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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

    2011-07-03

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

  2. Bipolar switching in chalcogenide phase change memory.

    PubMed

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

    2016-07-05

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

  3. 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.

  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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  6. 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

  7. Projected phase-change memory devices.

    PubMed

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

    2015-09-03

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

  8. 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

  9. Application of phase-change materials in memory taxonomy

    PubMed Central

    Wang, Lei; Tu, Liang; Wen, Jing

    2017-01-01

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

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

    PubMed

    Wang, Lei; Tu, Liang; Wen, Jing

    2017-01-01

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

  11. Crystal growth within a phase change memory cell.

    PubMed

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

    2014-07-07

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

  12. 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.

  13. 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.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Devasia, Archana

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  18. 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

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

    PubMed

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

    2015-09-01

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

  20. New developments in optical phase-change memory

    NASA Astrophysics Data System (ADS)

    Ovshinsky, Stanford R.; Czubatyj, Wolodymyr

    2001-02-01

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

  1. 16-Kbit SPI phase change memory chip with ECC scheme

    NASA Astrophysics Data System (ADS)

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

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

  2. 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.

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

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

    PubMed

    Esopenko, Carrie; Levine, Brian

    2017-04-01

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

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

    DTIC Science & Technology

    2015-09-02

    Energy-Efficient Phase-Change Memory with Graphene as a Thermal Barrier Chiyui Ahn,*,† Scott W. Fong,† Yongsung Kim,‡ Seunghyun Lee,† Aditya Sood...Samsung Advanced Institute of Technology (SAIT), Suwon, 443-803, South Korea *S Supporting Information ABSTRACT: Phase-change memory (PCM) is an important...cycles, and the graphene could further enhance the PCM endurance by limiting atomic migration or material segregation at the bottom electrode interface

  8. 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.

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

    PubMed

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

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  11. 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.

  12. Nonvolatile ``AND,'' ``OR,'' and ``NOT'' Boolean logic gates based on phase-change memory

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

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

    PubMed

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

    2015-06-11

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

  14. Program and read scaling trade-offs in phase change memories.

    PubMed

    Braga, Stefania; Cabrini, Alessandro; Torelli, Guido

    2011-12-01

    This paper investigates the scaling perspectives of Phase Change Memory technology by analyzing the effects of geometrical dimensions reduction and the read voltage scaling on program and read operations. To this end, we derive analytical expressions which allow us to estimate the dependence of the RESET and read current on key geometrical parameters of the memory cell, such as heater size and chalcogenide layer thickness.

  15. Size effect of nano scale phase change random access memory.

    PubMed

    Son, Ji Hoon; Choi, HongKyw; Jang, Nakwon; Kim, Hong Seung; Yi, Dong Young; Lee, Seong Hwan

    2010-05-01

    In this paper, we have investigated the size effect of nano scale PRAM using three-dimensional finite element analysis tool. The reset current and temperature profile of PRAM cells with top and bottom electrode contact hole size were calculated by the numerical method. And temperature profile of PRAM unit cell with size and thickness of GST thin film was simulated. As top electrode contact size was smaller, reset current decreased. But these variations couldn't affect to operate memory. On the other hand, as bottom electrode contact size was smaller, reset current abruptly decreased.

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  17. 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

  18. 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.

  19. Bond constraint theory studies of chalcogenide phase change memories

    SciTech Connect

    Paesler, M.A.; Baker, D.A.; Lucovsky, G.

    2008-07-08

    Studies of amorphous (a-) semiconductors have been driven by technological advances as well as fundamental theories. Observation of electrical switching, for example, fueled early interest in a-chalcogenides. More recently a-chalcogenide switching has been applied successfully to programmable memory devices as well as DVD technology where the quest for the discovery of better-suited materials continues. Thus, switching grants researchers today with an active arena of technological as well as fundamental study. Bond constraint theory (BCT) and rigidity theory provide a powerful framework for understanding the structure and properties of a-materials. Application of these theories to switching in a-chalcogenides holds the promise of finding the best composition suited for switching applications. Extended X-ray absorption fine structure (EXAFS) spectroscopy is an ideally suited technique to investigate the switching properties of these materials. Films of amorphous Ge{sub 2}Sb{sub 2}Te{sub 4}, Ge{sub 2}Sb{sub 2}Te{sub 5}, and Ge{sub 2}Sb{sub 2}Te{sub 7} exhibit differing bonding structures and bond statistics, which result in different electronic and optical properties. Results of new EXAFS experiments on these three critical compositions in the Ge-Sb-Te system are presented in light of BCT and rigidity theory.

  20. How important is the {103} plane of stable Ge2 Sb2 Te5 for phase-change memory?

    PubMed

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

    2015-07-01

    Closely correlating with {200} plane of cubic phase, {103} plane of hexagonal phase of Ge(2)Sb(2)Te(5) plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge(2)Sb(2)Te(5). The behaviors of {103} plane of hexagonal phase render the phase-change memory process as a nanoscale shape memory. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

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

    NASA Astrophysics Data System (ADS)

    Gyanathan, Ashvini; Yeo, Yee-Chia

    2012-11-01

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

  2. Logic computation in phase change materials by threshold and memory switching.

    PubMed

    Cassinerio, M; Ciocchini, N; Ielmini, D

    2013-11-06

    Memristors, namely hysteretic devices capable of changing their resistance in response to applied electrical stimuli, may provide new opportunities for future memory and computation, thanks to their scalable size, low switching energy and nonvolatile nature. We have developed a functionally complete set of logic functions including NOR, NAND and NOT gates, each utilizing a single phase-change memristor (PCM) where resistance switching is due to the phase transformation of an active chalcogenide material. The logic operations are enabled by the high functionality of nanoscale phase change, featuring voltage comparison, additive crystallization and pulse-induced amorphization. The nonvolatile nature of memristive states provides the basis for developing reconfigurable hybrid logic/memory circuits featuring low-power and high-speed switching. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Temperature dependence of SET switching characteristics in phase-change memory cells

    NASA Astrophysics Data System (ADS)

    He, Qiang; Li, Zhen; Liu, Chang; Meng, Xiang-ru; Peng, Ju-hong; Lai, Zhi-bo; Miao, Xiang-shui

    2016-09-01

    The temperature dependence of crystallization kinetics of phase-change materials raises a series of reliability issues, while phase-change memory cells work at high temperature or thermal-disturbance condition. These issues hinder the development of ultrahigh-density storage devices. We investigate the evolution of SET switching characteristics of phase-change memory cells at high operating temperature. We show that the high temperature strongly impacts the SET state resistance. As a result, SET failure has been observed with elevated ambient temperature. Our SPICE simulations indicate that transient amorphization behavior during a complete SET pulse period is considered as the potential mechanism of SET failure. By modifying the SET pulse intensity and width linearly, we successfully reduce the SET failure in the experiments. The results illustrate that the demonstrated linear properties may optimize SET pulse performance.

  4. GeTe/Sb7Te3 superlatticelike structure for lateral phase change memory

    NASA Astrophysics Data System (ADS)

    Yang, Hongxin; Chong, Chong Tow; Zhao, Rong; Lee, Hock Koon; Li, Jianming; Lim, Kian Guan; Shi, Luping

    2009-05-01

    A series of superlatticelike (SLL) structure incorporated with two phase-change materials GeTe and Sb7Te3 was applied in lateral phase change memory. Power consumption and lifetime were used as two criteria to optimize the SLL structure. It was found that with the thickness ratio of GeTe to Sb7Te3 at 1.6, the RESET current could be as low as 1.5 mA and the endurance could reach as high as 5.3×106 cycles. By varying the thickness ratio of GeTe to Sb7Te3, the crystallization temperature of SLL structures and the performance of lateral phase change memory with these SLL structures can be controlled.

  5. Material engineering of GexTe100-x compounds to improve phase-change memory performances

    NASA Astrophysics Data System (ADS)

    Navarro, G.; Sousa, V.; Persico, A.; Pashkov, N.; Toffoli, A.; Bastien, J.-C.; Perniola, L.; Maitrejean, S.; Roule, A.; Zuliani, P.; Annunziata, R.; De Salvo, B.

    2013-11-01

    In this paper we provide a detailed physical and electrical characterization of Germanium Telluride compounds (GexTe100-x) targeting phase-change memory applications. Thin films of Germanium-rich as well as Tellurium-rich phase-change materials are deposited for material analysis (XRD, resistivity and optical characterization). GexTe100-x compounds are then integrated in lance-type analytical phase-change memory devices allowing for a thorough analysis of the switching characteristics, data retention and endurance performances. Tellurium-rich GeTe alloys exhibit stable programming characteristics and can sustain endurance up to 107 cycles, while Germanium-rich compounds show an unstable RESET state during repeated write/erase cycles, probably affected by Ge segregation. Finally we demonstrate that data retention is strongly improved departing from Ge50Te50 stoichiometric composition.

  6. 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.

  7. Study on the impact of the initialization process on the phase change memory

    NASA Astrophysics Data System (ADS)

    Ren, Kun; Rao, Feng; Song, Zhitang; Lv, Shilong; Zhu, Min; Wu, Liangcai; Liu, Bo; Feng, Songlin

    2013-05-01

    The set processes of T-shape phase change memory (PCRAM) cell are compared to study the change caused by the initialization. After the initialization, PCRAM cell shows lower Vth and minor resistances than those of the 1st operation, which can be explained by the reduction of contact resistance caused by the formation of the crystalline phase change material interface (CPI) near the electrodes. The temperature transition regions between the programmed region and the electrodes preserve the CPI after its formation in the initial operation. Thus, we suggest the formation of CPI is the key role for the initialization.

  8. Role of an encapsulating layer for reducing resistance drift in phase change random access memory

    NASA Astrophysics Data System (ADS)

    Jin, Bo; Kim, Jungsik; Pi, Dong-Hai; Kim, Hyoung Seop; Meyyappan, M.; Lee, Jeong-Soo

    2014-12-01

    Phase change random access memory (PCRAM) devices exhibit a steady increase in resistance in the amorphous phase upon aging and this resistance drift phenomenon directly affects the device reliability. A stress relaxation model is used here to study the effect of a device encapsulating layer material in addressing the resistance drift phenomenon in PCRAM. The resistance drift can be increased or decreased depending on the biaxial moduli of the phase change material (YPCM) and the encapsulating layer material (YELM) according to the stress relationship between them in the drift regime. The proposed model suggests that the resistance drift can be effectively reduced by selecting a proper material as an encapsulating layer. Moreover, our model explains that reducing the size of the phase change material (PCM) while fully reset and reducing the amorphous/crystalline ratio in PCM help to improve the resistance drift, and thus opens an avenue for highly reliable multilevel PCRAM applications.

  9. 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.

  10. Programming power reduction in confined phase change memory cells with titanium dioxide clad layer

    NASA Astrophysics Data System (ADS)

    Chen, Liangliang; Zhang, Zhonghua; Song, Sannian; Song, Zhitang; Zheng, Qianqian; Zhang, Xin; Zhang, Juan; Zheng, Wanting; Shao, Hehong; Zhu, Xiuwei; Yu, Wenlei

    2017-01-01

    A confined structure phase change memory (PCM) cell has been fabricated based on the focused-ion beam technique. Furthermore, the titanium dioxide clad layer was proposed for promoting the temperature rise in the Ge0.61Sb2Te layer that causes the reduction in the reset voltage and current compared to the phase change memory cell without clad layer. Theoretical thermal simulation and calculation for the reset process are conducted to analyze the thermal effect of the titanium dioxide heating layer. The improved performance of the PCM cell with dioxide clad layer can be attributed to the fact that the buffer layer not only acted as heating layer but also efficiently reduced the cell dissipated power.

  11. Yttrium-Doped Sb2Te3: A Promising Material for Phase-Change Memory.

    PubMed

    Li, Zhen; Si, Chen; Zhou, Jian; Xu, Huibin; Sun, Zhimei

    2016-10-05

    Sb2Te3 exhibits outstanding performance among the candidate materials for phase-change memory; nevertheless, its low electrical resistivity and thermal stability hinder its practical application. Hence, numerous studies have been carried out to search suitable dopants to improve the performance; however, the explored dopants always cause phase separation and thus drastically reduce the reliability of phase-change memory. In this work, on the basis of ab initio calculations, we have identified yttrium (Y) as an optimal dopant for Sb2Te3, which overcomes the phase separation problem and significantly increases the resistivity of crystalline state by at least double that of Sb2Te3. The good phase stability of crystalline Y-doped Sb2Te3 (YST) is attributed to the same crystal structure between Y2Te3 and Sb2Te3 as well as their tiny lattice mismatch of only ∼1.1%. The significant increase in resistivity of c-YST is understood by our findings that Y can dramatically increase the carrier's effective mass by regulating the band structure and can also reduce the intrinsic carrier density by suppressing the formation of SbTe antisite defects. Y doping can also improve the thermal stability of amorphous YST based on our ab initio molecular dynamics simulations, which is attributed to the stronger interactions between Y and Te than that of Sb and Te.

  12. Sn2Se3: A conducting crystalline mixed valent phase change memory compound

    NASA Astrophysics Data System (ADS)

    Xing, Guangzong; Li, Yuwei; Fan, Xiaofeng; Zhang, Lijun; Zheng, Weitao; Singh, David J.

    2017-06-01

    Thin film Sn2Se3 is a promising new phase change memory material with a very high resistance contrast between insulating amorphous and conducting crystalline phases. We identify the structure of the Sn2Se3 crystalline phase using ab initio evolutionary structure search and report its properties. We find a structure based on Sn-Se ribbons with clear disproportionation of Sn into Sn(II) and Sn(IV) sites, similar to Sn2S3. The energy is only 9 meV/atom above the tie line between SnSe and SnSe2. Sn charge disproportionation is only marginally favored in this selenide, in contrast to sulfides. This leads to a semimetallic rather than semiconducting behavior. These findings, marginal stability of the crystalline phase and conducting character and close competition of disproportionated and non-disproportionated structures, are important for understanding the behavior of Sn2Se3 as a phase change memory material, specifically the fast low energy, the low temperature switching, and the high resistance contrast.

  13. Development and application of a new CMP slurry for phase change memory

    NASA Astrophysics Data System (ADS)

    Yu, Lei; Liu, Weili; Liu, Bo; Song, Zhitang

    2016-10-01

    In this paper, the development of a new chemical mechanical planarization (CMP) slurry for phase change material GeSbTe (GST) and its application in the manufacturing process of phase change memory based on GST is presented. The basic abrasive of the slurry was special colloid silica which was chosen from several kinds of colloid silica with different surface treatment and stable pH range. Oxidizer, chelator, inhibitor and protective agent were added to the colloid silica to accelerate the polishing rate and protect the surface. A series of CMP experiments were carried out on a 4-inch experimental platform to confirm and optimize the performance of the slurry with different ratio of reagents. After the recipe was frozen, the slurry was used in the CMP process of manufacturing the phase change memory on 12-inch wafers. The results on blanket wafers show that the remove rate, endurance life, residue control is at the same level with those of the old slurry, while the scratch control is much better than that of the old one. The final results on both metal line structure and blade structure show that the new slurry has much better performance than the old one on oxide loss, scratch and erosion control.

  14. 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

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

    PubMed

    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.

  16. Directed self-assembly patterning strategies for phase change memory applications

    NASA Astrophysics Data System (ADS)

    Bruce, Robert L.; Fraczak, Gloria; Papalia, John M.; Tsai, HsinYu; BrightSky, Matt; Miyazoe, Hiroyuki; Zhu, Yu; Engelmann, Sebastian U.; Lung, Hsiang-Lan; Masuda, Takeshi; Suu, Koukou; Liu, Chi-Chun; Tang, Hao; Arnold, John C.; Felix, Nelson; Lam, Chung H.

    2017-03-01

    Phase change material (PCM)-based memory cells have shown promise as an enabler for low power, high density memory. There is a current need to develop and improve patterning strategies to attain smaller device dimensions. In this work, two methods of patterning of PCM device structures was achieved using directed self-assembly (DSA) patterning: the formation of a high aspect ratio pore designed for atomic layer deposition (ALD) of etch damage-free PCM, and pillar formation by image reversal and plasma etch transfer into a PCM film. We show significant CD reduction (180 nm to 20 nm) of a lithographically defined hole by plasma etch shrink, DSA spin-coat and subsequent high selectivity pattern transfer. We then demonstrate structural fabrication of both DSA-defined SiN pores with ALD PCM and DSA-defined PCM pillars. Challenges to both pore and pillar fabrication are discussed.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. A power-efficient and non-volatile programmable logic array based on phase change memory

    NASA Astrophysics Data System (ADS)

    Du, Yuan; Ye, Yong; Kang, Yong; Xia, Yangyang; Song, Zhitang; Chen, Bomy

    2016-10-01

    Recently, numerous efforts have been made on NVM-based Field Programmable Gate Arrays (FPGAs) because the emerging non-volatile memory (NVM) technologies have the advantages of lower leakage power and higher density than Static Random Access Memory (SRAM) technology. However, the cost and the scale of FPGAs are so high and large that they can't be applied in the consumer electronics field and Internet of Things (IoT). Due to the small scale and low cost, Programmable Logic Array (PLA) is an ideal option for these fields. However, up to now there are few researches on non-volatile PLA based on emerging NVMs. In this paper, a power-efficient non-volatile PLA based on Phase Change Memory (PCM) is proposed. The proposed non-volatile PLA architecture has been evaluated using the 40 nm Complementary Metal Oxide Semiconductor (CMOS) technology, and the simulation results show the correct functionality of the PLA. After the PLA reads the configuration bits from the non-volatile programmable elements (PEs), the power of the programmable elements can be OFF. Therefore, the standby power of the programmable elements is much smaller than that of the commonly SRAM-based PLAs. The simulation results also show that the total power of nvPLA is reduced by about 53.6% when the supply power of Programmable Element is OFF.

  5. 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.

  6. Phase-Change Thermoplastic Elastomer Blends for Tunable Shape Memory by Physical Design

    SciTech Connect

    Mineart, Kenneth P.; Tallury, Syamal S.; Li, Tao; Lee, Byeongdu; Spontak, Richard J.

    2016-12-14

    Shape-memory polymers (SMPs) change shape upon exposure to an environmental stimulus.1-3 They are of considerable importance in the ongoing development of stimuli-responsive biomedical4,5 and deployable6 devices, and their function depends on the presence of two components.7 The first provides mechanical rigidity to ensure retention of one or more temporary strain states and also serves as a switch capable of releasing a temporary strain state. The second, a network-forming component, is required to restore the polymer to a prior strain state upon stimulation. In thermally-activated SMPs, the switching element typically relies on a melting or glass transition temperature,1-3,7 and broad or multiple switches permit several temporary strain states.8-10 Chemical integration of network-forming and switching species endows SMPs with specific properties.8,10,11 Here, we demonstrate that phase-change materials incorporated into network-forming macromolecules yield shape-memory polymer blends (SMPBs) with physically tunable switching temperatures and recovery kinetics for use in multi-responsive laminates and shape-change electronics.

  7. 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.

  8. 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.

  9. Electrophysical Properties of Ge-Sb-Te Thin Films for Phase Change Memory Devices

    NASA Astrophysics Data System (ADS)

    Lazarenko, P. I.; Kozyukhin, S. A.; Sherchenkov, A. A.; Babich, A. V.; Timoshenkov, S. P.; Gromov, D. G.; Zabolotskaya, A. V.; Kozik, V. V.

    2017-01-01

    In this work, we studied temperature dependences of the resistivity and current-voltage characteristics of amorphous thin films based on the materials of a Ge-Sb-Te system of compositions GeSb4Te7 (GST147), GeSb2Te4 (GST124), and Ge2Sb2Te5 (GST225) applied in the phase change memory devices. The effect of changes in the composition of thin films on the crystallization temperature, resistivity of films in amorphous and crystalline states, and on the activation energy of conductivity is determined. It is found that the peculiarity of these materials is the mechanism of two-channel conductivity where the contribution to the conductivity is made by charge carriers excited into localized states in the band tails and by carriers of the delocalized states in the valence band.

  10. 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

  11. 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.

  12. Can conventional phase-change memory devices be scaled down to single-nanometre dimensions?

    NASA Astrophysics Data System (ADS)

    Hayat, Hasan; Kohary, Krisztian; Wright, C. David

    2017-01-01

    The scaling potential of ‘mushroom-type’ phase-change memory devices is evaluated, down to single-nanometre dimensions, using physically realistic simulations that combine electro-thermal modelling with a Gillespie Cellular Automata phase-transformation approach. We found that cells with heater contact sizes as small as 6 nm could be successfully amorphized and re-crystallized (RESET and SET) using moderate excitation voltages. However, to enable the efficient formation of amorphous domes during RESET in small cells (heater contact diameters of 10 nm or less), it was necessary to improve the thermal confinement of the cell to reduce heat loss via the electrodes. The resistance window between the SET and RESET states decreased as the cell size reduced, but it was still more than an order of magnitude even for the smallest cells. As expected, the RESET current reduced as the cells got smaller; indeed, RESET current scaled with the inverse of the heater contact diameter and ultra-small RESET currents of only 19 μA were achieved for the smallest cells. Our results show that the conventional mushroom-type phase-change cell architecture is scalable and operable in the sub-10nm region.

  13. Sb7Te3/Ge multilayer films for low power and high speed phase-change memory

    NASA Astrophysics Data System (ADS)

    Chen, Shiyu; Wu, Weihua; Zhai, Jiwei; Song, Sannian; Song, Zhitang

    2017-06-01

    Phase-change memory has attracted enormous attention for its excellent properties as compared to flash memories due to their high speed, high density, better date retention and low power consumption. Here we present Sb7Te3/Ge multilayer films by using a magnetron sputtering method. The 10 years’ data retention temperature is significantly increased compared with pure Sb7Te3. When the annealing temperature is above 250 °C, the Sb7Te3/Ge multilayer thin films have better interface properties, which renders faster crystallization speed and high thermal stability. The decrease in density of ST/Ge multilayer films is only around 5%, which is very suitable for phase change materials. Moreover, the low RESET power benefits from high resistivity and better thermal stability in the PCM cells. This work demonstrates that the multilayer configuration thin films with tailored properties are beneficial for improving the stability and speed in phase change memory applications.

  14. 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.

  15. Optimization of J-V characteristic in diode array for phase change memory

    NASA Astrophysics Data System (ADS)

    Wang, Heng; Liu, Yan; Liu, Bo; Zhang, Chao; Song, Zhitang

    2016-10-01

    In this paper, current density-voltage (J-V) characteristic of dual trench diode array have been investigated by both TCAD model and experimental method. It is shown that the arsenic concentration in buried N+ layer (BNL), epitaxial (EPI) layer thickness, and the dosage of P region in PN junction are expected to be the prominent factors responsible for both of the leakage and drive current performance according to TCAD simulation. By introducing the optimal siliconbased results, the 4×4 diode arrays were successfully manufactured by 40nm CMOS technology. The median values of drive and reverse leakage current densities are 7.30×10-2 A/μm2 and 5.61×10-9 A/μm2, respectively. The breakdown voltages (BVDs) of diode array are exceeding 6V, and the Jon/Joff ratios of 109, which can satisfy the requirements of phase change memory (PCM) applications.

  16. 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

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

    SciTech Connect

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

    2014-04-28

    N doping is proposed to enlarge sensing margin of W{sub 0.08}(Sb{sub 2}Te){sub 0.92} based high-temperature phase-change memories (PCMs). The sensing margin is increased from 30 to 5 × 10{sup 3}, 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-W{sub 0.08}(Sb{sub 2}Te){sub 0.92} shows the fast operation speed of 30 ns and good cycling ability of >10{sup 3}. 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.

  18. Investigation on scalability of dual trench epitaxial diode for phase change memory

    NASA Astrophysics Data System (ADS)

    Wang, Heng; Liu, Bo; Liu, Yan; Zhang, Chao; Zhan, YiPeng; Xu, Zhen; Gao, Dan; Song, ZhiTang; Feng, Songlin

    2017-06-01

    In this paper, the scalability of dual trench epitaxial diode as the selector for phase change memory (PCM) has been analyzed. The 4 F2 diode with active area of 0.002916 μm2 has been fabricated using the standard 40 nm complementary metal oxide semiconductor process. The ratio of disturbance current between neighboring bit-lines (BLs) to drive current remains at average 2.0%. By introducing boron implantation into the device substrate, the punch-through voltage between neighboring word-lines (WLs) is larger than 6 V. Moreover, owing to the optimized P region in PN junction, the 4 F2 diode showed an excellent drive current of 431 μA. Finally, the resistances of 4/6.5/10/30 F2 diode array have been investigated, the series resistances of the buried N+ layer exhibited decreasing influence on drive current with the diode size scaling down.

  19. 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.

  20. Direct observation of nanometer-scale Joule and Peltier effects in phase change memory devices

    NASA Astrophysics Data System (ADS)

    Grosse, Kyle L.; Xiong, Feng; Hong, Sungduk; King, William P.; Pop, Eric

    2013-05-01

    We measure power dissipation in phase change memory (PCM) devices by scanning Joule expansion microscopy (SJEM) with ˜50 nm spatial and 0.2 K temperature resolution. The temperature rise in the Ge2Sb2Te5 (GST) is dominated by Joule heating, but at the GST-TiW contacts it is a combination of Peltier and current crowding effects. Comparison of SJEM and electrical measurements with simulations of the PCM devices uncovers a thermopower of ˜350 μV K-1 and a contact resistance of ˜2.0 × 10-8 Ω m2 (to TiW) for 25 nm thick films of face centered-cubic crystalline GST. Knowledge of such nanometer-scale Joule, Peltier, and current crowding effects is essential for energy-efficient design of future PCM technology.

  1. GeTe sequences in superlattice phase change memories and their electrical characteristics

    SciTech Connect

    Ohyanagi, T. Kitamura, M.; Takaura, N.; Araidai, M.; Kato, S.; Shiraishi, K.

    2014-06-23

    We studied GeTe structures in superlattice phase change memories (superlattice PCMs) with a [GeTe/Sb{sub 2}Te{sub 3}] stacked structure by X-ray diffraction (XRD) analysis. We examined the electrical characteristics of superlattice PCMs with films deposited at different temperatures. It was found that XRD spectra differed between the films deposited at 200 °C and 240 °C; the differences corresponded to the differences in the GeTe sequences in the films. We applied first-principles calculations to calculate the total energy of three different GeTe sequences. The results showed the Ge-Te-Ge-Te sequence had the lowest total energy of the three and it was found that with this sequence the superlattice PCMs did not run.

  2. Extracting the temperature distribution on a phase-change memory cell during crystallization

    NASA Astrophysics Data System (ADS)

    Bakan, Gokhan; Gerislioglu, Burak; Dirisaglik, Faruk; Jurado, Zoila; Sullivan, Lindsay; Dana, Aykutlu; Lam, Chung; Gokirmak, Ali; Silva, Helena

    2016-10-01

    Phase-change memory (PCM) devices are enabled by amorphization- and crystallization-induced changes in the devices' electrical resistances. Amorphization is achieved by melting and quenching the active volume using short duration electrical pulses (˜ns). The crystallization (set) pulse duration, however, is much longer and depends on the cell temperature reached during the pulse. Hence, the temperature-dependent crystallization process of the phase-change materials at the device level has to be well characterized to achieve fast PCM operations. A main challenge is determining the cell temperature during crystallization. Here, we report extraction of the temperature distribution on a lateral PCM cell during a set pulse using measured voltage-current characteristics and thermal modelling. The effect of the thermal properties of materials on the extracted cell temperature is also studied, and a better cell design is proposed for more accurate temperature extraction. The demonstrated study provides promising results for characterization of the temperature-dependent crystallization process within a cell.

  3. 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.

