Numerical Analysis Of Heat Transfer Parameters Using Ferrofluid

Heat transfer, thermal management, and acoustics are the important parameters that determine the effectiveness of any miniaturized electronic circuit. As the density of electronic components is increasing, the reliability of such systems is of great concern. The proposed work discusses a novel technique of a magnetic pumping fluid system without conventional cooling components. Here the integrated effect of the conjugate heat transfer and magnetic field is taken into account to study flow phenomena. Two different fluids—water and kerosene—as a base fluid for ferrofluid are evaluated for physical quantities such as pressure, temperature, and heat transfer coefficient to measure the performance of a magnetic cooling system. Flow in the cooling setup is optimized by using numerical analysis and number of experiments on the given setup. It was found that flow depends on the magnetic field gradient, temperature gradient, fluid properties, and material combination. In addition, flow characteristics depend on the influence of magnetic field and temperature of the fluid. Analysis results show that the heat transfer and pressure head in the kerosene-based ferrofluid are more stable compared to the water-based ferrofluid. A better magnetic fluid with both high magnetization and a high pyromagnetic coefficient can enhance the flowability of the ferrofluid to a large extent.     

Studies on the synthesis of electrospun PAN‐Ag composite nanofibers for antibacterial application

We have successfully synthesized polyacrylonitrile (PAN) nanofibers impregnated with Ag nanoparticles by electrospinning method at room temperature. Briefly, the PAN‐Ag composite nanofibers were prepared by electrospinning PAN (10% w/v) in dimethyl formamide (DMF) solvent containing silver nitrate (AgNO₃) in the amounts of 8% by weight of PAN. The silver ions were reduced into silver particles in three different methods i.e., by refluxing the solution before electrospinning, treating with sodium borohydride (NaBH₄), as reducing agent, and heating the prepared composite nanofibers at 160°C. The prepared PAN nanofibers functionalized with Ag nanoparticles were characterized by field emission scanning electron microscopy (FESEM), SEM elemental detection X‐ray analysis (SEM‐EDAX), transmission electron microscopy (TEM), and ultraviolet‐visible spectroscopy (UV‐VIS) analytical techniques. UV‐VIS spectra analysis showed distinct absorption band at 410 nm, suggesting the formation of Ag nanoparticles. TEM micrographs confirmed homogeneous dispersion of Ag nanoparticles on the surface of PAN nanofibers, and particle diameter was found to be 5–15 nm. It was found that all the three electrospun PAN‐Ag composite nanofibers showed strong antibacterial activity toward both gram positive and gram negative bacteria. However, the antibacterial activity of PAN‐Ag composite nanofibers membrane prepared by refluxed method was most prominent against S. aureus bacteria. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

An impact of bias and structure dependent L_\mathrm{SD} variation on the performance of GaN HEMTs based biosensor

In this paper, we discussed the effect of different bias and structures in relation to S-D distance variation on the device electrical and expected biosensing performance. Devices with source to drain length ( \(L_{SD})\) variations from 3.5, 5.0, 8.0, 14.0, 26.0 to \(52~\upmu \) m were simulated at low and high bias voltages. Different structures having gate recess and finger variations were investigated for the complete range of \(L_{SD}\) variations. Small and very large \(L_{SD}\) variations in non-recessed structure showed good values of drain current \((I_{ds})\) and transconductances \((g_{m})\) at different low and high bias voltages respectively. Therefore expected response time and sensitivity could be improved by choosing a proper bias condition for different biosensing \(L_{SD}\) lengths. A gate recess structure showed better \(g_{m}\) values at low bias conditions for all \(L_{SD}\) lengths. However, \(I_{ds}\) degraded for these structures and hence the expected response time. The non-recessed structure variations in terms of number of fingers and gate width did not change the effective trends in \(L_{SD}\) variation.     

Solid‐Supported Rhodium(0) Nano‐/Microparticles: An Efficient Ligand‐Free Heterogeneous Catalyst for Microwave‐Assisted Suzuki–Miyaura Cross‐Coupling Reaction

Solid‐supported nano‐ and microparticles of rhodium(0) (SS‐Rh) were prepared and applied as a ligand free heterogeneous catalyst for Suzuki–Miyaura cross‐coupling reaction with wide range of substrate scope. A hitherto unknown Rh‐catalyzed Suzuki cross‐coupling reaction of aldehyde and cyanohaloarenes was observed rather than the usual nucleophilic arylation.The catalyst can be removed by simple filtration and recycled upto twelve runs without any deterioration of activity.     

