流面上的Navier-Stokes方程及其维数分裂方法

该文首先提出了流面和流层的概念,然后推导出了半测地坐标系下流层内的三维NS (Navier-Stokes)方程,以及流面上的二维NS方程.通过引入流面上的流函数,得到了流函数方程的非线性初边值问题,并讨论了方程解的存在性和唯一性.基于以上讨论,提出了求解三维NS方程的维数分裂方法, 并给出了算例.     

Gas chromatography-mass spectrometry analysis of volatile compounds from Houttuynia cordata Thunb after extraction by solid-phase microextraction, flash evaporation and steam distillation

Various sampling techniques including flash evaporation (FE), headspace solid-phase microextraction (HS-SPME) and steam distillation (SD) were compared for the gas chromatography-mass spectrometry of volatile constituents present in Houttuynia cordata Thunb (HCT). 2-Undecanone (22.21%) and houttuynum (7.23%) were predominant components of HCT samples obtained by HS-SPME whereas those levels were 3.95 and 3.60% in the same samples by FE and 25.93 and 6.60% in those by SD, respectively. SPME with polydimethylsiloxane (PDMS) fibre was more selective and particularly efficient for the isolation of biologically active compounds and afforded a higher yield of total compounds than FE and SD. A total of 60 compounds were detected in SPME extracts. While in FE and SD extracts, the detected compounds were 41 and 51, respectively. The total amount of compounds isolated by SPME was much larger than that isolated by FE or SD. Some minor constituents were isolated by SPME, but not by SD and FE. This carries great significance because of the importance of the oil volatiles to clinical therapy. HS-SPME is a powerful tool for determining the volatile constitutes present in the TCMs.     

Reducing the calculation of the linear complexity of u2 v -periodic binary sequences to Games–Chan algorithm

We show that the linear complexity of a u2 ^v -periodic binary sequence, u odd, can easily be calculated from the linear complexities of certain 2 ^v -periodic binary sequences. Since the linear complexity of a 2 ^v -periodic binary sequence can efficiently be calculated with the Games-Chan algorithm, this leads to attractive procedures for the determination of the linear complexity of a u2 ^v -periodic binary sequence. Realizations are presented for u = 3, 5, 7, 15.      

Luby–Rackoff Revisited: On the Use of Permutations as Inner Functions of a Feistel Scheme

In this paper we are dealing with the security of the Feistel structure in the Luby–Rackoff model when the round functions are replaced by permutations. There is a priori no reason to think that the security bounds remain the same in this case, as illustrated by Knudsen’s attack [5]. It is why we revisit Luby–Rackoff’s proofs [6] in this specific case. The conclusion is that when the inner functions are random permutations, a 3-round (resp. 4-round) Feistel scheme remains secure against pseudorandom (resp. superpseudorandom) distinguishers as long as m 2^n/2 (with m the number of queries and 2n the block size). The main part of this work was carried out when the author was a member of the UCL Crypto Group (http://www.uclcrypto.org).     

Highly sensitive capillary electrophoresis-mass spectrometry for rapid screening and accurate quantitation of drugs of abuse in urine

The combination of capillary electrophoresis (CE) and mass spectrometry (MS) is particularly well adapted to bioanalysis due to its high separation efficiency, selectivity, and sensitivity; its short analytical time; and its low solvent and sample consumption. For clinical and forensic toxicology, a two-step analysis is usually performed: first, a screening step for compound identification, and second, confirmation and/or accurate quantitation in cases of presumed positive results. In this study, a fast and sensitive CE-MS workflow was developed for the screening and quantitation of drugs of abuse in urine samples. A CE with a time-of-flight MS (CE-TOF/MS) screening method was developed using a simple urine dilution and on-line sample preconcentration with pH-mediated stacking. The sample stacking allowed for a high loading capacity (20.5% of the capillary length), leading to limits of detection as low as 2 ng mL⁻¹ for drugs of abuse. Compound quantitation of positive samples was performed by CE-MS/MS with a triple quadrupole MS equipped with an adapted triple-tube sprayer and an electrospray ionization (ESI) source. The CE-ESI-MS/MS method was validated for two model compounds, cocaine (COC) and methadone (MTD), according to the Guidance of the Food and Drug Administration. The quantitative performance was evaluated for selectivity, response function, the lower limit of quantitation, trueness, precision, and accuracy. COC and MTD detection in urine samples was determined to be accurate over the range of 10–1000 ng mL⁻¹ and 21–1000 ng mL⁻¹, respectively.     

间接馈电柱-锥级联爆磁压缩发生器数值模拟

 为了研究间接馈电、两级级联柱-锥构型的爆磁压缩发生器的物理特性，发展了描述爆磁压缩物理过程的2维爆轰磁流体力学程序——MFCG（Ⅴ），并用其分析、计算了一系列模型。通过将计算结果与柱-柱构型的结果进行比较，表明了柱-锥构型更有利于功率放大：在同样的输出电流条件下，不仅爆磁压缩的时间缩短，而且输出功率也相应地增加。MFCG（Ⅴ）程序的建立以及相应的数值模拟结果有助于加深对柱-锥构型的爆磁压缩发生器物理过程的认识，并为实验设计提供参考。     

Resistance of a CAST-Like Encryption Algorithm to Linear and Differential Cryptanalysis

Linear cryptanalysis and differential cryptanalysis are two recently introduced, powerful methodologies for attacking private-key block ciphers. In this paper, we examine the application of these two cryptanalysis techniques to a CAST-like encryption algorithm. It is shown that, when randomly generated substitution boxes (s-boxes) are used in a CAST-like encryption algorithm, the resulting cipher is resistant to both the linear attack and the differential attack.     

A one-way coupled chaotic map lattice based self-synchronizing stream cipher

Self-synchronizing stream cipher (SSSC) has the advantage that the receiver can automatically synchronize with the sender after receiving previously transmitted ciphertext. However, it has also serious difficulty to keep security due to its self-synchronizing structure. In this paper, a new SSSC based on one-way coupled chaotic map lattice is proposed. By combining floating-point chaotic computations with algebraic operations, the cipher has high bit confusion and diffusion rates. It has both advantages of robustness of synchronization and strong security. The cipher can serve as a new type of SSSC candidate in software implementation.     

On improved asymptotic bounds for codes from global function fields

We analyse a binary cyclotomic sequence constructed via generalized cyclotomic classes by Bai et al. (IEEE Trans Inforem Theory 51: 1849–1853, 2005). First we determine the linear complexity of a natural generalization of this binary sequence to arbitrary prime fields. Secondly we consider k-error linear complexity and autocorrelation of these sequences and point out certain drawbacks of this construction. The results show that the parameters for the sequence construction must be carefully chosen in view of the respective application.      

Global subsonic and subsonic-sonic flows through infinitely long axially symmetric nozzles

In this paper, we establish existence of global subsonic and subsonic-sonic flows through infinitely long axially symmetric nozzles by combining variational method, various elliptic estimates and a compensated compactness method. More precisely, it is shown that there exist global subsonic flows in nozzles for incoming mass flux less than a critical value; moreover, uniformly subsonic flows always approach to uniform flows at far fields when nozzle boundaries tend to be flat at far fields, and flow angles for axially symmetric flows are uniformly bounded away from π/2; finally, when the incoming mass flux tends to the critical value, subsonic-sonic flows exist globally in nozzles in the weak sense by using angle estimate in conjunction with a compensated compactness framework.