Evaporation Heat Transfer Coefficient in a Capillary Pumped Loop and Loop Heat Pipe for Different Working Fluids

Capillary pumped loop (CPL) and loop heat pipe (LHP) are passive two-phase heat transport devices. They have been gaining importance as a part of the thermal control system of spacecraft. The evaporation heat transfer coefficient at the tooth-wick interface of an LHP or CPL has a significant impact on the evaporator temperature. It is also the main parameter in sizing of a CPL or LHP. Experimentally determined evaporation heat transfer coefficients from a three-port CPL with tubular axially grooved (TAG) evaporator and a TAG LHP with acetone, R-134A, and ammonia as working fluids are presented in this paper. The influences of working fluid, hydrodynamic blocks in the core, evaporator configuration (LHP or CPL), and adverse elevation (evaporator above condenser) on the heat transfer coefficient are presented.

Nanosphere Templated Metallic Grating Assisted Enhanced Fluorescence

In this paper, enhanced fluorescence from a silver film coated nanosphere templated grating is presented. Initially, numerical simulation was performed to determine the plasmon resonance wavelength by varying the thickness of the silver film on top of a monolayer of 400 nm nanospheres. The simulation results are verified experimentally and tested for enhancing fluorescence from fluorescein isothiocyanate whose excitation wavelength closely matches with the plasmon resonance wavelength of the substrate with 100 nm silver film over nanosphere. The 12 times enhancement in the intensity is attributed to the local field enhancement in addition to the excitation of surface plasmon polaritons along the surface.

Electrical Resistance and Seebeck Coefficient in PbTe Nanowires

We address a physics-based simplified analytical formulation of the diffusive electrical resistance ( (Omega)) and Seebeck coefficient () in a PbTe nanowire dominated by acoustic phonon scattering under the presence of a low static longitudinal electric field. The use of a second-order nonparabolic electron energy band structure involving a geometry-dependent band gap has been selected in principle to demonstrate that the electron mean free path (MFP) in such a system can reach as low as about 8 nm at room temperature for a 10-nm-wide PbTe nanowire. This is followed by the formulation of the carrier back-scattering coefficient for determination of (Omega) and as functions of wire dimensions, temperature, and the field, respectively. The present analytical formulation agrees well with the available experimental data and may find extensive use in determination of various electrothermal transport phenomena in PbTe-based one-dimensional electron devices.

An association and Wilson activity coefficient model for solubilities of aromatic solid pollutants in supercritical carbon dioxide

The solubilities of various solid pollutants in supercritical carbon dioxide were investigated. The intermolecular interactions play a significant role in determining the solubilities of solids in supercritical carbon dioxide. A new model equation was derived by using the concepts of association and activity coefficient model to correlate the solubilities of solids. The model equation combines the association and Wilson activity coefficient models and includes the interaction potentials between the molecules, which are useful in understanding the behavior of the solid solutes in SCCO2. The new model equation involves five adjustable parameters to correlate the solubilities of solids by incorporating the interactions between the molecules. The equation correlated 75 solid systems with an average AARD of around 9%, which was better than the correlations obtained from standard models such as Mendez Santiago-Teja (MT) model and association model. (C) 2012 Elsevier B.V. All rights reserved.

Quantum corrections to screening at strong coupling

We compute a certain class of corrections to (specific) screening lengths in strongly coupled non-abelian plasmas using the AdS/CFT correspondence. In this holographic framework, these corrections arise from various higher curvature interactions modifying the leading Einstein gravity action. The changes in the screening lengths are perturbative in inverse powers of the `t Hooft coupling or of the number of colors, as can be made precise in the context where the dual gauge theory is superconformal. We also compare the results of these holographic calculations to lattice results for the analogous screening lengths in QCD. In particular, we apply these results within the program of making quantitative comparisons between the strongly coupled quark-gluon plasma and holographic descriptions of conformal field theory. (c) 2012 Elsevier B.V. All rights reserved.

