A note on start-up and large amplitude oscillatory shear flow of multimode viscoelastic fluids

Start up of plane Couette flow and large amplitude oscillatory shear flow of single and multimode Maxwell fluids as well as Oldroyd-B fluids have been analyzed by analytical or semi-analytical procedures. The result of our analysis indicates that if a single or a multimode Maxwell fluid has a relaxation time comparable or smaller than the rate of change of force imparted on the fluid, then the fluid response is not singular as Elasticity Number (E ). However, if this is not the case, as E , perturbations of single and multimode Maxwell fluids give rise to highly oscillatory velocity and stress fields. Hence, their behavior is singular in this limit. Moreover, we have observed that transients in velocity and stresses that are caused by propagation of shear waves in Maxwell fluids are damped much more quickly in the presence of faster and faster relaxing modes. In addition, we have shown that the Oldroyd-B model gives rise to results quantitatively similar to multimode Maxwell fluids at times larger than the fastest relaxation time of the multimode Maxwell fluid. This suggests that the effect of fast relaxing modes is equivalent to viscous effects at times larger than the fastest relaxation time of the fluid. Moreover, the analysis of shear wave propagation in multimode Maxwell fluids clearly show that the dynamics of wave propagation are governed by an effective relaxation and viscosity spectra. Finally, no quasi-periodic or chaotic flows were observed as a result of interaction of shear waves in large amplitude oscillatory shear flows for any combination of frequency and amplitudes.     

Existence and nonexistence of global positive solutions to nonlinear diffusion problems with nonlinear absorption through the boundary

This paper deals with the existence and nonexistence of global positive solutions to in ,

and in . Here is a parameter, is a bounded smooth domain. After pointing out the mistakes in Global behavior of positive solutions to nonlinear diffusion problems with nonlinear absorption through the boundary, SIAM J. Math. Anal. 24 (1993), 317-326, by N. Wolanski, which claims that, for the ball of , the positive solution exists globally if and only if , we reconsider the same problem in general bounded domain and obtain that every positive solution exists globally if and only if .

     

Conformational studies of multichain copoly(α-amino acids)s in solution

The conformational transition of multichain copoly(-amino acid)s consisting of copoly(-methyl-L-glutamyl-L-lysine) as backbone molecule and poly(-benzyl-L-glutamate) as branch molecules was studied in chloroform and DCA mixtures. The helix stability of backbone molecule is strongly affected by the length of branch molecules. In the case of the multichain copolymer having short branch molecular chains, i.e.,DP _br <10, the helix conformation of the backbone molecule is strictly affected by some interferences among the randomly coiled molecular chains. In the case of water-soluble multichain copolymer having poly(L-glutamic acid) or poly(L-lysine) as branch molecules, the transitional process from coil to helix is observed by depressing hydrostatic repulsion among the ionized side chain of branch molecules. However, such conformational transition is depressed to a considerable extent by interferences among the branch molecules.Abbreviations used (shown alphabetically) A/I molar ratio of NCA to initiator - Cbz carbobenzyloxy - DCA dichloroacetic acid - DMF N,N-dimethylformamide - DP _br number-average degree of polymerization of branches of multichain copolymer - Fw _br weight fraction of-benzyl-L-glutamyl residues of multichain copolymer - Mn number-average molecular weight - NCA N-carboxy anhydride of-amino acid - ORD optical rotatory dispersion     

Blow‐up of solution of wave equation with internal and boundary source term and non‐porous viscoelastic acoustic boundary conditions

In this paper we study the blow‐up of solution of a mixed problem associated to a nonlinear wave equation with dissipative and source term in a bounded domain of . On a boundary portion of the domain we consider a non‐porous viscoelastic acoustic boundary conditions to a non‐locally reacting boundary.     

Synthesis of boron nitride nanotubes by Argon supported Thermal Chemical Vapor Deposition

Thermal Chemical Vapor Deposition technique is modified with the use of Argon gas flow inside the chamber as an alternative for vacuum and orientation of one end closed quartz test tube. The use of Argon gas not only simplified the experimental set up, but also made it ~ 18 % cost effective compared to the conventional set up. Field Emission Scanning Electron Microscopy micrographs show straight and long BNNTs along with some cotton like morphologies. Transmission electron microscopy revealed bamboo like structure inside the tube and ~0.34 nm interlayer spacing for highly crystalline nature of boron nitride nanotubes. X-ray photon spectroscopy shows B 1s peak at 191.08 eV and N 1s peak at 398.78 eV that represents h-BN. Whereas, Raman spectrum indicates a major peak at ~1379.60 (cm⁻¹) that correspond to E_2g mode of h-BN.     

Conformational analysis of a secondary hydroxamic acid in aqueous solution by NOE spectroscopy

Hydroxamic acids are metal‐binding compounds used by micro‐organisms and possess applications in medicine and industry. Hydroxamic acids favor two conformations, E and Z; metal binding is limited to the Z conformation. The Z conformation may be identifiable by NOE spectroscopy, but analysis is complicated by the potential for long‐range coupling as well as for relayed NOEs due to conformational switching. In this report, we re‐examine the reported conformational preference of N‐methyl acetohydroxamic acid (NMHA) in D₂O using NOE spectroscopy. We find that the favored conformation of NMHA in aqueous solution is the E conformation, contrary to an earlier report. NOE build‐up curves are proposed as a valuable tool to probe conformational behavior in similar systems. Copyright © 2013 John Wiley & Sons, Ltd.     

Studies on electron cloud instability in BEPCⅡ

Electron Cloud Instability has been studied in the operation of BEPC. The BEPCⅡ began the commissioning in November 2006 and the positron beam current has reached 500 mA. Because of such a high beam current, some instabilities such as ECI, bunch lengthening et al, have appeared during the operation. The experimental investigation on ECI during the commissioning of BEPCⅡ will be reported in this paper.     

存在随机解释变量的平行数据模型的处理

本文研究了平行数据模型中存在随机解释变量的解决方法:构造了模型设定的假设检验,给出了参数的一致估计量,并通过建立山东省城镇家庭烟草消费额模型进行了实证分析.     

Automated detection and removal of capillary electrophoresis artifacts due to spectral overlap

While DNA detection using capillary electrophoresis has enabled improvements in both resolution and throughput, the use of CE – particularly with multiple dye channels – can introduce artifacts that can complicate analyses. Undetected pull‐up artifacts can pose a challenge to investigators, especially in low‐level samples, while partial pull‐up peaks can distort peak height balance within a locus and impact the downstream likelihood ratio. Current methods for addressing pull‐up are typically manually implemented. This study presents an effective alternative: a series of mathematical models, created using symbolic regression achieved through genetic programming. The models estimate the amount of pull‐up expected in a peak from a true allele for a given dye‐dye relationship and instrument type. This leads to the removal of artifactual pull‐up peaks and peak height corrections when pull‐up is present within true alleles. When models are used in conjunction with a dynamic threshold, pull‐up peaks were automatically detected and removed with an accuracy rate of 96.1%. The removal of partial pull‐up from true allele peaks led to a more accurate heterozygote balance for the affected locus. These models have been optimized for use with any analytical threshold and can be implemented by any lab using a 3100 or 3500 instrument series.