  4. Study of phase change technology for computer memory using Se70Te30-xAgx system

    NASA Astrophysics Data System (ADS)

    Kumar, A.; Agarwal, Pragya; Saxena, Abhay

    2013-06-01

    The phase change memory is the revolutionary technology for computer world today. Phase change memory alloy is composed of chalcogenide glasses. In the present work Ag is doped in binary Se70Te30 system and activation energy of crystallization is calculated. These ternary alloys are explored in various fields like photo doping, optical imaging, and phase change optical recording. The crystallization kinetics of various ternary Se70Te30-xAgx(x = 0,2,4,6) alloys are studied by using Non-isothermal Iso-Conversional methods. The dependence of activation energy Ec is discussed by various methods. The result shows that the activation energy Ec plays a vital role in proving these materials as best applicable materials in optical phase change recording devices.

  5. 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.

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

    SciTech Connect

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

    2016-01-14

    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 Ge{sub 2}Sb{sub 2}Te{sub 5} 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.

  7. 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.

  8. Feasibility study of current pulse induced 2-bit/4-state multilevel programming in phase-change memory

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Fan, Xi; Chen, Houpeng; Wang, Yueqing; Liu, Bo; Song, Zhitang; Feng, Songlin

    2017-08-01

    In this brief, multilevel data storage for phase-change memory (PCM) has attracted more attention in the memory market to implement high capacity memory system and reduce cost-per-bit. In this work, we present a universal programing method of SET stair-case current pulse in PCM cells, which can exploit the optimum programing scheme to achieve 2-bit/ 4state resistance-level with equal logarithm interval. SET stair-case waveform can be optimized by TCAD real time simulation to realize multilevel data storage efficiently in an arbitrary phase change material. Experimental results from 1 k-bit PCM test-chip have validated the proposed multilevel programing scheme. This multilevel programming scheme has improved the information storage density, robustness of resistance-level, energy efficient and avoiding process complexity.

  9. Suppression of thermoelectric Thomson effect in silicon microwires under large electrical bias and implications for phase-change memory devices

    NASA Astrophysics Data System (ADS)

    Bakan, Gokhan; Gokirmak, Ali; Silva, Helena

    2014-12-01

    We have observed how thermoelectric effects that result in asymmetric melting of silicon wires are suppressed for increasing electric current density (J). The experimental results are investigated using numerical modeling of the self-heating process, which elucidates the relative contributions of the asymmetric thermoelectric Thomson heat (˜J) and symmetric Joule heating (˜J2) that lead to symmetric heating for higher current levels. These results are applied in modeling of the self-heating process in phase-change memory devices. While, phase-change memory devices show a clearly preferred operation polarity due to thermoelectric effects, nearly symmetric operation can be achieved with higher amplitude and shorter current pulses, which can lead to design of improved polarity-invariant memory circuitry.

  10. Investigation and solution of low yield problem for phase change memory with lateral fully-confined structure

    NASA Astrophysics Data System (ADS)

    Yaling, Zhou; Xiaofeng, Wang; Yingchun, Fu; Xiaodong, Wang; Fuhua, Yang

    2016-08-01

    This paper mainly focuses on solving the low yield problem for lateral phase change random access memory with a fully confined phase change material node. Improper over-etching and bad step-coverage of physical vapor deposition were the main reasons for the poor contact quality, which leads to the low yield problem. Process improvement was carried out to better control over-etching within 10 nm. Atomic layer deposition process was used to replace physical vapor deposition to guarantee good step coverage. Contrasting cross-sectional photos taken by scanning electron microscopy showed great improvement in contact quality. The atom layer deposition process was demonstrated to have good prospects in nano-contact for phase change memory application. Project supported by the National Basic Research Program of China (No. 2011CB922103), the National Natural Science Foundation of China (Nos. 61376420, 61404126, A040203), and the Science and Technology Project of Shenzhen (No. JCYJ20140509172609175).

  11. Investigation of data retention under current bias for phase change memory

    NASA Astrophysics Data System (ADS)

    Lu, Yao-Yao; Cai, Dao-Lin; Chen, Yi-Feng; Wang, Yue-Qing; Wei, Hong-Yang; Huo, Ru-Ru; Song, Zhi-Tang

    2016-10-01

    With Phase-change memory (PCM), information can be stored as different resistance states even when not powered. In order to accurately characterize the reliability of PCM devices, data retention has to be tested carefully. In this paper, a new test method is applied to measure the data retention of T-shaped PCM devices. This method makes it possible to accelerate crystallization in the amorphous area by using current bias. The new method works based on the field-induced crystallization theory, and could be able to gather fast and detailed information about high-resistance state's failure process, and at the same time, it could avoid issues related to high temperature. Experimental data for T-shaped PCM devices based on Ge2Sb2Te5 are presented and analyzed. An exponential trend-line of failure time t versus reciprocal bias current 1/I shows only negligible deviation of the measured data points, enabling the extrapolation of the retention behavior for ten-year lifetime. A maximum disturb current value of 5.08 μA is extracted to guarantee the ten years data retention requirement for PCM applications.

  12. Avalanche atomic switching in strain engineered Sb2Te3–GeTe interfacial phase-change memory cells

    NASA Astrophysics Data System (ADS)

    Zhou, Xilin; Behera, Jitendra K.; Lv, Shilong; Wu, Liangcai; Song, Zhitang; Simpson, Robert E.

    2017-09-01

    By confining phase transitions to the nanoscale interface between two different crystals, interfacial phase change memory heterostructures represent the state of the art for energy efficient data storage. We present the effect of strain engineering on the electrical switching performance of the {{Sb}}2{{Te}}3–GeTe superlattice van der Waals devices. Multiple Ge atoms switching through a two-dimensional Te layer reduces the activation barrier for further atoms to switch; an effect that can be enhanced by biaxial strain. The out-of-plane phonon mode of the GeTe crystal remains active in the superlattice heterostructures. The large in-plane biaxial strain imposed by the {{Sb}}2{{Te}}3 layers on the GeTe layers substantially improves the switching speed, reset energy, and cyclability of the superlattice memory devices. Moreover, carefully controlling residual stress in the layers of {{Sb}}2{{Te}}3–GeTe interfacial phase change memories provides a new degree of freedom to design the properties of functional superlattice structures for memory and photonics applications.

  13. 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.

  14. Role of mechanical stress in the resistance drift of Ge2Sb2Te5 films and phase change memories

    NASA Astrophysics Data System (ADS)

    Rizzi, M.; Spessot, A.; Fantini, P.; Ielmini, D.

    2011-11-01

    In a phase change memory (PCM), the device resistance increases slowly with time after the formation of the amorphous phase, thus affecting the stability of stored data. This work investigates the resistance drift in thin films of amorphous Ge2Sb2Te5 and in PCMs, demonstrating a common kinetic of drift in stressed/unstressed films and in the nanometer-size active volume of a PCM with different stress levels developed via stressor layers. It is concluded that stress is not the root cause of PCM drift, which is instead attributed to intrinsic structural relaxation due to the disordered, metastable nature of the amorphous chalcogenide phase.

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

    SciTech Connect

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

    2016-07-07

    In this work, we investigate the temperature-dependent thermal conductivities of few nanometer thick alternating stacks of amorphous dielectrics, specifically SiO{sub 2}/Al{sub 2}O{sub 3} and SiO{sub 2}/Si{sub 3}N{sub 4}. 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 SiO{sub 2}/Si{sub 3}N{sub 4} and SiO{sub 2}/Al{sub 2}O{sub 3} exhibit through-plane room temperature effective thermal conductivities of about 1.14 and 0.48 W/(m × K), respectively. In the case of SiO{sub 2}/Al{sub 2}O{sub 3}, the reduced conductivity is attributed to lowered film density (7.03 → 5.44 × 10{sup 28 }m{sup –3} for SiO{sub 2} and 10.2 → 8.27 × 10{sup 28 }m{sup –3} for Al{sub 2}O{sub 3}) caused by atomic layer deposition of thin-films as well as a small, finite, and repeating thermal boundary resistance (TBR) of 1.5 m{sup 2} 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.

  16. 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.

  17. 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.

  18. Te-free environmental materials of TixSb2.19Se applied in phase change memory

    NASA Astrophysics Data System (ADS)

    Zhu, Yueqin; Song, Sannian; Li, Le; Xie, Huaqing; Song, Zhitang; Liu, Bo; Wu, Junxing

    2016-10-01

    Environmental friendly Te-free phase change material of TixSb2.19Se was investigated for PCM application. As the important thermal properties, the crystallization temperature (Tc) and data retention for ten years for the best selected composition Ti0.34Sb2.19Se (TSS) are 234°C and 160‡C, respectively. Detection of the crystal structure of TSS by means of XRD, TEM and XPS reveals that the grains are more uniform compared with Ge2Sb2Te5 (GST). The Set and Reset operation voltages for TSS-based phase change memory devices are much lower than those of conventional GST-based ones. Remarkably, the TSS device exhibits an extremely high phase change speed of 10 ns.

  19. 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.

  20. Towards Multiple-Bit-Per-Cell Operation In a Single Active Layer-Phase Change Memory Cell

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    High contrast between 0 and 1 logic states in addition to other superior properties of phase change memory (PCM) brought out the possible application of multiple logic levels in a single bit in an effort to boost data storage density. The potential stabilization of resistance levels in between the 0 polycrystalline and 1 amorphous states enables storage of several data in a single device cell (such as 00, 01,10,11 levels). Here we report our investigation of the role of contact geometry and fabrication induced modification of phase change kinetics in stabilizing mixed phase states in an effort to obtain such multiple-bit per cell operation within a single layer PCM material system (Ge2Sb2Te5) . The nature of switching dynamics appears highly sensitive to exact programming current distribution and defect density such that a nanoscale square contact with effective current localization at the sharp corners facilitates the formation of stable intermediate phases as compared to a circular one. Resistance maps show that the top contact geometry and engineering of defects can be used as an effective handle to tune the resistance states to optimize memory cells for ultra-high density storage. This work has been supported by the European Commission FP7 Marie Curie IRG grant: PCM-256281.

  1. 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.

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

    PubMed

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

    2015-07-08

    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.

  3. 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.

  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. © The Author 2015. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  5. Phase Change

    NASA Technical Reports Server (NTRS)

    Hasan, Mohammad M.

    2004-01-01

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

  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. Threshold switching via electric field induced crystallization in phase-change memory devices

    NASA Astrophysics Data System (ADS)

    Vázquez Diosdado, Jorge A.; Ashwin, Peter; Kohary, Krisztian I.; Wright, C. David

    2012-06-01

    Phase-change devices exhibit characteristic threshold switching from the reset (off) to the set (on) state. Mainstream understanding of this electrical switching phenomenon is that it is initiated electronically via the influence of high electric fields on inter-band trap states in the amorphous phase. However, recent work has suggested that field induced (crystal) nucleation could instead be responsible. We compare and contrast these alternative switching "theories" via realistic simulations of device switching both with and without electric field dependent contributions to the system free energy. Results show that although threshold switching can indeed be obtained purely by electric field induced nucleation, the fields required are significantly larger than experimentally measured values.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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).

  13. Low power phase change memory switching of ultra-thin In3Sb1Te2 nanowires

    NASA Astrophysics Data System (ADS)

    Selmo, S.; Cecchini, R.; Cecchi, S.; Wiemer, C.; Fanciulli, M.; Rotunno, E.; Lazzarini, L.; Rigato, M.; Pogany, D.; Lugstein, A.; Longo, M.

    2016-11-01

    We report on the fabrication and electrical characterization of phase change memory (PCM) devices formed by In3Sb1Te2 chalcogenide nanowires (NWs), with diameters as small as 20 nm. The NWs were self-assembled by metal organic chemical vapor deposition via the vapor-liquid-solid method, catalyzed by Au nanoparticles. Reversible and well reproducible memory switching of the NWs between low and high resistance states was demonstrated. The conduction mechanism of the high resistance state was investigated according to a trap-limited model for electrical transport in the amorphous phase. The size of the amorphized portion of the NW and the critical electric field for the transition to the low resistance state were evaluated. The In3Sb1Te2 NW-based devices showed very low working parameters, such as RESET voltage (˜3 V), current (˜40 μA), and power (˜130 μW). Our results indicated that the studied NWs are suitable candidates for the realization of ultra-scaled, high performance PCM devices.

  14. Epitaxy of Ge-Sb-Te phase-change memory alloys

    SciTech Connect

    Braun, Wolfgang; Shayduk, Roman; Flissikowski, Timur; Ramsteiner, Manfred; Grahn, Holger T.; Riechert, Henning; Fons, Paul; Kolobov, Alex

    2009-01-26

    The authors demonstrate the epitaxy of Ge-Sb-Te alloys close to the Ge{sub 2}Sb{sub 2}Te{sub 5} composition on GaSb(001). Using molecular beam epitaxy with elemental sources, amorphous films are obtained at growth temperatures below 120 deg. C and films with a cubic structure and a predominant cube-on-cube epitaxial relationship above 180 deg. C. Using a high-power pulsed laser, the epitaxial films are switched between the crystalline and the amorphous phases. Streaks in the diffraction data help to resolve the apparent ambiguity in interatomic distances between earlier x-ray absorption and powder diffraction measurements. The structural changes are confirmed by Raman spectroscopy.

  15. 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.

  16. 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.

  17. Improved stability of a phase change memory device using Ge-doped SbTe at varying ambient temperature

    NASA Astrophysics Data System (ADS)

    Wu, Zhe; Lee, Suyoun; Park, Young-Wook; Ahn, Hyung-Woo; Jeong, Doo Seok; Jeong, Jeung-hyun; No, Kwangsoo; Cheong, Byung-ki

    2010-03-01

    Ge-doped SbTe (Ge-ST) was compared with Ge2Sb2Te5 (GST) for its potential use in the phase-change memory with improved stability at varying ambient temperature (TA). Device characteristics such as RESET current, RESET resistance, and SET resistance of Ge-ST devices were found to vary significantly less with TA than those of GST devices. From measured carrier density, mobility, and optical band gaps, these findings are interpreted to derive from a metallic nature of the crystalline Ge-ST in contrast with a semiconducting nature of the crystalline GST as well as a relatively weaker covalent bonding in amorphous Ge-ST.

  18. Phase change memory cell using Ge2Sb2Te5 and softly broken-down TiO2 films for multilevel operation

    NASA Astrophysics Data System (ADS)

    Choi, Byung Joon; Choi, Seol; Eom, Taeyong; Rha, Sang Ho; Kim, Kyung Min; Hwang, Cheol Seong

    2010-09-01

    A phase change memory cell was fabricated by stacking plasma-enhanced cyclic chemical-vapor-deposited Ge2Sb2Te5 (GST) and atomic layer deposited TiO2 thin films. Different pairs of resistance states were obtained by controlling the current flow, which can be used to achieve higher memory density by multilevel operation. The multiresistance states of the stacked cell were explained by the resistance switching phenomena of TiO2 and the thermoelectric phase change properties of GST. The phase change characteristics of GST could be altered by controlling the degree of filament formation in the TiO2 layer, which eventually changed the phase change volume in the GST.

  19. 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).

  20. Schottky-barrier diode array fabrication with self-aligned Ni silicidation for low power phase-change memory application

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Song, Zhitang; Liu, Bo; Chen, Houpeng; Wu, Guangping; Zhang, Chao; Wang, Lianhong; Wang, Lei; Feng, Songlin

    A high density design of Schottky-barrier diode array with self-aligned nickel-silicidation under 40nm technology node fabricated on epitaxial layer for low power phase-change memory application is proposed. According to N-type doping profile from simulation, large ON/OFF current ratio, the lower barrier height of ФB and series resistance RS are all determined by the dosage of buried N+ layer, epitaxial layer thickness. In addition, the temperature effect of the Schottky diode array is demonstrated by I-V electrical characteristics. From the optimal silicon-based results, a 9F2 16 × 16 diode array with the ideality factor of 1.21~1.40 shows a drive current density of ~14.9 mA/μm2, a Jon/Joff ratio of ~5.17×103, and crosstalk immunity. Furthermore, this calibrated physical model makes it possible to predict and improve the performance of accessing device array next generation for non-volatile memory application.

  1. 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.

  2. 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.

  3. Forming operation in Ge-rich GexSbyTez phase change memories

    NASA Astrophysics Data System (ADS)

    Palumbo, Elisabetta; Zuliani, Paola; Borghi, Massimo; Annunziata, Roberto

    2017-07-01

    Optimized Ge-rich GexSbyTez materials with improved crystallization temperature have been proven to guarantee code integrity after soldering thermal profile and data retention in extended temperature range for automotive application. Together with higher crystallization temperature, these materials show also peculiar characteristics of the crystalline state with respect to conventional GST (Ge2Sb2Te5). In particular integrated memory cell shows a very high virgin resistance and needs an electrical activation as last operation of the fabrication process. In this paper we investigate for the first time the role of this electrical activation we named forming operation. In particular we show that the level of the maximum current flowing into the cell at the first electrical activation (forming level) has an impact on cell programmability. An explanation of this behavior based on physical analysis is provided suggesting that it is related to the modulation of cell thermal efficiency. Finally it is shown how forming level can be used in order to optimize cell reliability with respect to requested specifications for high temperature data retention (HTDR) and endurance.

  4. 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.

  5. Addition of HfO2 interface layer for improved synaptic performance of phase change memory (PCM) devices

    NASA Astrophysics Data System (ADS)

    Suri, M.; Bichler, O.; Hubert, Q.; Perniola, L.; Sousa, V.; Jahan, C.; Vuillaume, D.; Gamrat, C.; DeSalvo, B.

    2013-01-01

    In this work, we will focus on the use of phase change memory (PCM) to emulate synaptic behavior in emerging neuromorphic system-architectures. In particular, we will show that the performance and energy-efficiency of large scale neuromorphic systems can be improved by engineering individual PCM devices used as synapses. This is obtained by adding a thin HfO2 interface layer to standard GST PCM devices, allowing for the lowering of the Set/Reset currents and the increase of the number of intermediate resistance states (or synaptic weights) in the synaptic potentiation characteristics. The experimentally obtained potentiation characteristics of such PCM devices are used to simulate a 2-layer ultra-dense spiking neural network (SNN) and to perform a complex visual pattern extraction from a test case based on real world data (i.e. cars passing on a 6-lane freeway). The total power dissipated in the learning mode, for the pattern extraction experiment is estimated to be as low as 60 μW. Average detection rate of cars is found to be greater than 90%.

  6. Influence of silicon oxide on the performance of TiN bottom electrode in phase change memory

    NASA Astrophysics Data System (ADS)

    Gao, Dan; Liu, Bo; Xu, Zhen; Wang, Heng; Xia, Yangyang; Wang, Lei; Zhu, Nanfei; Li, Ying; Zhan, Yipeng; Song, Zhitang; Feng, Songlin

    2016-10-01

    The stability of TiN which is the preferred bottom electrode contact (BEC) of phase change memory (PCM) due to its low thermal conductivity and suitable electrical conductivity, is very essential to the reliability of PCM devices. In this work, in order to investigate the effect of high aspect ratio process (HARP) SiO2 on the performance of TiN, both TiN/SiO2, TiN/SiN thin films and TiN BEC device structures are analyzed. By combining transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS), we found that the TiN would be oxidized after the deposition of HARP SiO2 and there exist a thin ( 4 nm) oxidation interfacial layer between TiN and SiO2. Electrical measurements were performed on the 1R PCM test-key die with 7 nm and 10 nm BEC-only cells. The statistical initial resistances of BEC have wide distribution and it is confirmed that the non-uniform oxidation of TiN BEC affects the astringency of the resistance of TiN BEC. The experimental results help to optimize the process of TiN BEC, and SiN is recommended as a better choice as the linear layer.

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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-1. This technique could facilitate improved measurements of thermoelectric phenomena and properties at the nanometer-scale.

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

    PubMed

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

    2014-09-01

    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(-1). This technique could facilitate improved measurements of thermoelectric phenomena and properties at the nanometer-scale.

  11. 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).

  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. 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.

  14. Investigation of thermal resistance and power consumption in Ga-doped indium oxide (In{sub 2}O{sub 3}) nanowire phase change random access memory

    SciTech Connect

    Jin, Bo; Lee, Jeong-Soo E-mail: ljs6951@postech.ac.kr; Lim, Taekyung; Ju, Sanghyun; Latypov, Marat I.; Pi, Dong-Hai; Seop Kim, Hyoung; Meyyappan, M. E-mail: ljs6951@postech.ac.kr

    2014-03-10

    The resistance stability and thermal resistance of phase change memory devices using ∼40 nm diameter Ga-doped In{sub 2}O{sub 3} nanowires (Ga:In{sub 2}O{sub 3} NW) with different Ga-doping concentrations have been investigated. The estimated resistance stability (R(t)/R{sub 0} ratio) improves with higher Ga concentration and is dependent on annealing temperature. The extracted thermal resistance (R{sub th}) increases with higher Ga-concentration and thus the power consumption can be reduced by ∼90% for the 11.5% Ga:In{sub 2}O{sub 3} NW, compared to the 2.1% Ga:In{sub 2}O{sub 3} NW. The excellent characteristics of Ga-doped In{sub 2}O{sub 3} nanowire devices offer an avenue to develop low power and reliable phase change random access memory applications.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Fast switching and low power of superlattice-like SnSe2/Sb thin films for phase change memory application

    NASA Astrophysics Data System (ADS)

    Wu, Weihua; He, Zifang; Chen, Shiyu; Zhai, Jiwei; Liu, Xinyi; Lai, Tianshu; Song, Sannian; Song, Zhitang

    2016-10-01

    Two non-promising phase change materials (SnSe2 and Sb) were prepared through the superlattice-like (SLL) method to explore the suitable phase change layer for phase change memory (PCM) application. The crystallization temperature, activation energy, and 10-year data retention of the SLL [SnSe2(10 nm)/Sb(2 nm)]4 ([SS(10)/S(2)]4) thin film are 185 °C, 3.03 eV, and 116 °C, respectively. The volume change of the SLL [SS(10)/S(2)]4 thin film during the crystallization is as small as 3.5%. The phase transition speed of the SLL [SS(10)/S(2)]4 thin film for crystallization is only about 11.9 ns. PCM cell based on the SLL [SS(10)/S(2)]4 thin film shows high operation speed (20 ns for SET/RESET) and lower power consumption (2.75 × 10-11 J for RESET operation).

  3. 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.

  4. Redefining the Speed Limit of Phase Change Memory Revealed by Time-resolved Steep Threshold-Switching Dynamics of AgInSbTe Devices

    PubMed Central

    Shukla, Krishna Dayal; Saxena, Nishant; Durai, Suresh; Manivannan, Anbarasu

    2016-01-01

    Although phase-change memory (PCM) offers promising features for a ‘universal memory’ owing to high-speed and non-volatility, achieving fast electrical switching remains a key challenge. In this work, a correlation between the rate of applied voltage and the dynamics of threshold-switching is investigated at picosecond-timescale. A distinct characteristic feature of enabling a rapid threshold-switching at a critical voltage known as the threshold voltage as validated by an instantaneous response of steep current rise from an amorphous off to on state is achieved within 250 picoseconds and this is followed by a slower current rise leading to crystallization. Also, we demonstrate that the extraordinary nature of threshold-switching dynamics in AgInSbTe cells is independent to the rate of applied voltage unlike other chalcogenide-based phase change materials exhibiting the voltage dependent transient switching characteristics. Furthermore, numerical solutions of time-dependent conduction process validate the experimental results, which reveal the electronic nature of threshold-switching. These findings of steep threshold-switching of ‘sub-50 ps delay time’, opens up a new way for achieving high-speed non-volatile memory for mainstream computing. PMID:27886266

  5. Redefining the Speed Limit of Phase Change Memory Revealed by Time-resolved Steep Threshold-Switching Dynamics of AgInSbTe Devices

    NASA Astrophysics Data System (ADS)

    Shukla, Krishna Dayal; Saxena, Nishant; Durai, Suresh; Manivannan, Anbarasu

    2016-11-01

    Although phase-change memory (PCM) offers promising features for a ‘universal memory’ owing to high-speed and non-volatility, achieving fast electrical switching remains a key challenge. In this work, a correlation between the rate of applied voltage and the dynamics of threshold-switching is investigated at picosecond-timescale. A distinct characteristic feature of enabling a rapid threshold-switching at a critical voltage known as the threshold voltage as validated by an instantaneous response of steep current rise from an amorphous off to on state is achieved within 250 picoseconds and this is followed by a slower current rise leading to crystallization. Also, we demonstrate that the extraordinary nature of threshold-switching dynamics in AgInSbTe cells is independent to the rate of applied voltage unlike other chalcogenide-based phase change materials exhibiting the voltage dependent transient switching characteristics. Furthermore, numerical solutions of time-dependent conduction process validate the experimental results, which reveal the electronic nature of threshold-switching. These findings of steep threshold-switching of ‘sub-50 ps delay time’, opens up a new way for achieving high-speed non-volatile memory for mainstream computing.

  6. 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.

  7. 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.

  8. Effect of Dielectric Material Films on Crystallization Characteristics of Ge2Sb2Te5 Phase-Change Memory Film

    NASA Astrophysics Data System (ADS)

    Nishiuchi, Kenichi; Yamada, Noboru; Kawahara, Katsumi; Kojima, Rie

    2007-11-01

    Reduction of the film thickness of phase-change film and the adoption of GeN- or ZrO2-based dielectric films are both effective in achieving good thermal stability in phase-change optical disks. It was experimentally confirmed that, at a heating rate of 10 °C/min, the crystallization temperature Tx of the Ge2Sb2Te5 amorphous film when sandwiched by ZnS-SiO2 films markedly increases from 162 to 197 °C, while the thickness of the Ge2Sb2Te5 film decreases from 10 to 3 nm. Tx also slightly increases when ZnS-SiO2 films are substituted for GeN-based films (from 162 to 165 °C) and ZrO2-based films (from 162 to 167 °C). At the same time, the activation energy of crystallization is 2.4 eV for both GeN- and ZrO2-based films, and is higher than 2.2 eV for ZnS-SiO2 films.

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

    NASA Astrophysics Data System (ADS)

    Skelton, J. M.; Elliott, S. R.

    2013-05-01

    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.

  10. 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.

  11. 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.

  12. 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 ...

  13. 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.

  14. 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.

  15. 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)

  16. 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)

  17. Simulation of phase-change random access memory with 35nm diameter of the TiN bottom electrode by finite element modeling

    NASA Astrophysics Data System (ADS)

    Jin, Qiuxue; Liu, Bo; Liu, Yan; Wang, Heng; Xu, Zhen; Gao, Dan; Wang, Qing; Xia, Yangyang; Wang, Weiwei; Song, Zhitang; Feng, Songlin

    2016-10-01

    A three-dimensional finite element model for Phase-Change Random Access Memory (PCRAM) is established to simulate thermal and electrical distribution during RESET operation. The establishment of the model is highly in accordance with the manufacture of PCRAM cell in the 40nm process and the model is applied to simulate the RESET behaviors of 35 nm diameter of titanium nitride (TiN) bottom electrode in the conventional mushroom structure (MS). By the simulations of thermal and electrical distribution, the highest temperature is observed in TiN bottom electrode contactor and meanwhile the voltage of the TiN bottom electrode accounts for as high as 65 percent of the total voltage. It induces high RESET current which suggests that the thermoelectric conductivity of MS is crucial in improving the heating efficiency in RESET process. Simulation results of RESET current and high resistance distribution during RESET operation are close to the data from the actual measurement. However those two values of low resistance are slightly different, probably due to the interface resistance between Ge2Sb2Te5 (GST) and other materials and the resistance caused by microstructural defects. This work reveals the importance of the thermoelectrical properties of materials in PCRAM cells and improves the quality of PCRAM simulations in industrial application.

