Ultrahigh speed OOK-to-PSK conversion using linear filtering in silicon ring resonators

A scheme to achieve ultrahigh speed all-optical format conversion from on-off keying (OOK) to phase-shift keying (PSK) by using the linear filtering in the silicon ring resonators is proposed. It is shown that the OOK-to-PSK conversion can be achieved through a linear signal processing. Simulation results are provided for the 160-Gb/s non-return-to-zero (NRZ)-to-PSK and carrier-suppressed (CS) return-to-zero (RZ)-to-(CS)RZPSK conversions.     

The sampling properties of Hurst exponent estimates

The classical rescaled adjusted range (R/S) statistic is a popular and robust tool for identifying fractal structures and long-term dependence in time-series data. Subsequent to Mandelbrot and Wallis [Water Resour. Res. 4 (1968) 909] who proposed the statistic be measured over several subseries contained within the whole series length, the use overlapping vs. contiguous subseries has been a source of some debate amongst R/S theorists. This study examines the distributional characteristics of rescaled adjusted range and Hurst exponent estimates derived using overlapping vs. contiguous subseries, henceforth closing debate on the issue of relative bias due to either technique. Confidence intervals for the statistical significance of the Hurst exponent are also determined.     

Aspects of large eddy simulation of homogeneous isotropic turbulence

HOMTY, a code for Large Eddy Simulation of homogeneous isotropic turbulence is proven by successful simulation of two experiments. The role of each term in the equations of motion and the concept of filtering is examined. It is shown that ‘prefiltering’ is unnecessary, and the resulting additional term in the equations, instead of transferring energy to the subgrid scales, backscatters energy from the resolved large wavenumerbers to the small ones. The kinetic energy decay exponent is shown to depend on the low wavenumber part of the velocity spectrum. Pressure statistics are computed and found to be in agreement with previous computations.     

Product operator analysis of the influence of chemical exchange on relaxation rates

Measurements of chemical-exchange processes by NMR are widely used to obtain valuable information about molecular dynamics and structure. Here, a computational method is introduced to assess the influence of chemical exchange on spin relaxation rates. The method is based on the inclusion of a random exchange process in product operator calculations on a microscopic level. This product operator approach can be applied to estimate exchange contributions when using sophisticated pulse sequences that cannot be easily described analytically. The method applies to the full range of exchange times measurable by NMR and can incorporate interference effects between exchange and other processes such as scalar coupling. To demonstrate its utility, simulated relaxation data were compared with theoretical predictions of spin-locking and Carr-Purcell spin-echo sequences with hard and adiabatic pulses, using different time scales for a two-site chemical-exchange process. Finally, simulations were used to examine a system in which a second random process is superimposed on a simple two-site exchange process. The method was found to provide a simple and robust tool to analyze pulse sequences and equations commonly used to study exchange-induced relaxation.     

Reduction of wave phenomena in high-field MRI experiments using absorbing layers

Wave behavior, such as constructive and destructive interference, can decrease RF field homogeneity. As the static magnetic field strengths increase, these effects become more significant, resulting in image inhomogeneities. For a surface coil, wave interference is due to reflections at boundaries separating regions with largely different dielectric constants. An approach is presented to eliminate wave reflections through the use of absorbing layers. A one-dimensional plane wave model and a three-dimensional finite difference time domain numerical model at 470 MHz are presented validating the theoretical effectiveness of the approach. The findings are verified experimentally with 1 H MRI on phantoms at 11.1 T, demonstrating greatly reduced interference patterns in the images.     

Computational screening and biochemical analysis of Pistacia integerrima and Pandanus odorifer plants to find effective inhibitors against Receptor-Binding domain (RBD) of the spike protein of SARS-Cov-2

