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Sample records for phase change memory

  1. Interfacial phase-change memory.

    PubMed

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

    2011-08-01

    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. PMID:21725305

  2. 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.

  3. Bipolar switching in chalcogenide phase change memory.

    PubMed

    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

  4. 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

  5. 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

  6. Projected phase-change memory devices.

    PubMed

    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

  7. 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

  8. Endurance characteristics of phase change memory cells

    NASA Astrophysics Data System (ADS)

    Ruru, Huo; Daolin, Cai; Chen, Bomy; Yifeng, Chen; Yuchan, Wang; Yueqing, Wang; Hongyang, Wei; Qing, Wang; Yangyang, Xia; Dan, Gao; Zhitang, Song

    2016-05-01

    The endurance characteristics of phase change memory are studied. With operational cycles, the resistances of reset and set states gradually change to the opposite direction. What is more, the operational conditions that are needed are also discussed. The failure and the changes are concerned with the compositional change of the phase change material. An abnormal phenomenon that the threshold voltage decreases slightly at first and then increases is observed, which is due to the coaction of interface contact and growing active volume size changing. Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA09020402), the National Key Basic Research Program of China (Nos. 2013CBA01900, 2010CB934300, 2011CBA00607, 2011CB932804), the National Integrate Circuit Research Program of China (No. 2009ZX02023-003), the National Natural Science Foundation of China (No. 61176122, 61106001, 61261160500, 61376006), and the Science and Technology Council of Shanghai (Nos. 12nm0503701, 13DZ2295700, 12QA1403900, 13ZR1447200, 14ZR1447500).

  9. Relaxation oscillations in chalcogenide phase change memory

    NASA Astrophysics Data System (ADS)

    Nardone, M.; Karpov, V. G.; Karpov, I. V.

    2010-03-01

    The results of a comprehensive experimental study of relaxation oscillations in chalcogenide phase change memory are presented. Extending the previous work, voltage and current oscillations were measured over much longer periods of time and with a broad range of applied voltages, load resistances, and device thicknesses. The effects of various reset voltage levels and material types were also considered. Several types of oscillation patterns were observed; most were continuous through the measurement period while others exhibited few or no oscillations. Also observed were two distinct regimes of oscillations; one of stable amplitudes followed by one of decaying amplitudes. The duration of the stable regime and the total time for oscillation decay were found to be directly proportional to the device thickness. In addition, temporal drift of the threshold voltage was observed which provided a method for measuring the variation in the drift coefficient between different materials. A numerical model was developed to simulate oscillations and extrapolate our results to lower circuit time constants. The physical mechanism of oscillations and their stochastic nature are effectively described in the framework of field-induced nucleation, while the transition from stable to decaying amplitudes is attributed to concomitant thermally induced nucleation.

  10. 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.

  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. 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.

  13. Phase-change Random Access Memory: A Scalable Technology

    SciTech Connect

    Raoux, S.; Burr, G; Breitwisch, M; Rettner, C; Chen, Y; Shelby, R; Salinga, M; Krebs, D; Chen, S; Lung, H

    2008-01-01

    Nonvolatile RAM using resistance contrast in phase-change materials [or phase-change RAM (PCRAM)] is a promising technology for future storage-class memory. However, such a technology can succeed only if it can scale smaller in size, given the increasingly tiny memory cells that are projected for future technology nodes (i.e., generations). We first discuss the critical aspects that may affect the scaling of PCRAM, including materials properties, power consumption during programming and read operations, thermal cross-talk between memory cells, and failure mechanisms. We then discuss experiments that directly address the scaling properties of the phase-change materials themselves, including studies of phase transitions in both nanoparticles and ultrathin films as a function of particle size and film thickness. This work in materials directly motivated the successful creation of a series of prototype PCRAM devices, which have been fabricated and tested at phase-change material cross-sections with extremely small dimensions as low as 3 nm x 20 nm. These device measurements provide a clear demonstration of the excellent scaling potential offered by this technology, and they are also consistent with the scaling behavior predicted by extensive device simulations. Finally, we discuss issues of device integration and cell design, manufacturability, and reliability.

  14. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Rewriting magnetic phase change memory by laser heating

    NASA Astrophysics Data System (ADS)

    Timmerwilke, John; Liou, Sy-Hwang; Cheng, Shu Fan; Edelstein, Alan S.

    2016-04-01

    Magnetic phase change memory (MAG PCM) consists of bits with different magnetic permeability values. The bits are read by measuring their effect on a magnetic probe field. Previously low permeability crystalline bits had been written in high permeability amorphous films of Metglas via laser heating. Here data is presented showing that by applying short laser pulses with the appropriate power to previously crystallized regions they can first be vitrified and then again crystallized. Thus, MAG PCM is rewriteable. Technical issues in processing the bits are discussed and results on thermal modeling are presented.

  17. 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.

  18. 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.

  19. 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. PMID:25133955

  20. Electrical conduction in chalcogenide glasses of phase change memory

    NASA Astrophysics Data System (ADS)

    Nardone, M.; Simon, M.; Karpov, I. V.; Karpov, V. G.

    2012-10-01

    Amorphous chalcogenides have been extensively studied over the last half century due to their application in rewritable optical data storage and in non-volatile phase change memory devices. Yet, the nature of the observed non-ohmic conduction in these glasses is still under debate. In this review, we consolidate and expand the current state of knowledge related to dc conduction in these materials. An overview of the pertinent experimental data is followed by a review of the physics of localized states that are peculiar to chalcogenide glasses. We then describe and evaluate twelve relevant transport mechanisms with conductivities that depend exponentially on the electric field. The discussed mechanisms include various forms of Poole-Frenkel ionization, Schottky emission, hopping conduction, field-induced delocalization of tail states, space-charge-limited current, field emission, percolation band conduction, and transport through crystalline inclusions. Most of the candidates provide more or less satisfactory fits of the observed non-linear IV data. Our analysis calls upon additional studies that would enable one to discriminate between the various alternative models.

  1. Flexible one diode-one phase change memory array enabled by block copolymer self-assembly.

    PubMed

    Mun, Beom Ho; You, Byoung Kuk; Yang, Se Ryeun; Yoo, Hyeon Gyun; Kim, Jong Min; Park, Woon Ik; Yin, You; Byun, Myunghwan; Jung, Yeon Sik; Lee, Keon Jae

    2015-04-28

    Flexible memory is the fundamental component for data processing, storage, and radio frequency communication in flexible electronic systems. Among several emerging memory technologies, phase-change random-access memory (PRAM) is one of the strongest candidate for next-generation nonvolatile memories due to its remarkable merits of large cycling endurance, high speed, and excellent scalability. Although there are a few approaches for flexible phase-change memory (PCM), high reset current is the biggest obstacle for the practical operation of flexible PCM devices. In this paper, we report a flexible PCM realized by incorporating nanoinsulators derived from a Si-containing block copolymer (BCP) to significantly lower the operating current of the flexible memory formed on plastic substrate. The reduction of thermal stress by BCP nanostructures enables the reliable operation of flexible PCM devices integrated with ultrathin flexible diodes during more than 100 switching cycles and 1000 bending cycles. PMID:25826001

  2. Thermal effect of Ge2Sb2Te5 in phase change memory device

    NASA Astrophysics Data System (ADS)

    Li, Jun-Tao; Liu, Bo; Song, Zhi-Tang; Ren, Kun; Zhu, Min; Xu, Jia; Ren, Jia-Dong; Feng, Gao-Ming; Ren, Wan-Chun; Tong, Hao

    2014-08-01

    In the fabrication of phase change random access memory (PRAM) devices, high temperature thermal processes are inevitable. We investigate the thermal stability of Ge2Sb2Te5 (GST) which is a prototypical phase change material. After high temperature process, voids of phase change material exist at the interface between Ge2Sb2Te5 and substrate in the initial open memory cell. This lower region of Ge2Sb2Te5 is found to be a Te-rich phase change layer. Phase change memory devices are fabricated in different process conditions and examined by scanning electron microscopy and energy dispersive X-ray. It is found that hot-chuck process, nitrogen-doping process, and lower temperature inter-metal dielectric (IMD) deposition process can ease the thermal impact of line-GST PRAM cell.

  3. Ultrafast response of phase-change memory materials

    NASA Astrophysics Data System (ADS)

    Lindenberg, Aaron

    2015-03-01

    We describe recent experiments probing the first steps in the amorphous-to-crystalline transition that underlies the behavior of phase-change materials, examining both electric-field-driven and optically-driven responses in GeSbTe and AgInSbTe alloys. First measurements using femtosecond x-ray pulses at the Linac Coherent Light Source will be described which enable direct snapshots of these transitions and associated intermediate states. We will also describe studies using single-cycle terahertz pulses as an all-optical means of biasing phase-change materials on femtosecond time-scales in order to examine the threshold-switching response on microscopically relevant time-scales. These studies indicate nonlinear scaling with the applied electric field and field-induced crystallization as evidenced by ultrafast optical reflectivity and conductivity measurements, from which a mechanistic understanding of these phase transitions can be obtained.

  4. Thermally efficient and highly scalable In2Se3 nanowire phase change memory

    NASA Astrophysics Data System (ADS)

    Jin, Bo; Kang, Daegun; Kim, Jungsik; Meyyappan, M.; Lee, Jeong-Soo

    2013-04-01

    The electrical characteristics of nonvolatile In2Se3 nanowire phase change memory are reported. Size-dependent memory switching behavior was observed in nanowires of varying diameters and the reduction in set/reset threshold voltage was as low as 3.45 V/6.25 V for a 60 nm nanowire, which is promising for highly scalable nanowire memory applications. Also, size-dependent thermal resistance of In2Se3 nanowire memory cells was estimated with values as high as 5.86×1013 and 1.04×106 K/W for a 60 nm nanowire memory cell in amorphous and crystalline phases, respectively. Such high thermal resistances are beneficial for improvement of thermal efficiency and thus reduction in programming power consumption based on Fourier's law. The evaluation of thermal resistance provides an avenue to develop thermally efficient memory cell architecture.

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

    PubMed Central

    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. PMID:22496956

  6. Oxygen incorporation into GST phase-change memory matrix

    NASA Astrophysics Data System (ADS)

    Golovchak, R.; Choi, Y. G.; Kozyukhin, S.; Chigirinsky, Yu.; Kovalskiy, A.; Xiong-Skiba, P.; Trimble, J.; Pafchek, R.; Jain, H.

    2015-03-01

    Structural changes in amorphous and crystallized GST-225 films induced by the reaction with oxygen are studied at different depth scales. The mechanism of interaction of the very top surface layers with oxygen is studied with low-energy ion scattering (LEIS) technique, while the modifications of chemistry in the underlying surface layers are investigated with high-resolution X-ray photoelectron spectroscopy (XPS). The changes averaged through the overall film thickness are characterized by micro-Raman spectroscopy. The oxygen exposure leads to a depletion of GST-225 film surfaces in Te and formation of the antimony and germanium oxides. The antimony oxide complexes are found throughout the whole thickness of the films after their prolonged storage in air, whereas no evidence for formation of pure GeO2 phase is found in the volume of the films through Raman spectroscopy. A tendency to form Ge-rich phase within the ∼10 nm surface layer is additionally observed by LEIS profiling during crystallization of GST-225 film at 300 °C in oxygen atmosphere.

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

    PubMed Central

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

    2015-01-01

    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. PMID:26068587

  8. Photo-induced optical activity in phase-change memory materials

    PubMed Central

    Borisenko, Konstantin B.; Shanmugam, Janaki; Williams, Benjamin A. O.; Ewart, Paul; Gholipour, Behrad; Hewak, Daniel W.; Hussain, Rohanah; Jávorfi, Tamás; Siligardi, Giuliano; Kirkland, Angus I.

    2015-01-01

    We demonstrate that optical activity in amorphous isotropic thin films of pure Ge2Sb2Te5 and N-doped Ge2Sb2Te5N phase-change memory materials can be induced using rapid photo crystallisation with circularly polarised laser light. The new anisotropic phase transition has been confirmed by circular dichroism measurements. This opens up the possibility of controlled induction of optical activity at the nanosecond time scale for exploitation in a new generation of high-density optical memory, fast chiroptical switches and chiral metamaterials. PMID:25740351

  9. Photo-induced optical activity in phase-change memory materials.

    PubMed

    Borisenko, Konstantin B; Shanmugam, Janaki; Williams, Benjamin A O; Ewart, Paul; Gholipour, Behrad; Hewak, Daniel W; Hussain, Rohanah; Jávorfi, Tamás; Siligardi, Giuliano; Kirkland, Angus I

    2015-01-01

    We demonstrate that optical activity in amorphous isotropic thin films of pure Ge2Sb2Te5 and N-doped Ge2Sb2Te5N phase-change memory materials can be induced using rapid photo crystallisation with circularly polarised laser light. The new anisotropic phase transition has been confirmed by circular dichroism measurements. This opens up the possibility of controlled induction of optical activity at the nanosecond time scale for exploitation in a new generation of high-density optical memory, fast chiroptical switches and chiral metamaterials. PMID:25740351

  10. Photo-induced optical activity in phase-change memory materials

    NASA Astrophysics Data System (ADS)

    Borisenko, Konstantin B.; Shanmugam, Janaki; Williams, Benjamin A. O.; Ewart, Paul; Gholipour, Behrad; Hewak, Daniel W.; Hussain, Rohanah; Jávorfi, Tamás; Siligardi, Giuliano; Kirkland, Angus I.

    2015-03-01

    We demonstrate that optical activity in amorphous isotropic thin films of pure Ge2Sb2Te5 and N-doped Ge2Sb2Te5N phase-change memory materials can be induced using rapid photo crystallisation with circularly polarised laser light. The new anisotropic phase transition has been confirmed by circular dichroism measurements. This opens up the possibility of controlled induction of optical activity at the nanosecond time scale for exploitation in a new generation of high-density optical memory, fast chiroptical switches and chiral metamaterials.

  11. Highly scalable non-volatile and ultra-low-power phase-change nanowire memory.

    PubMed

    Lee, Se-Ho; Jung, Yeonwoong; Agarwal, Ritesh

    2007-10-01

    The search for a universal memory storage device that combines rapid read and write speeds, high storage density and non-volatility is driving the exploration of new materials in nanostructured form. Phase-change materials, which can be reversibly switched between amorphous and crystalline states, are promising in this respect, but top-down processing of these materials into nanostructures often damages their useful properties. Self-assembled nanowire-based phase-change material memory devices offer an attractive solution owing to their sub-lithographic sizes and unique geometry, coupled with the facile etch-free processes with which they can be fabricated. Here, we explore the effects of nanoscaling on the memory-storage capability of self-assembled Ge2Sb2Te5 nanowires, an important phase-change material. Our measurements of write-current amplitude, switching speed, endurance and data retention time in these devices show that such nanowires are promising building blocks for non-volatile scalable memory and may represent the ultimate size limit in exploring current-induced phase transition in nanoscale systems. PMID:18654387

  12. The Oxidation Behaviour of Diamond Like Carbon for Phase-Change Probe Memory Application.

    PubMed

    Wang, Lei; Yang, Cihui; Wen, Jing; Yang, Guowei

    2015-06-01

    Phase-change probe memory, as a promising candidate for next-generation storage device, usually requires a capping layer to protect phase-change media from wear and corrosion. Diamond-like carbon film has been commonly used for capping layer due to its high mechanical hardness and easiness for tailoring physical properties. However, the possibility for such carbon thin film to react to surrounding oxygen when subjected to Joule heating during the recording process of phase-change probe memory is rarely investigated before from both experimental and simulation point of view. Therefore, a novel carbon oxidation model was developed to mimic the chemical reaction of carbon film to the surrounding oxygen in terms of the degradation of layer thickness. Results obtained from this model are in a good agreement with the experimental counterpart, indicating the physical reality of this proposed model. PMID:26369065

  13. 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. PMID:25809085

  14. Threshold-voltage modulated phase change heterojunction for application of high density memory

    SciTech Connect

    Yan, Baihan; Tong, Hao Qian, Hang; Miao, Xiangshui

    2015-09-28

    Phase change random access memory is one of the most important candidates for the next generation non-volatile memory technology. However, the ability to reduce its memory size is compromised by the fundamental limitations inherent in the CMOS technology. While 0T1R configuration without any additional access transistor shows great advantages in improving the storage density, the leakage current and small operation window limit its application in large-scale arrays. In this work, phase change heterojunction based on GeTe and n-Si is fabricated to address those problems. The relationship between threshold voltage and doping concentration is investigated, and energy band diagrams and X-ray photoelectron spectroscopy measurements are provided to explain the results. The threshold voltage is modulated to provide a large operational window based on this relationship. The switching performance of the heterojunction is also tested, showing a good reverse characteristic, which could effectively decrease the leakage current. Furthermore, a reliable read-write-erase function is achieved during the tests. Phase change heterojunction is proposed for high-density memory, showing some notable advantages, such as modulated threshold voltage, large operational window, and low leakage current.

  15. Dynamic switching characteristic dependence on sidewall angle for phase change memory

    NASA Astrophysics Data System (ADS)

    Long, X. M.; Miao, X. S.; Sun, J. J.; Cheng, X. M.; Tong, H.; Li, Y.; Yang, D. H.; Huang, J. D.; Liu, C.

    2012-01-01

    In this paper, the volume-minimized model of phase change memory (PCM) cell with Ge 2Sb 2Te 5 (GST) material has been established to study the dynamic switching (set-to-reset) characteristic dependence on the sidewall angle. Joule heating volume, threshold current, dynamic resistance and phase transition rate of PCM cells by current pulse are all calculated. The results show that the threshold current increases with decreasing the sidewall angle and is significantly impacted by the feature size and aspect ratio. The PCM cell of 90° sidewall angle exhibits the smallest Joule heating volume, the highest RESET resistance and the fastest phase transition property.

  16. Engineering of chalcogenide materials for embedded applications of Phase Change Memory

    NASA Astrophysics Data System (ADS)

    Zuliani, Paola; Palumbo, Elisabetta; Borghi, Massimo; Dalla Libera, Giovanna; Annunziata, Roberto

    2015-09-01

    Phase Change Memory technology can be a real breakthrough for process cost saving and performances for embedded applications. The feasibility at 90 nm technology node has been solidly proven in an industrial environment and the added value of this solution demonstrated. Nevertheless, for specific applications some improvement in High Temperature Data Retention (HTDR) characteristics is needed. In this work we present the engineering of chalcogenide materials in order to increase the stability of RESET state as a function of temperature. This goal has been achieved by exploring Ge-rich compounds in the Ge-Sb-Te ternary diagram. In particular, an optimized GexSbyTez Phase Change material, able to guarantee code integrity of the memory content after soldering thermal profile and data retention in extended temperature range has been obtained. Extrapolation of data retention at 10 years for temperatures higher than 150 °C cell-level has been demonstrated, thus enabling automotive applications.

  17. Threshold switching uniformity in In2Se3 nanowire-based phase change memory

    NASA Astrophysics Data System (ADS)

    Chen, Jian; Du, Gang; Liu, Xiao-Yan

    2015-05-01

    The uniformity of threshold voltage and threshold current in the In2Se3 nanowire-based phase change memory (PCM) devices is investigated. Based on the trap-limited transport model, amorphous layer thickness, trap density, and trap depth are considered to clarify their influences upon the threshold voltage and threshold current through simulations. Project supported by the National Basic Research Program of China (Grant No. 2011CBA00604).

  18. A candidate Zr-doped Sb2Te alloy for phase change memory application

    NASA Astrophysics Data System (ADS)

    Zheng, Yonghui; Cheng, Yan; Zhu, Min; Ji, Xinglong; Wang, Qing; Song, Sannian; Song, Zhitang; Liu, Weili; Feng, Songlin

    2016-02-01

    Here, Zr-doped Sb2Te alloy is proposed for phase change memory (PCM). Zr-doping enhances the crystallization temperature and thermal stability of Sb2Te alloy effectively. Crystalline Zr2(Sb2Te)98 film is manifested as a single phase without phase separation and the growth of crystal grain is dramatically suppressed. The density change of Zr2(Sb2Te)98 material between amorphous and crystalline is ˜2.65 ± 0.03%, which is much smaller than that of Ge2Sb2Te5 (6.5%). Phase change memory cells based on Zr2(Sb2Te)98 material can be reversibly switched by applying 40-400 ns width voltage pulses, and the reset current is relatively small when comparing with the prototypical Ge2Sb2Sb5 material. The resistance ON-OFF ratio of about 1.3 orders of magnitude is enough for figuring "0" and "1" out. Besides, endurance up to 4.1 × 104 cycles makes Zr-doped Sb2Te alloy a potential candidate for PCM.

  19. Understanding the early cycling evolution behaviors for phase change memory application

    NASA Astrophysics Data System (ADS)

    Wang, Yuchan; Chen, Yifeng; Cai, Daolin; Cheng, Yan; Chen, Xiaogang; Wang, Yueqing; Xia, Mengjiao; Zhou, Mi; Li, Gezi; Zhang, Yiyun; Gao, Dan; Song, Zhitang; Feng, Gaoming

    2014-11-01

    The RESET current of T-shaped phase change memory cells with 35 nm heating electrodes has been studied to understand the behavior of early cycling evolution. Results show that the RESET current has been significantly reduced after the early cycling evolution (1st RESET) operation. Compared the transmission electron microscope images, it is found that the hexagonal Ge2Sb2Te5 (GST) crystal grains are changed into the grains with face centered cubic structure after the early cycling evolution operation, which is taken as the major reason for the reduced RESET current, confirmed by a two-dimensional finite analysis and ab initio calculations.

  20. Balancing the Lifetime and Storage Overhead on Error Correction for Phase Change Memory

    PubMed Central

    An, Ning; Wang, Rui; Gao, Yuan; Yang, Hailong; Qian, Depei

    2015-01-01

    As DRAM is facing the scaling difficulty in terms of energy cost and reliability, some nonvolatile storage materials were proposed to be the substitute or supplement of main memory. Phase Change Memory (PCM) is one of the most promising nonvolatile memory that could be put into use in the near future. However, before becoming a qualified main memory technology, PCM should be designed reliably so that it can ensure the computer system’s stable running even when errors occur. The typical wear-out errors in PCM have been well studied, but the transient errors, that caused by high-energy particles striking on the complementary metal-oxide semiconductor (CMOS) circuit of PCM chips or by resistance drifting in multi-level cell PCM, have attracted little focus. In this paper, we propose an innovative mechanism, Local-ECC-Global-ECPs (LEGE), which addresses both soft errors and hard errors (wear-out errors) in PCM memory systems. Our idea is to deploy a local error correction code (ECC) section to every data line, which can detect and correct one-bit errors immediately, and a global error correction pointers (ECPs) buffer for the whole memory chip, which can be reloaded to correct more hard error bits. The local ECC is used to detect and correct the unknown one-bit errors, and the global ECPs buffer is used to store the corrected value of hard errors. In comparison to ECP-6, our method provides almost identical lifetimes, but reduces approximately 50% storage overhead. Moreover, our structure reduces approximately 3.55% access latency overhead by increasing 1.61% storage overhead compared to PAYG, a hard error only solution. PMID:26158524

  1. Novel device structure for phase change memory toward low-current operation

    NASA Astrophysics Data System (ADS)

    Kim, Eunha; Kang, Nam Soo; Yang, Hyung-Jun; Sutou, Yuji; Song, Yun-Heub

    2015-09-01

    We present a novel device architecture for low set and reset currents in phase change random access memory (PCRAM). In this structure, the sidewall of phase-change film is contacted with the vertical heating layer. In particular, to realize a small contact area of under 50 nm2 for low reset current, this structure includes stacked layers consisting of extremely thin phase change material (PCM) and conduction films, the fabrication method of which is proposed. We estimated set and reset currents for the proposed structure by the device simulation method. Here, we confirmed that a contact area of 30 nm2 in this structure, where Ge2Sb2Te5 is used as PCM, provides a reset current of 13.5 µA and a set current of 4 µA, which are promising for the scaling down of PCM. Furthermore, it is confirmed that the thinner PCM in this structure provides less thermal disturbance to the neighboring cell. From the results, we expect this structure to be a promising candidate for a high-density nonvolatile memory architecture with PCM.

  2. Phase-change memory function of correlated electrons in organic conductors

    NASA Astrophysics Data System (ADS)

    Oike, H.; Kagawa, F.; Ogawa, N.; Ueda, A.; Mori, H.; Kawasaki, M.; Tokura, Y.

    2015-01-01

    Phase-change memory (PCM), a promising candidate for next-generation nonvolatile memories, exploits quenched glassy and thermodynamically stable crystalline states as reversibly switchable state variables. We demonstrate PCM functions emerging from a charge-configuration degree of freedom in strongly correlated electron systems. Nonvolatile reversible switching between a high-resistivity charge-crystalline (or charge-ordered) state and a low-resistivity quenched state, charge glass, is achieved experimentally via heat pulses supplied by optical or electrical means in organic conductors θ -(BEDT-TTF)2X . Switching that is one order of magnitude faster is observed in another isostructural material that requires faster cooling to kinetically avoid charge crystallization, indicating that the material's critical cooling rate can be useful guidelines for pursuing a faster correlated-electron PCM function.

  3. Materials and other needs for advanced phase change memory (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Sosa, Norma E.

    2015-09-01

    Phase change memory (PCM), with its long history, may now hold its brightest promise to date. This bright future is being fueled by the "push" from big data. PCM is a non-volatile memory technology used to create solid-state random access memory devices that operate based the resistance properties of materials. Employing the electrical resistance differences-as opposed to differences in charge stored-between the amorphous and crystalline phases of the material, PCM can store bits, namely one's and zero's. Indeed, owing to the method of storage, PCM can in fact be designed to hold multiple bits thus leading to a high-density technology twice the storage density and less than half the cost of DRAM, the main kind found in typical personal computers. It has been long known that PCM can fill a need gap that spans 3 decades in performance from DRAM to solid state drive (NAND Flash). Furthermore, PCM devices can lead to performance and reliability improvements essential to enabling significant steps forward to supporting big data centric computing. This talk will focus on the science and challenges of aggressive scaling to realize the density needed, how this scaling challenge is intertwined with materials needs for endurance into the giga-cycles, and the associated forefront research aiming to realizing multi-level functionality into these nanoscale programmable resistor devices.

  4. Carbon-doped Ge2Sb2Te5 phase change material: A candidate for high-density phase change memory application

    NASA Astrophysics Data System (ADS)

    Zhou, Xilin; Wu, Liangcai; Song, Zhitang; Rao, Feng; Zhu, Min; Peng, Cheng; Yao, Dongning; Song, Sannian; Liu, Bo; Feng, Songlin

    2012-10-01

    Carbon-doped Ge2Sb2Te5 material is proposed for high-density phase-change memories. The carbon doping effects on electrical and structural properties of Ge2Sb2Te5 are studied by in situ resistance and x-ray diffraction measurements as well as optical spectroscopy. C atoms are found to significantly enhance the thermal stability of amorphous Ge2Sb2Te5 by increasing the degree of disorder of the amorphous phase. The reversible electrical switching capability of the phase-change memory cells is improved in terms of power consumption with carbon addition. The endurance of ˜2.1 × 104 cycles suggests that C-doped Ge2Sb2Te5 film will be a potential phase-change material for high-density storage application.

  5. Nanosecond switching in GeSe phase change memory films by atomic force microscopy

    SciTech Connect

    Bosse, James L.; Huey, Bryan D.; Grishin, Ilya; Kolosov, Oleg V.; Gyu Choi, Yong; Cheong, Byung-ki; Lee, Suyoun

    2014-02-03

    Nanosecond scale threshold switching is investigated with conducting atomic force microscopy (AFM) for an amorphous GeSe film. Switched bits exhibit 2–3 orders of magnitude variations in conductivity, as demonstrated in phase change based memory devices. Through the nm-scale AFM probe, this crystallization was achieved with pulse durations of as low as 15 ns, the fastest reported with scanning probe based methods. Conductance AFM imaging of the switched bits further reveals correlations between the switched volume, pulse amplitude, and pulse duration. The influence of film heterogeneities on switching is also directly detected, which is of tremendous importance for optimal device performance.

  6. Microstructural Characterization in Reliability Measurement of Phase Change Random Access Memory

    NASA Astrophysics Data System (ADS)

    Bae, Junsoo; Hwang, Kyuman; Park, Kwangho; Jeon, Seongbu; Kang, Dae-hwan; Park, Soonoh; Ahn, Juhyeon; Kim, Seoksik; Jeong, Gitae; Chung, Chilhee

    2011-04-01

    The cell failures after cycling endurance in phase-change random access memory (PRAM) have been classified into three groups, which have been analyzed by transmission electron microscopy (TEM). Both stuck reset of the set state (D0) and stuck set of the reset state (D1) are due to a void created inside GeSbTe (GST) film or thereby lowering density of GST film. The decrease of the both set and reset resistances that leads to the tails from the reset distribution are induced from the Sb increase with cycles.

  7. Empirical investigation of SET seasoning effects in Phase Change Memory arrays

    NASA Astrophysics Data System (ADS)

    Zambelli, C.; Chimenton, A.; Olivo, P.

    2011-04-01

    In this work we have investigated the seasoning effect in SET state occurring during cycling of multimegabit Phase Change Memory arrays. The impact of the erasing waveform on this phenomenon has been experimentally evaluated. The physical nature of the phenomenon has been discussed in relation to the electro-thermal characteristics of the active material. The study of such phenomenon is also important to comprehend the transition dynamics of the GST material towards its crystalline state and to develop accurate models allowing an estimate of the PCM cells behavior as a function of the operative cycles.

  8. Investigation of the Hydrogen Silsesquioxane (HSQ) Electron Resist as Insulating Material in Phase Change Memory Devices

    NASA Astrophysics Data System (ADS)

    Zhou, Jiao; Ji, Hongkai; Lan, Tian; Yan, Junbing; Zhou, Wenli; Miao, Xiangshui

    2015-01-01

    Phase change random access memory (PCRAM) affords many advantages over conventional solid-state memories due to its nonvolatility, high speed, and scalability. However, high programming current to amorphize the crystalline phase through the melt-quench process of PCRAM, known as the RESET current, poses a critical challenge and has become the most significant obstacle for its widespread commercialization. In this work, an excellent negative tone resist for high resolution electron beam lithography, hydrogen silsesquioxane (HSQ), has been investigated as the insulating material which locally blocks the contact between the bottom electrode and the phase change material in PCRAM devices. Fabrications of the highly scaled HSQ nanopore arrays (as small as 16 nm) are presented. The insulating properties of the HSQ material are studied, especially under e-beam exposure plus thermal curing. Some other critical issues about the thickness adjustment of HSQ films and the influence of the PCRAM electrode on electron scattering in e-beam lithography are discussed. In addition, the HSQ material was successfully integrated into the PCRAM devices, achieving ultra-low RESET current (sub-100 μA), outstanding on/off ratios (~50), and improved endurance at tens of nanometers.

  9. Investigation of the Hydrogen Silsesquioxane (HSQ) Electron Resist as Insulating Material in Phase Change Memory Devices

    NASA Astrophysics Data System (ADS)

    Zhou, Jiao; Ji, Hongkai; Lan, Tian; Yan, Junbing; Zhou, Wenli; Miao, Xiangshui

    2014-09-01

    Phase change random access memory (PCRAM) affords many advantages over conventional solid-state memories due to its nonvolatility, high speed, and scalability. However, high programming current to amorphize the crystalline phase through the melt-quench process of PCRAM, known as the RESET current, poses a critical challenge and has become the most significant obstacle for its widespread commercialization. In this work, an excellent negative tone resist for high resolution electron beam lithography, hydrogen silsesquioxane (HSQ), has been investigated as the insulating material which locally blocks the contact between the bottom electrode and the phase change material in PCRAM devices. Fabrications of the highly scaled HSQ nanopore arrays (as small as 16 nm) are presented. The insulating properties of the HSQ material are studied, especially under e-beam exposure plus thermal curing. Some other critical issues about the thickness adjustment of HSQ films and the influence of the PCRAM electrode on electron scattering in e-beam lithography are discussed. In addition, the HSQ material was successfully integrated into the PCRAM devices, achieving ultra-low RESET current (sub-100 μA), outstanding on/off ratios (~50), and improved endurance at tens of nanometers.

  10. Reversibility and stability of ZnO-Sb₂Te₃ nanocomposite films for phase change memory applications.

    PubMed

    Wang, Guoxiang; Chen, Yimin; Shen, Xiang; Li, Junjian; Wang, Rongping; Lu, Yegang; Dai, Shixun; Xu, Tiefeng; Nie, Qiuhua

    2014-06-11

    (ZnO)x(Sb2Te3)1-x materials with different ZnO contents have been systemically studied with an aim of finding the most suitable composition for phase change memory applications. It was found that ZnO-doping could improve thermal stability and electrical behavior of Sb2Te3 film. Sb2Te3-rich nanocrystals, surrounded by ZnO-rich amorphous phases, were observed in annealed ZnO-doped Sb2Te3 composite films, and the segregated domains exhibited a relatively uniform distribution. The ZnO-doped Sb2Te3 composite films, especially with 5.2 at% ZnO concentration were found to have higher crystallization temperature, higher crystalline resistance, and faster crystallization speed in comparison with Ge2Sb2Te5. A reversible repetitive optical switching behavior can be observed in (ZnO)5.2(Sb2Te3)94.8, confirming that the ZnO doping is responsible for a fast switching and the compound is stable with cycling. Therefore, it is promising for the applications in phase change memory devices. PMID:24802948

  11. Towards a drift-free multi-level Phase Change Memory

    NASA Astrophysics Data System (ADS)

    Cinar, Ibrahim; Ozdemir, Servet; Cogulu, Egecan; Gokce, Aisha; Stipe, Barry; Katine, Jordan; Aktas, Gulen; Ozatay, Ozhan

    For ultra-high density data storage applications, Phase Change Memory (PCM) is considered a potentially disruptive technology. Yet, the long-term reliability of the logic levels corresponding to the resistance states of a PCM device is an important issue for a stable device operation since the resistance levels drift uncontrollably in time. The underlying mechanism for the resistance drift is considered as the structural relaxation and spontaneous crystallization at elevated temperatures. We fabricated a nanoscale single active layer-phase change memory cell with three resistance levels corresponding to crystalline, amorphous and intermediate states by controlling the current injection site geometry. For the intermediate state and the reset state, the activation energies and the trap distances have been found to be 0.021 eV and 0.235 eV, 1.31 nm and 7.56 nm, respectively. We attribute the ultra-low and weakly temperature dependent drift coefficient of the intermediate state (ν = 0.0016) as opposed to that of the reset state (ν = 0.077) as being due to the dominant contribution of the interfacial defects in electrical transport in the case of the mixed phase. Our results indicate that the engineering of interfacial defects will enable a drift-free multi-level PCM device design.

  12. Ge2Sb2Te5 Confined Structures and Integration of 64 Mb Phase-Change Random Access Memory

    NASA Astrophysics Data System (ADS)

    Yeung, Fai; Ahn, Su-Jin; Hwang, Young-Nam; Jeong, Chang-Wook; Song, Yoon-Jong; Lee, Su-Youn; Lee, Se-Ho; Ryoo, Kyung-Chang; Park, Jae-Hyun; Shin, Jae-Min; Jeong, Won-Cheol; Kim, Young-Tae; Koh, Gwan-Hyeob; Jeong, Gi-Tae; Jeong, Hong-Sik; Kim, Kinam

    2005-04-01

    Phase-change random access memory is considered a potential challenger for conventional memories, such as dynamic random access memory and flash memory due to its numerous advantages. Nevertheless, high reset current is the ultimate problem in developing high-density phase-change random access memory (PRAM). We focus on the adoption of Ge2Sb2Te5 confined structures to achieve lower reset currents. By changing from a normal to a GST confined structure, the reset current drops to as low as 0.8 mA. Eventually, our integrated 64 Mb PRAM based on 0.18 μm CMOS technology offers a large sensing margin: Rreset ˜200 kΩ and Rset ˜2 kΩ, as well as reasonable reliability: an endurance of 1.0× 109 cycles and a retention time of 2 years at 85°C.

  13. High thermal stable and fast switching Ni-Ge-Te alloy for phase change memory applications

    NASA Astrophysics Data System (ADS)

    Cao, Liangliang; Wu, Liangcai; Zhu, Wenqing; Ji, Xinglong; Zheng, Yonghui; Song, Zhitang; Rao, Feng; Song, Sannian; Ma, Zhongyuan; Xu, Ling

    2015-12-01

    Ni-Ge-Te phase change material is proposed and investigated for phase change memory (PCM) applications. With Ni addition, the crystallization temperature, the data retention ability, and the crystallization speed are remarkably improved. The Ni-Ge-Te material has a high crystallization temperature (250 °C) and good data retention ability (149 °C). A reversible switching between SET and RESET state can be achieved by an electrical pulse as short as 6 ns. Up to ˜3 × 104 SET/RESET cycles are obtained with a resistance ratio of about two orders of magnitude. All of these demonstrate that Ni-Ge-Te alloy is a promising material for high speed and high temperature PCM applications.

  14. Electronic Transport properties of SET and REST states of interfacial phase-change memory

    NASA Astrophysics Data System (ADS)

    Nakamura, Hisao; Tominaga, Junji; Asai, Yoshihiro; Rungger, Ivan; Narayan, Awadhesh; Sanvito, Stefano

    2015-03-01

    The phase change memory (PCM) is one of most promising nonvolatile information storage technologies. Recently, the superlattice structure of GeTe/Sb2Te3 is proposed as PCM to reduce the restive switching energy. This PCM is called interfacial PCM (iPCM) and it is considered that SET and RESET states are realized only by the flip-flop transition of Ge atoms in crystal phase because of small loss of entropy. Furthermore, the GeTe is sandwiched by Sb2Te3 topological insulator. In this study, we performed the first principles electric transport calculations including spin-orbit interactions. We presents the mechanism of resistive switch by the transition of Ge atoms as well as the volume change effect and the role of spin-orbit interaction to resistance ration of SET and RESE states.

  15. Energy-Efficient Phase-Change Memory with Graphene as a Thermal Barrier.

    PubMed

    Ahn, Chiyui; Fong, Scott W; Kim, Yongsung; Lee, Seunghyun; Sood, Aditya; Neumann, Christopher M; Asheghi, Mehdi; Goodson, Kenneth E; Pop, Eric; Wong, H-S Philip

    2015-10-14

    Phase-change memory (PCM) is an important class of data storage, yet lowering the programming current of individual devices is known to be a significant challenge. Here we improve the energy-efficiency of PCM by placing a graphene layer at the interface between the phase-change material, Ge2Sb2Te5 (GST), and the bottom electrode (W) heater. Graphene-PCM (G-PCM) devices have ∼40% lower RESET current compared to control devices without the graphene. This is attributed to the graphene as an added interfacial thermal resistance which helps confine the generated heat inside the active PCM volume. The G-PCM achieves programming up to 10(5) cycles, and the graphene could further enhance the PCM endurance by limiting atomic migration or material segregation at the bottom electrode interface. PMID:26308280

  16. High thermal stability Sb3Te-TiN2 material for phase change memory application

    NASA Astrophysics Data System (ADS)

    Ji, Xinglong; Wu, Liangcai; Zhou, Wangyang; Zhu, Min; Rao, Feng; Song, Zhitang; Cao, Liangliang; Feng, Songlin

    2015-01-01

    For phase change memory (PCM) applications, it has been widely accepted that δ phase Sb-Te has fast operation speed and good phase stability. However, the fast growth crystallization mechanism will cause poor amorphous phase stability and overlarge grain size. We introduce TiN2 into δ phase Sb-Te (Sb3Te) to enhance the amorphous thermal stability and refine the grain size. With TiN2 incorporating, the temperature for 10-year data retention increases from 79 °C to 124 °C. And the grain size decreases to dozens of nanometers scale. Based on X-ray photoelectron spectroscopy and transmission electron microscopy results, we knew that nitrogen atoms bond with titanium, forming disorder region at the grain boundary of Sb3Te-TiN2 (STTN). Thus, STTN has a quite different crystallization mechanism from Sb3Te. Furthermore, PCM device based on STTN can realize reversible phase change under 20 ns electrical pulse.

  17. Scalability of Phase Change Materials in Non-Volatile Memory Devices

    NASA Astrophysics Data System (ADS)

    Jackson, Biyun Li

    This dissertation presents a study of the scaling limit of Phase Change Materials (PCM) for non-volatile memory device application. The approach is to obtain isolated true nano size Phase Change Materials through controllable deposition of PCM onto a template - nano pitted substrate. The fabrication of nano pitted substrate started from a di-block copolymer (DBC) film in hexagonal nano arrangement coated on thin SiO2 on Si (100) substrate. Then the DBC pattern was transferred to SiO2 - Si substrate by anisotropic dry oxide etch. Subsequently, a wet KOH etch with high crystallographic selectivity changed the circular pattern into an inverted pyramidal pit substrate. Thus, the dimension of the pits are controlled by the hole size of DBC, and the density of the pits are controlled by the interspacing between holes. Characterization tools such as SEM and TEM are intensively used to analyze the morphology, crystallographic, atomic ratio and phase transformation of the PCM. The dissertation discusses the critical fabrication tricks to produce high yield nano pitted substrate, illustrating the size effect of phase change materials upon crystallization and melting as well as the scaling limit of PCM. A proposal is also discussed for extending the study to device fabrication level and branch out the nano pitted substrate for the study of other materials in size and pressure effect.

  18. Understanding the early cycling evolution behaviors for phase change memory application

    SciTech Connect

    Wang, Yuchan Chen, Yifeng Cai, Daolin; Cheng, Yan; Chen, Xiaogang; Wang, Yueqing; Xia, Mengjiao; Zhou, Mi; Li, Gezi; Zhang, Yiyun; Gao, Dan; Song, Zhitang; Feng, Gaoming

    2014-11-28

    The RESET current of T-shaped phase change memory cells with 35 nm heating electrodes has been studied to understand the behavior of early cycling evolution. Results show that the RESET current has been significantly reduced after the early cycling evolution (1st RESET) operation. Compared the transmission electron microscope images, it is found that the hexagonal Ge{sub 2}Sb{sub 2}Te{sub 5} (GST) crystal grains are changed into the grains with face centered cubic structure after the early cycling evolution operation, which is taken as the major reason for the reduced RESET current, confirmed by a two-dimensional finite analysis and ab initio calculations.

  19. Investigation of electromigration in In2Se3 nanowire for phase change memory devices

    NASA Astrophysics Data System (ADS)

    Kang, Daegun; Rim, Taiuk; Baek, Chang-Ki; Meyyappan, M.; Lee, Jeong-Soo

    2013-12-01

    The decomposition of In2Se3 nanowire phase change memory devices during current-driving operation was investigated. The devices were subjected to thermal/electrical stress with current density and electric field during the reset operation at 0.24-0.38 MA/cm2 and 5.3-6.4 kV/cm, respectively. After multiple operation cycles, a change in morphology and composition of the In2Se3 nanowire was observed and led to the device failure. The transmission electron microscopy and energy dispersive analysis indicate that electromigration causes the catastrophic failure by void formation where In atoms migrate toward the cathode and Se atoms migrate toward the anode depending on their electronegativities.

  20. In-situ crystallization of GeTe\\GaSb phase change memory stacked films

    SciTech Connect

    Velea, A.; Borca, C. N.; Grolimund, D.; Socol, G.; Galca, A. C.; Popescu, M.; Bokhoven, J. A. van

    2014-12-21

    Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 °C and 198 °C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 °C. Furthermore, at 210 °C, the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples.

  1. Ultralow-power switching via defect engineering in germanium telluride phase-change memory devices

    PubMed Central

    Nukala, Pavan; Lin, Chia-Chun; Composto, Russell; Agarwal, Ritesh

    2016-01-01

    Crystal–amorphous transformation achieved via the melt-quench pathway in phase-change memory involves fundamentally inefficient energy conversion events; and this translates to large switching current densities, responsible for chemical segregation and device degradation. Alternatively, introducing defects in the crystalline phase can engineer carrier localization effects enhancing carrier–lattice coupling; and this can efficiently extract work required to introduce bond distortions necessary for amorphization from input electrical energy. Here, by pre-inducing extended defects and thus carrier localization effects in crystalline GeTe via high-energy ion irradiation, we show tremendous improvement in amorphization current densities (0.13–0.6 MA cm−2) compared with the melt-quench strategy (∼50 MA cm−2). We show scaling behaviour and good reversibility on these devices, and explore several intermediate resistance states that are accessible during both amorphization and recrystallization pathways. Existence of multiple resistance states, along with ultralow-power switching and scaling capabilities, makes this approach promising in context of low-power memory and neuromorphic computation. PMID:26805748

  2. Ultralow-power switching via defect engineering in germanium telluride phase-change memory devices.

    PubMed

    Nukala, Pavan; Lin, Chia-Chun; Composto, Russell; Agarwal, Ritesh

    2016-01-01

    Crystal-amorphous transformation achieved via the melt-quench pathway in phase-change memory involves fundamentally inefficient energy conversion events; and this translates to large switching current densities, responsible for chemical segregation and device degradation. Alternatively, introducing defects in the crystalline phase can engineer carrier localization effects enhancing carrier-lattice coupling; and this can efficiently extract work required to introduce bond distortions necessary for amorphization from input electrical energy. Here, by pre-inducing extended defects and thus carrier localization effects in crystalline GeTe via high-energy ion irradiation, we show tremendous improvement in amorphization current densities (0.13-0.6 MA cm(-2)) compared with the melt-quench strategy (∼50 MA cm(-2)). We show scaling behaviour and good reversibility on these devices, and explore several intermediate resistance states that are accessible during both amorphization and recrystallization pathways. Existence of multiple resistance states, along with ultralow-power switching and scaling capabilities, makes this approach promising in context of low-power memory and neuromorphic computation. PMID:26805748

  3. Ultralow-power switching via defect engineering in germanium telluride phase-change memory devices

    NASA Astrophysics Data System (ADS)

    Nukala, Pavan; Lin, Chia-Chun; Composto, Russell; Agarwal, Ritesh

    2016-01-01

    Crystal-amorphous transformation achieved via the melt-quench pathway in phase-change memory involves fundamentally inefficient energy conversion events; and this translates to large switching current densities, responsible for chemical segregation and device degradation. Alternatively, introducing defects in the crystalline phase can engineer carrier localization effects enhancing carrier-lattice coupling; and this can efficiently extract work required to introduce bond distortions necessary for amorphization from input electrical energy. Here, by pre-inducing extended defects and thus carrier localization effects in crystalline GeTe via high-energy ion irradiation, we show tremendous improvement in amorphization current densities (0.13-0.6 MA cm-2) compared with the melt-quench strategy (~50 MA cm-2). We show scaling behaviour and good reversibility on these devices, and explore several intermediate resistance states that are accessible during both amorphization and recrystallization pathways. Existence of multiple resistance states, along with ultralow-power switching and scaling capabilities, makes this approach promising in context of low-power memory and neuromorphic computation.

  4. Nanomechanical morphology of amorphous, transition, and crystalline domains in phase change memory thin films

    NASA Astrophysics Data System (ADS)

    Bosse, J. L.; Grishin, I.; Huey, B. D.; Kolosov, O. V.

    2014-09-01

    In the search for phase change materials (PCM) that may rival traditional random access memory, a complete understanding of the amorphous to crystalline phase transition is required. For the well-known Ge2Sb2Te5 (GST) and GeTe (GT) chalcogenides, which display nucleation and growth dominated crystallization kinetics, respectively, this work explores the nanomechanical morphology of amorphous and crystalline phases in 50 nm thin films. Subjecting these PCM specimens to a lateral thermal gradient spanning the crystallization temperature allows for a detailed morphological investigation. Surface and depth-dependent analyses of the resulting amorphous, transition and crystalline regions are achieved with shallow angle cross-sections, uniquely implemented with beam exit Ar ion polishing. To resolve the distinct phases, ultrasonic force microscopy (UFM) with simultaneous topography is implemented revealing a relative stiffness contrast between the amorphous and crystalline phases of 14% for the free film surface and 20% for the cross-sectioned surface. Nucleation is observed to occur preferentially at the PCM-substrate and free film interface for both GST and GT, while fine subsurface structures are found to be sputtering direction dependent. Combining surface and cross-section nanomechanical mapping in this manner allows 3D analysis of microstructure and defects with nanoscale lateral and depth resolution, applicable to a wide range of materials characterization studies where the detection of subtle variations in elastic modulus or stiffness are required.

  5. The effect of thermoelectric contributions in switching dynamics and resistance drift of Phase Change Memory devices

    NASA Astrophysics Data System (ADS)

    Cogulu, Egecan; Cinar, Ibrahim; Gokce, Aisha; Stipe, Barry; Katine, Jordan; Aktas, Gulen; Ozatay, Ozhan

    2015-03-01

    Phase Change Memory (PCM) is a promising non-volatile data storage technology that allows for multiple-bit-per-cell operation due to its high contrast in the resistance levels between 0 and 1 logic states. To visualize the complex nature and the stability of the switching dynamics in PCM devices with or without an intermediate resistance state, 3D finite element simulations were carried out in cells with a single Ge2Sb2Te5(GST) layer incorporating temperature and phase dependent thermal and electrical conductivities as well as thermoelectric effects. We compare our results with the experimental data and with our previous simulations to understand the influence of the thermo-electric effect on the phase switching. In addition, we integrated drift equations into our multiphysics simulation to get a complete picture of structural relaxation in time in amorphous and mixed phases of the GST. We compare our results with experimental resistance drift measurements to calculate a decay rate for defect concentration. Our results yield a complete picture of switching dynamics and post-switching resistance drift phenomena on the microscopic scale. TUBITAK fund 113F385, Bogazici Uni. Research Fund, 12B03M1, and European Union FP7 Marie Curie International Re-integration Grant PCM-256281.

  6. A Physics-Based Three Dimensional Model for Write and Read Performances of Phase-Change Probe Memory.

    PubMed

    Wang, Lei; Wright, C David; Aziz, Mustafa M; Ying, Jin; Yang, Guo Wei

    2015-04-01

    The write and read performances of phase-change probe memory were investigated for the first time by a physics-based pure three dimensional model. The written crystalline bit possessed from this developed model demonstrates the potential of phase-change probe memory for ultra-high density, low energy consumption, high data rate, and good readability. The cross-talk effect on the write and read performances of phase-change probe memory, which can not be modelled by previous two dimensional models, is also evaluated. The findings showed that the bit and track pitches should be remained sufficiently long so as to eliminate the undesired interferences. The simulated results exhibited a good agreement with the experimental observations, thus demonstrating the physical reality of the designed model. PMID:26353493

  7. Unsupervised Learning by Spike Timing Dependent Plasticity in Phase Change Memory (PCM) Synapses

    PubMed Central

    Ambrogio, Stefano; Ciocchini, Nicola; Laudato, Mario; Milo, Valerio; Pirovano, Agostino; Fantini, Paolo; Ielmini, Daniele

    2016-01-01

    We present a novel one-transistor/one-resistor (1T1R) synapse for neuromorphic networks, based on phase change memory (PCM) technology. The synapse is capable of spike-timing dependent plasticity (STDP), where gradual potentiation relies on set transition, namely crystallization, in the PCM, while depression is achieved via reset or amorphization of a chalcogenide active volume. STDP characteristics are demonstrated by experiments under variable initial conditions and number of pulses. Finally, we support the applicability of the 1T1R synapse for learning and recognition of visual patterns by simulations of fully connected neuromorphic networks with 2 or 3 layers with high recognition efficiency. The proposed scheme provides a feasible low-power solution for on-line unsupervised machine learning in smart reconfigurable sensors. PMID:27013934

  8. Investigation of Al doping on Ge55Te45 for phase change memory application

    NASA Astrophysics Data System (ADS)

    Ren, Kun; Rao, Feng; Song, Zhitang; Wu, Liangcai; Xia, Mengjiao; Liu, Bo; Feng, Songlin

    2013-06-01

    Al-doped Ge55Te45 materials are proposed for phase change memory application. Al incorporated in Ge55Te45 increases the crystallization temperature, band gap and 10-year data retention significantly. However, the crystallization speed of the Al-doped Ge55Te45 material will be lowered by excessive Al doping. The crystallization of the Al-doped Ge55Te45 film is observed to be growth-dominant, beginning with a random formation of spherical crystalline clusters. The 10-year data retention and crystallization speed of Al1Ge55Te45 are 117 °C and 5 ns, respectively, which makes the Al1Ge55Te45 a promising candidate for high speed PCM application. The 10-year data retention of 132 °C and good cyclic ability of ˜2 × 103 cycles of the Al2Ge55Te45 based PCM have shown its application potential in automotive fields.

