Analytic solution of nonlinear singularly perturbed initial value problems through iteration

This paper is concerned with singularly perturbed initial value problems for systems of ordinary differential equations. Here our emphasis will be on nonlinear phenomena and properties, particularly those with physical relevance. Since very few nonlinear systems can be solved explicitly, one must typically rely on a numerical scheme to accurately approximate the solution. However, numerical schemes do not always give accurate results, and we discuss the class of stiff differential equations, which present a more serious challenge to numerical analysts. In this paper, we derive in closed from, analytic solution of stiff nonlinear initial value problems, through iteration. The obtained sequence of iterates is based on the use of Lagrange multipliers. Moreover, the illustrative examples shows the efficiency of the method.     

Palladium-catalyzed asymmetric quaternary stereocenter formation

An efficient palladium catalyst is presented for the formation of benzylic quaternary stereocenters by conjugate addition of arylboronic acids to a variety of β,β-disubstituted carbocyclic, heterocyclic, and acyclic enones. The catalyst is readily prepared from PdCl(2), PhBOX, and AgSbF(6), and provides products in up to 99% enantiomeric excess, with good yields. Based on this strategy, (-)-α-cuparenone has been prepared in only two steps.     

Multifarious Applications of Photoacoustic Spectrophotometer and Its Importance in Forensic Investigation

Abstract: Photoacoustic spectrophotometer (PAS) has emerged as the most promising technology with its promise to resolve unmet issues in various domains. The advantages of PAS are nonvulnerability of the sample, trace quantity sample analysis, and short response time. Though it showed distinguished features close to its emergence, it is bereft of its importance in the present scenario. Certainly, there exists a transparent gap in understanding the current situation in forensic crime scene management and the application of PAS within the same discipline. This article aims to consolidate all this information to fill an existing knowledge gap and tries to establish trajectory of research done up to now. This article will also pinpoint the reasons behind why this advanced technique could not accomplish its respectable feat inside the market and restraint of optical business toward inventing and commercializing this merchandise.     

The swiss light source: The SLS team

The British Association (BA) Festival of Science is a special opportunity for any member of the public interested in science to meet together with scientists and discuss as well as review science and its achievements. One such opportunity arose when the turn of the northwest of England came to host the Annual BA Festival of Science at the University of Liverpool in September 2008. A session of synchrotron radiation science reviewing the contributions of the SRS as well as a look to the future was held. A review of accelerator science was given by Mike Poole, Director of ASTeC at STFC. John Helliwell, Professor of Structural Chemistry at Manchester University, reviewed biology and medicine; Bob Cernik, Professor of Materials Science at Manchester University, reviewed materials science; and Tracy Turner, of the Photon Science Department of STFC, reviewed future light sources.     

Water Vapor Sorption in Cementitious Materials—Measurement,Modeling and Interpretation

The rate and extent of uptake and release of moisture are critical in controlling the behavior of cementitious materials ranging from fluid transport to hygral deformations. While classically determined using an equilibrium (static) salt solution method (Baroghel-Bouny in Cem Concr Res 37:414–437, 2007), advanced capabilities offered by gravimetric dynamic vapor sorption (DVS) analyzers, are now permitting acquisition of sorption spectra at microgram ( $\upmu \hbox {g}$ ) resolution on the order of a few weeks. This work highlights new multicycle determinations of adsorption/desorption isotherms, acquired using a custom-built DVS analyzer for well-hydrated alite and ordinary portland cement pastes over a range of water-to-solid ratios ( $w/s$ , mass basis). Special focus is paid to describe measurement aspects relevant to acquiring reliable spectra, and their interpretation. Sorption isotherms are used to assess transport properties, and sorption hysteresis and its irreversibility following first drying. Based on an optimization-based criterion, the Young-Nelson model is selected to simulate sorption evolutions, including the effects of hysteresis. Sensitivity analyses carried out using this model are used to understand the role of parameters, including porosity and $w/s$ , on the hysteresis that develops from the first to subsequent sorption cycles.     

