TCP SACK突发分组丢失吞吐量模型

利用Gilbert分组丢失模型描述端对端突发分组丢失特性,提出了基于RFC6675的快重传和快恢复模型,推导并基于该模型建立TCP SACK吞吐量模型。数值实验和仿真实验表明,快重传和快恢复模型能准确描述基于RFC6675的快重传和快恢复过程;TCP SACK流吞吐量模型估计的准确性得到提升。     

浅谈计算机犯罪取证中数据恢复技术的应用

随着计算机技术的广泛应用,利用计算机进行犯罪的案件也不断增多。针对计算机进行调查取证已成为公安机关的一项重要工作。在取证过程中,公安机关利用高科技的数据恢复技术查找出被隐藏的犯罪证据,为破获计算机犯罪案件提供有力的技术保障。     

Signal-dependent noise removal for color videos using temporal and cross-channel priors

Noise widely exists in video acquisition, and is especially large under low illumination conditions. Existing video denoising methods are usually at the risk of losing perceptually crucial scene details and introducing unpleasant artifacts. Inspired by high sensitivity of human vision system to thin structures and color aberration in natural images, we incorporate two video priors into a joint optimization framework besides the constraint from the adopted Poisson–Gaussian noise model: (i) we force the motion compensated frames to be a low rank matrix to separate thin structures from large noise. (ii) we utilize the consistency of image pixel gradients in different color channels as a cross channel prior to eliminate color fringing artifacts. To solve this non-convex optimization model, we derive a numerical algorithm via the augmented Lagrangian multiplier method. The effectiveness of our approach is validated by a series of experiments, with both objective and subjective evaluations.     

Surface and interfacial properties of 1,3-dialkyl glyceryl ether hydroxypropyl sulfonates as surfactants for enhanced oil recovery

A series of double-chain anionic surfactants, 1,3-dialkyl glyceryl ether hydroxylpropyl sulfonates (diC_mGE-HS, m?=?8, 10, 12), were synthesized from renewable materials. These surfactants possess very low γ_cmc (～25?mN/m) at 25°C, and their mixtures with conventional surfactants can reduce Daqing crude oil/connate water IFT to ultralow at 45°C in wide total concentration range (0.625-10?mM) in the presence of 0.5?wt.% Na₂CO₃. It seems that diC₁₂GE-HS behaves as a hydrophobic component, whereas diC₁₀GE-HS and diC₈GE-HS behave as hydrophilic components in these mixtures. The mixtures also exhibit high resistance against adsorption by sandstone and good ability of keeping sandstone surface water-wet.     

Accessible and Cost-Effective Method of PDMS Microdevices Fabrication Using a Reusable Photopolymer Mold

This work describes a novel and cost-effective method of polydimethylsiloxane (PDMS) microchips fabrication by using a printing plate photopolymer called Flexcel as a master mold (Fmold). This method has demonstrated the ability to generate multiple devices from a single master, reaching a minimum channel size of 25 μm, structures height ranging from 53 to 1500 μm and achieving dimensions of 1270 × 2062 mm², which are larger than those obtained by the known techniques to date. Scanning electron microscopy, atomic force microscopy, and profilometry techniques have been employed to characterize the Fmold and PDMS replicas. The results showed high replication fidelity of Fmold to the PDMS replica. Furthermore, it was proved the reusability of the Fmold. In our study, up to 50 PDMS replicas have been fabricated without apparent degradation of the mold. The feasibility of the resulting PDMS replica was effectively demonstrated using a microfluidic device for enhanced oil recovery analysis. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1433–1442     

Environmentally Benign,Rapid, and Selective Extraction of Gold from Ores and Waste Electronic Materials

The extraction of gold from ores and electronic waste is an important topic worldwide, as this precious metal has immense value in a variety of fields. However, serious environmental pollution and high energy consumption due to the use of toxic oxidation reagents and harsh reaction conditions is a well‐known problem in the gold industry. Herein, we report a new chemical method based on the combined use of N ‐bromosuccinimide (NBS) and pyridine (Py), which has a greatly decreased environmental impact and reagent cost, as well as mild reaction requirements. This method can directly leach Au⁰ from gold ore and electronic waste to form Au^III in water. The process is achieved in a yield of approximately 90 % at room temperature and a nearly neutral pH. The minimum dose of NBS/Py is as low as 10 mm , which exhibits low toxicity towards mammalian cells and animals as well as aquatic creatures. The high leaching selectivity of Au over other metals during gold leaching is demonstrated, showing that this method has great potential for practical industrial application towards the sustainable refining of gold from ores and electronic waste.     