  9. Study on the nitrogen-doped W-Sb-Te material for phase change memory application

    NASA Astrophysics Data System (ADS)

    Ren, Kun; Xia, Mengjiao; Rao, Feng; Song, Zhitang; Ding, Keyuan; Ji, Xinglong; Wu, Liangcai; Liu, Bo; Feng, Songlin

    2014-04-01

    N doping is proposed to enlarge sensing margin of W0.08(Sb2Te)0.92 based high-temperature phase-change memories (PCMs). The sensing margin is increased from 30 to 5 × 103, with an increase from 145 °C to 158 °C in data retention. The grain size is reduced to 10 nm. The PCM based on N-W0.08(Sb2Te)0.92 shows the fast operation speed of 30 ns and good cycling ability of >103. By X-ray photoelectron spectroscopy and ab initio calculation, the W atoms are suggested to locate in the Sb positions and interstices of the lattice. The W atoms in interstice will bond to N atoms during N doping.

  10. Simulation study on heat conduction of a nanoscale phase-change random access memory cell.

    PubMed

    Kim, Junho; Song, Ki-Bong

    2006-11-01

    We have investigated heat transfer characteristics of a nano-scale phase-change random access memory (PRAM) cell using finite element method (FEM) simulation. Our PRAM cell is based on ternary chalcogenide alloy, Ge2Sb2Te5 (GST), which is used as a recording layer. For contact area of 100 x 100 nm2, simulations of crystallization and amorphization processes were carried out. Physical quantities such as electric conductivity, thermal conductivity, and specific heat were treated as temperature-dependent parameters. Through many simulations, it is concluded that one can reduce set current by decreasing both electric conductivities of amorphous GST and crystalline GST, and in addition to these conditions by decreasing electric conductivity of molten GST one can also reduce reset current significantly. PMID:17252792

  11. Unsupervised Learning by Spike Timing Dependent Plasticity in Phase Change Memory (PCM) Synapses.

    PubMed

    Ambrogio, Stefano; Ciocchini, Nicola; Laudato, Mario; Milo, Valerio; Pirovano, Agostino; Fantini, Paolo; Ielmini, Daniele

    2016-01-01

    We present a novel one-transistor/one-resistor (1T1R) synapse for neuromorphic networks, based on phase change memory (PCM) technology. The synapse is capable of spike-timing dependent plasticity (STDP), where gradual potentiation relies on set transition, namely crystallization, in the PCM, while depression is achieved via reset or amorphization of a chalcogenide active volume. STDP characteristics are demonstrated by experiments under variable initial conditions and number of pulses. Finally, we support the applicability of the 1T1R synapse for learning and recognition of visual patterns by simulations of fully connected neuromorphic networks with 2 or 3 layers with high recognition efficiency. The proposed scheme provides a feasible low-power solution for on-line unsupervised machine learning in smart reconfigurable sensors. PMID:27013934

  12. Distribution of nanoscale nuclei in the amorphous dome of a phase change random access memory

    SciTech Connect

    Lee, Bong-Sub Darmawikarta, Kristof; Abelson, John R.; Raoux, Simone; Shih, Yen-Hao; Zhu, Yu

    2014-02-17

    The nanoscale crystal nuclei in an amorphous Ge{sub 2}Sb{sub 2}Te{sub 5} bit in a phase change memory device were evaluated by fluctuation transmission electron microscopy. The quench time in the device (∼10 ns) afforded more and larger nuclei in the melt-quenched state than in the as-deposited state. However, nuclei were even more numerous and larger in a test structure with a longer quench time (∼100 ns), verifying the prediction of nucleation theory that slower cooling produces more nuclei. It also demonstrates that the thermal design of devices will strongly influence the population of nuclei, and thus the speed and data retention characteristics.

  13. Ultrafast switching in nanoscale phase-change random access memory with superlattice-like structures.

    PubMed

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

    2011-06-24

    Phase-change random access memory cells with superlattice-like (SLL) GeTe/Sb(2)Te(3) were demonstrated to have excellent scaling performance in terms of switching speed and operating voltage. In this study, the correlations between the cell size, switching speed and operating voltage of the SLL cells were identified and investigated. We found that small SLL cells can achieve faster switching speed and lower operating voltage compared to the large SLL cells. Fast amorphization and crystallization of 300 ps and 1 ns were achieved in the 40 nm SLL cells, respectively, both significantly faster than those observed in the Ge(2)Sb(2)Te(5) (GST) cells of the same cell size. 40 nm SLL cells were found to switch with low amorphization voltage of 0.9 V when pulse-widths of 5 ns were employed, which is much lower than the 1.6 V required by the GST cells of the same cell size. These effects can be attributed to the fast heterogeneous crystallization, low thermal conductivity and high resistivity of the SLL structures. Nanoscale PCRAM with SLL structure promises applications in high speed and low power memory devices. PMID:21572204

  14. Understanding phase-change behaviors of carbon-doped Ge₂Sb₂Te₅ for phase-change memory application.

    PubMed

    Zhou, Xilin; Xia, Mengjiao; Rao, Feng; Wu, Liangcai; Li, Xianbin; Song, Zhitang; Feng, Songlin; Sun, Hongbo

    2014-08-27

    Phase-change materials are highly promising for next-generation nonvolatile data storage technology. The pronounced effects of C doping on structural and electrical phase-change behaviors of Ge2Sb2Te5 material are investigated at the atomic level by combining experiments and ab initio molecular dynamics. C dopants are found to fundamentally affect the amorphous structure of Ge2Sb2Te5 by altering the local environments of Ge-Te tetrahedral units with stable C-C chains. The incorporated C increases the amorphous stability due to the enhanced covalent nature of the material with larger tetrahedral Ge sites. The four-membered rings with alternating atoms are reduced greatly with carbon addition, leading to sluggish phase transition and confined crystal grains. The lower RESET power is presented in the PCM cells with carbon-doped material, benefiting from its high resistivity and low thermal conductivity. PMID:25090618

  15. Evidence for thermally assisted threshold switching behavior in nanoscale phase-change memory cells

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    In spite of decades of research, the details of electrical transport in phase-change materials are still debated. In particular, the so-called threshold switching phenomenon that allows the current density to increase steeply when a sufficiently high voltage is applied is still not well understood, even though there is wide consensus that threshold switching is solely of electronic origin. However, the high thermal efficiency and fast thermal dynamics associated with nanoscale phase-change memory (PCM) devices motivate us to reassess a thermally assisted threshold switching mechanism, at least in these devices. The time/temperature dependence of the threshold switching voltage and current in doped Ge2Sb2Te5 nanoscale PCM cells was measured over 6 decades in time at temperatures ranging from 40 °C to 160 °C. We observe a nearly constant threshold switching power across this wide range of operating conditions. We also measured the transient dynamics associated with threshold switching as a function of the applied voltage. By using a field- and temperature-dependent description of the electrical transport combined with a thermal feedback, quantitative agreement with experimental data of the threshold switching dynamics was obtained using realistic physical parameters.

  16. Impact of thermoelectric phenomena on phase-change memory performance metrics and scaling.

    PubMed

    Lee, Jaeho; Asheghi, Mehdi; Goodson, Kenneth E

    2012-05-25

    The coupled transport of heat and electrical current, or thermoelectric phenomena, can strongly influence the temperature distribution and figures of merit for phase-change memory (PCM). This paper simulates PCM devices with careful attention to thermoelectric transport and the resulting impact on programming current during the reset operation. The electrothermal simulations consider Thomson heating within the phase-change material and Peltier heating at the electrode interface. Using representative values for the Thomson and Seebeck coefficients extracted from our past measurements of these properties, we predict a cell temperature increase of 44% and a decrease in the programming current of 16%. Scaling arguments indicate that the impact of thermoelectric phenomena becomes greater with smaller dimensions due to enhanced thermal confinement. This work estimates the scaling of this reduction in programming current as electrode contact areas are reduced down to 10 nm × 10 nm. Precise understanding of thermoelectric phenomena and their impact on device performance is a critical part of PCM design strategies. PMID:22543873

  17. Self-assembled incorporation of modulated block copolymer nanostructures in phase-change memory for switching power reduction.

    PubMed

    Park, Woon Ik; You, Byoung Kuk; Mun, Beom Ho; Seo, Hyeon Kook; Lee, Jeong Yong; Hosaka, Sumio; Yin, You; Ross, C A; Lee, Keon Jae; Jung, Yeon Sik

    2013-03-26

    Phase change memory (PCM), which exploits the phase change behavior of chalcogenide materials, affords tremendous advantages over conventional solid-state memory due to its nonvolatility, high speed, and scalability. However, high power consumption of PCM poses a critical challenge and has been the most significant obstacle to its widespread commercialization. Here, we present a novel approach based on the self-assembly of a block copolymer (BCP) to form a thin nanostructured SiOx layer that locally blocks the contact between a heater electrode and a phase change material. The writing current is decreased 5-fold (corresponding to a power reduction by 1/20) as the occupying area fraction of SiOx nanostructures is increased from a fill factor of 9.1% to 63.6%. Simulation results theoretically explain the current reduction mechanism by localized switching of BCP-blocked phase change materials. PMID:23451771

  18. Nanometer-scale temperature measurements of phase change memory and carbon nanomaterials

    NASA Astrophysics Data System (ADS)

    Grosse, Kyle Lane

    This work investigates nanometer-scale thermometry and thermal transport in new electronic devices to mitigate future electronic energy consumption. Nanometer-scale thermal transport is integral to electronic energy consumption and limits current electronic performance. New electronic devices are required to improve future electronic performance and energy consumption, but heat generation is not well understood in these new technologies. Thermal transport deviates significantly at the nanometer-scale from macroscopic systems as low dimensional materials, grain structure, interfaces, and thermoelectric effects can dominate electronic performance. This work develops and implements an atomic force microscopy (AFM) based nanometer-scale thermometry technique, known as scanning Joule expansion microscopy (SJEM), to measure nanometer-scale heat generation in new graphene and phase change memory (PCM) devices, which have potential to improve performance and energy consumption of future electronics. Nanometer-scale thermometry of chemical vapor deposition (CVD) grown graphene measured the heat generation at graphene wrinkles and grain boundaries (GBs). Graphene is an atomically-thin, two dimensional (2D) carbon material with promising applications in new electronic devices. Comparing measurements and predictions of CVD graphene heating predicted the resistivity, voltage drop, and temperature rise across the one dimensional (1D) GB defects. This work measured the nanometer-scale temperature rise of thin film Ge2Sb2Te5 (GST) based PCM due to Joule, thermoelectric, interface, and grain structure effects. PCM has potential to reduce energy consumption and improve performance of future electronic memory. A new nanometer-scale thermometry technique is developed for independent and direct observation of Joule and thermoelectric effects at the nanometer-scale, and the technique is demonstrated by SJEM measurements of GST devices. Uniform heating and GST properties are observed for

  19. Enhanced Performance of Phase Change Memory Cell Element by Initial Operation and Non-Cumulative Programming

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Feng; Song, Zhi-Tang; Chen, Xiao-Gang; Liu, Bo; Xu, Cheng; Feng, Gao-Ming; Wang, Liang-Yong; Zhong, Min; Feng, Song-Lin

    2010-10-01

    A phase change memory (PCM) device, based on the Ge2Sb2Te5 (GST) material, is fabricated using the standard 0.18-μm CMOS technology. After serials of detailed experiments on the phase transition behaviors, we find that the RESET process is strongly dependent on the state of the inactive area and the active area affects the SET process dramatically. By applying a 5-mA current-voltage (I — V) sweep as initial operation, we can reduce the voltage drop beyond the active area during the RESET process and the overall RESET voltage decreases from 3 V plus to 2.5 V. For the SET operation, a non-cumulative programming method is introduced to eliminate the impact of randomly formed amorphous active area, which is strongly related to the threshold switching process and SET voltage. Combining the two methods, the endurance performance of the PCM device has been remarkably improved beyond 1 × 106 cycles.

  20. Initial structure memory of pressure-induced changes in the phase-change memory alloy Ge2Sb2Te5.

    PubMed

    Krbal, M; Kolobov, A V; Haines, J; Fons, P; Levelut, C; Le Parc, R; Hanfland, M; Tominaga, J; Pradel, A; Ribes, M

    2009-09-11

    We demonstrate that while the metastable face-centered cubic (fcc) phase of Ge2Sb2Te5 becomes amorphous under hydrostatic compression at about 15 GPa, the stable trigonal phase remains crystalline. Upon higher compression, a body-centered cubic phase is obtained in both cases around 30 GPa. Upon decompression, the amorphous phase is retained for the starting fcc phase while the initial structure is recovered for the starting trigonal phase. We argue that the presence of vacancies and associated subsequent large atomic displacements lead to nanoscale phase separation and loss of initial structure memory in the fcc staring phase of Ge2Sb2Te5. PMID:19792382

  1. Impact of Ge-Sb-Te compound engineering on the set operation performance in phase-change memories

    NASA Astrophysics Data System (ADS)

    Boniardi, Mattia; Ielmini, Daniele; Tortorelli, Innocenzo; Redaelli, Andrea; Pirovano, Agostino; Allegra, Mario; Magistretti, Michele; Bresolin, Camillo; Erbetta, Davide; Modelli, Alberto; Varesi, Enrico; Pellizzer, Fabio; Lacaita, Andrea L.; Bez, Roberto

    2011-04-01

    The phase-change memory (PCM) technology is considered as one of the most attractive non-volatile memory concepts for next generation data storage. It relies on the ability of a chalcogenide material belonging to the Ge-Sb-Te compound system to reversibly change its phase between two stable states, namely the poly-crystalline low-resistive state and the amorphous high-resistive state, allowing the storage of the logical bit. A careful study of the phase-change material properties in terms of the set operation performance, the program window and the electrical switching parameters as a function of composition is very attractive in order to enlarge the possible PCM application spectrum. Concerning the set performance, a crystallization kinetics based interpretation of the observed behavior measured on different Ge-Sb-Te compounds is provided, allowing a physics-based comprehension of the reset-to-set transition.

  2. Characterization of Cu doping on GeTe for phase change memory application

    NASA Astrophysics Data System (ADS)

    Zhang, Zhonghua; Peng, Cheng; Song, Sannian; Song, Zhitang; Cheng, Yan; Ren, Kun; Li, Xiaoyun; Rao, Feng; Liu, Bo; Feng, Songlin

    2013-12-01

    In this paper, Cu-doped GeTe materials have been investigated for high-temperature phase change memory (PCM) application. Cu incorporated in GeTe increases the crystallization temperature, crystallization active energy, and band gap significantly. The incorporated Cu has effect on refining the crystal growth and brings more number of bonds in GeTe, and has remarkable effect on improving the thermal stability of GeTe. The 10-year data retention of Cu0.06(GeTe)0.94 and Cu0.13(GeTe)0.87 are 151 °C and 185 °C, which is higher than that of GeTe. PCM device based on Cu0.06(GeTe)0.94 exhibits faster switching speed than that of GeTe. In addition, Cu0.06(GeTe)0.94 shows endurance up to 2.8 × 103 cycles with an on/off ratio of two orders of magnitude.

  3. The impact of heater-recess and load matching in phase change memory mushroom cells.

    PubMed

    Cywar, Adam; Li, Jing; Lam, Chung; Silva, Helena

    2012-06-01

    Two-dimensional finite element simulations with rotational symmetry are used to analyze the impact of the bottom electrode recess on the reset operation of phase change memory elements with mushroom cell geometry (Ge2Sb2Te5 (GST) film over a patterned TiN pillar). Temperature dependent materials parameters are used for GST and TiN, and the latent heat of fusion in melting of GST is included to model melting. The results of this study indicate that a lower reset current and a more favorable thermal profile may be achieved by extending the active region of GST down into the pillar, due to the heat confinement. It is shown that the current through cells with an insufficient load condition for maximum power transfer can be maintained at a level lower than that which is sufficient for reset operation for extended periods of time due to the non-linear nature of temperature dependent electrical conductivity of GST. These results suggest that if the load condition is not matched, excessive voltage levels or pulse durations would be necessary to achieve successful reset operation across cell arrays. PMID:22571918

  4. The impact of heater-recess and load matching in phase change memory mushroom cells

    NASA Astrophysics Data System (ADS)

    Cywar, Adam; Li, Jing; Lam, Chung; Silva, Helena

    2012-06-01

    Two-dimensional finite element simulations with rotational symmetry are used to analyze the impact of the bottom electrode recess on the reset operation of phase change memory elements with mushroom cell geometry (Ge2Sb2Te5 (GST) film over a patterned TiN pillar). Temperature dependent materials parameters are used for GST and TiN, and the latent heat of fusion in melting of GST is included to model melting. The results of this study indicate that a lower reset current and a more favorable thermal profile may be achieved by extending the active region of GST down into the pillar, due to the heat confinement. It is shown that the current through cells with an insufficient load condition for maximum power transfer can be maintained at a level lower than that which is sufficient for reset operation for extended periods of time due to the non-linear nature of temperature dependent electrical conductivity of GST. These results suggest that if the load condition is not matched, excessive voltage levels or pulse durations would be necessary to achieve successful reset operation across cell arrays.

  5. Thermal conductivity measurement of amorphous dielectric multilayers for phase-change memory power reduction

    NASA Astrophysics Data System (ADS)

    Fong, S. W.; Sood, A.; Chen, L.; Kumari, N.; Asheghi, M.; Goodson, K. E.; Gibson, G. A.; Wong, H.-S. P.

    2016-07-01

    In this work, we investigate the temperature-dependent thermal conductivities of few nanometer thick alternating stacks of amorphous dielectrics, specifically SiO2/Al2O3 and SiO2/Si3N4. Experiments using steady-state Joule-heating and electrical thermometry, while using a micro-miniature refrigerator over a wide temperature range (100-500 K), show that amorphous thin-film multilayer SiO2/Si3N4 and SiO2/Al2O3 exhibit through-plane room temperature effective thermal conductivities of about 1.14 and 0.48 W/(m × K), respectively. In the case of SiO2/Al2O3, the reduced conductivity is attributed to lowered film density (7.03 → 5.44 × 1028 m-3 for SiO2 and 10.2 → 8.27 × 1028 m-3 for Al2O3) caused by atomic layer deposition of thin-films as well as a small, finite, and repeating thermal boundary resistance (TBR) of 1.5 m2 K/GW between dielectric layers. Molecular dynamics simulations reveal that vibrational mismatch between amorphous oxide layers is small, and that the TBR between layers is largely due to imperfect interfaces. Finally, the impact of using this multilayer dielectric in a dash-type phase-change memory device is studied using finite-element simulations.

  6. Influence of doping on the crystallization kinetics of Ge-Sb-Te thin films for phase-change memory application

    NASA Astrophysics Data System (ADS)

    Sherchenkov, Alexey A.; Kozyukhin, Sergey A.; Babich, Alexey V.; Shtern, Yuri I.; Mironov, Rostislav E.

    2014-12-01

    Crystallization kinetics in thin films of Ge2Sb2Te5 doped by Bi and Ti was studied. It has been shown that introduction of these impurities may have an impact on the kinetic parameters of the crystallization process. The possible recording and storage times of devices based on investigated materials were evaluated. It was shown that GST225 + 0,5 wt. % Bi has the best characteristics among the studied materials. Estimations showed that this composition can provide switching time of the phase-change memory cells less than 1 ns and it is extremely stable at room temperatures which is important for the reliable storage of information in memory cells.

  7. Three-Dimensional Multiscale Modeling of Stable Intermediate State Formation Mechanism in a Single Active Layer- Phase Change Memory Cell

    NASA Astrophysics Data System (ADS)

    Dincer, Onur; Cinar, Ibrahim; Karakas, Vedat; Aslan, Ozgur Burak; Gokce, Aisha; Stipe, Barry; Katine, Jordan A.; Aktas, Gulen; Ozatay, Ozhan

    2014-03-01

    Phase change memory (PCM) appears as a potential memory technology with its superior scalability which could be enhanced by a boost in storage density via multiple-bit per cell functionality. Given the large contrast between set and reset states of a PCM cell it is yet unclear whether it is possible to create intermediate logic states reproducibly and controllably in a device with a single active phase change layer. Here we report the results of a 3D finite element model that pinpoints the direct effect of current distribution and the indirect effect of device top contact fabrication induced defects through modification of phase change kinetics (crystallite nucleation and growth rates) on stabilization of intermediate states. A comprehensive picture of the electrical, thermal and phase change dynamics is obtained using a multiphysics approach. Our study shows that homogeneous and heterogeneous phase transition can be induced in the active region such that nonuniform temperature distribution and modification of switching dynamics with various contact shapes and sizes play a major role in the stabilization of a mixed phase state. This work has been supported by the European Commission FP7 Marie Curie IRG grant: PCM-256281 and TUBITAK grant: 113F385.

  8. Electrical performance of phase change memory cells with Ge3Sb2Te6 deposited by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Boschker, Jos E.; Boniardi, Mattia; Redaelli, Andrea; Riechert, Henning; Calarco, Raffaella

    2015-01-01

    Here, we report on the electrical characterization of phase change memory cells containing a Ge3Sb2Te6 (GST) alloy grown in its crystalline form by Molecular Beam Epitaxy (MBE). It is found that the high temperature growth on the amorphous substrate results in a polycrystalline film exhibiting a rough surface with a grain size of approximately 80-150 nm. A detailed electrical characterization has been performed, including I-V characteristic curves, programming curves, set operation performance, crystallization activation at low temperature, and resistance drift, in order to determine the material related parameters. The results indicate very good alignment of the electrical parameters with the current state-of-the-art GST, deposited by physical vapor deposition. Such alignment enables a possible employment of the MBE deposition technique for chalcogenide materials in the phase change memory technology, thus leading to future studies of as-deposited crystalline chalcogenides as integrated in electrical vehicles.

  9. A 4F2-cross-point phase change memory using nano-crystalline doped GeSbTe material

    NASA Astrophysics Data System (ADS)

    Takaura, Norikatsu; Kinoshita, Masaharu; Tai, Mitsuharu; Ohyanagi, Takasumi; Akita, Kenichi; Morikawa, Takahiro

    2015-04-01

    This paper reports on the use of nano-crystalline doped GeSbTe, or nano-GST, to fabricate a cross-point phase change memory with 4F2 cell size and test results obtained for it. We show the characteristics of a poly-Si diode select device with a high on-off ratio and data writing in a 4F2 memory cell array. The advantages of nano-GST over conventional GeSbTe are presented in terms of neighboring disturbance and 4F2 cross-point array formation. The memory cells’ high drivability, low power, and selective write and read performances are demonstrated. The scalability of the diode current density is also presented.

  10. Three dimensional finite element modeling and characterization of intermediate states in single active layer phase change memory devices

    NASA Astrophysics Data System (ADS)

    Cinar, I.; Aslan, O. B.; Gokce, A.; Dincer, O.; Karakas, V.; Stipe, B.; Katine, J. A.; Aktas, G.; Ozatay, O.

    2015-06-01

    The high contrast in the electrical resistivity between amorphous and crystalline states of a phase change material can potentially enable multiple memory levels for efficient use of a data storage medium. We report on our investigation of the role of the current injection site geometry (circular and square) in stabilizing such intermediate states within a nanoscale single-phase change material system (Ge2Sb2Te5). We have developed a three dimensional multiphysics model, which includes phase change kinetics, electrical, thermal, thermoelectric, and percolation effects, all as a function of temperature, using an iterative approach with coupled differential equations. Our model suggests that the physical origin of the formation of stable intermediate states in square top contact devices is mainly due to anisotropic heating during the application of a programming current pulse. Furthermore, the threshold current requirement and the width of the programming window are determined by crystallite nucleation and growth rates such that a higher crystallization rate leads to a narrower range of current pulses for switching to intermediate resistance level(s). The experimentally determined resistance maps, those that are indicative of the crystallinity, show good agreement with the simulated phase change behavior confirming the existence of stable intermediate states. Our model successfully predicts the required programming conditions for such mixed-phase levels, which can be used to optimize memory cells for future ultra-high density data storage applications.

  11. Coherent phonon study of (GeTe)l(Sb2Te3)m interfacial phase change memory materials

    NASA Astrophysics Data System (ADS)

    Makino, Kotaro; Saito, Yuta; Fons, Paul; Kolobov, Alexander V.; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki

    2014-10-01

    The time-resolved reflectivity measurements were carried out on the interfacial phase change memory (iPCM) materials ([(GeTe)2(Sb2Te3)4]8 and [(GeTe)2(Sb2Te3)1]20) as well as conventional Ge2Sb2Te5 alloy at room temperature and above the RESET-SET phase transition temperature. In the high-temperature phase, coherent phonons were clearly observed in the iPCM samples while drastic attenuation of coherent phonons was induced in the alloy. This difference strongly suggests the atomic rearrangement during the phase transition in iPCMs is much smaller than that in the alloy. These results are consistent with the unique phase transition model in which a quasi-one-dimensional displacement of Ge atoms occurs for iPCMs and a conventional amorphous-crystalline phase transition takes place for the alloy.

  12. Enhanced Memory Behavior in Phase-Change Nonvolatile-Memory Devices Using Multilayered Structure of Compositionally Modified Ge-Sb-Te Films

    NASA Astrophysics Data System (ADS)

    Yoon, Sung-Min; Lee, Seung-Yun; Jung, Soon-Won; Park, Young-Sam; Yu, Byoung-Gon

    2009-04-01

    A unique and novel phase-change memory device employing multilayered chalcogenide films was proposed and fabricated. In this structure, Ge18Sb39Te43, which corresponds to a 22 at. % Sb-excessive phase of typical stoichiometric Ge2Sb2Te5 (GST), was located in the middle and acted as the main operating region to exploit its superior properties, thus ensuring reliable memory operations. Thinner GST layers were inserted to above and below the middle layer. The introduction of a bottom GST layer promotes the temperature rise and the thermal insulation within the device operating volume owing to its lower thermal conductivity. The top GST layer effectively suppresses the undesirable interdiffusion between the top electrode of W and the Sb added to excess. Moreover, the upper and lower GST supplementary layers promote the initial crystallization stage during set operations owing to their higher crystallization rate compared with that of the Sb-rich phase of GST. As a result, the required current for reset, the required time for set, and the number of rewritable cycles of the proposed device with an active pore size of 0.5 ×0.5 µm2 were 6.1 mA, 80 ns, and 6.4 ×106, respectively, which are superior values compared with those for the device using a single layer of Ge18Sb39Te43. We can conclude that the proposed multilayered structure of compositionally modified GST films provides a very promising approach to enhancing all types of the memory behaviors required for the phase-change memory devices.

  13. Ge2Sb2Te5/SnSe2 nanocomposite multilayer thin films for phase change memory application

    NASA Astrophysics Data System (ADS)

    Feng, Xiaoyi; Wen, Ting; Zhai, Jiwei; Lai, Tianshu; Wang, Changzhou; Song, Sannian; Song, Zhitang

    2014-10-01

    By nanocompositing Ge2Sb2Te5 and SnSe2, the electrical and thermal proprieties of Ge2Sb2Te5/SnSe2 multilayer films for phase change random access memory (PCRAM) are better than those of Ge2Sb2Te5 films. The crystallization temperature rises and can be controlled. The resistance gap can reach approximately five orders of magnitude to ensure high data reliability. The activity energy (Ea) is more than 2.60 eV and the temperature for 10 year data retention reach 110 °C. The analysis of both XRD patterns and TEM images confirmed the reversible phase change transition between amorphous and crystalline state in Ge2Sb2Te5/SnSe2 nanocomposite multilayer films. According to transient photoreflectance traces, the speed of crystallization process was about 33 ns. Among different Ge2Sb2Te5/SnSe2 multilayer films, the film constitute of [Ge2Sb2Te5 (4 nm)/SnSe2(10 nm)]7 showed better properties and was manufactured by CMOS technology to phase change memory (PCM) cells. This result revealed that the Ge2Sb2Te5/SnSe2 nanocomposite multilayer film is a promising phase change material.

  14. Photoassisted amorphization of the phase-change memory alloy Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Fons, P.; Osawa, H.; Kolobov, A. V.; Fukaya, T.; Suzuki, M.; Uruga, T.; Kawamura, N.; Tanida, H.; Tominaga, J.

    2010-07-01

    Subnanosecond time-resolved x-ray absorption measurements have been used to probe dynamical changes in the local structure about Ge atoms in the phase-change alloy Ge2Sb2Te5 during the optical recording (amorphization) process using an optical pump and x-ray probe technique to examine the reversible phase transition from the metastable crystalline phase to the amorphous phase. We provide unambiguous evidence that the amorphization process does not proceed via the molten state but is a photoassisted process. We argue that the transition to the amorphous phase is a consequence of photoassisted destabilization of the resonant bonding present in the crystalline phase. This observation challenges the currently existing paradigm of the phase-change process which implicitly assumes the existence of the molten phase as a prerequisite for the creation of the amorphous phase. Implications from this finding are discussed, including the possibility to use the polarization of light as an extra coordinate for data recording.

  15. Cr-doped Ge2Sb2Te5 for ultra-long data retention phase change memory

    NASA Astrophysics Data System (ADS)

    Wang, Qing; Liu, Bo; Xia, Yangyang; Zheng, Yonghui; Huo, Ruru; Zhang, Qi; Song, Sannian; Cheng, Yan; Song, Zhitang; Feng, Songlin

    2015-11-01

    Phase change memory is regarded as one of the most promising candidates for the next-generation non-volatile memory. Its storage medium, phase change material, has attracted continuous exploration. Ge2Sb2Te5 (GST) is the most popular phase change material, but its thermal stability needs to be improved when used in some fields at high temperature (more than 120 °C). In this paper, we doped Cr atoms into GST and obtained Cr10(Ge2Sb2Te5)90 (labeled as Cr-GST) with high thermal stability. For Cr-GST film, the sheet resistance ratio between amorphous and crystalline states is high up to 3 orders of magnitude. The crystalline Cr-GST film inherits the phase structure of GST, with metastable face-centered cubic phase and/or stable hexagonal phase. The doped Cr atoms not only bond with other atoms but also help to improve the anti-oxidation property of Cr-GST. As for the amorphous thermal stability, the calculated temperature for 10-year-data-retention of Cr-GST film, based on the Arrhenius equation, is about 180 °C. The threshold current and threshold voltage of a cell based on Cr-GST are about 6 μA and 2.7 V. The cell could be operated by suitable voltages for more than 40 000 cycles. Thus, Cr-GST is proved to be a promising phase change material with ultra-long data retention.

  16. Performance improvement of Ge-Sb-Te material by GaSb doping for phase change memory

    NASA Astrophysics Data System (ADS)

    Lu, Yegang; Zhang, Zhonghua; Song, Sannian; Shen, Xiang; Wang, Guoxiang; Cheng, Limin; Dai, Shixun; Song, Zhitang

    2013-06-01

    Effects of GaSb doping on phase change characteristics of Ge-Sb-Te material are investigated by in situ resistance and x-ray diffraction measurement, optical spectroscopy, and x-ray photoelectron spectroscopy. The crystallization temperature and data retention of Ge-Sb-Te material increase significantly by the addition of GaSb, which results from the high thermal stability of amorphous GaSb. In addition, GaSb-doped Ge-Sb-Te material exhibits faster crystallization speed due to the change in electronic states as a result of the formation of chemical bonds with Ga element. Incorporation of GaSb is highly effective way to enhance the comprehensive performance of Ge-Sb-Te material for phase change memory.

  17. Performance improvement of Ge-Sb-Te material by GaSb doping for phase change memory

    SciTech Connect

    Lu, Yegang; Zhang, Zhonghua; Song, Sannian; Cheng, Limin; Song, Zhitang; Shen, Xiang; Wang, Guoxiang; Dai, Shixun

    2013-06-17

    Effects of GaSb doping on phase change characteristics of Ge-Sb-Te material are investigated by in situ resistance and x-ray diffraction measurement, optical spectroscopy, and x-ray photoelectron spectroscopy. The crystallization temperature and data retention of Ge-Sb-Te material increase significantly by the addition of GaSb, which results from the high thermal stability of amorphous GaSb. In addition, GaSb-doped Ge-Sb-Te material exhibits faster crystallization speed due to the change in electronic states as a result of the formation of chemical bonds with Ga element. Incorporation of GaSb is highly effective way to enhance the comprehensive performance of Ge-Sb-Te material for phase change memory.

  18. Programming Current Reduction via Enhanced Asymmetry-Induced Thermoelectric Effects in Vertical Nanopillar Phase-Change Memory Cells

    NASA Astrophysics Data System (ADS)

    Bahl, Jyotsna; Rajendran, Bipin; Muralidharan, Bhaskaran

    2015-12-01

    Thermoelectric effects are envisioned to reduce programming currents in nanopillar phase change memory cells. However, due to the inherent symmetry in such a structure, the contribution due to thermoelectric effects on programming currents is minimal. In this work, we propose a hybrid phase change memory structure which incorporates a two-fold asymmetry specifically aimed to favorably enhance thermoelectric effects. The first asymmetry is introduced via an interface layer of low thermal conductivity and high negative Seebeck coefficient, such as, polycrystalline SiGe, between the bottom electrode contact and the active region comprising the phase change material. This results in an enhanced Peltier heating of the active material. The second one is introduced structurally via a taper that results in an angle dependent Thomson heating within the active region. Various device geometries are analyzed using 2D-axis-symmetric simulations to predict the effect on programming currents as well as for different thicknesses of the interface layer. A programming current reduction of up to $60\\%$ is predicted for specific cell geometries. Remarkably, we find that due to an interplay of Thomson cooling in the electrode and the asymmetric heating profile inside the active region, the predicted programming current reduction is resilient to fabrication variability.

  19. Superlattice-like film for high data retention and high speed phase change random access memory

    NASA Astrophysics Data System (ADS)

    Li, Le; Song, Sannian; Zhang, Zhonghua; Chen, Liangliang; Song, Zhitang; Lv, Shilong; Liu, Bo; Guo, Tianqi

    2016-06-01

    Superlattice-like film (SLF) was formed alternately by Ti0.43Sb2Te3 (TST) and TiN, and TST is employed as phase change layers and TiN is employed as isolation layers of TST film. Comparing with single TST film with the same thickness, SLF owns higher data retention, higher phase change speed (5 ns) and endurance up to 1 × 105 cycles, and its power consumption of reset operation is significantly decreased by 65.2%. Two-dimensional thermal transient simulation of reset operation indicates that SLF-based device owns higher heating efficiency than 30-nm-thick TST-based device.

  20. Electrophysical properties of phase change memory materials on the pseudo-binary line GeTe-Sb2Te3

    NASA Astrophysics Data System (ADS)

    Yakubov, A. O.; Y Terekhov, D.; Sherchenkov, A. A.; Kozyuhhin, S. A.; Lazarenko, P. I.; Babich, A. V.; Timoshenkov, S. P.; Gromov, D. G.; Shuliatyev, A. S.

    2015-11-01

    The temperature dependences of the resistivity and current-voltage characteristics of amorphous thin films on the basis of GeSb4Te7, GeSb2Te4, and Ge2Sb2Te5 perspective for the phase change memory application were investigated. It was revealed that two-channel conduction mechanism with the transport of charge carriers by the localized states in the valence band tail and delocalized states of the valence band is characteristic feature of these materials.

  1. Ab Initio Molecular-Dynamics Simulation of Neuromorphic Computing in Phase-Change Memory Materials.

    PubMed

    Skelton, Jonathan M; Loke, Desmond; Lee, Taehoon; Elliott, Stephen R

    2015-07-01

    We present an in silico study of the neuromorphic-computing behavior of the prototypical phase-change material, Ge2Sb2Te5, using ab initio molecular-dynamics simulations. Stepwise changes in structural order in response to temperature pulses of varying length and duration are observed, and a good reproduction of the spike-timing-dependent plasticity observed in nanoelectronic synapses is demonstrated. Short above-melting pulses lead to instantaneous loss of structural and chemical order, followed by delayed partial recovery upon structural relaxation. We also investigate the link between structural order and electrical and optical properties. These results pave the way toward a first-principles understanding of phase-change physics beyond binary switching. PMID:26040531

  2. High thermal stability Sb{sub 3}Te-TiN{sub 2} material for phase change memory application

    SciTech Connect

    Ji, Xinglong; Zhou, Wangyang; Wu, Liangcai Zhu, Min; Rao, Feng; Song, Zhitang; Cao, Liangliang; Feng, Songlin

    2015-01-12

    For phase change memory (PCM) applications, it has been widely accepted that δ phase Sb-Te has fast operation speed and good phase stability. However, the fast growth crystallization mechanism will cause poor amorphous phase stability and overlarge grain size. We introduce TiN{sub 2} into δ phase Sb-Te (Sb{sub 3}Te) to enhance the amorphous thermal stability and refine the grain size. With TiN{sub 2} incorporating, the temperature for 10-year data retention increases from 79 °C to 124 °C. And the grain size decreases to dozens of nanometers scale. Based on X-ray photoelectron spectroscopy and transmission electron microscopy results, we knew that nitrogen atoms bond with titanium, forming disorder region at the grain boundary of Sb{sub 3}Te-TiN{sub 2} (STTN). Thus, STTN has a quite different crystallization mechanism from Sb{sub 3}Te. Furthermore, PCM device based on STTN can realize reversible phase change under 20 ns electrical pulse.

  3. Study on WSb3Te material for phase-change memory applications

    NASA Astrophysics Data System (ADS)

    Meng, Yun; Zhou, Xilin; Han, Peigao; Song, Zhitang; Wu, Liangcai; Zhu, Chengqiu; Guo, Wenjing; Xu, Ling; Ma, Zhongyuan; Song, Lianke

    2015-11-01

    The phase-change performance of WxSb3Te material were systemically investigated by in situ resistance-temperature measurement, X-ray diffraction (XRD), Raman scattering, adhesive strength test and transmission electron microscope (TEM) in this paper. Experimental results show that the thermal stability of Sb3Te was increased significantly with W doping. XRD and TEM results prove that the incorporation of W plays a role in suppressing the crystallization of Sb3Te films, causing smaller grain size. Furthermore, the adhesive strength between W electrode and phase-change material was increased obviously by W addition and a relatively rapid SET/RESET operation of 10 ns is realized with large sensing margin.

  4. Effect of Ti diffusion on the microstructure of Ge2Sb2Te5 in phase-change memory cell.

    PubMed

    Park, Jucheol; Bae, JunSoo

    2015-12-01

    The dependence of the microstructure of Ge2Sb2Te5 (GST) on Ti diffusion into GST by annealing in GST/Ti/TiN phase-change random access memory stack was studied by various transmission electron microscopy (TEM) techniques. The microstructure and crystal structure of GST were identified with high-resolution TEM (HRTEM) and image simulation technique, and the Ti diffusion into GST was revealed by scanning transmission electron microscope-energy-dispersive X-ray spectroscopy analysis. It was observed that Ti atoms of Ti/TiN thin layers were incorporated into GST cell through several thermal annealing steps and they could retard the phase transition from face-centered cubic (FCC) phase into hexagonal close-packed (HCP) phase partially and restrain the increase in grain size. Thus, it is concluded that Ti diffusion can affect the microstructure of GST including the type of the crystal phase and grain size of GST. It was shown that the insertion of diffusion barrier between TiN and GST could block Ti diffusion into GST and make it possible for FCC phase to completely transform into HCP phase. PMID:26185146

  5. Nonvolatile “AND,” “OR,” and “NOT” Boolean logic gates based on phase-change memory

    SciTech Connect

    Li, Y.; Zhong, Y. P.; Deng, Y. F.; Zhou, Y. X.; Xu, L.; Miao, X. S.

    2013-12-21

    Electronic devices or circuits that can implement both logic and memory functions are regarded as the building blocks for future massive parallel computing beyond von Neumann architecture. Here we proposed phase-change memory (PCM)-based nonvolatile logic gates capable of AND, OR, and NOT Boolean logic operations verified in SPICE simulations and circuit experiments. The logic operations are parallel computing and results can be stored directly in the states of the logic gates, facilitating the combination of computing and memory in the same circuit. These results are encouraging for ultralow-power and high-speed nonvolatile logic circuit design based on novel memory devices.

  6. Heterogeneous nanometer-scale Joule and Peltier effects in sub-25 nm thin phase change memory devices

    NASA Astrophysics Data System (ADS)

    Grosse, Kyle L.; Pop, Eric; King, William P.

    2014-09-01

    We measure heterogeneous power dissipation in phase change memory (PCM) films of 11 and 22 nm thin Ge2Sb2Te5 (GST) by scanning Joule expansion microscopy (SJEM), with sub-50 nm spatial and ˜0.2 K temperature resolution. The heterogeneous Joule and Peltier effects are explained using a finite element analysis (FEA) model with a mixture of hexagonal close-packed and face-centered cubic GST phases. Transfer length method measurements and effective media theory calculations yield the GST resistivity, GST-TiW contact resistivity, and crystal fraction of the GST films at different annealing temperatures. Further comparison of SJEM measurements and FEA modeling also predicts the thermopower of thin GST films. These measurements of nanometer-scale Joule, thermoelectric, and interface effects in PCM films could lead to energy-efficient designs of highly scaled PCM technology.

  7. Phase transformation behaviors of SiO2 doped Ge2Sb2Te5 films for application in phase change random access memory

    NASA Astrophysics Data System (ADS)

    Ryu, Seung Wook; Oh, Jin Ho; Lee, Jong Ho; Choi, Byung Joon; Kim, Won; Hong, Suk Kyoung; Hwang, Cheol Seong; Kim, Hyeong Joon

    2008-04-01

    The improvement in the phase change characteristics of Ge2Sb2Te5 (GST) films for phase change random access memory applications was investigated by doping the GST films with SiO2 using cosputtering at room temperature. As the sputtering power of SiO2 increased from 0to150W, the activation energy for crystallization increased from 2.1±0.2to3.1±0.15eV. SiO2 inhibited the crystallization of the amorphous GST films, which improved the long term stability of the metastable amorphous phase. The melting point decreased with increasing concentration of SiO2, which reduced the power consumption as well as the reset current.

  8. Ti-Sb-Te alloy: a candidate for fast and long-life phase-change memory.

    PubMed

    Xia, Mengjiao; Zhu, Min; Wang, Yuchan; Song, Zhitang; Rao, Feng; Wu, Liangcai; Cheng, Yan; Song, Sannian

    2015-04-15

    Phase-change memory (PCM) has great potential for numerous attractive applications on the premise of its high-device performances, which still need to be improved by employing a material with good overall phase-change properties. In respect to fast speed and high endurance, the Ti-Sb-Te alloy seems to be a promising candidate. Here, Ti-doped Sb2Te3 (TST) materials with different Ti concentrations have been systematically studied with the goal of finding the most suitable composition for PCM applications. The thermal stability of TST is improved dramatically with increasing Ti content. The small density change of T0.32Sb2Te3 (2.24%), further reduced to 1.37% for T0.56Sb2Te3, would greatly avoid the voids generated at phase-change layer/electrode interface in a PCM device. Meanwhile, the exponentially diminished grain size (from ∼200 nm to ∼12 nm), resulting from doping more and more Ti, enhances the adhesion between phase-change film and substrate. Tests of TST-based PCM cells have demonstrated a fast switching rate of ∼10 ns. Furthermore, because of the lower thermal conductivities of TST materials, compared with Sb2Te3-based PCM cells, T0.32Sb2Te3-based ones exhibit lower required pulse voltages for Reset operation, which largely decreases by ∼50% for T0.43Sb2Te3-based ones. Nevertheless, the operation voltages for T0.56Sb2Te3-based cells dramatically increase, which may be due to the phase separation after doping excessive Ti. Finally, considering the decreased resistance ratio, TixSb2Te3 alloy with x around 0.43 is proved to be a highly promising candidate for fast and long-life PCM applications. PMID:25805549

  9. Investigation of electromigration in In{sub 2}Se{sub 3} nanowire for phase change memory devices

    SciTech Connect

    Kang, Daegun; Rim, Taiuk; Baek, Chang-Ki; Meyyappan, M.; Lee, Jeong-Soo

    2013-12-02

    The decomposition of In{sub 2}Se{sub 3} nanowire phase change memory devices during current-driving operation was investigated. The devices were subjected to thermal/electrical stress with current density and electric field during the reset operation at 0.24–0.38 MA/cm{sup 2} and 5.3–6.4 kV/cm, respectively. After multiple operation cycles, a change in morphology and composition of the In{sub 2}Se{sub 3} nanowire was observed and led to the device failure. The transmission electron microscopy and energy dispersive analysis indicate that electromigration causes the catastrophic failure by void formation where In atoms migrate toward the cathode and Se atoms migrate toward the anode depending on their electronegativities.

  10. Sub 10 ns fast switching and resistance control in lateral GeTe-based phase-change memory

    NASA Astrophysics Data System (ADS)

    Yin, You; Zhang, Yulong; Takehana, Yousuke; Kobayashi, Ryota; Zhang, Hui; Hosaka, Sumio

    2016-06-01

    In this study, we investigated the fast switching and resistance control in a lateral GeTe-based phase-change memory (PCM). The resistivity of GeTe as a function of annealing temperature showed that it changed by more than 6 orders of magnitude in a very narrow temperature range. X-ray diffraction patterns of GeTe films indicated that GeTe had only one crystal structure, that is, face-centered cubic. It was demonstrated that the lateral device with a top conducting layer had a good performance. The operation characteristics of the GeTe-based lateral PCM device showed that it could be operated even when sub-10-ns voltage pulses were applied, making it much faster than a Ge2Sb2Te5-based device. The device resistance was successfully controlled by applying a staircase-like pulse, which enables the device to be used for fast multilevel storage.

  11. Phase change memory devices formed by using 2 dimensional layered Graphene-In2 Se3 van der Waals heterostructure

    NASA Astrophysics Data System (ADS)

    Choi, Min Sup; Yang, Chenxi; Ra, Chang Ho; Yoo, Won Jong

    Indium selenide (In2Se3) is one of the unique materials which have both a layered structure and phase change property. One of the advantages of using 2 dimensional (2D) materials is their potential to form van der Waals heterostructures which enable unique physical properties and novel quantum device functions, which cannot be achieved in 2D material alone. In this study, we fabricated vertically stacked graphene-In2Se3 heterostructured memory devices. The fabricated devices showed a rapid increase of current conduction, which is attributed to the phase transition of In2Se3. The TEM images demonstrated that In2Se3 transformed from polycrystalline to layered structure thanks to the effective thermal confinement effect between graphene and In2Se3, attributed to the low thermal conductivity of layered materials in vertical direction. In addition, the current conduction could be controlled effectively by applying different pulse voltages, showing stable retention and endurance characteristics. It is thought that the differently bonded states contribute to this control process. This study demonstrates the possibility of Graphene-In2Se3 van der Waals heterostructure as 2D based future memory electronics. This work was supported by the National Research Foundation of Korea(NRF) Grant funded by the Korea government(MEST) (No. 2013R1A2A2A01015516).

  12. Phase-change memory technology with self-aligned μTrench cell architecture for 90 nm node and beyond

    NASA Astrophysics Data System (ADS)

    Pirovano, A.; Pellizzer, F.; Tortorelli, I.; Riganó, A.; Harrigan, R.; Magistretti, M.; Petruzza, P.; Varesi, E.; Redaelli, A.; Erbetta, D.; Marangon, T.; Bedeschi, F.; Fackenthal, R.; Atwood, G.; Bez, R.

    2008-09-01

    A novel self-aligned μTrench-based cell architecture for phase change memory (PCM) process is presented. The low programming current and the good dimensional control of the sub-lithographic features achieved with the μTrench structure are combined with a self-aligned patterning strategy that simplify the integration process in term of alignment tolerances and of number of critical masks. The proposed architecture has been integrated in a 90 nm 128 Mb vehicle based on a pnp bipolar junction transistor for the array selection. The good active and leakage currents achieved by the purposely optimized selecting transistors combined with programming currents of 300 μA of the storage element and good distributions measured on the 128 Mb array demonstrate the suitability of the proposed architecture for the production of high-density PCM arrays at 90 nm and beyond.

  13. Ge2Sb2Te5/Sb superlattice-like thin film for high speed phase change memory application

    NASA Astrophysics Data System (ADS)

    Hu, Yifeng; Zou, Hua; Zhang, Jianhao; Xue, Jianzhong; Sui, Yongxing; Wu, Weihua; Yuan, Li; Zhu, Xiaoqin; Song, Sannian; Song, Zhitang

    2015-12-01

    In order to improve the operation speed of phase change memory (PCM), superlattice-like Ge2Sb2Te5/Sb (SLL GST/Sb) thin films were prepared in a sputtering method to explore the suitability as an active material for PCM application. Compared with GST, SLL GST/Sb thin film has a lower crystallization temperature, crystallization activation energy, thermal conductivity, and smaller crystalline grain size. A faster SET/RESET switching speed (10 ns) and a lower operation power consumption (the energy for RESET operation 9.1 × 10-13 J) are obtained. In addition, GST/Sb shows a good endurance of 8.3 × 104 cycles.

  14. Improved thermal stability of N-doped Sb materials for high-speed phase change memory application

    NASA Astrophysics Data System (ADS)

    Hu, Yifeng; Zhu, Xiaoqin; Zou, Hua; Zhang, Jianhao; Yuan, Li; Xue, Jianzhong; Sui, Yongxing; Wu, Weihua; Song, Sannian; Song, Zhitang

    2016-05-01

    Compared with pure Sb, N-doped Sb material was proved to be a promising candidate for the phase change memory (PCM) use because of its higher crystallization temperature (˜250 °C), larger crystallization activation energy (3.53 eV), and better data retention ability (166 °C for 10 years). N-doping also broadened the band gap and refined grain size. The reversible resistance transition could be achieved by an electric pulse as short as 8 ns for the PCM cell based on N-doped Sb material. A lower operation power consumption (the energy for RESET operation 2.2 × 10-12 J) was obtained. In addition, N-doped Sb material showed a good endurance of 1.8 × 105 cycles.

  15. Hybrid density functional study of electronic and optical properties of phase change memory material: Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Kaewmaraya, T.; Ramzan, M.; Löfâs, H.; Ahuja, Rajeev

    2013-01-01

    In this article, we use hybrid density functional (HSE06) to study the crystal and electronic structures and optical properties of well known phase change memory material Ge2Sb2Te5. We calculate the structural parameters, band gaps, and dielectric functions of three stable structures of this material. We also analyze the electron charge distribution using the Bader's theory of charge analysis. We find that hybrid density functional slightly overestimates the value of "c" parameter. However, overall, our results calculated with the use of hybrid density functional (HSE06) are very close to available experimental values than calculated with the use of Perdew Burke-Ernzerhof functional. Specifically, the electronic band gap values of this material calculated with HSE06 are in good agreement with the available experimental data in the literature. Furthermore, we perform the charge analysis and find that naive ionic model fails to explain the charge distribution between the constituent atoms, showing the complex nature of this compound.

  16. Ge-doped GaSb thin films with zero mass density change upon crystallization for applications in phase change memories

    NASA Astrophysics Data System (ADS)

    Putero, Magali; Coulet, Marie-Vanessa; Muller, Christophe; Baehtz, Carsten; Raoux, Simone; Cheng, Huai-Yu

    2016-03-01

    In order to optimize materials for phase change random access memories (PCRAM), the effect of Ge doping on Ga-Sb alloy crystallization was studied using combined in situ synchrotron x-ray techniques, electrical measurements, and static laser testing. The present data emphasize that the crystallization temperature can be increased up to 390 °C with subsequent higher thermal stability of the amorphous phase; phase segregation is evidenced with GaSb, Sb, and Ge phases that crystallize in a two-step crystallization process. The Ge-doped GaSb films exhibit a larger electrical contrast as compared to undoped GaSb alloy (up to ×100). The optical contrast measured by laser testing is shown to follow the mass density change variations upon crystallization, with a negative contrast (higher value in amorphous state) whatever Ge-doping levels. In situ x-ray reflectivity measurements show that zero mass density change can be achieved by low Ge-doping. Ge-doped GaSb alloys look promising since a phase change material with zero mass density change and higher crystallization temperature satisfactorily fulfills the specifications for reliable PCRAM cells in terms of endurance and data retention.

