Comprehensive experimental and theoretical study of fluid flow and heat transfer in a microscopic evaporating meniscus in a miniature heat exchanger

The complex physicochemical phenomena occurring in the contact line region of an evaporating meniscus are described using a unique combination of high-resolution experimental data and three complementary models. The following were used: (1) high-resolution experimental liquid profile data (thickness, slope, curvature and curvature gradient) to obtain the pressure gradient in the evaporating pentane meniscus in a vertical constrained vapor bubble (VCVB); (2) macroscopic outside surface temperature profile data; (3) a finite element model to obtain the two-dimensional heat conduction profile in the solid substrate wall (macro-model) and the solid–liquid interfacial temperature profile in the evaporating meniscus region; (4) a continuum fluid-dynamics model (micro-model) to obtain the liquid–vapor interfacial temperature, mass flow rate, Marangoni stresses, and evaporative heat flux profiles along the length of the evaporating meniscus; and (5) the Kelvin–Clapeyron model to obtain the vapor temperature profile (liquid–vapor interfacial temperature jump) in the evaporating meniscus region.The retarded dispersion constant and high-resolution thickness, slope, curvature and curvature gradient profiles were obtained from the experimental reflectivity profiles. There was a substantial increase in the measured curvature in the transition region, where the evaporation rate and flux are a maximum. To obtain numerical closure between the three complementary models, the continuum fluid dynamics model (micro-model) required slip at the solid–liquid interface to support the observed high mass flow rates in the evaporating pentane meniscus. Mass flow rates due to Marangoni stresses, capillary pressure and disjoining pressure are compared. Depending on the liquid thickness, Marangoni stresses can either enhance or hinder fluid flow towards the contact line for the evaporating pure pentane meniscus. Due to the high heat removal rate by the evaporating pentane meniscus in the transition region, dips in the vapor, liquid–vapor and solid–liquid interface temperature were obtained. The results demonstrate and describe the sensitivity and complexity of the phase change process in micro-regions.     

A 0.5 V tunable complex filter for Bluetooth and Zigbee using OTAs

A 12th-order low voltage tunable differential complex filter for bluetooth and Zigbee applications is proposed in this paper. The filter is based on improved controllable transconductors operating with the ultra-low supply voltage of 0.5 V. Simulation results using a triple-well 0.13 μm CMOS technology verify the filter operation fulfilling all the requirements for the complex filtering stage in bluetooth or Zigbee receivers. The in-band group delay variation is 0.79 μs for bluetooth and 0.46 μs for Zigbee. The image rejection ratio is greater than 71 dB and the achieved in-band spurious free dynamic range is 42 dB.     

Dynamic Electromechanical Hydrogel Matrices for Stem Cell Culture

Hydrogels have numerous biomedical applications including synthetic matrices for cell culture and tissue engineering. Here we report the development of hydrogel based multifunctional matrices that not only provide three‐dimensional structural support to the embedded cells but also can simultaneously provide potentially beneficial dynamic mechanical and electrical cues to the cells. A unique aspect of these matrices is that they undergo reversible, anisotropic bending dynamics in an electric field. The direction and magnitude of this bending can be tuned through the hydrogel crosslink density while maintaining the same electric potential gradient, allowing control over the mechanical strain imparted to the cells in a three‐dimensional environment. The conceptual design of these hydrogels was motivated through theoretical modeling of the osmotic pressure changes occurring at the gel‐solution interfaces in an electric field. These electro‐mechanical matrices support survival, proliferation, and differentiation of stem cells. Thus, these new three‐dimensional in vitro synthetic matrices, which mimic multiple aspects of the native cellular environment, take us one step closer to in vivo systems.     

Enhanced Erosion Protection of TWAS Coated Ti6Al4V Alloy Using Boride Bond Coat and Subsequent Laser Treatment

The material commonly used in low-pressure high-rating super critical/ultra super critical steam turbines as well as guide and moving blades of high speed aero compressors is Ti6Al4V alloy. These blades are severely affected owing to erosion which leads to drop in efficiency and increase in maintenance cost. This article deals with SHS 7170 coating on Ti6Al4V alloy using twin wire arc spraying (TWAS), enhancing its bonding by providing a thin bond coat and then treating with high-power diode laser (HPDL). Significant improvement in erosion resistance of this multilayer coating has been achieved because of the formation of fine-grained micro structure due to rapid heating and cooling rates associated with the laser surface treatment. After laser surface treatment, the fracture toughness of this multilayer has improved manifold. The water droplet and particulate erosion test results along with the damage mechanism are reported and discussed in this article.     

