Graphene oxide thin films for flexible nonvolatile memory applications

There has been strong demand for novel nonvolatile memory technology for low-cost, large-area, and low-power flexible electronics applications. Resistive memories based on metal oxide thin films have been extensively studied for application as next-generation nonvolatile memory devices. However, although the metal oxide based resistive memories have several advantages, such as good scalability, low-power consumption, and fast switching speed, their application to large-area flexible substrates has been limited due to their material characteristics and necessity of a high-temperature fabrication process. As a promising nonvolatile memory technology for large-area flexible applications, we present a graphene oxide based memory that can be easily fabricated using a room temperature spin-casting method on flexible substrates and has reliable memory performance in terms of retention and endurance. The microscopic origin of the bipolar resistive switching behavior was elucidated and is attributed to rupture and formation of conducting filaments at the top amorphous interface layer formed between the graphene oxide film and the top Al metal electrode, via high-resolution transmission electron microscopy and in situ X-ray photoemission spectroscopy. This work provides an important step for developing understanding of the fundamental physics of bipolar resistive switching in graphene oxide films, for the application to future flexible electronics.

[Stored electrograms in pacemakers and ICDs]

Stored electrograms (EGMs) represent an important development in pacemaker and ICD therapy. The most important issue in pacemaker EGMs is the confirmation of the detection of atrial tachyarrhythmias, especially atrial fibrillation. In ICD therapy, the discrimination between ventricular and supraventricular tachycardia (i.e., detection of inadequate therapy) is of central interest. Unfortunately, systematic"instructions" for interpreting stored EGMs in systems by different manufacturers are not available and the knowledge on this topic is limited to (too) few experts. The contributions in this issue aim at explaining the interpretation of stored EGMs in systems by different manufacturers, providing an understanding of marker annotations and EGM registrations in clinical examples. With the aim of improving pacemaker and ICD therapy, a broad distribution of knowledge on the usefulness and the practical use of stored EGMs is highly desirable.

Application of portable CDA for secure clinical-document exchange

Health Level Seven (HL7) organization published the Clinical Document Architecture (CDA) for exchanging documents among heterogeneous systems and improving medical quality based on the design method in CDA. In practice, although the HL7 organization tried to make medical messages exchangeable, it is still hard to exchange medical messages. There are many issues when two hospitals want to exchange clinical documents, such as patient privacy, network security, budget, and the strategies of the hospital. In this article, we propose a method for the exchange and sharing of clinical documents in an offline model based on the CDA-the Portable CDA. This allows the physician to retrieve the patient's medical record stored in a portal device, but not through the Internet in real time. The security and privacy of CDA data will also be considered.

Bulk heterojunction polymer memory devices with reduced graphene oxide as electrodes

A unique device structure with a configuration of reduced graphene oxide (rGO) /P3HT:PCBM/Al has been designed for the polymer nonvolatile memory device. The current-voltage (I-V) characteristics of the fabricated device showed the electrical bistability with a write-once-read-many-times (WORM) memory effect. The memory device exhibits a high ON/OFF ratio (10(4)-10(5)) and low switching threshold voltage (0.5-1.2 V), which are dependent on the sheet resistance of rGO electrode. Our experimental results confirm that the carrier transport mechanisms in the OFF and ON states are dominated by the thermionic emission current and ohmic current, respectively. The polarization of PCBM domains and the localized internal electrical field formed among the adjacent domains are proposed to explain the electrical transition of the memory device.

Acceleration of FDTD mode solver by high-performance computing techniques

A two-dimensional (2D) compact finite-difference time-domain (FDTD) mode solver is developed based on wave equation formalism in combination with the matrix pencil method (MPM). The method is validated for calculation of both real guided and complex leaky modes of typical optical waveguides against the bench-mark finite-difference (FD) eigen mode solver. By taking advantage of the inherent parallel nature of the FDTD algorithm, the mode solver is implemented on graphics processing units (GPUs) using the compute unified device architecture (CUDA). It is demonstrated that the high-performance computing technique leads to significant acceleration of the FDTD mode solver with more than 30 times improvement in computational efficiency in comparison with the conventional FDTD mode solver running on CPU of a standard desktop computer. The computational efficiency of the accelerated FDTD method is in the same order of magnitude of the standard finite-difference eigen mode solver and yet require much less memory (e.g., less than 10%). Therefore, the new method may serve as an efficient, accurate and robust tool for mode calculation of optical waveguides even when the conventional eigen value mode solvers are no longer applicable due to memory limitation.

