Hybrid photovoltaic–thermal solar collectors dynamic modeling

International Nuclear Information System (INIS)

Amrizal, N.; Chemisana, D.; Rosell, J.I.

2013-01-01

Highlights: ► A hybrid photovoltaic/thermal dynamic model is presented. ► The model, once calibrated, can predict the power output for any set of climate data. ► The physical electrical model includes explicitly thermal and irradiance dependences. ► The results agree with those obtained through steady-state characterization. ► The model approaches the junction cell temperature through the system energy balance. -- Abstract: A hybrid photovoltaic/thermal transient model has been developed and validated experimentally. The methodology extends the quasi-dynamic thermal model stated in the EN 12975 in order to involve the electrical performance and consider the dynamic behavior minimizing constraints when characterizing the collector. A backward moving average filtering procedure has been applied to improve the model response for variable working conditions. Concerning the electrical part, the model includes the thermal and radiation dependences in its variables. The results revealed that the characteristic parameters included in the model agree reasonably well with the experimental values obtained from the standard steady-state and IV characteristic curve measurements. After a calibration process, the model is a suitable tool to predict the thermal and electrical performance of a hybrid solar collector, for a specific weather data set.

Thermal transpiration: A molecular dynamics study

Energy Technology Data Exchange (ETDEWEB)

T, Joe Francis [Computational Nanotechnology Laboratory, School of Nano Science and Technology, National Institute of Technology Calicut, Kozhikode (India); Sathian, Sarith P. [Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai (India)

2014-12-09

Thermal transpiration is a phenomenon where fluid molecules move from the cold end towards the hot end of a channel under the influence of longitudinal temperature gradient alone. Although the phenomenon of thermal transpiration is observed at rarefied gas conditions in macro systems, the phenomenon can occur at atmospheric pressure if the characteristic dimensions of the channel is less than 100 nm. The flow through these nanosized channels is characterized by the free molecular flow regimes and continuum theory is inadequate to describe the flow. Thus a non-continuum method like molecular dynamics (MD) is necessary to study such phenomenon. In the present work, MD simulations were carried out to investigate the occurance of thermal transpiration in copper and platinum nanochannels at atmospheric pressure conditions. The mean pressure of argon gas confined inside the nano channels was maintained around 1 bar. The channel height is maintained at 2nm. The argon atoms interact with each other and with the wall atoms through the Lennard-Jones potential. The wall atoms are modelled using an EAM potential. Further, separate simulations were carried out where a Harmonic potential is used for the atom-atom interaction in the platinum channel. A thermally insulating wall was introduced between the low and high temperature regions and those wall atoms interact with fluid atoms through a repulsive potential. A reduced cut off radius were used to achieve this. Thermal creep is induced by applying a temperature gradient along the channel wall. It was found that flow developed in the direction of the increasing temperature gradient of the wall. An increase in the volumetric flux was observed as the length of the cold and the hot regions of the wall were increased. The effect of temperature gradient and the wall-fluid interaction strength on the flow parameters have been studied to understand the phenomenon better.

Thermal conductivity of graphene with defects induced by electron beam irradiation

Science.gov (United States)

Malekpour, Hoda; Ramnani, Pankaj; Srinivasan, Srilok; Balasubramanian, Ganesh; Nika, Denis L.; Mulchandani, Ashok; Lake, Roger K.; Balandin, Alexander A.

2016-07-01

We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management.We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is

Non-Fourier based thermal-mechanical tissue damage prediction for thermal ablation.

Science.gov (United States)

Li, Xin; Zhong, Yongmin; Smith, Julian; Gu, Chengfan

2017-01-02

Prediction of tissue damage under thermal loads plays important role for thermal ablation planning. A new methodology is presented in this paper by combing non-Fourier bio-heat transfer, constitutive elastic mechanics as well as non-rigid motion of dynamics to predict and analyze thermal distribution, thermal-induced mechanical deformation and thermal-mechanical damage of soft tissues under thermal loads. Simulations and comparison analysis demonstrate that the proposed methodology based on the non-Fourier bio-heat transfer can account for the thermal-induced mechanical behaviors of soft tissues and predict tissue thermal damage more accurately than classical Fourier bio-heat transfer based model.

Molecular Dynamics Studies of Thermal Induced Chemistry in Tatb

Science.gov (United States)

Quenneville, J.; Germann, T. C.; Thompson, A. P.; Kober, E. M.

2007-12-01

A reactive force field (ReaxFF) is used with molecular dynamics to probe the chemistry induced by intense heating (`accelerated cook-off') of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Large-system simulations are desired for TATB because of the high degree of carbon clustering expected in this material. Using small, 32-molecule simulations, we calculate the reaction rate as a function of temperature and compare the Arrhenius-predicted activation energy with experiment. Decomposition product evolution (mainly N2, H2O, CO2 and graphitic carbon clusters) is followed using a 576-molecule larger simulation, which also illustrates the effect of system size on both carbon clustering and reaction rate.

Interaction of alpha radiation with thermally-induced defects in silicon

International Nuclear Information System (INIS)

Ali, Akbar; Majid, Abdul

2008-01-01

The interaction of radiation-induced defects created by energetic alpha particles and thermally-induced defects in silicon has been studied using a Deep Level Transient Spectroscopy (DLTS) technique. Two thermally-induced defects at energy positions E c -0.48 eV and E c -0.25 eV and three radiation-induced defects E2, E3 and E5 have been observed. The concentration of both of the thermally-induced defects has been observed to increase on irradiation. It has been noted that production rates of the radiation-induced defects are suppressed in the presence of thermally-induced defects. A significant difference in annealing characteristics of thermally-induced defects in the presence of radiation-induced defects has been observed compared to the characteristics measured in pre-irradiated samples

Thermal-mechanical deformation modelling of soft tissues for thermal ablation.

Science.gov (United States)

Li, Xin; Zhong, Yongmin; Jazar, Reza; Subic, Aleksandar

2014-01-01

Modeling of thermal-induced mechanical behaviors of soft tissues is of great importance for thermal ablation. This paper presents a method by integrating the heating process with thermal-induced mechanical deformations of soft tissues for simulation and analysis of the thermal ablation process. This method combines bio-heat transfer theories, constitutive elastic material law under thermal loads as well as non-rigid motion dynamics to predict and analyze thermal-mechanical deformations of soft tissues. The 3D governing equations of thermal-mechanical soft tissue deformation are discretized by using the finite difference scheme and are subsequently solved by numerical algorithms. Experimental results show that the proposed method can effectively predict the thermal-induced mechanical behaviors of soft tissues, and can be used for the thermal ablation therapy to effectively control the delivered heat energy for cancer treatment.

Thermal coupling effect on the vortex dynamics of superconducting thin films: time-dependent Ginzburg–Landau simulations

Science.gov (United States)

Jing, Ze; Yong, Huadong; Zhou, Youhe

2018-05-01

In this paper, vortex dynamics of superconducting thin films are numerically investigated by the generalized time-dependent Ginzburg–Landau (TDGL) theory. Interactions between vortex motion and the motion induced energy dissipation is considered by solving the coupled TDGL equation and the heat diffusion equation. It is found that thermal coupling has significant effects on the vortex dynamics of superconducting thin films. Branching in the vortex penetration path originates from the coupling between vortex motion and the motion induced energy dissipation. In addition, the environment temperature, the magnetic field ramp rate and the geometry of the superconducting film also greatly influence the vortex dynamic behaviors. Our results provide new insights into the dynamics of superconducting vortices, and give a mesoscopic understanding on the channeling and branching of vortex penetration paths during flux avalanches.

Transient thermal driven bubble's surface and its potential ultrasound-induced damage

Science.gov (United States)

Movahed, Pooya; Freund, Jonathan B.

2017-11-01

Ultrasound-induced bubble activity in soft tissues is well-known to be a potential injury mechanism in therapeutic ultrasound treatments. We consider damage by transient thermal effects, including a hypothetical mechanism based on transient thermal phenomena, including viscous dissipation. A spherically symmetric compressible Navier-Stokes discretization is developed to solve the full governing equations, both inside and outside of the bubble, without the usual simplifications in the Rayleigh-Plesset bubble dynamics approach. Equations are solved in the Lagrangian framework, which provides a sharp and accurate representation of the interface as well as the viscous dissipation and thermal transport effects, which preclude reduction to the usual Rayleigh-Plesset ordinary differential equation. This method is used to study transient thermal effects at different frequencies and pressure amplitudes relevant to therapeutic ultrasound treatments. High temperatures achieved in the surrounding medium during the violent bubble collapse phase due to the viscous dissipation in the surrounding medium and thermal conduction from the bubble are expected to cause damage. This work was supported by NIH NIDDK Grant P01-DK043881.

Thermal dynamics of thermoelectric phenomena from frequency resolved methods

Directory of Open Access Journals (Sweden)

J. García-Cañadas

2016-03-01

Full Text Available Understanding the dynamics of thermoelectric (TE phenomena is important for the detailed knowledge of the operation of TE materials and devices. By analyzing the impedance response of both a single TE element and a TE device under suspended conditions, we provide new insights into the thermal dynamics of these systems. The analysis is performed employing parameters such as the thermal penetration depth, the characteristic thermal diffusion frequency and the thermal diffusion time. It is shown that in both systems the dynamics of the thermoelectric response is governed by how the Peltier heat production/absorption at the junctions evolves. In a single thermoelement, at high frequencies the thermal waves diffuse semi-infinitely from the junctions towards the half-length. When the frequency is reduced, the thermal waves can penetrate further and eventually reach the half-length where they start to cancel each other and further penetration is blocked. In the case of a TE module, semi-infinite thermal diffusion along the thickness of the ceramic layers occurs at the highest frequencies. As the frequency is decreased, heat storage in the ceramics becomes dominant and starts to compete with the diffusion of the thermal waves towards the half-length of the thermoelements. Finally, the cancellation of the waves occurs at the lowest frequencies. It is demonstrated that the analysis is able to identify and separate the different physical processes and to provide a detailed understanding of the dynamics of different thermoelectric effects.

Dynamic thermal analysis of machines in running state

CERN Document Server

Wang, Lihui

2014-01-01

With the increasing complexity and dynamism in today’s machine design and development, more precise, robust and practical approaches and systems are needed to support machine design. Existing design methods treat the targeted machine as stationery. Analysis and simulation are mostly performed at the component level. Although there are some computer-aided engineering tools capable of motion analysis and vibration simulation etc., the machine itself is in the dry-run state. For effective machine design, understanding its thermal behaviours is crucial in achieving the desired performance in real situation. Dynamic Thermal Analysis of Machines in Running State presents a set of innovative solutions to dynamic thermal analysis of machines when they are put under actual working conditions. The objective is to better understand the thermal behaviours of a machine in real situation while at the design stage. The book has two major sections, with the first section presenting a broad-based review of the key areas of ...

Effect of point defects on the thermal conductivity of UO2: molecular dynamics simulations

Energy Technology Data Exchange (ETDEWEB)

Liu, Xiang-Yang [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Stanek, Christopher Richard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Andersson, Anders David Ragnar [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2015-07-21

The thermal conductivity of uranium dioxide (UO₂) fuel is an important materials property that affects fuel performance since it is a key parameter determining the temperature distribution in the fuel, thus governing, e.g., dimensional changes due to thermal expansion, fission gas release rates, etc. [1] The thermal conductivity of UO₂ nuclear fuel is also affected by fission gas, fission products, defects, and microstructural features such as grain boundaries. Here, molecular dynamics (MD) simulations are carried out to determine quantitatively, the effect of irradiation induced point defects on the thermal conductivity of UO₂, as a function of defect concentrations, for a range of temperatures, 300 – 1500 K. The results will be used to develop enhanced continuum thermal conductivity models for MARMOT and BISON by INL. These models express the thermal conductivity as a function of microstructure state-variables, thus enabling thermal conductivity models with closer connection to the physical state of the fuel [2].

Haptization of molecular dynamics simulation with thermal display

International Nuclear Information System (INIS)

Tamura, Yuichi; Fujiwara, Susumu; Nakamura, Hiroaki

2010-01-01

Thermal display, which is a type of haptic display, is effective in providing intuitive information of temperature. However, in many studies, the user has assumed a sitting position during the use of these devices. In contrast, the user generally watches 3D objects while standing and walking around in large-scale virtual reality system, In addition, in scientific visualization, the response time is very important for observing physical phenomena, especially for dynamic numerical simulation. One solution is to provide two types of thermal information: information about the rate of thermal change and information about the actual temperature. We propose a thermal display with two Peltier elements which can show above two pairs of information and the result (for example energy and temperature, as thermal information) of numerical simulation. Finally, we represent an example of visualizing and haptizing the result of molecular dynamics simulation. (author)

Dynamic thermal characteristics of heat pipe via segmented thermal resistance model for electric vehicle battery cooling

Science.gov (United States)

Liu, Feifei; Lan, Fengchong; Chen, Jiqing

2016-07-01

Heat pipe cooling for battery thermal management systems (BTMSs) in electric vehicles (EVs) is growing due to its advantages of high cooling efficiency, compact structure and flexible geometry. Considering the transient conduction, phase change and uncertain thermal conditions in a heat pipe, it is challenging to obtain the dynamic thermal characteristics accurately in such complex heat and mass transfer process. In this paper, a ;segmented; thermal resistance model of a heat pipe is proposed based on thermal circuit method. The equivalent conductivities of different segments, viz. the evaporator and condenser of pipe, are used to determine their own thermal parameters and conditions integrated into the thermal model of battery for a complete three-dimensional (3D) computational fluid dynamics (CFD) simulation. The proposed ;segmented; model shows more precise than the ;non-segmented; model by the comparison of simulated and experimental temperature distribution and variation of an ultra-thin micro heat pipe (UMHP) battery pack, and has less calculation error to obtain dynamic thermal behavior for exact thermal design, management and control of heat pipe BTMSs. Using the ;segmented; model, the cooling effect of the UMHP pack with different natural/forced convection and arrangements is predicted, and the results correspond well to the tests.

Study of the thermal effect on silicon surface induced by ion beam from plasma focus device

Energy Technology Data Exchange (ETDEWEB)

Ahmad, Z., E-mail: pscientific5@aec.org.sy [Scientific Service Department, Atomic Energy Commission of Syria, P.O. Box: 6091, Damascus (Syrian Arab Republic); Ahmad, M. [IBA Laboratory, Atomic Energy Commission of Syria, P.O. Box: 6091, Damascus (Syrian Arab Republic); Chemistry Department, Atomic Energy Commission of Syria, P.O. Box: 6091, Damascus (Syrian Arab Republic); Al-Hawat, Sh.; Akel, M. [Physics Department, Atomic Energy Commission of Syria, P.O. Box: 6091, Damascus (Syrian Arab Republic)

2017-04-01

Structural modifications in form of ripples and cracks are induced by nitrogen ions from plasma focus on silicon surface. The investigation of such structures reveals correlation between ripples and cracks formation in peripheral region of the melt spot. The reason of such correlation and structure formation is explained as result of thermal effect. Melting and resolidification of the center of irradiated area occur within one micro second of time. This is supported by a numerical simulation used to investigate the thermal effect induced by the plasma focus ion beams on the silicon surface. This simulation provides information about the temperature profile as well as the dynamic of the thermal propagation in depth and lateral directions. In accordance with the experimental observations, that ripples are formed in latter stage after the arrival of last ion, the simulation shows that the thermal relaxation takes place in few microseconds after the end of the ion beam arrival. Additionally, the dependency of thermal propagation and relaxation on the distance of the silicon surface from the anode is presented.

Thermally induced magnonic spin current, thermomagnonic torques, and domain-wall dynamics in the presence of Dzyaloshinskii-Moriya interaction

Science.gov (United States)

Wang, X.-G.; Chotorlishvili, L.; Guo, G.-H.; Sukhov, A.; Dugaev, V.; Barnaś, J.; Berakdar, J.

2016-09-01

Thermally activated domain-wall (DW) motion in magnetic insulators has been considered theoretically, with a particular focus on the role of Dzyaloshinskii-Moriya interaction (DMI) and thermomagnonic torques. The thermally assisted DW motion is a consequence of the magnonic spin current due to the applied thermal bias. In addition to the exchange magnonic spin current and the exchange adiabatic and the entropic spin transfer torques, we also consider the DMI-induced magnonic spin current, thermomagnonic DMI fieldlike torque, and the DMI entropic torque. Analytical estimations are supported by numerical calculations. We found that the DMI has a substantial influence on the size and the geometry of DWs, and that the DWs become oriented parallel to the long axis of the nanostrip. Increasing the temperature smoothes the DWs. Moreover, the thermally induced magnonic current generates a torque on the DWs, which is responsible for their motion. From our analysis it follows that for a large enough DMI the influence of DMI-induced fieldlike torque is much stronger than that of the DMI and the exchange entropic torques. By manipulating the strength of the DMI constant, one can control the speed of the DW motion, and the direction of the DW motion can be switched, as well. We also found that DMI not only contributes to the total magnonic current, but also it modifies the exchange magnonic spin current, and this modification depends on the orientation of the steady-state magnetization. The observed phenomenon can be utilized in spin caloritronics devices, for example in the DMI based thermal diodes. By switching the magnetization direction, one can rectify the total magnonic spin current.

Carrier thermalization dynamics in single zincblende and wurtzite InP Nanowires.

Science.gov (United States)

Wang, Yuda; Jackson, Howard E; Smith, Leigh M; Burgess, Tim; Paiman, Suriati; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati

2014-12-10

Using transient Rayleigh scattering (TRS) measurements, we obtain photoexcited carrier thermalization dynamics for both zincblende (ZB) and wurtzite (WZ) InP single nanowires (NW) with picosecond resolution. A phenomenological fitting model based on direct band-to-band transition theory is developed to extract the electron-hole-plasma density and temperature as a function of time from TRS measurements of single nanowires, which have complex valence band structures. We find that the thermalization dynamics of hot carriers depends strongly on material (GaAs NW vs InP NW) and less strongly on crystal structure (ZB vs WZ). The thermalization dynamics of ZB and WZ InP NWs are similar. But a comparison of the thermalization dynamics in ZB and WZ InP NWs with ZB GaAs NWs reveals more than an order of magnitude slower relaxation for the InP NWs. We interpret these results as reflecting their distinctive phonon band structures that lead to different hot phonon effects. Knowledge of hot carrier thermalization dynamics is an essential component for effective incorporation of nanowire materials into electronic devices.

Direct current (DC) resistivity and induced polarization (IP) monitoring of active layer dynamics at high temporal resolution

DEFF Research Database (Denmark)

Doetsch, Joseph; Ingeman-Nielsen, Thomas; Christiansen, Anders V.

2015-01-01

With permafrost thawing and changes in active layer dynamics induced by climate change, interactions between biogeochemical and thermal processes in the ground are of great importance. Here, active layer dynamics have been monitored using direct current (DC) resistivity and induced polarization (IP...... in resistivity. While the freezing horizon generally moves deeper with time, some variations in the freezing depth are observed along the profile. Comparison with depth-specific soil temperature indicates an exponential relationship between resistivity and below-freezing temperature. Time-lapse inversions...

Direct current (DC) resistivity and Induced Polarization (IP) monitoring of active layer dynamics at high temporal resolution

DEFF Research Database (Denmark)

Doetsch, J.; Fiandaca, G.; Ingeman-Nielsen, Thomas

2015-01-01

With permafrost thawing and changes in active layer dynamics induced by climate change, interactions between biogeochemical and thermal processes in the ground are of great importance. Here, active layer dynamics have been monitored using direct current (DC) resistivity and induced polarization (IP...... the soil freezing as a strong increase in resistivity. While the freezing horizon generally moves deeper with time, some variations in the freezing depth are observed along the profile. Comparison with depth-specific soil temperature indicates an exponential relationship between resistivity and below...

Phase field modelling of dynamic thermal fracture in the context of irradiation damage

CERN Document Server

Schlüter, Alexander; Müller, Ralf; Tomut, Marilena; Trautmann , Christina; Weick, Helmut; Plate, Carolin

2015-01-01

This work presents a continuum mechanics approach to model fracturing processes in brittle materials that are subjected to rapidly applied high-temperature gradients. Such a type of loading typically occurs when a solid is exposed to an intense high-energy particle beam that deposits a large amount of energy into a small sample volume. Given the rapid energy deposition leading to a fast temperature increase, dynamic effects have to be considered. Our existing phase field model for dynamic fracture is thus extended in a way that allows modelling of thermally induced fracture. A finite element scheme is employed to solve the governing partial differential equations numerically. Finally, the functionality of our model is illustrated by two examples.

The Borexino Thermal Monitoring & Management System and simulations of the fluid-dynamics of the Borexino detector under asymmetrical, changing boundary conditions

Science.gov (United States)

Bravo-Berguño, D.; Mereu, R.; Cavalcante, P.; Carlini, M.; Ianni, A.; Goretti, A.; Gabriele, F.; Wright, T.; Yokley, Z.; Vogelaar, R. B.; Calaprice, F.; Inzoli, F.

2018-03-01

A comprehensive monitoring system for the thermal environment inside the Borexino neutrino detector was developed and installed in order to reduce uncertainties in determining temperatures throughout the detector. A complementary thermal management system limits undesirable thermal couplings between the environment and Borexino's active sections. This strategy is bringing improved radioactive background conditions to the region of interest for the physics signal thanks to reduced fluid mixing induced in the liquid scintillator. Although fluid-dynamical equilibrium has not yet been fully reached, and thermal fine-tuning is possible, the system has proven extremely effective at stabilizing the detector's thermal conditions while offering precise insights into its mechanisms of internal thermal transport. Furthermore, a Computational Fluid-Dynamics analysis has been performed, based on the empirical measurements provided by the thermal monitoring system, and providing information into present and future thermal trends. A two-dimensional modeling approach was implemented in order to achieve a proper understanding of the thermal and fluid-dynamics in Borexino. It was optimized for different regions and periods of interest, focusing on the most critical effects that were identified as influencing background concentrations. Literature experimental case studies were reproduced to benchmark the method and settings, and a Borexino-specific benchmark was implemented in order to validate the modeling approach for thermal transport. Finally, fully-convective models were applied to understand general and specific fluid motions impacting the detector's Active Volume.

Thermalization dynamics in a quenched many-body state

Science.gov (United States)

Kaufman, Adam; Preiss, Philipp; Tai, Eric; Lukin, Alex; Rispoli, Matthew; Schittko, Robert; Greiner, Markus

2016-05-01

Quantum and classical many-body systems appear to have disparate behavior due to the different mechanisms that govern their evolution. The dynamics of a classical many-body system equilibrate to maximally entropic states and quickly re-thermalize when perturbed. The assumptions of ergodicity and unbiased configurations lead to a successful framework of describing classical systems by a sampling of thermal ensembles that are blind to the system's microscopic details. By contrast, an isolated quantum many-body system is governed by unitary evolution: the system retains memory of past dynamics and constant global entropy. However, even with differing characteristics, the long-term behavior for local observables in quenched, non-integrable quantum systems are often well described by the same thermal framework. We explore the onset of this convergence in a many-body system of bosonic atoms in an optical lattice. Our system's finite size allows us to verify full state purity and measure local observables. We observe rapid growth and saturation of the entanglement entropy with constant global purity. The combination of global purity and thermalized local observables agree with the Eigenstate Thermalization Hypothesis in the presence of a near-volume law in the entanglement entropy.

Detailed Balance of Thermalization Dynamics in Rydberg-Atom Quantum Simulators.

Science.gov (United States)

Kim, Hyosub; Park, YeJe; Kim, Kyungtae; Sim, H-S; Ahn, Jaewook

2018-05-04

Dynamics of large complex systems, such as relaxation towards equilibrium in classical statistical mechanics, often obeys a master equation that captures essential information from the complexities. Here, we find that thermalization of an isolated many-body quantum state can be described by a master equation. We observe sudden quench dynamics of quantum Ising-like models implemented in our quantum simulator, defect-free single-atom tweezers in conjunction with Rydberg-atom interaction. Saturation of their local observables, a thermalization signature, obeys a master equation experimentally constructed by monitoring the occupation probabilities of prequench states and imposing the principle of the detailed balance. Our experiment agrees with theories and demonstrates the detailed balance in a thermalization dynamics that does not require coupling to baths or postulated randomness.

Detailed Balance of Thermalization Dynamics in Rydberg-Atom Quantum Simulators

Science.gov (United States)

Kim, Hyosub; Park, YeJe; Kim, Kyungtae; Sim, H.-S.; Ahn, Jaewook

2018-05-01

Dynamics of large complex systems, such as relaxation towards equilibrium in classical statistical mechanics, often obeys a master equation that captures essential information from the complexities. Here, we find that thermalization of an isolated many-body quantum state can be described by a master equation. We observe sudden quench dynamics of quantum Ising-like models implemented in our quantum simulator, defect-free single-atom tweezers in conjunction with Rydberg-atom interaction. Saturation of their local observables, a thermalization signature, obeys a master equation experimentally constructed by monitoring the occupation probabilities of prequench states and imposing the principle of the detailed balance. Our experiment agrees with theories and demonstrates the detailed balance in a thermalization dynamics that does not require coupling to baths or postulated randomness.

Activities and interconnections of thermal-fluid dynamics

International Nuclear Information System (INIS)

Celata, G.P.

1999-01-01

Thermal-fluid dynamics is a field of fundamental interest for a wide spectrum of past and present advanced 'applications': in nature, in the 'machines' of our everyday life and in industry. In particular, in today industry, its knowledge and the developments are of fundamental importance in understanding, modelling and in the advance design of heat and mass transfer process in energy conversion and transformation plants. Various examples of the role of the thermal-fluid dynamics to increase efficiency in energy utilization and in the design and in the development of new components and high performance system are exposed. New thermodynamic models and advanced analysis techniques together with necessary balance between theoretical advances codes for modelling and their experimental specific verifications are throughout discussed and illustrated

Thermally induced lensing determination from the coefficient of defocus aberration

CSIR Research Space (South Africa)

Bell, Teboho

2014-07-01

Full Text Available The effects of a temperature gradient in a laser crystal in an end-pumped configuration in a solid-state laser resonator results in thermally induced aberrations. Of particular interest we measure the thermally induced lens from the coefficient...

Thermal conductivity and thermal rectification in graphene nanoribbons: a molecular dynamics study.

Science.gov (United States)

Hu, Jiuning; Ruan, Xiulin; Chen, Yong P

2009-07-01

We have used molecular dynamics to calculate the thermal conductivity of symmetric and asymmetric graphene nanoribbons (GNRs) of several nanometers in size (up to approximately 4 nm wide and approximately 10 nm long). For symmetric nanoribbons, the calculated thermal conductivity (e.g., approximately 2000 W/m-K at 400 K for a 1.5 nm x 5.7 nm zigzag GNR) is on the similar order of magnitude of the experimentally measured value for graphene. We have investigated the effects of edge chirality and found that nanoribbons with zigzag edges have appreciably larger thermal conductivity than nanoribbons with armchair edges. For asymmetric nanoribbons, we have found significant thermal rectification. Among various triangularly shaped GNRs we investigated, the GNR with armchair bottom edge and a vertex angle of 30 degrees gives the maximal thermal rectification. We also studied the effect of defects and found that vacancies and edge roughness in the nanoribbons can significantly decrease the thermal conductivity. However, substantial thermal rectification is observed even in the presence of edge roughness.

Exploitation Strategies of Cabin and Galley Thermal Dynamics

OpenAIRE

Schlabe, Daniel; Zimmer, Dirk; Pollok, Alexander

2017-01-01

The thermal inertia of aircraft cabins and galleys is significant for commercial aircraft. The aircraft cabin is controlled by the Environment Control System (ECS) to reach, among other targets, a prescribed temperature. By allowing a temperature band of ± 2 K instead of a fixed temperature, it is possible to use this thermal dynamic of the cabin as energy storage. This storage can then be used to reduce electrical peak power, increase efficiency of the ECS, reduce thermal cooling peak power...

Electron thermal energy transport research based on dynamical relationship between heat flux and temperature gradient

International Nuclear Information System (INIS)

Notake, Takashi; Inagaki, Shigeru; Tamura, Naoki

2008-01-01

In the nuclear fusion plasmas, both of thermal energy and particle transport governed by turbulent flow are anomalously enhanced more than neoclassical levels. Thus, to clarify a relationship between the turbulent flow and the anomalous transports has been the most worthwhile work. There are experimental results that the turbulent flow induces various phenomena on transport processes such as non-linearity, transition, hysteresis, multi-branches and non-locality. We are approaching these complicated problems by analyzing not conventional power balance but these phenomena directly. They are recognized as dynamical trajectories in the flux and gradient space and must be a clue to comprehend a physical mechanism of arcane anomalous transport. Especially, to elucidate the mechanism for electron thermal energy transport is critical in the fusion plasma researches because the burning plasmas will be sustained by alpha-particle heating. In large helical device, the dynamical relationships between electron thermal energy fluxes and electron temperature gradients are investigated by using modulated electron cyclotron resonance heating and modern electron cyclotron emission diagnostic systems. Some trajectories such as hysteresis loop or line segments with steep slope which represent non-linear property are observed in the experiment. (author)

Thermal dynamic simulation of wall for building energy efficiency under varied climate environment

Science.gov (United States)

Wang, Xuejin; Zhang, Yujin; Hong, Jing

2017-08-01

Aiming at different kind of walls in five cities of different zoning for thermal design, using thermal instantaneous response factors method, the author develops software to calculation air conditioning cooling load temperature, thermal response factors, and periodic response factors. On the basis of the data, the author gives the net work analysis about the influence of dynamic thermal of wall on air-conditioning load and thermal environment in building of different zoning for thermal design regional, and put forward the strategy how to design thermal insulation and heat preservation wall base on dynamic thermal characteristic of wall under different zoning for thermal design regional. And then provide the theory basis and the technical references for the further study on the heat preservation with the insulation are in the service of energy saving wall design. All-year thermal dynamic load simulating and energy consumption analysis for new energy-saving building is very important in building environment. This software will provide the referable scientific foundation for all-year new thermal dynamic load simulation, energy consumption analysis, building environment systems control, carrying through farther research on thermal particularity and general particularity evaluation for new energy -saving walls building. Based on which, we will not only expediently design system of building energy, but also analyze building energy consumption and carry through scientific energy management. The study will provide the referable scientific foundation for carrying through farther research on thermal particularity and general particularity evaluation for new energy saving walls building.

Dynamic tuning of optical absorbers for accelerated solar-thermal energy storage.

Science.gov (United States)

Wang, Zhongyong; Tong, Zhen; Ye, Qinxian; Hu, Hang; Nie, Xiao; Yan, Chen; Shang, Wen; Song, Chengyi; Wu, Jianbo; Wang, Jun; Bao, Hua; Tao, Peng; Deng, Tao

2017-11-14

Currently, solar-thermal energy storage within phase-change materials relies on adding high thermal-conductivity fillers to improve the thermal-diffusion-based charging rate, which often leads to limited enhancement of charging speed and sacrificed energy storage capacity. Here we report the exploration of a magnetically enhanced photon-transport-based charging approach, which enables the dynamic tuning of the distribution of optical absorbers dispersed within phase-change materials, to simultaneously achieve fast charging rates, large phase-change enthalpy, and high solar-thermal energy conversion efficiency. Compared with conventional thermal charging, the optical charging strategy improves the charging rate by more than 270% and triples the amount of overall stored thermal energy. This superior performance results from the distinct step-by-step photon-transport charging mechanism and the increased latent heat storage through magnetic manipulation of the dynamic distribution of optical absorbers.

Evaluation of uranium dioxide thermal conductivity using molecular dynamics simulations

International Nuclear Information System (INIS)

Kim, Woongkee; Kaviany, Massoud; Shim, J. H.

2014-01-01

It can be extended to larger space, time scale and even real reactor situation with fission product as multi-scale formalism. Uranium dioxide is a fluorite structure with Fm3m space group. Since it is insulator, dominant heat carrier is phonon, rather than electrons. So, using equilibrium molecular dynamics (MD) simulation, we present the appropriate calculation parameters in MD simulation by calculating thermal conductivity and application of it to the thermal conductivity of polycrystal. In this work, we investigate thermal conductivity of uranium dioxide and optimize the parameters related to its process. In this process, called Green Kubo formula, there are two parameters i.e correlation length and sampling interval, which effect on ensemble integration in order to obtain thermal conductivity. Through several comparisons, long correlation length and short sampling interval give better results. Using this strategy, thermal conductivity of poly crystal is obtained and comparison with that of pure crystal is made. Thermal conductivity of poly crystal show lower value that that of pure crystal. In further study, we broaden the study to transport coefficient of radiation damaged structures using molecular dynamics. Although molecular dynamics is tools for treating microscopic scale, most macroscopic issues related to nuclear materials such as voids in fuel materials and weakened mechanical properties by radiation are based on microscopic basis. Thus, research on microscopic scale would be expanded in this field and many hidden mechanism in atomic scales will be revealed via both atomic scale simulations and experiments

Climate change impacts on lake thermal dynamics and ecosystem vulnerabilities

Science.gov (United States)

Sahoo, G. B; Forrest, A. L; Schladow, S. G ;; Reuter, J. E; Coats, R.; Dettinger, Michael

2016-01-01

Using water column temperature records collected since 1968, we analyzed the impacts of climate change on thermal properties, stability intensity, length of stratification, and deep mixing dynamics of Lake Tahoe using a modified stability index (SI). This new SI is easier to produce and is a more informative measure of deep lake stability than commonly used stability indices. The annual average SI increased at 16.62 kg/m2/decade although the summer (May–October) average SI increased at a higher rate (25.42 kg/m2/decade) during the period 1968–2014. This resulted in the lengthening of the stratification season by approximately 24 d. We simulated the lake thermal structure over a future 100 yr period using a lake hydrodynamic model driven by statistically downscaled outputs of the Geophysical Fluid Dynamics Laboratory Model (GFDL) for two different green house gas emission scenarios (the A2 in which greenhouse-gas emissions increase rapidly throughout the 21st Century, and the B1 in which emissions slow and then level off by the late 21st Century). The results suggest a continuation and intensification of the already observed trends. The length of stratification duration and the annual average lake stability are projected to increase by 38 d and 12 d and 30.25 kg/m2/decade and 8.66 kg/m2/decade, respectively for GFDLA2 and GFDLB1, respectively during 2014–2098. The consequences of this change bear the hallmarks of climate change induced lake warming and possible exacerbation of existing water quality, quantity and ecosystem changes. The developed methodology could be extended and applied to other lakes as a tool to predict changes in stratification and mixing dynamics.

Effect of thermal fluctuations in spin-torque driven magnetization dynamics

International Nuclear Information System (INIS)

Bonin, R.; Bertotti, G.; Serpico, C.; Mayergoyz, I.D.; D'Aquino, M.

2007-01-01

Nanomagnets with uniaxial symmetry driven by an external field and spin-polarized currents are considered. Anisotropy, applied field, and spin polarization are all aligned along the symmetry axis. Thermal fluctuations are described by adding a Gaussian white noise stochastic term to the Landau-Lifshitz-Gilbert equation for the deterministic dynamics. The corresponding Fokker-Planck equation is derived. It is shown that deterministic dynamics, thermal relaxation, and transition rate between stable states are governed by an effective potential including the effect of current injection

Effect of thermal fluctuations in spin-torque driven magnetization dynamics

Energy Technology Data Exchange (ETDEWEB)

Bonin, R. [INRiM, I-10135 Turin (Italy)]. E-mail: bonin@inrim.it; Bertotti, G. [INRiM, I-10135 Turin (Italy); Serpico, C. [Dipartimento di Ingegneria Elettrica, Universita di Napoli ' Federico II' I-80125 Naples (Italy); Mayergoyz, I.D. [Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742 (United States); D' Aquino, M. [Dipartimento per le Tecnologie, Universita di Napoli ' Parthenope' , I-80133 Naples (Italy)

2007-09-15

Nanomagnets with uniaxial symmetry driven by an external field and spin-polarized currents are considered. Anisotropy, applied field, and spin polarization are all aligned along the symmetry axis. Thermal fluctuations are described by adding a Gaussian white noise stochastic term to the Landau-Lifshitz-Gilbert equation for the deterministic dynamics. The corresponding Fokker-Planck equation is derived. It is shown that deterministic dynamics, thermal relaxation, and transition rate between stable states are governed by an effective potential including the effect of current injection.

Powder metallurgy and mechanical alloying effects on the formation of thermally induced martensite in an FeMnSiCrNi SMA

Directory of Open Access Journals (Sweden)

Pricop Bogdan

2015-01-01

Full Text Available By ingot metallurgy (IM, melting, alloying and casting, powder metallurgy (PM, using as-blended elemental powders and mechanical alloying (MA of 50 % of particle volume, three types of FeMnSiCrNi shape memory alloy (SMA specimens were fabricated, respectively. After specimen thickness reduction by hot rolling, solution treatments were applied, at 973 and 1273 K, to thermally induce martensite. The resulting specimens were analysed by X-ray diffraction (XRD and scanning electron microscopy (SEM, in order to reveal the presence of ε (hexagonal close-packed, hcp and α’ (body centred cubic, bcc thermally induced martensites. The reversion of thermally induced martensites, to γ (face centred cubic, fcc austenite, during heating, was confirmed by dynamic mechanical analysis (DMA, which emphasized marked increases of storage modulus and obvious internal friction maxima on DMA thermograms. The results proved that the increase of porosity degree, after PM processing, increased internal friction, while MA enhanced crystallinity degree.

Note: Local thermal conductivities from boundary driven non-equilibrium molecular dynamics simulations

International Nuclear Information System (INIS)

Bresme, F.; Armstrong, J.

2014-01-01

We report non-equilibrium molecular dynamics simulations of heat transport in models of molecular fluids. We show that the “local” thermal conductivities obtained from non-equilibrium molecular dynamics simulations agree within numerical accuracy with equilibrium Green-Kubo computations. Our results support the local equilibrium hypothesis for transport properties. We show how to use the local dependence of the thermal gradients to quantify the thermal conductivity of molecular fluids for a wide range of thermodynamic states using a single simulation

FEM modeling and histological analyses on thermal damage induced in facial skin resurfacing procedure with different CO2 laser pulse duration

Science.gov (United States)

Rossi, Francesca; Zingoni, Tiziano; Di Cicco, Emiliano; Manetti, Leonardo; Pini, Roberto; Fortuna, Damiano

2011-07-01

Laser light is nowadays routinely used in the aesthetic treatments of facial skin, such as in laser rejuvenation, scar removal etc. The induced thermal damage may be varied by setting different laser parameters, in order to obtain a particular aesthetic result. In this work, it is proposed a theoretical study on the induced thermal damage in the deep tissue, by considering different laser pulse duration. The study is based on the Finite Element Method (FEM): a bidimensional model of the facial skin is depicted in axial symmetry, considering the different skin structures and their different optical and thermal parameters; the conversion of laser light into thermal energy is modeled by the bio-heat equation. The light source is a CO2 laser, with different pulse durations. The model enabled to study the thermal damage induced into the skin, by calculating the Arrhenius integral. The post-processing results enabled to study in space and time the temperature dynamics induced in the facial skin, to study the eventual cumulative effects of subsequent laser pulses and to optimize the procedure for applications in dermatological surgery. The calculated data where then validated in an experimental measurement session, performed in a sheep animal model. Histological analyses were performed on the treated tissues, evidencing the spatial distribution and the entity of the thermal damage in the collageneous tissue. Modeling and experimental results were in good agreement, and they were used to design a new optimized laser based skin resurfacing procedure.

Dynamical thermalization in isolated quantum dots and black holes

Science.gov (United States)

Kolovsky, Andrey R.; Shepelyansky, Dima L.

2017-01-01

We study numerically a model of quantum dot with interacting fermions. At strong interactions with small conductance the model is reduced to the Sachdev-Ye-Kitaev black-hole model while at weak interactions and large conductance it describes a Landau-Fermi liquid in a regime of quantum chaos. We show that above the Åberg threshold for interactions there is an onset of dynamical themalization with the Fermi-Dirac distribution describing the eigenstates of an isolated dot. At strong interactions in the isolated black-hole regime there is also the onset of dynamical thermalization with the entropy described by the quantum Gibbs distribution. This dynamical thermalization takes place in an isolated system without any contact with a thermostat. We discuss the possible realization of these regimes with quantum dots of 2D electrons and cold ions in optical lattices.

Molecular dynamics simulation of thermal conductivities of superlattice nanowires

Institute of Scientific and Technical Information of China (English)

YANG; Juekuan(杨决宽); CHEN; Yunfei(陈云飞); YAN; Jingping(颜景平)

2003-01-01

Nonequilibrium molecular dynamics simulations were carried out to investigate heat transfer in superlattice nanowires. Results show that for fixed period length superlattice nanowires, the ratio of the total interfacial thermal resistance to the total thermal resistance and the effective thermal conductivities are invariant with the changes in interface numbers. Increasing the period length leads to an increase in the average interfacial thermal resistance, which indicates that the interfacial thermal resistance depends not only on the materials that constitute the alternating segments of superlattice nanowires, but also on the lattice strain throughout the segments. The modification of the lattice structure due to the lattice mismatch should be taken into account in the acoustic mismatch model. Simulation results also demonstrated the size confinement effect on the thermal conductivities for low dimensional structures, i.e. the thermal conductivities and the interfacial thermal resistance increase as the nanowire cross-sectional area increases.

Conditional repair by locally switching the thermal healing capability of dynamic covalent polymers with light

Science.gov (United States)

Fuhrmann, Anne; Göstl, Robert; Wendt, Robert; Kötteritzsch, Julia; Hager, Martin D.; Schubert, Ulrich S.; Brademann-Jock, Kerstin; Thünemann, Andreas F.; Nöchel, Ulrich; Behl, Marc; Hecht, Stefan

2016-12-01

Healable materials could play an important role in reducing the environmental footprint of our modern technological society through extending the life cycles of consumer products and constructions. However, as most healing processes are carried out by heat alone, the ability to heal damage generally kills the parent material's thermal and mechanical properties. Here we present a dynamic covalent polymer network whose thermal healing ability can be switched `on' and `off' on demand by light, thereby providing local control over repair while retaining the advantageous macroscopic properties of static polymer networks. We employ a photoswitchable furan-based crosslinker, which reacts with short and mobile maleimide-substituted poly(lauryl methacrylate) chains forming strong covalent bonds while simultaneously allowing the reversible, spatiotemporally resolved control over thermally induced de- and re-crosslinking. We reason that our system can be adapted to more complex materials and has the potential to impact applications in responsive coatings, photolithography and microfabrication.

Mathematical modelling of pasta dough dynamic viscosity, thermal conductivity and diffusivity

Directory of Open Access Journals (Sweden)

Andrei Ionuţ SIMION

2015-08-01

Full Text Available This work aimed to study the mathematical variation of three main thermodynamic properties (dynamic viscosity, thermal conductivity and thermal diffusivity of pasta dough obtained by mixing wheat semolina and water with dough humidity and deformation speed (for dynamic viscosity, respectively with dough humidity and temperature (for thermal diffusivity and conductivity. The realized regression analysis of existing graphical data led to the development of mathematical models with a high degree of accuracy. The employed statistical tests (least squares, relative error and analysis of variance revealed that the obtained equations are able to describe and predict the tendency of the dough thermodynamic properties.

Thermalization dynamics of two correlated bosonic quantum wires after a split

Science.gov (United States)

Huber, Sebastian; Buchhold, Michael; Schmiedmayer, Jörg; Diehl, Sebastian

2018-04-01

Cherently splitting a one-dimensional Bose gas provides an attractive, experimentally established platform to investigate many-body quantum dynamics. At short enough times, the dynamics is dominated by the dephasing of single quasiparticles, and well described by the relaxation towards a generalized Gibbs ensemble corresponding to the free Luttinger theory. At later times on the other hand, the approach to a thermal Gibbs ensemble is expected for a generic, interacting quantum system. Here, we go one step beyond the quadratic Luttinger theory and include the leading phonon-phonon interactions. By applying kinetic theory and nonequilibrium Dyson-Schwinger equations, we analyze the full relaxation dynamics beyond dephasing and determine the asymptotic thermalization process in the two-wire system for a symmetric splitting protocol. The major observables are the different phonon occupation functions and the experimentally accessible coherence factor, as well as the phase correlations between the two wires. We demonstrate that, depending on the splitting protocol, the presence of phonon collisions can have significant influence on the asymptotic evolution of these observables, which makes the corresponding thermalization dynamics experimentally accessible.

Importance of soil thermal dynamics on land carbon sequestration in Northern Eurasia during the 21st century

Science.gov (United States)

Kicklighter, David; Monier, Erwan; Sokolov, Andrei; Zhuang, Qianlai; Melillo, Jerry

2015-04-01

Recent modeling studies have suggested that carbon sinks in pan-arctic ecosystems may be weakening partially as a result of warming-induced increases in soil organic matter (SOM) decomposition and the exposure of previously frozen SOM to decomposition. This weakening of carbon sinks is likely to continue in the future as vast amount of carbon in permafrost soils is vulnerable to thaw. Here, we examine the importance of considering soil thermal dynamics when determining the effects of climate change and land-use change on carbon dynamics in Northern Eurasia during the 21st century. This importance is assessed by comparing results for a "business as usual" scenario between a version of the Terrestrial Ecosystem Model that does not consider soil thermal dynamics (TEM 4.4) and a version that does consider these dynamics (TEM 6.0). In this scenario, which is similar to the IPCC Representative Concentration Pathways (RCP) 8.5 scenario, the net area covered by food crops and pastures in Northern Eurasia is assumed to remain relatively constant over the 21st century, but the area covered by secondary forests is projected to double as a result of timber harvest and the abandonment of land associated with displacement of agricultural land. Enhanced decomposition from the newly exposed SOM from permafrost thaw also increases nitrogen availability for plant production so that the loss of carbon from the enhanced decomposition is partially compensated by enhanced uptake and storage of atmospheric carbon dioxide in vegetation. Our results indicate that consideration of soil thermal dynamics have a large influence on how simulated terrestrial carbon dynamics in Northern Eurasia respond to changes in climate, atmospheric chemistry (e.g., carbon dioxide fertilization, ozone pollution, nitrogen deposition) and disturbances.

Molecular Dynamics Studies on Ballistic Thermal Resistance of Graphene Nano-Junctions

International Nuclear Information System (INIS)

Yao Wen-Jun; Cao Bing-Yang

2015-01-01

Ballistic thermal resistance of graphene nano-junctions is investigated using non-equilibrium molecular dynamics simulation. The simulation system is consisted of two symmetrical trapezoidal or rectangular graphene nano-ribbons (GNRs) and a connecting nanoscale constriction in between. From the simulated temperature profile, a big temperature jump resulted from the constriction is found, which is proportional to the heat current and corresponds to a local ballistic thermal resistance. Fixing the constriction width and the length of GNRs, this ballistic thermal resistance is independent of the width of the GNRs bottom layer, i.e., the convex angle. But interestingly, this thermal resistance has obvious size effect. It is inversely proportional to the constriction width and will disappear with the constriction being wider. Moreover, based on the phonon dynamics theory, a theoretical model of the ballistic thermal resistance in two-dimensional nano-systems is developed, which gives a good explanation on microcosmic level and agrees well with the simulation result quantitatively and qualitatively. (paper)

Dynamics of quantum entanglement in de Sitter spacetime and thermal Minkowski spacetime

Directory of Open Access Journals (Sweden)

Zhiming Huang

2017-10-01

Full Text Available We investigate the dynamics of entanglement between two atoms in de Sitter spacetime and in thermal Minkowski spacetime. We treat the two-atom system as an open quantum system which is coupled to a conformally coupled massless scalar field in the de Sitter invariant vacuum or to a thermal bath in the Minkowski spacetime, and derive the master equation that governs its evolution. We compare the phenomena of entanglement creation, degradation, revival and enhancement for the de Sitter spacetime case with that for the thermal Minkowski spacetime case. We find that the entanglement dynamics of two atoms for these two spacetime cases behave quite differently. In particular, the two atoms interacting with the field in the thermal Minkowski spacetime (with the field in the de Sitter-invariant vacuum, under certain conditions, could be entangled, while they would not become entangled in the corresponding de Sitter case (in the corresponding thermal Minkowski case. Thus, although a single static atom in the de Sitter-invariant vacuum responds as if it were bathed in thermal radiation in a Minkowski universe, with the help of the different dynamic evolution behaviors of entanglement for two atoms one can in principle distinguish these two universes.

Lumped-Element Dynamic Electro-Thermal model of a superconducting magnet

Science.gov (United States)

Ravaioli, E.; Auchmann, B.; Maciejewski, M.; ten Kate, H. H. J.; Verweij, A. P.

2016-12-01

Modeling accurately electro-thermal transients occurring in a superconducting magnet is challenging. The behavior of the magnet is the result of complex phenomena occurring in distinct physical domains (electrical, magnetic and thermal) at very different spatial and time scales. Combined multi-domain effects significantly affect the dynamic behavior of the system and are to be taken into account in a coherent and consistent model. A new methodology for developing a Lumped-Element Dynamic Electro-Thermal (LEDET) model of a superconducting magnet is presented. This model includes non-linear dynamic effects such as the dependence of the magnet's differential self-inductance on the presence of inter-filament and inter-strand coupling currents in the conductor. These effects are usually not taken into account because superconducting magnets are primarily operated in stationary conditions. However, they often have significant impact on magnet performance, particularly when the magnet is subject to high ramp rates. Following the LEDET method, the complex interdependence between the electro-magnetic and thermal domains can be modeled with three sub-networks of lumped-elements, reproducing the electrical transient in the main magnet circuit, the thermal transient in the coil cross-section, and the electro-magnetic transient of the inter-filament and inter-strand coupling currents in the superconductor. The same simulation environment can simultaneously model macroscopic electrical transients and phenomena at the level of superconducting strands. The model developed is a very useful tool for reproducing and predicting the performance of conventional quench protection systems based on energy extraction and quench heaters, and of the innovative CLIQ protection system as well.

Observation of the dynamics of magnetic nanoparticles induced by a focused laser beam by using dark-field microscopy

Energy Technology Data Exchange (ETDEWEB)

Deng, Hai-Dong, E-mail: dhdong@scau.edu.cn [Department of Applied Physics, College of Science, South China Agricultural University, Guangzhou 510642 (China); Li, Guang-Can [Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006 (China); Li, Hai [Department of Applied Physics, College of Science, South China Agricultural University, Guangzhou 510642 (China)

2014-08-01

The dynamics of Fe{sub 3}O{sub 4} magnetic nanoparticles under the irradiation of a tightly focused laser beam was investigated by using a high-intensity dark-field microscopy. A depletion region of magnetic nanoparticles was found at the center of the laser beam where the dissipative force (absorption and scattering forces) dominated the dynamics of the magnetic nanoparticles. In contrast, the dynamics of magnetic nanoparticles was dominated by thermal and mass diffusions at the edge of the laser beam where the dissipative force was negligible. In addition, the transient variation in the concentration of magnetic nanoparticles was characterized by recording the transient scattering light intensity. The coefficients of thermal diffusion, mass diffusion and the Soret effect for this kind of magnetic nanoparticles were successfully extracted by using this technique. - Highlights: • The dynamics of magnetic nanoparticles induced by a focused laser beam was investigated by using dark-field microscopy. • The experimental results revealed that the dynamics of magnetic nanoparticles was dominated by different mechanisms. • A convenient technique to measure the Soret coefficient of nanoparticles was provided.

Time-dependent analytical thermal model to investigate thermally induced stresses in quasi-CW-pumped laser rods

CSIR Research Space (South Africa)

Bernhardi, EH

2008-01-01

Full Text Available that determines the temperature and the thermally induced stresses in isotropic rods is presented. Even though the model is developed for isotropic rods, it is shown that it can also be used to accurately estimate the thermal effects in anisotropic rods...

Chaos and thermal noise in the rf-biased Josephson junction

International Nuclear Information System (INIS)

Kautz, R.L.

1985-01-01

The effect of thermal noise on chaotic behavior in the rf-biased Josephson junction is studied through digital simulations. In instances for which chaotic behavior occurs in the noise-free system, it is found that the dynamics of the system are almost unchanged by the addition of thermal noise unless the level of thermal noise exceeds that of the chaotic state. In instances for which the only stable states of the noise-free system are periodic solutions, small amounts of thermal noise can induce the junction to hop between two different dynamical states, producing a low-frequency noise level much higher than that of the thermal noise. Such noise-induced hopping can occur either between two periodic solutions or between a periodic solution and a metastable chaotic solution. When a metastable chaotic state is involved, temperatures somewhat higher than those which produce hopping can destablize the periodic solution to the point where the system spends virtually all of its time in the metastable chaotic state, creating noise-induced chaos. The similarities between chaotic behavior at zero temperature and noise-induced chaos are sufficiently strong that it may be difficult to distinguish the two cases experimentally

Achieving dynamic behaviour and thermal expansion in the organic solid state via co-crystallization.

Science.gov (United States)

Hutchins, Kristin M; Groeneman, Ryan H; Reinheimer, Eric W; Swenson, Dale C; MacGillivray, Leonard R

2015-08-01

Thermal expansion involves a response of a material to an external stimulus that typically involves an increase in a crystallographic axis (positive thermal expansion (PTE)), although shrinking with applied heat (negative thermal expansion (NTE)) is known in rarer cases. Here, we demonstrate a means to achieve dynamic molecular motion and thermal expansions in organic solids via co-crystallizations. One co-crystal component is known to exhibit dynamic behaviour in the solid state while the second, when varied systematically, affords co-crystals with linear thermal expansion coefficients that range from colossal to nearly zero. Two co-crystals exhibit rare NTE. We expect the approach to guide the design of molecular solids that enable predesigned motion related to thermal expansion processes.

Lattice dynamics and thermal diffuse scattering for molecular crystals

International Nuclear Information System (INIS)

Kroon, P.A.

1977-01-01

Thermal diffuse scattering (TDS) corrections on the observed reflection intensities in the accurate determination of crystal structures by X-ray diffraction are emphasized. A lattice-dynamical model and procedure for lattice-dynamical calculations are set up. Expression for first- and second-order TDS intensity distributions are derived. A comparison with other models is made. First-order TDS corrections for naphtalene at 100 K are presented

Thermal dynamics of bomb calorimeters.

Science.gov (United States)

Lyon, Richard E

2015-12-01

The thermal dynamics of bomb calorimeters are modeled using a lumped heat transfer analysis in which heat is released in a pressure vessel/bomb immersed in a stirred water bath that is surrounded by a static air space bounded by an insulated (static) jacket, a constant/controlled temperature jacket (isoperibol), or a changing temperature (adiabatic) jacket. The temperature history of the water bath for each of these boundary conditions (methods) is well described by the two-term solution for the calorimeter response to a heat impulse (combustion), allowing the heat transfer coefficients and thermal capacities of the bomb and water bath to be determined parametrically. The validated heat transfer model provides an expression for direct calculation of the heat released in an arbitrary process inside a bomb calorimeter using the temperature history of the water bath for each of the boundary conditions (methods). This result makes possible the direct calculation of the heat of combustion of a sample in an isoperibol calorimeter from the recorded temperature history without the need for semi-empirical temperature corrections to account for non-adiabatic behavior. Another useful result is that the maximum temperature rise of the water bath in the static jacket method is proportional to the total heat generated, and the empirical proportionality constant, which is determined by calibration, accounts for all of the heat losses and thermal lags of the calorimeter.