A Novel Fiber Bragg Grating Based Sensing Methodology for Direct Measurement of Surface Strain on Body Muscles during Physical Exercises

The present work proposes a new sensing methodology, which uses Fiber Bragg Gratings (FBGs) to measure in vivo the surface strain and strain rate on calf muscles while performing certain exercises. Two simple exercises, namely ankle dorsi-flexion and ankle plantar-flexion, have been considered and the strain induced on the medial head of the gastrocnemius muscle while performing these exercises has been monitored. The real time strain generated has been recorded and the results are compared with those obtained using a commercial Color Doppler Ultrasound (CDU) system. It is found that the proposed sensing methodology is promising for surface strain measurements in biomechanical applications.

Angular amplification by a diffraction grating for chiro-optical measurements

The angles at which a light beam gets diffracted by a grating depend strongly on the direction of incidence for diffraction angles close to a right angle. Accordingly, it is possible to amplify small beam deflections by placing a grating at an optimal orientation to the light path. We use this principle to amplify small beam deviations arising out of a light beam refracting at the interface of an optically active medium, and demonstrate a new technique of enhancing the limit of detection of chiro-optical measurements. (C) 2012 Optical Society of America

MODELING HETEROSTRUCTURES WITH SCHRODINGER-POISSON-NAVIER ITERATIVE SCHEMES, EFFECT OF CARRIER CHARGE, AND INFLUENCE OF ELECTROMECHANICAL COUPLING

This paper presents a detailed investigation of the erects of piezoelectricity, spontaneous polarization and charge density on the electronic states and the quasi-Fermi level energy in wurtzite-type semiconductor heterojunctions. This has required a full solution to the coupled Schrodinger-Poisson-Navier model, as a generalization of earlier work on the Schrodinger-Poisson problem. Finite-element-based simulations have been performed on a A1N/GaN quantum well by using both one-step calculation as well as the self-consistent iterative scheme. Results have been provided for field distributions corresponding to cases with zero-displacement boundary conditions and also stress-free boundary conditions. It has been further demonstrated by using four case study examples that a complete self-consistent coupling of electromechanical fields is essential to accurately capture the electromechanical fields and electronic wavefunctions. We have demonstrated that electronic energies can change up to approximately 0.5 eV when comparing partial and complete coupling of electromechanical fields. Similarly, wavefunctions are significantly altered when following a self-consistent procedure as opposed to the partial-coupling case usually considered in literature. Hence, a complete self-consistent procedure is necessary when addressing problems requiring more accurate results on optoelectronic properties of low-dimensional nanostructures compared to those obtainable with conventional methodologies.

Evolution of structural phase coexistence in a half doped manganite Pr0.5Sr0.5MnO3: An evidence for magneto-structural coupling

Temperature dependent x-ray diffraction measurements have been performed to understand the implications of magnetic phase coexistence on crystallographic structure in a half-doped manganite Pr0.5Sr0.5MnO3. The compound shows a structural phase transition from high-temperature tetragonal-I4/mcm to low-temperature orthorhombic-Fmmm symmetry around the ferromagnetic to antiferro-magnetic transition. Rietveld analysis shows the coexistence of these two structures emerges at high temperature within the ferromagnetic state, and persists down to lowest temperature. Below around 40 K, however, this structural evolution stops, and a significant fraction (similar to 22%) of untransformed high-temperature phase remains. This agrees with earlier magnetization study, thus establishing its magneto-structural coupling. (C) 2012 Elsevier B.V. All rights reserved.

Palladium Catalyzed Coupling of Tosylhydrazones with Aryl and Heteroaryl Halides in the Absence of External Ligands: Synthesis of Substituted Olefins

Palladium catalyzed cross-coupling reaction of hydrazones with aryl halides in the absence of external ligand is reported. The versatility of this coupling reaction is demonstrated in showcasing the selectivity of coupling reaction in the presence of hydroxyl and amine functional groups. This method allows synthesizing a variety of heterocyclic compounds, which are difficult to access from other traditional methods and are not synthesized by employing similar coupling reactions. Application of the present methodology is validated in tandem reaction of ketones to the corresponding substituted olefins in a single pot experiment.

