Opportunities and challenges of the U.S. dollar as an increasingly global currency: a Federal Reserve perspective

The rapid growth of demand for U.S. currency over the past two decades, especially the proportion estimated to be held abroad, has posed challenges for the Federal Reserve in meeting its congressionally mandated responsibilities for currency availability and distribution. Those challenges lie in making certain that the Bureau of Engraving and Printing (BEP) prints adequate amounts of currency; that overseas distribution channels have sufficient capacity to distribute U.S. currency when and where it is needed; and that the integrity of U.S. currency is maintained by monitoring counterfeiting activity. In the process of meeting these challenges, the Federal Reserve has improved its methods of forecasting demand for U.S. currency, expanded currency distribution channels, and worked with the BEP and the U.S. Secret Service to protect against counterfeiting threats. This article gives an overview of the evolution of the Federal Reserve's responsibilities for U.S. currency, particularly in relation to the increase in foreign demand over the past two decades, and also discusses work on counterfeit deterrence.International finance ; Money ; Dollar, American

A character sum evaluation and Gaussian hypergeometric series

AbstractEvans has conjectured the value of a certain character sum. The conjecture is confirmed using properties of Gaussian hypergeometric series which are well known for hypergeometric series. Several related questions are discussed

An Investigation, Using Standard Experimental Techniques, to Determine FLCs at Elevated Temperature for Aluminium Alloys

An experimental procedure has been developed for the determination of FLCs at elevated temperatures. The GOM ARGUS system was employed for measuring surface strain based on pre-applied grids (pattern), and limit strains were determined according to the ISO 12004-2:2008 standard. Forming limit curves (FLCs) have been determined for AA5754 under warm forming conditions in an isothermal environment. The tests were carried out at various temperatures up to 300oC and forming speeds ranging from 5 – 300 mm s-1 . Results reveal the significant effect of both temperature and forming speed on FLCs of AA5754. Formability increases with increasing temperature above 200oC. Formability also increases with decreasing speed. The presented FLC results show that the best formability exists at low forming speed and the high temperature end of the warm forming range

16S rRNA gene sequencing of mock microbial populations- impact of DNA extraction method, primer choice and sequencing platform

peer-reviewedBackground Next-generation sequencing platforms have revolutionised our ability to investigate the microbiota composition of complex environments, frequently through 16S rRNA gene sequencing of the bacterial component of the community. Numerous factors, including DNA extraction method, primer sequences and sequencing platform employed, can affect the accuracy of the results achieved. The aim of this study was to determine the impact of these three factors on 16S rRNA gene sequencing results, using mock communities and mock community DNA. Results The use of different primer sequences (V4-V5, V1-V2 and V1-V2 degenerate primers) resulted in differences in the genera and species detected. The V4-V5 primers gave the most comparable results across platforms. The three Ion PGM primer sets detected more of the 20 mock community species than the equivalent MiSeq primer sets. Data generated from DNA extracted using the 2 extraction methods were very similar. Conclusions Microbiota compositional data differed depending on the primers and sequencing platform that were used. The results demonstrate the risks in comparing data generated using different sequencing approaches and highlight the merits of choosing a standardised approach for sequencing in situations where a comparison across multiple sequencing runs is required.This publication has emanated from research supported in part by a research grant from Science Foundation Ireland (SFI) under Grant Numbers SFI/12/RC/2273 and 11/PI/1137 and by FP7 funded CFMATTERS (Cystic Fibrosis Microbiome-determined Antibiotic Therapy Trial in Exacerbations: Results Stratified, Grant Agreement no. 603038)

Ultrafast spectroscopy of propagating coherent acoustic phonons in GaN/InGaN heterostructures

We show that large amplitude, coherent acoustic phonon wavepackets can be generated and detected in In$_x$Ga$_{1-x}$N/GaN epilayers and heterostructures in femtosecond pump-probe differential reflectivity experiments. The amplitude of the coherent phonon increases with increasing Indium fraction $x$ and unlike other coherent phonon oscillations, both \textit{amplitude} and \textit{period} are strong functions of the laser probe energy. The amplitude of the oscillation is substantially and almost instantaneously reduced when the wavepacket reaches a GaN-sapphire interface below the surface indicating that the phonon wavepackets are useful for imaging below the surface. A theoretical model is proposed which fits the experiments well and helps to deduce the strength of the phonon wavepackets. Our model shows that localized coherent phonon wavepackets are generated by the femtosecond pump laser in the epilayer near the surface. The wavepackets then propagate through a GaN layer changing the local index of refraction, primarily through the Franz-Keldysh effect, and as a result, modulate the reflectivity of the probe beam. Our model correctly predicts the experimental dependence on probe-wavelength as well as epilayer thickness.Comment: 11 pages, 14 figure

Reflection factorizations of Singer cycles

Abstract. The number of shortest factorizations into reflections for a Singer cycle inGLn(Fq) is shown to be (q n − 1) n−1. Formulas counting factorizations of any length, and counting those with reflections of fixed conjugacy classes are also given. Résumé. Nous prouvons que le nombre de factorisations de longueur minimale d’un cycle de Singer dans GLn(Fq) comme un produit de réflexions est (q n −1) n−1. Nous présentons aussi des formules donnant le nombre de factorisations de toutes les longueurs ainsi que des formules pour le nombre de factorisations comme produit de réflexions ayant des classes de conjugaison fixes