Laser-induced cracks in ice due to temperature gradient and thermal stress

Science.gov (United States)

Yang, Song; Yang, Ying-Ying; Zhang, Jing-Yuan; Zhang, Zhi-Yan; Zhang, Ling; Lin, Xue-Chun

2018-06-01

This work presents the experimental and theoretical investigations on the mechanism of laser-induce cracks in ice. The laser-induced thermal gradient would generate significant thermal stress and lead to the cracking without thermal melting in the ice. The crack density induced by a pulsed laser in the ice critically depends on the laser scanning speed and the size of the laser spot on the surface, which determines the laser power density on the surface. A maximum of 16 cracks within an area of 17 cm × 10 cm can be generated when the laser scanning speed is at 10 mm/s and the focal point of the laser is right on the surface of the ice with a laser intensity of ∼4.6 × 107 W/cm2. By comparing the infrared images of the ice generated at various experimental conditions, it was found that a larger temperature gradient would result in more laser-induced cracks, while there is no visible melting of the ice by the laser beam. The data confirm that the laser-induced thermal stress is the main cause of the cracks created in the ice.

Thermal conductivity of ZnTe investigated by molecular dynamics

International Nuclear Information System (INIS)

Wang Hanfu; Chu Weiguo

2009-01-01

The thermal conductivity of ZnTe with zinc-blende structure has been computed by equilibrium molecular dynamics method based on Green-Kubo formalism. A Tersoff's potential is adopted in the simulation to model the atomic interactions. The calculations are performed as a function of temperature up to 800 K. The calculated thermal conductivities are in agreement with the experimental values between 150 K and 300 K, while the results above the room temperature are comparable with the Slack's equation.

Thermal conductivity of pillared graphene-epoxy nanocomposites using molecular dynamics

Science.gov (United States)

Lakshmanan, A.; Srivastava, S.; Ramazani, A.; Sundararaghavan, V.

2018-04-01

Thermal conductivity in a pillared graphene-epoxy nanocomposite (PGEN) is studied using equilibrium molecular dynamics simulations. PGEN is a proposed material for advanced thermal management applications because it combines high in-plane conductivity of graphene with high axial conductivity of a nanotube to significantly enhance the overall conductivity of the epoxy matrix material. Anisotropic conductivity of PGEN has been compared with that of pristine and functionalized carbon nanotube-epoxy nanocomposites, showcasing the advantages of the unique hierarchical structure of PGEN. Compared to pure carbon allotropes, embedding the epoxy matrix also promotes a weaker dependence of conductivity on thermal variations. These features make this an attractive material for thermal management applications.

Thermally-induced bowing of CANDU fuel elements

International Nuclear Information System (INIS)

Suk, H.C.; Sim, K.S.; Park, J.H.; Park, G.S.

1995-01-01

Considering only the thermally-induced bending moments which are generated both within the sheath and between the fuel and sheath by an asymmetric temperature distribution with respect to the axis of an element, a generalized and explicit analytical formula for the thermally-induced bending is developed in this paper, based on the cases of 1) the bending of an empty tube treated by neglecting of the fuel/sheath mechanical interaction and 2) the fuel/sheath interaction due to the pellet and sheath temperature variations. In each of the cases, the temperature asymmetries in sheath are modelled to be caused by the combined effects of (i) non-uniform coolant temperature due to imperfect coolant mixing, (ii) variable sheath/coolant heat transfer coefficient, (iii) asymmetric heat generation due to neutron flux gradients across an element and so as to inclusively cover the uniform temperature distributions within the fuel and sheath with respect to the axial centerline. Investigating the relative importance of the various parameters affecting fuel element bowing, the element bowing is found to be greatly affected with the variations of element length, sheath diameter, pellet/sheath mechanical interaction and neutron flux depression factors, pellet thermal expansion coefficient, pellet/sheath heat transfer coefficient in comparison with those of other parameters such as sheath thickness, film heat transfer coefficient, sheath thermal expansion coefficient, and sheath and pellet thermal conductivities. Also, the element bowing of the standard 37-element bundle and CANFLEX 43-element bundle for the use in CANDU-6 reactors was analyzed with the formula, which could help to demonstrate the integrity of the fuel. All the required input data for the analyses were generated in terms of the reactor operation conditions on the reactor physics, thermal hydraulics and fuel performance by using various CANDU computer codes. The analysis results indicate that the CANFLEX 43-element

Electron-phonon thermalization in a scalable method for real-time quantum dynamics

Science.gov (United States)

Rizzi, Valerio; Todorov, Tchavdar N.; Kohanoff, Jorge J.; Correa, Alfredo A.

2016-01-01

We present a quantum simulation method that follows the dynamics of out-of-equilibrium many-body systems of electrons and oscillators in real time. Its cost is linear in the number of oscillators and it can probe time scales from attoseconds to hundreds of picoseconds. Contrary to Ehrenfest dynamics, it can thermalize starting from a variety of initial conditions, including electronic population inversion. While an electronic temperature can be defined in terms of a nonequilibrium entropy, a Fermi-Dirac distribution in general emerges only after thermalization. These results can be used to construct a kinetic model of electron-phonon equilibration based on the explicit quantum dynamics.

Some aspects of thermally induced martensite in Fe-30% Ni-5% Cu alloy

International Nuclear Information System (INIS)

Guener, M.; Gueler, E.; Yasar, E.; Aktas, H.

2007-01-01

Kinetical, morphological, crystallographical and several thermal properties of thermally induced martensite in the austenite phase of Fe-30% Ni-5% Cu alloy were investigated. Scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimetry (DSC) techniques were used during study. Kinetics of the transformation was found to be as athermal type. SEM and TEM observations revealed α' (BCC) martensite formation in the austenite phase of alloy by thermal effect. These thermally induced α' martensites exhibited a thin plate-like morphology with twinnings

Design and thermal dynamic analyses on the intermediate heat exchanger for HTGR

International Nuclear Information System (INIS)

Mori, M.; Mizuno, M.; Ito, M.; Urabe, S.

1986-01-01

The intermediate heat exchanger (IHX), one of the most important components in the high temperature gas cooled reactor (HTGR), is a high performance helium/helium (He/He) heat exchanger operated at a very high temperature above 900 0 C to transmit the nuclear heat from the reactor core to the nuclear heat utilization systems such as the chemical plant. Having to meet, in addition, the requirement of the pressure boundary as the Class-1 it demands the accurate estimation of thermal performance and analytical prediction of thermal behaviors to secure its integrity throughout the service life. In the present works, the newly-developed analytical codes carry out designing thermal performance and analyzing dynamic thermal behaviors of the IHX. These codes have been developed on a great deal of data and studies related to the research and development on the 1.5 MWt- and the 25 MWt-IHXs. This paper shows the design on the IHX, the results of the dynamic analyses on the 1.5 MWt-IHX with the comparison to the experimental data and the analytical predictions of the dynamic thermal behaviors on the 25 MWt-IHX. The results calculated are in fairly good agreement with the experimental data on the 1.5 MWt-IHX, the fact that has verified the analytical codes to be reasonable and much useful for the thermal design of the IHX. These presented results and data are available for the design of the IHX of HTGR

Negative thermal expansion induced by intermetallic charge transfer.

Science.gov (United States)

Azuma, Masaki; Oka, Kengo; Nabetani, Koichiro

2015-06-01

Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu 3 Fe 4 O 12 and LaCu 3 Fe 4- x Mn x O 12 , as well as in Bi or Ni substituted BiNiO 3 . The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding -70 × 10 -6 K -1 near room temperature, in the temperature range which can be controlled by substitution.

Analysis of molten salt thermal-hydraulics using computational fluid dynamics

International Nuclear Information System (INIS)

Yamaji, B.; Csom, G.; Aszodi, A.

2003-01-01

To give a good solution for the problem of high level radioactive waste partitioning and transmutation is expected to be a pro missing option. Application of this technology also could extend the possibilities of nuclear energy. Large number of liquid-fuelled reactor concepts or accelerator driven subcritical systems was proposed as transmutors. Several of these consider fluoride based molten salts as the liquid fuel and coolant medium. The thermal-hydraulic behaviour of these systems is expected to be fundamentally different than the behaviour of widely used water-cooled reactors with solid fuel. Considering large flow domains three-dimensional thermal-hydraulic analysis is the method seeming to be applicable. Since the fuel is the coolant medium as well, one can expect a strong coupling between neutronics and thermal-hydraulics too. In the present paper the application of Computational Fluid Dynamics for three-dimensional thermal-hydraulics simulations of molten salt reactor concepts is introduced. In our past and recent works several calculations were carried out to investigate the capabilities of Computational Fluid Dynamics through the analysis of different molten salt reactor concepts. Homogenous single region molten salt reactor concept is studied and optimised. Another single region reactor concept is introduced also. This concept has internal heat exchanges in the flow domain and the molten salt is circulated by natural convection. The analysis of the MSRE experiment is also a part of our work since it may form a good background from the validation point of view. In the paper the results of the Computational Fluid Dynamics calculations with these concepts are presented. In the further work our objective is to investigate the thermal-hydraulics of the multi-region molten salt reactor (Authors)

Lattice Dynamics Study of Phonon Instability and Thermal Properties of Type-I Clathrate K₈Si46 under High Pressure.

Science.gov (United States)

Zhang, Wei; Zeng, Zhao Yi; Ge, Ni Na; Li, Zhi Guo

2016-07-25

For a further understanding of the phase transitions mechanism in type-I silicon clathrates K₈Si 46 , ab initio self-consistent electronic calculations combined with linear-response method have been performed to investigate the vibrational properties of alkali metal K atoms encapsulated type-I silicon-clathrate under pressure within the framework of density functional perturbation theory. Our lattice dynamics simulation results showed that the pressure induced phase transition of K₈Si 46 was believed to be driven by the phonon instability of the calthrate lattice. Analysis of the evolution of the partial phonon density of state with pressure, a legible dynamic picture for both guest K atoms and host lattice, was given. In addition, based on phonon calculations and combined with quasi-harmonic approximation, the specific heat of K₈Si 46 was derived, which agreed very well with experimental results. Also, other important thermal properties including the thermal expansion coefficients and Grüneisen parameters of K₈Si 46 under different temperature and pressure were also predicted.

Thermal conductivity of armchair black phosphorus nanotubes: a molecular dynamics study

International Nuclear Information System (INIS)

Hao, Feng; Liao, Xiangbiao; Xiao, Hang; Chen, Xi

2016-01-01

The effects of size, strain, and vacancies on the thermal properties of armchair black phosphorus nanotubes are investigated based on qualitative analysis from molecular dynamics simulations. It is found that thermal conductivity has a remarkable size effect, because of the restricted paths for phonon transport, which is strongly dependent on the diameter and length of the nanotube. Owing to the intensified low-frequency phonons, axial tensile strain can facilitate thermal transport. In contrast, compressive strain weakens thermal transport due to the enhanced phonon scattering around the buckling of the nanotube. In addition, the thermal conductivity is dramatically reduced by single vacancies, particularly those with high defect concentrations. (paper)

Ultrafast Non-Thermal Electron Dynamics in Single Layer Graphene

Directory of Open Access Journals (Sweden)

Novoselov K.S.

2013-03-01

Full Text Available We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the non-equilibrium electron gas decay at early times.

Tutorial: Determination of thermal boundary resistance by molecular dynamics simulations

Science.gov (United States)

Liang, Zhi; Hu, Ming

2018-05-01

Due to the high surface-to-volume ratio of nanostructured components in microelectronics and other advanced devices, the thermal resistance at material interfaces can strongly affect the overall thermal behavior in these devices. Therefore, the thermal boundary resistance, R, must be taken into account in the thermal analysis of nanoscale structures and devices. This article is a tutorial on the determination of R and the analysis of interfacial thermal transport via molecular dynamics (MD) simulations. In addition to reviewing the commonly used equilibrium and non-equilibrium MD models for the determination of R, we also discuss several MD simulation methods which can be used to understand interfacial thermal transport behavior. To illustrate how these MD models work for various interfaces, we will show several examples of MD simulation results on thermal transport across solid-solid, solid-liquid, and solid-gas interfaces. The advantages and drawbacks of a few other MD models such as approach-to-equilibrium MD and first-principles MD are also discussed.

Comparative analyses on dynamic performances of photovoltaic–thermal solar collectors integrated with phase change materials

International Nuclear Information System (INIS)

Su, Di; Jia, Yuting; Alva, Guruprasad; Liu, Lingkun; Fang, Guiyin

2017-01-01

Highlights: • The dynamic model of photovoltaic–thermal collector with phase change material was developed. • The performances of photovoltaic–thermal collector are performed comparative analyses. • The performances of photovoltaic–thermal collector with phase change material were evaluated. • Upper phase change material mode can improve performances of photovoltaic–thermal collector. - Abstract: The operating conditions (especially temperature) of photovoltaic–thermal solar collectors have significant influence on dynamic performance of the hybrid photovoltaic–thermal solar collectors. Only a small percentage of incoming solar radiation can be converted into electricity, and the rest is converted into heat. This heat leads to a decrease in efficiency of the photovoltaic module. In order to improve the performance of the hybrid photovoltaic–thermal solar collector, we performed comparative analyses on a hybrid photovoltaic–thermal solar collector integrated with phase change material. Electrical and thermal parameters like solar cell temperature, outlet temperature of air, electrical power, thermal power, electrical efficiency, thermal efficiency and overall efficiency are simulated and analyzed to evaluate the dynamic performance of the hybrid photovoltaic–thermal collector. It is found that the position of phase change material layer in the photovoltaic–thermal collector has a significant effect on the performance of the photovoltaic–thermal collector. The results indicate that upper phase change material mode in the photovoltaic–thermal collector can significantly improve the thermal and electrical performance of photovoltaic–thermal collector. It is found that overall efficiency of photovoltaic–thermal collector in ‘upper phase change material’ mode is 10.7% higher than that in ‘no phase change material’ mode. Further, for a photovoltaic–thermal collector with upper phase change material, it is verified that 3 cm

Thermal Equilibrium Dynamic Control Based on DPWM Dual-Mode Modulation of High Power NPC Three-Level Inverter

Directory of Open Access Journals (Sweden)

Shi-Zhou Xu

2016-01-01

Full Text Available In some special applications of NPC three-level inverters, such as mine hoist, there exist special conditions of overloading during the whole hoisting process and large overload in starting stage, during which the power-loss calculation of power devices and thermal control are important factors affecting the thermal stability of inverters. The principles of SVPWM and DPWM were described in this paper firstly, based on which the dynamic power losses of the two modulations of hoist in single period were calculated. Secondly, a thermal equilibrium dynamic control based on DPMW dual-mode modulation was proposed, which can switch the modulation dynamically according to the change of dynamic power loss to realize dynamic control of power loss and thermal equilibrium of inverter. Finally, simulation and experiment prove the effectiveness of the proposed strategy.

Thermal Effects Induced by Laser Irradiation of Solids

International Nuclear Information System (INIS)

Galovic, S.

2004-01-01

A part of incident energy is absorbed within the irradiated sample when a solid is exposed to the influence of laser radiation, to more general electromagnetic radiation within the wide range of wavelengths (from microwaves, to infrared radiation to X-rays), or to the energy of particle beams (electronic, protonic, or ionic). The absorption process signifies a highly selective excitation of the electronic state of atoms or molecules, followed by thermal and non-thermal de-excitation processes. Non-radiation de-excitation-relaxation processes induce direct sample heating. In addition, a great number of non-thermal processes (e.g., photoluminescence, photochemistry, photovoltage) may also induce heat generation as a secondary process. This method of producing heat is called the photothermal effect.The photothermal effect and subsequent propagation of thermal waves on the surface and in the volume of the solid absorbing the exciting beam may produce the following: variations in the temperature on the surfaces of the sample; deformation and displacement of surfaces; secondary infrared radiation (photothermal radiation); the formation of the gradient of the refractivity index; changes in coefficients of reflection and absorbtion; the generation of sound (photoacoustic generation), etc. These phenomena may be used in the investigation and measurement of various material properties since the profile and magnitude of the generated signal depend upon the nature of material absorbing radiation. A series of non-destructive spectroscopic, microscopic and defectoscopic detecting techniques, called photothermal methods, is developed on the basis of the above-mentioned phenomena.This paper outlines the interaction between the intensity modulated laser beam and solids, and presents a mathematical model of generated thermal sources. Generalized models for a photothermal response of optically excited materials have been obtained, including thermal memory influence on the propagation

Simulation of Missing Pellet Surface thermal behavior with 3D dynamic gap element

International Nuclear Information System (INIS)

Kim, Hyo Chan; Yang, Yong Sik; Koo, Yang Hyun; Kang, Chang Hak; Lee Sung Uk; Yang, Dong Yol

2014-01-01

Most of the fuel performance codes that are able to simulate a multidimensional analysis are used to calculate the radial temperature distribution and perform a multidimensional mechanical analysis based on a one-dimensional (1D) temperature result. The FRAPCON-FRAPTRAN code system incorporates a 1D thermal module and two-dimensional (2D) mechanical module when FEM option is activated. In this method, the multidimensional gap conductance model is not required because one-dimensional thermal analysis is carried out. On the other hand, a gap conductance model for a multi-dimension should be developed in the code to perform a multidimensional thermal analysis. ALCYONE developed by CEA introduces an equivalent heat convection coefficient that represents the multidimensional gap conductance. However, the code does not employ dynamic gap conductance which is a function of gap thickness and gap characteristics in direct. The BISON code, which has been developed by INL (Idaho National Laboratory), employed a thermo-mechanical contact method that is specifically designed for tightly-coupled implicit solutions that employ Jacobian-free solution methods. Owing to tightly-coupled implicit solutions, the BISON code solves gap conductance and gap thickness simultaneously with given boundary conditions. In this paper, 3D dynamic gap element has been proposed to resolve convergence issue and nonlinear characteristic of multidimensional gap conductance. To evaluate 3D dynamic gap element module, 3D thermomechanical module using FORTRAN77 has been implemented incorporating 3D dynamic gap element. To demonstrate effect of 3D dynamic gap element, thermal behavior of missing pellet surface (MPS) has been simulated by the developed module. LWR fuel performance codes should incorporate thermo-mechanical loop to solve gap conductance problem, iteratively. However, gap conductance in multidimensional model is difficult issue owing to its nonlinearity and convergence characteristics. In

Influence of thermal effects induced by nonlinear absorption on four-wave mixing in silicon waveguides

DEFF Research Database (Denmark)

Pu, Minhao; Chen, Yaohui; Yvind, Kresten

2014-01-01

Influence of thermal effects induced by nonlinear absorption on four-wave mixing in silicon waveguides is investigated. A conversion bandwidth reduction up to 63% is observed in simulation due to the thermal effects.......Influence of thermal effects induced by nonlinear absorption on four-wave mixing in silicon waveguides is investigated. A conversion bandwidth reduction up to 63% is observed in simulation due to the thermal effects....

Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates.

Science.gov (United States)

Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

2016-06-03

A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.

Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates

Science.gov (United States)

Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

2016-06-01

A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.

Self-induced temperature gradients in Brownian dynamics

Science.gov (United States)

Devine, Jack; Jack, M. W.

2017-12-01

Brownian systems often surmount energy barriers by absorbing and emitting heat to and from their local environment. Usually, the temperature gradients created by this heat exchange are assumed to dissipate instantaneously. Here we relax this assumption to consider the case where Brownian dynamics on a time-independent potential can lead to self-induced temperature gradients. In the same way that externally imposed temperature gradients can cause directed motion, these self-induced gradients affect the dynamics of the Brownian system. The result is a coupling between the local environment and the Brownian subsystem. We explore the resulting dynamics and thermodynamics of these coupled systems and develop a robust method for numerical simulation. In particular, by focusing on one-dimensional situations, we show that self-induced temperature gradients reduce barrier-crossing rates. We also consider a heat engine and a heat pump based on temperature gradients induced by a Brownian system in a nonequilibrium potential.

Laser-induced photo-thermal strain imaging

Science.gov (United States)

Choi, Changhoon; Ahn, Joongho; Jeon, Seungwan; Kim, Chulhong

2018-02-01

Vulnerable plaque is the one of the leading causes of cardiovascular disease occurrence. However, conventional intravascular imaging techniques suffer from difficulty in finding vulnerable plaque due to limitation such as lack of physiological information, imaging depth, and depth sensitivity. Therefore, new techniques are needed to help determine the vulnerability of plaque, Thermal strain imaging (TSI) is an imaging technique based on ultrasound (US) wave propagation speed that varies with temperature of medium. During temperature increase, strain occurs in the medium and its variation tendency is depending on the type of tissue, which makes it possible to use for tissue differentiation. Here, we demonstrate laser-induced photo-thermal strain imaging (pTSI) to differentiate tissue using an intravascular ultrasound (IVUS) catheter and a 1210-nm continuous-wave laser for heating lipids intensively. During heating, consecutive US images were obtained from a custom-made phantom made of porcine fat and gelatin. A cross correlation-based speckle-tracking algorithm was then applied to calculate the strain of US images. In the strain images, the positive strain produced in lipids (porcine fat) was clearly differentiated from water-bearing tissue (gelatin). This result shows that laser-induced pTSI could be a new method to distinguish lipids in the plaque and can help to differentiate vulnerability of plaque.

Aeolian system dynamics derived from thermal infrared data

Science.gov (United States)

Scheidt, Stephen Paul

Thermal infrared (TIR) remote-sensing and field-based observations were used to study aeolian systems, specifically sand transport pathways, dust emission sources and Saharan atmospheric dust. A method was developed for generating seamless and radiometrically accurate mosaics of thermal infrared data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument. Using a combination of high resolution thermal emission spectroscopy results of sand samples and mosaic satellite data, surface emissivity was derived to map surface composition, which led to improvement in the understanding of sand accumulation in the Gran Desierto of northern Sonora, Mexico. These methods were also used to map sand transport pathways in the Sahara Desert, where the interaction between sand saltation and dust emission sources was explored. The characteristics and dynamics of dust sources were studied at White Sands, NM and in the Sahara Desert. At White Sands, an application was developed for studying the response of dust sources to surface soil moisture based on the relationship between soil moisture, apparent thermal inertia and the erosion potential of dust sources. The dynamics of dust sources and the interaction with sand transport pathways were also studied, focusing on the Bodele Depression of Chad and large dust sources in Mali and Mauritania. A dust detection algorithm was developed using ASTER data, and the spectral emissivity of observed atmospheric dust was related to the dust source area in the Sahara. At the Atmospheric Observatory (IZO) in Tenerife, Spain where direct measurement of the Saharan Air Layer could be made, the cycle of dust events occurring in July 2009 were examined. From the observation tower at the IZO, measurements of emitted longwave atmospheric radiance in the TIR wavelength region were made using a Forward Looking Infrared Radiometer (FLIR) handheld camera. The use of the FLIR to study atmospheric dust from the Saharan is a

Assessing thermally induced errors of machine tools by 3D length measurements

NARCIS (Netherlands)

Florussen, G.H.J.; Delbressine, F.L.M.; Schellekens, P.H.J.

2003-01-01

A new measurement technique is proposed for the assessment of thermally induced errors of machine tools. The basic idea is to measure changes of length by a telescopic double ball bar (TDEB) at multiple locations in the machine's workspace while the machine is thermally excited. In addition thermal

Multiphase Flow Dynamics 3 Thermal Interactions

CERN Document Server

Kolev, Nikolay Ivanov

2012-01-01

Multi-phase flows are part of our natural environment such as tornadoes, typhoons, air and water pollution and volcanic activities as well as part of industrial technology such as power plants, combustion engines, propulsion systems, or chemical and biological industry. The industrial use of multi-phase systems requires analytical and numerical strategies for predicting their behavior. .In its fourth extended edition the successful monograph package “Multiphase Flow Daynmics” contains theory, methods and practical experience for describing complex transient multi-phase processes in arbitrary geometrical configurations, providing a systematic presentation of the theory and practice of numerical multi-phase fluid dynamics. In the present third volume methods for describing of the thermal interactions in multiphase dynamics are provided. In addition a large number of valuable experiments is collected and predicted using the methods introduced in this monograph. In this way the accuracy of the methods is reve...

Thermal transport in semicrystalline polyethylene by molecular dynamics simulation

Science.gov (United States)

Lu, Tingyu; Kim, Kyunghoon; Li, Xiaobo; Zhou, Jun; Chen, Gang; Liu, Jun

2018-01-01

Recent research has highlighted the potential to achieve high-thermal-conductivity polymers by aligning their molecular chains. Combined with other merits, such as low-cost, corrosion resistance, and light weight, such polymers are attractive for heat transfer applications. Due to their quasi-one-dimensional structural nature, the understanding on the thermal transport in those ultra-drawn semicrystalline polymer fibers or films is still lacking. In this paper, we built the ideal repeating units of semicrystalline polyethylene and studied their dependence of thermal conductivity on different crystallinity and interlamellar topology using the molecular dynamics simulations. We found that the conventional models, such as the Choy-Young's model, the series model, and Takayanagi's model, cannot accurately predict the thermal conductivity of the quasi-one-dimensional semicrystalline polyethylene. A modified Takayanagi's model was proposed to explain the dependence of thermal conductivity on the bridge number at intermediate and high crystallinity. We also analyzed the heat transfer pathways and demonstrated the substantial role of interlamellar bridges in the thermal transport in the semicrystalline polyethylene. Our work could contribute to the understanding of the structure-property relationship in semicrystalline polymers and shed some light on the development of plastic heat sinks and thermal management in flexible electronics.

Novel dynamic thermal characterization of multifunctional concretes with microencapsulated phase change materials

Science.gov (United States)

Pisello, Anna Laura; Fabiani, Claudia; D'Alessandro, Antonella; Cabeza, Luisa F.; Ubertini, Filippo; Cotana, Franco

2017-04-01

Concrete is widely applied in the construction sector for its reliable mechanical performance, its easiness of use and low costs. It also appears promising for enhancing the thermal-energy behavior of buildings thanks to its capability to be doped with multifunctional fillers. In fact, key studies acknowledged the benefits of thermally insulated concretes for applications in ceilings and walls. At the same time, thermal capacity also represents a key property to be optimized, especially for lightweight constructions. In this view, Thermal-Energy Storage (TES) systems have been recently integrated into building envelopes for increasing thermal inertia. More in detail, numerical experimental investigations showed how Phase Change materials (PCMs), as an acknowledged passive TES strategy, can be effectively included in building envelope, with promising results in terms of thermal buffer potentiality. In particular, this work builds upon previous papers aimed at developing the new PCM-filled concretes for structural applications and optimized thermalenergy efficiency, and it is focused on the development of a new experimental method for testing such composite materials in thermal-energy dynamic conditions simulated in laboratory by exposing samples to environmentally controlled microclimate while measuring thermal conductivity and diffusivity by means of transient plane source techniques. The key findings show how the new composites are able to increasingly delay the thermal wave with increasing the PCM concentration and how the thermal conductivity varies during the course of the phase change, in both melting and solidification processes. The new analysis produces useful findings in proposing an effective method for testing composite materials with adaptive thermal performance, much needed by the scientific community willing to study building envelopes dynamics.

Harvesting thermal fluctuations: Activation process induced by a nonlinear chain in thermal equilibrium

International Nuclear Information System (INIS)

Reigada, Ramon; Sarmiento, Antonio; Romero, Aldo H.; Sancho, J. M.; Lindenberg, Katja

2000-01-01

We present a model in which the immediate environment of a bistable system is a molecular chain which in turn is connected to a thermal environment of the Langevin form. The molecular chain consists of masses connected by harmonic or by anharmonic springs. The distribution, intensity, and mobility of thermal fluctuations in these chains is strongly dependent on the nature of the springs and leads to different transition dynamics for the activated process. Thus, all else (temperature, damping, coupling parameters between the chain and the bistable system) being the same, the hard chain may provide an environment described as diffusion-limited and more effective in the activation process, while the soft chain may provide an environment described as energy-limited and less effective. The importance of a detailed understanding of the thermal environment toward the understanding of the activation process itself is thus highlighted. (c) 2000 American Institute of Physics

Sub-nanometer glass surface dynamics induced by illumination

International Nuclear Information System (INIS)

Nguyen, Duc; Nienhaus, Lea; Haasch, Richard T.; Lyding, Joseph; Gruebele, Martin

2015-01-01

Illumination is known to induce stress and morphology changes in opaque glasses. Amorphous silicon carbide (a-SiC) has a smaller bandgap than the crystal. Thus, we were able to excite with 532 nm light a 1 μm amorphous surface layer on a SiC crystal while recording time-lapse movies of glass surface dynamics by scanning tunneling microscopy (STM). Photoexcitation of the a-SiC surface layer through the transparent crystal avoids heating the STM tip. Up to 6 × 10 4 s, long movies of surface dynamics with 40 s time resolution and sub-nanometer spatial resolution were obtained. Clusters of ca. 3-5 glass forming units diameter are seen to cooperatively hop between two states at the surface. Photoexcitation with green laser light recruits immobile clusters to hop, rather than increasing the rate at which already mobile clusters hop. No significant laser heating was observed. Thus, we favor an athermal mechanism whereby electronic excitation of a-SiC directly controls glassy surface dynamics. This mechanism is supported by an exciton migration-relaxation-thermal diffusion model. Individual clusters take ∼1 h to populate states differently after the light intensity has changed. We believe the surrounding matrix rearranges slowly when it is stressed by a change in laser intensity, and clusters serve as a diagnostic. Such cluster hopping and matrix rearrangement could underlie the microscopic mechanism of photoinduced aging of opaque glasses

Thermodynamic model of a thermal storage air conditioning system with dynamic behavior

International Nuclear Information System (INIS)

Fleming, Evan; Wen, Shaoyi; Shi, Li; Silva, Alexandre K. da

2013-01-01

Highlights: • We developed an automotive thermal storage air conditioning system model. • The thermal storage unit utilizes phase change materials. • We use semi-analytic solution to the coupled phase change and forced convection. • We model the airside heat exchange using the NTU method. • The system model can incorporate dynamic inputs, e.g. variable inlet airflow. - Abstract: A thermodynamic model was developed to predict transient behavior of a thermal storage system, using phase change materials (PCMs), for a novel electric vehicle climate conditioning application. The main objectives of the paper are to consider the system’s dynamic behavior, such as a dynamic air flow rate into the vehicle’s cabin, and to characterize the transient heat transfer process between the thermal storage unit and the vehicle’s cabin, while still maintaining accurate solution to the complex phase change heat transfer. The system studied consists of a heat transfer fluid circulating between either of the on-board hot and cold thermal storage units, which we refer to as thermal batteries, and a liquid–air heat exchanger that provides heat exchange with the incoming air to the vehicle cabin. Each thermal battery is a shell-and-tube configuration where a heat transfer fluid flows through parallel tubes, which are surrounded by PCM within a larger shell. The system model incorporates computationally inexpensive semi-analytic solution to the conjugated laminar forced convection and phase change problem within the battery and accounts for airside heat exchange using the Number of Transfer Units (NTUs) method for the liquid–air heat exchanger. Using this approach, we are able to obtain an accurate solution to the complex heat transfer problem within the battery while also incorporating the impact of the airside heat transfer on the overall system performance. The implemented model was benchmarked against a numerical study for a melting process and against full system

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

Science.gov (United States)

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

2014-10-28

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

Transient, heat-induced thermal resistance in the small intestine of mouse

International Nuclear Information System (INIS)

Hume, S.P.; Marigold, J.C.L.

1980-01-01

Heat-induced thermal resistance has been investigated in mouse jejunum by assaying crypt survival 24 h after treatment. Hyperthermia was achieved by immersing an exteriorized loop of intestine in a bath of Krebs-Ringer solution. Two approaches have been used. In the first, thermal survival curves were obtained following single hyperthermal treatments at temperatures in the range 42 to 44 0 C. Transient thermal resistance, inducted by a plateau in the crypt survival curve, developed during heating at temperatures around 42.5 0 C after 60 to 80 min. In the second series of experiments, a priming heat treatment (40.0, 41.0, 41.5, or 42.0 0 C for 60 min) was followed at varying intervals by a test treatment at 43.0 0 C. A transient resistance to the second treatment was induced, the extent and time of development being dependent upon the priming treatment. Crypt survival curves for thermally resistant intestine showed an increase in thermal D 0 and a decrease in n compared with curves from previously unheated intestine

Full-size solar dynamic heat receiver thermal-vacuum tests

Science.gov (United States)

Sedgwick, L. M.; Kaufmann, K. J.; Mclallin, K. L.; Kerslake, T. W.

1991-01-01

The testing of a full-size, 102 kW, solar dynamic heat receiver utilizing high-temperature thermal energy storage is described. The purpose of the test program was to quantify receiver thermodynamic performance, operating temperatures, and thermal response to changes in environmental and power module interface boundary conditions. The heat receiver was tested in a vacuum chamber with liquid nitrogen cold shrouds and an aperture cold plate to partly simulate a low-Earth-orbit environment. The cavity of the receiver was heated by an infrared quartz lamp heater with 30 independently controllable zones to allow axially and circumferentially varied flux distributions. A closed-Brayton cycle engine simulator conditioned a helium-xenon gas mixture to specific interface conditions to simulate the various operational modes of the solar dynamic power module on the Space Station Freedom. Inlet gas temperature, pressure, and flow rate were independently varied. A total of 58 simulated orbital cycles, each 94 minutes in duration, was completed during the test period.

Response of a thermal barrier system to acoustic excitation in a gas turbine nuclear reactor

International Nuclear Information System (INIS)

Betts, W.S. Jr.; Blevins, R.D.

1980-11-01

A gas turbine located within a High-Temperature Gas-Cooled Reactor (HTGR) induces high acoustic sound pressure levels into the primary coolant (helium). This acoustic loading induces high cycle fatigue stresses which may control the design of the thermal barrier system. This study examines the dynamic response of a thermal barrier configuration consisting of a fibrous insulation compressed against the reactor vessel by a coverplate which is held in position by a central attachment fixture. The results of dynamic vibration analyses indicate the effect of the plate size and curvature and the attachment size on the response of the thermal barrier

Dynamics of a discrete geotropic sensor subject to rotation-induced gravity compensation

Energy Technology Data Exchange (ETDEWEB)

Silver, I.L.

1976-01-01

A clinostat achieves gravity compensation by providing circular rotation with uniform speed, about a horizontal axis. The dynamics of an assumed, discrete and free-moving subcellular gravity receptor, subject to clinostat rotation, is analyzed. The results imply that there is an optimum rotation rate; higher speeds result in circular motions with diameters more comparable to thermal noise fluctuations, but with greater linear velocities due to increasing centrifugal forces. An optimizing function is proposed. The nucleolus and mitochondrion is chosen as a gravity receptor for illustrating the use of this theory. The characteristics of their clinostat-induced motions are incorporated with experimental results on Avena plant shoots in an illustrative example.

Dynamic response analysis of an aircraft structure under thermal-acoustic loads

International Nuclear Information System (INIS)

Cheng, H; Li, H B; Zhang, W; Wu, Z Q; Liu, B R

2016-01-01

Future hypersonic aircraft will be exposed to extreme combined environments includes large magnitude thermal and acoustic loads. It presents a significant challenge for the integrity of these vehicles. Thermal-acoustic test is used to test structures for dynamic response and sonic fatigue due to combined loads. In this research, the numerical simulation process for the thermal acoustic test is presented, and the effects of thermal loads on vibro-acoustic response are investigated. To simulate the radiation heating system, Monte Carlo theory and thermal network theory was used to calculate the temperature distribution. Considering the thermal stress, the high temperature modal parameters are obtained with structural finite element methods. Based on acoustic finite element, modal-based vibro-acoustic analysis is carried out to compute structural responses. These researches are very vital to optimum thermal-acoustic test and structure designs for future hypersonic vehicles structure (paper)

Thermal quantum time-correlation functions from classical-like dynamics

Science.gov (United States)

Hele, Timothy J. H.

2017-07-01

Thermal quantum time-correlation functions are of fundamental importance in quantum dynamics, allowing experimentally measurable properties such as reaction rates, diffusion constants and vibrational spectra to be computed from first principles. Since the exact quantum solution scales exponentially with system size, there has been considerable effort in formulating reliable linear-scaling methods involving exact quantum statistics and approximate quantum dynamics modelled with classical-like trajectories. Here, we review recent progress in the field with the development of methods including centroid molecular dynamics , ring polymer molecular dynamics (RPMD) and thermostatted RPMD (TRPMD). We show how these methods have recently been obtained from 'Matsubara dynamics', a form of semiclassical dynamics which conserves the quantum Boltzmann distribution. We also apply the Matsubara formalism to reaction rate theory, rederiving t → 0+ quantum transition-state theory (QTST) and showing that Matsubara-TST, like RPMD-TST, is equivalent to QTST. We end by surveying areas for future progress.

Optimization of the dynamic and thermal performance of a resonant micro heat engine

International Nuclear Information System (INIS)

Bardaweel, H K; Richards, R F; Richards, C D; Anderson, M J

2008-01-01

The dynamic behavior of a flexing membrane micro heat engine is presented. The micro heat engine consists of a cavity filled with a saturated, two-phase working fluid bounded on the top by a flexible expander membrane and on the bottom by a stiff evaporator membrane. A lumped parameter model is developed to simulate the dynamic behavior of the micro heat engine. First, the model is validated against experimental data. Then, the model is used to investigate the effect of the duration of the heat addition process, the mass of the expander membrane and the thermal storage or thermal inertia associated with the engine cavity on the dynamic behavior of the micro engine. The results show the optimal duration for the heat addition process to be less than 10% of the engine cycle period. Increasing the mass of the flexible expander membrane is shown to reduce the resonant frequency of the engine to 130 Hz. Operating the engine at resonance leads to increased power output. The thermal storage or thermal inertia associated with the engine cavity is shown to have a strong effect on engine performance

Dynamical Dark Matter from thermal freeze-out

Science.gov (United States)

Dienes, Keith R.; Fennick, Jacob; Kumar, Jason; Thomas, Brooks

2018-03-01

In the Dynamical Dark-Matter (DDM) framework, the dark sector comprises a large number of constituent dark particles whose individual masses, lifetimes, and cosmological abundances obey specific scaling relations with respect to each other. In particular, the most natural versions of this framework tend to require a spectrum of cosmological abundances which scale inversely with mass, so that dark-sector states with larger masses have smaller abundances. Thus far, DDM model-building has primarily relied on nonthermal mechanisms for abundance generation such as misalignment production, since these mechanisms give rise to abundances that have this property. By contrast, the simplest versions of thermal freeze-out tend to produce abundances that increase, rather than decrease, with the mass of the dark-matter component. In this paper, we demonstrate that there exist relatively simple modifications of the traditional thermal freeze-out mechanism which "flip" the resulting abundance spectrum, producing abundances that scale inversely with mass. Moreover, we demonstrate that a far broader variety of scaling relations between lifetimes, abundances, and masses can emerge through thermal freeze-out than through the nonthermal mechanisms previously considered for DDM ensembles. The results of this paper thus extend the DDM framework into the thermal domain and essentially allow us to "design" our resulting DDM ensembles at will in order to realize a rich array of resulting dark-matter phenomenologies.

Optically induced structural phase transitions in ion Coulomb crystals

DEFF Research Database (Denmark)

Horak, Peter; Dantan, Aurelien Romain; Drewsen, Michael

2012-01-01

We investigate numerically the structural dynamics of ion Coulomb crystals confined in a three-dimensional harmonic trap when influenced by an additional one-dimensional optically induced periodical potential. We demonstrate that transitions between thermally excited crystal structures, such as b......We investigate numerically the structural dynamics of ion Coulomb crystals confined in a three-dimensional harmonic trap when influenced by an additional one-dimensional optically induced periodical potential. We demonstrate that transitions between thermally excited crystal structures...

Chronic vitamin C administration induces thermal hyperalgesia in ...

African Journals Online (AJOL)

Against a backdrop of neurological effects, the effects of acute and chronic administration of vitamin C (600mg/kg) on pain processing were investigated in male rats. Chronic administration of vitamin C induced significant thermal hyperalgesia while acute administration had no effect. In addition, the intraperitoneal ...

Phonon-mediated Thermal Conductivity in Ionic Solids by Lattice Dynamics-based Methods

Energy Technology Data Exchange (ETDEWEB)

Chernatynskiy, Aleksandr [Univ. of Florida, Gainesville, FL (United States); Turney, Joseph E. [Carnegie Mellon Univ., Pittsburgh, PA (United States); McGaughey, Alan J. H. [Carnegie Mellon Univ., Pittsburgh, PA (United States); Amon, Christina H. [Univ. of Toronto, ON (Canada); Phillpot, Simon R. [Univ. of Florida, Gainesville, FL (United States)

2011-07-22

Phonon properties predicted from lattice dynamics calculations and the Boltzmann Transport Equation (BTE) are used to elucidate the thermal-transport properties of ionic materials. It is found that a rigorous treatment of the Coulombic interactions within the harmonic analysis is needed for the analysis of the phonon structure of the solid, while a short-range approximation is sufficient for the third-order force constants. The effects on the thermal conductivity of the relaxation time approximation, the classical approximation to the phonon statistics, the direct summation method for the electrostatic interactions, and the quasi-harmonic approximation to lattice dynamics are quantified. Quantitative agreement is found between predictions from molecular dynamics simulations (a method valid at temperatures above the Debye temperature) and the BTE result within quasi-harmonic approximation over a wide temperature range.

Magnetic field induced dynamical chaos.

Science.gov (United States)

Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra

2013-12-01

In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x-y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

Nonlinear Modeling and Simulation of Thermal Effects in Microcantilever Resonators Dynamic

International Nuclear Information System (INIS)

Tadayon, M A; Sayyaadi, H; Jazar, G Nakhaie

2006-01-01

Thermal dependency of material characteristics in micro electromechanical systems strongly affects their performance, design, and control. Hence, it is essential to understand and model that in MEMS devices to optimize their designs. A thermal phenomenon introduces two main effects: damping due to internal friction, and softening due to Young modulus temperature relation. Based on some reported theoretical and experimental results, we model the thermal phenomena and use two Lorentzian functions to describe the restoring and damping forces caused by thermal phenomena. In order to emphasize the thermal effects, a nonlinear model of the MEMS, by considering capacitor nonlinearity, have been used. The response of the system is developed by employing multiple time scales perturbation method on nondimensionalized form of equations. Frequency response, resonant frequency and peak amplitude are examined for variation of dynamic parameters involved

Modeling interactions of soil hydrological dynamics and soil thermal and permafrost dynamics and their effects on carbon cycling in northern high latitudes

Science.gov (United States)

Zhuang, Q.; Tang, J.

2008-12-01

Large areas of northern high latitude ecosystems are underlain with permafrost. The warming temperature and fires deteriorate the stability of those permafrost, altering hydrological cycle, and consequently soil temperature and active layer depth. These changes will determine the fate of large carbon pools in soils and permafrost over the region. We developed a modeling framework of hydrology, permafrost, and biogeochemical dynamics based on our existing modules of these components. The framework was incorporated with a new snow dynamics module and the effects of soil moisture on soil thermal properties. The framework was tested for tundra and boreal forest ecosystems at field sites with respect to soil thermal and hydrological regimes in Alaska and was then applied to the whole Alaskan ecosystems for the period of 1923-2000 at a daily time step. Our two sets of simulations with and without considering soil moisture effects indicated that the soil temperature profile and active layer depth between two simulations are significant different. The differences of soil thermal regime would expect to result in different carbon dynamics. Next, we will verify the framework with the observed data of soil moisture and soil temperature at poor-drain, moderate-drain, and well-drain boreal forest sites in Alaska. With the verified framework, we will evaluate the effects of interactions of soil thermal and hydrological dynamics on carbon dynamics for the whole northern high latitudes.

Transient thermal stresses and stress intensity factors induced by thermal stratification in feedwater lines

International Nuclear Information System (INIS)

Sanchez Sarmiento, G.; Pardo, E.

1985-01-01

General analytical solutions for the thermal stresses and circumferential crack propagation in piping branches of nuclear power plants, that connect two circuits of the same fluid at different temperatures, are presented in this paper. Under certain conditions, two regions of the fluid possessing both temperatures with a separating layer of small thickness are formed ('flow stratification'). Dimensionless analytical expressions for the steady state temperature distribution in the pipe wall and the corresponding thermal stress are here derived, in terms of the basic geometrical and physical parameters. The position and thickness of the separating layer are considered as data of the model. Stress intensity ranges at any point of the tube wall are then determined. Finally, thermally induced stress intensity factors are calculated for hipothetically inside surface cracks. (orig.)

Comparison of radiation-induced and thermal oxidative aging of polyethylene in the presence of inhibitors

International Nuclear Information System (INIS)

Dalinkevich, A.A.; Piskarev, I.M.

1996-01-01

Thermal oxidative and radiation-induced oxidative aging of inhibited polyethylene of commercial brands with known properties was studied at 60, 80 and 140 deg C. Radiation-induced oxidative aging was carried out under X-ray radiation with E max = 25 keV at dose rates providing specimen oxidation in kinetic conditions. The value of activation energy of thermal oxidative destruction of inhibited polyethylene under natural conditions of its employment at 60-140 deg C (E a = 60 kJ/mol) was obtained by comparison of data for radiation-induced and thermal oxidative destruction

Molecular dynamics study on the thermal conductivity and thermal rectification in graphene with geometric variations of doped boron

Energy Technology Data Exchange (ETDEWEB)

Liang, Qi, E-mail: alfred_02030210@163.com; Wei, Yuan

2014-03-15

Thermal conductivity and thermal rectification of graphene with geometric variations have been investigated by using classical non-equilibrium molecular dynamics simulation, and analyzed theoretically the cause of the changes of thermal conductivity and thermal rectification. Two different structural models, triangular single-boron-doped graphene (SBDG) and parallel various-boron-doped graphene (VBDG), were considered. The results indicated that the thermal conductivities of two different models are about 54–63% lower than pristine graphene. And it was also found that the structure of parallel various-boron-doped graphene is inhibited more strongly on the heat transfer than that of triangular single-boron-doped graphene. The reduction in the thermal conductivities of two different models gradually decreases as the temperature rises. The thermal conductivities of triangular boron-doped graphene have a large difference in both directions, and the thermal rectification of this structure shows the downward trend with increasing temperature. However, the thermal conductivities of parallel various-boron-doped graphene are similar in both directions, and the thermal rectification effect is not obvious in this structure. The phenomenon of thermal rectification exits in SBDG. It implies that the SBDG might be a potential promising structure for thermal rectifier by controlling the boron-doped model.

Molecular dynamics study on the thermal conductivity and thermal rectification in graphene with geometric variations of doped boron

International Nuclear Information System (INIS)

Liang, Qi; Wei, Yuan

2014-01-01

Thermal conductivity and thermal rectification of graphene with geometric variations have been investigated by using classical non-equilibrium molecular dynamics simulation, and analyzed theoretically the cause of the changes of thermal conductivity and thermal rectification. Two different structural models, triangular single-boron-doped graphene (SBDG) and parallel various-boron-doped graphene (VBDG), were considered. The results indicated that the thermal conductivities of two different models are about 54–63% lower than pristine graphene. And it was also found that the structure of parallel various-boron-doped graphene is inhibited more strongly on the heat transfer than that of triangular single-boron-doped graphene. The reduction in the thermal conductivities of two different models gradually decreases as the temperature rises. The thermal conductivities of triangular boron-doped graphene have a large difference in both directions, and the thermal rectification of this structure shows the downward trend with increasing temperature. However, the thermal conductivities of parallel various-boron-doped graphene are similar in both directions, and the thermal rectification effect is not obvious in this structure. The phenomenon of thermal rectification exits in SBDG. It implies that the SBDG might be a potential promising structure for thermal rectifier by controlling the boron-doped model

Thermal parameter identification for non-Fourier heat transfer from molecular dynamics

Science.gov (United States)

Singh, Amit; Tadmor, Ellad B.

2015-10-01

Fourier's law leads to a diffusive model of heat transfer in which a thermal signal propagates infinitely fast and the only material parameter is the thermal conductivity. In micro- and nano-scale systems, non-Fourier effects involving coupled diffusion and wavelike propagation of heat can become important. An extension of Fourier's law to account for such effects leads to a Jeffreys-type model for heat transfer with two relaxation times. We propose a new Thermal Parameter Identification (TPI) method for obtaining the Jeffreys-type thermal parameters from molecular dynamics simulations. The TPI method makes use of a nonlinear regression-based approach for obtaining the coefficients in analytical expressions for cosine and sine-weighted averages of temperature and heat flux over the length of the system. The method is applied to argon nanobeams over a range of temperature and system sizes. The results for thermal conductivity are found to be in good agreement with standard Green-Kubo and direct method calculations. The TPI method is more efficient for systems with high diffusivity and has the advantage, that unlike the direct method, it is free from the influence of thermostats. In addition, the method provides the thermal relaxation times for argon. Using the determined parameters, the Jeffreys-type model is able to reproduce the molecular dynamics results for a short-duration heat pulse where wavelike propagation of heat is observed thereby confirming the existence of second sound in argon. An implementation of the TPI method in MATLAB is available as part of the online supplementary material.

Relaxation of a coherent, magnetic s–p model system coupled to one and two thermal baths and a laser pulse

Energy Technology Data Exchange (ETDEWEB)

Lefkidis, G. [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Box 3049, 67653 Kaiserslautern (Germany); School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an 710072 (China); Sold, S.; Hübner, W. [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Box 3049, 67653 Kaiserslautern (Germany)

2017-06-15

We study an s–p model magnetic system with a triplet ground state coupled to two temperature baths. By varying the temperatures we both generate non-thermal electronic distributions and create additional coherences in the density matrix of the system. Thus the thermally-induced magnetic response goes beyond the simple picture of majority-minority population dynamics. Furthermore, we discuss the influence of temperature induced relaxation effects on the dynamics induced by an optical perturbation for this quantum system.

Modelling of thermal field and point defect dynamics during silicon single crystal growth using CZ technique

Science.gov (United States)

Sabanskis, A.; Virbulis, J.

2018-05-01

Mathematical modelling is employed to numerically analyse the dynamics of the Czochralski (CZ) silicon single crystal growth. The model is axisymmetric, its thermal part describes heat transfer by conduction and thermal radiation, and allows to predict the time-dependent shape of the crystal-melt interface. Besides the thermal field, the point defect dynamics is modelled using the finite element method. The considered process consists of cone growth and cylindrical phases, including a short period of a reduced crystal pull rate, and a power jump to avoid large diameter changes. The influence of the thermal stresses on the point defects is also investigated.

Influence of gamma-irradiation on thermally-induced mesoscopic gelation of degalactosylated xyloglucans

International Nuclear Information System (INIS)

Todaro, S.; Sabatino, M.A.; Walo, M.; Mangione, M.R.; Bulone, D.; Dispenza, C.

2014-01-01

Thermoresponsive degalactosylated xyloglucans have been already proposed as in situ gelling scaffolds for tissue engineering, due to their reversible macroscopic thermal gelation at body temperature and biodegradability. The highly branched, hydroxyl group-rich molecular structure renders xyloglucans interesting raw materials also in the form of micro/nanoparticles for application as nanoscalar drug delivery devices in cosmetic and pharmaceutical formulations. Owing to their natural source, xyloglucans show high average molecular weight, broad molecular weight distribution and poor water solubility, as large and compact aggregates usually form via inter-molecular hydrogen bonding. 60 Co γ-irradiation has been here applied to reduce the molecular weight. The aqueous solutions of irradiated xyloglucan were characterized by dynamic light scattering measurements and gel filtration chromatography. The aggregation kinetics at 37 °C were studied by dynamic light scattering measurements to confirm the temperature-responsive behavior of this polymer even when dispersed in water at low concentration after γ-irradiation. Irradiation dose–molecular properties relationship has been sought. - Highlights: • Influence of γ-irradiation on a partially degalactosylated xyloglucan is investigated. • Molecular weight reduction is observed in the investigated dose range. • Modification of the temperature-induced mesoscopic gelation kinetics is evidenced

Semiquantum molecular dynamics simulation of thermal properties and heat transport in low-dimensional nanostructures

Science.gov (United States)

Savin, Alexander V.; Kosevich, Yuriy A.; Cantarero, Andres

2012-08-01

We present a detailed description of semiquantum molecular dynamics simulation of stochastic dynamics of a system of interacting particles. Within this approach, the dynamics of the system is described with the use of classical Newtonian equations of motion in which the effects of phonon quantum statistics are introduced through random Langevin-like forces with a specific power spectral density (the color noise). The color noise describes the interaction of the molecular system with the thermostat. We apply this technique to the simulation of thermal properties and heat transport in different low-dimensional nanostructures. We describe the determination of temperature in quantum lattice systems, to which the equipartition limit is not applied. We show that one can determine the temperature of such a system from the measured power spectrum and temperature- and relaxation-rate-independent density of vibrational (phonon) states. We simulate the specific heat and heat transport in carbon nanotubes, as well as the heat transport in molecular nanoribbons with perfect (atomically smooth) and rough (porous) edges, and in nanoribbons with strongly anharmonic periodic interatomic potentials. We show that the effects of quantum statistics of phonons are essential for the carbon nanotube in the whole temperature range T<500K, in which the values of the specific heat and thermal conductivity of the nanotube are considerably less than that obtained within the description based on classical statistics of phonons. This conclusion is also applicable to other carbon-based materials and systems with high Debye temperature like graphene, graphene nanoribbons, fullerene, diamond, diamond nanowires, etc. We show that the existence of rough edges and quantum statistics of phonons change drastically the low-temperature thermal conductivity of the nanoribbon in comparison with that of the nanoribbon with perfect edges and classical phonon dynamics and statistics. The semiquantum molecular

Power cables thermal protection by interval simulation of imprecise dynamical systems

Energy Technology Data Exchange (ETDEWEB)

Bontempi, G. [Universite Libre de Brussels (Belgium). Dept. d' Informatique; Vaccaro, A.; Villacci, D. [Universita del Sannio Benevento (Italy). Dept. of Engineering

2004-11-01

The embedding of advanced simulation techniques in power cables enables improved thermal protection because of higher accuracy, adaptiveness and. flexibility. In particular, they make possible (i) the accurate solution of differential equations describing the cables thermal dynamics and (ii) the adoption of the resulting solution in the accomplishment of dedicated protective functions. However, the use of model-based protective systems is exposed to the uncertainty affecting some model components (e.g. weather along the line route, thermophysical properties of the soil, cable parameters). When uncertainty can be described in terms of probability distribution, well-known techniques, such as Monte Carlo, are used to simulate the system behaviour. On the other hand, when the description of uncertainty in probabilistic terms is unfeasible or problematic, nonprobabilistic alternatives should be taken into consideration. This paper will discuss and compare three interval-based techniques as alternatives to probabilistic methods in the simulation of power cable dynamics. The experimental session will assess the interval-based approaches by simulating the thermal behaviour of medium voltage power cables.(author)

Effects of deformability and thermal motion of lipid membrane on electroporation: By molecular dynamics simulations

International Nuclear Information System (INIS)

Sun, Sheng; Yin, Guangyao; Lee, Yi-Kuen; Wong, Joseph T.Y.; Zhang, Tong-Yi

2011-01-01

Research highlights: → MD simulations show that deformability and thermal motion of membrane affect electroporation. → Stiffer membrane inhibits electroporation and makes water penetrate from both sides. → Higher temperature accelerates electroporation. -- Abstract: Effects of mechanical properties and thermal motion of POPE lipid membrane on electroporation were studied by molecular dynamics simulations. Among simulations in which specific atoms of lipids were artificially constrained at their equilibrium positions using a spring with force constant of 2.0 kcal/(mol A 2 ) in the external electric field of 1.4 kcal/(mol A e), only constraint on lateral motions of lipid tails prohibited electroporation while non-tail parts had little effects. When force constant decreased to 0.2 kcal/(mol A 2 ) in the position constraints on lipid tails in the external electric field of 2.0 kcal/(mol A e), water molecules began to enter the membrane. Position constraints of lipid tails allow water to penetrate from both sides of membrane. Thermal motion of lipids can induce initial defects in the hydrophobic core of membrane, which are favorable nucleation sites for electroporation. Simulations at different temperatures revealed that as the temperature increases, the time taken to the initial pore formation will decrease.

