Science.gov

Sample records for phase change wallboard

  1. Analysis of wallboard containing a phase change material

    NASA Astrophysics Data System (ADS)

    Tomlinson, J. J.; Heberle, D. P.

    Phase change materials (PCMs) used on the interior of buildings hold the promise for improved thermal performance by reducing the energy requirements for space conditioning and by improving thermal comfort by reducing temperature swings inside the building. Efforts are underway to develop a gypsum wallboard containing a hydrocarbon PCM. With a phase change temperature in the room temperature range, the PCM wallboard adds substantially to the thermal mass of the building while serving the same architectural function as conventional wallboard. To determine the thermal and economic performance of this PCM wallboard, the Transient Systems Simulation Program (TRNSYS) was modified to accommodate walls that are covered with PCM plasterboard, and to apportion the direct beam solar radiation to interior surfaces of a building. The modified code was used to simulate the performance of conventional and direct-gain passive solar residential-sized buildings with and without PCM wallboard. Space heating energy savings were determined as a function of PCM wallboard characteristics. Thermal comfort improvements in buildings containing the PCM were qualified in terms of energy savings. The report concludes with a present worth economic analysis of these energy savings and arrives at system costs and economic payback based on current costs of PCMs under study for the wallboard application.

  2. Wallboard with latent heat storage for passive solar applications

    SciTech Connect

    Kedl, R.J.

    1991-05-01

    Conventional wallboard impregnated with octadecane paraffin is being developed as a building material with latent heat storage for passive solar and other applications. Impregnation was accomplished simply by soaking the wallboard in molten wax. Concentrations of wax in the combined product as high as 35% by weight can be achieved. Scale-up of the soaking process, from small laboratory samples to full-sized 4- by 8-ft sheets, has been successfully accomplished. The required construction properties of wallboard are maintained after impregnation, that is, it can be painted and spackled. Long-term, high-temperature exposure tests and thermal cycling tests showed no tendency of the paraffin to migrate within the wallboard, and there was no deterioration of thermal energy storage capacity. In support of this concept, a computer model was developed to handle thermal transport and storage by a phase change material (PCM) dispersed in a porous media. The computer model was confirmed by comparison with known analytical solutions and also by comparison with temperatures measured in wallboard during an experimentally generated thermal transient. Agreement between the model and known solution was excellent. Agreement between the model and thermal transient was good, only after the model was modified to allow the PCM to melt over a temperature range, rather than at a specific melting point. When the melting characteristics of the PCM, as determined from a differential scanning calorimeter plot, were used in the model, agreement between the model and transient data was very good. 11 refs., 25 figs., 2 tabs.

  3. Wallboard with Latent Heat Storage for Passive Solar Applications

    SciTech Connect

    Kedl, R.J.

    2001-05-31

    Conventional wallboard impregnated with octadecane paraffin [melting point-23 C (73.5 F)] is being developed as a building material with latent heat storage for passive solar and other applications. Impregnation was accomplished simply by soaking the wallboard in molten wax. Concentrations of wax in the combined product as high as 35% by weight can be achieved. Scale-up of the soaking process, from small laboratory samples to full-sized 4- by 8-ft sheets, has been successfully accomplished. The required construction properties of wallboard are maintained after impregnation, that is, it can be painted and spackled. Long-term, high-temperature exposure tests and thermal cycling tests showed no tendency of the paraffin to migrate within the wallboard, and there was no deterioration of thermal energy storage capacity. In support of this concept, a computer model was developed to handle thermal transport and storage by a phase change material (PCM) dispersed in a porous media. The computer model was confirmed by comparison with known analytical solutions and also by comparison with temperatures measured in wallboard during an experimentally generated thermal transient. Agreement between the model and known solution was excellent. Agreement between the model and thermal transient was good, only after the model was modified to allow the PCM to melt over a temperature range, rather than at a specific melting point. When the melting characteristics of the PCM (melting point, melting range, and heat of fusion), as determined from a differential scanning calorimeter plot, were used in the model, agreement between the model and transient data was very good. The confirmed computer model may now be used in conjunction with a building heating and cooling code to evaluate design parameters and operational characteristics of latent heat storage wallboard for passive solar applications.

  4. Combined experimental and numerical evaluation of a prototype nano-PCM enhanced wallboard

    SciTech Connect

    Biswas, Kaushik; LuPh.D., Jue; Soroushian, Parviz; Shrestha, Som S

    2014-01-01

    In the United States, forty-eight (48) percent of the residential end-use energy consumption is spent on space heating and air conditioning. Reducing envelope-generated heating and cooling loads through application of phase change material (PCM)-enhanced building envelopes can facilitate maximizing the energy efficiency of buildings. Combined experimental testing and numerical modeling of PCM-enhanced envelope components are two important aspects of the evaluation of their energy benefits. An innovative phase change material (nano-PCM) was developed with PCM encapsulated with expanded graphite (interconnected) nanosheets, which is highly conductive for enhanced thermal storage and energy distribution, and is shape-stable for convenient incorporation into lightweight building components. A wall with cellulose cavity insulation and prototype PCM-enhanced interior wallboards was built and tested in a natural exposure test (NET) facility in a hot-humid climate location. The test wall contained PCM wallboards and regular gypsum wallboard, for a side-by-side annual comparison study. Further, numerical modeling of the walls containing the nano-PCM wallboard was performed to determine its actual impact on wall-generated heating and cooling loads. The model was first validated using experimental data, and then used for annual simulations using Typical Meteorological Year (TMY3) weather data. This article presents the measured performance and numerical analysis evaluating the energy-saving potential of the nano-PCM-enhanced wallboard.

  5. MOISTURE MOVEMENT (WICKING) WITHIN GYPSUM WALLBOARD

    EPA Science Inventory

    Gypsum wallboard with repeated or prolonged exposure to water or excess moisture can lose its structural integrity and provide a growth medium for biological contaminants. Poorly sealed buildings, leaking or failed plumbing systems, or improperly constructed HVAC systems can all ...

  6. MOISTURE MOVEMENT (WICKING) WITHIN GYPSUM WALLBOARD

    EPA Science Inventory

    Gypsum wallboard with repeated or prolonged exposure to water or excess moisture can lose its structural integrity and provide a growth medium for biological contaminants. Poorly sealed buildings, leaking or failed plumbing systems, or improperly constructed HVAC systems can all ...

  7. Characterization of dairy cattle manure/wallboard paper compost mixture.

    PubMed

    Saludes, Ronaldo B; Iwabuchi, Kazunori; Miyatake, Fumihito; Abe, Yoshiyuki; Honda, Yoshifumi

    2008-10-01

    The aim of this research was to evaluate the use of manufacturing wallboard paper scraps as an alternative bulking agent for dairy cattle manure composting. The characteristics of the composting process were studied based on the changes in physico-chemical parameters and final compost quality. Composting of dairy cattle manure with wallboard paper was performed in a 481-L cylindrical reactor with vacuum-type aeration. Rapid degradation of organic matter was observed during the thermophilic stage of composting due to high microbial activity. High temperature and alkaline pH conditions promoted intense ammonia emission during the early stage of composting. The number of mesophilic and thermophilic microorganisms were found to be affected by changes in temperature at different composting stages. The total nitrogen (N), phosphorus (P), potassium (K), and sodium (Na) concentrations of the mixture did not change significantly after 28days of composting. However, the presence of gypsum in the paper scraps increased the calcium content of the final compost. The wallboard paper had no phyto-inhibitory effects as shown by high germination index of final compost (GI=99%).

  8. Phase Change

    NASA Technical Reports Server (NTRS)

    Hasan, Mohammad M.

    2004-01-01

    Recent workshops to define strategic research on critical issues in microgravity fluids and transport phenomena in support of mission orientated needs of NASA and many technical conferences over the years in support of fundamental research targeting NASA's long range missions goal have identified several phase change processes needed to design advanced space and planetary based systems for long duration operations Recommendation noted that phase change processes are profoundly affected by gravitational environment.

  9. Characterizing synthetic gypsum for wallboard manufacture

    SciTech Connect

    Henkels, P.J.; Gynor, J.C.

    1996-12-31

    United States Gypsum Company (USGC) has developed specifications and guidelines covering the chemical and physical aspects of synthetic gypsum to help predict end use acceptability in wallboard manufacture. These guidelines are based in part on past experiences with natural and synthetic gypsum. Similarly, most wallboard manufacturers in North America have developed their own guidelines based in part on its unique history and particular experiences with synthetic gypsum. While there are similarities between manufacturers` guidelines, differences do exist. This paper discusses the importance of selected parameters contained in the FGD gypsum guidelines. In most cases, the parameters are equally relevant to other synthetic gypsums and the naturally occurring gypsum mineral as well.

  10. Gypsum Wallboard as a sink for formaldehyde

    EPA Science Inventory

    Formaldehyde (HCHO) has been of special concern as an indoor air pollutant because of its presence in a wide range of consumer products and its adverse health effects. Materials acting as HCHO sinks, such as painted gypsum wallboard, can become emission sources. However, adsorpti...

  11. Gypsum Wallboard as a sink for formaldehyde

    EPA Science Inventory

    Formaldehyde (HCHO) has been of special concern as an indoor air pollutant because of its presence in a wide range of consumer products and its adverse health effects. Materials acting as HCHO sinks, such as painted gypsum wallboard, can become emission sources. However, adsorpti...

  12. Desorption of a methamphetamine surrogate from wallboard under remediation conditions

    NASA Astrophysics Data System (ADS)

    Poppendieck, Dustin; Morrison, Glenn; Corsi, Richard

    2015-04-01

    Thousands of homes in the United States are found to be contaminated with methamphetamine each year. Buildings used to produce illicit methamphetamine are typically remediated by removing soft furnishings and stained materials, cleaning and sometimes encapsulating surfaces using paint. Methamphetamine that has penetrated into paint films, wood and other permanent materials can be slowly released back into the building air over time, exposing future occupants and re-contaminating furnishings. The objective of this study was to determine the efficacy of two wallboard remediation techniques for homes contaminated with methamphetamine: 1) enhancing desorption by elevating temperature and relative humidity while ventilating the interior space, and 2) painting over affected wallboard to seal the methamphetamine in place. The emission of a methamphetamine surrogate, N-isopropylbenzylamine (NIBA), from pre-dosed wallboard chambers over 20 days at 32 °C and two values of relative humidity were studied. Emission rates from wallboard after 15 days at 32 °C ranged from 35 to 1400 μg h-1 m-2. Less than 22% of the NIBA was removed from the chambers over three weeks. Results indicate that elevating temperatures during remediation and latex painting of impacted wallboard will not significantly reduce freebase methamphetamine emissions from wallboard. Raising the relative humidity from 27% to 49% increased the emission rates by a factor of 1.4. A steady-state model of a typical home using the emission rates from this study and typical residential building parameters and conditions shows that adult inhalation reference doses for methamphetamine will be reached when approximately 1 g of methamphetamine is present in the wallboard of a house.

  13. ASSESSMENT OF STACHYBOTRYS REGROWTH ON CONTAMINATED WALLBOARD AFTER TREATMENT WITH COMMON SURFACE CLEANERS/DISINFECTANTS

    EPA Science Inventory

    The paper describes results of experiments assessing the efficacy of treating mold-contaminated gypsum wallboard with cleaners and/or disinfectants. Although the accepted recommendations for handling Stachybotrys chartarum contaminated gypsum wallboard are removal and replacement...

  14. Seismic Experimental Study on New-Type Composite Exterior Wallboard with Integrated Structural Function and Insulation

    PubMed Central

    Ma, Shaochun; Jiang, Nan

    2015-01-01

    In order to evaluate the seismic performance of new-type composite exterior wallboard, a total of six exterior and interior wallboards were incorporated in the experiment of seismic performance. Seismic performance such as the stress process, damage mode, hysteresis and skeleton curve, load-carrying and ductility coefficient, damping and energy dissipation, stiffness degradation as well as material strain of the exterior wallboards were analyzed with emphasis and compared with interior wallboards. Results of the experiment and analysis showed that both interior and exterior wallboards exhibited outstanding seismic performance. Due to the existence of insulation layer and externally bonded single gypsum board, the capacity of elastoplastic deformation and seismic energy dissipation of the exterior wallboards was improved and each seismic performance indicator of the exterior wallboards outperformed the interior wallboards.

  15. ASSESSMENT OF STACHYBOTRYS REGROWTH ON CONTAMINATED WALLBOARD AFTER TREATMENT WITH COMMON SURFACE CLEANERS/DISINFECTANTS

    EPA Science Inventory

    The paper describes results of experiments assessing the efficacy of treating mold-contaminated gypsum wallboard with cleaners and/or disinfectants. Although the accepted recommendations for handling Stachybotrys chartarum contaminated gypsum wallboard are removal and replacement...

  16. Fate of Mercury in Synthetic Gypsum Used for Wallboard Production

    SciTech Connect

    Jessica Sanderson

    2007-12-31

    This report presents and discusses results from the project 'Fate of Mercury in Synthetic Gypsum Used for Wallboard Production', performed at five different full-scale commercial wallboard plants. Synthetic gypsum produced by wet flue gas desulfurization (FGD) systems on coal-fired power plants is commonly used in the manufacture of wallboard. This practice has long benefited the environment by recycling the FGD gypsum byproduct, which is becoming available in increasing quantities, decreasing the need to landfill this material, and increasing the sustainable design of the wallboard product. However, new concerns have arisen as recent mercury control strategies involve the capture of mercury in FGD systems. The objective of this study has been to determine whether any mercury is released into the atmosphere at wallboard manufacturing plants when the synthetic gypsum material is used as a feedstock for wallboard production. The project has been co-funded by the U.S. DOE National Energy Technology Laboratory (Cooperative Agreement DE-FC26-04NT42080), USG Corporation, and EPRI. USG Corporation is the prime contractor, and URS Group is a subcontractor. The project scope included seven discrete tasks, each including a test conducted at various USG wallboard plants using synthetic gypsum from different wet FGD systems. The project was originally composed of five tasks, which were to include (1) a base-case test, then variations representing differing power plant: (2) emissions control configurations, (3) treatment of fine gypsum particles, (4) coal types, and (5) FGD reagent types. However, Task 5,could not be conducted as planned and instead was conducted at conditions similar to Task 3. Subsequently an opportunity arose to test gypsum produced from the Task 5 FGD system, but with an additive expected to impact the stability of mercury, so Task 6 was added to the project. Finally, Task 7 was added to evaluate synthetic gypsum produced at a power plant from an additional

  17. Single-aliquot EPR dosimetry of wallboard (drywall).

    PubMed

    Mistry, R; Thompson, J W; Boreham, D R; Rink, W J

    2011-11-01

    Electron paramagnetic resonance spectra and dose-response curves are presented for a variety of wallboard samples obtained from different manufacturing facilities, as well as for source gypsum and anhydrite. The intensity of the CO(3)(-) paramagnetic centre (G2) is enhanced with gamma radiation. Isothermal decay curves are used to propose annealing methods for the removal of the radiosensitive CO(3)(-) radical without affecting the unirradiated baseline. Post-irradiation annealing of wallboard prevents recuperation of the radiosensitive CO(3)(-) radical with additional irradiation. A single-aliquot additive dose procedure is developed that successfully measures test doses as low as 0.76 Gy.

  18. MOLD GROWTH ON GYPSUM WALLBOARD--A RESEARCH SUMMARY

    EPA Science Inventory

    Reducing occupant exposure to mold growing on damp gypsum wallboard is a research objective of the U.S. Environmental Protection Agency. Often mold contaminated building materials are not properly removed but instead surface cleaners are used and then paint is applied in an attem...

  19. THE EFFECT OF MERCURY CONTROLS ON WALLBOARD MANUFACTURE

    SciTech Connect

    Sandra Meischen

    2004-07-01

    Pending EPA regulations may mandate 70 to 90% mercury removal efficiency from utility flue gas. A mercury control option is the trapping of oxidized mercury in wet flue gas desulfurization systems (FGD). The potential doubling of mercury in the FGD material and its effect on mercury volatility at temperatures common to wallboard manufacture is a concern that could limit the growing byproduct use of FGD material. Prediction of mercury fate is limited by lack of information on the mercury form in the FGD material. The parts per billion mercury concentrations prevent the identification of mercury compounds by common analytical methods. A sensitive analytical method, cold vapor atomic fluorescence, coupled with leaching and thermodecomposition methods were evaluated for their potential to identify mercury compounds in FGD material. The results of the study suggest that the mercury form is dominated by the calcium sulfate matrix and is probably associated with the sulfate form in the FGD material. Additionally, to determine the effect of high mercury concentration FGD material on wallboard manufacture, a laboratory FGD unit was built to trap the oxidized mercury generated in a simulated flue gas. Although the laboratory prepared FGD material did not contain the mercury concentrations anticipated, further thermal tests determined that mercury begins to evolve from FGD material at 380 to 390 F, consequently dropping the drying temperature should mitigate mercury evolution if necessary. Mercury evolution is also diminished as the weight of the wallboard sample increased. Consequently, mercury evolution may not be a significant problem in wallboard manufacture.

  20. MOLD GROWTH ON GYPSUM WALLBOARD--A RESEARCH SUMMARY

    EPA Science Inventory

    Reducing occupant exposure to mold growing on damp gypsum wallboard is a research objective of the U.S. Environmental Protection Agency. Often mold contaminated building materials are not properly removed but instead surface cleaners are used and then paint is applied in an attem...

  1. Fate of Mercury in Synthetic Gypsum Used for Wallboard Production

    SciTech Connect

    Jessica Marshall Sanderson

    2006-06-01

    This report presents and discusses results from Task 5 of the study ''Fate of Mercury in Synthetic Gypsum Used for Wallboard Production,'' performed at a full-scale commercial wallboard plant. Synthetic gypsum produced by wet flue gas desulfurization (FGD) systems on coal-fired power plants is commonly used in the manufacture of wallboard. The FGD process is used to control the sulfur dioxide emissions which would result in acid rain if not controlled. This practice has long benefited the environment by recycling the FGD gypsum byproduct, which is becoming available in increasing quantities, decreasing the need to landfill this material, and increasing the sustainable design of the wallboard product. However, new concerns have arisen as recent mercury control strategies developed for power plants involve the capture of mercury in FGD systems. The objective of this study is to determine whether any mercury is released into the atmosphere when the synthetic gypsum material is used as a feedstock for wallboard production. The project is being co-funded by the U.S. DOE National Energy Technology Laboratory (Cooperative Agreement DE-FC26-04NT42080), USG Corporation, and EPRI. USG Corporation is the prime contractor, and URS Group is a subcontractor. The project scope includes five discrete tasks, each conducted at various USG wallboard plants using synthetic gypsum from different FGD systems. The five tasks were to include (1) a baseline test, then variations representing differing power plant (2) emissions control configurations, (3) treatment of fine gypsum particles, (4) coal types, and (5) FGD reagent types. However, Task 5, which was to evaluate gypsum produced from an alternate FGD reagent, could not be conducted as planned. Instead, Task 5 was conducted at conditions similar to a previous task, Task 3, although with gypsum from an alternate FGD system. In this project, process stacks in the wallboard plant have been sampled using the Ontario Hydro method. The

  2. Demonstrating Phase Changes.

    ERIC Educational Resources Information Center

    Rohr, Walter

    1995-01-01

    Presents two experiments that demonstrate phase changes. The first experiment explores phase changes of carbon dioxide using powdered dry ice sealed in a piece of clear plastic tubing. The second experiment demonstrates an equilibrium process in which a crystal grows in equilibrium with its saturated solution. (PVD)

  3. Demonstrating Phase Changes.

    ERIC Educational Resources Information Center

    Rohr, Walter

    1995-01-01

    Presents two experiments that demonstrate phase changes. The first experiment explores phase changes of carbon dioxide using powdered dry ice sealed in a piece of clear plastic tubing. The second experiment demonstrates an equilibrium process in which a crystal grows in equilibrium with its saturated solution. (PVD)

  4. Fate of Mercury in Synthetic Gypsum Used for Wallboard Production

    SciTech Connect

    Jessica Sanderson; Gary M. Blythe; Mandi Richardson

    2006-12-01

    This report presents and discusses results from Task 6 of the study 'Fate of Mercury in Synthetic Gypsum Used for Wallboard Production,' performed at a full-scale commercial wallboard plant. Synthetic gypsum produced by wet flue gas desulfurization (FGD) systems on coal-fired power plants is commonly used in the manufacture of wallboard. This practice has long benefited the environment by recycling the FGD gypsum byproduct, which is becoming available in increasing quantities, decreasing the need to landfill this material, and increasing the sustainable design of the wallboard product. However, new concerns have arisen as recent mercury control strategies involve the capture of mercury in FGD systems. The objective of this study is to determine whether any mercury is released into the atmosphere when the synthetic gypsum material is used as a feedstock for wallboard production. The project is being co-funded by the U.S. DOE National Energy Technology Laboratory (Cooperative Agreement DE-FC26-04NT42080), USG Corporation, and EPRI. USG Corporation is the prime contractor, and URS Group is a subcontractor. The project scope now includes six discrete tasks, each conducted at various USG wallboard plants using synthetic gypsum from different FGD systems. The project was originally composed of five tasks, which were to include (1) a baseline test, then variations representing differing power plant: (2) emissions control configurations, (3) treatment of fine gypsum particles, (4) coal types, and (5) FGD reagent types. However, Task 5, which was to include testing with an alternate FGD reagent, could not be conducted as planned. Instead, Task 5 was conducted at conditions similar to Task 3, although with gypsum from an alternate FGD system. Subsequent to conducting Task 5 under these revised conditions, an opportunity arose to test gypsum produced at the same FGD system, but with an additive (Degussa Corporation's TMT-15) being used in the FGD system. TMT-15 was expected

  5. Optically stimulated luminescence dosimetry with gypsum wallboard (drywall).

    PubMed

    Thompson, Jeroen W; Burdette, Kevin E; Inrig, Elizabeth L; Dewitt, Regina; Mistry, Rajesh; Rink, W Jack; Boreham, Douglas R

    2010-09-01

    Gypsum wallboard (drywall) represents an attractive target for retrospective dosimetry by optically stimulated luminescence (OSL) in the event of a radiological accident or malicious use of nuclear material. In this study, wallboard is shown to display a radiation-induced luminescence signal (RIS) as well as a natural background signal (NS), which is comparable in intensity to the RIS. Excitation and emission spectra show that maximum luminescence intensity is obtained for stimulation with blue light-emitting diodes (470 nm) and for detection in the ultraviolet region (290-370 nm). It is necessary to decrease the optical stimulation power dramatically in order to adequately separate the RIS from the interfering background signal. The necessary protocols are developed for accurately measuring the absorbed dose as low as 500 mGy and demonstrate that the RIS decays logarithmically with storage time, with complete erasure expected within 1-4 d.

  6. Fun with Phase Changes

    ERIC Educational Resources Information Center

    Purvis, David

    2006-01-01

    A lot of good elementary science involves studying solids, liquids, and gases, and some inquiry-based activities that are easy to set up and do. In this article, the author presents activities pertaining to simple phase change. Using water as the example, these activities introduce upper-grade students to the idea of the arrangement of molecules…

  7. Phase change compositions

    DOEpatents

    Salyer, Ival O.

    1989-01-01

    Compositions containing crystalline, straight chain, alkyl hydrocarbons as phase change materials including cementitious compositions containing the alkyl hydrocarbons neat or in pellets or granules formed by incorporating the alkyl hydrocarbons in polymers or rubbers; and polymeric or elastomeric compositions containing alkyl hydrocarbons.

  8. Phase change compositions

    DOEpatents

    Salyer, Ival O.; Griffen, Charles W.

    1986-01-01

    Compositions containing crystalline, long chain, alkyl hydrocarbons as phase change materials including cementitious compositions containing the alkyl hydrocarbons neat or in pellets or granules formed by incorporating the alkyl hydrocarbons in polymers or rubbers; and polymeric or elastomeric compositions containing alkyl hydrocarbons.

  9. Fun with Phase Changes

    ERIC Educational Resources Information Center

    Purvis, David

    2006-01-01

    A lot of good elementary science involves studying solids, liquids, and gases, and some inquiry-based activities that are easy to set up and do. In this article, the author presents activities pertaining to simple phase change. Using water as the example, these activities introduce upper-grade students to the idea of the arrangement of molecules…

  10. Mitigation of efflorescence of wallboard by means of bio-mineralization

    PubMed Central

    Xue, Bin; Qian, Chunxiang

    2015-01-01

    Cement-based material is one of the most versatile and largest amounts of building materials which can not only be used in load-bearing structure but also be used as decoration materials, like brick, wallboard, and tile. However, white calcium carbonate always be found on the surface of wallboard. This phenomenon is generally called efflorescence, which has no damage to wallboard, but has aesthetic impact. In this research, Bacillus mucilaginosus was pre-added to the cement matrix to reduce the efflorescence of wallboard. Image processing, thermogravimetric analysis and permeability test were used to characterize the efflorescence degree of wallboard. The results showed that the bacterium captured atmospheric CO2 by carbonic anhydrase and promoted the CO2to react with Ca(OH)2. This process not only reduced the content of Ca(OH)2 but also improved the compactness of wallboard. In addition, the maximal decrease of efflorescence area of wallboard was gotten when the content of microbial was up to 4% of the mass of cementitious material and the proportion of efflorescence area reduced from 32 ± 3 to 5 ± 1% of the whole area of surface layer. At the same time, the values of compressive and flexural strength were the highest and the surface layer of wallboard was the most compact. The observed reduction of efflorescence was indeed due to the effect of bio-mineralization. This promising method was noted to be cheap, convenient, environment friendly, and which has the potential in various practical applications. PMID:26539182

  11. Coal Combustion Residual Beneficial Use Evaluation: Fly Ash Concrete and FGD Gypsum Wallboard

    EPA Pesticide Factsheets

    This page contains documents related to the evaluation of coal combustion residual beneficial use of fly ash concrete and FGD gypsum wallboard including the evaluation itself and the accompanying appendices

  12. Phase change materials handbook

    NASA Technical Reports Server (NTRS)

    Hale, D. V.; Hoover, M. J.; Oneill, M. J.

    1971-01-01

    This handbook is intended to provide theory and data needed by the thermal design engineer to bridge the gap between research achievements and actual flight systems, within the limits of the current state of the art of phase change materials (PCM) technology. The relationship between PCM and more conventional thermal control techniques is described and numerous space and terrestrial applications of PCM are discussed. Material properties of the most promising PCMs are provided; the purposes and use of metallic filler materials in PCM composites are presented; and material compatibility considerations relevant to PCM design are included. The engineering considerations of PCM design are described, especially those pertaining to the thermodynamic and heat transfer phenomena peculiar to PCM design. Methods of obtaining data not currently available are presented. The special problems encountered in the space environment are described. Computational tools useful to the designer are discussed. In summary, each aspect of the PCM problem important to the design engineer is covered to the extent allowed by the scope of this effort and the state of the art.

  13. PHASE CHANGE LIQUIDS

    SciTech Connect

    Susan S. Sorini; John F. Schabron

    2006-03-01

    Work is being performed to develop a new shipping system for frozen environmental samples (or other materials) that uses an optimal phase change liquid (PCL) formulation and an insulated shipping container with an on-board digital temperature data logger to provide a history of the temperature profile within the container during shipment. In previous work, several PCL formulations with temperatures of fusion ranging from approximately -14 to -20 C were prepared and evaluated. Both temperature of fusion and heat of fusion of the formulations were measured, and an optimal PCL formulation was selected. The PCL was frozen in plastic bags and tested for its temperature profile in a cooler using a digital temperature data logger. This testing showed that the PCL formulation can maintain freezer temperatures (< -7 to -20 C) for an extended period, such as the time for shipping samples by overnight courier. The results of the experiments described in this report provide significant information for use in developing an integrated freezer system that uses a PCL formulation to maintain freezer temperatures in coolers for shipping environmental samples to the laboratory. Experimental results show the importance of the type of cooler used in the system and that use of an insulating material within the cooler improves the performance of the freezer system. A new optimal PCL formulation for use in the system has been determined. The new formulation has been shown to maintain temperatures at < -7 to -20 C for 47 hours in an insulated cooler system containing soil samples. These results are very promising for developing the new technology.

  14. Phase Change Material Heat Exchangers

    NASA Image and Video Library

    NASA’s Game Changing Development is taking on a technologydevelopment and demonstration effort to design, build, and test the next generation of Phase Change Material Heat Exchangers (PCM HXs) on ...

  15. A Different Phase Change

    ERIC Educational Resources Information Center

    Link, Lyndsay B.; Christmann, Edwin P.

    2004-01-01

    This article provides instructions, and a list of supplies for a teacher performed class demonstration showing, change of state. Having students engage in technology-based inquiry activities is an excellent way for teachers to introduce topics that are driven by the National Science Education Standards (NRC 1996). Based on Content Standard B, this…

  16. A Different Phase Change

    ERIC Educational Resources Information Center

    Link, Lyndsay B.; Christmann, Edwin P.

    2004-01-01

    This article provides instructions, and a list of supplies for a teacher performed class demonstration showing, change of state. Having students engage in technology-based inquiry activities is an excellent way for teachers to introduce topics that are driven by the National Science Education Standards (NRC 1996). Based on Content Standard B, this…

  17. Pre-contamination of new gypsum wallboard with potentially harmful fungal species.

    PubMed

    Andersen, B; Dosen, I; Lewinska, A M; Nielsen, K F

    2017-01-01

    Gypsum wallboard is a popular building material, but is also very frequently overgrown by Stachybotrys chartarum after severe and/or undetected water damage. The purpose of this study was to determine whether Stachybotrys and other fungi frequently isolated from wet gypsum wallboard are already present in the panels directly from the factory. Surface-disinfected gypsum disks were wetted with sterile water, sealed, and incubated for 70 days. The results showed that Neosartorya hiratsukae (≡ Aspergillus hiratsukae) was the most dominant fungus on the gypsum wallboard followed by Chaetomium globosum and Stachybotrys chartarum. Our results suggest that these three fungal species are already embedded in the materials, presumably in the paper/carton layer surrounding the gypsum core, before the panels reach the retailers/building site.

  18. Interfacial phase-change memory.

    PubMed

    Simpson, R E; Fons, P; Kolobov, A V; Fukaya, T; Krbal, M; Yagi, T; Tominaga, J

    2011-07-03

    Phase-change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating or some other excitation process. For example, switching the composite Ge(2)Sb(2)Te(5) (GST) alloy from its covalently bonded amorphous phase to its resonantly bonded metastable cubic crystalline phase decreases the resistivity by three orders of magnitude, and also increases reflectivity across the visible spectrum. Moreover, phase-change memory based on GST is scalable, and is therefore a candidate to replace Flash memory for non-volatile data storage applications. The energy needed to switch between the two phases depends on the intrinsic properties of the phase-change material and the device architecture; this energy is usually supplied by laser or electrical pulses. The switching energy for GST can be reduced by limiting the movement of the atoms to a single dimension, thus substantially reducing the entropic losses associated with the phase-change process. In particular, aligning the c-axis of a hexagonal Sb(2)Te(3) layer and the 〈111〉 direction of a cubic GeTe layer in a superlattice structure creates a material in which Ge atoms can switch between octahedral sites and lower-coordination sites at the interface of the superlattice layers. Here we demonstrate GeTe/Sb(2)Te(3) interfacial phase-change memory (IPCM) data storage devices with reduced switching energies, improved write-erase cycle lifetimes and faster switching speeds.

  19. Stochastic phase-change neurons.

    PubMed

    Tuma, Tomas; Pantazi, Angeliki; Le Gallo, Manuel; Sebastian, Abu; Eleftheriou, Evangelos

    2016-08-01

    Artificial neuromorphic systems based on populations of spiking neurons are an indispensable tool in understanding the human brain and in constructing neuromimetic computational systems. To reach areal and power efficiencies comparable to those seen in biological systems, electroionics-based and phase-change-based memristive devices have been explored as nanoscale counterparts of synapses. However, progress on scalable realizations of neurons has so far been limited. Here, we show that chalcogenide-based phase-change materials can be used to create an artificial neuron in which the membrane potential is represented by the phase configuration of the nanoscale phase-change device. By exploiting the physics of reversible amorphous-to-crystal phase transitions, we show that the temporal integration of postsynaptic potentials can be achieved on a nanosecond timescale. Moreover, we show that this is inherently stochastic because of the melt-quench-induced reconfiguration of the atomic structure occurring when the neuron is reset. We demonstrate the use of these phase-change neurons, and their populations, in the detection of temporal correlations in parallel data streams and in sub-Nyquist representation of high-bandwidth signals.

  20. Stochastic phase-change neurons

    NASA Astrophysics Data System (ADS)

    Tuma, Tomas; Pantazi, Angeliki; Le Gallo, Manuel; Sebastian, Abu; Eleftheriou, Evangelos

    2016-08-01

    Artificial neuromorphic systems based on populations of spiking neurons are an indispensable tool in understanding the human brain and in constructing neuromimetic computational systems. To reach areal and power efficiencies comparable to those seen in biological systems, electroionics-based and phase-change-based memristive devices have been explored as nanoscale counterparts of synapses. However, progress on scalable realizations of neurons has so far been limited. Here, we show that chalcogenide-based phase-change materials can be used to create an artificial neuron in which the membrane potential is represented by the phase configuration of the nanoscale phase-change device. By exploiting the physics of reversible amorphous-to-crystal phase transitions, we show that the temporal integration of postsynaptic potentials can be achieved on a nanosecond timescale. Moreover, we show that this is inherently stochastic because of the melt-quench-induced reconfiguration of the atomic structure occurring when the neuron is reset. We demonstrate the use of these phase-change neurons, and their populations, in the detection of temporal correlations in parallel data streams and in sub-Nyquist representation of high-bandwidth signals.

  1. Microbial Volatile Organic Compound Emissions from Stachybotrys chartarum growing on Gypsum Wallboard and Ceiling tile

    EPA Science Inventory

    This study compared seven toxigenic strains of S. chartarum found in water-damaged buildings to characterize the microbial volatile organic compound (MVOC) emissions profile while growing on gypsum wallboard (W) and ceiling tile (C) coupons. The inoculated coupons with their sub...

  2. Microbial Volatile Organic Compound Emissions from Stachybotrys chartarum growing on Gypsum Wallboard and Ceiling tile

    EPA Science Inventory

    This study compared seven toxigenic strains of S. chartarum found in water-damaged buildings to characterize the microbial volatile organic compound (MVOC) emissions profile while growing on gypsum wallboard (W) and ceiling tile (C) coupons. The inoculated coupons with their sub...

  3. Children's Views Concerning Phase Changes.

    ERIC Educational Resources Information Center

    Bar, Varda; Travis, Anthony S.

    1991-01-01

    This article reports on answers by children (grades 1-9, n=83) to oral and written questions concerning the phase change from liquid to gas. The development of concepts was followed, proceeding from concrete to abstract ideas. Many students were found to experience difficulties in problem solving even though they may have had the necessary level…

  4. Thermal analysis of calcium sulfate dihydrate sources used to manufacture gypsum wallboard

    SciTech Connect

    Engbrecht, Dick C.; Hirschfeld, Deidre A.

    2016-07-27

    Gypsum wallboard has been used for over 100 years as a barrier to the spread of fire in residential and commercial structures. The gypsum molecule, CaSO4·2H2O, provides two crystalline waters that are released upon heating providing an endothermic effect. Manufacturers have recognized that the source of the gypsum ore is a factor that affects all aspects of its performance; thus, it is hypothesized that the impurities present in the gypsum ore are the causes of the performance differences. Differential Thermal Analysis/Thermogravimetric Analysis (DTA/TGA) and X-ray Diffraction (XRD) were used in this paper to compare and characterize samples of gypsum ore representing sources of natural, synthetic from a Flue Gas Desulfurization process (FGD) and blends thereof. The hemihydrate phase of representative natural, FGD, and reagent grade calcium sulfate were rehydrated with distilled water and evaluated by DTA/TGA. Analysis of the data shows distinct areas of similarity separated by the conversion to anhydrite ~250 °C. Compositional reconstructions based on DTA/TGA and XRD data were compared and although, the results were comparable, the DTA/TGA suggests thermally active compounds that were not detected by XRD. Anhydrite, silica and halite were reported by XRD but were not thermally reactive in the temperature range evaluated by DTA/TGA (ambient to 1050 °C). Finally, the presence of carbonate compounds (e.g., calcite and dolomite) were indicated by XRD and estimated from the thermal decomposition reaction ~700 °C.

  5. Thermal analysis of calcium sulfate dihydrate sources used to manufacture gypsum wallboard

    DOE PAGES

    Engbrecht, Dick C.; Hirschfeld, Deidre A.

    2016-07-27

    Gypsum wallboard has been used for over 100 years as a barrier to the spread of fire in residential and commercial structures. The gypsum molecule, CaSO4·2H2O, provides two crystalline waters that are released upon heating providing an endothermic effect. Manufacturers have recognized that the source of the gypsum ore is a factor that affects all aspects of its performance; thus, it is hypothesized that the impurities present in the gypsum ore are the causes of the performance differences. Differential Thermal Analysis/Thermogravimetric Analysis (DTA/TGA) and X-ray Diffraction (XRD) were used in this paper to compare and characterize samples of gypsum oremore » representing sources of natural, synthetic from a Flue Gas Desulfurization process (FGD) and blends thereof. The hemihydrate phase of representative natural, FGD, and reagent grade calcium sulfate were rehydrated with distilled water and evaluated by DTA/TGA. Analysis of the data shows distinct areas of similarity separated by the conversion to anhydrite ~250 °C. Compositional reconstructions based on DTA/TGA and XRD data were compared and although, the results were comparable, the DTA/TGA suggests thermally active compounds that were not detected by XRD. Anhydrite, silica and halite were reported by XRD but were not thermally reactive in the temperature range evaluated by DTA/TGA (ambient to 1050 °C). Finally, the presence of carbonate compounds (e.g., calcite and dolomite) were indicated by XRD and estimated from the thermal decomposition reaction ~700 °C.« less

  6. Controlled study of mold growth and cleaning procedure on treated and untreated wet gypsum wallboard in an indoor environment.

    PubMed

    Krause, Michael; Geer, William; Swenson, Lonie; Fallah, Payam; Robbins, Coreen

    2006-08-01

    The basis for some common gypsum wallboard mold remediation practices was examined. The bottom inch of several gypsum wallboard panels was immersed in bottled drinking water; some panels were coated and others were untreated. The panels were examined and tested for a period of 8 weeks. This study investigated: (a) whether mold growth, detectable visually or with tape lift samples, occurs within 1 week on wet gypsum wallboard; (b) the types, timing, and extent of mold growth on wet gypsum wallboard; (c) whether mold growth is present on gypsum wallboard surfaces 6 inches from visible mold growth; (d) whether some commonly used surface treatments affect the timing of occurrence and rate of mold growth; and (e) if moldy but dried gypsum wallboard can be cleaned with simple methods and then sealed with common surface treatments so that residual mold particles are undetectable with typical surface sampling techniques. Mold growth was not detected visually or with tape lift samples after 1 week on any of the wallboard panels, regardless of treatment, well beyond the 24-48 hours often mentioned as the incubation period. Growth was detected at 2 weeks on untreated gypsum. Penicillium, Cladosporium, and Acremonium were early colonizers of untreated panels. Aspergillus, Epicoccum, Alternaria, and Ulocladium appeared later. Stachybotrys was not found. Mold growth was not detected more than 6 inches beyond the margin of visible mold growth, suggesting that recommendations to remove gypsum wallboard more than 1 foot beyond visible mold are excessive. The surface treatments resulted in delayed mold growth and reduced the area of mold growth compared with untreated gypsum wallboard. Results showed that simple cleaning of moldy gypsum wallboard was possible to the extent that mold particles beyond "normal trapping" were not found on tape lift samples. Thus, cleaning is an option in some situations where removal is not feasible or desirable. In cases where conditions are not

  7. Phase change material storage heater

    DOEpatents

    Goswami, D. Yogi; Hsieh, Chung K.; Jotshi, Chand K.; Klausner, James F.

    1997-01-01

    A storage heater for storing heat and for heating a fluid, such as water, has an enclosure defining a chamber therein. The chamber has a lower portion and an upper portion with a heating element being disposed within the enclosure. A tube through which the fluid flows has an inlet and an outlet, both being disposed outside of the enclosure, and has a portion interconnecting the inlet and the outlet that passes through the enclosure. A densely packed bed of phase change material pellets is disposed within the enclosure and is surrounded by a viscous liquid, such as propylene glycol. The viscous liquid is in thermal communication with the heating element, the phase change material pellets, and the tube and transfers heat from the heating element to the pellets and from the pellets to the tube. The viscous fluid has a viscosity so that the frictional pressure drop of the fluid in contact with the phase change material pellets substantially reduces vertical thermal convection in the fluid. As the fluid flows through the tube heat is transferred from the viscous liquid to the fluid flowing through the tube, thereby heating the fluid.

  8. Interim Report on the Examination of Corrosion Damage in Homes Constructed With Imported Wallboard: Examination of Samples Received September 28, 2009.

    PubMed

    Pitchure, D J; Ricker, R E; Williams, M E; Claggett, S A

    2010-01-01

    Since many household systems are fabricated out of metallic materials, changes to the household environment that accelerate corrosion rates will increase the frequency of failures in these systems. Recently, it has been reported that homes constructed with imported wallboard have increased failure rates in appliances, air conditioner heat exchanger coils, and visible corrosion on electrical wiring and other metal components. At the request of the Consumer Product Safety Commission (CPSC), the National Institute of Standards and Technology (NIST) became involved through the Interagency Agreement CPSC-1-09-0023 to perform metallurgical analyses on samples and corrosion products removed from homes constructed using imported wallboard. This document reports on the analysis of the first group of samples received by NIST from CPSC. The samples received by NIST on September 28, 2009 consisted of copper tubing for supplying natural gas and two air conditioner heat exchanger coils. The examinations performed by NIST consisted of photography, metallurgical cross-sectioning, optical microscopy, scanning electron microscopy (SEM), and x-ray diffraction (XRD). Leak tests were also performed on the air conditioner heat exchanger coils. The objective of these examinations was to determine extent and nature of the corrosive attack, the chemical composition of the corrosion product, and the potential chemical reactions or environmental species responsible for accelerated corrosion. A thin black corrosion product was found on samples of the copper tubing. The XRD analysis of this layer indicated that this corrosion product was a copper sulfide phase and the diffraction peaks corresponded with those for the mineral digenite (Cu9S5). Corrosion products were also observed on other types of metals in the air conditioner coils where condensation would frequently wet the metals. The thickness of the corrosion product layer on a copper natural gas supply pipe with a wall thickness of 1

  9. Interim Report on the Examination of Corrosion Damage in Homes Constructed With Imported Wallboard: Examination of Samples Received September 28, 2009

    PubMed Central

    Pitchure, D. J.; Ricker, R. E.; Williams, M. E.; Claggett, S. A.

    2010-01-01

    Since many household systems are fabricated out of metallic materials, changes to the household environment that accelerate corrosion rates will increase the frequency of failures in these systems. Recently, it has been reported that homes constructed with imported wallboard have increased failure rates in appliances, air conditioner heat exchanger coils, and visible corrosion on electrical wiring and other metal components. At the request of the Consumer Product Safety Commission (CPSC), the National Institute of Standards and Technology (NIST) became involved through the Interagency Agreement CPSC-1-09-0023 to perform metallurgical analyses on samples and corrosion products removed from homes constructed using imported wallboard. This document reports on the analysis of the first group of samples received by NIST from CPSC. The samples received by NIST on September 28, 2009 consisted of copper tubing for supplying natural gas and two air conditioner heat exchanger coils. The examinations performed by NIST consisted of photography, metallurgical cross-sectioning, optical microscopy, scanning electron microscopy (SEM), and x-ray diffraction (XRD). Leak tests were also performed on the air conditioner heat exchanger coils. The objective of these examinations was to determine extent and nature of the corrosive attack, the chemical composition of the corrosion product, and the potential chemical reactions or environmental species responsible for accelerated corrosion. A thin black corrosion product was found on samples of the copper tubing. The XRD analysis of this layer indicated that this corrosion product was a copper sulfide phase and the diffraction peaks corresponded with those for the mineral digenite (Cu9S5). Corrosion products were also observed on other types of metals in the air conditioner coils where condensation would frequently wet the metals. The thickness of the corrosion product layer on a copper natural gas supply pipe with a wall thickness of 1

  10. Phase Change Fabrics Control Temperature

    NASA Technical Reports Server (NTRS)

    2009-01-01

    Originally featured in Spinoff in 1997, Outlast Technologies Inc. (formerly Gateway Technologies Inc.) has built its entire product line on microencapsulated phase change materials, developed in Small Business Innovation Research (SBIR) contracts with Johnson Space Center after initial development for the U.S. Air Force. The Boulder, Colorado-based company acquired the exclusive patent rights and now integrates these materials into textiles or onto finished apparel, providing temperature regulation in bedding materials and a full line of apparel for both ordinary and extreme conditions.

  11. Testing antimicrobial paint efficacy on gypsum wallboard contaminated with Stachybotrys chartarum.

    PubMed

    Menetrez, M Y; Foarde, K K; Webber, T D; Dean, T R; Betancourt, D A

    2008-02-01

    The goal of this research was to reduce occupant exposure to indoor mold through the efficacy testing of antimicrobial paints. An accepted method for handling Stachybotrys chartarum-contaminated gypsum wallboard (GWB) is removal and replacement. This practice is also recommended for water-damaged or mold-contaminated GWB but is not always followed completely. The efficacy of antimicrobial paints to eliminate or control mold regrowth on surfaces can be tested easily on nonporous surfaces. The testing of antimicrobial efficacy on porous surfaces found in the indoor environment, such as gypsum wallboard, can be more complicated and prone to incorrect conclusions regarding residual organisms. The mold S. chartarum has been studied for toxin production and its occurrence in water-damaged buildings. Research to control its growth using seven different antimicrobial paints and two commonly used paints on contaminated, common gypsum wallboard was performed in laboratory testing at high relative humidity. The results indicate differences in antimicrobial efficacy for the period of testing, and that proper cleaning and resurfacing of GWB with an antimicrobial paint can be an option in those unique circumstances when removal may not be possible.

  12. The use of epifluorescent microscopy and quantitative polymerase chain reaction to determine the presence/absence and identification of microorganisms associated with domestic and foreign wallboard samples

    USGS Publications Warehouse

    Griffin, Dale W.

    2011-01-01

    Epifluorescent microscopy and quantitative polymerase chain reaction (qPCR) were utilized to determine the presence, concentration and identification of bacteria, and more specifically sulfate reducing bacteria (SRB) in subsamples of Chinese and North American wallboard, and wallboard-mine rock. Bacteria were visible in most subsamples, which included wallboard-lining paper from each side of the wallboard, wallboard filler, wallboard tape and fragments of mined wallboard rock via microscopy. Observed bacteria occurred as single or small clusters of cells and no mass aggregates indicating colonization were noted. Universal 16S qPCR was utilized to directly examine samples and detected bacteria at concentrations ranging from 1.4 x 103 to 6.4 x 104 genomic equivalents per mm2 of paper or per gram of wallboard filler or mined rock, in 12 of 41 subsamples. Subsamples were incubated in sulfate reducing broth for ~30 to 60 days (enrichment assay) and then analyzed by universal 16S and SRB qPCR. Enrichment universal 16S qPCR detected bacteria in 32 of 41 subsamples at concentrations ranging from 1.5 x 104 to 4.2 x 107 genomic equivalents per ml of culture broth. Evaluation of enriched subsamples by SRB qPCR demonstrated that SRB were not detectable in most of the samples and if they were detected, detection was not reproducible (an indication of low concentrations, if present). Enrichment universal 16S and SRB qPCR demonstrated that viable bacteria were present in subsamples (as expected given exposure of the samples following manufacture, transport and use) but that SRB were either not present or present at very low numbers. Further, no differences in trends were noted between the various Chinese and North American wallboard samples. In all, the microscopy and qPCR data indicated that the suspected ‘sulfur emissions’ emanating from suspect wallboard samples is not due to microbial activity.

  13. Microbial volatile organic compound emissions from Stachybotrys chartarum growing on gypsum wallboard and ceiling tile

    PubMed Central

    2013-01-01

    Background Stachybotrys chartarum is a filamentous mold frequently identified among the mycobiota of water-damaged building materials. Growth of S. chartarum on suitable substrates and under favorable environmental conditions leads to the production of secondary metabolites such as mycotoxins and microbial volatile organic compounds (MVOCs). The aim of this study was to characterize MVOC emission profiles of seven toxigenic strains of S. chartarum, isolated from water-damaged buildings, in order to identify unique MVOCs generated during growth on gypsum wallboard and ceiling tile coupons. Inoculated coupons were incubated and monitored for emissions and growth using a closed glass environmental growth chamber maintained at a constant room temperature. Gas samples were collected from the headspace for three to four weeks using Tenax TA tubes. Results Most of the MVOCs identified were alcohols, ketones, ethers and esters. The data showed that anisole (methoxybenzene) was emitted from all of the S. chartarum strains tested on both types of substrates. Maximum anisole concentration was detected after seven days of incubation. Conclusions MVOCs are suitable markers for fungal identification because they easily diffuse through weak barriers like wallpaper, and could be used for early detection of mold growth in hidden cavities. This study identifies the production of anisole by seven toxigenic strains of Stachybotrys chartarum within a period of one week of growth on gypsum wallboard and ceiling tiles. These data could provide useful information for the future construction of a robust MVOC library for the early detection of this mold. PMID:24308451

  14. Microbial volatile organic compound emissions from Stachybotrys chartarum growing on gypsum wallboard and ceiling tile.

    PubMed

    Betancourt, Doris A; Krebs, Ken; Moore, Scott A; Martin, Shayna M

    2013-12-05

    Stachybotrys chartarum is a filamentous mold frequently identified among the mycobiota of water-damaged building materials. Growth of S. chartarum on suitable substrates and under favorable environmental conditions leads to the production of secondary metabolites such as mycotoxins and microbial volatile organic compounds (MVOCs). The aim of this study was to characterize MVOC emission profiles of seven toxigenic strains of S. chartarum, isolated from water-damaged buildings, in order to identify unique MVOCs generated during growth on gypsum wallboard and ceiling tile coupons. Inoculated coupons were incubated and monitored for emissions and growth using a closed glass environmental growth chamber maintained at a constant room temperature. Gas samples were collected from the headspace for three to four weeks using Tenax TA tubes. Most of the MVOCs identified were alcohols, ketones, ethers and esters. The data showed that anisole (methoxybenzene) was emitted from all of the S. chartarum strains tested on both types of substrates. Maximum anisole concentration was detected after seven days of incubation. MVOCs are suitable markers for fungal identification because they easily diffuse through weak barriers like wallpaper, and could be used for early detection of mold growth in hidden cavities. This study identifies the production of anisole by seven toxigenic strains of Stachybotrys chartarum within a period of one week of growth on gypsum wallboard and ceiling tiles. These data could provide useful information for the future construction of a robust MVOC library for the early detection of this mold.

  15. Testing antimicrobial cleaner efficacy on gypsum wallboard contaminated with Stachybotrys chartarum.

    PubMed

    Menetrez, Marc Y; Foarde, Karin K; Webber, Tricia D; Dean, Timothy R; Betancourt, Doris A

    2007-11-01

    Reducing occupant exposure to indoor mold is the goal of this research, through the efficacy testing of antimicrobial cleaners. Often mold contaminated building materials are not properly removed, but instead surface cleaners are applied in an attempt to alleviate the problem. The efficacy of antimicrobial cleaners to remove, eliminate or control mold growth on surfaces can easily be tested on non-porous surfaces. However, the testing of antimicrobial cleaner efficacy on porous surfaces, such as those found in the indoor environment such as gypsum board can be more complicated and prone to incorrect conclusions regarding residual organisms. The mold Stachybotrys chartarum has been found to be associated with idiopathic pulmonary hemorrhage in infants and has been studied for toxin production and its occurrence in water damaged buildings. Growth of S. chartarum on building materials such as gypsum wallboard has been frequently documented. Research to control S. chartarum growth using 13 separate antimicrobial cleaners on contaminated gypsum wallboard has been performed in laboratory testing. Popular brands of cleaning products were tested by following directions printed on the product packaging. A variety of gypsum wallboard surfaces were used to test these cleaning products at high relative humidity. The results indicate differences in antimicrobial efficacy for the six month period of testing. Results for the six types of GWB surfaces varied extensively. However, three cleaning products exhibited significantly better results than others. Lysol All-Purpose Cleaner-Orange Breeze (full strength) demonstrated results which ranked among the best in five of the six surfaces tested. Both Borax and Orange Glo Multipurpose Degreaser demonstrated results which ranked among the best in four of the six surfaces tested. The best antimicrobial cleaner to choose is often dependent on the type of surface to be cleaned of S. chartarum contamination. For Plain GWB, no paint, the

  16. Bipolar switching in chalcogenide phase change memory.

    PubMed

    Ciocchini, N; Laudato, M; Boniardi, M; Varesi, E; Fantini, P; Lacaita, A L; Ielmini, D

    2016-07-05

    Phase change materials based on chalcogenides are key enabling technologies for optical storage, such as rewritable CD and DVD, and recently also electrical nonvolatile memory, named phase change memory (PCM). In a PCM, the amorphous or crystalline phase affects the material band structure, hence the device resistance. Although phase transformation is extremely fast and repeatable, the amorphous phase suffers structural relaxation and crystallization at relatively low temperatures, which may affect the temperature stability of PCM state. To improve the time/temperature stability of the PCM, novel operation modes of the device should be identified. Here, we present bipolar switching operation of PCM, which is interpreted by ion migration in the solid state induced by elevated temperature and electric field similar to the bipolar switching in metal oxides. The temperature stability of the high resistance state is demonstrated and explained based on the local depletion of chemical species from the electrode region.

  17. Bipolar switching in chalcogenide phase change memory

    NASA Astrophysics Data System (ADS)

    Ciocchini, N.; Laudato, M.; Boniardi, M.; Varesi, E.; Fantini, P.; Lacaita, A. L.; Ielmini, D.

    2016-07-01

    Phase change materials based on chalcogenides are key enabling technologies for optical storage, such as rewritable CD and DVD, and recently also electrical nonvolatile memory, named phase change memory (PCM). In a PCM, the amorphous or crystalline phase affects the material band structure, hence the device resistance. Although phase transformation is extremely fast and repeatable, the amorphous phase suffers structural relaxation and crystallization at relatively low temperatures, which may affect the temperature stability of PCM state. To improve the time/temperature stability of the PCM, novel operation modes of the device should be identified. Here, we present bipolar switching operation of PCM, which is interpreted by ion migration in the solid state induced by elevated temperature and electric field similar to the bipolar switching in metal oxides. The temperature stability of the high resistance state is demonstrated and explained based on the local depletion of chemical species from the electrode region.

  18. Bipolar switching in chalcogenide phase change memory

    PubMed Central

    Ciocchini, N.; Laudato, M.; Boniardi, M.; Varesi, E.; Fantini, P.; Lacaita, A. L.; Ielmini, D.

    2016-01-01

    Phase change materials based on chalcogenides are key enabling technologies for optical storage, such as rewritable CD and DVD, and recently also electrical nonvolatile memory, named phase change memory (PCM). In a PCM, the amorphous or crystalline phase affects the material band structure, hence the device resistance. Although phase transformation is extremely fast and repeatable, the amorphous phase suffers structural relaxation and crystallization at relatively low temperatures, which may affect the temperature stability of PCM state. To improve the time/temperature stability of the PCM, novel operation modes of the device should be identified. Here, we present bipolar switching operation of PCM, which is interpreted by ion migration in the solid state induced by elevated temperature and electric field similar to the bipolar switching in metal oxides. The temperature stability of the high resistance state is demonstrated and explained based on the local depletion of chemical species from the electrode region. PMID:27377822

  19. Molecular mechanisms of phase change in locusts.

    PubMed

    Wang, Xianhui; Kang, Le

    2014-01-01

    Phase change in locusts is an ideal model for studying the genetic architectures and regulatory mechanisms associated with phenotypic plasticity. The recent development of genomic and metabolomic tools and resources has furthered our understanding of the molecular basis of phase change in locusts. Thousands of phase-related genes and metabolites have been highlighted using large-scale expressed sequence tags, microarrays, high-throughput transcriptomic sequences, or metabolomic approaches. However, only several key factors, including genes, metabolites, and pathways, have a critical role in phase transition in locusts. For example, CSP (chemosensory protein) and takeout genes, the dopamine pathway, protein kinase A, and carnitines were found to be involved in the regulation of behavioral phase change and gram-negative bacteria-binding proteins in prophylaxical disease resistance of gregarious locusts. Epigenetic mechanisms including small noncoding RNAs and DNA methylation have been implicated. We review these new advances in the molecular basis of phase change in locusts and present some challenges that need to be addressed.

  20. Utilization of Phase Change Materials (PCM) to Reduce Energy Consumption in Buildings

    DTIC Science & Technology

    2011-09-14

    lb/ft2 Wall Test Layer Configuration Section 1 Section 2 Section 3 Section 4 Room A 5/8-in Gypsum Wallboard 2.0-lb/ft2 PCM Mat R19 Fiberglass...insulation exposed to backside of Bio PCM mat Layer 3 Fiberglass insulation exposed to backside of gypsum wallboard Layer 4 Gypsum wallboard exposed to...Plywood, R-0.155(1) 0.0273 0.0273 EPE Foam, Rigid insulation, R-30 5.28 5.28 Glass Fiber mat ins, R-19 3.35 -- 6.25-in (2-in × 6-in) Wood

  1. Phase transitions in Ge-Sb phase change materials

    SciTech Connect

    Raoux, Simone; Virwani, Kumar; Hitzbleck, Martina; Salinga, Martin; Madan, Anita; Pinto, Teresa L.

    2009-03-15

    Thin films of the phase change material Ge-Sb with Ge concentrations between 7.3 and 81.1 at. % were deposited by cosputtering from elemental targets. Their crystallization behavior was studied using time-resolved x-ray diffraction, Auger electron spectroscopy, differential scanning calorimetry, x-ray reflectivity, profilometry, optical reflectivity, and resistivity versus temperature measurements. It was found that the crystallization temperature increases with Ge content. Calculations of the glass transition temperature (which is a lower limit for the crystallization temperature T{sub x}) also show an increase with Ge concentration closely tracking the measured values of T{sub x}. For low Ge content samples, Sb x-ray diffraction peaks occurred during a heating ramp at lower temperature than Ge diffraction peaks. The appearance of Ge peaks is related to Ge precipitation and agglomeration. For Ge concentrations of 59.3 at. % and higher, Sb and Ge peaks occurred at the same temperature. Upon crystallization, film mass density and optical reflectivity increase as well as electrical contrast (ratio of resistivity in amorphous phase to crystalline phase) all showed a maximum for the eutectic alloy (14.5 at. % Ge). For the alloy with 59.3 at. % Ge there was very little change in any of these parameters, while the alloy with 81.1 at. % Ge behaved opposite to a typical phase change alloy and showed reduced mass density and reflectivity and increased resistivity.

  2. Solar heat storage in phase change material

    SciTech Connect

    Phillips, H.J.

    1984-02-28

    The objective of this project was to develop a chemical heat storage system that had a phase change with release of latent heat at about 105/sup 0/F. The primary reason this kind on system was sought was that heat storage capacity of commonly used storage systems do not match the heat collection capacity of open air collectors. In addition to the phase change three other factors were considered: the cost of the material, the amount of heat the system would hold per unit volume, and the rate at which the system released sensible and latent heat. One hundred nineteen tests were made on 32 systems. Only data on six of the more promising are presented. In the six systems, borax was used as the major component with other materials used as nucleating agents toraise the temperature of phase change.

  3. Phase change thermal energy storage material

    DOEpatents

    Benson, David K.; Burrows, Richard W.

    1987-01-01

    A thermal energy storge composition is disclosed. The composition comprises a non-chloride hydrate having a phase change transition temperature in the range of 70.degree.-95.degree. F. and a latent heat of transformation of at least about 35 calories/gram.

  4. Polyolefin composites containing a phase change material

    DOEpatents

    Salyer, Ival O.

    1991-01-01

    A composite useful in thermal energy storage, said composite being formed of a polyolefin matrix having a phase change material such as a crystalline alkyl hydrocarbon incorporated therein, said polyolefin being thermally form stable; the composite is useful in forming pellets, sheets or fibers having thermal energy storage characteristics; methods for forming the composite are also disclosed.

  5. Locust dynamics: behavioral phase change and swarming.

    PubMed

    Topaz, Chad M; D'Orsogna, Maria R; Edelstein-Keshet, Leah; Bernoff, Andrew J

    2012-01-01

    Locusts exhibit two interconvertible behavioral phases, solitarious and gregarious. While solitarious individuals are repelled from other locusts, gregarious insects are attracted to conspecifics and can form large aggregations such as marching hopper bands. Numerous biological experiments at the individual level have shown how crowding biases conversion towards the gregarious form. To understand the formation of marching locust hopper bands, we study phase change at the collective level, and in a quantitative framework. Specifically, we construct a partial integrodifferential equation model incorporating the interplay between phase change and spatial movement at the individual level in order to predict the dynamics of hopper band formation at the population level. Stability analysis of our model reveals conditions for an outbreak, characterized by a large scale transition to the gregarious phase. A model reduction enables quantification of the temporal dynamics of each phase, of the proportion of the population that will eventually gregarize, and of the time scale for this to occur. Numerical simulations provide descriptions of the aggregation's structure and reveal transiently traveling clumps of gregarious insects. Our predictions of aggregation and mass gregarization suggest several possible future biological experiments.

  6. Phase-change materials in masonry construction

    NASA Astrophysics Data System (ADS)

    Lang, M.

    1982-01-01

    A demonstration project leading to commercialization of a passive thermal wall using phase change storage materials (PCM) in masonry construction is reported. Techniques of vacuum forming have been identified and characterized making it possible to produce high-volume low-cost packages for insertion into the core of cement blocks. PCM filled packages with aluminum laminated film produces a long life product capable of operating to store and release solar heat over long periods of time. Accelerated tests indicate operability over the life of the building. Five hundred accelerated test cycles have shown insignificant deterioration of capacity of the phase change material. The testing program shows that the wall is capable of both storing and transmitting heat in a similar manner to conventional trombe walls, but with increased thermal capability. Product cost data on return on investment estimates are low enough to be economically attractive.

  7. Dependence of phase transitions on small changes

    NASA Astrophysics Data System (ADS)

    Stoop, R.

    1993-06-01

    In this contribution, the generalized thermodynamic formalism is applied to a nonhyperbolic dynamical system in two comparable situations. The change from one situation to the other is small in the sense that the grammar and the singularities of the system are preserved. For the discussion of the effects generated by this change, the generalized entropy functions are calculated and the sets of the specific scaling functions which reflect the phase transition of the system are investigated. It is found that even under mild variations, this set is not invariant.

  8. Crystallization Properties of Ultrathin Phase Change Films

    SciTech Connect

    Raoux,S.; Jordan-Sweet, J.; Kellock, A.