QbD-driven development and validation of an efficient bioanalytical UPLC method for estimation of olmesartan medoxomil

The present studies describe quality by design-based development of bioanalytical ultra performance liquid chromatography method of olmesartan medoxomil. Initially, method objectives were defined and critical analytical attributes (CAAs) earmarked. Method optimization was conducted using a central composite design for optimizing mobile phase ratio and injection volume as the critical method parameters (CMPs) identified from risk assessment and factor screening studies, and evaluated for their influence on peak area, theoretical plates, and asymmetry factor as CAAs. Chromatographic separation was achieved using acetonitrile:water solvent system containing 0.1% orthophosphoric acid (54:46, v/v) as the mobile phase with UV detection at 243 nm. Further optimization of bioanalytical extraction process was accomplished using a Box–Behnken design selecting extraction time, centrifugation speed, and centrifugation time as the CMPs identified from failure mode and effect analysis, and evaluated for percent recovery, peak asymmetry, and theoretical plate count as the CAAs. Establishment of calibration curve indicated linearity between concentration range of 100 and 800 ng mL^?1, excellent accuracy and precision with limit of detection and limit of quantification as 6.2 and 19.0 ng mL^?1, respectively. Drug stability studies indicated mean percent recovery ranging between 92.4 and 97.3% under various stress conditions.     

Reversible data hiding in encrypted images based on absolute mean difference of multiple neighboring pixels

Recently, with the development of cloud computing, more and more secret data are stored in cloud. Reversible data hiding in encrypted images is a technique that makes contribution to cloud data management in privacy preserving and data security. In previous works, Zhang and Hong presented two reversible dada hiding methods in encrypted images, respectively. However, Zhang’s work neglected the pixels in the borders of image blocks, and Hong et al.’s research only considered two adjacent pixels of each pixel. In addition, their works only considered that all image blocks are embedded into additional data. In this paper, we propose a novel method of evaluating the complexity of image blocks, which considers multiple neighboring pixels according to the locations of different pixels. Furthermore, data embedding ratio is considered. Experiments show that this novel method can reduce average extracted-bit error rate when the block size is appropriate.     

A robust and adaptive recovery‐based discontinuous Galerkin method for the numerical solution of convection–diffusion equations

In this paper, we introduce and test the enhanced stability recovery (ESR) scheme. It is a robust and compact approach to the computation of diffusive fluxes in the framework of discontinuous Galerkin methods. The scheme is characterized by a new recovery basis and a new procedure for the weak imposition of Dirichlet boundary conditions. These features make the method flexible and robust, even in the presence of highly distorted meshes. The implementation is simplified with respect to the original recovery scheme (RDG1x). Furthermore, thanks to the proposed approach, a robust implementation of p‐adaptive algorithms is possible. Numerical tests on unstructured grids show a convergence rate equal to p + 1, where p is the reconstruction order. Comparisons are shown with the original recovery scheme RDG1x and the widely used BR2 method. Results show a significantly larger stability region for the proposed discretization when explicit Runge–Kutta time integration is employed. Interestingly, this advantage grows quickly when the reconstruction order is increased. The proposed procedure for the weak imposition of Dirichlet boundary conditions does not need the introduction of ghost cells, and it is truly local because it does not require data exchange with other elements. It can be easily used with curvilinear wall elements. Several test cases are considered. They include some benchmark tests with the heat equation and compressible Navier–Stokes equations, with test cases designed also to evaluate the behaviour of the scheme with very stretched elements and separated flows. Copyright © 2014 John Wiley & Sons, Ltd.     

DFT Study on the Recovery of Hoveyda–Grubbs‐Type Catalyst Precursors in Enyne and Diene Ring‐Closing Metathesis

DFT (B3LYP‐D) calculations have been used to better understand the origin of the recovered Hoveyda–Grubbs derivative catalysts after ring‐closing diene or enyne metathesis reactions. For that, we have considered the activation process of five different Hoveyda–Grubbs precursors in the reaction with models of usual diene and enyne reactants as well as the potential precursor regeneration through the release/return mechanism. The results show that, regardless of the nature of the initial precursor, the activation process needs to overcome relatively high energy barriers, which is in agreement with a relatively slow process. The precursor regeneration process is in all cases exergonic and it presents low energy barriers, particularly when compared to those of the activation process. This indicates that the precursor regeneration should always be feasible, unlike the moderate recoveries sometimes observed experimentally, which suggests that other competitive processes that hinder recovery should take place. Indeed, calculations presented in this work show that the reactions between the more abundant olefinic products and the active carbenes usually require lower energy barriers than those that regenerate the initial precatalyst, which could prevent precursor regeneration. On the other hand, varying the precursor concentration with time obtained from the computed energy barriers shows that, under the reaction conditions, the precursor activation is incomplete, thereby suggesting that the origin of the recovered catalyst probably arises from incomplete precursor activation.