Histological and Physiological Alterations Induced by Thermal Neutron Fluxes in Male Swiss Albino Mice

International Nuclear Information System (INIS)

Alzergy, A.A.; Emara, N.M.; Abd El-Latif, A.A.; El-Saady, S.M.M.; Emara, N.M.; Abd El-Latif, A.A.

2010-01-01

This work was performed to investigate the biological effects of different thermal neutron fluxes (0.27x10 8 , 0.52X10 8 , 1.089X10 8 , 2.16X10 8 and 4.32X10 8 ) on liver and kidney of male mice using neutron irradiation cell with Ra-Be(α,n) 3 mCi neutron source Leybold (55930). Exposed to various fluxes of thermal neutron induced a dramatic alterations in hepatic and renal functions as indicated by biochemical estimation of several parameters (bilirubin, SGT, and alkaline phosphate .Urea , total protein, and albumin) and confirmed by histological examinations Thermal neutron exposure induces marked increase in the serum activities of total bilirubin, alanine amino transaminase (ALT or GPT), and alkaline phosphate, whereas, urea, total protein and albumin showed marked decline as compared to control group. The physiological changes induced in thermal neutron fluxes dependent manner. Histopathological results revealed mild to severe type of necrosis, and degenerative changes in liver and kidney of male mice exposed to thermal neutron fluxes. Also it was found that the histopathological alterations induced in thermal neutron fluxes dependent manner. It was found that exposed to thermal neutron fluxes irradiation plays prominent role in the development of the physiological alterations in male Swiss albino mice. The Former up normalities as a result of the sequence events followed interaction of radiation with the former biological mater (liver and kidney) of male Swiss albino mice, which are, physical, physicochemical, chemical, and biological stages.

Geometric origin of dynamically induced freezing of quantum evolution

International Nuclear Information System (INIS)

Matos-Abiague, A.; Berakdar, J.

2006-01-01

The phenomenon of dynamical, field-induced freezing of quantum evolution is discussed. It occurs when a time-dependent state is dynamically driven in such a way that the evolution of the corresponding wave function is effectively localized within a small region in the projective Hilbert space. As a consequence, the dynamics of the system is frozen and the expectation values of all physical observables hardly change with time. Necessary and sufficient conditions for inducing dynamical freezing are inferred from a general analysis of the geometry of quantum evolution. The relevance of the dynamical freezing for a sustainable in time, dynamical control is discussed and exemplified by a study of the coherent control of the kicked rotor motion

Lattice Dynamics Study of Phonon Instability and Thermal Properties of Type-I Clathrate K8Si46 under High Pressure

Directory of Open Access Journals (Sweden)

Wei Zhang

2016-07-01

Full Text Available For a further understanding of the phase transitions mechanism in type-I silicon clathrates K8Si46, ab initio self-consistent electronic calculations combined with linear-response method have been performed to investigate the vibrational properties of alkali metal K atoms encapsulated type-I silicon-clathrate under pressure within the framework of density functional perturbation theory. Our lattice dynamics simulation results showed that the pressure induced phase transition of K8Si46 was believed to be driven by the phonon instability of the calthrate lattice. Analysis of the evolution of the partial phonon density of state with pressure, a legible dynamic picture for both guest K atoms and host lattice, was given. In addition, based on phonon calculations and combined with quasi-harmonic approximation, the specific heat of K8Si46 was derived, which agreed very well with experimental results. Also, other important thermal properties including the thermal expansion coefficients and Grüneisen parameters of K8Si46 under different temperature and pressure were also predicted.

Thermal equation of state for lattice Boltzmann gases

International Nuclear Information System (INIS)

Zheng, Ran

2009-01-01

The Galilean invariance and the induced thermo-hydrodynamics of the lattice Boltzmann Bhatnagar–Gross–Krook model are proposed together with their rigorous theoretical background. From the viewpoint of group invariance, recovering the Galilean invariance for the isothermal lattice Boltzmann Bhatnagar–Gross–Krook equation (LBGKE) induces a new natural thermal-dynamical system, which is compatible with the elementary statistical thermodynamics

Improved resistance of chemically-modified nanocellulose against thermally-induced depolymerization.

Science.gov (United States)

Agustin, Melissa B; Nakatsubo, Fumiaki; Yano, Hiroyuki

2017-05-15

The study demonstrated the improvement in the resistance of nanocellulose against thermally-induced depolymerization by esterification with benzoyl (BNZ) and pivaloyl (PIV). The change in the degree of polymerization (DP) and molecular weight distribution (MWD) after thermal treatment in nitrogen and in air was investigated using viscometry and gel permeation chromatography. BNZ and PIV nanocellulose esters without α-hydrogens gave higher DP and narrower MWD than pure bacterial cellulose; and the acetyl and myristoyl esters, which possess α-hydrogens. Results also showed that when depolymerization is suppressed, thermal discoloration is also reduced. Resistance against depolymerization inhibits the formation of reducing ends which can be active sites for thermal discoloration. Finally, the findings suggest that benzoylation and pivaloylation can be an excellent modification technique to improve the thermal stability of nanocellulose. Copyright © 2017 Elsevier Ltd. All rights reserved.

Thermal and dynamic range characterization of a photonics-based RF amplifier

Science.gov (United States)

Noque, D. F.; Borges, R. M.; Muniz, A. L. M.; Bogoni, A.; Cerqueira S., Arismar, Jr.

2018-05-01

This work reports a thermal and dynamic range characterization of an ultra-wideband photonics-based RF amplifier for microwave and mm-waves future 5G optical-wireless networks. The proposed technology applies the four-wave mixing nonlinear effect to provide RF amplification in analog and digital radio-over-fiber systems. The experimental analysis from 300 kHz to 50 GHz takes into account different figures of merit, such as RF gain, spurious-free dynamic range and RF output power stability as a function of temperature. The thermal characterization from -10 to +70 °C demonstrates a 27 dB flat photonics-assisted RF gain over the entire frequency range under real operational conditions of a base station for illustrating the feasibility of the photonics-assisted RF amplifier for 5G networks.

Effects of deformability and thermal motion of lipid membrane on electroporation: By molecular dynamics simulations

KAUST Repository

Sun, Sheng

2011-01-01

Effects of mechanical properties and thermal motion of POPE lipid membrane on electroporation were studied by molecular dynamics simulations. Among simulations in which specific atoms of lipids were artificially constrained at their equilibrium positions using a spring with force constant of 2.0kcal/(molÅ2) in the external electric field of 1.4kcal/(molÅe), only constraint on lateral motions of lipid tails prohibited electroporation while non-tail parts had little effects. When force constant decreased to 0.2kcal/(molÅ2) in the position constraints on lipid tails in the external electric field of 2.0kcal/(molÅe), water molecules began to enter the membrane. Position constraints of lipid tails allow water to penetrate from both sides of membrane. Thermal motion of lipids can induce initial defects in the hydrophobic core of membrane, which are favorable nucleation sites for electroporation. Simulations at different temperatures revealed that as the temperature increases, the time taken to the initial pore formation will decrease. © 2010 Elsevier Inc.

Inducible Laryngeal Obstruction: Excessive Dynamic Airway Collapse vs. Inducible Laryngeal Obstruction

Science.gov (United States)

2017-10-20

REPORT TYPE 10/20/2017 Poster 4. TITLE AND SUBTITLE Inducible Laryngeal Obstrnction: Excessive Dynamic Airway Collapse vs. Inducible Laryngeal...REPORT b.ABSTRACT c. THIS PAGE ABSTRACT OF PAGES 3. DATES COVERED (From - To) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER

Thermal interpretation of infrared dynamics in de Sitter

Energy Technology Data Exchange (ETDEWEB)

Rigopoulos, Gerasimos, E-mail: gerasimos.rigopoulos@ncl.ac.uk [School of Mathematics and Statistics, Newcastle University, Herschel Building, Newcastle upon Tyne, NE1 7RU U.K. (United Kingdom)

2016-07-01

The infrared dynamics of a light, minimally coupled scalar field in de Sitter spacetime with Ricci curvature R = 12 H {sup 2}, averaged over horizon sized regions of physical volume V {sub H} = (4π/3)(1/ H ){sup 3}, can be interpreted as Brownian motion in a medium with de Sitter temperature T {sub DS} = h-bar H /2π. We demonstrate this by directly deriving the effective action of scalar field fluctuations with wavelengths larger than the de Sitter curvature radius and generalizing Starobinsky's seminal results on stochastic inflation. The effective action describes stochastic dynamics and the fluctuating force drives the field to an equilibrium characterized by a thermal Gibbs distribution at temperature T {sub DS} which corresponds to a de Sitter invariant state. Hence, approach towards this state can be interpreted as thermalization. We show that the stochastic kinetic energy of the coarse-grained description corresponds to the norm of ∂{sub μ}φ and takes a well defined value per horizon volume ½((∇φ){sup 2}) = − ½ T {sub DS}/ V {sub H} . This approach allows for the non-perturbative computation of the de Sitter invariant stress energy tensor ( T {sub μν}) for an arbitrary scalar potential.

Symbiont dynamics during thermal acclimation using cnidarian-dinoflagellate model holobionts.

Science.gov (United States)

Núñez-Pons, Laura; Bertocci, Iacopo; Baghdasarian, Garen

2017-09-01

Warming oceans menace reef ecosystems by disrupting symbiosis between cnidarians and Symbiodinium zooxanthellae, thus triggering bleach episodes. Temperature fluctuations promote adjustments in physiological variables and symbiont composition, which can cause stress responses, but can also yield adaptation if fitter host-symbiont homeostasis are achieved. To understand such processes manipulative studies are required, but many reef-building cnidarians pose limitations to experimental prospects. We exposed Exaiptasia anemones to Gradual Thermal Stress (GTS) and Heat Shock (HS) exposures and monitored chlorophyll and symbiont dynamics to test the phenotypic plasticity of these photosynthetic holobionts. GTS enhanced chlorophyll concentrations and decreased Symbiodinium proliferation. A recovery period after GTS returned chlorophyll to lower concentrations and symbiont divisions to higher rates. HS triggered a stress response characterized by intense symbiont declines through degradation and expulsion, algal compensatory proliferation, and chlorophyll accumulation. Anemones pre-exposed to GTS displayed more acute signs of symbiont paucity after HS, demonstrating that recurrent stress does not always induce bleaching-resistance. Our study is the first documenting Symbiodinium C and D, along with the predominant Clade B1 in Exaiptasia anemones. C subclades found in outdoor specimens faded under laboratory exposures. Clade D emerged after HS treatments, and especially after GTS pre-exposure. This highlights the thermotolerance of D subclades found in E. pallida and shows that bleaching-recovery can involve shifts of background symbiont phylotypes. This study enlightens the capability of Exaiptasia anemones to acclimate to gradually increased temperatures, and explores into how thermal history influences in subsequent stress tolerance in symbiotic cnidarians. Copyright © 2017 Elsevier Ltd. All rights reserved.

Neutron and thermal dynamics of a gaseous core fission reactor

International Nuclear Information System (INIS)

van Dam, H.; Kuijper, J.C.; Stekelenburg, A.J.C.; Hoogenboom, J.E.; Boersma-Klein, W.; Kistemaker, J.

1989-01-01

In this paper neutron kinetics and thermal dynamics of a Gaseous Core Fission Reactor with magnetical pumping are shown to have many unconventional aspects. Attention is focused on the properties of the fuel gas, the non-linear neutron kinetics and the energy balance in thermodynamical cycles

Thermal- and urea-induced unfolding processes of glutathione S-transferase by molecular dynamics simulation.

Science.gov (United States)

Li, Jiahuang; Chen, Yuan; Yang, Jie; Hua, Zichun

2015-05-01

The Schistosoma juponicum 26 kDa glutathione S-transferase (sj26GST) consists of the N-terminal domain (N-domain), containing three alpha-helices (named H1-H3) and four anti-parallel beta-strands (S1-S4), and the C-terminal domain (C-domain), comprising five alpha-helices (named H4-H8). In present work, molecular dynamics simulations and fluorescence spectroscopic were used to gain insights into the unfolding process of sj26GST. The molecular dynamics simulations on sj26GST subunit both in water and in 8 M urea were carried out at 300 K, 400 K and 500 K, respectively. Spectroscopic measurements were employed to monitor structural changes. Molecular dynamics simulations of sj26GST subunit induced by urea and temperature showed that the initial unfolding step of sj26GST both in water and urea occurred on N-domain, involving the disruption of helices H2, H3 and strands S3 and S4, whereas H6 was the last region exposed to solution and was the last helix to unfold. Moreover, simulations analyses combining with fluorescence and circular dichroism spectra indicated that N-domain could not fold independent, suggesting that correct folding of N-domain depended on its interactions with C-domain. We further proposed that the folding of GSTs could begin with the hydrophobic collapse of C-domain whose H4, H5, H6 and H7 could move close to each other and form a hydrophobic core, especially H6 wrapped in the hydrophobic center and beginning spontaneous formation of the helix. S3, S4, H3, and H2 could form in the wake of the interaction between C-domain and N-domain. The paper can offer insights into the molecular mechanism of GSTs unfolding. © 2014 Wiley Periodicals, Inc.

Induced thermal resistance in the mouse ear

International Nuclear Information System (INIS)

Law, M.P.; Coultas, P.G.; Field, S.B.

1979-01-01

The mouse ear (pinna) was used to investigate the effect of two hyperthermic treatments. Heating was by immersion in hot water at 43.5 0 C. A single treatment of about 50 minutes was required to cause necrosis in 50% of the ears treated. When heat treatment was given in two equal fractions the total heating time had to be increased if the interval between fractions was greater than four hours. By 24 hours a total treatment of about 100 minutes was required, indicating almost complete recovery from the first heating. Priming treatments at 43.5 0 C induced thermal resistance to a second heat treatment at 43.5 0 C. Maximum resistance was observed one day after a 20 minute priming and two days after a 40 minute priming, when the heating time had to be increased to 120 minutes, an increase by a factor of 2.4. Shorter priming treatments induced less resistance, the minimum heating time to produce an effect being two minutes. In all cases the effect decreased during the next four to five days. These results indicate that the reduced response of tissues to fractionated hyperthermia is due both to the repair of sublethal heat damage and induction of thermal resistance. (author)

Thermalization and out-of-equilibrium dynamics in open quantum many-body systems

Energy Technology Data Exchange (ETDEWEB)

Buchhold, Michael

2015-06-30

In this thesis, we address both the question whether or not a quantum system driven away from equilibrium is able to relax to a thermal state, which fulfills detailed balance, and if one can identify universal behavior in the non-equilibrium relaxation dynamics. As a first realization of driven quantum systems out of equilibrium, we investigate a system of Ising spins, interacting with the quantized radiation field in an optical cavity. For multiple cavity modes, this system forms a highly entangled and frustrated state with infinite correlation times, known as a quantum spin glass. In the thermalized system, the features of the spin glass are mirrored onto the photon degrees of freedom, leading to an emergent photon glass phase. Exploiting the inherent photon loss of the cavity, we make predictions of possible measurements on the escaping photons, which contain detailed information of the state inside the cavity and allow for a precise, non-destructive measurement of the glass state. As a further set of non-equilibrium systems, we consider one-dimensional quantum fluids driven out of equilibrium, whose universal low energy theory is formed by the so-called Luttinger Liquid description. In this thesis, we derive for the first time a kinetic equation for interacting Luttinger Liquids, which describes the time evolution of the excitation densities for arbitrary initial states. The resonant character of the interaction makes a straightforward derivation of the kinetic equation, using Fermis golden rule, impossible and we have to develop non-perturbative techniques in the Keldysh framework. We derive a closed expression for the time evolution of the excitation densities in terms of self-energies and vertex corrections. Close to equilibrium, the kinetic equation describes the exponential decay of excitations, with a decay rate σ{sup R}=ImΣ{sup R}, determined by the self-energy at equilibrium. However, for long times τ, it also reveals the presence of dynamical slow

Current-induced dynamics in carbon atomic contacts

DEFF Research Database (Denmark)

Lu, Jing Tao; Gunst, Tue; Brandbyge, Mads

2011-01-01

voltage, which can be used to explore current-induced vibrational instabilities due the NC/BP forces. Furthermore, using tight-binding and the Brenner potential we illustrate how Langevin-type molecular-dynamics calculations including the Joule heating effect for the carbon-chain systems can be performed...... be used to explore current-induced dynamics and instabilities. We find instabilities at experimentally relevant bias and gate voltages for the carbon-chain system. © 2011 Lü et al....... carbon chain connecting electrically gated graphene electrodes. This illustrates how the device stability can be predicted solely from the modes obtained from the Langevin equation, including the current-induced forces. We point out that the gate offers control of the current, independent of the bias...

Induced topological pressure for topological dynamical systems

International Nuclear Information System (INIS)

Xing, Zhitao; Chen, Ercai

2015-01-01

In this paper, inspired by the article [J. Jaerisch et al., Stochastics Dyn. 14, 1350016, pp. 1-30 (2014)], we introduce the induced topological pressure for a topological dynamical system. In particular, we prove a variational principle for the induced topological pressure

Langevin dynamics of conformational transformations induced by the charge-curvature interaction

DEFF Research Database (Denmark)

Gaididei, Yuri Borisovich; Gorria, C.; Christiansen, Peter Leth

2009-01-01

The role of thermal fluctuations in the conformational dynamics of a single closed filament is studied. It is shown that, due to the interaction between charges and bending degrees of freedom, initially circular chains may undergo transformation to polygonal shape.......The role of thermal fluctuations in the conformational dynamics of a single closed filament is studied. It is shown that, due to the interaction between charges and bending degrees of freedom, initially circular chains may undergo transformation to polygonal shape....

Compton scattering at finite temperature: thermal field dynamics approach

International Nuclear Information System (INIS)

Juraev, F.I.

2006-01-01

Full text: Compton scattering is a classical problem of quantum electrodynamics and has been studied in its early beginnings. Perturbation theory and Feynman diagram technique enables comprehensive analysis of this problem on the basis of which famous Klein-Nishina formula is obtained [1, 2]. In this work this problem is extended to the case of finite temperature. Finite-temperature effects in Compton scattering is of practical importance for various processes in relativistic thermal plasmas in astrophysics. Recently Compton effect have been explored using closed-time path formalism with temperature corrections estimated [3]. It was found that the thermal cross section can be larger than that for zero-temperature by several orders of magnitude for the high temperature realistic in astrophysics [3]. In our work we use a main tool to account finite-temperature effects, a real-time finite-temperature quantum field theory, so-called thermofield dynamics [4, 5]. Thermofield dynamics is a canonical formalism to explore field-theoretical processes at finite temperature. It consists of two steps, doubling of Fock space and Bogolyubov transformations. Doubling leads to appearing additional degrees of freedom, called tilded operators which together with usual field operators create so-called thermal doublet. Bogolyubov transformations make field operators temperature-dependent. Using this formalism we treat Compton scattering at finite temperature via replacing in transition amplitude zero-temperature propagators by finite-temperature ones. As a result finite-temperature extension of the Klein-Nishina formula is obtained in which differential cross section is represented as a sum of zero-temperature cross section and finite-temperature correction. The obtained result could be useful in quantum electrodynamics of lasers and for relativistic thermal plasma processes in astrophysics where correct account of finite-temperature effects is important. (author)

Thermodynamic model of a thermal storage air conditioning system with dynamic behavior

Energy Technology Data Exchange (ETDEWEB)

Fleming, E; Wen, SY; Shi, L; da Silva, AK

2013-12-01

A thermodynamic model was developed to predict transient behavior of a thermal storage system, using phase change materials (PCMs), for a novel electric vehicle climate conditioning application. The main objectives of the paper are to consider the system's dynamic behavior, such as a dynamic air flow rate into the vehicle's cabin, and to characterize the transient heat transfer process between the thermal storage unit and the vehicle's cabin, while still maintaining accurate solution to the complex phase change heat transfer. The system studied consists of a heat transfer fluid circulating between either of the on-board hot and cold thermal storage units, which we refer to as thermal batteries, and a liquid-air heat exchanger that provides heat exchange with the incoming air to the vehicle cabin. Each thermal battery is a shell-and-tube configuration where a heat transfer fluid flows through parallel tubes, which are surrounded by PCM within a larger shell. The system model incorporates computationally inexpensive semianalytic solution to the conjugated laminar forced convection and phase change problem within the battery and accounts for airside heat exchange using the Number of Transfer Units (NTUs) method for the liquid-air heat exchanger. Using this approach, we are able to obtain an accurate solution to the complex heat transfer problem within the battery while also incorporating the impact of the airside heat transfer on the overall system performance. The implemented model was benchmarked against a numerical study for a melting process and against full system experimental data for solidification using paraffin wax as the PCM. Through modeling, we demonstrate the importance of capturing the airside heat exchange impact on system performance, and we investigate system response to dynamic operating conditions, e.g., air recirculation. (C) 2013 Elsevier Ltd. All rights reserved.

Multiphase Flow Dynamics 5 Nuclear Thermal Hydraulics

CERN Document Server

Kolev, Nikolay Ivanov

2012-01-01

The present Volume 5 of the successful book package "Multiphase Flow Dynamics" is devoted to nuclear thermal hydraulics which is a substantial part of nuclear reactor safety. It provides knowledge and mathematical tools for adequate description of the process of transferring the fission heat released in materials due to nuclear reactions into its environment. It step by step introduces into the heat release inside the fuel, temperature fields in the fuels, the "simple" boiling flow in a pipe described using ideas of different complexity like equilibrium, non equilibrium, homogeneity, non homogeneity. Then the "simple" three-fluid boiling flow in a pipe is described by gradually involving the mechanisms like entrainment and deposition, dynamic fragmentation, collisions, coalescence, turbulence. All heat transfer mechanisms are introduced gradually discussing their uncertainty. Different techniques are introduced like boundary layer treatments or integral methods. Comparisons with experimental data at each step...

Multiphase flow dynamics 5 nuclear thermal hydraulics

CERN Document Server

Kolev, Nikolay Ivanov

2015-01-01

This Volume 5 of the successful book package "Multiphase Flow Dynamics" is devoted to nuclear thermal hydraulics which is a substantial part of nuclear reactor safety. It provides knowledge and mathematical tools for adequate description of the process of transferring the fission heat released in materials due to nuclear reactions into its environment. It step by step introduces into the heat release inside the fuel, temperature fields in the fuels, the "simple" boiling flow in a pipe described using ideas of different complexity like equilibrium, non equilibrium, homogeneity, non homogeneity. Then the "simple" three-fluid boiling flow in a pipe is described by gradually involving the mechanisms like entrainment and deposition, dynamic fragmentation, collisions, coalescence, turbulence. All heat transfer mechanisms are introduced gradually discussing their uncertainty. Different techniques are introduced like boundary layer treatments or integral methods. Comparisons with experimental data at each step demons...

A novel test method for measuring the thermal properties of clothing ensembles under dynamic conditions

International Nuclear Information System (INIS)

Wan, X; Fan, J

2008-01-01

The dynamic thermal properties of clothing ensembles are important to thermal transient comfort, but have so far not been properly quantified. In this paper, a novel test procedure and new index based on measurements on the sweating fabric manikin-Walter are proposed to quantify and measure the dynamic thermal properties of clothing ensembles. Experiments showed that the new index is correlated to the changing rate of the body temperature of the wearer, which is an important indicator of thermal transient comfort. Clothing ensembles having higher values of the index means the wearer will have a faster changing rate of body temperature and shorter duration before approaching a dangerous thermo-physiological state, when he changes from 'resting' to 'exercising' mode. Clothing should therefore be designed to reduce the value of the index

On the analogy between thermally and irradiation induced creep

International Nuclear Information System (INIS)

Cozzarelli, F.A.; Huang, S.

1977-01-01

Employing an analogy between thermally induced and irradiation induced creep, physical arguments are used first to deduce a one-dimensional constitutive relation for metals under stress in a high temperature and high neutron flux field. This constitutive relation contains modified superposition integrals in which the temperature and flux dependence of the material parameters is included via the use of two reduced time scales; linear elastic, thermal expansion and swelling terms are also included. A systematic development based on thermodynamics, with the stress, temperature increment and defect density increment as independent variables in the Gibbs free energy, is then employed to obtain general three-dimensional memory integrals for strain; the entropy and coupled energy equation are also obtained. Modified superposition integrals similar to those previously obtained by physical argument are then obtained by substituting special functions into the results of the thermodynamic analysis, and the special case of an isotropic stress power law is examined in detail. (Auth.)

Analysis of dynamic effects in solar thermal energy conversion systems

Science.gov (United States)

Hamilton, C. L.

1978-01-01

The paper examines a study the purpose of which is to assess the performance of solar thermal power systems insofar as it depends on the dynamic character of system components and the solar radiation which drives them. Using a dynamic model, the daily operation of two conceptual solar conversion systems was simulated under varying operating strategies and several different time-dependent radiation intensity functions. These curves ranged from smoothly varying input of several magnitudes to input of constant total energy whose intensity oscillated with periods from 1/4 hour to 6 hours.

Evaluation of thermal control coatings for use on solar dynamic radiators in low earth orbit

Science.gov (United States)

Dever, Joyce A.; Rodriguez, Elvin; Slemp, Wayne S.; Stoyack, Joseph E.

1991-01-01

Thermal control coatings with high thermal emittance and low solar absorptance are needed for Space Station Freedom (SSF) solar dynamic power module radiator (SDR) surfaces for efficient heat rejection. Additionally, these coatings must be durable to low earth orbital (LEO) environmental effects of atomic oxygen, ultraviolet radiation and deep thermal cycles which occur as a result of start-up and shut-down of the solar dynamic power system. Eleven candidate coatings were characterized for their solar absorptance and emittance before and after exposure to ultraviolet (UV) radiation (200 to 400 nm), vacuum UV (VUV) radiation (100 to 200 nm) and atomic oxygen. Results indicated that the most durable and best performing coatings were white paint thermal control coatings Z-93, zinc oxide pigment in potassium silicate binder, and YB-71, zinc orthotitanate pigment in potassium silicate binder. Optical micrographs of these materials exposed to the individual environmental effects of atomic oxygen and vacuum thermal cycling showed that no surface cracking occurred.

Transitional free convection flows induced by thermal line sources

NARCIS (Netherlands)

Bastiaans, R.J.M.

1993-01-01

In the present study the usefullness of a large eddy simulation for transition is examined. Numerical results of such simulations are presented from a study to determine the characteristics of a flow induced by a thermal line source. The first bifurcation to time dependent motion and the route to

Dynamic Behavior of Fault Slip Induced by Stress Waves

Directory of Open Access Journals (Sweden)

Guang-an Zhu

2016-01-01

Full Text Available Fault slip burst is a serious dynamic hazard in coal mining. A static and dynamic analysis for fault slip was performed to assess the risk of rock burst. A numerical model FLAC3D was established to understand the stress state and mechanical responses of fault rock system. The results obtained from the analysis show that the dynamic behavior of fault slip induced by stress waves is significantly affected by mining depth, as well as dynamic disturbance intensity and the distance between the stope and the fault. The isolation effect of the fault is also discussed based on the numerical results with the fault angle appearing to have the strongest influence on peak vertical stress and velocity induced by dynamic disturbance. By taking these risks into account, a stress-relief technology using break-tip blast was used for fault slip burst control. This technique is able to reduce the stress concentration and increase the attenuation of dynamic load by fracturing the structure of coal and rock. The adoption of this stress-relief method leads to an effective reduction of fault slip induced rock burst (FSIRB occurrence.

Dynamic properties of a metal photo-thermal micro-actuator.

Science.gov (United States)

Shi, B; Zhang, H J; Wang, B; Yi, F T; Jiang, J Z; Zhang, D X

2015-02-20

This work presents the design, modeling, simulation, and characterization of a metal bent-beam photo-thermal micro-actuator. The mechanism of actuation is based on the thermal expansion of the micro-actuator which is irradiated by a laser, achieving noncontact control of the power supply. Models for micro-actuators were established and finite-element simulations were carried out to investigate the effects of various parameters on actuation properties. It is found that the thermal expansion coefficient, thermal conductivity, and the geometry size largely affected actuation behavior whereas heat capacity, density, and Young's modulus did not. Experiments demonstrated the dynamic properties of a Ni micro-actuator fabricated via LIGA technology with 1100/30/100 μm (long/wide/thick) arms. The tip displacement of the micro-actuator could achieve up to 42 μm driven by a laser beam (1064 nm wavelength, 1.2 W power, and a driving frequency of 1 HZ). It is found that the tip displacement decreases with increasing laser driving frequency. For 8 Hz driving frequency, 17 μm (peak-valley value) can be still reached, which is large enough for the application as micro-electro-mechanical systems. Metal photo-thermal micro actuators have advantages such as large displacement, simple structure, and large temperature tolerance, and therefore they will be promising in the fields of micro/nanotechnology.

Vegetation dynamics induced by phreatophyte--aquifer interactions.

Science.gov (United States)

Ridolfi, Luca; D'Odorico, Paolo; Laio, Francesco

2007-09-21

The dynamics of phreatophyte vegetation are strongly coupled to those of the shallow phreatic aquifers from which phreatophytes extract water. Vegetation is able to influence the depth of the water table, which, in turn, can induce stress in vegetation. These interactions are likely to affect the composition and structure of phreatophyte plant communities, as well as their successional dynamics. Despite the environmental and economical value of many wetland plant ecosystems around the world, the impact of vegetation-water table interactions on ecosystem succession and interspecies competition in phreatophyte plant communities remains poorly understood. This study develops a minimalistic modelling framework to investigate the dynamics of two phreatophyte species, and their interactions with the water table. In spite of its simplicity, the model exhibits a remarkable variety of dynamical behaviors, especially when the water table depth is forced by external drivers. It is shown that, even when one of the two species is dominant with respect to the other, these two species can coexist showing periodic, quasi-periodic, and chaotic dynamics. Moreover, in the presence of a random environmental forcing, noise-induced coexistence may emerge.

Dynamic indoor thermal comfort model identification based on neural computing PMV index

International Nuclear Information System (INIS)

Sahari, K S Mohamed; Jalal, M F Abdul; Homod, R Z; Eng, Y K

2013-01-01

This paper focuses on modelling and simulation of building dynamic thermal comfort control for non-linear HVAC system. Thermal comfort in general refers to temperature and also humidity. However in reality, temperature or humidity is just one of the factors affecting the thermal comfort but not the main measures. Besides, as HVAC control system has the characteristic of time delay, large inertia, and highly nonlinear behaviour, it is difficult to determine the thermal comfort sensation accurately if we use traditional Fanger's PMV index. Hence, Artificial Neural Network (ANN) has been introduced due to its ability to approximate any nonlinear mapping. Using ANN to train, we can get the input-output mapping of HVAC control system or in other word; we can propose a practical approach to identify thermal comfort of a building. Simulations were carried out to validate and verify the proposed method. Results show that the proposed ANN method can track down the desired thermal sensation for a specified condition space.

Ice Ih anomalies: Thermal contraction, anomalous volume isotope effect, and pressure-induced amorphization

Science.gov (United States)

Salim, Michael A.; Willow, Soohaeng Yoo; Hirata, So

2016-05-01

Ice Ih displays several anomalous thermodynamic properties such as thermal contraction at low temperatures, an anomalous volume isotope effect (VIE) rendering the volume of D2O ice greater than that of H2O ice, and a pressure-induced transition to the high-density amorphous (HDA) phase. Furthermore, the anomalous VIE increases with temperature, despite its quantum-mechanical origin. Here, embedded-fragment ab initio second-order many-body perturbation (MP2) theory in the quasiharmonic approximation (QHA) is applied to the Gibbs energy of an infinite, proton-disordered crystal of ice Ih at wide ranges of temperatures and pressures. The quantum effect of nuclei moving in anharmonic potentials is taken into account from first principles without any empirical or nonsystematic approximation to either the electronic or vibrational Hamiltonian. MP2 predicts quantitatively correctly the thermal contraction at low temperatures, which is confirmed to originate from the volume-contracting hydrogen-bond bending modes (acoustic phonons). It qualitatively reproduces (but underestimates) the thermal expansion at higher temperatures, caused by the volume-expanding hydrogen-bond stretching (and to a lesser extent librational) modes. The anomalous VIE is found to be the result of subtle cancellations among closely competing isotope effects on volume from all modes. Consequently, even ab initio MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets has difficulty reproducing this anomaly, yielding qualitatively varied predictions of the sign of the VIE depending on such computational details as the choice of the embedding field. However, the temperature growth of the anomalous VIE is reproduced robustly and is ascribed to the librational modes. These solid-state MP2 calculations, as well as MP2 Born-Oppenheimer molecular dynamics, find a volume collapse and a loss of symmetry and long-range order in ice Ih upon pressure loading of 2.35 GPa or higher. Concomitantly, rapid softening of

Ice Ih anomalies: Thermal contraction, anomalous volume isotope effect, and pressure-induced amorphization

Energy Technology Data Exchange (ETDEWEB)

Salim, Michael A.; Willow, Soohaeng Yoo; Hirata, So, E-mail: sohirata@illinois.edu [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801 (United States)

2016-05-28

Ice Ih displays several anomalous thermodynamic properties such as thermal contraction at low temperatures, an anomalous volume isotope effect (VIE) rendering the volume of D{sub 2}O ice greater than that of H{sub 2}O ice, and a pressure-induced transition to the high-density amorphous (HDA) phase. Furthermore, the anomalous VIE increases with temperature, despite its quantum-mechanical origin. Here, embedded-fragment ab initio second-order many-body perturbation (MP2) theory in the quasiharmonic approximation (QHA) is applied to the Gibbs energy of an infinite, proton-disordered crystal of ice Ih at wide ranges of temperatures and pressures. The quantum effect of nuclei moving in anharmonic potentials is taken into account from first principles without any empirical or nonsystematic approximation to either the electronic or vibrational Hamiltonian. MP2 predicts quantitatively correctly the thermal contraction at low temperatures, which is confirmed to originate from the volume-contracting hydrogen-bond bending modes (acoustic phonons). It qualitatively reproduces (but underestimates) the thermal expansion at higher temperatures, caused by the volume-expanding hydrogen-bond stretching (and to a lesser extent librational) modes. The anomalous VIE is found to be the result of subtle cancellations among closely competing isotope effects on volume from all modes. Consequently, even ab initio MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets has difficulty reproducing this anomaly, yielding qualitatively varied predictions of the sign of the VIE depending on such computational details as the choice of the embedding field. However, the temperature growth of the anomalous VIE is reproduced robustly and is ascribed to the librational modes. These solid-state MP2 calculations, as well as MP2 Born–Oppenheimer molecular dynamics, find a volume collapse and a loss of symmetry and long-range order in ice Ih upon pressure loading of 2.35 GPa or higher. Concomitantly, rapid

Rock properties and their effect on thermally-induced displacements and stresses

International Nuclear Information System (INIS)

Chan, T.; Hood, M.; Board, M.

1980-02-01

A discussion is given of the importance of material properties in the finite-element calculations for thermally induced displacements and stresses resulting from a heating experiment in an in-situ granitic rock, at Stripa, Sweden. Comparisons are made between field measurements and finite element method calculations using (1) temperature independent, (2) temperature dependent thermal and thermomechanical properties and (3) in-situ and laboratory measurements for Young's modulus. The calculations of rock displacements are influenced predominantly by the temperature dependence of the thermal expansion coefficient, whereas the dominant factor affecting predictions for rock stresses is the in-situ modulus

On the relation between quasi-static and dynamic stress induced reversible structural relaxation of amorphous alloys

International Nuclear Information System (INIS)

Krueger, P.; Stucky, T.; Boewe, M.; Neuhaeuser, H.

1993-01-01

Quasi-static stress relaxation and dynamic internal friction measurements of stress induced reversible structural relaxation were performed on the amorphous alloy Fe 40 Ni 40 B 20 . The kinetics can be well described by a stretched exponential Kohlrausch-Williams-Watts quasi-static relaxation. The thermally activated part of the internal friction shows an Arrhenius temperature behaviour for a fixed vibration frequency and an inverse power frequency behaviour for a fixed temperature. The activation energies calculated from the Arrhenius equation and from the frequency shift method are significantly different. In order to explain this discrepancy the relation between the quasi-static and the dynamic descriptions of the reversible relaxation is reexamined. In particular it is shown that these two activation energies are connected by the Kohlrausch exponent of the quasi-static relaxation. (orig.)

Evaluation of ethanol aged PVDF: diffusion, crystallinity and dynamic mechanical thermal properties

International Nuclear Information System (INIS)

Silva, Agmar J.J.; Costa, Marysilvia F.

2015-01-01

This work discuss firstly the effect of the ethanol fuel absorption by PVDF at 60°C through mass variation tests. A Fickian character was observed for the ethanol absorption kinetics of the aged PVDF at 60°C. In the second step, the dynamic mechanical thermal properties (E’, E’, E” and tan δ) of the PVDF were evaluated through dynamic mechanical thermal analysis (DMTA). The chemical structure of the materials was analyzed by X-ray diffraction analysis (XRD), and significant changes in the degree of crystallinity were verified after the aging. However, DMTA results showed a reduction in the storage modulus (E') of the aged PVDF, which was associated to diffusion of ethanol and swelling of the PVDF, which generated a prevailing plasticizing effect and led to reduction of its structural stiffness. (author)

Thermal and seismic impacts on the North Ramp at Yucca Mountain

International Nuclear Information System (INIS)

Lin, M.; Hardy, M.P.; Jung, J.

1994-01-01

The impacts of thermal and seismic loads on the stability of the Exploratory Studies Facility North Ramp at Yucca Mountain were assessed using both empirical and analytical approaches. This paper presents the methods and results of the analyses. Thermal loads were first calculated using the computer code STRES3D. This code calculates the conductive heat transfer through a semi-infinite elastic, isotropic, homogeneous solid and the resulting thermally-induced stresses. The calculated thermal loads, combined with simulated earthquake motion, were then modeled using UDEC and DYNA3D, numerical codes with dynamic simulation capabilities. The thermal- and seismic-induced yield zones were post-processed and presented for assessment of damage. Uncoupled bolt stress analysis was also conducted to evaluate the seismic impact on the ground support components

Investigation on seasonal variation of thermal-induced strain in flexible pavements based on field and laboratory measurements

Directory of Open Access Journals (Sweden)

Simita Biswas

2016-09-01

Full Text Available Pavement temperature variation has a large influence on the structural response of flexible pavements. Daily and seasonal temperature fluctuation causes expansion and contraction of pavement material, which then leads to the generation of thermal strain. In this study, field observation and laboratory tests were conducted to investigate seasonal variation of thermal-induced strain in flexible pavement. Field observations were conducted at the Integrated Road Research Facility (IRRF’s test road in Edmonton, Alberta, Canada, which is fully equipped with structural and environmental monitoring instruments. The main objective of the field study was to compare the variation of thermal-induced strain in warm and cold seasons. Field results indicated that thermal-induced strain is 1.4–2.0 times greater in cold seasons than in warm seasons following the same pavement temperature variations; however, strain generation rate was greater in warm seasons. Laboratory testing of asphalt slab and cylindrical samples produced comparable ratios. Moreover, field observation and laboratory testing showed a similar trend of temperature and thermal strain variations. Keywords: Thermal-induced strain, Asphalt strain gauge, Field observation, Flexible pavement, Laboratory testing, Seasonal variation

Molecular Dynamics Study of Thermally Augmented Nanodroplet Motion on Chemical Energy Induced Wettability Gradient Surfaces.

Science.gov (United States)

Chakraborty, Monojit; Chowdhury, Anamika; Bhusan, Richa; DasGupta, Sunando

2015-10-20

Droplet motion on a surface with chemical energy induced wettability gradient has been simulated using molecular dynamics (MD) simulation to highlight the underlying physics of molecular movement near the solid-liquid interface including the contact line friction. The simulations mimic experiments in a comprehensive manner wherein microsized droplets are propelled by the surface wettability gradient against forces opposed to motion. The liquid-wall Lennard-Jones interaction parameter and the substrate temperature are varied to explore their effects on the three-phase contact line friction coefficient. The contact line friction is observed to be a strong function of temperature at atomistic scales, confirming their experimentally observed inverse functionality. Additionally, the MD simulation results are successfully compared with those from an analytical model for self-propelled droplet motion on gradient surfaces.

Molecular dynamics study of interfacial thermal transport between silicene and substrates.

Science.gov (United States)

Zhang, Jingchao; Hong, Yang; Tong, Zhen; Xiao, Zhihuai; Bao, Hua; Yue, Yanan

2015-10-07

In this work, the interfacial thermal transport across silicene and various substrates, i.e., crystalline silicon (c-Si), amorphous silicon (a-Si), crystalline silica (c-SiO2) and amorphous silica (a-SiO2) are explored by classical molecular dynamics (MD) simulations. A transient pulsed heating technique is applied in this work to characterize the interfacial thermal resistance in all hybrid systems. It is reported that the interfacial thermal resistances between silicene and all substrates decrease nearly 40% with temperature from 100 K to 400 K, which is due to the enhanced phonon couplings from the anharmonicity effect. Analysis of phonon power spectra of all systems is performed to interpret simulation results. Contradictory to the traditional thought that amorphous structures tend to have poor thermal transport capabilities due to the disordered atomic configurations, it is calculated that amorphous silicon and silica substrates facilitate the interfacial thermal transport compared with their crystalline structures. Besides, the coupling effect from substrates can improve the interface thermal transport up to 43.5% for coupling strengths χ from 1.0 to 2.0. Our results provide fundamental knowledge and rational guidelines for the design and development of the next-generation silicene-based nanoelectronics and thermal interface materials.

Dynamic measurement of coal thermal properties and elemental composition of volatile matter during coal pyrolysis

Directory of Open Access Journals (Sweden)

Rohan Stanger

2014-01-01

Full Text Available A new technique that allows dynamic measurement of thermal properties, expansion and the elemental chemistry of the volatile matter being evolved as coal is pyrolysed is described. The thermal and other properties are measured dynamically as a function of temperature of the coal without the need for equilibration at temperature. In particular, the technique allows for continuous elemental characterisation of tars as they are evolved during pyrolysis and afterwards as a function of boiling point. The technique is demonstrated by measuring the properties of maceral concentrates from a coal. The variation in heats of reaction, thermal conductivity and expansion as a function of maceral composition is described. Combined with the elemental analysis, the results aid in the interpretation of the chemical processes contributing to the physical and thermal behaviour of the coal during pyrolysis. Potential applications in cokemaking studies are discussed.

Thermal conductivity of graphene nanoribbons under shear deformation: A molecular dynamics simulation

Science.gov (United States)

Zhang, Chao; Hao, Xiao-Li; Wang, Cui-Xia; Wei, Ning; Rabczuk, Timon

2017-01-01

Tensile strain and compress strain can greatly affect the thermal conductivity of graphene nanoribbons (GNRs). However, the effect of GNRs under shear strain, which is also one of the main strain effect, has not been studied systematically yet. In this work, we employ reverse nonequilibrium molecular dynamics (RNEMD) to the systematical study of the thermal conductivity of GNRs (with model size of 4 nm × 15 nm) under the shear strain. Our studies show that the thermal conductivity of GNRs is not sensitive to the shear strain, and the thermal conductivity decreases only 12–16% before the pristine structure is broken. Furthermore, the phonon frequency and the change of the micro-structure of GNRs, such as band angel and bond length, are analyzed to explore the tendency of thermal conductivity. The results show that the main influence of shear strain is on the in-plane phonon density of states (PDOS), whose G band (higher frequency peaks) moved to the low frequency, thus the thermal conductivity is decreased. The unique thermal properties of GNRs under shear strains suggest their great potentials for graphene nanodevices and great potentials in the thermal managements and thermoelectric applications. PMID:28120921

Gene Expression Dynamics Accompanying the Sponge Thermal Stress Response.

Science.gov (United States)

Guzman, Christine; Conaco, Cecilia

2016-01-01

Marine sponges are important members of coral reef ecosystems. Thus, their responses to changes in ocean chemistry and environmental conditions, particularly to higher seawater temperatures, will have potential impacts on the future of these reefs. To better understand the sponge thermal stress response, we investigated gene expression dynamics in the shallow water sponge, Haliclona tubifera (order Haplosclerida, class Demospongiae), subjected to elevated temperature. Using high-throughput transcriptome sequencing, we show that these conditions result in the activation of various processes that interact to maintain cellular homeostasis. Short-term thermal stress resulted in the induction of heat shock proteins, antioxidants, and genes involved in signal transduction and innate immunity pathways. Prolonged exposure to thermal stress affected the expression of genes involved in cellular damage repair, apoptosis, signaling and transcription. Interestingly, exposure to sublethal temperatures may improve the ability of the sponge to mitigate cellular damage under more extreme stress conditions. These insights into the potential mechanisms of adaptation and resilience of sponges contribute to a better understanding of sponge conservation status and the prediction of ecosystem trajectories under future climate conditions.

Dynamics and thermalization in violent collisions around 30 MeV/u

International Nuclear Information System (INIS)

Borderie, B.; Jouan, D.; Rivet, M.F.; Cabot, C.; Fuchs, H.; Gardes, D.; Gauvin, H.; Jacquet, D.; Monnet, F.; Montoya, M.

1990-01-01

In this paper, through exclusive measurements between heavy residues and light charged particles or intermediate-mass fragments, the dynamics of the different mechanisms involved in the Ar + nat Ag system at 27 MeV/u are described. Balances are presented. Finally the thermalization stage is discussed

Thermal singularity and droplet motion in one-component fluids on solid substrates with thermal gradients

KAUST Repository

Xu, Xinpeng

2012-06-26

Using a continuum model capable of describing the one-component liquid-gas hydrodynamics down to the contact line scale, we carry out numerical simulation and physical analysis for the droplet motion driven by thermal singularity. For liquid droplets in one-component fluids on heated or cooled substrates, the liquid-gas interface is nearly isothermal. Consequently, a thermal singularity occurs at the contact line and the Marangoni effect due to temperature gradient is suppressed. Through evaporation or condensation in the vicinity of the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. This effect on the contact angle can be used to move the droplets on substrates with thermal gradients. Our numerical results for this kind of droplet motion are explained by a simple fluid dynamical model at the droplet length scale. Since the mechanism for droplet motion is based on the change of contact angle, a separation of length scales is exhibited through a comparison between the droplet motion induced by a wettability gradient and that by a thermal gradient. It is shown that the flow field at the droplet length scale is independent of the statics or dynamics at the contact line scale.

Thermal singularity and droplet motion in one-component fluids on solid substrates with thermal gradients

KAUST Repository

Xu, Xinpeng; Qian, Tiezheng

2012-01-01

Using a continuum model capable of describing the one-component liquid-gas hydrodynamics down to the contact line scale, we carry out numerical simulation and physical analysis for the droplet motion driven by thermal singularity. For liquid droplets in one-component fluids on heated or cooled substrates, the liquid-gas interface is nearly isothermal. Consequently, a thermal singularity occurs at the contact line and the Marangoni effect due to temperature gradient is suppressed. Through evaporation or condensation in the vicinity of the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. This effect on the contact angle can be used to move the droplets on substrates with thermal gradients. Our numerical results for this kind of droplet motion are explained by a simple fluid dynamical model at the droplet length scale. Since the mechanism for droplet motion is based on the change of contact angle, a separation of length scales is exhibited through a comparison between the droplet motion induced by a wettability gradient and that by a thermal gradient. It is shown that the flow field at the droplet length scale is independent of the statics or dynamics at the contact line scale.

Further study on the wheel-rail impact response induced by a single wheel flat: the coupling effect of strain rate and thermal stress

Science.gov (United States)

Jing, Lin; Han, Liangliang

2017-12-01

A comprehensive dynamic finite-element simulation method was proposed to study the wheel-rail impact response induced by a single wheel flat based on a 3-D rolling contact model, where the influences of the structural inertia, strain rate effect of wheel-rail materials and thermal stress due to the wheel-rail sliding friction were considered. Four different initial conditions (i.e. pure mechanical loading plus rate-independent, pure mechanical loading plus rate-dependent, thermo-mechanical loading plus rate-independent, and thermo-mechanical loading plus rate-dependent) were involved into explore the corresponding impact responses in term of the vertical impact force, von-Mises equivalent stress, equivalent plastic strain and shear stress. Influences of train speed, flat length and axle load on the flat-induced wheel-rail impact response were discussed, respectively. The results indicate that the maximum thermal stresses are occurred on the tread of the wheel and on the top surface of the middle rail; the strain rate hardening effect contributes to elevate the von-Mises equivalent stress and restrain the plastic deformation; and the initial thermal stress due to the sliding friction will aggravate the plastic deformation of wheel and rail. Besides, the wheel-rail impact responses (i.e. impact force, von-Mises equivalent stress, equivalent plastic strain, and XY shear stress) induced by a flat are sensitive to the train speed, flat length and axle load.

distributions for the thermal neutron induced fission of 234U

Directory of Open Access Journals (Sweden)

Al-Adili A.

2016-01-01

In addition, the analysis of thermal neutron induced fission of 234U(n,f will be discussed. Currently analysis of data is ongoing, originally taken at the ILL reactor. The experiment is of particular interest since no measurement exist of the mass and energy distributions for this system at thermal energies. One main problem encountered during analysis was the huge background of 235U(nth,f. Despite the negligible isotopic traces in the sample, the cross section difference is enormous. Solution to this parasitic background will be highlighted.

Thermal conductivity of nanocrystalline SiGe alloys using molecular dynamics simulations

Science.gov (United States)

Abs da Cruz, Carolina; Katcho, Nebil A.; Mingo, Natalio; Veiga, Roberto G. A.

2013-10-01

We have studied the effect of nanocrystalline microstructure on the thermal conductivity of SiGe alloys using molecular dynamics simulations. Nanograins are modeled using both the coincidence site lattice and the Voronoi tessellation methods, and the thermal conductivity is computed using the Green-Kubo formalism. We analyze the dependence of the thermal conductivity with temperature, grain size L, and misorientation angle. We find a power dependence of L1/4 of the thermal conductivity with the grain size, instead of the linear dependence shown by non-alloyed nanograined systems. This dependence can be derived analytically underlines the important role that disorder scattering plays even when the grains are of the order of a few nm. This is in contrast to non-alloyed systems, where phonon transport is governed mainly by the boundary scattering. The temperature dependence is weak, in agreement with experimental measurements. The effect of angle misorientation is also small, which stresses the main role played by the disorder scattering.

Thermal conductivity of water: Molecular dynamics and generalized hydrodynamics results

Science.gov (United States)

Bertolini, Davide; Tani, Alessandro

1997-10-01

Equilibrium molecular dynamics simulations have been carried out in the microcanonical ensemble at 300 and 255 K on the extended simple point charge (SPC/E) model of water [Berendsen et al., J. Phys. Chem. 91, 6269 (1987)]. In addition to a number of static and dynamic properties, thermal conductivity λ has been calculated via Green-Kubo integration of the heat current time correlation functions (CF's) in the atomic and molecular formalism, at wave number k=0. The calculated values (0.67+/-0.04 W/mK at 300 K and 0.52+/-0.03 W/mK at 255 K) are in good agreement with the experimental data (0.61 W/mK at 300 K and 0.49 W/mK at 255 K). A negative long-time tail of the heat current CF, more apparent at 255 K, is responsible for the anomalous decrease of λ with temperature. An analysis of the dynamical modes contributing to λ has shown that its value is due to two low-frequency exponential-like modes, a faster collisional mode, with positive contribution, and a slower one, which determines the negative long-time tail. A comparison of the molecular and atomic spectra of the heat current CF has suggested that higher-frequency modes should not contribute to λ in this temperature range. Generalized thermal diffusivity DT(k) decreases as a function of k, after an initial minor increase at k=kmin. The k dependence of the generalized thermodynamic properties has been calculated in the atomic and molecular formalisms. The observed differences have been traced back to intramolecular or intermolecular rotational effects and related to the partial structure functions. Finally, from the results we calculated it appears that the SPC/E model gives results in better agreement with experimental data than the transferable intermolecular potential with four points TIP4P water model [Jorgensen et al., J. Chem. Phys. 79, 926 (1983)], with a larger improvement for, e.g., diffusion, viscosities, and dielectric properties and a smaller one for thermal conductivity. The SPC/E model shares

Keyhole formation and thermal fluid flow-induced porosity during laser fusion welding in titanium alloys: Experimental and modelling

International Nuclear Information System (INIS)

Panwisawas, Chinnapat; Perumal, Bama; Ward, R. Mark; Turner, Nathanael; Turner, Richard P.; Brooks, Jeffery W.; Basoalto, Hector C.

2017-01-01

High energy-density beam welding, such as electron beam or laser welding, has found a number of industrial applications for clean, high-integrity welds. The deeply penetrating nature of the joints is enabled by the formation of metal vapour which creates a narrow fusion zone known as a “keyhole”. However the formation of the keyhole and the associated keyhole dynamics, when using a moving laser heat source, requires further research as they are not fully understood. Porosity, which is one of a number of process induced phenomena related to the thermal fluid dynamics, can form during beam welding processes. The presence of porosity within a welded structure, inherited from the fusion welding operation, degrades the mechanical properties of components during service such as fatigue life. In this study, a physics-based model for keyhole welding including heat transfer, fluid flow and interfacial interactions has been used to simulate keyhole and porosity formation during laser welding of Ti-6Al-4V titanium alloy. The modelling suggests that keyhole formation and the time taken to achieve keyhole penetration can be predicted, and it is important to consider the thermal fluid flow at the melting front as this dictates the evolution of the fusion zone. Processing induced porosity is significant when the fusion zone is only partially penetrating through the thickness of the material. The modelling results are compared with high speed camera imaging and measurements of porosity from welded samples using X-ray computed tomography, radiography and optical micrographs. These are used to provide a better understanding of the relationship between process parameters, component microstructure and weld integrity.

Thermal conductivity predictions of herringbone graphite nanofibers using molecular dynamics simulations.

Science.gov (United States)

Khadem, Masoud H; Wemhoff, Aaron P

2013-02-28

Non-equilibrium molecular dynamics (NEMD) simulations are used to investigate the thermal conductivity of herringbone graphite nanofibers (GNFs) at room temperature by breaking down the axial and transverse conductivity values into intralayer and interlayer components. The optimized Tersoff potential is used to account for intralayer carbon-carbon interactions while the Lennard-Jones potential is used to model the interlayer carbon-carbon interactions. The intralayer thermal conductivity of the graphene layers near room temperature is calculated for different crease angles and number of layers using NEMD with a constant applied heat flux. The edge effect on a layer's thermal conductivity is investigated by computing the thermal conductivity values in both zigzag and armchair directions of the heat flow. The interlayer thermal conductivity is also predicted by imposing hot and cold Nosé-Hoover thermostats on two layers. The limiting case of a 90° crease angle is used to compare the results with those of single-layer graphene and few-layer graphene. The axial and transverse thermal conductivities are then calculated using standard trigonometric conversions of the calculated intralayer and interlayer thermal conductivities, along with calculations of few-layer graphene without a crease. The results show a large influence of the crease angle on the intralayer thermal conductivity, and the saturation of thermal conductivity occurs when number of layers is more than three. The axial thermal conductivity, transverse thermal conductivity in the crease direction, and transverse thermal conductivity normal to the crease for the case of a five-layer herringbone GNF with a 45° crease angle are calculated to be 27 W∕m K, 263 W∕m K, and 1500 W∕m K, respectively, where the axial thermal conductivity is in good agreement with experimental measurements.