Ferredoxin molecular thin film with intrinsic switching mechanism for biomemory application

A biomemory device consisting of cysteine modified ferredoxin molecules which possess a memory effect via a charge transfer mechanism was developed. For achieving an efficient bioelectronic device, cysteine modified ferredoxin was developed by embodying cysteine residues in ferredoxin by site--directed mutagenesis method to directly coordinate with the gold (Au) surface without use of any additional linkers. The thin film formation of ferredoxin molecules on Au electrode is confirmed by surface plasmon resonance (SPR) spectroscopy and scanning tunneling microscope (STM). Cyclic voltammetry (CV) and open circuit potential amperometry (OCPA) methods were used to verify the memory switching characteristics of the fabricated device. The charge transfer between ferredoxin protein molecules and Au electrode enables a bi-stable electrical conductivity allowing the system to be used as a digital memory device. Data storage is achieved by applying redox voltages which are within the range of -500 mV. These results suggest that the proposed device has a function of memory and can be used for the construction of a nano-scale bioelectronic device.

Analyzing fractal dynamics employing R

Recent empirical studies from cognitive, social and biological psychology revealed the fractal properties of many psychological phenomena. Employing methodologies from time- and frequency-domain analyses enabled detecting persistent long-range dependencies in various psychological and behavioral time series. These very slowly decaying autocorrelations are known as 1/f noise and typical for self-similar long memory processes. This paper evaluated different estimators of long memory parameters commonly available in the open source statistical software R concerning their ability to distinguish between fractional Brownian motions and fractional Gaussian noises, stationary and nonstationary fractal processes, short and long memory series. The following procedures implemented in the R packages fractal and fracdiff were considered: PSD (hurstSpec), DFA, the Whittle method (FDWhittle), semiparametric estimators of Reisen (fdSperio) and Geweke & Porter-Hudak (fdGPH) as well as the approximate ML algorithm of Haslett and Raftery (fracdiff). The key finding of the study was that the performance of the methods strongly depends on the complexity of the underlying process and parameterizations. Since in empirical settings the true structure is never known, an elaborated strategy for the estimation of the long memory parameter d combining different techniques was developed and demonstrated on an empirical example.

Organic nonvolatile memory devices based on ferroelectricity

A memory functionality is a prerequisite for many applications of electronic devices. Organic nonvolatile memory devices based on ferroelectricity are a promising approach toward the development of a low-cost memory technology. In this Review Article we discuss the latest developments in this area with a focus on three of the most important device concepts: ferroelectric capacitors, field-effect transistors, and diodes. Integration of these devices into larger memory arrays is also discussed.

[Stored electrograms in pacemakers and ICD systems from the Sorin Group]

Stored electrograms (EGMs) can improve therapy with pacemakers and ICDs by detecting technical problems (e.g., over- or undersensing) and medical problems (e.g., atrial tachyarrhythmias). Analysis of stored EGMs and their interpretation requires knowledge about EGM recording (e. g., channels, summation EGM) and marker annotations. This review presents stored EGMs in pacemaker and ICD systems from the Sorin Group with tips on the potential and interpretation of memory capabilities.

[Stored electrograms in pacemakers and ICDs from St. Jude Medical]

Stored electrograms (EGMs) significantly improve pacemaker and ICD therapy. In pacemaker systems, the main focus of stored EGMs concerns the manual control of device detection of atrial tachyarrhythmias, especially atrial fibrillation. In ICD therapy, stored EGMs allow the discrimination of adequate and inadequate detection of ventricular tachycardia. This review presents the implementation of stored EGMs in systems from St. Jude Medical and explains the mode of EGM storage and marker annotations, which are useful for interpretation of stored EGMs and to understand the way the device interprets the EGM. Clinical examples illustrate appropriate and inappropriate device classifications.

Convolutional perfectly matched layer for elastic second-order wave equation

In this work, a method is presented to extend the convolutional perfectly matched layer (C-PML) to simulate acoustic wave propagation in elastic media with a second-order equation formulation. This non-physical layer is used at the computational edge of a finite element method algorithm in frequency domain, and a pseudo-spectral algorithm in time domain, as an absorbing boundary condition (ABC) to truncate unbounded media. Numerical results show that the C-PML ABC attenuates the outgoing surface waves more effectively than classical PML ABC as proposed by Berenger [J. Comput. Phys. 114, 195-200 (1994)] for electromagnetic waves in the case of oblique incidence, where the PML method suffers from large spurious reflections. Moreover, a modification of the proposed C-PML formulation is also discussed in order to stabilize the absorbing layer in anisotropic solids where numerical instabilities can appear.

