flows

NASA Technical Reports Server (NTRS)

Simon, Frederick F.

1993-01-01

A method is presented for improving the numerical prediction of bypass transition heat transfer on a flat plate in a high-disturbance environment with zero or favorable pressure gradient. The method utilizes low Reynolds number k-epsilon turbulence models in combination with the characteristic parameters of the transition region. The parameters representing the characteristics of the transition region used are the intermittency, transition length and turbulent spot properties. An analysis is made of the transition length in terms of turbulent spot variables. The nondimensional spot formation rate, required for the prediction of the transition length, is shown by the analysis to be a function of the spot spreading angle, the dimensionless spot velocity ratio and the dimensionless spot area ratio. The intermittency form of the k-epsilon equations were derived from conditionally averaged equations which have been shown to be an improvement over global-time-averaged equations for the numerical calculation of the transition region. The numerical predictions are in general good agreement with the experimental data and indicate the potential use of the method in accelerating flows. Turbulence models of the k-epsilon type are known to underpredict the transition length. The present work demonstrates how incorporating transition region characteristics improves the ability of two-equation turbulence models to simulate bypass transition for flat plates with potential application to turbine vanes and blades.

Boundary layer turbulence in transitional and developed states

NASA Astrophysics Data System (ADS)

Park, George Ilhwan; Wallace, James M.; Wu, Xiaohua; Moin, Parviz

2012-03-01

Using the recent direct numerical simulations by Wu and Moin ["Transitional and turbulent boundary layer with heat transfer," Phys. Fluids 22, 85 (2010)] of a flat-plate boundary layer with a passively heated wall, statistical properties of the turbulence in transition at Reθ ≈ 300, from individual turbulent spots, and at Reθ ≈ 500, where the spots merge (distributions of the mean velocity, Reynolds stresses, kinetic energy production, and dissipation rates, enstrophy and its components) have been compared to these statistical properties for the developed boundary layer turbulence at Reθ = 1840. When the distributions in the transitional regions are conditionally averaged so as to exclude locations and times when the flow is not turbulent, they closely resemble the distributions in the developed turbulent state at the higher Reynolds number, especially in the buffer layer. Skin friction coefficients, determined in this conditional manner at the two Reynolds numbers in the transitional flow are, of course, much larger than when their values are obtained by including both turbulent and non-turbulent information there, and the conditional averaged values are consistent with the 1/7th power law approximation. An octant analysis based on the combinations of signs of the velocity and temperature fluctuations, u, v, and θ shows that the momentum and heat fluxes are predominantly of the mean gradient type in both the transitional and developed regions. The fluxes appear to be closely associated with vortices that transport momentum and heat toward and away from the wall in both regions of the flow. The results suggest that there may be little fundamental difference between the nonlinear processes involved in the formation of turbulent spots that appear in transition and those that sustain the turbulence when it is developed. They also support the view that the transport processes and the vortical structures that drive them in developed and transitional boundary layer turbulence are, in many dynamically important respects, similar.

The electrical properties and glass transition of some dental materials after temperature exposure.

PubMed

Marcinkowska, Agnieszka; Gauza-Wlodarczyk, Marlena; Kubisz, Leszek; Hedzelek, Wieslaw

2017-10-17

The physicochemical properties of dental materials will remain stable only when these materials in question are resistant to the changes in the oral cavity. The oral environment is subject to large temperature variations. The aim of the study was the assessment of electrical properties and glass transition of some dental materials after temperature exposure. Composite materials, compomers, materials for temporary prosthetic replacement and resin-based pit and fissure sealants were used in the study. The method used was electric conductivity of materials under changing temperature. The order of materials presenting the best characteristics for insulators was as follows: materials for temporary prosthetic replacement, resin-based pit and fissure sealants, composites, and compomers. Thanks to comparisons made between graphs during I and II heating run, the method could be used to observe changes in the heated material and determine whether the changes observed are reversible or permanent. The graphs also provided temperature values which contain information on glass transition during heating. In the oral cavity the effect of the constant temperature stimulus influences maturity of dental materials and improves their properties. But high temperatures over glass transition temperature can cause irreversible deformation and changes of the materials properties, even in a short time.

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

Weese, R K; Burnham, A K; Maienschein, J L

Dimensional changes related to temperature cycling of the beta and delta polymorphs of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) are important for a variety of applications. The coefficient of thermal expansion (CTE) of the beta and delta phases are measured and reported in this work over a temperature range of -20 C to 215 C. In addition, dimensional changes associated with the phase transition were measured, both through the transition and back down. Initially, differential scanning calorimetry (DSC) was used to investigate back conversion of the delta phase to the beta phase polymorph. The most successful approach was first to measure the amount ofmore » the beta to delta conversion, then after a given cooling period a repeat analysis, to measure the heat consumed by a second pass through the beta to delta phase transition. In addition, TMA is used to measure the dimensional change of a 0.20-gram sample of HMX during its initial heating and then three days later during a 2nd heating. This HMX shows the beta to delta phase transition a second time, thereby confirming the back conversion from delta to beta phase HMX.« less

Experimental Study of Hypersonic Inflatable Aerodynamic Decelerator (HIAD) Aeroshell with Axisymmetric Surface Deflection Patterns

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Hollingsworth, Kevin E.

2017-01-01

A wind tunnel test program was conducted to obtain aeroheating environment data on Hypersonic Inflatable Aerodynamic Decelerator aeroshells with flexible thermal protection systems. Data were obtained on a set of rigid wind tunnel models with surface deflection patterns of various heights that simulated a range of potential in-flight aeroshell deformations. Wind tunnel testing was conducted at Mach 6 at unit Reynolds numbers from 2.1 × 10(exp 6)/ft to 8.3 × 10(exp 6)/ft and angles of attack from 0 deg to 18 deg. Boundary-layer transition onset and global surface heating distribution measurements were performed using phosphor thermography and flow field images were obtained through schlieren photography. Surface deflections were found to both promote early transition of the boundary layer and to augment heating levels for both laminar and turbulent flows. A complimentary computational flow field study was also performed to provide heating predictions for comparison with the measurements as well as boundary layer flow field properties for use in correlating the data. Correlations of the wind tunnel data were developed to predict deflection effects on boundary layer transition and surface heating and were applied to both the wind tunnel test conditions and to the trajectory of NASA's successful IRVE-3 flight test. In general, the correlations produced at least qualitative agreement with the wind tunnel data, although the heating levels were underpredicted for some of the larger surface deflections. For the flight conditions, the correlations suggested that peak heating levels on the leeward side conical flank of the IRVE-3 vehicle may have exceeded those at nose for times late in the trajectory after the peak heating time point. However, the flight estimates were based on a conservative assumption of surface deflection magnitude (i.e., larger) than likely was produced in flight.

Simulation of the Plasma Density Evolution during Electron Cyclotron Resonance Heating at the T-10 Tokamak

NASA Astrophysics Data System (ADS)

Dnestrovskij, Yu. N.; Vershkov, V. A.; Danilov, A. V.; Dnestrovskij, A. Yu.; Zenin, V. N.; Lysenko, S. E.; Melnikov, A. V.; Shelukhin, D. A.; Subbotin, G. F.; Cherkasov, S. V.

2018-01-01

In ohmically heated (OH) plasma with low recycling, an improved particle confinement (IPC) mode is established during gas puffing. However, after gas puffing is switched off, this mode is retained only for about 100 ms, after which an abrupt phase transition into the low particle confinement (LPC) mode occurs in the entire plasma cross section. During such a transition, energy transport due to heat conduction does not change. The phase transition in OH plasma is similar to the effect of density pump-out from the plasma core, which occurs after electron cyclotron heating (ECH) is switched on. Analysis of the measured plasma pressure profiles in the T-10 tokamak shows that, after gas puffing in the OH mode is switched off, the plasma pressure profile in the IPC stage becomes more peaked and, after the peakedness exceeds a certain critical value, the IPC-LPC transition occurs. Similar processes are also observed during ECH. If the pressure profile is insufficiently peaked during ECH, then the density pump-out effect comes into play only after the critical peakedness of the pressure profile is reached. In the plasma core, the density and pressure profiles are close to the corresponding canonical profiles. This allows one to derive an expression for the particle flux within the canonical profile model and formulate a criterion for the IPC-LPC transition. The time evolution of the plasma density profile during phase transitions was simulated for a number of T-10 shots with ECH and high recycling. The particle transport coefficients in the IPC and LPC phases, as well as the dependences of these coefficients on the ECH power, are determined.

Origin of two maxima in specific heat in enthalpy relaxation under thermal history composed of cooling, annealing, and heating.

PubMed

Sakatsuji, Waki; Konishi, Takashi; Miyamoto, Yoshihisa

2016-12-01

The origin of two maxima in specific heat observed at the higher and the lower temperatures in the glass-transition region in the heating process has been studied for polymethyl methacrylate and polyvinyl chloride using differential scanning calorimetry, and the calculation was done using the phenomenological model equation under a thermal history of the typical annealing experiment composed of cooling, annealing, and heating. The higher maximum is observed above the glass-transition temperature, and it remains almost unchanged independent of annealing time t_{a}, while the lower one is observed above an annealing temperature T_{a} and shifts toward the higher one, increasing its magnitude with t_{a}. The analysis by the phenomenological model equation proposed in order to interpret the memory effect in the glassy state clarifies that under a typical annealing history, two maxima in specific heat essentially appear. The shift of the lower maximum toward higher temperatures from above T_{a} is caused by an increase in the amount of relaxation during annealing with t_{a}. The annealing temperature and the amount of relaxation during annealing play a major role in the determination of the number of maxima in the specific heat.

Transition from Forward Smoldering to Flaming in Small Polyurethane Foam Samples

NASA Technical Reports Server (NTRS)

Bar-Ilan, A.; Putzeys, O.; Rein, G.; Fernandez-Pello, A. C.

2004-01-01

Experimental observations are presented of the effect of the flow velocity and oxygen concentration, and of a thermal radiant flux, on the transition from smoldering to flaming in forward smoldering of small samples of polyurethane foam with a gas/solid interface. The experiments are part of a project studying the transition from smolder to flaming under conditions encountered in spacecraft facilities, i.e., microgravity, low velocity variable oxygen concentration flows. Because the microgravity experiments are planned for the International Space Station, the foam samples had to be limited in size for safety and launch mass reasons. The feasible sample size is too small for smolder to self propagate because of heat losses to the surrounding environment. Thus, the smolder propagation and the transition to flaming had to be assisted by reducing the heat losses to the surroundings and increasing the oxygen concentration. The experiments are conducted with small parallelepiped samples vertically placed in a wind tunnel. Three of the sample lateral-sides are maintained at elevated temperature and the fourth side is exposed to an upward flow and to a radiant flux. It is found that decreasing the flow velocity and increasing its oxygen concentration, and/or increasing the radiant flux enhances the transition to flaming, and reduces the delay time to transition. Limiting external ambient conditions for the transition to flaming are reported for the present experimental set-up. The results show that smolder propagation and the transition to flaming can occur in relatively small fuel samples if the external conditions are appropriate. The results also indicate that transition to flaming occurs in the char left behind by the smolder reaction, and it has the characteristics of a gas-phase ignition induced by the smolder reaction, which acts as the source of both gaseous fuel and heat.

Transcriptional profiling of the early stages of germination in Candida albicans by real-time RT-PCR.

PubMed

Toyoda, Mika; Cho, Tamaki; Kaminishi, Hidenori; Sudoh, Masayuki; Chibana, Hiroji

2004-12-01

By using real-time RT-PCR, we profiled the expression of CGR1, CaMSI3, EFG1, NRG1, and TUP1 in Candida albicans strains JCM9061 and CAI4 under several conditions, including induction of morphological transition, heat shock, and treatment with calcium inhibitors. Expression of CaMSI3 changed under these growth conditions except during heat shock. CGR1 expression increased during the early stages of hyphal growth in JCM9061, while expression was strain-dependent during heat shock. Both EFG1 and NRG1 were similarly expressed under hypha-inducing conditions and heat shock. Expression of TUP1 was slightly different from the expression of EFG1 or NRG1.

Heat Transfer Computations of Internal Duct Flows With Combined Hydraulic and Thermal Developing Length

NASA Technical Reports Server (NTRS)

Wang, C. R.; Towne, C. E.; Hippensteele, S. A.; Poinsatte, P. E.

1997-01-01

This study investigated the Navier-Stokes computations of the surface heat transfer coefficients of a transition duct flow. A transition duct from an axisymmetric cross section to a non-axisymmetric cross section, is usually used to connect the turbine exit to the nozzle. As the gas turbine inlet temperature increases, the transition duct is subjected to the high temperature at the gas turbine exit. The transition duct flow has combined development of hydraulic and thermal entry length. The design of the transition duct required accurate surface heat transfer coefficients. The Navier-Stokes computational method could be used to predict the surface heat transfer coefficients of a transition duct flow. The Proteus three-dimensional Navier-Stokes numerical computational code was used in this study. The code was first studied for the computations of the turbulent developing flow properties within a circular duct and a square duct. The code was then used to compute the turbulent flow properties of a transition duct flow. The computational results of the surface pressure, the skin friction factor, and the surface heat transfer coefficient were described and compared with their values obtained from theoretical analyses or experiments. The comparison showed that the Navier-Stokes computation could predict approximately the surface heat transfer coefficients of a transition duct flow.

Investigation of the critical edge ion heat flux for L-H transitions in Alcator C-Mod and its dependence on B T

NASA Astrophysics Data System (ADS)

Schmidtmayr, M.; Hughes, J. W.; Ryter, F.; Wolfrum, E.; Cao, N.; Creely, A. J.; Howard, N.; Hubbard, A. E.; Lin, Y.; Reinke, M. L.; Rice, J. E.; Tolman, E. A.; Wukitch, S.; Ma, Y.; ASDEX Upgrade Team; Alcator C-Mod Team

2018-05-01

This paper presents investigations on the role of the edge ion heat flux for transitions from L-mode to H-mode in Alcator C-Mod. Previous results from the ASDEX Upgrade tokamak indicated that a critical value of edge ion heat flux per particle is needed for the transition. Analysis of C-Mod data confirms this result. The edge ion heat flux is indeed found to increase linearly with density at given magnetic field and plasma current. Furthermore, the Alcator C-Mod data indicate that the edge ion heat flux at the L-H transition also increases with magnetic field. Combining the data from Alcator C-Mod and ASDEX Upgrade yields a general expression for the edge ion heat flux at the L-H transition. These results are discussed from the point of view of the possible physics mechanism of the L-H transition. They are also compared to the L-H power threshold scaling and an extrapolation for ITER is given.

Lattice Boltzmann modeling of boiling heat transfer: The boiling curve and the effects of wettability

DOE PAGES

Li, Q.; Kang, Q. J.; Francois, M. M.; ...

2015-03-03

A hybrid thermal lattice Boltzmann (LB) model is presented to simulate thermal multiphase flows with phase change based on an improved pseudopotential LB approach (Li et al., 2013). The present model does not suffer from the spurious term caused by the forcing-term effect, which was encountered in some previous thermal LB models for liquid–vapor phase change. Using the model, the liquid–vapor boiling process is simulated. The boiling curve together with the three boiling stages (nucleate boiling, transition boiling, and film boiling) is numerically reproduced in the LB community for the first time. The numerical results show that the basic featuresmore » and the fundamental characteristics of boiling heat transfer are well captured, such as the severe fluctuation of transient heat flux in the transition boiling and the feature that the maximum heat transfer coefficient lies at a lower wall superheat than that of the maximum heat flux. Moreover, the effects of the heating surface wettability on boiling heat transfer are investigated. It is found that an increase in contact angle promotes the onset of boiling but reduces the critical heat flux, and makes the boiling process enter into the film boiling regime at a lower wall superheat, which is consistent with the findings from experimental studies.« less

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.

Blunt body near wake flow field at Mach 6

NASA Technical Reports Server (NTRS)

Horvath, Thomas J.; McGinley, Catherine B.; Hannemann, Klaus

1996-01-01

Tests were conducted in a Mach 6 flow to examine the reattachment process of an axisymmetric free shear layer associated with the near wake of a 70 deg. half angle, spherically blunted cone with a cylindrical after body. Model angle of incidence was fixed at 0 deg. and free-stream Reynolds numbers based on body diameter ranged from 0.5 x 10(exp 6) to 4 x 10(exp 6). The sensitivity of wake shear layer transition on reattachment heating was investigated. The present perfect gas study was designed to compliment results obtained previously in facilities capable of producing real gas effects. The instrumented blunted cone model was designed primarily for testing in high enthalpy hypervelocity shock tunnels in both this country and abroad but was amenable for testing in conventional hypersonic blowdown wind tunnels as well. Surface heating rates were inferred from temperature - time histories from coaxial surface thermocouples on the model forebody and thin film resistance gages along the model base and cylindrical after body. General flow feature (bow shock, wake shear layer, and recompression shock) locations were visually identified by schlieren photography. Mean shear layer position and growth were determined from intrusive pitot pressure surveys. In addition, wake surveys with a constant temperature hot-wire anemometer were utilized to qualitatively characterize the state of the shear layer prior to reattachment. Experimental results were compared to laminar perfect gas predictions provided by a 3-D Navier Stokes code (NSHYP). Shear layer impingement on the instrumented cylindrical after body resulted in a localized heating maximum that was 21 to 29 percent of the forebody stagnation point heating. Peak heating resulting from the reattaching shear layer was found to be a factor of 2 higher than laminar predictions, which suggested a transitional shear layer. Schlieren flow visualization and fluctuating voltage time histories and spectra from the hot wire surveys across the shear layer substantiate this observation. The sensitivity of surface heating to forebody roughness was characterized for a reattaching shear layer. For example, at R(sub infinity), d = 4 x 10(exp 6), when the shear layer was transitional, the magnitude of peak heating from shear layer impingement was reduced by approximately 24 percent when transition grit was applied to the forebody. The spatial location of the local peak, however, remained unchanged.

Stochastic modeling of stock price process induced from the conjugate heat equation

NASA Astrophysics Data System (ADS)

Paeng, Seong-Hun

2015-02-01

Currency can be considered as a ruler for values of commodities. Then the price is the measured value by the ruler. We can suppose that inflation and variation of exchange rate are caused by variation of the scale of the ruler. In geometry, variation of the scale means that the metric is time-dependent. The conjugate heat equation is the modified heat equation which satisfies the heat conservation law for the time-dependent metric space. We propose a new model of stock prices by using the stochastic process whose transition probability is determined by the kernel of the conjugate heat equation. Our model of stock prices shows how the volatility term is affected by inflation and exchange rate. This model modifies the Black-Scholes equation in light of inflation and exchange rate.

Coupled Evolution with Tides of the Radius and Orbit of Transiting Giant Planets

NASA Astrophysics Data System (ADS)

Ibgui, Laurent; Burrows, A.

2009-12-01

Some transiting extrasolar giant planets have measured radii larger than predicted by the standard theory. We explore the possibility that an earlier episode of tidal heating can explain such radius anomalies and apply the formalism we develop to HD 209458b as an example. We find that for strong enough tides the planet's radius can undergo a transient phase of inflation that temporarily interrupts canonical, monotonic shrinking due to radiative losses. Importantly, an earlier episode of tidal heating can result in a planet with an inflated radius, even though its orbit has nearly circularized. Moreover, we confirm that at late times, and under some circumstances, by raising tides on the star itself a planet can spiral into its host. We note that a 3 to 10 solar planet atmospheric opacity with no tidal heating is sufficient to explain the observed radius of HD 209458b. However, our model demonstrates that with an earlier phase of episodic tidal heating we can fit the observed radius of HD 209458b even with lower (solar) atmospheric opacities. This work demonstrates that, if a planet is left with an appreciable eccentricity after early inward migration and/or dynamical interaction, coupling radius and orbit evolution in a consistent fashion that includes tidal heating, stellar irradiation, and detailed model atmospheres might offer a generic solution to the inflated radius puzzle for transiting extrasolar giant planets.

Aeroheating Environments for a Mars Smart Lander

NASA Technical Reports Server (NTRS)

Edquist, Karl T.; Liechty, Derek S.; Hollis, Brian R.; Alter, Stephen J.; Loomis, Mark P.

2002-01-01

A proposed Mars Smart Lander is designed to reach the surface via lifting-body atmospheric entry (alpha = 16 deg) to within 10 km of the target site. CFD (computational fluid dynamics) predictions of the forebody aeroheating environments are given for a direct entry from a 2005 launch. The solutions were obtained using an 8-species gas in thermal and chemical nonequilibrium with a radiative-equilibrium wall temperature boundary condition. Select wind tunnel data are presented from tests at NASA Langley Research Center. Turbulence effects are included to account for both smooth body transition and turbulence due to heatshield penetrations. Natural transition is based on a momentum-thickness Reynolds number value of 200. The effects of heatshield penetrations on turbulence are estimated from wind tunnel tests of various cavity sizes and locations. Both natural transition and heatshield penetrations are predicted to cause turbulence prior to the nominal trajectory peak heating time. Laminar and turbulent CFD predictions along the trajectory are used to estimate heat rates and loads. The predicted peak turbulent heat rate of 63 W/sq cm on the heatshield leeward flank is 70% higher than the laminar peak. The maximum integrated heat load for a fully turbulent heat pulse is 38% higher than the laminar load on the heatshield nose. The predicted aeroheating environments with uncertainty factors will be used to design a thermal protection system.

Study of the heat-transfer crisis on heat-release surfaces of annular channels with swirl and transit flows

NASA Astrophysics Data System (ADS)

Boltenko, E. A.

2016-10-01

The results of the experimental study of the heat-transfer crisis on heat-release surfaces of annular channels with swirl and transit flow are presented. The experiments were carried out using electric heated annular channels with one and (or) two heat-release surfaces. For the organization of transit flow on a convex heat-release surface, four longitudinal ribs were installed uniformly at its perimeter. Swirl flow was realized using a capillary wound tightly (without gaps) on the ribs. The ratio between swirl and transit flows in the annular gap was varied by applying longitudinal ribs of different height. The experiments were carried out using a closed-type circulatory system. The experimental data were obtained in a wide range of regime parameters. Both water heated to the temperature less than the saturation temperature and water-steam mixture were fed at the inlet of the channels. For the measurement of the temperature of the heat-release surfaces, chromel-copel thermocouples were used. It was shown that the presence of swirl flow on a convex heatrelease surface led to a significant decrease in critical heat flows (CHF) compared to a smooth surface. To increase CHF, it was proposed to use the interaction of swirl flows of the heat carrier. The second swirl flow was transit flow, i.e., swirl flow with the step equal to infinity. It was shown that CHF values for a channel with swirl and transit flow in all the studied range of regime parameters was higher than CHF values for both a smooth annular channel and a channel with swirl. The empirical ratios describing the dependence of CHF on convex and concave heat-release surfaces of annular channels with swirl and transit flow on the geometrical characteristics of channels and the regime parameters were obtained. The experiments were carried out at the pressure p = 3.0-16.0 MPa and the mass velocity ρw = 250-3000 kg/(m2s).

Supersonic/Hypersonic Correlations for In-Cavity Transition and Heating Augmentation

NASA Technical Reports Server (NTRS)

Everhart, Joel L.

2011-01-01

Laminar-entry cavity heating data with a non-laminar boundary layer exit flow have been retrieved from the database developed at Mach 6 and 10 in air on large flat plate models for the Space Shuttle Return-To-Flight Program. Building on previously published fully laminar and fully turbulent analysis methods, new descriptive correlations of the in-cavity floor-averaged heating and endwall maximum heating have been developed for transitional-to-turbulent exit flow. These new local-cavity correlations provide the expected flow and geometry conditions for transition onset; they provide the incremental heating augmentation induced by transitional flow; and, they provide the transitional-to-turbulent exit cavity length. Furthermore, they provide an upper application limit for the previously developed fully-laminar heating correlations. An example is provided that demonstrates simplicity of application. Heating augmentation factors of 12 and 3 above the fully laminar values are shown to exist on the cavity floor and endwall, respectively, if the flow exits in fully tripped-to-turbulent boundary layer state. Cavity floor heating data in geometries installed on the windward surface of 0.075-scale Shuttle wind tunnel models have also been retrieved from the boundary layer transition database developed for the Return-To-Flight Program. These data were independently acquired at Mach 6 and Mach 10 in air, and at Mach 6 in CF4. The correlation parameters for the floor-averaged heating have been developed and they offer an exceptionally positive comparison to previously developed laminar-cavity heating correlations. Non-laminar increments have been extracted from the Shuttle data and they fall on the newly developed transitional in-cavity correlations, and they are bounded by the 95% correlation prediction limits. Because the ratio of specific heats changes along the re-entry trajectory, turning angle into a cavity and boundary layer flow properties may be affected, raising concerns regarding the application validity of the heating augmentation predictions.

Time Dependent Predictive Modeling of DIII-D ITER Baseline Scenario using Predictive TRANSP

NASA Astrophysics Data System (ADS)

Grierson, B. A.; Andre, R. G.; Budny, R. V.; Solomon, W. M.; Yuan, X.; Candy, J.; Pinsker, R. I.; Staebler, G. M.; Holland, C.; Rafiq, T.

2015-11-01

ITER baseline scenario discharges on DIII-D are modeled with TGLF and MMM transitioning from combined ECH (3.3MW) +NBI(2.8MW) heating to NBI only (3.0 MW) heating maintaining βN = 2.0 on DIII-D predicting temperature, density and rotation for comparison to experimental measurements. These models capture the reduction of confinement associated with direct electron heating H98y2 = 0.89 vs. 1.0) consistent with stiff electron transport. Reasonable agreement between experimental and modeled temperature profiles is achieved for both heating methods, whereas density and momentum predictions differ significantly. Transport fluxes from TGLF indicate that on DIII-D the electron energy flux has reached a transition from low-k to high-k turbulence with more stiff high-k transport that inhibits an increase in core electron stored energy with additional electron heating. Projections to ITER also indicate high electron stiffness. Supported by US DOE DE-AC02-09CH11466, DE-FC02-04ER54698, DE-FG02-07ER54917, DE-FG02-92-ER54141.

The latent heat of vaporization of supercritical fluids

NASA Astrophysics Data System (ADS)

Banuti, Daniel; Raju, Muralikrishna; Hickey, Jean-Pierre; Ihme, Matthias

2016-11-01

The enthalpy of vaporization is the energy required to overcome intermolecular attractive forces and to expand the fluid volume against the ambient pressure when transforming a liquid into a gas. It diminishes for rising pressure until it vanishes at the critical point. Counterintuitively, we show that a latent heat is in fact also required to heat a supercritical fluid from a liquid to a gaseous state. Unlike its subcritical counterpart, the supercritical pseudoboiling transition is spread over a finite temperature range. Thus, in addition to overcoming intermolecular attractive forces, added energy simultaneously heats the fluid. Then, considering a transition from a liquid to an ideal gas state, we demonstrate that the required enthalpy is invariant to changes in pressure for 0 < p < 3pcr . This means that the classical pressure-dependent latent heat is merely the equilibrium part of the phase transition. The reduction at higher pressures is compensated by an increase in a nonequilibrium latent heat required to overcome residual intermolecular forces in the real fluid vapor during heating. At supercritical pressures, all of the transition occurs at non-equilibrium; for p -> 0 , all of the transition occurs at equilibrium.

Piloted Ignition to Flaming in Smoldering Fire-Retarded Polyurethane Foam

NASA Technical Reports Server (NTRS)

Putzeys, O.; Fernandez-Pello, A. C.; Urban, D. L.

2007-01-01

Experimental results are presented on the piloted transition from smoldering to flaming in the fire-retarded polyurethane foam Pyrell . The samples are small rectangular blocks with a square cross section, vertically placed in the wall of a vertical wind tunnel. Three of the vertical sample sides are insulated and the fourth side is exposed to an upward oxidizer flow of variable oxygen concentration and to a variable radiant heat flux. The gases emitted from the smoldering reaction pass upwards through a pilot, which consists of a coiled resistance heating wire. In order to compensate for the solid-phase and gas-phase effects of the fire retardants on the piloted transition from smoldering to flaming in Pyrell, it was necessary to assist the process by increasing the power supplied to the smolder igniter and the pilot (compared to that used for non-fire retarded foam). The experiments indicate that the piloted transition from smoldering to flaming occurs when the gaseous mixture at the pilot passes the lean flammability limit. It was found that increasing the oxygen concentration or the external heat flux increases the likelihood of a piloted transition from smoldering to flaming, and generally decreases the time delay to transition. The piloted transition to flaming is observed in oxygen concentrations of 23% and above in both low-density and high-density Pyrell. Comparisons with previous experiments show that the piloted transition from smoldering to flaming is possible under a wider range of external conditions (i.e. lower oxygen concentration) than the spontaneous transition from smoldering to flaming. The results show that the fire retardants in Pyrell are very effective in preventing the piloted transition to flaming in normal air, but Pyrell is susceptible to smoldering and the piloted transition to flaming in oxygen-enriched environments. Therefore, precautions should be taken in the design of applications of Pyrell in oxygen-enriched environments to reduce to the risk of a piloted transition to flaming.

MHD modeling of coronal loops: the transition region throat

NASA Astrophysics Data System (ADS)

Guarrasi, M.; Reale, F.; Orlando, S.; Mignone, A.; Klimchuk, J. A.

2014-04-01

Context. The expansion of coronal loops in the transition region may considerably influence the diagnostics of the plasma emission measure. The cross-sectional area of the loops is expected to depend on the temperature and pressure, and might be sensitive to the heating rate. Aims: The approach here is to study the area response to slow changes in the coronal heating rate, and check the current interpretation in terms of steady heating models. Methods: We study the area response with a time-dependent 2D magnetohydrodynamic (MHD) loop model, including the description of the expanding magnetic field, coronal heating and losses by thermal conduction, and radiation from optically thin plasma. We run a simulation for a loop 50 Mm long and quasi-statically heated to about 4 MK. Results: We find that the area can change substantially with the quasi-steady heating rate, e.g., by ~40% at 0.5 MK as the loop temperature varies between 1 MK and 4 MK, and, therefore, affects the interpretation of the differential emission measure vs. temperature (DEM(T)) curves. The movie associated to Fig. 4 is available in electronic form at http://www.aanda.org

Heating Augmentation Due to Compression Pad Cavities on the Project Orion CEV Heat Shield

NASA Technical Reports Server (NTRS)

Hollis, Brian R.

2009-01-01

An experimental study has been conducted to assess the effects of compression pad cavities on the aeroheating environment of the Project Orion CEV heat-shield. Testing was conducted in Mach 6 and Mach 10 perfect-gas wind tunnels to obtain heating measurements in and around the compression pads cavities using global phosphor thermography. Data were obtained over a wide range of Reynolds numbers that produced laminar, transitional, and turbulent flow within and downstream of the cavities. The effects of cavity dimensions on boundary-layer transition and heating augmentation levels were studied. Correlations were developed for transition onset and for the average cavity-heating augmentation.

Compression Pad Cavity Heating Augmentation on Orion Heat Shield

NASA Technical Reports Server (NTRS)

Hollis, Brian R.

2011-01-01

An experimental study has been conducted to assess the effects of compression pad cavities on the aeroheating environment of the Project Orion Crew Exploration Vehicle heat shield. Testing was conducted in Mach 6 and 10 perfect-gas wind tunnels to obtain heating measurements in and around the compression pads cavities using global phosphor thermography. Data were obtained over a wide range of Reynolds numbers that produced laminar, transitional, and turbulent flow within and downstream of the cavities. The effects of cavity dimensions on boundary-layer transition and heating augmentation levels were studied. Correlations were developed for transition onset and for the average cavity-heating augmentation.

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

Anameric, B.; Kawatra, S.K.

The pig iron nugget process is gaining in importance as an alternative to the traditional blast furnace. Throughout the process, self-reducing-fluxing dried greenballs composed of iron ore concentrate, reducing-carburizing agent (coal), flux (limestone) and binder (bentonite) are heat-treated. During the heat treatment, dried greenballs are first transformed into direct reduced iron (DRI), then to transition direct reduced iron (TDRI) and finally to pig iron nuggets. The furnace temperature and/or residence time and the corresponding levels of carburization, reduction and metallization dictate these transformations. This study involved the determination of threshold furnace temperatures and residence times for completion of all ofmore » the transformation reactions and pig iron nugget production. The experiments involved the heat treatment of self-reducing-fluxing dried greenballs at various furnace temperatures and residence times. The products of these heat treatments were identified by utilizing optical microscopy, apparent density and microhardness measurements.« less

L-H transitions driven by ion heating in scrape-off layer turbulence (SOLT) model simulations

NASA Astrophysics Data System (ADS)

Russell, D. A.; D'Ippolito, D. A.; Myra, J. R.

2015-11-01

The original SOLT model now includes the evolution of ion pressure consistent with drift-ordering. It is a two-dimensional, electrostatic reduced model wherein closure relations, obtained by integrating the equations along the B-field, model parallel physics that includes sheath-mediated current and heat flux in the scrape-off-layer and electron drift waves inside the separatrix. Low (L) and high (H) confinement regimes are observed in SOLT simulations, depending on the strength of an ion pressure (i.e., ion heating) source localized inside the separatrix: With increasing heating, particle and energy confinement times at first decrease in the L-mode then rise in the H-mode. The L-H transition is marked by distinct changes in sheared-flow profiles. The addition of ion pressure dynamics enables modeling the self-consistent interaction between the ion diamagnetic drift and the radial electric field (mean and zonal flows). The roles of these sheared flows in mediating the L-H transition are explored. A new diagnostic, based on the density correlation function, is applied to study blob velocities in different regimes. Work supported by the U.S. Department of Energy Office of Science, Office of Fusion Energy Sciences, under Award Number DE-FG02-97ER54392.

Optimization of Advanced ACTPol Transition Edge Sensor Bolometer Operation Using R(T,I) Transition Measurements

NASA Astrophysics Data System (ADS)

Salatino, Maria

2017-06-01

In the current submm and mm cosmology experiments the focal planes are populated by kilopixel transition edge sensors (TESes). Varying incoming power load requires frequent rebiasing of the TESes through standard current-voltage (IV) acquisition. The time required to perform IVs on such large arrays and the resulting transient heating of the bath reduces the sky observation time. We explore a bias step method that significantly reduces the time required for the rebiasing process. This exploits the detectors' responses to the injection of a small square wave signal on top of the dc bias current and knowledge of the shape of the detector transition R(T,I). This method has been tested on two detector arrays of the Atacama Cosmology Telescope (ACT). In this paper, we focus on the first step of the method, the estimate of the TES %Rn.

Evolution of Edge Pedestal Profiles Over the L-H Transition

NASA Astrophysics Data System (ADS)

Sayer, M. S.; Stacey, W. M.; Floyd, J. P.; Groebner, R. J.

2012-10-01

The detailed time evolution of thermal diffusivities, electromagnetic forces, pressure gradients, particle pinch and momentum transport frequencies (which determine the diffusion coefficient) have been analyzed during the L-H transition in a DIII-D discharge. Density, temperature, rotation velocity and electric field profiles at times just before and after the L-H transition are analyzed in terms of these quantities. The analysis is based on the fluid particle balance, energy balance, force balance and heat conduction equations, as in Ref. [1], but with much greater time resolution and with account for thermal ion orbit loss. The variation of diffusive and non-diffusive transport over the L-H transition is determined from the variation in the radial force balance (radial electric field, VxB force, and pressure gradient) and the variation in the interpreted diffusive transport coefficients. 6pt [1] W.M. Stacey and R.J. Groebner, Phys. Plasmas 17, 112512 (2010).

Development of diapiric structures in the upper mantle due to phase transitions

NASA Technical Reports Server (NTRS)

Liu, M.; Yuen, D. A.; Zhao, W.; Honda, S.

1991-01-01

Solid-state phase transition in time-dependent mantle convection can induce diapiric flows in the upper mantle. When a deep mantle plume rises toward phase boundaries in the upper mantle, the changes in the local thermal buoyancy, local heat capacity, and latent heat associated with the phase change at a depth of 670 kilometers tend to pinch off the plume head from the feeding stem and form a diapir. This mechanism may explain episodic hot spot volcanism. The nature of the multiple phase boundaries at the boundary between the upper and lower mantle may control the fate of deep mantle plumes, allowing hot plumes to go through and retarding the tepid ones.

Heating the sun's lower transition region with fine-scale electric currents

NASA Technical Reports Server (NTRS)

Rabin, D.; Moore, R.

1984-01-01

Analytical and observational data are presented to show that the lower transition zone, a 100 km thick region at 10,000-200,000 K between the solar chromosphere and corona, is heated by local electric currents. The study was spurred by correlations between the enhanced atmospheric heating and magnetospheric flux in the chromospheric network and active regions. Field aligned current heated flux loops are asserted to mainly reside in and make up most of the transition region. It is shown that thermal conduction from the sides of hot gas columns generated by the current dissipation is the source of the observed temperature distribution in the transition regions.

Surface energy exchanges along a tundra-forest transition and feedbacks to climate

USGS Publications Warehouse

Beringer, J.; Chapin, F. S.; Thompson, Catharine Copass; McGuire, A.D.

2005-01-01

Surface energy exchanges were measured in a sequence of five sites representing the major vegetation types in the transition from arctic tundra to forest. This is the major transition in vegetation structure in northern high latitudes. We examined the influence of vegetation structure on the rates of sensible heating and evapotranspiration to assess the potential feedbacks to climate if high-latitude warming were to change the distribution of these vegetation types. Measurements were made at Council on the Seward Peninsula, Alaska, at representative tundra, low shrub, tall shrub, woodland (treeline), and boreal forest sites. Structural differences across the transition from tundra to forest included an increase in the leaf area index (LAI) from 0.52 to 2.76, an increase in canopy height from 0.1 to 6.1 m, and a general increase in canopy complexity. These changes in vegetation structure resulted in a decrease in albedo from 0.19 to 0.10 as well as changes to the partitioning of energy at the surface. Bulk surface resistance to water vapor flux remained virtually constant across sites, apparently because the combined soil and moss evaporation decreased while transpiration increased along the transect from tundra to forest. In general, sites became relatively warmer and drier along the transect with the convective fluxes being increasingly dominated by sensible heating, as evident by an increasing Bowen ratio from 0.94 to 1.22. The difference in growing season average daily sensible heating between tundra and forest was 21 W m-2. Fluxes changed non-linearly along the transition, with both shrubs and trees substantially enhancing heat transfer to the atmosphere. These changes in vegetation structure that increase sensible heating could feed back to enhance warming at local to regional scales. The magnitude of these vegetation effects on potential high-latitude warming is two to three times greater than suggested by previous modeling studies. ?? 2005 Elsevier B.V. All rights reserved.

Dynamical Detection of Topological Phase Transitions in Short-Lived Atomic Systems.

PubMed

Setiawan, F; Sengupta, K; Spielman, I B; Sau, Jay D

2015-11-06

We demonstrate that dynamical probes provide direct means of detecting the topological phase transition (TPT) between conventional and topological phases, which would otherwise be difficult to access because of loss or heating processes. We propose to avoid such heating by rapidly quenching in and out of the short-lived topological phase across the transition that supports gapless excitations. Following the quench, the distribution of excitations in the final conventional phase carries signatures of the TPT. We apply this strategy to study the TPT into a Majorana-carrying topological phase predicted in one-dimensional spin-orbit-coupled Fermi gases with attractive interactions. The resulting spin-resolved momentum distribution, computed by self-consistently solving the time-dependent Bogoliubov-de Gennes equations, exhibits Kibble-Zurek scaling and Stückelberg oscillations characteristic of the TPT. We discuss parameter regimes where the TPT is experimentally accessible.

Dynamical Detection of Topological Phase Transitions in Short-Lived Atomic Systems

NASA Astrophysics Data System (ADS)

Setiawan, F.; Sengupta, K.; Spielman, I. B.; Sau, Jay D.

2015-11-01

We demonstrate that dynamical probes provide direct means of detecting the topological phase transition (TPT) between conventional and topological phases, which would otherwise be difficult to access because of loss or heating processes. We propose to avoid such heating by rapidly quenching in and out of the short-lived topological phase across the transition that supports gapless excitations. Following the quench, the distribution of excitations in the final conventional phase carries signatures of the TPT. We apply this strategy to study the TPT into a Majorana-carrying topological phase predicted in one-dimensional spin-orbit-coupled Fermi gases with attractive interactions. The resulting spin-resolved momentum distribution, computed by self-consistently solving the time-dependent Bogoliubov-de Gennes equations, exhibits Kibble-Zurek scaling and Stückelberg oscillations characteristic of the TPT. We discuss parameter regimes where the TPT is experimentally accessible.

Impact of radius and skew angle on areal density in heat assisted magnetic recording hard disk drives

NASA Astrophysics Data System (ADS)

Cordle, Michael; Rea, Chris; Jury, Jason; Rausch, Tim; Hardie, Cal; Gage, Edward; Victora, R. H.

2018-05-01

This study aims to investigate the impact that factors such as skew, radius, and transition curvature have on areal density capability in heat-assisted magnetic recording hard disk drives. We explore a "ballistic seek" approach for capturing in-situ scan line images of the magnetization footprint on the recording media, and extract parametric results of recording characteristics such as transition curvature. We take full advantage of the significantly improved cycle time to apply a statistical treatment to relatively large samples of experimental curvature data to evaluate measurement capability. Quantitative analysis of factors that impact transition curvature reveals an asymmetry in the curvature profile that is strongly correlated to skew angle. Another less obvious skew-related effect is an overall decrease in curvature as skew angle increases. Using conventional perpendicular magnetic recording as the reference case, we characterize areal density capability as a function of recording position.

IR thermography for dynamic detection of laminar-turbulent transition

NASA Astrophysics Data System (ADS)

Simon, Bernhard; Filius, Adrian; Tropea, Cameron; Grundmann, Sven

2016-05-01

This work investigates the potential of infrared (IR) thermography for the dynamic detection of laminar-turbulent transition. The experiments are conducted on a flat plate at velocities of 8-14 m/s, and the transition of the laminar boundary layer to turbulence is forced by a disturbance source which is turned on and off with frequencies up to 10 Hz. Three different heating techniques are used to apply the required difference between fluid and structure temperature: a heated aluminum structure is used as an internal structure heating technique, a conductive paint acts as a surface bounded heater, while an IR heater serves as an example for an external heating technique. For comparison of all heating techniques, a normalization is introduced and the frequency response of the measured IR camera signal is analyzed. Finally, the different heating techniques are compared and consequences for the design of experiments on laminar-turbulent transition are discussed.

Time-resolved x-ray diffraction and calorimetric studies at low scan rates

PubMed Central

Yao, Haruhiko; Hatta, Ichiro; Koynova, Rumiana; Tenchov, Boris

1992-01-01

The phase transitions of dipalmitoylphosphatidylethanolamine (DPPE) in excess water have been examined by low-angle time-resolved x-ray diffraction and calorimetry at low scan rates. The lamellar subgel/lamellar liquid-crystalline (Lc → Lα), lamellar gel/lamellar liquid-crystalline (Lβ → Lα), and lamellar liquid-crystalline/lamellar gel (Lα → Lβ) phase transitions proceed via coexistence of the initial and final phases with no detectable intermediates at scan rates 0.1 and 0.5°C/min. At constant temperature within the region of the Lβ → Lα transition the ratio of the two coexisting phases was found to be stable for over 30 min. The state of stable phase coexistence was preceded by a 150-s relaxation taking place at constant temperature after termination of the heating scan in the transition region. While no intermediate structures were present in the coexistence region, a well reproducible multipeak pattern, with at least four prominent heat capacity peaks separated in temperature by 0.4-0.5°C, has been observed in the cooling transition (Lα → Lβ) by calorimetry. The multipeak pattern became distinct with an increase of incubation time in the liquid-crystalline phase. It was also clearly resolved in the x-ray diffraction intensity versus temperature plots recorded at slow cooling rates. These data suggest that the equilibrium state of the Lα phase of hydrated DPPE is represented by a mixture of domains that differ in thermal behavior, but cannot be distinguished structurally by x-ray scattering. Imagesp689-aFIGURE 9 PMID:19431820

Experimental- Analitical Procedure Of Definition Of Thermal Fluxes On The Head Fairing Of Launch Vehicles

NASA Astrophysics Data System (ADS)

Yurchenko, I.; Karakotin, I.; Kudinov, A.

2011-05-01

Minimization of head fairing heat protection shield weight during spacecraft injecting in atmosphere dense layers is a complicated task. The identification of heat transfer coefficient on heat protection shield surface during injection can be considered as a primary task to be solved with certain accuracy in order to minimize heat shield weight as well as meet reliability requirements. The height of the roughness around sound point on the head fairing spherical nose tip has a great influence on the heat transfer coefficient calculation. As it has found out during flight tests the height of the roughness makes possible to create boundary layer transition criterion on the head fairing in flight. Therefore the second task is an assessment how height of the roughness influences on the total incoming heat flux to the head fairing. And finally the third task is associated with correct implementation of the first task results, as there are changing boundary conditions during a flight such as bubbles within heat shield surface paint and thermal protection ablation for instance. In the article we have considered results of flight tests carried out using launch vehicles which allowed us to measure heat fluxes in flight and to estimate dispersions of heat transfer coefficient. The experimental-analytical procedure of defining heat fluxes on the LV head fairings has been presented. The procedure includes: - calculation of general-purpose dimensionless heat transfer coefficient - Nusselt number Nueff - based on the proposed effective temperature Teff method. The method allows calculate the Nusselt number values for cylindrical surfaces as well as dispersions of heat transfer coefficient; - universal criterion of turbulent-laminar transition for blunted head fairings - Reynolds number Reek = [ρеUеk/μе]TR = const , which gives the best correlation of all dates of flight experiment carried out per Reda procedure to define turbulent-laminar transition in boundary layer. The criterion allows defining time margins when turbulent flux on space head surfaces exists. It was defined that in conditions when high background disturbances of free stream flux while main LV engines operating join with integrated roughness influence the critical value of Reynolds number is an order-diminished value compared to values obtained in wind tunnels and in free flight. Influence of minimization of height of surface roughness near sound point on head fairing nose has been estimated. It has been found that the criterion of turbulent-laminar transition for smooth head fairings elements - Reynolds number - reaches the limit value which is equal to 200. This value is obtained from momentum thickness Reynolds number when roughness height is close to zero. So the turbulent- laminar flux transition occurs earlier with decreased duration of effect of high turbulent heat fluxes to the heat shield. This will allow decreasing head shield thickness up to 30%

Mesoporous metal oxides and processes for preparation thereof

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

Suib, Steven L.; Poyraz, Altug Suleyman

A process for preparing a mesoporous metal oxide, i.e., transition metal oxide. Lanthanide metal oxide, a post-transition metal oxide and metalloid oxide. The process comprises providing an acidic mixture comprising a metal precursor, an interface modifier, a hydrotropic ion precursor, and a surfactant; and heating the acidic mixture at a temperature and for a period of time sufficient to form the mesoporous metal oxide. A mesoporous metal oxide prepared by the above process. A method of controlling nano-sized wall crystallinity and mesoporosity in mesoporous metal oxides. The method comprises providing an acidic mixture comprising a metal precursor, an interface modifier,more » a hydrotropic ion precursor, and a surfactant; and heating the acidic mixture at a temperature and for a period of time sufficient to control nano-sized wall crystallinity and mesoporosity in the mesoporous metal oxides. Mesoporous metal oxides and a method of tuning structural properties of mesoporous metal oxides.« less

An assessment of the impact of transition on advanced winged entry vehicle thermal protection system mass

NASA Technical Reports Server (NTRS)

Wurster, K. E.

1981-01-01

This study examines the impact of turbulent heating on thermal protection system (TPS) mass for advanced winged entry vehicles. Four basic systems are considered: insulative, metallic hot structures, metallic standoff, and hybrid systems. TPS sizings are performed using entry trajectories tailored specifically to the characteristics of each TPS concept under consideration. Comparisons are made between systems previously sized under the assumption of all laminar heating and those sized using a baseline estimate of transition and turbulent heating. The relative effect of different transition criteria on TPS mass requirements is also examined. Also investigated are entry trajectories tailored to alleviate turbulent heating. Results indicate the significant impact of turbulent heating on TPS mass and demonstrate the importance of both accurate transition criteria and entry trajectory tailoring.

Development of Instrumentation for Boundary Layer Transition Detection

DTIC Science & Technology

1991-01-01

assistance of Maj. Aaron Byerley were largely responsible for my decision to stay on. 4t Contents Abstract Acknowledgements Nomenclature Chapter 1...The use of shr sensitive liquid crystals in aerodynamic measurements has been a mor wPu imovation. Two different prcesses can be employed to...transition location. The steady-state heat transfer technique is unsuited for use on complex geometries, may be time consuming , and has an element of

Numerical analysis of flow resistance and heat transfer in the transitional regime of pipe flow with twisted-tape turbulators

NASA Astrophysics Data System (ADS)

Rossi, R.; Cattani, L.; Mocerino, A.; Bozzoli, F.; Rainieri, S.; Caminati, R.; Pagliarini, G.

2017-11-01

In this paper, we present the numerical analysis of the fully developed ow and heat transfer in pipes equipped with twisted-tape inserts in the laminar to transitional flow regime. The flow Reynolds number ranges from 210 to 3100 based on the pipe diameter, whereas the Prandtl number of the working fluid, a 40% mixture of water and ethylene glycol, is about 45 at the average film temperature. The numerical study is carried out via Scale Adaptive Simulations (SAS) where the k-ω SST model is employed for turbulence modeling. Using SAS and low-dissipation discretization schemes, the present study shows that it is possible to capture the transition from the laminar regime to the pulsating or pseudo-laminar flow regime induced by the twisted-tape at low Reynolds numbers, as well as the transition to moderate turbulent regime at the higher, yet non-turbulent for smooth pipes, range of Reynolds numbers. Numerical results, validated against experiments performed in a dedicated test rig, show very good agreement with measured data and an increase of the friction factor and Nusselt number in the range of 4 to 7 times and 6 to 15 times, respectively, of the values for an empty pipe.

Transition boiling heat transfer and the film transition regime

NASA Technical Reports Server (NTRS)

Ramilison, J. M.; Lienhard, J. H.

1987-01-01

The Berenson (1960) flat-plate transition-boiling experiment has been recreated with a reduced thermal resistance in the heater, and an improved access to those portions of the transition boiling regime that have a steep negative slope. Tests have been made in Freon-113, acetone, benzene, and n-pentane boiling on horizontal flat copper heaters that have been mirror-polished, 'roughened', or teflon-coated. The resulting data reproduce and clarify certain features observed by Berenson: the modest surface finish dependence of boiling burnout, and the influence of surface chemistry on both the minimum heat flux and the mode of transition boiling, for example. A rational scheme of correlation yields a prediction of the heat flux in what Witte and Lienhard (1982) previously identified as the 'film-transition boiling' region. It is also shown how to calculate the heat flux at the boundary between the pure-film, and the film-transition, boiling regimes, as a function of the advancing contact angle.

Transitions between refrigeration regions in extremely short quantum cycles

NASA Astrophysics Data System (ADS)

Feldmann, Tova; Kosloff, Ronnie

2016-05-01

The relation between the geometry of refrigeration cycles and their performance is explored. The model studied is based on a coupled spin system. Small cycle times, termed sudden refrigerators, develop coherence and inner friction. We explore the interplay between coherence and energy of the working medium employing a family of sudden cycles with decreasing cycle times. At the point of maximum coherence the cycle changes geometry. This region of cycle times is characterized by a dissipative resonance where heat is dissipated both to the hot and cold baths. We rationalize the change of geometry of the cycle as a result of a half-integer quantization which maximizes coherence. From this point on, increasing or decreasing the cycle time, eventually leads to refrigeration cycles. The transition point between refrigerators and short circuit cycles is characterized by a transition from finite to singular dynamical temperature. Extremely short cycle times reach a universal limit where all cycles types are equivalent.

On the reversibility of the Meissner effect and the angular momentum puzzle

NASA Astrophysics Data System (ADS)

Hirsch, J. E.

2016-10-01

It is generally believed that the laws of thermodynamics govern superconductivity as an equilibrium state of matter, and hence that the normal-superconductor transition in a magnetic field is reversible under ideal conditions. Because eddy currents are generated during the transition as the magnetic flux changes, the transition has to proceed infinitely slowly to generate no entropy. Experiments showed that to a high degree of accuracy no entropy was generated in these transitions. However, in this paper we point out that for the length of times over which these experiments extended, a much higher degree of irreversibility due to decay of eddy currents should have been detected than was actually observed. We also point out that within the conventional theory of superconductivity no explanation exists for why no Joule heat is generated in the superconductor to normal transition when the supercurrent stops. In addition we point out that within the conventional theory of superconductivity no mechanism exists for the transfer of momentum between the supercurrent and the body as a whole, which is necessary to ensure that the transition in the presence of a magnetic field respects momentum conservation. We propose a solution to all these questions based on the alternative theory of hole superconductivity. The theory proposes that in the normal-superconductor transition there is a flow and backflow of charge in direction perpendicular to the phase boundary when the phase boundary moves. We show that this flow and backflow explains the absence of Joule heat generated by Faraday eddy currents, the absence of Joule heat generated in the process of the supercurrent stopping, and the reversible transfer of momentum between the supercurrent and the body, provided the current carriers in the normal state are holes.

A stress-induced phase transition model for semi-crystallize shape memory polymer

NASA Astrophysics Data System (ADS)

Guo, Xiaogang; Zhou, Bo; Liu, Liwu; Liu, Yanju; Leng, Jinsong

2014-03-01

The developments of constitutive models for shape memory polymer (SMP) have been motivated by its increasing applications. During cooling or heating process, the phase transition which is a continuous time-dependent process happens in semi-crystallize SMP and the various individual phases form at different temperature and in different configuration. Then, the transformation between these phases occurred and shape memory effect will emerge. In addition, stress applied on SMP is an important factor for crystal melting during phase transition. In this theory, an ideal phase transition model considering stress or pre-strain is the key to describe the behaviors of shape memory effect. So a normal distributed model was established in this research to characterize the volume fraction of each phase in SMP during phase transition. Generally, the experiment results are partly backward (in heating process) or forward (in cooling process) compared with the ideal situation considering delay effect during phase transition. So, a correction on the normal distributed model is needed. Furthermore, a nonlinear relationship between stress and phase transition temperature Tg is also taken into account for establishing an accurately normal distributed phase transition model. Finally, the constitutive model which taking the stress as an influence factor on phase transition was also established. Compared with the other expressions, this new-type model possesses less parameter and is more accurate. For the sake of verifying the rationality and accuracy of new phase transition and constitutive model, the comparisons between the simulated and experimental results were carried out.

Magnetic, specific heat and electrical transport properties of Frank-Kasper cage compounds RTM2Al20 [R  =  Eu, Gd and La; TM  =  V, Ti

NASA Astrophysics Data System (ADS)

Kumar, K. Ramesh; Nair, Harikrishnan S.; Christian, Reinke; Thamizhavel, A.; Strydom, André M.

2016-11-01

Single crystals of Frank-Kasper compounds RTM2Al20 (R  =  Eu, Gd and La; TM  =  V and Ti) were grown by self-flux method and their physical properties were investigated through magnetization (M), magnetic susceptibility (χ), specific heat (C P) and electrical resistivity (ρ) measurements. Powder x-ray diffraction studies and structural analysis showed that these compounds crystallize in the cubic crystal structure with the space group Fd\\bar{3}m . The magnetic susceptibility for the compounds EuTi2Al20 and GdTi2Al20 showed a sudden jump below the Néel temperature T N indicative of plausible double magnetic transition. Specific heat (C P) and electrical resistivity (ρ) measurements also confirm the first-order magnetic transition (FOMT) and possible double magnetic transitions. Temperature variation of heat capacity showed a sharp phase transition and huge C P value for the (Eu/Gd)Ti2Al20 compounds’ full width at half-maximum (FWHM) (<0.2 K) which is reminiscent of a first-order phase transition and a unique attribute among RTM2Al20 compounds. In contrast, linear variation of C P is observed in the ordered state for (Eu/Gd)V2Al20 compounds suggesting a λ-type transition. We observed clear anomaly between heating and cooling cycle in temperature-time relaxation curve for the compounds GdTi2Al20 (2.38 K) and EuTi2Al20 (3.2 K) which is indicating a thermal arrest due to the latent heat. The temperature variation of S mag for GdTi2Al20 saturates to a value 0.95R\\ln 8 while the other magnetic systems exhibited still lower entropy saturation values in the high temperature limit. ≤ft({{C}\\text{P}}-γ T\\right)/{{T}3} versus T plot showed a maximum near 27 K for all the compounds indicating the presence of low frequency Einstein modes of vibrations. Resistivity measurements showed that all the samples behave as normal Fermi liquid type compounds and ρ (T) due to electron-phonon scattering follows Bloch-Grüneisen-Mott relation in the paramagnetic region.

The Shallow-to-Deep Transition in Convective Clouds During GoAmazon 2014/5

NASA Astrophysics Data System (ADS)

Jensen, M. P.; Gostic, C.; Giangrande, S. E.; Mechem, D. B.; Ghate, V. P.; Toto, T.

2016-12-01

Nearly two years of observations from the ARM Mobile Facility (AMF) deployed at Manacapuru, Brazil during the GOAmazon 2014/5 campaign are analyzed to investigate the environmental conditions controlling the transition from shallow to deep convective clouds. The Active Remote Sensing of Clouds (ARSCL) product, which combines radar and lidar observations to produce best estimates of cloud locations in the vertical column is used to qualitatively define four subsets of convective cloud conditions: 1,2) Transition cases (wet season, dry season), where a period of shallow convective clouds is followed by a period of deep convective clouds and 2) Non-transition cases (wet season, dry season), where shallow convective clouds persist without any subsequent development. For these subsets, observations of the time varying thermodynamic properties of the atmosphere, including the surface heat and radiative fluxes, the profiles of atmospheric state variables, and the ECMWF-derived large-scale advective tendencies, are composited to define averaged properties for each transition state. Initial analysis indicates that the transition state strongly depends on the pre-dawn free-tropospheric humidity, the convective inhibition and surface temperature and humidity with little dependence on the convective available potential energy and surface heat fluxes. The composited environmental thermodynamics are then used to force large-eddy simulations for the four transition states to further evaluate the sensitivity of the transition to the composite thermodynamics versus the importance of larger-scale forcing.

Nanofluids for power engineering: Emergency cooling of overheated heat transfer surfaces

NASA Astrophysics Data System (ADS)

Bondarenko, B. I.; Moraru, V. N.; Sidorenko, S. V.; Komysh, D. V.

2016-07-01

The possibility of emergency cooling of an overheated heat transfer surface using nanofluids in the case of a boiling crisis is explored by means of synchronous recording of changes of main heat transfer parameters of boiling water over time. Two nanofluids are tested, which are derived from a mixture of natural aluminosilicates (AlSi-7) and titanium dioxide (NF-8). It is found that the introduction of a small portions of nanofluid into a boiling coolant (distilled water) in a state of film boiling ( t heater > 500°C) can dramatically decrease the heat transfer surface temperature to 130-150°C, which corresponds to a transition to a safe nucleate boiling regime without affecting the specific heat flux. The fact that this regime is kept for a long time at a specific heat load exceeding the critical heat flux for water and t heater = 125-130°C is particularly important. This makes it possible to prevent a potential accident emergency (heater burnout and failure of the heat exchanger) and to ensure the smooth operation of the equipment.

A Method for Calculating Transient Surface Temperatures and Surface Heating Rates for High-Speed Aircraft

NASA Technical Reports Server (NTRS)

Quinn, Robert D.; Gong, Leslie

2000-01-01

This report describes a method that can calculate transient aerodynamic heating and transient surface temperatures at supersonic and hypersonic speeds. This method can rapidly calculate temperature and heating rate time-histories for complete flight trajectories. Semi-empirical theories are used to calculate laminar and turbulent heat transfer coefficients and a procedure for estimating boundary-layer transition is included. Results from this method are compared with flight data from the X-15 research vehicle, YF-12 airplane, and the Space Shuttle Orbiter. These comparisons show that the calculated values are in good agreement with the measured flight data.

