A polyhedral approach for the generalized assignment problem.

The generalized assignment problem (GAP) consists of finding a maximal profit assignment of n jobs over m capacity constrained agents, whereby each job has to be processed by only one agent. This contribution approaches the GAP from the polyhedral point of view. A good upper bound is obtained by approximating the convex hull of the knapsack constraints in the GAP-polytope using theoretical work of Balas. Based on this result, we propose a procedure for finding close-to-optimal solutions, which gives us a lower bound. Computational results on a set of 60representative and highly capacitated problems indicate that these solutions lie within 0.06% of the optimum. After applying some preprocessing techniques and using the obtained bounds, we solve the generated instances to optimality by branch and bound within reasonable computing time.Assignment;

Influence of the Cu-Te composition and microstructure on the resistive switching of Cu-Te/Al(2)O(3)/Si cells

In this letter, we explore the influence of the Cu(x)Te(1-x) layer composition (0.2 0.7 leads to large reset power, similar to pure-Cu electrodes, x < 0.3 results in volatile forming properties. The intermediate range 0.5< x < 0.7 shows optimum memory properties, featuring improved control of filament programming using <5 mu A as well as state stability at 85 degrees C. The composition-dependent programming control and filament stability are closely associated with the phases in the Cu(x)Te(1-x) layer and are explained as related to the chemical affinity between Cu and Te. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3621835

Microscopic origin of random telegraph noise fluctuations in aggressively scaled RRAM and its impact on read disturb variability

Random telegraph noise (RTN) is an important intrinsic phenomenon of any logic or memory device that is indicative of the reliability and stochastic variability in its performance. In the context of the resistive random access memory (RRAM), RTN becomes a key criterion that determines the read disturb immunity and memory window between the low (LRS) and high resistance states (HRS). With the drive towards ultra-low power memory (low reset current) and aggressive scaling to 10 × 10 nm2 area, contribution of RTN is significantly enhanced by every trap (vacancy) in the dielectric. The underlying mechanisms governing RTN in RRAM are yet to be fully understood. In this study, we aim to decode the role of conductance fluctuations caused by oxygen vacancy transport and inelastic electron trapping and detrapping processes. The influence of resistance state (LRS, shallow and deep HRS), reset depth and reset stop voltage (VRESET-STOP) on the conductance variability is also investigated. © 2013 IEEE

Factors associated with the intention of pregnant women to give birth with epidural analgesia: a cross-sectional study

Background In Belgium most women receive epidural analgesia during labour. Although, it offers satisfactory pain relief during labour, the risk on a series of adverse advents has been reported. The objective of this study was to determine factors associated with the intention of pregnant women, anticipating a vaginal birth, of requesting epidural analgesia during labour.Methods A cross-sectional study, using an online self-report questionnaire was performed, including socio-demographic and personal details. Associated factors were examined with the HEXACO-60 questionnaire, the Mental Health Inventory-5, the Tilburg Pregnancy Distress Scale and the Labour Pain Relief Attitude Questionnaire for pregnant women. The level of intention to request epidural analgesia was based on two questions: Do you intend to ask for epidural analgesia (1) at the start of your labour; (2) at some point during labour? Data were collected predominantly during the second and third trimester of pregnancy. Descriptive analysis and a multiple linear regression analysis were performed.Results 949 nulliparous (45.9%) and multiparous (54.1%) pregnant women, living in Flanders (Dutch-speaking part of Belgium) anticipating a vaginal birth completed the questionnaires. Birth-related anxiety (ß 0.096, p < 0.001), the attitude that because of the impact of pregnancy on the body, asking for pain relief is normal (ß 0.397, p < 0.001) and feeling more self-confident during labour when having pain relief (ß 0.034, p < 0.001) show a significant positive relationship with the intention for intrapartum epidural analgesia. The length of the gestational period (ß − 0.056, p 0.015), having a midwife as the primary care giver during pregnancy (ß − 0.048, p 0.044), and considering the partner in decision-making about pain relief (ß − 0.112, p < 0.001) show a significant negative relationship with the intention level of epidural analgesia. The explained variability by the multiple regression model is 54%.Conclusions A discussion during pregnancy about the underlying reason for epidural analgesia allows maternity care providers and partners to support women with pain management that is in line with women’s preferences. Because women’s intentions vary during the gestational period, pain relief should be an issue of conversation throughout pregnancy