  18. A weak electric field-assisted ultrafast electrical switching dynamics in In3SbTe2 phase-change memory devices

    NASA Astrophysics Data System (ADS)

    Pandey, Shivendra Kumar; Manivannan, Anbarasu

    2017-07-01

    Prefixing a weak electric field (incubation) might enhance the crystallization speed via pre-structural ordering and thereby achieving faster programming of phase change memory (PCM) devices. We employed a weak electric field, equivalent to a constant small voltage (that is incubation voltage, Vi of 0.3 V) to the applied voltage pulse, VA (main pulse) for a systematic understanding of voltage-dependent rapid threshold switching characteristics and crystallization (set) process of In3SbTe2 (IST) PCM devices. Our experimental results on incubation-assisted switching elucidate strikingly one order faster threshold switching, with an extremely small delay time, td of 300 ps, as compared with no incubation voltage (Vi = 0 V) for the same VA. Also, the voltage dependent characteristics of incubation-assisted switching dynamics confirm that the initiation of threshold switching occurs at a lower voltage of 0.82 times of VA. Furthermore, we demonstrate an incubation assisted ultrafast set process of IST device for a low VA of 1.7 V (˜18 % lesser compared to without incubation) within a short pulse-width of 1.5 ns (full width half maximum, FWHM). These findings of ultrafast switching, yet low power set process would immensely be helpful towards designing high speed PCM devices with low power operation.

  19. Memory strength versus memory variability in visual change detection.

    PubMed

    Nosofsky, Robert M; Gold, Jason

    2016-01-01

    Observers made change-detection judgments for colored squares in a paradigm that manipulated the retention interval, the magnitude of change, and objective change probability. The probability of change judgments increased across the retention interval for “same” and “small-change” test items but stayed the same or decreased for “large-change” and “far” test items. A variety of formal models were fitted to the individual-subject data. The modeling results provided evidence that, beyond changes in visual-memory precision, there were decreases in memory strength of individual study items across the retention interval. In addition, the modeling results provided evidence of a zero-information, absence-of-memory state that required guessing. The data were not sufficiently strong to sharply distinguish whether the losses in memory strength across the retention interval were continuous in nature or all-or-none. The authors argue that the construct of memory strength as distinct from memory variability is an important component of the nature of forgetting from visual working memory.

  20. 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…

  1. 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.

  2. 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.

  3. 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…

  4. Multi-level storage and ultra-high speed of superlattice-like Ge50Te50/Ge8Sb92 thin film for phase-change memory application

    NASA Astrophysics Data System (ADS)

    Wu, Weihua; Chen, Shiyu; Zhai, Jiwei; Liu, Xinyi; Lai, Tianshu; Song, Sannian; Song, Zhitang

    2017-10-01

    Superlattice-like Ge50Te50/Ge8Sb92 (SLL GT/GS) thin film was systematically investigated for multi-level storage and ultra-fast switching phase-change memory application. In situ resistance measurement indicates that SLL GT/GS thin film exhibits two distinct resistance steps with elevated temperature. The thermal stability of the amorphous state and intermediate state were evaluated with the Kissinger and Arrhenius plots. The phase-structure evolution revealed that the amorphous SLL GT/GS thin film crystallized into rhombohedral Sb phase first, then the rhombohedral GeTe phase. The microstructure, layered structure, and interface stability of SLL GT/GS thin film was confirmed by using transmission electron microscopy. The transition speed of crystallization and amorphization was measured by the picosecond laser pump-probe system. The volume variation during the crystallization was obtained from x-ray reflectivity. Phase-change memory (PCM) cells based on SLL GT/GS thin film were fabricated to verify the multi-level switching under an electrical pulse as short as 30 ns. These results illustrate that the SLL GT/GS thin film has great potentiality in high-density and high-speed PCM applications.

  5. Multi-level storage and ultra-high speed of superlattice-like Ge50Te50/Ge8Sb92 thin film for phase-change memory application.

    PubMed

    Wu, Weihua; Chen, Shiyu; Zhai, Jiwei; Liu, Xinyi; Lai, Tianshu; Song, Sannian; Song, Zhitang

    2017-10-06

    Superlattice-like Ge50Te50/Ge8Sb92 (SLL GT/GS) thin film was systematically investigated for multi-level storage and ultra-fast switching phase-change memory application. In situ resistance measurement indicates that SLL GT/GS thin film exhibits two distinct resistance steps with elevated temperature. The thermal stability of the amorphous state and intermediate state were evaluated with the Kissinger and Arrhenius plots. The phase-structure evolution revealed that the amorphous SLL GT/GS thin film crystallized into rhombohedral Sb phase first, then the rhombohedral GeTe phase. The microstructure, layered structure, and interface stability of SLL GT/GS thin film was confirmed by using transmission electron microscopy. The transition speed of crystallization and amorphization was measured by the picosecond laser pump-probe system. The volume variation during the crystallization was obtained from x-ray reflectivity. Phase-change memory (PCM) cells based on SLL GT/GS thin film were fabricated to verify the multi-level switching under an electrical pulse as short as 30 ns. These results illustrate that the SLL GT/GS thin film has great potentiality in high-density and high-speed PCM applications.

  6. 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

  7. 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.

  8. Stress-Induced Phase Transformations in Shape-Memory Polycrystals

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Kaushik; Schlömerkemper, Anja

    2010-06-01

    Shape-memory alloys undergo a solid-to-solid phase transformation involving a change of crystal structure. We examine model problems in the scalar setting motivated by the situation when this transformation is induced by the application of stress in a polycrystalline material made of numerous grains of the same crystalline solid with varying orientations. We show that the onset of transformation in a granular polycrystal with homogeneous elasticity is in fact predicted accurately by the so-called Sachs bound based on the ansatz of uniform stress. We also present a simple example where the onset of phase transformation is given by the Sachs bound, and the extent of phase transformation is given by the constant strain Taylor bound. Finally we discuss the stress-strain relations of the general problem using Milton-Serkov bounds.

  9. 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.

  10. 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.

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

    PubMed

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

    2013-09-11

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

  12. 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

  13. Phase Change Material Heat Exchangers

    NASA Image and Video Library

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

  14. Unpredictable visual changes cause temporal memory averaging.

    PubMed

    Ohyama, Junji; Watanabe, Katsumi

    2007-09-01

    Various factors influence the perceived timing of visual events. Yet, little is known about the ways in which transient visual stimuli affect the estimation of the timing of other visual events. In the present study, we examined how a sudden color change of an object would influence the remembered timing of another transient event. In each trial, subjects saw a green or red disk travel in circular motion. A visual flash (white frame) occurred at random times during the motion sequence. The color of the disk changed either at random times (unpredictable condition), at a fixed time relative to the motion sequence (predictable condition), or it did not change (no-change condition). The subjects' temporal memory of the visual flash in the predictable condition was as veridical as that in the no-change condition. In the unpredictable condition, however, the flash was reported to occur closer to the timing of the color change than actual timing. Thus, an unpredictable visual change distorts the temporal memory of another visual event such that the remembered moment of the event is closer to the timing of the unpredictable visual change.

  15. 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…

  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. 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.

  18. CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Simulation of SET Operation in Phase-Change Random Access Memories with Heater Addition and Ring-Type Contactor for Low-Power Consumption by Finite Element Modeling

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

    A three-dimensional finite element model for phase change random access memory (PCRAM) is established for comprehensive electrical and thermal analysis during SET operation. The SET behaviours of the heater addition structure (HS) and the ring-type contact in bottom electrode (RIB) structure are compared with each other. There are two ways to reduce the RESET current, applying a high resistivity interfacial layer and building a new device structure. The simulation results indicate that the variation of SET current with different power reduction ways is little. This study takes the RESET and SET operation current into consideration, showing that the RIB structure PCRAM cell is suitable for future devices with high heat efficiency and high-density, due to its high heat efficiency in RESET operation.

  19. Frontal GABA levels change during working memory.

    PubMed

    Michels, Lars; Martin, Ernst; Klaver, Peter; Edden, Richard; Zelaya, Fernando; Lythgoe, David J; Lüchinger, Rafael; Brandeis, Daniel; O'Gorman, Ruth L

    2012-01-01

    Functional neuroimaging metrics are thought to reflect changes in neurotransmitter flux, but changes in neurotransmitter levels have not been demonstrated in humans during a cognitive task, and the relationship between neurotransmitter dynamics and hemodynamic activity during cognition has not yet been established. We evaluate the concentration of the major inhibitory (GABA) and excitatory (glutamate + glutamine: Glx) neurotransmitters and the cerebral perfusion at rest and during a prolonged delayed match-to-sample working memory task. Resting GABA levels in the dorsolateral prefrontal cortex correlated positively with the resting perfusion and inversely with the change in perfusion during the task. Further, only GABA increased significantly during the first working memory run and then decreased continuously across subsequent task runs. The decrease of GABA over time was paralleled by a trend towards decreased reaction times and higher task accuracy. These results demonstrate a link between neurotransmitter dynamics and hemodynamic activity during working memory, indicating that functional neuroimaging metrics depend on the balance of excitation and inhibition required for cognitive processing.

  20. Critical behavior and magnetic entropy change at magnetic phase transitions in Ni50Mn35In14Si1 ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Das, R.; Alagarsamy, P.; Srinivasan, A.

    2014-12-01

    We have investigated critical behaviour and magnetocaloric effect in polycrystalline Ni50Mn35In14Si1 alloy near the second-order ferromagnetic phase transitions (SOPT) at austenite Curie temperature (TC,A) and at martensite Curie temperature (TC,M) by determining the critical exponents, β, γ and δ corresponding to the temperature dependence of spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively. The field dependence of the maximum value of the magnetic entropy change (Δ SM) at the two TC's was estimated using the Maxwell relation as well as from the values of the critical exponents. Values of Δ SM obtained by these two methods at both the SOPT are in remarkable agreement with each other. The critical exponents have been determined by analysing isothermal magnetization data using two different methods, viz., the modified Arrott plot method and the Widom scaling relation. The scaling plots depicted on linear as well as logarithmic scales confirm the reliability of the values of critical exponents obtained. The values of the critical exponents of polycrystalline Ni50Mn35In14Si1 alloy at both the TC's are close to those predicted by mean-field theory confirming the presence of long-range magnetic ordering in the investigated alloy.

  1. 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…

  2. 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…

  3. Dynamic Program Phase Detection in Distributed Shared-Memory Multiprocessors

    SciTech Connect

    Ipek, E; Martinez, J F; de Supinski, B R; McKee, S A; Schulz, M

    2006-03-06

    We present a novel hardware mechanism for dynamic program phase detection in distributed shared-memory (DSM) multiprocessors. We show that successful hardware mechanisms for phase detection in uniprocessors do not necessarily work well in DSM systems, since they lack the ability to incorporate the parallel application's global execution information and memory access behavior based on data distribution. We then propose a hardware extension to a well-known uniprocessor mechanism that significantly improves phase detection in the context of DSM multiprocessors. The resulting mechanism is modest in size and complexity, and is transparent to the parallel application.

  4. Modelling the phase diagram of magnetic shape memory Heusler alloys

    NASA Astrophysics Data System (ADS)

    Entel, P.; Buchelnikov, V. D.; Khovailo, V. V.; Zayak, A. T.; Adeagbo, W. A.; Gruner, M. E.; Herper, H. C.; Wassermann, E. F.

    2006-03-01

    We have modelled the phase diagram of magnetic shape memory alloys of the Heusler type by using the phenomenological Ginzburg-Landau theory. When fixing the parameters by realistic values taken from experiment we are able to reproduce most details of, for example, the phase diagram of Ni2+xMn1-xGa in the (T, x) plane. We present the results of ab initio calculations of the electronic and phonon properties of several ferromagnetic Heusler alloys, which allow one to characterize the structural changes associated with the martensitic instability leading to the modulated and tetragonal phases. From the ab initio investigations emerges a complex pattern of the interplay of magic valence electron per atom numbers (Hume-Rothery rules for magnetic ternary alloys), Fermi surface nesting and phonon instability. As the main result, we find that the driving force for structural transformations is considerably enhanced by the extremely low lying optical modes of Ni in the Ni-based Heusler alloys, which interfere with the acoustical modes enhancing phonon softening of the TA2 mode. In contrast, the ferromagnetic Co-based Heusler alloys show no tendency for phonon softening.

  5. Does Active Memory Capacity Change with Age?

    ERIC Educational Resources Information Center

    Halford, Graeme S.; And Others

    A series of experiments, which used the primary memory paradigm of Wickens et al. (1981, 1985) with university students, adults, and 8- and 9-year-old children, found an increase in primary memory capacity with age. Primary memory differs from secondary memory in that the latter is susceptible to proactive interference, whereas the former is not.…

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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…

  11. 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…

  12. Fully phase encrypted memory using cascaded extended fractional Fourier transform

    NASA Astrophysics Data System (ADS)

    Nishchal, Naveen K.; Joseph, Joby; Singh, Kehar

    2003-11-01

    In this paper, we implement a fully phase encrypted memory system using cascaded extended fractional Fourier transform (FRT). We encrypt and decrypt a two-dimensional image obtained from an amplitude image. The fully phase image to be encrypted is fractional Fourier transformed three times and random phase masks are placed in the two intermediate planes. Performing the FRT three times increases the key size, at an added complexity of one more lens. The encrypted image is holographically recorded in a photorefractive crystal and is then decrypted by generating through phase conjugation, conjugate of encrypted image. The decrypted phase image is converted into an amplitude image by using phase contrast technique. A lithium niobate crystal has been used as a phase contrast filter to reconstruct the phase image, alleviating the need of alignment in the Fourier plane, thereby making the system rugged.

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

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

    PubMed

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

    2017-12-01

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

  15. Vacancy-mediated three-center four-electron bonds in GeTe-Sb2Te3 phase-change memory alloys

    NASA Astrophysics Data System (ADS)

    Kolobov, Alexander V.; Fons, Paul; Tominaga, Junji; Ovshinsky, Stanford R.

    2013-04-01

    Although GeTe-Sb2Te3 (GST) alloys are widely used in data storage, many fundamental issues are still under debate. Here, we demonstrate that the presence of vacancies in the crystalline phase has far-reaching consequences, namely, a triad of twofold coordinated Te atoms with lone-pair electrons generated around the vacancy enables the formation of soft three-center four-electron bonds, whose properties provide an explanation for the unusual characteristics of GST, in particular, the increase in local disorder upon crystallization, the co-existence of a very fast switching rate with a large property contrast, the possibility of a solid-solid amorphization process that excludes conventional melting, and the drastic difference in crystallization behavior between GST and the ideal binary GeTe. Anisotropy of the three-center bonds may serve as an additional degree of freedom for information recording and provide a unified explanation for a variety of unique effects observed in lone-pair semiconductors.

  16. 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.

  17. 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.

  18. 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.

  19. Children's Views Concerning Phase Changes.

    ERIC Educational Resources Information Center

    Bar, Varda; Travis, Anthony S.

    1991-01-01

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

  20. Nanoscale martensitic phase transition at interfaces in shape memory materials

    NASA Astrophysics Data System (ADS)

    Dar, Rebecca D.; Chen, Ying

    2017-01-01

    In polycrystalline shape memory materials, mechanical interactions between martensitic transformation and grain boundaries at small scales play a critical role. Using a cobalt-based shape memory alloy, instrumented nanoindentation that probes nanoscale behavior reveals that grain boundary regions are resistant to transformation and have an adverse effect on shape memory possibly because an increase in strain energy outweighs reduction in interface energy. When grain boundaries are replaced by a thin, intergranular layer of a ductile and more malleable phase, grain boundary constraints are greatly alleviated, and transformation nearby can be well accommodated. Statistical analysis of results from a large number of nanoindents shows a decrease in shape recovery near grain boundaries and an increase in shape recovery near the new grain boundary phase, compared to grain interior. This is corroborated by analysis of nanoscale hardness and energy dissipation. Nanoscale martensitic transformation near interfaces depends largely on how the material across the interface accommodates transformation displacement. Engineering interfaces and enhancing local compatibility could drastically alter the energetics for phase transition at interfaces favorable for shape memory.

  1. Circadian phase and intertrial interval interfere with social recognition memory.

    PubMed

    Moura, Paula J; Gimenes-Júnior, João A; Valentinuzzi, Verónica S; Xavier, Gilberto F

    2009-01-08

    A modified version of the social habituation/dis-habituation paradigm was employed to examine social recognition memory in Wistar rats during two opposing (active and inactive) circadian phases, using different intertrial intervals (30 and 60 min). Wheel-running activity was monitored continuously to identify circadian phase. To avoid possible masking effects of the light-dark cycle, the rats were synchronized to a skeleton photoperiod, which allowed testing during different circadian phases under identical lighting conditions. In each trial, an infantile intruder was introduced into an adult's home-cage for a 5-minute interaction session, and social behaviors were registered. Rats were exposed to 5 trials per day for 4 consecutive days: on days 1 and 2, each resident was exposed to the same intruder; on days 3 and 4, each resident was exposed to a different intruder in each trial. The resident's social investigatory behavior was more intense when different intruders were presented compared to repeated presentation of the same intruder, suggesting social recognition memory. This effect was stronger when the rats were tested during the inactive phase and when the intertrial interval was 60 min. These findings suggest that social recognition memory, as evaluated in this modified habituation/dis-habituation paradigm, is influenced by the circadian rhythm phase during which testing is performed, and by intertrial interval.

  2. Superconducting phase domains for memory applications

    NASA Astrophysics Data System (ADS)

    Bakurskiy, S. V.; Klenov, N. V.; Soloviev, I. I.; Kupriyanov, M. Yu.; Golubov, A. A.

    2016-01-01

    In this work, we study theoretically the properties of S-F/N-sIS type Josephson junctions in the frame of the quasiclassical Usadel formalism. The structure consists of two superconducting electrodes (S), a tunnel barrier (I), a combined normal metal/ferromagnet (N/F) interlayer, and a thin superconducting film (s). We demonstrate the breakdown of a spatial uniformity of the superconducting order in the s-film and its decomposition into domains with a phase shift π. The effect is sensitive to the thickness of the s layer and the widths of the F and N films in the direction along the sIS interface. We predict the existence of a regime where the structure has two energy minima and can be switched between them by an electric current injected laterally into the structure. The state of the system can be non-destructively read by an electric current flowing across the junction.

  3. 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.

  4. 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

  5. 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.

  6. Operation cancellation at Chang Gung Memorial Hospital.

    PubMed

    Sung, Wei-Che; Chou, An-Hsun; Liao, Chia-Chih; Yang, Min-Wen; Chang, Chee-Jen

    2010-01-01

    Roughly 60,000 operations are performed at our medical center every year, so making efficient use of operating rooms (OR) is an important issue. Decreasing the cancellation rate of surgery is one method that could increase efficiency. We reviewed all OR cancellations in 2007 to survey the cancellation rates and causes. The present study was retrospective. Data were collected from the Department of Anesthesiology Quality Assurance Database of Chang Gung Memorial Hospital. We analyzed medical records for cancellations from January 1 to December 31, 2007. Data were analyzed using SPSS 16.0, employing descriptive measures and logistic regression. There were 61855 operations scheduled during this period; 229 were cancelled (0.37%). The mean age of patients in the cancelled group was significantly higher than that in the the non-cancelled group. We found a positive correlation between the cancellation rate and American Society of Anesthesiologists physical status. Cancellations for outpatient surgery were most frequent, as were those in the ophthalmology department. Forty-seven cases were cancelled because of cardiovascular problems; 136 operations were done later after the original cancellation issues were addressed while 11 were done under local anesthesia. Of all causes of cancellation of surgery, 54.1% were avoidable. Medical teams must communicate better with patients and relatives, identify and treat relevant comorbidities, and make adequate preparations for surgery.

  7. Sleep-induced changes in associative memory.

    PubMed

    Stickgold, R; Scott, L; Rittenhouse, C; Hobson, J A

    1999-03-01

    The notion that dreaming might alter the strength of associative links in memory was first proposed almost 200 years ago. But no strong evidence of such altered associative links has been obtained. Semantic priming can be used to quantify the strength of associative links between pairs of words; it is thought to measure the automatic spread of activation from a "node" representing one word to nodes representing semantically related words. Semantic priming could thus be used to test for global alterations in the strengths of associative links across the wake-sleep cycle. Awakenings from REM and nonREM (NREM) sleep produce a period of state carry-over during which performance is altered as a result of the brain's slow transition to full wakefulness, and cognitive testing in this period can provide information about the functioning of the brain during the prior sleep period. When subjects were tested across the night--before and after a night's sleep as well as immediately following forced awakenings from REM and NREM sleep--weak priming (e. g., thief-wrong) was found to be state dependent (p = 0.016), whereas strong priming (e.g., hot-cold) was not (p = 0.89). Weak primes were most effective in the presleep and REM sleep conditions and least effective in NREM and postsleep conditions. Most striking are analyses comparing weak and strong priming within each wake-sleep state. Contrary to the normal pattern of priming, subjects awakened from REM sleep showed greater priming by weak primes than by strong primes (p = 0.01). This result was seen in each of three protocols. In contrast, strong priming exceeded weak priming in NREM sleep. The shift in weak priming seen after REM sleep awakenings suggests that cognition during REM sleep is qualitatively different from that of waking and NREM sleep and may reflect a shift in associative memory systems, a shift that we hypothesize underlies the bizarre and hyperassociative character of REM-sleep dreaming. Known changes in

  8. On phase transformation behavior of porous Shape Memory Alloys.

    PubMed

    Liu, Bingfei; Dui, Guansuo; Zhu, Yuping

    2012-01-01

    This paper is concerned on the phase transformation mechanism of porous Shape Memory Alloys (SMAs). A unit-cell model is adopted to establish the constitutive relation for porous SMAs, the stress distributions, the phase distributions and the martensitic volume fractions for the model are then derived under both pure hydrostatic stress and uniaxial compression. Further, an example for the uniaxial response under compression for a porous Ni-Ti SMA material considering hydrostatic stress is supplied. Good agreement between the theoretical prediction of the proposed model and published experimental data is observed. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

  9. 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. Copyright © 2015 Elsevier Ltd. All rights reserved.

  10. Phase Change Fabrics Control Temperature

    NASA Technical Reports Server (NTRS)

    2009-01-01

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

  11. 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

  12. 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.

  13. Sleep promotes lasting changes in selective memory for emotional scenes

    PubMed Central

    Payne, Jessica D.; Chambers, Alexis M.; Kensinger, Elizabeth A.

    2012-01-01

    Although we know that emotional events enjoy a privileged status in our memories, we still have much to learn about how emotional memories are processed, stored, and how they change over time. Here we show a positive association between REM sleep and the selective consolidation of central, negative aspects of complex scenes. Moreover, we show that the placement of sleep is critical for this selective emotional memory benefit. When testing occurred 24 h post-encoding, subjects who slept soon after learning (24 h Sleep First group) had superior memory for emotional objects compared to subjects whose sleep was delayed for 16 h post-encoding following a full day of wakefulness (24 h Wake First group). However, this increase in memory for emotional objects corresponded with a decrease in memory for the neutral backgrounds on which these objects were placed. Furthermore, memory for emotional objects in the 24 h Sleep First group was comparable to performance after just a 12 h delay containing a night of sleep, suggesting that sleep soon after learning selectively stabilizes emotional memory. These results suggest that the sleeping brain preserves in long-term memory only what is emotionally salient and perhaps most adaptive to remember. PMID:23181013

  14. Sleep promotes lasting changes in selective memory for emotional scenes.

    PubMed

    Payne, Jessica D; Chambers, Alexis M; Kensinger, Elizabeth A

    2012-01-01

    Although we know that emotional events enjoy a privileged status in our memories, we still have much to learn about how emotional memories are processed, stored, and how they change over time. Here we show a positive association between REM sleep and the selective consolidation of central, negative aspects of complex scenes. Moreover, we show that the placement of sleep is critical for this selective emotional memory benefit. When testing occurred 24 h post-encoding, subjects who slept soon after learning (24 h Sleep First group) had superior memory for emotional objects compared to subjects whose sleep was delayed for 16 h post-encoding following a full day of wakefulness (24 h Wake First group). However, this increase in memory for emotional objects corresponded with a decrease in memory for the neutral backgrounds on which these objects were placed. Furthermore, memory for emotional objects in the 24 h Sleep First group was comparable to performance after just a 12 h delay containing a night of sleep, suggesting that sleep soon after learning selectively stabilizes emotional memory. These results suggest that the sleeping brain preserves in long-term memory only what is emotionally salient and perhaps most adaptive to remember.

  15. When lying changes memory for the truth.

    PubMed

    Otgaar, Henry; Baker, Alysha

    2017-06-22

    In the legal field, victims and offenders frequently lie to avoid talking about serious incidents, such as past experiences of sexual abuse or criminal involvement. Although these individuals may initially lie about an experienced event, oftentimes these same people eventually abandon their lies and are forthcoming with what truly happened. To date, it is unclear whether such lying affects later statements about one's memory for the experienced event. The impetus of the present review is to compile the current state of knowledge on the effects of lying on memory. Based on existing literature, we will describe how deceptive strategies (e.g., false denials) regarding what is remembered may affect memory in consequential ways, such as forgetting of details, falsely remembering features that were not present, or a combination of both. It will be argued that the current literature suggests that mnemonic outcome is contingent on the type of lie and we will propose a theoretical framework outlining which forms of lying likely result in certain memory outcomes. Potential avenues of future research also will be discussed.

  16. Pupil size changes during recognition memory.

    PubMed

    Otero, Samantha C; Weekes, Brendan S; Hutton, Samuel B

    2011-10-01

    Pupils dilate to a greater extent when participants view old compared to new items during recognition memory tests. We report three experiments investigating the cognitive processes associated with this pupil old/new effect. Using a remember/know procedure, we found that the effect occurred for old items that were both remembered and known at recognition, although it was attenuated for known compared to remembered items. In Experiment 2, the pupil old/new effect was observed when items were presented acoustically, suggesting the effect does not depend on low-level visual processes. The pupil old/new effect was also greater for items encoded under deep compared to shallow orienting instructions, suggesting it may reflect the strength of the underlying memory trace. Finally, the pupil old/new effect was also found when participants falsely recognized items as being old. We propose that pupils respond to a strength-of-memory signal and suggest that pupillometry provides a useful technique for exploring the underlying mechanisms of recognition memory.

  17. Dual origins of measured phase-amplitude coupling reveal distinct neural mechanisms underlying episodic memory in the human cortex.

    PubMed

    Vaz, Alex P; Yaffe, Robert B; Wittig, John H; Inati, Sara K; Zaghloul, Kareem A

    2017-03-01

    Phase-amplitude coupling (PAC) is hypothesized to coordinate neural activity, but its role in successful memory formation in the human cortex is unknown. Measures of PAC are difficult to interpret, however. Both increases and decreases in PAC have been linked to memory encoding, and PAC may arise due to different neural mechanisms. Here, we use a waveform analysis to examine PAC in the human cortex as participants with intracranial electrodes performed a paired associates memory task. We found that successful memory formation exhibited significant decreases in left temporal lobe and prefrontal cortical PAC, and these two regions exhibited changes in PAC within different frequency bands. Two underlying neural mechanisms, nested oscillations and sharp waveforms, were responsible for the changes in these regions. Our data therefore suggest that decreases in measured cortical PAC during episodic memory reflect two distinct underlying mechanisms that are anatomically segregated in the human brain.

  18. 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…

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

    PubMed

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

    2014-06-11

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

  20. 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

  1. Hippocampal Binding of Novel Information with Dominant Memory Traces Can Support Both Memory Stability and Change

    PubMed Central

    Voss, Joel L.