Lower solar chromosphere-corona transition region. II - Wave pressure effects for a specific form of the heating function

NASA Technical Reports Server (NTRS)

Woods, D. Tod; Holzer, Thomas E.; Macgregor, Keith B.

1990-01-01

Lower transition region models with a balance between mechanical heating and radiative losses are expanded to include wave pressure effects. The models are used to study the simple damping length form of the heating function. The results are compared to the results obtained by Woods et al. (1990) for solutions in the lower transition region. The results suggest that a mixture of fast-mode and slow-mode waves may provide the appropriate heating mechanism in the lower transition region, with the decline in effective vertical wave speed caused by the refraction and eventual total reflection of the fast-mode wave resulting from the decreasing atmospheric density.

Heat Capacity of Hydrous Silicate Melts

NASA Astrophysics Data System (ADS)

Robert, G.; Whittington, A. G.; Stechern, A.; Behrens, H.

2015-12-01

We determined the heat capacities of four series of glasses and liquids of basaltic and basaltic andesite compositions including two natural remelts from Fuego volcano, Guatemala, and two Fe-free analogs. The samples are low-alkali, Ca- and Mg-rich aluminosilicates with non-bridging oxygen to tetrahedrally-coordinated cation ratios (NBO/T) ranging between 0.33 and 0.67. Differential scanning calorimetry measurements were performed at atmospheric pressure between room temperature and ≈100 K above the glass transition for hydrous samples and up to ≈1800 K for dry samples. The water contents investigated range up to 5.34 wt.% (16.4 mol%). Water does not measurably affect the heat capacity of glasses (T

Coupled Evolution with Tides of the Radius and Orbit of Transiting Giant Planets: General Results

NASA Astrophysics Data System (ADS)

Ibgui, Laurent; Burrows, Adam

2009-08-01

Some transiting extrasolar giant planets (EGPs) have measured radii larger than predicted by the standard theory. In this paper, we explore the possibility that an earlier episode of tidal heating can explain such radius anomalies and apply the formalism we develop to HD 209458b as an example. We find that for strong enough tides the planet's radius can undergo a transient phase of inflation that temporarily interrupts canonical, monotonic shrinking due to radiative losses. Importantly, an earlier episode of tidal heating can result in a planet with an inflated radius, even though its orbit has nearly circularized. Moreover, we confirm that at late times, and under some circumstances, by raising tides on the star itself a planet can spiral into its host. We note that a 3× to 10× solar planet atmospheric opacity with no tidal heating is sufficient to explain the observed radius of HD 209458b. However, our model demonstrates that with an earlier phase of episodic tidal heating, we can fit the observed radius of HD 209458b even with lower (solar) atmospheric opacities. This work demonstrates that, if a planet is left with an appreciable eccentricity after early inward migration and/or dynamical interaction, coupling radius and orbit evolution in a consistent fashion that includes tidal heating, stellar irradiation, and detailed model atmospheres might offer a generic solution to the inflated radius puzzle for transiting EGPs such as WASP-12b, TrES-4, and WASP-6b.

Shock compression and flash-heating of molecular adsorbates on the picosecond time scale

NASA Astrophysics Data System (ADS)

Berg, Christopher Michael

An ultrafast nonlinear coherent laser spectroscopy termed broadband multiplex vibrational sum-frequency generation (SFG) with nonresonant suppression was employed to monitor vibrational transitions of molecular adsorbates on metallic substrates during laser-driven shock compression and flash-heating. Adsorbates were in the form of well-ordered self-assembled monolayers (SAMs) and included molecular explosive simulants, such as nitroaromatics, and long chain-length alkanethiols. Based on reflectance measurements of the metallic substrates, femtosecond flash-heating pulses were capable of producing large-amplitude temperature jumps with DeltaT = 500 K. Laser-driven shock compression of SAMs produced pressures up to 2 GPa, where 1 GPa ≈ 1 x 104 atm. Shock pressures were estimated via comparison with frequency shifts observed in the monolayer vibrational transitions during hydrostatic pressure measurements in a SiC anvil cell. Molecular dynamics during flash-heating and shock loading were probed with vibrational SFG spectroscopy with picosecond temporal resolution and sub-nanometer spatial resolution. Flash-heating studies of 4-nitrobenzenethiolate (NBT) on Au provided insight into effects from hot-electron excitation of the molecular adsorbates at early pump-probe delay times. At longer delay times, effects from the excitation of SAM lattice modes and lower-energy NBT vibrations were shown. In addition, flash-heating studies of alkanethiolates demonstrated chain disordering behaviors as well as interface thermal conductances across the Au-SAM junction, which was of specific interest within the context of molecular electronics. Shock compression studies of molecular explosive simulants, such as 4-nitrobenzoate (NBA), demonstrated the proficiency of this technique to observe shock-induced molecular dynamics, in this case orientational dynamics, on the picosecond time scale. Results validated the utilization of these refined shock loading techniques to probe the shock initiation or first bond-breaking reactions in molecular explosives such as delta-HMX: a necessary study for the development of safer and more effective energetic materials.

Process for preparing high-transition-temperature superconductors in the Nb-Al-Ge system

DOEpatents

Giorgi, A.L.; Szklarz, E.G.

1973-01-30

The patent describes a process for preparing superconducting materials in the Nb-Al-Ge system having transition temperatures in excess of 19K. The process comprises premixing powdered constituents, pressing them into a plug, heating the plug to 1,450-1,800C for 30 minutes to an hour under vacuum or an inert atmosphere, and annealing at moderate temperatures for reasonably long times (approximately 50 hours). High transition-temperature superconductors, including those in the Nb3(Al,Ge) system, prepared in accordance with this process exhibit little degradation in the superconducting transition temperature on being ground to -200 mesh powder. (GRA)

Melting temperature and enthalpy variations of phase change materials (PCMs): a differential scanning calorimetry (DSC) analysis

NASA Astrophysics Data System (ADS)

Sun, Xiaoqin; Lee, Kyoung Ok; Medina, Mario A.; Chu, Youhong; Li, Chuanchang

2018-06-01

Differential scanning calorimetry (DSC) analysis is a standard thermal analysis technique used to determine the phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy of phase change materials (PCMs). To determine the appropriate heating rate and sample mass, various DSC measurements were carried out using two kinds of PCMs, namely N-octadecane paraffin and calcium chloride hexahydrate. The variations in phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy were observed within applicable heating rates and sample masses. It was found that the phase transition temperature range increased with increasing heating rate and sample mass; while the heat of fusion varied without any established pattern. The specific heat decreased with the increase of heating rate and sample mass. For accuracy purpose, it is recommended that for PCMs with high thermal conductivity (e.g. hydrated salt) the focus will be on heating rate rather than sample mass.

Flow Topology Transition via Global Bifurcation in Thermally Driven Turbulence

NASA Astrophysics Data System (ADS)

Xie, Yi-Chao; Ding, Guang-Yu; Xia, Ke-Qing

2018-05-01

We report an experimental observation of a flow topology transition via global bifurcation in a turbulent Rayleigh-Bénard convection. This transition corresponds to a spontaneous symmetry breaking with the flow becomes more turbulent. Simultaneous measurements of the large-scale flow (LSF) structure and the heat transport show that the LSF bifurcates from a high heat transport efficiency quadrupole state to a less symmetric dipole state with a lower heat transport efficiency. In the transition zone, the system switches spontaneously and stochastically between the two long-lived metastable states.

Mesoscale evolution of voids and microstructural changes in HMX-based explosives during heating through the β-δ phase transition

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

Willey, Trevor M., E-mail: willey1@llnl.gov; Lauderbach, Lisa; Gagliardi, Franco

HMX-based explosives LX-10 and PBX-9501 were heated through the β-δ phase transition. Ultra-small angle x-ray scattering (USAXS) and molecular diffraction were simultaneously recorded as the HMX was heated. Mesoscale voids and structure dramatically change promptly with the β-δ phase transition, rather than with other thermal effects. Also, x-ray induced damage, observed in the USAXS, occurs more readily at elevated temperatures; as such, the dose was reduced to mitigate this effect. Optical microscopy performed during a similar heating cycle gives an indication of changes on longer length scales, while x-ray microtomography, performed before and after heating, shows the character of extensivemore » microstructural damage resulting from the temperature cycle and solid-state phase transition.« less

Mesoscale evolution of voids and microstructural changes in HMX-based explosives during heating through the β-δ phase transition

DOE PAGES

Willey, Trevor M.; Lauderbach, Lisa; Gagliardi, Franco; ...

2015-08-07

HMX-based explosives LX-10 and PBX-9501 were heated through the β-δ phase transition. Ultra-small angle x-ray scattering (USAXS) and molecular diffraction were simultaneously recorded as the HMX was heated. Mesoscale voids and structure dramatically change promptly with the β-δ phase transition, rather than with other thermal effects. Also, x-ray induced damage, observed in the USAXS, occurs more readily at elevated temperatures; as such, the dose was reduced to mitigate this effect. Optical microscopy performed during a similar heating cycle gives an indication of changes on longer length scales, while x-ray microtomography, performed before and after heating, shows the character of extensivemore » microstructural damage resulting from the temperature cycle and solid-state phase transition.« less

The frequency dependence of the discharge properties in a capacitively coupled oxygen discharge

NASA Astrophysics Data System (ADS)

Gudmundsson, J. T.; Snorrason, D. I.; Hannesdottir, H.

2018-02-01

We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 to explore the evolution of the charged particle density profiles, electron heating mechanism, the electron energy probability function (EEPF), and the ion energy distribution in a single frequency capacitively coupled oxygen discharge, with driving frequency in the range 12-100 MHz. At a low driving frequency and low pressure (5 and 10 mTorr), a combination of stochastic (α-mode) and drift ambipolar (DA) heating in the bulk plasma (the electronegative core) is observed and the DA-mode dominates the time averaged electron heating. As the driving frequency or pressure are increased, the heating mode transitions into a pure α-mode, where electron heating in the sheath region dominates. At low pressure (5 and 10 mTorr), this transition coincides with a sharp decrease in electronegativity. At low pressure and low driving frequency, the EEPF is concave. As the driving frequency is increased, the number of low energy electrons increases and the relative number of higher energy electrons (>10 eV) increases. At high driving frequency, the EEPF develops a convex shape or becomes bi-Maxwellian.

Investigation of the effects of pressure gradient, temperature and wall temperature ratio on the stagnation point heat transfer for circular cylinders and gas turbine vanes

NASA Technical Reports Server (NTRS)

Nagamatsu, H. T.; Duffy, R. E.

1984-01-01

Low and high pressure shock tubes were designed and constructed for the purpose of obtaining heat transfer data over a temperature range of 390 to 2500 K, pressures of 0.3 to 42 atm, and Mach numbers of 0.15 to 1.5 with and without pressure gradient. A square test section with adjustable top and bottom walls was constructed to produce the favorable and adverse pressure gradient over the flat plate with heat gages. A water cooled gas turbine nozzle cascade which is attached to the high pressure shock tube was obtained to measuse the heat flux over pressure and suction surfaces. Thin-film platinum heat gages with a response time of a few microseconds were developed and used to measure the heat flux for laminar, transition, and turbulent boundary layers. The laminar boundary heat flux on the shock tube wall agreed with Mirel's flat plate theory. Stagnation point heat transfer for circular cylinders at low temperature compared with the theoretical prediction, but for a gas temperature of 922 K the heat fluxes were higher than the predicted values. Preliminary flat plate heat transfer data were measured for laminar, transition, and turbulent boundary layers with and without pressure gradients for free-stream temperatures of 350 to 2575 K and flow Mach numbers of 0.11 to 1.9. The experimental heat flux data were correlated with the laminar and turbulent theories and the agreement was good at low temperatures which was not the case for higher temperatures.

Boundary Layer Transition in the Leading Edge Region of a Swept Cylinder in High Speed Flow

NASA Technical Reports Server (NTRS)

Coleman, Colin P.

1998-01-01

Experiments were conducted on a 76 degree swept cylinder to establish the behavior of the attachment line transition process in a low-disturbance level, Mach number 1.6 flow. For a near adiabatic wall condition, the attachment-line boundary layer remained laminar up to the highest attainable Reynolds number. The attachment-line boundary layer transition under the influence of trip wires depended on wind tunnel disturbance level, and a transition onset condition for this flow is established. Internal heating raised the surface temperature of the attachment line to induce boundary layer instabilities. This was demonstrated experimentally for the first time and the frequencies of the most amplified disturbances were determined over a range of temperature settings. Results were in excellent agreement to those predicted by a linear stability code, and provide the first experimental verification of theory. Transition onset along the heated attachment line at an R-bar of 800 under quiet tunnel conditions was found to correlate with an N factor of 13.2. Increased tunnel disturbance levels caused the transition onset to occur at lower cylinder surface temperatures and was found to correlate with an approximate N factor of 1 1.9, so demonstrating that the attachment-line boundary layer is receptive to increases in the tunnel disturbance level.

Recovery Temperature, Transition, and Heat Transfer Measurements at Mach 5

NASA Technical Reports Server (NTRS)

Brinich, Paul F.

1961-01-01

Schlieren, recovery temperature, and heat-transfer measurements were made on a hollow cylinder and a cone with axes alined parallel to the stream. Both the cone and cylinder were equipped with various bluntnesses, and the tests covered a Reynolds number range up to 20 x 10(exp 6) at a free-stream Mach number of 4.95 and wall to free-stream temperature ratios from 1.8 to 5.2 (adiabatic). A substantial transition delay due to bluntness was found for both the cylinder and the cone. For the present tests (Mach 4.95), transition was delayed by a factor of 3 on the cylinder and about 2 on the cone, these delays being somewhat larger than those observed in earlier tests at Mach 3.1. Heat-transfer tests on the cylinder showed only slight effects of wall temperature level on transition location; this is to be contrasted to the large transition delays observed on conical-type bodies at low surface temperatures at Mach 3.1. The schlieren and the peak-recovery-temperature methods of detecting transition were compared with the heat-transfer results. The comparison showed that the first two methods identified a transition point which occurred just beyond the end of the laminar run as seen in the heat-transfer data.

Rapid microwave-assisted preparation of binary and ternary transition metal sulfide compounds

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

Butala, Megan M.; Perez, Minue A.; Arnon, Shiri

Transition metal chalcogenides are of interest for energy applications, including energy generation in photoelectrochemical cells and as electrodes for next-generation electrochemical energy storage. Synthetic routes for such chalcogenides typically involve extended heating at elevated temperatures for multiple weeks. We demonstrate here the feasibility of rapidly preparing select sulfide compounds in a matter of minutes, rather than weeks, using microwave-assisted heating in domestic microwaves. We report the preparations of phase pure FeS2, CoS2, and solid solutions thereof from the elements with only 40 min of heating. Conventional furnace and rapid microwave preparations of CuTi2S4 both result in a majority of themore » targeted phase, even with the significantly shorter heating time of 40 min for microwave methods relative to 12 days using a conventional furnace. The preparations we describe for these compounds can be extended to related structures and chemistries and thus enable rapid screening of the properties and performance of various compositions of interest for electronic, optical, and electrochemical applications.« less

Sensing Floquet-Majorana fermions via heat transfer

NASA Astrophysics Data System (ADS)

Molignini, Paolo; van Nieuwenburg, Evert; Chitra, R.

2017-09-01

Time periodic modulations of the transverse field in the closed X Y spin-1/2 chain generate a very rich dynamical phase diagram, with a hierarchy of Zn topological phases characterized by differing numbers of Floquet-Majorana modes. This rich phase diagram survives when the system is coupled to dissipative end reservoirs. Circumventing the obstacle of preparing and measuring quasienergy configurations endemic to Floquet-Majorana detection schemes, we show that stroboscopic heat transport and spin density are robust observables to detect both the dynamical phase transitions and Majorana modes in dissipative settings. We find that the heat current provides very clear signatures of these Floquet topological phase transitions. In particular, we observe that the derivative of the heat current, with respect to a control parameter, changes sign at the boundaries separating topological phases with differing nonzero numbers of Floquet-Majorana modes. We present a simple scheme to directly count the number of Floquet-Majorana modes in a phase from the Fourier transform of the local spin density profile. Our results are valid provided the anisotropies are not strong and can be easily implemented in quantum engineered systems.

High-temperature heat capacity of Co3O4 spinel: thermally induced spin unpairing transition

USGS Publications Warehouse

Mocala, K.; Navrotsky, A.; Sherman, David M.

1992-01-01

A strong anomaly was found in the heat capacity of Co3O4 between 1000 K and the decomposition temperature. This anomaly is not related to the decomposition of Co3O4 to CoO. The measured entropy of transition, ??S=46??4 J mol-1 K-1 of Co3O4, supports the interpretation that this anomaly reflects a spin unpairing transition in octahedrally coordinated Co3+ cations. Experimental values of heat capacity, heat content and entropy of Co3O4 in the high temperature region are provided. The enthalpy of the spin unpairing transition is 53??4 kJ mol-1 of Co3O4. ?? 1992 Springer-Verlag.

The Distribution of Heat-Producing Radioactive Elements in the Deep Earth

NASA Astrophysics Data System (ADS)

Chidester, Bethany A.

The Earth is a heat engine, where large differences in temperature between the interior and the surface drive large-scale movement that manifests as plate tectonics and the geomagnetic field that protects us from the Sun's harmful charged particles. Decay of the long-lived radioactive elements U, Th, and K is expected to contribute as much as 45% of the current heat production in the Earth, and that heat production was five times higher early in Earth's history. It is unclear how this heat source affects the thermal and dynamic evolution of the Earth's core and mantle and how that contribution has changed over geologic time. This dissertation addresses this problem in several different ways. This work represents the first high-pressure, high-temperature metal-silicate partitioning experiments for U, Th, and K in the laser-heated diamond anvil cell at conditions relevant to core formation. A chemical model is developed using parameterization of these partitioning data to constrain the concentrations of each of these elements in the core. Using a numerical calculation, it is then determined how that radioactive heat would contribute to the core's energy and entropy budget through time. One finds that, despite its strong lithophile nature at the surface, U partitions significantly into the metallic phase at increasing temperatures. This may be due to a decrease in U valence from 4+ to 2+ in high-pressure silicate melts, which our data supports. However, K and Th do not exhibit a similar change in behavior at these conditions, and this may drive fractionation between U and Th in the deep mantle. At the most extreme conditions of core formation, enough U could exist in the core to produce up to 4.4 TW of heat 4.5 billion years ago. Potassium could produce much less heat than U early on (< 1 TW), and due to its short half-life, would have decayed away much faster. While this energy source is significantly greater than was previously thought to be possible, it is likely not enough to explain the presence of the geomagnetic field early in Earth's history. I have also completed a synchrotron-based study to determine the phase behavior and equations of state of UO2 and ThO2. ThO 2 undergoes a phase transition from the fluorite- type structure (thorianite) that is stable at ambient conditions to the previously identified cotunnite-type structure around 19 GPa and 1500 K. It remains in the cotunnite-type phase up to 60 GPa and 2500 K. UO2 undergoes several solid phase transitions at high pressure. The fluorite-type (uraninite) to cotunnite-type transition occurs around 20 GPa above 1100 K. At around 35 GPa, a new phase emerges; this phase has been indexed to a tetragonal crystal structure. Finally, at 80 GPa and above, UO2 undergoes another phase transition or dissociates into two separate oxides. This understanding of the phase behavior of the simplest actinide-bearing minerals provides insight into the mineralogical hosts for these radioactive elements, as well as other large cations, in the Earth's deep mantle.

Start-up Characteristics of Swallow-tailed Axial-grooved Heat Pipe under the conditions of Multiple Heat Sources

NASA Astrophysics Data System (ADS)

Zhang, Renping

2017-12-01

A mathematical model was developed for predicting start-up characteristics of Swallow-tailed Axial-grooved Heat Pipe under the conditions of Multiple Heat Sources. The effects of heat capacitance of heat source, liquid-vapour interfacial evaporation-condensation heat transfer, shear stress at the interface was considered in current model. The interfacial evaporating mass flow rate is based on the kinetic analysis. Time variations of evaporating mass rate, wall temperature and liquid velocity are studied from the start-up to steady state. The calculated results show that wall temperature demonstrates step transition at the junction between the heat source and non-existent heat source on the evaporator. The liquid velocity changes drastically at the evaporator section, however, it has slight variation at the evaporator section without heat source. When the effect of heat source is ignored, the numerical temperature demonstrates a quicker response. With the consideration of capacitance of the heat source, the data obtained from the proposed model agree well with the experimental results.

Quantum criticality at the superconductor-insulator transition revealed by specific heat measurements

PubMed Central

Poran, S.; Nguyen-Duc, T.; Auerbach, A.; Dupuis, N.; Frydman, A.; Bourgeois, Olivier

2017-01-01

The superconductor–insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, cp, measurements. Here we use a unique highly sensitive experiment to measure cp of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition. PMID:28224994

Quantum criticality at the superconductor-insulator transition revealed by specific heat measurements.

PubMed

Poran, S; Nguyen-Duc, T; Auerbach, A; Dupuis, N; Frydman, A; Bourgeois, Olivier

2017-02-22

The superconductor-insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, c p , measurements. Here we use a unique highly sensitive experiment to measure c p of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition.

Superconducting Hot-Electron Submillimeter-Wave Detector

NASA Technical Reports Server (NTRS)

Karasik, Boris; McGrath, William; Leduc, Henry

2009-01-01

A superconducting hot-electron bolometer has been built and tested as a prototype of high-sensitivity, rapid-response detectors of submillimeter-wavelength radiation. There are diverse potential applications for such detectors, a few examples being submillimeter spectroscopy for scientific research; detection of leaking gases; detection of explosive, chemical, and biological weapons; and medical imaging. This detector is a superconducting-transition- edge device. Like other such devices, it includes a superconducting bridge that has a low heat capacity and is maintained at a critical temperature (T(sub c)) at the lower end of its superconducting-transition temperature range. Incident photons cause transient increases in electron temperature through the superconducting-transition range, thereby yielding measurable increases in electrical resistance. In this case, T(sub c) = 6 K, which is approximately the upper limit of the operating-temperature range of silicon-based bolometers heretofore used routinely in many laboratories. However, whereas the response speed of a typical silicon- based laboratory bolometer is characterized by a frequency of the order of a kilohertz, the response speed of the present device is much higher characterized by a frequency of the order of 100 MHz. For this or any bolometer, a useful figure of merit that one seeks to minimize is (NEP)(tau exp 1/2), where NEP denotes the noise-equivalent power (NEP) and the response time. This figure of merit depends primarily on the heat capacity and, for a given heat capacity, is approximately invariant. As a consequence of this approximate invariance, in designing a device having a given heat capacity to be more sensitive (to have lower NEP), one must accept longer response time (slower response) or, conversely, in designing it to respond faster, one must accept lower sensitivity. Hence, further, in order to increase both the speed of response and the sensitivity, one must make the device very small in order to make its heat capacity very small; this is the approach followed in developing the present device.

Development of a real-time system for ITER first wall heat load control

NASA Astrophysics Data System (ADS)

Anand, Himank; de Vries, Peter; Gribov, Yuri; Pitts, Richard; Snipes, Joseph; Zabeo, Luca

2017-10-01

The steady state heat flux on the ITER first wall (FW) panels are limited by the heat removal capacity of the water cooling system. In case of off-normal events (e.g. plasma displacement during H-L transitions), the heat loads are predicted to exceed the design limits (2-4.7 MW/m2). Intense heat loads are predicted on the FW, even well before the burning plasma phase. Thus, a real-time (RT) FW heat load control system is mandatory from early plasma operation of the ITER tokamak. A heat load estimator based on the RT equilibrium reconstruction has been developed for the plasma control system (PCS). A scheme, estimating the energy state for prescribed gaps defined as the distance between the last closed flux surface (LCFS)/separatrix and the FW is presented. The RT energy state is determined by the product of a weighted function of gap distance and the power crossing the plasma boundary. In addition, a heat load estimator assuming a simplified FW geometry and parallel heat transport model in the scrape-off layer (SOL), benchmarked against a full 3-D magnetic field line tracer is also presented.

The α–β phase transition in volcanic cristobalite

PubMed Central

Damby, David E.; Llewellin, Edward W.; Horwell, Claire J.; Williamson, Ben J.; Najorka, Jens; Cressey, Gordon; Carpenter, Michael

2014-01-01

Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α–β phase transition in volcanic cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic cristobalite exists in the α form and has a larger cell volume than synthetic α-cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic cristobalite exhibits a lower degree of thermal expansion than synthetic cristobalite, and it also has a lower α–β transition temperature (∼473 K) compared with synthetic cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures. PMID:25242910

The α-β phase transition in volcanic cristobalite.

PubMed

Damby, David E; Llewellin, Edward W; Horwell, Claire J; Williamson, Ben J; Najorka, Jens; Cressey, Gordon; Carpenter, Michael

2014-08-01

Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al 3+ and Na + for Si 4+ ; similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α-β phase transition in volcanic cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic cristobalite exists in the α form and has a larger cell volume than synthetic α-cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic cristobalite exhibits a lower degree of thermal expansion than synthetic cristobalite, and it also has a lower α-β transition temperature (∼473 K) compared with synthetic cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al 3+ and Na + defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures.

Development of a high-speed real-time PCR system for rapid and precise nucleotide recognition

NASA Astrophysics Data System (ADS)

Terazono, Hideyuki; Takei, Hiroyuki; Hattori, Akihiro; Yasuda, Kenji

2010-04-01

Polymerase chain reaction (PCR) is a common method used to create copies of a specific target region of a DNA sequence and to produce large quantities of DNA. A few DNA molecules, which act as templates, are rapidly amplified by PCR into many billions of copies. PCR is a key technology in genome-based biological analysis, revolutionizing many life science fields such as medical diagnostics, food safety monitoring, and countermeasures against bioterrorism. Thus, many applications have been developed with the thermal cycling. For these PCR applications, one of the most important key factors is reduction in the data acquisition time. To reduce the acquisition time, it is necessary to decrease the temperature transition time between the high and low ends as much as possible. We have developed a novel rapid real-time PCR system based on rapid exchange of media maintained at different temperatures. This system consists of two thermal reservoirs and a reaction chamber for PCR observation. The temperature transition was achieved within 0.3 sec, and good thermal stability was achieved during thermal cycling with rapid exchange of circulating media. This system allows rigorous optimization of the temperatures required for each stage of the PCR processes. Resulting amplicons were confirmed by electrophoresis. Using the system, rapid DNA amplification was accomplished within 3.5 min, including initial heating and complete 50 PCR cycles. It clearly shows that the device could allow us faster temperature switching than the conventional conduction-based heating systems based on Peltier heating/cooling.

Microwave-assisted synthesis of carbon nanotubes from tannin, lignin, and derivatives

DOEpatents

Viswanathan, Tito

2014-06-17

A method of synthesizing carbon nanotubes. In one embodiment, the method includes the steps of: (a) dissolving a first amount of a first transition-metal salt and a second amount of a second transition-metal salt in water to form a solution; (b) adding a third amount of tannin to the solution to form a mixture; (c) heating the mixture to a first temperature for a first duration of time to form a sample; and (d) subjecting the sample to a microwave radiation for a second duration of time effective to produce a plurality of carbon nanotubes.

Correlations for Boundary-Layer Transition on Mars Science Laboratory Entry Vehicle Due to Heat-Shield Cavities

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Liechty, Derek S.

2008-01-01

The influence of cavities (for attachment bolts) on the heat-shield of the proposed Mars Science Laboratory entry vehicle has been investigated experimentally and computationally in order to develop a criterion for assessing whether the boundary layer becomes turbulent downstream of the cavity. Wind tunnel tests were conducted on the 70-deg sphere-cone vehicle geometry with various cavity sizes and locations in order to assess their influence on convective heating and boundary layer transition. Heat-transfer coefficients and boundary-layer states (laminar, transitional, or turbulent) were determined using global phosphor thermography.

Role of thermal heating on the voltage induced insulator-metal transition in VO2.

PubMed

Zimmers, A; Aigouy, L; Mortier, M; Sharoni, A; Wang, Siming; West, K G; Ramirez, J G; Schuller, Ivan K

2013-02-01

We show that the main mechanism for the dc voltage or dc current induced insulator-metal transition in vanadium dioxide VO(2) is due to local Joule heating and not a purely electronic effect. This "tour de force" experiment was accomplished by using the fluorescence spectra of rare-earth doped micron sized particles as local temperature sensors. As the insulator-metal transition is induced by a dc voltage or dc current, the local temperature reaches the transition temperature indicating that Joule heating plays a predominant role. This has critical implications for the understanding of the dc voltage or dc current induced insulator-metal transition and has a direct impact on applications which use dc voltage or dc current to externally drive the transition.

Overview of NASA supported Stirling thermodynamic loss research

NASA Technical Reports Server (NTRS)

Tew, Roy C.; Geng, Steven M.

1992-01-01

NASA is funding research to characterize Stirling machine thermodynamic losses. NASA's primary goal is to improve Stirling design codes to support engine development for space and terrestrial power. However, much of the fundamental data is applicable to Stirling cooling and heat pump applications. The research results are reviewed. Much was learned about oscillating flow hydrodynamics, including laminar/turbulent transition, and tabulated data was documented for further analysis. Now, with a better understanding of the oscillating flow field, it is time to begin measuring the effects of oscillating flow and oscillating pressure level on heat transfer in heat exchanger flow passages and in cylinders.

Ignitability of materials in transitional heating regimes

Treesearch

Mark A. Dietenberger

2004-01-01

Piloted ignition behavior of materials, particularly wood products, during transitions between heating regimes is measured and modeled in a cone calorimetry (ISO 5660) heating environment. These include (1) effect of material thickness, density, moisture content, and paint coating variations on thermal response characteristics, (2) effect of fire retardant treatment...

Ultra-Sensitive Transition-Edge Sensors (TESs) for Far-IR/Submm Space-Borne Spectroscopy

NASA Technical Reports Server (NTRS)

Kenyon, M.; Day, P. K.; Bradford, C. M.; Bock, J .J.; Leduc, H. G.

2011-01-01

We have built surface micromachined thin-film metallized Si(x)N(y) optical absorbers for transition-edge sensors (TESs) suitable for the Background - Limited far-IR/Submm Spectrograph (BLISS). BLISS is a broadband (38 micrometers - 433 micrometers), grating spectrometer consisting of five wavebands each with a modest resolution of R (is) approx. 1000. Because BLISS requires the effective noise equivalent power (NEP) of the TES to be below 10 (exp 19) W/Hz(exp 1/2), our TESs consist of four long (1000 micrometers), narrow (0.4 micrometers ), and thin (0.25 micrometers ) Si(x) N(y) support beams that reduce the thermal conductance G between the substrate and the optical absorber. To reduce the heat capacity of the absorber and make the response time tau fast enough for BLISS, our absorbers are patterned into a mesh geometry with a fill factor of less than 10%. We use a bilayer of Ti/Au to make the effective impedance of the absorber match the impedance of the incoming radiation for each band. Measurements of the response time of the metallized absorbers to heat pulses show that their heat capacity exceeds the predictions of the Debye model. Our results are suggestive that the surface of the low pressure chemical vapor deposition (LPCVD) Si(x)N(y) used in the absorbers' construction is the source of microstates that dominate the heat capacity.

Studies of Transitional Flow, Unsteady Separation Phenomena and Particle Induced Augmentation Heating on Ablated Nose Tips.

DTIC Science & Technology

1975-10-01

63 29 Variation of Profile Shape with Time for Axisyinmetric Camphor Models 63 30 The Development of Ablated Nose Shapes Over Which Flow...ablation tests using camphor models and inferred from downrange observation of full scale flight missions. Regions of gross instability on nose...been verified in wind tunnel tests of camphor models where shapes similar to those shown on Figure 29 can be developed under transitional conditions

High-transition-temperature superconductors in the Nb-Al-Ge system

DOEpatents

Giorgi, A.L.; Szklarz, E.G.

1972-09-26

The patent describes superconducting materials of the nominal composition Nb(x)Al(y)Ge(l-y), where x is in the range of 1.9 to 2.8 and y is in the range of 0.5 to 0.9, having transition temperatures in the 19 -20K. range which are readily produced by annealing arc-melted compositions, or cold-pressed, heat-treated compositions at moderate temperatures for reasonably long times (about 50 hours).

A physical mechanism for the onset of radial electric fields in magnetically confined plasmas

NASA Astrophysics Data System (ADS)

Moleti, A.

1996-04-01

A simple physical mechanism is described, which could trigger the Low-mode to High-mode (L-H) transition. The instantaneous ion density profile is significantly modified by a sudden temperature increase, because Larmor radii and banana orbit widths are proportional to thermal velocity. The electric fields that are observed in H-mode plasmas could be produced in the radial region where a large second derivative of the density profile exists, either by strong additional heating or by the heat pulse associated to a sawtooth crash. The L-H transition threshold for the time derivative of the ion temperature is of the order of magnitude of the values that are measured in the outer part of the plasma by electron temperature fast diagnostics at sawtooth crashes. This model agrees with the experimental evidence that L-H transitions are often triggered by a sawtooth crash, and the predicted dependence of the threshold on plasma parameters is fairly consistent with available data.

A simple model of entropy relaxation for explaining effective activation energy behavior below the glass transition temperature.

PubMed

Bisquert, Juan; Henn, François; Giuntini, Jean-Charles

2005-03-01

Strong changes in relaxation rates observed at the glass transition region are frequently explained in terms of a physical singularity of the molecular motions. We show that the unexpected trends and values for activation energy and preexponential factor of the relaxation time tau, obtained at the glass transition from the analysis of the thermally stimulated current signal, result from the use of the Arrhenius law for treating the experimental data obtained in nonstationary experimental conditions. We then demonstrate that a simple model of structural relaxation based on a time dependent configurational entropy and Adam-Gibbs relaxation time is sufficient to explain the experimental behavior, without invoking a kinetic singularity at the glass transition region. The pronounced variation of the effective activation energy appears as a dynamic signature of entropy relaxation that governs the change of relaxation time in nonstationary conditions. A connection is demonstrated between the peak of apparent activation energy measured in nonequilibrium dielectric techniques, with the overshoot of the dynamic specific heat that is obtained in calorimetry techniques.

Heat-pipe Earth.

PubMed

Moore, William B; Webb, A Alexander G

2013-09-26

The heat transport and lithospheric dynamics of early Earth are currently explained by plate tectonic and vertical tectonic models, but these do not offer a global synthesis consistent with the geologic record. Here we use numerical simulations and comparison with the geologic record to explore a heat-pipe model in which volcanism dominates surface heat transport. These simulations indicate that a cold and thick lithosphere developed as a result of frequent volcanic eruptions that advected surface materials downwards. Declining heat sources over time led to an abrupt transition to plate tectonics. Consistent with model predictions, the geologic record shows rapid volcanic resurfacing, contractional deformation, a low geothermal gradient across the bulk of the lithosphere and a rapid decrease in heat-pipe volcanism after initiation of plate tectonics. The heat-pipe Earth model therefore offers a coherent geodynamic framework in which to explore the evolution of our planet before the onset of plate tectonics.

Analysis of energy relaxation kinetics for control of the electron energy distributions in capacitively coupled RF discharges

NASA Astrophysics Data System (ADS)

Lee, Jung Yeol; Verboncoeur, John P.; Lee, Hae June

2018-04-01

The transition of electron energy probability functions (EEPFs) through the change of heating mode is an important issue in plasma science. A well-known example is that the increase of gas pressure, which was analyzed in terms of the ratio of the energy relaxation mean free path to the electrode gap distance, changes the EEPF from bi-Maxwellian to Maxwellian or Druyvesteyn. In this study, a new aspect of the temporal decay of kinetic energy during the energy relaxation time is theoretically analyzed and compared with a particle-in-cell Monte Carlo collision simulation of capacitively coupled plasmas. A fully kinetic description of electron transport and collisions shows drastic changes of EEPFs with the variation of the driving frequency due to the heating mode transition.

Influence of a heated leading edge on boundary layer growth, stability, and transition

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

Landrum, D.B.; Macha, J.M.

1987-06-01

This paper presents the results of a combined theoretical and experimental study of the influence of a heated leading edge on the growth, stability, and transition of a two-dimensional boundary layer. The findings are directly applicable to aircraft wings and nacelles that use surface heating for anti-icing protection. The potential effects of the non-adiabatic condition are particularly important for laminar-flow sections where even small perturbations can result in significantly degraded aerodynamic performance. The results of the study give new insight to the fundamental coupling between streamwise pressure gradient and surface heat flux in laminar and transitional boundary layers. 13 references.

Influence of a heated leading edge on boundary layer growth, stability, and transition

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

Landrum, D.B.; Macha, J.M.

1987-01-01

This paper presents the results of a combined theoretical and experimental study of the influence of a heated leading edge on the growth, stability, and transition of a two-dimensional boundary layer. The findings are directly applicable to aircraft wings and nacelles that use surface heating for anti-icing protection. The potential effects of the non-adiabatic condition are particularly important for laminar-flow sections where even small perturbations can result in significantly degraded aerodynamic performance. The results of the study give new insight to the fundamental coupling between streamwise pressure gradient and surface heat flux in laminar and transitional boundary layers.

Saturated fatty acids and fatty acid esters promote the polymorphic transition of clarithromycin metastable form I crystal.

PubMed

Watanabe, Miteki; Mizoguchi, Midori; Aoki, Hajime; Iwao, Yasunori; Noguchi, Shuji; Itai, Shigeru

2016-10-15

The phase transition of active pharmaceutical ingredients should be taken into account during manufacturing, processing- and storage, because different crystal forms lead to different physical properties of formulations. The phase transition of clarithromycin (CAM) metastable form I to stable form II was investigated on heating with additives such as fatty acids or fatty acid esters. Differential scanning calorimetry analyses revealed that when form I was heated with additives, the phase transition temperature of form I decreased close to the melting points of the additives. Powder X-ray diffraction analyses indicated the tentative presence of a non-crystalline component during the transition of form I to form II on heating with additives. These observations implied that CAM form I dissolved in the melted additives on heating and the dissolved CAM crystallized to form II. Reduction of transition temperatures in the presence of additives were also observed for the crystals of nifedipine form B and carbamazepine form III. These results suggested that the phenomena can be widely applicable for simultaneous crystalline phase transition and granulation using binder additives. Copyright © 2016 Elsevier B.V. All rights reserved.

Advanced Spectroscopic and Thermal Imaging Instrumentation for Shock Tube and Ballistic Range Facilities

NASA Technical Reports Server (NTRS)

Grinstead, Jay H.; Wilder, Michael C.; Reda, Daniel C.; Cruden, Brett A.; Bogdanoff, David W.

2010-01-01

The Electric Arc Shock Tube (EAST) facility and Hypervelocity Free Flight Aerodynamic Facility (HFFAF, an aeroballistic range) at NASA Ames support basic research in aerothermodynamic phenomena of atmospheric entry, specifically shock layer radiation spectroscopy, convective and radiative heat transfer, and transition to turbulence. Innovative optical instrumentation has been developed and implemented to meet the challenges posed from obtaining such data in these impulse facilities. Spatially and spectrally resolved measurements of absolute radiance of a travelling shock wave in EAST are acquired using multiplexed, time-gated imaging spectrographs. Nearly complete spectral coverage from the vacuum ultraviolet to the near infrared is possible in a single experiment. Time-gated thermal imaging of ballistic range models in flight enables quantitative, global measurements of surface temperature. These images can be interpreted to determine convective heat transfer rates and reveal transition to turbulence due to isolated and distributed surface roughness at hypersonic velocities. The focus of this paper is a detailed description of the optical instrumentation currently in use in the EAST and HFFAF.

Aerodynamic heating effects on wall-modeled large-eddy simulations of high-speed flows

NASA Astrophysics Data System (ADS)

Yang, Xiang; Urzay, Javier; Moin, Parviz

2017-11-01

Aerospace vehicles flying at high speeds are subject to increased wall-heating rates because of strong aerodynamic heating in the near-wall region. In wall-modeled large-eddy simulations (WMLES), this near-wall region is typically not resolved by the computational grid. As a result, the effects of aerodynamic heating need to be modeled using an LES wall model. In this investigation, WMLES of transitional and fully turbulent high-speed flows are conducted to address this issue. In particular, an equilibrium wall model is employed in high-speed turbulent Couette flows subject to different combinations of thermal boundary conditions and grid sizes, and in transitional hypersonic boundary layers interacting with incident shock waves. Specifically, the WMLES of the Couette-flow configuration demonstrate that the shear-stress and heat-flux predictions made by the wall model show only a small sensitivity to the grid resolution even in the most adverse case where aerodynamic heating prevails near the wall and generates a sharp temperature peak there. In the WMLES of shock-induced transition in boundary layers, the wall model is tested against DNS and experiments, and it is shown to capture the post-transition aerodynamic heating and the overall heat transfer rate around the shock-impingement zone. This work is supported by AFOSR.

Ultrasonic Method for Measuring Internal Temperature Profile in Heated Materials

NASA Astrophysics Data System (ADS)

Ihara, I.; Takahashi, M.

2008-02-01

A new ultrasonic method for internal temperature measurement is presented. The principle of the method is based on temperature dependence of the velocity of the ultrasonic wave propagating through the material. An inverse analysis to determine the temperature profile in a heated material is developed and an experiment is carried out to verify the validity of the developed method. A single side of a silicone rubber plate of 30 mm thickness is heated and ultrasonic pulse-echo measurements are then performed during heating. A change in transit time of ultrasonic wave in the heated rubber plate is monitored and used to determine the transient variation in internal temperature distribution of the rubber. The internal temperature distribution determined ultrasonically agrees well with both obtained using commercial thermocouples installed in the rubber and estimated theoretically.

On the Coupling Time of the Heat-Bath Process for the Fortuin-Kasteleyn Random-Cluster Model

NASA Astrophysics Data System (ADS)

Collevecchio, Andrea; Elçi, Eren Metin; Garoni, Timothy M.; Weigel, Martin

2018-01-01

We consider the coupling from the past implementation of the random-cluster heat-bath process, and study its random running time, or coupling time. We focus on hypercubic lattices embedded on tori, in dimensions one to three, with cluster fugacity at least one. We make a number of conjectures regarding the asymptotic behaviour of the coupling time, motivated by rigorous results in one dimension and Monte Carlo simulations in dimensions two and three. Amongst our findings, we observe that, for generic parameter values, the distribution of the appropriately standardized coupling time converges to a Gumbel distribution, and that the standard deviation of the coupling time is asymptotic to an explicit universal constant multiple of the relaxation time. Perhaps surprisingly, we observe these results to hold both off criticality, where the coupling time closely mimics the coupon collector's problem, and also at the critical point, provided the cluster fugacity is below the value at which the transition becomes discontinuous. Finally, we consider analogous questions for the single-spin Ising heat-bath process.

Switching dynamics of TaOx-based threshold switching devices

NASA Astrophysics Data System (ADS)

Goodwill, Jonathan M.; Gala, Darshil K.; Bain, James A.; Skowronski, Marek

2018-03-01

Bi-stable volatile switching devices are being used as access devices in solid-state memory arrays and as the active part of compact oscillators. Such structures exhibit two stable states of resistance and switch between them at a critical value of voltage or current. A typical resistance transient under a constant amplitude voltage pulse starts with a slow decrease followed by a rapid drop and leveling off at a low steady state value. This behavior prompted the interpretation of initial delay and fast transition as due to two different processes. Here, we show that the entire transient including incubation time, transition time, and the final resistance values in TaOx-based switching can be explained by one process, namely, Joule heating with the rapid transition due to the thermal runaway. The time, which is required for the device in the conducting state to relax back to the stable high resistance one, is also consistent with the proposed mechanism.

A study of photothermal laser ablation of various polymers on microsecond time scales.

PubMed

Kappes, Ralf S; Schönfeld, Friedhelm; Li, Chen; Golriz, Ali A; Nagel, Matthias; Lippert, Thomas; Butt, Hans-Jürgen; Gutmann, Jochen S

2014-01-01

To analyze the photothermal ablation of polymers, we designed a temperature measurement setup based on spectral pyrometry. The setup allows to acquire 2D temperature distributions with 1 μm size and 1 μs time resolution and therefore the determination of the center temperature of a laser heating process. Finite element simulations were used to verify and understand the heat conversion and heat flow in the process. With this setup, the photothermal ablation of polystyrene, poly(α-methylstyrene), a polyimide and a triazene polymer was investigated. The thermal stability, the glass transition temperature Tg and the viscosity above Tg were governing the ablation process. Thermal decomposition for the applied laser pulse of about 10 μs started at temperatures similar to the start of decomposition in thermogravimetry. Furthermore, for polystyrene and poly(α-methylstyrene), both with a Tg in the range between room and decomposition temperature, ablation already occurred at temperatures well below the decomposition temperature, only at 30-40 K above Tg. The mechanism was photomechanical, i.e. a stress due to the thermal expansion of the polymer was responsible for ablation. Low molecular weight polymers showed differences in photomechanical ablation, corresponding to their lower Tg and lower viscosity above the glass transition. However, the difference in ablated volume was only significant at higher temperatures in the temperature regime for thermal decomposition at quasi-equilibrium time scales.

Direct numerical simulation of transitional and turbulent flow over a heated flat plate using finite-difference schemes

NASA Technical Reports Server (NTRS)

Madavan, Nateri K.

1995-01-01

This report deals with the direct numerical simulation of transitional and turbulent flow at low Mach numbers using high-order-accurate finite-difference techniques. A computation of transition to turbulence of the spatially-evolving boundary layer on a heated flat plate in the presence of relatively high freestream turbulence was performed. The geometry and flow conditions were chosen to match earlier experiments. The development of the momentum and thermal boundary layers was documented. Velocity and temperature profiles, as well as distributions of skin friction, surface heat transfer rate, Reynolds shear stress, and turbulent heat flux, were shown to compare well with experiment. The results indicate that the essential features of the transition process have been captured. The numerical method used here can be applied to complex geometries in a straightforward manner.

Radiative bistability and thermal memory.

PubMed

Kubytskyi, Viacheslav; Biehs, Svend-Age; Ben-Abdallah, Philippe

2014-08-15

We predict the existence of a thermal bistability in many-body systems out of thermal equilibrium which exchange heat by thermal radiation using insulator-metal transition materials. We propose a writing-reading procedure and demonstrate the possibility to exploit the thermal bistability to make a volatile thermal memory. We show that this thermal memory can be used to store heat and thermal information (via an encoding temperature) for arbitrary long times. The radiative thermal bistability could find broad applications in the domains of thermal management, information processing, and energy storage.

The role of zonally asymmetric heating in the vertical and temporal structure of the global scale flow fields during FGGE SOP-1

NASA Technical Reports Server (NTRS)

Paegle, J.; Kalnay, E.; Baker, W. E.

1981-01-01

The global scale structure of atmospheric flow is best documented on time scales longer than a few days. Theoretical and observational studies of ultralong waves have emphasized forcing due to global scale variations of topography and surface heat flux, possibly interacting with baroclinically unstable or vertically refracting basic flows. Analyses of SOP-1 data in terms of global scale spherical harmonics is documented with emphasis upon weekly transitions.

Transitiometric analysis of solid II/solid I transition in anhydrous theophylline.

PubMed

Legendre, Bernard; Randzio, Stanislaw L

2007-10-01

For the first time, with the use of a high sensitivity, low heating rate, scanning transitiometry, it was possible to distinguish and characterise the polymorphic equilibrium transition between forms II and I in anhydrous theophylline. In this manner it was univocally proved, that forms II and I in theophylline are enantiotropically related. The temperature and enthalpy for that transition are as follows: T(trs)(II/I)=536.8+/-2.2K; Delta(trs)H(II/I)=1.99+/-0.09 kJ/mol. Making use of advantages of very slow heating rate and of a high energetic sensitivity of the transitiometer it was possible to observe in detail the polymorphic transition followed by melting of high temperature form I and to stop the solid I-liquid transition at a desired point of equilibrium. Such a solid I-liquid equilibrium could be stabilised and then displaced back to the crystallisation of form I with an adequate use of a precise temperature programming. In such a way a pure single phase of form I of theophylline was prepared. This fact was confirmed by X-ray powder diffraction patterns and calorimetric traces of fusion of the crystallised product. The temperature and enthalpy of the form I-liquid transition are as follows: T(fus)(I)=546.5+/-0.2K and Delta(fus)H(I)=29.37+/-0.29 kJ/mol.

Configurational entropy of polar glass formers and the effect of electric field on glass transition

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

Matyushov, Dmitry V., E-mail: dmitrym@asu.edu

2016-07-21

A model of low-temperature polar liquids is constructed that accounts for the configurational heat capacity, entropy, and the effect of a strong electric field on the glass transition. The model is based on the Padé-truncated perturbation expansions of the liquid state theory. Depending on parameters, it accommodates an ideal glass transition of vanishing configurational entropy and its avoidance, with a square-root divergent enumeration function at the point of its termination. A composite density-temperature parameter ρ{sup γ}/T, often used to represent combined pressure and temperature data, follows from the model. The theory is in good agreement with the experimental data formore » excess (over the crystal state) thermodynamics of molecular glass formers. We suggest that the Kauzmann entropy crisis might be a signature of vanishing configurational entropy of a subset of degrees of freedom, multipolar rotations in our model. This scenario has observable consequences: (i) a dynamical crossover of the relaxation time and (ii) the fragility index defined by the ratio of the excess heat capacity and excess entropy at the glass transition. The Kauzmann temperature of vanishing configurational entropy and the corresponding glass transition temperature shift upward when the electric field is applied. The temperature shift scales quadratically with the field strength.« less

Origin of nonlinear transport across the magnetically induced superconductor-metal-insulator transition in two dimensions.

PubMed

Seo, Y; Qin, Y; Vicente, C L; Choi, K S; Yoon, Jongsoo

2006-08-04

We have studied the effect of perpendicular magnetic fields and temperatures on nonlinear electronic transport in amorphous Ta superconducting thin films. The films exhibit a magnetic field-induced metallic behavior intervening the superconductor-insulator transition in the zero temperature limit. We show that the phase-identifying nonlinear transport in the superconducting and metallic phases arises from an intrinsic origin, not from an electron heating effect. The nonlinear transport is found to accompany an extraordinarily long voltage response time.

Premelting, Melting, and Degradation Properties of Molten Alkali Nitrates: LiNO3, NaNO3, KNO3, and Binary NaNO3-KNO3

NASA Astrophysics Data System (ADS)

Mohammad, Mehedi Bin; Brooks, Geoffrey Alan; Rhamdhani, Muhammad Akbar

2018-02-01

A simultaneous thermal analyzer (STA) was used to observe the transition and degradation events of LiNO3, NaNO3, KNO3, and binary NaNO3-KNO3 salts for potential use as phase change materials (PCMs) and heat transfer fluid (HTF). Samples were heated from 50 °C to 800 °C at 10 °C/min scanning rate in three atmospheres (argon, air, and oxygen) using an STA to observe decomposition behavior. Thermal stability increased for all salts at high partial pressure of O2 ( P_{{{O}2 }} = 1.0) compared to inert argon ( P_{{{O}2 }} = 0). O2, N2, NO, N2O, and NO2 were main evolved gases during nitrate decomposition. NO and O2 started to evolve at approximately the same temperature after melting, indicating that primary and secondary decomposition reactions were concurrent and overlapping. The solid-solid transition, liquidus and solidus temperatures, heat of transition, heat of melting, and heat of solidification were obtained at various heating-cooling rates (1, 2, 4, 5, 6, 8, 10, and 15 °C/min) using an STA. At all heating-cooling rates, a small gap exists between liquidus and solidus temperatures for all samples due to the salts exhibiting supercooling phenomena. This study showed that the degradation point depends on the blanket atmosphere top of the molten salts and that heating rates have a minor effect on transition events (peaks height, peaks width, and transition enthalpies).

Premelting, Melting, and Degradation Properties of Molten Alkali Nitrates: LiNO3, NaNO3, KNO3, and Binary NaNO3-KNO3

NASA Astrophysics Data System (ADS)

Mohammad, Mehedi Bin; Brooks, Geoffrey Alan; Rhamdhani, Muhammad Akbar

2018-06-01

A simultaneous thermal analyzer (STA) was used to observe the transition and degradation events of LiNO3, NaNO3, KNO3, and binary NaNO3-KNO3 salts for potential use as phase change materials (PCMs) and heat transfer fluid (HTF). Samples were heated from 50 °C to 800 °C at 10 °C/min scanning rate in three atmospheres (argon, air, and oxygen) using an STA to observe decomposition behavior. Thermal stability increased for all salts at high partial pressure of O2 ( P_{{{O}2 }} = 1.0) compared to inert argon ( P_{{{O}2 }} = 0). O2, N2, NO, N2O, and NO2 were main evolved gases during nitrate decomposition. NO and O2 started to evolve at approximately the same temperature after melting, indicating that primary and secondary decomposition reactions were concurrent and overlapping. The solid-solid transition, liquidus and solidus temperatures, heat of transition, heat of melting, and heat of solidification were obtained at various heating-cooling rates (1, 2, 4, 5, 6, 8, 10, and 15 °C/min) using an STA. At all heating-cooling rates, a small gap exists between liquidus and solidus temperatures for all samples due to the salts exhibiting supercooling phenomena. This study showed that the degradation point depends on the blanket atmosphere top of the molten salts and that heating rates have a minor effect on transition events (peaks height, peaks width, and transition enthalpies).

On the Induction of the First-Order Phase Magnetic Transitions by Acoustic Vibrations in MnSi

NASA Astrophysics Data System (ADS)

Pikin, S. A.

2017-12-01

The main result of the paper contains the conclusion that the magnetic phase transition in MnSi always remains first order at any temperature and magnetic field. In these aims, a model of coupling of an order parameter with other degrees of freedom is used. The coupling of magnetic order parameters with long-wave acoustic phonons, in the presence of the nonsingular parts of the bulk and shear moduli, a first-order transition occurs, participle near the transition the heat capacity and the compressibility remain finite, if the heat capacity becomes infinite in the system disregarding the acoustic phonons. The role of the Frenkel heterophase fluctuations is discussed. The impurity effect shows that, for some phases, the heat capacity of the system remains continuous and finite at the transition point. It is supposed that the transition is progressively smoothed by these fluctuations at the application of the magnetic field.

On the induction of the first-order phase magnetic transitions by acoustic vibrations in MnSi

NASA Astrophysics Data System (ADS)

Pikin, S. A.

2017-12-01

The main result of the paper contains the conclusion that the magnetic phase transition in MnSi always remains first order at any temperature and magnetic field. In these aims, a model of coupling of an order parameter with other degrees of freedom is used. The coupling of magnetic order parameters with longwave acoustic phonons, in the presence of the nonsingular parts of the bulk and shear moduli, a first-order transition occurs, participle near the transition the heat capacity and the compressibility remain finite, if in the system without allowance of the acoustic phonons the heat capacity becomes infinite. The role of the Frenkel heterophase fluctuations is discussed. The impurity effect shows that, for some phases, the heat capacity of the system remains continuous and finite at the transition point. It is supposed that the transition is progressively smoothed by these fluctuations at the application of the magnetic field.

Composite prepreg application device

NASA Technical Reports Server (NTRS)

Sandusky, Donald A. (Inventor); Marchello, Joseph M. (Inventor)

1995-01-01

A heated shoe and cooled pressure roller assembly for composite prepreg application is provided. The shoe assembly includes a heated forward contact surface having a curved pressure surface. The following cooled roller provides a continuous pressure to the thermoplastic while reducing the temperature to approximately 5 C below glass transition temperature. Electric heating coils inside the forward portion of the shoe heat a thermoplastic workpiece to approximately 100 C above the glass transition. Immediately following the heated contact surface, a cooled roller cools the work. The end sharpened shape of the heated shoe trailing edge tends to prevent slag buildup and maintain a uniform, relaxed stress fabrication.

Long-range Prethermal Time Crystals

NASA Astrophysics Data System (ADS)

Machado, Francisco; Meyer, Gregory D.; Else, Dominic; Olund, Christopher; Nayak, Chetan; Yao, Norman Y.

2017-04-01

Driven quantum systems have recently enabled the realization of a discrete time crystal - an intrinsically out-of-equilibrium phase of matter. One strategy to prevent the drive-induced, runaway heating of the time crystal is the presence of strong disorder leading to many-body localization (MBL). A more elegant, disorder-less approach is simply to work in the prethermal regime where time crystalline order can persist to exponentially long times. One key difference between prethermal and MBL time crystals is that the former is prohibited from existing in one dimensional systems with short-range interactions. In this work, we demonstrate that long-range interactions can stabilize a one dimensional prethermal time crystal. By numerically studying the pre-thermal regime, we find evidence for a phase transition out of the time crystal as a function of increasing energy density. Finally, generalizations of previous analytical bounds for the heating time-scale of driven quantum systems to long-range interactions will also be discussed.

Performance Impact of Deflagration to Detonation Transition Enhancing Obstacles

NASA Technical Reports Server (NTRS)

Paxson, Daniel E.; Schauer, Frederick; Hopper, David

2012-01-01

A sub-model is developed to account for the drag and heat transfer enhancement resulting from deflagration-to-detonation (DDT) inducing obstacles commonly used in pulse detonation engines (PDE). The sub-model is incorporated as a source term in a time-accurate, quasi-onedimensional, CFD-based PDE simulation. The simulation and sub-model are then validated through comparison with a particular experiment in which limited DDT obstacle parameters were varied. The simulation is then used to examine the relative contributions from drag and heat transfer to the reduced thrust which is observed. It is found that heat transfer is far more significant than aerodynamic drag in this particular experiment.

Synchronized Molecular-Dynamics simulation for thermal lubrication of a polymeric liquid between parallel plates

NASA Astrophysics Data System (ADS)

Yasuda, Shugo; Yamamoto, Ryoichi

2015-11-01

The Synchronized Molecular-Dynamics simulation which was recently proposed by authors is applied to the analysis of polymer lubrication between parallel plates. In the SMD method, the MD simulations are assigned to small fluid elements to calculate the local stresses and temperatures and are synchronized at certain time intervals to satisfy the macroscopic heat- and momentum-transport equations.The rheological properties and conformation of the polymer chains coupled with local viscous heating are investigated with a non-dimensional parameter, the Nahme-Griffith number, which is defined as the ratio of the viscous heating to the thermal conduction at the characteristic temperature required to sufficiently change the viscosity. The present simulation demonstrates that strong shear thinning and a transitional behavior of the conformation of the polymer chains are exhibited with a rapid temperature rise when the Nahme-Griffith number exceeds unity.The results also clarify that the reentrant transition of the linear stress-optical relation occurs for large shear stresses due to the coupling of the conformation of polymer chains with heat generation under shear flows. This study was financially supported by JSPS KAKENHI Grant Nos. 26790080 and 26247069.

Phase boundary of hot dense fluid hydrogen

PubMed Central

Ohta, Kenji; Ichimaru, Kota; Einaga, Mari; Kawaguchi, Sho; Shimizu, Katsuya; Matsuoka, Takahiro; Hirao, Naohisa; Ohishi, Yasuo

2015-01-01

We investigated the phase transformation of hot dense fluid hydrogen using static high-pressure laser-heating experiments in a laser-heated diamond anvil cell. The results show anomalies in the heating efficiency that are likely to be attributed to the phase transition from a diatomic to monoatomic fluid hydrogen (plasma phase transition) in the pressure range between 82 and 106 GPa. This study imposes tighter constraints on the location of the hydrogen plasma phase transition boundary and suggests higher critical point than that predicted by the theoretical calculations. PMID:26548442

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

Yeager, John David; Watkins, Erik Benjamin; Duque, Amanda Lynn

Thermal ignition via self-heating (cook-off) of cyclotetramethylene-tetranitramine (HMX)-containing plastic-bonded explosives (PBXs) is driven by the β → δ phase transition in the HMX, which is affected if not dominated by microstructure. Here, we studied the HMX-binder interface and phase transition for several variations of PBX 9404 (HMX with plasticized nitrocellulose [NC] binder). Neutron reflectometry was used to examine the interface under several conditions—pristine, after aging, and after thermal treatment. The initial interfacial structure depended on the plasticizer, but the interface homogenized over time. Thermal and optical analyses showed that all formulated materials had higher transition temperatures than neat HMX. Thismore » effect increased with NC content.« less

Heat transfer and pressure drop for air flow through enhanced passages

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

Obot, N.T.; Esen, E.B.

