A batch arrival retrial queue with general retrial times under Bernoulli vacation schedule for unreliable server and delaying repair

This paper deals with the steady state behaviour of an M^x/G/1 queue with general retrial time and Bernoulli vacation schedule for an unreliable server, which consists of a breakdown period and delay period. Here we assume that customers arrive according to compound Poisson processes. While the server is working with primary customers, it may breakdown at any instant and server will be down for short interval of time. Further concept of the delay time is also introduced. The primary customer finding the server busy, down or vacation are queued in the orbit in accordance with FCFS (first come first served) retrial policy. After the completion of a service, the server either goes for a vacation of random length with probability p or may continue to serve for the next customer, if any with probability (1 − p). We carry out an extensive analysis of this model. Finally, we obtain some important performance measures and reliability indices of this model.     

T型及KA分子筛膜的制备、修复及其天然气脱水蒸气性能研究

天然气在长距离输送之前必须进行脱水蒸气,膜分离法是天然气脱水蒸气的有效方法,其中膜材料是关键,而分子筛膜因具有均一的孔径、规则的孔道、良好的稳定性而备受关注。本研究选择孔径为3-5 μm,直径为2 cm的圆片状多孔氧化铝陶瓷作为成膜基底,通过在基底上预涂晶种后原位生长得到了T型和NaA分子筛膜,NaA分子筛膜进一步经过金属离子交换获得了KA分子筛膜,最后将两种分子筛膜应用于水蒸气含量为3.5%的甲烷气体(作为模型天然气)进行天然气脱水蒸气实验。研究结果表明,T型及KA分子筛膜对模型天然气脱水蒸气的H₂O/CH₄选择性分别为2.80和3.16。进而采用表面涂层法对分子筛膜中的缺陷进行了修复,从而有效提高了其模型天然气脱水蒸气性能,修复后的T型及KA分子筛膜的H₂O/CH₄选择性分别达到了10.52和17.71,水蒸气的渗透系数分别为104397 Barrer和28200 Barrer,甲烷损失率分别仅为2%和1%,修复后的两种分子筛膜皆具有良好的稳定性。     

Stem cells and their extracellular vesicles as natural and bioinspired carriers for the treatment of neurological disorders

One of the most explored strategies to cure neurological disorders is the transplantation of stem cells and their derived products. Different stem cells, as well as their extracellular vesicles (EV), modified or not, have been administrated in a large array of preclinical neurological disorder models. EV represent the hope of a “cell-free” therapy that would combine the therapeutic potential of stem cells without their drawbacks. Stem cells and EV showed various degrees of efficiency but, overall, provided benefits and improvements. The administration route has a considerable impact on stem cell and EV safety and therapeutic effect. However, despite evidences of preclinical success, the different strategies developed based on stem cells to treat neurological disorders do not exactly recapitulate in clinical trials. Discrepancies between preclinical and clinical experimental conditions and settings, cell availability and difficulties to scale up and to produce cells and EV in a Good Manufacturing Practices (GMP) environment limit translation.     

Ergodic and light traffic properties of a complex repairable system

A repairable system is composed of components ofI types. A component can be loaded, put on standby, queued or repaired. The repair facility is here assumed to be a queueing system of a rather general structure though interruption of repairs is not allowed. Typei components possess a lifetime distributionA _i (t) and repair time distributionB _t (t). The lifetime of componentj is exhausted with a state-dependent rate _j (t). A Markov process Z(t) with supplementary variables is built to investigate the system behaviour. An ergodic result, Theorem 1, is established under a set of conditions convenient for light traffic analysis. In Theorems 2 to 6, a light traffic limit is derived for the joint steady state distribution of supplementary variables. Applying these results, Theorems 7 to 10 derive light traffic properties of a busy period-measured random variable. Essentially, the concepts of light traffic equivalence due to Daley and Rolski (1992) and Asmussen (1992) are used. The asymptotic (light traffic) insensitivity of busy period and steady state parameters to the form ofA _i(t) [given their means and (in some cases) values of density functions for smallt], is observed under some analytic conditions.Some abbreviations & notations LHS, RHS lefthand side, righthand side - w.r.t. with respect to - (i.i.d.) r.v. (independent identically distributed) random variables - A ^c complement event - d.f., p.d.f. distribution function, probability density function - m.g.f. moment generating function - I _A indicator function of eventA - (t) =1–A(t)     

Transport and AC loss properties of the repaired multifilamentary REBCO superconducting tapes

For near-future applications of REBa₂Cu₃O₇ (REBCO) coated conductors to electric power cables, transformers and Superconducting Magnetic Energy Storage (SMES), the long taped wires with high performance in the transport properties have been designed and fabricated. Moreover, in order to drastically reduce AC losses in perpendicular field configuration, advanced multifilament YBCO coated conductors (MFYCCs) fabricated with technique of a laser scribing process have been also developed. In the present study, from engineering viewpoints to utilize such advanced conductors, we evaluated the transport and AC loss properties of short MFYCCs with a repaired part or a joint by a diffusion joint technique with the saddle-shaped pickup coil method.     