    2014-01-01

    Memory stability and change are considered opposite outcomes. We tested the counterintuitive notion that both depend on one process: hippocampal binding of memory features to associatively novel information, or associative novelty binding (ANB). Building on the idea that dominant memory features, or “traces,” are most susceptible to modification, we hypothesized that ANB would selectively involve dominant traces. Therefore, memory stability versus change should depend on whether the currently dominant trace is old versus updated; in either case, novel information will be bound with it, causing either maintenance (when old) or change (when updated). People in our experiment studied objects at locations within scenes (contexts). During reactivation in a new context, subjects moved studied objects to new locations either via active location recall or by passively dragging objects to predetermined locations. After active reactivation, the new object location became dominant in memory, whereas after passive reactivation, the old object location maintained dominance. In both cases, hippocampal ANB bound the currently dominant object-location memory with a context with which it was not paired previously (i.e., associatively novel). Stability occurred in the passive condition when ANB united the dominant original location trace with an associatively novel newer context. Change occurred in the active condition when ANB united the dominant updated object location with an associatively novel and older context. Hippocampal ANB of the currently dominant trace with associatively novel contextual information thus provides a single mechanism to support memory stability and change, with shifts in trace dominance during reactivation dictating the outcome. PMID:24501360

  2. Anticipatory alpha phase influences visual working memory performance.

    PubMed

    Zanto, Theodore P; Chadick, James Z; Gazzaley, Adam

    2014-01-15

    Alpha band (8-12 Hz) phase dynamics in the visual cortex are thought to reflect fluctuations in cortical excitability that influences perceptual processing. As such, visual stimuli are better detected when their onset is concurrent with specific phases of the alpha cycle. However, it is unclear whether alpha phase differentially influences cognitive performance at specific times relative to stimulus onset (i.e., is the influence of phase maximal before, at, or after stimulus onset?). To address this, participants performed a delayed-recognition, working memory (WM) task for visual motion direction during two separate visits. The first visit utilized functional magnetic resonance (fMRI) imaging to identify neural regions associated with task performance. Replicating previous studies, fMRI data showed engagement of visual cortical area V5, as well as a prefrontal cortical region, the inferior frontal junction (IFJ). During the second visit, transcranial magnetic stimulation (TMS) was applied separately to both the right IFJ and right V5 (with the vertex as a control region) while electroencephalography (EEG) was simultaneously recorded. During each trial, a single pulse of TMS (spTMS) was applied at one of six time points (-200, -100, -50, 0, 80, 160 ms) relative to the encoded stimulus onset. Results demonstrated a relationship between the phase of the posterior alpha signal prior to stimulus encoding and subsequent response times to the memory probe two seconds later. Specifically, spTMS to V5, and not the IFJ or vertex, yielded faster response times, indicating improved WM performance, when delivered during the peak, compared to the trough, of the alpha cycle, but only when spTMS was applied 100 ms prior to stimulus onset. These faster responses to the probe correlated with decreased early event related potential (ERP) amplitudes (i.e., P1) to the probe stimuli. Moreover, participants that were least affected by spTMS exhibited greater functional connectivity

  3. Model for resistance evolution in shape memory alloys including R-phase

    NASA Astrophysics Data System (ADS)

    Brammajyosula, Ravindra; Buravalla, Vidyashankar; Khandelwal, Ashish

    2011-03-01

    The electrical resistance behavior of a shape memory alloy (SMA) wire can be used for sensing the state of an SMA device. Hence, this study investigates the resistance evolution in SMAs. A lumped parameter model with cosine kinetics to capture the resistance variation during the phase transformation is developed. Several SMA materials show the presence of trigonal or rhombohedral (R) phase as an intermediate phase, apart from the commonly recognized austenite and martensite phases. Most of the SMA models ignore the R-phase effect in their prediction of thermomechanical response. This may be acceptable since the changes in thermomechanical response associated with the R-phase are relatively less. However, the resistivity related effects are pronounced in the presence of the R-phase and its appearance introduces non-monotonicity in the resistivity evolution. This leads to additional complexities in the use of resistance signal for sensing and control. Hence, a lumped model is developed here for resistance evolution including the R-phase effects. A phase-diagram-based model is proposed for predicting electro-thermomechanical response. Both steady state hysteretic response and transient response are modeled. The model predictions are compared with the available test data. Numerical studies have shown that the model is able to capture all the essential features of the resistance evolution in SMAs in the presence of the R-phase.

  4. 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.

  5. Electric Crosstalk Effect in Valence Change Resistive Random Access Memory

    NASA Astrophysics Data System (ADS)

    Sun, Jing; Wang, Hong; Wu, Shiwei; Song, Fang; Wang, Zhan; Gao, Haixia; Ma, Xiaohua

    2017-08-01

    Electric crosstalk phenomenon in valence change resistive switching memory (VCM) is systematically investigated. When a voltage is applied on the VCM device, an electric field is formed in the isolated region between the devices, which causes the oxygen vacancies in conductive filaments (CFs) to drift apart, leading to a consequent resistance degradation of the neighboring devices. The effects of distance between memory cells, electrodes widths and physical dimensions of CFs on the memory performance are investigated in this work. Furthermore, the strategies to mitigate electric crosstalk effects are developed. According to the simulation results, the crosstalk phenomenon can become more severe as the distance between memory cells or the electrode width decreases. In order to optimize the device performance, it is helpful to control the location of the break points of CFs in the device close to the top electrode. Alternatively, taking the integration density into account, switching materials with a small field accelerated parameter can also contribute to obtaining a stable performance.

  6. Subjective Age and Changes in Memory in Older Adults.

    PubMed

    Stephan, Yannick; Sutin, Angelina R; Caudroit, Johan; Terracciano, Antonio

    2016-07-01

    The subjective experience of aging, indexed by how old or young an individual feels, has been related to well-being and health-related outcomes among older adults. The present study examined whether subjective age is associated with memory level and changes, as indexed by measures of immediate and delayed recall. A complementary purpose was to test the mediating role of depressive symptoms and physical activity in the relation between subjective age and memory changes. Participants were drawn from three waves of the Health and Retirement Study. Subjective age, baseline memory measures, and covariates were assessed during the 2008 wave (N = 5809), depressive symptoms and physical activity were assessed again in the 2010 wave, and the follow-up memory measures were assessed in the 2012 wave. Regression analyses that included demographic, metabolic, and vascular covariates revealed that a younger subjective age at baseline was associated with better concurrent performance and with slower decline in immediate and delayed recall. Bootstrap procedures indicated that fewer depressive symptoms mediated these associations. Additional analyses revealed that memory level and change were unrelated to changes in subjective age. Beyond chronological age, the subjective experience of age is associated with cognitive aging. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  7. 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. Copyright © 2016

  8. 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.

  9. One order of magnitude faster phase change at reduced power in Ti-Sb-Te.

    PubMed

    Zhu, Min; Xia, Mengjiao; Rao, Feng; Li, Xianbin; Wu, Liangcai; Ji, Xinglong; Lv, Shilong; Song, Zhitang; Feng, Songlin; Sun, Hongbo; Zhang, Shengbai

    2014-07-08

    To date, slow Set operation speed and high Reset operation power remain to be important limitations for substituting dynamic random access memory by phase change memory. Here, we demonstrate phase change memory cell based on Ti0.4Sb2Te3 alloy, showing one order of magnitude faster Set operation speed and as low as one-fifth Reset operation power, compared with Ge2Sb2Te5-based phase change memory cell at the same size. The enhancements may be rooted in the common presence of titanium-centred octahedral motifs in both amorphous and crystalline Ti0.4Sb2Te3 phases. The essentially unchanged local structures around the titanium atoms may be responsible for the significantly improved performance, as these structures could act as nucleation centres to facilitate a swift, low-energy order-disorder transition for the rest of the Sb-centred octahedrons. Our study may provide an alternative to the development of high-speed, low-power dynamic random access memory-like phase change memory technology.

  10. 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

  11. Multilevel data storage in multilayer phase change material

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  12. The effects of velocity difference changes with memory on the dynamics characteristics and fuel economy of traffic flow

    NASA Astrophysics Data System (ADS)

    Yu, Shaowei; Zhao, Xiangmo; Xu, Zhigang; Zhang, Licheng

    2016-11-01

    To evaluate the effects of velocity difference changes with memory in the intelligent transportation environment on the dynamics and fuel consumptions of traffic flow, we first investigate the linkage between velocity difference changes with memory and car-following behaviors with the measured data in cities, and then propose an improved cooperative car-following model considering multiple velocity difference changes with memory in the cooperative adaptive cruise control strategy, finally carry out several numerical simulations under the periodic boundary condition and at signalized intersections to explore how velocity difference changes with memory affect car's velocity, velocity fluctuation, acceleration and fuel consumptions in the intelligent transportation environment. The results show that velocity difference changes with memory have obvious effects on car-following behaviors, that the improved cooperative car-following model can describe the phase transition of traffic flow and estimate the evolution of traffic congestion, that the stability and fuel economy of traffic flow simulated by the improved car-following model with velocity difference changes with memory is obviously superior to those without velocity difference changes, and that taking velocity difference changes with memory into account in designing the advanced adaptive cruise control strategy can significantly improve the stability and fuel economy of traffic flow.

  13. Changes in Semantic Memory in Early Stage Alzheimer's Disease Patients.

    ERIC Educational Resources Information Center

    Weingartner, Herbert J.; And Others

    1993-01-01

    Contrasts changes in semantic memory in elderly normal controls and Alzheimer's disease (AD) patients before patients expressed symptoms. Found that controls generated more uncommon exemplars from closed semantic categories (fruits and vegetables) than did AD patients prior to presumed onset of AD. AD patients were just as productive as controls…

  14. 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…

  15. 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…

  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.

  17. Thalamic theta phase alignment predicts human memory formation and anterior thalamic cross-frequency coupling.

    PubMed

    Sweeney-Reed, Catherine M; Zaehle, Tino; Voges, Jürgen; Schmitt, Friedhelm C; Buentjen, Lars; Kopitzki, Klaus; Hinrichs, Hermann; Heinze, Hans-Jochen; Rugg, Michael D; Knight, Robert T; Richardson-Klavehn, Alan

    2015-05-20

    Previously we reported electrophysiological evidence for a role for the anterior thalamic nucleus (ATN) in human memory formation (Sweeney-Reed et al., 2014). Theta-gamma cross-frequency coupling (CFC) predicted successful memory formation, with the involvement of gamma oscillations suggesting memory-relevant local processing in the ATN. The importance of the theta frequency range in memory processing is well-established, and phase alignment of oscillations is considered to be necessary for synaptic plasticity. We hypothesized that theta phase alignment in the ATN would be necessary for memory encoding. Further analysis of the electrophysiological data reveal that phase alignment in the theta rhythm was greater during successful compared with unsuccessful encoding, and that this alignment was correlated with the CFC. These findings support an active processing role for the ATN during memory formation.

  18. Thalamic theta phase alignment predicts human memory formation and anterior thalamic cross-frequency coupling

    PubMed Central

    Sweeney-Reed, Catherine M; Zaehle, Tino; Voges, Jürgen; Schmitt, Friedhelm C; Buentjen, Lars; Kopitzki, Klaus; Hinrichs, Hermann; Heinze, Hans-Jochen; Rugg, Michael D; Knight, Robert T; Richardson-Klavehn, Alan

    2015-01-01

    Previously we reported electrophysiological evidence for a role for the anterior thalamic nucleus (ATN) in human memory formation (Sweeney-Reed et al., 2014). Theta-gamma cross-frequency coupling (CFC) predicted successful memory formation, with the involvement of gamma oscillations suggesting memory-relevant local processing in the ATN. The importance of the theta frequency range in memory processing is well-established, and phase alignment of oscillations is considered to be necessary for synaptic plasticity. We hypothesized that theta phase alignment in the ATN would be necessary for memory encoding. Further analysis of the electrophysiological data reveal that phase alignment in the theta rhythm was greater during successful compared with unsuccessful encoding, and that this alignment was correlated with the CFC. These findings support an active processing role for the ATN during memory formation. DOI: http://dx.doi.org/10.7554/eLife.07578.001 PMID:25993559

  19. Gamma phase-synchrony in autobiographical memory: Evidence from magnetoencephalography and severely deficient autobiographical memory.

    PubMed

    Fuentemilla, Lluís; Palombo, Daniela J; Levine, Brian

    2017-08-16

    The subjective sense of recollecting events from one's past is an essential feature of episodic memory, but the neural mechanisms supporting this capacity are poorly understood. We examined the role of large-scale patterns of neural synchrony using whole-head MEG recordings in healthy adults and S.M., who has severely deficient autobiographical memory (SDAM; Palombo et al., 2015), a syndrome in which autobiographical recollection is absent but other functions (including other mnemonic functions), are normal. MEG was conducted while participants listened to prospectively collected recordings documenting unique personal episodes (PE) that normally evoke rich recollection, as well as a condition including general semantic information that is non-specific in place or time (GS; Levine et al., 2004). We predicted that PE (and not GS) would be associated with changes in patterns of large-scale neural synchrony in comparison subjects. We found large-scale neural synchrony, specifically in the gamma frequency ranges (i.e., 27-45Hz), specific to PE and not GS. These synchrony differences between PE and GS were not apparent in S.M. Our findings provide empirical evidence for the supporting role of large-scale gamma neural synchrony underlying autobiographical recollection. Copyright © 2017 Elsevier Ltd. All rights reserved.

  20. Memory under stress: from single systems to network changes.

    PubMed

    Schwabe, Lars

    2017-02-01

    Stressful events have profound effects on learning and memory. These effects are mainly mediated by catecholamines and glucocorticoid hormones released from the adrenals during stressful encounters. It has been known for long that both catecholamines and glucocorticoids influence the functioning of the hippocampus, a critical hub for episodic memory. However, areas implicated in other forms of memory, such as the insula or the dorsal striatum, can be affected by stress as well. Beyond changes in single memory systems, acute stress triggers the reconfiguration of large scale neural networks which sets the stage for a shift from thoughtful, 'cognitive' control of learning and memory toward more reflexive, 'habitual' processes. Stress-related alterations in amygdala connectivity with the hippocampus, dorsal striatum, and prefrontal cortex seem to play a key role in this shift. The bias toward systems proficient in threat processing and the implementation of well-established routines may facilitate coping with an acute stressor. Overreliance on these reflexive systems or the inability to shift flexibly between them, however, may represent a risk factor for psychopathology in the long-run.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  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. Age-Related Reversals in Neural Recruitment across Memory Retrieval Phases.

    PubMed

    Ford, Jaclyn H; Kensinger, Elizabeth A

    2017-05-17

    Over the last several decades, neuroimaging research has identified age-related neural changes that occur during cognitive tasks. These changes are used to help researchers identify functional changes that contribute to age-related impairments in cognitive performance. One commonly reported example of such a change is an age-related decrease in the recruitment of posterior sensory regions coupled with an increased recruitment of prefrontal regions across multiple cognitive tasks. This shift is often described as a compensatory recruitment of prefrontal regions due to age-related sensory-processing deficits in posterior regions. However, age is not only associated with spatial shifts in recruitment, but also with temporal shifts, in which younger and older adults recruit the same neural region at different points in a task trial. The current study examines the possible contribution of temporal modifications in the often-reported posterior-anterior shift. Participants, ages 19-85, took part in a memory retrieval task with a protracted retrieval trial consisting of an initial memory search phase and a subsequent detail elaboration phase. Age-related neural patterns during search replicated prior reports of age-related decreases in posterior recruitment and increases in prefrontal recruitment. However, during the later elaboration phase, the same posterior regions were associated with age-related increases in activation. Further, ROI and functional connectivity results suggest that these posterior regions function similarly during search and elaboration. These results suggest that the often-reported posterior-anterior shift may not reflect the inability of older adults to engage in sensory processing, but rather a change in when they recruit this processing.SIGNIFICANCE STATEMENT The current study provides evidence that the often-reported posterior-anterior shift in aging may not reflect a global sensory-processing deficit, as has often been reported, but rather a

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

    PubMed

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

    2017-08-09

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

  5. Dynamically Reconfigurable Metadevice Employing Nanostructured Phase-Change Materials

    DOE PAGES

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

    2017-07-01

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

  6. 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

  7. 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.

  8. 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.

  9. Visual Working Memory Load-Related Changes in Neural Activity and Functional Connectivity

    PubMed Central

    Li, Ling; Zhang, Jin-Xiang; Jiang, Tao

    2011-01-01

    Background Visual working memory (VWM) helps us store visual information to prepare for subsequent behavior. The neuronal mechanisms for sustaining coherent visual information and the mechanisms for limited VWM capacity have remained uncharacterized. Although numerous studies have utilized behavioral accuracy, neural activity, and connectivity to explore the mechanism of VWM retention, little is known about the load-related changes in functional connectivity for hemi-field VWM retention. Methodology/Principal Findings In this study, we recorded electroencephalography (EEG) from 14 normal young adults while they performed a bilateral visual field memory task. Subjects had more rapid and accurate responses to the left visual field (LVF) memory condition. The difference in mean amplitude between the ipsilateral and contralateral event-related potential (ERP) at parietal-occipital electrodes in retention interval period was obtained with six different memory loads. Functional connectivity between 128 scalp regions was measured by EEG phase synchronization in the theta- (4–8 Hz), alpha- (8–12 Hz), beta- (12–32 Hz), and gamma- (32–40 Hz) frequency bands. The resulting matrices were converted to graphs, and mean degree, clustering coefficient and shortest path length was computed as a function of memory load. The results showed that brain networks of theta-, alpha-, beta-, and gamma- frequency bands were load-dependent and visual-field dependent. The networks of theta- and alpha- bands phase synchrony were most predominant in retention period for right visual field (RVF) WM than for LVF WM. Furthermore, only for RVF memory condition, brain network density of theta-band during the retention interval were linked to the delay of behavior reaction time, and the topological property of alpha-band network was negative correlation with behavior accuracy. Conclusions/Significance We suggest that the differences in theta- and alpha- bands between LVF and RVF conditions in

  10. 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

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

    PubMed

    Batterink, Laura J; Creery, Jessica D; Paller, Ken A

    2016-01-27

    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. Slow-wave sleep (SWS) is characterized by synchronized neural activity alternating between active upstates and quiet downstates. The slow-oscillation upstates are thought to provide a

  12. Brain network changes and memory decline in aging.

    PubMed

    Beason-Held, Lori L; Hohman, Timothy J; Venkatraman, Vijay; An, Yang; Resnick, Susan M

    2016-06-18

    One theory of age-related cognitive decline proposes that changes within the default mode network (DMN) of the brain impact the ability to successfully perform cognitive operations. To investigate this theory, we examined functional covariance within brain networks using regional cerebral blood flow data, measured by (15)O-water PET, from 99 participants (mean baseline age 68.6 ± 7.5) in the Baltimore Longitudinal Study of Aging collected over a 7.4 year period. The sample was divided in tertiles based on longitudinal performance on a verbal recognition memory task administered during scanning, and functional covariance was compared between the upper (improvers) and lower (decliners) tertile groups. The DMN and verbal memory networks (VMN) were then examined during the verbal memory scan condition. For each network, group differences in node-to-network coherence and individual node-to-node covariance relationships were assessed at baseline and in change over time. Compared with improvers, decliners showed differences in node-to-network coherence and in node-to-node relationships in the DMN but not the VMN during verbal memory. These DMN differences reflected greater covariance with better task performance at baseline and both increasing and declining covariance with declining task performance over time for decliners. When examined during the resting state alone, the direction of change in DMN covariance was similar to that seen during task performance, but node-to-node relationships differed from those observed during the task condition. These results suggest that disengagement of DMN components during task performance is not essential for successful cognitive performance as previously proposed. Instead, a proper balance in network processes may be needed to support optimal task performance.

  13. Learning-induced and stathmin-dependent changes in microtubule stability are critical for memory and disrupted in ageing.

    PubMed

    Uchida, Shusaku; Martel, Guillaume; Pavlowsky, Alice; Takizawa, Shuichi; Hevi, Charles; Watanabe, Yoshifumi; Kandel, Eric R; Alarcon, Juan Marcos; Shumyatsky, Gleb P

    2014-07-10

    Changes in the stability of microtubules regulate many biological processes, but their role in memory remains unclear. Here we show that learning causes biphasic changes in the microtubule-associated network in the hippocampus. In the early phase, stathmin is dephosphorylated, enhancing its microtubule-destabilizing activity by promoting stathmin-tubulin binding, whereas in the late phase these processes are reversed leading to an increase in microtubule/KIF5-mediated localization of the GluA2 subunit of AMPA receptors at synaptic sites. A microtubule stabilizer paclitaxel decreases or increases memory when applied at the early or late phases, respectively. Stathmin mutations disrupt changes in microtubule stability, GluA2 localization, synaptic plasticity and memory. Aged wild-type mice show impairments in stathmin levels, changes in microtubule stability and GluA2 localization. Blocking GluA2 endocytosis rescues memory deficits in stathmin mutant and aged wild-type mice. These findings demonstrate a role for microtubules in memory in young adult and aged individuals.

  14. Learning-induced and stathmin-dependent changes in microtubule stability are critical for memory and disrupted in ageing

    PubMed Central

    Uchida, Shusaku; Martel, Guillaume; Pavlowsky, Alice; Takizawa, Shuichi; Hevi, Charles; Watanabe, Yoshifumi; Kandel, Eric R.; Alarcon, Juan Marcos; Shumyatsky, Gleb P.

    2014-01-01

    Changes in the stability of microtubules regulate many biological processes, but their role in memory remains unclear. Here we show that learning causes biphasic changes in the microtubule-associated network in the hippocampus. In the early phase, stathmin is dephosphorylated, enhancing its microtubule-destabilizing activity by promoting stathmin-tubulin binding, whereas in the late phase these processes are reversed leading to an increase in microtubule/KIF5-mediated localization of the GluA2 subunit of AMPA receptors at synaptic sites. A microtubule stabilizer paclitaxel decreases or increases memory when applied at the early or late phases, respectively. Stathmin mutations disrupt changes in microtubule stability, GluA2 localization, synaptic plasticity and memory. Aged wild-type mice show impairments in stathmin levels, changes in microtubule stability, and GluA2 localization. Blocking GluA2 endocytosis rescues memory deficits in stathmin mutant and aged wild-type mice. These findings demonstrate a role for microtubules in memory in young adult and aged individuals. PMID:25007915

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

    PubMed

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

    2017-01-11

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

  16. Metal organic chemical vapor deposition of phase change Ge1Sb2Te4 nanowires.

    PubMed

    Longo, Massimo; Fallica, Roberto; Wiemer, Claudia; Salicio, Olivier; Fanciulli, Marco; Rotunno, Enzo; Lazzarini, Laura

    2012-03-14

    The self-assembly of Ge(1)Sb(2)Te(4) nanowires (NWs) for phase change memories application was achieved by metal organic chemical vapor deposition, catalyzed by Au nanoislands in a narrow range of temperatures and deposition pressures. In the optimized conditions of 400 °C, 50 mbar, the NWs are Ge(1)Sb(2)Te(4) single hexagonal crystals. Phase change memory switching was reversibly induced by nanosecond current pulses through metal-contacted NWs with threshold voltage of about 1.35 V.

  17. Molecular mechanisms of phase change in locusts.

    PubMed

    Wang, Xianhui; Kang, Le

    2014-01-01

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

  18. The memory phase of the CD4 T-cell response to influenza virus infection maintains its diverse antigen specificity

    PubMed Central

    Richards, Katherine A; Chaves, Francisco A; Sant, Andrea J

    2011-01-01

    A major gap in our understanding of the immune response to pathogens and vaccines is how closely the antigen specificity in the memory phase mimics repertoire that is rapidly expanded upon priming. Understanding the diversity of the CD4 T-cell memory compartment after a primary response to pathogens is hampered by the technical challenges of epitope discovery and suitable models to study primary immune responses. Recently, we have used overlapping synthetic peptides to empirically map most of the specificities present in the primary response to live influenza infection. We found that the CD4 T-cell response can be exceptionally diverse, depending on the allele(s) of MHC class II molecules expressed. In the current study, using a mouse model of primary influenza infection and peptide-specific cytokine EliSpots, we have asked how this broad CD4 T-cell immunodominance hierarchy changes as the immune response contracts and memory is established. Our studies revealed that, for the most part, diversity is maintained, and most specificities, including those for relatively minor epitopes, are preserved in the memory CD4 T-cell compartment. A modest, but reproducible shift in specificity toward haemagglutinin-derived epitopes was observed, raising the possibility that protein or peptide persistence might play a role in the evolution of the memory phase of the CD4 T-cell response. PMID:21517839

  19. 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

  20. 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. Copyright © 2014 Elsevier Inc. All rights reserved.

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

    PubMed

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

    2011-03-01

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

  2. Phase transitions in Ge-Sb phase change materials

    SciTech Connect

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

    2009-03-15

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

  3. 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.

  4. Changes in cortical activity when subjects scan memory for tones.

    PubMed

    Kaufman, L; Curtis, S; Wang, J Z; Williamson, S J

    1992-04-01

    The magnetoencephalogram (MEG) was used to detect regional changes in spontaneous cortical activity accompanying short-term memory search. This method was chosen because magnetic fields are detectable only within a few centimeters of the projections of their sources onto the scalp. The specific hypothesis that auditory cortex is involved in scanning memory for tones was tested by sensing the field of the magnetic counterpart to N100 (N100m) which is known to originate in auditory cortex. N100m was measured at many different positions and the spontaneous cortical rhythms in the alpha bandwidth (8-12 Hz) were measured at the same places. These rhythms were found to be suppressed while subjects scanned memory for musical tones in a Sternberg paradigm. For 3 subjects, both the MEG suppression time (ST) and reaction time (RT) increased linearly with memory set size. The correlation between ST measured over the left hemisphere and set size was significant for two subjects but not significant for the third, and the slopes of the regression lines relating ST to set size were too shallow to be related to the time required to scan memory. However, the correlation between ST of the right hemisphere and set size was highly significant for all subjects, and the slopes of the regression lines were comparable to those relating RT to set size. The electroencephalogram (EEG) recorded with midline electrodes failed to reveal a significant relationship between suppression time and set size for 2 of the subjects, thus ruling out global alpha blockage and generalized arousal as the basis for the task-related suppression duration. The electric N100, measured at Cz, decreased significantly in amplitude with set size for 2 subjects, but it increased significantly in amplitude for the third subject. In contrast, RT increased with set size for all subjects. N100m measured over the right hemisphere was similar to the behavior of N100, while N100m measured over the left hemisphere showed

  5. Shape-Memory Alloy Tactical Feedback Actuator. Phase 1

    DTIC Science & Technology

    1990-08-01

    AAMRL-TR-90-039 00 " SHAPE-MEMORY ALLOY N TACTICAL FEEDBACK ACTUATOR I A. DAVID JOHNSON TIN! ALLOY COMPANY, INC. DTIC 1144 65th STREET ELECTE OAKLAND...DATES COVERED 1 Sep 89 Final 1 Feb 89 - 1Aug 89 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS PE - 65502F Shape-Memory Alloy Tactile Feedback Actuator PR...pad size arrays and that computer control is feasible. Actuation profiles and design techniques are discussed. 14. SUBJECT TERMS 15. NUMBER OF PAGES

  6. Memory

    MedlinePlus

    ... it has to decide what is worth remembering. Memory is the process of storing and then remembering this information. There are different types of memory. Short-term memory stores information for a few ...

  7. Longitudinal Changes in Component Processes of Working Memory.

    PubMed

    Rieckmann, Anna; Pudas, Sara; Nyberg, Lars

    2017-01-01

    Working memory (WM) entails maintenance and manipulation of information in the absence of sensory input. This study investigated the trajectories and neural basis of these component processes of WM functions in aging. Longitudinal human functional magnetic resonance imaging (fMRI) data are presented from 136 older individuals (55-80 years) who were scanned at baseline and again 4 years later. We obtained evidence that age-related changes in parietal and frontal components of the WM core network are dissociable in terms of their role in maintenance of perceptual representations and further manipulation of this information, respectively. Individual difference analyses in performance subgroups showed that only prefrontal changes in fMRI activation were accompanied by changes in performance, but parietal brain activity was related to study dropout. We discuss the results in terms of possible neurobiological causes underlying separable aging-related declines in inferior parietal cortex and lateral prefrontal cortex that differentially affect WM functions.

  8. Longitudinal Changes in Component Processes of Working Memory

    PubMed Central

    2017-01-01

    Abstract Working memory (WM) entails maintenance and manipulation of information in the absence of sensory input. This study investigated the trajectories and neural basis of these component processes of WM functions in aging. Longitudinal human functional magnetic resonance imaging (fMRI) data are presented from 136 older individuals (55–80 years) who were scanned at baseline and again 4 years later. We obtained evidence that age-related changes in parietal and frontal components of the WM core network are dissociable in terms of their role in maintenance of perceptual representations and further manipulation of this information, respectively. Individual difference analyses in performance subgroups showed that only prefrontal changes in fMRI activation were accompanied by changes in performance, but parietal brain activity was related to study dropout. We discuss the results in terms of possible neurobiological causes underlying separable aging-related declines in inferior parietal cortex and lateral prefrontal cortex that differentially affect WM functions. PMID:28374009

  9. Memory reconsolidation, emotional arousal, and the process of change in psychotherapy: New insights from brain science.