1992-06-01

An extensive experimental investigation was carried out to determine the pressure drop and heat transfer characteristics for laminar, transitional and turbulent flow of air through a smooth passage and twenty-three enhanced passages. The internal surfaces of all enhanced passages had spirally shaped geometries; these included fluted, finned/ribbed and indented surfaces. The Reynolds number (Re) was varied between 400 and 50000. The effect of heat transfer (wall cooling or fluid heating) on pressure drop is most significant within the transition region; the recorded pressure drop with heat transfer is much higher than that without heat transfer. The magnitude of this effectmore » depends markedly on the average surface temperature and, to a lesser extent, on the geometric characteristics of the enhanced surfaces. When the pressure drop data are reduced as values of the Fanning friction factor(f), the results are about the same with and without heat transfer for turbulent flow, with moderate differences in the laminar and transition regions.« less

Heat transfer and pressure drop for air flow through enhanced passages. Final report

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

Obot, N.T.; Esen, E.B.

1992-06-01

An extensive experimental investigation was carried out to determine the pressure drop and heat transfer characteristics for laminar, transitional and turbulent flow of air through a smooth passage and twenty-three enhanced passages. The internal surfaces of all enhanced passages had spirally shaped geometries; these included fluted, finned/ribbed and indented surfaces. The Reynolds number (Re) was varied between 400 and 50000. The effect of heat transfer (wall cooling or fluid heating) on pressure drop is most significant within the transition region; the recorded pressure drop with heat transfer is much higher than that without heat transfer. The magnitude of this effectmore » depends markedly on the average surface temperature and, to a lesser extent, on the geometric characteristics of the enhanced surfaces. When the pressure drop data are reduced as values of the Fanning friction factor(f), the results are about the same with and without heat transfer for turbulent flow, with moderate differences in the laminar and transition regions.« less

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

Willey, Trevor M.; Lauderbach, Lisa; Gagliardi, Franco

HMX-based explosives LX-10 and PBX-9501 were heated through the β-δ phase transition. Ultra-small angle x-ray scattering (USAXS) and molecular diffraction were simultaneously recorded as the HMX was heated. Mesoscale voids and structure dramatically change promptly with the β-δ phase transition, rather than with other thermal effects. Also, x-ray induced damage, observed in the USAXS, occurs more readily at elevated temperatures; as such, the dose was reduced to mitigate this effect. Optical microscopy performed during a similar heating cycle gives an indication of changes on longer length scales, while x-ray microtomography, performed before and after heating, shows the character of extensivemore » microstructural damage resulting from the temperature cycle and solid-state phase transition.« less

Universality of oscillating boiling in Leidenfrost transition

NASA Astrophysics Data System (ADS)

Tran, Tuan; Khavari, Mohammad

2017-11-01

The Leidenfrost transition leads a boiling system to the boiling crisis, a state in which the liquid loses contact with the heated surface due to excessive vapor generation. Here, using experiments of liquid droplets boiling on a heated surface, we report a new phenomenon, termed oscillating boiling, at the Leidenfrost transition. We show that oscillating boiling results from the competition between two effects: separation of liquid from the heated surface due to localized boiling, and rewetting. We argue theoretically that the Leidenfrost transition can be predicted based on its link with the oscillating boiling phenomenon, and verify the prediction experimentally for various liquids. This work was funded by Nanyang Technological University and A*STAR, Singapore.

Development of the oriental latrine fly, Chrysomya megacephala (Diptera: Calliphoridae), at five constant temperatures

USGS Publications Warehouse

Gruner, S. V.; Slone, D.H.; Capinera, J.L.; Turco, M. P.

2017-01-01

Chrysomya megacephala (Fabricius) is a forensically important fly that is found throughout the tropics and subtropics. We calculated the accumulated development time and transition points for each life stage from eclosion to adult emergence at five constant temperatures: 15, 20, 25, 30, and 35 °C. For each transition, the 10th, 50th, and 90th percentiles were calculated with a logistic linear model. The mean transition times and % survivorship were determined directly from the raw laboratory data. Development times of C. megacephala were compared with that of two other closely related species, Chrysomya rufifacies (Macquart) and Phormia regina (Meigen). Ambient and larval mass temperatures were collected from field studies conducted from 2001–2004. Field study data indicated that adult fly activity was reduced at lower ambient temperatures, but once a larval mass was established, heat generation occurred. These development times and durations can be used for estimation of a postmortem interval (PMI).

Numerical simulation for turbulent heating around the forebody fairing of H-II rocket

NASA Astrophysics Data System (ADS)

Nomura, Shigeaki; Yamamoto, Yukimitsu; Fukushima, Yukio

Concerning the heat transfer distributions around the nose fairing of the Japanese new launch vehicle H-II rocket, numerical simulations have been conducted for the conditions along its nominal ascent trajectory and some experimental tests have been conducted additionally to confirm the numerical results. The thin layer approximated Navier-Stokes equations with Baldwin-Lomax's algebraic turbulent model were solved by the time dependent finite difference method. Results of numerical simulations showed that a high peak heating would occur near the stagnation point on the spherical nose portion due to the transition to turbulent flow during the period when large stagnation point heating was predicted. The experiments were conducted under the condition of M = 5 and Re = 10 to the 6th which was similar to the flight condition where the maximum stagnation point heating would occur. The experimental results also showed a high peak heating near the stagnation point over the spherical nose portion.

Experimental investigation on the heat transfer characteristics and flow pattern in vertical narrow channels heated from one side

NASA Astrophysics Data System (ADS)

Huang, Lihao; Li, Gang; Tao, Leren

2016-07-01

Experimental investigation for the flow boiling of water in a vertical rectangular channel was conducted to reveal the boiling heat transfer mechanism and flow patterns map aspects. The onset of nucleate boiling went upward with the increasing of the working fluid mass flow rate or the decreasing of the inlet working fluid temperature. As the vapour quality was increased, the local heat transfer coefficient increased first, then decreased, followed by various flow patterns. The test data from other researchers had a similar pattern transition for the bubble-slug flow and the slug-annular flow. Flow pattern transition model analysis was performed to make the comparison with current test data. The slug-annular and churn-annular transition models showed a close trend with current data except that the vapor phase superficial velocity of flow pattern transition was much higher than that of experimental data.

Endotoxin inactivation via steam-heat treatment in dilute simethicone emulsions used in biopharmaceutical processes.

PubMed

Britt, Keith A; Galvin, Jeffrey; Gammell, Patrick; Nti-Gyabaah, Joseph; Boras, George; Kolwyck, David; Ramirez, José G; Presente, Esther; Naugle, Gregory

2014-01-01

Simethicone emulsion is used to regulate foaming in cell culture operations in biopharmaceutical processes. It is also a potential source of endotoxin contamination. The inactivation of endotoxins in dilute simethicone emulsions was assessed as a function of time at different steam temperatures using a Limulus amebocyte lysate kinetic chromogenic technique. Endotoxin inactivation from steam-heat treatment was fit to a four-parameter double exponential decay model, which indicated that endotoxin inactivation was biphasic, consisting of fast and slow regimes. In the fast regime, temperature-related effects were dominant. Transitioning into the slow regime, the observed temperature dependence diminished, and concentration-related effects became increasingly significant. The change in the Gibbs free energy moving through the transition state indicated that a large energy barrier must be overcome for endotoxin inactivation to occur. The corresponding Arrhenius pre-exponential factor was >10(12) s(-1) suggesting that endotoxins in aqueous solution exist as aggregates. The disorder associated with the endotoxin inactivation reaction pathway was assessed via the change in entropy moving through the transition state. This quantity was positive indicating that endotoxin inactivation may result from hydrolysis of individual endotoxin molecules, which perturbs the conformation of endotoxin aggregates, thereby modulating the biological activity observed. Steam-heat treatment decreased endotoxin levels by 1-2 logarithm (log) reduction (LRV), which may be practically relevant depending on incoming raw material endotoxin levels. Antifoam efficiency and cell culture performance were negligibly impacted following steam-heat treatment. The results from this study show that steam-heat treatment is a viable endotoxin control strategy that can be implemented to support large-scale biopharmaceutical manufacturing. © 2014 American Institute of Chemical Engineers.

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

NASA Astrophysics Data System (ADS)

Warren, Harry P.; Reep, Jeffrey W.; Crump, Nicholas A.; Simões, Paulo J. A.

2016-09-01

We exploit the high spatial resolution and high cadence of the Interface Region Imaging Spectrograph (IRIS) to investigate the response of the transition region and chromosphere to energy deposition during a small flare. Simultaneous observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager provide constraints on the energetic electrons precipitating into the flare footpoints, while observations of the X-Ray Telescope, Atmospheric Imaging Assembly, and Extreme Ultraviolet Imaging Spectrometer (EIS) allow us to measure the temperatures and emission measures from the resulting flare loops. We find clear evidence for heating over an extended period on the spatial scale of a single IRIS pixel. During the impulsive phase of this event, the intensities in each pixel for the Si IV 1402.770 Å, C II 1334.535 Å, Mg II 2796.354 Å, and O I 1355.598 Å emission lines are characterized by numerous small-scale bursts typically lasting 60 s or less. Redshifts are observed in Si IV, C II, and Mg II during the impulsive phase. Mg II shows redshifts during the bursts and stationary emission at other times. The Si IV and C II profiles, in contrast, are observed to be redshifted at all times during the impulsive phase. These persistent redshifts are a challenge for one-dimensional hydrodynamic models, which predict only short-duration downflows in response to impulsive heating. We conjecture that energy is being released on many small-scale filaments with a power-law distribution of heating rates.

Transition Analysis for the HIFiRE-1 Flight Experiment

NASA Technical Reports Server (NTRS)

Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan; Kimmel, Roger; Adamczak, David; Smith, Mark S.

2011-01-01

The HIFiRE-1 flight experiment provided a valuable database pertaining to boundary layer transition over a 7-degree half-angle, circular cone model from supersonic to hypersonic Mach numbers, and a range of Reynolds numbers and angles of incidence. This paper reports the initial findings from the ongoing computational analysis pertaining to the measured in-flight transition behavior. Transition during the ascent phase at nearly zero degree angle of attack is dominated by second mode instabilities except in the vicinity of the cone meridian where a roughness element was placed midway along the length of the cone. The first mode instabilities were found to be weak at all trajectory points analyzed from the ascent phase. For times less than approximately 18.5 seconds into the flight, the peak amplification ratio for second mode disturbances is sufficiently small because of the lower Mach numbers at earlier times, so that the transition behavior inferred from the measurements is attributed to an unknown physical mechanism, potentially related to step discontinuities in surface height near the locations of a change in the surface material. Based on the time histories of temperature and/or heat flux at transducer locations within the aft portion of the cone, the onset of transition correlated with a linear PSE N-factor of approximately 14.

Calculation of cracking under pulsed heat loads in tungsten manufactured according to ITER specifications

NASA Astrophysics Data System (ADS)

Arakcheev, A. S.; Skovorodin, D. I.; Burdakov, A. V.; Shoshin, A. A.; Polosatkin, S. V.; Vasilyev, A. A.; Postupaev, V. V.; Vyacheslavov, L. N.; Kasatov, A. A.; Huber, A.; Mertens, Ph; Wirtz, M.; Linsmeier, Ch; Kreter, A.; Löwenhoff, Th; Begrambekov, L.; Grunin, A.; Sadovskiy, Ya

2015-12-01

A mathematical model of surface cracking under pulsed heat load was developed. The model correctly describes a smooth brittle-ductile transition. The elastic deformation is described in a thin-heated-layer approximation. The plastic deformation is described with the Hollomon equation. The time dependence of the deformation and stresses is described for one heating-cooling cycle for a material without initial plastic deformation. The model can be applied to tungsten manufactured according to ITER specifications. The model shows that the stability of stress-relieved tungsten deteriorates when the base temperature increases. This proved to be a result of the close ultimate tensile and yield strengths. For a heat load of arbitrary magnitude a stability criterion was obtained in the form of condition on the relation of the ultimate tensile and yield strengths.

Local heat transfer in turbine disk-cavities. I - Rotor and stator cooling with hub injection of coolant

NASA Astrophysics Data System (ADS)

Bunker, R. S.; Metzger, D. E.; Wittig, S.

1990-06-01

Detailed radial heat-transfer coefficient distributions applicable to the cooling of disk-cavity regions of gas turbines are obtained experimentally from local heat-transfer data on both the rotating and stationary surfaces of a parallel-geometry disk-cavity system. Attention is focused on the hub injection of a coolant over a wide range of parameters including disk rotational Reynolds numbers of 200,000 to 50,000, rotor/stator spacing-to-disk ratios of 0.025 to 0.15, and jet mass flow rates between 0.10 and 0.40 times the turbulent pumped flow rate of a free disk. It is shown that rotor heat transfer exhibits regions of impingement and rotational domination with a transition region between, while stator heat transfer displays flow reattachment and convection regions with an inner recirculation zone.

Structural and magnetic transitions in spinel FeM n 2 O 4 single crystals

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

Nepal, Roshan; Zhang, Qiang; Dai, Samuel

Materials that form the spinel structure are known to exhibit geometric frustration, which can lead to magnetic frustration as well. Through magnetization and neutron diffraction measurements, we find that FeMn 2O 4 undergoes one structural and two magnetic transitions. The structural transition occurs at T s ~595K from cubic at high temperatures to tetragonal at low temperatures. Here, two magnetic transitions are ferrimagnetic at T FI–1 ~373K and T FI–2 ~50K, respectively. Further investigation of the specific heat, thermal conductivity, and Seebeck coefficient confirms both magnetic transitions. Of particular interest is that there is a significant magnetic contribution to themore » low-temperature specific heat and thermal conductivity, providing a unique system to study heat transport by magnetic excitations.« less

Structural and magnetic transitions in spinel FeM n 2 O 4 single crystals

DOE PAGES

Nepal, Roshan; Zhang, Qiang; Dai, Samuel; ...

2018-01-11

Materials that form the spinel structure are known to exhibit geometric frustration, which can lead to magnetic frustration as well. Through magnetization and neutron diffraction measurements, we find that FeMn 2O 4 undergoes one structural and two magnetic transitions. The structural transition occurs at T s ~595K from cubic at high temperatures to tetragonal at low temperatures. Here, two magnetic transitions are ferrimagnetic at T FI–1 ~373K and T FI–2 ~50K, respectively. Further investigation of the specific heat, thermal conductivity, and Seebeck coefficient confirms both magnetic transitions. Of particular interest is that there is a significant magnetic contribution to themore » low-temperature specific heat and thermal conductivity, providing a unique system to study heat transport by magnetic excitations.« less

A model to study finite-size and magnetic effects on the phase transition of a fermion interacting system

NASA Astrophysics Data System (ADS)

Corrêa, Emerson B. S.; Linhares, César A.; Malbouisson, Adolfo P. C.

2018-03-01

We present a model to study the effects from external magnetic field, chemical potential and finite size on the phase structures of a massive four- and six-fermion interacting systems. These effects are introduced by a method of compactification of coordinates, a generalization of the standard Matsubara prescription. Through the compactification of the z-coordinate and of imaginary time, we describe a heated system with the shape of a film of thickness L, at temperature β-1 undergoing first- or second-order phase transition. We have found a strong dependence of the temperature transition on the coupling constants λ and η. Besides inverse magnetic catalysis and symmetry breaking for both kinds of transition, we have found an inverse symmetry breaking phenomenon with respect to first-order phase transition.

An Analytic Formulation of the 21 cm Signal from the Early Phase of the Epoch of Reionization

NASA Astrophysics Data System (ADS)

Raste, Janakee; Sethi, Shiv

2018-06-01

We present an analytic formulation to model the fluctuating component of the H I signal from the epoch of reionization during the phase of partial heating. During this phase, we assume self-ionized regions, whose size distribution can be computed using excursion set formalism, to be surrounded by heated regions. We model the evolution of the heating profile around these regions (near zone) and their merger into the time-dependent background (far zone). We develop a formalism to compute the two-point correlation function for this topology, taking into account the heating autocorrelation and heating-ionization cross-correlation. We model the ionization and X-ray heating using four parameters: efficiency of ionization, ζ number of X-ray photons per stellar baryon, N heat; spectral index of X-ray photons, α and minimum frequency of X-ray photons, ν min. We compute the H I signal in the redshift range 10 < z < 20 for the ΛCDM model for a set of these parameters. We show that the H I signal for a range of scales 1–8 Mpc shows a peak strength of 100–1000 (mK)2 during the partially heated era. The redshift at which the signal makes a transition to a uniformly heated universe depends on the modeling parameters; e.g., if ν min is changed from 100 eV to 1 keV, this transition moves from z ≃ 15 to z ≃ 12. This result, along with the dependence of the H I signal on the modeling parameters, is in reasonable agreement with existing results from N-body simulations.

Tuning near field radiative heat flux through surface excitations with a metal insulator transition.

PubMed

van Zwol, P J; Ranno, L; Chevrier, J

2012-06-08

The control of heat flow is a formidable challenge due to lack of good thermal insulators. Promising new opportunities for heat flow control were recently theoretically discovered for radiative heat flow in near field, where large heat flow contrasts may be achieved by tuning electronic excitations on surfaces. Here we show experimentally that the phase transition of VO2 entails a change of surface polariton states that significantly affects radiative heat transfer in near field. In all cases the Derjaguin approximation correctly predicted radiative heat transfer in near field, but it underestimated the far field limit. Our results indicate that heat flow contrasts can be realized in near field that can be larger than those obtained in far field.

Composite prepreg application device

NASA Technical Reports Server (NTRS)

Sandusky, Donald A. (Inventor); Marchello, Joseph M. (Inventor)

1996-01-01

A heated shoe and cooled pressure roller assembly for composite prepreg application is provided. The shoe assembly includes a heated forward contact surface having a curved pressure surface. The following cooled roller provides a continuous pressure to the thermoplastic while reducing the temperature to approximately 5.degree. C. below glass transition temperature. Electric heating coils inside the forward portion of the shoe heat a thermoplastic workpiece to approximately 100.degree. C. above the glass transition. Immediately following the heated contact surface, a cooled roller cools the work. The end sharpened shape of the heated shoe trailing edge tends to prevent slag buildup and maintain a uniform, relaxed stress fabrication.

A study of start-up characteristics of a potassium heat pipe from the frozen state

NASA Technical Reports Server (NTRS)

Jang, Jong Hoon

1992-01-01

The start up characteristics of a potassium heat pipe were studied both analytically and experimentally. Using the radiation heat transfer mode the heat pipe was tested in a vacuum chamber. The transition temperature calculated for potassium was then compared with the experimental results of the heat pipe with various heat inputs. These results show that the heat pipe was inactive until it reached the transition temperature. In addition, during the start up period, the evaporator experienced dry-out with a heat input smaller than the capillary limit calculated at the steady state. However, when the working fluid at the condensor was completely melted, the evaporation was rewetted without external aid. The start up period was significantly reduced with a large heat input.

A research program for improving heat transfer prediction for the laminar to turbulent transition region of turbine vanes/blades

NASA Technical Reports Server (NTRS)

Simon, Frederick F.

1993-01-01

A program sponsored by NASA for the investigation of the heat transfer in the transition region of turbine vanes and blades with the objective of improving the capability for predicting heat transfer is described. The accurate prediction of gas-side heat transfer is important to the determination of turbine longevity, engine performance, and developmental costs. The need for accurate predictions will become greater as the operating temperatures and stage loading levels of advanced turbine engines increase. The present methods for predicting transition shear stress and heat transfer on turbine blades are based on incomplete knowledge and are largely empirical. To meet the objective of the NASA program, a team approach consisting of researchers from government, universities, a research institute, and a small business is presented. The research is divided into the areas of experiments, direct numerical simulations (DNS), and turbulence modeling. A summary of the results to date is given for the above research areas in a high-disturbance environment (bypass transition) with a discussion of the model development necessary for use in numerical codes.

Signatures of Steady Heating in Time Lag Analysis of Coronal Emission

NASA Technical Reports Server (NTRS)

Viall, Nicholeen M.; Klimchuk, James A.

2016-01-01

Among the multitude of methods used to investigate coronal heating, the time lag method of Viall Klimchuk is becoming increasingly prevalent as an analysis technique that is complementary to those that are traditionally used.The time lag method cross correlates light curves at a given spatial location obtained in spectral bands that sample different temperature plasmas. It has been used most extensively with data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. We have previously applied the time lag method to entire active regions and surrounding the quiet Sun and created maps of the results. We find that the majority of time lags are consistent with the cooling of coronal plasma that has been impulsively heated. Additionally, a significant fraction of the map area has a time lag of zero. This does not indicate a lack of variability. Rather, strong variability must be present, and it must occur in phase between the different channels. We have previously shown that these zero time lags are consistent with the transition region response to coronal nanoflares, although other explanations are possible. A common misconception is that the zero time lag indicates steady emission resulting from steady heating. Using simulated and observed light curves, we demonstrate here that highly correlated light curves at zero time lag are not compatible with equilibrium solutions. Such light curves can only be created by evolution

On the reversibility of the Meissner effect and the angular momentum puzzle

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

Hirsch, J.E., E-mail: jhirsch@ucsd.edu

It is generally believed that the laws of thermodynamics govern superconductivity as an equilibrium state of matter, and hence that the normal-superconductor transition in a magnetic field is reversible under ideal conditions. Because eddy currents are generated during the transition as the magnetic flux changes, the transition has to proceed infinitely slowly to generate no entropy. Experiments showed that to a high degree of accuracy no entropy was generated in these transitions. However, in this paper we point out that for the length of times over which these experiments extended, a much higher degree of irreversibility due to decay ofmore » eddy currents should have been detected than was actually observed. We also point out that within the conventional theory of superconductivity no explanation exists for why no Joule heat is generated in the superconductor to normal transition when the supercurrent stops. In addition we point out that within the conventional theory of superconductivity no mechanism exists for the transfer of momentum between the supercurrent and the body as a whole, which is necessary to ensure that the transition in the presence of a magnetic field respects momentum conservation. We propose a solution to all these questions based on the alternative theory of hole superconductivity. The theory proposes that in the normal-superconductor transition there is a flow and backflow of charge in direction perpendicular to the phase boundary when the phase boundary moves. We show that this flow and backflow explains the absence of Joule heat generated by Faraday eddy currents, the absence of Joule heat generated in the process of the supercurrent stopping, and the reversible transfer of momentum between the supercurrent and the body, provided the current carriers in the normal state are holes. - Highlights: • The normal-superconductor phase transition is reversible. • Within the conventional theory, Foucault currents give rise to irreversibility. • To suppress Foucault currents, charge has to flow in direction perpendicular to the phase boundary. • The charge carriers have to be holes. • This solves also the angular momentum puzzle associated with the Meissner effect.« less

Transition duration of ingested deuterium oxide to eccrine sweat during exercise in the heat.

PubMed

Church, Adam; Lee, Fanny; Buono, Michael J

2017-01-01

The time necessary for the initial appearance of ingested water as sweat during exercise in the heat remains unknown. Based on the current literature, we estimated fluid transition through the body, from ingestion to appearance as sweat, to have a minimum time duration of approximately three minutes. The purpose of this study was to test this prediction and identify the time necessary for the initial enrichment of deuterium oxide (D 2 O) in sweat following ingestion during exercise in the heat. Eight participants performed moderate intensity (40% of maximal oxygen uptake) treadmill exercise in an environmental chamber (40°C, 40% rH) to induce active sweating. After fifteen minutes, while continuing to walk, participants consumed D 2 O (0.15mlkg -1 ) in a final volume of 50ml water. Scapular sweat samples were collected one minute prior to and ten minutes post-ingestion. Samples were analyzed for sweat D 2 O concentration using isotope ratio mass spectrometry and compared to baseline. Mean±SD ∆ sweat D 2 O concentration at minutes one and two post-ingestion were not significantly higher than baseline (0min). Minutes three (9±3ppm) through ten (23±11ppm) post-ingestion had ∆ sweat D 2 O concentrations significantly (P<0.05) higher than baseline. Such results suggest that ingested water rapidly transports across the mucosal membrane of the alimentary canal into the vasculature space, enters the extravascular fluid, and is actively secreted by the eccrine sweat glands onto the surface of the skin for potential evaporation in as little as three minutes during exercise in the heat. Copyright © 2016 Elsevier Ltd. All rights reserved.

Coastal Wind and Turbulence Observations during the Morning and Evening Transitions over Tropical Terrain

DOE PAGES

Jensen, Derek D.; Price, Timothy A.; Nadeau, Daniel F.; ...

2017-12-15

Data collected during a multiyear, wind-resource assessment over a multi-land-use coastal environment in Belize are used to study the development and decay of wind and turbulence through the morning and evening transitions. Observations were made on three tall masts, forming an inland transect of approximately 5 km. The wind distribution is found to be bimodal and governed by synoptic scales, with onshore and offshore flow regimes. The behavior between the coastal and inland sites is found to be very similar when the flow is directed offshore; for onshore flow, stark differences occur. The mean wind speed at the coastal sitemore » is approximately 20% greater than the most inland site and is nearly constant throughout the diurnal cycle. Furthermore, for both flow regimes, the influence of the land–sea breeze circulation is inconsequential relative to the large-scale synoptic forcing. Composite time series are used to study the evolution of sensible heat flux and turbulence kinetic energy (TKE) throughout the morning and evening transitions. The TKE budget reveals that at the coastal site mechanical production of TKE is much more important than buoyant production. This allows for the unexpected case in which TKE increases through the ET despite the decrease of buoyant TKE production. Multiresolution flux decomposition is used to further study this phenomenon as well as the evolution of the sensible heat flux at differing time scales. We present an idealized schematic to illustrate the timing and structure of the morning and evening transitions for an inland site and a coastal site that are subjected to similar synoptic forcing.« less

Coastal Wind and Turbulence Observations during the Morning and Evening Transitions over Tropical Terrain

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

Jensen, Derek D.; Price, Timothy A.; Nadeau, Daniel F.

Data collected during a multiyear, wind-resource assessment over a multi-land-use coastal environment in Belize are used to study the development and decay of wind and turbulence through the morning and evening transitions. Observations were made on three tall masts, forming an inland transect of approximately 5 km. The wind distribution is found to be bimodal and governed by synoptic scales, with onshore and offshore flow regimes. The behavior between the coastal and inland sites is found to be very similar when the flow is directed offshore; for onshore flow, stark differences occur. The mean wind speed at the coastal sitemore » is approximately 20% greater than the most inland site and is nearly constant throughout the diurnal cycle. Furthermore, for both flow regimes, the influence of the land–sea breeze circulation is inconsequential relative to the large-scale synoptic forcing. Composite time series are used to study the evolution of sensible heat flux and turbulence kinetic energy (TKE) throughout the morning and evening transitions. The TKE budget reveals that at the coastal site mechanical production of TKE is much more important than buoyant production. This allows for the unexpected case in which TKE increases through the ET despite the decrease of buoyant TKE production. Multiresolution flux decomposition is used to further study this phenomenon as well as the evolution of the sensible heat flux at differing time scales. We present an idealized schematic to illustrate the timing and structure of the morning and evening transitions for an inland site and a coastal site that are subjected to similar synoptic forcing.« less

Kepler K2 observations of the transitional millisecond pulsar PSR J1023+0038

NASA Astrophysics Data System (ADS)

Kennedy, M. R.; Clark, C. J.; Voisin, G.; Breton, R. P.

2018-06-01

For 80 d in 2017, the Kepler Space Telescope continuously observed the transitional millisecond pulsar system PSR J1023+0038 in its accreting state. We present analyses of the 59-s cadence data, focusing on investigations of the orbital light curve of the irradiated companion star and of flaring activity in the neutron star's accretion disc. The underlying orbital modulation from the companion star retains a similar amplitude and asymmetric heating profile as seen in previous photometric observations of the system in its radio pulsar state, suggesting that the heating mechanism has not been affected by the state change. We also find tentative evidence that this asymmetry may vary with time. The light curve also exhibits `flickering' activity, evident as short time-scale flux correlations throughout the observations, and periods of rapid mode-switching activity on time-scales shorter than the observation cadence. Finally, the system spent ˜ 20 per cent of the observations in a flaring state, with the length of these flares varying from <2 min up to several hours. The flaring behaviour is consistent with a self-organized criticality mechanism, most likely related to the build-up and release of mass at the inner edge of the accretion disc.

Cooling of High-Power LED Lamp Using a Commercial Paraffin Wax

NASA Astrophysics Data System (ADS)

Zmywaczyk, J.; Zbińkowski, P.; Smogór, H.; Olejnik, A.; Koniorczyk, P.

2017-03-01

Commercial paraffin wax used by Bolsius Nederland B.V. for manufacturing various kinds of candles was applied as a phase-change material (PCM) for cooling a 28 W high-power light emitting diode (LED) panel during its operation. The main problem arising during operation of an LED is thermal management. According to the manufacturer's datasheet specifications (BioSolution Ltd. www.biosolution.pl, the operating temperature range for the LED street lamp UL28W is (-30 {°}C) to (+40 {°}C). The object of the present study was an LED panel containing 28 pieces of high-power 1W LEDs connected in series (4 LEDs in each of the 7 rows) mounted on an aluminum plate of dimensions 80 mm by 135 mm. The tested aluminum plate was placed in a block made of aluminum with a hollow compartment containing Bolsius paraffin wax of density 914 kg\\cdot m^{-3} at room temperature. Temperatures were recorded using K-type thermocouples at selected locations of the tested LED panel for several values of the power supplied to it, while utilizing PCM and without it. As the manufacturer of Bolsius wax candles does not provide any data on the thermal properties of the material used, it was necessary to carry out micro-calorimetric research. Thermophysical properties of the paraffin wax such as the apparent specific heat, enthalpy of phase transition and temperature of phase change transition during heating and cooling were determined using the Netzsch DSC 214 Polyma. The Netzsch TG 209F3 Tarsus was used for TG/DTG measurements. DSC investigations revealed the following thermal transitions taking place during the first heating: solid-solid transition (onset 30.4 {°}C, peak at 40.9 {°}C), solid-liquid transition (onset 47.7 {°}C, peak at 54.9 {°}C, end at 58.3 {°}C), latent heat of energy storage 201 J\\cdot g^{-1}, apparent specific heat corresponding to peak at 41.5 {°}C (5.498 J\\cdot g^{-1}\\cdot K^{-1}). DTG investigations revealed that the decomposition of paraffin wax is a two-step process. At 283 {°}C there was observed a slightly slower decomposition (9.43 %\\cdot min^{-1}) than that at 323 {°}C (12.5 %\\cdot min^{-1}). The experimental results obtained upon cooling the high-power LED lamp during its operation can be applied to verify results of numerical modeling of the heat transfer problems with phase-change transitions. An attempt at modeling such a problem based on 1D fixed grid with variable time step approach was undertaken in this work.

Roles of strain and domain boundaries on the phase transition stability of VO2 thin films

NASA Astrophysics Data System (ADS)

Jian, Jie; Chen, Aiping; Chen, Youxing; Zhang, Xinghang; Wang, Haiyan

2017-10-01

The fundamental phase transition mechanism and the stability of the semiconductor-to-metal phase transition properties during multiple thermal cycles have been investigated on epitaxial vanadium dioxide (VO2) thin films via both ex situ heating and in situ heating by transmission electron microscopy (TEM). VO2 thin films were deposited on c-cut sapphire substrates by pulsed laser deposition. Ex situ studies show the broadening of transition sharpness (ΔT) and the width of thermal hysteresis (ΔH) after 60 cycles. In situ TEM heating studies reveal that during thermal cycles, large strain was accumulated around the domain boundaries, which was correlated with the phase transition induced lattice constant change and the thermal expansion. It suggests that the degradation of domain boundary structures in the VO2 films not only caused the transition property reduction (e.g., the decrease in ΔT and ΔH) but also played an important role in preventing the film from fracture during thermal cycles.

Aerothermodynamic Design of the Mars Science Laboratory Heatshield

NASA Technical Reports Server (NTRS)

Edquist, Karl T.; Dyakonov, Artem A.; Wright, Michael J.; Tang, Chun Y.

2009-01-01

Aerothermodynamic design environments are presented for the Mars Science Laboratory entry capsule heatshield. The design conditions are based on Navier-Stokes flowfield simulations on shallow (maximum total heat load) and steep (maximum heat flux, shear stress, and pressure) entry trajectories from a 2009 launch. Boundary layer transition is expected prior to peak heat flux, a first for Mars entry, and the heatshield environments were defined for a fully-turbulent heat pulse. The effects of distributed surface roughness on turbulent heat flux and shear stress peaks are included using empirical correlations. Additional biases and uncertainties are based on computational model comparisons with experimental data and sensitivity studies. The peak design conditions are 197 W/sq cm for heat flux, 471 Pa for shear stress, 0.371 Earth atm for pressure, and 5477 J/sq cm for total heat load. Time-varying conditions at fixed heatshield locations were generated for thermal protection system analysis and flight instrumentation development. Finally, the aerothermodynamic effects of delaying launch until 2011 are previewed.

Transition to hard turbulence in thermal convection at infinite Prandtl number

NASA Technical Reports Server (NTRS)

Hansen, Ulrich; Yuen, David A.; Kroening, Sherri E.

1990-01-01

Direct numerical simulations of two-dimensional high Rayleigh (Ra) number, base-heated thermal convection in large aspect-ratio boxes are presented for infinite Prandtl number fluids, as applied to the earth's mantle. A transition is characaterized in the flow structures in the neighborhood of Ra between 10 to the 7th and 10 to the 8th. These high Ra flows consist of large-scale cells with strong intermittent, boundary-layer instabilities. For Ra exceeding 10 to the 7th it is found that the heat-transfer mechanism changes from one characterized by mushroom-like plumes to one consisting of disconnected ascending instabilities, which do not carry with them all the thermal anomaly from the bottom boundary layer. Plume-plume collisions become much more prominent in high Ra situations and have a tendency of generating a pulse-like behavior in the fixed plume. This type of instability represents a distinct mode of heat transfer in the hard turbulent regime. Predictions of this model can be used to address certain issues concerning the mode of time-dependent convection in the earth's mantle.

Thermophysical parameters of coconut oil and its potential application as the thermal energy storage system in Indonesia

NASA Astrophysics Data System (ADS)

Putri, Widya A.; Fahmi, Zulfikar; Sutjahja, I. M.; Kurnia, D.; Wonorahardjo, S.

2016-08-01

The high consumption of electric energy for room air conditioning (AC) system in Indonesia has driven the research of potential thermal energy storage system as a passive temperature controller. The application of coconut oil (CO) as the potential candidate for this purpose has been motivated since its working temperature just around the human thermal comfort zone in the tropical area as Indonesia. In this research we report the time-dependent temperature data of CO, which is adopting the T-history method. The analysis of the data revealed a set of thermophysical parameters, consist of the mean specific heats of the solid and liquid, as well as the latent heat of fusion for the phase change transition. The performance of CO to decrease the air temperature was measured in the thermal chamber. From the results it is shown that the latent phase of CO related to the solid-liquid phase transition show the highest capability in heat absorption, directly showing the potential application of CO as thermal energy storage system in Indonesia.

Fine flow structures in the transition region small-scale loops

NASA Astrophysics Data System (ADS)

Yan, L.; Peter, H.; He, J.; Wei, Y.

2016-12-01

The observation and model have suggested that the transition region EUV emission from the quiet sun region is contributed by very small scale loops which have not been resolved. Recently, the observation from IRIS has revealed that this kind of small scale loops. Based on the high resolution spectral and imaging observation from IRIS, much more detail work needs to be done to reveal the fine flow features in this kind of loop to help us understand the loop heating. Here, we present a detail statistical study of the spatial and temporal evolution of Si IV line profiles of small scale loops and report the spectral features: there is a transition from blue (red) wing enhancement dominant to red (blue) wing enhancement dominant along the cross-section of the loop, which is independent of time. This feature appears as the loop appear and disappear as the loop un-visible. This is probably the signature of helical flow along the loop. The result suggests that the brightening of this kind of loop is probably due to the current dissipation heating in the twisted magnetic field flux tube.

Analysis of oligomeric transition of silkworm small heat shock protein sHSP20.8 using high hydrostatic pressure native PAGE

NASA Astrophysics Data System (ADS)

Fujisawa, Tetsuro; Ueda, Toshifumi; Kameyama, Keiichi; Aso, Yoichi; Ishiguro, Ryo

2013-06-01

The small heat shock proteins (sHSPs) solubilize thermo-denatured proteins without adenosine triphosphate energy consumption to facilitate protein refolding. sHSP20.8 is one of the silkworm (Bombyx mori) sHSPs having only one cystein in the N-terminal domain: Cys43. We report a simple measurement of oligomeric transition of sHSP20.8 using high hydrostatic pressure native polyacrylamide gel electrophoresis (high hydrostatic pressure (HP) native polyacrylamide gel electrophoresis (PAGE)). At ambient pressure under oxydative condition, the native PAGE of thermal transition of sHSP20.8 oligomer displayed a cooperative association. In contrast, HP native PAGE clearly demonstrated that sHSP20.8 dissociated at 80 MPa and 25°C, and the resultant molecular species gradually reassociated with time under that condition. In addition, the reassociation process was suppressed in the presence of the reductant. These results are consistent with the idea that sHSP20.8 oligomer temporally dissociates at the first thermo-sensing step and reassociates with the oxidation of Cys43.

Dynamic melting of metals in the diamond cell: Clues for melt viscosity?

NASA Astrophysics Data System (ADS)

Boehler, R.; Karandikar, A.; Yang, L.

2011-12-01

From the observed decreasing mobility of liquid iron at high pressure in the laser-heated diamond cell and the gradual decrease in the shear modulus in shock experiments, one may derive high viscosity in the liquid outer core of the Earth. A possible explanation could be the presence of local structures in the liquid as has been observed for several transition metals. In order to bridge the large gap in the timescales between static and dynamic melting experiments, we have developed new experimental techniques to solve the large discrepancies in the melting curves of transition metals (Fe, W, Ta, Mo) measured statically in the laser-heated diamond cell and in shock experiments. The new methods employ "single-shot" laser heating in order to reduce problems associated with mechanical instabilities and chemical reactions of the samples subjected to several thousand degrees at megabar pressures. For melt detection, both synchrotron X-ray diffraction and Scanning Electron Microscopy (SEM) on recovered samples are used. A third approach is the measurement of latent heat effects associated with melting or freezing. This method employs simultaneous CW and pulse laser heating and monitoring the temperature-time history with fast photomultipliers. Using the SEM recovery method, we measured first melting temperatures of rhenium, which at high pressure may be one of the most refractory materials. From the melt textures of Re, we did not observe a significant pressure dependence of viscosity.

Heat capacity of free electrons at the degenerate-nondegenerate transition

NASA Astrophysics Data System (ADS)

Nimtz, G.; Stadler, J. P.

1985-04-01

In this Brief Report the heat capacity of an electron gas at the degenerate-nondegenerate transition is presented. The values are deduced from hot-carrier data of InSb with ~=1014 electrons/cm3 determined by Maneval, Zylberstejn, and Budd.

Thermomechanical modeling of the Colorado Plateau-Basin and range transition zone

NASA Technical Reports Server (NTRS)

Londe, M. D.

1985-01-01

The Colorado Plateau (CP) basin and range (B & R) boundary is marked by a transition zone on the order of 75 to 150 km in width. As one moves westward across this transition from the CP interior to the B & R there is a variation in the surface topography, surface heat flow, Bouguer gravity, seismicity, and crustal structure. This transition extends eastward into the western CP from the Wastach-Hurricane fault line and is largely coincident with the high plateaus of Utah and the Wasatch Mountains. It has been suggested that this transition zone marks a thermal and tectonic encroachment of the CP by the B & R. A simple two dimensional numerical model of the thermal regime for the transition zone was constructed to test the hypothesis that the observed geophysical signatures across the transition are due to lateral heat conduction from steady state uniform extension within the B & R lithosphere. Surface heat flow, uplift due to flexure from thermal buoyant loading, and regional Bouguer gravity are computed for various extension rates, crustal structures, and compensation depths.

The Thermal and Microstructural Effect of Plasticizing HMX-Nitrocellulose Composites

DOE PAGES

Yeager, John David; Watkins, Erik Benjamin; Duque, Amanda Lynn; ...

2017-03-15

Thermal ignition via self-heating (cook-off) of cyclotetramethylene-tetranitramine (HMX)-containing plastic-bonded explosives (PBXs) is driven by the β → δ phase transition in the HMX, which is affected if not dominated by microstructure. Here, we studied the HMX-binder interface and phase transition for several variations of PBX 9404 (HMX with plasticized nitrocellulose [NC] binder). Neutron reflectometry was used to examine the interface under several conditions—pristine, after aging, and after thermal treatment. The initial interfacial structure depended on the plasticizer, but the interface homogenized over time. Thermal and optical analyses showed that all formulated materials had higher transition temperatures than neat HMX. Thismore » effect increased with NC content.« less

The Thermal and Microstructural Effect of Plasticizing HMX-Nitrocellulose Composites

NASA Astrophysics Data System (ADS)

Yeager, John D.; Watkins, Erik B.; Higginbotham Duque, Amanda L.; Majewski, Jaroslaw

2018-01-01

Thermal ignition via self-heating (cook-off) of cyclotetramethylene-tetranitramine (HMX)-containing plastic-bonded explosives (PBXs) is driven by the β → δ phase transition in the HMX, which is affected if not dominated by microstructure. Here, the HMX-binder interface and phase transition were studied for several variations of PBX 9404 (HMX with plasticized nitrocellulose [NC] binder). Neutron reflectometry was used to examine the interface under several conditions-pristine, after aging, and after thermal treatment. The initial interfacial structure depended on the plasticizer, but the interface homogenized over time. Thermal and optical analyses showed that all formulated materials had higher transition temperatures than neat HMX. This effect increased with NC content.

Acoustic Behavior of Vapor Bubbles

NASA Technical Reports Server (NTRS)

Prosperetti, Andrea; Oguz, Hasan N.

1996-01-01

In a microgravity environment vapor bubbles generated at a boiling surface tend to remain near it for a long time. This affects the boiling heat transfer and in particular promotes an early transition to the highly inefficient film boiling regime. This paper describes the physical basis underlying attempts to remove the bubbles by means of pressure radiation forces.

Magnetic properties of mechanically alloyed Mn-Al-C powders

NASA Astrophysics Data System (ADS)

Kohmoto, O.; Kageyama, N.; Kageyama, Y.; Haji, H.; Uchida, M.; Matsushima, Y.

2011-01-01

We have prepared supersaturated-solution Mn-Al-C alloy powders by mechanical alloying using a planetary high-energy mill. The starting materials were pure Mn, Al and C powers. The mechanically-alloyed powders were subjected to a two-step heating. Although starting particles are Al and Mn with additive C, the Al peak disappears with MA time. With increasing MA time, transition from α-Mn to β-Mn does not occur; the α-Mn structure maintains. At 100 h, a single phase of supersaturated-solution α-Mn is obtained. The lattice constant of α-Mn decreases with increasing MA time. From the Scherrer formula, the crystallite size at 500 h is obtained as 200Å, which does not mean amorphous state. By two-step heating, high magnetization (66 emu/g) was obtained from short-time-milled powders (t=10 h). The precursor of the as-milled powder is not a single phase α-Mn but contains small amount of fcc Al. After two-step heating, the powder changes to τ-phase. Although the saturation magnetization increases, the value is less than that by conventional bulk MnAl (88 emu/g). Meanwhile, long-time-milled powder of single α-Mn phase results in low magnetization (5.2 emu/g) after two-step heating.

Distributed Roughness Effects on Blunt-Body Transition and Turbulent Heating

NASA Technical Reports Server (NTRS)

Hollis, Brian R.

2014-01-01

An experimental program has been conducted to obtain data on the effects of surface roughness on blunt bodies at laminar, transitional, and turbulent conditions. Wind tunnel models with distributed surface roughness heights from 0.06 mm to 1.75 mm were tested and heating data were obtained using global surface thermography. Heating rates of up to 85% higher than predicted, smooth-surface turbulent levels were measured.

Heat transfer and fluid mechanics measurements in transitional boundary layer flows

NASA Technical Reports Server (NTRS)

Wang, T.; Simon, T. W.; Buddhavarapu, J.

1985-01-01

Experimental results are presented to document hydrodynamic and thermal development of flat-plate boundary layers undergoing natural transition. Local heat transfer coefficients, skin friction coefficients and profiles of velocity, temperature and Reynolds normal and shear stresses are presented. A case with no transition and transitional cases with 0.68% and 2.0% free-stream disturbance intensities were investigated. The locations of transition are consistent with earlier data. A late-laminar state with significant levels of turbulence is documented. In late-transitional and early-turbulent flows, turbulent Prandtl number and conduction layer thickness values exceed, and the Reynolds analogy factor is less than, values previously measured in fully turbulent flows.

Proliferation of metallic domains caused by inhomogeneous heating near the electrically driven transition in VO2 nanobeams

NASA Astrophysics Data System (ADS)

Singh, Sujay; Horrocks, Gregory; Marley, Peter M.; Shi, Zhenzhong; Banerjee, Sarbajit; Sambandamurthy, G.

2015-10-01

We discuss the mechanisms behind the electrically driven insulator-metal transition in single-crystalline VO2 nanobeams. Our dc and ac transport measurements and the versatile harmonic analysis method employed show that nonuniform Joule heating causes electronic inhomogeneities to develop within the nanobeam and is responsible for driving the transition in VO2. A Poole-Frenkel-like purely electric-field-induced transition is found to be absent, and the role of percolation near and away from the electrically driven transition in VO2 is also identified. The results and the harmonic analysis can be generalized to many strongly correlated materials that exhibit electrically driven transitions.

Regimes of heating and dynamical response in driven many-body localized systems

NASA Astrophysics Data System (ADS)

Gopalakrishnan, Sarang; Knap, Michael; Demler, Eugene

2016-09-01

We explore the response of many-body localized (MBL) systems to periodic driving of arbitrary amplitude, focusing on the rate at which they exchange energy with the drive. To this end, we introduce an infinite-temperature generalization of the effective "heating rate" in terms of the spread of a random walk in energy space. We compute this heating rate numerically and estimate it analytically in various regimes. When the drive amplitude is much smaller than the frequency, this effective heating rate is given by linear response theory with a coefficient that is proportional to the optical conductivity; in the opposite limit, the response is nonlinear and the heating rate is a nontrivial power law of time. We discuss the mechanisms underlying this crossover in the MBL phase. We comment on implications for the subdiffusive thermal phase near the MBL transition, and for response in imperfectly isolated MBL systems.

Determination of thermodynamic properties of poly (cyclohexyl methacrylate) by inverse gas chromatography.

PubMed

Kaya, Ismet; Pala, Cigdem Yigit

2014-07-01

In this work, some thermodynamic properties of poly (cyclohexyl methacrylate) were studied by inverse gas chromatography (IGC). For this purpose, the polymeric substance was coated on Chromosorb W and which was filled into a glass column. The retention times (t(r)) of the probes were determined from the interactions of poly (cyclohexyl methacrylate) with n-pentane, n-hexane, n-heptane, n-octane, n-decane, methanol, ethanol, 2-propanol, butanol, acetone, ethyl methyl ketone, benzene, toluene and o-xylene by IGC technique. Then, the specific volume (Vg(0)) was determined for each probe molecule. By using (1/T; lnVg(0)) graphics, the glass transition temperature of poly (cyclohexyl methacrylate) was found to be 373 K. The adsorption heat under the glass transition temperature (deltaH(a)), and partial molar heat of sorption above the glass transition (deltaH1(S)), partial molar free energy of sorption (deltaG1(S)) and partial molar entropy of sorption (deltaS1(S)) belonging to sorption for every probe were calculated. The partial molar heat of mixing at infinite dilution (deltaH1(infinity)), partial molar free energy of mixing at infinite dilution (deltaG1(infinity)), Flory-Huggins interaction parameter (chi12(infinity)) and weight fraction activity coefficient (a1/w1)(infinity) values of polymer-solute systems were calculated at different column temperatures. The solubility parameters (delta2) of the polymer were obtained by IGC technique.

Detection of Second Order Melting Transitions in the HTSC's by Specific Heat Measurements?

NASA Astrophysics Data System (ADS)

Pierson, Stephen W.; Valls, Oriol T.

1997-03-01

The finite magnetic field phase transition in the high-temperature superconductors from the solid vortex lattice to the liquid has been under intense study recently. Detection of this melting is difficult but has been seen in magnetization and resistivity measurements. It has also been reported recently in specific heat measurements. In particular, in one case, evidence for a second order melting phase transition has been presented based on specific heat measurements.(M. Roulin, A. Junod, and E. Walker. Science 273), 1210 (1996). However, we present evidence that the feature in the specific heat data can be explained using a theory derived using the lowest-Landau-level approximation(Z. Tes)anović and A. V. Andreev, Phys. Rev. B 49, 4064 (1994) that does not invoke flux lattice melting arguments.

Multiphase numerical analysis of heat pipe with different working fluids for solar applications

NASA Astrophysics Data System (ADS)

Aswath, S.; Netaji Naidu, V. H.; Padmanathan, P.; Raja Sekhar, Y.

2017-11-01

Energy crisis is a prognosis predicted in many cases with the indiscriminate encroachment of conventional energy sources for applications on a massive scale. This prediction, further emboldened by the marked surge in global average temperatures, attributed to climate change and global warming, the necessity to conserve the environment and explore alternate sources of energy is at an all-time high. Despite being among the lead candidates for such sources, solar energy is utilized far from its vast potential possibilities due to predominant economic constraints. Even while there is a growing need for solar panels at more affordable rates, the other options to harness better out of sun’s energy is to optimize and improvise existing technology. One such technology is the heat pipe used in Evacuated Tube Collectors (ETC). The applications of heat pipe have been gaining momentum in various fields since its inception and substantial volumes of research have explored optimizing and improving the technology which is proving effective in heat recovery and heat transfer better than conventional systems. This paper carries out a computational analysis on a comparative simulation between two working fluids within heat pipe of same geometry. It further endeavors to study the multiphase transitions within the heat pipe. The work is carried out using ANSYS Fluent with inputs taken from solar data for the location of Vellore, Tamil Nadu. A wickless, gravity-assisted heat pipe (GAHP) is taken for the simulation. Water and ammonia are used as the working fluids for comparative multiphase analysis to arrive at the difference in heat transfer at the condenser section. It is demonstrated that a heat pipe ETC with ammonia as working fluid showed higher heat exchange (temperature difference) as against that of water as working fluid. The multiphase model taken aided in study of phase transitions within both cases and supported the result of ammonia as fluid being a better candidate.

Simultaneous Determination of Glass Transition Temperatures of Several Polymers.

PubMed

He, Jiang; Liu, Wei; Huang, Yao-Xiong

2016-01-01

A simple and easy optical method is proposed for the determination of glass transition temperature (Tg) of polymers. Tg was determined using the technique of microsphere imaging to monitor the variation of the refractive index of polymer microsphere as a function of temperature. It was demonstrated that the method can eliminate most thermal lag and has sensitivity about six fold higher than the conventional method in Tg determination. So the determined Tg is more accurate and varies less with cooling/heating rate than that obtained by conventional methods. The most attractive character of the method is that it can simultaneously determine the Tg of several polymers in a single experiment, so it can greatly save experimental time and heating energy. The method is not only applicable for polymer microspheres, but also for the materials with arbitrary shapes. Therefore, it is expected to be broadly applied to different fundamental researches and practical applications of polymers.

First-principles simulation on thermoelectric propertiesof transition metal dichalcogenide monolayers

NASA Astrophysics Data System (ADS)

Nakamura, Koichi

2018-06-01

Thermoelectric properties of transition metal dichalcogenide (TMDC) monolayer models, such as Seebeck coefficient and lattice heat capacity, were simulated on the basis of first-principles calculations. The calculated Seebeck coefficients are appropriate for the thermoelectric element of all the TMDC monolayer models introduced in this study. In the MoX2/WX2 (X = S, Se, and Te) heterojunction structure, carrier electrons and holes are respectively distributed in the MoX2 and WX2 regions by adopting a common Fermi energy for both electronic structures. In particular, in the X = Te case, the practical carrier concentration with a large Seebeck coefficient can be evaluated without doping. The lattice heat capacities and their temperature dependence tendencies can be classified on the basis of the minimum frequencies of the optical modes. The quotient of the lattice thermal conductivity over the phonon relaxation time gives the temperature-independent specific values according to the kind of TMDC monolayer.

Magnetospheric space plasma investigations

NASA Technical Reports Server (NTRS)

Comfort, Richard H.; Horwitz, James L.

1994-01-01

A time dependent semi-kinetic model that includes self collisions and ion-neutral collisions and chemistry was developed. Light ion outflow in the polar cap transition region was modeled and compared with data results. A model study of wave heating of O+ ions in the topside transition region was carried out using a code which does local calculations that include ion-neutral and Coulomb self collisions as well as production and loss of O+. Another project is a statistical study of hydrogen spin curve characteristics in the polar cap. A statistical study of the latitudinal distribution of core plasmas along the L=4.6 field line using DE-1/RIMS data was completed. A short paper on dual spacecraft estimates of ion temperature profiles and heat flows in the plasmasphere ionosphere system was prepared. An automated processing code was used to process RIMS data from 1981 to 1984.

Photoluminescence response of colloidal quantum dots on VO2 film across metal to insulator transition

PubMed Central

2014-01-01

We have proposed a method to probe metal to insulator transition in VO2 measuring photoluminescence response of colloidal quantum dots deposited on the VO2 film. In addition to linear luminescence intensity decrease with temperature that is well known for quantum dots, temperature ranges with enhanced photoluminescence changes have been found during phase transition in the oxide. Corresponding temperature derived from luminescence dependence on temperature closely correlates with that from resistance measurement during heating. The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition. Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition. It is a strong argument in favor of the proposed explanation based on the reflectance data. PACS 71.30. + h; 73.21.La; 78.47.jd PMID:25404877

Dynamic transport study of the plasmas with transport improvement in LHD and JT-60U

NASA Astrophysics Data System (ADS)

Ida, K.; Sakamoto, Y.; Inagaki, S.; Takenaga, H.; Isayama, A.; Matsunaga, G.; Sakamoto, R.; Tanaka, K.; Ide, S.; Fujita, T.; Funaba, H.; Kubo, S.; Yoshinuma, M.; Shimozuma, T.; Takeiri, Y.; Ikeda, K.; Michael, C.; Tokuzawa, T.; LHD experimental Group; JT-60 Team

2009-01-01

Transport analysis during the transient phase of heating (a dynamic transport study) applied to the plasma with internal transport barriers (ITBs) in the Large Helical Device (LHD) heliotron and the JT-60U tokamak is described. In the dynamic transport study the time of transition from the L-mode plasma to the ITB plasma is clearly determined by the onset of flattening of the temperature profile in the core region and a spontaneous phase transition from a zero curvature ITB (hyperbolic tangent shaped ITB) or a positive curvature ITB (concaved shaped ITB) to a negative curvature ITB (convex shaped ITB) and its back-transition are observed. The flattening of the core region of the ITB transition and the back-transition between a zero curvature ITB and a convex ITB suggest the strong interaction of turbulent transport in space.

Heat capacity and transport measurements in sputtered niobium-zirconium multilayers

NASA Astrophysics Data System (ADS)

Broussard, P. R.; Mael, D.

1989-08-01

We have studied the electrical resistivity and heat capacity for multilayers of niobium and zirconium prepared by magnetron sputtering for values of the bilayer period Λ varying from 4 to 950 Å. We find a transition in the thermal part of the resistivity that correlates with the coherent-to-incoherent transition seen in earlier work. The heat capacity data for the normal state show anomalous behavior for both the electronic coefficient γ and the Debye temperature. We also study the variation in Tc and the jump in the specific heat.

Fluid Mechanics and Heat Transfer in Transitional Boundary Layers

NASA Technical Reports Server (NTRS)

Wang, Ting

2007-01-01

Experiments have been performed to investigate the effects of elevated free-stream turbulence and streamwise acceleration on flow and thermal structures in transitional boundary layers. The free-stream turbulence ranges from 0.5 to 6.4% and the streamwise acceleration ranges from K = 0 to 0.8 x 10(exp -6). The onset of transition, transition length and the turbulent spot formation rate are determined. The statistical results and conditionally sampled results of th streamwise and cross-stream velocity fluctuations, temperature fluctuations, Reynolds stress and Reynolds heat fluxes are presented.

Analysis of Free-Flight Laminar, Transitional, and Turbulent Heat-Transfer Results at Free-Stream Mach Numbers Near 20 (Reentry F)

NASA Technical Reports Server (NTRS)

Zoby, Ernest V.; Rumsey, Charles B.

1971-01-01

Laminar, transitional, and turbulent heat-transfer data were measured during a reentry flight at a Mach number of 20 on a 5 deg half-angle cone 3.962 m (13 ft) long with an initial nose tip radius of 0.254 cm (0.1 in.). The free-stream Reynolds number increased during the prime data period from 7.0 x 10(exp 6) to 51.5 x 10(exp 6) per meter (2.1 x 10(exp 6) to 15.7 x 10(exp 6) per foot) and the ratio of wall to total temperature varied from 0.053 to 0.12. The angle of attack was less than 1deg for the prime data period. The experimental laminar and turbulent heating rates are compared with results from existing flat-plate prediction methods. At conditions of minimal tip blunting and angle of attack (above 26.8 km (88 000 ft)), values from a flat-plate laminar method agreed within 20 percent with the laminar data. The Schultz-Grunow skin-friction equation with reference enthalpy; conditions, with the Reynolds number based on distance from the transition location, and with the Colburn Reynolds analogy agreed within 10 percent with the experimental turbuleiit heating data. The Van Driest n skin-friction equation with Reynolds number greater than 10(exp 7) based on distance from the peak heating point and the Colburn Reynolds analogy was also within approximately 10 percent of the experimental turbulent heating data. A data correlation jbf the extent of transition and a simple empirical transition-zone heating correlation were also presented.

High-pressure and high-temperature study of the phase transition in anhydrite

NASA Astrophysics Data System (ADS)

Ma, Y. M.; Zhou, Q.; He, Z.; Li, F. F.; Yang, K. F.; Cui, Q. L.; Zou, G. T.

2007-10-01

The high-pressure and high-temperature behaviors of anhydrite (CaSO4) are studied up to 53.5 GPa and 1800 K using double-sided laser heating Raman spectroscopy and x-ray diffraction in diamond anvil cells. The evidence of phase transition from an anhydrite structure to the monazite type was observed at about 2 GPa under cold compression. Another phase transition and a change in color of the sample from transparent to black have been also observed at a pressure of 33.2 GPa after laser heating. The new phase after laser heating persists to 53.5 GPa and 1800 K.

Global two-fluid turbulence simulations of L-H transitions and edge localized mode dynamics in the COMPASS-D tokamak

NASA Astrophysics Data System (ADS)

Thyagaraja, A.; Valovič, M.; Knight, P. J.

2010-04-01

It is shown that the transition from L-mode to H-mode regimes in tokamaks can be reproduced using a two-fluid, fully electromagnetic, plasma model when a suitable particle sink is added at the edge. Such a model is implemented in the CUTIE code [A. Thyagaraja et al., Eur. J. Mech. B/Fluids 23, 475 (2004)] and is illustrated on plasma parameters that mimic those in the COMPASS-D tokamak with electron cyclotron resonance heating [Fielding et al., Plasma Phys. Contr. Fusion 42, A191 (2000)]. In particular, it is shown that holding the heating power, current, and magnetic field constant and increasing the fuelling rate to raise the plasma density leads spontaneously to the formation of an edge transport barrier (ETB) which occurs going from low to higher density experimentally. In the following quiescent period in which the stored energy of the plasma rises linearly with time, a dynamical transition occurs in the simulation with the appearance of features resembling strong edge localized modes. The simulation qualitatively reproduces many features observed in the experiment. Its relative robustness suggests that some, at least of the observed characteristics of ETBs and L-H transitions, can be captured in the global electromagnetic turbulence model.

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

Perez-Becker, Daniel; Showman, Adam P.