    2008-01-01

    The crystallization behavior of ultrathin phase change films was studied using time-resolved x-ray diffraction (XRD). Thin films of variable thickness between 1 and 50?nm of the phase change materials Ge2Sb2Te5 (GST), N-doped GST, Ge15Sb85, Sb2Te, and Ag- and In-doped Sb2Te were heated in a He atmosphere, and the intensity of the diffracted x-ray peaks was recorded. It was found for all materials that the crystallization temperature increases as the film thickness is reduced below 10?nm. The increase depends on the material and can be as high as 200? C for the thinnest films. The thinnest films that show XRD peaks are 2?nm for GST and N-GST, 1.5?nm for Sb2Te and AgIn-Sb2Te, and 1.3?nm for GeSb. This scaling behavior is very promising for the application of phase change materials to solid-state memory technology.

  9. Sprayable Phase Change Coating Thermal Protection Material

    NASA Technical Reports Server (NTRS)

    Richardson, Rod W.; Hayes, Paul W.; Kaul, Raj

    2005-01-01

    NASA has expressed a need for reusable, environmentally friendly, phase change coating that is capable of withstanding the heat loads that have historically required an ablative thermal insulation. The Space Shuttle Program currently relies on ablative materials for thermal protection. The problem with an ablative insulation is that, by design, the material ablates away, in fulfilling its function of cooling the underlying substrate, thus preventing the insulation from being reused from flight to flight. The present generation of environmentally friendly, sprayable, ablative thermal insulation (MCC-l); currently use on the Space Shuttle SRBs, is very close to being a reusable insulation system. In actual flight conditions, as confirmed by the post-flight inspections of the SRBs, very little of the material ablates. Multi-flight thermal insulation use has not been qualified for the Space Shuttle. The gap that would have to be overcome in order to implement a reusable Phase Change Coating (PCC) is not unmanageable. PCC could be applied robotically with a spray process utilizing phase change material as filler to yield material of even higher strength and reliability as compared to MCC-1. The PCC filled coatings have also demonstrated potential as cryogenic thermal coatings. In experimental thermal tests, a thin application of PCC has provided the same thermal protection as a much thicker and heavier application of a traditional ablative thermal insulation. In addition, tests have shown that the structural integrity of the coating has been maintained and phase change performance after several aero-thermal cycles was not affected. Experimental tests have also shown that, unlike traditional ablative thermal insulations, PCC would not require an environmental seal coat, which has historically been required to prevent moisture absorption by the thermal insulation, prevent environmental degradation, and to improve the optical and aerodynamic properties. In order to reduce

  10. interThermalPhaseChangeFoam-A framework for two-phase flow simulations with thermally driven phase change

    NASA Astrophysics Data System (ADS)

    Nabil, Mahdi; Rattner, Alexander S.

    The volume-of-fluid (VOF) approach is a mature technique for simulating two-phase flows. However, VOF simulation of phase-change heat transfer is still in its infancy. Multiple closure formulations have been proposed in the literature, each suited to different applications. While these have enabled significant research advances, few implementations are publicly available, actively maintained, or inter-operable. Here, a VOF solver is presented (interThermalPhaseChangeFoam), which incorporates an extensible framework for phase-change heat transfer modeling, enabling simulation of diverse phenomena in a single environment. The solver employs object oriented OpenFOAM library features, including Run-Time-Type-Identification to enable rapid implementation and run-time selection of phase change and surface tension force models. The solver is packaged with multiple phase change and surface tension closure models, adapted and refined from earlier studies. This code has previously been applied to study wavy film condensation, Taylor flow evaporation, nucleate boiling, and dropwise condensation. Tutorial cases are provided for simulation of horizontal film condensation, smooth and wavy falling film condensation, nucleate boiling, and bubble condensation. Validation and grid sensitivity studies, interfacial transport models, effects of spurious currents from surface tension models, effects of artificial heat transfer due to numerical factors, and parallel scaling performance are described in detail in the Supplemental Material (see Appendix A). By incorporating the framework and demonstration cases into a single environment, users can rapidly apply the solver to study phase-change processes of interest.

  11. Tunable hyperbolic metamaterials utilizing phase change heterostructures

    SciTech Connect

    Krishnamoorthy, Harish N. S.; Menon, Vinod M.; Zhou, You; Ramanathan, Shriram; Narimanov, Evgenii

    2014-03-24

    We present a metal-free tunable anisotropic metamaterial where the iso-frequency surface is tuned from elliptical to hyperbolic dispersion by exploiting the metal-insulator phase transition in the correlated material vanadium dioxide (VO{sub 2}). Using VO{sub 2}-TiO{sub 2} heterostructures, we demonstrate the transition in the effective dielectric constant parallel to the layers to undergo a sign change from positive to negative as the VO{sub 2} undergoes the phase transition. The possibility to tune the iso-frequency surface in real time using external perturbations such as temperature, voltage, or optical pulses creates new avenues for controlling light-matter interaction.

  12. Phase-Change Heat-Storage Module

    NASA Technical Reports Server (NTRS)

    Mulligan, James C.

    1989-01-01

    Heat-storage module accommodates momentary heating or cooling overload in pumped-liquid heat-transfer system. Large heat-storage capacity of module provided by heat of fusion of material that freezes at or near temperature desired to maintain object to be heated or cooled. Module involves relatively small penalties in weight, cost, and size and more than compensates by enabling design of rest of system to handle only average load. Latent heat of fusion of phase-change material provides large heat-storage capacity in small volume.

  13. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, I.O.

    1994-12-06

    A free flowing, conformable powder-like mix of silica particles and a phase change material (PCM) is provided. The silica particles have a critical size of about 0.005 to about 0.025 microns and the PCM must be added to the silica in an amount of 75% or less PCM per combined weight of silica and PCM. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and particularly in applications for heat protection for heat sensitive items, such as aircraft flight recorders, and for preventing brake fade in automobiles, buses, trucks and aircraft. 3 figures.

  14. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, Ival O.

    1995-01-01

    A free flowing, conformable powder-like mix of silica particles and a phase change material (PCM) is provided. The silica particles have a critical size of about 0.005 to about 0.025 microns and the PCM must be added to the silica in an amount of 75% or less PCM per combined weight of silica and PCM. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and particularly in applications for heat protection for heat sensitive items, such as aircraft flight recorders, and for preventing brake fade in automobiles, buses, trucks and aircraft.

  15. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, I.O.

    1995-12-26

    A free flowing, conformable powder-like mix of silica particles and a phase change material (PCM) is provided. The silica particles have a critical size of about 0.005 to about 0.025 microns and the PCM must be added to the silica in an amount of 75% or less PCM per combined weight of silica and PCM. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and particularly in applications for heat protection for heat sensitive items, such as aircraft flight recorders, and for preventing brake fade in automobiles, buses, trucks and aircraft. 3 figs.

  16. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, Ival O.

    1994-01-01

    A free flowing, conformable powder-like mix of silica particles and a phase change material (PCM) is provided. The silica particles have a critical size of about 0.005 to about 0.025 microns and the PCM must be added to the silica in an amount of 75% or less PCM per combined weight of silica and PCM. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and particularly in applications for heat protection for heat sensitive items, such as aircraft flight recorders, and for preventing brake fade in automobiles, buses, trucks and aircraft.

  17. Phase change based cooling for high burst mode heat loads with temperature regulation above the phase change temperature

    SciTech Connect

    The United States of America as represented by the United States Department of Energy

    2009-12-15

    An apparatus and method for transferring thermal energy from a heat load is disclosed. In particular, use of a phase change material and specific flow designs enables cooling with temperature regulation well above the fusion temperature of the phase change material for medium and high heat loads from devices operated intermittently (in burst mode). Exemplary heat loads include burst mode lasers and laser diodes, flight avionics, and high power space instruments. Thermal energy is transferred from the heat load to liquid phase change material from a phase change material reservoir. The liquid phase change material is split into two flows. Thermal energy is transferred from the first flow via a phase change material heat sink. The second flow bypasses the phase change material heat sink and joins with liquid phase change material exiting from the phase change material heat sink. The combined liquid phase change material is returned to the liquid phase change material reservoir. The ratio of bypass flow to flow into the phase change material heat sink can be varied to adjust the temperature of the liquid phase change material returned to the liquid phase change material reservoir. Varying the flowrate and temperature of the liquid phase change material presented to the heat load determines the magnitude of thermal energy transferred from the heat load.

  18. Phase Change Material Thermal Power Generator

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.

    2013-01-01

    An innovative modification has been made to a previously patented design for the Phase Change Material (PCM) Thermal Generator, which works in water where ocean temperature alternatively melts wax in canisters, or allows the wax to re-solidify, causing high-pressure oil to flow through a hydraulic generator, thus creating electricity to charge a battery that powers the vehicle. In this modification, a similar thermal PCM device has been created that is heated and cooled by the air and solar radiation instead of using ocean temperature differences to change the PCM from solid to liquid. This innovation allows the device to use thermal energy to generate electricity on land, instead of just in the ocean.

  19. Passive thermal management using phase change materials

    NASA Astrophysics Data System (ADS)

    Ganatra, Yash Yogesh

    The trend of enhanced functionality and reducing thickness of mobile devices has. led to a rapid increase in power density and a potential thermal bottleneck since. thermal limits of components remain unchanged. Active cooling mechanisms are not. feasible due to size, weight and cost constraints. This work explores the feasibility. of a passive cooling system based on Phase Change Materials (PCMs) for thermal. management of mobile devices. PCMs stabilize temperatures due to the latent heat. of phase change thus increasing the operating time of the device before threshold. temperatures are exceeded. The primary contribution of this work is the identification. of key parameters which influence the design of a PCM based thermal management. system from both the experiments and the numerical models. This work first identifies strategies for integrating PCMs in an electronic device. A. detailed review of past research, including experimental techniques and computational. models, yields key material properties and metrics to evaluate the performance of. PCMs. Subsequently, a miniaturized version of a conventional thermal conductivity. measurement technique is developed to characterize thermal resistance of PCMs. Further, latent heat and transition temperatures are also characterized for a wide. range of PCMs. In-situ measurements with PCMs placed on the processor indicate that some. PCMs can extend the operating time of the device by as much as a factor of 2.48. relative to baseline tests (with no PCMs). This increase in operating time is investigated. by computational thermal models that explore various integration locations, both at the package and device level.

  20. Metallic resist for phase-change lithography

    NASA Astrophysics Data System (ADS)

    Zeng, Bi Jian; Huang, Jun Zhu; Ni, Ri Wen; Yu, Nian Nian; Wei, Wei; Hu, Yang Zhi; Li, Zhen; Miao, Xiang Shui

    2014-06-01

    Currently, the most widely used photoresists in optical lithography are organic-based resists. The major limitations of such resists include the photon accumulation severely affects the quality of photolithography patterns and the size of the pattern is constrained by the diffraction limit. Phase-change lithography, which uses semiconductor-based resists such as chalcogenide Ge2Sb2Te5 films, was developed to overcome these limitations. Here, instead of chalcogenide, we propose a metallic resist composed of Mg58Cu29Y13 alloy films, which exhibits a considerable difference in etching rate between amorphous and crystalline states. Furthermore, the heat distribution in Mg58Cu29Y13 thin film is better and can be more easily controlled than that in Ge2Sb2Te5 during exposure. We succeeded in fabricating both continuous and discrete patterns on Mg58Cu29Y13 thin films via laser irradiation and wet etching. Our results demonstrate that a metallic resist of Mg58Cu29Y13 is suitable for phase change lithography, and this type of resist has potential due to its outstanding characteristics.

  1. Metallic resist for phase-change lithography

    PubMed Central

    Zeng, Bi Jian; Huang, Jun Zhu; Ni, Ri Wen; Yu, Nian Nian; Wei, Wei; Hu, Yang Zhi; Li, Zhen; Miao, Xiang Shui

    2014-01-01

    Currently, the most widely used photoresists in optical lithography are organic-based resists. The major limitations of such resists include the photon accumulation severely affects the quality of photolithography patterns and the size of the pattern is constrained by the diffraction limit. Phase-change lithography, which uses semiconductor-based resists such as chalcogenide Ge2Sb2Te5 films, was developed to overcome these limitations. Here, instead of chalcogenide, we propose a metallic resist composed of Mg58Cu29Y13 alloy films, which exhibits a considerable difference in etching rate between amorphous and crystalline states. Furthermore, the heat distribution in Mg58Cu29Y13 thin film is better and can be more easily controlled than that in Ge2Sb2Te5 during exposure. We succeeded in fabricating both continuous and discrete patterns on Mg58Cu29Y13 thin films via laser irradiation and wet etching. Our results demonstrate that a metallic resist of Mg58Cu29Y13 is suitable for phase change lithography, and this type of resist has potential due to its outstanding characteristics. PMID:24931505

  2. Material Engineering for Phase Change Memory

    NASA Astrophysics Data System (ADS)

    Cabrera, David M.

    As semiconductor devices continue to scale downward, and portable consumer electronics become more prevalent there is a need to develop memory technology that will scale with devices and use less energy, while maintaining performance. One of the leading prototypical memories that is being investigated is phase change memory. Phase change memory (PCM) is a non-volatile memory composed of 1 transistor and 1 resistor. The resistive structure includes a memory material alloy which can change between amorphous and crystalline states repeatedly using current/voltage pulses of different lengths and magnitudes. The most widely studied PCM materials are chalcogenides - Germanium-Antimony-Tellerium (GST) with Ge2Sb2Te3 and Germanium-Tellerium (GeTe) being some of the most popular stochiometries. As these cells are scaled downward, the current/voltage needed to switch these materials becomes comparable to the voltage needed to sense the cell's state. The International Roadmap for Semiconductors aims to raise the threshold field of these devices from 66.6 V/mum to be at least 375 V/mum for the year 2024. These cells are also prone to resistance drift between states, leading to bit corruption and memory loss. Phase change material properties are known to influence PCM device performance such as crystallization temperature having an effect on data retention and litetime, while resistivity values in the amorphous and crystalline phases have an effect on the current/voltage needed to write/erase the cell. Addition of dopants is also known to modify the phase change material parameters. The materials G2S2T5, GeTe, with dopants - nitrogen, silicon, titanium, and aluminum oxide and undoped Gallium-Antimonide (GaSb) are studied for these desired characteristics. Thin films of these compositions are deposited via physical vapor deposition at IBM Watson Research Center. Crystallization temperatures are investigated using time resolved x-ray diffraction at Brookhaven National Laboratory

  3. Phase changes in the BRCA policy domain.

    PubMed

    Modell, Stephen M; King, Susan B; Citrin, Toby; Kardia, Sharon L R

    2014-06-01

    The recent US Supreme Court ruling against gene patenting has been accompanied by the passage at the federal level of the Patient Protection and Affordable Care Act, both events representing a thawing or phase change in policies that will now make preventive techniques, such as BRCA genetic testing to predict risk for familial breast and ovarian cancer, more affordable and accessible. Authors including Yun-Han Huang in this journal have noted the judicial ruling is one step--a significant one--in the process of patent system reform. This commentary links such changes with policy formation and action taken by members of diverse religious communities in the aftermath of the Human Genome Project and continuing in today's genome sequencing area. Religious engagement has acted as a catalyzing force for change in the creation and dissemination of genetic developments. Religious perspectives are needed to solve the new ethical dilemmas posed by population screening for BRCA mutations and the rise of direct-to-consumer and provider marketing of such genetic tests, which have far-reaching consequences at the individual, family, and societal levels.

  4. A new method for the characterization of the degree of fire damage to gypsum wallboard for use in fire investigations.

    PubMed

    Gorbett, Gregory E; Morris, Sarah M; Meacham, Brian J; Wood, Christopher B

    2015-01-01

    A new method to characterize the degree of fire damage to gypsum wallboard is introduced, implemented, and tested to determine the efficacy of its application among novices. The method was evaluated by comparing degree of fire damage assessments of novices with and without the method. Thirty-nine "novice" raters assessed damage to a gypsum wallboard surface, completing 66 ratings, first without the method, and then again using the method. The inter-rater reliability was evaluated for ratings of damage without and with the method. For novice fire investigators rating degree of damage without the aid of the method, ICC(1,2) = 0.277 with 95% CI (0.211, 0.365), and with the method, ICC(2,1) = 0.593 with 95% CI (0.509, 0.684). Results indicate that the raters were more reliable in their analysis of the degree of fire damage when using the method, which support the use of standardized processes to decrease the variability in data collection and interpretation.

  5. Projected phase-change memory devices

    NASA Astrophysics Data System (ADS)

    Koelmans, Wabe W.; Sebastian, Abu; Jonnalagadda, Vara Prasad; Krebs, Daniel; Dellmann, Laurent; Eleftheriou, Evangelos

    2015-09-01

    Nanoscale memory devices, whose resistance depends on the history of the electric signals applied, could become critical building blocks in new computing paradigms, such as brain-inspired computing and memcomputing. However, there are key challenges to overcome, such as the high programming power required, noise and resistance drift. Here, to address these, we present the concept of a projected memory device, whose distinguishing feature is that the physical mechanism of resistance storage is decoupled from the information-retrieval process. We designed and fabricated projected memory devices based on the phase-change storage mechanism and convincingly demonstrate the concept through detailed experimentation, supported by extensive modelling and finite-element simulations. The projected memory devices exhibit remarkably low drift and excellent noise performance. We also demonstrate active control and customization of the programming characteristics of the device that reliably realize a multitude of resistance states.

  6. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, I.O.

    1993-05-18

    Free flowing, conformable powder-like mix of silica particles and a phase change material (p.c.m.) is disclosed. The silica particles have a critical size of about 7[times]10[sup [minus]3] to about 7[times]10[sup [minus]2] microns and the p.c.m. must be added to the silica in an amount of 80 wt. % or less p.c.m. per combined weight of silica and p.c.m. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and in cementitious compositions of the type in which it is beneficial to use a p.c.m. material. The silica-p.c.m. mix can also be admixed with soil to provide a soil warming effect and placed about a tree, flower, or shrub.

  7. Phase-change oscillations in silicon microwires

    NASA Astrophysics Data System (ADS)

    Cywar, A.; Bakan, G.; Boztug, C.; Silva, H.; Gokirmak, A.

    2009-02-01

    We have observed liquid-solid phase-change oscillations in 2-5.5 μm long silicon wires biased through a load resistor. Molten silicon resistivity is approximately 30 times lower than that of the room temperature solid-state resistivity of the highly doped nanocrystalline-silicon thin film used to fabricate the wires. Wires typically melt with 15-20 V electrical stresses, draining the parasitic capacitance introduced by the experimental setup within 1 μs. The power dissipated in the wire is not sufficient to keep it in molten state after the discharge, leading to repeated melting and resolidification of the wires with 1 MHz, 2-20 mA current oscillations.

  8. Projected phase-change memory devices

    PubMed Central

    Koelmans, Wabe W.; Sebastian, Abu; Jonnalagadda, Vara Prasad; Krebs, Daniel; Dellmann, Laurent; Eleftheriou, Evangelos

    2015-01-01

    Nanoscale memory devices, whose resistance depends on the history of the electric signals applied, could become critical building blocks in new computing paradigms, such as brain-inspired computing and memcomputing. However, there are key challenges to overcome, such as the high programming power required, noise and resistance drift. Here, to address these, we present the concept of a projected memory device, whose distinguishing feature is that the physical mechanism of resistance storage is decoupled from the information-retrieval process. We designed and fabricated projected memory devices based on the phase-change storage mechanism and convincingly demonstrate the concept through detailed experimentation, supported by extensive modelling and finite-element simulations. The projected memory devices exhibit remarkably low drift and excellent noise performance. We also demonstrate active control and customization of the programming characteristics of the device that reliably realize a multitude of resistance states. PMID:26333363

  9. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, I.O.

    1993-10-19

    Free flowing, conformable powder-like mix of silica particles and a phase change material (pcm) is disclosed. The silica particles have a critical size of about 7[times]10[sup [minus]3] to about 7[times]10[sup [minus]2] microns and the pcm must be added to the silica in an amount of 80 wt. % or less pcm per combined weight of silica and pcm. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and in cementitious compositions of the type in which it is beneficial to use a pcm material. The silica-pcm mix can also be admixed with soil to provide a soil warming effect and placed about a tree, flower, or shrub. 10 figures.

  10. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, I.O.

    1994-02-01

    Free flowing, conformable powder-like mix of silica particles and a phase change material (PCM) is provided. The silica particles have a critical size of about 0.005 to about 0.025 microns and the PCM must be added to the silica in an amount of 75% or less PCM per combined weight of silica and PCM. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and in cementitious compositions of the type in which it is beneficial to use a PCM material. The silica-PCM mix can also be admixed with soil to provide a soil warming effect and placed about a tree, flower, or shrub. 2 figures.

  11. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, Ival O.

    1992-01-01

    Free flowing, conformable powder-like mix of silica particles and a phase change material (p.c.m.) is disclosed. The silica particles have a critical size of about 7.times.10.sup.-3 to about 7.times.10.sup.-2 microns and the pcm must be added to the silica in an amount of 80 wt. % or less pcm per combined weight of silica and pcm. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and in cementitious compositions of the type in which it is beneficial to use a pcm material. The silica-pcm mix can also be admixed with soil to provide a soil warming effect and placed about a tree, flower, or shrub.

  12. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, Ival O.

    1993-01-01

    Free flowing, conformable powder-like mix of silica particles and a phase change material (p.c.m.) is disclosed. The silica particles have a critical size of about 7.times.10.sup.-3 to about 7.times.10.sup.-2 microns and the pcm must be added to the silica in an amount of 80 wt. % or less pcm per combined weight of silica and pcm. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garmets, quilts and blankets, and in cementitious compositions of the type in which it is beneficial to use a pcm material. The silica-pcm mix can also be admixed with soil to provide a soil warming effect and placed about a tree, flower, or shrub.

  13. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, Ival O.

    1993-01-01

    Free flowing, conformable powder-like mix of silica particles and a phase change material (p.c.m.) is disclosed. The silica particles have a critical size of about 7.times.10.sup.-3 to about 7.times.10.sup.-2 microns and the pcm must be added to the silica in an amount of 80 wt. % or less pcm per combined weight of silica and pcm. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and in cementitious compositions of the type in which it is beneficial to use a pcm material. The silica-pcm mix can also be admixed with soil to provide a soil warming effect and placed about a tree, flower, or shrub.

  14. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, Ival O.

    1994-01-01

    Free flowing, conformable powder-like mix of silica particles and a phase change material (PCM) is provided. The silica particles have a critical size of about 0.005 to about 0.025 microns and the PCM must be added to the silica in an amount of 75% or less PCM per combined weight of silica and PCM. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and in cementitious compositions of the type in which it is beneficial to use a PCM material. The silica-PCM mix can also be admixed with soil to provide a soil warming effect and placed about a tree, flower, or shrub.

  15. Projected phase-change memory devices.

    PubMed

    Koelmans, Wabe W; Sebastian, Abu; Jonnalagadda, Vara Prasad; Krebs, Daniel; Dellmann, Laurent; Eleftheriou, Evangelos

    2015-09-03

    Nanoscale memory devices, whose resistance depends on the history of the electric signals applied, could become critical building blocks in new computing paradigms, such as brain-inspired computing and memcomputing. However, there are key challenges to overcome, such as the high programming power required, noise and resistance drift. Here, to address these, we present the concept of a projected memory device, whose distinguishing feature is that the physical mechanism of resistance storage is decoupled from the information-retrieval process. We designed and fabricated projected memory devices based on the phase-change storage mechanism and convincingly demonstrate the concept through detailed experimentation, supported by extensive modelling and finite-element simulations. The projected memory devices exhibit remarkably low drift and excellent noise performance. We also demonstrate active control and customization of the programming characteristics of the device that reliably realize a multitude of resistance states.

  16. Dry powder mixes comprising phase change materials

    DOEpatents

    Salyer, I.O.

    1992-04-21

    A free flowing, conformable powder-like mix of silica particles and a phase change material (p.c.m.) is disclosed. The silica particles have a critical size of about 7 [times] 10[sup [minus]3] to about 7 [times] 10[sup [minus]2] microns and the pcm must be added to the silica in an amount of 80 wt. % or less pcm per combined weight of silica and pcm. The powder-like mix can be used in tableware items, medical wraps, tree wraps, garments, quilts and blankets, and in cementitious compositions of the type in which it is beneficial to use a pcm material. The silica-pcm mix can also be admixed with soil to provide a soil warming effect and placed about a tree, flower, or shrub. 9 figs.

  17. Phase change material thermal capacitor clothing

    NASA Technical Reports Server (NTRS)

    Buckley, Theresa M. (Inventor)

    2005-01-01

    An apparatus and method for metabolic cooling and insulation of a user in a cold environment. In its preferred embodiment the apparatus is a highly flexible composite material having a flexible matrix containing a phase change thermal storage material. The apparatus can be made to heat or cool the body or to act as a thermal buffer to protect the wearer from changing environmental conditions. The apparatus may also include an external thermal insulation layer and/or an internal thermal control layer to regulate the rate of heat exchange between the composite and the skin of the wearer. Other embodiments of the apparatus also provide 1) a path for evaporation or direct absorption of perspiration from the skin of the wearer for improved comfort and thermal control, 2) heat conductive pathways within the material for thermal equalization, 3) surface treatments for improved absorption or rejection of heat by the material, and 4) means for quickly regenerating the thermal storage capacity for reuse of the material. Applications of the composite materials are also described which take advantage of the composite's thermal characteristics. The examples described include a diver's wet suit, ski boot liners, thermal socks, gloves and a face mask for cold weather activities, and a metabolic heating or cooling blanket useful for treating hypothermia or fever patients in a medical setting and therapeutic heating or cooling orthopedic joint supports.

  18. Mechanics of Metals with Phase Changes

    SciTech Connect

    Lashley, Jason C.

    2001-01-01

    New experimental data is presented on some exotic metals that exhibit phase changes at cryogenic temperatures. The types of phase changes that were detected in the specific heat data range from martensitic (diffusion less) transitions to superconducting transitions. In addition, the charge density wave (CDW) state in uranium metal was detected in the specific heat. Specific-heat measurements were made in zero-magnetic field using an apparatus capable of obtaining temperatures as low as 0.4 K. Calibration performed on this apparatus, using a single-crystal copper sample, show its accuracy to be 0.50%, while the resolution was better than 0.1%. Our measurements demonstrate that similar high precision and accurate specific-heat measurements can be obtained on milligram-scale samples. In Chapters 2 and 3, specific-heat measurements are presented for the B2 (CsCl structure) alloy AuZn and for α-uranium (orthorhombic symmetry). The AuZn alloy exhibits a continuous transition at 64.75 K and an entropy of transition of (ΔStr) 2.02 J K-1 mol-1. Calculation of the Debye temperature, by extrapolating of the high temperature phase elastic constants to T = 0 K yields a value of 207 K (±2 K), in favorable agreement with the calorimetric value of 219 K (±0.50 K), despite the intervening martensitic transition. Reported results for single-crystal α-U show a low-temperature limiting θD of 256 K (±0.50 K) and four low-temperature anomalies: a superconducting transition below 1 K, an electronic transition at 22 K, and two anomalies at 38 K and at 42 K indicative of the CDW state. In order to continue the study of the actinide series of elements, a program was initiated to first purify and then grow single crystals of plutonium. Accordingly, the focus of Chapters 4 through 6 will be a description of plutonium sample preparation. In this program plutonium metal was purified via zone refining, using a levitated molten zone to minimize

  19. Phase Change Material Heat Exchanger Life Test

    NASA Technical Reports Server (NTRS)

    Lillibridge, Sean; Stephan, Ryan; Lee, Steve; He, Hung

    2008-01-01

    Low Lunar Orbit (LLO) poses unique thermal challenges for the orbiting space craft, particularly regarding the performance of the radiators. The emitted infrared (IR) heat flux from the lunar surface varies drastically from the light side to the dark side of the moon. Due to the extremely high incident IR flux, especially at low beta angles, a radiator is oftentimes unable to reject the vehicle heat load throughout the entire lunar orbit. One solution to this problem is to implement Phase Change Material (PCM) Heat Exchangers. PCM Heat Exchangers act as a "thermal capacitor," storing thermal energy when the radiator is unable to reject the required heat load. The stored energy is then removed from the PCM heat exchanger when the environment is more benign. Because they do not use an expendable resource, such as the feed water used by sublimators and evaporators, PCM Heat Exchangers are ideal for long duration Low Lunar Orbit missions. The Advanced Thermal Control project at JSC is completing a PCM heat exchanger life test to determine whether further technology development is warranted. The life test is being conducted on four nPentadecane, carbon filament heat exchangers. Fluid loop performance, repeatability, and measurement of performance degradation over 2500 melt-freeze cycles will be performed and reported in the current document.

  20. Phase Change Material Heat Exchanger Life Test

    NASA Technical Reports Server (NTRS)

    Lillibridge, Sean; Stephan, Ryan

    2009-01-01

    Low Lunar Orbit (LLO) poses unique thermal challenges for the orbiting space craft, particularly regarding the performance of the radiators. The IR environment of the space craft varies drastically from the light side to the dark side of the moon. The result is a situation where a radiator sized for the maximal heat load in the most adverse situation is subject to freezing on the dark side of the orbit. One solution to this problem is to implement Phase Change Material (PCM) Heat Exchangers. PCM Heat Exchangers act as a "thermal capacitor," storing thermal energy when there is too much being produced by the space craft to reject to space, and then feeding that energy back into the thermal loop when conditions are more favorable. Because they do not use an expendable resource, such as the feed water used by sublimators and evaporators, PCM Heat Exchangers are ideal for long duration LLO missions. In order to validate the performance of PCM Heat Exchangers, a life test is being conducted on four n-Pentadecane, carbon filament heat exchangers. Fluid loop performance, repeatability, and measurement of performance degradation over 2500 melt-freeze cycles will be performed.

  1. Phase Change Material Heat Exchanger Life Test

    NASA Technical Reports Server (NTRS)

    Lillibridge, Sean; Stephan, Ryan

    2009-01-01

    Low Lunar Orbit (LLO) poses unique thermal challenges for the orbiting space craft, particularly regarding the performance of the radiators. The IR environment of the space craft varies drastically from the light side to the dark side of the moon. The result is a situation where a radiator sized for the maximal heat load in the most adverse situation is subject to freezing on the dark side of the orbit. One solution to this problem is to implement Phase Change Material (PCM) Heat Exchangers. PCM Heat Exchangers act as a "thermal capacitor," storing thermal energy when there is too much being produced by the space craft to reject to space, and then feeding that energy back into the thermal loop when conditions are more favorable. Because they do not use an expendable resource, such as the feed water used by sublimators and evaporators, PCM Heat Exchangers are ideal for long duration LLO missions. In order to validate the performance of PCM Heat Exchangers, a life test is being conducted on four n-Pentadecane, carbon filament heat exchangers. Fluid loop performance, repeatability, and measurement of performance degradation over 2500 melt-freeze cycles will be performed.

  2. Phase Change Material Heat Exchanger Life Test

    NASA Technical Reports Server (NTRS)

    Lillibridge, Sean; Stephan, Ryan; Lee, Steve; He, Hung

    2008-01-01

    Low Lunar Orbit (LLO) poses unique thermal challenges for the orbiting space craft, particularly regarding the performance of the radiators. The emitted infrared (IR) heat flux from the lunar surface varies drastically from the light side to the dark side of the moon. Due to the extremely high incident IR flux, especially at low beta angles, a radiator is oftentimes unable to reject the vehicle heat load throughout the entire lunar orbit. One solution to this problem is to implement Phase Change Material (PCM) Heat Exchangers. PCM Heat Exchangers act as a "thermal capacitor," storing thermal energy when the radiator is unable to reject the required heat load. The stored energy is then removed from the PCM heat exchanger when the environment is more benign. Because they do not use an expendable resource, such as the feed water used by sublimators and evaporators, PCM Heat Exchangers are ideal for long duration Low Lunar Orbit missions. The Advanced Thermal Control project at JSC is completing a PCM heat exchanger life test to determine whether further technology development is warranted. The life test is being conducted on four nPentadecane, carbon filament heat exchangers. Fluid loop performance, repeatability, and measurement of performance degradation over 2500 melt-freeze cycles will be performed and reported in the current document.

  3. Reconfigurable Braille display with phase change locking

    NASA Astrophysics Data System (ADS)

    Soule, Cody W.; Lazarus, Nathan

    2016-07-01

    Automatically updated signs and displays for sighted people are common in today’s world. However, there is no cheap, low power equivalent available for the blind. This work demonstrates a reconfigurable Braille cell using the solid-to-liquid phase change of a low melting point alloy as a zero holding power locking mechanism. The device is actuated with the alloy in the liquid state, and is then allowed to solidify to lock the Braille dot in the actuated position. A low-cost manufacturing process is developed that includes molding of a rigid silicone to create pneumatic channels, and bonding of a thin membrane of a softer silicone on the surface for actuation. A plug of Field’s metal (melting point 62 °C) is placed in the pneumatic channels below each Braille dot to create the final device. The device is well suited for low duty cycle operation in applications such as signs, and is able to maintain its state indefinitely without additional power input. The display requires a pneumatic pressure of only 24 kPa for actuation, and reconfiguration has been demonstrated in less than a minute and a half.

  4. Application of phase-change materials in memory taxonomy

    PubMed Central

    Wang, Lei; Tu, Liang; Wen, Jing

    2017-01-01

    Abstract Phase-change materials are suitable for data storage because they exhibit reversible transitions between crystalline and amorphous states that have distinguishable electrical and optical properties. Consequently, these materials find applications in diverse memory devices ranging from conventional optical discs to emerging nanophotonic devices. Current research efforts are mostly devoted to phase-change random access memory, whereas the applications of phase-change materials in other types of memory devices are rarely reported. Here we review the physical principles of phase-change materials and devices aiming to help researchers understand the concept of phase-change memory. We classify phase-change memory devices into phase-change optical disc, phase-change scanning probe memory, phase-change random access memory, and phase-change nanophotonic device, according to their locations in memory hierarchy. For each device type we discuss the physical principles in conjunction with merits and weakness for data storage applications. We also outline state-of-the-art technologies and future prospects. PMID:28740557

  5. Application of phase-change materials in memory taxonomy.

    PubMed

    Wang, Lei; Tu, Liang; Wen, Jing

    2017-01-01

    Phase-change materials are suitable for data storage because they exhibit reversible transitions between crystalline and amorphous states that have distinguishable electrical and optical properties. Consequently, these materials find applications in diverse memory devices ranging from conventional optical discs to emerging nanophotonic devices. Current research efforts are mostly devoted to phase-change random access memory, whereas the applications of phase-change materials in other types of memory devices are rarely reported. Here we review the physical principles of phase-change materials and devices aiming to help researchers understand the concept of phase-change memory. We classify phase-change memory devices into phase-change optical disc, phase-change scanning probe memory, phase-change random access memory, and phase-change nanophotonic device, according to their locations in memory hierarchy. For each device type we discuss the physical principles in conjunction with merits and weakness for data storage applications. We also outline state-of-the-art technologies and future prospects.

  6. Procedure de caracterisation thermophysique d'un materiau a changement de phase composite pour le stockage thermique

    NASA Astrophysics Data System (ADS)

    Le Du, Mathieu

    The use of phase change materials (PCMs) allows to store and release large amounts of energy in reduced volumes by using latent heat storage through melting and solidifying at specific temperatures. Phase change materials received a great interest for reducing energy consumption by easing the implementation of passive solar heating and cooling. They can be integrated to buildings as wallboards to improve the heat storage capacity. In this study, an original experimental device has allowed to characterize the thermophysical proprieties of a composite wallboard constituted of PCMs. Generally, PCMs are characterized by calorimetric methods which use very small quantities of material. The device used can characterize large sample's dimensions, as they could be used in real condition. Apparent thermal conductivity and specific heat have been measured for various temperatures. During phase change process, total and latent heat storage capacities have been evaluated with the peak melting and freezing temperatures. Results are compared to the manufacturer's data and data from literature. Incoherencies have been found between sources. Despite several differences with published data, overall results are similar to the latest information, which allow validate the original experimental device. Thermal disturbances due to hysteresis have been noticed and discussed. Results allow suggesting recommendations on thermal procedure and experimental device to characterize efficiently this kind of materials. Temperature's ranges and heating and freezing rates affect results and it must be considered in the characterization. Moreover, experimental devices have to be designed to allow similar heating and freezing rates in order to compare results during melting and freezing. Key words: Phase change material, latent thermal storage, thermophysical characterization.

  7. Innovative Phase Change Approach for Significant Energy Savings

    DTIC Science & Technology

    2016-09-01

    FINAL REPORT Innovative Phase Change Approach for Significant Energy Savings ESTCP Project EW-201138 SEPTEMBER 2016 Dr. Aly H Shaaban Applied...5a. CONTRACT NUMBER W912HQ-11-C-0011 Innovative Phase Change Approach for Significant Energy Savings 5b. GRANT NUMBER 5c. PROGRAM...The HECU integrated heat exchangers filled with Phase Change Material (PCM) into a facility’s air conditioning system. The PCM acts as a thermal

  8. A Phase-Change Composite for Use in Building Envelopes

    SciTech Connect

    Graves, Ron S.

    1992-06-15

    The objective of this project is to develop composite thermal insulations containing phase-change materials for use in the building envelope. The use of a phase-change insulation composite in the building envelope could result in a significant increase in energy efficiency. PhD Research provided candidate phase-change composites, and ORNL performed analytical and experimental evaluations of their thermal performance. The thermal resistance of the prototype panels was somewhat less than that of commercial products, although their thermal capacity was greater. Using these results, PhD Research has been working to modify the design and to produce practical building elements that incorporate phase-change material.

  9. A numerical method for phase-change problems

    NASA Technical Reports Server (NTRS)

    Kim, Charn-Jung; Kaviany, Massoud

    1990-01-01

    A highly accurate and efficient finite-difference method for phase-change problems with multiple moving boundaries of irregular shape is developed by employing a coordinate transformation that immobilizes moving boundaries and preserves the conservative forms of the original governing equations. The numerical method is first presented for one-dimensional phase-change problems (involving large density variation between phases, heat generation, and multiple moving boundaries) and then extended to solve two-dimensional problems (without change of densities between phases). Numerical solutions are obtained non-iteratively using an explicit treatment of the interfacial mass and energy balances and an implicit treatment of the temperature field equations. The accuracy and flexibility of the present numerical method are verified by solving some phase-change problems and comparing the results with existing analytical, semi-analytical and numerical solutions. Results indicate that one- and two-dimensional phase-change problems can be handled easily with excellent accuracies.

  10. Crystal growth within a phase change memory cell.

    PubMed

    Sebastian, Abu; Le Gallo, Manuel; Krebs, Daniel

    2014-07-07

    In spite of the prominent role played by phase change materials in information technology, a detailed understanding of the central property of such materials, namely the phase change mechanism, is still lacking mostly because of difficulties associated with experimental measurements. Here, we measure the crystal growth velocity of a phase change material at both the nanometre length and the nanosecond timescale using phase-change memory cells. The material is studied in the technologically relevant melt-quenched phase and directly in the environment in which the phase change material is going to be used in the application. We present a consistent description of the temperature dependence of the crystal growth velocity in the glass and the super-cooled liquid up to the melting temperature.

  11. A numerical method for phase-change problems

    NASA Technical Reports Server (NTRS)

    Kim, Charn-Jung; Kaviany, Massoud

    1990-01-01

    A highly accurate and efficient finite-difference method for phase-change problems with multiple moving boundaries of irregular shape is developed by employing a coordinate transformation that immobilizes moving boundaries and preserves the conservative forms of the original governing equations. The numerical method is first presented for one-dimensional phase-change problems (involving large density variation between phases, heat generation, and multiple moving boundaries) and then extended to solve two-dimensional problems (without change of densities between phases). Numerical solutions are obtained non-iteratively using an explicit treatment of the interfacial mass and energy balances and an implicit treatment of the temperature field equations. The accuracy and flexibility of the present numerical method are verified by solving some phase-change problems and comparing the results with existing analytical, semi-analytical and numerical solutions. Results indicate that one- and two-dimensional phase-change problems can be handled easily with excellent accuracies.

  12. Visualization of the structural changes in plywood and gypsum board during the growth of Chaetomium globosum and Stachybotrys chartarum.

    PubMed

    Lewinska, Anna M; Hoof, Jakob B; Peuhkuri, Ruut H; Rode, Carsten; Lilje, Osu; Foley, Matthew; Trimby, Patrick; Andersen, Birgitte

    2016-10-01

    Fungal growth in indoor environments is associated with many negative health effects. Many studies focus on brown- and white-rot fungi and their effect on wood, but there is none that reveals the influence of soft-rot fungi, such as Stachybotrys spp. and Chaetomium spp., on the structure of building materials such as plywood and gypsum wallboard. This study focuses on using micro-computed tomography (microCT) to investigate changes of the structure of plywood and gypsum wallboard during fungal degradation by S. chartarum and C. globosum. Changes in the materials as a result of dampness and fungal growth were determined by measuring porosity and pore shape via microCT. The results show that the composition of the building material influenced the level of penetration by fungi as shown by scanning electron microscopy (SEM). Plywood appeared to be the most affected, with the penetration of moisture and fungi throughout the whole thickness of the sample. Conversely, fungi grew only on the top cardboard in the gypsum wallboard and they did not have significant influence on the gypsum wallboard structure. The majority of the observed changes in gypsum wallboard occurred due to moisture. This paper suggests that the mycelium distribution within building materials and the structural changes, caused by dampness and fungal growth, depend on the type of the material. Copyright © 2016 Elsevier B.V. All rights reserved.

  13. The Last Phase of Process Change - Deployment

    DTIC Science & Technology

    2008-11-01

    adoption of the change has reached Adoption infusion (depth) How deeply embedded into the practices of the organization is the new process Adoption business ... success Return on Investment data that determines if the effort to adopt the change was worthwhile Reference Suzanne Garcia and Richard Turner’s

  14. Heat storage system utilizing phase change materials government rights

    DOEpatents

    Salyer, Ival O.

    2000-09-12

    A thermal energy transport and storage system is provided which includes an evaporator containing a mixture of a first phase change material and a silica powder, and a condenser containing a second phase change material. The silica powder/PCM mixture absorbs heat energy from a source such as a solar collector such that the phase change material forms a vapor which is transported from the evaporator to the condenser, where the second phase change material melts and stores the heat energy, then releases the energy to an environmental space via a heat exchanger. The vapor is condensed to a liquid which is transported back to the evaporator. The system allows the repeated transfer of thermal energy using the heat of vaporization and condensation of the phase change material.

  15. Reflectance Changes during Shock-induced Phase Transformations in Metals

    SciTech Connect

    Stevens, G. D.; Turley, W. D.; Veeser, L. R.; Jensen, B. J.; Rigg, P. A.

    2010-06-01

    In performing shock wave experiments to study the characteristics of metals at high pressures, wave profiles (i.e., velocity measurements of the surface of the sample) are an established and useful way to study phase transformations. For example, a sudden change in the velocity or its slope can occur when the phase transformation induces a large volume change leading to a change in particle velocity. Allowing the shock to release into a transparent window that is in contact with the sample surface allows the study of conditions away from the shock Hugoniot. However, in cases where the wave profile is not definitive an additional phase-transformation diagnostic would be useful. Changes in the electronic structure of the atoms in the crystal offer opportunities to develop new phase-change diagnostics. We have studied optical reflectance changes for several phase transformations to see whether reflectance changes might be a generally applicable phase-transformation diagnostic. Shocks were produced by direct contact with explosives or with impacts from guns. Optical wavelengths for the reflectance measurements ranged from 355 to 700 nm. We studied samples of tin, iron, gallium, and cerium as each passed through a phase transformation during shock loading and, if observable, a reversion upon unloading. For solid-solid phase changes in tin and iron we saw small changes in the surface scattering characteristics, perhaps from voids or rough areas frozen into the surface of the sample as it transformed to a new crystal structure. For melt in gallium and cerium we saw changes in the wavelength dependence of the reflectance, and we surmise that these changes may result from changes in the crystal electronic structure. It appears that reflectance measurements can be a significant part of a larger suite of diagnostics to search for difficult-to-detect phase transformations.

  16. A Gibbs Formulation for Reactive Condensed Phase Materials with Phase Change

    NASA Astrophysics Data System (ADS)

    Stewart, D. Scott

    2014-03-01

    A large class of applications have pure, condensed phase constituents that come into contact, chemically react and simultaneously undergo phase change. Phase change in a given molecular material has often been considered to be separate from chemical reaction. Continuum modelers of phase change often use a phase field model whereby an indicator function is allowed to change from one value to another in regions of phase change, governed by evolutionary (Ginzburg-Landau) equations. Whereas classic chemical kinetics literally count species concentrations and derive evolution equations based on species mass transport. We argue that the latter is fundamental and is the same as the former, if all species, phase or chemical are treated as distinct chemical species. A self consistent continuum-thermomechanical model, must account for all significant energetic quantities and have correct molecular and continuum limits in the mixture. The use of Gibbs potentials for all relevant species, chemical and phase does this neatly and allows the use of classical potentials, while allowing for modeling of phase interaction terms and reaction rate and phase change kinetics. The phase field quantities are the mass fractions. One has a single stress tensor, and a single temperature. Office of Naval Research and Defense Threat Reduction Agency.

  17. Phase-change radiative thermal diode

    SciTech Connect

    Ben-Abdallah, Philippe; Biehs, Svend-Age

    2013-11-04

    A thermal diode transports heat mainly in one preferential direction rather than in the opposite direction. This behavior is generally due to the non-linear dependence of certain physical properties with respect to the temperature. Here we introduce a radiative thermal diode which rectifies heat transport thanks to the phase transitions of materials. Rectification coefficients greater than 70% and up to 90% are shown, even for small temperature differences. This result could have important applications in the development of future contactless thermal circuits or in the conception of radiative coatings for thermal management.

  18. Confined crystals of the smallest phase-change material.

    PubMed

    Giusca, Cristina E; Stolojan, Vlad; Sloan, Jeremy; Börrnert, Felix; Shiozawa, Hidetsugu; Sader, Kasim; Rümmeli, Mark H; Büchner, Bernd; Silva, S Ravi P

    2013-09-11

    The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales.

  19. Confined Crystals of the Smallest Phase-Change Material

    PubMed Central

    2013-01-01

    The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales. PMID:23984706

  20. PHASE CHANGE MATERIALS IN FLOOR TILES FOR THERMAL ENERGY STORAGE

    SciTech Connect

    Douglas C. Hittle

    2002-10-01

    Passive solar systems integrated into residential structures significantly reduce heating energy consumption. Taking advantage of latent heat storage has further increased energy savings. This is accomplished by the incorporation of phase change materials into building materials used in passive applications. Trombe walls, ceilings and floors can all be enhanced with phase change materials. Increasing the thermal storage of floor tile by the addition of encapsulated paraffin wax is the proposed topic of research. Latent heat storage of a phase change material (PCM) is obtained during a change in phase. Typical materials use the latent heat released when the material changes from a liquid to a solid. Paraffin wax and salt hydrates are examples of such materials. Other PCMs that have been recently investigated undergo a phase transition from one solid form to another. During this process they will release heat. These are known as solid-state phase change materials. All have large latent heats, which makes them ideal for passive solar applications. Easy incorporation into various building materials is must for these materials. This proposal will address the advantages and disadvantages of using these materials in floor tile. Prototype tile will be made from a mixture of quartz, binder and phase change material. The thermal and structural properties of the prototype tiles will be tested fully. It is expected that with the addition of the phase change material the structural properties will be compromised to some extent. The ratio of phase change material in the tile will have to be varied to determine the best mixture to provide significant thermal storage, while maintaining structural properties that meet the industry standards for floor tile.

  1. Polarization selective phase-change nanomodulator

    PubMed Central

    Appavoo, Kannatassen; Haglund Jr., Richard F.

    2014-01-01

    Manipulating optical signals below the diffraction limit is crucial for next-generation data-storage and telecommunication technologies. Although controlling the flow of light around nanoscale waveguides was achieved over a decade ago, modulating optical signals at terahertz frequencies within nanoscale volumes remains a challenge. Since the physics underlying any modulator relies on changes in dielectric properties, the incorporation of strongly electron-correlated materials (SECMs) has been proposed because they can exhibit orders of magnitude changes in electrical and optical properties with modest thermal, electrical or optical trigger signals. Here we demonstrate a hybrid nanomodulator of deep sub-wavelength dimensions with an active volume of only 0.002 µm3 by spatially confining light on the nanometre length scale using a plasmonic nanostructure while simultaneously controlling the reactive near-field environment at its optical focus with a single, precisely positioned SECM nanostructure. Since the nanomodulator functionality hinges on this near-field electromagnetic interaction, the modulation is also selectively responsive to polarization. This architecture suggests one path for designing reconfigurable optoelectronic building blocks with responses that can be tailored with exquisite precision by varying size, geometry, and the intrinsic materials properties of the hybrid elements. PMID:25346427

  2. Polarization selective phase-change nanomodulator

    SciTech Connect

    Appavoo, Kannatassen; Haglund Jr., Richard F.

    2014-10-27

    Manipulating optical signals below the diffraction limit is crucial for next-generation data-storage and telecommunication technologies. Although controlling the flow of light around nanoscale waveguides was achieved over a decade ago, modulating optical signals at terahertz frequencies within nanoscale volumes remains a challenge. Since the physics underlying any modulator relies on changes in dielectric properties, the incorporation of strongly electron-correlated materials (SECMs) has been proposed because they can exhibit orders of magnitude changes in electrical and optical properties with modest thermal, electrical or optical trigger signals. Here we demonstrate a hybrid nanomodulator of deep sub-wavelength dimensions with an active volume of only 0.002 µm3 by spatially confining light on the nanometre length scale using a plasmonic nanostructure while simultaneously controlling the reactive near-field environment at its optical focus with a single, precisely positioned SECM nanostructure. Since the nanomodulator functionality hinges on this near-field electromagnetic interaction, the modulation is also selectively responsive to polarization. Lastly, this architecture suggests one path for designing reconfigurable optoelectronic building blocks with responses that can be tailored with exquisite precision by varying size, geometry, and the intrinsic materials properties of the hybrid elements.

  3. Polarization selective phase-change nanomodulator

    DOE PAGES

    Appavoo, Kannatassen; Haglund Jr., Richard F.

    2014-10-27

    Manipulating optical signals below the diffraction limit is crucial for next-generation data-storage and telecommunication technologies. Although controlling the flow of light around nanoscale waveguides was achieved over a decade ago, modulating optical signals at terahertz frequencies within nanoscale volumes remains a challenge. Since the physics underlying any modulator relies on changes in dielectric properties, the incorporation of strongly electron-correlated materials (SECMs) has been proposed because they can exhibit orders of magnitude changes in electrical and optical properties with modest thermal, electrical or optical trigger signals. Here we demonstrate a hybrid nanomodulator of deep sub-wavelength dimensions with an active volume ofmore » only 0.002 µm3 by spatially confining light on the nanometre length scale using a plasmonic nanostructure while simultaneously controlling the reactive near-field environment at its optical focus with a single, precisely positioned SECM nanostructure. Since the nanomodulator functionality hinges on this near-field electromagnetic interaction, the modulation is also selectively responsive to polarization. Lastly, this architecture suggests one path for designing reconfigurable optoelectronic building blocks with responses that can be tailored with exquisite precision by varying size, geometry, and the intrinsic materials properties of the hybrid elements.« less

  4. Frequency, phase, and amplitude changes of the hydrogen maser oscillation

    NASA Technical Reports Server (NTRS)

    Audoin, Claude; Diener, William A.

    1992-01-01

    The frequency, the phase, and the amplitude changes of the hydrogen maser oscillation, which are induced by the modulation of the cavity resonant frequency, are considered. The results obtained apply specifically to one of the H-maser cavity autotuning methods which is actually implemented, namely the cavity frequency-switching method. The frequency, the phase, and the amplitude changes are analyzed theoretically. The phase and the amplitude variations are measured experimentally. It is shown, in particular, that the phase of oscillation is subjected to abrupt jumps at the times of the cavity frequency switching, whose magnitude is specified. The results given can be used for the design of a phase-locked loop (PLL) aimed at minimizing the transfer of the phase modulation to the slaved VCXO.

  5. Frequency, phase, and amplitude changes of the hydrogen maser oscillation

    NASA Technical Reports Server (NTRS)

    Audoin, Claude; Diener, William A.

    1992-01-01

    The frequency, the phase, and the amplitude changes of the hydrogen maser oscillation, which are induced by the modulation of the cavity resonant frequency, are considered. The results obtained apply specifically to one of the H-maser cavity autotuning methods which is actually implemented, namely the cavity frequency-switching method. The frequency, the phase, and the amplitude changes are analyzed theoretically. The phase and the amplitude variations are measured experimentally. It is shown, in particular, that the phase of oscillation is subjected to abrupt jumps at the times of the cavity frequency switching, whose magnitude is specified. The results given can be used for the design of a phase-locked loop (PLL) aimed at minimizing the transfer of the phase modulation to the slaved VCXO.

  6. Reconfigurable phase-change photomask for grayscale photolithography

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Yuan, G. H.; Kiang, K. S.; Sun, K.; Gholipour, B.; Rogers, E. T. F.; Huang, K.; Ang, S. S.; Zheludev, N. I.; Teng, J. H.

    2017-05-01

    We demonstrate a grayscale photolithography technique which uses a thin phase-change film as a photomask to locally control the exposure dose and allows three-dimensional (3D) sculpting photoresist for the manufacture of 3D structures. Unlike traditional photomasks, the transmission of the phase-change material photomask can be set to an arbitrary gray level with submicron lateral resolution, and the mask pattern can be optically reconfigured on demand, by inducing a refractive-index-changing phase-transition with femtosecond laser pulses. We show a spiral phase plate and a phase-type super-oscillatory lens fabricated on Si wafers to demonstrate the range of applications that can be addressed with this technique.

  7. Phase Change Material Thermal Power Generator

    NASA Technical Reports Server (NTRS)

    Jones, Jack A. (Inventor); Chao, Yi (Inventor); Valdez, Thomas I. (Inventor)

    2014-01-01

    An energy producing device, for example a submersible vehicle for descending or ascending to different depths within water or ocean, is disclosed. The vehicle comprises a temperature-responsive material to which a hydraulic fluid is associated. A pressurized storage compartment stores the fluid as soon as the temperature-responsive material changes density. The storage compartment is connected with a hydraulic motor, and a valve allows fluid passage from the storage compartment to the hydraulic motor. An energy storage component, e.g. a battery, is connected with the hydraulic motor and is charged by the hydraulic motor when the hydraulic fluid passes through the hydraulic motor. Upon passage in the hydraulic motor, the fluid is stored in a further storage compartment and is then sent back to the area of the temperature-responsive material.

  8. Phase change material thermal power generator

    NASA Technical Reports Server (NTRS)

    Jones, Jack A. (Inventor); Chao, Yi (Inventor); Valdez, Thomas I. (Inventor)

    2011-01-01

    An energy producing device, for example a submersible vehicle for descending or ascending to different depths within water or ocean, is disclosed. The vehicle comprises a temperature-responsive material to which a hydraulic fluid is associated. A pressurized storage compartment stores the fluid as soon as the temperature-responsive material changes density. The storage compartment is connected with a hydraulic motor, and a valve allows fluid passage from the storage compartment to the hydraulic motor. An energy storage component, e.g. a battery, is connected with the hydraulic motor and is charged by the hydraulic motor when the hydraulic fluid passes through the hydraulic motor. Upon passage in the hydraulic motor, the fluid is stored in a further storage compartment and is then sent back to the area of the temperature-responsive material.

  9. Aging mechanisms in amorphous phase-change materials.

    PubMed

    Raty, Jean Yves; Zhang, Wei; Luckas, Jennifer; Chen, Chao; Mazzarello, Riccardo; Bichara, Christophe; Wuttig, Matthias

    2015-06-24

    Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to a drift in the electrical resistance, which hinders the development of ultrahigh density storage devices. Here we elucidate the aging process in amorphous GeTe, a prototypical phase-change material, by advanced numerical simulations, photothermal deflection spectroscopy and impedance spectroscopy experiments. We show that aging is accompanied by a progressive change of the local chemical order towards the crystalline one. Yet, the glass evolves towards a covalent amorphous network with increasing Peierls distortion, whose structural and electronic properties drift away from those of the resonantly bonded crystal. This behaviour sets phase-change materials apart from conventional glass-forming systems, which display the same local structure and bonding in both phases.

  10. Anomalous phase change characteristics in Fe-Te materials

    SciTech Connect

    Fu, X. T.; Song, W. D.; Ji, R.; Ho, H. W.; Wang, L.; Hong, M. H.

    2012-05-14

    Phase change materials have become significantly attractive due to its unique characteristics for its extensive applications. In this paper, a kind of phase change material, which consists of Fe and Te components, is developed. The crystallization temperature of the Fe-Te materials is 180 deg. C for Fe{sub 1.19}Te and can be adjusted by the Fe/Te ratio. High-speed phase change in the Fe-Te materials has been demonstrated by nanosecond laser irradiation. Comparing to conventional phase change materials, the Fe-Te materials exhibit an anomalous optical property that has higher reflectivity at amorphous than crystalline state, which is useful for data storage design.

  11. A Gibbs Formulation for Reactive Materials with Phase Change

    NASA Astrophysics Data System (ADS)

    Stewart, D. Scott

    2015-06-01

    A large class of applications have pure, condensed phase constituents that come into contact, chemically react and simultaneously undergo phase change. Phase change in a given molecular material has often been considered to be separate from chemical reaction. Continuum modelers of phase change often use a phase field model whereby an indicator function is allowed to change from one value to another in regions of phase change, governed by evolutionary (Ginzburg-Landau) equations, whereas classic chemical kinetics literally count species concentrations and derive kinetics evolution equations based on species mass transport. We argue the latter is fundamental and is the same as the former, if all species, phase or chemical are treated as distinct chemical species. We pose a self-consistent continuum, thermo-mechanical model to account for significant energetic quantities with correct molecular and continuum limits in the mixture. A single stress tensor, and a single temperature is assumed for the mixture with specified Gibbs potentials for all relevant species, and interaction energies. We discuss recent examples of complex reactive material modeling, drawn from thermitic and propellant combustion that use this new model. Supported by HDTRA1-10-1-0020 (DTRA), N000014-12-1-0555 (ONR) and FA8651-10-1-0004 (AFRL/RW).

  12. A Gibbs Formulation for Reactive Materials with Phase Change

    NASA Astrophysics Data System (ADS)

    Stewart, D. Scott

    2015-11-01

    A large class of applications have pure, condensed phase constituents that come into contact, chemically react and simultaneously undergo phase change. Phase change in a given molecular material has often been considered to be separate from chemical reaction. Continuum modelers of phase change often use a phase field model whereby an indicator function is allowed to change from one value to another in regions of phase change, governed by evolutionary (Ginzburg-Landau) equations, whereas classic chemical kinetics literally count species concentrations and derive kinetics evolution equations based on species mass transport. We argue the latter is fundamental and is the same as the former, if all species, phase or chemical are treated as distinct chemical species. We pose a self-consistent continuum, thermo-mechanical model to account for significant energetic quantities with correct molecular and continuum limits in the mixture. A single stress tensor, and a single temperature is assumed for the mixture with specified Gibbs potentials for all relevant species, and interaction energies. We discuss recent examples of complex reactive material modeling, drawn from thermitic and propellant combustion that use this new model. DSS supported by DTRA, ONR and AFOSR.

  13. Phase change materials in energy sector - applications and material requirements

    NASA Astrophysics Data System (ADS)

    Kuta, Marta; Wójcik, Tadeusz M.

    2015-05-01

    Phase change materials (PCMs) have been applying in many areas. One of them is energy field. PCMs are interesting for the energy sector because their use enables thermal stabilization and storage of large amount of heat. It is major issue for safety of electronic devices, thermal control of buildings and vehicles, solar power and many others energy domains. This paper contains preliminary results of research on solid-solid phase change materials designed for thermal stabilisation of electronic devices.

  14. Recent Advances on Neuromorphic Systems Using Phase-Change Materials

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Lu, Shu-Ren; Wen, Jing

    2017-05-01

    Realization of brain-like computer has always been human's ultimate dream. Today, the possibility of having this dream come true has been significantly boosted due to the advent of several emerging non-volatile memory devices. Within these innovative technologies, phase-change memory device has been commonly regarded as the most promising candidate to imitate the biological brain, owing to its excellent scalability, fast switching speed, and low energy consumption. In this context, a detailed review concerning the physical principles of the neuromorphic circuit using phase-change materials as well as a comprehensive introduction of the currently available phase-change neuromorphic prototypes becomes imperative for scientists to continuously progress the technology of artificial neural networks. In this paper, we first present the biological mechanism of human brain, followed by a brief discussion about physical properties of phase-change materials that recently receive a widespread application on non-volatile memory field. We then survey recent research on different types of neuromorphic circuits using phase-change materials in terms of their respective geometrical architecture and physical schemes to reproduce the biological events of human brain, in particular for spike-time-dependent plasticity. The relevant virtues and limitations of these devices are also evaluated. Finally, the future prospect of the neuromorphic circuit based on phase-change technologies is envisioned.

  15. Recent Advances on Neuromorphic Systems Using Phase-Change Materials.

    PubMed

    Wang, Lei; Lu, Shu-Ren; Wen, Jing

    2017-12-01

    Realization of brain-like computer has always been human's ultimate dream. Today, the possibility of having this dream come true has been significantly boosted due to the advent of several emerging non-volatile memory devices. Within these innovative technologies, phase-change memory device has been commonly regarded as the most promising candidate to imitate the biological brain, owing to its excellent scalability, fast switching speed, and low energy consumption. In this context, a detailed review concerning the physical principles of the neuromorphic circuit using phase-change materials as well as a comprehensive introduction of the currently available phase-change neuromorphic prototypes becomes imperative for scientists to continuously progress the technology of artificial neural networks. In this paper, we first present the biological mechanism of human brain, followed by a brief discussion about physical properties of phase-change materials that recently receive a widespread application on non-volatile memory field. We then survey recent research on different types of neuromorphic circuits using phase-change materials in terms of their respective geometrical architecture and physical schemes to reproduce the biological events of human brain, in particular for spike-time-dependent plasticity. The relevant virtues and limitations of these devices are also evaluated. Finally, the future prospect of the neuromorphic circuit based on phase-change technologies is envisioned.

  16. Phase Change Material Systems for High Temperature Heat Storage.

    PubMed

    Perraudin, David Y S; Binder, Selmar R; Rezaei, Ehsan; Ortonaa, Alberto; Haussener, Sophia

    2015-01-01

    Efficient, cost effective, and stable high-temperature heat storage material systems are important in applications such as high-temperature industrial processes (metal processing, cement and glass manufacturing, etc.), or electricity storage using advanced adiabatic compressed air energy storage. Incorporating phase change media into heat storage systems provides an advantage of storing and releasing heat at nearly constant temperature, allowing steady and optimized operation of the downstream processes. The choice of, and compatibility of materials and encapsulation for the phase change section is crucial, as these must guarantee good and stable performance and long lifetime at low cost. Detailed knowledge of the material properties and stability, and the coupled heat transfer, phase change, and fluid flow are required to allow for performance and lifetime predictions. We present coupled experimental-numerical techniques allowing prediction of the long-term performance of a phase change material-based high-temperature heat storage system. The experimental investigations focus on determination of material properties (melting temperature, heat of fusion, etc.) and phase change material and encapsulation interaction (stability, interface reactions, etc.). The computational investigations focus on an understanding of the multi-mode heat transfer, fluid flow, and phase change processes in order to design the material system for enhanced performance. The importance of both the experimental and numerical approaches is highlighted and we give an example of how both approaches can be complementarily used for the investigation of long-term performance.