  17. Reduction of RESET current in phase change memory devices by carbon doping in GeSbTe films

    NASA Astrophysics Data System (ADS)

    Park, J. H.; Kim, S.-W.; Kim, J. H.; Wu, Z.; Cho, S. L.; Ahn, D.; Ahn, D. H.; Lee, J. M.; Nam, S. U.; Ko, D.-H.

    2015-03-01

    Phase Change Memory (PCM) has been proposed for use as a substitute for flash memory to satisfy the huge demands for high performance and reliability that promise to come in the next generation. In spite of its high scalability, reliability, and simple structure, high writing current, e.g., RESET current, has been a significant obstacle to achieving a high density in storage applications and the low power consumption required for use in mobile applications. We report herein on an attempt to determine the level of carbon incorporated into a GeSbTe (GST) film that is needed to reduce the RESET current of PCM devices. The crystal structure of the film was transformed into an amorphous phase by carbon doping, the stability of which was enhanced with increasing carbon content. This was verified by the small grain size and large band gap that are typically associated with carbon. The increased level of C-Ge covalent bonding is responsible for these enhancements. Thus, the resistance of the carbon doped Ge2Sb2Te5 film was higher than that for an undoped GST film by a factor of 2 orders of magnitude after producing a stable face-centered cubic phase by annealing. As a consequence, the PCM devices showed a significant reduction in RESET current as low as 23% when the carbon content was increased to 11.8 at. %. This can be attributed to the elevated SET resistance, which is proportional to the dynamic resistance of the PCM device, caused by the high resistance due to a carbon doped GST film.

  18. Low Power Phase Change Memory using Silicon Carbide as a Heater Layer

    NASA Astrophysics Data System (ADS)

    Aziz, M. S.; Yin, Y.; Hosaka, S.; Mohammed, Z.; Alip, R. I.

    2015-11-01

    The amorphous to crystalline transition of germanium-antimony-tellurium (GST) using two types heating element was investigated. With separate heater structure, simulation was done using COMSOL Multiphysic 5.0. Silicon carbide (SiC) and Titanium Sitride (TiSi3) has been selected as a heater and differences of them have been studied. The voltage boundary is 0.905V and temperature of the memory layer is 463K when using SIC as a heater. While the voltage boundary and temperature of memory layer when using TiSi3 are 1.103 V and 459K respectively. Based on the result of a simulation, the suitable material of heater layer for separate heater structure is Silicon carbide (SiC) compared with Titanium Sitride (TiSi3).

  19. Correlative transmission electron microscopy and electrical properties study of switchable phase-change random access memory line cells

    SciTech Connect

    Oosthoek, J. L. M.; Kooi, B. J.; Voogt, F. C.; Attenborough, K.; Verheijen, M. A.; Hurkx, G. A. M.; Gravesteijn, D. J.

    2015-02-14

    Phase-change memory line cells, where the active material has a thickness of 15 nm, were prepared for transmission electron microscopy (TEM) observation such that they still could be switched and characterized electrically after the preparation. The result of these observations in comparison with detailed electrical characterization showed (i) normal behavior for relatively long amorphous marks, resulting in a hyperbolic dependence between SET resistance and SET current, indicating a switching mechanism based on initially long and thin nanoscale crystalline filaments which thicken gradually, and (ii) anomalous behavior, which holds for relatively short amorphous marks, where initially directly a massive crystalline filament is formed that consumes most of the width of the amorphous mark only leaving minor residual amorphous regions at its edges. The present results demonstrate that even in (purposely) thick TEM samples, the TEM sample preparation hampers the probability to observe normal behavior and it can be debated whether it is possible to produce electrically switchable TEM specimen in which the memory cells behave the same as in their original bulk embedded state.

  20. TixSb2Te Thin Films for Phase Change Memory Applications

    NASA Astrophysics Data System (ADS)

    Tang, Shi-Yu; Li, Run; Ou, Xin; Xu, Han-Ni; Xia, Yi-Dong; Yin, Jiang; Liu, Zhi-Guo

    2014-07-01

    Sb2Te films with different Ti contents (TixSb2Te) are derived via the target-attachment method by using the magnetron sputtering technique. The effects of the Ti content on the phase change characteristics and the microstructures are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy and atom force microcopy. Resistance-temperature measurements are carried out to reveal the enhanced crystallization temperature of TixSb2Te films, indicating a better thermal stability in such films. Both the activation energy and the temperature for 10 y data retention increase with increasing the concentration of Ti. It indicates that the crystallization of the amorphous Sb2Te film could be suppressed by the introduction of Ti. The improvement of crystallization temperature and the thermal stability of the amorphous Sb2Te film results from the introduction of Ti in Sb-Te bond that decreases the binding energy of Sb 4d and Te 4d.

  1. Simulation of crystallization in Ge2Sb2Te5: A memory effect in the canonical phase-change material

    NASA Astrophysics Data System (ADS)

    Kalikka, J.; Akola, J.; Jones, R. O.

    2014-11-01

    Crystallization of amorphous Ge2Sb2Te5 (GST) has been studied using four extensive (460 atoms, up to 4 ns) density functional/molecular dynamics simulations at 600 K. This phase change material is a rare system where crystallization can be simulated without adjustable parameters over the physical time scale, and the results could provide insight into order-disorder processes in general. Crystallization is accompanied by an increase in the number of A B A B squares (A :Ge,Sb;B :Te), percolation, and the occurrence of low-frequency localized vibration modes. A sample with a history of order crystallizes completely in 1.2 ns, but ordering in others was less complete, even after 4 ns. The amorphous starting structures without memory display phases (>1 ns) with subcritical nuclei (10-50 atoms) ranging from nearly cubical blocks to stringlike configurations of A B A B squares and A B bonds extending across the cell. Percolation initiates the rapid phase of crystallization and is coupled to the directional p -type bonding in metastable GST. Cavities play a crucial role, and the final ordered structure is distorted rock salt with a face-centered cubic sublattice containing predominantly Te atoms. We comment on earlier models based on smaller and much shorter simulations.

  2. Phase-Change Memory Properties of Electrodeposited Ge-Sb-Te Thin Film

    NASA Astrophysics Data System (ADS)

    Huang, Ruomeng; Kissling, Gabriela P.; Jolleys, Andrew; Bartlett, Philip N.; Hector, Andrew L.; Levason, William; Reid, Gillian; De Groot, C. H. `Kees'

    2015-11-01

    We report the properties of a series of electrodeposited Ge-Sb-Te alloys with various compositions. It is shown that the Sb/Ge ratio can be varied in a controlled way by changing the electrodeposition potential. This method opens up the prospect of depositing Ge-Sb-Te super-lattice structures by electrodeposition. Material and electrical characteristics of various compositions have been investigated in detail, showing up to three orders of magnitude resistance ratio between the amorphous and crystalline states and endurance up to 1000 cycles.

  3. Phase-Change Memory Properties of Electrodeposited Ge-Sb-Te Thin Film.

    PubMed

    Huang, Ruomeng; Kissling, Gabriela P; Jolleys, Andrew; Bartlett, Philip N; Hector, Andrew L; Levason, William; Reid, Gillian; De Groot, C H 'Kees'

    2015-12-01

    We report the properties of a series of electrodeposited Ge-Sb-Te alloys with various compositions. It is shown that the Sb/Ge ratio can be varied in a controlled way by changing the electrodeposition potential. This method opens up the prospect of depositing Ge-Sb-Te super-lattice structures by electrodeposition. Material and electrical characteristics of various compositions have been investigated in detail, showing up to three orders of magnitude resistance ratio between the amorphous and crystalline states and endurance up to 1000 cycles. PMID:26525703

  4. Anisotropic lattice response induced by a linearly-polarized femtosecond optical pulse excitation in interfacial phase change memory material

    PubMed Central

    Makino, Kotaro; Saito, Yuta; Fons, Paul; Kolobov, Alexander V.; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki

    2016-01-01

    Optical excitation of matter with linearly-polarized femtosecond pulses creates a transient non-equilibrium lattice displacement along a certain direction. Here, the pump and probe pulse polarization dependence of the photo-induced ultrafast lattice dynamics in (GeTe)2/(Sb2Te3)4 interfacial phase change memory material is investigated under obliquely incident conditions. Drastic pump polarization dependence of the coherent phonon amplitude is observed when the probe polarization angle is parallel to the c–axis of the sample, while the pump polarization dependence is negligible when the probe polarization angle is perpendicular to the c–axis. The enhancement of phonon oscillation amplitude due to pump polarization rotation for a specific probe polarization angle is only found in the early time stage (≤2 ps). These results indicate that the origin of the pump and probe polarization dependence is dominantly attributable to the anisotropically-formed photo-excited carriers which cause the directional lattice dynamics. PMID:26805401

  5. Hysteretic melting and freezing of nanoscale indium islands using local thermal cycling for phase-change memory nodes

    NASA Astrophysics Data System (ADS)

    Brintlinger, Todd; Hussain Baloch, Kamal; Qi, Yi; Cullen, William G.; Goldhaber-Gordon, David; Cumings, John

    2007-03-01

    Using a transmission electron microscope (TEM) operating in dark-field mode, the melting and freezing transition in nanoscale (approximately 20-200nm diameter) metal islands can be imaged at video rates (33ms/frame). The metal, typically indium, islands are thermally evaporated on one side of a 100nm thick SiN membrane. Local thermal gradients produced by Joule heating of lithographically defined electrodes on the opposite side of the membrane show a hysteretic effect in the melting/freezing of the metal islands. Read and write cycles are accomplished with 5-10 microW power, while a quiescent power of 80-100 microW is required to keep an island near its melting point. The hysteresis indicates a finite nucleation energy during freezing of individual islands. While TEM is not a practical readout mechanism, the behavior suggests a type of phase-change memory node on an inherently nanometer scale. Results for all the aforementioned will be shown, including micrographs, video, and related discussion.

  6. Nanometer-scale temperature imaging for independent observation of Joule and Peltier effects in phase change memory devices

    SciTech Connect

    Grosse, Kyle L.; Pop, Eric; King, William P.

    2014-09-15

    This paper reports a technique for independent observation of nanometer-scale Joule heating and thermoelectric effects, using atomic force microscopy (AFM) based measurements of nanometer-scale temperature fields. When electrical current flows through nanoscale devices and contacts the temperature distribution is governed by both Joule and thermoelectric effects. When the device is driven by an electrical current that is both periodic and bipolar, the temperature rise due to the Joule effect is at a different harmonic than the temperature rise due to the Peltier effect. An AFM tip scanning over the device can simultaneously measure all of the relevant harmonic responses, such that the Joule effect and the Peltier effect can be independently measured. Here we demonstrate the efficacy of the technique by measuring Joule and Peltier effects in phase change memory devices. By comparing the observed temperature responses of these working devices, we measure the device thermopower, which is in the range of 30 ± 3 to 250 ± 10 μV K{sup −1}. This technique could facilitate improved measurements of thermoelectric phenomena and properties at the nanometer-scale.

  7. Anisotropic lattice response induced by a linearly-polarized femtosecond optical pulse excitation in interfacial phase change memory material.

    PubMed

    Makino, Kotaro; Saito, Yuta; Fons, Paul; Kolobov, Alexander V; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki

    2016-01-01

    Optical excitation of matter with linearly-polarized femtosecond pulses creates a transient non-equilibrium lattice displacement along a certain direction. Here, the pump and probe pulse polarization dependence of the photo-induced ultrafast lattice dynamics in (GeTe)2/(Sb2Te3)4 interfacial phase change memory material is investigated under obliquely incident conditions. Drastic pump polarization dependence of the coherent phonon amplitude is observed when the probe polarization angle is parallel to the c-axis of the sample, while the pump polarization dependence is negligible when the probe polarization angle is perpendicular to the c-axis. The enhancement of phonon oscillation amplitude due to pump polarization rotation for a specific probe polarization angle is only found in the early time stage (≤2 ps). These results indicate that the origin of the pump and probe polarization dependence is dominantly attributable to the anisotropically-formed photo-excited carriers which cause the directional lattice dynamics. PMID:26805401

  8. Three-Dimensional Numerical Simulation of Phase-Change Memory Cell with Probe like Bottom Electrode Structure

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Song, Zhitang; Ling, Yun; Gong, Yuefeng; Feng, Songlin

    2009-02-01

    A new device structure of phase-change memory (PCM) cell with a Probe like bottom electrode (PBE) was proposed and its electrical-thermal characteristics were investigated by three-dimensional finite element analysis. The programming region of the definition (GST) layer in the PBE cell is much smaller than that in a conventional normal-bottom-contact (NBC) cell after the RESET operation. The high concentrations of electric-field density and electric-current density in the small programming region of GST layer in the PBE cell have the advantages of reducing the power consumption and increasing the heating efficiency of PCM devices. Compared with the NBC cell, the RESET threshold current of the PBE cell is reduced from 1.2 to 0.45 mA and the heating efficiency increases from 28.7 to 44.1%. Therefore, the lower programming current, the smaller molten region of GST and the higher heating efficiency in the PBE cell will be propitious for developing the PCM with low power consumption and high integration density.

  9. Anisotropic lattice response induced by a linearly-polarized femtosecond optical pulse excitation in interfacial phase change memory material

    NASA Astrophysics Data System (ADS)

    Makino, Kotaro; Saito, Yuta; Fons, Paul; Kolobov, Alexander V.; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki

    2016-01-01

    Optical excitation of matter with linearly-polarized femtosecond pulses creates a transient non-equilibrium lattice displacement along a certain direction. Here, the pump and probe pulse polarization dependence of the photo-induced ultrafast lattice dynamics in (GeTe)2/(Sb2Te3)4 interfacial phase change memory material is investigated under obliquely incident conditions. Drastic pump polarization dependence of the coherent phonon amplitude is observed when the probe polarization angle is parallel to the c-axis of the sample, while the pump polarization dependence is negligible when the probe polarization angle is perpendicular to the c-axis. The enhancement of phonon oscillation amplitude due to pump polarization rotation for a specific probe polarization angle is only found in the early time stage (≤2 ps). These results indicate that the origin of the pump and probe polarization dependence is dominantly attributable to the anisotropically-formed photo-excited carriers which cause the directional lattice dynamics.

  10. The effect of oxygen plasma ashing on the resistance of TiN bottom electrode for phase change memory

    NASA Astrophysics Data System (ADS)

    Dan, Gao; Bo, Liu; Ying, Li; Zhitang, Song; Wanchun, Ren; Juntao, Li; Zhen, Xu; Shilong, Lü; Nanfei, Zhu; Jiadong, Ren; Yipeng, Zhan; Hanming, Wu; Songlin, Feng

    2015-05-01

    Phase change memory (PCM) has been regarded as a promising candidate for the next generation of nonvolatile memory. To decrease the power required to reset the PCM cell, titanium nitride (TiN) is preferred to be used as the bottom electrode of PCM due to its low thermal and suitable electrical conductivity. However, during the manufacture of PCM cell in 40 nm process node, abnormally high and discrete distribution of the resistance of TiN bottom electrode was found, which might be induced by the surface oxidation of TiN bottom electrode during the photoresist ashing process by oxygen plasma. In this work, we have studied the oxidation of TiN and found that with the increasing oxygen plasma ashing time, the thickness of the TiO2 layer became thicker and the state of the TiO2 layer changed from amorphous to crystalline, respectively. The resistance of TiN electrode contact chain with 4-5 nm TiO2 layer was confirmed to be almost three-orders of magnitude higher than that of pure TiN electrode, which led to the failure issue of PCM cell. We efficiently removed the oxidation TiO2 layer by a chemical mechanical polishing (CMP) process, and we eventually recovered the resistance of TiN bottom electrode from 1 × 105 Ω/via back to 6 × 102 Ω/via and successfully achieved a uniform resistance distribution of the TiN bottom electrode. Project supported by the National Key Basic Research Program of China (Nos. 2010CB934300, 2013CBA01900, 2011CBA00607, 2011CB932804), the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA09020402), the National Integrate Circuit Research Program of China (No. 2009ZX02023-003), the National Natural Science Foundation of China (Nos. 61176122, 61106001, 61261160500, 61376006), and the Science and Technology Council of Shanghai (Nos. 12nm0503701, 13DZ2295700, 12QA1403900, 13ZR1447200).

  11. Pressure tunes electrical resistivity by four orders of magnitude in amorphous Ge2Sb2Te5 phase-change memory alloy.

    PubMed

    Xu, M; Cheng, Y Q; Wang, L; Sheng, H W; Meng, Y; Yang, W G; Han, X D; Ma, E

    2012-05-01

    Ge-Sb-Te-based phase-change memory is one of the most promising candidates to succeed the current flash memories. The application of phase-change materials for data storage and memory devices takes advantage of the fast phase transition (on the order of nanoseconds) and the large property contrasts (e.g., several orders of magnitude difference in electrical resistivity) between the amorphous and the crystalline states. Despite the importance of Ge-Sb-Te alloys and the intense research they have received, the possible phases in the temperature-pressure diagram, as well as the corresponding structure-property correlations, remain to be systematically explored. In this study, by subjecting the amorphous Ge(2)Sb(2)Te(5) (a-GST) to hydrostatic-like pressure (P), the thermodynamic variable alternative to temperature, we are able to tune its electrical resistivity by several orders of magnitude, similar to the resistivity contrast corresponding to the usually investigated amorphous-to-crystalline (a-GST to rock-salt GST) transition used in current phase-change memories. In particular, the electrical resistivity drops precipitously in the P = 0 to 8 GPa regime. A prominent structural signature representing the underlying evolution in atomic arrangements and bonding in this pressure regime, as revealed by the ab initio molecular dynamics simulations, is the reduction of low-electron-density regions, which contributes to the narrowing of band gap and delocalization of trapped electrons. At P > 8 GPa, we have observed major changes of the average local structures (bond angle and coordination numbers), gradually transforming the a-GST into a high-density, metallic-like state. This high-pressure glass is characterized by local motifs that bear similarities to the body-centered-cubic GST (bcc-GST) it eventually crystallizes into at 28 GPa, and hence represents a bcc-type polyamorph of a-GST. PMID:22509004

  12. Pressure tunes electrical resistivity by four orders of magnitude in amorphous Ge[subscript 2]Sb[subscript 2]Te[subscript 5] phase-change memory alloy

    SciTech Connect

    Xu, M.; Cheng, Y.Q.; Wang, L.; Sheng, H.W.; Meng, Y.; Yang, W.G.; Hang, X.D.; Ma, E.

    2012-05-22

    Ge-Sb-Te-based phase-change memory is one of the most promising candidates to succeed the current flash memories. The application of phase-change materials for data storage and memory devices takes advantage of the fast phase transition (on the order of nanoseconds) and the large property contrasts (e.g., several orders of magnitude difference in electrical resistivity) between the amorphous and the crystalline states. Despite the importance of Ge-Sb-Te alloys and the intense research they have received, the possible phases in the temperature-pressure diagram, as well as the corresponding structure-property correlations, remain to be systematically explored. In this study, by subjecting the amorphous Ge{sub 2}Sb{sub 2}Te{sub 5} (a-GST) to hydrostatic-like pressure (P), the thermodynamic variable alternative to temperature, we are able to tune its electrical resistivity by several orders of magnitude, similar to the resistivity contrast corresponding to the usually investigated amorphous-to-crystalline (a-GST to rock-salt GST) transition used in current phase-change memories. In particular, the electrical resistivity drops precipitously in the P = 0 to 8 GPa regime. A prominent structural signature representing the underlying evolution in atomic arrangements and bonding in this pressure regime, as revealed by the ab initio molecular dynamics simulations, is the reduction of low-electron-density regions, which contributes to the narrowing of band gap and delocalization of trapped electrons. At P > 8 GPa, we have observed major changes of the average local structures (bond angle and coordination numbers), gradually transforming the a-GST into a high-density, metallic-like state. This high-pressure glass is characterized by local motifs that bear similarities to the body-centered-cubic GST (bcc-GST) it eventually crystallizes into at 28 GPa, and hence represents a bcc-type polyamorph of a-GST.

  13. Logic gates realized by nonvolatile GeTe/Sb2Te3 super lattice phase-change memory with a magnetic field input

    NASA Astrophysics Data System (ADS)

    Lu, Bin; Cheng, Xiaomin; Feng, Jinlong; Guan, Xiawei; Miao, Xiangshui

    2016-07-01

    Nonvolatile memory devices or circuits that can implement both storage and calculation are a crucial requirement for the efficiency improvement of modern computer. In this work, we realize logic functions by using [GeTe/Sb2Te3]n super lattice phase change memory (PCM) cell in which higher threshold voltage is needed for phase change with a magnetic field applied. First, the [GeTe/Sb2Te3]n super lattice cells were fabricated and the R-V curve was measured. Then we designed the logic circuits with the super lattice PCM cell verified by HSPICE simulation and experiments. Seven basic logic functions are first demonstrated in this letter; then several multi-input logic gates are presented. The proposed logic devices offer the advantages of simple structures and low power consumption, indicating that the super lattice PCM has the potential in the future nonvolatile central processing unit design, facilitating the development of massive parallel computing architecture.

  14. Performance improvement of phase-change memory cell using AlSb3Te and atomic layer deposition TiO2 buffer layer

    PubMed Central

    2013-01-01

    A phase change memory (PCM) cell with atomic layer deposition titanium dioxide bottom heating layer is investigated. The crystalline titanium dioxide heating layer promotes the temperature rise in the AlSb3Te layer which causes the reduction in the reset voltage compared to a conventional phase change memory cell. The improvement in thermal efficiency of the PCM cell mainly originates from the low thermal conductivity of the crystalline titanium dioxide material. Among the various thicknesses of the TiO2 buffer layer, 4 nm was the most appropriate thickness that maximized the improvement with negligible sacrifice of the other device performances, such as the reset/set resistance ratio, voltage window, and endurance. PMID:23414571

  15. Role of the nano amorphous interface in the crystallization of Sb2Te3 towards non-volatile phase change memory: insights from first principles.

    PubMed

    Wang, Xue-Peng; Chen, Nian-Ke; Li, Xian-Bin; Cheng, Yan; Liu, X Q; Xia, Meng-Jiao; Song, Z T; Han, X D; Zhang, S B; Sun, Hong-Bo

    2014-06-14

    The nano amorphous interface is important as it controls the phase transition for data storage. Yet, atomic scale insights into such kinds of systems are still rare. By first-principles calculations, we obtain the atomic interface between amorphous Si and amorphous Sb2Te3, which prevails in the series of Si-Sb-Te phase change materials. This interface model reproduces the experiment-consistent phenomena, i.e. the amorphous stability of Sb2Te3, which defines the data retention in phase change memory, and is greatly enhanced by the nano interface. More importantly, this method offers a direct platform to explore the intrinsic mechanism to understand the material function: (1) by steric effects through the atomic "channel" of the amorphous interface, the arrangement of the Te network is significantly distorted and is separated from the p-orbital bond angle in the conventional phase-change material; and (2) through the electronic "channel" of the amorphous interface, high localized electrons in the form of a lone pair are "projected" to Sb2Te3 from amorphous Si by a proximity effect. These factors set an effective barrier for crystallization and improve the amorphous stability, and thus data retention. The present research and scheme sheds new light on the engineering and manipulation of other key amorphous interfaces, such as Si3N4/Ge2Sb2Te5 and C/Sb2Te3, through first-principles calculations towards non-volatile phase change memory. PMID:24759902

  16. SiO2 doped Ge2Sb2Te5 thin films with high thermal efficiency for applications in phase change random access memory.

    PubMed

    Ryu, Seung Wook; Lyeo, Ho-Ki; Lee, Jong Ho; Ahn, Young Bae; Kim, Gun Hwan; Kim, Choon Hwan; Kim, Soo Gil; Lee, Se-Ho; Kim, Ka Young; Kim, Jong Hyeop; Kim, Won; Hwang, Cheol Seong; Kim, Hyeong Joon

    2011-06-24

    This study examined the various physical, structural and electrical properties of SiO(2) doped Ge(2)Sb(2)Te(5) (SGST) films for phase change random access memory applications. Interestingly, SGST had a layered structure (LS) resulting from the inhomogeneous distribution of SiO(2) after annealing. The physical parameters able to affect the reset current of phase change memory (I(res)) were predicted from the Joule heating and heat conservation equations. When SiO(2) was doped into GST, thermal conductivity largely decreased by ∼ 55%. The influence of SiO(2)-doping on I(res) was examined using the test phase change memory cell. I(res) was reduced by ∼ 45%. An electro-thermal simulation showed that the reduced thermal conductivity contributes to the improvement of cell efficiency as well as the reduction of I(res), while the increased dynamic resistance contributes only to the latter. The formation and presence of the LS thermal conductivity in the set state test cell after repeated switching was confirmed. PMID:21572208

  17. Electrical properties of the Ge2Sb2Te5 thin films for phase change memory application

    NASA Astrophysics Data System (ADS)

    Lazarenko, P. I.; Sherchenkov, A. A.; Kozyukhin, S. A.; Babich, A. V.; Timoshenkov, S. P.; Gromov, D. G.; Shuliatyev, A. S.; Redichev, E. N.

    2016-04-01

    In this study I-V characteristic, temperature dependence of resistivity, thermopower, switching and memory effect were investigated for GST225 thin films. Resistivities, ratio of the resistivities of amorphous and crystalline states, activation energies of conductivity, temperature of phase transition, Seebeck coefficient, transition time due to the transformation from OFF to ON states and full recording time were estimated. It was shown that transport mechanism based on the two-channel model has a good correlation with experimental results for Ohmic region of I-V characteristic, while space-charge limited current mechanism for power region.

  18. O-doped Si2Sb2Te5 nano-composite phase change material for application of chalcogenide random access memory.

    PubMed

    Zhang, Ting; Song, Zhitang; Liu, Bo; Wang, Feng; Feng, Songlin

    2009-02-01

    A method to prepare nano-composite phase change material was proposed and demonstrated by oxygen doping into Si2Sb2Te5 material. According to transmission electron microscope images, Si-Sb-Te-rich domains are separated from each other by SiOx-rich domains within the material. A proper dose of O-doping into Si2Sb2Te5 significantly reduces the grain size of the phase change material. Average size of Si-Sb-Te-rich domains is about 10 nm. Such separation will limit the phase-change to a relatively small volume. The reduction of grain size further results in the promotion of data retention and thermal stability of the material. Memory device based on O-doped Si2Sb2Te5 nano-composite phase change material, with a bottom electrode contact of 260 nm in diameter, was fabricated and characterized. The memory cell shows a better electrical performance compared with the Ge2Sb2Te5 based one. PMID:19441462

  19. Vanadium doped Sb{sub 2}Te{sub 3} material with modified crystallization mechanism for phase-change memory application

    SciTech Connect

    Ji, Xinglong; Zheng, Yonghui; Zhou, Wangyang; Wu, Liangcai Cao, Liangliang; Zhu, Min; Rao, Feng; Song, Zhitang; Feng, Songlin

    2015-06-15

    In this paper, V{sub 0.21}Sb{sub 2}Te{sub 3} (VST) has been proposed for phase-change memory applications. With vanadium incorporating, VST has better thermal stability than Sb{sub 2}Te{sub 3} and can maintain in amorphous phase at room temperature. Two resistance steps were observed in temperature dependent resistance measurements. By real-time observing the temperature dependent lattice structure evolution, VST presents as a homogenous phase throughout the whole thermal process. Combining Hall measurement and transmission electron microscopy results, we can ascribe the two resistance steps to the unique crystallization mechanism of VST material. Then, the amorphous thermal stability enhancement can also be rooted in the suppression of the fast growth crystallization mechanism. Furthermore, the applicability of VST is demonstrated by resistance-voltage measurement, and the phase transition of VST can be triggered by a 15 ns electric pulse. In addition, endurance up to 2.7×10{sup 4} cycles makes VST a promising candidate for phase-change memory applications.

  20. Sub-nanosecond threshold-switching dynamics and set process of In3SbTe2 phase-change memory devices

    NASA Astrophysics Data System (ADS)

    Pandey, Shivendra Kumar; Manivannan, Anbarasu

    2016-06-01

    Phase-change materials show promising features for high-speed, non-volatile, random access memory, however achieving a fast electrical switching is a key challenge. We report here, the dependence of electrical switching dynamics including transient parameters such as delay time, switching time, etc., on the applied voltage and the set process of In3SbTe2 phase-change memory devices at the picosecond (ps) timescale. These devices are found to exhibit threshold-switching at a critical voltage called threshold-voltage, VT of 1.9 ± 0.1 V, having a delay time of 25 ns. Further, the delay time decreases exponentially to a remarkably smaller value, as short as 300 ± 50 ps upon increasing the applied voltage up to 1.1VT. Furthermore, we demonstrate a rapid phase-change behavior from amorphous (˜10 MΩ) to poly-crystalline (˜10 kΩ) phase using time-resolved measurements revealing an ultrafast set process, which is primarily initiated by the threshold-switching process within 550 ps for an applied voltage pulse with a pulse-width of 1.5 ns and an amplitude of 2.3 V.

  1. Cr-doped Ge{sub 2}Sb{sub 2}Te{sub 5} for ultra-long data retention phase change memory

    SciTech Connect

    Wang, Qing; Xia, Yangyang; Zheng, Yonghui; Zhang, Qi; Liu, Bo Song, Sannian; Cheng, Yan; Song, Zhitang; Feng, Songlin; Huo, Ruru

    2015-11-30

    Phase change memory is regarded as one of the most promising candidates for the next-generation non-volatile memory. Its storage medium, phase change material, has attracted continuous exploration. Ge{sub 2}Sb{sub 2}Te{sub 5} (GST) is the most popular phase change material, but its thermal stability needs to be improved when used in some fields at high temperature (more than 120 °C). In this paper, we doped Cr atoms into GST and obtained Cr{sub 10}(Ge{sub 2}Sb{sub 2}Te{sub 5}){sub 90} (labeled as Cr-GST) with high thermal stability. For Cr-GST film, the sheet resistance ratio between amorphous and crystalline states is high up to 3 orders of magnitude. The crystalline Cr-GST film inherits the phase structure of GST, with metastable face-centered cubic phase and/or stable hexagonal phase. The doped Cr atoms not only bond with other atoms but also help to improve the anti-oxidation property of Cr-GST. As for the amorphous thermal stability, the calculated temperature for 10-year-data-retention of Cr-GST film, based on the Arrhenius equation, is about 180 °C. The threshold current and threshold voltage of a cell based on Cr-GST are about 6 μA and 2.7 V. The cell could be operated by suitable voltages for more than 40 000 cycles. Thus, Cr-GST is proved to be a promising phase change material with ultra-long data retention.

  2. Reactive ion etching of Si(x)Sb2Te in CF4/Ar plasma for nonvolatile phase-change memory device.

    PubMed

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

    2013-02-01

    Si(x)Sb2Te material system is novel for phase-change random access memory applications. Its properties are more outstanding than the widely used material Ge2Sb2Te5. Etching process is one of the critical steps in the device fabrication. The etching characteristics of phase-change material Si(x)Sb2Te were studied with CF4/Ar gas mixture by a reactive ion etching system. The changes of etching rate, etching profile and surface root-mean-square roughness resulted from variation of the gas-mixing ratio were investigated under constant pressure (50 mTorr) and applying power (200 W). Si0.34Sb2Te is with the highest phase-change speed and the lowest power consumption in the PCRAM memory among these compositions, which means it is the most promising candidate for the PCRAM applications. So the most optimized CF4/Ar gas ratio for Si0.34Sb2Te was studied, the value is 25/25. The etching rate is 155 nm/min, and the selectivity of Si0.34Sb2Te to SiO2 is as high as 3.4 times. Furthermore, the smooth surface was achieved with this optimized gas ratio. PMID:23646688

  3. Pressure-induced reversible amorphization and an amorphous–amorphous transition in Ge2Sb2Te5 phase-change memory material

    PubMed Central

    Sun, Zhimei; Zhou, Jian; Pan, Yuanchun; Song, Zhitang; Mao, Ho-Kwang; Ahuja, Rajeev

    2011-01-01

    Ge2Sb2Te5 (GST) is a technologically very important phase-change material that is used in digital versatile disks-random access memory and is currently studied for the use in phase-change random access memory devices. This type of data storage is achieved by the fast reversible phase transition between amorphous and crystalline GST upon heat pulse. Here we report pressure-induced reversible crystalline-amorphous and polymorphic amorphous transitions in NaCl structured GST by ab initio molecular dynamics calculations. We have showed that the onset amorphization of GST starts at approximately 18 GPa and the system become completely random at approximately 22 GPa. This amorphous state has a cubic framework (c-amorphous) of sixfold coordinations. With further increasing pressure, the c-amorphous transforms to a high-density amorphous structure with trigonal framework (t-amorphous) and an average coordination number of eight. The pressure-induced amorphization is investigated to be due to large displacements of Te atoms for which weak Te–Te bonds exist or vacancies are nearby. Upon decompressing to ambient conditions, the original cubic crystalline structure is restored for c-amorphous, whereas t-amorphous transforms to another amorphous phase that is similar to the melt-quenched amorphous GST. PMID:21670255

  4. Quantum memory based on phase matching control

    NASA Astrophysics Data System (ADS)

    Zhang, Xi-Wen; Kalachev, A.; Hemmer, P.; Scully, M. O.; Kocharovskaya, O.

    2014-09-01

    We discuss a class of quantum memory (QM) scheme based on phase matching control (PMC). A single-photon wave packet can be mapped into and retrieved on demand from a long-lived spin grating in the presence of a control field, forming along with the signal field a Raman configuration, when the wave vector of the control field is continuously changed in time. Such mapping and retrieval takes place due to the phase matching condition and requires neither a variation of the amplitude of the control field nor inhomogeneous broadening of the medium. We discuss the general model of PMC QM and its specific implementation via (i) modulation of the refractive index, (ii) angular scanning of the control field, and (iii) its frequency chirp. We show that the performance of the PMC QM protocol may be as good as those realized in the gradient echo memory (GEM) but achieved with less stringent requirements on the medium. We suggest the experimental realization of PMC QM in nitrogen vacancies (NV) and silicon vacancies (SiV) in diamond as well as in rare-earth doped crystals. We dedicate this paper to the memory of Professor Igor Yevseyev, the internationally renowned scientist, one of the pioneers of the field of quantum coherence effects. We have warm memories of many fruitful and pleasant communications with Professor Yevseyev during the International Laser Physics Workshops, which he so successfully organized and hosted.

  5. Improvement of reliability and speed of phase change memory devices with N7.9(Ge46.9Bi7.2Te45.9) films

    NASA Astrophysics Data System (ADS)

    Park, J. H.; Kim, S.-W.; Kim, J. H.; Ko, D.-H.; Wu, Z.; Cho, S. L.; Ahn, D.; Ahn, D. H.; Lee, J. M.; Nam, S. W.

    2015-08-01

    In this study, we propose a nitrogen-incorporated GeBiTe ternary phase of N7.9(Ge46.9Bi7.2Te45.9) as a phase change material for reliable PCM (Phase Change Memory) with high speed operation. We found that the N7.9(Ge46.9Bi7.2Te45.9) film shows the resistance value of 40 kΩ after annealing at 440oC for 10 minutes, which is much higher than the value of 3.4 kΩ in the case of conventional N7.0(Ge22.0Sb22.0Te56.0) films. A set operation time of 14 nsec was achieved in the devices due to the increased probability of the nucleation by the addition of the elemental Bi. The long data retention time of 10 years at 85oC on the base of 1% failure was obtained as the result of higher activation energy of 2.52 eV for the crystallization compared to the case of N7.0(Ge22.0Sb22.0Te56.0) film, in which the activation energy is 2.1 eV. In addition, a reset current reduction of 27% and longer cycles of endurance as much as 2 order of magnitude compared to the case of N7.0(Ge22.0Sb22.0Te56.0) were observed at a set operation time of 14 nsec. Our results show that N7.9(Ge46.9Bi7.2Te45.9) is highly promising for use as a phase change material in reliable PCMs with high performance and also in forthcoming storage class memory applications, too.

  6. Managing Chemotherapy Side Effects: Memory Changes

    MedlinePlus

    ... C ancer I nstitute Managing Chemotherapy Side Effects Memory Changes What is causing these changes? Your doctor ... thinking or remembering things Managing Chemotherapy Side Effects: Memory Changes Get help to remember things. Write down ...

  7. Nitrogen-doped Ge3Te2 materials with self-restricted active region for low power phase-change memory

    NASA Astrophysics Data System (ADS)

    Peng, Cheng; Yang, Pingxiong; Wu, Liangcai; Song, Zhitang; Rao, Feng; Song, Sannian; Zhou, Dong; Chu, Junhao

    2013-01-01

    In this paper, nitrogen-doped Ge3Te2 materials have been investigated for low power phase-change memory. Nitrogen incorporated in Ge3Te2 increases the crystallization temperature, electrical resistance, and band gap significantly. The introduced GeNx pile up at the grain-boundaries and suppress the crystal growth of Ge3Te2, which further leads to larger crystalline resistance and smaller active region. 10-year data retention of nitrogen-doped Ge3Te2 film reaches a peak value with a N2 flow of 2 sccm, while it decreases sharply as the N2 flow reaches 3 sccm. This is due to the formation of inhomogeneous nucleation sites at the GeNx-GeTe interface. Phase-change memory device based on nitrogen-doped Ge3Te2 film shows much lower RESET power consumption than that of pure Ge3Te2. It's considered that the self-restricted active region and effect of GeNx microheaters play an important role in cutting down the power consumption.

  8. Electrical performance of phase change memory cells with Ge{sub 3}Sb{sub 2}Te{sub 6} deposited by molecular beam epitaxy

    SciTech Connect

    Boschker, Jos E.; Riechert, Henning; Calarco, Raffaella; Boniardi, Mattia; Redaelli, Andrea

    2015-01-12

    Here, we report on the electrical characterization of phase change memory cells containing a Ge{sub 3}Sb{sub 2}Te{sub 6} (GST) alloy grown in its crystalline form by Molecular Beam Epitaxy (MBE). It is found that the high temperature growth on the amorphous substrate results in a polycrystalline film exhibiting a rough surface with a grain size of approximately 80–150 nm. A detailed electrical characterization has been performed, including I-V characteristic curves, programming curves, set operation performance, crystallization activation at low temperature, and resistance drift, in order to determine the material related parameters. The results indicate very good alignment of the electrical parameters with the current state-of-the-art GST, deposited by physical vapor deposition. Such alignment enables a possible employment of the MBE deposition technique for chalcogenide materials in the phase change memory technology, thus leading to future studies of as-deposited crystalline chalcogenides as integrated in electrical vehicles.

  9. Coherent phonon study of (GeTe){sub l}(Sb{sub 2}Te{sub 3}){sub m} interfacial phase change memory materials

    SciTech Connect

    Makino, Kotaro Saito, Yuta; Fons, Paul; Kolobov, Alexander V.; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki

    2014-10-13

    The time-resolved reflectivity measurements were carried out on the interfacial phase change memory (iPCM) materials ([(GeTe){sub 2}(Sb{sub 2}Te{sub 3}){sub 4}]{sub 8} and [(GeTe){sub 2}(Sb{sub 2}Te{sub 3}){sub 1}]{sub 20}) as well as conventional Ge{sub 2}Sb{sub 2}Te{sub 5} alloy at room temperature and above the RESET-SET phase transition temperature. In the high-temperature phase, coherent phonons were clearly observed in the iPCM samples while drastic attenuation of coherent phonons was induced in the alloy. This difference strongly suggests the atomic rearrangement during the phase transition in iPCMs is much smaller than that in the alloy. These results are consistent with the unique phase transition model in which a quasi-one-dimensional displacement of Ge atoms occurs for iPCMs and a conventional amorphous-crystalline phase transition takes place for the alloy.

  10. Evidence for phase change memory behavior in In2(SexTe1-x)3 thin films

    NASA Astrophysics Data System (ADS)

    Matheswaran, P.; Sathyamoorthy, R.; Asokan, K.

    2012-08-01

    Crystalline In2(Se0.5Te0.5)3 thin films are prepared by thermal evaporation and subsequently annealed at 300°C in Ar atmosphere. SEM image of the crystalline sample shows spherical nature of constituents, distributed uniformly throughout the surface. Island structure of the surface is clearly visible after switching. Elemental composition of the sample remains unchanged even after switching. Temperature dependent I-V analysis shows stoichiometric phase change at 80°C [from In2(Se0.5Te0.5)3 to In2Te3 and In2Se3 phase], where current switches three orders of magnitude higher than that in lower temperature. Further rise in temperature results increase in current only after switching, where threshold voltage remains constant.

  11. Memory Optimization for Phase-field Simulations

    SciTech Connect

    Derek Gaston; John Peterson; Andrew Slaughter; Cody Permann; David Andrs

    2014-08-01

    Phase-field simulations are computationally and memory intensive applications. Many of the phase-field simulations being conducted in support of NEAMS were not capable of running on “normal clusters” with 2-4GB of RAM per core, and instead required specialized “big-memory” clusters with 64GB per core. To address this issue, the MOOSE team developed a new Python-based utility called MemoryLogger, and applied it to locate, diagnose, and eradicate memory bottlenecks within the MOOSE framework. MemoryLogger allows for a better understanding of the memory usage of an application being run in parallel across a cluster. Memory usage information is captured for every individual process in a parallel job, and communicated to the head node of the cluster. Console text output from the application itself is automatically matched with this memory usage information to produce a detailed picture of memory usage over time, making it straightforward to identify the subroutines which contribute most to the application’s peak memory usage. The information produced by the MemoryLogger quickly and effectively narrows the search for memory optimizations to the most data-intensive parts of the simulation.

  12. In silico optimization of phase-change materials for digital memories: a survey of first-row transition-metal dopants for Ge₂Sb₂Te₅.

    PubMed

    Skelton, J M; Elliott, S R

    2013-05-22

    Phase-change materials are the alloys at the heart of an emerging class of next-generation, non-volatile digital memory technologies. However, the widely studied Ge-Sb-Te system possesses several undesirable properties, and enhancing its properties, e.g. by doping, is an area of active research. Various first-row transition-metal dopants have been shown to impart useful property enhancements, but a systematic study of the entire period has yet to be undertaken, and little has been done to investigate their interaction with the host material at the atomic level. We have carried out first-principles computer simulations of the complete phase-change cycle in Ge2Sb2Te5 doped with each of the ten first-row transition metals. In this article, we present a comprehensive survey of the electronic, magnetic and optical properties of these doped materials. We discuss in detail their atomic-level structure, and relate the microscopic behaviours of the dopant atoms to their influence on the Ge2Sb2Te5 host. By considering an entire family of similar materials, we identify trends and patterns which might be used to predict suitable dopants for optimizing materials for specific phase-change applications. The computational method employed here is general, and this materials-discovery approach could be applied in the future to study other families of potential dopants for such materials. PMID:23628772

  13. Enhancement of a cyclic endurance of phase change memory by application of a high-density C15(Ge21Sb36Te43) film

    NASA Astrophysics Data System (ADS)

    Park, J. H.; Kim, S. W.; Kim, J. H.; Ko, D. H.; Wu, Z.; Ahn, D.; Ahn, D. H.; Lee, J. M.; Kang, S. B.; Choi, S. Y.

    2016-02-01

    The lower cyclic endurance of Phase Change Memory (PCM) devices limits the spread of its applications for reliable memory. The findings reported here show that micro-voids and excess vacancies that are produced during the deposition process and the subsequent growth in sputtered carbon-doped GeSbTe films is one of the major causes of device failure in PCM with cycling. We found that the size of voids in C15(Ge21Sb36Te43) films increased with increasing annealing temperature and the activation energy for the growth rate of voids was determined to be 2.22 eV. The film density, which is closely related to voids, varies with the deposition temperature and sputtering power used. The lower heat of vaporization of elemental Sb and Te compared to that for elemental Ge and C is a major cause of the low density of the film. It was possible to suppress void formation to a considerable extent by optimizing the deposition conditions, which leads to a dramatic enhancement in cyclic endurance by 2 orders of magnitude in PCM devices prepared at 300oC-300W compared to one prepared at 240oC-500W without change of compositions.

  14. The role of contact resistance in GeTe and Ge2Sb2Te5 nanowire phase change memory reset switching current

    NASA Astrophysics Data System (ADS)

    Hwang, Inchan; Cho, Yong-Jun; Lee, Myoung-Jae; Jo, Moon-Ho

    2015-05-01

    Nanowire (NW) structures offer a model system for investigating material and scaling properties of phase change random access memory (PCRAM) at the nanometer scale. Here, we investigate the relationship between nanowire device contact resistance and reset current (Ireset) for varying diameters of NWs. Because the reset switching current directly affects possible device density of PCRAM NWs, it is considered one of the most important parameters for PCRAM. We found that the reset switching current, Ireset, was inversely proportional to the contact resistance of PCRAM NW devices decreasing as NW diameter was reduced from 250 nm to 20 nm. Our observations suggest that the reduction of power consumption of PCRAM in the sub-lithographic regime can be achieved by lowering the contact resistance.

  15. Scanning electron microscope for in situ study of crystallization of Ge2Sb2Te5 in phase-change memory.

    PubMed

    Yin, You; Niida, Daisuke; Ota, Kazuhiro; Sone, Hayato; Hosaka, Sumio

    2007-12-01

    By introducing electrical connections into the chamber of a scanning electron microscope (SEM) via its holder assembly, it has become feasible to in situ observe and electrically characterize electronic devices. The in situ SEM was applied to investigate electric-pulse-induced behavior of Ge(2)Sb(2)Te(5) in a lateral phase-change memory cell. Randomly distributed nuclei with sizes from 20 to 80 nm were initiated at a low voltage pulse. Initially, grain growth depended strongly on pulse amplitude at around 60.3 nm/V and then a weak pulse amplitude dependence was observed at around 13.5 nm/V. Device resistance during crystallization dropped by two to three orders of magnitude with two falling steps, which probably resulted from amorphous to face-centered-cubic and subsequently to hexagonal transitions, respectively. PMID:18163750

  16. High thermal stability and low density variation of carbon-doped Ge2Sb2Te5 for phase-change memory application

    NASA Astrophysics Data System (ADS)

    Zhou, Wangyang; Wu, Liangcai; Zhou, Xilin; Rao, Feng; Song, Zhitang; Yao, Dongning; Yin, Weijun; Song, Sannian; Liu, Bo; Qian, Bo; Feng, Songlin

    2014-12-01

    Carbon-doped Ge2Sb2Te5 (GSTC) film has been experimentally studied as a thermal stable material for high temperature applications. The 10-yr data retention temperature is remarkably increased through C doping. Furthermore, GSTC films have better interface properties after annealing at 410 °C for 30 min. The density variation of GSTC film is significantly improved, which is very important to device reliability. X-ray photoelectron spectroscopy results reveal that the thermal stability enhancement of GSTC film attributes to the forming of C-Ge, C-Sb, and C-Te bonds. The perfect thermal stability makes GSTC materials a good candidate in the actual production of phase-change memory.

  17. The reason for the increased threshold switching voltage of SiO2 doped Ge2Sb2Te5 thin films for phase change random access memory

    NASA Astrophysics Data System (ADS)

    Ryu, Seung Wook; Lee, Jong Ho; Ahn, Young Bae; Kim, Choon Hwan; Yang, Bong Seob; Kim, Gun Hwan; Kim, Soo Gil; Lee, Se-Ho; Hwang, Cheol Seong; Kim, Hyeong Joon

    2009-09-01

    This study examined the threshold switching voltage (VT) of 150 nm thick SiO2 doped Ge2Sb2Te5 (SGST) films for phase change random access memory applications. The VT of the SGST films increased from ˜0.9 V (for GST) to ˜1.5 V with increasing SiO2 content. The optical band gap and Urbach edge of the SGST films were similar regardless of the SiO2 concentration. The dielectric constant decreased by ˜37% and the electrical resistivity increased by ˜19%. The increase in VT of SGST films is associated with an effective increase in electric field and the decreased generation rate caused by impact ionization.

  18. Implementation of nitrogen-doped titanium-tungsten tunable heater in phase change random access memory and its effects on device performance

    SciTech Connect

    Tan, Chun Chia; Zhao, Rong Chong, Tow Chong; Shi, Luping

    2014-10-13

    Nitrogen-doped titanium-tungsten (N-TiW) was proposed as a tunable heater in Phase Change Random Access Memory (PCRAM). By tuning N-TiW's material properties through doping, the heater can be tailored to optimize the access speed and programming current of PCRAM. Experiments reveal that N-TiW's resistivity increases and thermal conductivity decreases with increasing nitrogen-doping ratio, and N-TiW devices displayed (∼33% to ∼55%) reduced programming currents. However, there is a tradeoff between the current and speed for heater-based PCRAM. Analysis of devices with different N-TiW heaters shows that N-TiW doping levels could be optimized to enable low RESET currents and fast access speeds.

  19. Associative memory in phasing neuron networks

    SciTech Connect

    Nair, Niketh S; Bochove, Erik J.; Braiman, Yehuda

    2014-01-01

    We studied pattern formation in a network of coupled Hindmarsh-Rose model neurons and introduced a new model for associative memory retrieval using networks of Kuramoto oscillators. Hindmarsh-Rose Neural Networks can exhibit a rich set of collective dynamics that can be controlled by their connectivity. Specifically, we showed an instance of Hebb's rule where spiking was correlated with network topology. Based on this, we presented a simple model of associative memory in coupled phase oscillators.

  20. Investigation of Ge2Sb2Te5/Si nano-multilayered films for phase-change memory applications

    NASA Astrophysics Data System (ADS)

    Zheng, Long; Gu, Xiaomin; Ma, Ligang; Wu, Xiaoshan; Zhu, Xiaoqin; Sui, Yongxing

    2016-01-01

    The phase-transition behavior and thermal stability of Ge2Sb2Te5/Si nano-multilayered films are investigated in this study. Our results reveal that the improvement in thermal stability and increase in the phase-transition temperature are not universal results for all nano-multilayered structures. The stress effect induced by thermal expansion during heating indeed could inhibit the crystallization of Ge2Sb2Te5/Si nano-multilayered films. The interface effect is believed to play a dominant role in thicker films, while the stress effect is active when the layer thickness is decreased. The gradual shift in the Raman peaks' position can support this scenario because they are modified by both the interface effect and the stress effect.

  1. Formation of large voids in the amorphous phase-change memory Ge2Sb2Te5 alloy.

    PubMed

    Sun, Zhimei; Zhou, Jian; Blomqvist, Andreas; Johansson, Börje; Ahuja, Rajeev

    2009-02-20

    On the basis of ab initio molecular dynamics simulations, large voids mainly surrounded by Te atoms are observed in molten and amorphous Ge2Sb2Te5, which is due to the clustering of two- and threefold coordinated Te atoms. Furthermore, pressure shows a significant effect on the clustering of the under coordinated Te atoms and hence the formation of large voids. The present results demonstrate that both vacancies and Te play an important role in the fast reversible phase transition process. PMID:19257687

  2. Investigation of Cr0.06(Sb4Te)0.94 alloy for high-speed and high-data-retention phase change random access memory applications

    NASA Astrophysics Data System (ADS)

    Li, Le; Song, Sannian; Zhang, Zhonghua; Song, Zhitang; Cheng, Yan; Lv, Shilong; Wu, Liangcai; Liu, Bo; Feng, Songlin

    2015-08-01

    The effects of Cr doping on the structural and electrical properties of Cr x (Sb4Te)1- x materials have been investigated in order to solve the contradiction between thermal stability and fast crystallization speed of Sb4Te alloys. Cr0.06(Sb4Te)0.94 alloy is considered to be a potential candidate for phase change random access memory (PCM), as evidenced by a higher crystallization temperature (204 °C), a better data retention ability (137.6 °C for 10 years), a lower melting point (558 °C), a lower energy consumption, and a faster switching speed in comparison with those of Ge2Sb2Te5. A reversible switching between set and reset states can be realized by an electric pulse as short as 5 ns for Cr0.06(Sb4Te)0.94-based PCM cell. In addition, Cr0.06(Sb4Te)0.94 shows good endurance up to 1.1 × 104 cycles with a resistance ratio of about two orders of magnitude.