Infrared light curves of transiting hot Jupiters present a trend in which the atmospheres of the hottest planets are less efficient at redistributing the stellar energy absorbed on their daysides—and thus have a larger day-night temperature contrast—than colder planets. To this day, no predictive atmospheric model has been published that identifies which dynamical mechanisms determine the atmospheric heat redistribution efficiency on tidally locked exoplanets. Here we present a shallow-water model of the atmospheric dynamics on synchronously rotating planets that explains why heat redistribution efficiency drops as stellar insolation rises. Our model shows that planets with weak friction and weak irradiationmore » exhibit a banded zonal flow with minimal day-night temperature differences, while models with strong irradiation and/or strong friction exhibit a day-night flow pattern with order-unity fractional day-night temperature differences. To interpret the model, we develop a scaling theory which shows that the timescale for gravity waves to propagate horizontally over planetary scales, τ{sub wave}, plays a dominant role in controlling the transition from small to large temperature contrasts. This implies that heat redistribution is governed by a wave-like process, similar to the one responsible for the weak temperature gradients in the Earth's tropics. When atmospheric drag can be neglected, the transition from small to large day-night temperature contrasts occurs when τ{sub wave}∼√(τ{sub rad}/Ω), where τ{sub rad} is the radiative relaxation time and Ω is the planetary rotation frequency. Alternatively, this transition criterion can be expressed as τ{sub rad} ∼ τ{sub vert}, where τ{sub vert} is the timescale for a fluid parcel to move vertically over the difference in day-night thickness. These results subsume the more widely used timescale comparison for estimating heat redistribution efficiency between τ{sub rad} and the horizontal day-night advection timescale, τ{sub adv}. Only because τ{sub adv} ∼ τ{sub vert} for hot Jupiters does the commonly assumed timescale comparison between τ{sub rad} and τ{sub adv} yield approximately correct predictions for the heat redistribution efficiency.« less

Dynamics of streamer-to-leader transition at reduced air densities and its implications for propagation of lightning leaders and gigantic jets

NASA Astrophysics Data System (ADS)

da Silva, Caitano L.; Pasko, Victor P.

2013-12-01

In this paper we present modeling studies of air heating by electrical discharges in a wide range of pressures. The developed model is capable of quantifying the different contributions for heating of air at the particle level and rigorously accounts for the vibration-dissociation-vibration coupling. The model is validated by calculating the breakdown times of short air gaps and comparing to available experimental data. Detailed discussion on the role of electron detachment in the development of the thermal-ionizational instability that triggers the spark development in short air gaps is presented. The dynamics of fast heating by quenching of excited electronic states is discussed and the scaling of its main channels with ambient air density is quantified. The developed model is employed to study the streamer-to-leader transition process and to obtain its scaling with ambient air density. Streamer-to-leader transition is the name given to a sequence of events occurring in a thin plasma channel through which a relatively strong current is forced through, culminating in heating of ambient gas and increase of the electrical conductivity of the channel. This process occurs during the inception of leaders (from sharp metallic structures, from hydrometeors inside the thundercloud, or in virgin air) and during their propagation (at the leader head or during the growth of a space leader). The development of a thermal-ionizational instability that culminates in the leader formation and propagation is characterized by a change in air ionization mechanism from electron impact to associative ionization and by contraction of the plasma channel. The introduced methodology for estimation of leader speeds shows that the propagation of a leader is limited by the air heating of every newly formed leader section. It is demonstrated that the streamer-to-leader transition time has an inverse-squared dependence on the ambient air density at near-ground pressures, in agreement with similarity laws for Joule heating in a streamer channel. Model results indicate that a deviation from this similarity scaling occurs at very low air densities, where the rate of electronic power deposition is balanced by the channel expansion, and air heating from quenching of excited electronic states is very inefficient. These findings place a limit on the maximum altitude at which a hot and highly conducting lightning leader channel can be formed in the Earth's atmosphere, result which is important for understating of the gigantic jet (GJ) discharges between thundercloud tops and the lower ionosphere. Simulations of leader speeds at GJ altitudes demonstrate that initial speeds of GJs are consistent with the leader propagation mechanism. The simulation of a GJ, escaping upward from a thundercloud top, shows that the lengthening of the leader streamer zone, in a medium of exponentially decreasing air density, determines the existence of an altitude at which the streamer zones of GJs become so long that they dynamically extend (jump) all the way to the ionosphere.

An Exercise in X-Ray Diffraction Using the Polymorphic Transition of Nickel Chromite.

ERIC Educational Resources Information Center

Chipman, David W.

1980-01-01

Describes a laboratory experiment appropriate for a course in either x-ray crystallography or mineralogy. The experiment permits the direct observation of a polymorphic transition in nickel chromite without the use of a special heating stage or heating camera. (Author/GS)

A Research Program for Improving Heat Transfer Prediction Capability for the Laminar to Turbulent Transition Region of Turbine Vanes/Blades

NASA Technical Reports Server (NTRS)

Simon, Frederick F.

2007-01-01

A program sponsored by the National Aeronautics and Space Administration (NASA) for the investigation of the heat transfer in the transition region of turbine vanes and blades with the object of improving the capability for predicting heat transfer is described,. The accurate prediction of gas-side heat transfer is important to the determination of turbine longevity, engine performance and developmental costs. The need for accurate predictions will become greater as the operating temperatures and stage loading levels of advanced turbine engines increase. The present methods for predicting transition shear stress and heat transfer on turbine blades are based on incomplete knowledge and are largely empirical. To meet the objectives of the NASA program, a team approach consisting of researchers from government, universities, a research institute, and a small business is presented. The research is divided into areas of experimentation, direct numerical simulation (DNS) and turbulence modeling. A summary of the results to date is given for the above research areas in a high-disturbance environment (bypass transition) with a discussion of the model development necessary for use in numerical codes.

Pluto's Polygonal Terrain Places Lower Limit on Planetary Heat Flow

NASA Astrophysics Data System (ADS)

Trowbridge, A.; Steckloff, J. K.; Melosh, H., IV; Freed, A. M.

2015-12-01

During its recent flyby of Pluto, New Horizons imaged an icy plains region (Sputnik Planum) whose surface is divided into polygonal blocks, ca. 20-30 km across, bordered by what appear to be shallow troughs. The lack of craters within these plains suggests they are relatively young, implying that the underlying material is recently active. The scale of these features argues against an origin by cooling and contraction. Here we investigate the alternative scenario that they are the surface manifestation of shallow convection in a thick layer of nitrogen ice. Typical Rayleigh-Bernard convective cells are approximately three times wider than the depth of the convecting layer, implying a layer depth of ca. 7-10 km. Our convection hypothesis requires that the Rayleigh number exceed a minimum of about 1000 in the nitrogen ice layer. We coupled a parameterized convection model with a temperature dependent rheology of nitrogen ice (Yamashita, 2008), finding a Rayleigh number 1500 to 7500 times critical for a plausible range of heat flows for Pluto's interior. The computed range of heat flow (3.5-5.2 mW/m2) is consistent with the radiogenic heat generated by a carbonaceous chondrite (CC) core implied by Pluto's bulk density. The minimum heat flow at the critical Rayleigh number is 0.13 mW/m2. Our model implies a core temperature of 44 K in the interior of the convecting layer. This is very close to the exothermic β-α phase transition in nitrogen ice at 35.6 K (for pure N2 ice; dissolved CO can increase this, depending on its concentration), suggesting that the warm cores of the rising convective cells may be β phase, whereas the cooler sinking limbs may be α phase. This transition may thus be observable due to the large difference in their spectral signature. Further applying our model to Pluto's putative water ice mantle, the heat flow from CC is consistent with convection in Pluto's mantle and the activity observed on its surface.

Convective sources of trajectories traversing the tropical tropopause layer

NASA Astrophysics Data System (ADS)

Tissier, Ann-Sophie; Legras, Bernard

2016-03-01

Transit properties across the tropical tropopause layer are studied using extensive forward and backward Lagrangian diabatic trajectories between cloud tops and the reference surface 380 K. After dividing the tropical domain into 11 subregions according to the distribution of land and convection, we estimate the contribution of each region to the upward mass flux across the 380 K surface and to the vertical distribution of convective sources and transit times over the period 2005-2008. The good agreement between forward and backward statistics is the basis of the results presented here. It is found that about 85 % of the tropical parcels at 380 K originate from convective sources throughout the year. From November to April, the sources are dominated by the warm pool which accounts for up to 70 % of the upward flux. During boreal summer, the Asian monsoon region is the largest contributor with similar contributions from the maritime and continental parts of the region; however, the vertical distributions and transit times associated with these two subregions are very different. Convective sources are generally higher over the continental part of the Asian monsoon region, with shorter transit times. We estimate the monthly averaged upward mass flux on the 380 K surface and show that the contribution from convective outflow accounts for 80 % on average and explains most of its seasonal variations. The largest contributor to the convective flux is the South Asian Pacific region (warm pool) at 39 % throughout the year followed by oceanic regions surrounding continental Asia at 18 % and Africa at 10.8 %. Continental Asian lowlands account for 8 %. The Tibetan Plateau is a minor overall contributor (0.8 %), but transport from convective sources in this region is very efficient due to its central location beneath the Asian upper level anticyclone. The core results are robust to uncertainties in data and methods, but the vertical source distributions and transit times exhibit some sensitivity to the representations of cloud tops and heating rates. The main sensitivity is to the radiative heating rates which vary among reanalyses.

Al 1s-2p absorption spectroscopy of shock-wave heating and compression in laser-driven planar foil

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

Sawada, H.; Regan, S. P.; Radha, P. B.

Time-resolved Al 1s-2p absorption spectroscopy is used to diagnose direct-drive, shock-wave heating and compression of planar targets having nearly Fermi-degenerate plasma conditions (T{sub e}{approx}10-40 eV, {rho}{approx}3-11 g/cm{sup 3}) on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. A planar plastic foil with a buried Al tracer layer was irradiated with peak intensities of 10{sup 14}-10{sup 15} W/cm{sup 2} and probed with the pseudocontinuum M-band emission from a point-source Sm backlighter in the range of 1.4-1.7 keV. The laser ablation process launches 10-70 Mbar shock waves into the CH/Al/CH target. The Al 1s-2p absorption spectramore » were analyzed using the atomic physic code PRISMSPECT to infer T{sub e} and {rho} in the Al layer, assuming uniform plasma conditions during shock-wave heating, and to determine when the heat front penetrated the Al layer. The drive foils were simulated with the one-dimensional hydrodynamics code LILAC using a flux-limited (f=0.06 and f=0.1) and nonlocal thermal-transport model [V. N. Goncharov et al., Phys. Plasmas 13, 012702 (2006)]. The predictions of simulated shock-wave heating and the timing of heat-front penetration are compared to the observations. The experimental results for a wide variety of laser-drive conditions and buried depths have shown that the LILAC predictions using f=0.06 and the nonlocal model accurately model the shock-wave heating and timing of the heat-front penetration while the shock is transiting the target. The observed discrepancy between the measured and simulated shock-wave heating at late times of the drive can be explained by the reduced radiative heating due to lateral heat flow in the corona.« less

Al 1s-2p Absorption Spectroscopy of Shock-Wave Heating and Compression in Laser-Driven Planar Foil

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

Sawada, H.; Regan, S.P.; Radha, P.B.

Time-resolved Al 1s-2p absorption spectroscopy is used to diagnose direct-drive, shock-wave heating and compression of planar targets having nearly Fermi-degenerate plasma conditions (Te ~ 10–40 eV, rho ~ 3–11 g/cm^3) on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. A planar plastic foil with a buried Al tracer layer was irradiated with peak intensities of 10^14–10^15 W/cm^2 and probed with the pseudocontinuum M-band emission from a point-source Sm backlighter in the range of 1.4–1.7 keV. The laser ablation process launches 10–70 Mbar shock waves into the CH/Al/CH target. The Al 1s-2p absorption spectra weremore » analyzed using the atomic physic code PRISMSPECT to infer Te and rho in the Al layer, assuming uniform plasma conditions during shock-wave heating, and to determine when the heat front penetrated the Al layer. The drive foils were simulated with the one-dimensional hydrodynamics code LILAC using a flux-limited (f =0.06 and f =0.1) and nonlocal thermal-transport model [V. N. Goncharov et al., Phys. Plasmas 13, 012702 (2006)]. The predictions of simulated shock-wave heating and the timing of heat-front penetration are compared to the observations. The experimental results for a wide variety of laser-drive conditions and buried depths have shown that the LILAC predictions using f = 0.06 and the nonlocal model accurately model the shock-wave heating and timing of the heat-front penetration while the shock is transiting the target. The observed discrepancy between the measured and simulated shock-wave heating at late times of the drive can be explained by the reduced radiative heating due to lateral heat flow in the corona.« less

Shape-Memory Wires Switch Rotary Actuator

NASA Technical Reports Server (NTRS)

Brudnicki, Myron J.

1992-01-01

Thermomechanical rotary actuator based on shape-memory property of alloy composed of equal parts of titanium and nickel. If alloy stretched while below transition temperature, it reverts to original length when heated above transition temperature. Two capstans on same shaft wrapped with shape-memory wires. As one wire heated, it contracts and stretches opposite wire. Wires heated in alternation so they switch shaft between two extreme angular positions; "on" and "off" positions of rotary valve.

Ion-scale turbulence in MAST: anomalous transport, subcritical transitions, and comparison to BES measurements

NASA Astrophysics Data System (ADS)

van Wyk, F.; Highcock, E. G.; Field, A. R.; Roach, C. M.; Schekochihin, A. A.; Parra, F. I.; Dorland, W.

2017-11-01

We investigate the effect of varying the ion temperature gradient (ITG) and toroidal equilibrium scale sheared flow on ion-scale turbulence in the outer core of MAST by means of local gyrokinetic simulations. We show that nonlinear simulations reproduce the experimental ion heat flux and that the experimentally measured values of the ITG and the flow shear lie close to the turbulence threshold. We demonstrate that the system is subcritical in the presence of flow shear, i.e., the system is formally stable to small perturbations, but transitions to a turbulent state given a large enough initial perturbation. We propose that the transition to subcritical turbulence occurs via an intermediate state dominated by low number of coherent long-lived structures, close to threshold, which increase in number as the system is taken away from the threshold into the more strongly turbulent regime, until they fill the domain and a more conventional turbulence emerges. We show that the properties of turbulence are effectively functions of the distance to threshold, as quantified by the ion heat flux. We make quantitative comparisons of correlation lengths, times, and amplitudes between our simulations and experimental measurements using the MAST BES diagnostic. We find reasonable agreement of the correlation properties, most notably of the correlation time, for which significant discrepancies were found in previous numerical studies of MAST turbulence.

Development of the Oriental Latrine Fly, Chrysomya megacephala (Diptera: Calliphoridae), at Five Constant Temperatures.

PubMed

Gruner, S V; Slone, D H; Capinera, J L; Turco, M P

2017-03-01

Chrysomya megacephala (Fabricius) is a forensically important fly that is found throughout the tropics and subtropics. We calculated the accumulated development time and transition points for each life stage from eclosion to adult emergence at five constant temperatures: 15, 20, 25, 30, and 35 °C. For each transition, the 10th, 50th, and 90th percentiles were calculated with a logistic linear model. The mean transition times and % survivorship were determined directly from the raw laboratory data. Development times of C. megacephala were compared with that of two other closely related species, Chrysomya rufifacies (Macquart) and Phormia regina (Meigen). Ambient and larval mass temperatures were collected from field studies conducted from 2001-2004. Field study data indicated that adult fly activity was reduced at lower ambient temperatures, but once a larval mass was established, heat generation occurred. These development times and durations can be used for estimation of a postmortem interval (PMI). © The Authors 2016. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Effect of water content on specific heat capacity of porcine septum cartilage

NASA Astrophysics Data System (ADS)

Chae, Yongseok; Lavernia, Enrique J.; Wong, Brian J.

2002-06-01

The effect of water content on specific heat capacity was examined using temperature modulated Differential Scanning Calorimetry (TMDSC). This research was motivated in part by the development laser cartilage reshaping operations, which use photothermal heating to accelerate stress relaxation and shape change. Deposition of thermal energy leads to mechanical stress relaxation and redistribution of cartilage internal stresses, which may lead to a permanent shape change. The specific heat of cartilage specimens (dia: 3 mm and thickness 1-2 mm) was measured using a heating rate of 2 degree(s)C/min for conventional DSC and 2 degree(s)C/min with an amplitude 0.38-0.45 degree(s)C and a period 60-100 sec for TMDSC. The amount of water in cartilaginous tissue was determined using thermogravimetry analysis (TGA) under ambient conditions. In order to correlate changes in heat flow with alterations in cartilage mechanical behavior, dynamic mechanical temperature analysis (DMTA) was used to estimate the specific transition temperatures where stress relaxation occurs. With decreasing water content, we identified a phase transition that shifted to a higher temperature after 35-45% water content was measured. The phase transition energy increased from 0.12 J/g to 1.68 J/g after a 45% weight loss. This study is a preliminary investigation focused on understanding the mechanism of the stress relaxation of cartilage during heating. The energy requirement of such a transition estimated using TMDSC and temperature range, where cartilage shape changes likely occur, was estimated.

Numerical prediction of turbulent oscillating flow and associated heat transfer

NASA Technical Reports Server (NTRS)

Koehler, W. J.; Patankar, S. V.; Ibele, W. E.

1991-01-01

A crucial point for further development of engines is the optimization of its heat exchangers which operate under oscillatory flow conditions. It has been found that the most important thermodynamic uncertainties in the Stirling engine designs for space power are in the heat transfer between gas and metal in all engine components and in the pressure drop across the heat exchanger components. So far, performance codes cannot predict the power output of a Stirling engine reasonably enough if used for a wide variety of engines. Thus, there is a strong need for better performance codes. However, a performance code is not concerned with the details of the flow. This information must be provided externally. While analytical relationships exist for laminar oscillating flow, there has been hardly any information about transitional and turbulent oscillating flow, which could be introduced into the performance codes. In 1986, a survey by Seume and Simon revealed that most Stirling engine heat exchangers operate in the transitional and turbulent regime. Consequently, research has since focused on the unresolved issue of transitional and turbulent oscillating flow and heat transfer. Since 1988, the University of Minnesota oscillating flow facility has obtained experimental data about transitional and turbulent oscillating flow. However, since the experiments in this field are extremely difficult, lengthy, and expensive, it is advantageous to numerically simulate the flow and heat transfer accurately from first principles. Work done at the University of Minnesota on the development of such a numerical simulation is summarized.

Latent heat effects of the major mantle phase transitions on low-angle subduction

NASA Astrophysics Data System (ADS)

van Hunen, Jeroen; van den Berg, Arie P.; Vlaar, Nico J.

2001-08-01

Very low to zero shallow dip angles are observed at several moderately young subduction zones with an active trenchward moving overriding plate. We have investigated the effects of latent heat for this situation, where mantle material is pushed through the major mantle phase transitions during shallow low-angle subduction below the overriding plate. The significance of the buoyancy forces, arising from the latent heat effects, on the dynamics of the shallowly subducting slab is examined by numerical modeling. When a 32-Ma-old slab is overridden with 2.5 cm/yr by a continent, flat subduction occurs with a 4-5 cm/yr convergence rate. When latent heat is included in the model, forced downwellings cause a thermal anomaly and consequently thermal and phase buoyancy forces. Under these circumstances, the flat slab segment subducts horizontally about 350 km further and for about 11 Ma longer than in the case without latent heat, before it breaks through the 400-km phase transition. The style of subduction strongly depends on the mantle rheology: increasing the mantle viscosity by one order of magnitude can change the style of subduction from steep to shallow. Similarly, an overriding velocity of less than 1 cm/yr leads to steep subduction, which gradually changes to flat subduction when increasing the overriding velocity. However, these model parameters do not change the aforementioned effect of the latent heat, provided that low-angle subduction occurs. In all models latent heat resulted in a substantial increase of the flat slab length by 300-400 km. Varying the olivine-spinel transition Clapeyron slope γ from 1 to 6 MPa/K reveals a roughly linear relation between γ and the horizontal length of the slab. Based on these results, we conclude that buoyancy forces due to latent heat of phase transitions play an important role in low-angle subduction below an overriding plate.

Crystalline-gel-molten phase transitions of water in calcium dipicolinate (Ca-DPA)

NASA Astrophysics Data System (ADS)

Tiwari, Subodh; Mishra, Ankit; Sheng, Chunyang; Rajak, Pankaj; Kalia, Rajiv; Nakano, Aiichiro; Vashishta, Priya

The heat resistance of bacterial spores directly correlates to the protoplast dehydration and presence of dipicolinic acid (DPA) and its associated metal salts at the core. Bacteria's structural integrity in moist heat conferred by high concentration of DPA and calcium DPA salts depends on the properties are additional water molecules and temperature. In our reactive MD simulations, we characterize different possible phases and the transport properties of water molecules. We observed solid-gel and gel-liquid phase transitions of the hydrated Ca-DPA system. These simulations reveal monotonically decreasing solid-gel-liquid transition temperatures with increasing cell hydration, reflecting the experimental trend of moist-heat resistance of bacterial spores. We also observed that the calcification of bacterial spores further increases the transition temperatures. This research is supported by DTRA Grant No. HDTRA1-14-1-0074.

A Transition to Metallic Hydrogen: Evidence of the Plasma Phase Transition

NASA Astrophysics Data System (ADS)

Silvera, Isaac; Zaghoo, Mohamed; Salamat, Ashkan

The insulator-metal transition in hydrogen is one of the most outstanding problems in condensed matter physics. The high-pressure metallic phase is now predicted to be liquid atomic from T =0 K to very high temperatures. We have conducted measurements of optical properties of hot dense hydrogen in the region of 1.1-1.7 Mbar and up to 2200 K in a diamond anvil cell using pulsed laser heating of the sample. We present evidence in two forms: a plateau in the heating curves (average laser power vs temperature) characteristic of a first-order phase transition with latent heat, and changes in transmittance and reflectance characteristic of a metal for temperatures above the plateau temperature. For thick films the reflectance saturates at ~0.5. The phase line of this transition has a negative slope in agreement with theories of the so-called plasma phase transition. The NSF, Grant DMR-1308641, the DOE Stockpile Stewardship Academic Alliance Program, Grant DE-FG52-10NA29656, and NASA Earth and Space Science Fellowship Program, Award NNX14AP17H supported this research.

Magnetism of Ho 1-xTb xAl₂ alloys: Critical dependence of a first-order transition on Tb concentration

DOE PAGES

Khan, Mahmud; Mudryk, Ya.; Gschneidner, K. A.; ...

2011-12-27

HoAl₂ exhibits a first-order spin reorientation transition at 20 K, which is manifested as a sharp peak in the heat capacity. When Ho is partially replaced by only 5% of Tb, the sharp heat-capacity peak in Ho 1-xTb xAl₂ (x = 0.05) disappears, and then reappears again for x ≥ 0.07. For x = 0.05, the anomaly corresponding to the spin reorientation transition is barely seen in the heat capacity, but as x exceeds 0.07 the weak anomaly transforms to a sharp peak. The spin reorientation transition temperature increases to 29 K for x = 0.05, and as x increasesmore » further the transition shifts to lower temperature and returns to ~20 K for x = 0.25. The transition is no longer observed when x exceeds 0.60. Temperature-dependent x-ray powder-diffraction data confirm the first-order nature of the spin reorientation transition for the alloy with x = 0.40, and indicate that the compound retains the room-temperature cubic structure within the sensitivity of the technique. Experimental observations are discussed considering the easy magnetization directions of HoAl₂ and TbAl₂.« less

Full-time response of starch subjected to microwave heating.

PubMed

Fan, Daming; Wang, Liyun; Zhang, Nana; Xiong, Lei; Huang, Luelue; Zhao, Jianxin; Wang, Mingfu; Zhang, Hao

2017-06-21

The effect of non-ionizing microwave radiation on starch is due to a gelatinization temperature range that changes starch structure and properties. However, the changes in starch upon microwave heating are observable throughout the heating process. We compared the effects on starch heating by microwaves to the effects by rapid and regular conventional heating. Our results show that microwave heating promotes the rapid rearrangement of starch molecules at low temperatures; starch showed a stable dielectric response and a high dielectric constant. Microwave heating changed the Cole-Cole curve and the polarization of starch suspension at low temperatures. A marked transition at 2.45 GHz resulted in a double-polarization phenomenon. At temperatures below gelatinization, microwave-induced dielectric rearrangement and changes in the polarization characteristics of starch suspensions reduced the absorption properties; at temperatures above gelatinization, these characteristics became consistent with conventional heating. Throughout the heating process, microwaves change the electrical response and polarization characteristics of the starch at low temperatures, but on the macro level, there is no enhancement of the material's microwave absorption properties. In contrast, with the warming process, the starch exhibited a "blocking effect", and the absorption properties of the starch quickly returned to the level observed in conductive heating after gelatinization.

Investigation on phase transitions of 1-decylammonium hydrochloride as the potential thermal energy storage material

NASA Astrophysics Data System (ADS)

Dan, Wen-Yan; Di, You-Ying; He, Dong-Hua; Liu, Yu-Pu

2011-02-01

1-Decylammonium hydrochloride was synthesized by the method of liquid phase synthesis. Chemical analysis, elemental analysis, and X-ray single crystal diffraction techniques were applied to characterize its composition and structure. Low-temperature heat capacities of the compounds were measured with a precision automated adiabatic calorimeter over the temperature range from 78 to 380 K. Three solid-solid phase transitions have been observed at the peak temperatures of 307.52 ± 0.13, 325.02 ± 0.19, and 327.26 ± 0.07 K. The molar enthalpies and entropies of three phase transitions were determined based on the analysis of heat capacity curves. Experimental molar heat capacities were fitted to two polynomial equations of the heat capacities as a function of temperature by least square method. Smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at intervals of 5 K based on the fitted polynomials.

Laminar, Transitional, and Turbulent Heating on Mid Lift-to-Drag Ratio Entry Vehicles

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Hollingsworth, Kevin E.

2013-01-01

The boundary-layer transition characteristics and convective aeroheating levels on mid lift-to-drag ratio entry vehicle configurations have been studied through wind-tunnel testing. Several configurations were investigated, including elliptically blunted cylinders with both circular and elliptically flattened cross sections, biconic geometries based on launch vehicle dual-use shrouds, and parametrically optimized analytic geometries. Vehicles of this class have been proposed for high-mass Mars missions, such as sample return and crewed exploration, for which the conventional sphere-cone entry-vehicle geometries of previous Mars missions are insufficient. Testing was conducted at Mach 6 over a range of Reynolds numbers sufficient to generate laminar, transitional, and turbulent flow. Transition onset locations, both straight-line and cross-flow, and heating rates were obtained through global phosphor thermography. Supporting computations were performed to obtain heating rates for comparison with the data. Laminar data and predictions agreed to well within the experimental uncertainty. Fully turbulent data and predictions also agreed well. However, in transitional flow regions, greater differences were observed.

Mechanical heating in the transition region

NASA Technical Reports Server (NTRS)

Withbroe, G.

1981-01-01

Attention is focused on the energy balance in the transition region and the role that mechanical heating plays in determining the temperature density structure of this region in a stellar atmosphere. Because of its role as the interface layer through which mass and energy flow between the chromospheres and corona, direct deposition of mechanical energy is a relatively unimportant factor in the overall energy balance in the transition region, except in the uppermost layers where the temperature approaches coronal values.

Ultraviolet absorption spectra of shock-heated carbon dioxide and water between 900 and 3050 K

NASA Astrophysics Data System (ADS)

Schulz, C.; Koch, J. D.; Davidson, D. F.; Jeffries, J. B.; Hanson, R. K.

2002-03-01

Spectrally resolved UV absorption cross-sections between 190 and 320 nm were measured in shock-heated CO 2 between 880 and 3050 K and H 2O between 1230 and 2860 K. Absorption spectra were acquired with 10 μs time resolution using a unique kinetic spectrograph, thereby enabling comparisons with time-dependent chemical kinetic modeling of post-shock thermal decomposition and chemical reactions. Although room temperature CO 2 is transparent (σ<10 -22 cm2) at wavelengths longer than 200 nm, hot CO 2 has significant absorption (σ>10 -20 cm2) extending to wavelengths longer than 300 nm. The temperature dependence of CO 2 absorption strongly suggests sharply increased transition probabilities from excited vibrational levels.

Experimental Investigations of Space Shuttle BX-265 Foam

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Sullivan, Roy M.

2009-01-01

This report presents a variety of experimental studies on the polyurethane foam, BX-265. This foam is used as a close-out foam insulation on the space shuttle external tank. The purpose of this work is to provide a better understanding of the foam s behavior and to support advanced modeling efforts. The following experiments were performed: Thermal expansion was measured for various heating rates. The in situ expansion of foam cells was documented by heating the foam in a scanning electron microscope. Expansion mechanisms are described. Thermogravimetric analysis was performed at various heating rates and for various environments. The glass transition temperature was also measured. The effects of moisture on the foam were studied. Time-dependent effects were measured to give preliminary data on viscoelastoplastic properties.

LC-circuit calorimetry

NASA Astrophysics Data System (ADS)

Bossen, O.; Schilling, A.

2011-09-01

We present a new type of calorimeter in which we couple an unknown heat capacity with the aid of Peltier elements to an electrical circuit. The use of an electrical inductance and an amplifier in the circuit allows us to achieve autonomous oscillations, and the measurement of the corresponding resonance frequency makes it possible to accurately measure the heat capacity with an intrinsic statistical uncertainty that decreases as ˜ t_m^{ -3/2} with measuring time tm, as opposed to a corresponding uncertainty ˜ t_m^{-1/2} in the conventional alternating current method to measure heat capacities. We have built a demonstration experiment to show the feasibility of the new technique, and we have tested it on a gadolinium sample at its transition to the ferromagnetic state.

Theoretical potential for low energy consumption phase change memory utilizing electrostatically-induced structural phase transitions in 2D materials

NASA Astrophysics Data System (ADS)

Rehn, Daniel A.; Li, Yao; Pop, Eric; Reed, Evan J.

2018-01-01

Structural phase-change materials are of great importance for applications in information storage devices. Thermally driven structural phase transitions are employed in phase-change memory to achieve lower programming voltages and potentially lower energy consumption than mainstream nonvolatile memory technologies. However, the waste heat generated by such thermal mechanisms is often not optimized, and could present a limiting factor to widespread use. The potential for electrostatically driven structural phase transitions has recently been predicted and subsequently reported in some two-dimensional materials, providing an athermal mechanism to dynamically control properties of these materials in a nonvolatile fashion while achieving potentially lower energy consumption. In this work, we employ DFT-based calculations to make theoretical comparisons of the energy required to drive electrostatically-induced and thermally-induced phase transitions. Determining theoretical limits in monolayer MoTe2 and thin films of Ge2Sb2Te5, we find that the energy consumption per unit volume of the electrostatically driven phase transition in monolayer MoTe2 at room temperature is 9% of the adiabatic lower limit of the thermally driven phase transition in Ge2Sb2Te5. Furthermore, experimentally reported phase change energy consumption of Ge2Sb2Te5 is 100-10,000 times larger than the adiabatic lower limit due to waste heat flow out of the material, leaving the possibility for energy consumption in monolayer MoTe2-based devices to be orders of magnitude smaller than Ge2Sb2Te5-based devices.

The direct heat measurement of mechanical energy storage metal-organic frameworks.

PubMed

Rodriguez, Julien; Beurroies, Isabelle; Loiseau, Thierry; Denoyel, Renaud; Llewellyn, Philip L

2015-04-07

In any process, the heat exchanged is an essential property required in its development. Whilst the work related to structural transitions of some flexible metal-organic frameworks (MOFs) has been quantified and linked with potential applications such as molecular springs or shock absorbers, the heat related to such transitions has never been directly measured. This has now been carried out with MIL-53(Al) using specifically devised calorimetry experiments. We project the importance of these heats in devices such as molecular springs or dampers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heat transfer characteristics of hypersonic waveriders with an emphasis on leading edge effects

NASA Technical Reports Server (NTRS)

Vanmol, Denis O.; Anderson, John D., Jr.

1992-01-01

The present analysis of the heat-transfer characteristics of a family of viscous-optimized, 60 m-long waverider hypersonic vehicles gives attention to the transition from laminar to turbulent flow, and to how the transition affects aerodynamic heating distributions over the waverider surface. Two different constant-dynamic-pressure flight trajectories are considered, at 0.2 and 1.0 freestream atmospheres. For Mach numbers below 10, it is found that passive radiative cooling of the surface is sufficient. The degree of leading-edge bluntness required by aerodynamic heating constraints does not significantly degrade the aerodynamic performance of these waveriders.

Ballistic near-field heat transport in dense many-body systems

NASA Astrophysics Data System (ADS)

Latella, Ivan; Biehs, Svend-Age; Messina, Riccardo; Rodriguez, Alejandro W.; Ben-Abdallah, Philippe

2018-01-01

Radiative heat transport mediated by near-field interactions is known to be superdiffusive in dilute, many-body systems. Here we use a generalized Landauer theory of radiative heat transfer in many-body planar systems to demonstrate a nonmonotonic transition from superdiffusive to ballistic transport in dense systems. We show that such a transition is associated to a change of the polarization of dominant modes. Our findings are complemented by a quantitative study of the relaxation dynamics of the system in the different regimes of heat transport. This result could have important consequences on thermal management at nanoscale of many-body systems.

Route to chaos in porous-medium thermal convection

NASA Astrophysics Data System (ADS)

Kimura, S.; Schubert, G.; Straus, J. M.

1986-05-01

The transition to chaos in two-dimensional single-cell time-dependent convection in a square cross section of porous material saturated with fluid and heated from below is investigated theoretically by means of pseudospectral numerical simulations. The results are presented graphically and discussed in terms of the time-averaged Nusselt number, the oscillation mechanism, and similarities to Hele-Shaw convection. As the Rayleigh number (R) increases, the system is found to proceed from the steady state to a simply periodic state, a quasi-periodic state with two basic frequencies, a second simply periodic state, and finally to chaos. The transitions occur at R = 4 pi squared, 380-400, 500-520, 560-570, and 850-1000. The intermediate and chaotic regimes are characterized in detail.

Kinetic synergistic transitions in the Ostwald ripening processes

NASA Astrophysics Data System (ADS)

Sachkov, I. N.; Turygina, V. F.; Dolganov, A. N.

2018-01-01

There is proposed approach to mathematical description of the kinetic transitions in Ostwald ripening processes of volatile substance in nonuniformly heated porous materials. It is based upon the finite element method. There are implemented computer software. The main feature of the software is to calculate evaporation and condensation fluxes on the walls of a nonuniformly heated cylindrical capillary. Kinetic transitions are detected for three modes of volatile substances migration which are different by condensation zones location. There are controlling dimensionless parameters of the kinetic transition which are revealed during research. There is phase diagram of the Ostwald ripening process modes realization.

Pressure Dependence of the Specific-Heat Jump at the Superfluid Transition and the Effective Mass of 3He

NASA Astrophysics Data System (ADS)

Alvesalo, T. A.; Haavasoja, T.; Manninen, M. T.; Soinne, A. T.

1980-04-01

The specific heat of liquid 3He has been measured from 1 to 10 mK between 0 and 32.5 bars. The values implied for the effective mass are considerably smaller than the currently accepted ones. Near zero pressure the specific-heat jump is close to the BCS value 1.43, and at 32.5 bars it has reached 1.90 in the B phase and 2.04 in the A phase. The temperature dependence of the specific heat in the B phase agrees with a model of Serene and Rainer. The latent heat at the A-B transition has been measured.

Methods of Helium Injection and Removal for Heat Transfer Augmentation

NASA Technical Reports Server (NTRS)

Haight, Harlan; Kegley, Jeff; Bourdreaux, Meghan

2008-01-01

While augmentation of heat transfer from a test article by helium gas at low pressures is well known, the method is rarely employed during space simulation testing because the test objectives usually involve simulation of an orbital thermal environment. Test objectives of cryogenic optical testing at Marshall Space Flight Center's X-ray Cryogenic Facility (XRCF) have typically not been constrained by orbital environment parameters. As a result, several methods of helium injection have been utilized at the XRCF since 1999 to decrease thermal transition times. A brief synopsis of these injection (and removal) methods including will be presented.

Methods of Helium Injection and Removal for Heat Transfer Augmentation

NASA Technical Reports Server (NTRS)

Kegley, Jeffrey

2008-01-01

While augmentation of heat transfer from a test article by helium gas at low pressures is well known, the method is rarely employed during space simulation testing because the test objectives are to simulate an orbital thermal environment. Test objectives of cryogenic optical testing at Marshall Space Flight Center's X-ray Calibration Facility (XRCF) have typically not been constrained by orbital environment parameters. As a result, several methods of helium injection have been utilized at the XRCF since 1999 to decrease thermal transition times. A brief synopsis of these injection (and removal) methods including will be presented.

Fast optical cooling of nanomechanical cantilever with the dynamical Zeeman effect.

PubMed

Zhang, Jian-Qi; Zhang, Shuo; Zou, Jin-Hua; Chen, Liang; Yang, Wen; Li, Yong; Feng, Mang

2013-12-02

We propose an efficient optical electromagnetically induced transparency (EIT) cooling scheme for a cantilever with a nitrogen-vacancy center attached in a non-uniform magnetic field using dynamical Zeeman effect. In our scheme, the Zeeman effect combined with the quantum interference effect enhances the desired cooling transition and suppresses the undesired heating transitions. As a result, the cantilever can be cooled down to nearly the vibrational ground state under realistic experimental conditions within a short time. This efficient optical EIT cooling scheme can be reduced to the typical EIT cooling scheme under special conditions.

LCM-seq reveals the crucial role of LsSOC1 in heat-promoted bolting of lettuce (Lactuca sativa L.).

PubMed

Chen, Zijing; Zhao, Wensheng; Ge, Danfeng; Han, Yingyan; Ning, Kang; Luo, Chen; Wang, Shenglin; Liu, Renyi; Zhang, Xiaolan; Wang, Qian

2018-05-17

Lettuce (Lactuca sativa L.) is one of the most economically important vegetables. The floral transition in lettuce is accelerated under high temperatures, which can significantly decrease yields. However, the molecular mechanism underlying the floral tranition in lettuce is poorly known. Using laser capture microdissection coupled with RNA sequencing, we isolated shoot apical meristem cells from the bolting-sensitive lettuce line S39 at four critical stages of development. Subsequently, we screened specifically for the flowering-related gene LsSOC1 during the floral transition through comparative transcriptomic analysis. Molecular biology, developmental biology, and biochemical tools were combined to investigate the biological function of LsSOC1 in lettuce. LsSOC1 knockdown by RNA interference resulted in a significant delay in the timing of bolting and insensitivity to high temperature, which indicated that LsSOC1 functions as an activator during heat-promoted bolting in lettuce. We determined that two heat-shock transcription factors, HsfA1e and HsfA4c, bound to the promoter of LsSOC1 to confirm that LsSOC1 played an important role in heat-promoted bolting. This study indicates that LsSOC1 plays a crucial role in the heat-promoted bolting process in lettuce. Further investigation of LsSOC1 may be useful for clarification of the bolting mechanism in lettuce. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Heat shock, but not temperature, is a biological trigger for the exsheathment of third-stage larvae of Haemonchus contortus.

PubMed

Bekelaar, Kiliana; Waghorn, Tania; Tavendale, Michael; McKenzie, Catherine; Leathwick, Dave

2018-05-21

Gastrointestinal parasites are an important health issue in grazing ruminants. Understanding the processes involved in the transition from the free living to the parasitic life stage of these nematodes is one avenue to identifying new targets amenable to future intervention. The transition to parasitism is initiated by exsheathment and is triggered by the sudden change in environment after ingestion of the infective larva by the host. Two major changes in environment are the increases in temperature and carbon dioxide (CO 2 ) levels. For CO 2 a role in exsheathment has been described previously, but the exact role of temperature was unclear. The current study is the first to investigate the importance of temperature in triggering exsheathment of Haemonchus contortus. Carbon dioxide induced exsheathment in H. contortus proved to be temperature dependent, as no exsheathment was observed at room temperatures. However, the temperature requirement to trigger exsheathment was quite specific. A rapid change in temperature (heat shock) very efficiently induced high levels of exsheathment. In contrast, when the larvae were exposed to a slow increase in temperature, the exsheathment response was smaller and delayed. Further investigation revealed that timing of the heat shock in relation to the CO 2 administration was crucial, as well as the final temperature and magnitude of the heat shock. In conclusion, these data indicate that heat shock rather than temperature itself is a crucial aspect in triggering the biological exsheathment cascade, and thus infection process, of H. contortus.

Preparation and Characterization of BaTiO3-PbZrTiO3 Coating for Pyroelectric Energy Harvesting

NASA Astrophysics Data System (ADS)

Raghavendra, R. M.; Praneeth, K. P. S. S.; Dutta, Soma

2017-01-01

Harvesting energy from waste heat is a promising field of research as there are significant energy recovery opportunities from various waste thermal energy sources. The present study reports pyroelectric energy harvesting using thick film prepared from a (x)BaTiO3-(1 - x)PbZr0.52Ti0.48O3 (BT-PZT) solid solution. The developed BT-PZT system is engineered to tune the ferro to paraelectric phase transition temperature of it in-between the phase transition temperature of BaTiO3 (393 K) and PbZrTiO3 (573 K) with higher pyroelectric figure-of-merit (FOM). The temperature-dependent dielectric behavior of the material has revealed the ferro- to paraelectric phase transition at 427 K with a maximum dielectric constant of 755. The room-temperature (298 K) pyroelectric coefficient (Pi) of the material was obtained as 738.63 μC/m2K which has yielded a significantly high FOM of 1745.8 J m-3 K-2. The enhancement in pyroelectric property is attributed to the morphotopic phase transition between tetragonal and rhombohedral PZT phases in the BT-PZT system. The developed BT-PZT system is capable of generating a power output of 1.3 mW/m2 near the Curie temperature with a constant rate (0.11 K/s) of heating. A signal conditioning circuit has been developed to rectify the time-varying current and voltage signals obtained from the harvester during heating cycles. The output voltage generated by the pyroelectric harvester has been stored in a capacitor for powering wearable electronics.

Stellar Activity at the End of the Main Sequence: GHRS Observations of the M8 Ve Star VB 10

NASA Technical Reports Server (NTRS)

Linsky, Jeffrey L.; Wood, Brian E.; Brown, Alexander; Giampapa, Mark S.; Ambruster, Carol

1995-01-01

We present Goddard High Resolution Spectrograph observations of the M8 Ve star VB 10 (equal to G1 752B), located very near the end of the stellar main sequence, and its dM3.5 binary companion G1 752A. These coeval stars provide a test bed for studying whether the outer atmospheres of stars respond to changes in internal structure as stars become fully convective near mass 0.3 solar mass (about spectral type M5), where the nature of the stellar magnetic dynamo presumably changes, and near the transition from red to brown dwarfs near mass 0.08 solar mass (about spectral type M9), when hydrogen burning ceases at the end of the main sequence. We obtain upper limits for the quiescent emission of VB 10 but observe a transition region spectrum during a large flare, which indicates that some type of magnetic dynamo must be present. Two indirect lines of evidence-scaling from the observed X-ray emission and scaling from a time-resolved flare on AD Leo suggest that the fraction of the stellar bolometric luminosity that heats the transition region of VB 10 outside of obvious flares is comparable to, or larger than, that for G1 752A. This suggests an increase in the magnetic heating rates, as measured by L(sub line)/L(sub bol) ratios, across the radiative/convective core boundary and as stars approach the red/brown dwarf boundary. These results provide new constraints for dynamo models and models of coronal and transition-region heating in late-type stars.

A review and analysis of boundary layer transition data for turbine application

NASA Technical Reports Server (NTRS)

Gaugler, R. E.

1984-01-01

A symposium on transition in turbines was held at the NASA Lewis Research Center. One recommendation of the working groups was the collection of existing transition data to provide standard cases against which models could be tested. A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information from the heat transfer data. The data sets reviewed cover a wide range of flow conditions, from low speed, flat plate tests to full scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

A review and analysis of boundary layer transition data for turbine application

NASA Technical Reports Server (NTRS)

Gaugler, R. E.

1985-01-01

A symposium on transition in turbines was held at the NASA Lewis Research Center. One recommendation of the working groups was the collection of existing transition data to provide standard cases against which models could be tested. A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information from the heat transfer data. The data sets reviewed cover a wide range of flow conditions, from low speed, flat plate tests to full scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

Low Stretch Solid-Fuel Flame Transient Response to a Step Change in Gravity

NASA Technical Reports Server (NTRS)

Armstrong, J. B.; Olson, S. L.; T'ien, J. S.

2003-01-01

The effect of a step change in gravity level on the stability of low stretch diffusion flames over a solid fuel is studied both numerically and experimentally. Drop tower experiments have been conducted in NASA Glenn Research Center's 5.2 Zero Gravity Facility. In the experiments burning PMMA cylinders, a dynamic transition is observed when the steadily burning 1g flame is dropped and becomes a 0g flame. To understand the physics behind this dynamic transition, a transient stagnation point model has been developed which includes gas-phase radiation and solid phase coupling to describe this dynamic process. In this paper, the experimental results are compared with the model predictions. Both model and experiment show that the interior of the solid phase does not have time to change significantly in the few seconds of drop time, so the experimental results are pseudo-steady in the gas-phase, but the solid is inherently unsteady over long time scales. The model is also used to examine the importance of fractional heat losses on extinction, which clearly demonstrates that as the feedback from the flame decreases, the importance of the ongoing heat losses becomes greater, and extinction is observed when these losses represent 80% or more of the flame feedback.

Mechanochemical effect in the iron(III) spin crossover complex [Fe(3-MeO-salenEt2]PF6 as studied by heat capacity calorimetry.

PubMed

Sorai, Michio; Burriel, Ramón; Westrum, Edgar F; Hendrickson, David N

2008-04-10

Magnetic and thermal properties of the iron(III) spin crossover complex [Fe(3MeO-salenEt)(2)]PF(6) are very sensitive to mechanochemical perturbations. Heat capacities for unperturbed and differently perturbed samples were precisely determined by adiabatic calorimetry at temperatures in the 10-300 K range. The unperturbed compound shows a cooperative spin crossover transition at 162.31 K, presenting a hysteresis of 2.8 K. The anomalous enthalpy and entropy contents of the transition were evaluated to be Delta(trs)H = 5.94 kJ mol(-1) and Delta(trs)S = 36.7 J K(-1) mol(-1), respectively. By mechanochemical treatments, (1) the phase transition temperature was lowered by 1.14 K, (2) the enthalpy and entropy gains at the phase transition due to the spin crossover phenomenon were diminished to Delta(trs)H = 4.94 kJ mol(-1) and Delta(trs)S = 31.1 J K(-1) mol(-1), and (3) the lattice heat capacities were larger than those of the unperturbed sample over the whole temperature range. In spite of different mechanical perturbations (grinding with a mortar and pestle and grinding in a ball-mill), two sets of heat capacity measurements provided basically the same results. The mechanochemical perturbation exerts its effect more strongly on the low-spin state than on the high-spin state. It shows a substantial increase of the number of iron(III) ions in the high-spin state below the transition temperature. The heat capacities of the diamagnetic cobalt(III) analogue [Co(3MeO-salenEt)(2)]PF(6) also were measured. The lattice heat capacity of the iron compounds has been estimated from either the measurements on the cobalt complex using a corresponding states law or the effective frequency distribution method. These estimations have been used for the evaluation of the transition anomaly.

Transition region fluxes in A-F Dwarfs: Basal fluxes and dynamo activity

NASA Technical Reports Server (NTRS)

Walter, Frederick M.; Schrijver, Carolus J.; Boyd, William

1988-01-01

The transition region spectra of 87 late A and early F dwarfs and subgiants were analyzed. The emission line fluxes are uniformly strong in the early F stars, and drop off rapidly among the late A stars. The basal flux level in the F stars is consistent with an extrapolation of that observed among the G stars, while the magnetic component displays the same flux-flux relations seen among solar-like stars. Despite the steep decrease in transition region emission flux for B-V less than 0.28, C II emission is detected in alpha Aql (B-V = 0.22). The dropoff in emission is inconsistent with models of the mechanically generated acoustic flux available. It is concluded that, although the nonmagnetic basal heating is an increasingly important source of atmospheric heating among the early F stars, magnetic heating occurs in any star which has a sufficiently thick convective zone to generate acoustic heating.

Calorimetry of a Bose–Einstein-condensed photon gas

PubMed Central

Damm, Tobias; Schmitt, Julian; Liang, Qi; Dung, David; Vewinger, Frank; Weitz, Martin; Klaers, Jan

2016-01-01

Phase transitions, as the condensation of a gas to a liquid, are often revealed by a discontinuous behaviour of thermodynamic quantities. For liquid helium, for example, a divergence of the specific heat signals the transition from the normal fluid to the superfluid state. Apart from liquid helium, determining the specific heat of a Bose gas has proven to be a challenging task, for example, for ultracold atomic Bose gases. Here we examine the thermodynamic behaviour of a trapped two-dimensional photon gas, a system that allows us to spectroscopically determine the specific heat and the entropy of a nearly ideal Bose gas from the classical high temperature to the Bose-condensed quantum regime. The critical behaviour at the phase transition is clearly revealed by a cusp singularity of the specific heat. Regarded as a test of quantum statistical mechanics, our results demonstrate a quantitative agreement with its predictions at the microscopic level. PMID:27090978

High-order corrections on the laser cooling limit in the Lamb-Dicke regime.

PubMed

Yi, Zhen; Gu, Wen-Ju

2017-01-23

We investigate corrections on the cooling limit of high-order Lamb-Dicke (LD) parameters in the double electromagnetically induced transparency (EIT) cooling scheme. Via utilizing quantum interferences, the single-phonon heating mechanism vanishes and the system evolves to a double dark state, from which we will obtain the mechanical occupation on the single-phonon excitation state. In addition, the further correction induced by two-phonon heating transitions is included to achieve a more accurate cooling limit. There exist two pathways of two-phonon heating transitions: direct two-phonon excitation from the dark state and further excitation from the single-phonon excited state. By adding up these two parts of correction, the obtained analytical predictions show a well consistence with numerical results. Moreover, we find that the two pathways can destructively interfere with each other, leading to the elimination of two-phonon heating transitions and achieving a lower cooling limit.

Experiments in Transitional Boundary Layers With Emphasis on High Free-Stream Disturbance Level, Surface Concave Curvature and Strong Favorable Streamwise Pressure Gradient Effects

NASA Technical Reports Server (NTRS)

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

2007-01-01

Experiments on boundary layer transition with flat, concave and convex walls and various levels of free-stream disturbance and with zero and strong streamwise acceleration have been conducted. Measurements of both fluid mechanics and heat transfer processes were taken. Examples are profiles of mean velocity and temperature; Reynolds normal and shear stresses; turbulent streamwise and cross-stream heat fluxed; turbulent Prandtl number; and streamwise variations of wall skin friction and heat transfer coefficient values. Free-stream turbulence levels were varied over the range from about 0.3 percent to about 8 percent. The effects of curvature on the onset of transition under low disturbance conditions are clear; concave curvature leads to an earlier and more rapid transition and the opposite is true for convex curvature This was previously known but little documentation of the transport processes in the flow was available

Measurements of Heat Transfer and Boundary-Layer Transition on an 8-Inch-Diameter Hemisphere-Cylinder in Free Flight for a Mach Number Range of 2.00 to 3.88

NASA Technical Reports Server (NTRS)

Garland, Benjamine J.; Chauvin, Leo T.

1957-01-01

Measurements of aerodynamic heat transfer have been made along the hemisphere and cylinder of a hemisphere-cylinder rocket-propelled model in free flight up to a Mach number of 3.88. The test Reynolds number based on free-stream condition and diameter of model covered a range from 2.69 x l0(exp 6) to 11.70 x 10(exp 6). Laminar, transitional, and turbulent heat-transfer coefficients were obtained. The laminar data along the body agreed with laminar theory for blunt bodies whereas the turbulent data along the cylinder were consistently lower than that predicted by the turbulent theory for a flat plate. Measurements of heat transfer at the stagnation point were, in general, lower than the theory for stagnation-point heat transfer. When the Reynolds number to the junction of the hemisphere-cylinder was greater than 6 x l0(exp 6), the transitional Reynolds number varied from 0.8 x l0(exp 6) to 3.0 x 10(exp 6); however, than 6 x l(exp 6) when the Reynolds number to the junction was less, than the transitional Reynolds number varied from 7.0 x l0(exp 6) to 24.7 x 10(exp 6).

Thermal Transport Model for Heat Sink Design

NASA Technical Reports Server (NTRS)

Chervenak, James A.; Kelley, Richard L.; Brown, Ari D.; Smith, Stephen J.; Kilbourne, Caroline a.

2009-01-01

A document discusses the development of a finite element model for describing thermal transport through microcalorimeter arrays in order to assist in heat-sinking design. A fabricated multi-absorber transition edge sensor (PoST) was designed in order to reduce device wiring density by a factor of four. The finite element model consists of breaking the microcalorimeter array into separate elements, including the transition edge sensor (TES) and the silicon substrate on which the sensor is deposited. Each element is then broken up into subelements, whose surface area subtends 10 10 microns. The heat capacity per unit temperature, thermal conductance, and thermal diffusivity of each subelement are the model inputs, as are the temperatures of each subelement. Numerical integration using the Finite in Time Centered in Space algorithm of the thermal diffusion equation is then performed in order to obtain a temporal evolution of the subelement temperature. Thermal transport across interfaces is modeled using a thermal boundary resistance obtained using the acoustic mismatch model. The document concludes with a discussion of the PoST fabrication. PoSTs are novel because they enable incident x-ray position sensitivity with good energy resolution and low wiring density.

Linking the micro and macro: L-H transition dynamics and threshold physics

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

Malkov, M. A., E-mail: mmalkov@ucsd.edu; Diamond, P. H.; Miki, K.

2015-03-15

The links between the microscopic dynamics and macroscopic threshold physics of the L → H transition are elucidated. Emphasis is placed on understanding the physics of power threshold scalings, and especially on understanding the minimum in the power threshold as a function of density P{sub thr} (n). By extending a numerical 1D model to evolve both electron and ion temperatures, including collisional coupling, we find that the decrease in P{sub thr} (n) along the low-density branch is due to the combination of an increase in collisional electron-to-ion energy transfer and an increase in the heating fraction coupled to the ions.more » Both processes strengthen the edge diamagnetic electric field needed to lock in the mean electric field shear for the L→H transition. The increase in P{sub thr} (n) along the high-density branch is due to the increase with ion collisionality of damping of turbulence-driven shear flows. Turbulence driven shear flows are needed to trigger the transition by extracting energy from the turbulence. Thus, we identify the critical transition physics components of the separatrix ion heat flux and the zonal flow excitation. The model reveals a power threshold minimum in density scans as a crossover between the threshold decrease supported by an increase in heat fraction received by ions (directly or indirectly, from electrons) and a threshold increase, supported by the rise in shear flow damping. The electron/ion heating mix emerges as important to the transition, in that it, together with electron-ion coupling, regulates the edge diamagnetic electric field shear. The importance of possible collisionless electron-ion heat transfer processes is explained.« less

Altered native stability is the dominant basis for susceptibility of α1-antitrypsin mutants to polymerization

PubMed Central

Irving, James A.; Haq, Imran; Dickens, Jennifer A.; Faull, Sarah V.; Lomas, David A.

2014-01-01

Serpins are protease inhibitors whose most stable state is achieved upon transition of a central 5-stranded β-sheet to a 6-stranded form. Mutations, low pH, denaturants and elevated temperatures promote this transition, which can result in a growing polymer chain of inactive molecules. Different types of polymer are possible, but, experimentally only heat has been shown to generate polymers in vitro consistent with ex vivo pathological specimens. Many mutations that alter the rate of heat-induced polymerization have been described, but interpretation is problematic because discrimination is lacking between the effect of global changes in native stability and specific effects on structural mechanism. We show that the temperature midpoint (Tm) of thermal denaturation reflects the transition of α1-antitrypsin to the polymerization intermediate, and determine the relationship with fixed-temperature polymerization half-times (t0.5) in the presence of stabilizing additives [TMAO (trimethylamine N-oxide), sucrose and sodium sulfate], point mutations and disulfide bonds. Combined with a retrospective analysis of 31 mutants characterized in the literature, the results of the present study show that global changes to native state stability are the predominant basis for the effects of mutations and osmolytes on heat-induced polymerization, summarized by the equation: ln(t0.5,mutant/t0.5,wild-type)=0.34×ΔTm. It is deviations from this relationship that hold key information about the polymerization process. PMID:24552432

Kinetics and mechanism of the pressure-induced lamellar order/disorder transition in phosphatidylethanolamine: a time-resolved X-ray diffraction study.

PubMed

Mencke, A P; Caffrey, M

1991-03-05

By using synchrotron radiation, a movie was made of the X-ray scattering pattern from a biological liquid crystal undergoing a phase transition induced by a pressure jump. The system studied includes the fully hydrated phospholipid dihexadecylphosphatidylethanolamine in the lamellar gel (L beta') phase at a temperature of 68 degrees C and a pressure of 9.7 MPa (1400 psig). Following the rapid release of pressure to atmospheric the L beta' phase transforms slowly into the lamellar liquid crystal (L alpha) phase. The pressure perturbation is applied with the intention of producing a sudden phase disequilibrium followed by monitoring the system as it relaxes to its new equilibrium condition. Remarkably, the proportion of sample in the L alpha phase grows linearly with time, taking 37 s to totally consume the L beta' phase. The time dependencies of radius, peak intensity, and width of the powder diffraction ring of the low-angle (001) lamellar reflections were obtained from the movie by image processing. The concept of an "effective pressure" is introduced to account for the temperature variations that accompany the phase transition and to establish that the observed large transit time is indeed intrinsic to the sample and not due to heat exchange with the environment. The reverse transformation, L alpha to L beta', induced by a sudden jump from atmospheric pressure to 9.7 MPa, is complete in less than 13 s. These measurements represent a new approach for studying the kinetics of lipid phase transitions and for gaining insights into the mechanism of the lamellar order/disorder transition.

What Is Happening at Spectral Type F5 in Hyades F Stars?

NASA Technical Reports Server (NTRS)

Boehm-Vitense, Erika; Robinson, Richard; Carpenter, Kenneth; Mena-Werth, Jose

2002-01-01

Aiming at a better understanding of the mechanisms heating the chromospheres, transition regions, and coronae of cool stars, we study ultraviolet, low-resolution Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra of Hyades main-sequence F stars. We study the B-V dependence(s) of the chromospheric and transition layer emission line fluxes and their dependences on rotational velocities. We find that the transition layer emission line fluxes and also those of strong chromospheric lines decrease steeply between B-V = 0.42 and 0.45, i.e., at spectral type F5, for which the rotational velocities also decrease steeply. The magnitude of the line-flux decrease increases for lines of ions with increasing degree of ionization. This shows that the line-flux decrease is not due to a change in the surface filling factor but rather due to a change of the relative importance of different heating mechanisms. For early F stars with B-V < 0.42 we find for the transition layer emission lines increasing fluxes for increasing v sin i, indicating magnetohydrodynamic heating. The v sin i dependence is strongest for the high-ionization lines. On the other hand, the low chromospheric lines show no dependence on v sin i, indicating acoustic shock heating for these layers. This also contributes to the heating of the transition layers. The Mg II and Ca II lines show decreasing fluxes for increasing v sin i, as long as v sin i is less than approx. 40 km/s. The coronal X-ray emission also decreases for increasing v sin i, except for v sin i larger than approx. 100 km/s. We have at present no explanation for this behavior. For late F stars the chromospheric lines show v sin i dependences similar to those observed for early F stars, again indicating acoustic heating for these layers. We were unable to determine the v sin i dependence of the transition layer lines because of too few single star targets. The decrease of emission line fluxes at the spectral type F5, with steeply decreasing v sin i, indicates, however, a decreasing contribution of magnetohydrodynamic heating for the late F stars. The X-ray emission for the late F stars increases for increasing v sin i, indicating magnetohydrodynamic heating for the coronae of the late F stars, different from the early F stars.