A facile synthesis of PEG-coated magnetite (Fe3O4) nanoparticles and their prevention of the reduction of cytochrome c

We report here a facile and green synthetic approach to prepare magnetite (Fe(3)O(4)) nanoparticles (NPs) with magnetic core and polyethylene glycol (PEG) surface coating. The interaction of the bare and PEG-coated Fe(3)O(4) NPs with cytochrome c (cyt c, an important protein with direct role in the electron transfer chain) is also reported in this study. With ultrasonication as the only peptization method and water as the synthesis medium, this method is easy, fast, and environmentally benign. The PEG coated NPs are highly water dispersible and stable. The bare NPs have considerable magnetism at room temperature; surface modification by PEG has resulted in softening the magnetization. This approach can very well be applicable to prepare biocompatible, surface-modified soft magnetic materials, which may offer enormous utility in the field of biomedical research. Detailed characterizations including XRD, FTIR, TG/DTA, TEM, and VSM of the PEG-coated Fe(3)O(4) NPs were carried out in order to ensure the future applicability of this method. Although the interaction of bare NPs with cyt c shows reduction of the protein, efficient surface modification by PEG prevents its reduction.     

Recombinase‐Based Isothermal Amplification of Nucleic Acids with Self‐Avoiding Molecular Recognition Systems (SAMRS)

Recombinase polymerase amplification (RPA) is an isothermal method to amplify nucleic acid sequences without the temperature cycling that classical PCR uses. Instead of using heat to denature the DNA duplex, RPA uses recombination enzymes to swap single‐stranded primers into the duplex DNA product; these are then extended using a strand‐displacing polymerase to complete the cycle. Because RPA runs at low temperatures, it never forces the system to recreate base‐pairs following Watson–Crick rules, and therefore it produces undesired products that impede the amplification of the desired product, complicating downstream analysis. Herein, we show that most of these undesired side products can be avoided if the primers contain components of a self‐avoiding molecular recognition system (SAMRS). Given the precision that is necessary in the recombination systems for them to function biologically, it is surprising that they accept SAMRS. SAMRS‐RPA is expected to be a powerful tool within the range of amplification techniques available to scientists.     

Surface hardening in N<Superscript>+</Superscript> implanted polycarbonate

The influence of low energy nitrogen ions on the surface hardness of polycarbonate has been studied by implanting some of these specimens with 100 keV N⁺ ions at a beam current of 1 μA/cm² in the dose range of 1 × 10¹⁵ to 1 × 10¹⁷ ions cm^?2. Knoop microhardness has been found to be increased nearly 24 times at a load of 9.8 mN, for the dose of 1 × 10¹⁷ ions cm^?2. The structural changes occurred in implanted specimens were studied by Raman analysis, UV–Visible spectroscopy, and X-ray diffraction techniques. Raman studies point toward the formation of a structure resembling hydrogenated amorphous carbon. Disordering in the surface structure (I _D/I _G ratio) has also been found to increase with ion fluence using Raman technique. UV–Visible spectroscopic analysis shows a clear enhancement in Urbach energy (disorder parameter) from a value of 0.61 eV (virgin sample) to 1.72 eV (at a fluence of 1 × 10¹⁷ N⁺ cm^?2) with increasing ion dose. The increase in Urbach energy has been found to be correlated linearly with the increase in Knoop microhardness number. Results of X-ray diffraction analysis also indicate disordering in implanted layers as a result of implantation. In the present work, the possible mechanism behind the formation of harder surfaces due to implantation has been discussed in detail.     

Primary hyperoxaluria causing ESRD and gangrene of extremities leading to amputation

Primary hyperoxaluria is an uncommon, inherited metabolic disorder due to hepatic enzyme deficiencies with consequent hepatic oxalate overproduction and attendant systemic complications. The diagnosis is established on a combination of clinical parameters, elevated urinary excretion of oxalate and glycolate and determination of alanine glyoxylate aminotransferase in the liver tissue. We describe a 45-year-old female with end-stage renal disease secondary to nephrolithiasis, who presented with a fulminating vascular syndrome before confirming the diagnosis of primary hyperoxaluria. This case illustrates that in this infrequent clinical entity, the diagnosis is often delayed with incorrect initial management.     

Supporting children's mental health in schools: Teacher perceptions of needs, roles, and barriers.

There is a significant research to practice gap in the area of mental health practices and interventions in schools. Understanding the teacher perspective can provide important information about contextual influences that can be used to bridge the research to practice gap in school-based mental health practices. The purpose of this study was to examine teachers' perceptions of current mental health needs in their schools; their knowledge, skills, training experiences and training needs; their roles for supporting children's mental health; and barriers to supporting mental health needs in their school settings. Participants included 292 teachers from 5 school districts. Teachers reported viewing school psychologists as having a primary role in most aspects of mental health service delivery in the school including conducting screening and behavioral assessments, monitoring student progress, and referring children to school-based or community services. Teachers perceived themselves as having primary responsibility for implementing classroom-based behavioral interventions but believed school psychologists had a greater role in teaching social emotional lessons. Teachers also reported a global lack of experience and training for supporting children's mental health needs. Implications of the findings are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)