  3. Investigation of transport mechanisms in Bi doped Ge2Sb2Te5 thin films for phase change memory application

    NASA Astrophysics Data System (ADS)

    Lazarenko, Petr I.; Sherchenkov, Alexey A.; Kozyukhin, Sergey S.; Shtern, Maxim Y.; Timoshenkov, Sergey P.; Gromov, Dmitry G.; Redichev, Evgeniy N.

    2014-12-01

    The influence of Bi doping on the charge carrier transport mechanism in GST225 thin films was investigated. The three regions with different current-voltage dependencies were established. The energy diagrams for Bi doped GST225 thin films for different regions were analyzed. Analysis of experimental data showed that space charge limited current is the most possible explanation for the nonlinear I-V dependence in the middle electrical field strength (103 < E < 104 V/cm). Position of the trap levels (Et) controlling transport mechanism, and density of traps (Nt) were estimated with using of Rose and Lampert theories. It was established that Bi doping can significantly change I-V characteristic, resistivity, mobility gap, Urbach energy, density distribution of localized states, and activation energy of conductivity. The most pronounced modification of current-voltage characteristic and parameters of the thin films was established for GST225 + 0,5 wt. % Bi. Thus, doping of Ge2Sb2Te5 by Bi expands the range of material properties, which is important for the optimization of PCM technology.

  4. 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)

  5. Memory Reconsolidation: Time to Change Your Mind

    PubMed Central

    Bailey, Matthew R.; Balsam, Peter D.

    2016-01-01

    A new study shows that temporal expectations about threats are a key part of fear memories and that changing this temporal expectation is enough to trigger the updating and reconsolidation of a previously learned fear. PMID:23518056

  6. 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.

  7. 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.

  8. 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…

  9. Drastic change in density of states upon martensitic phase transition for metamagnetic shape memory alloy Ni2Mn(1+x)In(1-x).

    PubMed

    Zhu, Siyuan; Ye, Mao; Shirai, Kaito; Taniguchi, Masaki; Ueda, Shigenori; Miura, Yoshio; Shirai, Masafumi; Umetsu, Rie Yamauchi; Kainuma, Ryosuke; Kanomata, Takeshi; Kimura, Akio

    2015-09-16

    We have unravelled the electronic structure of a class of metamagnetic shape memory alloy Ni2Mn1+x In1-x by combining bulk-sensitive hard x-ray photoelectron spectroscopy and first-principles density-functional calculations. A sharp drop in the Ni 3d e(g) density of states forming a pseudogap in the martensitic phase transition (MPT) for x   =   0.36 has been observed near the Fermi level. As a feature of MPT, hysteretic behaviour of this drop has been confirmed in both cooling and warming. This pseudogap is responsible for the giant negative magnetoresistance. The experimental result is well reproduced by the first principle calculation. We have also clarified theoretically that the MPT is linked to a competition of ferromagnetic and anti-ferromagnetic coupling between ordinary and anti-site Mn atoms. PMID:26289060

  10. Effects of germanium and nitrogen incorporation on crystallization of N-doped Ge2+xSb2Te5 (x = 0,1) thin films for phase-change memory

    NASA Astrophysics Data System (ADS)

    Cheng, Limin; Wu, Liangcai; Song, Zhitang; Rao, Feng; Peng, Cheng; Yao, Dongning; Liu, Bo; Xu, Ling

    2013-01-01

    The phase-change behavior and microstructure changes of N-doped Ge3Sb2Te5 [N-GST(3/2/5)] and Ge2Sb2Te5 [GST(2/2/5)] films during the phase transition from an amorphous to a crystalline phase were studied using in situ temperature-dependent sheet resistance measurements, X-ray diffraction, and transmission electron microscopy. The optical band gaps of N-GST(3/2/5) films are higher than that of GST(2/2/5) film in both the amorphous and face-centered-cubic (fcc) phases. Ge nitride formation by X-ray photoelectron spectroscopy analysis increased the optical band gap and suppressed crystalline grain growth, resulting in an increase in the crystallization temperature and resistance in the fcc phase. As a result, the Ge- and N-doped GST(2/2/5) composite films can be considered as a promising material for phase-change memory application because of improved thermal stability and reduced power consumption.

  11. Effects of germanium and nitrogen incorporation on crystallization of N-doped Ge{sub 2+x}Sb{sub 2}Te{sub 5} (x = 0,1) thin films for phase-change memory

    SciTech Connect

    Cheng Limin; Wu Liangcai; Song Zhitang; Rao Feng; Peng Cheng; Yao Dongning; Liu Bo; Xu Ling

    2013-01-28

    The phase-change behavior and microstructure changes of N-doped Ge{sub 3}Sb{sub 2}Te{sub 5}[N-GST(3/2/5)] and Ge{sub 2}Sb{sub 2}Te{sub 5}[GST(2/2/5)] films during the phase transition from an amorphous to a crystalline phase were studied using in situ temperature-dependent sheet resistance measurements, X-ray diffraction, and transmission electron microscopy. The optical band gaps of N-GST(3/2/5) films are higher than that of GST(2/2/5) film in both the amorphous and face-centered-cubic (fcc) phases. Ge nitride formation by X-ray photoelectron spectroscopy analysis increased the optical band gap and suppressed crystalline grain growth, resulting in an increase in the crystallization temperature and resistance in the fcc phase. As a result, the Ge- and N-doped GST(2/2/5) composite films can be considered as a promising material for phase-change memory application because of improved thermal stability and reduced power consumption.

  12. CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Simulation of Phase-Change Random Access Memory with Ring-Type Contactor for Low Reset Current by Finite Element Modelling

    NASA Astrophysics Data System (ADS)

    Gong, Yue-Feng; Ling, Yun; Song, Zhi-Tang; Feng, Song-Lin

    2008-09-01

    A three-dimensional finite element models for phase change random access memory (PCRAM) is established to simulate thermal and electrical behaviours during RESET operation. The RESET behaviours of the conventional structure (CS) and the ring-type contact in bottom electrode (RIB) are compared with each other. The simulation results indicate that the RIB cell has advantages of high heat efficiency for melting phase change material in cell, reduction of contact area and lower RESET current with maintaining good resistance contrast. The RESET current decreases from 1.26mA to 1.2mA and the heat consumption in GST material during programming increases from 12% to 37% in RIB structure. Thus the RIB structure PCRAM cell is suitable for future device with high heat efficiency and smaller RESET current.

  13. On the persuadability of memory: Is changing people's memories no more than changing their minds?

    PubMed

    Nash, Robert A; Wheeler, Rebecca L; Hope, Lorraine

    2015-05-01

    The observation of parallels between the memory distortion and persuasion literatures leads, quite logically, to the appealing notion that people can be 'persuaded' to change their memories. Indeed, numerous studies show that memory can be influenced and distorted by a variety of persuasive tactics, and the theoretical accounts commonly used by researchers to explain episodic and autobiographical memory distortion phenomena can generally predict and explain these persuasion effects. Yet, despite these empirical and theoretical overlaps, explicit reference to persuasion and attitude-change research in the memory distortion literature is surprisingly rare. In this paper, we argue that stronger theoretical foundations are needed to draw the memory distortion and persuasion literatures together in a productive direction. We reason that theoretical approaches to remembering that distinguish (false) beliefs in the occurrence of events from (false) memories of those events - compatible with a source monitoring approach - would be beneficial to this end. Such approaches, we argue, would provide a stronger platform to use persuasion findings to enhance the psychological understanding of memory distortion. PMID:24898340

  14. Spatial phase modulation from permanent memory in doped glass.

    PubMed

    Myint, Thandar; Alfano, R R

    2010-04-15

    Diffraction rings are observed from photoinduced permanent memory of doped glass. The permanent memory is created by the high-intensity picosecond laser beam. A 1 mm spot size of laser beam creates spatially variable refractive index memory, which appears as a void located inside the glass. When a probe laser beam passes through the memory region, the diffraction rings arisen from spatial phase modulation of the transverse phase of the input beam are created. Agreement between the observed and calculated beam pattern using Kirchhoff's diffraction integral is satisfactory. PMID:20410991

  15. Superlattice-like SnSb4/Ga3Sb7 thin films for ultrafast switching phase-change memory application

    NASA Astrophysics Data System (ADS)

    Hu, Yifeng; He, Zifang; Zhai, Jiwei; Wu, Pengzhi; Lai, Tianshu; Song, Sannian; Song, Zhitang

    2015-11-01

    The carrier concentration of Sb-rich phase SnSb4, Ga3Sb7 and superlattice-like [SnSb4(3.5 nm)/Ga3Sb7(4 nm)]7 (SLL-7) thin films as a function of annealing temperature was investigated to explain the reason of resistance change. The activation energy for crystallization was calculated with a Kissinger equation to estimate the thermal stability. In order to illuminate the transition mechanisms, the crystallization kinetics of SLL-7 were explored by using Johnson-Mehl-Avrami theory. The obtained values of Avrami indexes indicate that a one-dimensional growth-dominated mechanism is responsible for the set transition of SLL-7 thin film. X-ray diffractometer and Raman scattering spectra were recorded to investigate the change of crystalline structure. The measurement of atomic force microscopy indicated that SLL-7 thin film has a good smooth surface. A picosecond laser pump-probe system was used to test and verify phase-change speed of the SLL-7 thin film.

  16. Accounting for Change in Declarative Memory: A Cognitive Neuroscience Perspective

    ERIC Educational Resources Information Center

    Richmond, Jenny; Nelson, Charles A.

    2007-01-01

    The medial temporal lobe memory system matures relatively early and supports rudimentary declarative memory in young infants. There is considerable development, however, in the memory processes that underlie declarative memory performance during infancy. Here we consider age-related changes in encoding, retention, and retrieval in the context of…

  17. Phase-change materials handbook

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    Handbook describes relationship between phase-change materials and more conventional thermal control techniques and discusses materials' space and terrestrial applications. Material properties of most promising phase-change materials and purposes and uses of metallic filler materials in phase-change material composites are provided.

  18. 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.

  19. 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.

  20. High thermal stability and low density variation of carbon-doped Ge{sub 2}Sb{sub 2}Te{sub 5} for phase-change memory application

    SciTech Connect

    Zhou, Wangyang; Wu, Liangcai Zhou, Xilin; Rao, Feng; Song, Zhitang Yao, Dongning; Yin, Weijun; Song, Sannian; Liu, Bo; Feng, Songlin; Qian, Bo

    2014-12-15

    Carbon-doped Ge{sub 2}Sb{sub 2}Te{sub 5} (GSTC) film has been experimentally studied as a thermal stable material for high temperature applications. The 10-yr data retention temperature is remarkably increased through C doping. Furthermore, GSTC films have better interface properties after annealing at 410 °C for 30 min. The density variation of GSTC film is significantly improved, which is very important to device reliability. X-ray photoelectron spectroscopy results reveal that the thermal stability enhancement of GSTC film attributes to the forming of C-Ge, C-Sb, and C-Te bonds. The perfect thermal stability makes GSTC materials a good candidate in the actual production of phase-change memory.

  1. 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

  2. Metamemory ratings predict long-term changes in reactivated episodic memories

    PubMed Central

    Yacoby, Amnon; Dudai, Yadin; Mendelsohn, Avi

    2015-01-01

    Reactivation of long-term memory can render the memory item temporarily labile, offering an opportunity to modify it via behavioral or pharmacological intervention. Declarative memory reactivation is accompanied by a metamemory ability to subjectively assess the knowledge available concerning the target item (Feeling of knowing, FOK). We set out to examine whether FOK can predict the extent of change of long-term episodic memories by post-retrieval manipulations. To this end, participants watched a short movie and were immediately thereafter tested on their memory for it. A day later, they were reminded of that movie, and either immediately or 1 day later, were presented with a second movie. The reminder phase consisted of memory cues to which participants were asked to judge their FOK regarding the original movie. The memory performance of participants to whom new information was presented immediately after reactivating the original episode corresponded to the degree of FOK ratings upon reactivation such that the lower their FOK, the less their memory declined. In contrast, no relation was found between FOK and memory strength for those who learned new information 1 day after the reminder phase. Our findings suggest that the subjective accessibility of reactivated memories may determine the extent to which new information might modify those memories. PMID:25709571

  3. Phase Change Material Heat Exchangers

    NASA Video Gallery

    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 ...

  4. Changes in Memory Prediction Accuracy: Age and Performance Effects

    ERIC Educational Resources Information Center

    Pearman, Ann; Trujillo, Amanda

    2013-01-01

    Memory performance predictions are subjective estimates of possible memory task performance. The purpose of this study was to examine possible factors related to changes in word list performance predictions made by younger and older adults. Factors included memory self-efficacy, actual performance, and perceptions of performance. The current study…

  5. Transition of Bery Phase and Pancharatnam Phase and Phase Change

    NASA Astrophysics Data System (ADS)

    Fu, Guolan; Pan, Hui; Wang, Zisheng

    2016-07-01

    Berry Phase and time-dependent Pancharatnam phase are investigated for nuclear spin polarization in a liquid by a rotation magnetic field, where two-state mixture effect is exactly included in the geometric phases. We find that when the system of nuclear spin polarization is in the unpolarized state, the transitive phenomena of both Berry phase and Pancharatnam phase are taken place. For the polarized system, in contrast, such a transition is not taken place. It is obvious that the transitions of geometric phase correspond to the phase change of physical system.

  6. Topological phases and self-correcting memories in interacting anyon systems

    NASA Astrophysics Data System (ADS)

    Wootton, James R.

    2013-12-01

    Recent studies have shown that topological models with interacting anyonic quasiparticles can be used as self-correcting quantum memories. Here we study the behavior of these models at thermal equilibrium. It is found that the interactions allow topological order to exist at finite temperature, not only in an extension of the ground-state phase, but also in a novel form of topologically ordered phase. Both phases are found to support self-correction in all models considered, and the transition between them corresponds to a change in the scaling of memory lifetime with system size.

  7. 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…

  8. Sex and menstrual cycle phase at encoding influence emotional memory for gist and detail.

    PubMed

    Nielsen, Shawn E; Ahmed, Imran; Cahill, Larry

    2013-11-01

    Sex influences on emotional memory have received increasing interest over the past decade. However, only a subset of this previous work explored the influence of sex on memory for central information (gist) and peripheral detail in emotional versus neutral contexts. Here we examined the influence of sex and menstrual cycle phase at encoding on memory for either an emotional or neutral story, specifically with respect to the retention of gist and peripheral detail. Healthy naturally cycling women and men viewed a brief, narrated, three-phase story containing neutral or emotionally arousing elements. One week later, participants received a surprise free recall test for story elements. The results indicate that naturally cycling women in the luteal (high hormone) phase of the menstrual cycle at encoding show enhanced memory for peripheral details, but not gist, when in the emotional compared with neutral stories (p<.05). In contrast, naturally cycling women in the follicular (low hormone) phase of the menstrual cycle at encoding did not show enhanced memory for gist or peripheral details in the emotional compared with neutral stories. Men show enhanced memory for gist, but not peripheral details, in the emotional versus neutral stories (p<.05). In addition, these sex influences on memory cannot be attributed to differences in attention or arousal; luteal women, follicular women, and men performed similarly on measures of attention (fixation time percentage) and arousal (pupil diameter changes) during the most arousing phase of the emotional story. These findings suggest that sex and menstrual cycle phase at encoding influence long term memory for different types of emotional information. PMID:23891713

  9. Cortical Low-Frequency Power and Progressive Phase Synchrony Precede Successful Memory Encoding

    PubMed Central

    Haque, Rafi U.; Wittig, John H.; Damera, Srikanth R.; Inati, Sara K.

    2015-01-01

    Neural activity preceding an event can influence subsequent memory formation, yet the precise cortical dynamics underlying this activity and the associated cognitive states remain unknown. We investigate these questions here by examining intracranial EEG recordings as 28 participants with electrodes placed for seizure monitoring participated in a verbal paired-associates memory task. We found that, preceding successfully remembered word pairs, an orientation cue triggered a low-frequency 2–4 Hz phase reset in the right temporoparietal junction with concurrent increases in low-frequency power across cortical regions that included the prefrontal cortex and left temporal lobe. Regions that exhibited a significant increase in 2–4 Hz power were functionally bound together through progressive low-frequency 2–4 Hz phase synchrony. Our data suggest that the interaction between power and phase synchrony reflects the engagement of attentional networks that in large part determine the extent to which memories are successfully encoded. SIGNIFICANCE STATEMENT Here we investigate the spatiotemporal cortical dynamics that precede successful memory encoding. Using intracranial EEG, we observed significant changes in oscillatory power, intertrial phase consistency, and pairwise phase synchrony that predict successful encoding. Our data suggest that the interaction between power and phase synchrony reflects the engagement of attentional networks that in large part determine the extent to which memories are successfully encoded. PMID:26446212

  10. Research on phase locked loop in optical memory servo system

    NASA Astrophysics Data System (ADS)

    Qin, Liqin; Ma, Jianshe; Zhang, Jianyong; Pan, Longfa; Deng, Ming

    2005-09-01

    Phase locked loop (PLL) is a closed loop automatic control system, which can track the phase of input signal. It widely applies in each area of electronic technology. This paper research the phase locked loop in optical memory servo area. This paper introduces the configuration of digital phase locked loop (PLL) and phase locked servo system, the control theory, and analyses system's stability. It constructs the phase locked loop experiment system of optical disk spindle servo, which based on special chip. DC motor is main object, this system adopted phase locked servo technique and digital signal processor (DSP) to achieve constant linear velocity (CLV) in controlling optical spindle motor. This paper analyses the factors that affect the stability of phase locked loop in spindle servo system, and discusses the affection to the optical disk readout signal and jitter due to the stability of phase locked loop.

  11. Simulation studies of GST phase change alloys

    NASA Astrophysics Data System (ADS)

    Martyna, Glenn

    2008-03-01

    In order to help drive post-Moore's Law technology development, switching processes involving novel materials, in particular, GeSbTe (GST) alloys are being investigated for use in memory and eFuse applications. An anneal/quench thermal process crystallizes/amorphosizes a GST alloy which then has a low/high resistance and thereby forms a readable/writeable bit; for example, a ``one'' might be the low resistance, conducting crystalline state and a ``zero'' might be the high resistance, glassy state. There are many open questions about the precise nature of the structural transitions and the coupling to electronic structure changes. Computational and experimental studies of the effect of pressure on the GST materials were initiated in order to probe the physics behind the thermal switching process. A new pathway to reversible phase change involving pressure-induced structural metal insulator transitions was discovered. In a binary GS system, a room-temperature, direct, pressure-induced transformation from the high resistance amorphous phase to the low resistance crystalline phase was observed experimentally while the reverse process under tensile load was demonstrated via ab initio MD simulations performed on IBM's Blue Gene/L enabled by massively parallel software. Pressure induced transformations of the ternary material GST-225 (Ge2Sb2Te5) were, also, examined In the talk, the behavior of the two systems will be compared and insight into the nature of the phase change given.

  12. Accounting for change in declarative memory: A cognitive neuroscience perspective

    PubMed Central

    Richmond, Jenny; Nelson, Charles A.

    2007-01-01

    The medial temporal lobe memory system matures relatively early and supports rudimentary declarative memory in young infants. There is considerable development, however, in the memory processes that underlie declarative memory performance during infancy. Here we consider age-related changes in encoding, retention, and retrieval in the context of current knowledge about the brain systems that may underlie these memory processes. While changes in infants’ encoding may be attributed to rapid myelination during the first year of life, improvements in long-term retention and flexible retrieval are likely due to the prolonged development of the dentate gyrus. Future studies combining measures of brain and behavior are critical in improving our understanding of how brain development drives memory development during infancy and early childhood. PMID:18769510

  13. 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.

  14. 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. PMID:27183057

  15. 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.

  16. 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.

  17. Modulation of theta phase synchronization in the human electroencephalogram during a recognition memory task.

    PubMed

    Kim, Sung-Phil; Kang, Jae-Hwan; Choe, Seong-Hyun; Jeong, Ji Woon; Kim, Hyun Taek; Yun, Kyongsik; Jeong, Jaeseung; Lee, Seung-Hwan

    2012-08-01

    To the extent that recognition memory relies on interactions among widely distributed neural assemblies across the brain, phase synchronization between brain rhythms may play an important role in meditating those interactions. As the theta rhythm is known to modulate in power during the recognition memory process, we aimed to determine how the phase synchronization of the theta rhythms across the brain changes with recognition memory. Fourteen human participants performed a visual object recognition task in a virtual reality environment. Electroencephalograms were recorded from the scalp of the participants while they either recognized objects that had been presented previously or identified new objects. From the electroencephalogram recordings, we analyzed the phase-locking value of the theta rhythms, which indicates the degree of phase synchronization. We found that the overall phase-locking value recorded during the recognition of previously viewed objects was greater than that recorded during the identification of new objects. Specifically, the theta rhythms became strongly synchronized between the frontal and the left parietal areas during the recognition of previously viewed objects. These results suggest that the recognition memory process may involve an interaction between the frontal and the left parietal cortical regions mediated by theta phase synchronization. PMID:22610314

  18. 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.

  19. Conditions of steady switching in phase-transition memory cells

    SciTech Connect

    Popov, A. I. Salnikov, S. M.; Anufriev, Yu. V.

    2015-04-15

    Three types of non-volatile memory cells of different designs based on phase transitions are developed and implemented. The effect of the design features of the cells and their active-region sizes on the switching characteristics and normal operation of the cells is considered as a whole. The causes of failure of the cells are analyzed from the obtained series of scanning electron images upon level-by-level etching of the samples. It is shown that the cell design is the most critical factor from the viewpoint of switching to the high-resistance state. The causes of this fact are analyzed and the criterion for providing the steady operation of cells of non-volatile memory based on phase transitions is formulated.

  20. Medial prefrontal theta phase coupling during spatial memory retrieval.

    PubMed

    Kaplan, Raphael; Bush, Daniel; Bonnefond, Mathilde; Bandettini, Peter A; Barnes, Gareth R; Doeller, Christian F; Burgess, Neil

    2014-06-01

    Memory retrieval is believed to involve a disparate network of areas, including medial prefrontal and medial temporal cortices, but the mechanisms underlying their coordination remain elusive. One suggestion is that oscillatory coherence mediates inter-regional communication, implicating theta phase and theta-gamma phase-amplitude coupling in mnemonic function across species. To examine this hypothesis, we used non-invasive whole-head magnetoencephalography (MEG) as participants retrieved the location of objects encountered within a virtual environment. We demonstrate that, when participants are cued with the image of an object whose location they must subsequently navigate to, there is a significant increase in 4-8 Hz theta power in medial prefrontal cortex (mPFC), and the phase of this oscillation is coupled both with ongoing theta phase in the medial temporal lobe (MTL) and perceptually induced 65-85 Hz gamma amplitude in medial parietal cortex. These results suggest that theta phase coupling between mPFC and MTL and theta-gamma phase-amplitude coupling between mPFC and neocortical regions may play a role in human spatial memory retrieval. PMID:24497013

  1. Spatiotemporal oscillatory dynamics during the encoding and maintenance phases of a visual working memory task.

    PubMed

    Heinrichs-Graham, Elizabeth; Wilson, Tony W

    2015-08-01

    Many electrophysiology studies have examined neural oscillatory activity during the encoding, maintenance, and/or retrieval phases of various working memory tasks. Together, these studies have helped illuminate the underlying neural dynamics, although much remains to be discovered and some findings have not replicated in subsequent work. In this study, we examined the oscillatory dynamics that serve visual working memory operations using high-density magnetoencephalography (MEG) and advanced time-frequency and beamforming methodology. Specifically, we recorded healthy adults while they performed a high-load, Sternberg-type working memory task, and focused on the encoding and maintenance phases. We found significant 9-16 Hz desynchronizations in the bilateral occipital cortices, left dorsolateral prefrontal cortex (DLPFC), and left superior temporal areas throughout the encoding phase. Our analysis of the dynamics showed that the left DLPFC and superior temporal desynchronization became stronger as a function of time during the encoding period, and was sustained throughout most of the maintenance phase until sharply decreasing in the milliseconds preceding retrieval. In contrast, desynchronization in occipital areas became weaker as a function of time during encoding and eventually evolved into a strong synchronization during the maintenance period, consistent with previous studies. These results provide clear evidence of dynamic network-level processes during the encoding and maintenance phases of working memory, and support the notion of a dynamic pattern of functionally-discrete subprocesses within each working memory phase. The presence of such dynamic oscillatory networks may be a potential source of inconsistent findings in this literature, as neural activity within these networks changes dramatically with time. PMID:26043156

  2. 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.

  3. Phase front patterns in shape memory alloy strips

    SciTech Connect

    Lagoudas, D.C.; Howard, S.D.

    1995-12-31

    Uniaxial thermomechanical tests of Shape Memory Alloy (SMA) Nitinol strips, below the austenitic start temperature, have shown the formation of multiple phase front patterns forming at approximately 45 degrees angle with respect to the applied load. These phase fronts, that separate self-accommodating martensitic variants from detwinned martensite, propagate along the specimen in the direction of applied load, until fully detwinned martensite is developed. Similar patterns of martensitic-austenitic phase fronts occur when the temperature is raised above austenitic finish, and uniaxial loading is applied to the strip specimens. An experimental study of this phenomenon, together with some preliminary modelling results will be presented. In contrast to the above uniform loading case, experimental results and numerical simulations for the propagation of a phase transformation front, induced by an imposed temperature gradient, will also be presented.

  4. Changes in Context-Specificity during Memory Reconsolidation: Selective Effects of Hippocampal Lesions

    ERIC Educational Resources Information Center

    Winocur, Gordon; Frankland, Paul W.; Sekeres, Melanie; Fogel, Stuart; Moscovitch, Morris

    2009-01-01

    After acquisition, memories associated with contextual fear conditioning pass through a labile phase, in which they are vulnerable to hippocampal lesions, to a more stable state, via consolidation, in which they engage extrahippocampal structures and are resistant to such disruption. The process is accompanied by changes in the form of the memory…

  5. Correlates and moderators of change in subjective memory and memory performance: findings from the health and retirement study.

    PubMed

    Hülür, Gizem; Hertzog, Christopher; Pearman, Ann M; Gerstorf, Denis

    2015-01-01

    Aging researchers have long been interested in understanding individuals' subjective perceptions of their own memory functioning. Previous research has shown that subjective memory ratings are partly based on memory performance but also reflect the influence of other factors, such as depressive symptoms. The aim of the present study was to examine (1) longitudinal associations between trajectories of subjective memory and memory performance, (2) variables that predict levels of and changes in subjective memory and memory performance, and (3) variables that moderate associations between these constructs. We applied a latent growth curve model to four occasions of data from 15,824 participants of the Health and Retirement Study (HRS; mean age at baseline=64.27 years, SD=9.90; 58% women). Results revealed that latent changes in subjective memory were correlated with latent changes in memory performance (φ=0.49), indicating that participants who reported steeper declines of subjective memory indeed showed steeper declines of memory performance over time. Three major patterns of associations emerged with respect to predictors of subjective memory and subjective memory change. First, the level of memory performance showed stronger associations with age, gender, and education, whereas subjective memory was more strongly associated with subjective age and personality traits. For example, women performed better than men on the episodic memory test, but there were no gender differences in subjective memory. Also, older age was associated with steeper declines of memory performance but with less decline of subjective memory. Second, personality traits that predicted subjective memory intercepts did not predict subjective memory slopes. Third, the strength of associations between levels and slopes of subjective memory and memory performance varied as a function of gender, education, depressive symptoms, and personality traits. Conscientiousness moderated the relationship of

  6. 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.

  7. 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

  8. Multilevel phase and amplitude modulation method for holographic memories with programmable phase modulator

    NASA Astrophysics Data System (ADS)

    Honma, Satoshi; Sekiguchi, Toru

    2014-09-01

    The utilization of spatial quadrature amplitude modulation (SQAM) signals with amplitude and phase modulation is a simple method used to improve storage capacity in a holographic data storage system. We propose a multilevel phase and amplitude modulation method for holographic memories with a programmable phase modulator (PPM). In this method, holographic page data is recorded by a two-step exposure process for different phase-modulated data. There is no need to adjust the positions of spatial light modulators (SLM) with high accuracy because we use only one spatial modulator. We estimate the quality of 16 SQAM signals produced by our technique.

  9. Brain functional network changes following Prelimbic area inactivation in a spatial memory extinction task.

    PubMed

    Méndez-Couz, Marta; Conejo, Nélida M; Vallejo, Guillermo; Arias, Jorge L

    2015-01-01

    Several studies suggest a prefrontal cortex involvement during the acquisition and consolidation of spatial memory, suggesting an active modulating role at late stages of acquisition processes. Recently, we have reported that the prelimbic and infralimbic areas of the prefrontal cortex, among other structures, are also specifically involved in the late phases of spatial memory extinction. This study aimed to evaluate whether the inactivation of the prelimbic area of the prefrontal cortex impaired spatial memory extinction. For this purpose, male Wistar rats were implanted bilaterally with cannulae into the prelimbic region of the prefrontal cortex. Animals were trained during 5 consecutive days in a hidden platform task and tested for reference spatial memory immediately after the last training session. One day after completing the training task, bilateral infusion of the GABAA receptor agonist Muscimol was performed before the extinction protocol was carried out. Additionally, cytochrome c oxidase histochemistry was applied to map the metabolic brain activity related to the spatial memory extinction under prelimbic cortex inactivation. Results show that animals acquired the reference memory task in the water maze, and the extinction task was successfully completed without significant impairment. However, analysis of the functional brain networks involved by cytochrome oxidase activity interregional correlations showed changes in brain networks between the group treated with Muscimol as compared to the saline-treated group, supporting the involvement of the mammillary bodies at a the late stage in the memory extinction process. PMID:25813749

  10. Elastically driven metamagnetic-like phase transformations of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Danilevich, A. G.; L'vov, V. A.

    2016-03-01

    A theoretical model of metamagnetic-like (ferromagnetic-paramagnetic and ferromagnetic-antiferromagnetic) phase transitions is developed for the interpretation of experimental results obtained recently for the Ni-Mn-Co-X (X  =  In, Sn, Ga) shape memory alloys. The conditions of elastically driven (caused by the martensitic transformation of alloy) metamagnetic-like phase transitions are determined. These conditions are: high magnetic susceptibility of paramagnetic/antiferromagnetic phase; large (but real for some alloys) volume change during the martensitic transformation; and large value of volume magnetostriction caused by the metamagnetic-like phase transition. The magnetoelastic mechanism is proposed for the explanation of magnetic field influence on the martensitic transformation. The elastically driven ferromagnetic-paramagnetic phase transition is considered in more detail and the results of corresponding magnetic measurements are described.

  11. Effects of timbre and tempo change on memory for music.

    PubMed

    Halpern, Andrea R; Müllensiefen, Daniel

    2008-09-01

    We investigated the effects of different encoding tasks and of manipulations of two supposedly surface parameters of music on implicit and explicit memory for tunes. In two experiments, participants were first asked to either categorize instrument or judge familiarity of 40 unfamiliar short tunes. Subsequently, participants were asked to give explicit and implicit memory ratings for a list of 80 tunes, which included 40 previously heard. Half of the 40 previously heard tunes differed in timbre (Experiment 1) or tempo (Experiment 2) in comparison with the first exposure. A third experiment compared similarity ratings of the tunes that varied in timbre or tempo. Analysis of variance (ANOVA) results suggest first that the encoding task made no difference for either memory mode. Secondly, timbre and tempo change both impaired explicit memory, whereas tempo change additionally made implicit tune recognition worse. Results are discussed in the context of implicit memory for nonsemantic materials and the possible differences in timbre and tempo in musical representations. PMID:19086302

  12. 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. PMID:24798660

  13. Extinction Partially Reverts Structural Changes Associated with Remote Fear Memory

    ERIC Educational Resources Information Center

    Vetere, Gisella; Restivo, Leonardo; Novembre, Giovanni; Aceti, Massimiliano; Lumaca, Massimo; Ammassari-Teule, Martine

    2011-01-01

    Structural synaptic changes occur in medial prefrontal cortex circuits during remote memory formation. Whether extinction reverts or further reshapes these circuits is, however, unknown. Here we show that the number and the size of spines were enhanced in anterior cingulate (aCC) and infralimbic (ILC) cortices 36 d following contextual fear…

  14. Acute social stress before the planning phase improves memory performance in a complex real life-related prospective memory task.

    PubMed

    Glienke, Katharina; Piefke, Martina

    2016-09-01

    Successful execution of intentions, but also the failure to recall are common phenomena in everyday life. The planning, retention, and realization of intentions are often framed as the scientific concept of prospective memory. The current study aimed to examine the influence of acute stress on key dimensions of complex "real life" prospective memory. To this end, we applied a prospective memory task that involved the planning, retention, and performance of intentions during a fictional holiday week. Forty healthy males participated in the study. Half of the subjects were stressed with the Socially Evaluated Cold Pressor Test (SECPT) before the planning of intentions, and the other half of the participants underwent a control procedure at the same time. Salivary cortisol was used to measure the effectiveness of the SECPT stress induction. Stressed participants did not differ from controls in planning accuracy. However, when we compared stressed participants with controls during prospective memory retrieval, we found statistically significant differences in PM across the performance phase. Participants treated with the SECPT procedure before the planning phase showed improved prospective memory retrieval over time, while performance of controls declined. Particularly, there was a significant difference between the stress and control group for the last two days of the holiday week. Interestingly, control participants showed significantly better performance for early than later learned items, which could be an indicator of a primacy effect. This differential effect of stress on performance was also found in time- and event-dependent prospective memory. Our results demonstrate for the first time, that acute stress induced before the planning phase may improve prospective memory over the time course of the performance phase in time- and event-dependent prospective memory. Our data thus indicate that prospective memory can be enhanced by acute stress. PMID:27370532

  15. Controlling the Phase of Ferromagnetic Josephson Junctions for Cryogenic Memory Applications

    NASA Astrophysics Data System (ADS)

    Niedzielski, Bethany; Gingrich, Eric; Glick, Joseph; Wang, Yixing; Miller, Don; Loloee, Reza; Pratt, William, Jr.; Birge, Norman

    Josephson junctions containing ferromagnetic layers are currently of interest for use in cryogenic memory where either the phase or critical current can be switched between two distinct states. We present the first direct phase measurements of such a junction demonstrating control of the phase. If a junction contains one ferromagnetic layer, the thickness of that layer dictates the ground state phase between the superconducting electrodes, which can be either 0 or π. If the junction contains two ferromagnetic layers and the layer thicknesses are carefully chosen, then the phase of a single junction can be switched between 0 and π by changing the relative magnetization directions of the two layers from antiparallel to parallel. We have successfully fabricated and directly measured the relative phase of two such spin valve junctions in a SQUID loop to confirm the phase change from π to 0 and back again of each junction. We report our continued progress in optimizing the control of such systems. This work was supported by IARPA via ARO Contract W911NF-14-C-0115.

  16. Sleep supports cued fear extinction memory consolidation independent of circadian phase.

    PubMed

    Melo, Irene; Ehrlich, Ingrid

    2016-07-01

    Sleep promotes memory, particularly for declarative learning. However, its role in non-declarative, emotional memories is less well understood. Some studies suggest that sleep may influence fear-related memories, and thus may be an important factor determining the outcome of treatments for emotional disorders such as post-traumatic stress disorder. Here, we investigated the effect of sleep deprivation and time of day on fear extinction memory consolidation. Mice were subjected to a cued Pavlovian fear and extinction paradigm at the beginning of their resting or active phase. Immediate post-extinction learning sleep deprivation for 5h compromised extinction memory when tested 24h after learning. Context-dependent extinction memory recall was completely prevented by sleep-manipulation during the resting phase, while impairment was milder during the active phase and extinction memory retained its context-specificity. Importantly, control experiments excluded confounding factors such as differences in baseline locomotion, fear generalization and stress hormone levels. Together, our findings indicate that post-learning sleep supports cued fear extinction memory consolidation in both circadian phases. The lack of correlation between memory efficacy and sleep time suggests that extinction memory may be influenced by specific sleep events in the early consolidation period. PMID:27109918

  17. Caregiver perspectives of memory and behavior changes in stroke survivors.

    PubMed

    Clark, Patricia C; Dunbar, Sandra B; Aycock, Dawn M; Courtney, Elizabeth; Wolf, Steven L

    2006-01-01

    Post-stroke memory and behavior changes (MBC) are associated with negative outcomes for stroke survivors and caregivers. This article describes the types of MBC that occur most frequently and caregivers' responses to these behaviors. Data were obtained through in-person interviews and administration of questionnaires to 132 caregivers of first-time stroke survivors 3-9 months after stroke. MBC were measured with a modified version of a Memory and Behavior Problems checklist. On average, caregivers reported 7.7 +/- 3.6 (range 0-17) behaviors. Common stroke survivor MBC included appearing sad or depressed, interrupting the caregiver, and being restless or agitated. These MBC were distressing to caregivers. Caregivers may not recognize some MBC as potential symptoms of depression. In addition, caregiver misunderstanding of the amount of control survivors may have over some behaviors has implications for rehabilitation and caregivers' responses to these changes. PMID:16422042

  18. 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

  19. 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

    2014-01-01

    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

  20. Mechanisms of Change: Exploring Not Only When and What, but Also How Declarative Memory Develops

    ERIC Educational Resources Information Center

    Richmond, Jenny; DeBoer, Tracy

    2006-01-01

    Age-related changes in representational flexibility are a characteristic feature of declarative memory development. The authors suggest that a qualitative shift in the nature of infants' memory representations accounts for increasing memory flexibility with age. We will argue that a comprehensive theory of declarative memory development must (1)…

  1. The fate of object memory traces under change detection and change blindness.

    PubMed

    Busch, Niko A

    2013-07-01

    Observers often fail to detect substantial changes in a visual scene. This so-called change blindness is often taken as evidence that visual representations are sparse and volatile. This notion rests on the assumption that the failure to detect a change implies that representations of the changing objects are lost all together. However, recent evidence suggests that under change blindness, object memory representations may be formed and stored, but not retrieved. This study investigated the fate of object memory representations when changes go unnoticed. Participants were presented with scenes consisting of real world objects, one of which changed on each trial, while recording event-related potentials (ERPs). Participants were first asked to localize where the change had occurred. In an additional recognition task, participants then discriminated old objects, either from the pre-change or the post-change scene, from entirely new objects. Neural traces of object memories were studied by comparing ERPs for old and novel objects. Participants performed poorly in the detection task and often failed to recognize objects from the scene, especially pre-change objects. However, a robust old/novel effect was observed in the ERP, even when participants were change blind and did not recognize the old object. This implicit memory trace was found both for pre-change and post-change objects. These findings suggest that object memories are stored even under change blindness. Thus, visual representations may not be as sparse and volatile as previously thought. Rather, change blindness may point to a failure to retrieve and use these representations for change detection. PMID:23685191

  2. Precipitate Phases in Several High Temperature Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Yang, Fan

    Initiated by the aerospace industry, there has been a great interest to develop high temperature shape memory alloys (HTSMAs) for actuator type of application at elevated temperatures. Several NiTi based ternary systems have been shown to be potential candidates for HTSMAs and this work focuses on one or more alloys in the TiNiPt, TiNiPd, NiTiHf, NiPdTiHf systems. The sheer scope of alloys of varying compositions across all four systems suggests that the questions raised and addressed in this work are just the tip of the iceberg. This work focuses on materials characterization and aims to investigate microstructural evolution of these alloys as a function of heat treatment. The information gained through the study can serve as guidance for future alloy processing. The emphasis of this work is to describe novel precipitate phases that are formed under aging in the ternary systems and one quaternary system. Employing conventional transmission electron microscopy (TEM), high resolution high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), 3D atom probe tomography (3D APT), as well as ab initio calculations, the complete description of the unit cell for the new precipitates was determined. The methodology is summarized in the appendix to help elucidate some basics of such a process.

  3. Awareness of Memory Ability and Change: (In)Accuracy of Memory Self-Assessments in Relation to Performance

    PubMed Central

    Rickenbach, Elizabeth Hahn; Agrigoroaei, Stefan; Lachman, Margie E.

    2015-01-01

    Little is known about subjective assessments of memory abilities and decline among middle-aged adults or their association with objective memory performance in the general population. In this study we examined self-ratings of memory ability and change in relation to episodic memory performance in two national samples of middle-aged and older adults from the Midlife in the United States study (MIDUS II in 2005-06) and the Health and Retirement Study (HRS; every two years from 2002 to 2012). MIDUS (Study 1) participants (N=3,581) rated their memory compared to others their age and to themselves five years ago; HRS (Study 2) participants (N=14,821) rated their current memory and their memory compared to two years ago, with up to six occasions of longitudinal data over ten years. In both studies, episodic memory performance was the total number of words recalled in immediate and delayed conditions. When controlling for demographic and health correlates, self-ratings of memory abilities, but not subjective change, were related to performance. We examined accuracy by comparing subjective and objective memory ability and change. More than one third of the participants across the studies had self-assessments that were inaccurate relative to their actual level of performance and change, and accuracy differed as a function of demographic and health factors. Further understanding of self-awareness of memory abilities and change beginning in midlife may be useful for identifying early warning signs of decline, with implications regarding policies and practice for early detection and treatment of cognitive impairment. PMID:25821529

  4. Functional connectivity change across multiple cortical networks relates to episodic memory changes in aging.

    PubMed

    Fjell, Anders M; Sneve, Markus H; Grydeland, Håkon; Storsve, Andreas B; de Lange, Ann-Marie Glasø; Amlien, Inge K; Røgeberg, Ole J; Walhovd, Kristine B

    2015-12-01

    A major task of contemporary cognitive neuroscience of aging is to explain why episodic memory declines. Change in resting-state functional connectivity (rsFC) could be a mechanism accounting for reduced function. We addressed this through 3 studies. In study 1, 119 healthy participants (20-83 years) were followed for 3.5 years with verbal recall testing and magnetic resonance imaging. Independent of atrophy, recall change was related to change in rsFC in anatomically widespread areas. Striking age-effects were observed in that a positive relationship between rsFC and memory characterized older participants while a negative relationship was seen among the younger and middle-aged. This suggests that cognitive consequences of rsFC change are not stable across age. In study 2 and 3, the age-dependent differences in rsFC-memory relationship were replicated by use of a simulation model (study 2) and by a cross-sectional experimental recognition memory task (study 3). In conclusion, memory changes were related to altered rsFC in an age-dependent manner, and future research needs to detail the mechanisms behind age-varying relationships. PMID:26363813

  5. Visual long-term memory and change blindness: Different effects of pre- and post-change information on one-shot change detection using meaningless geometric objects.

    PubMed

    Nishiyama, Megumi; Kawaguchi, Jun

    2014-11-01

    To clarify the relationship between visual long-term memory (VLTM) and online visual processing, we investigated whether and how VLTM involuntarily affects the performance of a one-shot change detection task using images consisting of six meaningless geometric objects. In the study phase, participants observed pre-change (Experiment 1), post-change (Experiment 2), or both pre- and post-change (Experiment 3) images appearing in the subsequent change detection phase. In the change detection phase, one object always changed between pre- and post-change images and participants reported which object was changed. Results showed that VLTM of pre-change images enhanced the performance of change detection, while that of post-change images decreased accuracy. Prior exposure to both pre- and post-change images did not influence performance. These results indicate that pre-change information plays an important role in change detection, and that information in VLTM related to the current task does not always have a positive effect on performance. PMID:25282403

  6. Sign reversal of transformation entropy change in Co2Cr(Ga,Si) shape memory alloys

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Omori, Toshihiro; Nagasako, Makoto; Kanomata, Takeshi; Kainuma, Ryosuke

    2015-11-01

    In situ X-ray diffraction (XRD) measurements and compression tests were performed on Co2Cr(Ga,Si) shape memory alloys. The reentrant martensitic transformation behavior was directly observed during the in situ XRD measurements. The high-temperature parent phase and low-temperature reentrant parent phase were found to have a continuous temperature dependence of lattice parameter, therefore suggesting that they are the same phase in nature. Moreover, compression tests were performed on a parent-phase single crystal sample; an evolution from normal to inverse temperature dependence of critical stress for martensitic transformation was directly observed. Based on the Clausius-Clapeyron analysis, a sign reversal of entropy change can be expected on the same alloy.

  7. Phase of Spontaneous Slow Oscillations during Sleep Influences Memory-Related Processing of Auditory Cues

    PubMed Central

    Creery, Jessica D.; Paller, Ken A.

    2016-01-01

    Slow oscillations during slow-wave sleep (SWS) may facilitate memory consolidation by regulating interactions between hippocampal and cortical networks. Slow oscillations appear as high-amplitude, synchronized EEG activity, corresponding to upstates of neuronal depolarization and downstates of hyperpolarization. Memory reactivations occur spontaneously during SWS, and can also be induced by presenting learning-related cues associated with a prior learning episode during sleep. This technique, targeted memory reactivation (TMR), selectively enhances memory consolidation. Given that memory reactivation is thought to occur preferentially during the slow-oscillation upstate, we hypothesized that TMR stimulation effects would depend on the phase of the slow oscillation. Participants learned arbitrary spatial locations for objects that were each paired with a characteristic sound (eg, cat–meow). Then, during SWS periods of an afternoon nap, one-half of the sounds were presented at low intensity. When object location memory was subsequently tested, recall accuracy was significantly better for those objects cued during sleep. We report here for the first time that this memory benefit was predicted by slow-wave phase at the time of stimulation. For cued objects, location memories were categorized according to amount of forgetting from pre- to post-nap. Conditions of high versus low forgetting corresponded to stimulation timing at different slow-oscillation phases, suggesting that learning-related stimuli were more likely to be processed and trigger memory reactivation when they occurred at the optimal phase of a slow oscillation. These findings provide insight into mechanisms of memory reactivation during sleep, supporting the idea that reactivation is most likely during cortical upstates. SIGNIFICANCE STATEMENT Slow-wave sleep (SWS) is characterized by synchronized neural activity alternating between active upstates and quiet downstates. The slow-oscillation upstates are

  8. Neural correlates of auditory sensory memory and automatic change detection.

    PubMed

    Sabri, Merav; Kareken, David A; Dzemidzic, Mario; Lowe, Mark J; Melara, Robert D

    2004-01-01

    An auditory event-related potential component, the mismatch negativity (MMN), reflects automatic change detection and its prerequisite, sensory memory. This study examined the neural correlates of automatic change detection using BOLD fMRI and two rates of presentation previously shown to induce either a large or no MMN. A boxcar block design was employed in two functional scans, each performed twice. A block consisting of 1000-Hz standards (S) alternated with one consisting of 1000-Hz standards and 2000-Hz infrequent deviants (S + D). Presentation rate was either 150 or 2400 ms. Fourteen participants were instructed to ignore all auditory stimulation and concentrate on a film (no audio) by reading subtitles. Data analysis used SPM99 and random effects approach. Cluster statistics (P < 0.05, corrected) were employed at a height threshold of P < 0.001. At the short ISI, there was a significant BOLD response in the right superior temporal gyrus (STG), the left insula, and the left STG (including parts of primary auditory cortex). There were no suprathreshold clusters at the long rate, with S + D blocks inducing no greater activity than S blocks. These results support the hypothesis that the automatic detection of auditory change occurs in the STG bilaterally and relies on the maintenance of sensory memory traces. PMID:14741643

  9. 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.

  10. Vanadium Dioxide Phase Change Switches

    NASA Astrophysics Data System (ADS)

    Field, Mark; Hillman, Christopher; Stupar, Philip; Hacker, Jonathan; Griffith, Zachary; Lee, Kang-Jin

    2015-03-01

    We have built RF switches using vanadium dioxide thin films fabricated within a section of inverted transmission line with integrated on chip heaters to provide local thermal control. On heating the films above the metal insulator transition we obtain record low switch insertion loss of -0.13 dB at 50 GHz and -0.5 dB at 110 GHz. We investigate the device physics of these switches including the effect of a deposited insulator on the VO2 switching characteristics, the self-latching of the devices under high RF powers and the effect of resistance change with temperature on the device linearity. Finally we show how these devices can be integrated with silicon germanium RF circuits to produce a field programmable device where the RF signal routing can be selected under external control. Supported under the DARPA RF-FPGA Program, Contract HR0011-12-C-0092.

  11. 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

  12. Phase changes in liquid face seals

    NASA Technical Reports Server (NTRS)

    Hughes, W. F.

    1980-01-01

    Computer program predicts boiling (phase change) in liquid face seals. Program determines if and when boiling occurs, and calculates location of boiling interface, pressure and temperature profiles, and load.

  13. Memory.

    ERIC Educational Resources Information Center

    McKean, Kevin

    1983-01-01

    Discusses current research (including that involving amnesiacs and snails) into the nature of the memory process, differentiating between and providing examples of "fact" memory and "skill" memory. Suggests that three brain parts (thalamus, fornix, mammilary body) are involved in the memory process. (JN)

  14. 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. PMID:26415716

  15. Neural Changes Underlying the Development of Episodic Memory During Middle Childhood

    PubMed Central

    Ghetti, Simona; Bunge, Silvia A.

    2012-01-01

    Episodic memory is central to the human experience. In typically developing children, episodic memory improves rapidly during middle childhood. While the developmental cognitive neuroscience of episodic memory remains largely uncharted, recent research has begun to provide important insights. It has long been assumed that hippocampus-dependent binding mechanisms are in place by early childhood, and that improvements in episodic memory observed during middle childhood result from the protracted development of the prefrontal cortex. We revisit the notion that binding mechanisms are age-invariant, and propose that changes in the hippocampus and its projections to cortical regions also contribute to the development of episodic memory. We further review the role of developmental changes in lateral prefrontal and parietal cortices in this development. Finally, we discuss changes in white matter tracts connecting brain regions that are critical for episodic memory. Overall, we argue that changes in episodic memory emerge from the concerted effort of a network of relevant brain structures. PMID:22770728

  16. Thermoviscoplastic behaviors of anisotropic shape memory elastomeric composites for cold programmed non-affine shape change

    NASA Astrophysics Data System (ADS)

    Mao, Yiqi; Robertson, Jaimee M.; Mu, Xiaoming; Mather, Patrick T.; Jerry Qi, H.

    2015-12-01

    Shape memory polymers (SMPs) can fix a temporary shape and recover their permanent shape upon activation by an external stimulus. Most SMPs require programming at above their transition temperatures, normally well above the room temperature. In addition, most SMPs are programmed into shapes that are affine to the high temperature deformation. Recently, a cold-programmed anisotropic shape memory elastomeric composite was developed and showed interesting low temperature stretching induced shape memory behavior. There, simple, uniaxial stretching at low temperature transformed the composites into curled temporary shapes upon unloading. The exact geometry of the curled state depended on the microstructure of the composite, and the curled shape showed no affinity to the deformed shape. Heating the sample recovered the sample back to its original shape. This new composite consisted of an elastomeric matrix reinforced by aligned amorphous polymer fibers. By utilizing the plastic-like behavior of the amorphous polymer phase at low temperatures, a temporary shape could be fixed upon unloading since the induced plastic-like strain resists the recovery of the elastomer matrix. After heating to a high temperature, the permanent shape was recovered when the amorphous polymer softened and the elastomer matrix contracted. To set a theoretical foundation for capturing the cold-programmed shape memory effects and the dramatic non-affine shape change of this composite, a 3D anisotropic thermoviscoelastic constitutive model is developed in this paper. In this model, the matrix is modeled as a hyperelastic solid, and the amorphous phase of the fibrous mat is considered as a nonlinear thermoviscoplastic solid, whose viscous flow resistance is sensitive to both temperature and stress. The plastic-deformation like behavior demonstrated in the fiber is treated as nonlinear viscoplasticity with extremely high viscosity or long relaxation time at zero-stress state at low temperature. The

  17. Inducing chalcogenide phase change with ultra-narrow carbon nanotube heaters

    NASA Astrophysics Data System (ADS)

    Xiong, Feng; Liao, Albert; Pop, Eric

    2009-12-01

    Carbon nanotube (CNT) heaters with sub-5 nm diameter induce highly localized phase change in Ge2Sb2Te5 (GST) chalcogenide. A significant reduction in resistance of test structures is measured as the GST near the CNT heater crystallizes. Effective GST heating occurs at currents as low as 25 μA, significantly lower than in conventional phase change memory with metal electrodes (0.1-0.5 mA). Atomic force microscopy reveals nucleation sites associated with phase change in GST around the CNT heater. Finite element simulations confirm electrical characteristics consistent with the experiments, and reveal the current and phase distribution in GST.