Geophysical investigations of a geothermal anomaly at Wadi Ghadir, eastern Egypt

NASA Technical Reports Server (NTRS)

Morgan, P.; Boulos, F. K.; Hennin, S. F.; El-Sherif, A. A.; El-Sayed, A. A.; Basta, N. Z.; Melek, Y. S.

1984-01-01

During regional heat flow studies a geothermal anomaly was discovered approximately 2 km from the Red Sea coast at Wadi Ghadir, in the Red Sea Hills of Eastern Egypt. A temperature gradient of 55 C/km was measured in a 150 m drillhole at this location, indicating a heat flow of approximately 175 mw/sqm, approximately four times the regional background heat flow for Egypt. Gravity and magnetic data were collected along Wadi Ghadir, and combined with offshore gravity data, to investigate the source of the thermal anomaly. Magnetic anomalies in the profile do not coincide with the thermal anomaly, but were observed to correlate with outcrops of basic rocks. Other regional heat flow and gravity data indicate that the transition from continental to oceanic type lithosphere occurs close to the Red Sea margin, and that the regional thermal anomaly is possibly related to the formation of the Red Sea.

A New Look at the Structural and Magnetic Properties of Potassium Neptunate K2NpO4 Combining XRD, XANES Spectroscopy, and Low-Temperature Heat Capacity.

PubMed

Smith, Anna L; Colineau, Eric; Griveau, Jean-Christophe; Popa, Karin; Kauric, Guilhem; Martin, Philippe; Scheinost, Andreas C; Cheetham, Anthony K; Konings, Rudy J M

2017-05-15

The physicochemical properties of the potassium neptunate K 2 NpO 4 have been investigated in this work using X-ray diffraction, X-ray absorption near edge structure (XANES) spectroscopy at the Np-L 3 edge, and low-temperature heat capacity measurements. A Rietveld refinement of the crystal structure is reported for the first time. The Np(VI) valence state has been confirmed by the XANES data, and the absorption edge threshold of the XANES spectrum has been correlated to the Mössbauer isomer shift value reported in the literature. The standard entropy and heat capacity of K 2 NpO 4 have been derived at 298.15 K from the low-temperature heat capacity data. The latter suggest the existence of a magnetic ordering transition around 25.9 K, most probably of the ferromagnetic type.

Creation of a Data Base on Energetic Materials

DTIC Science & Technology

1987-08-10

Examples of booster explosives are Tetryl, RDX , and HMX . Examples of bursting explosives are Amatols, TNT, Compositions A, B, & C, and Picatrol. Within...Test Thermal Shock Resistance Glass Transition Temperature Toxicity Grain Size Viscosity Hardness Volatility Heat Capacity Water Resistance Heat of...Tensile Strength Flammability Thermal Conductivity Flexural Strength Thermal Expansion Coefficient Gap Test Thermal Shock Resistance Glass Transition

An Experiment in Physical Chemistry: Polymorphism and Phase Stability in Acetaminophen (Paracetamol)

ERIC Educational Resources Information Center

Myrick, Michael L.; Baranowski, Megan; Profeta, Luisa T. M.

2010-01-01

Differential scanning calorimetry analyses of two easily prepared polymorphs of acetaminophen (also known as paracetamol) are recorded. The density of the forms can be found in the literature. Rules for heats of transition, heats of fusion, and density, as well as methods for determining the solid-solid transition temperature between the forms,…

Nanocalorimeter platform for in situ specific heat measurements and x-ray diffraction at low temperature

NASA Astrophysics Data System (ADS)

Willa, K.; Diao, Z.; Campanini, D.; Welp, U.; Divan, R.; Hudl, M.; Islam, Z.; Kwok, W.-K.; Rydh, A.

2017-12-01

Recent advances in electronics and nanofabrication have enabled membrane-based nanocalorimetry for measurements of the specific heat of microgram-sized samples. We have integrated a nanocalorimeter platform into a 4.5 T split-pair vertical-field magnet to allow for the simultaneous measurement of the specific heat and x-ray scattering in magnetic fields and at temperatures as low as 4 K. This multi-modal approach empowers researchers to directly correlate scattering experiments with insights from thermodynamic properties including structural, electronic, orbital, and magnetic phase transitions. The use of a nanocalorimeter sample platform enables numerous technical advantages: precise measurement and control of the sample temperature, quantification of beam heating effects, fast and precise positioning of the sample in the x-ray beam, and fast acquisition of x-ray scans over a wide temperature range without the need for time-consuming re-centering and re-alignment. Furthermore, on an YBa2Cu3O7-δ crystal and a copper foil, we demonstrate a novel approach to x-ray absorption spectroscopy by monitoring the change in sample temperature as a function of incident photon energy. Finally, we illustrate the new insights that can be gained from in situ structural and thermodynamic measurements by investigating the superheated state occurring at the first-order magneto-elastic phase transition of Fe2P, a material that is of interest for magnetocaloric applications.

Particle signatures of magnetic topology at the magnetopause: AMPTE/CCE observations

NASA Technical Reports Server (NTRS)

Fuselier, S. A.; Anderson, B. J.; Onsager, T. G.

1995-01-01

Electron distributions at energies above 50 eV have been found to be a sensitive indicator of magnetic topology for magnetopause crossings of the AMPTE/CCE spacecraft. Progressing from the magnetosheath to the magnetosphere two abrupt transitions occur. First, the magnetosheath electron population directed either parallel or antiparallel to the magnetic field is replaced by a streaming, heated magnetosheath electron population. The other half of the distribution is unchanged. The region with unidirectional, heated magnetosheath electrons is identified as the magnetosheath boundary layer (MSBL). Second, the unheated magnetosheath electron population is replaced by a heated population nearly identical to the population encountered in the MSBL, resulting in a symmetric counterstreaming distribution. The region populated by the bidirectional heated magnetosheath electrons is identified as the low-latitude boundary layer (LLBL). The MSBL and LLBL identified by the electron transitions are the same as the regions identified using ion composition measurements. The magnetosheath-MSBL transition reflects a change in magnetic topology from a solar wind field line to one that threads the magnetopause, and the existence of a magnetosheath-MSBL transition implies that the magnetopause is open. When the current layer is easily identified, the MSBL-LLBL transition coincides with the magnetopause current layer, indicating that the magnetosheath electrons are heated in the current layer. Both magnetosheath-MSBL and MSBL-LLBL transitions are observed for low as well as high magnetic shears. Moreover, the transitions are particularly clear for low shear implying that magnetic topology boundaries are sharp even when abrupt changes in the field and other plasma parameters are absent. Furthermore, for low magnetic shear, solar wind ions with low parallel drift speeds make up the majority of the LLBL population indicating that the magnetosheath plasma has convected directly across the magnetosheath plasma has converted directly across the magnetopause. These observations are consistent with quasi-steady, high-latitude reconnection and indicate that the signatures of this reconnection geometry are commonly present in the subpolar region.

Transitions between three swimming gaits in Paramecium escape.

PubMed

Hamel, Amandine; Fisch, Cathy; Combettes, Laurent; Dupuis-Williams, Pascale; Baroud, Charles N

2011-05-03

Paramecium and other protists are able to swim at velocities reaching several times their body size per second by beating their cilia in an organized fashion. The cilia beat in an asymmetric stroke, which breaks the time reversal symmetry of small scale flows. Here we show that Paramecium uses three different swimming gaits to escape from an aggression, applied in the form of a focused laser heating. For a weak aggression, normal swimming is sufficient and produces a steady swimming velocity. As the heating amplitude is increased, a higher acceleration and faster swimming are achieved through synchronized beating of the cilia, which begin by producing oscillating swimming velocities and later give way to the usual gait. Finally, escape from a life-threatening aggression is achieved by a "jumping" gait, which does not rely on the cilia but is achieved through the explosive release of a group of trichocysts in the direction of the hot spot. Measurements through high-speed video explain the role of trichocysts in defending against aggressions while showing unexpected transitions in the swimming of microorganisms. These measurements also demonstrate that Paramecium optimizes its escape pattern by taking advantage of its inertia.

Transitions between three swimming gaits in Paramecium escape

PubMed Central

Hamel, Amandine; Fisch, Cathy; Combettes, Laurent; Dupuis-Williams, Pascale; Baroud, Charles N.

2011-01-01

Paramecium and other protists are able to swim at velocities reaching several times their body size per second by beating their cilia in an organized fashion. The cilia beat in an asymmetric stroke, which breaks the time reversal symmetry of small scale flows. Here we show that Paramecium uses three different swimming gaits to escape from an aggression, applied in the form of a focused laser heating. For a weak aggression, normal swimming is sufficient and produces a steady swimming velocity. As the heating amplitude is increased, a higher acceleration and faster swimming are achieved through synchronized beating of the cilia, which begin by producing oscillating swimming velocities and later give way to the usual gait. Finally, escape from a life-threatening aggression is achieved by a “jumping” gait, which does not rely on the cilia but is achieved through the explosive release of a group of trichocysts in the direction of the hot spot. Measurements through high-speed video explain the role of trichocysts in defending against aggressions while showing unexpected transitions in the swimming of microorganisms. These measurements also demonstrate that Paramecium optimizes its escape pattern by taking advantage of its inertia. PMID:21464291

Examination of nanosecond laser melting thresholds in refractory metals by shear wave acoustics

NASA Astrophysics Data System (ADS)

Abdullaev, A.; Muminov, B.; Rakhymzhanov, A.; Mynbayev, N.; Utegulov, Z. N.

2017-07-01

Nanosecond laser pulse-induced melting thresholds in refractory (Nb, Mo, Ta and W) metals are measured using detected laser-generated acoustic shear waves. Obtained melting threshold values were found to be scaled with corresponding melting point temperatures of investigated materials displaying dissimilar shearing behavior. The experiments were conducted with motorized control of the incident laser pulse energies with small and uniform energy increments to reach high measurement accuracy and real-time monitoring of the epicentral acoustic waveforms from the opposite side of irradiated sample plates. Measured results were found to be in good agreement with numerical finite element model solving coupled elastodynamic and thermal conduction governing equations on structured quadrilateral mesh. Solid-melt phase transition was handled by means of apparent heat capacity method. The onset of melting was attributed to vanished shear modulus and rapid radial molten pool propagation within laser-heated metal leading to preferential generation of transverse acoustic waves from sources surrounding the molten mass resulting in the delay of shear wave transit times. Developed laser-based technique aims for applications involving remote examination of rapid melting processes of materials present in harsh environment (e.g. spent nuclear fuels) with high spatio-temporal resolution.

Aerodynamic heating in transitional hypersonic boundary layers: Role of second-mode instability

NASA Astrophysics Data System (ADS)

Zhu, Yiding; Chen, Xi; Wu, Jiezhi; Chen, Shiyi; Lee, Cunbiao; Gad-el-Hak, Mohamed

2018-01-01

The evolution of second-mode instabilities in hypersonic boundary layers and its effects on aerodynamic heating are investigated. Experiments are conducted in a Mach 6 wind tunnel using fast-response pressure sensors, fluorescent temperature-sensitive paint, and particle image velocimetry. Calculations based on parabolic stability equations and direct numerical simulations are also performed. It is found that second-mode waves, accompanied by high-frequency alternating fluid compression and expansion, produce intense aerodynamic heating in a small region that rapidly heats the fluid passing through it. As the second-mode waves decay downstream, the dilatation-induced aerodynamic heating decreases while its shear-induced counterpart keeps growing. The latter brings about a second growth of the surface temperature when transition is completed.

Investigation of transition from thermal- to solutal-Marangoni flow in dilute alcohol/water mixtures using nano-plasmonic heaters

NASA Astrophysics Data System (ADS)

Namura, Kyoko; Nakajima, Kaoru; Suzuki, Motofumi

2018-02-01

We experimentally investigated Marangoni flows around a microbubble in diluted 1-butanol/water, 2-propanol/water, and ethanol/water mixtures using the thermoplasmonic effect of gold nanoisland film. A laser spot on the gold nanoisland film acted as a highly localized heat source that was utilized to generate stable air microbubbles with diameters of 32-48 μm in the fluid and to induce a steep temperature gradient on the bubble surface. The locally heated bubble has a flow along the bubble surface, with the flow direction showing a clear transition depending on the alcohol concentrations. The fluid is driven from the hot to cold regions when the alcohol concentration is lower than the transition concentration, whereas it is driven from the cold to hot regions when the concentration is higher than the transition concentration. In addition, the transition concentration increases as the carbon number of the alcohol decreases. The observed flow direction transition is explained by the balance of the thermal- and solutal-Marangoni forces that are cancelled out for the transition concentration. The selective evaporation of the alcohol at the locally heated surface allows us to generate stable and rapid thermoplasmonic solutal-Marangoni flows in the alcohol/water mixtures.

Using a Semiconductor-to-Metal Transition to Control Optical Transmission through Subwavelength Hole Arrays

DOE PAGES

Donev, E. U.; Suh, J. Y.; Lopez, R.; ...

2008-01-01

We describe a simple configuration in which the extraordinary optical transmission effect through subwavelength hole arrays in noble-metal films can be switched by the semiconductor-to-metal transition in an underlying thin film of vanadium dioxide. In these experiments, the transition is brought about by thermal heating of the bilayer film. The surprising reverse hysteretic behavior of the transmission through the subwavelength holes in the vanadium oxide suggest that this modulation is accomplished by a dielectric-matching condition rather than plasmon coupling through the bilayer film. The results of this switching, including the wavelength dependence, are qualitatively reproduced by a transfer matrix model.more » The prospects for effecting a similar modulation on a much faster time scale by using ultrafast laser pulses to trigger the semiconductor-to-metal transition are also discussed.« less

Numerical study of air ingress transition to natural circulation in a high temperature helium loop

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

Franken, Daniel; Gould, Daniel; Jain, Prashant K.

Here, the generation-IV high temperature gas cooled reactors (HTGRs) are designed with many passive safety features, one of which is the ability to passively remove heat under a loss of coolant accident (LOCA). However, several common reactor designs do not prevent against a large break in the coolant system and may therefore experience a depressurized LOCA. This would lead to air entering into the reactor system via several potential modes of ingress: diffusion, gravity currents, and natural circulation. At the onset of a LOCA, the initial rate of air ingress is expected to be very slow because it is governedmore » by molecular diffusion. However, after several hours, natural circulation would commence, thus, bringing the air into the reactor system at a much higher rate. As a consequence, air ingress would cause the high temperature graphite matrix to oxidize, leading to its thermal degradation and decreased passive heat (decay) removal capability. Therefore, it is essential to understand the transition of air ingress from molecular diffusion to natural circulation in an HTGR system. This paper presents results from a computational fluid dynamics (CFD) model to study the air ingress transition behavior. These results are validated against an h-shaped high temperature helium loop experiment. Details are provided to quantitatively predict the transition time from molecular diffusion to natural circulation.« less

Numerical study of air ingress transition to natural circulation in a high temperature helium loop

DOE PAGES

Franken, Daniel; Gould, Daniel; Jain, Prashant K.; ...

2017-09-21

Here, the generation-IV high temperature gas cooled reactors (HTGRs) are designed with many passive safety features, one of which is the ability to passively remove heat under a loss of coolant accident (LOCA). However, several common reactor designs do not prevent against a large break in the coolant system and may therefore experience a depressurized LOCA. This would lead to air entering into the reactor system via several potential modes of ingress: diffusion, gravity currents, and natural circulation. At the onset of a LOCA, the initial rate of air ingress is expected to be very slow because it is governedmore » by molecular diffusion. However, after several hours, natural circulation would commence, thus, bringing the air into the reactor system at a much higher rate. As a consequence, air ingress would cause the high temperature graphite matrix to oxidize, leading to its thermal degradation and decreased passive heat (decay) removal capability. Therefore, it is essential to understand the transition of air ingress from molecular diffusion to natural circulation in an HTGR system. This paper presents results from a computational fluid dynamics (CFD) model to study the air ingress transition behavior. These results are validated against an h-shaped high temperature helium loop experiment. Details are provided to quantitatively predict the transition time from molecular diffusion to natural circulation.« less

Thermal conductivity of Glycerol’s liquid, glass, and crystal states, glass-liquid-glass transition, and crystallization at high pressures

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

Andersson, Ove; Johari, G. P., E-mail: joharig@mcmaster.ca

2016-02-14

To investigate the effects of local density fluctuations on phonon propagation in a hydrogen bonded structure, we studied the thermal conductivity κ of the crystal, liquid, and glassy states of pure glycerol as a function of the temperature, T, and the pressure, p. We find that the following: (i) κ{sub crystal} is 3.6-times the κ{sub liquid} value at 140 K at 0.1 MPa and 2.2-times at 290 K, and it varies with T according to 138 × T{sup −0.95}; (ii) the ratio κ{sub liquid} (p)/κ{sub liquid} (0.1 MPa) is 1.45 GPa{sup −1} at 280 K, which, unexpectedly, is about themore » same as κ{sub crystal} (p)/κ{sub crystal} (0.1 MPa) of 1.42 GPa{sup −1} at 298 K; (iii) κ{sub glass} is relatively insensitive to T but sensitive to the applied p (1.38 GPa{sup −1} at 150 K); (iv) κ{sub glass}-T plots show an enhanced, pressure-dependent peak-like feature, which is due to the glass to liquid transition on heating; (v) continuous heating cold-crystallizes ultraviscous glycerol under pressure, at a higher T when p is high; and (vi) glycerol formed by cooling at a high p and then measured at a low p has a significantly higher κ than the glass formed by cooling at a low p. On heating at a fixed low p, its κ decreases before its glass-liquid transition range at that p is reached. We attribute this effect to thermally assisted loss of the configurational and vibrational instabilities of a glass formed at high p and recovered at low p, which is different from the usual glass-aging effect. While the heat capacity, entropy, and volume of glycerol crystal are less than those for its glass and liquid, κ{sub crystal} of glycerol, like its elastic modulus and refractive index, is higher. We discuss these findings in terms of the role of fluctuations in local density and structure, and the relations between κ and the thermodynamic quantities.« less

Solid-Solid Phase Transition Kinetics of FOX-7

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

Burnham, A K; Weese, R K; Wang, R

Since it was developed in the late 1990s, 1,1-diamino-2,2-dinitroethene (FOX-7), with lower sensitivity and comparable performance to RDX, has received increasing interest. This paper will present our results for the phase changes of FOX-7 using DSC and HFC (Heat Flow Calorimetry). DSC thermal curves recorded at linear heating rates of 0.10, 0.35 and 1.0 C min{sup -1} show two endothermic peaks and two exothermic peaks. The two endothermic peaks represent solid-solid phase transitions, which have been observed in the literature at 114 C ({beta}-{gamma}) and 159 C ({gamma}-{delta}) by both DSC and XPD (X-ray powder diffraction) measurements. The first transitionmore » shifts from 114.5 to 115.8 C as the heating rate increases from 0.10 to 1.0 C min{sup -1}, while the second transition shifts from 158.5 to 160.4 C. Cyclical heating experiments show the endotherms and exotherms for a first heating through the {gamma} phase to the {delta} phase, a cooling and reversion to the {alpha} or {beta} phase, and a second heating to the {gamma} and {delta} phases. The data are interpreted using kinetic models with thermodynamic constraints.« less

Study of Periodical Flow Heat Transfer in an Internal Combustion Engine

NASA Astrophysics Data System (ADS)

Luo, Xi

In-cylinder heat transfer is one of the most critical physical behaviors which has a direct influence on engine out emission and thermal efficiency for IC engine. In-cylinder wall temperature has to be precisely controlled to achieve high efficiency and low emission. However, this cannot be done without knowing gas-to-wall heat flux. This study reports on the development of a technique suitable for engine in-cylinder surface temperature measurement, as the traditional method is "hard to reach." A laser induced phosphorescence technique was used to study in-cylinder wall temperature effects on engine out unburned hydrocarbons during the engine transitional period (warm up). A linear correlation was found between the cylinder wall surface temperature and the unburned hydrocarbons at mediate and high charge densities. At low charge density, no clear correlation was observed because of miss-fire events. A new auto background correction infrared (IR) diagnostic was developed to measure the instantaneous in-cylinder surface temperature at 0.1 CAD resolution. A numerical mechanism was designed to suppress relatively low-frequency background noise and provide an accurate in-cylinder surface temperature measurements with an error of less than 1.4% inside the IC engine. In addition, a proposed optical coating reduced time delay errors by 50% compared to more conventional thermocouple techniques. A new cycle-averaged Res number was developed for an IC engine to capture the characteristics of engine flow. Comparison and scaling between different engine flow parameters are available by matching the averaged Res number. From experimental results, the engine flow motion was classified as intermittently turbulent, and it is different from the original fully developed turbulent assumption, which has previously been used in almost all engine simulations. The intermittent turbulence could have a great impact on engine heat transfer because of the transitional turbulence effect. Engine 3D CFD model further proves the existence of transitional turbulence flow. A new multi zone heat transfer model is proposed for IC engines only. The model includes pressure work effects and improved heat transfer prediction compared to the standard Law of the wall model.

Phase transition in the (Li 0.5-( x/2) K 0.5-( x/2) Cs x) 2SO 4 system

NASA Astrophysics Data System (ADS)

Hamed, A. E.; El-Aziz, Y. M. Abd.; Madi, N. K.; Kassem, M. E.

1995-12-01

Phase transition in the (Li 0.5-( x/2) K 0.5-( x/2) Cs x) 2SO 4 system was studied by measuring the specific heat at constant pressure, C p, as a function of temperature in the temperature range 300-800 K. For non-zero values of X ( X = 0.2%, 0.5%, 1% and 2%) the critical behaviour of the phase transition was found to change considerably compared with that of X = 0 or pure LiKSO 4. The observed change in the phase transition with increase of Cs 2SO 4 content ( X) was accompanied by a decrease in the thermodynamic parameters: the value of the specific heat at the transition point (Δ C P) max, the transition temperature, T1, and the value of the energy of ordering. The results were interpreted within the Landau thermodynamic theory of the phase transition.

Nature of the transition between a ferromagnetic metal and a spin-glass insulator in pyrochlore molybdates.

PubMed

Hanasaki, N; Watanabe, K; Ohtsuka, T; Kézsmárki, I; Iguchi, S; Miyasaka, S; Tokura, Y

2007-08-24

The metal-insulator transition has been investigated for pyrochlore molybdates R(2)Mo(2)O(7) with nonmagnetic rare-earth ions R. The dynamical scaling analysis of ac susceptibility reveals that the geometrical frustration causes the atomic spin-glass state. The reentrant spin-glass phase exists below the ferromagnetic transition. The electronic specific heat is enhanced as compared to the band calculation result, perhaps due to the orbital fluctuation in the half-metallic ferromagnetic state. The large specific heat is rather reduced upon the transition, likely because the short-range antiferromagnetic fluctuation shrinks the Fermi surface.

Water-induced convection in the Earth's mantle transition zone

NASA Astrophysics Data System (ADS)

Richard, Guillaume C.; Bercovici, David

2009-01-01

Water enters the Earth's mantle by subduction of oceanic lithosphere. Most of this water immediately returns to the atmosphere through arc volcanism, but a part of it is expected as deep as the mantle transition zone (410-660 km depth). There, slabs can be deflected and linger before sinking into the lower mantle. Because it lowers the density and viscosity of the transition zone minerals (i.e., wadsleyite and ringwoodite), water is likely to affect the dynamics of the transition zone mantle overlying stagnant slabs. The consequences of water exchange between a floating slab and the transition zone are investigated. In particular, we focus on the possible onset of small-scale convection despite the adverse thermal gradient (i.e., mantle is cooled from below by the slab). The competition between thermal and hydrous effects on the density and thus on the convective stability of the top layer of the slab is examined numerically, including water-dependent density and viscosity and temperature-dependent water solubility. For plausible initial water content in a slab (≥0.5 wt %), an episode of convection is likely to occur after a relatively short time delay (5-20 Ma) after the slab enters the transition zone. However, water induced rheological weakening is seen to be a controlling parameter for the onset time of convection. Moreover, small-scale convection above a stagnant slab greatly enhances the rate of slab dehydration. Small-scale convection also facilitates heating of the slab, which in itself may prolong the residence time of the slab in the transition zone.

Observations of brine plumes below melting Arctic sea ice

NASA Astrophysics Data System (ADS)

Peterson, Algot K.

2018-02-01

In sea ice, interconnected pockets and channels of brine are surrounded by fresh ice. Over time, brine is lost by gravity drainage and flushing. The timing of salt release and its interaction with the underlying water can impact subsequent sea ice melt. Turbulence measurements 1 m below melting sea ice north of Svalbard reveal anticorrelated heat and salt fluxes. From the observations, 131 salty plumes descending from the warm sea ice are identified, confirming previous observations from a Svalbard fjord. The plumes are likely triggered by oceanic heat through bottom melt. Calculated over a composite plume, oceanic heat and salt fluxes during the plumes account for 6 and 9 % of the total fluxes, respectively, while only lasting in total 0.5 % of the time. The observed salt flux accumulates to 7.6 kg m-2, indicating nearly full desalination of the ice. Bulk salinity reduction between two nearby ice cores agrees with accumulated salt fluxes to within a factor of 2. The increasing fraction of younger, more saline ice in the Arctic suggests an increase in desalination processes with the transition to the new Arctic.

Regulation of photochemical energy transfer accompanied by structural changes in thylakoid membranes of heat-stressed wheat.

PubMed

Marutani, Yoko; Yamauchi, Yasuo; Miyoshi, Akihito; Inoue, Kanako; Ikeda, Ken-ichi; Mizutani, Masaharu; Sugimoto, Yukihiro

2014-12-11

Photosystems of higher plants alleviate heat-induced damage in the presence of light under moderate stressed conditions; however, in the absence of light (i.e., in the dark), the same plants are damaged more easily. (Yamauchi and Kimura, 2011) We demonstrate that regulating photochemical energy transfer in heat-treated wheat at 40 °C with light contributed to heat tolerance of the photosystem. Chlorophyll fluorescence analysis using heat-stressed wheat seedlings in light showed increased non-photochemical quenching (NPQ) of chlorophyll fluorescence, which was due to thermal dissipation that was increased by state 1 to state 2 transition. Transmission electron microscopy revealed structural changes in thylakoid membranes, including unstacking of grana regions under heat stress in light. It was accompanied by the phosphorylation of thylakoid proteins such as D1 and D2 proteins and the light harvesting complex II proteins Lhcb1 and Lhcb2. These results suggest that heat stress at 40 °C in light induces state 1 to state 2 transition for the preferential excitation of photosystem I (PSI) by phosphorylating thylakoid proteins more strongly. Structural changes of thylakoid membrane also assist the remodeling of photosystems and regulation of energy distribution by transition toward state 2 probably contributes to plastoquione oxidation; thus, light-driven electrons flowing through PSI play a protective role against PSII damage under heat stress.

Rigid High Temperature Heat-Shrinkable Polyimide Tubes with Functionality as Reducer Couplings

PubMed Central

Kong, Deyan; Xiao, Xinli

2017-01-01

Flexible and semi-rigid heat-shrinkable tubes (HSTs) have been used in thousands of applications, and here rigid high temperature HSTs are reported for the first time. These rigid HSTs are prepared with shape memory polyimides possessing glass transition temperatures (Tgs) from 182 to 295 °C, and the relationships between Tg and their molecular structures are studied. The polyimide HSTs (PIHSTs) can fix expanded diameters and shrink back to original diameters very well, and the mechanisms of their heat-shrinkage performance are discussed. Their differences from commercially available HSTs in heat-shrinkage are also analyzed. They can withstand low temperature of −196 °C, much lower than those of other HSTs. The PIHSTs can also connect subjects of different sizes by heat-shrinkage and then fix them upon cooling like reducer couplings, and the possible mechanisms of their reducer coupling effect are analyzed. With their unique characteristics, PIHSTs will expand the application areas of HSTs enormously. PMID:28317905

Transient Convection Due to Imposed Heat Flux: Application to Liquid-Acquisition Devices

NASA Technical Reports Server (NTRS)

Duval, Walter M. B.; Chato, David J.; Doherty, Michael P.

2014-01-01

A model problem is considered that addresses the effect of heat load from an ambient laboratory environment on the temperature rise of liquid nitrogen inside an enclosure. This model has applications to liquid acquisition devices inside the cryogenic storage tanks used to transport vapor-free propellant to the main engine. We show that heat loads from Q = 0.001 to 10 W, with corresponding Rayleigh numbers from Ra = 109 to 1013, yield a range of unsteady convective states and temperature rise in the liquid. The results show that Q = 1 to 10 W (Ra = 1012 to 1013) yield temperature distributions along the enclosure height that are similar in trend to experimental measurements. Unsteady convection, which shows selfsimilarity in its planforms, is predicted for the range of heat-load conditions. The onset of convection occurs from a free-convection-dominated base flow that becomes unstable against convective instability generated at the bottom of the enclosure while the top of the enclosure is convectively stable. A number of modes are generated with small-scale thermals at the bottom of the enclosure in which the flow selforganizes into two symmetric modes prior to the onset of the propagation of the instability. These symmetric vertical modes transition to asymmetric modes that propagate as a traveling-wave-type motion of convective modes and are representative of the asymptotic convective state of the flow field. Intense vorticity production is created in the core of the flow field due to the fact that there is shear instability between the vertical and horizontal modes. For the higher Rayleigh numbers, 1012 to 1013, there is a transition from a stationary to a nonstationary response time signal of the flow and temperature fields with a mean value that increases with time over various time bands and regions of the enclosure.

Experimental measurements and modeling of convective heat transfer in the transitional rarefied regime

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

Strongrich, Andrew D.; Alexeenko, Alina A.

We present experimental measurements and numerical simulations of convective heat transfer performance in the transitional rarefied regime for an isolated rectangular beam geometry. Experiments were performed using single crystalline silicon beam elements having width-to-thickness aspect ratios of 8.5 and 17.4. Devices were enclosed in a vacuum chamber and heated resistively using a DC power supply. A range of pressures corresponding to Knudsen numbers between 0.096 and 43.2 in terms of device thickness were swept, adjusting applied power to maintain a constant temperature of 50 K above the ambient temperature. Both parasitic electrical resistance associated with the hardware and radiative exchangemore » with the environment were removed from measured data, allowing purely convective heat flux to be extracted. Numerical simulations were carried out deterministically through solution of the Ellipsoidal Statistical Bhatnagar-Gross-Krook collision model of the Boltzmann equation. Results agree with experimental data, revealing a strong coupling between dissipated heat flux and thermal stresses within the flowfield as well as a nonlinear transition between the free-molecule and continuum regimes.« less

Experimental Studies of the Aerothermal Characteristics of the Project Orion CEV heat Shield in High Speed Transitional and Turbulent Flows

NASA Technical Reports Server (NTRS)

Wadhams, T.P.; MacLean, M.; Holden, M.S.; Cassady, A.M.

2009-01-01

An experimental program has been completed by CUBRC exploring laminar, transitional, and turbulent flows over a 7.0% scale model of the Project ORION CEV geometry. This program was executed primarily to answer questions concerning the increase in heat transfer on the windward, or "hot shoulder" of the CEV heat shield from laminar to turbulent flow. To answer these questions CUBRC constructed and instrumented a 14.0 inch diameter Project ORION CEV model and ran a range of Reynolds numbers based on diameter from 1.0 to over 40 million at a Mach number of 8.0. These Reynolds numbers were selected to cover laminar to turbulent heating data on the "hot shoulder". Data obtained during these runs will be used to guide design decisions as they apply to heat shield thickness and extent. Several experiments at higher enthalpies were achieved to obtain data for code validation with real gas effects and transition. CUBRC also performed computation studies of these experiments to aid in the data reduction process and study turbulence modeling.

Motion control in free-standing shape-memory actuators

NASA Astrophysics Data System (ADS)

Belmonte, Alberto; Lama, Giuseppe C.; Cerruti, Pierfrancesco; Ambrogi, Veronica; Fernández-Francos, Xavier; De la Flor, Silvia

2018-07-01

In this work, free-standing shape-memory thermally triggered actuators are developed by laminating ‘thiol-epoxy’-based glassy thermoset (GT) and stretched liquid-crystalline network (LCN) films. A sequential curing process was used to obtain GTs with tailored thermomechanical properties and network relaxation dynamics, and also to assemble the final actuator. The actuation extent, rate and time were studied by varying the GT and the heating rate in thermo-actuation with an experimental approach. The results demonstrate that it is possible to tailor the actuation rate and time by designing GT materials with a glass transition temperature close to that of the liquid-crystalline-to-isotropic phase transition of the LCN, thus making it possible to couple the two processes. Such coupling is also possible in rapid heating processes even when the glass transition temperature of the GT is clearly lower than the isotropization temperature of the LCN, depending on the network relaxation dynamics of the GT and the presence of thermal gradients within the actuators. Interestingly, varying the GT network relaxation dynamics does not affect the actuation extent. As predicted by the analytical model developed in our previous work, the modulus of the GT layer is mainly responsible for the actuation extent. Finally, to demonstrate the enhanced control of the actuation, specifically designed actuators were assembled in a three-dimensional actuating device able to make complex motions (including ‘S-type’ bending). This approach makes it possible to engineer advanced functional materials for application in self-adaptable structures and soft robotics.

Zinc-blende to rocksalt transition in SiC in a laser-heated diamond-anvil cell

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

Daviau, Kierstin; Lee, Kanani K. M.

2017-04-18

We explore the stability of the ambient pressure zinc-blende polymorph (B3) structure of silicon carbide (SiC) at high pressures and temperatures where it transforms to the rocksalt (B1) structure. We find that the transition occurs ~40 GPa lower than previously measured when heated to moderately high temperatures. A lower transition pressure is consistent with the transition pressures predicted in numerous ab initio computations. We find a large volume decrease across the transition of ~17%, with the volume drop increasing at higher formation pressures, suggesting this transition is volume driven yielding a nearly pressure-independent Clapeyron slope. Such a dramatic density increasemore » occurring at pressure is important to consider in applications where SiC is exposed to extreme conditions, such as in industrial applications or planetary interiors.« less

Laminar, Transitional, and Turbulent Heating on Mid Lift-to-Drag Ratio Entry Vehicles

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Hollingsworth, Kevin E.

2012-01-01

The boundary-layer transition characteristics and convective aeroheating levels on mid lift-to-drag ratio entry vehicle configurations have been studied through wind tunnel testing. Several configurations were investigated, including elliptically-blunted cylinders with both circular and elliptically-flattened cross sections, biconic geometries based on launch vehicle dual-use shrouds, and parametrically-optimized analytic geometries. Vehicles of this class have been proposed for high-mass Mars missions, such as sample return and crewed exploration, for which the conventional sphere-cone entry-vehicle geometries of previous Mars missions are insufficient. Testing was conducted at Mach 6 over a range of Reynolds numbers sufficient to generate laminar, transitional, and turbulent flow. Transition onset locations - both straight-line and cross-flow - and heating rates were obtained through global phosphor thermography. Supporting computations were performed to obtain heating rates for comparison with the data. Laminar data and predictions agreed to well within the experimental uncertainty. Fully-turbulent data and predictions also agreed well. However, in transitional flow regions, greater differences were observed. Additional aerodynamic performance data were also generated through Modified-Newtonian analyses of the geometries.

Heating and cooling of the multiply charged ion nonequilibrium plasma in a high-current extended low-inductance discharge

NASA Astrophysics Data System (ADS)

Burtsev, V. A.; Kalinin, N. V.

2014-09-01

Using a radiation magnetohydrodynamics two-temperature model (RMHD model) of a high-current volumetric radiating Z-discharge, the heating and cooling of the nitrogen plasma in a pulsed pinched extended discharge is investigated as applied to the problem of creating a recombination laser based on 3 → 2 transitions of hydrogen-like nitrogen ions (λ = 13.4 nm). It is shown that the power supply of the discharge, which is represented by a dual storage-forming line and a transmission line, makes it possible to raise the power density of the nitrogen plasma to 0.01-1.00 TW/cm3. Accordingly, there arises the possibility of generating a fully ionized (i.e., consisting of bare nuclei and electrons) plasma through the heating (compression) of electrons owing to the self-magnetic field of the plasma current and Joule heat even if the plasma is cooled by its own radiation at this stage. Such a plasma is needed to produce the lasing (active) medium of a recombination laser based on electron transitions in hydrogen-like ions. At the second stage, it is necessary to rapidly and deeply cool the plasma to 20-40 eV for 1-2 ns. Cooling of the fully ionized expanding plasma was numerically simulated with the discharge current switched on and off by means of a switch with a rapidly rising resistance. In both cases, the plasma expansion in the discharge is not adiabatic. Even after the discharge current is fairly rapidly switched off, heating of electrons continues inside the plasma column for a time longer than the switching time. Discharge current switchoff improves the electron cooling efficiency only slightly. Under such conditions, the plasma cools down to 50-60 eV in the former case and to 46-54 eV in the latter case for 2-3 ns.

Convective thinning of the lithosphere - A mechanism for the initiation of continental rifting

NASA Technical Reports Server (NTRS)

Spohn, T.; Schubert, G.

1982-01-01

A model of lithospheric thinning, in which heat is convected to the base and conducted within the lithosphere, is presented. An analytical equation for determinining the amount of thinning attainable on increasing the heat flux from the asthenosphere is derived, and a formula for lithosphere thickness approximations as a function of time is given. Initial and final equilibrium thicknesses, thermal diffusivity, transition temperature profile, and plume temperature profile are all factors considered for performing rate of thinning determinations. In addition, between initial and final equilibrium states, lithospheric thinning occurs at a rate which is inversely proportional to the square root of the time. Finally, uplift resulting from thermal expansion upon lithospheric thinning is on the order of 10 to the 2nd to 10 to the 3rd m.

Gas heating dynamics during leader inception in long air gaps at atmospheric pressure

NASA Astrophysics Data System (ADS)

Liu, Lipeng; Becerra, Marley

2017-08-01

The inception of leader discharges in long air gaps at atmospheric pressure is simulated with a thermo-hydrodynamic model and a detailed kinetic scheme for N2/O2/H2O mixtures. In order to investigate the effect of humidity, the kinetic scheme includes the most important reactions with the H2O molecule and its derivatives, resulting in a scheme with 45 species and 192 chemical reactions. The heating of a thin plasma channel in front of an anode electrode during the streamer to leader transition is evaluated with a detailed 1D radial model. The analysis includes the simulation of the corresponding streamer bursts, dark periods and aborted leaders that may occur prior to the inception of a propagating leader discharge. The simulations are performed using the time-varying discharge current in two laboratory discharge events of positive polarity reported in the literature as input. Excellent agreement between the simulated and the experimental time variation of the thermal radius for a 1 m rod-plate air gap discharge event reported in the literature has been found. The role of different energy transfer and loss mechanisms prior to the inception of a stable leader is also discussed. It is found that although a small percentage of water molecules can accelerate the vibrational-translational relaxation to some extent, this effect leads to a negligible temperature increase during the streamer-to-leader transition. It is also found that the gas temperature should significantly exceed 2000 K for the transition to lead to the inception of a propagating leader. Otherwise, the strong convection loss produced by the gas expansion during the transition causes a drop in the translational temperature below 2000 K, aborting the incepted leader. Furthermore, it is shown that the assumptions used by the widely-used model of Gallimberti do not hold when evaluating the streamer-to-leader transition.

Simultaneous Determination of Glass Transition Temperatures of Several Polymers

PubMed Central

He, Jiang; Liu, Wei; Huang, Yao-Xiong

2016-01-01

Aims A simple and easy optical method is proposed for the determination of glass transition temperature (Tg) of polymers. Methods & Results Tg was determined using the technique of microsphere imaging to monitor the variation of the refractive index of polymer microsphere as a function of temperature. It was demonstrated that the method can eliminate most thermal lag and has sensitivity about six fold higher than the conventional method in Tg determination. So the determined Tg is more accurate and varies less with cooling/heating rate than that obtained by conventional methods. The most attractive character of the method is that it can simultaneously determine the Tg of several polymers in a single experiment, so it can greatly save experimental time and heating energy. Conclusion The method is not only applicable for polymer microspheres, but also for the materials with arbitrary shapes. Therefore, it is expected to be broadly applied to different fundamental researches and practical applications of polymers. PMID:26985670

Influence of repetition frequency on streamer-to-spark breakdown mechanism in transient spark discharge

NASA Astrophysics Data System (ADS)

Janda, M.; Martišovitš, V.; Buček, A.; Hensel, K.; Molnár, M.; Machala, Z.

2017-10-01

Streamer-to-spark transition in a self-pulsing positive transient spark (TS) discharge was investigated at different repetition frequencies. The temporal evolution of the TS was recorded, showing the primary streamer and the secondary streamer phases. A streak camera-like images were obtained using spatio-temporal reconstruction of the discharge emission detected by a photomultiplier tube with light collection system placed on a micrometric translation stage. With increasing TS repetition frequency f (from ~1 to 6 kHz), the increase of the propagation velocity of both the primary and the secondary streamer was observed. Acceleration of the primary and secondary streamers, and shortening of streamer-to-spark transition time τ with increasing f was attributed to the memory effect composed of pre-heating and gas composition changes induced by the previous TS pulses. Fast propagation of the secondary streamer through the entire gap and fast gas heating could explain the short τ (~100 ns) at f above ~3 kHz.

AlMn Transition Edge Sensors for Advanced ACTPol

NASA Technical Reports Server (NTRS)

Li, Dale; Austermann, Jason E.; Beall, James A.; Tucker, Daniel T.; Duff, Shannon M.; Gallardo, Patricio A.; Henderson, Shawn W.; Hilton, Gene C.; Ho, Shuay-Pwu; Hubmayr, Johannes;

AlMn Transition Edge Sensors for Advanced ACTPol

NASA Astrophysics Data System (ADS)

Li, Dale; Austermann, Jason E.; Beall, James A.; Becker, Daniel T.; Duff, Shannon M.; Gallardo, Patricio A.; Henderson, Shawn W.; Hilton, Gene C.; Ho, Shuay-Pwu; Hubmayr, Johannes; Koopman, Brian J.; McMahon, Jeffrey J.; Nati, Federico; Niemack, Michael D.; Pappas, Christine G.; Salatino, Maria; Schmitt, Benjamin L.; Simon, Sara M.; Staggs, Suzanne T.; Van Lanen, Jeff; Ward, Jonathan T.; Wollack, Edward J.

2016-07-01

Advanced ACTPol (AdvACT) will use an array of multichroic polarization-sensitive AlMn transition edge sensor (TES) bolometers read out through time-division multiplexing. Aluminum doped with a low concentration of manganese can be deposited to a bulk film thickness for a more reliable superconducting critical temperature uniformity compared to thin bilayers. To build the TES, the AlMn alloy is deposited, over Nb wiring, to a specific thickness to set the TES normal resistance. The doping concentration of manganese coarsely defines the TES critical temperature, while a fine tuning is achieved by heating the deposited film to a specific temperature. The TES island is connected to the thermal bath via four silicon-nitride membranes, where their geometry defines the thermal conductance to the temperature of the bath. Lastly, the TES heat capacity is increased by addition of PdAu electrically connected to the AlMn film. Designs and performance characteristics of these AlMn TESs are presented for use in AdvACT.

Critical phenomena and chemical potential of a charged AdS black hole

NASA Astrophysics Data System (ADS)

Wei, Shao-Wen; Liang, Bin; Liu, Yu-Xiao

2017-12-01

Inspired by the interpretation of the cosmological constant from the boundary gauge theory, we here treat it as the number of colors N and its conjugate quantity as the associated chemical potential μ in the black hole side. Then the thermodynamics and the chemical potential for a five-dimensional charged AdS black hole are studied. It is found that there exists a small-large black hole phase transition of van der Waals type. The critical phenomena are investigated in the N2-μ chart. The result implies that the phase transition can occur for large number of colors N , while is forbidden for small number. This to some extent implies that the interaction of the system increases with the number. In particular, in the reduced parameter space, all the thermodynamic quantities can be rescaled with the black hole charge such that these reduced quantities are charge-independent. Then we obtain the coexistence curve and the phase diagram. The latent heat is also numerically calculated. Moreover, the heat capacity and the thermodynamic scalar are studied. The result indicates that the information of the first-order black hole phase transition is encoded in the heat capacity and scalar. However, the phase transition point cannot be directly calculated with them. Nevertheless, the critical point linked to a second-order phase transition can be determined by either the heat capacity or the scalar. In addition, we calculate the critical exponents of the heat capacity and the scalar for the saturated small and large black holes near the critical point.

Temperature dependence of laser induced insulator-metal transition in VO2

NASA Astrophysics Data System (ADS)

Wang, Siming; Bar-Ad, Shimshon; Ramirez, Juan Gabriel; Huppert, Dan; Schuller, Ivan K.

2013-03-01

We performed optical pump-probe experiments on VO2 thin films with low laser fluence at temperatures ranging across the insulator-metal transition (IMT). At room temperature, the reflectivity of VO2 increases in the first 400-500 fs when pumped by 150 fs laser pulses. An exponential decay of the reflectivity is observed in the following 1 ps. Interestingly, as the temperature approaches the transition temperature (340 K), the reflectivity shows a second increase on an 80 ps time scale following the exponential decay, indicating an IMT. We propose that the decay of the reflectivity is due to electron-phonon thermalization, which raises the phonon temperature and causes a superheating of the lattice. This process provides the latent heat and induces the IMT on the 80 ps time scale. The coexistence of the insulating and metallic phases is observed in the reflectivity measurements for temperatures above 340 K. This work is supported by the Air Force Office of Scientific Research No. FA9550-12-1-0381.

Simultaneous detection of acoustic emission and Barkhausen noise during the martensitic transition of a Ni-Mn-Ga magnetic shape-memory alloy

NASA Astrophysics Data System (ADS)

Baró, Jordi; Dixon, Steve; Edwards, Rachel S.; Fan, Yichao; Keeble, Dean S.; Mañosa, Lluís; Planes, Antoni; Vives, Eduard

2013-11-01

We present simultaneous measurements of acoustic emission and magnetic Barkhausen noise during the thermally induced martensitic transition in a Ni-Mn-Ga single crystal. The range where structural acoustic emission avalanches are detected extends for more than 50 K for both cooling and heating ramps, with a hysteresis of ˜10 K. The magnetic activity occurs during the structural transition, exhibiting similar hysteresis, but concentrated in the lower half of the temperature range. Statistical analysis of individual signals allows characterization of the broad distributions of acoustic emission and Barkhausen amplitudes. By studying the times of arrival of the avalanche events we detect the existence of correlations between the two kinds of signals, with a number of acoustic emission signals occurring shortly after a Barkhausen signal. The order of magnitude of the observed delays is compatible with the time needed for the propagation of ultrasound through the sample, showing correlation of some of the signals.

Woven heat exchanger

DOEpatents

Piscitella, Roger R.

1987-01-01

In a woven ceramic heat exchanger using the basic tube-in-shell design, each heat exchanger consisting of tube sheets and tube, is woven separately. Individual heat exchangers are assembled in cross-flow configuration. Each heat exchanger is woven from high temperature ceramic fiber, the warp is continuous from tube to tube sheet providing a smooth transition and unitized construction.

Woven heat exchanger

DOEpatents

Piscitella, Roger R.

1987-05-05

In a woven ceramic heat exchanger using the basic tube-in-shell design, each heat exchanger consisting of tube sheets and tube, is woven separately. Individual heat exchangers are assembled in cross-flow configuration. Each heat exchanger is woven from high temperature ceramic fiber, the warp is continuous from tube to tube sheet providing a smooth transition and unitized construction.

Sensitizing effects of gallium citrate on hyperthermic cell killing in vitro.

PubMed

Miyazaki, N; Nakano, H; Kawakami, N; Kugotani, M; Nishihara, K; Aoki, Y; Shinohara, K

2000-01-01

The lethal effects of gallium citrate in combination with heat were studied using four cell lines, L5178Y, FM3A, P388 and HeLa. Cells were incubated with different concentrations (0.2 2 mM) of gallium citrate at 37 degrees C for 24 h and heated at a range of temperatures from 40-44 degrees C for various time periods up to 6 h in the absence of gallium citrate. Survival and cell viability were determined by clonogenic assay and the dye-exclusion test, respectively. All of the cell lines tested were insensitive to heat below 41 degrees C, but were very sensitive to heat above 43 degrees C. Gallium citrate was cytotoxic to these cell lines at different levels: P388 and HeLa were far more sensitive than L5178Y and FM3A. The killing effects of heat at 41 degrees C were greatly enhanced by gallium citrate in L5178Y and P388 cells. The Arrhenius analysis for the lethal effect of heat, determined by clonogenic assay, in L5178Y cells showed that the transition temperature was remarkably decreased for the gallium-treated cells from approximately 43 degrees C to 41 degrees C. The mechanism for this decrease in the transition temperature may be attributable to the additional effects of gallium citrate on energy metabolism. Preincubation with 0.05 mM gallium citrate at 37 degrees C for 7 days also enhanced heat sensitization at 41 degrees C in L5178Y. This preincubation condition may correspond to the condition for the continuous infusion of gallium that is clinically used for cancer treatment. In contrast, treatment with gallium did not greatly enhance the sensitivity of FM3A or HeLa cells to heat at 41 degrees C, but the effects of gallium were significant.

T(sub lambda) Depression by a Heat Current Along the lambda-Line

NASA Technical Reports Server (NTRS)

Liu, Yuanming; Larson, Melora; Iraelsson, Ulf E.

1999-01-01

We report measurements of the depression of the superfluid transition temperature by a heat current (1 less than or = Q less than or = 100 microW/sq cm) along the lambda-line (SVP less than or = P less than or = 21.6 bar). At P = 21.6 bar, measurements were also performed in a reduced gravity (0.2g). Experimental results show that the pressure dependence of the depression and the gravity effect on the measurements are small, in qualitative agreement with theoretical predictions. Keywords: superfluid helium; Lambda transition; heat current

Thermoelectric generator having a resiliently mounted removable thermoelectric module

DOEpatents

Purdy, David L.; Shapiro, Zalman M.; Hursen, Thomas F.; Maurer, Gerould W.

1976-11-02

An electrical generator having an Isotopic Heat Capsule including radioactive fuel rod 21 as a primary heat source and Thermoelectric Modules 41 and 43 as converters. The Biological Shield for the Capsule is suspended from Spiders at each end each consisting of pretensioned rods 237 and 239 defining planes at right angles to each other. The Modules are mounted in cups 171 of transition members 173 of a heat rejection Fin Assembly whose fins 195 and 197 extend from both sides of the transition member 173 for effective cooling.

Influence of phase transition on the instability of a liquid-vapor interface in a gravitational field

NASA Astrophysics Data System (ADS)

Konovalov, V. V.; Lyubimov, D. V.; Lyubimova, T. P.

2017-06-01

This study is concerned with the linear stability of the horizontal interface between thick layers of a viscous heat-conducting liquid and its vapor in a gravitational field subject to phase transition. We consider the case when the hydrostatic base state is consistent with a balanced heat flux at the liquid-vapor interface. The corrections to the growth rate of the most dangerous perturbations and cutoff wave number, characterizing the influence of phase transition on the Rayleigh-Taylor instability, are found to be different from the data in the literature. Most of the previous results were obtained in the framework of a quasiequilibrium approximation, which had been shown to conform to the limit of thin media layers under equality of the interface temperature to a saturation temperature. The main difference from the results obtained with the quasiequilibrium approach is new values of the proportionality coefficients that correlate our corrections with the intensity of weak heating. Moreover, at large values of the heat flux rate, when deviations from the approximate linear law are important, the effect of phase transition is limited and does not exceed the size of the vapor viscosity effect.

A Study of Al-Mn Transition Edge Sensor Engineering for Stability

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

George, E. M.; et al.

2013-11-10

The stability of Al-Mn transition edge sensor (TES) bolometers is studied as we vary the engineered TES transition, heat capacity, and/or coupling between the heat capacity and TES. We present thermal structure measurements of each of the 39 designs tested. The data is accurately fit by a two-body bolometer model, which allows us to extract the basic TES parameters that affect device stability. We conclude that parameters affecting device stability can be engineered for optimal device operation, and present the model parameters extracted for the different TES designs.

Toward a theory of the general-anesthetic-induced phase transition of the cerebral cortex. I. A thermodynamics analogy

NASA Astrophysics Data System (ADS)

Steyn-Ross, Moira L.; Steyn-Ross, D. A.; Sleigh, J. W.; Wilcocks, Lara C.

2001-07-01

In a recent paper the authors developed a stochastic model for the response of the cerebral cortex to a general anesthetic agent. The model predicted that there would be an anesthetic-induced phase change at the point of transition into unconsciousness, manifested as a divergence in the electroencephalogram spectral power, and a change in spectral energy distribution from being relatively broadband in the conscious state to being strongly biased towards much lower frequencies in the unconscious state. Both predictions have been verified in recent clinical measurements. In the present paper we extend the model by calculating the equilibrium distribution function for the cortex, allowing us to establish a correspondence between the cortical phase transition and the more familiar thermodynamic phase transitions. This correspondence is achieved by first identifying a cortical free energy function, then by postulating that there exists an inverse relationship between an anesthetic effect and a quantity we define as cortical excitability, which plays a role analogous to temperature in thermodynamic phase transitions. We follow standard thermodynamic theory to compute a cortical entropy and a cortical ``heat capacity,'' and we investigate how these will vary with anesthetic concentration. The significant result is the prediction that the entropy will decrease discontinuously at the moment of induction into unconsciousness, concomitant with a release of ``latent heat'' which should manifest as a divergence in the analogous heat capacity. There is clear clinical evidence of heat capacity divergence in historical anesthetic-effect measurements performed in 1977 by Stullken et al. [Anesthesiology 46, 28 (1977)]. The discontinuous step change in cortical entropy suggests that the cortical phase transition is analogous to a first-order thermodynamic transition in which the comatose-quiescent state is strongly ordered, while the active cortical state is relatively disordered.

Frustrated magnetism in the tetragonal CoSe analog of superconducting FeSe

NASA Astrophysics Data System (ADS)

Wilfong, Brandon; Zhou, Xiuquan; Vivanco, Hector; Campbell, Daniel J.; Wang, Kefeng; Graf, Dave; Paglione, Johnpierre; Rodriguez, Efrain

2018-03-01

Recently synthesized metastable tetragonal CoSe, isostructural to the FeSe superconductor, offers a new avenue for investigating systems in close proximity to the iron-based superconductors. We present magnetic and transport property measurements on powders and single crystals of CoSe. High field magnetic susceptibility measurements indicate a suppression of the previously reported 10 K ferromagnetic transition with the magnetic susceptibility, exhibiting time dependence below the proposed transition. Dynamic scaling analysis of the time dependence yields a critical relaxation time of τ*=0.064 ±0.008 s which in turn yields activation energy Ea*=14.84 ±0.59 K and an ideal glass temperature T0*=8.91 ±0.09 K from Vogel-Fulcher analysis. No transition is observed in resistivity and specific heat measurements, but both measurements indicate that CoSe is metallic. These results are interpreted on the basis of CoSe exhibiting frustrated magnetic ordering arising from competing magnetic interactions. Arrott analysis of single crystal magnetic susceptibility has indicated the transition temperature occurs in close proximity to previous reports and that the magnetic moment lies solely in the a b plane. The results have implications for understanding the relationship between magnetism and transport properties in the iron chalcogenide superconductors.

Mixture for producing fracture-resistant, fiber-reinforced ceramic material by microwave heating

DOEpatents

Meek, T.T.; Blake, R.D.

1985-04-03

A fracture-resistant, fiber-reinforced ceramic substrate is produced by a method which involves preparing a ceramic precursor mixture comprising glass material, a coupling agent, and resilient fibers, and then exposing the mixture to microwave energy. The microwave field orients the fibers in the resulting ceramic material in a desired pattern wherein heat later generated in or on the substrate can be dissipated in a desired geometric pattern parallel to the fiber pattern. Additionally, the shunt capacitance of the fracture-resistant, fiber-reinforced ceramic substrate is lower which provides for a quicker transit time for electronic pulses in any conducting pathway etched into the ceramic substrate.

Mixture for producing fracture-resistant, fiber-reinforced ceramic material by microwave heating

DOEpatents

Meek, Thomas T.; Blake, Rodger D.

1987-01-01

A fracture-resistant, fiber-reinforced ceramic substrate is produced by a method which involves preparing a ceramic precursor mixture comprising glass material, a coupling agent, and resilient fibers, and then exposing the mixture to microwave energy. The microwave field orients the fibers in the resulting ceramic material in a desired pattern wherein heat later generated in or on the substrate can be dissipated in a desired geometric pattern parallel to the fiber pattern. Additionally, the shunt capacitance of the fracture-resistant, fiber-reinforced ceramic substrate is lower which provides for a quicker transit time for electronic pulses in any conducting pathway etched into the ceramic substrate.

Phase relations of aluminous silica to 120 GPa and lowermost mantle dynamics

NASA Astrophysics Data System (ADS)

Tronnes, R. G.; Andrault, D.; Konopkova, Z.; Morgenroth, W.; Liermann, H.-P.

2012-04-01

Basalts have 3-10 times higher concentrations of Al, Ti, Ca and Na and more than 5 times lower concentration of Mg than peridotite. The resulting lower mantle basaltic mineralogy has no ferropericlase and low proportion of Mg-perovskite and post-perovskite with high Fe/Mg-ratio. Oversaturation of silica and alumina produces separate silica-dominated phases and Al-rich phases (NAL and Ca-ferrite phases). At pressures of 60-100 GPa common basalts crystallize 15-20% CaCl2-structured silica, 15-25% Ca-ferrite, 35-40% Mg-perovskite and 20-30% Ca-perovskite. The Fe-rich Mg-perovskite makes basaltic material denser than peridotite throughout the lower mantle below 720 km depth, with important implications for mantle dynamics. Partial separation of subducted basaltic crust from depleted lithosphere may occur within the strongly heterogeneous D" zone. The silica-dominated phases have considerable solubility of alumina [1]. At 3500-4000 K the transition from the CaCl2-phase to seifertite (a-PbO2-structure) of pure SiO2 occurs at 130-140 GPa, with a dp/dT-slope of about 10 MPa/K [2]. The transition pressure is reduced with Al-saturation. We investigated silica with 4 and 6 wt% alumina to 120 GPa, using LH-DAC at the Extreme Conditions Beamline (P02.2) at PETRA-III, DESY. Powdered glass mixed with 10-15 wt% Pt-powder was compressed and heated in NaCl pressure media in Re-gaskets. To delineate the phase transition, the samples were compressed incrementally with intermittent laser heating. Slow reaction rates required 20-40 min heating at 3500-4000 K for each heating step. The XRD data and pressure estimates were acquired repeatedly during heating and after quenching to room temperature. The first crystallization of seifertite at 3500-4000 K was recorded at about 118 and 108 GPa in samples with 4 and 6 wt% AlO1.5, respectively. The CaCl2-structured silica phase crystallized along with seifertite, consistent with a binary phase loop trending towards lower pressure with increasing Al-content. Due to the presence of the Al-rich Ca-ferrite phase (near the MgAl2O4-NaAlSiO4-join) in natural basaltic compositions, the Al-solubility limits for the silica-dominated phases in basaltic lithologies may be similar to those in the binary system SiO2-AlO1.5. Phase transitions in response to increasing pressure are generally associated with densification. Because of the strong partitioning of light and voluminous AlO1.5 into seifertite, however, the densification effect is more than offset by the lighter alumina component. The unit cell data of ref. [1] indicate a volume increase of about 3.8% associated with the transition. The associated density reduction would be strongly dependent on the substitution mechanism. O-vacancy and cation (3Si4+ → 4Al3+) substitutions yield density reductions of 5.4% and 1.9%, respectively [1]. The large density reduction accompanying the seifertite transition may limit the role of gravitational accretion of evolved MORB to the LLSVPs. Segregation of Fe-rich picritic, komatiitic or peridotitic rocks with no separate silica phase may be more likely. Deep-mantle cumulates and solidified melts of peridotitic to komatiitic composition were mostly produced in the Hadean and early Archean, indicating that the antipodal and near-equatorial LLSVPs, stabilized by Earth's rotation, could also represent ancient structures.

Evaluation of an Early-Warning System for Heat Wave-Related Mortality in Europe: Implications for Sub-seasonal to Seasonal Forecasting and Climate Services.