Real-time deep-tissue thermal sensing with sub-degree resolution by thermally improved Nd{sup 3+}:LaF{sub 3} multifunctional nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Rocha, Uéslen, E-mail: ueslen.silva@fis.ufal.br [Fluorescence Imaging Group, Departamento de Física de Materiales C-04, Instituto Nicolás Cabrera, Facultad de Ciencias, Universidad Autónoma de Madrid (Spain); Jacinto, Carlos; Kumar, Kagola Upendra [Grupo de Fotônica e Fluidos Complexos, Instituto de Física, Universidade Federal de Alagoas, 57072-970 Maceió, Alagoas (Brazil); López, Fernando J.; Bravo, David; Solé, José García [Fluorescence Imaging Group, Departamento de Física de Materiales C-04, Instituto Nicolás Cabrera, Facultad de Ciencias, Universidad Autónoma de Madrid (Spain); Jaque, Daniel, E-mail: daniel.jaque@uam.es [Fluorescence Imaging Group, Departamento de Física de Materiales C-04, Instituto Nicolás Cabrera, Facultad de Ciencias, Universidad Autónoma de Madrid (Spain); Instituto Ramón y Cajal de Investigación Sanitaria, Hospital Ramon y Cajal, Madrid 28034 (Spain)

2016-07-15

Nd{sup 3+} ion doped LaF{sub 3} dielectric nanoparticles have recently emerged as very attractive multifunctional nanoparticles capable of simultaneous sub-tissue heating and thermal sensing. Although they have been already used for selective photothermal treatment of cancer tumors in animal models, their real application as self-monitored photothermal agents require further optimization and development. Dynamic adjustment of the therapy parameters is mandatory for non-selective damage minimization. It would require real-time (sub-second) thermal sensing with a sub-degree thermal resolution. In this work we demonstrate that meeting this challenge is, indeed, possible by performing controlled thermal treatment on as-synthesized Nd{sup 3+} doped LaF{sub 3} nanoparticles. Temperature induced lattice ordering and defect re-combination have been concluded to induce, simultaneously, a line fluorescence narrowing, fluorescence brightness enhancement and a remarkable increment in thermal sensitivity. Ex-vivo experiments have demonstrated that, thanks to this multi-parameter optimization, Neodymium doped LaF{sub 3} nanoparticles are capable of real time sub-tissue thermal reading with a temperature resolution as low as 0.7 °C.

Effects of thermal vapor diffusion on seasonal dynamics of water in the unsaturated zone

Science.gov (United States)

Milly, Paul C.D.

1996-01-01

The response of water in the unsaturated zone to seasonal changes of temperature (T) is determined analytically using the theory of nonisothermal water transport in porous media, and the solutions are tested against field observations of moisture potential and bomb fallout isotopic (36Cl and 3H) concentrations. Seasonally varying land surface temperatures and the resulting subsurface temperature gradients induce thermal vapor diffusion. The annual mean vertical temperature gradient is close to zero; however, the annual mean thermal vapor flux is downward, because the temperature‐dependent vapor diffusion coefficient is larger, on average, during downward diffusion (occurring at high T) than during upward diffusion (low T). The annual mean thermal vapor flux is shown to decay exponentially with depth; the depth (about 1 m) at which it decays to e−1of its surface value is one half of the corresponding decay depth for the amplitude of seasonal temperature changes. This depth‐dependent annual mean flux is effectively a source of water, which must be balanced by a flux divergence associated with other transport processes. In a relatively humid environment the liquid fluxes greatly exceed the thermal vapor fluxes, so such a balance is readily achieved without measurable effect on the dynamics of water in the unsaturated zone. However, if the mean vertical water flux through the unsaturated zone is very small (theoretical prediction is supported by long‐term field measurements in the Chihuahuan Desert. The analysis also makes predictions, confirmed by the field observations, regarding the seasonal variations of matric potential at a given depth. The conceptual model of unsaturated zone water transport developed here implies the possibility of near‐surface trapping of any aqueous constituent introduced at the surface.

First-Principles Quantum Dynamics of Singlet Fission: Coherent versus Thermally Activated Mechanisms Governed by Molecular π Stacking

Science.gov (United States)

Tamura, Hiroyuki; Huix-Rotllant, Miquel; Burghardt, Irene; Olivier, Yoann; Beljonne, David

2015-09-01

Singlet excitons in π -stacked molecular crystals can split into two triplet excitons in a process called singlet fission that opens a route to carrier multiplication in photovoltaics. To resolve controversies about the mechanism of singlet fission, we have developed a first principles nonadiabatic quantum dynamical model that reveals the critical role of molecular stacking symmetry and provides a unified picture of coherent versus thermally activated singlet fission mechanisms in different acenes. The slip-stacked equilibrium packing structure of pentacene derivatives is found to enhance ultrafast singlet fission mediated by a coherent superexchange mechanism via higher-lying charge transfer states. By contrast, the electronic couplings for singlet fission strictly vanish at the C2 h symmetric equilibrium π stacking of rubrene. In this case, singlet fission is driven by excitations of symmetry-breaking intermolecular vibrations, rationalizing the experimentally observed temperature dependence. Design rules for optimal singlet fission materials therefore need to account for the interplay of molecular π -stacking symmetry and phonon-induced coherent or thermally activated mechanisms.

Thermal conductivity prediction of nanoscale phononic crystal slabs using a hybrid lattice dynamics-continuum mechanics technique

Directory of Open Access Journals (Sweden)

Charles M. Reinke

2011-12-01

Full Text Available Recent work has demonstrated that nanostructuring of a semiconductor material to form a phononic crystal (PnC can significantly reduce its thermal conductivity. In this paper, we present a classical method that combines atomic-level information with the application of Bloch theory at the continuum level for the prediction of the thermal conductivity of finite-thickness PnCs with unit cells sized in the micron scale. Lattice dynamics calculations are done at the bulk material level, and the plane-wave expansion method is implemented at the macrosale PnC unit cell level. The combination of the lattice dynamics-based and continuum mechanics-based dispersion information is then used in the Callaway-Holland model to calculate the thermal transport properties of the PnC. We demonstrate that this hybrid approach provides both accurate and efficient predictions of the thermal conductivity.

Investigation of statistical relationship between dynamic modulus and thermal strength of asphalt concrete

International Nuclear Information System (INIS)

Qadir, A.; Gular, M.

2011-01-01

Dynamic modulus is a performance indicator for asphalt concrete and is used to qualify asphalt mixtures based on stress-strain characteristics under repeated loading. Moreover, the low temperature cracking of asphalt concrete mixes are measured in terms of fracture strength and fracture temperature. Dynamic modulus test was selected as one of the simple performance tests in the AASHTO 2002 guidelines to rate mixtures according to permanent deformation performance. However, AASHTO 2002 guidelines is silent in relating dynamic modulus values to low temperature cracking, probably because of weak correlations reported between these two properties. The present study investigates the relation between these two properties under the influence of aggregate type and mix gradation. Mixtures were prepared with two types of aggregate and gradations, while maintaining the binder type and air voids constant. The mixtures were later tested for dynamic modulus and fracture strength using thermal stress restrained specimen test (TSRST). Results indicate that there exists a fair correlation between the thermal fracture strength and stiffness at a selected test temperature and frequency level. These correlations are highly dependent upon the type of aggregate and mix gradation. (author)

Hot colors: the nature and specificity of color-induced nasal thermal sensations.

Science.gov (United States)

Michael, George A; Galich, Hélène; Relland, Solveig; Prud'hon, Sabine

2010-03-05

The nature of the recently discovered color-induced nasal thermal sensations was investigated in four Experiments. Subjects were required to fixate a bottle containing a red or green solution presented centrally (Exp1 and Exp4) or laterally (Exp2) and to sniff another bottle, always the same one, but which they were not allowed to see, containing 10 ml of a colorless, odorless and trigeminal-free solution. Each nostril was tested separately, and subjects were asked whether the sniffed solution induced warming or cooling sensations (plus an ambient sensation in Exp4) in the nasal cavity. The results of Experiments 1 and 2 confirmed the warming/left nostril-cooling/right nostril dissociation, suggesting the existence of different lateralized processes for thermal processing. However, Experiment 2 failed to demonstrate dominance of warming responses when subjects' eyes were directed to the left or cooling responses when they were directed to the right. Nor did gaze direction interact with the tested nostril. This suggests that the color-induced thermal sensations are specifically related to the nasal trigeminal system, rather than a general process related to general hemispheric activity. When the exposed bottles were colorless (Exp3), no lateralized patterns were observed, suggesting, in combination with the results of Experiments 1 and 2, that both color cues and nasal stimulations are necessary for lateralized patterns to arise. Rendering the temperature judgment even more difficult (Exp4), made the lateralized patterns shift towards the associated (i.e., ambient) responses. The results are discussed in a general framework which considers that, even in the absence of real thermal stimulus, preparing to process thermal stimuli in the nasal cavity may activate the underlying lateralized neural mechanisms, and that those mechanisms are reflected in the responses. Copyright 2009 Elsevier B.V. All rights reserved.

Dynamic characteristics of rotating pretwisted clamped-clamped beam under thermal stress

International Nuclear Information System (INIS)

Zhang, Bo; Li, Yueming; Lu, Wei Zhen

2016-01-01

Effects of thermal stress on the vibration characteristics, buckling limit and critical speed of a rotating pretwisted beam clamped to rigid hub at a stagger angle were investigated. By considering the work done by thermal stress, the thermal influence on stiffness matrix was introduced in the dynamic model. The motion equations were derived based on Lagrange equation by employing three pure Cartesian deformation variables combined with nonlinear von Karman strain formula. Numerical investigations studied the modal characteristics of the beam. Numerical results calculated from a commercial finite element code and obtained with the present modeling method were in good agreement with the previous results reported in the literature. The combined softening effects due to the thermal stress and the rotation motion were observed. Furthermore, it is shown that the inclusion of thermal stress is necessary for blades operating under a high temperature field. Buckling thermal loads and the critical rotating speed were calculated through solving the corresponding nonlinear equations numerically, and some pertinent conclusions are outlined. It is also found that the peak value position of the first mode shape approaches to the tip of blade with the increment of rotating speed and hub radius. However, the variation in the environment temperature causes only a slight alteration in the mode shape

Dynamic characteristics of rotating pretwisted clamped-clamped beam under thermal stress

Energy Technology Data Exchange (ETDEWEB)

Zhang, Bo; Li, Yueming [State Key Laboratory for Strength and Vibration of Mechanical Structures, Shaanxi Key Laboratory of Environment and Control for Flight Vehicle, School of Aerospace, Xi' an Jiaotong UniversityXi' an (China); Lu, Wei Zhen [Dept. of Civil and Architectural Engineering, City University of Hong Kong, Hong Kong (China)

2016-09-15

Effects of thermal stress on the vibration characteristics, buckling limit and critical speed of a rotating pretwisted beam clamped to rigid hub at a stagger angle were investigated. By considering the work done by thermal stress, the thermal influence on stiffness matrix was introduced in the dynamic model. The motion equations were derived based on Lagrange equation by employing three pure Cartesian deformation variables combined with nonlinear von Karman strain formula. Numerical investigations studied the modal characteristics of the beam. Numerical results calculated from a commercial finite element code and obtained with the present modeling method were in good agreement with the previous results reported in the literature. The combined softening effects due to the thermal stress and the rotation motion were observed. Furthermore, it is shown that the inclusion of thermal stress is necessary for blades operating under a high temperature field. Buckling thermal loads and the critical rotating speed were calculated through solving the corresponding nonlinear equations numerically, and some pertinent conclusions are outlined. It is also found that the peak value position of the first mode shape approaches to the tip of blade with the increment of rotating speed and hub radius. However, the variation in the environment temperature causes only a slight alteration in the mode shape.

Spatiotemporal dynamics of the spin transition in [Fe (HB(tz)3) 2] single crystals

Science.gov (United States)

Ridier, Karl; Rat, Sylvain; Shepherd, Helena J.; Salmon, Lionel; Nicolazzi, William; Molnár, Gábor; Bousseksou, Azzedine

2017-10-01

The spatiotemporal dynamics of the spin transition have been thoroughly investigated in single crystals of the mononuclear spin-crossover (SCO) complex [Fe (HB (tz )3)2] (tz = 1 ,2 ,4-triazol-1-yl) by optical microscopy. This compound exhibits an abrupt spin transition centered at 334 K with a narrow thermal hysteresis loop of ˜1 K (first-order transition). Most single crystals of this compound reveal exceptional resilience upon repeated switching (several hundred cycles), which allowed repeatable and quantitative measurements of the spatiotemporal dynamics of the nucleation and growth processes to be carried out. These experiments revealed remarkable properties of the thermally induced spin transition: high stability of the thermal hysteresis loop, unprecedented large velocities of the macroscopic low-spin/high-spin phase boundaries up to 500 µm/s, and no visible dependency on the temperature scan rate. We have also studied the dynamics of the low-spin → high-spin transition induced by a local photothermal excitation generated by a spatially localized (Ø = 2 μ m ) continuous laser beam. Interesting phenomena have been evidenced both in quasistatic and dynamic conditions (e.g., threshold effects and long incubation periods, thermal activation of the phase boundary propagation, stabilization of the crystal in a stationary biphasic state, and thermal cutoff frequency). These measurements demonstrated the importance of thermal effects in the transition dynamics, and they enabled an accurate determination of the thermal properties of the SCO compound in the framework of a simple theoretical model.

Thermally-assisted Magma Emplacement Explains Restless Calderas.

Science.gov (United States)

Amoruso, Antonella; Crescentini, Luca; D'Antonio, Massimo; Acocella, Valerio

2017-08-11

Many calderas show repeated unrest over centuries. Though probably induced by magma, this unique behaviour is not understood and its dynamics remains elusive. To better understand these restless calderas, we interpret deformation data and build thermal models of Campi Flegrei caldera, Italy. Campi Flegrei experienced at least 4 major unrest episodes in the last decades. Our results indicate that the inflation and deflation of magmatic sources at the same location explain most deformation, at least since the build-up of the last 1538 AD eruption. However, such a repeated magma emplacement requires a persistently hot crust. Our thermal models show that this repeated emplacement was assisted by the thermal anomaly created by magma that was intruded at shallow depth ~3 ka before the last eruption. This may explain the persistence of the magmatic sources promoting the restless behaviour of the Campi Flegrei caldera; moreover, it explains the crystallization, re-melting and mixing among compositionally distinct magmas recorded in young volcanic rocks. Our model of thermally-assisted unrest may have a wider applicability, possibly explaining also the dynamics of other restless calderas.

True Triaxial Experimental Study of Rockbursts Induced By Ramp and Cyclic Dynamic Disturbances

Science.gov (United States)

Su, Guoshao; Hu, Lihua; Feng, Xiating; Yan, Liubin; Zhang, Gangliang; Yan, Sizhou; Zhao, Bin; Yan, Zhaofu

2018-04-01

A modified rockburst testing system was utilized to reproduce rockbursts induced by ramp and cyclic dynamic disturbances with a low-intermediate strain rate of 2 × 10-3-5 × 10-3 s-1 in the laboratory. The experimental results show that both the ramp and cyclic dynamic disturbances play a significant role in inducing rockbursts. In the tests of rockbursts induced by a ramp dynamic disturbance, as the static stress before the dynamic disturbance increases, both the strength of specimens and the kinetic energy of the ejected fragments first increase and then decrease. In the tests of rockbursts induced by a cyclic dynamic disturbance, there exists a rockburst threshold of the static stress and the dynamic disturbance amplitude, and the kinetic energy of the ejected fragments first increases and then decreases as the cyclic dynamic disturbance frequency increases. The main differences between rockbursts induced by ramp dynamic disturbances and those induced by cyclic dynamic disturbances are as follows: the rockburst development process of the former is characterized by an impact failure feature, while that of the latter is characterized by a fatigue failure feature; the damage evolution curve of the specimen of the former has a leap-developing form with a significant catastrophic feature, while that of the latter has an inverted S-shape with a remarkable fatigue damage characteristic; the energy mechanism of the former involves the ramp dynamic disturbance giving extra elastic strain energy to rocks, while that of the latter involves the cyclic dynamic disturbance decreasing the ultimate energy storage capacity of rocks.

Nonlinear thermally induced distortions of a laser beam in a cryogenic disk amplifier

International Nuclear Information System (INIS)

Vyatkin, A G; Khazanov, Efim A

2009-01-01

Taking into account the temperature dependences of the heat conductivity, the refractive index, and the thermal expansion coefficient, we calculated the temperature, elastic stresses, a thermally induced lens and depolarisation of a beam in a cryogenic disk amplifier (an Yb:YAG disk placed between a copper cylinder and a sapphire disk cooled by liquid nitrogen). When the active element (the thickness is 0.6 mm, the orientation is [001], the atomic concentration of Yb is 10%) is pumped by radiation from a diode laser (the beam diameter is 6 mm), the temperature does not exceed 140 K for the heat release power of 100 W. In this case, elastic stresses in the active element are six times lower than the maximum permissible value. The focal distance of the thermally induced lens is 5.5 m and the depolarisation rate is 0.038% per two passes through the active element. Although the heat conductivity of the active element rapidly decreases with temperature, the thermal load can be increased by 1.5-2 times when the dimensions of the active element remain constant. (active media)

Visualization of thermally activated nanocarriers using in situ atomic force microscopy

DEFF Research Database (Denmark)

Dong, M. D.; Howard, K. A.; Oupicky, D.

2007-01-01

Thermo-responsive nanocarriers aim to improve the delivery of drugs into target tissue by a process of size-mediated deposition activated by thermal stimuli. The direct imaging of thermally-induced changes in nanocarrier morphology was demonstrated using in situ liquid AFM over a nano-scale and t......-scale and temperature range relevant for clinical approaches. In situ AFM proved to be a unique method for investigating the dynamic conformational changes of individual nanoparticles, promoting its application in the future development of stimuli-responsive nanocarriers.......Thermo-responsive nanocarriers aim to improve the delivery of drugs into target tissue by a process of size-mediated deposition activated by thermal stimuli. The direct imaging of thermally-induced changes in nanocarrier morphology was demonstrated using in situ liquid AFM over a nano...

Preliminary analysis of the potential for thermally-induced rock fracture around high-level waste containers

International Nuclear Information System (INIS)

Ratigan, J.L.

1976-01-01

The major results are: the development of parametric formulations relating the potential for thermally induced fracturing in the high-level radioactive waste repository concept to the elastic and thermal properties of the site rock and the depth of the excavation, and the recognition of a need to determine the actual ''failure envelope'' for any potential site rock in the laboratory and adjust the parametric relations appropriately. Analysis of five rock types indicated that none would experience elastic/brittle failure due to the thermal stresses induced by the introduction of a 5 kW heat source. However, the rock strengths and elastic properties are laboratory values and not in situ values

Structure impact on the thermal and electronic properties of bismuth telluride by ab-initio and molecular dynamics calculations

International Nuclear Information System (INIS)

Termentzidis, K; Pokropivny, A; Xiong, S-Y; Chumakov, Y; Volz, S; Woda, M; Cortona, P

2012-01-01

We use molecular dynamics and ab-initio methods to predict the thermal and electronic properties of new materials with high figures of merit. The simulated systems are bulk bismuth tellurides with antisite and vacancy defects. Optimizations of the materials under investigation are performed by the SIESTA code for subsequent calculations of force constants, electronic properties, and Seebeck coefficients. The prediction of the thermal conductivity is made by Non-Equilibrium Molecular Dynamics (NEMD) using the LAMMPS code. The thermal conductivity of bulk bismuth telluride with different stoichiometry and with a number of substitution defects is calculated. We have found that the thermal conductivity can be decreased by 60% by introducing vacancy defects. The calculated thermal conductivities for the different structures are compared with the available experimental and theoretical results.

On the role of thermal fluid dynamics into the evolution of porosity during selective laser melting

International Nuclear Information System (INIS)

Panwisawas, C.; Qiu, C.L.; Sovani, Y.; Brooks, J.W.; Attallah, M.M.; Basoalto, H.C.

2015-01-01

Thermal fluid dynamics and experiments have been used to study the evolution of pores during selective laser melting of Ti-6Al-4V. Scanning electron micrographs show that the morphology of pores changed from near-spherical to elongated shape as the laser scan speed increased. Computational fluid dynamics suggests that this is caused by the change of flow pattern in the melt pool which is dictated by forces such as vapour pressure, gravitational force, capillary and thermal capillary forces exerted on the metallic/gaseous interface

Crack propagation under thermal cycling loading inducing a thermal gradient in the specimen thickness

International Nuclear Information System (INIS)

Le, H.N.

2009-05-01

This study aims to figure out the crack growth phenomenon by thermal fatigue induced by thermal gradient through thickness of specimen. Firstly, an experimental facility has been developed: a rectangular parallelepiped specimen is subjected to thermal cycling between 350 C and 100 C; the specimen is freed to expand and contract. Two semi-circular notches (0,1 mm depth and 4 mm length) have been machined on the surface of the specimen. A series of interrupted tests has been carried out to characterize and quantify the crack growth in depth and surface of the pre-existing crack. Next, a three-dimensional crack growth simulation has been implemented in ABAQUS. Automation using Python was used to simulate the propagation of a crack under thermal cycling, with re-meshing at crack front after each calculation step. No assumption has been taken on the crack front during the crack propagation. A comparison with test results showed very good agreement on the evolution of crack front shape and on the kinetics of propagation on the edge and the heart of pre-existing crack. An analytical approach was also developed based on the calculation of stress intensity factors (SIC). A two-dimensional approach was first introduced enabling us to better understand the influence of various thermal and geometric parameters. Finally, a three dimensional approach, with an elliptical assumption crack shape during the propagation, leading to a prediction of crack growth on the surface and in depth which is very similar to that obtained numerically, but with computational time much lower. (author)

Modeling surface energy fluxes and thermal dynamics of a seasonally ice-covered hydroelectric reservoir.

Science.gov (United States)

Wang, Weifeng; Roulet, Nigel T; Strachan, Ian B; Tremblay, Alain

2016-04-15

The thermal dynamics of human created northern reservoirs (e.g., water temperatures and ice cover dynamics) influence carbon processing and air-water gas exchange. Here, we developed a process-based one-dimensional model (Snow, Ice, WAater, and Sediment: SIWAS) to simulate a full year's surface energy fluxes and thermal dynamics for a moderately large (>500km(2)) boreal hydroelectric reservoir in northern Quebec, Canada. There is a lack of climate and weather data for most of the Canadian boreal so we designed SIWAS with a minimum of inputs and with a daily time step. The modeled surface energy fluxes were consistent with six years of observations from eddy covariance measurements taken in the middle of the reservoir. The simulated water temperature profiles agreed well with observations from over 100 sites across the reservoir. The model successfully captured the observed annual trend of ice cover timing, although the model overestimated the length of ice cover period (15days). Sensitivity analysis revealed that air temperature significantly affects the ice cover duration, water and sediment temperatures, but that dissolved organic carbon concentrations have little effect on the heat fluxes, and water and sediment temperatures. We conclude that the SIWAS model is capable of simulating surface energy fluxes and thermal dynamics for boreal reservoirs in regions where high temporal resolution climate data are not available. SIWAS is suitable for integration into biogeochemical models for simulating a reservoir's carbon cycle. Copyright © 2016 Elsevier B.V. All rights reserved.

Testing thermal gradient driving force for grain boundary migration using molecular dynamics simulations

International Nuclear Information System (INIS)

Bai, Xian-Ming; Zhang, Yongfeng; Tonks, Michael R.

2015-01-01

Strong thermal gradients in low-thermal-conductivity ceramics may drive extended defects, such as grain boundaries and voids, to migrate in preferential directions. In this work, molecular dynamics simulations are conducted to study thermal gradient driven grain boundary migration and to verify a previously proposed thermal gradient driving force equation, using uranium dioxide as a model system. It is found that a thermal gradient drives grain boundaries to migrate up the gradient and the migration velocity increases under a constant gradient owing to the increase in mobility with temperature. Different grain boundaries migrate at very different rates due to their different intrinsic mobilities. The extracted mobilities from the thermal gradient driven simulations are compared with those calculated from two other well-established methods and good agreement between the three different methods is found, demonstrating that the theoretical equation of the thermal gradient driving force is valid, although a correction of one input parameter should be made. The discrepancy in the grain boundary mobilities between modeling and experiments is also discussed.

Kraus map for non-Markovian quantum dynamics driven by a thermal reservoir

NARCIS (Netherlands)

van Wonderen, A.J.; Suttorp, L.G.

2013-01-01

Starting from unitary dynamics we study the evolution in time of a non-relativistic quantum system that exchanges energy with a thermal reservoir of harmonic oscillators. System and reservoir are assumed to be initially decorrelated. Reservoir correlation functions are factorized by means of a Kraus

Standoff laser-induced thermal emission of explosives

Science.gov (United States)

Galán-Freyle, Nataly Y.; Pacheco-Londoño, Leonardo C.; Figueroa-Navedo, Amanda; Hernandez-Rivera, Samuel P.

2013-05-01

A laser mediated methodology for remote thermal excitation of analytes followed by standoff IR detection is proposed. The goal of this study was to determine the feasibility of using laser induced thermal emission (LITE) from vibrationally excited explosives residues deposited on surfaces to detect explosives remotely. Telescope based FT-IR spectral measurements were carried out to examine substrates containing trace amounts of threat compounds used in explosive devices. The highly energetic materials (HEM) used were PETN, TATP, RDX, TNT, DNT and ammonium nitrate with concentrations from 5 to 200 μg/cm2. Target substrates of various thicknesses were remotely heated using a high power CO2 laser, and their mid-infrared (MIR) thermally stimulated emission spectra were recorded. The telescope was configured from reflective optical elements in order to minimize emission losses in the MIR frequencies and to provide optimum overall performance. Spectral replicas were acquired at a distance of 4 m with an FT-IR interferometer at 4 cm- 1 resolution and 10 scans. Laser power was varied from 4-36 W at radiation exposure times of 10, 20, 30 and 60 s. CO2 laser powers were adjusted to improve the detection and identification of the HEM samples. The advantages of increasing the thermal emission were easily observed in the results. Signal intensities were proportional to the thickness of the coated surface (a function of the surface concentration), as well as the laser power and laser exposure time. For samples of RDX and PETN, varying the power and time of induction of the laser, the calculated low limit of detections were 2 and 1 μg/cm2, respectively.

Current-induced magnetization dynamics in nanomagnets

International Nuclear Information System (INIS)

Bertotti, G.; Serpico, C.; Mayergoyz, I.D.; Bonin, R.; D'Aquino, M.

2007-01-01

An overview is given of the various approaches that have been proposed for the interpretation of spin-transfer-driven magnetization dynamics. Models of critical currents and critical fields for switching as well as for the onset of magnetization oscillations are discussed, together with methods for the construction of field-current stability diagrams. Finally, the role of thermal fluctuations is analyzed. Particular emphasis is given to the study of uniformly magnetized nanomagnets, which represents an essential step before moving to the numerical computation of more complex micromagnetic configurations

Current-induced magnetization dynamics in nanomagnets

Energy Technology Data Exchange (ETDEWEB)

Bertotti, G. [INRIM-Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, 10135 Turin (Italy)]. E-mail: g.bertotti@inrim.it; Serpico, C. [Department of Electrical Engineering, Universita degli Studi Federico II, Via Claudio 21, 80125 Naples (Italy); Mayergoyz, I.D. [Department of Electrical and Computer Engineering, University of Maryland, College Park, MD 20742 (United States); Bonin, R. [INRIM-Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, 10135 Turin (Italy); D' Aquino, M. [Department of Electrical Engineering, Universita degli Studi Federico II, Via Claudio 21, 80125 Naples (Italy)

2007-09-15

An overview is given of the various approaches that have been proposed for the interpretation of spin-transfer-driven magnetization dynamics. Models of critical currents and critical fields for switching as well as for the onset of magnetization oscillations are discussed, together with methods for the construction of field-current stability diagrams. Finally, the role of thermal fluctuations is analyzed. Particular emphasis is given to the study of uniformly magnetized nanomagnets, which represents an essential step before moving to the numerical computation of more complex micromagnetic configurations.

Molecular nonlinear dynamics and protein thermal uncertainty quantification

Science.gov (United States)

Xia, Kelin; Wei, Guo-Wei

2014-01-01

This work introduces molecular nonlinear dynamics (MND) as a new approach for describing protein folding and aggregation. By using a mode system, we show that the MND of disordered proteins is chaotic while that of folded proteins exhibits intrinsically low dimensional manifolds (ILDMs). The stability of ILDMs is found to strongly correlate with protein energies. We propose a novel method for protein thermal uncertainty quantification based on persistently invariant ILDMs. Extensive comparison with experimental data and the state-of-the-art methods in the field validate the proposed new method for protein B-factor prediction. PMID:24697365

Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion

Science.gov (United States)

Scholz, Robert; Floß, Gereon; Saalfrank, Peter; Füchsel, Gernot; Lončarić, Ivor; Juaristi, J. I.

2016-10-01

A Langevin model accounting for all six molecular degrees of freedom is applied to femtosecond-laser induced, hot-electron driven dynamics of Ru(0001)(2 ×2 ):CO. In our molecular dynamics with electronic friction approach, a recently developed potential energy surface based on gradient-corrected density functional theory accounting for van der Waals interactions is adopted. Electronic friction due to the coupling of molecular degrees of freedom to electron-hole pairs in the metal are included via a local density friction approximation, and surface phonons by a generalized Langevin oscillator model. The action of ultrashort laser pulses enters through a substrate-mediated, hot-electron mechanism via a time-dependent electronic temperature (derived from a two-temperature model), causing random forces acting on the molecule. The model is applied to laser induced lateral diffusion of CO on the surface, "hot adsorbate" formation, and laser induced desorption. Reaction probabilities are strongly enhanced compared to purely thermal processes, both for diffusion and desorption. Reaction yields depend in a characteristic (nonlinear) fashion on the applied laser fluence, as well as branching ratios for various reaction channels. Computed two-pulse correlation traces for desorption and other indicators suggest that aside from electron-hole pairs, phonons play a non-negligible role for laser induced dynamics in this system, acting on a surprisingly short time scale. Our simulations on precomputed potentials allow for good statistics and the treatment of long-time dynamics (300 ps), giving insight into this system which hitherto has not been reached. We find generally good agreement with experimental data where available and make predictions in addition. A recently proposed laser induced population of physisorbed precursor states could not be observed with the present low-coverage model.

Topology of a dissipative spin: Dynamical Chern number, bath-induced nonadiabaticity, and a quantum dynamo effect

Science.gov (United States)

Henriet, Loïc; Sclocchi, Antonio; Orth, Peter P.; Le Hur, Karyn

2017-02-01

We analyze the topological deformations of the ground state manifold of a quantum spin-1/2 in a magnetic field H =H (sinθ cosϕ ,sinθ sinϕ ,cosθ ) induced by a coupling to an ohmic quantum dissipative environment at zero temperature. From Bethe ansatz results and a variational approach, we confirm that the Chern number associated with the geometry of the reduced spin ground state manifold is preserved in the delocalized phase for α <1 . We report a divergence of the Berry curvature at αc=1 for magnetic fields aligned along the equator θ =π /2 . This divergence is caused by the complete quenching of the transverse magnetic field by the bath associated with a gap closing that occurs at the localization Kosterlitz-Thouless quantum phase transition in this model. Recent experiments in quantum circuits have engineered nonequilibrium protocols to access topological properties from a measurement of a dynamical Chern number defined via the out-of-equilibrium spin expectation values. Applying a numerically exact stochastic Schrödinger approach we find that, for a fixed field sweep velocity θ (t )=v t , the bath induces a crossover from (quasi)adiabatic to nonadiabatic dynamical behavior when the spin bath coupling α increases. We also investigate the particular regime H /ωc≪v /H ≪1 with large bath cutoff frequency ωc, where the dynamical Chern number vanishes already at α =1 /2 . In this regime, the mapping to an interacting resonance level model enables us to analytically describe the behavior of the dynamical Chern number in the vicinity of α =1 /2 . We further provide an intuitive physical explanation of the bath-induced breakdown of adiabaticity in analogy to the Faraday effect in electromagnetism. We demonstrate that the driving of the spin leads to the production of a large number of bosonic excitations in the bath, which strongly affect the spin dynamics. Finally, we quantify the spin-bath entanglement and formulate an analogy with an effective

Orion Active Thermal Control System Dynamic Modeling Using Simulink/MATLAB

Science.gov (United States)

Wang, Xiao-Yen J.; Yuko, James

2010-01-01

This paper presents dynamic modeling of the crew exploration vehicle (Orion) active thermal control system (ATCS) using Simulink (Simulink, developed by The MathWorks). The model includes major components in ATCS, such as heat exchangers and radiator panels. The mathematical models of the heat exchanger and radiator are described first. Four different orbits were used to validate the radiator model. The current model results were compared with an independent Thermal Desktop (TD) (Thermal Desktop, PC/CAD-based thermal model builder, developed in Cullimore & Ring (C&R) Technologies) model results and showed good agreement for all orbits. In addition, the Orion ATCS performance was presented for three orbits and the current model results were compared with three sets of solutions- FloCAD (FloCAD, PC/CAD-based thermal/fluid model builder, developed in C&R Technologies) model results, SINDA/FLUINT (SINDA/FLUINT, a generalized thermal/fluid network-style solver ) model results, and independent Simulink model results. For each case, the fluid temperatures at every component on both the crew module and service module sides were plotted and compared. The overall agreement is reasonable for all orbits, with similar behavior and trends for the system. Some discrepancies exist because the control algorithm might vary from model to model. Finally, the ATCS performance for a 45-hr nominal mission timeline was simulated to demonstrate the capability of the model. The results show that the ATCS performs as expected and approximately 2.3 lb water was consumed in the sublimator within the 45 hr timeline before Orion docked at the International Space Station.

Adsorption thermal energy storage for cogeneration in industrial batch processes: Experiment, dynamic modeling and system analysis

International Nuclear Information System (INIS)

Schreiber, Heike; Graf, Stefan; Lanzerath, Franz; Bardow, André

2015-01-01

Adsorption thermal energy storage is investigated for heat supply with cogeneration in industrial batch processes. The feasibility of adsorption thermal energy storage is demonstrated with a lab-scale prototype. Based on these experiments, a dynamic model is developed and successfully calibrated to measurement data. Thereby, a reliable description of the dynamic behavior of the adsorption thermal energy storage unit is achieved. The model is used to study and benchmark the performance of adsorption thermal energy storage combined with cogeneration for batch process energy supply. As benchmark, we consider both a peak boiler and latent thermal energy storage based on a phase change material. Beer brewing is considered as an example of an industrial batch process. The study shows that adsorption thermal energy storage has the potential to increase energy efficiency significantly; primary energy consumption can be reduced by up to 25%. However, successful integration of adsorption thermal storage requires appropriate integration of low grade heat: Preferentially, low grade heat is available at times of discharging and in demand when charging the storage unit. Thus, adsorption thermal energy storage is most beneficial if applied to a batch process with heat demands on several temperature levels. - Highlights: • A highly efficient energy supply for industrial batch processes is presented. • Adsorption thermal energy storage (TES) is analyzed in experiment and simulation. • Adsorption TES can outperform both peak boilers and latent TES. • Performance of adsorption TES strongly depends on low grade heat temperature.

Thermal behavior of natural zeolites

International Nuclear Information System (INIS)

Bish, D.L.

1993-01-01

Thermal behavior of natural zeolites impacts their application and identification and varies significantly from zeolite to zeolite. Zeolites evolve H 2 0 upon heating, but recent data show that distinct ''types'' of water (e.g., loosely bound or tightly bound zeolitic water) do not exist. Rather water is bound primarily to extra-framework cations with a continuum of energies, giving rise to pseudocontinuous loss of water accompanied by a dynamic interaction between remaining H 2 0 molecules and extra-framework cations. These interactions in the channels of zeolites give rise to dehydration dependent on the extra-framework cation, in addition to temperature and water vapor pressure. The dehydration reaction and the extra-framework cation also affect the thermal expansion/contraction. Most zeolites undergo dehydration-induced contractions that may be anisotropic, although minor thermal expansion can be seen with some zeolites. Such contractions can be partially or completely irreversible if they involve modifications of the tetrahedral framework and/or if rehydration is sluggish. Thermally induced structural modifications are also driven initially by dehydration and the concomitant contraction and migration of extra-framework cations. Contraction is accommodated by rotations of structural units and tetrahedral cation-oxygen linkages may break. Thermal reactions that involve breaking of tetrahedral cation-oxygen bonds markedly irreversible and may be kinetically limited, producing large differences between short- and long-term heating

Thermal distribution in biological tissue at laser induced fluorescence and photodynamic therapy

Science.gov (United States)

Krasnikov, I. V.; Seteikin, A. Yu.; Drakaki, E.; Makropoulou, M.

2012-03-01

Laser induced fluorescence spectroscopy and photodynamic therapy (PDT) are techniques currently introduced in clinical applications for visualization and local destruction of malignant tumours as well as premalignant lesions. During the laser irradiation of tissues for the diagnostic and therapeutic purposes, the absorbed optical energy generates heat, although the power density of the treatment light for surface illumination is normally low enough not to cause any significantly increased tissue temperature. In this work we tried to evaluate the utility of Monte Carlo modeling for simulating the temperature fields and the dynamics of heat conduction into the skin tissue under several laser irradiation conditions with both a pulsed UV laser and a continuous wave visible laser beam. The analysis of the results showed that heat is not localized on the surface, but it is collected inside the tissue. By varying the boundary conditions on the surface and the type of the laser radiation (continuous or pulsed) we can reach higher than normal temperature inside the tissue without simultaneous formation of thermally damaged tissue (e.g. coagulation or necrosis zone).

Silver-mediated base pairings: towards dynamic DNA nanostructures with enhanced chemical and thermal stability

International Nuclear Information System (INIS)

Swasey, Steven M; Gwinn, Elisabeth G

2016-01-01

The thermal and chemical fragility of DNA nanomaterials assembled by Watson–Crick (WC) pairing constrain the settings in which these materials can be used and how they can be functionalized. Here we investigate use of the silver cation, Ag + , as an agent for more robust, metal-mediated self-assembly, focusing on the simplest duplex building blocks that would be required for more elaborate Ag + –DNA nanostructures. Our studies of Ag + -induced assembly of non-complementary DNA oligomers employ strands of 2–24 bases, with varied base compositions, and use electrospray ionization mass spectrometry to determine product compositions. High yields of duplex products containing narrowly distributed numbers of Ag + can be achieved by optimizing solution conditions. These Ag + -mediated duplexes are stable to at least 60 mM Mg 2+ , higher than is necessary for WC nanotechnology schemes such as tile assemblies and DNA origami, indicating that sequential stages of Ag + -mediated and WC-mediated assembly may be feasible. Circular dichroism spectroscopy suggests simple helical structures for Ag + -mediated duplexes with lengths to at least 20 base pairs, and further indicates that the structure of cytosine-rich duplexes is preserved at high urea concentrations. We therefore propose an approach towards dynamic DNA nanomaterials with enhanced thermal and chemical stability through designs that combine sturdy silver-mediated ‘frames’ with WC paired ‘pictures’. (paper)

Parameter estimation of breast tumour using dynamic neural network from thermal pattern

Directory of Open Access Journals (Sweden)

Elham Saniei

2016-11-01

Full Text Available This article presents a new approach for estimating the depth, size, and metabolic heat generation rate of a tumour. For this purpose, the surface temperature distribution of a breast thermal image and the dynamic neural network was used. The research consisted of two steps: forward and inverse. For the forward section, a finite element model was created. The Pennes bio-heat equation was solved to find surface and depth temperature distributions. Data from the analysis, then, were used to train the dynamic neural network model (DNN. Results from the DNN training/testing confirmed those of the finite element model. For the inverse section, the trained neural network was applied to estimate the depth temperature distribution (tumour position from the surface temperature profile, extracted from the thermal image. Finally, tumour parameters were obtained from the depth temperature distribution. Experimental findings (20 patients were promising in terms of the model’s potential for retrieving tumour parameters.

Optimal Sizing of Energy Storage for Community Microgrids Considering Building Thermal Dynamics

Energy Technology Data Exchange (ETDEWEB)

Liu, Guodong [ORNL; Li, Zhi [ORNL; Starke, Michael R. [ORNL; Ollis, Ben [ORNL; Tomsovic, Kevin [University of Tennessee, Knoxville (UTK)

2017-07-01

This paper proposes an optimization model for the optimal sizing of energy storage in community microgrids considering the building thermal dynamics and customer comfort preference. The proposed model minimizes the annualized cost of the community microgrid, including energy storage investment, purchased energy cost, demand charge, energy storage degradation cost, voluntary load shedding cost and the cost associated with customer discomfort due to room temperature deviation. The decision variables are the power and energy capacity of invested energy storage. In particular, we assume the heating, ventilation and air-conditioning (HVAC) systems can be scheduled intelligently by the microgrid central controller while maintaining the indoor temperature in the comfort range set by customers. For this purpose, the detailed thermal dynamic characteristics of buildings have been integrated into the optimization model. Numerical simulation shows significant cost reduction by the proposed model. The impacts of various costs on the optimal solution are investigated by sensitivity analysis.

Thermal transport characterization of hexagonal boron nitride nanoribbons using molecular dynamics simulation

Directory of Open Access Journals (Sweden)

Asir Intisar Khan

2017-10-01

Full Text Available Due to similar atomic bonding and electronic structure to graphene, hexagonal boron nitride (h-BN has broad application prospects such as the design of next generation energy efficient nano-electronic devices. Practical design and efficient performance of these devices based on h-BN nanostructures would require proper thermal characterization of h-BN nanostructures. Hence, in this study we have performed equilibrium molecular dynamics (EMD simulation using an optimized Tersoff-type interatomic potential to model the thermal transport of nanometer sized zigzag hexagonal boron nitride nanoribbons (h-BNNRs. We have investigated the thermal conductivity of h-BNNRs as a function of temperature, length and width. Thermal conductivity of h-BNNRs shows strong temperature dependence. With increasing width, thermal conductivity increases while an opposite pattern is observed with the increase in length. Our study on h-BNNRs shows considerably lower thermal conductivity compared to GNRs. To elucidate these aspects, we have calculated phonon density of states for both h-BNNRs and GNRs. Moreover, using EMD we have explored the impact of different vacancies, namely, point vacancy, edge vacancy and bi-vacancy on the thermal conductivity of h-BNNRs. With varying percentages of vacancies, significant reduction in thermal conductivity is observed and it is found that, edge and point vacancies are comparatively more destructive than bi-vacancies. Such study would contribute further into the growing interest for accurate thermal transport characterization of low dimensional nanostructures.

ATLAST ULE mirror segment performance analytical predictions based on thermally induced distortions

Science.gov (United States)

Eisenhower, Michael J.; Cohen, Lester M.; Feinberg, Lee D.; Matthews, Gary W.; Nissen, Joel A.; Park, Sang C.; Peabody, Hume L.

2015-09-01

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for a 9.2 m aperture space-borne observatory operating across the UV/Optical/NIR spectra. The primary mirror for ATLAST is a segmented architecture with pico-meter class wavefront stability. Due to its extraordinarily low coefficient of thermal expansion, a leading candidate for the primary mirror substrate is Corning's ULE® titania-silicate glass. The ATLAST ULE® mirror substrates will be maintained at `room temperature' during on orbit flight operations minimizing the need for compensation of mirror deformation between the manufacturing temperature and the operational temperatures. This approach requires active thermal management to maintain operational temperature while on orbit. Furthermore, the active thermal control must be sufficiently stable to prevent time-varying thermally induced distortions in the mirror substrates. This paper describes a conceptual thermal management system for the ATLAST 9.2 m segmented mirror architecture that maintains the wavefront stability to less than 10 pico-meters/10 minutes RMS. Thermal and finite element models, analytical techniques, accuracies involved in solving the mirror figure errors, and early findings from the thermal and thermal-distortion analyses are presented.

Spin dynamics and thermal stability in L10 FePt

Science.gov (United States)

Chen, Tianran; Toomey, Wahida

Increasing the data storage density of hard drives remains one of the continuing goals in magnetic recording technology. A critical challenge for increasing data density is the thermal stability of the written information, which drops rapidly as the bit size gets smaller. To maintain good thermal stability in small bits, one should consider materials with high anisotropy energy such as L10 FePt. High anisotropy energy nevertheless implies high coercivity, making it difficult to write information onto the disk. This issue can be overcome by a new technique called heat-assisted magnetic recording, where a laser is used to locally heat the recording medium to reduce its coercivity while retaining relatively good thermal stability. Many of the microscopic magnetic properties of L10 FePt, however, have not been theoretically well understood. In this poster, I will focus on a single L10 FePt grain, typically of a few nanometers. Specifically, I will discuss its critical temperature, size effect and, in particular, spin dynamics in the writing process, a key to the success of heat-assisted magnetic recording. WCU URF16.

Thermal boundary resistance at Si/Ge interfaces by molecular dynamics simulation

Directory of Open Access Journals (Sweden)

Tianzhuo Zhan

2015-04-01

Full Text Available In this study, we investigated the temperature dependence and size effect of the thermal boundary resistance at Si/Ge interfaces by non-equilibrium molecular dynamics (MD simulations using the direct method with the Stillinger-Weber potential. The simulations were performed at four temperatures for two simulation cells of different sizes. The resulting thermal boundary resistance decreased with increasing temperature. The thermal boundary resistance was smaller for the large cell than for the small cell. Furthermore, the MD-predicted values were lower than the diffusion mismatch model (DMM-predicted values. The phonon density of states (DOS was calculated for all the cases to examine the underlying nature of the temperature dependence and size effect of thermal boundary resistance. We found that the phonon DOS was modified in the interface regions. The phonon DOS better matched between Si and Ge in the interface region than in the bulk region. Furthermore, in interface Si, the population of low-frequency phonons was found to increase with increasing temperature and cell size. We suggest that the increasing population of low-frequency phonons increased the phonon transmission coefficient at the interface, leading to the temperature dependence and size effect on thermal boundary resistance.

X-ray diffraction study of thermally and stress-induced phase transformations in single crystalline Ni-Mn-Ga alloys

International Nuclear Information System (INIS)

Martynov, V.V.

1995-01-01

Using in-situ single crystal X-ray diffraction methods, thermally- and stress-induced crystal structure evolution was investigated in two Ni-Mn-Ga Heusler-type alloys. For the 51at.%Ni-24at.%Mn-25at.%Ga alloy it was found that application of external stress in a temperature range ∼20 C above the M s at first causes intensity changes of X-ray diffuse scattering peaks in β-phase. Further stressing results in stress-induced phase transformations and under the appropriate conditions three successive martensitic transformations (one is parent-to-martensite and two are martensite-to-martensite transformations) can be stress induced. Of these only the parent-to-martensite transformation can be thermally-induced. Two successive structural transformations (thermally-induced parent-to-martensite and stress-induced martensite-to-martensite transformations) were found in 52at.%Ni-25at.%Mn-23at.%Ga alloy. Crystal structure, lattice parameters, type of modulation, and the length of modulation period for all martensites were identified. (orig.)

Dynamic modeling and sensitivity analysis of solar thermal energy conversion systems

Science.gov (United States)

Hamilton, C. L.

1977-01-01

Since the energy input to solar thermal conversion systems is both time variant and probabilistic, it is unlikely that simple steady-state methods for estimating lifetime performance will provide satisfactory results. The work described here uses dynamic modeling to begin identifying what must be known about input radiation and system dynamic characteristics to estimate performance reliably. Daily operation of two conceptual solar energy systems was simulated under varying operating strategies with time-dependent radiation intensity ranging from smooth input of several magnitudes to input of constant total energy whose intensity oscillated with periods from 1/4 hour to 6 hours. Integrated daily system output and efficiency were functions of both level and dynamic characteristics of insolation. Sensitivity of output to changes in total input was greater than one.

MR imaging and histopathologic correlations of thermal injuries induced by interstitial laser applications

International Nuclear Information System (INIS)

Anzai, Y.; Lufkin, R.B.; Castro, D.J.; Farahani, K.; Chen, H.W.; Hirchowiz, S.

1991-01-01

Interstitial laser phototherapy for deep-seated tumors may become an attractive therapeutic modality when a noninvasive, accurate monitoring system is developed. In this paper, to devaluate the ability of MR imaging to differentiate reversible and irreversible thermal injuries induced by laser therapy, the precise correlation of MR and histopathologic findings are investigated in the in vivo model. Nd:YAG lasers were applied to normal musculature of rabbits, and MR examinations were performed immediately after laser exposure and followed up for up to 10 weeks. The sequential MR images were correlated with histopathologic findings. T2-weighted MR imaging clearly showed laser-induced thermal injuries on any postoperative day. MR imaging of acute thermal injuries showed a central cavity, low-signal zone of coagulative necrosis and a peripheral high-signal layer of interstitial edema. The infiltration of neutrophils followed by fibrovascular response was identified on the marginal edema layer after 6 postoperative days

Light induced intraspecific variability in response to thermal stress in the hard coral Stylophora pistillata

NARCIS (Netherlands)

Tilstra, Arjen; Wijgerde, Tim; Dini-Andreote, Francisco; Eriksson, Britas Klemens; Salles, Joana Falcão; Pen, Ido; Osinga, Ronald; Wild, Christian

2017-01-01

Recent research suggests that prior exposure of several months to elevated irradiance induces enhanced thermal tolerance in scleractinian corals. While this tolerance has been reported at the species level, individual coral colonies may react differently due to individual variability in thermal

Thermal, chemical and pH induced unfolding of turmeric root lectin: modes of denaturation.

Directory of Open Access Journals (Sweden)

Himadri Biswas

Full Text Available Curcuma longa rhizome lectin, of non-seed origin having antifungal, antibacterial and α-glucosidase inhibitory activities, forms a homodimer with high thermal stability as well as acid tolerance. Size exclusion chromatography and dynamic light scattering show it to be a dimer at pH 7, but it converts to a monomer near pH 2. Circular dichroism spectra and fluorescence emission maxima are virtually indistinguishable from pH 7 to 2, indicating secondary and tertiary structures remain the same in dimer and monomer within experimental error. The tryptophan environment as probed by acrylamide quenching data yielded very similar data at pH 2 and pH 7, implying very similar folding for monomer and dimer. Differential scanning calorimetry shows a transition at 350.3 K for dimer and at 327.0 K for monomer. Thermal unfolding and chemical unfolding induced by guanidinium chloride for dimer are both reversible and can be described by two-state models. The temperatures and the denaturant concentrations at which one-half of the protein molecules are unfolded, are protein concentration-dependent for dimer but protein concentration-independent for monomer. The free energy of unfolding at 298 K was found to be 5.23 Kcal mol-1 and 14.90 Kcal mol-1 for the monomer and dimer respectively. The value of change in excess heat capacity upon protein denaturation (ΔCp is 3.42 Kcal mol-1 K-1 for dimer. The small ΔCp for unfolding of CLA reflects a buried hydrophobic core in the folded dimeric protein. These unfolding experiments, temperature dependent circular dichroism and dynamic light scattering for the dimer at pH 7 indicate its higher stability than for the monomer at pH 2. This difference in stability of dimeric and monomeric forms highlights the contribution of inter-subunit interactions in the former.

Magnetic field induced augmented thermal conduction phenomenon in magneto-nanocolloids

International Nuclear Information System (INIS)

Katiyar, Ajay; Dhar, Purbarun; Nandi, Tandra; Das, Sarit K.

2016-01-01

Magnetic field induced augmented thermal conductivity of magneto-nanocolloids involving nanoparticles, viz. Fe_2O_3, Fe_3O_4, NiO and Co_3O_4 dispersed in different base fluids have been reported. Experiments reveal the augmented thermal transport under external applied magnetic field. A maximum thermal conductivity enhancement ∼114% is attained at 7.0 vol% concentration and 0.1 T magnetic flux density for Fe_3O_4/EG magneto-nanocolloid. However, a maximum ∼82% thermal conductivity enhancement is observed for Fe_3O_4/kerosene magneto-nanocolloid for the same concentration but relatively at low magnetic flux density (∼0.06 T). Thereby, a strong effect of fluid as well as particle physical properties on the chain formation propensity, leading to enhanced conduction, in such systems is observed. Co_3O_4 nanoparticles show insignificant effect on the thermal conductivity enhancement of MNCs due to their minimal magnetic moment. A semi-empirical approach has been proposed to understand the mechanism and physics behind the thermal conductivity enhancement under external applied magnetic field, in tune with near field magnetostatic interactions as well as Neel relaxivity of the magnetic nanoparticles. Furthermore, the model is able to predict the phenomenon of enhanced thermal conductivity as a function of physical parameters and shows good agreement with the experimental observations. - Highlights: • Heat conduction in magneto-nanocolloids augments tremendously under magnetic field. • Oxide nanoparticles of Fe, Ni and Co dispersed in variant base fluids are used. • Enhancement in heat conduction is due to the formation of thermally conductive chains. • Proposed semi-empirical model shows good agreement with the experimental results.

Solar thermal - the new dynamics

International Nuclear Information System (INIS)

2017-01-01

This booklet is intended to engineering consultants and construction professionals and aims at showing them the real interest of solar thermal energy. It notably highlights the very high efficiency which can be reached, the high performance value compared to gas, the high rank of solar thermal energy in terms of profitability over a 20-year period, the fact that solar thermal energy is almost always the most economic solution for buildings and the less expensive in comparison with non renewable energies. It outlines that, as far as purchase is concerned, solar thermal energy is more than competitive, is also a leader as far as financing issues are concerned. It finally briefly describes how the SOCOL initiative can be a support at any step of a solar thermal project

Influence of TRPV1 on diabetes-induced alterations in thermal pain sensitivity

Directory of Open Access Journals (Sweden)

Pauza Mary E

2008-03-01

Full Text Available Abstract A common complication associated with diabetes is painful or painless diabetic peripheral neuropathy (DPN. The mechanisms and determinants responsible for these peripheral neuropathies are poorly understood. Using both streptozotocin (STZ-induced and transgene-mediated murine models of type 1 diabetes (T1D, we demonstrate that Transient Receptor Potential Vanilloid 1 (TRPV1 expression varies with the neuropathic phenotype. We have found that both STZ- and transgene-mediated T1D are associated with two distinct phases of thermal pain sensitivity that parallel changes in TRPV1 as determined by paw withdrawal latency (PWL. An early phase of hyperalgesia and a late phase of hypoalgesia are evident. TRPV1-mediated whole cell currents are larger and smaller in dorsal root ganglion (DRG neurons collected from hyperalgesic and hypoalgesic mice. Resiniferatoxin (RTX binding, a measure of TRPV1 expression is increased and decreased in DRG and paw skin of hyperalgesic and hypoalgesic mice, respectively. Immunohistochemical labeling of spinal cord lamina I and II, dorsal root ganglion (DRG, and paw skin from hyperalgesic and hypoalgesic mice reveal increased and decreased TRPV1 expression, respectively. A role for TRPV1 in thermal DPN is further suggested by the failure of STZ treatment to influence thermal nociception in TRPV1 deficient mice. These findings demonstrate that altered TRPV1 expression and function contribute to diabetes-induced changes in thermal perception.

