Design and analysis of a flow control scheme over wireless networks

This paper studies the problem of congestion control on wireless networks. A dynamical model for the end‐to‐end network flow control that exploits the differentiation between congestion loss and physical channel error loss is proposed. The introduction of a specific wireless model is motivated by the distinctive presence of channel errors, which are often not known exactly. We assume that each wireless link is associated with an additional error function that depends on the current flow along the link and that accounts for the packet loss rate caused by the physical channel. This leads to a new dynamic flow control scheme that naturally extends a known mathematical model for the fluid‐flow approximation of the Transmission Control Protocol for wireline networks. The main objective of this work is to study the dynamical properties of the new model: we analyze its nonlinear dynamics, derive its stability properties, and study its robustness to delays. We also present and discuss some ns‐2 simulations of its dynamics. This work additionally looks at the actual implementation of the proposed scheme: by requiring only modifications to the application layer rather than the transport one, no alterations to the network infrastructure or transport protocols are needed. The article argues that the new scheme appears to be not only theoretically meaningful but also practically relevant for an application layer implementation. Copyright © 2011 John Wiley & Sons, Ltd.     

Exponential stability of slowly varying discrete systems with multiple state delays

We give sufficient conditions for the exponential stability of a class of perturbed time‐varying difference equations with multiple delays and slowly varying coefficients. Under appropriate growth conditions on the perturbations, combined with the ‘freezing’ technique, we establish explicit conditions for global exponential stability. Copyright © 2012 John Wiley & Sons, Ltd.     

Environmental effects on the electrical behavior of pentacene thin-film transistors with a poly(methyl methacrylate) gate insulator

The electrical properties of top-contact pentacene thin-film transistors (TFTs) with a poly(methyl methacrylate) (PMMA) gate dielectric were analyzed in air and vacuum environments. Compared to the vacuum case, the pentacene TFT in air exhibited lower drain currents and more pronounced shifts in the threshold voltage upon reversal of the gate voltage sweep direction, together with a decrease in the field-effect mobility. These characteristic variations were explained in terms of two distinctive actions of polar H₂O molecules in pentacene TFT. H₂O molecules were suggested to diffuse under the source and drain contacts and interrupt the charge injection into the pentacene film, whereas those that permeate at the pentacene/PMMA interface retard hole depletion in and around the TFT channel. The diffusion process was much slower than the permeation process. The degraded TFT characteristics in air could be recovered mostly by storing the device under vacuum, which suggests that the air instability of TFTs is due mainly to the physical adsorption of H₂O molecules within the pentacene film.     

An error correcting code and its implementation†

The present paper describes an error correcting code. It is a linear systematic (7,4) code which is capable of detecting two errors and correcting a single error. The encoding and decoding circuits have also been described.     

Crack path stability in cracked panel

Abstract

The prediction of the crack growth path plays a significant role in the estimation of the final shape of broken solids and structures. Furthermore, the study of the crack path in broken specimens renders the loading conditions just before fracture. Experiments on brittle materials, pre‐cracked specimens of the same geometry, under similar loading conditions, occasionally result in different trajectories of the crack propagation. The already proposed theories for the prediction of the crack path (in) stability are based on the perturbation method in combination with analytical and finite elements methods; however, they require knowledge of the toughness equations. Therefore, they can only be applied in specimens with uncomplicated geometry and straightforward loadings. In the present paper the problem of the crack path (in) stability, is approached from a different viewpoint. Using a finite element program, the stres field is calculated, and consequently, a plotting program constructs the contours map of the strain energy density on the idealized geometry of the specimen or structure. For the determination of the predicted trajectory of the crack during unstable propagation, the minimum of the strain energy density criterion (SED) is used. The forecasted trajectory appears with the drawing of the “gorge” on the contours map of the strain energy density. Based on the estimation criterion, which claims that the degree of stability is a function of the distinctness of the gorge plot, we can predict the degree of the crack path stability. Therefore, this simple method offers good reliability in the prediction of the crack path stability for two as well as three‐dimensional problems with complex geometry structures and arbitrary loadings. In order to clarify the suggested prediction method, we apply it on the central cracked panel where a rich international practical experience exists. The results that are analysed in the present work, are in good agreement with equivalent published experimental results.     