PubMed

Lowe, Rachel; García-Díez, Markel; Ballester, Joan; Creswick, James; Robine, Jean-Marie; Herrmann, François R; Rodó, Xavier

2016-02-06

Heat waves have been responsible for more fatalities in Europe over the past decades than any other extreme weather event. However, temperature-related illnesses and deaths are largely preventable. Reliable sub-seasonal-to-seasonal (S2S) climate forecasts of extreme temperatures could allow for better short-to-medium-term resource management within heat-health action plans, to protect vulnerable populations and ensure access to preventive measures well in advance. The objective of this study is to assess the extent to which S2S climate forecasts could be incorporated into heat-health action plans, to support timely public health decision-making ahead of imminent heat wave events in Europe. Forecasts of apparent temperature at different lead times (e.g., 1 day, 4 days, 8 days, up to 3 months) were used in a mortality model to produce probabilistic mortality forecasts up to several months ahead of the 2003 heat wave event in Europe. Results were compared to mortality predictions, inferred using observed apparent temperature data in the mortality model. In general, we found a decreasing transition in skill between excellent predictions when using observed temperature, to predictions with no skill when using forecast temperature with lead times greater than one week. However, even at lead-times up to three months, there were some regions in Spain and the United Kingdom where excess mortality was detected with some certainty. This suggests that in some areas of Europe, there is potential for S2S climate forecasts to be incorporated in localised heat-health action plans. In general, these results show that the performance of this climate service framework is not limited by the mortality model itself, but rather by the predictability of the climate variables, at S2S time scales, over Europe.

Dynamically induced many-body localization

NASA Astrophysics Data System (ADS)

Choi, Soonwon; Abanin, Dmitry A.; Lukin, Mikhail D.

2018-03-01

We show that a quantum phase transition from ergodic to many-body localized (MBL) phases can be induced via periodic pulsed manipulation of spin systems. Such a transition is enabled by the interplay between weak disorder and slow heating rates. Specifically, we demonstrate that the Hamiltonian of a weakly disordered ergodic spin system can be effectively engineered, by using sufficiently fast coherent controls, to yield a stable MBL phase, which in turn completely suppresses the energy absorption from external control field. Our results imply that a broad class of existing many-body systems can be used to probe nonequilibrium phases of matter for a long time, limited only by coupling to external environment.

Quantum-to-classical transition and entanglement sudden death in Gaussian states under local-heat-bath dynamics

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

Goyal, Sandeep K.; Ghosh, Sibasish

2010-10-15

Entanglement sudden death (ESD) in spatially separated two-mode Gaussian states coupled to local thermal and squeezed thermal baths is studied by mapping the problem to that of the quantum-to-classical transition. Using Simon's criterion concerning the characterization of classicality in Gaussian states, the time to ESD is calculated by analyzing the covariance matrices of the system. The results for the two-mode system at T=0 and T>0 for the two types of bath states are generalized to n modes, and are shown to be similar in nature to the results for the general discrete n-qubit system.

Charting the Parameter Space of the 21-cm Power Spectrum

NASA Astrophysics Data System (ADS)

Cohen, Aviad; Fialkov, Anastasia; Barkana, Rennan

2018-05-01

The high-redshift 21-cm signal of neutral hydrogen is expected to be observed within the next decade and will reveal epochs of cosmic evolution that have been previously inaccessible. Due to the lack of observations, many of the astrophysical processes that took place at early times are poorly constrained. In recent work we explored the astrophysical parameter space and the resulting large variety of possible global (sky-averaged) 21-cm signals. Here we extend our analysis to the fluctuations in the 21-cm signal, accounting for those introduced by density and velocity, Lyα radiation, X-ray heating, and ionization. While the radiation sources are usually highlighted, we find that in many cases the density fluctuations play a significant role at intermediate redshifts. Using both the power spectrum and its slope, we show that properties of high-redshift sources can be extracted from the observable features of the fluctuation pattern. For instance, the peak amplitude of ionization fluctuations can be used to estimate whether heating occurred early or late and, in the early case, to also deduce the cosmic mean ionized fraction at that time. The slope of the power spectrum has a more universal redshift evolution than the power spectrum itself and can thus be used more easily as a tracer of high-redshift astrophysics. Its peaks can be used, for example, to estimate the redshift of the Lyα coupling transition and the redshift of the heating transition (and the mean gas temperature at that time). We also show that a tight correlation is predicted between features of the power spectrum and of the global signal, potentially yielding important consistency checks.

14 CFR 121.421 - Flight attendants: Initial and transition ground training.

Code of Federal Regulations, 2011 CFR

2011-01-01

... ground training. 121.421 Section 121.421 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... § 121.421 Flight attendants: Initial and transition ground training. (a) Initial and transition ground... equipment and the controls for cabin heat and ventilation. (b) Initial and transition ground training for...

14 CFR 121.421 - Flight attendants: Initial and transition ground training.

Code of Federal Regulations, 2010 CFR

2010-01-01

... ground training. 121.421 Section 121.421 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... § 121.421 Flight attendants: Initial and transition ground training. (a) Initial and transition ground... equipment and the controls for cabin heat and ventilation. (b) Initial and transition ground training for...

Heat transfer investigation of Langley Research Center transition models at a Mach number of 8, volume 2

NASA Technical Reports Server (NTRS)

Matthews, R. K.; Martindale, W. R.; Warmbrod, J. D.; Johnson, C. B.

1972-01-01

The results are presented of a wind tunnel test program to determine aerodynamic heat transfer distributions on delta body and straight body transition models of the space shuttle. Heat transfer rates were determined by the phase-change paint technique on Stycast and RTV models using Tempilag as the surface temperature indicator. The nominal test conditions were: Mach 8, length Reynolds numbers of 5 million and 7.4 million, and angles of attack of 20, 40, and 60 deg. Model details, test conditions, and reduced heat transfer data are included. Data reduction of the phase-change paint photographs was performed by utilizing a new technique.

X-38 Experimental Aeroheating at Mach 10

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Horvath, Thomas J.; Weilmuenster, K. James; Alter, Stephan J.; Merski, N. Ronald

2001-01-01

This report provides an update of the hypersonic aerothermodynamic wind tunnel test program conducted at the NASA Langley Research Center in support of the X-38 program. Global surface heat transfer distributions were measured on 0.0177 and 0.0236 scale models of the proposed X-38 configuration at Mach 10 in air. The parametrics that were investigated primarily include freestream unit Reynolds numbers of 0.6 to 2.2 million per foot and body flap deflections of 15, 20, and 25 deg for an angle-of-attack of 40 deg. The model-scale variance was tested to obtain laminar, transitional, and turbulent heating levels on the defected bodyflaps. In addition, a limited investigation of forced boundary layer transition through the use of discrete roughness elements was performed. Comparisons of the present experimental results to computational predictions and previous experimental data were conducted Laminar, transitional, and turbulent heating levels were observed on the deflected body flap, which compared favorably to the computational results and to the predicted heating based on the flight aerothermodynamic database.

MINIVER: Miniature version of real/ideal gas aero-heating and ablation computer program

NASA Technical Reports Server (NTRS)

Hendler, D. R.

1976-01-01

Computer code is used to determine heat transfer multiplication factors, special flow field simulation techniques, different heat transfer methods, different transition criteria, crossflow simulation, and more efficient thin skin thickness optimization procedure.

Boundary Layer Transition Correlations and Aeroheating Predictions for Mars Smart Lander

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Liechty, Derek S.

2002-01-01

Laminar and turbulent perfect-gas air, Navier-Stokes computations have been performed for a proposed Mars Smart Lander entry vehicle at Mach 6 over a free stream Reynolds number range of 6.9 x 10(exp 6)/m to 2.4 x 10(exp 7)/m (2.1 x 10(exp 6)/ft to 7.3 x 10(exp 6)/ft) for angles-of-attack of 0-deg, 11-deg, 16-deg, and 20-deg, and comparisons were made to wind tunnel heating data obtained a t the same conditions. Boundary layer edge properties were extracted from the solutions and used to correlate experimental data on the effects of heat-shield penetrations (bolt-holes where the entry vehicle would be attached to the propulsion module during transit to Mars) on boundary-layer transition. A non-equilibrium Martian-atmosphere computation was performed for the peak heating point on the entry trajectory in order to determine if the penetrations would produce boundary-layer transition by using this correlation.

Boundary Layer Transition Correlations and Aeroheating Predictions for Mars Smart Lander

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Liechty, Derek S.

2002-01-01

Laminar and turbulent perfect-gas air, Navier-Stokes computations have been performed for a proposed Mars Smart Lander entry vehicle at Mach 6 over a free stream Reynolds number range of 6.9 x 10(exp 6/m to 2.4 x 10(exp 7)m(2.1 x 10(exp 6)/ft to 7.3 x 10(exp 6)ft) for angles-of-attack of 0-deg, 11-deg, 16-deg, and 20-deg, and comparisons were made to wind tunnel heating data obtained at the same conditions. Boundary layer edge properties were extracted from the solutions and used to correlate experimental data on the effects of heat-shield penetrations (bolt-holes where the entry vehicle would be attached to the propulsion module during transit to Mars) on boundary-layer transition. A non-equilibrium Martian-atmosphere computation was performed for the peak heating point on the entry trajectory in order to determine if the penetrations would produce boundary-layer transition by using this correlation.

Role of Halides in the Ordered Structure Transitions of Heated Gold Nanocrystal Superlattices

PubMed Central

2015-01-01

Dodecanethiol-capped gold (Au) nanocrystal superlattices can undergo a surprisingly diverse series of ordered structure transitions when heated (Goodfellow, B. W.; Rasch, M. R.; Hessel, C. M.; Patel, R. N.; Smilgies, D.-M.; Korgel, B. A. Nano Lett.2013, 13, 5710–5714). These are the result of highly uniform changes in nanocrystal size, which subsequently force a spontaneous rearrangement of superlattice structure. Here, we show that halide-containing surfactants play an essential role in these transitions. In the absence of any halide-containing surfactant, superlattices of dodecanethiol-capped (1.9-nm-diameter) Au nanocrystals do not change size until reaching about 190–205 °C, at which point the gold cores coalesce. In the presence of halide-containing surfactant, such as tetraoctylphosphonium bromide (TOPB) or tetraoctylammounium bromide (TOAB), the nanocrystals ripen at much lower temperature and superlattices undergo various ordered structure transitions upon heating. Chloride- and iodide-containing surfactants induce similar behavior, destabilizing the Au–thiol bond and reducing the thermal stability of the nanocrystals. PMID:26013597

Thermal transistor utilizing gas-liquid transition.

PubMed

Komatsu, Teruhisa S; Ito, Nobuyasu

2011-01-01

We propose a simple thermal transistor, a device to control heat current. In order to effectively change the current, we utilize the gas-liquid transition of the heat-conducting medium (fluid) because the gas region can act as a good thermal insulator. The three terminals of the transistor are located at both ends and the center of the system, and are put into contact with distinct heat baths. The key idea is a special arrangement of the three terminals. The temperature at one end (the gate temperature) is used as an input signal to control the heat current between the center (source, hot) and another end (drain, cold). Simulating the nanoscale systems of this transistor, control of heat current is demonstrated. The heat current is effectively cut off when the gate temperature is cold and it flows normally when it is hot. By using an extended version of this transistor, we also simulate a primitive application for an inverter.

Malignant hyperthermia and calcium-induced heat production.

PubMed

Ueda, I; Shinoda, F; Kamaya, H; Krishna, P R

1994-05-01

The abnormal increase in intracellular Ca++ in malignant hyperthermia (MH) is well documented, but the link between the increased Ca++ concentration and high temperature remains speculative. We investigated the possibility that the Ca(++)-induced change in the state of cell membranes may contribute to the temperature elevation. Calcium ion transforms phospholipid membranes from the fluid to solid state. This is analogous to the freezing of water, and liberates latent heat. Differential titration calorimetry (DTC) measures heat production or absorption during ligand binding to macromolecules. When CaCl2 solution was added to anionic dimyristoylphosphatidic acid (DMPA) and dimyristoylphosphatidylglycerol (DMPG) vesicle membranes in incremental doses, DTC showed that the heat production suddenly increased when the Ca++ concentration exceeded about 120 microM. At this Ca++ concentration range, these lipid membranes underwent phase transition. The latent heat of transition was measured by differential scanning calorimetry (DSC). The values were 7.1 +/- 0.7 (SD, n = 4) kcal.mol-1 of DMPA and 6.8 +/- 0.7 (SD, n = 4) kcal.mol-1 of DMPG. The study shows that Ca++ produces heat when bound to lipid membranes. We are not proposing, however, that this is the sole source of heat. We contend that the lipid phase transition is one of the heat sources and it may trigger a hypermetabolic state by elevating the temperature of cell membranes. Because Ca++ is implicated as the second messenger in signal transduction, multiple systems may be involved. More studies are needed to clarify how Ca++ increases body temperature.

Reversible and Irreversible Behavior of Glass-forming Materials from the Standpoint of Hierarchical Dynamical Facilitation

NASA Astrophysics Data System (ADS)

Keys, Aaron

2013-03-01

Using molecular simulation and coarse-grained lattice models, we study the dynamics of glass-forming liquids above and below the glass transition temperature. In the supercooled regime, we study the structure, statistics, and dynamics of excitations responsible for structural relaxation for several atomistic models of glass-formers. Excitations (or soft spots) are detected in terms of persistent particle displacements. At supercooled conditions, we find that excitations are associated with correlated particle motions that are sparse and localized, and the statistics and dynamics of these excitations are facilitated and hierarchical. Excitations at one point in space facilitate the birth and death of excitations at neighboring locations, and space-time excitation structures are microcosms of heterogeneous dynamics at larger scales. Excitation-energy scales grow logarithmically with the characteristic size of the excitation, giving structural-relaxation times that can be predicted quantitatively from dynamics at short time scales. We demonstrate that these same physical principles govern the dynamics of glass-forming systems driven out-of-equilibrium by time-dependent protocols. For a system cooled and re-heated through the glass transition, non-equilibrium response functions, such as heat capacities, are notably asymmetric in time, and the response to melting a glass depends markedly on the cooling protocol by which the glass was formed. We introduce a quantitative description of this behavior based on the East model, with parameters determined from reversible transport data, that agrees well with irreversible differential scanning calorimetry. We find that the observed hysteresis and asymmetric response is a signature of an underlying dynamical transition between equilibrium melts with no trivial spatial correlations and non-equilibrium glasses with correlation lengths that are both large and dependent upon the rate at which the glass is prepared. The correlation length corresponds to the size of amorphous domains bounded by excitations that remain frozen on the observation time scale, thus forming stripes when viewed in space and time. We elucidate properties of the striped phase and show that glasses of this type, traditionally prepared through cooling, can be considered a finite-size realization of the inactive phase formed by the s-ensemble in the space-time thermodynamic limit.

Critical viewpoints on the methods of realizing the metal freezing points of the ITS-90

NASA Astrophysics Data System (ADS)

Ma, C. K.

1995-08-01

The time-honored method for realizing the freezing point tf of a metal (in practice necessarily a dilute alloy) is that of continuous, slow freezing where the plateau temperature (which is the result of solidifying material's being so pure that its phase-transition temperature is observably constant) is measured. The freezing point being an equilibrium temperature, Ancsin considers this method to be inappropriate in principle: equilibrium between the solid and liquid phases cannot be achieved while the solid is being cooled to dispose of the releasing latent heat and while it is accreting at the expense of the liquid. In place of the continuous freezing method he has employed the pulse-heating method (in which the sample is allowed to approach equilibrium after each heat pulse) in his study of Ag; his measurements suggest that freezing can produce non-negligible errors. Here we examine both methods and conclude that the freezing method, employing an inside solid-liquid interface thermally isolated by an outside interface, can provide realizations of the highest accuracy; in either method, perturbation, by inducing solid-liquid phase transition continuously or intermittently, is essential for detecting equilibrium thermally. The respective merits and disadvantages of these two methods and also of the inner-melt method are discussed. We conclude that in a freezing-point measurement what is being measured is in effect the however minutely varying phase transition, and nonconstitutional equilibrium, temperature ti at the solid-liquid interface. The objective is then to measure the ti that is the best measure of tf, which is, normally, the plateau temperature.

Temperature-Controlled High-Speed AFM: Real-Time Observation of Ripple Phase Transitions.

PubMed

Takahashi, Hirohide; Miyagi, Atsushi; Redondo-Morata, Lorena; Scheuring, Simon

2016-11-01

With nanometer lateral and Angstrom vertical resolution, atomic force microscopy (AFM) has contributed unique data improving the understanding of lipid bilayers. Lipid bilayers are found in several different temperature-dependent states, termed phases; the main phases are solid and fluid phases. The transition temperature between solid and fluid phases is lipid composition specific. Under certain conditions some lipid bilayers adopt a so-called ripple phase, a structure where solid and fluid phase domains alternate with constant periodicity. Because of its narrow regime of existence and heterogeneity ripple phase and its transition dynamics remain poorly understood. Here, a temperature control device to high-speed atomic force microscopy (HS-AFM) to observe dynamics of phase transition from ripple phase to fluid phase reversibly in real time is developed and integrated. Based on HS-AFM imaging, the phase transition processes from ripple phase to fluid phase and from ripple phase to metastable ripple phase to fluid phase could be reversibly, phenomenologically, and quantitatively studied. The results here show phase transition hysteresis in fast cooling and heating processes, while both melting and condensation occur at 24.15 °C in quasi-steady state situation. A second metastable ripple phase with larger periodicity is formed at the ripple phase to fluid phase transition when the buffer contains Ca 2+ . The presented temperature-controlled HS-AFM is a new unique experimental system to observe dynamics of temperature-sensitive processes at the nanoscopic level. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transition and Turbulence Modeling for Blunt-Body Wake Flows

NASA Technical Reports Server (NTRS)

Nance, Robert P.; Horvath, Thomas J.; Hassan, H. A.

1997-01-01

Aerobraking has been proposed as an efficient means of decelerating spacecraft for planetary missions. Most current aerobrake designs feature a blunt forebody shielding the payload from the intense heat generated during atmospheric entry. Although this forebody will absorb the largest portion of the heat pulse, accurate prediction of heating in the near wake is of great importance, since large local heating values can occur at points of shear-layer impingement. In order to address the various issues associated with these blunt-body wake flowfields, the Advisory Group for Aerospace Research and Development (AGARD) formed Working Group 18 in 1992. One of the objectives of this activity was to examine real-gas effects in high-speed flow fields around a 70 deg. blunted cone. To date, many researchers have conducted experiments using this geometry in various facilities, such as the Large Energy National Shock (LENS) tunnel at Cubric/Calspan and the HEG shock tunnel at DLR-Goettingen. Several computational studies have also been conducted in concert with these tests. Many of the experimental results have indicated the possible presence of a transitional shear layer through a large increase in heat transfer downstream of the reattachment point. The presence of transition could in fact lead to much higher peak heating than if the separated flow is entirely laminar or turbulent. In the shock-tunnel tests, however, it is difficult to separate such viscous-flow phenomena from real-gas effects. In order to help make this distinction, Horvath et al. recently conducted a set of experiments in the NASA Langley 20-Inch Mach 6 Tunnel, and compared the results to laminar Navier-Stokes calculations. They found heat-transfer distributions similar to those obtained in the high-enthalpy facilities, with the measured peak heating along the sting support markedly greater than that predicted by the laminar computations. These trends point to the need to find transitional and turbulent computational solutions for these flowfields.

Venus: No Breaks from an Extended Childhood

NASA Astrophysics Data System (ADS)

Moore, W. B.; Kankanamge, D. G. J.

2017-05-01

High surface temperatures lead to lower heat flow and lower stress as planets transition out of the heat-pipe mode into subsolidus convection. This causes Venus to miss the window for plate tectonics due to an extended heat-pipe childhood.

Unsteady Heat-Flux Measurements of Second-Mode Instability Waves in a Hypersonic Boundary Layer

NASA Technical Reports Server (NTRS)

Kergerise, Michael A.; Rufer, Shann J.

2016-01-01

In this paper we report on the application of the atomic layer thermopile (ALTP) heat- flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are in agreement with data previously reported in the literature. Heat flux time series, and the Morlet-wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was developed to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

Unsteady heat-flux measurements of second-mode instability waves in a hypersonic flat-plate boundary layer

NASA Astrophysics Data System (ADS)

Kegerise, Michael A.; Rufer, Shann J.

2016-08-01

In this paper, we report on the application of the atomic layer thermopile (ALTP) heat-flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat-plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors, and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are consistent with data previously reported in the literature. Heat flux time series, and the Morlet wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was used to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

The observable signature of late heating of the Universe during cosmic reionization.

PubMed

Fialkov, Anastasia; Barkana, Rennan; Visbal, Eli

2014-02-13

Models and simulations of the epoch of reionization predict that spectra of the 21-centimetre transition of atomic hydrogen will show a clear fluctuation peak, at a redshift and scale, respectively, that mark the central stage of reionization and the characteristic size of ionized bubbles. This is based on the assumption that the cosmic gas was heated by stellar remnants-particularly X-ray binaries-to temperatures well above the cosmic microwave background at that time (about 30 kelvin). Here we show instead that the hard spectra (that is, spectra with more high-energy photons than low-energy photons) of X-ray binaries make such heating ineffective, resulting in a delayed and spatially uniform heating that modifies the 21-centimetre signature of reionization. Rather than looking for a simple rise and fall of the large-scale fluctuations (peaking at several millikelvin), we must expect a more complex signal also featuring a distinct minimum (at less than a millikelvin) that marks the rise of the cosmic mean gas temperature above the microwave background. Observing this signal, possibly with radio telescopes in operation today, will demonstrate the presence of a cosmic background of hard X-rays at that early time.

Ignition, Transition, Flame Spread in Multidimensional Configurations in Microgravity

NASA Technical Reports Server (NTRS)

Kashiwagi, Takashi; Mell, William E.; McGrattan, Kevin B.; Baum, Howard R.; Olson, Sandra L.; Fujita, Osamu; Kikuchi, Masao; Ito, Kenichi

1997-01-01

Ignition of solid fuels by external thermal radiation and subsequent transition to flame spread are processes that not only are of considerable scientific interest but which also have fire safety applications. A material which undergoes a momentary ignition might be tolerable but a material which permits a transition to subsequent flame spread would significantly increase the fire hazard in a spacecraft. Therefore, the limiting condition under which flame cannot spread should be calculated from a model of the transition from ignition instead of by the traditional approach based on limits to a steady flame spread model. However, although the fundamental processes involved in ignition have been suggested there have been no definitive experimental or modeling studies due to the flow motion generated by buoyancy near the heated sample surface. In this study, microgravity experiments which required longer test times such as in air and surface smoldering experiment were conducted in the space shuttle STS-75 flight; shorter experimental tests such as in 35% and 50% oxygen were conducted in the droptower in the Japan Microgravity Center, JAMIC. Their experimental data along with theoretically calculated results from solving numerically the time-dependent Navier-Stokes equations are summarized in this paper.

Temperature decline thermography for laminar-turbulent transition detection in aerodynamics

NASA Astrophysics Data System (ADS)

von Hoesslin, Stefan; Stadlbauer, Martin; Gruendmayer, Juergen; Kähler, Christian J.

2017-09-01

Detailed knowledge about laminar-turbulent transition and heat transfer distribution of flows around complex aerodynamic components are crucial to achieve highest efficiencies in modern aerodynamical systems. Several measurement techniques have been developed to determine those parameters either quantitatively or qualitatively. Most of them require extensive instrumentation or give unreliable results as the boundary conditions are often not known with the required precision. This work introduces the simple and robust temperature decline method to qualitatively detect the laminar-turbulent transition and the respective heat transfer coefficients on a surface exposed to an air flow, according to patent application Stadlbauer et al. (Patentnr. WO2014198251 A1, 2014). This method provides results which are less sensitive to control parameters such as the heat conduction into the blade material and temperature inhomogeneities in the flow or blade. This method was applied to measurements with NACA0018 airfoils exposed to the flow of a calibration-free jet at various Reynolds numbers and angles of attack. For data analysis, a post-processing method was developed and qualified to determine a quantity proportional to the heat transfer coefficient into the flow. By plotting this quantity for each pixel of the surface, a qualitative, two-dimensional heat transfer map was obtained. The results clearly depicted the areas of onset and end of transition over the full span of the model and agreed with the expected behavior based on the respective flow condition. To validate the approach, surface hotfilm measurements were conducted simultaneously on the same NACA profile. Both techniques showed excellent agreement. The temperature decline method allows to visualize laminar-turbulent transitions on static or moving parts and can be applied on a very broad range of scales—from tiny airfoils up to large airplane wings.

MSFR TRU-burning potential and comparison with an SFR

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

Fiorina, C.; Cammi, A.; Franceschini, F.

2013-07-01

The objective of this work is to evaluate the Molten Salt Fast Reactor (MSFR) potential benefits in terms of transuranics (TRU) burning through a comparative analysis with a sodium-cooled FR. The comparison is based on TRU- and MA-burning rates, as well as on the in-core evolution of radiotoxicity and decay heat. Solubility issues limit the TRU-burning rate to 1/3 that achievable in traditional low-CR FRs (low-Conversion-Ratio Fast Reactors). The softer spectrum also determines notable radiotoxicity and decay heat of the equilibrium actinide inventory. On the other hand, the liquid fuel suggests the possibility of using a Pu-free feed composed onlymore » of Th and MA (Minor Actinides), thus maximizing the MA burning rate. This is generally not possible in traditional low-CR FRs due to safety deterioration and decay heat of reprocessed fuel. In addition, the high specific power and the lack of out-of-core cooling times foster a quick transition toward equilibrium, which improves the MSFR capability to burn an initial fissile loading, and makes the MSFR a promising system for a quick (i.e., in a reactor lifetime) transition from the current U-based fuel cycle to a novel closed Th cycle. (authors)« less

Towards a predictive thermal explosion model for energetic materials

NASA Astrophysics Data System (ADS)

Yoh, Jack J.; McClelland, Matthew A.; Maienschein, Jon L.; Wardell, Jeffrey F.

2005-01-01

We present an overview of models and computational strategies for simulating the thermal response of high explosives using a multi-physics hydrodynamics code, ALE3D. Recent improvements to the code have aided our computational capability in modeling the behavior of energetic materials systems exposed to strong thermal environments such as fires. We apply these models and computational techniques to a thermal explosion experiment involving the slow heating of a confined explosive. The model includes the transition from slow heating to rapid deflagration in which the time scale decreases from days to hundreds of microseconds. Thermal, mechanical, and chemical effects are modeled during all phases of this process. The heating stage involves thermal expansion and decomposition according to an Arrhenius kinetics model while a pressure-dependent burn model is employed during the explosive phase. We describe and demonstrate the numerical strategies employed to make the transition from slow to fast dynamics. In addition, we investigate the sensitivity of wall expansion rates to numerical strategies and parameters. Results from a one-dimensional model show that violence is influenced by the presence of a gap between the explosive and container. In addition, a comparison is made between 2D model and measured results for the explosion temperature and tube wall expansion profiles.

Complex magnetic behaviour and evidence of a superspin glass state in the binary intermetallic compound Er5Pd2

NASA Astrophysics Data System (ADS)

Sharma, Mohit K.; Yadav, Kavita; Mukherjee, K.

2018-05-01

The binary intermetallic compound Er5Pd2 has been investigated using dc and ac magnetic susceptibilities, magnetic memory effect, isothermal magnetization, non-linear dc susceptibility, heat capacity and magnetocaloric effect studies. Interestingly, even though the compound does not show geometrical frustration it undergoes glassy magnetic phase transition below 17.2 K. Investigation of dc magnetization and heat capacity data divulged absence of long-ranged magnetic ordering. Through the magnetic memory effect, time dependent magnetization and ac susceptibility studies it was revealed that the compound undergoes glass-like freezing below 17.2 K. Analysis of frequency dependence of this transition temperature through scaling and Arrhenius law; along with the Mydosh parameter indicate, that the dynamics in Er5Pd2 are due to the presence of strongly interacting superspins rather than individual spins. This phase transition was further investigated by non-linear dc susceptibility and was characterized by static critical exponents γ and δ. Our results indicate that this compound shows the signature of superspin glass at low temperature. Additionally, both conventional and inverse magnetocaloric effect was observed with a large value of magnetic entropy change and relative cooling power. Our results suggest that Er5Pd2 can be classified as a superspin glass system with large magnetocaloric effect.

Woven heat exchanger

DOEpatents

Piscitella, R.R.

1984-07-16

This invention relates to a heat exchanger for waste heat recovery from high temperature industrial exhaust streams. In a woven ceramic heat exchanger using the basic tube-in-shell design, each heat exchanger consisting of tube sheets and tube, is woven separately. Individual heat exchangers are assembled in cross-flow configuration. Each heat exchanger is woven from high temperature ceramic fiber, the warp is continuous from tube to tube sheet providing a smooth transition and unitized construction.

Constraints on active region coronal heating properties from observations and modeling of chromospheric, transition region, and coronal emission

NASA Astrophysics Data System (ADS)

Testa, P.; Polito, V.; De Pontieu, B.; Carlsson, M.; Reale, F.; Allred, J. C.; Hansteen, V. H.

2017-12-01

We investigate coronal heating properties in active region cores in non-flaring conditions, using high spatial, spectral, and temporal resolution chromospheric/transition region/coronal observations coupled with detailed modeling. We will focus, in particular, on observations with the Interface Region Imaging Spectrograph (IRIS), joint with observations with Hinode (XRT and EIS) and SDO/AIA. We will discuss how these observations and models (1D HD and 3D MHD, with the RADYN and Bifrost codes) provide useful diagnostics of the coronal heating processes and mechanisms of energy transport.

Impact of wall hydrophobicity on condensation flow and heat transfer in silicon microchannels

NASA Astrophysics Data System (ADS)

Fang, Chen; Steinbrenner, Julie E.; Wang, Fu-Min; Goodson, Kenneth E.

2010-04-01

While microchannel condensation has been the subject of several recent studies, the critical impact of wall hydrophobicity on the microchannel condensation flow has received very little attention. The paper experimentally studies steam condensation in a silicon microchannel 286 µm in hydraulic diameter with three different wall hydrophobicities. It is found that the channel surface wettability has a significant impact on the flow pattern, pressure drop and heat transfer characteristic. Spatial flow pattern transition is observed in both hydrophobic and hydrophilic channels. In the hydrophobic channel, the transition from dropwise/slugwise flow to plug flow is induced by the slug instability. In the hydrophilic channel, the flow transition is characterized by the periodic bubble detachment, a process in which pressure evolution is found important. Local temperature measurement is conducted and heat flux distribution in the microchannel is reconstructed. For the same inlet vapor flux and temperature, the hydrophobic microchannel yields higher heat transfer rate and pressure drop compared to the hydrophilic channel. The difference is attributed to the distinction in flow pattern and heat transfer mechanism dictated by the channel hydrophobicity. This study highlights the importance of the channel hydrophobicity control for the optimization of the microchannel condenser.

Numerical Simulations of the Boundary Layer Transition Flight Experiment

NASA Technical Reports Server (NTRS)

Tang, Chun Y.; Trumble, Kerry A.; Campbell, Charles H.; Lessard, Victor R.; Wood, William A.

2010-01-01

Computational Fluid Dynamics (CFD) simulations were used to study the possible effects that the Boundary Layer Transition (BLT) Flight Experiments may have on the heating environment of the Space Shuttle during its entry to Earth. To investigate this issue, hypersonic calculations using the Data-Parallel Line Relaxation (DPLR) and Langley Aerothermodynamic Upwind Relaxation (LAURA) CFD codes were computed for a 0.75 tall protuberance at flight conditions of Mach 15 and 18. These initial results showed high surface heating on the BLT trip and the areas surrounding the protuberance. Since the predicted peak heating rates would exceed the thermal limits of the materials selected to construct the BLT trip, many changes to the geometry were attempted in order to reduce the surface heat flux. The following paper describes the various geometry revisions and the resulting heating environments predicted by the CFD codes.

Quantitative analysis of the local phase transitions induced by the laser heating

DOE PAGES

Levlev, Anton V.; Susner, Michael A.; McGuire, Michael A.; ...

2015-11-04

Functional imaging enabled by scanning probe microscopy (SPM) allows investigations of nanoscale material properties under a wide range of external conditions, including temperature. However, a number of shortcomings preclude the use of the most common material heating techniques, thereby limiting precise temperature measurements. Here we discuss an approach to local laser heating on the micron scale and its applicability for SPM. We applied local heating coupled with piezoresponse force microscopy and confocal Raman spectroscopy for nanoscale investigations of a ferroelectric-paraelectric phase transition in the copper indium thiophosphate layered ferroelectric. Bayesian linear unmixing applied to experimental results allowed extraction of themore » Raman spectra of different material phases and enabled temperature calibration in the heated region. Lastly, the obtained results enable a systematic approach for studying temperature-dependent material functionalities in heretofore unavailable temperature regimes.« less

Hybrid microwave/conventionally heated calorimeter

NASA Astrophysics Data System (ADS)

Binner, Jon G. P.; Price, Duncan M.; Reading, Mike; Vaidhyanathan, Bala

2005-06-01

The design and construction of a calorimeter in which the specimen may be heated by microwave radiation and/or hot air is described. The apparatus was used to examine the effect of microwave radiation on the melting of benzil (89°C) and the solid-state phase transition of silver iodide (147°C). Reproducibility of transition temperature determinations were within ±1°C. No changes were observed for benzil but silver iodide exhibited an apparent reduction in transition temperature to around 120°C in the presence of microwaves, which increased with the level of microwave irradiation.

Heat Transfer in Conical Corner and Short Superelliptical Transition Ducts

NASA Technical Reports Server (NTRS)

Poinsatte, Philip; Thurman, Douglas; Hippensteele, Steven

2008-01-01

Local surface heat transfer measurements were experimentally mapped using a transient liquid-crystal heat-transfer technique on the surface of two circular-to-rectangular transition ducts. One has a transition cross section defined by conical corners (Duct 1) and the other by an elliptical equation with changing coefficients (Duct 2). Duct 1 has a length-to-diameter ratio of 0.75 and an exit plane aspect ratio of 1.5. Duct 2 has a length-to-diameter ratio of 1.0 and an exit plane aspect ratio of 2.9. Test results are reported for various inlet-diameter-based Reynolds numbers ranging from 0.45 106 to 2.39 106 and two freestream turbulence intensities of about 1 percent, which is typical of wind tunnels, and up to 16 percent, which may be more typical of real engine conditions.

Light-Induced Temperature Transitions in Biodegradable Polymer and Nanorod Composites**

PubMed Central

Hribar, Kolin C.; Metter, Robert B.; Ifkovits, Jamie L.; Troxler, Thomas

2010-01-01

Shape-memory materials (including polymers, metals, and ceramics) are those that are processed into a temporary shape and respond to some external stimuli (e.g., temperature) to undergo a transition back to a permanent shape.[1, 2] Shape memory polymers are finding use in a range of applications from aerospace to fabrics, to biomedical devices and microsystem components.[3–5] For many applications, it would be beneficial to initiate heating with an external trigger (e.g., transdermal light exposure). In this work, we formulated composites of gold nanorods (<1% by volume) and biodegradable networks, where exposure to infrared light induced heating and consequently, shape transitions. The heating is repeatable and tunable based on nanorod concentration and light intensity and the nanorods did not alter the cytotoxicity or in vivo tissue response to the networks. PMID:19408258

Nanocalorimeter platform for in situ specific heat measurements and x-ray diffraction at low temperature

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

Willa, K.; Diao, Z.; Campanini, D.

Recent advances in electronics and nanofabrication have enabled membrane-based nanocalorimetry for measurements of the specific heat of microgram-sized samples. We have integrated a nanocalorimeter platform into a 4.5 T split-pair vertical-field magnet to allow for the simultaneous measurement of the specific heat and x-ray scattering in magnetic fields and at temperatures as low as 4 K. This multi-modal approach empowers researchers to directly correlate scattering experiments with insights from thermodynamic properties including structural, electronic, orbital, and magnetic phase transitions. The use of a nanocalorimeter sample platform enables numerous technical advantages: precise measurement and control of the sample temperature, quantification ofmore » beam heating effects, fast and precise positioning of the sample in the x-ray beam, and fast acquisition of x-ray scans over a wide temperature range without the need for time-consuming re-centering and re-alignment. Furthermore, on an YBa2Cu3O7-delta crystal and a copper foil, we demonstrate a novel approach to x-ray absorption spectroscopy by monitoring the change in sample temperature as a function of incident photon energy. Finally, we illustrate the new insights that can be gained from in situ structural and thermodynamic measurements by investigating the superheated state occurring at the first-order magneto-elastic phase transition of Fe2P, a material that is of interest for magnetocaloric applications.« less

Quantitative method for measuring heat flux emitted from a cryogenic object

DOEpatents

Duncan, Robert V.

1993-01-01

The present invention is a quantitative method for measuring the total heat flux, and of deriving the total power dissipation, of a heat-fluxing object which includes the steps of placing an electrical noise-emitting heat-fluxing object in a liquid helium bath and measuring the superfluid transition temperature of the bath. The temperature of the liquid helium bath is thereafter reduced until some measurable parameter, such as the electrical noise, exhibited by the heat-fluxing object or a temperature-dependent resistive thin film in intimate contact with the heat-fluxing object, becomes greatly reduced. The temperature of the liquid helum bath is measured at this point. The difference between the superfluid transition temperature of the liquid helium bath surrounding the heat-fluxing object, and the temperature of the liquid helium bath when the electrical noise emitted by the heat-fluxing object becomes greatly reduced, is determined. The total heat flux from the heat-fluxing object is determined as a function of this difference between these temperatures. In certain applications, the technique can be used to optimize thermal design parameters of cryogenic electronics, for example, Josephson junction and infra-red sensing devices.

Quantitative method for measuring heat flux emitted from a cryogenic object

DOEpatents

Duncan, R.V.

1993-03-16

The present invention is a quantitative method for measuring the total heat flux, and of deriving the total power dissipation, of a heat-fluxing object which includes the steps of placing an electrical noise-emitting heat-fluxing object in a liquid helium bath and measuring the superfluid transition temperature of the bath. The temperature of the liquid helium bath is thereafter reduced until some measurable parameter, such as the electrical noise, exhibited by the heat-fluxing object or a temperature-dependent resistive thin film in intimate contact with the heat-fluxing object, becomes greatly reduced. The temperature of the liquid helum bath is measured at this point. The difference between the superfluid transition temperature of the liquid helium bath surrounding the heat-fluxing object, and the temperature of the liquid helium bath when the electrical noise emitted by the heat-fluxing object becomes greatly reduced, is determined. The total heat flux from the heat-fluxing object is determined as a function of this difference between these temperatures. In certain applications, the technique can be used to optimize thermal design parameters of cryogenic electronics, for example, Josephson junction and infrared sensing devices.

Transient lattice contraction in the solid-to-plasma transition

PubMed Central

Ferguson, Ken R.; Bucher, Maximilian; Gorkhover, Tais; Boutet, Sébastien; Fukuzawa, Hironobu; Koglin, Jason E.; Kumagai, Yoshiaki; Lutman, Alberto; Marinelli, Agostino; Messerschmidt, Marc; Nagaya, Kiyonobu; Turner, Jim; Ueda, Kiyoshi; Williams, Garth J.; Bucksbaum, Philip H.; Bostedt, Christoph

2016-01-01

In condensed matter systems, strong optical excitations can induce phonon-driven processes that alter their mechanical properties. We report on a new phenomenon where a massive electronic excitation induces a collective change in the bond character that leads to transient lattice contraction. Single large van der Waals clusters were isochorically heated to a nanoplasma state with an intense 10-fs x-ray (pump) pulse. The structural evolution of the nanoplasma was probed with a second intense x-ray (probe) pulse, showing systematic contraction stemming from electron delocalization during the solid-to-plasma transition. These findings are relevant for any material in extreme conditions ranging from the time evolution of warm or hot dense matter to ultrafast imaging with intense x-ray pulses or, more generally, any situation that involves a condensed matter-to-plasma transition. PMID:27152323

Polar Kerr Effect from Time-Reversal Symmetry Breaking in the Heavy-Fermion Superconductor PrOs4Sb12

NASA Astrophysics Data System (ADS)

Levenson-Falk, E. M.; Schemm, E. R.; Aoki, Y.; Maple, M. B.; Kapitulnik, A.

2018-05-01

We present polar Kerr effect measurements of the filled skutterudite superconductor PrOs4 Sb12 . Simultaneous ac susceptibility measurements allow us to observe the superconducting transition under the influence of heating from the optical beam. A nonzero Kerr angle θK develops below the superconducting transition, saturating at ˜300 nrad at low temperatures. This result is repeated across several measurements of multiple samples. By extrapolating the measured θK(T ) to zero optical power, we are able to show that the Kerr angle onset temperature in one set of measurements is consistent with the transition to the B phase at TC 2. We discuss the possible explanations for this result and its impact on the understanding of multiphase and inhomogeneous superconductivity in PrOs4 Sb12 .

The gabbro-eclogite phase transition and the elevation of mountain belts on Venus

NASA Astrophysics Data System (ADS)

Namiki, Noriyuki; Solomon, Sean C.

1992-12-01

Among the four mountain belts surrounding Lakshmi Planum, Maxwell Montes is the highest and stands up to 11 km above the mean planetary radius and 7 km above Lakshmi Planum. The bulk composition and radioactive heat production of the crust on Venus, where measured, are similar to those of terrestrial tholeiitic basalt. Because the thickness of the low-density crust may be limited by the gabbro-garnet granulite-eclogite phase transitions, the 7-11 km maximum elevation of Maxwell Montes is difficult to understand except in the unlikely situation that the crust contains a large volume of magma. A possible explanation is that the base of the crust is not in phase equilibrium. It has been suggested that under completely dry conditions, the gabbro-eclogite phase transition takes place by solid-state diffusion and may require a geologically significant time to run to completion. Solid-state diffusion is a strongly temperature-dependent process. In this paper we solve the thermal evolution of the mountain belt to attempt to constrain the depth of the gabbro-eclogite transition and thus to assess this hypothesis quantitatively. The one-dimensional heat equation is solved numerically by a finite difference approximation. The deformation of the horizontally shortening crustal and mantle portions of the thermal boundary layer is assumed to occur by pure shear, and therefore the vertical velocity is given by the product of the horizontal strain rate and depth.

The gabbro-eclogite phase transition and the elevation of mountain belts on Venus

NASA Technical Reports Server (NTRS)

Namiki, Noriyuki; Solomon, Sean C.

1992-01-01

Among the four mountain belts surrounding Lakshmi Planum, Maxwell Montes is the highest and stands up to 11 km above the mean planetary radius and 7 km above Lakshmi Planum. The bulk composition and radioactive heat production of the crust on Venus, where measured, are similar to those of terrestrial tholeiitic basalt. Because the thickness of the low-density crust may be limited by the gabbro-garnet granulite-eclogite phase transitions, the 7-11 km maximum elevation of Maxwell Montes is difficult to understand except in the unlikely situation that the crust contains a large volume of magma. A possible explanation is that the base of the crust is not in phase equilibrium. It has been suggested that under completely dry conditions, the gabbro-eclogite phase transition takes place by solid-state diffusion and may require a geologically significant time to run to completion. Solid-state diffusion is a strongly temperature-dependent process. In this paper we solve the thermal evolution of the mountain belt to attempt to constrain the depth of the gabbro-eclogite transition and thus to assess this hypothesis quantitatively. The one-dimensional heat equation is solved numerically by a finite difference approximation. The deformation of the horizontally shortening crustal and mantle portions of the thermal boundary layer is assumed to occur by pure shear, and therefore the vertical velocity is given by the product of the horizontal strain rate and depth.

Design and Testing of an Automated System using Thermochromatic Liquid Crystals to Determine Local Heat Transfer Coefficients for an Impinging Jet

NASA Technical Reports Server (NTRS)

Tan, Benjamin

1995-01-01

Using thermochromatic liquid crystal to measure surface temperature, an automated transient method with time-varying free-stream temperature is developed to determine local heat transfer coefficients. By allowing the free-stream temperature to vary with time, the need for complicated mechanical components to achieve a step temperature change is eliminated, and by using the thermochromatic liquid crystals as temperature indicators, the labor intensive task of installing many thermocouples is omitted. Bias associated with human perception of the transition of the thermochromatic liquid crystal is eliminated by using a high speed digital camera and a computer. The method is validated by comparisons with results obtained by the steady-state method for a circular Jet impinging on a flat plate. Several factors affecting the accuracy of the method are evaluated.

Free-stream turbulence and concave curvature effects on heated, transitional boundary layers

NASA Technical Reports Server (NTRS)

Kim, J.; Simon, T. W.

1991-01-01

An experimental investigation of the transition process on flat-plate and concave curved-wall boundary layers for various free-stream turbulence levels was performed. Results show that for transition of a flat-plate, the two forms of boundary layer behavior, identified as laminar-like and turbulent-like, cannot be thought of as separate Blasius and fully-turbulent profiles, respectively. Thus, simple transition models in which the desired quantity is assumed to be an average, weighted on intermittency, of the theoretical laminar and fully turbulent values is not expected to be successful. Deviation of the flow identified as laminar-like from theoretical laminar behavior is shown to be due to recovery after the passage of a turbulent spot, while deviation of the flow identified as turbulent-like from the full-turbulent values is thought to be due to incomplete establishment of the fully-turbulent power spectral distribution. Turbulent Prandtl numbers for the transitional flow, computed from measured shear stress, turbulent heat flux and mean velocity and temperature profiles, were less than unity. For the curved-wall case with low free-stream turbulence intensity, the existence of Gortler vortices on the concave wall within both laminar and turbulent flows was established using liquid crystal visualization and spanwise velocity and temperature traverses. Transition was found to occur via a vortex breakdown mode. The vortex wavelength was quite irregular in both the laminar and turbulent flows, but the vortices were stable in time and space. The upwash was found to be more unstable, with higher levels of u' and u'v', and lower skin friction coefficients and shape factors. Turbulent Prandtl numbers, measured using a triple-wire probe, were found to be near unity for all post-transitional profiles, indicating no gross violation of Reynolds analogy. No evidence of streamwise vortices was seen in the high turbulence intensity case.

Simplified Approach to Predicting Rough Surface Transition

NASA Technical Reports Server (NTRS)

Boyle, Robert J.; Stripf, Matthias

2009-01-01

Turbine vane heat transfer predictions are given for smooth and rough vanes where the experimental data show transition moving forward on the vane as the surface roughness physical height increases. Consiste nt with smooth vane heat transfer, the transition moves forward for a fixed roughness height as the Reynolds number increases. Comparison s are presented with published experimental data. Some of the data ar e for a regular roughness geometry with a range of roughness heights, Reynolds numbers, and inlet turbulence intensities. The approach ta ken in this analysis is to treat the roughness in a statistical sense , consistent with what would be obtained from blades measured after e xposure to actual engine environments. An approach is given to determ ine the equivalent sand grain roughness from the statistics of the re gular geometry. This approach is guided by the experimental data. A roughness transition criterion is developed, and comparisons are made with experimental data over the entire range of experimental test co nditions. Additional comparisons are made with experimental heat tran sfer data, where the roughness geometries are both regular as well a s statistical. Using the developed analysis, heat transfer calculatio ns are presented for the second stage vane of a high pressure turbine at hypothetical engine conditions.

Fabrication of carbon nanotube films from alkyne-transition metal complexes

DOEpatents

Iyer, Vivekanantan S [Delft, NL; Vollhardt, K Peter C. [Oakland, CA

2007-08-28

A simple method for the production or synthesis of carbon nanotubes as free-standing films or nanotube mats by the thermal decomposition of transition metal complexed alkynes with aryl, alkyl, alkenyl, or alkynyl substituents. In particular, transition metal (e.g. Co, Ni, Fe, Mo) complexes of diarylacetylenes, e.g. diphenylacetylene, and solid mixtures of these complexes with suitable, additional carbon sources are heated in a vessel. More specifically, the heating of the transition metal complex is completed at a temperature between 400-800.degree. C. and more particularly 550-700.degree. C. for between 0.1 to 24 hours and more particularly 0.5-3 hours in a sealed vessel under a partial pressure of argon or helium.

Chain Breakage in the Supercooled Liquid - Liquid Transition and Re-entry of the λ-transition in Sulfur.

PubMed

Zhang, Linji; Ren, Yang; Liu, Xiuru; Han, Fei; Evans-Lutterodt, Kenneth; Wang, Hongyan; He, Yali; Wang, Junlong; Zhao, Yong; Yang, Wenge

2018-03-14

Amorphous sulfur was prepared by rapid compression of liquid sulfur at temperatures above the λ-transition for to preserve the high-temperature liquid structure. We conducted synchrotron high-energy X-ray diffraction and Raman spectroscopy to diagnose the structural evolution of amorphous sulfur from room temperature to post-λ-transition temperature. Discontinuous changes of the first and second peaks in atomic pair-distribution-function, g(r), were observed during the transition from amorphous to liquid sulfur. The average first-neighbor coordination numbers showed an abrupt drop from 1.92 to 1.81. The evolution of the chain length clearly shows that the transition was accompanied by polymeric chains breaking. Furthermore, a re-entry of the λ-transition structure was involved in the heating process. The amorphous sulfur, which inherits the post-λ-transition structure from its parent melts, transformed to the pre-λ-transition liquid structure at around 391 K. Upon further heating, the pre-λ-transition liquid transformed to a post-λ-transition structure through the well-known λ-transition process. This discovery offers a new perspective on amorphous sulfur's structural inheritance from its parent liquid and has implications for understanding the structure, evolution and properties of amorphous sulfur and its liquids.

Transient and asymptotic behavior in a regular network model for the ice-albedo feedback under thermal forcing

NASA Astrophysics Data System (ADS)

Mueller-Stoffels, M.; Wackerbauer, R.

2010-12-01

The Arctic ocean and sea ice form a feedback system which plays an important role in the global climate. Variations of the global ice and snow distribution have a significant effect on the planetary albedo which governs the absorption of shortwave radiation. The complexity of highly parametrized GCMs makes it very difficult to assess single feedback processes in the climate system without the concurrent use of simple models where the physics are understood [1][2][3]. We introduce a complex systems model to investigate thermodynamic feedback processes in an Arctic ice-ocean layer. The ice-ocean layer is represented as a regular network of coupled cells. The state of each cell is determined by its energy content, which also defines the phase of the cell. The energy transport between cells is described with nonlinear and heterogeneous diffusion constants. And the time-evolution of the ice-ocean is driven by shortwave, longwave and lateral oceanic and atmospheric thermal forcing. This model is designed to study the stability of an ice cover under various heat intake scenarios. The network structure of the model allows to easily introduce albedo heterogeneities due to aging ice, wind blown snow cover, and ice movement to explore the time-evolution and pattern formation (melt ponds) processes in the Arctic sea ice. The solely thermodynamic model exhibits two stable states; one in the perennially ice covered domain and one in the perennially open water domain. Their existence is due to the temperature dependence of the longwave radiative budget. Transition between these states can be forced via lateral heat fluxes. During the transition from the ice covered to the open water stable state the ice albedo feedback effects are manifested as an increased warming rate of the ice cover together with enhanced seasonal energy oscillations. In the current model realization seasonal ice cover is present as a transient state only. Furthermore, the model exhibits hysteresis between the ice covered and the open water state when varying the lateral atmospheric (or oceanic) heat intake. Once the ice-ocean layer has transitioned from the ice covered to the open water stable state significant cooling (reduction of lateral fluxes) is necessary to return to the ice covered stable state. We also find that ocean heat fluxes are more efficient than atmospheric heat fluxes to melt Arctic sea ice; only small portions of heat entering from the bottom of the ice-ocean layer induce already a transition to the stable asymptotic state with perennial open water. This indicates that ocean currents, understood as heat conveyors, can play a significant role in melting continuous ice covers. This is consistent with the findings of Shimada et al. for the Canada basin [4]. References: [1] S. Bony et al., How well do we understand and evaluate climate change feedback processes?, J of Climate 19, 3445 (2006). [2]I. Eisenman and J.S. Wettlaufer, Nonlinear threshold behavior during the loss of Arctic sea ice, PNAS 106, 28 (2009). [3]A.S. Thorndike, A Toy Model Linking Atmospheric and Thermal Radiation and Sea Ice Growth, JGR 97, 9401 (1992). [4] K. Shimada et al., Paci[|#12#|]c Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean, GRL 33, L08605 (2006).

Aragonite→calcite transformation studied by EPR of Mn 2+ ions

NASA Astrophysics Data System (ADS)

Lech, J.; Śl|zak, A.

1989-05-01

The irreversible transformation aragonite→calcite has been studied both at different fixed heating rates (5, 10, 15 and 20 K/min) and at different fixed temperatures. Apparent progression rates of the transformation were observed above 685 K. At 730 K the transformation became sudden and violent. Time developments of the transformation at fixed temperatures have been discussed in terms of Avrami-Lichti's approach to transitions involving nucleation processes.

NUMERICAL SIMULATIONS OF CORONAL HEATING THROUGH FOOTPOINT BRAIDING

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

Hansteen, V.; Pontieu, B. De; Carlsson, M.

2015-10-01

Advanced three-dimensional (3D) radiative MHD simulations now reproduce many properties of the outer solar atmosphere. When including a domain from the convection zone into the corona, a hot chromosphere and corona are self-consistently maintained. Here we study two realistic models, with different simulated areas, magnetic field strength and topology, and numerical resolution. These are compared in order to characterize the heating in the 3D-MHD simulations which self-consistently maintains the structure of the atmosphere. We analyze the heating at both large and small scales and find that heating is episodic and highly structured in space, but occurs along loop-shaped structures, andmore » moves along with the magnetic field. On large scales we find that the heating per particle is maximal near the transition region and that widely distributed opposite-polarity field in the photosphere leads to a greater heating scale height in the corona. On smaller scales, heating is concentrated in current sheets, the thicknesses of which are set by the numerical resolution. Some current sheets fragment in time, this process occurring more readily in the higher-resolution model leading to spatially highly intermittent heating. The large-scale heating structures are found to fade in less than about five minutes, while the smaller, local, heating shows timescales of the order of two minutes in one model and one minutes in the other, higher-resolution, model.« less

Variability of absorption heat pump efficiency for domestic water heating and space heating based on time-weighted bin analysis

DOE PAGES

Ally, Moonis Raza; Sharma, Vishaldeep

2017-11-02

Natural gas-driven absorption heat pumps are under renewed scrutiny as a viable technology for space conditioning and water heating for residential and commercial applications because of natural gas production trends, pricing, and the speculation that it might be a “bridge fuel” in the global transition towards energy sustainability. Since any level of natural gas combustion contributes to atmospheric carbon dioxide accumulation, the merits of natural gas consuming absorption technology are re-examined in this paper from the point of view of expected efficiency throughout the United States using a time-weighted bin temperature analysis. Such analyses are necessary because equipment standards formore » rated performance is restricted to one set ambient condition, whereas in actual practice, the absorption heat pump (AHP) must perform over a considerably wider range of external conditions, where its efficiency may be vastly different from that at the rated condition. Quantification of variation in efficiency and system performance are imperative to address how to provide the desired utility with the least environmental impact. In this paper, we examine limiting features in absorption heat pumps and relate it to systemic performances in sixteen cities across all eight climate zones in the U.S, each containing fifteen bin temperatures. The results indicate that the true expectation of performance of an AHP is significantly less than what might be optimized for the rated condition. Statistical measures of the variation in water heating COPs show that for most cities, the COP at the rated conditions is outside the 95% Confidence Interval. Moreover, it is concluded that deployment of absorption heat pump water heaters (AHPWH) may be restricted geographically by outdoor temperature constraints.« less

Variability of absorption heat pump efficiency for domestic water heating and space heating based on time-weighted bin analysis

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

Ally, Moonis Raza; Sharma, Vishaldeep

Natural gas-driven absorption heat pumps are under renewed scrutiny as a viable technology for space conditioning and water heating for residential and commercial applications because of natural gas production trends, pricing, and the speculation that it might be a “bridge fuel” in the global transition towards energy sustainability. Since any level of natural gas combustion contributes to atmospheric carbon dioxide accumulation, the merits of natural gas consuming absorption technology are re-examined in this paper from the point of view of expected efficiency throughout the United States using a time-weighted bin temperature analysis. Such analyses are necessary because equipment standards formore » rated performance is restricted to one set ambient condition, whereas in actual practice, the absorption heat pump (AHP) must perform over a considerably wider range of external conditions, where its efficiency may be vastly different from that at the rated condition. Quantification of variation in efficiency and system performance are imperative to address how to provide the desired utility with the least environmental impact. In this paper, we examine limiting features in absorption heat pumps and relate it to systemic performances in sixteen cities across all eight climate zones in the U.S, each containing fifteen bin temperatures. The results indicate that the true expectation of performance of an AHP is significantly less than what might be optimized for the rated condition. Statistical measures of the variation in water heating COPs show that for most cities, the COP at the rated conditions is outside the 95% Confidence Interval. Moreover, it is concluded that deployment of absorption heat pump water heaters (AHPWH) may be restricted geographically by outdoor temperature constraints.« less

Unique Signatures of Population III Stars in the Global 21-cm Signal

NASA Astrophysics Data System (ADS)

Mirocha, Jordan; Mebane, Richard H.; Furlanetto, Steven R.; Singal, Krishma; Trinh, Donald

2018-05-01

We investigate the effects of Population III stars on the sky-averaged 21-cm background radiation, which traces the collective emission from all sources of ultraviolet and X-ray photons before reionization is complete. While UV photons from Pop III stars can in principle shift the onset of radiative coupling of the 21-cm transition - and potentially reionization - to early times, we find that the remnants of Pop III stars are likely to have a more discernible impact on the 21-cm signal than Pop III stars themselves. The X-rays from such sources preferentially heat the IGM at early times, which elongates the epoch of reheating and results in a more gradual transition from an absorption signal to emission. This gradual heating gives rise to broad, asymmetric wings in the absorption signal, which stand in contrast to the relatively sharp, symmetric signals that arise in models treating Pop II sources only. A stronger signature of Pop III, in which the position of the absorption minimum becomes inconsistent with Pop II-only models, requires extreme star-forming events that may not be physically plausible, lending further credence to predictions of relatively high frequency absorption troughs, νmin ˜ 100 MHz. As a result, though the trough location alone may not be enough to indicate the presence of Pop III, the asymmetric wings should arise even if only a few Pop III stars form in each halo before the transition to Pop II star formation occurs, provided that the Pop III IMF is sufficiently top-heavy and at least some Pop III stars form in binaries.

2D Micro-XAS mapping in Diamond Anvil Cell: Application for Post-Spinel Transition

NASA Astrophysics Data System (ADS)

Leonid, D.; Narygina, O.; Kantor, I.; Pascarelli, S.; Aquilanti, G.; Munoz, M.

2007-12-01

Energy Dispersive X-ray Absorption Spectroscopy (EDXAS) is a now a well-established method which has been applied to a broad range of applications. The advantages of an energy dispersive spectrometer, that features no movement of optics during acquisition leading to an enhanced stability of energy scale, spot size and position, combined with a micron sized spot and the option of fluorescence detection, has made it possible to address 2- dimensional mapping with micron resolution on heterogeneous samples, providing full XAS information on each pixel. It is worth noting that due to the absence of mechanical scanning of the monochromator, the spatial resolution is not affected by the energy scan and remains fixed to the dimensions of the probe. In addition, the energy scale is preserved. Moreover, the dwell time per pixel is short enough to make it practically possible to acquire 100 x 100 pixel images in a few hours. We tested 2D mapping in transmission mode to perform "in-situ" investigations in the diamond anvil cell. Maps of redox and speciation at extreme conditions of pressure and temperature yield information on possible phase transitions and/or chemical reactions that occur at P and T conditions in the Earth interiors. As test sample, we chose a major component of Earth's transition zone, ringwoodite [γ-(Mg,Fe)2SiO4]. Sample synthesized in large-volume press at 19 GPa and 1700 C from natural olivine (Mg0.88,Fe0.12)2SiO4 was polished, loaded into the DAC, compressed to desire pressure, and laser-heated. We aquired Fe K-edge XANES maps at different pressures, up to ~ 40 GPa, before and after laser heating, covering for each map an area of 200 x 200 m2 at 5 m resolution. We found that laser heating does not result in re-distribution of iron between heated and non-heated areas. Within precision of measurements there are no detectable changes in iron oxidation state upon decomposition of ringwoodite in to silicate perovskite and magnesowüstite. We also observe that iron preferably partitioning in to magnesowüstite.