    PubMed

    Lane, Richard D; Ryan, Lee; Nadel, Lynn; Greenberg, Leslie

    2015-01-01

    Since Freud, clinicians have understood that disturbing memories contribute to psychopathology and that new emotional experiences contribute to therapeutic change. Yet, controversy remains about what is truly essential to bring about psychotherapeutic change. Mounting evidence from empirical studies suggests that emotional arousal is a key ingredient in therapeutic change in many modalities. In addition, memory seems to play an important role but there is a lack of consensus on the role of understanding what happened in the past in bringing about therapeutic change. The core idea of this paper is that therapeutic change in a variety of modalities, including behavioral therapy, cognitive-behavioral therapy, emotion-focused therapy, and psychodynamic psychotherapy, results from the updating of prior emotional memories through a process of reconsolidation that incorporates new emotional experiences. We present an integrated memory model with three interactive components - autobiographical (event) memories, semantic structures, and emotional responses - supported by emerging evidence from cognitive neuroscience on implicit and explicit emotion, implicit and explicit memory, emotion-memory interactions, memory reconsolidation, and the relationship between autobiographical and semantic memory. We propose that the essential ingredients of therapeutic change include: (1) reactivating old memories; (2) engaging in new emotional experiences that are incorporated into these reactivated memories via the process of reconsolidation; and (3) reinforcing the integrated memory structure by practicing a new way of behaving and experiencing the world in a variety of contexts. The implications of this new, neurobiologically grounded synthesis for research, clinical practice, and teaching are discussed.

  10. Dynamic changes in parietal activation during encoding: implications for human learning and memory.

    PubMed

    Elman, Jeremy A; Rosner, Zachary A; Cohn-Sheehy, Brendan I; Cerreta, Adelle G; Shimamura, Arthur P

    2013-11-15

    The ventral posterior parietal cortex (vPPC) monitors successful memory retrieval, yet its role during learning remains unclear. Indeed, increased vPPC activation during stimulus encoding is often negatively correlated with subsequent memory performance, suggesting that this region is suppressed during learning. Alternatively, the vPPC may engage in learning-related processes immediately after stimulus encoding thus facilitating retrieval at a later time. To investigate this possibility, we assessed vPPC activity during item presentation and immediately following its offset when a cue to remember was presented. We observed a dynamic change in vPPC response such that activity was negatively correlated with subsequent memory during stimulus presentation but positively correlated immediately following the stimulus during the cue phase. Furthermore, regional differences in this effect suggest a degree of functional heterogeneity within the vPPC. These findings demonstrate that the vPPC is engaged during learning and acts to facilitate post-encoding memory processes that establish long-term cortical representations. Copyright © 2013 Elsevier Inc. All rights reserved.

  11. The Effect of Sex and Menstrual Phase on Memory Formation during Nap.

    PubMed

    Mednick, Sara C; Sattari, Negin; McDevitt, Elizabeth A; Panas, Dagmara; Niknazar, Mohammad; Ahmadi, Maryam; Naji, Mohsen; Baker, Fiona

    2017-09-16

    Memory formation can be influenced by sleep and sex hormones in both men and women, and by the menstrual cycle in women. Though many studies have shown that sleep benefits the consolidation of memories, it is not clear whether this effect differs between men and women in general or according to menstrual phase in women. The present study investigated the effect of sex and menstrual cycle on memory consolidation of face-name associations (FNA) following a daytime nap. Recognition memory was tested using a face-name paired associates task with a polysomnographic nap between morning and evening testing. Seventeen healthy women (age: 20.75 (1.98) years) were studied at two time points of their menstrual cycles, defined from self-report and separated by 2 weeks (perimenses: -5 days to + 6 days from the start of menses, and non-perimenses: outside of the perimenses phase) and compared with eighteen healthy men (age: 22.01 (2.91) years). Regardless of menstrual phase, women had better pre-nap performance than men. Further, menstrual phase affected post-nap memory consolidation, with women showing greater forgetting in their perimenses phase compared with their non-perimenses phase, and men. Interestingly, post-nap performance correlated with electrophysiological events during sleep (slow oscillations, spindles, and temporal coupling between the two), however, these correlations differed according to menstrual phase and sex. Men's performance improvement was associated with the temporal coupling of spindles and slow oscillations (i.e., spindle/SO coincidence) as well as spindles. Women, however, showed an association with slow oscillations during non-perimenses, whereas when they were in their perimenses phase of their cycle, women appeared to show an association only with sleep spindle events for consolidation. These findings add to the growing literature demonstrating sex and menstrual phase effects on memory formation during sleep. Copyright © 2017. Published by

  12. 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.

  13. 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.

  14. Theta Phase Synchronization Is the Glue that Binds Human Associative Memory.

    PubMed

    Clouter, Andrew; Shapiro, Kimron L; Hanslmayr, Simon

    2017-10-04

    Episodic memories are information-rich, often multisensory events that rely on binding different elements [1]. The elements that will constitute a memory episode are processed in specialized but distinct brain modules. The binding of these elements is most likely mediated by fast-acting long-term potentiation (LTP), which relies on the precise timing of neural activity [2]. Theta oscillations in the hippocampus orchestrate such timing as demonstrated by animal studies in vitro [3, 4] and in vivo [5, 6], suggesting a causal role of theta activity for the formation of complex memory episodes, but direct evidence from humans is missing. Here, we show that human episodic memory formation depends on phase synchrony between different sensory cortices at the theta frequency. By modulating the luminance of visual stimuli and the amplitude of auditory stimuli, we directly manipulated the degree of phase synchrony between visual and auditory cortices. Memory for sound-movie associations was significantly better when the stimuli were presented in phase compared to out of phase. This effect was specific to theta (4 Hz) and did not occur in slower (1.7 Hz) or faster (10.5 Hz) frequencies. These findings provide the first direct evidence that episodic memory formation in humans relies on a theta-specific synchronization mechanism. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

  16. Corticothalamic phase synchrony and cross-frequency coupling predict human memory formation.

    PubMed

    Sweeney-Reed, Catherine M; Zaehle, Tino; Voges, Juergen; Schmitt, Friedhelm C; Buentjen, Lars; Kopitzki, Klaus; Esslinger, Christine; Hinrichs, Hermann; Heinze, Hans-Jochen; Knight, Robert T; Richardson-Klavehn, Alan

    2014-12-23

    The anterior thalamic nucleus (ATN) is thought to play an important role in a brain network involving the hippocampus and neocortex, which enables human memories to be formed. However, its small size and location deep within the brain have impeded direct investigation in humans with non-invasive techniques. Here we provide direct evidence for a functional role for the ATN in memory formation from rare simultaneous human intrathalamic and scalp electroencephalogram (EEG) recordings from eight volunteering patients receiving intrathalamic electrodes implanted for the treatment of epilepsy, demonstrating real-time communication between neocortex and ATN during successful memory encoding. Neocortical-ATN theta oscillatory phase synchrony of local field potentials and neocortical-theta-to-ATN-gamma cross-frequency coupling during presentation of complex photographic scenes predicted later memory for the scenes, demonstrating a key role for the ATN in human memory encoding.

  17. Corticothalamic phase synchrony and cross-frequency coupling predict human memory formation

    PubMed Central

    Sweeney-Reed, Catherine M; Zaehle, Tino; Voges, Juergen; Schmitt, Friedhelm C; Buentjen, Lars; Kopitzki, Klaus; Esslinger, Christine; Hinrichs, Hermann; Heinze, Hans-Jochen; Knight, Robert T; Richardson-Klavehn, Alan

    2014-01-01

    The anterior thalamic nucleus (ATN) is thought to play an important role in a brain network involving the hippocampus and neocortex, which enables human memories to be formed. However, its small size and location deep within the brain have impeded direct investigation in humans with non-invasive techniques. Here we provide direct evidence for a functional role for the ATN in memory formation from rare simultaneous human intrathalamic and scalp electroencephalogram (EEG) recordings from eight volunteering patients receiving intrathalamic electrodes implanted for the treatment of epilepsy, demonstrating real-time communication between neocortex and ATN during successful memory encoding. Neocortical-ATN theta oscillatory phase synchrony of local field potentials and neocortical-theta-to-ATN-gamma cross-frequency coupling during presentation of complex photographic scenes predicted later memory for the scenes, demonstrating a key role for the ATN in human memory encoding. DOI: http://dx.doi.org/10.7554/eLife.05352.001 PMID:25535839

  18. Episodic sequence memory is supported by a theta-gamma phase code

    PubMed Central

    Heusser, Andrew C.; Poeppel, David; Ezzyat, Youssef; Davachi, Lila

    2016-01-01

    The meaning we derive from our experiences is not a simple static extraction of the elements, but is largely based on the order in which those elements occur. Models propose that sequence encoding is supported by interactions between high and low frequency oscillations, such that elements within an experience are represented by neural cell assemblies firing at higher frequencies (i.e. gamma) and sequential order is coded by the specific timing of firing with respect to a lower frequency oscillation (i.e. theta). During episodic sequence memory formation in humans, we provide evidence that items in different sequence positions exhibit relatively greater gamma power along distinct phases of a theta oscillation. Furthermore, this segregation is related to successful temporal order memory. These results provide compelling evidence that memory for order, a core component of an episodic memory, capitalizes on the ubiquitous physiological mechanism of theta-gamma phase-amplitude coupling. PMID:27571010

  19. 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.

  20. Locust dynamics: behavioral phase change and swarming.

    PubMed

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

    2012-01-01

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

  1. 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

  2. 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)

  3. 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)

  4. Phase-amplitude coupling and long-range phase synchronization reveal frontotemporal interactions during visual working memory.

    PubMed

    Daume, Jonathan; Gruber, Thomas; Engel, Andreas K; Friese, Uwe

    2016-11-30

    It has been suggested that cross-frequency phase-amplitude coupling (PAC) particularly in temporal brain structures serves as a neural mechanism for coordinated working memory storage. In this magnetoencephalography study, we show that during visual working memory maintenance, temporal cortex regions, which exhibit enhanced PAC, interact with prefrontal cortex via enhanced low-frequency phase synchronization. Healthy human participants were engaged in a visual delayed-matching-to-sample task with pictures of natural objects. During the delay period, we observed increased spectral power of beta (20-28 Hz) and gamma band (40-94 Hz) as well as decreased power of theta/alpha band (7-9 Hz) oscillations in visual sensory areas. Enhanced PAC between the phases of theta/alpha and the amplitudes of beta oscillations was found in the left inferior temporal cortex (IT) - an area known to be involved in visual object memory. Furthermore, the IT was functionally connected to the prefrontal cortex by increased low-frequency phase synchronization within the theta/alpha band. Taken together, these results point to a mechanism, in which the combination of PAC and long-range phase synchronization subserves enhanced large-scale brain communication. They suggest that distant brain regions might coordinate their activity in the low-frequency range to engage local stimulus-related processing in higher frequencies via the combination of long-range within-frequency phase synchronization and local cross-frequency PAC. Working memory maintenance, like other cognitive functions, requires the coordinated engagement of brain areas in local and large-scale networks. However, the mechanisms by which spatially distributed brain regions share and combine information remain largely unknown. We show that the combination of long-range low-frequency phase synchronization and local cross-frequency phase-amplitude coupling might serve as a mechanism to coordinate memory processes across distant brain

  5. Phase-Amplitude Coupling and Long-Range Phase Synchronization Reveal Frontotemporal Interactions during Visual Working Memory.

    PubMed

    Daume, Jonathan; Gruber, Thomas; Engel, Andreas K; Friese, Uwe

    2017-01-11

    It has been suggested that cross-frequency phase-amplitude coupling (PAC), particularly in temporal brain structures, serves as a neural mechanism for coordinated working memory storage. In this magnetoencephalography study, we show that during visual working memory maintenance, temporal cortex regions, which exhibit enhanced PAC, interact with prefrontal cortex via enhanced low-frequency phase synchronization. Healthy human participants were engaged in a visual delayed match-to-sample task with pictures of natural objects. During the delay period, we observed increased spectral power of beta (20-28 Hz) and gamma (40-94 Hz) bands as well as decreased power of theta/alpha band (7-9 Hz) oscillations in visual sensory areas. Enhanced PAC between the phases of theta/alpha and the amplitudes of beta oscillations was found in the left inferior temporal cortex (IT), an area known to be involved in visual object memory. Furthermore, the IT was functionally connected to the prefrontal cortex by increased low-frequency phase synchronization within the theta/alpha band. Together, these results point to a mechanism in which the combination of PAC and long-range phase synchronization subserves enhanced large-scale brain communication. They suggest that distant brain regions might coordinate their activity in the low-frequency range to engage local stimulus-related processing in higher frequencies via the combination of long-range, within-frequency phase synchronization and local cross-frequency PAC. Working memory maintenance, like other cognitive functions, requires the coordinated engagement of brain areas in local and large-scale networks. However, the mechanisms by which spatially distributed brain regions share and combine information remain primarily unknown. We show that the combination of long-range, low-frequency phase synchronization and local cross-frequency phase-amplitude coupling might serve as a mechanism to coordinate memory processes across distant brain areas

  6. 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

  7. A Reevaluation of Age-Related Changes in Associative Memory Organization.

    ERIC Educational Resources Information Center

    Lindauer, Barbara K.; Paris, Scott G.

    This paper focuses on a study which replicates and extends earlier work employing a recognition memory paradigm to investigate children's memory and developmental changes in dominant word associations. On the recognition test the implicit associative response can lead to better memory for the original items (this is the hit rate), and it can also…

  8. 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.

  9. 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

  10. 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

    2016-06-16

    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.

  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. Changing disturbance regimes, ecological memory, and forest resilience

    USGS Publications Warehouse

    Johnstone, Jill F.; Allen, Craig D.; Franklin, Jerry F.; Frelich, Lee E.; Harvey, Brian J.; Higuera, Philip E.; Mack, Michelle C.; Meentemeyer, Ross K.; Metz, Margaret R.; Perry, George LW; Schoennagel, Tania; Turner, Monica G.

    2016-01-01

    Ecological memory is central to how ecosystems respond to disturbance and is maintained by two types of legacies – information and material. Species life-history traits represent an adaptive response to disturbance and are an information legacy; in contrast, the abiotic and biotic structures (such as seeds or nutrients) produced by single disturbance events are material legacies. Disturbance characteristics that support or maintain these legacies enhance ecological resilience and maintain a “safe operating space” for ecosystem recovery. However, legacies can be lost or diminished as disturbance regimes and environmental conditions change, generating a “resilience debt” that manifests only after the system is disturbed. Strong effects of ecological memory on post-disturbance dynamics imply that contingencies (effects that cannot be predicted with certainty) of individual disturbances, interactions among disturbances, and climate variability combine to affect ecosystem resilience. We illustrate these concepts and introduce a novel ecosystem resilience framework with examples of forest disturbances, primarily from North America. Identifying legacies that support resilience in a particular ecosystem can help scientists and resource managers anticipate when disturbances may trigger abrupt shifts in forest ecosystems, and when forests are likely to be resilient.

  13. Phase-change materials in masonry construction

    NASA Astrophysics Data System (ADS)

    Lang, M.

    1982-01-01

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

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

    PubMed

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

    2004-10-01

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

  15. Memory for centrally attended changing objects in an incidental real-world change detection paradigm.

    PubMed

    Levin, Daniel T; Simons, Daniel J; Angelone, Bonnie L; Chabris, Christopher F

    2002-08-01

    People often have difficulty detecting visual changes in scenes, a phenomenon referred to as 'change blindness'. Although change blindness is usually observed in pictures of objects that are not the focus of attention, it also occurs for attended objects in the real world. Here, we further explore the finding that many participants fail to detect the unexpected substitution of one conversation partner for another. We show that change blindness for a conversation partner occurs in a variety of situations. Furthermore, when tested with a photographic lineup following the change, participants who noticed the substitution showed better memory for both pre- and post-change experimenters than participants who did not detect the change. We conclude that change blindness in this case is associated with relatively ineffective or inaccessible representations of previously attended objects, and we contrast these results with others indicating that change blindness arises from a failure to compare the original and changed object.

  16. Dependence of phase transitions on small changes

    NASA Astrophysics Data System (ADS)

    Stoop, R.

    1993-06-01

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

  17. 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.

  18. 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

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Ihalawela, Chandrasiri A.

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

  1. 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

  2. Rapid Changes in the Light/Dark Cycle Disrupt Memory of Conditioned Fear in Mice

    PubMed Central

    Loh, Dawn H.; Navarro, Juliana; Hagopian, Arkady; Wang, Louisa M.; Deboer, Tom; Colwell, Christopher S.

    2010-01-01

    Background Circadian rhythms govern many aspects of physiology and behavior including cognitive processes. Components of neural circuits involved in learning and memory, e.g., the amygdala and the hippocampus, exhibit circadian rhythms in gene expression and signaling pathways. The functional significance of these rhythms is still not understood. In the present study, we sought to determine the impact of transiently disrupting the circadian system by shifting the light/dark (LD) cycle. Such “jet lag” treatments alter daily rhythms of gene expression that underlie circadian oscillations as well as disrupt the synchrony between the multiple oscillators found within the body. Methodology/Principal Findings We subjected adult male C57Bl/6 mice to a contextual fear conditioning protocol either before or after acute phase shifts of the LD cycle. As part of this study, we examined the impact of phase advances and phase delays, and the effects of different magnitudes of phase shifts. Under all conditions tested, we found that recall of fear conditioned behavior was specifically affected by the jet lag. We found that phase shifts potentiated the stress-evoked corticosterone response without altering baseline levels of this hormone. The jet lag treatment did not result in overall sleep deprivation, but altered the temporal distribution of sleep. Finally, we found that prior experience of jet lag helps to compensate for the reduced recall due to acute phase shifts. Conclusions/Significance Acute changes to the LD cycle affect the recall of fear-conditioned behavior. This suggests that a synchronized circadian system may be broadly important for normal cognition and that the consolidation of memories may be particularly sensitive to disruptions of circadian timing. PMID:20824058

  3. Circadian waveform bifurcation, but not phase-shifting, leaves cued fear memory intact.

    PubMed

    Harrison, E M; Carmack, S A; Block, C L; Sun, J; Anagnostaras, S G; Gorman, M R

    2017-02-01

    In mammals, memory acquisition and retrieval can be affected by time of day, as well as by manipulations of the light/dark cycle. Under bifurcation, a manipulation of circadian waveform, two subjective days and nights are experimentally induced in rodents. We examined the effect of bifurcation on Pavlovian fear conditioning, a prominent model of learning and memory. Here we demonstrate that bifurcation of the circadian waveform produces a small deficit in acquisition, but not on retrieval of fear memory. In contrast, repeated phase-shifting in a simulated jet-lag protocol impairs retrieval of memory for cued fear. The results have implications for those attempting to adjust to shift-work or other challenging schedules. Copyright © 2016 Elsevier Inc. All rights reserved.

  4. DNA methylation changes in plasticity genes accompany the formation and maintenance of memory.

    PubMed

    Halder, Rashi; Hennion, Magali; Vidal, Ramon O; Shomroni, Orr; Rahman, Raza-Ur; Rajput, Ashish; Centeno, Tonatiuh Pena; van Bebber, Frauke; Capece, Vincenzo; Garcia Vizcaino, Julio C; Schuetz, Anna-Lena; Burkhardt, Susanne; Benito, Eva; Navarro Sala, Magdalena; Javan, Sanaz Bahari; Haass, Christian; Schmid, Bettina; Fischer, Andre; Bonn, Stefan

    2016-01-01

    The ability to form memories is a prerequisite for an organism's behavioral adaptation to environmental changes. At the molecular level, the acquisition and maintenance of memory requires changes in chromatin modifications. In an effort to unravel the epigenetic network underlying both short- and long-term memory, we examined chromatin modification changes in two distinct mouse brain regions, two cell types and three time points before and after contextual learning. We found that histone modifications predominantly changed during memory acquisition and correlated surprisingly little with changes in gene expression. Although long-lasting changes were almost exclusive to neurons, learning-related histone modification and DNA methylation changes also occurred in non-neuronal cell types, suggesting a functional role for non-neuronal cells in epigenetic learning. Finally, our data provide evidence for a molecular framework of memory acquisition and maintenance, wherein DNA methylation could alter the expression and splicing of genes involved in functional plasticity and synaptic wiring.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

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

    PubMed

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

    2016-12-13

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

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Nabil, Mahdi; Rattner, Alexander S.

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

  10. 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.

  11. 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.

  12. Phase memory across two single-photon interferometers including wavelength conversion

    NASA Astrophysics Data System (ADS)

    Heuer, A.; Raabe, S.; Menzel, R.

    2014-10-01

    Spontaneous parametric down-conversion (SPDC) in a nonlinear crystal generates two single photons (signal and idler) with random phases. Thus, no first-order interference between them occurs. However, coherence can be induced in a cascaded setup of two crystals if, e.g., the idler modes of both crystals are aligned to be indistinguishable. Due to the effect of phase memory it is found that the first-order interference of the signal beams can be controlled by the phase delay between the pump beams. Even for pump photon delays much larger than the coherence length of the SPDC photons, the visibility is above 90%. The high visibilities reported here prove an almost perfect phase memory effect across the two interferometers for the pump and the signal photon modes.

  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. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Sleep, Memory, and Aging: The Link Between Slow-Wave Sleep and Episodic Memory Changes from Younger to Older Adults

    PubMed Central

    Scullin, Michael K.

    2012-01-01

    In younger adults, recently learned episodic memories are reactivated and consolidated during slow-wave sleep (SWS). Interestingly, SWS declines across the lifespan but little research has examined whether sleep-dependent memory consolidation occurs in older adults. In the present study, younger adults and healthy older adults encoded word pairs in the morning or evening and then returned following a sleep or no-sleep interval. Sleep stage scoring was obtained using a home sleep-stage monitoring system. In the younger adult group, there was a positive correlation between word retention and amount of SWS. In contrast, the older adults demonstrated no significant positive correlations, but one significant negative correlation, between memory and SWS. These findings suggest that the link between episodic memory and SWS that is typically observed in younger adults may be weakened or otherwise changed in the healthy elderly. PMID:22708533

  19. 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…

  20. 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…

  1. 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.

  2. 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.

  3. 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.

  4. Developmental changes in memory encoding: insights from event-related potentials.

    PubMed

    Rollins, Leslie; Riggins, Tracy

    2013-07-01

    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 previous ERP studies have examined subsequent memory effects in children. This represents a critical gap in the literature because encoding processes, and changes in neural correlates supporting encoding, partially account for age-related improvements in children's memory performance. Results revealed that subsequent memory effects differed between children and adults temporally, directionally, and topographically. These findings lend support to the hypothesis that encoding processes and their neural correlates are an important source of change in memory development. A video abstract of this article can be viewed at http://youtu.be/sH83_qVimgc. © 2013 John Wiley & Sons Ltd.

  5. Neural change following different memory training approaches in very preterm born children - A pilot study.

    PubMed

    Everts, Regula; Mürner-Lavanchy, Ines; Schroth, Gerhard; Steinlin, Maja

    2017-01-01

    There is mixed evidence regarding neural change following cognitive training. Brain activation increase, decrease, or a combination of both may occur. We investigated training-induced neural change using two different memory training approaches. Very preterm born children (aged 7-12 years) were randomly allocated to a memory strategy training, an intensive working memory practice or a waiting control group. Before and immediately after the trainings and the waiting period, brain activation during a visual working memory task was measured using fMRI and cognitive performance was assessed. Following both memory trainings, there was a significant decrease of fronto-parietal brain activation and a significant increase of memory performance. In the control group, no neural or performance change occurred after the waiting period. These pilot data point towards a training-related decrease of brain activation, independent of the training approach. Our data highlight the high training-induced plasticity of the child's brain during development.

  6. 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…

  7. 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…

  8. Passive thermal management using phase change materials

    NASA Astrophysics Data System (ADS)

    Ganatra, Yash Yogesh

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

  9. Metallic resist for phase-change lithography

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  10. 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

  11. Hippocampal theta phase-contingent memory retrieval in delay and trace eyeblink conditioning.

    PubMed

    Waselius, Tomi; Pöllänen, Eveliina; Wikgren, Jan; Penttonen, Markku; Nokia, Miriam S

    2017-09-04

    Hippocampal theta oscillations (3-12Hz) play a prominent role in learning. It has been suggested that encoding and retrieval of memories are supported by different phases of the theta cycle. Our previous study on trace eyeblink conditioning in rabbits suggests that the timing of the conditioned stimulus (CS) in relation to theta phase affects encoding but not retrieval of the memory trace. Here, we directly tested the effects of hippocampal theta phase on memory retrieval in two experiments conducted on adult female New Zealand White rabbits. In Experiment 1, animals were trained in trace eyeblink conditioning followed by extinction, and memory retrieval was tested by presenting the CS at troughs and peaks of the theta cycle during different stages of learning. In Experiment 2, animals were trained in delay conditioning either contingent on a high level of theta or at a random neural state. Conditioning was then followed by extinction conducted either at a random state, contingent on theta trough or contingent on theta peak. Our current results indicate that the phase of theta at CS onset has no effect on the performance of the behavioral learned response at any stage of classical eyeblink conditioning or extinction. In addition, theta-contingent trial presentation does not improve learning during delay eyeblink conditioning. The results are consistent with our earlier findings and suggest that the theta phase alone is not sufficient to affect learning at the behavioral level. It seems that the retrieval of recently acquired memories and consequently performing a learned response is moderated by neural mechanisms other than hippocampal theta. Copyright © 2017 Elsevier B.V. All rights reserved.

  12. 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

  13. Effect of circadian phase on memory acquisition and recall: operant conditioning vs. classical conditioning.

    PubMed

    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.

  14. 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.

  15. The influence of the memory effect on preparative separations using the amylose tris(3,5-dimethylphenylcarbamate) stationary phase.

    PubMed

    Putnam, Joel; Guiochon, Georges

    2011-08-05

    Acid/base mobile phase modifiers affect enantioseparations in ways that are not yet understood for the lack of systematic studies, which makes the scale-up of preparative separations difficult to predict. Shifts of the selectivity of certain pairs of enantiomers upon exposure of the column to these modifiers is amply documented. Furthermore, once the modifier has been removed from the mobile phase, the improved selectivity remains, this phenomenon has been named the memory effect. We selected four enantiomeric pairs for a systematic study of this memory effect. The selectivity of 4-chlorophenylalanine ethyl ester (4CPEE) improves after a solution of ethanesulfonic acid (ESA) is percolated through the column. The selectivity of propranolol HCl and Tröger's base increases after a solution of diiospropylethylamine is percolated through the column. The selectivity of these three pairs of enantiomers is inversely affected by percolation of the opposite acid/base solution. Each of these four compounds reached an equilibrium concentration that maintained the separation of the enantiomeric pairs. In contrast, the selectivity of trans-stilbene oxide (TSO) is not affected by either acid/base modifier. Preparative separations can be used to detect changes in the active surface of the chiral polymer stationary phase by measuring the change in selectivity and resolution when modifiers are used. Preparative method development was carried out on analytical columns and scale-up to 1cm ID columns were performed in this study.

  16. 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. Copyright © 2015 Elsevier Inc. All rights reserved.

  17. Functional and evolutionary trade-offs co-occur between two consolidated memory phases in Drosophila melanogaster.

    PubMed

    Lagasse, Fabrice; Moreno, Celine; Preat, Thomas; Mery, Frederic

    2012-10-07

    Memory is a complex and dynamic process that is composed of different phases. Its evolution under natural selection probably depends on a balance between fitness benefits and costs. In Drosophila, two separate forms of consolidated memory phases can be generated experimentally: anaesthesia-resistant memory (ARM) and long-term memory (LTM). In recent years, several studies have focused on the differences between these long-lasting memory types and have found that, at the functional level, ARM and LTM are antagonistic. How this functional relationship will affect their evolutionary dynamics remains unknown. We selected for flies with either improved ARM or improved LTM over several generations, and found that flies selected specifically for improvement of one consolidated memory phase show reduced performance in the other memory phase. We also found that improved LTM was linked to decreased longevity in male flies but not in females. Conversely, males with improved ARM had increased longevity. We found no correlation between either improved ARM or LTM and other phenotypic traits. This is, to our knowledge, the first evidence of a symmetrical evolutionary trade-off between two memory phases for the same learning task. Such trade-offs may have an important impact on the evolution of cognitive capacities. On a neural level, these results support the hypothesis that mechanisms underlying these forms of consolidated memory are, to some degree, antagonistic.