  17. Mantle plume interaction with an endothermic phase change

    NASA Technical Reports Server (NTRS)

    Schubert, Gerald; Anderson, Charles; Goldman, Peggy

    1995-01-01

    High spatial resolution numerical simulations of mantle plumes impinging from below on the endothermic phase change at 660-km depth are used to investigate the effects of latent heat release on the plume-phase change interaction. Both axisymmetric and planar upflows are considered, and the strong temperature dependence of mantle viscosity is taken into account. For plume strengths considered, a Clapeyron slope of -4 MPa/K prevents plume penetration of the phase change. Plumes readily penetrate the phase change for a Clapeyron slope of -2 MPa/K and arrive in the upper mantle considerably hotter than if they had not traversed the phase change. For the same amount of thermal drive, i.e., the same excess basal temperature, axisymmetric plumes are hotter upon reaching the upper mantle than are planar upwellings. Heating of plumes by their passage through the spinel-perovskite endothermic phase change can have important consequences for the ability of the plume to thermally thin the lithosphere and cause melting and volcanism.

  18. A latchable thermally activated phase change actuator for microfluidic systems

    NASA Astrophysics Data System (ADS)

    Richter, Christiane; Sachsenheimer, Kai; Rapp, Bastian E.

    2016-03-01

    Complex microfluidic systems often require a high number of individually controllable active components like valves and pumps. In this paper we present the development and optimization of a latchable thermally controlled phase change actuator which uses a solid/liquid phase transition of a phase change medium and the displacement of the liquid phase change medium to change and stabilize the two states of the actuator. Because the phase change is triggered by heat produced with ohmic resistors the used control signal is an electrical signal. In contrast to pneumatically activated membrane valves this concept allows the individual control of several dozen actuators with only two external pressure lines. Within this paper we show the general working principle of the actuator and demonstrate its general function and the scalability of the concept at an example of four actuators. Additionally we present the complete results of our studies to optimize the response behavior of the actuator - the influence of the heating power as well as the used phase change medium on melting and solidifying times.

  19. Numerical Simulation of Two-phase flow with Phase Change Using the Level-set Method

    NASA Astrophysics Data System (ADS)

    Li, Hongying; Lou, Jing; Pan, Lunsheng; Yap, Yitfatt

    2016-11-01

    Multiphase flow with phase change is widely encountered in many engineering applications. A distinct feature involves in these applications is the phase transition from one phase to another due to the non-uniform temperature distribution. Such kind of process generally releases or absorbs large amount of energy with mass transfer happened simultaneously. It demands great cautions occasionally such as the high pressure due to evaporation. This article presents a numerical model for simulation of two-fluid flow with phase change problem. In these two fluids, one of them changes its state due to phase change. Such a problem then involves two substances with three phases as well as two different interfaces, i.e. the interface between two substances and the interface of one substance between its two phases. Two level-set functions are used to capture the two interfaces in the current problem. The current model is validated against one-dimensional and two-dimensional liquid evaporation. With the code validated, it is applied to different phase change problems including (1) a falling evaporating droplet and the rising of one bubble and (2) two-fluid stratified flow with solidification of one fluid. Comparisons on the bubble and droplet topologies, flow and temperature fields are made for the first case between the falling evaporating droplet and the falling droplet without evaporation. For the second demonstration case, the effect of the superheated temperature on the solidification process is investigated.

  20. Phase change material in floor tiles for thermal energy storage

    NASA Astrophysics Data System (ADS)

    Lee, Amy Sarah

    Traditional passive solar systems have relied on sensible heat storage for energy savings. Recent research has investigated taking advantage of latent heat storage for additional energy savings. This is accomplished by the incorporation of phase change material into building materials used in traditional passive applications. Trombe walls, ceilings and floors can all be enhanced with phase change materials. This research introduces a new flooring material that incorporates a phase change material ready for commercial manufacture. An agglomerate floor tile containing 20% by mass of encapsulated octadecane has been manufactured. Flexural and compressive strength of 7.4 MPa and 24.5 MPa respectively, were measured for the tile. Peak melting transition temperature was determined to be 27.2°C with a latent heat of 33.9 J/g of tile. Structural and thermal performance of the tile surpassed that of a typical ceramic tile. Each tile was composed of quartz, resin and phase change material. Statistical modeling was performed to analyze the response of flexural and compressive strength on varying amounts of quartz, resin and phase change material. Resulting polynomials described the effect of adding phase change material into the tile. With as little as 10% by mass of phase change material, the strength was reduced to less than 50% of tile without phase change material. It was determined that the maximum phase change material content to attain structural integrity greater than ceramic tile was 20% by mass. The statistical analysis used for this research was based on mixture experiments. A procedure was developed to simplify the selection of data points used in the fit of the polynomials to describe the response of flexural and compressive strengths. Analysis of energy savings using this floor tile containing 20% by mass of phase change material was performed as an addendum to this research. A known static simulation method, SLR (solar load ratio), was adapted to include

  1. Synthesis of the Research on Educational Change: Implementation Phase.

    ERIC Educational Resources Information Center

    Busick, Kathleen U.; Inos, Rita Hocog

    As Pacific educational leaders strive to make their educational systems meaningful for their own island people, lessons can be learned from the research on change. This is the second in a series of three papers on the broad phases of educational change: initiation, implementation, and institutionalization and renewal. The Concerns Based Adoption…

  2. Development of PCM wallboard for heating and cooling of residential buildings

    SciTech Connect

    Salyer, I.O.; Sircar, A.K.

    1989-03-01

    The goals of this project were to find, test, and develop an effective phase change material (PCM) for heating and cooling of residential buildings. Specifications for the PCM included thermal storage of at least 30 cal/gm, congruent melting and freezing, at 25{degrees}C, nontoxic, noncorrosive, nonhygroscopic, low-cost, and commercially available in quantity. The PCM must be able to be incorporated into ordinary building materials (plasterboard, concrete, floor tile) by processes adaptable to commercial manufacture. The goals of the original program have been substantially achieved by identifying a series of linear crystalline alkyl hydrocarbon PCM that are commercially available from petroleum refining (lower cost, lower {open_quotes}purity{close_quotes}), and from polymerization of ethylene (higher cost, higher {open_quotes}purity{close_quotes}). Four alternate processes have been developed whereby these PCM can be incorporated into plasterboard and concrete building materials. Two of the processes have been successfully demonstrated in the laboratories of the two largest U.S. manufacturers of plasterboard, and collaborative development leading toward commercialization is still ongoing. Problem areas remaining to be resolved include: establishing unequivocably the economic viability of the system, developing environmentally acceptable fire retarding procedures, scale up of the manufacturing processes and evaluating effects of long-term thermocycling. We are scaling up the immersion process to include imbibing and testing 4-ft x 8-ft plasterboard panels. Successful completion is expected to encourage a plasterboard manufacturer to commercialize the technology. Five U.S. patents have been issuedand U.S. and foreign patents are pending. One foreign license has been negotiated. Spin-offs of the technology likely to be commercialized soon in the U.S. include tableware, hot and cold medical wraps, and wraps to prevent the overnight freezing of citrus tree trunks.

  3. Adversary phase change detection using SOMs and text data.

    SciTech Connect

    Speed, Ann Elizabeth; Doser, Adele Beatrice; Warrender, Christina E.

    2010-05-01

    In this work, we developed a self-organizing map (SOM) technique for using web-based text analysis to forecast when a group is undergoing a phase change. By 'phase change', we mean that an organization has fundamentally shifted attitudes or behaviors. For instance, when ice melts into water, the characteristics of the substance change. A formerly peaceful group may suddenly adopt violence, or a violent organization may unexpectedly agree to a ceasefire. SOM techniques were used to analyze text obtained from organization postings on the world-wide web. Results suggest it may be possible to forecast phase changes, and determine if an example of writing can be attributed to a group of interest.

  4. Preservice Elementary Teachers' Knowledge of Observable Moon Phases and Pattern of Change in Phases

    ERIC Educational Resources Information Center

    Trundle, Kathy Cabe; Atwood, Ronald K.; Christopher, John E.

    2006-01-01

    The purpose of this study was to describe selected content knowledge held by 52 preservice elementary teachers about the observable phases of the moon and the monthly pattern of change in observable phases. Data were obtained from participants in a physics course before and after they received inquiry-based instruction designed to promote…

  5. Preservice Elementary Teachers' Knowledge of Observable Moon Phases and Pattern of Change in Phases

    ERIC Educational Resources Information Center

    Trundle, Kathy Cabe; Atwood, Ronald K.; Christopher, John E.

    2006-01-01

    The purpose of this study was to describe selected content knowledge held by 52 preservice elementary teachers about the observable phases of the moon and the monthly pattern of change in observable phases. Data were obtained from participants in a physics course before and after they received inquiry-based instruction designed to promote…

  6. Quantitative Phase-Change Thermodynamics and Metastability of Perovskite-Phase Cesium Lead Iodide.

    PubMed

    Dastidar, Subham; Hawley, Christopher J; Dillon, Andrew D; Gutierrez-Perez, Alejandro D; Spanier, Jonathan E; Fafarman, Aaron T

    2017-03-16

    The perovskite phase of cesium lead iodide (α-CsPbI3 or "black" phase) possesses favorable optoelectronic properties for photovoltaic applications. However, the stable phase at room temperature is a nonfunctional "yellow" phase (δ-CsPbI3). Black-phase polycrystalline thin films are synthesized above 330 °C and rapidly quenched to room temperature, retaining their phase in a metastable state. Using differential scanning calorimetry, it is shown herein that the metastable state is maintained in the absence of moisture, up to a temperature of 100 °C, and a reversible phase-change enthalpy of 14.2 (±0.5) kJ/mol is observed. The presence of atmospheric moisture hastens the black-to-yellow conversion kinetics without significantly changing the enthalpy of the transition, indicating a catalytic effect, rather than a change in equilibrium due to water adduct formation. These results delineate the conditions for trapping the desired phase and highlight the significant magnitude of the entropic stabilization of this phase.

  7. A Gibbs formulation for reactive materials with phase change

    NASA Astrophysics Data System (ADS)

    Stewart, D. Scott

    2017-01-01

    Energetic material condensed phase constituents come into contact, chemically react and simultaneously undergo phase change. Phase change in a given molecular material is often considered separately from chemical reaction. Continuum phase field models often use a indicator function to change the phase in different regions according to an evolutionary (Ginzburg-Landau) equation. But chemical kinetic descriptions of change (according to physical chemistry formulations) count species or component concentrations and derive kinetic evolution equations based on component mass transport. We argue the latter is fundamental and that all components, designated by both phase and chemical characters are treated as distinct chemical species. We pose a self-consistent continuum, thermo-mechanical model based on specified Gibbs potentials for all relevant species/components that are present in a single material. Therefore a single stress tensor, and a single temperature is assumed for the material for all relevant component-species, for all equilibrium potentials, interaction energies and material properties. We discuss recent examples where we have applied the Gibbs formulation to model behavior of complex reactive materials.

  8. Vegetative phase change and shoot maturation in plants.

    PubMed

    Poethig, R Scott

    2013-01-01

    As a plant shoot develops, it produces different types of leaves, buds, and internodes, and eventually acquires the capacity to produce structures involved in sexual reproduction. Morphological and anatomical traits that change in coordinated fashion at a predictable time in vegetative development allow this process to be divided into several more-or-less discrete phases; the transition between these phases is termed "vegetative phase change." Vegetative phase change is regulated by a decrease in the expression of the related microRNAs, miR156, and miR157, which act by repressing the expression of squamosa promoter binding protein/SBP-like (SBP/SPL) transcription factors. SBP/SPL proteins regulate a wide variety of processes in shoot development, including flowering time and inflorescence development. Answers to long-standing questions about the relationship between vegetative and reproductive maturation have come from genetic analyses of the transcriptional and posttranscriptional regulatory networks in which these proteins are involved. Studies conducted over several decades indicate that carbohydrates have a significant effect on phase-specific leaf traits, and recent research suggests that sugar may be the leaf signal that promotes vegetative phase change.

  9. Vegetative phase change and shoot maturation in plants

    PubMed Central

    Poethig, R. Scott

    2014-01-01

    As a plant shoot develops, it produces different types of leaves, buds, and internodes, and eventually acquires the capacity to produce structures involved in sexual reproduction. Morphological and anatomical traits that change in coordinated fashion at a predictable time in vegetative development allow this process to be divided into several more-or-less discrete phases; the transition between these phases is termed vegetative phase change. Vegetative phase change is regulated by a decrease in the expression of the related microRNAs, miR156 and miR157, which act by repressing the expression of SBP/SPL transcription factors. SBP/SPL proteins regulate a wide variety of processes in shoot development, including flowering time and inflorescence development. Answers to long-standing questions about the relationship between vegetative and reproductive maturation have come from genetic analyses of the transcriptional and post-transcriptional regulatory networks in which these proteins are involved. Studies conducted over several decades indicate that carbohydrates have a significant effect on phase-specific leaf traits, and recent research suggests that sugar may be the leaf signal that promotes vegetative phase change. PMID:23962841

  10. Effects of phase change on reflection in phase-measuring interference microscopy.

    PubMed

    Dubois, Arnaud

    2004-03-01

    We show by analytical and numerical calculations that the phase change on reflection that occurs in interference microscopy is almost independent of the numerical aperture of the objective. The shift of the microscope interferogram response due to the phase change on reflection, however, increases with the numerical aperture. Measurements of the interferogram shift are made with a Linnik interference microscope equipped with various numerical-aperture objectives and are reported and compared with theory.

  11. Understanding Phase-Change Memory Alloys from a Chemical Perspective

    PubMed Central

    Kolobov, A.V.; Fons, P.; Tominaga, J.

    2015-01-01

    Phase-change memories (PCM) are associated with reversible ultra-fast low-energy crystal-to-amorphous switching in GeTe-based alloys co-existing with the high stability of the two phases at ambient temperature, a unique property that has been recently explained by the high fragility of the glass-forming liquid phase, where the activation barrier for crystallisation drastically increases as the temperature decreases from the glass-transition to room temperature. At the same time the atomistic dynamics of the phase-change process and the associated changes in the nature of bonding have remained unknown. In this work we demonstrate that key to this behavior is the formation of transient three-center bonds in the excited state that is enabled due to the presence of lone-pair electrons. Our findings additionally reveal previously ignored fundamental similarities between the mechanisms of reversible photoinduced structural changes in chalcogenide glasses and phase-change alloys and offer new insights into the development of efficient PCM materials. PMID:26323962

  12. Rayleigh-Taylor instability of viscous fluids with phase change.

    PubMed

    Kim, Byoung Jae; Kim, Kyung Doo

    2016-04-01

    Film boiling on a horizontal surface is a typical example of the Rayleigh-Taylor instability. During the film boiling, phase changes take place at the interface, and thus heat and mass transfer must be taken into consideration in the stability analysis. Moreover, since the vapor layer is not quite thick, a viscous flow must be analyzed. Existing studies assumed equal kinematic viscosities of two fluids, and/or considered thin viscous fluids. The purpose of this study is to derive the analytical dispersion relation of the Rayleigh-Taylor instability for more general conditions. The two fluids have different properties. The thickness of the vapor layer is finite, but the liquid layer is thick enough to be nearly semi-infinite in view of perturbation. Initially, the vapor is in equilibrium with the liquid at the interface, and the direction of heat transfer is from the vapor side to the liquid side. In this case, the phase change has a stabilizing effect on the growth rate of the interface. When the vapor layer is thin, there is a coupled effect of the vapor viscosity, phase change, and vapor thickness on the critical wave number. For the other limit of a thick vapor, both the liquid and vapor viscosities influence the critical wave number. Finally, the most unstable wavelength is investigated. When the vapor layer is thin, the most unstable wavelength is not affected by phase change. When the vapor layer is thick, however, it increases with the increasing rate of phase change.

  13. Understanding Phase-Change Memory Alloys from a Chemical Perspective.

    PubMed

    Kolobov, A V; Fons, P; Tominaga, J

    2015-09-01

    Phase-change memories (PCM) are associated with reversible ultra-fast low-energy crystal-to-amorphous switching in GeTe-based alloys co-existing with the high stability of the two phases at ambient temperature, a unique property that has been recently explained by the high fragility of the glass-forming liquid phase, where the activation barrier for crystallisation drastically increases as the temperature decreases from the glass-transition to room temperature. At the same time the atomistic dynamics of the phase-change process and the associated changes in the nature of bonding have remained unknown. In this work we demonstrate that key to this behavior is the formation of transient three-center bonds in the excited state that is enabled due to the presence of lone-pair electrons. Our findings additionally reveal previously ignored fundamental similarities between the mechanisms of reversible photoinduced structural changes in chalcogenide glasses and phase-change alloys and offer new insights into the development of efficient PCM materials.

  14. New developments in optical phase-change memory

    NASA Astrophysics Data System (ADS)

    Ovshinsky, Stanford R.; Czubatyj, Wolodymyr

    2001-02-01

    Phase change technology has progressed from the original invention of Ovshinsky to become the leading choice for rewritable optical disks. ECD's early work in phase change materials and methods for operating in a direct overwrite fashion were crucial to the successes that have been achieved. Since the introduction of the first rewritable phase change products in 1991, the market has expanded from CD-RW into rewritable DVD with creative work going on worldwide. Phase change technology is ideally suited to address the continuous demand for increased storage capacity. First, laser beams can be focused to ever-smaller spot sizes using shorter wavelength lasers and higher performance optics. Blue lasers are now commercially viable and high numerical aperture and near field lenses have been demonstrated. Second, multilevel approaches can be used to increase capacity by a factor of three or more with concomitant increases in data transfer rate. In addition, ECD has decreased manufacturing costs through the use of innovative production technology. These factors combine to accelerate the widespread use of phase change technology. As in all our technologies, such as thin film photovoltaics, nickel metal hydride batteries, hydrogen storage systems, fuel cells, electrical memory, etc., we have invented the materials, the products, the production machines and the production processes for high rate, low-cost manufacture.

  15. Atomic structure and pressure-induced phase transformations in a phase-change alloy

    NASA Astrophysics Data System (ADS)

    Xu, Ming

    Phase-change materials exist in at least two phases under the ambient condition. One is the amorphous state and another is crystalline phase. These two phases have vastly different physical properties, such as electrical conductivity, optical reflectivity, mass density, thermal conductivity, etc. The distinct physical properties and the fast transformation between amorphous and crystalline phases render these materials the ability to store information. For example, the DVD and the Blue-ray discs take advantage of the optical reflectivity contrast, and the newly developed solid-state memories make use of the large conductivity difference. In addition, both the amorphous and crystalline phases in phase-change memories (PCMs) are very stable at room temperature, and they are easy to be scaled up in the production of devices with large storage density. All these features make phase-change materials the ideal candidates for the next-generation memories. Despite of the fast development of these new memory materials in industry, many fundamental physics problems underlying these interesting materials are still not fully resolved. This thesis is aiming at solving some of the key issues in phase-change materials. Most of phase-change materials are composed of Ge-Sb-Te constituents. Among all these Ge-Sb-Te based materials, Ge2Sb2Te5 (GST) has the best performance and has been frequently studied as a prototypical phase-change material. The first and foremost issue is the structure of the two functioning phases. In this thesis, we investigate the unique atomic structure and bonding nature of amorphous GST (a-GST) and crystalline GST ( c-GST), using ab initio tools and X-ray diffraction (XRD) methods. Their local structures and bonding scenarios are then analyzed using electronic structure calculations. In order to gain insight into the fast phase transformation mechanism, we also carried out a series of high-pressure experiments on GST. Several new polymorphs and their

  16. Dielectric properties of amorphous phase-change materials

    NASA Astrophysics Data System (ADS)

    Chen, C.; Jost, P.; Volker, H.; Kaminski, M.; Wirtssohn, M.; Engelmann, U.; Krüger, K.; Schlich, F.; Schlockermann, C.; Lobo, R. P. S. M.; Wuttig, M.

    2017-03-01

    The dielectric function of several amorphous phase-change materials has been determined by employing a combination of impedance spectroscopy (9 kHz-3 GHz) and optical spectroscopy from the far- (20 c m-1 , 0.6 THz) to the near- (12 000 c m-1 , 360 THz) infrared, i.e., from the DC limit to the first interband transition. While phase-change materials undergo a change from covalent bonding to resonant bonding on crystallization, the amorphous and crystalline phases of ordinary chalcogenide semiconductors are both governed by virtually the same covalent bonds. Here, we study the dielectric properties of amorphous phase-change materials on the pseudobinary line between GeTe and S b2T e3 . These data provide important insights into the charge transport and the nature of bonding in amorphous phase-change materials. No frequency dependence of permittivity and conductivity is discernible in the impedance spectroscopy measurements. Consequently, there are no dielectric relaxations. The frequency-independent conductivity is in line with charge transport via extended states. The static dielectric constant significantly exceeds the optical dielectric constant. This observation is corroborated by transmittance measurements in the far infrared, which show optical phonons. From the intensity of these phonon modes, a large Born effective charge is derived. Nevertheless, it is known that crystalline phase-change materials such as GeTe possess even significantly larger Born effective charges. Crystallization is hence accompanied by a huge increase in the Born effective charge, which reveals a significant change of bonding upon crystallization. In addition, a clear stoichiometry trend in the static dielectric constant along the pseudobinary line between GeTe and S b2T e3 has been identified.

  17. Optical response of phase change material for metasurface (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Chu, Cheng Hung; Tseng, Ming Lun; Chen, Jie; Wu, Hui Jun; Wang, Hsiang-Chu; Chen, Ting-Yu; Tsai, Din Ping

    2016-09-01

    Phase change materials are used as the recording layer in optical data storage, electronic storage and nanolithography due to the enormous physical difference between crystalline and amorphous states. In recent years, they are demonstrated to exploit in various tunable plasmonic devices, such as perfect absorber, planar lenses, plasmonic antenna, Fano resonance and so on. However, in these researches, the phase change material merely plays a role as a refractive index switchable substrate. In this paper, we study the intrinsic optical properties of phase change material Ge2Sb2Te5 (GST) in the near-infrared regime. A clear insight into the dipole resonance system of GST is provided. The reflection phase retardation and intensity of each unit cells depending on the phase state and geometry are estimated. Further, we introduce the concept of reconfigurable gradient metasurface, which has different anomalous reflection angles by switching the combination of nanorods with different geometries and phase states. The research has great potential in the area of tunable metamaterial device (metadevice) in the future.

  18. A Study on Phase Changes of Heterogeneous Composite Materials

    NASA Astrophysics Data System (ADS)

    Hirasawa, Yoshio; Saito, Akio; Takegoshi, Eisyun

    In this study, a phase change process in heterogeneous composite materials which consist of water and coiled copper wires as conductive solid is investigated by four kinds of typical calculation models : 1) model-1 in which the effective thermal conductivity of the composite material is used, 2) model-2 in which a fin metal acts for many conductive solids, 3) model-3 in which the effective thermal conductivities between nodes are estimated and three-dimensional calculation is performed, 4) model-4 proposed by authors in the previous paper in which effective thermal conductivity is not needed. Consequently, model-1 showed the phase change rate considerably lower than the experimental results. Model-2 gave the larger amount of the phase change rate. Model-3 agreed well with the experiment in the case of small coil diameter and relatively large Vd. Model-4 showed a very well agreement with the experiment in the range of this study.

  19. Microcapsule Buckling Triggered by Compression-Induced Interfacial Phase Change.

    PubMed

    Salmon, Andrew Roy; Parker, Richard M; Groombridge, Alexander S; Maestro, Armando; Coulston, Roger J; Hegemann, Jonas; Kierfeld, Jan; Scherman, Oren A; Abell, Chris

    2016-10-04

    There is an emerging trend towards the fabrication of microcapsules at liquid interfaces. In order to control the parameters of such capsules, the interfacial processes governing their formation must be understood. Here, poly(vinyl alcohol) films are assembled at the interface of water-in-oil microfluidic droplets. The polymer is cross-linked using cucurbit[8]uril ternary supramolecular complexes. It is shown that compression-induced phase change causes the onset of buckling in the interfacial film. On evaporative compression, the interfacial film both increases in density and thickens, until it reaches a critical density and a phase change occurs. We show that this increase in density can be simply related to the film Poisson ratio and area compression. This description captures fundamentals of many compressive interfacial phase changes and can also explain the observation of a fixed thickness-to-radius ratio at buckling, (T/R)buck.

  20. Zero-static-power phase-change optical modulator.

    PubMed

    Jafari, Mohsen; Rais-Zadeh, Mina

    2016-03-15

    This Letter presents an innovative design of an electro-optical modulator using germanium telluride (GeTe) phase change material with an integrated nano-heater. The refractive index and the electrical conductivity of GeTe significantly change as the GeTe goes though the crystallographic phase change. Amorphization and crystallization of GeTe is achieved using the Joule heating method by passing current through an array of metal gratings, where GeTe fills the slits between the metal lines. These metal slits also increase the contrast between the amorphous (on) and crystalline (off) phases of the modulator by having extraordinary transmission and reflection response based on interactions of surface plasmon polaritons (SPPs) with the incoming light. The modulator is designed for 1550 nm wavelength, where GeTe is transparent in the amorphous phase and provides high optical on/off contrast. The metal-insulator-metal (MIM) is designed in such a way to only support SPP excitation when GeTe is crystalline and slit resonance when it is amorphous to increase the modulation index. The modulator is stable in both phases with higher than 12 dB change in transmission with zero static power consumption at room temperature.

  1. Finite-element model for phase-change recording

    NASA Astrophysics Data System (ADS)

    Brusche, J. H.; Segal, A.; Urbach, H. P.

    2005-04-01

    The finite-element method is applied to model phase-change recording in a grooved recording stack. A rigorous model for the scattering of a three-dimensional focused spot by a one-dimensional periodic grating is used to determine the absorbed light in a three-dimensional region inside the phase-change layer. The optical model is combined with a three-dimensional thermal model to compute the temperature distribution. Land and groove recording and polarization dependence are studied, and the model is applied to the Blu-ray Disc.

  2. Lightweight Phase-Change Material For Solar Power

    NASA Technical Reports Server (NTRS)

    Stark, Philip

    1993-01-01

    Lightweight panels containing phase-change materials developed for use as heat-storage elements of compact, lightweight, advanced solar dynamic power system. During high insolation, heat stored in panels via latent heat of fusion of phase-change material; during low insolation, heat withdrawn from panels. Storage elements consist mainly of porous carbon-fiber structures imbued with germanium. Developed for use aboard space station in orbit around Earth, also adapted to lightweight, compact, portable solar-power systems for use on Earth.

  3. Inserting Phase Change Lines into Microsoft Excel® Graphs.

    PubMed

    Dubuque, Erick M

    2015-10-01

    Microsoft Excel® is a popular graphing tool used by behavior analysts to visually display data. However, this program is not always friendly to the graphing conventions used by behavior analysts. For example, adding phase change lines has typically been a cumbersome process involving the insertion of line objects that do not move when new data is added to a graph. The purpose of this article is to describe a novel way to add phase change lines that move when new data is added and when graphs are resized.

  4. Lightweight Phase-Change Material For Solar Power

    NASA Technical Reports Server (NTRS)

    Stark, Philip

    1993-01-01

    Lightweight panels containing phase-change materials developed for use as heat-storage elements of compact, lightweight, advanced solar dynamic power system. During high insolation, heat stored in panels via latent heat of fusion of phase-change material; during low insolation, heat withdrawn from panels. Storage elements consist mainly of porous carbon-fiber structures imbued with germanium. Developed for use aboard space station in orbit around Earth, also adapted to lightweight, compact, portable solar-power systems for use on Earth.

  5. Using adversary text to detect adversary phase changes.

    SciTech Connect

    Speed, Ann Elizabeth; Doser, Adele Beatrice; Warrender, Christina E.

    2009-05-01

    The purpose of this work was to help develop a research roadmap and small proof ofconcept for addressing key problems and gaps from the perspective of using text analysis methods as a primary tool for detecting when a group is undergoing a phase change. Self- rganizing map (SOM) techniques were used to analyze text data obtained from the tworld-wide web. Statistical studies indicate that it may be possible to predict phase changes, as well as detect whether or not an example of writing can be attributed to a group of interest.

  6. Phase change material for temperature control and material storage

    NASA Technical Reports Server (NTRS)

    Wessling, Jr., Francis C. (Inventor); Blackwood, James M. (Inventor)

    2011-01-01

    A phase change material comprising a mixture of water and deuterium oxide is described, wherein the mole fraction of deuterium oxide is selected so that the mixture has a selected phase change temperature within a range between 0.degree. C. and 4.degree. C. The mixture is placed in a container and used for passive storage and transport of biomaterials and other temperature sensitive materials. Gels, nucleating agents, freezing point depression materials and colorants may be added to enhance the characteristics of the mixture.

  7. Extracting changes in air temperature using acoustic coda phase delays.

    PubMed

    Marcillo, Omar; Arrowsmith, Stephen; Whitaker, Rod; Morton, Emily; Scott Phillips, W

    2014-10-01

    Blast waves produced by 60 high-explosive detonations were recorded at short distances (few hundreds of meters); the corresponding waveforms show charge-configuration independent coda-like features (i.e., similar shapes, amplitudes, and phases) lasting several seconds. These features are modeled as reflected and/or scattered waves by acoustic reflectors/scatters surrounding the explosions. Using explosion pairs, relative coda phase delays are extracted and modeled as changes in sound speed due to changes in air temperature. Measurements from nearby weather towers are used for validation.

  8. Vibration damping and heat transfer using material phase changes

    DOEpatents

    Kloucek, Petr; Reynolds, Daniel R.

    2009-03-24

    A method and apparatus wherein phase changes in a material can dampen vibrational energy, dampen noise and facilitate heat transfer. One embodiment includes a method for damping vibrational energy in a body. The method comprises attaching a material to the body, wherein the material comprises a substrate, a shape memory alloy layer, and a plurality of temperature change elements. The method further comprises sensing vibrations in the body. In addition, the method comprises indicating to at least a portion of the temperature change elements to provide a temperature change in the shape memory alloy layer, wherein the temperature change is sufficient to provide a phase change in at least a portion of the shape memory alloy layer, and further wherein the phase change consumes a sufficient amount of kinetic energy to dampen at least a portion of the vibrational energy in the body. In other embodiments, the shape memory alloy layer is a thin film. Additional embodiments include a sensor connected to the material.

  9. Vibration damping and heat transfer using material phase changes

    NASA Technical Reports Server (NTRS)

    Kloucek, Petr (Inventor); Reynolds, Daniel R. (Inventor)

    2009-01-01

    A method and apparatus wherein phase changes in a material can dampen vibrational energy, dampen noise and facilitate heat transfer. One embodiment includes a method for damping vibrational energy in a body. The method comprises attaching a material to the body, wherein the material comprises a substrate, a shape memory alloy layer, and a plurality of temperature change elements. The method further comprises sensing vibrations in the body. In addition, the method comprises indicating to at least a portion of the temperature change elements to provide a temperature change in the shape memory alloy layer, wherein the temperature change is sufficient to provide a phase change in at least a portion of the shape memory alloy layer, and further wherein the phase change consumes a sufficient amount of kinetic energy to dampen at least a portion of the vibrational energy in the body. In other embodiments, the shape memory alloy layer is a thin film. Additional embodiments include a sensor connected to the material.

  10. Compensating temperature-induced ultrasonic phase and amplitude changes

    NASA Astrophysics Data System (ADS)

    Gong, Peng; Hay, Thomas R.; Greve, David W.; Junker, Warren R.; Oppenheim, Irving J.

    2016-04-01

    In ultrasonic structural health monitoring (SHM), environmental and operational conditions, especially temperature, can significantly affect the propagation of ultrasonic waves and thus degrade damage detection. Typically, temperature effects are compensated using optimal baseline selection (OBS) or optimal signal stretch (OSS). The OSS method achieves compensation by adjusting phase shifts caused by temperature, but it does not fully compensate phase shifts and it does not compensate for accompanying signal amplitude changes. In this paper, we develop a new temperature compensation strategy to address both phase shifts and amplitude changes. In this strategy, OSS is first used to compensate some of the phase shifts and to quantify the temperature effects by stretching factors. Based on stretching factors, empirical adjusting factors for a damage indicator are then applied to compensate for the temperature induced remaining phase shifts and amplitude changes. The empirical adjusting factors can be trained from baseline data with temperature variations in the absence of incremental damage. We applied this temperature compensation approach to detect volume loss in a thick wall aluminum tube with multiple damage levels and temperature variations. Our specimen is a thick-walled short tube, with dimensions closely comparable to the outlet region of a frac iron elbow where flow-induced erosion produces the volume loss that governs the service life of that component, and our experimental sequence simulates the erosion process by removing material in small damage steps. Our results show that damage detection is greatly improved when this new temperature compensation strategy, termed modified-OSS, is implemented.

  11. Unusual crystallization behavior in Ga-Sb phase change alloys

    SciTech Connect

    Putero, Magali Coulet, Marie-Vanessa; Ouled-Khachroum, Toufik; Muller, Christophe; Baehtz, Carsten; Raoux, Simone

    2013-12-01

    Combined in situ X-ray scattering techniques using synchrotron radiation were applied to investigate the crystallization behavior of Sb-rich Ga-Sb alloys. Measurements of the sheet resistance during heating indicated a reduced crystallization temperature with increased Sb content, which was confirmed by in situ X-ray diffraction. The electrical contrast increased with increasing Sb content and the resistivities in both the amorphous and crystalline phases decreased. It was found that by tuning the composition between Ga:Sb = 9:91 (in at.%) and Ga:Sb = 45:55, the change in mass density upon crystallization changes from an increase in mass density which is typical for most phase change materials to a decrease in mass density. At the composition of Ga:Sb = 30:70, no mass density change is observed which should be very beneficial for phase change random access memory (PCRAM) applications where a change in mass density during cycling is assumed to cause void formation and PCRAM device failure.

  12. Multilevel data storage in multilayer phase change material

    NASA Astrophysics Data System (ADS)

    Lu, Yegang; Wang, Miao; Song, Sannian; Xia, Mengjiao; Jia, Yu; shen, Xiang; Wang, Guoxiang; Dai, Shixun; Song, Zhitang

    2016-10-01

    Superlattice-like GaSb/Sb4Te phase change film was proposed for multilevel phase change memory with the feature of three stable resistance states. Two distinct transition temperatures of around 170 and 230 °C were observed in the superlattice-like GaSb/Sb4Te thin film. Under elevated temperature, the precipitated rhombohedral Sb phase was found in the Sb4Te layer, which was followed by the crystallization of rhombohedral Sb2Te3, whereas the GaSb layer remained almost in the amorphous state except the impinged Sb grains. The formation of percolation path for crystallization in the GaSb layer can account for the multilevel resistance states. For the GaSb/Sb4Te-based device, the reversibly electrical switching was realized under the electrical pulse as short as 10 ns, and the endurance was achieved at least 105 cycles among different resistance states.

  13. High-pressure Raman spectroscopy of phase change materials

    SciTech Connect

    Hsieh, Wen-Pin Mao, Wendy L.; Zalden, Peter; Wuttig, Matthias; Lindenberg, Aaron M.

    2013-11-04

    We used high-pressure Raman spectroscopy to study the evolution of vibrational frequencies of the phase change materials (PCMs) Ge{sub 2}Sb{sub 2}Te{sub 5}, GeSb{sub 2}Te{sub 4}, and SnSb{sub 2}Te{sub 4}. We found that the critical pressure for triggering amorphization in the PCMs decreases with increasing vacancy concentration, demonstrating that the presence of vacancies, rather than differences in the atomic covalent radii, is crucial for pressure-induced amorphization in PCMs. Compared to the as-deposited amorphous phase, the pressure-induced amorphous phase has a similar vibrational spectrum but requires much lower laser power to transform into the crystalline phase, suggesting different kinetics of crystallization, which may have implications for applications of PCMs in non-volatile data storage.

  14. Phase-change devices for simultaneous optical-electrical applications.

    PubMed

    Au, Yat-Yin; Bhaskaran, Harish; Wright, C David

    2017-08-29

    We present a viable pathway to the design and characterization of phase-change devices operating in a mixed-mode optical-electrical, or optoelectronic, manner. Such devices have potential applications ranging from novel displays to optically-gated switches to reconfigurable metamaterials-based devices. With this in mind, a purpose-built optoelectronics probe station capable of simultaneous optical-electrical excitation and simultaneous optical-electrical response measurement has been designed and constructed. Two prototype phase-change devices that might exploit simultaneous optical and electrical effects and/or require simultaneous optical and electrical characterisation, namely a mixed-mode cross-bar type structure and a microheater-based structure, have been designed, fabricated and characterized. The microheater-based approach was shown to be capable of successful thermally-induced cycling, between amorphous and crystalline states, of large-area phase-change devices, making it attractive for practicable pixel fabrication in phase-change display applications.

  15. Phase Change Permeation Technology For Environmental Control Life Support Systems

    NASA Technical Reports Server (NTRS)

    Wheeler, Raymond M.

    2014-01-01

    Use of a phase change permeation membrane (Dutyion [Trademark]) to passively and selectively mobilize water in microgravity to enable improved water recovery from urine/brine for Environment Control and Life Support Systems (ECLSS) and water delivery to plans for potential use in microgravity.

  16. Kodak phase-change media for optical tape applications

    NASA Technical Reports Server (NTRS)

    Tyan, Yuan-Sheng; Preuss, Donald R.; Olin, George R.; Vazan, Fridrich; Pan, Kee-Chuan; Raychaudhuri, Pranab. K.

    1993-01-01

    The SbInSn phase-change write-once optical medium developed by Eastman Kodak Company is particularly suitable for development into the next generation optical tape media. Its performance for optical recording has already been demonstrated in some of the highest performance optical disk systems. Some of the key performance features are presented.

  17. New Actuator Utilizing Phase Change of Functional Fluids

    NASA Astrophysics Data System (ADS)

    Tanaka, Chigusa; Mai, Jianqiang; Nakagawa, Masamichi; Oshima, Shuzo; Yamane, Ryuichiro; Park, Myeng-Kwan

    This paper proposes a new actuator utilizing the phase change of the ER fluid. The dielectric coolant was used for the solvent and silica gel particles for the dispersion particle. The dynamic characteristics of the actuator was determined for the several patterns of the working conditions.

  18. Method for preparing polyolefin composites containing a phase change material

    DOEpatents

    Salyer, Ival O.

    1990-01-01

    A composite useful in thermal energy storage, said composite being formed of a polyolefin matrix having a phase change material such as a crystalline alkyl hydrocarbon incorporated therein. The composite is useful in forming pellets, sheets or fibers having thermal energy storage characteristics; methods for forming the composite are also disclosed.

  19. Ultrafast characterization of phase-change material crystallization properties in the melt-quenched amorphous phase.

    PubMed

    Jeyasingh, Rakesh; Fong, Scott W; Lee, Jaeho; Li, Zijian; Chang, Kuo-Wei; Mantegazza, Davide; Asheghi, Mehdi; Goodson, Kenneth E; Wong, H-S Philip

    2014-06-11

    Phase change materials are widely considered for application in nonvolatile memories because of their ability to achieve phase transformation in the nanosecond time scale. However, the knowledge of fast crystallization dynamics in these materials is limited because of the lack of fast and accurate temperature control methods. In this work, we have developed an experimental methodology that enables ultrafast characterization of phase-change dynamics on a more technologically relevant melt-quenched amorphous phase using practical device structures. We have extracted the crystallization growth velocity (U) in a functional capped phase change memory (PCM) device over 8 orders of magnitude (10(-10) < U < 10(-1) m/s) spanning a wide temperature range (415 < T < 580 K). We also observed direct evidence of non-Arrhenius crystallization behavior in programmed PCM devices at very high heating rates (>10(8) K/s), which reveals the extreme fragility of Ge2Sb2Te5 in its supercooled liquid phase. Furthermore, these crystallization properties were studied as a function of device programming cycles, and the results show degradation in the cell retention properties due to elemental segregation. The above experiments are enabled by the use of an on-chip fast heater and thermometer called as microthermal stage (MTS) integrated with a vertical phase change memory (PCM) cell. The temperature at the PCM layer can be controlled up to 600 K using MTS and with a thermal time constant of 800 ns, leading to heating rates ∼10(8) K/s that are close to the typical device operating conditions during PCM programming. The MTS allows us to independently control the electrical and thermal aspects of phase transformation (inseparable in a conventional PCM cell) and extract the temperature dependence of key material properties in real PCM devices.

  20. Dynamic observation of phase transformation behaviors in indium(III) selenide nanowire based phase change memory.

    PubMed

    Huang, Yu-Ting; Huang, Chun-Wei; Chen, Jui-Yuan; Ting, Yi-Hsin; Lu, Kuo-Chang; Chueh, Yu-Lun; Wu, Wen-Wei

    2014-09-23

    Phase change random access memory (PCRAM) has been extensively investigated for its potential applications in next-generation nonvolatile memory. In this study, indium(III) selenide (In2Se3) was selected due to its high resistivity ratio and lower programming current. Au/In2Se3-nanowire/Au phase change memory devices were fabricated and measured systematically in an in situ transmission electron microscope to perform a RESET/SET process under pulsed and dc voltage swept mode, respectively. During the switching, we observed the dynamic evolution of the phase transformation process. The switching behavior resulted from crystalline/amorphous change and revealed that a long pulse width would induce the amorphous or polycrystalline state by different pulse amplitudes, supporting the improvement of the writing speed, retention, and endurance of PCRAM.

  1. Irreversible altering of crystalline phase of phase-change Ge-Sb thin films

    SciTech Connect

    Krusin-Elbaum, L.; Shakhvorostov, D.; Cabral, C. Jr.; Raoux, S.; Jordan-Sweet, J. L.

    2010-03-22

    The stability of the crystalline phase of binary phase-change Ge{sub x}Sb{sub 1-x} films is investigated over a wide range of Ge content. From Raman spectroscopy we find the Ge-Sb crystalline structure irreversibly altered after exposure to a laser beam. We show that with increasing beam intensity/temperature Ge agglomerates and precipitates out in the amount growing with x. A simple empirical relation links Ge precipitation temperature T{sub Ge}{sup p} to the rate of change dT{sub cryst}/dx of crystallization, with the precipitation easiest on the mid-range x plateau, where T{sub cryst} is nearly constant. Our findings point to a preferable 15% < or approx. x < 50% window, that may achieve the desired cycling/archival properties of a phase-change cell.

  2. An ALE Finite Element Approach for Two-Phase Flow with Phase Change

    NASA Astrophysics Data System (ADS)

    Gros, Erik; Anjos, Gustavo; Thome, John; Ltcm Team; Gesar Team

    2016-11-01

    In this work, two-phase flow with phase change is investigated through the Finite Element Method (FEM) in the Arbitrary Lagrangian-Eulerian (ALE) framework. The equations are discretized on an unstructured mesh where the interface between the phases is explicitly defined as a sub-set of the mesh. The two-phase interface position is described by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The methodology proposed for computing the curvature leads to very accurate results with moderate programming effort and computational costs. Such a methodology can be employed to study accurately many two-phase flow and heat transfer problems in industry such as oil extraction and refinement, design of refrigeration systems, modelling of microfluidic and biological systems and efficient cooling of electronics for computational purposes. The latter is the principal aim of the present research. The numerical results are discussed and compared to analytical solutions and reference results, thereby revealing the capability of the proposed methodology as a platform for the study of two-phase flow with phase change.

  3. Thermoelectric Effects in Simulations of Phase Change Memory Mushroom Cells

    NASA Astrophysics Data System (ADS)

    Faraclas, Azer; Bakan, Gokhan; Gokirmak, Ali; Silva, Helena

    2012-02-01

    Phase change memory is a potential candidate for the future of high-speed non-volatile memory, however significant improvements in cell design is crucial for its success in the mainstream market. Due to the asymmetric geometry of phase change mushroom cells and the high temperature gradients generated, thermoelectric effects play a key role in determining energy consumption, cell performance, and reliability. In this study, rotationally symmetric 2D finite element simulations using COMSOL Multiphysics are implemented for GeSbTe (GST). Temperature dependent material parameters (electrical conductivity, thermal conductivity, heat capacity, and Seebeck coefficient) are included in the model for accuracy. Switching the direction of current shows a large change in peak molten volume within the cell, as well as current and power consumption.

  4. Irradiation induced structural change in Mo2Zr intermetallic phase

    DOE PAGES

    Gan, J.; Keiser, Jr., D. D.; Miller, B. D.; ...

    2016-05-14

    The Mo2Zr phase has been identified as a major interaction product at the interface of U-10Mo and Zr. Transmission electron microscopy in-situ irradiation with Kr ions at 200 °C with doses up to 2.0E+16 ions/cm2 was carried out to investigate the radiation stability of the Mo2Zr. The Mo2Zr undergoes a radiation-induced structural change, from a large cubic (cF24) to a small cubic (cI2), along with an estimated 11.2% volume contraction without changing its composition. The structural change begins at irradiation dose below 1.0E+14 ions/cm2. Furthermore, the transformed Mo2Zr phase demonstrates exceptional radiation tolerance with the development of dislocations without bubblemore » formation.« less

  5. Three phase partitioning leads to subtle structural changes in proteins.

    PubMed

    Rather, Gulam Mohmad; Gupta, Munishwar Nath

    2013-09-01

    Three phase partitioning consists of precipitation of proteins due to simultaneous presence of ammonium sulphate and t-butanol. The technique has been successfully used for purification and refolding of proteins. There are however indications that the structures of proteins subjected to three phase partitioning are different from native structure of proteins. Taking several proteins, the present work examines the structural changes in proteins by comparing their thermal stabilities, secondary structure contents, surface hydrophobicities, hydrodynamic radii and solubilities in the presence of ammonium sulphate. The results show that while the nature or extent of structural changes may vary, in all the cases the changes are rather subtle and not drastic in nature. Hence, the technique can be safely used for protein purification and refolding.

  6. Phase Transformation Volume Change Control of Strain and Instability Mechanisms

    NASA Astrophysics Data System (ADS)

    Green, H. W.

    2011-12-01

    Phase transformations that are accompanied by significant change in volume self-organize the transformation process under stress to enhance strain and/or decrease stress. When the kinetics of the reaction are reasonably rapid, this occurs by nucleation and growth of phase(s) on grain boundaries of appropriate orientation to facilitate strain. When the kinetics of reaction are sluggish (ratio of nucleation rate to growth rate >> 1) and the reaction is polymorphic and exothermic, under specific conditions this process can lead to shearing instability in which the volume change of reaction drives runaway nucleation at stress concentrations leading to macroscopic faulting. Under these conditions, the detailed processes and microstructures produced depend on the sign of volume change but the failure is very similar whether volume change is positive or negative. The microstructures confirm that the mesoscale physics of this process (self-organization of primary features and nucleation/propagation of a fault) is the same as for brittle shear fracture, despite the large difference in the fundamental microscopic physics (formation of nanocrystalline microlenses instead of tensile cracks, and fault propagation by grain-boundary sliding rather than frictional sliding). When volume change is negative and the kinetics of reaction are less sluggish (ratio of nucleation rate to growth rate of order 1), nucleation of the new (denser) phase occurs preferentially on grain boundaries normal to maximum compression and new crystals nucleated on any orientation of grain boundary grow parallel to maximum compression. The result is stylolite-like volume loss normal to maximum compression. Observations of polyphase metamorphic rocks suggest that similar creep can occur during prograde metamorphism by nucleation of more-dense phases and less-dense phases on different populations of phase-boundary orientations such that the overall pattern achieves a macroscopic strain by volume transfer

  7. Simulations of Lithium-Magnetite Electrodes Incorporating Phase Change

    DOE PAGES

    Knehr, Kevin W.; Cama, Christina A.; Brady, Nicholas W.; ...

    2017-04-09

    In this work, the phase changes occurring in magnetite (Fe3O4) during lithiation and voltage recovery experiments are modeled using a model that simulates the electrochemical performance of a Fe3O4 electrode by coupling the lithium transport in the agglomerate and nano-crystal length-scales to thermodynamic and kinetic expressions. Phase changes are described using kinetic expressions based on the Avrami theory for nucleation and growth. Also, simulated results indicate that the slow, linear voltage change observed at long times during the voltage recovery experiments can be attributed to a slow phase change from α-LixFe3O4 to β-Li4Fe3O4. In addition, the long voltage plateau atmore » ~1.2 V observed during lithiation of electrodes is attributed to conversion from α-LixFe3O4 to γ-(4 Li2O + 3 Fe). Simulations for the lithiation of 6 and 32 nm Fe3O4 suggest the rate of conversion to γ-(4 Li2O + 3 Fe) decreases with decreasing crystal size.« less

  8. Disorder-induced localization in crystalline phase-change materials.

    PubMed

    Siegrist, T; Jost, P; Volker, H; Woda, M; Merkelbach, P; Schlockermann, C; Wuttig, M

    2011-03-01

    Localization of charge carriers in crystalline solids has been the subject of numerous investigations over more than half a century. Materials that show a metal-insulator transition without a structural change are therefore of interest. Mechanisms leading to metal-insulator transition include electron correlation (Mott transition) or disorder (Anderson localization), but a clear distinction is difficult. Here we report on a metal-insulator transition on increasing annealing temperature for a group of crystalline phase-change materials, where the metal-insulator transition is due to strong disorder usually associated only with amorphous solids. With pronounced disorder but weak electron correlation, these phase-change materials form an unparalleled quantum state of matter. Their universal electronic behaviour seems to be at the origin of the remarkable reproducibility of the resistance switching that is crucial to their applications in non-volatile-memory devices. Controlling the degree of disorder in crystalline phase-change materials might enable multilevel resistance states in upcoming storage devices.

  9. Phase field modeling of rapid crystallization in the phase-change material AIST

    NASA Astrophysics Data System (ADS)

    Tabatabaei, Fatemeh; Boussinot, Guillaume; Spatschek, Robert; Brener, Efim A.; Apel, Markus

    2017-07-01

    We carry out phase field modeling as a continuum simulation technique in order to study rapid crystallization processes in the phase-change material AIST (Ag4In3Sb67Te26). In particular, we simulate the spatio-temporal evolution of the crystallization of a molten area of the phase-change material embedded in a layer stack. The simulation model is adapted to the experimental conditions used for recent measurements of crystallization rates by a laser pulse technique. Simulations are performed for substrate temperatures close to the melting temperature of AIST down to low temperatures when an amorphous state is involved. The design of the phase field model using the thin interface limit allows us to retrieve the two limiting regimes of interface controlled (low temperatures) and thermal transport controlled (high temperatures) dynamics. Our simulations show that, generically, the crystallization velocity presents a maximum in the intermediate regime where both the interface mobility and the thermal transport, through the molten area as well as through the layer stack, are important. Simulations reveal the complex interplay of all different contributions. This suggests that the maximum switching velocity depends not only on material properties but also on the precise design of the thin film structure into which the phase-change material is embedded.

  10. Non-equilibrium model of two-phase porous media flow with phase change

    NASA Astrophysics Data System (ADS)

    Cueto-Felgueroso, L.; Fu, X.; Juanes, R.

    2014-12-01

    The efficient simulation of multi-phase multi-component flow through geologic porous media is challenging and computationally intensive, yet quantitative modeling of these processes is essential in engineering and the geosciences. Multiphase flow with phase change and complex phase behavior arises in numerous applications, including enhanced oil recovery, steam injection in groundwater remediation, geologic CO2 storage and enhanced geothermal energy systems. A challenge of multiphase compositional simulation is that the number of existing phases varies with position and time, and thus the number of state variables in the saturation-based conservation laws is a function of space and time. The tasks of phase-state identification and determination of the composition of the different phases are performed assuming local thermodynamic equilibrium. Here we investigate a thermodynamically consistent formulation for non-isothermal two-phase flow, in systems where the hypothesis of instantaneous local equilibrium does not hold. Non-equilibrium effects are important in coarse-scale simulations where the assumption of complete mixing in each gridblock is not realistic. We apply our model to steam injection in water-saturated porous media.

  11. Ultrafast phase-change logic device driven by melting processes.

    PubMed

    Loke, Desmond; Skelton, Jonathan M; Wang, Wei-Jie; Lee, Tae-Hoon; Zhao, Rong; Chong, Tow-Chong; Elliott, Stephen R

    2014-09-16

    The ultrahigh demand for faster computers is currently tackled by traditional methods such as size scaling (for increasing the number of devices), but this is rapidly becoming almost impossible, due to physical and lithographic limitations. To boost the speed of computers without increasing the number of logic devices, one of the most feasible solutions is to increase the number of operations performed by a device, which is largely impossible to achieve using current silicon-based logic devices. Multiple operations in phase-change-based logic devices have been achieved using crystallization; however, they can achieve mostly speeds of several hundreds of nanoseconds. A difficulty also arises from the trade-off between the speed of crystallization and long-term stability of the amorphous phase. We here instead control the process of melting through premelting disordering effects, while maintaining the superior advantage of phase-change-based logic devices over silicon-based logic devices. A melting speed of just 900 ps was achieved to perform multiple Boolean algebraic operations (e.g., NOR and NOT). Ab initio molecular-dynamics simulations and in situ electrical characterization revealed the origin (i.e., bond buckling of atoms) and kinetics (e.g., discontinuouslike behavior) of melting through premelting disordering, which were key to increasing the melting speeds. By a subtle investigation of the well-characterized phase-transition behavior, this simple method provides an elegant solution to boost significantly the speed of phase-change-based in-memory logic devices, thus paving the way for achieving computers that can perform computations approaching terahertz processing rates.

  12. Dynamically Reconfigurable Metadevice Employing Nanostructured Phase-Change Materials.

    PubMed

    Zhu, Zhihua; Evans, Philip G; Haglund, Richard F; Valentine, Jason G

    2017-08-09

    Mastering dynamic free-space spectral control and modulation in the near-infrared (NIR) and optical regimes remains a challenging task that is hindered by the available functional materials at high frequencies. In this work, we have realized an efficient metadevice capable of spectral control by minimizing the thermal mass of a vanadium dioxide phase-change material (PCM) and placing the PCM at the feed gap of a bow-tie field antenna. The device has an experimentally measured tuning range of up to 360 nm in the NIR and a modulation depth of 33% at the resonant wavelength. The metadevice is configured for integrated and local heating, leading to faster switching and more precise spatial control compared with devices based on phase-change thin films. We envisage that the combined advantages of this device will open new opportunities for signal processing, memory, security, and holography at optical frequencies.

  13. Nanoscale phase change memory with graphene ribbon electrodes

    NASA Astrophysics Data System (ADS)

    Behnam, Ashkan; Xiong, Feng; Cappelli, Andrea; Wang, Ning C.; Carrion, Enrique A.; Hong, Sungduk; Dai, Yuan; Lyons, Austin S.; Chow, Edmond K.; Piccinini, Enrico; Jacoboni, Carlo; Pop, Eric

    2015-09-01

    Phase change memory (PCM) devices are known to reduce in power consumption as the bit volume and contact area of their electrodes are scaled down. Here, we demonstrate two types of low-power PCM devices with lateral graphene ribbon electrodes: one in which the graphene is patterned into narrow nanoribbons and the other where the phase change material is patterned into nanoribbons. The sharp graphene "edge" contacts enable switching with threshold voltages as low as ˜3 V, low programming currents (<1 μA SET and <10 μA RESET) and OFF/ON resistance ratios >100. Large-scale fabrication with graphene grown by chemical vapor deposition also enables the study of heterogeneous integration and that of variability for such nanomaterials and devices.

  14. Thermal energy storage using a phase change material

    SciTech Connect

    Hamdan, M.A.; Elwerr, F.A.

    1996-12-31

    A two-dimensional melting process of a solid phase change material investigated theoretically. The material contained in a rectangular enclosure heated from one side, while all the other sides are assumed to be adiabatic ones. In this study convection mode was considered to be the dominant mode of heat transfer within the melted region, except within the region very close to the solid surface at the bottom where conduction mode was only taken into considerations. It was found that the obtained results are in good agreement with previous ones. Finally the present analysis was used to predict the melted fraction of the phase change material and hence the amount of stored energy. 8 refs., 8 figs.

  15. Dynamically Reconfigurable Metadevice Employing Nanostructured Phase-Change Materials

    DOE PAGES

    Haglund, Richard F.; Valentine, Jason; Zhu, Zhihua; ...

    2017-07-01

    Mastering dynamic free-space spectral control and modulation in the near-infrared (NIR) and optical regimes remains a challenging task that is hindered by the available functional materials at high frequencies. In this work, we have realized an efficient metadevice capable of spectral control by minimizing the thermal mass of a vanadium dioxide phase-change material (PCM) and placing the PCM at the feed gap of a bow-tie field antenna. The device has an experimentally measured tuning range of up to 360 nm in the NIR and a modulation depth of 33% at the resonant wavelength. The metadevice is configured for integrated andmore » local heating, leading to faster switching and more precise spatial control compared with devices based on phase-change thin films. We envisage that the combined advantages of this device will open new opportunities for signal processing, memory, security, and holography at optical frequencies.« less

  16. Round-Robin Test of Paraffin Phase-Change Material

    NASA Astrophysics Data System (ADS)

    Vidi, S.; Mehling, H.; Hemberger, F.; Haussmann, Th.; Laube, A.

    2015-11-01

    A round-robin test between three institutes was performed on a paraffin phase-change material (PCM) in the context of the German quality association for phase-change materials. The aim of the quality association is to define quality and test specifications for PCMs and to award certificates for successfully tested materials. To ensure the reproducibility and comparability of the measurements performed at different institutes using different measuring methods, a round-robin test was performed. The sample was unknown. The four methods used by the three participating institutes in the round-robin test were differential scanning calorimetry, Calvet calorimetry and three-layer calorimetry. Additionally, T-history measurements were made. The aim of the measurements was the determination of the enthalpy as a function of temperature. The results achieved following defined test specifications are in excellent agreement.

  17. All-dielectric phase-change reconfigurable metasurface

    NASA Astrophysics Data System (ADS)

    Karvounis, Artemios; Gholipour, Behrad; MacDonald, Kevin F.; Zheludev, Nikolay I.

    2016-08-01

    We harness non-volatile, amorphous-crystalline transitions in the chalcogenide phase-change medium germanium antimony telluride (GST) to realize optically-switchable, all-dielectric metamaterials. Nanostructured, subwavelength-thickness films of GST present high-quality resonances that are spectrally shifted by laser-induced structural transitions, providing reflectivity and transmission switching contrast ratios of up to 5:1 (7 dB) at visible/near-infrared wavelengths selected by design.

  18. Inverse heat conduction problem in a phase change memory device

    NASA Astrophysics Data System (ADS)

    Battaglia, Jean-Luc; De, Indrayush; Sousa, Véronique

    2017-01-01

    An invers heat conduction problem is solved considering the thermal investigation of a phase change memory device using the scanning thermal microscopy. The heat transfer model rests on system identification for the probe thermal impedance and on a finite element method for the device thermal impedance. Unknown parameters in the model are then identified using a nonlinear least square algorithm that minimizes the quadratic gap between the measured probe temperature and the simulated one.

  19. Microencapsulated Phase-Change Materials For Storage Of Heat

    NASA Technical Reports Server (NTRS)

    Colvin, David P.

    1989-01-01

    Report describes research on engineering issues related to storage and transport of heat in slurries containing phase-change materials in microscopic capsules. Specific goal of project to develop lightweight, compact, heat-management systems used safely in inhabited areas of spacecraft. Further development of obvious potential of technology expected to lead to commercialization and use in aircraft, electronic equipment, machinery, industrial processes, and other sytems in which requirements for management of heat compete with severe restrictions on weight or volume.

  20. Thermal Performance of Microencapsulated Phase Change Material Slurry

    DTIC Science & Technology

    2008-03-01

    tetradec- ane-containing microcapsules with an average size of 4.4 μm. Yamagishi et al. (1999) obtained empirical data for microencapsulated octadecane ob...MPCM slurry (90 – 150 μm). It should be noted that the mass of an average microcapsule is equal to the mass of microencapsulated PCM and the mass...ER D C TR -0 8 -4 Basic Research/Military Construction Thermal Performance of Microencapsulated Phase Change Material Slurry Jorge L

  1. Thermal Performance of Microencapsulated Phase Change Material Survey

    DTIC Science & Technology

    2008-03-01

    tetradec- ane-containing microcapsules with an average size of 4.4 μm. Yamagishi et al. (1999) obtained empirical data for microencapsulated octadecane ob...MPCM slurry (90 – 150 μm). It should be noted that the mass of an average microcapsule is equal to the mass of microencapsulated PCM and the mass...ER D C TR -0 8 -4 Basic Research/Military Construction Thermal Performance of Microencapsulated Phase Change Material Slurry Jorge L

  2. Voice and speech changes in various phases of menstrual cycle.

    PubMed

    Çelik, Öner; Çelik, Aygen; Ateşpare, Altay; Boyacı, Zerrin; Çelebi, Saban; Gündüz, Tonguç; Aksungar, Fehime Benli; Yelken, Kürşat

    2013-09-01

    The reproductive system in females undergoes a regular cyclic change known as the menstrual cycle. Laryngeal changes are evident and fluctuate systematically during the reproductive years with the menstrual cycle. The impact of estrogens in concert with progesterone produces the characteristics of the female voice, with a fundamental frequency (F(0)) higher than that of male. To characterize changes in voice and speech in adolescent females in different phases of the menstrual cycle--during menstruation, after menstruation, mid-menstrual cycle, and premenstruation. Sixteen adult females who were nonusers of oral contraceptives participated in a cross-sectional study of menstrual cycle influences on voicing and speaking tasks. Acoustic analysis (F(0), intensity, perturbation measurements [jitter and shimmer], and harmonic-to-noise ratio), maximum phonation time (MPT), s/z ratio, and perceptual assessments (grade [G], roughness [R], breathiness [B], asthenia [A], and strain [S] [GRBAS] and Voice Handicap Index-10 [VHI-10]) scales were performed during all phases. None of the acoustic analysis parameters and MPT and s/z ratio measurements revealed statistically significant difference (P > 0.05). Perceptual voice assessment scales either clinician based or patients self-evaluated showed significant differences among phases (P < 0.05). The objective voice analysis methods, such as acoustic analysis, MPT, and s/z ratio, determined no difference; however, the subjective voice analysis methods, such as clinician-based perceptual assessment (GRBAS) and patients self-evaluation (VHI-10) scales, demonstrated significant changes during different phases of menstrual cycle. Copyright © 2013 The Voice Foundation. Published by Mosby, Inc. All rights reserved.