Differential evolution applied for reliability optimization of radial distribution systems

This paper describes a methodology for reliability enhancement of radial distribution system by determining optimal values of repair times and failure rates of each section. Penalty cost functions have been constructed as function of failure rates and repair times. Constraints on customer and energy based indices, i.e. SAIFI, SAIDI, CAIDI and AENS have been considered. The problem has been decomposed in two stages. One stage determines the optimum failure rates and second stage optimizes repair times satisfying constraints. A population based approach, i.e. differential evolution (DE) has been used as optimization technique. The algorithm has been implemented on a sample test system. Results obtained have been compared with those obtained using particle swarm optimization (PSO) and co-ordinated aggregation based particle swarm optimization techniques (CAPSO).     

An impression of coffee carbohydrates

Coffee is one of the most popular beverages in the world. It is consumed for its refreshing and stimulating properties. Carbohydrates are the major constituents of coffee beans and serve various functions like binding of aroma, stabilization of foam, formation of sedimentation, and increased viscosity of the extract. The principal low molecular weight carbohydrate is sucrose and no evidence of other simple oligosaccharides has been found. Polysaccharide fraction from green coffee is dominated by arabinogalactan, galactomannan, and cellulose. The polysaccharide content is reduced during roasting due to degradation to low molecular weight carbohydrates (viz., mono and oligosaccharide) and become more extractable. Various methods that can be employed to extract the carbohydrate from roasted coffee are sequential extraction, acid hydroloysis, hot water extraction, enzymatic extraction etc. Carbohydrates from coffee can be quantitatively determined by liquid chromatography, high performance anion exchange chromatography, size exclusion chromatography, and high performance liquid chromatography. Besides improving the organoleptic quality of the coffee beverage, carbohydrates also possess various biological activities such as lowering colon cancer risk. Besides their sheer mass, a variety of evidences testify to the important contribution that the polysaccharide content makes to the character of the final brew. Although a number of chemical and enzymatic methods have been devised to isolate and quantify the carbohydrates of R&G coffee, till date hot water extraction is the only method which can be accepted as a most feasible process and hence, there is wide scope of further research for the efficient and economically viable technology for extraction of carbohydrates from coffee.     

New approaches toward recognition of nucleic acid triple helices

A DNA duplex can be recognized sequence-specifically in the major groove by an oligodeoxynucleotide (ODN). The resulting structure is a DNA triple helix, or triplex. The scientific community has invested significant research capital in the study of DNA triplexes because of their robust potential for providing new applications, including molecular biology tools and therapeutic agents. The triplex structures have inherent instabilities, however, and the recognition of DNA triplexes by small molecules has been attempted as a means of strengthening the three-stranded complex. Over the decades, the majority of work in the field has focused on heterocycles that intercalate between the triplex bases. In this Account, we present an alternate approach to recognition and stabilization of DNA triplexes. We show that groove recognition of nucleic acid triple helices can be achieved with aminosugars. Among these aminosugars, neomycin is the most effective aminoglycoside (groove binder) for stabilizing a DNA triple helix. It stabilizes both the TAT triplex and mixed-base DNA triplexes better than known DNA minor groove binders (which usually destabilize the triplex) and polyamines. Neomycin selectively stabilizes the triplex (TAT and mixed base) without any effect on the DNA duplex. The selectivity of neomycin likely originates from its potential and shape complementarity to the triplex Watson-Hoogsteen groove, making it the first molecule that selectively recognizes a triplex groove over a duplex groove. The groove recognition of aminoglycosides is not limited to DNA triplexes, but also extends to RNA and hybrid triple helical structures. Intercalator-neomycin conjugates are shown to simultaneously probe the base stacking and groove surface in the DNA triplex. Calorimetric and spectrosocopic studies allow the quantification of the effect of surface area of the intercalating moiety on binding to the triplex. These studies outline a novel approach to the recognition of DNA triplexes that incorporates the use of noncompeting binding sites. These principles of dual recognition should be applicable to the design of ligands that can bind any given nucleic acid target with nanomolar affinities and with high selectivity.     

