Numerical modeling and experimental study of the frontal polymerization of the diglycidyl ether of bisphenol A/diethylenetriamine epoxy system

Frontal polymerization is a process in which a spatially localized reaction zone propagates through a monomer by converting it into a polymer. In particular, the heat produced during the curing process is exploited to promote the reaction of the monomer lying next to the propagating front, making this latter able to self‐sustain. This approach represents an alternative solution to traditional polymerization methods and can be successfully applied to the preparation of many polymeric materials. In this study, frontal polymerization was numerically modeled to better understand it and to provide the basis for processing simulation. A finite‐difference method was used to solve the thermal problem coupled with the equation describing the cure evolution for a reactor with a cylindrical geometry. The implicit backward time–centered space method was used. First, a one‐dimensional model, able to describe the process in an adiabatic tube, was developed. The front ignition was simulated as if it were a hot surface warming one end of the reactor to trigger reactant polymerization. The model was able to predict the formation of a reactive front advancing in the unreacted zone with a constant speed. The influence of the chemical and physical properties of the resin on process evolution was also investigated. By applying the alternate direction implicit method, a more detailed two‐dimensional model able to describe a three‐dimensional problem for a cylindrical reactor was also developed. With this model, it was possible to study the influence of boundary conditions on process evolution, considering a convective heat exchange with the environment through the reactor walls. Diglycidyl ether of bisphenol A, cured with diethylenetriamine (DETA), was used as the model system. Differential scanning calorimetry was used to produce a phenomenological model able to describe the cure process and to determine the physical properties of the resin. The validity of the approach was confirmed experimentally using a small cylindrical reactor. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1756–1766, 2005     

An Optimization Approach to Multiarea State Estimation

This paper proposes a simple multiarea decentralized state estimation procedure. This procedure allows estimating the state of a multiarea electric energy system while preserving the independence of each area. Information interchange among area operators reduces to just border information. The proposed algorithm is both simple and robust. The procedure developed is illustrated through several case studies carried out using the IEEE Reliability Test System. Conclusions are duly drawn     

Using vanishing points for camera calibration

In this article a new method for the calibration of a vision system which consists of two (or more) cameras is presented. The proposed method, which uses simple properties of vanishing points, is divided into two steps. In the first step, the intrinsic parameters of each camera, that is, the focal length and the location of the intersection between the optical axis and the image plane, are recovered from a single image of a cube. In the second step, the extrinsic parameters of a pair of cameras, that is, the rotation matrix and the translation vector which describe the rigid motion between the coordinate systems fixed in the two cameras are estimated from an image stereo pair of a suitable planar pattern. Firstly, by matching the corresponding vanishing points in the two images the rotation matrix can be computed, then the translation vector is estimated by means of a simple triangulation. The robustness of the method against noise is discussed, and the conditions for optimal estimation of the rotation matrix are derived. Extensive experimentation shows that the precision that can be achieved with the proposed method is sufficient to efficiently perform machine vision tasks that require camera calibration, like depth from stereo and motion from image sequence.     

Influence of the carrier diffusion process on the transient response of vertical‐cavity surface‐emitting lasers

We investigate the transverse mode dynamics of weakly index‐guided vertical‐cavity surface‐emitting lasers (VCSEL). The turn‐on time of transverse modes are calculated by implementing a model for the VCSEL dynamics including diffusion and transport/capture phenomena. It takes into account the spatial dependence of the two carrier density profiles associated with the confined carriers in the quantum wells, and with the unconfined carriers in the barrier region. Devices of different aperture diameter under different excitation conditions are also studied. The model displays the correct turn‐on time dependence on the injection current density when compared with the experimental data available. We show that the turn‐on time of the modes increases when capture time increases and escape time decreases and also when diffusion increases. Copyright © 2002 John Wiley & Sons, Ltd.     

