Bounds on non-linear errors for variance computation with stochastic rounding *

The main objective of this work is to investigate non-linear errors and pairwise summation using stochastic rounding (SR) in variance computation algorithms. We estimate the forward error of computations under SR through two methods: the first is based on a bound of the variance and Bienaym{\'e}-Chebyshev inequality, while the second is based on martingales and Azuma-Hoeffding inequality. The study shows that for pairwise summation, using SR results in a probabilistic bound of the forward error proportional to log(n)u rather than the deterministic bound in O(log(n)u) when using the default rounding mode. We examine two algorithms that compute the variance, called ''textbook'' and ''two-pass'', which both exhibit non-linear errors. Using the two methods mentioned above, we show that these algorithms' forward errors have probabilistic bounds under SR in O(\sqrt nu) instead of nu for the deterministic bounds. We show that this advantage holds using pairwise summation for both textbook and two-pass, with probabilistic bounds of the forward error proportional to log(n)u

Phytochemical, antimicrobial and cytotoxicity screening of ethanol extract of Acacia ehrenbergiana Hayne grown in Jazan Region of Saudi Arabia

Purpose: To explore the phytoconstituents of Acacia ehrenbergiana Hayne as well as its biological effects. Methods: Determination of phytoconstituents of ethanol extract of the plant was performed by gas chromatography-mass spectrometry (GC-MS) technique. Antibacterial screening was conducted against the isolates of Gram-positive and Gram-negative microbes while the anti-carcinogenic properties of the ethanol extract on cancerous cells were investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) cytotoxicity assay against breast MCF7, ovary cancer A2780 and colon cancer HT29 cells, respectively, in addition to normal MRC5 fibroblast cells. Results: GC-MS analysis identified 15 different phytochemicals in the ethanol extract. The extract exerted significant antimicrobial activity with the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) in the range 1.56 - 6.25 and 3.12 – 12.5 mg/L, respectively, against all test bacterial strains. Cytotoxic activity, obtained by MTT assay, was 28.81 ± 0.99, 12.50 ± 2.50, 23.90 ± 0.74 and 50.58 ± 3.24 μg/mL, against the three cancer cell lines and normal fibroblast, respectively. MTT cytotoxicity results was further confirmed by clonogenic survival assay on MCF7 cells. Conclusion: This study highlights the potential interesting ethnopharmacological applications of Acacia ehrenbergiana Hayne to treat drug-resistant pathogens as standardized extract. Keywords: Acacia ehrenbergiana, Phytochemistry, Antimicrobial, Cytotoxicit

Hot-Carrier Cooling in High-Quality Graphene is Intrinsically Limited by Optical Phonons

Many promising optoelectronic devices, such as broadband photodetectors, nonlinear frequency converters, and building blocks for data communication systems, exploit photoexcited charge carriers in graphene. For these systems, it is essential to understand, and eventually control, the cooling dynamics of the photoinduced hot-carrier distribution. There is, however, still an active debate on the different mechanisms that contribute to hot-carrier cooling. In particular, the intrinsic cooling mechanism that ultimately limits the cooling dynamics remains an open question. Here, we address this question by studying two technologically relevant systems, consisting of high-quality graphene with a mobility >10,000 cm$^2$V$^{-1}$s$^{-1}$ and environments that do not efficiently take up electronic heat from graphene: WSe$_2$-encapsulated graphene and suspended graphene. We study the cooling dynamics of these two high-quality graphene systems using ultrafast pump-probe spectroscopy at room temperature. Cooling via disorder-assisted acoustic phonon scattering and out-of-plane heat transfer to the environment is relatively inefficient in these systems, predicting a cooling time of tens of picoseconds. However, we observe much faster cooling, on a timescale of a few picoseconds. We attribute this to an intrinsic cooling mechanism, where carriers in the hot-carrier distribution with enough kinetic energy emit optical phonons. During phonon emission, the electronic system continuously re-thermalizes, re-creating carriers with enough energy to emit optical phonons. We develop an analytical model that explains the observed dynamics, where cooling is eventually limited by optical-to-acoustic phonon coupling. These fundamental insights into the intrinsic cooling mechanism of hot carriers in graphene will play a key role in guiding the development of graphene-based optoelectronic devices

Understanding Novel Superconductors with Ab Initio Calculations

This chapter gives an overview of the progress in the field of computational superconductivity. Following the MgB2 discovery (2001), there has been an impressive acceleration in the development of methods based on Density Functional Theory to compute the critical temperature and other physical properties of actual superconductors from first-principles. State-of-the-art ab-initio methods have reached predictive accuracy for conventional (phonon-mediated) superconductors, and substantial progress is being made also for unconventional superconductors. The aim of this chapter is to give an overview of the existing computational methods for superconductivity, and present selected examples of material discoveries that exemplify the main advancements.Comment: 38 pages, 10 figures, Contribution to Springer Handbook of Materials Modellin

System-wide profiling of RNA-binding proteins uncovers key regulators of virus infection

International audienceGraphical Abstract Highlights d A quarter of the RBPome changes upon SINV infection d Alterations in RBP activity are largely explained by changes in RNA availability d Altered RBPs are crucial for viral infection efficacy d GEMIN5 binds to the 5 0 end of SINV RNAs and regulates viral gene expressio

Reassessing the effect of colour on attitude and behavioural intentions in promotional activities: The moderating role of mood and involvement

The present research examines the effect of background colour on attitude and behavioural intentions in various promotional activities taking into consideration the moderating role of mood and involvement. Three experiments reflecting different promotional activities (window display, consumer trade show, guerrilla marketing) were conducted for this purpose. Overall, findings indicate that cool background colours, in contrast to warm colours, induce more positive attitudes and behavioural intentions mainly in positive mood, and low involvement conditions. Implications are also discussed