Measurements of Particulate (PM2.5), BC and Trace Gases Over the Northwestern Himalayan Region of India

Ambient trace gases (NH₃, NO, NO₂ and SO₂) and black carbon (BC) were measured along with particulate matter (PM_2.5) over the northwestern Himalayan region (Palampur, Kullu, Shimla, Solan and Nahan) of Himachal Pradesh (HP), India in a campaign mode during 12–22 March 2013 to evaluate the ambient air quality of the region. The average mixing ratio of ambient NH₃, NO, NO₂ and SO₂ were recorded as 7.1 ± 2.6, 3.1 ± 1.3, 3.9 ± 1.4 and 1.7 ± 0.7 ppb respectively over the northwestern Himalayan region. The average concentration of BC was estimated as 2.2 ± 0.5 µg m^?3 over the region whereas average concentration of PM_2.5 mass was estimated as 41.8 ± 7.9 µg m^?3. The spatial variation of ambient trace gases (NH₃, NO, NO₂ and SO₂), BC and PM_2.5 over the northwestern Himalayan region, India reveals that the region is mainly influenced by local activities, i.e., tourism activities, agricultural activities, biomass burning and vehicular emission. A significant positive linear correlation of NH₃ and NH₄ ⁺ with SO₄ ^2?, NO₃ ^? and Cl^? (NH₄ ⁺ vs. SO₄ ^2? , r ² = 0.652; NH₄ ⁺ vs. NO₃ ^?, r ² = 0.701; and NH₄ ⁺ vs. Cl^?, r ² = 0.627) of the PM_2.5 indicates the possible formation of (NH₄)₂SO₄, NH₄NO₃ and NH₄Cl aerosols over the region.     

Time-dependent oscillating systems with damping,slowly varying parameters,and delay

Summary Mechanical and physical oscillating systems with slowly varying parameters, delay, and large damping, modeled by certain nonlinear ordinary and partial differential equations are considered. The time-dependent terms in these eqiations may not be periodic in time. The study is based on an extension of the asymptotic method of Krylow-Bogoliubov-Mitropolskii.

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Zeitabhängige Schwingungssysteme mit Dämpfung, langsam veränderlichen Parametern und Verzögerung

Zusammenfassung Es werden mechanische und physikalische Schwingungssysteme mit langsam veränderlichen Parametern, Verzögerung und großer Dämpfung behandelt, welche durch bestimmte nichtlineare, gewöhnliche und partielle Differentialgleichungen beschrieben werden. Die zeitabhängigen Glieder in diesen Gleichungen müssen nicht zeitlich periodisch sein. Diese Arbeit basiert auf einer Erweiterung der asymptotischen Methode von Krylow-Bogoliubov-Mitropolskii.

     

Gold nanoparticle-polyaniline composite films for glucose sensing

Gold nanoparticles (AuNPs) have been self-assembled onto electrochemically deposited polyaniline (PANI) films on indium-tin-oxide (ITO) coated glass plates to fabricate glucose biosensor. The covalent immobilization of glucose oxidase (GOx) in the near vicinity of gold nanoparticles has been obtained using N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS), chemistry between amino groups of PANI and COOH groups of GOx. These AuNPs-PANI/ ITO and GOx/AuNPs-PANI/ITO composite films have been characterized using Fourier transform infra red (FTIR) and cyclic voltammetry (CV) techniques, respectively. The fast electron transfer from the modified PANI surface to electrode is indicated by the observed increase in amperometric response current of these GOx/AuNPs-PANI/ITO bioelectrodes. These GOx/AuNPs-PANI/ITO bioelectrodes exhibit response time of 10 s, linearity from 50 to 300 mg/dl and show value of apparent Michaelis-Menten constant (Km(app)) of 2.2 mM.