RTN in GexSe1-x OTS Selector Devices

Random telegraph noise (RTN) signals in GexSe1-x ovonic threshold switching (OTS) selector have been analyzed in this work, both before and after the first-fire (FF) operation and at on- and off-states. It is observed that RTN appears after the FF, and its absolute amplitude at the off-state is small and negligible in comparison with the RTN signals in RRAM devices. At the on-state, large RTN signals are observed, which can either partially or fully block the conduction path, supporting that a conductive filament is formed or activated by FF and then modulated during switching. Statistical analysis reveals that the relative RTN amplitude at on-state in GexSe1-x OTS selector is smaller than or equivalent to those in RRAM devices

Stochastic computing based on volatile GeSe ovonic threshold switching selectors

Stochastic computing (SC) is a special type of digital compute strategy where values are represented by the probability of 1 and 0 in stochastic bit streams, which leads to superior hardware simplicity and error-tolerance. In this paper, we propose and demonstrate SC with GeSe based Ovonic Threshold Switching (OTS) selector devices by exploiting their probabilistic switching behavior. The stochastic bit streams generated by OTS are demonstrated with good computation accuracy in both multiplication operation and image processing circuit. Moreover, the bit distribution has been statistically studied and linked to the collective defect de/localization behavior in the chalcogenide material. Weibull distribution of the delay time supports the origin of such probabilistic switching, facilitates further optimization of the operation condition, and lays the foundation for device modelling and circuit design. Considering its other advantages such as simple structure, fast speed, and volatile nature, OTS is a promising material for implementing SC in a wide range of novel applications, such as image processors, neural networks, control systems and reliability analysis

Measurement and simulation of the neutron response of the Nordball liquid scintillator array

The response of the liquid scintillator array Nordball to neutrons in the energy range 1.5 < T_n < 10 MeV has been measured by time of flight using a 252Cf fission source. Fission fragments were detected by means of a thin-film plastic scintillator. The measured differential and integral neutron detection efficiencies agree well with predictions of a Monte Carlo simulation of the detector which models geometry accurately and incorporates the measured, non-linear proton light output as a function of energy. The ability of the model to provide systematic corrections to photoneutron cross sections, measured by Nordball at low energy, is tested in a measurement of the two-body deuteron photodisintegration cross section in the range E_gamma=14-18 MeV. After correction the present 2H(gamma,n)p measurements agree well with a published evaluation of the large body of 2H(gamma,p)n data.Comment: 20 pages 10 figures, submitted Nucl. Instr. Meth.

A computational analysis of lower bounds for big bucket production planning problems

In this paper, we analyze a variety of approaches to obtain lower bounds for multi-level production planning problems with big bucket capacities, i.e., problems in which multiple items compete for the same resources. We give an extensive survey of both known and new methods, and also establish relationships between some of these methods that, to our knowledge, have not been presented before. As will be highlighted, understanding the substructures of difficult problems provide crucial insights on why these problems are hard to solve, and this is addressed by a thorough analysis in the paper. We conclude with computational results on a variety of widely used test sets, and a discussion of future research

Investigation of pre-existing and generated defects in non-filamentary a-Si/TiO2 RRAM and their impacts on RTN amplitude distribution

An extensive investigation of the pre-existing and generated defects in amorphous-Si/TiO2 based non-filamentary (a-VMCO) RRAM device has been carried out in this work to identify the switching and degradation mechanisms, through a combination of random-telegraph-noise (RTN) and constant- voltage-stress (CVS) analysis. The amplitude of RTN, which leads to read instability, is also evaluated statistically at different stages of cell degradation and correlated with different defects, for the first time. It is found that the switching between low and high resistance states (LRS and HRS) are correlated with the profile modulation of pre-existing defects in the ‘defect-less’ region near the a-Si/TiO2 interface. The RTN amplitude observed at this stage is small and has a tight distribution. At longer stress times, a percolation path is formed due to defects generation, which introduces larger RTN amplitude and a significant tail in its distribution