The Effect of Particle Morphology on the Physical Stability of Pharmaceutical Powder Mixtures: The Effect of Surface Roughness of the Carrier on the Stability of Ordered Mixtures

The effect of particle morphology of the components on the physical stability of ordered mixtures was determined for a model system comprised of a mixture of micronized aspirin and a monodisperse carrier. Spray-dried lactose, crystallized lactose, microcrystalline cellulose, and dextrate were used as carriers. The surface texture of the carriers was quantified in terms of the ratio of the perimeter of the particles to that of an idealized shape at a constant magnification. Mixtures containing highly textured carriers segregated to a lesser extent than those containing smoother textured carriers. This was postulated to be due to the presence of a higher concentration of surface asperities on the coarse carriers that can constitute potentially strong adhesion sites for the fine component because of their higher energy relative to adjacent areas on the surface. The effect of the addition of a ternary component, magnesium stearate, on the stability of the above mixtures was studied. The observed differences in the segregation response were attributed to electrostatic charge effects.     

Physicochemical stability,pharmacokinetic, and biodistribution evaluation of paclitaxel solid dispersion prepared using supercritical antisolvent process

Aim: To investigate the physicochemical stability, pharmacokinetics (PK), and biodistribution of paclitaxel (PTX) from paclitaxel solid dispersion (PSD) prepared by supercritical antisolvent (SAS) process.

Methods: Physicochemical stability was performed in accelerated (40°C 70?±?5% RH) and stress (60°C) storage conditions for a period of 6 months and 4 weeks, respectively. PK and biodistribution studies were performed in rats following i.v. administration of PTX equivalent to 6 and 12?mg/kg formulations.

Results: Physical stability of PSD showed excellent stability with no recrystallization of the amorphous form. Chemical stability of PSD in terms of % PTX remaining was 98.2?±?0.6% at 6 months and 97.9?±?0.3% at 4 weeks of accelerated and stress conditions, respectively. The PK study showed a nonlinear increase in AUC with increasing dose, that is, 100% increase in dose (from 6 to 12?mg/kg) resulted in 405.90% increase in AUC. Unlike PK study, the organ distribution study of PTX from PSD showed linear relationship with dose escalation. The order of organ distribution of PTX from highest to lowest for both PSD and Taxol^® was liver>kidney>lung>brain.

Conclusions: This study demonstrated excellent physicochemical stability with insight information on the PK and biodistribution of PTX from PSD prepared by SAS process.     

Effect of strain-induced martensitic phase transformation on the formability of nitrogen-alloyed metastable austenitic stainless steels

Strain-induced martensitic phase transformation and its influence on the formability of newly developed nitrogen-alloyed metastable austenitic stainless steels were systematically investigated. Yield strength for the asreceived steels bearing lownickel content was around 300 MPa and their elongation ratios varied from 55. 2% to61. 7%. Erichsen numbers of these samples differed from 13. 82 to 14. 57 mm. Although its Cu content was lower than that of other samples,steel D2 exhibited better plasticity and formability,which was attributed to γ→α'martensitic phase transformation. EBSD,XRD,and magnetism tests showed that increases in deformation ratio gradually increased the α' martensite phase of a sample,thereby contributing to its strain and inducing the optimal transformation-induced plasticity effect. An M_(d30/50) temperature of around 20 ℃,which is close to the deformation temperature,provided the austenite with adequate stability and gradually transformed it into martensite,thereby endowing lean ASS with better formability.     

A necessary and sufficient condition for input-to-state stability of quantised feedback systems

For zooming-out/in method used in the design of quantised feedback systems, the property of the duration of zoom-out mode (this duration is defined as capture time) is essential to input-to-state stability (ISS) of systems. This paper shows that a necessary and sufficient condition of achieving ISS with respect to external disturbances for quantised feedback systems is that capture time under the proposed coding scheme is uniformly bounded. It further shows that the coding scheme under which capture time is only bounded and not uniformly bounded cannot guarantee ISS of systems. A coding scheme is designed for uniformly bounded capture time and therefore achieves ISS of systems.