  18. Growth resumption from stationary phase reveals memory in Escherichia coli cultures

    PubMed Central

    Jõers, Arvi; Tenson, Tanel

    2016-01-01

    Frequent changes in nutrient availability often result in repeated cycles of bacterial growth and dormancy. The timing of growth resumption can differ among isogenic cells and delayed growth resumption can lead to antibiotic tolerant persisters. Here we describe a correlation between the timing of entry into stationary phase and resuming growth in the next period of cell proliferation. E. coli cells can follow a last in first out rule: the last ones to shut down their metabolism in the beginning of stationary phase are the first to recover in response to nutrients. This memory effect can last for several days in stationary phase and is not influenced by environmental changes. We observe that the speed and heterogeneity of growth resumption depends on the carbon source. A good carbon source (glucose) can promote rapid growth resumption even at low concentrations, and is seen to act more like a signal than a growth substrate. Heterogeneous growth resumption can protect the population from adverse effect of stress, investigated here using heat-shock, because the stress-resilient dormant cells are always present. PMID:27048851

  19. Growth resumption from stationary phase reveals memory in Escherichia coli cultures.

    PubMed

    Jõers, Arvi; Tenson, Tanel

    2016-01-01

    Frequent changes in nutrient availability often result in repeated cycles of bacterial growth and dormancy. The timing of growth resumption can differ among isogenic cells and delayed growth resumption can lead to antibiotic tolerant persisters. Here we describe a correlation between the timing of entry into stationary phase and resuming growth in the next period of cell proliferation. E. coli cells can follow a last in first out rule: the last ones to shut down their metabolism in the beginning of stationary phase are the first to recover in response to nutrients. This memory effect can last for several days in stationary phase and is not influenced by environmental changes. We observe that the speed and heterogeneity of growth resumption depends on the carbon source. A good carbon source (glucose) can promote rapid growth resumption even at low concentrations, and is seen to act more like a signal than a growth substrate. Heterogeneous growth resumption can protect the population from adverse effect of stress, investigated here using heat-shock, because the stress-resilient dormant cells are always present. PMID:27048851

  20. Memory-based mismatch response to frequency changes in rats.

    PubMed

    Astikainen, Piia; Stefanics, Gabor; Nokia, Miriam; Lipponen, Arto; Cong, Fengyu; Penttonen, Markku; Ruusuvirta, Timo

    2011-01-01

    Any occasional changes in the acoustic environment are of potential importance for survival. In humans, the preattentive detection of such changes generates the mismatch negativity (MMN) component of event-related brain potentials. MMN is elicited to rare changes ('deviants') in a series of otherwise regularly repeating stimuli ('standards'). Deviant stimuli are detected on the basis of a neural comparison process between the input from the current stimulus and the sensory memory trace of the standard stimuli. It is, however, unclear to what extent animals show a similar comparison process in response to auditory changes. To resolve this issue, epidural potentials were recorded above the primary auditory cortex of urethane-anesthetized rats. In an oddball condition, tone frequency was used to differentiate deviants interspersed randomly among a standard tone. Mismatch responses were observed at 60-100 ms after stimulus onset for frequency increases of 5% and 12.5% but not for similarly descending deviants. The response diminished when the silent inter-stimulus interval was increased from 375 ms to 600 ms for +5% deviants and from 600 ms to 1000 ms for +12.5% deviants. In comparison to the oddball condition the response also diminished in a control condition in which no repetitive standards were presented (equiprobable condition). These findings suggest that the rat mismatch response is similar to the human MMN and indicate that anesthetized rats provide a valuable model for studies of central auditory processing. PMID:21915297

  1. Similarity solutions for phase-change problems

    NASA Technical Reports Server (NTRS)

    Canright, D.; Davis, S. H.

    1989-01-01

    A modification of Ivantsov's (1947) similarity solutions is proposed which can describe phase-change processes which are limited by diffusion. The method has application to systems that have n-components and possess cross-diffusion and Soret and Dufour effects, along with convection driven by density discontinuities at the two-phase interface. Local thermal equilibrium is assumed at the interface. It is shown that analytic solutions are possible when the material properties are constant.

  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. Thermal transport in phase-change materials from atomistic simulations

    NASA Astrophysics Data System (ADS)

    Sosso, Gabriele C.; Donadio, Davide; Caravati, Sebastiano; Behler, Jörg; Bernasconi, Marco

    2012-09-01

    We computed the thermal conductivity (κ) of amorphous GeTe by means of classical molecular dynamics and lattice dynamics simulations. GeTe is a phase change material of interest for applications in nonvolatile memories. An interatomic potential with close-to-ab initio accuracy was used as generated by fitting a huge ab initio database with a neural network method. It turns out that the majority of heat carriers are nonpropagating vibrations (diffusons), the small percentage of propagating modes giving a negligible contribution to the total value of κ. This result is in contrast with the properties of other amorphous semiconductors such as Si for which nonpropagating and propagating vibrations account for about one half of the value of κ each. This outcome suggests that the value of κ measured for the bulk amorphous phase can be used to model the thermal transport of GeTe and possibly of other materials in the same class also in nanoscaled memory devices. Actually, the contribution from propagating modes, which may endure ballistic transport at the scale of 10-20 nm, is negligible.

  4. Stress and memory retrieval in women: no strong impairing effect during the luteal phase.

    PubMed

    Schoofs, Daniela; Wolf, Oliver T

    2009-06-01

    Stress has been shown to impair delayed memory retrieval, but so far no study has been conducted solely with naturally cycling women. In a crossover design, 36 women (all in the luteal phase) participated in two experimental conditions (stress vs. control). Delayed memory retrieval of a wordlist learned 24 hours earlier was tested after stress or control treatment. Although stressed subjects showed a strong cortisol increase following stress, no influence on memory retrieval occurred. In an additional data analysis, subjects were split up into a cortisol responder and a cortisol nonresponder group. However, again no evidence for a stress-induced retrieval impairment became apparent. Similarly, no correlation was observed between the stress-induced cortisol increase and memory. This study failed to find an influence of stress on memory retrieval in women tested in the luteal phase. The findings are in contrast to our previous results obtained with men. Evidence is discussed that the luteal phase, which is characterized by elevated gonadal steroids, is associated with reduced glucocorticoid sensitivity. This might underlie the missing impact of stress on memory. PMID:19485561

  5. Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane

    2012-01-01

    The deformation and transformation mechanisms of polycrystalline Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 (in at.%) shape memory alloys were investigated by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The thermomechanical response of the low temperature martensite, the high temperature austenite phases, and changes between these two states during thermomechanical cycling were probed and reported. In the cubic austenite phase, stress-induced martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were compared to the bulk macroscopic response. When cycling between these two phases, the evolution of inelastic strains, along with the shape setting procedures were examined and used for the optimization of the transformation properties as a function of deformation levels and temperatures. Finally, this work was extended to the development of multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory.

  6. 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.

  7. Five Phases for Managing Change in Education.

    ERIC Educational Resources Information Center

    Bowsher, Jack E.

    1989-01-01

    Educators should make learning more work related and companies should make work more learning related. A five-phase system for managing educational change includes (1) unstructured education; (2) inventory of education programs and costs; (3) planning, measurement, and organization; (4) implementation of structured education; and (5) refining…

  8. 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.

  9. Expectancy effects in source memory: how moving to a bad neighborhood can change your memory.

    PubMed

    Kroneisen, Meike; Woehe, Larissa; Rausch, Leonie Sophie

    2015-02-01

    Enhanced memory for cheaters could be suited to avoid social exchange situations in which we run the risk of getting exploited by others. Several experiments demonstrated that we have better source memory for faces combined with negative rather than positive behavior (Bell & Buchner, Memory & Cognition, 38, 29-41, 2010) or for cheaters and cooperators showing unexpected behavior (Bell, Buchner, Kroneisen, Giang, Journal of Experimental Psychology: Learning, Memory, and Cognition, 38, 1512-1529, 2012). In the present study, we compared two groups: Group 1 just saw faces combined with aggressive, prosocial or neutral behavior descriptions, but got no further information, whereas group 2 was explicitly told that they would now see the behavior descriptions of very aggressive and unsocial persons. To measure old-new discrimination, source memory, and guessing biases separately, we used a multinomial model. When having no expectancies about the behavior of the presented people, enhanced source memory for aggressive persons was found. In comparison, source memory for faces combined with prosocial behavior descriptions was significantly higher in the group expecting only aggressive persons. These findings can be attributed to a mechanism that focuses on expectancy-incongruent information, representing a more flexible and therefore efficient memory strategy for remembering exchange-relevant information. PMID:24838306

  10. Developmental Change in Working Memory Strategies: From Passive Maintenance to Active Refreshing

    ERIC Educational Resources Information Center

    Camos, Valerie; Barrouillet, Pierre

    2011-01-01

    Change in strategies is often mentioned as a source of memory development. However, though performance in working memory tasks steadily improves during childhood, theories differ in linking this development to strategy changes. Whereas some theories, such as the time-based resource-sharing model, invoke the age-related increase in use and…

  11. Formation of visual memories controlled by gamma power phase-locked to alpha oscillations

    NASA Astrophysics Data System (ADS)

    Park, Hyojin; Lee, Dong Soo; Kang, Eunjoo; Kang, Hyejin; Hahm, Jarang; Kim, June Sic; Chung, Chun Kee; Jiang, Haiteng; Gross, Joachim; Jensen, Ole

    2016-06-01

    Neuronal oscillations provide a window for understanding the brain dynamics that organize the flow of information from sensory to memory areas. While it has been suggested that gamma power reflects feedforward processing and alpha oscillations feedback control, it remains unknown how these oscillations dynamically interact. Magnetoencephalography (MEG) data was acquired from healthy subjects who were cued to either remember or not remember presented pictures. Our analysis revealed that in anticipation of a picture to be remembered, alpha power decreased while the cross-frequency coupling between gamma power and alpha phase increased. A measure of directionality between alpha phase and gamma power predicted individual ability to encode memory: stronger control of alpha phase over gamma power was associated with better memory. These findings demonstrate that encoding of visual information is reflected by a state determined by the interaction between alpha and gamma activity.

  12. Formation of visual memories controlled by gamma power phase-locked to alpha oscillations

    PubMed Central

    Park, Hyojin; Lee, Dong Soo; Kang, Eunjoo; Kang, Hyejin; Hahm, Jarang; Kim, June Sic; Chung, Chun Kee; Jiang, Haiteng; Gross, Joachim; Jensen, Ole

    2016-01-01

    Neuronal oscillations provide a window for understanding the brain dynamics that organize the flow of information from sensory to memory areas. While it has been suggested that gamma power reflects feedforward processing and alpha oscillations feedback control, it remains unknown how these oscillations dynamically interact. Magnetoencephalography (MEG) data was acquired from healthy subjects who were cued to either remember or not remember presented pictures. Our analysis revealed that in anticipation of a picture to be remembered, alpha power decreased while the cross-frequency coupling between gamma power and alpha phase increased. A measure of directionality between alpha phase and gamma power predicted individual ability to encode memory: stronger control of alpha phase over gamma power was associated with better memory. These findings demonstrate that encoding of visual information is reflected by a state determined by the interaction between alpha and gamma activity. PMID:27306959

  13. Formation of visual memories controlled by gamma power phase-locked to alpha oscillations.

    PubMed

    Park, Hyojin; Lee, Dong Soo; Kang, Eunjoo; Kang, Hyejin; Hahm, Jarang; Kim, June Sic; Chung, Chun Kee; Jiang, Haiteng; Gross, Joachim; Jensen, Ole

    2016-01-01

    Neuronal oscillations provide a window for understanding the brain dynamics that organize the flow of information from sensory to memory areas. While it has been suggested that gamma power reflects feedforward processing and alpha oscillations feedback control, it remains unknown how these oscillations dynamically interact. Magnetoencephalography (MEG) data was acquired from healthy subjects who were cued to either remember or not remember presented pictures. Our analysis revealed that in anticipation of a picture to be remembered, alpha power decreased while the cross-frequency coupling between gamma power and alpha phase increased. A measure of directionality between alpha phase and gamma power predicted individual ability to encode memory: stronger control of alpha phase over gamma power was associated with better memory. These findings demonstrate that encoding of visual information is reflected by a state determined by the interaction between alpha and gamma activity. PMID:27306959

  14. 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. PMID:25197044

  15. An improved car-following model considering headway changes with memory

    NASA Astrophysics Data System (ADS)

    Yu, Shaowei; Shi, Zhongke

    2015-03-01

    To describe car-following behaviors in complex situations better, increase roadway traffic mobility and minimize cars' fuel consumptions, the linkage between headway changes with memory and car-following behaviors was explored with the field car-following data by using the gray correlation analysis method, and then an improved car-following model considering headway changes with memory on a single lane was proposed based on the full velocity difference model. Some numerical simulations were carried out by employing the improved car-following model to explore how headway changes with memory affected each car's velocity, acceleration, headway and fuel consumptions. The research results show that headway changes with memory have significant effects on car-following behaviors and fuel consumptions and that considering headway changes with memory in designing the adaptive cruise control strategy can improve the traffic flow stability and minimize cars' fuel consumptions.

  16. Locust Dynamics: Behavioral Phase Change and Swarming

    PubMed Central

    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. PMID:22916003

  17. Three-dimensional nanomechanical mapping of amorphous and crystalline phase transitions in phase-change materials.

    PubMed

    Grishin, Ilja; Huey, Bryan D; Kolosov, Oleg V

    2013-11-13

    The nanostructure of micrometer-sized domains (bits) in phase-change materials (PCM) that undergo switching between amorphous and crystalline phases plays a key role in the performance of optical PCM-based memories. Here, we explore the dynamics of such phase transitions by mapping PCM nanostructures in three dimensions with nanoscale resolution by combining precision Ar ion beam cross-sectional polishing and nanomechanical ultrasonic force microscopy (UFM) mapping. Surface and bulk phase changes of laser written submicrometer to micrometer sized amorphous-to-crystalline (SET) and crystalline-to-amorphous (RESET) bits in chalcogenide Ge2Sb2Te5 PCM are observed with 10-20 nm lateral and 4 nm depth resolution. UFM mapping shows that the Young's moduli of crystalline SET bits exceed the moduli of amorphous areas by 11 ± 2%, with crystalline content extending from a few nanometers to 50 nm in depth depending on the energy of the switching pulses. The RESET bits written with 50 ps pulses reveal shallower depth penetration and show 30-50 nm lateral and few nanometer vertical wavelike topography that is anticorrelated with the elastic modulus distribution. Reverse switching of amorphous RESET bits results in the full recovery of subsurface nanomechanical properties accompanied with only partial topography recovery, resulting in surface corrugations attributed to quenching. This precision sectioning and nanomechanical mapping approach could be applicable to a wide range of amorphous, nanocrystalline, and glass-forming materials for 3D nanomechanical mapping of amorphous-crystalline transitions. PMID:24111915

  18. Changing Conception of Sources of Memory Development. 1985/23.

    ERIC Educational Resources Information Center

    Chi, Michelene T. H.

    1985-01-01

    Explanations for memory development have tended to focus on acquistion of general strategies and metaknowledge. Recently, emphasis has been given to the knowledge base as a whole, including general world-knowledge and domain-specific knowledge and procedures. Evidence is presented from the memory development literature showing why strategies and…

  19. Late Protein Synthesis-Dependent Phases in CTA Long-Term Memory: BDNF Requirement

    PubMed Central

    Martínez-Moreno, Araceli; Rodríguez-Durán, Luis F.; Escobar, Martha L.

    2011-01-01

    It has been proposed that long-term memory (LTM) persistence requires a late protein synthesis-dependent phase, even many hours after memory acquisition. Brain-derived neurotrophic factor (BDNF) is an essential protein synthesis product that has emerged as one of the most potent molecular mediators for long-term synaptic plasticity. Studies in the rat hippocampus have been shown that BDNF is capable to rescue the late-phase of long-term potentiation as well as the hippocampus-related LTM when protein synthesis was inhibited. Our previous studies on the insular cortex (IC), a region of the temporal cortex implicated in the acquisition and storage of conditioned taste aversion (CTA), have demonstrated that intracortical delivery of BDNF reverses the deficit in CTA memory caused by the inhibition of IC protein synthesis due to anisomycin administration during early acquisition. In this work, we first analyze whether CTA memory storage is protein synthesis-dependent in different time windows. We observed that CTA memory become sensible to protein synthesis inhibition 5 and 7 h after acquisition. Then, we explore the effect of BDNF delivery (2 μg/2 μl per side) in the IC during those late protein synthesis-dependent phases. Our results show that BDNF reverses the CTA memory deficit produced by protein synthesis inhibition in both phases. These findings support the notion that recurrent rounds of consolidation-like events take place in the neocortex for maintenance of CTA memory trace and that BDNF is an essential component of these processes. PMID:21960964

  20. Late Protein Synthesis-Dependent Phases in CTA Long-Term Memory: BDNF Requirement.

    PubMed

    Martínez-Moreno, Araceli; Rodríguez-Durán, Luis F; Escobar, Martha L

    2011-01-01

    It has been proposed that long-term memory (LTM) persistence requires a late protein synthesis-dependent phase, even many hours after memory acquisition. Brain-derived neurotrophic factor (BDNF) is an essential protein synthesis product that has emerged as one of the most potent molecular mediators for long-term synaptic plasticity. Studies in the rat hippocampus have been shown that BDNF is capable to rescue the late-phase of long-term potentiation as well as the hippocampus-related LTM when protein synthesis was inhibited. Our previous studies on the insular cortex (IC), a region of the temporal cortex implicated in the acquisition and storage of conditioned taste aversion (CTA), have demonstrated that intracortical delivery of BDNF reverses the deficit in CTA memory caused by the inhibition of IC protein synthesis due to anisomycin administration during early acquisition. In this work, we first analyze whether CTA memory storage is protein synthesis-dependent in different time windows. We observed that CTA memory become sensible to protein synthesis inhibition 5 and 7 h after acquisition. Then, we explore the effect of BDNF delivery (2 μg/2 μl per side) in the IC during those late protein synthesis-dependent phases. Our results show that BDNF reverses the CTA memory deficit produced by protein synthesis inhibition in both phases. These findings support the notion that recurrent rounds of consolidation-like events take place in the neocortex for maintenance of CTA memory trace and that BDNF is an essential component of these processes. PMID:21960964

  1. Expectations about Memory Change Across the Life Span Are Impacted By Aging Stereotypes

    PubMed Central

    Lineweaver, Tara T.; Berger, Andrea K.; Hertzog, Christopher

    2008-01-01

    This study examined whether expectations about memory change with age vary for different personality types. Four adjectives from each of Hummert’s age-stereotype trait sets were selected to create 11 adjective clusters varying in both valence (positive versus negative) and relevance to memory functioning. Three hundred and seventy three participants in three age groups rated the memory abilities of target adults, defined by the adjective clusters, across the adult life span. Consistent with past studies, participants believed in age-related memory decline. However, participants rated target adults with positive personality traits as having better memory ability and less age-related memory decline than target adults with negative personality traits. This effect was larger when the traits were relevant to memory than when they were not. Finally, older participants were more strongly influenced by both the valence and the relevance of the personality descriptions than younger participants. PMID:19290748

  2. Why Narrating Changes Memory: A Contribution to an Integrative Model of Memory and Narrative Processes.

    PubMed

    Smorti, Andrea; Fioretti, Chiara

    2016-06-01

    This paper aims to reflect on the relation between autobiographical memory (ME) and autobiographical narrative (NA), examining studies on the effects of narrating on the narrator and showing how studying these relations can make more comprehensible both memory's and narrating's way of working. Studies that address explicitly on ME and NA are scarce and touch this issue indirectly. Authors consider different trends of studies of ME and NA: congruency vs incongruency hypotheses on retrieving, the way of organizing memories according to gist or verbatim format and their role in organizing positive and negative emotional experiences, the social roots of ME and NA, the rules of conversation based on narrating. Analysis of investigations leads the Authors to point out three basic results of their research. Firstly, NA transforms ME because it narrativizes memories according to a narrative format. This means that memories, when are narrated, are transformed in stories (verbal language) and socialised. Secondly, the narrativization process is determined by the act of telling something within a communicative situation. Thus, relational situation of narrating act, by modifying the story, modifies also memories. The Authors propose the RE.NA.ME model (RElation, NArration, MEmory) to understand and study ME and NA. Finally, this study claims that ME and NA refer to two different types of processes having a wide area of overlapping. This is due to common social, developmental and cultural roots that make NA to include part of ME (narrative of memory) and ME to include part of NA (memory of personal events that have been narrated). PMID:26433588

  3. Direct observation of titanium-centered octahedra in titanium-antimony-tellurium phase-change material

    NASA Astrophysics Data System (ADS)

    Rao, Feng; Song, Zhitang; Cheng, Yan; Liu, Xiaosong; Xia, Mengjiao; Li, Wei; Ding, Keyuan; Feng, Xuefei; Zhu, Min; Feng, Songlin

    2015-11-01

    Phase-change memory based on Ti0.4Sb2Te3 material has one order of magnitude faster Set speed and as low as one-fifth of the Reset energy compared with the conventional Ge2Sb2Te5 based device. However, the phase-transition mechanism of the Ti0.4Sb2Te3 material remains inconclusive due to the lack of direct experimental evidence. Here we report a direct atom-by-atom chemical identification of titanium-centered octahedra in crystalline Ti0.4Sb2Te3 material with a state-of-the-art atomic mapping technology. Further, by using soft X-ray absorption spectroscopy and density function theory simulations, we identify in amorphous Ti0.4Sb2Te3 the titanium atoms preferably maintain the octahedral configuration. Our work may pave the way to more thorough understanding and tailoring of the nature of the Ti-Sb-Te material, for promoting the development of dynamic random access memory-like phase-change memory as an emerging storage-class memory to reform current memory hierarchy.

  4. Direct observation of titanium-centered octahedra in titanium-antimony-tellurium phase-change material.

    PubMed

    Rao, Feng; Song, Zhitang; Cheng, Yan; Liu, Xiaosong; Xia, Mengjiao; Li, Wei; Ding, Keyuan; Feng, Xuefei; Zhu, Min; Feng, Songlin

    2015-01-01

    Phase-change memory based on Ti0.4Sb2Te3 material has one order of magnitude faster Set speed and as low as one-fifth of the Reset energy compared with the conventional Ge2Sb2Te5 based device. However, the phase-transition mechanism of the Ti0.4Sb2Te3 material remains inconclusive due to the lack of direct experimental evidence. Here we report a direct atom-by-atom chemical identification of titanium-centered octahedra in crystalline Ti0.4Sb2Te3 material with a state-of-the-art atomic mapping technology. Further, by using soft X-ray absorption spectroscopy and density function theory simulations, we identify in amorphous Ti0.4Sb2Te3 the titanium atoms preferably maintain the octahedral configuration. Our work may pave the way to more thorough understanding and tailoring of the nature of the Ti-Sb-Te material, for promoting the development of dynamic random access memory-like phase-change memory as an emerging storage-class memory to reform current memory hierarchy. PMID:26610374

  5. Direct observation of titanium-centered octahedra in titanium–antimony–tellurium phase-change material

    PubMed Central

    Rao, Feng; Song, Zhitang; Cheng, Yan; Liu, Xiaosong; Xia, Mengjiao; Li, Wei; Ding, Keyuan; Feng, Xuefei; Zhu, Min; Feng, Songlin

    2015-01-01

    Phase-change memory based on Ti0.4Sb2Te3 material has one order of magnitude faster Set speed and as low as one-fifth of the Reset energy compared with the conventional Ge2Sb2Te5 based device. However, the phase-transition mechanism of the Ti0.4Sb2Te3 material remains inconclusive due to the lack of direct experimental evidence. Here we report a direct atom-by-atom chemical identification of titanium-centered octahedra in crystalline Ti0.4Sb2Te3 material with a state-of-the-art atomic mapping technology. Further, by using soft X-ray absorption spectroscopy and density function theory simulations, we identify in amorphous Ti0.4Sb2Te3 the titanium atoms preferably maintain the octahedral configuration. Our work may pave the way to more thorough understanding and tailoring of the nature of the Ti–Sb–Te material, for promoting the development of dynamic random access memory-like phase-change memory as an emerging storage-class memory to reform current memory hierarchy. PMID:26610374

  6. Memory load modulates graded changes in distracter filtering.

    PubMed

    Shimi, Andria; Woolrich, Mark W; Mantini, Dante; Astle, Duncan E

    2014-01-01

    Our ability to maintain small amounts of information in mind is critical for successful performance on a wide range of tasks. However, it remains unclear exactly how this maintenance is achieved. One possibility is that it is brought about using mechanisms that overlap with those used for attentional control. That is, the same mechanisms that we use to regulate and optimize our sensory processing may be recruited when we maintain information in visual short-term memory (VSTM). We aimed to test this hypothesis by exploring how distracter filtering is modified by concurrent VSTM load. We presented participants with sequences of target items, the order and location of which had to be maintained in VSTM. We also presented distracter items alongside the targets, and these distracters were graded such that they could be either very similar or dissimilar to the targets. We analyzed scalp potentials using a novel multiple regression approach, which enabled us to explore the neural mechanisms by which the participants accommodated these variable distracters on a trial-to-trial basis. Critically, the effect of distracter filtering interacted with VSTM load; the same graded changes in perceptual similarity exerted effects of a different magnitude depending upon how many items participants were already maintaining in VSTM. These data provide compelling evidence that maintaining information in VSTM recruits an overlapping set of attentional control mechanisms that are otherwise used for distracter filtering. PMID:25610387

  7. Phase change thermal energy storage material

    SciTech Connect

    Benson, D.K.; Burrows, R.W.

    1987-10-27

    A thermal energy storage tank is described comprising a containment vessel arranged for exposure to thermal energy, and a thermal energy storage composition disposed within the vessel and comprising a non-chloride hydrate having a phase change transition temperature in the range of 70/sup 0/-95/sup 0/F and a latent heat of transformation of greater than about 35 calories/gram. The non-chloride hydrate comprises trimethyol ethane hydrate.

  8. Changing Behavior by Memory Aids: A Social Psychological Model of Prospective Memory and Habit Development Tested with Dynamic Field Data

    ERIC Educational Resources Information Center

    Tobias, Robert

    2009-01-01

    This article presents a social psychological model of prospective memory and habit development. The model is based on relevant research literature, and its dynamics were investigated by computer simulations. Time-series data from a behavior-change campaign in Cuba were used for calibration and validation of the model. The model scored well in…

  9. Martensitic phase transformation and ferromagnetic shape memory effect in iron palladium single crystal

    NASA Astrophysics Data System (ADS)

    Cui, Jun

    In this thesis the ferromagnetic shape memory effect in Fe70Pd 30 alloys is studied in three stages. The first stage is to grow a single crystal of Fe70Pd30 using Bridgman method; the second stage focuses on the characterization of material properties. Both x-ray analysis and DSC measurements show that the FCC-FCT transformation is a weak first order thermoelastic transition. The average lattice parameters are a = 3.822 A and c = 3.6298 A for the FCT martensite, and a0 = 3.7557 A for the cubic austenite. The latent heat is 10.79 +/- 11 J/cm3. The Curie temperature is 300°C. The saturation magnetization is ms = 1217 emu/cm3 for the martensite and ms = 1081 emu/cm 3 for the austenite in Fe70Pd30 alloy; the easy axis is in the [100] or [010] direction (the long axis of the FCT lattice). The magnetic anisotropy is -4.8 x 103 erg/cm 3 for the austenite at 60°C, and it is 3.46 x 10 5 erg/cm3 for the martensite at -20°C. In addition, the effect of heat treatment on the materials properties is investigated. The third stage is to characterize the ferromagnetic shape memory effect of this alloy using magnetomechanical tests and the results are compared with micromagnetic theory. The sign of the field-induced strain agrees with the constrained theory. The maximum ferromagnetic strain in this material is about 0.9%, which is 1/4 of the theoretical prediction. The blocking stress is about -4 MPa, and the work output is about 20 x 103 J/m 3 per cycle at -12 MPa and 10°C. Furthermore, stress has large effect on the phase transformation temperature, for the compressive stress, it is 0.7°C/MPa. The phase transformation temperature can also be changed by applying a magnetic field during cooling or heating. The direction and the degree of changes depends on the direction of the field. The most significant change happens at a [001] field less than 1700 G, where [001] refers to the short axis of the FCT lattice.

  10. Numerical simulations of phase change in microgravity

    SciTech Connect

    Juric, D.; Tryggvason, G.

    1996-12-31

    Direct numerical simulations of liquid-solid and liquid-vapor phase change are conducted under microgravity conditions. The time-dependent governing equations are solved using a two-dimensional finite-difference/front-tracking method. Large interface deformations, topology change, latent heat, surface tension and unequal material properties between the phases are included in the simulations. Results are presented for two specific problems: directional solidification of a dilute binary alloy and the rapid evaporation of a superheated liquid (vapor explosion). For the directional solidification problem, solution of the fully coupled solute and energy equations reveals the evolution of morphologically complex structures such as tip splitting, coarsening and droplet detachment from deep intercellular grooves. A variety of important solute segregation patterns such as necking, coring and banding are also observed. The boiling problem couples the phase change with fluid flow. This requires the solution of the Navier-Stokes and energy equations with interphase mass transfer. The energetic growth of instabilities on planar and circular interfaces during the unstable explosive evaporation of a superheated liquid in microgravity is demonstrated.

  11. Subjective and Objective Memory Changes in Old Age across Five Years.

    PubMed

    Zimprich, Daniel; Kurtz, Tanja

    2015-01-01

    Typically, subjective memory assessments (be it in form of single items or questionnaires) in old age only weakly correlate with the performance in objective memory tests at cross-section. It thus appears as if individual differences in subjective memory assessments hardly reflect individual differences in memory in old age. A shortcoming of cross-sectional studies, however, is that subjective assessments may rely on different individual standards, which are not taken into account. One solution to this problem has been to investigate subjective and objective memory longitudinally, thereby focusing on individual differences in intraindividual changes. Results from studies using this approach have been mixed, with some studies showing a significantly stronger relation between changes than between levels, and other studies showing no such significant difference. Using data from the Zurich Longitudinal Study on Cognitive Aging (n=236), we find that 5-year changes in subjective assessments of memory capacity and memory changes correlate with objective memory changes of 0.54 and -0.44, respectively. These correlations are significantly stronger than at cross-section. After controlling for age, depressive affect, and subjective health at the first measurement occasion, correlations are slightly attenuated, but the basic findings remain the same. PMID:25791780

  12. TOPICAL REVIEW Nanoscale memory devices

    NASA Astrophysics Data System (ADS)

    Chung, Andy; Deen, Jamal; Lee, Jeong-Soo; Meyyappan, M.

    2010-10-01

    This article reviews the current status and future prospects for the use of nanomaterials and devices in memory technology. First, the status and continuing scaling trends of the flash memory are discussed. Then, a detailed discussion on technologies trying to replace flash in the near-term is provided. This includes phase change random access memory, Fe random access memory and magnetic random access memory. The long-term nanotechnology prospects for memory devices include carbon-nanotube-based memory, molecular electronics and memristors based on resistive materials such as TiO2.

  13. 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

  14. Different Phases of Long-Term Memory Require Distinct Temporal Patterns of PKA Activity after Single-Trial Classical Conditioning

    ERIC Educational Resources Information Center

    Michel, Maximilian; Kemenes, Ildiko; Muller, Uli; Kemenes, Gyorgy

    2008-01-01

    The cAMP-dependent protein kinase (PKA) is known to play a critical role in both transcription-independent short-term or intermediate-term memory and transcription-dependent long-term memory (LTM). Although distinct phases of LTM already have been demonstrated in some systems, it is not known whether these phases require distinct temporal patterns…

  15. X-ray diffraction study of the phase transformations in NiTi shape memory alloy

    SciTech Connect

    Uchil, J.; Fernandes, F.M. Braz . E-mail: kkmahesh@rediffmail.com

    2007-03-15

    The phase transformations occurring in heat-treated NiTi shape memory alloys have been studied through the analysis of variation in integrated peak area (integrated intensity) with temperature, under the XRD peak profiles in the transformation temperature range. For this purpose, integrated peak area under the prominent peak corresponding to (110) plane of the austenitic phase has been chosen. The results so obtained are compared with those got from the DSC method. The XRD method is found to be more sensitive.

  16. 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.

  17. Changes in the Capacity of Visual Working Memory in 5- to 10-Year-Olds

    ERIC Educational Resources Information Center

    Riggs, Kevin J.; McTaggart, James; Simpson, Andrew; Freeman, Richard P. J.

    2006-01-01

    Using the Luck and Vogel change detection paradigm, we sought to investigate the capacity of visual working memory in 5-, 7-, and 10-year-olds. We found that performance on the task improved significantly with age and also obtained evidence that the capacity of visual working memory approximately doubles between 5 and 10 years of age, where it…

  18. Developmental Changes in Memory Encoding: Insights from Event-Related Potentials

    ERIC Educational Resources Information Center

    Rollins, Leslie; Riggins, Tracy

    2013-01-01

    The aim of the present study was to investigate developmental changes in encoding processes between 6-year-old children and adults using event-related potentials (ERPs). Although episodic memory ("EM") effects have been reported in both children and adults at retrieval and subsequent memory effects have been established in adults, no…

  19. Memory for surface features of unfamiliar melodies: independent effects of changes in pitch and tempo.

    PubMed

    Schellenberg, E Glenn; Stalinski, Stephanie M; Marks, Bradley M

    2014-01-01

    A melody's identity is determined by relations between consecutive tones in terms of pitch and duration, whereas surface features (i.e., pitch level or key, tempo, and timbre) are irrelevant. Although surface features of highly familiar recordings are encoded into memory, little is known about listeners' mental representations of melodies heard once or twice. It is also unknown whether musical pitch is represented additively or interactively with temporal information. In two experiments, listeners heard unfamiliar melodies twice in an initial exposure phase. In a subsequent test phase, they heard the same (old) melodies interspersed with new melodies. Some of the old melodies were shifted in key, tempo, or key and tempo. Listeners' task was to rate how well they recognized each melody from the exposure phase while ignoring changes in key and tempo. Recognition ratings were higher for old melodies that stayed the same compared to those that were shifted in key or tempo, and detrimental effects of key and tempo changes were additive in between-subjects (Experiment 1) and within-subjects (Experiment 2) designs. The results confirm that surface features are remembered for melodies heard only twice. They also imply that key and tempo are processed and stored independently. PMID:23385775

  20. Effect of Circadian Phase on Memory Acquisition and Recall: Operant Conditioning vs. Classical Conditioning

    PubMed Central

    Garren, Madeleine V.; Sexauer, Stephen B.; Page, Terry L.

    2013-01-01

    There have been several studies on the role of circadian clocks in the regulation of associative learning and memory processes in both vertebrate and invertebrate species. The results have been quite variable and at present it is unclear to what extent the variability observed reflects species differences or differences in methodology. Previous results have shown that following differential classical conditioning in the cockroach, Rhyparobia maderae, in an olfactory discrimination task, formation of the short-term and long-term memory is under strict circadian control. In contrast, there appeared to be no circadian regulation of the ability to recall established memories. In the present study, we show that following operant conditioning of the same species in a very similar olfactory discrimination task, there is no impact of the circadian system on either short-term or long-term memory formation. On the other hand, ability to recall established memories is strongly tied to the circadian phase of training. On the basis of these data and those previously reported for phylogenetically diverse species, it is suggested that there may be fundamental differences in the way the circadian system regulates learning and memory in classical and operant conditioning. PMID:23533587

  1. Intensive Working Memory Training Produces Functional Changes in Large-scale Frontoparietal Networks.

    PubMed

    Thompson, Todd W; Waskom, Michael L; Gabrieli, John D E

    2016-04-01

    Working memory is central to human cognition, and intensive cognitive training has been shown to expand working memory capacity in a given domain. It remains unknown, however, how the neural systems that support working memory are altered through intensive training to enable the expansion of working memory capacity. We used fMRI to measure plasticity in activations associated with complex working memory before and after 20 days of training. Healthy young adults were randomly assigned to train on either a dual n-back working memory task or a demanding visuospatial attention task. Training resulted in substantial and task-specific expansion of dual n-back abilities accompanied by changes in the relationship between working memory load and activation. Training differentially affected activations in two large-scale frontoparietal networks thought to underlie working memory: the executive control network and the dorsal attention network. Activations in both networks linearly scaled with working memory load before training, but training dissociated the role of the two networks and eliminated this relationship in the executive control network. Load-dependent functional connectivity both within and between these two networks increased following training, and the magnitudes of increased connectivity were positively correlated with improvements in task performance. These results provide insight into the adaptive neural systems that underlie large gains in working memory capacity through training. PMID:26741799

  2. 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. PMID:27430363

  3. Changes in Neural Connectivity and Memory Following a Yoga Intervention for Older Adults: A Pilot Study

    PubMed Central

    Eyre, Harris A.; Acevedo, Bianca; Yang, Hongyu; Siddarth, Prabha; Van Dyk, Kathleen; Ercoli, Linda; Leaver, Amber M.; Cyr, Natalie St.; Narr, Katherine; Baune, Bernhard T.; Khalsa, Dharma S.; Lavretsky, Helen

    2016-01-01

    Background: No study has explored the effect of yoga on cognitive decline and resting-state functional connectivity. Objectives: This study explored the relationship between performance on memory tests and resting-state functional connectivity before and after a yoga intervention versus active control for subjects with mild cognitive impairment (MCI). Methods: Participants ( ≥ 55 y) with MCI were randomized to receive a yoga intervention or active “gold-standard” control (i.e., memory enhancement training (MET)) for 12 weeks. Resting-state functional magnetic resonance imaging was used to map correlations between brain networks and memory performance changes over time. Default mode networks (DMN), language and superior parietal networks were chosen as networks of interest to analyze the association with changes in verbal and visuospatial memory performance. Results: Fourteen yoga and 11 MET participants completed the study. The yoga group demonstrated a statistically significant improvement in depression and visuospatial memory. We observed improved verbal memory performance correlated with increased connectivity between the DMN and frontal medial cortex, pregenual anterior cingulate cortex, right middle frontal cortex, posterior cingulate cortex, and left lateral occipital cortex. Improved verbal memory performance positively correlated with increased connectivity between the language processing network and the left inferior frontal gyrus. Improved visuospatial memory performance correlated inversely with connectivity between the superior parietal network and the medial parietal cortex. Conclusion:Yoga may be as effective as MET in improving functional connectivity in relation to verbal memory performance. These findings should be confirmed in larger prospective studies. PMID:27060939

  4. Working memory activation of neural networks in the elderly as a function of information processing phase and task complexity.

    PubMed

    Charroud, Céline; Steffener, Jason; Le Bars, Emmanuelle; Deverdun, Jérémy; Bonafe, Alain; Abdennour, Meriem; Portet, Florence; Molino, François; Stern, Yaakov; Ritchie, Karen; Menjot de Champfleur, Nicolas; Akbaraly, Tasnime N

    2015-11-01

    Changes in working memory are sensitive indicators of both normal and pathological brain aging and associated disability. The present study aims to further understanding of working memory in normal aging using a large cohort of healthy elderly in order to examine three separate phases of information processing in relation to changes in task load activation. Using covariance analysis, increasing and decreasing neural activation was observed on fMRI in response to a delayed item recognition task in 337 cognitively healthy elderly persons as part of the CRESCENDO (Cognitive REServe and Clinical ENDOphenotypes) study. During three phases of the task (stimulation, retention, probe), increased activation was observed with increasing task load in bilateral regions of the prefrontal cortex, parietal lobule, cingulate gyrus, insula and in deep gray matter nuclei, suggesting an involvement of central executive and salience networks. Decreased activation associated with increasing task load was observed during the stimulation phase, in bilateral temporal cortex, parietal lobule, cingulate gyrus and prefrontal cortex. This spatial distribution of decreased activation is suggestive of the default mode network. These findings support the hypothesis of an increased activation in salience and central executive networks and a decreased activation in default mode network concomitant to increasing task load. PMID:26456114

  5. 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.

  6. Optical correlation aspect of holography: from ghost-imaging to static phase-conjugation holographic associative memories

    NASA Astrophysics Data System (ADS)

    Polyanskii, P. V.; Husak, Ye. M.

    2013-12-01

    We highlight the milestones of fifty-year history of emerging holographic associative memory as the chronologically first proposed practical application of the laser holographic techniques (van Heerden, 1963). Holographic associative memories are considered here as an important aspect of correlation optics, and the forming associative response is interpreted with account of fine phase relations among numerous partial images involved into discrimination mechanism of reconstruction. Three main approaches proposed for implementation of holographic associative memories are discussed and compared, namely, classical 'linear' ghost-image holography, the associateve memories based on resonator architectures using optical feedback and thresholding algorithms, and the quadric (second-order) hologrambased associative memories.

  7. One-Dimensional Phase-Change Nanomaterials for Information Storage Applications

    NASA Astrophysics Data System (ADS)

    Sun, Xuhui; Yu, Bin; Ng, Garrick; Meyyappan, M.

    The electrically operated phase-change random access memory (PRAM) features faster write/read, improved endurance, and much simpler fabrication as compared with the traditional transistor-based nonvolatile semiconductor memories. Low-dimensional phase-change materials in nanoscale dimensions offer advantages over their bulk or thin-film counterparts in several aspects such as reduced programmable volume and reduced thermal energies in phase transition. These features contribute to low-power operation, excellent scalability, and fast write/erase time. In this chapter, we present a general bottom-up synthesis approach and systematic material analysis study of one-dimensional chalcogenide-based phase-change materials including germanium telluride (GeTe), and indium selenide (In2Se3) nanowires that are targeted for nonvolatile resistive switching data storage. The phase-change nanowires have been synthesized via thermal evaporation method under vaporliquid—solid (VLS) mechanism. The morphology, composition, and crystal structure of the synthesized nanowires were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy. The as-synthesized nanowires are structurally uniform with single crystalline structures. The one-dimensional phase-change chalcogenide nanowires exhibit significantly reduced melting points, low activation energy, and excellent morphology, making them promising nanomaterials for data storage devices with very low energy consumption and excellent scalability.

  8. Quantum memory and phase gate in Optical cavities based on EIT

    NASA Astrophysics Data System (ADS)

    Borges, Halyne; Villas-Bôas, Celso

    In this work we investigate theoretically the implementation of an optical quantum memory in a system composed by a single atom, trapped in a high finesse optical cavity. In order to analyse the feasibility of implementing a quantum memory in the atom-cavity system based on the EIT phenomenon, we investigated in detail which parameter configuration the memory efficiency is optimized considering the two different setups. Our results shows that for a asymmetric one-sided cavity, which is the experimental setup commonly used to observe the EIT effect, the memory efficiency value saturates at about 8 . 5 % . Meanwhile, for an one-sided cavity, we observe for a sufficiently high value of the coupling constant g, the efficiency has its maximum value increased considerably, close to 100 % . However, this experimental setup is not suitable to observe cavity-EIT in the transmission spectrum, being necessary another kind of experiment, such as measurements phase difference field that leaves the cavity induced by the control field. Considering this configuration we also showed the implementation of a quantum phase gate based on the same nonlinear effect, where the pulse probe can experience a phase shift on the order of π, due to the presence or absence of a control pulse. Supported by FAPESP (Proc. 2014/12740-1) and INCT-IQ.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Detection of the Number of Changes in a Display in Working Memory

    PubMed Central

    Cowan, Nelson; Hardman, Kyle; Saults, J. Scott; Blume, Christopher L.; Clark, Katherine M.; Sunday, Mackenzie A.

    2015-01-01

    Here we examine a new task to assess working memory for visual arrays in which the participant must judge how many items changed from a studied array to a test array. As a clue to processing, on some trials in the first two experiments, participants carried out a metamemory judgment in which they were to decide how many items were in working memory. Trial-to-trial fluctuations in these working memory storage judgments correlated with performance fluctuations within an individual, indicating a need to include trial-to-trial variation within capacity models (through either capacity fluctuation or some other attention parameter). Mathematical modeling of the results achieved a good fit to a complex pattern of results, suggesting that working memory capacity limits can apply even to judgments that involve an entire array rather than just a single item that may have changed, thus providing the expected conscious access to at least some of the contents of working memory. PMID:26375783

  15. 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.

  16. 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.

  17. On phase change in thermocapillary flows

    NASA Astrophysics Data System (ADS)

    Saenz, Pedro; Valluri, Prashant; Sefiane, Khellil; Karapetsas, George; Matar, Omar

    2012-11-01

    We present the findings from our 3D direct numerical study of thermocapillary flows undergoing phase change. A liquid-gas model with VOF interface-tracking technique is employed to investigate stable and unstable (hydrothermal waves) scenarios. The spatiotemporal evolution of the local evaporation flux is determined with the assumption that vapour phase just above interface is at a local thermodynamic equilibrium with the liquid phase below. The transient vapour distribution in the gas is also accounted for by means of the solution of an advection-diffusion equation. We calculate the resulting spatially non-uniform flux and illustrate its controlling mechanisms, which involve the Marangoni effect and non-uniform vapour-pressure distribution due to the externally-imposed thermal gradient. We also present the flux's non-linear evolution due to the transient liquid-level reduction and its stabilizing-destabilizing effect on the thermal and physical interface fluctuations. The oscillatory temperature- and vapour-fields in the gas, tightly coupled with advection rolls observed, are also shown. EPSRC DTA.

  18. A phase code for memory could arise from circuit mechanisms in entorhinal cortex

    PubMed Central

    Hasselmo, Michael E.; Brandon, Mark P.; Yoshida, Motoharu; Giocomo, Lisa M.; Heys, James G.; Fransen, Erik; Newman, Ehren L.; Zilli, Eric A.

    2009-01-01

    Neurophysiological data reveals intrinsic cellular properties that suggest how entorhinal cortical neurons could code memory by the phase of their firing. Potential cellular mechanisms for this phase coding in models of entorhinal function are reviewed. This mechanism for phase coding provides a substrate for modeling the responses of entorhinal grid cells, as well as the replay of neural spiking activity during waking and sleep. Efforts to implement these abstract models in more detailed biophysical compartmental simulations raise specific issues that could be addressed in larger scale population models incorporating mechanisms of inhibition. PMID:19656654

  19. Cultural differences in rated typicality and perceived causes of memory changes in adulthood.

    PubMed

    Bottiroli, Sara; Cavallini, Elena; Fastame, Maria Chiara; Hertzog, Christopher

    2013-01-01

    This study examined cultural differences in stereotypes and attributions regarding aging and memory. Two subcultures belonging to the same country, Italy, were compared on general beliefs about memory. Sardinians live longer than other areas of Italy, which is a publically shared fact that informs stereotypes about that subculture. An innovative instrument evaluating simultaneously aging stereotypes and attributions about memory and memory change in adulthood was administered to 52 Sardinian participants and 52 Milanese individuals divided into three age groups: young (20-30), young-old (60-70), and old-old (71-85) adults. Both Milanese and Sardinians reported that memory decline across the life span is more typical than a pattern of stability or improvement. However, Sardinians viewed stability and improvement in memory as more typical than did the Milanese. Interestingly, cultural differences emerged in attributions about memory improvement. Although all Sardinian age groups rated nutrition and heredity as relevant causes in determining the memory decline, Sardinians' rated typicality of life-span memory improvement correlated strongly with causal attributions to a wide number of factors, including nutrition and heredity. PMID:23571129

  20. 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

  1. Metallic resist for phase-change lithography.

    PubMed

    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. Suppression of aversive memories associates with changes in early and late stages of neurocognitive processing.

    PubMed

    Chen, Chunping; Liu, Chao; Huang, Ruiwang; Cheng, Dazhi; Wu, Haiyan; Xu, Pengfei; Mai, Xiaoqin; Luo, Yue-Jia

    2012-10-01

    Unwanted memories, such as emotionally negative, can be intentionally suppressed through voluntary control in humans. Memory suppression is thought to be mediated by the interplay of a chain of neurocognitive processes. However, empirical data in support of this notion is lacking. Using high-temporal resolution event-related potential (ERP) technique, we investigated the time course of ERPs associated with suppression of negative and neutral memories in a Think/No-Think paradigm in young, healthy participants. Results showed that participants had greater difficulty in suppressing emotionally negative memories than neutral ones. ERPs and source analyses demonstrated that memory suppression processing for negative and neutral memories were generally associated with changes during early components of a time window of 70-260 ms, such as P1 and N2, mainly at the right inferior frontal gyrus and occipital lobe; suppression of aversive memories was associated with two major late ERP components between 380 and 800 ms, with significantly smaller later negativity (LN) but larger late parietal positivity (LPP), primarily at the right medial and superior frontal gyri. These results suggest that differences in early components may reflect early stages of suppression processing including visual awareness, attention reallocation, and executive processing. Differences in late components between suppression of aversive and neutral memories may reflect a process of down-regulating conscious recollection of memory representations supported by prefrontal and parietal networks. A less effective control of this process, as evidenced by smaller LN and larger LPP, may explain the fact that emotionally negative memories were harder to be suppressed. Altogether, these findings suggest that suppression of aversive memories requires down-regulation of late conscious recollection, which can be dissociated from early visual and attention processing in memory suppression. PMID:22917568

  3. Working Memory Training: Improving Intelligence--Changing Brain Activity

    ERIC Educational Resources Information Center

    Jausovec, Norbert; Jausovec, Ksenija

    2012-01-01

    The main objectives of the study were: to investigate whether training on working memory (WM) could improve fluid intelligence, and to investigate the effects WM training had on neuroelectric (electroencephalography--EEG) and hemodynamic (near-infrared spectroscopy--NIRS) patterns of brain activity. In a parallel group experimental design,…

  4. Developmental Changes in the Interface between Perception and Memory Retrieval.

    ERIC Educational Resources Information Center

    Bhatt, Ramesh S.; And Others

    1994-01-01

    Four experiments examined how perception affects delayed recognition, visual pop out, and memory reactivation (priming) in six month olds. Infants discriminated cues differing in spatial arrangement or number of primitive perceptual units (textons) in a delayed recognition task and exhibited adultlike visual pop-out effects in a priming task. (MDM)

  5. Effects of Developmental Changes in Affective Meaning Structure on Memory.

    ERIC Educational Resources Information Center

    Ghatala, Elizabeth S.; And Others

    In an incidental memory task, second, sixth, and tenth-grade students performed three orientating tasks on different subsets of items in a list of common nouns. In one condition (EPA), children judged words on the Evaluative, Potency and Activity dimensions of the semantic differential. In another condition (EEE) children made phonetic judgments.…

  6. Leptin attenuates the detrimental effects of β-amyloid on spatial memory and hippocampal later-phase long term potentiation in rats.