Curcumin prevents cisplatin-induced renal alterations in mitochondrial bioenergetics and dynamic.

Science.gov (United States)

Ortega-Domínguez, Bibiana; Aparicio-Trejo, Omar Emiliano; García-Arroyo, Fernando E; León-Contreras, Juan Carlos; Tapia, Edilia; Molina-Jijón, Eduardo; Hernández-Pando, Rogelio; Sánchez-Lozada, Laura Gabriela; Barrera-Oviedo, Diana; Pedraza-Chaverri, José

2017-09-01

Cisplatin is widely used as chemotherapeutic agent for treatment of diverse types of cancer, however, acute kidney injury (AKI) is an important side effect of this treatment. Diverse mechanisms have been involved in cisplatin-induced AKI, such as oxidative stress, apoptosis and mitochondrial damage. On the other hand, curcumin is a polyphenol extracted from the rhizome of Curcuma longa L. Previous studies have shown that curcumin protects against the cisplatin-induced AKI; however, it is unknown whether curcumin can reduce alterations in mitochondrial bioenergetics and dynamic in this model. It was found that curcumin prevents cisplatin-induced: (a) AKI and (b) alterations in the following mitochondrial parameters: bioenergetics, ultrastructure, hydrogen peroxide production and dynamic. In fact, curcumin prevented the increase of mitochondrial fission 1 protein (FIS1), the decrease of optic atrophy 1 protein (OPA1) and the decrease of NAD + -dependent deacetylase sirtuin-3 (SIRT3), a mitochondrial dynamic regulator as well as the increase in the mitophagy associated proteins parkin and phosphatase and tensin homologue (PTEN)-induced putative kinase protein 1 (PINK1). In conclusion, the protective effect of curcumin in cisplatin-induced AKI was associated with the prevention of the alterations in mitochondrial bioenergetics, ultrastructure, redox balance, dynamic, and SIRT3 levels. Copyright © 2017 Elsevier Ltd. All rights reserved.

Addressing Thermal and Performance Variability Issues in Dynamic Processors

Energy Technology Data Exchange (ETDEWEB)

Yoshii, Kazutomo [Argonne National Lab. (ANL), Argonne, IL (United States); Llopis, Pablo [Univ. Carlos III de Madrid (Spain); Zhang, Kaicheng [Northwestern Univ., Evanston, IL (United States); Luo, Yingyi [Northwestern Univ., Evanston, IL (United States); Ogrenci-Memik, Seda [Northwestern Univ., Evanston, IL (United States); Memik, Gokhan [Northwestern Univ., Evanston, IL (United States); Sankaran, Rajesh [Argonne National Lab. (ANL), Argonne, IL (United States); Beckman, Pete [Argonne National Lab. (ANL), Argonne, IL (United States)

2017-03-01

As CMOS scaling nears its end, parameter variations (process, temperature and voltage) are becoming a major concern. To overcome parameter variations and provide stability, modern processors are becoming dynamic, opportunistically adjusting voltage and frequency based on thermal and energy constraints, which negatively impacts traditional bulk-synchronous parallelism-minded hardware and software designs. As node-level architecture is growing in complexity, implementing variation control mechanisms only with hardware can be a challenging task. In this paper we investigate a software strategy to manage hardwareinduced variations, leveraging low-level monitoring/controlling mechanisms.

Nuclear dynamics in heavy ion induced fusion-fission reactions

International Nuclear Information System (INIS)

Kapoor, S.S.

1992-01-01

Heavy ion induced fission and fission-like reactions evolve through a complex nuclear dynamics encountered in the medium energy nucleus-nucleus collisions. In the recent years, measurements of the fragment-neutron and fragment-charged particle angular correlations in heavy ion induced fusion-fission reactions, have provided new information on the dynamical times of nuclear deformations of the initial dinuclear complex to the fission saddle point and the scission point. From the studies of fragment angular distributions in heavy ion induced fission it has been possible to infer the relaxation times of the dinuclear complex in the K-degree of freedom and our recent measurements on the entrance channel dependence of fragment anisotropies have provided an experimental signature of the presence of fissions before K-equilibration. This paper reviews recent experimental and theoretical status of the above studies with particular regard to the questions relating to dynamical times, nuclear dissipation and the effect of nuclear dissipation on the K-distributions at the fission saddle in completely equilibrated compound nucleus. (author). 19 refs., 9 figs

Tuning the thermal conductivity of silicon carbide by twin boundary: a molecular dynamics study

International Nuclear Information System (INIS)

Liu, Qunfeng; Wang, Liang; Shen, Shengping; Luo, Hao

2017-01-01

Silicon carbide (SiC) is a semiconductor with excellent mechanical and physical properties. We study the thermal transport in SiC by using non-equilibrium molecular dynamics simulations. The work is focused on the effects of twin boundaries and temperature on the thermal conductivity of 3C-SiC. We find that compared to perfect SiC, twinned SiC has a markedly reduced thermal conductivity when the twin boundary spacing is less than 100 nm. The Si–Si twin boundary is more effective to phonon scattering than the C–C twin boundary. We also find that the phonon scattering effect of twin boundary decreases with increasing temperature. Our findings provide insights into the thermal management of SiC-based electronic devices and thermoelectric applications. (paper)

Thermal-Acoustic Fatigue of a Multilayer Thermal Protection System in Combined Extreme Environments

Directory of Open Access Journals (Sweden)

Liu Liu

2014-06-01

Full Text Available In order to ensure integrity of thermal protection system (TPS structure for hypersonic vehicles exposed to severe operating environments, a study is undertaken to investigate the response and thermal-acoustic fatigue damage of a representative multilayer TPS structure under combined thermal and acoustic loads. An unsteady-state flight of a hypersonic vehicle is composed of a series of steady-state snapshots, and for each snapshot an acoustic load is imposed to a static steady-state TPS structure. A multistep thermal-acoustic fatigue damage intensity analysis procedure is given and consists of a heat transfer analysis, a nonlinear thermoelastic analysis, and a random response analysis under a combined loading environment and the fatigue damage intensity has been evaluated with two fatigue analysis techniques. The effects of thermally induced deterministic stress and nondeterministic dynamic stress due to the acoustic loading have been considered in the damage intensity estimation with a maximum stress fatigue model. The results show that the given thermal-acoustic fatigue intensity estimation procedure is a viable approach for life prediction of TPS structures under a typical mission cycle with combined loadings characterized by largely different time-scales. A discussion of the effects of the thermal load, the acoustic load, and fatigue analysis methodology on the fatigue damage intensity has been provided.

Nonlinear dynamic modeling of a V-shaped metal based thermally driven MEMS actuator for RF switches

Science.gov (United States)

Bakri-Kassem, Maher; Dhaouadi, Rached; Arabi, Mohamed; Estahbanati, Shahabeddin V.; Abdel-Rahman, Eihab

2018-05-01

In this paper, we propose a new dynamic model to describe the nonlinear characteristics of a V-shaped (chevron) metallic-based thermally driven MEMS actuator. We developed two models for the thermal actuator with two configurations. The first MEMS configuration has a small tip connected to the shuttle, while the second configuration has a folded spring and a wide beam attached to the shuttle. A detailed finite element model (FEM) and a lumped element model (LEM) are proposed for each configuration to completely characterize the electro-thermal and thermo-mechanical behaviors. The nonlinear resistivity of the polysilicon layer is extracted from the measured current-voltage (I-V) characteristics of the actuator and the simulated corresponding temperatures in the FEM model, knowing the resistivity of the polysilicon at room temperature from the manufacture’s handbook. Both developed models include the nonlinear temperature-dependent material properties. Numerical simulations in comparison with experimental data using a dedicated MEMS test apparatus verify the accuracy of the proposed LEM model to represent the complex dynamics of the thermal MEMS actuator. The LEM and FEM simulation results show an accuracy ranging from a maximum of 13% error down to a minimum of 1.4% error. The actuator with the lower thermal load to air that includes a folded spring (FS), also known as high surface area actuator is compared to the actuator without FS, also known as low surface area actuator, in terms of the I-V characteristics, power consumption, and experimental static and dynamic responses of the tip displacement.

Dynamic model reduction using data-driven Loewner-framework applied to thermally morphing structures

Science.gov (United States)

Phoenix, Austin A.; Tarazaga, Pablo A.

2017-05-01

The work herein proposes the use of the data-driven Loewner-framework for reduced order modeling as applied to dynamic Finite Element Models (FEM) of thermally morphing structures. The Loewner-based modeling approach is computationally efficient and accurately constructs reduced models using analytical output data from a FEM. This paper details the two-step process proposed in the Loewner approach. First, a random vibration FEM simulation is used as the input for the development of a Single Input Single Output (SISO) data-based dynamic Loewner state space model. Second, an SVD-based truncation is used on the Loewner state space model, such that the minimal, dynamically representative, state space model is achieved. For this second part, varying levels of reduction are generated and compared. The work herein can be extended to model generation using experimental measurements by replacing the FEM output data in the first step and following the same procedure. This method will be demonstrated on two thermally morphing structures, a rigidly fixed hexapod in multiple geometric configurations and a low mass anisotropic morphing boom. This paper is working to detail the method and identify the benefits of the reduced model methodology.

Formation dynamics of UV and EUV induced hydrogen plasma

NARCIS (Netherlands)

Dolgov, A.A.; Lee, Christopher James; Yakushev, O.; Lopaev, D.V.; Abrikosov, A.; Krivtsun, V.M.; Zotovich, A.; Bijkerk, F.

2014-01-01

The comparative study of the dynamics of ultraviolet (UV) and extreme ultraviolet (EUV) induced hydrogen plasma was performed. It was shown that for low H2 pressures and bias voltages, the dynamics of the two plasmas are significantly different. In the case of UV radiation, the plasma above the

Thermal Structure and Mantle Dynamics of Rocky Exoplanets

Science.gov (United States)

Wagner, F. W.; Tosi, N.; Hussmann, H.; Sohl, F.

2011-12-01

The confirmed detections of CoRoT-7b and Kepler-10b reveal that rocky exoplanets exist. Moreover, recent theoretical studies suggest that small planets beyond the Solar System are indeed common and many of them will be discovered by increasingly precise observational surveys in the years ahead. The knowledge about the interior structure and thermal state of exoplanet interiors provides crucial theoretical input not only for classification and characterization of individual planetary bodies, but also to better understand the origin and evolution of the Solar System and the Earth in general. These developments and considerations have motivated us to address several questions concerning thermal structure and interior dynamics of terrestrial exoplanets. In the present study, depth-dependent structural models of solid exoplanet interiors have been constructed in conjunction with a mixing length approach to calculate self-consistently the radial distribution of temperature and heat flux. Furthermore, 2-D convection simulations using the compressible anelastic approximation have been carried through to examine the effect of thermodynamic quantities (e.g., thermal expansivity) on mantle convection pattern within rocky planets more massive than the Earth. In comparison to parameterized convection models, our calculated results predict generally hotter planetary interiors, which are mainly attributed to a viscosity-regulating feedback mechanism involving temperature and pressure. We find that density and thermal conductivity increase with depth by a factor of two to three, however, thermal expansivity decreases by more than an order of magnitude across the mantle for planets as massive as CoRoT-7b or Kepler-10b. The specific heat capacity is observed to stay almost constant over an extended region of the lower mantle. The planform of mantle convection is strongly modified in the presence of depth-dependent thermodynamic quantities with hot upwellings (plumes) rising across

Magnetic field induced augmented thermal conduction phenomenon in magneto-nanocolloids

Energy Technology Data Exchange (ETDEWEB)

Katiyar, Ajay, E-mail: ajay_cim@rediffmail.com [Research and Innovation Centre (DRDO), Indian Institute of Technology Madras Research Park, Chennai 600 113 (India); Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India); Dhar, Purbarun, E-mail: purbarun@iitrpr.ac.in [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India); Nandi, Tandra, E-mail: tandra_n@rediffmail.com [Defence Materials and Stores Research and Development Establishment (DRDO), G.T. Road, Kanpur 208 013 (India); Das, Sarit K., E-mail: skdas@iitrpr.ac.in [Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India)

2016-12-01

Magnetic field induced augmented thermal conductivity of magneto-nanocolloids involving nanoparticles, viz. Fe{sub 2}O{sub 3}, Fe{sub 3}O{sub 4}, NiO and Co{sub 3}O{sub 4} dispersed in different base fluids have been reported. Experiments reveal the augmented thermal transport under external applied magnetic field. A maximum thermal conductivity enhancement ∼114% is attained at 7.0 vol% concentration and 0.1 T magnetic flux density for Fe{sub 3}O{sub 4}/EG magneto-nanocolloid. However, a maximum ∼82% thermal conductivity enhancement is observed for Fe{sub 3}O{sub 4}/kerosene magneto-nanocolloid for the same concentration but relatively at low magnetic flux density (∼0.06 T). Thereby, a strong effect of fluid as well as particle physical properties on the chain formation propensity, leading to enhanced conduction, in such systems is observed. Co{sub 3}O{sub 4} nanoparticles show insignificant effect on the thermal conductivity enhancement of MNCs due to their minimal magnetic moment. A semi-empirical approach has been proposed to understand the mechanism and physics behind the thermal conductivity enhancement under external applied magnetic field, in tune with near field magnetostatic interactions as well as Neel relaxivity of the magnetic nanoparticles. Furthermore, the model is able to predict the phenomenon of enhanced thermal conductivity as a function of physical parameters and shows good agreement with the experimental observations. - Highlights: • Heat conduction in magneto-nanocolloids augments tremendously under magnetic field. • Oxide nanoparticles of Fe, Ni and Co dispersed in variant base fluids are used. • Enhancement in heat conduction is due to the formation of thermally conductive chains. • Proposed semi-empirical model shows good agreement with the experimental results.

Coupled Monitoring and Inverse Modeling to Investigate Surface - Subsurface Hydrological and Thermal Dynamics in the Arctic Tundra

Science.gov (United States)

Tran, A. P.; Dafflon, B.; Hubbard, S. S.; Bisht, G.; Peterson, J.; Ulrich, C.; Romanovsky, V. E.; Kneafsey, T. J.; Wu, Y.

2015-12-01

Quantitative characterization of the soil surface-subsurface hydrological and thermal processes is essential as they are primary factors that control the biogeochemical processes, ecological landscapes and greenhouse gas fluxes. In the Artic region, the surface-subsurface hydrological and thermal regimes co-interact and are both largely influenced by soil texture and soil organic content. In this study, we present a coupled inversion scheme that jointly inverts hydrological, thermal and geophysical data to estimate the vertical profiles of clay, sand and organic contents. Within this inversion scheme, the Community Land Model (CLM4.5) serves as a forward model to simulate the land-surface energy balance and subsurface hydrological-thermal processes. Soil electrical conductivity (from electrical resistivity tomography), temperature and water content are linked together via petrophysical and geophysical models. Particularly, the inversion scheme accounts for the influences of the soil organic and mineral content on both of the hydrological-thermal dynamics and the petrophysical relationship. We applied the inversion scheme to the Next Generation Ecosystem Experiments (NGEE) intensive site in Barrow, AK, which is characterized by polygonal-shaped arctic tundra. The monitoring system autonomously provides a suite of above-ground measurements (e.g., precipitation, air temperature, wind speed, short-long wave radiation, canopy greenness and eddy covariance) as well as below-ground measurements (soil moisture, soil temperature, thaw layer thickness, snow thickness and soil electrical conductivity), which complement other periodic, manually collected measurements. The preliminary results indicate that the model can well reproduce the spatiotemporal dynamics of the soil temperature, and therefore, accurately predict the active layer thickness. The hydrological and thermal dynamics are closely linked to the polygon types and polygon features. The results also enable the

Thermal fatigue. Fluid-structure interaction at thermal mixing events

International Nuclear Information System (INIS)

Schuler, X.; Herter, K.H.; Moogk, S.; Laurien, E.; Kloeren, D.; Kulenovic, R.; Kuschewski, M.

2012-01-01

In the framework of the network research project ''Thermal Fatigue - Basics of the system-, outflow- and material-characteristics of piping under thermal fatigue'' funded by the German Federal Ministry of Education and Research (BMBF) fundamental numerical and experimental investigations on the material behaviour under transient thermal-mechanical stress conditions (high cycle fatigue - HCF) are carried out. The project's background and its network of scientific working groups with their individual working tasks are briefly introduced. The main focus is especially on the joint research tasks within the sub-projects of MPA and IKE which are dealing with thermal mixing of flows in a T-junction configuration and the fluidstructure- interactions (FSI). Therefore, experiments were performed with the newly established FSI test facility at MPA which enables single-phase flow experiments of water in typical power plant piping diameters (DN40 and DN80) at high pressure (maximum 75 bar) and temperatures (maximum 280 C). The experimental results serve as validation data base for numerical modelling of thermal flow mixing by means of thermo-fluid dynamics simulations applying CFD techniques and carried out by IKE as well as for modelling of thermal and mechanical loads of the piping structure by structural mechanics simulations with FEM methods which are executed by MPA. The FSI test facility will be described inclusively the applied measurement techniques, e. g. in particular the novel near-wall LED-induced Fluorescence method for non-intrusive flow temperature measurements. First experimental data and numerical results from CFD and FEM simulations of the thermal mixing of flows in the T-junction are presented.

Numerical analysis of the thermally induced flow in a strongly rotating gas centrifuge

Energy Technology Data Exchange (ETDEWEB)

Novelli, P.

1982-04-01

The present work is concerned with the numerical analysis of the thermally induced flow in a rapidly gas centrifuge. The primary purpose for this work is to investigate the dependence of the flow field on the thermal boundary conditions, angular speed, aspect ratio of the cylinder, holdup. Some of our results are compared with the predictions of asymptotic theories, particularly those of Sakurai-Mtsuda and Brouwers, and with the numerical results of Dickinson-Jones.

Laser-Induced Thermal Acoustics Theory and Expected Experimental Errors when Applied to a Scramjet Isolator Model

Science.gov (United States)

Middleton, Troy F.; Balla, Robert Jeffrey; Baurle, Robert A.; Wilson, Lloyd G.

2011-01-01

A scramjet isolator model test apparatus is being assembled in the Isolator Dynamics Research Lab (IDRL) at the NASA Langley Research Center in Hampton, Virginia. The test apparatus is designed to support multiple measurement techniques for investigating the flow field in a scramjet isolator model. The test section is 1-inch high by 2-inch wide by 24-inch long and simulates a scramjet isolator with an aspect ratio of two. Unheated, dry air at a constant stagnation pressure and temperature is delivered to the isolator test section through a Mach 2.5 planar nozzle. The isolator test section is mechanically back-pressured to contain the resulting shock train within the 24-inch isolator length and supports temperature, static pressure, and high frequency pressure measurements at the wall. Additionally, nonintrusive methods including laser-induced thermal acoustics (LITA), spontaneous Raman scattering, particle image velocimetry, and schlieren imaging are being incorporated to measure off-wall fluid dynamic, thermodynamic, and transport properties of the flow field. Interchangeable glass and metallic sidewalls and optical access appendages permit making multiple measurements simultaneously. The measurements will be used to calibrate computational fluid dynamics turbulence models and characterize the back-pressured flow of a scramjet isolator. This paper describes the test apparatus, including the optical access appendages; the physics of the LITA method; and estimates of LITA measurement uncertainty for measurements of the speed of sound and temperature.

Thermal effects induced by laser ablation in non-homogeneous limestone covered by an impurity layer

Science.gov (United States)

Cocean, Alexandru; Pelin, Vasile; Cazacu, Marius Mihai; Cocean, Iuliana; Sandu, Ion; Gurlui, Silviu; Iacomi, Felicia

2017-12-01

This paper reports preliminary results concerning thermal effects induced by urban/industrial air pollutants deposited on a limestone rock when heated by pulsed laser in the cleaning process. The process of laser cleaning treatment of the crust is simulated using COMSOL Multiphysics 4.4, finite element analysis software. Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy and Laser Induced Breakdown Spectroscopy techniques have been used to analyze the chemical composition of the samples. Two elements found as being present into the dust and in the crust, such as iron and magnesium particles are used for simulation in COMSOL. Therefore, the profiles heat evolutions on the crust surface and inside limestone are obtained as thermal interactions between the three components (iron, magnesium and limestone), simulating the non-homogeneous materials. It has been observed that iron impurities caused by the dust deposition may damage the limestone through a process of overheating, as a consequence of a high thermal conduction phenomenon, recorded for the region with iron impurities and sizes of micrometric order are localized. The thermal contact between the three components results in plots that reflect their thermal interactions.

Thermal Fluid-Dynamic Study for the thermal control of the new ALICE Central Detectors

CERN Document Server

AUTHOR|(CDS)2216237

The Inner Tracking System Detector of the ALICE Experiment at CERN laboratory will be replaced in 2020 with a new Detector. It will have to provide, among others, higher spatial resolution, higher tracking precision and faster data read-out. These goals will be attained thanks to new pixel sensors chips and new electronic components, which will have a high impact in terms of dissipated heat. Therefore, one of the critical aspects for the success of the Upgrade project is the design of the Detector cooling system. This thesis work has been developed at CERN in Geneva in close contact with the group responsible for the Mechanics and Cooling of the Detector. The aim of the thermal fluid dynamic study devised is to deliver to the group a reliable and accurate description of the air flow inside the New Inner Tracking System Detector. After a first part of problem definition and design study, a Computational Fluid Dynamic (CFD) analysis has been developed with the ANSYS Fluent software. The CFD model built in this ...

Dynamic response of SWEMAAIR 300 thermal anemometer with SWA-01 velocity transducer

Energy Technology Data Exchange (ETDEWEB)

Melikov, A K; Popiolek, Z

1996-06-01

The objective of this study is to identify the dynamic response of the SwemaAir 300 thermal anemometer to downward airflow with different amplitude and frequency of the velocity fluctuations and changing direction. An important aim is to find to what extend the accuracy of the velocity measurements is effected at the above described conditions. (au)

Dynamic Thermal Analysis of DFIG Rotor-side Converter during Balanced Grid Fault

DEFF Research Database (Denmark)

Zhou, Dao; Blaabjerg, Frede

2014-01-01

and the rotor voltage during the balanced grid fault is firstly addressed. By using the traditional demagnetizing control, the damping of the stator flux and the safety operation area are theoretically evaluated with various amounts of demagnetizing current. It is observed that the higher demagnetizing current...... leads to faster stator flux damping and lower induced rotor voltage, but it brings higher loss as well as the thermal cycling of the power device. Based on the simulation of the stator flux evolution and the thermal behavior of each power semiconductor, it is concluded that there is a trade...

Does thermal ecology influence dynamics of side-blotched lizards and their micro-parasites?

Science.gov (United States)

Paranjpe, Dhanashree A; Medina, Dianna; Nielsen, Erica; Cooper, Robert D; Paranjpe, Sharayu A; Sinervo, Barry

2014-07-01

Hosts and parasites form interacting populations that influence each other in multiple ways. Their dynamics can also be influenced by environmental and ecological factors. We studied host-parasite dynamics in a previously unexplored study system: side-blotched lizards and their micro-parasites. Compared with uninfected lizards, the infected lizards elected to bask at lower temperatures that were outside their range of preferred temperatures. Infected lizards also were not as precise as uninfected lizards in maintaining their body temperatures within a narrow range. At the ecological scale, areas with higher infection rates coincided with more thermally heterogeneous microhabitats as well as with the areas where lizards tended to live longer. Thermal heterogeneity of lizards' microhabitats may provide important clues to the spatial and temporal distribution of infections. © The Author 2014. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.

Dynamic electro-thermal modeling of all-vanadium redox flow battery with forced cooling strategies

International Nuclear Information System (INIS)

Wei, Zhongbao; Zhao, Jiyun; Xiong, Binyu

2014-01-01

Highlights: • A dynamic electro-thermal model is proposed for VRB with forced cooling. • The Foster network is adopted to model the battery cooling process. • Both the electrolyte temperature and terminal voltage can be accurately predicted. • The flow rate of electrolyte and coolant significantly impact battery performance. - Abstract: The present study focuses on the dynamic electro-thermal modeling for the all-vanadium redox flow battery (VRB) with forced cooling strategies. The Foster network is adopted to dynamically model the heat dissipation of VRB with heat exchangers. The parameters of Foster network are extracted by fitting the step response of it to the results of linearized CFD model. Then a complete electro-thermal model is proposed by coupling the heat generation model, Foster network and electrical model. Results show that the established model has nearly the same accuracy with the nonlinear CFD model in electrolyte temperature prediction but drastically improves the computational efficiency. The modeled terminal voltage is also benchmarked with the experimental data under different current densities. The electrolyte temperature is found to be significantly influenced by the flow rate of coolant. As compared, although the electrolyte flow rate has unremarkable impact on electrolyte temperature, its effect on system pressure drop and battery efficiency is significant. Increasing the electrolyte flow rate improves the coulombic efficiency, voltage efficiency and energy efficiency simultaneously but at the expense of higher pump power demanded. An optimal flow rate exists for each operating condition to maximize the system efficiency

A Lumped Thermal Model Including Thermal Coupling and Thermal Boundary Conditions for High Power IGBT Modules

DEFF Research Database (Denmark)

Bahman, Amir Sajjad; Ma, Ke; Blaabjerg, Frede

2018-01-01

Detailed thermal dynamics of high power IGBT modules are important information for the reliability analysis and thermal design of power electronic systems. However, the existing thermal models have their limits to correctly predict these complicated thermal behavior in the IGBTs: The typically used...... thermal model based on one-dimensional RC lumps have limits to provide temperature distributions inside the device, moreover some variable factors in the real-field applications like the cooling and heating conditions of the converter cannot be adapted. On the other hand, the more advanced three......-dimensional thermal models based on Finite Element Method (FEM) need massive computations, which make the long-term thermal dynamics difficult to calculate. In this paper, a new lumped three-dimensional thermal model is proposed, which can be easily characterized from FEM simulations and can acquire the critical...

Laser-induced vibrational dynamics of ozone in solid argon

DEFF Research Database (Denmark)

Hansen, Flemming Yssing; Amstrup, B.; Henriksen, Niels Engholm

1997-01-01

We consider the vibrational dynamics, induced by an intense infrared laser pulse, in an ozone molecule with isotopic substitution, that is, (OOO)-O-16-O-16-O-18 and compare the dynamics in the gas phase and in solid ar on. not perturbed by argon on a time-scale of a few picoseconds and selective...

Thermal conductivity of a h-BCN monolayer.

Science.gov (United States)

Zhang, Ying-Yan; Pei, Qing-Xiang; Liu, Hong-Yuan; Wei, Ning

2017-10-18

A hexagonal graphene-like boron-carbon-nitrogen (h-BCN) monolayer, a new two-dimensional (2D) material, has been synthesized recently. Herein we investigate for the first time the thermal conductivity of this novel 2D material. Using molecular dynamics simulations based on the optimized Tersoff potential, we found that the h-BCN monolayers are isotropic in the basal plane with close thermal conductivity magnitudes. Though h-BCN has the same hexagonal lattice as graphene and hexagonal boron nitride (h-BN), it exhibits a much lower thermal conductivity than the latter two materials. In addition, the thermal conductivity of h-BCN monolayers is found to be size-dependent but less temperature-dependent. Modulation of the thermal conductivity of h-BCN monolayers can also be realized by strain engineering. Compressive strain leads to a monotonic decrease in the thermal conductivity while the tensile strain induces an up-then-down trend in the thermal conductivity. Surprisingly, the small tensile strain can facilitate the heat transport of the h-BCN monolayers.

Parvovirus induced alterations in nuclear architecture and dynamics.

Directory of Open Access Journals (Sweden)

Teemu O Ihalainen

2009-06-01

Full Text Available The nucleus of interphase eukaryotic cell is a highly compartmentalized structure containing the three-dimensional network of chromatin and numerous proteinaceous subcompartments. DNA viruses induce profound changes in the intranuclear structures of their host cells. We are applying a combination of confocal imaging including photobleaching microscopy and computational methods to analyze the modifications of nuclear architecture and dynamics in parvovirus infected cells. Upon canine parvovirus infection, expansion of the viral replication compartment is accompanied by chromatin marginalization to the vicinity of the nuclear membrane. Dextran microinjection and fluorescence recovery after photobleaching (FRAP studies revealed the homogeneity of this compartment. Markedly, in spite of increase in viral DNA content of the nucleus, a significant increase in the protein mobility was observed in infected compared to non-infected cells. Moreover, analysis of the dynamics of photoactivable capsid protein demonstrated rapid intranuclear dynamics of viral capsids. Finally, quantitative FRAP and cellular modelling were used to determine the duration of viral genome replication. Altogether, our findings indicate that parvoviruses modify the nuclear structure and dynamics extensively. Intranuclear crowding of viral components leads to enlargement of the interchromosomal domain and to chromatin marginalization via depletion attraction. In conclusion, parvoviruses provide a useful model system for understanding the mechanisms of virus-induced intranuclear modifications.

Modeling the effects of the variability of temperature-related dynamic viscosity on the thermal-affected zone of groundwater heat-pump systems

Science.gov (United States)

Lo Russo, Stefano; Taddia, Glenda; Cerino Abdin, Elena

2018-01-01

Thermal perturbation in the subsurface produced in an open-loop groundwater heat pump (GWHP) plant is a complex transport phenomenon affected by several factors, including the exploited aquifer's hydrogeological and thermal characteristics, well construction features, and the temporal dynamics of the plant's groundwater abstraction and reinjection system. Hydraulic conductivity has a major influence on heat transport because plume propagation, which occurs primarily through advection, tends to degrade following conductive heat transport and convection within moving water. Hydraulic conductivity is, in turn, influenced by water reinjection because the dynamic viscosity of groundwater varies with temperature. This paper reports on a computational analysis conducted using FEFLOW software to quantify how the thermal-affected zone (TAZ) is influenced by the variation in dynamic viscosity due to reinjected groundwater in a well-doublet scheme. The modeling results demonstrate non-negligible groundwater dynamic-viscosity variation that affects thermal plume propagation in the aquifer. This influence on TAZ calculation was enhanced for aquifers with high intrinsic permeability and/or substantial temperature differences between abstracted and post-heat-pump-reinjected groundwater.

Molecular dynamics calculations of the thermal expansion properties and melting points of Si and Ge

International Nuclear Information System (INIS)

Timon, V; Brand, S; Clark, S J; Abram, R A

2006-01-01

The thermal expansion properties and melting points of silicon and germanium are calculated using molecular dynamics simulations within the density functional theory framework. An isothermal-isobaric (NPT) ensemble is considered in a periodic system with a relatively small number of particles per unit cell to obtain the thermal expansion data over a range of temperatures, and it is found that the calculated thermal expansion coefficients and bond lengths agree well with experimental data. Also, the positions of discontinuities in the potential energy as a function of temperature are in good agreement with the experimental melting points

Spin-pump-induced spin transport in a thermally evaporated pentacene film

Energy Technology Data Exchange (ETDEWEB)

Tani, Yasuo; Shikoh, Eiji, E-mail: shikoh@elec.eng.osaka-cu.ac.jp [Graduate School of Engineering, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585 (Japan); Teki, Yoshio [Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585 (Japan)

2015-12-14

We report the spin-pump-induced spin transport properties of a pentacene film prepared by thermal evaporation. In a palladium(Pd)/pentacene/Ni{sub 80}Fe{sub 20} tri-layer sample, a pure spin-current is generated in the pentacene layer by the spin-pumping of Ni{sub 80}Fe{sub 20}, which is independent of the conductance mismatch problem in spin injection. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current at room temperature in pentacene films prepared by thermal evaporation.

Thermal conductivity enhancement of paraffin by adding boron nitride nanostructures: A molecular dynamics study

International Nuclear Information System (INIS)

Lin, Changpeng; Rao, Zhonghao

2017-01-01

Highlights: • Different contributions to thermal conductivity are obtained. • Thermal conductivity of paraffin could be improved by boron nitride. • Crystallization effect from boron nitride was the key factor. • Paraffin nanocomposite is the desirable candidate for thermal energy storage. - Abstract: While paraffin is widely used in thermal energy storage today, its low thermal conductivity has become a bottleneck for the further applications. Here, we construct two kinds of paraffin-based phase change material nanocomposites through introducing boron nitride (BN) nanostructures into n-eicosane to enhance the thermal conductivity. Molecular dynamics (MD) simulation was adopted to estimate their thermal conductivities and related thermal properties. The results indicate that, after adding BN nanostructures, the latent heat of composites is reduced compared with the pure paraffin and they both show a glass-like thermal conductivity which increases as the temperature rises. This happens because the increasing temperature leads to gradually smaller inconsistency in vibrational density of state along three directions and increasingly significant overlaps among them. Furthermore, by decomposing the thermal conductivity, it is found that the major contribution to the overall thermal conductivity comes from BN nanostructures, while the contribution of n-eicosane is insignificant. Though the thermal conductivity from n-eicosane term is small, it has been improved greatly compared with amorphous state of n-eicosane, mainly due to the crystallization effects from BN nanostructures. This work will provide microscopic views and insights into the thermal mechanism of paraffin and offer effective guidances to enhance the thermal conductivity.

Three-Dimensional Graphene Foam Induces Multifunctionality in Epoxy Nanocomposites by Simultaneous Improvement in Mechanical, Thermal, and Electrical Properties.

Science.gov (United States)

Embrey, Leslie; Nautiyal, Pranjal; Loganathan, Archana; Idowu, Adeyinka; Boesl, Benjamin; Agarwal, Arvind

2017-11-15

Three-dimensional (3D) macroporous graphene foam based multifunctional epoxy composites are developed in this study. Facile dip-coating and mold-casting techniques are employed to engineer microstructures with tailorable thermal, mechanical, and electrical properties. These processing techniques allow capillarity-induced equilibrium filling of graphene foam branches, creating epoxy/graphene interfaces with minimal separation. Addition of 2 wt % graphene foam enhances the glass transition temperature of epoxy from 106 to 162 °C, improving the thermal stability of the polymer composite. Graphene foam aids in load-bearing, increasing the ultimate tensile strength by 12% by merely 0.13 wt % graphene foam in an epoxy matrix. Digital image correlation (DIC) analysis revealed that the graphene foam cells restrict and confine the deformation of the polymer matrix, thereby enhancing the load-bearing capability of the composite. Addition of 0.6 wt % graphene foam also enhances the flexural strength of the pure epoxy by 10%. A 3D network of graphene branches is found to suppress and deflect the cracks, arresting mechanical failure. Dynamic mechanical analysis (DMA) of the composites demonstrated their vibration damping capability, as the loss tangent (tan δ) jumps from 0.1 for the pure epoxy to 0.24 for ∼2 wt % graphene foam-epoxy composite. Graphene foam branches also provide seamless pathways for electron transfer, which induces electrical conductivity exceeding 450 S/m in an otherwise insulator epoxy matrix. The epoxy-graphene foam composite exhibits a gauge factor as high as 4.1, which is twice the typical gauge factor for the most common metals. Simultaneous improvement in thermal, mechanical, and electrical properties of epoxy due to 3D graphene foam makes epoxy-graphene foam composite a promising lightweight and multifunctional material for aiding load-bearing, electrical transport, and motion sensing in aerospace, automotive, robotics, and smart device structures.

Effects of iron on the lattice thermal conductivity of Earth's deep mantle and implications for mantle dynamics.

Science.gov (United States)

Hsieh, Wen-Pin; Deschamps, Frédéric; Okuchi, Takuo; Lin, Jung-Fu

2018-04-17

Iron may critically influence the physical properties and thermochemical structures of Earth's lower mantle. Its effects on thermal conductivity, with possible consequences on heat transfer and mantle dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-mantle ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8-10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-mantle thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower mantle. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.

Pressure-induced reversal between thermal contraction and expansion in ferroelectric PbTiO3.

Science.gov (United States)

Zhu, Jinlong; Zhang, Jianzhong; Xu, Hongwu; Vogel, Sven C; Jin, Changqing; Frantti, Johannes; Zhao, Yusheng

2014-01-15

Materials with zero/near zero thermal expansion coefficients are technologically important for applications in thermal management and engineering. To date, this class of materials can only be produced by chemical routes, either by changing chemical compositions or by composting materials with positive and negative thermal expansion. Here, we report for the first time a physical route to achieve near zero thermal expansion through application of pressure. In the stability field of tetragonal PbTiO3 we observed pressure-induced reversals between thermal contraction and expansion between ambient pressure and 0.9 GPa. This hybrid behavior leads to a mathematically infinite number of crossover points in the pressure-volume-temperature space and near-zero thermal expansion coefficients comparable to or even smaller than those attained by chemical routes. The observed pressures for this unusual phenomenon are within a small range of 0.1-0.9 GPa, potentially feasible for designing stress-engineered materials, such as thin films and nano-crystals, for thermal management applications.

Effects of thermal cracking on the dynamic behavior of reinforced concrete containment structures

International Nuclear Information System (INIS)

Castellani, A.; Fontana, A.

1977-01-01

Thick concrete cylinders acted on by horizontal dynamic forces are analyzed. According to the dimensions they may simulate a containment structure or a reactor core support. In particular, the effects of thermal cracking on their dynamic behavior are investigated; up to now the tests are confined to vertical cracking which is likely to appear under a thermal gradient of approximately 35 to 45 0 C on the wall. At higher temperatures, the number and extension of these cracks increase, till a stabilized crack pattern is reached. This is the main subject of the present investigation. The horizontal forces call for a shear transmission along the crack. According to the literature, shear stresses can be transmitted by aggregate interlock, by shear friction, and by the dowel action provided by horizontal reinforcement. These effects may accomodate the shear transmission along the crack required to resist a given distribution of horizontal forces. On the other hand, the shear rigidity of the structure may be negatively affected by the cracking, depending on the crack width and distribution and on the amplitude of the applied forces. In this case a dynamic behavior of the structure is to be analyzed with proper consideration to the existing cracking

Decadal trends and common dynamics of the bio-optical and thermal characteristics of the African Great Lakes.

Directory of Open Access Journals (Sweden)

Steven Loiselle

Full Text Available The Great Lakes of East Africa are among the world's most important freshwater ecosystems. Despite their importance in providing vital resources and ecosystem services, the impact of regional and global environmental drivers on this lacustrine system remains only partially understood. We make a systematic comparison of the dynamics of the bio-optical and thermal properties of thirteen of the largest African lakes between 2002 and 2011. Lake surface temperatures had a positive trend in all Great Lakes outside the latitude of 0° to 8° south, while the dynamics of those lakes within this latitude range were highly sensitive to global inter-annual climate drivers (i.e. El Niño Southern Oscillation. Lake surface temperature dynamics in nearly all lakes were found to be sensitive to the latitudinal position of the Inter Tropical Convergence Zone. Phytoplankton dynamics varied considerably between lakes, with increasing and decreasing trends. Intra-lake differences in both surface temperature and phytoplankton dynamics occurred for many of the larger lakes. This inter-comparison of bio-optical and thermal dynamics provides new insights into the response of these ecosystems to global and regional drivers.

Equilibrium Limit of Boundary Scattering in Carbon Nanostructures: Molecular Dynamics Calculations of Thermal Transport

Science.gov (United States)

Haskins, Justin; Kinaci, Alper; Sevik, Cem; Cagin, Tahir

2012-01-01

It is widely known that graphene and many of its derivative nanostructures have exceedingly high reported thermal conductivities (up to 4000 W/mK at 300 K). Such attractive thermal properties beg the use of these structures in practical devices; however, to implement these materials while preserving transport quality, the influence of structure on thermal conductivity should be thoroughly understood. For graphene nanostructures, having average phonon mean free paths on the order of one micron, a primary concern is how size influences the potential for heat conduction. To investigate this, we employ a novel technique to evaluate the lattice thermal conductivity from the Green-Kubo relations and equilibrium molecular dynamics in systems where phonon-boundary scattering dominates heat flow. Specifically, the thermal conductivities of graphene nanoribbons and carbon nanotubes are calculated in sizes up to 3 microns, and the relative influence of boundary scattering on thermal transport is determined to be dominant at sizes less than 1 micron, after which the thermal transport largely depends on the quality of the nanostructure interface. The method is also extended to carbon nanostructures (fullerenes) where phonon confinement, as opposed to boundary scattering, dominates, and general trends related to the influence of curvature on thermal transport in these materials are discussed.

Lattice dynamics of lithium oxide

Indian Academy of Sciences (India)

Abstract. Li2O finds several important technological applications, as it is used in solid- state batteries, can be used as a blanket breeding material in nuclear fusion reactors, etc. Li2O exhibits a fast ion phase, characterized by a thermally induced dynamic disorder in the anionic sub-lattice of Li+, at elevated temperatures ...

Effects of deformability and thermal motion of lipid membrane on electroporation: By molecular dynamics simulations

KAUST Repository

Sun, Sheng; Yin, Guangyao; Lee, Yi-Kuen; Wong, Joseph T.Y.; Zhang, Tong-Yi

2011-01-01

Effects of mechanical properties and thermal motion of POPE lipid membrane on electroporation were studied by molecular dynamics simulations. Among simulations in which specific atoms of lipids were artificially constrained at their equilibrium

Contributions to thermal and fluid dynamic problems in nuclear technology

International Nuclear Information System (INIS)

Mueller, U.; Krebs, L.; Rust, K.

1984-02-01

The majority of contributions compiled in this report deals with thermal and fluid dynamic problems in nuclear engineering. Especially problems of heat transfer and cooling are represented which may arise during and afer a loss-of-coolant accident both in light water reactors and in liquid metal cooled fast breeder reactors. Papers on the mass transfer in pressurized water, tribological problems in sodium cooled reactors, the fluid dynamics of pulsed column, and fundamental investigations of convective flows supplement these contributions on problems connected with accidents. Furthermore, a keynote paper presents the individual activities relating to the reliability of reactor components, a field recently included in our research program. Technical solutions to special problems are closely connected to the investigations based on experiments. Therefore, several contributions deal with new developments in technology and measuring techniques. (orig.) [de

Thermally induced degradation of sulfur-containing aliphatic glucosinolates in broccoli sprouts (Brassica oleracea var. italica) and model systems.

Science.gov (United States)

Hanschen, Franziska S; Platz, Stefanie; Mewis, Inga; Schreiner, Monika; Rohn, Sascha; Kroh, Lothar W

2012-03-07

Processing reduces the glucosinolate (GSL) content of plant food, among other aspects due to thermally induced degradation. Since there is little information about the thermal stability of GSL and formation of corresponding breakdown products, the thermally induced degradation of sulfur-containing aliphatic GSL was studied in broccoli sprouts and with isolated GSL in dry medium at different temperatures as well as in aqueous medium at different pH values. Desulfo-GSL have been analyzed with HPLC-DAD, while breakdown products were estimated using GC-FID. Whereas in the broccoli sprouts structural differences of the GSL with regard to thermal stability exist, the various isolated sulfur-containing aliphatic GSL degraded nearly equally and were in general more stable. In broccoli sprouts, methylsulfanylalkyl GSL were more susceptible to degradation at high temperatures, whereas methylsulfinylalkyl GSL were revealed to be more affected in aqueous medium under alkaline conditions. Besides small amounts of isothiocyanates, the main thermally induced breakdown products of sulfur-containing aliphatic GSL were nitriles. Although they were most rapidly formed at comparatively high temperatures under dry heat conditions, their highest concentrations were found after cooking in acidic medium, conditions being typical for domestic processing.

Thermal transport property of Ge34 and d-Ge investigated by molecular dynamics and the Slack's equation

International Nuclear Information System (INIS)

Han-Fu, Wang; Wei-Guo, Chu; Yan-Jun, Guo; Hao, Jin

2010-01-01

In this study, we evaluate the values of lattice thermal conductivity κ L of type II Ge clathrate (Ge 34 ) and diamond phase Ge crystal (d-Ge) with the equilibrium molecular dynamics (EMD) method and the Slack's equation. The key parameters of the Slack's equation are derived from the thermodynamic properties obtained from the lattice dynamics (LD) calculations. The empirical Tersoff's potential is used in both EMD and LD simulations. The thermal conductivities of d-Ge calculated by both methods are in accordance with the experimental values. The predictions of the Slack's equation are consistent with the EMD results above 250 K for both Ge 34 and d-Ge. In a temperature range of 200–1000 K, the κ L value of d-Ge is about several times larger than that of Ge 34 . (condensed matter: structure, thermal and mechanical properties)

TOLERANCE TIME OF EXPERIMENTAL THERMAL PAIN (COLD INDUCED) IN VOLUNTEERS.

Science.gov (United States)

Vaid, V N; Wilkhoo, N S; Jain, A K

1998-10-01

Perception of thermal pain (cold induced) was studied in 106 volunteers from troops and civilians deployed in J & K. Thermal stimulus devised was "holding ice". Tolerance time of holding ice was taken to be a measure of thermal sensitivity, volunteers were classified based on their native areas, addiction habits and socio-economic status, out of 106 volunteers, 81 could & 25 could not hold ice over 10 min. Sixteen out of 40 from coastline States and 9 out of 66 from non-coast line States failed to hold ice over 10 min. In "below average" "average" and "high average" socio-economic groups, three out of 27, 19 out of 73 and 03 out of 6 failed to hold ice over 10 min respectively. Fifteen out of 64 from "addiction habit group" and 10 out of 42 from "no addiction habit group" failed to hold ice over 10 min. Statistically no classification used in the study revealed significant difference in "tolerance times" of volunteers except the one based on coastline and non-coastline States.

Dynamic modeling of human thermal comfort after the transition from an indoor to an outdoor hot environment.

Science.gov (United States)

Katavoutas, George; Flocas, Helena A; Matzarakis, Andreas

2015-02-01

Thermal comfort under non-steady-state conditions primarily deals with rapid environmental transients and significant alterations of the meteorological conditions, activity, or clothing pattern within the time scale of some minutes. In such cases, thermal history plays an important role in respect to time, and thus, a dynamic approach is appropriate. The present study aims to investigate the dynamic thermal adaptation process of a human individual, after his transition from a typical indoor climate to an outdoor hot environment. Three scenarios of thermal transients have been considered for a range of hot outdoor environmental conditions, employing the dynamic two-node IMEM model. The differences among them concern the radiation field, the activity level, and the body position. The temporal pattern of body temperatures as well as the range of skin wettedness and of water loss have been investigated and compared among the scenarios and the environmental conditions considered. The structure and the temporal course of human energy fluxes as well as the identification of the contribution of body temperatures to energy fluxes have also been studied and compared. In general, the simulation results indicate that the response of a person, coming from the same neutral indoor climate, varies depending on the scenario followed by the individual while being outdoors. The combination of radiation field (shade or not) with the kind of activity (sitting or walking) and the outdoor conditions differentiates significantly the thermal state of the human body. Therefore, 75% of the skin wettedness values do not exceed the thermal comfort limit at rest for a sitting individual under the shade. This percentage decreases dramatically, less than 25%, under direct solar radiation and exceeds 75% for a walking person under direct solar radiation.

Large-k exciton dynamics in GaN epilayers: Nonthermal and thermal regimes

Science.gov (United States)

Vinattieri, Anna; Bogani, Franco; Cavigli, Lucia; Manzi, Donatella; Gurioli, Massimo; Feltin, Eric; Carlin, Jean-François; Martin, Denis; Butté, Raphaël; Grandjean, Nicolas

2013-02-01

We present a detailed investigation performed at low temperature (T<50 K) concerning the exciton dynamics in GaN epilayers grown on c-plane sapphire substrates, focusing on the exciton formation and the transition from the nonthermal to the thermal regime. The time-resolved kinetics of longitudinal-optical-phonon replicas is used to address the energy relaxation in the excitonic band. From picosecond time-resolved spectra, we bring evidence for a long lasting nonthermal excitonic distribution, which accounts for the first 50 ps. Such a behavior is confirmed in different experimental conditions when both nonresonant and resonant excitations are used. At low excitation power density, the exciton formation and their subsequent thermalization are dominated by impurity scattering rather than by acoustic phonon scattering. The estimate of the average energy of the excitons as a function of delay after the excitation pulse provides information on the relaxation time, which describes the evolution of the exciton population to the thermal regime.

Evaluating CO2 and CH4 dynamics of Alaskan ecosystems during the Holocene Thermal Maximum

Science.gov (United States)

He, Yujie; Jones, Miriam C.; Zhuang, Qianlai; Bochicchio, Christopher; Felzer, B. S.; Mason, Erik; Yu, Zicheng

2014-01-01

The Arctic has experienced much greater warming than the global average in recent decades due to polar amplification. Warming has induced ecological changes that have impacted climate carbon-cycle feedbacks, making it important to understand the climate and vegetation controls on carbon (C) dynamics. Here we used the Holocene Thermal Maximum (HTM, 11–9 ka BP, 1 ka BP = 1000 cal yr before present) in Alaska as a case study to examine how ecosystem Cdynamics responded to the past warming climate using an integrated approach of combining paleoecological reconstructions and ecosystem modeling. Our paleoecological synthesis showed expansion of deciduous broadleaf forest (dominated by Populus) into tundra and the establishment of boreal evergreen needleleaf and mixed forest during the second half of the HTM under a warmer- and wetter-than-before climate, coincident with the occurrence of the highest net primary productivity, cumulative net ecosystem productivity, soil C accumulation and CH4 emissions. These series of ecological and biogeochemical shifts mirrored the solar insolation and subsequent temperature and precipitation patterns during HTM, indicating the importance of climate controls on C dynamics. Our simulated regional estimate of CH4 emission rates from Alaska during the HTM ranged from 3.5 to 6.4 Tg CH4 yr−1 and highest annual NPP of 470 Tg C yr−1, significantly higher than previously reported modern estimates. Our results show that the differences in static vegetation distribution maps used in simulations of different time slices have greater influence on modeled C dynamics than climatic fields within each time slice, highlighting the importance of incorporating vegetation community dynamics and their responses to climatic conditions in long-term biogeochemical modeling.

Electron cyclotron heating and supra-thermal electron dynamics in the TCV Tokamak

Energy Technology Data Exchange (ETDEWEB)

Gnesin, S.

2011-10-15

This thesis is concerned with the physics of supra-thermal electrons in thermonuclear, magnetically confined plasmas. Under a variety of conditions, in laboratory as well as space plasmas, the electron velocity distribution function is not in thermodynamic equilibrium owing to internal or external drives. Accordingly, the distribution function departs from the equilibrium Maxwellian, and in particular generally develops a high-energy tail. In tokamak plasmas, this occurs especially as a result of injection of high-power electromagnetic waves, used for heating and current drive, as well as a result of internal magnetohydrodynamic (MHD) instabilities. The physics of these phenomena is intimately tied to the properties and dynamics of this supra-thermal electron population. This motivates the development of instrumental apparatus to measure its properties as well as of numerical codes to simulate their dynamics. Both aspects are reflected in this thesis work, which features advanced instrumental development and experimental measurements as well as numerical modeling. The instrumental development consisted of the complete design of a spectroscopic and tomographic system of four multi-detector hard X-ray (HXR) cameras for the TCV tokamak. The goal is to measure bremsstrahlung emission from supra-thermal electrons with energies in the 10-300 keV range, with the ultimate aim of providing the first full tomographic reconstruction at these energies in a noncircular plasma. In particular, supra-thermal electrons are generated in TCV by a high-power electron cyclotron heating (ECH) system and are also observed in the presence of MHD events, such as sawtooth oscillations and disruptive instabilities. This diagnostic employs state-of-the-art solid-state detectors and is optimized for the tight space requirements of the TCV ports. It features a novel collimator concept that combines compactness and flexibility as well as full digital acquisition of the photon pulses, greatly

Electron cyclotron heating and supra-thermal electron dynamics in the TCV Tokamak

International Nuclear Information System (INIS)

Gnesin, S.

2011-10-01

This thesis is concerned with the physics of supra-thermal electrons in thermonuclear, magnetically confined plasmas. Under a variety of conditions, in laboratory as well as space plasmas, the electron velocity distribution function is not in thermodynamic equilibrium owing to internal or external drives. Accordingly, the distribution function departs from the equilibrium Maxwellian, and in particular generally develops a high-energy tail. In tokamak plasmas, this occurs especially as a result of injection of high-power electromagnetic waves, used for heating and current drive, as well as a result of internal magnetohydrodynamic (MHD) instabilities. The physics of these phenomena is intimately tied to the properties and dynamics of this supra-thermal electron population. This motivates the development of instrumental apparatus to measure its properties as well as of numerical codes to simulate their dynamics. Both aspects are reflected in this thesis work, which features advanced instrumental development and experimental measurements as well as numerical modeling. The instrumental development consisted of the complete design of a spectroscopic and tomographic system of four multi-detector hard X-ray (HXR) cameras for the TCV tokamak. The goal is to measure bremsstrahlung emission from supra-thermal electrons with energies in the 10-300 keV range, with the ultimate aim of providing the first full tomographic reconstruction at these energies in a noncircular plasma. In particular, supra-thermal electrons are generated in TCV by a high-power electron cyclotron heating (ECH) system and are also observed in the presence of MHD events, such as sawtooth oscillations and disruptive instabilities. This diagnostic employs state-of-the-art solid-state detectors and is optimized for the tight space requirements of the TCV ports. It features a novel collimator concept that combines compactness and flexibility as well as full digital acquisition of the photon pulses, greatly

Electro-thermal dynamic stripping process : integrating environmentalism with bitumen production

Energy Technology Data Exchange (ETDEWEB)

McGee, B.C.W.; McDonald, C.W. [Society of Petroleum Engineers, Canadian Section, Calgary, AB (Canada)]|[E-T Energy, Calgary, AB (Canada); Little, L. [Society of Petroleum Engineers, Canadian Section, Calgary, AB (Canada)]|[Alberta Energy Research Inst., Edmonton, AB (Canada)

2008-10-15

This paper presented a new method of in situ oil sands extraction developed by Calgary-based E-T Energy. The Electro-Thermal Dynamic Stripping Process (ET-DSP) uses electricity to melt oil sands deposits that are too deep for open pit mining. The energy intensity of production compares favourably with alternative thermal bitumen extraction techniques and water consumption for the process is comparatively low, with all produced water being re-injected into the producing formation without any treatment. With ET-DSP, electrodes are drilled and completed next to the oil sands formation which ensures that the electrical currents are forced to flow to the oil sands formation. The viscosity of the bitumen is lowered by the heat from the current, thereby making the fluid flow more readily into vertical extraction wells. ET-DSP uses electricity directly from the power grid, and does not produce any greenhouse gas (GHG) emissions of its own. The process has the potential to allow operators to focus on areas of oil sands reservoirs that have remained inaccessible. Field studies confirmed that the production of bitumen using this method was achieved with reduced greenhouse gas emissions as compared to other thermal recovery process. The bitumen had trace amount of sand and no emulsions. 5 refs., 5 figs.

Thermal fatigue. Fluid-structure interaction at thermal mixing events

Energy Technology Data Exchange (ETDEWEB)

Schuler, X.; Herter, K.H.; Moogk, S. [Stuttgart Univ. (Germany). MPA; Laurien, E.; Kloeren, D.; Kulenovic, R.; Kuschewski, M. [Stuttgart Univ. (Germany). Inst. of Nuclear Technology and Energy Systems

2012-07-01

In the framework of the network research project ''Thermal Fatigue - Basics of the system-, outflow- and material-characteristics of piping under thermal fatigue'' funded by the German Federal Ministry of Education and Research (BMBF) fundamental numerical and experimental investigations on the material behaviour under transient thermal-mechanical stress conditions (high cycle fatigue - HCF) are carried out. The project's background and its network of scientific working groups with their individual working tasks are briefly introduced. The main focus is especially on the joint research tasks within the sub-projects of MPA and IKE which are dealing with thermal mixing of flows in a T-junction configuration and the fluidstructure- interactions (FSI). Therefore, experiments were performed with the newly established FSI test facility at MPA which enables single-phase flow experiments of water in typical power plant piping diameters (DN40 and DN80) at high pressure (maximum 75 bar) and temperatures (maximum 280 C). The experimental results serve as validation data base for numerical modelling of thermal flow mixing by means of thermo-fluid dynamics simulations applying CFD techniques and carried out by IKE as well as for modelling of thermal and mechanical loads of the piping structure by structural mechanics simulations with FEM methods which are executed by MPA. The FSI test facility will be described inclusively the applied measurement techniques, e. g. in particular the novel near-wall LED-induced Fluorescence method for non-intrusive flow temperature measurements. First experimental data and numerical results from CFD and FEM simulations of the thermal mixing of flows in the T-junction are presented.

