Pressure-tuning of the c-f hybridization in Yb metal detected by infrared spectroscopy up to 18 GPa

It has been known that the elemental Yb, a divalent metal at mbient pressure, becomes a mixed-valent metal under external pressure, with its valence reaching ~2.6 at 30 GPa. In this work, infrared spectroscopy has been used to probe the evolution of microscopic electronic states associated with the valence crossover in Yb at external pressures up to 18 GPa. The measured infrared reflectivity spectrum R(w) of Yb has shown large variations with pressure. In particular, R(w) develops a deep minimum in the mid-infrared, which shifts to lower energy with increasing pressure. The dip is attributed to optical absorption due to a conduction c-f electron hybridization state, similarly to those previously observed for heavy fermion compounds. The red shift of the dip indicates that the $c$-$f$ hybridization decreases with pressure, which is consistent with the increase of valence.Comment: 2 pages, to appear in J. Phys. Soc. Jpn. Supp

Mutation of Directed Graphs -- Corresponding Regular Expressions and Complexity of Their Generation

Directed graphs (DG), interpreted as state transition diagrams, are traditionally used to represent finite-state automata (FSA). In the context of formal languages, both FSA and regular expressions (RE) are equivalent in that they accept and generate, respectively, type-3 (regular) languages. Based on our previous work, this paper analyzes effects of graph manipulations on corresponding RE. In this present, starting stage we assume that the DG under consideration contains no cycles. Graph manipulation is performed by deleting or inserting of nodes or arcs. Combined and/or multiple application of these basic operators enable a great variety of transformations of DG (and corresponding RE) that can be seen as mutants of the original DG (and corresponding RE). DG are popular for modeling complex systems; however they easily become intractable if the system under consideration is complex and/or large. In such situations, we propose to switch to corresponding RE in order to benefit from their compact format for modeling and algebraic operations for analysis. The results of the study are of great potential interest to mutation testing

Metamaterial Polarization Converter Analysis: Limits of Performance

In this paper we analyze the theoretical limits of a metamaterial converter that allows for linear-to- elliptical polarization transformation with any desired ellipticity and ellipse orientation. We employ the transmission line approach providing a needed level of the design generalization. Our analysis reveals that the maximal conversion efficiency for transmission through a single metamaterial layer is 50%, while the realistic re ection configuration can give the conversion efficiency up to 90%. We show that a double layer transmission converter and a single layer with a ground plane can have 100% polarization conversion efficiency. We tested our conclusions numerically reaching the designated limits of efficiency using a simple metamaterial design. Our general analysis provides useful guidelines for the metamaterial polarization converter design for virtually any frequency range of the electromagnetic waves.Comment: 10 pages, 11 figures, 2 table

Optimal seed solver: Optimizing seed selection in read mapping

Motivation: Optimizing seed selection is an important problem in read mapping. The number of non-overlapping seeds a mapper selects determines the sensitivity of the mapper while the total frequency of all selected seeds determines the speed of the mapper. Modern seed-and-extend mappers usually select seeds with either an equal and fixed-length scheme or with an inflexible placement scheme, both of which limit the ability of the mapper in selecting less frequent seeds to speed up the mapping process. Therefore, it is crucial to develop a new algorithm that can adjust both the individual seed length and the seed placement, as well as derive less frequent seeds. Results: We present the Optimal Seed Solver (OSS), a dynamic programming algorithm that discovers the least frequently-occurring set of x seeds in an L-base-pair read in O(x×L) operations on average and in O(x×L2) operations in the worst case, while generating a maximum of O(L2) seed frequency database lookups. We compare OSS against four state-of-the-art seed selection schemes and observe that OSS provides a 3-fold reduction in average seed frequency over the best previous seed selection optimizations. Availability and implementation: We provide an implementation of the Optimal Seed Solver in C++ at: https://github.com/CMU-SAFARI/Optimal-Seed-Solver. Supplementary information: Supplementary data are available at Bioinformatics online. © 2015 The Author 2015. Published by Oxford University Press. All rights reserved

TESS asteroseismology of the known red-giant host stars HD 212771 and HD 203949

International audienc

Seismic Constraints on Helium Abundances from the TESS Southern CVZ

Poster for Cool Stars 21 Stellar helium abundances strongly determine their structure and evolution. However, since helium cannot be detected directly in the photospheres of cool stars, helium abundances are one of the most poorly-constrained inputs to stellar models. It is therefore typical to assume a relationship with the initial abundances of other heavy elements, typically of linear form described by a gradient ΔY/ΔZ. Attempts to determine from globular-cluster stellar populations and Galactic H-II regions have so far not yielded any consensus about empirically reasonable values of ΔY/ΔZ, or, for that matter, even whether such a linear relation is observationally justifiable. Separately, asteroseismology permits the inference of stellar helium abundances, either directly through acoustic-glitch measurements, or indirectly through the forward modelling of stellar oscillation mode frequencies. Using constraints on the initial helium abundance derived from ensemble asteroseismology and stellar forward modelling against individual mode frequencies of a collection of field stars in the TESS, Kepler, and K2 fields, we characterise the helium-metallicity relation of the brightest cool stars in the solar neighbourhood. We find a large spread of seismic initial helium abundances for any given metallicity, rather than a single well-defined linear enrichment law

Aging-Aware Request Scheduling for Non-Volatile Main Memory

Modern computing systems are embracing non-volatile memory (NVM) to implement high-capacity and low-cost main memory. Elevated operating voltages of NVM accelerate the aging of CMOS transistors in the peripheral circuitry of each memory bank. Aggressive device scaling increases power density and temperature, which further accelerates aging, challenging the reliable operation of NVM-based main memory. We propose HEBE, an architectural technique to mitigate the circuit aging-related problems of NVM-based main memory. HEBE is built on three contributions. First, we propose a new analytical model that can dynamically track the aging in the peripheral circuitry of each memory bank based on the bank's utilization. Second, we develop an intelligent memory request scheduler that exploits this aging model at run time to de-stress the peripheral circuitry of a memory bank only when its aging exceeds a critical threshold. Third, we introduce an isolation transistor to decouple parts of a peripheral circuit operating at different voltages, allowing the decoupled logic blocks to undergo long-latency de-stress operations independently and off the critical path of memory read and write accesses, improving performance. We evaluate HEBE with workloads from the SPEC CPU2017 Benchmark suite. Our results show that HEBE significantly improves both performance and lifetime of NVM-based main memory.Comment: To appear in ASP-DAC 202