    PubMed

    Tong, Jia-Qing; Zhang, Jun; Hao, Ming; Yang, Ju; Han, Yu-Fei; Liu, Xiao-Jie; Shi, Hui; Wu, Mei-Na; Liu, Qing-Song; Qi, Jin-Shun

    2015-07-01

    β-Amyloid (Aβ) is the main component of amyloid plaques developed in the brain of patients with Alzheimer's disease (AD). The increasing burden of Aβ in the cortex and hippocampus is closely correlated with memory loss and cognition deficits in AD. Recently, leptin, a 16kD peptide derived mainly from white adipocyte tissue, has been appreciated for its neuroprotective function, although less is known about the effects of leptin on spatial memory and synaptic plasticity. The present study investigated the neuroprotective effects of leptin against Aβ-induced deficits in spatial memory and in vivo hippocampal late-phase long-term potentiation (L-LTP) in rats. Y maze spontaneous alternation was used to assess short term working memory, and the Morris water maze task was used to assess long term reference memory. Hippocampal field potential recordings were performed to observe changes in L-LTP. We found that chronically intracerebroventricular injection of leptin (1μg) effectively alleviated Aβ1-42 (20μg)-induced spatial memory impairments of Y maze spontaneous alternation and Morris water maze. In addition, chronic administration of leptin also reversed Aβ1-42-induced suppression of in vivo hippocampal L-LTP in rats. Together, these results suggest that chronic leptin treatments reversed Aβ-induced deficits in learning and memory and the maintenance of L-LTP. PMID:26135065

  7. Coordinated Changes in DNA Methylation in Antigen-Specific Memory CD4 T Cells

    PubMed Central

    Ogoshi, Katsumi; Sasaki, Atsushi; Abe, Jun; Qu, Wei; Nakatani, Yoichiro; Ahsan, Budrul; Oshima, Kenshiro; Shand, Francis H. W.; Ametani, Akio; Suzuki, Yutaka; Kaneko, Shuichi; Wada, Takashi; Hattori, Masahira; Sugano, Sumio; Morishita, Shinichi; Matsushima, Kouji

    2013-01-01

    Memory CD4+ T cells are central regulators of both humoral and cellular immune responses. T cell differentiation results in specific changes in chromatin structure and DNA methylation of cytokine genes. Although the methylation status of a limited number of gene loci in T cells has been examined, the genome-wide DNA methylation status of memory CD4+ T cells remains unexplored. To further elucidate the molecular signature of memory T cells, we conducted methylome and transcriptome analyses of memory CD4+ T cells generated using T cells from TCR-transgenic mice. The resulting genome-wide DNA methylation profile revealed 1144 differentially methylated regions (DMRs) across the murine genome during the process of T cell differentiation, 552 of which were associated with gene loci. Interestingly, the majority of these DMRs were located in introns. These DMRs included genes such as CXCR6, Tbox21, Chsy1, and Cish, which are associated with cytokine production, homing to bone marrow, and immune responses. Methylation changes in memory T cells exposed to specific Ag appeared to regulate enhancer activity rather than promoter activity of immunologically relevant genes. In addition, methylation profiles differed between memory T cell subsets, demonstrating a link between T cell methylation status and T cell differentiation. By comparing DMRs between naive and Ag-specific memory T cells, this study provides new insights into the functional status of memory T cells. PMID:23509353

  8. Relation between bandgap and resistance drift in amorphous phase change materials.

    PubMed

    Rütten, Martin; Kaes, Matthias; Albert, Andreas; Wuttig, Matthias; Salinga, Martin

    2015-01-01

    Memory based on phase change materials is currently the most promising candidate for bridging the gap in access time between memory and storage in traditional memory hierarchy. However, multilevel storage is still hindered by the so-called resistance drift commonly related to structural relaxation of the amorphous phase. Here, we present the temporal evolution of infrared spectra measured on amorphous thin films of the three phase change materials Ag4In3Sb67Te26, GeTe and the most popular Ge2Sb2Te5. A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials. Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled. The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift. PMID:26621533

  9. Relation between bandgap and resistance drift in amorphous phase change materials

    NASA Astrophysics Data System (ADS)

    Rütten, Martin; Kaes, Matthias; Albert, Andreas; Wuttig, Matthias; Salinga, Martin

    2015-12-01

    Memory based on phase change materials is currently the most promising candidate for bridging the gap in access time between memory and storage in traditional memory hierarchy. However, multilevel storage is still hindered by the so-called resistance drift commonly related to structural relaxation of the amorphous phase. Here, we present the temporal evolution of infrared spectra measured on amorphous thin films of the three phase change materials Ag4In3Sb67Te26, GeTe and the most popular Ge2Sb2Te5. A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials. Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled. The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift.

  10. Relation between bandgap and resistance drift in amorphous phase change materials

    PubMed Central

    Rütten, Martin; Kaes, Matthias; Albert, Andreas; Wuttig, Matthias; Salinga, Martin

    2015-01-01

    Memory based on phase change materials is currently the most promising candidate for bridging the gap in access time between memory and storage in traditional memory hierarchy. However, multilevel storage is still hindered by the so-called resistance drift commonly related to structural relaxation of the amorphous phase. Here, we present the temporal evolution of infrared spectra measured on amorphous thin films of the three phase change materials Ag4In3Sb67Te26, GeTe and the most popular Ge2Sb2Te5. A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials. Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled. The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift. PMID:26621533

  11. Dysfunction in different phases of working memory in schizophrenia: evidence from ERP recordings.

    PubMed

    Zhao, Yan Li; Tan, Shu Ping; Yang, Fu De; Wang, Li Li; Feng, Wen Feng; Chan, Raymond C K; Gao, Xiao; Zhou, Dong Feng; Li, Bin Bin; Song, Chong Sheng; Fan, Feng Mei; Tan, Yun Long; Zhang, Jin Guo; Wang, Yun Hui; Zou, Yi Zhuang

    2011-12-01

    The present study combined a time-locked paradigm and high-time-resolution event-related potential (ERP) recordings to examine different phases of working memory, including early visual processing and late memory-related processes of encoding, maintenance, and retrieval, in 67 adults with schizophrenia and 46 healthy controls. Alterations in ERP components were correlated with task performance. Patients performed significantly worse in the working memory task than healthy subjects, although all subjects' accuracy exceeded 80%. During encoding, the N1 and P2 component amplitudes were lower while the P300 amplitude was higher in schizophrenic patients compared to healthy controls. There were no differences between groups with respect to the mean amplitudes of the negative slow waves in the early stage (the first 400 ms) of the maintenance phase. However, in the next 500-ms time window, the patients exhibited a more negative deflection in the middle fronto-central region than the control group. Likewise, a similar pattern was observed in the second 500-ms period in the middle fronto-central region, although the effect was marginally significant. There were no differences between groups in the remaining 1000 ms. During retrieval, the P1, N1 and P2 amplitudes were lower while the P300 amplitude and latency were higher in schizophrenic patients. The present results indicate early visual deficits in the working memory task in adults with schizophrenia. Impairments in the maintenance phase were confined to the late rehearsal stage. The increased P300 amplitude at the fronto-central electrode sites along with the poorer behavioral performance suggests that schizophrenic patients have an inefficient working memory system. PMID:22014837

  12. 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. PMID:24599711

  13. Memories.

    ERIC Educational Resources Information Center

    Brand, Judith, Ed.

    1998-01-01

    This theme issue of the journal "Exploring" covers the topic of "memories" and describes an exhibition at San Francisco's Exploratorium that ran from May 22, 1998 through January 1999 and that contained over 40 hands-on exhibits, demonstrations, artworks, images, sounds, smells, and tastes that demonstrated and depicted the biological,…

  14. When asking the question changes the ultimate answer: Metamemory judgments change memory.

    PubMed

    Mitchum, Ainsley L; Kelley, Colleen M; Fox, Mark C

    2016-02-01

    Self-report measurements are ubiquitous in psychology, but they carry the potential of altering processes they are meant to measure. We assessed whether a common metamemory measure, judgments of learning, can change the ongoing process of memorizing and subsequent memory performance. Judgments of learning are a form of metamemory monitoring described as conscious reflection on one's own memory performance or encoding activities for the purpose of exerting strategic control over one's study and retrieval activities (T. O. Nelson & Narens, 1990). Much of the work examining the conscious monitoring of encoding relies heavily on a paradigm in which participants are asked to estimate the probability that they will recall a given item in a judgment of learning. In 5 experiments, we find effects of measuring judgments of learning on how people allocate their study time to difficult versus easy items, and on what they will recall. These results suggest that judgments of learning are partially constructed in response to the measurement question. The tendency of judgments of learning to alter performance places them in the company of other reactive verbal reporting methods, counseling researchers to consider incorporating control groups, creating alternative scales, and exploring other verbal reporting methods. Less directive methods of accessing participants' metacognition and other judgments should be considered as an alternative to response scales. PMID:27045282

  15. Toward the ultimate limit of phase change in Ge(2)Sb(2)Te(5).

    PubMed

    Simpson, R E; Krbal, M; Fons, P; Kolobov, A V; Tominaga, J; Uruga, T; Tanida, H

    2010-02-10

    The limit to which the phase change memory material Ge(2)Sb(2)Te(5) can be scaled toward the smallest possible memory cell is investigated using structural and optical methodologies. The encapsulation material surrounding the Ge(2)Sb(2)Te(5) has an increasingly dominant effect on the material's ability to change phase, and a profound increase in the crystallization temperature is observed when the Ge(2)Sb(2)Te(5) layer is less than 6 nm thick. We have found that the increased crystallization temperature originates from compressive stress exerted from the encapsulation material. By minimizing the stress, we have maintained the bulk crystallization temperature in Ge(2)Sb(2)Te(5) films just 2 nm thick. PMID:20041706

  16. Phase change water processing for Space Station

    NASA Technical Reports Server (NTRS)

    Zdankiewicz, E. M.; Price, D. F.

    1985-01-01

    The use of a vapor compression distillation subsystem (VCDS) for water recovery on the Space Station is analyzed. The self-contained automated system can process waste water at a rate of 32.6 kg/day and requires only 115 W of electric power. The improvements in the mechanical components of VCDS are studied. The operation of VCDS in the normal mode is examined. The VCDS preprototype is evaluated based on water quality, water production rate, and specific energy. The relation between water production rate and fluids pump speed is investigated; it is concluded that a variable speed fluids pump will optimize water production. Components development and testing currently being conducted are described. The properties and operation of the proposed phase change water processing system for the Space Station, based on vapor compression distillation, are examined.

  17. Cooling of Electronics with Phase Change Materials

    NASA Astrophysics Data System (ADS)

    Saha, S. K.; Dutta, P.

    2010-10-01

    This paper deals with phase change materials (PCMs), used in conjunction with thermal conductivity enhancer (TCE), as means of thermal management of electronic systems. This work was motivated by the need for short term thermal management of high packing density equipments (such as in avionics). Eicosane is used as PCM, while aluminium pin or plate fins are used as TCE. The test section considered in all cases is 42×42 mm square base with TCE height of 25 mm. An electronic heater producing 4, 6 and 8 W was used to simulate the heat generation of electronic chips. Various volumetric percentages of TCE in the conglomerate of PCM and TCE were considered, namely, 0, 2, 8, 18 and 27%. The case with 8% volumetric percentage of TCE was found to have the best thermal performance. A numerical model was developed to enable interpretation of experimental results and to perform parametric studies.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Sign reversal of transformation entropy change in Co{sub 2}Cr(Ga,Si) shape memory alloys

    SciTech Connect

    Xu, Xiao Omori, Toshihiro; Kainuma, Ryosuke; Nagasako, Makoto; Kanomata, Takeshi

    2015-11-02

    In situ X-ray diffraction (XRD) measurements and compression tests were performed on Co{sub 2}Cr(Ga,Si) shape memory alloys. The reentrant martensitic transformation behavior was directly observed during the in situ XRD measurements. The high-temperature parent phase and low-temperature reentrant parent phase were found to have a continuous temperature dependence of lattice parameter, therefore suggesting that they are the same phase in nature. Moreover, compression tests were performed on a parent-phase single crystal sample; an evolution from normal to inverse temperature dependence of critical stress for martensitic transformation was directly observed. Based on the Clausius-Clapeyron analysis, a sign reversal of entropy change can be expected on the same alloy.

  7. Refractive index modulation of Sb70Te30 phase-change thin films by multiple femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Lei, Kai; Wang, Yang; Jiang, Minghui; Wu, Yiqun

    2016-05-01

    In this study, the controllable effective refractive index modulation of Sb70Te30 phase-change thin films between amorphous and crystalline states was achieved experimentally by multiple femtosecond laser pulses. The modulation mechanism was analyzed comprehensively by a spectral ellipsometer measurement, surface morphology observation, and two-temperature model calculations. We numerically demonstrate the application of the optically modulated refractive index of the phase-change thin films in a precisely adjustable color display. These results may provide further insights into ultrafast phase-transition mechanics and are useful in the design of programmable photonic and opto-electrical devices based on phase-change memory materials.

  8. Age-related Changes in the Sleep-dependent Reorganization of Declarative Memories.

    PubMed

    Baran, Bengi; Mantua, Janna; Spencer, Rebecca M C

    2016-06-01

    Consolidation of declarative memories has been associated with slow wave sleep in young adults. Previous work suggests that, in spite of changes in sleep, sleep-dependent consolidation of declarative memories may be preserved with aging, although reduced relative to young adults. Previous work on young adults shows that, with consolidation, retrieval of declarative memories gradually becomes independent of the hippocampus. To investigate whether memories are similarly reorganized over sleep at the neural level, we compared functional brain activation associated with word pair recall following a nap and equivalent wake in young and older adults. SWS during the nap predicted better subsequent memory recall and was negatively associated with retrieval-related hippocampal activation in young adults. In contrast, in older adults there was no relationship between sleep and memory performance or with retrieval-related hippocampal activation. Furthermore, compared with young adults, postnap memory retrieval in older adults required strong functional connectivity of the hippocampus with the PFC, whereas there were no differences between young and older adults in the functional connectivity of the hippocampus following wakefulness. These results suggest that, although neural reorganization takes place over sleep in older adults, the shift is unique from that seen in young adults, perhaps reflecting memories at an earlier stage of stabilization. PMID:26918588

  9. Mechanics of metals with phase changes

    NASA Astrophysics Data System (ADS)

    Lashley, Jason C.

    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 (diffusionless) 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 per cent, while the resolution was better than 0.1 per cent. 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 alpha-uranium (orthorhombic symmetry). The AuZn alloy exhibits a continuous transition at 64.75 K and an entropy of transition of (DeltaStr ) 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 alpha-U show a low-temperature limiting 19, of 256 K (+/-0.50 K) and four low-temperature anamolies: a superconducting transition below 1 K, an electronic transition at 22 K, and two anamolies 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 the introduction

  10. The distinctive germinal center phase of IgE+ B lymphocytes limits their contribution to the classical memory response

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The mechanisms involved in the maintenance of memory IgE responses are poorly understood, and the role played by germinal center (GC) IgE+ cells in memory responses is particularly unclear. IgE B cell differentiation is characterized by a transient GC phase, a bias towards the plasma cell (PC) fate,...

  11. 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.

  12. Changes in global and regional modularity associated with increasing working memory load

    PubMed Central

    Stanley, Matthew L.; Dagenbach, Dale; Lyday, Robert G.; Burdette, Jonathan H.; Laurienti, Paul J.

    2014-01-01

    Using graph theory measures common to complex network analyses of neuroimaging data, the objective of this study was to explore the effects of increasing working memory processing load on functional brain network topology in a cohort of young adults. Measures of modularity in complex brain networks quantify how well a network is organized into densely interconnected communities. We investigated changes in both the large-scale modular organization of the functional brain network as a whole and regional changes in modular organization as demands on working memory increased from n = 1 to n = 2 on the standard n-back task. We further investigated the relationship between modular properties across working memory load conditions and behavioral performance. Our results showed that regional modular organization within the default mode and working memory circuits significantly changed from 1-back to 2-back task conditions. However, the regional modular organization was not associated with behavioral performance. Global measures of modular organization did not change with working memory load but were associated with individual variability in behavioral performance. These findings indicate that regional and global network properties are modulated by different aspects of working memory under increasing load conditions. These findings highlight the importance of assessing multiple features of functional brain network topology at both global and regional scales rather than focusing on a single network property. PMID:25520639

  13. TMS-induced theta phase synchrony reveals a bottom-up network in working memory.

    PubMed

    Miyauchi, Eri; Kitajo, Keiichi; Kawasaki, Masahiro

    2016-05-27

    Global theta phase synchronization between the frontal and sensory areas has been suggested to connect the relevant areas for executive processes of working memory (WM). However, little is known regarding network directionality (i.e. top-down or bottom-up) of this interaction. To address the issue, the present study conducted transcranial magnetic stimulation (TMS)-electroencephalography (EEG) experiment during WM tasks. Results showed that TMS-induced increases in theta phase synchronization were observed only when TMS was delivered to the sensory areas but not the frontal area. These findings suggest that network directionality represented in WM is bottom-up rather than top-down. PMID:27063284

  14. Topological insulating in GeTe/Sb2Te3 phase-change superlattice.

    PubMed

    Sa, Baisheng; Zhou, Jian; Sun, Zhimei; Tominaga, Junji; Ahuja, Rajeev

    2012-08-31

    GeTe/Sb2Te3 superlattice phase-change memory devices demonstrated greatly improved performance over that of Ge2Sb2Te5, a prototype record media for phase-change random access memory. In this work, we show that this type of GeTe/Sb2Te3 superlattice exhibits topological insulating behavior on the basis of ab initio calculations. The analysis of the band structures and parities as well as Z2 topological invariants unravels the topological insulating nature in these artificial materials. Furthermore, the topological insulating character remains in the GeTe/Sb2Te3 superlattice under small compressive strains, whereas it is not observed as more Sb2Te3 building blocks introduced in the superlattice. The present results show that multifunctional data storages may be achieved in the GeTe/Sb2Te3 superlattice. Such kinds of artificial materials can be used in phase-change random access memory, spintronics, and quantum computing. PMID:23002870

  15. Ultrafast optical manipulation of atomic motion in multilayer Ge-Sb-Te phase change materials

    NASA Astrophysics Data System (ADS)

    Makino, K.; Tominaga, J.; Kolobov, A. V.; Fons, P.; Hase, M.

    2013-03-01

    Phase change random access memory devices have evolved dramatically with the recent development of superlattice structure of Ge-Sb-Te material (GST-SL) in terms of its low power consumption. The phase change in GST-SL is mainly characterized by the displacement of Ge atoms. Here we examine a new phase change method, that is the manipulation of Ge-Te bonds using linearly-polarized femtosecond near-infrared optical pulses. As a result, we found that the p-polarized pump pulse is more effective in inducing the reversible and irreversible displacement of Ge atoms along [111] direction in the local structure. This structural change would be induced by the anisotropic carrier-phonon interaction along the [111] direction created by the p-polarized pulse.

  16. Detection of the Number of Changes in a Display in Working Memory

    ERIC Educational Resources Information Center

    Cowan, Nelson; Hardman, Kyle; Saults, J. Scott; Blume, Christopher L.; Clark, Katherine M.; Sunday, Mackenzie A.

    2016-01-01

    Here we examine a new task to assess working memory for visual arrays in which the participant must judge how many items changed from a studied array to a test array. As a clue to processing, on some trials in the first 2 experiments, participants carried out a metamemory judgment in which they were to decide how many items were in working memory.…

  17. Changing maladaptive memories through reconsolidation: A role for sleep in psychotherapy?

    PubMed

    Diekelmann, Susanne; Forcato, Cecilia

    2015-01-01

    Like Lane et al., we believe that change in psychotherapy comes about by updating dysfunctional memories with new adaptive experiences. We suggest that sleep is essential to (re-)consolidate such corrective experiences. Sleep is well-known to strengthen and integrate new memories into pre-existing networks. Targeted sleep interventions might be promising tools to boost this process and thereby increase therapy effectiveness. PMID:26050697

  18. Multiscale model for phase transformation in magnetic shape memory alloy single crystals

    NASA Astrophysics Data System (ADS)

    Stoilov, Vesselin

    2006-03-01

    This paper investigates the nano-macro transition in magnetic shape memory alloy(MSMA) thin films using a recently developed sharp phase front-based three-dimensional (3D) constitutive model outlined by Stoilov (JSMS 2005), and originally proposed in the 1D context by Stoilov and Bhattacharyya (Acta Mat 2002). The key ingredient in the model is the recognition of martensitic variants as separate phases in a MSMA domain. Evolution of the interface between these phases is taken as an indicator of the process of reorientation in progress. A formulation of the Helmholtz free energy potential based on Ising model has been derived. The implications of the external magnetic field on the initiation of phase transformation are studied for various mechanical loading modes.

  19. Stochastic cortical neurodynamics underlying the memory and cognitive changes in aging.

    PubMed

    Rolls, Edmund T; Deco, Gustavo

    2015-02-01

    The relatively random spiking times of individual neurons provide a source of noise in the brain. We show how this noise interacting with altered depth in the basins of attraction of networks involved in short-term memory, attention, and episodic memory provide an approach to understanding some of the cognitive changes in normal aging. The effects of the neurobiological changes in aging that are considered include reduced synaptic modification and maintenance during learning produced in part through reduced acetylcholine in normal aging, reduced dopamine which reduces NMDA-receptor mediated effects, reduced noradrenaline which increases cAMP and thus shunts excitatory synaptic inputs, and the effects of a reduction in acetylcholine in increasing spike frequency adaptation. Using integrate-and-fire simulations of an attractor network implementing memory recall and short-term memory, it is shown that all these changes associated with aging reduce the firing rates of the excitatory neurons, which in turn reduce the depth of the basins of attraction, resulting in a much decreased probability in maintaining in short-term memory what has been recalled from the attractor network. This stochastic dynamics approach opens up new ways to understand and potentially treat the effects of normal aging on memory and cognitive functions. PMID:25536108

  20. 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.

  1. White matter and memory in healthy adults: Coupled changes over two years.

    PubMed

    Bender, Andrew R; Prindle, John J; Brandmaier, Andreas M; Raz, Naftali

    2016-05-01

    Numerous cross-sectional studies have used diffusion tensor imaging (DTI) to link age-related differences in white matter (WM) anisotropy and concomitant decrements in cognitive ability. Due to a dearth of longitudinal evidence, the relationship between changes in diffusion properties of WM and cognitive performance remains unclear. Here we examine the relationship between two-year changes in WM organization and cognitive performance in healthy adults (N=96, age range at baseline=18-79 years). We used latent change score models (LCSM) to evaluate changes in age-sensitive cognitive abilities - fluid intelligence and associative memory. WM changes were assessed by fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) in WM regions that are considered part of established memory networks and exhibited individual differences in change. In modeling change, we postulated reciprocal paths between baseline measures and change factors, within and between WM and cognition domains, and accounted for individual differences in baseline age. Although baseline cross-sectional memory performance was positively associated with FA and negatively with RD, longitudinal effects told an altogether different story. Independent of age, longitudinal improvements in associative memory were significantly associated with linear reductions in FA and increases in RD. The present findings demonstrate the sensitivity of DTI-derived indices to changes in the brain and cognition and affirm the importance of longitudinal models for evaluating brain-cognition relations. PMID:26545457

  2. 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. PMID:24663836

  3. Mechanics of Metals with Phase Changes

    SciTech Connect

    Lashley, J.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 {alpha}-uranium (orthorhombic symmetry). The AuZn alloy exhibits a continuous transition at 64.75 K and an entropy of transition of ({Delta}S{sub tr}) 2.02 J K{sup {minus}1} mol{sup {minus}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 {alpha}-U show a low-temperature limiting {Theta}{sub D} 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

  4. 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.

  5. 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.

  6. 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.

  7. Electric Field Induced Reversible Phase Transition in Li Doped Phosphorene: Shape Memory Effect and Superelasticity.

    PubMed

    Deng, Junkai; Chang, Zhenyue; Zhao, Tong; Ding, Xiangdong; Sun, Jun; Liu, Jefferson Zhe

    2016-04-13

    Phosphorene, the single-layer form of black phosphorus, as a new member of atomically thin material family, has unique puckered atomistic structure and remarkable physical and chemical properties. In this paper, we report a discovery of an unexpected electromechanical energy conversion phenomenon-shape memory effect-in Li doped phosphorene P4Li2, using ab initio density functional theory simulations. Two stable phases are found for the two-dimensional (2D) P4Li2 crystal. Applying an external electric field can turn on or off the unique adatom switches in P4Li2 crystals, leading to a reversible structural phase transition and thereby the shape memory effect with an tunable strain output as high as 2.06%. Our results demonstrate that multiple temporary shapes are attainable in one piece of P4Li2 material, offering programmability that is particularly useful for device designs. Additionally, the P4Li2 displays superelasticity that can generate a pseudoelastic tensile strain up to 6.2%. The atomic thickness, superior flexibility, excellent electromechanical strain output, the special shape memory phenomenon, and the programmability feature endow P4Li2 with great application potential in high-efficient energy conversion at nanoscale and flexible nanoelectromechanical systems. PMID:27043220

  8. A 3-D constitutive model for pressure-dependent phase transformation of porous shape memory alloys.

    PubMed

    Ashrafi, M J; Arghavani, J; Naghdabadi, R; Sohrabpour, S

    2015-02-01

    Porous shape memory alloys (SMAs) exhibit the interesting characteristics of porous metals together with shape memory effect and pseudo-elasticity of SMAs that make them appropriate for biomedical applications. In this paper, a 3-D phenomenological constitutive model for the pseudo-elastic behavior and shape memory effect of porous SMAs is developed within the framework of irreversible thermodynamics. Comparing to micromechanical and computational models, the proposed model is computationally cost effective and predicts the behavior of porous SMAs under proportional and non-proportional multiaxial loadings. Considering the pressure dependency of phase transformation in porous SMAs, proper internal variables, free energy and limit functions are introduced. With the aim of numerical implementation, time discretization and solution algorithm for the proposed model are also presented. Due to lack of enough experimental data on multiaxial loadings of porous SMAs, we employ a computational simulation method (CSM) together with available experimental data to validate the proposed constitutive model. The method is based on a 3-D finite element model of a representative volume element (RVE) with random pores pattern. Good agreement between the numerical predictions of the model and CSM results is observed for elastic and phase transformation behaviors in various thermomechanical loadings. PMID:25528691

  9. The Less Things Change, the More They Are Different: Contributions of Long-Term Synaptic Plasticity and Homeostasis to Memory

    ERIC Educational Resources Information Center

    Schacher, Samuel; Hu, Jiang-Yuan

    2014-01-01

    An important cellular mechanism contributing to the strength and duration of memories is activity-dependent alterations in the strength of synaptic connections within the neural circuit encoding the memory. Reversal of the memory is typically correlated with a reversal of the cellular changes to levels expressed prior to the stimulation. Thus, for…

  10. Developmental Changes in Infants' Visual Short-Term Memory for Location

    ERIC Educational Resources Information Center

    Oakes, Lisa M.; Hurley, Karinna B.; Ross-Sheehy, Shannon; Luck, Steven J.

    2011-01-01

    To examine the development of visual short-term memory (VSTM) for location, we presented 6- to 12-month-old infants (N = 199) with two side-by-side stimulus streams. In each stream, arrays of colored circles continually appeared, disappeared, and reappeared. In the "changing" stream, the location of one or more items changed in each cycle; in the…

  11. Glutamate and GABA concentration changes in the globus pallidus internus of Parkinson's patients during performance of implicit and declarative memory tasks: a report of two subjects.

    PubMed

    Buchanan, Robert J; Gjini, Klevest; Darrow, David; Varga, Georgeta; Robinson, Jennifer L; Nadasdy, Zoltan

    2015-03-01

    The basal ganglia, typically associated with motor function, are involved in human cognitive processes, as demonstrated in behavioral, lesion, and noninvasive functional neuroimaging studies. Here we report task-contingent changes in concentrations of the neurotransmitters glutamate (Glu) and gamma-aminobutyric acid (GABA) in the globus pallidus internus (GPi) of two patients with Parkinson's disease undergoing deep brain stimulation surgery by utilizing in-vivo microdialysis measurements during performance of implicit and declarative memory tasks. Performance of an implicit memory task (weather prediction task-WPT) was associated with increased levels of glutamate and GABA in the GPi compared to their concentrations at baseline. On the other hand, performance of a declarative memory task (verbal learning task-VLT) was associated with decreased levels of glutamate and GABA in GPi compared to baseline during the encoding and immediate recall phase with less conclusive results during the delayed recall phase. These results are in line with hypothesized changes in these neurotransmitter levels: an increase of excitatory (Glu) input from subthalamic nucleus (STN) to GPi during implicit memory task performance and a decrease of inhibitory inputs (GABA) from globus pallidus externus (GPe) and striatum to GPi during declarative memory performance. Consistent with our previous report on in-vivo neurotransmitter changes during tasks in STN, these data provide corroborative evidence for the direct involvement of basal ganglia in cognitive functions and complements our model of the functional circuitry of basal ganglia in the healthy and Parkinson's disease affected brain. PMID:25596441

  12. Aluminum-Centered Tetrahedron-Octahedron Transition in Advancing Al-Sb-Te Phase Change Properties

    PubMed Central

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

    2015-01-01

    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. PMID:25709082

  13. 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

    2015-01-01

    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. PMID:25709082

  14. Aluminum-Centered Tetrahedron-Octahedron Transition in Advancing Al-Sb-Te Phase Change Properties

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  15. Splenectomy Associated Changes in IgM Memory B Cells in an Adult Spleen Registry Cohort

    PubMed Central

    Cameron, Paul U.; Jones, Penelope; Gorniak, Malgorzata; Dunster, Kate; Paul, Eldho; Lewin, Sharon; Woolley, Ian; Spelman, Denis

    2011-01-01

    Asplenic patients have a lifelong risk of overwhelming post-splenectomy infection and have been reported to have low numbers of peripheral blood IgM memory B cells. The clinical value of quantitation of memory B cells as an indicator of splenic abnormality or risk of infection has been unclear. To assess changes in B cell sub-populations after splenectomy we studied patients recruited to a spleen registry (n = 591). A subset of 209 adult asplenic or hyposplenic subjects, and normal controls (n = 140) were tested for IgM memory B cells. We also determined a) changes in IgM memory B cells with time after splenectomy using the cross-sectional data from patients on the registry and b) the kinetics of changes in haematological markers associated with splenectomy(n = 45). Total B cells in splenectomy patients did not differ from controls, but memory B cells, IgM memory B cells and switched B cells were significantly (p<0.001) reduced. The reduction was similar for different indications for splenectomy. Changes of asplenia in routine blood films including presence of Howell-Jolly bodies (HJB), occurred early (median 25 days) and splenectomy associated thrombocytosis and lymphocytosis peaked by 50 days. There was a more gradual decrease in IgM memory B cells reaching a stable level within 6 months after splenectomy. IgM memory B cells as proportion of B cells was the best discriminator between splenectomized patients and normal controls and at the optimal cut-off of 4.53, showed a true positive rate of 95% and false positive rate of 20%. In a survey of 152 registry patients stratified by IgM memory B cells around this cut-off there was no association with minor infections and no registry patients experienced OPSI during the study. Despite significant changes after splenectomy, conventional measures of IgM memory cells have limited clinical utility in this population. PMID:21829713

  16. Developmental Changes in Item and Source Memory: Evidence from an ERP Recognition Memory Study with Children, Adolescents, and Adults

    ERIC Educational Resources Information Center

    Sprondel, Volker; Kipp, Kerstin H.; Mecklinger, Axel

    2011-01-01

    Event-related potential (ERP) correlates of item and source memory were assessed in 18 children (7-8 years), 20 adolescents (13-14 years), and 20 adults (20-29 years) performing a continuous recognition memory task with object and nonobject stimuli. Memory performance increased with age and was particularly low for source memory in children. The…

  17. Direct Observation of Amorphous to Crystalline Phase Transitions in Nano-Particle Arrays of Phase Change Materials

    SciTech Connect

    Raoux,S.; Rettner, C.; Jordan-Sweet, J.; Kellock, A.; Topuria, T.; Rice, P.; Miller, D.

    2007-01-01

    We have used time-resolved x-ray diffraction to study the amorphous-crystalline phase transition in 20-80?nm particles of the phase change materials Ge2Sb2Te5, nitrogen-doped Ge2Sb2Te5, Ge15Sb85, Sb2Te, and Sb2Te doped with Ag and In. We find that all samples undergo the phase transition with crystallization temperatures close to those of similarly prepared blanket films of the same materials with the exception of Sb2Te that shows the transition at a temperature that is about 40? C higher than that of blanket films. Some of the nanoparticles show a difference in crystallographic texture compared to thick films. Large area arrays of these nanoparticles were fabricated using electron-beam lithography, keeping the sample temperatures well below the crystallization temperatures so as to produce particles that were entirely in the amorphous phase. The observation that particles with diameters as small as 20?nm can still undergo this phase transition indicates that phase change solid-state memory technology should scale to these dimensions.

  18. Realization of multifunctional shape-memory ferromagnets in all-d-metal Heusler phases

    SciTech Connect

    Wei, Z. Y.; Liu, E. K. Chen, J. H.; Xi, X. K.; Zhang, H. W.; Wang, W. H.; Wu, G. H.; Li, Y.; Liu, G. D.; Luo, H. Z.

    2015-07-13

    Heusler ferromagnetic shape-memory alloys (FSMAs) normally consist of transition-group d-metals and main-group p-elements. Here, we report the realization of FSMAs in Heusler phases that completely consist of d metals. By introducing the d-metal Ti into NiMn alloys, cubic B2-type Heusler phase is obtained and the martensitic transformation temperature is decreased efficiently. Strong ferromagnetism is established by further doping Co atoms into the B2-type antiferromagnetic Ni-Mn-Ti austenite. Based on the magnetic-field-induced martensitic transformations, collective multifunctional properties are observed in Ni(Co)-Mn-Ti alloys. The d metals not only facilitate the formation of B2-type Heusler phases but also establish strong ferromagnetic coupling and offer the possibility to tune the martensitic transformation.

  19. Changes in neuronal excitability serve as a mechanism of long-term memory for operant conditioning

    PubMed Central

    Mozzachiodi, Riccardo; Lorenzetti, Fred D.; Baxter, Douglas A.; Byrne, John H.

    2016-01-01

    Learning can lead to changes in the intrinsic excitability of neurons. However, it is unclear to what extent these changes persist and what role they play in the expression of memory. Here, we report that in vitro analogues of operant conditioning produce a long-term (24 h) increase in the excitability of an identified neuron (B51) critical for the expression of feeding in Aplysia. This increase in excitability, which is cAMP dependent, contributes to the associative modification of the feeding circuitry, providing a mechanism for long-term memory storage. PMID:18776897

  20. Phase behavior of shape-changing spheroids

    NASA Astrophysics Data System (ADS)

    Teixeira, P. I. C.; Masters, A. J.

    2015-12-01

    We introduce a simple model for a biaxial nematic liquid crystal. This consists of hard spheroids that can switch shape between prolate (rodlike) and oblate (platelike) subject to an energy penalty Δ ɛ . The spheroids are approximated as hard Gaussian overlap particles and are treated at the level of Onsager's second-virial description. We use both bifurcation analysis and a numerical minimization of the free energy to show that, for additive particle shapes, (i) there is no stable biaxial phase even for Δ ɛ =0 (although there is a metastable biaxial phase in the same density range as the stable uniaxial phase) and (ii) the isotropic-to-nematic transition is into either one of two degenerate uniaxial phases, rod rich or plate rich. We confirm that even a small amount of shape nonadditivity may stabilize the biaxial nematic phase.

  1. The change probability effect: incidental learning, adaptability, and shared visual working memory resources.

    PubMed

    van Lamsweerde, Amanda E; Beck, Melissa R

    2011-12-01

    Statistical properties in the visual environment can be used to improve performance on visual working memory (VWM) tasks. The current study examined the ability to incidentally learn that a change is more likely to occur to a particular feature dimension (shape, color, or location) and use this information to improve change detection performance for that dimension (the change probability effect). Participants completed a change detection task in which one change type was more probable than others. Change probability effects were found for color and shape changes, but not location changes, and intentional strategies did not improve the effect. Furthermore, the change probability effect developed and adapted to new probability information quickly. Finally, in some conditions, an improvement in change detection performance for a probable change led to an impairment in change detection for improbable changes. PMID:21963330

  2. Changes in spatial memory and BDNF expression to simultaneous dietary restriction and forced exercise.

    PubMed

    Khabour, Omar F; Alzoubi, Karem H; Alomari, Mahmoud A; Alzubi, Mohammad A

    2013-01-01

    Previous literature suggests that learning and memory formation can be influenced by diet and exercise. In the current study, we investigated the combined effects of forced swimming exercise (FSE) and every other day fasting (EODF) on spatial memory formation and on the levels of brain-derived neurotrophic factor (BDNF) in the hippocampus of Wistar male rats. The radial arm water maze (RAWM) paradigm was used to assess changes in learning and memory formation, whereas ELISA assay was used to measure BDNF protein levels. The FSE and/or EODF were simultaneously instituted for 6 weeks. Results show that FSE improved learning, short-term as well as long-term memory formation, and significantly increased BDNF protein in the hippocampus (p<0.05). However, EODF had no effect on either spatial learning and memory formation or the levels of hippocamapal BDNF protein (p>0.05). In addition, EODF did not modulate beneficial effect of swimming exercise on cognitive function (p>0.05). Thus exercise enhanced, while EODF did not affect spatial learning and memory formation. PMID:23000024

  3. Context Memory Decline in Middle Aged Adults is Related to Changes in Prefrontal Cortex Function.

    PubMed

    Kwon, Diana; Maillet, David; Pasvanis, Stamatoula; Ankudowich, Elizabeth; Grady, Cheryl L; Rajah, M Natasha

    2016-06-01

    The ability to encode and retrieve spatial and temporal contextual details of episodic memories (context memory) begins to decline at midlife. In the current study, event-related fMRI was used to investigate the neural correlates of context memory decline in healthy middle aged adults (MA) compared with young adults (YA). Participants were scanned while performing easy and hard versions of spatial and temporal context memory tasks. Scans were obtained at encoding and retrieval. Significant reductions in context memory retrieval accuracy were observed in MA, compared with YA. The fMRI results revealed that overall, both groups exhibited similar patterns of brain activity in parahippocampal cortex, ventral occipito-temporal regions and prefrontal cortex (PFC) during encoding. In contrast, at retrieval, there were group differences in ventral occipito-temporal and PFC activity, due to these regions being more activated in MA, compared with YA. Furthermore, only in YA, increased encoding activity in ventrolateral PFC, and increased retrieval activity in occipital cortex, predicted increased retrieval accuracy. In MA, increased retrieval activity in anterior PFC predicted increased retrieval accuracy. These results suggest that there are changes in PFC contributions to context memory at midlife. PMID:25882039

  4. Correlating structural and resistive changes in Ti:NiO resistive memory elements.

    SciTech Connect

    Holt, M.; Heinonen, O.; Siegert, M.; Roelofe, A.; Petford-Long, A. K.; Li, W.; d'Aquila, K.; Seagate Technology; Northwestern Univ.

    2010-03-08

    Structural and resistive changes in Ti-doped NiO resistive random access memory structures that occur upon electroforming have been investigated using hard x-ray microscopy. Electroforming leads to structural changes in regions of size up to about one micrometer, much larger than the grain size of the structure. Such changes are consistent with a migration of ionic species or defects during electroforming over regions containing many crystalline grains.

  5. Nano composite phase change materials microcapsules

    NASA Astrophysics Data System (ADS)

    Song, Qingwen

    MicroPCMs with nano composite structures (NC-MicroPCMs) have been systematically studied. NC-MicroPCMs were fabricated by the in situ polymerization and addition of silver NPs into core-shell structures. A full factorial experiment was designed, including three factors of core/shell, molar ratio of formaldehyde/melamine and NPs addition. 12 MicroPCMs samples were prepared. The encapsulated efficiency is approximately 80% to 90%. The structural/morphological features of the NC-MicroPCMs were evaluated. The size was in a range of 3.4 mu m to 4.0 mu m. The coarse appearance is attributed to NPs and NPs are distributed on the surface, within the shell and core. The NC-MicroPCMs contain new chemical components and molecular groups, due to the formation of chemical bonds after the pretreatment of NPs. Extra X-ray diffraction peaks of silver were found indicating silver nano-particles were formed into an integral structure with the core/shell structure by means of chemical bonds and physical linkages. Extra functionalities were found, including: (1) enhancement of IR radiation properties; (2) depression of super-cooling, and (3) increase of thermal stabilities. The effects of SERS (Surface Enhanced Raman Spectroscopy) arising from the silver nano-particles were observed. The Raman scattering intensity was magnified more than 100 times. These effects were also exhibited in macroscopic level in the fabric coatings as enhanced IR radiation properties were detected by the "Fabric Infrared Radiation Management Tester" (FRMT). "Degree of Crystallinity" (DOC) was measured and found the three factors have a strong influence on it. DOC is closely related to thermal stability and MicroPCMs with a higher DOC show better temperature resistance. The thermal regulating effects of the MicroPCMs coatings were studied. A "plateau regions" was detected around the temperature of phase change, showing the function of PCMs. Addition of silver nano-particles to the MicroPCMs has a positive

  6. Oscillation Phase Locking and Late ERP Components of Intracranial Hippocampal Recordings Correlate to Patient Performance in a Working Memory Task

    PubMed Central

    Kleen, Jonathan K.; Testorf, Markus E.; Roberts, David W.; Scott, Rod C.; Jobst, Barbara J.; Holmes, Gregory L.; Lenck-Santini, Pierre-Pascal

    2016-01-01

    In working memory tasks, stimulus presentation induces a resetting of intracranial temporal lobe oscillations in multiple frequency bands. To further understand the functional relevance of this phenomenon, we investigated whether working memory performance depends on the phase precision of ongoing oscillations in the hippocampus. We recorded intra-hippocampal local field potentials in individuals performing a working memory task. Two types of trials were administered. For high memory trials presentation of a list of four letters (“List”) was followed by a single letter memory probe (“Test”). Low memory load trials, consisting of four identical letters (AAAA) followed by a probe with the same letter (A), were interspersed. Significant phase locking of ongoing oscillations across trials, estimated by the Pairwise Phase Consistency Index (PPCI) was observed in delta (0.5–4 Hz), theta (5–7 Hz), and alpha (8–12 Hz) bands during stimulus presentation and recall but was increased in low memory load trials. Across patients however, higher delta PPCIs during recall in the left hippocampus were associated with faster reaction times. Because phase locking could also be interpreted as a consequence of a stimulus evoked potential, we performed event related potential analysis (ERP) and examined the relationship of ERP components with performance. We found that both amplitude and latency of late ERP components correlated with both reaction time and accuracy. We propose that, in the Sternberg task, phase locking of oscillations, or alternatively its ERP correlate, synchronizes networks within the hippocampus and connected structures that are involved in working memory. PMID:27378885

  7. 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.

  8. Microscopic origin of resistance drift in the amorphous state of the phase-change compound GeTe

    NASA Astrophysics Data System (ADS)

    Gabardi, S.; Caravati, S.; Sosso, G. C.; Behler, J.; Bernasconi, M.

    2015-08-01

    Aging is a common feature of the glassy state. In the case of phase-change chalcogenide alloys the aging of the amorphous state is responsible for an increase of the electrical resistance with time. This phenomenon called drift is detrimental in the application of these materials in phase-change nonvolatile memories, which are emerging as promising candidates for storage class memories. By means of combined molecular dynamics and electronic structure calculations based on density functional theory, we have unraveled the atomistic origin of the resistance drift in the prototypical phase-change compound GeTe. The drift results from a widening of the band gap and a reduction of Urbach tails due to structural relaxations leading to the removal of chains of Ge-Ge homopolar bonds. The same structural features are actually responsible for the high mobility above the glass transition which boosts the crystallization speed exploited in the device.

  9. Toward structural/chemical cotailoring of phase-change Ge-Sb-Te in a transmission electron microscope.

    PubMed

    Zhang, W; Kim, J-G; Zheng, W T; Cui, X Q; Kim, Y-J; Song, S A

    2015-03-01

    Ge2Sb2Te5, as the prototype material for phase-change memory, can be transformed from amorphous phase into nanoscale rocksalt-type GeTe provided with an electron irradiation assisted by heating to 520°C in a 1250 kV transmission electron microscope. This sheds a new light into structural and chemical cotailoring of materials through coupling of thermal and electrical fields. PMID:25623497

  10. The effect of memory and context changes on color matches to real objects.

    PubMed

    Allred, Sarah R; Olkkonen, Maria

    2015-07-01

    Real-world color identification tasks often require matching the color of objects between contexts and after a temporal delay, thus placing demands on both perceptual and memory processes. Although the mechanisms of matching colors between different contexts have been widely studied under the rubric of color constancy, little research has investigated the role of long-term memory in such tasks or how memory interacts with color constancy. To investigate this relationship, observers made color matches to real study objects that spanned color space, and we independently manipulated the illumination impinging on the objects, the surfaces in which objects were embedded, and the delay between seeing the study object and selecting its color match. Adding a 10-min delay increased both the bias and variability of color matches compared to a baseline condition. These memory errors were well accounted for by modeling memory as a noisy but unbiased version of perception constrained by the matching methods. Surprisingly, we did not observe significant increases in errors when illumination and surround changes were added to the 10-minute delay, although the context changes alone did elicit significant errors. PMID:25824887

  11. 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. PMID:23003059

  12. Thermo-mechanical Response and Damping Behavior of Shape Memory Alloy-MAX Phase Composites

    NASA Astrophysics Data System (ADS)

    Kothalkar, Ankush Dilip; Benitez, Rogelio; Hu, Liangfa; Radovic, Miladin; Karaman, Ibrahim

    2014-05-01

    NiTi/Ti3SiC2 interpenetrating composites that combine two unique material systems—a shape memory alloy (SMA) and a MAX phase—demonstrating two different pseudoelastic mechanisms, were processed using spark plasma sintering. The goal of mixing these two material systems was to enhance the damping behavior and thermo-mechanical response of the composite by combining two pseudoelastic mechanisms, i.e., reversible stress-induced martensitic transformation in SMA and reversible incipient kink band formation in MAX phase. Equal volume fractions of equiatomic NiTi and Ti3SiC2 were used. Microstructural characterization was conducted using scanning electron microscopy to study the distribution of NiTi, Ti3SiC2, and remnant porosity in the composite. Thermo-mechanical testing in the form of thermal cycles under constant stress levels was performed in order to characterize shape memory behavior and thereby introducing residual stresses in the composites. Evolution of two-way shape memory effect was studied and related to the presence of residual stresses in the composites. Damping behavior, implying the energy dissipation per loading-unloading cycle under increasing compressive stresses, of pure NiTi, pure Ti3SiC2, as-sintered, and thermo-mechanically cycled (TC) NiTi/Ti3SiC2 composites, was investigated and compared to the literature data. In this study, the highest energy dissipation was observed for the TC composite followed by the as-sintered (AS) composite, pure NiTi, and pure Ti3SiC2 when compared at the same applied stress levels. Both the AS and TC composites showed higher damping up to 200 MPa stress than any of the metal—MAX phase composites reported in the literature to date. The ability to enhance the performance of the composite by controlling the thermo-mechanical loading paths was further discussed.

  13. Short-Term Longitudinal Changes in Memory, Intelligence and Perceived Competence in Older Adults.

    ERIC Educational Resources Information Center

    Gilewski, Michael J.; Schaie, K. Warner

    Previous research on intelligence and aging has relied on tests developed for younger adults, which often incorporate many factors that could impede optimal performance in elderly populations. To investigate short-term longitudinal changes in memory, intelligence, and perceived competence in everyday situations among older adults, 227 adults were…

  14. Developmental Change in Proactive Interference across the Life Span: Evidence from Two Working Memory Tasks

    ERIC Educational Resources Information Center

    Loosli, Sandra V.; Rahm, Benjamin; Unterrainer, Josef M.; Weiller, Cornelius; Kaller, Christoph P.

    2014-01-01

    Working memory (WM) as the ability to temporarily maintain and manipulate various kinds of information is known to be affected by proactive interference (PI) from previously relevant contents, but studies on developmental changes in the susceptibility to PI are scarce. In the present study, we investigated life span development of item-specific…

  15. Developmental changes in visual short-term memory in infancy: evidence from eye-tracking

    PubMed Central

    Oakes, Lisa M.; Baumgartner, Heidi A.; Barrett, Frederick S.; Messenger, Ian M.; Luck, Steven J.

    2013-01-01

    We assessed visual short-term memory (VSTM) for color in 6- and 8-month-old infants (n = 76) using a one-shot change detection task. In this task, a sample array of two colored squares was visible for 517 ms, followed by a 317-ms retention period and then a 3000-ms test array consisting of one unchanged item and one item in a new color. We tracked gaze at 60 Hz while infants looked at the changed and unchanged items during test. When the two sample items were different colors (Experiment 1), 8-month-old infants exhibited a preference for the changed item, indicating memory for the colors, but 6-month-olds exhibited no evidence of memory. When the two sample items were the same color and did not need to be encoded as separate objects (Experiment 2), 6-month-old infants demonstrated memory. These results show that infants can encode information in VSTM in a single, brief exposure that simulates the timing of a single fixation period in natural scene viewing, and they reveal rapid developmental changes between 6 and 8 months in the ability to store individuated items in VSTM. PMID:24106485

  16. Age-Related Changes in Duration Reproduction: Involvement of Working Memory Processes

    ERIC Educational Resources Information Center

    Baudouin, Alexia; Vanneste, Sandrine; Pouthas, Viviane; Isingrini, Michel

    2006-01-01

    The aim of the present research was to study age-related changes in duration reproduction by differentiating the working memory processes underlying this time estimation task. We compared performances of young and elderly adults in a duration reproduction task performed in simple and concurrent task conditions. Participants were also administered…

  17. 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.

  18. Competing covalent and ionic bonding in Ge-Sb-Te phase change materials

    DOE PAGESBeta

    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 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 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

  20. Competing covalent and ionic bonding in Ge-Sb-Te phase change materials.

    PubMed

    Mukhopadhyay, Saikat; Sun, Jifeng; Subedi, Alaska; Siegrist, Theo; Singh, David J

    2016-01-01

    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

  1. Seymour Sarason in Memorial: Prospects for Community and Social Change

    ERIC Educational Resources Information Center

    Maton, Kenneth I.

    2012-01-01

    Seymour Sarason passed away on January 10, 2010 at the age of 91. He was the author of more than 40 books, including The Culture of the School and the Problem of Change (1971), The Creation of Settings and the Future Societies (1972), and The Psychological Sense of Community: Prospects for a Community Psychology (1974). His groundbreaking ideas…

  2. Structural Phase Transition Effect on Resistive Switching Behavior of MoS2 -Polyvinylpyrrolidone Nanocomposites Films for Flexible Memory Devices.

    PubMed

    Zhang, Peng; Gao, Cunxu; Xu, Benhua; Qi, Lin; Jiang, Changjun; Gao, Meizhen; Xue, Desheng

    2016-04-01

    The 2H phase and 1T phase coexisting in the same molybdenum disulfide (MoS2 ) nanosheets can influence the electronic properties of the materials. The 1T phase of MoS2 is introduced into the 2H-MoS2 nanosheets by two-step hydrothermal synthetic methods. Two types of nonvolatile memory effects, namely write-once read-many times memory and rewritable memory effect, are observed in the flexible memory devices with the configuration of Al/1T@2H-MoS2 -polyvinylpyrrolidone (PVP)/indium tin oxide (ITO)/polyethylene terephthalate (PET) and Al/2H-MoS2 -PVP/ITO/PET, respectively. It is observed that structural phase transition in MoS2 nanosheets plays an important role on the resistive switching behaviors of the MoS2 -based device. It is hoped that our results can offer a general route for the preparation of various promising nanocomposites based on 2D nanosheets of layered transition metal dichalcogenides for fabricating the high performance and flexible nonvolatile memory devices through regulating the phase structure in the 2D nanosheets. PMID:26938882

  3. Effects of twin boundary mobility on domain microstructure evolution in magnetic shape memory alloys: Phase field simulation

    SciTech Connect

    Jin, Yongmei M.

    2009-02-09

    Effects of twin boundary mobility on domain microstructure evolution during magnetic field-induced deformation in magnetic shape memory alloys are studied by phase field micromagnetic microelastic modeling. The simulations show that different twin boundary mobilities lead to drastically different domain microstructures and evolution pathways, yielding very different magnetization and strain responses, even with opposite signs. The study also reveals complex domain phenomena in magnetic shape memory alloys.

