A new method to estimate parameters of linear compartmental models using artificial neural networks

At present, the preferred tool for parameter estimation in compartmental analysis is an iterative procedure; weighted nonlinear regression. For a large number of applications, observed data can be fitted to sums of exponentials whose parameters are directly related to the rate constants/coefficients of the compartmental models. Since weighted nonlinear regression often has to be repeated for many different data sets, the process of fitting data from compartmental systems can be very time consuming. Furthermore the minimization routine often converges to a local (as opposed to global) minimum. In this paper, we examine the possibility of using artificial neural networks instead of weighted nonlinear regression in order to estimate model parameters. We train simple feed-forward neural networks to produce as outputs the parameter values of a given model when kinetic data are fed to the networks' input layer. The artificial neural networks produce unbiased estimates and are orders of magnitude faster than regression algorithms. At noise levels typical of many real applications, the neural networks are found to produce lower variance estimates than weighted nonlinear regression in the estimation of parameters from mono- and biexponential models. These results are primarily due to the inability of weighted nonlinear regression to converge. These results establish that artificial neural networks are powerful tools for estimating parameters for simple compartmental models.     

A Specific Stability Indicating Hplc Method to Determine Diclofenac Sodium in Raw Materials and Pharmaceutical Solid Dosage Forms

A high performance liquid chromatography method is described for the determination of diclofenac sodium, its related compounds and degradation products in commercial sources of raw materials and solid dosage forms. This method is specific, accurate and stability indicating. The method employs a reverse-phase octylsilane (C18) column with a mobile phase composed of acetonitrile/methanol/pic B-6 (25:25:50) and detection at 229 nm. The method resolves six principal related compounds with quantitation in the range 0.3-1.5%. Assay recoveries by spiking commercial formulations with diclofenac sodium were 99.64 ± 1.30%. Drug content in several commercial formulations are reported. Accelerated stability tests were conducted on raw materials and drug products and 1-(2,6-dichlorophenyl)-2-indolin-2-one was identified for the first time as a degradation product in solid dosage forms which are stressed under humidity and heat.     

Social Profile Aware AODV Protocol for Ad-Hoc Social Networks

Wireless Personal Communications - Ad-hoc social networks are required to strengthen local communication between people. Mobile ad-hoc social networks have emerged as self-configuring and...     

Highly Conductive Carbon Nanotube‐Graphene Hybrid Yarn

An efficient procedure for the fabrication of highly conductive carbon nanotube/graphene hybrid yarns has been developed. To start, arrays of vertically aligned multi‐walled carbon nanotubes (MWNT) are converted into indefinitely long MWNT sheets by drawing. Graphene flakes are then deposited onto the MWNT sheets by electrospinning to form a composite structure that is transformed into yarn filaments by twisting. The process is scalable for yarn fabrication on an industrial scale. Prepared materials are characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It is found that the electrical conductivity of the composite MWNT‐graphene yarns is over 900 S/cm. This value is 400% and 1250% higher than electrical conductivity of pristine MWNT yarns or graphene paper, respectively. The increase in conductivity is asssociated with the increase of the density of states near the Fermi level by a factor of 100 and a decrease in the hopping distance by an order of magnitude induced by grapene flakes. It is found also that the MWNT‐graphene yarn has a strong electrochemical response with specific capacitance in excess of 111 Fg^?1. This value is 425% higher than the capacitance of pristine MWNT yarn. Such substantial improvements of key properties of the hybrid material can be associated with the synergy of MWNT and graphene layers in the yarn structure. Prepared hybrid yarns can benefit such applications as high‐performance supercapacitors, batteries, high current capable cables, and artificial muscles.     

Proton spin–spin relaxation time of peel and flesh of navel orange varieties exposed to freezing temperature

Proton spin–spin relaxation times (T₂) of peel (albedo and flavedo) and juice sacs (flesh segments) of navel oranges were measured at 10 MHz using a Bruker Minispec PC 110 NMR spectrometer. The oranges were subjected to chilling (5 °C) and freezing (−7 °C) temperatures for 20 h and warmed to room temperature before peeling for T₂ measurements. The exposure to chilling or freezing temperature did not affect the T₂ values of peel, but freezing caused an appreciable decrease (∼15%) in the T₂ values of flesh segments of the varieties of navel oranges studied. When the peel was exposed to −20 °C, the T₂ showed a drastic reduction suggesting that the peel did not freeze at −7 °C. The possible cause of reduction in the T₂ values when exposed to freezing temperature may be damage to the juice sac membrane and leakage of juice out of the sac. The difference in the T₂ values between juice sacs of freeze-affected and normal oranges can potentially be used for detection of freeze-damaged fruits. Copyright © 2005 Society of Chemical Industry     

Procedural outcome and follow-up results of balloon angioplasty versus new device interventions for treatment of true bifurcation stenoses

Strategies for dilatation of bifurcation stenoses have continued to evolve over the past several years. However, there is limited experience on the efficacy of various nonballoon interventional devices and their results in comparison with balloon angioplasty. We, therefore, analysed our data in 72 patients of coronary artery disease with true bifurcation stenoses with balloon angioplasty or new device interventions (NDI). All patients underwent dilatation of both the primary vessel and side branch ostial stenosis. Balloon angioplasty using double guidewire with sequential or simultaneous (kissing balloon) balloon inflation in the two vessels was performed in 42 patients. Thirty patients underwent NDI, using directional coronary atherectomy (DCA) in 12, rotablation in 6 and elective coronary stents in 12 patients. There were no significant differences in the baseline clinical and angiographic variables between patients in the two groups. While the preprocedural luminal diameter stenosis was similar, the residual stenosis was significantly less, both in the primary vessel and side branch, after NDI compared to balloon angioplasty. The procedure was successful in 96.6 percent patients treated with NDI and 83.3 percent with balloon angioplasty (p < 0.01) with relief of obstruction in both branches without any major complications. Freedom from subsequent coronary events in the form of angina, myocardial infarction, PTCA, bypass graft surgery of death was significantly more, both at 6 months (92% versus 65.6%, p < 0.001) and 12 months (81.8% versus 53.1%, p < 0.001) in the group of patients treated with NDI compared to balloon angioplasty. It is, therefore, concluded that NDI including DCA, rotablation and elective stenting are associated with higher rate of success, lesser complications and better event-free survival in comparison to balloon angioplasty for treatment of true bifurcation stenoses.     

Pharmacological actions of Pongamia pinnata seeds--a preliminary study

Direct ethanolic and sequential petroleum ether, chloroform, acetone and ethanolic extracts (50-100 mg/kg, i.p.) of P. pinnata seeds given 30-60 min before revealed anti-inflammatory, analgesic and anti-ulcerogenic activities in rats. The activities were present maximum in petroleum ether and chloroform extracts. However, the extracts also showed shortening of pentobarbitone induced 'sleep time' in rats.