A 4.43 Ga Transition from Mega-impact to Habitability Deduced from Microstructural Geochronology of Martian Zircon and Baddeleyite

NASA Astrophysics Data System (ADS)

Moser, D.; Reinhard, D. A.; Larson, D. J.; McCubbin, F. M.; Darling, J.; White, L. F.; Arcuri, G.; Irving, A. J.; Tait, K.; Barker, I.

2017-12-01

The rates at which early planetary surfaces like those of Mars and Earth transitioned to stability within the heavy bombardment epoch are poorly constrained. Here we show through analysis of the shock history of the earliest mineral remnants of Mars crust, specifically the accessory and highly refractory phases zircon and baddeleyite in martian meteorites, that the transition for Mars was relatively rapid and early. The Moon-sized impactor widely believed to have generated the martian hemispheric dichotomy, would have caused catastrophic heating, impact metamorphism and global re-surfacing by magma.This process would either destroy any primordial accessory phases through melting and vaporization, or impart micro- or nano-structural signatures of ultra-high temperature and/or pressure metamorphism on survivor crystals. We have conducted atom probe and/or correlative electron microscopy on intensely shocked and heated zircon and baddeleyite reference samples from Earth and the Moon, as well as from 4.43 Ga grains occurring as crystals and in lithic clasts in six polished surfaces of the Rabt Sbayta suite of martian polymict regolith breccias (NWA 7475, NWA 7034, NWA 7906, Rabt Sbayta 003). The martian population (n=68) shows no micro- or nano-signatures of ultra high temperature or pressure metamorphism. Instead, it exhibits mostly low-grade shock and thermal features consistent with regolith formation at 1.5 Ga and recent low pressure ( 5GPa) launch to Earth. Taken together with the time for decay of the mega-impact heat effects, as well as the 4.50 Ga age estimate for martian mantle solidification (modelled by other workers) our results indicate an early, 70 million year long transition from initiation of the hemispheric dichotomy to establishment of at least one domain of persistently stable and potentially habitable crust. The accelerated deep mantle convection prompted by mega-impact may have also increased the transport rate of volatiles to the Martian exterior during this transition, permitting the inference that early, planet-shaping impacts may ultimately promote habitability pathways in planetary systems.

Ultrafast Dynamics in Vanadium Dioxide: Separating Spatially Segregated Mixed Phase Dynamics in the Time-domain

NASA Astrophysics Data System (ADS)

Hilton, David

2011-10-01

In correlated electronic systems, observed electronic and structural behavior results from the complex interplay between multiple, sometimes competing degrees-of- freedom. One such material used to study insulator-to-metal transitions is vanadium dioxide, which undergoes a phase transition from a monoclinic-insulating phase to a rutile-metallic phase when the sample is heated to 340 K. The major open question with this material is the relative influence of this structural phase transition (Peirels transition) and the effects of electronic correlations (Mott transition) on the observed insulator-to-metal transition. Answers to these major questions are complicated by vanadium dioxide's sensitivity to perturbations in the chemical structure in VO2. For example, related VxOy oxides with nearly a 2:1 ratio do not demonstrate the insulator-to- metal transition, while recent work has demonstrated that W:VO2 has demonstrated a tunable transition temperature controllable with tungsten doping. All of these preexisting results suggest that the observed electronic properties are exquisitely sensitive to the sample disorder. Using ultrafast spectroscopic techniques, it is now possible to impulsively excite this transition and investigate the photoinduced counterpart to this thermal phase transition in a strongly nonequilibrium regime. I will discuss our recent results studying the terahertz-frequency conductivity dynamics of this photoinduced phase transition in the poorly understood near threshold temperature range. We find a dramatic softening of the transition near the critical temperature, which results primarily from the mixed phase coexistence near the transition temperature. To directly study this mixed phase behavior, we directly study the nucleation and growth rates of the metallic phase in the parent insulator using non-degenerate optical pump-probe spectroscopy. These experiments measure, in the time- domain, the coexistent phase separation in VO2 (spatially separated insulator and metal islands) and, more importantly, their dynamic evolution in response to optical excitation.

Transition between free, mixed and forced convection

NASA Astrophysics Data System (ADS)

Jaeger, W.; Trimborn, F.; Niemann, M.; Saini, V.; Hering, W.; Stieglitz, R.; Pritz, B.; Fröhlich, J.; Gabi, M.

2017-07-01

In this contribution, numerical methods are discussed to predict the heat transfer to liquid metal flowing in rectangular flow channels. A correct representation of the thermo-hydraulic behaviour is necessary, because these numerical methods are used to perform design and safety studies of components with rectangular channels. Hence, it must be proven that simulation results are an adequate representation of the real conditions. Up to now, the majority of simulations are related to forced convection of liquid metals flowing in circular pipes or rod bundle, because these geometries represent most of the components in process engineering (e.g. piping, heat exchanger). Open questions related to liquid metal heat transfer, among others, is the behaviour during the transition of the heat transfer regimes. Therefore, this contribution aims to provide useful information related to the transition from forced to mixed and free convection, with the focus on a rectangular flow channel. The assessment of the thermo-hydraulic behaviour under transitional heat transfer regimes is pursued by means of system code simulations, RANS CFD simulations, LES and DNS, and experimental investigations. Thereby, each of the results will compared to the others. The comparison of external experimental data, DNS data, RANS data and system code simulation results shows that the global heat transfer can be consistently represented for forced convection in rectangular flow channels by these means. Furthermore, LES data is in agreement with RANS CFD results for different Richardson numbers with respect to temperature and velocity distribution. The agreement of the simulation results among each other and the hopefully successful validation by means of experimental data will fosters the confidence in the predicting capabilities of numerical methods, which can be applied to engineering application.

Shuttle ascent and shock impingement aerodynamic heating studies

NASA Technical Reports Server (NTRS)

Lanning, W. D.; Hung, F. T.

1971-01-01

The collection and analysis of aerodynamic heating data obtained from shock impingement experimental investigation were completed. The data were categorized into four interference areas; fin leading edge, wing/fuselage fin/plate corners, and space shuttle configurations. The effects of shock impingement were found to increase the heating rates 10 to 40 times the undisturbed values. A test program was completed at NASA/Langley Research Center to investigate the magnitudes and surface patterns of the mated shock interference flowfield. A 0.0065 scale thin-skin model of the MDAC 256-20 space shuttle booster mated with a Stycast model of the MDAC Internal tank orbiter was tested in the 20-inch M=6 tunnel, the 31-inch M=10 tunnel, and the 48-inch Unitary Plan Tunnel. The gap region of the ascent configuration was the principal area of interest where both thermocouple and phase-change paint data were obtained. Pressure and heat transfer distributions data on the leeward surface of a 75-degree sweep slab delta wing are presented. The effects of surface roughness on boundary layer transition and aerodynamic heating were investigated.

Thermophysical Properties of Solid and Liquid Ti-6Al-4V (TA6V) Alloy

NASA Astrophysics Data System (ADS)

Boivineau, M.; Cagran, C.; Doytier, D.; Eyraud, V.; Nadal, M.-H.; Wilthan, B.; Pottlacher, G.

2006-03-01

Ti-6Al-4V (TA6V) titanium alloy is widely used in industrial applications such as aeronautic and aerospace due to its good mechanical properties at high temperatures. Experiments on two different resistive pulse heating devices (CEA Valduc and TU-Graz) have been carried out in order to study thermophysical properties (such as electrical resistivity, volume expansion, heat of fusion, heat capacity, normal spectral emissivity, thermal diffusivity, and thermal conductivity) of both solid and liquid Ti-6Al-4V. Fast time-resolved measurements of current, voltage, and surface radiation and shadowgraphs of the volume have been undertaken. At TU-Graz, a fast laser polarimeter has been used for determining the emissivity of liquid Ti-6Al-4V at 684.5 nm and a differential scanning calorimeter (DSC) for measuring the heat capacity of solid Ti-6Al-4V. This study deals with the specific behavior of the different solid phase transitions (effect of heating rate) and the melting region, and emphasizes the liquid state ( T > 2000 K).

Oxidation and alpha-case formation in Ti–6Al–2Sn–4Zr–2Mo alloy

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

Gaddam, Raghuveer, E-mail: raghuveer.gaddam@ltu.se; Sefer, Birhan; Pederson, Robert

2015-01-15

Isothermal heat treatments in ambient air were performed on wrought Ti–6Al–2Sn–4Zr–2Mo (Ti-6242) material at 500, 593 and 700°C for times up to 500 h. In the presence of oxygen at elevated temperatures simultaneous reactions occurred in Ti-6242 alloy, which resulted in the formation of an oxide scale and a layer with higher oxygen concentration (termed as alpha-case). Total weight gain analysis showed that there was a transition in the oxidation kinetics. At 500°C, the oxidation kinetics obeyed a cubic relationship up to 200 h and thereafter changed to parabolic at prolonged exposure times. At 593°C, it followed a parabolic relationship.more » After heat treatment at 700°C, the oxidation obeyed a parabolic relationship up to 200 h and thereafter changed to linear at prolonged exposure times. The observed transition is believed to be due to the differences observed in the oxide scale. The activation energy for parabolic oxidation was estimated to be 157 kJ/mol. In addition, alpha-case layer was evaluated using optical microscope, electron probe micro-analyser and microhardness tester. The thickness of the alpha-case layer was found to be a function of temperature and time, increasing proportionally, and following a parabolic relationship. The activation energy for the formation of alpha-case layer was estimated to be 153 kJ/mol. - Highlights: • Transition in oxidation kinetics was observed in Ti–6Al–2Sn–4Zr–2Mo alloy in the temperature range 500–700°C. • The activation energy for parabolic oxidation and for alpha-case formation is about 157 kJ/mol and 153 kJ/mol. • Thickness of alpha-case layer estimated by optical microscopy and electron probe microanalysis is comparable.« less

Evidence for the role of turbulence-induced poloidal flow shear in triggering the L-H transition

NASA Astrophysics Data System (ADS)

Yu, C. X.; Xu, Y. H.; Jiang, Y.; Luo, J. R.; Mao, J. S.; Liu, B. H.; Li, J. G.

1999-11-01

We have studied the role of turbulence-driven Reynolds stress induced poloidal flow shear in triggering the L-H transition induced by turbulent heating (TH) on HT-6M tokamak. This improved confinement regime has a set of features similar to that of H-mode are commonly observed in large tokamaks. The time evolution indicates that V_θ begins to evolve 0.1ms prior to the change in Er which precedes any measurable change in local confinement characteristics. The measurements of the turbulence-driven Reynolds stress S shows that S and its gradient in the edge region evolve sharply after the start of the TH pulse. Moreover, the time evolution and the temporal structure of the poloidal velocity computed from the measured Reynolds stress profile and the directly measured V_θ look remarkably similar. The time behavior and magnitude of the Reynolds stress-induced-V_θ B_φ term are also found to be in good correlation with that of the measured E_r. These results suggest that the turbulence-driven Reynolds stress might be the dominant mechanism to generate the poloidal flow shear which causes the rapid changes in Er and its shear to trigger the transition.

Measuring temperature induced phase change kinetics in subcutaneous fatty tissues using near infrared spectroscopy, magnetic resonance imaging and optical coherence tomography (Conference Presentation)

NASA Astrophysics Data System (ADS)

Sajjadi, Amir Y.; Carp, Stefan A.; Manstein, Dieter

2017-02-01

Monitoring phase transition in adipose tissue and formation of lipid crystals is important in Cryo-procedures such as cryosurgery or Selective Cryolipolysis (SC). In this work, we exploited a Near-Infrared Spectroscopy (NIRS) method to monitor the onset of fat freezing/melting. Concurrent measurements using frequency domain NIRS and MR Spectroscopy during cooling/heating were performed on an in vitro porcine skin sample with a thick subcutaneous fat layer in a human MR scanner. The NIRS probe was placed on the skin measuring the average optical scattering of the fatty layer. Two fiber optic temperature probes were inserted in the area of the MRS and NIRS measurements. To further investigate the microscopic features of the phase-transition, an identical cooling/heating procedure was replicated on the same fat tissue while being imaged by Optical Coherence Tomography. The temperature relationships of optical scattering, MRS peak characteristics and OCT reflection intensity were analyzed to find signatures related to the onset of phase transition. The optical scattering in the fatty tissues decreases during the heating and increases by cooling. However, there is an inflexion in the rate of change of the scattering while the phase transition happens in the fatty layer. The methylene fat peaks on the MR Spectrum are also shown to be broadened during the cooling. OCT intensity displays a sharp increase at the transition temperature. The results from multiple samples show two transition points around 5-10 ˚C (cooling) and 15-20 ˚C (heating) through all three methods, demonstrating that adipose tissue phase change can be monitored non-invasively.

Light masking of circadian rhythms of heat production, heat loss, and body temperature in squirrel monkeys

NASA Technical Reports Server (NTRS)

Robinson, E. L.; Fuller, C. A.

1999-01-01

Whole body heat production (HP) and heat loss (HL) were examined to determine their relative contributions to light masking of the circadian rhythm in body temperature (Tb). Squirrel monkey metabolism (n = 6) was monitored by both indirect and direct calorimetry, with telemetered measurement of body temperature and activity. Feeding was also measured. Responses to an entraining light-dark (LD) cycle (LD 12:12) and a masking LD cycle (LD 2:2) were compared. HP and HL contributed to both the daily rhythm and the masking changes in Tb. All variables showed phase-dependent masking responses. Masking transients at L or D transitions were generally greater during subjective day; however, L masking resulted in sustained elevation of Tb, HP, and HL during subjective night. Parallel, apparently compensatory, changes of HL and HP suggest action by both the circadian timing system and light masking on Tb set point. Furthermore, transient HL increases during subjective night suggest that gain change may supplement set point regulation of Tb.

Accessing thermoplastic processing windows in metallic glasses using rapid capacitive discharge

PubMed Central

Kaltenboeck, Georg; Harris, Thomas; Sun, Kerry; Tran, Thomas; Chang, Gregory; Schramm, Joseph P.; Demetriou, Marios D.; Johnson, William L.

2014-01-01

The ability of the rapid-capacitive discharge approach to access optimal viscosity ranges in metallic glasses for thermoplastic processing is explored. Using high-speed thermal imaging, the heating uniformity and stability against crystallization of Zr35Ti30Cu7.5Be27.5 metallic glass heated deeply into the supercooled region is investigated. The method enables homogeneous volumetric heating of bulk samples throughout the entire supercooled liquid region at high rates (~105 K/s) sufficient to bypass crystallization throughout. The crystallization onsets at temperatures in the vicinity of the “crystallization nose” were identified and a Time-Temperature-Transformation diagram is constructed, revealing a “critical heating rate” for the metallic glass of ~1000 K/s. Thermoplastic process windows in the optimal viscosity range of 100–104 Pa·s are identified, being confined between the glass relaxation and the eutectic crystallization transition. Within this process window, near-net forging of a fine precision metallic glass part is demonstrated. PMID:25269892

Review and assessment of the HOST turbine heat transfer program

NASA Technical Reports Server (NTRS)

Gladden, Herbert J.

1988-01-01

The objectives of the HOST Turbine Heat Transfer subproject were to obtain a better understanding of the physics of the aerothermodynamic phenomena occurring in high-performance gas turbine engines and to assess and improve the analytical methods used to predict the fluid dynamics and heat transfer phenomena. At the time the HOST project was initiated, an across-the-board improvement in turbine design technology was needed. Therefore, a building-block approach was utilized, with research ranging from the study of fundamental phenomena and analytical modeling to experiments in simulated real-engine environments. Experimental research accounted for 75 percent of the project, and analytical efforts accounted for approximately 25 percent. Extensive experimental datasets were created depicting the three-dimensional flow field, high free-stream turbulence, boundary-layer transition, blade tip region heat transfer, film cooling effects in a simulated engine environment, rough-wall cooling enhancement in a rotating passage, and rotor-stator interaction effects. In addition, analytical modeling of these phenomena was initiated using boundary-layer assumptions as well as Navier-Stokes solutions.

Experimental and Computational Studies of the Flow Over a Sting Mounted Planetary Probe Configuration

NASA Technical Reports Server (NTRS)

Holden, Michael S.; Harvey, John K.; Boyd, Iain D.; George, Jyothish; Horvath, Thomas J.

1997-01-01

This paper summarizes the results of a series of experimental studies in the LENS shock tunnel and computations with DSMC and Navier Stokes codes which have been made to examine the aerothermal and flowfield characteristics of the flow over a sting-supported planetary probe configuration in hypervelocity air and nitrogen flows. The experimental program was conducted in the LENS hypervelocity shock tunnel at total enthalpies of 5and 10 MJkg for a range of reservoir pressure conditions from 70 to 500 bars. Heat transfer and pressure measurements were made on the front and rear face of the probe and along the supporting sting. High-speed and single shot schlieren photography were also employed to examine the flow over the model and the time to establish the flow in the base recirculation region. Predictions of the flowfield characteristics and the distributions of heat transfer and pressure were made with DSMC codes for rarefied flow conditions and with the Navier-Stokes solvers for the higher pressure conditions where the flows were assumed to be laminar. Analysis of the time history records from the heat transfer and pressure instrumentation on the face of the probe and in the base region indicated that the base flow was fully established in under 4 milliseconds from flow initiation or between 35 and 50 flow lengths based on base height. The measurements made in three different tunnel entries with two models of identical geometries but with different instrumentation packages, one prepared by NASA Langley and the second prepared by CUBRC, demonstrated good agreement between heat transfer measurements made with two different types of thin film and coaxial gage instrumentation. The measurements of heat transfer and pressure to the front face of the probe were in good agreement with theoretical predictions from both the DSMC and Navier Stokes codes. For the measurements made in low density flows, computations with the DSMC code were found to compare well with the pressure and heat transfer measurements on the sting, although the computed heat transfer rates in the recirculation region did not exhibit the same characteristics as the measurements. For the 10MJkg and 500 bar reservoir match point condition, the measurements and heat transfer along the sting from the first group of studies were in agreement with the Navier Stokes solutions for laminar conditions. A similar set of measurements made in later tests where the model was moved to a slightly different position in the test section indicated that the boundary layer in the reattachment compression region was close to transition or transitional where small changes in the test environment can result in larger than laminar heating rates. The maximum heating coefficients on the sting observed in the present studies was a small fraction of similar measurements obtained at nominally the same conditions in the HEG shock tunnel, where it is possible for transition to occur in the base flow, and in the low enthalpy studies conducted in the NASA Langley high Reynolds number Mach 10 tunnel where the base flow was shown to be turbulent. While the hybrid Navier- StokedDMSC calculations by Gochberg et al. (Reference 1) suggested that employing the Navier- Stokes calculations for the entire flowfield could be seriously in error in the base region for the 10 MJkg, 500 bar test case, similar calculations performed by Cornell, presented here, do not.

Transit forecasting accuracy : ridership forecasts and capital cost estimates, final research report.

DOT National Transportation Integrated Search

2009-01-01

In 1992, Pickrell published a seminal piece examining the accuracy of ridership forecasts and capital cost estimates for fixed-guideway transit systems in the US. His research created heated discussions in the transit industry regarding the ability o...

Research activities at the Center for Modeling of Turbulence and Transition

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing

1993-01-01

The main research activities at the Center for Modeling of Turbulence and Transition (CMOTT) are described. The research objective of CMOTT is to improve and/or develop turbulence and transition models for propulsion systems. The flows of interest in propulsion systems can be both compressible and incompressible, three dimensional, bounded by complex wall geometries, chemically reacting, and involve 'bypass' transition. The most relevant turbulence and transition models for the above flows are one- and two-equation eddy viscosity models, Reynolds stress algebraic- and transport-equation models, pdf models, and multiple-scale models. All these models are classified as one-point closure schemes since only one-point (in time and space) turbulent correlations, such as second moments (Reynolds stresses and turbulent heat fluxes) and third moments, are involved. In computational fluid dynamics, all turbulent quantities are one-point correlations. Therefore, the study of one-point turbulent closure schemes is the focus of our turbulence research. However, other research, such as the renormalization group theory, the direct interaction approximation method, and numerical simulations are also pursued to support the development of turbulence modeling.

Simulation of Solar Energy Use in Livelihood of Buildings

NASA Astrophysics Data System (ADS)

Lvocich, I. Ya; Preobrazhenskiy, A. P.; Choporov, O. N.

2017-11-01

Solar energy can be considered as the most technological and economical type of renewable energy. The purpose of the paper is to increase the efficiency of solar energy utilization on the basis of the mathematical simulation of the solar collector. A mathematical model of the radiant heat transfer vacuum solar collector is clarified. The model was based on the process of radiative heat transfer between glass and copper walls with the defined blackness degrees. A mathematical model of the ether phase transition point is developed. The dependence of the reservoir walls temperature change on the ambient temperature over time is obtained. The results of the paper can be useful for the development of prospective sources using solar energy.

Mixture for producing fracture-resistant, fiber-reinforced ceramic material by microwave heating

DOEpatents

Meek, T.T.; Blake, R.D.

1987-09-22

A fracture-resistant, fiber-reinforced ceramic substrate is produced by a method which involves preparing a ceramic precursor mixture comprising glass material, a coupling agent, and resilient fibers, and then exposing the mixture to microwave energy. The microwave field orients the fibers in the resulting ceramic material in a desired pattern wherein heat later generated in or on the substrate can be dissipated in a desired geometric pattern parallel to the fiber pattern. Additionally, the shunt capacitance of the fracture-resistant, fiber-reinforced ceramic substrate is lower which provides for a quicker transit time for electronic pulses in any conducting pathway etched into the ceramic substrate. 2 figs.

Characteristic power spectrum of diffusive interface dynamics in the two-dimensional Ising model

NASA Astrophysics Data System (ADS)

Masumoto, Yusuke; Takesue, Shinji

2018-05-01

We investigate properties of the diffusive motion of an interface in the two-dimensional Ising model in equilibrium or nonequilibrium situations. We focused on the relation between the power spectrum of a time sequence of spins and diffusive motion of an interface which was already clarified in one-dimensional systems with a nonequilibrium phase transition like the asymmetric simple exclusion process. It is clarified that the interface motion is a diffusion process with a drift force toward the higher-temperature side when the system is in contact with heat reservoirs at different temperatures and heat transfers through the system. Effects of the width of the interface are also discussed.

A kinetic study of solar wind electrons in the transition region from collision dominated to collisionless flow

NASA Technical Reports Server (NTRS)

Lie-Svendsen, O.; Leer, E.

1995-01-01

We have studied the evolution of the velocity distribution function of a test population of electrons in the solar corona and inner solar wind region, using a recently developed kinetic model. The model solves the time dependent, linear transport equation, with a Fokker-Planck collision operator to describe Coulomb collisions between the 'test population' and a thermal background of charged particles, using a finite differencing scheme. The model provides information on how non-Maxwellian features develop in the distribution function in the transition region from collision dominated to collisionless flow. By taking moments of the distribution the evolution of higher order moments, such as the heat flow, can be studied.

Production of Transitional Diffused Layers by Electrospark Coating

NASA Astrophysics Data System (ADS)

Smolentsev, Vladislav P.; Boldyrev, Alexander I.; Smolentsev, Evgeniy V.; Boldyrev, Alexander A.; Mozgalin, Vladislav L.

2018-03-01

The article presents a new method for production of diffused transitional layers with nano- and microthickness by local removal of nanofilms on aluminum alloys. This allows procuring of high-quality coatings on fusible alloys (for example, on aluminum ones) by materials, the melting point of which is 2-3 times higher than that of the basis (for example, of cast iron). This permits imparting new useful properties to workpieces made from light alloys with decent values for electrochemical working. The authors show that application of coatings provides minimum heating of workpieces. This enables the regulation in temperature condition of operating environment and permits efficiency improving during the process of electrochemical working by means of higher density current supply.

Influence of defects on the charge density wave of ([SnSe] 1+δ) 1(VSe 2) 1 ferecrystals

DOE PAGES

Falmbigl, Matthias; Putzky, Daniel; Ditto, Jeffrey; ...

2015-07-14

A series of ferecrystalline compounds ([SnSe] 1+δ) 1(VSe 2) 1 with varying Sn/V ratios were synthesized using the modulated elemental reactant technique. Temperature-dependent specific heat data reveal a phase transition at 102 K, where the heat capacity changes abruptly. An abrupt increase in electrical resistivity occurs at the same temperature, correlated with an abrupt increase in the Hall coefficient. Combined with the magnitude and nature of the specific heat discontinuity, this suggests that the transition is similar to the charge density wave transitions in transition metal dichalcogenides. An ordered intergrowth was formed over a surprisingly wide compositional range of Sn/Vmore » ratios of 0.89 ≤ 1 + δ ≤ 1.37. X-ray diffraction and transmission electron microscopy reveal the formation of various volume defects in the compounds in response to the nonstoichiometry. The electrical resistivity and Hall coefficient data of samples with different Sn/V ratios show systematic variation in the carrier concentration with the Sn/V ratio. There is no significant change in the onset temperature of the charge density wave transition, only a variation in the carrier densities before and after the transition. Given the sensitivity of the charge density wave transitions of transition metal dichalcogenides to variations in composition, it is very surprising that the charge density wave transition observed at 102 K for ([SnSe] 1.15) 1(VSe 2) 1 is barely influenced by the nonstoichiometry and structural defects. As a result, this might be a consequence of the two-dimensional nature of the structurally independent VSe 2 layers.« less

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

Perry, William L; Gunderson, Jake A; Dickson, Peter M

There has been a long history of interest in the decomposition kinetics of HMX and HMX-based formulations due to the widespread use of this explosive in high performance systems. The kinetics allow us to predict, or attempt to predict, the behavior of the explosive when subjected to thermal hazard scenarios that lead to ignition via impact, spark, friction or external heat. The latter, commonly referred to as 'cook off', has been widely studied and contemporary kinetic and transport models accurately predict time and location of ignition for simple geometries. However, there has been relatively little attention given to the problemmore » of localized ignition that results from the first three ignition sources of impact, spark and friction. The use of a zero-order single-rate expression describing the exothermic decomposition of explosives dates to the early work of Frank-Kamanetskii in the late 1930s and continued through the 60's and 70's. This expression provides very general qualitative insight, but cannot provide accurate spatial or timing details of slow cook off ignition. In the 70s, Catalano, et al., noted that single step kinetics would not accurately predict time to ignition in the one-dimensional time to explosion apparatus (ODTX). In the early 80s, Tarver and McGuire published their well-known three step kinetic expression that included an endothermic decomposition step. This scheme significantly improved the accuracy of ignition time prediction for the ODTX. However, the Tarver/McGuire model could not produce the internal temperature profiles observed in the small-scale radial experiments nor could it accurately predict the location of ignition. Those factors are suspected to significantly affect the post-ignition behavior and better models were needed. Brill, et al. noted that the enthalpy change due to the beta-delta crystal phase transition was similar to the assumed endothermic decomposition step in the Tarver/McGuire model. Henson, et al., deduced the kinetics and thermodynamics of the phase transition, providing Dickson, et al. with the information necessary to develop a four-step model that included a two-step nucleation and growth mechanism for the {beta}-{delta} phase transition. Initially, an irreversible scheme was proposed. That model accurately predicted the spatial and temporal cook off behavior of the small-scale radial experiment under slow heating conditions, but did not accurately capture the endothermic phase transition at a faster heating rate. The current version of the four-step model includes reversibility and accurately describes the small-scale radial experiment over a wide range of heating rates. We have observed impact-induced friction ignition of PBX 9501 with grit embedded between the explosive and the lower anvil surface. Observation was done using an infrared camera looking through the sapphire bottom anvil. Time to ignition and temperature-time behavior were recorded. The time to ignition was approximately 500 microseconds and the temperature was approximately 1000 K. The four step reversible kinetic scheme was previously validated for slow cook off scenarios. Our intention was to test the validity for significantly faster hot-spot processes, such as the impact-induced grit friction process studied here. We found the model predicted the ignition time within experimental error. There are caveats to consider when evaluating the agreement. The primary input to the model was friction work over an area computed by a stress analysis. The work rate itself, and the relative velocity of the grit and substrate both have a strong dependence on the initial position of the grit. Any errors in the analysis or the initial grit position would affect the model results. At this time, we do not know the sensitivity to these issues. However, the good agreement does suggest the four step kinetic scheme may have universal applicability for HMX systems.« less

Evaluation of an Early-Warning System for Heat Wave-Related Mortality in Europe: Implications for Sub-seasonal to Seasonal Forecasting and Climate Services

PubMed Central

Lowe, Rachel; García-Díez, Markel; Ballester, Joan; Creswick, James; Robine, Jean-Marie; Herrmann, François R.; Rodó, Xavier

2016-01-01

Heat waves have been responsible for more fatalities in Europe over the past decades than any other extreme weather event. However, temperature-related illnesses and deaths are largely preventable. Reliable sub-seasonal-to-seasonal (S2S) climate forecasts of extreme temperatures could allow for better short-to-medium-term resource management within heat-health action plans, to protect vulnerable populations and ensure access to preventive measures well in advance. The objective of this study is to assess the extent to which S2S climate forecasts could be incorporated into heat-health action plans, to support timely public health decision-making ahead of imminent heat wave events in Europe. Forecasts of apparent temperature at different lead times (e.g., 1 day, 4 days, 8 days, up to 3 months) were used in a mortality model to produce probabilistic mortality forecasts up to several months ahead of the 2003 heat wave event in Europe. Results were compared to mortality predictions, inferred using observed apparent temperature data in the mortality model. In general, we found a decreasing transition in skill between excellent predictions when using observed temperature, to predictions with no skill when using forecast temperature with lead times greater than one week. However, even at lead-times up to three months, there were some regions in Spain and the United Kingdom where excess mortality was detected with some certainty. This suggests that in some areas of Europe, there is potential for S2S climate forecasts to be incorporated in localised heat–health action plans. In general, these results show that the performance of this climate service framework is not limited by the mortality model itself, but rather by the predictability of the climate variables, at S2S time scales, over Europe. PMID:26861369

Design, Construction, and Qualification of a Microscale Heater Array for Use in Boiling Heat Transfer

NASA Technical Reports Server (NTRS)

Rule, T. D.; Kim, J.; Kalkur, T. S.

1998-01-01

Boiling heat transfer is an efficient means of heat transfer because a large amount of heat can be removed from a surface using a relatively small temperature difference between the surface and the bulk liquid. However, the mechanisms that govern boiling heat transfer are not well understood. Measurements of wall temperature and heat flux near the wall would add to the database of knowledge which is necessary to understand the mechanisms of nucleate boiling. A heater array has been developed which contains 96 heater elements within a 2.5 mm square area. The temperature of each heater element is held constant by an electronic control system similar to a hot-wire anemometer. The voltage that is being applied to each heater element can be measured and digitized using a high-speed A/D converter, and this digital information can be compiled into a series of heat-flux maps. Information for up to 10,000 heat flux maps can be obtained each second. The heater control system, the A/D system and the heater array construction are described in detail. Results are presented which show that this is an effective method of measuring the local heat flux during nucleate and transition boiling. Heat flux maps are obtained for pool boiling in FC-72 on a horizontal surface. Local heat flux variations are shown to be three to six times larger than variations in the spatially averaged heat flux.

Signatures Of Coronal Heating Driven By Footpoint Shuffling: Closed and Open Structures.

NASA Astrophysics Data System (ADS)

Velli, M. C. M.; Rappazzo, A. F.; Dahlburg, R. B.; Einaudi, G.; Ugarte-Urra, I.

2017-12-01

We have previously described the characteristic state of the confined coronal magnetic field as a special case of magnetically dominated magnetohydrodynamic (MHD) turbulence, where the free energy in the transverse magnetic field is continuously cascaded to small scales, even though the overall kinetic energy is small. This coronal turbulence problem is defined by the photospheric boundary conditions: here we discuss recent numerical simulations of the fully compressible 3D MHD equations using the HYPERION code. Loops are forced at their footpoints by random photospheric motions, energizing the field to a state with continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Only a fraction of the coronal mass and volume gets heated at any time. Temperature and density are highly structured at scales that, in the solar corona, remain observationally unresolved: the plasma of simulated loops is multithermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. We will also compare Reduced MHD simulations with fully compressible simulations and photospheric forcings with different time-scales compared to the Alfv'en transit time. Finally, we will discuss the differences between the closed field and open field (solar wind) turbulence heating problem, leading to observational consequences that may be amenable to Parker Solar Probe and Solar Orbiter.

Thermodynamic properties of methane hydrate in quartz powder.

PubMed

Voronov, Vitaly P; Gorodetskii, Evgeny E; Safonov, Sergey S

2007-10-04

Using the experimental method of precision adiabatic calorimetry, the thermodynamic (equilibrium) properties of methane hydrate in quartz sand with a grain size of 90-100 microm have been studied in the temperature range of 260-290 K and at pressures up to 10 MPa. The equilibrium curves for the water-methane hydrate-gas and ice-methane hydrate-gas transitions, hydration number, latent heat of hydrate decomposition along the equilibrium three-phase curves, and the specific heat capacity of the hydrate have been obtained. It has been experimentally shown that the equilibrium three-phase curves of the methane hydrate in porous media are shifted to the lower temperature and high pressure with respect to the equilibrium curves of the bulk hydrate. In these experiments, we have found that the specific heat capacity of the hydrate, within the accuracy of our measurements, coincides with the heat capacity of ice. The latent heat of the hydrate dissociation for the ice-hydrate-gas transition is equal to 143 +/- 10 J/g, whereas, for the transition from hydrate to water and gas, the latent heat is 415 +/- 15 J/g. The hydration number has been evaluated in the different hydrate conditions and has been found to be equal to n = 6.16 +/- 0.06. In addition, the influence of the water saturation of the porous media and its distribution over the porous space on the measured parameters has been experimentally studied.

Thermal-hydraulic behavior of a mixed chevron single-pass plate-and-frame heat exchanger

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

Manglik, R.M.; Muley, A.

1995-12-31

Effective heat exchange is very critical for improving the process efficiency and operating economy of chemical and process plants. Here, experimental friction factor and heat transfer data for single-phase water flows in a plate-and-frame heat exchanger are presented. A mixed chevron plate arrangement with {beta} = 30{degree}/60{degree} in a single-pass U-type, counterflow configuration is employed. The friction factor and heat transfer data are for isothermal flow and cooling conditions, respectively, and the flow rates correspond to transition and turbulent flow regimes (300 < Re < 6,000 and 2.4 < Pr < 4.5). Based on these data, Nusselt number and frictionmore » factor correlations for fully developed turbulent flows (Re {ge} 1,000) are presented. The results highlight the effects of {beta} on the thermal-hydraulic performance, transition to turbulent flows, and the relative impact of using symmetric or mixed chevron plate arrangements.« less

Near-field thermal rectification devices using phase change periodic nanostructure.

PubMed

Ghanekar, Alok; Tian, Yanpei; Ricci, Matthew; Zhang, Sinong; Gregory, Otto; Zheng, Yi

2018-01-22

We theoretically analyze two near-field thermal rectification devices: a radiative thermal diode and a thermal transistor that utilize a phase change material to achieve dynamic control over heat flow by exploiting metal-insulator transition of VO 2 near 341 K. The thermal analogue of electronic diode allows high heat flow in one direction while it restricts the heat flow when the polarity of temperature gradient is reversed. We show that with the introduction of 1-D rectangular grating, thermal rectification is dramatically enhanced in the near-field due to reduced tunneling of surface waves across the interfaces for negative polarity. The radiative thermal transistor also works around phase transition temperature of VO 2 and controls heat flow. We demonstrate a transistor-like behavior wherein heat flow across the source and the drain can be greatly varied by making a small change in gate temperature.

Ultra thin metallic coatings to control near field radiative heat transfer

NASA Astrophysics Data System (ADS)

Esquivel-Sirvent, R.

2016-09-01

We present a theoretical calculation of the changes in the near field radiative heat transfer between two surfaces due to the presence of ultra thin metallic coatings on semiconductors. Depending on the substrates, the radiative heat transfer is modulated by the thickness of the ultra thin film. In particular we consider gold thin films with thicknesses varying from 4 to 20 nm. The ultra-thin film has an insulator-conductor transition close to a critical thickness of dc = 6.4 nm and there is an increase in the near field spectral heat transfer just before the percolation transition. Depending on the substrates (Si or SiC) and the thickness of the metallic coatings we show how the near field heat transfer can be increased or decreased as a function of the metallic coating thickness. The calculations are based on available experimental data for the optical properties of ultrathin coatings.

XRD and FTIR studies the effect of heat treatment and doping the transition metal oxide on LiNbO3 and LiNb3O8 nano-crystallite phases in lithium borate glass system.

PubMed

Kashif, Ismail; Soliman, Ashia A; Sakr, Elham M; Ratep, Asmaa

2013-09-01

Glasses of various compositions in the system 90 Li2B4O7-10 Nb2O5 mixed with T.M ions (where T.M is the transition metal) were prepared by quenching technique. Heat-treatment of the parent glasses was performed at 540, 570 and 620 °C, for 5 and 16 h. The glass structure evolution during the controlled crystallization was examined by XRD and FT-IR spectroscopy analysis. The crystalline phases present in the glass ceramics were identified via X-ray diffraction as a function of heat treatment. The FT-IR data propose for these glasses and heat-treated glass network structures mainly built by: di-, tri-, tetra-, penta-and ortho-borate groups. It was found that the quantitative evolution of these various borate species in the glass structures is influenced by the transition metal. A detailed discussion relating to the N4 evolution with the T.M content was made. Copyright © 2013 Elsevier B.V. All rights reserved.

Magnetic transition in Y-site doped multiferroic YMnO3

NASA Astrophysics Data System (ADS)

Thakur, Rajesh K.; Thakur, Rasna; Gaur, N. K.

2016-05-01

We have synthesized polycrystalline hexagonal Y1-xSrxMnO3 (x=0.02, 0.1) compounds by using conventional solid state reaction method. The detailed structural investigations are carried out by using XRD studies which reveals the single phase formation of the reported compounds with hexagonal structure and space group P63cm (JCPDS: 25-1079). Further the XRD data of reported compounds were analyzed by RIETVELD (FULLPROFF) method which shows the decrease in the lattice parameter with increasing concentration of divalent strontium to Y-site. The observed pointed kinks in the specific heat study are indicative of the probable coupling in between the electric and magnetic orders in this class of materials. The reported systematic specific heat studies shows that the antiferromagnetic (AFM) transition temperature (TN) shifts to higher value with increasing concentration of Sr2+ ion in the YMnO3 compound which is attributed to the enhanced lattice contribution to the specific heat in the this compound. The present compound shows the independence of specific heat and magnetic transition temperature with applied magnetic field of 8T and 12T.

Tuning transitions in rotating Rayleigh-Bénard convection

NASA Astrophysics Data System (ADS)

Joshi, Pranav; Kunnen, Rudie; Clercx, Herman

2015-11-01

Turbulent rotating Rayleigh-Bénard convection, depending on the system parameters, exhibits multiple flow states and transitions between them. The present experimental study aims to control the transitions between the flow regimes, and hence the system heat transfer characteristics, by introducing particles in the flow. We inject near-neutrally buoyant silver coated hollow ceramic spheres (~100 micron diameter) and measure the system response, i.e. the Nusselt number, at different particle concentrations and rotation rates. Both for rotating and non-rotating cases, most of the particles settle on the top and bottom plates in a few hours following injection. This rapid settling may be a result of ``trapping'' of particles in the laminar boundary layers at the horizontal walls. These particle layers on the heat-transfer surfaces reduce their effective conductivity, and consequently, lower the heat transfer rate. We calculate the effective system parameters by estimating, and accounting for, the temperature drop across the particle layers. Preliminary analysis suggests that the thermal resistance of the particle layers may affect the flow structure and delay the transition to the ``geostrophic'' regime. Financial support from Foundation for Fundamental Research on Matter.

Nonlinear Dynamics of the Superfluid Transition: What may We learn on orbit?

NASA Technical Reports Server (NTRS)

Duncan, Rob

2003-01-01

Linear response (specifically, Fourier's Law) in He-4 has been observed to fail in heat flow experiments near the superfluid transition. A detailed analysis of the data suggests that the hydrostatic pressure gradient across the helium column limits the divergence of the correlation length in our earth-based experiments. This is consistent with other observations, such as the surprising lack of mutual friction and hysteresis near the superfluid transition, and a 'rounding' of the transition that appears to be independent of heat flux in the low heat flux limit. I will discuss these unusual results from earth-based measurements, and will show predictions for the very different results that may result when we make our measurements on orbit as part of the M1 Mission of the Low- Temperature, Microgravity Physics Facility. This work has been funded by the Fundamental Physics Discipline within the Physical Sciences Research Office of NASA, and is conducted by the DYNAMX (UNM) and CQ (Caltech) Groups, with assistance from the Low Temperature Science and Quantum Sensors Group at JPL.

The glass transition, crystallization and melting in Au-Pb-Sb alloys

NASA Technical Reports Server (NTRS)

Lee, M. C.; Allen, J. L.; Fecht, H. J.; Perepezko, J. H.; Ohsaka, K.

1988-01-01

The glass transition, crystallization and melting of Au(55)Pb(22.5)Sb(22.5) alloys have been studied by differential scanning calorimetry DSC. Crystallization on heating above the glass transition temperature Tg (45 C) begins at 64 C. Further crystallization events are observed at 172 C and 205 C. These events were found to correspond to the formation of the intermetallic compounds AuSb2, Au2Pb, and possibly AuPb2, respectively. Isothermal DSC scans of the glassy alloy above Tg were used to monitor the kinetics of crystallization. The solidification behavior and heat capacity in the glass-forming composition range were determined with droplet samples. An undercooling level of 0.3T(L) below the liquidus temperature T(L) was achieved, resulting in crystallization of different stable and metastable phases. The heat capacity C(P) of the undercooled liquid was measured over an undercooling range of 145 C.

Investigation of Heat Transfer in Straight and Curved Rectangular Ducts for Laminar and Transition Flows.

DTIC Science & Technology

1981-06-01

in order that the complete theoretical solution of the effects of the Taylor- Gortler vortices on heat transfer be explained. In 1977, - R. Kahawita ...Kelleher, M.D., "Taylor- Gortler Vortices and Their Effect on Heat Transfer" Journal of Heat Transfer, V.92, pp. 101-112, February 1970. 20. Kahawita , R

Shuttle Return To Flight Experimental Results: Protuberance Effects on Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Berry, Scott A.; Horvath, Thomas J.

2006-01-01

The effect of isolated roughness elements on the windward boundary layer of the Shuttle Orbiter has been experimentally examined in the Langley Aerothermodynamic Laboratory in support of an agency-wide effort to prepare the Shuttle Orbiter for return to flight. This experimental effort was initiated to provide a roughness effects database for developing transition criteria to support on-orbit decisions to repair damage to the thermal protection system. Boundary layer transition results were obtained using trips of varying heights and locations along the centerline and attachment lines of 0.0075-scale models. Global heat transfer images using phosphor thermography of the Orbiter windward surface and the corresponding heating distributions were used to infer the state of the boundary layer (laminar, transitional, or turbulent). The database contained within this report will be used to formulate protuberance-induced transition correlations using predicted boundary layer edge parameters.

Thermodynamics around the first-order ferromagnetic phase transition of Fe2P single crystals

NASA Astrophysics Data System (ADS)

Hudl, M.; Campanini, D.; Caron, L.; Höglin, V.; Sahlberg, M.; Nordblad, P.; Rydh, A.

2014-10-01

The specific heat and thermodynamics of Fe2P single crystals around the first-order paramagnetic to ferromagnetic (FM) phase transition at TC≃217 K are empirically investigated. The magnitude and direction of the magnetic field relative to the crystal axes govern the derived H -T phase diagram. Strikingly different phase contours are obtained for fields applied parallel and perpendicular to the c axis of the crystal. In parallel fields, the FM state is stabilized, while in perpendicular fields the phase transition is split into two sections, with an intermediate FM phase where there is no spontaneous magnetization along the c axis. The zero-field transition displays a textbook example of a first-order transition with different phase stability limits on heating and cooling. The results have special significance since Fe2P is the parent material to a family of compounds with outstanding magnetocaloric properties.

Secondary fuel delivery system

DOEpatents

Parker, David M.; Cai, Weidong; Garan, Daniel W.; Harris, Arthur J.

2010-02-23

A secondary fuel delivery system for delivering a secondary stream of fuel and/or diluent to a secondary combustion zone located in the transition piece of a combustion engine, downstream of the engine primary combustion region is disclosed. The system includes a manifold formed integral to, and surrounding a portion of, the transition piece, a manifold inlet port, and a collection of injection nozzles. A flowsleeve augments fuel/diluent flow velocity and improves the system cooling effectiveness. Passive cooling elements, including effusion cooling holes located within the transition boundary and thermal-stress-dissipating gaps that resist thermal stress accumulation, provide supplemental heat dissipation in key areas. The system delivers a secondary fuel/diluent mixture to a secondary combustion zone located along the length of the transition piece, while reducing the impact of elevated vibration levels found within the transition piece and avoiding the heat dissipation difficulties often associated with traditional vibration reduction methods.

FILM-30: A Heat Transfer Properties Code for Water Coolant

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

MARSHALL, THERON D.

2001-02-01

A FORTRAN computer code has been written to calculate the heat transfer properties at the wetted perimeter of a coolant channel when provided the bulk water conditions. This computer code is titled FILM-30 and the code calculates its heat transfer properties by using the following correlations: (1) Sieder-Tate: forced convection, (2) Bergles-Rohsenow: onset to nucleate boiling, (3) Bergles-Rohsenow: partially developed nucleate boiling, (4) Araki: fully developed nucleate boiling, (5) Tong-75: critical heat flux (CHF), and (6) Marshall-98: transition boiling. FILM-30 produces output files that provide the heat flux and heat transfer coefficient at the wetted perimeter as a function ofmore » temperature. To validate FILM-30, the calculated heat transfer properties were used in finite element analyses to predict internal temperatures for a water-cooled copper mockup under one-sided heating from a rastered electron beam. These predicted temperatures were compared with the measured temperatures from the author's 1994 and 1998 heat transfer experiments. There was excellent agreement between the predicted and experimentally measured temperatures, which confirmed the accuracy of FILM-30 within the experimental range of the tests. FILM-30 can accurately predict the CHF and transition boiling regimes, which is an important advantage over current heat transfer codes. Consequently, FILM-30 is ideal for predicting heat transfer properties for applications that feature high heat fluxes produced by one-sided heating.« less

Fatigue Failure Modes of the Grain Size Transition Zone in a Dual Microstructure Disk

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.; Kantzos, Pete T.; Palsa, Bonnie; Telesman, Jack; Gayda, John; Sudbrack, Chantal K.

2012-01-01

Mechanical property requirements vary with location in nickel-based superalloy disks. In order to maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored grain microstructures. In this study, fatigue failure modes of a grain size transition zone in a dual microstructure disk were evaluated. A specialized heat treatment method was applied to produce varying grain microstructure in the bore to rim portions of a powder metallurgy processed nickel-based superalloy disk. The transition in grain size was concentrated in a zone of the disk web, between the bore and rim. Specimens were extracted parallel and transversely across this transition zone, and multiple fatigue tests were performed at 427 C and 704 C. Grain size distributions were characterized in the specimens, and related to operative failure initiation modes. Mean fatigue life decreased with increasing maximum grain size, going out through the transition zone. The scatter in limited tests of replicates was comparable for failures of uniform gage specimens in all transition zone locations examined.

Superionic phase transition in silver chalcogenide nanocrystals realizing optimized thermoelectric performance.

PubMed

Xiao, Chong; Xu, Jie; Li, Kun; Feng, Jun; Yang, Jinlong; Xie, Yi

2012-03-07

Thermoelectric has long been recognized as a potentially transformative energy conversion technology due to its ability to convert heat directly into electricity. However, how to optimize the three interdependent thermoelectric parameters (i.e., electrical conductivity σ, Seebeck coefficient S, and thermal conductivity κ) for improving thermoelectric properties is still challenging. Here, we put forward for the first time the semiconductor-superionic conductor phase transition as a new and effective way to selectively optimize the thermoelectric power factor based on the modulation of the electric transport property across the phase transition. Ultra low value of thermal conductivity was successfully retained over the whole investigated temperature range through the reduction of grain size. As a result, taking monodisperse Ag(2)Se nanocrystals for an example, the maximized ZT value can be achieved around the temperature of phase transition. Furthermore, along with the effective scattering of short-wavelength phonons by atomic defects created by alloying, the alloyed ternary silver chalcogenide compounds, monodisperse Ag(4)SeS nanocrystals, show better ZT value around phase transition temperature, which is cooperatively contributed by superionic phase transition and alloying at nanoscale. © 2012 American Chemical Society

A heated vapor cell unit for dichroic atomic vapor laser lock in atomic rubidium.

PubMed

McCarron, Daniel J; Hughes, Ifan G; Tierney, Patrick; Cornish, Simon L

2007-09-01

The design and performance of a compact heated vapor cell unit for realizing a dichroic atomic vapor laser lock (DAVLL) for the D(2) transitions in atomic rubidium is described. A 5 cm long vapor cell is placed in a double-solenoid arrangement to produce the required magnetic field; the heat from the solenoid is used to increase the vapor pressure and correspondingly the DAVLL signal. We have characterized experimentally the dependence of important features of the DAVLL signal on magnetic field and cell temperature. For the weaker transitions both the amplitude and gradient of the signal are increased by an order of magnitude.

High accuracy heat capacity measurements through the lambda transition of helium with very high temperature resolution

NASA Technical Reports Server (NTRS)

Fairbanks, W. M.; Lipa, J. A.

1984-01-01

A measurement of the heat capacity singularity of helium at the lambda transition was performed with the aim of improving tests of the Renormalization Group (RG) predictions for the static thermodynamic behavior near the singularity. The goal was to approach as closely as possible to the lambda-point while making heat capacity measurements of high accuracy. To do this, a new temperature sensor capable of unprecedented resolution near the lambda-point, and two thermal control systems were used. A short description of the theoretical background and motivation is given. The initial apparatus and results are also described.

DNS and Embedded DNS as Tools for Investigating Unsteady Heat Transfer Phenomena in Turbines

NASA Technical Reports Server (NTRS)

vonTerzi, Dominic; Bauer, H.-J.

2010-01-01

DNS is a powerful tool with high potential for investigating unsteady heat transfer and fluid flow phenomena, in particular for cases involving transition to turbulence and/or large coherent structures. - DNS of idealized configurations related to turbomachinery components is already possible. - For more realistic configurations and the inclusion of more effects, reduction of computational cost is key issue (e.g., hybrid methods). - Approach pursued here: Embedded DNS ( segregated coupling of DNS with LES and/or RANS). - Embedded DNS is an enabling technology for many studies. - Pre-transitional heat transfer and trailing-edge cutback film-cooling are good candidates for (embedded) DNS studies.

Synthesis of Binary Transition Metal Nitrides, Carbides and Borides from the Elements in the Laser-Heated Diamond Anvil Cell and Their Structure-Property Relations

PubMed Central

Friedrich, Alexandra; Winkler, Björn; Juarez-Arellano, Erick A.; Bayarjargal, Lkhamsuren

2011-01-01

Transition metal nitrides, carbides and borides have a high potential for industrial applications as they not only have a high melting point but are generally harder and less compressible than the pure metals. Here we summarize recent advances in the synthesis of binary transition metal nitrides, carbides and borides focusing on the reaction of the elements at extreme conditions generated within the laser-heated diamond anvil cell. The current knowledge of their structures and high-pressure properties like high-(p,T) stability, compressibility and hardness is described as obtained from experiments. PMID:28824101

Demonstration of Wavelet Techniques in the Spectral Analysis of Bypass Transition Data

NASA Technical Reports Server (NTRS)

Lewalle, Jacques; Ashpis, David E.; Sohn, Ki-Hyeon

1997-01-01

A number of wavelet-based techniques for the analysis of experimental data are developed and illustrated. A multiscale analysis based on the Mexican hat wavelet is demonstrated as a tool for acquiring physical and quantitative information not obtainable by standard signal analysis methods. Experimental data for the analysis came from simultaneous hot-wire velocity traces in a bypass transition of the boundary layer on a heated flat plate. A pair of traces (two components of velocity) at one location was excerpted. A number of ensemble and conditional statistics related to dominant time scales for energy and momentum transport were calculated. The analysis revealed a lack of energy-dominant time scales inside turbulent spots but identified transport-dominant scales inside spots that account for the largest part of the Reynolds stress. Momentum transport was much more intermittent than were energetic fluctuations. This work is the first step in a continuing study of the spatial evolution of these scale-related statistics, the goal being to apply the multiscale analysis results to improve the modeling of transitional and turbulent industrial flows.

High-temperature measurements of methane and acetylene using quantum cascade laser absorption near 8 μm

NASA Astrophysics Data System (ADS)

Sajid, M. B.; Javed, T.; Farooq, A.

2015-04-01

The mid-infrared wavelength region near 8 μm contains absorption bands of several molecules such as water vapor, hydrogen peroxide, nitrous oxide, methane and acetylene. A new laser absorption sensor based on the ν4 band of methane and the ν4+ν5 band of acetylene is reported for interference-free, time-resolved measurements under combustion-relevant conditions. A detailed line-selection procedure was used to identify optimum transitions. Methane and acetylene were measured at the line centers of Q12 (1303.5 cm-1) and P23 (1275.5 cm-1) transitions, respectively. High-temperature absorption cross sections of methane and acetylene were measured at peaks (on-line) and valleys (off-line) of the selected absorption transitions. The differential absorption strategy was employed to eliminate interference absorption from large hydrocarbons. Experiments were performed behind reflected shock waves over a temperature range of 1200-2200 K, between pressures of 1-4 atm. The diagnostics were then applied to measure the respective species time-history profiles during the shock-heated pyrolysis of n-pentane.

Phonon Mechanisms for Excess Heat Capacity in Membrane Isolated Superconducting Transition Edge Sensors

NASA Technical Reports Server (NTRS)

Chervenak, James A.

2012-01-01

The mechanics of phonon transport in membrane-isolated superconducting transition edge sensors is discussed. Surveys of the literature on this type of sensor reveal a number of designs with excess heat capacity and a smaller subset that exhibit decoupling of the superconducting film from the underlying dielectric. A simple model is addressed in which the membrane, despite its thermal isolation, fails to fully thermalize to the temperature of the metal film heating it. A population of phonons exists which is emitted by the metal film, partially thermalizes the dielectric and is then reabsorbed in the metal film without escaping from the device structure to the thermal bath. The size of this population and its contribution to the heat capacity are estimated for several device scenarios.

Specific heat measurement set-up for quench condensed thin superconducting films.

PubMed

Poran, Shachaf; Molina-Ruiz, Manel; Gérardin, Anne; Frydman, Aviad; Bourgeois, Olivier

2014-05-01

We present a set-up designed for the measurement of specific heat of very thin or ultra-thin quench condensed superconducting films. In an ultra-high vacuum chamber, materials of interest can be thermally evaporated directly on a silicon membrane regulated in temperature from 1.4 K to 10 K. On this membrane, a heater and a thermometer are lithographically fabricated, allowing the measurement of heat capacity of the quench condensed layers. This apparatus permits the simultaneous thermal and electrical characterization of successively deposited layers in situ without exposing the deposited materials to room temperature or atmospheric conditions, both being irreversibly harmful to the samples. This system can be used to study specific heat signatures of phase transitions through the superconductor to insulator transition of quench condensed films.

Chromospheric counterparts of solar transition region unresolved fine structure loops

NASA Astrophysics Data System (ADS)

Pereira, Tiago M. D.; Rouppe van der Voort, Luc; Hansteen, Viggo H.; De Pontieu, Bart

2018-04-01

Low-lying loops have been discovered at the solar limb in transition region temperatures by the Interface Region Imaging Spectrograph (IRIS). They do not appear to reach coronal temperatures, and it has been suggested that they are the long-predicted unresolved fine structures (UFS). These loops are dynamic and believed to be visible during both heating and cooling phases. Making use of coordinated observations between IRIS and the Swedish 1-m Solar Telescope, we study how these loops impact the solar chromosphere. We show for the first time that there is indeed a chromospheric signal of these loops, seen mostly in the form of strong Doppler shifts and a conspicuous lack of chromospheric heating. In addition, we find that several instances have a inverse Y-shaped jet just above the loop, suggesting that magnetic reconnection is driving these events. Our observations add several puzzling details to the current knowledge of these newly discovered structures; this new information must be considered in theoretical models. Two movies associated to Fig. 1 are available at http://https://www.aanda.org

Simulated tempering based on global balance or detailed balance conditions: Suwa-Todo, heat bath, and Metropolis algorithms.

PubMed

Mori, Yoshiharu; Okumura, Hisashi

2015-12-05

Simulated tempering (ST) is a useful method to enhance sampling of molecular simulations. When ST is used, the Metropolis algorithm, which satisfies the detailed balance condition, is usually applied to calculate the transition probability. Recently, an alternative method that satisfies the global balance condition instead of the detailed balance condition has been proposed by Suwa and Todo. In this study, ST method with the Suwa-Todo algorithm is proposed. Molecular dynamics simulations with ST are performed with three algorithms (the Metropolis, heat bath, and Suwa-Todo algorithms) to calculate the transition probability. Among the three algorithms, the Suwa-Todo algorithm yields the highest acceptance ratio and the shortest autocorrelation time. These suggest that sampling by a ST simulation with the Suwa-Todo algorithm is most efficient. In addition, because the acceptance ratio of the Suwa-Todo algorithm is higher than that of the Metropolis algorithm, the number of temperature states can be reduced by 25% for the Suwa-Todo algorithm when compared with the Metropolis algorithm. © 2015 Wiley Periodicals, Inc.

Stochastic effects in a thermochemical system with Newtonian heat exchange.

PubMed

Nowakowski, B; Lemarchand, A

2001-12-01

We develop a mesoscopic description of stochastic effects in the Newtonian heat exchange between a diluted gas system and a thermostat. We explicitly study the homogeneous Semenov model involving a thermochemical reaction and neglecting consumption of reactants. The master equation includes a transition rate for the thermal transfer process, which is derived on the basis of the statistics for inelastic collisions between gas particles and walls of the thermostat. The main assumption is that the perturbation of the Maxwellian particle velocity distribution can be neglected. The transition function for the thermal process admits a continuous spectrum of temperature changes, and consequently, the master equation has a complicated integro-differential form. We perform Monte Carlo simulations based on this equation to study the stochastic effects in the Semenov system in the explosive regime. The dispersion of ignition times is calculated as a function of system size. For sufficiently small systems, the probability distribution of temperature displays transient bimodality during the ignition period. The results of the stochastic description are successfully compared with those of direct simulations of microscopic particle dynamics.

Streamer Evaporation

NASA Technical Reports Server (NTRS)

Suess, Steven T.; Wang, A. H.; Wu, Shi T.; Nerney, S.

1998-01-01

Evaporation is the consequence of slow plasma heating near the tops of streamers where the plasma is only weakly contained by the magnetic field. The form it takes is the slow opening of field lines at the top of the streamer and transient formation of new solar wind. It was discovered in polytropic model calculations, where due to the absence of other energy loss mechanisms in magnetostatic streamers, its ultimate endpoint is the complete evaporation of the streamer. This takes, for plausible heating rates, weeks to months in these models. Of course streamers do not behave this way, for more than one reason. One is that there are losses due to thermal conduction to the base of the streamer and radiation from the transition region. Another is that streamer heating must have a characteristic time constant and depend on the ambient physical conditions. We use our global Magnetohydrodynamics (MHD) model with thermal conduction to examine a few examples of the effect of changing the heating scale height and of making ad hoc choices for how the heating depends on ambient conditions. At the same time, we apply and extend the analytic model of streamers, which showed that streamers will be unable to contain plasma for temperatures near the cusp greater than about 2xl0(exp 6) K. Slow solar wind is observed to come from streamers through transient releases. A scenario for this that is consistent with the above physical process is that heating increases the near-cusp temperature until field lines there are forced open. The subsequent evacuation of the flux tubes by the newly forming slow wind decreases the temperature and heating until the flux tubes are able to reclose. Then, over a longer time scale, heating begins to again refill the flux tubes with plasma and increase the temperature until the cycle repeats itself. The calculations we report here are first steps towards quantitative evaluation of this scenario.