Computational tools for mechanistic discrimination in the reductive and metathesis coupling reactions mediated by titanium(IV) isopropoxide

A theoretical study has been carried out at the B3LYP/LANL2DZ level to compare the reactivity of phenyl isocyanate and phenyl isothiocyanate towards titanium(IV) alkoxides. Isocyanates are shown to favour both mono insertion and double insertion reactions. Double insertion in a head-to-tail fashion is shown to be more exothermic than double insertion in a head-to-head fashion. The head-to-head double insertion leads to the metathesis product, a carbodiimide, after the extrusion of carbon dioxide. In the case of phenyl isothiocyanate, calculations favour the formation of only mono insertion products. Formation of a double insertion product is highly unfavourable. Further, these studies indicate that the reverse reaction involving the metathesis of N,N-'-diphenyl carbodiimide with carbon dioxide is likely to proceed more efficiently than the metathesis reaction with carbon disulphide. This is in excellent agreement with experimental results as metathesis with carbon disulphide fails to occur. In a second study, multilayer MM/QM calculations are carried out on intermediates generated from reduction of titanium(IV) alkoxides to investigate the effect of alkoxy bridging on the reactivity of multinuclear Ti species. Bimolecular coupling of imines initiated by Ti(III) species leads to a mixture of diastereomers and not diastereoselective coupling of the imine. However if the reaction is carried out by a trimeric biradical species, diastereoselective coupling of the imine is predicted. The presence of alkoxy bridges greatly favours the formation of the d,l (+/-) isomer, whereas the intermediate without alkoxy bridges favours the more stable meso isomer. As a bridged trimeric species, stabilized by bridging alkoxy groups, correctly explains the diastereoselective reaction, it is the most likely intermediate in the reaction.

Coupling of photomechanical and electromechanical actuations in carbon nanotubes

It is known that carbon nanotubes (CNTs) possess multifunctional characteristics, which are applicable for a wide variety of engineering applications. CNT is also recognized as a radiation sensitive material, for example for detecting infrared (IR) radiations. One of the direct implications of exposing CNTs to radiation is the photomechanical actuation and generation of a photovoltage/photocurrent. The present work focuses on coupling electromechanical and photomechanical characteristics to enhance the resulting induced-strain response in CNTs. We have demonstrated that after applying an electric field the induced strain in CNT sheet is enhanced to about similar to 2.18 times for the maximum applied electric field at 2 V as compared to the photo-actuation response alone. This enhancement of the strain at higher bias voltages (> 1 V) can be considered as a sum of individual contributions of the bias voltage and IR stimulus. However, at lower voltage (< 1 V) the enhancement in the resulting strain has been attributed to the associated electrostatic effects when CNTs are stimulated with IR radiation under external bias conditions. This report reveals that voltage bias or IR stimulus alone could not produce the observed strain in the CNT sheet under lower bias conditions.

Analysis of rectangular folded waveguide SWS with grating on the broad wall

An E-plane rectangular folded-waveguide slow-wave structure with metal grating on the broad wall of the waveguide along the direction of the electric field has been proposed and analyzed for the dispersion and interaction impedance characteristics through three dimensional electromagnetic modeling in CST Studio. The effects of the presence of grating on the bandwidth and interaction impedance are demonstrated.

High power microwave coupling with a buried twisted pair cable

This paper deals with the coupling of High Power Microwaves with a buried twisted pair cable. The electric field at a distance of 1km from the HPM antenna has been computed and is used for further computation of induced voltage and current. It is found that the peak of the induced current and voltage in a buried unshielded twisted pair cable at a distance of 1km from an HPM antenna of power level 10GW is 20A and 2kV respectively.

Calibration of etched fiber bragg grating sensor arrays for measurement of molecular surface adsorption

Etched Fiber Bragg Grating (EFBG) sensors are attractive from the point of the inherently high multiplexing ability of fiber based sensors. However, the strong dependence of the sensitivity of EFBG sensors on the fiber diameter requires robust methods for calibration when used for distributed sensing in a large array format. Using experimental data and numerical modelling, we show that knowledge of the wavelength shift during the etch process is necessary for high-fidelity calibration of EFBG arrays. However as this approach requires the monitoring of every element of the sensor array during etching, we also proposed and demonstrated a calibration scheme using data from bulk refractometry measurements conducted post-fabrication without needing any information about the etching process. Although this approach is not as precise as the first one, it may be more practical as there is no requirement to monitor each element of the sensor array. We were able to calibrate the response of the sensors to within 3% with the approach using information acquired during etching and to within 5% using the post-fabrication bulk refractometry approach in spite of the sensitivities of the array element differing by more than a factor of 4. These two approaches present a tradeoff between accuracy and practicality.