  4. Biophysical Modeling of Phase Changes in BOLD fMRI

    PubMed Central

    Feng, Zhaomei; Caprihan, Arvind; Blagoev, Krastan B.; Calhoun, Vince D

    2009-01-01

    In BOLD fMRI, stimulus related phase changes have been repeatedly observed in humans. However, virtually all fMRI processing utilizes the magnitude information only, while ignoring the phase. This results in an unnecessary loss of physiological information and signal-to-noise efficiency. A widely held view is that the BOLD phase change is zero for a voxel containing randomly orientated blood vessels and that phase changes are only due to the presence of large vessels. Based on a previously developed theoretical model, we show through simulations and experimental human BOLD fMRI data that a non-zero phase change can be present in a region with randomly oriented vessels. Using simulations of the model, we first demonstrate that a spatially distributed susceptibility results in a non-zero phase distribution. Next, experimental data in a finger-tapping experiment show consistent bipolar phase distribution across multiple subjects. This model is then used to show that in theory a bipolar phase distribution can also be produced by the model. Finally, we show that the model can produce a bipolar phase pattern consistent with that observed in the experimental data. Understanding of the mechanisms behind the experimentally observed phase changes in BOLD fMRI would be an important step forward and will enable biophysical model based methods for integrating the phase and magnitude information in BOLD fMRI experiments. PMID:19426815

  5. Sub-nanometre resolution of atomic motion during electronic excitation in phase-change materials

    PubMed Central

    Mitrofanov, Kirill V.; Fons, Paul; Makino, Kotaro; Terashima, Ryo; Shimada, Toru; Kolobov, Alexander V.; Tominaga, Junji; Bragaglia, Valeria; Giussani, Alessandro; Calarco, Raffaella; Riechert, Henning; Sato, Takahiro; Katayama, Tetsuo; Ogawa, Kanade; Togashi, Tadashi; Yabashi, Makina; Wall, Simon; Brewe, Dale; Hase, Muneaki

    2016-01-01

    Phase-change materials based on Ge-Sb-Te alloys are widely used in industrial applications such as nonvolatile memories, but reaction pathways for crystalline-to-amorphous phase-change on picosecond timescales remain unknown. Femtosecond laser excitation and an ultrashort x-ray probe is used to show the temporal separation of electronic and thermal effects in a long-lived (>100 ps) transient metastable state of Ge2Sb2Te5 with muted interatomic interaction induced by a weakening of resonant bonding. Due to a specific electronic state, the lattice undergoes a reversible nondestructive modification over a nanoscale region, remaining cold for 4 ps. An independent time-resolved x-ray absorption fine structure experiment confirms the existence of an intermediate state with disordered bonds. This newly unveiled effect allows the utilization of non-thermal ultra-fast pathways enabling artificial manipulation of the switching process, ultimately leading to a redefined speed limit, and improved energy efficiency and reliability of phase-change memory technologies. PMID:26868451

  6. Sub-nanometre resolution of atomic motion during electronic excitation in phase-change materials

    NASA Astrophysics Data System (ADS)

    Mitrofanov, Kirill V.; Fons, Paul; Makino, Kotaro; Terashima, Ryo; Shimada, Toru; Kolobov, Alexander V.; Tominaga, Junji; Bragaglia, Valeria; Giussani, Alessandro; Calarco, Raffaella; Riechert, Henning; Sato, Takahiro; Katayama, Tetsuo; Ogawa, Kanade; Togashi, Tadashi; Yabashi, Makina; Wall, Simon; Brewe, Dale; Hase, Muneaki

    2016-02-01

    Phase-change materials based on Ge-Sb-Te alloys are widely used in industrial applications such as nonvolatile memories, but reaction pathways for crystalline-to-amorphous phase-change on picosecond timescales remain unknown. Femtosecond laser excitation and an ultrashort x-ray probe is used to show the temporal separation of electronic and thermal effects in a long-lived (>100 ps) transient metastable state of Ge2Sb2Te5 with muted interatomic interaction induced by a weakening of resonant bonding. Due to a specific electronic state, the lattice undergoes a reversible nondestructive modification over a nanoscale region, remaining cold for 4 ps. An independent time-resolved x-ray absorption fine structure experiment confirms the existence of an intermediate state with disordered bonds. This newly unveiled effect allows the utilization of non-thermal ultra-fast pathways enabling artificial manipulation of the switching process, ultimately leading to a redefined speed limit, and improved energy efficiency and reliability of phase-change memory technologies.

  7. Sub-nanometre resolution of atomic motion during electronic excitation in phase-change materials.

    PubMed

    Mitrofanov, Kirill V; Fons, Paul; Makino, Kotaro; Terashima, Ryo; Shimada, Toru; Kolobov, Alexander V; Tominaga, Junji; Bragaglia, Valeria; Giussani, Alessandro; Calarco, Raffaella; Riechert, Henning; Sato, Takahiro; Katayama, Tetsuo; Ogawa, Kanade; Togashi, Tadashi; Yabashi, Makina; Wall, Simon; Brewe, Dale; Hase, Muneaki

    2016-01-01

    Phase-change materials based on Ge-Sb-Te alloys are widely used in industrial applications such as nonvolatile memories, but reaction pathways for crystalline-to-amorphous phase-change on picosecond timescales remain unknown. Femtosecond laser excitation and an ultrashort x-ray probe is used to show the temporal separation of electronic and thermal effects in a long-lived (>100 ps) transient metastable state of Ge2Sb2Te5 with muted interatomic interaction induced by a weakening of resonant bonding. Due to a specific electronic state, the lattice undergoes a reversible nondestructive modification over a nanoscale region, remaining cold for 4 ps. An independent time-resolved x-ray absorption fine structure experiment confirms the existence of an intermediate state with disordered bonds. This newly unveiled effect allows the utilization of non-thermal ultra-fast pathways enabling artificial manipulation of the switching process, ultimately leading to a redefined speed limit, and improved energy efficiency and reliability of phase-change memory technologies. PMID:26868451

  8. Sub-nanometre resolution of atomic motion during electronic excitation in phase-change materials

    DOE PAGESBeta

    Mitrofanov, Kirill V.; Fons, Paul; Makino, Kotaro; Terashima, Ryo; Shimada, Toru; Kolobov, Alexander V.; Tominaga, Junji; Bragaglia, Valeria; Giussani, Alessandro; Calarco, Raffaella; et al

    2016-02-12

    Phase-change materials based on Ge-Sb-Te alloys are widely used in industrial applications such as nonvolatile memories, but reaction pathways for crystalline-to-amorphous phase-change on picosecond timescales remain unknown. Femtosecond laser excitation and an ultrashort x-ray probe is used to show the temporal separation of electronic and thermal effects in a long-lived (>100 ps) transient metastable state of Ge2Sb2Te5 with muted interatomic interaction induced by a weakening of resonant bonding. Due to a specific electronic state, the lattice undergoes a reversible nondestructive modification over a nanoscale region, remaining cold for 4 ps. An independent time-resolved x-ray absorption fine structure experiment confirms themore » existence of an intermediate state with disordered bonds. Furthermore, this newly unveiled effect allows the utilization of non-thermal ultra-fast pathways enabling artificial manipulation of the switching process, ultimately leading to a redefined speed limit, and improved energy efficiency and reliability of phase-change memory technologies.« less

  9. Effects of experimentally necessary changes in husbandry on olfactory memory: Chronic food restriction and social isolation.

    PubMed

    Manella, Laura; Woldeyohannes, Leuk; McMahon, Devon; Linster, Christiane

    2016-03-01

    Changes to typical procedures in animal husbandry are often necessary to accommodate the needs of behavioral experiments. Two common changes in husbandry for rodents are light chronic food restriction (to motivate animals in reward-association tasks) and social isolation (to accommodate individual feeding schedules or need to reduce interactions because of implants for example). Each of these intervention individually has been shown to modulate behavioral state and with it performance in behavioral tasks. We here systematically test how social isolation and light chronic food restriction modulate olfactory memory in rats. Our results show a strong modulation of olfactory memory after both types of husbandry interventions. These results suggest that common changes in animal husbandry promote distinct and relevant changes in animal behavior. PMID:26655783

  10. Phase Transformation and Creep Behavior in Ti50Pd30Ni20 High Temperature Shape Memory Alloy in Compression

    NASA Technical Reports Server (NTRS)

    Kumar, Parikshith K.; Desai, Uri; Monroe, James; Lagoudas, Dimitris C.; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glenn

    2010-01-01

    The creep behavior and the phase transformation of Ti50Pd30Ni20 High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

  11. Dynamic Thermo-Mechanical Phase-Field Models for Martensitic Transformations in Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Dhote, Rakesh

    Shape memory alloys (SMAs) exhibit complex microstructures and non-linear hysteretic behaviors that arise from a strong interaction between mechanical and thermal phenomena. It is imperative to couple the thermal physics and the mechanical dynamics to study the influence of such coupling on the mechanical properties of SMA systems, including nanostructures. However, the majority of phase-field models in the literature related to SMAs account for structural physics only. With the aim to incorporate thermal physics, in this thesis, first the 2D and 3D dynamic fully coupled thermo-mechanical phase-field models are developed based on the strain-based order parameters. The developed models are highly nonlinear, strongly hysteretic with fourth-order spatial differential terms, which impose several computational challenges. Secondly, to overcome these computational challenges, a numerical formulation based on the isogeometric analysis is developed for a straightforward solution to the fourth-order differential equations using continuously differentiable non-uniform rational B-splines (NURBS). Several numerical examples of microstructure evolution in SMA systems, in particular nanostructures of different geometries, under temperature and stress induced loadings illustrated the flexibility, accuracy and robustness of the developed numerical formulation. The numerical simulations revealed a significant impact of the temperature dynamics on mechanical properties of SMAs. The developed models successfully captured experimentally observed mechanical and thermal hysteresis phenomena, local non-uniform phase transformations and corresponding non-uniform temperature and deformations distributions. The predicted microstructure evolution is in qualitative agreement with the results reported in the literature. The material properties of austenite and martensite phases are different, as observed experimentally during phase transformations. However, the majority of macroscale non

  12. 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.

  13. Age-related changes in neural activity during source memory encoding in young, middle-aged and elderly adults.

    PubMed

    Cansino, Selene; Trejo-Morales, Patricia; Hernández-Ramos, Evelia

    2010-07-01

    Source memory, the ability to remember contextual information present at the moment an event occurs, declines gradually during normal aging. The present study addressed whether source memory decline is related to changes in neural activity during encoding across age. Event-related potentials (ERPs) were recorded in three groups of 14 subjects each: young (21-26 years), middle-aged (50-55 years) and older adults (70-77 years). ERPs were recorded while the subjects performed a natural/artificial judgment on images of common objects that were presented randomly in one of the quadrants of the screen (encoding phase). At retrieval, old images mixed with new ones were presented at the center of the screen and the subjects judged whether each image was new or old and, if old, were asked to indicate at which position of the screen the image was presented in the encoding session. The neurophysiological activity recorded during encoding was segregated for the study items according to whether their context was correctly retrieved or not, so as to search for subsequent memory effects (SME). These effects, which consisted of larger amplitude for items subsequently attracting a correct source judgment than an incorrect one, were observed in the three groups, but their onset was delayed across the age groups. The amplitude of the SME was similar across age groups at the frontal and central electrode sites, but was manifested more at the posterior sites in middle-aged and older adults, suggesting that source memory decline may be related to less efficient encoding mechanisms. PMID:20441775

  14. How Japanese adults perceive memory change with age: middle-aged adults with memory performance as high as young adults evaluate their memory abilities as low as older adults.

    PubMed

    Kinjo, Hikari; Shimizu, Hiroyuki

    2014-01-01

    The characteristics of self-referent beliefs about memory change with age. The relationship between beliefs and memory performance of three age groups of Japanese adults was investigated. The beliefs measured by the Personal Beliefs about Memory Instrument (Lineweaver & Hertzog, 1998) differed among the age groups and between sexes. In most scales, the ratings by middle-aged adults were as low as those by older adults, which were lower than those by young adults. Women perceived their memory abilities as lower than men's, with no interaction between age and sex, suggesting the difference remains across the lifespan. For middle-aged adults, the better they performed in cued-recall, free recall, and recognition, the lower they evaluated their memory self-efficacy, while few relationships were found for other groups. Our results suggest that cognitive beliefs change with age and that investigating the beliefs of the middle-aged adults is indispensable to elucidate the transition of beliefs. PMID:24669510

  15. Influence of Dynamic Compression on Phase Transformation of Martensitic NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Qiu, Ying; Young, Marcus L.; Nie, Xu

    2015-10-01

    Shape memory alloys (SMAs) exhibit high damping capacity in both austenitic and martensitic phases, due to either a stress-induced martensite phase transformation or a stress-induced martensite variant reorientation, making them ideal candidates for vibration suppression devices to protect structural components from damage due to external forces. In this study, both quasi-static and dynamic compression was conducted on a martensitic NiTi SMA using a mechanical loading frame and on a Kolsky compression bar, respectively, to examine the relationship between microstructure and phase transformation characteristics of martensitic NiTi SMAs. Both endothermic and exothermic peaks disappear completely after experiencing deformation at a strain rate of 103 s-1 and to a strain of about 10 pct. The phase transformation peaks reappear after the deformed specimens were annealed at 873 K (600 °C) for 30 minutes. As compared to samples from quasi-static loading, where a large amount of twinning is observed with a small amount of grain distortion and fracture, samples from dynamic loading show much less twinning with a larger amount of grain distortion and fracture.

  16. A study to evaluate non-uniform phase maps in shape memory alloys using finite element method

    NASA Astrophysics Data System (ADS)

    Motte, Naren

    The unique thermo-mechanical behavior of Shape Memory Alloys (SMAs), such as their ability to recover the original shape upon heating or being able to tolerate large deformations without undergoing plastic transformations, makes them a good choice for actuators. This work studies their application in the aerospace and defense industries where SMA components can serve as release mechanisms for gates of enclosures that have to be deployed remotely. This work provides a novel approach in evaluating the stress and heat induced change of phase in a SMA, in terms of the transformation strain tensor. In particular, the FEA tool ANSYS has been used to perform a 2-D analysis of a Cu-Al-Zn-Mn SMA specimen undergoing a nontraditional loading path in two steps with stress and heating loads. In the first load step, tensile displacement is applied, followed by the second load step in which the specimen is heated while the end displacements are held constant. A number of geometric configurations are examined under the two step loading path. Strain results are used to calculate transformation strain which provides a quantitative measure of phase at a material point; when transformation strain is zero, the material point is either twinned martensite, or austenite depending on the temperature. Transformation strain value of unity corresponds to detwinned martensite. A value between zero and one indicates mixed phase. In this study, through two step loading in conjunction with transformation strain calculations, a method for mapping transient non-uniform distribution of phases in an SMA is introduced. Ability to obtain drastically different phase distributions under same loading path by modifying the geometry is demonstrated. The failure behavior of SMAs can be designed such that the load level the crack initiates and the path it propagates can be customized.

  17. The Decay of Motor Memories Is Independent of Context Change Detection

    PubMed Central

    Brennan, Andrew E.; Smith, Maurice A.

    2015-01-01

    When the error signals that guide human motor learning are withheld following training, recently-learned motor memories systematically regress toward untrained performance. It has previously been hypothesized that this regression results from an intrinsic volatility in these memories, resulting in an inevitable decay in the absence of ongoing error signals. However, a recently-proposed alternative posits that even recently-acquired motor memories are intrinsically stable, decaying only if a change in context is detected. This new theory, the context-dependent decay hypothesis, makes two key predictions: (1) after error signals are withheld, decay onset should be systematically delayed until the context change is detected; and (2) manipulations that impair detection by masking context changes should result in prolonged delays in decay onset and reduced decay amplitude at any given time. Here we examine the decay of motor adaptation following the learning of novel environmental dynamics in order to carefully evaluate this hypothesis. To account for potential issues in previous work that supported the context-dependent decay hypothesis, we measured decay using a balanced and baseline-referenced experimental design that allowed for direct comparisons between analogous masked and unmasked context changes. Using both an unbiased variant of the previous decay onset analysis and a novel highly-powered group-level version of this analysis, we found no evidence for systematically delayed decay onset nor for the masked context change affecting decay amplitude or its onset time. We further show how previous estimates of decay onset latency can be substantially biased in the presence of noise, and even more so with correlated noise, explaining the discrepancy between the previous results and our findings. Our results suggest that the decay of motor memories is an intrinsic feature of error-based learning that does not depend on context change detection. PMID:26111244

  18. Matrix Metalloproteinase-9 Is Required for Hippocampal Late-Phase Long-Term Potentiation and Memory

    PubMed Central

    Nagy, Vanja; Bozdagi, Ozlem; Matynia, Anna; Balcerzyk, Marcin; Okulski, Pawel; Dzwonek, Joanna; Costa, Rui M.; Silva, Alcino J.; Kaczmarek, Leszek; Huntley, George W.

    2015-01-01

    Matrix metalloproteinases (MMPs) are extracellular proteases that have well recognized roles in cell signaling and remodeling in many tissues. In the brain, their activation and function are customarily associated with injury or pathology. Here, we demonstrate a novel role for MMP-9 in hippocampal synaptic physiology, plasticity, and memory. MMP-9 protein levels and proteolytic activity are rapidly increased by stimuli that induce late-phase long-term potentiation (L-LTP) in area CA1. Such regulation requires NMDA receptors and protein synthesis. Blockade of MMP-9 pharmacologically prevents induction of L-LTP selectively; MMP-9 plays no role in, nor is regulated during, other forms of short-term synaptic potentiation or long-lasting synaptic depression. Similarly, in slices from MMP-9 null-mutant mice, hippocampal LTP, but not long-term depression, is impaired in magnitude and duration; adding recombinant active MMP-9 to null-mutant slices restores the magnitude and duration of LTP to wild-type levels. Activated MMP-9 localizes in part to synapses and modulates hippocampal synaptic physiology through integrin receptors, because integrin function-blocking reagents prevent an MMP-9-mediated potentiation of synaptic signal strength. The fundamental importance of MMP-9 function in modulating hippocampal synaptic physiology and plasticity is underscored by behavioral impairments in hippocampal-dependent memory displayed by MMP-9 null-mutant mice. Together, these data reveal new functions for MMPs in synaptic and behavioral plasticity. PMID:16481424

  19. Properties of triple shape memory composites prepared via polymerization-induced phase separation.

    PubMed

    Torbati, Amir H; Nejad, Hossein Birjandi; Ponce, Mileysa; Sutton, James P; Mather, Patrick T

    2014-05-01

    Research in the field of shape memory polymers has recently witnessed the introduction of increasing complexity of material response, including such phenomena as triple/multishape behavior, temperature memory, and reversible actuation. Ordinarily, such complexity in physical behaviour is achieved through comparable complexity in material composition and synthesis. Seeking to achieve a triple shape behaviour with a simple route to materials synthesis, we introduce here a method that utilizes polymerization induced phase separation (PIPS) to yield the requisite combination of microstructure and composition. Thus, two blends incorporating epoxy and poly(ε-caprolactone) were developed using commercially available reactants, one featuring a semicrystalline epoxy and the other featuring an amorphous epoxy. We show that both blends exhibited distinct transition temperatures and three modulus-temperature plateaus needed for triple shape behaviour. Despite these similarities, their physical character at room temperature is vastly different: the semicrystalline epoxy material is elastomeric and the amorphous epoxy material is highly stiff. Characterization of the triple shape behaviour revealed an ability of both systems to fix two separate deformations independently, one by PCL crystallization and a second one by epoxy crystallization or vitrification, and recover both programmed shapes separately upon heating. Given the simplicity of fabrication, we envision application as multi-shape coatings, adhesives, and films. PMID:24695693

  20. Low-power switching of phase-change materials with carbon nanotube electrodes.

    PubMed

    Xiong, Feng; Liao, Albert D; Estrada, David; Pop, Eric

    2011-04-29

    Phase-change materials (PCMs) are promising candidates for nonvolatile data storage and reconfigurable electronics, but high programming currents have presented a challenge to realize low-power operation. We controlled PCM bits with single-wall and small-diameter multi-wall carbon nanotubes. This configuration achieves programming currents of 0.5 microampere (set) and 5 microamperes (reset), two orders of magnitude lower than present state-of-the-art devices. Pulsed measurements enable memory switching with very low energy consumption. Analysis of over 100 devices finds that the programming voltage and energy are highly scalable and could be below 1 volt and single femtojoules per bit, respectively. PMID:21393510

  1. Can color changes alter the neural correlates of recognition memory? Manipulation of processing affects an electrophysiological indicator of conceptual implicit memory.

    PubMed

    Cui, Xiaoyu; Gao, Chuanji; Zhou, Jianshe; Guo, Chunyan

    2016-09-28

    It has been widely shown that recognition memory includes two distinct retrieval processes: familiarity and recollection. Many studies have shown that recognition memory can be facilitated when there is a perceptual match between the studied and the tested items. Most event-related potential studies have explored the perceptual match effect on familiarity on the basis of the hypothesis that the specific event-related potential component associated with familiarity is the FN400 (300-500 ms mid-frontal effect). However, it is currently unclear whether the FN400 indexes familiarity or conceptual implicit memory. In addition, on the basis of the findings of a previous study, the so-called perceptual manipulations in previous studies may also involve some conceptual alterations. Therefore, we sought to determine the influence of perceptual manipulation by color changes on recognition memory when the perceptual or the conceptual processes were emphasized. Specifically, different instructions (perceptually or conceptually oriented) were provided to the participants. The results showed that color changes may significantly affect overall recognition memory behaviorally and that congruent items were recognized with a higher accuracy rate than incongruent items in both tasks, but no corresponding neural changes were found. Despite the evident familiarity shown in the two tasks (the behavioral performance of recognition memory was much higher than at the chance level), the FN400 effect was found in conceptually oriented tasks, but not perceptually oriented tasks. It is thus highly interesting that the FN400 effect was not induced, although color manipulation of recognition memory was behaviorally shown, as seen in previous studies. Our findings of the FN400 effect for the conceptual but not perceptual condition support the explanation that the FN400 effect indexes conceptual implicit memory. PMID:27489100

  2. Adolphe Abrahams memorial lecture, 1988. Exercise and lifestyle change.

    PubMed Central

    Shephard, R J

    1989-01-01

    While the evidence for a clustering of health habits is not particularly strong, there are both pedagogic and economic arguments in favour of a multifaceted approach to health education. The present review thus examines the impact of regular physical exercise upon other forms of health behaviour, testing the extent to which an activity programme can be a catalyst of improved lifestyle in both primary and secondary preventive therapy. The conceptual framework of health promotion is examined with particular reference to the models of Skinner, Becker, Fishbein, Triandis and Rokeach. Certain differences are noted between the decision to exercise and the marketing decisions for which Fishbein's model was originally designed. Nevertheless, in its later modifications, it provides a basic framework for understanding how human lifestyle is shaped. Theoretical mechanisms are suggested whereby exercise could influence such behaviours as cigarette smoking, alcohol consumption and drug usage, seat-belt usage, hypertension, body mass, lipid profile, promiscuous sexual behaviour, the carrying of lethal weapons, and acceptance of regular preventive medical examinations. The empirical evidence from both cross-sectional and longitudinal experiments shows a relatively weak association between exercise habits and other desirable forms of health behaviour. Moreover, it is arguable that other forms of health intervention such as smoking withdrawal or dieting might be equally effective as a primary change agent, and much of the observed association between exercise and other health habits could be attributable to a common dependence on demographic and socio-economic factors. On the other hand, the apparent weakness of associations may arise in part from difficulties in measuring both habitual physical activity and other forms of health behaviour, with a resultant attenuation of correlations. Possibly, a stronger association between exercise participation and other favourable health

  3. tACS Phase Locking of Frontal Midline Theta Oscillations Disrupts Working Memory Performance

    PubMed Central

    Chander, Bankim S.; Witkowski, Matthias; Braun, Christoph; Robinson, Stephen E.; Born, Jan; Cohen, Leonardo G.; Birbaumer, Niels; Soekadar, Surjo R.

    2016-01-01

    Background: Frontal midline theta (FMT) oscillations (4–8 Hz) are strongly related to cognitive and executive control during mental tasks such as memory processing, arithmetic problem solving or sustained attention. While maintenance of temporal order information during a working memory (WM) task was recently linked to FMT phase, a positive correlation between FMT power, WM demand and WM performance was shown. However, the relationship between these measures is not well understood, and it is unknown whether purposeful FMT phase manipulation during a WM task impacts FMT power and WM performance. Here we present evidence that FMT phase manipulation mediated by transcranial alternating current stimulation (tACS) can block WM demand-related FMT power increase (FMTΔpower) and disrupt normal WM performance. Methods: Twenty healthy volunteers were assigned to one of two groups (group A, group B) and performed a 2-back task across a baseline block (block 1) and an intervention block (block 2) while 275-sensor magnetoencephalography (MEG) was recorded. After no stimulation was applied during block 1, participants in group A received tACS oscillating at their individual FMT frequency over the prefrontal cortex (PFC) while group B received sham stimulation during block 2. After assessing and mapping phase locking values (PLV) between the tACS signal and brain oscillatory activity across the whole brain, FMT power and WM performance were assessed and compared between blocks and groups. Results: During block 2 of group A but not B, FMT oscillations showed increased PLV across task-related cortical areas underneath the frontal tACS electrode. While WM task-related FMTΔpower and WM performance were comparable across groups in block 1, tACS resulted in lower FMTΔpower and WM performance compared to sham stimulation in block 2. Conclusion: tACS-related manipulation of FMT phase can disrupt WM performance and influence WM task-related FMTΔpower. This finding may have important

  4. 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. PMID:25008527

  5. 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.

  6. The scene and the unseen: manipulating photographs for experiments on change blindness and scene memory: image manipulation for change blindness.

    PubMed

    Ball, Felix; Elzemann, Anne; Busch, Niko A

    2014-09-01

    The change blindness paradigm, in which participants often fail to notice substantial changes in a scene, is a popular tool for studying scene perception, visual memory, and the link between awareness and attention. Some of the most striking and popular examples of change blindness have been demonstrated with digital photographs of natural scenes; in most studies, however, much simpler displays, such as abstract stimuli or "free-floating" objects, are typically used. Although simple displays have undeniable advantages, natural scenes remain a very useful and attractive stimulus for change blindness research. To assist researchers interested in using natural-scene stimuli in change blindness experiments, we provide here a step-by-step tutorial on how to produce changes in natural-scene images with a freely available image-processing tool (GIMP). We explain how changes in a scene can be made by deleting objects or relocating them within the scene or by changing the color of an object, in just a few simple steps. We also explain how the physical properties of such changes can be analyzed using GIMP and MATLAB (a high-level scientific programming tool). Finally, we present an experiment confirming that scenes manipulated according to our guidelines are effective in inducing change blindness and demonstrating the relationship between change blindness and the physical properties of the change and inter-individual differences in performance measures. We expect that this tutorial will be useful for researchers interested in studying the mechanisms of change blindness, attention, or visual memory using natural scenes. PMID:24311058

  7. Genetic analysis of phase change in Bordetella pertussis.

    PubMed Central

    Weiss, A A; Falkow, S

    1984-01-01

    Avirulent-phase derivatives of Bordetella pertussis (those which have simultaneously lost the ability to synthesize several virulence-associated factors) and the genetic mechanism of the phase change were studied. Increased tolerance to erythromycin was shown to be an avirulent-phase marker. By the use of efficiency of plating on erythromycin, the proportion of avirulent-phase (Vir) variants in a virulent-phase (Vir+) population was determined to be between 10(-3) and 10(-6), depending on the strain. We showed that the phase shift is reversible and detected a complete Vir- to Vir+ to Vir- to cycle. In other experiments, hybridization studies with avirulent-phase mutants obtained by Tn5 mutagenesis suggested that a single region located at a unique site in the B. pertussis chromosome controls the phase change. One of the avirulent Tn5 mutants was used as a recipient in a conjugative cross with a virulent-phase donor. All recombinants which had reacquired the virulence-associated factors also lost Tn5, indicating the loss of Tn5 was required to restore the Vir+ phenotype. The Tn5 avirulent-phase mutants behave as if the insertion interrupted the function of a transacting gene product which is required for the expression of the other virulent-phase genes. A model of the molecular basis of the phase regulation is presented. Images PMID:6317569

  8. Divided attention can enhance early-phase memory encoding: the attentional boost effect and study trial duration.

    PubMed

    Mulligan, Neil W; Spataro, Pietro

    2015-07-01

    Divided attention during encoding typically produces marked reductions in later memory. The attentional boost effect (ABE) is a surprising variation on this phenomenon. In this paradigm, each study stimulus (e.g., a word) is presented along with a target or a distractor (e.g., different colored circles) in a detection task. Later memory is better for stimuli co-occurring with targets. The present experiments indicate that the ABE arises during an early phase of memory encoding that involves initial stimulus perception and comprehension rather than at a later phase entailing controlled, elaborative rehearsal. Experiment 1 demonstrated that the ABE was robust at a short study duration (700 ms) and did not increase with increasing study trial durations (1,500 ms and 4,000 ms). Furthermore, the target condition is boosted to the level of memory performance in a full-attention condition for the short duration but not the long duration. Both results followed from the early-phase account. This account also predicts that for very short study times (limiting the influence of late-phase controlled encoding and thus minimizing the usual negative effect of divided attention), the target condition will produce better memory than will the full-attention condition. Experiment 2 used a study time of 400 ms and found that words presented with targets lead to greater recognition accuracy than do either words presented with distractors or words in the full-attention condition. Consistent with the early-phase account, a divided attention condition actually produced superior memory than did the full-attention condition, a very unusual but theoretically predicted result. PMID:25181494

  9. 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

  10. 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

  11. Polarization selective phase-change nanomodulator

    DOE PAGESBeta

    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

  12. 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.

  13. Three-dimensional optical memory using photoluminescence change in Sm-doped sodium borate glass

    SciTech Connect

    Lim, Jinhyong; Lee, Myeongkyu; Kim, Eunkyoung

    2005-05-09

    The feasibility of three-dimensional (3D) optical memory has been demonstrated by utilizing the photoluminescence (PL) spectrum change in a Sm-doped fluoride glass [K. Miura, J. Qiu, S. Fujiwara, S. Sakasuchi, and K. Hirao, Appl. Phys. Lett. 80 2263 (2002)]. We here report on a femtosecond laser-induced PL change in a Sm-doped sodium borate glass that is easier to synthesize and its potential application to 3D memory. Irradiation with a femtosecond pulsed laser (800 nm, 1 kHz, 100 fs) induced a PL peak near 682 nm, resulting from the photoreduction of the Sm ions. A multilayer pattern (bit size=1 {mu}m,layer separation=8 {mu}m) formed by femtosecond laser irradiation was read out by a reflection-type fluorescent confocal microscope, which detected the emission at 682 nm as a signal. High-contrast pattern images were obtained without crosstalk.

  14. 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.

  15. 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.

  16. 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.

  17. Working memory gating mechanisms explain developmental change in rule-guided behavior.

    PubMed

    Unger, Kerstin; Ackerman, Laura; Chatham, Christopher H; Amso, Dima; Badre, David

    2016-10-01

    Cognitive control requires choosing contextual information to update into working memory (input gating), maintaining it there (maintenance) stable against distraction, and then choosing which subset of maintained information to use in guiding action (output gating). Recent work has raised the possibility that the development of rule-guided behavior, in the transition from childhood to adolescence, is linked specifically to changes in the gating components of working memory (Amso, Haas, McShane, & Badre, 2014). Given the importance of effective rule-guided behavior for decision making in this developmental transition, we used hierarchical rule tasks to probe the precise developmental dynamics of working memory gating. This mechanistic precision informs ongoing efforts to train cognitive control and working memory operations across typical and atypical development. The results of Experiment 1 verified that the development of rule-guided behavior is uniquely linked to increasing hierarchical complexity but not to increasing maintenance demands across 1st, 2nd, and 3rd order rule tasks. Experiment 2 then investigated whether this developmental trajectory in rule-guided behavior is best explained by change in input gating or output gating. Further, as input versus output gating also tend to correlate with a more proactive versus reactive control strategy in these tasks, we assessed developmental change in the degree to which these two processes were deployed efficiently given the task. Experiment 2 shows that the developmental change observed in Experiment 1 and in Amso et al. (2014) is likely a result of increased efficacy of output gating processes, as well as greater strategic efficiency in that adolescents opt for this costly process less often than children. PMID:27336178

  18. Working memory in ALS patients: preserved performance but marked changes in underlying neuronal networks.

    PubMed

    Zaehle, Tino; Becke, Andreas; Naue, Nicole; Machts, Judith; Abdulla, Susanne; Petri, Susanne; Kollewe, Katja; Dengler, Reinhard; Heinze, Hans-Jochen; Vielhaber, Stefan; Müller, Notger G

    2013-01-01

    Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease which affects the motor system but also other frontal brain regions. In this study we investigated changes in functional neuronal networks including posterior brain regions that are not directly affected by the neurodegenerative process. To this end, we analyzed the contralateral delay activity (CDA), an ERP component considered an online marker of memory storage in posterior cortex, while 23 ALS patients and their controls performed a delayed-matching-to-sample working memory (WM) task. The task required encoding of stimuli in the cued hemifield whilst ignoring stimuli in the other hemifield. Despite their unimpaired behavioral performance patients displayed several changes in the neuronal markers of the memory processes. Their CDA amplitude was smaller; it showed less load-dependent modulation and lacked the reduction observed when controls performed the same task three months later. The smaller CDA in the patients could be attributed to more ipsilateral cortical activity which may indicate that ALS patients unnecessarily processed the irrelevant stimuli as well. The latter is presumably related to deterioration of the frontal cortex in the patient group which was indicated by slight deficits in tests of their executive functions that increased over time. The frontal pathology presumably affected their top-down control of memory storage in remote regions in the posterior brain. In sum, the present results demonstrate functional changes in neuronal networks, i.e. neuroplasticity, in ALS that go well beyond the known structural changes. They also show that at least in WM tasks, in which strategic top-down control demands are relatively low, the frontal deficit can be compensated for by intact low level processes in posterior brain regions. PMID:23951274

  19. Working Memory in ALS Patients: Preserved Performance but Marked Changes in Underlying Neuronal Networks

    PubMed Central

    Zaehle, Tino; Becke, Andreas; Naue, Nicole; Machts, Judith; Abdulla, Susanne; Petri, Susanne; Kollewe, Katja; Dengler, Reinhard; Heinze, Hans-Jochen; Vielhaber, Stefan; Müller, Notger G.

    2013-01-01

    Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease which affects the motor system but also other frontal brain regions. In this study we investigated changes in functional neuronal networks including posterior brain regions that are not directly affected by the neurodegenerative process. To this end, we analyzed the contralateral delay activity (CDA), an ERP component considered an online marker of memory storage in posterior cortex, while 23 ALS patients and their controls performed a delayed-matching-to-sample working memory (WM) task. The task required encoding of stimuli in the cued hemifield whilst ignoring stimuli in the other hemifield. Despite their unimpaired behavioral performance patients displayed several changes in the neuronal markers of the memory processes. Their CDA amplitude was smaller; it showed less load-dependent modulation and lacked the reduction observed when controls performed the same task three months later. The smaller CDA in the patients could be attributed to more ipsilateral cortical activity which may indicate that ALS patients unnecessarily processed the irrelevant stimuli as well. The latter is presumably related to deterioration of the frontal cortex in the patient group which was indicated by slight deficits in tests of their executive functions that increased over time. The frontal pathology presumably affected their top-down control of memory storage in remote regions in the posterior brain. In sum, the present results demonstrate functional changes in neuronal networks, i.e. neuroplasticity, in ALS that go well beyond the known structural changes. They also show that at least in WM tasks, in which strategic top-down control demands are relatively low, the frontal deficit can be compensated for by intact low level processes in posterior brain regions. PMID:23951274

  20. The microsurgery fellowship at chang gung memorial hospital: blossom of caterpillars.

    PubMed

    Abdelrahman, Mohamed

    2015-04-01

    Against a background of globalization and medical migration, issues have been raised regarding training outside the clinician's own context. Fellowship was not commonly used as a career step, or a means of migration, but as a process of professional and personal development. Taking Chang Gung Memorial Hospital Microsurgery Fellowship as the case study, I would like to highlight an example of a long-running successful training program in a special field such as plastic surgery. PMID:25973354

  1. BEHAVIORAL AND MEMORY CHANGES IN Mus musculus COINFECTED BY Toxocara canis AND Toxoplasma gondii

    PubMed Central

    Corrêa, Flávia Motta; Chieffi, Pedro Paulo; Lescano, Susana A. Zevallos; dos Santos, Sergio Vieira

    2014-01-01

    Several researchers have stated that parasites can alter the behavior of their hosts, in order to increase the transmission rate, principally when prey-predator relationships are a reliable way of infection transmission. The aim of this study was to verify the occurrence of changes in anxiety and short-term memory patterns in experimentally infected Mus musculus by Toxocara canis and/or Toxoplasma gondii. Forty male Mus musculus (Balb/c) eight-week-old were divided into four groups of 10 mice each. One group was infected with 300 eggs of Toxocara canis; a second group was submitted to infection with 10 cysts of Toxoplasma gondii; a third group was concomitantly infected with both parasites with the same inoculums and the last group was maintained without infection. The anxiety levels were evaluated using an elevated plus maze and an actometer; the short-term memory was determined by a two-way active avoidance equipment. The determination of anxiety levels were conducted 40 and 70 days after infection and the short-term memory was evaluated 140 days after infection. Mice chronically infected by Toxoplasma gondii showed impaired learning and short-term memory, but no significant differences were found in mice infected by Toxocara canis or concomitantly infected by Toxocara canis and Toxoplasma gondii when compared to non infected mice. PMID:25076438

  2. Aging mechanisms in amorphous phase-change materials

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

  3. 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.

  4. 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).

  5. Solid–Liquid Phase Change Driven by Internal Heat Generation

    SciTech Connect

    John Crepeau; Ali s. Siahpush

    2012-07-01

    This article presents results of solid-liquid phase change, the Stefan Problem, where melting is driven internal heat generation, in a cylindrical geometry. The comparison between a quasi-static analytical solution for Stefan numbers less than one and numerical solutions shows good agreement. The computational results of phase change with internal heat generation show how convection cells form in the liquid region. A scale analysis of the same problem shows four distinct regions of the melting process.

  6. Learning about frequency on the fly: Recent experience changes strategies regarding linguistic frequency in recognition memory.

    PubMed

    Miller, Jeremy K

    2010-01-01

    In the present study, the author examines whether participants can adjust recognition response strategies to account for the effects of linguistic frequency. Experiment 1 used a counterfeit-list technique to replicate findings that indicate that participants exhibit a bias toward choosing high-frequency lures. Experiment 2 demonstrates that when participants are exposed to a training phase that includes an opportunity to recognize high- and low-frequency words, participants no longer demonstrate a significant bias toward choosing high-frequency items on the counterfeit list task. Experiments 3 and 4 examine how participants learn to adjust for linguistic frequency by manipulating the information available during training. The results demonstrate that participants use information from the training phase indicating that high word frequency is a good cue to oldness to guide their memory decisions during the counterfeit list task, but do not use training phase information indicating that low frequency is the best cue to oldness in a similar fashion. PMID:20441131

  7. 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.

  8. 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. PMID:26842330

  9. 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.

  10. Development and implementation of configurational forces based constitutive phase field models for shape memory alloys

    NASA Astrophysics Data System (ADS)

    Agboola, Babatunde Omogbolahan

    Continuum thermodynamic constitutive phase field models are developed to simulate the rate dependent, thermomechanical response and precipitate formation in shape memory alloys (SMAs). The two models are based on the application of the balance of configurational forces, a scalar order parameter (a phase field) and atomic concentration to extend standard continuum thermodynamics approach. Constitutive field equations that capture the kinetics of solid-solid martensitic phase transition in SMA and the diffusion mediated precipitate formation in an elastic solid are developed. The coupled set of thermodynamically consistent field equations results from balance of configuration forces, balance of linear momentum, balance of energy and balance of atomic species mass. The field equations capture the kinetics of phase transition, deformation and elastic wave, heat transfer and atomic diffusion respectively. The first model is thermomechanical and is used to simulate the macroscopic response of SMA such as pseudoelasticity; transformation induced pseudo-creep, stress relaxation as well as the effect of cooling rate on mechanical and thermally induced phase transformation of SMA. The second model couples diffusion with elasticity to simulate growth and coarsening of precipitate and experimentally observed concentration depletion near the precipitates Results of the simulations of the macroscopic SMA response are in very good agreement with experimental observation. Simulations suggest that rate dependent and complex thermomechanical response of SMA are due to the interaction of an inherent time scale ( as well as length scale) of phase transformation, introduced through the balance of configurational forces, with other time scales. This work contributes to improved SMA modeling, scientific understanding and design. In particular, for aerospace application under stringent requirement and severe environmental conditions. Contribution of fundamental use of balance of

  11. Thermal analysis of metal foam matrix composite phase change material

    NASA Astrophysics Data System (ADS)

    Song, Xiange

    2015-06-01

    In this paper, CPCM (Composite Phase Change Material) was manufactured with metal foam matrix used as filling material. The temperature curves were obtained by experiment. The performance of heat transfer was analyzed. The experimental results show that metal foam matrix can improve temperature uniformity in phase change thermal storage material and enhance heat conduction ability. The thermal performance of CPCM is significantly improved. The efficiency of temperature control can be obviously improved by adding metal foam in phase change material. CPCM is in solid-liquid two-phase region when temperature is close to phase change point of paraffin. An approximate plateau appears. The plateau can be considered as the temperature control zone of CPCM. Heat can be transferred from hot source and be uniformly spread in thermal storage material by using metal foam matrix since thermal storage material has the advantage of strong heat storage capacity and disadvantage of poor heat conduction ability. Natural convection promotes the melting of solid-liquid phase change material. Good thermal conductivity of foam metal accelerates heat conduction of solid-liquid phase change material. The interior temperature difference decreases and the whole temperature becomes more uniform. For the same porosity with a metal foam, melting time of solid-liquid phase change material decreases. Heat conduction is enhanced and natural convection is suppressed when pore size of metal foam is smaller. The thermal storage time decreases and heat absorption rate increases when the pore size of metal foam reduces. The research results can be used to guide fabricating the CPCM.

  12. A four-component model of age-related memory change.

    PubMed

    Healey, M Karl; Kahana, Michael J

    2016-01-01

    We develop a novel, computationally explicit, theory of age-related memory change within the framework of the context maintenance and retrieval (CMR2) model of memory search. We introduce a set of benchmark findings from the free recall and recognition tasks that include aspects of memory performance that show both age-related stability and decline. We test aging theories by lesioning the corresponding mechanisms in a model fit to younger adult free recall data. When effects are considered in isolation, many theories provide an adequate account, but when all effects are considered simultaneously, the existing theories fail. We develop a novel theory by fitting the full model (i.e., allowing all parameters to vary) to individual participants and comparing the distributions of parameter values for older and younger adults. This theory implicates 4 components: (a) the ability to sustain attention across an encoding episode, (b) the ability to retrieve contextual representations for use as retrieval cues, (c) the ability to monitor retrievals and reject intrusions, and (d) the level of noise in retrieval competitions. We extend CMR2 to simulate a recognition memory task using the same mechanisms the free recall model uses to reject intrusions. Without fitting any additional parameters, the 4-component theory that accounts for age differences in free recall predicts the magnitude of age differences in recognition memory accuracy. Confirming a prediction of the model, free recall intrusion rates correlate positively with recognition false alarm rates. Thus, we provide a 4-component theory of a complex pattern of age differences across 2 key laboratory tasks. PMID:26501233

  13. Social, demographic, and environmental influences on perceptions and memories of weather, climate, and climate change

    NASA Astrophysics Data System (ADS)

    Malmberg, Julie Suzanne

    This research seeks to understand how people in the Denver metropolitan area perceive and remember weather, climate, and climate change and how social, demographic, and environmental factors might influence these perceptions and memories. To do this, an online survey was completed in 2006 and in-person interviews were conducted in 2010 and 2011. The online survey and the in-person interviews both asked questions about recent weather, seasonal climate for specific years, beliefs about climate change and human impact on climate change, and social and demographic information. During the 2010--2011 in-person interviews, ambient meteorological conditions were recorded. For climate recollections, overall accuracy was about 20%. In general, women who were politically liberal, majored in a science field, believed in climate change, and were in a good mood were the most accurate for past climates. However, this accuracy was still only about 30%. For recent weather memories, the accuracy was about 50%. Time was the biggest indicator of accuracy, with the most recent weather being remembered the most accurately. When asked to rate the weather from positive to negative for specific events, respondents reported the weather with a negative bias for extremely negative flashbulb memory events. For perceptions about climate change, over 80% of the respondents in the Denver metropolitan area believed global warming was occurring and that humans had an impact on global warming. Over 80% of respondents believed that global warming will impact the Denver metropolitan area, however not all of these people knew how climate change would impact them personally.

  14. Brain-like associative learning using a nanoscale non-volatile phase change synaptic device array

    PubMed Central

    Eryilmaz, Sukru B.; Kuzum, Duygu; Jeyasingh, Rakesh; Kim, SangBum; BrightSky, Matthew; Lam, Chung; Wong, H.-S. Philip

    2014-01-01

    Recent advances in neuroscience together with nanoscale electronic device technology have resulted in huge interests in realizing brain-like computing hardwares using emerging nanoscale memory devices as synaptic elements. Although there has been experimental work that demonstrated the operation of nanoscale synaptic element at the single device level, network level studies have been limited to simulations. In this work, we demonstrate, using experiments, array level associative learning using phase change synaptic devices connected in a grid like configuration similar to the organization of the biological brain. Implementing Hebbian learning with phase change memory cells, the synaptic grid was able to store presented patterns and recall missing patterns in an associative brain-like fashion. We found that the system is robust to device variations, and large variations in cell resistance states can be accommodated by increasing the number of training epochs. We illustrated the tradeoff between variation tolerance of the network and the overall energy consumption, and found that energy consumption is decreased significantly for lower variation tolerance. PMID:25100936

  15. 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

  16. Predictors of longitudinal changes in memory, visuospatial, and verbal functioning in very old demented adults.

    PubMed

    Small, B J; Bäckman, L

    1998-01-01

    Longitudinal changes in memory, visuospatial and verbal functioning in a sample of demented persons were examined. The role of several demographic, psychometric, and biological indices in predicting the rate of cognitive deterioration was also investigated. The sample consisted of 31 very old (mean age at entry = 83.5 years, range = 75-95) persons with Alzheimer's disease (n = 22) and vascular dementia (n = 9) from a community-based study. Subjects were tested on two occasions separated by approximately 2.5 years. Results indicated significant longitudinal decline in verbal fluency and visuospatial ability, but only on 1 of 3 measures of episodic memory. Results from regression analyses indicated that a variety of putatively important variables, including age, gender, education, digit span, as well as a number of biological (vitamin B12, TSH), dementia etiology, and psychometric (digit span) indicators, exhibited no relationship to rate of memory, visuospatial, or verbal decline. The results suggest that the rate of cognitive deterioration in dementia is highly variable, and this variability in change appears to include a variety of characteristics. A possible reason thereof may be that the role of individual-difference variables for cognitive functioning in dementia is overshadowed by the pathogenetic process itself. PMID:9701677

  17. The future of memory

    NASA Astrophysics Data System (ADS)

    Marinella, M.

    In the not too distant future, the traditional memory and storage hierarchy of may be replaced by a single Storage Class Memory (SCM) device integrated on or near the logic processor. Traditional magnetic hard drives, NAND flash, DRAM, and higher level caches (L2 and up) will be replaced with a single high performance memory device. The Storage Class Memory paradigm will require high speed (< 100 ns read/write), excellent endurance (> 1012), nonvolatility (retention > 10 years), and low switching energies (< 10 pJ per switch). The International Technology Roadmap for Semiconductors (ITRS) has recently evaluated several potential candidates SCM technologies, including Resistive (or Redox) RAM, Spin Torque Transfer RAM (STT-MRAM), and phase change memory (PCM). All of these devices show potential well beyond that of current flash technologies and research efforts are underway to improve the endurance, write speeds, and scalabilities to be on-par with DRAM. This progress has interesting implications for space electronics: each of these emerging device technologies show excellent resistance to the types of radiation typically found in space applications. Commercially developed, high density storage class memory-based systems may include a memory that is physically radiation hard, and suitable for space applications without major shielding efforts. This paper reviews the Storage Class Memory concept, emerging memory devices, and possible applicability to radiation hardened electronics for space.

  18. Overgeneral autobiographical memory predicts changes in depression in a community sample.

    PubMed

    Van Daele, Tom; Griffith, James W; Van den Bergh, Omer; Hermans, Dirk

    2014-01-01

    This study investigated whether overgeneral autobiographical memory (OGM) predicts the course of symptoms of depression and anxiety in a community sample, after 5, 6, 12 and 18 months. Participants (N=156) completed the Autobiographical Memory Test and the Depression Anxiety Stress Scales-21 (DASS-21) at baseline and were subsequently reassessed using the DASS-21 at four time points over a period of 18 months. Using latent growth curve modelling, we found that OGM was associated with a linear increase in depression. We were unable to detect changes over time in anxiety. OGM may be an important marker to identify people at risk for depression in the future, but more research is needed with anxiety. PMID:24467645

  19. Imagery Rescripting: The Impact of Conceptual and Perceptual Changes on Aversive Autobiographical Memories

    PubMed Central

    Slofstra, Christien; Nauta, Maaike H.; Holmes, Emily A.; Bockting, Claudi L. H.

    2016-01-01

    Background Imagery rescripting (ImRs) is a process by which aversive autobiographical memories are rendered less unpleasant or emotional. ImRs is thought only to be effective if a change in the meaning-relevant (semantic) content of the mental image is produced, according to a cognitive hypothesis of ImRs. We propose an additional hypothesis: that ImRs can also be effective by the manipulation of perceptual features of the memory, without explicitly targeting meaning-relevant content. Methods In two experiments using a within-subjects design (both N = 48, community samples), both Conceptual-ImRs—focusing on changing meaning-relevant content—and Perceptual-ImRs—focusing on changing perceptual features—were compared to Recall-only of aversive autobiographical image-based memories. An active control condition, Recall + Attentional Breathing (Recall+AB) was added in the first experiment. In the second experiment, a Positive-ImRs condition was added—changing the aversive image into a positive image that was unrelated to the aversive autobiographical memory. Effects on the aversive memory’s unpleasantness, vividness and emotionality were investigated. Results In Experiment 1, compared to Recall-only, both Conceptual-ImRs and Perceptual-ImRs led to greater decreases in unpleasantness, and Perceptual-ImRs led to greater decreases in emotionality of memories. In Experiment 2, the effects on unpleasantness were not replicated, and both Conceptual-ImRs and Perceptual-ImRs led to greater decreases in emotionality, compared to Recall-only, as did Positive-ImRs. There were no effects on vividness, and the ImRs conditions did not differ significantly from Recall+AB. Conclusions Results suggest that, in addition to traditional forms of ImRs, targeting the meaning-relevant content of an image during ImRs, relatively simple techniques focusing on perceptual aspects or positive imagery might also yield benefits. Findings require replication and extension to clinical

  20. Shock-Induced Magnetic and Structural Changes in Magnetite: New Insights Towards Strain Memory Mechanisms

    NASA Astrophysics Data System (ADS)

    Kontny, A. M.; Reznik, B.; Lied, P.; Holzwarth, A.; Göttlicher, J.; Boubnov, A.

    2014-12-01

    Shock recovery experiments using an air gun (5 GPa) and high-explosive set-up (10, 20, 30 GPa) were done from natural stoichiometric magnetite ore samples consisting mainly of multidomain magnetite and quartz. The aim of this study is to investigate the potential of changes in magnetic transition temperatures in magnetite as a geobarometer for extreme conditions like those observed in a meteorite impact on Earth material or in meteorites. We used the temperature dependence of magnetic susceptibility along with XANES and X-ray diffraction for monitoring magnetic and structural changes. We will demonstrate that the shocked samples show a shift in the Verwey transition temperature (Fig. 1a and b) compared to the unshocked magnetite. Although the Curie temperature itself is very similar for all investigated samples, the shape as well as the amplitude of the heating and cooling curves are nearly reversible for the unshocked "0 GPa" sample but irreversible for the shocked samples. While the amplitude changes before the Curie temperature and above the Verwey transition temperature (Fig. 1a and c) are related to reduction in magnetic domain sizes due to fragmentation, the shift in the Verwey transition temperature and the irreversibility of Curie temperature cannot be explained by this mechanism and we suspect that chemical (Fe2+/Fe3+ ratio in Fe3O4) or structural (lattice distortion) changes occur. These findings help to constrain data for a possible strain memory of magnetic transition temperatures in magnetite and help to explore the potential use of changes in magnetic transition temperatures as a strain memory as earlier suggested by Carporzen and Gilder (2010). Carporzen, L., Gilder, S.A., 2010: Strain memory of the Verwey transition, J. Geophys. Res., 115, B05103, doi: 10.1029/2009JB006813.