Exposure and health impact evaluation based on simultaneous measurement of indoor and ambient PM2.5 in Haidian, Beijing.

PubMed

Qi, Meng; Zhu, Xi; Du, Wei; Chen, Yilin; Chen, Yuanchen; Huang, Tianbo; Pan, Xuelian; Zhong, Qirui; Sun, Xu; Zeng, Eddy Y; Xing, Baoshan; Tao, Shu

2017-01-01

Because people spend most of their time indoors, the characterization of indoor air quality is important for exposure assessment. Unfortunately, indoor air data are scarce, leading to a major data gap in risk assessment. In this study, PM 2.5 concentrations in both indoor and outdoor air were simultaneously measured using on-line particulate counters in 13 households in Haidian, Beijing for both heating and non-heating seasons. A bimodal distribution of PM 2.5 concentrations suggests rapid transitions between polluted and non-polluted situations. The PM 2.5 concentrations in indoor and outdoor air varied synchronously, with the indoor variation lagging. The lag time in the heating season was longer than that in the non-heating season. The particle sizes in indoor air were smaller than those in ambient air in the heating season and vice versa in the non-heating season. PM 2.5 concentrations in indoor air were generally lower than those in ambient air except when ambient concentrations dropped sharply to very low levels or there were internal emissions from cooking or other activities. The effectiveness of an air cleaner to reduce indoor PM 2.5 concentrations was demonstrated. Non-linear regression models were developed to predict indoor air PM 2.5 concentrations based on ambient data with lag time incorporated. The models were applied to estimate the overall population exposure to PM 2.5 and the health consequences in Haidian. The health impacts would be significantly overestimated without the indoor exposure being taken into consideration, and this bias would increase as the ambient air quality improved in the future. Copyright © 2016 Elsevier Ltd. All rights reserved.

Non-equilibrium phase transitions in a liquid crystal

NASA Astrophysics Data System (ADS)

Dan, K.; Roy, M.; Datta, A.

2015-09-01

The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min-1, consistent with a glass transition, a clear peak for β ≤ 5 K min-1 and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the anisotropy, goes to zero from nematic to isotropic phase. To a point below the transition temperature, the order parameter is constant but decreases linearly with increase in temperature below that indicating the dependence of nematic ordering on the initial temperature during heating consistent with the non-equilibrium nature of nematic-isotropic phase transition.

Flamelet Formation In Hele-Shaw Flow

NASA Technical Reports Server (NTRS)

Wichman, I. S.; Olson, S. L.

2003-01-01

A Hele-Shaw flow apparatus constructed at Michigan State University (MSU) produces conditions that reduce influences of buoyancy-driven flows. In addition, in the MSU Hele-Shaw apparatus it is possible to adjust the heat losses from the fuel sample (0.001 in. thick cellulose) and the flow speed of the approaching oxidizer flow (air) so that the "flamelet regime of flame spread" is entered. In this regime various features of the flame-to-smolder (and vice versa) transition can be studied. For the relatively wide (approx. 17.5 cm) and long (approx. 20 cm) samples used, approximately ten flamelets existed at all times. The flamelet behavior was studied mechanistically and statistically. A heat transfer analysis of the dominant heat transfer mechanisms was conducted. Results indicate that radiation and conduction processes are important, and that a simple 1-D model using the Broido-Shafizadeh model for cellulose decomposition chemistry can describe aspects of the flamelet spread process. Introduction

Thermally induced vibrations of smart solar panel in a low-orbit satellite

NASA Astrophysics Data System (ADS)

Azadi, E.; Fazelzadeh, S. Ahmad; Azadi, M.

2017-03-01

In this paper, a smart flexible satellite moving in a circular orbit with two flexible panels are studied. The panels have been modeled as clamped-free-free-free rectangular plates with attached piezoelectric actuators. It is assumed that the satellite has a pitch angle rotation maneuver. Rapid temperature changes at day-night transitions in orbit generate time dependent bending moments. Satellite maneuver and temperature varying induce vibrations in the appendages. So, to simulate the system, heat radiation effects on the appendages have been considered. The nonlinear equations of motion and the heat transfer equations are coupled and solved simultaneously. So, the governing equations of motion are nonlinear and very complicated ones. Finally, the whole system is simulated and the effects of the heat radiation, radius of the orbit, piezoelectric voltages, and piezoelectric locations on the response of the system are studied.

Electronic structure and quantum spin fluctuations at the magnetic phase transition in MnSi

NASA Astrophysics Data System (ADS)

Povzner, A. A.; Volkov, A. G.; Nogovitsyna, T. A.

2018-05-01

The effect of spin fluctuations on the heat capacity and homogeneous magnetic susceptibility of the chiral magnetic MnSi in the vicinity of magnetic transition has been investigated by using the free energy functional of the coupled electron and spin subsystems and taking into account the Dzyaloshinsky-Moriya interaction. For helical ferromagnetic ordering, we found that zero-point fluctuations of the spin density are large and comparable with fluctuations of the non-uniform magnetization. The amplitude of zero-point spin fluctuations shows a sharp decrease in the region of the magnetic phase transition. It is shown that sharp decrease of the amplitude of the quantum spin fluctuations results in the lambda-like maxima of the heat capacity and the homogeneous magnetic susceptibility. Above the temperature of the lambda anomaly, the spin correlation radius becomes less than the period of the helical structure and chiral fluctuations of the local magnetization appear. It is shown that formation of a "shoulder" on the temperature dependence of the heat capacity is due to disappearance of the local magnetization. Our finding allows to explain the experimentally observed features of the magnetic phase transition of MnSi as a result of the crossover of quantum and thermodynamic phase transitions.

Polar Kerr Effect from Time-Reversal Symmetry Breaking in the Heavy-Fermion Superconductor PrOs 4 Sb 12

DOE PAGES

Levenson-Falk, Eli M.; Schemm, E. R.; Aoki, Y.; ...

2018-05-04

Here, we present polar Kerr effect measurements of the filled skutterudite superconductor PrOs 4Sb 12. Simultaneous ac susceptibility measurements allow us to observe the superconducting transition under the influence of heating from the optical beam. A nonzero Kerr angle θ K develops below the superconducting transition, saturating at ~300 nrad at low temperatures. This result is repeated across several measurements of multiple samples. By extrapolating the measured θ K(T) to zero optical power, we are able to show that the Kerr angle onset temperature in one set of measurements is consistent with the transition to the B phase at Tmore » C2. We discuss the possible explanations for this result and its impact on the understanding of multiphase and inhomogeneous superconductivity in PrOs 4Sb 12.« less

Polar Kerr Effect from Time-Reversal Symmetry Breaking in the Heavy-Fermion Superconductor PrOs 4 Sb 12

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

Levenson-Falk, Eli M.; Schemm, E. R.; Aoki, Y.

Here, we present polar Kerr effect measurements of the filled skutterudite superconductor PrOs 4Sb 12. Simultaneous ac susceptibility measurements allow us to observe the superconducting transition under the influence of heating from the optical beam. A nonzero Kerr angle θ K develops below the superconducting transition, saturating at ~300 nrad at low temperatures. This result is repeated across several measurements of multiple samples. By extrapolating the measured θ K(T) to zero optical power, we are able to show that the Kerr angle onset temperature in one set of measurements is consistent with the transition to the B phase at Tmore » C2. We discuss the possible explanations for this result and its impact on the understanding of multiphase and inhomogeneous superconductivity in PrOs 4Sb 12.« less

Parametric electroconvection in a weakly conducting fluid in a horizontal parallel-plate capacitor

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

Kartavykh, N. N.; Smorodin, B. L., E-mail: bsmorodin@yandex.ru; Il’in, V. A.

2015-07-15

We study the flows of a nonuniformly heated weakly conducting fluid in an ac electric field of a horizontal parallel-plate capacitor. Analysis is carried out for fluids in which the charge formation is governed by electroconductive mechanism associated with the temperature dependence of the electrical conductivity of the medium. Periodic and chaotic regimes of fluid flow are investigated in the limiting case of instantaneous charge relaxation and for a finite relaxation time. Bifurcation diagrams and electroconvective regimes charts are constructed. The regions where fluid oscillations synchronize with the frequency of the external field are determined. Hysteretic transitions between electroconvection regimesmore » are studied. The scenarios of transition to chaotic oscillations are analyzed. Depending on the natural frequency of electroconvective system and the external field frequency, the transition from periodic to chaotic oscillations can occur via quasiperiodicity, a subharmonic cascade, or intermittence.« less

Dynamic contraction of the positive column of a self-sustained glow discharge in air flow

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

Shneider, M. N.; Mokrov, M. S.; Milikh, G. M.

We study the dynamic contraction of a self-sustained glow discharge in air in a rectangular duct with convective cooling. A two dimensional numerical model of the plasma contraction was developed in a cylindrical frame. The process is described by a set of time-dependent continuity equations for the electrons, positive and negative ions; gas and vibrational temperature; and equations which account for the convective heat and plasma losses by the transverse flux. Transition from the uniform to contracted state was analyzed. It was shown that such transition experiences a hysteresis, and that the critical current of the transition increases when themore » gas density drops. Possible coexistence of the contracted and uniform state of the plasma in the discharge, where the current flows along the density gradient of the background gas, is discussed.« less

Transition Heat Transfer Modeling Based on the Characteristics of Turbulent Spots

NASA Technical Reports Server (NTRS)

Simon, Fred; Boyle, Robert

1998-01-01

While turbulence models are being developed which show promise for simulating the transition region on a turbine blade or vane, it is believed that the best approach with the greatest potential for practical use is the use of models which incorporate the physics of turbulent spots present in the transition region. This type of modeling results in the prediction of transition region intermittency which when incorporated in turbulence models give a good to excellent prediction of the transition region heat transfer. Some models are presented which show how turbulent spot characteristics and behavior can be employed to predict the effect of pressure gradient and Mach number on the transition region. The models predict the spot formation rate which is needed, in addition to the transition onset location, in the Narasimha concentrated breakdown intermittency equation. A simplified approach is taken for modeling turbulent spot growth and interaction in the transition region which utilizes the turbulent spot variables governing transition length and spot generation rate. The models are expressed in terms of spot spreading angle, dimensionless spot velocity, dimensionless spot area, disturbance frequency and Mach number. The models are used in conjunction with a computer code to predict the effects of pressure gradient and Mach number on the transition region and compared with VKI experimental turbine data.

Evaluation of heat hyperalgesia and anxiety like-behaviors in a rat model of orofacial cancer.

PubMed

Gambeta, Eder; Kopruszinski, Caroline Machado; Dos Reis, Renata Cristiane; Zanoveli, Janaina Menezes; Chichorro, Juliana Geremias

2016-04-21

Pain and anxiety are commonly experienced by cancer patients and both significantly impair their quality of life. Some authors claim that there is a relationship between pain and anxiety, while others suggest that there is not a direct association. In any case, there is indeed a consensus that anxiety impairs the pain condition beyond be under diagnosed and undertreated in cancer pain patients. Herein we investigated if rats presenting heat hyperalgesia induced by orofacial cancer cell inoculation would display anxiety-like behaviors. In addition, we evaluated if pain blockade would result in alleviation of anxiety behaviors, as well as, if blockade of anxiety would result in pain relief. Orofacial cancer was induced in male Wistar rats by inoculation of Walker-256 cells into the right vibrissal pad. Heat facial hyperalgesia was assessed on day 6 after the inoculation, and on this time point rats were submitted to the elevated plus maze and the light-dark transition tests. The influence of lidocaine and midazolam on heat hyperalgesia and anxiety-like behaviors was assessed. The peak of facial heat hyperalgesia was detected 6 days after cancer cells inoculation, and at this time point, rats exhibited increased anxiety-like behaviors. Local treatment with lidocaine (2%/50μL) caused a marked reduction of heat hyperalgesia, but failed to affect the anxiety-like behaviors, while midazolam (0.5mg/kg, i.p.) treatment failed to change the heat threshold, but induced an anxiolytic-like effect. Altogether, our data demonstrated that rats with orofacial cancer present pain- and anxiety-like behaviors, but brief heat hyperalgesia relief does not affect the anxiety-like behaviors, and vice-versa, in our experimental conditions. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Catalysts for the hydrodenitrogenation of organic materials and process for the preparation of the catalysts

DOEpatents

Laine, R.M.; Hirschon, A.S.; Wilson, R.B. Jr.

1987-12-29

A process is described for the preparation of a multimetallic catalyst for the hydrodenitrogenation of an organic feedstock, which process comprises: (a) forming a precatalyst itself comprising: (1) a first metal compound selected from compounds of nickel, cobalt or mixtures thereof; (2) a second metal compound selected from compounds of chromium, molybdenum, tungsten, or mixtures thereof; and (3) an inorganic support; (b) heating the precatalyst of step (a) with a source of sulfide in a first non-oxidizing gas at a temperature and for a time effective to presulfide the precatalyst; (c) adding in a second non-oxidizing gas to the sulfided precatalyst of step (b) an organometallic transition metal moiety selected from compounds of iridium, rhodium, iron, ruthenium, tungsten or mixtures thereof for a time and at a temperature effective to chemically combine the metal components; and (d) optionally heating the chemically combined catalyst of step (b) in vacuum at a temperature and for a time effective to remove residual volatile organic materials. 12 figs.

Numerical Simulation of Liquid Nitrogen Chilldown of a Vertical Tube

NASA Technical Reports Server (NTRS)

Darr, Samuel; Hu, Hong; Schaeffer, Reid; Chung, Jacob; Hartwig, Jason; Majumdar, Alok

2015-01-01

This paper presents the results of a one-dimensional numerical simulation of the transient chilldown of a vertical stainless steel tube with liquid nitrogen. The direction of flow is downward (with gravity) through the tube. Heat transfer correlations for film, transition, and nucleate boiling, as well as critical heat flux, rewetting temperature, and the temperature at the onset of nucleate boiling were used to model the convection to the tube wall. Chilldown curves from the simulations were compared with data from 55 recent liquid nitrogen chilldown experiments. With these new correlations the simulation is able to predict the time to rewetting temperature and time to onset of nucleate boiling to within 25% for mass fluxes ranging from 61.2 to 1150 kg/(sq m s), inlet pressures from 175 to 817 kPa, and subcooled inlet temperatures from 0 to 14 K below the saturation temperature.

An experimental study of high-pressure droplet combustion

NASA Technical Reports Server (NTRS)

Norton, Chris M.; Litchford, Ron J.; Jeng, San-Mou

1990-01-01

The results are presented of an experimental study on suspended n-heptane droplet combustion in air for reduced pressures up to P(r) = 2.305. Transition to fully transient heat-up through the critical state is demonstrated above a threshold pressure corresponding to P(r) of roughly 1.4. A silhouette imaging technique resolves the droplet surface for reduced pressures up to about P(r) roughly 0.63, but soot formation conceals the surface at higher pressures. Images of the soot plumes do not show any sudden change in behavior indicative of critical transition. Mean burning rate constants are computed from the d-squared variation law using measured effective droplet diameters at ignition and measured burn times, and corrected burning times are computed for an effective initial droplet diameter. The results show that the burning rates increase as the fuel critical pressure is approached and decrease as the pressure exceeds the fuel critical pressure. Corrected burning times show inverse behavior.

Specific heat in the pure gauge SU(2) theory

NASA Astrophysics Data System (ADS)

Mitrjushkin, V. K.; Zadorozhny, A. M.

1989-12-01

We calculated the specific heat Cv in pure gauge SU(2) theory. Calculations were done on the 3·8 3 lattice in the vicinity of the phase transition temperature. It is shown that the dependence of its electric ( CEv) and magnetic ( CMV) compone nts differ drastically near the phase transition point. Their behaviour is in full agreement with our previous calculations of the electric and magnetic components of the internal energy density and pressure.

Comparative study of helimagnets MnSi and Cu2OSeO3 at high pressures

NASA Astrophysics Data System (ADS)

Stishov, Sergei; Sidorov, Vladimir; Petrova, Alla; Berdonosov, Peter; Dolgikh, Valery

2014-03-01

The heat capacity of helical magnets Cu2OSeO3 and MnSi has been investigated at high pressures by the ac-calorimetric technique. Despite the differing nature of their magnetic moments, Cu2OSeO3 and MnSi demonstrate a surprising similarity in behavior of their magnetic and thermodynamic properties at the phase transition. Two characteristic features of the heat capacity at the phase transitions of both substances (peak and shoulder) behave also in a similar way at high pressures if analyzed as a function of temperature. This probably implies that the longitudinal spin fluctuations typical of weak itinerant magnets like MnSi contribute little to the phase transition. The shoulders of the heat capacity curves shrink with decreasing temperature suggesting that they arise from classical fluctuations. In case of MnSi the sharp peak and shoulder at the heat capacity disappear simultaneously probably signifying the existence of a tricritical point and confirming the fluctuation nature of the first order phase transition in MnSi as well as in Cu2OSeO3. This work was supported by the Russian Foundation for Basic Research (grant 12-02-00376-a, 12-03-92604), Program of the Physics Department of RAS on Strongly Correlated Electron Systems and Program of the Presidium of RAS on Strongly Compressed Matter.

Heat Pipe Planets

NASA Astrophysics Data System (ADS)

Moore, W. B.; Simon, J. I.

2018-05-01

We propose that cooling via volcanic heat pipes may provide a universal model of the way terrestrial bodies transition from a magma-ocean state into subsequent single-plate, stagnant-lid convection or plate tectonic phases.

Relationship between morphological change and crystalline phase transitions of polyethylene-poly(ethylene oxide) diblock copolymers, revealed by the temperature-dependent synchrotron WAXD/SAXS and infrared/Raman spectral measurements.

PubMed

Weiyu, Cao; Tashiro, Kohji; Hanesaka, Makoto; Takeda, Shinichi; Masunaga, Hiroyasu; Sasaki, Sono; Takata, Masaki

2009-02-26

The phase transition behaviors of low-molecular-weight polyethylene-poly(ethylene oxide) (PE-b-PEO) diblock copolymers with the monomeric units of PE/PEO = 17/40 and 39/86 have been successfully investigated through the temperature-dependent measurements of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), infrared and Raman spectra, as well as thermal analysis. These diblock copolymers had been believed to show only order-to-disorder transition of lamellar morphology in a wide temperature region, but it has been found here for the first time that this copolymer clearly exhibits the three stages of transitions among lamella, gyroid, cylinder, and spherical phases in the heating and cooling processes. The WAXD and IR/Raman spectral measurements allowed us to relate these morphological changes to the microscopic changes in the aggregation states of PEO and PE segments. In the low-temperature region the PEO segments form the monoclinic crystal of (7/2) helical chain conformation and the PE segments of planar-zigzag form take the orthorhombic crystalline phase. These crystalline lamellae of PEO and PE segments are alternately stacked with the long period of 165 Angstroms. In a higher temperature region, where the PEO crystalline parts are on the way of melting but the PE parts are still in the orthorhombic phase, the gyroid morphology is detected in the SAXS data. By heating further, the gyroid morphology changes to the hexagonally packed cylindrical morphology, where the orthorhombic phase of PE segments is gradually disordered because of thermally activated molecular motion and finally transforms to the pseudohexagonal or rotator phase. Once the PE segments are perfectly melted, the higher-order structure changes from the cylinder to the spherical morphology. These morphological transitions might relate to the thermally activated motions of two short chain segments of the diblock copolymer, although the details of the transition mechanism are unclear at the present stage.

Good News for Borehole Climatology

NASA Astrophysics Data System (ADS)

Rath, Volker; Fidel Gonzalez-Rouco, J.; Goosse, Hugues

2010-05-01

Though the investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories, there are many open questions concerning the significance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last glacial Maximum (LGM) is still present in borehole temperature profiles. It influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries. This is shown using Monte Carlo experiments on past surface temperature change, using plausible distributions for the most important parameters, i.e.,amplitude and timing of the glacial-interglacial transition, the prior average temperature, and petrophysical properties. It has been argued that the signature of the last glacial-interglacial transition could be responsible for the high amplitudes of millennial temperature reconstructions. However, in shallow boreholes the additional effect of past climate can reasonably approximated by a linear variation of temperature with depth, and thus be accommodated by a "biased" background heat flow. This is good news for borehole climate, but implies that the geological heat flow values have to be interpreted accordingly. Borehole climate reconstructions from these shallow are most probably underestimating past variability due to the diffusive character of the heat conduction process, and the smoothness constraints necessary for obtaining stable solutions of this ill-posed inverse problem. A simple correction based on subtracting an appropriate prior surface temperature history shows promising results reducing these errors considerably, also with deeper boreholes, where the heat flow signal can not be approximated linearly, and improves the comparisons with AOGCM modeling results.

EARLY-PHASE PHOTOMETRY AND SPECTROSCOPY OF TRANSITIONAL TYPE Ia SN 2012ht: DIRECT CONSTRAINT ON THE RISE TIME

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

Yamanaka, Masayuki; Nogami, Daisaku; Maeda, Keiichi

We report photometric and spectroscopic observations of the nearby Type Ia Supernova (SN Ia) 2012ht from –15.8 days to +49.1 days after B-band maximum. The decline rate of the light curve is Δm {sub 15}(B) = 1.39 ± 0.05 mag, which is intermediate between normal and subluminous SNe Ia, and similar to that of the ''transitional'' Type Ia SN 2004eo. The spectral line profiles also closely resemble those of SN 2004eo. We were able to observe SN 2012ht at a very early phase, when it was still rising and was about three magnitudes fainter than at the peak. The rise time to the B-bandmore » maximum is estimated to be 17.6 ± 0.5 days and the time of the explosion is MJD 56277.98 ± 0.13. SN 2012ht is the first transitional SN Ia whose rise time is directly measured without using light curve templates, and the fifth SN Ia overall. This rise time is consistent with those of the other four SNe within the measurement error, even including the extremely early detection of SN 2013dy. The rising part of the light curve can be fitted by a quadratic function, and shows no sign of a shock-heating component due to the interaction of the ejecta with a companion star. The rise time is significantly longer than that inferred for subluminous SNe such as SN 1991bg, which suggests that a progenitor and/or explosion mechanism of transitional SNe Ia are more similar to normal SNe Ia rather than to subluminous SNe Ia.« less

Transition-Region/Coronal Signatures of Penumbral Microjets: Hi-C, SDO/AIA and Hinode (SOT/FG) Observations

NASA Technical Reports Server (NTRS)

Tiwari, Sanjiv K.; Alpert, Shane E.; Moore, Ronald L.; Winebarger, Amy R.

2014-01-01

Penumbral microjets are bright, transient features seen in the chromosphere of sunspot penumbrae. Katsuaka et al. (2007) noted their ubiquity and characterized them using the Ca II H-line filter on Hinode's Solar Optical Telescope (SOT). The jets are 1000{4000 km in length, 300{400 km in width, and last less than one minute. It was proposed that these penumbral microjets could contribute to the transition-region and coronal heating above sunspots. We examine whether these microjets appear in the transition-region (TR) and/or corona or are related{ temporally and spatially{ to similar brightenings in the TR and/or corona. First, we identify penumbral microjets with the SOT's Ca II H-line filter. The chosen sunspot is observed on July 11, 2012 from 18:50:00 UT to 20:00:00 UT at approx. 14 inches, -30 inches. We then examine the sunspot in the same field of view and at the same time in other wavelengths. We use the High Resolution Coronal Imager Telescope (Hi-C) at 193A and the 1600A, 304A, 171A, 193A, and 94A passbands of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamic Observatory. We include examples of these jets and where they should appear in the other passbands, but find no signifcant association, except for a few jets with longer lifetimes and bigger sizes seen at locations in the penumbra with repeated stronger brightenings. We conclude that the normal microjets are not heated to transition-region/coronal temperatures, but the larger jets are.

The Effect of Solution Thermal History on Chicken Egg White Lysozyme Nucleation

NASA Technical Reports Server (NTRS)

Burke, Michael W.; Judge, Russell A.; Pusey, Marc L.

2001-01-01

Proteins are highly flexible molecules and often exhibit defined conformational changes in response to changes in the ambient temperature. Chicken egg white lysozyme has been previously shown to undergo an apparent structural change when warmed above the tetragonal/orthorhombic phase transition temperature. This is reflected by a change in the habit of the tetragonal and orthorhombic crystals so formed. In this study, we show that possible conformational changes induced by heating are stable and apparently non-reversible by simple cooling. Exposure of protein solutions to temperatures above the phase change transition temperature, before combining with precipitant solution to begin crystallization, reduces final crystal numbers. Protein that is briefly warmed to 37 C, then cooled shows no sign of reversal to the unheated nucleation behavior even after storage for four weeks at 4 C. The change in nucleation behavior of tetragonal lysozyme crystals, attributed to a structural shift, occurs faster the greater the exposure to temperature above the equi-solubility point for the two phases. Heating for 2 hours at 48 C reduces crystal numbers by 20 fold in comparison to the same solution heated for the same time at 30 C. Thermal treatment of solutions is therefore a possible tool to reduce crystal numbers and increase crystal size. The effects of a protein's previous thermal history are now shown to be a potentially critical factor in subsequent macromolecule crystal nucleation and growth studies.

The Effect of Solution Thermal History on Chicken Egg White Lysozyme Nucleation

NASA Technical Reports Server (NTRS)

Burke, Michael W.; Judge, Russell A.; Pusey, Marc L.; Rose, M. Franklin (Technical Monitor)

2000-01-01

Proteins are highly flexible molecules and often exhibit defined conformational changes in response to changes in the ambient temperature. Chicken egg white lysozyme has been previously shown to undergo an apparent structural change when warmed above the tetragonal/orthorhombic phase transition temperature. This is reflected by a change in the habit of the tetragonal and orthorhombic crystals so formed. In this study we show that possible conformational changes induced by heating are stable and apparently non- reversible by simple cooling. Exposure of protein solutions to temperatures above the phase change transition temperature, before combining with precipitant solution to begin crystallization, reduces final crystal numbers. Protein that is briefly warmed to 37 C, then cooled shows no sign of reversal to the unheated nucleation behavior even after storage for 4 weeks at 4 C. The change in nucleation behavior of tetragonal lysozyme crystals, attributed to a structural shift, occurs faster the greater the exposure to temperature above the equi-solubility point for the two phases. Heating for 2 h at 48 C reduces crystal numbers by 20 fold in comparison to the same solution heated for the same time at 30 C. Thermal treatment of solutions is therefore a possible tool to reduce crystal numbers and increase crystal size. The effects of a protein's previous thermal history are now shown to be a potentially critical factor in subsequent macromolecule crystal nucleation and growth studies.

Dynamical heat transport amplification in a far-field thermal transistor of VO{sub 2} excited with a laser of modulated intensity

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

Ordonez-Miranda, Jose, E-mail: jose.ordonez@cnrs.pprime.fr; Ezzahri, Younès; Drevillon, Jérémie

2016-05-28

Far-field radiative heat transport in a thermal transistor made up of a vanadium dioxide base excited with a laser of modulated intensity is analytically studied and optimized. This is done by solving the equation of energy conservation for the steady-state and modulated components of the temperature and heat fluxes that the base exchanges with the collector and emitter. The thermal bistability of VO{sub 2} is used to find an explicit condition on the laser intensity required to maximize these heat fluxes to values higher than the incident flux. For a 1 μm-thick base heated with a modulation frequency of 0.5 Hz, itmore » is shown that both the DC and AC components of the heat fluxes are about 4 times the laser intensity, while the AC temperature remains an order of magnitude smaller than the DC one at around 343 K. Higher AC heat fluxes are obtained for thinner bases and/or lower frequencies. Furthermore, we find that out of the bistability temperatures associated with the dielectric-to-metal and metal-to-dielectric transitions of VO{sub 2}, the amplification of the collector-to-base and base-to-emitter heat fluxes is still possible, but at modulation frequencies lower than 0.1 Hz.« less

Single-electron thermal devices coupled to a mesoscopic gate

NASA Astrophysics Data System (ADS)

Sánchez, Rafael; Thierschmann, Holger; Molenkamp, Laurens W.

2017-11-01

We theoretically investigate the propagation of heat currents in a three-terminal quantum dot engine. Electron-electron interactions introduce state-dependent processes which can be resolved by energy-dependent tunneling rates. We identify the relevant transitions which define the operation of the system as a thermal transistor or a thermal diode. In the former case, thermal-induced charge fluctuations in the gate dot modify the thermal currents in the conductor with suppressed heat injection, resulting in huge amplification factors and the possible gating with arbitrarily low energy cost. In the latter case, enhanced correlations of the state-selective tunneling transitions redistribute heat flows giving high rectification coefficients and the unexpected cooling of one conductor terminal by heating the other one. We propose quantum dot arrays as a possible way to achieve the extreme tunneling asymmetries required for the different operations.

Strategy Guideline. Transitioning HVAC Companies to Whole House Performance Contractors

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

Burdick, Arlan

2012-05-01

This report describes the findings from research IBACOS conducted related to heating, ventilation, and air conditioning (HVAC) companies who have made the decision to transition to whole house performance contracting (WHPC).

Shear induced phase transitions induced in edible fats

NASA Astrophysics Data System (ADS)

Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.

2003-03-01

The food industry crystallizes fats under different conditions of temperature and shear to obtain products with desired crystalline phases. Milk fat, palm oil, cocoa butter and chocolate were crystallized from the melt in a temperature controlled Couette cell. Synchrotron x-ray diffraction studies were conducted to examine the role of shear on the phase transitions seen in edible fats. The shear forces on the crystals induced acceleration of the alpha to beta-prime phase transition with increasing shear rate in milk fat and palm oil. The increase was slow at low shear rates and became very strong above 360 s-1. In cocoa butter the acceleration between beta-prime-III and beta-V phase transition increased until a maximum of at 360 s-1, and then decreased, showing competition between enhanced heat transfer and viscous heat generation.

Correlation between thermal annealing temperature and Joule-heating based insulator-metal transition in VO2 nanobeams

NASA Astrophysics Data System (ADS)

Rathi, Servin; Park, Jin-Hyung; Lee, In-yeal; Jin Kim, Min; Min Baik, Jeong; Kim, Gil-Ho

2013-11-01

Rapid thermal annealing of VO2 nanobeams in an ambient argon environment has been carried out at various temperatures after device fabrication. Our analysis revealed that increasing the annealing temperature from 200 °C to 400 °C results in the reduction of both ohmic and nanobeam resistances with an appreciable decrease in joule-heating based transition voltage and transition temperature, while samples annealed at 500 °C exhibited a conducting rutile-phase like characteristics at room temperature. In addition, these variation trends were explored using a physical model and the results were found to be in agreement with the observed results, thus verifying the model.

Fragility and glass transition for binary mixtures of 1,2-propanediol and LiBF4

NASA Astrophysics Data System (ADS)

Terashima, Y.; Mori, M.; Sugimoto, N.; Takeda, K.

2014-04-01

The fragility and glass transition for binary mixtures of 1,2-propanediol and LiBF4 were investigated by measuring the heating rate dependence of glass transition temperature (Tg) using differential scanning calorimetry. With increasing LiBF4 mole fraction, x, up to 0.25, fragility, m, increased rapidly from 53 to 85, and then remained approximately unchanged for x > 0.25. The concentration dependences of Tg and heat capacity jump at Tg also showed anomalies around x = 0.25. We suggest this mixture transformed from a moderate to quite fragile liquid at x = 0.25 because of a structural change from a hydrogen-bonding- to ionic-interaction-dominant system.

Anhydrous octyl-glucoside phase transition from lamellar to isotropic induced by electric and magnetic fields.

PubMed

Hashim, Rauzah; Sugimura, Akihiko; Nguan, Hock-Seng; Rahman, Matiur; Zimmermann, Herbert

2017-02-28

A static deuterium nuclear magnetic resonance ( 2 HNMR) technique (magnetic field, B = 7.05 T) was employed to monitor the thermotropic lamellar phase of the anhydrous 1:1 mixture sample of octyl-b-D-glucoside (βOG) and that of partially deuterium labelled at the alpha position on the chain, i.e.,βOG-d 2 In the absence of an electric field, the 2 H NMR spectrum of the mixture gives a typical quadrupolar doublet representing the aligned lamellar phase. Upon heating to beyond the clearing temperature at 112 °C, this splitting converts to a single line expected for an isotropic phase. Simultaneous application of magnetic and electric fields (E = 0.4 MV/m) at 85 °C in the lamellar phase, whose direction was set to be parallel or perpendicular to the magnetic field, resulted in the change of the doublet into a single line and this recovers to the initial doublet with time for both experimental geometries. This implies E- and B-field-induced phase transitions from the lamellar to an isotropic phase and a recovery to the lamellar phase again with time. Moreover, these phase transformations are accompanied by a transient current. A similar observation was made in a computational study when an electric field was applied to a water cluster system. Increasing the field strength distorts the water cluster and weakens its hydrogen bonds leading to a structural breakdown beyond a threshold field-strength. Therefore, we suggest the observed field-induced transition is likely due to a structure change of the βOG lamellar assembly caused by the field effect and not due to Joule heating.

Navy Expeditionary Technology Transition Program (NETTP)

DTIC Science & Technology

2012-03-02

water vapor from feed air using a zeolite membrane •Temperature/Humidity levels can be met in warm, humid climates without reheating •Allows higher...UNCLASSIFIED, Distribution Unlimited Modular Thermal Hub •Small, efficient absorption cooling •Energy source: Combustion, low- grade waste heat, solar... thermal energy •Reversible operation enables space cooling and heating, and water heating •Modular cooling and heating unit •Monolithic packaging offers

Superconducting properties and μSR study of the noncentrosymmetric superconductor Nb0.5Os0.5.

PubMed

Singh, D; Barker, J A T; Thamizhavel, A; Hillier, A D; Paul, D McK; Singh, R P

2018-01-22

The properties of the noncentrosymmetric superconductor (α-[Formula: see text] structure) Nb 0.5 Os 0.5 have been investigated using resistivity, magnetization, specific heat, and muon spin relaxation and rotation (μSR) measurements. These measurements suggest that Nb 0.5 Os 0.5 is a weakly coupled ([Formula: see text]) type-II superconductor ([Formula: see text]), having a bulk superconducting transition temperature T c   =  3.07 K. The specific heat data fits well with the single-gap BCS model indicating nodeless s-wave superconductivity in Nb 0.5 Os 0.5 . The μSR measurements also confirm [Formula: see text]-wave superconductivity with the preserved time-reversal symmetry.

Photonic Shape Memory Polymer with Stable Multiple Colors

PubMed Central

2017-01-01

A photonic shape memory polymer film that shows large color response (∼155 nm) in a wide temperature range has been fabricated from a semi-interpenetrating network of a cholesteric polymer and poly(benzyl acrylate). The large color response is achieved by mechanical embossing of the photonic film above its broad glass transition temperature. The embossed film, as it recovers to its original shape on heating through the broad thermal transition, exhibits multiple structural colors ranging from blue to orange. The relaxation behavior of the embossed film can be fully described using a Kelvin–Voigt model, which reveals that the influence of temperature on the generation of colors is much stronger than that of time, thereby producing stable multiple colors. PMID:28840717

Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic Insulating BaFeO_{3} Thin Films.

PubMed

Tsuyama, T; Chakraverty, S; Macke, S; Pontius, N; Schüßler-Langeheine, C; Hwang, H Y; Tokura, Y; Wadati, H

2016-06-24

We studied the electronic and magnetic dynamics of ferromagnetic insulating BaFeO_{3} thin films by using pump-probe time-resolved resonant x-ray reflectivity at the Fe 2p edge. By changing the excitation density, we found two distinctly different types of demagnetization with a clear threshold behavior. We assigned the demagnetization change from slow (∼150  ps) to fast (<70  ps) to a transition into a metallic state induced by laser excitation. These results provide a novel approach for locally tuning magnetic dynamics. In analogy to heat-assisted magnetic recording, metallization can locally tune the susceptibility for magnetic manipulation, allowing one to spatially encode magnetic information.

Magnetic transition in Y-site doped multiferroic YMnO{sub 3}

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

Thakur, Rajesh K., E-mail: thakur.rajesh2009@gmail.com; Thakur, Rasna, E-mail: rasnathakur@yahoo.com; Gaur, N. K., E-mail: srl-nkgaur@yahoo.co.in

2016-05-06

We have synthesized polycrystalline hexagonal Y{sub 1-x}Sr{sub x}MnO{sub 3} (x=0.02, 0.1) compounds by using conventional solid state reaction method. The detailed structural investigations are carried out by using XRD studies which reveals the single phase formation of the reported compounds with hexagonal structure and space group P6{sub 3}cm (JCPDS: 25-1079). Further the XRD data of reported compounds were analyzed by RIETVELD (FULLPROFF) method which shows the decrease in the lattice parameter with increasing concentration of divalent strontium to Y-site. The observed pointed kinks in the specific heat study are indicative of the probable coupling in between the electric and magneticmore » orders in this class of materials. The reported systematic specific heat studies shows that the antiferromagnetic (AFM) transition temperature (T{sub N}) shifts to higher value with increasing concentration of Sr{sup 2+} ion in the YMnO{sub 3} compound which is attributed to the enhanced lattice contribution to the specific heat in the this compound. The present compound shows the independence of specific heat and magnetic transition temperature with applied magnetic field of 8T and 12T.« less

The transition from natural convection to thermomagnetic convection of a magnetic fluid in a non-uniform magnetic field

NASA Astrophysics Data System (ADS)

Szabo, Peter S. B.; Früh, Wolf-Gerrit

2018-02-01

Magnetic fluid flow and heat transfer by natural and thermomagnetic convection was studied numerically in a square enclosure. The aim was to investigate the transition from natural convection to thermomagnetic convection by exploring situations where buoyancy and the Kelvin body force would be opposing each other such that the magnetic effects would in some cases be the dominant factor throughout the domain and in other cases only in a part of the fluid. The numerical model coupled the solution of the magnetostatic field equation with the heat and fluid flow equations to simulate the fluid flow under a realistic magnetic field generated by a permanent magnet. The results suggest that the domain of influence over the flow field is largely aligned with the domain of dominance of the respective driving force. The result is that the transition from a single buoyancy-driven convection cell to a single thermomagnetically driven cell is via a two-cell structure and that the local effect on the flow field leads to a global effect on the heat transfer with a minimum of the Nusselt number in the transition region.

Melting of the Dipalmitoylphosphatidylcholine Monolayer.

PubMed

Xu, Lu; Bosiljevac, Gordon; Yu, Kyle; Zuo, Yi Y

2018-04-17

Langmuir monolayer self-assembled at the air-water interface represents an excellent model for studying phase transition and lipid polymorphism in two dimensions. Compared with numerous studies of phospholipid phase transitions induced by isothermal compression, there are very scarce reports on two-dimensional phase transitions induced by isobaric heating. This is mainly due to technical difficulties of continuously regulating temperature variations while maintaining a constant surface pressure in a classical Langmuir-type film balance. Here, with technological advances in constrained drop surfactometry and closed-loop axisymmetric drop shape analysis, we studied the isobaric heating process of the dipalmitoylphosphatidylcholine (DPPC) monolayer. It is found that temperature and surface pressure are two equally important intensive properties that jointly determine the phase behavior of the phospholipid monolayer. We have determined a critical point of the DPPC monolayer at a temperature of 44 °C and a surface pressure of 57 mN/m. Beyond this critical point, no phase transition can exist in the DPPC monolayer, either by isothermal compression or by isobaric heating. The melting process of the DPPC monolayer studied here provides novel insights into the understanding of a wide range of physicochemical and biophysical phenomena, such as surface thermodynamics, critical phenomena, and biophysical study of pulmonary surfactants.

Minnowbrook IV: 2003 Workshop on Transition and Unsteady Aspects of Turbomachinery Flows

NASA Technical Reports Server (NTRS)

LaGraff, John E. (Editor); Ashpis, David E.

2004-01-01

This Minnowbrook IV 2003 workshop on Transition and Unsteady Aspects of Turbomachinery Flows includes the following topics: 1) Current Issues in Unsteady Turbomachinery Flows; 2) Global Instability and Control of Low-Pressure Turbine Flows; 3) Influence of End Wall Leakage on Secondary Flow Development in Axial Turbines; 4) Active and Passive Flow Control on Low Pressure Turbine Airfoils; 5) Experimental and Numerical Investigation of Transitional Flows as Affected by Passing Wakes; 6) Effects of Freestream Turbulence on Turbine Blade Heat Transfer; 7) Bypass Transition Via Continuous Modes and Unsteady Effects on Film Cooling; 8) High Frequency Surface Heat Flux Imaging of Bypass Transition; 9) Skin Friction and Heat Flux Oscillations in Upstream Moving Wave Packets; 10) Transition Mechanisms and Use of Surface Roughness to Enhance the Benefits of Wake Passing in LP Turbines; 11) Transient Growth Approach to Roughness-Induced Transition; 12) Roughness- and Freestream-Turbulence-Induced Transient Growth as a Bypass Transition Mechanism; 13) Receptivity Calculations as a Means to Predicting Transition; 14) On Streamwise Vortices in a Curved Wall Jet and Their Effect on the Mean Flow; 15) Plasma Actuators for Separation Control of Low Pressure Turbine Blades; 16) Boundary-Layer Separation Control Under Low-Pressure-Turbine Conditions Using Glow-Discharge Plasma Actuators; 17) Control of Separation for Low Pressure Turbine Blades: Numerical Simulation; 18) Effects of Elevated Free-Stream Turbulence on Active Control of a Separation Bubble; 19) Wakes, Calming and Transition Under Strong Adverse Pressure Gradients; 20) Transitional Bubble in Periodic Flow Phase Shift; 21) Modelling Spots: The Calmed Region, Pressure Gradient Effects and Background; 22) Modeling of Unsteady Transitional Flow on Axial Compressor Blades; 23) Challenges in Predicting Component Efficiencies in Turbomachines With Low Reynolds Number Blading; 24) Observations on the Causal Relationship Between Blade Count and Developing Rotating Stall in a Four Stage Axial Compressor; 25) Experimental and Numerical Study of Non-Linear Interactions in Transonic Nozzle Flow; 26) Clocking Effects on a Modern Stage and One-Half Transonic Turbine; 27) DNS and LES of Transition on Turbine Blades; 28) The Use of Cellular Automata in Modeling the Transition; 29) Predicting Unsteady Buffet Onset Using RANS Solutions; 30) Transition Modelling With the SST Turbulence Model and an Intermittency Transport; and 31) Equation Workshop Summary Transcript

Vertical structure and physical processes of the Madden-Julian Oscillation: Biases and uncertainties at short range

NASA Astrophysics Data System (ADS)

Xavier, Prince K.; Petch, Jon C.; Klingaman, Nicholas P.; Woolnough, Steve J.; Jiang, Xianan; Waliser, Duane E.; Caian, Mihaela; Cole, Jason; Hagos, Samson M.; Hannay, Cecile; Kim, Daehyun; Miyakawa, Tomoki; Pritchard, Michael S.; Roehrig, Romain; Shindo, Eiki; Vitart, Frederic; Wang, Hailan

2015-05-01

An analysis of diabatic heating and moistening processes from 12 to 36 h lead time forecasts from 12 Global Circulation Models are presented as part of the "Vertical structure and physical processes of the Madden-Julian Oscillation (MJO)" project. A lead time of 12-36 h is chosen to constrain the large-scale dynamics and thermodynamics to be close to observations while avoiding being too close to the initial spin-up of the models as they adjust to being driven from the Years of Tropical Convection (YOTC) analysis. A comparison of the vertical velocity and rainfall with the observations and YOTC analysis suggests that the phases of convection associated with the MJO are constrained in most models at this lead time although the rainfall in the suppressed phase is typically overestimated. Although the large-scale dynamics is reasonably constrained, moistening and heating profiles have large intermodel spread. In particular, there are large spreads in convective heating and moistening at midlevels during the transition to active convection. Radiative heating and cloud parameters have the largest relative spread across models at upper levels during the active phase. A detailed analysis of time step behavior shows that some models show strong intermittency in rainfall and differences in the precipitation and dynamics relationship between models. The wealth of model outputs archived during this project is a very valuable resource for model developers beyond the study of the MJO. In addition, the findings of this study can inform the design of process model experiments, and inform the priorities for field experiments and future observing systems.

Characterization of BaTiO3 nanocubes assembled into highly ordered monolayers using micro- and nano-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Itasaka, Hiroki; Mimura, Ken-ichi; Nishi, Masayuki; Kato, Kazumi

2018-05-01

We investigated the influence of heat treatment on the crystallographic structure and ferroelectric phase transition behavior of barium titanate (BaTiO3, BT) nanocubes assembled into highly ordered monolayers, using tip-enhanced Raman spectroscopy (TERS), temperature-dependent micro-Raman spectroscopy, and scanning transmission electron microscopy (STEM). TER spectra from individual BT nanocubes with the size of about 20 nm were obtained with a side-illumination optical setup, and revealed that heat treatment enhances their tetragonality. The result of temperature-dependent micro-Raman spectroscopy showed that the ferroelectric phase transition behavior of the monolayers becomes similar to that of bulk BT through heat treatment in spite of their thickness. STEM observation for the cross-section of the heated BT nanocube monolayer showed that amorphous layers exist at the interface between BT nanocubes in face-to-face contact. These results indicate that the tetragonal crystal structure of BT nanocubes is stabilized by heat treatment and the formation of the interfacial amorphous layer during heat treatment may be a key to this phenomenon.

Effects of Freestream Turbulence on Turbine Blade Heat Transfer

NASA Technical Reports Server (NTRS)

Boyle, Robert J.; Giel, Paul W.; Ames, Forrest E.

2004-01-01

Experiments have shown that moderate turbulence levels can nearly double turbine blade stagnation region heat transfer. Data have also shown that heat transfer is strongly affected by the scale of turbulence as well as its level. In addition to the stagnation region, turbulence is often seen to increase pressure surface heat transfer. This is especially evident at low to moderate Reynolds numbers. Vane and rotor stagnation region, and vane pressure surface heat transfer augmentation is often seen in a pre-transition environment. Accurate predictions of transition and relaminarization are critical to accurately predicting blade surface heat transfer. An approach is described which incorporates the effects of both turbulence level and scale into a CFD analysis. The model is derived from experimental data for cylindrical and elliptical leadng edges. Results using this model are compared to experimental data for both vane and rotor geometries. The comparisons are made to illustrate that using a model which includes the effects of turbulence length scale improves agreement with data, and to illustrate where improvements in the modeling are needed.

Convective heat transfer studies at high temperatures with pressure gradient for inlet flow Mach number of 0.45

NASA Technical Reports Server (NTRS)

Pedrosa, A. C. F.; Nagamatsu, H. T.; Hinckel, J. A.

1984-01-01

Heat transfer measurements were determined for a flat plate with and without pressure gradient for various free stream temperatures, wall temperature ratios, and Reynolds numbers for an inlet flow Mach number of 0.45, which is a representative inlet Mach number for gas turbine rotor blades. A shock tube generated the high temperature and pressure air flow, and a variable geometry test section was used to produce inlet flow Mach number of 0.45 and accelerate the flow over the plate to sonic velocity. Thin-film platinum heat gages recorded the local heat flux for laminar, transition, and turbulent boundary layers. The free stream temperatures varied from 611 R (339 K) to 3840 R (2133 K) for a T(w)/T(r,g) temperature ratio of 0.87 to 0.14. The Reynolds number over the heat gages varied from 3000 to 690,000. The experimental heat transfer data were correlated with laminar and turbulent boundary layer theories for the range of temperatures and Reynolds numbers and the transition phenomenon was examined.

Determination of heat transfer coefficients in plastic French straws plunged in liquid nitrogen.

PubMed

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

2014-12-01

The knowledge of the thermodynamic process during the cooling of reproductive biological systems is important to assess and optimize the cryopreservation procedures. The time-temperature curve of a sample immersed in liquid nitrogen enables the calculation of cooling rates and helps to determine whether it is vitrified or undergoes phase change transition. When dealing with cryogenic liquids, the temperature difference between the solid and the sample is high enough to cause boiling of the liquid, and the sample can undergo different regimes such as film and/or nucleate pool boiling. In the present work, the surface heat transfer coefficients (h) for plastic French straws plunged in liquid nitrogen were determined using the measurement of time-temperature curves. When straws filled with ice were used the cooling curve showed an abrupt slope change which was attributed to the transition of film into nucleate pool boiling regime. The h value that fitted each stage of the cooling process was calculated using a numerical finite element program that solves the heat transfer partial differential equation under transient conditions. In the cooling process corresponding to film boiling regime, the h that best fitted experimental results was h=148.12±5.4 W/m(2) K and for nucleate-boiling h=1355±51 W/m(2) K. These values were further validated by predicting the time-temperature curve for French straws filled with a biological fluid system (bovine semen-extender) which undergoes freezing. Good agreement was obtained between the experimental and predicted temperature profiles, further confirming the accuracy of the h values previously determined for the ice-filled straw. These coefficients were corroborated using literature correlations. The determination of the boiling regimes that govern the cooling process when plunging straws in liquid nitrogen constitutes an important issue when trying to optimize cryopreservation procedures. Furthermore, this information can lead to improvements in the design of cooling devices in the cryobiology field. Copyright © 2014 Elsevier Inc. All rights reserved.

One-Way Multishape-Memory Effect and Tunable Two-Way Shape Memory Effect of Ionomer Poly(ethylene-co-methacrylic acid).

PubMed

Lu, Lu; Li, Guoqiang

2016-06-15

Reversible elongation by cooling and contraction by heating, without the need for repeated programming, is well-known as the two-way shape-memory effect (2W-SME). This behavior is contrary to the common physics-contraction when cooling and expansion when heating. Materials with such behavior may find many applications in real life, such as self-sufficient grippers, fastening devices, optical gratings, soft actuators, and sealant. Here, it is shown that ionomer Surlyn 8940, a 50-year old polymer, exhibits both one-way multishape-memory effects and tunable two-way reversible actuation. The required external tensile stress to trigger the tunable 2W-SME is very low when randomly jumping the temperatures within the melting transition window. With a proper one-time programming, "true" 2W-SME (i.e., 2W-SME without the need for an external tensile load) is also achieved. A long training process is not needed to trigger the tunable 2W-SME. Instead, a proper one-time tensile programming is sufficient to trigger repeated and tunable 2W-SME. Because the 2W-SME of the ionomer Surlyn is driven by the thermally reversible network, here crystallization and melting transitions of the semicrystalline poly(ethylene-co-methacrylic acid), it is believed that a class of thermally reversible polymers should also exhibit tunable 2W-SMEs.

Shape transition with temperature of the pear-shaped nuclei in covariant density functional theory

DOE PAGES

Zhang, Wei; Niu, Yi-Fei

2017-11-10

The shape evolutions of the pear-shaped nucleimore » $$^{224}$$Ra and even-even $$^{144-154}$$Ba with temperature are investigated by the finite-temperature relativistic mean field theory with the treatment of pairing correlations by the BCS approach. We study the free energy surfaces as well as the bulk properties including deformations, pairing gaps, excitation energy, and specific heat for the global minimum. For $$^{224}$$Ra, three discontinuities found in the specific heat curve indicate the pairing transition at temperature 0.4 MeV, and two shape transitions at temperatures 0.9 and 1.0 MeV, namely one from quadrupole-octupole deformed to quadrupole deformed, and the other from quadrupole deformed to spherical. Furthermore, the gaps at $N$=136 and $Z$=88 are responsible for stabilizing the octupole-deformed global minimum at low temperatures. Similar pairing transition at $$T\\sim$$0.5 MeV and shape transitions at $T$=0.5-2.2 MeV are found for even-even $$^{144-154}$$Ba. Finally, the transition temperatures are roughly proportional to the corresponding deformations at the ground states.« less

The deconfining phase transition in and out of equilibrium

NASA Astrophysics Data System (ADS)

Bazavov, Oleksiy

Recent experiments carried out at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory provide strong evidence that a matter can be driven from a confined, low-temperature phase, observed in our every day world into a deconfined high-temperature phase of liberated quarks and gluons. The equilibrium and dynamical properties of the deconfining phase transition are thus of great theoretical interest, since they also provide an information about the first femtoseconds of the evolution of our Universe, when the hot primordial soup while cooling has undergone a chain of phase transitions. The aspects of the deconfining phase transition studied in this work include: the dynamics of the SU(3) gauge theory after the heating quench (which models rapid heating in the heavy-ion collisions), equilibrium properties of the phase transition in the SU(3) gauge theory with boundaries at low temperature (small volumes at RHIC suggest that boundary effects cannot be neglected and periodic boundary conditions normally used in lattice simulations do not correspond to the experimental situation), and a study of the order of the transition in U(1) gauge theory.

Thermal Analysis Methods and Basic Heat-Transfer Data for a Turbulent Heating Flight Experiment at Mach 20 (Reentry F)

NASA Technical Reports Server (NTRS)

Howard, Floyd G.

1971-01-01

A heat-transfer experiment was flight conducted on a 5 deg half-angle cone, 396.2 cm (13 ft) in length, as it entered the sensible atmosphere under laminar, transitional, and turbulent boundary-layer conditions at a free-stream Mach number of about 20. Accurate turbulent-heat-transfer data with natural transition were obtained for correlation with theories in regions of simultaneous high Mach number, Reynolds number, enthalpy, and total-to-wall temperature ratio. Temperatures were measured at four depths through the 15.24-mm-thick (0.600-in.) beryllium wall. Experimental heating rates at 20 stations on the cone were determined independently from the outermost temperature measurement and from the temperature measurement at the second depth by a single-thermocouple inverse method and also from the temperature histories at all four depths by an integral method. The thermal data analysis procedure, associated problems, and results are presented herein.

Fundamental Boiling and RP-1 Freezing Experiments

NASA Technical Reports Server (NTRS)

Goode, Brian

2002-01-01

The prestart thermal conditioning of the hardware in LOX (liquid oxygen) systems involve heat transfer between LOX and metal where boiling plays a large role. Information is easily found on nucleate boiling, maximum heat flux, minimum heat flux and film boiling for common fluids like water. After looking at these standard correlations it was felt more data was needed for the cool down side transition boiling for the LN2 and LOX. In particular interest is the film boiling values, the temperature at which transition begins and the slope as peak heat flux is approached. The ultimate goal is an array of boiling heat transfer coefficient as a function of surface temperature which can be used in the chilldown model of the feed system, engine and bleed system for X-34. The first experiment consisted of an actual MC-1 LOX Impeller which had been machined backwards, that was instrumented with 17 surface thermocouples and submerged in liquid nitrogen. The thermocouples were installed on metal thicknesses varying from the thin inducer to the thick hub.

Influence of the variable thermophysical properties on the turbulent buoyancy-driven airflow inside open square cavities

NASA Astrophysics Data System (ADS)

Zamora, Blas; Kaiser, Antonio S.

2012-01-01

The effects of the air variable properties (density, viscosity and thermal conductivity) on the buoyancy-driven flows established in open square cavities are investigated, as well as the influence of the stated boundary conditions at open edges and the employed differencing scheme. Two-dimensional, laminar, transitional and turbulent simulations are obtained, considering both uniform wall temperature and uniform heat flux heating conditions. In transitional and turbulent cases, the low-Reynolds k - ω turbulence model is employed. The average Nusselt number and the dimensionless mass-flow rate have been obtained for a wide and not yet covered range of the Rayleigh number varying from 103 to 1016. The results obtained taking into account variable properties effects are compared with those calculated assuming constant properties and the Boussinesq approximation. For uniform heat flux heating, a correlation for the critical heating parameter above which the burnout phenomenon can be obtained is presented, not reported in previous works. The effects of variable properties on the flow patterns are analyzed.

Turbulent heat flux measurements in a transitional boundary layer

NASA Technical Reports Server (NTRS)

Sohn, K. H.; Zaman, K. B. M. Q.; Reshotko, E.

1992-01-01

During an experimental investigation of the transitional boundary layer over a heated flat plate, an unexpected result was encountered for the turbulent heat flux (bar-v't'). This quantity, representing the correlation between the fluctuating normal velocity and the temperature, was measured to be negative near the wall under certain conditions. The result was unexpected as it implied a counter-gradient heat transfer by the turbulent fluctuations. Possible reasons for this anomalous result were further investigated. The possible causes considered for this negative bar-v't' were: (1) plausible measurement error and peculiarity of the flow facility, (2) large probe size effect, (3) 'streaky structure' in the near wall boundary layer, and (4) contributions from other terms usually assumed negligible in the energy equation including the Reynolds heat flux in the streamwise direction (bar-u't'). Even though the energy balance has remained inconclusive, none of the items (1) to (3) appear to be contributing directly to the anomaly.

Correlation of HIFiRE-5 Flight Data with Computed Pressure and Heat Transfer (Postprint)

DTIC Science & Technology

2015-06-01

AFRL-RQ-WP-TP-2015-0149 CORRELATION OF HIFiRE-5 FLIGHT DATA WITH COMPUTED PRESSURE AND HEAT TRANSFER (POSTPRINT) Joseph S. Jewell...results with St was compared to flight heat transfer measurements, and transition locations were inferred. Finally, a computational heat conduction...HIFiRE-5 Flight Data With Computed Pressure and Heat Transfer Joseph S. Jewell,1 James H. Miller,2 and Roger L. Kimmel3 U.S. Air Force Research

Optical absorption in recycled waste plastic polyethylene

NASA Astrophysics Data System (ADS)

Aji, M. P.; Rahmawati, I.; Priyanto, A.; Karunawan, J.; Wati, A. L.; Aryani, N. P.; Susanto; Wibowo, E.; Sulhadi

2018-03-01

We investigated the optical properties of UV spectrum absorption in recycled waste plastic from polyethylene polymer type. Waste plastic polyethylene showed an optical spectrum absorption after it’s recycling process. Spectrum absorption is determined using spectrophotometer UV-Nir Ocean Optics type USB 4000. Recycling method has been processed using heating treatment around the melting point temperature of the polyethylene polymer that are 200°C, 220°C, 240°C, 260°C, and 280°C. In addition, the recycling process was carried out with time variations as well, which are 1h, 1.5h, 2h, and 2.5h. The result of this experiment shows that recycled waste plastic polyethylene has a spectrum absorption in the ∼ 340-550 nm wavelength range. The absorbance spectrum obtained from UV light which is absorbed in the orbital n → π* and the orbital π → π*. This process indicates the existence of electron transition phenomena. This mechanism is affected by the temperature and the heating time where the intensity of absorption increases and widens with the increase of temperature and heating time. Furthermore this study resulted that the higher temperature affected the enhancement of the band gap energy of waste plastic polyethylene. These results show that recycled waste plastic polyethylene has a huge potential to be absorber materials for solar cell.

Heat accumulation period in the Mediterranean region: phenological response of the olive in different climate areas (Spain, Italy and Tunisia).

PubMed

Aguilera, Fátima; Ruiz, Luis; Fornaciari, Marco; Romano, Bruno; Galán, Carmen; Oteros, Jose; Ben Dhiab, Ali; Msallem, Monji; Orlandi, Fabio

2014-07-01

The main characteristics of the heat accumulation period and the possible existence of different types of biological response to the environment in different populations of olive through the Mediterranean region have been evaluated. Chilling curves to determine the start date of the heat accumulation period were constructed and evaluated. The results allow us to conclude that the northern olive populations have the greatest heat requirements for the development of their floral buds, and they need a period of time longer than olives in others areas to completely satisfy their biothermic requirements. The olive trees located in the warmest winter areas have a faster transition from endogenous to exogenous inhibition once the peak of chilling is met, and they show more rapid floral development. The lower heat requirements are due to better adaptation to warmer regions. Both the threshold temperature and the peak of flowering date are closely related to latitude. Different types of biological responses of olives to the environment were found. The adaptive capacity shown by the olive tree should be considered as a useful tool with which to study the effects of global climatic change on agro-ecosystems.