Inverse-phosphocholine lipids: a remix of a common phospholipid

Zwitterionic inverse-phosphocholine (iPC) lipids contain headgroups with an inverted charge orientation relative to phosphocholine (PC) lipids. The iPC lipid headgroup has a quaternary amine adjacent to the bilayer interface and a phosphate that extends into the aqueous phase. Neutral iPC lipids with ethylated phosphate groups (CPe) and anionic iPC lipids nonethylated phosphate groups (CP) were synthesized. The surface potential of CPe liposomes remains negative across a broad pH range and in the presence of up to 10 mM Ca(2+). CP liposomes aggregate in the presence of Ca(2+), but at a slower rate than other anionic lipids. Hydrolysis of CP lipids by alkaline phosphatases generates a cationic lipid. CPe liposomes release encapsulated anionic carboxyfluorescein (CF) 20 times faster than PC liposomes and release uncharged glucose twice as fast as PC liposomes. As such, iPC lipids afford a unique opportunity to investigate the biophysical and bioactivity-related ramifications of a charge inversion at the bilayer surface.     

Performance analysis of traffic groomed optical network

In this paper we carry out the performance analysis of traffic groomed multilayer optical networks. It is seen that the number of wavelength channels required decreases as the wavelength grooming factor increases. We have evaluated blocking probability for different load and grooming factor. The performance of the network has been evaluated for different conditions; first for fixed number of links with grooming factor set to 3 and subsequently with increase in grooming factor up to 18 in steps. The load on each link is selected as 2, 5, 9, 12, 15 and 20 Erlangs and the blocking probability as function of number of optical channels has been evaluated. In this work the effect of number of wavelength channels, traffic load and grooming factor on network blocking probability has been studied. The investigation reveals that the blocking probability decreases with increase in wavelength channels. Similarly we found that the blocking probability increases with increase in traffic load which is quite evident. Further it is shown that when the grooming factor is increased to significant value (16), the number of wavelengths requirement (8) becomes relatively stable.     

Noise conversion from pump to the passively mode-locked fiber lasers at 1.5 μm

We characterize the noise conversion from the pump relative intensity noise (RIN) to the RIN and phase noise of passively mode-locked lasers at 1.5 μm. Two mode locking mechanisms, nonlinear polarization rotation (NPR) and semiconductor saturable absorber mirror (SESAM), are compared for noise conversion for the first time. It is found that the RIN and the phase noise of both types of lasers are dominated by the noise converted from the pump RIN and thus, can be predicted with the measured pump RIN and noise conversion ratios. The SESAM laser is found to show an excess noise conversion from the laser RIN to the laser phase noise due to the slow saturable absorber effect.     

Wendelstein 7‐X: An Alternative Route to a Fusion Reactor

With the ITER tokamak magnetic confinement fusion is making the decisive step to realize a burning fusion plasma and prepare the basis for a demonstration power plant (DEMO). Despite the advantages of an intrinsically steady state magnetic field and better stability properties, the development of stellarators lags behind by about 1 1/2 device generations, because of the difficulties to realize the desired magnetic field configuration. The goal of the optimized stellarator Wendelstein 7‐X is to overcome the principal deficiencies of the stellarator concept and demonstrate its reactor capability, combining sufficiently good thermal and fast ion confinement with reactor relevant ß and collisionality under steady state conditions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Effective Conjugation Length Is Responsible for the Red/Green Spectral Tuning in the Cyanobacteriochrome Slr1393g3

The origin of the spectral shift from a red‐ to a green‐absorbing form in a cyanobacteriochrome, Slr1393g3, was identified by combined quantum mechanics/molecular mechanics simulations. This protein, related to classical phytochromes, carries the open‐chain tetrapyrrole chromophore phycocyanobilin. Our calculations reveal that the effective conjugation length in the chromophore becomes shorter upon conversion from the red to the green form. This is related to the planarity of the entire chromophore. A large distortion was found for the terminal pyrrole rings A and D; however, the D ring contributes more strongly to the photoproduct tuning, despite a larger change in the twist of the A ring. Our findings implicate that the D ring twist can be exploited to regulate the absorption of the photoproduct. Hence, mutations that affect the D ring twist can lead to rational tuning of the photoproduct absorption, allowing the tailoring of cyanobacteriochromes for biotechnological applications such as optogenetics and bioimaging.