  18. 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).

  19. 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.

  20. Neuronal Oscillations Indicate Sleep-dependent Changes in the Cortical Memory Trace.

    PubMed

    Köster, Moritz; Finger, Holger; Kater, Maren-Jo; Schenk, Christoph; Gruber, Thomas

    2017-04-01

    Sleep promotes the consolidation of newly acquired associative memories. Here we used neuronal oscillations in the human EEG to investigate sleep-dependent changes in the cortical memory trace. The retrieval activity for object-color associations was assessed immediately after encoding and after 3 hr of sleep or wakefulness. Sleep had beneficial effects on memory performance and led to reduced event-related theta and gamma power during the retrieval of associative memories. Furthermore, event-related alpha suppression was attenuated in the wake group for memorized and novel stimuli. There were no sleep-dependent changes in retrieval activity for missed items or items retrieved without color. Thus, the sleep-dependent reduction in theta and gamma oscillations was specific for the retrieval of associative memories. In line with theoretical accounts on sleep-dependent memory consolidation, decreased theta may indicate reduced mediotemporal activity because of a transfer of information into neocortical networks during sleep, whereas reduced parietal gamma may reflect effects of synaptic downscaling. Changes in alpha suppression in the wake group possibly index reduced attentional resources that may also contribute to a lower memory performance in this group. These findings indicate that the consolidation of associative memories during sleep is associated with profound changes in the cortical memory trace and relies on multiple neuronal processes working in concert.

  1. Wearless scratch on NiTi shape memory alloy due to phase transformational shakedown

    NASA Astrophysics Data System (ADS)

    Feng, Xi-Qiao; Qian, Linmao; Yan, Wenyi; Sun, Qingping

    2008-03-01

    Cyclic microscratch tests were performed to examine the scratching behavior of NiTi shape memory alloy. It shows a superior wear resistance within the temperature range of 22-120°C, but the corresponding physical mechanisms are different at low and high temperatures. We introduced the concept of phase transformational shakedown to interpret the wear-resistant behavior. At room temperature, a scratch groove may be caused by repeated scratching, but its depth stops increasing after a certain number of scratching cycles once the phase transformational shakedown state has been achieved. The groove will be self-healed upon heating as a result of the shape memory effect. At 60 and 120°C, however, no evident scratch groove is observed under the same load due to the pseudoelastic effect and the increase in the phase transition stress with temperature.

  2. Memory load modulates graded changes in distracter filtering

    PubMed Central

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

    2015-01-01

    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

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

    PubMed

    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.

  4. 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

  5. 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.

  6. Long-term memory and volatility clustering in high-frequency price changes

    NASA Astrophysics Data System (ADS)

    oh, Gabjin; Kim, Seunghwan; Eom, Cheoljun

    2008-02-01

    We studied the long-term memory in diverse stock market indices and foreign exchange rates using Detrended Fluctuation Analysis (DFA). For all high-frequency market data studied, no significant long-term memory property was detected in the return series, while a strong long-term memory property was found in the volatility time series. The possible causes of the long-term memory property were investigated using the return data filtered by the AR(1) model, reflecting the short-term memory property, the GARCH(1,1) model, reflecting the volatility clustering property, and the FIGARCH model, reflecting the long-term memory property of the volatility time series. The memory effect in the AR(1) filtered return and volatility time series remained unchanged, while the long-term memory property diminished significantly in the volatility series of the GARCH(1,1) filtered data. Notably, there is no long-term memory property, when we eliminate the long-term memory property of volatility by the FIGARCH model. For all data used, although the Hurst exponents of the volatility time series changed considerably over time, those of the time series with the volatility clustering effect removed diminish significantly. Our results imply that the long-term memory property of the volatility time series can be attributed to the volatility clustering observed in the financial time series.

  7. 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

  8. 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.

  9. Fully phase-encrypted memory using cascaded extended fractional Fourier transform

    NASA Astrophysics Data System (ADS)

    Nishchal, Naveen Kumar; Joseph, Joby; Singh, Kehar

    2004-08-01

    In this paper, we implement a fully phase-encrypted memory system using cascaded extended fractional Fourier transform (FRT). We encrypt and decrypt a two-dimensional image obtained from an amplitude image. The full phase image to be encrypted is fractional Fourier transformed three times and random phase masks are placed in the two intermediate planes. Performing the FRT three times increases the key size, at an added complexity of one more lens. The encrypted image is holographically recorded in a photorefractive crystal and is then decrypted by generating through phase conjugation, the conjugate of the encrypted image. A lithium niobate crystal has been used as a phase contrast filter to reconstruct the decrypted phase image, alleviating the need of alignment in the Fourier plane making the system rugged.

  10. 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.

  11. Phase-change oscillations in silicon microwires

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Irreversible reactions studied with nanosecond transmission electron microscopy movies: Laser crystallization of phase change materials

    NASA Astrophysics Data System (ADS)

    Santala, M. K.; Reed, B. W.; Raoux, S.; Topuria, T.; LaGrange, T.; Campbell, G. H.

    2013-04-01

    We use multi-frame, nanosecond-scale photo-emission transmission electron microscopy to create movies of irreversible reactions that occur too rapidly to capture with conventional microscopy. The technique is applied to the crystallization of phase change materials used for optical and resistive memory. For those applications, laser- or current-induced crystallization is orders of magnitude too fast to capture with other imaging techniques. We recorded movies of laser-induced crystallization and measured crystal growth rates at temperatures close to where the maximum growth rate occurs. This paves the way for studying crystallization kinetics of phase change materials over the whole range of technologically relevant temperatures.

  20. 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…

  1. 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…

  2. 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. © 2015 S. Karger AG, Basel

  3. 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.

  4. 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.

  5. Basic perceptual changes that alter meaning and neural correlates of recognition memory.

    PubMed

    Gao, Chuanji; Hermiller, Molly S; Voss, Joel L; Guo, Chunyan

    2015-01-01

    It is difficult to pinpoint the border between perceptual and conceptual processing, despite their treatment as distinct entities in many studies of recognition memory. For instance, alteration of simple perceptual characteristics of a stimulus can radically change meaning, such as the color of bread changing from white to green. We sought to better understand the role of perceptual and conceptual processing in memory by identifying the effects of changing a basic perceptual feature (color) on behavioral and neural correlates of memory in circumstances when this change would be expected to either change the meaning of a stimulus or to have no effect on meaning (i.e., to influence conceptual processing or not). Abstract visual shapes ("squiggles") were colorized during study and presented during test in either the same color or a different color. Those squiggles that subjects found to resemble meaningful objects supported behavioral measures of conceptual priming, whereas meaningless squiggles did not. Further, changing color from study to test had a selective effect on behavioral correlates of priming for meaningful squiggles, indicating that color change altered conceptual processing. During a recognition memory test, color change altered event-related brain potential (ERP) correlates of memory for meaningful squiggles but not for meaningless squiggles. Specifically, color change reduced the amplitude of frontally distributed N400 potentials (FN400), implying that these potentials indicated conceptual processing during recognition memory that was sensitive to color change. In contrast, color change had no effect on FN400 correlates of recognition for meaningless squiggles, which were overall smaller in amplitude than for meaningful squiggles (further indicating that these potentials signal conceptual processing during recognition). Thus, merely changing the color of abstract visual shapes can alter their meaning, changing behavioral and neural correlates of memory

  6. Basic perceptual changes that alter meaning and neural correlates of recognition memory

    PubMed Central

    Gao, Chuanji; Hermiller, Molly S.; Voss, Joel L.; Guo, Chunyan

    2015-01-01

    It is difficult to pinpoint the border between perceptual and conceptual processing, despite their treatment as distinct entities in many studies of recognition memory. For instance, alteration of simple perceptual characteristics of a stimulus can radically change meaning, such as the color of bread changing from white to green. We sought to better understand the role of perceptual and conceptual processing in memory by identifying the effects of changing a basic perceptual feature (color) on behavioral and neural correlates of memory in circumstances when this change would be expected to either change the meaning of a stimulus or to have no effect on meaning (i.e., to influence conceptual processing or not). Abstract visual shapes (“squiggles”) were colorized during study and presented during test in either the same color or a different color. Those squiggles that subjects found to resemble meaningful objects supported behavioral measures of conceptual priming, whereas meaningless squiggles did not. Further, changing color from study to test had a selective effect on behavioral correlates of priming for meaningful squiggles, indicating that color change altered conceptual processing. During a recognition memory test, color change altered event-related brain potential (ERP) correlates of memory for meaningful squiggles but not for meaningless squiggles. Specifically, color change reduced the amplitude of frontally distributed N400 potentials (FN400), implying that these potentials indicated conceptual processing during recognition memory that was sensitive to color change. In contrast, color change had no effect on FN400 correlates of recognition for meaningless squiggles, which were overall smaller in amplitude than for meaningful squiggles (further indicating that these potentials signal conceptual processing during recognition). Thus, merely changing the color of abstract visual shapes can alter their meaning, changing behavioral and neural correlates of

  7. OPC for edge post structures using chrome-less phase shifting mask in 3-D memory

    NASA Astrophysics Data System (ADS)

    Chen, Yung-Tin; Lee, M. T.

    2005-11-01

    Matrix Semiconductor have successfully implemented chrome-less phase shifting mask to their 0.13μm half pitch, 3D memory circuit process using 0.7NA KrF photolithography. The K1 factor is 0.37. OPC for post structures at the edge of memory array presents a special challenge for 3-D memory circuits. As 3-D memory circuits are stacked vertically, the topography also accumulates to the top of memory layers, thus resulting in reduced process margin due to "peeling off" of edge posts. Ruled based and model based OPC for edge posts are studied in this paper. A simple ruled based OPC is developed to compensate the size difference between the posts at array center and the ones at array edge. A manufacturing oriented OPC strategy is used to gain optimum process windows. The wafer printing results from ruled based OPC are compared to the model prediction from commercial lithography software. Discrepancy between wafer printing results and model prediction using thin film mask approximation is reported. A new model based OPC method for chrome-less PSM in the application to post structures is proposed from this study.

  8. Design rules for phase-change materials in data storage applications.

    PubMed

    Lencer, Dominic; Salinga, Martin; Wuttig, Matthias

    2011-05-10

    Phase-change materials can rapidly and reversibly be switched between an amorphous and a crystalline phase. Since both phases are characterized by very different optical and electrical properties, these materials can be employed for rewritable optical and electrical data storage. Hence, there are considerable efforts to identify suitable materials, and to optimize them with respect to specific applications. Design rules that can explain why the materials identified so far enable phase-change based devices would hence be very beneficial. This article describes materials that have been successfully employed and dicusses common features regarding both typical structures and bonding mechanisms. It is shown that typical structural motifs and electronic properties can be found in the crystalline state that are indicative for resonant bonding, from which the employed contrast originates. The occurence of resonance is linked to the composition, thus providing a design rule for phase-change materials. This understanding helps to unravel characteristic properties such as electrical and thermal conductivity which are discussed in the subsequent section. Then, turning to the transition kinetics between the phases, the current understanding and modeling of the processes of amorphization and crystallization are discussed. Finally, present approaches for improved high-capacity optical discs and fast non-volatile electrical memories, that hold the potential to succeed present-day's Flash memory, are presented.

  9. 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. Copyright © 2015 Elsevier Inc. All rights reserved.

  10. 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…

  11. 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…

  12. An analytical model for nanoscale electrothermal probe recording on phase-change media

    NASA Astrophysics Data System (ADS)

    Aziz, Mustafa M.; Wright, C. David

    2006-02-01

    Scanning probe memories are now emerging as a means of achieving nanoscale resolution data storage. The use of microscopic conductive tips in contact with a phase-change material to record data as amorphous and crystalline marks is one such approach, making use of the large difference in electrical conductivity between the two phases to distinguish between two binary states on replay and hence provide a memory function. The writing process is complex and involves electronic, thermal, and phase-change processes that are difficult to model and study except using numerical techniques. A simplified analytical model of electrothermal writing by probe on a basic two-layer phase-change structure is developed here, and used to predict the required voltage levels for recording and the expected diameters of recorded crystalline and amorphous marks. A simplified model of cooling and solidification was also developed to study the cooling rates during amorphization. The predictions are shown to be in agreement with published experimental measurements and numerical simulations. The developed analytical models were extended to investigate the effects of introducing coating layers on recording voltage levels, to study the depth profiles of recorded marks, and to derive expressions for the capacitance and resistance of the phase-change layer that contribute to the transient behavior of the recording system.

  13. 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.

  14. Distractor-resistant Short-Term Memory Is Supported by Transient Changes in Neural Stimulus Representations.

    PubMed

    Derrfuss, Jan; Ekman, Matthias; Hanke, Michael; Tittgemeyer, Marc; Fiebach, Christian J

    2017-09-01

    Goal-directed behavior in a complex world requires the maintenance of goal-relevant information despite multiple sources of distraction. However, the brain mechanisms underlying distractor-resistant working or short-term memory (STM) are not fully understood. Although early single-unit recordings in monkeys and fMRI studies in humans pointed to an involvement of lateral prefrontal cortices, more recent studies highlighted the importance of posterior cortices for the active maintenance of visual information also in the presence of distraction. Here, we used a delayed match-to-sample task and multivariate searchlight analyses of fMRI data to investigate STM maintenance across three extended delay phases. Participants maintained two samples (either faces or houses) across an unfilled pre-distractor delay, a distractor-filled delay, and an unfilled post-distractor delay. STM contents (faces vs. houses) could be decoded above-chance in all three delay phases from occipital, temporal, and posterior parietal areas. Classifiers trained to distinguish face versus house maintenance successfully generalized from pre- to post-distractor delays and vice versa, but not to the distractor delay period. Furthermore, classifier performance in all delay phases was correlated with behavioral performance in house, but not face, trials. Our results demonstrate the involvement of distributed posterior, but not lateral prefrontal, cortices in active maintenance during and after distraction. They also show that the neural code underlying STM maintenance is transiently changed in the presence of distractors and reinstated after distraction. The correlation with behavior suggests that active STM maintenance is particularly relevant in house trials, whereas face trials might rely more strongly on contributions from long-term memory.

  15. Age-related changes in parietal lobe activation during an episodic memory retrieval task.

    PubMed

    Oedekoven, Christiane S H; Jansen, Andreas; Kircher, Tilo T; Leube, Dirk T

    2013-05-01

    The crucial role of lateral parietal regions in episodic memory has been confirmed in previous studies. While aging has an influence on retrieval of episodic memory, it remains to be examined how the involvement of lateral parietal regions in episodic memory changes with age. We investigated episodic memory retrieval in two age groups, using faces as stimuli and retrieval success as a measure of episodic memory. Young and elderly participants showed activation within a similar network, including lateral and medial parietal as well as prefrontal regions, but elderly showed a higher level of brain activation regardless of condition. Furthermore, we examined functional connectivity in the two age groups and found a more extensive network in the young group, including correlations of parietal and prefrontal regions. In the elderly, the overall stronger activation related to memory performance may indicate a compensatory process for a less extensive functional network.

  16. 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

  17. Thermoplastic High Strain Multishape Memory Polymer: Side-Chain Polynorbornene with Columnar Liquid Crystalline Phase.

    PubMed

    Zhao, Ruiying; Zhao, Tipeng; Jiang, Xuqiang; Liu, Xin; Shi, Dong; Liu, Chenyang; Yang, Shuang; Chen, Er-Qiang

    2017-03-01

    A thermoplastic high strain multishape memory polymer can be fabricated using a hemiphasmid side-chain polynorbornene (P1) with hexagonal columnar liquid crystalline (ΦH ) phase. Without any chemical crosslinks, P1 can memorize multiple temporary shapes with high strain and exhibit excellent shape fixity and shape recovery. As the building blocks of ΦH , the multichain columns in P1 act as robust physical crosslinks. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Functional cerebral changes in multiple sclerosis patients during an autobiographical memory test.

    PubMed

    Ernst, Alexandra; Noblet, Vincent; Denkova, Ekaterina; Blanc, Frédéric; de Seze, Jérôme; Gounot, Daniel; Manning, Liliann

    2015-01-01

    Our aim was to investigate the functional underpinnings of autobiographical memory (AM) impairment in multiple sclerosis (MS) patients. To that end, 18 patients and 18 controls underwent the autobiographical interview (AI). Subsequently, the 36 participants underwent a functional magnetic resonance imaging (fMRI) session designed to assess the construction and elaboration of AMs. A categorical control task was also presented. Patients were trained in the fMRI procedure to optimise the procedural aspects accompanying the task itself. Although the patients obtained significantly poorer AI scores (p < .001), their performance on the easier AM fMRI task was efficiently carried out, allowing relevant comparisons with healthy controls. Relatively to healthy controls, the patients showed increased and bilateral cerebral activations (p < .005) during the construction and elaboration phases. The prefrontal, temporal and posterior cerebral region activations were located within the core network sustaining AM, with the bilateral prefrontal region being centrally involved. The parametric neural responses to the difficulty of access and amount of details of memories were also significantly different for the two groups, with the right hippocampal region showing a particularly increased recruitment (p < .005). The findings suggested the presence of functional cerebral changes during AM performance and supported the presence of AM retrieval deficit in MS patients.

  19. Mechanics of Metals with Phase Changes

    SciTech Connect

    Lashley, Jason C.

    2001-01-01

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

  20. 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.

  1. Phase Change Material Heat Exchanger Life Test

    NASA Technical Reports Server (NTRS)

    Lillibridge, Sean; Stephan, Ryan

    2009-01-01

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

  2. Phase Change Material Heat Exchanger Life Test

    NASA Technical Reports Server (NTRS)

    Lillibridge, Sean; Stephan, Ryan

    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.

  3. 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.

  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. Synthesis and Screening of Phase Change Chalcogenide Thin Film Materials for Data Storage.

    PubMed

    Guerin, Samuel; Hayden, Brian; Hewak, Daniel W; Vian, Chris

    2017-07-10

    A combinatorial synthetic methodology based on evaporation sources under an ultrahigh vacuum has been used to directly synthesize compositional gradient thin film libraries of the amorphous phases of GeSbTe alloys at room temperature over a wide compositional range. An optical screen is described that allows rapid parallel mapping of the amorphous-to-crystalline phase transition temperature and optical contrast associated with the phase change on such libraries. The results are shown to be consistent with the literature for compositions where published data are available along the Sb2Te3-GeTe tie line. The results reveal a minimum in the crystallization temperature along the Sb2Te3-Ge2Te3 tie line, and the method is able to resolve subsequent cubic-to-hexagonal phase transitions in the GST crystalline phase. HT-XRD has been used to map the phases at sequentially higher temperatures, and the results are reconciled with the literature and trends in crystallization temperatures. The results clearly delineate compositions that crystallize to pure GST phases and those that cocrystallize Te. High-throughput measurement of the resistivity of the amorphous and crystalline phases has allowed the compositional and structural correlation of the resistivity contrast associated with the amorphous-to-crystalline transition, which range from 5-to-8 orders of magnitude for the compositions investigated. The results are discussed in terms of the compromises in the selection of these materials for phase change memory applications and the potential for further exploration through more detailed secondary screening of doped GST or similar classes of phase change materials designed for the demands of future memory devices.

  6. Brain Events Underlying Episodic Memory Changes in Aging: A Longitudinal Investigation of Structural and Functional Connectivity.

    PubMed

    Fjell, Anders M; Sneve, Markus H; Storsve, Andreas B; Grydeland, Håkon; Yendiki, Anastasia; Walhovd, Kristine B

    2016-03-01

    Episodic memories are established and maintained by close interplay between hippocampus and other cortical regions, but degradation of a fronto-striatal network has been suggested to be a driving force of memory decline in aging. We wanted to directly address how changes in hippocampal-cortical versus striatal-cortical networks over time impact episodic memory with age. We followed 119 healthy participants (20-83 years) for 3.5 years with repeated tests of episodic verbal memory and magnetic resonance imaging for quantification of functional and structural connectivity and regional brain atrophy. While hippocampal-cortical functional connectivity predicted memory change in young, changes in cortico-striatal functional connectivity were related to change in recall in older adults. Within each age group, effects of functional and structural connectivity were anatomically closely aligned. Interestingly, the relationship between functional connectivity and memory was strongest in the age ranges where the rate of reduction of the relevant brain structure was lowest, implying selective impacts of the different brain events on memory. Together, these findings suggest a partly sequential and partly simultaneous model of brain events underlying cognitive changes in aging, where different functional and structural events are more or less important in various time windows, dismissing a simple uni-factorial view on neurocognitive aging. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

  7. Age-related changes to the neural correlates of working memory which emerge after midlife.

    PubMed

    Macpherson, Helen N; White, David J; Ellis, Kathryn A; Stough, Con; Camfield, David; Silberstein, Richard; Pipingas, Andrew

    2014-01-01

    Previous research has indicated that the neural processes which underlie working memory change with age. Both age-related increases and decreases to cortical activity have been reported. This study investigated which stages of working memory are most vulnerable to age-related changes after midlife. To do this we examined age-differences in the 13 Hz steady state visually evoked potential (SSVEP) associated with a spatial working memory delayed response task. Participants were 130 healthy adults separated into a midlife (40-60 years) and an older group (61-82 years). Relative to the midlife group, older adults demonstrated greater bilateral frontal activity during encoding and this pattern of activity was related to better working memory performance. In contrast, evidence of age-related under activation was identified over left frontal regions during retrieval. Findings from this study suggest that after midlife, under-activation of frontal regions during retrieval contributes to age-related decline in working memory performance.

  8. 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

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

    USDA-ARS?s Scientific Manuscript database

    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,...

  10. 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.

  11. 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.

  12. 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.

  13. Lessons from a crab: molecular mechanisms in different memory phases of Chasmagnathus.

    PubMed

    Romano, Arturo; Locatelli, Fernando; Freudenthal, Ramiro; Merlo, Emiliano; Feld, Mariana; Ariel, Pablo; Lemos, Darío; Federman, Noel; Fustiñana, Maria Sol

    2006-06-01

    Consolidation of long-term memory requires the activation of several transduction pathways that lead to post-translational modifications of synaptic proteins and to regulation of gene expression, both of which promote stabilization of specific changes in the activated circuits. In search of the molecular mechanisms involved in such processes, we used the context-signal associative learning paradigm of the crab Chasmagnathus. In this model, we studied the role of some molecular mechanisms, namely cAMP-dependent protein kinase (PKA), extracellular-signal-regulated kinase (ERK), the nuclear factor kappa B (NF-kappaB) transcription factor, and the role of synaptic proteins such as amyloid beta precursor protein, with the object of describing key mechanisms involved in memory processing. In this article we review the most salient results obtained over a decade of research in this memory model.

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

    PubMed

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

    2015-02-24

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

  15. Damping characteristics of R-phase NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wu, Kuang-Hsi; Dalip, S. K.; Liu, Y. Q.; Pu, Zhongjie J.

    1995-05-01

    This paper focuses on the study of damping behavior associated with the R-phase in NiTi shape memory alloy. The variation of the tan((delta) ) and Young's modulus as a function of temperature, ramp rate, frequency, and applied amplitude are systematically studied using a dynamic mechanical analyzer (DMA). It was found that the tan((delta) ) versus the temperature curve exhibits four peaks during the thermal cycle, two peaks each in the heating and in the cooling process. These peaks correspond to the martensite to R-phase, R-phase to austenite, austenite to R-phase, and R-phase to martensite transformations. The value of the tan((delta) ) at each peak is in proportion to the ramp rate and in reverse proportion to frequency. The vibration amplitude tends to have a minor effect on the tan((delta) ). The variation of these peaks with ramp rate, frequency, and amplitude are discussed based on the Delorme and De Jonghe damping model. In addition, the experimental results show that an isotropic softening occurs in the Young's modulus during martensite to R-phase, R-phase to austenite, austenite to R-phase, and R-phase to martensite transformations.

  16. Neural changes underlying the development of episodic memory during middle childhood.

    PubMed

    Ghetti, Simona; Bunge, Silvia A

    2012-10-01

    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. Copyright © 2012 Elsevier Ltd. All rights reserved.

  17. Developmental Changes in Working Memory, Updating, and Math Achievement

    ERIC Educational Resources Information Center

    Lee, Kerry; Bull, Rebecca

    2016-01-01

    Children with higher working memory or updating (WMU) capacity perform better in math. What is less clear is whether and how this relation varies with grade. Children (N = 673, kindergarten to Grade 9) participated in a 4-year cross-sequential study. Data from 3 WMU (Listening Recall, Mr. X, and an updating task) and a standardized math task…

  18. 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,…

  19. 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)

  20. 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.…

  1. Developmental Changes in Working Memory, Updating, and Math Achievement

    ERIC Educational Resources Information Center

    Lee, Kerry; Bull, Rebecca

    2016-01-01

    Children with higher working memory or updating (WMU) capacity perform better in math. What is less clear is whether and how this relation varies with grade. Children (N = 673, kindergarten to Grade 9) participated in a 4-year cross-sequential study. Data from 3 WMU (Listening Recall, Mr. X, and an updating task) and a standardized math task…

  2. 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,…

  3. 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.

  4. Electrical properties of Cr-doped Sb2Te3 phase change material

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    Phase Change Memory (PCM) is regarded as one of the most promising candidates for the next-generation nonvolatile memory. Its storage medium, phase change material, has attracted continuous exploration. Sb2Te3 is a high-speed phase change material matrix with low crystallization temperature. Cr-doped Sb2Te3 (CST) films with suitable composition have been studied and proved to be a promising novel phase change material with high speed and good thermal stability. In this paper, detailed Rs-T characteristics and Hall characteristics of the CST films are studied. We find that, when more parts of the film crystallizes into the ordered structure, the activation energy for electrical conduction (Eσ) decreases, indicating that the semiconductor property is weakened. And with the increase of Cr-dopants, Eσ of the As-deposited (As-de) amorphous CST films decreases, thus the thermal stability of resistance is improved. Hall results show that Sb2Te3 and CST films are all in P-type. For As-de amorphous films, with the increase of Cr-dopants, the carrier mobility decreases all along, while the carrier density decreases at first and then increases. For the crystalline films, with the increase of Cr-dopants, the carrier mobility decreases, while the carrier density increases.

  5. 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

  6. 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.

  7. A Dynamic Neural Field Model of Visual Working Memory and Change Detection

    PubMed Central

    Johnson, Jeffrey S.; Spencer, John P.; Luck, Steven J.; Schöner, Gregor

    2009-01-01

    Efficient visually guided behavior depends on the ability to form, retain, and compare visual representations for objects that may be separated in space and time. This ability relies on a short-term form of memory known as visual working memory. Although a considerable body of research has begun to shed light on the neurocognitive systems subserving this form of memory, few theories have addressed these processes in an integrated, neurally plausible framework. We describe a layered neural architecture that implements encoding and maintenance, and links these processes to a plausible comparison process. In addition, the model makes the novel prediction that change detection will be enhanced when metrically similar features are remembered. Results from experiments probing memory for color and for orientation were consistent with this novel prediction. These findings place strong constraints on models addressing the nature of visual working memory and its underlying mechanisms. PMID:19368698

  8. A dynamic neural field model of visual working memory and change detection.

    PubMed

    Johnson, Jeffrey S; Spencer, John P; Luck, Steven J; Schöner, Gregor

    2009-05-01

    Efficient visually guided behavior depends on the ability to form, retain, and compare visual representations for objects that may be separated in space and time. This ability relies on a short-term form of memory known as visual working memory. Although a considerable body of research has begun to shed light on the neurocognitive systems subserving this form of memory, few theories have addressed these processes in an integrated, neurally plausible framework. We describe a layered neural architecture that implements encoding and maintenance, and links these processes to a plausible comparison process. In addition, the model makes the novel prediction that change detection will be enhanced when metrically similar features are remembered. Results from experiments probing memory for color and for orientation were consistent with this novel prediction. These findings place strong constraints on models addressing the nature of visual working memory and its underlying mechanisms.