  1. Hemodynamic changes in the prefrontal cortex during working memory in essential hypertension.

    PubMed

    Grant, Hercules; Bhambhani, Yagesh; Singhal, Anthony

    2015-08-01

    Behavioral performance and hemodynamic changes in the prefrontal cortex (PFC) represent cerebrovascular reserve and may indicate functional deficits related to essential hypertension. Fifteen stage 1 hypertensive and normotensive males (19-55 years) were compared on four tests of working memory (digit span and auditory consonant trigrams), and accompanying hemodynamic changes measured by functional near infrared spectroscopy (fNIRS). With participants blindfolded, the four tests were randomized while fNIRS was used to monitor bilateral PFC changes in oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb), total hemoglobin (tHb), and hemoglobin difference. The hypertensive group demonstrated significant impairment in performance on the working memory tests with a trend of decreased efficiency performance scores (tests score/O2Hb and tHb changes). Significant correlations were noted in the hypertensive group between test performance and changes in O2Hb and tHb in both the left and right PFC. These findings suggest that fNIRS combined with cognitive testing may provide important measures of cerebrovascular reserve in essential hypertension. PMID:26206381

  2. 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.

  3. Metal - Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials.

    PubMed

    Bragaglia, Valeria; Arciprete, Fabrizio; Zhang, Wei; Mio, Antonio Massimiliano; Zallo, Eugenio; Perumal, Karthick; Giussani, Alessandro; Cecchi, Stefano; Boschker, Jos Emiel; Riechert, Henning; Privitera, Stefania; Rimini, Emanuele; Mazzarello, Riccardo; Calarco, Raffaella

    2016-01-01

    Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows. PMID:27033314

  4. Metal - Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials

    PubMed Central

    Bragaglia, Valeria; Arciprete, Fabrizio; Zhang, Wei; Mio, Antonio Massimiliano; Zallo, Eugenio; Perumal, Karthick; Giussani, Alessandro; Cecchi, Stefano; Boschker, Jos Emiel; Riechert, Henning; Privitera, Stefania; Rimini, Emanuele; Mazzarello, Riccardo; Calarco, Raffaella

    2016-01-01

    Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows. PMID:27033314

  5. Phase Change Nanodot Arrays Fabricated Using a Self-Assembly Diblock Copolymer Approach

    SciTech Connect

    Zhang,Y.; Wong, H.; Raoux, S.; Cha, J.; Rettner, C.; Krupp, L.; Topuria, T.; Milliron, D.; Rice, P.; Jordan-Sweet, J.

    2007-01-01

    Self-assembling diblock copolymer, polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP), was used as the template for fabricating phase change nanostructures. The high density GeSb nanodots were formed by etching into an amorphous GeSb thin film using silica hard mask which was patterned on top of polymer. The nanodot arrays are 15 nm in diameter with 30 nm spacing. This is smaller than most structures obtained by e-beam lithography. Time-resolved x-ray diffraction studies showed that the phase transition occurred at 235 {sup o}C, which is 5 {sup o}C lower than blanket GeSb film but higher than that of Ge{sub 2}Sb{sub 2}Te{sub 5} (150 {sup o}C). GeSb showed good temperature stability for fabrication of small memory devices.

  6. Metal - Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials

    NASA Astrophysics Data System (ADS)

    Bragaglia, Valeria; Arciprete, Fabrizio; Zhang, Wei; Mio, Antonio Massimiliano; Zallo, Eugenio; Perumal, Karthick; Giussani, Alessandro; Cecchi, Stefano; Boschker, Jos Emiel; Riechert, Henning; Privitera, Stefania; Rimini, Emanuele; Mazzarello, Riccardo; Calarco, Raffaella

    2016-04-01

    Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows.

  7. Cortical phase changes measured using 7-T MRI in subjects with subjective cognitive impairment, and their association with cognitive function.

    PubMed

    van Rooden, Sanneke; Buijs, Mathijs; van Vliet, Marjolein E; Versluis, Maarten J; Webb, Andrew G; Oleksik, Ania M; van de Wiel, Lotte; Middelkoop, Huub A M; Blauw, Gerard Jan; Weverling-Rynsburger, Annelies W E; Goos, Jeroen D C; van der Flier, Wiesje M; Koene, Ted; Scheltens, Philip; Barkhof, Frederik; van de Rest, Ondine; Slagboom, P Eline; van Buchem, Mark A; van der Grond, Jeroen

    2016-09-01

    Studies have suggested that, in subjects with subjective cognitive impairment (SCI), Alzheimer's disease (AD)-like changes may occur in the brain. Recently, an in vivo study has indicated the potential of ultra-high-field MRI to visualize amyloid-beta (Aβ)-associated changes in the cortex in patients with AD, manifested by a phase shift on T2 *-weighted MRI scans. The main aim of this study was to investigate whether cortical phase shifts on T2 *-weighted images at 7 T in subjects with SCI can be detected, possibly implicating the deposition of Aβ plaques and associated iron. Cognitive tests and T2 *-weighted scans using a 7-T MRI system were performed in 28 patients with AD, 18 subjects with SCI and 27 healthy controls (HCs). Cortical phase shifts were measured. Univariate general linear modeling and linear regression analysis were used to assess the association between diagnosis and cortical phase shift, and between cortical phase shift and the different neuropsychological tests, adjusted for age and gender. The phase shift (mean, 1.19; range, 1.00-1.35) of the entire cortex in AD was higher than in both SCI (mean, 0.85; range, 0.73-0.99; p < 0.001) and HC (mean, 0.94; range, 0.79-1.10; p < 0.001). No AD-like changes, e.g. increased cortical phase shifts, were found in subjects with SCI compared with HCs. In SCI, a significant association was found between memory function (Wechsler Memory Scale, WMS) and cortical phase shift (β = -0.544, p = 0.007). The major finding of this study is that, in subjects with SCI, an increased cortical phase shift measured at high field is associated with a poorer memory performance, although, as a group, subjects with SCI do not show an increased phase shift compared with HCs. This increased cortical phase shift related to memory performance may contribute to the understanding of SCI as it is still unclear whether SCI is a sign of pre-clinical AD. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25522735

  8. Neonatal anoxia in rats: hippocampal cellular and subcellular changes related to cell death and spatial memory.

    PubMed

    Takada, S H; dos Santos Haemmerle, C A; Motta-Teixeira, L C; Machado-Nils, A V; Lee, V Y; Takase, L F; Cruz-Rizzolo, R J; Kihara, A H; Xavier, G F; Watanabe, I-S; Nogueira, M I

    2015-01-22

    Neonatal anoxia in rodents has been used to understand brain changes and cognitive dysfunction following asphyxia. This study investigated the time-course of cellular and subcellular changes and hippocampal cell death in a non-invasive model of anoxia in neonatal rats, using Terminal deoxynucleotidyl transferase-mediated dUTP Nick End Labeling (TUNEL) to reveal DNA fragmentation, Fluoro-Jade® B (FJB) to show degenerating neurons, cleaved caspase-3 immunohistochemistry (IHC) to detect cells undergoing apoptosis, and transmission electron microscopy (TEM) to reveal fine ultrastructural changes related to cell death. Anoxia was induced by exposing postnatal day 1 (P1) pups to a flow of 100% gaseous nitrogen for 25 min in a chamber maintained at 37 °C. Control rats were similarly exposed to this chamber but with air flow instead of nitrogen. Brain changes following anoxia were evaluated at postnatal days 2, 14, 21 and 60 (P2, P14, P21 and P60). In addition, spatial reference memory following anoxia and control treatments was evaluated in the Morris water maze, starting at P60. Compared to their respective controls, P2 anoxic rats exhibited (1) higher TUNEL labeling in cornus ammonis (CA) 1 and the dentate gyrus (DG), (2) higher FJB-positive cells in the CA2-3, and (3) somato-dendritic swelling, mitochondrial injury and chromatin condensation in irregular bodies, as well as other subcellular features indicating apoptosis, necrosis, autophagy and excitotoxicity in the CA1, CA2-3 and DG, as revealed by TEM. At P14, P21 and P60, both groups showed small numbers of TUNEL-positive and FJB-positive cells. Stereological analysis at P2, P14, P21 and P60 revealed a lack of significant differences in cleaved caspase-3 IHC between anoxic and control subjects. These results suggest that the type of hippocampal cell death following neonatal anoxia is likely independent of caspase-3 activation. Neonatal anoxia induced deficits in acquisition and performance of spatial reference

  9. 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. PMID:27176406

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

    NASA Astrophysics Data System (ADS)

    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.

  11. 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…

  12. Associative memory of phase-coded spatiotemporal patterns in leaky Integrate and Fire networks.

    PubMed

    Scarpetta, Silvia; Giacco, Ferdinando

    2013-04-01

    We study the collective dynamics of a Leaky Integrate and Fire network in which precise relative phase relationship of spikes among neurons are stored, as attractors of the dynamics, and selectively replayed at different time scales. Using an STDP-based learning process, we store in the connectivity several phase-coded spike patterns, and we find that, depending on the excitability of the network, different working regimes are possible, with transient or persistent replay activity induced by a brief signal. We introduce an order parameter to evaluate the similarity between stored and recalled phase-coded pattern, and measure the storage capacity. Modulation of spiking thresholds during replay changes the frequency of the collective oscillation or the number of spikes per cycle, keeping preserved the phases relationship. This allows a coding scheme in which phase, rate and frequency are dissociable. Robustness with respect to noise and heterogeneity of neurons parameters is studied, showing that, since dynamics is a retrieval process, neurons preserve stable precise phase relationship among units, keeping a unique frequency of oscillation, even in noisy conditions and with heterogeneity of internal parameters of the units. PMID:23053861

  13. Early age-related changes in episodic memory retrieval as revealed by event-related potentials.

    PubMed

    Guillaume, Cécile; Clochon, Patrice; Denise, Pierre; Rauchs, Géraldine; Guillery-Girard, Bérengère; Eustache, Francis; Desgranges, Béatrice

    2009-01-28

    Familiarity is better preserved than recollection in ageing. The age at which changes first occur and the slope of the subsequent decline, however, remain unclear. In this study, we investigated changes in episodic memory, by using event-related potentials (ERPs) in young (m=24), middle-aged (m=58) and older (m=70) adults. Although behavioural performance did not change before the age of 65 years, changes in ERP correlates were already present in the middle-aged adults. The ERP correlates of recollection and monitoring processes were the first to be affected by ageing, with a linear decrease as age increased. Conversely, the ERP correlate of familiarity remained unchanged, at least up to the age of 65 years. These results suggest a differential time course for the age effects on episodic retrieval. PMID:19104457

  14. Why Phase-Change Media Are Fast and Stable: A New Approach to an Old Problem

    NASA Astrophysics Data System (ADS)

    Kolobov, Alexander V.; Fons, Paul; Tominaga, Junji; Frenkel, Anatoly I.; Ankudinov, Alexei L.; Yannopoulos, Spyros N.; Andrikopoulos, Konstantinos S.; Uruga, Tomoya

    2005-05-01

    Present-day multimedia strongly relies on re-writable phase-change optical memories. We find that, different from current consensus Ge2Sb2Te5 (GST), the material of choice in digital versatile discs—random access memory (DVD-RAM), possesses a structure similar to ferroelectric GeTe, namely that Ge and Sb atoms are located off-center giving rise to a net dipole moment. Amorphisation of both GeTe and GST results in a significant shortening of covalent bonds and a decrease in the mean-square relative displacement concomitant with a drastic change in the short-range order. We demonstrate that the order-disorder transition in GeTe and GST is primarily due to a flip of Ge atoms from an octahedral position into a tetrahedral position without rupture of strong covalent bonds. It is this nature of the transformation that ensures large changes in reflectivity, fast disk performance and repeatable switching over millions cycles.

  15. A three-dimensional non-isothermal Ginzburg-Landau phase-field model for shape memory alloys

    NASA Astrophysics Data System (ADS)

    Dhote, R.; Fabrizio, M.; Melnik, R.; Zu, J.

    2014-12-01

    In this paper, a macroscopic three-dimensional non-isothermal model is proposed for describing hysteresis phenomena and phase transformations in shape memory alloys (SMAs). The model is of phase-field type and is based on the Ginzburg-Landau theory. The hysteresis and phase transformations are governed by the kinetic phase evolution equation using the scalar order parameter, laws of conservation of the momentum and energy and a nonlinear coupling of the stress, the strain and the order parameter in a differential form. One of the important features of the model is that the phase transformation is governed by the stress tensor, as opposed to the transformation strain tensor typically used in the literature. The model takes into account different properties of austenite and martensite phases based on the compliance tensor as a function of the order parameter and stress. Representative numerical simulations on an SMA specimen reproduce hysteretic behaviors observed experimentally in the literature.

  16. Detection of small orientation changes and the precision of visual working memory.

    PubMed

    Salmela, Viljami R; Saarinen, Jussi

    2013-01-14

    We investigated the precision of orientation representations with two tasks, change detection and recall. Previously change detection has been measured only with relatively large orientation changes compared to psychophysical thresholds. In the first experiment, we measured the observers' ability (d') to detect small changes in orientation (5-30°) with 1-4 Gabor items. With one item even a 10° change was well detected (average d'=2.5). As the amount of change increased to 30°, the d' increased to 5.2. When the number of items was increased, the d's gradually decreased. In the second experiment, we used a recall task and the observers adjusted the orientation of a probe Gabor to match the orientation of a Gabor held in the memory. The standard deviation (s.d.) of errors was calculated from the Gaussian distribution fitted to the data. As the number of items increased from 1 to 6, the s.d. increased from 8.6° to 19.6°. Even with six items, the observers did not make any random adjustments. The results show a square root relation between the d'/s.d. and the number of items. The d' in change detection is directly proportional to the square root of (1/n) and the orientation change. The increase of the s.d. in recall task is inversely proportional to square root of (1/n). The results suggest that limited resources and precision of representations, without additional assumptions, determine the memory performance. PMID:23085239

  17. 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

  18. The objects of visuospatial short-term memory: Perceptual organization and change detection.

    PubMed

    Nikolova, Atanaska; Macken, Bill

    2016-01-01

    We used a colour change-detection paradigm where participants were required to remember colours of six equally spaced circles. Items were superimposed on a background so as to perceptually group them within (a) an intact ring-shaped object, (b) a physically segmented but perceptually completed ring-shaped object, or (c) a corresponding background segmented into three arc-shaped objects. A nonpredictive cue at the location of one of the circles was followed by the memory items, which in turn were followed by a test display containing a probe indicating the circle to be judged same/different. Reaction times for correct responses revealed a same-object advantage; correct responses were faster to probes on the same object as the cue than to equidistant probes on a segmented object. This same-object advantage was identical for physically and perceptually completed objects, but was only evident in reaction times, and not in accuracy measures. Not only, therefore, is it important to consider object-level perceptual organization of stimulus elements when assessing the influence of a range of factors (e.g., number and complexity of elements) in visuospatial short-term memory, but a more detailed picture of the structure of information in memory may be revealed by measuring speed as well as accuracy. PMID:26286369

  19. Changes in pattern completion – a key mechanism to explain age-related recognition memory deficits?

    PubMed Central

    Vieweg, Paula; Stangl, Matthias; Howard, Lorelei R.; Wolbers, Thomas

    2016-01-01

    Accurate memory retrieval from partial or degraded input requires the reactivation of memory traces, a hippocampal mechanism termed pattern completion. Age-related changes in hippocampal integrity have been hypothesized to shift the balance of memory processes in favor of the retrieval of already stored information (pattern completion), to the detriment of encoding new events (pattern separation). Using a novel behavioral paradigm, we investigated the impact of cognitive aging (1) on recognition performance across different levels of stimulus completeness, and (2) on potential response biases. Participants were required to identify previously learned scenes among new ones. Additionally, all stimuli were presented in gradually masked versions to alter stimulus completeness. Both young and older adults performed increasingly poorly as the scenes became less complete, and this decline in performance was more pronounced in elderly participants indicative of a pattern completion deficit. Intriguingly, when novel scenes were shown, only the older adults showed an increased tendency to identify these as familiar scenes. In line with theoretical models, we argue that this reflects an age-related bias towards pattern completion. PMID:25597525

  20. The objects of visuospatial short-term memory: Perceptual organization and change detection

    PubMed Central

    Nikolova, Atanaska; Macken, Bill

    2016-01-01

    We used a colour change-detection paradigm where participants were required to remember colours of six equally spaced circles. Items were superimposed on a background so as to perceptually group them within (a) an intact ring-shaped object, (b) a physically segmented but perceptually completed ring-shaped object, or (c) a corresponding background segmented into three arc-shaped objects. A nonpredictive cue at the location of one of the circles was followed by the memory items, which in turn were followed by a test display containing a probe indicating the circle to be judged same/different. Reaction times for correct responses revealed a same-object advantage; correct responses were faster to probes on the same object as the cue than to equidistant probes on a segmented object. This same-object advantage was identical for physically and perceptually completed objects, but was only evident in reaction times, and not in accuracy measures. Not only, therefore, is it important to consider object-level perceptual organization of stimulus elements when assessing the influence of a range of factors (e.g., number and complexity of elements) in visuospatial short-term memory, but a more detailed picture of the structure of information in memory may be revealed by measuring speed as well as accuracy. PMID:26286369

  1. Working memory-related changes in functional connectivity persist beyond task disengagement

    PubMed Central

    Gordon, Evan M.; Breeden, Andrew L.; Bean, Stephanie E.; Vaidya, Chandan J.

    2013-01-01

    We examined whether altered connectivity in functional networks during working memory performance persists following conclusion of that performance, into a subsequent resting state. We conducted functional magnetic resonance imaging (fMRI) in 50 young adults during an initial resting state, followed by an N-back working memory task and a subsequent resting state, in order to examine changes in functional connectivity within and between the default-mode network (DMN) and the task-positive network (TPN) across the three states. We found that alterations in connectivity observed during the N-back task persisted into the subsequent resting state within the TPN and between the DMN and TPN, but not within the DMN. Further, speed of working memory performance and TPN connectivity strength during the N-back task predicted connectivity strength in the subsequent resting state. Finally, DMN connectivity measured before and during the N-back task predicted individual differences in self-reported inattentiveness, but this association was not found during the post-task resting state. Together, these findings have important implications for models of how the brain recovers following effortful cognition, as well as for experimental designs using resting and task scans. PMID:23281202

  2. Mechanical behavior and phase stability of NiAl-based shape memory alloys

    SciTech Connect

    George, E.P.; Liu, C.T.; Horton, J.A.; Kunsmann, H.; King, T.; Kao, M.

    1993-12-31

    NiAl-based shape memory alloys (SMAs) can be made ductile by alloying with 100--300 wppm B and 14--20 at.% Fe. The addition of Fe has the undesirable effect that it lowers the temperature (A{sub p}) of the martensite {yields} austenite phase transformation. Fortunately, however, A can be raised by lowering the ``equivalent`` amount of Al in the alloy. In this way a high A{sub p} temperature of {approximately}190 C has been obtained without sacrificing ductility. Furthermore, a recoverable strain of 0.7% has been obtained in a Ni-Al-Fe alloy with A{sub p} temperature of {approximately}140 C. Iron additions do not suppress the aging-induced embrittlement that occurs in NiAl alloys at 300--500 C as a result of Ni{sub 5}Al{sub 3} precipitation. Manganese additions (up to 10 at.%) have the effect of lowering A{sub p}, degrading hot workability, and decreasing room-temperature ductility.

  3. Response-time evidence for mixed memory states in a sequential-presentation change-detection task.

    PubMed

    Nosofsky, Robert M; Donkin, Chris

    2016-02-01

    Response-time (RT) and choice-probability data were obtained in a rapid visual sequential-presentation change-detection task in which memory set size, study-test lag, and objective change probabilities were manipulated. False "change" judgments increased dramatically with increasing lag, consistent with the idea that study items with long lags were ejected from a discrete-slots buffer. Error RTs were nearly invariant with set size and lag, consistent with the idea that the errors were produced by a stimulus-independent guessing process. The patterns of error and RT data could not be explained in terms of encoding limitations, but were consistent with the hypothesis that long retention lags produced a zero-stimulus-information state that required guessing. Formal modeling of the change-detection RT and error data pointed toward a hybrid model of visual working memory. The hybrid model assumed mixed states involving a combination of memory and guessing, but with higher memory resolution for items with shorter retention lags. The work raises new questions concerning the nature of the memory representations that are produced across the closely related tasks of change detection and visual memory search. PMID:26706291

  4. Enhanced thermoelectric performance driven by high-temperature phase transition in the phase change material Ge4SbTe5

    DOE PAGESBeta

    Williams, Jared B.; Lara-Curzio, Edgar; Cakmak, Ercan; Watkins, Thomas R.; Morelli, Donald T.

    2015-05-15

    Phase change materials are identified for their ability to rapidly alternate between amorphous and crystalline phases and have large contrast in the optical/electrical properties of the respective phases. The materials are primarily used in memory storage applications, but recently they have also been identified as potential thermoelectric materials. Many of the phase change materials researched today can be found on the pseudo-binary (GeTe)1-x(Sb2Te3)x tie-line. While many compounds on this tie-line have been recognized as thermoelectric materials, here we focus on Ge4SbTe5, a single phase compound just off of the (GeTe)1-x(Sb2Te3)x tie-line, that forms in a stable rocksalt crystal structure atmore » room temperature. We find that stoichiometric and undoped Ge4SbTe5 exhibits a thermal conductivity of ~1.2 W/m-K at high temperature and a large Seebeck coefficient of ~250 μV/K. The resistivity decreases dramatically at 623 K due to a structural phase transition which lends to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. In a more general sense the research presents evidence that phase change materials can potentially provide a new route to highly efficient thermoelectric materials for power generation at high temperature.« less

  5. Characterization of Fe-doped In-Sb-Te (Fe: 10 at.%) material with individual electrical-phase-change and magnetic properties

    NASA Astrophysics Data System (ADS)

    Lee, Young Mi; Dung, Dang Duc; Cho, Sunglae; Jung, Min Sang; Choi, Duck Kyun; Ahn, Docheon; Kim, Min Kyu; Kim, Jae-Young; Jung, Min-Cherl

    2011-06-01

    We propose a new electrical-phase-change magnetic material, namely Fe-doped In-Sb-Te (FIST), for possible non-volatile multi-bit memory applications. FIST was formed by typical co-sputter method with Fe 10 at.% doping in In3Sb1Te2. FIST offers the electrical-phase-change and magnetic properties by way of the change of In 4d chemical bonding density and embedded Fe nanoclusters with the size of 4˜5 nm, respectively. It maintained the amorphous phase on the electrical-phase-change. Chemical state of In was only changed to increase the density of In-In chemical bonding during the electrical-phase-change without Fe nanoclusters contribution. Also, the magnetic property by Fe nanoclusters was not changed by the electrical-phase-change. On this basis, we propose the FIST material with the individual electrical-phase-change and magnetic properties for the multi-bit nonvolatile memory materials.

  6. Picosecond Electric-Field-Induced Threshold Switching in Phase-Change Materials.

    PubMed

    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

    2016-08-01

    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 Ag_{4}In_{3}Sb_{67}Te_{26}. 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. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch. PMID:27541475

  7. Picosecond Electric-Field-Induced Threshold Switching in Phase-Change Materials

    NASA Astrophysics Data System (ADS)

    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.

    2016-08-01

    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. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

  8. Phase change dispersion of plasmonic nano-objects.

    PubMed

    Zeng, Xie; Hu, Haifeng; Gao, Yongkang; Ji, Dengxin; Zhang, Nan; Song, Haomin; Liu, Kai; Jiang, Suhua; Gan, Qiaoqiang

    2015-01-01

    Phase is an inherent and important feature for coherent processes, which, unfortunately, has not been completely understood for surface plasmon polariton (SPP) and matter interactions. Here we propose a practical approach to extract the phase change dispersion during the interaction between free-space light, SPPs and nanogroove/slit based on far-field information only. Numerical simulation and experimental validation were both presented using nanoslit-groove plasmonic interferometers, agreeing well with theoretical near-field analysis. This approach is generally feasible to extract the intrinsic phase dispersion of other plasmonic nanostructures and can reveal more fundamental features of SPP-matter interactions. PMID:26219831

  9. Measurement of crystal growth velocity in a melt-quenched phase-change material

    PubMed Central

    Salinga, Martin; Carria, Egidio; Kaldenbach, Andreas; Bornhöfft, Manuel; Benke, Julia; Mayer, Joachim; Wuttig, Matthias

    2013-01-01

    Phase-change materials are the basis for next-generation memory devices and reconfigurable electronics, but fundamental understanding of the unconventional kinetics of their phase transitions has been hindered by challenges in the experimental quantification. Here we obtain deeper understanding based on the temperature dependence of the crystal growth velocity of the phase-change material AgInSbTe, as derived from laser-based time-resolved reflectivity measurements. We observe a strict Arrhenius behaviour for the growth velocity over eight orders of magnitude (from ~10 nm s−1 to ~1 m s−1). This can be attributed to the formation of a glass at elevated temperatures because of rapid quenching of the melt. Further, the temperature dependence of the viscosity is derived, which reveals that the supercooled liquid phase must have an extremely high fragility (>100). Finally, the new experimental evidence leads to an interpretation, which comprehensively explains existing data from various different experiments reported in literature. PMID:23986035

  10. Working Memory Network Changes in ALS: An fMRI Study

    PubMed Central

    Vellage, Anne-Katrin; Veit, Maria; Kobeleva, Xenia; Petri, Susanne; Vielhaber, Stefan; Müller, Notger G.

    2016-01-01

    We used amyotrophic lateral sclerosis (ALS) as a model of prefrontal dysfunction in order to re-assess the potential neuronal substrates of two sub processes of working memory, namely information storage and filtering. To date it is unclear which exact neuronal networks sustain these two processes and the prefrontal cortex was suggested to play a crucial role both for filtering out of irrelevant information and for the storage of relevant information in memory. Other research has attributed information storage to more posterior brain regions, including the parietal cortex and stressed the role of subcortical areas in information filtering. We studied 14 patients suffering from ALS and the same number of healthy controls in an fMRI-task that allowed calculating separate storage and filtering scores. A brain volume analysis confirmed prefrontal atrophy in the patient group. Regarding their performance in the working memory task, we observed a trend toward slightly impaired storage capabilities whereas filtering appeared completely intact. Despite the rather subtle behavioral deficits we observed marked changes in neuronal activity associated with ALS: Compared to healthy controls patients showed significantly reduced hemodynamic responses in the left occipital cortex and right prefrontal cortex in the storage contrast. The filter contrast on the other hand revealed a relative hyperactivation in the superior frontal gyrus of the ALS patients. This hyperactivation might reflect a possible compensational mechanism for the prefrontal degeneration found in ALS. The reduced hemodynamic responses in the storage contrast might reflect a disruption of prefrontal top-down control of posterior brain regions, a process which was especially relevant in the most difficult high load memory task. Taken together, the present study demonstrates marked neurophysiological changes in ALS patients compared to healthy controls during the filtering and storage of information in spite of

  11. 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. PMID:26977663

  12. Slow-Theta-to-Gamma Phase-Amplitude Coupling in Human Hippocampus Supports the Formation of New Episodic Memories.

    PubMed

    Lega, Bradley; Burke, John; Jacobs, Joshua; Kahana, Michael J

    2016-01-01

    Phase-amplitude coupling (PAC) has been proposed as a neural mechanism for coordinating information processing across brain regions. Here we sought to characterize PAC in the human hippocampus, and in temporal and frontal cortices, during the formation of new episodic memories. Intracranial recordings taken as 56 neurosurgical patients studied and recalled lists of words revealed significant hippocampal PAC, with slow-theta activity (2.5-5 Hz) modulating gamma band activity (34-130 Hz). Furthermore, a significant number of hippocampal electrodes exhibited greater PAC during successful than unsuccessful encoding, with the gamma activity at these sites coupled to the trough of the slow-theta oscillation. These same conditions facilitate LTP in animal models, providing a possible mechanism of action for this effect in human memory. Uniquely in the hippocampus, phase preference during item encoding exhibited a biphasic pattern. Overall, our findings help translate between the patterns identified during basic memory tasks in animals and those present during complex human memory encoding. We discuss the unique properties of human hippocampal PAC and how our findings relate to influential theories of information processing based on theta-gamma interactions. PMID:25316340

  13. 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.

  14. 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.

  15. 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.

  16. Hydrogen doping in HfO2 resistance change random access memory

    NASA Astrophysics Data System (ADS)

    Duncan, D.; Magyari-Köpe, B.; Nishi, Y.

    2016-01-01

    The structures and energies of hydrogen-doped monoclinic hafnium dioxide were calculated using density-functional theory. The electronic interactions are described within the LDA + U formalism, where on-site Coulomb corrections are applied to the 5d orbital electrons of Hf atoms and 2p orbital electrons of the O atoms. The effects of charge state, defect-defect interactions, and hydrogenation are investigated and compared with experiment. It is found that hydrogenation of HfO2 resistance-change random access memory devices energetically stabilizes the formation of oxygen vacancies and conductive vacancy filaments through multiple mechanisms, leading to improved switching characteristic and device yield.

  17. Microstructural changes in memory and reticular formation neural pathway after simple concussion☆

    PubMed Central

    Ouyang, Lin; Shi, Rongyue; Xiao, Yuhui; Meng, Jiarong; Guo, Yihe; Lu, Guangming

    2012-01-01

    Patients with concussion often present with temporary disturbance of consciousness. The microstructural and functional changes in the brain associated with concussion, as well as the relationship with transient cognitive disorders, are currently unclear. In the present study, a rabbit model of simple concussion was established. Magnetic resonance-diffusion tensor imaging results revealed that the corona radiata and midbrain exhibited significantly decreased fractional anisotropy values in the neural pathways associated with memory and the reticular formation. In addition, the apparent diffusion coefficient values were significantly increased following injury compared with those before injury. Following a 1-hour period of quiet rest, the fractional anisotropy values significantly increased, and apparent diffusion coefficient values significantly decreased, returning to normal pre-injury levels. In contrast, the fractional anisotropy values and apparent diffusion coefficient values in the corpus callosum, thalamus and hippocampus showed no statistical significant alterations following injury. These findings indicate that the neural pathways associated with memory and the reticular formation pathway exhibit reversible microstructural white matter changes when concussion occurs, and these changes are exhibited to a different extent in different regions. PMID:25538741

  18. A Novel Paradigm for Nonassociative Long-Term Memory in Drosophila: Predator-Induced Changes in Oviposition Behavior

    PubMed Central

    Kacsoh, Balint Z.; Bozler, Julianna; Hodge, Sassan; Ramaswami, Mani; Bosco, Giovanni

    2015-01-01

    Learning processes in Drosophila have been studied through the use of Pavlovian associative memory tests, and these paradigms have been extremely useful in identifying both genetic factors and neuroanatomical structures that are essential to memory formation. Whether these same genes and brain compartments also contribute to memory formed from nonassociative experiences is not well understood. Exposures to environmental stressors such as predators are known to induce innate behavioral responses and can lead to new memory formation that allows a predator response to persist for days after the predator threat has been removed. Here, we utilize a unique form of nonassociative behavior in Drosophila where female flies detect the presence of endoparasitoid predatory wasps and alter their oviposition behavior to lay eggs in food containing high levels of alcohol. The predator-induced change in fly oviposition preference is maintained for days after wasps are removed, and this persistence in behavior requires a minimum continuous exposure time of 14 hr. Maintenance of this behavior is dependent on multiple long-term memory genes, including orb2, dunce, rutabaga, amnesiac, and Fmr1. Maintenance of the behavior also requires intact synaptic transmission of the mushroom body. Surprisingly, synaptic output from the mushroom body (MB) or the functions of any of these learning and memory genes are not required for the change in behavior when female flies are in constant contact with wasps. This suggests that perception of this predator that leads to an acute change in oviposition behavior is not dependent on the MB or dependent on learning and memory gene functions. Because wasp-induced oviposition behavior can last for days and its maintenance requires a functional MB and the wild-type products of several known learning and memory genes, we suggest that this constitutes a paradigm for a bona fide form of nonassociative long-term memory that is not dependent on associated

  19. Possible Overlapping Time Frames of Acquisition and Consolidation Phases in Object Memory Processes: A Pharmacological Approach

    ERIC Educational Resources Information Center

    Akkerman, Sven; Blokland, Arjan; Prickaerts, Jos

    2016-01-01

    In previous studies, we have shown that acetylcholinesterase inhibitors and phosphodiesterase inhibitors (PDE-Is) are able to improve object memory by enhancing acquisition processes. On the other hand, only PDE-Is improve consolidation processes. Here we show that the cholinesterase inhibitor donepezil also improves memory performance when…

  20. Structure Analysis of a Precipitate Phase in an Ni-Rich High Temperature NiTiHf Shape Memory Alloy

    SciTech Connect

    Yang, Fan; Coughlin, D. R.; Phillips, Patrick J.; Yang, L.; Devaraj, Arun; Kovarik, Libor; Noebe, Ronald D.; Mills, M. J.

    2013-03-22

    Thermal aging of the high temperature shape memory alloy 50.3Ni-29.7Ti-20Hf (at.%) introduces a novel precipitate phase, which plays an important role in improving shape memory properties. The precipitate phase was investigated by conventional electron diffraction, high resolution scanning transmission electron microscopy (STEM) and three dimensional atom probe tomography. An unrelaxed orthorhombic atomic structural model is proposed based on these observations. This model was subsequently relaxed by ab initio calculations. As a result of the relaxation, atom shuffle displacements occur, which in turn yields improved agreement with the STEM images. The relaxed structure, which is termed the “H-phase”, has also been verified to be thermodymanically stable at 0 K.

  1. Extended investigation of intermartensitic transitions in Ni-Mn-Ga magnetic shape memory alloys: A detailed phase diagram determination

    SciTech Connect

    Çakir, Asli; Aktürk, Selçuk; Righi, Lara

    2013-11-14

    Martensitic transitions in shape memory Ni-Mn-Ga Heusler alloys take place between a high temperature austenite and a low temperature martensite phase. However, intermartensitic transformations have also been encountered that occur from one martensite phase to another. To examine intermartensitic transitions in magnetic shape memory alloys in detail, we carried out temperature dependent magnetization, resistivity, and x-ray diffraction measurements to investigate the intermartensitic transition in Ni{sub 50}Mn{sub 50–x}Ga{sub x} in the composition range 12≤x≤25 at. %. Rietveld refined x-ray diffraction results are found to be consistent with magnetization and resistivity data. Depending on composition, we observe that intermartensitic transitions occur in the sequences 7M→L1{sub 0}, 5M→7M, and 5M→7M→L1{sub 0} with decreasing temperature. The L1{sub 0} non-modulated structure is most stable at low temperature.

  2. Changes in regional boreal climate due to historic and future structural vegetation changes and variations in soil moisture memory

    NASA Astrophysics Data System (ADS)

    Rydsaa, Johanne H.; Stordal, Frode; Tallaksen, Lena M.

    2014-05-01

    Amplified warming at high latitudes over the past decades already has led to, and will continue to lead to, changes in the boreal and arctic part of the climate system. Climate change induced alterations include structural shifts in high latitude ecosystems such as boreal forest expansion towards higher latitudes and altitudes, and shrub-ecosystems replacing tundra in large areas of the arctic. These shifts affect surface physical qualities such as albedo, roughness length, and soil properties. Shifts in vegetation species may also lead to alterations in soil- and boundary layer moisture. Resultant changes in land surface properties and processes provide important feedbacks to regional climate by changes in radiation, and water and energy fluxes. Structural vegetation changes that appear on local scale may through these feedback mechanisms also propagate to affect large scale climatic features. In this study, the Weather Research and Forecasting model (WRF) with the Noah Land surface model is used in a series of experiments in order to investigate the influence of observed and anticipated structural changes in the boreal ecosystem on changes in the land-atmosphere feedbacks. MODIS land surface data are used together with observational data and dynamical vegetation model output from the CMIP5 database, to simulate the influence of historical and future structural vegetation changes over the Northern European Boreal domain. In a series of three experiments the MODIS dataset is manually altered in order to reflect observed and anticipated changes in Boreal forest geography on summer water and energy fluxes at the surface, including Bowen ratio changes. As results are highly sensitive to soil moisture variations, experiments are conducted under wet and dry soil moisture regimes, to take into account uncertainties in future soil state projections and to estimate sensitivity to soil moisture memory in surface flux estimates.

  3. 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.

  4. High-resolution transmission electron microscopy study of electrically-driven reversible phase change in ge2sb2te5 nanowires.

    PubMed

    Jung, Yeonwoong; Nam, Sung-Wook; Agarwal, Ritesh

    2011-03-01

    By combining high-resolution transmission electron microscopy (HRTEM) characterization and electrical measurements on a unique device platform, we study the reversible electrically-driven phase-change characteristics of self-assembled Ge(2)Sb(2)Te(5) nanowires. Detailed HRTEM analyses are used to correlate and understand the effect of full and intermediate structural transformations on the measured electrical properties of the nanowire devices. The study demonstrates that our unique approach has the potential to provide new information regarding the dynamic structural and electrical states of phase-change materials at the nanoscale, which will aid the design of future phase-change memory devices. PMID:21271735

  5. 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.

  6. 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.

  7. Performance enhancement of hermetic compressor using phase change materials

    NASA Astrophysics Data System (ADS)

    Mahmoud, I. M.; Rady, M. A.; Huzayyin, A. S.

    2015-08-01

    The present study is motivated by the need for the research of simple measures for increasing energy efficiency of hermetic compressor. The measure is the application of phase change materials for performance enhancement. The first experimental study should be guide for choice of PCM. It has been performed to investigate the effects of thermostat setting temperature on the performance of hermetic compressor. The effects of thermostat setting temperature with and without load on power consumption have been analyzed. Performance enhancement using phase change materials (PCMs) has been studied by employing a phase change material Rubitherm-42 (RT-42) on the top surface of compressor. Choice of PCM material is based on basic compressor performance measured in the first part of the present study. Experiments have been carried out for different load values and different quantities of PCM. The quantity and phase change characteristic of PCM are essential parameters that determine the percentage of performance enhancement in term of energy consumption. Reduction of energy consumption of about 10% has been achieved in the present study by using PCM. The present study shows that how to reduce the electrical power consumption to enhance compressor heat dissipation method to improve efficiency.

  8. 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.

  9. Surface expression of NMDA receptor changes during memory consolidation in the crab Neohelice granulata.

    PubMed

    Hepp, Yanil; Salles, Angeles; Carbo-Tano, Martin; Pedreira, Maria Eugenia; Freudenthal, Ramiro

    2016-08-01

    The aim of the present study was to analyze the surface expression of the NMDA-like receptors during the consolidation of contextual learning in the crab Neohelice granulata Memory storage is based on alterations in the strength of synaptic connections between neurons. The glutamatergic synapses undergo various forms of N-methyl-D aspartate receptor (NMDAR)-dependent changes in strength, a process that affects the abundance of other receptors at the synapse and underlies some forms of learning and memory. Here we propose a direct regulation of the NMDAR. Changes in NMDAR's functionality might be induced by the modification of the subunit's expression or cellular trafficking. This trafficking does not only include NMDAR's movement between synaptic and extra-synaptic localizations but also the cycling between intracellular compartments and the plasma membrane, a process called surface expression. Consolidation of contextual learning affects the surface expression of the receptor without affecting its general expression. The surface expression of the GluN1 subunit of the NMDAR is down-regulated immediately after training, up-regulated 3 h after training and returns to naïve and control levels 24 h after training. The changes in NMDAR surface expression observed in the central brain are not seen in the thoracic ganglion. A similar increment in surface expression of GluN1 in the central brain is observed 3 h after administration of the competitive GABAA receptor antagonist, bicuculline. These consolidation changes are part of a plasticity event that first, during the down-regulation, stabilizes the trace and later, at 3-h post-training, changes the threshold for synapse activation. PMID:27421895

  10. Changes of subtests of Wechsler Memory Scale and cognitive function in subjects with subclinical hypothyroidism following treatment with levothyroxine

    PubMed Central

    Aghili, Rokhsareh; Khamseh, Mohammad E.; Malek, Mojtaba; Hadian, Ali; Baradaran, Hamid R.; Emami, Zahra

    2012-01-01

    Introduction Subclinical hypothyroidism has been reported to be associated with disturbed cognitive function. In this study, changes of subtests of the Wechsler Memory Scale and memory quotient were investigated in subjects with subclinical hypothyroidism following treatment with levothyroxine. The aim of the study was a randomized double blind placebo-controlled clinical trial. Material and methods Sixty subjects (51 females and 9 males) with subclinical hypothyroidism were enrolled. Memory quotient was evaluated at the beginning of the study and three months after enrollment, using Wechsler's memory test. Subclinical hypothyroidism was defined as serum TSH level between 4.5 mU/l and 10 mU/l in the presence of normal free-T4 (0.8-2 ng/dl) and positive anti-TPO-Ab. The intervention and control groups received levothyroxine and placebo respectively for 3 months. Re-evaluation was done using the Wechsler Memory Scale at the end of the study. Results The mean age was 34 ±10 years, mean TSH level was 8.25 ±3.64 muIU/l. Memory quotient was similar in both groups at the beginning of the study: 105.70 ±2.1 in intervention group vs. 105.87 ±2.1 in control group (p = 0.89). At the end of the study, the memory quotient rose by 9.3 points in the intervention group and by 3.23 in the controls (p = 0.002). Analysis of the scores of Wechsler Memory subtests in the intervention group indicated significant improvement of mental control (p = 0.002), logical memory (p < 0.001), associate learning (p = 0.014), age corrected score (p = 0.002), and memory quotient (p < 0.001). Conclusions This study showed the efficacy of levothyroxine for cognitive function of subjects with subclinical hypothyroidism. PMID:23319987

  11. Entropy change and phase transitions in an expanding Universe

    NASA Astrophysics Data System (ADS)

    Iqbal, N.; Masood, T.; Demir, N.

    2015-12-01

    The work compiles a correlated study of a gravitational quasi equilibrium thermodynamic approach for establishing and signifying a unique behavior of the cosmological entropy and phase transitions in an expanding Universe. On the basis of prescribed boundary conditions for the cluster temperature a relation for the intra-cluster medium (ICM) of galaxy clusters has been derived. A more productive and signifying approach of the correlation functions used for galaxy clustering phenomena shows a unique behavior of the entropy change where a phenomenon known as the gravitational phase transition occurs. This unique behavior occurs with a symmetry breaking from mild clustering to low clustering and from mild clustering to high clustering which differs from a normal symmetry breaking in material sciences. We also derive results for the specific latent heat associated with the phase transitions of 3.20 T_c and 0.55 T_c for the mildly clustered phase to the low clustered phase and from the mildly clustered phase to the highly clustered phase, respectively.

  12. Irradiation induced structural change in Mo2Zr intermetallic phase

    DOE PAGESBeta

    Gan, J.; Keiser, Jr., D. D.; Miller, B. D.; Eriksson, N.; Sohn, Y. H.; Kirk, M.

    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 developmentmore » of dislocations without bubble formation.« less

  13. Dynamic changes in neural circuitry during adolescence are associated with persistent attenuation of fear memories

    PubMed Central

    Pattwell, Siobhan S.; Liston, Conor; Jing, Deqiang; Ninan, Ipe; Yang, Rui R.; Witztum, Jonathan; Murdock, Mitchell H.; Dincheva, Iva; Bath, Kevin G.; Casey, B. J.; Deisseroth, Karl; Lee, Francis S.

    2016-01-01

    Fear can be highly adaptive in promoting survival, yet it can also be detrimental when it persists long after a threat has passed. Flexibility of the fear response may be most advantageous during adolescence when animals are prone to explore novel, potentially threatening environments. Two opposing adolescent fear-related behaviours—diminished extinction of cued fear and suppressed expression of contextual fear—may serve this purpose, but the neural basis underlying these changes is unknown. Using microprisms to image prefrontal cortical spine maturation across development, we identify dynamic BLA-hippocampal-mPFC circuit reorganization associated with these behavioural shifts. Exploiting this sensitive period of neural development, we modified existing behavioural interventions in an age-specific manner to attenuate adolescent fear memories persistently into adulthood. These findings identify novel strategies that leverage dynamic neurodevelopmental changes during adolescence with the potential to extinguish pathological fears implicated in anxiety and stress-related disorders. PMID:27215672

  14. Dynamic changes in neural circuitry during adolescence are associated with persistent attenuation of fear memories.

    PubMed

    Pattwell, Siobhan S; Liston, Conor; Jing, Deqiang; Ninan, Ipe; Yang, Rui R; Witztum, Jonathan; Murdock, Mitchell H; Dincheva, Iva; Bath, Kevin G; Casey, B J; Deisseroth, Karl; Lee, Francis S

    2016-01-01

    Fear can be highly adaptive in promoting survival, yet it can also be detrimental when it persists long after a threat has passed. Flexibility of the fear response may be most advantageous during adolescence when animals are prone to explore novel, potentially threatening environments. Two opposing adolescent fear-related behaviours-diminished extinction of cued fear and suppressed expression of contextual fear-may serve this purpose, but the neural basis underlying these changes is unknown. Using microprisms to image prefrontal cortical spine maturation across development, we identify dynamic BLA-hippocampal-mPFC circuit reorganization associated with these behavioural shifts. Exploiting this sensitive period of neural development, we modified existing behavioural interventions in an age-specific manner to attenuate adolescent fear memories persistently into adulthood. These findings identify novel strategies that leverage dynamic neurodevelopmental changes during adolescence with the potential to extinguish pathological fears implicated in anxiety and stress-related disorders. PMID:27215672

  15. The wisdom of elders: Inuvialuit social memories of continuity and change in the twentieth century.

    PubMed

    Lyons, Natasha

    2010-01-01

    The Inuvialuit of the Canadian Western Arctic are no strangers to change. From the arrival of whalers ca. 1890, they underwent a century of monumental societal upheaval. Perhaps against the odds, they sustained many of their traditional socioeconomic activities and continued to follow a land-based lifestyle through much of the twentieth century. With a few notable exceptions, historical accounts of this period were written by cultural outsiders who conveyed their own perspectives on Inuvialuit culture. This paper focuses on the social memories of present-day Inuvialuit Elders who recount aspects of their lifeways throughout the twentieth century, including seasonal practices, traditional skills they maintained, and responses to the historical events that challenged their ways of living and spurred continuous change. These oral narratives form part of a larger history for succeeding generations, and a platform from which to construct contemporary identities and to negotiate a collective future. PMID:20648982

  16. Evidence for segregation of Te in ``phase-change" thin chalcogenide Ge-Sb-Te films

    NASA Astrophysics Data System (ADS)

    Cabral, C., Jr.; Krusin-Elbaum, L..; Chen, K. N.; Copel, M.; Bruley, J.; Deline, V. R.

    2007-03-01

    The novel chalcogenide phase-change materials are promising candidates for new technologies such as nonvolatile memories and programmable switches in 3D integration and planar logic. They are typically thin Ge-Sb-Te (GST) films, where a thermally induced amorphous-to-crystalline phase transformation can be fast and reversible, with the corresponding large swing in resistance values between the two stable structural states. Here we report on the structural evolution of GST films during thermal cycling and demonstrate using high-resolution (0.5 nm focused probe STEM) scans that Te segregates to the grain boundaries at fairly low temperatures. We show that diffusion of Te along grain boundaries results in its pileup at the free surface and interaction with Ti in adhesion layers in device- compatible stacks. This is consistent with impeded grain growth and with post-crystallization stress release. This motion may impact the ultimate life-cycle of phase-change based devices and should guide the optimal GST material design.

  17. Structural transformations in amorphous ↔ crystalline phase change of Ga-Sb alloys

    SciTech Connect

    Edwards, T. G.; Sen, S.; Hung, I.; Gan, Z.; Kalkan, B.; Raoux, S.

    2013-12-21

    Ga-Sb alloys with compositions ranging between ∼12 and 50 at. % Ga are promising materials for phase change random access memory applications. The short-range structures of two such alloys with compositions Ga{sub 14}Sb{sub 86} and Ga{sub 46}Sb{sub 54} are investigated, in their amorphous and crystalline states, using {sup 71}Ga and {sup 121}Sb nuclear magnetic resonance spectroscopy and synchrotron x-ray diffraction. The Ga and Sb atoms are fourfold coordinated in the as-deposited amorphous Ga{sub 46}Sb{sub 54} with nearly 40% of the constituent atoms being involved in Ga-Ga and Sb-Sb homopolar bonding. This necessitates extensive bond switching and elimination of homopolar bonds during crystallization. On the other hand, Ga and Sb atoms are all threefold coordinated in the as-deposited amorphous Ga{sub 14}Sb{sub 86}. Crystallization of this material involves phase separation of GaSb domains in Sb matrix and a concomitant increase in the Ga coordination number from 3 to 4. Results from crystallization kinetics experiments suggest that the melt-quenching results in the elimination of structural “defects” such as the homopolar bonds and threefold coordinated Ga atoms in the amorphous phases of these alloys, thereby rendering them structurally more similar to the corresponding crystalline states compared to the as-deposited amorphous phases.

  18. First Principles Study of structural characteristics and phase change mechanism of Ge-Sb-Te based materials

    NASA Astrophysics Data System (ADS)

    Park, Hanjin; Kim, Cheol-Woon; Lee, Hyung-June; Song, Hosin; Kwon, Young-Kyun

    Using ab initio density functional theory, we investigate the structural properties and their phase transition mechanism of the crystalline and amorphous phases of Ge-Sb-Te (GST) based phase change materials, which would be utilized for phase change random access memory. Among various stochiometries of GST, we focus on compositions along the (GeTe)n(Sb2Te3)m pseudo-binary line, denoted simply by (n , m) with integer n and m. We explore various GST materials corresponding (n , m) sets including (1,0), (0,1), (1,1), (2,1) and (1,2) by modeling their both phases. Especially, their amorphous phases can be constructed based on experimental data available or molecular dynamics (MD) simulations performing melt-quench processes. To understand the phase transition mechanism, we evaluate their coordination numbers, radial distribution functions, and angle distribution functions, which enables us to identify the characteristic local geometry representing each phase. We further investigate the thermal properties of various phases by evaluating their phonon densities of states obtained by Fourier-transforming the velocity autocorrelation functions calculated directly from our MD simulation.

  19. The distinctive germinal center phase of IgE+ B lymphocytes limits their contribution to the classical memory response

    PubMed Central

    He, Jin-Shu; Meyer-Hermann, Michael; Xiangying, Deng; Zuan, Lim Yok; Jones, Leigh Ann; Ramakrishna, Lakshmi; de Vries, Victor C.; Dolpady, Jayashree; Aina, Hoi; Joseph, Sabrina; Narayanan, Sriram; Subramaniam, Sharrada; Puthia, Manoj; Wong, Glenn; Xiong, Huizhong; Poidinger, Michael; Urban, Joseph F.; Lafaille, Juan J.

    2013-01-01

    The mechanisms involved in the maintenance of memory IgE responses are poorly understood, and the role played by germinal center (GC) IgE+ cells in memory responses is particularly unclear. IgE+ B cell differentiation is characterized by a transient GC phase, a bias toward the plasma cell (PC) fate, and dependence on sequential switching for the production of high-affinity IgE. We show here that IgE+ GC B cells are unfit to undergo the conventional GC differentiation program due to impaired B cell receptor function and increased apoptosis. IgE+ GC cells fail to populate the GC light zone and are unable to contribute to the memory and long-lived PC compartments. Furthermore, we demonstrate that direct and sequential switching are linked to distinct B cell differentiation fates: direct switching generates IgE+ GC cells, whereas sequential switching gives rise to IgE+ PCs. We propose a comprehensive model for the generation and memory of IgE responses. PMID:24218137

  20. Reconsolidation-induced memory persistence: Participation of late phase hippocampal ERK activation.

    PubMed

    Krawczyk, M C; Navarro, N; Blake, M G; Romano, A; Feld, M; Boccia, M M

    2016-09-01

    Persistence is an attribute of long-term memories (LTM) that has recently caught researcher's attention in search for mechanisms triggered by experience that assure memory perdurability. Up-to-date, scarce evidence of relationship between reconsolidation and persistence has been described. Here, we characterized hippocampal ERK participation in LTM reconsolidation and persistence using an inhibitory avoidance task (IA) at different time points. Intra-dorsal-hippocampal (dHIP) administration of an ERK inhibitor (PD098059, PD, 1.0μg/hippocampus) 3h after retrieval did not affect reconsolidation of a strong IA, when tested 24h apart. However, the same manipulation impaired performance when animals were tested at 7d, regardless of the training's strength; and being specific to memory reactivation. To the best of our knowledge, this is the first report showing that persistence might be triggered after memory reactivation involving an ERK/MAPK-dependent process. PMID:27321160