  3. Using Adversary Text to Detect Adversary Phase Changes

    DTIC Science & Technology

    2009-08-10

    government of Sri Lanka . The island of Sri Lanka is approximately 80% Buddhist , and 12% Tamil Hindu . Many Hindus feel that they are persecuted by...of Sri Lanka , commonly referred to as the Tamil Tigers, as a study group. For more than 25 years, the LTTE has been engaged in a civil war with the...signed between the LTTE and the Government of Sri Lanka (GoSL). There were many phase changes exhibited by the Tigers before the ceasefire fully

  4. Microencapsulated Phase-Change Materials For Storage Of Heat

    NASA Technical Reports Server (NTRS)

    Colvin, David P.

    1989-01-01

    Report describes research on engineering issues related to storage and transport of heat in slurries containing phase-change materials in microscopic capsules. Specific goal of project to develop lightweight, compact, heat-management systems used safely in inhabited areas of spacecraft. Further development of obvious potential of technology expected to lead to commercialization and use in aircraft, electronic equipment, machinery, industrial processes, and other sytems in which requirements for management of heat compete with severe restrictions on weight or volume.

  5. Study of large nonlinear change phase in Hibiscus Sabdariffa

    NASA Astrophysics Data System (ADS)

    Trejo-Durán, M.; Alvarado-Méndez, E.; Andrade-Lucio, J. A.; Rojas-Laguna, R.; Vázquez-Guevara, M. A.

    2015-09-01

    High intensities electromagnetic energy interacting with organic media gives rise to nonlinear optical effects. Hibiscus Sabdariffa is a flower whose concentrated solution presents interesting nonlinear optical properties. This organic material shows an important self-phase modulation with changes bigger than 2π. We present a diffraction ring patterns study of the Hibiscus Sabdariffa solution. Numerical results of transmittance, with refraction and simultaneous absorption, are shown.

  6. Phase-Changing Ionic Liquids: CO2 Capture with Ionic Liquids Involving Phase Change

    SciTech Connect

    2010-07-01

    IMPACCT Project: Notre Dame is developing a new CO2 capture process that uses special ionic liquids (ILs) to remove CO2 from the gas exhaust of coal-fired power plants. ILs are salts that are normally liquid at room temperature, but Notre Dame has discovered a new class of ILs that are solid at room temperature and change to liquid when they bind to CO2. Upon heating, the CO2 is released for storage, and the ILs re-solidify and donate some of the heat generated in the process to facilitate further CO2 release. These new ILs can reduce the energy required to capture CO2 from the exhaust stream of a coal-fired power plant when compared to state-ofthe- art technology.

  7. Epigenetic Regulation of Vegetative Phase Change in Arabidopsis

    PubMed Central

    Xu, Mingli; Hu, Tieqiang; Smith, Michael R.; Poethig, R. Scott

    2016-01-01

    Vegetative phase change in flowering plants is regulated by a decrease in the level of miR156. The molecular mechanism of this temporally regulated decrease in miR156 expression is still unknown. Most of the miR156 in Arabidopsis thaliana shoots is produced by MIR156A and MIR156C. We found that the downregulation of these genes during vegetative phase change is associated with an increase in their level of histone H3 lysine 27 trimethylation (H3K27me3) and requires this chromatin modification. The increase in H3K27me3 at MIR156A/MIR156C is associated with an increase in the binding of PRC2 to these genes and is mediated redundantly by the E(z) homologs SWINGER and CURLY LEAF. The CHD3 chromatin remodeler PICKLE (PKL) promotes the addition of H3K27me3 to MIR156A/MIR156C but is not responsible for the temporal increase in this chromatin mark. PKL is bound to the promoters of MIR156A/MIR156C, where it promotes low levels of H3K27ac early in shoot development and stabilizes the nucleosome at the +1 position. These results suggest a molecular mechanism for the initiation and maintenance of vegetative phase change in plants. PMID:26704382

  8. Epigenetic Regulation of Vegetative Phase Change in Arabidopsis.

    PubMed

    Xu, Mingli; Hu, Tieqiang; Smith, Michael R; Poethig, R Scott

    2016-01-01

    Vegetative phase change in flowering plants is regulated by a decrease in the level of miR156. The molecular mechanism of this temporally regulated decrease in miR156 expression is still unknown. Most of the miR156 in Arabidopsis thaliana shoots is produced by MIR156A and MIR156C. We found that the downregulation of these genes during vegetative phase change is associated with an increase in their level of histone H3 lysine 27 trimethylation (H3K27me3) and requires this chromatin modification. The increase in H3K27me3 at MIR156A/MIR156C is associated with an increase in the binding of PRC2 to these genes and is mediated redundantly by the E(z) homologs SWINGER and CURLY LEAF. The CHD3 chromatin remodeler PICKLE (PKL) promotes the addition of H3K27me3 to MIR156A/MIR156C but is not responsible for the temporal increase in this chromatin mark. PKL is bound to the promoters of MIR156A/MIR156C, where it promotes low levels of H3K27ac early in shoot development and stabilizes the nucleosome at the +1 position. These results suggest a molecular mechanism for the initiation and maintenance of vegetative phase change in plants.

  9. Forced Ion Migration for Chalcogenide Phase Change Memory Device

    NASA Technical Reports Server (NTRS)

    Campbell, Kristy A (Inventor)

    2013-01-01

    Non-volatile memory devices with two stacked layers of chalcogenide materials comprising the active memory device have been investigated for their potential as phase-change memories. The devices tested included GeTe/SnTe, Ge2Se3/SnTe, and Ge2Se3/SnSe stacks. All devices exhibited resistance switching behavior. The polarity of the applied voltage with respect to the SnTe or SnSe layer was critical to the memory switching properties, due to the electric field induced movement of either Sn or Te into the Ge-chalcogenide layer. One embodiment of the invention is a device comprising a stack of chalcogenide-containing layers which exhibit phase-change switching only after a reverse polarity voltage potential is applied across the stack causing ion movement into an adjacent layer and thus "activating" the device to act as a phase-change random access memory device or a reconfigurable electronics device when the applied voltage potential is returned to the normal polarity. Another embodiment of the invention is a device that is capable of exhibiting more than two data states.

  10. Forced ion migration for chalcogenide phase change memory device

    NASA Technical Reports Server (NTRS)

    Campbell, Kristy A. (Inventor)

    2011-01-01

    Non-volatile memory devices with two stacked layers of chalcogenide materials comprising the active memory device have been investigated for their potential as phase change memories. The devices tested included GeTe/SnTe, Ge.sub.2Se.sub.3/SnTe, and Ge.sub.2Se.sub.3/SnSe stacks. All devices exhibited resistance switching behavior. The polarity of the applied voltage with respect to the SnTe or SnSe layer was critical to the memory switching properties, due to the electric field induced movement of either Sn or Te into the Ge-chalcogenide layer. One embodiment of the invention is a device comprising a stack of chalcogenide-containing layers which exhibit phase change switching only after a reverse polarity voltage potential is applied across the stack causing ion movement into an adjacent layer and thus "activating" the device to act as a phase change random access memory device or a reconfigurable electronics device when the applied voltage potential is returned to the normal polarity. Another embodiment of the invention is a device that is capable of exhibiting more that two data states.

  11. Forced ion migration for chalcogenide phase change memory device

    NASA Technical Reports Server (NTRS)

    Campbell, Kristy A. (Inventor)

    2012-01-01

    Non-volatile memory devices with two stacked layers of chalcogenide materials comprising the active memory device have been investigated for their potential as phase-change memories. The devices tested included GeTe/SnTe, Ge.sub.2Se.sub.3/SnTe, and Ge.sub.2Se.sub.3/SnSe stacks. All devices exhibited resistance switching behavior. The polarity of the applied voltage with respect to the SnTe or SnSe layer was critical to the memory switching properties, due to the electric field induced movement of either Sn or Te into the Ge-chalcogenide layer. One embodiment of the invention is a device comprising a stack of chalcogenide-containing layers which exhibit phase-change switching only after a reverse polarity voltage potential is applied across the stack causing ion movement into an adjacent layer and thus "activating" the device to act as a phase-change random access memory device or a reconfigurable electronics device when the applied voltage potential is returned to the normal polarity. Another embodiment of the invention is a device that is capable of exhibiting more than two data states.

  12. Towards integrating chalcogenide based phase change memory with silicon microelectronics

    NASA Astrophysics Data System (ADS)

    Devasia, Archana

    The continued dominance of floating gate technology as the premier non-volatile memory (NVM) technology is expected to hit a roadblock due to issues associated with its inability to catch up with CMOS scaling. The uncertain future of floating gate memory has led to a host of unorthodox NVM technologies to surface as potential heirs. Among the mix is phase change memory (PCM), which is a non-volatile, resistance variable, memory technology wherein the state of the memory bit is defined by the resistance of the memory material. This research study examines novel, bilayer chalcogenide based materials composed of Ge-chalcogenide (GeTe or Ge2Se3) and Sn-chalcogenide (SnTe or SnSe) for phase change memory applications and explores their integration with CMOS technology. By using a layered arrangement, it is possible to induce phase change response in materials, which normally do not exhibit such behavior, and thus form new materials which may have lower threshold voltage and programming current requirements. Also, through the incorporation of a metal containing layer, the phase transition characteristics of the memory layer can be tailored in order to obtain in-situ, a material with optimized phase change properties. Using X-ray diffraction (XRD) and time resolved XRD, it has been demonstrated that stacked phase change memory films exhibit both structural and compositional dependency with annealing temperature. The outcome of the structural transformation of the bottom layer, is an annealing temperature dependent residual stress. By the incorporation of a Sn layer, the phase transition characteristics of Ge-chalcogenide thin films can be tuned. Clear evidence of thermally induced Ge, Sn and chalcogen inter-diffusion, has been discerned via transmission electron microscopy and parallel electron energy loss spectroscopy. The presence of Al2O3 as capping layer has been found to mitigate volatilization and metallic Sn phase separation at high temperatures. Two terminal PCM

  13. Cryogenic two-phase flow and phase-change heat transfer in microgravity

    NASA Astrophysics Data System (ADS)

    Tai, Cheng-Feng

    The applications of cryogenic flow and heat transfer are found in many different types of industries, whether it be the liquid fuel for propulsion or the cryogenic cooling in medical applications. It is very common to find the transportation of cryogenic flow under microgravity in space missions. For example, the liquid oxygen and hydrogen are used to power launch vehicles and helium is used for pressurizing the fuel tank. During the transportation process in pipes, because of high temperature and heat flux from the pipe wall, the cryogenic flow is always in a two-phase condition. As a result, the physics of cryogenic two-phase flow and heat transfer is an important topic for research. In this research, numerical simulation is employed to study fluid flow and heat transfer. The Sharp Interface Method (SIM) with a Cut-cell approach (SIMCC) is adopted to handle the two-phase flow and heat transfer computation. In SIMCC, the background grid is Cartesian and explicit true interfaces are immersed into the computational domain to divide the entire domain into different sub-domains/phases. In SIMCC, each phase comes with its own governing equations and the interfacial conditions act as the bridge to connect the information between the two phases. The Cut-cell approach is applied to handle nonrectangular cells cut by the interfaces and boundaries in SIMCC. With the Cut-cell approach, the conservative properties can be maintained better near the interface. This research will focus on developing the numerical techniques to simulate the two-phase flow and phase change phenomena for one of the major flow patterns in film boiling, the inverted annular flow.

  14. Two-bit multi-level phase change random access memory with a triple phase change material stack structure

    NASA Astrophysics Data System (ADS)

    Gyanathan, Ashvini; Yeo, Yee-Chia

    2012-11-01

    This work demonstrates a novel two-bit multi-level device structure comprising three phase change material (PCM) layers, separated by SiN thermal barrier layers. This triple PCM stack consisted of (from bottom to top), Ge2Sb2Te5 (GST), an ultrathin SiN barrier, nitrogen-doped GST, another ultrathin SiN barrier, and Ag0.5In0.5Sb3Te6. The PCM layers can selectively amorphize to form 4 different resistance levels ("00," "01," "10," and "11") using respective voltage pulses. Electrical characterization was extensively performed on these devices. Thermal analysis was also done to understand the physics behind the phase changing characteristics of the two-bit memory devices. The melting and crystallization temperatures of the PCMs play important roles in the power consumption of the multi-level devices. The electrical resistivities and thermal conductivities of the PCMs and the SiN thermal barrier are also crucial factors contributing to the phase changing behaviour of the PCMs in the two-bit multi-level PCRAM device.

  15. Pulse voltage induced phase change characteristics of the ZnxSbyTez phase-change prototype device

    NASA Astrophysics Data System (ADS)

    Li, Rui; Xu, Ling; Fang, Henan; Lu, Ronghua; Wu, Tao; Yang, Fei; Ma, Zhongyuan; Xu, Jun

    2016-10-01

    ZnxSbyTez thin films are deposited on quartz or glass substrates by the electron beam evaporation technique in an ultra-high vacuum. A prototype phase change memory device using the ZST (ZnxSbyTez) thin film is fabricated. The current-voltage test results of the device show the threshold voltage of ZST531 (Zn5.18Sb3.75Te1.10 at.%) is 2.4 V, which is similar to that of the device based on pure Ge2Sb2Te5. It is shown that the phase-change device with the ZST film is able to perform several reading and writing cycles and the off/on resistance ratio is nearly 10 under pulse voltage. The switching performance of the device is also investigated. Most importantly, the results of the in situ resistance measurements show that the increase of crystallization temperature and the higher 10-year data retention temperature are as high as 300 °C and 191 °C, respectively. This indicates that the ZnxSbyTez material is quite stable, and thus appropriate for use in phase-change memory.

  16. Effect of "phase change" complex on postoperative adhesion prevention.

    PubMed

    Li, Xiao-Dong; Xia, Dong-Lin; Shen, Ling-Ling; He, Hong; Chen, Chao; Wang, Yu-Fei; Chen, Yan-Pei; Guo, Ling-Yan; Gu, Hai-Ying

    2016-05-01

    Postsurgical peritoneal adhesion is a major clinical problem. Numerous anti-adhesion products have been studied, but none could be easily used to provide a physical barrier. In this study, we developed a "phase change" anti-adhesion barrier for reducing peritoneal adhesion by cross-linked copolymerization of O-carboxymethyl chitosan (CMC) and CaCl2 and addition of cyclosporin A (CsA). The CMC-CaCl2-CsA compound was characterized by equilibrium swelling rate, weight loss, releasing effect, and coagulation test, and its biosafety was characterized by acute oral toxicity, hemolysis, and cytotoxicity. Intestinal adhesion model was applied on 64 Sprague-Dawley rats, which received CMC, CMC-CaCl2, or CMC-CaCl2-CsA treatment. At postoperative days 7 and 14, the rats were euthanized, and adhesions were graded by an investigator blinded to the treatment groups, using a predetermined adhesion scoring system. The cecum and adhesion tissue were stained with hematoxylin and eosin and antibodies for matrix metalloproteinase-9 and TIMP-1 for further histopathologic examination. The phase change anti-adhesive material exhibited effective blood clotting and were nontoxic in clotting experiments and acute toxicity test. The degradation rate could be adjusted using phosphate-buffered solution with varying pH. Adhesions were significantly reduced in the CMC-CaCl2-CsA treatment group compared with the control group (P < 0.001). Expression of matrix metalloproteinase-9 was stronger in CMC-CaCl2-CsA treatment group at 7 days after surgery. "Phase-change" adhesive can undergo changes after application, and it inhibits the formation of abdominal adhesions after surgery. The material is convenient for using by surgeons and provides an effective tool for intestinal adhesion prevention. Copyright © 2016 Elsevier Inc. All rights reserved.

  17. Controlled Phase Changes of Titania Using Nitrogen Plasma

    NASA Astrophysics Data System (ADS)

    Trejo-Tzab, R.; Caballero-Espada, Liliana; Quintana, P.; Ávila-Ortega, Alejandro; Medina-Esquivel, R. A.

    2017-01-01

    In this work, the development of a new crystallization technique is reported, using nitrogen plasma (AC) to obtain nanostructured anatase and rutile from amorphous titanium oxide (TiO2). This methodology increases throughput and minimizes thermal effects. Nanostructured amorphous TiO2 was obtained by the sol-gel method and subsequently subjected to AC treatment, at a controlled pressure, applying different powers and treatment times in order to obtain phase changes. The obtained samples were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The results show the crystallization in parallel with anatase and rutile phases with a proportion that is directly related to the applied power in the plasma and the treatment time. This technique allows us to obtain smaller crystals in comparison with those of classic thermal methodologies. It is also demonstrated that the application of plasma represents a novel and innovative method to obtain phase polymorphic changes in titanium oxide without needing to apply prolonged heat treatments at high temperatures and can therefore be taken into consideration as a technique with low energy costs, in comparison with conventional heat treatments.

  18. A phenomenological approach of solidification of polymeric phase change materials

    NASA Astrophysics Data System (ADS)

    Bahrani, Seyed Amir; Royon, Laurent; Abou, Bérengère; Osipian, Rémy; Azzouz, Kamel; Bontemps, André

    2017-01-01

    Phase Change Materials (PCMs) are widely used in thermal energy storage and thermal management systems due to their small volume for a given stored energy and their capability for maintaining nearly constant temperatures. However, their performance is limited by their low thermal conductivity and possible leaks while in the liquid phase. One solution is to imprison the PCM inside a polymer mesh to create a Polymeric Phase Change Material (PPCM). In this work, we have studied the cooling and solidification of five PPCMs with different PCMs and polymer fractions. To understand the heat transfer mechanisms involved, we have carried out micro- and macrorheological measurements in which Brownian motion of tracers embedded in PPCMs has been depicted and viscoelastic moduli have been measured, respectively. Beyond a given polymer concentration, it was shown that the Brownian motion of the tracers is limited by the polymeric chains and that the material exhibits an elastic behavior. This would suggest that heat transfer essentially occurs by conduction, instead of convection. Experiments were conducted to measure temperature variation during cooling of the five samples, and a semi-empirical model based on a phenomenological approach was proposed as a practical tool to choose and size PPCMs.

  19. Controlled Phase Changes of Titania Using Nitrogen Plasma.

    PubMed

    Trejo-Tzab, R; Caballero-Espada, Liliana; Quintana, P; Ávila-Ortega, Alejandro; Medina-Esquivel, R A

    2017-12-01

    In this work, the development of a new crystallization technique is reported, using nitrogen plasma (AC) to obtain nanostructured anatase and rutile from amorphous titanium oxide (TiO2). This methodology increases throughput and minimizes thermal effects. Nanostructured amorphous TiO2 was obtained by the sol-gel method and subsequently subjected to AC treatment, at a controlled pressure, applying different powers and treatment times in order to obtain phase changes. The obtained samples were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The results show the crystallization in parallel with anatase and rutile phases with a proportion that is directly related to the applied power in the plasma and the treatment time. This technique allows us to obtain smaller crystals in comparison with those of classic thermal methodologies. It is also demonstrated that the application of plasma represents a novel and innovative method to obtain phase polymorphic changes in titanium oxide without needing to apply prolonged heat treatments at high temperatures and can therefore be taken into consideration as a technique with low energy costs, in comparison with conventional heat treatments.

  20. Small RNAs of Sequoia sempervirens during rejuvenation and phase change.

    PubMed

    Chen, Y-T; Shen, C-H; Lin, W-D; Chu, H-A; Huang, B-L; Kuo, C-I; Yeh, K-W; Huang, L-C; Chang, I-F

    2013-01-01

    In this work, the population of small RNAs (sRNAs) was studied in the gymnosperm Sequoia sempervirens during phase changes, specifically in the juvenile, adult and rejuvenated plants obtained in vitro. The potential target genes of Sequoia sRNAs were predicted through bioinformatics. Rejuvenation is a pivotal process in woody plants that enables them to regain their growth potential, which results in the recovery of physiologic and molecular characteristics that were lost when the juveniles mature into adult plants. The results from the five repeated graftings of juvenile, adult and rejuvenated plants in vitro showed that sRNAs could be classified into structural RNAs (Group I), small interfering RNAs (Group II), annotated microRNAs (Group III, and unannotated sRNAs (Group IV). The results indicate that only 573 among 15,485,415 sRNAs (Groups III and IV) had significantly different expression patterns associated with rejuvenation and phase change. A total of 215 sRNAs exhibited up-regulated expression patterns in adult shoots, and 358 sRNAs were down-regulated. Expression profiling and prediction of possible target genes of these unique small RNAs indicate possible functions in the control of photosynthetic efficiency and rooting competence abundance during plant rejuvenation. Moreover, the increase in SsmiR156 and decrease in SsmiR172 during plant rejuvenation suggested that these two microRNAs extensively affect phase transition.

  1. Phase transformation changes in thermocycled nickel-titanium orthodontic wires.

    PubMed

    Berzins, David W; Roberts, Howard W

    2010-07-01

    In the oral environment, orthodontic wires will be subject to thermal fluctuations. The purpose of this study was to investigate the effect of thermocycling on nickel-titanium (NiTi) wire phase transformations. Straight segments from single 27 and 35 degrees C copper NiTi (Ormco), Sentalloy (GAC), and Nitinol Heat Activated (3M Unitek) archwires were sectioned into 5mm segments (n=20). A control group consisted of five randomly selected non-thermocycled segments. The remaining segments were thermocycled between 5 and 55 degrees C with five randomly selected segments analyzed with differential scanning calorimetry (DSC; -100<-->150 degrees C at 10 degrees C/min) after 1000, 5000, and 10,000 cycles. Thermal peaks were evaluated with results analyzed via ANOVA (alpha=0.05). Nitinol HA and Sentalloy did not demonstrate qualitative or quantitative phase transformation behavior differences. Significant differences were observed in some of the copper NiTi transformation temperatures, as well as the heating enthalpy with the 27 degrees C copper NiTi wires (p<0.05). Qualitatively, with increased thermocycling the extent of R-phase in the heating peaks decreased in the 35 degrees C copper NiTi, and an austenite to martensite peak shoulder developed during cooling in the 27 degrees C copper NiTi. Repeated temperature fluctuations may contribute to qualitative and quantitative phase transformation changes in some NiTi wires. Copyright 2010 Academy of Dental Materials. All rights reserved.

  2. Fabrication, chemical composition change and phase evolution of biomorphic hydroxyapatite.

    PubMed

    Qian, Junmin; Kang, Yahong; Zhang, Wei; Li, Zhe

    2008-11-01

    Biomorphous, highly porous hydroxyapatite (HA) ceramics have been prepared by a combination of a novel biotemplating process and a sol-gel method, using natural plants like cane and pine as biotemplates. A HA sol was first synthesized from triethylphosphate and calcium nitrate used as the phosphorus and calcium precursors, respectively, and infiltrated into the biotemplates, and subsequently they were sintered at elevated temperatures to obtain porous HA ceramics. The microstructural changes, phase and chemical composition evolutions during the biotemplate-to-HA conversion were investigated by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy. The XRD and FT-IR analysis revealed that the dominant phase of the product was HA, which contained a small amount of mixed A/B-type carbonated HA, closely resembling that of human bone apatite. Moreover, the appearance of a small amount of secondary phase CaCO(3) seemed unavoidable. The HA was not transformed to the other calcium phosphate phases up to 1400 degrees C, but it contained a trace amount of CaO when sintered at above 1100 degrees C. The possible transformation mechanism was proposed. The SEM observation and mechanical property test showed that as-produced HA ceramics retained the macro-/micro-porous structures of the biotemplates with high precision, and possessed acceptable mechanical strength, which is suggested to be potential scaffolds for bone tissue engineering.

  3. Microencapsulated Phase Change Composite Materials for Energy Efficient Buildings

    NASA Astrophysics Data System (ADS)

    Thiele, Alexander

    This study aims to elucidate how phase change material (PCM)-composite materials can be leveraged to reduce the energy consumption of buildings and to provide cost savings to ratepayers. Phase change materials (PCMs) can store thermal energy in the form of latent heat when subjected to temperatures exceeding their melting point by undergoing a phase transition from solid to liquid state. Reversibly, PCMs can release this thermal energy when the system temperature falls below their solidification point. The goal in implementing composite PCM walls is to significantly reduce and time-shift the maximum thermal load on the building in order to reduce and smooth out the electricity demand for heating and cooling. This Ph.D. thesis aims to develop a set of thermal design methods and tools for exploring the use of PCM-composite building envelopes and for providing design rules for their practical implementation. First, detailed numerical simulations were used to show that the effective thermal conductivity of core-shell-matrix composites depended only on the volume fraction and thermal conductivity of the constituent materials. The effective medium approximation reported by Felske (2004) was in very good agreement with numerical predictions of the effective thermal conductivity. Second, a carefully validated transient thermal model was used to simulate microencapsulated PCM-composite walls subjected to diurnal or annual outdoor temperature and solar radiation flux. It was established that adding microencapsulated PCM to concrete walls both substantially reduced and delayed the thermal load on the building. Several design rules were established, most notably, (i) increasing the volume fraction of microencapsulated PCM within the wall increases the energy savings but at the potential expense of mechanical properties [1], (ii) the phase change temperature leading to the maximum energy and cost savings should equal the desired indoor temperature regardless of the climate

  4. Engineering the Phase Front of Light with Phase-Change Material Based Planar lenses

    PubMed Central

    Chen, Yiguo; Li, Xiong; Sonnefraud, Yannick; Fernández-Domínguez, Antonio I.; Luo, Xiangang; Hong, Minghui; Maier, Stefan A.

    2015-01-01

    A novel hybrid planar lens is proposed to engineer the far-field focusing patterns. It consists of an array of slits which are filled with phase-change material Ge2Sb2Te5 (GST). By varying the crystallization level of GST from 0% to 90%, the Fabry-Pérot resonance supported inside each slit can be spectrally shifted across the working wavelength at 1.55 µm, which results in a transmitted electromagnetic phase modulation as large as 0.56π. Based on this geometrically fixed platform, different phase fronts can be constructed spatially on the lens plane by assigning the designed GST crystallization levels to the corresponding slits, achieving various far-field focusing patterns. The present work offers a promising route to realize tunable nanophotonic components, which can be used in optical circuits and imaging applications. PMID:25726864

  5. Speed Measurement and Motion Analysis of Chang'E-3 Rover Based on Differential Phase Delay

    NASA Astrophysics Data System (ADS)

    Chao, Pan; Qing-hui, Liu; Xin, Zheng; Qing-bao, He; Ya-jun, Wu

    2016-04-01

    On 14th December 2013, the Chang'E-3 made a successful soft landing on the lunar surface, and then carried out the tasks of separating the lander and the rover, and taking pictures of each other. With the same beam VLBI (Very Long Baseline Interferometry) technique to observe the signals transmitted by the lander and the rover simultaneously, the differential phase delay between them is calculated, which can reflect the minor changes of the rover's position on a scale of a few centimeters. Based on the high sensitivity of differential phase delay, the rover's speeds during 5 movements are obtained with an average of 0.056 m/s. The relationship between the rover's shake in the moving process and the lunar terrain is analyzed by using the spectrum of the residual of the differential phase delay after the first-order polynomial fitting.

  6. Speed Measurement and Motion Analysis of Chang'E-3 Rover Based on Differential Phase Delay

    NASA Astrophysics Data System (ADS)

    Pan, C.; Liu, Q. H.; Zheng, X.; He, Q. B.; Wu, Y. J.

    2015-07-01

    On 2013 December 14, the Chang'E-3 made a successful soft landing on the lunar surface, and then carried out the tasks of separating the lander and the rover, and taking the photos of each other. With the same beam VLBI (Very long baseline interferometry) technique to observe the signals transmitted by the lander and the rover simultaneously, the differential phase delay between them is calculated, which can reflect a minor change of the rover's position on a scale of a few centimeters. Based on the high sensitivity of differential phase delay, the rover's speeds during 5 movements are obtained with an average of 0.056 m/s. The relationship between the rover's shake in moving process, and lunar terrain is analyzed by using the spectrum of the residual of the differential phase delay after the first-order polynomial fitting.

  7. Two different phase-change origins with chemical- and structural-phase-changes in C doped (1.5 wt.%) In3Sb1Te2

    NASA Astrophysics Data System (ADS)

    Lee, Y. M.; Lee, S. Y.; Sasaki, T.; Kim, K.; Ahn, D.; Jung, M.-C.

    2016-12-01

    We fabricated C-doped (1.5 wt.%) In3Sb1Te2 (CIST) thin films with amorphous phase (a-CIST) using a sputter method. Two electrical-phase-changes at 250 and 275 °C were observed in the sheet resistance measurement. In order to understand the origin of these electrical-phase-changes, all samples were characterized by XRD, TEM, and HRXPS with synchrotron radiation. In a-CIST, only weak Sb-C bonding was observed. In the first electrical-phase-change at 250 °C, strong Sb-C bonding occurred without an accompanying structural/phase change (still amorphous). On the other hand, the second electrical-phase-change at 275 °C was due to the structural/phase change from amorphous to crystalline without a chemical state change.

  8. Two different phase-change origins with chemical- and structural-phase-changes in C doped (1.5 wt.%) In3Sb1Te2.

    PubMed

    Lee, Y M; Lee, S Y; Sasaki, T; Kim, K; Ahn, D; Jung, M-C

    2016-12-08

    We fabricated C-doped (1.5 wt.%) In3Sb1Te2 (CIST) thin films with amorphous phase (a-CIST) using a sputter method. Two electrical-phase-changes at 250 and 275 °C were observed in the sheet resistance measurement. In order to understand the origin of these electrical-phase-changes, all samples were characterized by XRD, TEM, and HRXPS with synchrotron radiation. In a-CIST, only weak Sb-C bonding was observed. In the first electrical-phase-change at 250 °C, strong Sb-C bonding occurred without an accompanying structural/phase change (still amorphous). On the other hand, the second electrical-phase-change at 275 °C was due to the structural/phase change from amorphous to crystalline without a chemical state change.

  9. Two different phase-change origins with chemical- and structural-phase-changes in C doped (1.5 wt.%) In3Sb1Te2

    PubMed Central

    Lee, Y. M.; Lee, S. Y.; Sasaki, T.; Kim, K.; Ahn, D.; Jung, M.-C.

    2016-01-01

    We fabricated C-doped (1.5 wt.%) In3Sb1Te2 (CIST) thin films with amorphous phase (a-CIST) using a sputter method. Two electrical-phase-changes at 250 and 275 °C were observed in the sheet resistance measurement. In order to understand the origin of these electrical-phase-changes, all samples were characterized by XRD, TEM, and HRXPS with synchrotron radiation. In a-CIST, only weak Sb-C bonding was observed. In the first electrical-phase-change at 250 °C, strong Sb-C bonding occurred without an accompanying structural/phase change (still amorphous). On the other hand, the second electrical-phase-change at 275 °C was due to the structural/phase change from amorphous to crystalline without a chemical state change. PMID:27929133

  10. Phase-Change Contrast Agents for Imaging and Therapy

    PubMed Central

    Sheeran, Paul S.; Dayton, Paul A.

    2016-01-01

    Phase-change contrast agents (PCCAs) for ultrasound-based applications have resulted in novel ways of approaching diagnostic and therapeutic techniques beyond what is possible with microbubble contrast agents and liquid emulsions. When subjected to sufficient pressures delivered by an ultrasound transducer, stabilized droplets undergo a phase-transition to the gaseous state and a volumetric expansion occurs. This phenomenon, termed acoustic droplet vaporization, has been proposed as a means to address a number of in vivo applications at the microscale and nanoscale. In this review, the history of PCCAs, physical mechanisms involved, and proposed applications are discussed with a summary of studies demonstrated in vivo. Factors that influence the design of PCCAs are discussed, as well as the need for future studies to characterize potential bioeffects for administration in humans and optimization of ultrasound parameters. PMID:22352770

  11. Thermodynamic design of a phase change thermal storage module

    SciTech Connect

    Conti, M.; Bellecci, C.; Charach, C.

    1996-05-01

    This paper analyzes the irreversibilities due to the heat transfer processes in a latent heat thermal storage system. The Thermal Storage Module (TSM) consists of a cylindrical shell that surrounds an internal coaxial tube. The shell side is filled by a Phase Change Material (PCM); a fluid flows through the inner tube and exchanges heat along the way. The most fundamental assumption underlying this study is that the exergy of the hot fluid stream in the active phase is discharged into the environment and completely destroyed, unless it is partially intercepted by the storage system. A numerical study is conducted to identify and to minimize the thermodynamic losses of the storage and removal processes. The dependence of the second-law efficiency of the system on various design parameters is investigated and discussed.

  12. Low-energy phase change memory with graphene confined layer

    NASA Astrophysics Data System (ADS)

    Zhu, Chengqiu; Ma, Jun; Ge, Xiaoming; Rao, Feng; Ding, Keyuan; Lv, Shilong; Wu, Liangcai; Song, Zhitang

    2016-06-01

    How to reduce the Reset operation energy is the key scientific and technological problem in the field of phase change memory (PCM). Here, we show in the Ge2Sb2Te5 based PCM cell, inserting an additional graphene monolayer in the Ge2Sb2Te5 layer can remarkably decrease both the Reset current and energy. Because of the small out-of-plane electrical and thermal conductivities of such monolayer graphene, the Set resistance and the heat dissipation towards top TiN electrode of the modified PCM cell are significantly increased and decreased, respectively. The mushroom-typed larger active phase transition volume thus can be confined inside the underlying thinner GST layer, resulting in the lower power consumption.

  13. Aluminum Foam-Phase Change Material Composites as Heat Exchangers

    SciTech Connect

    Hong, Sung-tae; Herling, Darrell R.

    2007-04-07

    The effects of geometric parameters of open-cell aluminum foams on the performance of aluminum foam-phase change material (PCM) composites as heat sinks are investigated by experiments. Three types of open-cell aluminum 6061 foams with similar relative densities and different cell sizes are used. Paraffin is selected as the PCM due to its excellent thermal stability and ease of handling. The experimental results show that the performance of the heat sink is significantly affected by the surface area density of the aluminum foam. In general, as the surface area density of the foam increases, the performance of the heat sink is improved regardless of the current phase of the PCM.

  14. Heat transfer and phase change in an impinging droplet

    NASA Astrophysics Data System (ADS)

    Rangchian, Aysan; Shirazi, Nikki L.; Kavehpour, H. Pirouz

    2016-11-01

    Non isothermal droplet impact on solid surfaces has several industrial applications such as spray cooling and 3D printing. Impinging of a droplet on a surface involves an initial phase of spreading followed by a subsequent return to the equilibrium shape. Thermal energy exchanged within the droplet fluid as well as between liquid/solid during the impact has been studied using an ultra high speed infrared camera. Variable parameters in the experiment include droplet temperature and kinetic energy of the droplet during the impact. The evolution of droplet shape viewed by IR camera is similar to what previously observed by high speed photography. The thermal map of droplet over time in these experiments agrees with previously reported numerical simulation. In addition, spacial and temporal temperature variations of liquid droplets on a surface as they solidify are presented. IR camera provides an accurate temperature diagram as the phase change occurs, which is essential for understanding the physics of 3D printing.

  15. Phase-Change Modelling in Severe Nuclear Accidents

    NASA Astrophysics Data System (ADS)

    Pain, Christopher; Pavlidis, Dimitrios; Xie, Zhihua; Percival, James; Gomes, Jefferson; Matar, Omar; Moatamedi, Moji; Tehrani, Ali; Jones, Alan; Smith, Paul

    2014-11-01

    This paper describes progress on a consistent approach for multi-phase flow modelling with phase-change. Although, the developed methods are general purpose the applications presented here cover core melt phenomena at the lower vessel head. These include corium pool formation, coolability and solidification. With respect to external cooling, comparison with the LIVE experiments (from Karlsruhe) is undertaken. Preliminary re-flooding simulation results are also presented. These include water injection into porous media (debris bed) and boiling. Numerical simulations follow IRSN's PEARL experimental programme on quenching/re-flooding. The authors wish to thank Prof. Timothy Haste of IRSN. Dr. D. Pavlidis is funded by EPSRC Consortium ``Computational Modelling for Advanced Nuclear Plants,'' Grant Number EP/I003010/1.

  16. Gradient Augmented Level Set Method for Two Phase Flow Simulations with Phase Change

    NASA Astrophysics Data System (ADS)

    Anumolu, C. R. Lakshman; Trujillo, Mario F.

    2016-11-01

    A sharp interface capturing approach is presented for two-phase flow simulations with phase change. The Gradient Augmented Levelset method is coupled with the two-phase momentum and energy equations to advect the liquid-gas interface and predict heat transfer with phase change. The Ghost Fluid Method (GFM) is adopted for velocity to discretize the advection and diffusion terms in the interfacial region. Furthermore, the GFM is employed to treat the discontinuity in the stress tensor, velocity, and temperature gradient yielding an accurate treatment in handling jump conditions. Thermal convection and diffusion terms are approximated by explicitly identifying the interface location, resulting in a sharp treatment for the energy solution. This sharp treatment is extended to estimate the interfacial mass transfer rate. At the computational cell, a d-cubic Hermite interpolating polynomial is employed to describe the interface location, which is locally fourth-order accurate. This extent of subgrid level description provides an accurate methodology for treating various interfacial processes with a high degree of sharpness. The ability to predict the interface and temperature evolutions accurately is illustrated by comparing numerical results with existing 1D to 3D analytical solutions.

  17. Lattice-Boltzmann-based two-phase thermal model for simulating phase change.

    PubMed

    Kamali, M R; Gillissen, J J J; van den Akker, H E A; Sundaresan, Sankaran

    2013-09-01

    A lattice Boltzmann (LB) method is presented for solving the energy conservation equation in two phases when the phase change effects are included in the model. This approach employs multiple distribution functions, one for a pseudotemperature scalar variable and the rest for the various species. A nonideal equation of state (EOS) is introduced by using a pseudopotential LB model. The evolution equation for the pseudotemperature variable is constructed in such a manner that in the continuum limit one recovers the well known macroscopic energy conservation equation for the mixtures. Heats of reaction, the enthalpy change associated with the phase change, and the diffusive transport of enthalpy are all taken into account; but the dependence of enthalpy on pressure, which is usually a small effect in most nonisothermal flows encountered in chemical reaction systems, is ignored. The energy equation is coupled to the LB equations for species transport and pseudopotential interaction forces through the EOS by using the filtered local pseudotemperature field. The proposed scheme is validated against simple test problems for which analytical solutions can readily be obtained.

  18. Heat transfer characteristics of building walls using phase change material

    NASA Astrophysics Data System (ADS)

    Irsyad, M.; Pasek, A. D.; Indartono, Y. S.; Pratomo, A. W.

    2017-03-01

    Minimizing energy consumption in air conditioning system can be done with reducing the cooling load in a room. Heat from solar radiation which passes through the wall increases the cooling load. Utilization of phase change material on walls is expected to decrease the heat rate by storing energy when the phase change process takes place. The stored energy is released when the ambient temperature is low. Temperature differences at noon and evening can be utilized as discharging and charging cycles. This study examines the characteristics of heat transfer in walls using phase change material (PCM) in the form of encapsulation and using the sleeve as well. Heat transfer of bricks containing encapsulated PCM, tested the storage and released the heat on the walls of the building models were evaluated in this study. Experiments of heat transfer on brick consist of time that is needed for heat transfer and thermal conductivity test as well. Experiments were conducted on a wall coated by PCM which was exposed on a day and night cycle to analyze the heat storage and heat release. PCM used in these experiments was coconut oil. The measured parameter is the temperature at some points in the brick, walls and ambient temperature as well. The results showed that the use of encapsulation on an empty brick can increase the time for thermal heat transfer. Thermal conductivity values of a brick containing encapsulated PCM was lower than hollow bricks, where each value was 1.3 W/m.K and 1.6 W/m.K. While the process of heat absorption takes place from 7:00 am to 06:00 pm, and the release of heat runs from 10:00 pm to 7:00 am. The use of this PCM layer can reduce the surface temperature of the walls of an average of 2°C and slows the heat into the room.

  19. Polymeric compositions incorporating polyethylene glycol as a phase change material

    DOEpatents

    Salyer, Ival O.; Griffen, Charles W.

    1989-01-01

    A polymeric composition comprising a polymeric material and polyethylene glycol or end-capped polyethylene glycol as a phase change material, said polyethylene glycol and said end-capped polyethylene glycol having a molecular weight greater than about 400 and a heat of fusion greater than about 30 cal/g; the composition is useful in making molded and/or coated materials such as flooring, tiles, wall panels and the like; paints containing polyethylene glycols or end-capped polyethylene glycols are also disclosed.

  20. Phase change thermal storage for a solar total energy system

    NASA Technical Reports Server (NTRS)

    Rice, R. E.; Cohen, B. M.

    1978-01-01

    An analytical and experimental program is being conducted on a one-tenth scale model of a high-temperature (584 K) phase-change thermal energy storage system for installation in a solar total energy test facility at Albuquerque, New Mexico, U.S.A. The thermal storage medium is anhydrous sodium hydroxide with 8% sodium nitrate. The program will produce data on the dynamic response of the system to repeated cycles of charging and discharging simulating those of the test facility. Data will be correlated with a mathematical model which will then be used in the design of the full-scale system.

  1. Covert thermal barcodes based on phase change nanoparticles

    PubMed Central

    Duong, Binh; Liu, Helin; Ma, Liyuan; Su, Ming

    2014-01-01

    An unmet need is to develop covert barcodes that can be used to track-trace objects, and authenticate documents. This paper describes a new nanoparticle-based covert barcode system, in which a selected panel of solid-to-liquid phase change nanoparticles with discrete and sharp melting peaks is added in a variety of objects such as explosive derivative, drug, polymer, and ink. This method has high labeling capacity owing to the small sizes of nanoparticles, sharp melting peaks, and large scan range of thermal analysis. The thermal barcode can enhance forensic investigation by its technical readiness, structural covertness, and robustness. PMID:24901064

  2. 16-Kbit SPI phase change memory chip with ECC scheme

    NASA Astrophysics Data System (ADS)

    Zhang, Yiyun; Chen, Houpeng; Song, Zhitang; Li, Xi; Hong, Xiao; Wang, Qian; Jin, Rong; Wang, Zhaomin; Cai, Daoling

    A serial peripheral interface (SPI) 16-Kbit phase change memory chip based on 0.13μm CMOS process is designed. It contains a parallel error correcting code (ECC) circuit, which can correct 2 bits in every 8 bits without clock delay, enabling the write and read operations performed at bus speed. All the data transfers in 8-bit groups and can be read or written with write protection scheme by unlimited cycle, in which address can automatically increase one by one. Simulation results show that the chip can work correctly in SPI mode and with ECC scheme. It is now under testing.

  3. Satellite thermal storage systems using metallic phase-change materials

    SciTech Connect

    Lauf, R.J.; Hamby, C.

    1989-01-01

    Solar (thermal) dynamic power systems for satellites require a heat storage system capable of operating the engine during eclipse. This paper describes a system in which the phase-change material (PCM) is a metal rather than the more conventional fluoride salts. Thermal storage modules consisting of germanium contained in graphite have good thermal conductivity, low parasitic mass, and are physically and chemically stable. We describe the result of thermal cycle testing of graphite capsules containing germanium and several germanium- and silicon-based alloys, as well as some initial tests of the compatibility of graphite with Nb-1%Zr structural materials. 7 refs., 7 figs., 3 tabs.

  4. Covert thermal barcodes based on phase change nanoparticles

    NASA Astrophysics Data System (ADS)

    Duong, Binh; Liu, Helin; Ma, Liyuan; Su, Ming

    2014-06-01

    An unmet need is to develop covert barcodes that can be used to track-trace objects, and authenticate documents. This paper describes a new nanoparticle-based covert barcode system, in which a selected panel of solid-to-liquid phase change nanoparticles with discrete and sharp melting peaks is added in a variety of objects such as explosive derivative, drug, polymer, and ink. This method has high labeling capacity owing to the small sizes of nanoparticles, sharp melting peaks, and large scan range of thermal analysis. The thermal barcode can enhance forensic investigation by its technical readiness, structural covertness, and robustness.

  5. Phase change thermal storage for a solar total energy system

    NASA Technical Reports Server (NTRS)

    Rice, R. E.; Cohen, B. M.

    1978-01-01

    An analytical and experimental program is being conducted on a one-tenth scale model of a high-temperature (584 K) phase-change thermal energy storage system for installation in a solar total energy test facility at Albuquerque, New Mexico, U.S.A. The thermal storage medium is anhydrous sodium hydroxide with 8% sodium nitrate. The program will produce data on the dynamic response of the system to repeated cycles of charging and discharging simulating those of the test facility. Data will be correlated with a mathematical model which will then be used in the design of the full-scale system.

  6. Polymerase chain reaction with phase change as intrinsic thermal control

    NASA Astrophysics Data System (ADS)

    Hsieh, Yi-Fan; Yonezawa, Eri; Kuo, Long-Sheng; Yeh, Shiou-Hwei; Chen, Pei-Jer; Chen, Ping-Hei

    2013-04-01

    This research demonstrated that without any external temperature controller, the capillary convective polymerase chain reaction (ccPCR) powered by a candle can operate with the help of phase change. The candle ccPCR system productively amplified hepatitis B virus 122 base-pairs DNA fragment. The detection sensitivity can achieve at an initial DNA concentration to 5 copies per reaction. The results also show that the candle ccPCR system can operate functionally even the ambient temperature varies from 7 °C to 45 °C. These features imply that the candle ccPCR system can provide robust medical detection services.

  7. Automated baseline change detection phase I. Final report

    SciTech Connect

    1995-12-01

    The Automated Baseline Change Detection (ABCD) project is supported by the DOE Morgantown Energy Technology Center (METC) as part of its ER&WM cross-cutting technology program in robotics. Phase 1 of the Automated Baseline Change Detection project is summarized in this topical report. The primary objective of this project is to apply robotic and optical sensor technology to the operational inspection of mixed toxic and radioactive waste stored in barrels, using Automated Baseline Change Detection (ABCD), based on image subtraction. Absolute change detection is based on detecting any visible physical changes, regardless of cause, between a current inspection image of a barrel and an archived baseline image of the same barrel. Thus, in addition to rust, the ABCD system can also detect corrosion, leaks, dents, and bulges. The ABCD approach and method rely on precise camera positioning and repositioning relative to the barrel and on feature recognition in images. In support of this primary objective, there are secondary objectives to determine DOE operational inspection requirements and DOE system fielding requirements.

  8. Controllable Thermal Rectification Realized in Binary Phase Change Composites

    PubMed Central

    Chen, Renjie; Cui, Yalong; Tian, He; Yao, Ruimin; Liu, Zhenpu; Shu, Yi; Li, Cheng; Yang, Yi; Ren, Tianling; Zhang, Gang; Zou, Ruqiang

    2015-01-01

    Phase transition is a natural phenomenon happened around our daily life, represented by the process from ice to water. While melting and solidifying at a certain temperature, a high heat of fusion is accompanied, classified as the latent heat. Phase change material (PCM) has been widely applied to store and release large amount of energy attributed to the distinctive thermal behavior. Here, with the help of nanoporous materials, we introduce a general strategy to achieve the binary eicosane/PEG4000 stuffed reduced graphene oxide aerogels, which has two ends with different melting points. It's successfully demonstrated this binary PCM composites exhibits thermal rectification characteristic. Partial phase transitions within porous networks instantaneously result in one end of the thermal conductivity saltation at a critical temperature, and therefore switch on or off the thermal rectification with the coefficient up to 1.23. This value can be further raised by adjusting the loading content of PCM. The uniqueness of this device lies in its performance as a normal thermal conductor at low temperature, only exhibiting rectification phenomenon when temperature is higher than a critical value. The stated technology has broad applications for thermal energy control in macroscopic scale such as energy-efficiency building or nanodevice thermal management. PMID:25748640

  9. Controllable Thermal Rectification Realized in Binary Phase Change Composites

    NASA Astrophysics Data System (ADS)

    Chen, Renjie; Cui, Yalong; Tian, He; Yao, Ruimin; Liu, Zhenpu; Shu, Yi; Li, Cheng; Yang, Yi; Ren, Tianling; Zhang, Gang; Zou, Ruqiang

    2015-03-01

    Phase transition is a natural phenomenon happened around our daily life, represented by the process from ice to water. While melting and solidifying at a certain temperature, a high heat of fusion is accompanied, classified as the latent heat. Phase change material (PCM) has been widely applied to store and release large amount of energy attributed to the distinctive thermal behavior. Here, with the help of nanoporous materials, we introduce a general strategy to achieve the binary eicosane/PEG4000 stuffed reduced graphene oxide aerogels, which has two ends with different melting points. It's successfully demonstrated this binary PCM composites exhibits thermal rectification characteristic. Partial phase transitions within porous networks instantaneously result in one end of the thermal conductivity saltation at a critical temperature, and therefore switch on or off the thermal rectification with the coefficient up to 1.23. This value can be further raised by adjusting the loading content of PCM. The uniqueness of this device lies in its performance as a normal thermal conductor at low temperature, only exhibiting rectification phenomenon when temperature is higher than a critical value. The stated technology has broad applications for thermal energy control in macroscopic scale such as energy-efficiency building or nanodevice thermal management.

  10. Analysis of Lipoplex Structure and Lipid Phase Changes

    SciTech Connect

    Koynova, Rumiana

    2012-07-18

    Efficient delivery of genetic material to cells is needed for tasks of utmost importance in the laboratory and clinic, such as gene transfection and gene silencing. Synthetic cationic lipids can be used as delivery vehicles for nucleic acids and are now considered the most promising nonviral gene carriers. They form complexes (lipoplexes) with the polyanionic nucleic acids. A critical obstacle for clinical application of the lipid-mediated DNA delivery (lipofection) is its unsatisfactory efficiency for many cell types. Understanding the mechanism of lipid-mediated DNA delivery is essential for their successful application, as well as for a rational design and synthesis of novel cationic lipoid compounds for enhanced gene delivery. A viewpoint now emerging is that the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids. In particular, recent studies showed that the phase evolution of lipoplex lipids upon interaction and mixing with membrane lipids appears to be decisive for transfection success: specifically, lamellar lipoplex formulations, which were readily susceptible to undergoing lamellar-nonlamellar phase transition upon mixing with cellular lipids and were found rather consistently associated with superior transfection potency, presumably as a result of facilitated DNA release. Thus, understanding the lipoplex structure and the phase changes upon interacting with membrane lipids is important for the successful application of the cationic lipids as gene carriers.

  11. Integrating Phase-Change Materials into Automotive Thermoelectric Generators

    NASA Astrophysics Data System (ADS)

    Klein Altstedde, Mirko; Rinderknecht, Frank; Friedrich, Horst

    2014-06-01

    Because the heat emitted by conventional combustion-engine vehicles during operation has highly transient properties, automotive thermoelectric generators (TEG) are intended for a particular operating state (design point). This, however, leads to two problems. First, whenever the combustion engine runs at low load, the maximum operating temperature cannot be properly utilised; second, a combustion engine at high load requires partial diversion of exhaust gas away from the TEG to protect the thermoelectric modules. An attractive means of stabilising dynamic exhaust behaviour (thereby keeping the TEG operating status at the design point for as long as possible) is use of latent heat storage, also known as phase-change materials (PCM). By positioning PCM between module and exhaust heat conduit, and choosing a material with a phase-change temperature matching the module's optimum operating temperature, it can be used as heat storage. This paper presents results obtained during examination of the effect of integration of latent heat storage on the potential of automotive TEG to convert exhaust heat. The research resulted in the development of a concept based on the initial integration idea, followed by proof of concept by use of a specially created prototype. In addition, the potential amount of energy obtained by use of a PCM-equipped TEG was calculated. The simulations indicated a significant increase in electrical energy was obtained in the selected test cycle.

  12. Metallic phase change material thermal storage for Dish Stirling

    DOE PAGES

    Andraka, C. E.; Kruizenga, A. M.; Hernandez-Sanchez, B. A.; ...

    2015-06-05

    Dish-Stirling systems provide high-efficiency solar-only electrical generation and currently hold the world record at 31.25%. This high efficiency results in a system with a high possibility of meeting the DOE SunShot goal of $0.06/kWh. However, current dish-Stirling systems do not incorporate thermal storage. For the next generation of non-intermittent and cost-competitive solar power plants, we propose adding a thermal energy storage system that combines latent (phase-change) energy transport and latent energy storage in order to match the isothermal input requirements of Stirling engines while also maximizing the exergetic efficiency of the entire system. This paper reports current findings in themore » area of selection, synthesis and evaluation of a suitable high performance metallic phase change material (PCM) as well as potential interactions with containment alloy materials. The metallic PCM's, while more expensive than salts, have been identified as having substantial performance advantages primarily due to high thermal conductivity, leading to high exergetic efficiency. Systems modeling has indicated, based on high dish Stirling system performance, an allowable cost of the PCM storage system that is substantially higher than SunShot goals for storage cost on tower systems. Several PCM's are identified with suitable melting temperature, cost, and performance.« less

  13. Preliminary Trade Study of Phase Change Heat Sinks

    NASA Technical Reports Server (NTRS)

    Anderson, Molly; Leimkeuhler, Thomas; Quinn, Gregory; Golliher, Eric

    2006-01-01

    For short durations, phase change based heat rejection systems are a very effective way of removing heat from spacecraft. Future NASA vehicles, such as the Crew Exploration Vehicle (CEV), will require non-radiative heat rejection systems during at least a portion of the planned mission, just as their predecessors have. While existing technologies are available to modify, such as Apollo era sublimators, or the Space Shuttle Flash Evaporator System (FES), several new technologies are under development or investigation to progress beyond these existing heat rejection systems. Examples include the Multi-Fluid Evaporator developed by Hamilton Sundstrand, improvements upon the Contaminant Insensitive Sublimator originally developed for the X-38 program, and a Compact Flash Evaporator System (CFES). Other possibilities evaluate new ways of operating existing designs. The new developments are targeted at increasing operating life, expanding the environments in which the system can operate, improving the mass and volume characteristics, or some combination of these or other improvements. This paper captures the process and results of a preliminary trade study performed at Johnson Space Center to compare the various existing and proposed phase change based heat rejection systems for the CEV. Because the new systems are still in development, and the information on existing systems is extrapolation, this trade study is not meant to suggest a final decision for future vehicles. The results of this early trade study are targeted to aid the development efforts for the new technologies by identifying issues that could reduce the chances of selection for the CEV.

  14. Metallic phase change material thermal storage for Dish Stirling

    SciTech Connect

    Andraka, C. E.; Kruizenga, A. M.; Hernandez-Sanchez, B. A.; Coker, E. N.

    2015-06-05

    Dish-Stirling systems provide high-efficiency solar-only electrical generation and currently hold the world record at 31.25%. This high efficiency results in a system with a high possibility of meeting the DOE SunShot goal of $0.06/kWh. However, current dish-Stirling systems do not incorporate thermal storage. For the next generation of non-intermittent and cost-competitive solar power plants, we propose adding a thermal energy storage system that combines latent (phase-change) energy transport and latent energy storage in order to match the isothermal input requirements of Stirling engines while also maximizing the exergetic efficiency of the entire system. This paper reports current findings in the area of selection, synthesis and evaluation of a suitable high performance metallic phase change material (PCM) as well as potential interactions with containment alloy materials. The metallic PCM's, while more expensive than salts, have been identified as having substantial performance advantages primarily due to high thermal conductivity, leading to high exergetic efficiency. Systems modeling has indicated, based on high dish Stirling system performance, an allowable cost of the PCM storage system that is substantially higher than SunShot goals for storage cost on tower systems. Several PCM's are identified with suitable melting temperature, cost, and performance.

  15. Phase change energy storage for solar dynamic power systems

    NASA Technical Reports Server (NTRS)

    Chiaramonte, F. P.; Taylor, J. D.

    1992-01-01

    This paper presents the results of a transient computer simulation that was developed to study phase change energy storage techniques for Space Station Freedom (SSF) solar dynamic (SD) power systems. Such SD systems may be used in future growth SSF configurations. Two solar dynamic options are considered in this paper: Brayton and Rankine. Model elements consist of a single node receiver and concentrator, and takes into account overall heat engine efficiency and power distribution characteristics. The simulation not only computes the energy stored in the receiver phase change material (PCM), but also the amount of the PCM required for various combinations of load demands and power system mission constraints. For a solar dynamic power system in low earth orbit, the amount of stored PCM energy is calculated by balancing the solar energy input and the energy consumed by the loads corrected by an overall system efficiency. The model assumes an average 75 kW SD power system load profile which is connected to user loads via dedicated power distribution channels. The model then calculates the stored energy in the receiver and subsequently estimates the quantity of PCM necessary to meet peaking and contingency requirements. The model can also be used to conduct trade studies on the performance of SD power systems using different storage materials.

  16. Phase change energy storage for solar dynamic power systems

    NASA Technical Reports Server (NTRS)

    Chiaramonte, F. P.; Taylor, J. D.

    1992-01-01

    This paper presents the results of a transient computer simulation that was developed to study phase change energy storage techniques for Space Station Freedom (SSF) solar dynamic (SD) power systems. Such SD systems may be used in future growth SSF configurations. Two solar dynamic options are considered in this paper: Brayton and Rankine. Model elements consist of a single node receiver and concentrator, and takes into account overall heat engine efficiency and power distribution characteristics. The simulation not only computes the energy stored in the receiver phase change material (PCM), but also the amount of the PCM required for various combinations of load demands and power system mission constraints. For a solar dynamic power system in low earth orbit, the amount of stored PCM energy is calculated by balancing the solar energy input and the energy consumed by the loads corrected by an overall system efficiency. The model assumes an average 75 kW SD power system load profile which is connected to user loads via dedicated power distribution channels. The model then calculates the stored energy in the receiver and subsequently estimates the quantity of PCM necessary to meet peaking and contingency requirements. The model can also be used to conduct trade studies on the performance of SD power systems using different storage materials.

  17. The Study of the Thermoelectric Properties of Phase Change Materials

    NASA Astrophysics Data System (ADS)

    Yin, Ming; Abdi, Mohammed; Noimande, Zibusisu; Mbamalu, Godwin; Alameeri, Dheyaa; Datta, Timir

    We study thermoelectric property that is electrical phenomena occurring in conjunction with the flow of heat of phase-change materials (PCM) in particular GeSbTe (GST225). From given sets of material parameters, COMSOL Multiphysics heat-transfer module is used to compute maps of temperature and voltage distribution in the PCM samples. These results are used to design an apparatus including the variable temperature sample holder set up. An Arbitrary/ Function generator and a circuit setup is also designed to control the alternation of heaters embedded on the sample holder in order to ensure sequential back and forward flow of heat current from both sides of the sample. Accurate values of potential differences and temperature distribution profiles are obtained in order to compute the Seebeck coefficient of the sample. The results of elemental analysis and imaging studies such as XRD, UV-VIS, EDEX and SEM of the sample are obtained. Factors affecting the thermoelectric properties of phase change memory are also discussed. NNSA/ DOD Consortium for Materials and Energy Studies.

  18. Phase Change Effects on Immiscible Flow Displacements in Radial Injection

    NASA Astrophysics Data System (ADS)

    Ahmadlouydarab, Majid; Azaiez, Jalel; Chen, Zhangxin

    2014-11-01

    We report a systematic simulation of immiscible fluid-fluid displacements in radial injection in the presence of phase change. Due to the presence of two fluid-fluid interfaces in the system, a special treatment has been adopted. To track the leading interface position, two highly accurate methods including Level Set and Immersed Interface Method were used, while for locating the trailing interface an energy equation was adopted assuming the existence of a constant thin condensate layer. Dimensional analysis led to three important dimensionless groups including capillary number (Ca), Jacob number (Ja) and viscosity ratios (M) of the three fluids. Simulation results indicate significant influences of these parameters on the development of the instability and the interfacial morphology of fingers. Increasing Ca or M tends to amplify the interfacial instability, fingertip splitting, and results in longer fingers. In contrast, increasing Ja has stabilizing effects due to an increase of the thickness of the condensate layer. On the other hand at lower viscosity ratios as well as lower Ca, because of compensation effects of the phase change, both leading and trailing interfaces are found to be less unstable. Moreover accumulated condensate and oil saturation depletion curves show increasing and decreasing trends, respectively, when the Ca increases. Although viscosity ratio and Ja have similar effects on the accumulated condensate, they do not show any effect on the oil depletion saturation.

  19. Natural convection during a phase change of sodium acetate trihydrate

    NASA Astrophysics Data System (ADS)

    Ouchi, Yasunori; Someya, Satoshi; Munakata, Tetsuo

    2014-11-01

    A latent heat storage system has higher storage capacity than a sensible heat storage system. Sodium acetate trihydrate has large latent heat at the temperature, 58°C, suitable for a hot-water supply system. The present study focused on convection in a phase change process to understand the heat transfer from the phase change material (PCM). The convection occurred only in certain conditions of supercooling temperature and PCM concentration. A spicular crystal grew quickly and the thermal convection couldn't be detected at large supercooling temperature with high concentration of PCM. In the range of 5 ~ 13°C of supercooling temperature, the buoyancy driven convection due to the latent heat of PCM was measured using the PIV. It was also observed that a part of CH3COONa-3H2O solution was sucked into the growing spicular crystals to supply CH3COONa at the condition with small concentration and at 5 ~ 13°C of supercooling temperature.

  20. Subscale Water Based Phase Change Material Heat Exchanger Development

    NASA Technical Reports Server (NTRS)

    Sheth, Rubik; Hansen, Scott

    2016-01-01

    Supplemental heat rejection devices are required in many spacecraft as the radiators are not sized to meet the full heat rejection demand. One means of obtaining additional heat rejection is through the use of phase change material heat exchangers (PCM HX's). PCM HX's utilize phase change to store energy in unfavorable thermal environments (melting) and reject the energy in favorable environments (freezing). Traditionally, wax has been used as a PCM on spacecraft. However, water is an attractive alternative because it is capable of storing about 40% more energy per unit mass due to its higher latent heat of fusion. The significant problem in using water as a PCM is its expansion while freezing, leading to structural integrity concerns when housed in an enclosed heat exchanger volume. Significant investigation and development has taken place over the past five years to understand and overcome the problems associated with water PCM HX's. This paper reports on the final efforts by Johnson Space Center's Thermal Systems Branch to develop a water based PCM HX. The test article developed and reported on is a subscale version of the full-scale water-based PCM HX's constructed by Mezzo Technologies. The subscale unit was designed by applying prior research on freeze front propagation and previous full-scale water PCM HX development. Design modifications to the subscale unit included use of urethane bladder, decreased aspect ratio, perforated protection sheet, and use of additional mid-plates. Testing of the subscale unit was successful and 150 cycles were completed without fail.

  1. Direct numerical simulation of incompressible multiphase flow with phase change

    NASA Astrophysics Data System (ADS)

    Lee, Moon Soo; Riaz, Amir; Aute, Vikrant

    2017-09-01

    Simulation of multiphase flow with phase change is challenging because of the potential for unphysical pressure oscillations, spurious velocity fields and mass flux errors across the interface. The resulting numerical errors may become critical when large density contrasts are present. To address these issues, we present a new approach for multiphase flow with phase change that features, (i) a smooth distribution of sharp velocity jumps and mass flux within a narrow region surrounding the interface, (ii) improved mass flux projection from the implicit interface onto the uniform Cartesian grid and (iii) post-advection velocity correction step to ensure accurate velocity divergence in interfacial cells. These new features are implemented in combination with a sharp treatment of the jumps in pressure and temperature gradient. A series of 1-D, 2-D, axisymmetric and 3-D problems are solved to verify the improvements afforded by the new approach. Axisymmetric film boiling results are also presented, which show good qualitative agreement with heat transfer correlations as well as experimental observations of bubble shapes.

