The COVID-19 containment in Vietnam: What are we doing?

This viewpoint provides an explanation from the public health policies of Vietnamese government to contain the contagious disease with regard to COVID-19 pandemic. A combination of an early lockdown, increase in “virality” of the health information, encouragement in health declaration, regulation for wearing mask in the public, and country’s unity have been the effective ways to cope with this deadly virus in Vietnam, a developing country, which became the first country to halt the SARS spread successfully in 2003

Stable scalable control of soliton propagation in broadband nonlinear optical waveguides

We develop a method for achieving scalable transmission stabilization and switching of $N$ colliding soliton sequences in optical waveguides with broadband delayed Raman response and narrowband nonlinear gain-loss. We show that dynamics of soliton amplitudes in $N$-sequence transmission is described by a generalized $N$-dimensional predator-prey model. Stability and bifurcation analysis for the predator-prey model are used to obtain simple conditions on the physical parameters for robust transmission stabilization as well as on-off and off-on switching of $M$ out of $N$ soliton sequences. Numerical simulations for single-waveguide transmission with a system of $N$ coupled nonlinear Schr\"odinger equations with $2 \le N \le 4$ show excellent agreement with the predator-prey model's predictions and stable propagation over significantly larger distances compared with other broadband nonlinear single-waveguide systems. Moreover, stable on-off and off-on switching of multiple soliton sequences and stable multiple transmission switching events are demonstrated by the simulations. We discuss the reasons for the robustness and scalability of transmission stabilization and switching in waveguides with broadband delayed Raman response and narrowband nonlinear gain-loss, and explain their advantages compared with other broadband nonlinear waveguides.Comment: 37 pages, 7 figures, Eur. Phys. J. D (accepted

Fast two-pulse collisions in linear diffusion-advection systems with weak quadratic loss in spatial dimension 2

We investigate the dynamics of fast two-pulse collisions in linear diffusion-advection systems with weak quadratic loss in spatial dimension 2. We introduce a two-dimensional perturbation method, which generalizes the perturbation method used for studying two-pulse collisions in spatial dimension 1. We then use the generalized perturbation method to show that a fast collision in spatial dimension 2 leads to a change in the pulse shape in the direction transverse to the advection velocity vector. Moreover, we show that in the important case of a separable initial condition, the longitudinal part in the expression for the amplitude shift has a simple universal form, while the transverse part does not. Additionally, we show that anisotropy in the initial condition leads to a complex dependence of the amplitude shift on the orientation angle between the pulses. Our perturbation theory predictions are in very good agreement with results of extensive numerical simulations with the weakly perturbed diffusion-advection model. Thus, our study significantly enhances and generalizes the results of previous works on fast collisions in diffusion-advection systems, which were limited to spatial dimension 1.Comment: The paper presents a perturbation method for fast two-pulse collisions in diffusion-advection systems with weak nonlinear loss in dimension higher than 1. It generalizes the method that was used in arXiv:1702.05583 and arXiv:1808.04323 for the 1-dimensional problem. It complements the method that was presented in arXiv:2102.07438 for the high-dimensional problem in weakly nonlinear optical medi

When Tether says “JUMP!” Bitcoin asks “How low?”

While stablecoins such as Tether closely track the peg, there is some evidence for recurring spikes in stablecoins’ intraday volatilities rendering stablecoin volatilities unstable (Grobys et al., 2021). Using the Barndorff-Nielsen and Shephard (2006a) methodology, the purpose of our study is to examine whether jumps in Tether have an impact on (subsequent) Bitcoin returns. We retrieve hourly data for Bitcoin and Tether from Bitfinex covering the November 2018 to June 2021 period and encode the binary choice (1 – ‘jump’ and 0 – ‘no jump’) using bi-power variation based on asymptotic distribution theory at 5% significance level for each trading day. Our results show that the joint effect of positive jumps in Tether in association with an 1% increase in Tether returns on the prior day significantly predict negative prices changes in Bitcoin ranging from -3.65% to -8.49% in daily terms. Our results remain robust even after controlling for various other variables.© 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed

Theoretical Design and Analysis of Multivolume Digital Assays with Wide Dynamic Range Validated Experimentally with Microfluidic Digital PCR

This paper presents a protocol using theoretical methods and free software to design and analyze multivolume digital PCR (MV digital PCR) devices; the theory and software are also applicable to design and analysis of dilution series in digital PCR. MV digital PCR minimizes the total number of wells required for “digital” (single molecule) measurements while maintaining high dynamic range and high resolution. In some examples, multivolume designs with fewer than 200 total wells are predicted to provide dynamic range with 5-fold resolution similar to that of single-volume designs requiring 12 000 wells. Mathematical techniques were utilized and expanded to maximize the information obtained from each experiment and to quantify performance of devices and were experimentally validated using the SlipChip platform. MV digital PCR was demonstrated to perform reliably, and results from wells of different volumes agreed with one another. No artifacts due to different surface-to-volume ratios were observed, and single molecule amplification in volumes ranging from 1 to 125 nL was self-consistent. The device presented here was designed to meet the testing requirements for measuring clinically relevant levels of HIV viral load at the point-of-care (in plasma, 1 000 000 molecules/mL), and the predicted resolution and dynamic range was experimentally validated using a control sequence of DNA. This approach simplifies digital PCR experiments, saves space, and thus enables multiplexing using separate areas for each sample on one chip, and facilitates the development of new high-performance diagnostic tools for resource-limited applications. The theory and software presented here are general and are applicable to designing and analyzing other digital analytical platforms including digital immunoassays and digital bacterial analysis. It is not limited to SlipChip and could also be useful for the design of systems on platforms including valve-based and droplet-based platforms. In a separate publication by Shen et al. (J. Am. Chem. Soc., 2011, DOI: 10.1021/ja2060116), this approach is used to design and test digital RT-PCR devices for quantifying RNA

Computer Aided Traumatic Pelvic Injury Decision-making

Traumatic pelvic injury is one of the most dangerous injuries because it is often associated with severe hemorrhage as well as serious complications. It is therefore vital to provide immediate medical treatment to increase the survival rate of pelvic injury patients. However, it is often difficult to make treatment decisions, as cases are complex and display similar patterns. It has been suggested that the use of computer aided decision-making in a trauma support system is the most efficient way to reduce the cost of trauma care. In our previous work, we found that creating rules using all available variables results in lower accuracy than when using only significant variables. This is because less relevant attributes and/or less reliable attributes with regards to the means of measurement can result in random correlation that is clinically meaningless. Based on this knowledge, we designed an efficient computer assisted trauma decision making system for traumatic pelvic injuries using a machine learning algor thm. More specifically, a rule-based system was designed to create a reliable method of making predictions/recommendations on the status and exact outcome – i.e. home or rehabilitation - of pelvic trauma patients using a nonlinear regression and classification (CART) method. The resulting computer aided system can aid physicians in making rapid and accurate decisions. Three machine learning algorithms were compared to evaluate the proposed method

Institutional investment activities and stock market volatility amid COVID-19 in India

This article examines institutional investors’ investment activities and the impact of their trading styles on market volatility amidst COVID-19 in India. Specifically, it seeks to offer a comprehensive analysis of foreign portfolio investors’ (FPIs) and domestic mutual fund managers’ (MFs) investment on equity and debt securities. It examines whether their trading activities drive market volatility during the pandemic period. Also, it explores the impact of COVID-19 on the Indian equity market. This study finds that the growth of COVID-19 does not significantly affect the stock market volatility during the study period. Precisely, the findings reveal that the FPI’s net selling of equity and their overall trading activities in the debt instruments positively impact the market volatility. Findings also show that the FPI’s momentum buys and contrarian sales induce market volatility, whereas the MF’s trading style does not significantly influence the volatility. The Granger causality tests indicate that the FPI’s net sales of equity instruments cause the return volatility and that the market volatility does not drive the equity net sales. Findings also reveal that mutual-fund managers’ trading behavior does not Granger cause market volatility; instead, volatility causes MF’s net selling of debt instruments