Although World Health Organization-approved emergency vaccines are available in many countries, the mortality rate from COVID-19 remains high due to the fourth or fifth wave and the delta variant of the coronavirus. Thus, an effective mechanistic investigation in treating this disease is urgently needed. In this work, we extracted phytochemicals from two mangrove plants, Pistacia integerrima and Pandanus odorifer, assessing their potential actions against the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2. The antioxidant activities of Pistacia integerrima leaves and fruits were 142.10 and 97.13 µg/mL, respectively, whereas Pandanus odorifer leaves and fruits were 112.50 and 292.71 µg/mL, respectively. Furthermore, leaf extracts from both plants had lower cytotoxicity against Artemia salina than fruit extracts. Gas chromatography-mass spectrometry analysis revealed a total of 145 potential phytochemicals from these extracts. Three phytochemicals, 28-demethyl-beta-amyrone, 24-Noroleana-3,12-diene, and stigmasterol, displayed binding free energy values of ? 8.3, ?7.5, and ? 8.1 Kcal/mol, respectively, in complexes with the spike protein of SARS-CoV-2. The root-mean-square deviation, solvent-accessible surface area, radius of gyration, root-mean-square fluctuations, and hydrogen bonds were used to ensure the binding stability of the docked complexes in the atomistic simulation. Thus, wet-lab validations are necessary to support these findings.     

The effect of pH adjusted electrolytes on capillary isoelectric focusing assessed by high-resolution dynamic computer simulation

The effect of the composition of electrolytes on capillary IEF is assessed for systems with carrier ampholytes covering two pH units and with catholytes of decreased pH, anolytes of increased pH, and both electrode solutions with adjusted pH values. For electrolytes composed of formic acid as anolyte and ammonium hydroxide as catholyte, simulation is demonstrated to provide the expected IEF system in which analytes with pI values within the formed pH gradient are focused and become immobile. Addition of formic acid to the catholyte results in the formation of an isotachophoretic zone structure that migrates toward the cathode. With ammonium hydroxide added to the anolyte migration occurs toward the anode. In the two cases, all carrier components and amphoteric analytes migrate isotachophoretically as cations or anions, respectively. The data reveal that millimolar amounts of a counter ion are sufficient to convert an IEF pattern into an ITP system. With increasing amounts of the added counter ion, the overall length of the migrating zone structure shrinks, the range of the pH gradient changes, and the migration rate increases. The studied examples indicate that systems of this type reported in the literature should be classified as ITP and not IEF. When both electrolytes are titrated, a non-uniform background electrolyte composed of formic acid and ammonium hydroxide is established in which analytes migrate according to local pH and conductivity without forming IEF or ITP zone structures. Simulation data are in qualitative agreement with previously published experimental data.     

基于计算机模拟技术对JAK2抑制剂的定量构效关系、分子设计和分子动力学研究

本文选取了52个对Janus激酶2(JAK2)有抑制作用的小分子化合物,分别使用3D-QSAR中的CoMFA和CoMSIA方法构建了两个可靠的、具有预测能力的模型,并利用分子对接分析数据集化合物与JAK2蛋白的相互作用,表明化合物主要通过氢键和范德华作用与JAK2靶蛋白结合。根据3D-QSAR模型的分析结果,设计了40个化合物,利用构建的模型预测其抑制活性;使用软件预测了化合物的药代动力学(ADME)参数,开展分子对接模拟,最终选择化合物D01和D22与JAK2靶蛋白进行了分子动力学模拟研究,结果显示两个复合物结合构象稳定,与分子对接结果趋势一致。本研究的结果可以为JAK2抑制剂的研发提供一些新的思路,为临床开发此类药物提供理论支撑。     

Étude de la convergence numérique d'une méthode vortex pour un écoulement a grand nombre de Reynolds dans un mélangeurNumerical convergence of vortex method for a high Reynolds number 2D bluff-body flow

In this paper the convergence of the RVM for a complex flow is studied, in function of three discretization parameters. Two of these parameters are related to the spatial discretization of the vorticity Γ (sheet or blob strength) and h (sheet length or core radius) and the third one to the time discretization Δt. Two main events are observed: first, the computation works but the convergence is not attained, secondly the computation fails. The first behaviour is attributed to a lack of accuracy and the second to a lack of numerical stability. Once the stability conditions are satisfied, decreasing the value of parameters always leads to convergence. To cite this article: I. Mortazavi et al., C. R. Mecanique 330 (2002) 409–416.     

Fermetures entropiques pour les systèmes bifluides à sept équations

In this Note, we propose a way to obtain two-fluid two-pressures multiphase models that satisfy an entropy inequality. We first notice that the continuous model associated to the discrete model of Abgrall and Saurel (2003) satisfies the entropy principles. Thanks to this, we show how to modify existing models in order to achieve the second law of thermodynamics. To cite this article: M. Papin, R. Abgrall, C. R. Mecanique 333 (2005).