  2. Innovative Phase Change Thermal Energy Storage Solution for Baseload Power Phase 1 Final Report

    SciTech Connect

    Qiu, Songgang

    2013-05-15

    The primary purpose of this project is to develop and validate an innovative, scalable phase change salt thermal energy storage (TES) system that can interface with Infinia’s family of free-piston Stirling engines (FPSE). This TES technology is also appropriate for Rankine and Brayton power converters. Solar TES systems based on latent heat of fusion rather than molten salt temperature differences, have many advantages that include up to an order of magnitude higher energy storage density, much higher temperature operation, and elimination of pumped loops for most of Infinia’s design options. DOE has funded four different concepts for solar phase change TES, including one other Infinia awarded project using heat pipes to transfer heat to and from the salt. The unique innovation in this project is an integrated TES/pool boiler heat transfer system that is the simplest approach identified to date and arguably has the best potential for minimizing the levelized cost of energy (LCOE). The Phase 1 objectives are to design, build and test a 1-hour TES proof-of-concept lab demonstrator integrated with an Infinia 3 kW Stirling engine, and to conduct a preliminary design of a 12-hour TES on-sun prototype.

  3. Dynamics of plumes in a compressible mantle with phase changes: Implications for phase boundary topography

    NASA Astrophysics Data System (ADS)

    Bossmann, Andrea B.; van Keken, Peter E.

    2013-11-01

    While plumes rising from the deep mantle may be responsible for hotspot volcanism, their existence has not yet been unambiguously confirmed by seismological studies. Several seismic studies reported that the topography of the 670-km discontinuity is flat below hotspots, which disagrees with the elevation expected due to its negative Clapeyron slope and plume excess temperature. An improved numerical method that includes compressibility and consistently implemented phase transitions is used to study plume evolution in the Earth’s mantle. The influence of latent heat on plume behavior for varying convective vigor and Clapeyron slope of the endothermic phase change at 670 km depth is studied in axisymmetric spherical shell geometry. Minor differences in plume dynamics are found for models considering and neglecting latent heat. Three regimes of plume behavior at the endothermic phase boundary are observed: besides complete plume inhibition and penetration along the symmetry axis an intermediate regime in which the plume forms a ring around the symmetry axis is found. These models also predict that the 670-km discontinuity is flat below hotspots due to a large plume head in the lower mantle of about 1000 km diameter that significantly thins as it rises into the upper mantle. This is explained by the lower viscosity in the upper mantle and the spreading of the temporarily inhibited plume below the endothermic phase boundary, which reconciles the flat 670-km discontinuity with a deep mantle plume origin.

  4. Consideration of a Phase Change Model Based on Apparent Phase Equilibrium

    NASA Astrophysics Data System (ADS)

    Kashiwada, S.; Iga, Y.

    2015-12-01

    It has been known that cavity volume is underestimated and there is a discrepancy between predicted and measured breakdown characteristics for the numerical simulation of unsteady cavitation around a hydrofoil at high angle of attack. Therefore, in this study, in order to predict the cavity volume with high accuracy, the phenomena that gas phase increases even at a pressure higher than saturated vapour pressure which is known as aeration is modelled, and applied to phase change term. It was assumed that the precipitation of dissolved air is promoted by mechanical stimulation such as Reynolds stress in unsteady flow. The effectivity of the proposed model is discussed through the comparison among some kinds of components of the pressure variation.

  5. A zero density change phase change memory material: GeTe-O structural characteristics upon crystallisation.

    PubMed

    Zhou, Xilin; Dong, Weiling; Zhang, Hao; Simpson, Robert E

    2015-06-11

    Oxygen-doped germanium telluride phase change materials are proposed for high temperature applications. Up to 8 at.% oxygen is readily incorporated into GeTe, causing an increased crystallisation temperature and activation energy. The rhombohedral structure of the GeTe crystal is preserved in the oxygen doped films. For higher oxygen concentrations the material is found to phase separate into GeO2 and TeO2, which inhibits the technologically useful abrupt change in properties. Increasing the oxygen content in GeTe-O reduces the difference in film thickness and mass density between the amorphous and crystalline states. For oxygen concentrations between 5 and 6 at.%, the amorphous material and the crystalline material have the same density. Above 6 at.% O doping, crystallisation exhibits an anomalous density change, where the volume of the crystalline state is larger than that of the amorphous. The high thermal stability and zero-density change characteristic of Oxygen-incorporated GeTe, is recommended for efficient and low stress phase change memory devices that may operate at elevated temperatures.

  6. MULTI-PHASE FRACTURE-MATRIX INTERACTIONS UNDER STRESS CHANGES

    SciTech Connect

    A.S. Grader; D. Elsworth; P.M. Halleck; F. Alvarado; H. Yasuhara; A. Alajmi; Z. Karpyn

    2002-10-28

    The main objectives of this project are to quantify the changes in fracture porosity and multiphase transport properties as a function of confining stress. These changes will be integrated into conceptual and numerical models that will improve our ability to predict and optimize fluid transport in fractured system. This report details our progress on: (1) developing the direct experimental measurements of fracture aperture and topology using high-resolution x-ray microtomography, (2) modeling of fracture permeability in the presence of asperities and confining stress, and (3) simulation of two-phase fluid flow in a fracture and a layered matrix. The three-dimensional surface that describes the large-scale structure of the fracture in the porous medium can be determined using x-ray micro-tomography with significant accuracy. The distribution of fracture aperture is a difficult issue that we are studying and developing methods of quantification. The difficulties are both numerical and conceptual. Numerically, the three-dimensional data sets include millions, and sometimes, billions of points, and pose a computational challenge. The conceptual difficulties derive from the rough nature of the fracture surfaces, and the heterogeneous nature of the rock matrix. However, the high-resolution obtained by the imaging system provides us a much needed measuring environment on rock samples that are subjected to simultaneous fluid flow and confining stress. Pilot multi-phase experiments have been performed, proving the ability to detect two phases in certain large fractures. The absolute permeability of a fracture depends on the behavior of the asperities that keep it open. A model is being developed that predicts the permeability and average aperture of a fracture as a function of time under steady flow of water including the pressure solution at the asperity contact points. Several two-phase flow experiments in the presence of a fracture tip were performed in the past. At the

  7. NGNP Process Heat Utilization: Liquid Metal Phase Change Heat Exchanger

    SciTech Connect

    Piyush Sabharwall; Mike Patterson; Vivek Utgikar; Fred Gunnerson

    2008-09-01

    One key long-standing issue that must be overcome to fully realize the successful growth of nuclear power is to determine other benefits of nuclear energy apart from meeting the electricity demands. The Next Generation Nuclear Plant (NGNP) will most likely be producing electricity and heat for the production of hydrogen and/or oil retrieval from oil sands and oil shale to help in our national pursuit of energy independence. For nuclear process heat to be utilized, intermediate heat exchange is required to transfer heat from the NGNP to the hydrogen plant or oil recovery field in the most efficient way possible. Development of nuclear reactor - process heat technology has intensified the interest in liquid metals as heat transfer media because of their ideal transport properties. Liquid metal heat exchangers are not new in practical applications. An important rational for considering liquid metals is the potential convective heat transfer is among the highest known. Thus explains the interest in liquid metals as coolant for intermediate heat exchange from NGNP. For process heat it is desired that, intermediate heat exchangers (IHX) transfer heat from the NGNP in the most efficient way possible. The production of electric power at higher efficiency via the Brayton Cycle, and hydrogen production, requires both heat at higher temperatures and high effectiveness compact heat exchangers to transfer heat to either the power or process cycle. Compact heat exchangers maximize the heat transfer surface area per volume of heat exchanger; this has the benefit of reducing heat exchanger size and heat losses. High temperature IHX design requirements are governed in part by the allowable temperature drop between the outlet and inlet of the NGNP. In order to improve the characteristics of heat transfer, liquid metal phase change heat exchangers may be more effective and efficient. This paper explores the overall heat transfer characteristics and pressure drop of the phase change

  8. Optimized Structures for Low-Profile Phase Change Thermal Spreaders

    NASA Astrophysics Data System (ADS)

    Sharratt, Stephen Andrew

    Thin, low-profile phase change thermal spreaders can provide cooling solutions for some of today's most pressing heat flux dissipation issues. These thermal issues are only expected to increase as future electronic circuitry requirements lead to denser and potentially 3D chip packaging. Phase change based heat spreaders, such as heat pipes or vapor chambers, can provide a practical solution for effectively dissipating large heat fluxes. This thesis reports a comprehensive study of state-of-the-art capillary pumped wick structures using computational modeling, micro wick fabrication, and experimental analysis. Modeling efforts focus on predicting the shape of the liquid meniscus inside a complicated 3D wick structure. It is shown that this liquid shape can drastically affect the wick's thermal resistance. In addition, knowledge of the liquid meniscus shape allows for the computation of key parameters such as permeability and capillary pressure which are necessary for predicting the maximum heat flux. After the model is validated by comparison to experimental results, the wick structure is optimized so as to decrease overall wick thermal resistance and increase the maximum capillary limited heat flux before dryout. The optimized structures are then fabricated out of both silicon and copper using both traditional and novel micro-fabrication techniques. The wicks are made super-hydrophilic using chemical and thermal oxidation schemes. A sintered monolayer of Cu particles is fabricated and analyzed as well. The fabricated wick structures are experimentally tested for their heat transfer performance inside a well controlled copper vacuum chamber. Heat fluxes as high as 170 W/cm2 are realized for Cu wicks with structure heights of 100 μm. The structures optimized for both minimized thermal resistance and high liquid supply ability perform much better than their non-optimized counterparts. The super-hydrophilic oxidation scheme is found to drastically increase the maximum

  9. Surface topographical changes measured by phase-locked interferometry

    NASA Technical Reports Server (NTRS)

    Lauer, J. L.; Fung, S. S.

    1984-01-01

    An electronic optical laser interferometer capable of resolving depth differences of as low as 30 A and planar displacements of 6000 A was constructed to examine surface profiles of bearing surfaces without physical contact. Topological chemical reactivity was determined by applying a drop of dilute alcoholic hydrochloric acid and measuring the profile of the solid surface before and after application of this probe. Scuffed bearing surfaces reacted much faster than virgin ones but that bearing surfaces exposed to lubricants containing an organic chloride reacted much more slowly. The reactivity of stainless steel plates, heated in a nitrogen atmosphere to different temperatures, were examined later at ambient temperature. The change of surface contour as a result of the probe reaction followed Arrhenius-type relation with respect to heat treatment temperature. The contact area of the plate of a ball/plate sliding elastohydrodynamic contact run on trimethylopropane triheptanoate with or without additives was optically profiled periodically. As scuffing was approached, the change of profile within the contact region changed much more rapidly by the acid probe and assumed a constant high value after scuffing. A nonetching metallurgical phase was found in the scuff mark, which was apparently responsible for the high reactivity.

  10. Phase Change Material Heat Sink for an ISS Flight Experiment

    NASA Technical Reports Server (NTRS)

    Quinn, Gregory; Stieber, Jesse; Sheth, Rubik; Ahlstrom, Thomas

    2015-01-01

    A flight experiment is being constructed to utilize the persistent microgravity environment of the International Space Station (ISS) to prove out operation of a microgravity compatible phase change material (PCM) heat sink. A PCM heat sink can help to reduce the overall mass and volume of future exploration spacecraft thermal control systems (TCS). The program is characterizing a new PCM heat sink that incorporates a novel phase management approach to prevent high pressures and structural deformation that often occur with PCM heat sinks undergoing cyclic operation in microgravity. The PCM unit was made using brazed aluminum construction with paraffin wax as the fusible material. It is designed to be installed into a propylene glycol and water cooling loop, with scaling consistent with the conceptual designs for the Orion Multipurpose Crew Vehicle. This paper reports on the construction of the PCM heat sink and on initial ground test results conducted at UTC Aerospace Systems prior to delivery to NASA. The prototype will be tested later on the ground and in orbit via a self-contained experiment package developed by NASA Johnson Space Center to operate in an ISS EXPRESS rack.

  11. Diffusion and phase change characterization by mass spectrometry

    NASA Technical Reports Server (NTRS)

    Koslin, M. E.; White, F. A.

    1979-01-01

    The high temperature diffusion of trace elements in metals and alloys was investigated. Measurements were made by high sensitivity mass spectrometry in which individual atoms were detected, and quantitative data was obtained for zircaloy-2, 304 stainless steel, and tantalum. Additionally, a mass spectrometer was also an analytical tool for determining an allotropic phase change for stainless steel at 955 C, and a phase transition region between 772 C and 1072 C existing for zircaloy-2. Diffusion rates were measured in thin (0.001" (0.0025 cm) and 0.0005" (0.0013 cm)) ribbons which were designed as high temperature thermal ion sources, with the alkali metals as naturally occurring impurities. In the temperature and pressure regime where diffusion measurements were made, the solute atoms evaporated from the ribbon filaments when the impurities diffused to the surface, with a fraction of these impurity atoms ionized according to the Langmuir-Saha relation. The techniques developed can be applied to many other alloys important to space vehicles and supersonic transports; and, with appropriate modifications, to the diffusion of impurities in composites.

  12. Enabling tunable micromechanical bandpass filters through phase-change materials

    NASA Astrophysics Data System (ADS)

    Cao, Yunqi; Torres, David; Wang, Tongyu; Tan, Xiaobo; Sepúlveda, Nelson

    2017-08-01

    Vanadium dioxide (VO2), one of the most promising phase-change smart materials, has shown strong frequency tuning capabilities in MEMS resonators. In this paper, we demonstrate the potential use of VO2-based MEMS devices as second-order kilohertz (kHz) bandpass filters with tunable band selectivity and adjustable bandwidth (BW). Two identical on-chip micro resonators are actuated using mechanical excitation and measured using optical detection. One of the resonators is not actuated while the other is tuned by applying electric currents across an integrated resistive heater, which induces the phase transition of the VO2, and consequently a large stress to the mechanical structure. The responses of both MEMS resonators are combined, resulting in a resonant peak of tunable BW controlled by the input current. The BW can be extended to 2.62 times by using two bridges or 2.39 times by implementing one pair of cantilevers. The results for both devices are discussed.

  13. Plastic phase change material and articles made therefrom

    DOEpatents

    Abhari, Ramin

    2016-04-19

    The present invention generally relates to a method for manufacturing phase change material (PCM) pellets. The method includes providing a melt composition, including paraffin and a polymer. The paraffin has a melt point of between about 10.degree. C. and about 50.degree. C., and more preferably between about 18.degree. C. and about 28.degree. C. In one embodiment, the melt composition includes various additives, such as a flame retardant. The method further includes forming the melt composition into PCM pellets. The method further may include the step of cooling the melt to increase the melt viscosity before pelletizing. Further, PCM compounds are provided having an organic PCM and a polymer. Methods are provided to convert the PCM compounds into various form-stable PCMs. A method of coating the PCMs is included to provide PCMs with substantially no paraffin seepage and with ignition resistance properties.

  14. Understanding the phase-change mechanism of rewritable optical media.

    PubMed

    Kolobov, Alexander V; Fons, Paul; Frenkel, Anatoly I; Ankudinov, Alexei L; Tominaga, Junji; Uruga, Tomoya

    2004-10-01

    Present-day multimedia strongly rely on rewritable phase-change optical memories. We demonstrate that, different from the current consensus, Ge(2)Sb(2)Te(5), the material of choice in DVD-RAM, does not possess the rocksalt structure but more likely consists of well-defined rigid building blocks that are randomly oriented in space consistent with cubic symmetry. Laser-induced amorphization results in drastic shortening of covalent bonds and a decrease in the mean-square relative displacement, demonstrating a substantial increase in the degree of short-range ordering, in sharp contrast to the amorphization of typical covalently bonded solids. This novel order-disorder transition is due to an umbrella-flip of Ge atoms from an octahedral position into a tetrahedral position without rupture of strong covalent bonds. It is this unique two-state nature of the transformation that ensures fast DVD performance and repeatable switching over ten million cycles.

  15. Bearing and retention apparatus for a camshaft phase change device

    SciTech Connect

    Danieli, O.G.

    1992-10-06

    This patent describes a phase change device. It comprises: an output member, in input member, bearing means supporting the input member for rotation on the output member, an advancing member received between the input and output member and being operative upon axial movement thereof to effect limited relative rotation between the input and output member, drum means engaged with the advancing member to effect the axial movement of the advancing member when a retarding force is applied to the drum means, and actuating means operable to apply the retarding force. This patent describes improvement in the bearing means. It comprises a first peripheral groove formed in the input member, a second peripheral groove formed in the output member, and a plurality of balls received in the first and second grooves.

  16. Thermal analysis of n-alkane phase change material mixtures

    SciTech Connect

    Chio, Y.I.; Choi, E.; Lorsch, H.G.

    1991-03-31

    Tests were performed to characterize the thermal behavior of it number of n-alkanes to be used as phase change materials (PCMs) in district cooling applications. Hexadecane and tetradecane were mixed in different fractions, and their thermal behavior was experimentally evaluated. Test results for melting temperature and fusion energy for laboratory grade hexadecane and tetradecane showed good agreement with datain the literature. However, values for commercial grade hexadecane were found to be considerably lower. In the range of temperatures of interest for district cooling, mixtures of tetradecane and hexadecane can be treated as homogeneous substances. However, their heats of fusion are slightly lower than those of the pure substances. Their melting temperatures are also lower by an amount that can be predicted.

  17. Modeling of subcooling and solidification of phase change materials

    NASA Astrophysics Data System (ADS)

    Günther, Eva; Mehling, Harald; Hiebler, Stefan

    2007-12-01

    Phase change materials (PCM) are able to store thermal energy in small temperature intervals very efficiently due to their high latent heat. Particularly high storage capacity is found in salt hydrates. Salt hydrates however often show subcooling, thus inhibiting the release of the stored heat. In the state of the art simulations of PCM, the effect of subcooling is almost always neglected. This is a practicable approach for small subcooling, but it is problematic for subcooling in the order of the driving temperature gradient on unloading the storage. In this paper, we first present a new algorithm to simulate subcooling in a physically proper way. Then, we present a parametric study to demonstrate the main features of the algorithm and a comparison of computed and experimentally obtained data. The new algorithm should be particularly useful in simulating applications with low cooling rates, for example building applications.

  18. Control surface wettability with nanoparticles from phase-change materials

    NASA Astrophysics Data System (ADS)

    ten Brink, G. H.; van het Hof, P. J.; Chen, B.; Sedighi, M.; Kooi, B. J.; Palasantzas, G.

    2016-12-01

    The wetting state of surfaces can be controlled physically from the highly hydrophobic to hydrophilic states using the amorphous-to-crystalline phase transition of Ge2Sb2Te5 (GST) nanoparticles as surfactant. Indeed, contact angle measurements show that by increasing the surface coverage of the amorphous nanoparticles the contact angle increases to high values ˜140°, close to the superhydrophobic limit. However, for crystallized nanoparticle assemblies after thermal annealing, the contact angle decreases down to ˜40° (significantly lower than that of the bare substrate) leading to an increased hydrophilicity. Moreover, the wettability changes are also manifested on the capillary adhesion forces by being stronger for the crystallized GST state.

  19. Pickering Emulsification to Mass Produce Nanoencapsulated Phase-change-material

    NASA Astrophysics Data System (ADS)

    Wang, Xuezhen; Zhang, Lecheng; Yu, Yi-Hsien; Mannan, S. Sam; Chen, Ying; Cheng, Zhengdong; Cheng's Group Team, Dr.

    2015-03-01

    Phase changing materials (PCM) have useful applications in thermal management. However, mass production of micro and nano encapsulated PCM has been a challenge. Here, we present a simple and scalable method via a two-step Pickering emulsification method. We have developed interface active nanoplates by asymmetric modification of nanoplates of layered crystal materials. Nanoencapsulated PCM is realized with exfoliated monolayer nanoplates surfactants using very little energy input for emulsification. Further chemical reactions are performed to convert the emulsions into core-shell structures. The resulted capsules are submicron in size with remarkable uniformity in size distribution. DSC characterization showed that the capsulation efficiency of NEPCM was 58.58% and were thermal stable which was characterized by the DSC data for the sample after 200 thermal cycling.

  20. Self-tracking phase change concentrator device demonstrator

    NASA Astrophysics Data System (ADS)

    Zagolla, V.; Tremblay, E.; Moser, C.

    2014-10-01

    Concentration photovoltaic systems uses free-space optics to concentrate sunlight onto photovoltaic cells, using mechanical trackers to accurately track the sun's position and keep the focal spot on the PV cell. We recently proposed and demonstrated a proof-of concept of a self-tracking mechanism using a phase-change material to greatly extend the acceptance angle of the concentration device. The light responsive mechanism allows for efficient waveguide coupling and light concentration independent of the angle of incidence inside its angular range of acceptance. The system uses a lens pair to achieve a flat Petzval field curvature over the acceptance angle range. A waveguide slab acts as the concentrating device. The use of a dichroic prism membrane separates the solar spectrum into two parts, lower wavelengths (<750nm) are coupled into the waveguide, while the energy of higher wavelengths (>750nm) is used to power the self-tracking mechanism. The energy in this part of the spectrum is absorbed by a carbon black paraffin wax mixture that undergoes a phase change and subsequently creates a coupling feature due to thermal expansion which allows the lower wavelength part to be coupled into the waveguide. We show the extension of our proof-of concept to a device-like demonstrator, featuring the extension to a lens array and much larger dimensions. All parts of the proof-of-concept device have been upscaled to meet the requirements of a larger scale demonstrator. The demonstrator has an acceptance angle of +/- 16 degrees and can achieve an effective concentration factor of 20x. We present experimental and simulation results of the demonstration device.

  1. Heat transfer in vertically aligned phase change energy storage systems

    SciTech Connect

    El-Dessouky, H.T.; Bouhamra, W.S.; Ettouney, H.M.; Akbar, M.

    1999-05-01

    Convection effects on heat transfer are analyzed in low temperature and vertically aligned phase change energy storage systems. This is performed by detailed temperature measurements in the phase change material (PCM) in eighteen locations forming a grid of six radial and three axial positions. The system constitutes a double pipe configuration, where commercial grade paraffin wax is stored in the annular space between the two pipes and water flows inside the inner pipe. Vertical alignment of the system allowed for reverse of the flow direction of the heat transfer fluid (HTF), which is water. Therefore, the PCM is heated from the bottom for HTF flow from bottom to top and from the top as the HTF flow direction is reversed. For the former case, natural convection affects the melting process. Collected data are used to study variations in the transient temperature distribution at axial and radial positions as well as for the two-dimensional temperature field. The data are used to calculate the PCM heat transfer coefficient and to develop correlations for the melting Fourier number. Results indicate that the PCM heat transfer coefficient is higher for the case of PCM heating from bottom to top. Nusselt number correlations are developed as a function of Rayleigh, Stefan, and Fourier numbers for the HTF flow from bottom to top and as a function of Stefan and Fourier numbers for HTF flow from top to bottom. The enhancement ratio for heat transfer caused by natural convection increases and then levels off as the inlet temperature of the HTF is increased.

  2. MULTI-PHASE FRACTURE-MATRIX INTERACTIONS UNDER STRESS CHANGES

    SciTech Connect

    A.S. Grader; D. Elsworth; P.M. Halleck; F. Alvarado; A. Alajmi; Z. Karpyn; N. Mohammed; S. Al-Enezi

    2005-06-15

    The main objectives of this project are to quantify the changes in fracture porosity and multiphase transport properties as a function of confining stress. These changes will be integrated into conceptual and numerical models that will improve our ability to predict and optimize fluid transport in fractured system. This report details our progress on: (a) developing the direct experimental measurements of fracture aperture and topology and fluid occupancy using high-resolution x-ray micro-tomography, (b) quantifying the effect of confining stress on the distribution of fracture aperture, and (c) characterization of shear fractures and their impact on multi-phase flow. The three-dimensional surface that describes the large-scale structure of the fracture in the porous medium can be determined using x-ray micro-tomography with significant accuracy. Several fractures have been scanned and the fracture aperture maps have been extracted. The success of the mapping of fracture aperture was followed by measuring the occupancy of the fracture by two immiscible phases, water and decane, and water and kerosene. The distribution of fracture aperture depends on the effective confining stress on the nature of the rock and the type and distribution of the asperities that keep the fracture open. Fracture apertures at different confining stresses were obtained by micro-tomography covering a range of about two thousand psig. Initial analysis of the data shows a significant aperture closure with increase in effective confining stress. Visual descriptions of the process are shown in the report while detailed analysis of the behavior of the distribution of fracture aperture is in progress. Both extensional and shear fractures are being considered. The initial multi-phase flow tests were done in extensional fractures. Several rock samples with induced shear fracture are being studies, and some of the new results are presented in this report. These samples are being scanned in order to

  3. Consistent implementation of phase changes into geodynamic models

    NASA Astrophysics Data System (ADS)

    Hetényi, György; Connolly, James A. D.; Godard, Vincent; Cattin, Rodolphe

    2010-05-01

    Numerical modelling of geodynamic processes occurring on geologic timescales is a rapidly evolving field of research. Despite this rapid growth, one of the initial simplifying assumptions of early numerical models is still overlooked, as the continuity equation regarding mass is mostly left out of consideration. In fluid dynamics this is known as the Boussinesq approximation. In visco-elastic models of the lithosphere this manifests in using phase equilibria calculations to modify the density of rocks without considering any volumetric effect. We explore the consequences of this simplification by developing an approach that allows us to obtain rigorously correct solutions for continuity. In technical terms, we use the finite element thermo-mechanical modelling tool Cast3M. This tool was previously developed for geodynamic applications, and handles elastic and visco-elastic rheology, erosion laws, as well as remeshing. We further develop the numerical code to incorporate the volumetric changes due to mineralogic phase transformations through modification of the regional stress-field. Exact density values are derived from petrogenetic grid calculated by software Perple_X. Our application focuses on mountain range evolution. We study the evolution of its deformation at surface as well as at depth, with and without different modelling conditions to evaluate their respective importance: elastic vs. visco-elastic behaviour; erosion; horizontal convergence; hydration level of the mafic lower crust; and consistent application of phase changes. We focus on the metamorphic reactions occurring in the lower crust, as this is where the largest density and hence volumetric effects are expected to occur in the lithosphere. The results after 4 Myr simulation time show that, when enforcing continuity, metamorphic reactions play an important role on the deformation of the orogen: the effects on the evolution of topography are of the same order of magnitude as effects resulting from

  4. MULTI-PHASE FRACTURE-MATRIX INTERACTIONS UNDER STRESS CHANGES

    SciTech Connect

    A.S. Grader; D. Elsworth; P.M. Halleck; F. Alvarad; H. Yasuhara; A. Alajmi

    2002-04-20

    The main objectives of this project are to quantify the changes in fracture porosity and multi-phase transport properties as a function of confining stress. These changes will be integrated into conceptual and numerical models that will improve our ability to predict and optimize fluid transport in fractured system. This report details our progress on: (1) developing the direct experimental measurements of fracture aperture and topology using high-resolution x-ray micro-tomography, (2) modeling of fracture permeability in the presence of asperities and confining stress, and (3) simulation of two-phase fluid flow in a fracture and a layered matrix. The three-dimensional surface that describes the large-scale structure of the fracture in the porous medium can be determined using x-ray micro-tomography with significant accuracy. The distribution of fracture aperture is a difficult issue that we are studying and developing methods of quantification. The difficulties are both numerical and conceptual. Numerically, the three-dimensional data sets include millions, and sometimes, billions of points, and pose a computational challenge. The conceptual difficulties derive from the rough nature of the fracture surfaces, and the heterogeneous nature of the rock matrix. However, the high-resolution obtained by the imaging system provides us a much needed measuring environment on rock samples that are subjected to simultaneous fluid flow and confining stress. The absolute permeability of a fracture depends on the behavior of the asperities that keep it open. A model is being developed that predicts the permeability and average aperture of a fracture as a function of time under steady flow of water including the pressure solution at the asperity contact points. Several two-phase flow experiments in the presence of a fracture tip were performed in the past. At the present time, we are developing an inverse process using a simulation model to understand the fluid flow patterns in

  5. MULTI-PHASE FRACTURE-MATRIX INTERACTIONS UNDER STRESS CHANGES

    SciTech Connect

    A.S. Grader; D. Elsworth; P.M. Halleck; F. Alvarado; A. Alajmi; Z. Karpyn; N. Mohammed; S. Al-Enezi

    2005-06-15

    The main objectives of this project are to quantify the changes in fracture porosity and multiphase transport properties as a function of confining stress. These changes will be integrated into conceptual and numerical models that will improve our ability to predict and optimize fluid transport in fractured system. This report details our progress on: (a) developing the direct experimental measurements of fracture aperture and topology and fluid occupancy using high-resolution x-ray micro-tomography, (b) quantifying the effect of confining stress on the distribution of fracture aperture, and (c) characterization of shear fractures and their impact on multi-phase flow. The three-dimensional surface that describes the large-scale structure of the fracture in the porous medium can be determined using x-ray micro-tomography with significant accuracy. Several fractures have been scanned and the fracture aperture maps have been extracted. The success of the mapping of fracture aperture was followed by measuring the occupancy of the fracture by two immiscible phases, water and decane, and water and kerosene. The distribution of fracture aperture depends on the effective confining stress on the nature of the rock and the type and distribution of the asperities that keep the fracture open. Fracture apertures at different confining stresses were obtained by micro-tomography covering a range of about two thousand psig. Initial analysis of the data shows a significant aperture closure with increase in effective confining stress. Visual descriptions of the process are shown in the report while detailed analysis of the behavior of the distribution of fracture aperture is in progress. Both extensional and shear fractures are being considered. The initial multi-phase flow tests were done in extensional fractures. Several rock samples with induced shear fracture are being studied, and some of the new results are presented in this report. These samples are being scanned in order to

  6. Phase Change Characteristics of a Nanoemulsion as a Latent Heat Storage Material

    NASA Astrophysics Data System (ADS)

    Fumoto, Koji; Sato, Noriaki; Kawaji, Masahiro; Kawanami, Tsuyoshi; Inamura, Takao

    2014-10-01

    The primary objective of this study was to investigate the fundamental phase change characteristics of a nanoemulsion using differential scanning calorimetry (DSC). Tetradecane, which has a slightly higher melting point than water, was utilized as the phase change material for the nanoemulsion. The melting point of the nanoemulsion, the melting peak temperature, and latent heat were examined in detail. Regarding the fundamental phase change characteristics of the nanoemulsion, it was found that its phase change characteristics were strongly affected by the temperature-scanning rate of the DSC. Moreover, it was confirmed that the phase change behavior does not change with repeated solidification and melting.

  7. Sb-Te Phase-change Materials under Nanoscale Confinement

    NASA Astrophysics Data System (ADS)

    Ihalawela, Chandrasiri A.

    Size, speed and efficiency are the major challenges of next generation nonvolatile memory (NVM), and phase-change memory (PCM) has captured a great attention due to its promising features. The key for PCM is rapid and reversible switching between amorphous and crystalline phases with optical or electrical excitation. The structural transition is associated with significant contrast in material properties which can be utilized in optical (CD, DVD, BD) and electronic (PCRAM) memory applications. Importantly, both the functionality and the success of PCM technology significantly depend on the core material and its properties. So investigating PC materials is crucial for the development of PCM technology to realized enhanced solutions. In regards to PC materials, Sb-Te binary plays a significant role as a basis to the well-known Ge-Sb-Te system. Unlike the conventional deposition methods (sputtering, evaporation), electrochemical deposition method is used due to its multiple advantages, such as conformality, via filling capability, etc. First, the controllable synthesis of Sb-Te thin films was studied for a wide range of compositions using this novel deposition method. Secondly, the solid electrolytic nature of stoichiometric Sb2Te3 was studied with respect to precious metals. With the understanding of 2D thin film synthesis, Sb-Te 1D nanowires (18 - 220 nm) were synthesized using templated electrodeposition, where nanoporous anodic aluminum oxide (AAO) was used as a template for the growth of nanowires. In order to gain the controllability over the deposition in high aspect ratio structures, growth mechanisms of both the thin films and nanowires were investigated. Systematic understanding gained thorough previous studies helped to formulate the ultimate goal of this dissertation. In this dissertation, the main objective is to understand the size effect of PC materials on their phase transition properties. The reduction of effective memory cell size in conjunction with

  8. Phase change thermal control materials, method and apparatus

    NASA Technical Reports Server (NTRS)

    Buckley, Theresa M. (Inventor)

    2001-01-01

    An apparatus and method for metabolic cooling and insulation of a user in a cold environment. In its preferred embodiment the apparatus is a highly flexible composite material having a flexible matrix containing a phase change thermal storage material. The apparatus can be made to heat or cool the body or to act as a thermal buffer to protect the wearer from changing environmental conditions. The apparatus may also include an external thermal insulation layer and/or an internal thermal control layer to regulate the rate of heat exchange between the composite and the skin of the wearer. Other embodiments of the apparatus also provide 1) a path for evaporation or direct absorption of perspiration from the skin of the wearer for improved comfort and thermal control, 2) heat conductive pathways within the material for thermal equalization, 3) surface treatments for improved absorption or rejection of heat by the material, and 4) means for quickly regenerating the thermal storage capacity for reuse of the material. Applications of the composite materials are also described which take advantage of the composite's thermal characteristics. The examples described include a diver's wet suit, ski boot liners, thermal socks, gloves and a face mask for cold weather activities, and a metabolic heating or cooling blanket useful for treating hypothermia or fever patients in a medical setting and therapeutic heating or cooling orthopedic joint supports.

  9. Flexible composite material with phase change thermal storage

    NASA Technical Reports Server (NTRS)

    Buckley, Theresa M. (Inventor)

    2001-01-01

    A highly flexible composite material having a flexible matrix containing a phase change thermal storage material. The composite material can be made to heat or cool the body or to act as a thermal buffer to protect the wearer from changing environmental conditions. The composite may also include an external thermal insulation layer and/or an internal thermal control layer to regulate the rate of heat exchange between the composite and the skin of the wearer. Other embodiments of the PCM composite also provide 1) a path for evaporation or direct absorption of perspiration from the skin of the wearer for improved comfort and thermal control, 2) heat conductive pathways within the material for thermal equalization, 3) surface treatments for improved absorption or rejection of heat by the material, and 4) means for quickly regenerating the thermal storage capacity for reuse of the material. Applications of the composite materials are also described which take advantage of the composite's thermal characteristics. The examples described include a diver's wet suit, ski boot liners, thermal socks, ,gloves and a face mask for cold weather activities, and a metabolic heating or cooling blanket useful for treating hypothermia or fever patients in a medical setting and therapeutic heating or cooling orthopedic joint supports.

  10. Flexible composite material with phase change thermal storage

    NASA Technical Reports Server (NTRS)

    Buckley, Theresa M. (Inventor)

    1999-01-01

    A highly flexible composite material having a flexible matrix containing a phase change thermal storage material. The composite material can be made to heat or cool the body or to act as a thermal buffer to protect the wearer from changing environmental conditions. The composite may also include an external thermal insulation layer and/or an internal thermal control layer to regulate the rate of heat exchange between the composite and the skin of the wearer. Other embodiments of the PCM composite also provide 1) a path for evaporation or direct absorption of perspiration from the skin of the wearer for improved comfort and thermal control, 2) heat conductive pathways within the material for thermal equalization, 3) surface treatments for improved absorption or rejection of heat by the material, and 4) means for quickly regenerating the thermal storage capacity for reuse of the material. Applications of the composite materials are also described which take advantage of the composite's thermal characteristics. The examples described include a diver's wet suit, ski boot liners, thermal socks, gloves and a face mask for cold weather activities, and a metabolic heating or cooling blanket useful for treating hypothermia or fever patients in a medical setting and therapeutic heating or cooling orthopedic joint supports.

  11. FPGA-based prototype storage system with phase change memory

    NASA Astrophysics Data System (ADS)

    Li, Gezi; Chen, Xiaogang; Chen, Bomy; Li, Shunfen; Zhou, Mi; Han, Wenbing; Song, Zhitang

    2016-10-01

    With the ever-increasing amount of data being stored via social media, mobile telephony base stations, and network devices etc. the database systems face severe bandwidth bottlenecks when moving vast amounts of data from storage to the processing nodes. At the same time, Storage Class Memory (SCM) technologies such as Phase Change Memory (PCM) with unique features like fast read access, high density, non-volatility, byte-addressability, positive response to increasing temperature, superior scalability, and zero standby leakage have changed the landscape of modern computing and storage systems. In such a scenario, we present a storage system called FLEET which can off-load partial or whole SQL queries to the storage engine from CPU. FLEET uses an FPGA rather than conventional CPUs to implement the off-load engine due to its highly parallel nature. We have implemented an initial prototype of FLEET with PCM-based storage. The results demonstrate that significant performance and CPU utilization gains can be achieved by pushing selected query processing components inside in PCM-based storage.

  12. Multi-Phase Fracture-Matrix Interactions Under Stress Changes

    SciTech Connect

    A.S. Grader; D. Elsworth; P.M. Halleck; F. Alvarao; A. Alajmi; Z. Karpyn; N. Mohammed; S. Al-Enezi

    2005-12-07

    The main objectives of this project are to quantify the changes in fracture porosity and multi-phase transport properties as a function of confining stress. These changes will be integrated into conceptual and numerical models that will improve our ability to predict and optimize fluid transport in fractured system. This report details our progress on: (a) developing the direct experimental measurements of fracture aperture and topology and fluid occupancy using high-resolution x-ray micro-tomography, (b) counter-current fluid transport between the matrix and the fracture, (c) studying the effect of confining stress on the distribution of fracture aperture and two-phase flow, and (d) characterization of shear fractures and their impact on multi-phase flow. The three-dimensional surface that describes the large-scale structure of the fracture in the porous medium can be determined using x-ray micro-tomography with significant accuracy. Several fractures have been scanned and the fracture aperture maps have been extracted. The success of the mapping of fracture aperture was followed by measuring the occupancy of the fracture by two immiscible phases, water and decane, and water and kerosene. The distribution of fracture aperture depends on the effective confining stress, on the nature of the rock, and the type and distribution of the asperities that keep the fracture open. Fracture apertures at different confining stresses were obtained by micro-tomography covering a range of about two thousand psig. Initial analysis of the data shows a significant aperture closure with increase in effective confining stress. Visual and detailed descriptions of the process are shown in the report. Both extensional and shear fractures have been considered. A series of water imbibition tests were conducted in which water was injected into a fracture and its migration into the matrix was monitored with CT and DR x-ray techniques. The objective was to understand the impact of the

  13. Development of Phase Change Materials for RF Switch Applications

    NASA Astrophysics Data System (ADS)

    King, Matthew Russell

    For decades chalcogenide-based phase change materials (PCMs) have been reliably implemented in optical storage and digital memory platforms. Owing to the substantial differences in optical and electronic properties between crystalline and amorphous states, device architectures requiring a "1" and "0" or "ON" and "OFF" states are attainable with PCMs if a method for amorphizing and crystallizing the PCM is demonstrated. Taking advantage of more than just the binary nature of PCM electronic properties, recent reports have shown that the near-metallic resistivity of some PCMs allow one to manufacture high performance RF switches and related circuit technologies. One of the more promising RF switch technologies is the Inline Phase Change Switch (IPCS) which utilizes GeTe as the active material. Initial reports show that an electrically isolated, thermally coupled thin film heater can successfully convert GeTe between crystalline and amorphous states, and with proper design an RF figure of merit cutoff frequency (FCO) of 12.5 THz can be achieved. In order to realize such world class performance a significant development effort was undertaken to understand the relationship between fundamental GeTe properties, thin film deposition method and resultant device properties. Deposition pressure was found to be the most important deposition process parameter, as it was found to control Ge:Te ratio, oxygen content, Ar content, film density and surface roughness. Ultimately a first generation deposition process produced GeTe films with a crystalline resistivity of 3 ohm-mum. Upon implementing these films into IPCS devices, post-cycling morphological analysis was undertaken using STEM and related analyses. It was revealed that massive structural changes occur in the GeTe during switching, most notably the formation of an assembly of voids along the device centerline and large GeTe grains on either side of the so-called active region. Restructuring of this variety was tied to

  14. Continued Water-Based Phase Change Material Heat Exchanger Development

    NASA Technical Reports Server (NTRS)

    Hansen, Scott W.; Sheth, Rubik B.; Poynot, Joe; Giglio, Tony; Ungar, Gene K.

    2015-01-01

    In a cyclical heat load environment such as low Lunar orbit, a spacecraft's radiators are not sized to meet the full heat rejection demands. Traditionally, a supplemental heat rejection device (SHReD) such as an evaporator or sublimator is used to act as a "topper" to meet the additional heat rejection demands. Utilizing a Phase Change Material (PCM) heat exchanger (HX) as a SHReD provides an attractive alternative to evaporators and sublimators as PCM HX's do not use a consumable, thereby leading to reduced launch mass and volume requirements. In continued pursuit of water PCM HX development two full-scale, Orion sized water-based PCM HX's were constructed by Mezzo Technologies. These HX's were designed by applying prior research on freeze front propagation to a full-scale design. Design options considered included bladder restraint and clamping mechanisms, bladder manufacturing, tube patterns, fill/drain methods, manifold dimensions, weight optimization, and midplate designs. Two units, Units A and B, were constructed and differed only in their midplate design. Both units failed multiple times during testing. This report highlights learning outcomes from these tests and are applied to a final sub-scale PCM HX which is slated to be tested on the ISS in early 2017.

  15. Water Based Phase Change Material Heat Exchanger Development

    NASA Technical Reports Server (NTRS)

    Hansen, Scott W.; Sheth, Ribik B.; Atwell, Matt; Cheek, Ann; Agarwal, Muskan; Hong, Steven; Patel, Aashini,; Nguyen, Lisa; Posada, Luciano

    2014-01-01

    In a cyclical heat load environment such as low Lunar orbit, a spacecraft’s radiators are not sized to reject the full heat load requirement. Traditionally, a supplemental heat rejection device (SHReD) such as an evaporator or sublimator is used to act as a “topper” to meet the additional heat rejection demands. Utilizing a Phase Change Material (PCM) heat exchanger (HX) as a SHReD provides an attractive alternative to evaporators and sublimators as PCM HXs do not use a consumable, thereby leading to reduced launch mass and volume requirements. Studies conducted in this paper investigate utilizing water’s high latent heat of formation as a PCM, as opposed to traditional waxes, and corresponding complications surrounding freezing water in an enclosed volume. Work highlighted in this study is primarily visual and includes understanding ice formation, freeze front propagation, and the solidification process of water/ice. Various test coupons were constructed of copper to emulate the interstitial pin configuration (to aid in conduction) of the proposed water PCM HX design. Construction of a prototypic HX was also completed in which a flexible bladder material and interstitial pin configurations were tested. Additionally, a microgravity flight was conducted where three copper test articles were frozen continuously during microgravity and 2-g periods and individual water droplets were frozen during microgravity.

  16. Pelletization and roll encapsulation of phase change materials

    NASA Astrophysics Data System (ADS)

    Chen, J.; Nelson, R.; Polinski, F. X.

    1982-02-01

    Based on the criteria of high latent heats of fusion, low cost, and ease of pelletization, seven phase change materials (PCM's) with melting points in the ranges suitable for absorption cooling, active heating, and passive space conditioning applications have been pressed into pellets about 12 mm in diameter and then encapsulated with organic coating materials by a roll coating process. Capsules of four of the seven PCM candidates have shown retention of integrity in various aqueous heat exchange fluids in accelerated thermal cycling tests ranging between 1500 to 2900 heating and cooling cycles. Capsules of PCM's melting near room temperature have also shown good stability in laboratory air environment. The objective of this effort is to develop reliable and cost effective PCM's for use in: (1) active heat exchange packed bed assemblies of simple design that are capable of providing heat exchange efficiency and storage capacity superior to those of conventional heat storge systems, and (2) passive heat storage systems consisting of building products incorporating thermal energy storage materials. The feasibility of this approach is supported by a favorable cost analysis.

  17. Applications of fibrous substrates containing insolubilized phase change polymers

    NASA Technical Reports Server (NTRS)

    Vigo, Tyrone L.; Bruno, Joseph S.

    1993-01-01

    Incorporation of polyethylene glycols into fibrous substrates produces several improved functional properties when they are insolubilized by crosslinking with a methylolamide resin or by polyacetal formation by their reaction with glyoxal. The range of molecular weights of polyols that may be insolubilized is broad as are the curing conditions (0.25-10 min at 80-200C). Most representative fiber types and blends (natural and synthetic) and all types of fabric constructions (woven, nonwoven and knit) have been modified by incorporation of the bound polyols. The most novel property is the thermal adaptability of the modified substrates to many climatic conditions. This adaptability is due to the high latent heat of the crosslinked polyols that function as phase change materials, the hydrophilic nature of the crosslinked polymer and its enhanced thermal conductivity. Other enhanced properties imparted to fabrics include flex and flat abrasion, antimicrobial activity, reduced static charge, resistance to oily soils, resiliency, wind resistance and reduced lint loss. Applications commercialized in the U.S. and Japan include sportswear and skiwear. Several examples of electric sets of properties useful for specific end uses are given. In addition, other uses are biomedical horticultural, aerospace, indoor insulation, automotive interiors and components and packaging material.

  18. Precision manufacture of phase-change perfluorocarbon droplets using microfluidics.

    PubMed

    Martz, Thomas D; Sheeran, Paul S; Bardin, David; Lee, Abraham P; Dayton, Paul A

    2011-11-01

    Liquid perfluorocarbon droplets have been of interest in the medical acoustics community for use as acoustically activated particles for tissue occlusion, imaging and therapeutics. To date, methods to produce liquid perfluorocarbon droplets typically result in a polydisperse size distribution. Because the threshold of acoustic activation is a function of diameter, there would be benefit from a monodisperse population to preserve uniformity in acoustic activation parameters. Through use of a microfluidic device with flow-focusing technology, the production of droplets of perfluoropentane with a uniform size distribution is demonstrated. Stability studies indicate that these droplets are stable in storage for at least two weeks. Acoustic studies illustrate the thresholds of vaporization as a function of droplet diameter, and a logarithmic relationship is observed between acoustic pressure and vaporization threshold within the size ranges studied. Droplets of uniform size have very little variability in acoustic vaporization threshold. Results indicate that microfluidic technology can enable greater manufacturing control of phase-change perfluorocarbons for acoustic droplet vaporization applications.

  19. Experimental Investigation of Ice Phase Change Material Heat Exchangers

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Stephan, Ryan A.

    2012-01-01

    Phase change materials (PCM) may be useful for spacecraft thermal control systems that involve cyclical heat loads or cyclical thermal environments. Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. This can result in a decreased turndown ratio for the radiator and a reduced system mass. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents an overview of the results of this investigation from the past three years.

  20. University of South Florida- Phase Change Materials (PCM)

    ScienceCinema

    Goswami, Yogi; Stefanakos, Lee

    2016-07-12

    USF is developing low-cost, high-temperature phase-change materials (PCMs) for use in thermal energy storage systems. Heat storage materials are critical to the energy storage process. In solar thermal storage systems, heat can be stored in these materials during the day and released at night--when the sun is not out--to drive a turbine and produce electricity. In nuclear storage systems, heat can be stored in these materials at night and released to produce electricity during daytime peak-demand hours. Most PCMs do not conduct heat very well. Using an innovative, electroless encapsulation technique, USF is enhancing the heat transfer capability of its PCMs. The inner walls of the capsules will be lined with a corrosion-resistant, high-infrared emissivity coating, and the absorptivity of the PCM will be controlled with the addition of nano-sized particles. USF's PCMs remain stable at temperatures from 600 to 1,000°C and can be used for solar thermal power storage, nuclear thermal power storage, and other applications.

  1. Experimental Investigation of Ice Phase Change Material Heat Exchangers

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Stephan, Ryan A.

    2011-01-01

    Phase change materials (PCM) may be useful for spacecraft thermal control systems that involve cyclical heat loads or cyclical thermal environments. Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. This can result in a decreased turndown ratio for the radiator and a reduced system mass. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents an overview of the results of this investigation from the past three years.

  2. Numerical Modeling of Liquid-Vapor Phase Change

    NASA Technical Reports Server (NTRS)

    Esmaeeli, Asghar; Arpaci, Vedat S.

    2001-01-01

    We implemented a two- and three-dimensional finite difference/front tracking technique to solve liquid-vapor phase change problems. The mathematical and the numerical features of the method were explained in great detail in our previous reports, Briefly, we used a single formula representation which incorporated jump conditions into the governing equations. The interfacial terms were distributed as singular terms using delta functions so that the governing equations would be the same as conventional conservation equations away from the interface and in the vicinity of the interface they would provide correct jump conditions. We used a fixed staggered grid to discretize these equations and an unstructured grid to explicitly track the front. While in two dimensions the front was simply a connection of small line segments, in three dimensions it was represented by a connection of small triangular elements. The equations were written in conservative forms and during the course of computations we used regriding to control the size of the elements of the unstructured grid. Moreover, we implemented a coalescence in two dimensions which allowed the merging of different fronts or two segments of the same front when they were sufficiently close. We used our code to study thermocapillary migration of bubbles, burst of bubbles at a free surface, buoyancy-driven interactions of bubbles, evaporation of drops, rapid evaporation of an interface, planar solidification of an undercooled melt, dendritic solidification, and a host of other problems cited in the reference.

  3. Radiation and phase change of lithium fluoride in an annulus

    NASA Technical Reports Server (NTRS)

    Lund, Kurt O.

    1993-01-01

    A one-dimensional thermal model is developed to evaluate the effect of radiation on the phase change of lithium-fluoride (LiF) in an annular canister under gravitational and microgravitational conditions. Specified heat flux at the outer wall of the canister models focused solar flux; adiabatic and convective conditions are considered for the inner wall. A two-band radiation model is used for the combined-mode heat transfer within the canister, and LiF optical properties relate metal surface properties in vacuum to those in LiF. For axial gravitational conditions, the liquid LiF remains in contact with the two bounding walls, whereas a void gap is used at the outer wall to model possible microgravitational conditions. For the adiabatic cases, exact integrals are obtained for the time required for complete melting of the LiF. Melting was found to occur primarily from the outer wall in the 1-g model, whereas it occurred primarily from the inner wall in the mu-g model. For the convective cases, partially melted steady-state conditions and fully melted conditions are determined to depend on the source flux level, with radiation extending the melting times.

  4. University of South Florida- Phase Change Materials (PCM)

    SciTech Connect

    Goswami, Yogi; Stefanakos, Lee

    2014-03-07

    USF is developing low-cost, high-temperature phase-change materials (PCMs) for use in thermal energy storage systems. Heat storage materials are critical to the energy storage process. In solar thermal storage systems, heat can be stored in these materials during the day and released at night--when the sun is not out--to drive a turbine and produce electricity. In nuclear storage systems, heat can be stored in these materials at night and released to produce electricity during daytime peak-demand hours. Most PCMs do not conduct heat very well. Using an innovative, electroless encapsulation technique, USF is enhancing the heat transfer capability of its PCMs. The inner walls of the capsules will be lined with a corrosion-resistant, high-infrared emissivity coating, and the absorptivity of the PCM will be controlled with the addition of nano-sized particles. USF's PCMs remain stable at temperatures from 600 to 1,000°C and can be used for solar thermal power storage, nuclear thermal power storage, and other applications.

  5. Electromagnetic brake for a camshaft phase change device

    SciTech Connect

    Muir, D.J.; Brune, J.E.; Van Deusen, B.K.; Day, J.K.

    1991-07-16

    This patent describes a phase change device. It comprises a first shaft; an input member supported for rotation on the first shaft; an output member fixed to the first shaft; advancing means interconnecting the input and output members, the advancing means being operative upon axial movement to effect limited relative rotation between the input and output members; drum means supported for rotation on the first shaft and engaged with the advancing means to effect the axial movement of the advancing means when a retarding force is applied to the drum means; and actuating means operable to apply the retarding force; the improvement wherein the actuating means comprises an electromagnetic brake assembly, the electromagnetic brake assembly comprising an annular housing defining pole pieces of the electromagnet, a magnetic coil received in the housing, a nonmagnetic plate member enclosing the housing, friction material adhered to the plate member, a brake disc surface formed on the drum, and means for mounting the housing on the first shaft in juxtaposition with the brake disc surface in a substantially fixed angular position while permitting limited axial movement relative to the disc surface.

  6. Phase-change materials in architecture-opportunities and constraints

    SciTech Connect

    Kando, P.

    1985-01-01

    Affordability, which implies minimizing both construction and operating costs, is probably the central challenge of architecture today. The twin demands can be met only by simultaneously increasing construction quality and energy efficiency, while keeping its cost down. Innovative, labor- and time-saving construction techniques tend to rely on lighter weight structural components and the utilization of premanufactured components. Under these circumstances, phase change materials (PCM's) offer about the only opportunity to introduce thermal mass into modern buildings. The opportunities discussed here have to do with the relatively light weight of these materials compared to traditional means of providing mass in buildings; and with the flexibility with which these materials may be introduced into structures. The constraints are presented by aesthetic consideration on the one hand, and heat transfer considerations on the other. Ultimately the architectural challenge is to integrate these materials with both the traditional and the emerging techniques to construct buildings and provide them with indoor comfort safely at a reasonable cost.

  7. Pelletization and roll encapsulation of phase-change materials

    SciTech Connect

    Chen, J.

    1981-01-01

    Based on the criteria of high latent heats of fusion, low cost, and ease of pelletization, seven phase change materials (PCMs) with melting points in the ranges suitable for absorption cooling, active heating, and passive space conditioning applications have been pressed into pellets about 12 mm in diameter and then encapsulated with organic coating materials by a roll coating process. Capsules of four of the seven PCM candidates have shown retention of integrity in various aqueous heat exchange fluids in accelerated thermal cycling tests ranging between 1500 to 2900 heating and cooling cycles. Capsules of PCMs melting near room temperature have also shown good stability in laboratory air environment. The objective of this effort is to develop reliable and cost effective PCMs for use in: (i) active heat exchange packed-bed assemblies of simple design that are capable of providing heat exchange efficiency and storage capacity superior to those of conventional heat storage systems, and (ii) passive heat storage systems consisting of building products incorporating thermal energy storage (TES) materials. The feasibility of this approach is supported by a favorable cost analysis.

  8. Radiation and phase change of lithium fluoride in an annulus

    NASA Technical Reports Server (NTRS)

    Lund, Kurt O.

    1993-01-01

    A one-dimensional thermal model is developed to evaluate the effect of radiation on the phase change of lithium-fluoride (LiF) in an annular canister under gravitational and microgravitational conditions. Specified heat flux at the outer wall of the canister models focused solar flux; adiabatic and convective conditions are considered for the inner wall. A two-band radiation model is used for the combined-mode heat transfer within the canister, and LiF optical properties relate metal surface properties in vacuum to those in LiF. For axial gravitational conditions, the liquid LiF remains in contact with the two bounding walls, whereas a void gap is used at the outer wall to model possible microgravitational conditions. For the adiabatic cases, exact integrals are obtained for the time required for complete melting of the LiF. Melting was found to occur primarily from the outer wall in the 1-g model, whereas it occurred primarily from the inner wall in the mu-g model. For the convective cases, partially melted steady-state conditions and fully melted conditions are determined to depend on the source flux level, with radiation extending the melting times.

  9. Precision Manufacture of Phase-Change Perfluorocarbon Droplets using Microfluidics

    PubMed Central

    Martz, Thomas D.; Sheeran, Paul S.; Bardin, David; Lee, Abraham P.; Dayton, Paul A.

    2011-01-01

    Liquid perfluorocarbon droplets have been of interest in the medical acoustics community for use as acoustically activated particles for tissue occlusion, imaging, and therapeutics. To date, methods to produce liquid perfluorocarbon droplets typically result in a polydisperse size distribution. Since the threshold of acoustic activation is a function of diameter, there would be benefit from a monodisperse population to preserve uniformity in acoustic activation parameters. Through the use of a microfluidic device with flow focusing technology, the production of droplets of perfluoropentane with a uniform size distribution is demonstrated. Stability studies indicate that these droplets are stable in storage for at least two weeks. Acoustic studies illustrate the thresholds of vaporization as a function of droplet diameter, and a logarithmic relationship is observed between acoustic pressure and vaporization threshold within the size ranges studied. Droplets of uniform size have very little variability in acoustic vaporization threshold. Results indicate that microfluidic technology can enable greater manufacturing control of phase change perfluorocarbons for acoustic droplet vaporization applications. PMID:21963036

  10. Continued Water-Based Phase Change Material Heat Exchanger Development

    NASA Technical Reports Server (NTRS)

    Hansen, Scott; Poynot, Joe

    2014-01-01

    In a cyclical heat load environment such as low Lunar orbit, a spacecraft's radiators are not sized to reject the full heat load requirement. Traditionally, a supplemental heat rejection device (SHReD) such as an evaporator or sublimator is used to act as a "topper" to meet the additional heat rejection demands. Utilizing a Phase Change Material (PCM) heat exchanger (HX) as a SHReD provides an attractive alternative to evaporators and sublimators as PCM HXs do not use a consumable, thereby leading to reduced launch mass and volume requirements. In continued pursuit of water PCM HX development two full-scale, Orion sized water-based PCM HX's were constructed by Mezzo Technologies. These HX's were designed by applying prior research and experimentation to the full scale design. Design options considered included bladder restraint and clamping mechanisms, bladder manufacturing, tube patterns, fill/drain methods, manifold dimensions, weight optimization, and midplate designs. Design and construction of these HX's led to successful testing of both PCM HX's.

  11. Personality Change in the Preclinical Phase of Alzheimer Disease.

    PubMed

    Terracciano, Antonio; An, Yang; Sutin, Angelina R; Thambisetty, Madhav; Resnick, Susan M

    2017-09-20

    Changes in behavior and personality are 1 criterion for the diagnosis of dementia. It is unclear, however, whether such changes begin before the clinical onset of the disease. To determine whether increases in neuroticism, declines in conscientiousness, and changes in other personality traits occur before the onset of mild cognitive impairment or dementia. A cohort of 2046 community-dwelling older adults who volunteered to participate in the Baltimore Longitudinal Study of Aging were included. The study examined personality and clinical assessments obtained between 1980 and July 13, 2016, from participants with no cognitive impairment at first assessment who were followed up for as long as 36 years (mean [SD], 12.05 [9.54] years). The self-report personality scales were not considered during consensus diagnostic conferences. Change in self-rated personality traits assessed in the preclinical phase of Alzheimer disease and other dementias with the Revised NEO Personality Inventory, a 240-item questionnaire that assesses 30 facets, 6 for each of the 5 major dimensions: neuroticism, extraversion, openness, agreeableness, and conscientiousness. Of the 2046 participants, 931 [45.5%] were women; mean (SD) age at first assessment was 62.56 (14.63) years. During 24 569 person-years, mild cognitive impairment was diagnosed in 104 (5.1%) individuals, and all-cause dementia was diagnosed in 255 (12.5%) participants, including 194 (9.5%) with Alzheimer disease. Multilevel modeling that accounted for age, sex, race, and educational level found significant differences on the intercept of several traits: individuals who developed dementia scored higher on neuroticism (β = 2.83; 95% CI, 1.44 to 4.22; P < .001) and lower on conscientiousness (β = -3.34; 95% CI, -4.93 to -1.75; P < .001) and extraversion (β = -1.74; 95% CI, -3.23 to -0.25; P = .02). Change in personality (ie, slope), however, was not significantly different between the nonimpaired and

  12. SixSb2Te materials with stable phase for phase change random access memory applications

    NASA Astrophysics Data System (ADS)

    Gu, Yifeng; Song, Sannian; Song, Zhitang; Cheng, Yan; Du, Xiaofeng; Liu, Bo; Feng, Songlin

    2012-03-01

    The physical and electrical properties of SixSb2Te system materials with various Si contents have been systemically studied with the aim of finding the most suitable composition for the phase change random access memory (PCRAM) applications. SixSb2Te shows better thermal stability than Ge2Sb2Te5 due to no Te separation under high annealing temperatures. The increase of Si content can enhance the data retention ability of SixSb2Te materials. When the value of x is larger than 0.44, the 10-year data retention temperature for SixSb2Te will exceed 110 °C, which meets the long-term data retention requirement. Furthermore, Si-rich SixSb2Te materials exhibit the improvement on thickness change after annealing compared with Ge2Sb2Te5. In addition, the PCRAM devices based on SixSb2Te (x = 0.31, 0.44) were fabricated and the electrical operations were carried out. Both of them show the outstanding performances with long-term operations.

  13. The use of lipids as phase change materials for thermal energy storage

    USDA-ARS?s Scientific Manuscript database

    Phase change materials (PCMs) are substances capable of absorbing and releasing large 2 amounts of thermal energy (heat or cold) as latent heat over constant temperature as they 3 undergo a change in state of matter (phase transition), commonly, between solid and 4 liquid phases. Since the late 194...

  14. Performance of Thermal Insulation Containing Microencapsulated Phase Change Material

    SciTech Connect

    Kosny, Jan; Yarbrough, David; Syed, Azam M

    2007-01-01

    The objective of this study is dynamic thermal performance microencapsulated phase change material (PCM) blended with loose-fill cellulose insulation. Dynamic hot-box testing and heat-flux measurements have been made for loose-fill cellulose insulation with and without uniformly distributed microencapsulated PCM. The heat flux measurements were made with a heat-flow-meter (HFM) apparatus built in accordance with ASTM C 518. Data were obtained for 1.6 lb{sub m}/ft{sup 3} cellulose insulation containing 0 to 40 wt% PCM. Heat-flux data resulting from a rapid increase in the temperature on one side of a test specimen initially at uniform temperature were analyzed to access the effect of PCM on total heat flow. The heat flux was affected by the PCM for about 100 minutes after the temperature increase. The total heat flow during this initial period decreased linearly with PCM content from 6.5 Btu/ft{sup 2} at 0% PCM to 0.89 Btu/ft{sup 2} for 40 wt% PCM. The cellulose insulation with PCM discharged heat faster than the untreated cellulose when the hot-side temperature of the test specimen was reduced. In addition, hot-box apparatus built in accordance with ASTM C 1363 was utilized for dynamic hot-box testing of a wood stud wall assembly containing PCM-enhanced cellulose insulation. Experimental data obtained for wood-frame wall cavities containing cellulose insulation with PCM was compared with results obtained from cavities containing only cellulose insulation.