  9. Size-dependent and tunable crystallization of GeSbTe phase-change nanoparticles.

    PubMed

    Chen, Bin; Ten Brink, Gert H; Palasantzas, George; Kooi, Bart J

    2016-12-20

    Chalcogenide-based nanostructured phase-change materials (PCMs) are considered promising building blocks for non-volatile memory due to their high write and read speeds, high data-storage density, and low power consumption. Top-down fabrication of PCM nanoparticles (NPs), however, often results in damage and deterioration of their useful properties. Gas-phase condensation based on magnetron sputtering offers an attractive and straightforward solution to continuously down-scale the PCMs into sub-lithographic sizes. Here we unprecedentedly present the size dependence of crystallization for Ge2Sb2Te5 (GST) NPs, whose production is currently highly challenging for chemical synthesis or top-down fabrication. Both amorphous and crystalline NPs have been produced with excellent size and composition control with average diameters varying between 8 and 17 nm. The size-dependent crystallization of these NPs was carefully analyzed through in-situ heating in a transmission electron microscope, where the crystallization temperatures (Tc) decrease when the NPs become smaller. Moreover, methane incorporation has been observed as an effective method to enhance the amorphous phase stability of the NPs. This work therefore elucidates that GST NPs synthesized by gas-phase condensation with tailored properties are promising alternatives in designing phase-change memories constrained by optical lithography limitations.

  10. Size-dependent and tunable crystallization of GeSbTe phase-change nanoparticles

    PubMed Central

    Chen, Bin; ten Brink, Gert H.; Palasantzas, George; Kooi, Bart J.

    2016-01-01

    Chalcogenide-based nanostructured phase-change materials (PCMs) are considered promising building blocks for non-volatile memory due to their high write and read speeds, high data-storage density, and low power consumption. Top-down fabrication of PCM nanoparticles (NPs), however, often results in damage and deterioration of their useful properties. Gas-phase condensation based on magnetron sputtering offers an attractive and straightforward solution to continuously down-scale the PCMs into sub-lithographic sizes. Here we unprecedentedly present the size dependence of crystallization for Ge2Sb2Te5 (GST) NPs, whose production is currently highly challenging for chemical synthesis or top-down fabrication. Both amorphous and crystalline NPs have been produced with excellent size and composition control with average diameters varying between 8 and 17 nm. The size-dependent crystallization of these NPs was carefully analyzed through in-situ heating in a transmission electron microscope, where the crystallization temperatures (Tc) decrease when the NPs become smaller. Moreover, methane incorporation has been observed as an effective method to enhance the amorphous phase stability of the NPs. This work therefore elucidates that GST NPs synthesized by gas-phase condensation with tailored properties are promising alternatives in designing phase-change memories constrained by optical lithography limitations. PMID:27996054

  11. Size-dependent and tunable crystallization of GeSbTe phase-change nanoparticles

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Ten Brink, Gert H.; Palasantzas, George; Kooi, Bart J.

    2016-12-01

    Chalcogenide-based nanostructured phase-change materials (PCMs) are considered promising building blocks for non-volatile memory due to their high write and read speeds, high data-storage density, and low power consumption. Top-down fabrication of PCM nanoparticles (NPs), however, often results in damage and deterioration of their useful properties. Gas-phase condensation based on magnetron sputtering offers an attractive and straightforward solution to continuously down-scale the PCMs into sub-lithographic sizes. Here we unprecedentedly present the size dependence of crystallization for Ge2Sb2Te5 (GST) NPs, whose production is currently highly challenging for chemical synthesis or top-down fabrication. Both amorphous and crystalline NPs have been produced with excellent size and composition control with average diameters varying between 8 and 17 nm. The size-dependent crystallization of these NPs was carefully analyzed through in-situ heating in a transmission electron microscope, where the crystallization temperatures (Tc) decrease when the NPs become smaller. Moreover, methane incorporation has been observed as an effective method to enhance the amorphous phase stability of the NPs. This work therefore elucidates that GST NPs synthesized by gas-phase condensation with tailored properties are promising alternatives in designing phase-change memories constrained by optical lithography limitations.

  12. Changes in working memory after traumatic brain injury in children.

    PubMed

    Levin, Harvey S; Hanten, Gerri; Zhang, Lifang; Swank, Paul R; Ewing-Cobbs, Linda; Dennis, Maureen; Barnes, Marcia A; Max, Jeffrey; Schachar, Russell; Chapman, Sandra B; Hunter, Jill V

    2004-04-01

    The impact of traumatic brain injury (TBI) on working memory (WM) was studied in 144 children (79 with mild, 23 with moderate, and 42 with severe injuries) who underwent magnetic resonance imaging (MRI) at 3 months and were tested at baseline and at 3, 6, 12, and 24 months postinjury. An n-back WM task for letter identity was administered with memory load ranging from 1- to 3-back and a 0-back condition. A TBI Severity x Quadratic Tune interaction showed that net percentage correct (correct detections of targets minus false alarms) was significantly lower in severe than in mild TBI groups. The Left Frontal Lesions x Age interaction approached significance. Mechanisms mediating late decline in WM and the effects of left frontal lesions are discussed.

  13. Phase diagram kinetics for shape memory alloys: a robust finite element implementation

    NASA Astrophysics Data System (ADS)

    Gao, Xiujie; Qiao, Rui; Brinson, L. Catherine

    2007-12-01

    A physically based one-dimensional shape memory alloy (SMA) model is implemented into the finite element software ABAQUS via a user interface. Linearization of the SMA constitutive law together with complete transformation kinetics is performed and tabulated for implementation. Robust rules for transformation zones of the phase diagram are implemented and a new strategy for overlapping transformation zones is developed. The iteration algorithm, switching point updates and solution strategies are developed and are presented in detail. The code is validated via baseline simulations including the shape memory effect and pseudoelasticity and then further tested with complex loading paths. A hybrid composite with self-healing function is then simulated using the developed code. The example demonstrates the usefulness of the methods for the design and simulation of materials or structures actuated by SMA wires or ribbons.

  14. Innovative Phase Change Approach for Significant Energy Savings

    DTIC Science & Technology

    2016-09-01

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

  15. 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,…

  16. 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,…

  17. Dynamic changes in large-scale functional network organization during autobiographical memory retrieval.

    PubMed

    Inman, Cory S; James, G Andrew; Vytal, Katherine; Hamann, Stephan

    2017-09-23

    Autobiographical memory (AM), episodic memory for life events, involves the orchestration of multiple dynamic cognitive processes, including memory access and subsequent elaboration. Previous neuroimaging studies have contrasted memory access and elaboration processes in terms of regional brain activation and connectivity within large, multi-region networks. Although interactions between key memory-related regions such as the hippocampus and prefrontal cortex (PFC) have been shown to play an important role in AM retrieval, it remains unclear how such connectivity between specific, individual regions involved in AM retrieval changes dynamically across the retrieval process and how these changes relate to broader memory networks throughout the whole brain. The present functional magnetic resonance imaging (fMRI) study sought to assess the specific changes in interregional connectivity patterns across the AM retrieval processes to understand network level mechanisms of AM retrieval and further test current theoretical accounts of dynamic AM retrieval processes. We predicted that dynamic connections would reflect two hypothesized memory processes, with initial processes reflecting memory-access related connections between regions such as the anterior hippocampal and ventrolateral PFC regions, and later processes reflecting elaboration-related connections between dorsolateral frontal working memory regions and parietal-occipital visual imagery regions. One week prior to fMRI scanning, fifteen healthy adult participants generated AMs using personally selected cue words. During scanning, participants were cued to retrieve the AMs. We used a moving-window functional connectivity analysis and graph theoretic measures to examine dynamic changes in the strength and centrality of connectivity among regions involved in AM retrieval. Consistent with predictions, early, access-related processing primarily involved a ventral frontal to temporal-parietal network associated with

  18. 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.

  19. 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.

  20. Cross-talk in phase encoded volume holographic memories employing unitary matrices

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Berger, G.; Dietz, M.; Denz, C.

    2006-12-01

    The cross-talk noise in phase encoded holographic memories employing unitary matrices is theoretically investigated. After reviewing some earlier work in this area, we derive a relationship for the noise-to-signal ratio for phase-code multiplexing with unitary matrices. The noise-to-signal ratio rises in a zigzag way on increasing the storage capacity. Cross-talk is mainly caused by high-frequency phase codes. Unitary matrices of even orders have only one bad code, while unitary matrices of odd orders have four bad codes. The signal-to-noise ratios of all other codes can in each case be drastically improved by omission of these bad codes. We summarize the optimal orders of Hadamard and unitary matrices for recording a given number of holograms. The unitary matrices can enable us to adjust the available spatial light modulators to achieve the maximum possible storage capacity in both circumstances with and without bad codes.

  1. Changes in memory before and after stroke differ by age and sex, but not by race.

    PubMed

    Wang, Qianyi; Mejía-Guevara, Iván; Rist, Pamela M; Walter, Stefan; Capistrant, Benjamin D; Glymour, M Maria

    2014-01-01

    Post-stroke memory impairment is more common among older adults, women and blacks. It is unclear whether post-stroke differences reflect differential effects of stroke per se or differences in prestroke functioning. We compare memory trajectories before and after stroke by age, sex and race. Health and Retirement Study participants aged ≥50 years (n = 17,341), with no stroke history at baseline, were interviewed biennially up to 10 years for first self- or proxy-reported stroke (n = 1,574). Segmented linear regression models were used to compare annual rates of memory change before and after stroke among 1,169 stroke survivors, 405 stroke decedents and 15,767 stroke-free participants. Effect modification was evaluated with analyses stratified by baseline age (≤70 vs. >70), sex and race (white vs. nonwhite), and using interaction terms between age/sex/race indicators and annual memory change. Older (>70 years) adults experienced a faster memory decline before stroke (-0.19 vs. -0.10 points/year for survivors, -0.24 vs. -0.13 points/year for decedents, p < 0.001 for both interactions), and among stroke survivors, larger memory decrements (-0.64 vs. -0.26 points, p < 0.001) at stroke and faster memory decline (-0.15 vs. -0.07 points/year, p = 0.003) after stroke onset, compared to younger adults. Female stroke survivors experienced a faster prestroke memory decline than male stroke survivors (-0.14 vs. -0.10 points/year, p < 0.001). However, no sex differences were seen for other contrasts. Although whites had higher post-stroke memory scores than nonwhites, race was not associated with rate of memory decline during any period of time; i.e. race did not significantly modify the rate of decline before or after stroke or the immediate effect of stroke on memory. Older age predicted worse memory change before, at and after stroke onset. Sex and race differences in post-stroke memory outcomes might be attributable to prestroke disparities, which may be unrelated to

  2. 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

  3. A numerical method for phase-change problems

    NASA Technical Reports Server (NTRS)

    Kim, Charn-Jung; Kaviany, Massoud

    1990-01-01

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

  4. A numerical method for phase-change problems

    NASA Technical Reports Server (NTRS)

    Kim, Charn-Jung; Kaviany, Massoud

    1990-01-01

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

  5. 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.

  6. 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.

  7. 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.

  8. Acute pre-learning stress and declarative memory: impact of sex, cortisol response and menstrual cycle phase.

    PubMed

    Espin, Laura; Almela, Mercedes; Hidalgo, Vanesa; Villada, Carolina; Salvador, Alicia; Gomez-Amor, Jesus

    2013-05-01

    This study explores the influence of pre-learning stress on performance on declarative memory tasks in healthy young adults in relation to sex and menstrual cycle phase. The sample was composed of 119 students (32 men and 87 women) from 18 to 25 years of age. The women were tested in different hormonal stages (30 in follicular phase, 34 in luteal phase, and 23 using oral contraceptives). The participants were exposed to the Trier Social Stress Test (TSST) or a control condition. Afterwards, their memory performance was measured using a standardized memory test (Rey's Auditory Verbal Learning Test). In the control condition, all groups of women recalled more words than men, but these differences disappeared in the group exposed to TSST because men's performance on the memory test improved, but only to the level of women. In addition, our data suggest that in women the relationship between cortisol and memory can be modulated by sex hormone levels, since in luteal women a negative relationship was found between memory performance and peak cortisol level. These results confirm that sex differences need to be considered in the relationship between pre-learning stress and memory performance.

  9. 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.

  10. 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.…

  11. 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.…

  12. A semi-Markov model with memory for price changes

    NASA Astrophysics Data System (ADS)

    D'Amico, Guglielmo; Petroni, Filippo

    2011-12-01

    We study the high-frequency price dynamics of traded stocks by means of a model of returns using a semi-Markov approach. More precisely we assume that the intraday returns are described by a discrete time homogeneous semi-Markov model which depends also on a memory index. The index is introduced to take into account periods of high and low volatility in the market. First of all we derive the equations governing the process and then theoretical results are compared with empirical findings from real data. In particular we analyzed high-frequency data from the Italian stock market from 1 January 2007 until the end of December 2010.

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

    SciTech Connect

    Subedi, Alaska; Siegrist, Theo; Singh, David J.; Mukhopadhyay, Saikat; Sun, Jifeng

    2016-05-19

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionic and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. As a result, this different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties.

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

    DOE PAGES

    Subedi, Alaska; Siegrist, Theo; Singh, David J.; ...

    2016-05-19

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionicmore » and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. As a result, this different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties.« less

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

    PubMed

    Mukhopadhyay, Saikat; Sun, Jifeng; Subedi, Alaska; Siegrist, Theo; Singh, David J

    2016-05-19

    Ge2Sb2Te5 and related phase change materials are highly unusual in that they can be readily transformed between amorphous and crystalline states using very fast melt, quench, anneal cycles, although the resulting states are extremely long lived at ambient temperature. These states have remarkably different physical properties including very different optical constants in the visible in strong contrast to common glass formers such as silicates or phosphates. This behavior has been described in terms of resonant bonding, but puzzles remain, particularly regarding different physical properties of crystalline and amorphous phases. Here we show that there is a strong competition between ionic and covalent bonding in cubic phase providing a link between the chemical basis of phase change memory property and origins of giant responses of piezoelectric materials (PbTiO3, BiFeO3). This has important consequences for dynamical behavior in particular leading to a simultaneous hardening of acoustic modes and softening of high frequency optic modes in crystalline phase relative to amorphous. This different bonding in amorphous and crystalline phases provides a direct explanation for different physical properties and understanding of the combination of long time stability and rapid switching and may be useful in finding new phase change compositions with superior properties.

  16. 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.

  17. 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

  18. Changes of memory B- and T-cell subsets in lupus nephritis patients.

    PubMed

    Kosalka, Joanna; Jakiela, Bogdan; Musial, Jacek

    2016-01-01

    Renal involvement in systemic lupus erythematosus (SLE) is associated with production of antibodies to double stranded DNA, deposition of immune complexes and organ damage. These processes have been linked with abnormalities in B- and T-cell memory compartments. The aim of the study was to analyze subsets of peripheral memory B-cells and T-cells in lupus nephritis (LN) patients. We used multicolor flow cytometry to analyze major memory subsets of peripheral blood B-cells (defined by CD27, IgD and CD21) and T-cells (CD45RA, CD45RO, CCR7) in 32 patients with active or inactive LN, and 23 control subjects. Lupus nephritis patients were characterized by increased percentage of immature/early-transitional B-cells (CD27-IgD+CD21-), higher frequency of activated switched memory (SM, CD27+IgD-CD21-) and exhausted memory B-cells (CD27-IgD-), and decrease in non-switched memory (NSM, CD27+IgD+) B-cells. CD21low subsets (immature and activated B-cells) were particularly expanded in patients with active disease. In both groups of LN patients we observed decline in the absolute count of NSM B-cells. It was paralleled by lymphopenia in naïve CD4+ T-cell compartment and increase in the frequency of effector memory T-cells, and these changes were more pronounced in active LN. B-cell memory compartment in LN is deficient in NSM cells and during active disease it is further skewed towards SM and exhausted memory phenotypes, most likely as a cause of chronic antigenic stimulation. Parallel changes in T-helper cell subsets suggest a similar mechanism of SLE-related lymphopenia for both B-cell and T-cell compartment.

  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.

  20. An ultra-fast optical shutter exploiting total light absorption in a phase change material

    NASA Astrophysics Data System (ADS)

    Jafari, Mohsen; Guo, L. Jay; Rais-Zadeh, Mina

    2017-02-01

    In this paper, we present an ultra-fast and high-contrast optical shutter with applications in atomic clock assemblies, integrated photonic systems, communication hardware, etc. The shutter design exploits the total light absorption phenomenon in a thin phase change (PC) material placed over a metal layer. The shutter switches between ON and OFF states by changing PC material phase and thus its refractive index. The PC material used in this work is Germanium Telluride (GeTe), a group IV-VI chalcogenide compound, which exhibits good optical contrast when switching from amorphous to crystalline state and vice versa. The stable phase changing behavior and reliability of GeTe and GeSbTe (GST) have been verified in optical memories and RF switches. Here, GeTe is used as it has a lower extinction coefficient in near-IR regions compared to GST. GeTe can be thermally transitioned between two phases by applying electrical pulses to an integrated heater. The memory behavior of GeTe results in zero static power consumption which is useful in applications requiring long time periods between switching activities. We previously demonstrated a meta-surface employing GeTe in sub-wavelength slits with >14 dB isolation at 1.5 μm by exciting the surface plasmon polariton and localized slit resonances. In this work, strong interference effects in a thin layer of GeTe over a gold mirror result in near total light absorption of up to 40 dB (21 dB measured) in the amorphous phase of the shutter at 780 nm with much less fabrication complexity. The optical loss at the shutter ON state is less than 1.5 dB. A nickel chrome (NiCr) heater provides the Joule heating energy required to achieve the crystallographic phase change. The measured switching speed is 2 μs.

  1. A Two-Phase Model of Resource Allocation in Visual Working Memory.

    PubMed

    Ye, Chaoxiong; Hu, Zhonghua; Li, Hong; Ristaniemi, Tapani; Liu, Qiang; Liu, Taosheng

    2017-03-02

    Two broad theories of visual working memory (VWM) storage have emerged from current research, a discrete slot-based theory and a continuous resource theory. However, neither the discrete slot-based theory or continuous resource theory clearly stipulates how the mental commodity for VWM (discrete slot or continuous resource) is allocated. Allocation may be based on the number of items via stimulus-driven factors, or it may be based on task demands via voluntary control. Previous studies have obtained conflicting results regarding the automaticity versus controllability of such allocation. In the current study, we propose a two-phase allocation model, in which the mental commodity could be allocated only by stimulus-driven factors in the early consolidation phase. However, when there is sufficient time to complete the early phase, allocation can enter the late consolidation phase, where it can be flexibly and voluntarily controlled according to task demands. In an orientation recall task, we instructed participants to store either fewer items at high-precision or more items at low-precision. In 3 experiments, we systematically manipulated memory set size and exposure duration. We did not find an effect of task demands when the set size was high and exposure duration was short. However, when we either decreased the set size or increased the exposure duration, we found a trade-off between the number and precision of VWM representations. These results can be explained by a two-phase model, which can also account for previous conflicting findings in the literature. (PsycINFO Database Record

  2. The Last Phase of Process Change - Deployment

    DTIC Science & Technology

    2008-11-01

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

  3. White Matter and Memory in Healthy Adults: Coupled Changes over Two Years

    PubMed Central

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

    2016-01-01

    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

  4. Microstructure and electrical properties of Sb2Te phase-change material

    NASA Astrophysics Data System (ADS)

    Liu, Guangyu; Wu, Liangcai; Li, Tao; Rao, Feng; Song, Sannian; Liu, Bo; Song, Zhitang

    2016-10-01

    Phase Change Memory (PCM) has great potential for commercial applications of next generation non-volatile memory (NVM) due to its high operation speed, high endurance and low power consumption. Sb2Te (ST) is a common phase-change material and has fast crystallization speed, while thermal stability is relatively poor and its crystallization temperature is about 142°C. According to the Arrhenius law, the extrapolated failure temperature is about 55°C for ten years. When heated above the crystallization temperature while below the melting point, its structure can be transformed from amorphous phase to hexagonal phase. Due to the growth-dominated crystallization mechanism, the grain size of ST film is large and the diameter of about 300 nm is too large compared with Ge2Sb2Te5 (GST), which may deteriorate the device performance. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) were employed to study the microstructures and the results indicate that the crystal plane is {110}. In addition, device cells were manufactured and their current-voltage (I-V) and resistance-voltage characteristics were tested, and the results reveal that the threshold voltage (Vth) of ST film is 0.87 V. By researching the basic properties of ST, we can understand its disadvantages and manage to improve its performance by doping or other proper methods. Finally, the improved ST can be a candidate for optical discs and PCM.

  5. 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

  6. Amorphous blue phase III polymer scaffold as a sub-millisecond switching electro-optical memory device

    NASA Astrophysics Data System (ADS)

    Gandhi, Sahil Sandesh; Kim, Min Su; Hwang, Jeoung-Yeon; Chien, Liang-Chy

    2017-02-01

    We demonstrate the application of the nanostructured scaffold of BPIII as a resuable EO device that retains the BPIII ordering and sub-millisecond EO switching characteristics, that is, "EO-memory" of the original BPIII even after removal of the cholesteric blue phase liquid crystal (LC) and subsequent refilling with different nematic LCs. We also fabricate scaffolds mimicking the isotropic phase and cubic blue phase I (BPI) to demonstrate the versatility of our material system to nano-engineer EO-memory scaffolds of various structures. We envisage that this work will promote new experimental investigations of the mysterious BPIII and the development of novel device architectures and optically functional nanomaterials.

  7. Confined martensitic phase transformation kinetics and lattice dynamics in Ni–Co–Fe–Ga shape memory alloys

    SciTech Connect

    Cong, Daoyong; Rule, Kirrily Clair; Li, Wen-Hsien; Lee, Chi-Hung; Zhang, Qinghua; Wang, Haoliang; Hao, Yulin; Wang, Yandong; Huang, E-Wen

    2016-09-02

    Here we describe insights into the phase transformation kinetics and lattice dynamics associated with the newly discovered confined martensitic transformation, which are of great significance to the in-depth understanding of the phase transformation behavior responsible for the rich new physical phenomena in shape memory alloys and could shed light on the design of novel multifunctional properties through tuning the confined martensitic transformation.

  8. Interrelations between subjective health and episodic memory change in Swedish and Canadian samples of older adults.

    PubMed

    Wahlin, Ake; Maitland, Scott B; Bäckman, Lars; Dixon, Roger A

    2003-01-01

    Recent research has documented associations between subjective health ratings and objective indicators of disease and death. Less is known about relations between subjective health ratings and level of cognitive performance in older adults. In this study, we explored whether subjective health ratings are related to episodic memory performance, both concurrently and across a three-year longitudinal interval. Persons aged 75-84 years, and participating in the Swedish Kungsholmen Project (n = 105) or the Canadian Victoria Longitudinal Study (n = 71), were examined. Results showed that in both samples, while the cross-sectional relationship was non-significant, longitudinal change in perceptions of subjective health were related to change in episodic memory performance. Next, the two samples were combined in additional analyses. Here, results further revealed that the associations between longitudinal change in subjective health and memory performance generalized across samples independently of demographic, changing physical health status, and subjective memory decline differences. Thus, the present findings suggest that subjective health may be added to the growing number of individual-difference variables that are predictive of episodic memory change in very old age.

  9. 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.

  10. Differential trajectories of age-related changes in components of executive and memory processes.

    PubMed

    Goh, Joshua O; An, Yang; Resnick, Susan M

    2012-09-01

    Several studies have demonstrated age-related declines in general executive function and memory. In this study, we examined cross-sectional and longitudinal age effects in more specific cognitive processes that constitute executive function and memory. We postulated that, whereas some components of executive and memory functions would show age differences and longitudinal declines, other specific abilities would be maintained or even improve with repeated testing. In a sample of individuals ≥55 years old from the Baltimore Longitudinal Study of Aging, we found longitudinal declines in inhibition, manipulation, semantic retrieval, phonological retrieval, switching, and long-term memory over a maximum of 14 years follow-up. In contrast, abstraction, capacity, chunking, discrimination, and short-term memory were maintained or even improved longitudinally, probably due in part to repeated testing. Moreover, whereas several different abilities were correlated across participants' cross-sectional performance, longitudinal changes in performance showed more heterogeneous trajectories. Finally, compared with cross-sectional performance, longitudinal trajectories showed better distinction between participants with and those without later cognitive impairment. These results show that longitudinal cognitive aging of executive and memory functions is not a uniform process but a heterogeneous one and suggest that certain executive and memory functions remain stable despite age-related declines in other component processes.

  11. 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…

  12. 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…

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

    SciTech Connect

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

    2010-06-01

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

  14. Phase change properties of Ti-Sb-Te thin films deposited by thermal atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Song, Sannian; Shen, Lanlan; Song, Zhitang; Yao, Dongning; Guo, Tianqi; Li, Le; Liu, Bo; Wu, Liangcai; Cheng, Yan; Ding, Yuqiang; Feng, Songlin

    2016-10-01

    Phase change random access memory (PCM) appears to be the strongest candidate for next-generation high density nonvolatile memory. The fabrication of ultrahigh density PCM depends heavily on the thin film growth technique for the phase changing chalcogenide material. In this study, TiSb2Te4 (TST) thin films were deposited by thermal atomic layer deposition (ALD) method using TiCl4, SbCl3, (Et3Si)2Te as precursors. The threshold voltage for the cell based on thermal ALD-deposited TST is about 2.0 V, which is much lower than that (3.5 V) of the device based on PVD-deposited Ge2Sb2Te5 (GST) with the identical cell architecture. Tests of TST-based PCM cells have demonstrated a fast switching rate of 100 ns. Furthermore, because of the lower melting point and thermal conductivities of TST materials, TST-based PCM cells exhibit 19% reduction of pulse voltages for Reset operation compared with GST-based PCM cells. These results show that thermal ALD is an attractive method for the preparation of phase change materials.

  15. Sub-nanometre resolution of atomic motion during electronic excitation in phase-change materials

    SciTech Connect

    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

    2016-02-12

    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 the 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.

  16. Sub-nanometre resolution of atomic motion during electronic excitation in phase-change materials

    DOE PAGES

    Mitrofanov, Kirill V.; Fons, Paul; Makino, Kotaro; ...

    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

  17. 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.

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

    NASA Astrophysics Data System (ADS)

    Stewart, D. Scott

    2014-03-01

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

  19. 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…

  20. Effects of capacity limits, memory loss, and sound type in change deafness.

    PubMed

    Gregg, Melissa K; Irsik, Vanessa C; Snyder, Joel S

    2017-08-30

    Change deafness, the inability to notice changes to auditory scenes, has the potential to provide insights about sound perception in busy situations typical of everyday life. We determined the extent to which change deafness to sounds is due to the capacity of processing multiple sounds and the loss of memory for sounds over time. We also determined whether these processing limitations work differently for varying types of sounds within a scene. Auditory scenes composed of naturalistic sounds, spectrally dynamic unrecognizable sounds, tones, and noise rhythms were presented in a change-detection task. On each trial, two scenes were presented that were same or different. We manipulated the number of sounds within each scene to measure memory capacity and the silent interval between scenes to measure memory loss. For all sounds, change detection was worse as scene size increased, demonstrating the importance of capacity limits. Change detection to the natural sounds did not deteriorate much as the interval between scenes increased up to 2,000 ms, but it did deteriorate substantially with longer intervals. For artificial sounds, in contrast, change-detection performance suffered even for very short intervals. The results suggest that change detection is generally limited by capacity, regardless of sound type, but that auditory memory is more enduring for sounds with naturalistic acoustic structures.

  1. Cross-phase modulation and entanglement in a compound gradient echo memory

    NASA Astrophysics Data System (ADS)

    Fu, Shuangshuang; Carvalho, André R. R.; Hush, Michael R.; James, Matthew R.