[Stored electrograms in pacemakers and ICDs from Boston Scientific]

The storage of electrograms in pacemakers and ICDs represents an important step forward in the detection of asymptomatic arrhythmias (e.g., paroxysmal atrial fibrillation) and the distinction between appropriate and inappropriate therapies. This review presents via clinical examples the information provided in stored electrograms in systems from Boston Scientific and tips how to interpret them.

[Analysis of intracardial electrograms in pacemakers and ICD systems by Biotronik]

Detailed analysis of stored electrograms is essential for the interpretation of arrhythmias, programming changes, and optimization of the medical therapy in patients with implanted pacemakers and defibrillators. The physician who cares for patients with implantable electrical devices has to be able to understand the detection and treatment algorithms of those devices. Biotronik pacemakers of newer generations are capable of storing intracardiac electrograms. Earlier devices store up to 12 electrograms of 10 s duration after certain trigger events, like atrial tachycardia or high ventricular rates. Cardiac resynchronization systems can store electrograms after patient activation with magnets in addition to the above mentioned trigger-activated electrograms. Defibrillators store intracardiac electrograms during tachycardia episodes with near-field and far-field electrograms of the right ventricular lead in addition to the markers in single and dual chamber defibrillators (in addition to an atrial electrogram) and near field electrograms of the atrial, the right, and the left ventricular electrode in addition to the markers in resynchronization systems. Each channel has a maximum storing capacity of 32 min. If there are more episodes than storing capacity, electrograms of older episodes will be overwritten, but if the newer episodes are all classified as supraventricular, the last two ventricular episodes (VT or VF) will remain in the episode memory. This article describes stored electrograms, detection, and treatment algorithms of implantable cardiac devices manufactured by Biotronik.

[Stored electrograms in pacemakers and ICDs from Medtronic]

Modern pacemakers and implantable defibrillators provide a multitude of technical algorithms and parameters, which can be programmed individually and can treat different forms of arrhythmias. Stored electrograms offer the possibility to obtain valuable information during follow-up (but also in real-time) about arrhythmias and device function or malfunction. This results in improved treatment of cardiac arrhythmias and heart disease. Due to constant innovation and development of these systems, it requires, however, profound biomedical and technical knowledge, since stored electrograms may display complex arrhythmias and device reactions that are not easy to interpret. Understanding of stored device information improves follow-up and facilitates individual care for the patient.

Assessing the relationship between computational speed and precision: a case study comparing an interpreted versus compiled programming language using a stochastic simulation model in diabetes care

BACKGROUND

Simulation techniques are well suited to modelling diseases yet can be computationally intensive. This study explores the relationship between modelled effect size, statistical precision, and efficiency gains achieved using variance reduction and an executable programming language.

METHODS

A published simulation model designed to model a population with type 2 diabetes mellitus based on the UKPDS 68 outcomes equations was coded in both Visual Basic for Applications (VBA) and C++. Efficiency gains due to the programming language were evaluated, as was the impact of antithetic variates to reduce variance, using predicted QALYs over a 40-year time horizon.

RESULTS

The use of C++ provided a 75- and 90-fold reduction in simulation run time when using mean and sampled input values, respectively. For a series of 50 one-way sensitivity analyses, this would yield a total run time of 2 minutes when using C++, compared with 155 minutes for VBA when using mean input values. The use of antithetic variates typically resulted in a 53% reduction in the number of simulation replications and run time required. When drawing all input values to the model from distributions, the use of C++ and variance reduction resulted in a 246-fold improvement in computation time compared with VBA - for which the evaluation of 50 scenarios would correspondingly require 3.8 hours (C++) and approximately 14.5 days (VBA).

CONCLUSIONS

The choice of programming language used in an economic model, as well as the methods for improving precision of model output can have profound effects on computation time. When constructing complex models, more computationally efficient approaches such as C++ and variance reduction should be considered; concerns regarding model transparency using compiled languages are best addressed via thorough documentation and model validation.

PIYAS-proceeding to intelligent service oriented memory allocation for flash based data centric sensor devices in wireless sensor networks

Flash memory has become a more widespread storage medium for modern wireless devices because of its effective characteristics like non-volatility, small size, light weight, fast access speed, shock resistance, high reliability and low power consumption. Sensor nodes are highly resource constrained in terms of limited processing speed, runtime memory, persistent storage, communication bandwidth and finite energy. Therefore, for wireless sensor networks supporting sense, store, merge and send schemes, an efficient and reliable file system is highly required with consideration of sensor node constraints. In this paper, we propose a novel log structured external NAND flash memory based file system, called Proceeding to Intelligent service oriented memorY Allocation for flash based data centric Sensor devices in wireless sensor networks (PIYAS). This is the extended version of our previously proposed PIYA [1]. The main goals of the PIYAS scheme are to achieve instant mounting and reduced SRAM space by keeping memory mapping information to a very low size of and to provide high query response throughput by allocation of memory to the sensor data by network business rules. The scheme intelligently samples and stores the raw data and provides high in-network data availability by keeping the aggregate data for a longer period of time than any other scheme has done before. We propose effective garbage collection and wear-leveling schemes as well. The experimental results show that PIYAS is an optimized memory management scheme allowing high performance for wireless sensor networks.