  15. Geometric structure and information change in phase transitions

    NASA Astrophysics Data System (ADS)

    Kim, Eun-jin; Hollerbach, Rainer

    2017-06-01

    We propose a toy model for a cyclic order-disorder transition and introduce a geometric methodology to understand stochastic processes involved in transitions. Specifically, our model consists of a pair of forward and backward processes (FPs and BPs) for the emergence and disappearance of a structure in a stochastic environment. We calculate time-dependent probability density functions (PDFs) and the information length L , which is the total number of different states that a system undergoes during the transition. Time-dependent PDFs during transient relaxation exhibit strikingly different behavior in FPs and BPs. In particular, FPs driven by instability undergo the broadening of the PDF with a large increase in fluctuations before the transition to the ordered state accompanied by narrowing the PDF width. During this stage, we identify an interesting geodesic solution accompanied by the self-regulation between the growth and nonlinear damping where the time scale τ of information change is constant in time, independent of the strength of the stochastic noise. In comparison, BPs are mainly driven by the macroscopic motion due to the movement of the PDF peak. The total information length L between initial and final states is much larger in BPs than in FPs, increasing linearly with the deviation γ of a control parameter from the critical state in BPs while increasing logarithmically with γ in FPs. L scales as |lnD | and D-1 /2 in FPs and BPs, respectively, where D measures the strength of the stochastic forcing. These differing scalings with γ and D suggest a great utility of L in capturing different underlying processes, specifically, diffusion vs advection in phase transition by geometry. We discuss physical origins of these scalings and comment on implications of our results for bistable systems undergoing repeated order-disorder transitions (e.g., fitness).

  16. Signal intensity changes of the fetal liver on MRI in-phase and out-of-phase sequence.

    PubMed

    Li, Xiaobing; Brugger, Peter C; Huang, Min; Kasprian, Gregor; Li, Hong; Bettelheim, Dieter; Prayer, Daniela

    2013-04-01

    To study signal intensity (SI) of the fetal liver by MRI in-phase and out-of-phase over gestational age (GA). A total of 91 pregnant women from 19 to 38 gestational weeks were imaged using MRI. Liver-to-spleen SI ratios of the right and left fetal liver lobes on in-phase and out-of-phase were measured, calculated, and compared with each other. Curves of liver-to-spleen SI ratio of the right and left liver lobe were plotted by GA. Liver-to-spleen SI ratio of the right lobe on in-phase was different from that of the left liver lobe (t = 3.95; p < 0.001). A statistically significant difference was also found for out-of-phase SI ratios (t = 3.69; p < 0.001). Curves of liver-to-spleen SI ratio of the fetal liver on in-phase and out-of-phase showed changes against GA. Liver-to-spleen SI ratio is different between the right and left liver lobe, which probably results from the different blood supply. Curves of liver-to-spleen SI ratios between 19 to 38 gestational weeks reflect the changes of decreasing function of blood production by fetal liver. In-phase and out-of-phase may have clinical use in the early detection of disordered fetal growth and metabolism. © 2013 John Wiley & Sons, Ltd.

  17. Negative P-T slopes characterize phase change processes: Case of the Ge1Sb2Te4 phase change alloy

    NASA Astrophysics Data System (ADS)

    Kalkan, B.; Sen, S.; Aitken, B. G.; Raju, S. V.; Clark, S. M.

    2011-07-01

    The crystalline, liquid and amorphous phase stabilities and transformations of the Ge1Sb2Te4 (GST124) alloy are investigated as a function of pressure and temperature using synchrotron diffraction experiments in a diamond anvil cell. The results indicate that the solid-state amorphization of the cubic GST124 phase under high pressure may correspond to a metastable extension of the stability field of the GST124 liquid along a hexagonal crystal-liquid phase boundary with a negative P-T slope. The internal pressures generated during phase change are shown to be too small to affect phase stability. However, they may be important in understanding reliability issues related to thermomechanical stress development in phase change random access memory structures.

  18. Nature of phase transitions in crystalline and amorphous GeTe-Sb2Te3 phase change materials.

    PubMed

    Kalkan, B; Sen, S; Clark, S M

    2011-09-28

    The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge(1)Sb(2)Te(4) (GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic → amorphous → orthorhombic → bcc and hexagonal → orthorhombic → bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope. © 2011 American Institute of Physics

  19. Maxwell rigidity and topological constraints in amorphous phase-change networks

    SciTech Connect

    Micoulaut, M.; Otjacques, C.; Raty, J.-Y.; Bichara, C.

    2011-12-12

    By analyzing first-principles molecular-dynamics simulations of different telluride amorphous networks, we develop a method for the enumeration of radial and angular topological constraints, and show that the phase diagram of the most popular system Ge-Sb-Te can be split into two compositional elastic phases: a tellurium rich flexible phase and a stressed rigid phase that contains most of the materials used in phase-change applications. This sound atomic scale insight should open new avenues for the understanding of phase-change materials and other complex amorphous materials from the viewpoint of rigidity.

  20. A design handbook for phase change thermal control and energy storage devices. [selected paraffins

    NASA Technical Reports Server (NTRS)

    Humphries, W. R.; Griggs, E. I.

    1977-01-01

    Comprehensive survey is given of the thermal aspects of phase change material devices. Fundamental mechanisms of heat transfer within the phase change device are discussed. Performance in zero-g and one-g fields are examined as it relates to such a device. Computer models for phase change materials, with metal fillers, undergoing conductive and convective processes are detailed. Using these models, extensive parametric data are presented for a hypothetical configuration with a rectangular phase change housing, using straight fins as the filler, and paraffin as the phase change material. These data are generated over a range of realistic sizes, material properties, and thermal boundary conditions. A number of illustrative examples are given to demonstrate use of the parametric data. Also, a complete listing of phase change material property data are reproduced herein as an aid to the reader.

  1. Finite element simulations involving simultaneous multiple interface fronts in phase change problems

    NASA Technical Reports Server (NTRS)

    Ouyang, Tianhong; Tamma, Kumar K.

    1992-01-01

    The present paper describes the simulation of phase change problems involving simultaneous multiple interface fronts employing the finite element method. Much of the past investigations employing finite elements have been restricted to primarily a single phase change situation. The existence of more than one phase, that is, the presence of multiple phase fronts poses certain challenges and further complications. However, the results provide a very interesting thermal behavior for this class of problems. In this paper, attention is focused on fixed grid methods and the trapezoidal family of one-step methods using the enthalpy formulations. Illustrative examples which handle simultaneous multiple fronts in phase change problems are presented.

  2. Phase Variation and Genomic Architecture Changes in Azospirillum

    PubMed Central

    Vial, Ludovic; Lavire, Céline; Mavingui, Patrick; Blaha, Didier; Haurat, Jacqueline; Moënne-Loccoz, Yvan; Bally, René; Wisniewski-Dyé, Florence

    2006-01-01

    The plant growth-promoting rhizobacterium Azospirillum lipoferum 4B generates in vitro at high frequency a stable nonswimming phase variant designated 4VI, which is distinguishable from the wild type by the differential absorption of dyes. The frequency of variants generated by a recA mutant of A. lipoferum 4B was increased up to 10-fold. The pleiotropic modifications characteristic of the phase variant are well documented, but the molecular processes involved are unknown. Here, the objective was to assess whether genomic rearrangements take place during phase variation of strain 4B. The random amplified polymorphic DNA (RAPD) profiles of strains 4B and 4VI differed. RAPD fragments observed only with the wild type were cloned, and three cosmids carrying the corresponding fragments were isolated. The three cosmids hybridized with a 750-kb plasmid and pulse-field gel electrophoresis analysis revealed that this replicon was missing in the 4VI genome. The same rearrangements took place during phase variation of 4BrecA. Large-scale genomic rearrangements during phase variation were demonstrated for two additional strains. In Azospirillum brasilense WN1, generation of stable variants was correlated with the disappearance of a replicon of 260 kb. For Azospirillum irakense KBC1, the variant was not stable and coincided with the formation of a new replicon, whereas the revertant recovered the parental genomic architecture. This study shows large-scale genomic rearrangements in Azospirillum strains and correlates them with phase variation. PMID:16855225

  3. The Ramsey phase-change hypothesis. [for development of earth core

    NASA Technical Reports Server (NTRS)

    Lyttleton, R. A.

    1978-01-01

    Ramsey's (1948, 1949, 1950, 1954) arguments for the phase-change interpretation of the nature of the terrestrial core are summarized. Some of the successes of the phase-change theory in accounting for hitherto unexplained properties of earth's interior are discussed. Evidence in favor of the phase-change theory is reviewed, and calculations are examined which indicate that the liquid-core material is far more compressible at any relevant pressure than is the mantle material. Implications of the phase-change theory for Venus, Mars, Mercury, and the moon are considered.

  4. The Ramsey phase-change hypothesis. [for development of earth core

    NASA Technical Reports Server (NTRS)

    Lyttleton, R. A.

    1978-01-01

    Ramsey's (1948, 1949, 1950, 1954) arguments for the phase-change interpretation of the nature of the terrestrial core are summarized. Some of the successes of the phase-change theory in accounting for hitherto unexplained properties of earth's interior are discussed. Evidence in favor of the phase-change theory is reviewed, and calculations are examined which indicate that the liquid-core material is far more compressible at any relevant pressure than is the mantle material. Implications of the phase-change theory for Venus, Mars, Mercury, and the moon are considered.

  5. Onset of Convection in Two Liquid Layers with Phase Change

    SciTech Connect

    McFadden, G B; Coriell, S R; Gurski, K F; Cotrell, D L

    2006-09-14

    We perform linear stability calculations for horizontal fluid bilayers that can undergo a phase transformation, taking into account both buoyancy effects and thermocapillary effects in the presence of a vertical temperature gradient. We compare the familiar case of the stability of two immiscible fluids in a bilayer geometry with the less-studied case that the two fluids represent different phases of a single-component material, e.g., the water-steam system. The two cases differ in their interfacial boundary conditions: the condition that the interface is a material surface is replaced by the continuity of mass flux across the interface, together with an assumption of thermodynamic equilibrium that in the linearized equations represents the Clausius-Clapeyron relation relating the interfacial temperature and pressures. For the two-phase case, we find that the entropy difference between the phases plays a crucial role in determining the stability of the system. For small values of the entropy difference between the phases, the two-phase system can be linearly unstable to either heating from above or below. The instability is due to the Marangoni effect in combination with the effects of buoyancy (for heating from below). For larger values of the entropy difference the two-phase system is unstable only for heating from below, and the Marangoni effect is masked by effects of the entropy difference. To help understand the mechanisms driving the instability on heating from below we have performed both long-wavelength and short-wavelength analyses of the two-phase system. The short-wavelength analysis shows that the instability is driven by a coupling between the flow normal to the interface and the latent heat generation at the interface. The mechanism for the large wavelength instability is more complicated, and the detailed form of the expansion is found to depend on the Crispation and Bond numbers as well as the entropy difference. The two-phase system allows a

  6. Solid-liquid phase changes in simulated isoenergetic Ar13

    NASA Astrophysics Data System (ADS)

    Jellinek, Julius; Beck, Thomas L.; Berry, R. Stephen

    1986-03-01

    Simulations by molecular dynamics of 13-particle clusters of argon display distinct nonrigid, liquid-like and near-rigid, solid-like ``phases.'' The simulations, conducted at constant total energy, display a low-energy region in which only the solid-like form appears, a high-energy region in which only the liquid-like form appears, and an intermediate band of energy—a ``coexistence region''— in which clusters exhibit both forms. The intervals of time spent in each phase in the two-form coexistence region are long compared with the intervals required to establish equilibrium-like properties distinctive of each form, such as mean square displacement and power spectrum, so that well-defined phases can be said to exist. The fraction of time spent in each phase is a function of the energy. When a long simulation is separated into regions of solid-like and liquid-like behavior, the curve of the derived caloric equation of state is double valued in the two-phase range of energy, forming two well-defined, smooth branches. When, instead, the caloric curve is constructed from averages over all of a long run, its form is smooth and monotonic showing no trace of the ``loop'' that had been reported for earlier treatments with much shorter molecular dynamics runs, and which we could also reproduce with short runs.

  7. Microstructure characterization of multi-phase composites and utilization of phase change materials and recycled rubbers in cementitious materials

    NASA Astrophysics Data System (ADS)

    Meshgin, Pania

    2011-12-01

    This research focuses on two important subjects: (1) Characterization of heterogeneous microstructure of multi-phase composites and the effect of microstructural features on effective properties of the material. (2) Utilizations of phase change materials and recycled rubber particles from waste tires to improve thermal properties of insulation materials used in building envelopes. Spatial pattern of multi-phase and multidimensional internal structures of most composite materials are highly random. Quantitative description of the spatial distribution should be developed based on proper statistical models, which characterize the morphological features. For a composite material with multi-phases, the volume fraction of the phases as well as the morphological parameters of the phases have very strong influences on the effective property of the composite. These morphological parameters depend on the microstructure of each phase. This study intends to include the effect of higher order morphological details of the microstructure in the composite models. The higher order statistics, called two-point correlation functions characterize various behaviors of the composite at any two points in a stochastic field. Specifically, correlation functions of mosaic patterns are used in the study for characterizing transport properties of composite materials. One of the most effective methods to improve energy efficiency of buildings is to enhance thermal properties of insulation materials. The idea of using phase change materials and recycled rubber particles such as scrap tires in insulation materials for building envelopes has been studied.

  8. Multilayer SnSb4-SbSe Thin Films for Phase Change Materials Possessing Ultrafast Phase Change Speed and Enhanced Stability.

    PubMed

    Liu, Ruirui; Zhou, Xiao; Zhai, Jiwei; Song, Jun; Wu, Pengzhi; Lai, Tianshu; Song, Sannian; Song, Zhitang

    2017-08-16

    A multilayer thin film, comprising two different phase change material (PCM) components alternatively deposited, provides an effective means to tune and leverage good properties of its components, promising a new route toward high-performance PCMs. The present study systematically investigated the SnSb4-SbSe multilayer thin film as a potential PCM, combining experiments and first-principles calculations, and demonstrated that these multilayer thin films exhibit good electrical resistivity, robust thermal stability, and superior phase change speed. In particular, the potential operating temperature for 10 years is shown to be 122.0 °C and the phase change speed reaches 5 ns in the device test. The good thermal stability of the multilayer thin film is shown to come from the formation of the Sb2Se3 phase, whereas the fast phase change speed can be attributed to the formation of vacancies and a SbSe metastable phase. It is also demonstrated that the SbSe metastable phase contributes to further enhancing the electrical resistivity of the crystalline state and the thermal stability of the amorphous state, being vital to determining the properties of the multilayer SnSb4-SbSe thin film.

  9. Phase Change Heat Transfer Device for Process Heat Applications

    SciTech Connect

    Piyush Sabharwall; Mike Patterson; Vivek Utgikar; Fred Gunnerson

    2010-10-01

    The next generation nuclear plant (NGNP) will most likely produce electricity and process heat, with both being considered for hydrogen production. To capture nuclear process heat, and transport it to a distant industrial facility requires a high temperature system of heat exchangers, pumps and/or compressors. The heat transfer system is particularly challenging not only due to the elevated temperatures (up to approx.1300 K) and industrial scale power transport (=50MW), but also due to a potentially large separation distance between the nuclear and industrial plants (100+m) dictated by safety and licensing mandates. The work reported here is the preliminary analysis of two-phase thermosyphon heat transfer performance with alkali metals. A thermosyphon is a thermal device for transporting heat from one point to another with quite extraordinary properties. In contrast to single-phased forced convective heat transfer via ‘pumping a fluid’, a thermosyphon (also called a wickless heat pipe) transfers heat through the vaporization/condensing process. The condensate is further returned to the hot source by gravity, i.e., without any requirement of pumps or compressors. With this mode of heat transfer, the thermosyphon has the capability to transport heat at high rates over appreciable distances, virtually isothermally and without any requirement for external pumping devices. Two-phase heat transfer by a thermosyphon has the advantage of high enthalpy transport that includes the sensible heat of the liquid, the latent heat of vaporization, and vapor superheat. In contrast, single-phase forced convection transports only the sensible heat of the fluid. Additionally, vapor-phase velocities within a thermosyphon are much greater than single-phase liquid velocities within a forced convective loop. Thermosyphon performance can be limited by the sonic limit (choking) of vapor flow and/or by condensate entrainment. Proper thermosyphon requires analysis of both.

  10. Phase change in 080A42 plain carbon steel

    NASA Astrophysics Data System (ADS)

    de'Ath, James; Proud, William; Appleby-Thomas, Gareth; Millett, Jeremy

    2011-06-01

    Under shock loading conditions, mild steel undergoes a solid-solid phase transition at approximately 13GPa. In this work 080A42 plain carbon steel bright round rolled bar, was machined and heat-treated to produce an annealed or a martensitic structure. These samples were shock loaded, by plate impact, and the material response recorded using in-situ manganin stress gauges and heterodyne velocimetry. The Hugoniot stress and material characteristics both above and below the phase transition pressure have been recorded.

  11. Phase change in 080M40 plain carbon steel

    NASA Astrophysics Data System (ADS)

    De'Ath, James Michael; Proud, William; Millett, Jeremy; Appleby-Thomas, Gareth James

    2012-03-01

    Under shock loading conditions, mild steel undergoes a solid-solid phase transition at approximately 13GPa. In this work 080M40 plain carbon steel bright round rolled bar, was machined and heat-treated to produce an annealed or a martensitic structure. These samples were shock loaded, by plate impact, and the material response recorded using in-situ manganin stress gauges and heterodyne velocimetry. The Hugoniot stress and material characteristics both above and below the phase transition pressure have been recorded.

  12. Non-invasive temperature measurement by using phase changes in electromagnetic waves in a cavity resonator.

    PubMed

    Ishihara, Yasutoshi; Ohwada, Hiroshi

    2011-01-01

    To improve the efficacy of hyperthermia treatment, a novel method of non-invasive measurement of changes in body temperature is proposed. The proposed method is based on phase changes with temperature in electromagnetic waves in a heating applicator and the temperature dependence of the dielectric constant. An image of the temperature change inside a body is reconstructed by applying a computed tomography algorithm. This method can be combined easily with a heating applicator based on a cavity resonator and can be used to treat cancer effectively while non-invasively monitoring the heating effect. In this paper the phase change distributions of electromagnetic waves with temperature changes are measured experimentally, and the accuracy of reconstruction is discussed. The phase change distribution is reconstructed by using a prototype system with a rectangular aluminum cavity resonator that can be rotated 360° around an axis of rotation. To make measurements without disturbing the electromagnetic field distribution, an optical electric field sensor is used. The phase change distribution is reconstructed from 4-projection data by using a simple back-projection algorithm. The paper demonstrates that the phase change distribution can be reconstructed. The difference between phase changes obtained experimentally and by numerical analysis is about 20% and is related mainly to the limited signal detection sensitivity of electromagnetic waves. A temperature change inside an object can be reconstructed from the measured phase changes in a cavity resonator.

  13. Phase change dispersion, potentially a new class of heat transfer fluids

    NASA Astrophysics Data System (ADS)

    Fischer, L. J.; von Arx, S.; Wechsler, U.; Züst, S.; Worlitschek, J.

    2016-09-01

    The authors present values and an application of a phase change dispersion, where the dispersed phase change material within water changes from solid to liquid while absorbing heat and changes from liquid to solid while releasing heat at constant temperature. The phase change enthalpy increases the “apparent specific heat capacity” significantly in comparison to water. As the heat transfer takes place at constant temperature, the heat transfer fluid itself remains at constant temperature while absorbing heat. Isothermal heating and cooling of devices with a liquid is feasible.

  14. Comparison of the solid-phase fragment condensation and phase-change approaches in the synthesis of salmon I calcitonin.

    PubMed

    Gatos, D; Tzavara, C

    2001-02-01

    Salmon I calcitonin was synthesized using both phase-change and conventional solid-phase fragment condensation (SPFC) approaches, utilizing the Rink amide linker (Fmoc-amido-2,4-dimethoxybenzyl-4-phenoxyacetic acid) combined with 2-chlorotrityl resin and the Fmoc/tBu(Trt)-based protection scheme. Phase-change synthesis, performed by the selective detachment of the fully protected C-terminal 22-mer peptide-linker from the resin and subsequent condensation in solution with the N-terminal 1-10 fragment, gave a product of slightly less purity (85 vs. 92%) than the corresponding synthesis on the solid-phase. In both cases salmon I calcitonin was easily obtained in high purity.

  15. High speed, high temperature electrical characterization of phase change materials: metastable phases, crystallization dynamics, and resistance drift

    NASA Astrophysics Data System (ADS)

    Dirisaglik, Faruk; Bakan, Gokhan; Jurado, Zoila; Muneer, Sadid; Akbulut, Mustafa; Rarey, Jonathan; Sullivan, Lindsay; Wennberg, Maren; King, Adrienne; Zhang, Lingyi; Nowak, Rebecca; Lam, Chung; Silva, Helena; Gokirmak, Ali

    2015-10-01

    During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K.During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05512a

  16. Ultrafast phase-change logic device driven by melting processes

    PubMed Central

    Loke, Desmond; Skelton, Jonathan M.; Wang, Wei-Jie; Lee, Tae-Hoon; Zhao, Rong; Chong, Tow-Chong; Elliott, Stephen R.

    2014-01-01

    The ultrahigh demand for faster computers is currently tackled by traditional methods such as size scaling (for increasing the number of devices), but this is rapidly becoming almost impossible, due to physical and lithographic limitations. To boost the speed of computers without increasing the number of logic devices, one of the most feasible solutions is to increase the number of operations performed by a device, which is largely impossible to achieve using current silicon-based logic devices. Multiple operations in phase-change–based logic devices have been achieved using crystallization; however, they can achieve mostly speeds of several hundreds of nanoseconds. A difficulty also arises from the trade-off between the speed of crystallization and long-term stability of the amorphous phase. We here instead control the process of melting through premelting disordering effects, while maintaining the superior advantage of phase-change–based logic devices over silicon-based logic devices. A melting speed of just 900 ps was achieved to perform multiple Boolean algebraic operations (e.g., NOR and NOT). Ab initio molecular-dynamics simulations and in situ electrical characterization revealed the origin (i.e., bond buckling of atoms) and kinetics (e.g., discontinuouslike behavior) of melting through premelting disordering, which were key to increasing the melting speeds. By a subtle investigation of the well-characterized phase-transition behavior, this simple method provides an elegant solution to boost significantly the speed of phase-change–based in-memory logic devices, thus paving the way for achieving computers that can perform computations approaching terahertz processing rates. PMID:25197044

  17. Gene conversion accounts for pilin structural changes and for reversible piliation "phase" changes in gonococci.

    PubMed

    Swanson, J; Bergstrom, S; Boslego, J; Koomey, M

    1987-01-01

    Pilus+ "wild-type" gonococci (Gc) frequently display gene conversion of their expressed complete pilin gene (CPG); a copy of DNA derived from one of the Gc genome's multiple silent partial pilin genes (PPG) is recombinationally-inserted into the CPG's central and 3' portions with formation of a new, chimeric CPG. Expression of that new CPG leads to either 1) retention of pilus+ phenotype but change in pilin primary structure/antigenicity, or 2) phase change to pilus- phenotype capable of reverting. This study utilizes pilus revertants of P-rp +/- Gc and P+ colony morphotype variants spawned by P++ Gc to examine pilin gene conversion in strain MS11mk Gc in greater detail. Each revertant's and variant's expressed pilin gene's sequence (as pilin mRNA) was defined to learn whether their differences are due to gene conversion by different PPGs, or by varying stretches from the same PPG, or both. Gene conversion by PPG pilS1 copy 2 has been documented in Gc recovered from a human volunteer's urethra previously inoculated with pilus Gc (strain MS11). The pilus+ Gc isolated expressed structurally/antigenically distinct pilins.

  18. High speed, high temperature electrical characterization of phase change materials: metastable phases, crystallization dynamics, and resistance drift.

    PubMed

    Dirisaglik, Faruk; Bakan, Gokhan; Jurado, Zoila; Muneer, Sadid; Akbulut, Mustafa; Rarey, Jonathan; Sullivan, Lindsay; Wennberg, Maren; King, Adrienne; Zhang, Lingyi; Nowak, Rebecca; Lam, Chung; Silva, Helena; Gokirmak, Ali

    2015-10-28

    During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K.

  19. Program For Finite-Element Analyses Of Phase-Change Fluids

    NASA Technical Reports Server (NTRS)

    Viterna, L. A.

    1995-01-01

    PHASTRAN analyzes heat-transfer and flow behaviors of materials undergoing phase changes. Many phase changes operate over range of accelerations or effective gravitational fields. To analyze such thermal systems, it is necessary to obtain simultaneous solutions for equations of conservation of energy, momentum, and mass, and for equation of state. Written in APL2.

  20. Thermal Characteristics of Pitch Based Carbon Foam and Phase Change Materials

    DTIC Science & Technology

    2005-03-01

    communications systems. Carbon foam derived from a blown mesophase pitch precursor can be considered to be an interconnected network of graphitic...THERMAL CHARACTERISTICS OF PITCH BASED CARBON FOAM AND PHASE CHANGE MATERIALS THESIS Kevin...APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. THERMAL CHARACTERISTICS OF PITCH BASED CARBON FOAM AND PHASE CHANGE MATERIALS

  1. On the stability of natural circulation loops with phase change

    NASA Astrophysics Data System (ADS)

    Haskin, Troy C.

    The stability of a simple, closed-loop, water-cooled natural circulation system was characterized over a range of single phase and two-phase states. The motivation for this investigation is a Next Generation Nuclear Plant safety cooling system called the Reactor Cavity Cooling System (RCCS). One of the proposed designs for the RCCS is a closed-circuit of network piping using water as a working fluid. One of the safety considerations for such a system is the stability of the system at steady-state under a large number of unknown states. This work provides a derivation of the commonly used one-dimensional conservation laws used in thermohydraulic system modeling and a novel discretization scheme that allows for exact integration of the computational domain for accurate calculation of eigenvalues of a linearized system. The steady-state solution of the discretized equations is then performed using a fully nonlinear Jacobian-Free Newton Krylov Method for a number of temperatures, pressures, and heat loads both in single and two-phase conditions. All of the single and two-phase state exhibit linear stability to small perturbations in values. The linear stability is also found to increase with increasing heat load due to the greater inertia of the system damping out small perturbation effectively and with increasing pressure due to the greater stiffness of the fluid. Nonlinear stability was also examined for a point power insertion of varying intensity from two steady-states. The loop exhibited stability for all power insertions from both steady-states, returning to the initial steady value shortly after the pulse.

  2. Dynamic changes of phase in a van der Waals fluid

    NASA Astrophysics Data System (ADS)

    Hagan, R.; Serrin, J.

    1984-03-01

    This paper gives sufficient conditions to guarantee the existence of a shock layer solution connecting two different equilibrium states in a van der Waals fluid. In particular, the equilibrium states can belong to two different phases of the fluid. The constitutive laws come from a modified Korteweg theory which is compatible with the Clausius Duhem inequality. The Clausius Duhem inequality in turn gives rise to a Liapunov function. The main mathematical tool is the LaSalle invariance principle.

  3. Phase change thermal storage materials with crust forming stabilizers

    SciTech Connect

    Telkes, M.

    1980-02-05

    A body for the storage of heat or for the storage of coolness is, in its solid phase, a conglomerate of a mass of crystalline particles of a salt-hydrate, and a rigid cellular support structure in the form of a crust formed by a chemical reaction with the surfaces of the crystalline particles. By way of example , strontium nitrate is reacted with uniformly sized crystalline particles of sodium sulfate decahydrate to form an integral support crust structure of the compound strontium sulfate, which compound is insoluble in water. When the crystalline particles are transformed to the liquid phase, the liquid is confined within the cells of the support structure. The body is enclosed in a moisture impermeable skin to prevent evaporation of the water of crystallization in the liquid phase. Several methods of fabricating such a body are disclosed, including the mixing of the crystalline particles with a solution of soluble strontium nitrate in sufficient quantity to provide the desired supporting crust structure, pouring that mixture into a suitable mold, and providing the desired moisture impervious skin for the cast.

  4. Evidence for Electronic Gap-Driven Metal-Semiconductor Transition in Phase-Change Materials

    SciTech Connect

    Shakhvorostov, D.; Nistor, R; Krusin-Elbaum, L; Martyna, G; Newns, D; Elmegreen, B; Liu, X; Hughes, Z; Paul, S; et. al.

    2009-01-01

    Phase-change materials are functionally important materials that can be thermally interconverted between metallic (crystalline) and semiconducting (amorphous) phases on a very short time scale. Although the interconversion appears to involve a change in local atomic coordination numbers, the electronic basis for this process is still unclear. Here, we demonstrate that in a nearly vacancy-free binary GeSb system where we can drive the phase change both thermally and, as we discover, by pressure, the transformation into the amorphous phase is electronic in origin. Correlations between conductivity, total system energy, and local atomic coordination revealed by experiments and long time ab initio simulations show that the structural reorganization into the amorphous state is driven by opening of an energy gap in the electronic density of states. The electronic driving force behind the phase change has the potential to change the interconversion paradigm in this material class.

  5. Vegetative phase change and photosynthesis in Eucalyptus occidentalis: architectural simplification prolongs juvenile traits.

    PubMed

    Jaya, Elizabeth; Kubien, David S; Jameson, Paula E; Clemens, John

    2010-03-01

    To understand the effect of shoot architecture on vegetative and reproductive phase changes, seedlings of Eucalyptus occidentalis (Myrtaceae) were grown as free-branching or as single-stem plants, the latter treatment resulting from the continual removal of axillary vegetative buds. In E. occidentalis, vegetative phase change was characterized by increasing leaf length/width ratios. In contrast to the behaviour of other woody species subjected to architectural manipulation of this kind, vegetative phase change was faster in branched plants than in single-stem plants, which continued to exhibit juvenile leaf morphology throughout the duration of this study. However, the first appearance of flowers occurred approximately synchronously in both treatments after 9 months, demonstrating that vegetative phase change and floral transition are developmentally uncoupled in this species. Leaf morphological changes that characterized phase change lagged behind changes in leaf anatomy and gas exchange. In single-stem plants with juvenile leaves, leaf intercellular airspace (20.9%) was almost double that in branched plants with adult foliage (11.2%). Photosynthetic gas exchange analyses indicated that the juvenile leaves of single-stem plants had greater Rubisco and electron transport capacities than those of free-branching plants. Higher leaf N concentrations were recorded in single-stem plants than in branched plants. These observations support the hypothesis that the complexity of shoot architecture impacts the rate of vegetative phase change, but does not affect reproductive phase change in this species.

  6. Investigation of surface changes of nanoparticles using TM-AFM phase imaging.

    PubMed

    Dong, Rong; Yu, Liya E

    2003-06-15

    Tapping-mode AFM (TM-AFM) phase imaging was utilized to characterize the surface changes of nanosize particles, in regard to the effects of different amounts of condensed water and organic coatings on particle surfaces. Model nanoparticles were continuously examined under various relative humidity (RH) levels by concurrently obtaining both topographic and phase images. The condensed water appeared to soften particle surfaces and to increase tip-sample attractive interaction over relatively stiff surfaces, which were shown with dark phase contrasts and negative phase shift values in phase images. Under high RH, a massive amount of water gave the particles a droplet-like surface, which reversed the original negative phase shifts to positive values with bright contrasts. Glutaric-acid coatings provided a compliant surface with high viscosity resulting in a dark phase contrast, whereas water droplets containing relatively low viscosity gave a bright phase contrast and positive phase shift. Overall, our results show that it is essential to describe the physical properties of a sample surface as solid, soft, or droplet-like material in order to derive a meaningful understanding of the surface changes of nanosize particles based on TM-AFM phase images. In contrast to other phase imaging studies, this work clearly correlates continuous surface changes with phase images, demonstrating a promising approach to characterize environmental nanoparticles.

  7. Bubbles in liquids with phase transition. Part 1. On phase change of a single vapor bubble in liquid water

    NASA Astrophysics Data System (ADS)

    Dreyer, Wolfgang; Duderstadt, Frank; Hantke, Maren; Warnecke, Gerald

    2012-11-01

    In the forthcoming second part of this paper a system of balance laws for a multi-phase mixture with many dispersed bubbles in liquid is derived where phase transition is taken into account. The exchange terms for mass, momentum and energy explicitly depend on evolution laws for total mass, radius and temperature of single bubbles. Therefore in the current paper we consider a single bubble of vapor and inert gas surrounded by the corresponding liquid phase. The creation of bubbles, e.g. by nucleation is not taken into account. We study the behavior of this bubble due to condensation and evaporation at the interface. The aim is to find evolution laws for total mass, radius and temperature of the bubble, which should be as simple as possible but consider all relevant physical effects. Special attention is given to the effects of surface tension and heat production on the bubble dynamics as well as the propagation of acoustic elastic waves by including slight compressibility of the liquid phase. Separately we study the influence of the three phenomena heat conduction, elastic waves and phase transition on the evolution of the bubble. We find ordinary differential equations that describe the bubble dynamics. It turns out that the elastic waves in the liquid are of greatest importance to the dynamics of the bubble radius. The phase transition has a strong influence on the evolution of the temperature, in particular at the interface. Furthermore the phase transition leads to a drastic change of the water content in the bubble. It is shown that a rebounding bubble is only possible, if it contains in addition an inert gas. In Part 2 of the current paper the equations derived are sought in order to close the system of equations for multi-phase mixture balance laws for dispersed bubbles in liquids involving phase change.

  8. Highly stable phase change material emulsions fabricated by interfacial assembly of amphiphilic block copolymers during phase inversion.

    PubMed

    Park, Hanhee; Han, Dong Wan; Kim, Jin Woong

    2015-03-10

    This study introduced a robust and promising approach to fabricate highly stable phase change material (PCM) emulsions consisting of n-tetradecane as a dispersed phase and a mixture of meso-2,3-butanediol (m-BDO) and water as a continuous phase. We showed that amphiphilic poly(ethylene oxide)-b-poly(ε-caprolactone) block copolymers assembled to form a flexible but tough polymer membrane at the interface during phase inversion from water-in-oil emulsion to oil-in-water emulsion, thus remarkably improving the emulsion stability. Although the incorporation of m-BDO into the emulsion lowered the phase changing enthalpy, it provided a useful means to elevate the melting temperature of the emulsions near to 15 °C. Interestingly, supercooling was commonly observed in our PCM emulsions. We attributed this to the fact that the PCM molecules confined in submicron-scale droplets could not effectively nucleate to grow molecular crystals. Moreover, the presence of m-BDO in the continuous phase rather dominated the heat emission of the emulsion system during freezing, which made the supercooling more favorable.

  9. Change in the crystalline structure during the phase transition of the palladium-hydrogen system.

    PubMed

    Kawasaki, Akio; Itoh, Satoshi; Shima, Kunihiro; Kato, Kenichi; Ohashi, Haruhiko; Ishikawa, Tetsuya; Yamazaki, Toshimitsu

    2015-10-14

    We performed an X-ray diffraction experiment while a palladium bulk absorbed and desorbed hydrogen to investigate the behavior of the crystalline lattice during the phase transition between the α phase and the β phase. Fast growth of the β phase was observed at around x = 0.1 and x = 0.45 of PdHx, and the phase transition rate has an exponential behavior in between. In addition, slight compression of the lattice at a high hydrogen concentration, an increase in the lattice constant, and broadening of the line width of the α phase after a cycle of absorption and desorption of hydrogen were observed. These behaviors correlated with the change in the sample length, which may infer that the change in shape was related to the phase transition.

  10. Changes in phase space during learning an unstable balance.

    PubMed

    Mégrot, Fabrice; Bardy, Benoît G

    2006-07-10

    Six participants learned to maintain an unstable balance on a stabilometer, during 6 consecutive days of practice (total of 90 trials). Lateral and angular variations of body segments and body center of mass were analysed, and their evolution over the learning period was compared to the changes in dimensional variables capturing the structure of the movement itself (embedding and correlation dimension, largest Lyapunov exponent). Results indicated that (i) learning occurred, (ii) was accompanied by persistence in the dimension of the movement, and (iii) by a reduction in chaotic (or stochastic) components. Compared to other results in the learning literature, these results suggest that dimensional changes over learning are task-specific.

  11. IMPACTS OF TECHNOLOGICAL CHANGES IN WAREHOUSING, PHASE I.

    ERIC Educational Resources Information Center

    HAMILTON, PHYLLIS D.; KINCAID, HARRY V.

    THE OBJECTIVES OF THIS STUDY WERE (1) TO DETERMINE THE AVAILABILITY, NATURE, AND RELIABILITY OF DATA ON THE RAPID CHANGE IN THE WAREHOUSING FUNCTION IN INDUSTRY AND (2) TO PROVIDE A BASIS FOR DECISIONS CONCERNING THE DESIRABILITY AND FEASIBILITY OF CONDUCTING SUBSEQUENT STUDIES. THREE MAJOR SOURCES OF INFORMATION ON CALIFORNIA, OREGON, WASHINGTON,…

  12. Temperature-driven topological quantum phase transitions in a phase-change material Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Eremeev, S. V.; Rusinov, I. P.; Echenique, P. M.; Chulkov, E. V.

    2016-12-01

    The Ge2Sb2Te5 is a phase-change material widely used in optical memory devices and is a leading candidate for next generation non-volatile random access memory devices which are key elements of various electronics and portable systems. Despite the compound is under intense investigation its electronic structure is currently not fully understood. The present work sheds new light on the electronic structure of the Ge2Sb2Te5 crystalline phases. We demonstrate by predicting from first-principles calculations that stable crystal structures of Ge2Sb2Te5 possess different topological quantum phases: a topological insulator phase is realized in low-temperature structure and Weyl semimetal phase is a characteristic of the high-temperature structure. Since the structural phase transitions are caused by the temperature the switching between different topologically non-trivial phases can be driven by variation of the temperature. The obtained results reveal the rich physics of the Ge2Sb2Te5 compound and open previously unexplored possibility for spintronics applications of this material, substantially expanding its application potential.

  13. Temperature-driven topological quantum phase transitions in a phase-change material Ge2Sb2Te5.

    PubMed

    Eremeev, S V; Rusinov, I P; Echenique, P M; Chulkov, E V

    2016-12-13

    The Ge2Sb2Te5 is a phase-change material widely used in optical memory devices and is a leading candidate for next generation non-volatile random access memory devices which are key elements of various electronics and portable systems. Despite the compound is under intense investigation its electronic structure is currently not fully understood. The present work sheds new light on the electronic structure of the Ge2Sb2Te5 crystalline phases. We demonstrate by predicting from first-principles calculations that stable crystal structures of Ge2Sb2Te5 possess different topological quantum phases: a topological insulator phase is realized in low-temperature structure and Weyl semimetal phase is a characteristic of the high-temperature structure. Since the structural phase transitions are caused by the temperature the switching between different topologically non-trivial phases can be driven by variation of the temperature. The obtained results reveal the rich physics of the Ge2Sb2Te5 compound and open previously unexplored possibility for spintronics applications of this material, substantially expanding its application potential.

  14. Temperature-driven topological quantum phase transitions in a phase-change material Ge2Sb2Te5

    PubMed Central

    Eremeev, S. V.; Rusinov, I. P.; Echenique, P. M.; Chulkov, E. V.

    2016-01-01

    The Ge2Sb2Te5 is a phase-change material widely used in optical memory devices and is a leading candidate for next generation non-volatile random access memory devices which are key elements of various electronics and portable systems. Despite the compound is under intense investigation its electronic structure is currently not fully understood. The present work sheds new light on the electronic structure of the Ge2Sb2Te5 crystalline phases. We demonstrate by predicting from first-principles calculations that stable crystal structures of Ge2Sb2Te5 possess different topological quantum phases: a topological insulator phase is realized in low-temperature structure and Weyl semimetal phase is a characteristic of the high-temperature structure. Since the structural phase transitions are caused by the temperature the switching between different topologically non-trivial phases can be driven by variation of the temperature. The obtained results reveal the rich physics of the Ge2Sb2Te5 compound and open previously unexplored possibility for spintronics applications of this material, substantially expanding its application potential. PMID:27958321

  15. Autobiographical memory and structural brain changes in chronic phase TBI.

    PubMed

    Esopenko, Carrie; Levine, Brian

    2017-04-01

    Traumatic brain injury (TBI) is associated with a range of neuropsychological deficits, including attention, memory, and executive functioning attributable to diffuse axonal injury (DAI) with accompanying focal frontal and temporal damage. Although the memory deficit of TBI has been well characterized with laboratory tests, comparatively little research has examined retrograde autobiographical memory (AM) at the chronic phase of TBI, with no prior studies of unselected patients drawn directly from hospital admissions for trauma. Moreover, little is known about the effects of TBI on canonical episodic and non-episodic (e.g., semantic) AM processes. In the present study, we assessed the effects of chronic-phase TBI on AM in patients with focal and DAI spanning the range of TBI severity. Patients and socioeconomic- and age-matched controls were administered the Autobiographical Interview (AI) (Levine, Svoboda, Hay, Winocur, & Moscovitch, 2002) a widely used method for dissociating episodic and semantic elements of AM, along with tests of neuropsychological and functional outcome. Measures of episodic and non-episodic AM were compared with regional brain volumes derived from high-resolution structural magnetic resonance imaging (MRI). Severe TBI (but not mild or moderate TBI) was associated with reduced recall of episodic autobiographical details and increased recall of non-episodic details relative to healthy comparison participants. There were no significant associations between AM performance and neuropsychological or functional outcome measures. Within the full TBI sample, autobiographical episodic memory was associated with reduced volume distributed across temporal, parietal, and prefrontal regions considered to be part of the brain's AM network. These results suggest that TBI-related distributed volume loss affects episodic autobiographical recollection.

  16. Space observations of cold-cloud phase change.

    PubMed

    Choi, Yong-Sang; Lindzen, Richard S; Ho, Chang-Hoi; Kim, Jinwon

    2010-06-22

    This study examines the vertically resolved cloud measurements from the cloud-aerosol lidar with orthogonal polarization instrument on Aqua satellite from June 2006 through May 2007 to estimate the extent to which the mixed cloud-phase composition can vary according to the ambient temperature, an important concern for the uncertainty in calculating cloud radiative effects. At -20 degrees C, the global average fraction of supercooled clouds in the total cloud population is found to be about 50% in the data period. Between -10 and -40 degrees C, the fraction is smaller at lower temperatures. However, there are appreciable regional and temporal deviations from the global mean (> +/- 20%) at the isotherm. In the analysis with coincident dust aerosol data from the same instrument, it appears that the variation in the supercooled cloud fraction is negatively correlated with the frequencies of dust aerosols at the -20 degrees C isotherm. This result suggests a possibility that dust particles lifted to the cold cloud layer effectively glaciate supercooled clouds. Observations of radiative flux from the clouds and earth's radiant energy system instrument aboard Terra satellite, as well as radiative transfer model simulations, show that the 20% variation in the supercooled cloud fraction is quantitatively important in cloud radiative effects, especially in shortwave, which are 10-20 W m(-2) for regions of mixed-phase clouds affected by dust. In particular, our results demonstrate that dust, by glaciating supercooled water, can decrease albedo, thus compensating for the increase in albedo due to the dust aerosols themselves. This has important implications for the determination of climate sensitivity.

  17. Space observations of cold-cloud phase change

    PubMed Central

    Choi, Yong-Sang; Lindzen, Richard S.; Ho, Chang-Hoi; Kim, Jinwon

    2010-01-01

    This study examines the vertically resolved cloud measurements from the cloud-aerosol lidar with orthogonal polarization instrument on Aqua satellite from June 2006 through May 2007 to estimate the extent to which the mixed cloud-phase composition can vary according to the ambient temperature, an important concern for the uncertainty in calculating cloud radiative effects. At -20 °C, the global average fraction of supercooled clouds in the total cloud population is found to be about 50% in the data period. Between -10 and -40 °C, the fraction is smaller at lower temperatures. However, there are appreciable regional and temporal deviations from the global mean (>  ± 20%) at the isotherm. In the analysis with coincident dust aerosol data from the same instrument, it appears that the variation in the supercooled cloud fraction is negatively correlated with the frequencies of dust aerosols at the -20 °C isotherm. This result suggests a possibility that dust particles lifted to the cold cloud layer effectively glaciate supercooled clouds. Observations of radiative flux from the clouds and earth’s radiant energy system instrument aboard Terra satellite, as well as radiative transfer model simulations, show that the 20% variation in the supercooled cloud fraction is quantitatively important in cloud radiative effects, especially in shortwave, which are 10 - 20 W m-2 for regions of mixed-phase clouds affected by dust. In particular, our results demonstrate that dust, by glaciating supercooled water, can decrease albedo, thus compensating for the increase in albedo due to the dust aerosols themselves. This has important implications for the determination of climate sensitivity. PMID:20534562

  18. Oxygen Tuned Local Structure and Phase-Change Performance of Germanium Telluride.

    PubMed

    Zhou, Xilin; Du, Yonghua; Behera, Jitendra K; Wu, Liangcai; Song, Zhitang; Simpson, Robert E

    2016-08-10

    The effect of oxygen on the local structure of Ge atoms in GeTe-O materials has been investigated. Oxygen leads to a significant modification to the vibrational modes of Ge octahedra, which results from a decrease in its coordination. We find that a defective octahedral Ge network is the crucial fingerprint for rapid and reversible structural transitions in GeTe-based phase change materials. The appearance of oxide Raman modes confirms phase separation into GeO and TeO at high level O doping. Counterintuitively, despite the increase in crystallization temperature of oxygen doped GeTe-O phase change materials, when GeTe-O materials are used in electrical phase change memory cells, the electrical switching energy is lower than the pure GeTe material. This switching energy reduction is ascribed to the smaller change in volume, and therefore smaller enthalpy change, for the oxygen doped GeTe materials.

  19. Enabling universal memory by overcoming the contradictory speed and stability nature of phase-change materials.

    PubMed

    Wang, Weijie; Loke, Desmond; Shi, Luping; Zhao, Rong; Yang, Hongxin; Law, Leong-Tat; Ng, Lung-Tat; Lim, Kian-Guan; Yeo, Yee-Chia; Chong, Tow-Chong; Lacaita, Andrea L

    2012-01-01

    The quest for universal memory is driving the rapid development of memories with superior all-round capabilities in non-volatility, high speed, high endurance and low power. Phase-change materials are highly promising in this respect. However, their contradictory speed and stability properties present a key challenge towards this ambition. We reveal that as the device size decreases, the phase-change mechanism changes from the material inherent crystallization mechanism (either nucleation- or growth-dominated), to the hetero-crystallization mechanism, which resulted in a significant increase in PCRAM speeds. Reducing the grain size can further increase the speed of phase-change. Such grain size effect on speed becomes increasingly significant at smaller device sizes. Together with the nano-thermal and electrical effects, fast phase-change, good stability and high endurance can be achieved. These findings lead to a feasible solution to achieve a universal memory.

  20. Enabling Universal Memory by Overcoming the Contradictory Speed and Stability Nature of Phase-Change Materials

    NASA Astrophysics Data System (ADS)

    Wang, Weijie; Loke, Desmond; Shi, Luping; Zhao, Rong; Yang, Hongxin; Law, Leong-Tat; Ng, Lung-Tat; Lim, Kian-Guan; Yeo, Yee-Chia; Chong, Tow-Chong; Lacaita, Andrea L.

    2012-04-01

    The quest for universal memory is driving the rapid development of memories with superior all-round capabilities in non-volatility, high speed, high endurance and low power. Phase-change materials are highly promising in this respect. However, their contradictory speed and stability properties present a key challenge towards this ambition. We reveal that as the device size decreases, the phase-change mechanism changes from the material inherent crystallization mechanism (either nucleation- or growth-dominated), to the hetero-crystallization mechanism, which resulted in a significant increase in PCRAM speeds. Reducing the grain size can further increase the speed of phase-change. Such grain size effect on speed becomes increasingly significant at smaller device sizes. Together with the nano-thermal and electrical effects, fast phase-change, good stability and high endurance can be achieved. These findings lead to a feasible solution to achieve a universal memory.

  1. Numerical Simulation of Two-Phase Critical Flow with the Phase Change in the Nozzle Tube

    NASA Astrophysics Data System (ADS)

    Ishigaki, Masahiro; Watanabe, Tadashi; Nakamura, Hideo

    Two-phase critical flow in the nozzle tube is analyzed numerically by the best estimate code TRACE and the CFD code FLUENT, and the performance of the mass flow rate estimation by the numerical codes is discussed. For the best estimate analysis by the TRACE code, the critical flow option is turned on. The mixture model is used with the cavitation model and the evaporation-condensation model for the numerical simulation by the FLUENT code. Two test cases of the two-phase critical flow are analyzed. One case is the critical flashing flow in a convergent-divergent nozzle (Super Moby Dick experiment), and the other case is the break nozzle flow for a steam generator tube rupture experiment of pressurized water reactors at Large Scale Test Facility of Japan Atomic Energy Agency. The calculation results of the mass flow rates by the numerical simulations show good agreements with the experimental results.

  2. Thermal modeling with solid/liquid phase change of the thermal energy storage experiment

    NASA Technical Reports Server (NTRS)

    Skarda, J. Raymond Lee

    1991-01-01

    A thermal model which simulates combined conduction and phase change characteristics of thermal energy storage (TES) materials is presented. Both the model and results are presented for the purpose of benchmarking the conduction and phase change capabilities of recently developed and unvalidated microgravity TES computer programs. Specifically, operation of TES-1 is simulated. A two-dimensional SINDA85 model of the TES experiment in cylindrical coordinates was constructed. The phase change model accounts for latent heat stored in, or released from, a node undergoing melting and freezing.

  3. On entropy change measurements around first order phase transitions in caloric materials.

    PubMed

    Caron, Luana; Ba Doan, Nguyen; Ranno, Laurent

    2017-02-22

    In this work we discuss the measurement protocols for indirect determination of the isothermal entropy change associated with first order phase transitions in caloric materials. The magneto-structural phase transitions giving rise to giant magnetocaloric effects in Cu-doped MnAs and FeRh are used as case studies to exemplify how badly designed protocols may affect isothermal measurements and lead to incorrect entropy change estimations. Isothermal measurement protocols which allow correct assessment of the entropy change around first order phase transitions in both direct and inverse cases are presented.

  4. On entropy change measurements around first order phase transitions in caloric materials

    NASA Astrophysics Data System (ADS)

    Caron, Luana; Doan, Nguyen Ba; Ranno, Laurent

    2017-02-01

    In this work we discuss the measurement protocols for indirect determination of the isothermal entropy change associated with first order phase transitions in caloric materials. The magneto-structural phase transitions giving rise to giant magnetocaloric effects in Cu-doped MnAs and FeRh are used as case studies to exemplify how badly designed protocols may affect isothermal measurements and lead to incorrect entropy change estimations. Isothermal measurement protocols which allow correct assessment of the entropy change around first order phase transitions in both direct and inverse cases are presented.

  5. Microgravity experiments on phase change of self-rewetting fluids.

    PubMed

    Abe, Yoshiyuki; Iwasaki, Akira; Tanaka, Kotaro

    2004-11-01

    A series of microgravity experiments on self-rewetting fluids has been conducted at the 10-second drop shaft of the Japan Microgravity Center (JAMIC). In all the experiments, 1.5 wt% of 1-butanol aqueous solution were employed as a self-rewetting fluid. The objective of the first experiment was to observe the boiling behavior of two-dimensional adjacent dual vapor bubbles with the aid of a two-wavelength interferometer and tracer particles. A significant difference was observed between a self-rewetting fluid and a normal fluid (CFC-113 in this experiment) in bubble interaction and flow developed along vapor/bubble interface. The second experiment focused on the flow at the bubble/heater contact area and around the three-phase interline, visualized with tracer particles. Differing behavior among three fluids, 1-butanol aqueous solution, CFC-113, and ethanol aqueous solution, was observed. The last microgravity experiment was a demonstration of wickless heat pipes containing three different fluids as a working fluid, 1-butanol aqueous solution, water, and ethanol aqueous solution. The temperature variation of working fluid in the heat pipe was monitored, and the liquid flow returning from the condensation region to the evaporation region was visualized by tracer particles. In addition to microgravity experiments, the performance of conventional heat pipes with 1-butanol aqueous solution was evaluated on the ground, and compared with water heat pipes. Our preliminary results are presented.

  6. Reversible solvent vapor-mediated phase changes in nanocrystal superlattices.

    PubMed

    Goodfellow, Brian W; Korgel, Brian A

    2011-04-26

    Colloidal nanocrystals are being explored for use in a variety of applications, from solar cells to transistors to medical diagnostics and therapy. Ordered assemblies of nanocrystals, or superlattices, are one particularly interesting class of these materials, in which the nanocrystals serve as modular building blocks to construct nanostructures by self-assembly with spatial and temporal complexity and unique properties. From a fundamental perspective, the nanocrystals are simple molecular models that can be manipulated and studied to test statistical mechanical and thermodynamic models of crystallization and disorder. An article by Bian et al. in this issue of ACS Nano reports surprising new phase behavior in semiconductor nanocrystal superlattices: reversible transitions between non-close-packed body-centered cubic (bcc) and body-centered tetragonal (bct) structures, and close-packed face-centered cubic (fcc) structures, observed by real-time in situ grazing incidence small-angle X-ray scattering (GISAXS) measurements, upon solvent vapor exposure and increased interparticle separation. These studies offer new insight and raise new questions about superlattice structure and the forces that control self-assembly. Accompanying computer simulations show that ligand-ligand interactions are important. Furthermore, it appears that ligand-coated nanocrystals have more in common with soft microphase-separated materials, like diblock copolymers and surfactant assemblies, than previously realized.

  7. Automated baseline change detection -- Phases 1 and 2. Final report

    SciTech Connect

    Byler, E.

    1997-10-31

    The primary objective of this project is to apply robotic and optical sensor technology to the operational inspection of mixed toxic and radioactive waste stored in barrels, using Automated Baseline Change Detection (ABCD), based on image subtraction. Absolute change detection is based on detecting any visible physical changes, regardless of cause, between a current inspection image of a barrel and an archived baseline image of the same barrel. Thus, in addition to rust, the ABCD system can also detect corrosion, leaks, dents, and bulges. The ABCD approach and method rely on precise camera positioning and repositioning relative to the barrel and on feature recognition in images. The ABCD image processing software was installed on a robotic vehicle developed under a related DOE/FETC contract DE-AC21-92MC29112 Intelligent Mobile Sensor System (IMSS) and integrated with the electronics and software. This vehicle was designed especially to navigate in DOE Waste Storage Facilities. Initial system testing was performed at Fernald in June 1996. After some further development and more extensive integration the prototype integrated system was installed and tested at the Radioactive Waste Management Facility (RWMC) at INEEL beginning in April 1997 through the present (November 1997). The integrated system, composed of ABCD imaging software and IMSS mobility base, is called MISS EVE (Mobile Intelligent Sensor System--Environmental Validation Expert). Evaluation of the integrated system in RWMC Building 628, containing approximately 10,000 drums, demonstrated an easy to use system with the ability to properly navigate through the facility, image all the defined drums, and process the results into a report delivered to the operator on a GUI interface and on hard copy. Further work is needed to make the brassboard system more operationally robust.

  8. Exploring the Limits of Fast Phase Change Materials

    DTIC Science & Technology

    2001-04-01

    upon short laser pulse irradiation. The sheet resistance was measured with a four-point probe setup following the procedure proposed by van der Pauw...transition can be determined using Kissinger plots [8]. Figure I shows the temperature dependence of the sheet resistance (Rs) of 80 nm thin Ge2Sb 2Te5...Temperature dependence of the sheet resistance Rs of 80 nm GeSbTes (left) and 80 rn Ge4SbTe5 (right) with different heating rates leading to a change in the

  9. Phase change in the cathode side of a proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Khajeh-Hosseini-Dalasm, N.; Fushinobu, Kazuyoshi; Okazaki, Ken

    A three-dimensional steady state two-phase non-isothermal model which highly couples the water and thermal management has been developed to numerically investigate the spatial distribution of the interfacial mass transfer phase-change rate in the cathode side of a proton exchange membrane fuel cell (PEMFC). A non-equilibrium evaporation-condensation phase change rate was incorporated in the model which allowed supersaturation and undersaturation take place. The most significant effects of phase-change rate on liquid saturation and temperature distributions are highlighted. A parametric study was also carried out to investigate the effects of operating conditions; namely as the channel inlet humidity, cell operating temperature, and inlet mass flow rate on the phase-change rate. It was also found that liquid phase assumption for produced water in the cathode catalyst layer (CL) changed the local distribution of phase-change rate. The maximum evaporation rate zone (above the channel near the CL) coincided with the maximum temperature zone and resulted in lowering the liquid saturation level. Furthermore, reduction of the channel inlet humidity and an increase of the operation temperature and inlet mass flow rate increased the evaporation rate and allowed for dehydration process of the gas diffusion layer (GDL) to take place faster.

  10. Mixed-Mode Operation of Hybrid Phase-Change Nanophotonic Circuits.

    PubMed

    Lu, Yegang; Stegmaier, Matthias; Nukala, Pavan; Giambra, Marco A; Ferrari, Simone; Busacca, Alessandro; Pernice, Wolfram H P; Agarwal, Ritesh

    2017-01-11

    Phase change materials (PCMs) are highly attractive for nonvolatile electrical and all-optical memory applications because of unique features such as ultrafast and reversible phase transitions, long-term endurance, and high scalability to nanoscale dimensions. Understanding their transient characteristics upon phase transition in both the electrical and the optical domains is essential for using PCMs in future multifunctional optoelectronic circuits. Here, we use a PCM nanowire embedded into a nanophotonic circuit to study switching dynamics in mixed-mode operation. Evanescent coupling between light traveling along waveguides and a phase-change nanowire enables reversible phase transition between amorphous and crystalline states. We perform time-resolved measurements of the transient change in both the optical transmission and resistance of the nanowire and show reversible switching operations in both the optical and the electrical domains. Our results pave the way toward on-chip multifunctional optoelectronic integrated devices, waveguide integrated memories, and hybrid processing applications.

  11. Enhancing heat capacity of colloidal suspension using nanoscale encapsulated phase-change materials for heat transfer.

    PubMed

    Hong, Yan; Ding, Shujiang; Wu, Wei; Hu, Jianjun; Voevodin, Andrey A; Gschwender, Lois; Snyder, Ed; Chow, Louis; Su, Ming

    2010-06-01

    This paper describes a new method to enhance the heat-transfer property of a single-phase liquid by adding encapsulated phase-change nanoparticles (nano-PCMs), which absorb thermal energy during solid-liquid phase changes. Silica-encapsulated indium nanoparticles and polymer-encapsulated paraffin (wax) nanoparticles have been made using colloid method, and suspended into poly-alpha-olefin (PAO) and water for potential high- and low-temperature applications, respectively. The shells prevent leakage and agglomeration of molten phase-change materials, and enhance the dielectric properties of indium nanoparticles. The heat-transfer coefficients of PAO containing indium nanoparticles (30% by mass) and water containing paraffin nanoparticles (10% by mass) are 1.6 and 1.75 times higher than those of corresponding single-phase fluids. The structural integrity of encapsulation allows repeated use of such nanoparticles for many cycles in high heat generating devices.

  12. An optoelectronic framework enabled by low-dimensional phase-change films.

    PubMed

    Hosseini, Peiman; Wright, C David; Bhaskaran, Harish

    2014-07-10

    The development of materials whose refractive index can be optically transformed as desired, such as chalcogenide-based phase-change materials, has revolutionized the media and data storage industries by providing inexpensive, high-speed, portable and reliable platforms able to store vast quantities of data. Phase-change materials switch between two solid states--amorphous and crystalline--in response to a stimulus, such as heat, with an associated change in the physical properties of the material, including optical absorption, electrical conductance and Young's modulus. The initial applications of these materials (particularly the germanium antimony tellurium alloy Ge2Sb2Te5) exploited the reversible change in their optical properties in rewritable optical data storage technologies. More recently, the change in their electrical conductivity has also been extensively studied in the development of non-volatile phase-change memories. Here we show that by combining the optical and electronic property modulation of such materials, display and data visualization applications that go beyond data storage can be created. Using extremely thin phase-change materials and transparent conductors, we demonstrate electrically induced stable colour changes in both reflective and semi-transparent modes. Further, we show how a pixelated approach can be used in displays on both rigid and flexible films. This optoelectronic framework using low-dimensional phase-change materials has many likely applications, such as ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent 'smart' glasses, 'smart' contact lenses and artificial retina devices.

  13. An optoelectronic framework enabled by low-dimensional phase-change films

    NASA Astrophysics Data System (ADS)

    Hosseini, Peiman; Wright, C. David; Bhaskaran, Harish

    2014-07-01

    The development of materials whose refractive index can be optically transformed as desired, such as chalcogenide-based phase-change materials, has revolutionized the media and data storage industries by providing inexpensive, high-speed, portable and reliable platforms able to store vast quantities of data. Phase-change materials switch between two solid states--amorphous and crystalline--in response to a stimulus, such as heat, with an associated change in the physical properties of the material, including optical absorption, electrical conductance and Young's modulus. The initial applications of these materials (particularly the germanium antimony tellurium alloy Ge2Sb2Te5) exploited the reversible change in their optical properties in rewritable optical data storage technologies. More recently, the change in their electrical conductivity has also been extensively studied in the development of non-volatile phase-change memories. Here we show that by combining the optical and electronic property modulation of such materials, display and data visualization applications that go beyond data storage can be created. Using extremely thin phase-change materials and transparent conductors, we demonstrate electrically induced stable colour changes in both reflective and semi-transparent modes. Further, we show how a pixelated approach can be used in displays on both rigid and flexible films. This optoelectronic framework using low-dimensional phase-change materials has many likely applications, such as ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent `smart' glasses, `smart' contact lenses and artificial retina devices.

  14. Ethylene-associated phase change from juvenile to mature phenotype of daylily (Hemerocallis) in vitro

    NASA Technical Reports Server (NTRS)

    Smith, D. L.; Kelly, K.; Krikorian, A. D.

    1989-01-01

    Hemerocallis plantlets maintained in vitro for extended periods of time in tightly closed culture vessels frequently show a phenotype, albeit on a miniaturized scale, typical of more mature, field-grown plants. The positive relationship of elevated ethylene in the headspace of such vessels to the phase shift from juvenile to mature form is established. Rigorous restriction in air exchange with the external environment by means of silicone grease seals hastens the phase change and improves uniformity of response. Although some plantlets may take longer to accumulate enough ethylene in sealed jars to undergo change, added ethylene and ethylene-releasing agents promote it. Ethylene adsorbants (e.g. mercuric perchlorate) block the shift of juvenile to mature form. Critical ambient ethylene level for the shift is ca 1 microliter l-1. Levels up to 1000 microliters l-1 do not hasten the response but are not toxic. The phase change is fully reversible when air exchange permits ethylene to drop below 1 microliter l-1. At least 1 microliter l-1 ethylene is required to sustain the mature phenotype. The ethylene synthesis inhibitor aminoethoxyvinylglycine (AVG) prevents the phase change, while the ethylene biosynthesis intermediate 1-aminocyclopropanecarboxylic acid (ACC) improves it. KOH, as a CO2 absorbent, does not prevent the phase change. Histology sections demonstrate subtle changes in the form of shoot tips of plantlets undergoing phase change.