Molecular dynamics study of the thermal expansion coefficient of silicon

Energy Technology Data Exchange (ETDEWEB)

Nejat Pishkenari, Hossein, E-mail: nejat@sharif.edu; Mohagheghian, Erfan; Rasouli, Ali

2016-12-16

Due to the growing applications of silicon in nano-scale systems, a molecular dynamics approach is employed to investigate thermal properties of silicon. Since simulation results rely upon interatomic potentials, thermal expansion coefficient (TEC) and lattice constant of bulk silicon have been obtained using different potentials (SW, Tersoff, MEAM, and EDIP) and results indicate that SW has a better agreement with the experimental observations. To investigate effect of size on TEC of silicon nanowires, further simulations are performed using SW potential. To this end, silicon nanowires of different sizes are examined and their TEC is calculated by averaging in different directions ([100], [110], [111], and [112]) and various temperatures. Results show that as the size increases, due to the decrease of the surface effects, TEC approaches its bulk value. - Highlights: • MD simulations of TEC and lattice constant of bulk silicon. • Effects of four potentials on the results. • Comparison to experimental data. • Investigating size effect on TEC of silicon nanowires.

Mass spectrometric comparison of swift heavy ion-induced and anaerobic thermal degradation of polymers

Science.gov (United States)

Lima, V.; Hossain, U. H.; Walbert, T.; Seidl, T.; Ensinger, W.

2018-03-01

The study of polymers irradiated by highly energetic ions and the resulting radiation-induced degradation is of major importance for space and particle accelerator applications. The mechanism of ion-induced molecular fragmentation of polyethylene, polyethyleneimine and polyamide was investigated by means of mass spectrometry and infrared spectroscopy. The results show that the introduction of nitrogen and oxygen into the polymer influences the stability rendering aliphatic polymers with heteroatoms less stable. A comparison to thermal decomposition data from literature reveals that ion-induced degradation is different in its bond fracture mechanism. While thermal degradation starts at the weakest bond, which is usually the carbon-heteroatom bond, energetic ion irradiation leads in the first step to scission of all types of bonds creating smaller molecular fragments. This is due to the localized extreme energy input under non-equilibrium conditions when the ions transfer kinetic energy onto electrons. These findings are of relevance for the choice of polymers for long-term application in both space and accelerator facilities.

Thermal analysis of heat storage canisters for a solar dynamic, space power system

Science.gov (United States)

Wichner, R. P.; Solomon, A. D.; Drake, J. B.; Williams, P. T.

1988-01-01

A thermal analysis was performed of a thermal energy storage canister of a type suggested for use in a solar receiver for an orbiting Brayton cycle power system. Energy storage for the eclipse portion of the cycle is provided by the latent heat of a eutectic mixture of LiF and CaF2 contained in the canister. The chief motivation for the study is the prediction of vapor void effects on temperature profiles and the identification of possible differences between ground test data and projected behavior in microgravity. The first phase of this study is based on a two-dimensional, cylindrical coordinates model using an interim procedure for describing void behavor in 1-g and microgravity. The thermal analysis includes the effects of solidification front behavior, conduction in liquid/solid salt and canister materials, void growth and shrinkage, radiant heat transfer across the void, and convection in the melt due to Marangoni-induced flow and, in 1-g, flow due to density gradients. A number of significant differences between 1-g and o-g behavior were found. This resulted from differences in void location relative to the maximum heat flux and a significantly smaller effective conductance in 0-g due to the absence of gravity-induced convection.

Glutamate Induced Thermal Equilibrium Intermediate and Counteracting Effect on Chemical Denaturation of Proteins.

Science.gov (United States)

Anumalla, Bramhini; Prabhu, N Prakash

2018-01-25

When organisms are subjected to stress conditions, one of their adaptive responses is accumulation of small organic molecules called osmolytes. These osmolytes affect the structure and stability of the biological macromolecules including proteins. The present study examines the effect of a negatively charged amino acid osmolyte, glutamate (Glu), on two model proteins, ribonuclease A (RNase A) and α-lactalbumin (α-LA), which have positive and negative surface charges at pH 7, respectively. These proteins follow two-state unfolding transitions during both heat and chemical induced denaturation processes. The addition of Glu stabilizes the proteins against temperature and induces an early equilibrium intermediate during unfolding. The stability is found to be enthalpy-driven, and the free energy of stabilization is more for α-LA compared to RNase A. The decrease in the partial molar volume and compressibility of both of the proteins in the presence of Glu suggests that the proteins attain a more compact state through surface hydration which could provide a more stable conformation. This is also supported by molecule dynamic simulation studies which demonstrate that the water density around the proteins is increased upon the addition of Glu. Further, the intermediates could be completely destabilized by lower concentrations (∼0.5 M) of guanidinium chloride and salt. However, urea subverts the Glu-induced intermediate formed by α-LA, whereas it only slightly destabilizes in the case of RNase A which has a positive surface charge and could possess charge-charge interactions with Glu. This suggests that, apart from hydration, columbic interactions might also contribute to the stability of the intermediate. Gdm-induced denaturation of RNase A and α-LA in the absence and the presence of Glu at different temperatures was carried out. These results also show the Glu-induced stabilization of both of the proteins; however, all of the unfolding transitions followed two

Design of performance and analysis of dynamic and transient thermal behaviors on the intermediate heat exchanger for HTGR

International Nuclear Information System (INIS)

Mori, Michitsugu; Mizuno, Minoru; Itoh, Mitsuyoshi; Urabe, Shigemi

1985-01-01

The intermediate heat exchanger (IHX) is designed as the high temperature heat exchanger for HTGR (High Temperature Gas-cooled Reactor), which transmits the primary coolant helium's heat raised up to about 950 0 C in the reactor core to the secondary helium or the nuclear heat utilization. Having to meet, in addition, the requirement of the primary coolant pressure boundary as the Class-1 component, it must be secured integrity throughout the service life. This paper will show (1) the design of the thermal performance; (2) the results of the dynamic analyses of the 1.5 MWt-IHX with its comparison to the experimental data; (3) the analytical predictions of the dynamic thermal behaviors under start-up and of the transient thermal behaviors during the accident on the 25 MWt-IHX. (author)

Thermally induced delamination of multilayers

DEFF Research Database (Denmark)

Sørensen, Bent F.; Sarraute, S.; Jørgensen, O.

1998-01-01

Steady-state delamination of multilayered structures, caused by stresses arising during processing due to thermal expansion mismatch, is analyzed by a fracture mechanics model based on laminate theory. It is found that inserting just a few interlayers with intermediate thermal expansion coefficie...... coefficients may be an effective way of reducing the delamination energy release rate. Uneven layer thickness and increasing elastic mismatch are shown to raise the energy release rate. Experimental work confirms important trends of the model.......Steady-state delamination of multilayered structures, caused by stresses arising during processing due to thermal expansion mismatch, is analyzed by a fracture mechanics model based on laminate theory. It is found that inserting just a few interlayers with intermediate thermal expansion...

Molecular-dynamics simulation of crystalline 18-crown-6: thermal shortening of covalent bonds

NARCIS (Netherlands)

van Eerden, J.; Harkema, Sybolt; Feil, D.

1990-01-01

Molecular-dynamics simulations of crystalline 18-crown-6 have been performed in a study of the apparent thermal shortening of covalent bonds observed in crystal structures. At 100 K, a shortening of 0.006 _+ 0.001 A for C----C and C----O bonds was obtained. This result was found to be independent of

Gradual plasticity alters population dynamics in variable environments: thermal acclimation in the green alga Chlamydomonas reinhartdii.

Science.gov (United States)

Kremer, Colin T; Fey, Samuel B; Arellano, Aldo A; Vasseur, David A

2018-01-10

Environmental variability is ubiquitous, but its effects on populations are not fully understood or predictable. Recent attention has focused on how rapid evolution can impact ecological dynamics via adaptive trait change. However, the impact of trait change arising from plastic responses has received less attention, and is often assumed to optimize performance and unfold on a separate, faster timescale than ecological dynamics. Challenging these assumptions, we propose that gradual plasticity is important for ecological dynamics, and present a study of the plastic responses of the freshwater green algae Chlamydomonas reinhardtii as it acclimates to temperature changes. First, we show that C. reinhardtii 's gradual acclimation responses can both enhance and suppress its performance after a perturbation, depending on its prior thermal history. Second, we demonstrate that where conventional approaches fail to predict the population dynamics of C. reinhardtii exposed to temperature fluctuations, a new model of gradual acclimation succeeds. Finally, using high-resolution data, we show that phytoplankton in lake ecosystems can experience thermal variation sufficient to make acclimation relevant. These results challenge prevailing assumptions about plasticity's interactions with ecological dynamics. Amidst the current emphasis on rapid evolution, it is critical that we also develop predictive methods accounting for plasticity. © 2018 The Author(s).

Radioactive waste combustion-vitrification under arc plasma: thermal and dynamic modelling

International Nuclear Information System (INIS)

Barthelemy, B.

2003-06-01

This thesis concerns the thermal and dynamic modelling for a combustion/vitrification process of surrogate radioactive waste under transferred arc plasma. The writer presents the confinement processes for radioactive waste using arc plasma and the different software used to model theses processes. This is followed by a description of our experimental equipment including a plasma arc reactor and an inductive system allowing the homogenization of glass temperature. A combustion/vitrification test is described. Thermal and material balances were discussed. The temperature fields of plasma arc and the glass frit conductivity are measured. Finally, the writer describes and clarifies the equations solved for the simulations of the electrically plasma arc and the glass melting including the thin layer of glass frit coating the crucible cold walls. The modelling results are presented in the form of spatial distribution of temperature, velocity and voluminal power... (author)

Radioactive waste combustion / vitrification under arc plasma: thermal and dynamic modelling

International Nuclear Information System (INIS)

Barthelemy, B.

2003-01-01

This thesis concerns the thermal and dynamic modelling for a combustion/vitrification process of surrogate radioactive waste under transferred arc plasma. The writer presents the confinement processes for radioactive waste using arc plasma and the different software used to model theses processes. This is followed by a description of our experimental equipment including a plasma arc reactor and an inductive system allowing the homogenization of glass temperature. A combustion/vitrification test is described. Thermal and material balances were discussed. The temperature fields of plasma arc and the glass frit conductivity are measured. Finally, the writer describes and clarifies the equations solved for the simulations of the electrically plasma arc and the glass melting including the thin layer of glass frit coating the crucible cold walls. The modelling results are presented in the form of spatial distribution of temperature, velocity and volume power... (author)

Dynamic Thermal Model And Control Of A Pem Fuel Cell System

DEFF Research Database (Denmark)

Liso, Vincenzo; Nielsen, Mads Pagh

2013-01-01

the fuel cell system. A PID temperature control is implemented to study the effect of stack temperature on settling times of other variables such as stack voltage, air flow rate, oxygen excess ratio and net power of the stack. The model allows an assessment of the effect of operating parameters (stack...... power output, cooling water flow rate, air flow rate, and environmental temperature) and parameter interactions on the system thermal performance. The model represents a useful tool to determine the operating temperatures of the various components of the thermal system, and thus to fully assess......A lumped parameter dynamic model is developed for predicting the stack performance, temperatures of the exit reactant gases and coolant liquid outlet in a proton-exchange membrane fuel cell (PEMFC) system. The air compressor, humidifier and cooling heat exchanger models are integrated to study...

Electron momentum spectroscopy of aniline taking account of nuclear dynamics in the initial electronic ground state

International Nuclear Information System (INIS)

Farasat, M; Golzan, M M; Shojaei, S H R; Morini, F; Deleuze, M S

2016-01-01

The electronic structure, electron binding energy spectrum and (e, 2e) momentum distributions of aniline have been theoretically predicted at an electron impact energy of 1.500 keV on the basis of Born–Oppenheimer molecular dynamical simulations, in order to account for thermally induced nuclear motions in the initial electronic ground state. Most computed momentum profiles are rather insensitive to thermally induced alterations of the molecular structure, with the exception of the profiles corresponding to two ionization bands at electron binding energies comprised between ∼10.0 and ∼12.0 eV (band C) and between ∼16.5 and ∼20.0 eV (band G). These profiles are found to be strongly influenced by nuclear dynamics in the electronic ground state, especially in the low momentum region. The obtained results show that thermal averaging smears out most generally the spectral fingerprints that are induced by nitrogen inversion. (paper)

A molecular dynamics study of thermal transport in nanoparticle doped Argon like solid

Energy Technology Data Exchange (ETDEWEB)

Shahadat, Muhammad Rubayat Bin, E-mail: rubayat37@gmail.com; Ahmed, Shafkat; Morshed, A. K. M. M. [Department of Mechanical Engineering Bangladesh University of Engineering and Technology (BUET) Dhaka (Bangladesh)

2016-07-12

Interfacial phenomena such as mass and type of the interstitial atom, nano scale material defect influence heat transfer and the effect become very significant with the reduction of the material size. Non Equilibrium Molecular Dynamics (NEMD) simulation was carried out in this study to investigate the effect of the interfacial phenomena on solid. Argon like solid was considered in this study and LJ potential was used for atomic interaction. Nanoparticles of different masses and different molecular defects were inserted inside the solid. From the molecular simulation, it was observed that a large interfacial mismatch due to change in mass in the homogenous solid causes distortion of the phonon frequency causing increase in thermal resistance. Position of the doped nanoparticles have more profound effect on the thermal conductivity of the solid whereas influence of the mass ratio is not very significant. Interstitial atom positioned perpendicular to the heat flow causes sharp reduction in thermal conductivity. Structural defect caused by the molecular defect (void) also observed to significantly affect the thermal conductivity of the solid.

Theory of laser-induced demagnetization at high temperatures

KAUST Repository

Manchon, Aurelien

2012-02-17

Laser-induced demagnetization is theoretically studied by explicitly taking into account interactions among electrons, spins, and lattice. Assuming that the demagnetization processes take place during the thermalization of the subsystems, the temperature dynamics is given by the energy transfer between the thermalized interacting baths. These energy transfers are accounted for explicitly through electron-magnon and electron-phonon interactions, which govern the demagnetization time scale. By properly treating the spin system in a self-consistent random phase approximation, we derive magnetization dynamic equations for a broad range of temperature. The dependence of demagnetization on the temperature and pumping laser intensity is calculated in detail. In particular, we show several salient features for understanding magnetization dynamics near the Curie temperature. While the critical slowdown in dynamics occurs, we find that an external magnetic field can restore the fast dynamics. We discuss the implication of the fast dynamics in the application of heat-assisted magnetic recording.

Theory of laser-induced demagnetization at high temperatures

KAUST Repository

Manchon, Aurelien; Li, Q.; Xu, L.; Zhang, S.

2012-01-01

Laser-induced demagnetization is theoretically studied by explicitly taking into account interactions among electrons, spins, and lattice. Assuming that the demagnetization processes take place during the thermalization of the subsystems, the temperature dynamics is given by the energy transfer between the thermalized interacting baths. These energy transfers are accounted for explicitly through electron-magnon and electron-phonon interactions, which govern the demagnetization time scale. By properly treating the spin system in a self-consistent random phase approximation, we derive magnetization dynamic equations for a broad range of temperature. The dependence of demagnetization on the temperature and pumping laser intensity is calculated in detail. In particular, we show several salient features for understanding magnetization dynamics near the Curie temperature. While the critical slowdown in dynamics occurs, we find that an external magnetic field can restore the fast dynamics. We discuss the implication of the fast dynamics in the application of heat-assisted magnetic recording.

A sharp interface immersed boundary method for vortex-induced vibration in the presence of thermal buoyancy

Science.gov (United States)

Garg, Hemanshul; Soti, Atul K.; Bhardwaj, Rajneesh

2018-02-01

We report the development of an in-house fluid-structure interaction solver and its application to vortex-induced vibration (VIV) of an elastically mounted cylinder in the presence of thermal buoyancy. The flow solver utilizes a sharp interface immersed boundary method, and in the present work, we extend it to account for the thermal buoyancy using Boussinesq approximation and couple it with a spring-mass system of the VIV. The one-way coupling utilizes an explicit time integration scheme and is computationally efficient. We present benchmark code verifications of the solver for natural convection, mixed convection, and VIV. In addition, we verify a coupled VIV-thermal buoyancy problem at a Reynolds number, Re = 150. We numerically demonstrate the onset of the VIV in the presence of the thermal buoyancy for an insulated cylinder at low Re. The buoyancy is induced by two parallel plates, kept in the direction of flow and symmetrically placed around the cylinder. The plates are maintained at the hot and cold temperature to the same degree relative to the ambient. In the absence of the thermal buoyancy (i.e., the plates are at ambient temperature), the VIV does not occur for Re ≤ 20 due to stable shear layers. By contrast, the thermal buoyancy induces flow instability and the vortex shedding helps us to achieve the VIV at Re ≤ 20, lower than the critical value of Re (≈21.7), reported in the literature, for a self-sustained VIV in the absence of the thermal buoyancy. The present simulations show that the lowest Re to achieve VIV in the presence of the thermal buoyancy is around Re ≈ 3, at Richardson number, Ri = 1. We examine the effect of the reduced velocity (UR), mass ratio (m), Prandtl number (Pr), Richardson number (Ri) on the displacement of the cylinder, lift coefficient, oscillation frequency, the phase difference between displacement and lift force, and wake structures. We obtain a significantly larger vibration amplitude of the cylinder over a wide

Holographic lessons for quark dynamics

Science.gov (United States)

Chernicoff, Mariano; García, J. Antonio; Güijosa, Alberto; Pedraza, Juan F.

2012-05-01

We give a brief overview of recent results obtained through the gauge/gravity correspondence, concerning the propagation of a heavy quark in strongly coupled conformal field theories (such as {N}=4 super-Yang-Mills), both at zero and finite temperature. In the vacuum, we discuss energy loss, radiation damping, signal propagation and radiation-induced fluctuations. In the presence of a thermal plasma, our emphasis is on early-time energy loss, screening and quark-antiquark evolution after pair creation. Throughout, quark dynamics is seen to be efficiently encapsulated in the usual string worldsheet dynamics.

Opposite patterns of change in perception of imagined and physically induced pain over the course of repeated thermal stimulations.

Science.gov (United States)

Gács, B; Szolcsányi, T; Csathó, Á

2017-08-01

Individuals frequently show habituation to repeated noxious heat. However, given the defensive function of human pain processing, it is reasonable to assume that individuals anticipate that they would become increasingly sensitive to repeated thermal pain stimuli. No previous studies have, however, been addressed to this assumption. Therefore, in the current study, we investigated how healthy human individuals imagine the intensity of repeated thermal pain stimulations, and compared this with the intensity ratings given after physically induced thermal pain trials. Healthy participants (N = 20) gave pain intensity ratings in two conditions: imagined and real thermal pain. In the real pain condition, thermal pain stimuli of two intensities (minimal and moderate pain) were delivered in four consecutive trials. The duration of the peak temperature was 20 s, and stimulation was always delivered to the same location. In each trial, participants rated the pain intensity twice, 5 and 15 s after the onset of the peak temperature. In the imagined pain condition, participants were subjected to a reference pain stimulus and then asked to imagine and rate the same sequence of stimulations as in the induced pain condition. Ratings of imagined pain and physically induced pain followed opposite courses over repeated stimulations: Ratings of imagined pain indicated sensitization, whereas ratings for physically induced pain indicated habituation. The findings were similar for minimal and moderate pain intensities. The findings suggest that, rather than habituating to pain, healthy individuals imagine that they would become increasingly sensitive to repeated thermal pain stimuli. This study identified opposite patterns of change in perception of imagined pain (sensitization) and physically induced pain (habituation). The findings show that individuals anticipate that they would become increasingly sensitive to repeated pain stimuli, which might also have clinical implications. �

Selection of high temperature thermal energy storage materials for advanced solar dynamic space power systems

Science.gov (United States)

Lacy, Dovie E.; Coles-Hamilton, Carolyn; Juhasz, Albert

1987-01-01

Under the direction of NASA's Office of Aeronautics and Technology (OAST), the NASA Lewis Research Center has initiated an in-house thermal energy storage program to identify combinations of phase change thermal energy storage media for use with a Brayton and Stirling Advanced Solar Dynamic (ASD) space power system operating between 1070 and 1400 K. A study has been initiated to determine suitable combinations of thermal energy storage (TES) phase change materials (PCM) that result in the smallest and lightest weight ASD power system possible. To date the heats of fusion of several fluoride salt mixtures with melting points greater than 1025 K have been verified experimentally. The study has indicated that these salt systems produce large ASD systems because of their inherent low thermal conductivity and low density. It is desirable to have PCMs with high densities and high thermal conductivities. Therefore, alternate phase change materials based on metallic alloy systems are also being considered as possible TES candidates for future ASD space power systems.

Multicharged Ion-induced simple molecule fragmentation dynamics

International Nuclear Information System (INIS)

Tarisien, M.

2003-10-01

The aim of this work is to study the dynamics of swift multicharged ion-induced fragmentation of diatomic (CO) and triatomic (CO 2 ) molecules. Performed at the GANIL facility, this study used the Recoil Ion Momentum Spectroscopy technique (RIMS), which consists of a time-of-flight mass spectrometer, coupled with a multi-hit capability position sensitive detector (delay line anode). The high-resolution measurement of the kinetic energy distribution released (KER) during the CO fragmentation points out the limitation of the Coulomb Explosion Model, revealing, for example, the di-cation CO 2 + electronic state contribution in the case of C + /O + fragmentation pathway. Furthermore, the multi-ionization cross section dependence with the orientation of the internuclear axis of CO is compared with a geometrical model calculation. Finally, different behaviours are observed for the dissociation dynamics of a triatomic molecule (CO 2 ). While triple ionization leads mainly to a synchronous concerted fragmentation dynamics, a weak fraction of dissociating molecule follows a sequential dynamics involving CO 2 + metastable states. In the case of double ionization, (CO 2 ) 2+ di-cation dissociation dynamics is asynchronously concerted and has been interpreted using a simple model involving an asymmetrical vibration of the molecule. (author)

Hyperbaric oxygen therapy attenuates central sensitization induced by a thermal injury in humans

DEFF Research Database (Denmark)

Rasmussen, V M; Borgen, A E; Jansen, E C

2015-01-01

BACKGROUND: Hyperbaric oxygen (HBO2 ) treatment has in animal experiments demonstrated antinociceptive effects. It was hypothesized that these effects would attenuate secondary hyperalgesia areas (SHAs), an expression of central sensitization, after a first-degree thermal injury in humans. METHODS...... was demonstrated. However, in the nine volunteers starting with the control session, a statistical significant attenuation of SHAs was demonstrated in the HBO2 session (P = 0.004). CONCLUSIONS: The results indicate that HBO2 therapy in humans attenuates central sensitization induced by a thermal skin injury......, compared with control. These new and original findings in humans corroborate animal experimental data. The thermal injury model may give impetus to future human neurophysiological studies exploring the central effects of hyperbaric oxygen treatment....

First principles calculations of thermal conductivity with out of equilibrium molecular dynamics simulations

Science.gov (United States)

Puligheddu, Marcello; Gygi, Francois; Galli, Giulia

The prediction of the thermal properties of solids and liquids is central to numerous problems in condensed matter physics and materials science, including the study of thermal management of opto-electronic and energy conversion devices. We present a method to compute the thermal conductivity of solids by performing ab initio molecular dynamics at non equilibrium conditions. Our formulation is based on a generalization of the approach to equilibrium technique, using sinusoidal temperature gradients, and it only requires calculations of first principles trajectories and atomic forces. We discuss results and computational requirements for a representative, simple oxide, MgO, and compare with experiments and data obtained with classical potentials. This work was supported by MICCoM as part of the Computational Materials Science Program funded by the U.S. Department of Energy (DOE), Office of Science , Basic Energy Sciences (BES), Materials Sciences and Engineering Division under Grant DOE/BES 5J-30.

Kalman Filtered MR Temperature Imaging for Laser Induced Thermal Therapies

OpenAIRE

Fuentes, D.; Yung, J.; Hazle, J. D.; Weinberg, J. S.; Stafford, R. J.

2011-01-01

The feasibility of using a stochastic form of Pennes bioheat model within a 3D finite element based Kalman filter (KF) algorithm is critically evaluated for the ability to provide temperature field estimates in the event of magnetic resonance temperature imaging (MRTI) data loss during laser induced thermal therapy (LITT). The ability to recover missing MRTI data was analyzed by systematically removing spatiotemporal information from a clinical MR-guided LITT procedure in human brain and comp...

Impact of vacancies on the thermal conductivity of graphene nanoribbons: A molecular dynamics simulation study

Directory of Open Access Journals (Sweden)

Maliha Noshin

2017-01-01

Full Text Available Equilibrium molecular dynamics simulation using 2nd generation Reactive Bond Order interatomic potential has been performed to model the thermal transport of nanometer sized zigzag defected graphene nanoribbons (GNRs containing several types of vacancies. We have investigated the thermal conductivity of defected GNRs as a function of vacancy concentration within a range of 0.5% to 5% and temperature ranging from 300K to 600K, along with a comparative analysis of those for pristine GNRs. We find that, a vacancy concentration of 0.5% leads to over 90% reduction in the thermal conductivity of GNRs. At low defect concentration, the decay rate is faster but ceases gradually at higher defect concentration. With the increasing temperature, thermal conductivity of defected GNRs decreases but shows less variation in comparison with that of pristine GNRs at higher temperatures. Such comprehensive study on several vacancy type defects in GNRs can provide further insight to tune up the thermal transport characteristics of low dimensional carbon nanostructures. This eventually would encourage the characterization of more stable thermal properties in thermal devices at an elevated temperature as well as the potential applicability of GNRs as thermoelectrics.

Pharmaceutical applications of dynamic mechanical thermal analysis.

Science.gov (United States)

Jones, David S; Tian, Yiwei; Abu-Diak, Osama; Andrews, Gavin P

2012-04-01

The successful development of polymeric drug delivery and biomedical devices requires a comprehensive understanding of the viscoleastic properties of polymers as these have been shown to directly affect clinical efficacy. Dynamic mechanical thermal analysis (DMTA) is an accessible and versatile analytical technique in which an oscillating stress or strain is applied to a sample as a function of oscillatory frequency and temperature. Through cyclic application of a non-destructive stress or strain, a comprehensive understanding of the viscoelastic properties of polymers may be obtained. In this review, we provide a concise overview of the theory of DMTA and the basic instrumental/operating principles. Moreover, the application of DMTA for the characterization of solid pharmaceutical and biomedical systems has been discussed in detail. In particular we have described the potential of DMTA to measure and understand relaxation transitions and miscibility in binary and higher-order systems and describe the more recent applications of the technique for this purpose. © 2011 Elsevier B.V. All rights reserved.

Factors Affecting the Thickness of Thermal Aureoles

Directory of Open Access Journals (Sweden)

Catherine Annen

2017-10-01

Full Text Available Intrusions of magma induce thermal aureoles in the country rock. Analytical solutions predict that the thickness of an aureole is proportional to the thickness of the intrusion. However, in the field, thermal aureoles are often significantly thinner or wider than predicted by simple thermal models. Numerical models show that thermal aureoles are wider if the heat transfer in the magma is faster than in the country rock due to contrasts in thermal diffusivities or the effect of magma convection. Large thermal aureoles can also be caused by repeated injection close to the contact. Aureoles are thin when heat transfer in the country rock is faster than heat transfer within the magma or in case of incrementally, slowly emplaced magma. Absorption of latent heat due to metamorphic reactions or water volatilization also affects thermal aureoles but to a lesser extent. The way these parameters affect the thickness of a thermal aureole depends on the isotherm under consideration, hence on which metamorphic phase is used to draw the limit of the aureole. Thermal aureoles provide insight on the dynamics of intrusions emplacement. Although available examples are limited, asymmetric aureoles point to magma emplacement by over-accretion for mafic cases and by under-accretion for felsic cases, consistent with geochronological data.

Femtosecond quantum dynamics and laser-cooling in thermal molecular systems

International Nuclear Information System (INIS)

Warmuth, C.

2000-01-01

This work deals with coherent and incoherent vibrational phenomena in thermal systems, wave packet motion and laser-cooling. In the first part, the principle of COIN (Coherence Observation by Interference Noise) has been applied as a new approach to measuring wave packet motion. In the experiment pairs of phase-randomized femtosecond pulses with relative delay-time τ prepare interference fluctuations in the excited state population, so the variance of the correlated fluorescence intensity directly mimics the dynamics of the propagating wave packet. The scheme is demonstrated by measuring the vibrational coherence of wave packet-motion in the B-state of gaseous iodine. The COIN-interferograms obtained recover propagation, recurrences, spreading, and revivals as the typical signature of wave packets. Due to the disharmony of the B-state-potential, fractional revivals have also been found showing the potential of the COIN-technique in quantum-dynamical research. In the second part the fluorescence lifetime of trans-stilbene, isolated and in the presence of 1 atm of Ar gas, respectively, was measured as a function of the detuning of the excitation frequency from the frequency of the 0-0-transition ω 0 . The lifetime was found to decrease on both sides of ω 0 , but the dependence of the lifetime on detuning in the presence of Ar gas is much weaker than for the isolated molecule. Both observations corroborate previous theoretical predictions of laser-cooling of thermal trans-stilbene upon excitation at the ω 0 frequency. The experimental results are in good agreement with theoretical analysis. (author)

Factors influencing the thermally-induced strength degradation of B/Al composites

International Nuclear Information System (INIS)

Dicarlo, J.A.

1983-01-01

Literature data related to the thermally-induced strength degradation of B/Al composites were examined in the light of fracture theories based on reaction-controlled fiber weakening. Under the assumption of a parabolic time-dependent growth for the interfacial reaction product, a Griffith-type fracture model was found to yield simple equations whose predictions were in good agreement with data for boron fiber average strength and for B/Al axial fracture strain. The only variables in these equations were the time and temperature of the thermal exposure and an empirical factor related to fiber surface smoothness prior to composite consolidation. Such variables as fiber diameter and aluminum alloy composition were found to have little influence. The basic and practical implications of the fracture model equations are discussed

Universal slow dynamics in granular solids

Science.gov (United States)

TenCate; Smith; Guyer

2000-07-31

Experimental properties of a new form of creep dynamics are reported, as manifest in a variety of sandstones, limestone, and concrete. The creep is a recovery behavior, following the sharp drop in elastic modulus induced either by nonlinear acoustic straining or rapid temperature change. The extent of modulus recovery is universally proportional to the logarithm of the time after source discontinuation in all samples studied, over a scaling regime covering at least 10(3) s. Comparison of acoustically and thermally induced creep suggests a single origin based on internal strain, which breaks the symmetry of the inducing source.

Anderson localized state as a predissipative state: irreversible emission of thermalized quanta from a dynamically delocalized state.

Science.gov (United States)

Yamada, Hiroaki; Ikeda, Kensuke S

2002-04-01

It was shown that localization in one-dimensional disordered (quantum) electronic system is destroyed against coherent harmonic perturbations and the delocalized electron exhibits an unlimited diffusive motion [Yamada and Ikeda, Phys. Rev. E 59, 5214 (1999)]. The appearance of diffusion implies that the system has potential for irreversibility and dissipation. In the present paper, we investigate dissipative property of the dynamically delocalized state, and we show that an irreversible quasistationary energy flow indeed appears in the form of a "heat" flow when we couple the system with another dynamical degree of freedom. In the concrete we numerically investigate dissipative properties of a one-dimensional tight-binding electronic system perturbed by time-dependent harmonic forces, by coupling it with a quantum harmonic oscillator or a quantum anharmonic oscillator. It is demonstrated that if the on-site potential is spatially irregular an irreversible energy transfer from the scattered electron to the test oscillator occurs. Moreover, the test oscillator promptly approaches a thermalized state characterized by a well-defined time-dependent temperature. On the contrary, such a relaxation process cannot be observed at all for periodic potential systems. Our system is one of the minimal quantum systems in which a distinct nonequilibrium statistical behavior is self-induced.

Thermal Dynamics of Xanthene Dye in Polymer Matrix Excited by Double Pulse Laser Radiation

Science.gov (United States)

Samusev, Ilia; Borkunov, Rodion; Tsarkov, Maksim; Konstantinova, Elizaveta; Antipov, Yury; Demin, Maksim; Bryukhanov, Valery

2018-01-01

Double-pulse laser excitation of the eosin and silver nanoparticles embedded into polymer media is known to be a method of electronic-vibrational energy deactivation kinetic process information obtaining and polymer thermal dynamics investigation. We have studied the vibrational relaxation processes in dye molecules (eosin) and nanoparticles in polyvinyl alcohol after two time-shifted laser pulses with fast and delayed fluorescence kinetics study. In order to simulate thermal and photophysical processes caused by double photon excitation, we solved heat transfer and energy deactivation differential equations numerically. The simulation allowed us to obtain the value of heat conductivity coefficient of polymer matrix.

Dynamic simulation and thermo-economic analysis of a PhotoVoltaic/Thermal collector heating system for an indoor–outdoor swimming pool

International Nuclear Information System (INIS)

Buonomano, Annamaria; De Luca, Giuseppina; Figaj, Rafal Damian; Vanoli, Laura

2015-01-01

Highlights: • A PV/T heating system for indoor–outdoor swimming pools is proposed. • A comparison among some thermal pool models available in literature is carried out. • Dynamic simulations of the thermal behavior of the swimming-pools are performed. • PV/T thermal energy is used to heat the swimming pool and for DHW production. • Energy and economic parametric analyses of the proposed system are presented. - Abstract: This paper presents an analysis of an innovative renewable energy plant serving an existing indoor/outdoor swimming pool located in Naples. The proposed solar hybrid system is designed in order to balance the remarkable energy demand of the swimming pool facility and to ensure suitable comfort conditions for swimmers. With the aim to accomplish such goals, the dynamic thermal behavior of the swimming pool was analyzed as a function of the thermo-hygrometric conditions of the indoor space and on the meteorological conditions of the pool site. In order to properly design and size the proposed renewable energy system, different thermal pool loss formulations for the calculation of the swimming pool thermal balance, in indoor and outdoor regimes, are adopted. The solar hybrid system consists of a water cooled photovoltaic/thermal collectors plant (PV/T), designed to meet a part of the facility demands of electricity and heat. Electricity is completely utilized by the facility, while the produced thermal energy is primarily used to meet the pool thermal demand and secondarily for sanitary hot water scopes. In order to carry out dynamic simulations and sensitivity analyses, the system performance is designed and dynamically simulated in TRNSYS environment. The developed simulation model enables the calculation of both the indoor and outdoor swimming pool thermal losses and the overall energy and economic system performance. Such results are obtained as a function of the thermo-hygrometric conditions of the environment, of the occupants and the

Molecular dynamics study on interfacial thermal conductance of unirradiated and irradiated SiC/C

International Nuclear Information System (INIS)

Wang, Qingyu; Wang, Chenglong; Zhang, Yue; Li, Taosheng

2014-01-01

SiC f /SiC composite materials have been considered as candidate structural materials for several types of advanced nuclear reactors. Both experimental and computer simulations studies have revealed the degradation of thermal conductivity for this material after irradiation. The objective of this study is to investigate the effect of SiC/graphite interface structure and irradiation on the interfacial thermal conductance by using molecular dynamics simulation. Five SiC/graphite composite models were created with different interface structures, and irradiation was introduced near the interfaces. Thermal conductance was calculated by means of reverse-NEMD method. Results show that there is a positive correlation between the interfacial energy and interfacial C–Si bond quantity, and irradiated models showed higher interfacial energy compared with their unirradiated counterparts. Except the model with graphite atom plane parallel to the interface, the interfacial thermal conductance of unirradiated and irradiated (1000 eV) models, increases as the increase of interfacial energy, respectively. For all irradiated models, lattice defects are of importance in impacting the interfacial thermal conductance depending on the interface structure. For the model with graphite layer parallel to the interface, the interfacial thermal conductance increased after irradiation, for the other models the interfacial thermal conductance decreased. The vibrational density of states of atoms in the interfacial region was calculated to analyze the phonon mismatch at the interface

Dynamic Exergy Analysis for the Thermal Storage Optimization of the Building Envelope

Directory of Open Access Journals (Sweden)

Valentina Bonetti

2017-01-01

Full Text Available As a measure of energy “quality”, exergy is meaningful for comparing the potential for thermal storage. Systems containing the same amount of energy could have considerably different capabilities in matching a demand profile, and exergy measures this difference. Exergy stored in the envelope of buildings is central in sustainability because the environment could be an unlimited source of energy if its interaction with the envelope is optimised for maintaining the indoor conditions within comfort ranges. Since the occurring phenomena are highly fluctuating, a dynamic exergy analysis is required; however, dynamic exergy modelling is complex and has not hitherto been implemented in building simulation tools. Simplified energy and exergy assessments are presented for a case study in which thermal storage determines the performance of seven different wall types for utilising nocturnal ventilation as a passive cooling strategy. Hourly temperatures within the walls are obtained with the ESP-r software in free-floating operation and are used to assess the envelope exergy storage capacity. The results for the most suitable wall types were different between the exergy analysis and the more traditional energy performance indicators. The exergy method is an effective technique for selecting the construction type that results in the most favourable free-floating conditions through the analysed passive strategy.

Delay-Induced Consensus and Quasi-Consensus in Multi-Agent Dynamical Systems

NARCIS (Netherlands)

Yu, Wenwu; Chen, Guanrong; Cao, Ming; Ren, Wei

2013-01-01

This paper studies consensus and quasi-consensus in multi-agent dynamical systems. A linear consensus protocol in the second-order dynamics is designed where both the current and delayed position information is utilized. Time delay, in a common perspective, can induce periodic oscillations or even

Temporal dynamics of distinct CA1 cell populations during unconscious state induced by ketamine.

Directory of Open Access Journals (Sweden)

Hui Kuang

2010-12-01

Full Text Available Ketamine is a widely used dissociative anesthetic which can induce some psychotic-like symptoms and memory deficits in some patients during the post-operative period. To understand its effects on neural population dynamics in the brain, we employed large-scale in vivo ensemble recording techniques to monitor the activity patterns of simultaneously recorded hippocampal CA1 pyramidal cells and various interneurons during several conscious and unconscious states such as awake rest, running, slow wave sleep, and ketamine-induced anesthesia. Our analyses reveal that ketamine induces distinct oscillatory dynamics not only in pyramidal cells but also in at least seven different types of CA1 interneurons including putative basket cells, chandelier cells, bistratified cells, and O-LM cells. These emergent unique oscillatory dynamics may very well reflect the intrinsic temporal relationships within the CA1 circuit. It is conceivable that systematic characterization of network dynamics may eventually lead to better understanding of how ketamine induces unconsciousness and consequently alters the conscious mind.

Thermally-assisted Magma Emplacement Explains Restless Calderas

Science.gov (United States)

Amoruso, A.; Crescentini, L.; D'Antonio, M.; Acocella, V.

2017-12-01

Many calderas show repeated unrest over centuries. Though probably induced by magma, this unique behaviour is not understood and its dynamics remains elusive. To better understand these restless calderas, we interpret deformation data and build thermal models of Campi Flegrei, Italy, which is the best-known, yet most dangerous calderas, lying to the west of Naples and restless since the 1950s at least.Our elaboration of the geodetic data indicates that the inflation and deflation of magmatic sources at the same location explain most deformation, at least since the build-up of the last 1538 AD eruption. However, such a repeated magma emplacement requires a persistently hot crust.Our thermal models show that the repeated emplacement was assisted by the thermal anomaly created by magma that was intruded at shallow depth 3 ka before the last eruption and, in turn, contributed to maintain the thermal anomaly itself. This may explain the persistence of the magmatic sources promoting the restless behaviour of the Campi Flegrei caldera; moreover, it explains the crystallization, re-melting and mixing among compositionally distinct magmas recorded in young volcanic rocks.Available information at other calderas highlights similarities to Campi Flegrei, in the pattern and cause of unrest. All monitored restless calderas have either geodetically (Yellowstone, Aira Iwo-Jima, Askja, Fernandina and, partly, Long Valley) or geophysically (Rabaul, Okmok) detected sill-like intrusions inducing repeated unrest. Some calderas (Yellowstone, Long Valley) also show stable deformation pattern, where inflation insists on and mimics the resurgence uplift. The common existence of sill-like sources, also responsible for stable deformation patterns, in restless calderas suggests close similarities to Campi Flegrei. This suggests a wider applicability of our model of thermally-assisted sill emplacement, to be tested by future studies to better understand not only the dynamics of restless

Kalman filtered MR temperature imaging for laser induced thermal therapies.

Science.gov (United States)

Fuentes, D; Yung, J; Hazle, J D; Weinberg, J S; Stafford, R J

2012-04-01

The feasibility of using a stochastic form of Pennes bioheat model within a 3-D finite element based Kalman filter (KF) algorithm is critically evaluated for the ability to provide temperature field estimates in the event of magnetic resonance temperature imaging (MRTI) data loss during laser induced thermal therapy (LITT). The ability to recover missing MRTI data was analyzed by systematically removing spatiotemporal information from a clinical MR-guided LITT procedure in human brain and comparing predictions in these regions to the original measurements. Performance was quantitatively evaluated in terms of a dimensionless L(2) (RMS) norm of the temperature error weighted by acquisition uncertainty. During periods of no data corruption, observed error histories demonstrate that the Kalman algorithm does not alter the high quality temperature measurement provided by MR thermal imaging. The KF-MRTI implementation considered is seen to predict the bioheat transfer with RMS error 10 sec.

Modeling thermal spike driven reactions at low temperature and application to zirconium carbide radiation damage

Science.gov (United States)

Ulmer, Christopher J.; Motta, Arthur T.

2017-11-01

The development of TEM-visible damage in materials under irradiation at cryogenic temperatures cannot be explained using classical rate theory modeling with thermally activated reactions since at low temperatures thermal reaction rates are too low. Although point defect mobility approaches zero at low temperature, the thermal spikes induced by displacement cascades enable some atom mobility as it cools. In this work a model is developed to calculate "athermal" reaction rates from the atomic mobility within the irradiation-induced thermal spikes, including both displacement cascades and electronic stopping. The athermal reaction rates are added to a simple rate theory cluster dynamics model to allow for the simulation of microstructure evolution during irradiation at cryogenic temperatures. The rate theory model is applied to in-situ irradiation of ZrC and compares well at cryogenic temperatures. The results show that the addition of the thermal spike model makes it possible to rationalize microstructure evolution in the low temperature regime.

Study of Error Propagation in the Transformations of Dynamic Thermal Models of Buildings

Directory of Open Access Journals (Sweden)

Loïc Raillon

2017-01-01

Full Text Available Dynamic behaviour of a system may be described by models with different forms: thermal (RC networks, state-space representations, transfer functions, and ARX models. These models, which describe the same process, are used in the design, simulation, optimal predictive control, parameter identification, fault detection and diagnosis, and so on. Since more forms are available, it is interesting to know which one is the most suitable by estimating the sensitivity of the model to transform into a physical model, which is represented by a thermal network. A procedure for the study of error by Monte Carlo simulation and of factor prioritization is exemplified on a simple, but representative, thermal model of a building. The analysis of the propagation of errors and of the influence of the errors on the parameter estimation shows that the transformation from state-space representation to transfer function is more robust than the other way around. Therefore, if only one model is chosen, the state-space representation is preferable.

Preparation of multishell ICF target plastic-foam cushion materials by thermally induced phase-inversion processes

International Nuclear Information System (INIS)

Young, A.T.; Moreno, D.K.; Marsters, R.G.

1981-01-01

Homogenous, low-density plastic foams for ICF targets have been prepared by thermally induced phase inversion processes. Uniform, open cell foams have been obtained by the rapid freezing of water solutions of modified cellulose polymers with densities in the range of 5 mg/cm 3 to 0.7 mg/cm 3 and respective average cell sizes of 2 to 40 micrometers. In addition, low-density, microcellular foams have been prepared from the hydrocarbon polymer poly(4-methyl-l-pentene) via a similar phase inversion process using homogenous solutions in organic solvents. These foams have densities from 2 to 5 mg/cm 3 and average cell sizes of 20 micrometers. The physical-chemical aspects of the thermally induced phase inversion process is presented

Remarkable reduction of thermal conductivity in phosphorene phononic crystal

International Nuclear Information System (INIS)

Xu, Wen; Zhang, Gang

2016-01-01

Phosphorene has received much attention due to its interesting physical and chemical properties, and its potential applications such as thermoelectricity. In thermoelectric applications, low thermal conductivity is essential for achieving a high figure of merit. In this work, we propose to reduce the thermal conductivity of phosphorene by adopting the phononic crystal structure, phosphorene nanomesh. With equilibrium molecular dynamics simulations, we find that the thermal conductivity is remarkably reduced in the phononic crystal. Our analysis shows that the reduction is due to the depressed phonon group velocities induced by Brillouin zone folding, and the reduced phonon lifetimes in the phononic crystal. Interestingly, it is found that the anisotropy ratio of thermal conductivity could be tuned by the ‘non-square’ pores in the phononic crystal, as the phonon group velocities in the direction with larger projection of pores is more severely suppressed, leading to greater reduction of thermal conductivity in this direction. Our work provides deep insight into thermal transport in phononic crystals and proposes a new strategy to reduce the thermal conductivity of monolayer phosphorene. (paper)

Factors influencing the thermally-induced strength degradation of B/Al composites

Science.gov (United States)

Dicarlo, J. A.

1983-01-01

Literature data related to the thermally-induced strength degradation of B/Al composites were examined in the light of fracture theories based on reaction-controlled fiber weakening. Under the assumption of a parabolic time-dependent growth for the interfacial reaction product, a Griffith-type fracture model was found to yield simple equations whose predictions were in good agreement with data for boron fiber average strength and for B/Al axial fracture strain. The only variables in these equations were the time and temperature of the thermal exposure and an empirical factor related to fiber surface smoothness prior to composite consolidation. Such variables as fiber diameter and aluminum alloy composition were found to have little influence. The basic and practical implications of the fracture model equations are discussed. Previously announced in STAR as N82-24297

Splenectomy attenuates severe thermal trauma-induced intestinal barrier breakdown in rats.

Science.gov (United States)

Liu, Xiang-dong; Chen, Zhen-yong; Yang, Peng; Huang, Wen-guang; Jiang, Chun-fang

2015-12-01

The severe local thermal trauma activates a number of systemic inflammatory mediators, such as TNF-α, NF-κB, resulting in a disruption of gut barrier. The gastrointestinal tight junction (TJ) is highly regulated by membrane-associated proteins including zonula occludens protein-1 (ZO-1) and occludin, which can be modulated by inflammatory cytokines. As splenectomy has been shown to reduce secretion of cytokines, we hypothesized that (1) severe scald injury up-regulates TNF-α and NF-κB, meanwhile down-regulates expression of ZO-1 and occludin, leading to the increased intestinal permeability, and (2) splenectomy can prevent the burn-induced decrease in ZO-1 and occludin expression, resulting in improved intestinal barrier. Wistar rats undergoing a 30% total body surface area (TBSA) thermal trauma were randomized to receive an accessorial splenectomy meanwhile or not. Intestinal injury was assessed by histological morphological analysis, and serum endotoxin levels, TNF-α, NF-κB, ZO-1 and occludin levels were detected by Western blotting in the terminal ileum mucosal tissue. 30% TBSA burn caused a significant increase in serum endotoxin levels, but NF-κB, and TNF-α, and the average intestinal villus height and mucosal thickness were decreased significantly. Burn injury could also markedly decrease the levels of ZO-1 and occludin in terminal ileum mucosal tissue (all PSplenectomy at 7th day after burn significantly reversed the burn-induced breakdown of ZO-1 and occludin (all PSplenectomy may provide a therapeutic benefit in restoring burn-induced intestinal barrier by decreasing the release of inflammatory cytokines and recovering TJ proteins.

Impact of the surface quality on the thermal shock performance of beryllium armor tiles for first wall applications

Energy Technology Data Exchange (ETDEWEB)

Spilker, B., E-mail: b.spilker@fz-juelich.de; Linke, J.; Pintsuk, G.; Wirtz, M.

2016-11-01

Highlights: • Different surface qualities of S-65 beryllium are tested under high heat flux conditions. • After 1000 thermal shocks, the loaded area exhibits a crucial destruction. • Stress accelerated grain boundary oxidation/dynamic embrittlement effects are linked to the thermal shock performance of beryllium. • Thermally induced cracks form between 1 and 10 pulses and grow wider and deeper between 10 and 100 pulses. • Thermally induced cracks form and propagate independently from surface grooves and the surface quality. - Abstract: Beryllium will be applied as first wall armor material in ITER. The armor has to sustain high steady state and transient power fluxes. For transient events like edge localized modes, these transient power fluxes rise up to 1.0 GW m{sup −2} with a duration of 0.5–0.75 ms in the divertor region and a significant fraction of this power flux is deposited on the first wall as well. In the present work, the reference beryllium grade for the ITER first wall application S-65 was prepared with various surface conditions and subjected to transient power fluxes (thermal shocks) with ITER relevant loading parameters. After 1000 thermal shocks, a crucial destruction of the entire loaded area was observed and linked to the stress accelerated grain boundary oxidation (SAGBO)/dynamic embrittlement (DE) effect. Furthermore, the study revealed that the majority of the thermally induced cracks formed between 1 and 10 pulses and then grew wider and deeper with increasing pulse number. The surface quality did not influence the cracking behavior of beryllium in any detectable way. However, the polished surface demonstrated the highest resistance against the observed crucial destruction mechanism.

Thermal and dynamic mechanical properties of grafted kenaf filled poly (vinyl chloride)/ethylene vinyl acetate composites

International Nuclear Information System (INIS)

Bakar, Nurfatimah Abu; Chee, Ching Yern; Abdullah, Luqman Chuah; Ratnam, Chantara Thevy; Ibrahim, Nor Azowa

2015-01-01

Highlights: • Study on thermal and dynamic mechanical properties of PVC/EVA/PMMA grafted kenaf fiber. • PMMA grafted kenaf fiber showed good interaction with PVC/EVA blends. • Thermal stability of the composites increase upon PMMA grafting on kenaf fiber. • The crystallinity of the composites decrease upon PMMA grafting on kenaf fiber. • PMMA grafted fiber provides more reinforcement on PVC/EVA/grafted PMMA composite. - Abstract: The effects of kenaf and poly (methyl methacrylate grafted kenaf on the thermal and dynamic mechanical properties of poly (vinyl chloride), PVC and ethylene vinyl acetate, EVA blends were investigated. The PVC/EVA/kenaf composites were prepared by mixing the grafted and ungrafted kenaf fiber and PVC/EVA blend using HAAKE Rheomixer at a temperature of 150 °C and the rotor speed at 50 rpm for 20 min. The composites were subjected to Differential Scanning Calorimetric (DSC), Thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR) and Scanning Electron Microscopy (SEM) studies. The DSC data revealed that the crystallinity of the EVA decreased with the addition of 30% grafted and ungrafted kenaf fibers. TGA and derivative thermogravimetric (DTG) curves displayed an increase in the thermal stability of the composites upon grafting of the fiber. Studies on DMA indicate that the T g of the PVC and EVA in the PVC/EVA/kenaf composites has been shifted to higher temperature with the addition of the kenaf fiber. The presence of PMMA on the surface of grafted kenaf fiber was further confirmed by the analytical results from FTIR. The morphology of fractured surfaces of the composites, which was examined by a scanning electron microscope, showed the adhesion between the kenaf fiber and the PVC/EVA matrix was improved upon grafting of the kenaf fiber

Thermal and dynamic mechanical characterization of thermoplastic polyurethane/organoclay nanocomposites prepared by melt compounding

International Nuclear Information System (INIS)

Barick, A.K.; Tripathy, D.K.

2010-01-01

Thermoplastic polyurethane (TPU) nanocomposites based on organically modified layered silicate (OMLS) were prepared by melt intercalation process followed by compression molding. Different percentage of organoclays was incorporated into the TPU matrix in order to examine the influence of the nanoscaled fillers on nanostructure morphology and material properties. The microscopic morphology of the nanocomposites was evaluated by wide angle X-ray diffraction (WAXD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The observation revealed that both nanoclay-polymer interactions and shear stress developed during melt mixing are responsible for the effectively organoclay dispersion in TPU matrix resulting intercalated/exfoliated morphology. Thermal stability of the nanocomposites measured by thermogravimetric analysis (TGA) was improved significantly with the addition of nanoclay. The differential scanning calorimetry (DSC) analysis reveals that melting point of the nanocomposites increased with incorporation of nanoclay. The dynamic mechanical properties of the TPU nanocomposites were analyzed using a dynamic mechanical thermal analyzer (DMTA), which indicates that the storage modulus (E'), loss modulus (E''), and glass transition temperature (T g ) are significantly increased with increasing nanoclay content.

Applications of laser-induced gratings to spectroscopy and dynamics

Energy Technology Data Exchange (ETDEWEB)

Rohlfing, E.A. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

This program has traditionally emphasized two principal areas of research. The first is the spectroscopic characterization of large-amplitude motion on the ground-state potential surface of small, transient molecules. The second is the reactivity of carbonaceous clusters and its relevance to soot and fullerene formation in combustion. Motivated initially by the desire to find improved methods of obtaining stimulated emission pumping (SEP) spectra of transients, most of our recent work has centered on the use of laser-induced gratings or resonant four-wave mixing in free-jet expansions. These techniques show great promise for several chemical applications, including molecular spectroscopy and photodissociation dynamics. The author describes recent applications of two-color laser-induced grating spectroscopy (LIGS) to obtain background-free SEP spectra of transients and double resonance spectra of nonfluorescing species, and the use of photofragment transient gratings to probe photodissociation dynamics.

Thermally induced outdiffusion studies of deuterium in ceramic breeder blanket materials after irradiation

Energy Technology Data Exchange (ETDEWEB)

González, Maria, E-mail: maria.gonzalez@ciemat.es [LNF-CIEMAT, Materials for Fusion Group, Madrid (Spain); Carella, Elisabetta; Moroño, Alejandro [LNF-CIEMAT, Materials for Fusion Group, Madrid (Spain); Kolb, Matthias H.H.; Knitter, Regina [Karlsruhe Institute of Technology, Institute for Applied Materials (IAM-WPT), Karlsruhe (Germany)

2015-10-15

Highlights: • Surface defects in Lithium-based ceramics are acting as trapping centres for deuterium. • Ionizing radiation affects the deuterium sorption and desorption processes. • By extension, the release of the tritium produced in a fusion breeder will be effective. - Abstract: Based on a KIT–CIEMAT collaboration on the radiation damage effects of light ions sorption/desorption in ceramic breeder materials, candidate materials for the ITER EU TBM were tested for their outgassing behavior as a function of temperature and radiation. Lithium orthosilicate based pebbles with different metatitanate contents and pellets of the individual oxide components were exposed to a deuterium atmosphere at room temperature. Then the thermally induced release of deuterium gas was registered up to 800 °C. This as-received behavior was studied in comparison with that after exposing the deuterium-treated samples to 4 MGy total dose of gamma radiation. The thermal desorption spectra reveal differences in deuterium sorption/desorption behavior depending on the composition and the induced ionizing damage. In these breeder candidates, strong desorption rate at approx. 300 °C takes place, which slightly increases with increasing amount of the titanate second phase. For all studied materials, ionizing radiation induces electronic changes disabling a number of trapping centers for D{sub 2} adsorption.