    2016-02-01

    We present a theoretical model for a Kerr-like interaction between two registers of a compound gradient echo memory (GEM). This type of interaction is known to generate cross-phase modulation (XPM) between optical fields, an effect that is limited by the typically small values of nonlinearities in crystals. Here we show that in GEM systems the phase shift increases linearly with the interaction time and quadratically with the strength of the field. Increasing storage (interaction) times would then lead to stronger XPM effects even with fields with very low intensity. This interaction also generates two other effects: entanglement between the registers, which depends on the strength of the interaction and its spatial profile, and an interaction-induced gradient. We show that the latter produces leakage during the storage stage depending on the shape of the stored pulses, an undesirable consequence that can be minimized by carefully designing the temporal profile of the input fields.

  2. Magnetically induced nonvolatile magnetoresistance and resistance memory effect in phase-separated manganite thin films

    NASA Astrophysics Data System (ADS)

    Li, Qian; Cao, Qingqi; Wang, Dunhui; Du, Youwei

    2017-03-01

    We report the observation of magnetically induced resistance memory effect in a typical electronic phase-separated manganite La5/8‑x Pr x Ca3/8MnO3 (x  =  0.3) thin film. In the hysteresis region of metal-to-insulator transition, the resistance exhibits a sharp drop with the application of magnetic field and maintains the low resistance state after the removal of field, showing a nonvolatile magnetoresistance effect. The high resistance state can be recovered until the temperature is warmed. More explicit measurements at the hysteresis region exhibit the non-volatility and irreversibility of magnetoresistance, which can be ascribed to the percolative feature in the electronic phase-separated manganite. The origin and potential applications of these interesting effects are discussed.

  3. Phase-change radiative thermal diode

    SciTech Connect

    Ben-Abdallah, Philippe; Biehs, Svend-Age

    2013-11-04

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

  4. Nap and melatonin-induced changes in hippocampal activation and their role in verbal memory consolidation.

    PubMed

    Gorfine, Tali; Yeshurun, Yaara; Zisapel, Nava

    2007-11-01

    Overnight sleep contributes to memory consolidation; even a short nap improves memory performance. Such improvement has been linked to hippocampal activity during sleep. Melatonin has been shown to affect the human hippocampus and to induce 'sleep like' changes in brain activation. We therefore conducted and compared two functional magnetic resonance imaging studies: the first study assessed the effect of a 2-hr mid-day nap versus an equal amount of wakefulness on a verbal memory task (unrelated word pair association); the second assessed the effect of melatonin versus placebo (both conditions without nap) on a similar task. We report that following a nap relative to wakefulness, successful retrieval-related activation in the parahippocampus is decreased. A smaller decrease is seen in wakefulness with melatonin but not placebo. In parallel, an improvement in verbal memory recall was found after a nap compared with wakefulness but not with melatonin during wakefulness compared with placebo. Our findings demonstrate effects of melatonin that resemble those of sleep on verbal memory processing in the hippocampus thus suggesting that melatonin, like sleep, can initiate offline plastic changes underlying memory consolidation; they also suggest that concomitant rest without interferences is necessary for enhanced performance.

  5. 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.

  6. 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…

  7. 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…

  8. Phase-locking and amplitude modulations of EEG alpha: Two measures reflect different cognitive processes in a working memory task.

    PubMed

    Herrmann, Christoph S; Senkowski, Daniel; Röttger, Stefan

    2004-01-01

    It has been demonstrated in numerous experiments that oscillatory EEG responses in the alpha frequency band (8-12 Hz) increase with memory load during the retention interval in working memory tasks. However, the findings diverge with respect to which measurement of alpha activity is influenced by memory processes. Here, we differentiate between evoked and total alpha activity in order to separate effects of phase-locking and amplitude modulation. We present data from a delayed-matching-to-sample task (S1-S2 paradigm) for which we compared EEG alpha responses between a perception and a memory condition. Increased total alpha activity was found in the retention interval for the memory as compared to the perception condition. Evoked alpha activity, however, did not differentiate between memory and perception conditions but, instead, was increased for the more complex condition of processing non-Kanizsa figures as compared to Kanizsa figures. Thus, our results demonstrate a functional differentiation between evoked and total alpha activity. While alpha phase locking seemed to be influenced mainly by task complexity, alpha amplitude clearly reflected memory demands in our paradigm.

  9. 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.

  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. Development of Phase Change Materials for RF Switch Applications

    NASA Astrophysics Data System (ADS)

    King, Matthew Russell

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

  12. 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.

  13. Picosecond electric-field-induced threshold switching in phase-change materials [THz-induced threshold switching and crystallization of phase-change materials

    SciTech Connect

    Zalden, Peter; Shu, Michael J.; Chen, Frank; Wu, Xiaoxi; Zhu, Yi; Wen, Haidan; Johnston, Scott; Shen, Zhi -Xun; Landreman, Patrick; Brongersma, Mark; Fong, Scott W.; Wong, H. -S. Philip; Sher, Meng -Ju; Jost, Peter; Kaes, Matthias; Salinga, Martin; von Hoegen, Alexander; Wuttig, Matthias; Lindenberg, Aaron M.

    2016-08-05

    Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag4In3Sb67Te26. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales—faster than crystals can nucleate. As a result, this supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

  14. Picosecond electric-field-induced threshold switching in phase-change materials [THz-induced threshold switching and crystallization of phase-change materials

    DOE PAGES

    Zalden, Peter; Shu, Michael J.; Chen, Frank; ...

    2016-08-05

    Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag4In3Sb67Te26. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales—faster than crystals can nucleate. As a result, this supports purely electronic models of threshold switching and reveals potentialmore » applications as an ultrafast electronic switch.« less

  15. Picosecond electric-field-induced threshold switching in phase-change materials [THz-induced threshold switching and crystallization of phase-change materials

    SciTech Connect

    Zalden, Peter; Shu, Michael J.; Chen, Frank; Wu, Xiaoxi; Zhu, Yi; Wen, Haidan; Johnston, Scott; Shen, Zhi -Xun; Landreman, Patrick; Brongersma, Mark; Fong, Scott W.; Wong, H. -S. Philip; Sher, Meng -Ju; Jost, Peter; Kaes, Matthias; Salinga, Martin; von Hoegen, Alexander; Wuttig, Matthias; Lindenberg, Aaron M.

    2016-08-05

    Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag4In3Sb67Te26. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales—faster than crystals can nucleate. As a result, this supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

  16. Attention bias modification training under working memory load increases the magnitude of change in attentional bias.

    PubMed

    Clarke, Patrick J F; Branson, Sonya; Chen, Nigel T M; Van Bockstaele, Bram; Salemink, Elske; MacLeod, Colin; Notebaert, Lies

    2017-12-01

    Attention bias modification (ABM) procedures have shown promise as a therapeutic intervention, however current ABM procedures have proven inconsistent in their ability to reliably achieve the requisite change in attentional bias needed to produce emotional benefits. This highlights the need to better understand the precise task conditions that facilitate the intended change in attention bias in order to realise the therapeutic potential of ABM procedures. Based on the observation that change in attentional bias occurs largely outside conscious awareness, the aim of the current study was to determine if an ABM procedure delivered under conditions likely to preclude explicit awareness of the experimental contingency, via the addition of a working memory load, would contribute to greater change in attentional bias. Bias change was assessed among 122 participants in response to one of four ABM tasks given by the two experimental factors of ABM training procedure delivered either with or without working memory load, and training direction of either attend-negative or avoid-negative. Findings revealed that avoid-negative ABM procedure under working memory load resulted in significantly greater reductions in attentional bias compared to the equivalent no-load condition. The current findings will require replication with clinical samples to determine the utility of the current task for achieving emotional benefits. These present findings are consistent with the position that the addition of a working memory load may facilitate change in attentional bias in response to an ABM training procedure. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Shape-memory-actuated change in scaffold fiber alignment directs stem cell morphology.

    PubMed

    Tseng, Ling-Fang; Mather, Patrick T; Henderson, James H

    2013-11-01

    Tissue engineering scaffolds have traditionally been static physical structures poorly suited to mimicking the complex dynamic behavior of in vivo microenvironments. Here we present a thermoresponsive scaffold that can be programmed to change macroscopic shape and microscopic architecture during cell culture. The scaffold, which was prepared by electrospinning a shape memory polymer (SMP), was used to test the hypothesis that a shape-memory-actuated change in scaffold fiber alignment could be used to control the behavior of attached and viable cells. To test this hypothesis, we stretched an SMP scaffold of randomly oriented fibers and fixed the scaffold in a temporary but stable elongated shape in which fibers were aligned by the strain. Following seeding and culture of human adipose-derived stem cells on the strain-aligned scaffold, the scaffold was triggered to transition back to its initial shape and random fiber orientation via shape memory actuation using a cytocompatible temperature increase. We found that cells preferentially aligned along the fiber direction of the strain-aligned scaffold before shape memory actuation. After shape memory actuation, cells remained attached and viable but lost preferential alignment. These results demonstrate that shape-memory-actuated changes in scaffold fiber alignment can be achieved with attached and viable cells and can control cell morphological behavior. The incorporation of shape memory into cytocompatible scaffolds is anticipated to facilitate the development, delivery and functionality of tissue engineering scaffolds and the in vitro and in vivo study and application of mechanobiology. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  18. Modeling Longitudinal Changes in Older Adults’ Memory for Spoken Discourse: Findings from the ACTIVE Cohort

    PubMed Central

    Payne, Brennan R.; Gross, Alden L.; Parisi, Jeanine M.; Sisco, Shannon M.; Stine-Morrow, Elizabeth A. L.; Marsiske, Michael; Rebok, George W.

    2014-01-01

    Episodic memory shows substantial declines with advancing age, but research on longitudinal trajectories of spoken discourse memory (SDM) in older adulthood is limited. Using parallel process latent growth curve models, we examined 10 years of longitudinal data from the no-contact control group (N = 698) of the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) randomized controlled trial in order to test (a) the degree to which SDM declines with advancing age, (b) predictors of these age-related declines, and (c) the within-person relationship between longitudinal changes in SDM and longitudinal changes in fluid reasoning and verbal ability over 10 years, independent of age. Individuals who were younger, White, had more years of formal education, were male, and had better global cognitive function and episodic memory performance at baseline demonstrated greater levels of SDM on average. However, only age at baseline uniquely predicted longitudinal changes in SDM, such that declines accelerated with greater age. Independent of age, within-person decline in reasoning ability over the 10-year study period was substantially correlated with decline in SDM (r = .87). An analogous association with SDM did not hold for verbal ability. The findings suggest that longitudinal declines in fluid cognition are associated with reduced spoken language comprehension. Unlike findings from memory for written prose, preserved verbal ability may not protect against developmental declines in memory for speech. PMID:24304364

  19. Modelling longitudinal changes in older adults' memory for spoken discourse: findings from the ACTIVE cohort.

    PubMed

    Payne, Brennan R; Gross, Alden L; Parisi, Jeanine M; Sisco, Shannon M; Stine-Morrow, Elizabeth A L; Marsiske, Michael; Rebok, George W

    2014-01-01

    Episodic memory shows substantial declines with advancing age, but research on longitudinal trajectories of spoken discourse memory (SDM) in older adulthood is limited. Using parallel process latent growth curve models, we examined 10 years of longitudinal data from the no-contact control group (N = 698) of the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) randomised controlled trial in order to test (1) the degree to which SDM declines with advancing age, (2) the predictors of these age-related declines and (3) the within-person relationship between longitudinal changes in SDM and longitudinal changes in fluid reasoning and verbal ability over 10 years, independent of age. Individuals who were younger, were White, had more years of formal education, were male and had better global cognitive function and episodic memory performance at baseline demonstrated greater levels of SDM on average. However, only age at baseline uniquely predicted longitudinal changes in SDM, such that declines accelerated with greater age. Independent of age, within-person decline in reasoning ability over the 10-year study period was substantially correlated with decline in SDM (r = .87). An analogous association with SDM did not hold for verbal ability. The findings suggest that longitudinal declines in fluid cognition are associated with reduced spoken language comprehension. Unlike findings from memory for written prose, preserved verbal ability may not protect against developmental declines in memory for speech.

  20. Genetic and lifestyle predictors of 15-year longitudinal change in episodic memory.

    PubMed

    Josefsson, Maria; de Luna, Xavier; Pudas, Sara; Nilsson, Lars-Göran; Nyberg, Lars

    2012-12-01

    To reveal distinct longitudinal trajectories in episodic memory over 15 years and to identify demographic, lifestyle, health-related, and genetic predictors of stability or decline. Prospective cohort study. The Betula Project, Umeå, Sweden. One thousand nine hundred fifty-four healthy participants aged 35 to 85 at baseline. Memory was assessed according to validated episodic memory tasks in participants from a large population-based sample. Data were analyzed using a random-effects pattern-mixture model that considered the effect of attrition over two to four longitudinal sessions. Logistic regression was used to determine significant predictors of stability or decline relative to average change in episodic memory. Of 1,558 participants with two or more test sessions, 18% were classified as maintainers and 13% as decliners, and 68% showed age-typical average change. More educated and more physically active participants, women, and those living with someone were more likely to be classified as maintainers, as were carriers of the met allele of the catechol-O-methyltransferase gene. Less educated participants, those not active in the labor force, and men were more likely to be classified as decliners, and the apolipoprotein E ~4 allele was more frequent in decliners. Quantitative, attrition-corrected assessment of longitudinal changes in memory can reveal substantial heterogeneity in aging trajectories, and genetic and lifestyle factors predict such heterogeneity. © 2012, Copyright the Authors Journal compilation © 2012, The American Geriatrics Society.

  1. Running wheel training does not change neurogenesis levels or alter working memory tasks in adult rats

    PubMed Central

    Rojas, Manuel J.; Cardenas P., Fernando

    2017-01-01

    Background Exercise can change cellular structure and connectivity (neurogenesis or synaptogenesis), causing alterations in both behavior and working memory. The aim of this study was to evaluate the effect of exercise on working memory and hippocampal neurogenesis in adult male Wistar rats using a T-maze test. Methods An experimental design with two groups was developed: the experimental group (n = 12) was subject to a forced exercise program for five days, whereas the control group (n = 9) stayed in the home cage. Six to eight weeks after training, the rats’ working memory was evaluated in a T-maze test and four choice days were analyzed, taking into account alternation as a working memory indicator. Hippocampal neurogenesis was evaluated by means of immunohistochemistry of BrdU positive cells. Results No differences between groups were found in the behavioral variables (alternation, preference index, time of response, time of trial or feeding), or in the levels of BrdU positive cells. Discussion Results suggest that although exercise may have effects on brain structure, a construct such as working memory may require more complex changes in networks or connections to demonstrate a change at behavioral level. PMID:28503368

  2. Electron spin echo studies of the internal motion of radicals in crystals: Phase memory vs correlation time

    NASA Astrophysics Data System (ADS)

    Kispert, Lowell D.; Bowman, Michael K.; Norris, James R.; Brown, Meta S.

    1982-01-01

    An electron spin echo (ESE) study of the internal motion of the CH2 protons in irradiated zinc acetate dihydrate crystals shows that quantitative measurements of the motional correlation time can be obtained quite directly from pulsed measurements. In the slow motional limit, the motional correlation time is equal to the phase memory time determined by ESE. In the fast motional limit, the motional correlation time is proportional to the no motion spectral second moment divided by the ESE phase memory time. ESE offers a convenient method of studying motion, electron transfer, conductivity, etc. in a variety of systems too complicated for study by ordinary EPR. New systems for study by ESE include biological samples, organic polymers, liquid solutions of radicals with unresolved hyperfine, etc. When motion modulates large anisotropic hyperfine couplings, ESE measurements of the phase memory time are sensitive to modulation of pseudosecular hyperfine interactions.

  3. Phase diagram of FeNiCoAlTaB ferrous shape memory alloy on aging time

    NASA Astrophysics Data System (ADS)

    Zhou, Zhijian; Cui, Jian; Ren, Xiaobing

    2017-04-01

    Ferrous shape memory alloy, Fe41Ni28Co17Al11.5Ta2.5B0.05, has shown large superelastic strain and strength in previous study. In the fabrication of this alloy, aging process is crucial for the formation of shape memory effect/superelasticity. However, its phase evolution on aging time is not clearly known. In this study, we systematically studied the phase diagram of this alloy on aging time. It is found that the unaged alloy shows a strain glass transition. With the aging time proceeding, the martensitic transformation gradually emerges. The phase diagram can be explained by the formation of coherent precipitates induced by aging. The heterogeneous strain between coherent precipitates and matrix is the driving force responsible for the emerging martensitic transformation. The generic explanation is supposed to be useful in martensitic transformation engineering for developing novel shape memory alloys from non-transforming materials.

  4. Evaluating working memory: Comparing change-detection tasks and Wechsler working memory subtests in school-age children.

    PubMed

    Colbert, Alison; Bo, Jin

    2017-09-01

    Among a number of methods for assessing working memory (WM), span tasks have been commonly utilized in clinical psychology, whereas change-detection tasks are often used in experimental or cognitive psychology. This study sought to understand the use of change-detection tasks in children and to evaluate the relationship between change-detection tasks and clinical WM measures in the Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV). Results revealed that the overall pattern of performance in change-detection tasks for children was similar to adults' performance in the literature; with increased array size, response accuracy systematically decreased. Significant age-related improvements on visuospatial and verbal WM capacities were found in school-age children. Although WISC-IV WM measures were significantly correlated with each other, only the Arithmetic subtest was significantly correlated with visuospatial WM as measured by the change-detection task, and none were significantly correlated with verbal WM as measured by the change-detection task. These results suggest the clinical WISC-IV WM subtests may not elicit the same construct as experimental change-detection WM measures, with the possible exception of the Arithmetic subtest.

  5. 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.

  6. 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

  7. Impact of Perinatally Acquired HIV Disease Upon Longitudinal Changes in Memory and Executive Functioning.

    PubMed

    Malee, Kathleen M; Chernoff, Miriam C; Sirois, Patricia A; Williams, Paige L; Garvie, Patricia A; Kammerer, Betsy L; Harris, Lynnette L; Nozyce, Molly L; Yildirim, Cenk; Nichols, Sharon L

    2017-08-01

    Little is known regarding effects of perinatally acquired HIV infection (PHIV) on longitudinal change in memory and executive functioning (EF) during adolescence despite the importance of these skills for independence in adulthood. PHIV (n = 144) and perinatally HIV-exposed uninfected youth (PHEU, n = 79), ages 12-17, completed standardized tests of memory and EF at baseline and 2 years later. Changes from baseline for each memory and EF outcome were compared between PHEU and PHIV youth with (PHIV/C, n = 39) and without (PHIV/non-C, n = 105) history of CDC class C (AIDS-defining) diagnoses. Among PHIV youth, associations of baseline and past disease severity with memory and EF performance at follow-up were evaluated using adjusted linear regression models. Participants were primarily black (79%); 16% were Hispanic; 55% were female. Mean memory and EF scores at follow-up generally fell in the low-average to average range. Pairwise comparison of adjusted mean change from baseline to follow-up revealed significantly greater change for PHIV/non-C compared with PHEU youth in only one verbal recognition task, with a difference in mean changes for PHIV/non-C versus PHEU of -0.99 (95% CI: -1.80 to -0.19; P = 0.02). Among youth with PHIV, better immunologic status at baseline was positively associated with follow-up measures of verbal recall and recognition and cognitive inhibition/flexibility. Past AIDS-defining diagnoses and higher peak viral load were associated with lower performance across multiple EF tasks at follow-up. Youth with PHIV demonstrated stable memory and EF during a 2-year period of adolescence, allowing cautious optimism regarding long-term outcomes.

  8. A Flicker Change Detection Task Reveals Object-in-Scene Memory Across Species.

    PubMed

    Chau, Vivian L; Murphy, Emily F; Rosenbaum, R Shayna; Ryan, Jennifer D; Hoffman, Kari L

    2011-01-01

    Tests of recognition memory in macaques typically assay memory for objects or isolated images, over time spans of seconds to hours from stimulus presentation, and/or require extensive training. Here, we propose a new application of the flicker change detection task that could measure object-in-scene memory days after single-trial exposures. In three experiments, participants searched for a changing object - or "target" - embedded within a scene as their eye movements were tracked. For new targets-in-scenes, the change is difficult to detect and requires extensive search. Once the target is found, however, the change becomes obvious. We reasoned that the decreased times required to find a target in a repeated scene would indicate memory for the target. In humans, targets were found faster when the targets-and-scenes were explicitly remembered than when they were forgotten, or had never been seen before. This led to faster repeated-trial compared to novel-trial search times. Based solely on repeated-trial search times, we were able to select distributions comprised of predominantly remembered or predominantly forgotten trials. Macaques exhibited the same repetition effects as humans, suggesting that remembered trials could be dissociated from novel or forgotten trials using the same procedures we established in humans. Finally, an anterograde amnesic patient with damage that included the medial temporal lobe (MTL) showed no search time differences, suggesting that memory revealed through search times on this task requires MTL integrity. Together, these findings indicate that the time required to locate a changing object reveals object-in-scene memory over long retention intervals in humans and macaques.

  9. A Flicker Change Detection Task Reveals Object-in-Scene Memory Across Species

    PubMed Central

    Chau, Vivian L.; Murphy, Emily F.; Rosenbaum, R. Shayna; Ryan, Jennifer D.; Hoffman, Kari L.

    2011-01-01

    Tests of recognition memory in macaques typically assay memory for objects or isolated images, over time spans of seconds to hours from stimulus presentation, and/or require extensive training. Here, we propose a new application of the flicker change detection task that could measure object-in-scene memory days after single-trial exposures. In three experiments, participants searched for a changing object – or “target” – embedded within a scene as their eye movements were tracked. For new targets-in-scenes, the change is difficult to detect and requires extensive search. Once the target is found, however, the change becomes obvious. We reasoned that the decreased times required to find a target in a repeated scene would indicate memory for the target. In humans, targets were found faster when the targets-and-scenes were explicitly remembered than when they were forgotten, or had never been seen before. This led to faster repeated-trial compared to novel-trial search times. Based solely on repeated-trial search times, we were able to select distributions comprised of predominantly remembered or predominantly forgotten trials. Macaques exhibited the same repetition effects as humans, suggesting that remembered trials could be dissociated from novel or forgotten trials using the same procedures we established in humans. Finally, an anterograde amnesic patient with damage that included the medial temporal lobe (MTL) showed no search time differences, suggesting that memory revealed through search times on this task requires MTL integrity. Together, these findings indicate that the time required to locate a changing object reveals object-in-scene memory over long retention intervals in humans and macaques. PMID:21960963

  10. Hierarchically Self-Assembled Block Copolymer Blends for Templating Hollow Phase-Change Nanostructures with an Extremely Low Switching Current

    DOE PAGES

    Park, Woon Ik; Kim, Jong Min; Jeong, Jae Won; ...

    2015-03-17

    Phase change memory (PCM) is one of the most promising candidates for next-generation nonvolatile memory devices because of its high speed, excellent reliability, and outstanding scalability. But, the high switching current of PCM devices has been a critical hurdle to realize low-power operation. Although one solution is to reduce the switching volume of the memory, the resolution limit of photolithography hinders further miniaturization of device dimensions. Here, we employed unconventional self-assembly geometries obtained from blends of block copolymers (BCPs) to form ring-shaped hollow PCM nanostructures with an ultrasmall contact area between a phase-change material (Ge2Sb2Te5) and a heater (TiN) electrode.more » The high-density (approximately 0.1 terabits per square inch) PCM nanoring arrays showed extremely small switching current of 2-3 mu A. Furthermore, the relatively small reset current of the ring-shaped PCM compared to the pillar-shaped devices is attributed to smaller switching volume, which is well supported by electro-thermal simulation results. Our approach may also be extended to other nonvolatile memory device applications such as resistive switching memory and magnetic storage devices, where the control of nanoscale geometry can significantly affect device performances.« less

  11. Hierarchically Self-Assembled Block Copolymer Blends for Templating Hollow Phase-Change Nanostructures with an Extremely Low Switching Current

    SciTech Connect

    Park, Woon Ik; Kim, Jong Min; Jeong, Jae Won; Hur, Yoon Hyoung; Choi, Young Joong; Kwon, Se-Hun; Hong, Seungbum; Yin, You; Jung, Yeon Sik; Kim, Kwang Ho

    2015-03-17

    Phase change memory (PCM) is one of the most promising candidates for next-generation nonvolatile memory devices because of its high speed, excellent reliability, and outstanding scalability. But, the high switching current of PCM devices has been a critical hurdle to realize low-power operation. Although one solution is to reduce the switching volume of the memory, the resolution limit of photolithography hinders further miniaturization of device dimensions. Here, we employed unconventional self-assembly geometries obtained from blends of block copolymers (BCPs) to form ring-shaped hollow PCM nanostructures with an ultrasmall contact area between a phase-change material (Ge2Sb2Te5) and a heater (TiN) electrode. The high-density (approximately 0.1 terabits per square inch) PCM nanoring arrays showed extremely small switching current of 2-3 mu A. Furthermore, the relatively small reset current of the ring-shaped PCM compared to the pillar-shaped devices is attributed to smaller switching volume, which is well supported by electro-thermal simulation results. Our approach may also be extended to other nonvolatile memory device applications such as resistive switching memory and magnetic storage devices, where the control of nanoscale geometry can significantly affect device performances.

  12. EEG-power and -coherence changes in a unimodal and a crossmodal working memory task with visual and kinesthetic stimuli.

    PubMed

    Seemüller, A; Müller, E M; Rösler, F

    2012-01-01

    We investigated EEG-power and EEG-coherence changes in a unimodal and a crossmodal matching-to-sample working memory task with either visual or kinesthetic stimuli. Angle-shaped trajectories were used as stimuli presented either as a moving dot on a screen or as a passive movement of a haptic device. Effects were evaluated during the different phases of encoding, maintenance, and recognition. Alpha power was modulated during encoding by the stimulus modality, and in crossmodal conditions during encoding and maintenance by the expected modality of the upcoming test stimulus. These power modulations were observed over modality-specific cortex regions. Systematic changes of coherence for crossmodal compared to unimodal tasks were not observed during encoding and maintenance but only during recognition. There, coherence in the theta-band increased between electrode sites over left central and occipital cortex areas in the crossmodal compared to the unimodal conditions. The results underline the importance of modality-specific representations and processes in unimodal and crossmodal working memory tasks. Crossmodal recognition of visually and kinesthetically presented object features seems to be related to a direct interaction of somatosensory/motor and visual cortex regions by means of long-range synchronization in the theta-band and such interactions seem to take place at the beginning of the recognition phase, i.e. when crossmodal transfer is actually necessary.

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

    PubMed Central

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

    2016-01-01

    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

  14. 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.

  15. 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.

  16. Changes in spatial memory and BDNF expression to concurrent dietary restriction and voluntary exercise.

    PubMed

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

    2010-05-01

    Substantial data suggest that cognitive function can be influenced by many lifestyle activities associated with changes in energy metabolism such as exercise and diet. In the current study, we investigated the combined effects of voluntary exercise (access to running wheels) and dietary restriction (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. Spatial learning and memory formation was assessed using the radial arm water maze (RAWM) paradigm, while BDNF protein was measured using ELISA test. Voluntary exercise and/or EODF were instituted for 6 weeks. Voluntary exercise alone significantly enhanced short-term, intermediate-term, and long-term memory formation, and increased BDNF protein levels in the hippocampus. EODF enhanced mean running wheel activity by approximately twofold. However, EODF did not modulate the effects of exercise on memory formation and expression of BDNF. In addition, EODF alone had no effect on memory and BDNF protein in the hippocampus. In conclusion, results of this study indicate that exercise enhanced while EODF had neutral effect on both spatial memory formation and hippocampus BDNF levels.

  17. 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

  18. 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.

  19. Polarization selective phase-change nanomodulator

    DOE PAGES

    Appavoo, Kannatassen; Haglund Jr., Richard F.

    2014-10-27

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

  20. 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.