  15. Chalcogenide phase-change thin films used as grayscale photolithography materials.

    PubMed

    Wang, Rui; Wei, Jingsong; Fan, Yongtao

    2014-03-10

    Chalcogenide phase-change thin films are used in many fields, such as optical information storage and solid-state memory. In this work, we present another application of chalcogenide phase-change thin films, i.e., as grayscale photolithgraphy materials. The grayscale patterns can be directly inscribed on the chalcogenide phase-change thin films by a single process through direct laser writing method. In grayscale photolithography, the laser pulse can induce the formation of bump structure, and the bump height and size can be precisely controlled by changing laser energy. Bumps with different height and size present different optical reflection and transmission spectra, leading to the different gray levels. For example, the continuous-tone grayscale images of lifelike bird and cat are successfully inscribed onto Sb(2)Te(3) chalcogenide phase-change thin films using a home-built laser direct writer, where the expression and appearance of the lifelike bird and cat are fully presented. This work provides a way to fabricate complicated grayscale patterns using laser-induced bump structures onto chalcogenide phase-change thin films, different from current techniques such as photolithography, electron beam lithography, and focused ion beam lithography. The ability to form grayscale patterns of chalcogenide phase-change thin films reveals many potential applications in high-resolution optical images for micro/nano image storage, microartworks, and grayscale photomasks.

  16. Finite element developments for two dimensional multiple-interface phase change problems

    NASA Technical Reports Server (NTRS)

    Ouyang, Tianhong; Tamma, Kumar K.

    1992-01-01

    Finite element developments for multiple phase change problems in two-dimensional models are presented for the first time. The enthalpy method is used to simulate latent heat release in conjunction with fixed grid techniques. An unconditionally stable implicit method is used for the time integration. The effects of boundary conditions and the different phase regions on the multiple phase front developments are examined for numerous examples. Discussions and conclusions are appropriately addressed.

  17. Graphene/phase change material nanocomposites: light-driven, reversible electrical resistivity regulation via form-stable phase transitions.

    PubMed

    Wang, Yunming; Mi, Hongyi; Zheng, Qifeng; Ma, Zhenqiang; Gong, Shaoqin

    2015-02-04

    Innovative photoresponsive materials are needed to address the complexity of optical control systems. Here, we report a new type of photoresponsive nanomaterial composed of graphene and a form-stable phase change material (PCM) that exhibited a 3 orders of magnitude change in electrical resistivity upon light illumination while retaining its overall original solid form at the macroscopic level. This dramatic change in electrical resistivity also occurred reversibly through the on/off control of light illumination. This was attributed to the reversible phase transition (i.e., melting/recrystallization) behavior of the microscopic crystalline domains present in the form-stable PCM. The reversible phase transition observed in the graphene/PCM nanocomposite was induced by a reversible temperature change through the on/off control of light illumination because graphene can effectively absorb light energy and convert it to thermal energy. In addition, this graphene/PCM nanocomposite also possessed excellent mechanical properties. Such photoresponsive materials have many potential applications, including flexible electronics.

  18. Aluminum-centered tetrahedron-octahedron transition in advancing Al-Sb-Te phase change properties.

    PubMed

    Xia, Mengjiao; Ding, Keyuan; Rao, Feng; Li, Xianbin; Wu, Liangcai; Song, Zhitang

    2015-02-24

    Group IIIA elements, Al, Ga, or In, etc., doped Sb-Te materials have proven good phase change properties, especially the superior data retention ability over popular Ge2Sb2Te5, while their phase transition mechanisms are rarely investigated. In this paper, aiming at the phase transition of Al-Sb-Te materials, we reveal a dominant rule of local structure changes around the Al atoms based on ab initio simulations and nuclear magnetic resonance evidences. By comparing the local chemical environments around Al atoms in respective amorphous and crystalline Al-Sb-Te phases, we believe that Al-centered motifs undergo reversible tetrahedron-octahedron reconfigurations in phase transition process. Such Al-centered local structure rearrangements significantly enhance thermal stability of amorphous phase compared to that of undoped Sb-Te materials, and facilitate a low-energy amorphization due to the weak links among Al-centered and Sb-centered octahedrons. Our studies may provide a useful reference to further understand the underlying physics and optimize performances of all IIIA metal doped Sb-Te phase change materials, prompting the development of NOR/NAND Flash-like phase change memory technology.

  19. Simplified computer program for the analysis of phase change in liquid face seals

    NASA Technical Reports Server (NTRS)

    Birchak, M.; Hughes, W. F.

    1977-01-01

    A simplified computer program is presented which allows for the prediction of boiling (phase change) in liquid face seals. The program determines if and when boiling occurs and then calculates the location of the boiling interface, pressure and temperature profiles, and load. The main assumption which allows for a simplified analysis is the assumption of an isothermal gas phase.

  20. Estuary 2100 Project, Phase 1: Resilient Watersheds for a Changing Climate

    EPA Pesticide Factsheets

    Information about the SFBWQP Estuary 2100 Project, Phase 1: Resilient Watersheds for a Changing Climate , part of an EPA competitive grant program to improve SF Bay water quality focused on restoring impaired waters and enhancing aquatic resources.

  1. Radiation Heat Transfer Modeling Improved for Phase-Change, Thermal Energy Storage Systems

    NASA Technical Reports Server (NTRS)

    Kerslake, Thomas W.; Jacqmin, David A.

    1998-01-01

    Spacecraft solar dynamic power systems typically use high-temperature phase-change materials to efficiently store thermal energy for heat engine operation in orbital eclipse periods. Lithium fluoride salts are particularly well suited for this application because of their high heat of fusion, long-term stability, and appropriate melting point. Considerable attention has been focused on the development of thermal energy storage (TES) canisters that employ either pure lithium fluoride (LiF), with a melting point of 1121 K, or eutectic composition lithium-fluoride/calcium-difluoride (LiF-20CaF2), with a 1040 K melting point, as the phase-change material. Primary goals of TES canister development include maximizing the phase-change material melt fraction, minimizing the canister mass per unit of energy storage, and maximizing the phase-change material thermal charge/discharge rates within the limits posed by the container structure.

  2. Advection Scheme for Phase-changing Porous Media Flow of Fluids with Large Density Ratio

    NASA Astrophysics Data System (ADS)

    Zhang, Duan; Padrino, Juan

    2015-11-01

    Many flows in a porous media involve phase changes between fluids with a large density ratio. For instance, in the water-steam phase change the density ratio is about 1000. These phase changes can be results of physical changes, or chemical reactions, such as fuel combustion in a porous media. Based on the mass conservation, the velocity ratio between the fluids is of the same order of the density ratio. As the result the controlling Courant number for the time step in a numerical simulation is determined by the high velocity and low density phase, leading to small time steps. In this work we introduce a numerical approximation to increase the time step by taking advantage of the large density ratio. We provide analytical error estimation for this approximate numerical scheme. Numerical examples show that using this approximation about 40-fold speedup can be achieved at the cost of a few percent error. Work partially supported by LDRD project of LANL.

  3. Development and evaluation of germanium telluride phase change material based ohmic switches for RF applications

    NASA Astrophysics Data System (ADS)

    Wang, Muzhi; Rais-Zadeh, Mina

    2017-01-01

    We report on the device structure and performance of germanium telluride phase change material based ohmic RF switches. Two main types of the phase change switches using direct and indirect heating methods have been designed, fabricated and measured to analyze and compare the performance of germanium telluride in RF switch applications. Both types of switches are proven to have an insertion loss of less than 0.6 dB and an isolation of more than 13 dB for up to 20 GHz. Good linearity and power handling capability results are also measured. A reconfigurable bandpass filter using the indirectly heated phase change switch has also been developed, and shows promising performance. Efforts have been made to further analyze the issues with switching reliability, and explore possible ways of improving the performance of phase change RF switches.

  4. Some aspects of the computer simulation of conduction heat transfer and phase change processes

    SciTech Connect

    Solomon, A. D.

    1982-04-01

    Various aspects of phase change processes in materials are discussd including computer modeling, validation of results and sensitivity. In addition, the possible incorporation of cognitive activities in computational heat transfer is examined.

  5. Phase change nanocomposites with tunable melting temperature and thermal energy storage density.

    PubMed

    Liu, Minglu; Wang, Robert Y

    2013-08-21

    Size-dependent melting decouples melting temperature from chemical composition and provides a new design variable for phase change material applications. To demonstrate this potential, we create nanocomposites that exhibit stable and tunable melting temperatures through numerous melt-freeze cycles. These composites consist of a monodisperse ensemble of Bi nanoparticles (NPs) embedded in a polyimide (PI) resin matrix. The Bi NPs operate as the phase change component whereas the PI resin matrix prevents nanoparticle coalescence during melt-freeze cycles. We tune melting temperature and enthalpy of fusion in these composites by varying the NP diameter. Adjusting the NP volume fraction also controls the composite's thermal energy storage density. Hence it is possible to leverage size effects to tune phase change temperature and energy density in phase change materials.

  6. Thermal modeling of phase change solidification in thermal control devices including natural convection effects

    NASA Technical Reports Server (NTRS)

    Ukanwa, A. O.; Stermole, F. J.; Golden, J. O.

    1972-01-01

    Natural convection effects in phase change thermal control devices were studied. A mathematical model was developed to evaluate natural convection effects in a phase change test cell undergoing solidification. Although natural convection effects are minimized in flight spacecraft, all phase change devices are ground tested. The mathematical approach to the problem was to first develop a transient two-dimensional conduction heat transfer model for the solidification of a normal paraffin of finite geometry. Next, a transient two-dimensional model was developed for the solidification of the same paraffin by a combined conduction-natural-convection heat transfer model. Throughout the study, n-hexadecane (n-C16H34) was used as the phase-change material in both the theoretical and the experimental work. The models were based on the transient two-dimensional finite difference solutions of the energy, continuity, and momentum equations.

  7. Spectral changes induced by a phase modulator acting as a time lens

    SciTech Connect

    Plansinis, B. W.; Donaldson, W. R.; Agrawal, G. P.

    2015-07-06

    We show both numerically and experimentally that a phase modulator, acting as a time lens in the Fourier-lens configuration, can induce spectral broadening, narrowing, or shifts, depending on the phase of the modulator cycle. These spectral effects depend on the maximum phase shift that can be imposed by the modulator. In our numerical simulations, pulse spectrum could be compressed by a factor of 8 for a 30 rad phase shift. Experimentally, spectral shifts over a 1.35 nm range and spectral narrowing and broadening by a factor of 2 were demonstrated using a lithium niobate phase modulator with a maximum phase shift of 16 rad at a 10 GHz modulation frequency. All spectral changes were accomplished without employing optical nonlinear effects such as self- or cross-phase modulation.

  8. Synthesis and characteristics of form-stable n-octadecane/expanded graphite composite phase change materials

    NASA Astrophysics Data System (ADS)

    Li, Hui; Liu, Xu; Fang, Gui-Yin

    2010-09-01

    N-octadecane/expanded graphite composite phase-change materials were prepared by absorbing liquid n-octadecane into the expanded graphite. The n-octadecane was used as the phase-change material for thermal energy storage, and the expanded graphite acted as the supporting material. Fourier transformation infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal diffusivity measurement were used to determine the chemical structure, crystalline phase, microstructure and thermal diffusivity of the composite phase-change materials, respectively. The thermal properties and thermal stability were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC results indicated that the composite phase-change materials exhibited the same phase-transition characteristics as the n-octadecane and their latent heat increased with the n-octadecane content in composite phase-change materials. The SEM results showed that the n-octadecane was well absorbed in the porous network of the expanded graphite, and there was no leakage of the n-octadecane from the composites even when it was in the molten state.

  9. Energy-Efficient Phase-Change Memory with Graphene as a Thermal Barrier

    DTIC Science & Technology

    2015-09-02

    Energy-Efficient Phase-Change Memory with Graphene as a Thermal Barrier Chiyui Ahn,*,† Scott W. Fong,† Yongsung Kim,‡ Seunghyun Lee,† Aditya Sood...Samsung Advanced Institute of Technology (SAIT), Suwon, 443-803, South Korea *S Supporting Information ABSTRACT: Phase-change memory (PCM) is an important...cycles, and the graphene could further enhance the PCM endurance by limiting atomic migration or material segregation at the bottom electrode interface

  10. Change of shoot architecture during juvenile-to-adult phase transition in soybean.

    PubMed

    Yoshikawa, Takanori; Ozawa, Suguru; Sentoku, Naoki; Itoh, Jun-Ichi; Nagato, Yasuo; Yokoi, Shuji

    2013-07-01

    Juvenile-to-adult phase change is an indispensable event which guarantees a successful life cycle. Phase change has been studied in maize, Arabidopsis and rice, but is mostly unknown in other species. Soybean/Fabaceae plants undergo drastic changes of shoot architecture at the early vegetative stage including phyllotactic change and leaf type alteration from simple to compound. These characteristics make soybean/Fabaceae plants an interesting taxon for investigating vegetative phase change. Following the expansion of two cotyledons, two simple leaves simultaneously emerge in opposite phyllotaxy. The phyllotaxy of the third and fourth leaves is not fixed; both opposite and distichous phyllotaxis are observed within the same population. Leaves were compound from the third leaf. But the third leaf was rarely simple. Morphological and quantitative changes in early vegetative phase were recognized in leaf size, leaf shape, number of trichomes, stipule size and shape, and shoot meristem shape. Two microRNA genes, miR156 and miR172, are known to be associated with vegetative phase change. Examination of the expression level revealed that miR156 expression was high in the first two leaves and subsequently down-regulated, and that of miR172 showed the inverse expression pattern. These expression patterns coincided with the case of other species. Taken all data together, the first and second leaves represent juvenile phase, the fifth and upper leaves adult phase, and the third and fourth leaves intermediate stage. Further investigation of soybean phase change would give fruitful understandings on plant development.

  11. Understanding rapid changes in phase partitioning between cloud liquid and ice in an Arctic stratiform mixed-phase cloud

    NASA Astrophysics Data System (ADS)

    Kalesse, Heike; de Boer, Gijs; Solomon, Amy; Oue, Mariko; Ahlgrimm, Maike; Zhang, Damao; Shupe, Matthew; Luke, Edward; Protat, Alain

    2016-04-01

    In the Arctic, a region particularly sensitive to climate change, mixed-phase clouds occur as persistent single or multiple stratiform layers. For many climate models, the correct partitioning of hydrometeor phase (liquid vs. ice) remains a challenge. However, this phase partitioning plays an important role for precipitation processes and the radiation budget. To better understand the partitioning of phase in Arctic clouds, observations using a combination of surface-based remote sensors are useful. In this study, the focus is on a persistent low-level single-layer stratiform Arctic mixed-phase cloud observed during March 11-12, 2013 at the US Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) permanent site in Barrow, Alaska. This case is of particular interest due to two significant shifts in observed precipitation intensity over a 36 hour period. For the first 12 hours of this case, the observed liquid portion of the cloud cover featured a stable cloud top height with a gradually descending liquid cloud base and continuous ice precipitation. Then the ice precipitation intensity significantly decreased. A second decrease in ice precipitation intensity was observed a few hours later coinciding with the advection of a cirrus over the site. Through analysis of the data collected by extensive ground-based remote-sensing and in-situ observing systems as well as Nested Weather Research and Forecasting (WRF) simulations and ECMWF radiation scheme simulations, we try to shed light on the processes responsible for these rapid changes in precipitation rates. A variety of parameters such as the evolution of the internal dynamics and microphysics of the low-level mixed-phase cloud and the influence of the cirrus cloud are evaluated.

  12. Crystallization and Phase Changes in Paracetamol from the Amorphous Solid to the Liquid Phase

    PubMed Central

    2014-01-01

    For the case of paracetamol, we show how terahertz time-domain spectroscopy can be used to characterize the solid and liquid phase dynamics. Heating of supercooled amorphous paracetamol from 295 K in a covered sample under vacuum leads to its crystallization at 330 K. First, form III is formed followed by the transformation of form III to form II at 375 K, to form I at 405 K, and finally melting is observed around 455 K. We discuss the difference between the featureless spectra of the supercooled liquid and its liquid melt. Lastly, we studied the onset of crystallization from the supercooled liquid in detail and quantified its kinetics based on the Avrami–Erofeev model. We determined an effective rate constant of k = 0.056 min–1 with a corresponding onset of crystallization at T = 329.5 K for a heating rate of 0.4 K min–1. PMID:24579729

  13. Quasi-stationary phase change heat transfer on a fin

    NASA Astrophysics Data System (ADS)

    Orzechowski, Tadeusz; Stokowiec, Katarzyna

    2016-03-01

    The paper presents heat transfer research basing on a long fin with a circular cross-section. Its basis is welded to the pipe where the hot liquid paraffin, having a temperature of 70°C at the inflow, is pumped. The analyzed element is a recurrent part of a refrigeration's condenser, which is immersed in a paraffin. The temperature of the inflowing liquid is higher than the temperature of the melting process for paraffin, which allows the paraffin to liquify. The temperature at the basis of the rib changes and it is assumed that the heat transfer is quasi-stationary. On this basis the estimation of the mean value of heat transfer coefficient was conducted. The unsteady thermal field of the investigated system was registered with an infrared camera V50 produced by a Polish company Vigo System. This device is equipped with a microbolometric detector with 384 × 288 elements and the single pixel size 25 × 25 μm. Their thermal resolution is lower than 70 mK at a temperature of 30 °C. The camera operates at 7,5 ÷ 14 μm long-wave infrared radiation range. For a typical lens 35 mm the special resolution is 0.7 mrad. The result of the calculations is mean heat transfer coefficient for the considered time series. It is equal to 50 W m -2 K-1 and 47 W m -2 K-1 on the left and right side of the fin, respectively. The distance between the experimental data and the curve approximating the temperature distribution was assessed with the standard deviation, Sd = 0.04 K.

  14. Initial Atomic Motion Immediately Following Femtosecond-Laser Excitation in Phase-Change Materials.

    PubMed

    Matsubara, E; Okada, S; Ichitsubo, T; Kawaguchi, T; Hirata, A; Guan, P F; Tokuda, K; Tanimura, K; Matsunaga, T; Chen, M W; Yamada, N

    2016-09-23

    Despite the fact that phase-change materials are widely used for data storage, no consensus exists on the unique mechanism of their ultrafast phase change and its accompanied large and rapid optical change. By using the pump-probe observation method combining a femtosecond optical laser and an x-ray free-electron laser, we substantiate experimentally that, in both GeTe and Ge_{2}Sb_{2}Te_{5} crystals, rattling motion of mainly Ge atoms takes place with keeping the off-center position just after femtosecond-optical-laser irradiation, which eventually leads to a higher symmetry or disordered state. This very initial rattling motion in the undistorted lattice can be related to instantaneous optical change due to the loss of resonant bonding that characterizes GeTe-based phase change materials. Based on the amorphous structure derived by first-principles molecular dynamics simulation, we infer a plausible ultrafast amorphization mechanism via nonmelting.

  15. Qualitative observation of reversible phase change in astrochemical ethanethiol ices using infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Pavithraa, S.; Methikkalam, R. R. J.; Gorai, P.; Lo, J.-I.; Das, A.; Raja Sekhar, B. N.; Pradeep, T.; Cheng, B.-M.; Mason, N. J.; Sivaraman, B.

    2017-05-01

    Here we report the first evidence for a reversible phase change in an ethanethiol ice prepared under astrochemical conditions. InfraRed (IR) spectroscopy was used to monitor the morphology of the ice using the Ssbnd H stretching vibration, a characteristic vibration of thiol molecules. The deposited sample was able to switch between amorphous and crystalline phases repeatedly under temperature cycles between 10 K and 130 K with subsequent loss of molecules in every phase change. Such an effect is dependent upon the original thickness of the ice. Further work on quantitative analysis is to be carried out in due course whereas here we are reporting the first results obtained.

  16. Phase changes of the water hexamer and octamer in the gas phase and adsorbed on polycyclic aromatic hydrocarbons.

    PubMed

    Oliveira, Luiz Fernando L; Cuny, Jérôme; Morinière, Maxime; Dontot, Léo; Simon, Aude; Spiegelman, Fernand; Rapacioli, Mathias

    2015-07-14

    We investigate thermodynamic properties of small water clusters adsorbed on polycyclic aromatic hydrocarbons (PAHs), which are relevant systems in the context of astrophysical and atmospheric chemistry. We present heat capacity curves computed from parallel-tempering molecular dynamics and Monte Carlo simulations that were performed using the self-consistent-charge density-functional based tight-binding method. These curves are characteristic of the phase changes occurring in the aggregates and provide useful information on the evolution of the interaction between the water molecules and the PAHs as a function of temperature. After benchmarking our approach on the water hexamer and octamer in the gas phase, we present some results for these same clusters adsorbed on coronene and circumcoronene. When compared to the curves obtained for the isolated water clusters, the phase change temperature significantly decreases for the (H2O)8-PAH clusters whereas it depends on the nature of the PAH in the case of the hexamer. We analyse these differences as connected to the relative energies of the optimized characteristic isomers and to their dynamical behavior. We also evidence the population changes of the various cluster isomers as a function of temperature.

  17. Refraction-Assisted Solar Thermoelectric Generator based on Phase-Change Lens.

    PubMed

    Kim, Myoung-Soo; Kim, Min-Ki; Jo, Sung-Eun; Joo, Chulmin; Kim, Yong-Jun

    2016-06-10

    Solar thermoelectric generators (STEGs), which are used for various applications, (particularly small size electronic devices), have optical concentration systems for high energy conversion efficiency. In this study, a refraction-assisted STEG (R-STEG) is designed based on phase-change materials. As the phase-change material (PCM) changes phase from solid to liquid, its refractive index and transmittance also change, resulting in changes in the refraction of the sunlight transmitted through it, and concentration of solar energy in the phase-change lens. This innovative design facilitates double focusing the solar energy through the optical lens and a phase-change lens. This mechanism resulted in the peak energy conversion efficiencies of the R-STEG being 60% and 86% higher than those of the typical STEG at solar intensities of 1 kW m(-2) and 1.5 kW m(-2), respectively. In addition, the energy stored in PCM can help to generate steady electrical energy when the solar energy was removed. This work presents significant progress regarding the optical characteristic of PCM and optical concentration systems of STEGs.

  18. Refraction-Assisted Solar Thermoelectric Generator based on Phase-Change Lens

    PubMed Central

    Kim, Myoung-Soo; Kim, Min-Ki; Jo, Sung-Eun; Joo, Chulmin; Kim, Yong-Jun

    2016-01-01

    Solar thermoelectric generators (STEGs), which are used for various applications, (particularly small size electronic devices), have optical concentration systems for high energy conversion efficiency. In this study, a refraction-assisted STEG (R-STEG) is designed based on phase-change materials. As the phase-change material (PCM) changes phase from solid to liquid, its refractive index and transmittance also change, resulting in changes in the refraction of the sunlight transmitted through it, and concentration of solar energy in the phase-change lens. This innovative design facilitates double focusing the solar energy through the optical lens and a phase-change lens. This mechanism resulted in the peak energy conversion efficiencies of the R-STEG being 60% and 86% higher than those of the typical STEG at solar intensities of 1 kW m−2 and 1.5 kW m−2, respectively. In addition, the energy stored in PCM can help to generate steady electrical energy when the solar energy was removed. This work presents significant progress regarding the optical characteristic of PCM and optical concentration systems of STEGs. PMID:27283350

  19. An experimental and theoretical evaluation of increased thermal diffusivity phase change devices

    NASA Technical Reports Server (NTRS)

    White, S. P.; Golden, J. O.; Stermole, F. J.

    1972-01-01

    This study was to experimentally evaluate and mathematically model the performance of phase change thermal control devices containing high thermal conductivity metal matrices. Three aluminum honeycomb filters were evaluated at five different heat flux levels using n-oct-adecane as the test material. The system was mathematically modeled by approximating the partial differential equations with a three-dimensional implicit alternating direction technique. The mathematical model predicts the system quite well. All of the phase change times are predicted. The heating of solid phase is predicted exactly while there is some variation between theoretical and experimental results in the liquid phase. This variation in the liquid phase could be accounted for by the fact that there are some heat losses in the cell and there could be some convection in the experimental system.

  20. Thermodynamic nonequilibrium phase change behavior and thermal properties of biological solutions for cryobiology applications.

    PubMed

    Han, Bumsoo; Bischof, John C

    2004-04-01

    Understanding the phase change behavior of biomaterials during freezing/thawing including their thermal properties at low temperatures is essential to design and improve cryobiology applications such as cryopreservation and cryosurgery. However, knowledge of phase change behavior and thermal properties of various biomaterials is still incomplete, especially at cryogenic temperatures (< or = -40 degrees C). Moreover, in these applications, chemicals are often added to improve their outcome, which can result in significant variation in the phase change behavior and thermal properties from those of the original biomaterials. These chemical additives include cryoprotective agents (CPAs), antifreeze protein (AFP), or cryosurgical adjuvants like sodium chloride (NaCl). In the present study, phase change behavior and thermal properties of saline solutions--either water-NaCl or phosphate buffered saline (PBS)--with various chemical additives were investigated. The chemical additives studied are glycerol and raffinose as CPAs, an AFP (Type III, molecular weight = 6500), and NaCl as a cryosurgical adjuvant. The phase change behavior was investigated using a differential scanning calorimeter (DSC) and a cryomicroscope. The specific and latent heat of these solutions were also measured with the DSC. The saline solutions have two distinct phase changes--water/ice and eutectic phase changes. During freezing, eutectic solidification of both water-NaCl and PBS are significantly supercooled below their thermodynamic equilibrium eutectic temperatures. However, their melting temperatures are close to thermodynamic equilibrium during thawing. These eutectic phase changes disappear when even a small amount (0.1 M glycerol) of CPA was added, but they are still observed after the addition of an AFP. The specific heats of these solutions are close to that of ice at very low temperatures (< or = -100 degrees C) regardless of the additives, but they increase between -100 degrees C and -30

  1. Titanium defect structure change after gas-phase hydrogenation at different temperatures and cooling rates

    NASA Astrophysics Data System (ADS)

    Mikhaylov, Andrey A.; Laptev, Roman S.; Kudiiarov, Viktor N.; Volokitina, Tatiana L.

    2016-11-01

    Influence of gas-phase hydrogenation temperature and cooling rate on defect structure of commercially pure titanium alloy was experimentally studied by means of positron annihilation spectroscopy. The change of temperature in the process of gas-phase hydrogenation was in the range of 500-700°C, while the change of cooling rate was in the range of 0.4-10.4°C/min. With increasing of gas-phase hydrogenation temperature, significant increase of hydrogen sorption rate was found. High temperature gas-phase hydrogenation of commercially pure titanium alloy lead to the formation of vacancy and hydrogen-vacancy complexes. For the same concentration of hydrogen, temperature variation or variation of cooling rate had no effect on the type of defect. However, this variation provides significant changes in defect concentration.

  2. Morphology and polymorphic phase changes of calcium carbonate micro/nanocrystals using fruit extracts.

    PubMed

    Ankamwar, Balaprasad

    2011-05-01

    This study reveals the morphology and polymorphic phase changes of calcium carbonate crystals into a mixture of calcite and aragonite micro/nanocrystals of interesting morphology at room temperature by a simple reaction with fruit extracts of Tamarindus indica and Emblica officinalis respectively by mixing CaCO3 solutions with their corresponding extracts. The control experiments were carried out to establish the plausible role of tartaric acid from Tamarindus indica and ascorbic acid from Emblica officinalis in this regard. The quantitative determination of CaCO3 phases was done based on the use of intensities obtained from corresponding XRD spectrum. The molar % of aragonite was found to be more in case of TA and AA rather than TI and EO respectively, however the calcite was observed to be the predominant phase in all four reactions. Interestingly, the TI changes the rhombohedral morphology of calcite to elongated rods, whereas EO induces a great polymorphic phase change.

  3. Role of an encapsulating layer for reducing resistance drift in phase change random access memory

    NASA Astrophysics Data System (ADS)

    Jin, Bo; Kim, Jungsik; Pi, Dong-Hai; Kim, Hyoung Seop; Meyyappan, M.; Lee, Jeong-Soo

    2014-12-01

    Phase change random access memory (PCRAM) devices exhibit a steady increase in resistance in the amorphous phase upon aging and this resistance drift phenomenon directly affects the device reliability. A stress relaxation model is used here to study the effect of a device encapsulating layer material in addressing the resistance drift phenomenon in PCRAM. The resistance drift can be increased or decreased depending on the biaxial moduli of the phase change material (YPCM) and the encapsulating layer material (YELM) according to the stress relationship between them in the drift regime. The proposed model suggests that the resistance drift can be effectively reduced by selecting a proper material as an encapsulating layer. Moreover, our model explains that reducing the size of the phase change material (PCM) while fully reset and reducing the amorphous/crystalline ratio in PCM help to improve the resistance drift, and thus opens an avenue for highly reliable multilevel PCRAM applications.

  4. Materials research for passive solar systems: solid-state phase-change materials

    SciTech Connect

    Benson, D.K.; Webb, J.D.; Burrows, R.W.; McFadden, J.D.O.; Christensen, C.

    1985-03-01

    A set of solid-state phase-change materials is being evaluated for possible use in passive solar thermal energy storage systems. The most promising materials are organic solid solutions of pentaerythritol (C/sub 5/H/sub 12/O/sub 4/), pentaglycerinve (C/sub 5/H/sub 12/O/sub 3/), and neopentyl glycol (C/sub 5/H/sub 12/O/sub 2/). Solid solution mixtures of these compounds can be tailored so that they exhibit solid-to-solid phase transformations at any desired temperature betweeen 25/sup 0/C and 188/sup 0/C, and have latent heats of transformation between 20 and 70 cal/g. Transformation temperatures, specific heats, and latent heats of transformation have been measured for a number of these materials. Limited cyclic experiments suggest that the solid solutions are stable. These phase-change materials exhibit large amounts of undercooling; however, the addition of certain nucleating agents as particulate dispersions in the solid phase-change material greatly reduces this effect. Computer simulations suggest that the use of an optimized solid-state phase-change material in a Trombe wall could provide better performance than a concrete Trombe wall four times thicker and nine times heavier. Nevertheless, a higher cost of the phase-change materials (approx. =$0.70 per pound) is likely to limit their applicability in passive solar systems unless their performance can be significantly improved through further research.

  5. Auditory cortical neurons are sensitive to static and continuously changing interaural phase cues.

    PubMed

    Reale, R A; Brugge, J F

    1990-10-01

    1. The interaural-phase-difference (IPD) sensitivity of single neurons in the primary auditory (AI) cortex of the anesthetized cat was studied at stimulus frequencies ranging from 120 to 2,500 Hz. Best frequencies of the 43 AI cells sensitive to IPD ranged from 190 to 2,400 Hz. 2. A static IPD was produced when a pair of low-frequency tone bursts, differing from one another only in starting phase, were presented dichotically. The resulting IPD-sensitivity curves, which plot the number of discharges evoked by the binaural signal as a function of IPD, were deeply modulated circular functions. IPD functions were analyzed for their mean vector length (r) and mean interaural phase (phi). Phase sensitivity was relatively independent of best frequency (BF) but highly dependent on stimulus frequency. Regardless of BF or stimulus frequency within the excitatory response area the majority of cells fired maximally when the ipsilateral tone lagged the contralateral signal and fired least when this interaural-phase relationship was reversed. 3. Sensitivity to continuously changing IPD was studied by delivering to the two ears 3-s tones that differed slightly in frequency, resulting in a binaural beat. Approximately 26% of the cells that showed a sensitivity to static changes in IPD also showed a sensitivity to dynamically changing IPD created by this binaural tonal combination. The discharges were highly periodic and tightly synchronized to a particular phase of the binaural beat cycle. High synchrony can be attributed to the fact that cortical neurons typically respond to an excitatory stimulus with but a single spike that is often precisely timed to stimulus onset. A period histogram, binned on the binaural beat frequency (fb), produced an equivalent IPD-sensitivity function for dynamically changing interaural phase. For neurons sensitive to both static and continuously changing interaural phase there was good correspondence between their static (phi s) and dynamic (phi d

  6. Nucleation of a new phase on a surface that is changing irreversibly with time.

    PubMed

    Sear, Richard P

    2014-02-01

    Nucleation of a new phase almost always starts at a surface. This surface is almost always assumed not to change with time. However, surfaces can roughen, partially dissolve, and change chemically with time. Each of these irreversible changes will change the nucleation rate at the surface, resulting in a time-dependent nucleation rate. Here we use a simple model to show that partial surface dissolution can qualitatively change the nucleation process in a way that is testable in experiment. The changing surface means that the nucleation rate is increasing with time. There is an initial period during which no nucleation occurs, followed by relatively rapid nucleation.

  7. Phase changes at the end of a microtubule with a GTP cap.

    PubMed Central

    Hill, T L; Chen, Y

    1984-01-01

    Examination of Monte Carlo kinetic simulations, based on a realistic set of microscopic rate constants that apply to the end of a microtubule with a GTP cap, suggests that the end of a microtubule alternates between two quasimacroscopic phases. In one phase, the microtubule end has a GTP cap that fluctuates in size; in the other phase, the GTP cap has been lost. These repeated phase changes take place at any given tubulin concentration in a wide range of concentrations. While in the first phase, the microtubule grows slowly; while in the second phase, it shortens rapidly and may disappear completely. These results are closely related to the recent experimental work of Mitchison and Kirschner [Mitchison, T. & Kirschner, M.W. (1984) Nature (London), in press]. PMID:6592585

  8. An Automatic Phase-Change Detection Technique for Colloidal Hard Sphere Suspensions

    NASA Technical Reports Server (NTRS)

    McDowell, Mark; Gray, Elizabeth; Rogers, Richard B.

    2005-01-01

    Colloidal suspensions of monodisperse spheres are used as physical models of thermodynamic phase transitions and as precursors to photonic band gap materials. However, current image analysis techniques are not able to distinguish between densely packed phases within conventional microscope images, which are mainly characterized by degrees of randomness or order with similar grayscale value properties. Current techniques for identifying the phase boundaries involve manually identifying the phase transitions, which is very tedious and time consuming. We have developed an intelligent machine vision technique that automatically identifies colloidal phase boundaries. The algorithm utilizes intelligent image processing techniques that accurately identify and track phase changes vertically or horizontally for a sequence of colloidal hard sphere suspension images. This technique is readily adaptable to any imaging application where regions of interest are distinguished from the background by differing patterns of motion over time.

  9. Modeling of a Two-Phase Jet Pump with Phase Change, Shocks and Temperature-Dependent Properties

    NASA Technical Reports Server (NTRS)

    Sherif, S. A.

    1998-01-01

    One of the primary motivations behind this work is the attempt to understand the physics of a two-phase jet pump which constitutes part of a flow boiling test facility at NASA-Marshall. The flow boiling apparatus is intended to provide data necessary to design highly efficient two-phase thermal control systems for aerospace applications. The facility will also be capable of testing alternative refrigerants and evaluate their performance using various heat exchangers with enhanced surfaces. The test facility is also intended for use in evaluating single-phase performance of systems currently using CFC refrigerants. Literature dealing with jet pumps is abundant and covers a very wide array of application areas. Example application areas include vacuum pumps which are used in the food industry, power station work, and the chemical industry; ejector systems which have applications in the aircraft industry as cabin ventilators and for purposes of jet thrust augmentation; jet pumps which are used in the oil industry for oil well pumping; and steam-jet ejector refrigeration, to just name a few. Examples of work relevant to this investigation includes those of Fairuzov and Bredikhin (1995). While past researchers have been able to model the two-phase flow jet pump using the one-dimensional assumption with no shock waves and no phase change, there is no research known to the author apart from that of Anand (1992) who was able to account for condensation shocks. Thus, one of the objectives of this work is to model the dynamics of fluid interaction between a two-phase primary fluid and a subcooled liquid secondary fluid which is being injected employing atomizing spray injectors. The model developed accounts for phase transformations due to expansion, compression, and mixing. It also accounts for shock waves developing in the different parts of the jet pump as well as temperature and pressure dependencies of the fluid properties for both the primary two-phase mixture and the

  10. Study on the impact of the initialization process on the phase change memory

    NASA Astrophysics Data System (ADS)

    Ren, Kun; Rao, Feng; Song, Zhitang; Lv, Shilong; Zhu, Min; Wu, Liangcai; Liu, Bo; Feng, Songlin

    2013-05-01

    The set processes of T-shape phase change memory (PCRAM) cell are compared to study the change caused by the initialization. After the initialization, PCRAM cell shows lower Vth and minor resistances than those of the 1st operation, which can be explained by the reduction of contact resistance caused by the formation of the crystalline phase change material interface (CPI) near the electrodes. The temperature transition regions between the programmed region and the electrodes preserve the CPI after its formation in the initial operation. Thus, we suggest the formation of CPI is the key role for the initialization.

  11. Presence of acute phase changes in zinc, iron, and copper metabolism in turkey embryos

    SciTech Connect

    Klasing, K.C.; Richards, M.P.; Darcey, S.E.; Laurin, D.E.

    1987-01-01

    Acute phase changes in trace mineral metabolism were examined in turkey embryos. An endotoxin injection resulted in increased concentrations of serum copper and liver zinc and decreased concentrations of serum zinc in embryos incubated either in ovo or ex ovo. Changes in zinc and copper metabolism occurred when endotoxin either was injected intramuscularly, into the amnionic fluid, or administered onto the chorioallantoic membrane. Unlike poults, embryos did not respond to an inflammatory challenge with decreased serum iron concentrations. Acute phase changes in embryo serum zinc and copper as well as liver zinc concentrations were similar to those in poults. Increased liver zinc concentrations were associated with increased zinc in metallothionein (MT). An injection of a crude interleukin 1 preparation into embryos resulted in similar increases in hepatic zinc and MT concentrations as an endotoxin injection, suggesting a role for this cytokine in mediating the acute phase changes in embryonic zinc metabolism.

  12. Non-binary Colour Modulation for Display Device Based on Phase Change Materials.

    PubMed

    Ji, Hong-Kai; Tong, Hao; Qian, Hang; Hui, Ya-Juan; Liu, Nian; Yan, Peng; Miao, Xiang-Shui

    2016-12-19

    A reflective-type display device based on phase change materials is attractive because of its ultrafast response time and high resolution compared with a conventional display device. This paper proposes and demonstrates a unique display device in which multicolour changing can be achieved on a single device by the selective crystallization of double layer phase change materials. The optical contrast is optimized by the availability of a variety of film thicknesses of two phase change layers. The device exhibits a low sensitivity to the angle of incidence, which is important for display and colour consistency. The non-binary colour rendering on a single device is demonstrated for the first time using optical excitation. The device shows the potential for ultrafast display applications.

  13. Adversary phase change detection using S.O.M. and text data.

    SciTech Connect

    Speed, Ann Elizabeth; Doser, Adele Beatrice; Warrender, Christina E.

    2011-01-01

    In this work, we developed a self-organizing map (SOM) technique for using web-based text analysis to forecast when a group is undergoing a phase change. By 'phase change', we mean that an organization has fundamentally shifted attitudes or behaviors. For instance, when ice melts into water, the characteristics of the substance change. A formerly peaceful group may suddenly adopt violence, or a violent organization may unexpectedly agree to a ceasefire. SOM techniques were used to analyze text obtained from organization postings on the world-wide web. Results suggest it may be possible to forecast phase changes, and determine if an example of writing can be attributed to a group of interest.

  14. Adversary phase change detection using S.O.M. and text data.

    SciTech Connect

    Speed, Ann Elizabeth; Doser, Adele Beatrice; Warrender, Christina E.

    2010-09-01

    In this work, we developed a self-organizing map (SOM) technique for using web-based text analysis to forecast when a group is undergoing a phase change. By 'phase change', we mean that an organization has fundamentally shifted attitudes or behaviors. For instance, when ice melts into water, the characteristics of the substance change. A formerly peaceful group may suddenly adopt violence, or a violent organization may unexpectedly agree to a ceasefire. SOM techniques were used to analyze text obtained from organization postings on the world-wide web. Results suggest it may be possible to forecast phase changes, and determine if an example of writing can be attributed to a group of interest.

  15. Non-binary Colour Modulation for Display Device Based on Phase Change Materials

    PubMed Central

    Ji, Hong-Kai; Tong, Hao; Qian, Hang; Hui, Ya-Juan; Liu, Nian; Yan, Peng; Miao, Xiang-Shui

    2016-01-01

    A reflective-type display device based on phase change materials is attractive because of its ultrafast response time and high resolution compared with a conventional display device. This paper proposes and demonstrates a unique display device in which multicolour changing can be achieved on a single device by the selective crystallization of double layer phase change materials. The optical contrast is optimized by the availability of a variety of film thicknesses of two phase change layers. The device exhibits a low sensitivity to the angle of incidence, which is important for display and colour consistency. The non-binary colour rendering on a single device is demonstrated for the first time using optical excitation. The device shows the potential for ultrafast display applications. PMID:27991523

  16. Differences among trainees in client outcomes associated with the phase model of change.

    PubMed

    Budge, Stephanie L; Owen, Jesse J; Kopta, S Mark; Minami, Takuya; Hanson, Matthew R; Hirsch, Glenn

    2013-06-01

    This study investigated psychotherapy trainees' ability to facilitate change in outcomes (e.g., well-being, symptom reduction, and life functioning) specifically related to the phase model. Four different psychotherapist experience levels (beginning practicum, advanced practicum, intern/postdoc, and psychologist) were compared to determine whether there are training differences related to significant change for psychotherapy outcomes according to the phase model. A total of 1,318 clients from a university counseling center, treated by 64 psychotherapists, were included in the analysis for this study. Results indicate that interns/postdocs' clients achieve more significant change than psychologists' and advanced practicum students' clients related to life functioning. In addition, interns/postdocs' clients achieve more significant change related to symptom reduction, when compared with the clients of psychologists. Implications for these results, given the hypotheses of both the phase model and competency models, are discussed.

  17. Competing covalent and ionic bonding in Ge-Sb-Te phase change materials

    SciTech Connect

    Subedi, Alaska; Siegrist, Theo; Singh, David J.; Mukhopadhyay, Saikat; Sun, Jifeng

    2016-05-19

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionic and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. As a result, this different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties.

  18. Competing covalent and ionic bonding in Ge-Sb-Te phase change materials

    DOE PAGES

    Subedi, Alaska; Siegrist, Theo; Singh, David J.; ...

    2016-05-19

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionicmore » and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. As a result, this different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties.« less

  19. Competing covalent and ionic bonding in Ge-Sb-Te phase change materials.

    PubMed

    Mukhopadhyay, Saikat; Sun, Jifeng; Subedi, Alaska; Siegrist, Theo; Singh, David J

    2016-05-19

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionic and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. This different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties.

  20. Competing covalent and ionic bonding in Ge-Sb-Te phase change materials

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Saikat; Sun, Jifeng; Subedi, Alaska; Siegrist, Theo; Singh, David J.

    2016-05-01

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionic and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. This different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties.

  1. Competing covalent and ionic bonding in Ge-Sb-Te phase change materials

    PubMed Central

    Mukhopadhyay, Saikat; Sun, Jifeng; Subedi, Alaska; Siegrist, Theo; Singh, David J.

    2016-01-01

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionic and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. This different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties. PMID:27193531

  2. Synthesis and Screening of Phase Change Chalcogenide Thin Film Materials for Data Storage.

    PubMed

    Guerin, Samuel; Hayden, Brian; Hewak, Daniel W; Vian, Chris

    2017-07-10

    A combinatorial synthetic methodology based on evaporation sources under an ultrahigh vacuum has been used to directly synthesize compositional gradient thin film libraries of the amorphous phases of GeSbTe alloys at room temperature over a wide compositional range. An optical screen is described that allows rapid parallel mapping of the amorphous-to-crystalline phase transition temperature and optical contrast associated with the phase change on such libraries. The results are shown to be consistent with the literature for compositions where published data are available along the Sb2Te3-GeTe tie line. The results reveal a minimum in the crystallization temperature along the Sb2Te3-Ge2Te3 tie line, and the method is able to resolve subsequent cubic-to-hexagonal phase transitions in the GST crystalline phase. HT-XRD has been used to map the phases at sequentially higher temperatures, and the results are reconciled with the literature and trends in crystallization temperatures. The results clearly delineate compositions that crystallize to pure GST phases and those that cocrystallize Te. High-throughput measurement of the resistivity of the amorphous and crystalline phases has allowed the compositional and structural correlation of the resistivity contrast associated with the amorphous-to-crystalline transition, which range from 5-to-8 orders of magnitude for the compositions investigated. The results are discussed in terms of the compromises in the selection of these materials for phase change memory applications and the potential for further exploration through more detailed secondary screening of doped GST or similar classes of phase change materials designed for the demands of future memory devices.

  3. Preparation and characterization of novel anion phase change heat storage materials.

    PubMed

    Hong, Wei; Lil, Qingshan; Sun, Jing; Di, Youbo; Zhao, Zhou; Yu, Wei'an; Qu, Yuan; Jiao, TiFeng; Wang, Guowei; Xing, Guangzhong

    2013-10-01

    In this paper, polyurethane phase change material was successfully prepared with TDI with BDO for hard segments and PEG for soft segments. Moreover, based on this the solid-solid phase change material, A-PCM1030 which can release anions was prepared with the successful addition of anion additives A1030 for the first time. Then the test of the above material was conducted utilizing FT-IR, DSC, TEM, WAXD and Air Ion Detector. The Results indicated that the polyurethane phase change material possesses excellent thermal stability since there was no appearance of liquid leakage and phase separation after 50 times warming-cooling thermal cycles. It also presented reversibility on absorbing and releasing heat. In addition, adding a little A1030 can increase the thermal stability and reduce phase transition temperatures, as well as reduce the undercooling of the polyurethane phase change material. In addition, the anion test results suggested that the supreme amount of anion released by A-PCM1030 could reach 2510 anions/cm3 under dynamic conditions, which is beneficial for human health.

  4. Modulation of behavioral phase changes of the migratory locust by the catecholamine metabolic pathway

    PubMed Central

    Ma, Zongyuan; Guo, Wei; Guo, Xiaojiao; Wang, Xianhui; Kang, Le

    2011-01-01

    The migratory locust, Locusta migratoria, shows a striking phenotypic plasticity. It transitions between solitary and gregarious phases in response to population density changes. However, the molecular mechanism underlying the phase-dependent behavior changes remains elusive. Here we report a genome-wide gene expression profiling of gregarious and solitary nymphs at each stadium of the migratory locust, and we identified the most differentially expressed genes in the fourth stadium of the two phases. Bioinformatics analysis indicated that the catecholamine metabolic pathway was the most significant pathway up-regulated in the gregarious phase. We found pale, henna, and vat1, involved in dopamine biosynthesis and synaptic release, were critical target genes related to behavioral phase changes in the locusts. The roles of these genes in mediating behavioral changes in the gregarious individuals were confirmed by RNAi and pharmacological intervention. A single injection of dopamine or its agonist initiated gregarious behavior. Moreover, continuous and multiple injections of a dopamine agonist coupled with crowding resulted in more pronounced gregarious behavior. Our study thus provides insights into the relationships between genes and behavior in phase transition of this important pest species. PMID:21325054

  5. Visualising phase change in a brushite-based calcium phosphate ceramic.

    PubMed

    Bannerman, A; Williams, R L; Cox, S C; Grover, L M

    2016-09-08

    The resorption of brushite-based bone cements has been shown to be highly unpredictable, with strong dependence on a number of conditions. One of the major factors is phase transformation, with change to more stable phases such as hydroxyapatite affecting the rate of resorption. Despite its importance, the analysis of phase transformation has been largely undertaken using methods that only detect crystalline composition and give no information on the spatial distribution of the phases. In this study confocal Raman microscopy was used to map cross-sections of brushite cylinders aged in Phosphate Buffered Saline, Foetal Bovine Serum, Dulbecco's - Minimum Essential Medium (with and without serum). Image maps showed the importance of ageing medium on the phase composition throughout the ceramic structure. When aged without serum, there was dissolution of the brushite phase concomitant to the deposition of octacalcium phosphate (OCP) around the periphery of the sample. The deposition of OCP was detectable within five days and reduced the rate of brushite dissolution from the material. The use of serum, even at a concentration of 10vol% prevented phase transformation. This paper demonstrates the value of confocal Raman microscopy in monitoring phase change in biocements; it also demonstrates the problems with assessing material degradation in non-serum containing media.

  6. Visualising phase change in a brushite-based calcium phosphate ceramic

    NASA Astrophysics Data System (ADS)

    Bannerman, A.; Williams, R. L.; Cox, S. C.; Grover, L. M.

    2016-09-01

    The resorption of brushite-based bone cements has been shown to be highly unpredictable, with strong dependence on a number of conditions. One of the major factors is phase transformation, with change to more stable phases such as hydroxyapatite affecting the rate of resorption. Despite its importance, the analysis of phase transformation has been largely undertaken using methods that only detect crystalline composition and give no information on the spatial distribution of the phases. In this study confocal Raman microscopy was used to map cross-sections of brushite cylinders aged in Phosphate Buffered Saline, Foetal Bovine Serum, Dulbecco’s – Minimum Essential Medium (with and without serum). Image maps showed the importance of ageing medium on the phase composition throughout the ceramic structure. When aged without serum, there was dissolution of the brushite phase concomitant to the deposition of octacalcium phosphate (OCP) around the periphery of the sample. The deposition of OCP was detectable within five days and reduced the rate of brushite dissolution from the material. The use of serum, even at a concentration of 10vol% prevented phase transformation. This paper demonstrates the value of confocal Raman microscopy in monitoring phase change in biocements; it also demonstrates the problems with assessing material degradation in non-serum containing media.

  7. Visualising phase change in a brushite-based calcium phosphate ceramic

    PubMed Central

    Bannerman, A.; Williams, R. L.; Cox, S. C.; Grover, L. M.

    2016-01-01

    The resorption of brushite-based bone cements has been shown to be highly unpredictable, with strong dependence on a number of conditions. One of the major factors is phase transformation, with change to more stable phases such as hydroxyapatite affecting the rate of resorption. Despite its importance, the analysis of phase transformation has been largely undertaken using methods that only detect crystalline composition and give no information on the spatial distribution of the phases. In this study confocal Raman microscopy was used to map cross-sections of brushite cylinders aged in Phosphate Buffered Saline, Foetal Bovine Serum, Dulbecco’s – Minimum Essential Medium (with and without serum). Image maps showed the importance of ageing medium on the phase composition throughout the ceramic structure. When aged without serum, there was dissolution of the brushite phase concomitant to the deposition of octacalcium phosphate (OCP) around the periphery of the sample. The deposition of OCP was detectable within five days and reduced the rate of brushite dissolution from the material. The use of serum, even at a concentration of 10vol% prevented phase transformation. This paper demonstrates the value of confocal Raman microscopy in monitoring phase change in biocements; it also demonstrates the problems with assessing material degradation in non-serum containing media. PMID:27604149

  8. Electro- and photodriven phase change composites based on wax-infiltrated carbon nanotube sponges.

    PubMed

    Chen, Liangjie; Zou, Ruqiang; Xia, Wei; Liu, Zhenpu; Shang, Yuanyuan; Zhu, Jinlong; Wang, Yingxia; Lin, Jianhua; Xia, Dingguo; Cao, Anyuan

    2012-12-21

    Organic phase change materials are usually insulating in nature, and they are unlikely to directly trigger latent heat storage through an electrical way. Here we report a multifunctional phase change composite in which the energy storage can be driven by small voltages (e.g., 1.5 V) or light illumination with high electro-to-heat or photo-to-thermal storage efficiencies (40% to 60%). The composite is composed of paraffin wax infiltrated into a porous, deformable carbon nanotube sponge; the latter not only acts as a flexible encapsulation scaffold for wax but also maintains a highly conductive network during the phase change process (for both solid and liquid states). Uniform interpenetration between the nanotube network and paraffin wax with high affinity results in enhanced phase change enthalpy and thermal conductivity compared to pure paraffin wax. Our phase change composite can store energy in practical ways such as by sunlight absorption or under voltages applied by conventional lithium-ion batteries.

  9. Quantitative stability analyses of multiwall carbon nanotube nanofluids following water/ice phase change cycling.

    PubMed

    Ivall, Jason; Langlois-Rahme, Gabriel; Coulombe, Sylvain; Servio, Phillip

    2017-02-03

    Multiwall carbon nanotube nanofluids are regularly investigated for phase change enhancement between liquid and solid states owing to their improved heat transfer properties. The potential applications are numerous, the most notable being latent heat thermal energy storage, but the success of all nanofluid-assisted technologies hinges greatly on the ability of nanoparticles to remain stably dispersed after repeated phase change cycles. In this report, the stability of aqueous nanofluids made from oxygen-functionalized multiwall carbon nanotubes (f-MWCNTs) was profiled over the course of 20 freeze/thaw cycles. Sonication was used after each cycle to re-disperse clusters formed from the crystallization process. This study offers a quantitative evaluation of f-MWCNT-nanofluid stability as a result of phase change through optical characterization of concentration and particle size. It also provides insight into the integrity of the surface functionalities through zeta potential and XPS analyses. Concentration and particle size measurements showed moderate and consistent recoverability of f-MWCNT dispersion following ultrasonication. XPS measurements of solid-state MWCNTs exposed to freeze/thaw cycling in water, and zeta potential analyses of the nanofluids indicate that the surface oxygen content is preserved throughout phase change and over repeated cycles. These results suggest a resilience of oxygen-functionalized MWCNTs to the freezing and thawing of water, which is ideal for their utilization as phase change enhancers.

  10. Quantitative stability analyses of multiwall carbon nanotube nanofluids following water/ice phase change cycling

    NASA Astrophysics Data System (ADS)

    Ivall, Jason; Langlois-Rahme, Gabriel; Coulombe, Sylvain; Servio, Phillip

    2017-02-01

    Multiwall carbon nanotube nanofluids are regularly investigated for phase change enhancement between liquid and solid states owing to their improved heat transfer properties. The potential applications are numerous, the most notable being latent heat thermal energy storage, but the success of all nanofluid-assisted technologies hinges greatly on the ability of nanoparticles to remain stably dispersed after repeated phase change cycles. In this report, the stability of aqueous nanofluids made from oxygen-functionalized multiwall carbon nanotubes (f-MWCNTs) was profiled over the course of 20 freeze/thaw cycles. Sonication was used after each cycle to re-disperse clusters formed from the crystallization process. This study offers a quantitative evaluation of f-MWCNT-nanofluid stability as a result of phase change through optical characterization of concentration and particle size. It also provides insight into the integrity of the surface functionalities through zeta potential and XPS analyses. Concentration and particle size measurements showed moderate and consistent recoverability of f-MWCNT dispersion following ultrasonication. XPS measurements of solid-state MWCNTs exposed to freeze/thaw cycling in water, and zeta potential analyses of the nanofluids indicate that the surface oxygen content is preserved throughout phase change and over repeated cycles. These results suggest a resilience of oxygen-functionalized MWCNTs to the freezing and thawing of water, which is ideal for their utilization as phase change enhancers.

  11. Effect of water-ice phase change on thermal performance of building materials

    NASA Astrophysics Data System (ADS)

    Kočí, Václav; Černý, Robert

    2016-07-01

    The effect of water ice-phase change on thermal performance of integrated building material is investigated in this paper. As a characteristic construction, simple external wall made of aerated autoclaved concrete was assumed which was exposed to dynamic climatic condition of Šerák, Czech Republic. The computational modelling of hygrothermal performance was carried out using computer codes HEMOT and SIFEL that work on the basis of finite element method. The effect of phase change was taken into account by fixed-domain method, when experimentally determined effective specific heat capacity was used as a material parameter. It comprises also the effect of heat consumption and heat release that accompany the water-ice phase change. Comparing to the results with specific heat capacity, the effect of phase change on thermal performance could be quantified. The results showed that temperature fields can differ more than 6 °C. Additionally, the amount energy transported through the wall may be higher up to 4 %. This confirmed, that the effect water-ice phase change should be included in all the relevant energy calculations.

  12. A model and practical solution for freezing phase change material aboard the International Space Station

    NASA Astrophysics Data System (ADS)

    Blackwood, James

    A need exists to send and return temperature-critical science payloads from the International Space Station to the earth. A Low Temperature low Energy Carrier (LoTEC) has been designed to meet this need. It is a passive device that gains its cooling power by using phase change material. This phase change material can be stored in containers on the International Space Station. Before it can be employed by LoTEC for a return trip, it must first be frozen. Most phase change materials are water-based and therefore expanding upon freezing. This expansion can cause a rupture in station freezers and/or an inability to fit inside LoTEC due to small tolerances. To solve this problem a simple analytical model of the phase change process for water is examined to give guidance for a higher fidelity numerical model. This three-dimensional numerical model is used to predict ice formation and final ice shape. The numerical model also gives guidance for devising a freezing method to ensure a desirable final ice shape for the phase change material. Finally, ground-based experiments are conducted to add validity to the model and freezing method.

  13. Phase change of nickel phosphide catalysts in the conversion of cellulose into sorbitol.

    PubMed

    Yang, Pengfei; Kobayashi, Hirokazu; Hara, Kenji; Fukuoka, Atsushi

    2012-05-01

    Nickel phosphide catalysts supported on activated carbon were tested for the conversion of cellulose in water. High sorbitol yields of over 60% were obtained with high cellulose conversions at 503 K and 5 MPa of H(2) . It is interesting that an amorphous nickel phosphide phase is generated from a crystalline phase during the increase in temperature and that the amorphous phase is responsible for the high yield of sorbitol. The optimization of the reaction parameters indicates that the increase of the amorphous part in the cellulose is the key to obtaining high yields of sorbitol. A phase change of the nickel phosphide is observed, which can be correlated to the change in catalytic activity.

  14. Ultrafast Ge-Te bond dynamics in a phase-change superlattice

    NASA Astrophysics Data System (ADS)

    Malvestuto, Marco; Caretta, Antonio; Casarin, Barbara; Cilento, Federico; Dell'Angela, Martina; Fausti, Daniele; Calarco, Raffaella; Kooi, Bart J.; Varesi, Enrico; Robertson, John; Parmigiani, Fulvio

    2016-09-01

    A long-standing question for avant-garde data storage technology concerns the nature of the ultrafast photoinduced phase transformations in the wide class of chalcogenide phase-change materials (PCMs). Overall, a comprehensive understanding of the microstructural evolution and the relevant kinetics mechanisms accompanying the out-of-equilibrium phases is still missing. Here, after overheating a phase-change chalcogenide superlattice by an ultrafast laser pulse, we indirectly track the lattice relaxation by time resolved x-ray absorption spectroscopy (tr-XAS) with a sub-ns time resolution. The approach to the tr-XAS experimental results reported in this work provides an atomistic insight of the mechanism that takes place during the cooling process; meanwhile a first-principles model mimicking the microscopic distortions accounts for a straightforward representation of the observed dynamics. Finally, we envisage that our approach can be applied in future studies addressing the role of dynamical structural strain in PCMs.

  15. How important is the {103} plane of stable Ge2 Sb2 Te5 for phase-change memory?

    PubMed

    Zhang, W; Zheng, W T; Kim, J-G; Cui, X Q; Li, L; Qi, J G; Kim, Y-J; Song, S A

    2015-07-01

    Closely correlating with {200} plane of cubic phase, {103} plane of hexagonal phase of Ge(2)Sb(2)Te(5) plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge(2)Sb(2)Te(5). The behaviors of {103} plane of hexagonal phase render the phase-change memory process as a nanoscale shape memory. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

  16. Dynamic digital speckle interferometry applied to optical diagnosis of gas-liquid phase change

    NASA Astrophysics Data System (ADS)

    Song, Yaozu; Zhang, Hongling; Zhang, Wei; Jiao, Tianfeng

    2001-11-01

    In this paper, a Dynamic Digital Speckle Interferometry (DDSI) applied to optical diagnosis of gas-liquid phase change is proposed. The basic principle and experimental system of the DDSI are presented. This technology of flow optical diagnosis has the following three main advantages. First, DDSI uses a CCD camera as record device of a specklegram and a microcomputer, which processes the specklegrams to obtain a speckle interferogram. Therefore, the DDSI does not need the photographic film and optical dark room that usually are needed for holographic interferometry and speckle photography. Second, in DDSI technique, the information of density field in flow is obtained by using a double exposure with and without flow variation respectively. As a result, it can automatically eliminate the effect of the density nonuniformity of the optical windows of test section on the density measurement (like holographic interferometry). Third, the DDSI can be used for dynamic visualization and real time measurement of continuous variation of density with time in flow (like M-Z interferometry). The gas-liquid phase change process of freon R13 is investigated experimentally. By means of the DDSI technique, both density distributions in gas phase and liquid phase of R13, which are located on two sides of gas-liquid interface respectively, can be measured when gas-liquid phase change occurs. It is also observed that the interface between gas-phase and liquid-phase has a thickness of the order of hundreds micrometers, when the temperature of R13 flow comes close to its critical temperature. The variation laws of the interface thickness with the temperature of R13 are discussed. The interface behaviors of movement, disappearance and renewal are presented. The investigations show that DDSI is very suitable for the optical diagnosis of gas-liquid phase change in mini or micro scale. It provides an effective method for experimental investigations on heat transfer and flow in mini or micro

  17. Fundamental heat transfer processes related to phase change thermal storage media

    SciTech Connect

    Sparrow, E. M.; Ramsey, J. W.

    1981-01-01

    Research on fundamental heat transfer processes which occur in phase-change thermal storage systems is described. The research encompasses both melting and freezing, and includes both experiment and analysis. The status of four research problems is discussed. One of the freezing problems was focused on investigating, via experiment, the extent to which freezing can be enhanced by the attachment of fins to the external surface of a cooled vertical tube situated in a liquid phase-change medium. Very substantial enhancements were encountered which neutralize the degradation of freezing due to the thermal resistance of the frozen layer and to natural convection in the liquid phase. The second of the freezing problems was analytical in nature and sought to obtain solutions involving both the phase-change medium and the heat transfer fluid used either to add heat to or extract heat from the medium. For freezing on a plane wall, it was possible to obtain a closed-form analytical solution, while for freezing about a coolant-carrying circular tube, a new numerical methodology was devised to obtain finite-difference solutions. For melting, quantitative design-quality heat transfer coefficients were determined experimentally for melting adjacent to a heated vertical tube. These experiments explored the effects of solid-phase subcooling and of open versus closed top containment on the coefficients. A dimensionless correlation enables these results to be used for a wide range of phase-change media. Studies on melting of a phase-change material situated within a circular tube are in progress.

  18. microRNA172 down-regulates glossy15 to promote vegetative phase change in maize

    PubMed Central

    Lauter, Nick; Kampani, Archana; Carlson, Shawn; Goebel, Mark; Moose, Stephen P.