Nanocomposite of photocurable epoxy-acrylate resin and carbon nanotubes: dynamic-mechanical, thermal and tribological properties

Directory of Open Access Journals (Sweden)

Marcos Nunes dos Santos

2013-04-01

Full Text Available In this study, the thermal, dynamic-mechanical and tribological behavior of nanocomposites of a photocurable epoxy-acrylate resin and multiwalled carbon nanotubes (MWCNT are investigated. A route consisting of a combination of sonication, mechanical and magnetic stirring is used to disperse 0.25-0.75 wt. (% MWCNT into the resin. Two photocuring cycles using 12 hours and 24 hours of UV-A radiation are studied. The storage modulus, the loss modulus and the tan delta are obtained by dynamic mechanical analysis. Thermal stability is investigated by thermogravimetry, morphology by transmission electronic microscopy (TEM and tribological performance using a pin-on-disk apparatus. The results indicate an increase in stiffness and higher ability to dissipate energy, as well as a shift in the glass transition temperature for the nanocomposites. The addition of nanofillers also decreased friction coefficient and wear rate of the nanocomposites but did not change the observed wear mechanisms.

Nanocomposite of photocurable epoxy-acrylate resin and carbon nanotubes: dynamic-mechanical, thermal and tribological properties

Directory of Open Access Journals (Sweden)

Marcos Nunes dos Santos

2012-01-01

Full Text Available In this study, the thermal, dynamic-mechanical and tribological behavior of nanocomposites of a photocurable epoxy-acrylate resin and multiwalled carbon nanotubes (MWCNT are investigated. A route consisting of a combination of sonication, mechanical and magnetic stirring is used to disperse 0.25-0.75 wt. (% MWCNT into the resin. Two photocuring cycles using 12 hours and 24 hours of UV-A radiation are studied. The storage modulus, the loss modulus and the tan delta are obtained by dynamic mechanical analysis. Thermal stability is investigated by thermogravimetry, morphology by transmission electronic microscopy (TEM and tribological performance using a pin-on-disk apparatus. The results indicate an increase in stiffness and higher ability to dissipate energy, as well as a shift in the glass transition temperature for the nanocomposites. The addition of nanofillers also decreased friction coefficient and wear rate of the nanocomposites but did not change the observed wear mechanisms.

Record Dynamics and the Parking Lot Model for granular dynamics

Science.gov (United States)

Sibani, Paolo; Boettcher, Stefan

Also known for its application to granular compaction (E. Ben-Naim et al., Physica D, 1998), the Parking Lot Model (PLM) describes the random parking of identical cars in a strip with no marked bays. In the thermally activated version considered, cars can be removed at an energy cost and, in thermal equilibrium, their average density increases as temperature decreases. However, equilibration at high density becomes exceedingly slow and the system enters an aging regime induced by a kinematic constraint, the fact that parked cars may not overlap. As parking an extra car reduces the available free space,the next parking event is even harder to achieve. Records in the number of parked cars mark the salient features of the dynamics and are shown to be well described by the log-Poisson statistics known from other glassy systems with record dynamics. Clusters of cars whose positions must be rearranged to make the next insertion possible have a length scale which grows logarithmically with age, while their life-time grows exponentially with size. The implications for a recent cluster model of colloidal dynamics,(S. Boettcher and P. Sibani, J. Phys.: Cond. Matter, 2011 N. Becker et al., J. Phys.: Cond. Matter, 2014) are discussed. Support rom the Villum Foundation is gratefully acknowledged.

Effects of Heating Rate on the Dynamic Tensile Mechanical Properties of Coal Sandstone during Thermal Treatment

Directory of Open Access Journals (Sweden)

Ming Li

2017-01-01

Full Text Available The effects of coal layered combustion and the heat injection rate on adjacent rock were examined in the process of underground coal gasification and coal-bed methane mining. Dynamic Brazilian disk tests were conducted on coal sandstone at 800°C and slow cooling from different heating rates by means of a Split Hopkinson Pressure Bar (SHPB test system. It was discovered that thermal conditions had significant effects on the physical and mechanical properties of the sandstone including longitudinal wave velocity, density, and dynamic linear tensile strength; as the heating rates increased, the thermal expansion of the sandstone was enhanced and the damage degree increased. Compared with sandstone at ambient temperature, the fracture process of heat-treated sandstone was more complicated. After thermal treatment, the specimen had a large crack in the center and cracks on both sides caused by loading; the original cracks grew and mineral particle cracks, internal pore geometry, and other defects gradually appeared. With increasing heating rates, the microscopic fracture mode transformed from ductile fracture to subbrittle fracture. It was concluded that changes in the macroscopic mechanical properties of the sandstone were result from changes in the composition and microstructure.

Thermal dynamic behavior during selective laser melting of K418 superalloy: numerical simulation and experimental verification

Science.gov (United States)

Chen, Zhen; Xiang, Yu; Wei, Zhengying; Wei, Pei; Lu, Bingheng; Zhang, Lijuan; Du, Jun

2018-04-01

During selective laser melting (SLM) of K418 powder, the influence of the process parameters, such as laser power P and scanning speed v, on the dynamic thermal behavior and morphology of the melted tracks was investigated numerically. A 3D finite difference method was established to predict the dynamic thermal behavior and flow mechanism of K418 powder irradiated by a Gaussian laser beam. A three-dimensional randomly packed powder bed composed of spherical particles was established by discrete element method. The powder particle information including particle size distribution and packing density were taken into account. The volume shrinkage and temperature-dependent thermophysical parameters such as thermal conductivity, specific heat, and other physical properties were also considered. The volume of fluid method was applied to reconstruct the free surface of the molten pool during SLM. The geometrical features, continuity boundaries, and irregularities of the molten pool were proved to be largely determined by the laser energy density. The numerical results are in good agreement with the experiments, which prove to be reasonable and effective. The results provide us some in-depth insight into the complex physical behavior during SLM and guide the optimization of process parameters.

Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics – a Comparative Study with Gallium Nitride

Science.gov (United States)

Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L.; Roy, Ajit K.; Luo, Tengfei

2016-01-01

Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN) – another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics. PMID:26928396

Interring Gas Dynamic Analysis of Piston in a Diesel Engine considering the Thermal Effect

Directory of Open Access Journals (Sweden)

Wanyou Li

2015-01-01

Full Text Available Understanding the interaction between ring dynamics and gas transport in ring pack systems is crucial and needs to be imperatively studied. The present work features detailed interring gas dynamics of piston ring pack behavior in internal combustion engines. The model is developed for a ring pack with four rings. The dynamics of ring pack are simulated. Due to the fact that small changes in geometry of the grooves and lands would have a significant impact on the interring gas dynamics, the thermal deformation of piston has been considered during the ring pack motion analysis in this study. In order to get the temperature distribution of piston head more quickly and accurately, an efficient method utilizing the concept of inverse heat conduction is presented. Moreover, a sensitive analysis based on the analysis of partial regression coefficients is presented to investigate the effect of groove parameters on blowby.

New model for surface fracture induced by dynamical stress

OpenAIRE

Andersen, J. V.; Lewis, L. J.

1997-01-01

We introduce a model where an isotropic, dynamically-imposed stress induces fracture in a thin film. Using molecular dynamics simulations, we study how the integrated fragment distribution function depends on the rate of change and magnitude of the imposed stress, as well as on temperature. A mean-field argument shows that the system becomes unstable for a critical value of the stress. We find a striking invariance of the distribution of fragments for fixed ratio of temperature and rate of ch...

Numerical simulation of temperature and thermal stress for nuclear piping by using computational fluid dynamics analysis and Green’s function

Energy Technology Data Exchange (ETDEWEB)

Boo, Myung-Hwan [Korea Hydro and Nuclear Power Company, Daejeon (Korea, Republic of); Oh, Chang-Kyun; Kim, Hyun-Su [KEPCO Engineering and Construction Company, Gimcheon (Korea, Republic of); Choi, Choeng-Ryul [ELSOLTEC, Inc., Yongin (Korea, Republic of)

2017-05-15

Owing to the fact that thermal fatigue is a well-known damage mechanism in nuclear power plants, accurate stress and fatigue evaluation are highly important. Operating experience shows that the design condition is conservative compared to the actual one. Therefore, various fatigue monitoring methods have been extensively utilized to consider the actual operating data. However, defining the local temperature in the piping is difficult because temperature-measuring instruments are limited. The purpose of this paper is to define accurate local temperature in the piping and evaluate thermal stress using Green’s function (GF) by performing a series of computational fluid dynamics analyses considering the complex fluid conditions. Also, the thermal stress is determined by adopting GF and comparing it with that of the design condition. The fluid dynamics analysis result indicates that the fluid temperature slowly varies compared to the designed one even when the flow rate changes abruptly. In addition, the resulting thermal stress can significantly decrease when reflecting the actual temperature.

Tuning the Dynamics of Particles and Drops at Engineered Nanostructured Interfaces

Science.gov (United States)

Colosqui, Carlos; Checco, Antonio

2015-11-01

Harnessing the full potential of current nanofabrication capabilities requires significant progress in understanding non-equilibrium phenomena produced by nanoscale interfacial structure and thermal motion. In diverse colloidal systems relevant to complex fluids and soft materials, the nanoscale interfacial structure can induce transitions from fast dynamics dominated by (deterministic) hydrodynamic and surface forces to arrested dynamics dominated by (random) thermally-activated processes. Recent work provides guidelines for engineering geometries and surface structures to tune the dynamic behavior of nano/microscale particles and droplets. For example, small reductions of the radius of a microparticle can lead to dramatic increases in the time for adsorption at liquid interfaces or membranes. Similarly, reducing the radius of a millimeter-sized droplet can lead to arrested spreading dynamics with logarithmic-in-time relaxation. Furthermore, nanostructured surfaces with directional asymmetry can convert thermal motion into directed transport processes at controllable rates. This talk will discuss theoretical and computational predictions that have been confirmed in recent experimental work by our and other groups and new predictions that can guide future experimental studies.

Heterogeneity in induced thermal resistance of rat tumor cell clones

International Nuclear Information System (INIS)

Tomasovic, S.P.; Rosenblatt, P.L.; Heitzman, D.

1983-01-01

Four 13762NF rat mammary adenocarcinoma clones were examined for their survival response to heating under conditions that induced transient thermal resistance (thermotolerance). Clones MTC and MTF7 were isolated from the subcutaneous locally growing tumor, whereas clones MTLn2 and MTLn3 were derived from spontaneous lung metastases. There was heterogeneity among these clones in thermotolerance induced by either fractionated 45 0 C or continuous 42 0 C heating, but the order of sensitivity was not necessarily the same. The clones developed thermal resistance at different rates and to different degrees within the same time intervals. There was heterogeneity between clones isolated from within either the primary site or metastatic lesions. However, clones derived from metastatic foci did not intrinsically acquire more or less thermotolerance to fractionated 45 0 C or continuous 42 0 C heating than did clones from the primary tumor. Further, there was no apparent relationship between any phenotypic properties that conferred more or less thermotolerance in vitro and any phenotypic properties that conferred enhanced metastatic success of these same clones by spontaneous (subcutaneous) or experimental (intravenous) routes in vivo. These tumor clones also differ in their karyotype, metastatic potential, cell surface features, sensitivity to x-irradiation and drugs, and ability to repair sublethal radiation damage. These results provide further credence to the concept that inherent heterogeneity within tumors may be as important in therapeutic success as other known modifiers of outcome such as site and treatment heterogeneity

Mode coupling theory for nonequilibrium glassy dynamics of thermal self-propelled particles.

Science.gov (United States)

Feng, Mengkai; Hou, Zhonghuai

2017-06-28

We present a mode coupling theory study for the relaxation and glassy dynamics of a system of strongly interacting self-propelled particles, wherein the self-propulsion force is described by Ornstein-Uhlenbeck colored noise and thermal noises are included. Our starting point is an effective Smoluchowski equation governing the distribution function of particle positions, from which we derive a memory function equation for the time dependence of density fluctuations in nonequilibrium steady states. With the basic assumption of the absence of macroscopic currents and standard mode coupling approximation, we can obtain expressions for the irreducible memory function and other relevant dynamic terms, wherein the nonequilibrium character of the active system is manifested through an averaged diffusion coefficient D[combining macron] and a nontrivial structural function S 2 (q) with q being the magnitude of wave vector q. D[combining macron] and S 2 (q) enter the frequency term and the vertex term for the memory function, and thus influence both the short time and the long time dynamics of the system. With these equations obtained, we study the glassy dynamics of this thermal self-propelled particle system by investigating the Debye-Waller factor f q and relaxation time τ α as functions of the persistence time τ p of self-propulsion, the single particle effective temperature T eff as well as the number density ρ. Consequently, we find the critical density ρ c for given τ p shifts to larger values with increasing magnitude of propulsion force or effective temperature, in good accordance with previously reported simulation work. In addition, the theory facilitates us to study the critical effective temperature T for fixed ρ as well as its dependence on τ p . We find that T increases with τ p and in the limit τ p → 0, it approaches the value for a simple passive Brownian system as expected. Our theory also well recovers the results for passive systems and can be

Characterising thermal resistances and capacitances of GaN high-electron-mobility transistors through dynamic electrothermal measurements

DEFF Research Database (Denmark)

Wei, Wei; Mikkelsen, Jan H.; Jensen, Ole Kiel

2014-01-01

This study presents a method to characterise thermal resistances and capacitances of GaN high-electron-mobility transistors (HEMTs) through dynamic electrothermal measurements. A measured relation between RF gain and the channel temperature (Tc) is formed and used for indirect measurements...

WE-FG-202-01: Early Prediction of Radiotherapy Induced Skin Reactions Using Dynamic Infrared Imaging

Energy Technology Data Exchange (ETDEWEB)

Biswal, N [Rutgers Cancer Institute of New Jersey, New Brunswick, NJ (United States); Cifter, G [Boston, MA (United States); Sun, J [Argonne National Laboratory, Lemont, IL (United States); Sen, N; Wang, D; Diaz, A; Griem, K [Rush University Medical Center, Chicago, IL (United States); Chu, J [Rush University Medical Center, Oak Brook, IL (United States)

2016-06-15

Purpose: To predict radiotherapy induced skin reactions using dynamic infrared imaging. Methods: Thermal images were captured by our homebuilt system consisting of two flash lamps and an infrared (IR) camera. The surface temperature of the skin was first raised by ∼ 6 oC from ∼1 ms flashes. The camera then captured a series of IR images for 10 seconds. For each image, a baseline skin temperature was recorded for 0.5sec before heat impulse. The temporal temperature gradients were calculated between a reference point (immediately after the flash) and at a time point 9sec after that. Thermal effusivity, an intrinsic thermal property of a material, was calculated from the surface temperature decay of skin. We present experimental data in five patients undergoing radiation therapy, of which 2 were Head & Neck, 1 was Sarcoma and 2 were Breast cancer patients. The prescribed doses were 45 – 60 Gy in 25 – 30 fractions. Each patient was imaged before treatment and after every fifth fraction until end of the treatment course. An area on the skin, outside the radiation field, was imaged as control region. During imaging, each patient’s irradiated skins were scored based on RTOG skin morbidity scoring criteria. Results: Temperature gradient, which is the temperature recovery rate, depends on the thermal properties of underlying tissue. It was observed that, the skin temperature and temporal temperature gradient increases with delivered radiation dose and skin RTOG score. The treatment does not change effusivity of superficial skin layer, however there was a significant difference in effusivity between treated and control areas at depth of ∼ 1.5 – 1.8 mm, increases with dose. Conclusion: The higher temporal temperature gradient and effusivity from irradiated areas suggest that there is more fluid under the irradiated skin, which causes faster temperature recovery. The mentioned effects may be predictors of Moist Desquamation.

Simulation study of the thermal and the thermoelastic effects induced by pulsed laser absorption in human skin

Science.gov (United States)

Kim, Jae-Young; Jang, Kyungmin; Yang, Seung-Jin; Baek, Jun-Hyeok; Park, Jong-Rak; Yeom, Dong-Il; Kim, Ji-Sun; Kim, Hyung-Sik; Jun, Jae-Hoon; Chung, Soon-Cheol

2016-04-01

We studied the thermal and the mechanical effects induced by pulsed laser absorption in human skin by numerically solving the heat-transfer and the thermoelastic wave equations. The simulation of the heat-transfer equation yielded the spatiotemporal distribution of the temperature increase in the skin, which was then used in the driving term of the thermoelastic wave equation. We compared our simulation results for the temperature increase and the skin displacements with the measured and numerical results, respectively. For the comparison, we used a recent report by Jun et al. [Sci. Rep. 5, 11016 (2015)], who measured in vivo skin temperature and performed numerical simulation of the thermoelastic wave equation using a simple assumption about the temporal evolution of the temperature distribution, and found their results to be in good agreement with our results. In addition, we obtained solutions for the stresses in the human skin and analyzed their dynamic behaviors in detail.

Noise spectroscopy of CoFeB/MgO/CoFeB magnetic tunnel junctions in the presence of thermal gradients

Energy Technology Data Exchange (ETDEWEB)

Liebing, N. [Physikalisch-Technische Bundesanstalt, Bundesallee 100, d-38116 Braunschweig (Germany); Serrano-Guisan, S., E-mail: santiago.serrano-guisan@inl.int [International Iberian Nanotechnology Laboratory, Avenida Mestre Jose Veiga, 4715-330 Braga (Portugal); Rott, K.; Reiss, G. [University of Bielefeld, Department of Physics, Univesitätesstr. 25, d-33615 Bielefeld (Germany); Schumacher, H.W., E-mail: hans.w.schumacher@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, d-38116 Braunschweig (Germany)

2016-02-15

We present experimental data of the precessional dynamics of the free layer of CoFeB/MgO/CoFeB based magnetic tunnel junctions (MTJ) in the presence of thermal gradients across the MTJ. The free layer precession is investigated by noise spectroscopy. Thermal gradients of the order of tens of mK/nm across the MTJ are generated by electrical heating. Without applied thermal gradients we find spin transfer torque modified magnetization precession. With increasing thermal gradients we generally observe a decrease of the precession frequency which could be related to an increasing overall free layer temperature. However an asymmetry of the line width behavior for parallel and antiparallel orientation points towards additional effects beyond thermal activation. This could be a hint for the modification of the precessional dynamics in magnetic tunnel junctions by thermal spin torques. - Highlights: • Thermal gradients induced magnetization dynamics on MTJ structures are explored. • Magnetic noise spectroscopy is carried out to study the efficiency of such effects. • A decrease of resonance frequency is observed at both MTJ states for large ∇T. • An asymmetric linewidth behavior is observed for both MTJ states under ∇T. • Additional thermal effects beyond thermal activation must be considered.

Moisture-Induced Delamination Video of an Oxidized Thermal Barrier Coating

Science.gov (United States)

Smialek, James L.; Zhu, Dongming; Cuy, Michael D.

2008-01-01

PVD TBC coatings were thermally cycled to near-failure at 1150 C. Normal failure occurred after 200 to 300 1-hr cycles with only moderate weight gains (0.5 mg/sq cm). Delamination and buckling was often delayed until well after cooldown (desktop spallation), but could be instantly induced by the application of water drops, as shown in a video clip which can be viewed by clicking on figure 2 of this report. Moisture therefore plays a primary role in delayed desktop TBC failure. Hydrogen embrittlement is proposed as the underlying mechanism.

Thermal-hydraulics stability of natural circulation BWR under startup. Flashing effects

International Nuclear Information System (INIS)

Hu, Rui; Kazimi, Mujid S.

2009-01-01

To help achieve the necessary natural circulation flow, a fairly long chimney is installed in a boiling natural circulation reactor like the ESBWR. In such systems, thermal-hydraulic stability during low pressure start-up should be examined while considering the flashing induced by the pressure drop in the channel and the chimney due to gravity head. In this work, a BWR stability analysis code in the frequency domain, named FISTAB (Flashing-Induced STability Analysis for BWR), was developed to address the issue of flashing-induced instability. A thermal-hydraulics non-homogeneous equilibrium model (NHEM) based on a drift flux formulation along with a lumped fuel dynamics model is incorporated in the work. The vapor generation rate is derived from the mixture energy conservation equation while considering the effect of flashing. The functionality of the FISTAB code was confirmed by comparison to experimental results from SIRIUS-N facility at CRIEPI, Japan. Both stationary and perturbation results agree well with the experimental results. (author)

Facility at CIRUS reactor for thermal neutron induced prompt γ-ray spectroscopic studies

International Nuclear Information System (INIS)

Biswas, D.C.; Danu, L.S.; Mukhopadhyay, S.; Kinage, L.A.; Prashanth, P.N.; Goswami, A.; Sahu, A.K.; Shaikh, A.M.; Chatterjee, A.; Choudhury, R.K.; Kailas, S.

2013-01-01

A facility for prompt γ-ray spectroscopic studies using thermal neutrons from a radial beam line of Canada India Research Utility Services (CIRUS) reactor, Bhabha Atomic Research Centre (BARC), has been developed. To carry out on-line spectroscopy experiments, two clover germanium detectors were used for the measurement of prompt γ rays. For the first time, the prompt γ–γ coincidence technique has been used to study the thermal neutron induced fission fragment spectroscopy (FFS) in 235 U(n th , f). Using this facility, experiments have also been carried out for on-line γ-ray spectroscopic studies in 113 Cd(n th , γ) reaction

Temperature and Pressure Dependence of Signal Amplitudes for Electrostriction Laser-Induced Thermal Acoustics

Science.gov (United States)

Herring, Gregory C.

2015-01-01

The relative signal strength of electrostriction-only (no thermal grating) laser-induced thermal acoustics (LITA) in gas-phase air is reported as a function of temperature T and pressure P. Measurements were made in the free stream of a variable Mach number supersonic wind tunnel, where T and P are varied simultaneously as Mach number is varied. Using optical heterodyning, the measured signal amplitude (related to the optical reflectivity of the acoustic grating) was averaged for each of 11 flow conditions and compared to the expected theoretical dependence of a pure-electrostriction LITA process, where the signal is proportional to the square root of [P*P /( T*T*T)].

Current-induced atomic dynamics, instabilities, and Raman signals

DEFF Research Database (Denmark)

Lu, Jing Tao; Brandbyge, Mads; Hedegard, Per

2012-01-01

We derive and employ a semiclassical Langevin equation obtained from path integrals to describe the ionic dynamics of a molecular junction in the presence of electrical current. The electronic environment serves as an effective nonequilibrium bath. The bath results in random forces describing Joule...... heating, current-induced forces including the nonconservative wind force, dissipative frictional forces, and an effective Lorentz-type force due to the Berry phase of the nonequilibrium electrons. Using a generic two-level molecular model, we highlight the importance of both current-induced forces...... and Joule heating for the stability of the system. We compare the impact of the different forces, and the wide-band approximation for the electronic structure on our result. We examine the current-induced instabilities (excitation of runaway "waterwheel" modes) and investigate the signature...

Mobility of point defects induced by subthreshold collisions

International Nuclear Information System (INIS)

Tenenbaum, A.; Nguyen Van Doan

1976-01-01

The effect of thermal vibrations on atomic collision focusing was studied with the view to demonstrate that such collisions may induce point defect migration through the crystal. The persistence of the phenomenon of focused atomic collisions in a crystal at thermal equilibrium was studied, using a computer simulation by the Molecular Dynamics Technique. In the temperature range (0 to 500K) matter and momentum transfers in c.f.c. crystals proceed mainly by focused collisions along and directions. Their contribution to the induced migration of radiation defects was determined from the threshold energy of every primary able to be involved in the process. As an example, the quantitative model is applied to electron irradiation along the crystallographic directions [fr

ESR Study Applied To Thermal Stability Of Radiation-Induced Species Of Solid Ketoprofen

International Nuclear Information System (INIS)

Maltar-Strmecki, N.; Katusin-Razem, B.; Razem, D.

2015-01-01

Ketoprofen [2-(3-benzoylphenyl) propionic acid] is a non-steroidal anti-inflammatory drug. It has been widely used in human and veterinary medicine. Radiation processing of drugs and its ingredients is recognized as a safe and effective method among the existing technologies for sterilization and protocols that can be found in ISO 11137-1. Radiosterilization of drugs or other medical products by a suitable dose of ionizing radiation conducted in an appropriate environment ensures sterile conditions by destroying or removing vegetative and sporulating microbes from the ingredients or environment. In earlier studies the effects of gamma radiation was evaluated by selected physico-chemical methods and the observations showed that solid ketoprofen is relatively stable toward ionizing irradiation and that radiosterilization might be a suitable method for the sterilization of solid ketoprofen. The studies reported in this work were undertaken to analyse thermal stability of free radicals by accelerated aging method with a view to the determination of shelf-life. The expiration date (shelf-life) of a product is based on evaluation of both, thermal stability of free radicals, as well as on the time evolution of stable radiolysis products. Namely, storage time is determined by the time required by any degradation product in the dosage form to achieve a sufficient level to represent a risk to the patient. This work shows that ESR spectroscopy provides means for determination of thermal stability of radicals induced by gamma-irradiation in solid drugs. Therefore, despite the complex mixture of individual free radicals induced by gamma-irradiation in solid ketoprofen, the overall lifetime of free radicals could be determined by using isothermal and isochronal annealing. This study shows that radicals induced by gamma-irradiation in solid ketoprofen are stable for at least about 6 months. (author).

Concurrency-Induced Transitions in Epidemic Dynamics on Temporal Networks.

Science.gov (United States)

Onaga, Tomokatsu; Gleeson, James P; Masuda, Naoki

2017-09-08

Social contact networks underlying epidemic processes in humans and animals are highly dynamic. The spreading of infections on such temporal networks can differ dramatically from spreading on static networks. We theoretically investigate the effects of concurrency, the number of neighbors that a node has at a given time point, on the epidemic threshold in the stochastic susceptible-infected-susceptible dynamics on temporal network models. We show that network dynamics can suppress epidemics (i.e., yield a higher epidemic threshold) when the node's concurrency is low, but can also enhance epidemics when the concurrency is high. We analytically determine different phases of this concurrency-induced transition, and confirm our results with numerical simulations.

Concurrency-Induced Transitions in Epidemic Dynamics on Temporal Networks

Science.gov (United States)

Onaga, Tomokatsu; Gleeson, James P.; Masuda, Naoki

2017-09-01

Social contact networks underlying epidemic processes in humans and animals are highly dynamic. The spreading of infections on such temporal networks can differ dramatically from spreading on static networks. We theoretically investigate the effects of concurrency, the number of neighbors that a node has at a given time point, on the epidemic threshold in the stochastic susceptible-infected-susceptible dynamics on temporal network models. We show that network dynamics can suppress epidemics (i.e., yield a higher epidemic threshold) when the node's concurrency is low, but can also enhance epidemics when the concurrency is high. We analytically determine different phases of this concurrency-induced transition, and confirm our results with numerical simulations.

Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals.

Science.gov (United States)

Tang, Jau

2008-04-28

In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi-Pasta-Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit "breathing" standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.

Cancelation of thermally induced frequency shifts in bimaterial cantilevers by nonlinear optomechanical interactions

Energy Technology Data Exchange (ETDEWEB)

Vy, Nguyen Duy, E-mail: nguyenduyvy@tdt.edu.vn [Theoretical Physics Research Group, Ton Duc Thang University, Ho Chi Minh City 756636 (Viet Nam); Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 756636 (Viet Nam); Tri Dat, Le [Faculty of Physics and Engineering Physics, University of Science, Ho Chi Minh City 748355 (Viet Nam); Iida, Takuya [Department of Physical Science, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan)

2016-08-01

Bimaterial cantilevers have recently been used in, for example, the calorimetric analysis with picowatt resolution in microscopic space based on state-of-the-art atomic force microscopes. However, thermally induced effects usually change physical properties of the cantilevers, such as the resonance frequency, which reduce the accuracy of the measurements. Here, we propose an approach to circumvent this problem that uses an optical microcavity formed between a metallic layer coated on the back of the cantilever and one coated at the end of an optical fiber irradiating the cantilever. In addition to increasing the sensitivity, the optical rigidity of this system diminishes the thermally induced frequency shift. For a coating thickness of several tens of nanometers, the input power is 5–10 μW. These values can be evaluated from parameters derived by directly irradiating the cantilever in the absence of the microcavity. The system has the potential of using the cantilever both as a thermometer without frequency shifting and as a sensor with nanometer-controlled accuracy.

Thermal Equilibrium Dynamic Control Based on DPWM Dual-Mode Modulation of High Power NPC Three-Level Inverter

OpenAIRE

Xu, Shi-Zhou; He, Feng-You

2016-01-01

In some special applications of NPC three-level inverters, such as mine hoist, there exist special conditions of overloading during the whole hoisting process and large overload in starting stage, during which the power-loss calculation of power devices and thermal control are important factors affecting the thermal stability of inverters. The principles of SVPWM and DPWM were described in this paper firstly, based on which the dynamic power losses of the two modulations of hoist in single pe...

Pronounced low-frequency vibrational thermal transport in C60 fullerite realized through pressure-dependent molecular dynamics simulations

Science.gov (United States)

Giri, Ashutosh; Hopkins, Patrick E.

2017-12-01

Fullerene condensed-matter solids can possess thermal conductivities below their minimum glassy limit while theorized to be stiffer than diamond when crystallized under pressure. These seemingly disparate extremes in thermal and mechanical properties raise questions into the pressure dependence on the thermal conductivity of C60 fullerite crystals, and how the spectral contributions to vibrational thermal conductivity changes under applied pressure. To answer these questions, we investigate the effect of strain on the thermal conductivity of C60 fullerite crystals via pressure-dependent molecular dynamics simulations under the Green-Kubo formalism. We show that the thermal conductivity increases rapidly with compressive strain, which demonstrates a power-law relationship similar to their stress-strain relationship for the C60 crystals. Calculations of the density of states for the crystals under compressive strains reveal that the librational modes characteristic in the unstrained case are diminished due to densification of the molecular crystal. Over a large compression range (0-20 GPa), the Leibfried-Schlömann equation is shown to adequately describe the pressure dependence of thermal conductivity, suggesting that low-frequency intermolecular vibrations dictate heat flow in the C60 crystals. A spectral decomposition of the thermal conductivity supports this hypothesis.

Interactions between soil thermal and hydrological dynamics in the response of Alaska ecosystems to fire disturbance

Science.gov (United States)

Yi, Shuhua; McGuire, A. David; Harden, Jennifer; Kasischke, Eric; Manies, Kristen L.; Hinzman, Larry; Liljedahl, Anna K.; Randerson, J.; Liu, Heping; Romanovsky, Vladimir E.; Marchenko, Sergey S.; Kim, Yongwon

2009-01-01

Soil temperature and moisture are important factors that control many ecosystem processes. However, interactions between soil thermal and hydrological processes are not adequately understood in cold regions, where the frozen soil, fire disturbance, and soil drainage play important roles in controlling interactions among these processes. These interactions were investigated with a new ecosystem model framework, the dynamic organic soil version of the Terrestrial Ecosystem Model, that incorporates an efficient and stable numerical scheme for simulating soil thermal and hydrological dynamics within soil profiles that contain a live moss horizon, fibrous and amorphous organic horizons, and mineral soil horizons. The performance of the model was evaluated for a tundra burn site that had both preburn and postburn measurements, two black spruce fire chronosequences (representing space-for-time substitutions in well and intermediately drained conditions), and a poorly drained black spruce site. Although space-for-time substitutions present challenges in model-data comparison, the model demonstrates substantial ability in simulating the dynamics of evapotranspiration, soil temperature, active layer depth, soil moisture, and water table depth in response to both climate variability and fire disturbance. Several differences between model simulations and field measurements identified key challenges for evaluating/improving model performance that include (1) proper representation of discrepancies between air temperature and ground surface temperature; (2) minimization of precipitation biases in the driving data sets; (3) improvement of the measurement accuracy of soil moisture in surface organic horizons; and (4) proper specification of organic horizon depth/properties, and soil thermal conductivity.

Nonlocal microstructure-dependent dynamic stability of refined porous FG nanoplates in hygro-thermal environments

Science.gov (United States)

Reza Barati, Mohammad

2017-10-01

Based on the generalized nonlocal strain gradient theory (NSGT), dynamic modeling and analysis of nanoporous inhomogeneous nanoplates is presented. Therefore, it is possible to capture both stiffness-softening and stiffness-hardening effects for a more accurate dynamic analysis of nanoplates. The nanoplate is in hygro-thermal environments and is subjected to an in-plane harmonic load. Porosities are incorporated to the model based on a modified rule of mixture. Modeling of the porous nanoplate is conducted according to a refined four-variable plate theory with fewer field variables than in the first-order plate theory. The governing equations and related classical and nonclassical boundary conditions are derived based on Hamilton's principle. These equations are solved for hinged nanoplates via Galerkin's method. It is shown that porosities, moisture rise, temperature rise, nonlocal parameter, strain gradient parameter, material gradation, elastic foundation and uniform dynamic load have a remarkable influence on the dynamic behavior of nanoscale plates.

Molecular dynamics simulations of thermally activated edge dislocation unpinning from voids in α -Fe

Science.gov (United States)

Byggmästar, J.; Granberg, F.; Nordlund, K.

2017-10-01

In this study, thermal unpinning of edge dislocations from voids in α -Fe is investigated by means of molecular dynamics simulations. The activation energy as a function of shear stress and temperature is systematically determined. Simulations with a constant applied stress are compared with dynamic simulations with a constant strain rate. We found that a constant applied stress results in a temperature-dependent activation energy. The temperature dependence is attributed to the elastic softening of iron. If the stress is normalized with the softening of the specific shear modulus, the activation energy is shown to be temperature-independent. From the dynamic simulations, the activation energy as a function of critical shear stress was determined using previously developed methods. The results from the dynamic simulations are in good agreement with the constant stress simulations, after the normalization. This indicates that the computationally more efficient dynamic method can be used to obtain the activation energy as a function of stress and temperature. The obtained relation between stress, temperature, and activation energy can be used to introduce a stochastic unpinning event in larger-scale simulation methods, such as discrete dislocation dynamics.

Controlling Thermal Expansion: A Metal-Organic Frameworks Route.

Science.gov (United States)

Balestra, Salvador R G; Bueno-Perez, Rocio; Hamad, Said; Dubbeldam, David; Ruiz-Salvador, A Rabdel; Calero, Sofia

2016-11-22

Controlling thermal expansion is an important, not yet resolved, and challenging problem in materials research. A conceptual design is introduced here, for the first time, for the use of metal-organic frameworks (MOFs) as platforms for controlling thermal expansion devices that can operate in the negative, zero, and positive expansion regimes. A detailed computer simulation study, based on molecular dynamics, is presented to support the targeted application. MOF-5 has been selected as model material, along with three molecules of similar size and known differences in terms of the nature of host-guest interactions. It has been shown that adsorbate molecules can control, in a colligative way, the thermal expansion of the solid, so that changing the adsorbate molecules induces the solid to display positive, zero, or negative thermal expansion. We analyze in depth the distortion mechanisms, beyond the ligand metal junction, to cover the ligand distortions, and the energetic and entropic effect on the thermo-structural behavior. We provide an unprecedented atomistic insight on the effect of adsorbates on the thermal expansion of MOFs as a basic tool toward controlling the thermal expansion.

Controlling Thermal Expansion: A Metal–Organic Frameworks Route

Science.gov (United States)

2016-01-01

Controlling thermal expansion is an important, not yet resolved, and challenging problem in materials research. A conceptual design is introduced here, for the first time, for the use of metal–organic frameworks (MOFs) as platforms for controlling thermal expansion devices that can operate in the negative, zero, and positive expansion regimes. A detailed computer simulation study, based on molecular dynamics, is presented to support the targeted application. MOF-5 has been selected as model material, along with three molecules of similar size and known differences in terms of the nature of host–guest interactions. It has been shown that adsorbate molecules can control, in a colligative way, the thermal expansion of the solid, so that changing the adsorbate molecules induces the solid to display positive, zero, or negative thermal expansion. We analyze in depth the distortion mechanisms, beyond the ligand metal junction, to cover the ligand distortions, and the energetic and entropic effect on the thermo-structural behavior. We provide an unprecedented atomistic insight on the effect of adsorbates on the thermal expansion of MOFs as a basic tool toward controlling the thermal expansion. PMID:28190918

Thermal Dynamics in Newborn and Juvenile Models Cooled by Total Liquid Ventilation.

Science.gov (United States)

Nadeau, Mathieu; Sage, Michael; Kohlhauer, Matthias; Vandamme, Jonathan; Mousseau, Julien; Robert, Raymond; Tissier, Renaud; Praud, Jean-Paul; Walti, Herve; Micheau, Philippe

2016-07-01

Total liquid ventilation (TLV) consists in filling the lungs with a perfluorocarbon (PFC) and using a liquid ventilator to ensure a tidal volume of oxygenated, CO 2 -free and temperature-controlled PFC. Having a much higher thermal capacity than air, liquid PFCs assume that the filled lungs become an efficient heat exchanger with pulmonary circulation. The objective of the present study was the development and validation of a parametric lumped thermal model of a subject in TLV. The lungs were modeled as one compartment in which the control volume varied as a function of the tidal volume. The heat transfer in the body was modeled as seven parallel compartments representing organs and tissues. The thermal model of the lungs and body was validated with two groups of lambs of different ages and weights (newborn and juvenile) undergoing an ultrafast mild therapeutic hypothermia induction by TLV. The model error on all animals yielded a small mean error of -0.1 ±0.4  (°)C for the femoral artery and 0.0 ±0.1   (°)C for the pulmonary artery. The resulting experimental validation attests that the model provided an accurate estimation of the systemic arterial temperature and the venous return temperature. This comprehensive thermal model of the lungs and body has the advantage of closely modeling the rapid thermal dynamics in TLV. The model can explain how the time to achieve mild hypothermia between newborn and juvenile lambs remained similar despite of highly different physiological and ventilatory parameters. The strength of the model is its strong relationship with the physiological parameters of the subjects, which suggests its suitability for projection to humans.

Two-dimensional simulation of the thermal stress effect on static and dynamic VDMOS characteristics

International Nuclear Information System (INIS)

Alwan, M.; Beydoun, B.; Ketata, K.; Zoaeter, M.

2005-01-01

Using a two-dimensional simulator, the effect of the thermal stress on static and dynamic vertical double-diffusion metal oxide semiconductor (VDMOS) characteristics have been investigated. The use of the device under certain thermal stress conditions can produce modifications of its physical and electrical properties. Based on physics and 2D simulations, this paper proposes an analysis of this stress effect observed on the electrical characteristics of the device. Parameters responsible of these modifications are determined. Approximate expressions of the ionization coefficients and breakdown voltage in terms of temperature are proposed. Non-punch-through junction theory is used to express the breakdown voltage and the space charge extension with respect to the impurity concentration and the temperature. The capacitances of the device have been also studied. The effect of the stress on C-V characteristics is observed and analyzed. We notice that the drain-gate, drain-source and gate-source capacitances are shifted due to the degradation of device physical properties versus thermal stress

Thermal conductivity of electron-irradiated graphene

Science.gov (United States)

Weerasinghe, Asanka; Ramasubramaniam, Ashwin; Maroudas, Dimitrios

2017-10-01

We report results of a systematic analysis of thermal transport in electron-irradiated, including irradiation-induced amorphous, graphene sheets based on nonequilibrium molecular-dynamics simulations. We focus on the dependence of the thermal conductivity, k, of the irradiated graphene sheets on the inserted irradiation defect density, c, as well as the extent of defect passivation with hydrogen atoms. While the thermal conductivity of irradiated graphene decreases precipitously from that of pristine graphene, k0, upon introducing a low vacancy concentration, c reduction of the thermal conductivity with the increasing vacancy concentration exhibits a weaker dependence on c until the amorphization threshold. Beyond the onset of amorphization, the dependence of thermal conductivity on the vacancy concentration becomes significantly weaker, and k practically reaches a plateau value. Throughout the range of c and at all hydrogenation levels examined, the correlation k = k0(1 + αc)-1 gives an excellent description of the simulation results. The value of the coefficient α captures the overall strength of the numerous phonon scattering centers in the irradiated graphene sheets, which include monovacancies, vacancy clusters, carbon ring reconstructions, disorder, and a rough nonplanar sheet morphology. Hydrogen passivation increases the value of α, but the effect becomes very minor beyond the amorphization threshold.

Thermal energy storage for organic Rankine cycle solar dynamic space power systems

Science.gov (United States)

Heidenreich, G. R.; Parekh, M. B.

An organic Rankine cycle-solar dynamic power system (ORC-SDPS) comprises a concentrator, a radiator, a power conversion unit, and a receiver with a thermal energy storage (TES) subsystem which charges and discharges energy to meet power demands during orbital insolation and eclipse periods. Attention is presently given to the criteria used in designing and evaluating an ORC-SDPS TES, as well as the automated test facility employed. It is found that a substantial data base exists for the design of an ORC-SDPS TES subsystem.

Dynamic strain-induced transformation: An atomic scale investigation

International Nuclear Information System (INIS)

Zhang, H.; Pradeep, K.G.; Mandal, S.; Ponge, D.; Springer, H.; Raabe, D.

2015-01-01

Phase transformations provide the most versatile access to the design of complex nanostructured alloys in terms of grain size, morphology, local chemical constitution etc. Here we study a special case of deformation induced phase transformation. More specifically, we investigate the atomistic mechanisms associated with dynamic strain-induced transformation (DSIT) in a dual-phased multicomponent iron-based alloy at high temperatures. DSIT phenomena and the associated secondary phase nucleation were observed at atomic scale using atom probe tomography. The obtained local chemical composition was used for simulating the nucleation process which revealed that DSIT, occurring during load exertion, proceeds by a diffusion-controlled nucleation process

Colour centre recovery in yttria-stabilised zirconia: photo-induced versus thermal processes

Science.gov (United States)

Costantini, Jean-Marc; Touati, Nadia; Binet, Laurent; Lelong, Gérald; Guillaumet, Maxime; Beuneu, François

2018-05-01

The photo-annealing of colour centres in yttria-stabilised zirconia (YSZ) was studied by electron paramagnetic resonance spectroscopy upon UV-ray or laser light illumination, and compared to thermal annealing. Stable hole centres (HCs) were produced in as-grown YSZ single crystals by UV-ray irradiation at room temperature (RT). The HCs produced by 200-MeV Au ion irradiation, as well as the F+-type centres (? centres involving oxygen vacancies) were left unchanged upon UV illumination. In contrast, a significant photo-annealing of the latter point defects was achieved in 1.4-MeV electron-irradiated YSZ by 553-nm laser light irradiation at RT. Almost complete photo-bleaching was achieved by laser irradiation inside the absorption band of ? centres centred at a wavelength 550 nm. Thermal annealing of these colour centres was also followed by UV-visible absorption spectroscopy showing full bleaching at 523 K. Colour-centre evolutions by photo-induced and thermally activated processes are discussed on the basis of charge exchange processes between point defects.

Dynamic thermal analysis of a concentrated photovoltaic system

Science.gov (United States)

Avrett, John T., II; Cain, Stephen C.; Pochet, Michael

2012-02-01

Concentrated photovoltaic (PV) technology represents a growing market in the field of terrestrial solar energy production. As the demand for renewable energy technologies increases, further importance is placed upon the modeling, design, and simulation of these systems. Given the U.S. Air Force cultural shift towards energy awareness and conservation, several concentrated PV systems have been installed on Air Force installations across the country. However, there has been a dearth of research within the Air Force devoted to understanding these systems in order to possibly improve the existing technologies. This research presents a new model for a simple concentrated PV system. This model accurately determines the steady state operating temperature as a function of the concentration factor for the optical part of the concentrated PV system, in order to calculate the optimum concentration that maximizes power output and efficiency. The dynamic thermal model derived is validated experimentally using a commercial polysilicon solar cell, and is shown to accurately predict the steady state temperature and ideal concentration factor.

Double light-cone dynamics establish thermal states in integrable 1D Bose gases

Science.gov (United States)

Langen, T.; Schweigler, T.; Demler, E.; Schmiedmayer, J.

2018-02-01

We theoretically investigate the non-equilibrium dynamics in a quenched pair of one-dimensional Bose gases with density imbalance. We describe the system using its low-energy effective theory, the Luttinger liquid model. In this framework the system shows strictly integrable relaxation dynamics via dephasing of its approximate many-body eigenstates. In the balanced case, this leads to the well-known light-cone-like establishment of a prethermalized state, which can be described by a generalized Gibbs ensemble. In the imbalanced case the integrable dephasing leads to a state that, counter-intuitively, closely resembles a thermal equilibrium state. The approach to this state is characterized by two separate light-cone dynamics with distinct characteristic velocities. This behavior is a result of the fact that in the imbalanced case observables are not aligned with the conserved quantities of the integrable system. We discuss a concrete experimental realization to study this effect using matterwave interferometry and many-body revivals on an atom chip.

Polyurethane scaffold formation via a combination of salt leaching and thermally induced phase separation

NARCIS (Netherlands)

Heijkants, R. G. J. C.; van Calck, R. V.; van Tienen, T. G.; de Groot, J. H.; Pennings, A. J.; Buma, P.; Veth, R. P. H.; Schouten, A. J.

2008-01-01

Porous scaffolds have been made from two polyurethanes based on thermally induced phase separation of polymer dissolved in a DMSO/water mixture in combination with salt leaching. It is possible to obtain very porous foams with a very high interconnectivity. A major advantage of this method is that

Dynamics and mechanisms of chemotherapy-induced ovarian follicular depletion in women of fertile age

DEFF Research Database (Denmark)

Rosendahl, Mikkel; Andersen, Claus Yding; la Cour Freiesleben, Nina

2010-01-01

To study ovarian follicular dynamics during chemotherapy to understand the mechanisms behind chemotherapy-induced ovarian follicular depletion and to evaluate whether pretreatment levels of ovarian reserve markers were predictive of the posttreatment levels.......To study ovarian follicular dynamics during chemotherapy to understand the mechanisms behind chemotherapy-induced ovarian follicular depletion and to evaluate whether pretreatment levels of ovarian reserve markers were predictive of the posttreatment levels....

Somatic mutation and recombination induced with reactor thermal neutrons in Drosophila melanogaster

International Nuclear Information System (INIS)

Zambrano A, F.; Guzman R, J.; Paredes G, L.; Delfin L, A.

1997-01-01

The SMART test of Drosophila melanogaster was used to quantify the effect over the somatic mutation and recombination induced by thermal and fast neutrons at the TRIGA Mark III reactor of the ININ at the power of 300 k W for times of 30, 60 and 120 minutes with total equivalent doses respectively of 20.8, 41.6 and 83.2 Sv. A linear relation between the radiation equivalent dose and the frequency of the genetic effects such as mutation and recombination was observed. The obtained results allow to conclude that SMART is a sensitive system to the induced damage by neutrons, so this can be used for studying its biological effects. (Author)

A thermal modelling of displacement cascades in uranium dioxide

Energy Technology Data Exchange (ETDEWEB)

Martin, G., E-mail: guillaume.martin@cea.fr [CEA – DEN/DEC/SESC/LLCC, Bât. 352, 13108 Saint-Paul-Lez-Durance Cedex (France); Garcia, P.; Sabathier, C. [CEA – DEN/DEC/SESC/LLCC, Bât. 352, 13108 Saint-Paul-Lez-Durance Cedex (France); Devynck, F.; Krack, M. [Laboratory for Reactor Physics and Systems Behaviour, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Maillard, S. [CEA – DEN/DEC/SESC/LLCC, Bât. 352, 13108 Saint-Paul-Lez-Durance Cedex (France)

2014-05-01

The space and time dependent temperature distribution was studied in uranium dioxide during displacement cascades simulated by classical molecular dynamics (MD). The energy for each simulated radiation event ranged between 0.2 keV and 20 keV in cells at initial temperatures of 700 K or 1400 K. Spheres into which atomic velocities were rescaled (thermal spikes) have also been simulated by MD to simulate the thermal excitation induced by displacement cascades. Equipartition of energy was shown to occur in displacement cascades, half of the kinetic energy of the primary knock-on atom being converted after a few tenths of picoseconds into potential energy. The kinetic and potential parts of the system energy are however subjected to little variations during dedicated thermal spike simulations. This is probably due to the velocity rescaling process, which impacts a large number of atoms in this case and would drive the system away from a dynamical equilibrium. This result makes questionable MD simulations of thermal spikes carried out up to now (early 2014). The thermal history of cascades was compared to the heat equation solution of a punctual thermal excitation in UO{sub 2}. The maximum volume brought to a temperature above the melting temperature during the simulated cascade events is well reproduced by this simple model. This volume eventually constitutes a relevant estimate of the volume affected by a displacement cascade in UO{sub 2}. This definition of the cascade volume could also make sense in other materials, like iron.

Non-invasive and non-intrusive gas flow measurement based on the dynamic thermal characteristics of a pipeline

Science.gov (United States)

Fan, Zichuan; Cai, Maolin; Xu, Weiqing

2012-10-01

This paper proposes a non-intrusive and non-invasive method for measuring the gas flow rate in pneumatic industry. A heater unit is fixed on the partial circumference of the external wall of a pipeline and emits specific thermal pulses in a predetermined mode. Two sensors attached to the external wall detect the upstream temperature, and the gas flow can be measured according to the relationship between the flow rate and the dynamic thermal characteristics of the pipeline. To determine the preferable relationship, the temperature field model of the measurement system is built. Then, based on the measurement modes and the corresponding simulations, the objective functions for the gas flow specified on different dynamic thermal characteristics are established. Additionally, the minimum measurement time of the method, named reference time scale, is proposed. Further, robustness tests of the measurement method are derived by considering the influences of multiple factors on the objective functions. The experiments confirm that this method does not need to open the pipeline and disturb the flow regime in order to obtain the data; this method also avoids the typical time-consuming and complex operations, resists ambient temperature disturbance and achieves approximately acceptable results.

Non-invasive and non-intrusive gas flow measurement based on the dynamic thermal characteristics of a pipeline

International Nuclear Information System (INIS)

Fan, Zichuan; Cai, Maolin; Xu, Weiqing

2012-01-01

This paper proposes a non-intrusive and non-invasive method for measuring the gas flow rate in pneumatic industry. A heater unit is fixed on the partial circumference of the external wall of a pipeline and emits specific thermal pulses in a predetermined mode. Two sensors attached to the external wall detect the upstream temperature, and the gas flow can be measured according to the relationship between the flow rate and the dynamic thermal characteristics of the pipeline. To determine the preferable relationship, the temperature field model of the measurement system is built. Then, based on the measurement modes and the corresponding simulations, the objective functions for the gas flow specified on different dynamic thermal characteristics are established. Additionally, the minimum measurement time of the method, named reference time scale, is proposed. Further, robustness tests of the measurement method are derived by considering the influences of multiple factors on the objective functions. The experiments confirm that this method does not need to open the pipeline and disturb the flow regime in order to obtain the data; this method also avoids the typical time-consuming and complex operations, resists ambient temperature disturbance and achieves approximately acceptable results. (paper)

Data of thermal degradation and dynamic mechanical properties of starch-glycerol based films with citric acid as crosslinking agent.

Science.gov (United States)

González Seligra, Paula; Medina Jaramillo, Carolina; Famá, Lucía; Goyanes, Silvia

2016-06-01

Interest in biodegradable edible films as packaging or coating has increased because their beneficial effects on foods. In particular, food products are highly dependents on thermal stability, integrity and transition process temperatures of the packaging. The present work describes a complete data of the thermal degradation and dynamic mechanical properties of starch-glycerol based films with citric acid (CA) as crosslinking agent described in the article titled: "Biodegradable and non-retrogradable eco-films based on starch-glycerol with citric acid as crosslinking agent" González Seligra et al. (2016) [1]. Data describes thermogravimetric and dynamical mechanical experiences and provides the figures of weight loss and loss tangent of the films as a function of the temperature.

Intraluminal bubble dynamics induced by lithotripsy shock wave

Science.gov (United States)

Song, Jie; Bai, Jiaming; Zhou, Yufeng

2016-12-01

Extracorporeal shock wave lithotripsy (ESWL) has been the first option in the treatment of calculi in the upper urinary tract since its introduction. ESWL-induced renal injury is also found after treatment and is assumed to associate with intraluminal bubble dynamics. To further understand the interaction of bubble expansion and collapse with the vessel wall, the finite element method (FEM) was used to simulate intraluminal bubble dynamics and calculate the distribution of stress in the vessel wall and surrounding soft tissue during cavitation. The effects of peak pressure, vessel size, and stiffness of soft tissue were investigated. Significant dilation on the vessel wall occurs after contacting with rapid and large bubble expansion, and then vessel deformation propagates in the axial direction. During bubble collapse, large shear stress is found to be applied to the vessel wall at a clinical lithotripter setting (i.e. 40 MPa peak pressure), which may be the mechanism of ESWL-induced vessel rupture. The decrease of vessel size and viscosity of soft tissue would enhance vessel deformation and, consequently, increase the generated shear stress and normal stresses. Meanwhile, a significantly asymmetric bubble boundary is also found due to faster axial bubble expansion and shrinkage than in radial direction, and deformation of the vessel wall may result in the formation of microjets in the axial direction. Therefore, this numerical work would illustrate the mechanism of ESWL-induced tissue injury in order to develop appropriate counteractive strategies for reduced adverse effects.

On the thermal phase structure of QCD at vanishing chemical potentials

CERN Document Server

Kabana, S

2011-01-01

The hypothesis is investigated, that the thermal structure of QCD phases at and near zero chemical potentials is determined by long range coherence, inducing the gauge boson pair condensate. The latter reflects the dynamical nature of gauge boson Bogoliubov transformations at the origin of localization of all color fields inside hadrons at low temperature in contrast to loss of such localization above a unique critical temperature.

Role of field-induced nanostructures, zippering and size polydispersity on effective thermal transport in magnetic fluids without significant viscosity enhancement

Science.gov (United States)

Vinod, Sithara; Philip, John

2017-12-01

Magnetic nanofluids or ferrofluids exhibit extraordinary field dependant tunable thermal conductivity (k), which make them potential candidates for microelectronic cooling applications. However, the associated viscosity enhancement under an external stimulus is undesirable for practical applications. Further, the exact mechanism of heat transport and the role of field induced nanostructures on thermal transport is not clearly understood. In this paper, through systematic thermal, rheological and microscopic studies in 'model ferrofluids', we demonstrate for the first time, the conditions to achieve very high thermal conductivity to viscosity ratio. Highly stable ferrofluids with similar crystallite size, base fluid, capping agent and magnetic properties, but with slightly different size distributions, are synthesized and characterized by X-ray diffraction, small angle X-ray scattering, transmission electron microscopy, dynamic light scattering, vibrating sample magnetometer, Fourier transform infrared spectroscopy and thermo-gravimetry. The average hydrodynamic diameters of the particles were 11.7 and 10.1 nm and the polydispersity indices (σ), were 0.226 and 0.151, respectively. We observe that the system with smaller polydispersity (σ = 0.151) gives larger k enhancement (130% for 150 G) as compared to the one with σ = 0.226 (73% for 80 G). Further, our results show that dispersions without larger aggregates and with high density interfacial capping (with surfactant) can provide very high enhancement in thermal conductivity, with insignificant viscosity enhancement, due to minimal interfacial losses. We also provide experimental evidence for the effective heat conduction (parallel mode) through a large number of space filling linear aggregates with high aspect ratio. Microscopic studies reveal that the larger particles act as nucleating sites and facilitate lateral aggregation (zippering) of linear chains that considerably reduces the number density of space

Incomplete Thermalization from Trap-Induced Integrability Breaking: Lessons from Classical Hard Rods

Science.gov (United States)

Cao, Xiangyu; Bulchandani, Vir B.; Moore, Joel E.