Locality of optimal binary codes

The locality of locally repairable codes (LRCs) for a distributed storage system is the number of nodes that participate in the repair of failed nodes, which characterizes the repair cost. In this paper, we first determine the locality of MacDonald codes, then propose three constructions of LRCs with $r=1,2\text{ and }3$. Based on these results, for $2\le k\le 7$ and $n\ge k+2$, we give an optimal linear $[n,k,d]$ code with small locality. The distance optimality of these linear codes can be judged by the codetable of M. Grassl for $n<2(2^k-1)$ and by the Griesmer bound for $n\ge 2(2^k-1)$. Almost all the $[n,k,d]$ codes ($2\le k\le 7$) have locality $r\le 3$ except for the three codes, and most of the $[n,k,d]$ code with $n<2(2^k-1)$ achieves the Cadambe–Mazumdar bound for LRCs.     

Theoretical study of fast repair of DNA damage by cistanoside C and analogs: Mechanism and docking

Experiments show that the natural substances phenylpropanoid glycosides (PPGs) extracted from pelicularis spicata are capable of repairing DNA damaged by oxygen radicals. Based on kinetic measurements and experiments on tumor cells, a theoretical study of the interaction between PPG molecules and isolated DNA bases, as well as a DNA fragment has been performed. An interaction mechanism reported early has been refined. The docking calculations performed using junction minimization of nucleic acids (JUMNA) software showed that the PPG molecules can be docked into the minor groove of DNA and form complexes with the geometry suitable for an electron transfer between guanine radical and the ligand. Such complexes can be formed without major distortions of DNA structure and are further stabilized by the interaction with the rhamnosyl side-groups.     

Fracture mechanics and crack contact analyses of the active repair of multi-layered piezoelectric patches bonded on cracked structures

In this paper, two-dimensional plane strain finite element analyses of the active repair for cracked structures by using multi-layered piezoelectric patches have been studied. The reductions of stress intensity factors and strain energy density factor at the crack tips are obtained. Also, the repair voltages for various conditions are obtained for estimating the repair performances. Lower repair voltage is a better choice because it is low-energy-consuming and safer for the operation. From the results of numerical fracture mechanics, it shows the crack contact conditions must be considered in the analysis. However, the friction on the crack has few effects on the repair performances for this mode-I dominated case. The better design choices for the piezoelectric patch are as follows: increasing the layer number, increasing the patch length, and reducing the patch thickness. In additions, it is not a good idea to use higher input voltage that is larger than the repair voltage because it will enlarge the crack open near the crack tip. Too long patch length has no advantage for the active repair.     

A Theoretical Model for the Simulation of Microdamage Accumulation and Repair in Compact Bone*

This paper describes a new theoretical approach to bone microdamage, in which a population of cracks is explicitly modelled. A given sample of bone is assumed to contain a certain number of cracks, whose growth characteristics are described with an equation containing stochastic variables to create statistical differences from one crack to another. This type of model allows us to predict a wide variety of data. The present paper illustrates the different types of prediction which can be made, including: (i) standard damage parameters such as the number and length of cracks and the reduction in stiffness; (ii) fatigue test data such as the number of cycles to failure as a function of stress level, including scatter; (iii) effects due to the living system, including repair, remodelling and adaptation. A useful feature of the model is our ability to examine the statistics of the crack population in detail to find, for example, the number of cracks which are potentially dangerous as opposed to those which are dormant, and to investigate the reasons for increased crack numbers in the bones of older people. The potential also exists to use the model to investigate different theories of bone remodelling and adaptation.     

环模修复机模孔定位关键技术研究

环模在饲料加工机械中是一个易阻塞的核心部件。国内外常见清理手段是人工手动逐孔清理。针对现有技术存在清理效率低、易产生误操作及毁坏环模等瓶颈,提出了一套有效的环模模孔定位方法。首先运用磁敏元件检测漏磁原理,分析了模孔定位方法的可行性;然后根据电磁屏蔽对屏蔽材料的选择角度,制作关键探测探头;最后根据捕获模孔的信号特征,基于高效的黄金分割优化搜索的设计思想,构建了环模模孔定位算法模型,分析了模孔定位方案的有效性。结果表明研制的修复机系统模孔定位精度在mm级以下,模孔刮伤率大大降低,进而环模的使用寿命得到延长。