    2005-01-01

    Shoot development in many higher plant species is characterized by phase change, where meristems and organs transition from one set of identities to another. The transition from a juvenile to adult leaf identity in maize is regulated by the APETALA2-like gene glossy15 (gl15). We demonstrate here that increasing gl15 activity in transgenic maize not only increases the number of leaves expressing juvenile traits, but also delays the onset of reproductive development, indicating that gl15 plays a primary role in the maintenance of the juvenile phase. We also show that the accumulation of a maize microRNA homologous to miR172 increases during shoot development and mediates gl15 mRNA degradation. These data indicate that vegetative phase change in maize is regulated by the opposing actions of gl15 and miR172, with gl15 maintaining the juvenile phase and miR172 promoting the transition to the adult phase by down-regulation of gl15. Our results also suggest that the balance of activities between APETALA2-like genes and miR172 may be a general mechanism for regulating vegetative phase change in higher plants. PMID:15958531

  19. Differential proteomic analysis during the vegetative phase change and the floral transition in Malus domestica.

    PubMed

    Zeng, Guang J; Li, Chun M; Zhang, Xin Z; Han, Zhen H; Yang, Feng Q; Gao, Yan; Chen, Dong M; Zhao, Yong B; Wang, Yi; Teng, Yun L; Dong, Wen X

    2010-09-01

    In order to identify the proteomic changes of apple (Malus domestica Borkh.) during the vegetative phase change and the floral transition, leaf protein of juvenile, adult vegetative and reproductive phase in a seedling ('Jonathan' × 'Golden Delicious') was extracted and analyzed by 2-D electrophoresis and Matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Seventy two gel spots with significant expression differences between ontogenetic phases were obtained. Five protein spots were only detected in leaves of juvenile phase and 11 were not; 17 spots were found exclusively in adult vegetative leaves; and only one spot solely appeared in reproductive leaves while 12 did not. Twenty six of the differentially expressed proteins identified were involved in photosynthesis. Seven enzymes were related to respiration and carbohydrate metabolism. Fifteen other proteins also presented qualitative or quantitative differences among developmental phases. The spatial distribution of one differentially expressed protein, serine hydroxymethyltransferase, was confirmed by enzyme linked immunosorbent assay and immunohistochemistry. These results strongly support the idea that the vegetative phase change and the floral transition are regulated independently during developmental process.

  20. Design rules for phase-change materials in data storage applications.

    PubMed

    Lencer, Dominic; Salinga, Martin; Wuttig, Matthias

    2011-05-10

    Phase-change materials can rapidly and reversibly be switched between an amorphous and a crystalline phase. Since both phases are characterized by very different optical and electrical properties, these materials can be employed for rewritable optical and electrical data storage. Hence, there are considerable efforts to identify suitable materials, and to optimize them with respect to specific applications. Design rules that can explain why the materials identified so far enable phase-change based devices would hence be very beneficial. This article describes materials that have been successfully employed and dicusses common features regarding both typical structures and bonding mechanisms. It is shown that typical structural motifs and electronic properties can be found in the crystalline state that are indicative for resonant bonding, from which the employed contrast originates. The occurence of resonance is linked to the composition, thus providing a design rule for phase-change materials. This understanding helps to unravel characteristic properties such as electrical and thermal conductivity which are discussed in the subsequent section. Then, turning to the transition kinetics between the phases, the current understanding and modeling of the processes of amorphization and crystallization are discussed. Finally, present approaches for improved high-capacity optical discs and fast non-volatile electrical memories, that hold the potential to succeed present-day's Flash memory, are presented.

  1. Direct numerical simulations of fluid flow, heat transfer and phase changes

    NASA Technical Reports Server (NTRS)

    Juric, D.; Tryggvason, G.; Han, J.

    1997-01-01

    Direct numerical simulations of fluid flow, heat transfer, and phase changes are presented. The simulations are made possible by a recently developed finite difference/front tracking method based on the one-field formulation of the governing equations where a single set of conservation equations is written for all the phases involved. The conservation equations are solved on a fixed rectangular grid, but the phase boundaries are kept sharp by tracking them explicitly by a moving grid of lower dimension. The method is discussed and applications to boiling heat transfer and the solidification of drops colliding with a wall are shown.

  2. Morphological analysis of GeTe in inline phase change switches

    SciTech Connect

    King, Matthew R.; El-Hinnawy, Nabil; Salmon, Mike; Gu, Jitty; Wagner, Brian P.; Jones, Evan B.; Howell, Robert S.; Nichols, Doyle T.; Young, Robert M.; Borodulin, Pavel

    2015-09-07

    Crystallization and amorphization phenomena in indirectly heated phase change material-based devices were investigated. Scanning transmission electron microscopy was utilized to explore GeTe phase transition processes in the context of the unique inline phase change switch (IPCS) architecture. A monolithically integrated thin film heating element successfully converted GeTe to ON and OFF states. Device cycling prompted the formation of an active area which sustains the majority of structural changes during pulsing. A transition region on both sides of the active area consisting of polycrystalline GeTe and small nuclei (<15 nm) in an amorphous matrix was also observed. The switching mechanism, determined by variations in pulsing parameters, was shown to be predominantly growth-driven. A preliminary model for crystallization and amorphization in IPCS devices is presented.

  3. Logic computation in phase change materials by threshold and memory switching.

    PubMed

    Cassinerio, M; Ciocchini, N; Ielmini, D

    2013-11-06

    Memristors, namely hysteretic devices capable of changing their resistance in response to applied electrical stimuli, may provide new opportunities for future memory and computation, thanks to their scalable size, low switching energy and nonvolatile nature. We have developed a functionally complete set of logic functions including NOR, NAND and NOT gates, each utilizing a single phase-change memristor (PCM) where resistance switching is due to the phase transformation of an active chalcogenide material. The logic operations are enabled by the high functionality of nanoscale phase change, featuring voltage comparison, additive crystallization and pulse-induced amorphization. The nonvolatile nature of memristive states provides the basis for developing reconfigurable hybrid logic/memory circuits featuring low-power and high-speed switching. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Temperature dependence of SET switching characteristics in phase-change memory cells

    NASA Astrophysics Data System (ADS)

    He, Qiang; Li, Zhen; Liu, Chang; Meng, Xiang-ru; Peng, Ju-hong; Lai, Zhi-bo; Miao, Xiang-shui

    2016-09-01

    The temperature dependence of crystallization kinetics of phase-change materials raises a series of reliability issues, while phase-change memory cells work at high temperature or thermal-disturbance condition. These issues hinder the development of ultrahigh-density storage devices. We investigate the evolution of SET switching characteristics of phase-change memory cells at high operating temperature. We show that the high temperature strongly impacts the SET state resistance. As a result, SET failure has been observed with elevated ambient temperature. Our SPICE simulations indicate that transient amorphization behavior during a complete SET pulse period is considered as the potential mechanism of SET failure. By modifying the SET pulse intensity and width linearly, we successfully reduce the SET failure in the experiments. The results illustrate that the demonstrated linear properties may optimize SET pulse performance.

  5. Morphological analysis of GeTe in inline phase change switches

    NASA Astrophysics Data System (ADS)

    King, Matthew R.; El-Hinnawy, Nabil; Salmon, Mike; Gu, Jitty; Wagner, Brian P.; Jones, Evan B.; Borodulin, Pavel; Howell, Robert S.; Nichols, Doyle T.; Young, Robert M.

    2015-09-01

    Crystallization and amorphization phenomena in indirectly heated phase change material-based devices were investigated. Scanning transmission electron microscopy was utilized to explore GeTe phase transition processes in the context of the unique inline phase change switch (IPCS) architecture. A monolithically integrated thin film heating element successfully converted GeTe to ON and OFF states. Device cycling prompted the formation of an active area which sustains the majority of structural changes during pulsing. A transition region on both sides of the active area consisting of polycrystalline GeTe and small nuclei (<15 nm) in an amorphous matrix was also observed. The switching mechanism, determined by variations in pulsing parameters, was shown to be predominantly growth-driven. A preliminary model for crystallization and amorphization in IPCS devices is presented.

  6. GeTe/Sb7Te3 superlatticelike structure for lateral phase change memory

    NASA Astrophysics Data System (ADS)

    Yang, Hongxin; Chong, Chong Tow; Zhao, Rong; Lee, Hock Koon; Li, Jianming; Lim, Kian Guan; Shi, Luping

    2009-05-01

    A series of superlatticelike (SLL) structure incorporated with two phase-change materials GeTe and Sb7Te3 was applied in lateral phase change memory. Power consumption and lifetime were used as two criteria to optimize the SLL structure. It was found that with the thickness ratio of GeTe to Sb7Te3 at 1.6, the RESET current could be as low as 1.5 mA and the endurance could reach as high as 5.3×106 cycles. By varying the thickness ratio of GeTe to Sb7Te3, the crystallization temperature of SLL structures and the performance of lateral phase change memory with these SLL structures can be controlled.

  7. A 63 K phase change unit integrating with pulse tube cryocoolers

    NASA Astrophysics Data System (ADS)

    Chunhui, Kong; Liubiao, Chen; Sixue, Liu; Yuan, Zhou; Junjie, Wang

    2017-02-01

    This article presents the design and computer model results of an integrated cooler system which consists of a single stage pulse tube cryocooler integrated with a small amount of a phase change material. A cryogenic thermal switch was used to thermally connect the phase change unit to the cold end of the cryocooler. During heat load operation, the cryogenic thermal switch is turned off to avoid vibrations. The phase change unit absorbs heat loads by melting a substance in a constant pressure-temperature-volume process. Once the substance has been melted, the cryogenic thermal turned on, the cryocooler can then refreeze the material. Advantages of this type of cooler are no vibrations during sensor operations; the ability to absorb increased heat loads; potentially longer system lifetime; and a lower mass, volume and cost. A numerical model was constructed from derived thermodynamic relationships for the cooling/heating and freezing/melting processes.

  8. Change in Photosystem II Photochemistry During Algal Growth Phases of Chlorella vulgaris and Scenedesmus obliquus.

    PubMed

    Oukarroum, Abdallah

    2016-06-01

    Sensitivity of photosynthetic processes towards environmental stress is used as a bioanalytical tool to evaluate the responses of aquatic plants to a changing environment. In this paper, change of biomass density, chlorophyll a fluorescence and photosynthetic parameters during growth phases of two microalgae Chlorella vulgaris and Scenedesmus obliquus were studied. The photosynthetic growth behaviour changed significantly with cell age and algae species. During the exponential phase of growth, the photosynthesis capacity reached its maximum and decreased in ageing algal culture during stationary phase. In conclusion, the chlorophyll a fluorescence OJIP method and the derived fluorescence parameters would be an accurate method for obtaining information on maximum photosynthetic capacities and monitoring algal cell growth. This will contribute to more understanding, for example, of toxic actions of pollutants in microalgae test.

  9. Hybrid transfinite element modeling/analysis of nonlinear heat conduction problems involving phase change

    NASA Technical Reports Server (NTRS)

    Tamma, Kumar K.; Railkar, Sudhir B.

    1988-01-01

    The present paper describes the applicability of hybrid transfinite element modeling/analysis formulations for nonlinear heat conduction problems involving phase change. The methodology is based on application of transform approaches and classical Galerkin schemes with finite element formulations to maintain the modeling versatility and numerical features for computational analysis. In addition, in conjunction with the above, the effects due to latent heat are modeled using enthalpy formulations to enable a physically realistic approximation to be dealt computationally for materials exhibiting phase change within a narrow band of temperatures. Pertinent details of the approach and computational scheme adapted are described in technical detail. Numerical test cases of comparative nature are presented to demonstrate the applicability of the proposed formulations for numerical modeling/analysis of nonlinear heat conduction problems involving phase change.

  10. Transient analysis of a thermal storage unit involving a phase change material

    NASA Technical Reports Server (NTRS)

    Griggs, E. I.; Pitts, D. R.; Humphries, W. R.

    1974-01-01

    The transient response of a single cell of a typical phase change material type thermal capacitor has been modeled using numerical conductive heat transfer techniques. The cell consists of a base plate, an insulated top, and two vertical walls (fins) forming a two-dimensional cavity filled with a phase change material. Both explicit and implicit numerical formulations are outlined. A mixed explicit-implicit scheme which treats the fin implicity while treating the phase change material explicitly is discussed. A band algorithmic scheme is used to reduce computer storage requirements for the implicit approach while retaining a relatively fine grid. All formulations are presented in dimensionless form thereby enabling application to geometrically similar problems. Typical parametric results are graphically presented for the case of melting with constant heat input to the base of the cell.

  11. Phase-Change Characteristic Analysis of Partially Melted Sodium Acetate Trihydrate Using DSC

    NASA Astrophysics Data System (ADS)

    Jin, Xing; Medina, Mario A.; Zhang, Xiaosong; Zhang, Shuanglong

    2014-01-01

    Sodium acetate trihydrate (SAT), which is a kind of phase-change material, offers high potential for application in thermal energy storage. However, SAT has a natural tendency to supercool during its solidification process. Adding nucleating agents has been suggested as a possible solution. In this paper, the phase-change characteristics of the partially melted SAT were analyzed using a differential scanning calorimeter (DSC). A phenomenon related to SAT undergoing phase change was discovered and analyzed. The results showed that if SAT were cooled when it was partially melted, it would release heat and quickly solidify without adding any nucleating agents. Therefore, if the temperature range of SAT was controlled properly, supercooling could be significantly prevented.

  12. Material engineering of GexTe100-x compounds to improve phase-change memory performances

    NASA Astrophysics Data System (ADS)

    Navarro, G.; Sousa, V.; Persico, A.; Pashkov, N.; Toffoli, A.; Bastien, J.-C.; Perniola, L.; Maitrejean, S.; Roule, A.; Zuliani, P.; Annunziata, R.; De Salvo, B.

    2013-11-01

    In this paper we provide a detailed physical and electrical characterization of Germanium Telluride compounds (GexTe100-x) targeting phase-change memory applications. Thin films of Germanium-rich as well as Tellurium-rich phase-change materials are deposited for material analysis (XRD, resistivity and optical characterization). GexTe100-x compounds are then integrated in lance-type analytical phase-change memory devices allowing for a thorough analysis of the switching characteristics, data retention and endurance performances. Tellurium-rich GeTe alloys exhibit stable programming characteristics and can sustain endurance up to 107 cycles, while Germanium-rich compounds show an unstable RESET state during repeated write/erase cycles, probably affected by Ge segregation. Finally we demonstrate that data retention is strongly improved departing from Ge50Te50 stoichiometric composition.

  13. Hybrid transfinite element modeling/analysis of nonlinear heat conduction problems involving phase change

    NASA Technical Reports Server (NTRS)

    Tamma, Kumar K.; Railkar, Sudhir B.

    1988-01-01

    The present paper describes the applicability of hybrid transfinite element modeling/analysis formulations for nonlinear heat conduction problems involving phase change. The methodology is based on application of transform approaches and classical Galerkin schemes with finite element formulations to maintain the modeling versatility and numerical features for computational analysis. In addition, in conjunction with the above, the effects due to latent heat are modeled using enthalpy formulations to enable a physically realistic approximation to be dealt computationally for materials exhibiting phase change within a narrow band of temperatures. Pertinent details of the approach and computational scheme adapted are described in technical detail. Numerical test cases of comparative nature are presented to demonstrate the applicability of the proposed formulations for numerical modeling/analysis of nonlinear heat conduction problems involving phase change.

  14. Phase changes of filled ice Ih methane hydrate under low temperature and high pressure.

    PubMed

    Tanaka, Takehiko; Hirai, Hisako; Matsuoka, Takahiro; Ohishi, Yasuo; Yagi, Takehiko; Ohtake, Michika; Yamamoto, Yoshitaka; Nakano, Satoshi; Irifune, Tetsuo

    2013-09-14

    Low-temperature and high-pressure experiments were performed with filled ice Ih structure of methane hydrate under 2.0-77.0 GPa and 30-300 K using diamond anvil cells and a helium-refrigeration cryostat. In situ X-ray diffractometry revealed distinct changes in the compressibility of the axial ratios of the host framework with pressure. Raman spectroscopy showed a split in the C-H vibration modes of the guest methane molecules, which was previously explained by the orientational ordering of the guest molecules. The pressure and temperature conditions at the split of the vibration modes agreed well with those of the compressibility change. The results indicate the following: (i) the orientational ordering of the guest methane molecules from an orientationally disordered state occurred at high pressures and low temperatures; and (ii) this guest ordering led to anisotropic contraction in the host framework. Such guest orientational ordering and subsequent anisotropic contraction of the host framework were similar to that reported previously for filled ice Ic hydrogen hydrate. Since phases with different guest-ordering manners were regarded as different phases, existing regions of the guest disordered-phase and the guest ordered-phase were roughly estimated by the X-ray study. In addition, above the pressure of the guest-ordered phase, another high-pressure phase developed in the low-temperature region. The deuterated-water host samples were also examined, and the influence of isotopic effects on guest ordering and phase transformation was observed.

  15. Growth phase dependent changes in the structure and protein composition of nucleoid in Escherichia coli.

    PubMed

    Talukder, AliAzam; Ishihama, Akira

    2015-09-01

    The genomic DNA of bacteria is highly compacted in a single or a few bodies known as nucleoids. Here, we have isolated Escherichia coli nucleoid by sucrose density gradient centrifugation. The sedimentation rates, structures as well as protein/ DNA composition of isolated nucleoids were then compared under various growth phases. The nucleoid structures were found to undergo changes during the cell growth; i. e., the nucleoid structure in the stationary phase was more tightly compacted than that in the exponential phase. In addition to factor for inversion stimulation (Fis), histone-like nucleoid structuring protein (H-NS), heat-unstable nucleoid protein (HU) and integration host factor (IHF) here we have identified, three new candidates of E. coli nucleoid, namely DNA-binding protein from starved cells (Dps), host factor for phage Qβ (Hfq) and suppressor of td(-) phenotype A (StpA). Our results reveal that the major components of exponential phase nucleoid are Fis, HU, H-NS, StpA and Hfq, while Dps occupies more than half of the stationary phase nucleoid. It has been known for a while that Dps is the main nucleoid-associated protein at stationary phase. From these results and the prevailing information, we propose a model for growth phase dependent changes in the structure and protein composition of nucleoid in E. coli.

  16. Electronic Structure and Spin Configuration Trends of Single Transition Metal Impurity in Phase Change Material

    NASA Astrophysics Data System (ADS)

    Li, H.; Pei, J.; Shi, L. P.

    2016-10-01

    Fe doped phase change material GexSbyTez has shown experimentally the ability to alter its magnetic properties by phase change. This engineered spin degree of freedom into the phase change material offers the possibility of logic devices or spintronic devices where they may enable fast manipulation of ferromagnetism by a phase change mechanism. The electronic structures and spin configurations of isolated transition metal dopant in phase change material (iTM-PCM) is important to understand the interaction between localized metal d states and the unique delocalized host states of phase change material. Identifying an impurity center that has, in isolation, a nonvanishing magnetic moment is the first step to study the collective magnetic ordering, which originates from the interaction among close enough individual impurities. Theoretical description of iTM-PCM is challenging. In this work, we use a screened exchange hybrid functional to study the single 3d transition metal impurity in crystalline GeTe and GeSb2Te4. By curing the problem of local density functional (LDA) such as over-delocalization of the 3d states, we find that Fe on the Ge/Sb site has its majority d states fully occupied while its minority d states are empty, which is different from the previously predicted electronic configuration by LDA. From early transition metal Cr to heavier Ni, the majority 3d states are gradually populated until fully occupied and then the minority 3d states begin to be filled. Interpretive orbital interaction pictures are presented for understanding the local and total magnetic moments.

  17. Heat transfer characteristics of coconut oil as phase change material to room cooling application

    NASA Astrophysics Data System (ADS)

    Irsyad, M.; Harmen

    2017-03-01

    Thermal comfort in a room is one of human needs in the workplace and dwellings, so that the use of air conditioning system in tropical countries is inevitable. This equipment has an impact on the increase of energy consumption. One method of minimizing the energy use is by using the phase change material (PCM) as thermal energy storage. This material utilizes the temperature difference between day and night for the storage and release of thermal energy. PCM development on application as a material for air cooling inlet, partitioning and interior needs to be supported by the study of heat transfer characteristics when PCM absorbs heat from ambient temperature. This study was conducted to determine the heat transfer characteristics on coconut oil as a phase change material. There are three models of experiments performed in this research. Firstly, an experiment was conducted to analyze the time that was needed by material to phase change by varying the temperature. The second experiment analyzed the heat transfer characteristics of air to PCM naturally convection. The third experiment analyzed the forced convection heat transfer on the surface of the PCM container by varying the air velocity. The data of experimental showed that, increasing ambient air temperature resulted in shorter time for phase change. At temperatures of 30°C, the time for phase change of PCM with the thickness of 8 cm was 1700 min, and it was stable at temperatures of 27°C. Increasing air temperature accelerated the phase change in the material. While for the forced convection heat transfer, PCM could reduce the air temperature in the range of 30 to 35°C at about 1 to 2°C, with a velocity of 1-3 m/s.

  18. An analytical model for nanoscale electrothermal probe recording on phase-change media

    NASA Astrophysics Data System (ADS)

    Aziz, Mustafa M.; Wright, C. David

    2006-02-01

    Scanning probe memories are now emerging as a means of achieving nanoscale resolution data storage. The use of microscopic conductive tips in contact with a phase-change material to record data as amorphous and crystalline marks is one such approach, making use of the large difference in electrical conductivity between the two phases to distinguish between two binary states on replay and hence provide a memory function. The writing process is complex and involves electronic, thermal, and phase-change processes that are difficult to model and study except using numerical techniques. A simplified analytical model of electrothermal writing by probe on a basic two-layer phase-change structure is developed here, and used to predict the required voltage levels for recording and the expected diameters of recorded crystalline and amorphous marks. A simplified model of cooling and solidification was also developed to study the cooling rates during amorphization. The predictions are shown to be in agreement with published experimental measurements and numerical simulations. The developed analytical models were extended to investigate the effects of introducing coating layers on recording voltage levels, to study the depth profiles of recorded marks, and to derive expressions for the capacitance and resistance of the phase-change layer that contribute to the transient behavior of the recording system.

  19. Changes in functioning of mesolimbic incentive processing circuits during the premenstrual phase

    PubMed Central

    van Wingen, Guido A.; Kooijman, Sabine C.; Bäckström, Torbjörn; Fernández, Guillén; Hermans, Erno J.

    2011-01-01

    The premenstrual phase of the menstrual cycle is associated with marked changes in normal and abnormal motivated behaviors. Animal studies suggest that such effects may result from actions of gonadal hormones on the mesolimbic dopamine (DA) system. We therefore investigated premenstrual changes in reward-related neural activity in terminal regions of the DA system in humans. Twenty-eight healthy young women underwent functional magnetic resonance imaging on 2 days during the menstrual cycle, once during the late follicular phase and once during the premenstrual phase, in counterbalanced order. Using a modified version of the monetary incentive delay task, we assessed responsiveness of the ventral striatum to reward anticipation. Our results show enhanced ventral striatal responses during the premenstrual as compared to the follicular phase. Moreover, this effect was most pronounced in women reporting more premenstrual symptoms. These findings provide support for the notion that changes in functioning of mesolimbic incentive processing circuits may underlie premenstrual changes in motivated behaviors. Notably, increases in reward-cue responsiveness have previously been associated with DA withdrawal states. Our findings therefore suggest that the sharp decline of gonadal hormone levels in the premenstrual phase may trigger a similar withdrawal-like state. PMID:20817665

  20. A computational framework for mapping the timing of vegetative phase change.

    PubMed

    Xu, Meng; Jiang, Libo; Zhu, Sheng; Zhou, Chunguo; Ye, Meixia; Mao, Ke; Sun, Lidan; Su, Xiaohua; Pan, Huixin; Zhang, Shougong; Huang, Minren; Wu, Rongling

    2016-07-01

    Phase change plays a prominent role in determining the form of growth and development. Although considerable attention has been focused on identifying the regulatory control mechanisms of phase change, a detailed understanding of the genetic architecture of this phenomenon is still lacking. We address this issue by deriving a computational model. The model is founded on the framework of functional mapping aimed at characterizing the interplay between quantitative trait loci (QTLs) and development through biologically meaningful mathematical equations. A multiphasic growth equation was implemented into functional mapping, which, via a series of hypothesis tests, allows the quantification of how QTLs regulate the timing and pattern of vegetative phase transition between independently regulated, temporally coordinated processes. The model was applied to analyze stem radial growth data of an interspecific hybrid family derived from two Populus species during the first 24 yr of ontogeny. Several key QTLs related to phase change have been characterized, most of which were observed to be in the adjacent regions of candidate genes. The identification of phase transition QTLs, whose expression is regulated by endogenous and environmental signals, may enhance our understanding of the evolution of development in changing environments. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

  1. One order of magnitude faster phase change at reduced power in Ti-Sb-Te.

    PubMed

    Zhu, Min; Xia, Mengjiao; Rao, Feng; Li, Xianbin; Wu, Liangcai; Ji, Xinglong; Lv, Shilong; Song, Zhitang; Feng, Songlin; Sun, Hongbo; Zhang, Shengbai

    2014-07-08

    To date, slow Set operation speed and high Reset operation power remain to be important limitations for substituting dynamic random access memory by phase change memory. Here, we demonstrate phase change memory cell based on Ti0.4Sb2Te3 alloy, showing one order of magnitude faster Set operation speed and as low as one-fifth Reset operation power, compared with Ge2Sb2Te5-based phase change memory cell at the same size. The enhancements may be rooted in the common presence of titanium-centred octahedral motifs in both amorphous and crystalline Ti0.4Sb2Te3 phases. The essentially unchanged local structures around the titanium atoms may be responsible for the significantly improved performance, as these structures could act as nucleation centres to facilitate a swift, low-energy order-disorder transition for the rest of the Sb-centred octahedrons. Our study may provide an alternative to the development of high-speed, low-power dynamic random access memory-like phase change memory technology.

  2. One order of magnitude faster phase change at reduced power in Ti-Sb-Te

    PubMed Central

    Zhu, Min; Xia, Mengjiao; Rao, Feng; Li, Xianbin; Wu, Liangcai; Ji, Xinglong; Lv, Shilong; Song, Zhitang; Feng, Songlin; Sun, Hongbo; Zhang, Shengbai

    2014-01-01

    To date, slow Set operation speed and high Reset operation power remain to be important limitations for substituting dynamic random access memory by phase change memory. Here, we demonstrate phase change memory cell based on Ti0.4Sb2Te3 alloy, showing one order of magnitude faster Set operation speed and as low as one-fifth Reset operation power, compared with Ge2Sb2Te5-based phase change memory cell at the same size. The enhancements may be rooted in the common presence of titanium-centred octahedral motifs in both amorphous and crystalline Ti0.4Sb2Te3 phases. The essentially unchanged local structures around the titanium atoms may be responsible for the significantly improved performance, as these structures could act as nucleation centres to facilitate a swift, low-energy order-disorder transition for the rest of the Sb-centred octahedrons. Our study may provide an alternative to the development of high-speed, low-power dynamic random access memory-like phase change memory technology. PMID:25001009

  3. MICRO- AND NANOSCALE MEASUREMENT METHODS FOR PHASE CHANGE HEAT TRANSFER ON PLANAR AND STRUCTURED SURFACES

    SciTech Connect

    Buongiorno, J; Cahill, DG; Hidrovo, CH; Moghaddam, S; Schmidt, AJ; Shi, L

    2014-07-23

    In this opinion piece, we discuss recent advances in experimental methods for characterizing phase change heat transfer. We begin with a survey of techniques for high-resolution measurements of temperature and heat flux at the solid surface and in the working fluid. Next, we focus on diagnostic tools for boiling heat transfer and describe techniques for visualizing the temperature and velocity fields, as well as measurements at the single bubble level. Finally, we discuss techniques to probe the kinetics of vapor formation within a few molecular layers of the interface. We conclude with our outlook for future progress in experimental methods for phase change heat transfer.

  4. Review of development survey of phase change material models in building applications.

    PubMed

    Akeiber, Hussein J; Wahid, Mazlan A; Hussen, Hasanen M; Mohammad, Abdulrahman Th

    2014-01-01

    The application of phase change materials (PCMs) in green buildings has been increasing rapidly. PCM applications in green buildings include several development models. This paper briefly surveys the recent research and development activities of PCM technology in building applications. Firstly, a basic description of phase change and their principles is provided; the classification and applications of PCMs are also included. Secondly, PCM models in buildings are reviewed and discussed according to the wall, roof, floor, and cooling systems. Finally, conclusions are presented based on the collected data.

  5. Structural and phase changes in carbides of the high-speed steel upon heat treatment

    NASA Astrophysics Data System (ADS)

    Chaus, A. S.

    2016-07-01

    The effect of austenitizing temperature on structural and phase changes in carbides of the tungsten-molybdenum high-speed steel has been studied. The results of metallographic analysis and energy dispersive microanalysis have been discussed. It has been shown that an increase in austenitizing temperature from 1180 to 1260°C causes structural transformations in carbide particles of eutectic origin crushed upon hot plastic deformation, which are related to their dissolution and coalescence, and changes in the phase composition of the carbides themselves.

  6. Review of Development Survey of Phase Change Material Models in Building Applications

    PubMed Central

    Akeiber, Hussein J.; Wahid, Mazlan A.; Hussen, Hasanen M.; Mohammad, Abdulrahman Th.

    2014-01-01

    The application of phase change materials (PCMs) in green buildings has been increasing rapidly. PCM applications in green buildings include several development models. This paper briefly surveys the recent research and development activities of PCM technology in building applications. Firstly, a basic description of phase change and their principles is provided; the classification and applications of PCMs are also included. Secondly, PCM models in buildings are reviewed and discussed according to the wall, roof, floor, and cooling systems. Finally, conclusions are presented based on the collected data. PMID:25313367

  7. Phase volume changes accompanying water extraction from aqueous electrolyte solutions by 1-octanol

    SciTech Connect

    Sun, Y.; Moyer, B.A.

    1995-03-01

    The extraction of water by 1-octanol was calculated as a function of aqueous electrolyte concentration and initial O/A volume ratio for a series of representative salts, including LiCl, NaCl, KCl, NaNO{sub 3}, NaClO{sub 4}, MgCl{sub 2}, and CaCl{sub 2}. These results were then used to calculate the resultant phase-volume changes and aqueous-electrolyte-concentration changes. Such corrections are necessitated for precise extraction measurements employing 1-octanol as a diluent, especially as the O/A phase ratio exceeds unity. 20 refs., 2 figs., 1 tab.

  8. Irreversible reactions studied with nanosecond transmission electron microscopy movies: Laser crystallization of phase change materials

    NASA Astrophysics Data System (ADS)

    Santala, M. K.; Reed, B. W.; Raoux, S.; Topuria, T.; LaGrange, T.; Campbell, G. H.

    2013-04-01

    We use multi-frame, nanosecond-scale photo-emission transmission electron microscopy to create movies of irreversible reactions that occur too rapidly to capture with conventional microscopy. The technique is applied to the crystallization of phase change materials used for optical and resistive memory. For those applications, laser- or current-induced crystallization is orders of magnitude too fast to capture with other imaging techniques. We recorded movies of laser-induced crystallization and measured crystal growth rates at temperatures close to where the maximum growth rate occurs. This paves the way for studying crystallization kinetics of phase change materials over the whole range of technologically relevant temperatures.

  9. Metal organic chemical vapor deposition of phase change Ge1Sb2Te4 nanowires.

    PubMed

    Longo, Massimo; Fallica, Roberto; Wiemer, Claudia; Salicio, Olivier; Fanciulli, Marco; Rotunno, Enzo; Lazzarini, Laura

    2012-03-14

    The self-assembly of Ge(1)Sb(2)Te(4) nanowires (NWs) for phase change memories application was achieved by metal organic chemical vapor deposition, catalyzed by Au nanoislands in a narrow range of temperatures and deposition pressures. In the optimized conditions of 400 °C, 50 mbar, the NWs are Ge(1)Sb(2)Te(4) single hexagonal crystals. Phase change memory switching was reversibly induced by nanosecond current pulses through metal-contacted NWs with threshold voltage of about 1.35 V.

  10. Parametric Analysis of Cyclic Phase Change and Energy Storage in Solar Heat Receivers

    NASA Technical Reports Server (NTRS)

    Hall, Carsie A., III; Glakpe, Emmanuel K.; Cannon, Joseph N.; Kerslake, Thomas W.

    1997-01-01

    A parametric study on cyclic melting and freezing of an encapsulated phase change material (PCM), integrated into a solar heat receiver, has been performed. The cyclic nature of the present melt/freeze problem is relevant to latent heat thermal energy storage (LHTES) systems used to power solar Brayton engines in microgravity environments. Specifically, a physical and numerical model of the solar heat receiver component of NASA Lewis Research Center's Ground Test Demonstration (GTD) project was developed. Multi-conjugate effects such as the convective fluid flow of a low-Prandtl-number fluid, coupled with thermal conduction in the phase change material, containment tube and working fluid conduit were accounted for in the model. A single-band thermal radiation model was also included to quantify reradiative energy exchange inside the receiver and losses through the aperture. The eutectic LiF-CaF2 was used as the phase change material (PCM) and a mixture of He/Xe was used as the working fluid coolant. A modified version of the computer code HOTTube was used to generate results in the two-phase regime. Results indicate that parametric changes in receiver gas inlet temperature and receiver heat input effects higher sensitivity to changes in receiver gas exit temperatures.

  11. Investigation of phase-change coatings for variable thermal control of spacecraft

    NASA Technical Reports Server (NTRS)

    Kelliher, W. C.; Young, P. R.

    1972-01-01

    An investigation was conducted to determine the feasibility of producing a spacecraft coating system that could vary the ratio of its solar absorptance to thermal emittance to adjust automatically for changes in the thermal balance of a spacecraft. This study resulted in a new concept called the phase-change effect which uses the change that occurs in the optical properties of many materials during the phase transition from a crystalline solid to an amorphous material. A series of two-component model coatings was developed which, when placed on a highly reflecting substrate, exhibited a sharp decrease in solar absorptance within a narrow temperature range. A variable thermal control coating can have a significant amount of temperature regulation with the phase-change effect. Data are presented on several crystallite-polymer formulations, their physical and optical properties, and associated phase-change temperatures. Aspects pertaining to their use in a space environment and an example of the degree of thermal regulation attainable with these coatings is also given.

  12. Changes in phase structure and conformational state of wood components during flash autohydrolysis

    SciTech Connect

    Teeyaer, R.E.; Gravitis, Ya.A.; Erin'sh, P.P.; Pugulis, Ya.A.; Kul'kevits, A.Ya.; Gromov, V.S.; Lippmaa, E.T.

    1986-12-01

    The authors studied the structural changes occurring in wood as the result of flash autohydrolysis by a high resolution /sup 13/C NMR method in a solid phase, using a Bruker SXP-200 spectrometer (GFR), while the sample was rotated under a magnetic angle in the direction of magnetic field (54/sup 0/44'). Besides the chemical changes, with this method changes in the conformation and orderlines of macromolecules could be followed, as well as the compatibility (miscibility) of different macromolecules. They studied the changes in birch, white alder, aspen, pine, and spruce woods.

  13. The seasonally changing cloud feedbacks contribution to the ENSO seasonal phase-locking

    NASA Astrophysics Data System (ADS)

    Dommenget, Dietmar; Yu, Yanshan

    2016-12-01

    ENSO variability has a seasonal phase-locking, with SST anomalies on average decreasing during the beginning of the year and SST anomalies increasing during the second half of the year. As a result of this, the ENSO SST variability is smallest in April and the so call `spring barrier' exists in the predictability of ENSO. In this study we analysis how the seasonal phase-locking of surface short wave radiation associated with cloud cover feedbacks contribute to this phenomenon. We base our analysis on observations and simplified climate model simulations. At the beginning of the year, the warmer mean SST in the eastern equatorial Pacific leads to deeper clouds whose anomalous variability are positively correlated with the underlying SST anomalies. These observations highlight a strong negative surface short wave radiation feedback at the beginning of the year in the eastern Pacific (NINO3 region). This supports the observed seasonal phase-locking of ENSO SST variability. This relation also exists in model simulations of the linear recharge oscillator and in the slab ocean model coupled to a fully complex atmospheric GCM. The Slab ocean simulation has seasonal phase-locking similar to observed mostly caused by similar seasonal changing cloud feedbacks as observed. In the linear recharge oscillator simulations seasonal phase-locking is also similar to observed, but is not just related to seasonal changing cloud feedbacks, but is also related to changes in the sensitivity of the zonal wind stress and to a lesser extent to seasonally change sensitivities to the thermocline depth. In summary this study has shown that the seasonal phase-locking, as observed and simulated, is linked to seasonally changing cloud feedbacks.

  14. Monitoring small changes in blood hematocrit using phase sensitive spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Manne, Venu G. R.; Manapuram, Ravi Kiran; Sudheendran, Narendran; Larin, Kirill V.

    2010-02-01

    A new method for monitoring ultra-small changes in blood hematocrit (~0.2%) based on measurement of refractive index changes in vitro using Phase Sensitive Spectral Domain Optical Coherence Tomography modality (PhS-SDOCT) is introduced. The developed system has an axial resolution of ~8 μm, phase sensitivity of +/-0.01 radians, imaging depth of 3.4 +/- 0.01 mm in air, and image acquisition speed of 29 kHz. The experimental accuracy for monitoring refractive index changes as a function of hematocrit level in blood is found to be +/-1.5x10-4 (+/-0.2%). Obtained results indicate that the PhS-SDOCT can be used to monitor ultra-small changes in the hematocrit and in vitro and, potentially, in tissue blood vessels in vivo.

  15. On the penetration of the 660 km phase change by mantle downflows

    NASA Technical Reports Server (NTRS)

    Bercovici, David; Schubert, Gerald; Tackley, Paul J.

    1993-01-01

    We present a simple analytic model of the interaction of cold convective downwelling currents with an endothermic phase change. The model describes the ponding and lateral spreading of downflows along the phase transition interface. A simple comparison of the vertical forces on the ponding material provides a necessary condition for a downflow to penetrate the phase boundary. This condition is fundamentally dependent on the geometry of the downflow. For planar downwellings, the model predicts a minimum ponding time before the structure can penetrate the phase boundary. For columnar (axisymmetric) downflows, there is no minimum time of spreading required before penetration can proceed. The model thus provides an explanation for the observation that in numerical models of three-dimensional convection with an endothermic phase change, cylindrical downflows penetrate the phase interface while planar ones do not. Since descending slabs in the Earth's mantle display a wide spectrum of geometries between planar and cylindrical (given various trench curvatures, as well as intersections of two or more subduction zones), this phenomenon may explain, in part, why some slabs appear to extend into the lower mantle while others are deflected at the 660 km discontinuity.

  16. Discharge, Relaxation, and Charge Model for the Lithium Trivanadate Electrode: Reactions, Phase Change, and Transport

    SciTech Connect

    Brady, Nicholas W.; Zhang, Qing; Knehr, K. W.; Liu, Ping; Marschilok, Amy C.; J. Takeuchi, Kenneth; Takeuchi, Esther S.; West, Alan C.

    2016-10-26

    The electrochemical behavior of lithium trivanadate (LiV3O8) during lithiation, delithiation, and voltage recovery experiments is simulated using a crystal-scale model that accounts for solid-state diffusion, charge-transfer kinetics, and phase transformations. The kinetic expression for phase change was modeled using an approach inspired by the Avrami formulation for nucleation and growth. Numerical results indicate that the solid-state diffusion coefficient of lithium in LiV3O8 is ~ 10-13 cm2 s-1 and the equilibrium compositions in the two phase region (~2.5 V) are Li2.5V3O8:Li4V3O8. Agreement between the simulated and experimental results is excellent. Relative to the lithiation curves, the experimental delithiation curves show significantly less overpotential and at low levels of lithiation (end of charge). Simulations are only able to capture this result by assuming that the solid-state mass-transfer resistance is less during delithiation. The proposed rationale for this difference is that the (100) face is inactive during lithiation, but active during delithiation. Finally, by assuming non-instantaneous phase-change kinetics, estimates are made for the overpotential due to imperfect phase change (supersaturation).

  17. Discharge, Relaxation, and Charge Model for the Lithium Trivanadate Electrode: Reactions, Phase Change, and Transport

    DOE PAGES

    Brady, Nicholas W.; Zhang, Qing; Knehr, K. W.; ...

    2016-10-26

    The electrochemical behavior of lithium trivanadate (LiV3O8) during lithiation, delithiation, and voltage recovery experiments is simulated using a crystal-scale model that accounts for solid-state diffusion, charge-transfer kinetics, and phase transformations. The kinetic expression for phase change was modeled using an approach inspired by the Avrami formulation for nucleation and growth. Numerical results indicate that the solid-state diffusion coefficient of lithium in LiV3O8 is ~ 10-13 cm2 s-1 and the equilibrium compositions in the two phase region (~2.5 V) are Li2.5V3O8:Li4V3O8. Agreement between the simulated and experimental results is excellent. Relative to the lithiation curves, the experimental delithiation curves show significantlymore » less overpotential and at low levels of lithiation (end of charge). Simulations are only able to capture this result by assuming that the solid-state mass-transfer resistance is less during delithiation. The proposed rationale for this difference is that the (100) face is inactive during lithiation, but active during delithiation. Finally, by assuming non-instantaneous phase-change kinetics, estimates are made for the overpotential due to imperfect phase change (supersaturation).« less

  18. A Newton method with adaptive finite elements for solving phase-change problems with natural convection

    NASA Astrophysics Data System (ADS)

    Danaila, Ionut; Moglan, Raluca; Hecht, Frédéric; Le Masson, Stéphane

    2014-10-01

    We present a new numerical system using finite elements with mesh adaptivity for the simulation of solid-liquid phase change systems. In the liquid phase, the natural convection flow is simulated by solving the incompressible Navier-Stokes equations with Boussinesq approximation. A variable viscosity model allows the velocity to progressively vanish in the solid phase, through an intermediate mushy region. The phase change is modeled by introducing an implicit enthalpy source term in the heat equation. The final system of equations describing the liquid-solid system by a single domain approach is solved using a Newton iterative algorithm. The space discretization is based on a P2-P1 Taylor-Hood finite elements and mesh adaptivity by metric control is used to accurately track the solid-liquid interface or the density inversion interface for water flows. The numerical method is validated against classical benchmarks that progressively add strong non-linearities in the system of equations: natural convection of air, natural convection of water, melting of a phase-change material and water freezing. Very good agreement with experimental data is obtained for each test case, proving the capability of the method to deal with both melting and solidification problems with convection. The presented numerical method is easy to implement using FreeFem++ software using a syntax close to the mathematical formulation.

  19. Strongly Nonlinear Optical Glass Fibers from Noncentrosymmetric Phase-Change Chalcogenide Materials

    SciTech Connect

    Chung, In; Jang, Joon I.; Malliakas, Christos D.; Ketterson, John B.; Kanatzidis, Mercouri G.

    2010-08-27

    We report that the one-dimensional polar selenophosphate compounds APSe{sub 6} (A = K, Rb), which show crystal-glass phase-change behavior, exhibit strong second harmonic generation (SHG) response in both crystal and glassy forms. The crystalline materials are type-I phase-matchable with SHG coefficients {chi}{sup (2)} of 151.3 and 149.4 pm V{sup -1} for K{sup +} and Rb{sup +} salts, respectively, which is the highest among phase-matchable nonlinear optical (NLO) materials with band gaps over 1.0 eV. The glass of APSe{sub 6} exhibits comparable SHG intensities to the top infrared NLO material AgGaSe{sub 2} without any poling treatments. APSe{sub 6} exhibit excellent mid-IR transparency. We demonstrate that starting from noncentrosymmetric phase-change materials such as APSe{sub 6} (A = K, Rb), we can obtain optical glass fibers with strong, intrinsic, and temporally stable second-order nonlinear optical (NLO) response. The as-prepared glass fibers exhibit SHG and difference frequency generation (DFG) responses over a wide range of wavelengths. Raman spectroscopy and pair distribution function (PDF) analyses provide further understanding of the local structure in amorphous state of KPSe{sub 6} bulk glass and glass fiber. We propose that this approach can be widely applied to prepare permanent NLO glass from materials that undergo a phase-change process.

  20. Crystal-amorphous transformation via defect-templating in phase-change materials

    NASA Astrophysics Data System (ADS)

    Nukala, Pavan

    Phase-change materials (PCM) such as GeTe and Ge-Sb-Te alloys are potential candidates for non-volatile memory applications, because they can reversibly and rapidly transform between a crystalline phase and an amorphous phase with medium-range order. Traditionally, crystal-amorphous transformation in these materials has been carried out via melt-quench pathway, where the crystalline phase is heated beyond its melting point by the rising edge of an electric pulse, and the melt phase is quenched by the falling edge into a glassy phase. Formation of an intermediate melt phase in this transformation pathway requires usage of large switching current densities, resulting in energy wastage, and device degradation issues. Furthermore, melt-quench pathway is a brute force strategy of amorphizing PCM, and does not utilize the peculiar structural properties in crystalline phase. It will be beneficial from a device perspective that crystal-amorphous transformation is carried out via subtler solid-state pathways. Single-crystalline nanowire phase-change memory, owing to its lateral geometry and large volumes of active material, offers a platform to construct a crystal-amorphous transformation pathway via gradually increasing disorder in the crystalline phase, and study it. Using in situ transmission electron microscopy on GeTe and Ge2Sb2Te5 systems, we showed that the application of an electric pulse (heat-shock) creates dislocations in the PCM that migrate with the hole-wind force, and interact with the already existing ferroelectric boundaries in case of GeTe, changing their nature. We adapted novel tools such as optical second harmonic generation polarimety to carefully study these defect interactions. These defects accumulate at a region of local inhomogeneity, and upon addition of defects beyond a critical limit to that region via electrical pulsing, an amorphous phase "nucleates". We also studied the effect of defect dynamics on carrier transport using temperature

  1. Qualitative observation of reversible phase change in astrochemical ethanethiol ices using infrared spectroscopy.

    PubMed

    Pavithraa, S; Methikkalam, R R J; Gorai, P; Lo, J-I; Das, A; Raja Sekhar, B N; Pradeep, T; Cheng, B-M; Mason, N J; Sivaraman, B

    2017-05-05

    Here we report the first evidence for a reversible phase change in an ethanethiol ice prepared under astrochemical conditions. InfraRed (IR) spectroscopy was used to monitor the morphology of the ice using the SH stretching vibration, a characteristic vibration of thiol molecules. The deposited sample was able to switch between amorphous and crystalline phases repeatedly under temperature cycles between 10K and 130K with subsequent loss of molecules in every phase change. Such an effect is dependent upon the original thickness of the ice. Further work on quantitative analysis is to be carried out in due course whereas here we are reporting the first results obtained. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. Thermally induced phase changes, lateral heterogeneity of the mantle, continental roots, and deep slab anomalies

    NASA Technical Reports Server (NTRS)

    Anderson, Don L.

    1987-01-01

    Factors which influence the lateral heterogeneity in density and seismic velocity with depth in the upper earth mantle are discussed. It is emphasized that most of the increases in density and seismic velocity with depth are caused by pressure-induced solid-solid phase changes in the high-density high-velocity phases of mineral assemblage, due to variations in temperature. In particular, the ilmenite form of MgSiO3 and the gamma-spinel form of Mg2SiO4 have broad stability fields in cold mantle and are not stable in hotter mantle. It is emphasized that the density and velocity anomalies associated with temperature-induced phase changes in mineral assemblage must be taken into account in the thermal models of the slabs; when these effects are accounted for, the geoid and seismic anomalies associated with subducted slabs are consistent with slab confinement to the upper mantle and with layered models of mantle convection.

  3. The tropicalization of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts

    PubMed Central

    Vergés, Adriana; Steinberg, Peter D.; Hay, Mark E.; Poore, Alistair G. B.; Campbell, Alexandra H.; Ballesteros, Enric; Heck, Kenneth L.; Booth, David J.; Coleman, Melinda A.; Feary, David A.; Figueira, Will; Langlois, Tim; Marzinelli, Ezequiel M.; Mizerek, Toni; Mumby, Peter J.; Nakamura, Yohei; Roughan, Moninya; van Sebille, Erik; Gupta, Alex Sen; Smale, Dan A.; Tomas, Fiona; Wernberg, Thomas; Wilson, Shaun K.

    2014-01-01

    Climate-driven changes in biotic interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to ‘barrens’ when temperate urchin grazing increases. Here, we propose a novel phase-shift away from macroalgal dominance caused by tropical herbivores extending their range into temperate regions. We argue that this phase shift is facilitated by poleward-flowing boundary currents that are creating ocean warming hotspots around the globe, enabling the range expansion of tropical species and increasing their grazing rates in temperate areas. Overgrazing of temperate macroalgae by tropical herbivorous fishes has already occurred in Japan and the Mediterranean. Emerging evidence suggests similar phenomena are occurring in other temperate regions, with increasing occurrence of tropical fishes on temperate reefs. PMID:25009065

  4. Computation of solid/liquid phase change including free convection - Comparison with data

    NASA Technical Reports Server (NTRS)

    Schneider, G. E.

    1990-01-01

    A computational model is presented for solid/liquid phase-change energy transport including free convection fluid flow in the liquid phase. The computational model considers the velocity components of all nonliquid control volumes to be zero but fully solves the coupled mass-momentum problem within the liquid. The thermal energy model includes the entire domain and employs an enthalpy-like model and a recently developed method for handling the phase-change interface nonlinearity. Convergence studies are performed and comparisons made with experimental data for two different problems. Grid independence is achieved, and the comparison with experimental data indicates excellent quantitative prediction of the melt fraction evolution. Qualitative data are also provided as velocity vector and isotherm plots. The computational costs incurred are quite low by comparison with other models.

  5. Nanostructured thin film-based near-infrared tunable perfect absorber using phase-change material

    NASA Astrophysics Data System (ADS)

    Kocer, Hasan

    2015-01-01

    Nanostructured thin film absorbers embedded with phase-change thermochromic material can provide a large level of absorption tunability in the near-infrared region. Vanadium dioxide was employed as the phase-change material in the designed structures. The optical absorption properties of the designed structures with respect to the geometric and material parameters were systematically investigated using finite-difference time-domain computations. Absorption level of the resonance wavelength in the near-IR region was tuned from the perfect absorption level to a low level (17%) with a high positive dynamic range of near-infrared absorption intensity tunability (83%). Due to the phase transition of vanadium dioxide, the resonance at the near-infrared region is being turned on and turned off actively and reversibly under the thermal bias, thereby rendering these nanostructures suitable for infrared camouflage, emitters, and sensors.

  6. Computation of solid/liquid phase change including free convection - Comparison with data

    NASA Technical Reports Server (NTRS)

    Schneider, G. E.

    1990-01-01

    A computational model is presented for solid/liquid phase-change energy transport including free convection fluid flow in the liquid phase. The computational model considers the velocity components of all nonliquid control volumes to be zero but fully solves the coupled mass-momentum problem within the liquid. The thermal energy model includes the entire domain and employs an enthalpy-like model and a recently developed method for handling the phase-change interface nonlinearity. Convergence studies are performed and comparisons made with experimental data for two different problems. Grid independence is achieved, and the comparison with experimental data indicates excellent quantitative prediction of the melt fraction evolution. Qualitative data are also provided as velocity vector and isotherm plots. The computational costs incurred are quite low by comparison with other models.

  7. The tropicalization of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts.

    PubMed

    Vergés, Adriana; Steinberg, Peter D; Hay, Mark E; Poore, Alistair G B; Campbell, Alexandra H; Ballesteros, Enric; Heck, Kenneth L; Booth, David J; Coleman, Melinda A; Feary, David A; Figueira, Will; Langlois, Tim; Marzinelli, Ezequiel M; Mizerek, Toni; Mumby, Peter J; Nakamura, Yohei; Roughan, Moninya; van Sebille, Erik; Gupta, Alex Sen; Smale, Dan A; Tomas, Fiona; Wernberg, Thomas; Wilson, Shaun K

    2014-08-22

    Climate-driven changes in biotic interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to 'barrens' when temperate urchin grazing increases. Here, we propose a novel phase-shift away from macroalgal dominance caused by tropical herbivores extending their range into temperate regions. We argue that this phase shift is facilitated by poleward-flowing boundary currents that are creating ocean warming hotspots around the globe, enabling the range expansion of tropical species and increasing their grazing rates in temperate areas. Overgrazing of temperate macroalgae by tropical herbivorous fishes has already occurred in Japan and the Mediterranean. Emerging evidence suggests similar phenomena are occurring in other temperate regions, with increasing occurrence of tropical fishes on temperate reefs.

  8. Metasurfaces Based on Phase-Change Material as a Reconfigurable Platform for Multifunctional Devices

    PubMed Central

    Raeis-Hosseini, Niloufar; Rho, Junsuk

    2017-01-01

    Integration of phase-change materials (PCMs) into electrical/optical circuits has initiated extensive innovation for applications of metamaterials (MMs) including rewritable optical data storage, metasurfaces, and optoelectronic devices. PCMs have been studied deeply due to their reversible phase transition, high endurance, switching speed, and data retention. Germanium-antimony-tellurium (GST) is a PCM that has amorphous and crystalline phases with distinct properties, is bistable and nonvolatile, and undergoes a reliable and reproducible phase transition in response to an optical or electrical stimulus; GST may therefore have applications in tunable photonic devices and optoelectronic circuits. In this progress article, we outline recent studies of GST and discuss its advantages and possible applications in reconfigurable metadevices. We also discuss outlooks for integration of GST in active nanophotonic metadevices. PMID:28878196

  9. Metasurfaces Based on Phase-Change Material as a Reconfigurable Platform for Multifunctional Devices.

    PubMed

    Raeis-Hosseini, Niloufar; Rho, Junsuk

    2017-09-06

    Integration of phase-change materials (PCMs) into electrical/optical circuits has initiated extensive innovation for applications of metamaterials (MMs) including rewritable optical data storage, metasurfaces, and optoelectronic devices. PCMs have been studied deeply due to their reversible phase transition, high endurance, switching speed, and data retention. Germanium-antimony-tellurium (GST) is a PCM that has amorphous and crystalline phases with distinct properties, is bistable and nonvolatile, and undergoes a reliable and reproducible phase transition in response to an optical or electrical stimulus; GST may therefore have applications in tunable photonic devices and optoelectronic circuits. In this progress article, we outline recent studies of GST and discuss its advantages and possible applications in reconfigurable metadevices. We also discuss outlooks for integration of GST in active nanophotonic metadevices.

  10. Te-centric view of the phase change mechanism in Ge-Sb-Te alloys.

    PubMed

    Sen, S; Edwards, T G; Cho, J-Y; Joo, Y-C

    2012-05-11

    The short-range structure of amorphous and fcc Ge1Sb2Te4 and Ge2Sb2Te5 phase-change alloys is investigated using 125Te NMR spectroscopy. Both amorphous and fcc structures consist solely of heteropolar Ge/Sb-Te bonds that may enable rapid displacive phase transformation without the need for extensive atomic rearrangement. The vacancy distribution is random in microcrystalline fcc phases while significant clustering is observed in their nanocrystalline counterparts that may result in the formation of tetrahedrally coordinated Ge atoms in the latter. This structural commonality may further facilitate the kinetics of transformation between amorphous and nanocrystalline fcc phases, a situation relevant for high-density memory storage.

  11. Picosecond electric-field-induced threshold switching in phase-change materials [THz-induced threshold switching and crystallization of phase-change materials

    SciTech Connect

    Zalden, Peter; Shu, Michael J.; Chen, Frank; Wu, Xiaoxi; Zhu, Yi; Wen, Haidan; Johnston, Scott; Shen, Zhi -Xun; Landreman, Patrick; Brongersma, Mark; Fong, Scott W.; Wong, H. -S. Philip; Sher, Meng -Ju; Jost, Peter; Kaes, Matthias; Salinga, Martin; von Hoegen, Alexander; Wuttig, Matthias; Lindenberg, Aaron M.

    2016-08-05

    Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag4In3Sb67Te26. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales—faster than crystals can nucleate. As a result, this supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

  12. Picosecond electric-field-induced threshold switching in phase-change materials [THz-induced threshold switching and crystallization of phase-change materials

    DOE PAGES

    Zalden, Peter; Shu, Michael J.; Chen, Frank; ...

    2016-08-05

    Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag4In3Sb67Te26. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales—faster than crystals can nucleate. As a result, this supports purely electronic models of threshold switching and reveals potentialmore » applications as an ultrafast electronic switch.« less

  13. Picosecond electric-field-induced threshold switching in phase-change materials [THz-induced threshold switching and crystallization of phase-change materials

    SciTech Connect

    Zalden, Peter; Shu, Michael J.; Chen, Frank; Wu, Xiaoxi; Zhu, Yi; Wen, Haidan; Johnston, Scott; Shen, Zhi -Xun; Landreman, Patrick; Brongersma, Mark; Fong, Scott W.; Wong, H. -S. Philip; Sher, Meng -Ju; Jost, Peter; Kaes, Matthias; Salinga, Martin; von Hoegen, Alexander; Wuttig, Matthias; Lindenberg, Aaron M.

    2016-08-05

    Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag4In3Sb67Te26. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales—faster than crystals can nucleate. As a result, this supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

  14. Molecular simulation of excess isotherm and excess enthalpy change in gas-phase adsorption.

    PubMed

    Do, D D; Do, H D; Nicholson, D

    2009-01-29

    We present a new approach to calculating excess isotherm and differential enthalpy of adsorption on surfaces or in confined spaces by the Monte Carlo molecular simulation method. The approach is very general and, most importantly, is unambiguous in its application to any configuration of solid structure (crystalline, graphite layer or disordered porous glass), to any type of fluid (simple or complex molecule), and to any operating conditions (subcritical or supercritical). The behavior of the adsorbed phase is studied using the partial molar energy of the simulation box. However, to characterize adsorption for comparison with experimental data, the isotherm is best described by the excess amount, and the enthalpy of adsorption is defined as the change in the total enthalpy of the simulation box with the change in the excess amount, keeping the total number (gas + adsorbed phases) constant. The excess quantities (capacity and energy) require a choice of a reference gaseous phase, which is defined as the adsorptive gas phase occupying the accessible volume and having a density equal to the bulk gas density. The accessible volume is defined as the mean volume space accessible to the center of mass of the adsorbate under consideration. With this choice, the excess isotherm passes through a maximum but always remains positive. This is in stark contrast to the literature where helium void volume is used (which is always greater than the accessible volume) and the resulting excess can be negative. Our definition of enthalpy change is equivalent to the difference between the partial molar enthalpy of the gas phase and the partial molar enthalpy of the adsorbed phase. There is no need to assume ideal gas or negligible molar volume of the adsorbed phase as is traditionally done in the literature. We illustrate this new approach with adsorption of argon, nitrogen, and carbon dioxide under subcritical and supercritical conditions.

  15. Non-Toxic, Non-Flammable, -80 C Phase Change Materials

    NASA Technical Reports Server (NTRS)

    Cutbirth, J. Michael

    2013-01-01

    The objective of this effort was to develop a non-toxic, non-flammable, -80 C phase change material (PCM) to be used in NASA's ICEPAC capsules for biological sample preservation in flight to and from Earth orbit. A temperature of about -68 C or lower is a critical temperature for maintaining stable cell, tissue, and cell fragment storage.

  16. Replacement of Ablators with Phase-Change Material for Thermal Protection of STS Elements

    NASA Technical Reports Server (NTRS)

    Kaul, Raj K.; Stuckey, Irvin; Munafo, Paul M. (Technical Monitor)

    2002-01-01

    As part of the research and development program to develop new Thermal Protection System (TPS) materials for aerospace applications at NASA's Marshall Space Flight Center (MSFC), an experimental study was conducted on a new concept for a non-ablative TPS material. Potential loss of TPS material and ablation by-products from the External Tank (ET) or Solid Rocket Booster (SRB) during Shuttle flight with the related Orbiter tile damage necessitates development of a non-ablative thermal protection system. The new Thermal Management Coating (TMC) consists of phase-change material encapsulated in micro spheres and a two-part resin system to adhere the coating to the structure material. The TMC uses a phase-change material to dissipate the heat produced during supersonic flight rather than an ablative material. This new material absorbs energy as it goes through a phase change during the heating portion of the flight profile and then the energy is slowly released as the phase-change material cools and returns to its solid state inside the micro spheres. The coating was subjected to different test conditions simulating design flight environments at the NASA/MSFC Improved Hot Gas Facility (IHGF) to study its performance.

  17. Preparation of CMC-modified melamine resin spherical nano-phase change energy storage materials.

    PubMed

    Hu, Xiaofeng; Huang, Zhanhua; Zhang, Yanhua

    2014-01-30

    A novel carboxymethyl cellulose (CMC)-modified melamine-formaldehyde (MF) phase change capsule with excellent encapsulation was prepared by in situ polymerization. Effects of CMC on the properties of the capsules were studied by Fourier transformation infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), X-ray diffractometry (XRD), and thermogravimetric analysis (TGA). The results showed that the CMC-modified capsules had an average diameter of about 50nm and good uniformity. The phase change enthalpy of the capsules was increased and the cracking ratio decreased by incorporating a suitable amount of CMC. The optimum phase change enthalpy of the nanocapsules was 83.46J/g, and their paraffin content was 63.1%. The heat resistance of the capsule shells decreased after CMC modification. In addition, the nanocapsule cracking ratio of the nanocapsules was 11.0%, which is highly attractive for their application as nano phase change materials. Copyright © 2013 Elsevier Ltd. All rights reserved.

  18. Experimental data showing the thermal behavior of a flat roof with phase change material.

    PubMed

    Tokuç, Ayça; Başaran, Tahsin; Yesügey, S Cengiz

    2015-12-01

    The selection and configuration of building materials for optimal energy efficiency in a building require some assumptions and models for the thermal behavior of the utilized materials. Although the models for many materials can be considered acceptable for simulation and calculation purposes, the work for modeling the real time behavior of phase change materials is still under development. The data given in this article shows the thermal behavior of a flat roof element with a phase change material (PCM) layer. The temperature and energy given to and taken from the building element are reported. In addition the solid-liquid behavior of the PCM is tracked through images. The resulting thermal behavior of the phase change material is discussed and simulated in [1] A. Tokuç, T. Başaran, S.C. Yesügey, An experimental and numerical investigation on the use of phase change materials in building elements: the case of a flat roof in Istanbul, Build. Energy, vol. 102, 2015, pp. 91-104.

  19. Functional differentiation of the sugar beet root system as indicator of developmental phase change

    USDA-ARS?s Scientific Manuscript database

    Developmental phase transition in the plant root system has not been well characterized. In this study we compared the dynamics of sucrose accumulation with gene expression changes analyzed with cDNA-AFLP in the tap root system of sugar beet (Beta vulgaris L.) during the first nine weeks after emerg...

  20. Analysis of thermal energy storage material with change-of-phase volumetric effects

    NASA Technical Reports Server (NTRS)

    Kerslake, Thomas W.; Ibrahim, Mounir B.

    1990-01-01

    NASA's Space Station Freedom proposed hybrid power system includes photovoltaic arrays with nickel hydrogen batteries for energy storage and solar dynamic collectors driving Brayton heat engines with change-of-phase Thermal Energy Storage (TES) devices. A TES device is comprised of multiple metallic, annular canisters which contain a eutectic composition LiF-CaF2 Phase Change Material (PCM) that melts at 1040 K. A moderately sophisticated LiF-CaF2 PCM computer model is being developed in three stages considering 1-D, 2-D, and 3-D canister geometries, respectively. The 1-D model results indicate that the void has a marked effect on the phase change process due to PCM displacement and dynamic void heat transfer resistance. Equally influential are the effects of different boundary conditions and liquid PCM natural convection. For the second stage, successful numerical techniques used in the 1-D phase change model are extended to a 2-D (r,z) PCM containment canister model. A prototypical PCM containment canister is analyzed and the results are discussed.