2018-04-01

We study a one-dimensional gas of hard rods trapped in a harmonic potential, which breaks integrability of the hard-rod interaction in a nonuniform way. We explore the consequences of such broken integrability for the dynamics of a large number of particles and find three distinct regimes: initial, chaotic, and stationary. The initial regime is captured by an evolution equation for the phase-space distribution function. For any finite number of particles, this hydrodynamics breaks down and the dynamics becomes chaotic after a characteristic timescale determined by the interparticle distance and scattering length. The system fails to thermalize over the timescale studied (1 04 natural units), but the time-averaged ensemble is a stationary state of the hydrodynamic evolution. We close by discussing logical extensions of the results to similar systems of quantum particles.

Mechanisms of thermally induced threshold voltage instability in GaN-based heterojunction transistors

International Nuclear Information System (INIS)

Yang, Shu; Liu, Shenghou; Liu, Cheng; Lu, Yunyou; Chen, Kevin J.

2014-01-01

In this work, we attempt to reveal the underlying mechanisms of divergent V TH -thermal-stabilities in III-nitride metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) and MOS-Channel-HEMT (MOSC-HEMT). In marked contrast to MOSC-HEMT featuring temperature-independent V TH , MIS-HEMT with the same high-quality gate-dielectric/III-nitride interface and similar interface trap distribution exhibits manifest thermally induced V TH shift. The temperature-dependent V TH of MIS-HEMT is attributed to the polarized III-nitride barrier layer, which spatially separates the critical gate-dielectric/III-nitride interface from the channel and allows “deeper” interface trap levels emerging above the Fermi level at pinch-off. This model is further experimentally validated by distinct V G -driven Fermi level movements at the critical interfaces in MIS-HEMT and MOSC-HEMT. The mechanisms of polarized III-nitride barrier layer in influencing V TH -thermal-stability provide guidelines for the optimization of insulated-gate III-nitride power switching devices

Light induced intraspecific variability in response to thermal stress in the hard coral Stylophora pistillata

Directory of Open Access Journals (Sweden)

Arjen Tilstra

2017-10-01

Full Text Available Recent research suggests that prior exposure of several months to elevated irradiance induces enhanced thermal tolerance in scleractinian corals. While this tolerance has been reported at the species level, individual coral colonies may react differently due to individual variability in thermal tolerance. As thermal anomalies are predicted to become common in the upcoming future, intraspecific variation may be key to the survival of coral populations. In order to study light-history based thermal stress responses on individual colonies, we developed a preliminary microcosm experiment where three randomly chosen, aquacultured colonies of the model coral Stylophora pistillata were exposed to two irradiance treatments (200 and 400 μmol photons m−2 s−1 for 31 days, followed by artificially induced heat stress (∼33.4 °C. We found different responses to occur at both the intraspecific and the intracolonial levels, as indicated by either equal, less severe, delayed, and/or even non-necrotic responses of corals previously exposed to the irradiance of 400 compared to 200 μmol photons m−2 s−1. In addition, all individual colonies revealed light-enhanced calcification. Finally, elevated irradiance resulted in a lower chlorophyll a concentration in one colony compared to the control treatment, and the same colony displayed more rapid bleaching compared to the other ones. Taken together, this study highlights the potential importance of intra-individual variability in physiological responses of scleractinian corals and provides recommendations for improving methodological designs for future studies.

Thermal ripples in model molybdenum disulfide monolayers

Energy Technology Data Exchange (ETDEWEB)

Remsing, Richard C.; Klein, Michael L. [Institute for Computational Molecular Science, Center for the Computational, Design of Functional Layered Materials, and Department of Chemistry, Temple University, 1925 N. 12th St., 19122, Philadelphia, PA (United States); Waghmare, Umesh V. [Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, 560 064, Jakkur, Bangalore (India)

2017-01-15

Molybdenum disulfide (MoS{sub 2}) monolayers have the potential to revolutionize nanotechnology. To reach this potential, it will be necessary to understand the behavior of this two-dimensional (2D) material on large length scales and under thermal conditions. Herein, we use molecular dynamics (MD) simulations to investigate the nature of the rippling induced by thermal fluctuations in monolayers of the 2H and 1T phases of MoS{sub 2}. The 1T phase is found to be more rigid than the 2H phase. Both monolayer phases are predicted to follow long wavelength scaling behavior typical of systems with anharmonic coupling between vibrational modes as predicted by classic theories of membrane-like systems. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Dynamic correlation of photo-excited electrons: Anomalous levels induced by light–matter coupling

Energy Technology Data Exchange (ETDEWEB)

Jiang, Xiankai [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Huai, Ping, E-mail: huaiping@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800 (China); Song, Bo, E-mail: bosong@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, P.O. Box 800-204, Shanghai 201800 (China)

2014-04-01

Nonlinear light–matter coupling plays an important role in many aspects of modern physics, such as spectroscopy, photo-induced phase transition, light-based devices, light-harvesting systems, light-directed reactions and bio-detection. However, excited states of electrons are still unclear for nano-structures and molecules in a light field. Our studies unexpectedly present that light can induce anomalous levels in the electronic structure of a donor–acceptor nanostructure with the help of the photo-excited electrons transferring dynamically between the donor and the acceptor. Furthermore, the physics underlying is revealed to be the photo-induced dynamical spin–flip correlation among electrons. These anomalous levels can significantly enhance the electron current through the nanostructure. These findings are expected to contribute greatly to the understanding of the photo-excited electrons with dynamic correlations, which provides a push to the development and application of techniques based on photosensitive molecules and nanostructures, such as light-triggered molecular devices, spectroscopic analysis, bio-molecule detection, and systems for solar energy conversion.

Spin-motive Force Induced by Domain Wall Dynamics in the Antiferromagnetic Spin Valve

Science.gov (United States)

Sugano, Ryoko; Ichimura, Masahiko; Takahashi, Saburo; Maekawa, Sadamichi; Crest Collaboration

2014-03-01

In spite of no net magnetization in antiferromagnetic (AF) textures, the local magnetic properties (Neel magnetization) can be manipulated in a similar fashion to ferromagnetic (F) ones. It is expected that, even in AF metals, spin transfer torques (STTs) lead to the domain wall (DW) motion and that the DW motion induces spin-motive force (SMF). In order to study the Neel magnetization dynamics and the resultant SMF, we treat the nano-structured F1/AF/F2 junction. The F1 and F2 leads behave as a spin current injector and a detector, respectively. Each F lead is fixed in the different magnetization direction. Torsions (DW in AF) are introduced reflecting the fixed magnetization of two F leads. We simulated the STT-induced Neel magnetization dynamics with the injecting current from F1 to F2 and evaluate induced SMF. Based on the adiabatic electron dynamics in the AF texture, Langevin simulations are performed at finite temperature. This research was supported by JST, CREST, Japan.

Micromachined single-level nonplanar polycrystalline SiGe thermal microemitters for infrared dynamic scene projection

Science.gov (United States)

Malyutenko, V. K.; Malyutenko, O. Yu.; Leonov, V.; Van Hoof, C.

2009-05-01

The technology for self-supported membraneless polycrystalline SiGe thermal microemitters, their design, and performance are presented. The 128-element arrays with a fill factor of 88% and a 2.5-μm-thick resonant cavity have been grown by low-pressure chemical vapor deposition and fabricated using surface micromachining technology. The 200-nm-thick 60×60 μm2 emitting pixels enforced with a U-shape profile pattern demonstrate a thermal time constant of 2-7 ms and an apparent temperature of 700 K in the 3-5 and 8-12 μm atmospheric transparency windows. The application of the devices to the infrared dynamic scene simulation and their benefit over conventional planar membrane-supported emitters are discussed.

Multi-thermal dynamics and energetics of a coronal mass ejection in the low solar atmosphere

Science.gov (United States)

Hannah, I. G.; Kontar, E. P.

2013-05-01

Aims: The aim of this work is to determine the multi-thermal characteristics and plasma energetics of an eruptive plasmoid and occulted flare observed by the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA). Methods: We study a 2010 Nov. 3 event (peaking at 12:20 UT in GOES soft X-rays) of a coronal mass ejection and occulted flare that demonstrates the morphology of a classic erupting flux rope. The high spatial and time resolution and six coronal channels of the SDO/AIA images allows the dynamics of the multi-thermal emission during the initial phases of eruption to be studied in detail. The differential emission measure is calculated, using an optimized version of a regularized inversion method, for each pixel across the six channels at different times, resulting in emission measure maps and movies in a variety of temperature ranges. Results: We find that the core of the erupting plasmoid is hot (8-11, 11-14 MK) with a similarly hot filamentary "stem" structure connecting it to the lower atmosphere, which could be interpreted as the current sheet in the flux rope model, though is wider than these models suggest. The velocity of the leading edge of the eruption is 597-664 km s-1 in the temperature range ≥3-4 MK and between 1029-1246 km s-1 for ≤2-3 MK. We estimate the density (in 11-14 MK) of the erupting core and stem during the impulsive phase to be about 3 × 109 cm-3, 6 × 109 cm-3, 9 × 108 cm-3 in the plasmoid core, stem, and surrounding envelope of material. This gives thermal energy estimates of 5 × 1029 erg, 1 × 1029 erg, and 2 × 1030 erg. The kinetic energy for the core and envelope is slightly lower. The thermal energy of the core and current sheet grows during the eruption, suggesting continuous influx of energy presumably via reconnection. Conclusions: The combination of the optimized regularized inversion method and SDO/AIA data allows the multi-thermal characteristics (i.e. velocity, density, and thermal energies) of the

Thermal buckling behavior of defective CNTs under pre-load: A molecular dynamics study.

Science.gov (United States)

Mehralian, Fahimeh; Tadi Beni, Yaghoub; Kiani, Yaser

2017-05-01

Current study is concentrated on the extraordinary properties of defective carbon nanotubes (CNTs). The role of vacancy defects in thermal buckling response of precompressed CNTs is explored via molecular dynamics (MD) simulations. Defective CNTs are initially compressed at a certain ratio of their critical buckling strain and then undergo a uniform temperature rise. Comprehensive study is implemented on both armchair and zigzag CNTs with different vacancy defects including monovacancy, symmetric bivacancy and asymmetric bivacancy. The results reveal that defects have a pronounced impact on the buckling behavior of CNTs; interestingly, defective CNTs under compressive pre-load show higher resistance to thermal buckling than pristine ones. In the following, the buckling response of defective CNTs is shown to be dependent on the vacancy defects, location of defects and chirality. Copyright © 2017 Elsevier Inc. All rights reserved.

Thermal Stress-Induced Depolarization Loss in Conventional and Panda-Shaped Photonic Crystal Fiber Lasers

Science.gov (United States)

Mousavi, Seyedeh Laleh; Sabaeian, Mohammad

2016-10-01

We report on the modeling of the depolarization loss in the conventional and panda-shaped photonic crystal fiber lasers (PCFLs) due to the self-heating of the fiber, which we call it thermal stress-induced depolarization loss (TSIDL). We first calculated the temperature distribution over the fiber cross sections and then calculated the thermal stresses/strains as a function of heat load per meter. Thermal stress-induced birefringence (TSIB), which is defined as | n x - n y |, in the core and cladding regions was calculated. Finally, TSIDL was calculated for the conventional and panda-shaped PCFLs as a function of fiber length and, respectively, saturated values of 22 and 25 % were obtained which were independent of heat load per meter. For panda-shaped PCFLs, prior to being saturated, an oscillating and damping behavior against the fiber length was seen where in some lengths reached 35 %. The results are close to an experimental value of 30 % reported for a pulsed PCFL (Limpert et al., Opt Express 12:1313-1319, 2004) where the authors reported a degree of polarization of 70 % (i.e., a depolarization of 30 %). The most important result of this work is a saturation behavior of TSIDL at long-enough lengths of the fiber laser which is independent of heat load per meter. To our knowledge, this the first report of TSIBL for PCFLs.

Spectroscopic Evidence for Exceptional Thermal Contribution to Electron-Beam Induced Fragmentation

Energy Technology Data Exchange (ETDEWEB)

Caldwell, Marissa A.; Haynor, Ben; Aloni, Shaul; Ogletree, D. Frank; Wong, H.-S. Philip; Urban, Jeffrey J.; Milliron, Delia J.

2010-11-16

While electron beam induced fragmentation (EBIF) has been reported to result in the formation of nanocrystals of various compositions, the physical forces driving this phenomenon are still poorly understood. We report EBIF to be a much more general phenomenon than previously appreciated, operative across a wide variety of metals, semiconductors and insulators. In addition, we leverage the temperature dependent bandgap of several semiconductors to quantify -- using in situ cathodoluminescence spectroscopy -- the thermal contribution to EBIF, and find extreme temperature rises upwards of 1000K.

A dynamic model for air-based photovoltaic thermal systems working under real operating conditions

International Nuclear Information System (INIS)

Sohel, M. Imroz; Ma, Zhenjun; Cooper, Paul; Adams, Jamie; Scott, Robert

2014-01-01

Highlights: • A dynamic model suitable for air-based photovoltaic thermal (PVT) systems is presented. • The model is validated with PVT data from two unique buildings. • The simulated output variables match very well with the experimental data. • The performance of the PVT system under changing working condition is analysed. - Abstract: In this paper a dynamic model suitable for simulating real operating conditions of air-based photovoltaic thermal (PVT) systems is presented. The performance of the model is validated by using the operational data collected from the building integrated photovoltaic (PVT) systems installed in two unique buildings. The modelled air outlet temperature and electrical power match very well with the experimental data. In Solar Decathlon house PVT, the average (RMS) error in air outlet temperatures was 4.2%. The average (RMS) error in electrical power was also 4.2%. In the Sustainable Buildings Research Centre PVT, the average errors (RMS) of PV and air temperatures were 3.8% and 2.2%, respectively. The performance of the PVT system under changing working condition is also analysed in this paper. The analysis includes the effect of ambient air temperature, air inlet temperature, air flow rate and solar irradiation on thermal, electrical, first law and second law efficiencies. Both the thermal and the 1st law efficiencies almost linearly increased with the increase of the ambient temperature. However, the PVT electrical efficiency and the second law efficiency decreased with the increase of the ambient temperature. All efficiencies expect the second law efficiency decreased with increase of the PVT air inlet temperature. The second law efficiency first increased and then reduced. With increasing the air flow rate all the efficiencies increased. The electrical and second law efficiencies become less sensitive when the air flow rate exceeded 300 l/s. Both the thermal and the 1st law efficiencies decreased while the electrical

Thermal evolution of the CO stretching band in carboxy-myoglobin in the light of neutron scattering and molecular dynamics simulations

Energy Technology Data Exchange (ETDEWEB)

Cordone, Lorenzo [Dipartimento di Scienze Fisiche ed Astronomiche, Universita di Palermo and CNISM, Via Archirafi 36, I-90123 Palermo (Italy)], E-mail: cordone@fisica.unipa.it; Cottone, Grazia; Giuffrida, Sergio; Librizzi, Fabio [Dipartimento di Scienze Fisiche ed Astronomiche, Universita di Palermo and CNISM, Via Archirafi 36, I-90123 Palermo (Italy)

2008-04-18

As it is well known, the thermal behaviour of the CO stretching band in MbCO reflects the interconversion among protein's taxonomic and lower tier substates. We compare here FTIR data on the thermal behaviour of the CO stretching band in MbCO embedded in non-liquid, water-trehalose matrixes, and neutron scattering data on dry and hydrated proteins and nucleic acids. The comparison, also in the light of simulative data, gives relevant information on the relationship between the mean square displacements of hydrogen atoms and the heme pocket thermal rearrangements in MbCO, as experienced by the bound CO, in the temperature region 100-200 K, and at higher temperature when large scale protein motions take place, following the so-called dynamic transition. The reported results point out how FTIR is a useful tool to study the protein internal dynamics, and complement information from neutron scattering measurements.

CFD (Computational Fluid Dynamics) simulators and thermal cracking of heavy oil and ultraheavy residues using microreactor

Energy Technology Data Exchange (ETDEWEB)

Jardini, Andre L.; Bineli, Aulus R.R.; Viadana, Adriana M.; Maciel, Maria Regina Wolf; Maciel Filho, Rubens [State University of Campinas (UNICAMP), SP (Brazil). School of Chemical Engineering; Medina, Lilian C.; Gomes, Alexandre de O. [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES); Barros, Ricardo S. [University Foundation Jose Bonifacio (FUJB), Rio de Janeiro, RJ (Brazil)

2008-07-01

In this paper, the design of microreactor with microfluidics channels has been carried out in Computer Aided Design Software (CAD) and constructed in rapid prototyping system to be used in chemical reaction processing of the heavy oil fractions. The flow pattern properties of microreactor (fluid dynamics, mixing behavior) have been considered through CFD (computational fluid dynamics) simulations. CFD calculations are also used to study the design and specification of new microreactor developments. The potential advantages of using a microreactor include better control of reaction conditions, improved safety and portability. A more detailed crude assay of the raw national oil, whose importance was evidenced by PETROBRAS/CENPES allows establishing the optimum strategies and processing conditions, aiming at a maximum utilization of the heavy oil fractions, towards valuable products. These residues are able to be processed in microreactor, in which conventional process like as hydrotreating, catalytic and thermal cracking may be carried out in a much more intensified fashion. The whole process development involves a prior thermal study to define the possible operating conditions for a particular task, the microreactor design through computational fluid dynamics and construction using rapid prototyping. This gives high flexibility for process development, shorter time, and costumer/task oriented process/product development. (author)

Summer and Winter Effect of Innovative Cool Roof Tiles on the Dynamic Thermal Behavior of Buildings

Directory of Open Access Journals (Sweden)

Anna Laura Pisello

2014-04-01

Full Text Available Cool roofs represent an acknowledged passive cooling technique to reduce building energy consumption for cooling and to mitigate urban heat island effects. This paper concerns the evaluation of the dynamic effect of new cool roof clay tiles on building thermal performance in summer and winter conditions. To this end, these properties have been analyzed on traditional roof brick tiles through an indoor and outdoor two-year long continuous monitoring campaign set up in a residential building located in central Italy. The analysis and the cooperation with industrial companies producing brick tiles and reflective coatings allowed the production of a new tile with notable “cool roof” properties through the traditional industrial manufacturing path of such tiles. Notable results show that during summer the high reflection tiles are able to decrease the average external roof surface temperature by more than 10 °C and the indoor operative temperature by more than 3 °C. During winter the average external surface temperature is lower with high reflection tiles by about 1 °C. Singular optic-thermal phenomena are registered while evaluating the dynamics of the cool roof effect. Interesting findings show how the sloped cool roof application could suggest further considerations about the dynamic effect of cool roofs.

Impact of tensile strain on the thermal transport of zigzag hexagonal boron nitride nanoribbon: An equilibrium molecular dynamics study

Science.gov (United States)

Navid, Ishtiaque Ahmed; Intisar Khan, Asir; Subrina, Samia

2018-02-01

The thermal conductivity of single layer strained hexagonal boron nitride nanoribbon (h-BNNR) has been computed using the Green—Kubo formulation of Equilibrium Molecular Dynamics (EMD) simulation. We have investigated the impact of strain on thermal transport of h-BNNR by varying the applied tensile strain from 1% upto 5% through uniaxial loading. The thermal conductivity of h-BNNR decreases monotonically with the increase of uniaxial tensile strain keeping the sample size and temperature constant. The thermal conductivity can be reduced upto 86% for an applied uniaxial tensile strain of 5%. The impact of temperature and width variation on the thermal conductivity of h-BNNR has also been studied under different uniaxial tensile strain conditions. With the increase in temperature, the thermal conductivity of strained h-BNNR exhibits a decaying characteristics whereas it shows an opposite pattern with the increasing width. Such study would provide a good insight on the strain tunable thermal transport for the potential device application of boron nitride nanostructures.

The coke drum thermal kinetic effects

Energy Technology Data Exchange (ETDEWEB)

Aldescu, Maria M.; Romero, Sim; Larson, Mel [KBC Advanced Technologies plc, Surrey (United Kingdom)

2012-07-01

The coke drum thermal kinetic dynamics fundamentally affect the coker unit yields as well as the coke product properties and unit reliability. In the drum the thermal cracking and polymerization or condensation reactions take place in a semi-batch environment. Understanding the fundamentals of the foaming kinetics that occur in the coke drums is key to avoiding a foam-over that could result in a unit shutdown for several months. Although the most dynamic changes with time occur during drum filling, other dynamics of the coker process will be discussed as well. KBC has contributed towards uncovering and modelling the complexities of heavy oil thermal dynamics. (author)

Thermal conductivity at the nanoscale: A molecular dynamics study

Science.gov (United States)

Lyver, John W., IV

With the growing use of nanotechnology and nanodevices in many fields of engineering and science, a need for understanding the thermal properties of such devices has increased. The ability for nanomaterials to conduct heat is highly dependent on the purity of the material, internal boundaries due to material changes and the structure of the material itself. Experimentally measuring the heat transport at the nanoscale is extremely difficult and can only be done as a macro output from the device. Computational methods such as various Monte Carlo (MC) and molecular dynamics (MD) techniques for studying the contribution of atomic vibrations associated with heat transport properties are very useful. The Green--Kubo method in conjunction with Fourier's law for calculating the thermal conductivity, kappa, has been used in this study and has shown promise as one approach well adapted for understanding nanosystems. Investigations were made of the thermal conductivity using noble gases, modeled with Lennard-Jones (LJ) interactions, in solid face-centered cubic (FCC) structures. MC and MD simulations were done to study homogeneous monatomic and binary materials as well as slabs of these materials possessing internal boundaries. Additionally, MD simulations were done on silicon carbide nanowires, nanotubes, and nanofilaments using a potential containing two-body and three-body terms. The results of the MC and MD simulations were matched against available experimental and other simulations and showed that both methods can accurately simulate real materials in a fraction of the time and effort. The results of the study show that in compositionally disordered materials the selection of atomic components by their mass, hard-core atomic diameter, well depth, and relative concentration can change the kappa by as much as an order of magnitude. It was found that a 60% increase in mass produces a 25% decrease in kappa. A 50% increase in interatomic strength produces a 25% increase in

Dynamic Characterization of an Inflatable Concentrator for Solar Thermal Propulsion

Science.gov (United States)

Leigh, Larry; Hamidzadeh, Hamid; Tinker, Michael L.; Rodriguez, Pedro I. (Technical Monitor)

2001-01-01

An inflatable structural system that is a technology demonstrator for solar thermal propulsion and other applications is characterized for structural dynamic behavior both experimentally and computationally. The inflatable structure is a pressurized assembly developed for use in orbit to support a Fresnel lens or inflatable lenticular element for focusing sunlight into a solar thermal rocket engine. When the engine temperature reaches a pre-set level, the propellant is injected into the engine, absorbs heat from an exchanger, and is expanded through the nozzle to produce thrust. The inflatable structure is a passively adaptive system in that a regulator and relief valve are utilized to maintain pressure within design limits during the full range of orbital conditions. Modeling and test activities are complicated by the fact that the polyimide film material used for construction of the inflatable is nonlinear, with modulus varying as a function of frequency, temperature, and level of excitation. Modal vibration testing and finite element modeling are described in detail in this paper. The test database is used for validation and modification of the model. This work is highly significant because of the current interest in inflatable structures for space application, and because of the difficulty in accurately modeling such systems.

Laser irradiation and thermal treatment inducing selective crystallization in Sb2O3-Sb2S3 glassy films

Science.gov (United States)

Avila, L. F.; Pradel, A.; Ribeiro, S. J. L.; Messaddeq, Y.; Nalin, M.

2015-02-01

The influence of both thermal treatment and laser irradiation on the structural and optical properties of films in the Sb2O3-Sb2S3 system was investigated. The films were prepared by RF-sputtering using glass compositions as raw materials. Irreversible photodarkening effect was observed after exposure the films to a 458 nm solid state laser. It is shown, for the first time, the use of holographic technique to measure "in situ", simultaneously and independently, the phase and amplitude modulations in glassy films. The films were also photo-crystallized and analysed "in situ" using a laser coupled to a micro-Raman equipment. Results showed that Sb2S3 crystalline phase was obtained after irradiation. The effect of thermal annealing on the structure of the films was carried out. Different from the result obtained by irradiation, thermal annealing induces the crystallization of the Sb2O3 phase. Photo and thermal induced effects on films were studied using UV-Vis and Raman spectroscopy, atomic force microscopy (AFM), thermal analysis (DSC), X-ray diffraction, scanning electron microscopy (MEV) and energy-dispersive X-ray spectroscopy (EDX).

Carbon Nanotubes as Thermally Induced Water Pumps

DEFF Research Database (Denmark)

Oyarzua, Elton; Walther, Jens Honore; Megaridis, Constantine M

2017-01-01

Thermal Brownian motors (TBMs) are nanoscale machines that exploit thermal fluctuations to provide useful work. We introduce a TBM-based nanopump which enables continuous water flow through a carbon nanotube (CNT) by imposing an axial thermal gradient along its surface. We impose spatial asymmetry...

Applying thermal neutron radiography to non-destructive assays of dynamic systems

International Nuclear Information System (INIS)

Silvani, Maria I.; Almeida, Gevaldo L. de; Goncalves, Marcelo J.; Lopes, Ricardo T.

2008-01-01

Dynamic processes or systems frequently can not have their behavior directly analyzed due to safety reasons or because they require destructive assays, which can not be always afforded when high-cost equipment, devices and components are involved. Under these circumstances, some kind of non-destructive technique should be applied to preserve the safety of the personnel performing the assay, as well as the integrity of the piece being inspected. Thermal neutrons are specially suited as a tool for this purpose, thanks to their capability to pass through metallic materials, which could be utterly opaque to X-rays. This paper describes the accomplishments achieved at the Instituto de Engenharia Nuclear / CNEN, Brazil, aiming at the development of an Image Acquisition System capable to perform non-destructive assays using thermal neutrons. It is comprised of a thermal neutron source provided by the Argonauta research reactor, a converter-scintillating screen, and a CCD-based video camera optically coupled to the screen through a dark chamber equipped with a mirror. The developed system has been used to acquire 2D neutron radiographic images of static devices to reveal their inner structure, as well as movies of running systems and working devices to verify its functioning and soundness. Radiographic images of objects taken at different angles would be later on used as projections to retrieve - through a proper unfolding software - their 3D images expressed as attenuation coefficients for thermal neutrons. A quantitative performance of the system has been assessed through its Modulation Transfer Function - MTF. In order to determine this curve, unique collimators designed to simulate different spatial frequencies have been manufactured. Besides that, images of some objects have been acquired with the system being developed as well as using the conventional radiographic film, allowing thus a qualitative comparison between them. (author)

Effects of Thermally Induced Microcracking on the Quasi Static and Dynamic Response of Salem Limestone

Science.gov (United States)

2017-06-30

elastic material, e.g., a high strength steel. A third bar, the striker bar, is propelled (typically by a gas gun) into the end of the incident bar...Sciences 36:433-448. Ferrero, A. M., and P. Marini. 2001. Experimental studies on the mechanical behaviour of two thermal cracked marbles. Rock

Non-thermal plasma instabilities induced by deformation of the electron energy distribution function

Science.gov (United States)

Dyatko, N. A.; Kochetov, I. V.; Napartovich, A. P.

2014-08-01

Non-thermal plasma is a key component in gas lasers, microelectronics, medical applications, waste gas cleaners, ozone generators, plasma igniters, flame holders, flow control in high-speed aerodynamics and others. A specific feature of non-thermal plasma is its high sensitivity to variations in governing parameters (gas composition, pressure, pulse duration, E/N parameter). This sensitivity is due to complex deformations of the electron energy distribution function (EEDF) shape induced by variations in electric field strength, electron and ion number densities and gas excitation degree. Particular attention in this article is paid to mechanisms of instabilities based on non-linearity of plasma properties for specific conditions: gas composition, steady-state and decaying plasma produced by the electron beam, or by an electric current pulse. The following effects are analyzed: the negative differential electron conductivity; the absolute negative electron mobility; the stepwise changes of plasma properties induced by the EEDF bi-stability; thermo-current instability and the constriction of the glow discharge column in rare gases. Some of these effects were observed experimentally and some of them were theoretically predicted and still wait for experimental confirmation.

Research Update: Utilizing magnetization dynamics in solid-state thermal energy conversion

Directory of Open Access Journals (Sweden)

Stephen R. Boona

2016-10-01

Full Text Available We review the spin-Seebeck and magnon-electron drag effects in the context of solid-state energy conversion. These phenomena are driven by advective magnon-electron interactions. Heat flow through magnetic materials generates magnetization dynamics, which can strongly affect free electrons within or adjacent to the magnetic material, thereby producing magnetization-dependent (e.g., remnant electric fields. The relative strength of spin-dependent interactions means that magnon-driven effects can generate significantly larger thermoelectric power factors as compared to classical thermoelectric phenomena. This is a surprising situation in which spin-based effects are larger than purely charge-based effects, potentially enabling new approaches to thermal energy conversion.

Thermal injury lowers the threshold for radiation-induced neuroinflammation and cognitive dysfunction.

Science.gov (United States)

Cherry, Jonathan D; Williams, Jacqueline P; O'Banion, M Kerry; Olschowka, John A

2013-10-01

The consequences of radiation exposure alone are relatively well understood, but in the wake of events such as the World War II nuclear detonations and accidents such as Chernobyl, other critical factors have emerged that can substantially affect patient outcome. For example, ~70% of radiation victims from Hiroshima and Nagasaki received some sort of additional traumatic injury, the most common being thermal burn. Animal data has shown that the addition of thermal insult to radiation results in increased morbidity and mortality. To explore possible synergism between thermal injury and radiation on brain, C57BL/6J female mice were exposed to either 0 or 5 Gy whole-body gamma irradiation. Irradiation was immediately followed by a 10% total-body surface area full thickness thermal burn. Mice were sacrificed 6 h, 1 week or 6 month post-injury and brains and plasma were harvested for histology, mRNA analysis and cytokine ELISA. Plasma analysis revealed that combined injury synergistically upregulates IL-6 at acute time points. Additionally, at 6 h, combined injury resulted in a greater upregulation of the vascular marker, ICAM-1 and TNF-α mRNA. Enhanced activation of glial cells was also observed by CD68 and Iba1 immunohistochemistry at all time points. Additionally, doublecortin staining at 6 months showed reduced neurogenesis in all injury conditions. Finally, using a novel object recognition test, we observed that only mice with combined injury had significant learning and memory deficits. These results demonstrate that thermal injury lowers the threshold for radiation-induced neuroinflammation and long-term cognitive dysfunction.

Computational Fluid Dynamics Model for Solar Thermal Storage Tanks with Helical Jacket Heater and Upper Spiral Coil Heater

Energy Technology Data Exchange (ETDEWEB)

Baek, Seung Man [Seoul Nat' l Univ., Seoul (Korea, Republic of); Zhong, Yiming; Nam, Jin Hyun [Daegu Univ., Daegu (Korea, Republic of); Chung, Jae Dong [Sejong Univ., Seoul (Korea, Republic of); Hong, Hiki [Kyung Hee Univ., Seoul (Korea, Republic of)

2013-04-15

In a solar domestic hot water (Shadow) system, solar energy is collected using collector panels, transferred to a circulating heat transfer fluid (brine), and eventually stored in a thermal storage tank (Test) as hot water. In this study, a computational fluid dynamics (CAD) model was developed to predict the solar thermal energy storage in a hybrid type Test equipped with a helical jacket heater (mantle heat exchanger) and an immersed spiral coil heater. The helical jacket heater, which is the brine flow path attached to the side wall of a Test, has advantages including simple system design, low brine flow rate, and enhanced thermal stratification. In addition, the spiral coil heater further enhances the thermal performance and thermal stratification of the Test. The developed model was validated by the good agreement between the CAD results and the experimental results performed with the hybrid-type Test in Shadow settings.

Computational Fluid Dynamics Model for Solar Thermal Storage Tanks with Helical Jacket Heater and Upper Spiral Coil Heater

International Nuclear Information System (INIS)

Baek, Seung Man; Zhong, Yiming; Nam, Jin Hyun; Chung, Jae Dong; Hong, Hiki

2013-01-01

In a solar domestic hot water (Shadow) system, solar energy is collected using collector panels, transferred to a circulating heat transfer fluid (brine), and eventually stored in a thermal storage tank (Test) as hot water. In this study, a computational fluid dynamics (CAD) model was developed to predict the solar thermal energy storage in a hybrid type Test equipped with a helical jacket heater (mantle heat exchanger) and an immersed spiral coil heater. The helical jacket heater, which is the brine flow path attached to the side wall of a Test, has advantages including simple system design, low brine flow rate, and enhanced thermal stratification. In addition, the spiral coil heater further enhances the thermal performance and thermal stratification of the Test. The developed model was validated by the good agreement between the CAD results and the experimental results performed with the hybrid-type Test in Shadow settings

Nonequilibrium Distribution of the Microscopic Thermal Current in Steady Thermal Transport Systems

KAUST Repository

Yukawa, Satoshi; Ogushi, Fumiko; Shimada, Takashi; Ito, Nobuyasu

2010-01-01

Nonequilibrium distribution of the microscopic thermal current is investigated by direct molecular dynamics simulations. The microscopic thermal current in this study is defined by a flow of kinetic energy carried by a single particle. Asymptotic parallel and antiparallel tails of the nonequilibrium distribution to an average thermal current are identical to ones of equilibrium distribution with different temperatures. These temperatures characterizing the tails are dependent on a characteristic length in which a memory of dynamics is completely erased by several particle collisions. This property of the tails of nonequilibrium distribution is confirmed in other thermal transport systems. In addition, statistical properties of a particle trapped by a harmonic potential in a steady thermal conducting state are also studied. This particle feels a finite force parallel to the average thermal current as a consequence of the skewness of the distribution of the current. This force is interpreted as the microscopic origin of thermophoresis.

Thermal induced carrier's transfer in bimodal size distribution InAs/GaAs quantum dots

Science.gov (United States)

Ilahi, B.; Alshehri, K.; Madhar, N. A.; Sfaxi, L.; Maaref, H.

2018-06-01

This work reports on the investigation of the thermal induced carriers' transfer mechanism in vertically stacked bimodal size distribution InAs/GaAs quantum dots (QD). A model treating the QD as a localized states ensemble (LSE) has been employed to fit the atypical temperature dependence of the photoluminescence (PL) emission energies and linewidth. The results suggest that thermally activated carriers transfer within the large size QD family occurs through the neighboring smaller size QD as an intermediate channel before direct carriers redistribution. The obtained activation energy suggests also the possible contribution of the wetting layer (WL) continuum states as a second mediator channel for carriers transfer.

Dynamics of CO and D{sub 2}O on Cu(111). Laser induced and thermally induced processes Dynamik von CO und D{sub 2}O auf Cu(111); Dynamik von CO und D{sub 2}O auf Cu(111). Laserinduzierte und thermisch induzierte Prozesse

Energy Technology Data Exchange (ETDEWEB)

Mehlhorn, M.

2005-07-15

In this thesis the concept and the experimental realisation of a combined fs-laser low temperature scanning tunneling microscope for investigations of dynamics in molecule- metal-systems on atomic scale is presented. With the highly reproducible focusing of the laserspot under the tunneling tip it is possible to analyse reaction rates and therefore to understand the underlying reaction paths. The capability of this combination is demonstrated on the system CO/Cu(111). Diffusion, dimer formation, and desorption are induced with fs-laser pulses. The diffusion is mediated through non-thermalized and thermalized electrons. In the electronic friction model this results in a diffusion barrier of (96{+-}3) meV. The formation of dimers is also electron mediated and represents a basic step of a chemical reaction on surfaces, namely the adsorption of reactants on adjacent lattice sites. With the desorption of molecules from the edge of close packed CO-islands a dependence on the local environment could be directly identified for the first time. Due to the high stability of the scanning tunneling microscope with tunneling currents in the low pA range the study of extremely sensitive molecule-metal-systems such as D{sub 2}O on Cu(111) is possible. In particular, different metastable structures occurring during thermally activated transition from amorphous to crystalline ice are investigated. The starting point are amorphous three dimensional ice clusters. Heating removes the pores from the clusters before the molecules are then rearranged in a hexagonal lattice. The amorphous solid water (ASW) as well as the resulting buckled hexagonal ice bilayers are imaged in real space for the first time. A further annealing of the bilayers results in a faceted crystalline surface, on which pyramidal islands are stabilized at higher temperatures. The thermodynamically most stable structures are nano-crystallites, which appear at the beginning of desorption. The dissociation of D{sub 2}O

A framework of induced hyperspace dynamical systems equipped with the hit-or-miss topology

International Nuclear Information System (INIS)

Wang Yangeng; Wei Guo; Campbell, William H.; Bourquin, Steven

2009-01-01

For any dynamical system (E,d,f), where E is Hausdorff locally compact second countable (HLCSC), let F (resp., 2 E ) denote the space of all closed subsets (resp., non-empty closed subsets) of E equipped with the hit-or-miss topology τ f . Both F and 2 E are again HLCSC (F actually compact), thus metrizable. Let ρ be such a metric (three metrics available). The main purpose is to determine the conditions on f that ensure the continuity of the induced hyperspace maps 2 f :F→F and 2 f :2 E →2 E defined by 2 f (F)=f(F). With this setting, the induced hyperspace systems (F,ρ,2 f ) and (2 E ,ρ,2 f ) are compact and locally compact dynamical systems, respectively. Consequently, dynamical properties, particularly metric related dynamical properties, of the given system (E,d,f) can be explored through these hyperspace systems. In contrast, when the Vietoris topology τ v is equipped on 2 E , the space of the induced hyperspace topological dynamical system (2 E ,τ v ,2 f ) is not metrizable if E is not compact metrizable, e.g., E=R n , implying that metric related dynamical concepts cannot be defined for (2 E ,τ v ,2 f ). Moreover, two examples are provided to illustrate the advantages of the hit-or-miss topology as compared to the Vietoris topology.

SEVERAL PROBLEMS IN THERMOFLUID DYNAMICS

Institute of Scientific and Technical Information of China (English)

过增元

1991-01-01

A new cross-discipline, the thermofluid dynamics, has been established, which is relatedto heat transfer, fluid dynamics and thermodynamics with emphasis on the effect of thermalprocess on fluid flow. Its subject areas are (i) thermal drag, (ii) thermal roundabout flow,(iii) thermal drive and thermal instability, and (iv) thermal optimization.

Single molecule manipulation at low temperature and laser scanning tunnelling photo-induced processes analysis through time-resolved studies

International Nuclear Information System (INIS)

Riedel, Damien

2010-01-01

This paper describes, firstly, the statistical analysis used to determine the processes that occur during the manipulation of a single molecule through electronically induced excitations with a low temperature (5 K) scanning tunnelling microscope (STM). Various molecular operation examples are described and the ability to probe the ensuing molecular manipulation dynamics is discussed within the excitation context. It is, in particular, shown that such studies can reveal reversible manipulation for tuning dynamics through variation of the excitation energy. Secondly, the photo-induced process arising from the irradiation of the STM junction is also studied through feedback loop dynamics analysis, allowing us to distinguish between photo-thermally and photo-electronically induced signals.

Equilibrium Molecular Dynamics (MD Simulation Study of Thermal Conductivity of Graphene Nanoribbon: A Comparative Study on MD Potentials

Directory of Open Access Journals (Sweden)

Asir Intisar Khan

2015-12-01

Full Text Available The thermal conductivity of graphene nanoribbons (GNRs has been investigated using equilibrium molecular dynamics (EMD simulation based on Green-Kubo (GK method to compare two interatomic potentials namely optimized Tersoff and 2nd generation Reactive Empirical Bond Order (REBO. Our comparative study includes the estimation of thermal conductivity as a function of temperature, length and width of GNR for both the potentials. The thermal conductivity of graphene nanoribbon decreases with the increase of temperature. Quantum correction has been introduced for thermal conductivity as a function of temperature to include quantum effect below Debye temperature. Our results show that for temperatures up to Debye temperature, thermal conductivity increases, attains its peak and then falls off monotonically. Thermal conductivity is found to decrease with the increasing length for optimized Tersoff potential. However, thermal conductivity has been reported to increase with length using 2nd generation REBO potential for the GNRs of same size. Thermal conductivity, for the specified range of width, demonstrates an increasing trend with the increase of width for both the concerned potentials. In comparison with 2nd generation REBO potential, optimized Tersoff potential demonstrates a better modeling of thermal conductivity as well as provides a more appropriate description of phonon thermal transport in graphene nanoribbon. Such comparative study would provide a good insight for the optimization of the thermal conductivity of graphene nanoribbons under diverse conditions.

A molecular dynamics study of liquid layering and thermal conductivity enhancement in nanoparticle suspensions

Science.gov (United States)

Paul, J.; Madhu, A. K.; Jayadeep, U. B.; Sobhan, C. B.; Peterson, G. P.

2018-03-01

Liquid layering is considered to be one of the factors contributing to the often anomalous enhancement in thermal conductivity of nanoparticle suspensions. The extent of this layering was found to be significant at lower particle sizes, as reported in an earlier work by the authors. In continuation to that work, an investigation was conducted to better understand the fundamental parameters impacting the reported anomalous enhancement in thermal conductivity of nanoparticle suspensions (nanofluids), utilizing equilibrium molecular dynamics simulations in a copper-argon system. Nanofluids containing nanoparticles of size less than 6 nm were investigated and studied analytically. The heat current auto-correlation function in the Green-Kubo formulation for thermal conductivity was decomposed into self-correlations and cross-correlations of different species and the kinetic, potential, collision and enthalpy terms of the dominant portion of the heat current vector. The presence of liquid layering around the nanoparticle was firmly established through simulations that show the dominant contribution of Ar-Ar self-correlation and the trend displayed by the kinetic-potential cross-correlation within the argon species.

Relationship between dynamic infrared thermal images and blood perfusion rate of the tongue in anaemia patients

Science.gov (United States)

Xie, Haiwei; Zhang, Yan

2018-03-01

The relationship between dynamic infrared (IR) thermal images and blood perfusion rate of the tongues of anaemia patients was investigated. Blood perfusion rates at multiple locations on the tongues of 62 anaemia patients and 70 control subjects were measured. For both groups of subjects, dynamic IR thermal images were also recorded within 16 s after the mouth opened. The results showed that the blood perfusion rates at different sites (apex, middle, left side and right side) on the tongues in anaemia patients (3.49, 3.71, 3.85 and 3.77 kg/s m-3) were significantly lower than those at the corresponding sites in control subjects (4.45, 4.66, 4.81 and 4.70 kg/s m-3). After the mouth opened, the tongue temperature decreased more rapidly in anaemia patients than in control subjects. To analyse the heat transfer mechanism, a transient heat transfer model of the tongue was developed. The tongue temperatures in anaemia patients and control subjects were calculated using this model and compared to the tongue temperatures measured by the IR thermal imager. The relationship between the tongue surface temperature and the tongue blood perfusion rate was analysed. The simulation results indicated that the low blood perfusion rate and the correlated changes in anaemia patients can cause faster temperature decreases of the tongue surface.

Thermal-hydraulic causes of increase of dynamic stresses and cracks in the covers of vessel reactors

International Nuclear Information System (INIS)

Proskuryakov, K.N.

2006-01-01

Paper presents data of measurements and of analysis of the WWER-1000 reactor NPP equipment process noises manifesting occurrence of the latent dynamic processes. The NPP is shown to have unused abilities to prolong the equipment service life and to reduce possibility of the equipment thermally and hydraulically caused unexpected malfunctions [ru

Does the thermal spike affect low energy ion-induced interfacial mixing?

International Nuclear Information System (INIS)

Suele, P.; Menyhard, M.; Nordlund, K.

2003-01-01

Molecular dynamics simulations have been used to obtain the three-dimensional distribution of interfacial mixing and cascade defects in Ti/Pt multilayer system due to single 1 keV Ar + impact at grazing angle of incidence. The Ti/Pt system was chosen because of its relatively high heat of mixing in the binary alloy and therefore a suitable candidate for testing the effect of heat of mixing on ion-beam mixing. However, the calculated mixing profile is not sensitive to the heat of mixing. Therefore the thermal spike model of mixing is not fully supported under these irradiation conditions. Instead we found that the majority of mixing occurs after the thermal spike during the relaxation process. These conclusions are supported by liquid, vacancy as well as adatom analysis. The interfacial mixing is in various aspects anomalous in this system: the time evolution of mixing is leading to a phase delay for Ti mixing, and Pt exhibits an unexpected double peaked mixing evolution. The reasons to these effects are discussed

Development of Computational Tools for Predicting Thermal- and Radiation-Induced Solute Segregation at Grain Boundaries in Fe-based Alloys

Energy Technology Data Exchange (ETDEWEB)

Yang, Ying [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2016-09-30

Radiation-induced segregation (RIS) has been frequently reported in structural materials such as austenitic, ferritic, and ferritic-martensitic stainless steels (SS) that have been widely used in light water reactors (LWRs). RIS has been linked to secondary degradation effects in SS including irradiation-induced stress corrosion cracking (IASCC). Earlier studies on thermal segregation in Fe-based alloys found that metalloids elements such as P, S, Si, Ge, Sn, etc., embrittle the materials when enrichment was observed at grain boundaries (GBs). RIS of Fe-Cr-Ni-based austenitic steels has been modeled in the U.S. 2015 fiscal year (FY2015), which identified the pre-enrichment due to thermal segregation can have an important role on the subsequent RIS. The goal of this work is to develop thermal segregation models for alloying elements in steels for future integration with RIS modeling.

Role of rainwater induced subsurface flow in water-level dynamics and thermoerosion of shallow thermokarst ponds on the Northeastern Qinghai-Tibet Plateau

Science.gov (United States)

Pan, X.; Yu, Q.; You, Y.

2014-12-01

Understanding hydrological and thermal regimes of thermokarst lakes is of great importance for predicting their responses to climate change. However, mechanism of water-level dynamics and associated thermal effects on thermoerosion of thermokarst lakes are still not well understood on the Qinghai-Tibet Plateau (QTP). In this study, we investigate two typical shallow thermokarst ponds (namely small lakes) in a warm permafrost region with thick active layer on the northeastern QTP through quantifying water budget. Results demonstrate that, rainfall induced subsurface lateral flow dominates pond water-level regime. Annual variation of pond water-level relies on areal water budget of surrounding active layer, particularly the high variable of precipitation. Besides, it is worth noting the extraordinary warming during the late ice-cover period, because marked air gap between upper ice-cover and underlying water, led by the upward thawing of thick ice-cover, might result in greenhouse-like condition due to the unique weather that strong solar radiation and little snowpack. This hydrological mechanism also exerts evident impacts on thermal regime and thermoerosion of the shallow thermokarst ponds, and they are closely related to retreat of thermokarst pondshore and underlying permafrost degradation. These findings imply a localized model addressing the unique hydrological and thermal regimes of thermokarst lakes would be essential to study the evolution of these shallow rainwater dominated thermokarst ponds on the QTP.

Compensation for thermally induced birefringence in polycrystalline ceramic active elements

International Nuclear Information System (INIS)

Kagan, M A; Khazanov, E A

2003-01-01

Polycrystalline ceramics differ significantly from single crystals in that the crystallographic axes (and hence of the axes of thermally induced birefringence) are oriented randomly in each granule of the ceramic. The quaternion formalism is employed to calculate the depolarisation in the ceramics and the efficiency of its compensation. The obtained analytic expressions are in good agreement with the numerical relations. It is shown that the larger the ratio of the sample length to the granule size, the closer the properties of the ceramics to those of a single crystal with the [111] orientation (in particular, the uncompensated depolarisation is inversely proportional to this ratio). (active media)

Dynamics of defect-induced dark solitons in an exciton-polariton condensate

Science.gov (United States)

Opala, Andrzej; Pieczarka, Maciej; Bobrovska, Nataliya; Matuszewski, Michał

2018-04-01

We study theoretically the emission of dark solitons induced by a moving defect in a nonresonantly pumped exciton-polariton condensate. The number of created dark solitons per unit of time is found to be strongly dependent on the pump power. We relate the observed dynamics of this process to the oscillations of the drag force experienced by the condensate. We investigate the stability of the polariton quantum fluid and present various types of dynamics depending on the condensate and moving obstacle parameters. Furthermore, we provide analytical expressions for dark soliton dynamics using the variational method adapted to the nonequilibrium polariton system. The determined dynamical equations are found to be in excellent agreement with the results of numerical simulations.

Nuclear dynamics of radiation-induced foci in euchromatin and heterochromatin

International Nuclear Information System (INIS)

Chiolo, Irene; Tang, Jonathan; Georgescu, Walter; Costes, Sylvain V.

2013-01-01

Repair of double strand breaks (DSBs) is essential for cell survival and genome integrity. While much is known about the molecular mechanisms involved in DSB repair and checkpoint activation, the roles of nuclear dynamics of radiation-induced foci (RIF) in DNA repair are just beginning to emerge. Here, we summarize results from recent studies that point to distinct features of these dynamics in two different chromatin environments: heterochromatin and euchromatin. We also discuss how nuclear architecture and chromatin components might control these dynamics, and the need of novel quantification methods for a better description and interpretation of these phenomena. These studies are expected to provide new biomarkers for radiation risk and new strategies for cancer detection and treatment

Nuclear dynamics of radiation-induced foci in euchromatin and heterochromatin

Energy Technology Data Exchange (ETDEWEB)

Chiolo, Irene; Tang, Jonathan; Georgescu, Walter; Costes, Sylvain V.

2013-10-01

Repair of double strand breaks (DSBs) is essential for cell survival and genome integrity. While much is known about the molecular mechanisms involved in DSB repair and checkpoint activation, the roles of nuclear dynamics of radiation-induced foci (RIF) in DNA repair are just beginning to emerge. Here, we summarize results from recent studies that point to distinct features of these dynamics in two different chromatin environments: heterochromatin and euchromatin. We also discuss how nuclear architecture and chromatin components might control these dynamics, and the need of novel quantification methods for a better description and interpretation of these phenomena. These studies are expected to provide new biomarkers for radiation risk and new strategies for cancer detection and treatment.

Multifragmentation of gold nuclei by light relativistic ions - thermal break-up versus dynamic disintegration

International Nuclear Information System (INIS)

Avdeev, S.P.; Karnaukhov, V.A.; Petrov, L.A.

2000-01-01

Multiple emission of intermediate-mass fragments has been studied for the collisions of p, 4 He and 12 C on Au with the 4π setup FASA. The mean IMF multiplicities saturate at a value of around 2 for incident energies above 6 GeV. An attempt to describe the observed IMF multiplicities in the two-stage scenario, a fast cascade followed by a statistical multifragmentation, fails. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate expansion phase and modifying empirically the excitation energies and masses of the remnants. The angular distributions and energy spectra from the p-induced collisions are in agreement with the scenario of 'thermal' multifragmentation of a hot and expanded target-spectator. In the case of 12 C+Au (22.4 GeV) and 4 He (14.6 GeV) +Au collisions, deviations from a pure thermal break-up are seen in the emitted-fragment energy spectra, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow with the expansion velocity at the surface of about 0.1 s (for 12 C + Au collisions)

A method for the dynamic and thermal stress analysis of space shuttle surface insulation

Science.gov (United States)

Ojalvo, I. U.; Levy, A.; Austin, F.

1975-01-01

The thermal protection system of the space shuttle consists of thousands of separate insulation tiles bonded to the orbiter's surface through a soft strain-isolation layer. The individual tiles are relatively thick and possess nonuniform properties. Therefore, each is idealized by finite-element assemblages containing up to 2500 degrees of freedom. Since the tiles affixed to a given structural panel will, in general, interact with one another, application of the standard direct-stiffness method would require equation systems involving excessive numbers of unknowns. This paper presents a method which overcomes this problem through an efficient iterative procedure which requires treatment of only a single tile at any given time. Results of associated static, dynamic, and thermal stress analyses and sufficient conditions for convergence of the iterative solution method are given.

Quantum chaos induced by nonadiabatic coupling in wave-packet dynamics

International Nuclear Information System (INIS)

Higuchi, Hisashi; Takatsuka, Kazuo

2002-01-01

The effect of nonadiabatic coupling due to breakdown of the Born-Oppenheimer approximation on chaos is investigated. A couple of measures (indicators) that detect the extent of chaos in wave-packet dynamics on coupled potential functions are devised. Using them, we show that chaos is indeed induced by a nonadiabatic coupling in individual time-dependent wave-packet dynamics. This chaos is genuinely of quantum nature, since it arises from bifurcation and merging of a wave packet at the quasicrossing region of two coupled potential functions

Thermal domains in inhomogeneous current-carrying superconductors. Current-voltage characteriscs and dynamics of domain formation after current jumps

International Nuclear Information System (INIS)

Bezuglyj, A.I.; Shklovskij, V.A.

1984-01-01

The static and dynamic behavior of thermal domains in inhomogeneous superconducting films, where the inhomogeneity behaves like a portion of the film with a reduced critical current, have been studied theoretically within the framework of the phenomenological approach, using the heat balance equation and the dependence of the superconductor critical current on temperature. Depending on the size of the inhomogeneity (local or extended) and on the relative values of parameters of the homogeneous and inhomogeneous regions, different types of current-voltage characteristics are obtained. The nonstationary problem of thermal domain formation near the inhomogeneity after a current jump has been solved, and the domain boundary (kink) dynamics at a distance from the inhomogeneity has been analyzed. A combination of the results allows one to describe the whole process of normal phase formation and its spread throughout the superconducting film

Dynamic, large-deflection, inelastic and thermal stress analysis by the finite element method

International Nuclear Information System (INIS)

Haisler, W.E.; Stricklin, J.A.

1975-01-01

A finite element theory and computer program have been developed for predicting the dynamic, large displacement, inelastic and thermal response of stiffened and layered structures. The dependence of material properties on temperature is explicitly accounted for and any arbitrary, transient mechanical or thermal load history is allowed. The shell may have internal or external stiffeners and be constructed with up to three layers. The equations of motion are developed by using the pseudo force approach to represent all nonlinearities and are then solved by using either the Houbolt method or central differences. Moderately large rotations are allowed. The program is based on an incremental theory of plasticity using the Von Mises yield condition and associated flow rule. The post yield or work-hardening behavior is idealized with either the isotropic hardening or mechanical sublayer models. Two models are utilized since it has been found through comparison with experimental results that isotropic hardening is best for simple loading conditions while the mechanical sublayer model is better for reverse and cyclic loading. Strain-rate effects are also accounted for in the program by using a power-law type model based on the strain rate. The dependence of material properties on temperature is taken into account in the pseudo forces. Young's modulus, Poisson's ratio, thermal coefficient of expansion, the yield stress, and the entire stress strain curve are treated as functions of the applied temperature. Containment vessels subjected to transient and shock-type mechanical and thermal loads have been analyzed

Thermal/structural analysis of radiators for heavy-duty trucks

International Nuclear Information System (INIS)