Double renal allografts successfully increase utilization of kidneys from older donors within a single organ procurement organization

BACKGROUND: In 1994, a policy of double renal allografting (DUAL) was used at two centers within our local organ procurement organization to increase utilization of kidneys from older donors that would otherwise be discarded. Both kidneys from an older donor (age > 60 years) were selectively transplanted into a single adult recipient. METHODS: The relative impact of a DUAL policy on the utilization of older donor kidneys is examined for the period of April 1994 to April 1996. Actual utilization is compared with the hypothetical case in which a DUAL policy is not present. RESULTS: In the actual setting, a total of 75 kidneys from older donors (> 60 years) were accepted for transplantation. Thirty-six kidneys were transplanted as singlets, and 16 additional kidneys were transplanted as DUAL renal allografts. Thus, a 44% increase in transplantable kidneys, and a 22% increase in patients transplanted with kidneys from older donors, was realized. In the actual setting, 23 older kidneys were discarded; without the DUAL policy, 39 kidneys would have been deemed untransplantable. When compared with the actual (n = 52) and hypothetical number of kidneys transplanted without a policy of DUAL transplantation (n = 36), the DUAL policy significantly increased the utilization of older donor kidneys (P = 0.01). The actuarial 1-year graft survival rate of the dual kidneys was 100%, with a mean follow-up of 11.1 +/- 2.9 months. Mean 6-month and 1-year serum creatinine level were 1.76 +/- 0.4 and 1.63 +/- 0.6 mg/dl, respectively. CONCLUSIONS: A DUAL policy significantly increased the number of older donor kidneys transplanted in a single organ procurement organization and reduced the rate of discard of older donor kidneys over a 2-year period. Long-term follow-up is necessary to substantiate satisfactory graft function in DUAL from older donors.     

The Contribution of Wnt Signaling to Vascular Complications in Type 2 Diabetes Mellitus

Vascular complications are the leading cause of morbidity and mortality among patients with type 2 diabetes mellitus (T2DM). These vascular abnormalities result in a chronic hyperglycemic state, which influences many signaling molecular pathways that initially lead to increased oxidative stress, increased inflammation, and endothelial dysfunction, leading to both microvascular and macrovascular complications. Endothelial dysfunction represents the initial stage in both types of vascular complications; it represents “mandatory damage” in the development of microvascular complications and only “introductory damage” in the development of macrovascular complications. Increasing scientific evidence has revealed an important role of the Wnt pathway in the pathophysiology of the vascular wall. It is well known that the Wnt pathway is altered in patients with T2DM. This review aims to be an update of the current literature related to the Wnt pathway molecules that are altered in patients with T2DM, which may also be the cause of damage to the vasculature. Both microvascular complications (retinopathy, nephropathy, and neuropathy) and macrovascular complications (coronary artery disease, cerebrovascular disease, and peripheral arterial disease) are analyzed. This review aims to concisely concentrate all the evidence to facilitate the view on the vascular involvement of the Wnt pathway and its components by highlighting the importance of exploring possible therapeutic strategy for patients with T2DM who develop vascular pathologies.     

Fast Preisach-based magnetization model and fast inverse hysteresismodel

Fast computational methods for Preisach-based models and their inverses are presented. The methods are based on a differential equation approach to computing a sequence of magnetization values due to a sequence of applied fields. The method used to speed up calculations can be applied to any Preisach model. The Della Torre, Oti, Kadar model was used here as an illustration. Sequential computations for the magnetization model are substantially faster than for standard Preisach models with comparable output error. Computations for the inverse hysteresis model are even faster than for the model. Using the inverse, open loop control of magnetic hysteresis is simulated, showing hysteretic material tracking a desired magnetization in a linear manner for both major loops and minor loops, with less than 2% error in inversion for the waveforms used. The effect of misidentification of material parameters on operation of the inverse is also investigated through simulations     

Eunomos,a legal document and knowledge management system for the Web to provide relevant,reliable and up-to-date information on the law

This paper describes the Eunomos software, an advanced legal document and knowledge management system, based on legislative XML and ontologies. We describe the challenges of legal research in an increasingly complex, multi-level and multi-lingual world and how the Eunomos software helps users cut through the information overload to get the legal information they need in an organized and structured way and keep track of the state of the relevant law on any given topic. Using NLP tools to semi-automate the lower-skill tasks makes this ambitious project a realistic commercial prospect as it helps keep costs down while at the same time allowing greater coverage. We describe the core system from workflow and technical perspectives, and discuss applications of the system for various user groups.