Two-terminal nonvolatile memories based on single-walled carbon nanotubes

Reproducible current hysteresis is observed in semiconducting single-walled carbon nanotubes (SWCNTs) measured in a two-terminal configuration without a gate electrode. On the basis of this hysteresis, a two-terminal nonvolatile memory is realized by applying voltage pulses of opposite polarities across the SWCNT. Charge trapping at the SWCNT/SiO(2) interface is proposed to account for the observed phenomena; this explanation is supported by the direct correlation between the switching behaviors and SWCNT carrier types. In particular, a change in dominant carrier type induced by adsorbates in air leads to the direct transition of hysteresis evolution in the same device, providing further evidence for the proposed mechanism.

Charge retention of self-assembled ferredoxin monolayer by the reduction-oxidation control for biomemory device

The oxidation-reduction control to store charges in self-assembled ferredoxin layer was investigated by scanning electrochemical method. Micro sized spot arrays consisting of ferredoxin proteins which used as the storage element were formed on chemically modified gold coated glass by micro contanct printing method. The formation of ferredoxin array was confirmed by the atomic force microscopy. The charge store was investigated by external applied reduction potential to ferredoxin as a write function, and the stored reducing charge was measured as a read function of storage applications. In the reduction state, the stored charge was maintained for around 90 sec. This ferredoxin layer can be used as the molecular size information storage by applying the reducing potential and measuring the current flow when achieving the current of individual ferredoxin molecule.

Memory effects based on random networks of single-walled carbon nanotubes

We have fabricated memory devices based on random networks of single-walled carbon nanotubes (SWNTs) on a glass substrate. The characteristics of the nonvolatile memory were investigated as a function of gate voltage, pulse time, and temperature. The program/erase window was greater than approximately 3.2 V. The gate voltage sensitivity of the erase speed was greater ( approximately 1.9 times) than that of the program speed. The activation energy was about 0.273 eV. The mechanism could be explained from the polarization of water molecules, and may provide an important insight into the program/erase operation of memory devices. We have also discussed a fast erase speed due to a work function difference and oxide trapped charges.

Optimality based repetitive controller design for track-following servo system of optical disk drives

In an optical disk drive servo system, to attenuate the external periodic disturbances induced by inevitable disk eccentricity, repetitive control has been used successfully. The performance of a repetitive controller greatly depends on the bandwidth of the low-pass filter included in the repetitive controller. However, owing to the plant uncertainty and system stability, it is difficult to maximize the bandwidth of the low-pass filter. In this paper, we propose an optimality based repetitive controller design method for the track-following servo system with norm-bounded uncertainties. By embedding a lead compensator in the repetitive controller, both the system gain at periodic signal's harmonics and the bandwidth of the low-pass filter are greatly increased. The optimal values of the repetitive controller's parameters are obtained by solving two optimization problems. Simulation and experimental results are provided to illustrate the effectiveness of the proposed method.

A multiplexed quantum memory

A quantum repeater is a system for long-distance quantum communication that employs quantum memory elements to mitigate optical fiber transmission losses. The multiplexed quantum memory (O. A. Collins, S. D. Jenkins, A. Kuzmich, and T. A. B. Kennedy, Phys. Rev. Lett. 98, 060502 (2007)) has been shown theoretically to reduce quantum memory time requirements. We present an initial implementation of a multiplexed quantum memory element in a cold rubidium gas. We show that it is possible to create atomic excitations in arbitrary memory element pairs and demonstrate the violation of Bell's inequality for light fields generated during the write and read processes.

Memories for life: a review of the science and technology

This paper discusses scientific, social and technological aspects of memory. Recent developments in our understanding of memory processes and mechanisms, and their digital implementation, have placed the encoding, storage, management and retrieval of information at the forefront of several fields of research. At the same time, the divisions between the biological, physical and the digital worlds seem to be dissolving. Hence, opportunities for interdisciplinary research into memory are being created, between the life sciences, social sciences and physical sciences. Such research may benefit from immediate application into information management technology as a testbed. The paper describes one initiative, memories for life, as a potential common problem space for the various interested disciplines.